Human hepatic cortisol reductase activities: enzymatic properties and substrate specificities of cytosolic cortisol delta 4-5 beta-reductase and dihydrocortisol-3 alpha-oxidoreductase(s)

Management aspects of congenital adrenal hyperplasia during adolescence and transition to adult care

The adolescent period is characterised by fundamental hormonal changes, which affect sex steroid production, cortisol metabolism and insulin sensitivity. These physiological changes have a significant impact on patients with congenital adrenal hyperplasia (CAH). An essential treatment aim across the lifespan in patients with CAH is to replace glucocorticoids sufficiently to avoid excess adrenal androgen production but equally to avoid cardiometabolic risks associated with excess glucocorticoid intake. The changes to the hormonal milieu at puberty, combined with poor adherence to medical therapy, often result in unsatisfactory control exacerbating androgen excess and increasing the risk of metabolic complications due to steroid over-replacement. With the physical and cognitive maturation of the adolescent with CAH, fertility issues and sexual function become a new focus of patient care in the paediatric clinic. This requires close surveillance for gonadal dysfunction, such as irregular periods/hirsutism or genital surgery-associated symptoms in girls and central hypogonadism or testicular adrenal rest tumours in boys. To ensure good health outcomes across the lifespan, the transition process from paediatric to adult care of patients with CAH must be planned carefully and early from the beginning of adolescence, spanning over many years into young adulthood. Its key aims are to empower the young person through education with full disclosure of their medical history, to ensure appropriate follow-up with experienced physicians and facilitate access to multispecialist teams addressing the complex needs of patients with CAH.

iTRAQ-based quantitative proteomic analyses the cycle chronic heat stress affecting liver proteome in yellow-feather chickens

Heat stress (HS) is one of the main environmental factors affecting the efficiency of poultry production. The yellow-feather chickens (YFC) as an indigenous strain of chicken is a popular poultry breed in China. Our previous study used the RNA-seq to analyze the gene expression profiles of male YFC under HS and showed that the lipid and energy metabolism pathways are activated in livers of YFC exposed to acute HS (38°C, 4 h and 25°C recovery 2 h). In this study, we used quantitative proteome analysis based on iTRAQ to study the liver response of YFC to cycle chronic HS (38 ± 1°C, 8 h/d, 7 d, CyCHS). The male YFCs treatment used the CyCHS from 22 to 28 days of age. The liver tissue samples were collected at 28 d old. A total of 39,327 unique peptides matches were detected using iTRAQ analysis and 4,571 proteins exhibited a false discovery rate of 1% or less. Forty-six significant differentially expressed proteins (DEPs) were detected in the CyCHS group compared with the control group for the liver samples, including up- and down-regulated DEPs were 18 and 28, respectively. We found that the enriched biological process terms of the DEPs expressed in the liver were related to DNA metabolic process, oxidation-reduction process, oxidative stress and gluconeogenesis. In KEGG pathway analysis. Most of the hepatic DEPs were annotated to glutathione metabolism and TCA cycle in response to CyCHS. The up-regulation of 5 DEPs (GPX1, GSTT1, GSTT1L, RRM2, and LOC100859645) in the glutathione metabolism pathway likely reflects an attempt to deal with oxidative damage by CyCHS. The down-regulation of 3 DEPs (Isocitrate dehydrogenase [IDH3A], IDH3B, and phosphoenolpyruvate carboxykinase 1) in the TCA cycle pathway contributes to the regulation mechanism of energy metabolism and probably to cope with the balance of heat production and dissipation during CyCHS in order to adapt to high temperature environments. Our results provide insights into the potential molecular mechanism in heat-induced oxidative stress and energy in YFCs and future studies will investigate the functional genes associated with the response to HS.

Improved Urinary Cortisol Metabolome in Addison Disease: A Prospective Trial of Dual-Release Hydrocortisone

CONTEXT

Oral once-daily dual-release hydrocortisone (DR-HC) replacement therapy has demonstrated an improved metabolic profile compared to conventional 3-times-daily (TID-HC) therapy among patients with primary adrenal insufficiency. This effect might be related to a more physiological cortisol profile, but also to a modified pattern of cortisol metabolism.

