Heat indicators of oxidative stress, inflammation and metal transport show dependence of cadmium pollution history in the liver of female zebrafish

Inflammation as a pathway for heavy metal-induced liver damage-Insights from a repeated-measures study in residents exposed to metals and bioinformatics analysis

BACKGROUND

Epidemiological studies on heavy metal exposure and liver injury are predominantly cross-sectional, lacking longitudinal data and exploration of potential mechanisms.

METHOD

We conducted a repeated-measures study in Northeast China from 2016 to 2019, involving 322 participants. Linear mixed models (LMM) and Bayesian kernel machine regression (BKMR) were employed to explore the associations between individual and mixed blood metal concentrations [chromium (Cr), cadmium (Cd), vanadium (V), manganese (Mn), lead (Pb)] and liver function biomarkers [alanine aminotransferase (ALT), aspartate aminotransferase (AST), albumin (ALB), globulin (GLB), total protein (TP)]. Mediation and enrichment analyses were used to determine whether the inflammatory response is a critical pathway for heavy metal-induced liver damage.

RESULT

We obtained a total of 958 observations. The results from LMM and BKMR indicated significant associations between individual and mixed heavy metals and liver function biomarkers. Longitudinal analysis revealed associations between Cd and the annual increase rate of ALT (β = 2.61; 95% CI: 0.97, 4.26), the annual decrease rate of ALB (β = -0.21; 95% CI: -0.39, -0.03), Mn and the annual increase rate of GLB (β = 0.38; 95% CI: 0.05, 0.72), and V and the annual decrease rate of ALB/GLB (β = -1.15; 95% CI: -2.00, -0.31). Mediation analysis showed that high-sensitivity C-reactive protein (hsCRP) mediated the associations between Cd and AST, TP, with mediation effects of 27.7% and 13.4%, respectively. Additionally, results from Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses supported the role of inflammatory response pathways.

CONCLUSION

Our findings indicate that heavy metal exposure leads to liver damage, with the inflammatory response potentially serving as a crucial pathway in this process. This study offers a novel perspective on understanding heavy metal-induced liver injury and provides insights for preventive measures against the health damage caused by heavy metals.

Quercetin attenuates environmental Avermectin-induced ROS accumulation and alleviates gill damage in carp through activation of the Nrf2 pathway

Avermectin (AVM) is one of the most often used insecticides which is toxic to aquatic organisms, and cause oxidative-induced damages to the fish respiratory organ, the "gills". To better understand the mechanism by which an antioxidant reduces AVM-induced gill damage, we investigated the effects of Quercetin (Que) on AVM induction of oxidative stress to inhibit damages to the gills using common carp as a model organism. The Que is a fruit and vegetable rich flavonoid with antioxidant activity. In this study, four groups were created: the Control group, the Que group (400 mg/kg), the AVM group (2.404 μg/L), and the Que plus AVM group. The analytical methods were pathological structure examination, qPCR, Reactive Oxygen Species (ROS) and Western blot. The results showed that Que alleviated AVM-induced oxidative stress, inflammatory damage and apoptosis in the carp gills by activating the Nrf2 pathway. The mechanism was that Que alleviated the accumulation of ROS, reduced the balance between oxidation and antioxidant disrupted by AVM exposure, lowered the content of lipid peroxidation produced malondialdehyde (MDA), and increased the content of antioxidant enzymes including glutathione (GSH) and catalase (CAT). Nrf2 pathway was activated. Meanwhile, Que inhibited gill apoptosis in carp by decreasing the levels of Bax, Cytochrome C, Caspase9, Cleaved-Caspase3 and reduced Bcl2. This has important implications for future studies on Que and AVM. New suggestions are provided to reduce the threat of aquatic environmental pollution.

