Glomerular hemodynamics in severe obesity

Telmisartan attenuates diabetic nephropathy by suppressing oxidative stress in db/db mice

BACKGROUND/AIMS

Telmisartan, an angiotensin II type 1 receptor blocker, is widely used to treat hypertension and kidney diseases, including diabetic nephropathy, because of its renoprotective effects. However, the mechanism by which telmisartan prevents proteinuria and renal dysfunction in diabetic nephropathy is still unclear. In this study, we examined the effects of telmisartan against diabetic nephropathy in db/db mice.

METHODS

Telmisartan was administered at a dose of 5 mg/kg/day for 3 weeks to db/db (diabetic) and db/m (control) mice. Urinary albumin excretion, renal histology, and the gene expression of oxidative stress and inflammatory markers in renal tissue were determined. To evaluate the effects of telmisartan on reactive oxygen species (ROS) production, superoxide was detected by dihydroethidium (DHE) staining in vivo and in vitro.

RESULTS

Telmisartan reduced albuminuria, mesangial matrix expansion, macrophage infiltration, and the expression of ROS markers (NADPH oxidase 4- and 8-hydroxydeoxyguanosine) and inflammatory cytokines (monocyte chemoattractant protein-1, osteopontin, and transforming growth factor-β) in the kidney. DHE staining showed that telmisartan decreased ROS generation in the kidney and in cultured mesangial and proximal tubular epithelial cells.

CONCLUSIONS

Taken together, these findings indicate that telmisartan protects against diabetic nephropathy by reducing diabetes-induced oxidative stress.

Changes in renal function following Roux-en-Y gastric bypass: a prospective study

BACKGROUND

Studies of the impact of Roux-en-Y gastric bypass (RYGB) on renal function have shown mixed results. We constructed this prospective repeated-measures controlled study to characterize this response and identify the best method of gauging renal function in this setting.

METHODS

Clinical data, serum creatinine (SC), and 24-h urine were collected 1 week before and 6 months following RYGB. Glomerular filtration rate (GFR) was calculated utilizing the Modification of Diet in Renal Disease formula. Creatinine clearance (CCL) was measured as a 24-h collection (24 CCL) and calculated by the Cockcroft-Gault (CG) formula.

RESULTS

The study population of 37 patients (81% women) had a mean age of 47 ± 11 years, had mean BMI of 47.6 ± 6.3 kg/m(2), and achieved a mean % excess weight loss (EWL) of 60.9 ± 17.1%. SC decreased from 0.83 ± 0.21 mg/dl to 0.72 ± 0.16 mg/dl (p < 0.001) and mean GFR improved from 91.6 ± 29.7 ml/min/1.73 m(2) to 104.9 ± 23.5 ml/min/1.73 m(2) (p < 0.01). Preoperatively, CG significantly overestimated CCL when compared with 24 CCL (197.1 ± 88.2 ml/min vs. 136.5 ± 53.0 ml/min, p < 0.001). In all patients, improvement in 24 CCL correlated with EWL (r = 0.32) and %EWL (r = 0.16), and significantly correlated with decrease in BMI (r = 0.51, p < 0.005). In hypertensive patients, improvement in 24 CCL significantly correlated with EWL (r = 0.43, p < 0.05), %EWL (r = 0.40, p < 0.05), and decrease in BMI (r = 0.60, p < 0.001) and was negatively correlated with age (r = -0.45, p < 0.05).

CONCLUSIONS

This study demonstrates that renal function improves following RYGB and is best identified by change in GFR. Improvement in 24 CCL is correlated with the EWL success of the patient, especially hypertensive patients.

Clinical features and long-term renal outcomes of Japanese patients with obesity-related glomerulopathy

BACKGROUND

Studies have suggested that obesity-related glomerulopathy (ORG) is one of the important disease entities leading to end-stage renal disease. However, information is limited regarding the clinical features and renal outcomes of Japanese ORG patients.

METHODS

Among the patients whose renal biopsy was performed at our institute during the past 10 years, we identified 28 ORG patients. Among them, the renal prognosis of the 20 patients with more than 2 years of follow-up was further analyzed. The clinical features at biopsy and the renal outcomes were compared with those of other ORG cohorts.

RESULTS

The average values at diagnosis were a body mass index of 32.0 kg/m(2), eGFR of 65 ml/min/1.73 m(2), and urinary protein excretion of 1.7 g/day. These features were less serious than those of the US cohort or the Spanish cohort and were compatible with those of the Chinese cohort. At the last observation, seven patients (35%) showed a 50% increase in their serum creatinine, and two patients (10%) had a 100% increase in serum creatinine and/or end-stage renal disease (end point). A multivariate analysis identified the time-averaged proteinuria during follow-up as an independent factor that was associated with the slope of renal function. The annual rate of patients reaching the end point in the US cohort, the Spanish cohort and the current cohort were 6.7, 6.9 and 1.6% per year, respectively.

CONCLUSION

The long-term outcomes of Japanese ORG patients include progression to renal failure, emphasizing the importance of an accurate early diagnosis of this entity.

Advances in the surgical treatment of morbid obesity

Due to the rapidly expanding prevalence of obesity, bariatric surgery is becoming an increasingly popular treatment option. Bariatric surgeries including Roux-en-Y gastric bypass (RYGB) and vertical sleeve gastrectomy (VSG) produce long-term weight loss and metabolic improvement, reducing mortality. This review discusses the important benefits and risks of RYGB and VSG, highlighting hypothesized mechanisms for these effects. We present data suggesting that VSG, albeit a newer procedure, may be as effective as RYGB with fewer adverse effects including less surgical risk, reduced nutritional deficiency, and less incidence of dumping syndrome. This may position VSG as an increasingly important procedure, particularly for the treatment of pediatric obesity.

