Exposure to Sri Lanka's local groundwater in a CKDu prevalent area causes kidney damage in zebrafish

Metabolome evidence of CKDu risks after chronic exposure to simulated Sri Lanka drinking water in zebrafish

It is still a serious public health issue that chronic kidney disease of uncertain etiology (CKDu) in Sri Lanka poses challenges in identification, prevention, and treatment. What environmental factors in drinking water cause kidney damage remains unclear. This study aimed to investigate the risks of various environmental factors that may induce CKDu, including water hardness, fluoride (HF), heavy metals (HM), microcystin-LR (MC-LR), and their combined exposure (HFMM). The research focused on comprehensive metabolome analysis, and correlation with transcriptomic and gut microbiota changes. Results revealed that chronic exposure led to kidney damage and pancreatic toxicity in adult zebrafish. Metabolomics profiling showed significant alterations in biochemical processes, with enriched metabolic pathways of oxidative phosphorylation, folate biosynthesis, arachidonic acid metabolism, FoxO signaling pathway, lysosome, pyruvate metabolism, and purine metabolism. The network analysis revealed significant changes in metabolites associated with renal function and diseases, including 20-Hydroxy-LTE4, PS(18:0/22:2(13Z,16Z)), Neuromedin N, 20-Oxo-Leukotriene E4, and phenol sulfate, which are involved in the fatty acyls and glycerophospholipids class. These metabolites were closely associated with the disrupted gut bacteria of g_ZOR0006, g_Pseudomonas, g_Tsukamurella, g_Cetobacterium, g_Flavobacterium, which belonged to dominant phyla of Firmicutes and Proteobacteria, etc., and differentially expressed genes (DEGs) such as egln3, ca2, jun, slc2a1b, and gls2b in zebrafish. Exploratory omics analyses revealed the shared significantly changed pathways in transcriptome and metabolome like calcium signaling and necroptosis, suggesting potential biomarkers for assessing kidney disease.

Kidney injury contributes to edema of zebrafish larvae caused by quantum dots

Edema represents a notable outcome in fishes exposed to aquatic pollutants, yet the underlying etiology remains inadequately understood. This investigation delves into the etiological factors of edema formation in 7 days post fertilization (dpf) zebrafish larvae following their exposure to InP/ZnS quantum dots (QDs), which was chosen as a prototypical edema inducer. Given the fundamental role of the kidney in osmoregulation, we used transgenic zebrafish lines featuring fluorescent protein labeling of the glomerulus, renal tubule, and blood vessels, in conjunction with histopathological scrutiny. We identified the pronounced morphological and structural aberrations within the pronephros. By means of tissue mass spectrometry imaging and hyperspectral microscopy, we discerned the accumulation of InP/ZnS QDs in the pronephros. Moreover, InP/ZnS QDs impeded the renal clearance capacity of the pronephros, as substantiated by diminished uptake of FITC-dextran. InP/ZnS QDs also disturbed the expression levels of marker genes associated with kidney development and osmoregulatory function at the earlier time points, which preceded the onset of edema. These results suggest that impaired fluid clearance most likely resulting from pronephros injury contributes to the emergence of zebrafish edema. Briefly, our study provides a perspective: the kidney developmental injury induced by exogenous substances may regulate edema in a zebrafish model.

Effects of water fluoridation on early embryonic development of zebrafish

Fluoride has strong electronegativity and exposes diversely in nature. Water fluoridation is the most pervasive form of occurrence, representing a significant threat to human health. In this study, we investigate the morphometric and physiological alterations triggered by fluoride stimulation during the embryogenesis of zebrafish and reveal its putative effects of stage- and/or dose-dependent. Fluoride exhibits potent biological activity and can be extensively absorbed by the yolk sac, exerting significant effects on the development of multiple organs. This is primarily manifested as restricted nutrient utilization and elevated levels of lipid peroxidation, further leading to the accumulation of superoxide in the yolk sac, liver, and intestines. Moreover, pericardial edema exerts pressure on the brain and eye development, resulting in spinal curvature and reduced body length. Besides, acute fluoride exposure with varying concentrations has led to diverse teratogenic outcomes. A low dose of water fluoridation tends to induce abnormal development of the embryonic yolk sac, while vascular malformation is widely observed in all fluoride-treated groups. The effect of fluoride exposure on blood circulation is universally present, even in zebrafish larvae that do not exhibit obvious deformities. Their swimming behavior is also affected by water fluoridation, resulting in reduced activity and delayed reactions. In conclusion, this study provides valuable insights into the monitoring of environmental quality related to water fluoridation and disease prevention.

