Effects of exogenous desmopressin on a model of heat stress nephropathy in mice

Acute heat stress upregulates Akr1b3 through Nrf-2 to increase endogenous fructose leading to kidney injury

In recent years, the prevalence of extremely high-temperature climates has led to an increase in cases of acute heat stress (HS), which has been identified as a contributing factor to various kidney diseases. Fructose, the end product of the polyol pathway, has been linked to kidney conditions such as kidney stones, chronic kidney disease, and acute kidney injury. However, the relationship between acute HS and kidney injury caused by endogenous fructose remains unclear. The study found that acute HS triggers the production of reactive oxygen species, which in turn activate the Nrf-2 and Akr1b3 leading to an increase in endogenous fructose levels in kidney cells. It was further demonstrated that the elevated levels of endogenous fructose play a crucial role in causing damage to kidney cells. Moreover, inhibiting Nrf-2 effectively mitigated kidney damage induced by acute HS by reducing endogenous fructose levels. These findings underscore the detrimental impact of excessive fructose resulting from acute stress on kidney function, offering a novel perspective for future research on the prevention and treatment of acute HS-induced kidney injury.

The effect of consuming a sucrose-containing sports drink on acute kidney injury risk during a 4 h simulated occupational heat stress

Occupational heat stress increases acute kidney injury risk. Drinking a soft drink sweetened with high fructose corn syrup further elevates this acute kidney injury risk. However, the impact of sucrose, another fructose-containing sweetener, on acute kidney injury risk remains unexplored. We tested the hypothesis that drinking a sucrose-containing sports drink increases acute kidney injury risk when compared to drinking a sugar-free sports drink during 4 h of simulated occupational heat stress. Ten healthy adults consumed a sucrose-containing or sugar-free sport drink ad libitum during 4 h exposures to wet bulb globe temperatures of ∼28 °C. Thirty min of work and 30 min of rest were completed each hour. Work involved treadmill walking at a fixed rate of metabolic heat production (sucrose-containing: 6.0 ± 1.2 W/kg, sugar-free: 5.5 ± 0.9 W/kg, p = 0.267). The product of urinary insulin-like growth factor-binding protein 7 and tissue inhibitor of metalloproteinase-2, normalized to urine specific gravity ([IGFBP7·TIMP-2]USG), provided an acute kidney injury risk index. Mean core (intestinal: n = 13, rectal: n = 7) temperature (sucrose-containing: 37.5 ± 0.1 °C, sugar-free: 37.5 ± 0.3 °C; p = 0.914), peak core temperature (sucrose-containing: 37.8 ± 0.2 °C, sugar-free: 37.9 ± 0.3 °C; p = 0.398), and percent changes in body mass (sucrose-containing: -0.5 ± 0.4%, sugar-free: -0.3 ± 0.6%; p = 0.386) did not differ between groups. [IGFBP7∙TIMP-2]USG increased in both groups (time effect: p = 0.025) with no drink (p = 0.675) or interaction (p = 0.715) effects. Peak change [IGFBP7∙TIMP-2]USG did not differ between sucrose-containing (median 0.0116 [-0.0012, 0.1760] (ng/mL)2/1000) and sugar-free (median 0.0021 [0.0003, 0.2077] (ng/mL)2/1000; p = 0.796). Sucrose-containing sports drink consumption during simulated occupational heat stress does not modify acute kidney injury risk when compared to sugar free-sport drink consumption.

Diagnostic accuracy of thermal, hydration, and heart rate assessments in discriminating positive acute kidney injury risk following physical work in the heat

Occupational heat stress increases the risk of acute kidney injury (AKI). This study presents a secondary analysis to generate novel hypotheses for future studies by investigating the diagnostic accuracy of thermal, hydration, and heart rate assessments in discriminating positive AKI risk following physical work in the heat in unacclimatized individuals. Unacclimatized participants (n = 13, 3 women, age: ∼23 years) completed four trials involving 2 h of exercise in a 39.7 ± 0.6 °C, 32 ± 3% relative humidity environment that differed by experimental manipulation of hyperthermia (i.e., cooling intervention) and dehydration (i.e., water drinking). Diagnostic accuracy was assessed via receiver operating characteristic curve analysis. Positive AKI risk was identified when the product of concentrations insulin-like growth factor binding protein 7 and tissue inhibitor of metalloproteinase-2 [IGFBP7∙TIMP-2] exceeded 0.3 (ng∙mL-1)2∙1000-1. Peak absolute core temperature had the acceptable discriminatory ability (AUC = 0.71, p = 0.009), but a relatively large variance (AUC 95% CI: 0.57-0.86). Mean body temperature, urine specific gravity, urine osmolality, peak heart rate, and the peak percent of both maximum heart rate and heart rate reserve had poor discrimination (AUC = 0.66-0.69, p ≤ 0.051). Mean skin temperature, percent change in body mass and plasma volume, and serum sodium and osmolality had no discrimination (p ≥ 0.072). A peak increase in mean skin temperature of >4.7 °C had a positive likelihood ratio of 11.0 which suggests clinical significance. These data suggest that the absolute value of peak core temperature and the increase in mean skin temperature may be valuable to pursue in future studies as a biomarker for AKI risk in unacclimatized workers.

