Bioaccumulation and physiological responses in juvenile Marsupenaeus japonicus exposed to cadmium

Caffeic acid attenuates memory dysfunction and restores the altered activity of cholinergic, monoaminergic and purinergic in brain of cadmium chloride exposure rats

Objectives This study aims to evaluate the neuroprotective effect of caffeic acid (CAF) against cadmium chloride (CdCl2) in rats via its effect on memory index as well as on altered enzymatic activity in the brain of CdCl2-induced neurotoxicity. Methods The experimental rats were divided into seven groups (n=6 rats per group) of healthy rats (group 1), CdCl2 -induced (CD) (3 mg/kg BW) rats (group 2), CD rats + Vitamin C (group 3), CD rats + CAF (10 and 20 mg/kg BW respectively) (group 4 & 5), and healthy rat + CAF (10 and 20 mg/kg BW respectively) (group 6 & 7). Thereafter, CdCl2 and CAF were administered orally to the experimental rats in group 2 to group 5 on daily basis for 14 days. Then, the Y-maze test was performed on the experimental rats to ascertain their memory index. Results CdCl2 administration significantly altered cognitive function, the activity of cholinesterase, monoamine oxidase, arginase, purinergic enzymes, nitric oxide (NOx), and antioxidant status of Cd rats (untreated) when compared with healthy rats. Thereafter, CD rats treated with vitamin C and CAF (10 and 20 mg/kg BW) respectively exhibited an improved cognitive function, and the observed altered activity of cholinesterase, monoamine oxidase, arginase, purinergic were restored when compared with untreated CD rats. Also, the level of brain NOx and antioxidant status were significantly (p<0.05) enhanced when compared with untreated CD rats. In the same vein, CAF administration offers neuro-protective effect in healthy rats vis-à-vis improved cognitive function, reduction in the activity of some enzymes linked to the progression of cognitive dysfunction, and improved antioxidant status when compared to healthy rats devoid of CAF. Conclusions This study demonstrated the neuroprotective effect of CAF against CdCl2 exposure and in healthy rats.

Sources, bioaccumulation, and toxicity mechanisms of cadmium in Chlamys farreri

The Potentially toxic elements (PTEs) cadmium (Cd) is one of the most serious stressors polluting the marine environment. Marine bivalves have specific high enrichment capacity for Cd. Previous studies have investigated the tissue distribution changes and toxic effects of Cd in bivalves, but the sources of Cd enrichment, migration regulation during growth, and toxicity mechanisms in bivalves have not been fully explained. Here, we used stable-isotope labeling to investigate the contributions of Cd from different sources to scallop tissues. We sampled the entire growth cycle of Chlamys farreri, which is widely cultured in northern China, from juveniles to adult scallops. We found tissue variability in the bioconcentration-metabolism pattern of Cd in different bound states, with Cd in the aqueous accounting for a significant contribution. The accumulation pattern of Cd in all tissues during growth was more significant in the viscera and gills. Additionally, we combined a multi-omics approach to reveal a network of oxidative stress-induced toxicity mechanisms of Cd in scallops, identifying differentially expressed genes and proteins involved in metal ion binding, oxidative stress, energy metabolism, and apoptosis. Our findings have important implications for both ecotoxicology and aquaculture. They also provide new insights into marine environmental assessment and mariculture development.

Heavy metals and metalloid in aquatic invertebrates: A review of single/mixed forms, combination with other pollutants, and environmental factors

Heavy metals (HMs) and metalloid occur naturally and are found throughout the Earth's crust but they are discharged into aquatic environments at high concentrations by human activities, increasing heavy metal pollution. HMs can bioaccumulate in higher organisms through the food web and consequently affect humans. In an aquatic environment, various HMs mixtures can be present. Furthermore, HMs adsorb on other environmental pollutants, such as microplastics and persistent organic pollutants, causing a synergistic or antagonistic effect on aquatic organisms. Therefore, to understand the biological and physiological effects of HMs on aquatic organisms, it is important to evaluate the effects of exposure to combinations of complex HM mixtures and/or pollutants and other environmental factors. Aquatic invertebrates occupy an important niche in the aquatic food chain as the main energy link between higher and lower organisms. The distribution of heavy metals and the resulting toxic effects in aquatic invertebrates have been extensively studied, but few reports have dealt with the relationship between HMs, pollutants, and environmental factors in biological systems with regard to biological availability and toxicity. This review describes the overall properties of individual HM and their effects on aquatic invertebrates and comprehensively reviews physiological and biochemical endpoints in aquatic invertebrates depending on interactions among HMs, other pollutants, and environmental factors.

