Clinical and Experimental Pharmacology and Physiology (2005) 32, 70–75 PROTECTIVE ROLE OF TEA CATECHINS AGAINST OXIDATION-INDUCED DAMAGE OF TYPE 2 DIABETIC ERYTHROCYTES Syed Ibrahim Rizvi, Mohd Abu Zaid, Rafat Anis and Neetu Mishra Department of Biochemistry, University of Allahabad, Allahabad, India SUMMARY 1. Oxidative stress is recognized as a major contributing factor for the development of late complications of diabetes. 2. Tea contains polyphenolic compounds (catechins), which have many important biological properties, including strong anti-oxidant activity. 3. The present study was undertaken to evaluate the effect of tea catechins (epigallocatechin gallate (EGCG), epigallocate- chin (EGC), epicatechin gallate (ECG) and epicatechin (EC)) on markers of oxidative stress (malondialdehyde (MDA), reduced glutathione (GSH) and membrane -SH group) in erythrocytes from type 2 diabetics. 4. Oxidative stress was induced in normal and type 2 diabetic erythrocytes by incubating with tert-butyl hydro- peroxide (t-BHP). 5. Diabetic erythrocytes have higher MDA and decreased GSH and membrane -SH groups compared with normal erythrocytes. 6. Our results show that tea catechins protect erythrocytes from t-BHP-induced oxidative stress, the effect being more pronounced in diabetic erythrocytes. The relative effectiveness of individual catechins are in the order of EGCG > ECG > EGC > EC. 7. We hypothesise that a higher intake of catechin-rich food by diabetic patients may provide some protection against the development of long-term complications of diabetes. Key words: erythrocytes, oxidative stress, tea catechins, type 2 diabetes. INTRODUCTION Diabetes is one of the most common non-communicable diseases globally. It is estimated that by the year 2010 the total number of people with diabetes will reach 221 million, the areas likely to be most affected being Asia and Africa. 1 Complications from diabetes, such as coronary artery and peripheral vascular disease, stroke, diabetic neuropathy, amputations, renal failure and blind- ness, result in increasing disability, reduced life expectancy and enormous health costs. Genetic susceptibility to type 2 diabetes coupled with lifestyle changes is a major factor for the growing incidence of diabetes in Asian countries. 2 Although little can be done to avert genetic susceptibility, efforts can be made to delay/ prevent the development of diabetic complications. Several studies have emphasised the importance of anti-oxidants in diabetes and low levels of plasma anti-oxidants have been implicated as a risk factor for the development of the disease. 3 In diabetes mellitus, chronic hyperglycaemia produces multiple biochemical sequelae and diabetes-induced oxidative stress could play a role in the onset and progression of disease. Many of the complications of diabetes, including retinopathy and athero- sclerotic vascular disease, the leading cause of mortality in diabetes, have been linked to oxidative stress. 4 A rational extension of the proposed role for oxidative stress is the suggestion that the different susceptibility of diabetic patients to micro- and macro- vascular complications may be a function of the endogenous anti- oxidant status. 4 Many in vitro and in vivo studies have demonstrated that several parameters of erythrocyte function and integrity are negatively affected by increased oxidative stress. In fact, changes in membrane fluidity and inactivation of membrane-bound receptors and enzymes, 5 ionic parameters, 6 an increase in lipid peroxidation, 7 oxidation of glutathione and protein sulphydryl group 8 and activ- ation of proteolysis 9 have all been described following the applic- ation of oxidative stress to erythrocytes. Decreased erythrocyte anti-oxidative capacity in non-insulin-dependent diabetes mellitus (NIDDM) has been shown to be correlated with several diabetic complications. Atherosclerosis and microvascular complications in diabetes are reported to be linked with a reduced anti-oxidant status of diabetic erythrocytes. 10 The importance of erythrocytes in diabetes research is highlighted by the observation that anti- oxidant deficiency and excessive peroxide-mediated damage in erythrocytes precede the development of the frank diabetic state. 11 Tea (Camellia sinensis) is the most popular beverage worldwide. Epidemiological studies indicate that tea consumption may reduce the risk of cardiovascular disease. 12 Tea contains polyphenolic compounds, collectively known as catechins, belonging to the flavonoid family. Quantitatively, the most important catechins in green tea are epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG) and epicatechin (EC) (Fig. 1). Catechins are known to posses anti-oxidant, 13 anticancer, 14 vasorelaxant 15 and hypoglycaemic 16 activities. The exact Correspondence: Syed Ibrahim Rizvi, Department of Biochemistry, University of Allahabad, Allahabad, 211 002, India. Email: rzv@rediffmail.com Received 6 June 2004; revision 2 September 2004; accepted 24 October 2004.