Vasopressin Mediates the Renal Damage Induced by Limited Fructose Rehydration in Recurrently Dehydrated Rats

A study on the early metabolic effects of salt and fructose consumption: the protective role of water

Increasing serum osmolality has recently been linked with acute stress responses, which over time can lead to increased risk for obesity, hypertension, and other chronic diseases. Salt and fructose are two major stimuli that can induce acute changes in serum osmolality. Here we investigate the early metabolic effects of sodium and fructose consumption and determine whether the effects of sodium or fructose loading can be mitigated by blocking the change in osmolality with hydration. Forty-four healthy subjects without disease and medication were recruited into four groups. After overnight fasting, subjects in Group 1 drank 500 mL of salty soup, while those in Group 2 drank 500 mL of soup without salt for 15 min. Subjects in Group 3 drank 500 mL of 100% apple juice in 5 min, while subjects in Group 4 drank 500 mL of 100% apple juice and 500 mL of water in 5 min. Blood pressure (BP), plasma sodium, and glucose levels were measured every 15 min in the first 2 h. Serum and urine osmolarity, serum uric acid, cortisol, fibroblast growth factor 21 (FGF21), aldosterone, adrenocorticotropic hormone (ACTH) level, and plasma renin activity (PRA) were measured at the baseline and 2 h. Both acute intake of salt or fructose increased serum osmolality (maximum ∼4 mOsm/L peaking at 75 min) associated with a rise in systolic and diastolic BP, PRA, aldosterone, ACTH, cortisol, plasma glucose, uric acid, and FGF21. Salt tended to cause greater activation of the renin-angiotensin-system (RAS), while fructose caused a greater rise in glucose and FGF21. In both cases, hydration could prevent the osmolality and largely block the acute stress response. Acute changes in serum osmolality can induce remarkable activation of the ACTH-cortisol, RAS, glucose metabolism, and uric acid axis that is responsive to hydration. In addition to classic dehydration, salt, and fructose-containing sugars can activate these responses. Staying well hydrated may provide benefits despite exposure to sugar and salt. More studies are needed to investigate whether hydration can block the chronic effects of sugar and salt on disease.

Sports drinks do not increase acute kidney injury risk in males during industrial work in the heat when euhydration is maintained, a randomized crossover trial

Industrial workers regularly perform physical labor under high heat stress, which may place them at risk for dehydration and acute kidney injury. Current guidelines recommend that workers should consume sports drinks to maintain euhydration during work shifts. However, the impact of fructose sweetened sports drinks on acute kidney injury risk is unknown. The purpose of this study was to investigate the effects of sports drink consumption on markers of acute kidney injury following simulated industrial work in the heat. Twenty males completed two matched 2 h simulated industrial work trial visits in a warm and humid environment (30 °C and 55% relative humidity). During and following the bout of simulated work, participants consumed either a commercially available sports drink or a noncaloric placebo. Urine and blood samples, collected pre-, post-, and 16 h post-work were assayed for markers of hydration (plasma/urine osmolality, and urine specific gravity) and acute kidney injury (KIM-1 and NGAL). There were no differences in physiological or perceptual responses to the bout of work (interaction p > 0.05 for all indices), and markers of hydration were similar between trials (interaction p > 0.05 for all indices). KIM-1 (Placebo: Δ Ln 1.18 ± 1.64; Sports drink: Δ Ln 1.49 ± 1.10 pg/mL; groupwide d = 0.89, p < 0.001) and NGAL (Placebo: Δ Ln 0.44 ± 1.11; Sports drink: Δ Ln 0.67 ± 1.22 pg/mL; groupwide d = 0.39, p = 0.03) were elevated pre- to post-work, but there were no differences between trials (interaction p > 0.05). These data provide no evidence that consumption of fructose sweetened sports drinks increases the risk of acute kidney injury during physical work in the heat.

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.

Short-term impact of extreme temperatures, relative humidity and air pollution on emergency hospital admissions due to kidney disease and kidney-related conditions in the Greater Madrid area (Spain)

While some studies report a possible association between heat waves and kidney disease and kidney-related conditions, there still is no consistent scientific consensus on the matter or on the role played by other variables, such as air pollution and relative humidity. Ecological retrospective time series study 01-01-2013 to 31-12-2018). Dependent variables: daily emergency hospitalisations due to kidney disease (KD), acute kidney injury (AKI), lithiasis (L), dysnatraemia (DY) and hypovolaemia (HPV). Independent variables: maximum and minimum daily temperature (Tmax, Tmin, °C), and daily relative humidity (RH, %). Other variables were also calculated, such as the daily temperature for risk of kidney disease (Theat, °C) and low daily hazardous relative humidity (HRH%). As variables of air pollution, we used the daily mean concentrations of PM10, PM2.5, NO2 and O3 in μg/m3. Based on these, we then calculated their daily excesses over World Health Organisation (WHO) guideline levels (hPM10, hPM2.5, hNO2 and hO3 respectively). Poisson family generalised linear models (GLMs) (link = log) were used to calculate relative risks (RRs), and attributable risks and attributable admissions. In the models, we controlled for the covariates included: seasonalities, trend, autoregressive component, day of the week, month and year. A statistically significant association was found between Theat and all the dependent variables analysed. The greatest AKI disease burden was attributable to Theat (2.2 % (1.7, 2.6) of attributable hospital admissions), followed by hNO2 (1.7 % (0.9, 3.4)) and HRH (0.8 (0.6, 1.1)). In the case of hypovolaemia and dysnatraemia, the greatest disease burden again corresponded to Theat, with 6.9 % (6.2, 7.6) and 5.7 (4.8, 6.6) of attributable hospital admissions respectively. Episodes of extreme heat exacerbate daily emergency hospital admissions due to kidney disease and kidney-related conditions; and attributable risks are likewise seen for low relative humidity and high ozone levels.

Heat exposure and hospitalizations for chronic kidney disease in China: a nationwide time series study in 261 major Chinese cities

BACKGROUND

Climate change profoundly shapes the population health at the global scale. However, there was still insufficient and inconsistent evidence for the association between heat exposure and chronic kidney disease (CKD).