Effects of lead pollution on bacterial communities in biofilm attached to submerged plants

Submerged plants and biofilms have significant advantages in hydro-ecology rehabilitation, but their tolerance and physiological responses to heavy metal stress have thus far been under-investigated. This study investigated the influence of lead on physiological and biochemical responses, as well as variation in bacterial communities and functional characteristics of submerged plant biofilms. The results showed that chlorophyll a content of two submerged plants decreased with increased lead concentration. The concentration of malondialdehyde of both submerged plants was higher under high lead concentrations than under low lead concentrations, and the concentrations of malondialdehyde and hydrogen peroxide in Vallisneria natans were more stable. The antioxidant enzyme systems of the two plants played protective roles against lead stress. High lead concentration can inhibit the bacterial community and lead to decreased diversity. The most abundant bacterial phyla were Proteobacteria (40.9%), Cyanobacteria (21.5%), and Bacteroidetes (14.3%). Proteobacteria abundance decreased with increased lead concentration, while Cyanobacteria abundance increased. The lead concentration in plants (19.7%, P < 0.01) and the lead concentration in aquatic environment (17.7%, P < 0.01) were significantly correlated with variation in bacterial communities. High lead concentration inhibits the activity of these bacteria related to the conversion of nitrogen and sulfur.

Organ-specific accumulation of cadmium and zinc in Gammarus fossarum exposed to environmentally relevant metal concentrations

One of the best approaches for improving the assessment of metal toxicity in aquatic organisms is to study their organotropism (i.e., the distribution of metals among organs) through a dynamical approach (i.e., via kinetic experiments of metal bioaccumulation), to identify the tissues/organs that play a key role in metal regulation (e.g., storage or excretion). This study aims at comparing the organ-specific metal accumulation of a non-essential (Cd) and an essential metal (Zn), at their environmentally relevant exposure concentrations, in the gammarid Gammarus fossarum. Gammarids were exposed for 7 days to ¹⁰⁹Cd- or ⁶⁵Zn-radiolabeled water at a concentration of 52.1 and 416 ng.L^-1 (stable equivalent), respectively, and then placed in clean water for 21 days. At different time intervals, the target organs (i.e., caeca, cephalons, intestines, gills, and remaining tissues) were collected and ¹⁰⁹Cd or ⁶⁵Zn contents were quantified by gamma-spectrometry. A one-compartment toxicokinetic (TK) model was fitted by Bayesian inference to each organ/metal dataset in order to establish TK parameters. Our results indicate: i) a contrasting distribution pattern of concentrations at the end of the accumulation phase (7^th day): gills > caeca ≈ intestines > cephalons > remaining tissues for Cd and intestines > caeca > gills > cephalons > remaining tissues for Zn; ii) a slower elimination of Cd than of Zn by all organs, especially in the gills in which the Cd concentration remained constant during the 21-day depuration phase, whereas Zn concentrations decreased sharply in all organs after 24 h in the depuration phase; iii) a major role of intestines in the uptake of waterborne Cd and Zn at environmentally relevant concentrations.

Effects of copper on non-specific immunity and antioxidant in the oriental river prawn (Macrobrachium nipponense)

The copper, as heavy metal has important impacts on the antioxidant and immune defense systems in aquatic organisms, and the toxic effects of copper can be accumulated and magnified with the food chain, thus posing a threat to food safety as well as ecosystems. This study explored the response of the antioxidant system and non-specific immunity in M. nipponense to copper stress. Low concentration of copper (0.05, 0.1 mg L^-1) had positive effects on the non-specific immunity in M. nipponense, while the non-specific immunity in M. nipponense could be affect negatively or even be inhibited by high copper concentration (0.15 mg L^-1). Even low concentrations of copper could cause oxidative stress, and high copper concentration (0.15 mg L^-1) could induce oxidative damage and even apoptosis, and thus causing damage to the antioxidant defense system in M. nipponense. Low concentration of copper could affect the gill and hepatopancreas structure in M. nipponense, but high level oxidative stress caused by high copper concentration could cause oxidative damage to these tissue, resulting in the destruction of gill and hepatopancreas. This study provides the safety concentration for using copper-containing fish drugs in the actual culture of M. nipponense and provides basic data for the toxicity mechanism of copper to M. nipponense.

