Effects of insulin and acarbose alone and in combination in the female streptozotocin-induced diabetic rat

Antidiabetic properties of purified polysaccharide fromHedysarum polybotrys

Hedysarum polybotrys polysaccharide (HPS) is the principal active fraction responsible for the antidiabetic properties of this species. The aim of this study was to determine the antidiabetic properties of 4 purified fractions of different molecular weight range HPSs (HPS1, HPS2, HPS3, HPS4). HPS3 was selected for examination of its hypoglycemic mechanism because of its significant hypoglycemic effect in alloxan-induced diabetic mice. The changes in blood glucose levels and oral glucose tolerance tests (OGTT) showed that hypoglycemia was more pronounced in HPS3-treated groups than in the diabetes mellitus model (DM) control group. The interleukin-6, tumor necrosis factor-α, leptin, and free fatty acid levels were significantly lower in the HPS3-treated groups and HPS3 + metformin (HPS3+MET) group than in the DM control group, while plasma insulin, hepatic glycogen, superoxide dismutase, and nitric oxide synthetase activity were significantly higher. Treatment with HPS3 or HPS3+MET also significantly lowered malonaldehyde levels compared with the DM control group, while it elevated the nitric oxide and total antioxidant capacity. HPS3 altered the plasma lipid levels by lowering cholesterol and triglyceride concentrations, while elevating the plasma high-density lipoprotein cholesterol level. Therefore, these results suggest that HPS3 may partly ameliorate hyperglycemia and hyperlipidemia associated with type 2 diabetes through increased insulin secretion, inhibition of lipid peroxidation, promotion of sensitivity to insulin, suppression of gluconeogenesis and reduction in the biosynthesis fatty acid, cholesterol and cell cytokines related to insulin resistance, and it could be a useful adjunct therapy to a proven first-line therapy for type 2 diabetes using metformin.

A comparative study on hypoglycemic and hypocholesterolemic effects of high and low molecular weight chitosan in streptozotocin-induced diabetic rats

The hypoglycemic and hypocholesterolemic effects of high and low molecular weight chitosan were evaluated in streptozotocin (STZ)-induced diabetic rats. Rats were divided into three groups of normal rats (Experiment I) and three groups of diabetic rats (Experiment II). The first group received a cellulose (control) diet, the second group received a low MW (1.4 x 10(4)Da) chitosan diet and the third group received a high MW (1.0 x 10(6)Da) chitosan diet. All three diets were containing 0.5% cholesterol. Experiment I: rats fed with high MW or low MW chitosan diet had increased high density lipoprotein (HDL) cholesterol. However, chitosan did not affect plasma glucose in normal rats. Experiment II: significantly decreased plasma glucose and total cholesterol and increased HDL cholesterol and fecal cholesterol excretion were observed in diabetic rats fed with high MW chitosan diet than animals fed with cellulose diet. However, no statistical significant difference in plasma glucose and total cholesterol was observed in diabetic rats fed with low MW chitosan. The total content of SCFAs in cecum was significantly increased and the ratio of acetate to propionate was slight but significantly decreased in diabetic rats after consuming high MW chitosan diet. The activities of hepatic hexokinase were significantly increased and the intestinal disaccharidases including sucrase and maltase were significantly decreased in normal and diabetic rats fed with high MW chitosan diet. Results obtained from the present study demonstrated the potential of high MW chitosan in reducing hyperglycemia and hypercholesterolemia in STZ-induced diabetic rats.

Effects of the alpha-glucosidase inhibitor acarbose on the development of long-term complications in diabetic animals: pathophysiological and therapeutic implications

Short-term studies with acarbose have demonstrated its efficacy in reducing postprandial blood glucose levels and glycated haemoglobin (HbA(1c)) levels. These effects would be expected to translate into improvements in long-term complications of diabetes, but such data are not yet available due to the long follow-up times required. Animal models of diabetes have, however, demonstrated the efficacy of acarbose in combating the long-term complications of the disease. The 18 animal studies reviewed here showed that acarbose treatment reduced postprandial blood glucose concentrations and decreased protein glycation. Through these actions, acarbose delayed or prevented the onset of renal, retinal, lens and neurological changes and the development of ischaemic myocardial lesions. Acarbose treatment can therefore be expected to benefit patients with Type 2 and, in combination with insulin, Type 1 diabetes. This is being investigated in ongoing clinical studies in patients with Type 2 diabetes and impaired glucose tolerance (IGT).