Transplantation in obese patient

Obesity is a worldwide epidemic leading to severe comorbidity that damages end-organ function. Overall transplant outcomes in this population are inferior to those in nonobese patients. Large population studies show decreased patient and graft survival in obese kidney transplant patients. Despite the poorer outcomes, kidney transplantation is considered because of the survival benefit as compared with the wait-listed dialysis patients. In liver transplantation, the benefit to transplantation as compared with remaining on the list is obvious, as there is no viable liver dialysis at this time. Obesity in potential organ donors impacts both medical and surgical issues. Obesity-related kidney disease affects both the remaining and transplanted kidney. Pancreas donor organs are associated with decreased early graft survival. Liver donor organs with significant steatosis lead to an increased risk for delayed or nonfunction of the organ. Immunosuppressive drugs with variable lipophilicity and altered volume of distribution can greatly affect the therapeutic usefulness of these drugs. Transplant candidates benefit from a multidisciplinary team approach to their care. As the epidemic progresses and less-invasive treatments for metabolic surgery evolve, we are likely to require more patients to lose weight prior to transplantation as we continue to strive for improved outcomes.

Pathophysiology of obesity-related renal dysfunction contributes to diabetic nephropathy

Recent studies have demonstrated the role of insulin resistance in renal injury related to obesity, with hyperfiltration leading to glomerulomegaly in a pattern similar to that found in diabetic nephropathy. Similarities in the histologic patterns of damage from obesity and diabetes point to overlapping mechanisms of injury. In this review, we will examine the hormonal mechanisms, signaling pathways and injury patterns in renal injury resulting from obesity and attempt to draw conclusions on the reasons for these similarities.

The effect of weight loss in obesity and chronic kidney disease

Several epidemiologic investigations have confirmed that obesity is a significant risk factor for the appearance of proteinuria and end-stage kidney disease in a normal population. Weight loss induced by low-calorie diets, physical exercise, or bariatric surgery is accompanied by an important antiproteinuric effect. Reduction in proteinuria is already observed after a few weeks from the onset of weight loss and it is evident even in patients with modest weight losses. Reduction in proteinuria by weight loss has been described in chronic proteinuric nephropathies of different etiologies. The mechanisms through which weight loss may reverse proteinuria are likely to be plural: better control of blood pressure, improvement of serum lipid profile, improvement of insulin sensitivity, better glycemic control in diabetes patients, decrease of circulating leptin levels, reversal of glomerular hyperfiltration, and decreased activation of the renin-angiotensin-aldosterone system.

The link between the renin-angiotensin-aldosterone system and renal injury in obesity and the metabolic syndrome

Obesity is a risk factor for type 2 diabetes mellitus (DM) and is associated with chronic kidney disease. Activation of the renin-angiotensin-aldosterone system (RAAS) is common in obesity. The RAAS is an important mediator of hypertension. Mechanisms involved in activation of the RAAS in obesity include sympathetic stimulation, synthesis of adipokines in the RAAS by visceral fat, and hemodynamic alterations. The RAAS is known for its role in regulating blood pressure and fluid and electrolyte homeostasis. The role of local/tissue RAAS in specific tissues has been a focus of research. Urinary angiotensinogen (UAGT) provides a specific index of the intrarenal RAAS. Investigators have demonstrated that sex steroids can modulate the expression and activity of the different components of the intrarenal RAAS and other tissues. Our data suggest that obese women without DM and hypertension have significantly higher levels of UAGT than their male counterparts. These differences existed without any background difference in the ratio of microalbumin to creatinine in the urine or the estimated glomerular filtration rate, raising a question about the importance of baseline gender differences in the endogenous RAAS in the clinical spectrum of cardiovascular diseases and the potential utility of UAGT as a marker of the intrarenal RAAS. Animal studies have demonstrated that modifying the amount of angiotensin, the biologically active component of the RAAS, directly influences body weight and adiposity. This article reviews the role of the RAAS in renal injury seen in obesity and the metabolic syndrome.

Comparative effects of low-carbohydrate high-protein versus low-fat diets on the kidney

BACKGROUND AND OBJECTIVES

Concerns exist about deleterious renal effects of low-carbohydrate high-protein weight loss diets. This issue was addressed in a secondary analysis of a parallel randomized, controlled long-term trial.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

Between 2003 and 2007, 307 obese adults without serious medical illnesses at three United States academic centers were randomly assigned to a low-carbohydrate high-protein or a low-fat weight-loss diet for 24 months. Main outcomes included renal filtration (GFR) indices (serum creatinine, cystatin C, creatinine clearance); 24-hour urinary volume; albumin; calcium excretion; and serum solutes at 3, 12, and 24 months.

RESULTS

Compared with the low-fat diet, low-carbohydrate high-protein consumption was associated with minor reductions in serum creatinine (relative difference, -4.2%) and cystatin C (-8.4%) at 3 months and relative increases in creatinine clearance at 3 (15.8 ml/min) and 12 (20.8 ml/min) months; serum urea at 3 (14.4%), 12 (9.0%), and 24 (8.2%) months; and 24-hour urinary volume at 12 (438 ml) and 24 (268 ml) months. Urinary calcium excretion increased at 3 (36.1%) and 12 (35.7%) months without changes in bone density or clinical presentations of new kidney stones.

CONCLUSIONS

In healthy obese individuals, a low-carbohydrate high-protein weight-loss diet over 2 years was not associated with noticeably harmful effects on GFR, albuminuria, or fluid and electrolyte balance compared with a low-fat diet. Further follow-up is needed to determine even longer-term effects on kidney function.

Systolic Heart Function, Kidney Filtration and the Number of Coronary Atherosclerotic Plaques in Lean and Overweight Patients

The objective of this study was to quantify the number of vessels with stenotic points in the coronary circulation of lean and overweight individuals submitted to coronary angiography and ventriculography to verify the possible associations with glomerular filtration and the systolic ventricular function. Eighty-six patients with a previous history of myocardial ischemia were studied. Two groups were formed: non-elderly (G1), n = 38, 52.8 ± 1.2 years old, and elderly (G2), n = 48, 70.1 ± 1.2 years old. Both groups were divided into 2 subgroups according to the estimated glomerular filtration rate (eGFR): ≥60 and <60 ml/min/m(2). The results showed that G1 had 0.36 ± 0.11 versus 1.25 ± 0.45 stenoses/patient (≥60 vs. <60 ml/min/m(2); p < 0.05, respectively) and G2 had 0.91 ± 0.28 versus 1.83 ± 0.33 stenoses/patient (≥60 vs. <60 ml/min/m(2), respectively). The other variables, such as central and brachial arterial blood pressures, did not manifest significant differences in relation to the eGFR. The following significant correlations were observed: between the quantity of coronary stenotic points and the eGFR (R(2) = 11.2%; r = -0.33; p < 0.001), and between eGFR and the ventricular ejection fraction (R(2) = 5.1%; r = 0.57; p < 0.0001). The ejection fraction correlated significantly with the number of vessels with stenoses in the coronary bed (R(2) = 13.4%; r = -0.36; p < 0.008). In conclusion, although the correlations are considered weak, interrelationships between heart and kidney were demonstrated in this study.