Abamectin induced brain and liver toxicity in carp: The healing potential of silybin and potential molecular mechanisms

Abamectin (ABM) abuse contaminated aquatic environment and posed a potential threat to fish health as well as public safety. Silybin (SIL), a flavonoid, has been widely used as a novel feed additive to promote fish health. This research was to explore the potential antagonistic mechanism between ABM and SIL on brain and liver toxicity was investigated in common carp. Sixty carp were divided into four groups at random: the Control group, the SIL group, the ABM group, and ABM + SIL group. This experiment lasted for 30 d. According to behavioral observation, the detection of levels of acetylcholinesterase (AchE), iron, and mRNA expression levels of blood-brain barrier (BBB) related tight junction proteins (ZO-1, Claudin7, Occludin, MMP2, MMP9, and MMP13) in brain tissues, it was found that SIL relieved neurobehavioral disorders caused by ABM-induced BBB destruction in carp. H&E staining showed SIL mitigated nerve injury and liver injury caused by ABM. Oil Red O staining and liver-related parameters showed that SIL alleviated hepatotoxicity and lipid metabolism disorder caused by ABM exposure. Furthermore, this work also explored the specific molecular mechanism of SIL in liver protection and neuroprotection. It was shown that SIL lowered ROS levels in liver and brain tissues via the GSK-3β/TSC2/TOR pathway. Simultaneously, SIL inhibited NF-κB signaling pathway and played an anti-inflammatory role. In conclusion, we believed that SIL supplementation has a protective effect on the brain and liver by regulating oxidative stress and inflammation.

Protective effect of quercetin on avermectin induced splenic toxicity in carp: Resistance to inflammatory response and oxidative damage

Avermectin pollution is an important problem that cannot be ignored in aquatic system in recent years. It has brought great trouble to freshwater aquaculture, especially fishery aquaculture. Plant-derived quercetin has anti-inflammatory and antioxidant properties and is widely used as a dietary additive, but its protective effect on immune damage induced by avermectin in freshwater carp remains unclear. This study evaluated the role of dietary additive quercetin supplementation in chronic avermectin exposure of carp spleen. Sixty carp were divided into 4 groups (n = 15/ group), including control group, avermectin treatment group, quercetin treatment group, quercetin and avermectin co-treatment group. Carp were exposed to a 1/10 96 h LC₅₀ dose of avermectin for 30 d and fed a carp diet containing 400 mg/kg quercetin twice a day (3% body weigh/ carp). The results showed that chronic avermectin exposure caused the loose parenchymal structure of carp spleen tissue and the increase of inflammatory cells, accompanied by increased transcription levels of pro-inflammatory il-1β, il-6, tnf-α and decreased levels of anti-inflammatory factors il-10 and tgf-β1, ROS accumulation in spleen tissue. MDA content increased and T-AOC, CAT and GSH levels decreased. Quercetin down-regulates the NF-κB pathway by inhibiting the expression of iNOS and activating p38 MAPK, blocking the transcription of inflammatory factors, and alleviating the inflammation of carp spleen caused by chronic avermectin exposure. In addition, quercetin inhibits the over-activation of Nrf2/Keap-1 signaling axis, blocks ROS accumulation, and restores the spleen REDOX homeostasis. In conclusion, quercetin, as a dietary additive for carp feed, can effectively improve the immune damage caused by avermectin pollution in aquatic environment, resist spleen inflammation and oxidative stress, and provide a theoretical basis for clinical development of freshwater carp feed.

Nano-Selenium Antagonized Cadmium-Induced Liver Fibrosis in Chicken

Cadmium is a global ecological toxic pollutant; in animals, hepatotoxic fibrosis is caused by bioaccumulation of Cd through food chains. We determined the path of nano-Se antagonism in Cd-induced hepatocyte pyroptosis by targeting the APJ-AMPK-PGC1α pathway, using an in vivo model of hepatotoxicity. All 1-day-old chicks were treated with Cd (140 mg/kg BW/day) and/or nano-Se (0.3 or 0.6 mg/kg BW/day) for 90 days. The result showed that Cd (1.55 ± 0.148) activated NLRP3 inflammasome 49.903% as compared to the Con group (1.034 ± 0.008) to release the inflammasome as a result of hepatocyte pyroptosis (2.824 ± 0.057). Compared with the Con group (1.010 ± 0.021), Kupffer cells were 219.109% more to activate astrocytes through the APJ-AMPK-PGC1α pathway, resulting in 185.149% more hepatic fibrosis. However, the fibrosis degree of the H-Se + Cd group (1.252 ± 0.056) was 56.5278% (p < 0.001) lower than that of the Cd group (2.880 ± 0.124). Therefore, this study established that pyroptotic hepatocytes and Kupffer cells could be targeted for nano-Se antagonizing Cd toxicity, which reveals a potential new approach targeting astrocytes for the treatment of liver fibrosis triggered by Cd pollution.

