Age-dependent Protein Abundance of Cytosolic Alcohol and Aldehyde Dehydrogenases in Human Liver

Abstract

Hepatic cytosolic alcohol and aldehyde dehydrogenases (ADHs and ALDHs) catalyze the biotransformation of xenobiotics (e.g., cyclophosphamide and ethanol) and vitamin A. Because age-dependent hepatic abundance of these proteins is unknown, we quantified protein expression of ADHs and ALDH1A1 in a large cohort of pediatric and adult human livers by liquid chromatography coupled with tandem mass spectrometry proteomics. Purified proteins were used as calibrators. Two to three surrogate peptides per protein were quantified in trypsin digests of liver cytosolic samples and calibrator proteins under optimal conditions of reproducibility. Neonatal levels of ADH1A, ADH1B, ADH1C, and ALDH1A1 were 3-, 8-, 146-, and 3-fold lower than the adult levels, respectively. For all proteins, the abundance steeply increased during the first year of life, which mostly reached adult levels during early childhood (age between 1 and 6 years). Only for ADH1A protein abundance in adults (age > 18 year) was ∼40% lower relative to the early childhood group. Abundances of ADHs and ALDH1A1 were not associated with sex in samples with age > 1 year compared with males. Known single nucleotide polymorphisms had no effect on the protein levels of these proteins. Quantification of ADHs and ALDH1A1 protein levels could be useful in predicting disposition and response of substrates of these enzymes in younger children.

Fig. 1.

Age-dependent abundance of ADH1A, ADH1B, ADH1C, and ALDH1A1 in human liver cytosol samples. Age classification: neonatal (0–27 days), infancy (28–364 days), toddler/early childhood (1 year to <6 years), middle childhood (6 years to < 12 years), adolescence (12– 18 years) and adulthood (>18 years). The number of subjects in each age category are indicated in parentheses in the x-axis of categorical data. Dot plots are displayed with mean protein abundance as the horizontal line together with S.D. Representative pie chart is showing change in protein abundance of ADHs and ALDH1A1 from neonatal to adulthood. For all proteins, the abundance steeply increases during the first 2 years of life, reaching adult levels during early childhood. ADH1A protein abundance in adults (>18 years) is ∼39% lower compared with children and adolescents. *, ** and *** represents P values < 0.05, < 0.01, and < 0.001, respectively.

Fig. 2.

Continuous age-dependent abundance of ADH1A, ADH1B, ADH1C, and ALDH1A1 in human liver cytosol samples. Table presents fitted values of abundance at birth (E0), average adult abundance (Adult_max), and 50% protein abundance is observed (Age₅₀). Additional parameters are reported in Supplemental Table 4S. Only protein expression data until age 18 were used to calculate above parameters. ND, not defined; SE, standard error; CI, confidence intervals.