Substance P Upregulates LTB4 in Rat Adherent Macrophages from Granuloma Induced by KMnO4

Substance P (SP) is an important neuropeptide involved in neurogenic inflammation and most of its pathophysiological functions are mediated through binding to the neurokinin-1 receptor. SP exerts various proinflammatory actions on immune-cells, including macrophages. Several compounds such as cytokines have the capacity to activate and stimulate macrophages to produce arachidonic acid oxygenation and lipoxygenation products. Leukotriene B4 (LTB4) is one of the most important mediators of leukocyte activation in acute and chronic inflammatory reactions. LTB4 stimulates chemotaxis, lysosomal enzyme release, and cell aggregation. In this report, we studied the effect of SP on rat adherent granuloma macrophages (RAGMs). The chronic granuloma in rat was induced by dorsal injections of a potassium permanganate (KMnO4) saturated crystal solution (200 mu l of a 1:40 dilution). After 7 days, all rats developed a subcutaneous granuloma in the injection site from which infiltrated macrophages were extracted, isolated, and cultured in vitro. We tested the hypothesis that SP stimulates the production of LTB4 in RAGMs and increases lipoxygenase expression. Here we show that the cell-free supernatant of RAGMs stimulated with SP (10 mu M), resulted in statistically significant increases of LTB4. Preincubation of RAGMs with NDGA (nordihydroguaiaretic acid (10 mu M), completely abolished the production of LTB4 in the supernatants and lipoxygenase expression on RAGMs challenged with SP, or the cation ionophore A23187 (positive control). Similar effects were obtained when the cells were pretreated with dexamethasone (10 mu M). Our results suggest that SP is able to stimulate the release of LTB4 and lipoxygenase expression in macrophages from chronic inflammatory granuloma and provide further evidence for a neuroinflammatory pathway.