The authors have nothing to disclose.

1. INS-1E Cells: Maintenance and Plating
<ol>
	<li>Maintain INS-1E cells in a humidified 37 &#730;C/5% CO2 incubator and cultured with RPMI 1640 medium supplemented with 5% (v/v) heat-inactivated fetal bovine serum, 2 mM L-glutamine, 10 mM HEPES, 1 mM sodium pyruvate, 100 U/mL Penicillin/Streptomycin solution, 50 &#181;M &#946;-mercaptoethanol. Culture cells in 10 mL complete RPMI 1640 medium (per plate), until they reach 80 - 90% confluence, when they can be trypsinized and passaged or used for the insulin ...

<ol>
	<li>Taniguchi, C. M., Emanuelli, B., Kahn, C. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Critical+nodes+in+signalling+pathways:+Insights+into+insulin+action.">Critical nodes in signalling pathways: Insights into insulin action.</a> Nat Rev Mol Cell Biol. 7 (2), 85-96 (2006).</li><li>Vetere, A., Choudhary, A., Burns, S. M., Wagner, B. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Targeting+the+pancreatic+beta-cell+to+treat+diabetes.">Targeting the pancreatic beta-cell to treat diabetes.</a> Nat Rev Drug Discov. 13 (4), 278-289 (2014).</li><li>Despres, J. P., Lemieux, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Abdominal+obesity+and+metabolic+syndrome.">Abdominal obesity and metabolic syndrome.</a> Nature. 444 (7121), 881-887 (2006).</li><li>Kahn, S. E., Hull, R. L., Utzschneider, K. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanisms+linking+obesity+to+insulin+resistance+and+type+2+diabetes.">Mechanisms linking obesity to insulin resistance and type 2 diabetes.</a> Nature. 444 (7121), 840-846 (2006).</li><li>Barg, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanisms+of+exocytosis+in+insulin-secreting+B-cells+and+glucagon-secreting+A-cells.">Mechanisms of exocytosis in insulin-secreting B-cells and glucagon-secreting A-cells.</a> Pharmacol Toxicol. 92 (1), 3-13 (2003).</li><li>Braun, M., Ramracheya, R., Rorsman, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Autocrine+regulation+of+insulin+secretion.">Autocrine regulation of insulin secretion.</a> Diabetes Obes Metab. 14 Suppl 3, 143-151 (2012).</li><li>Farino, Z. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+a+rapid+insulin+assay+by+homogenous+time-resolved+fluorescence.">Development of a rapid insulin assay by homogenous time-resolved fluorescence.</a> PLoS One. 11 (2), e0148684 (2016).</li><li>Simpson, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dopamine-mediated+autocrine+inhibitory+circuit+regulating+human+insulin+secretion+in+vitro.">Dopamine-mediated autocrine inhibitory circuit regulating human insulin secretion in vitro.</a> Mol Endocrinol. 26 (10), 1757-1772 (2012).</li><li>Heyduk, E., Moxley, M. M., Salvatori, A., Corbett, J. A., Heyduk, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Homogeneous+insulin+and+C-Peptide+sensors+for+rapid+assessment+of+insulin+and+C-peptide+secretion+by+the+islets.">Homogeneous insulin and C-Peptide sensors for rapid assessment of insulin and C-peptide secretion by the islets.</a> Diabetes. 59 (10), 2360-2365 (2010).</li><li>Heyduk, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measuring+protein+conformational+changes+by+FRET/LRET.">Measuring protein conformational changes by FRET/LRET.</a> Curr Opin Biotechnol. 13 (4), 292-296 (2002).</li><li>Degorce, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=HTRF((R)):+Pioneering+technology+for+high-throughput+screening.">HTRF((R)): Pioneering technology for high-throughput screening.</a> Expert Opin Drug Discov. 1 (7), 753-764 (2006).</li><li>Degorce, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=HTRF:+A+technology+tailored+for+drug+discovery+-+a+review+of+theoretical+aspects+and+recent+applications.">HTRF: A technology tailored for drug discovery - a review of theoretical aspects and recent applications.</a> Curr Chem Genomics. 3, 22-32 (2009).</li><li>Mathis, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=HTRF(R)+Technology.">HTRF(R) Technology.</a> J Biomol Screen. 4 (6), 309-314 (1999).</li><li>Daijo, J. E., Sportsman, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+time-resolved+fluorescence+immunoassay+for+insulin+in+rodent+plasma.">A time-resolved fluorescence immunoassay for insulin in rodent plasma.</a> J Pharm Biomed Anal. 19 (3-4), 335-342 (1999).</li><li>Merglen, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Glucose+sensitivity+and+metabolism-secretion+coupling+studied+during+two-year+continuous+culture+in+INS-1E+insulinoma+cells.">Glucose sensitivity and metabolism-secretion coupling studied during two-year continuous culture in INS-1E insulinoma cells.</a> Endocrinology. 145 (2), 667-678 (2004).</li><li>Ustione, A., Piston, D. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dopamine+synthesis+and+D3+receptor+activation+in+pancreatic+beta-cells+regulates+insulin+secretion+and+intracellular+[Ca(2+)]+oscillations.">Dopamine synthesis and D3 receptor activation in pancreatic beta-cells regulates insulin secretion and intracellular [Ca(2+)] oscillations.</a> Mol Endocrinol. 26 (11), 1928-1940 (2012).</li><li>Ustione, A., Piston, D. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+simple+introduction+to+multiphoton+microscopy.">A simple introduction to multiphoton microscopy.</a> J Microsc. 243 (3), 221-226 (2011).</li><li>Ustione, A., Piston, D. W., Harris, P. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Minireview:+Dopaminergic+regulation+of+insulin+secretion+from+the+pancreatic+islet.">Minireview: Dopaminergic regulation of insulin secretion from the pancreatic islet.</a> Mol Endocrinol. 27 (8), 1198-1207 (2013).</li><li>Rubi, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dopamine+D2-like+receptors+are+expressed+in+pancreatic+beta+cells+and+mediate+inhibition+of+insulin+secretion.">Dopamine D2-like receptors are expressed in pancreatic beta cells and mediate inhibition of insulin secretion.</a> J Biol Chem. 280 (44), 36824-36832 (2005).</li><li>Garcia-Tornadu, I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Disruption+of+the+dopamine+d2+receptor+impairs+insulin+secretion+and+causes+glucose+intolerance.">Disruption of the dopamine d2 receptor impairs insulin secretion and causes glucose intolerance.</a> Endocrinology. 151 (4), 1441-1450 (2010).</li><li>Garcia-Tornadu, I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=New+insights+into+the+endocrine+and+metabolic+roles+of+dopamine+D2+receptors+gained+from+the+Drd2+mouse.">New insights into the endocrine and metabolic roles of dopamine D2 receptors gained from the Drd2 mouse.</a> Neuroendocrinology. 92 (4), 207-214 (2010).</li><li>Lopez Vicchi, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dopaminergic+drugs+in+type+2+diabetes+and+glucose+homeostasis.">Dopaminergic drugs in type 2 diabetes and glucose homeostasis.</a> Pharmacol Res. 109, 74-80 (2016).</li><li>Kalra, S., Kalra, B., Agrawal, N., Kumar, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dopamine:+The+forgotten+felon+in+type+2+diabetes.">Dopamine: The forgotten felon in type 2 diabetes.</a> Recent Pat Endocr Metab Immune Drug Discov. 5 (1), 61-65 (2011).</li><li>Mahajan, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bromocriptine+mesylate:+FDA-approved+novel+treatment+for+type-2+diabetes.">Bromocriptine mesylate: FDA-approved novel treatment for type-2 diabetes.</a> Indian J Pharmacol. 41 (4), 197-198 (2009).</li><li>Caicedo, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Paracrine+and+autocrine+interactions+in+the+human+islet:+more+than+meets+the+eye.">Paracrine and autocrine interactions in the human islet: more than meets the eye.</a> Semin Cell Dev Biol. 24 (1), 11-21 (2013).</li><li>Ballon, J. S., Pajvani, U., Freyberg, Z., Leibel, R. L., Lieberman, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+pathophysiology+of+metabolic+effects+of+antipsychotic+medications.">Molecular pathophysiology of metabolic effects of antipsychotic medications.</a> Trends Endocrinol Metab. , (2014).</li><li>Freyberg, Z., Aslanoglou, D., Shah, R., Ballon, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intrinsic+and+antipsychotic+drug-induced+metabolic+dysfunction+in+schizophrenia.">Intrinsic and antipsychotic drug-induced metabolic dysfunction in schizophrenia.</a> Front Neurosci. 11, 432 (2017).</li><li>de Leeuw van Weenen, E. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+dopamine+receptor+D2+agonist+bromocriptine+inhibits+glucose-stimulated+insulin+secretion+by+direct+activation+of+the+alpha2-adrenergic+receptors+in+beta+cells.">The dopamine receptor D2 agonist bromocriptine inhibits glucose-stimulated insulin secretion by direct activation of the alpha2-adrenergic receptors in beta cells.</a> Biochem Pharmacol. 79 (12), 1827-1836 (2010).</li></ol>