Multi-omics reveal mechanisms underlying chronic kidney disease of unknown etiology (CKDu) pathogenesis using zebrafish

Chronic kidney disease of unknown etiology (CKDu) is an endemic disease in the dry zone of farming communities, Sri Lanka. The drinking water in a CKDu prevalent area contains a high concentration of F-, hardness and other environmental pollutants, including heavy metals and microcystin, which are considered possible etiology of CKDu in these areas. Here, multi-omics data with host transcriptome, metabolome and gut microbiomes were obtained using simulated local drinking water of Sri Lanka after their exposure to adult zebrafish. Based on an integrated multi-omics analysis in the context of host physiology in the kidney injury samples with different pathologic grades, two common pathways necroptosis and purine metabolism were identified as potentially important pathways that affect kidney injury. The key metabolite acetyl adenylate in the purine metabolism pathway was significantly positively correlated with Comamonas (rho = 0.72) and significantly negatively correlated with Plesiomonas (rho = -0.58). This crucial metabolite and two key gut bacteria genera may not only be potential markers but also potential therapeutic targets in the uric acid metabolic pathway, which is an important factor in the pathogenesis of acute kidney injury (AKI) in general, as well as of chronic kidney disease (CKD). Based on this, we revealed the urea metabolism pathway of kidney injury in zebrafish and provided a new avenue for the treatment of CKDu in Sri Lanka.

Food-mediated exposure of Hofmeister ions in Oryza sativa (Rice) from selected CKDu endemic regions in Sri Lanka

The objectives of this study were to determine selected Hofmeister anions and cations that are important for kidney health, in raw rice samples from selected Chronic Kidney Disease of unknown etiology (CKDu) endemic and non-endemic areas in Sri Lanka and their intake. The anions and cations were analyzed by Ion Chromatography and Microwave Plasma Atomic Emission Spectrometry (MP-AES), respectively, after alkaline and acid digestion in thirty raw rice samples each from CKDu endemic and non-endemic areas, and the dietary intake was estimated. The mean concentrations of fluoride (F-), chloride (Cl-), phosphate (PO43-), sulfate (SO42-), sodium (Na+), magnesium (Mg2+), potassium (K+), and calcium (Ca2+) in raw rice in CKDu endemic areas were 53.317, 1515.3, 2799.6, 2704.9, 30.603, 300.76, 1001.3, and 90.075 mg/kg, respectively. The mean concentration of the anions and cations in raw rice from CKDu non-endemic areas were 22.850, 947.52, 4418.7, 6080.2, 23.862, 364.45, 955.78, and 96.780 mg/kg, respectively. Significantly higher differences (p < 0.05) were reported in the mean concentration of F-, Cl-, and Na+ in raw rice from CKDu endemic areas in comparison with the samples from non-endemic areas. The aggregated estimated daily intake (EDI) and cumulative EDI of F- via consumption of cooked non-traditional samba rice from CKDu endemic areas for adults were the highest (0.155 and 0.172 mg/kg bw/d, respectively), which were higher than the recommended tolerable upper intake value (0.15-0.2 mg/kg bw/d). In contrast, the traditional rice from CKDu non-endemic areas for adolescents, reported the lowest values (0.0210 and 0.0470 mg/kg bw/d, respectively). Adults who consume non-traditional samba rice from CKDu endemic areas were at health risk, while children were the most vulnerable group due to their low body weight. These results indicate that the consumption of rice rich in Hofmeister ions may contribute to the total intake and act as risk factors to negatively affect weak kidneys in CKDu endemic areas. Further research to analyze Hofmeister ions in cooked rice and rice from different countries is recommended.