Hypohydration induced by prolonged cycling in the heat increases biomarkers of renal injury in males

PURPOSE

Recent studies have shown that hypohydration can increase renal injury. However, the contribution of hypohydration to the extent of renal injury is often confounded by exercise induced muscle damage. Therefore, the aim of the present study was to investigate the effect of manipulating hydration status during moderate-intensity cycling in the heat on biomarkers of renal injury.

METHODS

Following familiarisation, fourteen active males (age: 21 [20-22] y; BMI: 22.1 ± 1.9 kg/m2; V ˙ O2peak: 55 ± 9 mL/kg/min) completed two experimental trials, in a randomised cross-over design. Experimental trials consisted of up to 120 min of intermittent cycling (~ 50% Wpeak) in the heat (~ 35 °C, ~ 50% relative humidity). During exercise, subjects consumed either a water volume equal to 100% body mass losses (EU) or minimal water (HYP; 75-100 mL) to induce ~ 3% body mass loss. Blood and urine samples were collected at baseline, 30 min post-exercise and 24 h post-baseline, with an additional urine sample collected immediately post-exercise.

RESULTS

Thirty minutes post-exercise, body mass and plasma volume were lower in HYP than EU (P < 0.001), whereas serum and urine osmolality (P < 0.001), osmolality-corrected urinary kidney injury molecule-1 concentrations (HYP: 2.74 [1.87-5.44] ng/mOsm, EU: 1.15 [0.84-2.37] ng/mOsm; P = 0.024), and percentage change in osmolality-corrected urinary neutrophil gelatinase-associated lipocalin concentrations (HYP: 61 [17-141] %, EU: 7.1 [- 4 to 24] %; P = 0.033) were greater in HYP than EU.

CONCLUSION

Hypohydration produced by cycling in the heat increased renal tubular injury, compared to maintaining euhydration with water ingestion.

Clinical findings and kidney morphology in chronic kidney disease of unknown cause in India

BACKGROUND

Chronic kidney disease of unknown cause (CKDu) is an emerging health problem in India and other countries worldwide. However, clinical descriptions, including kidney pathology, are scarce.

METHODS

This is a descriptive case series of patients with CKDu from an endemic region in India, with a focus on clinical and biochemical characteristics, kidney biopsy findings, and environmental exposure. Patients with suspected CKDu, aged 20-65, and eGFR 30-80 mL/min/1.73 m2 from rural areas with endemic prevalence of CKDu were included. The exclusion criteria were diabetes mellitus, uncontrolled hypertension, proteinuria >1 g/24 h, or other known kidney diseases. The participants underwent kidney biopsies, and blood and urine samples were collected.

RESULTS

Fourteen participants (3 females, 11 males) with a mean eGFR of 53 (range 29-78) mL/min/1.73 m2 were included. Kidney biopsies showed a combination of chronic tubulointerstitial damage, glomerulosclerosis, and glomerular hypertrophy, with varying degrees of interstitial inflammation. Eight participants had polyuria (diuresis ≥ 3 L/day). The urinary sediments were bland, with no haematuria. Serum potassium and sodium levels were, in most cases, normal but within the lower reference interval.

CONCLUSION

The kidney morphology and clinical characteristics in patients with CKDu in India were similar to those described for CKDu in Central America and Sri Lanka.

Macrophages promote heat stress nephropathy in mice via the C3a-C3aR-TNF pathway

Heat-stress nephropathy (HSN) is associated with recurrent dehydration. However, the mechanisms underlying HSN remain largely unknown. In this study, we evaluated the role of dehydration in HSN and kidney injury in mice. Firstly, we found that complement was strongly activated in the mice that were exposed to dehydration; and among complement components, the interaction between C3a and its receptor, C3aR, was more closely associated with kidney injury. Then two-month-old mice were intraperitoneally injected with 2% dimethyl sulfoxide (DMSO) or the C3aR inhibitor SB290157 during dehydration. DMSO-treated mice exhibited excessive macrophage infiltration, renal cell apoptosis, and kidney fibrosis. In contrast, SB290157-treated mice had no apparent kidney injury. By fluorescence-activated cell sorting (FACS), we found that SB290157 treatment in mice remarkably inhibited macrophage infiltration and suppressed CCR2 expression in macrophages. In addition, C3a binding to C3aR promoted macrophage polarization toward the M1 phenotype and increased the production of TNF-α, which induced renal tubular epithelial cell (RTEC) apoptosis in vivo and in vitro. Interestingly, C3a treatment failed to directly induce TNF-α production and apoptosis in RTECs. However, TNF-α production in response to C3a treatment was significantly elevated when RTECs were cocultured with macrophages, suggesting that macrophages rather than RTECs are the target of C3a-C3aR interaction. At last, we proved that infusion of macrophages which highly expressed TNF-α would significantly deteriorate HSN in TNF-KO mice when they were exposed to recurrent dehydration. This study uncovers a novel mechanism underlying the pathogenesis of HSN, and a potential pathway to prevent kidney injury during dehydration.

Nephroprotective plant species used in traditional Mayan Medicine for renal-associated diseases

ETHNOPHARMACOLOGICAL RELEVANCE

The prevalence of kidney disease has increased rapidly in recent years and has emerged as one of the leading causes of mortality worldwide. Natural products have been suggested as valuable nephroprotective agents due to their multi-target and synergistic effects on modulating important proteins involved in kidney injury. There is a large number of plant species that have been used traditionally for kidney-related conditions in Mesoamerican medicine by different cultural groups that could provide a valuable source of nephroprotective therapeutic candidates and could lead to potential drug discovery.

