Burnt sugarcane harvesting is associated with acute renal dysfunction

Derangement in Nicotinamide Adenine Dinucleotide Metabolism is Observed During Acute Kidney Injury Among Male Agricultural Workers at Risk for Mesoamerican Nephropathy

Introduction

Mesoamerican nephropathy (MeN) is a chronic kidney disease (CKD) which may be caused by recurrent acute kidney injury (AKI). We investigated urinary quinolinate-to-tryptophan ratio (Q/T), a validated marker of nicotinamide adenine dinucleotide (NAD+) biosynthesis that is elevated during ischemic and inflammatory AKI, in a sugarcane worker population in Nicaragua with high rates of MeN.

Methods

Among 693 male sugarcane workers studied, we identified 45 who developed AKI during the harvest season. We matched them 1:1 based on age and job category with 2 comparison groups: (i) "no kidney injury," active sugarcane workers with serum creatinine (sCr) <1.1 mg/dl; and (ii) "CKD," individuals no longer working in sugarcane due to their CKD, who had additional 1:1 matching for sCr. We measured urine metabolites using liquid chromatography coupled tandem mass spectrometry (LC-MS/MS) and compared Q/T and other metabolic features between the AKI and comparison groups.

Results

Urine Q/T was significantly higher in workers with AKI than in those with no kidney injury (median interquartile Range [IQR]: 0.104 [0.074-0.167] vs. 0.060 [0.045-0.091], P < 0.0001) and marginally higher than in workers with CKD (0.086 [0.063-0.142], P = 0.059). Urine levels of the NAD+ precursor nicotinamide were lower in the AKI group than in comparison groups.

Conclusion

Workers at risk for MeN who develop AKI demonstrate features of impaired NAD+ biosynthesis, thereby providing new insights into the metabolic mechanisms of injury in this population. Therapeutic use of oral nicotinamide, which may ameliorate NAD+ biosynthetic derangement and fortify against kidney injury, should be investigated to prevent AKI in this setting.

Ten tips on how to care for your CKD patients in episodes of extreme heat

Climate change is responsible for ≈75% of extreme heat events throughout the world. Heat events are associated with an increased risk for acute kidney injury, which contributes to the development of chronic kidney disease (CKD) and cardiovascular events. Patients with CKD are especially vulnerable to heat stress for a variety of reasons. A disproportionate percentage of patients with CKD live in poverty; experience homelessness, mental illness or disabilities; work outside or are elderly, all demographics that overlap with populations most susceptible to episodes of extreme heat. Therefore, it is reasonable to conclude that exposure to episodes of extreme heat can lead to the progression of CKD and increases morbidity and mortality. Given these concerns, clinicians must be prepared to promptly recognize complications of heat in CKD patients and to help patients appropriately acclimate. We propose the following tips for clinicians to effectively care for their CKD patients during extreme heat days.

Health burden of sugarcane burning on agricultural workers and nearby communities

Sugarcane is the most widely cultivated crop in the world, with equatorial developing nations performing most of this agriculture. Burning sugarcane is a common practice to facilitate harvest, producing extremely high volumes of respirable particulate matter in the process. These emissions are known to have deleterious effects on agricultural workers and nearby communities, but the extent of this exposure and potential toxicity remain poorly characterized. As the epidemicof chronic kidney disease of an unknown etiology (CKDu) and its associated mortality continue to increase along with respiratory distress, there is an urgent need to investigate the causes, determine viable interventions to mitigate disease andimprove outcomes for groups experiencing disproportionate impact. The goal of this review is to establish the state of available literature, summarize what is known in terms of human health risk, and provide recommendations for what areas should be prioritized in research.

Occupational risks associated with chronic kidney disease of non-traditional origin (CKDnt) in Brazil: it is time to dig deeper into a neglected problem

In the past decades, an epidemic of chronic kidney disease (CKD) has been associated with environmental and occupational factors (heat stress from high workloads in hot temperatures and exposure to chemicals, such as pesticides and metals), which has been termed CKD of non-traditional origin (CKDnt). This descriptive review aims to present recent evidence about heat stress, pesticides, and metals as possible causes of CKDnt and provide an overview of the related Brazilian regulation, enforcement, and health surveillance strategies. Brazilian workers are commonly exposed to extreme heat conditions and other CKDnt risk factors, including increasing exposure to pesticides and metals. Furthermore, there is a lack of adequate regulation (and enforcement), public policies, and strategies to protect the kidney health of workers, considering the main risk factors. CKDnt is likely to be a significant cause of CKD in Brazil, since CKD's etiology is unknown in many patients and several conditions for its development are present in the country. Further epidemiological studies may be conducted to explore causal associations and estimate the impact of heat, pesticides, and metals on CKDnt in Brazil. Moreover, public policies should prioritize reducing workers´ exposure and promoting their health and safety.

Chronic Interstitial Nephritis in Agricultural Communities: Observational and Mechanistic Evidence Supporting the Role of Nephrotoxic Agrochemicals

Chronic interstitial nephritis in agricultural communities (CINAC) is an epidemic of kidney disease affecting specific tropical and subtropical regions worldwide and is characterized by progressive CKD in the absence of traditional risk factors, such as hypertension and diabetes. CINAC prevalence is higher among young, male agricultural workers, but it also affects women, children, and nonagricultural workers in affected areas. Biopsies from patients with CINAC across regions commonly demonstrate tubular injury with lysosomal aggregates, tubulointerstitial inflammation, and fibrosis and variable glomerular changes. Each endemic area holds environmental risk factors and patient/genetic milieus, resulting in uncertainty about the cause(s) of the disease. Currently, there is no specific treatment available for CINAC. We highlight survey findings of Houston-based migrant workers with CINAC and draw similarities between kidney injury phenotype of patients with CINAC and mice treated chronically with paraquat, an herbicide used worldwide. We propose potential pathways and mechanisms for kidney injury in patients with CINAC, which may offer clues for potential therapies.

Intranasal Administration of Sugarcane Ash Causes Chronic Kidney Disease in Rats

Background. Silica nanoparticles found in sugarcane ash have been postulated to be a toxicant contributing to chronic kidney disease of unknown etiology (CKDu). However, while the administration of manufactured silica nanoparticles is known to cause chronic tubulointerstitial disease in rats, the effect of administering sugarcane ash on kidney pathology remains unknown. Here we investigate whether sugarcane ash can induce CKD in rats. Methods. Sugarcane ash was administered for 13 weeks into the nares of rats (5 mg/day for 5d/week), and blood, urine and kidney tissues were collected at 13 weeks (at the end of ash administration) and in a separate group of rats at 24 weeks (11 weeks after stopping ash administration). Kidney histology was evaluated, and inflammation and fibrosis (collagen deposition) measured. Results. Sugarcane ash exposure led to the accumulation of silica in the kidneys, lungs, liver and spleen of rats. Mild proteinuria developed although renal function was largely maintained. However, biopsies showed focal glomeruli with segmental glomerulosclerosis, and tubulointerstitial inflammation and fibrosis that tended to worsen even after the ash administration had been stopped. Staining for the lysosomal marker, LAMP-1, showed decreased staining in ash administered rats consistent with lysosomal activation. Conclusion. Sugarcane ash containing silica nanoparticles can cause CKD in rats.

Chronic Tubulointerstitial Nephropathy of Agricultural Communities

Chronic interstitial nephritis in agricultural communities is an emerging public health concern affecting numerous agricultural communities in tropical countries, including regions in India, with a significant impact on the health and well-being of affected individuals. The affected individuals suffer from various psychosocial, nutritional, and metabolic challenges due to organ failure, which affects their quality of life. The etiology remains poorly understood, and various risk factors, which include various environmental and occupational hazards, have been implicated in its development. The recent discovery of lysosomal proximal tubulopathy has reignited interest in its pathogenesis. Along with the representative feature of chronic interstitial nephritis, changes suggestive of tubular injury have also been reported. It is suggested to use the term “chronic tubulointerstitial nephropathy of agricultural community” instead of chronic interstitial nephritis of the agricultural communities. Chronic tubulointerstitial nephropathy in agricultural communities is a slowly progressive disease that initially does not cause any symptoms in patients and most patients have a delayed onset of symptoms. Several diagnostic criteria have been introduced over the past years and one introduced by the Ministry of Health of Sri Lanka is widely used. The management of this chronic illness is no different from other causes of chronic interstitial nephritis and our focus should be on implementing various preventive strategies to reduce its incidence in agricultural communities and protect the health and well-being of agricultural workers. By disseminating knowledge about chronic tubulointerstitial nephropathy in agricultural communities, we can contribute to the development of evidence-based interventions to reduce the burden of the disease on affected communities. Moreover, we would like to sensitize physicians to this entity to increase awareness and identify potential endemic areas in various agricultural communities.