Probiotics mitigate kidney damage after exposure to Sri Lanka's local groundwater from chronic kidney disease with uncertain etiology (CKDu) prevalent area in zebrafish

Groundwater in Sri Lanka, contaminated with environmental toxins, is suspected to potentially induce chronic kidney disease of uncertain etiology (CKDu) in humans. This study aims to elucidate the potential mitigating effects of probiotics on kidney damage induced by exposure to this local groundwater (LW) in zebrafish. We used zebrafish as a model organism and exposed them to local groundwater to evaluate the risk of CKDu. Probiotics were then added at a concentration of 108 colony-forming units per milliliter (CFU/mL). Our findings revealed that exposure to local groundwater resulted in abnormalities, such as tail deletion and spinal curvature in zebrafish larvae. However, the addition of probiotics mitigated these effects, improving the hatching rate, heart rate, length, weight, deformity rate, survival rate, and abnormal behavior of zebrafish. It also positively influenced the differential expression levels of kidney development and immunity-related genes (dync2h1, foxj1, pkd2, gata3, slc20a1, il1β, and lyso). Furthermore, exposure to LW decreased both the diversity and abundance of microbiota in zebrafish larvae. However, treatment with probiotics, such as L. plantarum and L. rhamnosus partially restored the disrupted gut microbiota and significantly impacted the cellular process pathways of the microbial community, as determined by KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis. In conclusion, this study highlights the risks associated with Sri Lanka's local groundwater from a CKDu prevalent area and confirms the beneficial effects of different probiotics. These findings may provide new insights into bacterial function in host kidney health.

Elucidating environmental factors and their combined effects on CKDu in Sri Lanka using zebrafish

Chronic kidney disease with uncertain etiology (CKDu) in Sri Lanka has attracted much attention as a global health issue. However, how environmental factors in local drinking water induce kidney damage in organisms is still elusive. We investigated multiple environmental factors including water hardness and fluoride (HF), heavy metals (HM), microcystin-LR (MC-LR), and their combined exposure (HFMM) to elucidate their toxic effects on CKDu risk in zebrafish. Acute exposure affected renal development and inhibited the fluorescence of Na, K-ATPase alpha1A4:GFP zebrafish kidney. Chronic exposure influenced the body weight of both genders of adult fish and induced kidney damage by histopathological analyses. Furthermore, the exposure significantly disturbed differential expression genes (DEGs), diversity and richness of gut microbiota, and critical metabolites related to renal functions. The transcriptomic analysis revealed that kidney-related DEGs were linked with renal cell carcinoma, proximal tubule bicarbonate reclamation, calcium signaling pathway, and HIF-1 signaling pathway. The significantly disrupted intestinal microbiota was closely related to the environmental factors and H&E score, which demonstrated the mechanisms of kidney risks. Notably, the Spearman correlation analysis indicated that the changed bacteria such as Pseudomonas, Paracoccus, and ZOR0006, etc were significantly connected to the DEGs and metabolites. Therefore, the assessment of multiple environmental factors provided new insights on "bio-markers" as potential therapies of the target signaling pathways, metabolites, and gut bacteria to monitor or protect residents from CKDu.

Eugenol exposure inhibits embryonic development and swim bladder formation in zebrafish