OBJECTIVE

This work aimed to study cortisol metabolism during DR-HC and TID-HC.

DESIGN

A randomized, 12-week, crossover study was conducted.

INTERVENTION AND PARTICIPANTS

DC-HC and same daily dose of TID-HC were administered to patients with primary adrenal insufficiency (n = 50) vs healthy individuals (n = 124) as controls.

MAIN OUTCOME MEASURES

Urinary corticosteroid metabolites were measured by gas chromatography/mass spectrometry at 24-hour urinary collections.

RESULTS

Total cortisol metabolites decreased during DR-HC compared to TID-HC (P < .001) and reached control values (P = .089). During DR-HC, 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) activity measured by tetrahydrocortisol + 5α-tetrahydrocortisol/tetrahydrocortisone ratio was reduced compared to TID-HC (P < .05), but remained increased vs controls (P < .001). 11β-HSD2 activity measured by urinary free cortisone/free cortisol ratio was decreased with TID-HC vs controls (P < .01) but normalized with DR-HC (P = .358). 5α- and 5β-reduced metabolites were decreased with DR-HC compared to TID-HC. Tetrahydrocortisol/5α-tetrahydrocortisol ratio was increased during both treatments, suggesting increased 5β-reductase activity.

CONCLUSIONS

The urinary cortisol metabolome shows striking abnormalities in patients receiving conventional TID-HC replacement therapy, with increased 11β-HSD1 activity that may account for the unfavorable metabolic phenotype in primary adrenal insufficiency. Its change toward normalization with DR-HC may mediate beneficial metabolic effects. The urinary cortisol metabolome may serve as a tool to assess optimal cortisol replacement therapy.

The distorting effect of varying diets on fecal glucocorticoid measurements as indicators of stress: a cautionary demonstration using laboratory mice

The physiological stress response is frequently gauged in animals, non-invasively, through measuring glucocorticoids in excreta. A concern with this method is, however, the unknown effect of variations in diets on the measurements. With an energy dense diet, leading to reduced defecation, will low concentrations of glucocorticoids be artificially inflated? Can this effect be overcome by measuring the total output of glucocorticoids in excreta? In a controlled laboratory setting we explored the effect in mice. When standard mouse chow - high in dietary fiber - was replaced with a 17% more energy-dense diet, fecal mass was significantly reduced. As circulating levels of corticosterone and the total output of corticosterone metabolites over time remained unaffected, the result was an overestimation - more than a doubling - of the corticosterone metabolite excretion if expressed as concentrations. Similar results were obtained for testosterone metabolites. Although measuring the total output is not feasible in, for example, wildlife studies, the present findings highlight the perilousness of relying on concentrations of hormones in excreta with no associated information of the dietary intake as even moderate changes can exert a great influence.

Role of aldo-keto reductase family 1 (AKR1) enzymes in human steroid metabolism

Human aldo-keto reductases AKR1C1-AKR1C4 and AKR1D1 play essential roles in the metabolism of all steroid hormones, the biosynthesis of neurosteroids and bile acids, the metabolism of conjugated steroids, and synthetic therapeutic steroids. These enzymes catalyze NADPH dependent reductions at the C3, C5, C17 and C20 positions on the steroid nucleus and side-chain. AKR1C1-AKR1C4 act as 3-keto, 17-keto and 20-ketosteroid reductases to varying extents, while AKR1D1 acts as the sole Δ(4)-3-ketosteroid-5β-reductase (steroid 5β-reductase) in humans. AKR1 enzymes control the concentrations of active ligands for nuclear receptors and control their ligand occupancy and trans-activation, they also regulate the amount of neurosteroids that can modulate the activity of GABAA and NMDA receptors. As such they are involved in the pre-receptor regulation of nuclear and membrane bound receptors. Altered expression of individual AKR1C genes is related to development of prostate, breast, and endometrial cancer. Mutations in AKR1C1 and AKR1C4 are responsible for sexual development dysgenesis and mutations in AKR1D1 are causative in bile-acid deficiency.

