Michael R. Quinn

The production of superoxide anion and nitric oxide by cultured murine leukocytes and the accumulation of TNF-α in the conditioned media is inhibited by taurine chloramine

Taurine chloramine (Tau-Cl) inhibits production of nitric oxide (NO) by activated peritoneal macrophages and attenuates accumulation of tumor necrosis factor-alpha (TNF-alpha) in the culture media, similar to that previously reported for activated RAW 264.7 cells. In addition, the effect of Tau-Cl and taurine on superoxide anion (O2-) production in murine peritoneal exudate polymorphonuclear leukocytes (PMN) was examined. Tau-Cl inhibited O2- production in a manner that was dose-dependent and reversible. Taurine also inhibited O2- production by stimulated PMN, but at higher concentrations and to a lesser extent than Tau-Cl. The effects of taurine on O2- production was attributed to the in vitro formation of Tau-Cl catalyzed by PMN associated halide-dependent myeloperoxidase. In contrast, production of NO by activated peritoneal macrophages and accumulation of TNF-alpha in the media was inhibited by Tau-Cl while taurine was without effect. These data lend support to the notion that Tau-Cl may participate in the inflammatory response by modulating production of inflammatory mediators.

Taurine protects against oxidant-induced lung injury: possible mechanism(s) of action.

It is thought that oxidant-induced tissue damage is not a direct effect of the oxidant per se, but rather results from the inflammatory response that occurs thereafter. As a result of inflammation following oxidant exposure, there are neutrophils, monocytes, and macrophages with myeloperoxidase-H2O2-halide activity in the lung. Leukocytes and especially neutrophils contain high intracellular concentrations (22-50mM) of taurine (6, 8, 11, 20). Taurine acts as a trap for toxic hypochlorous acid (HOCl) and forms the less reactive metabolite, N-chlorotaurine (5-6). Thus, the biological activity of halide-dependent myeloperoxidase may be regulated by endogenous taurine. Although taurine had no effect in the present study, polymorphonuclear leukocytes have an active myeloperoxidase system capable of producing N-chlorotaurine (9, 19) and would be present at the site of inflammation in oxidant-exposed lungs. Our data suggest that taurine via N-chlorotaurine formation may protect the lung from oxidant injury, at least in part, by inhibiting production of nitrite and TNF-alpha. Moreover, lavage cells isolated from rats pretreated with taurine and exposed to O3 have a significant decrease in the production of nitrite and TNF-alpha, compared with lavage cells from rats exposed to O3 without taurine supplementation (preliminary studies). Both the concentration of taurine and the effects of N-chlorotaurine strengthen the potential impact of this chlorinated amine in vivo. N-Chlorotaurine may protect against oxidant-induced lung injury by inhibiting production of nitrite and the release of TNF-alpha which are both known to be directly linked to tissue injury.

Taurine Chloramine Inhibits the Production of Superoxide Anion, IL-6 and IL-8 in Activated Human Polymorphonuclear Leukocytes

Polymorphonuclear leukocytes (PMN) are the initial cells recruited to the site of inflammation where foreign invaders such as microorganisms, toxic gases and chemicals elicit an inflammation reaction4,6,12. Activated PMN produce various oxygen and hydroxyl radicals which kill bacteria and fungi but may also induce indiscriminate cellular damage14. For example, HOCl/OCl- produced by the halide-dependent myeloperoxidase of PMN is highly toxic. Taurine attenuates the damage caused by HOCl/OCl- by forming taurine chloramine (Tau-Cl), a relatively non-toxic and long-lived oxidant7,9,13,15. Previously we demonstrated that Tau-Cl suppressed the production of nitric oxide (NO), tumor necrosis factor-α (TNF-α) and prostaglandin E2 (PGE2) in activated murine peritoneal macrophages and/or RAW 264.7, a murine macrophage cell line8,10,11. Tau-Cl also inhibits the production of superoxide anion in activated murine peritoneal PMN5. Since human PMN produce Tau-Cl by halide-dependent myeloperoxidase, we investigated the effect of Tau-Cl on the production of various cytokines and superoxide anion by activated human PMN. In this report we demonstrate that Tau-Cl down-regulates the production of superoxide anion, IL-6 and IL-8 by activated human PMN.

