Association Between Alternative Complement Pathway and Carotid Plaque and the Underlying Gut Microbial and...

The alternative pathway (AP) plays a crucial role in triggering complement activation and promoting chronic inflammation. This study aims to investigate the longitudinal association between AP and atherosclerosis, and explore the potential role of gut microbiota and inflammatory factors in their association.

This study was based on a 9-year prospective cohort of 3382 participants from Guangzhou, China (mean age±SD, 57.75±5.85 years; 68.8% female), with data on serum APACPs (AP-associated complement proteins) and carotid plaque (measured by ultrasound) repeatedly measured up to 3×. Baseline inflammatory markers were evaluated in 923 participants, and gut shotgun metagenome data were obtained from 1567 participants. Mendelian randomization analysis was performed using genome-wide significant genetic variants as instrumental variables to suggest potential causal associations.

Both longitudinal and prospective analyses consistently demonstrated positive associations between carotid plaque and 3 complement components: C3 (complement C3; odds ratios [95% Cl] for the highest versus lowest quartiles, 1.36 [1.07-1.74] in longitudinal analysis and 1.29 [1.06-1.56] in prospective analysis), CFB (complement factor B; 1.36 [1.07-1.72] in longitudinal analysis and 1.39 [1.15-1.69] in prospective analysis), and CFH (complement factor H; 1.39 [1.10-1.76] in longitudinal analysis and 1.31 [1.07-1.61] in prospective analysis). Mendelian randomization analysis suggested a potential causal association between CFB and carotid plaque. Inflammatory factors (CRP [C-reactive protein] and IL-6 [interleukin-6]) and microbial species (Ruminococcus bromii, Roseburia hominis, Rothia mucilaginosa, Collinsella stercoris, Olsenella scatoligenes, and Bacteroides massiliensis) were significantly associated with both APACPs and carotid plaque (P<0.05). For example, butyrate-producing bacterium R bromii was inversely associated with CFB and carotid plaque (odds ratios [95% CI], 0.83 [0.79-0.88]) and may mediate the CFB-carotid plaque association (proportion mediated, 13.5%; P=0.005). Microbial risk score (weighted sum of selected microbial species; proportion mediated, 42.6%; P<0.001) and total immune factors (the sum of all inflammatory factors; proportion mediated, 19.0%; P=0.002) mediated the association between Total-APACPs (sum of standardized carotid plaque-related APACPs [C3, CFB, and CFH]) and carotid plaque.

Our study showed a negative association between the AP and carotid plaque in a longitudinal cohort. Gut microbiota and inflammatory biomarkers may provide mechanistic insights into the association between the AP and atherosclerosis. Our findings pave the way for the development of new therapeutic targets for atherosclerosis.