Uptake and metabolism of sulphated steroids by the blood-brain barrier in the adult male rat.

Little is known about the origin of the neuroactive steroids dehydroepiandrosterone sulphate (DHEAS) and pregnenolone sulphate (PregS) in the brain or of their subsequent metabolism. Using rat brain perfusion in situ, we have found 3 H-PregS to enter more rapidly than 3 H-DHEAS and both to undergo extensive (> 50%) desulphation within 0.5 min of uptake. Enzyme activity for the steroid sulphatase catalysing this deconjugation was enriched in the capillary fraction of the blood-brain barrier and its mRNA expressed in cultures of rat brain endothelial cells and astrocytes. Although permeability measurements suggested a net efflux, addition of the efflux inhibitors GF120918 and/or MK571 to the perfusate reduced rather than enhanced the uptake of 3 H-DHEAS and 3 H-PregS; a further reduction was seen upon the addition of unlabelled steroid sulphate, suggesting a saturable uptake transporter. Analysis of brain fractions after 0.5 min perfusion with the 3 H-steroid sulphates showed no further metabolism of PregS beyond the liberation of free steroid pregnenolone. By contrast, DHEAS underwent 17-hydroxylation to form androstenediol in both the steroid sulphate and the free steroid fractions, with some additional formation of androstenedione in the latter. Our results indicate a gain of free steroid from circulating steroid sulphates as hormone precursors at the blood-brain barrier, with implications for ageing, neurogenesis, neuronal survival, learning and memory.

Elevation of brain allopregnanolone rather than 5-HT release by short term, low dose fluoxetine treatment prevents the estrous cycle-linked increase in stress sensitivity in female rats.

Withdrawal from long-term dosing with exogenous progesterone precipitates increased anxiety-linked changes in behavior in animal models due to the abrupt decrease in brain concentration of allopregnanolone (ALLO), a neuroactive metabolite of progesterone. We show that a withdrawal-like effect also occurs during the late diestrus phase (LD) of the natural ovarian cycle in rats, when plasma progesterone and ALLO are declining but estrogen secretion maintains a stable low level. This effect at LD was prevented by short-term treatment with low dose fluoxetine. During LD, but not at other stages of the estrous cycle, exposure to anxiogenic stress induced by whole body vibration at 4 Hz for 5 min evoked a significant decrease in tail flick latency (stress-induced hyperalgesia) and a decrease in the number of Fos-positive neurons present in the periaqueductal gray (PAG). The threshold to evoke fear-like behaviors in response to electrical stimulation of the dorsal PAG was lower in the LD phase, indicating an increase in the intrinsic excitability of the PAG circuitry. All these effects were blocked by short-term administration of fluoxetine (2 × 1.75 mg kg(-1) i.p.) during LD. This dosage increased the whole brain concentration of ALLO, as determined using gas chromatography-mass spectrometry, but was without effect on the extracellular concentration of 5-HT in the dorsal PAG, as measured by microdialysis. We suggest that fluoxetine-induced rise in brain ALLO concentration during LD offsets the sharp physiological decline, thus removing the trigger for the development of anxiogenic withdrawal effects.

Altered brain gene expression but not steroid biochemistry in a genetic mouse model of neurodevelopmental disorder.

BACKGROUND: The 39,XY*O mouse, which lacks the orthologues of the ADHD and autism candidate genes STS (steroid sulphatase) and ASMT (acetylserotonin O-methyltransferase), exhibits behavioural phenotypes relevant to developmental disorders. The neurobiology underlying these phenotypes is unclear, although there is evidence for serotonergic abnormalities in the striatum and hippocampus. METHODS: Using microarray and quantitative gene expression analyses, and gas chromatography-mass spectrometry, we compared brain gene expression and steroid biochemistry in wildtype (40,XY) and 39,XY*O adult mice to identify non-obvious genetic and endocrine candidates for between-group differences in behaviour and neurochemistry. We also tested whether acute STS inhibition by COUMATE in wildtype (40,XY) adult male mice recapitulated any significant gene expression or biochemical findings from the genetic comparison. Data were analysed by unpaired t-test or Mann Whitney U-test depending on normality, with a single factor of KARYOTYPE. RESULTS: Microarray analysis indicated seven robust gene expression differences between the two groups (Vmn2r86, Sfi1, Pisd-ps1, Tagap1, C1qc, Metap1d, Erdr1); Erdr1 and C1qc expression was significantly reduced in the 39,XY*O striatum and hippocampus, whilst the expression of Dhcr7 (encoding 7-dehydrocholesterol reductase, a modulator of serotonin system development), was only reduced in the 39,XY*O hippocampus. None of the confirmed gene expression changes could be recapitulated by COUMATE administration. We detected ten free, and two sulphated steroids in 40,XY and 39,XY*O brain; surprisingly, the concentrations of all of these were equivalent between groups. CONCLUSIONS: Our data demonstrate that the mutation in 39,XY*O mice: i) directly disrupts expression of the adjacent Erdr1 gene, ii) induces a remarkably limited suite of downstream gene expression changes developmentally, with several of relevance to associated neurobehavioural phenotypes and iii) does not elicit large changes in brain steroid biochemistry. It is possible that individuals with STS/ASMT deficiency exhibit a similarly specific pattern of gene expression changes to the 39,XY*O mouse, and that these contribute towards their abnormal neurobiology. Future work may focus on whether complement pathway function, mitochondrial metabolism and cholesterol biosynthesis pathways are perturbed in such subjects.

