The purpose of this study was to explore whether nontraditional risk factors, such as apolipoprotein C-III (Apo C-III) and its corresponding Apo B lipoprotein (Lp) subclasses, contribute to the risk of cardiovascular disease in rheumatoid arthritis (RA) patients.
Apolipoprotein and lipoproteins were measured in 152 RA patients by immunoturbidimetric procedures, electroimmunoassay, and immunoprecipitation. Patients had a coronary artery calcium (CAC) score assessed at baseline and at year 3. Differences in the CAC scores between baseline and year 3 were calculated and dichotomized at 0, where patients with a difference score >0 were denoted as progressors and the rest were denoted as nonprogressors. Differences between means were tested with a 2-sided independent Student's t-test with Satterthwaite's adjustment. Proportion differences were tested with a chi-square test. Multiple logistic regression was performed to assess the relationship between apolipoprotein and lipoprotein levels and the dichotomized CAC score.
Progressors accounted for almost 60% of the cohort. Progressors had significantly higher levels of triglycerides, very low-density lipoprotein (VLDL) cholesterol, total cholesterol/high-density lipoprotein (HDL), triglycerides/HDL, Apo B, LpA-II:B:C:D:E, LpB:C, Apo B/Apo A-I, Apo C-III, and Apo C-III-heparin precipitate than the nonprogressors. After adjusting for age, sex, statin use (yes/no), and hypertension (yes/no), significant risk factors of progressors were total cholesterol, triglycerides, VLDL cholesterol, LDL cholesterol, Apo B, LpB:C, Apo C-III, and Apo B/Apo A-I.
Apo C-III-containing Apo B lipoprotein subclasses were found to be significantly elevated in progressors compared to nonprogressors. Many of these same lipoproteins were found to be associated with an increase in CAC scores among progressors. These lipoproteins may be considered new risk factors for progression of atherosclerosis in RA patients.