Substrate specificity and inhibitor analyses of human steroid 5β-reductase (AKR1D1)

Human steroid 5β-reductase (aldo-keto reductase 1D1) catalyzes the stereospecific NADPH-dependent reduction of the C4-C5 double bond of Δ(4)-ketosteroids to yield an A/B cis-ring junction. This cis-configuration is crucial for bile acid biosynthesis and plays important roles in steroid metabolism. The biochemical properties of the enzyme have not been thoroughly studied and conflicting data have been reported, partially due to the lack of highly homogeneous protein. In the present study, we systematically determined the substrate specificity of homogeneous human recombinant AKR1D1 using C18, C19, C21, and C27 Δ(4)-ketosteroids and assessed the pH-rate dependence of the enzyme. Our results show that AKR1D1 proficiently reduced all the steroids tested at physiological pH, indicating AKR1D1 is the only enzyme necessary for all the 5β-steroid metabolites present in humans. Substrate inhibition was observed with C18 to C21 steroids provided that the C11 position was unsubstituted. This structure activity relationship can be explained by the existence of a small alternative substrate binding pocket revealed by the AKR1D1 crystal structure. Non-steroidal anti-inflammatory drugs which are potent inhibitors of the related AKR1C enzymes do not inhibit AKR1D1. By contrast chenodeoxycholate and ursodeoxycholate were found to be potent non-competitive inhibitors suggesting that bile-acids may regulate their own synthesis at the level of AKR1D1 inhibition.

The effect of disease associated point mutations on 5β-reductase (AKR1D1) enzyme function

The stereospecific 5β-reduction of Δ(4)-3-ketosterols is very difficult to achieve chemically and introduces a 90° bend between ring A and B of the planar steroid. In mammals, the reaction is catalyzed by steroid 5β-reductase, a member of the aldo-keto reductase (AKR) family. The human enzyme, AKR1D1, plays an essential role in bile-acid biosynthesis since the 5β-configuration is required for the emulsifying properties of bile. Deficient 5β-reductase activity can lead to cholestasis and neo-natal liver failure and is often lethal if it remains untreated. In five patients with 5β-reductase deficiency, sequencing revealed individual, non-synonymous point mutations in the AKR1D1 gene: L106F, P133R, G223E, P198L and R261C. However, mapping these mutations to the AKR1D1 crystal structure failed to reveal any obvious involvement in substrate or cofactor binding or catalytic mechanism, and it remained unclear whether these mutations could be causal for the observed disease. We analyzed the positions of the reported mutations and found that they reside in highly conserved portions of AKR1D1 and hypothesized that they would likely lead to changes in protein folding, and hence enzyme activity. Attempts to purify the mutant enzymes for further characterization by over-expression in Escherichia coli yielded sufficient amounts of only one mutant (P133R). This enzyme exhibited reduced K(m) and k(cat) values with the bile acid intermediate Δ(4)-cholesten-7α-ol-3-one as substrate reminiscent of uncompetitive inhibition. In addition, P133R displayed no change in cofactor affinity but was more thermolabile as judged by CD-spectroscopy. When all AKR1D1 mutants were expressed in HEK 293 cells, protein expression levels and enzyme activity were dramatically reduced. Furthermore, cycloheximide treatment revealed decreased stability of several of the mutants compared to wild type. Our data show, that all five mutations identified in patients with functional bile acid deficiency strongly affected AKR1D1 enzyme functionality and therefore may be causal for this disease.

