Non-stereo-selective cytosolic human brain tissue 3-ketosteroid reductase is refractory to inhibition by AKR1C inhibitors

• Published in: Biochimica et biophysica acta 2010-11, Vol.1801 (11), p.1221-1231
• Main Authors: Steckelbroeck, Stephan, Lütjohann, Dieter, Bauman, David R., Ludwig, Michael, Friedl, Anke, Hans, Volkmar H.J., Penning, Trevor M., Klingmüller, Dietrich
• Format: Article
• Language: English
• Subjects: 20-Hydroxysteroid Dehydrogenases - antagonists & inhibitors; 20-Hydroxysteroid Dehydrogenases - genetics; 3-Hydroxysteroid Dehydrogenases - metabolism; 3alpha/3beta-hydroxysteroid dehydrogenase; Adult; Aged; Aldo-keto reductase; Brain - metabolism; Brain - pathology; Cell Line, Tumor; Chromatography, Thin Layer - methods; Female; GABA-A receptor; Gas Chromatography-Mass Spectrometry - methods; Gene Expression Regulation, Enzymologic; HSD; Human brain; Humans; Infant; Middle Aged; Stereo-selective; Steroid 17-alpha-Hydroxylase - genetics; Steroids - chemistry; Temporal Lobe - pathology
• ISSN: 1388-1981; 0006-3002; 1879-2618
• DOI: 10.1016/j.bbalip.2010.07.005

Cerebral 3α-hydroxysteroid dehydrogenase (3α-HSD) activity was suggested to be responsible for the local directed formation of neuroactive 5α,3α-tetrahydrosteroids (5α,3α-THSs) from 5α-dihydrosteroids. We show for the first time that within human brain tissue 5α-dihydroprogesterone and 5α-dihydrotestosterone are converted via non-stereo-selective 3-ketosteroid reductase activity to produce the respective 5α,3α-THSs and 5α,3β-THSs. Apart from this, we prove that within the human temporal lobe and limbic system cytochrome P450c17 and 3β-HSD/Δ 5–4 ketosteroid isomerase are not expressed. Thus, it appears that these brain regions are unable to conduct de novo biosynthesis of Δ 4-3-ketosteroids from Δ 5-3β-hydroxysteroids. Consequently, the local formation of THSs will depend on the uptake of circulating Δ 4-3-ketosteroids such as progesterone and testosterone. 3α- and 3β-HSD activity were (i) equally enriched in the cytosol, (ii) showed equal distribution between cerebral neocortex and subcortical white matter without sex- or age-dependency, (iii) demonstrated a strong and significant positive correlation when comparing 46 different specimens and (iv) exhibited similar sensitivities to different inhibitors of enzyme activity. These findings led to the assumption that cerebral 3-ketosteroid reductase activity might be catalyzed by a single enzyme and is possibly attributed to the expression of a soluble AKR1C aldo-keto reductase. AKR1Cs are known to act as non-stereo-selective 3-ketosteroid reductases; low AKR1C mRNA expression was detected. However, the cerebral 3-ketosteroid reductase was clearly refractory to inhibition by AKR1C inhibitors indicating the expression of a currently unidentified enzyme. Its lack of stereo-selectivity is of physiological significance, since only 5α,3α-THSs enhance the effect of GABA on the GABA A receptor, whereas 5α,3β-THSs are antagonists. ►In the human brain 5α-dihydrosteroids are converted via 3α/β-HSD activity. ►The human brain is unable to conduct de novo biosynthesis of Δ 4-3-ketosteroids. ►The local formation of tetrahydrosteroids depends on the uptake of Δ 4-3-ketosteroids. ►Cytosolic cerebral 3α/β-HSD activity might be catalyzed by a single enzyme. ►AKR1Cs are expressed. ►The cerebral 3α/β-HSD activity is not affected by AKR1C inhibitors. ►The lack of stereo-selectivity is of physiological significance. ►Only 5α,3α-tetrahydrosteroids enhance the effect of GABA on the GABA A receptor. ►5α,3β-tetrahydrosteroids are antag