MCI-826 is a potent and selective antagonist of peptide leukotrienes (p-LTs) and has characteristics distinctive from those of FPL 55712

Cysteinyl leukotriene-dependent interleukin-5 production leading to eosinophilia during late asthmatic response in guinea-pigs

BACKGROUND

Allergic airway eosinophilia is suppressed by cysteinyl leukotriene (CysLT) receptor (CysLT1 receptor) antagonists in several species including humans and guinea-pigs, suggesting that CysLTs are directly or indirectly involved in induction of the response.

OBJECTIVE

We examined the effect of CysLT antagonists (pranlukast and MCI-826) on antigen inhalation-induced eosinophilia in peripheral blood and lung, and on IL-5 activity in serum during late increase of airway resistance (late asthmatic response, LAR) in sensitized guinea-pigs.

METHODS

Guinea-pigs inhaled ovalbumin (OVA) + Al(OH)3 and OVA mists alternately for sensitization and challenge, respectively, once every 2 weeks. At the fifth challenge, the effects of CysLT antagonists and an anti-IL-5 antibody (TRFK-5) on the occurrence of LAR, and blood and lung eosinophilia, which appeared at 5 h after challenge, were examined. The time-course of IL-5 activity in the serum after the challenge was evaluated by measuring in vitro 'eosinophil survival prolongation activity'. The influence of CysLT antagonists on IL-5 activity was assessed.

RESULTS

CysLT antagonists and TRFK-5 completely abolished blood and lung eosinophilia. LAR was suppressed by both MCI-826 and TRFK-5 by 40-50%. Sera obtained from sensitized, challenged animals 3 h and 4 h after challenge induced an obvious prolongation of eosinophil survival. The activity of the sera was completely neutralized by prior exposure to TRFK-5, suggesting that it reflected IL-5 activity. Increased IL-5 activity in the serum was inhibited by both pranlukast and MCI-826 by over 90%.

CONCLUSIONS

CysLTs produced after antigen provocation sequentially induced IL-5 production from some immune component cells via CysLT1 receptor activation. Thus, it is likely that CysLTs indirectly cause antigen-induced eosinophilia through IL-5 production.

Inhibitory effect of ONO-1078 on specific binding of peptide leukotrienes to human lung crude membrane

We investigated the effects of ONO-1078, a newly synthesized peptide leukotriene (p-LT antagonist, on the specific binding of radiolabelled [3H]-LTC4, [3H]-LTD4 and [3H]-LTE4 to a human lung crude membrane fraction (HLMF). The binding assay was performed under conditions in which [3H]-LTC4 and [3H]-LTD4 were not metabolized by HLMF; that is, the metabolism of LTC4 to LTD4 or LTE4 was almost completely prevented by pretreating HLMF with 5 mM acivicin at 37 degrees C for 180 min, and metabolism of LTD4 to LTE4 was inhibited by including 5 mM L-cysteine and 5 mM glycine in the assay. [3H]-LTD4 specific binding was potently and concentration-dependently dissociated by ONO-1078. Its potency was 180-fold stronger than that of FPL 55712, a standardized p-LT antagonist, whereas high concentrations of ONO-1078 similar to those of FPL 55712 were required to inhibit [3H]-LTC4 specific binding. The rank order of the inhibitory potencies of p-LT agonists and antagonists for [3H]-LTD4 specific binding was LTD4 > ONO-1078 > LTE4 > LTC4 > FPI 55712. On the other hand, not only high concentrations of ONO-1078 and FPL 55712 but also more than a 100-fold excess of unlabelled LTE4 was required to inhibit [3H]-LTE4 specific binding, indicating that the binding sites do not appear to be receptors of LTE4. From these results, it is suggested that ONO-1078 is a highly potent LTD4 antagonist which is expected to be very effective on bronchial asthma.