Investigating potential mechanisms of obesity by metabolomics

Obesity is a serious health problem with an increased risk of several common diseases including diabetes, cardiovascular disease, and cancer. Metabolomics is an emerging analytical technique for systemic determination of metabolite profiles, which is useful for understanding the biochemical changes in obesity or related diseases both in individual organs and at the organism level. Increasingly, this technology has been applied to the study of obesity, complementing transcriptomics and/or proteomics analyses. Indeed, the alterations of metabolites in biofluids/tissues are direct indicators of variations in physiology or pathology. In this paper, we will examine the obesity-related alterations in significant metabolites that have been identified by metabolomics as well as their metabolic pathway associations. Issues concerning the screening of biologically significant metabolites related to obesity will also be discussed.

Inflammation and oxidative stress in obesity-related glomerulopathy

Obesity-related glomerulopathy is an increasing cause of end-stage renal disease. Obesity has been considered a state of chronic low-grade systemic inflammation and chronic oxidative stress. Augmented inflammation in adipose and kidney tissues promotes the progression of kidney damage in obesity. Adipose tissue, which is accumulated in obesity, is a key endocrine organ that produces multiple biologically active molecules, including leptin, adiponectin, resistin, that affect inflammation, and subsequent deregulation of cell function in renal glomeruli that leads to pathological changes. Oxidative stress is also associated with obesity-related renal diseases and may trigger the initiation or progression of renal damage in obesity. In this paper, we focus on inflammation and oxidative stress in the progression of obesity-related glomerulopathy and possible interventions to prevent kidney injury in obesity.

Application of a systems approach to the bottom-up assessment of pharmacokinetics in obese patients: expected variations in clearance

BACKGROUND AND OBJECTIVES

The maintenance dose of a drug is dependent on drug clearance, and thus any biochemical and physiological changes in obesity that affect parameters such as cardiac output, renal function, expression of drug-metabolizing enzymes and protein binding may result in altered clearance compared with that observed in normal-weight subjects (corrected or uncorrected for body weight). Because of the increasing worldwide incidence of obesity, there is a need for more information regarding the optimal dosing of drug therapy to be made available to prescribers. This is usually provided via clinical studies in obese people; however, such studies are not available for all drugs that might be used in obese subjects. Incorporation of the relevant physiological and biochemical changes into predictive bottom-up pharmacokinetic models in order to optimize dosage regimens may offer a logical way forward for the cases where no clinical data exist. The aims of the current report are to apply such a 'systems approach' to identify the likelihood of observing variations in the clearance of drugs in obesity and morbid obesity for a set of compounds for which clinical data, as well as the necessary in vitro information, are available, and to provide a framework for assessing other drugs in the future.

METHODS

The population-specific changes in demographic, physiological and biochemical parameters that are known to be relevant to obese and morbidly obese subjects were collated and incorporated into two separate population libraries. These libraries, together with mechanistic in vitro-in vivo extrapolations (IVIVE) within the Simcyp Population-based Simulator™, were used to predict the clearance of oral alprazolam, oral caffeine, oral chlorzoxazone, oral ciclosporin, intravenous and oral midazolam, intravenous phenytoin, oral theophylline and oral triazolam. The design of the simulated studies was matched as closely as possible with that of the clinical studies. Outcome was measured by the predicted ratio of the clearance of the drug in obese and lean subjects ± its 90% confidence interval, compared with observed values. The overall statistical measures of the performance of the model to detect differences in compound clearance between obese and lean populations were investigated by measuring sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV). A power calculation was carried out to investigate the impact of the sample size on the overall outcome of clinical studies.

RESULTS

The model was successful in predicting clearance in obese subjects, with the degree to which simulations could mimic the outcome of in vivo studies being greater than 60% for six of the eight drugs. A clear difference in the clearance of chlorzoxazone was correctly picked up via simulation. The overall statistical measures of the performance of the Simcyp Simulator were 100% sensitivity, 66% specificity, 60% PPV and 100% NPV. Studies designed on the basis of the ratio of the absolute values required substantial numbers of participants in order to detect a significant difference, except for phenytoin and chlorzoxazone, where the ratios of the weight-normalized clearances generally showed statistically significant differences with a smaller number of subjects.

CONCLUSION

Extension of a mechanistic predictive pharmacokinetic model to accommodate physiological and biochemical changes associated with obesity and morbid obesity allowed prediction of changes in drug clearance on the basis of in vitro data, with reasonable accuracy across a range of compounds that are metabolized by different enzymes. Prediction of the effects of obesity on drug clearance, normalized by various body size scalars, is of potential value in the design of clinical studies during drug development and in the introduction of dosage adjustments that are likely to be needed in clinical practice.

Low glomerular density with glomerulomegaly in obesity-related glomerulopathy

BACKGROUND AND OBJECTIVES

Obesity-related glomerulopathy is a secondary form of glomerular disease that may occur in obese individuals. It is histologically characterized by marked glomerulomegaly closely related to glomerular hyperfiltration. This study examined glomerular density (nonsclerotic glomerular number per renal cortical area of biopsy specimen) in patients with obesity-related glomerulopathy to determine whether any differences in this measure is associated with disease status.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Glomerular density and glomerular volume in renal biopsy samples from patients with obesity-related glomerulopathy were compared with those of kidney transplant donors and patients with IgA nephropathy. Kidneys obtained from persons without renal diseases during autopsy were also analyzed to investigate the effects of obesity on glomerular density and glomerular volume.

