Evaluation of skin sensitization potential of melatonin and nimesulide by murine local lymph node assay

Melatonin is a good candidate for transdermal delivery considering its shor t plasma half life, low molecular weight and a favorable octanol:water part ition coefficient. Nimesulide is a nonsteroidal anti-inflammatory agent use d orally and rectally for inflammatory disorders. The objective of this stu dy was to investigate the skin sensitization potential of melatonin and nim esulide using the standard murine local lymph node assay (LLNA). Melatonin (0.5, 2.5, 5.0 and 10.0%, w/v) and nimesulide (0.5, 2.5, 5.0 and 10.0%, w/v ) dissolved in acetone:olive oil (4:1, AOO) was applied (25 mul) on the dor sal surface of each ear of female CBA/Ca mice for three consecutive days. O n the sixth day, [H-3]methyl thymidine was administered intravenously and t he uptake of [AH]methyl thymidine (dpm) by the draining lymph nodes was det ermined by established methods. Dinitrochlorobenzene (DNCB, 0.25%, w/v) and para-aminobenzoic acid (PABA. 2.5%, w/v) were used as positive and negativ e control, respectively. The mean dpm obtained with melatonin and nimesulid e treatment at all concentrations were not significantly different (P >0.05 ) from that of AOO. The stimulation index (SI) values of melatonin and nime sulide at different concentrations were close to 1. The results of the pres ent study using the standard LLNA approved by US Interagency Coordinating C ommittee in the Validation of Alternative Methods (ICCVAM) indicate that me latonin and nimesulide are not skin sensitizers. However. since LLNA has sh own false negatives with many drugs. clinical trials are certainly needed t o exclude the possibility of a weak or delayed type skin sensitization reac tion. Further studies using modified LLNA procedures (extended exposure, al ternative vehicle systems. pre-abrasion, etc.) may be useful in identifying the weak or delayed type skin sensitization reactions. (C) 2001 Elsevier S cience B.V. All rights reserved.