Chronic kidney disease of unknown aetiology in Sri Lanka and the exposure to environmental chemicals: a review of literature

Exposome and Metabolome Analysis of Sugarcane Workers Reveals Predictors of Kidney Injury

Introduction

Sugarcane workers are exposed to potentially hazardous agrochemicals, including pesticides, heavy metals, and silica. Such occupational exposures present health risks and have been implicated in a high rate of kidney disease seen in these workers.

Methods

To investigate potential biomarkers and mechanisms that could explain chronic kidney disease (CKD) among this worker population, paired urine samples were collected from sugarcane cutters at the beginning and end of a harvest season in Guatemala. Workers were then separated into 2 groups, namely those with or without kidney function decline (KFD) across the harvest season. Urine samples from these 2 groups underwent elemental analysis and untargeted metabolomics.

Results

Urine profiles demonstrated increases in silicon, certain pesticides, and phosphorus levels in all workers, whereas heavy metals remained low. The KFD group had a reduction in estimated glomerular filtration rate (eGFR) across the harvest season; however, kidney injury marker 1 did not significantly change. Cross-harvest metabolomic analysis found trends of fatty acid accumulation, perturbed amino acid metabolism, presence of pesticides, and other known signs of impaired kidney function.

Conclusion

Silica and certain pesticides were significantly elevated in the urine of sugarcane workers with or without KFD. Future work should determine whether long-term occupational exposure to silica and pesticides across multiple seasons contributes to CKD in these workers. Overall, these results confirmed that multiple exposures are occurring in sugarcane workers and may provide insight into early warning signs of kidney injury and may help explain the increased incidence of CKD among agricultural workers.

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.

The association between urinary metals/metalloids and chronic kidney disease among general adults in Wuhan, China

The relation between exposure to single metal/metalloid and the risk of chronic kidney disease (CKD) remains unclear. We aimed to determine the single and mixed associations of 21 heavy metals/metalloids exposure and the risk of CKD. We performed a cross-sectional study that recruited 4055 participants. Multivariate logistic regression, linear regression and weighted quantile sum (WQS) regression were conducted to explore the possible effects of single and mixed metals/metalloids exposure on the risk of CKD, the risk of albuminuria and changes in the estimated glomerular filtration rate (eGFR). In single-metal models, Cu, Fe, and Zn were positively associated with increased risks of CKD (P-trend < 0.05). Compared to the lowest level, the highest quartiles of Cu (OR = 2.94; 95% CI: 1.70, 5.11; P-trend < 0.05), Fe (OR = 2.39; 95% CI: 1.42, 4.02; P-trend < 0.05), and Zn (OR = 2.35; 95% CI: 1.31, 4.24; P-trend < 0.05) were associated with an increased risk of CKD. After multi-metal adjustment, the association with the risk of CKD remained robust for Cu (P < 0.05). Weighted quantile sum regression revealed a positive association between mixed metals/metalloids and the risk of CKD, and the association was largely driven by Cu (43.7%). Specifically, the mixture of urinary metals/metalloids was positively associated with the risk of albuminuria and negatively associated with eGFR.

Threshold effect of urinary chromium on kidney function biomarkers: Evidence from a repeated-measures study

Chronic kidney disease (CKD) is a public health concern worldwide, and chromium exposure may be a risk factor due to its potential nephrotoxicity. However, research on the association between chromium exposure and kidney function especially the potential threshold effect of chromium exposure is limited. A repeated-measures study involving 183 adults (641 observations) was conducted from 2017 to 2021 in Jinzhou, China. Urinary albumin-to-creatinine ratio (UACR) and estimated glomerular filtration rate (eGFR) were measured as kidney function biomarkers. Generalized mixed models and two-piecewise linear spline mixed models were used to assess the dose-response relationship and potential threshold effect of chromium on kidney function, respectively. Temporal analysis was conducted by the latent process mixed model to depict the longitudinal change of kidney function over age. Urinary chromium was associated with CKD (odds ratio [OR] = 1.29; 95 % confidence interval [CI], 6.41, 14.06) and UACR (Percent change = 10.16 %; 95 % CI, 6.41 %, 14.06 %), and we did not find significant association between urinary chromium and eGFR (Percent change = 0.06 %; 95 % CI, -0.80 %, 0.95 %). The threshold analyses suggested the existence of threshold effects of urinary chromium, with inflection points at 2.74 μg/L for UACR and 3.95 μg/L for eGFR. Furthermore, we found that chromium exposure exhibited stronger kidney damage over age. Our study provided evidence for the threshold effects of chromium exposure on kidney function biomarkers and the heightened nephrotoxicity of chromium in older adults. More attention should be paid to the supervision of chromium exposure concentrations for preventing kidney damage, especially in older adults.

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.

Exposure of patients with chronic kidney disease on dialysis to pesticides

INTRODUCTION

Pesticides can trigger kidney disease.

OBJECTIVE

To describe the exposure to pesticides of patients with chronic kidney disease on dialysis.

