Cadmium disrupts melanocortin 2 receptor signaling in rainbow trout

Transcriptome analysis of Sparidentex hasta larvae exposed to water-accommodated fraction of Kuwait crude oil

Anthropogenic activities have been shown to significantly affect marine life. Water pollution and oil spills are particularly deleterious to the fish population, especially during their larval stage. In this study, Sobaity-sea bream Sparidentex hasta (Valenciennes, 1830) larvae were exposed to serial dilutions of water-accommodated fraction of Kuwait crude oil (KCO-WAF) for varying durations (3, 6, 24, 48, 72 or 96 h) in acute exposure regime. Gene expression was assessed using RNA sequencing and validated through RT-qPCR. The RNA sequencing data were aligned to the sequenced genome, and differentially expressed genes were identified in response to treatment with or without KCO-WAF at various exposure times. The highest number of differentially expressed genes was observed at the early time point of 6 h of post-exposure to KCO-WAF. The lowest number of differentially expressed genes were noticed at 96 h of treatment indicating early response of the larvae to KCO-WAF contaminant. The acquired information on the differentially expressed genes was then used for functional and pathway analysis. More than 90% of the differentially expressed genes had a significant BLAST match, with the two most common matching species being Acanthopagrus latus and Sparus aurata. Approximately 65% of the differentially expressed genes had Gene Ontology annotations, whereas > 35% of the genes had KEGG pathway annotations. The differentially expressed genes were found to be enriched for various signaling pathways (e.g., MAPK, cAMP, PI3K-Akt) and nervous system-related pathways (e.g., neurodegeneration, axon guidance, glutamatergic synapse, GABAergic synapse). Early exposure modulated the signaling pathways, while KCO-WAF exposure of larvae for a longer duration affected the neurodegenerative/nervous system-related pathways. RT-qPCR analysis confirmed the differential expression of genes at each time point. These findings provide insights into the underlying molecular mechanisms of the deleterious effects of acute exposure to oil pollution-on marine fish populations, particularly at the early larval stage of Sparidentex hasta.

Co-exposure to sodium hypochlorite and cadmium induced locomotor behavior disorder by influencing neurotransmitter secretion and cardiac function in larval zebrafish

Sodium hypochlorite (NaClO) and cadmium (Cd) are widely co-occurring in natural aquatic environment; however, no study has been conducted on effects of their combined exposure on aquatic organisms. To assess effects of exposure to NaClO and Cd in zebrafish larvae, we designed six treatment groups, as follows: control group, NaClO group (300 μg/L), 1/100 Cd group (48 μg/L), 1/30 Cd group (160 μg/L), NaClO+1/100 Cd group, and NaClO+1/30 Cd group analyzed behavior, neurological function and cardiac function. Results revealed that exposure to 1/30 Cd and NaClO+1/30 Cd caused abnormal embryonic development in larvae by altering body morphology and physiological indicators. Combined exposure to NaClO and 1/30 Cd affected the free-swimming activity and behavior of larvae in response to light-dark transition stimuli. Moreover, exposure to 1/30 Cd or NaClO+1/30 Cd resulted in a significant increase in tyrosine hydroxylase and acetylcholinesterase activities, as well as significant changes of various neurotransmitters. Lastly, exposure to 1/30 Cd or NaClO+1/30 Cd influenced the transcription of cardiac myosin-related genes and disturbed the myocardial contractile function. Altogether, our results suggested that combined exposure to NaClO and Cd induced oxidative damage in larvae, resulting in detrimental effects on nervous system and cardiac function, thus altering their swimming behavior.

A multi-targeted investigation of Deepwater Horizon crude oil exposure impacts on the marine teleost stress axis

The toxicity of the polycyclic aromatic hydrocarbons (PAHs) in Deepwater Horizon (DWH) oil is well-established, but a knowledge gap exists regarding how this combination of PAHs affects the vertebrate stress axis. We hypothesized that (1) marine vertebrates exposed to DWH PAHs experience stress axis impairment, and co-exposure to an additional chronic stressor may exacerbate these effects, (2) serotonin (5-hydroxytryptamine; 5-HT) may act as a secondary cortisol secretagogue in DWH PAH-exposed fish to compensate for impairment, and (3) the mechanism of stress axis impairment may involve downregulation of cyclic adenosine monophosphate (cAMP; as proxy for melanocortin 2 receptor (MC2R) functionality), total cholesterol, and/or mRNA expression of CYP1A and steroidogenic proteins StAR, P450scc, and 11β-h at the level of the kidney. We found that in vivo plasma cortisol and plasma adrenocorticotropic hormone (ACTH) concentrations in Gulf toadfish exposed to an environmentally relevant DWH PAH concentration (ΣPAH₅₀= 4.6 ± 1.6 μg/L) for 7 days were not significantly different from controls, whether fish were chronically stressed or not. However, the rate of cortisol secretion by isolated kidneys after acute stimulation with ACTH was significantly lower in PAH-exposed toadfish compared to clean seawater (SW) controls. 5-HT does not appear to be acting as a secondary cortisol secretagogue, rather, PAH-exposed + stressed toadfish exhibited significantly lower plasma 5-HT concentrations than clean SW + stressed fish as well as a reduced sensitivity to 5-HT at the level of the kidney. There was a tendency for kidney cAMP concentrations to be lower in PAH-exposed fish (p = 0.069); however, mRNA expression of steroidogenic proteins between control and PAH-exposed toadfish were not significantly different and a significant elevation in total cholesterol concentration in PAH-exposed toadfish compared to controls was measured. Future work is needed to establish whether the slower cortisol secretion rate by isolated kidneys of PAH-exposed fish is detrimental, to determine the potential role of other secretagogues in compensating for the impaired kidney interrenal cell function, and to determine whether there is a reduction in MC2R mRNA expression or an impairment in the function of steroidogenic proteins.

