Effects of acute heat stress on liver damage, apoptosis and inflammation of pikeperch (Sander lucioperca).

Pikeperch (Sander lucioperca) is a sub-cold water fish species with high aquaculture potential. Its culture is seriously affected by increasing summer temperatures in recent years. Aim to investigate the effects of heat stress on apoptosis, oxidative stress, and the immune response in pikeperch. the fish were heat stressed at 30 °C, 32 °C and 34 °C for 2h respectively, followed by a 48h recovery period. The results showed that as temperature increased, the contents of malondialdehyde (MDA) and hydrogen peroxide (H2O2) in the liver increased significantly. Meanwhile, acute heat stress results in progressive deleterious alterations in liver tissue, especially vascular rupture, blood infiltration, and severe vacuolation at 34 °C. TUNEL staining revealed that the apoptosis level increased significantly with the rising temperature. Acute heat stress significantly induced the mRNA expression of apoptosis-related genes, including tumor suppressor (p53), B-cell lymphoma-2 (bcl-2), bcl-2-associated X (bax), apoptotic protease activating factor-1 (apaf-1), cysteinyl aspartate specific proteinase (caspase-3 and caspase-9), and the expression of p53 was also positively correlated with bax expression and the bax/bcl-2 ratio. Additionally, caspase-3 and caspase-9 activity increased significantly at 34 °C compared with the control group (23 °C). Innate immune genes, including tumor necrosis factor (tnf-α), interleukins (il-7, il-8, il-10 and il-1ß), complement 3 (c3) were activated under acute heat stress, and H2O2 content was positively correlated with the expressions of tnf-α and il-1ß. After the temperature reached again 23 °C, most measured indexes in heat-stressed groups didn't return to stress-free levels, and liver tissue also didn't return to its normal state in the histopathology. It was found that p53-mediated mitochondrial apoptosis pathway was triggered in pikeperch under acute heat stress, and there may be a vicious cycle between oxidative stress and inflammation. In summary, the present study is helpful to elucidate how acute heat stress mediates liver injury of pikeperch through mitochondrial pathway, inflammation and oxidative stress.

Alterations to transcriptomic profile, histopathology, and oxidative stress in liver of pikeperch (Sander lucioperca) under heat stress.

Pikeperch (Sander lucioperca) is an economically important cool-water fish. In recent years, its cultivation has become threatened by higher temperatures in summer. We previously investigated the effects of heat stress on pikeperch liver under different temperatures, but the molecular mechanism of the heat-stress response is still unknown. This study applied consistent heat stress (29 °C, 0-48 h) to pikeperch juveniles, and a transcriptomic profile of pikeperch liver under heat stress (29 °C, 0 h) was performed by RNA-Seq. The antioxidant status, changes in liver histology, and antioxidant gene expression at different time points were examined. We identified 403 differentially expressed genes (DEGs), many of which were enriched in KEGG pathways, including protein processing in endoplasmic reticulum (ER), insulin signaling, and immune-related pathways. Among these, the most significant heat-stress-related pathway was protein processing in ER, indicating that this pathway is critical for the heat-stress response. After consistent heat stress at 29 °C, the total antioxidant capacity (T-AOC), the activities of total superoxide dismutase (T-SOD) and catalase (CAT), and the mRNA expression of manganese SOD (Mn-SOD), CAT, and glutathione peroxidase 1 and 7 (GPx1 and GPx7) in the treated groups showed the same trend of first increasing and then decreasing. Levels of malondialdehyde (MDA) content did not show significant differences between samples at 0 h and 3 h, but significantly increased by 6 h, and thereafter decreased. The liver tissue was normal at 0 h (29 °C); however, it suffered histological damage with increased duration of the heat stress. Above all, heat stress at 29 °C seemed to cause oxidative damage and dysfunction in pikeperch liver between 3 h and 48 h. The present results indicate that pikeperch have the capacity to defend against heat stress and maintain relative balance of oxidation-reduction reactions mainly through activating the antioxidant system, protein processing in ER, the insulin-signaling pathway, and immune-related pathways.

Physicochemical changes in liver and Hsc70 expression in pikeperch Sander lucioperca under heat stress.