The HTRF insulin assay described here offers a rapid, efficient system to measure insulin secretion from a cultured cell-based system. Among its most important advantages, this assay offers a low background signal due to the high signal-to-noise ratio. Additionally, we have confirmed that the HTRF signal is stable for extended periods of time (&#62;24 h)7. Nevertheless, since the insulin-binding monoclonal antibodies quickly reach binding saturation after addition to the assay, kinetics of antibod...

The regulation of energy metabolism is fine-tuned by a major anabolic hormone, insulin. Insulin is synthesized and released by pancreatic beta cells in response to increased extracellular glucose levels. The released insulin triggers the uptake of glucose by insulin-sensitive tissues1,2. Physiologically, this is linked to the elevation of glucose concentration after a meal, followed by secretion of insulin to regulate glucose uptake. Disturbances in glucose homeostasis lead to metabolic impairments culminating in insulin resistance and ultimately in the onset of type 2 diabetes2,3,4.
Although insulin secretion has been extensively studied, its regulatory mechanisms remain poorly understood. A critical area of investigation has been identification of novel modulators of insulin secretion by beta cells5,6,7,8. These studies require a better understanding of the coupling relationship between glucose stimulation and insulin secretion. Therefore, the ability to accurately monitor and quantify the levels of glucose-stimulated insulin secretion (GSIS) has been essential. To date, however, only a limited number of methods were available to allow quantification of GSIS using insulin-secreting cell lines and/or pancreatic islets. One is radioimmunoassay (RIA), which utilizes radioisotope-tagged insulin and antibodies. The main limitations of this approach include safety issues due to the handling and disposal of radioactive materials. Additionally, this method is labor-intensive, involving multiple long washing and incubation steps. Enzyme-linked immunosorbent assay (ELISA) is another costly and labor-intensive approach that utilizes antibodies for insulin detection. Variation in antibody affinities and in the efficiency of recognizing insulin are limiting factors of this method and can affect the reproducibility of the results. Neither ELISA nor RIA was designed for high-throughput experiments. AlphaScreen is a homogeneous assay used for detecting and measuring levels of insulin secretion. AlphaScreen technology is based on the conversion of ambient oxygen into an excited oxygen singlet state that can react with chemiluminescent species, resulting in the generation of chemiluminescence. Because the assay is homogenous, many of the washing steps associated with RIA and ELISA are eliminated. However, the instability of the signal due to the nature of the reaction is a limiting factor that may affect the readout of the assay. (TR-PINCER, developed by Heyduk and colleagues9, is another homogenous approach to insulin measurement based on the binding of two separate antibodies to different epitopes on the insulin molecule. The antibodies are each chemically linked to double stranded DNA with short complementary single stranded DNA overhangs. Binding of the antibodies to insulin brings them together and leads to a double stranded DNA duplex. Each antibody is also associated with a respective donor or acceptor fluorophore, and the association of the DNA duplex brings together these fluorophores to generate F&#246;rster resonance energy transfer (FRET). One potential limitation of TR-PINCER, however, rests with the FRET itself. The inability to rapidly dissipate background fluorescence during the FRET reaction may lead to relatively high levels of background fluorescence and a low signal to noise ratio within the assay. Therefore, a need still exists for a reliable, robust, and cost-effective assay for quantifying GSIS in a high-throughput manner.
Recent advances in biophysics have culminated in the development of a homogeneous time-resolved fluorescence energy resonance transfer (HTRF) based assay. Specifically, while the energy transfer within the assay may be described as FRET-based, more accurately, HTRF relies on luminescence energy resonance transfer (LRET)10 which is the non-radiative transfer of energy between the donor and acceptor species11,12,13. This distinction is important, since the timing of a fluorescence or quenching based FRET interaction is much different than it is for LRET, though the same types of gating can be used for FRET and LRET. Moreover, the use of rare earth lanthanide cryptate compounds such as europium or terbium cryptate in HTRF produces long fluorescence half-lives12,14. This offers the unique advantage of the introduction of a time delay (&#181;sec) between donor excitation and the measurement of emission from the acceptor (i.e., time-resolved assay). This time delay allows for sufficient time for the background fluorescence to dissipate prior to measurement of acceptor emission fluorescence. Consequently, the readout is free of non-specific fluorescence and thus, a high signal-to-noise ratio is achieved (Figure 1). Furthermore, the homogenous nature of HTRF eliminates the need for washing steps to wash off the unbound species, making the assay much more rapid than ELISA or RIA-based methods.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57531/57531fig1.jpg" /> 
Figure 1: Schematic of the mechanism for HTRF insulin detection. Two independently generated monoclonal antibodies specifically recognize and bind to insulin at separate sites. These antibodies are conjugated to either the europium cryptate donor or the XL665 acceptor. Excitation of the donor at 337 nm results in emission at 620 nm. The resulting energy transfer causes XL665 to emit at a longer wavelength, 665 nm. <a href="/files/ftp_upload/57531/57531fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Here, we provide a detailed protocol for using an HTRF-based approach to determine the levels of GSIS from INS-1E cells, a well-established insulin-secreting beta cell-derived rat insulinoma cell line15. In addition, this assay may be used for identifying the pharmacological profile of molecular regulators of insulin secretion. We apply this HTRF-based insulin assay to examine dopamine D2-like receptor regulation of GSIS. Increasing studies have revealed that the neurotransmitter dopamine is an important regulator of GSIS8,16,17,18,19,20,21,22. Dopamine affects GSIS in a negative autocrine/paracrine manner via actions on the dopamine D2-like receptors (D2, D3, D4 receptors) expressed at the surface of beta pancreatic cells8,16,19. Using this assay, we confirm dopamine&#39;s role as a negative regulator of GSIS and demonstrate that the dopamine D2-like receptor agonists bromocriptine and quinpirole also reduce GSIS.

