Human IgM Antibodies to Malondialdehyde Conjugated With Albumin Are Negatively Associated With Cardiovascular Disease Among 60-Year-Olds

Abstract

Background: Malondialdehyde (MDA) is generated during lipid peroxidation as in oxidized low-density lipoprotein, but antibodies against oxidized low-density lipoprotein show variable results in clinical studies. We therefore studied the risk of cardiovascular disease (CVD) associated with IgM antibodies against MDA conjugated with human albumin (anti-MDA).

Methods and results: In a 5- to 7-year follow-up of 60-year-old men and women from Stockholm County previously screened for cardiovascular risk factors (2039 men, 2193 women), 209 incident CVD cases (defined as new events of coronary heart disease, fatal and nonfatal myocardial infarction, ischemic stroke, and hospitalization for angina pectoris) and 620 age- and sex-matched controls were tested for IgM anti-MDA by ELISA. Antibody peptide/protein characterization was done using a proteomics de novo sequencing approach. After adjustment for smoking, body-mass index, type 2 diabetes mellitus, hyperlipidemia, and hypertension, an increased CVD risk was observed in the low IgM anti-MDA percentiles (below 10th and 25th) (odds ratio and 95% CI: 2.0; 1.19-3.36 and 1.67; 1.16-2.41, respectively). Anti-MDA above the 66th percentile was associated with a decreased CVD risk (odds ratio 0.68; CI: 0.48-0.98). After stratification by sex, associations were only present among men. IgM anti-MDA levels were lower among cases (median [interquartile range]: 141.0 [112.7-164.3] versus 147.4 [123.5-169.6]; P=0.0177), even more so among men (130.6 [107.7-155.3] versus 143.0 [120.1-165.2]; P=0.001). The IgM anti-MDA variable region profiles are distinctly different and also more homologous in their content (correlates strongly with fewer peptides) than control antibodies (not binding MDA).

Conclusions: IgM anti-MDA is a protection marker for CVD. This finding could have diagnostic and therapeutic implications.

Keywords: antibody; cardiovascular disease; cardiovascular disease risk factors; immune system; malondialdehyde; oxidation; proteomics.

Figure 1

Numbers of peptides quantified in the anti‐MDA and in the flow through (FT) control samples. MDA indicates malondialdehyde.

Figure 2

Differences in the variable chain region between polyclonal anti‐MDA IgM and non‐anti‐MDA IgM (flow through, FT). A, Distribution in heavy variable (HV), kappa variable (KV), and lambda variable (LV) chains in the anti‐MDA and non‐anti‐MDA FT samples. B, Peptides from the HV and KV regions that were elevated in the anti‐MDA IgM. Numbers indicate significant P‐values. CDR indicates complementary determining region; FR, framework region; ns, not significant. MDA indicates malondialdehyde.

Figure 3

Multivariate analysis of the anti‐MDA and flow through (FT) samples using heavy variable, lambda variable, and kappa variable chain peptides that were identified in both FT and anti‐MDA samples or identified in anti‐MDA only. A, Principal component analysis (PCA), scores plot. The anti‐MDA and FT samples are distinctly separated along component 1 (t[1], R ²=0.59, Q²=0.37). B, Orthogonal Projections to Latent Structures–Discriminant Analysis (OPLS‐DA) loading plot. The plot shows which peptides are most distinctly different between the 2 IgM profile types (ie, anti‐MDA and FT). Only peptides correlating with 95% CI with respective sample type are shown. From the plot it is evident that the majority of peptides correlate with the FT, but a small number of specific peptides are correlating with the anti‐MDA IgM. It is noteworthy that no lambda chain sequences correlated with anti‐MDA. Heavy variable (HV), kappa variable (KV), and lambda variable (LV) sequences are shown. MDA indicates malondialdehyde.