Effects of cadmium and lead co-exposure on glucocorticoid levels in rural residents of northwest China

Cadmium (Cd) and lead (Pb) are important environmental endocrine disruptors that are associated with adverse health problems. However, the effects of co-exposure to Cd and Pb on glucocorticoids (GCs) in the body at environmental levels are limited. A total of 468 subjects from the Dongdagou-Xinglong cohort (DDG-XL) were included in this study. We measured the serum levels of two representative endogenous GCs [cortisol (CRL) and cortisone (CRN)], and whole blood levels of Cd and Pb. Multiple linear regression models were constructed to explore the associations of single or combined Cd and Pb exposure with serum CRL and CRN levels. The interactive effects of Cd and Pb on GCs were further assessed using mediation analysis and moderation analysis. Single-heavy metal exposure analysis with adjustment for potential confounders showed that the serum CRL level decreased when the blood Cd or Pb concentration gradually increased (P trend <0.01). Additionally, subjects with high Cd or Pb exposure (Q4) had significantly reduced serum CRN levels compared to those with low Cd or Pb exposure (Q1) (P < 0.05). In Cd and Pb co-exposure analysis, significant negative dose-response relationships were observed between co-exposure to Cd and Pb and serum CRL and CRN levels. Furthermore, mediation analysis showed that Cd completely mediated the relationship between Pb and GCs, and moderation analysis suggested that Pb might weaken the negative relationship between Cd and GCs. These findings suggest that single or combined exposure to Cd and Pb interferes with the homeostasis of serum CRL and CRN levels. Furthermore, we innovatively propose that Cd and Pb may have interactive effects on GCs levels, and Pb can antagonize the negative relationship between Cd and GCs, which may provide clues for further studies on endocrine and metabolic disorders related to these heavy metals.

Transgenerational effects of co-exposure to cadmium and carbofuran on zebrafish based on biochemical and transcriptomic analyses

The combined toxicity of heavy metals and pesticides to aquatic organisms is still largely unexplored. In this study, we investigated the combined impacts of cadmium (Cd) and carbofuran (CAR) on female zebrafish (F0 generation) and their following F1 generation. Results showed that mixtures of Cd and CAR induced acute synergistic effects on both zebrafish adults of the F0 generation and embryos of the F1 generation. Combined exposure to Cd and CAR could obviously alter the hepatic VTG level of females, and the individual exposures increased the relative mRNA levels of vtg1 and vtg2. Through maternal transmission, co-exposure of Cd and CAR caused toxicity to 4-day-old larvae of the F1 generation, evidenced by the significant changes in T4 and VTG levels, CYP450 activity, and the relative transcriptional levels of genes related to the hormone, oxidative stress, and apoptosis. These effects were also reflected by the global gene expression pattern to 7-day-old larvae of F1 generation using the transcriptomic analysis, and they could also affect energy metabolism. Our results provided a more comprehensive insight into the transgenerational toxic impacts of heavy metal and pesticide mixtures. These findings highlighted that it was highly necessary to consider transgenerational exposures in the ecological risk assessment of chemical mixtures.