<table border="0" cellpadding="0" cellspacing="0" width="773">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">96-well white half area plate</td>
			<td style="width:104px;">Greiner Bio-One</td>
			<td style="width:139px;">82050-042</td>
			<td style="width:315px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">384-well white low-volume, round-bottom plate</td>
			<td style="width:104px;">Corning</td>
			<td>15100157</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Insulin High Range Kit</td>
			<td style="width:104px;">Cisbio Bioassays</td>
			<td style="width:139px;">62IN1PEH&#160;</td>
			<td>10,000 test HTRF-based insulin assay kit</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">PHERAstar FSX plate reader</td>
			<td style="width:104px;">BMG Labtech</td>
			<td>FSX</td>
			<td>Plate reader adapted for HTRF-based assay readings</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Plate sealers</td>
			<td style="width:104px;">Fisher Scientific</td>
			<td style="width:139px;">DY992</td>
			<td>To seal plate while antibodies incubate</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Hemocytometer</td>
			<td style="width:104px;">Hausser Scientific</td>
			<td style="width:139px;">3100</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">RPMI Medium 1640 (1x)</td>
			<td style="width:104px;">Gibco&#160;</td>
			<td style="width:139px;">11875-093</td>
			<td>[+] L-glutamine</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Trypsin 0.05%&#160;</td>
			<td style="width:104px;">Corning</td>
			<td style="width:139px;">25-052-CI</td>
			<td>0.53 mM EDTA, (-) sodium bicarbonate</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">DPBS (Dulbecco&#39;s phosphate buffered saline)</td>
			<td style="width:104px;">Corning</td>
			<td style="width:139px;">21-031-CV</td>
			<td>Without calcium and magnesium</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Fetal Bovine Serum</td>
			<td style="width:104px;">Corning</td>
			<td style="width:139px;">35-010-CV</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">HEPES</td>
			<td style="width:104px;">Gibco&#160;</td>
			<td style="width:139px;">156-30-080</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Sodium pyruvate</td>
			<td style="width:104px;">Gibco&#160;</td>
			<td style="width:139px;">11360070</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Penicillin/Streptomycin solution 100x</td>
			<td style="width:104px;">Corning</td>
			<td style="width:139px;">30-002 CT</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">2-mercaptoethanol</td>
			<td style="width:104px;">Sigma</td>
			<td style="width:139px;">M1348</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Trypan Blue Stain (0.4%)</td>
			<td style="width:104px;">Gibco&#160;</td>
			<td style="width:139px;">15250-061</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Dopamine hydrochloride</td>
			<td style="width:104px;">Sigma</td>
			<td style="width:139px;">8502</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Bromocriptine mesylate</td>
			<td style="width:104px;">Tocris</td>
			<td style="width:139px;">427</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">(-)-Quinpirole hydrochloride</td>
			<td style="width:104px;">Tocris</td>
			<td style="width:139px;">1061</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Bovine Serum Albumin</td>
			<td style="width:104px;">Calbiochem</td>
			<td style="width:139px;">12659</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Poly-L-Lysine</td>
			<td style="width:104px;">Sigma</td>
			<td style="width:139px;">P4832</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Glucose</td>
			<td style="width:104px;">Sigma</td>
			<td style="width:139px;">G7021</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">DMSO (Dimethyl sulfoxide)</td>
			<td style="width:104px;">Sigma</td>
			<td style="width:139px;">276855</td>
			<td></td>
		</tr>
	</tbody>
</table>

homogeneous time-resolved f&#246;rster resonance energy transfer-based assay for detection of insulin secretion

The detection of insulin secretion is critical for elucidating mechanisms of regulated secretion as well as in studies of metabolism. Though numerous insulin assays have existed for decades, the recent advent of homogeneous time-resolved F&#246;rster Resonance Energy Transfer (HTRF) technology has significantly simplified these measurements. This is a rapid, cost-effective, reproducible, and robust optical assay reliant upon antibodies conjugated to bright fluorophores with long lasting emission which facilitates time-resolved F&#246;rster Resonance Energy Transfer. Moreover, HTRF insulin detection is amenable for the development of high-throughput screening assays. Here we use HTRF to detect insulin secretion in INS-1E cells, a rat insulinoma-derived cell line. This allows us to estimate basal levels of insulin and their changes in response to glucose stimulation. In addition, we use this insulin detection system to confirm the role of dopamine as a negative regulator of glucose-stimulated insulin secretion (GSIS). In a similar manner, other dopamine D2-like receptor agonists, quinpirole, and bromocriptine, reduce GSIS in a concentration-dependent manner. Our results highlight the utility of the HTRF insulin assay format in determining the role of numerous drugs in GSIS and their pharmacological profiles.

