Selective inhibition of extracellular oxidants liberated from human neutrophils—A new mechanism potentially involved in the anti-inflammatory activity of hydroxychloroquine

• Hydroxychloroquine:Decreased the activity of neutrophils in rats with adjuvant arthritis
• Diminished the oxidants released from neutrophils and involved in tissue damage
• Protected the radicals formed inside neutrophils which fulfil a regulatory role
• Antiradical effects corresponded with the phosphorylation of protein kinases C and p40phox.
• Inhibited mobilisation of intracellular calcium in neutrophils

Hydroxychloroquine is used in the therapy of rheumatoid arthritis or lupus erythematosus. Although these diseases are often accompanied by activation of neutrophils, there are still few data relating to the impact of hydroxychloroquine on these cells.We investigated the effect of orally administered hydroxychloroquine on neutrophil oxidative burst in rats with adjuvant arthritis. In human neutrophils, extra- and intracellular formation of oxidants, mobilisation of intracellular calcium and the phosphorylation of proteins regulating NADPH oxidase assembly were analysed.Administration of hydroxychloroquine decreased the concentration of oxidants in blood of arthritic rats. The inhibition was comparable with the reference drug methotrexate, yet it was not accompanied by a reduction in neutrophil count. When both drugs were co-applied, the effect became more pronounced. In isolated human neutrophils, treatment with hydroxychloroquine resulted in reduced mobilisation of intracellular calcium, diminished concentration of external oxidants and in decreased phosphorylation of Ca2 +-dependent protein kinase C isoforms PKCα and PKCβII, which regulate activation of NADPH oxidase on plasma membrane. On the other hand, no reduction was observed in intracellular oxidants or in the phosphorylation of p40phox and PKCδ, two proteins directing the oxidase assembly to intracellular membranes.Hydroxychloroquine reduced neutrophil-derived oxidants potentially involved in tissue damage and protected those capable to suppress inflammation. The observed effects may represent a new mechanism involved in the anti-inflammatory activity of this drug.