5alpha-reduced C21 steroids are substrates for human cytochrome P450c17

Interpretation of Steroid Biomarkers in 21-Hydroxylase Deficiency and Their Use in Disease Management

The most common form of congenital adrenal hyperplasia is 21-hydroxylase deficiency (21OHD), which in the classic (severe) form occurs in roughly 1:16 000 newborns worldwide. Lifelong treatment consists of replacing cortisol and aldosterone deficiencies, and supraphysiological dosing schedules are typically employed to simultaneously attenuate production of adrenal-derived androgens. Glucocorticoid titration in 21OHD is challenging as it must balance the consequences of androgen excess vs those from chronic high glucocorticoid exposure, which are further complicated by interindividual variability in cortisol kinetics and glucocorticoid sensitivity. Clinical assessment and biochemical parameters are both used to guide therapy, but the specific purpose and goals of each biomarker vary with age and clinical context. Here we review the approach to medication titration for children and adults with classic 21OHD, with an emphasis on how to interpret adrenal biomarker values in guiding this process. In parallel, we illustrate how an understanding of the pathophysiologic and pharmacologic principles can be used to avoid and to correct complications of this disease and consequences of its management using existing treatment options.

Human cytochrome P450 17A1 structures with metabolites of prostate cancer drug abiraterone reveal substrate-binding plasticity and a second binding site

Abiraterone acetate is a first-line therapy for castration-resistant prostate cancer. This prodrug is deacetylated in vivo to abiraterone, which is a potent and specific inhibitor of cytochrome P450 17A1 (CYP17A1). CYP17A1 performs two sequential steps that are required for the biosynthesis of androgens that drive prostate cancer proliferation, analogous to estrogens in breast cancer. Abiraterone can be further metabolized in vivo on the steroid A ring to multiple metabolites that also inhibit CYP17A1. Despite its design as an active-site-directed substrate analog, abiraterone and its metabolites demonstrate mixed competitive/noncompetitive inhibition. To understand their binding, we solved the X-ray structures of CYP17A1 with three primary abiraterone metabolites. Despite different conformations of the steroid A ring and substituents, all three bound in the CYP17A1 active site with the steroid core packed against the I helix and the A ring C3 keto or hydroxyl oxygen forming a hydrogen bond with N202 similar to abiraterone itself. The structure of CYP17A1 with 3-keto, 5α-abiraterone was solved to 2.0 Å, the highest resolution to date for a CYP17A1 complex. This structure had additional electron density near the F/G loop, which is likely a second molecule of the inhibitor and which may explain the noncompetitive inhibition. Mutation of the adjacent Asn52 to Tyr positions its side chain in this space, maintains enzyme activity, and prevents binding of the peripheral ligand. Collectively, our findings provide further insight into abiraterone metabolite binding and CYP17A1 function.

Allopregnanolone: Metabolism, Mechanisms of Action, and Its Role in Cancer

Allopregnanolone (3α-THP) has been one of the most studied progesterone metabolites for decades. 3α-THP and its synthetic analogs have been evaluated as therapeutic agents for pathologies such as anxiety and depression. Enzymes involved in the metabolism of 3α-THP are expressed in classical and nonclassical steroidogenic tissues. Additionally, due to its chemical structure, 3α-THP presents high affinity and agonist activity for nuclear and membrane receptors of neuroactive steroids and neurotransmitters, such as the Pregnane X Receptor (PXR), membrane progesterone receptors (mPR) and the ionotropic GABA_A receptor, among others. 3α-THP has immunomodulator and antiapoptotic properties. It also induces cell proliferation and migration, all of which are critical processes involved in cancer progression. Recently the study of 3α-THP has indicated that low physiological concentrations of this metabolite induce the progression of several types of cancer, such as breast, ovarian, and glioblastoma, while high concentrations inhibit it. In this review, we explore current knowledge on the metabolism and mechanisms of action of 3α-THP in normal and tumor cells.

Androgen Metabolism and Response in Prostate Cancer Anti-Androgen Therapy Resistance

All aspects of prostate cancer evolution are closely related to androgen levels and the status of the androgen receptor (AR). Almost all treatments target androgen metabolism pathways and AR, from castration-sensitive prostate cancer (CSPC) to castration-resistant prostate cancer (CRPC). Alterations in androgen metabolism and its response are one of the main reasons for prostate cancer drug resistance. In this review, we will introduce androgen metabolism, including how the androgen was synthesized, consumed, and responded to in healthy people and prostate cancer patients, and discuss how these alterations in androgen metabolism contribute to the resistance to anti-androgen therapy.

Classic and backdoor pathways of androgen biosynthesis in human sexual development

Both genes and hormones regulate human sexual development. Although ovarian hormones are not essential for female external genitalia development, male sexual development requires the action of testicular testosterone and dihydrotestosterone (DHT). DHT is the most active endogenous androgen formed by the conversion of testosterone in genital skin. This synthesis route from cholesterol to DHT is called the conventional classic pathway. Recent investigations have reported an alternative ("backdoor") route for DHT formation that bypasses fetal testicular testosterone. This alternative route plays a crucial role in human hyperandrogenic disorders like congenital adrenal hyperplasia caused by P450c21 deficiency, polycystic ovary syndrome, and P450 oxidoreductase deficiency. In addition, mutations in AKR1C2 and AKR1C4, genes encoding 3α-reductases, have been implicated in disorders of sexual development, indicating that both the classic and backdoor routes are required for normal human male sexual development. More recently, androsterone was found to be the primary androgen of the human backdoor route. Androsterone and steroidal substrates specific to the backdoor route are predominantly found in the placenta, liver, and adrenal glands rather than in the testes. These findings are essential to understanding human sexual development.

Altered Steroidome in Women with Gestational Diabetes Mellitus: Focus on Neuroactive and Immunomodulatory Steroids from the 24th Week of Pregnancy to Labor

Gestational diabetes mellitus (GDM) is a complication in pregnancy, but studies focused on the steroidome in patients with GDM are not available in the public domain. This article evaluates the steroidome in GDM+ and GDM- women and its changes from 24 weeks (± of gestation) to labor. The study included GDM+ (n = 44) and GDM- women (n = 33), in weeks 24-28, 30-36 of gestation and at labor and mixed umbilical blood after delivery. Steroidomic data (101 steroids quantified by GC-MS/MS) support the concept that the increasing diabetogenic effects with the approaching term are associated with mounting progesterone levels. The GDM+ group showed lower levels of testosterone (due to reduced AKR1C3 activity), estradiol (due to a shift from the HSD17B1 towards HSD17B2 activity), 7-oxygenated androgens (competing with cortisone for HSD11B1 and shifting the balance from diabetogenic cortisol towards the inactive cortisone), reduced activities of SRD5As, and CYP17A1 in the hydroxylase but higher CYP17A1 activity in the lyase step. With the approaching term, the authors found rising activities of CYP3A7, AKR1C1, CYP17A1 in its hydroxylase step, but a decline in its lyase step, rising conjugation of neuroinhibitory and pregnancy-stabilizing steroids and weakening AKR1D1 activity.

Back where it belongs: 11β-hydroxyandrostenedione compels the re-assessment of C11-oxy androgens in steroidogenesis

Adrenal steroidogenesis has, for decades, been depicted as three biosynthesis pathways -the mineralocorticoid, glucocorticoid and androgen pathways with aldosterone, cortisol and androstenedione as the respective end products. 11β-hydroxyandrostenedione was not included as an adrenal steroid despite the adrenal output of this steroid being twice that of androstenedione. While it is the end of the line for aldosterone and cortisol, as it is in these forms that they exhibit their most potent receptor activities prior to inactivation and conjugation, 11β-hydroxyandrostenedione is another matter entirely. The steroid, which is weakly androgenic, has its own designated pathway yielding 11-ketoandrostenedione, 11β-hydroxytestosterone and the potent androgens, 11-ketotestosterone and 11-ketodihydrotestosterone, primarily in the periphery. Over the last decade, these C11-oxy C₁₉ steroids have once again come to the fore with the rising number of studies contradicting the generally accepted notion that testosterone and it's 5α-reduced product, dihydrotestosterone, are the principal potent androgens in humans. These C11-oxy androgens have been shown to contribute to the androgen milieu in adrenal disorders associated with androgen excess and in androgen dependant disease progression. In this review, we will highlight these overlooked C11-oxy C₁₉ steroids as well as the C11-oxy C₂₁ steroids and their contribution to congenital adrenal hyperplasia, polycystic ovarian syndrome and prostate cancer. The focus is on new findings over the past decade which are slowly but surely reshaping our current outlook on human sex steroid biology.