End-stage renal disease incidence in a cohort of US firefighters from San Francisco, Chicago, and Philadelphia

BACKGROUND

Firefighters perform strenuous work in hot environments, which may increase their risk of chronic kidney disease. The purpose of this study was to evaluate the risk of end-stage renal disease (ESRD) and types of ESRD among a cohort of US firefighters compared to the US general population, and to examine exposure-response relationships.

METHODS

ESRD from 1977 through 2014 was identified through linkage with Medicare data. ESRD incidence in the cohort compared to the US population was evaluated using life table analyses. Associations of all ESRD, systemic ESRD, hypertensive ESRD, and diabetic ESRD with exposure surrogates (exposed days, fire runs, and fire hours) were examined in Cox proportional hazards models adjusted for attained age (the time scale), race, birth date, fire department, and employment duration.

RESULTS

The incidence of all ESRD was less than expected (standardized incidence ratio (SIR) = 0.79; 95% confidence interval = 0.69-0.89, observed = 247). SIRs for ESRD types were not significantly increased. Positive associations of all ESRD, systemic ESRD, and hypertensive ESRD with exposed days were observed: however, 95% confidence intervals included one.

CONCLUSIONS

We found little evidence of increased risk of ESRD among this cohort of firefighters. Limitations included the inability to evaluate exposure-response relationships for some ESRD types due to small observed numbers, the limitations of the surrogates of exposure, and the lack of information on more sensitive outcome measures for potential kidney effects.

Kidney Function in Factory Workers Exposed to Heat Stress: A 2-Year Follow-up Study

OBJECTIVES

The aims of the study are to re-evaluate kidney function in workers exposed and not exposed to heat stress after 2 years and to compare kidney function cross-shift using creatinine and cystatin C.

METHODS

Participants were workers from a metallurgical industry. The clinical and biochemical markers of hydration and kidney function were evaluated before and after a single shift in work.

RESULTS

We included 14 workers (6 in the heat group and 8 in the control group). The serum creatinine levels did not change during the follow-up period. Cross-shift, creatinine-based eGFR (estimated glomerular filtration rate) decreased, and cystatin C-based eGFR was maintained in the heat and control groups.

CONCLUSIONS

Workers exposed to heat stress maintained their kidney function after a 2-year follow-up. Cystatin C is a better kidney function marker than creatinine for cross-shift assessments in this setting.

The impact of heat on kidney health: A PRISMA-compliant bibliometric analysis

BACKGROUND

Exposure to excessive heat can impact kidney health. Climate change is projected to aggravate this impact. An analysis of articles published between 1958 and 2021 was conducted to explore the progress of the research on this issue.

METHODS

This study included a bibliometric analysis wherein Web of Science was used to generate a list of all published articles related to the impact of heat on kidney health. Basic information about the articles, such as titles, authors' names, keywords, and citations, were recorded and analyzed.

RESULTS

A total of 226 published articles related to the impact of heat on kidney health were identified as of November 20, 2021. Most of these articles (93%) were published within the last decade. The United States was the most prominent country in terms of research productivity and collaboration. Researchers from the United States were well represented among the top 20 contributors of published articles on the study issue. The productivity of the top 20 authors varied between 6 and 32 articles each. A total of 25 common words used by the authors were identified. The most frequently used keywords were chronic kidney disease, heat stress, acute kidney injury, Mesoamerican nephropathy, and climate change. Keyword analysis revealed 3 distinct major research clusters in the existing scientific research on the impact of heat on kidney health: chronic kidney disease of unknown etiology, heat stress and renal physiology, and the effect of climate change on kidney health.

CONCLUSIONS

Research on heat-related kidney injury has witnessed rapid development in recent decades, motivated by the emergence of chronic kidney disease of unknown etiology and climate change. Developing countries in hot regions must increase their productivity in this research area through international collaboration and partnerships.

Kidney Function in Rice Workers Exposed to Heat and Dehydration in Costa Rica

The aim of this study was to evaluate heat exposure, dehydration, and kidney function in rice workers over the course of three months, in Guanacaste, Costa Rica. We collected biological and questionnaire data across a three-month-period in male field (n = 27) and other (n = 45) workers from a rice company where chronic kidney disease of unknown origin (CKDu) is endemic. We used stepwise forward regression to determine variables associated with estimated glomerular filtration rate eGFR at enrollment and/or change in eGFR, and Poisson regression to assess associations with incident kidney injury (IKI) over the course of three months. Participants were 20−62 years old (median = 40 in both groups). Dehydration was common (≥37%) in both groups, particularly among other workers at enrollment, but field workers were more exposed to heat and had higher workloads. Low eGFR (<60 mL/min/1.73 m2) was more prevalent in field workers at enrollment (19% vs. 4%) and follow-up (26% vs. 7%). Field workers experienced incident kidney injury (IKI) more frequently than other workers: 26% versus 2%, respectively. Age (β = −0.71, 95%CI: −1.1, −0.4), current position as a field worker (β = −2.75, 95%CI: −6.49, 0.99) and past work in construction (β = 3.8, 95%CI: −0.1, 7.6) were included in the multivariate regression model to explain eGFR at enrollment. The multivariate regression model for decreased in eGFR over three month included current field worker (β = −3.9, 95%CI: −8.2, 0.4), current smoking (β= −6.2, 95%CI: −13.7−1.3), dehydration (USG ≥ 1.025) at both visits (β= −3.19, 95%CI: −7.6, 1.2) and pain medication at follow-up (β= −3.2, 95%CI: −8.2, 1.95). Current fieldwork [IR (incidence rate) = 2.2, 95%CI 1.1, 5.8) and being diabetic (IR = 1.8, 95%CI 0.9, 3.6) were associated with IKI. Low eGFR was common in field workers from a rice company in Guanacaste, and being a field worker was a risk factor for IKI, consistent with the hypothesis that occupational heat exposure is a critical risk factor for CKDu in Mesoamerica.

Prevalence and risk factors associated with chronic kidney disease in Moroccan rural communes: Fez-Meknes region

BACKGROUND AND AIMS

Chronic kidney disease is a worldwide public health issue. It can be a serious problem, especially in developing countries including Morocco. However, few studies have explored the factors influencing chronic kidney disease in this country. Hence, using the definitions proposed by Kidney Disease Improving Global Outcomes in 2012, we have conducted this study to establish the prevalence and risk factors of chronic kidney disease particularly in rural communities in the Fez-Meknes region.

METHODS

Weight, height, blood pressure, proteinuria, hematuria, plasma creatinine, estimated glomerular filtration rate (using the Modification of Diet in Renal Disease formula), and fasting glycemia were measured. Abnormal results were controlled within two weeks; estimated Glomerular filtration rate was retested at 3 months. Furthermore, to determine the factors associated with chronic kidney disease, multivariate logistic regression was used.

RESULTS

A total of 431 patients participated in the study; the prevalence of confirmed proteinuria, hematuria, and reduced estimated Glomerular filtration rate was 5.3%, 1.8%, and 3%, respectively. Overall, chronic kidney disease was found to be present in 6.5% of the population. Chronic kidney disease 1 and 2 accounted for 32.1% and 21.4% of the overall chronic kidney disease population, respectively, while chronic kidney disease 3 accounted for 46.4% (3A: 38.2%; 3B: 7.14%). Chronic kidney disease 4 and 5 were not present in the total chronic kidney disease population. Chronic kidney disease was strongly linked with advanced age (OR 2.65; 95%CI: 1.05-6.65), hypertension (OR 2.41; 95%CI: 1.03-5.63), agricultural occupation (OR 1.02; 95%CI: 1.00-1.04) and contact with Agrochemicals (OR 1.40; 95%CI: 0.81-2.71).

CONCLUSIONS

It is important to note that screening for kidney damage and being aware of the risks linked to it, is key for the early detection and management of chronic kidney disease; they are also crucial to provide in a database for the development of a national prevention policy.

Heat exposure and workers' health: a systematic review

OBJECTIVES

Several studies on the health effects of heat exposure on workers have been reported; however, only few studies have summarized the overall and systematic health effects of heat exposure on workers. This study aims to review the scientific reports on the health status of workers exposed to high temperatures in the workplace.

METHODS

We reviewed literature from databases such as PubMed and Google Scholar, using Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines to identify studies that address health effects of heat exposure among workers.

RESULTS

In total, 459 articles were identified, and finally, 47 articles were selected. Various health effects of heat exposure on workers have been reported, such as heat-related diseases, deaths, accidents or injuries, effects on the urinary system, reproductive system, and on the psychological system.