AIM OF REVIEW

This review aims to provide an overview of the currently known efficacy of plant species used traditionally in Mesoamerica by Mayan groups to treat kidney-related conditions and to analyze the phytochemical, pharmacological, molecular, toxicological, and clinical evidence to contribute to public health efforts and for directing future research.

METHODS

Primary sources of plant use reports for traditional kidney-related disorders in Mesoamerica were searched systematically from library catalogs, theses, and scientific databases (PubMed, Google Scholar; and Science Direct), and were filtered according to usage frequency in Mayan groups and plant endemism. The database of traditional plants was further analyzed based on associations with published reports of the phytochemical, pharmacological, molecular, toxicological, and clinical evidence.

RESULTS

The most reported kidney-related conditions used traditionally in Mayan medicine involve reducing renal damage (a cultural interpretation that considers an inflammatory or infectious condition), cleaning or purifying the blood and kidney, reducing kidney pain, and eliminating kidney stones. A total of 208 plants used for kidney-related problems by 10 Mayan groups were found, representing 143 native species, where only 42 have reported pharmacological activity against kidney damage, mainly approached by in vitro and in vivo models of chemical- or drug-induced nephrotoxicity, diabetes nephropathy, and renal injury produced by hypertension. Nephroprotective effects are mainly mediated by reducing oxidative stress, inflammatory response, fibrosis mechanisms, and apoptosis in the kidney. The most common nephroprotective compounds associated with traditional Mayan medicine were flavonoids, terpenoids, and phenolic acids. The most widely studied traditional plants in terms of pharmacological evidence, bioactive compounds, and mechanisms of action, are Annona muricata L., Carica papaya L., Ipomoea batatas (L.) Lam., Lantana camara L., Sechium edule (Jacq.) Sw., Tagetes erecta L., and Zea mays L. Most of the plant species with reported pharmacological activity against kidney damage were considered safe in toxicological studies.

CONCLUSION

Available pharmacological reports suggest that several herbs used in traditional Mayan medicine for renal-associated diseases may have nephroprotective effects and consistent pharmacological evidence, nephroprotective compounds, and mechanisms of action in different models of kidney injury. However, more research is required to fully understand the potential of traditional Mayan medicine in drug discovery given the limited ethnobotanical studies and data available for most species with regards to identification on bioactive components, pharmacological mechanisms, and the scarce number of clinical studies.

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.

Current Hydration Habits: The Disregarded Factor for the Development of Renal and Cardiometabolic Diseases

Improper hydration habits are commonly disregarded as a risk factor for the development of chronic diseases. Consuming an intake of water below recommendations (underhydration) in addition to the substitution of sugar-sweetened beverages (SSB) for water are habits deeply ingrained in several countries. This behavior is due to voluntary and involuntary dehydration; and because young children are exposed to SSB, the preference for a sweet taste is profoundly implanted in the brain. Underhydration and SSB intake lead to mild hyperosmolarity, which stimulates biologic processes, such as the stimulation of vasopressin and the polyol-fructose pathway, which restore osmolarity to normal but at the expense of the continued activation of these biological systems. Unfortunately, chronic activation of the vasopressin and polyol-fructose pathways has been shown to mediate many diseases, such as obesity, diabetes, metabolic syndrome, chronic kidney disease, and cardiovascular disease. It is therefore urgent that we encourage educational and promotional campaigns that promote the evaluation of personal hydration status, a greater intake of potable water, and a reduction or complete halting of the drinking of SSB.

Tubular injury in diabetic ketoacidosis: Results from the diabetic kidney alarm study

OBJECTIVE

Glomerular injury is a recognized complication of diabetic ketoacidosis (DKA), yet the tubular lesions are poorly understood. The aim of this prospective study was to evaluate the presence and reversibility of tubular injury during DKA in children with type 1 diabetes (T1D).

RESEARCH DESIGN AND METHODS

Blood and urine samples were collected from 40 children with DKA (52% boys, mean age 11 ± 4 years, venous pH 7.2 ± 0.1, glucose 451 ± 163 mg/dL) at three timepoints: 0-8 and 12-24 h after starting insulin, and 3 months after discharge. Mixed-effects models evaluated the changes in tubular injury markers over time (neutrophil gelatinase-associated lipocalin [NGAL], kidney injury molecule 1 [KIM-1], and interleukin 18 [IL-18]). We also evaluated the relationships among the tubular injury biomarkers, copeptin, a vasopressin surrogate, and serum uric acid (SUA).

RESULTS

Serum NGAL, KIM-1, and IL-18 were highest at 0-8 h (306.5 ± 45.9 ng/mL, 128.9 ± 10.1 pg/mL, and 564.3 ± 39.2 pg/mL, respectively) and significantly decreased over 3 months (p = 0.03, p = 0.01, and p < 0.001, respectively). There were strong relationships among increases in copeptin and SUA and rises in tubular injury biomarkers. At 0-8 h, participants with acute kidney injury (AKI) [17%] showed significantly higher concentrations of tubular injury markers, copeptin, and SUA.

CONCLUSIONS

DKA was characterized by tubular injury, and the degree of injury associated with elevated copeptin and SUA. Tubular injury biomarkers, copeptin and SUA may be able to predict AKI in DKA.

