Interindividual variability in hepatic hydrolytic enzymes: Effects of age, sex, and race on the abundance of drug-metabolizing hydrolases.

Hydrolases represent a diverse class of drug-metabolizing enzymes that catalyze the hydrolytic cleavage of a broad spectrum of xenobiotics including certain novel drug modalities, thereby modulating pharmacokinetics and potentially influencing pharmacodynamics. However, many hydrolases remain poorly characterized, and their developmental expression and interindividual variability are not well understood. This study aimed to systematically characterize hydrolase expression in the human liver. Human hepatocytes obtained from 8 adult and 50 pediatric donors were subjected to global proteomics analysis to quantify hydrolase abundance and assess variability across demographic factors. Two hundred and thirty-nine hydrolases were studied for the influence of age, sex, and race on their abundance. The key enzymes included arylacetamide deacetylase (AADAC), alpha/beta hydrolase domain-containing protein 10 (ABHD10), alkaline phosphatase, tissue-nonspecific isozyme (ALPL), acyl-peptide hydrolase (APEH), bleomycin hydrolase (BLMH), valacyclovir hydrolase (BPHL), cytidine deaminase (CDA), carboxylesterase 1 (CES1), CES2, carboxymethylenebutenolidase homolog (CMBL), cathepsin A (CTSA), cathepsin B (CTSB), dipeptidyl peptidase 4 (DPP4), epoxide hydrolase 1 (EPHX1), EPHX2, EPHX3, guanine deaminase (GDA), paraoxonase 1 (PON1), PON2, PON3, and deoxynucleoside triphosphate triphosphohydrolase SAMHD1 (SAMHD1). Notably, several enzymes exhibited age-dependent increases in the abundance from neonates to adults (fold), including CDA (>200), GDA (53), CES1 (14), EPHX3 (12), ALPL (10), CES2 (3.5), sialate O-acetylesterase (SIAE) (3), and CMBL (2.6). In contrast, BLMH, CTSA, DPP4, PON2, and SAMHD1 displayed approximately 2-fold to 3-fold lower abundance in adults than in neonates. PON1 was 42% higher in Black individuals compared with White individuals, whereas PON3 abundance was 32% higher in males than in females. This study provides the first systematic quantitative characterization of a broad panel of hydrolases and provides a key foundation for physiologically-based pharmacokinetic and quantitative systems pharmacology modeling of the substrates of hydrolytic enzymes. SIGNIFICANCE STATEMENT: Interindividual variability, including ontogeny, is well characterized for many drug-metabolizing enzymes but remains poorly defined for most hydrolases. The influence of age, sex, and race on 239 hepatic hydrolases was evaluated, revealing important demographic determinants. These data provide a critical foundation for physiologically-based pharmacokinetic modeling. Incorporation of proteomics-informed variability into physiologically-based pharmacokinetic models has the potential to improve the prediction of drug pharmacokinetics, particularly in pediatric populations.