Effect of Dose and 5α-Reductase Inhibition on the Circulating Testosterone Metabolite Profile of Men Administered Oral Testosterone

Development of new hormonal male contraception for the couple

BACKGROUND

Current options for male contraception are limited to condoms, the withdrawal method, or a vasectomy. Studies indicate that men have expressed growing interest in bearing responsibility for family planning.

OBJECTIVES

To review prior studies investigating the role of an androgen-only or androgen with progestin regimen for hormonal male contraception and to provide an update of a promising new hormonal agent, a transdermal gel.

DISCUSSION

Thus far, there have been six studies conducted in couples evaluating the contraceptive efficacy of an androgen-only or androgen co-administered with a progestin regimen for hormonal male contraception. The only ongoing study is by the National Institute of Child Health and Human Development, in collaboration with the Population Council. They have developed a novel transdermal gel containing testosterone and segesterone acetate (Nestorone), a progestin. An ongoing phase II study enrolling more than 460 couples has shown great potential with respect to the product's efficacy, safety, reversibility, and acceptability. As this agent advances in development, a rapid at-home test for sperm concentration will provide couples with immediate feedback regarding their potential for pregnancy.

CONCLUSION

There is promise for the first-of-its-kind hormonal male contraceptive, a transdermal gel, to achieve market approval for distribution in the United States and elsewhere. Its safety, efficacy, reversibility, and user-control are all appealing qualities that make it readily adoptable for clinical practice.

Profiling of urinary steroids aided by lithium ion adduction-based ultrahigh-performance liquid chromatography-tandem mass spectrometry

RATIONALE

As 3-OH-containing steroids are prone to dehydration by conventional electrospray ionization, reducing detection sensitivity, Li ion adduction-based ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC/MS/MS), developed to prevent dehydration and effectively detect 3-OH steroids, was applied for profiling total and free steroids in urine.

METHODS

Free urinary steroids were isolated directly from urine by solid-phase extraction (SPE) with 80% acetonitrile. The total steroids were prepared by enzymatic treatment of urine with a cocktail of sulfatase and glucronidase, protein precipitation, and separation with the above SPE. In order to detect as many steroid types as possible, UHPLC/MS/MS (Li method) with Li+ solution added after the column was used for analysis in addition to the conventional method of detecting protonated ions (H method). The 13 3-OH steroids and the remaining 16 steroids were quantified by standard curves prepared using product ion transitions derived from [M + Li]+ and MH+ , respectively.

RESULTS

Two groups of human urine, male and female urine, were analyzed. 3-OH steroids could be detected with greater sensitivity using the Li method than the conventional method. The absolute amounts of each steroid were normalized based on creatinine levels. The difference between the male and female groups are clearly attributable to sex steroids.

CONCLUSIONS

Twenty-nine total steroids and 19 free steroids were identified in a limited volume (240 mL) of urine. Of these, 13 3-OH steroids were better detected by Li+ adduction-based UHPLC/MS/MS.

Relevance of Human Aldoketoreductases and Microbial β-Glucuronidases in Testosterone Disposition

Testosterone exhibits high variability in pharmacokinetics and glucuronidation after oral administration. Although testosterone metabolism has been studied for decades, the impact of UGT2B17 gene deletion and the role of gut bacterial β-glucuronidases on its disposition are not well characterized. We first performed an exploratory study to investigate the effect of UGT2B17 gene deletion on the global liver proteome, which revealed significant increases in proteins from multiple biological pathways. The most upregulated liver proteins were aldoketoreductases [AKR1D1, AKR1C4, AKR7A3, AKR1A1, and 7-dehydrocholesterol reductase (DHCR7)] and alcohol or aldehyde dehydrogenases (ADH6, ADH1C, ALDH1A1, ALDH9A1, and ALDH5A). In vitro assays revealed that AKR1D1 and AKR1C4 inactivate testosterone to 5β-dihydrotestosterone (5β-DHT) and 3α,5β-tetrahydrotestosterone (3α,5β-THT), respectively. These metabolites also appeared in human hepatocytes treated with testosterone and in human serum collected after oral testosterone dosing in men. Our data also suggest that 5β-DHT and 3α, 5β-THT are then eliminated through glucuronidation by UGT2B7 in UGT2B17 deletion individuals. Second, we evaluated the potential reactivation of testosterone glucuronide (TG) after its secretion into the intestinal lumen. Incubation of TG with purified gut microbial β-glucuronidase enzymes and with human fecal extracts confirmed testosterone reactivation into testosterone by gut bacterial enzymes. Both testosterone metabolic switching and variable testosterone activation by gut microbial enzymes are important mechanisms for explaining the disposition of orally administered testosterone and appear essential to unraveling the molecular mechanisms underlying UGT2B17-associated pathophysiological conditions. SIGNIFICANCE STATEMENT: This study investigated the association of UGT2B17 gene deletion and gut bacterial β-glucuronidases with testosterone disposition in vitro. The experiments revealed upregulation of AKR1D1 and AKR1C4 in UGT2B17 deletion individuals, and the role of these enzymes to inactivate testosterone to 5β-dihydrotestosterone and 3α, 5β-tetrahydrotestosterone, respectively. Key gut bacterial species responsible for testosterone glucuronide activation were identified. These data are important for explaining the disposition of exogenously administered testosterone and appear essential to unraveling the molecular mechanisms underlying UGT2B17-associated pathophysiological conditions.