METHODS

In the present study, we studied the association of heat exposure with hospitalizations for cause-specific CKD using a national inpatient database in China during the study period of hot season from 2015 to 2018. Standard time-series regression models and random-effects meta-analysis were developed to estimate the city-specific and national averaged associations at a 7 lag-day span, respectively.

RESULTS

A total of 768,129 hospitalizations for CKD was recorded during the study period. The results showed that higher temperature was associated with elevated risk of hospitalizations for CKD, especially in sub-tropical cities. With a 1 °C increase in daily mean temperature, the cumulative relative risks (RR) over lag 0-7 d were 1.008 [95% confidence interval (CI) 1.003-1.012] for nationwide. The attributable fraction of CKD hospitalizations due to high temperatures was 5.50%. Stronger associations were observed among younger patients and those with obstructive nephropathy. Our study also found that exposure to heatwaves was associated with added risk of hospitalizations for CKD compared to non-heatwave days (RR = 1.116, 95% CI 1.069-1.166) above the effect of daily mean temperature.

CONCLUSIONS

Short-term heat exposure may increase the risk of hospitalization for CKD. Our findings provide insights into the health effects of climate change and suggest the necessity of guided protection strategies against the adverse effects of high temperatures.

Fructose: A New Variable to Consider in SIADH and the Hyponatremia Associated With Long-Distance Running?

Fructose has recently been proposed to stimulate vasopressin secretion in humans. Fructose-induced vasopressin secretion is not only postulated to result from ingestion of fructose-containing drinks but may also occur from endogenous fructose production via activation of the polyol pathway. This raises the question of whether fructose might be involved in some cases of vasopressin-induced hyponatremia, especially in situations where the cause is not fully known such as in the syndrome of inappropriate secretion of diuretic hormone (SIADH) and exercise-associated hyponatremia, which has been observed in marathon runners. Here we discuss the new science of fructose and vasopressin, and how it may play a role in some of these conditions, as well as in the complications associated with rapid treatment (such as the osmotic demyelination syndrome). Studies to test the role of fructose could provide new pathophysiologic insights as well as novel potential treatment strategies for these common conditions.

Associations between short-term temperature exposure and kidney-related conditions in New York State: The influence of temperature metrics across four dimensions

BACKGROUND

Evidence describing the relationship between short-term temperature exposure and kidney-related conditions is insufficient. It remains unclear how temperature specification affects estimation of these associations. This study aimed to assess associations between short-term temperature exposure and seven kidney-related conditions and to evaluate the influence of temperature specification.

METHODS

We obtained data on hospital encounters in New York State (2007-2016). We assessed associations with a case-crossover design using conditional logistic regression with distributed lag non-linear models. We compared model performance (i.e., AIC) and association curves using 1) five temperature spatial resolutions; 2) temperature on an absolute versus relative scale; 3) seven temperature metrics incorporating humidity, wind speed, and/or solar radiation; and 4) five intraday temperature measures (e.g., daily minimum and daytime mean).

RESULTS

We included 1,209,934 unplanned adult encounters. Temperature metric and intraday measure had considerably greater influence than spatial resolution and temperature scale. For outcomes not associated with temperature exposure, almost all metrics or intraday measures showed good model performance; for outcomes associated with temperature, there were meaningful differences in performance across metrics or intraday measures. For parsimony, we modelled daytime mean outdoor wet-bulb globe temperature, which showed good performance for all outcomes. At lag 0-6 days, we observed increased risk at the 95^th percentile of temperature versus the minimum morbidity temperature for acute kidney failure (odds ratio [OR] = 1.36, 95% confidence interval [CI]: 1.09, 1.69), urolithiasis (OR = 1.41, 95% CI: 1.16, 1.70), dysnatremia (OR = 1.26, 95% CI: 1.01, 1.59), and volume depletion (OR = 1.88, 95% CI: 1.41, 2.51), but not for glomerular diseases, renal tubulo-interstitial diseases, and chronic kidney disease.

CONCLUSIONS

High-temperature exposure over one week is a risk factor for acute kidney failure, urolithiasis, dysnatremia, and volume depletion. The differential model performance across temperature metrics and intraday measures indicates the importance of careful selection of exposure metrics when estimating temperature-related health burden.

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.

High-Fructose Diet-Induced Hyperuricemia Accompanying Metabolic Syndrome-Mechanisms and Dietary Therapy Proposals

Fructose is often used as a food ingredient due to its low production costs and sweetening power. In recent years, it has been noticed that people on a Western diet high in fructose have high levels of uric acid in their blood. It was recognized that the specific metabolism of fructose in the body might cause increased production of uric acid, which then may affect the intensification of lipogenesis and the development of metabolic syndrome (MetS), insulin resistance, gout, cardiovascular diseases, leptin resistance, or non-alcoholic fatty liver disease. So far, to treat hyperuricemia, it has been recommended to use a low-purine diet characterized by limiting protein-containing products. However, this recommendation often leads to an increased intake of carbohydrate-rich foods that may contain fructose. Increased fructose consumption may enhance the secretion of uric acid again and, consequently, does not have therapeutic effects. Therefore, instead of a low-purine diet, using healthy diets, such as DASH or the Mediterranean diet, which can benefit metabolic parameters, could be a better proposal. This article provides an overview of this approach, focusing on MetS and hyperuricemia among high-fructose dieters.

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.

Negative Effects of Chronic High Intake of Fructose on Lung Diseases

In the modern diet, excessive fructose intake (>50 g/day) had been driven by the increase, in recent decades, of the consumption of sugar-sweetened beverages. This phenomenon has dramatically increased within the Caribbean and Latin American regions. Epidemiological studies show that chronic high intake of fructose related to sugar-sweetened beverages increases the risk of developing several non-communicable diseases, such as chronic obstructive pulmonary disease and asthma, and may also contribute to the exacerbation of lung diseases, such as COVID-19. Evidence supports several mechanisms—such as dysregulation of the renin−angiotensin system, increased uric acid production, induction of aldose reductase activity, production of advanced glycation end-products, and activation of the mTORC1 pathway—that can be implicated in lung damage. This review addresses how these pathophysiologic and molecular mechanisms may explain the lung damage resulting from high intake of fructose.

