Early glomerular changes in streptozotocin diabetes of the guinea pig

A model of type 2 diabetes in the guinea pig using sequential diet-induced glucose intolerance and streptozotocin treatment

Type 2 diabetes is a leading cause of morbidity and mortality among noncommunicable diseases, and additional animal models that more closely replicate the pathogenesis of human type 2 diabetes are needed. The goal of this study was to develop a model of type 2 diabetes in guinea pigs, in which diet-induced glucose intolerance precedes β-cell cytotoxicity, two processes that are crucial to the development of human type 2 diabetes. Guinea pigs developed impaired glucose tolerance after 8 weeks of feeding on a high-fat, high-carbohydrate diet, as determined by oral glucose challenge. Diet-induced glucose intolerance was accompanied by β-cell hyperplasia, compensatory hyperinsulinemia, and dyslipidemia with hepatocellular steatosis. Streptozotocin (STZ) treatment alone was ineffective at inducing diabetic hyperglycemia in guinea pigs, which failed to develop sustained glucose intolerance or fasting hyperglycemia and returned to euglycemia within 21 days after treatment. However, when high-fat, high-carbohydrate diet-fed guinea pigs were treated with STZ, glucose intolerance and fasting hyperglycemia persisted beyond 21 days post-STZ treatment. Guinea pigs with diet-induced glucose intolerance subsequently treated with STZ demonstrated an insulin-secretory capacity consistent with insulin-independent diabetes. This insulin-independent state was confirmed by response to oral antihyperglycemic drugs, metformin and glipizide, which resolved glucose intolerance and extended survival compared with guinea pigs with uncontrolled diabetes. In this study, we have developed a model of sequential glucose intolerance and β-cell loss, through high-fat, high-carbohydrate diet and extensive optimization of STZ treatment in the guinea pig, which closely resembles human type 2 diabetes. This model will prove useful in the study of insulin-independent diabetes pathogenesis with or without comorbidities, where the guinea pig serves as a relevant model species.

A computational model of flow and species transport in the mesangium

A variety of macromolecules accumulate in the glomerular mesangium in many different diseases, but the physics of the transport of these molecules within the mesangial matrix has not been extensively studied. We present a computational model of convection and diffusion within the porous mesangial matrix and apply this model to the specific instance of immunoglobulin A (IgA) transport in IgA nephropathy. We examine the influence of physiological factors including glomerular basement membrane (GBM) thickness and mesangial matrix density on the total accumulation of IgA. Our results suggest that IgA accumulation can be understood by relating convection and diffusion, thus demonstrating the importance of intrinsic glomerular factors.

Choline acetyltransferase and inducible nitric oxide synthase are increased in myenteric plexus of diabetic guinea pig

Alterations in enzymes in myenteric neurons from ileum were investigated in guinea pigs treated with either the pancreatic beta cell toxin streptozotocin or vehicle. After 5-6 weeks, expressions of choline acetyltransferase, neuronal nitric oxide synthase and inducible nitric oxide synthase were determined in longitudinal and myenteric plexus preparations using indirect immunohistochemistry. In ileum from streptozotocin-treated animals, the density of choline acetyltransferase-immunoreactive nerve fibers within the tertiary plexus and the percent total myenteric neurons expressing inducible nitric oxide synthase were increased, but the percent total myenteric neurons expressing neuronal nitric oxide synthase was not changed. Diabetes resulted in selective alterations in myenteric neurons including an increased density of cholinergic tertiary fibers and percentage of neurons expressing the inducible isoform of nitric oxide synthase. These adaptive changes by myenteric neurons to diabetes may contribute to gastrointestinal dysfunctions associated with diabetes.

Effect of vitamin C on sorbitol in the lens of guinea-pigs made diabetic with streptozotocin

Marginally vitamin C-deficient guinea-pigs treated with the diabetogenic agent streptozotocin were compared with those liberally supplied with vitamin C, for functional indices of vitamin C status, particularly in the eye lens. Weanling male Dunkin-Hartley guinea-pigs were fed on diets with 0.1 g vitamin C/kg (marginally deficient), or 5 g/kg (liberally supplied), and some received intraperitoneal streptozotocin (two doses of 150 mg/kg body-weight). About half the streptozotocin-treated animals had high urinary glucose following an oral glucose dose; these animals also grew more slowly than the others. At 4 months after streptozotocin the animals were killed for measurement of tissue vitamin C, glucose and sorbitol. Streptozotocin moderately increased the concentration of glucose in plasma, lens and aqueous humour. Lens sorbitol levels increased only in the group exposed to streptozotocin plus marginal vitamin C. There was a significant (P less than 0.02) positive correlation between urinary glucose and lens sorbitol levels overall. Liberal vitamin C intake may thus counteract the effect of streptozotocin diabetes on lens sorbitol, suggesting a new function of vitamin C, possibly related to cataractogenesis and to the biochemical lesions associated with diabetes.