The pikeperch Sander lucioperca is an economically important freshwater species that is currently threatened by higher summer temperatures caused by global warming. To clarify the physiological state of pikeperch reared under relatively high temperatures and to acquire valuable biomarkers to monitor heat stress in this species, 100 fish were subjected to five different temperature treatments, ranging from 23 °C (control) to 36 °C. The physiological and biochemical indexes of liver and blood were determined, and heat-shock cognate 70 kDa protein (Hsc70) mRNA expression profiles were analyzed. The results showed that the activities of superoxide dismutase, catalase, and glutathione peroxidase in heat-stressed pikeperch first increased and then decreased, exhibiting peaks at 34 °C, 28 °C, and 28 °C, respectively. The level of thiobarbituric acid-reactive substances (TBARS) in all experimental groups was significantly higher than that of the control. The numbers of red blood cells, the packed-cell volume, and the contents of hemoglobin were significantly higher in the 34 °C and 36 °C treatment groups. Under heat stress, the albumin, cholesterol, and triglycerides contents decreased with increasing temperatures. Real-time fluorescence-based quantitative RT-PCR showed that Hsc70 mRNA levels increased in all eight of the tested tissues under heat stress. Expression reached maximum levels at 34 °C in the muscle, heart and gill tissues, and at 36 °C in the other five tissues. These results demonstrate that several physiological and biochemical phenotypes, such as oxidative stress, antioxidant enzymes and molecular chaperones, could be important biomarkers of heat stress in pikeperch, and are potentially valuable to uncover the mechanisms of heat-stress responses in fish.

Antimony isotope fractionation and the key controls in the soil profiles of an antimony smelting area.

The controlling factors of antimony migration and transformation in soil profiles are still unclear. Antimony isotopes might be a useful tool to trace it. In this paper, antimony isotopic compositions of plant and smelter-derived samples, and two soil profiles were measured for the first time. The δ123Sb values of the surface and bottom layers of the two soil profiles varied in 0.23‰-1.19‰ and 0.58‰-0.66‰, respectively, while δ123Sb of the smelter-derived samples varied in 0.29‰-0.38‰. The results show that the antimony isotopic compositions in the soil profiles are affected by post-depositional biogeochemical processes. The enrichment and loss of light isotopes at 0-10 cm and 10-40 cm layers of the contrasted soil profile may be controlled by plant uptake process. The loss and enrichment of heavy isotopes in the 0-10 cm and 10-25 cm layers of the antimony from smelting source in the polluted soil profile may be controlled by the adsorption process, while the enrichment of light isotopes in the 25-80 cm layer may be related to the reductive dissolution process. The conclusion emphasizes that the promotion of the Sb isotope fractionation mechanism will play a crucial role in understanding the migration and transformation behaviors of Sb in soil systems.

Contamination, oral bioaccessibility and human health risk assessment of thallium and other metal(loid)s in farmland soils around a historic TlHg mining area.

In this study, tweenty-nine soil samples were collected from a historic TlHg mining area, located in southwest Guizhou, China. Total concentrations of metal(loid)s in soils and in vitro extracts were analysed by ICP-MS, and the bioaccessibility of metal(loid)s was conducted by two often used in vitro extraction methods, Simplified bioaccessibility Extraction Test (SBET) and Physiologically Based Extraction Test (PBET). The health risk assessment based on total concentrations of metal(loid)s, bioaccessibility of SBET and PBET through soil ingestion were investigated. Results indicated that the collected cultivated soils contained elevated concentrations of Tl (44.8 ± 67.7 mg kg-1), Hg (110 ± 193 mg kg-1), As (84.4 ± 89.2 mg kg-1) and Sb (14.8 ± 24.8 mg kg-1), exceeding the regional background values of Guizhou province, China and the Chinese farmland risk screening values. However, the bioaccessibility of Tl, Hg, As and Sb were relatively low, usually less than 30% for most samples and varied greatly among metal(loid)s and sampling sites. The average bioaccessibility values of Tl, Hg, As and Sb by SBET were lower than those by PBET. The non-carsinogenic risk (HQ and HI) and Carcinogenic Risk (CR) values were significantly reduced when incorporating the bioaccessibiltiy of metal(loid)s into health risk assessment. It is worth noting that the health risk to children exceeded adults. Moreover, Tl and As contributed the most to the risk, indicating that more attention should be paid on Tl and As during the daily environmental regulation and management of contaminated soils in Lanmuchang.