Harold and Margaret Milliken Hatch, Laboratory of Neuroendocrinology, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA.
J Steroid Biochem Mol Biol. 2013 Nov;138:290-7. doi: 10.1016/j.jsbmb.2013.07.001. Epub 2013 Jul 12.
The neuroprotective action of dehydroepiandrosterone (DHEA) in the absence of a known specific receptor has been attributed to its metabolism by different cell types in the brain to various steroids, with a preference to its 7-hydroxylated products. The E(t)C cerebellar granule cell line converts DHEA almost exclusively to 7α-hydroxy-DHEA (7α-OH-DHEA). It has been postulated that DHEA's 7-OH and 7-oxo metabolites can decrease glucocorticoid levels by an interactive mechanism involving 11β-hydroxysteroid dehydrogenase (11β-HSD). In order to study the relationship of 7-hydroxylation of DHEA and glucocorticoid metabolism in intact brain cells, we examined whether E(t)C cerebellar neurons, which are avid producers of 7α-OH-DHEA, could also metabolize glucocorticoids. We report that E(t)C neuronal cells exhibit 11β-HSD1 reductase activity, and are able to convert 11-dehydrocorticosterone into corticosterone, whereas they do not demonstrate 11β-HSD2 dehydrogenase activity. Consequently, E(t)C cells incubated with DHEA did not yield 7-oxo- or 7β-OH-DHEA. Our findings are supported by the reductive environment of E(t)C cells through expression of hexose-6-phosphate dehydrogenase (H6PDH), which fosters 11β-HSD1 reductase activity. To further explore the role of 7α-OH-DHEA in E(t)C neuronal cells, we examined the effect of preventing its formation using the CYP450 inhibitor ketoconazole. Treatment of the cells with this drug decreased the yield of 7α-OH-DHEA by about 75% without the formation of alternate DHEA metabolites, and had minimal effects on glucocorticoid conversion. Likewise, elevated levels of corticosterone, the product of 11β-HSD1, had no effect on the metabolic profile of DHEA. This study shows that in a single population of whole-cells, with a highly reductive environment, 7α-OH-DHEA is unable to block the reducing activity of 11β-HSD1, and that 7-hydroxylation of DHEA does not interfere with the activation of glucocorticoids. Our investigation on the metabolism of DHEA in E(t)C neuronal cells suggest that other alternate mechanisms must be at play to explain the in vivo anti-glucocorticoid properties of DHEA and its 7-OH-metabolites.
脱氢表雄酮（DHEA）在没有已知特定受体的情况下发挥神经保护作用，这归因于它在大脑不同细胞类型中代谢为各种类固醇，偏爱其 7-羟化产物。E(t)C 小脑颗粒细胞系几乎专门将 DHEA 转化为 7α-羟基-DHEA（7α-OH-DHEA）。有人假设 DHEA 的 7-OH 和 7-氧代代谢物可以通过涉及 11β-羟甾脱氢酶（11β-HSD）的相互作用机制降低糖皮质激素水平。为了研究 DHEA 的 7-羟化与完整脑细胞中糖皮质激素代谢的关系，我们研究了是否 E(t)C 小脑神经元（其是 7α-OH-DHEA 的强烈产生者）也可以代谢糖皮质激素。我们报告说，E(t)C 神经元细胞表现出 11β-HSD1 还原酶活性，并且能够将 11-去氢皮质酮转化为皮质酮，而它们不表现出 11β-HSD2 脱氢酶活性。因此，用 DHEA 孵育的 E(t)C 细胞不会产生 7-氧代或 7β-OH-DHEA。我们的发现得到了 E(t)C 细胞还原性环境的支持，通过表达己糖-6-磷酸脱氢酶（H6PDH）促进 11β-HSD1 还原酶活性。为了进一步探索 7α-OH-DHEA 在 E(t)C 神经元细胞中的作用，我们研究了使用 CYP450 抑制剂酮康唑阻止其形成的效果。用该药物处理细胞可使 7α-OH-DHEA 的产量减少约 75%，而不会形成替代的 DHEA 代谢物，并且对糖皮质激素转化的影响很小。同样，皮质酮水平升高，即 11β-HSD1 的产物，对 DHEA 的代谢谱没有影响。这项研究表明，在具有高度还原性环境的单个全细胞群体中，7α-OH-DHEA 不能阻断 11β-HSD1 的还原活性，并且 DHEA 的 7-羟化不干扰糖皮质激素的激活。我们对 E(t)C 神经元细胞中 DHEA 代谢的研究表明，为了解释 DHEA 及其 7-OH 代谢物的体内抗糖皮质激素特性，其他替代机制必须发挥作用。
