Effects of two antihypertensive agents, labetalol and metoprolol, on the production of reactive oxygen species by normal polymorphonuclear leukocytes in vitro.

Objective: Increased lipid peroxidation is a putative causal factor for preeclampsia. Because oxygen free radicals are involved in inducing the lipid oxidation chain reaction, we evaluated two beta adrenoreceptor blockers, labetalol and metoprolol, currently used for treating hypertension with regard to their ability to inhibit the formation of reactive oxygen species during respiratory burst of human normal polymorphonuclear leukocytes in vitro.

Methods: We determined whether labetalol or metoprolol have antioxidative activity in a model of polymorphonuclear leukocytes stimulated in vitro with phorbol-12-myristate-13-acetate (PMA) and N-formyl-methionin-leucin-phenylalanin (fMLP). We also studied the scavenging properties of these two drugs using acellular systems.

Results: Labetalol inhibits O2-. production by neutrophils activated by fMLP (IC50 = 17.5 mg/L) and weakly by PMA (43.6% inhibition at 100 mg/L). It also possesses a significant activity on OH. production (IC50 = 65 mg/L) that may depend in part on its ability to interfere with iron in the Fenton reaction. The same assays performed with metoprolol did not show any inhibitory effect on O2.- generation. It decreased weak OH. production by neutrophils, as a result of cellular and scavenging effects.

Conclusion: Labetalol shows important antioxidative properties in vitro with regard to normal leukocyte oxidative metabolism.