Toxicological responses of juvenile Chinese shrimp Fenneropenaeus chinensis and swimming crab Portunus trituberculatus exposed to cadmium

Cadmium (Cd) is one of the typical metal pollutants in the Bohai Sea. To evaluate the acute toxicological effects of Cd on marine crustaceans, juvenile Fenneropenaeus chinensis and Portunus trituberculatus were exposed to Cd at environmentally relevant concentrations (5 and 50 μg/L) for 96 h. Cd accumulation, antioxidants and metabolite profiles were characterized to elucidate the responses of juvenile crustaceans to Cd stress. Significant Cd accumulation was observed in both juvenile crustaceans in 50 μg/L Cd-treated group. Results showed that Cd exposure induced hormesis based on the alterations of GSH, SOD and CAT activities (i.e. increased levels in the low concentration of Cd treatment and recovered levels in the high concentration of Cd treatment) in juvenile P. trituberculatus. Similarly, the responses of GSH contents presented hormesis pattern in Cd-treated juvenile F. chinensis. Na+-K+-ATPase contents were significantly elevated in 50 μg/L Cd-treated group. In addition, untargeted NMR-based metabolomics indicated Cd caused the disturbance in osmotic regulation and energy consumption in both juvenile F. chinensis and P. trituberculatus via different pathways. The immunotoxicity and movement disorder were uniquely demonstrated in juvenile P. trituberculatus after Cd exposure.

Metabolomic Alterations in the Digestive System of the Mantis Shrimp Oratosquilla oratoria Following Short-Term Exposure to Cadmium

Mantis shrimp Oratosquilla oratoria is an economically critical aquatic species along the coast of China but strongly accumulates marine pollutant cadmium (Cd) in its digestive system. It is necessary to characterize the toxicity of Cd in the digestive system of mantis shrimp. The metabolic process is an essential target of Cd toxicity response. In this work, we used ultra-performance liquid chromatography coupled with time-of-flight mass spectrometry (UPLC-TOF-MS) for untargeted metabolomics to characterize the metabolic changes in the digestive system of O. oratoria, exposed to 0.05 mg/L for 96 h. The aim of this study was to further investigate the effect of O. oratoria on Cd response to toxicity and develop biomarkers. Metabolomics analysis showed the alteration of metabolism in the digestive system of mantis shrimp under Cd stress. A total of 91 metabolites were differentially expressed and their main functions were classified into amino acids, phospholipids, and fatty acid esters. The enrichment results of differential metabolite functional pathways showed that biological processes such as amino acid metabolism, transmembrane transport, energy metabolism, and signal transduction are significantly affected. Based on the above results, the Cd-induced oxidative stress and energy metabolism disorders were characterized by the differential expression of amino acids and ADP in mantis shrimp, while the interference of transmembrane transport and signal transduction was due to the differential expression of phospholipids. Overall, this work initially discussed the toxicological response of Cd stress to O. oratoria from the metabolic level and provided new insights into the mechanism.

Effects of cadmium on antioxidant and non-specific immunity of Macrobrachium nipponense

As a non-essential and toxic element, cadmium poses an important threat to aquatic organisms and human food safety. In this study, the effects of cadmium on antioxidant and non-specific immunity of Macrobrachium nipponense were studied from the physiological and biochemical indexes, histology and expression of related genes. These results showed that low concentrations (0.01, 0.02 mg/L) of cadmium have a positive effect on the non-specific immunity of M. nipponense, but high concentration (0.04 mg/L) of cadmium could inhibit or even damage the non-specific immunity of M. nipponense. The cadmium could induce oxidative stress in M. nipponense, and M. nipponense actived the antioxidant defense system to deal with oxidative stress, but high concentration (0.04 mg/L) of cadmium could inhibit the antioxidant defense system of M. nipponense, leading to oxidative damage, and may induce apoptosis in severe case. At the same time, the results of histology showed that cadmium can damage the structure of gill and hepatopancreas tissues of M. nipponense. This study provides theoretical data for evaluating the influences of heavy metal cadmium on M. nipponense and the toxic mechanism of heavy metal cadmium.

