Brain 11β‐hydroxysteroid dehydrogenase activity: which enzyme?

Abstract

We studied 11β‐HSD activity in rat kidney (positive control) and brain homogenates and subcellular fractions. Samples were incubated with 0.5 mM NAD+ or NADP+ and [1,2 3H] corticosterone for 1h at 37° C. Steroids were extracted, separated by TLC, and the radioactivity represented by corticosterone and 11‐dehydrocorticosterone read by a bioscanner. Conversion of corticosterone to dehdrocorticosterone by homogenates was significantly increased by NADP+, but not NAD+: Cerebel: Control‐24.1±0.4%, NADP+‐60.9±0.8%, NAD+‐21.9±0.7%; Hypothal: Control‐8.2±0.1%, NADP+‐23.6±0.8%, NAD+‐ 7.3±0.0%; Hippoc: Control‐24.2±0.9%, NADP+‐62.1±0.6%, NAD+‐21.9±0.2%, p<0.001 in all). Conversion was significantly greater isolated in microsomes compared to nuclei and mitochondria, and for NADP+ vs NAD+: Cerebel microsomes: NAD+‐5.4±1.7%, NADP+‐34.3±4.6%, p<0.001; Hypothal microsomes: NAD+‐0%; NADP+‐9.2±1.8%, p<0.001; and Hippoc microsomes: NAD+ 0.6±0.6% vs NADP+ 23.1±1.4%, p<0.001). Thiram inhibited NAD+‐dependent HSD activity in 11‐β HSD2‐ transfected CHO cells; it did not in the brain. These data suggest a novel NADP+‐dependent 11β‐HSD that may allow aldosterone to activate some brain mineralocorticoid receptors.Support: VA Medical Research Funds, NIH HL27255 & HL75321, CAPES & FAPESP