RESUMO
Paradigms of insulin gene therapy for type 1 diabetes should incorporate vigorous control for insulin gene expression to be effective in correcting postprandial hyperglycemia and to be safe in preventing fasting hypoglycemia. We hypothesize that hepatic insulin gene expression auto-regulated positively by glucose and negatively by insulin might be both effective and safe in the treatment of type 1 diabetes. Expression of the glucose 6-phosphatase (G6Pase) gene in the liver is both stimulated by glucose and suppressed by insulin. The G6Pase promoter incorporated with intronic enhancers of the aldolase B gene was used to direct insulin gene expression in the liver of streptozotocin-induced diabetic nude rats. In the treated animals, blood insulin levels were elevated after feeding, and nonfasting hyperglycemia was significantly reduced. Glucose tolerance testing also illustrated that the treated animals exhibited accelerated glucose utilization rates. Upon fasting, blood glucose was reduced to normoglycemic range within 4 h and maintained at that level during the prolonged fasting of 16 h. No hypoglycemia was observed in any treated animals at any time throughout the fasting period, as blood insulin gradually declined to the normal range. These results suggest that auto-regulated hepatic insulin expression can potentially be developed as an effective and safe treatment modality for type 1 diabetes.
