In vitro steroid metabolic studies in testicular 17 beta-reduction deficiency

Natural potent androgens: lessons from human genetic models

Male pseudohermaphroditism due to 17 beta-hydroxysteroid dehydrogenase-3 (17 beta-HSD-3) deficiency and 5 alpha-reductase-2 (5 alpha-RD-2) deficiency provides natural human genetic models to elucidate androgen actions. To date, five 17 beta-HSD isozymes have been cloned that catalyse the oxidoreduction of androstenedione and testosterone and dihydrotestosterone (DHT), oestrone and oestradiol. Mutations in the isozyme 17 beta-HSD-3 gene are responsible for male pseudohermaphroditism due to 17 beta-HSD deficiency. The type 3 isozyme preferentially catalyses the reduction of androstenedione to testosterone and is primarily expressed in the testes. Fourteen mutations in the 17 beta-HSD-3 gene have been identified from different ethnic groups. Affected males with the 17 beta-HSD-3 gene defect have normal wolffian structures but ambiguous external genitalia at birth. Many are raised as girls but virilize at the time of puberty and adopt a male gender role. Some develop gynaecomastia at puberty, which appears to be related to the testosterone/oestradiol ratio. Two 5 alpha-reductase (5 alpha-RD) isozymes, types 1 and 2, have been identified, which convert testosterone to the more potent androgen DHT. Mutations in the 5 alpha-RD-2 gene cause male pseudohermaphroditism, and 31 mutations in the 5 alpha-RD-2 gene have been reported from various ethnic groups. Such individuals also have normal wolffian structure but ambiguous external genitalia at birth and are raised as girls. Virilization occurs at puberty, often with a gender role change. The prostate remains infantile and facial hair is decreased. Balding has not been reported.

Kinetic analysis of enzymic activities: prediction of multiple forms of 17 beta-hydroxysteroid dehydrogenase

An overview of the application of kinetic methods to the delineation of 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) heterogeneity in mammalian tissues is presented. Early studies of 17 beta-HSD activity in animal liver and kidney subcellular fractions were suggestive of multiple forms of the enzyme. Subsequently, detailed characterization of activity in cytosol and subcellular membrane fractions of human placenta, with particular emphasis on inhibition kinetics, yielded evidence of two kinetically-differing forms of 17 beta-HSD in that organ. Gene cloning and transfection experiments have confirmed the identity of these two proteins as products of separate genes. 17 beta-HSD type 1 is a cytosolic enzyme highly specific for C18 steroids such as 17 beta-estradiol (E2) and estrone (E1). 17 beta-HSD type 2 is a membrane bound enzyme reactive with testosterone (T) and androstenedione (A), as well as E2 and E1. Useful parameters for the detection of multiple forms of 17 beta-HSD appear to be the E2/T activity ratio, NAD/NADP activity ratios, steroid inhibitor specificity and inhibition patterns over a wide range of putative inhibitor concentrations. Evaluation of these parameters for microsomes from samples of human breast tissue suggests the presence of 17 beta-HSD type 2. The 17 beta-HSD enzymology of human testis microsomes appears to differ from placenta. Analysis of human ovary indicates granulosa cells are particularly enriched in the type 1 enzyme with type 2-like activity in stroma/theca. Mouse ovary appears to contain forms of 17 beta-HSD which differ from 17 beta-HSD type 1 and type 2 in their kinetic properties.

A study of androgen biosynthesis by the human testis in vitro

The biosynthetic pathways in human testicular tissue have been studied extensively in our laboratory without the use of radioisotopes. Experiments were conducted with normal testicular tissue from patients undergoing orchiectomy for prostatic cancer. These studies have shown that the preferred pathway of testosterone biosynthesis is influenced by the nature and concentration of cofactor added to the incubation medium. Four enzymes are involved in the transformation of pregnenolone to testosterone, that is, 3 beta-hydroxysteroid dehydrogenase, 17 alpha-hydroxylase, C17-C20 lyase and 17 beta-hydroxysteroid oxidoreductase. Our studies show that the 4-ene pathway predominates in the biosynthesis of testosterone from pregnenolone. Analysis of several samples of human testicular vein blood supports the contention that 4-androsten-3,17-dione is the immediate precursor of testosterone.

