The enzyme 5-lipoxygenase catalyzes the metabolism of arachidonic acid to form products that have been implicated in the airway obstruction of asthma. We hypothesized that if products of the 5-lipoxygenase pathway are important in mediating this obstruction, then prevention of their formation should decrease the severity of an induced asthmatic response.

In a randomized, double-blind, placebo-controlled, crossover study, we examined the effect of A-64077, a 5-lipoxygenase inhibitor, on the bronchoconstriction induced by hyperventilation of cold, dry air in 13 patients with asthma. The completeness of 5-lipoxygenase inhibition was confirmed by examining the profile of eicosanoids produced in whole blood ex vivo after activation with the calcium ionophore A-23187.

A-64077 decreased the mean (±SEM) ionophore-induced synthesis of leukotriene B₄, a 5-lipoxygenase product, by 74 percent (from 265.3±30.3 to 69.5±21.5 ng per milliliter, P<0.001), but it did not affect the ionophore-induced synthesis of thromboxane B₂, a cyclooxygenase metabolite of arachidonic acid (80.0±17.1 ng per milliliter before A-64077 vs. 75.8±14.3 ng per milliliter after A-64077). In concert with the selective inhibition of 5-lipoxygenase by A-64077, the amount of cold, dry air (expressed as respiratory heat exchange) required to reduce the forced expiratory volume in one second by 10 percent was increased by 47 percent after A-64077 (3.0 kJ per minute for placebo vs. 4.4 kJ per minute for A-64077, P<0.002). Similar results were obtained when minute ventilation was used as an indicator of outcome (27.5 liters per minute for placebo vs. 39.8 liters per minute for A-64077, P<0.005).

Selective inhibition of 5-lipoxygenase by A-64077 is associated with a significant amelioration of the asthmatic response to cold, dry air, suggesting that 5-lipoxygenase products are involved in this response. This approach may be useful in the treatment of asthma. (N Engl J Med 1990; 323:1740–4.)