Differential proteomics analysis of JEG-3 and JAR placental cell models and the effect of androgen treatment

The placenta is a vital fetal organ that plays an important role in maintaining fetal sex hormone homeostasis. Xenobiotics can alter placental sex-steroidogenic enzymes and transporters, including enzymes such as aromatase (CYP19A1) and the hydroxysteroid dehydrogenases (HSDs) but studying how compounds disrupt in vivo placental metabolism is complex. Utilizing high-throughput in vitro models is critical to predict the disruption of placental sex-steroidogenic enzymes and transporters, particularly by drug candidates in the early stages of drug discovery. JAR and JEG-3 cells are the most common, simple, and cost-effective placental cell models that are capable of high-throughput screening, but how well they express the sex-steroidogenic enzymes and transporters is not well known. Here, we compared the proteomes of JAR and JEG-3 cells in the presence and absence of physiologically relevant concentrations of dehydroepiandrosterone (DHEA, 8 µM) and testosterone (15 nM) to aid the characterization of sex-steroidogenic enzymes and transporters in these cell models. Global proteomics analysis detected 2931 and 3449 proteins in JAR cells and JEG-3 cells, respectively. However, dramatic differences in sex-steroidogenic enzymes and transporters were observed between these cells. In particular, the basal expression of steroid sulfatase (STS), HSD17B1, and HSD17B7 were unique to JEG-3 cells. JEG-3 cells also showed significantly higher protein levels of aldo-keto reductase (AKR) 1A1 and AKR1B1, while JAR cells showed significantly higher levels of HSD17B4 and HSDB12. Aldehyde dehydrogenase (ALDH) 3A2 and HSD17B11 enzymes as well as the transporters sterol O-acyltransferase (SOAT) 1 and ATP binding cassette subfamily G2 (ABCG2) were comparable between the cell lines, whereas sulfotransferases (SULTs) were uniquely present within JAR cells. Androgen treatments significantly lowered HSD17B11, HSD17B4, HSD17B12, and ALDH3A2 levels in JAR cells. DHEA treatment significantly raised the level of HSD17B1 by 51 % in JEG-3 cells, whereas CYP19A1 was increased to significant levels in both JAR and JEG-3 cells after androgen treatments. The proteomics data were supported by a complementary targeted metabolomics analysis of culture media in the DHEA (8 µM) and testosterone (15 nM) treated groups. This study has indicated that untreated JEG-3 cells express more sex-steroidogenic enzymes and transporters. Nevertheless, JEG-3 and JAR cells are unique and their respective proteomics data can be used to select the best model depending on the hypothesis.

Impact of Microbiome on Hepatic Metabolizing Enzymes and Transporters in Mice during Pregnancy

The microbiome and pregnancy are known to alter drug disposition, yet the interplay of the two physiologic factors on the expression and/or activity of drug metabolizing enzymes and transporters (DMETs) is unknown. This study investigated the effects of microbiome on host hepatic DMETs in mice during pregnancy by comparing four groups of conventional (CV) and germ-free (GF) female mice and pregnancy status, namely, CV nonpregnant, GF non-pregnant, CV pregnant, and GF pregnant mice. Transcriptomic and targeted proteomics of hepatic DMETs were profiled by using multiomics. Plasma bile acid and steroid hormone levels were quantified by liquid chromatography tandem mass spectrometry. CYP3A activities were measured by mouse liver microsome incubations. The trend of pregnancy-induced changes in the expression or activity of hepatic DMETs in CV and GF mice was similar; however, the magnitude of change was noticeably different. For certain DMETs, pregnancy status had paradoxical effects on mRNA and protein expression in both CV and GF mice. For instance, the mRNA levels of Cyp3a11, the murine homolog of human CYP3A4, were decreased by 1.7-fold and 3.3-fold by pregnancy in CV and GF mice, respectively; however, the protein levels of CYP3A11 were increased similarly ∼twofold by pregnancy in both CV and GF mice. Microsome incubations revealed a marked induction of CYP3A activity by pregnancy that was 10-fold greater in CV mice than that in GF mice. This is the first study to show that the microbiome can alter the expression and/or activity of hepatic DMETs in pregnancy. SIGNIFICANCE STATEMENT: We demonstrated for the first time that microbiome and pregnancy can interplay to alter the expression and/or activity of hepatic drug metabolizing enzymes and transporters. Though the trend of pregnancy-induced changes in the expression or activity of hepatic drug metabolizing enzymes and transporters in conventional and germ-free mice was similar, the magnitude of change was noticeably different.