Non-Classic Disorder of Adrenal Steroidogenesis and Clinical Dilemmas in 21-Hydroxylase Deficiency Combined with Backdoor Androgen Pathway. Mini-Review and Case Report

Congenital adrenal hyperplasia (CAH) is the most common cause of primary adrenal insufficiency in children and adolescents. It comprises several clinical entities associated with mutations in genes, encoding enzymes involved in cortisol biosynthesis. The mutations lead to considerable (non-classic form) to almost complete (classic form) inhibition of enzymatic activity, reflected by different phenotypes and relevant biochemical alterations. Up to 95% cases of CAH are due to mutations in CYP21A2 gene and subsequent 21α-hydroxylase deficiency, characterized by impaired cortisol synthesis and adrenal androgen excess. In the past two decades an alternative ("backdoor") pathway of androgens' synthesis in which 5α-androstanediol, a precursor of the 5α-dihydrotestosterone, is produced from 17α-hydroxyprogesterone, with intermediate products 3α,5α-17OHP and androsterone, in the sequence and with roundabout of testosterone as an intermediate, was reported in some studies. This pathway is not always considered in the clinical assessment of patients with hyperandrogenism. The article describes the case of a 17-year-old female patient with menstrual disorders and androgenization (persistent acne, advanced hirsutism). Her serum dehydroepiandrosterone sulfate and testosterone were only slightly elevated, along with particularly high values for 5α-dihydrotestosterone. In 24 h urine collection, an increased excretion of 16α-OHDHEA-a dehydroepiandrosterone metabolite-and pregnanetriolone-a 17α-hydroxyprogesterone metabolite-were observed. The investigations that we undertook provided evidence that the girl suffered from non-classic 21α-hydroxylase deficiency with consequent enhancement of the androgen "backdoor" pathway in adrenals, peripheral tissues or both, using adrenal origin precursors. The paper presents diagnostic dilemmas and strategies to differentiate between various reasons for female hyperandrogenism, especially in childhood and adolescence.

CYP17A1 exhibits 17αhydroxylase/17,20-lyase activity towards 11β-hydroxyprogesterone and 11-ketoprogesterone metabolites in the C11-oxy backdoor pathway

Cytochrome P450 17α-hydroxylase/17,20-lyase (CYP17A1) plays a pivotal role in the regulation of adrenal and gonadal steroid hormone biosynthesis. More recent studies highlighted the enzyme's role in the backdoor pathway leading to androgen production. Increased CYP17A1 activity in endocrine disorders and diseases are associated with elevated C₂₁ and C₁₉ steroids which include 17α-hydroxyprogesterone and androgens, as well as C11-oxy C₂₁ and C11-oxy C₁₉ steroids. We previously reported that 11β-hydroxyprogesterone (11OHP4), 21-deoxycortisol (21dF) and their keto derivatives are converted by 5α-reductases and hydroxysteroid dehydrogenases yielding C₁₉ steroids in the backdoor pathway. In this study the 17α-hydroxylase and 17,20-lyase activity of CYP17A1 towards the unconventional C11-oxy C₂₁ steroid substrates and their 5α- and 3α,5α-reduced metabolites was investigated in transfected HEK-293 cells. CYP17A1 catalysed the 17α-hydroxylation of 11OHP4 to 21dF and 11-ketoprogesterone (11KP4) to 21-deoxycortisone (21dE) with negligible hydroxylation of their 5α-reduced metabolites while no lyase activity was detected. The 3α,5α-reduced C11-oxy C₂₁ steroids-5α-pregnan-3α,11β-diol-20-one (3,11diOH-DHP4) and 5α-pregnan-3α-ol-11,20-dione (alfaxalone) were rapidly hydroxylated to 5α-pregnan-3α,11β,17α-triol-20-one (11OH-Pdiol) and 5α-pregnan-3α,17α-diol-11,20-dione (11K-Pdiol), with the lyase activity subsequently catalysing to conversion to the C11-oxy C₁₉ steroids, 11β-hydroxyandrosterone and 11-ketoandrosterone, respectively. Docking of 11OHP4, 11KP4 and the 5α-reduced metabolites, 5α-pregnan-11β-ol-3,20-dione (11OH-DHP4) and 5α-pregnan-3,11,20-trione (11K-DHP4) with human CYP17A1 showed minimal changes in the orientation of these C11-oxy C₂₁ steroids in the active pocket when compared with the binding of progesterone suggesting the 17,20-lyase is impaired by the C11-hydroxyl and keto moieties. The structurally similar 3,11diOH-DHP4 and alfaxalone showed a greater distance between C17 and the heme group compared to the natural substrate, 17α-hydroxypregnenolone potentially allowing more orientational freedom and facilitating the conversion of the C11-oxy C₂₁ to C11-oxy C₁₉ steroids. In summary, our in vitro assays showed that while CYP17A1 readily hydroxylated 11OHP4 and 11KP4, the enzyme was unable to catalyse the 17,20-lyase reaction of these C11-oxy C₂₁ steroid products. Although CYP17A1 exhibited no catalytic activity towards the 5α-reduced intermediates, once the C4-C5 double bond and the keto group at C3 were reduced, both the hydroxylation and lyase reactions proceeded efficiently. These findings show that the C11-oxy C₂₁ steroids could potentially contribute to the androgen pool in tissue expressing steroidogenic enzymes in the backdoor pathway.

Human steroid biosynthesis, metabolism and excretion are differentially reflected by serum and urine steroid metabolomes: A comprehensive review

Advances in technology have allowed for the sensitive, specific, and simultaneous quantitative profiling of steroid precursors, bioactive steroids and inactive metabolites, facilitating comprehensive characterization of the serum and urine steroid metabolomes. The quantification of steroid panels is therefore gaining favor over quantification of single marker metabolites in the clinical and research laboratories. However, although the biochemical pathways for the biosynthesis and metabolism of steroid hormones are now well defined, a gulf still exists between this knowledge and its application to the measured steroid profiles. In this review, we present an overview of steroid hormone biosynthesis and metabolism by the liver and peripheral tissues, specifically highlighting the pathways linking and differentiating the serum and urine steroid metabolomes. A brief overview of the methodology used in steroid profiling is also provided.

Alternative pathway androgen biosynthesis and human fetal female virilization

In the classic androgen biosynthesis pathway, testosterone is converted to 5α-dihydrotestosterone, a step crucially required for normal male genital virilization. Congenital adrenal hyperplasia (CAH) due to P450 oxidoreductase deficiency (PORD) is an inborn disorder that disrupts classic androgen biosynthesis. However, some affected girls present with severe genital virilization at birth. We hypothesized that this is explained by a prenatally active, alternative biosynthesis pathway to 5α-dihydrotestosterone. We show that adrenals and genital skin cooperate to produce androgens via the alternative pathway during the major period of human sexual differentiation and that neonates with PORD still produce alternative pathway androgens during the first weeks of life. This indicates that alternative pathway androgen biosynthesis drives prenatal virilization in CAH due to PORD.

Androgen biosynthesis in the human fetus proceeds through the adrenal sex steroid precursor dehydroepiandrosterone, which is converted to testosterone in the gonads, followed by further activation to 5α-dihydrotestosterone in genital skin, thereby facilitating male external genital differentiation. Congenital adrenal hyperplasia due to P450 oxidoreductase deficiency results in disrupted dehydroepiandrosterone biosynthesis, explaining undervirilization in affected boys. However, many affected girls are born virilized, despite low circulating androgens. We hypothesized that this is due to a prenatally active, alternative androgen biosynthesis pathway from 17α-hydroxyprogesterone to 5α-dihydrotestosterone, which bypasses dehydroepiandrosterone and testosterone, with increased activity in congenital adrenal hyperplasia variants associated with 17α-hydroxyprogesterone accumulation. Here we employ explant cultures of human fetal organs (adrenals, gonads, genital skin) from the major period of sexual differentiation and show that alternative pathway androgen biosynthesis is active in the fetus, as assessed by liquid chromatography–tandem mass spectrometry. We found androgen receptor expression in male and female genital skin using immunohistochemistry and demonstrated that both 5α-dihydrotestosterone and adrenal explant culture supernatant induce nuclear translocation of the androgen receptor in female genital skin primary cultures. Analyzing urinary steroid excretion by gas chromatography–mass spectrometry, we show that neonates with P450 oxidoreductase deficiency produce androgens through the alternative androgen pathway during the first weeks of life. We provide quantitative in vitro evidence that the corresponding P450 oxidoreductase mutations predominantly support alternative pathway androgen biosynthesis. These results indicate a key role of alternative pathway androgen biosynthesis in the prenatal virilization of girls affected by congenital adrenal hyperplasia due to P450 oxidoreductase deficiency.