Effects of ambient temperature on hospital admissions for obstructive nephropathy in Wuhan, China: A time-series analysis

Under the background of global warming, it has been confirmed that heat exposure has a huge impact on human health. The current study aimed to evaluate the effects of daily mean ambient temperature on hospital admissions for obstructive nephropathy (ON) at the population level. A total of 19,494 hospitalization cases for ON in Wuhan, China from January 1, 2015 to December 31, 2018 were extracted from a nationwide inpatient database in tertiary hospitals according to the International Classification of Diseases (ICD)- 10 codes. Daily ambient meteorological and pollution data during the same period were also collected. A quasi-Poisson Generalized Linear Model (GLM) combined with a distributed lag non-linear model (DLNM) was applied to analyze the lag-exposure-response relationship between daily mean temperature and daily hospital admissions for ON. Results showed that there were significantly positive associations between the daily mean temperature and ON hospital admissions. Relative to the minimum-risk temperature (-3.4 ℃), the risk of hospital admissions for ON at moderate hot temperature (25 ℃, 75th percentile) occurred from lag day 4 and stayed to lag day 12 (cumulative relative risk [RR] was 1.846, 95 % confidence interval [CI]: 1.135-3.005, over lag 0-12 days). Moreover, the risk of extreme hot temperature (32 ℃, 99th percentile) appeared immediately and lasted for 8 days (RR = 2.019, 95 % CI: 1.308-3.118, over lag 0-8 days). Subgroup analyses indicated that the middle-aged and elderly (≥45 years) patients might be more susceptible to the negative effects of high temperature, especially at moderate hot conditions. Our findings suggest that temperature may have a significant impact on the acute progression and onset of ON. Higher temperature is associated with increased risks of hospital admissions for ON, which indicates that early interventions should be taken in geographical settings with relatively high temperatures, particularly for the middle-aged and elderly.

Short-term association of NO2 with hospital visits for chronic kidney disease and effect modification by temperature in Hefei, China: A time series study

BACKGROUND

A large body of evidence has linked air pollution and temperature with chronic kidney disease (CKD) prevalence and hospitalizations. However, most studies have focused on the influence of heat stress on CKD prevalence, and the potential effect modification of temperature on the association between air pollution and CKD has not been well-investigated. In this study, we examined the associations of the whole temperature spectrum and air pollution with CKD-related hospital visits and explored whether temperature modifies the short-term association of air pollution with CKD-related hospital visits.

METHODS AND FINDINGS

We collected 40 276 CKD-related hospital visits from the first Affiliated Hospital of Anhui Medical University and Anhui Provincial Hospital in Hefei, China, during 2015-2019. A two-stage time-series design was conducted to investigate the associations of air pollution and daily mean temperature with CKD-related hospital visits. First, we estimated the associations between air pollution and CKD-related hospital visits as well as temperature and CKD-related hospital visits. Second, we analyzed the associations of air pollution with CKD hospital visits at different temperatures. We found that NO₂ exposure and low temperature were associated with an increased risk of CKD-related hospital visits. Low temperature enhanced the association between NO₂ exposure and CKD-related hospital visits, with an increase of 4.30% (95% CI: 2.47-5.92%) per 10 μg/m³ increment in NO₂ at low temperature. Effect modification of the association between NO₂ and the risk of CKD-related hospital visits was stronger at low temperature across the whole population.

CONCLUSIONS

Our findings indicate that low temperature-related chronic kidney damage should be of immediate public health concern. Impact of NO₂ exposure on the risk of CKD-related hospital visits may increase under the low temperature, which suggests the need for NO₂ exposure mitigation strategies in the context of climate change and an enhanced understanding of the mechanisms underlying the temperature variance of air pollution effect to help reduce the magnitude of the CKD burden on the healthcare systems.

Relationships between short-term ambient temperature exposure and kidney disease hospitalizations in the warm season in Vietnam: A case-crossover study

BACKGROUND

Under a warming climate, adverse health effects of heat are an increasing concern. We evaluated associations between short-term ambient temperature exposure and hospital admission for kidney disease in Vietnam.

METHODS

We linked province-level meteorologic data with admission data from 14 province-level hospitals (2003-2015). We used a case-crossover design to evaluate associations between daily ambient temperature metrics (mean, maximum, and minimum temperature and mean heat index) and risk of hospitalization for four kidney disease subtypes: glomerular diseases, renal tubulo-interstitial diseases, chronic kidney disease, and urolithiasis, including lagged (≤lag 14 days) and cumulative (≤lag 0-6 days) associations, during the warm season. We also evaluated independent associations with extreme heat days (defined as days with daily maximum temperature >95^th percentile of the provincial daily maximum temperature distribution). Akaike's information criterion and patterns of risk estimates across cumulative exposure time windows and single-day lags informed our selection of final models.

RESULTS

We included 58,330 hospital admissions during the warm season. Daily mean temperature averaged over the same day and the previous six days (lag 0-6 days) was associated with risk of hospitalization for each kidney disease outcome with odds ratios (per 1 °C increase in daily mean temperature) of 1.07 (95% confidence interval [CI]: 0.99, 1.16) for glomerular diseases, 1.06 (95% CI: 0.96, 1.17) for renal tubulo-interstitial diseases, 1.12 (95% CI: 1.00, 1.24) for chronic kidney disease, and 1.09 (95% CI: 1.02, 1.16) for urolithiasis. We found no additional independent associations with extreme heat. Results for the four temperature metrics were similar.

CONCLUSIONS

High ambient temperature was associated with increased risk of hospitalization for each kidney disease subtype, with the most convincing associations for chronic kidney disease and urolithiasis. Further laboratory and epidemiologic research is needed to confirm the findings and disentangle the underlying mechanisms.

