N Rajora

alpha-Melanocyte-stimulating hormone (alpha-MSH) is a potent inhibitory agent in all major forms of inflammation. To identify a potential mechanism of antiinflammatory action of alpha-MSH, we tested its effects on production of nitric oxide (NO), believed to be a mediator common to all forms of inflammation. We measured NO and alpha-MSH production in RAW 264.7 cultured murine macrophages stimulated with bacterial lipopolysaccharide and interferon gamma. alpha-MSH inhibited production of NO, as estimated from nitrite production and nitration of endogenous macrophage proteins. This occurred through inhibition of production of NO synthase II protein; steady-state NO synthase II mRNA abundance was also reduced. alpha-MSH increased cAMP accumulation in RAW cells, characteristic of alpha-MSH receptors in other cell types. RAW cells also expressed mRNA for the primary alpha-MSH receptor (melanocortin 1). mRNA for proopiomelanocortin, the precursor molecular of alpha-MSH, was expressed in RAW cells, and tumor necrosis factor alpha increased production and release of alpha-MSH. These results suggest that the proinflammatory cytokine tumor necrosis factor alpha can induce macrophages to increase production of alpha-MSH, which then becomes available to act upon melanocortin receptors on the same cells. Such stimulation of melanocortin receptors could modulate inflammation by inhibiting the production of NO. The results suggest that alpha-MSH is an autocrine factor in macrophages which modulates inflammation by counteracting the effects of proinflammatory cytokines.

alpha-Melanocyte-stimulating hormone (alpha-MSH), a tridecapeptide derived from pro-opiomelanocortin, has potent antiinflammatory activity in laboratory animals. alpha-MSH inhibits nitric oxide production by murine macrophages, an influence believed to reflect activation of an autocrine circuit in these cells, one that is based on production and release of alpha-MSH and subsequent stimulation of melanocortin receptors. We found that THP-1 cells, human monocytic cells, produced alpha-MSH; this production was increased by interleukin-6, tumor necrosis factor a, or concanavalin A. These cells also expressed the gene for the human alpha-MSH receptor MC1. Unlike murine macrophages, THP-1 cells produced little nitrite in response to interferon-gamma (IFN-gamma) and lipopolysaccharide, and a-MSH inhibited this production only slightly. However, production of neopterin, a presumed primate homologue of nitric oxide in lower animals, was increased in THP-1 cells stimulated with INF-gamma plus TNF-alpha and alpha-MSH significantly inhibited this production. The evidence indicates that an autocrine regulatory circuit based on alpha-MSH occurs in human monocyte/macrophages much as in murine macrophages. alpha-MSH-induced modulation of specific inflammatory mediators/cytotoxic agents appears to differ depending on the importance of the mediators in the myelomonocytic cells of different species.

Tumor necrosis factor (TNF-alpha) underlies pathological processes and functional disturbances in acute and chronic neurological disease and injury. The neuroimmunomodulatory peptide alpha-MSH modulates actions and production of proinflammatory cytokines including TNF-alpha, but there is no prior evidence that it alters TNF-alpha induced within the brain. To test for this potential influence of the peptide, TNF-alpha was induced centrally by local injection of bacterial lipopolysaccharide (LPS). alpha-MSH given once i.c.v. with LPS challenge, twice daily intraperitoneally (i.p.) for 5 d between central LPS injections, or both i.p. and centrally, inhibited production of TNF-alpha within brain tissue. Inhibition of TNF-alpha protein formation by alpha-MSH was confirmed by inhibition of TNF-alpha mRNA. Plasma TNF-alpha concentration was elevated markedly after central LPS, indicative of an augmented peripheral host response induced by the CNS signal. The increase was inhibited by alpha-MSH treatments, in relation to inhibition of central TNF-alpha. Presence within normal mouse brain of mRNA for the alpha-MSH receptor MC-1 suggests that the inhibitory effects of alpha-MSH on brain and plasma TNF-alpha might be mediated by this receptor subtype. The inhibitory effect of alpha-MSH on brain TNF-alpha did not depend on circulating factors because the effect also occurred in brain tissue in vitro. This indicates that alpha-MSH can act directly on brain cells to inhibit their production of TNF-alpha. If central TNF-alpha contributes to pathology in CNS disease and injury, and promotes inflammation in the periphery, agents that act on brain alpha-MSH receptors should decrease the pathological TNF-alpha reaction and promote tissue survival.

The hypothesis that macrophages contain an autocrine circuit based on melanocortin [ACTH and alpha-melanocyte-stimulating hormone (alpha-MSH)] peptides has major implications for neuroimmunomodulation research and inflammation therapy. To test this hypothesis, cells of the THP-1 human monocyte/macrophage line were stimulated with lipopolysaccharide (LPS) in the presence and absence of alpha-MSH. The inflammatory cytokine tumor necrosis factor (TNF)-alpha was inhibited in relation to alpha-MSH concentration. Similar inhibitory effects on TNF-alpha were observed with ACTH peptides that contain the alpha-MSH amino acid sequence and act on melanocortin receptors. Nuclease protection assays indicated that expression of the human melanocortin-1 receptor subtype (hMC-1R) occurs in THP-1 cells; Southern blots of RT-PCR product revealed that additional subtypes, hMC-3R and hMC-5R, also occur. Incubation of resting macrophages with antibody to hMC-1R increased TNF-alpha concentration; the antibody also markedly reduced the inhibitory influence of alpha-MSH on TNF-alpha in macrophages treated with LPS. These results in cells known to produce alpha-MSH at rest and to increase secretion of the peptide when challenged are consistent with an endogenous regulatory circuit based on melanocortin peptides and their receptors. Targeting of this neuroimmunomodulatory circuit in inflammatory diseases in which myelomonocytic cells are prominent should be beneficial.

Paraquat is a salt widely used as a herbicide. Although paraquat poisoning is rare in the general population, it may be considered as one of the most toxic poisons frequently used for suicide attempts, and is associated with serious complications including: acute kidney injury,pneumonitis and death. We report a fatal case of a16 year old girl who presented with dysphagia, cough and dyspnoea following ingestion of paraquat. She subsequently developed acute kidney injury (AKI) that resolved but she succumbed to respiratory complications despite use of antibiotics, corticosteroids and haemodialysis.Key words: Paraquat poisoning, Acute Kidney Injury, Haemodialysis, Pneumonitis.