Increased plasma levels of the lipoperoxyl radical-derived vitamin E metabolite α-tocopheryl quinone are an early indicator of lipotoxicity in fatty liver subjects

• Published in: Free radical biology & medicine 2019-02, Vol.131, p.115-125
• Main Authors: Torquato, Pierangelo, Bartolini, Desirée, Giusepponi, Danilo, Piroddi, Marta, Sebastiani, Bartolomeo, Saluti, Giorgio, Galarini, Roberta, Galli, Francesco
• Format: Article
• Language: English
• Subjects: 4-HNE; Adult; Alanine Transaminase - blood; Aldehydes - blood; alpha-Tocopherol - administration & dosage; alpha-Tocopherol - blood; Bilirubin - blood; Cholesterol, LDL - blood; Cross-Sectional Studies; Eicosanoids; Fatty Acids, Unsaturated - blood; Fatty liver; Female; Free Radical Scavengers - administration & dosage; Free Radical Scavengers - blood; Gas Chromatography-Mass Spectrometry; Hepatocytes - metabolism; Hepatocytes - pathology; Humans; Lipid Peroxidation; Liver - metabolism; Liver - pathology; Male; Middle Aged; NAFLD; NASH; Non-alcoholic Fatty Liver Disease - blood; Non-alcoholic Fatty Liver Disease - diagnosis; Non-alcoholic Fatty Liver Disease - pathology; Pilot Projects; Polyunsaturated fatty acids; Triglycerides - blood; Vitamin E; Vitamin E - analogs & derivatives; Vitamin E - blood; α-tocopherol; α-tocopheryl quinone
• ISSN: 0891-5849; 1873-4596
• DOI: 10.1016/j.freeradbiomed.2018.11.036

Lipid peroxidation is one of the earliest pathogenic events of non-alcoholic fatty liver disease (NAFLD). In this context, an increased oxidation of the lipoperoxyl radical scavenger α-tocopherol (α-TOH) should occur already in the subclinical phases of the disease to compensate for the increase oxidation of the lipid excess of liver and possibly of other tissues. However, this assumption remains unsupported by direct analytical evidence. In this study, GC-MS/MS and LC-MS/MS procedures have been developed and applied for the first time to measure the vitamin E oxidation metabolite α-tocopheryl quinone (α-TQ) in plasma of fatty liver (FL) subjects that were compared in a pilot cross-sectional study with healthy controls. The protein adducts of 4-hydroxynonenal (4-HNE) and the free form of polyunsaturated free fatty acids (PUFA) were measured as surrogate indicators of lipid peroxidation. α-TQ formation was also investigated in human liver cells after supplementation with α-TOH and/or fatty acids (to induce steatosis). Compared with controls, FL subjects showed increased (absolute and α-TOH-corrected) levels of plasma α-TQ and 4-HNE, and decreased concentrations of PUFA. α-TQ levels positively correlated with indices of liver damage and metabolic dysfunction, such as alanine aminotransferase, bilirubin and triglycerides, and negatively correlated with HDL cholesterol. Fatty acid supplementation in human hepatocytes stimulated the generation of cellular oxidants and α-TOH uptake leading to increased α-TQ formation and secretion in the extracellular medium - both were markedly stimulated by α-TOH supplementation. In conclusion, plasma α-TQ represents an early biomarker of the lipoperoxyl radical-induced oxidation of vitamin E and lipotoxicity of the fatty liver. [Display omitted] •α-TQ is a major lipoperoxyl radical-derived oxidation metabolite of α-TOH.•Steatosis promotes vitamin E accumulation and oxidation in liver cells.•Plasma concentrations of α-TQ are increased in fatty liver subjects.•Plasma α-TQ accumulation is associated with increased indices of lipid peroxidation.•α-TQ levels correlate with indices of liver damage and metabolic dysfunction.