Immunohistochemical, ultrastructural, and hormonal studies on the endocrine pancreas of voles (Microtus arvalis) with monosodium aspartate-induced diabetes

The types of endocrine cells in the pancreas of Sunda porcupine (Hystrix javanica)

Aim:

To identify the types of endocrine cells in the pancreas of the Sunda porcupine (Hystrix javanica) and its immunolocalization.

Materials and Methods:

Five adult H. javanica were used without sexual distinction. The presences of endocrine cells (glucagon, insulin, somatostatin, and pancreatic polypeptide [PP]) in pancreatic tissues were detected using the avidin-biotin-peroxidase complex method.

Results:

The fusiform, round, and oval form endocrine cells were detected in the islets of Langerhans and exocrine parts. Most of the insulin cells were found in the central area, glucagon cells were identified in the central and peripheral areas, and somatostatin and PP cells were detected in the mantle area of the islets of Langerhans. Glucagon and somatostatin cells were also detected in smaller numbers of peripheral parts of the islet. In all of the islet parts, glucagon endocrine cells were most prevalent cell type and then, somatostatin, insulin, and PP. In the exocrine parts, PP, somatostatin, glucagon, and insulin endocrine cells were found in the inter-acinus part with moderate, moderate, a few and rare numbers, in that order. In the pancreatic duct, glucagon and somatostatin cells were found between epithelial cells in rare numbers.

Conclusion:

The pancreas of Sunda porcupine (H. javanica) contains four types of major pancreatic endocrine cells with approximately similar distribution patterns to the other rodents, except for abundant glucagon cells in the peripheral area of the islets of Langerhans.

Genetic models rule out a major role of beta cell glycogen in the control of glucose homeostasis

AIMS/HYPOTHESIS

Glycogen accumulation occurs in beta cells of diabetic patients and has been proposed to partly mediate glucotoxicity-induced beta cell dysfunction. However, the role of glycogen metabolism in beta cell function and its contribution to diabetes pathophysiology remain poorly understood. We investigated the function of beta cell glycogen by studying glucose homeostasis in mice with (1) defective glycogen synthesis in the pancreas; and (2) excessive glycogen accumulation in beta cells.

METHODS

Conditional deletion of the Gys1 gene and overexpression of protein targeting to glycogen (PTG) was accomplished by Cre-lox recombination using pancreas-specific Cre lines. Glucose homeostasis was assessed by determining fasting glycaemia, insulinaemia and glucose tolerance. Beta cell mass was determined by morphometry. Glycogen was detected histologically by periodic acid-Schiff's reagent staining. Isolated islets were used for the determination of glycogen and insulin content, insulin secretion, immunoblots and gene expression assays.

RESULTS

Gys1 knockout (Gys1 (KO)) mice did not exhibit differences in glucose tolerance or basal glycaemia and insulinaemia relative to controls. Insulin secretion and gene expression in isolated islets was also indistinguishable between Gys1 (KO) and controls. Conversely, despite effective glycogen overaccumulation in islets, mice with PTG overexpression (PTG(OE)) presented similar glucose tolerance to controls. However, under fasting conditions they exhibited lower glycaemia and higher insulinaemia. Importantly, neither young nor aged PTG(OE) mice showed differences in beta cell mass relative to age-matched controls. Finally, a high-fat diet did not reveal a beta cell-autonomous phenotype in either model.

CONCLUSIONS/INTERPRETATION

Glycogen metabolism is not required for the maintenance of beta cell function. Glycogen accumulation in beta cells alone is not sufficient to trigger the dysfunction or loss of these cells, or progression to diabetes.

Partial regeneration of beta-cells in the islets of Langerhans by Nymphayol a sterol isolated from Nymphaea stellata (Willd.) flowers

Reduction of the beta-cell mass is critical in the pathogenesis of diabetes mellitus. The discovery of agents which induce regeneration of pancreatic beta-cells would be useful to develop new therapeutic approaches to treat diabetes. The present study was aimed at identifying a new agent for the control of diabetes through regeneration of pancreatic beta cells and insulin secretory potential. Nymphaea stellata flower chloroform extract (NSFCExt) showed significant plasma glucose lowering effect. Further NSFCExt was utilized to isolate and identify the lead compound based on bioassay guided fractionation; we found Nymphayol (25,26-dinorcholest-5-en-3beta-ol) a new crystal [space group P2(1) (No. 4), a=9.618(5), b=7.518(5), c=37.491(5)]. It was purified by repeat column. The structure was determined on the basis of X-ray crystallography and spectral data. Oral administration of Nymphayol for 45 days significantly (p<0.05) lowered the blood glucose level and more importantly it effectively increased the insulin content in diabetic rats. In addition, Nymphayol increased the number of beta cell mass enormously. Islet-like cell clusters in the islets of Langerhans were clearly observed based on histochemical and immunohistochemical study.

A 90-day toxicity study of L-asparagine, a food additive, in F344 rats

L-asparagine is an amino acid listed as an existing food additive in Japan. The present 90-day toxicity study in F344/DuCrlCrj rats was conducted for safety assessment and to determine a no observed adverse effect level (NOAEL) of L-asparagine. Groups of 10 males and 10 females were given the material at dose levels of 0%, 1.25%, 2.5% or 5% in diet for 90 days. During the experiment, there were no remarkable changes in general conditions and no deaths occurred in any group. Final body weights of male 5% and 1.25% groups were significantly decreased. There were also significant increases in relative organ weights of the brain, kidney and testis in 5% males. On serological examination, GLU, PL, K and ALT were increased significantly in 5% females, and GLU was increased significantly and CRN was decreased significantly in the female 1.25% group. However, histopathological examination did not reveal any significant variation in development of lesions among the groups. Changes in body and organ weights, as well as other parameters, were concluded to be due to treatment with 5% L-asparagine. The NOAEL was determined to be 2.5% in the diet (males, 1.65 g/kg body weight/day; females, 1.73 g/kg body weight/day).

