Indexed on: 22 Oct '08Published on: 22 Oct '08Published in: Life Sciences
The kidney metabolizes endogenous glucocorticoids using one of 2 isoforms of the enzyme 11ss-Hydroxysteroid Dehydrogenase (11ss-HSD). 11ss-HSD1 is located in the later portion of the proximal tubule and interstitial cells and 11ss-HSD2 is found in the mineralocorticoid sensitive collecting duct. Both renal isoforms appear to function as dehydrogenases, inactivating glucocorticoids. Since our laboratory has established that both renal cyclo-oxygenase-2 (COX-2) and 11ss-HSD1 co-localize in human kidney, we hypothesized that the two enzymes might functionally interact and influence each other's expression and/or activity.Using immuno-histochemistry staining with specific antibodies, both enzymes co-localize in later segments of proximal tubules in rat kidney and in rat hepatocytes. There was no co-localization with 11ss-HSD2 in the kidney. The co-localization was confirmed by Western blot and by immuno-precipitation in cultured rat proximal tubular cells (IRPTC). IRPTC incubated with corticosterone 1 microM or with corticosterone 10 nM plus the 11ss-HSD inhibitor carbenoxolone 1 microM demonstrated a decrease in the expression of COX-2 by Western blot at 24 h. When IRPTC were exposed to the COX-2 inhibitor, celecoxib, 11ss-HSD1 dehydrogenase activity was inhibited in a dose dependent manner with an IC50 of 1.4 microM. Celecoxib 2 microM had minimal effect on reductase activity in liver slices.Thus, COX-2 and 11ss-HSD1 co-localize in renal proximal tubules and in hepatocytes. In the kidney, each can influence the biological function of the other. The NSAID celecoxib may exert some of its anti-inflammatory effects on the kidney by locally prolonging the biologic half-life of endogenous glucocorticoids.