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Summary
The aim of this study was to investigate the effects of rooibos tea as a natural source of a wide scale of antioxidants on the prevention and treatment of oxidative stress in streptozotocin-induced diabetic rats. Expected significant changes of biochemical parameters characteristic for experimental diabetic state were found in plasma and tissues eight weeks after single dose streptozotocin application. Administration of aqueous and alkaline extracts of rooibos tea (or N-acetyl-L-cysteine for comparison) to diabetic rats did not affect markers of the diabetic status (glucose, glycated hemoglobin and fructosamine). Besides the parameters characterizing hepatotoxic effect of streptozotocin, rooibos tea significantly lowered advanced glycation end-products (AGEs) and malondialdehyde (MDA) in the plasma and in different tissues of diabetic rats, particularly MDA concentration in the lens. From these results we can conclude that antioxidant compounds in rooibos tea partially prevent oxidative stress and they are effective in both hydrophobic and hydrophilic biological systems. Therefore, rooibos tea as a commonly used beverage can be recommended as an excellent adjuvant support for the prevention and therapy of diabetic vascular complications, particularly for protecting ocular membrane systems against their peroxidation by reactive oxygen species.
Key words
Rooibos tea * Aspalathus linearis * Oxidative stress * Streptozotocin-induced diabetes
Introduction
Many current studies indicated that elevated oxidation of glucose leads to increased production of free radicals and other reactive oxygen species (ROS) as H^sub 2^O^sub 2^, organic peroxides and also singlet oxygen, which are believed together with glycation (Bucala and Cerami 1992) to be the main causes of a wide scale of diabetic complications such as nephropathy, diabetic cataract and retinopathy, neuropathy, cardiovascular diseases and others (West 2000, Bayraktutan 2002). In such a case of excessive production of ROS, endogenous protective mechanisms may not be sufficient to limit ROS and the damage they cause (Sies 1993). As additional mechanisms of dietary antioxidants may be of great importance, many artificial and natural agents possessing antioxidative and radical scavenging properties have been proposed to prevent and to treat oxidative damage induced by ROS developed pathological states (MartinezCayuela 1995, Furst 1996, Kucharská et al. 2004).
As mentioned above, along with a wide scale of artificially prepared antioxidants, numerous naturally occurring plants and fruits, containing compounds with antioxidative and radical scavenging properties, have been...