Environmental risk factors for reduced kidney function due to undetermined cause in India: an environmental epidemiologic analysis

BACKGROUND

An epidemic of chronic kidney disease is occurring in rural communities in low-income and middle-income countries that do not share common kidney disease risk factors such as diabetes and hypertension. This chronic kidney disease of unknown etiology occurs primarily in agricultural communities in Central America and South Asia. Consequently, environmental risk factors including heat stress, heavy metals exposure, and low altitude have been hypothesized as risk factors. We conducted an environmental epidemiological analysis investigating these exposures in India which reports the disease.

METHODS

We used a random sample population in rural and urban sites in Northern and Southern India in 2010, 2011, and 2014 (n = 11,119). We investigated associations of the heat index, altitude, and vicinity to cropland with estimated glomerular filtration rate (eGFR) using satellite-derived data assigned to residential coordinates. We modeled these exposures with eGFR using logistic regression to estimate the risk of low eGFR, and linear mixed models (LMMs) to analyze site-specific eGFR-environment associations.

RESULTS

Being over 55 years of age, male, and living in proximity to cropland was associated with increased risk of low eGFR [odds ratio (OR) (95% confidence interval (CI) = 2.24 (1.43, 3.56), 2.32 (1.39, 3.88), and 1.47 (1.16, 2.36)], respectively. In LMMs, vicinity to cropland was associated with low eGFR [-0.80 (-0.44, -0.14)]. No associations were observed with temperature or altitude.

CONCLUSIONS

Older age, being male, and living in proximity to cropland were negatively associated with eGFR. These analyses are important in identifying subcommunities at higher risk and can help direct future environmental investigations.

Hypohydration produced by high-intensity intermittent running increases biomarkers of renal injury in males

Purpose

Whilst there is evidence to suggest that hypohydration caused by physical work in the heat increases renal injury, whether this is the case during exercise in temperate conditions remains unknown. This study investigated the effect of manipulating hydration status during high-intensity intermittent running on biomarkers of renal injury.

Methods

After familiarisation, 14 males (age: 33 ± 7 years; V̇O_2peak: 57.1 ± 8.6 ml/kg/min; mean ± SD) completed 2 trials in a randomised cross-over design, each involving 6, 15 min blocks of shuttle running (modified Loughborough Intermittent Shuttle Test protocol) in temperate conditions (22.3 ± 1.0 °C; 47.9 ± 12.9% relative humidity). During exercise, subjects consumed either a volume of water equal to 90% of sweat losses (EU) or 75 mL water (HYP). Body mass, blood and urine samples were taken pre-exercise (baseline/pre), 30 min post-exercise (post) and 24 h post-baseline (24 h).

Results

Post-exercise, body mass loss, serum osmolality and urine osmolality were greater in HYP than EU (P ≤ 0.024). Osmolality-corrected urinary kidney injury molecule-1 (uKIM-1) concentrations were increased post-exercise (P ≤ 0.048), with greater concentrations in HYP than EU (HYP: 2.76 [1.72–4.65] ng/mOsm; EU: 1.94 [1.1–2.54] ng/mOsm; P = 0.003; median [interquartile range]). Osmolality-corrected urinary neutrophil gelatinase-associated lipocalin (uNGAL) concentrations were increased post-exercise (P < 0.001), but there was no trial by time interaction effect (P = 0.073).

Conclusion

These results suggest that hypohydration produced by high-intensity intermittent running increases renal injury, compared to when euhydration is maintained, and that the site of this increased renal injury is at the proximal tubules.

Acute Kidney Injury in Pediatric Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a common complication of type 1 and 2 diabetes and often presents during adolescence and young adulthood. Given the growing incidence of both type 1 and type 2 diabetes in children and adolescents, DKD represents a significant public health problem. Acute kidney injury (AKI) in youth with diabetes is strongly associated with risk of DKD development. This review will summarize the epidemiology and pathophysiology of AKI in children with diabetes, the relationship between AKI and DKD, and the potential therapeutic interventions. Finally, we will appraise the impact of the recent COVID-19 infection pandemic on AKI in children with diabetes.

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.

High-fructose corn syrup-sweetened soft drink consumption increases vascular resistance in the kidneys at rest and during sympathetic activation

We first tested the hypothesis that consuming a high-fructose corn syrup (HFCS)-sweetened soft drink augments kidney vasoconstriction to sympathetic stimulation compared with water (study 1). In a second study, we examined the mechanisms underlying these observations (study 2). In study 1, 13 healthy adults completed a cold pressor test, a sympathoexcitatory maneuver, before (preconsumption) and 30 min after drinking 500 mL of decarbonated HFCS-sweetened soft drink or water (postconsumption). In study 2, venous blood samples were obtained in 12 healthy adults before and 30 min after consumption of 500 mL water or soft drinks matched for caffeine content and taste, which were either artificially sweetened (Diet trial), sucrose-sweetened (Sucrose trial), or sweetened with HFCS (HFCS trial). In both study 1 and study 2, vascular resistance was calculated as mean arterial pressure divided by blood velocity, which was measured via Doppler ultrasound in renal and segmental arteries. In study 1, HFCS consumption increased vascular resistance in the segmental artery at rest (by 0.5 ± 0.6 mmHg·cm^-1·s^-1, P = 0.01) and during the cold pressor test (average change: 0.5 ± 1.0 mmHg·cm^-1·s^-1, main effect: P = 0.05). In study 2, segmental artery vascular resistance increased in the HFCS trial (by 0.8 ± 0.7 mmHg·cm^-1·s^-1, P = 0.02) but not in the other trials. Increases in serum uric acid were greater in the HFCS trial (0.3 ± 0.4 mg/dL, P ≤ 0.04) compared with the Water and Diet trials, and serum copeptin increased in the HFCS trial (by 0.8 ± 1.0 pmol/L, P = 0.06). These findings indicate that HFCS acutely increases vascular resistance in the kidneys, independent of caffeine content and beverage osmolality, which likely occurs via simultaneous elevations in circulating uric acid and vasopressin.