METHODS

Quantitative and descriptive field research, with 90 patients with chronic kidney disease on dialysis in two hemodialysis units in the state of Santa Catarina, through the application of a structured questionnaire. Participants were divided into two groups: with and without exposure to pesticides. The questionnaire was applied in hemodialysis clinics during treatment. Laboratory test values were collected from clinical records. Data were analyzed using descriptive statistics and association using the chi-square test. For laboratory test data, a comparison of means was performed using the unpaired Student's t-test between the groups.

RESULTS

The mean age of exposed participants was 58 years (±13.7; minimum = 23; maximum = 75) and that of non-exposed participants was 64 years old (±13.9; minimum = 35; maximum = 96). Of the 90 patients, 30% were exposed to pesticides. The mean exposure time was 6.7 ± 3.8 hours/day. There was a statistically significant association between the preparation of the mixture with pesticides and diabetes (p ≤ 0.048). There was no statistically significant difference between the results of laboratory tests in the exposed and non-exposed groups.

CONCLUSION

This study shows that pesticides can be triggering factors for chronic kidney disease (CKD); however, we must expand research in this field to prove the relationship between exposure to pesticides and CKD.

Fluorescence characteristics and source analysis of DOM in groundwater during the wet season in the CKDu zone of North Central Province, Sri Lanka

The dissolved organic matter (DOM) should be purified for safe drinking water due to disinfection by-products (DBPs) produced by disinfectants reaction with DOM. Current research on groundwater in the chronic kidney disease with unknown etiology (CKDu) zone of the North Central Province (NCP) in Sri Lanka has focused mainly on aquatic chemistry, with limited attention paid to the spatial distribution, compositional sources and factors of DOM. Therefore, the structure, composition, source and spatial distribution of the DOM of two kinds of groundwater samples collected from dug well and tube well in the NCP during the wet season were determined, compared and analyzed by analytical tools such as parallel factor analysis (PARAFAC). Results show that the average concentrations of TOC in these two groundwater samples are generally higher than 5.0 mg/L, and the concentration of TOC in the groundwater of the shallow weathered aquifer is higher than that of the deep hard rock aquifer, while its distribution of the two aquifers are on contrary. The DOM in the dug well has three types and four components, including humus-like component C1 (33.36%) and C2 (38.60%), protein-like component C3 (13.09%) and heterogeneous organic component C4 (14.95%). In the tube well, two types and two components of the DOM are determined, including humus-like component CⅠ (69.80%) widely existing in natural water and soluble microbial by-product CⅡ (30.20%) produced by microbial community activities. In the dug well, DOM is mainly exogenous input, the higher ion concentration in water affected the fluorescence intensity of humus and protein components. And in the tube well, DOM has obvious endogenous characteristics, and higher pH value may inhibit the production of protein like fluorescent substances to a certain extent.

Urinary MicroRNA Analysis Indicates an Epigenetic Regulation of Chronic Kidney Disease of Unknown Etiology in Sri Lanka

BACKGROUND

Chronic kidney disease of unknown etiology (CKDu) is reported among male paddy farmers in the dry zone of Sri Lanka. The exact cause of this disease remains undetermined. Genetic susceptibility is identified as a major risk factor for CKDu Objectives: In this study, small urinary RNAs were characterized in CKDu patients, healthy endemic and non-endemic controls. Differently expressed urinary miRNAs and their associated pathways were identified in the study population.

METHODS

Healthy and diseased male volunteers (n = 9) were recruited from Girandurukotte (endemic) and Mawanella (non-endemic) districts. Urinary small RNAs were purified and sequenced using Illumina MiSeqTM. The sequence trace files were assembled and analyzed. Differentially ex-pressed miRNAs among these three groups were identified and pathway analysis was conducted.

RESULTS

The urine samples contained 130,623 sequence reads identified as non-coding RNAs, PIWI-interacting RNAs (piRNA), and miRNAs. Approximately four percent of the total small RNA reads represented miRNA, and 29% represented piRNA. A total of 409 miRNA species were ex-pressed in urine. Interestingly, both diseased and endemic controls population showed significantly low expression of miRNA and piRNA. Regardless of the health status, the endemic population ex-pressed significantly low levels of miR-10a, miR-21, miR-148a, and miR-30a which have been linked with several environmental toxins Conclusion: Significant downregulation of miRNA and piRNA expression in both diseased and healthy endemic samples indicates an epigenetic regulation of CKDu involving genetic and environmental interaction. Further studies of specific miRNA species are required to develop a miRNA panel to identify individuals susceptible to CKDu.

Evaluation of the developmental effects of a glyphosate-based herbicide complexed with copper, zinc, and manganese metals in zebrafish