Alternative (backdoor) androgen production and masculinization in the human fetus

Masculinization of the external genitalia in humans is dependent on formation of 5α-dihydrotestosterone (DHT) through both the canonical androgenic pathway and an alternative (backdoor) pathway. The fetal testes are essential for canonical androgen production, but little is known about the synthesis of backdoor androgens, despite their known critical role in masculinization. In this study, we have measured plasma and tissue levels of endogenous steroids in second trimester human fetuses using multidimensional and high-resolution mass spectrometry. Results show that androsterone is the principal backdoor androgen in the male fetal circulation and that DHT is undetectable (<1 ng/mL), while in female fetuses, there are significantly lower levels of androsterone and testosterone. In the male, intermediates in the backdoor pathway are found primarily in the placenta and fetal liver, with significant androsterone levels also in the fetal adrenal. Backdoor intermediates, including androsterone, are only present at very low levels in the fetal testes. This is consistent with transcript levels of enzymes involved in the alternate pathway (steroid 5α-reductase type 1 [SRD5A1], aldo-keto reductase type 1C2 [AKR1C2], aldo-keto reductase type 1C4 [AKR1C4], cytochrome P450 17A1 [CYP17A1]), as measured by quantitative PCR (qPCR). These data identify androsterone as the predominant backdoor androgen in the human fetus and show that circulating levels are sex dependent, but also that there is little de novo synthesis in the testis. Instead, the data indicate that placental progesterone acts as substrate for synthesis of backdoor androgens, which occurs across several tissues. Masculinization of the human fetus depends, therefore, on testosterone and androsterone synthesis by both the fetal testes and nongonadal tissues, leading to DHT formation at the genital tubercle. Our findings also provide a solid basis to explain why placental insufficiency is associated with disorders of sex development in humans.

Fetal human masculinisation depends on testosterone production by the testes and an alternative “backdoor” androgen. This study shows that this androgen is likely to be androsterone, which is sexually dimorphic in the fetus but does not come from the testes; instead, synthesis probably depends on placental substrates.

The human penis starts to develop before birth from a structure called the genital tubercle. This process is dependent on the secretion of testosterone from the fetal testes and subsequent conversion of testosterone into dihydrotestosterone (DHT) by enzymes in the genital tubercle. Recently, an alternative "backdoor" route to the formation of DHT, which does not require testosterone, has also been shown to be essential for normal development of the human penis. In this study we provide evidence indicating that androsterone is the major backdoor androgen involved in human masculinization and that it is produced in nongonadal tissues. Steroid hormone levels were measured in the plasma of second trimester human fetuses, and testosterone and androsterone were the only androgens with higher levels in males than in females. Analysis of tissue steroid levels showed that plasma androsterone did not primarily originate from the testes but, instead, was probably formed in other tissues via metabolism of placental progesterone. These data indicate, therefore, that masculinization of the human fetus depends on steroid hormone secretion from both the testes and the placenta, and would explain why placental dysfunction is associated with disorders of sex development.

Canonical and Noncanonical Androgen Metabolism and Activity

Androgens are critical drivers of prostate cancer. In this chapter we first discuss the canonical pathways of androgen metabolism and their alterations in prostate cancer progression, including the classical, backdoor and 5α-dione pathways, the role of pre-receptor DHT metabolism, and recent findings on oncogenic splicing of steroidogenic enzymes. Next, we discuss the activity and metabolism of non-canonical 11-oxygenated androgens that can activate wild-type AR and are less susceptible to glucuronidation and inactivation than the canonical androgens, thereby serving as an under-recognized reservoir of active ligands. We then discuss an emerging literature on the potential non-canonical role of androgen metabolizing enzymes in driving prostate cancer. We conclude by discussing the potential implications of these findings for prostate cancer progression, particularly in context of new agents such as abiraterone and enzalutamide, which target the AR-axis for prostate cancer therapy, including mechanisms of response and resistance and implications of these findings for future therapy.

Mutation of HSD3B2 Gene and Fate of Dehydroepiandrosterone

3βHSD2 enzyme is crucial for adrenal and gonad steroid biosynthesis. In enzyme deficiency states, due to recessive loss-of-function HSD3B2 mutations, steroid flux is altered and clinical manifestations result. Deficiency of 3βHSD2 activity in the adrenals precludes normal aldosterone and cortisol synthesis and the alternative backdoor and 11-oxygenated C19 steroid pathways and the flooding of cortisol precursors along the Δ5 pathway with a marked rise in DHEA and DHEAS production. In gonads, it precludes normal T and estrogen synthesis. Here, we review androgen-dependent male differentiation of the external genitalia in humans and link this to female development and steroidogenesis in the developing adrenal cortex. The molecular mechanisms governing postnatal adrenal cortex zonation and ZR development were also revised. This chapter will review relevant clinical, hormonal, and genetic aspects of 3βHSD2 deficiency with emphasis on the significance of alternate fates encountered by steroid hormone precursors in the adrenal gland and gonads. Our current knowledge of the process of steroidogenesis and steroid action is derived from pathological conditions. In humans the 3βHSD2 deficiency represents a model of nature that reinforces our knowledge about the role of the steroidogenic alternative pathway in sex differentiation in both sexes. However, the physiological role of the high serum DHEAS levels in fetal life as well as after adrenarche remains to be elucidated.

Intracrine androgen biosynthesis, metabolism and action revisited

Androgens play an important role in metabolic homeostasis and reproductive health in both men and women. Androgen signalling is dependent on androgen receptor activation, mostly by testosterone and 5α-dihydrotestosterone. However, the intracellular or intracrine activation of C₁₉ androgen precursors to active androgens in peripheral target tissues of androgen action is of equal importance. Intracrine androgen synthesis is often not reflected by circulating androgens but rather by androgen metabolites and conjugates. In this review we provide an overview of human C₁₉ steroid biosynthesis including the production of 11-oxygenated androgens, their transport in circulation and uptake into peripheral tissues. We conceptualise the mechanisms of intracrinology and review the intracrine pathways of activation and inactivation in selected human tissues. The contribution of liver and kidney as organs driving androgen inactivation and renal excretion are also highlighted. Finally, the importance of quantifying androgen metabolites and conjugates to assess intracrine androgen production is discussed.

The in vitro metabolism of 11β-hydroxyprogesterone and 11-ketoprogesterone to 11-ketodihydrotestosterone in the backdoor pathway

Increased circulating 11β-hydroxyprogesterone (11OHP4), biosynthesised in the human adrenal, is associated with 21-hydroxylase deficiency in congenital adrenal hyperplasia. 17α-hydroxyprogesterone levels are also increased, with the steroid's metabolism to dihydrotestosterone in the backdoor pathway contributing to hyperandrogenic clinical conditions. In this study we investigated the in vitro biosynthesis and downstream metabolism of 11OHP4. Both cytochrome P450 11β-hydroxylase and aldosterone synthase catalyse the biosynthesis of 11OHP4 from progesterone (P4) which is converted to 11-ketoprogesterone (11KP4) by 11β-hydroxysteroid dehydrogenase type 2, while type 1 readily catalysed the reverse reaction. We showed in HEK-293 cells that these C11-oxy C₂₁ steroids were metabolised by steroidogenic enzymes in the backdoor pathway-5α-reductase (SRD5A) and 3α-hydroxysteroid type 3 (AKR1C2) converted 11OHP4 to 5α-pregnan-11β-ol,3,20-dione and 5α-pregnan-3α,11β-diol-20-one, while 11KP4 was converted to 5α-pregnan-3,11,20-trione and 5α-pregnan-3α-ol-11,20-dione (alfaxalone), respectively. Cytochrome P450 17α-hydroxylase/17,20-lyase catalysed the hydroxylase and lyase reaction to produce the C11-oxy C₁₉ steroids demonstrated in the conversion of alfaxalone to 11-oxy steroids demonstrated in the conversion of alfaxalone to 11ketoandrosterone. In LNCaP cells, a prostate cancer cell model endogenously expressing the relevant enzymes, 11OHP4 and 11KP4 were metabolised to the potent androgen, 11-ketodihydrotestosterone (11KDHT), thus suggesting the C11-oxy C₂₁ steroids contribute to the pool of validating the in vitro biosynthesis of C11-oxy C₁₉ steroids from C11-oxy C₂₁ steroids. The in vitro reduction of 11KP4 at C3 and C5 by AKR1C2 and SRD5A has confirmed the metabolic route of the urinary metabolite, 3α,20α-dihydroxy-5β-pregnan-11-one. Although our assays have demonstrated the conversion of 11OHP4 and 11KP4 by steroidogenic enzymes in the backdoor pathway yielding 11KDHT, thus suggesting the C11-oxy C₂₁ steroids contribute to the pool of potent androgens, the in vivo confirmation of this metabolic route remains challenging.

