Fatty acids in non-alcoholic steatohepatitis: Focus on pentadecanoic acid

<div><p>Non-alcoholic fatty liver disease (NAFLD) is the most common form of liver disease and ranges from isolated steatosis to NASH. To determine whether circulating fatty acids could serve as diagnostic markers of NAFLD severity and whether specific fatty acids could contribute to the pathogenesis of NASH, we analyzed two independent NAFLD patient cohorts and used the methionine- and choline-deficient diet (MCD) NASH mouse model. We identified six fatty acids that could serve as non-invasive markers of NASH in patients with NAFLD. Serum levels of 15:0, 17:0 and 16:1n7t negatively correlated with NAFLD activity scores and hepatocyte ballooning scores, while 18:1n7c serum levels strongly correlated with fibrosis stage and liver inflammation. Serum levels of 15:0 and 17:0 also negatively correlated with fasting glucose and AST, while 16:1n7c and 18:1n7c levels positively correlated with AST and ferritin, respectively. Inclusion of demographic and clinical parameters improved the performance of the fatty acid panels in detecting NASH in NAFLD patients. The panel [15:0, 16:1n7t, 18:1n7c, 22:5n3, age, ferritin and APRI] predicted intermediate or advanced fibrosis in NAFLD patients, with 82% sensitivity at 90% specificity [AUROC = 0.92]. 15:0 and 18:1n7c were further selected for functional studies <i>in vivo</i>. Mice treated with 15:0-supplemented MCD diet showed reduced AST levels and hepatic infiltration of ceroid-laden macrophages compared to MCD-treated mice, suggesting that 15:0 deficiency contributes to liver injury in NASH. In contrast, 18:1n7c-supplemented MCD diet didn’t affect liver pathology. In conclusion, 15:0 may serve as a promising biomarker or therapeutic target in NASH, opening avenues for the integration of diagnosis and treatment.</p></div

Fatty acids that showed significantly different levels in serum between patients with NAFLD activity scores (NAS) 1–4 (n = 68) and patients with NAS ≥5 (n = 38).

<p>(A) Saturated fatty acids (SFAs), pentadecanoic (15:0) and heptadecanoic (17:0) acid, (B) monounsaturated fatty acids (MUFAs), palmitelaidic (16:1n7t), palmitoleic (16:1n7c) and vaccenic (18:1n7c) acid. Fatty acids were measured as percentage of the phospholipid fraction. P-value was calculated using two-tailed student’s T-test.</p

Correlation of fatty acid levels with parameters of liver injury and metabolic syndrome.

<p>(A) Correlation of pentadecanoic (15:0) with fasting glucose levels and aspartate transaminase (AST), (B) correlation of heptadecanoic (17:0) with AST and alanine transaminase (ALT) levels, (C) correlation of palmitoleic acid (16:1n7c) with AST levels, (D) correlation of vaccenic acid (18:1n7c) with ferritin levels, and (E) correlation of docosapentaenoic acid (22:5n3) with albumin levels. Spearman correlation was calculated using GraphPad Prism 6 and Bonferroni correction was used to select the significant correlations.</p

Comparison of physiological parameters with 15:0 treatments <i>in vivo</i>.

<p>Comparison of physiological parameters with 15:0 treatments <i>in vivo</i>.</p

Characteristics of the patient population.

<p>Characteristics of the patient population.</p

Pentadecanoic acid (15:0), vaccenic acid (18:1n7c) and docosapentaenoic acid (22:5n3) serum levels in patients.

<p>Isolated steatosis (n = 27), NASH patients with fibrosis stage 0–1 (n = 45) and NASH patients with fibrosis stage 2–4 (n = 34). Fatty acids were measured as percentage of the phospholipid fraction. Statistical significance was done using ANOVA test and then pairwise comparison using Tukey’s test was performed.</p

Receiver operating characteristic (ROC) analysis.

<p>(A) based on NAFLD activity scores (NAS)–patients with NAS 1–4 versus patients with NAS ≥5. (B) Based on fibrosis scores—patients with fibrosis 0–1 versus patients with fibrosis 2–4.</p

Correlation of fatty acids with NASH parameters.

<p>(A) Correlation of pentadecanoic (15:0), heptadecanoic (17:0) acid and palmitelaidic (16:1n7t) with NAFLD activity scores (NAS), (B) correlation of pentadecanoic (15:0), heptadecanoic (17:0) acid and palmitelaidic (16:1n7t) with hepatocyte ballooning scores, (C) correlation of vaccenic acid (18:1n7c) with liver inflammation scores, and (D) correlation of vaccenic acid (18:1n7c) with fibrosis scores. Fatty acid levels are presented as a percentage of the phospholipid fraction. Statistical significance was done using ANOVA test and then pairwise comparison using Tukey’s test was performed. Spearman correlation was calculated using GraphPad Prism 6 and Bonferroni correction was used to select significant correlations.</p