Steroid 17β-hydroxysteroid dehydrogenase deficiency in man: an inherited form of male pseudohermaphroditism

Sixty-eight males with testicular 17β-hydroxysteroid dehydrogenase deficiency (17β-HSD) were identified among a highly inbred Arab population in Israel, and 45 studied over the last 15 years. The founders of this defect originated in the mountainous region of present Lebanon and Syria, but most of the families now live in Jerusalem, Hebron, the Tel-Aviv area, and in particular Gaza, where the frequency of affected males is estimated at 1 in 100 to 150. Affected individuals (46,XY) are born with ambiguity of the genitalia and reared as females until puberty. Thereafter marked virilization occurs, leading in many cases to the spontaneous adoption of a male gender role. Adults develop a male habitus with abundant body hair and beard, and the phallus and testes enlarge to adult proportions. Gender reassignment was possible only when enough erectile tissue was present at birth and developed into a normal size penis with systemic testosterone. male genitoplasty was performed in 15 children and 8 post-pubertal patients, and female genitoplasty in 2 children and 4 post-pubertal patients. In adults the defect is characterized by markedly increased concentrations of 4-androstendione (4-A) with borderline low to normal testosterone (T) levels, and a high 4-A/T ratio. Dihydrotestosterone (DHT) concentrations were either moderately decreased, normal, or high, and dehydroepiandrosterone levels were high. The estrogen pathway was also impaired, even though both estrone and estradiol-17β levels were elevated. Children had low basal levels of all androgens, but the defect could be demonstrated after prolonged stimulation with human chorionic gonadotropin. LH and FSH levels were very high after puberty, and normal in childhood. However, an over-response to gonadotropin-releasing hormone was found at all ages. Studies in testicular tissue revealed various abnormalities in steroid metabolism. Tissue from pre-pubertal patients metabolized progesterone (P) only to 4-A, while tissue from post-pubertal patients metabolized P to 16α- and 16β-hydroxyprogesterone (5.4- to 10.3-fold greater production), 17α-hydroxyprogesterone (5.4- to 8-fold smaller production), 4-A and T. 4-A was also metabolized to T, indicating that 17β-HSD was no longer deficient. Flow studies with equimolar concentrations of [¹⁴C]P and [³H]pregnenolone showed that the 5-ene pathway was the preferential one for androgen biosynthesis. Both in vivo and in vitro studies indicate that the severity of testicular 17β-HSD deficiency changes with age. Whereas the enzyme activity is absent in childhood, there is a progressive restoration after puberty. Androgen production increases progressively to normal so that T and DHT concentrations are sufficiently high to gradually induce somatic and genital virilization, thus enabling an adequate male gender function.

Molecular genetics of steroid 5 alpha-reductase 2 deficiency

Two isozymes of steroid 5 alpha-reductase encoded by separate loci catalyze the conversion of testosterone to dihydrotestosterone. Inherited defects in the type 2 isozyme lead to male pseudohermaphroditism in which affected males have a normal internal urogenital tract but external genitalia resembling those of a female. The 5 alpha-reductase type 2 gene (gene symbol SRD5A2) was cloned and shown to contain five exons and four introns. The gene was localized to chromosome 2 band p23 by somatic cell hybrid mapping and chromosomal in situ hybridization. Molecular analysis of the SRD5A2 gene resulted in the identification of 18 mutations in 11 homozygotes, 6 compound heterozygotes, and 4 inferred compound heterozygotes from 23 families with 5 alpha-reductase deficiency. 6 apparent recurrent mutations were detected in 19 different ethnic backgrounds. In two patients, the catalytic efficiency of the mutant enzymes correlated with the severity of the disease. The high proportion of compound heterozygotes suggests that the carrier frequency of mutations in the 5 alpha-reductase type 2 gene may be higher than previously thought.