The use of glyphosate-based herbicides (GBH) has increased dramatically, being currently the most used herbicides worldwide. Glyphosate acts as a chelating agent, capable of chelate metals. The synergistic effects of metals and agrochemicals may pose an environmental problem as they have been shown to induce neurological abnormalities and behavioural changes in aquatic species. However, as their ecotoxicity effects are poorly understood, evaluating the impacts of GBH complexed with metals is an ecological priority. The main objective of the study was to evaluate the potentially toxic effects caused by exposure to a GBH (1 μg a.i. mL^-1), alone or complexed with metals (Copper, Manganese, and Zinc (100 μg L^-1)), at environmentally relevant concentrations, during the early period of zebrafish (Danio rerio) embryo development (96 h post-fertilization), a promising model for in vivo developmental studies. To clarify the mechanisms of toxicity involved, lethal and sublethal development endpoints were assessed. At the end of the exposure, biochemical and cell death parameters were evaluated and, 24 h later, different behavioural responses were assessed. The results showed that metals induced higher levels of toxicity. Copper caused high mortality, low hatching, malformations, and changes in biochemical parameters, such as decreased Catalase (CAT) activity, increased Glutathione Peroxidase (GPx), Glutathione S-Transferase (GST), reduced Glutathione (GSH) and decreased Acetylcholinesterase (AChE) activity, also inducing apoptosis and changes in larval behaviour. Manganese increased the activity of SODs enzymes. Zinc increased mortality, reactive oxygen species (ROS) levels, superoxide dismutase activity (SODs) and caused a decrease in AChE activity. Embryos/larvae exposed to the combination of GBH/Metal also showed teratogenic effects during their development but in smaller proportions than the metal alone. Although more studies are needed, the results suggest that GBH may interfere with the mechanisms of metal toxicity at the biochemical, physiological, and behavioural levels of zebrafish.

Exposição de pacientes com doença renal crônica em tratamento dialítico aos agrotóxicos

Resumo Introdução: O uso de agrotóxicos pode desencadear doença renal. Objetivo: Descrever a exposição a agrotóxicos de pacientes com doença renal crônica em tratamento dialítico. Métodos: Pesquisa de campo, quantitativa e descritiva, com 90 portadores de doença renal crônica em tratamento dialítico em duas unidades de hemodiálise no estado de Santa Catarina, por meio da aplicação de um questionário estruturado. Os participantes foram divididos em dois grupos: sem e com exposição a agrotóxicos. O questionário foi aplicado nas clínicas de hemodiálise durante o tratamento. Foram coletados valores de exames laboratoriais dos prontuários clínicos. Os dados foram analisados pela estatística descritiva e associação pelo teste qui-quadrado. Para os dados dos exames laboratoriais, foi realizada comparação de médias pelo teste t de Student não pareado entre os grupos. Resultados: A idade média dos participantes expostos foi de 58 anos (±13,7; mínimo = 23; máximo = 75) e a dos não expostos, de 64 anos (±13,9; mínimo = 35; máximo = 96). Dos 90 pacientes, 30% foram expostos a agrotóxicos. O tempo médio de exposição foi de 6,7 ± 3,8 horas/dia. Houve associação estatística significativa entre o preparo da calda com agrotóxicos e a presença de diabetes (p ≤ 0,048). Não houve diferença estatística significativa entre os resultados dos exames laboratoriais do grupo exposto e do não exposto. Conclusão Esta pesquisa evidencia que os agrotóxicos podem ser fatores desencadeadores da doença renal crônica (DRC), entretanto sugere-se ampliar pesquisas na área que possam comprovar a relação entre exposição a agrotóxicos e DRC.

Renoprotective and Oxidative Stress-Modulating Effects of Taxifolin against Cadmium-Induced Nephrotoxicity in Mice

Cadmium (Cd) is an inessential trace metal that accumulates in the kidney and may lead to renal toxicity by mediating oxidative stress (OS), inflammatory reactions, and apoptosis. The main objective of this experiment was to inspect the protecting potential of taxifolin (TA) on Cd-induced renal toxicity. Adult male mice were allocated into equal five groups as follows: control, TA-treated (50 mg/kg, oral), CdCl₂-treated (4 mg/kg body weight (BW), p.o.), pretreated with TA (25 mg/kg) 1 h before CdCl₂ injection (4 mg/kg BW, p.o.), and pretreated with TA (50 mg/kg) 1 h before CdCl₂ injection (4 mg/kg BW, p.o.) for 14 days. Cd-intoxicated mice revealed higher serum urea and creatinine levels and notable histopathological alterations in the renal tissues. Malondialdehyde (MDA), nitric oxide (NO), nuclear factor-kappa B (NF-κB) p65, tumor necrosis factor-α (TNF-α), and IL-1β were increased. In contrast, glutathione levels, catalase and superoxide dismutase activities, and IL-10 levels were decreased under Cd-administered effects. Conversely, the TA pre-treatment highly protected tissues from Cd-toxicity, improved renal function, decreased MDA and NO levels, attenuated inflammation, and improved redox status in the renal tissues of Cd-intoxicated mice. The TA pre-treatment of Cd-intoxicated mice showed down-regulation of both Bax and caspase-3 protein and up-regulation of Bcl-2 protein expression in the kidney. Furthermore, TA pre-treatment induced higher upregulation of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase 1 (HO-1) expression in kidney cells of Cd-intoxicated mice. Therefore, TA can protect renal tissues against Cd-induced nephrotoxicity via improving redox status, modulating inflammation, diminishing cell apoptosis, and activating the Nrf2/HO-1 signaling pathway.

Environmental metal exposures and kidney function of Guatemalan sugarcane workers

BACKGROUND

Exposure to environmental metals can cause nephrotoxicity. There is an international epidemic of chronic kidney disease of unknown cause (CKDu). Whether metal exposures contribute to kidney dysfunction in populations at risk for CKDu remains unresolved.

