Tissue accumulation and toxicity of isothiazolinone in Ctenopharyngodon idellus (grass carp): association with P-glycoprotein expression and location within tissues

Toxicities of polystyrene microplastics (MPs) and hexabromocyclododecane (HBCD), alone or in combination, to the hepatopancreas of the whiteleg shrimp, Litopenaeus vannamei

The hepatopancreas is one of the largest organs playing crucial roles in metabolism and detoxification in crustacean invertebrates. Although toxicities have been increasingly documented for the two ubiquitous pollutants, hexabromocyclododecane (HBCD) and microplastics (MPs), in model animals, little is known about their impacts on the hepatopancreas of crustaceans. To fill this knowledge gap, the effects of MPs and HBCD, alone or in combination, on the hepatopancreas were evaluated in a commercially important crustacean species (the whiteleg shrimp) by histological observation as well as quantification of hepatic lesion-, metabolism-, and detoxification-related parameters. In addition, to reveal potential mechanisms underlying the hepatoxicity observed, the accumulation of HBCD in the shrimp and the status of oxidative stress were also investigated. Our results demonstrated that exposure of the whiteleg shrimp to MPs and HBCD for 4 weeks resulted in evident histological injury in the hepatopancreas and marked elevation in hepatic lesion markers (alanine aminotransferase and aspartate aminotransferase) in the hemolymph. Moreover, both metabolism (activity of phosphofructokinase, contents of lactic acid and adenosine triphosphate, and expression of metabolism-related genes) and detoxification (contents of cytochrome P450, UDP-glucuronosyltransferase, and glutathione, activity of glutathione S-transferase, and expression of detoxification-related genes) were found to be disrupted by the pollutants tested. In addition, exposure to MPs and HBCD also led to alterations in the contents and/or activities of antioxidant enzymes and resulted in oxidative damage to the hepatopancreas (indicated by marked elevation in malondialdehyde content). Furthermore, a significant amount of HBCD accumulated in shrimp treated with HBCD-containing seawater. The data also illustrated that HBCD-MP coexposure was more toxic than single exposure to these pollutants. These findings suggest that MPs and HBCD may exert hepatotoxic impacts on whiteleg shrimp by accumulating in vivo and inducing oxidative stress, which could pose a severe threat to the health of this important crustacean species.

Variation of Tolerance to Isothiazolinones Among Daphnia pulex Clones

Isothiazolinones are a family of broad-spectrum biocides widely used in industry and consumer products. Chloro- and methyl-isothiazolinones (CMIT and MIT) are documented as strong irritants, yet they are still used in a wide variety of applications, including cosmetics, cleansers, hygienic products, and various industrial applications. The subsequent substantial release of these molecules from urban sources into freshwater environments, and their potential impacts on aquatic species, have nevertheless received little attention so far, with few studies reporting on the toxicity of either CMIT or MIT to nontarget organisms. The present study addresses this current knowledge gap by evaluating the acute toxicity to Daphnia pulex (Cladocera) of CMIT/MIT (3:1) and MIT, the two formulations most commonly used by manufacturers. In addition, genetic diversity is known to be a major component of variability in phenotypic responses, although it is largely overlooked in typical toxicity tests. Thus the potential range of responses inherent to genetic diversity is rarely considered. Therefore, to account for intraspecific variations in sensitivity, our design involved eight clonal lines of D. pulex stemming from distinct natural populations or commercial strains. Clones exhibited strong variation in their responses, with median lethal concentration (LC50) values ranging from 0.10 to 1.84 mg/L for the mixture CMIT/MIT, and from 0.68 to 2.84 mg/L for MIT alone. These intraspecific ranges of LC50 values challenge the use of single clones of daphnids in standard ecotoxicological tests and the predictions based on their results. The present study brings new evidence that assessing ecological risk of chemicals while ignoring genotype diversity is neither ecologically relevant, nor a representative evaluation of the diversity of potential adverse outcomes. Environ Toxicol Chem 2023;42:805-814. © 2023 SETAC.