Eugenol is a natural phenolic essential oil extracted from cloves, that has analgesic and anesthetic effects and is widely used in fishery anesthesia. However, the potential safety risks of aquaculture production associated with the massive use of eugenol and its developmental toxicity during early life stages of fish have been overlooked. In this study, zebrafish (Danio rerio) embryos at 24 hours post-fertilization (hpf) were exposed to eugenol at concentrations of 0, 10, 15, 20, 25, or 30 mg/L for 96 h. Eugenol exposure delayed the hatching of zebrafish embryos, and reduced the body length and the inflation rate of the swim bladder. The accumulated number of dead zebrafish larvae in the eugenol-exposed groups was higher than that of the control group, and it was dose-dependent. Real-time quantitative polymerase chain reaction (qPCR) analysis showed that the Wnt/β-catenin signaling pathway that regulates the development of the swim bladder during the hatching and mouth-opening stages was inhibited after eugenol exposure. Specifically, the expression of wif1, a Wnt signaling pathway inhibitor, was significantly up-regulated, whereas the expression of fzd3b, fzd6, ctnnb1, and lef1 involved in the Wnt/β-catenin pathway was significantly down-regulated. These results suggest that the failure of zebrafish larvae to inflate their swim bladders as a result of eugenol exposure may be caused by the inhibition of the Wnt/β-catenin signaling pathway inhibited. In addition, the inability to catch food due to the abnormal development of the swim bladder may be the key to the death of zebrafish larvae during the mouth-opening stage.

Machine learning approach for assessment of arsenic levels using physicochemical properties of water, soil, elevation, and land cover

Groundwater is an essential resource; around 2.5 billion people depend on it for drinking and irrigation. Groundwater arsenic contamination is due to natural and anthropogenic sources. The World Health Organization (WHO) has proposed a guideline value for arsenic concentration in groundwater samples of 10[Formula: see text]g/L. Continuous consumption of arsenic-contaminated water causes various carcinogenic and non-carcinogenic health risks. In this paper, we introduce a geospatial-based machine learning method for classifying arsenic concentration levels as high (1) or low (0) using physicochemical properties of water, soil type, land use land cover, digital elevation, subsoil sand, silt, clay, and organic content of the region. The groundwater samples were collected from multiple sites along the river Ganga's banks of Varanasi district in Uttar Pradesh, India. The dataset was subjected to descriptive statistics and spatial analysis for all parameters. This study assesses the various contributing parameters responsible for the occurrence of arsenic in the study area based on the Pearson correlation feature selection method. The performance of machine learning models, i.e., Extreme Gradient Boosting (XGBoost), Gradient Boosting Machine (GBM), Decision Tree, Random Forest, Naïve Bayes, and Deep Neural Network (DNN), were compared to validate the parameters responsible for the dissolution of arsenic in groundwater aquifers. Among all the models, the DNN algorithm outclasses other classifiers as it has a high accuracy of 92.30%, a sensitivity of 100%, and a specificity of 75%. Policymakers can utilize the accuracy of the DNN model to approximate individuals prone to arsenic poisoning and formulate mitigation strategies based on spatial maps.

Bacteriophage-based techniques for elucidating the function of zebrafish gut microbiota

Bacteriophages (or phages) are unique viruses that can specifically infect bacteria. Since their discovery by Twort and d'Herelle, phages with bacterial specificity have played important roles in microbial regulation. The intestinal microbiota and host health are intimately linked with nutrient, metabolism, development, and immunity aspects. However, the mechanism of interactions between the composition of the microbiota and their functions in maintaining host health still needs to be further explored. To address the lack of methodology and functions of intestinal microbiota in the host, we first proposed that, with the regulations of special intestinal microbiota and applications of germ-free (GF) zebrafish model, phages would be used to infect and reduce/eliminate the defined gut bacteria in the conventionally raised (CR) zebrafish and compared with the GF zebrafish colonized with defined bacterial strains. Thus, this review highlighted the background and roles of phages and their functional characteristics, and we also summarized the phage-specific infection of target microorganisms, methods to improve the phage specificity, and their regulation within the zebrafish model and gut microbial functional study. Moreover, the primary protocol of phage therapy to control the intestinal microbiota in zebrafish models from larvae to adults was recommended including phage screening from natural sources, identification of host ranges, and experimental design in the animal. A well understanding of the interaction and mechanism between phages and gut bacteria in the host can potentially provide powerful strategies or techniques for preventing bacteria-related human diseases by precisely regulating in vitro and in vivo, which will provide novel insights for phages' application and combined research in the future. KEY POINTS: • Zebrafish models for clarifying the microbial and phages' functions were discussed • Phages infect host bacteria with exquisite specificity and efficacy • Phages can reduce/eliminate the defined gut bacteria to clarify their function.