Gradual increase of temperature trigger metabolic and oxidative responses in plasma and body tissues in the Antarctic fish Notothenia rossii.

Antarctica is considered a thermally stable ecosystem; however, climate studies point to increases in water temperatures in this region. These thermal changes may affect the biological processes and promote metabolic changes in the adapted organisms that live in this region, rendering the animals more vulnerable to oxidative damage. This study assessed the effect of acclimation temperature on the levels of stress response markers in plasma, kidney, gill, liver, and brain tissues of Notothenia rossii subjected to gradual temperature changes of 0.5 °C/day until reaching temperatures of 2, 4, 6, and 8 °C. Under the effect of the 0.5 °C/day acclimation rate, gill tissue showed increased glutathione-S-transferase (GST) activity; kidney tissue showed increased H+-ATPase activity. In the liver, there was also an increase in GSH. In plasma, gradual decreases in the concentrations of total proteins and globulins were observed. These responses indicate a higher production of reactive oxygen species ROS, an imbalance in energy demand, and a lack in protein synthesis. Gradual increase in temperature may cause opposite responses to the thermal shock model in N. rossii.

Biomarkers of oxidative stress and cell damage in freshwater bivalves Diplodon parodizi exposed to landfill leachate.

Landfill is a public and environmental health problem; establishing and understanding methodologies to decrease its toxicity are thus necessary. Leachate samples were collected, at a sanitary landfill, immediately after the exit from the landfill, i.e. raw leachate (collection point A), after conventional treatment (point B) and after treatment by wetlands (point C). D. parodizi specimens were exposed to 3%, 10% and control (0%) dilutions of leachate from these collection points for 7 days. Markers of antioxidant defences and cell damage were analysed. At point B, the gills of D. parodizi showed higher glutathione-S-transferase (GST) and glutathione reductase (GR) activity; the latter is a supplier of glutathione reductase (GSH). The low GST activity at point A was associated with the hormesis effect. Higher levels of superoxide dismutase (SOD), ethoxyresorufin-O-deethylase (EROD) and glutathione peroxidase (GPx) occurred at point A. Glucose-6-phosphate dehydrogenase (G6PDH) was inhibited at the points with the highest pollutant load and at the highest leachate dilutions. Higher levels of markers at point A may be related to the high pollutant charge and specific compounds present in the untreated leachate. The multi-xenobiotic resistance mechanism (MXR), metallothionein-like proteins (MT) and lipid peroxidation (LPO) did not vary among treatments. The biomarker responses showed negative effects of the leachate on the freshwater bivalve and simultaneously showed that the wetland treatment employed at the Caximba sanitary landfill is effective.

Effect of gradual temperature increase on the carbohydrate energy metabolism responses of the Antarctic fish Notothenia rossii.

The warming of the Southern Ocean waters may affect the biological processes and the performance of the fish inhabiting it. The notothenioid group is metabolically specialized to low-temperature environments and may be vulnerable to the climatic changes imposed on the Antarctic continent. However, gradual temperature changes potentially allow an opportunity for plasticity adjustments. The present study evaluated the effect of gradual increase of temperature on the enzymatic and nonenzymatic parameters of energy metabolism in renal, branchial, hepatic, and encephalic tissue of Notothenia rossii subjected to a gradual temperature change of 0.5 °C/day until reaching 2 °C, 4 °C, 6 °C, and 8 °C. Under the effect of an acclimation rate of 0.5 °C/day, the gill tissue showed increased phosphofructokinase (PFK) enzyme activity. In the kidney, there was increased activity of the malate dehydrogenase (MDH), glucose-6-phosphatase (G6PDH), and glycogen phosphorylase (GP) enzymes. There was an increase in lactate concentration in the liver and an increase in GP enzyme activity in the brain. The specific tissue responses indicate the presence of thermal plasticity and an attempt to regulate energy metabolism to mitigate thermal stress in this species under these experimental conditions, possibly through the activation of glycolysis, gluconeogenesis, and glycogenolysis.

Effect of long-term thermal challenge on the Antarctic notothenioid Notothenia rossii.

The thermal stability of the Antarctic Ocean raises questions concerning the metabolic plasticity of Antarctic notothenioids to changes in the environmental temperature. In this study, Notothenia rossii survived 90 days at 8 °C, and their condition factor level was maintained. However, their hepatosomatic (0.29×) index decreased, indicating a decrease in nutrient storage as a result of changes in the energy demands to support survival. At 8 °C, the plasma calcium, magnesium, cholesterol, and triglyceride concentrations decreased, whereas the glucose (1.91×) and albumin (1.26×) concentrations increased. The main energy substrate of the fish changed from lipids to glucose due to a marked increase in lactate dehydrogenase activity, as demonstrated by an increase in anaerobic metabolism. Moreover, malate dehydrogenase activity increased in all tissues, suggesting that fish acclimated at 8 °C exhibit enhanced gluconeogenesis. The aerobic demand increased only in the liver due to an increase (2.23×) in citrate synthase activity. Decreases in the activities of superoxide dismutase, catalase, and glutathione-S-transferase to levels that are most likely sufficient at 8 °C were observed, establishing a new physiological activity range for antioxidant defense. Our findings indicate that N. rossii has some compensatory mechanisms that enabled its long-term survival at 8 °C.

