Toxicity of manganese metallodrugs toward Danio rerio

Mn(III) O^N^O Complexes as Water-tolerant and Environmentally Benign Catalysts for Polyurethane Foam Synthesis

Polyurethanes are synthesized on industrial scale by the reaction of diisocyanates with diols in the presence of catalysts which are commonly based on tin complexes and amines. However, due to the toxicity and volatility of these tin catalysts and amines, there is the need to develop new catalysts that are more environmentally benign. Herein, we report the synthesis of O^N^O pincer-ligated Mn(III) and Fe(III) complexes that serve as suitable catalysts for urethane formation and are stable to hydrolysis as predicted by computations and observed experimentally. The O^N^O pincer scaffold is vital to the activity of these catalysts, simultaneously ensuring increased solubility in the reaction medium as well as providing a stable framework upon dissociation of co-ligands in the catalytic cycle. In silico mechanistic investigations for urethane formation show that the stabilization of active species in square-planar geometries enabled by these O^N^O ligands permit the simultaneous coordination of alcohol and isocyanate in suitable configuration at the metal center.

Manganese Exposure Induces Cellular Aggregates and the Accumulation of β-Catenin in Skin of Zebrafish Embryos

The effects of manganese (Mn) toxicity in different organs and tissues in humans and other vertebrates have been studied since the beginning of the past century, but most of its cellular effects remain largely unknown. In this study, we studied the effects of Mn in zebrafish, at the cellular level, due to the transparent nature of zebrafish larvae that enables a powerful analysis under the light microscope. The collection of our results shows that environmental concentrations of 0.5 mg/L affect swim bladder inflation; at concentration of 50 and 100 mg/L Mn (1) induces alterations in viability, swim bladder, heart, and size of zebrafish larvae, (2) induces an increase in melanocyte area and the formation of cellular aggregates in the skin, and (3) induces an accumulation of β-Catenin in mesenchymal cells in the caudal fin of zebrafish larvae. Our data suggest that increased levels of Mn induce cell aggregate formation in the skin and the presence of more melanocytes in the zebrafish caudal fin. Interestingly, the adhesion protein β-Catenin was activated in mesenchymal cells near the cell aggregates. These results open important new questions on the role of Mn toxicity on cellular organization and β-Catenin responses in fishes.

Effects of low-dose methylcyclopentadienyl manganese tricarbonyl-derived manganese on the development of diencephalic dopaminergic neurons in zebrafish

Fuel additive methylcyclopentadienyl manganese tricarbonyl (MMT) is counted as an organic manganese (Mn)-derived compound. The toxic effects of Mn (alone and complexed) on dopaminergic (DA) neurotransmission have been investigated in both cellular and animal models. However, the impact of environmentally relevant Mn exposure on DA neurodevelopment is rather poorly understood. In the present study, the MMT dose of 100 μM (about 5 mg Mn/L) caused up-regulation of DA-related genes in association with cell body swelling and increase in the number of DA neurons of the ventral diencephalon subpopulation DC2. Furthermore, our analysis identified significant brain Mn bioaccumulation and enhancement of total dopamine levels in association with locomotor hyperactivity. Although DA levels were restored at adulthood, we observed a deficit in the acquisition and consolidation of memory. Collectively, these findings suggest that developmental exposure to low-level MMT-derived Mn is responsible for the selective alteration of diencephalic DA neurons and with long-lasting effects on fish explorative behaviour in adulthood.

Health risk estimation of metals bioaccumulated in commercial fish from coastal areas and rivers in Bangladesh

