Niacin and triglycerides

Vitamin B3, also known as niacin, is used alone and with other medications to decrease blood triglyceride levels and prevent the progression of atherosclerosis. However, the mechanisms by which niacin affects these lipid levels is not yet fully understood. A study in the December issue of the Journal of Lipid Research presents important findings about the activity of a common niacin receptor.

The intramembranous G-protein-coupled receptor GPR109A/HCA2 readily binds niacin and mediates many of its effects. The receptor is expressed predominantly in adipose tissue and immune cells such as macrophages, specialized white blood cells that engulf and digest foreign particles. Previous research has shown niacin treatment does not affect lipid levels in mice lacking this receptor. It also has shown that triglyceride accumulation occurs when the normal innate immune response activates macrophages.

In the JLR study, a research team led by Kenneth R. Feingold at the University of California, San Francisco, treated mouse cells with lipopolysaccharide, a component of Gram-negative bacteria’s outer membranes. The treatment activated macrophages, which increased expression of the receptor.

The team then targeted the receptor with small interfering RNA, or siRNAs. That decreased the receptor’s expression. Also, the team observed a small but statistically significant increase in triglyceride accumulation in macrophages in cells with targeted siRNA.

Feingold, a JLR associate editor, explains: “If one inhibits the increase in GPR109A/HCA2 that is induced by inflammation, the ability of the macrophages to accumulate lipid is increased. This indicates that the increase in GPR109A/HCA2 is playing a role in preventing or decreasing the increase in lipids in macrophages that would typically occur with immune activation.”

The finding that increased expression and activation of this receptor with niacin or other ligands can inhibit feedback is novel and may inform researchers studying diabetes and atherosclerosis, common diseases with roots in inflammation.

Mary L. ChangMary L. Chang (mchang@asbmb.org) is publications manager for ASBMB.

ASBMB journal articles optimized for the Web

The American Society for Biochemistry and Molecular Biology is piloting a new article-reading tool on its three journal websites. Called Lens, the tool allows a website visitor to view figures, legends, references and other parts ofan article alongside the text and with backward and forward linking.

ASBMB is one of six publishers on the Highwire platform that are piloting Lens, an open-source tool introduced originally by the journal eLife. Visit the online versions of the Journal of Biological Chemistry, Journalof Lipid Research and Molecular & Cellular Proteomics to test it out.