We validated our insulin HTRF assay by generating an insulin standard curve using purified human insulin standards of predefined concentrations (Figure 2). Generation of the standard curve permitted us to extrapolate the ratiometric fluorescence readings and thus to determine the secreted insulin levels in response to the drug treatments (Figure 2). Intraplate variation for curve fitting was minimal (R2 = 0.99...

Watch this Scientific Journal Video about Homogeneous Time-resolved FÃ¶rster Resonance Energy Transfer-based Assay for Detection of Insulin Secretion at JoVE.com

Homogeneous Time-resolved F&amp;#246;rster Resonance Energy Transfer-based Assay for Detection of Insulin Secretion

Here, we present homogeneous time resolved FRET (HTRF) as an efficient method for rapid detection of insulin secreted from cells.

Homogeneous Time-resolved F&#246;rster Resonance Energy Transfer-based Assay for Detection of Insulin Secretion

The detection of insulin secretion is critical for elucidating mechanisms of regulated secretion as well as in studies of metabolism. Though numerous ...

The overall goal of this procedure is to induce and accurately quantify the levels of secreted insulin from insulin secreting cells. This method can help answer key questions in the diabetes field, such as the main mechanisms under glucose-stimulated insulin secretion in pancreatic beta cells. The main advantage of this technique is that it can accurately and rapidly quantify insulin secretion in response to glucose stimulation and detect potential drug effects on secretion.The implications of this technique extend toward therapy and drug discovery for treating Type 2 diabetes, because it will allow us to better understand the mechanisms of drug-induced metabolic dysfunction. Though this method can provide insight into insulin secretion from immortalized beta cell lines, it can also be applied to other systems, such as intact pancreatic islets. Generally, individuals new to this method will struggle, because of multiple cell handling steps and drug preparations.We first had the idea for this method when we wanted to come up with a rapid assay to investigate the actions of dopaminergic drugs on insulin secretion. Visual demonstration of this method is critical, as the cell handling steps are difficult to learn because of the delicate nature of the cells and the importance of precision to ensure consistency of the assay between experiments. First, grow the INS-1E cells as outlined in the text protocol.Once the cells reach the desired confluency, aspirate the medium. Wash the cells with five milliliters of phosphate buffered saline. Next, add 0.5 milliliters of 025%trypsin to the cells then leave the cells in the incubator for three to four minutes at 37 degrees Celsius.Deactivate the trypsin by adding nine milliliters of complete medium. Next, transfer the cells to a 15 milliliter centrifuge tube. Then centrifuge the cells to form a pellet.After centrifugation, dissolve the pellet in five milliliters of fresh medium. Pipette out 10 microliters of the re-suspended cells from the tube and mix with 10 microliters of trypan blue vital dye to assess viability. Next, use a hemocytometer to count the number of living and dead cells and ensure that 90%of the cells are living.After counting, add one million cells per milliliter in fresh RPMI 1640 medium, then seed 0.5 milliliters of 500, 000 INS-1E cells in each well of a poly-L-lysine coated 24-well plate. Leave the plate in the incubator for one whole day. The next day, remove the media and add 500 microliters of fresh RPMI 1640 medium in each of the wells.Incubate the plate for another 24 hours for the cells to spread on the well surfaces. To perform the assay, first prepare the KRB buffer, then aspirate the medium from each of the wells and wash with pre-warmed phosphate buffered saline, twice. Next, add 450 microliters of KRB buffer, supplemented with bovine serum albumin, but no glucose, in each well.Leave the culture plate at 37 degrees Celsius and 5%carbon dioxide for an hour. Prepare serial dilutions of the drugs in KRB buffer, supplemented with 10X final concentration of 200 millimolar glucose. After the glucose starvation step, pipette 50 microliters of serially diluted drugs in each of the corresponding wells.For glucose stimulation, add the respective serially diluted drugs in the presence of 20 millimolar glucose. Then incubate the cells at 37 degrees Celsius for 90 minutes. Once the stimulation is over, collect the supernatants and transfer them to labeled 1.5 milliliter centrifuge tubes.Transfer 10 microliters of each collected supernatant into a 96-well plate. Add 90 microliters of KRB to each well to achieve a one to 10 dilution ratio. Mix the dilutions to ensure homogeneity.Then, obtain the insulin standard curve for the HTRF insulin assay. Next, add 10 microliters each of the standard insulin samples and the diluted assay supernatants to a 96-well plate. Prepare the antibody mix in a one to two donor to accept a ratio in the detection buffer.After preparing the antibody mix, add 30 microliters of it to each of the wells in a 96-well plate. Seal the plate and incubate at room temperature. After two hours of incubation, read the plate with the antibody mix on the plate reader.Use the appropriate HTRF optic module at 665 and 620 nanometers for the reading and use 200 flashes for each well. First, an insulin standard curve is plotted to extrapolate the actual values of insulin from the assay samples. The standard curve shows that the ratiometric fluorescence reading obtained significantly increases as a function of the pre-defined standard human insulin concentrations.Next, the basal level of insulin secretion from the INS-1E cells is studied in the presence or absence of 20 millimolar glucose. From the plot, it shows that the cells secrete approximately 100 nanograms per milliliter of insulin in the presence of glucose. Interestingly, the insulin level is almost half at approximately 15 nanograms per milliliter in the absence of glucose.Next, the cells are incubated in the presence of increasing concentrations of dopamine with 20 millimolar glucose. The insulin secreted is normalized to the average value of the percent maximum insulin from each well. The plot shows that dopamine inhibits GSIS, thereby indicating the functional importance of dopaminergic receptors in GSIS.This plot shows that bromocriptine, a Type 2 diabetes drug, is more potent in inducing GSIS than dopamine. This plots shows that with increasing concentration of quinpirole, a D2 agonist, although less efficient than bromocriptine, shows similar potency like dopamine in stimulating GSIS. Once mastered, this technique can be done in four to five hours if it's performed properly.While attempting this procedure, it's important to remember to pipette carefully and consistently. Following this procedure, other functional assays like cyclic AMP HDRF assay can be performed in order to answer additional questions, like dopaminergic drug effects on downstream signaling. After its development, this technique paved the way for researchers in the field of metabolism to explore other endocrine secretory pathways in both immortalized cell lines and pancreatic islets.After watching this video, you should have a good understanding of how to accurately measure insulin secretion from cells using HDRF.

homogeneous-time-resolved-forster-resonance-energy-transfer-based

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JoVE Journal

Medicine

9.1K ビュー.  University of Pittsburgh. The overall goal of this procedure is to induce and accurately quantify the levels of secreted insulin from insulin secreting cells. This method can help answer key questions in the diabetes field, such as the main mechanisms under glucose-stimulated insulin secretion in pancreatic beta cells. The main advantage of this technique is that it can accurately and rapidly quantify insulin secretion in response to glucose stimulation and detect potential drug effects on secretion.The implica...

