The authors would like to acknowledge the strong support of the DHMRI CLAS animal care staff, Facility Manager Mr. Daniel Peralta and attending veterinarian, Dr. Glicerio Ignacio, DVM MRCVS.

All animal procedures were approved by the David H. Murdock Research Institute IACUC located on the North Carolina Research Campus (NCRC), under protocol 14-017, Characterization of a nonhuman primate model of diabetes and prediabetes/insulin resistance and efficacy of therapeutics to improve insulin sensitivity and metabolic function.
1. Animal Selection and Study Preparation
<ol>
	<li>Select diet and weight stable animals based on monthly food intake and body weight records. 
	NOTE: Animals that have exhibited a recent decline in appetite should not be characterized until their food intake has stabilized.
	<ol>
		<li>For mature animals (&#62; 5 - 6 yr), do not select animals whose body weights between consecutive months differ by more than 10% without first examining the monkey and ruling out causes other than changing metabolic status for the dramatic change in weight.</li>
	</ol>
	</li>
	<li>For glucose, insulin and c-peptide analytes, prepare K2EDTA sample collection tubes with protease inhibitor (Aprotinin and DPP4I). 
	NOTE: The DPP4I + Aprotinin cocktail provides a broad spectrum of protease inhibition should this be required for additional analytes (glucagon, GLP-1). In the event that additional analytes are not collected, the blood tubes should be prepared in the same way to maintain consistency in sample collection. Samples for assays not validated for this method should be collected separately, according to the recommendations of the manufacturer.
	<ol>
		<li>Prepare the protease inhibitor cocktail by mixing 100 mg lyophilized Aprotinin with 10 ml of DPP4I. Add 10 &#181;l of the Aprotinin + DPP4I mixture to each blood tube for every milliliter of blood collected.</li>
		<li>Add an additional 10 &#181;l of the protease inhibitor cocktail to each tube for possible collection overage. Store the treated-blood tubes at -20 &#176;C until use. Keep the tubes on wet ice during the procedure and spin at 4 &#176;C.</li>
		<li>Use a serum separator tube to collect a blood sample at baseline for standard serum chemistry analysis. For the Complete Blood Cell count (CBC), use a standard K2EDTA without protease inhibitors. Use cryovials to aliquot plasma and serum after the blood samples have been spun down.</li>
		<li>Label the blood tubes and the cryovials appropriately with the animal identification, date, procedure, timepoint, and sample volume. Label the cryovials with the analyte(s) in plasma for appropriate assay.</li>
	</ol>
	</li>
	<li>Prepare the heparinized saline flush by injecting 0.15 ml of 1,000 USP units per ml heparin into a 250 ml bag of normal saline. Obtain a solution of 0.06 mg heparin/ml. Draw 40 - 60 ml of this solution into a saline lock for flushing between samples. Draw an additional 1 ml and 5 ml into separate syringes for flushing the dextrose infusion port before and after the infusion, respectively.</li>
</ol>
2. Animal Sedation and Preparation
<ol>
	<li>Remove food from the animal&#39;s cage no less than 14 hr before the procedure, and no more than 18 hr. 
	NOTE: It is important that animals be fasted for the procedure to avoid any post-prandial variation in glycemic values. It is also a precaution to avoid regurgitation and aspiration of stomach contents while anesthetized.</li>
	<li>Sedate animals for the duration of the IVGTT procedure with ketamine given intramuscularly as a general anesthetic, at 10 mg/kg. Administer additional ketamine (5 - 10 mg/kg) at intervals of 20 - 30 min, or as needed, during the procedure.
	<ol>
		<li>Weigh the sedated animal. Place the animal in a laterally recumbent position on a heated procedure table.</li>
		<li>Monitor clinical parameters every 15 to 20 min to ensure the animal is in a stable plane of anesthesia. Measure heart rate (100 - 200 bpm) and SPO2 (&#62; 92%) with a pulse oximeter. Measure respiratory rate (20 - 50 breaths/min) with a stopwatch, counting respirations visually or by hand over fifteen seconds and multiplying by four. Measure temperature (&#62; 97 &#176;F) rectally. Monitor the color of the mucous membrane around the gum and lips (moist, pink).</li>
	</ol>
	</li>
	<li>Prepare two cannula sites. Use hair clippers to trim the hair from the area of interest where the catheter will be inserted, and sterilize the entire region with alternating scrubs of chlorhexidine and 70% alcohol.
	<ol>
