Serum cholesterol loading capacity of macrophages is regulated by seropositivity and C-reactive protein in rheumatoid arthritis patients

Objective: Excessive cholesterol accumulation in macrophages is the pivotal step underlying atherosclerotic plaque formation. We here explore factors in the serum of patients with RA, and mechanisms through which they interact with and influence cholesterol loading capacity (CLC) of macrophages.

Methods: In a cross-sectional observational cohort of 104 patients with RA, CLC was measured as intracellular cholesterol content in human THP-1-derived macrophages after incubation with patient serum. Low-density lipoprotein (LDL) oxidation was measured in terms of oxidized phospholipids on apoB100-containing particles (oxPL-apoB100). Antibodies against oxidized LDL (anti-oxLDL), proprotein convertase subtilisin/Kexin type-9 (PCSK9) and high-sensitivity CRP were also quantified. All analyses adjusted for atherosclerotic cardiovascular disease (ASCVD) risk score, obesity, total LDL, statin use, age at diagnosis, and anti-oxLDL IgM.

Results: OxPL-apoB100, anti-oxLDL IgG and PCSK9 were positively associated with CLC (all P < 0.020). OxPL-apoB100 directly influenced CLC only in dual RF- and ACPA-positive patients [unstandardized b (95% bootstrap CI)=2.08 (0.38, 3.79)]. An indirect effect of oxPL-apoB100 on CLC through anti-oxLDL IgG increased, along with level of CRP [index of moderated mediation = 0.55 (0.05-1.17)]. CRP also moderated yet another indirect effect of oxPL-apoB100 on CLC through upregulation of PCSK9, but only among dual-seropositive patients [conditional indirect effect = 0.64 (0.13-1.30)].

Conclusion: Oxidized LDL can directly influence CLC in dual-seropositive RA patients. Two additional and independent pathways-via anti-oxLDL IgG and PCSK9-may mediate the effects of oxPL-apoB100 on CLC, depending on CRP and seropositivity status. If externally validated, these findings may have clinical implications for cardiovascular risk prevention.