OBJECTIVE

Urinary metals (arsenic, cadmium, nickel, and uranium) were examined in 222 sugarcane cutters in Guatemala at three time points over 1 year.

METHODS

We explored the relationships between metal concentrations and markers of kidney function using multivariable linear mixed-effect models.

RESULTS

Arsenic, cadmium, and nickel were detected in the majority of the 340 urine samples and were generally within limits previously considered to be nonnephrotoxic. Nevertheless, higher urine cadmium was inversely associated with estimated glomerular filtration rate (eGFR) (β: -4.23, 95% confidence interval [CI]: -6.92, -1.54) and positively associated with neutrophil gelatinase-associated lipocalin (NGAL) (β: 2.92, 95% CI: 1.20, 4.64). Higher urine arsenic was also inversely associated with eGFR (β: -4.36, 95% CI: -7.07, -1.64).

SIGNIFICANCE

Our findings suggest that exposures to metals, including cadmium and arsenic, might contribute to kidney toxicity seen in workers at risk for CKDu. These findings are consistent with the potential for metal nephrotoxicity at lower than expected levels in the setting of manual work in a very hot environment.

Neuroprotective effect of sodium alginate against chromium-induced brain damage in rats

Oral exposure to chromium hexavalent [Cr(VI)] has disastrous impacts and affects many people worldwide. Cr(VI) triggers neurotoxicity via its high oxidation potential by generating high amount of ROS. Meanwhile, alginates are known by their chelating activity and ability to bind heavy metals and toxins, in addition to their antioxidant, anti-inflammatory, and anti-apoptotic activities. So, this study aimed to explore the neuroprotective potential of sodium alginate (SA) against cellular injury, DNA damage, macromolecule alterations, and apoptosis induced by oral ingestion of Cr. Forty Wistar male rats were divided into 4 groups; group I: standard control ingested with the vehicle solution, group II: Cr-intoxicated group received 10 mg/kg b.w. of potassium dichromate orally by gavage and kept without treatment, group III: SA group in which rats were orally exposed to 200 mg/kg b.w. of SA only, and group IV: SA-treated group that received 200 mg/kg b.w. of SA along with Cr for 28 consecutive days. Neurotransmitters such as Acetyl choline esterase (AchE), Monoamine oxidase A (MAOA) concentrations, Dopamine (DA) and 5-Hydroxytryptamine (5-HT) levels were assessed in brain homogenate tissues. Neurobiochemical markers; NAD⁺ and S100B protein were investigated in the brain tissues and serum, respectively. Levels of HSP70, caspase-3, protein profiling were evaluated. DNA damage was determined using the Comet assay. Results revealed a significant reduction in the AchE and MAOA concentrations, DA, 5-HT, and NAD⁺ levels, with an increase in the S100B protein levels. Cr(VI) altered protein pattern and caused DNA damage. High levels of HSP70 and caspase-3 proteins were observed. Fortunately, oral administration of SA prevented the accumulation of Cr in brain homogenates and significantly improved all investigated parameters. SA attenuated the ROS production and relieved the oxidative stress by its active constituents. SA can protect against cellular and DNA damage and limit apoptosis. SA could be a promising neuroprotective agent against Cr(VI)-inducing toxicity.

Comprehensive Groundwater Quality Analysis in Chronic Kidney Disease of Unknown Etiology (CKDu) Prevalence Areas of Sri Lanka to Investigate the Responsible Culprit

Chronic kidney disease of unknown etiology (CKDu) is a serious health problem in Sri Lanka especially among agricultural communities in dry zone since 19th century. In the present study, several water quality parameters were studied in well water samples and only four parameters, namely, hardness, cadmium level, fluoride level, and strontium level have shown a relationship with the CKDu prevalence. Higher percentage of well water samples collected from CKDu prevalent area in both pre and postmonsoon seasons have exceeded the WHO recommended levels of hardness. Further, water samples collected in postmonsoon seasons had significantly higher hardness than the well water samples collected in premonsoon season ( $P<0.05$ ). This may be due to the dissolution of calcium carbonate by water recharge. Moreover, cadmium and fluoride contents have exceeded the recommended levels in high-risk area during the premonsoon period. Furthermore, according to principal component analysis (PCA), four clusters were identified depending on the different levels of fluoride, cadmium, hardness, and strontium contents. The control area (Am) fell in to separate cluster with low contents of fluoride, cadmium, hardness, and strontium than in CKDu prevalent area. Since it has been found that the above species are directly involved in renal damage, it can be concluded that a synergetic effect of cadmium, fluoride, hardness, and strontium in well water may be a main cause for CKDu in Sri Lanka.

