Characterization of Vitamin A Metabolome in Healthy and Diseased Human Liver Using LC‐MS/MS Analysis

Abstract

Retinoids are important endogenous compounds responsible for regulating multiple biological events. Currently, the qualitative and quantitative information about retinoid concentrations in human tissues is limited. This prevents a deeper understanding how retinoid homeostasis is regulated in vivo. In this study the hepatic vitamin A metabolome in 50 normal human liver samples was quantified using novel LC‐MS/MS methods and isotope‐labeled internal standards. Measured retinoids included retinyl palmitate (RP; median, 276 nmols/g; range, 35.1–4,282 nmols/g), retinol (ROL; median, 4.9 nmols/g; range, 0.8–39 nomls/g), all‐trans retinoic acid (atRA; median, 39.8 pmols/g; range, 14.9–670.5 pmols/g), 13‐cis‐RA (median, 8.3 pmols/g; range, 1.4–43.5 pmols/g), 4‐oxo‐atRA (median, 18.3 pmols/g; range, 1.8–376.3 pmols/g) and 4‐oxo‐13‐cis‐RA (median, 13.0 pmols/g; range, 5.3–64.0 pmols/g). Two 4‐oxo‐RA isomers were, for the first time, detected in human tissues and their concentrations were comparable to RA isomers. As 4‐oxo‐atRA also activates retinoic acid receptors (RARs), its presence in human liver suggests that 4‐oxo‐atRA is essential in the regulation of retinoid homeostasis. Additionally, atRA concentration was positively correlated with that of other retinoids in normal livers, but not with the relative mRNA expression of LRAT, ALDH1A1, CYP26A1, RARα and RARβ, all of which are retinoid‐related genes. Finally, the vitamin A metabolome was also measured in livers from subjects with non‐alcoholic fatty liver disease (NAFLD) (steatosis, n=9; nonalcoholic steatohepatitis (NASH), n=13) to explore whether the development of NAFLD is associated with disturbed vitamin A homeostasis. The data showed a decrease of hepatic concentrations of RP, atRA, 13‐cis‐RA, 4‐oxo‐atRA and 4‐oxo‐13‐cis‐RA in NAFLD liver samples when compared to normal liver samples, while the hepatic ROL level remained unchanged, indicating that hepatic vitamin A homeostasis is disrupted in NAFLD.Support or Funding InformationThis work was supported in part by grants from the National Institutes of Health R01 GM111772 and T32 DK 007247.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.