Immunotoxicity of β-Diketone Antibiotic Mixtures to Zebrafish (Danio rerio) by Transcriptome Analysis

An environmentally relevant concentration of antibiotics impairs the immune system of zebrafish (Danio rerio) and increases susceptibility to virus infection

In this work, we analysed the transcriptome and metatranscriptome profiles of zebrafish exposed to an environmental concentration of the two antibiotics most frequently detected in European inland surface water, sulfamethoxazole (SMX) and clarithromycin (CLA). We found that those animals exposed to antibiotics (SMX+CLA) for two weeks showed a higher bacterial load in both the intestine and kidney; however, significant differences in the relative abundance of certain bacterial classes were found only in the intestine, which also showed an altered fungal profile. RNA-Seq analysis revealed that the complement/coagulation system is likely the most altered immune mechanism, although not the only one, in the intestine of fish exposed to antibiotics, with numerous genes inhibited compared to the control fish. On the other hand, the effect of SMX+CLA in the kidney was more modest, and an evident impact on the immune system was not observed. However, infection of both groups with spring viremia of carp virus (SVCV) revealed a completely different response to the virus and an inability of the fish exposed to antibiotics to respond with an increase in the transcription of complement-related genes, a process that was highly activated in the kidney of the untreated zebrafish after SVCV challenge. Together with the higher susceptibility to SVCV of zebrafish treated with SMX+CLA, this suggests that complement system impairment is one of the most important mechanisms involved in antibiotic-mediated immunosuppression. We also observed that zebrafish larvae exposed to SMX+CLA for 7 days showed a lower number of macrophages and neutrophils.

Antibiotics in elderly Chinese population and their relations with hypertension and pulse pressure

Although antibiotic exposure in the general population has been well documented by a biomonitoring approach, epidemiologic data on the relationships between urinary antibiotic burden in the elderly with blood pressure (BP) are still lacking. The current study revealed thirty-four antibiotics in urine specimens from 990 elderly patients in Lu'an City, China, with detection frequencies ranging from 0.2 to 35.5%. Among the elderly, the prevalence of hypertension was 72.0%, and 12 antibiotics were detected in more than 10% of individuals with hypertension. The elderly with hypertension had the maximum daily exposure (5450.45 μg/kg/day) to fluoroquinolones (FQs). Multiple linear regression analyses revealed significant associations of BP and pulse pressure (PP) with exposure to specific antibiotics. The estimated β values (95% confidence interval) of associations with systolic blood pressure (SBP) in the right arm were 4.42 (1.15, 7.69) for FQs, 4.26 (0.52, 8.01) for the preferred as human antibiotics (PHAs), and 3.48 (0.20, 6.77) for the mixtures (FQs + tetracyclines [TCs] (tertile 3 vs. tertile 1)), respectively. Increased concentrations of TCs were associated with decreased diastolic BP (DBP; tertile 3: -1.75 [-3.39, -0.12]) for the right arm. Higher levels of FQs (tertile 3: 4.28 [1.02, 7.54]), PHAs (tertile 3: 4.25 [0.49, 8.01]), and FQs + TCs (tertile 3: 3.99 [0.71, 7.26]) were associated with increased SBP, and an increase in DBP for FQs (tertile 3: 1.82 [0.22, 3.42]) was shown in the left arm. Also, higher urinary concentrations of FQs (tertile 3: 3.18 [0.53, 5.82]), PHAs (tertile 3: 3.42 [0.40, 6.45]), and FQs + TCs (tertile 3: 3.06 [0.40, 5.72]) were related to increased PP, whereas a decline in PP for TCs (tertile 2: -2.93 [-5.60, -0.25]) in the right arm. And increased concentrations of penicillin V (tertile 3: 5.31 [1.53, 9.10]) and FQs + TCs (tertile 3: 2.84 [0.19, 5.49]) were related to higher PP in the left arm. By utilizing restricted cubic splines, our current study revealed a potential nonlinear dose-response association between FQ exposure and hypertension risk. In conclusion, this investigation is the first to present antibiotic exposure using a biomonitoring approach, and informs understanding of impacts of antibiotic residues, as emerging hazardous pollutants, on the hypertension risk in the elderly.

Antimicrobial Resistance in Rivers: A Review of the Genes Detected and New Challenges

River ecosystems are very important parts of the water cycle and an excellent habitat, food, and drinking water source for many organisms, including humans. Antibiotics are emerging contaminants which can enter rivers from various sources. Several antibiotics and their related antibiotic resistance genes (ARGs) have been detected in these ecosystems by various research programs and could constitute a substantial problem. The presence of antibiotics and other resistance cofactors can boost the development of ARGs in the chromosomes or mobile genetic elements of natural bacteria in rivers. The ARGs in environmental bacteria can also be transferred to clinically important pathogens. However, antibiotics and their resistance genes are both not currently monitored by national or international authorities responsible for controlling the quality of water bodies. For example, they are not included in the contaminant list in the European Water Framework Directive or in the US list of Water-Quality Benchmarks for Contaminants. Although ARGs are naturally present in the environment, very few studies have focused on non-impacted rivers to assess the background ARG levels in rivers, which could provide some useful indications for future environmental regulation and legislation. The present study reviews the antibiotics and associated ARGs most commonly measured and detected in rivers, including the primary analysis tools used for their assessment. In addition, other factors that could enhance antibiotic resistance, such as the effects of chemical mixtures, the effects of climate change, and the potential effects of the coronavirus disease 2019 pandemic, are discussed. Environ Toxicol Chem 2022;41:687-714. © 2022 SETAC.

