Modulatory effects of N-acetyl-L-cysteine on human eosinophil apoptosis

Eosinophils are oxidant-sensitive cells considered relevant in allergic inflammation. The present study aimed to examine the effects of the antioxidant N-acetyl-L-cysteine (NAC) on constitutive and cytokine-delayed apoptosis in human isolated eosinophils. Human eosinophils were purified from the blood of healthy donors by a magnetic separation system. Apoptosis and cellular glutathione were assessed by cytofluorometric analysis and nuclear factor (NF)-kappaB binding activity assessed by electrophoresis mobility shift assay. The rate of spontaneous apoptosis of human eosinophils after 24 h culture, as assessed by annexin-V-positive staining, was mean+/-sem 48.2+/-1.4%, n = 5. Granulocyte-macrophage colony-stimulating factor (GM-CSF; 10 ng.mL(-1)) decreased apoptosis to 19.4+/-1.8%, n = 5. NAC (5 mM) inhibited spontaneous apoptosis (33.6+/-2.7%, n = 5) but augmented apoptosis in the presence of GM-CSF (30.9+/-1.5%, n = 5). NAC (5 mM) also increased the rate of apoptosis in the presence of tumour necrosis factor (TNF)-alpha (10 ng.mL(-1)) and interleukin-5 (5 ng.mL(-1)). NAC (5 mM) increased eosinophil glutathione content. The increase in eosinophil NF-kappaB binding activity induced by GM-CSF and TNF-alpha was suppressed by NAC. In conclusion, N-acetylcysteine modulates eosinophil apoptosis by inhibiting constitutive apoptosis but reversing the survival effect produced by inflammatory cytokines in human eosinophils.