Longitudinal serum and urine steroid metabolite profiling in a 46,XY infant with prenatally identified POR deficiency

Although POR deficiency (PORD) is assumed to be accompanied by excessive placental androgen accumulation and enhanced adrenal and testicular androgen production via the backdoor pathway as well as compromised testicular androgen production via the frontdoor pathway, there is no direct evidence for the flux of excessive placental androgens into the fetal circulation and for the production of dihydrotestosterone (DHT) via the backdoor pathway. We examined longitudinal serum and urine steroid metabolite profiles in a 46,XY infant with PORD who was prenatally identified because of the progressive fetal masculinization and maternal virilization from the mid-gestation and the presence of fetal radio-humeral synostosis and was confirmed to have compound heterozygous mutations of POR (p.Q201X and p.R457H). The results showed (1) markedly and inappropriately elevated serum androstenedione and testosterone (T) values at birth, (2) a markedly increased serum DHT value with a normal DHT/T ratio at birth, (3) transient elevation of serum T and DHT values accompanied by a normal DHT/T ratio and concomitant elevations of intermediate steroid metabolites on both the frontdoor and backdoor pathways at 30 days of age, and (4) persistent PORD-compatible urine steroid profiles. Although the data obtained from a single infantile patient are too premature to be generalized, they imply: (1) the transfer of excessive placental androgens into the fetal as well as the maternal circulations from the mid-gestation, (2) lack of a clinically discernible amount of DHT production via the adrenal backdoor pathway around birth, and (3) the activation of both the frontdoor and backdoor pathways in the testis around the mini-puberty, with no production of a clinically discernible amount of DHT via the testicular backdoor pathway.

Steroidogenesis: Unanswered Questions

Until the mid-1980s studies of steroidogenesis largely depended on identifying steroid structures and measuring steroid concentrations in body fluids. The molecular biology revolution radically revolutionized studies of steroidogenesis with the cloning of known steroidogenic enzymes, by identifying novel factors, and delineating the genetic basis of known and newly discovered diseases. Unfortunately, this dramatic success has led many young research-oriented endocrinologists to regard steroidogenesis as a 'solved area'. However, many important and exciting questions remain, especially concerning the mechanisms of cholesterol delivery to the steroidogenic machinery, the biochemistry of androgen synthesis, the regulation and biological role of adrenarche, fetal adrenal development and involution, the roles of steroids made in 'extraglandular' cells, and the search for genetic disorders. This review outlines some of these questions, but this list is necessarily incomplete.

Adrenal C11-oxy C21 steroids contribute to the C11-oxy C19 steroid pool via the backdoor pathway in the biosynthesis and metabolism of 21-deoxycortisol and 21-deoxycortisone

21-Hydroxylase deficiency presents with increased levels of cytochrome P450 21-hydroxylase substrates, progesterone and 17α-hydroxyprogesterone, which have been implicated in the production of androgens via the backdoor pathway. This study shows the biosynthesis of C11-oxy C₂₁ steroids, 21-deoxycortisol and 21-deoxycortisone, and their metabolism by steroidogenic enzymes in the backdoor pathway yielding novel steroid metabolites: 5α-pregnan-11β,17α-diol-3,20-dione; 5α-pregnan-17α-ol-3,11,20-trione; 5α-pregnan-3α,11β,17α-triol-20-one and 5α-pregnan-3α,17α-diol-11,20-dione. The metabolism of 21-deoxycortisol was validated in LNCaP cells expressing the relevant steroidogenic enzymes showing for the first time that the steroid, produced at high levels in 21OHD, is metabolised via the C11-oxy derivatives of 5α-pregnan-17α-ol-3,20-dione and 5α-pregnan-3α,17α-diol-20-one to substrates for the lyase activity of CYP17A1, leading to the production of C11-oxy C₁₉ steroids. 21-Deoxycortisol thus contributes to the pool of potent androgens in 21OHD, with novel steroid metabolites also presenting possible biomarkers in disease identification.

Androgenic potential of human fetal adrenals at the end of the first trimester

The onset of steroidogenesis in human fetal adrenal glands (HFA) during the first trimester is poorly investigated. An unresolved question is the capacity of the HFA to produce potent androgen DHT via conventional and/or the backdoor pathway(s) at the end of first trimester, when androgen-responsive organs are developed. Our aim was to explore steroidogenesis and the expression of steroidogenic enzymes and transcription factors in HFA at gestational weeks (GW) 9-12 with focus on their androgenic potential. Steroids in the HFA were analyzed by gas chromatography/mass spectrometry. The expression of steroidogenic enzymes and transcription factors in the HFA at GW9-12 was investigated by qPCR, automated Western blotting and immunohistochemistry. We demonstrated that during GW9-12 HFA produced steroids of the ∆⁵, ∆⁴ and the backdoor pathways of the biosynthesis of DHT, though the latter was limited to production of 17α-OH-dihydroprogesterone, androsterone and androstanedione without further conversion to DHT. The only androgens identified in the HFA were testosterone and androsterone, a precursor in the biosynthesis of DHT. We also observed higher levels of CYP17A1 but low expression of 3βHSD2 at GW11-12 in the HFA. Elevated levels of CYP17A1 were associated with an increased expression of SF-1 and GATA-6. Altogether, our data demonstrate that of those steroids analyzed, the only potent androgen directly produced by the HFA at GW9-12 was testosterone. The onset of steroidogenesis in the HFA is a complex process that is regulated by the coordinated action of related transcription factors.

Role of cytochrome b5 in the modulation of the enzymatic activities of cytochrome P450 17α-hydroxylase/17,20-lyase (P450 17A1)

Cytochrome b5 (cyt b5) is a small hemoprotein that plays a significant role in the modulation of activities of an important steroidogenic enzyme, cytochrome P450 17α-hydroxylase/17,20-lyase (P450 17A1, CYP17A1). Located in the zona fasciculata and zona reticularis of the adrenal cortex and in the gonads, P450 17A1 catalyzes two different reactions in the steroidogenic pathway; the 17α-hydroxylation and 17,20-lyase, in the endoplasmic reticulum of these respective tissues. The activities of P450 17A1 are regulated by cyt b5 that enhances the 17,20-lyase reaction by promoting the coupling of P450 17A1 and cytochrome P450 reductase (CPR), allosterically. Cyt b5 can also act as an electron donor to enhance the 16-ene-synthase activity of human P450 17A1. In this review, we discuss the many roles of cyt b5 and focus on the modulation of CYP17A1 activities by cyt b5 and the mechanisms involved.

Genes and proteins of the alternative steroid backdoor pathway for dihydrotestosterone synthesis are expressed in the human ovary and seem enhanced in the polycystic ovary syndrome

Recently, dihydrotestosterone biosynthesis through the backdoor pathway has been implicated for the human testis in addition to the classic pathway for testosterone (T) synthesis. In the human ovary, androgen precursors are crucial for estrogen synthesis and hyperandrogenism in pathologies such as the polycystic ovary syndrome is partially due to ovarian overproduction. However, a role for the backdoor pathway is only established for the testis and the adrenal, but not for the human ovary. To investigate whether the backdoor pathway exists in normal and PCOS ovaries, we performed specific gene and protein expression studies on ovarian tissues. We found aldo-keto reductases (AKR1C1-1C4), 5α-reductases (SRD5A1/2) and retinol dehydrogenase (RoDH) expressed in the human ovary, indicating that the ovary might produce dihydrotestosterone via the backdoor pathway. Immunohistochemical studies showed specific localization of these proteins to the theca cells. PCOS ovaries show enhanced expression, what may account for the hyperandrogenism.

The metabolic fate and receptor interaction of 16α-hydroxyprogesterone and its 5α-reduced metabolite, 16α-hydroxy-dihydroprogesterone

16α-hydroxyprogesterone (16OHP4) is not well characterised in terms of metabolism and receptor interaction. We therefore investigated its metabolism by adrenal CYP11B and peripheral steroidogenic enzymes, SRD5A and AKR1C2. UHPLC-MS/MS analyses identified novel steroids: the biosynthesis of 4-pregnen-11β,16α-diol-3,20-dione catalysed by CYP11B2; the 5α-reduction of the latter and 16OHP4 catalysed by SRD5A yielding 5α-pregnan-11β,16α-diol-3,20-diovne and 5α-pregnan-16α-ol-3,20-dione (16OH-DHP4); and 16OH-DHP4 converted by AKR1C2 to 5α-pregnan-3α,16α-diol-20-one. Receptor studies showed 16OHP4, 16OH-DHP4, progesterone and dihydroprogesterone (DHP4) were weak partial AR agonists; 16OHP4, 16OH-DHP4 and DHP4 exhibited weak partial agonist activity towards PR-B with DHP4 also exhibiting partial agonist activity towards PR-A. Data showed that while the 5α-reduction of P4 decreased PR activation significantly, 16OHP4 and 16OH-DHP4 exhibited comparable receptor activation. Although the clinical relevance of 16OHP4 remains unclear the elevated 16OHP4 levels characteristic of 21OHD, CAH, PCOS, prostate cancer, testicular feminization syndrome and cryptorchidism likely contribute towards these clinical conditions, inducing receptor-activated target genes.

