Koigoora Srikanth

Glutathione and its dependent enzymes' modulatory responses to toxic metals and metalloids in fish: a review

Toxic metals and metalloid are being rapidly added from multiple pathways to aquatic ecosystem and causing severe threats to inhabiting fauna including fish. Being common in all the type of aquatic ecosystems such as freshwater, marine and brackish water fish are the first to get prone to toxic metals and metalloids. In addition to a number of physiological/biochemical alterations, toxic metals and metalloids cause enhanced generation of varied reactive oxygen species (ROS) ultimately leading to a situation called oxidative stress. However, as an important component of antioxidant defence system in fish, the tripeptide glutathione (GSH) directly or indirectly regulates the scavenging of ROS and their reaction products. Additionally, several other GSH-associated enzymes such as GSH reductase (GR, EC 1.6.4.2), GSH peroxidase (EC 1.11.1.9), and GSH sulfotransferase (glutathione-S-transferase (GST), EC 2.5.1.18) cumulatively protect fish against ROS and their reaction products accrued anomalies under toxic metals and metalloids stress conditions. The current review highlights recent research findings on the modulation of GSH, its redox couple (reduced glutathione/oxidised glutathione), and other GSH-related enzymes (GR, glutathione peroxidase, GST) involved in the detoxification of harmful ROS and their reaction products in toxic metals and metalloids-exposed fish.

Oxidative stress and changes in locomotor behavior and gill morphology of Gambusia affinis exposed to chromium

Sublethal effects of chromium trioxide on mosquito fish, Gambusia affinis, were carried out for 28 days on day 4, 8, 12, 16, 20, 24, and 28. The sublethal effects of chromium (LC10, 77.62 mg L−1) on antioxidant enzymes, thiobarbituric acid reactive substance (TBARS), locomotor behavior, and gill morphology were studied. The antioxidant enzymes like superoxide dismutase (SOD) and catalase were induced throughout the exposure span of 28 days. Percent induction was also increase with the days of exposure. Lipid peroxidation product, malondialdehyde was enhanced in the viscera tissue of chromium-exposed fish. Perturbation of locomotor behavior like decrease in distance travelled (m min−1) and in swimming speed (cm s−1) was observed in exposed fish. Chromium toxicity caused alterations in gill morphology like hypertrophy and hyperplasia in secondary lamellae followed by detached epithelium with severe necrosis. It can be concluded from the results that Cr intoxication in Gambusia fish, caused induction in antioxidant enzymes and lipid peroxidation, plus changes in gill morphology and locomotor behavior.

Plasmatocyte-spreading peptide influences hemocyte behavior via eicosanoids

Hemocyte-spreading behavior is required for expressing a cellular immune response, nodulation, which clears the vast majority of invading microbes from circulation. The nodulation response is completed by a layer of plasmatocytes, which spread over the nodule and initiate a malanization process leading to darkened nodules. Plasmatocyte-spreading peptide (PSP), the first reported insect cytokine, is responsible for mediating the spreading and attachment of some subclasses of plasmatocytes to nodules. Prostaglandins (PGs), one group of eicosanoids formed from arachidonic acid (AA), also mediate plasmatocyte spreading (PS), although the potential interactions between the PSP and PG signal transduction pathways have not been investigated. We tested our hypothesis that PSP acts via biosynthesis of eicosanoids, specifically PGs, in the beet armyworm, Spodoptera exigua. In this study, we report that (1) PSP and PGE(2) independently stimulated Ca(++)-dependent PS, (2) inhibitors of PG biosynthesis reversibly blocked PS, (3) dsRNA silencing the gene encoding proPSP blocked PS, which was rescued by PSP and by AA, (4) PSP-stimulated PS was reversibly impaired by inhibitors of PG biosynthesis, and (5) the inhibitor-impaired spreading was rescued by AA. Taken together, these points strongly support our model showing that PSP acts via a plasmatocyte-surface receptor, which stimulates biosynthesis of the PGs responsible for mediating plasmatocytes spreading.

