Manganese Potentiates In Vitro Production of Proinflammatory Cytokines and Nitric Oxide by Microglia Through a Nuclear Factor kappa B-Dependent Mechanism

Abstract

Recent evidence suggests that the mechanism of manganese (Mn) neurotoxicity involves activation of microglia and/or astrocytes; as a consequence, neurons adjacent to the activated microglia may be injured. Mn modulation of proinflammatory cytokine expression by microglia has not been investigated. Therefore, the objectives of this research were to (1) assess whether Mn induces proinflammatory cytokine expression and/or modulates lipopolysaccharide (LPS)-induced expression of proinflammatory cytokines and (2) investigate possible mechanisms for such an induction. N9 microglia were exposed in vitro to increasing concentrations (50-1000 microM) of Mn in the presence or absence of LPS (10, 100, or 500 ng/ml). After various incubation times (up to 48 h), media levels of several cytokines and nitric oxide (NO) were determined, as was the expression of the inducible form of NO synthase (iNOS). Lactate dehydrogenase (LDH) release into the medium and the cellular uptake of Neutral Red were used as general measures for cytotoxicity. In the absence of LPS, Mn moderately increased interleukin-6 and tumor necrosis factor alpha (TNF-a) production only at higher Mn concentrations, which were cytotoxic. At all LPS doses, however, proinflammatory cytokine production was dose-dependently increased by Mn. Similarly, LPS-induced NO production and iNOS expression were substantially enhanced by Mn. Pharmacological manipulations indicated that nuclear factor kappa B (NFkappaB) activation is critical for the observed enhancement of cytokine and NO production. Within the context of inflammation, increased production of proinflammatory cytokines and NO by Mn could be an important part of the mechanism by which Mn exerts its neurotoxicity.

Glucagon-like peptide-1 inhibits adipose tissue macrophage infiltration and inflammation in an obese mouse model of diabetes

“…Reduction of NF-κB, ERK1/2 and JNK activation in adipose tissue of rAd-GLP-1-treated mice Activation of NF-κB is involved mainly in the expression of inflammatory responsive genes such as Il6 and Tnfa [20,21]. As pro-inflammatory cytokine production is reduced by rAd-GLP-1 treatment, we used EMSA to examine the activation of NF-κB in epididymal fat at 2 weeks after rAd-GLP-1 treatment.…”

Manganese and its Role in Parkinson’s Disease: From Transport to Neuropathology

“…Mn enhances the release of inflammatory cytokines interleukin-6 and TNF-α from microglial cells (Chang and Liu 1999;Filipov et al 2005) that can promote the activation of astrocytes and subsequent release of inflammatory mediators such as prostaglandin E2 and nitric oxide (NO) Hirsch et al 1998;Spranger et al 1998). Mn also strongly potentiates NO production in cytokine-stimulated astrocytes, leading to apoptosis in co-cultured neurons Spranger et al 1998;Tjalkens et al 2008).…”

“…This observation is supported by studies demonstrating increased expression of NOS2 in activated astrocytes surrounding degenerating neurons in the striatum and globus pallidus of Mn-treated mice . Mn also enhances the capacity of bacterial lipopolysaccharide to promote NO production in both astroglial (Barhoumi et al 2004) and microglial (Filipov et al 2005) cells. Low concentrations of Mn can increase the capacity of TNF-α, interferon-γ, and IL-1β to induce expression of NOS2 and production of NO in astrocytes by promoting activation of the transcription factor NF-κB (Liu et al 2005;Spranger et al 1998).…”

Inhibition of Lipopolysaccharide Activation of Kupffer Cells by Transition Metals

“…The studies showing pretreatment with Mn++ increased survival of rats treated with endotoxin supports this idea [7]. Manganese is neurotoxic and studies have shown that it affects microgilia by increasing the production of pro-inflammatory cytokines and nitric oxide [17]. However, another example showed that Zinc pretreatment of mice attenuates TNF-α production and reduces liver injury caused by alcohol [18].…”