Hydrogen peroxide induces leukocyte rolling: Modulation by endogenous antioxidant mechanisms including NO

In this study, intravital microscopy was used to examine the mechanisms that regulate H₂O₂-induced leukocyte rolling within rat mesenteric venules in vivo. H₂O₂ elicited leukocyte rolling within a narrow response window between 10 and 500 μM H₂O₂. Continuous superfusion with 100 μM H₂O₂ induced a large but transient increase in the flux of rolling leukocytes, whereas a short 5-min pulse elicited a sustained increase in rolling flux. Both treatments caused increases in leukocyte adhesion. H₂O₂-induced increases in leukocyte flux and adhesion could be prevented with an anti-P- selectin antibody. Inhibition of endogenous catalase (aminotriazole), glutathione (diethyl maleate), or nitric oxide (N(G)-nitro-L-arginine methyl ester) shifted the effective concentration of H₂O₂; continuous superfusion with 10 μM H₂O₂ now elicited large and sustained increases in leukocyte rolling flux, whereas 100 μM H₂O₂ elicited less than optimal responses. Dual antioxidant inhibition further reduced the effective H₂O₂ concentration to 1 μM H₂O₂. A nitric oxide donor prevented the increased rolling flux induced by 100 μM H₂O₂. These findings suggest that endogenous antioxidants are important regulators of H₂O₂-induced, P- selectin-dependent leukocyte rolling in vivo.