THIRSTY FOR FRUCTOSE: Arginine Vasopressin, Fructose, and the Pathogenesis of Metabolic and Renal Disease

We review the pathways by which arginine vasopressin (AVP) and hydration influence the sequelae of the metabolic syndrome induced by high fructose consumption. AVP and inadequate hydration have been shown to worsen the severity of two phenotypes associated with metabolic syndrome induced by high fructose intake-enhanced lipogenesis and insulin resistance. These findings have implications for those who frequently consume sweeteners such as high fructose corn syrup (HFCS). Patients with metabolic syndrome are at higher risk for microalbuminuria and/or chronic kidney disease; however, it is difficult to discriminate the detrimental renal effects of the metabolic syndrome from those of hypertension, impaired glucose metabolism, and obesity. It is not surprising the prevalence of chronic renal insufficiency is growing hand in hand with obesity, insulin resistance, and metabolic syndrome in those who consume large amounts of fructose. Higher AVP levels and low hydration status worsen the renal insufficiency found in patients with metabolic syndrome. This inter-relationship has public health consequences, especially among underserved populations who perform physical labor in environments that place them at risk for dehydration. MesoAmerican endemic nephropathy is a type of chronic kidney disease highly prevalent in hot ambient climates from southwest Mexico through Latin America. There is growing evidence that this public health crisis is being spurred by greater fructose consumption in the face of dehydration and increased dehydration-dependent vasopressin secretion. Work is needed at unraveling the mechanism(s) by which fructose consumption and increased AVP levels can worsen the renal disease associated with components of the metabolic syndrome.

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.

Ambient temperature, humidity, and urinary system diseases: a population-based study in Western China

Climate has received an increasing attention due to its adverse effects on human health, but the effects on the urinary system are still short of enough evidence. Therefore, we carry out this study to analyze the relationship between meteorological factors and urinary system health in arid areas of western China. In this study, the daily numbers of outpatients with the urinary system diseases from multiple hospitals in three cities in Gansu province (Lanzhou, Zhangye, and Tianshui city) were collected and used for analysis. The distributed lag non-linear models (DLNM) with a quasi-Poisson distribution were used to estimate the associations between meteorological factors and daily outpatients for urinary system diseases in these three cities, and then a multivariate meta-analysis was applied to pool the estimates of city-specific effects. We found that the ambient temperature (AT) and relative humidity (RH) were significantly associated with the outpatient visits of urinary system diseases. The effects of meteorological factors on outpatients with urinary system diseases for both males and females were statistically significant at different lag days. The higher AT and lower RH were associated with the higher risk of urinary system diseases. We also observed substantial lag effects of meteorological factors on outpatients for both males and females. Among all disease types, renal tubule-interstitial diseases had the strongest relationships with meteorological factors. Our results indicate that the higher AT and lower RH may increase the outpatient visits for urinary system diseases, with significant lag effects in semi-arid areas.

Hyponatraemia in heart failure: time for new solutions?

Hyponatraemia is very common in heart failure (HF), especially in decompensated patients. It is associated with increased mortality and morbidity and considered a marker of advanced disease. Recognition of hyponatraemia and its causes may help guide treatment strategy. Historically, therapy has primarily focused on water restriction, decongestion with loop diuretics in case of volume overload (dilutional hyponatraemia) and sodium repletion in case of depletion. In this review, we summarise the potential benefits of established and emerging HF therapies on sodium homeostasis, with a focus on dual vasopressin antagonists, angiotensin receptor-neprilysin inhibitors, sodium-glucose cotransporter 2 inhibitors and hypertonic saline, and propose a potential therapeutic approach for hyponatraemia in HF.

Hemodynamic phenotyping of transgenic rats with ubiquitous expression of an angiotensin-(1-7)-producing fusion protein

Activation of the angiotensin (Ang)-converting enzyme (ACE) 2/Ang-(1-7)/MAS receptor pathway of the renin-angiotensin system (RAS) induces protective mechanisms in different diseases. Herein, we describe the cardiovascular phenotype of a new transgenic rat line (TG7371) that expresses an Ang-(1-7)-producing fusion protein. The transgene-specific mRNA and the corresponding protein were shown to be present in all evaluated tissues of TG7371 with the highest expression in aorta and brain. Plasma Ang-(1-7) levels, measured by radioimmunoassay (RIA) were similar to control Sprague-Dawley (SD) rats, however high Ang-(1-7) levels were found in the hypothalamus. TG7371 showed lower baseline mean arterial pressure (MAP), assessed in conscious or anesthetized rats by telemetry or short-term recordings, associated with increased plasma atrial natriuretic peptide (ANP) and higher urinary sodium concentration. Moreover, evaluation of regional blood flow and hemodynamic parameters with fluorescent microspheres showed a significant increase in blood flow in different tissues (kidneys, mesentery, muscle, spleen, brown fat, heart and skin), with a resulting decrease in total peripheral resistance (TPR). TG7371 rats, on the other hand, also presented increased cardiac and global sympathetic tone, increased plasma vasopressin (AVP) levels and decreased free water clearance. Altogether, our data show that expression of an Ang-(1-7)-producing fusion protein induced a hypotensive phenotype due to widespread vasodilation and consequent fall in peripheral resistance. This phenotype was associated with an increase in ANP together with an increase in AVP and sympathetic drive, which did not fully compensate the lower blood pressure (BP). Here we present the hemodynamic impact of long-term increase in tissue expression of an Ang-(1-7)-fusion protein and provide a new tool to investigate this peptide in different pathophysiological conditions.

Physiological and Pathological Roles of Aldose Reductase

Aldose reductase (AR) is an aldo-keto reductase that catalyzes the first step in the polyol pathway which converts glucose to sorbitol. Under normal glucose homeostasis the pathway represents a minor route of glucose metabolism that operates in parallel with glycolysis. However, during hyperglycemia the flux of glucose via the polyol pathway increases significantly, leading to excessive formation of sorbitol. The polyol pathway-driven accumulation of osmotically active sorbitol has been implicated in the development of secondary diabetic complications such as retinopathy, nephropathy, and neuropathy. Based on the notion that inhibition of AR could prevent these complications a range of AR inhibitors have been developed and tested; however, their clinical efficacy has been found to be marginal at best. Moreover, recent work has shown that AR participates in the detoxification of aldehydes that are derived from lipid peroxidation and their glutathione conjugates. Although in some contexts this antioxidant function of AR helps protect against tissue injury and dysfunction, the metabolic transformation of the glutathione conjugates of lipid peroxidation-derived aldehydes could also lead to the generation of reactive metabolites that can stimulate mitogenic or inflammatory signaling events. Thus, inhibition of AR could have both salutary and injurious outcomes. Nevertheless, accumulating evidence suggests that inhibition of AR could modify the effects of cardiovascular disease, asthma, neuropathy, sepsis, and cancer; therefore, additional work is required to selectively target AR inhibitors to specific disease states. Despite past challenges, we opine that a more gainful consideration of therapeutic modulation of AR activity awaits clearer identification of the specific role(s) of the AR enzyme in health and disease.

