No abstract

The inflammatory reaction induced by the intradermal injection of arachidonic acid into the rabbit dermis has been investigated. Plasma extravasation was measured by the leakage of 125I‐albumin into the tissues and polymorphonuclear leukocyte (PMNL) accumulation was assessed histologically. Arachidonic, 5,8,11,14,17‐eicosapentaenoic and 8,11,14‐eicosatrienoic acids, but not oleic, linoleic or linolenic acids, caused a concentration‐related plasma extravasation following their intra‐dermal injection. The plasma extravasation induced by arachidonic acid was dependent on PMNLs. PMNL infiltration and plasma extravasation into arachidonic acid‐injected skin sites was inhibited by the mixed cyclo‐oxygenase‐lipoxygenase inhibitor, BW755C. Arachidonic acid‐induced plasma extravasation was inhibited by cyclo‐oxygenase and 5‐lipoxygenase inhibitors but not by the Paf antagonist, kadsurenone. The inflammation induced by arachidonic acid in the rabbit dermis may be a useful model for evaluating 5‐lipoxygenase inhibitors which could be potentially useful anti‐inflammatory agents for the treatment of psoriasis and other inflammatory diseases.

The efficacy of non-steroidal anti-inflammatory drugs (NSAIDs) is generally accepted to be due to the inhibition of cyclooxygenase (CO) and the subsequent reduction of blood flow and plasma exudation within the inflammatory lesion. It is speculated that drugs which prevent the accumulation of leukocytes into inflammatory lesions may also be clinically beneficial. One approach towards finding such a drug is based on the observation that leukotriene B4 (LTB4) is a potent leukotactic agent in several species including man. Therefore, reducing the levels of LTB4 through inhibition of 5-1ipoxygenase (LPO) may provide a means of inhibiting leukocyte migration.We have investigated the relationship between the effects of drugs on arachidonate metabolism and the inflammatory parameters of leukocyte migration and plasma exudation in the carrageenin-soaked sponge implant model in rats [1]. Our objectives were to investigate the role of LTB4 in the recruitment of leukocytes into the sponges and to assess the suitability of the model for evaluating the anti-inflammatory efficacy of LPO inhibitors.Agents were dosed p.o. in 1% carboxymethylcellulose one hour prior to the subcutaneous implant of sponges soaked in 0.5% 2 carrageenin and the various parameters were measured 4 hours post implant. Ex vivo LPO and CO activity were determined by stimulation of the inflammatory exudate with the calcium ionophore A23187, as described by SALMON et al. [1]. Prostaglandin E 2 and LTB4 generated by ionophore were measured by radioimmunoassay [2]. To authenticate the nature of the immunoreactive LTB4, ionophore-stimulated exudate was extracted with methylformate [3] and the extracted lipids subjected to RPHPLC using a 5/~Spherisorb ODS2 column and linear gradient from 60-95% methanol in 0.1% acetic acid and water, pH 5.6. A single peak of immunoreactive material was identified which co-eluted with synthetic LTB4 standard. No other immunoreactive materials were evident.The NSAIDs flurbiprofen and indomethacin (table) inhibited leukocyte migration, exudate volume and CO activity but failed to inhibit LPO activity. In fact these agents actually elevated immunoreactive LTB4 levels, an observation noted elsewhere [1]. Similar anti-leukotactic profiles were observed for other NSAIDs. Nafazatrom (Bayer g6575), quercetin and NDGA, which inhibit LPO activity in RBL and human PMNL 105,000 x g cytosol [4,5] had no effect on leukocyte migration, exudate volume, LPO or CO activity when dosed at 100 nag kg -1 p.o. These agents were also inactive when administered twice at 16 and 1 hour prior to sponge implant. The mixed cyclooxygenaselipoxygenase inhibitors BW755C and phenidone were equipotent inhibitors of LPO but BW755C was 10 times more potent than phenidone against CO (table). BW755C was also > 10 more potent than phenidone at inhibiting