PNPLA3 I148M variant influences circulating retinol in adults with nonalcoholic fatty liver disease or obesity

Background: Retinol is a lipid-soluble essential nutrient that is stored as retinyl esters in lipid droplets of hepatic stellate cells. Patatin-like phospholipase domain-containing 3 (PNPLA3), through its retinyl-palmitate lipase activity, releases retinol from lipid droplets in hepatic stellate cells in vitro and ex vivo. We have shown that the genetic variant I148M (rs738409) reduces the PNPLA3 retinyl-palmitate lipase activity. Objective: The aim of the present genetic association study was to test whether overweight/obese carriers of the PNPLA3 148M mutant allele had lower circulating concentrations of retinol than individuals who are homozygous for the 148I allele. Methods: PNPLA3 I148M (rs738409) was genotyped by Taqman assay in 76 overweight/obese individuals [BMI (kg/m²) ≥25; mean ± SD age: 59.7 ± 11.4 y; male gender: 70%] with a histologic diagnosis of nonalcoholic fatty liver disease (NAFLD; namely the Milan NAFLD cohort) and in 413 obese men (BMI ≥30; mean ± SD age: 57.1 ± 4.9 y) from the a-Tocopherol, β-Carotene Cancer Prevention (ATBC) Study. Serum concentrations of retinol and a-tocopherol were measured by HPLC in both cohorts. β-Carotene concentrations in the ATBC study were measured by using HPLC. Results: The PNPLA3 148M mutant allele was associated with lower fasting circulating concentrations of retinol (β = -0.289, P = 0.03) in adults with NAFLD (Milan NAFLD cohort). The PNPLA3 148M mutant allele was also associated with lower fasting circulating concentrations of retinol in adults with a BMI ≥30 (ATBC study; β = -0.043, P = 0.04). Conclusion: We showed for the first time, to our knowledge, that carriers of the PNPLA3 148M allele with either fatty liver plus obesity or obesity alone have lower fasting circulating retinol concentrations.