Comparative transcriptome analysis of the gills of Procambarus clarkii provide novel insights into the response mechanism of ammonia stress tolerance

Procambarus clarkii is an important model crustacean organism in many researches. Ammonia nitrogen is one of common contaminants in aquatic environment, influencing the health of aquatic organisms. The primary objective of this study was to investigate molecular mechanisms on ammonia stress in gills of P. clarkii to provide new insights into the strategies of aquatic animals in responding to high concentration of ammonia in the environment. Procambarus clarkii were randomly assigned into two groups (ammonia stress group, AG; control group, CG), and gill samples were dependently excised from AG and CG. Then response mechanisms on ammonia stress were investigated based on transcriptome data of P. clarkii. 9237 differentially expressed genes were identified in ammonia stress group. The genes of ion transport enzymes (NKA and SLC6A5S) were significantly up-regulated. Whereas the immune-related genes (e.g. MAP3K7, HSP70, HSP90A, CTSF, CTSL1, CHI and CTL4) and pathways were significantly up-regulated, which played an important role in reacting to ammonia stress. Procambarus clarkii may enhance immune defense to counteract ammonia toxicity by the up-regulation of immune-related genes and signaling pathways. The activities of ion transport enzymes are changed to mobilise signal transduction and ion channel regulation for adapting to ammonia environment. These previous key genes play an important role in resistance to ammonia stress to better prepare for survival in high concentration of ammonia.

Accumulation and Depuration of Cd and its Effect on the Expressions of Metallothionein and Apoptotic Genes in Litopenaeus vannamei

We investigated cadmium (Cd) accumulation in muscles, gills and hepatopancreas of Litopenaeus vannamei following 48 h exposure to 5.25 mg/L, and depuration of Cd in these tissues on 1, 5 and 15 d post exposure. We also detected the expressions of metallothionein (MT), caspase-3 and p53 in hepatopancreas of shrimp exposed to 0, 5.25 and 10.5 mg/L Cd (the 24 h median lethal concentration, 24 h LC₅₀) at 0, 3, 12, 24 and 48 h. Cd accumulated with high concentration in hepatopancreas, and low concentration in muscles. Cd depurated fast in hepatopancreas and gills. MT expression increased in a time-dependent manner after Cd exposure. The p53 and caspase-3 increased at 12 and 24 h in 10.5 mg/L group. In conclusion, the accumulation and depuration of Cd in three tissues were tissues-specific. The changes of the expressions of MT, p53 and caspase-3, were stress response of L. vannamei under Cd exposure.

Cadmium-induced oxidative stress, metabolic dysfunction and metal bioaccumulation in adult palaemonid shrimp Palaemon macrodactylus (Rathbun, 1902)

The Palaemonid shrimp Palaemon macrodactylus is widely distributed in coastal areas and estuaries which are easily contaminated by various pollutants. However, the responses of this species to environmental toxicants are not well described. In the present study, adult individuals of P. macrodactylus were exposed to gradient concentrations of Cadmium (Cd) to evaluate its acute toxic effects, including bioaccumulation, induced oxidative stress and changed energy metabolism in this species. The medium lethal concentration (LC₅₀) of Cd at 24 h, 48 h, 72 h, and 96 h were 2.60, 0.88, 0.49 and 0.37 mg/L, respectively. Cd bioaccumulations in tissues of shrimp increased in a concentration-dependent manner, and higher concentration (50% 96 h-LC₅₀, 0.185 mg/L) of Cd exposure led to a maximum increase of Cd concentration by 14.8, 145.5 and 15.8 folds in gill, hepatopancreas and abdominal muscle. Cd exposure caused a significant inhibition on the activity of catalase (CAT), and total superoxide dismutase (T-SOD), decrease in the total antioxidant capacity (T-AOC), and an increase of malonadehyde (MDA) content, which indicated a damage to the antioxidant system of shrimp. Meanwhile, Cd exposure also led to a significant up-regulation in the expression level of metallothionein gene (MT), and down-regulations at the mRNA level of heat shock protein 70 (HSP70) and CAT. Moreover, Cd exposure significantly inhibited the oxygen consumption rate (22%), and increased the ammonia excretion rate (43%), hence lead to a significant decrease of the O:N ratio (45%) in shrimp. The results indicated that Cd exposure could induce obvious oxidative stress, energy metabolic dysfunction and bioaccumulation of Cd in P. macrodactylus. The data obtained from the present study would provide useful information for further understanding on the toxicological mechanism of Cd to crustaceans in coastal areas and estuaries.