		<li>Place one catheter in the region of the left or right cephalic or saphenous veins and attach it to a heparin saline flush (0.06 mg heparin/ml) with a three-way stopcock. This is the sampling blood draw site.</li>
		<li>Place the second catheter in another leg or arm in the region of the cephalic or saphenous veins and attach a port. Use this site for the dextrose infusion. Use a small, 1 ml flush of heparinized saline to keep the cannula patent prior to dextrose infusion.</li>
	</ol>
	</li>
</ol>
3. IVGTT Procedure
NOTE: The IVGTT procedure consists of 8 blood draw sampling time-points (Table 1).
<ol>
	<li>Take the baseline sample and use a hand held glucometer to measure the fasting blood glucose level. Obtain a serum sample for standard chemistry analysis, as well as a whole blood sample for a CBC in order to assess the overall health of the animal. Collect plasma samples to assay glucose and insulin levels from the baseline sample using a kit validated for use with macaques as per the manufacturer&#39;s instructions 8, 9. 
	NOTE: It is important to have a pre-draw of 0.5 ml taken from the cannula prior to taking any sample for blood collection to remove residual blood or heparin in the dead-space of the cannula.</li>
	<li>After obtaining the baseline sample, infuse the dose of 50% dextrose (250 mg/kg) over 30 sec into the dextrose infusion port. 
	NOTE: Higher dose models (500 mg/kg) can be used, though the dose should be fixed across procedures in order to make longitudinal comparisons.
	<ol>
		<li>Flush the infusion port with 5 ml of heparinized saline to make sure that there is no dextrose left in the port. The end of the infusion is the T0. Have the technician replace the gloves, as residual dextrose from the infusion may contaminate subsequent blood samples.</li>
	</ol>
	</li>
	<li>The first post-infusion sample time point is at T3 min, from the end of dextrose infusion, followed by T5 min, T7 min, T10 min, T15 min, T20 min, and the last sample time point is at T30 min. Collect plasma from each timepoint to assay glucose and insulin levels with the baseline sample (see step 3.1).
	<ol>
		<li>At the T3 min time point, use the hand held glucometer to once again check the blood glucose level. 
		NOTE: The glucometer readings at baseline and T3 are only to confirm the infusion of the dextrose. The blood glucose level at the T3 min time point should be ~100 mg/dl higher compared to the fasting baseline plasma glucose level.</li>
	</ol>
	</li>
</ol>
4. Animal Recovery and Sample Processing
<ol>
	<li>Remove the cannulas and apply pressure to the catheterized sites for hemostasis after the T30 min time-point. Monitor the animal until it has regained consciousness and is sitting up. Offer feed once the animal is fully recovered.</li>
	<li>Immediately place each whole blood sample into K2EDTA tubes on ice. Centrifuge at 3,000 rpm at a temperature of 4 &#176;C within 10 min of collection. Aliquot plasma samples into cryovials, freeze and store at -80 &#176;C until analysis.
	<ol>
		<li>Allow the blood into the serum tube for standard serum chemistry analysis to sit at room temperature for no less than 20 min and no more than 30 min before centrifugation at 3,000 rpm at RT. Freeze the serum samples until assayed within 48 hr of collection. 
		NOTE: Refrigerate the whole blood samples collected for CBC analysis until assayed within 24 hr of collection.</li>
	</ol>
	</li>
</ol>
5. Data Treatment
<ol>
	<li>After establishing the plasma insulin and glucose curves, determine the glucose clearance rate K from the slope of the natural log of glucose values above baseline 16, 17. 
	NOTE: A healthy NHP may be expected to have a glucose clearance rate K well above 1, often greater than 2 or more, as a healthy animal will often return to their baseline glucose values within 30 min. As insulin production drops off, the glucose clearance rate K will drop more dramatically, falling below 1.</li>
	<li>Calculate the AUC as a whole, as the sum of totals of the area of the trapezoids representing the area under the curve of each line segment between time-points, through T30 16, 17. 
	NOTE: Traditionally, the AUC of the first ten minutes of the procedure is considered the acute insulin response to glucose (AIR), while the AUC from the last 20 min of the procedure is considered the late insulin response (LIR). As the animal becomes more dysmetabolic, the insulin AUC will increase, reflecting compensation for increasing insulin insensitivity. As the animal transitions to overt diabetes, however, the AUC will decrease, often initially in the acute insulin phase, captured by the AIR.</li>
</ol>