RESULTS

Glomerular density of kidneys from patients with obesity-related glomerulopathy (1.7±0.6/mm(2)) was significantly lower than that in biopsy samples from kidney transplant donors (3.1±1.0/mm(2)) and patients with IgA nephropathy (3.5±1.5/mm(2)). However, an analysis of autopsy cases without renal diseases showed that the glomerular density in overweight (2.9±0.7/mm(2)) or obese (3.1±1.1/mm(2)) persons was similar to that in nonobese (3.1±0.6/mm(2)) individuals. Biopsy specimens of patients with obesity-related glomerulopathy showed marked glomerulomegaly. However, glomerular volume was only modestly increased in the autopsy-examined kidneys from overweight or obese persons without renal diseases.

CONCLUSIONS

Low glomerular density associated with glomerulomegaly may be a characteristic histologic finding of patients with obesity-related glomerulopathy.

Comparative evaluation of the Cockcroft-Gault Equation and the Modification of Diet in Renal Disease (MDRD) study equation for drug dosing: an opinion of the Nephrology Practice and Research Network of the American College of Clinical Pharmacy

Accurate assessment of kidney function is an important component of determining appropriate drug dosing regimens. Nearly all manufacturer-recommended dosage adjustments are based on creatinine clearance ranges derived from clinical pharmacokinetic studies performed during the drug development process. The Cockcroft-Gault (CG) equation provides an estimate of creatinine clearance and is the equation most commonly used to determine drug dosages in patients with impaired kidney function. The Modification of Diet in Renal Disease (MDRD) study equation has also been proposed for this purpose. Published studies report that drug dosages determined by the two equations do not agree in 10-40% of cases. However, interpretation and comparison of these studies are complicated by the variable creatinine methods used for calculating CG and MDRD estimates, the patient populations studied, and a lack of outcomes data demonstrating the clinical significance of dosing discrepancies. Moreover, the impact of reporting standardized serum creatinine values on the accuracy of the CG equation and corresponding drug dosing regimens have been questioned. Currently, no prospective pharmacokinetic studies have been conducted with use of the MDRD equation to generate dosing recommendations, and limited data are available to support its use in some patient populations representing demographic extremes. Collectively, these issues have resulted in considerable confusion among clinicians and have fueled a healthy debate on whether or not to use the MDRD equation to determine drug dosages. Each of these issues is reviewed, and a proposed algorithm for using creatinine-based kidney function assessments in drug dosing is provided. Knowledge of the advantages, limitations, and clinical role of each equation will facilitate their safe and effective use in drug dosing.

Renal hyperfiltration related to diabetes mellitus and obesity in human disease

High intraglomerular pressure is associated with renal hyperfiltration, leading to the initiation and progression of kidney disease in experimental models of diabetes mellitus (DM). In humans, hyperfiltration is observed in patients with type 1 and type 2 DM, and is also seen in patients with pre-diabetic conditions, such as the metabolic syndrome. From a mechanistic perspective, both vascular and tubular factors likely contribute to the pathogenesis of hyperfiltration. Until now, human studies have primarily focused on the use of medications that inhibit the renin angiotensin system to reduce efferent vasoconstriction and thereby improve hyperfiltration. More recent advances in the development of investigational adenosine antagonists and inhibitors of sodium glucose co-transport may help to elucidate tubular factors that contribute to afferent vasodilatation. In this review, we summarize available data from experimental and human studies of type 1 and type 2 DM and obesity to provide an overview of factors that contribute to the hyperfiltration state. We have focused on the renin angiotensin system, cyclooxygenase-2 system, nitric oxide, protein kinase C and endothelin as vascular determinants of hyperfiltration. We also discuss relevant tubular factors, since experimental models have suggested that inhibition of sodium-glucose cotransport may be renoprotective.

Obesity-related glomerulopathy and podocyte injury: a mini review

Obesity-related glomerulopathy (ORG) is morphologically defined as focal segmental glomerulosclerosis and glomerulomegaly. Podocyte hypertrophy and reduced density are related to proteinuria which in a portion of patients is in the nephrotic range and evolvs towards renal failure. This article reviews the pathogenetic mechanisms of podocyte injury or dysfunction and lists new possible antiproteinuric strategies based on pharmaceutical targeting of the reported pathogenetic mechanisms. The pathogenetic mechnisms discussed include: renin angiotensin system, plasminogen activation inhibitor-1 (PAI-1), lipid metabolism, adiponectin, macrophages and proinflammatory cytokines, oxidative stress. The proposed antiproteinuric strategies include: AT2 receptor blockers; adipokine complement C19 TNF-related protein-1 blocker; selective PAI-1 inhibitor; farnesoid x receptor activation; increase of circulating adiponectin; selective antiinflammatory drugs; more potent antioxidants (Heme oxigenase, NOX4 inhibitors). However, because ORG is a rare disease, the need for a long term pharmaceutical approach in obese proteinuric patients should be carefully evaluated and limited to the cases with progressive loss of renal function.

IGF-1 levels link estimated glomerular filtration rate to insulin resistance in obesity: a study in obese, but metabolically healthy, subjects and obese, insulin-resistant subjects

BACKGROUND AND AIMS

Metabolically healthy but obese (MHO) subjects have a favourable cardio-metabolic risk profile, but whether they are also at lower risk for kidney dysfunction is still questionable.

METHODS AND RESULTS

A total of 106 MHO, 122 normal-weight and 212 insulin-resistant obese (IRO) subjects were stratified on the basis of their insulin sensitivity and body mass index (BMI). The CKD-EPI equation was used to estimate glomerular filtration rate (eGFR) and ISI index was used to estimate insulin sensitivity. eGFR was significantly lower in IRO as compared to MHO subjects after adjusting for age, gender and BMI (P = 0.008). In a logistic regression model adjusted for age, gender and BMI, IRO subjects showed an increased risk of having eGFR in the lowest quartile (odds ratio (OR) 1.91, 95% confidence interval (CI) 1.01-3.58; P = 0.04) as compared with MHO subjects. This association was maintained when waist, lean body mass, blood pressure, HDL cholesterol, triglyceride, fasting glucose and insulin levels were additionally included into the model (OR 2.49, 95%CI 1.17-5.27; P = 0.01), but its independence was not retained with further inclusion of insulin-like growth factor-1 (IGF-1) levels (OR 2.16, 95%CI 0.93-5.04; P = 0.07) No differences in eGFR were observed between non-obese and MHO individuals.