The role of Nrf2 in mitigating cadmium-induced oxidative stress of Marsupenaeus japonicus

Nuclear factor-erythroid 2-related factor-2 (Nrf2) is an important modulator of cellular responses against Cd in mammalian cells. However, whether such modulation is conserved in Marsupenaeus japonicas remains unknown.In our study, the shrimps were injected with dsRNA targeting Nrf2 at 4 μg g^-1 body weight (b.w.) or sulforaphane (SFN) at 5 μg g^-1 b.w., and then were exposed to 40 mg L^-1 CdCl₂ for 48 h. After Nrf2 knockdown, the Cd content increased, but decreased in the SFN group. This suggested that Nrf2 could promote Cd excretion. A terminal deoxynulceotidyl transferase nick-end-labeling (TUNEL) assay revealed that the Nrf2 knockdown increased the number of apoptotic cells in M. japonicas, while SFN decreased the number of apoptotic cells. After Nrf2 knockdown, the total antioxidant capacity (T-AOC), superoxide dismutase (Sod) activity, and related gene expression decreased significantly, while the malondialdehyde (MDA) content increased remarkably. By contrast, SFN injection alleviated the oxidative stress, as evidenced by increased T-AOC, Sod activity, sod mRNA expression and a reduced MDA content. Similarly, detoxification related enzyme activities (ethoxyresorufin O-deethylase and glutathione-S-transferase (GST)) and their corresponding gene expressions (cyp3a (cytochrome P450 family 3 subfamily A) and gst) were suppressed in the ds-Nrf2 injection group, while they were elevated in the SFN group. In addition, ds-Nrf2 activated mitochondrial apoptotic pathway, as evidenced the mRNA and protein levels of caspase-3, Bcl2 associated X protein (Bax), and p53, while SFN treatment suppressed them. These results displayed that in M. japonicus Cd-induced cellular oxidative damage probably acts via the Nrf2 pathway.

iTRAQ and PRM-based comparative proteomic profiling in gills of white shrimp Litopenaeus vannamei under copper stress

Crustaceans are particularly sensitive to heavy metal pollution. Copper (Cu) is one of typical heavy metal pollutants in aquatic ecosystems. However, limited attention has been paid on the proteomic responses of shrimp under Cu stress. White shrimp Litopenaeus vannamei held in 5‰ seawater were exposed to 5 mg L^-1 Cu for 3 h, and the regulatory mechanism in the gills was elucidated using iTRAQ-based quantitative proteomics. The results showed that a total of 5034 proteins were identified, 385 differentially expressed proteins (DEPs), including 147 differentially up-regulated proteins (DUPs) and 238 differentially down-regulated proteins (DDPs) were found. Bioinformatics analysis indicated the DEPs responding to Cu stress mainly involved in cytoskeleton, immune response, stress response, protein synthesis, detoxification, ion homeostasis and apoptosis. Furthermore, we still performed PRM analysis on sarcoplasmic calcium binding protein (SCP), serine proteinase inhibitor B3 (SPIB3), C-type lectin 4 (CTL4), cathepsin L (CATHL), JHE-like carboxylesterase 1 (CXE1) and paramyosin (PMY), and biochemical analysis on Cu/Zn-superoxide dismutase (Cu/Zn-SOD) to validate the iTRAQ results, respectively. The present proteome analysis revealed that Cu stress disrupted the ion homeostasis and protein synthesis, and L.vannamei mainly regulates a series of molecular pathways which contained many key proteins involved in the immune process to protect the organism from Cu stress. Our data provides more insight about the underlying mechanisms that related to the stress response of Cu exposure in crustacean.