Rapid plant uptake of isothiazolinone biocides and formation of metabolites by hydroponic Arabidopsis

Isothiazolinones biocides are water-soluble, low molecular weight, nitrogenous compounds widely used to prevent microbial growth in a variety of applications including personal care products and building façade materials. Because isothiazolinones from buildings wash off and enter stormwater, interactions with terrestrial plants may represent an important part of the environmental fate of these compounds (e.g., in green stormwater infrastructure). Using the model plant Arabidopsis thaliana grown hydroponically, we observed rapid (≥99% within 24 hours), plant-driven removal of four commonly used isothiazolinones: benzisothiazolinone (BIT), chloromethylisothiazolinone, methylisothiazolinone, and octylisothiazolinone. No significant differences in uptake rate occurred between the four compounds; therefore, BIT was used for further detailed investigation. BIT uptake by Arabidopsis was concentration-dependent in a manner that implicates transporter-mediated substrate inhibition. BIT uptake was also minimally impacted by multiple BIT spikes, suggesting constituently active uptake. BIT plant uptake rate was robust, unaffected by multiple inhibitors. We investigated plant metabolism as a relevant removal process. Proposed major metabolites that significantly increased in the BIT-exposure treatment compared to the control included: endogenous plant compounds nicotinic acid (confirmed with a reference standard) and phenylthioacetohydroximic acid, a possible amino acid-BIT conjugate, and two accurate masses of interest. Two of the compounds (phenylthioacetohydroximic acid and TP 470) were also present in increased amounts in the hydroponic medium after BIT exposure, possibly via plant excretion. Upregulation of endogenous plant compounds is environmentally significant because it demonstrates that BIT impacts plant biology. The rapid plant-driven isothiazolinone removal observed here indicates that plant-isothiazolinone processes could be relevant to the environmental fate of these stormwater compounds.

Regulation of glutathione-dependent antioxidant defense system of grass carp Ctenopharyngodon idella under the combined stress of mercury and temperature

In this study, we investigated the combined effects of temperatures fluencies and mercury (Hg) on glutathione-dependent antioxidant system in fish, by measuring the oxidative stress indicator (LPO, lipid peroxidation) and the parameters involved in the glutathione-related antioxidant defense system (GPx, glutathione peroxidase; GR, glutathione reductase; GST, glutathione S-transferase; GSH, reduced glutathione), as well as the expression of related genes in grass carp, Ctenopharyngodon idella. Fish (45.37 ± 3.58 g) were exposed to 10 test groups, e.g., 15 °C with/without Hg, 20 °C with/without Hg, 25 °C with/without Hg, 30 °C with/without Hg, 35 °C with/without Hg for 4 weeks. Three-way ANOVA was used to analyze the correlation between the measured parameters and experimental conditions (water temperature, Hg exposure, exposure time, and their interactions.). Our results show that there is no interaction between mercury and low temperature, but the combined effect at high temperature has been confirmed, which indicated the glutathione-dependent enzyme system in grass carp has a complex regulatory mechanism with temperature fluctuations. In the actual field monitoring, it is necessary to consider the impact of extreme temperature on the toxicity of pollutants in the aquatic ecosystem.

Gender-differentiated metabolic abnormalities of adult zebrafish with zinc pyrithione (ZPT) -induced hepatotoxicity

