Anti-diabetic efficacy of combination treatment with the nitric oxide metabolite nitrite and the endogenous antioxidant glutathione in diabetic mice: glutathione combination does not hamper the anti-diabetic effect of nitrite.

ABSTRACT

OBJECTIVE: The nitric oxide (NO) metabolite nitrite has been shown to attenuate hyperglycemia via its increase in insulin sensitivity and glucose uptake. However, the oral use of nitrite is limited due to its potential formation of the carcinogenic N-nitrosamines via reaction of acidic nitrite and the secondary amines. We investigated the anti-diabetic effect of sodium nitrite (SN) combined with glutathione (GSH) in streptozotocin (STZ)-induced diabetic mice for potential use of GSH as a protective agent in future nitrite therapy. MATERIALS AND METHODS: STZ-induced diabetic mice were orally treated for 5 weeks with vehicle, SN, GSH or SN + GSH. Oral glucose tolerance test and the measurement of fasting blood glucose (FBG) and glycosylated hemoglobin (HbA1c) levels were carried out to evaluate anti-diabetic effects of SN and SN + GSH. Plasma levels of total NO metabolites (NOx) were measured to confirm nitrite absorption. RESULTS: SN and SN + GSH significantly improved the glucose tolerance (p < 0.05), but GSH alone did not. The efficacy of combination treatment with SN and GSH in improving the glucose tolerance was higher than that of SN alone. Oral treatment with SN or SN + GSH significant reduced FBG and HbA1c levels (p < 0.05). Interestingly, daily oral administration of SN + GSH was more effective in reducing FBG and HbA1c levels than that of SN alone. Administration of SN or SN + GSH significantly increased plasma NOx levels (p < 0.05), and combination treatment with SN + GSH was more effective in increasing plasma NOx levels than that with SN alone. CONCLUSIONS: Combination treatment with SN and GSH is more effective in controlling hyperglycemia and increasing the plasma NOx levels in an experimental mouse model of diabetes. Since oral administration of GSH has been shown to be non-toxic in humans, the combination of SN and GSH may be important in potential future nitrite therapy.