Environmental co-exposure of high temperature and Cu induce hormonal disturbance of cortisol signaling and altered responses of cellular defense genes in zebrafish

Global warming is causing a continuous increase in environmental temperatures, which simultaneously activates toxic environmental stresses, such as heavy metal exposure, in aquatic ecosystems. The present study aimed at evaluating the effects of Cu toxicity along with increased temperature during zebrafish embryogenesis. Decreased survival rates were observed following combined exposure to high temperature and Cu. Heart rates of zebrafish embryos were significantly increased only during heat stress. An abnormal morphology with curved body shape was induced by exposure to a combination of Cu and heat stress. Furthermore, heat stress also triggered Cu-induced intracellular reactive oxygen species (ROS) production, with upregulation of superoxide dismutase (SOD) and glutathione s-transferase (GST) expression, and cell death with modified expression of p53 and B-cell lymphoma-2 (Bcl-2) in zebrafish embryos. Finally, increased cortisol levels and altered expression of cortisol-signaling genes were observed following exposure to Cu and high temperatures. These results highlight that realistic exposure to combined stressors induces developmental disturbances via stress-induced responses involving oxidative stress and cell death as well as transcriptional alterations leading to cortisol signaling in fish.

Combined effects of temperature and nutrients on the toxicity of cadmium in duckweed (Lemna aequinoctialis)

Global anthropogenic changes are altering the temperature and nutrients of the ecosystem, which might also affect the extent of cadmium (Cd) toxicity in organisms. This study aimed to investigate the combined effects of temperature and nutrient availability (here, nitrogen [N] and phosphorus [P]) on Cd toxicity in duckweed (Lemna aequinoctialis). The growth parameters, nutrient uptake, and Cd tolerance of plantlets reached their highest values for duckweed grown in medium with 28 mg/L N and 2.4 mg/L P (N:P = 11.67) at 25 °C under 1 mg/L CdCl₂ exposure. Raising the temperature (from 18 °C to 25 °C) and levels of N and P (from 0.01 N/P to 2 N/P) enhanced photosynthetic capacity and nutrient uptake, thus promoting plant growth and diluting the toxic effects of Cd. Although Cd uptake increased with increasing temperature, duckweed with relatively high biomass exhibited a lower accumulation of the toxic metal because their growth rate exceeded Cd uptake rate. Increasing N and P supply also enhanced the tolerance of duckweed to Cd by limiting Cd bioavailability. Our study therefore suggests the importance of combined effects from temperature and nutrients for Cd toxicity and provides novel insights for a comprehensive analysis of Cd toxicity associated with the environmental factors of a particular ecosystem.

Characterization, expression, and function analysis of AKR1A1 gene from yellow catfish (Tachysurus fulvidraco)

Aldehyde reductase (AKR1A1) is a carbonyl detoxification protein in toxic aldehyde removal. In the present study, the full-length cDNA of yellow catfish AKR1A1 (TfAKR1A1) was cloned. As expected, yellow catfish AKR1A1 showed similarities with that of other species. Subsequently, prokaryotic expression vector was constructed and recombinant TfAKR1A1 (rTfAKR1A1) was successfully induced and purified. rTfAKR1A1 exhibited reductive activity to many aldehydes and ketones. To determine whether TfAKR1A1 could confer stress tolerance in vitro, the viability of control and TfAKR1A1 expression E. coli under abiotic stress was compared by spot assay. Results showed that the recombinant strain had better stress resistance under cadmium, hydrogen peroxide, and DL-glyceraldehyde stress. Then, effects of an intraperitoneal injection of rTfAKR1A1 protein on cadmium-induced oxidative stress were evaluated. Results displayed that TfAKR1A1 and Nrf2 expression levels were significantly decreased, CAT and SOD expression levels were significantly increased, BCL-2 and IL-10 expression levels were significantly increased, and caspase3a, NF-κB, and IL-1β expression levels were significantly decreased in protein-injection group. Furthermore, oxidative stress indexes in livers under different protein injection doses were examined by ELISA. Results showed that CAT, SOD, and GSH-Px activities were upregulated, ROS and T-AOC contents were also improved, while MDA content was significantly decreased both in lower and middle dose injection groups. Finally, liver pathological section analysis was performed. Results displayed that liver injury degree in protein-injected groups was lower than that of PBS group under cadmium stress. These results suggested that TfAKR1A1 played important roles in response to cadmium stress in yellow catfish.