Zebrafish as a Screening Model to Study the Single and Joint Effects of Antibiotics

The overuse of antibiotics combined with the limitation of wastewater facilities has resulted in drug residue accumulation in the natural environment. Thus, in recent years, the presence of antibiotic residues in the environment has raised concerns over the potential harmful effects on ecosystems and human health. The in vivo studies represent an essential step to study the potential impact induced by pharmaceutical exposure. Due to the limitations of traditional vertebrate model systems, zebrafish (Danio rerio) has recently emerged as a promising animal model to study the toxic effects of drugs and their therapeutic efficacy. The present review summarizes the recent advances made on the toxicity of seven representative classes of antibiotics, namely aminoglycosides, β-lactams, macrolides, quinolones, sulfonamides, tetracyclines and polyether antibiotics, in zebrafish, as well as the combined effects of antibiotic mixtures, to date. Despite a significant amount of the literature describing the impact of single antibiotic exposure, little information exists on the effects of antibiotic mixtures using zebrafish as an animal model. Most of the research papers on this topic have focused on antibiotic toxicity in zebrafish across different developmental stages rather than on their efficacy assessment.

Transcriptomic analysis of bisphenol AF on early growth and development of zebrafish (Danio rerio) larvae

Bisphenol AF (BPAF), an alternative to bisphenol A, is widely detected in aquatic environments. Owing to health concerns, the toxic effects of BPAF on organisms are drawing attention. The present study aims to evaluate the toxicity of BPAF, combining the results of omics techniques and experiment. Employing transcriptome sequencing (RNA-seq), we obtained 391, 648, 512, and 545 differentially expressed genes (DEGs) in 0.1, 1, 10, and 100 μg/L BPAF-exposed zebrafish larvae, respectively. Gene ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment revealed the early development, stimulus-response, and MAPK signaling pathway were significantly affected by BPAF. In addition, five hub genes (fgf3, fgf4, map2k1, myca, and casp3b) were highlighted as the key genes in MAPK signaling pathway using the protein-protein interaction network. Therefore, the RNA-seq results showed that early development and stimulus-response were the main processes affected by BPAF, which was consistent with our morphological and pathological results. The hatching rate of zebrafish embryos in 1 and 10 μg/L BPAF groups was significantly inhibited, and the oxidative stress indexes, including the level of total antioxidant capacity (T-AOC), superoxide dismutase (SOD), and lipid peroxidation (LPO), were significantly increased by the 100 μg/L BPAF treatment. Moreover, the activity of alkaline phosphatase (AKP) was significantly decreased in all BPAF exposure groups. In conclusion, exposure to BPAF at environmental relevant concentrations affected the early development and immune system of zebrafish larvae by modulating MAPK signaling pathway, and our results provide solid evidence for the future studies on the toxicity of bisphenols.

[Effect of ceftriaxone on the intestinal epithelium and microbiota in neonatal mice]

OBJECTIVE

To investigate the effect of ceftriaxone on the intestinal epithelium and microbiota in mice in the early-life stage, as well as the recovery of the intestinal epithelium and reconstruction of intestinal microbiota in adult mice.

METHODS

A total of 36 BALB/C neonatal mice were randomly divided into control group and experimental group, with 18 mice in each group. The mice in the experimental group were given ceftriaxone 100 mg/kg every day by gavage within 21 days after birth. Those in the control group were given an equal volume of normal saline by gavage. Immunohistochemistry was used to measure the expression of Ki67, Muc2, and ZO-1 in the intestinal epithelium. qPCR and next-generation sequencing were used to analyze the overall concentration and composition of fecal bacteria.

RESULTS

After 21 days of ceftriaxone intervention, the experimental group had a significant reduction in body weight, a significant reduction in the expression of Ki67 and ZO-1 and a significant increase in the expression of Muc2 in intestinal epithelial cells, a significant reduction in the overall concentration of fecal bacteria, and a significant increase in the diversity of fecal bacteria compared with the control group (P<0.05). Firmicutes was the most common type of fecal bacteria in the experimental group, and there were large amounts of Staphylococcus and Enterococcus. The experimental group had a certain degree of recovery of the intestinal epithelium, but there were still significant differences in body weight and the structure of intestinal microbiota between the two groups at 56 days after birth (P<0.05).