Metal contaminations in commercial fish have become a great public health concern worldwide including Bangladesh. The current study was conducted to provide preliminary evidence of nine metals in three commercially significant fish namely Pampus argenteus, Sardinella longiceps and Tenualosa ilisha collected from four coastal stations- Kuakata, Pathorghata, Cox's Bazar, and Pirojpur, and eight stations of five rivers- Padma, Meghna, Jamuna, Katcha, and Nobogonga in Bangladesh. High magnitudes of Pb (0.74-4.59 mg/kg ww), Cd (0.07-0.24 mg/kg ww), and Mn (0.45-2.03 mg/kg ww) were recorded in the sampling stations that exceeded the maximum permissible limits (MPL) proposed by different recognized organizations. Significant mean differences of metal concentrations were observed (p < 0.05) between species and stations. In fish samples, excessive metals accumulations were recorded from Kuakata (St.1) at the coastal area, and Nobogonga (St. 12) among the rivers. The health risk assessment (HRA) was carried out comprehensively via the estimated daily intake (EDI), target hazard quotient (THQ), hazard index (HI), and target cancer risk (TR) calculations. The outcomes of EDI, THQ, and HI suggest that chronic exposure to towering Pb content might pose potential health threats to inhabitants particularly living in highly polluted stations of the coastal area. In addition, the massive TR values of Cd intake through fish consumption from the coastal area might create cancer risks. Accordingly, the ingestion of metals contaminated fish portends chronic as well as acute health risks to Bangladeshi people living both at home and abroad.

Assessment of selected trace metals in fish feeds, pond water and edible muscles of Oreochromis mossambicus and the evaluation of human health risk associated with its consumption in Vhembe district of Limpopo Province, South Africa

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Fish from Luvuvhu River recorded lower levels of trace metals than those from commercial fish ponds.

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Edible muscles of Oreochromis mossambicus had higher concentrations of trace metals than pond water.

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Low and moderate bioaccumulation factor (BF<5000) was recorded for most of the metals.

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There is no potential non-carcinogenic health risks from consumption of Oreochromis mossambicus in the study area.

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Cancer risk is more likely to occur in children than in adult consuming fish from the study area.

Fish is a rich source of proteins for humans and is widely consumed in various places in the world. This study assessed the levels of twenty trace metals (B, Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Mo, Cd, Sn, Sb, Ba, Hg and Pb) in fish feeds (n = 2), water (n = 27), and edible muscles of Oreochromis mossambicus (n = 20 from 8 ponds) from fish farms and Luvuvhu River (n = 3 from 1 river site) in Vhembe district of Limpopo Province, South Africa. Physicochemical parameters of water in the study area were analysed. Temperature ranged between 21.4–30.47 °C, pH: 5.59–7.28, electrical conductivity: 608–1216 μS/cm, total dissolved solids: 156–675 mg/l, dissolved oxygen: 0.28 - 0.56 mg/l, turbidity: 3.92–356.7 NTU, respectively. Levels of most trace metals such as Cr (2 μg/l and 1000 μg/kg), Mn (100 μg/l and 500 μg/kg), Fe (10 μg/l and 300 μg/kg), Ni (20 μg/l and 100 μg/kg), As (50 μg/l and 3 μg/kg), Pb (10 μg/l and 300 μg/kg) and Cu (2 μg/l and 2250 μg/kg) in water and O. mossambicus muscles were mostly below the World Health Organization (WHO), Food and Agricultural Organization (FAO)/WHO and European Commission (EC) recommended limit in the collected samples (Tshifulalani site and Duthuni site). However, Cu and Fe recorded concentration above the recommended limit at the control site (Luvuvhu River) in water and O. mossambicus muscles, respectively. Results from the bioaccumulation factor (BF), suggests the presence of metals in the water which can bioaccumulate in the fish muscles. Most of the metals (As, Cd, Hg, Mo, Sr, Sb and Sn) that recorded no possible bioaccumulation also recorded levels that complied with their maximum permissible limit (MPL) of WHO, FAO/WHO and EC guideline values in the fish feeds except for Se and Co. Moderate bioaccumulation was recorded for Cr, Mn, Fe and Zn in some of the sampling sites. Pb and Ni showed extreme bioaccumulation (BF > 5000) in one of the sampling sites and also recorded elevated levels in the fish feeds. Average daily dose (ADD), hazard quotient (HQ) and total hazard quotient (THQ) computed were less than 1. The Cancer risk (CR) evaluated were all below 10⁻⁴ except in one site for children (Tshifulanani 2) but the overall average result showed no carcinogenic health risk to the consumers of the O. mossambicus. Therefore, O. mossambicus intake in the study area should be constantly monitored to prevent future health implications.

