Effects of (−)-epigallocatechin-3-gallate on pancreatic beta-cell damage in streptozotocin-induced diabetic rats

Oxygen free radicals, which are produced as a result of chronic hyperglycemia, are implicated in many diabetic complications. (−)-Epigallocatechin-3-gallate (EGCG), a green tea polyphenol, has been shown to have both antioxidant and pro-oxidant activities, but its effect on oxidative stress of pancreatic beta cells in vivo is unclear. Here we evaluated the effects of nanomolar concentrations of EGCG on beta-cell survival and the response to high glucose loading in streptozotocin-induced diabetic rats. A 4-day intraperitoneal treatment with EGCG (5 mg/kg/day) further impaired the beta-cell response to high glucose in the diabetic rats. EGCG exacerbated the loss of islet cell mass and insulin-immunoreactivity in beta cells. These results suggest that, even at nanomolar plasma concentrations, EGCG acts as a pro-oxidant rather than an antioxidant, at least in beta cells in vivo.