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<li>Wang, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Quantification+of+beta-cell+insulin+secretory+function+using+a+graded+glucose-infusion+with+C-peptide+deconvolution+in+dysmetabolic%2C+and+diabetic+cynomolgus+monkeys%5BTitle%5D)+AND+%22Diabetology+and+Metabolic+Syn%22%5BJournal%5D)">Quantification of beta-cell insulin secretory function using a graded glucose-infusion with C-peptide deconvolution in dysmetabolic, and diabetic cynomolgus monkeys.</a> Diabetology and Metabolic Syn. 5, 40(2013).</li>
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</ol>

The authors are affiliated with a contract research organization (Crown Bioscience) active in the field of metabolic disease.

The IVGTT assesses the capacity of glucose-stimulated insulin release by a single dextrose infusion based on body weight 5, 12, 13. From the assay, the fasting blood glucose and insulin level is attained, and it allows an assessment of the animal&#39;s capacity to release insulin and return the elevated glucose level towards baseline. This provides the user with information to characterize the animal as a normal glucose and insulin level healthy control, a hyperinsulinemic dysmetabolic animal with normoglycemi...

The IVGTT is a convenient functional assay that is routinely used to determine the &#946;-cell function in humans at different metabolic states 5, 7. In animal models of T2D, it is well recognized as a tool to characterize animals that show metabolic disease progression from a healthy to a dysmetabolic hyperglycemic state 8, 9. The closest animal model of T2D is demonstrated in nonhuman primates (NHPs), of which rhesus and cynomolgus macaques are notable examples. These animals naturally develop T2D with the same risk factors of age and obesity contributing to its incidence as in humans 10. Furthermore, there is a similar disease progression and pancreatic pathology showing amyloid deposits as the dysmetabolic disease progresses 11.
Here we report on our standard method of performing an IVGTT in NHPs as part of our colony characterization of metabolic status in these animals. This method is easy to perform relative to other, more time consuming and costly techniques 2. The IVGTT is useful for characterizing a large colony of animals rapidly and frequently. When taken into consideration with the level of glycated hemoglobin (HbA1C), the animal&#39;s diet and food intake history, as well as their percent lean mass and body fat, the IVGTT is normally sufficient for characterizing an animal&#39;s metabolic status and progression toward overt diabetes 6, 8.
HbA1C represents the average glycemic level over the life of a red blood cell, providing a reliable measure of glucose levels over the previous six weeks to three months. When measured from the fasted baseline blood sample of the IVGTT, this value provides a window into glycemic control during the months between procedures. If the animal has transitioned from dysmetabolic to diabetic since their last IVGTT, an HbA1C value much higher than their previous value would indicate that the transition began soon after their last IVGTT, whereas, an HbA1C value closer to their previous value would indicate that they have only recently transitioned. In general, in rhesus macaques, HbA1C values greater than 6% are considered abnormal, and indicate poor glycemic control 10, 23.
Glycemic levels should be interpreted within the context of the behavior and general health of the animal as a whole. Diabetic macaques &#8212; like humans &#8212; exhibit hyperphagia, polydipsia, and polyuria. Group housing of animals provides significant challenges to measurement of these indicators and the individual care required for dysmetabolic and diabetic monkeys. We recommend singly housing the animals in order that more personalized care may be provided, and behavioral markers of the health of the monkey more easily be monitored 8. Additionally, diabetic macaques will exhibit weight loss, as well as an elevated lipid profile (increased cholesterol, hypertriglyceridemia) and disturbed mineral metabolism in serum chemistry. It is important to measure markers of liver and kidney function in serum chemistry, as damage to these organs are often complications of advancing metabolic disorder/diabetes, and may be co-determinants of glycemic, lipid and mineral imbalances 9, 11, 18, 24.
When using this method, the historic values generated from multiple, frequent characterizations over the life of a monkey are of particular value. If other procedures, such as a glucose clamp or graded glucose infusion (GGI), are needed to fully assess an animal&#39;s health, it is commonly upon initial characterization when their history is unavailable. However, once a baseline has been established, repeated IVGTTs of a frequency of every three months are normally sufficient to track an animal&#39;s progress. This is particularly important when the animals are enrolled into multiple studies throughout a calendar year based upon their metabolic status. While their health may remain relatively stable for years at a time, when the metabolic status of an animal worsens, a dramatic increase in insulin resistance and glucose intolerance can occur very rapidly. HbA1C values allow for some interpolation of the decline or improvement of the health status of the animal between procedures scheduled three months apart. For this reason, this method is ideal for characterizing animals used in multiple, longitudinal studies over the course of their natural lifespan.

