In a recent study published in Nature Medicine, researchers utilized an untargeted metabolomics technique to look for new compounds and pathways that may contribute to residual cardiovascular disease (CVD) risk.
Study: A terminal metabolite of niacin promotes vascular inflammation and contributes to cardiovascular disease risk. Image Credit: Dragana Gordic/Shutterstock.com
Background
CVD is a worldwide health problem, with only a tiny proportion of the risk linked to known risk factors. Despite breakthroughs in therapeutics, the risk of CVD remains high, indicating the presence of other unidentified variables.
Niacin, an essential vitamin in dietary staples, is critical in CVD. Treatment groups had mean LDL levels <50 mg/dl but significant cardiovascular event rates. Individuals with high inflammatory markers have an increased chance of developing CVD. However, dietary niacin intake has increased due to the increasing consumption of processed and fast food, raising concerns regarding the efficiency of therapeutic niacin in lowering CVD risk.
About the study
In the present study, researchers used untargeted mass spectrometry technology to identify circulating small molecules that predict incident CVD event risks without established risk factors.
The researchers investigated clinical, genetic, and mechanistic links between the terminal breakdown products of excess niacin and the incidence of major adverse cardiac events (MACE). They conducted untargeted metabolomics analyses on fasting plasma from stable cardiac patients in a prospective discovery cohort and subjects with elective diagnostic cardiac examinations.
The researchers postulated that the putative MACE-related analyte with m/z values of 153 Da may be a combination of two co-eluted structural isomers: the N1-methyl-2-pyridone-5-carboxamide (or 2PY) metabolite and the N1-methyl-4-pyridone-3-carboxamide (or 4PY) metabolite. They chemically synthesized both metabolite standards and conducted several chemical characterization tests.
The team used stable-isotope-dilution liquid chromatography with tandem mass spectrometry (LC-MS/MS) to examine the relationship between structural isomer levels in circulation and new-onset major-type adverse cardiovascular event risk in two validation populations [United States (US) cohort of 2,331 individuals and the European cohort of 832 individuals]. They performed a sensitivity analysis on validation cohort data to account for confounding with known risk variables.
The researchers used a genome-wide association study (GWAS) approach and meta-analyses to investigate the genetic determinants of circulating 2PY and 4PY levels. They combined the study results from the United States validation cohort with publicly available summary statistics for 2PY and 4PY levels from various multi-ancestry datasets. They reduced Acmsd expression in vivo by injecting mice with a liver-tropic adeno-associated virus (AAV) expressing either a short hairpin RNA (shRNA) targeting Acmsd or a scrambled control shRNA to directly test the notion that ACMSD influences 2PY and 4PY levels.
The researchers also used Mendelian randomization (MR) analysis to determine if genetically higher 2PY and 4PY levels were causally associated with CVD outcomes. They conducted in vitro and in vivo functional studies to investigate whether 2PY or 4PY would induce VCAM-1 expression on endothelial cells. They used in vivo methods to investigate the immediate effects of 2PY or 4PY on arterial VCAM-1 expression and function.
Results
Niacin metabolites were associated with an increase in major adverse CVD events (MACEs). Chemical production of authentic 2PY and 4PY standards and additional chemical characterization tests demonstrated that the MACE-associated blood 'analyte' with m/z values of 153 Da was a combination of the co-eluting structural isomers 2PY and 4PY with the same elemental composition.
In the US and European validation cohorts, serological 2PY and 4PY levels showed associations with increased three-year major-type adverse cardiovascular event risk [adjusted hazard ratios (HRs) for 2PY of 1.6 and 2.0, respectively; and for the 4PY metabolite: 1.9 and 2.0, respectively). Elevated 4PY levels were still strongly related to the incidence of major-type adverse cardiovascular event risk in both persons with relatively maintained and compromised renal function.
A phenome-level association study of the rs10496731 genetic variant, strongly correlated with both metabolite levels, found a link to soluble-type vascular adhesion molecule 1 (sVCAM-1). A meta-analysis found a link between rs10496731 and sVCAM-1 in 106,000 individuals, including 53,075 women. The validation group (974 individuals, 333 females) showed a significant correlation between sVCAM-1 expression and the niacin metabolites.
4PY metabolite (but not 2PY) administration in physiological amounts increased VCAM-1 expression and leukocyte adhesion to the vascular endothelial cells in murine animals. Both niacin metabolites were related to residual cardiovascular disease risk. The team also proposed an inflammation-dependent mechanism for the clinical connection between the 4PY metabolite and major adverse CVD events.
The study findings showed that two terminal metabolites of niacin and NAD metabolism, 2PY and 4PY, are associated with CVD regardless of established risk factors. Both metabolites genetically link to vascular inflammation, with a gene variation strongly associated with circulating 2PY and 4PY levels and sVCAM-1 levels. Excess niacin, particularly 4PY, is linked to increased MACE risks and may contribute to residual cardiovascular disease risk via inflammatory pathways. Further research is required to improve understanding of these relationships.
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