Modulatory effects of carvacrol against cadmium-induced hepatotoxicity and nephrotoxicity by molecular targeting regulation

AIM

Cadmium (Cd) is a toxic heavy metal that causes severe toxic effects on different tissues including liver and kidney. Therefore the research for alternatives to reduce the damage caused by Cd has substantial importance. This study was performed to examine the possible modulatory effects of carvacrol (CRV) against Cd-induced hepatorenal toxicities and the possible mechanisms underlying these effects.

MATERIALS AND METHODS

In the present study, 35 male Wistar rats were randomly divided into 5 groups. The rats were treated with Cd (25 mg/kg) and treated with CRV (25 and 50 mg/kg body weight) for 7 consecutive days.

KEY FINDINGS

CRV could modulate Cd-induced elevations of ALT, ALP, AST, urea, creatinine, MDA and enhance antioxidant enzymes' activities such as SOD, CAT, and GPx, and GSH's level. CRV also reversed the changes in levels of inflammatory biomarker and apoptotic genes that include NF-κB, Bcl-3, MAPK-14, iNOS, COX-2, MPO, PGE2, Bax, Bcl-2, P53, Caspase-9, Caspase-6 and Caspase-3 in both tissues. The levels of 8-OHdG in the Cd-induced liver and kidney tissues were modulated after CRV treatment. Furthermore, CRV treatment considerably lowered Cd, Na, Fe, and Zn content while increased K, Ca, Mg and Cu contents in both tissues as compared to the Cd-exposed rats.

SIGNIFICANCE

The results of the present study revealed that CRV supplementation could be a promising strategy to protect the liver and kidney tissues against Cd-induced oxidative damage, inflammation and apoptosis.

Caffeic acid phenethyl ester mitigates cadmium-induced hepatotoxicity in mice: Role of miR-182-5p/TLR4 axis

Cadmium (Cd), an environmental pollutant, is evidenced to cause hepatotoxicity. In this study, the potential protective effect of caffeic acid phenethyl ester (CAPE) on cadmium-induced liver damage was investigated. Forty male mice were treated daily with either CdCl₂ (1.5 mg/kg body weight (b.w.), gavage) or CAPE (10 μmol/kg b.w., gavage) or both for 4 weeks. CAPE administration significantly reduced Cd level and liver and body weight, and increased AST, ALT and ALP level. Moreover, CAPE prevented CdCl₂-induced oxidative stress via PI3K/Akt/mTOR pathway and inhibited apoptosis by regulating apoptosis markers. CAPE also suppressed the CdCl₂-induced inflammation by reducing the inflammatory mediators, including TNF-α, IL-6 and IL-1β. Furthermore, CAPE alleviated CdCl₂-induced reduction of TLR4. It should be noted that this effect was achieved by targeting miR-182-5p, and CAPE improved miR-182-5p level. The improvement of the liver tissue histopathology by CAPE confirmed the biochemical data. These results show for the first time that miR-182-5p/TLR4 axis involved in CAPE's protection against CdCl₂-induced hepatotoxicity, and may provide novel insights into the treatment of cadmium-related diseases.