Zinc pyrithione (ZPT) is an extensively used microbicidal agent and its toxicity to multiple organs has been gradually recognized. However, details of the mechanism of ZPT toxicity are lacking and profile studies at metabolic level are still greatly limited. In this work we investigated the effects of ZPT on metabolic pathways of zebrafish liver after twenty-one days of exposure. Our integrated approach was underpinned by gas chromatography coupled with mass spectroscopy (GC-MS) and liver function analysis. Metabolomic profiles were generated from the livers of ZPT-treated zebrafish and 172 significantly altered metabolite peaks were detected. As a result, ZPT caused altered perturbation of metabolic pathways in male and female zebrafish liver. Moreover, ZPT induced the liver injury with the changes of the metabolites 2,4-diaminobutyric acid (2,4-DABA) with significant distinction between male and female zebrafish. ZPT caused gender-differentiated liver metabolic changes associated with the disruption of glycogenolysis and glycolysis metabolism, purine and pyrimidine metabolism, oxidative phosphorylation, arginine biosynthesis, and amino acid metabolism. Conclusively, exposure of ZPT may result in gender-differentiated metabolic abnormalities of adult zebrafish with induced hepatotoxicity.

Asymmetric Disulfanylbenzamides as Irreversible and Selective Inhibitors of Staphylococcus aureus Sortase A

Staphylococcus aureus is one of the most frequent causes of nosocomial and community-acquired infections, with drug-resistant strains being responsible for tens of thousands of deaths per year. S. aureus sortase A inhibitors are designed to interfere with virulence determinants. We have identified disulfanylbenzamides as a new class of potent inhibitors against sortase A that act by covalent modification of the active-site cysteine. A broad series of derivatives were synthesized to derive structure-activity relationships (SAR). In vitro and in silico methods allowed the experimentally observed binding affinities and selectivities to be rationalized. The most active compounds were found to have single-digit micromolar Ki values and caused up to a 66 % reduction of S. aureus fibrinogen attachment at an effective inhibitor concentration of 10 μM. This new molecule class exhibited minimal cytotoxicity, low bacterial growth inhibition and impaired sortase-mediated adherence of S. aureus cells.

Effects of emodin on ABC transporter gene expression in grass carp (Ctenopharyngodon idellus) exposed to diazinon

This study aimed to investigate the function of ATP-binding cassette (ABC) transporter genes in grass carp treated with emodin combined with diazinon (DZN) exposure. The transcription levels of five ABC transporter genes in different tissues of grass carp and at different time points were measured by real-time quantitative PCR (qRT-PCR). The analysis of different tissues showed higher ABCB1 expression in the skin (26-fold) and gill (2-fold) than in the liver. In addition, ABCB11 expression was higher in the skin (109-fold) and gill (57-fold) than in the liver, ABCC1 was more highly expressed in the gill (50-fold) than in the liver, and ABCG2 was expressed at higher levels in the skin (659-fold, p < 0.01), gill (628-fold, p < 0.01) and liver (659-fold, p < 0.01) than in brain tissue. The analysis of different time points revealed that the ABCB1, ABCB11, ABCC1, ABCC2 and ABCG2 genes were highly expressed at 24 h in the liver in the experimental group. However, analysis of the intestinal tissue of the experimental group showed that the expression of ABCB1 and ABCB11 peaked at 6 h, the expression of ABCC1 and ABCC2 peaked at 5 d, and the expression of ABCG2 peaked at 3 d. Furthermore, the emodin concentrations in the liver and intestine reached their peak levels (50.18 and 117.24 μg·ml⁻¹, respectively) after 48 and 1 h of treatment with emodin combined with DZN, respectively. The peak DZN concentrations in the liver (1.42 ng·ml⁻¹) and intestine (0.2 ng·ml⁻¹) were detected 3 and 6 h after emodin treatment combined with DZN, respectively. In conclusion, this study shows that the transcript levels of ABC transporters respond to the presence of emodin, which indicates their potential involvement in and contribution with the metabolic process in grass carp.

