Background: The metabolic syndrome (MS) is associated with an increased production of nitrogen metabolites and elevated oxidative stress, which favors progression of nonalcoholic fatty liver disease (NAFLD). Subjects with the phenotype known as metabolically unhealthy obese (MUO) meet most of the MS cardiometabolic risk criteria and show a higher risk of advanced NAFLD severity, compared with the so-widely known metabolically healthy obese (MHO). Obese individuals with MS are more susceptible to abnormal lipid accumulation in different tissues, whereas oxidative stress and nitrogen metabolites are increased in MS and/or obesity. This study aimed to explore whether plasma- or liver tissue-determined biomarkers of nitrogen metabolism and oxidative stress relate to NAFLD severity and/or metabolic phenotype. Methods: This cross-sectional study included candidates for bariatric surgery with biopsy-proven NAFLD diagnosis and staging. For comparison, the study population was divided according to NAFLD damage (steatohepatitis F0-F1 vs. steatohepatitis F2-F4) and metabolic phenotype (MHO vs MUO, based on the MS criteria). Hepatic and plasma concentrations of nitrogen metabolites and oxidative stress biomarkers were determined by enzymatic kinetics assays, enzyme-linked immunosorbent assay, and Greiss reaction. Results: The study population (N = 45) was constituted by patients with obesity and higher prevalence of dyslipidemia, diabetes mellitus, and hypertension. According to plasma biomarkers, MUO phenotype was related to higher cardiometabolic risk; meanwhile, advanced NAFLD damage was related to higher glycated hemoglobin (HbA1c) and triglycerides. Elevated hepatic concentrations of ammonium, nitrites, arginine, and citrulline were found in MUO phenotype, but only higher plasma concentration of malondialdehyde was found as specifically related to advanced NAFLD damage. Conclusions: Circulating biomarkers of redox state were selectively related to advanced NAFLD damage, suggesting prognostic and therapeutic targets. Hepatic concentrations of nitrogen metabolism biomarkers may be more related to cardiometabolic risk.
Keywords: NAFLD progression; metabolic syndrome; nitrogen metabolism; obesity; pro-oxidative biomarkers.