Background Substance P (SP) is a neuropeptide involved in the neurogenic inflammation of rheumatoid arthritis (RA) and is increased in serum and synovial fluid of patients with the disease.

Objectives To evaluate the possible correlation between SP serum levels and RA activity assessed by disease activity score (DAS) 28 joints-C reactive protein (CRP) and German 7-Joint Ultrasound Score (GUS7).

Methods Ninety RA patients (32 in remission, 8 with low disease activity, 42 with moderate disease activity and 8 with high disease activity assessed by DAS28-PCR) and 24 healthy controls were included. GUS7 was performed by evaluating synovitis and synovial/tenosynovial vascularity semiquantitatively (grade 0–3) by gray-scale (GS) and power Doppler (PD) ultrasound using an 18-mHz linear transducer. SP serum levels were measured by enzyme-linked immunosorbent assay. Correlation was estimated by Spearman's correlation coefficient.

Results SP serum levels were statistically different between controls and patients in remission or with different grades of disease activity (P≤0.05). Furthermore, positive tendency between SP serum levels and RA activity was observed. SP showed significant correlation with DAS28-CRP, tender joint count, swollen joint count and visual analog scale (VAS) by Spearman's correlation coefficient. No correlation was found between SP and CRP or GUS7.

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Conclusions SP appears to be a potential RA activity biomarker. Notwithstanding, it is unlikely that SP itself provides sufficient discrimination in regard to rheumatoid arthritis activity given the complexity and heterogeneous etiology of this disease. In this regard, further studies of SP as a biological marker are necessary for its inclusion in a multi-biomarker equation that considers the neurogenic pathway participation in the pathogenesis of RA.

References

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4. Origuchi T, Iwamoto N, Kawashiri SY, Fujikawa K, Aramaki T, Tamai M, et al. Reduction in serum levels of substance P in patients with rheumatoid arthritis by etanercept, a tumor necrosis factor inhibitor. Mod Rheumatol 2011; 21:244–250.

Disclosure of Interest None declared