Risk factors for endemic chronic kidney disease of unknown etiology in Sri Lanka: Retrospect of water security in the dry zone

The prevalence of chronic kidney disease of unknown etiology (CKDu) is receiving considerable attention due to the serious threat to human health throughout the world. However, the roles of geo-socio-environmental factors in the prevalence of the CKDu endemic areas are still unknown. Sri Lanka is one of the countries most seriously affected by CKDu, where 10 out of 25 districts have been identified as the areas with the high prevalence of CKDu (10-20%). This review summarizes the geographical distribution of CKDu and its probable geochemical, behavioral, sociological, and environmental risk factors based on research related to hydrogeochemical influences on CKDu in Sri Lanka. More than 98% of CKDu patients have consumed groundwater as their primary water source in daily life, indicating the interactions of geogenic contaminants (such as F^-, total dissolved solids, Hofmeister ions) in groundwater is responsible for the disease. Apart from the hydrogeochemical factors, mycotoxins, cyanotoxins, use of some herbal medicines, dehydration, and exposure to agrochemicals were alleged as risk factors. Sociological factors, including poverty, living habits and anthropogenic activities, may also provoke the emergence of CKDu. Therefore, the interaction of geo-socio environmental risk factors should be sociologically and scientifically considered to prevent the prevalence of CKDu. Future in-depth studies are required to reveal the individual role of each of the postulated etiological factors, possibly using machine learning and advanced statistics.

The Groundwater Geochemistry and the Human Health Risk Assessment of Drinking Water in an Area with a High Prevalence of Chronic Kidney Disease of Unknown Etiology (CKDu), Sri Lanka

Chronic kidney disease of unknown etiology (CKDu) has become an alarming health issue in Sri Lanka. The disease is more notable among farming communities and people who consume groundwater as their main source of drinking water. To assess the possible links between drinking water chemistry and expansion of CKDu, the study was compared with hydrogeochemical data of drinking water sources in a CKDu prevalent area (Girandurukotte GND, Badulla District) and a reference area (Dambethalawa GND, Ampara District) in Sri Lanka. Based on the results, nephrotoxic heavy metal (Cd, Cr, Pb, and As) concentrations were significantly higher in the CKDu prevalent site than the reference area, compromised the harmful consequences to the people in the CKDu hotspot. Results of the inverse distance weighted (IDW) interpolation tool indicated the nephrotoxic heavy metals contents including Cd, Pb, As, and Cr in CKDu hotspot were changed in the ranges of 9.78–187.25 μg/L, 0.08–0.66 μg/L, 20.76–103.30 μg/L, and 0.03–0.34 μg/L. The random distribution patterns were shown by the result in Moran’s index values. Noteworthy, the results have emphasized a strong association between fluoride and water hardness. The frequency of occurrence above the threshold limit of fluoride was 28% in non-CKDu water samples, while 81% in CKDu prevalent sites. The hardness values in the CKDu prevalent site indicated “moderately hard water,” while the non-CKDu area indicated the “soft water.” Furthermore, this paper quantified overall water quality and heavy metal contamination and assessed the human health risks associated with drinking water. According to the results of the water quality index, 90% of the samples in the CKDu prevalent area were classified as “poor water” and “very poor water” for drinking purposes, while 73.33% of the samples in the non-CKDu area were “good” and “excellent” for drinking usage. Calculated chronic daily intake (CDIoral) and hazard quotient (HQoral) of nephrotoxicants were higher in CKDu hotspot than the non-CKDu site. Besides, the hazard index (HI) values obtained for the CKDu prevalent area exceeding the acceptable limit (HI = 1) indicated potential health risks to the people in those areas. This study suggests that long-term exposure to nephrotoxic heavy metals, water hardness, and fluoride present in drinking water may threaten human health and affect kidney functions. Therefore, regular monitoring and better management of water supplies in CKDu prevalent areas are essential to determine the contamination load and reduce the health impacts due to excessive and long-term exposure to the nephrotoxicants.

Sugarcane Workweek Study: Risk Factors for Daily Changes in Creatinine

INTRODUCTION

Agricultural workers laboring in thermally stressful environments are at increased risk for kidney injury and chronic kidney disease of unknown origin (CKDu), and their environmental and occupational exposures have been considered to be important risk factors. This study examined the effects of repeated kidney stress from the simultaneous strain of work and other factors experienced by workers in Guatemala during a typical workweek.

METHODS

We collected data from 107 sugarcane workers across 7 consecutive work shifts. Data included information on daily occupational, meteorological, environmental, and lifestyle factors. We used multivariable linear mixed models to evaluate associations of these factors with percent change in creatinine.

RESULTS

We observed that increasing wet bulb globe temperature (β = 2.5%, 95% confidence interval [CI] = 0.3%, 4.7%) and increasing diastolic blood pressure (β = 6.2%, 95% CI = 0.9%, 11.6%) were associated with increases in creatinine across the shift, whereas consumption of water from chlorinated dormitory tanks as compared to artesian well water (β = -17.5%, 95% CI = -29.6%, -5.4%) and increasing number of rest breaks (β = -5.8%, 95% CI = -9.0%, -2.6%) were found to be protective against increases in creatinine. Workers reporting drinking tank water had lower concentrations of urine creatinine-corrected arsenic, lead, uranium, and glyphosate compared to workers reporting the use of well water or municipal water.

CONCLUSION

These results reinforce the need to focus on preventive actions that reduce kidney injury among this worker population, including strategies to reduce heat stress, managing blood pressure, and examining water sources of workers for nephrotoxic contaminants.