Manganese: The overlooked contaminant in the world largest mine tailings dam collapse

Manganese (Mn) is an abundant element in terrestrial and coastal ecosystems and an essential micronutrient in the metabolic processes of plants and animals. Mn is generally not considered a potentially toxic element due to its low content in both soil and water. However, in coastal ecosystems, the Mn dynamic (commonly associated with the Fe cycle) is mostly controlled by redox processes. Here, we assessed the potential contamination of the Rio Doce estuary (SE Brazil) by Mn after the world's largest mine tailings dam collapse, potentially resulting in chronic exposure to local wildlife and humans. Estuarine soils, water, and fish were collected and analyzed seven days after the arrival of the tailings in 2015 and again two years after the dam collapse in 2017. Using a suite of solid-phase analyses including X-ray absorption spectroscopy and sequential extractions, our results indicated that a large quantity of Mn^II arrived in the estuary in 2015 bound to Fe oxyhydroxides. Over time, dissolved Mn and Fe were released from soils when Fe^III oxyhydroxides underwent reductive dissolution. Due to seasonal redox oscillations, both Fe and Mn were then re-oxidized to Fe^III, Mn^III, and Mn^IV and re-precipitated as poorly crystalline Fe oxyhydroxides and poorly crystalline Mn oxides. In 2017, redox conditions (Eh: -47 ± 83 mV; pH: 6.7 ± 0.5) favorable to both Fe and Mn reduction led to an increase (~880%) of dissolved Mn (average for 2015: 66 ± 130 µg L^-1; 2017: 582 ± 626 µg L^-1) in water and a decrease (~75%, 2015: 547 ± 498 mg kg^-1; 2017: 135 ± 80 mg kg^-1) in the total Mn content in soils. The crystalline Fe oxyhydroxides content significantly decreased while the fraction of poorly ordered Fe oxides increased in the soils limiting the role of Fe in Mn retention. The high concentration of dissolved Mn found within the estuary two years after the arrival of mine tailings indicates a possible chronic contamination scenario, which is supported by the high levels of Mn in two species of fish living in the estuary. Our work suggests a high risk to estuarine biota and human health due to the rapid Fe and Mn biogeochemical dynamic within the impacted estuary.

Distribution, source identification, and assessment of heavy metal pollution in the surface and pore waters of Cipeles River, West Java, Indonesia

The Cipeles watershed is the largest subsystem of the Cimanuk watershed, which is located in an agricultural area. Some segments of the Cipeles River are appropriate for aquatic life habitat. To assess the pollutant risk from heavy metals, which tend to accumulate in the environment, this study determined the heavy metal concentrations as a basic database, calculate the heavy metal pollution index (HMPI), and assess the correlation between heavy metals from the surface and pore waters of Cipeles River. Samples from 11 sampling stations at the end of the wet season were collected, preserved, and characterized using inductively coupled plasma mass spectrometry. The heavy metal concentrations were then plotted on a map using a geographic information system. As a result, the heavy metal occurrence in pore water was found to be Mn > Fe > Ba > Co > Zn > Cu > Pb > Cr in the order of abundance, while the order was slightly different in surface water, i.e., Fe > Mn > Zn > Ba > Cu > Pb > Co > Cr. Both pore and surface waters showed similar dominance for iron and manganese, where they mostly originated from the run-off water from the laterite and alluvial soils at the sampling locations. The other micro-concentrations of heavy metals indicate the anthropogenic source of pollutants. The HMPI indicated a low level in the upstream area, medium to high levels in the city center, and high levels in the downstream area. Moreover, there is a significant correlation between the heavy metal concentration at pore and surface waters, especially for Mn and Co in the city area and also Zn and Ba in the downstream area.

