R Veluthakal1, I Khan, M Tannous, A Kowluru. 1. Department of Pharmaceutical Sciences, Wayne State University and beta Cell Biochemistry Research Laboratory, John D. Dingell VA Medical Center, Detroit, MI 48201, USA.
Abstract
AIMS/HYPOTHESIS: It is well established that long-term exposure of isolated beta cells to cytokines [e.g., IL-1beta] results in increased expression of inducible nitric oxide synthase and subsequent release of nitric oxide, which in turn, has been shown to mediate a wide array of effects, including alterations in cellular high-energy metabolism. In this context, several extant studies have demonstrated significant reduction in adenine and guanine nucleotide triphosphate levels in beta cells exposed to IL-1beta. Herein, we examined the functional status of glyceraldehyde-3-phosphate dehydrogenase [GAPDH] in insulin-secreting cells exposed to IL-1beta, since it represents the first enzyme in the glycolytic pathway that is involved in the generation of ATP. METHODS: GAPDH was assayed spectrophotometrically in the cytosolic fraction derived from control and IL-1beta -treated [300 pM for 24 hrs] insulin-secreting cell lines [HIT-T15 and RINm5F]. RESULTS: IL-treatment resulted in marked attenuation of GAPDH activity in HIT and RIN cells; such a reduction in this activity was not due to inhibition of its expression by IL-1. Instead, we observed that incubation of HIT and RIN lysates with peroxynitrite, a reactive intermediate of nitric oxide with superoxide anion, resulted in significant reduction in the GAPDH activity. CONCLUSION/ INTERPRETATION: These results identify a GAPDH as one of the biochemical loci for the effects of IL-derived peroxynitrite in the islet beta cell. The previously reported reduction in high-energy phosphate levels in an IL-treated beta cell may, in part, be due to inhibition of GAPDH activity, and subsequent reduction in the glycolytic efficiency of the beta cell.
AIMS/HYPOTHESIS: It is well established that long-term exposure of isolated beta cells to cytokines [e.g., IL-1beta] results in increased expression of inducible nitric oxide synthase and subsequent release of nitric oxide, which in turn, has been shown to mediate a wide array of effects, including alterations in cellular high-energy metabolism. In this context, several extant studies have demonstrated significant reduction in adenine and guanine nucleotide triphosphate levels in beta cells exposed to IL-1beta. Herein, we examined the functional status of glyceraldehyde-3-phosphate dehydrogenase [GAPDH] in insulin-secreting cells exposed to IL-1beta, since it represents the first enzyme in the glycolytic pathway that is involved in the generation of ATP. METHODS:GAPDH was assayed spectrophotometrically in the cytosolic fraction derived from control and IL-1beta -treated [300 pM for 24 hrs] insulin-secreting cell lines [HIT-T15 and RINm5F]. RESULTS: IL-treatment resulted in marked attenuation of GAPDH activity in HIT and RIN cells; such a reduction in this activity was not due to inhibition of its expression by IL-1. Instead, we observed that incubation of HIT and RIN lysates with peroxynitrite, a reactive intermediate of nitric oxide with superoxide anion, resulted in significant reduction in the GAPDH activity. CONCLUSION/ INTERPRETATION: These results identify a GAPDH as one of the biochemical loci for the effects of IL-derived peroxynitrite in the islet beta cell. The previously reported reduction in high-energy phosphate levels in an IL-treated beta cell may, in part, be due to inhibition of GAPDH activity, and subsequent reduction in the glycolytic efficiency of the beta cell.