ビデオ: Homogeneous Time-resolved F&#246;rster Resonance Energy Transfer-based Assay for Detection of Insulin Secretion

Here, we present homogeneous time resolved FRET (HTRF) as an efficient method for rapid detection of insulin secreted from...

fast grid preparation for time-resolved cryo-electron microscopy

Fast Grid Preparation for Time-Resolved Cryo-Electron Microscopy

Here, we provide a detailed protocol for the use of a rapid grid making device for both fast grid-making and for rapid mixing and freezing to conduct time-resolved...

millifluidics for chemical synthesis and time-resolved mechanistic studies

Millifluidics for Chemical Synthesis and Time-resolved Mechanistic Studies

Millifluidic devices are utilized for controlled synthesis of nanomaterials, time-resolved analysis of reaction mechanisms and continuous flow...

time-resolved photoluminescence spectroscopy of semiconductor nanocrystals and other fluorophores

Time-Resolved Photoluminescence Spectroscopy of Semiconductor Nanocrystals and Other Fluorophores

This paper presents an experimental how-to on time-resolved photoluminescence. The hardware used in many single photon-counting setups will be described and a basic how-to will be presented. This is intended to help students and experimenters understand the key system parameters and how to correctly set them in time-resolved photoluminescence...

preparation of functionalized magnetic nanoparticles for time-resolved fluorescent imaging

Preparation of Functionalized Magnetic Nanoparticles for Time-Resolved Fluorescent Imaging

utilizing time-resolved protein-induced fluorescence enhancement to identify stable local conformations one &#945;-synuclein monomer at a time

Utilizing Time-Resolved Protein-Induced Fluorescence Enhancement to Identify Stable Local Conformations One &amp;#945;-Synuclein Monomer at a Time

Time-resolved single-molecule protein-induced fluorescence enhancement is a useful fluorescence spectroscopic proximity sensor sensitive to local structural changes in proteins. Here we show it can be used to uncover stable local conformations in &#945;-Synuclein, which is otherwise known as globularly unstructured and unstable when measured using the longer range FRET...

Utilizing Time-Resolved Protein-Induced Fluorescence Enhancement to Identify Stable Local Conformations One &#945;-Synuclein Monomer at a Time

recombination dynamics in thin-film photovoltaic materials via time-resolved microwave conductivity

Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity

A Time Resolved Microwave Conductivity technique for investigating direct and trap-mediated recombination dynamics and determining carrier mobilities of thin film semiconductors is presented...

time-resolved forster resonance energy transfer for monitoring protein phosphorylation in cells

This video describes the time-resolved F&#246;rster resonance energy transfer or TR-FRET assay to determine endogenous protein phosphorylation with the help of donor and acceptor fluorophores tagged on antibodies specific to a test protein. This technique is designed to measure the phosphorylation of test proteins in cell...

Time-Resolved Forster Resonance Energy Transfer for Monitoring Protein Phosphorylation in Cells

homogeneous equilibria for gaseous reactions

Equilibria for Gaseous Reactions: Relation Between Kp &amp; Kc

Homogeneous Equilibria for Gaseous Reactions For gas-phase reactions, the equilibrium constant may be expressed in terms of either the molar concentrations (Kc) or partial pressures (Kp) of the reactants and products. A relation between these two K values may be simply derived from the ideal gas equation and the definition of molarity. According to the ideal gas equation: Molar concentration or molarity is given by number of moles divided by the volume: Thus, where P is partial pressure, V...

Homogeneous Equilibria for Gaseous Reactions

f distribution

F Distribution

The F distribution was named after Sir Ronald Fisher, an English statistician. The F statistic is a ratio (a fraction) with two sets of degrees of freedom; one for the numerator and one for the denominator. The F distribution is derived from the Student&#39;s t distribution. The values of the F distribution are squares of the corresponding values of the t distribution. One-Way ANOVA expands the t test for comparing more than two groups. The scope of that derivation is beyond the level of this...

F Distribution

ultrafast time-resolved near-ir stimulated raman measurements of functional &#960;-conjugate systems

Ultrafast Time-resolved Near-IR Stimulated Raman Measurements of Functional &amp;#960;-conjugate Systems

Details of signal generation and optimization, measurement, data acquisition, and data handling for a femtosecond time-resolved near-IR stimulated Raman spectrometer are described. A near infrared stimulated Raman study on the excited-state dynamics of &#946;-carotene in toluene is shown as a representative...

Ultrafast Time-resolved Near-IR Stimulated Raman Measurements of Functional &#960;-conjugate Systems

The following day, prepare intermediate two-fold and four-fold dilution series of the test compounds, by serially diluting the compound in a serum-free medium, across 12 wells of a polypropylene 96-well plate. For cell stimulation, add 50 microliters of serum-free medium, containing the stimulator at a 2X concentration, and incubate the cells for the pre-optimized time at either room temperature or 37...

Production and Detection of Reactive Oxygen Species (ROS) in Cancers

Reactive oxygen species include a number of molecules that damage DNA and RNA and oxidize proteins and lipids (lipid peroxydation). These reactive molecules contain an oxygen and include H2O2 (hydrogen peroxide), NO (nitric oxide), O2- (oxide anion), peroxynitrite (ONOO-), hydrochlorous acid (HOCl), and hydroxyl radical (OH-).
Oxidative species are produced not only under pathological situations (cancers, ischemic/reperfusion, neurologic and cardiovascular pathologies, infectious diseases, inflammatory diseases 1, autoimmune diseases 2, etc&hellip;) but also during physiological (non-pathological) situations such as cellular metabolism 3, 4. Indeed, ROS play important roles in many cellular signaling pathways (proliferation, cell activation 5, 6, migration 7 etc..). ROS can be detrimental (it is then referred to as "oxidative and nitrosative stress") when produced in high amounts in the intracellular compartments and cells generally respond to ROS by upregulating antioxidants such as superoxide dismutase (SOD) and catalase (CAT), glutathione peroxidase (GPx) and glutathione (GSH) that protects them by converting dangerous free radicals to harmless molecules (i.e. water). Vitamins C and E have also been described as ROS scavengers (antioxidants).
Free radicals are beneficial in low amounts 3. Macrophage and neutrophils-mediated immune responses involve the production and release of NO, which inhibits viruses, pathogens and tumor proliferation 8. NO also reacts with other ROS and thus, also has a role as a detoxifier (ROS scavenger). Finally NO acts on vessels to regulate blood flow which is important for the adaptation of muscle to prolonged exercise 9, 10. Several publications have also demonstrated that ROS are involved in insulin sensitivity 11, 12.
Numerous methods to evaluate ROS production are available. In this article we propose several simple, fast, and affordable assays; these assays have been validated by many publications and are routinely used to detect ROS or its effects in mammalian cells. While some of these assays detect multiple ROS, others detect only a single ROS.