Human efflux transport of testosterone, epitestosterone and other androgen glucuronides

Several drug-metabolizing enzymes are known to control androgen homeostasis in humans. UDP-glucuronosyltransferases convert androgens to glucuronide conjugates in the liver and intestine, which enables subsequent elimination of these conjugated androgens via urine. The most important androgen is testosterone, while others are the testosterone metabolites androsterone and etiocholanolone, and the testosterone precursor dehydroepiandrosterone. Epitestosterone is another endogenous androgen, which is included as a crucial marker in urine doping tests. Since glucuronide conjugates are hydrophilic, efflux transporters mediate their excretion from tissues. In this study, we employed the membrane vesicle assay to identify the efflux transporters for glucuronides of androsterone, dehydroepiandrosterone, epitestosterone, etiocholanolone and testosterone. The human hepatic and intestinal transporters MRP2 (ABCC2), MRP3 (ABCC3), MRP4 (ABCC4), BCRP (ABCG2) and MDR1 (ABCB1) were studied in vitro. Of these transporters, only MRP2 and MRP3 transported the androgen glucuronides investigated. In kinetic analyses, MRP3 transported glucuronides of androsterone, epitestosterone and etiocholanolone at low K_m values, between 0.4 and 4 μM, while the K_m values for glucuronides of testosterone and dehydroepiandrosterone were 14 and 51 μM, respectively. MRP2 transported the glucuronides at lower affinity, as indicated by K_m values over 100 μM. Interestingly, the MRP2-mediated transport of androsterone and epitestosterone glucuronides was best described by sigmoidal kinetics. The inability of BCRP to transport any of the androgen glucuronides investigated is drastically different from its highly active transport of several estrogen conjugates. Our results explain the transporter-mediated disposition of androgen glucuronides in humans, and shed light on differences between the human efflux transporters MRP2, MRP3, MRP4, BCRP and MDR1.

Normalized Testosterone Glucuronide as a Potential Urinary Biomarker for Highly Variable UGT2B17 in Children 7-18 Years

UDP-glucuronosyltransferase 2B17 (UGT2B17) is a highly variable androgen-metabolizing and drug-metabolizing enzyme. UGT2B17 exhibits a unique ontogeny profile characterized by a dramatic increase in hepatic protein expression from prepubertal age to adulthood. Age, sex, copy number variation (CNV), and single nucleotide polymorphisms only explain 26% of variability in protein expression, highlighting the need for a phenotypic biomarker for predicting interindividual variability in glucuronidation of UGT2B17 substrates. Here, we propose testosterone glucuronide (TG) normalized by androsterone glucuronide (TG/AG) as a urinary UGT2B17 biomarker, and examine the associations among urinary TG/AG and age, sex, and CNV. We performed targeted metabolomics of 12 androgen conjugates with liquid-chromatography tandem mass spectrometry in 63 pediatric subjects ages 7-18 years followed over 7 visits in 3 years. Consistent with the reported developmental trajectory of UGT2B17 protein expression, urinary TG/AG is significantly associated with age, sex, and CNV. In conclusion, TG/AG shows promise as a phenotypic urinary UGT2B17 biomarker.

The gut microbiota is a major regulator of androgen metabolism in intestinal contents

Androgens exert important effects both in androgen-responsive tissues and in the intestinal tract. To determine the impact of the gut microbiota (GM) on intestinal androgen metabolism, we measured unconjugated (free) and glucuronidated androgen levels in intestinal contents from the small intestine, with a low bacterial density, and from cecum and colon, with a high bacterial density. Using a specific, sensitive gas chromatography-tandem mass spectrometry method, we detected high levels of glucuronidated testosterone (T) and dihydrotestosterone (DHT) in small intestinal content of mice of both sexes, whereas in the distal intestine we observed remarkably high levels of free DHT, exceeding serum levels by >20-fold. Similarly, in young adult men high levels of unconjugated DHT, >70-fold higher than in serum, were detected in feces. In contrast to mice with a normal GM composition, germ-free mice had high levels of glucuronidated T and DHT, but very low free DHT levels, in the distal intestine. These findings demonstrate that the GM is involved in intestinal metabolism and deglucuronidation of DHT and T, resulting in extremely high free levels of the most potent androgen, DHT, in the colonic content of young and healthy mice and men.

