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Introduction: 1-Methylnicotinamide (MNA), a major metabolite of nicotinamide (NA), is known to exert anti-inflammatory effects in vivo. Treatment of inflammatory skin diseases by topical application of MNA provides certain advantages over the use of NA. However, in contrast to NA, the molecular mechanisms of the anti-inflammatory properties of MNA are not well known. In this study the influence of exogenous MNA and NA in vitro on the generation of inflammatory mediators by macrophages (Mφ) was investigated. Materials and Methods: Peritoneal Mφ of CBA/J mice were activated in vitro with lipopolysaccharide and incubated with MNA or NA. The effect of these compounds on biological functions of Mφ was measured by evaluation of the production of reactive oxygen species (ROS) by luminol-dependent chemiluminescence, cytokines and prostaglandin E 2 (PGE 2 ) by ELISA, and nitric oxide (NO) by the Griess method. Moreover, the expressions of inducible NO synthase and cyclooxygenase-2 were measured by Western blotting. Results: It was shown that at non-cytotoxic concentrations, NA inhibits the production of a variety of pro-inflammatory agents, such as tumor necrosis factor α, interleukin 6, NO, PGE 2 , and the generation of ROS. In contrast to NA, exogenous MNA inhibited only the generation of ROS, while its effect on the synthesis of other mediators was negligible. Conclusions: These results indicate that the anti-inflammatory properties of MNA demonstrated previously in vivo do not depend on its capacity to suppress the functions of immune cells, but more likely may be related to its action on vascular endothelium. The authors suggest that the limited permeability for exogenous MNA, in contrast to that for NA, may be responsible for its lack of suppressor activity against Mφ.

Chronic active colitis (including inflammatory bowel disease - IBD) is maintained by a variety of pro-inflammatory mediators. Certain intestinal bacterial strains may induce colitis, whereas some strains (e.g. Lactobacillus spp.) show a protective effect in colitis owing to their anti-inflammatory activity. In this study, we have examined the production of selected inflammatory cytokines, reactive oxygen species (ROS), nitric oxide (NO) and the expression of haeme oxygenase-1 (HO-1) by murine peritoneal macrophages stimulated in vitro by the intestinal bacterial strains, isolated from mice with colitis. Lactobacillus strains (Lactobacillus reuteri, L. johnsonii, L. animalis/murinus) and two potentially pathogenic bacteria (Escherichia coli and Enterococcus faecalis) induced the production of substantial amounts of cytokines with a strain specific profile. Despite some interstrain differences, all lactobacilli induced production of anti-inflammatory cytokines (IL-10(high), IL-6(low), IL-12p70(low)). Conversely, E. faecalis and E. coli induced the production of proinflammatory cytokines (TNF-alpha, IL-12p70), the cytokines essential for chronic IBD. Macrophages released comparably substantial amounts of ROS in response to all Lactobacillus strains tested, while E. coli and E. faecalis ability to induce generation of ROS was negligible. In contrast to ROS, the production of NO/NO(2) (-) by macrophages activated with all bacterial strains tested was similar. Moreover, for the first time, it has been shown that intestinal bacteria differed in their ability to induce expression of HO-1, a stress-inducible enzyme with antioxidant and anti-inflammatory properties. The beneficial immunoregulatory properties of candidate probiotic bacteria for the treatment of IBD are discussed.

Summary Leukotriene B4 (LTB4) and cysteinyl leukotrienes (CysLTs) are known as potent mediators of inflammation, whereas their role in the regulation of adaptive immunity remains poorly characterized. Dendritic cells (DCs) are specialized antigen‐presenting cells, uniquely capable to initiate primary immune responses. We have found that zymosan, but not lipopolysaccharide (LPS) stimulates murine bone marrow‐derived dendritic cells (BM‐DCs) to produce large amounts of CysLTs and LTB4 from endogenous substrates. A selective inhibitor of leukotriene synthesis MK886 as well as an antagonist of the high affinity LTB4 receptor (BLT1) U‐75302 slightly inhibited zymosan‐, but not LPS‐stimulated interleukin (IL)‐10 release from BM‐DCs. In contrast, U‐75302 increased zymosan‐stimulated release of IL‐12 p40 by ∼23%. Pre‐treatment with transforming growth factor‐β1 enhanced both stimulated leukotriene synthesis and the inhibitory effect of U‐75302 and MK886 on IL‐10 release from DCs. Consistent with the effects of leukotriene antagonists, exogenous LTB4 enhanced LPS‐stimulated IL‐10 release by ∼39% and inhibited IL‐12 p40 release by ∼22%. Both effects were mediated by the BLT1 receptor. Ligands of the high affinity CysLTs receptor (CysLT1), MK‐571 and LTD4 had little or no effect on cytokine release. Agonists of the nuclear LTB4 receptor peroxisome proliferator‐activated receptor‐α, 8(S)‐hydroxyeicosatetraenoic acid and 5,8,11,14‐eicosatetraynoic acid, inhibited release of both IL‐12 p40 and IL‐10. Our results indicate that both autocrine and paracrine leukotrienes may modulate cytokine release from DCs, in a manner that is consistent with previously reported T helper 2‐polarizing effects of leukotrienes.