Steroid 17-hydroxylase and 17,20-lyase deficiencies, genetic and pharmacologic

Steroid 17-hydroxylase 17,20-lyase (cytochrome P450c17, P450 17A1, CYP17A1) catalyzes two major reactions: steroid 17-hydroxylation followed by the 17,20-lyase reactions. The most severe mutations in the cognate CYP17A1 gene abrogate all activities and cause combined 17-hydroxylase/17,20-lyase deficiency (17OHD), a biochemical phenotype that is replicated by treatment with the potent CYP17A1 inhibitor abiraterone acetate. The adrenals of patients with 17OHD synthesize 11-deoxycorticosterone (DOC) and corticosterone but no 19-carbon steroids, similar to the rodent adrenal, and DOC causes hypertension and hypokalemia. Loss of 17,20-lyase activity precludes sex steroid synthesis and leads to sexual infantilism. Rare missense CYP17A1 mutations minimally disrupt 17-hydroxylase activity but cause isolated 17,20-lyase deficiency (ILD), Mutations in the POR gene encoding the required cofactor protein cytochrome P450-oxidoreductase causes a spectrum of disease from ILD to 17OHD combined with 21-hydroxylase and aromatase deficiencies, sometimes including skeletal malformations. Mutations in the CYB5A gene encoding a second cofactor protein cytochrome b₅ also selectively disrupt 17,20-lyase activity and cause the purest form of ILD. The clinical manifestations of these conditions are best understood in the context of the biochemistry of CYP17A1.

An improved micro-method for the measurement of steroid profiles by APPI-LC-MS/MS and its use in assessing diurnal effects on steroid concentrations and optimizing the diagnosis and treatment of adrenal insufficiency and CAH

Our goals were to (1) develop an improved micro-method usable for neonates for steroid profile measurements and a method to measure androsterone, a key steroid in the recently described androgen backdoor pathway together, with dehydroepiandrosterone and (2) to assess if dehydroepiandrosterone diurnal concentration fluctuations exist potentially necessitating strict adherence to time of blood sample draw and requirement of separate time-dependent reference intervals. Liquid chromatography-tandem mass spectrometry was performed with an atmospheric pressure photoionization source [1]. For each sample 50μL (100μL for the backdoor pathway) of serum was deproteinized by adding 75μL (150μL for the backdoor pathway) of acetonitrile containing the internal standards. After centrifugation, 75μL (150μL for the backdoor pathway) of supernatant was diluted with 250μL of water and injected onto a Poroshell 120 EC-C8 column (SB-C8 column for the backdoor pathway). Within-run coefficients of variation ranged from 2.4 to 10.4% and between-day coefficients of variation from 2.9 to 11.2%. Comparison studies yielded correlation coefficient between 0.97 and 1.00 with recoveries of 90% or greater. Our methods analyze a 9 steroid profile and an additional 2 steroid profile (backdoor pathway) with minimal sample volume (usable in neonates optimizing early diagnosis of endocrinopathies and genetic diseases). Low limits of quantitation make these methods ideal for steroid measurement in women and prepubertal children. As diurnal variations of dehydroepiandrosterone and other steroids [2] concentrations are clinically significant we recommend that separate reference intervals be developed for 8 am, 8 pm, and midnight sample draws. The use of this approach in improving the diagnosis of patients with adrenal insufficiency and congenital adrenal hyperplasia is discussed.

Cytochrome b5 Activates the 17,20-Lyase Activity of Human Cytochrome P450 17A1 by Increasing the Coupling of NADPH Consumption to Androgen Production

Human cytochrome P450 17A1 is required for all androgen biosynthesis and is the target of abiraterone, a drug used widely to treat advanced prostate cancer. P450 17A1 catalyzes both 17-hydroxylation and subsequent 17,20-lyase reactions with pregnenolone, progesterone, and allopregnanolone. The presence of cytochrome b5 (b5) markedly stimulates the 17,20-lyase reaction, with little effect on 17-hydroxylation; however, the mechanism of this b5 effect is not known. We determined the influence of b5 on coupling efficiency-defined as the ratio of product formation to NADPH consumption-in a reconstituted system using these 3 pairs of substrates for the 2 reactions. Rates of NADPH consumption ranged from 4 to 13 nmol/min/nmol P450 with wild-type P450 17A1. For the 17-hydroxylase reaction, progesterone oxidation was the most tightly coupled (∼50%) and negligibly changed upon addition of b5. Rates of NADPH consumption were similar for the 17-hydroxylase and corresponding 17,20-lyase reactions for each steroid series, and b5 only slightly increased NADPH consumption. For the 17,20-lyase reactions, b5 markedly increased product formation and coupling in parallel with all substrates, from 6% to 44% with the major substrate 17-hydroxypregnenolone. For the naturally occurring P450 17A1 mutations E305G and R347H, which impair 17,20-lyase activity, b5 failed to rescue the poor coupling with 17-hydroxypregnenolone (2-4%). When the conserved active-site threonine was mutated to alanine (T306A), both the activity and coupling were markedly decreased with all substrates. We conclude that b5 stimulation of the 17,20-lyase reaction primarily derives from more efficient use of NADPH for product formation rather than side products.

Impaired 17,20-Lyase Activity in Male Mice Lacking Cytochrome b5 in Leydig Cells

Androgen and estrogen biosynthesis in mammals requires the 17,20-lyase activity of cytochrome P450 17A1 (steroid 17-hydroxylase/17,20-lyase). Maximal 17,20-lyase activity in vitro requires the presence of cytochrome b₅ (b5), and rare cases of b5 deficiency in human beings causes isolated 17,20-lyase deficiency. To study the consequences of conditional b5 removal from testicular Leydig cells in an animal model, we generated Cyb5^flox/flox:Sf1-Cre (LeyKO) mice. The LeyKO male mice had normal body weights, testis and sex organ weights, and fertility compared with littermates. Basal serum and urine steroid profiles of LeyKO males were not significantly different than littermates. In contrast, marked 17-hydroxyprogesterone accumulation (100-fold basal) and reduced testosterone synthesis (27% of littermates) were observed after human chorionic gonadotropin stimulation in LeyKO animals. Testis homogenates from LeyKO mice showed reduced 17,20-lyase activity and a 3-fold increased 17-hydroxylase to 17,20-lyase activity ratio, which were restored to normal upon addition of recombinant b5. We conclude that Leydig cell b5 is required for maximal androgen synthesis and to prevent 17-hydroxyprogesterone accumulation in the mouse testis; however, the b5-independent 17,20-lyase activity of mouse steroid 17-hydroxylase/17,20-lyase is sufficient for normal male genital development and fertility. LeyKO male mice are a good model for the biochemistry but not the physiology of isolated 17,20-lyase deficiency in human beings.

The diverse chemistry of cytochrome P450 17A1 (P450c17, CYP17A1)

The steroid hydroxylation and carbon-carbon bond cleavage activities of cytochrome P450 17A1 (CYP17A1) are responsible for the production of glucocorticoids and androgens, respectively. The inhibition of androgen synthesis is an important strategy to treat androgen-dependent prostate cancer. We discuss the different enzymatic activities towards the various substrates of CYP17A1, demonstrating its promiscuity. Additionally, a novel interhelical interaction is proposed between the F-G loop and the B'-helix to explain the 16α-hydroxylase activity of human CYP17A1 with progesterone as the substrate. The techniques used by biochemists to study this important enzyme are also summarized. This article is part of a Special Issue entitled 'Steroid/Sterol signaling'.

Cytochrome b5 modulates multiple reactions in steroidogenesis by diverse mechanisms

Cytochrome b5 (cyt-b5) is a relatively small haemoprotein which plays an important role in the regulation of mammalian steroidogenesis. This unique protein has the ability to modulate the activity of key steroidogenic enzymes via a number of diverse reaction mechanisms. Cyt-b5 can augment the 17,20-lyase activity of CYP17A1 by promoting the interaction of CYP17A1 and POR; enhance the 16-ene-synthase activity of CYP17A1 by acting as an electron donor; and enhance the activity of 3βHSD by increasing the affinity of 3βHSD for its cofactor NAD(+). We review the modulation of CYP17A1 and 3βHSD activity by cyt-b5 and discuss the reaction mechanisms associated with each activity. The physiological importance of cyt-b5 in regulating mammalian steroidogenesis is presented and the impact of inactivating cyt-b5 mutations are reviewed. This article is part of a Special Issue entitled 'Steroid/Sterol signaling'.

