Obese NHP Resource

To develop metabolic research at ONPRC, Dr. Kevin Grove and his colleagues have established two colonies of macaques that become obese when fed a high-fat/high-calorie diet (HF diet). The Diet-Induced Obesity (DIO) NHP models under development at ONPRC are being expanded in an effort to understand the progression of the disease as well as to understand the full spectrum of complications that are associated with obesity. Briefly, the two models are:

1) Gestational obesity studies using Japanese macaques. The studies of Japanese macaques use a breeding colony of animals maintained on a high-fat/calorie diet (HF diet). These animals are housed as small groups comprising 8-10 young adult females and two males. This colony consists of about 75 animals total and produces 30-40 pregnancies per year. These animals support studies on the effects of maternal diet and metabolic health on the development of metabolic systems in the offspring.

2) DIO using Rhesus macaques. These studies involve singly housed animals that have extensive phenotypic characterization, including glucose tolerance, insulin tolerance, food intake, energy expenditure, activity, and cardiovascular function. These macaques have been used in studies to test pharmaceutical therapeutics for obesity, insulin resistance, and cardiovascular disease.

This resource is being expanded for internal and external studies. The primary goals for the Obese NHP Resource are:

• To encourage interdisciplinary, collaborative studies that will specifically lead to additional funding in the various metabolic disease areas. This will be accomplished through interaction with the Metabolic Disease Working Group.
• To understand the timeline for the progression of the different aspects of the metabolic disease; i.e., obesity, diabetes, cardiovascular disease, and immune dysfunction.
• To determine the characteristics (i.e., genetic and behavioral) that make some animals susceptible to diet induced obesity, while other animals are highly resistant.
• To determine how the two species of macaques (Rhesus and Japanese) differ or are similar in their suitability as models for human metabolic disease.
• Provide oversight and coordination of all internal and external research projects, including promotion of collaborative efforts.

Technical approaches employed by the Resource:

Magnetic resonance spectroscopy (MRS). The ONPRC has recently obtained a 3T magnet from the main OHSU campus. One of the possible applications of this technology to the Obese NHP resource is through MRS analysis of ectopic lipid accumulation in the liver and muscle (as well as other tissues). This has become a valuable and powerful technique used in humans to investigate fatty liver disease and the correlation of ectopic lipid accumulation with insulin resistance and the progression to diabetes.

Dual energy X-ray analysis (DEXA). Last year, the ONPRC purchased a new Hologic Discovery A DEXA scanner for doing body composition analysis. This is the same machine used in OHSU clinics. This machine is available through charge-backs ($50 per animal), which covers its maintenance contract and upgrades.

Ex vivo islet culture system. A large-capacity physiological culture system has been recently established that enables the analysis of cells and organelles such as pancreatic islets under conditions that approximate in vivoconditions of CO₂, O₂, temperature, and 3-dimensional suspension culture. This system is being optimized for NHP islets, and is also amenable to analysis of immune cells relevant to chronic inflammation and follicles for planned studies of PCOS.

Energy expenditure. Double-labeled water analysis is commonly used in humans (children and adults) to measure basal energy expenditure. This technique has been validated in NHPs as well. This is a non-invasive technique that relies on two forms of labeled water (H₂¹⁸O and ²H₂O) and the utilization of these substrates to generate CO₂. This is a valuable technique to use in NHPs because it can be performed on large numbers of animals, which makes it ideal for both individually housed animals as well as group-housed animals.

Telemetry systems. DSI telemetry systems that measure blood pressure, heart rate, activity, body temperature, and ECG are employed for individually housed animals, and Actiwatch accelerometers can be used in both single and group-housed animals.

Hyperinsulinemic-euglycemic clamps. This is an important technique for extensive analysis of insulin resistance. While glucose and insulin tolerance tests (both used extensively at ONPRC) can give an indirect measure of whole-animal insulin resistance, clamp studies are used to detect insulin resistance in peripheral tissues (i.e., muscle and fat). These studies use the infusion of labeled substrates while clamping insulin at high levels and infusing glucose to maintain euglycemia.

Contrast-enhanced ultrasound CEU). This is a technique to measure vascular reactivity and tissue perfusion. This non-invasive perfusion imaging technique relies on the ultrasound detection of microbubble contrast agents during their tissue microvascular transit. Encapsulated microbubble contrast agents that are currently used for CEU imaging are ideal for the assessment of perfusion, since they are inert and remain in the vascular compartment, and their microvascular rheology is similar to that of red blood cells.

Immune function. Through Pathobiology and VGTI investigators, there is vast array of expertise to study NHP immune function. It is well accepted that obesity and diabetes in humans is associated with immune disorders and inflammation, and that this condition may contribute to the progression of the disease and the pathology.

The Obese Nonhuman Primate Resource is a critical component of the Metabolic Disease Working Group.

Kevin L. Grove, Ph.D., Head