Major glucuronide metabolites of testosterone are primarily transported by MRP2 and MRP3 in human liver, intestine and kidney

Testosterone glucuronide (TG), androsterone glucuronide (AG), etiocholanolone glucuronide (EtioG) and dihydrotestosterone glucuronide (DHTG) are the major metabolites of testosterone (T), which are excreted in urine and bile. Glucuronides can be deconjugated to active androgen in gut lumen after biliary excretion, which in turn can affect physiological levels of androgens. The goal of this study was to quantitatively characterize the mechanisms by which TG, AG, EtioG and DHTG are eliminated from liver, intestine, and kidney utilizing relative expression factor (REF) approach. Using vesicular transport assay with recombinant human MRP2, MRP3, MRP4, MDR1 and BCRP, we first identified that TG, AG, EtioG, and DHTG were primarily substrates of MRP2 and MRP3, although lower levels of transport were also observed with MDR1 and BCRP vesicles. The transport kinetic analyses revealed higher intrinsic clearances of TG by MRP2 and MRP3 as compared to that of DHTG, AG, and EtioG. MRP3 exhibited higher affinity for the transport of the studied glucuronides than MRP2. We next quantified the protein abundances of these efflux transporters in vesicles and compared the same with pooled total membrane fractions isolated from human tissues by quantitative LC-MS/MS proteomics. The fractional contribution of individual transporters (f_t) was estimated by proteomics-based physiological scaling factors, i.e., transporter abundance in whole tissue versus vesicles, and corrected for inside-out vesicles (determined by 5'-nucleotidase assay). The glucuronides of inactive androgens, AG and EtioG were preferentially transported by MRP3, whereas the glucuronides of active androgens, TG and DHTG were mainly transported by MRP2 in liver. Efflux by bile canalicular transport may indicate the potential role of enterohepatic recirculation in regulating the circulating active androgens after deconjugation in the gut. In intestine, MRP3 possibly contributes most to the efflux of these glucuronides. In kidney, all studied glucuronides seemed to be preferentially effluxed by MRP2 and MDR1 (for EtioG). These REF based analysis need to be confirmed with in vivo findings. Overall, characterization of the efflux mechanisms of T glucuronide metabolites is important for predicting the androgen disposition and interindividual variability, including drug-androgen interaction in humans. The mechanistic data can be extrapolated to other androgen relevant organs (e.g. prostate, testis and placenta) by integrating these data with quantitative tissue proteomics data.

Quantitative characterization of UDP-glucuronosyltransferase 2B17 in human liver and intestine and its role in testosterone first-pass metabolism

Protein abundance and activity of UGT2B17, a highly variable drug- and androgen-metabolizing enzyme, were quantified in microsomes, S9 fractions, and primary cells isolated from human liver and intestine by validated LC-MS/MS methods. UGT2B17 protein abundance showed >160-fold variation (mean ± SD, 1.7 ± 2.7 pmol/mg microsomal protein) in adult human liver microsomes (n = 26) and significant correlation (r2 = 0.77, p < 0.001) with testosterone glucuronide (TG) formation. Primary role of UGT2B17 in TG formation compared to UGT2B15 was confirmed by performing activity assays in UGT2B17 gene deletion samples and with a selective UGT2B17 inhibitor, imatinib. Human intestinal microsomes isolated from small intestine (n = 6) showed on average significantly higher protein abundance (7.4 ± 6.6 pmol/mg microsomal protein, p = 0.016) compared to liver microsomes, with an increasing trend towards distal segments of the gastrointestinal (GI) tract. Commercially available pooled microsomes and S9 fractions confirmed greater abundance and activity of UGT2B17 in intestinal fractions compared to liver fractions. To further investigate the quantitative role of UGT2B17 in testosterone metabolism in whole cell system, a targeted metabolomics study was performed in hepatocytes (n = 5) and enterocytes (n = 16). TG was the second most abundant metabolite after androstenedione in both cell systems. Reasonable correlation between UGT2B17 abundance and activity were observed in enterocytes (r2 = 0.69, p = 0.003), but not in hepatocytes. These observational and mechanistic data will be useful in developing physiologically-based pharmacokinetic (PBPK) models for predicting highly-variable first-pass metabolism of testosterone and other UGT2B17 substrates.