CONCLUSIONS

These results indicate that heterogeneity in obese phenotypes may account for conflicting evidence regarding the significance of obesity as a risk factor for chronic kidney disease. Our findings suggest that obesity is associated with lower kidney function only when insulin sensitivity is reduced, and that plasma IGF-1 is likely to be an important mechanism linking the IRO phenotype with reduced eGFR.

Blood cadmium and estimated glomerular filtration rate in Korean adults

BACKGROUND

Cadmium is a nephrotoxicant at high exposure levels. Few studies have evaluated the role of cadmium in kidney function at low-exposure levels.

OBJECTIVE

We evaluated the association of blood cadmium with estimated glomerular filtration rate (eGFR) in the Korean adult population.

METHODS

We evaluated 1,909 adults ≥ 20 years of age who participated in the 2005 Korean National Health and Nutrition Examination Survey and had blood cadmium determinations. eGFR was calculated using the Modification of Diet in Renal Disease equation.

RESULTS

Blood cadmium geometric means were 1.57 μg/L for men and 1.49 μg/L for women. The difference in eGFR levels that compared participants in the highest versus lowest cadmium tertiles, after multivariable adjustment, was -1.85 [95% confidence interval (CI): -3.55, -0.16] mL/min per 1.73 m2 in women and 0.67 (-1.16, 2.50) mL/min per 1.73 m2 in men. Among men, the association between blood cadmium and eGFR was modified by blood lead levels (p-value for interaction = 0.048). The fully adjusted differences in eGFR levels for a 2-fold increase in blood cadmium levels were -1.14 (-3.35, 1.07) and 1.84 (0.54, 3.14) mL/min per 1.73 m2 in men with blood lead levels below and above the median (2.75 μg/dL), respectively.

CONCLUSION

Elevated blood cadmium levels were associated with lower eGFR in women, which supports the role of cadmium as a risk factor for chronic kidney disease. In men, there was no overall association, although elevated blood cadmium levels were associated with higher eGFR levels in men with high blood lead levels and nonstatistically associated with lower eGFR levels in men with low blood lead levels.

The Cockcroft-Gault: a better predictor of renal function in an overweight and obese diabetic population

BACKGROUND

The performance of the Cockcroft-Gault (CG) equation, the Modification of Diet in Renal Disease (MDRD) formula, and the Chronic Kidney Disease Epidemiology Collaboration equation (CKD-EPI) was evaluated in body mass index (BMI) categories.

MATERIAL AND METHODS

In this retrospective cohort study in diabetic patients, creatinine clearance was measured by collecting 24-hour urines. Renal function was estimated using the CG, MDRD, and CKD-EPI. The performance of the equations was evaluated using correlation, Krippendorff's coefficient, bias, precision, and accuracy.

RESULTS

The bias of the MDRD and CKD-EPI increased from -13.9 ml/min/1.73 m(2) and -14.0 ml/min/1.73 m(2) (BMI < 25 kg/m(2)), respectively, to -31.7 ml/min/1.73 m(2) and -29.6 ml/min/1.73 m(2) (BMI > 30 kg/m(2)), respectively. Bias of the CG decreased from -13.4 ml/min (BMI < 25 kg/m(2)) to -3.2 ml/min (BMI > 30 kg/m(2)). With an accepted 30% dispersion, CG had the largest accuracy in the overweight and obese group (76.9 and 76.8%, respectively). The MDRD and CKD-EPI had an accuracy of 45.8 and 34.0% (overweight group), respectively,and 51.9 and 37.3% (obese group), respectively.

CONCLUSIONS

All renal function prediction equations are biased when used in overweight or obese diabetic populations with preserved renal function. The CG provides the best estimate of kidney function. The limitations of renal function prediction equations should be kept in mind when making clinical decisions.

Cigarette smoking and the association with glomerular hyperfiltration and proteinuria in healthy middle-aged men

BACKGROUND AND OBJECTIVES

Glomerular hyperfiltration and albuminuria accompanied by early-stage diabetic kidney disease predict future renal failure. Cigarette smoking has reported to be associated with elevated GFR in cross-sectional studies and with renal deterioration in longitudinal studies. The degree of glomerular hyperfiltration and proteinuria associated with smoking, which presumably is a phenomenon of early renal damage, has not been investigated in a satisfying manner so far.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This study included 10,118 Japanese men aged 40 to 55 years without proteinuria or renal dysfunction at entry. Estimated GFR was calculated using the Modification of Diet in Renal Disease equation for Japanese. Glomerular hyperfiltration was defined as estimated GFR ≥117.0 ml/min per 1.73 m(2), which was the upper 2.5th percentile value of estimated GFR in the total population. Proteinuria was detected using standard dipstick.

RESULTS

During the 6-year observation period, there were 449 incident cases of glomerular hyperfiltration and 1653 cases of proteinuria. Current smokers had a 1.32-time higher risk for the development of glomerular hyperfiltration and a 1.51-time higher risk for proteinuria than nonsmokers after adjustment for baseline age, body mass index, systolic and diastolic BP, antihypertensive medication, diabetes, alcohol consumption, regular leisure-time physical activity, and estimated GFR. Both daily and cumulative cigarette consumption were associated with an increased risk for glomerular hyperfiltration and proteinuria in a dose-response manner.

CONCLUSIONS

In middle-aged Japanese men, smoking was associated with an increased risk of glomerular hyperfiltration and dipstick proteinuria. Of importance, past smokers did not exhibit any increased risk for these conditions.

Impact of obesity on childhood kidney

Obese patients are known to have greater risks to develop hypertension, coronary vascular disease, and insulin resistance, and more attention has been recently paid to the impact of obesity on kidney. This study was conducted to investigate whether obese children have higher risk of renal injury as well as adults. Eighteen hundred and thirty school children aged 6-14 years with abnormal urinary findings on thrice occasions detected by the screening program for renal disease in Japan were enrolled. Of them, 27 children with nephritis or suspected nephritis diagnosed by persistent proteinuria with hematuria were compared to 588 without urinary abnormalities regarding their body mass index (BMI), blood pressure (BP), and serum level of total cholesterol. BMI and systolic BP (mmHg) were significantly higher in the former than in the latter. As a result, obesity may be associated with the development of renal injury even in childhood.

