Search

CI-986 (5-[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]-1,3, 4-thiadizole-2(3H)-thione, choline salt) was evaluated for its effect on arachidonic acid metabolism by human neutrophils in response to different stimuli. Leukotriene B4 (LTB4) release in response to calcium ionophore A23187 was 15 to 35 fold greater than the responses to N-formyl-methionyl-leucyl-phenylalanine (FMLP) or serum-opsonized zymosan (SOZ), respectively, while the thromboxane B2 (TXB2) release response was similar for the three stimuli tested. CI-986 inhibited the release of LTB4 and TXB2 in response to A23187 with IC50s of 63.4 and 1.6 microM, respectively. In comparison, the compound inhibited SOZ-stimulated LTB4 release with an IC50 of 11.2 microM, while having no effect on TXB2 at concentrations up to 100 microM. Conversely, CI-986 inhibited FMLP-stimulated LTB4 release by 42% at 100 microM, while inhibiting TXB2 release with an IC50 of 0.13 microM. These results demonstrate a stimulus-dependent inhibitory effect of CI-986 on human neutrophil eicosanoid metabolism.

The cell activation inhibitor CI-959 [5-methoxy-3-(1-methylethoxy)-N-1H-tetrazol-5-ylbenzo[b]thiophene-2-carboxamide, monosodium salt] was evaluated for its effects on human neutrophil functions. CI-959 inhibited spontaneous migration and chemotaxis toward N-formyl–methionyl-l-leucyl-l-phenylalanine (fMLP) with 50% inhibition (IC50) values of 3.6 and 3.1 μM, respectively. CI-959 also inhibited superoxide anion generation in response to C5a, fMLP, serum-opsonized zymosan (SOZ), concanavalin A (Con A), and calcium ionophore A23187 with IC50 values of 2.5, 4.7, 14.5, 5.4, and 14.8 μM, respectively. In comparison, CI-959 inhibited myeloperoxidase release in response to C5a, fMLP, SOZ, and Con A with IC50 values of 11.6, 16.1, 7.5, and 100 μM). These results demonstrate that CI-959 inhibits cellular responses to stimuli that mobilize intracellular calcium. For cellular responses to ionophore-mediated calcium influx, only oxygen radical production was inhibited by CI-959. CI-959 was further evaluated for its effects on neutrophil stimulus-response coupling. At 100 μM, CI-959 had no effect on human neutrophil phospholipase C or protein kinase C. CI-959 inhibited fMLP-stimulated intracellular calcium mobilization and calcium influx with IC50 values of 16.7 and 3.1 μM, respectively, and exhibited less potent calmodulin antagonist activity (IC50 = 90.5 μM). These results indicate that CI-959 may exert its stimulus- and response-specific inhibitory effects on neutrophil functions, in part, through inhibition of calcium-regulated signalling mechanisms. J. Leukoc. Biol. 55: 443–451; 1994.

L-PIA, a standard A1-selective adenosine agonist, was evaluated orally in carrageenan (CRG)- and reverse passive arthus-pleurisy. White blood cell (WBC) and exudate accumulation were assessed four hours after induction of the inflammatory response. L-PIA inhibited WBC accumulation in both models with ID50's of 4.37 and 4.42 mg/kg, respectively. In contrast, exudate was inhibited by L-PIA only in the CRG pleurisy model (ID50=1.01 mg/kg). In mechanistic studies, L-PIA reversed the drop in circulating neutrophil count which occurred within 15 minutes after CRG injection, suggesting that L-PIA may inhibit adhesion of the cells to the endothelium. The effects of L-PIA on several parameters of rat neutrophil function were determined. Enzyme release, O 2 − , TXB2, and LTB4 production were monitored in response to FMLP and opsonized zymosan (SOZ) stimulation. At high concentrations L-PIA had a mild inhibitory effect on O 2 − release in response to FMLP and had a moderate effect on arachidonic acid metabolite production, in response to both stimuli. The other response were unaffected. These results suggest that L-PIA may prevent diapedisis or neutrophil adhesion to the endothelium, but has a minimal effect on enzyme release O 2 − , LTB4 and TXB2 production.