CONCLUSIONS

Our review suggests that many workers are vulnerable to heat exposure, and this has a health effect on workers.

Body Composition, Anemia, and Kidney Function among Guatemalan Sugarcane Workers

Rates of anemia among agricultural workers, who are also at risk for kidney injury and chronic kidney disease of unknown cause (CKDu), are unknown. We evaluated body composition through the sum of three skinfolds among 203 male sugarcane cutters and assessed the relationship of variables related to nutrition, anemia (hemoglobin < 13 g/dL), and elevated hemoglobin A1c (HbA1c ≥ 5.7%) with estimated glomerular filtration rate (eGFR) using linear regression. Eleven percent of workers were at the level of essential body fat (2-5%). Anemia was present among 13% of workers, 70% of which were normochromic normocytic, a type of anemia suggesting potential underlying chronic disease. Anemia was more common among those with lower BMI and fat free mass. The prevalence of elevated HbA1c was 21%. A moderate negative correlation was found between hemoglobin and HbA1c (Pearson's r = -0.32, p <0.01) which suggests that HbA1c values should be interpreted with caution in populations that have high rates of anemia. Twelve percent of workers had reduced kidney function with an eGFR < 90 mL/min/1.73 m². On average, the eGFR was 18 mL/min per 1.73 m² lower [(95% CI:-24, -12), p <0.01)] for those with anemia than those without, and 8 mL/min per 1.73 m² lower among those with elevated HbA1c [(95% CI: -13, -2), p < 0.01]. Results will inform future studies examining the role of anemia in the evaluation of CKDu and interventions to improve nutrition for workers in low-resource settings.

Mesoamerican nephropathy: A not so unknown chronic kidney disease

From 2000, Mesoamerican region has reached an important rate of chronic kidney disease of unknown etiology. Under the name of Meroamerican Nephropathy (MeN) several hypotheses (including dehydration, heat stress, environmental or toxic exposure or even infections) have tried to explain the etiology this new disease. MeN affects young men, agricultural workers exposed to high temperatures. MeN courses with unspecific symptoms as low-grade fever and dysuria and progressive kidney disease with impaired renal function and hydroelectrolyte disturbances. The diagnosis requires kidney biopsy showing tubule-interstitial nephritis (usually at chronic stage). Although MeN conditions a high morbi-mortality in endemic regions, there is a lack of specific treatment and only preventive measures have demonstrated some effect of prognosis (avoid heat stress, constant hydration). In this review we aim to summarize the available information of MeN, illustrating the information in a case report.

Using social security number to identify sub-populations vulnerable to the health impacts from extreme heat in Florida, U.S

BACKGROUND

Some socioeconomically vulnerable groups may experience disproportionately higher risk of extreme heat illness than other groups, but no study has utilized the presence/absence of a social security number (SSN) as a proxy for vulnerable sub-populations.

METHODS

This study focused on the warm season from 2008 to 2012 in Florida, U.S. With a total number of 8,256,171 individual level health outcomes, we devised separate case-crossover models for five heat-sensitive health outcomes (cardiovascular disease, dehydration, heat-related illness, renal disease, and respiratory disease), type of health care visit (emergency department (ED) and hospitalization), and patients reporting/not reporting an SSN. Each stratified model also considered potential effect modification by sex, age, or race/ethnicity.

RESULTS

Mean temperature raised the odds of five heat-sensitive health outcomes with the highest odds ratios (ORs) for heat-related illness. Sex significantly modified heat exposure effects for dehydration ED visits (Males: 1.145, 95 % CI: 1.137-1.153; Females: 1.110, 95 % CI: 1.103-1.117) and hospitalization (Males: 1.116, 95 % CI: 1.110-1.121; Females: 1.100, 95 % CI: 1.095-1.105). Patients not reporting an SSN between 25 and 44 years (1.264, 95 % CI: 1.192-1.340) exhibited significantly higher dehydration ED ORs than those reporting an SSN (1.146, 95 % CI: 1.136-1.157). We also observed significantly higher ORs for cardiovascular disease hospitalization from the no SSN group (SSN: 1.089, 95 % CI: 1.088-1.090; no SSN: 1.100, 95 % CI: 1.091-1.110).

CONCLUSIONS

This paper partially supports the idea that individuals without an SSN could experience higher risks of dehydration (for those 25-45 years), renal disease, and cardiovascular disease than those with an SSN.

Longitudinal assessment of kidney function in migrant farm workers

Chronic kidney disease of unknown etiology (CKDu) is an epidemic that affects young agricultural workers in several warm regions of the world. However, there is a lack of monitoring of kidney issues in regions with extremely warm environments such as the Northwest of Mexico, a semi-arid region with a growing agricultural industry, where migrant and seasonal farm workers (MSFWs) travel to work in the fields. The objective of this study was to longitudinally assess kidney functioning of MSFWs in relation to pesticide exposure, heat stress and dehydration in a large-scale farm in Mexico. We enrolled 101 MSFWs, of whom 50 were randomly selected to work in an organic certified area and 51 were randomly selected to work in a conventional area. We also enrolled 50 office workers within the same region as a reference group. We collected urine and blood samples from all workers in addition to demographic, behavioral, and occupational characteristics. The physiological strain index (PSI) was used to estimate workers' heat strain. Sampling was conducted at pre-harvest (March) and late in the harvest (July). Linear mixed models were built with the estimated glomerular filtration rate (eGFR) as the dependent variable. We found a significant decrease in kidney function in MSFWs compared to office workers. By the late harvest, one MSFW developed kidney disease, two MSFWs suffered a kidney injury, and 14 MSFWs were at risk of a kidney injury. We found that the eGFR in MSFWs decreased significantly from pre-harvest (125 ± 13.0 mL/min/1.73 m2) to late harvest (109 ± 13.6 mL/min/1.73 m2) (p < 0.001), while no significant change was observed in office workers. The eGFR was significantly lower in MSFWs who worked in the conventional field (101.2 ± 19.4 mL/min/1.73 m2) vs the organic field (110.9 ± 13.6 mL/min/1.73 m2) (p = 0.002). In our final model, we found that dehydration was associated with the decrease of eGFR. We also found an interaction between heat strain and job category, as a significant decline in eGFR by job category (conventional/organic MSFWs and office workers) was related to an increase in heat strain. This suggests that pesticide exposure needs to be considered in combination with heat stress and dehydration. This study provides valuable information on kidney function in MSFWs, and it shows the importance of early long-term monitoring in farm workers in other regions where CKDu has not been evaluated yet.

Electrolyte Beverage Intake to Promote Hydration and Maintain Kidney Function in Guatemalan Sugarcane Workers Laboring in Hot Conditions

OBJECTIVES

To evaluate impact of electrolyte supplementation on hydration status and health outcomes in Guatemalan agricultural workers performing heavy work under hot climatic conditions.

METHODS

A 3-week pragmatic trial was conducted with a group of 50 workers during the 2017 to 2018 sugarcane harvest. Workers received an electrolyte hydration intervention during 2 of the 3 weeks. Blood and urine samples were collected each week.

RESULTS

Increased electrolyte intake resulted in less muscle injury. Kidney function was maintained across the intervention period. Workers were adequately hydrated and average electrolyte levels remained in normal ranges. Mild indications of hyponatremia occurred at higher levels of fluid intake.

CONCLUSIONS

This trial demonstrates the feasibility of maintaining workers' electrolyte levels under extremely hot and humid conditions while mitigating muscle injury. Electrolyte supplementation should be added to standard workplace water, rest, and shade interventions to protect workers.

Mesoamerican nephropathy: A not so unknown chronic kidney disease

From 2000, Mesoamerican region has reached an important rate of chronic kidney disease of unknown etiology. Under the name of Meroamerican Nephropathy (MeN) several hypotheses (including dehydration, heat stress, environmental or toxic exposure or even infections) have tried to explain the etiology this new disease. MeN affects young men, agricultural workers exposed to high temperatures. MeN courses with unspecific symptoms as low-grade fever and dysuria and progressive kidney disease with impaired renal function and hydroelectrolyte disturbances. The diagnosis requires kidney biopsy showing tubule-interstitial nephritis (usually at chronic stage). Although MeN conditions a high morbi-mortality in endemic regions, there is a lack of specific treatment and only preventive measures have demonstrated some effect of prognosis (avoid heat stress, constant hydration). In this review we aim to summarize the available information of MeN, illustrating the information in a case report.