Sublethal Effects of Profenofos on Locomotor Behavior and Gill Architecture of the Mosquito Fish,Gambusia affinis

Subacute studies of profenofos on mosquito fish, Gambusia affinis, were carried out for 20 days to assess the locomotor behavior and structural integrity of gill in relation to bioaccumulation and targeted enzyme acetylcholinesterase (AChE; EC 3.1.1.7). The sublethal concentration of 0.13 mg/L (1/5 of LC50) altered locomotor behavior such as distance traveled and swimming speed in exposed fish. This could be due to inhibition in the activity of acetylcholinesterase and deformities in the primary and secondary lamella of gill. The bioaccumulation values indicated that the accumulation of profenofos was highest in viscera followed by head and body. The average bioconcentration factor values are 254.83, 6.18, and 2.52 μg/g for viscera, head, and body. The findings revealed that profenofos is highly toxic even at sublethal concentrations to the mosquito fish, Gambusia affinis.

Environmental contamination using accumulation of metals in marine sponge, Sigmadocia fibulata inhabiting the coastal waters of Gulf of Mannar, India

Coastal marine ecosystems in many parts of the world are under unrelenting stress caused by urban development, pollutants and other ecological impacts such as building of infrastructure, land reclamation for port and industrial development, habitat modification, tourism and recreational activities. The present work is a first extensive field study using the marine sponge, Sigmadocia fibulata as a bioindicator to detect metal pollution between inshore and offshore environment of the ‘Gulf of Mannar’, India. Samples of S. fibulata were collected from different places of inshore (0.1–0.5 km) and offshore (3–5 kms) locations. Metal concentrations in water and bioaccumulation in sponges were determined by ICP-MS (Inductively coupled plasma-mass spectrometry). Enrichment of metal contamination was more in the inshore, when compared to offshore environment. Higher concentrations of metals Fe, Al, Ni, Mn, Cu, Cr, Co, Ba, Zn, V, Pb and Cd in inshore waters (3–6.4 times than offshore) may be due to the discharge of monsoonal rains, carrying a discharge of industrial and agricultural wastes and sewage directly into the coast. This is substantiated by a highly significant positive correlation between concentrations of metals in the water and accumulation in sponges. The bioaccumulation of metals in sponge tissue were in order of Fe > Al > Ni > Mn > Cu > Cr > Co > Ba > Zn > V > Cd > Pb in both the inshore and offshore regions. Apparently, the macromolecule composition (sugars, proteins and lipids) was significantly reduced by the accumulation of metals in inshore sponges. The current findings indicated that the frequent monitoring is necessary to assess the eco-health of the marine environment by choosing bio-indicator species like S. fibulata, which provide accurate, reliable measurements of environmental quality.

Acute toxicity bioassay using Paramecium caudatum , a key member to study the effects of monocrotophos on swimming behaviour, morphology and reproduction

The toxic effects of an organophosphorous insecticide, monochrotophos (MCP) were investigated on Paramecium caudatum in static acute toxicity tests (10 min and 2 h). The lethal concentrations (50%) were determined by probit method, for technical monocrotophos as 60 and 40.6 mg L−1, respectively. We have combined conventional light microscopy and a computerized video tracking system to determine behavioural and morphological changes in paramecium on exposure to MCP. Paramecia exposed to highest concentrations (90–100 mg L−1) used for 10 min exposure, exhibited initial increase with subsequent decrease in mobility with enormous blebbing, leading to lysis of cells. In the second set of experiments, the cells exposed to lethal concentration (40.6 mg L−1) for 2 h were under stress, and reduced their locomotor behaviour, i.e. distance travelled per unit time (mm in 6 min) and swimming speed (mm s−1) with increased time of exposure. In the third set of experiments, the number of generations and generation time in 24 h was evaluated with respect to the different sub lethal concentrations (5, 10, 15 and 20 mg L−1) of toxicant. The number of generations decreased and generation time extended significantly in a concentration dependent manner. The results indicate that the Paramecium toxicity assay could be used as a complimentary system to rapidly elucidate the cytotoxic potential of insecticides.

