The effect of acarbose on the intestinal metabolism of glucose in vitro

Acarbose improved survival for Apc+/Min mice

Acarbose blocks the digestion of complex carbohydrates, and the NIA Intervention Testing Program (ITP) found that it improved survival when fed to mice. Yet, we do not know if lifespan extension was caused by its effect on metabolism with regard to the soma or cancer suppression. Cancer caused death for ~80% of ITP mice. The ITP found rapamycin, an inhibitor to the pro-growth mTORC1 (mechanistic target of rapamycin complex 1) pathway, improved survival and it suppressed tumors in Apc+/Min mice providing a plausible rationale to ask if acarbose had a similar effect. Apc+/Min is a mouse model prone to intestinal polyposis and a mimic of familial adenomatous polyposis in people. Polyp-associated anemia contributed to their death. To address this knowledge gap, we fed two doses of acarbose to Apc+/Min mice. Acarbose improved median survival at both doses. A cross-sectional analysis was performed next. At both doses, ACA fed mice exhibited reduced intestinal crypt depth, weight loss despite increased food consumption and reduced postprandial blood glucose and plasma insulin, indicative of improved insulin sensitivity. Dose-independent and dose-dependent compensatory liver responses were observed for AMPK and mTORC1 activities, respectively. Only mice fed the high dose diet exhibited reductions in tumor number with higher hematocrits. Because low-dose acarbose improved lifespan but failed to reduced tumors, its effects seem to be independent of cancer. These data implicate the importance of improved carbohydrate metabolism on survival.

alpha-Glucosidase inhibitors prevent diet-induced increases in intestinal sugar transport in diabetic mice

The recommended diet for diabetes mellitus is rich in complex carbohydrates. We have previously shown that high carbohydrate levels in the intestinal lumen induce adaptive increases in sugar absorption which in turn exacerbate postprandial hyperglycemia in diabetic mice. alpha-Glucosidase inhibitors (AGIs) hinder digestion of complex carbohydrates and therefore alleviate postprandial glycemic excursions. In this study, we tested the hypothesis that AGIs prevent the carbohydrate-induced upregulation of intestinal glucose and fructose transport in diabetes. Streptozotocin-diabetic mice were fed the following isocaloric diets: high carbohydrate (H), H plus acarbose (HA), H plus deoxy-nojirimycin (HD), and low carbohydrate (L), then nutrient uptakes were determined after 2 and 4 weeks. Body weight, intestinal weight, and length were independent of diet. Fasting and postprandial blood glucose levels were lower in HA and HD than in H mice. Uptakes of D-glucose and D-fructose were 2 to 3 times greater in H than in L mice, but HA and HM diets gradually reduced D-glucose uptakes to rates similar to L mice. Only HA diets reduced D-fructose uptake. Intestinal proline, aspartate, and glutamine uptakes were each greater in L than in H, HA, and HD mice. alpha-Glucosidase inhibitors did not alter intestinal permeability and amino acid transport rates. alpha-Glucosidase inhibitor-inhibitable increases in total intestinal absorptive capacity for sugars were due to carbohydrate-induced increases in V(max) of glucose transport. Clearly, one potential mechanism by which AGIs blunt postprandial glycemic excursions and lower fasting blood glucose concentrations in individuals consuming carbohydrate-containing diets is by preventing carbohydrate-induced increases in intestinal sugar transport.

Acarbose partially inhibits microvascular retinopathy in the Zucker Diabetic Fatty rat (ZDF/Gmi-fa)

We compared quantitative capillary retinopathic changes between non-insulin-dependent diabetic Zucker Diabetic Fatty (ZDF) rats and heterozygous nondiabetic Zucker controls and evaluated the effect of an orally administered glucosidase inhibitor, acarbose, on retinopathy in these animals. Four groups of eight rats were analyzed: treated and untreated ZDF and treated and untreated Zuckers. Retinal capillary basement membrane thickening and retinal capillary cell density were determined from transmission electron microscopy and trypsin digestion preparations. ZDF rats had thicker basement membranes (p<0.0001) and more cells per unit capillary length (p=0.0003) compared to Zuckers. Acarbose treatment significantly reduced basement membrane thickening in the treated ZDF rats (p=0.001), but the effects on cell density showed only a favorable trend. Acarbose treatment has an ameliorative effect on the development of microvascular retinopathy in the ZDF rat, probably due to lessening of hyperglycemia.