Niacin increases diet-induced hepatic steatosis in B6129 mice

Nonalcoholic fatty liver disease (NAFLD) is a very common disorder affecting between 20 and 30% of adults in the United States. However, there is no effective pharmacotherapy for treating NAFLD. Niacin, a water-soluble vitamin (B3), at pharmacological doses, decreases hepatic triglyceride (TG) content in NAFLD through inhibition of diacylglycerol acyltransferase 2, a key enzyme that catalyzes the final step in TG synthesis. Alternatively, some studies indicate that niacin induces fatty liver in high-fat diet (HFD)-fed rats. Therefore, in this study we investigated whether niacin is beneficial in treating NAFLD in two strains of mice, C57BL/6J (B6) and B6129SF2/J (B6129) mice, with 20 weeks of HFD feeding. Niacin treatment was started from week 5 until the end of the study. Niacin treatment increased normalized liver weight, hepatic TG content and NAFLD score in HFD-fed B6129 mice but had no impact on B6 mice. Metabolomics analysis revealed that in B6129 mice, 4-hydroxyphenylpyruvic acid (4-HPP), which is associated with fatty acid oxidation, did not change with HFD feeding but significantly decreased with niacin treatment. Lipidomics analysis discovered that the abundance of phosphocholine (PC), which is critical for very low-density lipoprotein (VLDL)–TG production and secretion, was decreased in HFD-fed B6129 with niacin treatment. In conclusion, niacin had no impact on diet-induced NAFLD development in B6 mice but potentiated hepatic steatosis in HFD-fed B6129 mice due to impaired fatty acid oxidation and decreased VLDL-TG production and secretion.