Taurine chloramine inhibits prostaglandin E2 production in activated raw 264.7 cells by post-transcriptional effects on inducible cyclooxygenase expression

Taurine chloramine (Tau-Cl) was recently demonstrated to inhibit production of nitric oxide and tumor necrosis factor-alpha (TNF-alpha) by activated macrophages. Since increased production of prostaglandin E2 (PGE2), a reaction catalyzed by induction of cyclooxygenase-2 (COX-2), is also associated with the inflammatory response, we determined the effects of Tau-Cl on PGE2 production and on expression of COX-2 protein and COX-2 mRNA in activated RAW 264.7 cells, a murine macrophage-like cell line. Tau-Cl inhibited production of PGE2 in a concentration dependent manner with an IC50 of 0.4 mM. The decrease in PGE2 production was largely accounted for by decreased expression of COX-2 protein. Although the kinetics of COX-2 mRNA expression was altered in Tau-Cl treated cells, mRNA expression appeared to be quantitatively unimpaired. These results suggest that Tau-Cl affects the post-transcriptional regulation of COX-2 expression and support the idea that Tau-Cl may function as an inhibitory modulator of the inflammatory response.

Chemokine production by rat alveolar macrophages is inhibited by taurine chloramine

Taurine protects lung tissue from oxidant-induced damage in a variety of models that involve inflammation as a pathogenic feature. The mechanism of taurine protection is thought to be related to the formation and subsequent action of taurine chloramine (Tau-Cl). Tau-Cl results from the activity of a halide-dependent myeloperoxidase system associated with neutrophils. Since chemokines are secreted by activated alveolar macrophages and are prominently involved in propagating the inflammatory response in lung, we determined the effects of Tau-Cl on MCP-1 and MIP-2 production in NR8383, a cloned cell line derived from rat alveolar macrophages. Activation of NR8383 cells with LPS and IFN-gamma resulted in accumulation of MCP-1 and MIP-2 in the conditioned media over the following 24-h and this was inhibited by Tau-Cl in a concentration dependent fashion. Northern blot analyses of MCP-1 and MIP-2 mRNA expression revealed concentration dependent inhibition by Tau-Cl. Expression of MCP-1 transcripts was more potently inhibited by Tau-Cl relative to that of MIP-2. Since the promoter regions of these chemokine genes are regulated by NF-kappaB, nuclear protein extracts were evaluated for NF-kappaB binding to its sequence specific recognition site (EMSA). Tau-Cl treated cells expressed reduced nuclear NF-kappaB binding relative to the activated control cells. The composition of the NF-kappaB dimer contained predominately p50 and p65 subunits, but some c-Rel was also present. These results suggest that Tau-Cl inhibits production of chemokines by activated NR8383 cells through a mechanism that involves, in part, the NF-kappaB signaling pathway.

Monocyte chemoattractant protein-1 and macrophage inflammatory protein-2 production is inhibited by taurine chloramine in rat C6 glioma cells

Taurine monochloramine (Tau-Cl) is formed through the actions of a halide-dependent myeloperoxidase system associated with polymorphonuclear leukocytes (PMN). Tau-Cl inhibits production of inflammatory mediators by activated macrophages, and PMN. Recently, Tau-Cl was shown to inhibit production of nitric oxide and prostaglandin E2 by activated C6 glioma cells. Since chemokines, secreted by activated glial cells, play a prominent role in eliciting inflammatory responses in the central nervous system, the effects of Tau-Cl on production of monocyte chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-2 (MIP-2) were determined in activated C6 glioma cells. Tau-Cl inhibited production of MCP-1 and MIP-2 in a concentration-dependent manner, and was most potent against MCP-1. Tau-Cl exerted a transient inhibition of the temporal expression of MCP-1 and MIP-2 mRNAs during the first 4 h of activation. Although both chemokine mRNA levels were similar to those of control cells after 8-24 h of activation, production of the chemokine proteins, especially MCP-1, remained markedly low. These results suggest that Tau-Cl inhibits production of MCP-1 and MIP-2 in activated C6 cells primarily through post-transcriptional mechanisms.

Production of Nitric Oxide by Activated Microglial Cells Is Inhibited by Taurine Chloramine

Microglia are considered to be brain resident macrophages and along with astrocytes are the major immunoresponsive cells in the CNS1,2. When activated by bacterial endotoxin or cytokines, microglia respond rapidly by proliferating, changing morphology, and by producing proinflammatory cytokines and NO2-4. Although transient activation of microglia contributes to brain repair processes, chronic activation as occurs in CNS viral infections5, AIDS dementia complex6, Alzheimer’s disease7, multiple sclerosis8,9, traumatic injury, and stroke, leads to neuronal cell death as a result of inflammation and oxidative stress2,4,10 Production of nitric oxide is of particular importance in the pathology of several CNS disorders because of the toxicity of its byproducts, e.g. peroxynitrite. The increased production of NO by activated microglia results primarily from increased expression of the iNOS gene. The therapeutic potential of downregulating activation of microglia and/or production of NO may be of significant clinical value in developing strategies for treatment of neurodegeneative diseases.