Antidiabetic role of a novel protein from garlic via NO in expression of Glut-4/insulin in liver of alloxan induced diabetic mice

Introduction: Garlic has been reported to stimulate nitric-oxide (NO) synthesis in various cells. The role of aqueous-extract of garlic (AEG) and a purified NO-generating protein from garlic (NGPG) was investigated to control hyperglycemia by hepatic insulin synthesis through NGPG induced synthesis of NO via glucose-activated NO-synthase and glucose transporter-4 (Glut-4) in the hepatocytes. Methods: Type-1-diabetic mellitus mice were prepared by alloxan treatment, NO was determined by methemoglobin method, insulin synthesis was quantitated by ELISA. TNF-alpha and NF kappa beta was quantitated by ELISA. The AEG-induced Glut-4 synthesis was determined by in-vitro translation of mRNA from the hepatocytes. The NO-generating protein from AEG was purified to homogeneity by chromatography on DEAE-cellulose and Sephadex G-50 columns and sequenced/characterized by Mass-spectral-analysis. Results: Purified NGPG injection to diabetic mice significantly reduced the blood-sugar and increase insulin level in diabetic animal. It also increases insulin-release, Glut-4 synthesis, glucose-uptake in both liver and beta-cells of diabetic mice. NGPG down regulated pro-inflammatory cytokine TNF-alpha and the stress responsive NF kappa B-expression in liver cell of diabetic mice. Injection of AEG to the diabetic mice reduced the blood glucose level from 550 +/- 10 mg/dL to 125 +/- 10 mg/dL in 16 h with simultaneous increase of plasma NO from 0 nmol/h to 2.5 nmol/h and insulin 2 +/- 1.1 mu unit/mL to 15 mu unit/mL at 16 h. Oral administration of AEG to adult diabetic mice increased NO, insulin and Glut-4 synthesis in the hepatocytes. Conclusion: AEG and the purified-NGPG protein can control hyperglycemia through the stimulation of NO by glucose-activated NO-synthase that would play an important role in the synthesis of insulin/Glut-4 in liver-cells.