Characterization of Lysosomal Hydrolases and Transporters and Their Age-Dependent Variability: Relevance to Drug Metabolism and Transport of Small Molecule and Biologic Drugs.

Lysosomes play a key role in the accumulation, catabolism, and transport of endogenous and exogenous metabolites and proteins and are involved in drug metabolism and prodrug activation. However, the protein abundance and interindividual variability of lysosomal drug-metabolizing enzymes and transporters (DMETs) remain underexplored. In this study, we performed a global proteomics analysis of the enriched human liver lysosomal fraction to characterize and annotate lysosomal proteins and compared these results with the proteomics data of hepatocyte homogenates and the liver microsomal fraction. We annotated and quantified 66 hydrolases and 41 membrane transporters in the lysosomal fractions. These included proteins involved in prodrug activation, transport, and metabolism or functioning as drug targets. After confirming the identity of lysosomal proteins, we investigated age-dependent changes in the abundance of these proteins in human hepatocytes (n = 58) across various age groups, ranging from neonatal (0-12 days) to adulthood (>18 years). We observed age-specific variations in the expression of key hydrolases (CTSA, CTSL, NAGLU, PLD3, and GALNS) and transporters (ATP6V1B2, ATP6V1C1, TMEM63A, and SLC39A14). Together, these findings highlight the lysosomal localization of proteins involved in drug disposition and their dynamic developmental changes, providing critical insights for refining physiologically based pharmacokinetic (PBPK) models to support precision dosing and improve therapeutic outcomes in pediatric populations.