Effects of thermal stress-induced lead (Pb) toxicity on apoptotic cell death, inflammatory response, oxidative defense, and DNA methylation in zebrafish (Danio rerio) embryos

Lead (Pb) is a toxic environmental pollutant that is frequently present in effluents from urban, mining, and industrial sources. The combinatorial effects of heavy metal exposure and temperature in aquatic organisms have received considerable attention as heat stress occurs simultaneously in conjunction with several contaminants in a natural environment. In this study, we examined the potential effects of Pb exposure in conditions of thermal stress (34 °C) in zebrafish (Danio rerio) embryos. Thermal stress at 34 °C induced a dramatic decrease in the survival rate, although exposure to Pb at 26 °C decreased the survival rate of the embryos. Malformations, such as the curved body shape, were increased in response to exposure to a combination of Pb and heat stress. The combination of Pb and heat stress also caused a decrease in the heart rate. Moreover, Pb and high-temperature exposure induced the upregulation of SOD, CAT, TNF-α, IL-1β, p53, and BAX transcripts, and downregulation of Dnmt1 and Dnmt3b transcripts. Thermal stress enhanced transcriptional responses of eight indicator genes following Pb toxicity. The induction of cell death in response to combined exposures was also confirmed in the body of zebrafish by fluorescence intensity image analysis. These data indicated that thermal stress enhanced the poisonous effects of Pb exposure on antioxidant defense, inflammation, and apoptotic mechanisms. Transcriptional inhibition of DNA methylation-related genes might serve as a crucial factor contributing to the possibility of epigenetic adaptation by altering combined stress. We suggest that a careful evaluation of the potential effects of climate change (especially temperature) should be considered when investigating the toxic levels of metal pollution, such as Pb, in an aquatic environment.

High salinity acclimatization alleviated cadmium toxicity in Dunaliella salina: Transcriptomic and physiological evidence

In the present study, we tested the hypothesis that high salinity acclimatization can mitigate cadmium (Cd) toxicity in the microalga Dunaliella salina. To this end, microalgal cells were subjected to high salinity (60 g/L) for 12 weeks until the growth rate remained stable between generations and were then exposed to 2.5 mg/L of Cd for 4 days. Acute Cd toxicity impaired cell growth by increasing Cd bioaccumulation and lipid peroxidation, which reduced cellular pigment, total protein, and glutathione content. It also significantly weakened photosynthetic efficiency and total antioxidant capacity. However, acclimatization to high salinity alleviated these negative effects under Cd stress. To understand the potential mechanisms behind this phenomenon, 12 cDNA libraries from control, Cd-exposed (Cd), high salinity-acclimated (Salinity), and high salinity-acclimated with Cd exposure (Salinity + Cd) cells were derived using RNA sequencing. A total of 2019, 1799, 2150 and 1256 differentially expressed genes (DEGs) were identified from sample groups Salinity / Control, Cd / Control, Salinity + Cd / Control, and Salinity + Cd / Cd, respectively. Some of these DEGs were significantly enriched in ribosome, photosynthesis, stress defense, and photosynthesis-antenna proteins. Among these genes, 82 ribosomal genes were up-regulated in Salinity / Control (corrected P = 3.8 × 10^-28), while 81 were down-regulated in Cd / Control (corrected P = 1.1 × 10^-24). Moreover, high salinity acclimatization up-regulated 8 photosynthesis genes and 18 stress defense genes compared with the control. Additionally, 3 photosynthesis genes, 11 stress defense genes and 11 genes encoding light harvesting proteins were up-regulated by high salinity acclimatization under Cd exposure. Overall, high salinity acclimatization mitigated Cd toxicity, possibly by up-regulating the transcription of photosynthesis, stress defense, and ribosomal genes. These results provide new insights on cross-tolerance in microalgae.

Effects of combined stressors to cadmium and high temperature on antioxidant defense, apoptotic cell death, and DNA methylation in zebrafish (Danio rerio) embryos