Bariatric surgery and renal function

Obesity causes a significant healthcare burden and has been shown to be an important risk factor in the development of cardiovascular disease, type 2 diabetes, and increasingly chronic kidney disease. Bariatric surgery is the most effective treatment for obesity and has been shown to drastically improve both blood pressure and diabetic control. However, the interaction of bariatric surgery and renal function is less clear. This review focuses on the effect of bariatric surgery on renal function both in the acute situation, with respect to acute kidney injury, and also on changes in renal function parameters post-bariatric surgery weight loss. The interaction of obesity, bariatric surgery, and nephrolithiasis as a precipitant of acute kidney injury will also be considered. The role of bariatric surgery in pre- and post-renal transplant recipients is discussed as well as possible mechanisms underlying the improvement in renal function.

Metabolic syndrome and chronic kidney disease

Obesity is fast becoming a bane for the present civilization, as a result of sedentary lifestyle, atherogenic diet, and a susceptible thrifty genotype. The concept of metabolic syndrome, which is a constellation of metabolic disturbances, has crystallized over the last 80 years with the aim of identifying those at greater risk of developing type 2 diabetes and cardiovascular disease. These patients have visceral obesity and insulin resistance characterized by hypertyriglyceridemia. Recently, it has been realized that they are also at an increased risk of chronic renal disease. Release of adipocytokines leads to endothelial dysfunction. There is also activation of systemic and local renin-angiotensin-aldosterone system, oxidative stress, and impaired fibrinolysis. This leads to glomerular hyperfiltration, proteinuria, focal segmental glomerulosclerosis (FSGS), and ultimately end-stage renal disease (ESRD). Treatment consists of lifestyle modifications along with optimal control of blood pressure, blood sugar and lipids. Metformin and thiazolidenidiones reduce insulin resistance; while angiotensin converting enzyme inhibitors and angiotensin receptor blockers reduce proteinuria and have a renoprotective effect. Exciting new medical therapies on the horizon include rimonabant a cannabinoid receptor type 1 antagonist, soy proteins, and peroxisome proliferator-activated receptor (PPAR) agonist. Bariatric surgery for morbid obesity has also been shown to be effective in treating metabolic syndrome.

Renal glomerular and tubular injury after gastric bypass in obese rats

OBJECTIVE

Roux-en-Y gastric bypass (RYGB) surgery is the most common surgical intervention for long-term weight loss in morbidly obese patients. By decreasing obesity-associated hyperfiltration, diabetes, and hypertension, RYGB is touted to stabilize, if not prevent, progression of chronic renal disease. To test this, the renal histology of diet-induced obese rats that underwent RYGB surgery was compared with that of pair-fed and sham obese controls.

METHODS

Sprague-Dawley rats, fed a high-fat, low-oxalate diet to induce gross obesity, were randomized to RYGB (n = 6), gastrointestinal-intact sham-operated obese controls (sham, n = 4), or gastrointestinal-intact sham-operated obese pair-fed controls (fed, n = 8). Daily body weight and food intake were recorded. On postoperative day 42, renal histology and immunohistochemistry were examined. Renal pathology was assessed by a categorical glomerular lesion score and a quantitative glomerular/tubular scoring system by experienced veterinary pathologists. Osteopontin and ED-1 (monocyte/macrophage cell) stainings were estimated by the percentage of stained area and the number of counted cells/high-power field, respectively.

RESULTS

Compared with sham and fed controls, RYGB rats had significant decreases in body weight (P < 0.001), more glomerular lesions (P = 0.02), and received higher glomerular and tubular lesion scores (P < 0.01). RYGB rodents had significantly stronger staining for osteopontin within the inner medullary region (P < 0.005) and ED-1 within the outer medullary region (P < 0.02) compared with sham and fed controls.

CONCLUSION

In this diet-induced obese rat model, RYGB is associated with chronic glomerulosclerosis and tubulointerstitial nephritis, confirmed by histology and immunohistochemistry. Prospective studies to better define the injurious mechanisms in this model are underway.

Effects of dietary protein and fat contents on renal function and inflammatory cytokines in rats with adriamycin-induced nephrotic syndrome

The effects of dietary protein and fat on renal function-related blood and urine parameters, such as albumin, urinary protein,and inflammatory cytokines were investigated in adriamycin- (ADR) induced nephrotic syndrome rats. ADR (2 mg/kg BW) was injected i.p. weekly for six weeks to develop nephrotic syndrome; thereafter rats were fed low-protein/high-fat (LPHF) or high-protein/low-fat (HPLF) diets for five weeks. Renal function-related blood and urine parameters were measured before and after dietary intervention. Serum levels of albumin, TG, and creatinine were significantly higher in the LPHF group than in the HPLF group. Serum levels of albumin were low and urinary protein excretion protein was high in HPLF group. BUN and UUN levels were higher in the HPLF group than in the LPHF. Urinary excretion of creatinine was significantly higher in the HPLF group than in the LPHF group. Serum inflammatory cytokine levels did not differ between the two groups, however the levels of IL-6, TNF-α, and IL-13 in splenocyte supernatants were significantly higher in the LPHF group than in the HPLF group. We confirmed that protein and fat contents in diet affect renal function-related blood and urine parameters and splenocyte inflammatory cytokine levels in ADR-induced nephrotic syndrome rats.

Implications for kidney disease in obese children and adolescents

Increasing attention has been focused on the implications of obesity in adults on the development of kidney disease, but data on the obese pediatric population are lacking. The aim of this study was to investigate whether changes in various renal function indexes/markers, as expressed by the glomerular filtration rate [GFR, as estimated by the Schwartz formula (eGFR)], serum cystatin C (CysC) level, albumin excretion rate (AER), and modifications in nitric oxide (NO; an important modulator of renal function and morphology), urinary isoprostanes (markers of oxidative stress), and blood pressure (BP), can be detected in obese children and adolescents when compared to normal weight controls. Blood and urinary samples were collected to evaluate markers of renal function, serum and urinary NO, and urinary isoprostanes in 107 obese Caucasian subjects and 50 controls. Ambulatory BP monitoring (ABPM) was performed in all cases. Obesity was expressed by the body mass index standard deviation score (SDS-BMI), and insulin resistance by the homeostasis model assessment of insulin resistance (HOMA-IR). CysC and eGFR did not significantly differ between the two groups; AER was increased in obese children. CysC and GFR were related to HOMA-IR, and AER was related to HOMA-IR and SDS-BMI. Obese subjects had reduced NO levels and increased urinary isoprostanes and BP measurements; all three parameters were related to SDS-BMI and insulin resistance. ABPM showed an increased incidence of hypertension and non-dipping in the obese group. Based on our comparison of obese and nonobese children, we conclude that renal involvement is not an early clinically evident manifestation of adiposity in childhood, since no overt changes in eGFR and only a mild albuminuria were detected. A longer exposure to obesity is probably needed before renal function impairment appears.