<table><tbody><tr><td>Allegra X-15R Centrifuge</td><td></td><td></td><td>plasma: 4 &amp;#176;C at 3,000 rpm for 10 min</td></tr><tr><td>Sorvall ST16R Centrifuge</td><td></td><td></td><td>serum: 22 &amp;#176;C at 3,000 rpm for 10 min</td></tr><tr><td>Thermo Scientific -86 &amp;#176;C Freezer, Forma 88000 Series</td><td></td><td>Model: 88500A</td><td></td></tr><tr><td>Dextrose 50% (D50)</td><td>Webster</td><td>07-8008986</td><td>I.V. glucose infusate</td></tr><tr><td>3 ml Luer Lock Syringe</td><td>Midwest Veterinary Suppy</td><td></td><td>serial blood draws</td></tr><tr><td>5 ml Luer Lock Syringe</td><td>Midwest Veterinary Suppy</td><td></td><td>heparinized saline flush</td></tr><tr><td>10 ml Luer Lock Syringe</td><td>Midwest Veterinary Suppy</td><td></td><td>delivery of I.V. D50</td></tr><tr><td>Gauze sponges 2 x 2</td><td>Midwest Veterinary Suppy</td><td>366.23000.4</td><td>Used Dry, w/ 70% Alcohol, and 2% Chlorohex Solution</td></tr><tr><td>4 ml serum separator tubes&amp;nbsp;</td><td>Midwest Veterinary Supply</td><td>366.45000.4</td><td>blood collection tube for superchem panel</td></tr><tr><td>K&lt;sub&gt;2&lt;/sub&gt;EDTA, 2 ml</td><td>VWR</td><td>95057-239</td><td>blood collection tubes</td></tr><tr><td>Aprotinin, 100 mg</td><td>Sigma</td><td>A1153-100MG</td><td>blood collection tube protease additive</td></tr><tr><td>22 G x 1&quot; Catheters</td><td>Midwest Veterinary Suppy</td><td>193.75250.2</td><td>I.V. catheter&amp;nbsp;</td></tr><tr><td>Injection Plug W/ Cap</td><td>Midwest Veterinary Suppy</td><td>001.11500.2</td><td>%50 dextrose infusion port</td></tr><tr><td>Porus Tape, 1/2&quot; x 10 yd</td><td>Midwest Veterinary Suppy</td><td>001.85000.2</td><td>maintain adherance of catheters and hep. Locks</td></tr><tr><td>Chlorhexidine Solution 2%</td><td>Midwest Veterinary Suppy</td><td>193.08855.3</td><td>prep catheter site</td></tr><tr><td>70% Ethanol</td><td>VWR</td><td>71001-654</td><td>prep catheter site</td></tr><tr><td>tourniquet</td><td>Webster</td><td>07-8003432</td><td></td></tr><tr><td>3-way stopcock</td><td>Midwest Veterinary Supply</td><td>366.28510.4</td><td>hep. lock</td></tr><tr><td>37&quot; extension set</td><td>Webster</td><td>07-8454200</td><td>hep. lock</td></tr><tr><td>Exel 50-60cc LL Syringes</td><td>Midwest Veterinary Suppy</td><td>001.12250.2</td><td>Heparinized saline flush</td></tr><tr><td>250 ml bag 0.9% saline</td><td>Webster</td><td>07-8365593</td><td>flush</td></tr><tr><td>1,000 U Heparin, 10 ml</td><td>Webster</td><td>07-883-4916</td><td></td></tr><tr><td>Ketamine (Ketaset) 100&amp;nbsp;mg/ml</td><td>Fort Dodge</td><td>(AV ordered)</td><td></td></tr><tr><td>Precision Xtra glucose test strips 50/bx</td><td>Abbott (American Diabetes Wholesale)</td><td>9381599728K7</td><td>test baseline/T3 blood glucose levels</td></tr><tr><td>Masimo Rad 57</td><td>DRE</td><td>6052057V</td><td>pulse-oximeter</td></tr><tr><td>Pavia rectal thermometer</td><td>Patterson</td><td>07-8391335</td><td></td></tr><tr><td>Precision Xtra Glucometer</td><td>Abbott</td><td>9381599728K7</td><td>Handheld glucometer</td></tr></tbody></table>

characterization of metabolic status in nonhuman primates with the intravenous glucose tolerance test

The intravenous glucose tolerance test (IVGTT) plays a key role in the characterization of glucose homeostasis. When taken together with serum biochemical profiles, inclusive of blood glucose levels in both the fed and fasted state, HbA1c, insulin levels, clinical history of diet, body composition, and body weight status, an assessment of normal and abnormal glycemic control can be made. Interpretation of an IVGTT is done through measurement of changes in glucose and insulin levels over time in relation to the dextrose challenge. Critical components to be considered are: peak glucose and insulin levels reached in relation to T0 (end of glucose infusion), the glucose clearance rate K derived from the slope of rapid glucose clearance in the first 20 min (T1 to T20), the time to return to glucose baseline, and the area under the curve (AUC). These IVGTT measures will show characteristic changes as glucose homeostasis moves from a healthy to a diseased metabolic state5. Herein we will describe the characterization of nonhuman primates (Rhesus and Cynomolgus macaques), which are the most relevant animal model of Type II diabetes (T2D) in humans and the IVGTT and clinical profiles of these animals from a lean healthy, to obese dysmetabolic, and T2D state 8, 10, 11.