Climate change and nephrology

Climate change should be of special concern for the nephrologist, as the kidney has a critical role in protecting the host from dehydration, but it is also a favorite target of heat stress and dehydration. Here we discuss how rising temperatures and extreme heat events may affect the kidney. The most severe presentation of heat stress is heat stroke, which can result in severe electrolyte disturbance and both acute and chronic kidney disease (CKD). However, lesser levels of heat stress also have multiple effects, including exacerbating kidney disease and precipitating cardiovascular events in subjects with established kidney disease. Heat stress can also increase the risk for kidney stones, cause multiple electrolyte abnormalities and induce both acute and chronic kidney disease. Recently there have been multiple epidemics of CKD of uncertain etiology in various regions of the world, including Mesoamerica, Sri Lanka, India and Thailand. There is increasing evidence that climate change and heat stress may play a contributory role in these conditions, although other causes, including toxins, could also be involved. As climate change worsens, the nephrologist should prepare for an increase in diseases associated with heat stress and dehydration.

The Speed of Ingestion of a Sugary Beverage Has an Effect on the Acute Metabolic Response to Fructose

BACKGROUND

The consumption of sweetened beverages is associated with increased risk of metabolic syndrome, cardiovascular disease, and type 2 diabetes mellitus.

OBJECTIVE

We hypothesized that the metabolic effects of fructose in sugary beverages might be modulated by the speed of ingestion in addition to the overall amount.

DESIGN

Thirty healthy subjects free of any disease and medication were recruited into two groups. After overnight fasting, subjects in group 1 drank 500 mL of apple juice over an hour by drinking 125 mL every 15 min, while subjects in group 2 drank 500 mL of apple juice over 5 min. Blood samples were collected at time zero and 15, 30, 60, and 120 min after ingestion to be analyzed for serum glucose, insulin, homeostatic model assessment (HOMA-IR) score, fibroblast growth factor 21, copeptin, osmolarity, sodium, blood urea nitrogen (BUN), lactate, uric acid, and phosphate levels.

RESULTS

Serum glucose, insulin, HOMA-IR, fibroblast growth factor 21, copeptin, osmolarity, sodium, BUN, and lactate levels increased following apple juice ingestion. The increases were greater in the fast-drinking group, which were more significant after 15 min and 30 min compared to baseline. The changes in uric acid were not statistically different between the groups. Phosphate levels significantly increased only in the fast-drinking group.

CONCLUSION

Fast ingestion of 100% apple juice causes a significantly greater metabolic response, which may be associated with negative long-term outcomes. Our findings suggest that the rate of ingestion must be considered when evaluating the metabolic impacts of sweetened beverage consumption.

Fructose and Uric Acid as Drivers of a Hyperactive Foraging Response: A Clue to Behavioral Disorders Associated with Impulsivity or Mania?

Several behavioral disorders, including attention deficit hyperactivity disorder (ADHD), bipolar disorder, and aggressive behaviors are linked with sugar intake and obesity. The reason(s) for this association has been unclear. Here we present a hypothesis supporting a role for fructose, a component of sugar and high fructose corn syrup (HFCS), and uric acid (a fructose metabolite), in increasing the risk for these behavioral disorders. Recent studies have shown that the reason fructose intake is strongly associated with development of metabolic syndrome is that fructose intake activates an evolutionary-based survival pathway that stimulates foraging behavior and the storage of energy as fat. While modest intake may aid animals that would like to store fat as a protective response from food shortage or starvation, we propose that high intake of sugar and HFCS causes a hyperactive foraging response that stimulates craving, impulsivity, risk taking and aggression that increases the risk for ADHD, bipolar disease and aggressive behavior. High glycemic carbohydrates and salty foods may also contribute as they can be converted to fructose in the body. Some studies suggest uric acid produced during fructose metabolism may mediate some of these effects. Chronic stimulation of the pathway could lead to desensitization of hedonic responses and induce depression. In conclusion, a hyperactive foraging response driven by high glycemic carbohydrates and sugars may contribute to affective disorders.

Osthol Ameliorates Kidney Damage and Metabolic Syndrome Induced by a High-Fat/High-Sugar Diet

Excessive intake of fructose results in metabolic syndrome (MS) and kidney damage, partly mediated by its metabolism by fructokinase-C or ketohexokinase-C (KHK-C). Osthol has antioxidant properties, is capable of regulating adipogenesis, and inhibits KHK-C activity. Here, we examined the potential protective role of osthol in the development of kidney disease induced by a Western (high-fat/high-sugar) diet. Control rats fed with a high-fat/high-sugar diet were compared with two groups that also received two different doses of osthol (30 mg/kg/d or 40 mg/kg/d body weight BW). A fourth group served as a normal control and received regular chow. At the end of the follow-up, kidney function, metabolic markers, oxidative stress, and lipogenic enzymes were evaluated. The Western diet induced MS (hypertension, hyperglycemia, hypertriglyceridemia, obesity, hyperuricemia), a fall in the glomerular filtration rate, renal tubular damage, and increased oxidative stress in the kidney cortex, with increased expression of lipogenic enzymes and increased kidney KHK expression. Osthol treatment prevented the development of MS and ameliorated kidney damage by inhibiting KHK activity, preventing oxidative stress via nuclear factor erythroid 2-related factor (Nrf2) activation, and reducing renal lipotoxicity. These data suggest that the nutraceutical osthol might be an ancillary therapy to slow the progression of MS and kidney damage induced by a Western diet.

