Total Adipose Retinol Concentrations Are Correlated with Total Liver Retinol Concentrations in Male Mongolian Gerbils, but Only Partially Explained by Chylomicron Deposition Assessed with Total α-Retinol

BACKGROUND: Liver vitamin A (VA) concentration is the gold standard for VA status, but is not routinely accessible. Adipose tissue VA concentrations, as retinol and retinyl esters, may be correlated to liver VA. α-VA (as α-retinol) is a cleavage product of α-carotene that traces postprandial VA distribution to tissues but cannot recirculate from hepatic stores, providing insight into tissue VA sources. OBJECTIVE: We performed a secondary analysis of VA and α-VA in Mongolian gerbil liver and adipose to determine the suitability of adipose tissue VA as a biomarker of VA status. METHODS: Gerbils (n = 186) consumed feeds containing 0–15.9 μg (0–55.6 nmol) retinol activity equivalents/g as preformed VA and/or provitamin A carotenoids for 36–62 d in 3 studies. Body fat percentage was determined in the final study by MRI. Serum and liver retinol, α-retinol, and retinyl esters were extracted and analyzed by HPLC or ultra-performance LC (UPLC). Epididymal and retroperitoneal adipose tissue retinol and α-retinol were determined by UPLC after homogenization, saponification, and extraction. Linear regression models with appropriate data transformations identified determinants of adipose VA concentrations. RESULTS: Liver VA did not predict serum retinol concentrations. After logarithmic transformation of adipose and liver values, liver VA positively predicted both adipose depots’ VA concentrations (P < 0.001, R(2) > 0.7). Adding serum retinol or body fat percentage did not significantly increase the adjusted R(2). In liver, α-VA concentration explained much of the variation of VA (P < 0.001, R(2) > 0.7), but far less in epididymal and retroperitoneal adipose (P = 0.004 and 0.012, respectively, R(2) < 0.4). CONCLUSIONS: Adipose VA is correlated with liver VA and is a potential biomarker of VA status. It is not fully explained by chylomicron deposition and is negatively affected by serum retinol. Adipose biopsy validation is needed for human applications.