The effects of traditional antidiabetic plants on in vitro glucose diffusion
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.
Section snippets
Plant materials and preparation of plant extracts
Dried material of 10 plants (Agaricus campestris (mushroom), Agrimony eupatoria (agrimony), Coriandrum sativum (coriander), Eucalyptus globulus (eucalyptus), Juniperus communis (juniper), Medicago sativa (lucerne), Persea americana (avocado), Sambucus nigra (elder), Urtica diocia (nettle), and Viscum album (mistletoe) were obtained from a commercial source in Birmingham (West Midlands, UK). These were homogenised to a fine powder and stored at room temperature (20 ± 2°C) in opaque screw-top
Effects of plant extracts on glucose diffusion in vitro
After 26 h without plant extract (control), glucose movement out of dialysis had reached a plateau with a mean glucose concentration in the external solution was 9.6 ± 0.3 mmol/l (Fig. 1). Agrimony and avocado extracts were the most potent inhibitors of glucose movement in the model system. In the presence of agrimony extract (50 g/l) glucose diffusion was significantly decreased after 2 h and external glucose concentrations were 3.5 ± 0.3 mmol/l after 26 h (Fig. 1). This corresponds to an
Discussion
Over 400 plants have been documented as being useful for control of blood glucose concentration; however, the majority of these plants have yet to be scientifically or medically evaluated [10]. Dietary control of diabetes is fundamental to the management and treatment of NIDDM. In the last few decades, a number of studies have indicated the value of plant fibre or complex carbohydrates, including highly viscous soluble fibres such as guar gum and (β-glucan, for control of blood glucose
Acknowledgements
These studies were supported by the Department of Health and Social Services, Northern Ireland and the University of Ulster research strategy funding.
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