Vasopressin and copeptin release during sepsis and septic shock

Sepsis is defined as a potentially fatal organ dysfunction caused by a dysregulated host response to infection. Despite tremendous progress in the medical sciences, sepsis remains one of the leading causes of morbidity and mortality worldwide. The host response to sepsis and septic shock involves changes in the immune, autonomic, and neuroendocrine systems. Regarding neuroendocrine changes, studies show an increase in plasma vasopressin (AVP) concentrations followed by a decline, which may be correlated with septic shock. AVP is a peptide hormone derived from a larger precursor (preprohormone), along with two peptides, neurophysin II and copeptin. AVP is synthesized in the hypothalamus, stored and released from the neurohypophysis into the bloodstream by a wide range of stimuli. The measurement of AVP has limitations due to its plasma instability and short half-life. Copeptin is a more stable peptide than AVP, and its immunoassay is feasible. The blood concentrations of copeptin mirror those of AVP in many physiological states; paradoxically, during sepsis-related organ dysfunction, an uncoupling between copeptin and AVP blood levels appears to happen. In this review, we focus on clinical and experimental studies that analyzed AVP and copeptin blood concentrations over time in sepsis. The findings suggest that AVP and copeptin behave similarly in the early stages of sepsis; however, we did not find a proportional decrease in copeptin concentrations as seen with AVP during septic shock. Copeptin levels were higher in nonsurvivors than in survivors, suggesting that copeptin may work as a marker of severity or sepsis-related organ dysfunction.

Fluid Intake Restriction Concomitant to Sweetened Beverages Hydration Induce Kidney Damage

Currently, there is the paradox of low water intake but increased intake of sugar-sweetened beverages (SB) in several populations; those habits are associated with an increased prevalence of metabolic derangements and greater chronic disease mortality. Persistent heat dehydration and increased SB intake stimulate the continued release of vasopressin and overactivation of the polyol-fructokinase pathway, synergizing each other, an effect partially mediated by oxidative stress. The objective of the present study was to evaluate whether water restriction concurrent with SB hydration can cause renal damage by stimulating similar pathways as heat dehydration. Three groups of male Wistar rats (n = 6) were fluid restricted; from 10 am to 12 pm animals could rehydrate with tap water (W), or sweetened beverages, one prepared with 11% of a fructose-glucose combination (SB), or with the noncaloric edulcorant stevia (ST). A normal control group of healthy rats was also studied. The animals were followed for 4 weeks. Markers of dehydration and renal damage were evaluated at the end of the study. Fluid restriction and water hydration mildly increased urine osmolality and induced a 15% fall in CrCl while increased the markers of tubular damage by NAG and KIM-1. Such changes were in association with a mild overexpression of V1a and V2 renal receptors, polyol fructokinase pathway overactivation, and increased renal oxidative stress with reduced expression of antioxidant enzymes. Hydration with SB significantly amplified those alterations, while in stevia hydrated rats, the changes were similar to the ones observed in water hydrated rats. These data suggest that current habits of hydration could be a risk factor in developing kidney damage.

Restricted Water Intake and Hydration with Fructose-Containing Beverages during Infancy Predispose to Aggravate an Acute Renal Ischemic Insult in Adolescent Rats

We aimed to investigate the effects of chronic fluid restriction and hydration with a sweetened beverage (SB) in rats from weaning until adolescence, in a posterior acute kidney injury (AKI) event induced by ischemia-reperfusion (I/R). We followed 5 groups of weaning rats: control group (C); two groups with 22 h/day fluid restriction, a group hydrated for two hours with water (-W) and a group hydrated with SB; one group receiving SB ad libitum all day (+SB); and one group in which water consumption was increased using a gel diet. The rats that reached adolescence were submitted to I/R. Fluid restriction and/or SB hydration induced mild renal alterations that were significantly accentuated in the -SB group and resulted in worse outcomes after I/R-induced AKI that resulted in a catastrophic fall in creatinine clearance and diffuse acute tubular necrosis. In summary, low tap water intakes, as well as SB intake in infancy, prompt kidney worse outcomes in a later event of AKI during adolescence and both insults magnify kidney damage. Studies on hydration habits in children are recommended to disclose the potentially harmful effects that those behavioral patterns might carry to future renal health.

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.

Cerebral Fructose Metabolism as a Potential Mechanism Driving Alzheimer's Disease

The loss of cognitive function in Alzheimer's disease is pathologically linked with neurofibrillary tangles, amyloid deposition, and loss of neuronal communication. Cerebral insulin resistance and mitochondrial dysfunction have emerged as important contributors to pathogenesis supporting our hypothesis that cerebral fructose metabolism is a key initiating pathway for Alzheimer's disease. Fructose is unique among nutrients because it activates a survival pathway to protect animals from starvation by lowering energy in cells in association with adenosine monophosphate degradation to uric acid. The fall in energy from fructose metabolism stimulates foraging and food intake while reducing energy and oxygen needs by decreasing mitochondrial function, stimulating glycolysis, and inducing insulin resistance. When fructose metabolism is overactivated systemically, such as from excessive fructose intake, this can lead to obesity and diabetes. Herein, we present evidence that Alzheimer's disease may be driven by overactivation of cerebral fructose metabolism, in which the source of fructose is largely from endogenous production in the brain. Thus, the reduction in mitochondrial energy production is hampered by neuronal glycolysis that is inadequate, resulting in progressive loss of cerebral energy levels required for neurons to remain functional and viable. In essence, we propose that Alzheimer's disease is a modern disease driven by changes in dietary lifestyle in which fructose can disrupt cerebral metabolism and neuronal function. Inhibition of intracerebral fructose metabolism could provide a novel way to prevent and treat this disease.

Impact of passive heat acclimation on markers of kidney function during heat stress

NEW FINDINGS

What is the central question of this study? Does passive heat acclimation alter glomerular filtration rate and urine-concentrating ability in response to passive heat stress? What is the main finding and its importance? Glomerular filtration rate remained unchanged after passive heat stress, and heat acclimation did not alter this response. However, heat acclimation mitigated the reduction in urine-concentrating ability and reduced the incidence of albuminuria in young healthy adults after passive heat stress. Collectively, these results suggest that passive heat acclimation might improve structural integrity and reduce glomerular permeability during passive heat stress.

