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

Abstract

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.UDP-glucuronosyltransferase 2B17 (UGT2B17) is a highly variable androgen-metabolizing and drug-metabolizing enzyme, showing over a 3,000-fold variability in hepatic protein expression. 1 It is one of the most commonly deleted genes in the human genome with the frequency of the gene deletion event ranging from 16% in Caucasians subjects up to 96% in Asian subjects. 2 However, even among expressers carrying two copies of the UGT2B17 gene, > 160-fold variability in expression has been reported, 3 suggesting that copy number variation (CNV) is not the only determinant of the variability. Indeed, factors such as age, sex, and single nucleotide polymorphisms also affect UGT2B17 expression and activity. Still, only 26% of the variability can be explained by all these factors combined. 4 UGT2B17 also exhibits a unique developmental trajectory. UGT2B17 is minimally expressed in children under 9 years of age (0.11 ± 0.02 pmol/mg protein) but increases ~ 10-fold throughout adolescence to adulthood (1.31 ± 0.15 pmol/mg protein) in its hepatic protein expression. The increase is much more prominent in males compared to females, and adult males have, on average, 2.6-fold higher levels compared to females (1.75 ± 0.20 vs. 0.65 ± 0.18 pmol/mg protein, respectively). 4 Major endogenous substrates for UGT2B17 are C19 androgen steroids, such as

Ontogeny of Hepatic Transporters and Drug-Metabolizing Enzymes in Humans and in Nonclinical Species

“…Examples include the use of the urinary 6-b-hydroxycortisol/cortisol ratio for CYP3A activity, thiamine for OCT1 activity, and dehydroepiandrosterone sulfate (DHEAS) for OATP1B1/3 activity (Muller et al, 2018). Recently, testosterone glucuronide normalized by andosterone glucuronide was shown to be promising as a urinary biomarker to phenotype UGT2B17 activity in children 7-18 years (Zhang et al, 2020). Using endogenous substrates to phenotype DTs and DMEs does not require administration of an exogenous probe, thereby overcoming one of the challenges in pediatric research.…”

Metabolomics reveals biomarkers in human urine and plasma to predict cytochrome P450 2D6 (CYP2D6) activity

“…Biomarkers help monitor the evolution of a disease and the corresponding response to drugs, as well as better predict the clinical outcomes (Kohler et al, 2017 ). For instance, testosterone glucuronide, when normalized by glucuronide, can be used as a urinary biomarker of UDP‐glucuronosyltransferase 2B17 (UGT2B17), an androgen‐ and drug‐metabolizing enzyme, as recently shown through targeted metabolomic analysis (Zhang et al, 2020 ). Five ω‐ and (ω‐1)‐hydroxylated medium‐chain acylcarnitines have also been identified as novel CYP3A biomarkers using an untargeted metabolomic approach (Kim et al, 2018 ).…”

Current knowledge, challenges and innovations in developmental pharmacology: A combined conect4children Expert Group and European Society for Developmental, Perinatal and Paediatric Pharmacology White Paper

“…In line with the developmental pattern of UGT2B17 expression, this marker was significantly associated with sex, age and copy number variation. 188 …”