Rat Leydig cell and granulosa cell 17-ketosteroid reductase activity: subcellular localization and substrate specificity

The potent gonadal steroids testosterone and estradiol are synthesized from the biologically weak precursors, androstenedione and estrone, by enzymatic reduction of the ketone group at carbon-17 of the steroid nucleus (17-ketosteroid reductase). To test the hypothesis that Leydig and granulosa cells may contain a distinct 17-ketosteroid reductase enzyme, the subcellular localization and the substrate specificity of the enzyme was examined in each cell type. In Leydig cells, the 17-ketosteroid reductase activity was concentrated in the microsomal fraction of the cell. In granulosa cells, the 17-ketosteroid reductase activity was concentrated in the cytosolic fraction of the cell. In Leydig cell microsomes, the apparent Michaelis-Menten constant for the conversion of androstenedione to testosterone was 0.41 mumol/L and for the conversion of estrone to estradiol it was 12 mumol/L. In granulosa cell cytosol, the apparent Michaelis-Menten constant for the conversion of estrone to estradiol was 1.1 mumol/L and for the conversion of androstenedione to testosterone it was 15 mumol/L. These results demonstrate that rat Leydig and granulosa cells each contain a 17-ketosteroid reductase enzyme with unique subcellular localization and substrate specificity.

Steroid metabolism in testes of patients with incomplete masculinization due to androgen insensitivity or 17 beta-hydroxysteroid dehydrogenase deficiency and normally differentiated males

For purposes of establishing suitable controls in studies of patients with a suspected enzyme deficiency, activities of enzymes involved in the biosynthesis of testosterone were compared in testes of patients with androgen insensitivity syndrome (AIS) and normally differentiated males with carcinoma of the prostate (Ca prostate) or testis (Ca testis). Activities of 17,20-desmolase and of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) were higher in the testes of pre-, peri- or postpubertal patients with AIS than in elderly men (58-80 yr) with Ca prostate. Activities of 17 beta-HSD (reductive direction) and 3 beta-HSD tended to be higher in peri- or postpubertal than in prepubertal patients with AIS. Activity of 3 beta-HSD was low in the patient with Ca testis. In a peripubertal (12 yr) patient with incomplete masculinization due to a severe deficiency of 17 beta-HSD, reductive activity of 17 beta-HSD was very low compared with that of patients with Ca prostate, Ca testis or AIS. In contrast, in testes from the younger sibling (4 yr), in whom the deficiency of 17 beta-HSD was less severe, 17 beta-HSD reduction of dehydroepiandrosterone was as high as that of men with Ca prostate, yet deficient in comparison with that of more closely age-matched patients with AIS. This emphasizes the desirability of using age-matched tissue for control purposes in enzyme studies.

Prepubertal male pseudohermaphroditism due to 17-ketosteroid reductase deficiency: diagnostic value of a hCG test and lack of HLA association

Most patients with male pseudohermaphroditism (MPH) due to 17-ketosteroid reductase (17-KSR) deficiency were diagnosed at or after puberty when significant virilization occurred. We report 2 prepubertal sibs (Case 1, 4 yr and Case 2, 10 yr) unambiguously raised as females, with clitoral enlargement, separate urethral and vaginal orifices and gonads palpable at the inguinal canal bilaterally. Basal serum LH, FSH, 17-hydroxyprogesterone, testosterone (T), dihydrotestosterone and dehydroepiandrosterone (DHEA) were normal for age. delta 4-Androstenedione (delta 4-A) was slightly elevated in Case 2 but nondiagnostic. Steroid measurements after human chorionic gonadotropin (hCG) stimulation were compared with those of boys with male external genitalia submitted to the same hCG protocol: peak T was subnormal (Case 1, 80, Case 2, 91, vs normal 329 +/- 129 ng/dl, mean +/- 1SD), peak delta 4-A elevated (Case 1, 477, Case 2, 264, vs normal 44 +/- 26 ng/dl) resulting in an abnormally elevated delta 4-A/T ratio (Case 1, 6.0, Case 2, 2.9, vs normal 0.12 +/- 0.09) and establishing the diagnosis of 17-KSR deficiency. This diagnosis was confirmed in vitro by minimal T production when testicular tissue of both patients was incubated with tritiated delta 4-A. The 2 sibs did not share a single haplotype for the HLA complex indicating lack of association between HLA and the locus of the gene for 17-KSR. In conclusion, in 2 sibs with MPH the subnormal T and elevated delta 4-A response to the hCG test indicated the diagnosis of 17-KSR deficiency followed by orchiectomy to avoid later virilization at puberty.

