Search Results - (Author, Cooperation:Steckelbroeck)

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Dehydroepiandrosterone and its sulphate are important factors for vitality, development and functions of the CNS. They were found to be subjects to a series of enzyme-mediated conversions within the rodent CNS. In the present study, we were able to demonstrate for the first time that membrane-associated dehydroepiandrosterone 7α-hydroxylase activity occurs within the human brain. The cytochrome P450 enzyme demonstrated a sharp pH optimum between 7.5 and 8.0 and a mean KM value of 5.4 µm, corresponding with the presence of the oxysterol 7α-hydroxylase CYP7B1. Real-time RT–PCR analysis verified high levels of CYP7B1 mRNA expression in the human CNS. The additionally observed conversion of dehydroepiandrosterone via cytosolic 17β-hydroxysteroid dehydrogenase activity could be ascribed to the activity of an enzyme with a broad pH optimum and an undetectably high KM value. Subsequent experiments with cerebral neocortex and subcortical white matter specimens revealed that 7α-hydroxylase activity is significantly higher in the cerebral neocortex than in the subcortical white matter (p 〈 0.0005), whereas in the subcortical white matter, 17β-hydroxysteroid dehydrogenase activity is significantly higher than in the cerebral neocortex (p 〈 0.0005). No sex differences were observed. In conclusion, the high levels of CYP7B1 mRNA in brain tissue as well as in a variety of other tissues in combination with the ubiquitous presence of 7α-hydroxylase activity in the human temporal lobe led us to assume a neuroprotective function of the enzyme such as regulation of the immune response or counteracting the deleterious effects of neurotoxic glucocorticoids, rather than a distinct brain specific function such as neurostimulation or neuromodulation.

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Dehydroepiandrosterone (DHEA) and its sulfate (DHEAS) are suggested to be important neurosteroids. We investigated steroid sulfatase (STS) in human temporal lobe biopsies in the context of possible cerebral DHEA(S) de novo biosynthesis. Formation of DHEA(S) in mature human brain tissue has not yet been studied. 17α-Hydroxylase/C17-20-lyase and hydroxysteroid sulfotransferase catalyze the formation of DHEA from pregnenolone and the subsequent sulfoconjugation, respectively. Neither their mRNA nor activity were detected, indicating that DHEA(S) are not produced within the human temporal lobe. Conversely, strong activity and mRNA expression of DHEAS desulfating STS was found, twice as high in cerebral neocortex than in subcortical white matter. Cerebral STS resembled the characteristics of the known placental enzyme. Immunohistochemistry revealed STS in adult cortical neurons as well as in fetal and adult Cajal-Retzius cells. Organic anion transporting proteins OATP-A, -B, -D, and -E showed high mRNA expression levels with distinct patterns in cerebral neocortex and subcortical white matter. Although it is not clear whether they are expressed at the blood–brain barrier and facilitate an influx rather than an efflux, they might well be involved in the transport of steroid sulfates from the blood. Therefore, we hypothesize that DHEAS and/or other sulfated 3β-hydroxysteroids might enter the human temporal lobe from the circulation where they would be readily converted via neuronal STS activity.

Electronic Resource

1365-2826

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Sex steroids exert important effects on the central nervous system (CNS). Although the formation of 17β-hydroxysteroid dehydrogenase (17β-HSD) metabolites in the CNS was discovered almost 30 years ago, conclusive studies concerning 17β-HSD activity in the human brain are still lacking. Therefore, we investigated 17β-HSD in vitro activity in human temporal lobe biopsies of 13 women and 13 men using radioactively labelled androstenedione, testosterone, oestrone and 17β-oestradiol and compared it to that in human placenta, liver, testis and prostate. We could demonstrate androgenic and oestrogenic 17β-HSD activities in all tissues under investigation. The reduction of androstenedione and oestrone in brain was NADPH dependent with a broad pH optimum between 6.5 and 9.0, whereas the oxidation of testosterone and 17β-oestradiol was NAD dependent with a pH optimum of ≥9.0. Using optimum cofactors sex differences of brain 17β-HSD activities were not observed. Conversion of androstenedione, testosterone, oestrone and 17β-oestradiol was significantly higher in the subcortical white matter than in the cerebral cortex. We could demonstrate a significant formation of testosterone in the brain tissue of all patients under investigation. Substrate specificity and cofactor requirement patterns as well as pH optima and kinetic properties suggest the occurrence of 17β-HSD type 3 and type 4 in the human temporal lobe.

Electronic Resource