Canine and Feline Diabetes Mellitus: Nature or Nurture?

There is evidence for the role of genetic and environmental factors in feline and canine diabetes. Type 2 diabetes is the most common form of diabetes in cats. Evidence for genetic factors in feline diabetes includes the overrepresentation of Burmese cats with diabetes. Environmental risk factors in domestic or Burmese cats include advancing age, obesity, male gender, neutering, drug treatment, physical inactivity, and indoor confinement. High-carbohydrate diets increase blood glucose and insulin levels and may predispose cats to obesity and diabetes. Low-carbohydrate, high-protein diets may help prevent diabetes in cats at risk such as obese cats or lean cats with underlying low insulin sensitivity. Evidence exists for a genetic basis and altered immune response in the pathogenesis of canine diabetes. Seasonal effects on the incidence of diagnosis indicate that there are environmental influences on disease progression. At least 50% of diabetic dogs have type 1 diabetes based on present evidence of immune destruction of beta-cells. Epidemiological factors closely match those of the latent autoimmune diabetes of adults form of human type 1 diabetes. Extensive pancreatic damage, likely from chronic pancreatitis, causes approximately 28% of canine diabetes cases. Environmental factors such as feeding of high-fat diets are potentially associated with pancreatitis and likely play a role in the development of pancreatitis in diabetic dogs. There are no published data showing that overt type 2 diabetes occurs in dogs or that obesity is a risk factor for canine diabetes. Diabetes diagnosed in a bitch during either pregnancy or diestrus is comparable to human gestational diabetes.

Insulin sensitivity decreases with obesity, and lean cats with low insulin sensitivity are at greatest risk of glucose intolerance with weight gain

This study quantifies the effects of marked weight gain on glucose and insulin metabolism in 16 cats which increased their weight by an average of 44.2% over 10 months. Significantly, the development of feline obesity was accompanied by a 52% decrease in tissue sensitivity to insulin and diminished glucose effectiveness. In addition, glucose intolerance and abnormal insulin response occurred in some cats. An important finding was that normal weight cats with low insulin sensitivity and glucose effectiveness were at increased risk of developing impaired glucose tolerance with obesity. High basal insulin concentrations or low acute insulin response to glucose also independently increased the risk for developing impaired glucose tolerance. Male cats gained more weight relative to females and this, combined with their tendency to lower insulin sensitivity and higher insulin concentrations, may explain why male cats are at greater risk for diabetes. Results suggest an underlying predisposition for glucose intolerance in some cats, which is exacerbated by obesity. These cats may be more at risk of progressing to overt type 2 diabetes mellitus.

Pathogenesis of feline diabetes mellitus

Cats are one of the few species that develop a form of diabetes mellitus that is clinically and histologically analogous to human type 2 diabetes mellitus. Figure 9 summarizes the etiologic factors thought to be involved in the development of feline and human type 2 diabetes. The main metabolic characteristics of type 2 diabetes mellitus are impaired insulin secretion and resistance to the action of insulin in its target tissues. Impaired beta cell function occurs before histologic changes become evident. The characteristic histologic finding in cats with type 2 diabetes is deposition of amyloid in pancreatic islets. Amyloid deposition occurs before the onset of clinical signs, but does not seem to be the primary defect. Pancreatic amyloid is derived form the recently discovered pancreatic hormone amylin. Amylin is synthesized in pancreatic beta cells, and is co-stored and co-secreted with insulin. Amylin has been postulated to be involved in the pathogenesis of feline diabetes mellitus both through its metabolic effects, which include inhibition of insulin secretion and induction of insulin resistance, and via progressive amyloid deposition and beta cell degeneration. Increased amylin concentration has been documented intracellularly in cats with impaired glucose tolerance and in the plasma of diabetic cats, and supports the hypothesis that amylin is involved in the pathogenesis of type 2 diabetes. Obesity is a common finding in diabetic felines and is a contributing factor to the insulin resistance present in type 2 diabetes. Clinical signs of diabetes develop once total insulin secretion decreases to 20% to 25% of normal levels. Many diabetic cats have been treated successfully with oral hypoglycemics, but 50% to 70% of diabetic cats are insulin dependent. Based on histologic evidence, this is the result of extensive amyloid deposition and subsequent beta cell degeneration, rather than autoimmune destruction of pancreatic beta cells associated with type 1 diabetes. Alternative ways of treating type 2 diabetes currently are being investigated. Amylin antagonists recently have been proposed as a novel treatment to reverse the deleterious effects of excessive amylin concentrations. The gastrointestinal hormone glucagon-like peptide-1 may also prove useful in treating diabetic cats, because of its stimulatory effect on insulin secretion and synthesis, and the absence of significant hypoglycemic effect.

A review of new developments in type 2 diabetes in human beings and cats

Cats appear to be one of the few non-human species that develop a type of diabetes mellitus analogous to human Type 2, or non-insulin-dependent diabetes mellitus (NIDDM). In this review, some current theories on diabetogenesis are discussed. In both cats and human beings, Type 2 diabetes is characterized by impaired insulin secretion due to a functional defect in pancreatic beta-cells, and insulin resistance. In both species, amyloid deposition occurs in pancreatic islets and is derived from the newly discovered pancreatic hormone islet amyloid polypeptide (IAPP), or amylin. Amylin also reduces insulin secretion and induces insulin resistance. Thus, the hypothesis of amylin being intimately involved in the pathogenesis of human and feline Type 2 diabetes appears justified. Obesity is a frequent concomitant problem in feline and human Type 2 diabetes and contributes to the insulin resistance characteristic of the disease.