Regulation of cortisol production during chronic social stress in rainbow trout

Chronic stress resulting from social interactions impacts the endocrine stress response in many vertebrates, including teleost fishes. Juvenile rainbow trout held in pairs form a dominance hierarchy with the subordinate individual exhibiting chronic elevation of plasma cortisol and an attenuated cortisol response to an additional acute stressor. The current study investigated the mechanisms underlying this apparent dichotomy in cortisol production at the level of the head kidney (adrenal homolog). Following four days of chronic social stress, subordinate rainbow trout exhibited elevated plasma cortisol levels that correlated with basal cortisol production by the head kidney in vitro. Subordinate trout had higher transcript abundances of steroidogenic acute regulatory protein and cytochrome p450 side chain cleavage enzyme, which facilitate key steps in steroidogenesis, as well as two paralogs of steroidogenic factor 1. Despite elevation of basal steroidogenesis, acute cortisol production in response to ACTH (in vivo and in vitro) was lower in subordinate trout. Transcript abundances of the ACTH receptor accessory proteins were elevated in subordinate fish, but head kidney cortisol production in response to a cAMP analogue was lower than in dominant fish. Together, the data suggest that the attenuated acute cortisol response of subordinate trout reflects limitations on cortisol production downstream of cAMP signalling in steroidogenic cells of the head kidney, despite the increased basal abundance of key components of the steroidogenic pathway.

G protein-coupled receptors (GPCRs) in rotifers and cladocerans: Potential applications in ecotoxicology, ecophysiology, comparative endocrinology, and pharmacology

The G protein-coupled receptor (GPCR) superfamily plays a fundamental role in both sensory functions and the regulation of homeostasis, and is highly conserved across the eukaryote taxa. Its functional diversity is related to a conserved seven-transmembrane core and invariant set of intracellular signaling mechanisms. The interplay between these properties is key to the evolutionary success of GPCR. As this superfamily originated from a common ancestor, GPCR genes have evolved via lineage-specific duplications through the process of adaptation. Here we summarized information on GPCR gene families in rotifers and cladocerans based on their evolutionary position in aquatic invertebrates and their potential application in ecotoxicology, ecophysiology, comparative endocrinology, and pharmacology. Phylogenetic analyses were conducted to examine the evolutionary significance of GPCR gene families and to provide structural insight on their role in aquatic invertebrates. In particular, most GPCR gene families have undergone sporadic evolutionary processes, but some GPCRs are highly conserved across species despite the dynamics of GPCR evolution. Overall, this review provides a better understanding of GPCR evolution in aquatic invertebrates and expand our knowledge of the potential application of these receptors in various fields.

Phylogeny of the HO family in cyprinus carpio and the response of the HO-1 gene to adding Bacillus coagulans in feed under Cd2+ stress

The heavy metal cadmium (Cd²⁺) is an environmental pollutant that poses serious health hazards. Due to the increasing contamination of aquatic systems with Cd²⁺, the increased accumulation of Cd²⁺ in fish has become a food safety and public health concern. Heme oxygenase (HO) is an important antioxidant enzyme that plays a key role in defending the body against oxidative damage, but little research has been done in common carp. In this study, 6 HO genes were identified in the common carp genome database. Comparative genomics analysis showed considerable expansion of the HO genes and verified the four-round whole genome duplication (WGD) event in common carp. Phylogenetic analysis revealed that all HO genes of common carp were clustered into orthologous groups, indicating high conservation during evolution. In addition, the tissue distribution results showed that most HO genes had extensive tissue distribution and showed tissue-specific expression patterns. Exposure to 0.5 mg/L Cd²⁺ significantly reduced the expression of TGF-β and IL-10 in common carp, which may indicate that Cd²⁺ exposure can destroy the physical barrier function of the intestine, inhibit intestinal immune defense and induce intestinal inflammation. To find a suitable concentration of Bacillus coagulans that could activate HO-1 genes and the immunity of the organism, we investigated the changes in HO-1 gene expression levels in the intestinal tract of common carp under Cd²⁺ stress at 30 days and 60 days by adding different concentrations of B. coagulans to the feed. Compared with the Cd²⁺ stress group without supplementation, the expression levels of the HO-1 gene in the gut of three different concentrations of B. coagulans were almost increased. And B. coagulans with L2 concentrations had better activation effect on the HO-1 gene. Similarly, compared to the Cd²⁺ stressed group, adding B. coagulans to the diet can almost cause the early upregulation of IL-10 and TGF-β genes. Therefore, the addition of appropriate concentrations of B. coagulans may be a good way to activate HO-1, IL-10, and TGF-β genes, reduce oxidative damage, and encourage the immune.

Transcriptome expression analysis of the gene regulation mechanism of bacterial mineralization tolerance to high concentrations of Cd2

Cadmium (Cd) pollution is a pressing environmental issue that must be addressed. In recent years, microbial mineralization biotechnology has been developed into an effective and eco-friendly heavy metal bioremediation solution. In the present research, RNA-Seq technology was utilized to reveal the molecular mechanism through which Bacillus velezensis LB002 induced the mineralization and Cd²⁺ fixation under high-concentration Cd²⁺ stress. The metabolic pathways involved in the genes that were significant differentially expressed in the process of bacterial mineralization were also investigated. The results showed that the physiological response of bacteria to Cd²⁺ toxicity may include bacterial chemotaxis, siderophore complexation, and transport across cell membranes. Bacteria subjected to high-concentration Cd²⁺ stress can up-regulate genes of argH, argF, hutU, hutH, lpdA, and acnA related to arginine synthesis, histidine metabolism, and citric acid cycle metabolism pathways, inducing vaterite formation and Cd²⁺ fixation. Thus, the toxicity of Cd²⁺ was decreased and bacteria were allowed to grow. Real-time quantitative polymerase chain reaction (RT-qPCR) results confirmed the data obtained by RNA-Seq, indicating that bacteria can reduce Cd²⁺ toxicity by regulating the expression of related genes to induce mineralization. A basic bioremediation strategy to deal with high-concentration heavy-metal pollution was proposed from the perspective of gene regulation.