Association of Copeptin, a Surrogate Marker of Arginine Vasopressin, with Decreased Kidney Function in Sugarcane Workers in Guatemala

BACKGROUND

Vasopressin is elevated in response to heat and dehydration and has been postulated to have a role in the chronic kidney disease of unknown origin being observed in Central America. The aims of this study were to examine whether the vasopressin pathway, as measured by copeptin, is associated with the presence of kidney dysfunction, and to examine whether higher fluid intake is associated with lower circulating copeptin and thereby preserves kidney health among sugarcane workers exposed to hot conditions.

METHODS

Utilizing a longitudinal study of 105 workers in Guatemala, we examined relationships between hydration indices, plasma copeptin concentrations, and kidney function markers at 3 times during the 6-month harvest. We also examined whether baseline copeptin concentrations increased the odds of developing an estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m2.

RESULTS

Copeptin concentrations were positively associated with serum creatinine (β 1.41, 95% CI 0.88-2.03) and negatively associated with eGFR (β -1.07, 95% CI -1.43 to -0.70). In addition, as workers improved their hydration (measured by increases in fluid balance), copeptin concentrations were reduced, and this reduction was associated with an improvement in kidney function.

CONCLUSIONS

Results suggest that copeptin should be studied as a potential prognostic biomarker.

Both hyperthermia and dehydration during physical work in the heat contribute to the risk of acute kidney injury

Occupational heat stress increases the risk of acute kidney injury (AKI) and kidney disease. This study tested the hypothesis that attenuating the magnitude of hyperthermia (i.e., increase in core temperature) and/or dehydration during prolonged physical work in the heat attenuates increases in AKI biomarkers. Thirteen healthy adults (3 women, 23 ± 2 yr) exercised for 2 h in a 39.7 ± 0.6°C, 32 ± 3% relative-humidity environmental chamber. In four trials, subjects received water to remain euhydrated (Water), continuous upper-body cooling (Cooling), a combination of both (Water + Cooling), or no intervention (Control). The magnitude of hyperthermia (increased core temperature of 1.9 ± 0.3°C; P < 0.01) and dehydration (percent loss of body mass of -2.4 ± 0.5%; P < 0.01) were greatest in the Control group. There were greater increases in the urinary biomarkers of AKI in the Control trial: albumin (increase of 13 ± 11 μg/mL; P ≤ 0.05 compared with other trials), neutrophil gelatinase-associated lipocalin (NGAL) (increase of 16 ± 14 ng/dL, P ≤ 0.05 compared with Cooling and Water + Cooling groups), and insulin-like growth factor-binding protein 7 (IGFBP7) (increase of 227 ± 190 ng/mL; P ≤ 0.05 compared with other trials). Increases in IGFBP7 in the Control trial persisted after correcting for urine production/concentration. There were no differences in the AKI biomarker tissue inhibitor of metalloproteinase 2 (TIMP-2) between trials (P ≥ 0.11). Our findings indicate that the risk of AKI is highest with greater magnitudes of hyperthermia and dehydration during physical work in the heat. Additionally, the differential findings between IGFBP7 (preferentially secreted in proximal tubules) and TIMP-2 (distal tubules) suggest the proximal tubules as the location of potential renal injury.NEW & NOTEWORTHY We demonstrate that the risk for acute kidney injury (AKI) is higher in humans with greater magnitudes of hyperthermia and dehydration during physical work in the heat and that alleviating the hyperthermia and/or limiting dehydration equally reduce the risk of AKI. The biomarker panel employed in this study suggests the proximal tubules as the location of potential renal injury.

Serum osmolarity as a potential predictor for contrast-induced nephropathy following elective coronary angiography

BACKGROUND AND OBJECTIVES

Contrast-induced nephropathy (CIN) is a relatively common complication following primary coronary angiography (CAG) or percutaneous coronary intervention (PCI), especially in at-risk patients. The goal of this study is to evaluate the role of pre-procedural serum osmolarity as a risk factor for CIN in patients undergoing elective CAG for stable coronary artery disease (CAD).

MATERIALS AND METHODS

A total of 356 stable CAD patients scheduled to undergo CAG or PCI were included in this two-center study. Serum osmolarity was calculated on admission. CIN was defined according to the KDIGO criteria.