A Systematic Review of Renal Pathology in Chronic Kidney Disease of Uncertain Etiology

INTRODUCTION

Despite much research on chronic kidney disease of uncertain etiology (CKDu) in Sri Lanka and the Mesoamerican nephropathy, the etiology and pathogenesis of this disease remains elusive. The pathology has broadly been described as chronic tubulointerstitial nephritis and no specific signature lesions have been identified.

METHODS

A scoping review was conducted through MEDLINE and Google Scholar databases for peer-reviewed publications on biopsy studies related to CKDu - Sri Lanka and Mesoamerican nephropathy to develop a comparative and critical analysis of the renal pathology found in these patients.

RESULTS

Thirteen studies met the selection criteria. Interstitial fibrosis was the predominant lesion in all the studies. Tubulointerstitial and glomerular abnormalities showed a more variable distribution. No characteristic histopathological feature was reported other than a proximal tubular lysosomal inclusion body which was claimed to indicate a toxic etiology. Three main pathogenetic mechanisms were postulated: repeated acute insults leading to scarring, low-grade chronic insults leading to non-inflammatory fibrosis, and tubulointerstitial damage in combination with glomerular injury. The main limitations in the interpretation and comparative analysis of these studies were the heterogeneity in case selection and biopsy reporting.

CONCLUSIONS

Although no characteristic histopathological feature could be found in CKDu-Sri Lanka or Mesoamerican nephropathy, there are noticeable differences between these two groups in the frequency and severity of the glomerular and tubulointerstitial changes which warrant more explorative studies preferably on kidneys in early stages of the disease. Future strategies should ensure that more uniform selection criteria and reporting methods are used.

Dysuria, heat stress, and muscle injury among Nicaraguan sugarcane workers at risk for Mesoamerican nephropathy

Objectives:

Nicaraguan sugarcane workers, particularly cane cutters, have an elevated prevalence of chronic kidney disease of unknown origin, also referred to as Mesoamerican nephropathy (MeN). The pathogenesis of MeN may include recurrent heat stress, crystalluria, and muscle injury with subsequent kidney injury. Yet, studies examining the frequency of such events in long-term, longitudinal studies are limited.

Methods:

Using employment and medical data for male workers at a Nicaraguan sugarcane company, we classified months of active work as either work as a cane cutter or other sugarcane job and determined occurrence of dysuria, heat events and muscle events. Work months and events occurred January 1997 to June 2010. Associations between cane cutting and each outcome were analyzed using logistic regression based on generalized estimating equations for repeated events, controlling for age.

Results:

Among 242 workers with 7257 active work months, 19.5% of person-months were as a cane cutter. There were 160, 21, and 16 episodes of dysuria, heat events, and muscle events, respectively. Compared with work months in other jobs, cane cutting was associated with an elevated odds of dysuria [odds ratio 2.40 (95% confidence interval 1.56–3.68)]. The number of heat and muscle events by cane cutter and other job were limited.

Conclusions:

Working as a cane cutter compared with other jobs in the sugarcane industry was associated with increased dysuria, supporting the hypothesis that cane cutters are at increased risk of events suspected of inducing or presaging clinically evident kidney injury.

An ecological study of chronic kidney disease in five Mesoamerican countries: associations with crop and heat

BACKGROUND

Mesoamerica is severely affected by an epidemic of Chronic Kidney Disease of non-traditional origin (CKDnt), an epidemic with a marked variation within countries. We sought to describe the spatial distribution of CKDnt in Mesoamerica and examine area-level crop and climate risk factors.

METHODS

CKD mortality or hospital admissions data was available for five countries: Mexico, Guatemala, El Salvador, Nicaragua and Costa Rica and linked to demographic, crop and climate data. Maps were developed using Bayesian spatial regression models. Regression models were used to analyze the association between area-level CKD burden and heat and cultivation of four crops: sugarcane, banana, rice and coffee.

RESULTS

There are regions within each of the five countries with elevated CKD burden. Municipalities in hot areas and much sugarcane cultivation had higher CKD burden, both compared to equally hot municipalities with lower intensity of sugarcane cultivation and to less hot areas with equally intense sugarcane cultivation, but associations with other crops at different intensity and heat levels were not consistent across countries.

CONCLUSION

Mapping routinely collected, already available data could be a first step to identify areas with high CKD burden. The finding of higher CKD burden in hot regions with intense sugarcane cultivation which was repeated in all five countries agree with individual-level studies identifying heavy physical labor in heat as a key CKDnt risk factor. In contrast, no associations between CKD burden and other crops were observed.

Heat Stress and Kidney Function in Farmworkers in the US: A Scoping Review

Chronic kidney disease of unknown etiology (CKDu) has been well described in farmworkers in Latin America. Agricultural workers in the United States (US) are exposed to similar hot and humid working conditions, but CKDu in the US is under-described. This review aims to better understand the current literature describing the connection between heat stress and kidney function in farmworkers in the United States. Utilizing a scoping review methodology, we searched CINAHL, Embase, PubMed, and Web of Science databases to better understand the current state of the heat stress and kidney function research in farmworkers within the United States. In this review, 229 pieces of literature were screened. Ultimately, 4 articles were chosen to be included in the scoping review. Common themes within the articles were variations in study protocol lengths and type of heat stress measurement. Additionally, the majority of the work completed was quantitative to date, with only one study providing a critical social lens for analysis of CKDu in the United States. We found evidence that more work is needed within the US to understand the relationship between working in the heat and kidney function in agricultural and other workers who experience high heat conditions at work and are susceptible to the deleterious effects of working in said conditions.

Occupational Paraquat and Glyphosate Exposure May Decline Renal Functions among Rural Farming Communities in Sri Lanka

Extensive use of herbicides is common among rural agricultural workers in Sri Lanka. Recent studies have postulated their role in the development of chronic kidney disease of unknown etiology (CKDu). Paraquat and glyphosate are leading herbicides used by sugarcane farmers (SF), hence occupational exposure is inevitable. This study examined the expression of urinary paraquat, glyphosate and biomarkers among residential SF in CKDu emerging regions, Warunagama (WA) and Rahathangama (RH), in the Uva Province with non-endemic Matara (MA) in the Southern Province of Sri Lanka. Urinary glyphosate, Paraquat, kidney injury molecule -1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL) and β2-microglobulin (B2M) were determined using enzyme-linked immunosorbent assays (ELISA). Urinary creatinine, microalbumin, serum creatinine (SCr), serum cystatin C, estimated glomerular filtration rate (eGFR), and albumin creatinine ratio (ACR) were also assessed. Generally, herbicide residues and kidney injury biomarkers were higher in SF compared to the non-endemic MA. Creatinine-adjusted urinary glyphosate and paraquat levels were significantly higher in WA compared to MA. ACR in RH (median 14.9; IQR 5.4-393.1 mg/g) and WA (23.7; 11.5-64.6) was significantly higher than MA (4.3; 2.2-6.7). This study reports 39 individuals with impaired kidney function among SF in Sri Lanka for the first time. Urinary NGAL levels were significantly higher in both WA (median 2.14; IQR 1.28-6.15 ng/mg Cr) and RH (3.09; 1.15-9.09) compared to MA (1.28; 0.56-2.81). However, urinary KIM-1 levels in RH (3.2; 1.29-106.1 ng/g Cr) and WA (3.6; 1.94-115.1) were not significantly higher in MA (1.74; 0.76-116.9). Urinary NGAL (r = 0.493), eGFR (r = -0.147) and ACR (r = 0.171) significantly correlated with urinary glyphosate, but not with urinary paraquat levels. Urinary KIM-1 levels did not correlate with either urinary glyphosate or paraquat, while urinary B2M and serum cystatin C levels showed significant correlation with urinary glyphosate levels. The current study reports higher urinary herbicide levels among sugarcane farmers in WA and RH, and that is potentially linked to the subsequent decline in kidney function, as indicated by ACR, eGFR, and NGAL. We posit that these indicators may serve as markers to detect renal injury among herbicide-exposed SF in Rural Sri Lanka.

A Preliminary Evaluation of the Kidney Function of Sugarcane Cutters From Brazil

OBJECTIVE

To evaluate clinical parameters, markers of kidney function, and skeletal muscle damage in a group of sugarcane cutters during harvesting season.

METHODS

Seventeen volunteers were assessed for anthropometrics and cardiorespiratory fitness. Blood and urine samples were collected 48-hours after the last work session. Blood was analyzed for glucose, creatine kinase, cholesterol, and a complete hemogram. Urine and blood samples were also analyzed for markers related to kidney function.

RESULTS

Volunteers were young (26 ± 6 y), had low body fat (13 ± 5%), and good cardiorespiratory fitness (41 ± 6 mL/kg/min). Classical markers of kidney function (eGFR, creatinine, cystatin C) were within the normal range. However, ten volunteers presented elevated resting serum creatine kinase (221 ± 68 U/L).