The results shown in Figure 1 are demonstrative of typical glucose and insulin curves from mature, healthy and diabetic cynomolgus macaques over the course of a 30 min IVGTT. Data from healthy and advanced diabetic monkeys are shown in order to contrast the obvious differences between animals from both extreme ends of the range of metabolic characterization. This IVGTT protocol has been used successfully by the authors in rhesus macaques with similar results.
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Characterization of Metabolic Status in Nonhuman Primates with the Intravenous Glucose Tolerance Test

The goal of this protocol is to present a standard method to perform intravenous glucose tolerance tests (IVGTTs) to assess glycemic control in nonhuman primates and assess their metabolic status from healthy to dysmetabolic.

The intravenous glucose tolerance test (IVGTT) plays a key role in the characterization of glucose homeostasis. When taken together with serum biochemical ...

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Research

JoVE Journal

Medicine

10.9K Views.  Crown Bioscience.  Het doel van dit protocol is om een ​​standaard methode te presenteren aan intraveneuze glucose tolerantie testen (IVGTTs) uit te voeren om de glykemische controle van niet-menselijke primaten te evalueren en hun metabolische status dysmetabolic beoordelen van gezonde. 

Video: Characterization of Metabolic Status in Nonhuman Primates with the Intravenous Glucose Tolerance Test

Analysis of Non-Human Primate Pancreatic Islet Oxygen Consumption

The measurement of oxygen consumption in spheroid clusters of cells, such as ex vivo pancreatic islets, has historically been challenging. We demonstrate the measurement of islet oxygen consumption using a 96-well microplate designed for the measurement of oxygen consumption in spheroids. In this assay, spheroid microplates are coated with a cell and tissue adhesive on the day prior to the assay. We utilize a small volume of adhesive solution to encourage islet adherence to only the bottom of the well. On the day of the assay, 15 islets are loaded directly into the base of each well using a technique that ensures optimal positioning of islets and accurate measurement of oxygen consumption. Various aspects of mitochondrial respiration are probed pharmacologically in non-human primate islets, including ATP-dependent respiration, maximal respiration, and proton leak. This method allows for consistent, reproducible results using only a small number of islets per well. It can theoretically be applied to any cultured spheroids of similar size.

This protocol demonstrates the accurate and reproducible measurement of oxygen consumption in non-human primate pancreatic islets. The islet loading techniques and coating of the microplate provide a framework for efficient measurement of respiration in other types of cultured spheroids.

The measurement of oxygen consumption in spheroid clusters of cells, such as ex vivo pancreatic islets, has historically been challenging. We demonstrate ...

Developmental Biology

Intraperitoneal Glucose Tolerance Test, Measurement of Lung Function, and Fixation of the Lung to Study the Impact of Obesity and Impaired Metabolism on Pulmonary Outcomes

Obesity and respiratory disorders are major health problems. Obesity is becoming an emerging epidemic with an expected number of over 1 billion obese individuals worldwide by 2030, thus representing a growing socioeconomic burden. Simultaneously, obesity-related comorbidities, including diabetes as well as heart and chronic lung diseases, are continuously on the rise. Although obesity has been associated with increased risk for asthma exacerbations, worsening of respiratory symptoms, and poor control, the functional role of obesity and perturbed metabolism in the pathogenesis of chronic lung disease is often underestimated, and underlying molecular mechanisms remain elusive. This article aims to present methods to assess the effect of obesity on metabolism, as well as lung structure and function. Here, we describe three techniques for mice studies: (1) assessment of intraperitoneal glucose tolerance (ipGTT) to analyze the effect of obesity on glucose metabolism; (2) measurement of airway resistance (Res) and respiratory system compliance (Cdyn) to analyze the effect of obesity on lung function; and (3) preparation and fixation of the lung for subsequent quantitative histological assessment. Obesity-related lung diseases are probably multifactorial, stemming from systemic inflammatory and metabolic dysregulation that potentially adversely influence lung function and the response to therapy. Therefore, a standardized methodology to study molecular mechanisms and the effect of novel treatments is essential.

