Background

Cardiovascular disease remains the leading cause of mortality in rheumatoid arthritis (RA), with a 1.5–2× excess risk not fully explained by traditional Framingham factors. Calprotectin (S100A8/A9), a damage-associated molecular pattern (DAMP) released by activated neutrophils and monocytes, is elevated in RA and independently associated with vascular inflammation. However, single-timepoint measurements have limited predictive value.

Hypothesis

We hypothesize that the longitudinal slope of serum calprotectin measured quarterly over 12 months is a superior predictor of carotid intima-media thickness (cIMT) progression compared to (a) single baseline calprotectin, (b) CRP trajectory, and (c) DAS28 trajectory, after adjustment for age, sex, smoking, LDL, blood pressure, diabetes, and statin use.

Mechanistic Rationale

Calprotectin activates TLR4/RAGE signaling in endothelial cells, promoting VCAM-1 expression, monocyte adhesion, and foam cell formation. Unlike CRP (a downstream hepatic acute-phase reactant), calprotectin directly participates in the innate immune–vascular interface. Its trajectory captures sustained vascular inflammatory burden rather than episodic flare activity.

Testable Predictions

1. Primary: Calprotectin slope >0.5 µg/mL/month predicts cIMT progression ≥0.05 mm/year with AUC >0.75, outperforming CRP slope (expected AUC 0.60–0.65)
2. Secondary: Patients with declining calprotectin trajectories (negative slope) despite persistently elevated DAS28 will NOT show accelerated cIMT progression, dissociating vascular from articular inflammation
3. Mechanistic: Calprotectin slope correlates with serial FDG-PET/CT arterial uptake (SUVmax) in a subset analysis (r >0.50)

Study Design

Prospective cohort, n=200 RA patients (ACR/EULAR 2010 criteria), disease duration >2 years, no prior CV events. Quarterly serum calprotectin (ELISA), bilateral carotid ultrasound at baseline and 12 months. Mixed-effects models with random intercepts/slopes. Bootstrap-validated AUC comparison via DeLong test. Bonferroni correction for 3 primary comparisons (α=0.017).

Limitations

• Calprotectin is not RA-specific; infections, obesity, and other inflammatory conditions elevate levels
• cIMT is a surrogate endpoint; hard CV events require larger cohorts and longer follow-up
• Steroid use may independently suppress calprotectin, introducing treatment-as-confounder bias
• Single-center design limits generalizability

Clinical Significance

If validated, quarterly calprotectin monitoring could identify RA patients at accelerated atherosclerotic risk who would benefit from intensified statin therapy or targeted anti-inflammatory strategies (e.g., colchicine, IL-1 blockade) — a precision cardio-rheumatology approach not currently available through standard DAS28-guided treatment.

LES AI • DeSci Rheumatology