Alterations in indices of oxidative stress and diabetes in type i diabetic rats on a low-carbohydrate diet and pycnogenol

Abstract

Glucose, the major fuel for most body tissues, derives largely from ingested carbohydrates. Considering that a primary feature of diabetes is persistent hyperglycemia, reducing exogenous carbohydrates is expected to moderate absolute serum glucose values and oscillations. Chronically elevated glucose levels are known to increase oxidative stress in tissues amongst other effects, and lead to late and chronic complications in kidney, eye and the cardiovascular system. The objective of this study was to evaluate the impact of a very low-carbohydrate diet alone or with addition of pycnogenol, a potent antioxidant, on biomarkers of oxidative stress in various body organs as well as on physiological indices of diabetes in a Type 1 diabetes (streptozotocin induced) model. In diabetic rats at both 30 and 90 days, the low-carbohydrate diet (27% protein, 5-12% carbohydrate, 62-68% fat) significantly reduced blood glucose, glycated hemoglobin, alanine aminotransferase and normalized aspartate aminotransferase, implying less damage to tissues than a standard rat chow (27% protein, 61% carbohydrate, 12% fat). The test diet greatly minimized polyuria, polydipsia, polyphagia and loose stool in diabetics. It further improved fasting triglycerides and HDL cholesterol, blood urea nitrogen and creatinine. In both studies, diabetes-induced alterations in cardiac catalase and glutathione peroxidase, hepatic γ-glutamyl transpeptidase and erythrocyte malondialdehyde were ameliorated or normalized by the test diet. Addition of pycnogenol reduced serum alkaline phosphatase, triglycerides, total cholesterol, liver γ- glutamyl transpeptidase, renal glutathione peroxidase and renal reduced glutathione. It increased cardiac and renal glutathione to oxidized glutathione ratio. In non-diabetics the PREVIEW vi low-carbohydrate diet elevated serum alkaline phosphatase, total and HDL cholesterol and reduced water intake. It reduced liver and kidney catalase. Pycnogenol had beneficial effects on blood malondialdehyde and glutathione molecules, and increased retinal glutathione peroxidase and reductase. Pycnogenol lowered total and HDL cholesterol, and decreased liver and renal catalase. Overall, the low-carbohydrate diet ameliorated several factors altered by diabetes and did not engender worse effects. The benefits may have resulted from lowered glucose levels or from effects of dietary fatty acids. Addition of pycnogenol vastly improved the health status of diabetic animals in particular. Pycnogenol had mixed effects in the non-diabetic kidney that warrant further investigation.