CONCLUSION

Manual sugarcane harvesting is associated with sustained skeletal muscle damage which may increase the risk for kidney injury in Brazilian sugarcane cutters.

CKD and CKDu in northern Peru: a cross-sectional analysis under the DEGREE protocol

BACKGROUND

This study estimated the prevalence and risk factors for decreased estimated glomerular filtration rate (eGFR) in those without known hypertension, type 2 diabetes mellitus, or heavy proteinuria as a surrogate marker for chronic kidney disease of unknown cause (CKDu) among adults in the North of Peru.

METHODS

A cross-sectional study was conducted following the Disadvantaged Populations eGFR Epidemiology (DEGREE) Study protocol. Low eGFR was defined based on a single eGFR ≤60 mL/min/1.7m² estimated using the CKD-EPI equation. Environmental conditions related to CKDu (i.e., work in agriculture or sugarcane, water source, heat intolerance, and pesticide exposure) were evaluated, in addition to traditional risk factors for CKD (i.e., smoking, heavy drinking, physical activity, hypertension, type 2 diabetes mellitus, urolithiasis, among others).

RESULTS

A total of 1514 subjects were included in the study, mean age 45.1 (SD: 16.4), and 55.2% were females. Overall, only 26 cases (1.7%; 95%CI: 1.1-2.5%) had an eGFR < 60 mL/min/1.7m² compatible with CKD definition; when those with hypertension and type-2 diabetes or heavy proteinuria were excluded, according to the DEGREE protocol, the estimate fell to 0.9% (95%CI: 0.4-1.5%). Low physical activity levels (OR = 1.99; 95%CI: 1.18-3.34), hypertension (OR = 2.07; 1.26-3.41), and urolithiasis (OR = 1.97; 95%CI: 1.18-3.27) were factors associated with low eGFR.

CONCLUSIONS

A low population-based prevalence of low eGFR (as a surrogate for CKDu), both in rural and urban settings areas, in the Northern Peru, was found. Low physical activity levels, hypertension and urolithiasis were factors associated with low eGFR. Interventions to prevent CKD cases may be focused on well-known CV risk factors and urolithiasis.

A comparative review: Chronic Kidney Disease of unknown etiology (CKDu) research conducted in Latin America versus Asia

INTRODUCTION

The incidence of chronic kidney disease of unknown or uncertain etiology (CKDu) is recognized as a global non-communicable health crisis. The goal of this work is to compare the types of research studies in Latin America and Asia, two regions with increasing CKDu incidence.

METHODS

A comparative literature review was conducted to evaluate the CKDu research design for peer-reviewed articles published from 2015 to 2019. Full texts were reviewed to identify study location, study type, study design, risk factors evaluated, and if applicable, sample type and number.

RESULTS

In Asia and Latin America, 82 and 65 articles were identified in total, respectively, with 55 field studies in Asia versus 34 in Latin America. In Asia, research was focused on drinking water (34), heavy metals (20), and agrochemical product usage (19) as potential risk factors. In Latin America, research focused mostly on heat stress/dehydration (36) and agrochemical product usage (18) as potential CKDu risk factors. Biological samples were collected more frequently than environmental samples, especially in Latin America.

DISCUSSION

Research to pinpoint the risk factors associated with CKDu to date is not standardized and typically limited in geographical scope. The emphasis of CKDu research varies by geographic region, with a greater priority placed on water quality and chemical exposure in Asia, versus dehydration and heat stress in Latin America. Using a harmonized approach to CKDu research would yield improved understanding of the risk factors associated with CKDu and how they compare across affected regions.

Condições de trabalho no cultivo da cana-de-açúcar no Brasil e repercussões sobre a saúde dos canavieiros

Resumo Objetivo: analisar as condições de trabalho na cultura de cana-de-açúcar no Brasil e as suas repercussões na saúde do trabalhador. Métodos: revisão de literatura realizada nas bases LILACS, PubMed/MEDLINE e SciELO. Foram incluídos estudos originais publicados em português, inglês e espanhol, de 1970 a 2018. Resultados: inicialmente foram identificados 622 estudos e, após a aplicação dos critérios de exclusão, 69 artigos foram selecionados para a revisão. A análise dos trabalhos evidenciou o sistemático descumprimento das normas trabalhistas, previdenciárias e de saúde. Os estudos constataram ausências de intervalos de descanso, jornadas excessivas de trabalho, deficiência na distribuição dos equipamentos de proteção individual (EPIs) e na oferta de treinamentos para o seu uso, precariedade da distribuição e orientação sobre uso de repositores hidroeletrolíticos, inadequadas condições dos alojamentos e da alimentação dos trabalhadores, pressões e conflitos existentes no ambiente de trabalho, vínculos de trabalho precários, baixos salários e pagamento por produção. Exaustão física e psíquica dos trabalhadores, afecções musculoesqueléticas e articulares, hipertermia e acidentes de trabalho são comuns. Conclusão: as condições de trabalho nas lavouras de cana-de-açúcar, aliadas às diferentes vulnerabilidades existentes nos territórios, levam ao adoecimento e à morte, demonstrando que frequentemente os interesses econômicos se sobrepõem aos cuidados com a saúde dos trabalhadores.

Kidney physiology and pathophysiology during heat stress and the modification by exercise, dehydration, heat acclimation and aging

The kidneys' integrative responses to heat stress aid thermoregulation, cardiovascular control, and water and electrolyte regulation. Recent evidence suggests the kidneys are at increased risk of pathological events during heat stress, namely acute kidney injury (AKI), and that this risk is compounded by dehydration and exercise. This heat stress related AKI is believed to contribute to the epidemic of chronic kidney disease (CKD) occurring in occupational settings. It is estimated that AKI and CKD affect upwards of 45 million individuals in the global workforce. Water and electrolyte disturbances and AKI, both of which are representative of kidney-related pathology, are the two leading causes of hospitalizations during heat waves in older adults. Structural and physiological alterations in aging kidneys likely contribute to this increased risk. With this background, this comprehensive narrative review will provide the first aggregation of research into the integrative physiological response of the kidneys to heat stress. While the focus of this review is on the human kidneys, we will utilize both human and animal data to describe these responses to passive and exercise heat stress, and how they are altered with heat acclimation. Additionally, we will discuss recent studies that indicate an increased risk of AKI due to exercise in the heat. Lastly, we will introduce the emerging public health crisis of older adults during extreme heat events and how the aging kidneys may be more susceptible to injury during heat stress.

Cross-shift change of acute kidney injury biomarkers in sugarcane farmers and cutters

Sugarcane farmers and cutters have been reported to be at high risk of acute kidney injury. This cross-sectional study aimed to assess acute kidney injury biomarkers, and cross-shift change among 150 sugarcane cutters and 98 sugarcane farmers in Thailand. Physical health examination, environmental measurements, and measured urinary neutrophil gelatinase-associated lipocalin (NGAL) were assessed. Cross-shift change of urine creatinine (uCr), albumin creatinine ratio (ACR), and NGAL between sugarcane farmers and cutters was compared. Factors influencing abnormal post-shift ACR and NGAL were analyzed by binary logistic regression adjusted with covariates. Sugarcane cutters were significantly more likely to take nonsteroidal anti-inflammatory drugs (NSAID) and herbs to relieve pain than sugarcane farmers. Males were more likely to be current smokers and drinkers although 62% of cutters and 56% of farmers were female. Sugarcane farmers and cutters had similar post-shift estimated glomerular filtration rate (eGFR) and ACR levels. Cross-shift measurements showed that both sugarcane cutters and sugarcane farmers had significantly higher post-shift geometric mean (GM) urinary NGAL, but that the cross-shift changes of NGAL were significantly higher for sugarcane cutters (182%) vs. sugarcane farmers (112%). Water intake less than recommendation of subjects was a significant predictor of a higher risk for an abnormal post-shift ACR after controlling for covariates, while being a sugarcane cutter was a predictor of a lower risk of an abnormal risk of a post-shift NGAL after controlling for covariates. Measurements of heat stress (WBGT plus workload) found that sugarcane cutters exceeded recommended exposures while sugarcane farmers were compliance to the TLV. These findings suggest that to protect sugarcane farmers and cutters, preventative measures are needed.