A-ring modified steroidal azoles retaining similar potent and slowly reversible CYP17A1 inhibition as abiraterone

Abiraterone acetate is a potent inhibitor of human cytochrome P450c17 (CYP17A1, 17α-hydroxylase/17,20-lyase) and is clinically used in combination with prednisone for the treatment of castration-resistant prostate cancer. Although many studies have documented the potency of abiraterone (Abi) in a variety of in vitro and in vivo systems for several species, the exact potency of Abi for human CYP17A1 enzyme has not yet been determined, and the structural requirements for high-potency steroidal azole inhibitors are not established. We synthesized 4 Abi analogs differing in the A-B ring substitution patterns: 3α-hydroxy-Δ(4)-Abi (13), 3-keto-Δ(4)-Abi (11), 3-keto-5α-Abi (6), and 3α-hydroxy-5α-Abi (5). We measured the spectral binding constants (Ks) using purified and modified human CYP17A1 along with the determination constants (Ki) applying a native human CYP17A1 enzyme in yeast microsomes for these compounds as well as for ketoconazole. For Abi, 3-keto-Δ(4)-Abi, 3-keto-5α-Abi, and 3α-hydroxy-5α-Abi, the type 2 spectral changes gave the best fit for a quadratic equation, since in these experiments Ks values were 0.1-2.6nM, much lower than that for ketoconazole and 3α-hydroxy-Δ(4)-Abi (Ks values were 140 and 1660nM, respectively). Inhibition experiments showed mixed inhibition patterns with Ki values of 7-80nM. Abi dissociation from the CYP17A1-Abi complex was incomplete and slow; the t1/2 for dissociation was 1.8h, with 55% of complex remaining after 5h. We conclude that Abi and the 3 related steroidal azoles (3-keto-Δ(4)-Abi, 3-keto-5α-Abi, and 3α-hydroxy-5α-Abi), which also mimic natural substrates, are extraordinarily potent inhibitors of human CYP17A1, whereas the 3α-hydroxy-Δ(4)-Abi is moderately potent and comparable to ketoconazole.

Beyond T and DHT - novel steroid derivatives capable of wild type androgen receptor activation

While androgen deprivation therapy (ADT) remains the primary treatment for metastatic prostate cancer (PCa), castration does not eliminate androgens from the prostate tumor microenvironment, and residual intratumoral androgens are implicated in nearly every mechanism by which androgen receptor (AR)-mediated signaling promotes castration-resistant disease. The uptake and intratumoral (intracrine) conversion of circulating adrenal androgens such as dehydroepiandrosterone sulfate (DHEA-S) to steroids capable of activating the wild type AR is a recognized driver of castration resistant prostate cancer (CRPC). However, less well-characterized adrenal steroids, including 11-deoxcorticosterone (DOC) and 11beta-hydroxyandrostenedione (11OH-AED) may also play a previously unrecognized role in promoting AR activation. In particular, recent data demonstrate that the 5α-reduced metabolites of DOC and 11OH-AED are activators of the wild type AR. Given the well-recognized presence of SRD5A activity in CRPC tissue, these observations suggest that in the low androgen environment of CRPC, alternative sources of 5α-reduced ligands may supplement AR activation normally mediated by the canonical 5α-reduced agonist, 5α-DHT. Herein we review the emerging data that suggests a role for these alternative steroids of adrenal origin in activating the AR, and discuss the enzymatic pathways and novel downstream metabolites mediating these effects. We conclude by discussing the potential implications of these findings for CRPC progression, particularly in context of new agents such as abiraterone and enzalutamide which target the AR-axis for prostate cancer therapy.

5α-reductase type 3 enzyme in benign and malignant prostate

BACKGROUND

Currently available 5α-reductase inhibitors are not completely effective for treatment of benign prostate enlargement, prevention of prostate cancer (CaP), or treatment of advanced castration-recurrent (CR) CaP. We tested the hypothesis that a novel 5α-reductase, 5α-reductase-3, contributes to residual androgen metabolism, especially in CR-CaP.

METHODS

A new protein with potential 5α-reducing activity was expressed in CHO-K1 cellsandTOP10 E. coli for characterization. Protein lysates and total mRNA were isolated from preclinical and clinical tissues. Androgen metabolism was assessed using androgen precursors and thin layer chromatography or liquid chromatography tandem mass spectrometry.

RESULTS

The relative mRNA expression for the three 5α-reductase enzymes in clinical samples of CR-CaP was 5α-reductase-3 ≫ 5α-reductase-1> 5α-reductase-2. Recombinant 5α-reductase-3 protein incubations converted testosterone, 4-androstene-3,17-dione (androstenedione) and 4-pregnene-3,20-dione (progesterone) to dihydrotestosterone, 5α-androstan-3,17-dione, and 5α-pregnan-3,20-dione, respectively. 5α-Reduced androgen metabolites were measurable in lysates from androgen-stimulated (AS) CWR22 and CR-CWR22 tumors and clinical specimens of AS-CaP and CR-CaP pre-incubated with dutasteride (a bi-specific inhibitor of 5α-reductase-1 and 2).

CONCLUSION

Human prostate tissues contain a third 5α-reductase that was inhibited poorly by dutasteride at high androgen substrate concentration in vitro, and it may promote DHT formation in vivo, through alternative androgen metabolism pathways when testosterone levels are low.

Mechanisms of androgen receptor activation in castration-resistant prostate cancer

Systemic treatment of advanced prostate cancer is initiated with androgen deprivation therapy by gonadal testosterone depletion. Response durations are variable and tumors nearly always become resistant as castration-resistant prostate cancer (CRPC), which is driven, at least in part, by a continued dependence on the androgen receptor (AR). The proposed mechanisms that underlie AR function in this clinical setting are quite varied. These include intratumoral synthesis of androgens from inactive precursors, increased AR expression, AR activation through tyrosine kinase-dependent signaling, alterations in steroid receptor coactivators, and expression of a truncated AR with constitutive activity. Various pharmacologic interventions have clinically validated some of these mechanisms, such as those that require the AR ligand-binding domain. Clinical studies have failed to validate other mechanisms, and additional mechanisms have yet to be tested in patients with CRPC. Here, we review the mechanisms that elicit AR activity in CRPC, with a particular focus on recent developments.

The implication of neuroactive steroids in Tourette's syndrome pathogenesis: A role for 5α-reductase?

Tourette's syndrome (TS) is a neurodevelopmental disorder characterised by recurring motor and phonic tics. The pathogenesis of TS is considered to reflect dysregulations in the signalling of dopamine (DA) and other neurotransmitters, which lead to excitation/inhibition imbalances in cortico-striato-thalamocortical circuits. The causes of these deficits may reflect complex gene × environment × sex (G × E × S) interactions; indeed, the disorder is markedly predominant in males, with a male-to-female prevalence ratio of approximately 4 : 1. Converging lines of evidence point to neuroactive steroids as being likely molecular candidates to account for G × E × S interactions in TS. Building on these premises, our group has begun examining the possibility that alterations in the steroid biosynthetic process may be directly implicated in TS pathophysiology; in particular, our research has focused on 5α-reductase (5αR), the enzyme catalysing the key rate-limiting step in the synthesis of pregnane and androstane neurosteroids. In clinical and preclinical studies, we found that 5αR inhibitors exerted marked anti-DAergic and tic-suppressing properties, suggesting a central role for this enzyme in TS pathogenesis. Based on these data, we hypothesise that enhancements in 5αR activity in early developmental stages may lead to an inappropriate activation of the 'backdoor' pathway for androgen synthesis from adrenarche until the end of puberty. We predict that the ensuing imbalances in steroid homeostasis may impair the signalling of DA and other neurotransmitters, ultimately resulting in the facilitation of tics and other behavioural abnormalities in TS.

Role of microsomal steroid hydroxylases in Δ7-steroid biosynthesis

CYP17 (steroid 17α-hydroxylase/17,20-lyase) is a key enzyme in steroid hormone biosynthesis. It catalyzes two independent reactions at the same active center and has a unique ability to differentiate Δ(4)-steroids and Δ(5)-steroids in the 17,20-lyase reaction. The present work presents a complex experimental analysis of the role of CYP17 in the metabolism of 7-dehydrosteroids. The data indicate the existence of a possible alternative pathway of steroid hormone biosynthesis using 7-dehydrosteroids. The major reaction products of CYP17 catalyzed hydroxylation of 7-dehydropregnenolone have been identified. Catalytic activity of CYP17 from different species with 7-dehydropregnenolone has been estimated. It is shown that CYP21 cannot use Δ(5)-Δ(7) steroids as a substrate.