ABSTRACT

Little is known about the effect of heat acclimation on kidney function during heat stress. The purpose of this study was to determine the impact of passive heat stress and subsequent passive heat acclimation on markers of kidney function. Twelve healthy adults (seven men and five women; 26 ± 5 years of age; 72.7 ± 8.6 kg; 172.4 ± 7.5 cm) underwent passive heat stress before and after a 7 day controlled hyperthermia heat acclimation protocol. The impact of passive heat exposure on urine and serum markers of kidney function was evaluated before and after heat acclimation. Glomerular filtration rate, determined from creatinine clearance, was unchanged with passive heat stress before (pre, 133 ± 41 ml min^-1 ; post, 127 ± 51 ml min^-1 ; P = 0.99) and after (pre, 129 ± 46 ml min^-1 ; post, 130 ± 36 ml min^-1 ; P = 0.99) heat acclimation. The urine-to-serum osmolality ratio was reduced after passive heating (P < 0.01), but heat acclimation did not alter this response. In comparison to baseline, free water clearance was greater after passive heating before (pre, -0.86 ± 0.67 ml min^-1 ; post, 0.40 ± 1.01 ml min^-1 ; P < 0.01) but not after (pre, -0.16 ± 0.57 ml min^-1 ; post, 0.76 ± 1.2 ml min^-1 ; P = 0.11) heat acclimation. Furthermore, passive heating increased the fractional excretion rate of potassium (P < 0.03) but not sodium (P = 0.13) or chloride (P = 0.20). Lastly, heat acclimation reduced the fractional incidence of albuminuria after passive heating (before, 58 ± 51%; after, 8 ± 29%; P = 0.03). Collectively, these results demonstrate that passive heat stress does not alter the glomerular filtration rate. However, heat acclimation might improve urine-concentrating ability and filtration within the glomerulus.

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.

Tolvaptan add-on therapy in patients with acute heart failure: A systematic review and meta-analysis

This study aimed to investigate the short-term efficacy and safety of tolvaptan as an add-on to traditional diuretics in patients with acute heart failure (AHF). The PubMed, EMBASE, Cochrane Library, and Web of Science databases were comprehensively searched for all randomized controlled trials (RCTs) that examined AHF patients treated with tolvaptan as a combination therapy with traditional diuretics published on or before December 2, 2019. Efficacy indicators such as improved dyspnea, reduced edema, and changes in urine output and body weight were evaluated. In-hospital mortality and worsening renal function (WRF) were measured as safety indicators. Data from the published literature included in this study were independently extracted by two reviewers. The Cochrane risk of bias tool was used to evaluate the quality of the included RCTs. Twelve RCTs involving 5577 patients admitted for AHF were included. Compared with traditional diuretics alone, add-on tolvaptan significantly relieved dyspnea, reduced weight, increased total urine volume and changes in urine volume from baseline, reduced edema, and increased serum sodium concentration in the short term without increasing the mortality. Most importantly, a low dose of tolvaptan (7.5-15 mg/d) significantly reduced the incidence of WRF, while a high dose (30 mg/d) had the opposite effect. Short-term add-on tolvaptan in hospitalized AHF patients could significantly relieve shortness of breath, reduce body weight, improve edema, and increase urine output and serum sodium concentrations without increasing mortality. The protective effects of add-on tolvaptan against WRF, however, were observed at low doses, but not at high doses.

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.

Fructose metabolism as a common evolutionary pathway of survival associated with climate change, food shortage and droughts

Mass extinctions occur frequently in natural history. While studies of animals that became extinct can be informative, it is the survivors that provide clues for mechanisms of adaptation when conditions are adverse. Here, we describe a survival pathway used by many species as a means for providing adequate fuel and water, while also providing protection from a decrease in oxygen availability. Fructose, whether supplied in the diet (primarily fruits and honey), or endogenously (via activation of the polyol pathway), preferentially shifts the organism towards the storing of fuel (fat, glycogen) that can be used to provide energy and water at a later date. Fructose causes sodium retention and raises blood pressure and likely helped survival in the setting of dehydration or salt deprivation. By shifting energy production from the mitochondria to glycolysis, fructose reduced oxygen demands to aid survival in situations where oxygen availability is low. The actions of fructose are driven in part by vasopressin and the generation of uric acid. Twice in history, mutations occurred during periods of mass extinction that enhanced the activity of fructose to generate fat, with the first being a mutation in vitamin C metabolism during the Cretaceous-Paleogene extinction (65 million years ago) and the second being a mutation in uricase that occurred during the Middle Miocene disruption (12-14 million years ago). Today, the excessive intake of fructose due to the availability of refined sugar and high-fructose corn syrup is driving 'burden of life style' diseases, including obesity, diabetes and high blood pressure.

18α-Glycyrrhetinic acid (GA) ameliorates fructose-induced nephropathy in mice by suppressing oxidative stress, dyslipidemia and inflammation

Excessive fructose (FRU) intake can result in insulin resistance and metabolic disorder, which are related to renal injury.18α-Glycyrrhetinic acid (GA) is a bioactive component mainly extracted from Glycyrrhiza radix, and has anti-oxidant and anti-inflammatory activities. However, its effects on FRU-induced renal injury still remain unclear. In this study, we found that 18α-GA treatments could significantly ameliorate the cell viability in FRU-treated tubule epithelial cells, accompanied with improved mitochondrial membrane potential. Furthermore, reactive oxygen species (ROS) accumulation in FRU-stimulated cells was markedly reduced by 18α-GA, which were associated with the activation of nuclear factor (erythroid-derived-2)-like 2 (Nrf-2) and the blockage of MAPKs signaling. Additionally, dyslipidemia detected in FRU-treated cells was greatly inhibited by 18α-GA. We also found that 18α-GA significantly ameliorated FRU-induced inflammation in cells through reducing the expression of pro-inflammatory cytokines and chemokine. The anti-inflammatory effects regulated by 18α-GA were mainly related to the repression of nuclear factor-κB(NF-κB) signaling. Furthermore, the protective effects of 18α-GA against ROS production, lipid accumulation and inflammation were verified in renal tissues from FRU-challenged mice, consequently improving metabolic disorder and kidney injury. Taken together, these findings demonstrated that 18α-GA exerted renal protective effects through reducing oxidative stress, lipid deposition and inflammatory response, and thus could be considered as a promising therapeutic strategy for metabolic stress-induced kidney injury.