A Pilot Study to Assess Inhalation Exposures among Sugarcane Workers in Guatemala: Implications for Chronic Kidney Disease of Unknown Origin

Background: Sugarcane workers in Central America experience a heavy burden of chronic kidney disease of unknown origin. We conducted a pilot study among worker proxies in Guatemala to characterize exposures to particulate matter, silica, heavy metals, and glyphosate, as well as to examine potential nephrotoxic exposures. Methods: Air, soil, and ash samples were collected and analyzed using scanning electron microscopy, X-ray diffraction, inductively coupled plasma mass spectrometry, and an enzyme-linked immunosorbent assay. Results: The average mass concentration for particulate matter (PM)_2.5 and PM₁₀₀ exposures were 360 µg/m³ (range: 32 to 1500 µg/m³) and 555 µg/m³ (range: 229 to 1170 µg/m³), respectively. The elemental composition of particles was largely silicon. The amount of crystalline silica was below 5 μg, yet the percentage of total silica was ~17% by weight. Putatively, the silica was in the amorphous form. Concentrations of aluminum and calcium ranged from 2–7 μg/m³. Glyphosate was not detectable in analyzed air samples but was detectable at concentrations ranging from 81–165 ppb in soil samples. Conclusion: Sugarcane workers are exposed to high concentrations of particulate matter. Future studies should investigate the potential role of silica, heavy metals, and agrochemicals in the etiology of chronic kidney disease in this population.

Creatinine Fluctuations Forecast Cross-Harvest Kidney Function Decline Among Sugarcane Workers in Guatemala

Background

Chronic kidney disease of unknown origin (CKDu) is an epidemic that disproportionately affects young agriculture workers in hot regions. It has been hypothesized that repeated acute kidney injury (AKI) may play a role in the development of disease.

Methods

Latent class mixed models were used to identify groups of Guatemalan sugarcane harvesters based on their daily changes in creatinine over 6 consecutive days in 2018. Exponential smoothing state space models were used to forecast end-of-season creatinine between the identified groups. Percent change in estimated glomerular filtration rate (eGFR) across the harvest was compared between groups.

Results

Twenty-nine percent (n = 30) of the 103 workers experienced repeated severe fluctuations in creatinine across shift. The model with multiplicative error, multiplicative trend, and multiplicative seasonality was able to accurately forecast end-of-season creatinine in the severe group (mean percentage error [MPE]: −4.7%). eGFR of workers in the severe group on average decreased 20% across season compared to 11% decline for those in the moderate group (95% confidence interval for difference: −17% to 0%).

Conclusions

Daily fluctuations in creatinine can be used to forecast end-of-season creatinine in sugarcane harvesters. Workers who experience repeat severe daily fluctuations in creatinine, on average, experience a greater reduction in kidney function across the season.

Pathophysiological Mechanisms by which Heat Stress Potentially Induces Kidney Inflammation and Chronic Kidney Disease in Sugarcane Workers

BACKGROUND

Chronic kidney disease of non-traditional origin (CKDnt) is common among Mesoamerican sugarcane workers. Recurrent heat stress and dehydration is a leading hypothesis. Evidence indicate a key role of inflammation.

METHODS

Starting in sports and heat pathophysiology literature, we develop a theoretical framework of how strenuous work in heat could induce kidney inflammation. We describe the release of pro-inflammatory substances from a leaky gut and/or injured muscle, alone or in combination with tubular fructose and uric acid, aggravation by reduced renal blood flow and increased tubular metabolic demands. Then, we analyze longitudinal data from >800 sugarcane cutters followed across harvest and review the CKDnt literature to assess empirical support of the theoretical framework.

RESULTS

Inflammation (CRP elevation and fever) and hyperuricemia was tightly linked to kidney injury. Rehydrating with sugary liquids and NSAID intake increased the risk of kidney injury, whereas electrolyte solution consumption was protective. Hypokalemia and hypomagnesemia were associated with kidney injury.

DISCUSSION

Heat stress, muscle injury, reduced renal blood flow and fructose metabolism may induce kidney inflammation, the successful resolution of which may be impaired by daily repeating pro-inflammatory triggers. We outline further descriptive, experimental and intervention studies addressing the factors identified in this study.

Risk of Kidney Injury among Construction Workers Exposed to Heat Stress: A Longitudinal Study from Saudi Arabia

Saudi Arabia (SA) is one of the hottest countries in the world. This study was conducted to assess the impact of summer heat stress in Southeastern SA on short-term kidney injury (KI) among building construction workers and to identify relevant risk factors. Measurements of urinary albumin-creatinine ratio (ACR), height, weight, hydration, symptoms, daily work and behavioral factors were collected in June and September of 2016 from a cohort of construction workers (n = 65) in Al-Ahsa Province, SA. KI was defined as ACR ≥ 30 mg/g. Multivariate linear regression analysis was used to assess factors related to cross-summer changes in ACR. A significant increase in ACR occurred among most workers over the study period; incidence of KI was 18%. Risk factors associated with an increased ACR included dehydration, short sleep, and obesity. The findings suggest that exposure to summer heat may lead to the development of KI among construction workers in this region. Adequate hydration and promotion of healthy habits among workers may help reduce the risk of KI. A reduction in work hours may be the most effective intervention because this action can reduce heat exposure and improve sleep quality.

Dehydration-associated chronic kidney disease: a novel case of kidney failure in China

BACKGROUND

Mesoamerican nephropathy (MeN) is a pattern of chronic kidney disease (CKD) prevalent among Central American men who work in agriculture, and its underlying cause has not been elucidated. Currently, experts hypothesize that MeN is related to repeated episodes of occupational heat stress leading to water loss and hence it is also called dehydration-associated CKD.

CASE PRESENTATION

We report a case of a 40-year-old man, whose first admission to Peking Union Medical College Hospital was due to acute kidney injury (AKI). The clinical and pathological processes were consistent with acute tubular necrosis (ATN). However, after full recovery, CKD developed 1 year later. The second renal biopsy showed characteristics of ischemic renal disease but there was no evidence of vascular disease. It is worth noting that the patient had been taking part in long-distance running without drinking adequate water for years, which would have markedly decrease his renal blood flow. Thus, this patient may have developed chronic dehydration-associated kidney disease sharing the similar etiology of MeN.

CONCLUSIONS

We report here a case of dehydration-associated CKD in a Chinese patient which shared similar etiology to MeN. Even in non-agricultural areas, this etiology of CKD should be noted to obtain a relevant history and prompt diagnosis.

Other Potential CKD Hotspots in the World: The Cases of Mexico and the United States

Hotspots of chronic kidney disease of unknown etiology (CKDu) have been identified throughout the globe, of which the Mesoamerican nephropathy in Central America is the most conspicuous example. It affects mainly agricultural workers, heat exposure during extenuating shifts leading to sudden dehydration and subsequent acute kidney injury (AKI) episodes is the main hypothesis, with other factors such as environmental and social determinants playing an underlying role. Recent reports have suggested that Mexico and the United States may have newly identified CKDu hotspots. Studies from Tierra Blanca, a rural region in Mexico, have shown that the prevalence of probable CKD is high (25%) among the population, of which almost half of the identified cases had no known risk factor (such as diabetes or hypertension). Studies in Hispanic agricultural workers from California and Florida have shown that heat stress and dehydration is frequent and is correlated with AKI episodes after a work shift (33% of workers in one shift). Because recurrent AKI is an established risk factor for CKD, these studies strengthen the evidence that suggests an association between this occupational exposure and CKD. Whether the etiology responsible for the entities described is the same as in other CKDu hotspots in the world remains unknown. The development of preventative and intervention strategies is the most urgent priority to address this issue.

Genetic and Developmental Factors in Chronic Kidney Disease Hotspots

Chronic kidney disease increasingly is being recognized as an important global public health problem. Interindividual susceptibility to kidney disease is high and likely is dependent on risk modulation through genetics, fetal and early childhood development, environmental circumstances, and comorbidities. Traditionally, the chronic kidney disease burden has been ascribed largely to hypertension and diabetes. Increasingly, evidence is accumulating that nontraditional risk factors may predominate in some regions and populations, contributing to epidemics of kidney disease. Such nontraditional risk factors include environmental exposures, traditional medicines, fetal and maternal factors, infections, kidney stones, and acute kidney injury. Genetic factors may predispose patients to chronic kidney disease in some populations. Chronic kidney disease of unknown origin has its epicenters in Central America and South Asia. Such clustering of CKD may represent either genetic or environmentally driven kidney disease, or combinations of both. Developmental conditions impacting kidney development often are related to poverty and structural factors that persist throughout life. In this article, we explore the possibilities that genetic and developmental factors may be important contributors to the epidemics in these regions and suggest that optimization of factors impacting kidney development hold promise to reduce the risk of kidney disease in future generations.

Workload and cross-harvest kidney injury in a Nicaraguan sugarcane worker cohort

Objectives

To examine the association between workload and kidney injury in a fieldworker cohort with different levels of physically demanding work over a sugarcane harvest, and to assess whether the existing heat prevention efforts at a leading occupational safety and health programme are sufficient to mitigate kidney injury.