Metabolic responses in Antarctic Nototheniidae brains subjected to thermal stress.

Antarctic Nototheniidae is an attractive group for studying metabolic and physiological responses at high temperatures. The present work investigated the metabolic responses of the carbohydrate metabolism and antioxidant system to thermal stress at 8 °C (for 2-144 h) in the brains of Notothenia rossii and Notothenia coriiceps. In N. coriiceps, glycogenolysis was essential in the first hours of exposure (2 h) at 8 °C and, in addition to inhibiting glucose-6-phosphatase activity, was important for activating the pentose phosphate pathway. In N. rossii, anaerobic metabolism was reduced in the first hours of exposure (2 and 6 h) at 8 °C, followed by reduced hexokinase activity, suggesting energy regulation between neurons and astrocytes. The antioxidant system results indicated the importance of the actions of the glutathione-dependent antioxidant enzymes glutathione-S-transferase and glutathione peroxidase as well as those of catalase in N. coriiceps and the action of glutathione-S-transferase, glutathione peroxidase and glutathione reductase in N. rossii, especially during the first 12 h of thermal stress exposure. These results indicate tissue-specific patterns and species-specific responses to this stress.

Heat stress in the heart and muscle of the Antarctic fishes Notothenia rossii and Notothenia coriiceps: Carbohydrate metabolism and antioxidant defence.

Carbohydrate metabolism and the antioxidant defence system of heart and muscle of the Antarctic notothenioids Notothenia rossii and Notothenia coriiceps were evaluated in response to heat stress (8 °C) over 144 h. N. rossii heart exhibited decreased glycolysis and aerobic metabolism after up to 12 h of exposure to 8 °C, and anaerobiosis was inhibited within 24 h. However, these pathways were stimulated after 72 h at 8 °C. The consumption of glucose-6-phosphate, derived from hexokinase (HK), by glucose-6-phosphate dehydrogenase (G6PDH) decreased in N. rossii heart within 6 h at 8 °C, with a subsequent increase at 72 h. In N. rossii muscle at 8 °C, glycolysis was stimulated within 2 h by an increase in pyruvate kinase (PK), and aerobic metabolism was stimulated at 144 h, together with anaerobiosis. In N. coriiceps heart at 8 °C, glucose break down by HK decreased within 2 h and subsequently increased at 12 and 24 h. Increased glucose-6-phosphate consumption by G6PDH occurred within 6 h at 8 °C. In N. coriiceps muscle at 8 °C, glycolysis was stimulated at 2 and 6 h, with subsequent inhibition within 24 h, as indicated by HK activity. Aerobic metabolism was inhibited at 72 and 144 h at 8 °C through the inhibition of citrate synthase (CS). Heat stress caused responses were only occasional and transient in antioxidant defence system of both species in the heart and muscle, leading to increased glutathione (GSH) and decreased levels of lipoperoxidation in the heart of both species. The results obtained in this study in the heart and muscles indicate that under heat stress at 8 °C, N. rossii is more responsive than N. coriiceps with respect to carbohydrate metabolism.

Effects of heat stress on the renal and branchial carbohydrate metabolism and antioxidant system of Antarctic fish.

The objective of the present study was to assess the effect of short-term (2-144 h) heat stress (8 °C) on energy production processes and antioxidant defense systems in the kidneys and gills of Notothenia rossii and Notothenia coriiceps. Heat stress affected energy metabolism and oxidative stress parameters in a time-, tissue-, and species-dependent manner, and gills were more sensitive than kidneys to heat stress. N. rossii kidneys were able to stabilize carbohydrate metabolism after 12 h of heat stress, whereas the glycogen levels in N. coriiceps kidneys fluctuated in response to varying glucose-6-phosphatase (G6Pase) levels. The gills of N. rossii were able to stabilize their energy demand and aerobic metabolism under heat stress, whereas in the gills of N. coriiceps, changes in carbohydrate metabolic pathways depended on the exposure time: initially, anaerobiosis was activated after 6 h; the energy demand, characterized by glycogen consumption, increased after 72 h, and aerobic metabolism was activated within 144 h. With regard to the antioxidant defenses of the N. rossii kidney, it was found that levels of antioxidant enzymes were reduced during the first hours of heat stress, contributing to increased lipid peroxidation, whereas N. coriiceps kidneys did not show signs of oxidative damage. The gills of N. rossii exhibited more pronounced oxidative damage in response to heat stress than those of N. coriiceps despite the presence of increasing levels of antioxidants, likely due to tissue hypoxia.