Of marsupials and men: "Backdoor" dihydrotestosterone synthesis in male sexual differentiation

Following development of the fetal bipotential gonad into a testis, male genital differentiation requires testicular androgens. Fetal Leydig cells produce testosterone that is converted to dihydrotestosterone in genital skin, resulting in labio-scrotal fusion. An alternative 'backdoor' pathway of dihydrotestosterone synthesis that bypasses testosterone has been described in marsupials, but its relevance to human biology has been uncertain. The classic and backdoor pathways share many enzymes, but a 3α-reductase, AKR1C2, is unique to the backdoor pathway. Human AKR1C2 mutations cause disordered sexual differentiation, lending weight to the idea that both pathways are required for normal human male genital development. These observations indicate that fetal dihydrotestosterone acts both as a hormone and as a paracrine factor, substantially revising the classic paradigm for fetal male sexual development.

Prenatal diagnosis of congenital adrenal hyperplasia caused by P450 oxidoreductase deficiency

CONTEXT

Mutations in the electron donor enzyme P450 oxidoreductase (POR) result in congenital adrenal hyperplasia with apparent combined 17α-hydroxylase/17,20 lyase and 21-hydroxylase deficiencies, also termed P450 oxidoreductase deficiency (PORD). Major clinical features present in PORD are disordered sex development in affected individuals of both sexes, glucocorticoid deficiency, and multiple skeletal malformations.

OBJECTIVE

The objective of the study was to establish a noninvasive approach to prenatal diagnosis of PORD including assessment of malformation severity to facilitate optimized prenatal diagnosis and timely treatment.

DESIGN

We analyzed 20 pregnancies with children homozygous or compound heterozygous for disease-causing POR mutations and 1 pregnancy with a child carrying a heterozygous POR mutation by recording clinical and biochemical presentations and fetal ultrasound findings. In 4 of the pregnancies (3 homozygous and 1 heterozygous for disease-causing POR mutations), prenatal analysis of steroid metabolite excretion in maternal urine was carried out by gas chromatography/mass spectrometry during gestational weeks 11-23.

RESULTS

Pregnancy complications in our cohort included maternal virilization (6 of 20) with onset in the second trimester. Seven pregnant women presented with low unconjugated estriol at prenatal screening (triple or quadruple antenatal screening test). Overt dysmorphic features were noted in 19 of the 20 babies at birth but observed in only 5 by prenatal ultrasound. These 5 had the most severe malformation phenotypes and poor outcome, whereas the other babies showed normal development. Steroid profiling of maternal urine revealed significantly increased steroids of fetal origin, namely the pregnenolone metabolite epiallopregnanediol and the androgen metabolite androsterone, with concomitant low values for estriol. Diagnostic steroid ratios conclusively indicated PORD as early as gestational week 12. In the heterozygous pregnancy, steroid ratios were only slightly elevated and estriol excretion was normal.

CONCLUSION

Prenatal diagnosis in PORD is readily established via urinary steroid metabolite analysis of maternal urine. Visible malformations at prenatal ultrasound predict a severe malformation phenotype.

The activities of 5α-reductase and 17,20-lyase determine the direction through androgen synthesis pathways in patients with 21-hydroxylase deficiency

OBJECTIVE

The 'backdoor' pathway provides an efficient route from 17α-hydroxyprogesterone (17-OHP) to dihydrotestosterone (DHT) in patients with 21-hydroxylase deficiency (21-OHD). 17-OHP is a good substrate for 5α-reductase leading to 17α-hydroxyallopregnanolone, which is an excellent substrate for the 17,20-lyase activity of CYP17A1. 5α-Reductase and CYP17A1 are therefore two crucial enzymes in the backdoor route. The 17,20-lyase activity of CYP17A1 additionally promotes the conversion of 17-OHP and 17α-hydroxypregnenolone to androgens in the classical Δ(4) and Δ(5) pathways. Thus, we hypothesised that the activities of 5α-reductase and 17,20-lyase should determine the flux through the androgen synthesis pathways in patients with 21-OHD.

DESIGN AND METHODS

We compared retrospectively urinary steroid hormone profiles determined by gas chromatography-mass spectrometry of 142 untreated 21-OHD patients (age range: 1 day to 25.4 years; 51 males) with 138 control subjects.

RESULTS

The relative activities of the backdoor pathway and 5α-reductase correlated significantly (p<0.0001). Neonates with 21-OHD demonstrated a moderate activity of the 5α-reductase leading to moderate 17α-hydroxyallopregnanolone generation in the backdoor pathway. Due to substantial 17,20-lyase activity, 17α-hydroxyallopregnanolone is converted rapidly to androsterone. During infancy, the activity of 5α-reductase is very high leading to a high activity of the backdoor pathway until the generation of 17α-hydroxyallopregnanolone. Only a moderate androsterone production is the result of low 17,20-lyase activity. Children show a low 5α-reductase and a high 17,20-lyase activity leading to a low androsterone generation via the backdoor pathway.

CONCLUSION

The 5α-reductase is the gatekeeper of the backdoor pathway, whereas the 17,20-lyase activity of CYP17A1 is the regulator of the flux through the androgen pathways.

Increased activation of the alternative "backdoor" pathway in patients with 21-hydroxylase deficiency: evidence from urinary steroid hormone analysis

BACKGROUND

17-Hydroxyprogesterone (17-OHP) can be converted to dihydrotestosterone (DHT) via an alternative "backdoor" route that bypasses the conventional intermediates androstenedione and testosterone. In this backdoor pathway, 17-OHP is converted to 5α-pregnane-3α,17α-diol-20-one (pdiol), which is an excellent substrate for the 17,20 lyase activity of CYP17A1 to produce androsterone. OBJECTIVE AND HYPOTHESES: The objective of this study was to obtain evidence for the presence of the backdoor pathway in patients with 21-hydroxylase deficiency (21-OHD).

METHODS

We compared urinary steroid hormone profiles determined by gas chromatography-mass spectrometry of 142 untreated 21-OHD patients (age range, 1 d to 25.4 yr; 51 males) with 138 control subjects. The activity of the backdoor pathway was assessed using the ratios of the urinary concentrations of pdiol to those of the metabolites of the classic Δ4 and Δ5 pathways. In contrast to etiocholanolone, which originates almost exclusively from the classic pathways, androsterone may be derived additionally from the backdoor pathway. Therefore, the androsterone to etiocholanolone ratio can be used as an indicator for the presence of the backdoor pathway.

RESULTS

Untreated 21-OHD subjects showed increased urinary ratios of pdiol to the Δ4 and Δ5 pathway metabolites and a higher androsterone to etiocholanolone ratio.

CONCLUSIONS

The elevated ratios of pdiol to the Δ4 and Δ5 pathway metabolites as well as the higher androsterone to etiocholanolone ratio in patients with 21-OHD indicate postnatal activity of the backdoor pathway with maximum activity during early infancy. Our data provide new insights into the pathophysiology of androgen biosynthesis of 21-OHD.

Genotype-phenotype analysis in congenital adrenal hyperplasia due to P450 oxidoreductase deficiency

CONTEXT

P450 oxidoreductase deficiency (PORD) is a unique congenital adrenal hyperplasia variant that manifests with glucocorticoid deficiency, disordered sex development (DSD), and skeletal malformations. No comprehensive data on genotype-phenotype correlations in Caucasian patients are available.

OBJECTIVE

The objective of the study was to establish genotype-phenotype correlations in a large PORD cohort.

DESIGN

The design of the study was the clinical, biochemical, and genetic assessment including multiplex ligation-dependent probe amplification (MLPA) in 30 PORD patients from 11 countries.

RESULTS

We identified 23 P450 oxidoreductase (POR) mutations (14 novel) including an exonic deletion and a partial duplication detected by MLPA. Only 22% of unrelated patients carried homozygous POR mutations. p.A287P was the most common mutation (43% of unrelated alleles); no other hot spot was identified. Urinary steroid profiling showed characteristic PORD metabolomes with variable impairment of 17α-hydroxylase and 21-hydroxylase. Short cosyntropin testing revealed adrenal insufficiency in 89%. DSD was present in 15 of 18 46,XX and seven of 12 46,XY individuals. Homozygosity for p.A287P was invariably associated with 46,XX DSD but normal genitalia in 46,XY individuals. The majority of patients with mild to moderate skeletal malformations, assessed by a novel scoring system, were compound heterozygous for missense mutations, whereas nearly all patients with severe malformations carried a major loss-of-function defect on one of the affected alleles.

