The effects of traditional antidiabetic plants on in vitro glucose diffusion

Abstract

Plants represent a vast source of potentially useful dietary supplements for improving blood glucose control and preventing long-term complications in type 2 diabetes mellitus. Ten aqueous plant extracts with proven antihyperglycemic properties were examined at a concentration of 50g plant extract/l using an in vitro method to assess their possible effects on glucose diffusion across the gastrointestinal tract. Agrimony eupatoria (agrimony) and Persea americana (avocado) decreased glucose movement in vitro more than 50%. Aqueous extracts of Agaricus campestris (mushroom), Coriandrum sativum (coriander), Eucalyptus globulus (eucalyptus), Juniperus communis (juniper), Medicago sativa (lucerne), and Viscum album (mistletoe) decreased significantly glucose movement but were less effective than agrimony and avocado. Urtica diocia (nettle) and Sambucus nigra (elder) extracts did not significantly decrease glucose diffusion. The effects of agrimony, avocado, coriander and mushroom extracts were found to be concentration-dependent. These results suggest that part of the antihyperglycemic actions of these plants may be by decreasing glucose absorption in vivo.

Introduction

Diabetes mellitus is characterised by hyperglycemia that is induced by decreased cellular glucose uptake and metabolism [1]. Control of plasma glucose concentrations is vital to decrease the incidence and severity of long-term diabetic complications [2]. Currently, dietary changes, oral hypoglycaemic agents, or insulin injections are utilised to prevent hyperglycemia. At present, drug therapies either alone or in combination cannot restore normal blood glucose homeostasis, and many limitations exist in their use [3]. While external insulin is necessary for control of type 1 diabetes mellitus, the use of drug therapy in type 2 diabetes is initiated only after dietary and lifestyle modifications [4].

Various dietary regimes have been considered for prevention of hyperglycaemia in diabetes [5]. Jenkins et al. [6] proposed the use of plant derived products containing high concentrations of dietary fibre and complex polysaccharides. Inclusion of viscous polysaccharides in the diet decreased postprandial blood glucose concentrations in subjects with type 2 diabetes [7]. In particular, guar gum has decreased postprandial blood glucose concentrations in several experiments [8]. However, the highly viscous and unpalatable nature of guar gum has limited its use in dietary management of type 2 diabetes [9].

More than 400 plants world-wide have been documented as beneficial in the treatment of diabetes [10]. The majority of traditional antidiabetic plants await proper scientific and medical evaluation for their ability to improve blood glucose control [3], [11]. However, a few comprehensive studies of traditional antidiabetic plants have been carried out [12], [13], [14]. The antidiabetic actions of 37 European plants, traditionally used as adjuncts to the treatment of diabetes, were investigated by dietary administration to streptozotocin-treated mice and db/db mice [15]. These studies identified 21 plants with general beneficial effects, including 11 with significant antihyperglycemic activity [15].

Further studies with the most effective plants (Table 1) demonstrated that the antihyperglycemic activities were in part explained by the ability of water soluble plant components to increase glucose transport and metabolism in muscle and/or to stimulate insulin secretion [16], [17], [18], [19], [20], [21], [22]. To date no research has been carried out to evaluate the potential of these plants to additionally retard the diffusion and movement of glucose in the intestinal tract. The present study was undertaken to investigate the effects of 9 previously studied antidiabetic plants and Persea americana (avocado; Table 1) on glucose movement across dialysis membrane into external solution, which is a convenient model for assessing factors affecting glucose absorption in vitro.