Flutamide decreases cortisol clearance in patients with congenital adrenal hyperplasia

Classic congenital adrenal hyperplasia due to 21-hydroxylase deficiency is characterized by a defect in cortisol and aldosterone secretion and adrenal hyperandrogenism. Current treatment is to provide adequate glucocorticoid and mineralocorticoid substitution to prevent adrenal crises and to suppress excess adrenal androgen secretion. Satisfactory adrenocortical suppression often requires supraphysiological doses of hydrocortisone, which may produce an unacceptable degree of hypercortisolism. A new four-drug treatment regimen of flutamide, testolactone, reduced hydrocortisone dose, and 9alpha-fludrocortisone has been shown to achieve normal growth and development after 2 yr of therapy and may, therefore, represent a potential alternative approach to the treatment of children with classic congenital adrenal hyperplasia. We investigated the effect of flutamide and testolactone, and flutamide alone, on cortisol clearance by performing clearance studies twice in 13 children (6 males and 7 females; age range, 7.0-14.5 yr) with classic 21-hydroxylase deficiency. All studies were conducted at least 3 months after institution of the four-drug treatment regimen. In eight patients (group 1), the first cortisol clearance study was performed on the four-drug regimen, and the second study was performed after a 48-h washout period off flutamide and testolactone. In five patients (group 2), the first study was conducted 1 wk after discontinuation of testolactone and while patients were receiving flutamide, hydrocortisone and 9alpha-fludrocortisone, and the second study was performed after a 48-h washout period off flutamide. Oral hydrocortisone was held on the day of the clearance studies, and all patients received a continuous infusion of hydrocortisone (0.6 mg/m(2).h) from 1800 h to 0200 h, with cortisol concentrations measured once hourly. In addition, an in vitro study was conducted to exclude the possibility of an analytical interference of flutamide, 2-hydroxyflutamide, and testolactone with the serum cortisol immunoassay. Total body cortisol clearance was significantly lower during treatment with the four-drug regimen than during treatment with hydrocortisone and 9alpha-fludrocortisone (153.5 +/- 26.8 vs.355.4 +/- 65.8 ml/min; P = 0.001). Similar results were obtained comparing flutamide, hydrocortisone, and 9alpha-fludrocortisone therapy to hydrocortisone and 9alpha-fludrocortisone therapy (155.8 +/- 26.5 vs. 281.8 +/- 96.2 ml/min; P = 0.037). The in vitro study indicated that an interference with the serum cortisol immunoassay was unlikely. These findings indicate that the addition of flutamide and testolactone to the treatment regimen of hydrocortisone and 9alpha-fludrocortisone decreases cortisol clearance in patients with classic 21-hydroxylase deficiency, and this effect seems to be due to flutamide. Glucocorticoid replacement doses should be reduced when flutamide is added to the treatment regimen of patients receiving hydrocortisone.

Congenital adrenal hyperplasia due to 21-hydroxylase deficiency: alterations in cortisol pharmacokinetics at puberty

In congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency, treatment with glucocorticoid and mineralocorticoid substitution is not always satisfactory. Suboptimal control is often observed in pubertal patients, despite adequate replacement doses and adherence to treatment. We investigated whether the pubertal process is associated with alterations in cortisol pharmacokinetics resulting in a loss of control of the hypothalamic-pituitary-adrenal axis. We determined the pharmacokinetics of hydrocortisone administered iv as a bolus. A dose of 15 mg/m(2) body surface area was given to 14 prepubertal (median age, 9.4 yr; range, 6.1--10.8 yr), 20 pubertal (median, 13.5 yr; range, 10.6--16.8 yr), and 6 postpubertal (median, 18.2 yr; range, 17.2--20.3 yr) patients with salt-wasting CAH. All patients were on standard replacement therapy with hydrocortisone and 9 alpha-fludrocortisone. Serum total cortisol concentrations were measured at 10-min intervals for 6 h following iv hydrocortisone bolus and analyzed using a solid-phase RIA. The serum total cortisol clearance curve was monoexponential. Mean clearance was significantly higher in the pubertal group (mean, 427.0 mL/min; SD, 133.4) compared with the prepubertal (mean, 248.7 mL/min; SD, 100.6) and postpubertal (mean, 292.4 mL/min; SD, 106.3) (one-way ANOVA, F = 9.8, P < 0.001) groups. This effect persisted after adjustment for body mass index. The mean volume of distribution was also significantly higher in the pubertal (mean, 49.5 L; SD, 12.2) than the prepubertal (mean, 27.1 L; SD, 8.4) patients but not in the postpubertal (mean, 40.8 L; SD, 16) (ANOVA, F = 15.2, P < 0.001) patients. The significance remained after correction for body mass index. There was no significant difference in mean half-life of total cortisol in prepubertal (mean, 80.2 min; SD, 19.4), pubertal (mean, 84.4 min; SD, 24.9), and postpubertal (mean, 96.7 min; SD, 9.9) patients. Similar differences between groups were observed when the pharmacokinetic parameters of free cortisol were examined. In addition, the half-life of free cortisol was significantly shorter in females compared with males (P = 0.04). These data suggest that puberty is associated with alterations in cortisol pharmacokinetics resulting in increased clearance and volume of distribution with no change in half-life. These alterations probably reflect changes in the endocrine milieu at puberty and may have implications for therapy of CAH and other conditions requiring cortisol substitution in the adolescent years.

