Estimation of proinflammatory biomarkers of skin irritation by dermal microdialysis following exposure with irritant chemicals

The aim of the present study was to quantify the release of proinflammatory biomarkers by dermal microdialysis after topical exposure with irritant chemicals, Jet fuel (JP-8) and xylene in rat skin. Occlusive dermal exposure (2 h) was carried out with 230 μl of JP-8 or xylene using Hill top chambers®. Linear microdialysis probes (10 mm) were inserted in the dermis under urethane anesthesia. The dialysis fluid was pumped at a flow rate of 2 μl/min and the dialysate was collected for 7 h following probe insertion. The expression of substance P (SP), calcitonin-gene related peptide (CGRP) and prostaglandin E2 (PGE2) in the dialysate following microdialysis was measured by enzyme immunoassay (EIA). The effect of pretreatment with an SP antagonist (SR-140333) and a PGE2 inhibitor (celecoxib), 6 and 18 h before the application of JP-8 was also assessed to further establish the sensitivity of the microdialysis set up. On similar lines, untreated and capsaicin treated control experiments were performed to compare with the SP release following JP-8 treatment. Further, we also investigated the SP release following topical application of xylene. The mean concentrations of SP after the application of JP-8 (90.01 ± 3.31) and 3 h after its removal (58.66 ± 9.36) indicated that JP-8 induced significantly higher release of SP as compared to the baseline value (P < 0.05). The release of SP following JP-8 treatment (58.66 ± 9.36 pg/ml) was comparable to capsaicin (58.18 ± 11.29 pg/ml). JP-8 exposure resulted in a significant increase (P < 0.001) in PGE2 levels over the baseline control at the end of 1 and 2 h of exposure. JP-8 treatment also produced significant increase (P < 0.001) in PGE2 levels as compared to the untreated control during occlusion and 1 h following its removal. There was a significant drop (P < 0.05) in the PGE2 levels by the end of 3 h following exposure. Pretreatment with SR-140333 and celecoxib significantly reduced (P < 0.05) SP and PGE2 release induced by JP-8. The mean concentrations of SP following xylene exposure (25.50 ± 8.80 pg/ml) and 3 h after its removal (34.37 ± 5.61 pg/ml) indicated its skin irritation potential. Unlike JP-8, xylene produced a significant increase in SP release only after the removal of occlusion. Pretreatment with SR-140333 significantly blocked the xylene induced SP release. CGRP was not detected in any of the samples. This study demonstrates that dermal microdialysis can be used to quantify skin irritation potential of JP-8 and related irritant chemicals.