Heme oxygenase 1 plays a crucial role in swamp eel response to oxidative stress induced by cadmium exposure or Aeromonas hydrophila infection

Oxidative stress contributes a lot to initiation and progression of pathological conditions. Heme oxygenase 1 (HO1), a cytoprotective enzyme, is usually upregulated to alleviate oxidative stress in vivo. The function of teleost HO1 in the response to oxidative stress induced by heavy metal exposure and in pathogenic bacterial infection remains uncertain. In the present study, both complementary DNA and genomic sequence of a HO1-like gene cloned from the liver of swamp eel (Monopterus albus) are reported. Sequence analysis showed that the putative amino acid sequence contained a conserved heme oxygenase signature and displayed higher similarity to HO1 genes of other teleosts. Expression profile of swamp eel HO1 was investigated in healthy tissues and in tissues following stimulation with pathogenic bacteria (Aeromonas hydrophila) or cadmium chloride (CdCl₂) exposure. Results demonstrated that HO1 messenger RNA (mRNA) was highly expressed in the liver and relatively less in other tissues. Bacterial infection with A. hydrophila significantly changed HO1 mRNA expression in the liver, spleen, and kidney, and the mRNA expression of HO1 and Nrf2 in the liver was elevated after the fish were exposed to CdCl₂. Subsequently, the swamp eel HO1 was subcloned into a pET28a expression vector and transformed into Escherichia coli BL21 (DE3). Recombinant HO1 (rHO1) was successfully induced by 0.1 mmol/l IPTG and purified by Ni-NTA His Bind Resin purification system. To determine whether the rHO1 could confer stress tolerance in vitro, the viability of control and HO1-expressing E. coli under CdCl₂ stress was compared by spot assay. The rHO1 protein significantly increased survival rates of the bacterial hosts. To evaluate whether intraperitoneal injection with rHO1 protected the liver of swamp eel against A. hydrophila-induced oxidative stress, mRNA expression of HO1, Nrf2, hepcidin, and IL-1β as well as the oxidative stress-related parameters (ROS and total antioxidant capacity (T-AOC)) in the liver were examined. The results showed that exogenous rHO1 could significantly upgrade the mRNA expression of HO1 and hepcidin, coupled with increased ROS and T-AOC levels. However, Nrf2 and IL-1β expression levels were significantly downregulated and upregulated, respectively. These results suggested that HO1 should not only play a protective role in oxidative stress response and its adverse effects deserved further investigation.

Comparative accumulation and transcriptomic analysis of juvenile Marsupenaeus japonicus under cadmium or copper exposure

Waterborne metals may be hazardous to aquatic organisms and trigger stress responses. The present study aimed to assess the effect of exposure to 100 μg/L cadmium (Cd) or copper (Cu) for 48 h on juvenile Marsupenaeus japonicus, in terms of bioaccumulation and the whole body transcriptome. The results demonstrated that Cu accumulation in M. japonicas was much higher than that of Cd. Meanwhile, transcriptome analysis identified 1802 and 2670 differentially expressed genes (DEGs) after 48 h exposure to 100 μg/L Cd and Cu, respectively. Among them, 851 DEGs responded to both metals. Cd and Cu stress shared genes were related to the cytoskeleton, immunity, antioxidation, and detoxification. Metallothionein 1 (MT1) was specifically induced in the Cd-stress response, while glycometabolism, heat shock protein 90 (HSP90), metallothionein 2 (MT2), apoptosis, and iron transport-related genes were changed specifically in response to Cu stress. In addition, real-time PCR was used to verify the expression patterns of 28 randomly selected DEGs. The sequencing and real-time PCR results were consistent. Moreover, based on the number of significantly modulated genes and their expression levels, we deduced that Cu acts as a stronger stress inducer than Cd in M. japonicus. The identified Cd and Cu stress related genes and pathways will provide new insights into the common and different molecular mechanisms underlying Cd and Cu toxicity effects in M. japonicus.