Fish are frequently affected by environmental stressors, such as temperature changes and heavy metal exposure, in aquatic ecosystems. In this study, we evaluated the combined effects of cadmium (Cd) toxicity and temperature (rearing temperature of 26 °C and heat stress at 34 °C) on zebrafish (Danio rerio) embryos. The survival and heart rates of zebrafish embryos decreased at relatively high Cd concentrations of 0.07 and 0.1 mg L^-1. Abnormal morphology was induced by exposure to a combination of Cd toxicity and heat stress. The yolk sac edema size was not significantly different between the control- and Cd-treated groups. Cd exposure induced reactive oxygen species (ROS) production and cell death in the live zebrafish. High temperature (34 °C) triggered Cd-induced cell death and intracellular ROS production to a greater extent than the rearing temperature of 26 °C. Transcriptional levels of six genes-CAT, SOD, p53, BAX, Dnmt1, and Dnmt3b-were investigated. The mRNA expression of CAT and SOD, molecular indicators of oxidative stress, was increased significantly at 34 °C after Cd exposure. The mRNA expression of CAT was more sensitive to temperature than that of SOD in Cd-treated zebrafish. p53 and BAX, apoptosis-related genes, were upregulated upon combined exposure to high temperature and Cd. In addition, at 34 °C, the expression of Dnmt1 and Dnmt3b transcripts, markers of DNA methylation, was increased upon exposure of zebrafish to all concentrations of Cd. Overall, these results suggest that high temperature facilitates the potential role of Cd toxicity in the transcriptional regulation of genes involved in the antioxidant system, apoptosis, and DNA methylation.

Selenium prevent cadmium-induced hepatotoxicity through modulation of endoplasmic reticulum-resident selenoproteins and attenuation of endoplasmic reticulum stress

Cadmium (Cd), a heavy metal contaminant, exists in humans and animals throughout life and closely associate with severe hepatotoxicity. Selenium (Se) has been recognized as an effective chemo-protectant of Cd, but the underlying mechanisms remain unclear. The objective of the present study is to illustrate the antagonistic effect of Se against Cd-induced hepatotoxicity. Primary hepatocytes were cultured in the presence of 5 μM Cd, 1 μM Se and the mixture of 1 μM Se and 5 μM Cd for 24 h. Cell viability and morphology, antioxidant status, endoplasmic reticulum (ER) stress response and selenotranscriptome were assessed. It was observed that Se treatment dramatically alleviated Cd-induced hepatocytes death and morphological change. Simultaneously, Se mitigated Cd-induced oxidative stress by reducing ROS production, increasing reduced glutathione (GSH) level and increasing selenoenzyme (glutathione peroxidase, GPX) activity. Cd induced hepatotoxicity via disordering ER-resident selenoproteins transcription and triggering ER stress and unfolded protein response. Supplementary Se evidently relieved hepatocytes injury via modulating ER-resident selenoproteins transcription to inhibit ER stress. Collectively, our findings showed a potential protection of Se against Cd-induced hepatotoxicity via suppressing ER stress response.

Genomic regions and pathways associated with thermotolerance in layer-type strain Taiwan indigenous chickens

This study aimed to investigate genetic markers and candidate genes associated with thermotolerance in a layer-type strain Taiwan indigenous chickens exposed to acute heat stress. One hundred and ninety-two 30-week-old roosters were subjected to acute heat stress. Changes in body temperature (BT, ΔT) were calculated by measuring the difference between the initial BT and the highest BT during heat stress and the results were categorized into dead, susceptible, tolerant, and intermediate groups depending on their survival and ΔT values at the end of the experiment. A genome-wide association study on survival and ΔT values was conducted using the Cochran-Armitage trend test and Fisher's exact test. Association analyses identified 80 significant SNPs being annotated to 23 candidate genes, 440 SNPs to 71 candidate genes, 64 SNPs to 25 candidate genes, and 378 SNPs to 78 candidate genes in the dead versus survivor, tolerant versus susceptible, intermediate versus tolerant, and intermediate versus susceptible groups, respectively. The annotated genes were associated with apoptosis, cellular stress responses, DNA repair, and metabolic oxidative stress. In conclusion, the identified SNPs of candidate genes provide insights into the potential mechanisms underlying physiological responses to acute heat stress in chickens.

The effects of cadmium exposure in the induction of inflammation

Inflammation is a physiological process essential for maintaining homeostatic mechanisms in human, but however, exaggerated inflammatory responses are closely related to many chronic diseases. Cadmium (Cd) is a heavy metal with high toxicity when present in food, water and air has the potential of eliciting inflammatory reactions, with a major health risk to human. This review aimed to elucidate on the major routes of Cd exposure, the main organs affected by the exposure, the degree of toxicity as well as the roles of the toxic effects on the immune system which results to inflammatory responses. Immune modulation by Cd may cause serious adverse health effects in humans. Various studies have highlighted the ability of Cd as an environmental pollutant involved in the modulation of the innate, adaptive and mucosal immune responses in relations to the release of chemokine, gene expression, and susceptibility to microbial infections.

