Quantifying joint blood flow in a rat model of rheumatoid arthritis with dynamic contrast-enhanced near-infrared spectroscopy

The current standard of care for treating rheumatoid arthritis (RA) involves early use of disease modifying antirheumatic drugs (DMARDs). Nevertheless, 30% of RA patients still fail their first DMARD and it takes 3–6 months to detect treatment failure with current monitoring methods; this places patients at a higher risk of irreversible joint damage. We previously developed a dynamic contrast-enhanced time-resolved near-infrared spectroscopy technique (DCE TR-NIRS) for quantifying joint blood flow (BF). We now aim to investigate whether joint BF, as measured with DCE TR-NIRS, can be used to monitor disease activity and treatment response in a rat model of RA. Arthritis was induced in 4 adult male Lewis rats using the well-established adjuvant-induced arthritis model. Baseline measurements were acquired prior to adjuvant injection on day 0. Arthritis progressed until day 20 (“Pre-treatment” phase), after which rats received DMARD treatment (Enbrel®: 0.5 ml/kg; intramuscular injection) once every 5 days (“Treatment” phase). Starting on day 0, ankle joint BF was measured every 5 days until the end of the study on day 40. Mean rat ankle joint BF (mL/min/100g) increased from 7.94±3.71 at baseline to 15.77±4.58 during the Pre-treatment phase. Following treatment, mean joint BF decreased to 12.15±1.82 mL/min/100g. This is an ongoing study and the preliminary results shown here suggest that joint BF measured with DCE TR-NIRS is sensitive to RA disease activity and could detect response to treatment.