EFFECTS OF MITOGEN-ACTIVATED PROTEIN-KINASE KINASE INHIBITOR PD-098059 ON ANTIGEN CHALLENGE OF GUINEA-PIG AIRWAYS IN-VITRO

1 It has been shown that activation of protein tyrosine kinases is the earliest detectable signalling response to Fc epsilon RI: cross-linki ng on mast cell. Following tyrosine kinase activation, a family of mit ogen-activated protein kinases (MAPKs) was found to be activated as we ll. The present study examined the role of MAPK signalling cascade in in vitro model of allergic asthma using a specific MAPK kinase inhibit or PD 098059. 2 Guinea-pigs were passively sensitized with IgG antibod y raised against ovalbumin (OA). Effects of PD 098059 on OA-induced an aphylactic contraction of isolated bronchi and release of histamine an d peptidoleukotrienes from chopped lung preparations were studied. 3 P D 098059 (10-50 mu M) produced only minor reduction of maximal OA-indu ced bronchial contraction. In contrast, the rate of relaxation of OA-i nduced bronchial contraction was markedly faster in the presence of PD 098059 than the vehicle control in a concentration-dependent manner. 4 These observations corroborate well with the inability of PD 098059 (5-50 mu M) to substantially block the OA-induced release of histamine and with marked inhibition of OA-induced release of peptidoleukotrien es from lung fragments in the presence of PD 098059. Exogenous arachid onic acid-induced release of peptidoleukotrienes from lung fragments w as not blocked by PD 098059. 5 In immunoblotting study, we found that p42(MAPK) was constitutively expressed in guinea-pig bronchi. However, treatment with OA, histamine or LTD4 did not cause activation of p42( MAPK). These findings together with the lack of inhibitory effects of PD 098059 on bronchial contraction induced by histamine or LTD4 sugges t that histamine- and LTD4-induced bronchial contractions are not medi ated by p42(MAPK) activation. 6 Taken together, our findings show that inhibition of MAPK signalling cascade by PD 098059 significantly redu ced the OA-triggered release of peptidoleukotrienes leading to rapid r elaxation of anaphylactic bronchial contraction. On the other hand, p4 2MAPK did not play a role in histamine- or LTD4-induced bronchial smoo th muscle contraction suggesting that PD 098059 exerts its inhibitory effects on OA-induced bronchial contraction primarily through inhibiti on of peptidoleukotrienes release from mast cells.