RESULTS

There were 45 (12.6%) patients who developed CIN 48-72 h after CAG or PCI. CIN patients had a higher prevalence of diabetes (51.1% in those with CIN vs 24.4% in those without CIN, p < 0.001), higher serum glucose (129 mg/dL in those with CIN vs 108 mg/dL in those without CIN, p < 0.001), blood urea nitrogen (22.4 mg/dL in those with CIN vs 19.0 mg/dL in those without CIN, p = 0.01) and serum osmolarity (294.2 mOsm in those with CIN vs 290.1 mOsm in those without CIN, p < 0.001) levels, had received a higher dose of contrast (250 mL in those with CIN vs 200 mL in those without CIN, p = 0.03) but had lower hemoglobin (12.9 g/dL in those with CIN vs 13.6 g/dL in those without CIN, p = 0.04) level. In multivariate analysis, serum osmolarity [odds ratio (OR) 1.11; 95% confidence interval (CI) 1.04-1.18 for each mOsm/L increase; p = 0.001], diabetes (OR 2.43, 95% CI 1.26-4.71; p = 0.01), C-reactive protein (OR 1.04, 95% CI 1.01-1.08 for each mg/dL increase; p = 0.02) and contrast volume (OR 34.66, 95% CI 1.25-962.22 for each L increase; p = 0.04) remained as independent predictors of CIN. Serum sodium, glucose and blood urea nitrogen contributed to the excess serum osmolarity of CIN patients.

CONCLUSION

Serum osmolarity is a cheap and widely available marker that can reliably predict CIN after CAG or PCI. Future research should focus on determining a clinically optimal cutoff for serum osmolarity that would warrant preventive interventions. Furthermore, later research may investigate the role of serum osmolarity not only as a risk factor but also as a pathogenetic mechanism underlying CIN.

Antidiuretic Hormone and Serum Osmolarity Physiology and Related Outcomes: What Is Old, What Is New, and What Is Unknown?

CONTEXT

Although the physiology of sodium, water, and arginine vasopressin (AVP), also known as antidiuretic hormone, has long been known, accumulating data suggest that this system operates as a more complex network than previously thought.

EVIDENCE ACQUISITION

English-language basic science and clinical studies of AVP and osmolarity on the development of kidney and cardiovascular disease and overall outcomes.

EVIDENCE SYNTHESIS

Apart from osmoreceptors and hypovolemia, AVP secretion is modified by novel factors such as tongue acid-sensing taste receptor cells and brain median preoptic nucleus neurons. Moreover, pharyngeal, esophageal, and/or gastric sensors and gut microbiota modulate AVP secretion. Evidence is accumulating that increased osmolarity, AVP, copeptin, and dehydration are all associated with worse outcomes in chronic disease states such as chronic kidney disease (CKD), diabetes, and heart failure. On the basis of these pathophysiological relationships, an AVP receptor 2 blocker is now licensed for CKD related to polycystic kidney disease.

CONCLUSION

From a therapeutic perspective, fluid intake may be associated with increased AVP secretion if it is driven by loss of urine concentration capacity or with suppressed AVP if it is driven by voluntary fluid intake. In the current review, we summarize the literature on the relationship between elevated osmolarity, AVP, copeptin, and dehydration with renal and cardiovascular outcomes and underlying classical and novel pathophysiologic pathways. We also review recent unexpected and contrasting findings regarding AVP physiology in an attempt to explain and understand some of these relationships.

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.

Genes and environment in chronic kidney disease hotspots

PURPOSE OF REVIEW

Chronic kidney disease (CKD) can cluster in geographic locations or in people of particular genetic ancestries. We explore APOL1 nephropathy and Balkan nephropathy as examples of CKD clustering that illustrate genetics and environment conspiring to cause high rates of kidney disease. Unexplained hotspots of kidney disease in Asia and Central America are then considered from the perspective of potential gene × environment interactions.

RECENT FINDINGS

We report on evidence supporting both genes and environment in these CKD hotspots. Differing genetic susceptibility between populations and within populations may explain why causal environmental risk factors have been so hard to identify conclusively. Similarly, one cannot explain why these epidemics of kidney disease are happening now without invoking environmental changes.

SUMMARY

Approaches to these CKD hotspots are of necessity becoming more holistic. Genetic studies may help us identify the environmental triggers by teaching us about disease biology and may empower environmental risk factor studies by allowing for stratification of study participants by genetic susceptibility.

Soft drink consumption during and following exercise in the heat elevates biomarkers of acute kidney injury

The purpose of this study was to test the hypothesis that consuming a soft drink (i.e., a high-fructose, caffeinated beverage) during and following exercise in the heat elevates biomarkers of acute kidney injury (AKI) in humans. Twelve healthy adults drank 2 liters of an assigned beverage during 4 h of exercise in the heat [35.1 (0.1)°C, 61 (5)% relative humidity] in counterbalanced soft drink and water trials, and ≥1 liter of the same beverage after leaving the laboratory. Stage 1 AKI (i.e., increased serum creatinine ≥0.30 mg/dl) was detected at postexercise in 75% of participants in the Soft Drink trial compared with 8% in Water trial ( P = 0.02). Furthermore, urinary neutrophil gelatinase-associated lipocalin (NGAL), a biomarker of AKI, was higher during an overnight collection period after the Soft Drink trial compared with Water in both absolute concentration [6 (4) ng/dl vs. 5 (4) ng/dl, P < 0.04] and after correcting for urine flow rate [6 (7) (ng/dl)/(ml/min) vs. 4 (4) (ng/dl)/(ml/min), P = 0.03]. Changes in serum uric acid from preexercise were greater in the Soft Drink trial than the Water trial at postexercise ( P < 0.01) and 24 h ( P = 0.05). There were greater increases from preexercise in serum copeptin, a stable marker of vasopressin, at postexercise in the Soft Drink trial ( P < 0.02) than the Water trial. These findings indicate that consuming a soft drink during and following exercise in the heat induces AKI, likely via vasopressin-mediated mechanisms.