Pursuing the Elixir of Life: In Vivo Antioxidative Effects of Manganosalen Complexes

Manganosalen complexes are coordination compounds that possess a chelating salen-type ligand, a class of bis-Schiff bases obtained by condensation of salicylaldehyde and a diamine. They may act as catalytic antioxidants mimicking both the structure and the reactivity of the native antioxidant enzymes active site. Thus, manganosalen complexes have been shown to exhibit superoxide dismutase, catalase, and glutathione peroxidase activities, and they could potentially facilitate the scavenging of excess reactive oxygen species (ROS), thereby restoring the redox balance in damaged cells and organs. Initial catalytic studies compared the potency of these compounds as antioxidants in terms of rate constants of the chemical reactivity against ROS, giving catalytic values approaching and even exceeding that of the native antioxidative enzymes. Although most of these catalytic studies lack of biological relevance, subsequent in vitro studies have confirmed the efficiency of many manganosalen complexes in oxidative stress models. These synthetic catalytic scavengers, cheaper than natural antioxidants, have accordingly attracted intensive attention for the therapy of ROS-mediated injuries. The aim of this review is to focus on in vivo studies performed on manganosalen complexes and their activity on the treatment of several pathological disorders associated with oxidative damage. These disorders, ranging from the prevention of fetal malformations to the extension of lifespan, include neurodegenerative, inflammatory, and cardiovascular diseases; tissue injury; and other damages related to the liver, kidney, or lungs.

Effects of manganese on fat snook Centropomus parallelus (Carangaria: Centropomidae) exposed to different temperatures

ABSTRACT This study evaluates the effects of exposure to manganese (Mn2+) for 96 hours at two different temperatures (24 and 27°C) on juveniles of Centropomus parallelus through the activities of glutathione S-transferase (GST) and catalase (CAT), micronuclei test (MN) and comet assay. The GST activity did not show any significant difference between the groups exposed to Mn2+ and the respective control groups; in contrast, a major increase in the CAT activity was observed at 27°C in the group exposed to Mn2+ compared to the control group. The genotoxic analyses showed that in all animals exposed to Mn2+, the number of red cells with micronuclei increased significantly compared to the respective control groups. There was also a significant increase in the incidence of DNA damage in the groups exposed to Mn2+. At a temperature of 24ºC, animals exposed to Mn2+ had more DNA damage than those at 27°C. It is likely that the increase in temperature can also induce oxidative stress. Thus, we conclude that manganese is toxic to the fat snook juveniles, causing genotoxic damage, and when associated with an increase in temperature, manganese can also provoke an increase in oxidative stress.

Plasma metabolites, ions and thyroid hormones levels, and hepatic enzymes׳ activity in Caspian roach (Rutilus rutilus caspicus) exposed to waterborne manganese

To investigate the effect of waterborne manganese on plasma biochemical characteristics in fish, Caspian roach (Rutilus rutilus caspicus) was exposed to 0 (control), 60 (M60), 150 (M150) and 300 (M300) mg/L water manganese for 96h. Thereafter, plasma biochemical characteristics were studied. Plasma glucose level significantly increased in M60 and decreased in M150 and M300 groups, compared to the control. M300 had significantly lower hematocrit compared to the control. Albumin remained unchanged after manganese exposure, however, the manganese-exposed fish showed significant increase in plasma total protein levels. M150 and M300 showed significant increase in the plasma cholesterol and triglyceride levels compared to the control and M60. M60 and M150 had significantly higher alkaline phosphatase (ALP) activity compared to the control. The manganese-exposed groups had significantly higher alanine aminotransferase (ALT) activity compared to the control. M150 and M300 had aspartate aminotransferase (AST) activity significantly higher than those of the control and M60. M300 had significantly higher triiodothyronine (T3) levels than the other groups. All manganese-exposed fish had significantly higher thyroxin (T4) levels than the control. The plasma levels of chloride showed a significant decrease in the manganese-exposed fish, compared to the control. M150 and M300 had significantly lower sodium levels, compared to the control. M60 and M150 had significantly lower plasma calcium levels compared to the other groups. It is concluded that clinical chemistry along with thyroid hormones levels can be the useful tools to monitor manganese toxicity in fish. The possible mechanisms involving in the biochemical changes were discussed.