Inhibition of leukotriene biosynthesis abrogates the host control of Mycobacterium tuberculosis

Differential kinase requirement for enhancement of Fc gammaR-mediated phagocytosis in alveolar macrophages by leukotriene B4 vs. D4

In alveolar macrophages, leukotriene (LT) B(4) and cysteinyl LTs (LTC(4), LTD(4) and LTE(4)) both enhance Fc gamma receptor (Fc gammaR)-mediated phagocytosis. In the present study we investigated the role of specific PKC isoforms (PKC-alpha and -delta), the MAP kinases p38 and ERK 1/2, and PI3K in mediating the potentiation of Fc gammaR-mediated phagocytosis induced by addition of leukotrienes to the AMs. It was found that exogenously added LTB(4) and LTD(4) both enhanced PKC-delta and -alpha phosphorylation during Fc gammaR engagement. Studies with isoform-selective inhibitors indicated that exogenous LTB(4) effects were dependent on both PKC-alpha and -delta, while LTD(4) effects were exclusively due to PKC-delta activation. Although both exogenous LTB(4) and LTD(4) enhanced p38 and ERK 1/2 activation, LTB(4) required only ERK 1/2, while LTD(4) required only p38 activation. Activation by both LTs was dependent on PI3K activation. Effects of endogenous LTs on kinase activation were also investigated using selective LT receptor antagonists. Endogenous LTB(4) contributed to Fc gammaR-mediated activation of PKC-alpha, ERK 1/2 and PI3K, while endogenous cysLTs contributes to activation of PKC-delta, p38 and PI3K. Taken together, our data show that the capacities of LTB(4) and LTD(4) to enhance Fc gammaR-mediated phagocytosis reflect their differential activation of specific kinase programs.

Cyclooxygenase (COX) and 5-lipoxygenase (5-LOX) selectivity of COX inhibitors

In vitro evaluations of the selectivity of COX inhibitors are based on a great variety of experimental protocols. As a result, data available on cyclooxygenase (COX)-1/COX-2/5- lipoxygenase (LOX) selectivity of COX inhibitors lack consistency. We, therefore, performed a systematic analysis of the COX-1/COX-2/5-LOX selectivity of 14 compounds with selective COX inhibitory activity (Coxibs). The compounds belonged to different structural classes and were analyzed employing the well-recognized whole-blood assay. 5-LOX activity was also tested on isolated human polymorphonuclear leukocytes. Among COX inhibitors, celecoxib and ML-3000 (licofelone) inhibited 5-LOX in human neutrophils at micromolar ranges. Surprisingly, ML-3000 had no effect on 5-LOX product synthesis in whole-blood assay. In addition, we could show that inhibition of COX pathways did not increase the transformation of arachidonic acid by the 5-LOX pathway.