Production and Detection of Reactive Oxygen Species ROS in Cancers

Here we propose simple methods to test and evaluate the presence of reactive oxygen species in cells.

Reactive oxygen species include a number of molecules that damage DNA and RNA and oxidize proteins and lipids (lipid peroxydation). These reactive ...

Improving IV Insulin Administration in a Community Hospital

Diabetes mellitus is a major independent risk factor for increased morbidity and mortality in the hospitalized patient, and elevated blood glucose concentrations, even in non-diabetic patients, predicts poor outcomes.1-4 The 2008 consensus statement by the American Association of Clinical Endocrinologists (AACE) and the American Diabetes Association (ADA) states that "hyperglycemia in hospitalized patients, irrespective of its cause, is unequivocally associated with adverse outcomes."5 It is important to recognize that hyperglycemia occurs in patients with known or undiagnosed diabetes as well as during acute illness in those with previously normal glucose tolerance.
The Normoglycemia in Intensive Care Evaluation-Survival Using Glucose Algorithm Regulation (NICE-SUGAR) study involved over six thousand adult intensive care unit (ICU) patients who were randomized to intensive glucose control or conventional glucose control.6 Surprisingly, this trial found that intensive glucose control increased the risk of mortality by 14% (odds ratio, 1.14; p=0.02). In addition, there was an increased prevalence of severe hypoglycemia in the intensive control group compared with the conventional control group (6.8% vs. 0.5%, respectively; p&lt;0.001). From this pivotal trial and two others,7,8 Wyoming Medical Center (WMC) realized the importance of controlling hyperglycemia in the hospitalized patient while avoiding the negative impact of resultant hypoglycemia. 
Despite multiple revisions of an IV insulin paper protocol, analysis of data from usage of the paper protocol at WMC shows that in terms of achieving normoglycemia while minimizing hypoglycemia, results were suboptimal. Therefore, through a systematical implementation plan, monitoring of patient blood glucose levels was switched from using a paper IV insulin protocol to a computerized glucose management system. By comparing blood glucose levels using the paper protocol to that of the computerized system, it was determined, that overall, the computerized glucose management system resulted in more rapid and tighter glucose control than the traditional paper protocol. Specifically, a substantial increase in the time spent within the target blood glucose concentration range, as well as a decrease in the prevalence of severe hypoglycemia (BG &lt; 40 mg/dL), clinical hypoglycemia (BG &lt; 70 mg/dL), and hyperglycemia (BG &gt; 180 mg/dL), was witnessed in the first five months after implementation of the computerized glucose management system. The computerized system achieved target concentrations in greater than 75% of all readings while minimizing the risk of hypoglycemia. The prevalence of hypoglycemia (BG &lt; 70 mg/dL) with the use of the computer glucose management system was well under 1%.

When compared to the previous paper protocol, implementation of a computerized glucose management system results in a substantial increase in blood glucose concentration measurements within the target range. Using a computerized glucose management system to monitor blood glucose levels, decreases in severe hypoglycemia (&lt;40 mg/dL), clinical hypoglycemia (&lt;70 mg/dL), and hyperglycemia (&gt;180 mg/dL) also can be observed.

Diabetes mellitus is a major independent risk factor for increased morbidity and mortality in the hospitalized patient, and elevated blood glucose ...

Cerenkov Luminescence Imaging (CLI) for Cancer Therapy Monitoring

In molecular imaging, positron emission tomography (PET) and optical imaging (OI) are two of the most important and thus most widely used modalities1-3. PET is characterized by its excellent sensitivity and quantification ability while OI is notable for non-radiation, relative low cost, short scanning time, high throughput, and wide availability to basic researchers. However, both modalities have their shortcomings as well. PET suffers from poor spatial resolution and high cost, while OI is mostly limited to preclinical applications because of its limited tissue penetration along with prominent scattering optical signals through the thickness of living tissues.
 Recently a bridge between PET and OI has emerged with the discovery of Cerenkov Luminescence Imaging (CLI)4-6. CLI is a new imaging modality that harnesses Cerenkov Radiation (CR) to image radionuclides with OI instruments. Russian Nobel laureate Alekseyevich Cerenkov and his colleagues originally discovered CR in 1934. It is a form of electromagnetic radiation emitted when a charged particle travels at a superluminal speed in a dielectric medium7,8. The charged particle, whether positron or electron, perturbs the electromagnetic field of the medium by displacing the electrons in its atoms. After passing of the disruption photons are emitted as the displaced electrons return to the ground state. For instance, one 18F decay was estimated to produce an average of 3 photons in water5. 
 Since its emergence, CLI has been investigated for its use in a variety of preclinical applications including in vivo tumor imaging, reporter gene imaging, radiotracer development, multimodality imaging, among others4,5,9,10,11. The most important reason why CLI has enjoyed much success so far is that this new technology takes advantage of the low cost and wide availability of OI to image radionuclides, which used to be imaged only by more expensive and less available nuclear imaging modalities such as PET.
 Here, we present the method of using CLI to monitor cancer drug therapy. Our group has recently investigated this new application and validated its feasibility by a proof-of-concept study12. We demonstrated that CLI and PET exhibited excellent correlations across different tumor xenografts and imaging probes. This is consistent with the overarching principle of CR that CLI essentially visualizes the same radionuclides as PET. We selected Bevacizumab (Avastin; Genentech/Roche) as our therapeutic agent because it is a well-known angiogenesis inhibitor13,14. Maturation of this technology in the near future can be envisioned to have a significant impact on preclinical drug development, screening, as well as therapy monitoring of patients receiving treatments.

Cerenkov Luminescence Imaging CLI for Cancer Therapy Monitoring

Use of Cerenkov Luminescence Imaging (CLI) for monitoring preclinical cancer treatment is described here. This method takes advantage of Cerenkov Radiation (CR) and optical imaging (OI) to visualize radiolabeled probes and thus provides an alternative to PET in preclinical therapeutic monitoring and drug screening.

In  molecular imaging, positron emission tomography (PET) and optical imaging (OI)  are two of the most important and thus most widely used modalities1-3. ...

