The effect of dietary energy restriction on body weight gain and the development of noninsulin-dependent diabetes mellitus (NIDDM) in Psammomys obesus

Psammomys obesus: a Natural Diet-Controlled Model for Diabetes and Cardiovascular Diseases

PURPOSE OF REVIEW

This review specifically summarises and reports terrestrial mammals of the gerbil subfamily, known as Israeli sand rats or Psammomys obesus (P. obesus) as a diet-controlled, unique, polygenic rodent model for research in the areas of obesity, type 2 diabetes, and cardiovascular diseases. The animal model closely mimics phenotypic and pathophysiological resemblance with human populations.

RECENT FINDINGS

The physiological status and biochemical composition in P. obesus can be manipulated effectively by controlling its nutritional intake, making it a natural model for cardiovascular and diabetic research. Humans exhibit remarkable disparity in physiology and pathology, which are inter-dependent factors. However, variations in these factors in most animal models currently being used for cardiovascular/diabetes research are insignificant. Consequently, it is a necessity to identify and develop animal models exhibiting physiological variations mimicking human pathological conditions. We have compiled research developments conducted with this rodent model manifesting pathophysiology, closely mimicking that in human beings, thereby enabling better translation of novel therapeutic and diagnostic discoveries.

Synthetic protease inhibitor camostat prevents and reverses dyslipidemia, insulin secretory defects, and histological abnormalities of the pancreas in genetically obese and diabetic rats

BACKGROUND

Otsuka Long-Evans Tokushima Fatty (OLETF) rat, a model of type 2 diabetes, lacks the expression of cholecystokinin-1 receptor mRNA and exhibits inflammation and degeneration of the pancreas and eventually develops insulinopenic diabetes. Protease inhibitors are known to modulate inflammatory response and fibrosis as well as inhibit proteases activity.

AIM

To examine the effects of long-term treatment with camostat, a synthetic protease inhibitor, on metabolic and histopathological changes in the islets of OLETF rats.

METHOD

OLETF rats were fed either camostat-containing food (200 mg/100 g) from 12 or 28 weeks of age to 72 weeks of age, or fed standard rat diet.

RESULTS

Camostat-fed rats gained less weight or lost weight, although they consumed more food than the control rat when food intake was adjusted for body weight. Camostat reduced visceral adipose depots and fasting serum concentrations of triglyceride, free fatty acids, cholesterol, glucose, and insulin. Pancreatic insulin content in camostat-treated rats was significantly higher than in control rats. Immunohistochemistry revealed marked suppression of expressions of tumor necrosis factor alpha , interleukin 1 beta , interleukin 6, and alpha-smooth muscle actin in the islets of camostat-treated rats, compared with control rats. Histologically, disruption of the islets and pancreatic fibrosis were noted in control rats but not in camostat-fed rats.

CONCLUSION

Our findings suggest that camostat prevents and reverses obesity, hyperinsulinemia, hyperglycemia, and hyperlipidemia and markedly inhibits inflammation, fibrosis, and disruption of the islets in the genetically obese diabetic OLETF rats.

Seasonal variations in the function of the endocrine pancreas in Psammomys obesus

The aim of this work was to determine whether Psammomys obesus living in its natural habitat displays variation in the function of the endocrine pancreas. Live animals were collected regularly through the year by strip sampling. Plasma glucose varied during the year. Glucose levels were higher in periods I and III (autumn and spring) than in periods II and IV (winter and summer). Pancreatic insulin contents were higher in periods I and II than in periods III and IV. Plasma insulin also varied with the season in synchrony with glucose variations except during period IV, in which elevated levels of insulin were associated with low levels of glucose. The high insulin levels observed in period IV were resistant to the effects of food restriction in that period and were probably related to the presence of the greater levels of insulin in period III (spring). The dry season (period IV) corresponding to the period of restricted diet appears necessary to restore elevated levels of insulin to baseline. Morphometric quantitation of the insulin, glucagon, and somatostatin positive islet cells did not reveal seasonal variation. However, the volume density of A and D cells in P. obesus reached high values of 32 and 15%, respectively. The volume density of insulin cells amounted to about 53%. It is concluded that P. obesus living in its natural habitat is a nondiabetic healthy gerbil adapted to desert subsistence by endocrine feedback, imposed by the seasonal variation in food availability.