Possible role for the thioredoxin system in the protective effects of probucol in the pancreatic islets of diabetic rats.

1. Probucol, a lipid-lowering agent with a potent anti-oxidant action, protects diabetic pancreatic islets by an as yet unknown mechanism. Thioredoxin-interacting protein (TXNIP), an endogenous inhibitor of the ubiquitous thiol oxidoreductase thioredoxin (TRX), has been associated with oxidative stress in diabetic rat islets. The aim of the present study was to examine the effects of probucol on diabetic islet function and expression of TRX and TXNIP. 2. Thirty rats were randomly assigned to one of three groups: a normal control group, a diabetic group and a probucol-treated diabetic group. After 8 weeks treatment with probucol (500 mg/kg per day), plasma malondialdehyde (MDA), superoxide dismutase (SOD) and catalase (CAT) activity were determined using chemical colourimetric methods. In addition, the expression of insulin, TRX and TXNIP in islets was analysed using immunohistochemical, western blot and reverse transcription-polymerase chain reaction methods. 3. The expression of TRX and insulin in islets and plasma SOD and CAT activity were lower, but the expression of TXNIP in islets and plasma MDA were higher, in diabetic compared with normal control rats. Upregulated expression of TRX and insulin and downregulated expression of TXNIP were observed in probucol-treated diabetic rats. Probucol treatment increased plasma SOD, decreased plasma MDA and improved hypoinsulinaemia in diabetic rats. 4. The results indicate that treatment with probucol decreases TXNIP expression and increases TRX expression, which may alleviate hypoinsulinaemia by reducing oxidative stress. Therefore, probucol shows promise as a supplemental therapy for islet protection in Type 2 diabetes mellitus.