Negative effects of acute cadmium on stress defense, immunity, and metal homeostasis in liver of zebrafish: The protective role of environmental zinc dpre-exposure

In the study, zebrafish were exposed to 0 and 200 μg/L Zn for 8 weeks, and then both groups were transferred to water including 0, 100, and 200 μg/L Cd for 4 days, respectively. Acute Cd exposure caused negative effects on stress defense, immune, and metal transport systems by increasing lipid peroxidation, iNOS activity and mRNA levels of il-6 and inos, and decreasing Cu/Zn-SOD and HSP70 levels, and mRNA levels of sod1, cat, hsp70, p65, mtf-1, znt5, zip7, atp7a, and atp7b. Lipid peroxidation was significantly reduced by Zn pre-exposure under Cd exposure, which may be explained by the enhanced stress defense capacity and the weaken inflammatory response. Firstly, Zn pre-exposure increased MTs and HSP70 levels and CAT activity in Cd-free water, which may facilitate fish quick response to Cd. Secondly, Zn pre-exposure reduced Cd accumulation at 100 and 200 μg/L Cd, down-regulated il-6 and il-1β at 100 μg/L Cd and p65 at 200 μg/L Cd, and increased Cu/Zn-SOD and CAT activities at 200 μg/L Cd. Thirdly, Zn pre-exposure alone up-regulated transcription factors (hsf1, hsf2, and mtf-1, and nrf2) and their target genes (sod1, cat, hsp70, and mt2) under Cd exposure in a dose-dependent manner. It should be noted that Zn pre-exposure down-regulated several metal transport genes dramatically at 0 and 100 μg/L Cd, which may be an important mechanism for reducing Cd import into livers. Overall, long-term and environmental Zn pre-exposure mitigated Cd toxicity by the enhanced stress defense capacity and the down-regulated metal transport and inflammatory responses.

The role of Nrf2-Keap1 signaling pathway in the antioxidant defense response induced by PAHs in the calm Ruditapes philippinarum

The NF-E2-related factor 2 (Nrf2) is a master regulator of cellular responses against environmental stresses. In this study we cloned the full-length cDNAs of the RpNrf2 encompassed 2823 bp from the clam Ruditapes philippinarum (R. philippinarum). Sequences alignment and phylogenetic analysis showed that Nrf2 was highly specific in the clams. RpNrf2 expression was detected in gill, digestive gland, mantle and adductor, which the highest transcription level was observed in gill and digestive gland. The gene expressions of RpNrf2, Kelch-like-ECH-associated Protein 1 (Keap1), Cul3-based E3 Ubiquitin Ligase (E3), Glutathione S-transferase (GST-pi), Superoxide Dismutase (SOD), Catalase (CAT) and Glutathione Peroxidase (GPx) in digestive gland was evaluated by real-time PCR after being exposed to benzo(a)pyrene (BaP) (0.25, 1and 4 μg/L) for 15 days, which showed that the expression of Nrf2 significantly increased at day 1 and day 6 after exposure (p < 0.05), and there was a negative relationship between the mRNA levels of Nrf2 and Keap1 that indicates the enhancement of Keap1 expression stimulating Nrf2 degradation. RNA interference experiments were conducted to examine the expression profiles of RpNrf2, antioxidant and detoxification genes (GST-pi, Cu/Zn-SOD, CAT and GPx) and Lipid Peroxidase (LPO) level in digestive gland exposed to BaP. The results showed that the mRNA level of Nrf2 was significantly decreased by 63.2%, and the changes of antioxidant and detoxification genes expression were consistent with the Nrf2 gene suggesting that Nrf2 is required for the induction of antioxidant and detoxification genes. Besides, the LPO levels expressed by malondialdehyde (MDA) contents were significant higher compared with the control group at 72 h post dsRNA-Nrf2 injection. In conclusion, our data demonstrated that Keap1 can sense nucleophilic or oxidative stress factors to regulate the Nrf2 signaling pathway together with E3 and Nrf2 signaling pathway plays an important role in modulating gene expression of antioxidant enzymes in bivalve mollusks.