Methods

Biological and questionnaire data were collected before (n=545) and at the end (n=427) of harvest among field support staff (low workload), drip irrigation workers (moderate), seed cutters (high) and burned sugarcane cutters (very high). Dropouts were contacted (87%) and reported the reason for leaving work. Cross-harvest incident kidney injury (IKI) was defined as serum creatinine increase ≥0.30 mg/dL or ≥1.5 times the baseline value, or among dropouts reporting kidney injury leading to leaving work.

Results

Mean cross-harvest estimated glomerular filtration rate change was significantly associated with workload, increasing from 0 mL/min/1.73 m² in the low-moderate category to −5 mL/min/1.73 m² in the high and −9 mL/min/1.73 m² in the very high workload group. A similar pattern occurred with IKI, where low-moderate workload had 2% compared with 27% in the very high workload category. A healthy worker selection effect was detected, with 32% of dropouts reporting kidney injury. Fever and C reactive protein elevation were associated with kidney injury.

Conclusions

Workers considered to have the highest workload had more cross-harvest kidney damage than workers with less workload. Work practices preventing heat stress should be strengthened and their role in preventing kidney damage examined further. Future occupational studies on chronic kidney disease of unknown aetiology should account for a healthy worker effect by pursuing those lost to follow-up.

Occupational effect of sugarcane biomass burning on the conjunctival mucin profile of harvest workers and residents of an adjacent town - A Brazilian panel study

Pre-harvest burning of sugarcane fields produces large amounts of air pollutants which are known to cause health problems, including ocular surface abnormalities. In this study, we evaluated the effect of biomass burning on mucus quality and mucin gene expression (MUC1, MUC5AC, MUC16) in the conjunctiva of sugarcane workers (SWs) and residents of an adjacent town (RTs). Impression cytology samples of the inferior tarsal and bulbar conjunctiva of 78 SWs and 32 RTs were collected before (T1) and immediately after (T2) a 6-month harvest period. The neutral, acid and total mucus content of goblet cells was determined by PAS and AB staining. The levels of MUC5AC, MUC1 and MUC16 mRNA in the conjunctiva were measured by real-time PCR. Compared to RTs, SWs had higher levels of bulbar acid mucus and MUC16 mRNA and tarsal MUC5AC mRNA at T2 and lower levels of neutral mucus at T1 and T2. In the SW group, MUC1 mRNA levels were higher at T2 than at T1, but the levels of neutral and acid mucus were similar. In the RT group, acid mucus decreased and neutral mucus increased in the bulbar and tarsal conjunctiva at T2. In conclusion, our findings show that sugarcane harvesting is associated with abnormalities in mucus quality and content and changes in mucin mRNA levels on the ocular surface. This may help explain the ocular inflammatory signs and symptoms observed in subjects exposed to air pollutants and high temperatures from sugarcane biomass burning.

Daily ambient temperature is associated with biomarkers of kidney injury in older Americans

BACKGROUND

Increases in ambient temperature have recently been associated with increased emergency department visits and hospital admissions for acute renal failure. However, potential biological mechanisms through which short-term ambient temperature affects kidney function are not known.

METHODS

We used multiple regression models to evaluate the association between 1- and 3-day average, ambient temperature levels and two biomarkers of kidney injury (neutrophil gelatinase-associated lipocalin (NGAL) and adiponectin), among 3377 individuals over 57 years of age enrolled in the National Social Life, Health, and Aging Project. Ambient temperature was estimated on a 6-km grid covering the conterminous United States using ambient temperature measurements obtained from the National Climatic Data Center (NCDC). NGAL and adiponectin levels were measured from whole blood collected for each participant. All health effect models were adjusted for a number of demographics, socioeconomic, health behavior, medical history variables, with non-linear exposure-response relationships examined using natural cubic splines.

RESULTS

The relationship between 1- and 3-day average temperature and both NGAL and adiponectin levels was significant and non-linear, with largely null associations below 10 °C, and positive association for temperatures >10 °C. In fully adjusted, linear multiple regression models restricted to >10 °C, NGAL and adiponectin levels increased by 1.89% (95% CI: 0.77, 3.91) and 2.51% (95% CI: 1.34, 3.69), respectively, for a 1 °C increase in daily average temperature. Additionally, every 1 °C increase in temperature over 10 °C was associated with a 1.83% increased odds of having plasma NGAL levels consistent with acute kidney injury (>150 μg/L).

CONCLUSIONS

In a cohort of older men and women in the United States, our study is the first to observe that short-term ambient temperature exposures were significantly associated with biomarkers of kidney injury. These associations suggest that ambient temperature exposures could be an important risk factor for renal pathology.

Risk Factors for Declines in Kidney Function in Sugarcane Workers in Guatemala

Objectives:

To characterize kidney function of sugarcane workers in Guatemala over the 6-month harvest and identify risk factors associated with changes in kidney function.

Methods:

Demographic and biological data were collected for 330 sugarcane cutters at the beginning and end of the harvest. Multivariable regression analyses were used to assess factors related to kidney function.

Results:

A decline in kidney function across the harvest was observed in 36% of the participants. Risk factors associated with this decline included working at a particular plantation mill, local area workers compared with highland workers, and current smokers.

Conclusion:

Results showed both occupational and behavioral factors play significant roles in declines in kidney function. These results underline the need for a comprehensive approach to the epidemic as well as further investigation of risk factors to guide research and interventions.

Evaluation of heat stress and cumulative incidence of acute kidney injury in sugarcane workers in Guatemala

OBJECTIVE

Agricultural workers worldwide exposed to heat stress could be at the risk of kidney injury, which could lead to chronic kidney disease of an unknown origin (CKDu). Hydration has been promoted as a key measure to reduce kidney injury. In the presence of a hydration intervention, the incidence of acute kidney injury (AKI) was calculated in a sugarcane worker population in Guatemala and several risk factors were evaluated.

METHODS

We measured kidney function at the beginning and end of the work shift at three time points in 517 sugarcane workers. We defined AKI as an increase in serum creatinine of 26.5 µmol/L or 50% or more from the pre-shift value. Associations between AKI and risk factors were examined, including interactions with hydration status.

RESULTS

The prevalence of dehydration post-shift (> 1.020 specific gravity) was 11% in February, 9% in March, and 6% in April. Cumulative incidence of AKI was 53% in February, 54% in March, and 51% in April. AKI was associated with increasing post-shift specific gravity, a dehydration marker, (OR 1.24, 95% CI 1.02-1.52) and with lower electrolyte solution intake (OR 0.94, 95% CI 0.89-0.99).

CONCLUSIONS

Dehydration and insufficient electrolyte consumption are risk factors for AKI. However even well-hydrated sugarcane workers routinely experience AKI. While hydration is important and protective, there is a need to understand other contributors to risk of AKI and identify prevention strategies with these workers.

The Potential for Renal Injury Elicited by Physical Work in the Heat

An epidemic of chronic kidney disease (CKD) is occurring in laborers who undertake physical work in hot conditions. Rodent data indicate that heat exposure causes kidney injury, and when this injury is regularly repeated it can elicit CKD. Studies in humans demonstrate that a single bout of exercise in the heat increases biomarkers of acute kidney injury (AKI). Elevations in AKI biomarkers in this context likely reflect an increased susceptibility of the kidneys to AKI. Data largely derived from animal models indicate that the mechanism(s) by which exercise in the heat may increase the risk of AKI is multifactorial. For instance, heat-related reductions in renal blood flow may provoke heterogenous intrarenal blood flow. This can promote localized ischemia, hypoxemia and ATP depletion in renal tubular cells, which could be exacerbated by increased sodium reabsorption. Heightened fructokinase pathway activity likely exacerbates ATP depletion occurring secondary to intrarenal fructose production and hyperuricemia. Collectively, these responses can promote inflammation and oxidative stress, thereby increasing the risk of AKI. Equivalent mechanistic evidence in humans is lacking. Such an understanding could inform the development of countermeasures to safeguard the renal health of laborers who regularly engage in physical work in hot environments.

