TRPA1 Activation Contributes to Acute Inflammatory Response and Mediates Carrageenan-Induced Paw Edema

Lauri J. Moilanen1, Mirka Laavola1, Meiju Kukkonen1, Riku Korhonen1, Tiina Leppänen1, Edward D. Högestätt2, Peter M. Zygmunt2, Riina M. Nieminen1, Eeva Moilanen1. 1The Immunopharmacology Research Group, University of Tampere School of Medicine and Tampere University Hospital, Tampere, Finland, 2Department of Clinical Chemistry and Pharmacology, Lund University and Lund University Pain Research Center, Lund, Sweden.

Introduction: Transient receptor potential ankyrin 1 (TRPA1) is an ion channel which is activated by a variety of plant-derived and environmental irritants such as allyl isothiosyanate (AITC) and acrolein. TRPA1 is involved in nociceptive chemo-, mechano- and thermosensation. Of great interest is its role in inflammatory pain as many oxidants formed in inflammatory reactions have been identified as endogenous TRPA1 agonists. However, our understanding of TRPA1-mediated responses in the inflammatory process is limited. In the present study, we tested the hypothesis that TRPA1 is involved in the development of acute inflammatory edema.

Materials and Methods: Wild type (WT) and TRPA1 deficient C57BL76 mice (male, n = 6 per group) were used in the experiments. The animals were treated intraperitoneally with the TRPA1 antagonist HC-030031 (300 mg/kg) or with the COX-inhibitor ibuprofen (100 mg/kg) 2h before inflammatory paw edema was induced by intraplantar injection of carrageenan or AITC. Further, COX-2 expression was investigated in HEK 293 cells transfected with hTRPA1 and treated with AITC alone or together with HC-030031.

Results: In WT mice, AITC induced an inflammatory edema comparable to that caused by carrageenan. HC-030031 inhibited not only AITC but also carrageenan-induced edema. Also, ibuprofen suppressed both AITC and carrageenan-induced responses. TRPA1 deficient mice showed an attenuated response to carrageenan and practically no response to AITC. To investigate the mechanisms in further detail, we used HEK 293 cells transfected with hTRPA1. Carrageenan did not cause a direct activation of TRPA1. Interestingly, AITC enhanced COX-2 expression when measured by RT-PCR, and the response was reversed by treatment with HC-030031.

Conclusions: The results suggest that activation of TRPA1 induces an acute inflammatory COX-dependent edema. In addition, TRPA1 mediates carrageenan-induced paw edema, a widely used model for studying drug effects on acute inflammation.