Meal Frequency and Skipping Breakfast Are Associated with Chronic Kidney Disease

Chronic underhydration and malnutrition can be associated with irreversible renal damage. This study investigated the association of meal frequency and breakfast skipping with chronic kidney disease (CKD) in South Korea. Participants (4370 participants from the Korean National Health and Nutrition Examination Survey VI 2013-2014) were divided into two groups based on meal frequency: ≥ 15 or < 15 meals/week. They were further divided into four groups based on the frequency of breakfast, lunch, and dinner consumed in the previous year. The data were analyzed with complex samples logistic regression. We found that 9.6% of the participants (n = 412) had CKD, which was associated with gender, body mass index, serum fasting glucose, daily calorie intake, hypertension, diabetes, and cerebrovascular accident. Participants consuming <15 meals/week had a higher risk of CKD than those who consumed ≥15 meals/week (adjusted odds ratio [OR] 1.531, 95% confidence interval [CI] 1.209-1.938). Participants who rarely had breakfast showed a higher risk of CKD than those who had breakfast 5-7 times/week (adjusted OR 1.572, 95% CI 1.108-2.231). Our findings suggest that <15 meals/week or skipping breakfast is associated with a higher risk of CKD in the general South Korean population, especially for men or persons aged 42-64 years.

A Role for Both V1a and V2 Receptors in Renal Heat Stress Injury Amplified by Rehydration with Fructose

Chronic vasopressin secretion induced by recurrent mild heat stress exposure is significantly enhanced by limited rehydration with a fructose-containing beverage both in rodents and in humans. Moreover, this effect has been associated with upregulation of the polyol–fructokinase pathway and increased renal oxidative stress. Previously, we have shown that pharmacological inhibition of both V1a and V2 vasopressin receptors with conivaptan improved such renal alterations. The aim of this study was to evaluate the independent contributions of V1a and V2 receptors to the renal damage caused by mild heat stress and limited rehydration with a fructose-containing beverage. Osmotic minipumps were used to deliver either relcovaptan (0.64 mg/day) or tolvaptan (0.25 mg/day) in male Wistar rats for two weeks. Corresponding dilution vehicles were used as controls. To induce dehydration, rats were exposed to mild heat stress (37 °C for 1 h, Monday to Friday). All groups received a 10% fructose solution as a rehydration fluid for 2 h after mild heat stress. For the remainder of the day and on weekends, rats received tap water. The independent blockade of either the V1a or the V2 receptor prevented renal damage, reduced oxidative stress, and decreased plasma cortisol and systemic inflammation. However, the beneficial effects were regulated by different mechanisms. Tolvaptan inhibited polyol–fructokinase pathway overactivation, while relcovaptan prevented upregulation of the renin–angiotensin system and SGK1 expression. These data suggest that both V1a and V2 receptors participate in renal damage caused by heat stress-induced dehydration when fructose-containing beverages are used as rehydration fluids.

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.

Antioxidant supplements as a novel mean for blocking recurrent heat stress-induced kidney damage following rehydration with fructose-containing beverages

Recently repeated heat stress and dehydration have been reported to cause oxidative stress and kidney damage that is enhanced by rehydrating with fructose solutions. We hypothesized that antioxidants might provide a novel way to prevent kidney damage. To test this hypothesis, mild heat stress was induced by exposing rats to 37 °C during 1 h in a closed chamber. The supplementation with water-soluble antioxidants (Antiox), ascorbic acid 1% plus N-acetyl cysteine 600 mg/L was done either in the 10% fructose 2 h rehydration fluid immediately after heat stress (Fructose 10% + Antiox), and/or in the tap water (Water + Antiox) for the remainder of the day, or in both fluids. After 4 weeks, control rats exposed to heat with fructose rehydration developed impaired renal function, tubular injury, intrarenal oxidative stress, a reduction in Nrf2-Keap1 antioxidant pathway, stimulation of vasopressin and the intrarenal polyol-fructokinase pathway. In contrast, dosing the antioxidants in the tap water (i.e., before the heat exposure and rehydration with fructose) preserved renal function, prevented renal tubule dysfunction and avoided the increase in systemic blood pressure. These effects were likely due to the amplification of the antioxidant defenses through increased Nrf2 nuclear translocation stimulated by the antioxidants and by the prevention of polyol fructokinase pathway overactivation. More studies to understand the mechanisms implicated in this pathology are warranted as there is recent evidence that they may be operating in humans as well.

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.

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.

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.

Heat acclimatization blunts copeptin responses to hypertonicity from dehydrating exercise in humans

Acclimatization favors greater extracellular tonicity from lower sweat sodium, yet hyperosmolality may impair thermoregulation during heat stress. Enhanced secretion or action of vasopressin could mitigate this through increased free water retention. Aims were to determine responses of the vasopressin surrogate copeptin to dehydrating exercise and investigate its relationships with tonicity during short and long-term acclimatization. Twenty-three participants completed a structured exercise programme following arrival from a temperate to a hot climate. A Heat Tolerance Test (HTT) was conducted on Day-2, 6, 9 and 23, consisting of 60-min block-stepping at 50% VO2 peak, with no fluid intake. Resting sweat [Na+ ] was measured by iontophoresis. Changes in body mass (sweat loss), core temperature, heart rate, osmolality (serum and urine) and copeptin and aldosterone (plasma) were measured with each Test. From Day 2 to Day 23, sweat [Na+ ] decreased significantly (adjusted P < 0.05) and core temperature and heart rate fell. Over the same interval, HTT-associated excursions were increased for serum osmolality (5 [-1, 9] vs. 9 [5, 12] mosm·kg-1 ), did not differ for copeptin (9.6 [6.0, 15.0] vs. 7.9 [4.3, 14.7] pmol·L-1 ) and were reduced for aldosterone (602 [415, 946] vs. 347 [263, 537] pmol·L-1 ). Urine osmolality was unchanging and related consistently to copeptin at end-exercise, whereas the association between copeptin and serum osmolality was right-shifted (P = 0.0109) with acclimatization. Unchanging urine:serum osmolality argued against increased renal action of vasopressin. In conclusion, where exercise in the heat is performed without fluid replacement, heat acclimatization does not appear to enhance AVP-mediated free water retention in humans.

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.