Hirsutism, polycystic ovarian disease, and ovarian 17-ketosteroid reductase deficiency

We studied an 18-year-old woman with progressive hirsutism, secondary amenorrhea, and polycystic ovarian disease. Excess androstenedione was secreted by the ovaries, most likely because of a genetic deficiency of ovarian 17-ketosteroid reductase, the enzyme that converts androstenedione to testosterone. Markedly elevated basal plasma levels of androstenedione, estrone, and testosterone were regulated by gonadotropin but not by ACTH. The rate of androstenedione production in the patient's blood at base line and after administration of dexamethasone was very high (10.0 to 11.6 mg per day; value in control women with hirsutism, less than 4.1 mg per day), whereas her blood production of testosterone was 0.64 to 0.7 mg per day, similar to or higher than that in control women with hirsutism. The fractional blood conversion ratio of androstenedione to testosterone was normal (5.6 percent). Thus, 88 to 93 percent of the testosterone in the blood was derived from the peripheral conversion of androstenedione, and very little testosterone was secreted by the ovaries. These in vivo biochemical data suggest that the patient had a deficiency of ovarian 17-ketosteroid reductase activity but normal pubertal activity. The patient's two younger sisters with peripubertal symptoms of androgen excess also had elevated serum levels of androstenedione. We propose that the increased secretion of androstenedione in the three siblings in this family was probably due to a genetic deficiency of ovarian 17-ketosteroid reductase.

Incomplete masculinization due to a deficiency of 17 beta-hydroxysteroid dehydrogenase: comparison of prepubertal and peripubertal siblings

Incomplete masculinization due to a deficiency of 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) was investigated in siblings aged 4 years (Case 1) and 12 years (Case 2). Diagnosis was based on increased ratios of androstenedione (A) to testosterone (T) in blood, and impaired reduction of A to T by 17 beta-HSD in vitro in the testes. Impairment was total in Case 2 but partial in Case 1. Case 2 also showed deficient conversion of dehydroepiandrosterone (DHA) to androstenediol and of oestrone to oestradiol by 17 beta-HSD which were normal in Case 1. Oxidation of T to A by 17 beta-HSD and conversion of 17 alpha-hydroxyprogesterone to A by 17,20 desmolase were normal in the testes of both siblings. 3 beta-HSD conversion of DHA to A was normal in Case 1, but markedly increased in Case 2. In contrast to testicular findings, 17 beta-HSD reduction of A to T in genital skin fibroblasts from Case 2 was normal and diagnosis would not have been possible from studies of measurements of this enzyme in skin. The severity of the testicular 17 beta-HSD deficiency in the peripubertal compared with the prepubertal sibling suggests either considerable intra-familial variation in the extent of the enzyme defect or that puberty may aggravate this disorder. The normal reductive action of 17 beta-HSD in skin, despite impaired action in testes, suggests involvement of more than one iso-enzyme.

Follicle regulatory protein noncompetitively inhibits microsomal 3 beta-hydroxysteroid dehydrogenase activity

A heat- and trypsin-labile follicular fluid protein (FRP) extracted from both human and porcine follicular fluid has been shown to modulate ovarian steroidogenesis. To further investigate the effects of FRP, its effect on the kinetics of 3 beta-hydroxysteroid dehydrogenase activity (3 beta-HSD) was evaluated in cell-free microsomal preparations from human placenta. Test fractions of follicular fluid protein were preincubated with placental microsomes followed by the addition of various substrate concentrations (pregnenolone + NAD). Subsequent progesterone formation was interpreted as the velocity of the reaction. The 50% inhibitory dose (ID50) of FRP for 3 beta-HSD for the three substrate concentrations was 300 micrograms/ml. Although a clear decrease in 3 beta-HSD activity typically occurred after pre-incubation with 730 micrograms/ml of FRP, a paradoxical augmentation in 3 beta-HSD activity was present with the lower concentrations of FRP (10-30 micrograms/ml) and the more concentrated microsomal preparations. Double reciprocal plots of these reactions demonstrated a Km for 3 beta-HSD of 1.8-2.1 X 10(-6) M. Analysis of all reactions was found to be consistent with a noncompetitive mode of enzyme inhibition with an apparent Ki of 120 ng/ml or approximately 10(-8) M assuming a mol. wt of 16,000 Daltons for FRP. This derived Ki for FRP is within the biological concentration of FRP in follicular fluid.