Metabolic abnormalities in the genetically obese and diabetic Otsuka Long-Evans Tokushima Fatty rat can be prevented and reversed by alpha-glucosidase inhibitor

The recently developed Otsuka Long-Evans Tokushima Fatty (OLETF) rat is known to develop insulinopenic diabetes after a prolonged period in a condition resembling non-insulin-dependent diabetes mellitus (NIDDM). We examined the effect of pharmacological intervention with a potent intestinal alpha-glucosidase inhibitor, acarbose, on the metabolic and histopathologic changes in this rat model. The first two groups of rats received an acarbose-rich diet (150 mg/100 g normal chow) from 12 weeks of age (ie, before the onset of diabetes) or from 28 weeks of age (ie, after the onset of diabetes), while a third group received the acarbose-rich diet for the initial 16 weeks only (from 12 to 28 weeks of age). A control group received standard rat chow. Acarbose-fed rats gained less weight or lost weight despite increased food intake when switched to the acarbose-rich diet. Acarbose also reduced visceral adipose depots and fasting triglyceride (TG), glucose, and insulin levels. At the end of the study at 72 weeks, the pancreatic wet weight and insulin content were significantly higher in the treated groups versus control rats. The morphological changes observed in control rats, such as atrophy of the pancreas and reduced number and size of islets, were not present in acarbose-treated rats. Rats fed acarbose from 12 to 28 weeks of age gradually gained weight after switching to standard chow, and hyperinsulinemia, hyperglycemia, and hyperlipidemia appeared (in that order). The pancreatic insulin content in these rats was significantly higher and the visceral adipose depot was significantly smaller than in control rats. Our study demonstrates that acarbose prevented and reversed the metabolic derangement and histopathological changes in genetically diabetic rats. Moreover, treatment with acarbose even for a short period produced a marked delay in the development of insulin insensitivity and frank diabetes.

Positive effects of acarbose in the diabetic rat are not altered by feeding schedule

We previously demonstrated that chronic dietary treatment with acarbose, an alpha-glucosidase inhibitor, improves glucose homeostasis in the streptozotocin (STZ)-induced diabetic rat. In this study we evaluated the effects of 4 weeks of acarbose treatment on glucose homeostasis in STZ-diabetic rats for both meal-fed (three times daily) and ad libitum feeding conditions. Sprague Dawley male rats (n = 58) were started on a daily meal-feeding paradigm consisting of three 2-h feeding periods: 0700 to 0900 hours, 1300 to 1500 hours, and 1900 to 2100 hours. Following 2 weeks of adaptation, half of the animals were switched to ad libitum feeding. The feeding paradigm itself (meal fed versus ad lib.) affected neither body weight nor daily food intake. Twenty animals from each feeding group then received STZ (60 mg/kg i.v.), whereas control animals received vehicle injections only. Two days later, the diet of 10 STZ-treated animals from each paradigm was supplemented with acarbose (40 mg of BAY G 5421/100-g diet), and the groups were treated for 4 weeks. Untreated diabetic rats had lower body weight than vehicle-injected control rats at all time points after STZ treatment. Acarbose treatment delayed this effect on body weight. STZ treatment induced hyperphagia regardless of feeding paradigm, which was significantly attenuated by acarbose only for the first week of treatment. Untreated diabetic rats had fasting blood glucose values 4 times those of vehicle-injected controls in both the meal-fed and ad libitum-fed conditions. Acarbose significantly lowered fasting blood glucose in the treated STZ groups. Blood glucose was also assessed 0, 90, and 180 min following the start of a meal. The postprandial rise in blood glucose was significantly reduced in acarbose-treated meal-fed diabetic rats, to values not significantly different from those of vehicle-injected control rats. During the fourth week of treatment glycated hemoglobin levels were significantly higher in untreated diabetic groups compared to vehicle-injected control groups. Acarbose treatment significantly reduced this rise, regardless of the feeding paradigm. Collectively, the results demonstrate that acarbose reduces diabetes-induced increases of blood glucose and glycated hemoglobin and that the glycemic effects of acarbose are most apparent during the absorptive period. Feeding paradigm (ad lib. versus meal fed) has little or no influence on acarbose's metabolic effects, indicating that large meals are not required to realize the beneficial effects of the drug. The meal-fed STZ-diabetic rat may be a good model with which to test meal-based diabetes treatments.