Advantages of omics technology for evaluating cadmium toxicity in zebrafish

Transcriptomic analysis reveals particulate hexavalent chromium regulates key inflammatory pathways in human lung fibroblasts as a possible mechanism of carcinogenesis

Hexavalent chromium [Cr(VI)] is considered a major environmental health concern and lung carcinogen. However, the exact mechanism by which Cr(VI) causes lung cancer in humans remains unclear. Since several reports have demonstrated a role for inflammation in Cr(VI) toxicity, the present study aimed to apply transcriptomics to examine the global mRNA expression in human lung fibroblasts after acute (24 h) or prolonged (72 and 120 h) exposure to 0.1, 0.2 and 0.3 μg/cm2 zinc chromate, with a particular emphasis on inflammatory pathways. The results showed Cr(VI) affected the expression of multiple genes and these effects varied according to Cr(VI) concentration and exposure time. Bioinformatic analysis of RNA-Seq data based on the Gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) and MetaCore databases revealed multiple inflammatory pathways were affected by Cr(VI) treatment. qRT-PCR data corroborated RNA-Seq findings. This study showed for the first time that Cr(VI) regulates key inflammatory pathways in human lung fibroblasts, providing novel insights into the mechanisms by which Cr(VI) causes lung cancer.

Effect of long-term exposure to dyeing wastewater treatment plant effluent on growth and gut microbiota of adult zebrafish (Danio rerio)

Strict standards have been put forward for the treatment and discharge of dyeing wastewater worldwide. However, there are still traces amount of pollutants, especially emerging pollutants in dyeing wastewater treatment plant (DWTP) effluent. Few studies have focused on the chronic biological toxicity effect and mechanism of DWTP effluent. In this study, 3-month chronic compound toxic effects were investigated by the exposure of DWTP effluent using adult zebrafish. Significantly higher mortality and fatness and significantly lower body weight and body length were found in the treatment group. In addition, long-term exposure to DWTP effluent also obviously reduced liver-body weight ratio of zebrafish, causing abnormal liver development of zebrafish. Moreover, DWTP effluent led to obvious changes in the gut microbiota and microbial diversity of zebrafish. At phylum level, significantly higher of Verrucomicrobia but lower Tenericutes, Actinobacteria, and Chloroflexi were found in the control group. At genus level, the treatment group had significantly higher abundance of Lactobacillus, but significantly lower abundance of Akkermansia, Prevotella, Bacteroides, and Sutterella. These results suggested that long-term exposure to DWTP effluent led to imbalance of gut microbiota in zebrafish. In general, this research indicated that DWTP effluent pollutants could result in negative health outcomes to aquatic organisms.

Toxic Effects of Cadmium on Fish

Large amounts of enriched cadmium (Cd) in the environment seriously threatens the healthy and sustainable development of the aquaculture industry and greatly restricts the development of the food processing industry. Studying the distribution and toxic effects of Cd in fish, as well as the possible toxic effects of Cd on the human body, is very significant. A large number of studies have shown that the accumulation and distribution of Cd in fish are biologically specific, cause tissue differences, and seriously damage the integrity of tissue structure and function, the antioxidant defense system, the reproductive regulation system, and the immune system. The physiological, biochemical, enzyme, molecular, and gene expression levels change with different concentrations and times of Cd exposure, and these changes are closely related to the target sites of Cd action and tissues in fish. Therefore, the toxic effects of Cd on fish occur with multiple tissues, systems, and levels.

Altered life history traits and transcripts of molting- and reproduction-related genes by cadmium in Daphnia magna

Cadmium (Cd) is a non-essential element and can be toxic to aquatic organisms at low concentrations. Despite its well-known toxicity to Daphnia magna, the effects of Cd on physiological parameters (heart rate and thoracic limb activity) and molting- and reproduction-related genes are relatively understudied. In this study, D. magna were exposed to 0 (control), 25, 50 and 75 μg L^-1 of Cd for 7 d and 21 d to determine the toxicity of Cd. The results showed that the Cd body burden in D. magna was significantly increased with elevated Cd concentrations, up to 13.4 μg Cd/g dry weight (dw) after exposure to 75 μg L^-1 for 21 d. After 21 d of exposure, the body length and body weight of D. magna were significantly decreased in all Cd treatments compared to the control. The heart rate and thoracic limb activity were reduced by 4.3-11.7 and 5.0-10.3%, respectively. The levels of malondialdehyde (MDA) were increased by ~24-37% and the activity of catalase (CAT) was inhibited by ~50% compared to the control. The reproductive parameters (i.e., size of the first brood, the total number of offspring per female and the number of offspring per brood) were remarkably reduced, causing adverse effects on the population dynamics. In addition, the transcripts of genes (cyp314, cyp18a1, ecra, usp, hr3, cut, cht and cht3) related to the molting of D. magna were altered, whereas the transcripts of genes (vtg1, vtg2 and vmo1) related to reproduction were down-regulated. This study helps better understand the effects of Cd at different biological levels.