Search

Human exposure to relatively low levels of methylmercury is worrying, especially in terms of its genotoxicity. It is currently unknown as to whether exposure to low levels of mercury (below established limits) is safe. Genotoxicity was already shown in lymphocytes, but studies with cells of the CNS (as the main target organ) are scarce. Moreover, disturbances in the cell cycle and cellular proliferation have previously been observed in neuronal cells, but no data are presently available for glial cells. Interestingly, cells of glial origin accumulate higher concentrations of methylmercury than those of neuronal origin. Thus, the aim of this work was to analyze the possible genotoxicity and alterations in the cell cycle and cell proliferation of a glioma cell line (C6) exposed to a low, non-lethal and non-apoptotic methylmercury concentration. Biochemical (mitochondrial activity) and morphological (integrity of the membrane) assessments confirmed the absence of cell death after exposure to 3 μM methylmercury for 24 hours. Even without promoting cell death, this treatment significantly increased genotoxicity markers (DNA fragmentation, micronuclei, nucleoplasmic bridges and nuclear buds). Changes in the cell cycle profile (increased mitotic index and cell populations in the S and G2/M phases) were observed, suggesting arrest of the cycle. This delay in the cycle was followed, 24 hours after methylmercury withdrawal, by a decrease number of viable cells, reduced cellular confluence and increased doubling time of the culture. Our work demonstrates that exposure to a low sublethal concentration of MeHg considered relatively safe according to current limits promotes genotoxicity and disturbances in the proliferation of cells of glial origin with sustained consequences after methylmercury withdrawal. This fact becomes especially important, since this cellular type accumulates more methylmercury than neurons and displays a vital role protecting the CNS, especially in chronic intoxication with this heavy metal., Competing Interests: The authors have declared that no competing interests exist.

Neuroglia interactions are essential for the nervous system and in the retina Müller cells interact with most of the neurons in a symbiotic manner. Glutathione (GSH) is a low-molecular weight compound that undertakes major antioxidant roles in neurons and glia, however, whether this compound could act as a signaling molecule in neurons and/or glia is currently unknown. Here we used embryonic avian retina to obtain mixed retinal cells or purified Müller glia cells in culture to evaluate calcium shifts induced by GSH. A dose response curve (0.1-10 mM) showed that 5-10 mM GSH, induced calcium shifts exclusively in glial cells (later labeled and identified as 2M6 positive cells), while neurons responded to 50 mM KCl (labeled as βIII tubulin positive cells). BBG 100 nM, a P2X7 blocker, inhibited the effects of GSH on Müller glia. However, addition of DNQX 70 μM and MK-801 20 μM, non-NMDA and NMDA blockers, had no effect on GSH calcium induced shift. Oxidized glutathione (GSSG) at 5 mM failed to induce calcium mobilization in glia cells, indicating that the antioxidant and/or structural features of GSH are essential to promote elevations in cytoplasmic calcium levels. Indeed, a short GSH pulse (60s) protects Müller glia from oxidative damage after 30 min of incubation with 0.1% H2O2. Finally, GSH induced GABA release from chick embryonic retina, mixed neuron-glia or from Müller cell cultures, which were inhibited by BBG or in the absence of sodium. GSH also induced propidium iodide uptake in Müller cells in culture in a P2X7 receptor dependent manner. Our data suggest that GSH, in addition to antioxidant effects, could act signaling calcium shifts at the millimolar range particularly in Müller glia, and could regulate the release of GABA, with additional protective effects on retinal neuron-glial circuit.

Mercury is an extremely dangerous environmental contaminant responsible for episodes of human intoxication throughout the world. Methylmercury, the most toxic compound of this metal, mainly targets the central nervous system, accumulating preferentially in cells of glial origin and causing oxidative stress. Despite studies demonstrating the current exposure of human populations, the consequences of mercury intoxication and concomitant use of drugs targeting the central nervous system (especially drugs used in long-term treatments, such as analgesics) are completely unknown. Morphine is a major option for pain management; its global consumption more than quadrupled in the last decade. Controversially, morphine has been proposed to function in oxidative stress independent of the activation of the opioid receptors. In this work, a therapeutic concentration of morphine partially protected the cellular viability of cells from a C6 glioma cell line exposed to methylmercury. Morphine treatment also reduced lipid peroxidation and totally prevented increases in nitrite levels in those cells. A mechanistic study revealed no alteration in sulfhydryl groups or direct scavenging at this opioid concentration. Interestingly, the opioid antagonist naloxone completely eliminated the protective effect of morphine against methylmercury intoxication, pointing to opioid receptors as the major contributor to this action. Taken together, the experiments in the current study provide the first demonstration that a therapeutic concentration of morphine is able to reduce methylmercury-induced oxidative damage and cell death by activating the opioid receptors. Thus, these receptors may be a promising pharmacological target for modulating the deleterious effects of mercury intoxication. Although additional studies are necessary, our results support the clinical safety of using this opioid in methylmercury-intoxicated patients, suggesting that normal analgesic doses could confer an additional degree of protection against the cytotoxicity of this xenobiotic.

Kojic acid (KA) is a fungal metabolite used as a topical treatment skin-whitening cosmetic agent for melasma in humans; however its potential as an anti-leishmanial agent is unknown. Chemotherapy is one of the most effective treatments for Leishmaniasis. However, the drugs available are expensive, invasive, require long-term treatment and have severe side effects. Thus, the development of new effective leishmanicidal agents is a necessity. In this study we investigated the anti-leishmanial effect of KA on L. amazonensis, following in vitro and in vivo infections. KA (50 μg/mL) was found to decrease the growth by 62% (IC50 34 μg/mL) and 79% (IC50 27.84 μg/mL) of promastigotes and amastigotes in vitro, respectively. Ultrastructural analysis of KA-treated amastigotes showed the presence of vesicles bodies into the flagellar pocket, and an intense intracellular vacuolization and swelling of the mitochondrion. During the in vitro interaction of parasites and the host cell, KA reverses the superoxide anions (O2-) inhibitory mechanism promoted by parasite. In addition, 4 weeks after KA-topical formulation treatment of infected animals, a healing process was observed with a high production of collagen fibers and a decrease in parasite burden. Thus, these results demonstrated the great potential of KA as an anti-leishmanial compound.