Background: 11beta-Hydroxysteroid dehydrogenase types 1 and 2 (11betaHSD1 and 11betaHSD2) are two isoenzymes that convert inactive glucocorticoids (e.g., cortisone) to their active forms (e.g., cortisol) and vice versa. Abundant evidence indicates that 11betaHSD2 is expressed as mRNA and protein in both adrenal cortex and adrenal tumors. In contrast, 11betaHSD1 has been investigated to a much lesser degree. We therefore studied and compared the expression and activity of the two isoenzymes in the human adrenal cortex (HAC) and cortisol-secreting adenomas (CSAs).
Methods: Six HAC and six CSA specimens were studied. 11betaHSD1 and 11betaHSD2 gene expression was studied by conventional and semiquantitative reverse transcription-polymerase chain reaction. 11betaHSD1 and 11betaHSD2 activity was assayed by measuring the capacity of both microsomal fraction and tissue fragments to convert [3H]cortisone to [3H]cortisol and vice versa. Steroid hormones were separated and purified by high-performance liquid chromatography, and cortisol concentration was measured by radioimmunoassay.
Results: Semiquantitative reverse transcription-polymerase chain reaction and enzymatic assay demonstrated higher 11betaHSD1 expression and activity and lower 11betaHSD2 expression and activity in CSAs than in HACs. CSA slices secreted larger amounts of cortisol than did HAC specimens, and the cholesterol side-chain-cleaving enzyme inhibitor aminoglutethimide, by blocking the early step of steroid synthesis, reduced cortisol secretion by approximately 70%. Aminoglutethimide decreased [3H]cortisol production from [3H]cortisone and increased [3H]cortisone production from [3H]cortisol in both tissues, thereby annulling differences in 11betaHSD1 and 11betaHSD2 activity between HACs and CSAs.
Conclusion: Collectively, our findings indicate that 1) both 11betaHSD isoenzymes are expressed as mRNA and proteins in the HAC and CSA, with 11betaHSD1 upregulated and 1betaHSD2 downregulated in CSAs; and 2) 11betaHSD1 and 11betaHSD2 activity is positively and negatively correlated with the intracellular concentration of steroid hormones. Hence, 11betaHSD isoenzymes could act as amplifiers of the secretagogue effect of agonists and could contribute to the elevated hormonal secretion of CSAs.