The incidence of obesity is rising and increases the risk of chronic lung diseases. To establish the underlying mechanisms and preventive strategies, well-defined animal models are needed. Here, we provide three methods (glucose-tolerance-test, body plethysmography, and lung fixation) to study the effect of obesity on pulmonary outcomes in mice.

Obesity and respiratory disorders are major health problems. Obesity is becoming an emerging epidemic with an expected number of over 1 billion obese ...

Immunology and Infection

Determining Glucose Metabolism Kinetics Using 18F-FDG Micro-PET/CT

This paper describes the use of 18F-FDG and micro-PET/CT imaging to determine in vivo glucose metabolism kinetics in mice (and is transferable to rats). Impaired uptake and metabolism of glucose in multiple organ systems due to insulin resistance is a hallmark of type 2 diabetes. The ability of this technique to extract an image-derived input function from the vena cava using an iterative deconvolution method eliminates the requirement of the collection of arterial blood samples. Fitting of tissue and vena cava time activity curves to a two-tissue, three compartment model permits the estimation of kinetic micro-parameters related to the 18F-FDG uptake from the plasma to the intracellular space, the rate of transport from intracellular space to plasma and the rate of 18F-FDG phosphorylation. This methodology allows for multiple measures of glucose uptake and metabolism kinetics in the context of longitudinal studies and also provides insights into the efficacy of therapeutic interventions.

Determining Glucose Metabolism Kinetics Using 18F-FDG Micro-PET/CT

This study describes a protocol that uses 18F-FDG and positron emission tomography/computed tomography (PET/CT) imaging, together with kinetic modelling, to quantify the in vivo, real-time uptake of 18F-FDG into tissues.

This paper describes the use of 18F-FDG and micro-PET/CT imaging to determine in vivo glucose metabolism kinetics in mice (and is transferable to rats). ...

Study of In Vivo Glucose Metabolism in High-fat Diet-fed Mice Using Oral Glucose Tolerance Test (OGTT) and Insulin Tolerance Test (ITT)

Obesity represents the most important single risk factor in the pathogenesis of type 2 diabetes, a disease which is characterized by a resistance to insulin-stimulated glucose uptake and a gross decompensation of systemic glucose metabolism. Despite considerable progress in the understanding of glucose metabolism, the molecular mechanisms of its regulation in health and disease remain under-investigated, while novel approaches to prevent and treat diabetes are urgently needed. Diet derived glucose stimulates the pancreatic secretion of insulin, which serves as the principal regulator of cellular anabolic processes during the fed-state and thus balances blood glucose levels to maintain systemic energy status. Chronic overfeeding triggers meta-inflammation, which leads to alterations in peripheral insulin receptor-associated signaling and thus reduces the sensitivity to insulin-mediated glucose disposal. These events ultimately result in elevated fasting glucose and insulin levels as well as a reduction in glucose tolerance, which in turn serve as important indicators of insulin resistance. Here, we present a protocol for the generation and metabolic characterization of high-fat diet (HFD)-fed mice as a frequently used model of diet-induced insulin resistance. We illustrate in detail the oral glucose tolerance test (OGTT), which monitors the peripheral disposal of an orally administered glucose load and insulin secretion over time. Additionally, we present a protocol for the insulin tolerance test (ITT) to monitor whole-body insulin action. Together, these methods and their downstream applications represent powerful tools to characterize the general metabolic phenotype of mice as well as to specifically assess alterations in glucose metabolism. They may be especially useful in the broad research field of insulin resistance, diabetes and obesity to provide a better understanding of pathogenesis as well as to test the effects of therapeutic interventions.

Study of In Vivo Glucose Metabolism in High-fat Diet-fed Mice Using Oral Glucose Tolerance Test OGTT and Insulin Tolerance Test ITT

The current article describes the generation and metabolic characterization of high-fat diet-fed mice as a model of diet-induced insulin resistance and obesity. It further features detailed protocols to perform the oral glucose tolerance test and the insulin tolerance test, monitoring whole-body alterations of glucose metabolism in vivo.

Obesity represents the most important single risk factor in the pathogenesis of type 2 diabetes, a disease which is characterized by a resistance to ...