CONCLUSIONS

Early ceftriaxone intervention significantly affects the development of the intestinal epithelium and the construction of intestinal microbiota in the early-life stage. The injury of the intestinal microbiota in the early-life stage may continue to the adult stage and affect growth and development and physiological metabolism.

Omics and cytokine discovery in fish: Presenting the Yellowtail kingfish (Seriola lalandi) as a case study

A continued programme of research is essential to overcome production bottlenecks in any aquacultured fish species. Since the introduction of genetic and molecular techniques, the quality of immune research undertaken in fish has greatly improved. Thousands of species specific cytokine genes have been discovered, which can be used to conduct more sensitive studies to understand how fish physiology is affected by aquaculture environments or disease. Newly available transcriptomic technologies, make it increasingly easier to study the immunogenetics of farmed species for which little data exists. This paper reviews how the application of transcriptomic procedures such as RNA Sequencing (RNA-Seq) can advance fish research. As a case study, we present some preliminary findings using RNA-Seq to identify cytokine related genes in Seriola lalandi. These will allow in-depth investigations to understand the immune responses of these fish in response to environmental change or disease and help in the development of therapeutic approaches.

Reproductive toxicity of β-diketone antibiotic mixtures to zebrafish (Danio rerio)

So far, few data are available on the reproductive toxicological assessment of β-diketone antibiotics (DKAs), a class of ubiquitous pseudo-persistent pollutant, in zebrafish (Danio rerio). Herein, we reported the reproductive effects of DKAs by means of transcriptome analysis (F1-zebrafish), changes in a series of reproductive indices (F0-zebrafish) and histopathological observations. A total of 1170, 983 and 1399 genes were found to be differentially expressed when compared control vs. 6.25mg/L, control vs. 12.5mg/L and 6.25 vs. 12.5mg/L DKA-exposure treatments, respectively. Among three comparison groups, 670, 569 and 821 genes were respectively assigned for GO analyses based on matches with sequences of known functions. In 149 KEGG-noted metabolic pathways, the preferential one was the MAPK (mitogen-activated protein kinase) signaling pathway, followed by oxidative phosphorylation, neuroactive ligand-receptor interaction and so on. By qPCR verification, 6 genes (c6ast4, igfbp1b, mrpl42, tnnc2, emc4 and ddit4) showed consistent gene expression with those identified by transcriptome sequencing. Due to DKA-exposure, the concentrations of plasma estradiol and testosterone, and the gonado-somatic index were significantly dose-dependently declined. Also, DKA-exposure led to declining in zebrafish reproductive capacity, reflecting in fertilization, hatchability and egg production. Histopathological observations demonstrated that zebrafish ovary and testis suffered serious damage after DKA-exposure. The 4-oxo-TEMP signals increased obviously with increasing DKA-exposed concentrations, implying disruption of balance between generation and clearance of ¹O₂. In summary, DKAs not only produce reproductive toxicological effects on F0-zebrafish, but also result in adverse consequences for growth and development of F1-zebrafish.

Screening and functional identification of lncRNAs under β-diketone antibiotic exposure to zebrafish (Danio rerio) using high-throughput sequencing

Long non-coding RNAs (lncRNAs) have attracted considerable research interest, but so far no data are available on the roles of lncRNAs and their target genes under chronic β-diketone antibiotic (DKAs) exposure to zebrafish (Danio rerio). Herein, we identified 1.66, 3.07 and 3.36×10⁴ unique lncRNAs from the 0, 6.25 and 12.5mg/L DKA treatment groups, respectively. In comparison with the control group, the 6.25 and 12.5mg/L treatments led to up-regulation of 2064 and 2479 lncRNAs, and down-regulation of 778 and 954 lncRNAs, respectively. Of these, 44 and 39 lncRNAs in the respective 6.25 and 12.5mg/L treatments displayed significant differential expression. Volcano and Venn diagrams of the differentially expressed lncRNAs were constructed on the basis of the differentially expressed lncRNAs. After analyzing 10 lncRNAs and potential target genes, a complex interaction network was constructed between them. The consistency of 7 target genes (tenm3, smarcc1b, myo9ab, ubr4, hoxb3a, mycbp2 and CR388046.3), co-regulated by 3 lncRNAs (TCONS_00129029, TCONS_00027240 and TCONS_00017790), was observed between their qRT-PCR and transcriptomic sequencing. By in situ hybridization (ISH), abnormal expression of 3 lncRNAs was observed in hepatic and spleen tissues, suggesting that they might be target organs for DKAs. A similar abnormal expression of two immune-related target genes (plk3 and syt10), co-regulated by the 3 identified lncRNAs, was observed in liver and spleen by ISH. Histopathological observations demonstrated hepatic parenchyma vacuolar degeneration and clot formation in hepatic tissues, and uneven distribution of brown metachromatic granules and larger nucleus in spleen tissues resulting from DKA exposure. Overall, DKA exposure led to abnormal expression of some lncRNAs and their potential target genes, and these genes might play a role in immune functions of zebrafish.