Green Tea Antioxidants May Prevent or Delay Type 1 Diabetes Onset
November 6, 2008
Epigallocatechin gallate (EGCG), a green tea polyphenol, possesses potent antioxidant, anti-apoptotic, anti-inflammatory, and autoantigen-inhibitory properties. It is therefore extensively studied for probable health benefits against oxidative stress-related diseases including cancer. Now, a study published in the recent issue of the journal Life Sciences has reported that EGCG may also prevent or delay the onset of insulin-dependent type 1 diabetes in mice models. Researchers from the Medical College of Georgia (MCG) uncovered the promising findings while they were investigating the effectiveness of EGCG against Sjogren syndrome (SS).
Sjogren syndrome, an autoimmune disorder, affects moisture-producing glands, leading to xerostomia and keratoconjunctivitis sicca. It may occur alone or in combination with other autoimmune disorders such as rheumatoid arthritis, lupus erythematosus, or scleroderma.
Dr Stephen Hsu, a molecular/cell biologist in the School of Dentistry, MCG, and coworkers, conducted a study to determine the effects of EGCG against autoimmune-induced pathological changes in the salivary glands of non-obese diabetic mouse model for SS. The animals were treated with either water (controls) or water containing 0.2% EGCG. Submandibular salivary gland tissue and serum samples were collected at the age of 8, 16 and 22 weeks for pathological and serological analyses. At 16 weeks of age, lymphocyte infiltration was reduced in the EGCG-fed animals, while there was a considerable amount of infiltration in controls. In comparison to the EGCG group, water-fed animals showed high levels of serum total anti-nuclear antibody and enhanced apoptotic activity within the lymphocytic infiltrates by 22 weeks. The scientists found that the EGCG-fed mice were 6.1 and 4.2 times more likely to be diabetes-free than the water-fed group, at 16 and 22 weeks, respectively. The scientists concluded that EGCG could normalize abnormal proliferation of the salivary gland, a characteristic of the mouse models for Sjogren syndrome. Also, the antioxidant may protect submandibular glands of mice from autoimmune-induced inflammation and reduce serum autoantibody levels, thereby having the potential to delay or control SS-like autoimmune disorders. The researchers plan to conduct further larger studies to verify the positive findings of EGCG in humans.
Earlier, Wolfram, et al. (The Journal of Nutrition, 2006) conducted a study to determine the antidiabetic effects of EGCG in rodent models with type 2 diabetes mellitus and H4IIE rat hepatoma cells. The glucose and insulin tolerance in diabetic (db/db) mice and Zucker diabetic fatty (ZDF) rat models were measured following the treatment with EGCG. Additionally, the effect of EGCG on gene expression was also analyzed using gene microarray and real-time quantitative RT-PCR (reverse transcription-polymerase chain reaction). In a dose-dependant manner, EGCG improved oral glucose tolerance and blood glucose in food-deprived rats. There was an increase in glucose-stimulated insulin secretion and a reduction in the plasma concentrations of triacylglycerol. It was also noted that the genes involved in gluconeogenesis, and the synthesis of fatty acids, triacylgycerol and cholesterol were downregulated by EGCG in the rat hepatoma cells. Considering the findings, the researchers proposed that the tea polyphenol could modify glucose and lipid metabolism with an enhancement of glucose tolerance in diabetic rodents, thus suggesting its efficacy in preventing or treating type 2 diabetes.
EGCG, the most abundant catechin in tea, is known to protect human DNA from ultraviolet and visible radiation-induced damage. Additionally, it may promote fat oxidation, reduce bodyweight and unlike medications (steroids) used for autoimmune diseases, is not associated with adverse-effects.
Currently, the National Institutes of Health (NIH) estimates approximately 23.5 million Americans suffer from an autoimmune disease. Type 1 diabetes, a type of autoimmune disorder, is characterized by the loss of insulin-producing beta cells of the pancreas leading to inadequate production of insulin. According to National Diabetes Information Clearinghouse (NDIC), approximately 5 to 10 % of all diagnosed adult cases of diabetes account for type 1 diabetes in the US. Currently, there is no known cure or preventive treatment for diabetes, and it is managed by insulin replacement therapy.
Several studies are being conducted in the pursuit of developing novel nutritional and exercise strategies for the prevention or treatment of the deadly disease. With the current research identifying the potential health benefits of EGCG in preventing or delaying the onset of type 1 diabetes in mice models, the natural plant extract could serve as an effective dietary supplement against several autoimmune disorders including Sjogren syndrome when proven in human trials.
References
1. Gillespie K, Kodani I, Dickinson DP, et al. Effects of oral consumption of the green tea polyphenol EGCG in a murine model for human Sjogren’s syndrome, an autoimmune disease. Life Sci. 2008 Oct 24;83(17-18):581-8. Epub 2008 Sep 6.
2. Wolfram S, Raederstorff D, Preller M, et al. Epigallocatechin gallate supplementation alleviates diabetes in rodents. J Nutr. 2006 Oct;136(10):2512-8.
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