Body Composition and Metabolic Caging Analysis in High Fat Fed Mice

Alterations to body composition (fat or lean mass), metabolic parameters such as whole-body oxygen consumption, energy expenditure, and substrate utilization, and behaviors such as food intake and physical activity can provide important information regarding the underlying mechanisms of disease. Given the importance of body composition and metabolism to the development of obesity and its subsequent sequelae, it is necessary to make accurate measures of these parameters in the pre-clinical research setting. Advances in technology over the past few decades have made it possible to derive these measures in rodent models in a non-invasive and longitudinal fashion. Consequently, these metabolic measures have proven useful when assessing the response of genetic manipulations (for example knockout or transgenic mice, viral knock-down or overexpression of genes), experimental drug/compound screening and dietary, behavioral or physical activity interventions. Herein, we describe the protocols used to measure body composition and metabolic parameters using an animal monitoring system in chow-fed and high fat diet-fed mice.

This protocol describes the use of a body composition analyzer and metabolic animal monitoring system to characterize body composition and metabolic parameters in mice. An obesity model induced by high-fat feeding is used as an example for the application of these techniques.

Alterations to body composition (fat or lean mass), metabolic parameters such as whole-body oxygen consumption, energy expenditure, and substrate ...

Acclimation Prior to an Intraperitoneal Insulin Tolerance Test to Mitigate Stress-Induced Hyperglycemia in Conscious Mice

The insulin tolerance test is commonly used in metabolic studies to assess whole body insulin sensitivity in rodents. It is a relatively simple test that involves measurement of blood glucose levels over time following a single intraperitoneal injection of insulin. Given that it is performed in the conscious state and blood is often collected via a tail snip, it has the potential to elicit a stress response from animals due to anxiety associated with handling and blood collection. As such, a stress-induced rise in blood glucose can occur, making it difficult to detect and interpret the primary endpoint measure, namely an insulin-mediated reduction in blood glucose. This has been seen in many mouse strains, and is quite common in diabetic db/db mice, where glucose levels can increase, rather than decrease, after insulin administration. Here, we describe a method of acclimating mice to handling, injections and blood sampling prior to performing the insulin tolerance test. We find that this lowers stress-induced hyperglycemia and results in data that more accurately reflects whole body insulin sensitivity.

Stress-induced elevations in glucose levels can confound interpretation of data derived from a conscious intraperitoneal insulin tolerance test in mice. In this article, we describe a method to acclimate the mice to handling, injections and blood sampling prior to performing the insulin tolerance test in order to limit stress-induced hyperglycemia.

The insulin tolerance test is commonly used in metabolic studies to assess whole body insulin sensitivity in rodents. It is a relatively simple test that ...

Evaluation of Hepatic Glucose Production in a Polycystic Ovary Syndrome Mouse Model

Polycystic ovary syndrome (PCOS) is a common disease that results in disorders of glucose metabolism, such as insulin resistance and glucose intolerance. Dysregulated glucose metabolism is an important manifestation of the disease and is the key to its pathogenesis. Therefore, studies involving evaluation of glucose metabolism in PCOS are of utmost importance. Very few studies have quantified hepatic glucose production directly in PCOS models using non-radioactive glucose tracers. In this study, we discuss step-by-step instructions for the quantification of the rate of hepatic glucose production in a PCOS mouse model by measuring M+2 enrichment of [6,6-2H2]glucose, a stable isotopic glucose tracer, via gas chromatography - mass spectrometry (GCMS). This procedure involves creation of stable isotopic glucose tracer solution, use of tail vein catheter placement and infusion of the glucose tracer in both fasting and glucose-rich states in the same mouse in tandem. The enrichment of [6,6-2H2]glucose is measured using pentaacetate derivative in GCMS. This technique can be applied to a wide variety of studies involving direct measurement of the rate of hepatic glucose production.

This study describes the direct measurement of hepatic glucose production in a polycystic ovary syndrome mouse model by using a stable isotopic glucose tracer via tail vein in both fasting and glucose-rich states in tandem.

Polycystic ovary syndrome (PCOS) is a common disease that results in disorders of glucose metabolism, such as insulin resistance and glucose intolerance. ...

Glucose Uptake Measurement and Response to Insulin Stimulation in In Vitro Cultured Human Primary Myotubes

Skeletal muscle is the largest glucose deposit in mammals and largely contributes to glucose homeostasis. Assessment of insulin sensitivity of muscle cells is of major relevance for all studies dedicated to exploring muscle glucose metabolism and characterizing metabolic alterations. In muscle cells, glucose transporter type 4 (GLUT4) proteins translocate to the plasma membrane in response to insulin, thus allowing massive entry of glucose into the cell. The ability of muscle cells to respond to insulin by increasing the rate of glucose uptake is one of the standard readouts to quantify muscle cell sensitivity to insulin. Human primary myotubes are a suitable in vitro model, as the cells maintain many features of the donor phenotype, including insulin sensitivity. This in vitro model is also suitable for the test of any compounds that could impact insulin responsiveness. Measurements of the glucose uptake rate in differentiated myotubes reflect insulin sensitivity.
In this method, human primary muscle cells are cultured in vitro to obtain differentiated myotubes, and glucose uptake rates with and without insulin stimulation are measured. We provide a detailed protocol to quantify passive and active glucose transport rates using radiolabeled [3H] 2-deoxy-D-Glucose ([3H]2dG). Calculation methods are provided to quantify active basal and insulin-stimulated rates, as well as stimulation fold.