Interaction between 1,2-benzisothiazol-3(2H)-one and microalgae: Growth inhibition and detoxification mechanism

Isothiazolinones, such as 1,2-benzisothiazol-3(2H)-one (BIT), are widely used as biocides for bacterial growth control in many domestic and industrial processes. Despite their advantages as biocides, they are highly toxic and pose a potential risk to the environment. This study investigated the inhibition process and detoxification mechanism involved in microalgal survival and growth recovery after BIT poisoning. BIT could seriously inhibit the growth of Scenedesmus sp. LX1, Chlorella sp. HQ, and Chlamydomonas reinhardtii with half maximal effective concentrations at 72 h (72h-EC₅₀) of 1.70, 0.41, and 1.16 mg/L, respectively. The primary inhibition mechanism was the BIT-induced damage to microalgal photosynthetic systems. However, the inhibited strains could recover when their growth was not completely inhibited. The influence of this inhibiting effect on subsequent algal regrowth was negligible or weak. BIT consumption was the primary reason for their recovery. Notably, algae did not die even if their growth was completely inhibited. If the BIT concentration did not exceed a certain high level, then the inhibited algae could recover their growth relatively well. Microalgal generation of reduced glutathione (GSH) and the oxygen radical scavenging enzymes, superoxide dismutase (SOD) and catalase (CAT), played a key role in detoxification against BIT poisoning.

Tolerance and resistance characteristics of microalgae Scenedesmus sp. LX1 to methylisothiazolinone

Methylisothiazolinone (MIT) has been widely used to control bacterial growth in reverse osmosis (RO) systems. However, MIT's toxicity on microalgae should be determined because residual MIT is concentrated into RO concentrate (ROC) and might have a severe impact on microalgae-based ROC treatment. This study investigated the tolerance of Scenedesmus sp. LX1 to MIT and revealed the mechanism of algal growth inhibition and toxicity resistance. Scenedesmus sp. LX1 was inhibited by MIT with a half-maximal effective concentration at 72 h (72 h-EC₅₀) of 1.00 mg/L, but the strain recovered from the inhibition when its growth was not completely inhibited. It was observed that this inhibition's effect on subsequent growth was weak, and the removal of MIT was the primary reason for the recovery. Properly increasing the initial algal density significantly shortened the adaptation time for accelerated recovery in a MIT-containing culture. Photosynthesis damage by MIT was one of the primary reasons for growth inhibition, but microalgal cell respiration and adenosine triphosphate (ATP) synthesis were not completely inhibited, and the algae were still alive even when growth was completely inhibited, which was notably different from observations made with bacteria and fungi. The algae synthesized more chlorophyll, antioxidant enzymes of superoxide dismutase (SOD) and catalase (CAT), and small molecules, such as reduced glutathione (GSH), to resist MIT poisoning. The microalgae-based process could treat the MIT-containing ROC, since MIT was added for only several hours a week in municipal wastewater reclamation RO processes, and the MIT average concentration was considerably lower than the maximum concentration that algae could tolerate.

Toxicity and accumulation of zinc pyrithione in the liver and kidneys of Carassius auratus gibelio: association with P-glycoprotein expression

Zinc pyrithione (ZPT) is a broad-spectrum antibacterial and antifungal agent; therefore, it is widely used in industry and civilian life. It is discharged into the aquatic environment with industrial and civilian waste water. Carassius sp. is one of the most widely distributed and farmed fish in China. The effects of aquatic ZPT on Carassius sp. remain unknown. In this study, we determined the acute toxicity of ZPT on Carassius sp. The results showed that the median lethal concentration (LC50 96 h) of ZPT on Carassius sp. cultivated in freshwater or water with 1.5 or 3 ‰ salinity was 0.163, 0.126, and 0.113 mg/L, respectively. ZPT has a higher affinity to the liver than the kidney, with a prolonged tissue residual time. P-glycoprotein (P-gp), an ATP-binding cassette transporter, was found to be induced in the liver and kidney tissues of these Carassius spp. after ZPT treatment, based on the determination of its mRNA and protein levels by quantitative real-time reverse transcription polymerase chain reaction and immunohistochemistry, respectively. The ZPT accumulation and magnitude of P-gp induction were also affected by the salinity of the cultivation water. These results suggest that aquatic ZPT is potentially toxic to Carassius sp. We speculate that P-gp induction may play a protective role for Carassius sp. Our findings provide a basis for assessing the potential risk of ZPT to aquatic animals including Carassius sp.