Increase of core temperature affected the progression of kidney injury by repeated heat stress exposure

An epidemic of chronic kidney disease of unknown etiology (Mesoamerican nephropathy) has emerged in hot regions of Central America. We have demonstrated that dehydration associated with recurrent heat exposure causes chronic kidney disease in animal models. However, the independent influence of core body temperature on kidney injury has not been explored. In the present study, we tested the hypothesis that kidney injury could be accelerated by increasing body temperature independent of external temperature. Wild-type mice were exposed to heat (39.5°C, 30 min, 2 times daily) with or without the mitochondrial uncoupling agent 2,4-dinitrophenol (DNP) for 10 days. Core temperature, renal function, proteinuria, and renal histological and biochemical analyses were performed. Isolated mitochondria markers of oxidative stress were evaluated from kidney tissue. DNP increased body core temperature in response to heat by 1°C (42 vs. 41°C), which was transient. The mild increase in temperature correlated with worsening albuminuria (R = 0.715, P < 001), renal tubular injury, and interstitial infiltration of monocytes/macrophages. Tubular injury was marked in the outer medulla. This was associated with a reduction in kidney tissue ATP levels (nonheated control: 16.71 ± 1.33 nmol/mg and DNP + heat: 13.08 ± 1.12 nmol/mg, P < 0.01), reduced mitochondria, and evidence for mitochondrial oxidative stress. The results of the present study suggest that kidney injury in heat stress is markedly worsened by increasing core temperature. This is consistent with the hypothesis that clinical and subclinical heat stroke may play a role in Mesoamerican nephropathy.

The presence of dehydration in paddy farmers in an area with chronic kidney disease of unknown aetiology

AIM

Kidney disease of unknown aetiology (CKDu) has been a health problem in the rural farming community of the North Central province of Sri Lanka since the 1990s and various environmental factors have been postulated as contributing factors for this disease. The aim of our study was to find out whether farmers undergo dehydration which would lead to concentration of urine and the water soluble potentially toxic substance in the kidney, leading to damage of the renal tubules. Therefore, we studied a sample of healthy farmers who were CKDu-free to determine whether they were dehydrated.

METHODS

Sample included healthy male paddy farmers of Padaviya in the Anuradhapura district. Plasma and urine osmolarity were recorded upon waking up in the morning and evening during the non-farming and farming seasons. Basic statistics and a 2 × 2 anova was done to test the interaction of time of day with farming activity.

RESULTS

Farmers were dehydrated according to the plasma osmolarity especially in the mornings, irrespective of whether they were farming or not. Approximately 40% of the sample also demonstrated acute dehydration at the end of the day due to farming activity as indicated by both plasma and urine osmolarity and specific gravity.

CONCLUSION

This study revealed that the farmers of the Padaviya area were either dehydrated or at the upper limit of euhydration sometime during the day irrespective of their activities during the day.

Risk Factors and Mechanisms Underlying Cross-Shift Decline in Kidney Function in Guatemalan Sugarcane Workers

OBJECTIVE

Identify early biomarkers and mechanisms of acute kidney injury in workers at risk of developing chronic kidney disease of unknown origin (CKDu).

METHODS

We assessed cross-shift changes in kidney function and biomarkers of injury in 105 healthy sugarcane workers. We obtained pre-harvest clinical data as well as daily environmental, clinical, and productivity data for each worker.

RESULTS

The average percent decline in cross-shift estimated glomerular filtration rate (eGFR) was 21.8% (standard deviation [SD] 13.6%). Increasing wet bulb globe temperature (WBGT), high uric acid, decreased urine pH, urinary leukocyte esterase, and serum hyperosmolality were risk factors for decline in kidney function.

CONCLUSIONS

Sugarcane workers with normal kidney function experience recurrent subclinical kidney injury, associated with elevations in biomarkers of injury that suggest exposure to high temperatures and extreme physical demands.

Burnt sugarcane harvesting work: effects on pulmonary and systemic inflammatory markers

Objective: To evaluate the effects of burnt sugarcane harvesting on the plasmatic and urinary concentrations of the club cell secretory protein (CC16) and inflammatory systemic biomarkers in a group of sugarcane cutters. Methods: Seventy-eight sugar cane workers were evaluated. The plasmatic and urinary concentrations of CC16, a pulmonary damage marker and inflammatory systemic biomarkers were collected at three time points: before, three months after and six months after the onset of the burnt sugarcane harvesting period. All evaluations were performed at ∼7 am, before the daily work shift. In the three-month evaluation, a post-work shift assessment (acute effect) was also performed. Results: The age of the workers was 37.9 ± 11.0 years. The PM_2.5 concentrations were 27.0 (23.0-33.0) and 101.0 (31.0-139.5) µg/m³ in the pre harvest and harvest periods, respectively (p < .001). Burnt sugarcane harvesting was associated with a reduction, throughout the work during burnt sugarcane harvesting (subchronic effect), in plasmatic and urinary CC16 concentrations. Acutely, there was a decrease in plasmatic concentrations. There were acute and subchronic increases in inflammatory markers (neutrophils, monocytes) and muscle damage markers (CK and LDH) and a decrease in red blood cells. Conclusions: Harvesting of burnt sugarcane was associated with acute and subchronic reductions in the plasmatic and urinary concentrations of CC16 protein and changes in systemic inflammatory markers.

Acute Kidney Injury in Sugarcane Workers at Risk for Mesoamerican Nephropathy

RATIONALE & OBJECTIVE

Mesoamerican nephropathy (MeN), a form of chronic kidney disease (CKD) of unknown cause in Central America, affects young individuals working in physically strenuous occupations. Repeated episodes of work-related kidney injury may lead to CKD in this setting. We aimed to better understand the burden and natural history of acute kidney injury (AKI) in workers at risk for MeN.

STUDY DESIGN

Cross-sectional study of active sugarcane workers, followed by prospective follow-up of individuals with AKI.

SETTING & PARTICIPANTS

326 sugarcane workers with normal preharvest serum creatinine (Scr) values and no history of CKD in an MeN hotspot in Nicaragua near the end of the harvest, and prospective follow-up of workers with AKI.

PREDICTOR

AKI during the harvest, as defined by Scr level increase ≥ 0.3mg/dL over baseline to a level ≥ 1.3mg/dL.

OUTCOMES

Kidney function trajectory and development of CKD over 12 months.

ANALYTICAL APPROACH

Linear regression models were used to analyze the association between job category and kidney function. For workers with AKI, the effect of time on Scr level was evaluated using linear mixed effects.

RESULTS

34 of 326 participants were found to have AKI, with a median late-harvest Scr level of 1.64mg/dL in the AKI group. Workers without AKI had a median Scr level of 0.88mg/dL. AKI was more common among cane cutters compared with other field workers. Participants with AKI had variable degrees of kidney function recovery, with median 6- and 12-month Scr values of 1.25 and 1.27mg/dL, respectively (P < 0.001 for each follow-up value compared to late-harvest Scr). When we compared workers' kidney function before the AKI episode to their kidney function at last follow-up, 10 participants with AKI developed de novo estimated glomerular filtration rate < 60mL/min/1.73m² and 11 had a >30% decrease in estimated glomerular filtration rate.

LIMITATIONS

Follow-up limited to 1 year and some loss to follow-up in the prospective component of the study. Broad definition of AKI that includes both acute and subacute kidney injury.

CONCLUSIONS

In a group of sugarcane workers with normal preharvest kidney function, newly decreased kidney function developing during the harvest season was common. Of those with kidney injury, nearly half had established CKD 12 months later.

Unadjusted point of care creatinine results overestimate acute kidney injury incidence during field testing in Guatemala

OBJECTIVE

Acute kidney injury (AKI) occurs at high rates among agricultural workers (12-33%) in tropical environments. Because of the remote locations affected, traditional laboratory services are often unavailable. In this study we compare point of care (POC) creatinine values to standardized laboratory values, and examine the effect of POC testing on the interpretation of AKI rates under tropical field conditions.

METHODS

Blood samples were collected from 104 sugarcane workers from two time points in January 2018 as a derivation cohort, and from 105 workers from February to April 2017 as a validation cohort. Finger stick and venipuncture samples were drawn at the end of a worker's shift to measure creatinine. Laboratory samples were tested in Guatemala City, Guatemala, in duplicate using the Jaffe Generation 2 method. An adjustment factor to improve agreement with serum creatinine was statistically derived and validated, and then used to determine impact on observed rates of acute kidney injury based on across shift changes in creatinine.

RESULTS

POC creatinine and serum creatinine measures showed that POC consistently overestimated the creatinine by an average of 22% (95% CI: 19.8%, 24.7%) and the disagreement appeared greater at higher values of serum creatinine. An adjustment factor of 0.7775 was applied, which led to significantly greater agreement between the two measures. Rates of AKI in the two combined groups fell from 72% before adjustment to 57% afterwards.

CONCLUSIONS

POC testing under tropical field conditions routinely overestimates creatinine compared to laboratory testing, which leads to overestimation of rates of acute kidney injury. The application of an adjustment factor significantly improved the accuracy of the POC value.