Structural requirements of sesquiterpene lactones to inhibit LPS-induced nitric oxide synthesis in RAW 264.7 macrophages

Some sesquiterpene lactones were recently demonstrated to inhibit inducible nitric oxide synthase (iNOS)-dependent nitric oxide (NO) synthesis. The pr imary objective of the present study was, therefore, to find evidence for s tructural requirements of sesquiterpene lactones regarding their capability to inhibit iNOS-dependent NO synthesis. Sesquiterpene lactones 1-11 were e xamined for their influence on nitrite accumulation in cell culture superna tants of LPS-induced RAW 264.7 macrophages. Except the taraxinic acid beta -D-glucopyranosylester 8 all compounds showed a dose-dependent inhibition o f nitrite accumulation in cell culture supernatants with IC50 values rangin g from 0.5 to 36.8 muM High activity seemed to be dependent on an alpha -me thylene-gamma -lactone functionality. Cytotoxicity and the ability to inhib it activation of transcription factor NF-kappaB are further biological acti vities of sesquiterpene lactones. The second point of interest was, therefo re, whether the structural requirements of sesquiterpene lactones for these activities may differ or be the same for those needed to inhibit iNOS-depe ndent NO synthesis. Using concentrations of 111 required to inhibit NO synt hesis cell viability was determined and NF-kappaB binding activity was meas ured by gel-shift experiments. Interestingly, compounds almost equally effe ctive in inhibiting nitrite accumulation did not show the same cytotoxic po tential, and most sesquiterpene lactones inhibited nitrite accumulation at concentrations where inhibition of NF-kappaB activation was not significant . These results suggest that different biological activities of sesquiterpe ne lactones have different structural requirements. (C) 2000 Elsevier Scien ce Ltd. All rights reserved.