Aluminium oxide nanoparticles induced morphological changes, cytotoxicity and oxidative stress in Chinook salmon (CHSE-214) cells

Aluminium oxide nanoparticles (Al2O3 NPs) are increasingly used in diverse applications that has raised concern about their safety. Recent studies suggested that Al2O3 NPs induced oxidative stress may be the cause of toxicity in algae, Ceriodaphnia dubia, Caenorhabditis elegans and Danio rerio. However, there is paucity on the toxicity of Al2O3 NPs on fish cell lines. The current study was aimed to investigate Al2O3 NPs induced cytotoxicity, oxidative stress and morphological abnormality of Chinnok salmon cells (CHSE‐214). A dose‐dependent decline in cell viability was observed in CHSE‐214 cells exposed to Al2O3 NPs. Oxidative stress induced by Al2O3 NPs in CHSE‐214 cells has resulted in the significant reduction of superoxide dismutase, catalase and glutathione in a dose‐dependent manner. However, a significant increase in glutathione sulfo‐transferase and lipid peroxidation was observed in CHSE‐214 cells exposed to Al2O3 NPs in a dose‐dependent manner. Significant morphological changes in CHSE‐214 cells were observed when exposed to Al2O3 NPs at 6, 12 and 24 h. The cells started to detach and appear spherical at 6 h followed by loss of cellular contents resulting in the shrinking of the cells. At 24 h, the cells started to disintegrate and resulted in cell death. Our data demonstrate that Al2O3 NPs induce cytotoxicity and oxidative stress in a dose‐dependent manner in CHSE‐214 cells. Thus, our current work may serve as a base‐line study for future evaluation of toxicity studies using CHSE‐214 cells. Copyright

Graphene oxide induces cytotoxicity and oxidative stress in bluegill sunfish cells: Graphene oxide cytotoxic to blue gill sunfish cells

Graphene oxide (GO) is considered a promising material for biological application due to its unique properties. However, the potential toxicity of GO to aquatic organism particularly bluegill sun fish cells (BF‐2) is unexplored or remains poorly understood. GO‐induced cytotoxicity and oxidative stress in BF‐2 cells were assessed using a battery of biomarkers. Two different biological assays (3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl tetrazolium bromide and neutral red uptake were used to evaluate the cytotoxicity of GO on BF‐2 cells. It was found that GO induced dose‐ and time‐dependent cytotoxicity on BF‐2 cells. BF‐2 cells exposed to lower concentration of GO (40 μg ml–1) for 24 induced morphological changes when compared to their respective controls. As evidence for oxidative stress lipid peroxidation, superoxide dismutase, catalase, reactive oxygen species and 8‐hydroxy‐2′‐deoxyguanosine levels were increased and glutathione levels were found to decline in BF‐2 cells after treatment with GO. Our findings demonstrate that GO when exposed to BF‐2 fish cells cause oxidative stress.

Sponges as Biomonitors of Metal Toxicity in the Aquatic Systems

Aquatic ecosystems around the world are subjected to unrelenting stress caused by urban sprawl, discharge of effluents from domestic and other ecological impacts such as infrastructure, land reclamation for port and industrial development and habitat destruction. Sponges are efficient to accumulate the metals in their tissues if the concentration of these metals is low in the ambient environment. Difference in the accumulation of metals was observed in different species of sponges collected from the studied areas. Their strong capacity to accumulate metals and the diversity of sponges in the different coastal regions of the world make them ideal biomonitors of metal contamination of the confined region.

Seasonal Trend of Potential Toxic Elements in Seawater and Sediments from Tuticorin Coast

Potential toxic elements (PTEs) concentration was analyzed seasonally in seawater and sediment samples from Tuticorin coast, India. The extent of PTEs contamination in Tuticorin coast has been revealed by measuring the concentrations of iron (Fe), nickel (Ni), zinc (Zn), copper (Cu), cadmium (Cd), and lead (Pb) using inductively coupled plasma mass spectrophotometer (ICP-MS) seasonally. The concentration of all the PTEs in seawater samples was higher in summer and least in spring. The concentration of all the PTEs was significantly different within and among the season except for Zn and Cu. The concentration of PTEs in sediment samples was higher in winter and least in summer seasons. Exceptionally, the concentration of Cd was not significant among and within the seasons. The concentration of the PTEs in seawater and sediment samples exceeded the WHO-recommended limits. The contamination factor (CF) and geoaccumulation index (Igeo) values indicated significant contamination of PTEs in the sediment samples collected in different seasons. Variations in the concentration of PTEs could be due to changes in levels of pollution discharge over time, availability of PTEs for adsorption, as well as variations in the sampling season. The presence of a number of industries surrounding the Tuticorin coast and the release of the effluents from both industries and domestic sources are the main source of pollution at Tuticorin coast and are the prime reasons for the loss of existing diverse ecosystem.