RESUMO
An aqueous fraction (10-300 micrograms/mL) of the ethanol extract of the leaves of Cissampelos sympodialis Eichl inhibited N-formyl-Met-Leu-Phe (fMLP)-induced release of lysozyme and myeloperoxidase from human neutrophils. Inhibition by the fraction, as well as by dibutyryl-cAMP and prostaglandin E2, was substantially greater when the cells were pretreated with the phosphodiesterase (PDE) inhibitor isobutyl methyl xanthine (IBMX) indicating that the effect may be mediated by cAMP. Measurement of intracellular cAMP levels showed that the fraction (30-100 micrograms/mL) increased the nucleotide levels in IBMX-pretreated neutrophils which was unaffected by propranolol. Cyclic AMP dependent protein kinase A activity was also increased by the fraction (1.5-100 micrograms/mL). Superoxide anion generation induced by fMLP in cytochalasin B-treated cells primed with PAF was not inhibited by the aqueous fraction. The results indicate that the aqueous fraction of Cissampelos sympodialis inhibits neutrophil degranulation by a cAMP-dependent mechanism which may be relevant to the use of the plant as an anti-asthmatic agent in folk medicine.
Assuntos
Neutrófilos/efeitos dos fármacos , Extratos Vegetais/farmacologia , Plantas Medicinais/química , Brasil , AMP Cíclico/metabolismo , Proteínas Quinases Dependentes de AMP Cíclico/metabolismo , Etanol , Humanos , Técnicas In Vitro , Muramidase/metabolismo , Neutrófilos/enzimologia , Neutrófilos/metabolismo , Peroxidase/metabolismo , Folhas de Planta/química , Solventes , Superóxidos/metabolismo , ÁguaRESUMO
The biosynthesis of leukotrienes is known to occur through a series of complex processes which, in part, can be influenced by cell-cell interactions. Several studies have suggested that arachidonic acid availability is a major limiting step for leukotriene biosynthesis and that its transfer between cells can represent a significant source of this precursor. Accordingly, effect of time and source of arachidonic acid on transcellular leukotriene synthesis was studied in mixed platelet/neutrophil populations challenged with the calcium ionophore A23187. A time-dependent contribution of platelet-derived as well as neutrophil-derived arachidonate was found in the selective formation of neutrophil 5-lipoxygenase metabolites. Utilization of platelet or neutrophil arachidonate was followed by incorporation of radiolabeled arachidonic acid into platelet or neutrophil phospholipids prior to stimulation. Specific activity of liberated arachidonic acid along with numerous 5-lipoxygenase products (including LTB4, 20-hydroxy-LTB4, 5-HETE and LTC4) was determined in order to follow mass and radiolabel. A large amount of platelet-derived arachidonic acid was released in the first 1.5 min, whereas 10 min platelet-derived arachidonate was much lower in amount but significantly higher in specific activity, suggesting different precursor pools. The platelet-derived arachidonate was heavily utilized by the neutrophils at the early time points for formation of 5-HETE and delta 6-trans-LTB4 isomers, but appeared to contribute only marginally to the constitutive metabolism of neutrophil arachidonate into LTB4. Results from these experiments suggest different pools of 5-lipoxygenase in the neutrophil and indicate a time and source dependent modulation of arachidonate metabolism in mixed cell interactions.