On the in vitro metabolism of androstenedione and progesterone in human testicular tissue from fetal age to senescence

The conversion of [3H]-androstenedione to testosterone regulated by the enzyme 17 beta-ketosteroid reductase and the conversion of [3H]-progesterone to 17 alpha-hydroxyprogesterone and onwards along the delta 4 metabolic pathway was studied in vitro in human testicular tissue from 32 males (2 fetuses, 25 adult, infertile men and 5 elderly men with prostatic carcinoma). Additionally, two prepubertal boys were studied with respect to the conversion of [3H]-androstenedione to testosterone in vitro, whereas another seven boys were studied with reference to the conversion of [3H]-progesterone in vitro. It appeared, that in all cases, the conversion of androstenedione to testosterone was larger than the conversion of progesterone to 17 alpha-hydroxyprogesterone by way of the 17 alpha-hydroxylase and onwards along the delta 4 metabolic pathway. It is thus concluded that the 17 beta ketosteroid reductase is not a rate-limiting enzyme along the delta 4 metabolic pathway. No case of deficient 17 beta-ketosteroid reductase was found among the 25 infertile patients studied.

Male pseudohermaphroditism due to 17 beta-hydroxysteroid dehydrogenase deficiency: studies on the natural history of the defect and effect of androgens on gender role

Studies within the Arab population in Israel revealed 25 pseudohermaphrodites due to 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) deficiency. Twenty-three individuals, presently living in the Gaza strip, belong to a very large inbred kinship which extends over 8 generations. All affected subjects (46, XY) were born with mild to moderate degrees of ambiguity of an apparently normal-looking female genitalia and therefore were reared as girls. In childhood, genital abnormalities consisted of a clitoral-like phallus surrounded by a chordee, non-fused labial-scrotal folds and a urogenital sinus. The testes were in the inguinal canals, or rarely, in the labial-scrotal folds. Wolffian structures were normally differentiated while Mullerian structures were absent. At puberty, subjects developed a male body habitus with abundant body hair and beard. Gynecomastia was absent. The phallus and testes enlarged to adult proportions while the prostate remained small. Together with the physical change from girls to boys they developed a male identity having erections and ejaculations, which in 7 cases led to the spontaneous adoption of a male gender role. In adults the hormonal abnormalities consisted of greatly elevated delta 4-androstenedione (delta 4) (350-1267 ng/dl) associated with subnormal testosterone (T) levels (0.9-3.1 ng/ml). Dihydrotestosterone (DHT) levels, with the exception of 1 patient, were relatively low in all cases (27-35 ng/dl). Children had low levels of delta 4, T and DHT, which were normal for age. Although from puberty on there was a significant rise of the 3 androgens, delta 4 always remained extremely elevated and T and DHT relatively low when compared to normal controls. Dexamethasone failed to suppress the androgen pattern while HCG augmented the defect, making the diagnosis possible in 2 prepubertal children. Dehydroepiandrosterone (DHEA) and 17-hydroxyprogesterone (17-OHP) levels were normal or moderately elevated. Estradiol (E2) levels were normal in children and all but 2 adults, who had high levels. LH and FSH levels were very high after puberty, but normal before. However, there was an overresponse to LHRH in all age groups. The contrast between the lack of intrauterine virilization of the external genitalia in fetuses with 17 beta-HSD deficiency versus the marked masculinization that occurs after puberty still remains a puzzling phenomenon. It is conceivable that the postpubertal development of a male phenotype with change of gender identity and role occurs due to the joint effect of delta 4, T and DHT, even though secreted in inadequate proportions. Thus masculinization in these individuals is a slow process requiring a longer period of time than that of normal puberty to be completed.