A recent in vitro study demonstrated that tofacitinib, a JAK1/JAK3 inhibitor, effectively reduced inflammation in cellular models of rheumatoid arthritis but did not mitigate the prothrombotic changes in vascular endothelial cells, raising concerns about its cardiovascular safety profile.

Study Design and Methodology

Researchers conducted coculture experiments using peripheral blood mononuclear cells (PBMCs) activated with phytohemagglutinin and combined them with rheumatoid arthritis (RA) synoviocytes or endothelial cells (ECs). These models simulated the inflammatory microenvironment of RA joints and vasculature. Tofacitinib was administered at increasing concentrations: 0.1, 1, 10, and 100 μM. Cytokine secretion was assessed using ELISA, and gene expression was evaluated via RT-qPCR.

Key Findings in Synovial Cocultures

Tofacitinib strongly suppressed inflammatory cytokine production:

• IFN-γ levels dropped significantly, from 74.5% at 0.1 μM to near-complete inhibition at ≥1 μM (2.6%, 0.4%, 0.6% for 1, 10, and 100 μM respectively; P < .001).

• IL-17A decreased from 74.4% at 0.1 μM to 8.5% at 100 μM (P < .001).

• IL-10, an anti-inflammatory cytokine, was paradoxically reduced by 67.2% at 0.1 μM and remained at ~35% at higher doses.

• TNF declined gradually, with statistical significance only at 100 μM (32.3% remaining; P = .05).

Key Findings in Vascular Cocultures

In cocultures of ECs and activated PBMCs:

• IFN-γ secretion decreased significantly at 0.1 μM (68.6%), and was fully suppressed at ≥10 μM (P < .001).

• TNF decreased to 15.5% at 100 μM (P < .05).

• IL-6 declined to 1.8% and IL-8 to 20.2% at 100 μM (P < .001).

• IL-17A and IL-10 showed moderate reductions but remained detectable across all concentrations.

Endothelial Activation and Procoagulant Profile

Despite its anti-inflammatory effects, tofacitinib did not mitigate endothelial prothrombotic activation:

• Tissue Factor (TF) expression—key in coagulation—remained unaffected at all concentrations.

• VCAM-1 expression increased by 77% at 10 μM in ECs stimulated with TNF + IL-17A (P < .05).

• Thrombomodulin, an anticoagulant protein, was reduced by 43% at 1 μM (0.71 vs 1.25 in DMSO control; P < .05).

• E-selectin expression remained elevated regardless of tofacitinib treatment.

These findings were corroborated by both gene and protein expression data, visualized in Figures 3–5 of the source article.

Interpretation and Clinical Relevance

Lead author Aliki Zavoriti and coauthor Pierre Miossec concluded:

Tofacitinib inhibits synovium and vascular inflammation but fails to prevent the prothrombotic effects of inflammatory cytokines on ECs.

The authors suggest that incomplete inhibition of IL-17A and TNF, reduction of protective IL-10, and unchanged TF expression may perpetuate endothelial dysfunction despite control of systemic inflammation. Notably:

• IFN-γ is fully blocked due to its reliance on the JAK-STAT pathway.

• IL-17A, however, is regulated by non–JAK-dependent cytokines (e.g., IL-1β), explaining its partial resistance to inhibition.

This mechanistic insight may explain why patients treated with JAK inhibitors, including tofacitinib, have a higher incidence of cardiovascular events, even with improved RA symptom control.

Conclusion

While tofacitinib effectively suppresses inflammatory cytokines in joint and vascular models, it does not sufficiently counteract prothrombotic endothelial activation. These findings support the need for further investigation into combination therapies that also target coagulation pathways or EC-specific inflammation to reduce cardiovascular risk in patients with RA.

Full disclosures can be found in the published study.

Source: ACR Open Rheumatology