GIS, Multivariate Statistics Analysis and Health Risk Assessment of Water Supply Quality for Human Use in Central Mexico

The spatial assessments of water supply quality from wells, springs, and surface bodies were performed during the dry and rainy seasons in six municipalities in the eastern regions of Michoacán (Central Mexico). Different physicochemical parameters were used to determine the supplies’ Water Quality Index (WQI); all of the communities presented good quality. The analysis indicates that many water quality parameters were within limits set by the international standards, showing levels of “excellent and good quality” according to WQI, mainly during the dry season (except at San Pedro Jácuaro and Irimbo communities in the rainy season). However, some sites showed “poor quality” and “unsuitable drinking water” related to low pH levels (<5) and high levels of turbidity, color, Fe, Al, Mn, and arsenic. Multivariate statistical analysis techniques (Principal Component and Hierarchical Cluster) and geographic information system (GIS) identify potential sources of water pollution and estimate the geographic extension of parameters with negative effects on human health (mainly in communities without sampling). According to multivariate analysis, the Na+/K+ ratio and water temperature (22–42 °C) in various sites suggest that the WQI values were affected by geological and geothermal conditions and physical changes between seasons, but were not from anthropogenic activity. The GIS established predictions about the probable spatial distribution of arsenic levels, pH, temperature, acidity, and hardness in the study area, which provides valuable information on these parameters in the communities where the sampling was not carried out. The health risk assessment for dermal contact and ingestion showed that the noncancer risk level exceeded the recommended criteria (HQ > 1) in the rainy season for three target groups. At the same time, the carcinogenic risk (1 × 10−3) exceeded the acceptability criterion in the rainy season, which suggests that the As mainly represents a threat to the health of adults, children, and infants.

Biomarkers of effect as determined in human biomonitoring studies on hexavalent chromium and cadmium in the period 2008-2020

A number of human biomonitoring (HBM) studies have presented data on exposure to hexavalent chromium [Cr(VI)] and cadmium (Cd), but comparatively few include results on effect biomarkers. The latter are needed to identify associations between exposure and adverse outcomes (AOs) in order to assess public health implications. To support improved derivation of EU regulation and policy making, it is of great importance to identify the most reliable effect biomarkers for these heavy metals that can be used in HBM studies. In the framework of the Human Biomonitoring for Europe (HBM4EU) initiative, our study aim was to identify effect biomarkers linking Cr(VI) and Cd exposure to selected AOs including cancer, immunotoxicity, oxidative stress, and omics/epigenetics. A comprehensive PubMed search identified recent HBM studies, in which effect biomarkers were examined. Validity and applicability of the markers in HBM studies are discussed. The most frequently analysed effect biomarkers regarding Cr(VI) exposure and its association with cancer were those indicating oxidative stress (e.g., 8-hydroxy-2'-deoxyguanosine (8-OHdG), malondialdehyde (MDA), glutathione (GSH)) and DNA or chromosomal damage (comet and micronucleus assays). With respect to Cd and to some extent Cr, β-2-microglobulin (B2-MG) and N-acetyl-β-D-glucosaminidase (NAG) are well-established, sensitive, and the most common effect biomarkers to relate Cd or Cr exposure to renal tubular dysfunction. Neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule (KIM)-1 could serve as sensitive biomarkers of acute kidney injury in response to both metals, but need further investigation in HBM studies. Omics-based biomarkers, i.e., changes in the (epi-)genome, transcriptome, proteome, and metabolome associated with Cr and/or Cd exposure, are promising effect biomarkers, but more HBM data are needed to confirm their significance. The combination of established effect markers and omics biomarkers may represent the strongest approach, especially if based on knowledge of mechanistic principles. To this aim, also mechanistic data were collected to provide guidance on the use of more sensitive and specific effect biomarkers. This also led to the identification of knowledge gaps relevant to the direction of future research.

Development of a sensitive direct injection LC-MS/MS method for the detection of glyphosate and aminomethylphosphonic acid (AMPA) in hard waters

Glyphosate is currently the most widely used herbicide in the world; however, the zwitterionic and highly polar properties of glyphosate make current pesticide analysis methods unsuitable for its trace analysis in natural waters. Additionally, current glyphosate analysis methods do not account for waters of varying hardness, which is vital as glyphosate can complex with cationic species such as Ca2+ and Mg2+ in the environment. We detail here a robust LC-MS/MS method for the quantitation of glyphosate and its primary transformation product aminomethylphosphonic acid (AMPA) in environmental waters of varying water hardness. Chromatographic separation was achieved with a reversed-phase and weak anion-exchange mixed-mode column. We found that the addition of EDTA into hard water samples increases the response of both glyphosate and AMPA in the mass spectrometer. Limits of detection of 0.23 and 0.30 μg L-1 for glyphosate and AMPA in EDTA-amended hard water were achieved, respectively. We have demonstrated that the accuracy of the method was consistent over a wide range of water hardness levels up to a maximum of ~340 mg mL-1 CaCO3 hardness. We validated the method using matrix fortification of uncontaminated environmental samples from US river water. We then demonstrated that the method was successful at quantifying glyphosate and AMPA across surface and drinking water samples of varying water hardness from North Carolina and Sri Lanka. Measured concentrations of glyphosate and AMPA ranged from 1.6 to 13 μg L-1 and 0.50 to 2.5 μg L-1, respectively. This study represents a significant increase in sensitivity for LC-MS/MS analysis of glyphosate in hard water systems. Graphical abstract.