Metabolism of neuroactive steroids in day-old chick brain.

Metabolism of the neuroactive steroids pregnenolone (PREG), progesterone (PROG), dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulphate (DHEAS) was investigated in day-old chick brain following direct injection of the (3)H-labelled compounds into the intermediate medial mesopallium and sampling at times known to be crucial for memory formation in this brain region. (3)H-label from these steroids was cleared rapidly from the brain, decreasing to barely detectable levels within 5 h. Following extraction and fractionation, the (3)H-labelled brain steroids were identified by TLC, coupled with acetylation and/or separation in different solvent systems. PREG and PROG were converted within 10 min mostly to 20beta-dihydropregnenolone (20beta-DHPREG) and 5beta-dihydroprogesterone, respectively. There was no detectable metabolism of DHEA. Label from DHEAS persisted for longer (half-time 18.9 min) than the free steroid but with no detectable metabolism other than a small amount (4%) of desulphation to DHEA. Further investigation of chick brain steroid metabolism by incubation of subcellular fractions (1-3 h, 37 degrees C) with PREG, PROG or DHEA plus NADPH led to the formation of the following compounds: 20beta-DHPREG from PREG (particularly in cytosol); 5beta-dihydroprogesterone and 3alpha,5beta-tetrahydroprogesterone from PROG and no detectable metabolism of DHEA. Following incubation of the same brain fractions and labelled steroids with NAD(+), there was no detectable metabolism of PREG or PROG but some conversion of DHEA to androstenedione, especially in the nuclear fraction. The results suggest direct actions of DHEA(S) on the early stages of memory formation in the chick and introduce the possibility that PREG may act indirectly via 20beta-DHPREG.

Glucocorticoids trigger Alzheimer disease-like pathobiochemistry in rat neuronal cells expressing human tau.

Amyloid precursor protein (APP) mis-processing and aberrant tau hyperphosphorylation are causally related to the pathogenesis and neurodegenerative processes that characterize Alzheimer's disease (AD). Abnormal APP metabolism leads to the generation of neurotoxic amyloid beta (Abeta), whereas tau hyperphosphorylation culminates in cytoskeletal disturbances, neuronal dysfunction and death. Many AD patients hypersecrete glucocorticoids (GC) while neuronal structure, function and survival are adversely influenced by elevated GC levels. We report here that a rat neuronal cell line (PC12) engineered to express the human ortholog of the tau protein (PC12-htau) becomes more vulnerable to the toxic effects of either Abeta or GC treatment. Importantly, APP metabolism in GC-treated PC12-htau cells is selectively shifted towards increased production of the pro-amyloidogenic peptide C99. Further, GC treatment results in hyperphosphorylation of human tau at AD-relevant sites, through the cyclin-dependent kinase 5 (E.C. 2.7.11.26) and GSK3 (E.C. 2.7.11.22) protein kinases. Pulse-chase experiments revealed that GC treatment increased the stability of tau protein rather than its de novo synthesis. GC treatment also induced accumulation of transiently expressed EGFP-tau in the neuronal perikarya. Together with previous evidence showing that Abeta can activate cyclin-dependent kinase 5 and GSK3, these results uncover a potential mechanism through which GC may contribute to AD neuropathology.

The steroid sulfatase inhibitor COUMATE attenuates rather than enhances access of dehydroepiandrosterone sulfate to the brain in the mouse.

Intraperitoneal injection of adult male mice with the neuroactive steroid dehydroepiandrosterone sulfate (DHEAS) at 1 and 40 mg/kg caused dose-dependent increases in the concentration of both this compound and its corresponding free steroid DHEA in brain within 1 h of injection. Pretreatment of these animals for 24 h with the steroid sulfatase inhibitor COUMATE at a dose (10 mg/kg, p.o.) shown previously to cause almost complete inhibition of this enzyme in liver and brain was expected to increase the amount of the DHEAS dose reaching the brain. Surprisingly however, the increases in brain concentrations of DHEAS and DHEA after injection of DHEAS i.p. were attenuated by pretreatment with COUMATE. The results suggest that the arylsulfamate based steroid sulfatase inhibitors such as COUMATE interfere with the influx of the DHEAS anion into the brain.