Coculture Analysis of Extracellular Protein Interactions Affecting Insulin Secretion by Pancreatic Beta Cells

Interactions between cell-surface proteins help coordinate the function of neighboring cells. Pancreatic beta cells are clustered together within pancreatic islets and act in a coordinated fashion to maintain glucose homeostasis. It is becoming increasingly clear that interactions between transmembrane proteins on the surfaces of adjacent beta cells are important determinants of beta-cell function.
Elucidation of the roles of particular transcellular interactions by knockdown, knockout or overexpression studies in cultured beta cells or in vivo necessitates direct perturbation of mRNA and protein expression, potentially affecting beta-cell health and/or function in ways that could confound analyses of the effects of specific interactions. These approaches also alter levels of the intracellular domains of the targeted proteins and may prevent effects due to interactions between proteins within the same cell membrane to be distinguished from the effects of transcellular interactions.
Here a method for determining the effect of specific transcellular interactions on the insulin secreting capacity and responsiveness of beta cells is presented. This method is applicable to beta-cell lines, such as INS-1 cells, and to dissociated primary beta cells. It is based on coculture models developed by neurobiologists, who found that exposure of cultured neurons to specific neuronal proteins expressed on HEK293 (or COS) cell layers identified proteins important for driving synapse formation. Given the parallels between the secretory machinery of neuronal synapses and of beta cells, we reasoned that beta-cell functional maturation might be driven by similar transcellular interactions. We developed a system where beta cells are cultured on a layer of HEK293 cells expressing a protein of interest. In this model, the beta-cell cytoplasm is untouched while extracellular protein-protein interactions are manipulated. Although we focus here primarily on studies of glucose-stimulated insulin secretion, other processes can be analyzed; for example, changes in gene expression as determined by immunoblotting or qPCR.

Transcellular protein interactions are important determinants of pancreatic beta-cell function. Detailed here is a method&#x2014;adapted from a coculture model of synaptogenesis&#x2014;for investigating how specific transmembrane proteins influence insulin secretion. Transfected HEK293 cells express proteins of interest; beta cells do not need to be transfected or otherwise directly perturbed.

Interactions between cell-surface proteins help coordinate the function of neighboring cells. Pancreatic beta cells are clustered together within ...

Combined Intravital Microscopy and Contrast-enhanced Ultrasonography of the Mouse Hindlimb to Study Insulin-induced Vasodilation and Muscle Perfusion

It has been demonstrated that insulin's vascular actions contribute to regulation of insulin sensitivity. Insulin's effects on muscle perfusion regulate postprandial delivery of nutrients and hormones to insulin-sensitive tissues. We here describe a technique for combining intravital microscopy (IVM) and contrast-enhanced ultrasonography (CEUS) of the adductor compartment of the mouse hindlimb to simultaneously visualize muscle resistance arteries and perfusion of the microcirculation in vivo. Simultaneously assessing insulin's effect at multiple levels of the vascular tree is important to study relationships between insulin's multiple vasoactive effects and muscle perfusion. Experiments in this study were performed in mice. First, the tail vein cannula is inserted for the infusion of anesthesia, vasoactive compounds and ultrasound contrast agent (lipid-encapsulated microbubbles). Second, a small incision is made in the groin area to expose the arterial tree of the adductor muscle compartment. The ultrasound probe is then positioned at the contralateral upper hindlimb to view the muscles in cross-section. To assess baseline parameters, the arterial diameter is assessed and microbubbles are subsequently infused at a constant rate to estimate muscle blood flow and microvascular blood volume (MBV). When applied before and during a hyperinsulinemic-euglycemic clamp, combined IVM and CEUS allow assessment of insulin-induced changes of arterial diameter, microvascular muscle perfusion and whole-body insulin sensitivity. Moreover, the temporal relationship between responses of the microcirculation and the resistance arteries to insulin can be quantified. It is also possible to follow-up the mice longitudinally in time, making it a valuable tool to study changes in vascular and whole-body insulin sensitivity.

Insulin-induced vasodilation regulates muscle perfusion and increases the microvascular surface area (microvascular recruitment) available for solute exchange between blood and tissue interstitium. Combined intravital microscopy and contrast-enhanced ultrasonography is presented to simultaneously assess insulin&#39;s action at the larger vessels and the microcirculation in vivo.

It has been demonstrated that insulin's vascular actions contribute to regulation of insulin sensitivity. Insulin's effects on muscle perfusion regulate ...

Cardiac Magnetic Resonance Imaging at 7 Tesla

CMR at an ultra-high field (magnetic field strength B0&#160;&#8805; 7 Tesla) benefits from the signal-to-noise ratio (SNR) advantage inherent at higher magnetic field strengths and potentially provides improved signal contrast and spatial resolution. While promising results have been achieved, ultra-high field CMR is challenging due to energy deposition constraints and physical phenomena such as transmission field non-uniformities and magnetic field inhomogeneities. In addition, the magneto-hydrodynamic effect renders the synchronization of the data acquisition with the cardiac motion difficult. The challenges are currently addressed by explorations into novel magnetic resonance technology. If all impediments can be overcome, ultra-high field CMR may generate new opportunities for functional CMR, myocardial tissue characterization, microstructure imaging or metabolic imaging. Recognizing this potential, we show that multi-channel radio frequency (RF) coil technology tailored for CMR at 7 Tesla together with higher order B0 shimming and a backup signal for cardiac triggering facilitates high fidelity functional CMR. With the proposed setup, cardiac chamber quantification can be accomplished in examination times similar to those achieved at lower field strengths. To share this experience and to support the dissemination of this expertise, this work describes our setup and protocol tailored for functional CMR at 7 Tesla.

The sensitivity gain inherent to ultrahigh field magnetic resonance holds promise for high spatial resolution imaging of the heart. Here, we describe a protocol customized for functional cardiovascular magnetic resonance (CMR) at 7 Tesla using an advanced multi-channel radio-frequency coil, magnetic field shimming and a triggering concept.

CMR at an ultra-high field (magnetic field strength B0&#160;&#8805; 7 Tesla) benefits from the signal-to-noise ratio (SNR) advantage inherent at higher ...