Metabolic syndrome, components, and cardiovascular disease prevalence in chronic kidney disease: findings from the Chronic Renal Insufficiency Cohort (CRIC) Study

BACKGROUND/AIMS

Metabolic syndrome may increase the risk for incident cardiovascular disease (CVD) and all-cause mortality in the general population. It is unclear whether, and to what degree, metabolic syndrome is associated with CVD in chronic kidney disease (CKD). We determined metabolic syndrome prevalence among individuals with a broad spectrum of kidney dysfunction, examining the role of the individual elements of metabolic syndrome and their relationship to prevalent CVD.

METHODS

We evaluated four models to compare metabolic syndrome or its components to predict prevalent CVD using prevalence ratios in the Chronic Renal Insufficiency Cohort (CRIC) Study.

RESULTS

Among 3,939 CKD participants, the prevalence of metabolic syndrome was 65% and there was a significant association with prevalent CVD. Metabolic syndrome was more common in diabetics (87.5%) compared with non-diabetics (44.3%). Hypertension was the most prevalent component, and increased triglycerides the least prevalent. Using the bayesian information criterion, we found that the factors defining metabolic syndrome, considered as a single interval-scaled variable, was the best of four models of metabolic syndrome, both for CKD participants overall and for diabetics and non-diabetics separately.

CONCLUSION

The predictive value of this model for future CVD outcomes will subsequently be validated in longitudinal analyses.

Metabolic syndrome, chronic kidney disease, and cardiovascular disease: a dynamic and life-threatening triad

The metabolic syndrome (MS) and chronic kidney disease (CKD) have both become global public health problems, with increasing social and economic impact due to their high prevalence and remarkable impact on morbidity and mortality. The causality between MS and CKD, and its clinical implications, still does remain not completely understood. Moreover, prophylactic and therapeutic interventions do need to be properly investigated in this field. Herein, we critically review the existing clinical evidence that associates MS with renal disease and cardiovascular disease, as well as the associated pathophysiologic mechanisms and actual treatment options.

Weight loss: a neglected intervention in the management of chronic kidney disease

PURPOSE OF REVIEW

Obesity is being increasingly implicated as an independent risk factor for the development of chronic kidney disease (CKD), raising the question whether reversing obesity can be utilized as a mainstay or an adjunct therapy for CKD and possibly for its prevention. The purpose of this review is to examine the impact of treatment of obesity on renal outcomes.

RECENT FINDINGS

Many observations have pointed to improvement in renal parameters following weight loss. In fact, both surgical and nonsurgical approaches appear to be effective at reducing blood pressure and proteinuria. Weight loss has also been shown to lower glomerular filtration rate (GFR) in obese patients, not an insignificant benefit considering that intra-glomerular hypertension and the subsequent hyperfiltration in the setting of obesity might be a main driver for the development of CKD.

SUMMARY

Urinary protein excretion, blood pressure, and GFR improve with surgical and nonsurgical weight loss interventions. Whether improvements in these surrogate outcomes after weight loss actually translate into a reduction in the risk of CKD or amelioration in the rate of progression of established CKD is yet to be determined.

Renal function and severity of bright liver. Relationship with insulin resistance, intrarenal resistive index, and glomerular filtration rate

AIMS

Relationships of renal function and liver disease are described in acute and chronic liver failure. The aim of the study is to investigate which relationship, if any, is present between severity of non-alcoholic fatty liver disease (NAFLD), assessed by bright liver score (BLS) versus mild-moderate renal insufficiency assessed by glomerular filtration rate (GFR) and by ultrasound intra-renal arterial resistive index (RRI). Moreover, which difference, if any, can be found in NAFLD patients with normal versus increased transaminases.

PATIENTS

The study enrolled 323 NAFLD and 176 non-NAFLD consecutive patients, comparable for age, gender distribution, GFR, and RRI referred to a university clinical day hospital after an ultrasound diagnosis of bright liver, for clinical-nutritional counselling. Personalized computerized mediterranean diet, physical activity increase, and smoking withdrawal integrated counselling were provided.

RESULTS

In NAFLD patients, homoeostasis model (HOMA) has a significant correlation with BLS. According to the severity of BLS, grade II-III versus grade I patients have significantly higher values of HOMA, body mass index (BMI), triglycerides, and longitudinal right liver length. By odds ratio, more severe BLS, increased HOMA, and transaminases are associated with lower GFR. Increased transaminases are associated with higher grades of BLS, HOMA, and BMI. By multiple linear regression waist-to-hip ratio, RRI, and BLS, as significant independent factors (p < 0.0001), explain significantly variance to GFR. This is not observed in normal control group, in which only RRI is a factor explaining GFR.

CONCLUSION

Greater RRI, abdominal obesity, and greater BLS account for a lower GFR in NAFLD patients suggesting the hypothesis that inter-related factors can be operating early in the natural history of obesity-related kidney and liver disease.

Bardet-Biedl syndrome highlights the major role of the primary cilium in efficient water reabsorption

Studies of the primary cilium, now known to be present in all cells, have undergone a revolution, in part, because mutation of many of its proteins causes a large number of diseases, including cystic kidney disease. Bardet-Biedl syndrome (BBS) is an inherited ciliopathy characterized, among other dysfunctions, by renal defects for which the precise role of the cilia in kidney function remains unclear. We studied a cohort of patients with BBS where we found that these patients had a urinary concentration defect even when kidney function was near normal and in the absence of major cyst formation. Subsequent in vitro analysis showed that renal cells in which a BBS gene was knocked down were unciliated, but did not exhibit cell cycle defects. As the vasopressin receptor 2 is located in the primary cilium, we studied BBS-derived unciliated renal epithelial cells and found that they were unable to respond to luminal arginine vasopressin treatment and activate their luminal aquaporin 2. The ability to reabsorb water was restored by treating these unciliated renal epithelial cells with forskolin, a receptor-independent adenylate cyclase activator, showing that the intracellular machinery for water absorption was present but not activated. These findings suggest that the luminal receptor located on the primary cilium may be important for efficient transepithelial water absorption.