Lead (Pb) exposure and heart failure risk

Lead (Pb) is a heavy metal with widespread industrial use, but it is also a widespread environmental contaminant with serious toxicological consequences to many species. Pb exposure adversely impacts the cardiovascular system in humans, leading to cardiac dysfunction, but its effects on heart failure risk remain poorly elucidated. To better understand the pathophysiological effects of Pb, we review potential mechanisms by which Pb exposure leads to cardiac dysfunction. Adverse effects of Pb exposure on cardiac function include heart failure risk, pressure overload, arrhythmia, myocardial ischemia, and cardiotoxicity. The data reviewed clearly establish that Pb exposure can play an important role in the occurrence and development of heart failure. Future epidemiological and mechanistic studies should be developed to better understand the involvement of Pb exposure in heart failure.

Flacourtia indica fruit extract modulated antioxidant gene expression, prevented oxidative stress and ameliorated kidney dysfunction in isoprenaline administered rats

This study evaluated the effect of Flacourtia indica fruit extract against isoprenaline (ISO) induced renal damage in rats. This investigation showed that ISO administration in rats increased the level oxidative stress biomarkers such as malondialdehyde (MDA), nitric oxide (NO), advanced protein oxidation product (APOP) in kidneys followed by a decrease in antioxidant enzymes functions. Flacourtia indica fruit extract, which is rich in strong antioxidants, also reduced the MDA, NO and APOP level in kidney of ISO administered rats. Inflammation and necrosis was also visible in kidney section of ISO administered rats which was significantly prevented by atenolol and Flacourtia indica fruit extract. Moreover, atenolol and Flacourtia indica fruit extract also modulated the genes expressions related to inflammation and oxidative stress in kidneys. The beneficial effects could be attributed to the presence of a number of phenolic antioxidants. This study suggests that Flacourtia indica fruit extract may prevent kidney dysfunction in ISO administered rats, probably by preventing oxidative stress and inflammation.

Associations among Heavy Metals and Proteinuria and Chronic Kidney Disease

Background: The prevalence of chronic kidney disease (CKD) is increasing annually in Taiwan. In addition to traditional risk factors, heavy metals contribute to the development of CKD. The aim of this study was to investigate associations among heavy metals and proteinuria and CKD in the general population in Southern Taiwan. We also explored the interaction and synergetic effects among heavy metals on proteinuria. Methods: We conducted a health survey in the general population living in Southern Taiwan between June 2016 and September 2018. Seven heavy metals were measured: blood lead (Pb) and urine nickel (Ni), chromium (Cr), manganese (Mn), arsenic (As), copper (Cu), and cadmium (Cd). Proteinuria was measured using reagent strips. CKD was defined as an estimated glomerular filtration rate (eGFR) of <60 mL/min/1.73 m². Results: The mean age of the 2447 participants was 55.1 ± 13.2 years and included 977 males and 1470 females. Participants with high blood Pb and high urine Ni, Mn, Cu, and Cd were significantly associated with proteinuria. Interactions between blood Pb and urine Cr, and between urine Cd and Cu, had significant effects on proteinuria. The participants with high blood Pb and high urine Cu were significantly associated with an eGFR of <60 mL/min/1.73 m². Conclusion: High blood Pb and high urine Cu may be associated with proteinuria and an eGFR of <60 mL/min/1.73 m². High urine Ni, Mn, and Cd were significantly associated with proteinuria. Co-exposure to Cd and Cu, and Pb and Cr, may have synergistic effects on proteinuria.

Renal tubular injury induced by glyphosate combined with hard water: the role of cytosolic phospholipase A2

Background

The combined effects of glyphosate and hard water on chronic kidney disease of unknown etiology (CDKu) have attracted much interest, but the mechanisms remain unknown. Cytoplasmic phospholipase A₂ (cPLA₂) plays a key role in the acute and chronic inflammatory reactions. This study explored the effect of glyphosate combined with hard water on renal tubules and the possible targets and mechanisms involved.

Methods

In vivo experiments were conducted to investigate the synergistic effects and potential mechanisms of glyphosate and hard water on renal tubular injury in mice.

Results

Administration of glyphosate in mice resulted in elevated levels of β2-microglobulin (β₂-MG), albumin (ALB), and serum creatinine (SCr) compared to control mice. This increase was more pronounce when glyphosate was combined with hard water. In the glyphosate-treated mice, small areas of the kidney revealed fibroblast proliferation and vacuolar degeneration, particularly at the higher dose of 400 mg/kg glyphosate. However, the combination of glyphosate and hard water induced an even greater degree of pathological changes in the kidney. Immunofluorescence and western blot analyses showed that glyphosate and hard water had a coordinated effect on calcium ions (Ca²⁺)-activated phospholipase A₂ and the activation may play a key role in inflammation and renal tubular injury. Exposure to glyphosate alone or glyphosate plus hard water increased the levels of oxidative stress markers and inflammatory biomarkers, namely, thromboxane A₂ (TX-A₂), leukotriene B₄ (LTB₄), prostaglandin E₂ (PGE₂), nitric oxide synthase (NOS), and nitric oxide (NO). Parameters of oxidative stress, including the levels of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were decreased. Further analysis showed that the levels of these biomarkers were significantly different between the mice treated with glyphosate plus hard water and the mice treated with glyphosate alone.