Selected physical and biochemical parameters in the streptozotocin-treated guinea pig: insights into the diabetic guinea pig model

Since evidence suggests that ascorbic acid deficits may provoke certain diabetic complications, it becomes necessary to develop a diabetic animal model which, like man, is unable to synthesize this vitamin. To this end, the present study monitored the diabetogenic effects of streptozotocin (STZ, 150 mg/kg) in the male guinea pig, a species rarely used in diabetes research. Over a 3-week period, body weight and relative food intake were lower in the STZ group compared to controls. The mean daily water intake and urine volume of the STZ group after 1 week were 175 and 270% of their initial pretreatment values, respectively, while control values were unchanged. The STZ group also exhibited a persistent glycosuria throughout the study. At the end of 3 weeks, aldehyde fuchsin staining of pancreatic beta cell granules (an index of stored insulin) was 58% lower in the STZ group compared to controls. Plasma C-peptide (indicator of insulin secretion) was expressed in human equivalents (mean +/- SEM). C-peptide was reduced in the STZ group (103 +/- 65 pg/ml) compared to controls (549 +/- 96 pg/ml); however, no change in plasma glucose was observed. Plasma ascorbic acid levels also were lower for STZ animals (150 +/- 26 micrograms%) versus controls (410 +/- 28 micrograms%). This study 1) demonstrates a diabetic syndrome in the STZ-treated guinea pig based on a reduced growth rate, beta cell dysfunction, polydipsia, polyuria and glycosuria, and 2) suggests the usefulness of this diabetic model in studies of pathologic mechanisms influenced by ascorbic acid.

Effects of streptozotocin in the male guinea pig: a potential animal model for studying diabetes

The effects of acutely administered streptozotocin in the male guinea pig were studied for a period of 18 days following treatment. A single intracardiac injection of streptozotocin (150 mg/kg) was administered on Day 0. On Day 2, plasma glucose concentrations were not significantly different from control levels. On Day 7 and 18, an oral glucose tolerance test was performed with streptozotocin-treated animals receiving an acute injection of either insulin (18 U/kg, i.m.) or saline 90 minutes prior to glucose loading. On Day 7, streptozotocin-treated animals receiving saline had significantly elevated plasma and urine glucose concentrations at 3 hours after glucose loading when compared to controls. Streptozotocin-treated animals receiving insulin however, had significantly lower plasma glucose concentrations at 3 hours while urinary glucose was equal to control values. The second glucose tolerance test performed on Day 18 yielded similar results. Necropsies were performed on animals that died after Day 6. Lesions found in the streptozotocin-treated animals included: small and irregular pancreatic islets, pyknotic nuclei and degranulation of beta cells, renal proximal tubule swelling and vacuolization, adrenal cortical hyperplasia, hepatocyte vacuolization, and visceral fat atrophy. Animals surviving until Day 18 were sacrificed and found to have significantly elevated kidney and adrenal weights compared to controls. These changes illustrate the effectiveness of streptozotocin in the acute chemical induction of diabetes in an animal model (guinea pig) which, like humans, requires a dietary source of ascorbic acid.

Glomerular alterations in experimental diabetes of the rat

To detect structural glomerular alterations in the early stages of diabetes mellitus glomeruli from young streptozotocin diabetic rats were studied by light microscopy with morphometric methods 2, 8, 12 and 24 weeks after induction of diabetes. It was found that there is a marked increase in the percentage mesangial surface as compared with the control animals already two weeks after induction of diabetes. The relative mesangial surface fraction was greater in the diabetic animals than in the controls at all test times. It was also demonstrated that the endothelial cell count was reduced in the diabetic animals in the first few weeks of the study. High-grade glycosuria and proteinuria were likewise observed in the diabetic animals. Hence the mesangium appears to be one of the glomerular structures which shows the first changes in the initial stages of diabetes mellitus. Possibly the most likely cause of the changes based on the present study is the diabetic metabolic state (or the insulin deficiency).

Mesangium in rats after E. coli neurotoxin shock: a morphometric and light microscopic analysis

The renal corpuscles of 28 specific-pathogen-free Wistar rats fixed by perfusion were examined light microscopically and morphometrically following experimental protracted neurotoxin shock. The mean diameter of the center sections of 420 renal corpuscles was 113.0 micrometers. The mesangial portion occupied 9.5% of the total area of the renal corpuscle in control rats and increased to a maximum of 17.25% in experimental rats. The number of mesangial nuclei per renal corpuscle in rats with protracted shock showed that expansion of the mesangium with compression of capillary loops was not caused solely by an increase in the number of cells. Furthermore, there was an enlargement of the mesangial cytoplasm and matrix. Activation and proliferation of connective tissue in rats with protracted shock could be observed in the interstitium of various organs as well as in the mesangium of the glomerulus.

Effect of islet transplantation on the glomerular changes in streptozotocin-diabetic rats

Glomerular changes develop in rats with streptozotocin diabetes. The structure of these lesions (nodular and diffuse glomerulosclerosis, mesangial cell proliferation, basement membrane thickening, glomerular aneurysms, fibrinoid caps, glomerular adhesions) is described in the present paper and the effect of normalization of metabolism by islet transplantation on the glomerular changes is studied with histological, immunohistological and morphometric methods. Isogenous islets were transplanted into the portal vein of streptozotocin-diabetic rats after diabetes of 7 months' duration. The kidneys of normal, diabetic and transplanted animals of the same age were studied 2.5 months later. Studies of the kinetics of immunocomplexes in the mesangium were also performed. The renal changes (glomerulosclerosis, mesangial cell proliferation) were largely reversible after islet transplantation and the blood glucose level and glucose tolerance were normalized. In the diabetic animals the delayed uptake and elimination of immunocomplexes in the mesangium was normalized after the transplantation. It is possible, that the cause of the lesions is a functional disturbance of the mesangium induced by insulin deficiency and/or hyperglycaemia.