| Summary: | 碩士 === 長庚大學 === 天然藥物研究所 === 97 === Human neutrophils are known to play important roles in the host to defend against microorganisms. However, the extensive or inappropriate activation of neutrophils may cause inflammatory diseases, such as asthma, myocardial infarction, chronic obstructive pulmonary disease, and rheumatoid arthritis. In a search for new anti-inflammatory agent with high efficacy and low toxicity, the effects of imperatorin, a furocoumarin derivative, on superoxide anion and elastase release in human neutrophils were tested. Imperatorin concentration-dependently inhibited superoxide (O2.-) production with an IC50 value of 0.17±0.02 μM, but not elastase release, in formyl-methionyl-leucyl-phenylalanine (FMLP)-activated human neutrophils. However, imperatorin did not affect protein kinase (PK)C activator-induced O2.- generation. Furthermore, imperatorin displayed no antioxidant or O2.- scavenging ability, and it failed to alter the subcellular NADPH oxidase activity. Significantly, the inhibitory effect of imperatorin on O2.- production was reversed by a PKA inhibitor, but not by a PKG inhibitor. Indeed, imperatorin and rolipram notably increased cAMP levels and PKA activity in FMLP-stimulated human neutrophils. Additionally, the peak [Ca2+]i value was unaltered by imperatorin and rolipram, but the time taken for [Ca2+]i to return to half of the peak values was significantly shorted in FMLP-activated neutrophils. Imperatorin reduced FMLP- induced phosphorylation of extracellular regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and protein kinase B (AKT), but not p38 mitogen-activated protein kinase. The inhibitory effects of imperatorin on mobilization of Ca2+ and activation of ERK, JNK and AKT were reversed by PKA inhibitor. In summary, these results demonstrate that inhibition of O2.- release in human neutrophils by imperatorin is associated with an elevation of cellular cAMP levels and PKA activity.
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