Conclusions

These findings suggested that hard water combined with glyphosate can induce renal tubular injury in mice, and this may involve mitogen-activated protein kinases (MAPK)/cytosolic phospholipase A₂ (cPLA₂)/arachidonic acid (AA) and its downstream factors.

Kidney developmental effects of metal-herbicide mixtures: Implications for chronic kidney disease of unknown etiology

Chronic kidney disease of unknown etiology (CKDu) is an emerging global concern affecting several agricultural communities in the Americas and South Asia. Environmental contaminants such as heavy metals (e.g., Cd, As, Pb, and V) and organic pesticides (e.g., glyphosate) in the drinking water have been hypothesized to play a role in childhood onset and progression of this disease. However, a comprehensive analysis of chemical contaminants in the drinking water and effects of these compounds and their mixtures on kidney development and function remains unknown. Here, we conducted targeted and non-targeted chemical analyses of sediment and drinking water in CKDu affected regions in Sri Lanka, one of the most affected countries. Using zebrafish Danio rerio, a toxicology and kidney disease model, we then examined kidney developmental effects of exposure to (i) environmentally derived samples from CKDu endemic and non-endemic regions and (ii) Cd, As, V, Pb, and glyphosate as individual compounds and in mixtures. We found that drinking water is contaminated with various organic chemicals including nephrotoxic compounds as well as heavy metals, but at levels considered safe for drinking. Histological studies and gene expression analyses examining markers of kidney development (pax2a) and kidney injury (kim1) showed novel metal and glyphosate-metal mixture specific effects on kidney development. Mitochondrial dysfunction is directly linked to kidney failure, and examination of mixture specific mitochondrial toxicity showed altered mitochondrial function following treatment with environmental samples from endemic regions. Collectively, we show that metals in drinking water, even at safe levels, can impede kidney development at an early age, potentiating increased susceptibility to other agrochemicals such as glyphosate. Drinking water contaminant effects on mitochondria can further contribute to progression of kidney dysfunction and our mitochondrial assay may help identify regions at risk of CKDu.

The water chemistry and microbiome of household wells in Medawachchiya, Sri Lanka, an area with high prevalence of chronic kidney disease of unknown origin (CKDu)

Chronic kidney disease (CKD) of unknown etiology (CKDu) mostly affects agricultural communities in Central America, South Asia, Africa, but likely also in North America and Australia. One such area with increased CKDu prevalence is the Medawachchiya District Secretariat Division of the Anuradhapura District in the North Central Province of Sri Lanka. Recent research has focused on the presence of various microbial pathogens in drinking water as potential causal or contributing factors to CKDu, yet no study to date has performed a more comprehensive microbial and water chemistry assessment of household wells used for domestic water supply in areas of high CKDu prevalence. In this study, we describe the chemical composition and total microbial content in 30 domestic household wells in the Medawachchiya District Secretariat Division. While the chemical composition in the tested wells mostly lies within standard drinking water limits, except for high levels of fluoride (F), magnesium (Mg), sodium (Na), chloride (Cl) and calcium (Ca) in some samples, we find a frequent presence of cyanotoxin-producing Microcystis, confirming earlier studies in Sri Lanka. Since the total microbial content of drinking water also directly influences the composition of the human gut microbiome, it can be considered an important determinant of health. Several bacterial phyla were previously reported in the gut microbiome of patients with CKD. Using these bacteria phyla to define operational taxonomic units, we found that these bacteria also occur in the microbiome of the sampled well water. Based on available environmental data, our study demonstrates associations between the abundances of these bacteria with geographical distribution, well water temperature and likely fertilizer use in the local surface water catchment area of the individual household wells. Our results reinforce the recommendation that household wells with stagnant or infrequently used water should be purged prior to use for drinking water, bathing and irrigation. The latter is suggested because of the reported potential accumulation of bacterial toxins by agricultural crops. The observation that bacteria previously found in chronic kidney disease patients are also present in household wells requires a more detailed systematic study of both the human gut and drinking water microbiomes in CKDu patients, in relation to disease prevalence and progression.

Chronic kidney disease of unknown etiology (CKDu): Using a system dynamics model to conceptualize the multiple environmental causative pathways of the epidemic

A chronic kidney disease of unknown etiology is devastating agricultural communities of Sri Lanka, Central America, areas of India, and Egypt. Researchers are yet to agree on its etio-pathogenesis despite many cross-sectional, case-control and cohort studies done in these countries. These approaches are broadly based on a reductionist approach. We propose a complementary paradigm based on complexity science to deepen our understanding of the disease. Complexity science views a population as system that has several dynamically interacting and inter-dependent sub-systems and is 'open' to the 'outer' environment. Health outcomes or epidemics are viewed as 'emergent' properties of the population. Using available literature from Sri Lanka, the paper presents a system dynamics model incorporating exposures from pesticides and heavy metals, drinking hard water with high levels of fluoride, poverty, low birth weight, micronutrient deficiencies and heat stress. This approach can be used to model the epidemic, understand the impacts of different factors, predict potential populations at risk, and formulate multi-pronged prevention strategies that target leverage points of the system.