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We have examined the effect of the oral gold compound auranofin (AF) on calcium ionophore A23187-induced arachidonic acid metabolism in the rat alveolar macrophage. Both reverse-phase high performance liquid chromatographic and radioimmunoassay analyses revealed that AF dose-dependently inhibited leukotriene B4 and 5-hydroxyeicosatetraenoic acid synthesis in a parallel fashion with an IC50 approximately 4.3 micrograms/ml. At the same time, AF augmented A23187-induced arachidonate release and cyclooxygenase metabolism. A possible mechanism for the inhibition of 5-lipoxygenase was suggested by the capacity of AF to dose-dependently deplete ATP (IC50 approximately 5.9 micrograms/ml), a cofactor for 5-lipoxygenase. These data indicate that, at therapeutic concentrations, AF acts in vitro as a selective inhibitor of macrophage 5-lipoxygenase metabolism. This likely represents an important mechanism of action of AF in chronic inflammatory disorders.

Lipoxygenase metabolites of arachidonic acid have been proposed as possible mediators of hypoxic pulmonary vasoconstriction (HPV) in the rat. Since reduced glutathione (GSH) is a required substrate for the synthesis of the sulfidopeptide eicosanoid leukotriene C4 (LTC4), we reasoned that this specific GSH dependence of LTC4 synthesis might allow us to distinguish between the roles of sulfidopeptide leukotrienes and other 5-lipoxygenase metabolites of arachidonic acid. In the present study we have examined the effect of in vivo pretreatment with the GSH synthesis inhibitor buthionine sulfoximine (BSO) on both the hypoxic pressor response and lung leukotriene synthesis in the rat. The intraperitoneal administration of 4 mmol/kg of BSO 30, 20, and 4 h prior to lung excision significantly depleted total lung glutathione as compared to saline-pretreated controls. This depletion of glutathione was associated with a significant attenuation of HPV in isolated perfused lungs but no alteration in pressor response to angiotensin II or KCl. In addition, hypoxia-associated LTC4 levels in lung homogenates were significantly lower in animals pretreated with BSO than in saline-pretreated controls. The specificity of the effects of BSO on lung leukotriene synthesis was examined by quantitating immunoreactive leukotrienes produced by unstimulated and ionophore A23187-stimulated parenchymal lung fragments, lonophore stimulation of lung fragments from BSO-pretreated rats produced 76 +/- 12.2% as much LTC4 and 127 +/- 22.3% as much leukotriene B4 as did fragments from saline-pretreated rats. Our data demonstrating that GSH depletion caused parallel reductions in both HPV and hypoxia-associated lung LTC4 levels are therefore consistent with the hypothesis that sulfidopeptide leukotrienes are involved in this pressor response in the rat.

Long-circulating lipospheres containing 6-mercaptopurine (6-MP) were prepared by solidification of warm microemulsion at low temperature. Palmitoyl PEG was incorporated in the system to confer stealth-type nature. The size of lipospheres was in the range of 60-70 nm and was inversely proportional to sonication time. The size range was attained after 8 h. of sonication. The entrapped 6-MP contained 0.12 mmol/mole of lipid. The coating efficiency of 63-71% was attained. The zeta potential substantially decreased after PEG coating, however, the lipospheres were stable due to steric repulsion and exhibited no aggregation. The release of 6-MP was found to be 18-25% of administered dose in 24 h. and followed a mixed profile for stealth lipospheres. The percent dose remaining in plasma was found to be high even after 24 h as compared to control, indicating an increase in circulation time of lipospheres. Tissue accumulation of drug correlated with the pharmacokinetic behavior of lipospheres. The system seems to be an ideal carrier for anticancer drug delivery.