Fructose increases risk for kidney stones: potential role in metabolic syndrome and heat stress

Background

Fructose intake, mainly as table sugar or high fructose corn syrup, has increased in recent decades and is associated with increased risk for kidney stones. We hypothesized that fructose intake alters serum and urinary components involved in stone formation.

Methods

We analyzed a previously published randomized controlled study that included 33 healthy male adults (40–65 years of age) who ingested 200 g of fructose (supplied in a 2-L volume of 10% fructose in water) daily for 2 weeks. Participants were evaluated at the Unit of Nephrology of the Mateo Orfila Hospital in Menorca. Changes in serum levels of magnesium, calcium, uric acid, phosphorus, vitamin D, and intact PTH levels were evaluated. Urine magnesium, calcium, uric acid, phosphorus, citrate, oxalate, sodium, potassium, as well as urinary pH, were measured.

Results

Ingestion of fructose was associated with an increased serum level of uric acid (p < 0.001), a decrease in serum ionized calcium (p = 0.003) with a mild increase in PTH (p < 0.05) and a drop in urinary pH (p = 0.02), an increase in urine oxalate (p = 0.016) and decrease in urinary magnesium (p = 0.003).

Conclusions

Fructose appears to increase urinary stone formation in part via effects on urate metabolism and urinary pH, and also via effects on oxalate. Fructose may be a contributing factor for the development of kidney stones in subjects with metabolic syndrome and those suffering from heat stress.

Trial registration

ClinicalTrials.gov NCT00639756 March 20, 2008.

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.

MicroRNA-132 controls water homeostasis through regulating MECP2-mediated vasopressin synthesis

Fine-tuning of the body’s water balance is regulated by vasopressin (AVP), which induces the expression and apical membrane insertion of aquaporin-2 water channels and subsequent water reabsorption in the kidney. Here we demonstrate that silencing of microRNA-132 (miR-132) in mice causes severe weight loss due to acute diuresis coinciding with increased plasma osmolality, reduced renal total and plasma membrane expression of aquaporin-2, and abrogated increase in AVP levels. Infusion with synthetic AVP fully reversed the antagomir-132-induced diuresis, and low-dose intracerebroventricular administration of antagomir-132 similarly caused acute diuresis. Central and intracerebroventricular antagomir-132 injection both decreased hypothalamic AVP mRNA levels. At the molecular level, antagomir-132 increased the in vivo and in vitro mRNA expression of methyl-CpG-binding protein-2 (MECP2), which is a miR-132 target and which blocks AVP gene expression by binding its enhancer region. In line with this, treatment of hypothalamic N6 cells with a high-salt solution increased its miR-132 levels, whereas it attenuated endogenous Mecp2 mRNA levels. In conclusion, we identified miR-132 as a first miRNA regulating the osmotic balance by regulating the hypothalamic AVP gene mRNA expression.

Rehydration with fructose worsens dehydration-induced renal damage

Background

Increasing evidence suggests heat stress induced chronic kidney disease (CKD) may be mediated by endogenous fructose generation and may be exacerbated by rehydration by fructose-containing solutions. We have recently reported a model of CKD induced by heat stress. Here we test the hypothesis that rehydration with fructose may induce worse kidney injury than rehydration with equal amounts of water, and we also test if this fructose-induced injury is associated with activation of inflammasomes in the kidney.

Methods

Mice were recurrently exposed to heat (39.5 C⁰ for 30 min/h, 5 times daily for 5 wks) with rehydration consisting of 6 ml each night of water (Heat, n = 7) or fructose (Heat+F, 10%, n = 7), and were compared to control mice on water (Control, n = 7) or fructose (Fructose, n = 7). Various markers of renal injury were assessed.

Results

Compared to control animals, there was a progressive worsening of renal injury (inflammation and fibrosis) with fructose alone, heat stress alone, and heat stress with fructose rehydration (P < 0.01 by ANOVA). The combination of heat stress with rehydration with fructose was associated with increased intrarenal expression of the inflammasome markers, NLRP3 and IL-18, compared to heat stress alone. In addition, heat stress with or without fructose was associated with increased expression of caspase − 3 and monocyte chemoattractant protein-1 levels. Fructose administration was also associated with an increase in serum copeptin levels (a biomarker of vasopressin) and elevated copeptin was also observed in mice undergoing heat stress alone.

Conclusions

These studies suggest that heat stress may activate intrarenal inflammasomes leading to inflammation and renal injury, and provide evidence that rehydration with fructose may accelerate the renal injury and inflammatory response.