Evidence for the involvement of 3-oxo-delta 4 intermediates in ecdysteroid biosynthesis

Although the involvement of 3-oxo-delta 4 compounds as intermediates in arthropod ecdysteroid biosynthesis has been postulated for a long time, it has not yet been directly demonstrated. In the present study, 3-oxo-delta 4-steroids have been synthesized and incubated in vitro with dissociated moulting gland cells from the crab Carcinus maenas. The tritiated compounds were converted into 3-dehydroecdysone, ecdysone and/or 25-deoxyecdysone, i.e. final ecdysteroids. This means that the 3-oxo-delta 4 compounds had undergone a 5 beta-reduction, to give the 5 beta-conformation of ecdysteroids. Our results suggest that the 3-oxo-delta 4-steroid 4,7-cholestadien-14 alpha-ol-3,6-dione may be an intermediate in the biosynthetic pathway. The 5 beta-reduction reaction involves a cytosolic enzyme which requires NADPH as electron donor and seems specific for 3-oxo-delta 4 substrates. This reaction was the most active in crab Y-organs, as compared with other tissues. The characteristics of the 5 beta-reductase (subcellular localization, substrate and cofactor requirements) appear similar to those of the vertebrate 3-oxo-delta 4-steroid 5 beta-reductase involved in steroid hormone catabolism and bile acid biosynthesis.

Cortisol metabolism in vitro--III. Inhibition of microsomal 6 beta-hydroxylase and cytosolic 4-ene-reductase

The in vitro metabolism of cortisol in human liver fractions is highly complex and variable. Cytosolic metabolism proceeds predominantly via A-ring reduction (to give 3 alpha,5 beta-tetrahydrocortisol; 3 alpha,5 beta-THF), while microsomal incubations generate upto 7 metabolites, including 6 beta-hydroxycortisol (6 beta-OHF), and 6 beta-hydroxycortisone (6 beta-OHE), products of the cytochrome P450 (CYP) 3A subfamily. The aim of the present study was, therefore, to examine two of the main enzymes involved in cortisol metabolism, namely, microsomal 6 beta-hydroxylase and cytosolic 4-ene-reductase. In particular, we wished to assess the substrate specificity of these enzymes and identify compounds with inhibitory potential. Incubations for 30 min containing [3H]cortisol, potential inhibitors, microsomal or cytosolic protein (3 mg), and co-factors were followed by radiometric HPLC analysis. The Km value for 6 beta-OHF and 6 beta-OHE formation was 15.2 +/- 2.1 microM (mean +/- SD; n = 4) and the Vmax value 6.43 +/- 0.45 pmol/min/mg microsomal protein. The most potent inhibitor of cortisol 6 beta-hydroxylase was ketoconazole (Ki = 0.9 +/- 0.4 microM; n = 4), followed by gestodene (Ki = 5.6 +/- 0.6 microM) and cyclosporine (Ki = 6.8 +/- 1.4 microM). Both betamethasone and dexamethasone produced some inhibition (Ki = 31.3 and 54.5 microM, respectively). However, substrates for CYP2C (tolbutamide), CYP2D (quinidine), and CYP1A (theophylline) were essentially non-inhibitory. The Km value for cortisol 4-ene-reductase was 26.5 +/- 11.2 microM (n = 4) and the Vmax value 107.7 +/- 46.0 pmol/min/mg cytosolic protein. The most potent inhibitors were androstendione (Ki = 17.8 +/- 3.3 microM) and gestodene (Ki = 23.8 +/- 3.8 microM). Although both compounds have identical A-rings to cortisol, and undergo reduction, inhibition was non-competitive.

