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>
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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>

We thank Nicolas Pierre (Cisbio Bioassays) for helpful advice and Dr. Pierre Maechler (University of Geneva) for generously providing INS-1E cells. This work was supported by funding from the Department of Defense (grant PR141292 to Z.F.), and the John F. and Nancy A. Emmerling Fund of The Pittsburgh Foundation (to Z.F.).

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.

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9.1K vues.  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...