CONCLUSIONS

We report clinical, biochemical, and genetic findings in a large PORD cohort and show that MLPA is a useful addition to POR mutation analysis. Homozygosity for the most frequent mutation in Caucasians, p.A287P, allows for prediction of genital phenotype and moderate malformations. Adrenal insufficiency is frequent, easily overlooked, but readily detected by cosyntropin testing.

Role of a disordered steroid metabolome in the elucidation of sterol and steroid biosynthesis

In 1937 Butler and Marrian found large amounts of the steroid pregnanetriol in urine from a patient with the adrenogenital syndrome, a virilizing condition known to be caused by compromised adrenal secretion even in this pre-cortisol era. This introduced the concept of the study of altered excretion of metabolites as an in vivo tool for understanding sterol and steroid biosynthesis. This approach is still viable and has experienced renewed significance as the field of metabolomics. From the first cyclized sterol lanosterol to the most downstream product estradiol, there are probably greater than 30 steps. Based on a distinctive metabolome clinical disorders have now been attributed to about seven post-squalene cholesterol (C) biosynthetic steps and around 15 en-route to steroid hormones or needed for further metabolism of such hormones. Forty years ago it was widely perceived that the principal steroid biosynthetic defects were known but interest rekindled as novel metabolomes were documented. In his career this investigator has been involved in the study of many steroid disorders, the two most recent being P450 oxidoreductase deficiency and apparent cortisone reductase deficiency. These are of interest as they are due not to mutations in the primary catalytic enzymes of steroidogenesis but in ancillary enzymes needed for co-factor oxido-reduction A third focus of this researcher is Smith-Lemli-Opitz syndrome (SLOS), a cholesterol synthesis disorder caused by 7-dehydrocholesterol reductase mutations. The late George Schroepfer, in whose honor this article has been written, contributed greatly to defining the sterol metabolome of this condition. Defining the cause of clinically severe disorders can lead to improved treatment options. We are now involved in murine gene therapy studies for SLOS which, if successful could in the future offer an alternative therapy for this severe condition.

Why human cytochrome P450c21 is a progesterone 21-hydroxylase

Human cytochrome P450c21 (steroid 21-hydroxylase, CYP21A2) catalyzes the 21-hydroxylation of progesterone (P4) and its preferred substrate 17α-hydroxyprogestrone (17OHP4). CYP21A2 activities, which are required for cortisol and aldosterone biosynthesis, involve the formation of energetically disfavored primary carbon radicals. Therefore, we hypothesized that the binding of P4 and 17OHP4 to CYP21A2 restricts access of the reactive heme-oxygen complex to the C-21 hydrogen atoms, suppressing oxygenation at kinetically more favorable sites such as C-17 and C-16, which are both hydroxylated by cytochrome P450c17 (CYP17A1). We reasoned that expansion of the CYP21A2 substrate-binding pocket would increase substrate mobility and might yield additional hydroxylation activities. We built a computer model of CYP21A2 based principally on the crystal structure of CYP2C5, which also 21-hydroxylates P4. Molecular dynamics simulations indicate that binding of the steroid nucleus perpendicular to the plane of the CYP21A2 heme ring limits access of the heme oxygen to the C-21 hydrogen atoms. Residues L107, L109, V470, I471, and V359 were found to contribute to the CYP21A2 substate-binding pocket. Mutation of V470 and I471 to alanine or glycine preserved P4 21-hydroxylase activity, and mutations of L107 or L109 were inactive. Mutations V359A and V359G, in contrast, acquired 16α-hydroxylase activity, accounting for 40% and 90% of the P4 metabolites, respectively. We conclude that P4 binds to CYP21A2 in a fundamentally different orientation than to CYP17A1 and that expansion of the CYP21A2 substrate-binding pocket allows additional substrate trajectories and metabolic switching.

The molecular biology, biochemistry, and physiology of human steroidogenesis and its disorders

Steroidogenesis entails processes by which cholesterol is converted to biologically active steroid hormones. Whereas most endocrine texts discuss adrenal, ovarian, testicular, placental, and other steroidogenic processes in a gland-specific fashion, steroidogenesis is better understood as a single process that is repeated in each gland with cell-type-specific variations on a single theme. Thus, understanding steroidogenesis is rooted in an understanding of the biochemistry of the various steroidogenic enzymes and cofactors and the genes that encode them. The first and rate-limiting step in steroidogenesis is the conversion of cholesterol to pregnenolone by a single enzyme, P450scc (CYP11A1), but this enzymatically complex step is subject to multiple regulatory mechanisms, yielding finely tuned quantitative regulation. Qualitative regulation determining the type of steroid to be produced is mediated by many enzymes and cofactors. Steroidogenic enzymes fall into two groups: cytochrome P450 enzymes and hydroxysteroid dehydrogenases. A cytochrome P450 may be either type 1 (in mitochondria) or type 2 (in endoplasmic reticulum), and a hydroxysteroid dehydrogenase may belong to either the aldo-keto reductase or short-chain dehydrogenase/reductase families. The activities of these enzymes are modulated by posttranslational modifications and by cofactors, especially electron-donating redox partners. The elucidation of the precise roles of these various enzymes and cofactors has been greatly facilitated by identifying the genetic bases of rare disorders of steroidogenesis. Some enzymes not principally involved in steroidogenesis may also catalyze extraglandular steroidogenesis, modulating the phenotype expected to result from some mutations. Understanding steroidogenesis is of fundamental importance to understanding disorders of sexual differentiation, reproduction, fertility, hypertension, obesity, and physiological homeostasis.

At the crossroads of steroid hormone biosynthesis: the role, substrate specificity and evolutionary development of CYP17

Cytochrome P450s play critical roles in the metabolism of various bioactive compounds. One of the crucial functions of cytochrome P450s in Chordata is in the biosynthesis of steroid hormones. Steroid 17alpha-hydroxylase/17,20-lyase (CYP17) is localized in endoplasmic reticulum membranes of steroidogenic cells. CYP17 catalyzes the 17alpha-hydroxylation reaction of delta4-C₂₁ steroids (progesterone derivatives) and delta5-C₂₁ steroids (pregnenolone derivatives) as well as the 17,20-lyase reaction producing C₁₉-steroids, a key branch point in steroid hormone biosynthesis. Depending on CYP17 activity, the steroid hormone biosynthesis pathway is directed to either the formation of mineralocorticoids and glucocorticoids or sex hormones. In the present review, the current information on CYP17 is analyzed and discussed.

46,XX DSD: the masculinised female

The 46,XX disorders of sex development (DSDs) cause virilisation or masculinisation of the female foetus. The final common pathway of all 46,XX DSDs is excess dihydrotestosterone (DHT) or potent foreign androgen in the genital tissue during the critical period of sexual differentiation. Whereas the foetal testis is source of androgen in the male, it is the foetal adrenal that produces the DHT precursors in the female. By understanding the principles of human steroid biosynthesis, the pathogenesis of each disorder may be logically deduced, and treatment strategies are rationally constructed. In practice, however, therapies for many of these diseases are fraught with complications and caveats, and current approaches leave much room for improvement. This review discusses these diseases, their pathogenesis and approaches to therapy. We emphasise areas where improved treatments are sorely needed.

Steroidogenesis in the fetal testis and its susceptibility to disruption by exogenous compounds

Masculinization depends on adequate production of testosterone by the fetal testis within a specific "masculinization programming window." Disorders resulting from subtle deficiencies in this process are common in humans, and environmental exposures/lifestyle could contribute causally because common therapeutic and environmental compounds can affect steroidogenesis. This evidence derives mainly from rodent studies, but because there are major species differences in regulation of steroidogenesis in the fetal testis, this may not always be a guide to potential effects in the human. In addition to direct study of the effects of compounds on steroidogenesis, information also derives from study of masculinization disorders that result from mutations in genes in pathways regulating steroidogenesis. This review addresses this issue by critically reviewing the comparative timing of production and regulation of steroidogenesis in the fetal testis of humans and of rodents and its susceptibility to disruption; where there is limited information for the fetus, evidence from effects on steroidogenesis in the adult testis is considered. There are a number of fundamental regulatory differences between the human and rodent fetal testis, most notably in the importance of paracrine vs. endocrine drives during masculinization such that inactivating LH receptor mutations block masculinization in humans but not in rodents. Other large differences involve the steroidogenic response to estrogens and GnRH analogs and possibly phthalates, whereas for other compounds there may be differences in sensitivity to disruption (ketoconazole). This comparison identifies steroidogenic targets that are either vulnerable (mitochondrial cholesterol transport, CYP11A, CYP17) or not (cholesterol uptake) to chemical interference.