Experimental heat stress nephropathy and liver injury are improved by allopurinol

An epidemic of chronic kidney disease (CKD) has been observed in Central America among workers in the sugarcane fields. One hypothesis is that the CKD may be caused by recurrent heat stress and dehydration, and potentially by hyperuricemia. Accordingly, we developed a murine model of kidney injury associated with recurrent heat stress. In the current experiment, we tested whether treatment with allopurinol (a xanthine oxidase inhibitor that reduces serum urate) provides renal protection against recurrent heat stress and dehydration. Eight-week-old male C57BL/6 mice were subjected to recurrent heat stress (39.5°C for 30 min, 7 times daily, for 5 wk) with or without allopurinol treatment and were compared with control animals with or without allopurinol treatment. Mice were allowed ad libitum access to normal laboratory chow (Harlan Teklad). Kidney histology, liver histology, and renal function were examined. Heat stress conferred both kidney and liver injury. Kidneys showed loss of proximal tubules, infiltration of monocyte/macrophages, and interstitial collagen deposition, while livers of heat-stressed mice displayed an increase in macrophages, collagen deposition, and myofibroblasts. Allopurinol provided significant protection and improved renal function in the heat-stressed mice. The renal protection was associated with reduction in intrarenal uric acid concentration and heat shock protein 70 expression. Heat stress-induced renal and liver injury can be protected with allopurinol treatment. We recommend a clinical trial of allopurinol for individuals developing renal injury in rural areas of Central America where the epidemic of chronic kidney disease is occurring.

Copeptin reflects physiological strain during thermal stress

PURPOSE

To prevent heat-related illnesses, guidelines recommend limiting core body temperature (T c) ≤ 38 °C during thermal stress. Copeptin, a surrogate for arginine vasopressin secretion, could provide useful information about fluid balance, thermal strain and health risks. It was hypothesised that plasma copeptin would rise with dehydration from occupational heat stress, concurrent with sympathoadrenal activation and reduced glomerular filtration, and that these changes would reflect T c responses.

METHODS

Volunteers (n = 15) were recruited from a British Army unit deployed to East Africa. During a simulated combat assault (3.5 h, final ambient temperature 27 °C), T c was recorded by radiotelemetry to differentiate volunteers with maximum T c > 38 °C versus ≤ 38 °C. Blood was sampled beforehand and afterwards, for measurement of copeptin, cortisol, free normetanephrine, osmolality and creatinine.

RESULTS

There was a significant (P < 0.05) rise in copeptin from pre- to post-assault (10.0 ± 6.3 vs. 16.7 ± 9.6 pmol L-1, P < 0.001). Although osmolality did not increase, copeptin correlated strongly with osmolality after the exposure (r = 0.70, P = 0.004). In volunteers with maximum T c > 38 °C (n = 8) vs ≤ 38 °C (n = 7) there were significantly greater elevations in copeptin (10.4 vs. 2.4 pmol L-1) and creatinine (10 vs. 2 μmol L-1), but no differences in cortisol, free normetanephrine or osmolality.

CONCLUSIONS

Changes in copeptin reflected T c response more closely than sympathoadrenal markers or osmolality. Dynamic relationships with tonicity and kidney function may help to explain this finding. As a surrogate for integrated physiological strain during work in a field environment, copeptin assay could inform future measures to prevent heat-related illnesses.

Tolvaptan in Later-Stage Autosomal Dominant Polycystic Kidney Disease

BACKGROUND

In a previous trial involving patients with early autosomal dominant polycystic kidney disease (ADPKD; estimated creatinine clearance, ≥60 ml per minute), the vasopressin V₂-receptor antagonist tolvaptan slowed the growth in total kidney volume and the decline in the estimated glomerular filtration rate (GFR) but also caused more elevations in aminotransferase and bilirubin levels. The efficacy and safety of tolvaptan in patients with later-stage ADPKD are unknown.

METHODS

We conducted a phase 3, randomized withdrawal, multicenter, placebo-controlled, double-blind trial. After an 8-week prerandomization period that included sequential placebo and tolvaptan run-in phases, during which each patient's ability to take tolvaptan without dose-limiting side effects was assessed, 1370 patients with ADPKD who were either 18 to 55 years of age with an estimated GFR of 25 to 65 ml per minute per 1.73 m² of body-surface area or 56 to 65 years of age with an estimated GFR of 25 to 44 ml per minute per 1.73 m² were randomly assigned in a 1:1 ratio to receive tolvaptan or placebo for 12 months. The primary end point was the change in the estimated GFR from baseline to follow-up, with adjustment for the exact duration that each patient participated (interpolated to 1 year). Safety assessments were conducted monthly.

RESULTS

The change from baseline in the estimated GFR was -2.34 ml per minute per 1.73 m² (95% confidence interval [CI], -2.81 to -1.87) in the tolvaptan group, as compared with -3.61 ml per minute per 1.73 m² (95% CI, -4.08 to -3.14) in the placebo group (difference, 1.27 ml per minute per 1.73 m²; 95% CI, 0.86 to 1.68; P<0.001). Elevations in the alanine aminotransferase level (to >3 times the upper limit of the normal range) occurred in 38 of 681 patients (5.6%) in the tolvaptan group and in 8 of 685 (1.2%) in the placebo group. Elevations in the aminotransferase level were reversible after stopping tolvaptan. No elevations in the bilirubin level of more than twice the upper limit of the normal range were detected.

CONCLUSIONS

Tolvaptan resulted in a slower decline than placebo in the estimated GFR over a 1-year period in patients with later-stage ADPKD. (Funded by Otsuka Pharmaceuticals and Otsuka Pharmaceutical Development and Commercialization; REPRISE ClinicalTrials.gov number, NCT02160145 .).