Glucose Uptake Measurement and Response to Insulin Stimulation in In Vitro Cultured Human Primary Myotubes

In this method, human primary muscle cells are cultured in vitro to obtain differentiated myotubes and glucose uptake rates are measured. We provide a detailed protocol to quantify rates in basal and insulin-stimulated states using radiolabeled [3H] 2-deoxy-D-Glucose.

Skeletal muscle is the largest glucose deposit in mammals and largely contributes to glucose homeostasis. Assessment of insulin sensitivity of muscle ...

Biology

Using a Combination of Indirect Calorimetry, Infrared Thermography, and Blood Glucose Levels to Measure Brown Adipose Tissue Thermogenesis in Humans

In mammals, brown adipose tissue (BAT) is activated rapidly in response to cold in order to maintain body temperature. Although BAT has been studied greatly in small animals, it is difficult to measure the activity of BAT in humans. Therefore, little is known about the heat-generating capacity and physiological significance of BAT in humans, including the degree to which components of the diet can activate BAT. This is due to the limitations in the currently most used method to assess the activation of BAT-radiolabeled glucose (fluorodeoxyglucose or 18FDG) measured by positron emission tomography-computerized tomography (PET-CT).
This method is usually performed in fasted subjects, as feeding induces glucose uptake by the muscles, which can mask the glucose uptake into the BAT. This paper describes a detailed protocol for quantifying total-body human energy expenditure and substrate utilization from BAT thermogenesis by combining indirect calorimetry, infrared thermography, and blood glucose monitoring in carbohydrate-loaded adult males. To characterize the physiological significance of BAT, measures of the impact of BAT activity on human health are critical. We demonstrate a protocol to achieve this by combining carbohydrate loading and indirect calorimetry with measurements of supraclavicular changes in temperature. This novel approach will help to understand the physiology and pharmacology of BAT thermogenesis in humans.

Here, we present a protocol to quantify the physiological significance of the impact of brown adipose tissue (BAT) activity on human metabolism. This is achieved by combining carbohydrate loading and indirect calorimetry with measurements of supraclavicular changes in temperature. This novel approach can help develop a pharmacological target for BAT thermogenesis in humans.

In mammals, brown adipose tissue (BAT) is activated rapidly in response to cold in order to maintain body temperature. Although BAT has been studied ...

Assessment of the Metabolic Effects of Isocaloric 2:1 Intermittent Fasting in Mice

Intermittent fasting (IF), a dietary intervention involving periodic energy restriction, has been considered to provide numerous benefits and counteract metabolic abnormalities. So far, different types of IF models with varying durations of fasting and feeding periods have been documented. However, interpreting the outcomes is challenging, as many of these models involve multifactorial contributions from both time- and calorie-restriction strategies. For example, the alternate day fasting model, often used as a rodent IF regimen, can result in underfeeding, suggesting that health benefits from this intervention are likely mediated via both caloric restriction and fasting-refeeding cycles. Recently, it has been successfully demonstrated that 2:1 IF, comprising 1 day of fasting followed by 2 days of feeding, can provide protection against diet-induced obesity and metabolic improvements without a reduction in overall caloric intake. Presented here is a protocol of this isocaloric 2:1 IF intervention in mice. Also described is a pair-feeding (PF) protocol required to examine a mouse model with altered eating behaviors, such as hyperphagia. Using the 2:1 IF regimen, it is demonstrated that isocaloric IF leads to reduced body weight gain, improved glucose homeostasis, and elevated energy expenditure. Thus, this regimen may be useful to investigate the health impacts of IF on various disease conditions.

The current article describes a detailed protocol for isocaloric 2:1 intermittent fasting to protect and treat against obesity and impaired glucose metabolism in wild-type and ob/ob mice.

Intermittent fasting (IF), a dietary intervention involving periodic energy restriction, has been considered to provide numerous benefits and counteract ...

Characterization of Metabolic Status in Nonhuman Primates with the Intravenous Glucose Tolerance Test

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