Phytoremediation of toxic metals present in soil and water environment: a critical review

Heavy metals are one of the most hazardous inorganic contaminants of both water and soil environment composition. Normally, heavy metals are non-biodegradable in nature because of their long persistence in the environment. Trace amounts of heavy metal contamination may pose severe health problems in human beings after prolonged consumption. Many instrumental techniques such as atomic absorption spectrophotometry, inductively coupled plasma-mass spectrometry, X-ray fluorescence, neutron activation analysis, etc. have been developed to determine their concentration in water as well as in the soil up to ppm, ppb, or ppt levels. Recent advances in these techniques along with their respective advantages and limitations are being discussed in the present paper. Moreover, some possible remedial phytoremediation approaches (phytostimulation, phytoextraction, phyotovolatilization, rhizofiltration, phytostabilization) have been presented for the removal of the heavy metal contamination from the water and soil environments.

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.

Cadmium-induced developmental alteration and upregulation of serine-type endopeptidase transcripts in wild freshwater populations of Chironomus plumosus

Cadmium, a toxic heavy metal, is a persistent environmental contaminant with irreversible toxicity to aquatic organisms. Chironomus plumosus, a natural species, is the largest sediment-burrowing aquatic midge in freshwater environments. In this study, we evaluated developmental defects in C. plumosus resulting from Cd exposure. In C. plumosus larvae, Cd exposure induced decreased survival and growth rates, reduction of emergence rate and sex ratio, and delayed emergence, as well as elevating the incidence of split tooth deformities. To identify potential biomarker genes to assess environmental pollutants such as Cd, we identified differentially expressed genes (DEGs) in C. plumosus exposed to various Cd concentrations. Among fourteen characterized DEGs, serine-type endopeptidase (SP) and heat shock protein 70 (HSP70) genes exhibited significant upregulation in C. plumosus larvae after Cd exposure. Therefore, we evaluated SP and HSP70 responses in natural C. plumosus populations collected from three sites of a Korean river and analyzed their correlations with eighteen environmental quality characteristics using principal component analysis. The highest expression of SP and HSP70 transcripts was observed in C. plumosus populations from Yeosu in Korea, which has high concentrations of polluting heavy metals. SP transcript expression was positively correlated with concentrations of Cd, Pb, Al, Fe, NO2, and NO3. These results suggested that environmental pollutants such as Cd can impair proteolytic activity in the digestive system of C. plumosus and may ultimately induce developmental alterations. We therefore suggest SP as a potential biomarker to assess the effects of environmental pollutants in aquatic ecosystems.

Multimetal tolerance mechanisms in bacteria: The resistance strategies acquired by bacteria that can be exploited to 'clean-up' heavy metal contaminants from water

Heavy metal pollution is one of the major environmental concerns worldwide. Toxic heavy metals when untreated get accumulated in environment and can pose severe threats to living organisms. It is well known that metals play a major role either directly or indirectly in different metabolic processes of bacteria. This allows bacterial cells to grow even in the presence of some toxic heavy metals. Microbial biotechnology has thus emerged as an effective and eco friendly solution in recent years for bioremediation of heavy metals. Therefore, this review is focused on summarising bacterial adaptation mechanisms for various heavy metals. It also shares some applications of have metal tolerant bacteria in bioremediation. Bacteria have evolved a number of processes for heavy metal tolerance viz., transportation across cell membrane, accumulation on cell wall, intra as well as extracellular entrapment, formation of complexes and redox reactions which form the basis of different bioremediation strategies. The genetic determinants for most of these resistances are located on plasmids however some may be chromosomal as well. Bacterial cells can uptake heavy by both ATP dependent and ATP independent processes. Bacterial cell wall also plays a very important role in accumulating heavy metals by bacterial cells. Gram-positive bacteria accumulate much higher concentrations of heavy metals on their cell walls than that of metals gram -ve bacteria. The role of bacterial metallothioneins (MTs) in heavy metal has also been reported. Thus, heavy metal tolerant bacteria are important for bioremediation of heavy metal pollutants from areas containing high concentrations of particular heavy metals.