Studying the Hypothalamic Insulin Signal to Peripheral Glucose Intolerance with a Continuous Drug Infusion System into the Mouse Brain

Insulin regulates systematic metabolism in the hypothalamus and the peripheral insulin response. An inflammatory reaction in peripheral adipose tissues contributes to type 2 diabetes mellitus (T2DM) development and appetite regulation in the hypothalamus. Chemokine CCL5 and C-C chemokine receptor type 5 (CCR5) levels have been suggested to mediate arteriosclerosis and glucose intolerance in type 2 diabetes mellitus (T2DM). In addition, CCL5 plays a neuroendocrine role in the hypothalamus by regulating food intake and body temperature, thus, prompting us to investigate its function in hypothalamic insulin signaling and the regulation of peripheral glucose metabolism.
The micro-osmotic pump brain infusion system is a quick and precise way to manipulate CCL5 function and study its effect in the brain. It also provides a convenient alternative approach to generating a transgenic knockout animal. In this system, CCL5 signaling was blocked by intracerebroventricular (ICV) infusion of its antagonist, MetCCL5, using a micro-osmotic pump. The peripheral glucose metabolism and insulin responsiveness was detected by the Oral Glucose Tolerance Test (OGTT) and Insulin Tolerance Test (ITT). Insulin signaling activity was then analyzed by protein blot from tissue samples derived from the animals.
After 7-14 days of MetCCL5 infusion, the glucose metabolism and insulin responsiveness was impaired in mice, as seen in the results of the OGTT and ITT. The IRS-1 serine302 phosphorylation was increased and the Akt activity was reduced in mice hypothalamic neurons following CCL5 inhibition. Altogether, our data suggest that blocking CCL5 in the mouse brain increases the phosphorylation of IRS-1 S302 and interrupts hypothalamic insulin signaling, leading to a decrease in insulin function in peripheral tissues as well as the impairment of glucose metabolism.

This protocol studies the role of chemokine (C-C motif) ligand 5 (CCL5) in the hypothalamus by delivering an antagonist, MetCCL5, into the mouse brain using a micro-osmotic pump brain infusion system. This transient inhibition of CCL5 activity interrupted hypothalamic insulin signaling, leading to glucose intolerance and peripheral systemic insulin sensitivity.

Insulin regulates systematic metabolism in the hypothalamus and the peripheral insulin response. An inflammatory reaction in peripheral adipose tissues ...

Endotoxin Activity Assay for the Detection of Whole Blood Endotoxemia in Critically Ill Patients

Lipopolysaccharide, also known as endotoxin, is a fundamental component of gram-negative bacteria and plays a crucial role in the development of sepsis and septic shock. The early identification of an infectious process that is rapidly evolving to a critical illness might prompt a quicker and more intensive treatment, thereby potentially leading to better patient outcomes. The Endotoxin Activity (EA) assay can be used at the bedside as a reliable biomarker of systemic endotoxemia. The detection of elevated endotoxin activity levels has been repeatedly shown to be associated with an increased disease severity in patients with sepsis and septic shock. The assay is quick and easy to perform. Briefly, after sampling, an aliquot of whole blood is mixed with an anti-endotoxin antibody and with added LPS. Endotoxin activity is measured as the relative oxidative burst of primed neutrophils as detected by chemioluminescence. The assay&#39;s output is expressed on a scale from 0 (absent) to 1 (maximal) and categorized as &#8220;low&#8221; (&#60;0.4 units), &#8220;intermediate&#8221; (0.4&#8211;0.59 units), or &#8220;high&#8221; (&#8805;0.6 units). The detailed methodology and rationale for the implementation of the EA assay are reported in this manuscript.

We hereby present a protocol to measure at the bedside the endotoxin activity of human whole blood samples. The Endotoxin Activity assay is a simple test to perform and may be a useful biomarker in critically ill patients with sepsis.

Lipopolysaccharide, also known as endotoxin, is a fundamental component of gram-negative bacteria and plays a crucial role in the development of sepsis ...

Mechanisms Underlying Gut Hormone Secretion Using the Isolated Perfused Rat Small Intestine

The gut is the largest endocrine organ of the body, producing more than 15 different peptide hormones that regulate appetite and food intake, digestion, nutrient absorption and distribution, and post-prandial glucose excursions. Understanding the molecular mechanisms that regulate gut hormone secretion is fundamental for understanding and translating gut hormone physiology. Traditionally, the mechanisms underlying gut hormone secretion are either studied in vivo (in experimental animals or humans) or using gut hormone-secreting primary mucosal cell cultures or cell lines. Here, we introduce an isolated perfused rat small intestine as an alternative method for studying gut hormone secretion. The virtues of this model are that it relies on the intact gut, meaning that it recapitulates most of the physiologically important parameters responsible for the secretion in in vivo studies, including mucosal polarization, paracrine relationships and routes of perfusion/stimulus exposure. In addition, and unlike in vivo studies, the isolated perfused rat small intestine allows for almost complete experimental control and direct assessment of secretion. In contrast to in vitro studies, it is possible to study both the magnitude and the dynamics of secretion and to address important questions, such as what stimuli cause secretion of different gut hormones, from which side of the gut (luminal or vascular) is secretion stimulated, and to analyze in detail molecular sensors underlying the secretory response. In addition, the preparation is a powerful model for the study of intestinal absorption and details regarding the dynamics of intestinal absorption including the responsible transporters.

Here, we present a powerful and physiological model to study the molecular mechanisms underlying gut hormone secretion and intestinal absorption &#8212; the isolated perfused rat small intestine.

The gut is the largest endocrine organ of the body, producing more than 15 different peptide hormones that regulate appetite and food intake, digestion, ...

Human Fetal Blood Flow Quantification with Magnetic Resonance Imaging and Motion Compensation

Magnetic resonance imaging (MRI) is an important tool for the clinical assessment of cardiovascular morphology and heart function. It is also the recognized standard-of-care for blood flow quantification based on phase contrast MRI. While such measurement of blood flow has been possible in adults for decades, methods to extend this capability to fetal blood flow have only recently been developed.
Fetal blood flow quantification in major vessels is important for monitoring fetal pathologies such as congenital heart disease (CHD) and fetal growth restriction (FGR). CHD causes alterations in the cardiac structure and vasculature that change the course of blood in the fetus. In FGR, the path of blood flow is altered through the dilation of shunts such that the oxygenated blood supply to the brain is increased. Blood flow quantification enables assessment of the severity of the fetal pathology, which in turn allows for suitable&#160;in utero&#160;patient management and planning for postnatal care.
The primary challenges of applying phase contrast MRI to the human fetus include small blood vessel size, high fetal heart rate, potential MRI data corruption due to maternal respiration, unpredictable fetal movements, and lack of conventional cardiac gating methods to synchronize data acquisition. Here, we describe recent technical developments from our lab that have enabled the quantification of fetal blood flow using phase contrast MRI, including advances in accelerated imaging, motion compensation, and cardiac gating.

Here we present a protocol for measuring fetal blood flow rapidly with MRI and retrospectively performing motion correction and cardiac gating.