Cortisol metabolism by human liver in vitro--IV. Metabolism of 9 alpha-fluorocortisol by human liver microsomes and cytosol

The oxidative and reductive biotransformations of 9 alpha-fluorocortisol (fluorocortisol) by human liver microsomes and cytosol have been characterized. 9 alpha-Fluorination greatly simplified cortisol metabolism in microsomes: dehydrogenation of the 11 beta-hydroxyl group and A-ring (4-ene-5 beta and 3 alpha-keto) reduction, the principle pathways, were completely blocked. Fluorocortisol was essentially metabolized by the remaining pathways, 20 beta-reduction and 6 beta-hydroxylation. In cytosol, 20 beta-reduction replaced the A-ring reduction of cortisol as the sole biotransformation. The major structure-metabolism relationships of fluorocortisol in man, i.e. complete and extensive inhibition of 11 beta-dehydrogenation and 4-ene-5 beta-reduction, respectively, were attributed to hepatic enzyme systems. Their mechanistic basis is discussed with reference to the electronic and conformational changes induced by 9 alpha-fluorination.

Cortisol metabolism in vitro--II. Species difference

It has been suggested that cortisol 6 beta-hydroxylase activity specifically reflects cytochrome P4503A (CYP3A) levels in the liver. However, we have previously reported that the metabolism of cortisol in human liver fractions in vitro is extremely complex and variable, and therefore complete metabolite analysis must be undertaken if 6 beta-hydroxycortisol is to be used as a marker of CYP3A activity. In the present study, the metabolism of [3H]cortisol by hepatic microsomes from various animal species, and by cytosol from male and female rats, has been defined and compared with metabolites formed by human liver microsomes. Metabolites were characterized by co-chromatography with authentic standards, mass spectrometry, and quantified by radiometric HPLC. The results show that all microsomes prepared from animal species studied (male and female rat, male and female guinea-pig, male hamsters and mice) can metabolize cortisol, although the metabolic profiles are both quantitatively and qualitatively different from that obtained with human microsomes. In general the metabolic profiles for animal microsomes are simpler: hamster, mouse and guinea pig show only 6 beta-hydroxylase and 11 beta-dehydrogenase activity, although male rat shows both of these and 20 beta-reductase activity while the female rat possesses all of the above as well as the ability to reduce the A-ring (delta 4-reductase and 3-oxidoreductase activities). The female rat also produces two metabolites undetected in humans. Incubations with male rat cytosol generated 20 beta-dihydrocortisone as the major metabolite, and several unidentified minor polar metabolites, whereas female cytosolic products were identical to those generated by human cytosol, the major metabolite being 3 alpha,5 beta-tetrahydrocortisol. In conclusion, our studies have shown that hepatic cortisol metabolism is extremely variable amongst the species investigated and that the hamster provides the simplest model with which to explore cortisol 6 beta-hydroxylase activity.

Cortisol metabolism by human liver in vitro--I. Metabolite identification and inter-individual variability

