The enhancement of the hyperglycemic effect of S-nitrosoglutathione and S-nitroso-N-acetylpenicillamine by vitamin C in an animal model

Understanding the in-vivo relevance of S-nitrosothiols in insulin action

Insulin sensitivity is maximal in the postprandial state, decreasing with a fasting period through a mechanism that is dependent on the integrity of the hepatic parasympathetic nerves/nitric oxide (NO) production and increased hepatic glutathione (GSH) levels. GSH and NO react to form S-nitrosoglutathione (GSNO), an S-nitrosothiol (RSNO) for which the in-vivo effects are still being determined. The goal of this study was to test the hypothesis that in-vivo administration of RSNOs, GSNO, or S-nitroso-N-acetylpenicillamine (SNAP) increases insulin sensitivity in fasted or fed-denervated animals, but not in fed animals, where full postprandial insulin sensitivity is achieved. Fasted, fed, or fed-denervated male Wistar rats were used as models for different insulin sensitivity conditions. The rapid insulin sensitivity test (RIST) was used to measure insulin-stimulated glucose disposal before and after drug administration (GSNO, SNAP, or 3-morpholinosydnonimine (SIN-1), intravenous (i.v.) or to the portal vein (i.p.v.)). Fast insulin sensitivity was not altered by administration of SIN-1 (neither i.v. nor i.p.v.). Intravenous infusion of RSNOs in fasted and fed hepatic denervated rats increased insulin sensitivity by 126.35% ± 35.43% and 82.7% ± 12.8%, respectively. In fed animals, RSNOs decreased insulin sensitivity indicating a negative feedback mechanism. These results suggest that RSNOs incremental effect on insulin sensitivity represent a promising therapeutical tool in insulin resistance states.

Role of nuclear factor (erythroid-derived 2)-like 2 in metabolic homeostasis and insulin action: A novel opportunity for diabetes treatment?

Redox balance is fundamentally important for physiological homeostasis. Pathological factors that disturb this dedicated balance may result in oxidative stress, leading to the development or aggravation of a variety of diseases, including diabetes mellitus, cardiovascular diseases, metabolic syndrome as well as inflammation, aging and cancer. Thus, the capacity of endogenous free radical clearance can be of patho-physiological importance; in this regard, the major reactive oxygen species defense machinery, the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) system needs to be precisely modulated in response to pathological alterations. While oxidative stress is among the early events that lead to the development of insulin resistance, the activation of Nrf2 scavenging capacity leads to insulin sensitization. Furthermore, Nrf2 is evidently involved in regulating lipid metabolism. Here we summarize recent findings that link the Nrf2 system to metabolic homeostasis and insulin action and present our view that Nrf2 may serve as a novel drug target for diabetes and its complications.