Changes of cellular stress response related hsp70 and abcb1 transcript and Hsp70 protein levels in Siberian freshwater amphipods upon exposure to cadmium chloride in the lethal concentration range

The induction of cellular stress response systems, heat shock protein hsp70/Hsp70 and multixenobiotic transporter abcb1, by cadmium chloride (CdCl₂) was explored in amphipod species with different stress adaptation strategies from the Lake Baikal area. Based on the lethal concentrations (LC) of CdCl₂, the sensitivities of the different species to CdCl₂ were ranked (24 hr LC50 in mg/L CdCl₂ (mean/95% confidence interval)): Gammarus lacustris (1.7/1.3–2.4) < Eulimnogammarus cyaneus (2.9/2.1–4.0) < Eulimnogammarus verrucosus (5.7/3.8–8.7) < Eulimnogammarus vittatus (18.1/12.4–26.6). Conjugated dienes, indicating lipid peroxidation, were significantly increased after 24 hr exposures to 5 mg/L CdCl₂ only in the more CdCl₂-sensitive species G. lacustris and E. cyaneus. Upon treatment with 0.54 to 5.8 mg/L CdCl₂ for 1, 6 and 24 hrs, hsp70 transcript levels were generally more increased after the longer exposure times and in the more CdCl₂-sensitive species. Relating the CdCl₂ exposure concentrations to LCx values revealed that across the species the increases of hsp70 transcript levels were comparatively low (up to 2.6-fold) at CdCl₂ concentrations ≤LC50. Relative hsp70 transcript levels were maximally increased in E. cyaneus by 5 mg/L CdCl₂ (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$\hat {=}$\end{document}= ˆLC70) at 24 hrs (9.1-fold increase above the respective control). When G. lacustris was exposed to 5 mg/L CdCl₂ (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$\hat {=}$\end{document}= ˆLC90) for 24 hrs, the increase in hsp70 was in comparison to E. cyaneus considerably less pronounced (3.0-fold increase in hsp70 levels relative to control). Upon exposure of amphipods to 5 mg/L CdCl₂, increases in Hsp70 protein levels compared to untreated controls were highest in E. cyaneus at 1 and 6 hrs (5 mg/L CdCl₂\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$\hat {=}$\end{document}= ˆ LC70) and in E. verrucosus at 24 hrs (5 mg/L CdCl₂\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$\hat {=}$\end{document}= ˆ LC45). Thus, when the fold increases in Hsp70 protein levels in the different amphipod species were related to the respective species-specific LCx values a similar bell-shaped trend as for hsp70 transcript levels was seen across the species. Transcript levels of abcb1 in CdCl₂exposed individuals of the different amphipod species varied up to 4.7-fold in relation to the respective controls. In contrast to hsp70/Hsp70, abcb1 transcripts in CdCl₂ exposed individuals of the different amphipod species did not indicate similar levels of induction of abcb1 at equal LCx levels across the species. Induction of hsp70 and abcb1 genes and Hsp70 proteins by CdCl₂ in the lethal concentration range shows that these cellular responses are rather insensitive to CdCl₂ stress in the examined amphipod species. Furthermore, the increase of expression of these cellular defense systems at such high stress levels suggests that induction of these genes is not related to the maintenance of normal metabolism but to mitigation of the effects of severe toxic stress.

A 28.6-kD small heat shock protein (MnHSP28.6) protects Macrobrachium nipponense against heavy metal toxicity and oxidative stress by virtue of its anti-aggregation activity

Small heat shock proteins (sHSPs) are ATP-independent chaperones and involved into various physiological and stress processes. In the present study, a 28.6-kD sHSP coding gene, MnHSP28.6, was cloned and characterized from the oriental river prawn Macrobrachium nipponense. Tissue distribution analysis via qPCR and western blot revealed that MnHSP28.6 predominantly expressed in muscle. The temporal transcription of MnHSP28.6 in muscle after bacterial challenge, heavy metal exposure and doxorubicin (DOX) injection was investigated by qPCR. The results showed that the expression of MnHSP28.6 were strongly enhanced by both Cd²⁺ and Cu²⁺ exposure, as well as DOX injection, but not by bacterial infection. Aggregation assays showed that recombinant MnHSP28.6 could effectively prevent temperature-induced aggregation of citrate synthase, and reduction-induced aggregation of insulin in vitro. MnHSP28.6 also could protect muscle extracts from heat-induced protein denaturation and superoxide dismutase (SOD) inactivation. Expressing MnHSP28.6 in E. coli conferred host cell impressive protection against H₂O₂ compared to control. These results suggest a protective role of MnHSP28.6 in maintaining protein homeostasis, preventing aggregation, promoting resistance to heavy metal and keeping redox balance.