The measurement of urinary 6 beta-hydroxycortisol (6 beta-OHF) has been widely used as a non-invasive clinical test to detect cytochrome P450 induction. Although only a minor biotransformation, 6 beta-OHF formation represents a sensitive target for many P450-inducing drugs and environmental chemicals in man. There is good evidence that an isozyme of the P450IIIA subfamily is predominantly responsible for 6 beta-hydroxylase activity and therefore it has been suggested that urinary 6 beta-OHF is a marker of the induction of P450IIIA. The basis of the present study was that in order to realistically assign to 6 beta-OHF the status of a P450IIIA marker we should characterize all the metabolites of cortisol produced by human liver and assess inter-liver variability. Incubations at 37 degrees C for 2 h contained [3H]cortisol (0.1 microCi, 1 or 50 microM), MgCl2 (10 mM), microsomal or cytosolic protein (3 mg), an NADPH-regenerating system and 1/15 M phosphate buffer (pH 7.4) to give a final volume of 0.5 ml. Extraction with ethyl acetate (2 x 2 ml) was followed by radiometric HPLC analysis. Metabolites were identified by co-chromatography with authentic standards and mass spectrometry (electron impact and chemical ionization). All the microsomal incubations (n = 6 livers) produced 6 alpha-hydroxycortisol (6 alpha-OHF), 6 beta-OHF, 20 beta-dihydroxycortisol, 20 beta-dihydroxycortisone, cortisone, and 3 alpha, 5 beta-tetrahydrocortisone (3 alpha, 5 beta-THE), while five produced 6 beta-hydroxycortisone and four produced 3 alpha, 5 beta-tetrahydrocortisol (3 alpha, 5 beta-THF). The cytosolic incubations gave a much simpler metabolic profile, with 3 alpha, 5 beta-THF the major metabolite and 3 alpha, 5 beta-THE a minor metabolite. There was considerable inter-individual variability in metabolite profiles from microsomal incubations. 6 beta-OHF varied from 2.8 to 31.7%. Major metabolites were cortisone and 3 alpha, 5 beta-THE. Inter-liver variability was less for cytosolic incubations, the major metabolite always being 3 alpha, 5 beta-THF. In conclusion we have rigorously identified the hepatic metabolites of cortisol formed in vitro. The highly complex and variable hepatic metabolism of cortisol clearly limits the use of urinary 6 beta-OHF excretion as a marker of baseline P450IIIA activity in man.

Purification and properties of human hepatic 3 alpha-hydroxysteroid dehydrogenase

3 alpha-Hydroxysteroid dehydrogenase (3 alpha-HSD) was purified greater than 500-fold from human liver cytosol. The purification was monitored using 5 beta-[3H]dihydrocortisol (5 beta-DHF) as substrate. Electrophoretically homogeneous enzyme was obtained using a procedure that involved ammonium sulfate precipitation and three successive column chromatography steps: DEAE-cellulose, hydroxylapatite and Blue-Sepharose. The enzyme is a monomer since the native molecular weight was found to be 37,000, using a calibrated Sephadex G-75 column, and the denatured subunit molecular weight was determined to be 38,500, by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. The enzyme had a pI of 5.6-5.9. The 3-ketosteroids: cortisol, testosterone, progesterone and androstenedione, were not substrates for 3 alpha-HSD indicating that a saturated 4,5 double bond was required for substrate activity. The conformation at the 5 position, however, did not influence substrate activity since 5 alpha- and 5 beta-DHF and 5 alpha-dihydrotestosterone were all reduced at similar rates. The purified enzyme preferred NADPH to NADH as a cofactor and showed a broad peak of activity in the pH range of 6.8-7.4. The apparent Km for 5 beta-DHF was 18 microM. The enzyme was markedly stabilized by 50 mM phosphate buffer containing 10 to 20% glycerol at 4 degrees C. Freezing and thawing of the enzyme resulted in a large loss of activity during early stages of the purification. This is the first report of the purification to homogeneity of 3 alpha-HSD from human tissue.

Human hepatic 3 alpha-hydroxysteroid dehydrogenase: possible identity with human hepatic chlordecone reductase

3 alpha-Hydroxysteroid dehydrogenase is a cytosolic, monomeric, NADPH-dependent oxidoreductase which reduces 3-keto-5-dihydrosteroids to their tetrahydro products. We present here the first partial amino acid sequence data for the human liver enzyme and show these sequences to be identical to the deduced amino acid sequence for human hepatic chlordecone reductase. In addition, these two enzymes exhibit similar substrate and cofactor specificities and immunological reactivity. The results suggest that the natural substrates for chlordecone reductase are 3-keto-5-dihydrosteroids and that these two proteins may be identical.