The conflicting effects of maternal nutrient restriction and early-life obesity on renal health

Epidemiological and animal studies have demonstrated that early-life nutrition alters the metabolic responses and generates structural changes in complex tissues, such as the kidneys, which may lead to a reduction in the offspring lifespan. Independently, obesity induces a spontaneous low-grade chronic inflammatory response by modulating several of the major metabolic pathways that ultimately compromise long-term renal health. However, the combined effects of maternal nutrition and early-life obesity in the development of renal diseases are far from conclusive. Previous results, using the ovine model, demonstrated that the combination of a reduction in fetal nutrition and juvenile obesity induced a series of adaptations associated with severe metabolic syndrome in the heart and adipose tissue. Surprisingly, exposure to an obesogenic environment in the kidney of those offspring produced an apparent reduction in glomerulosclerosis in relation to age- and weight-matched controls. However, this reduction in cellular apoptosis was accompanied by a rise in glomerular filtration rate and blood pressure of equal intensity when compared with obese controls. The intention of this review is to explain the adaptive responses observed in this model, based on insights into the mechanism of renal fetal programming, and their potential interactions with some of the metabolic changes produced by obesity.

[Renal consequences of obesity]

The steady increase in the prevalence of obesity contributes to the increase in the prevalence of chronic kidney disease, through renal damages associated with type-2 diabetes and hypertension. Obesity is also an independent risk factor for the kidney, since it is associated with an increased risk of albuminuria and glomerulosclerosis, and worsens the course of chronic kidney disease regardless of the primary renal disease. The existence of a metabolic syndrome, constant in type-2 diabetes, and associated with abdominal obesity, is not the only requirement for renal anomalies of which the translation is a functional hyperfiltration, a clinical microalbuminuria and histologically a glomerulomegaly and glomerulosclerosis. The estimated glomerular filtration rate (GFR) in obese patients is strongly influenced by the weight or indexation to body surface area, and it is logical to take into account the value of non-indexed GFR to assess renal risk and treatment effects, especially if they lead to weight loss. Hypertension is promoted by salt sensitivity, potentially reversible, and overactivity of the renin-angiotensin system (RAS) in part due to adipose tissue. The cytokines secreted by adipose tissue (adipokines), induce sympathetic hyperactivity through leptin, and low-grade inflammatory state that contributes to the development of glomerular sclerosis lesions, especially because a resistance to adiponectin. The treatment relies on weight loss, possibly through bariatric surgery, and antagonists of the RAS.

Oxygen regulation of the epithelial Na channel in the collecting duct

The PO(2) within the kidney changes dramatically from cortex to medulla. The present experiments examined the effect of changing PO(2) on epithelial Na channel (ENaC)-mediated Na transport in the collecting duct using the mpkCCD-c14 cell line. Decreasing ambient O(2) concentration from 20 to 8% decreased ENaC activity by 40%; increasing O(2) content to 40% increased ENaC activity by 50%. The O(2) effect required several hours to develop and was not mimicked by the acid pH that developed in monolayers incubated in low-O(2) medium. Corticosteroids increased ENaC activity at each O(2) concentration; there was no interaction. The pathways for O(2) and steroid regulation of ENaC are different since O(2) did not substantially affect Sgk1, α-ENaC, Gilz, or Usp2-45 mRNA levels, genes involved in steroid-mediated ENaC regulation. The regulation of ENaC activity by these levels of O(2) appears not to be mediated by changes in hypoxia-inducible factor-1α or -2α activity or a change in AMP kinase activity. Changes in O(2) concentration had minimal effect on α- or γ-ENaC mRNA and protein levels; there were moderate effects on β-ENaC levels. However, 40% O(2) induced substantially greater total β- and γ-ENaC on the apical surface compared with 8% O(2); both subunits demonstrated a greater increase in the mature forms. The α-ENaC subunit was difficult to detect on the apical surface, perhaps because our antibodies do not recognize the major mature form. These results identify a mechanism of ENaC regulation that may be important in different regions of the kidney and in responses to changes in dietary NaCl.

Possible Link between Metabolic Syndrome and Chronic Kidney Disease in the Development of Cardiovascular Disease

Metabolic syndrome (MetS) is a clinical syndrome that consists of visceral obesity, dyslipidemia, hypertension, and impaired insulin sensitivity. Although individual components of MetS have been implicated in the development of chronic kidney disease (CKD), few studies have examined the effect of combinations of the components of MetS on the development of CKD and cardiovascular disease (CVD). The prevalence of MetS is increasing worldwide in both developing and developed countries, and early detection and treatment of MetS would be a cost-effective strategy for preventing the development of CKD. Visceral obesity and insulin resistance are two important features of MetS that may be associated with renal damage. Lifestyle modifications, including caloric restriction and exercise, are necessary to treat MetS. Initial antihypertensive therapy should consist of an angiotensin-converting enzyme inhibitor or angiotensin receptor blocker. An improved understanding of the mechanism responsible for the association between MetS and renal damage should be helpful in determining the treatment regimens directed at cardiovascular and renal protection.

The clinical significance of hyperfiltration in diabetes

Glomerular filtration rate is commonly elevated in early diabetes and patients with this symptom are arbitrarily considered to have hyperfiltration. The prevalence of hyperfiltration in type 1 diabetes varies from less than 25% to more than 75%. The corresponding figures in type 2 diabetes are significantly lower, ranging between 0% and more than 40%. Several factors, methodological and biological, may contribute to the wide variation in estimates of hyperfiltration prevalence. Methodological differences in measurement and evaluation of GFR apply in particular to the handling of plasma disappearance curves of filtration markers. Biological factors that may influence GFR in the hyperfiltration range include glycaemic control, diabetes duration, BMI, sex, pubertal status in type 1 diabetes and age in type 2 diabetes. Hyperglycaemia may influence GFR and albuminuria, and may therefore confound the evaluation of hyperfiltration as an independent risk factor for diabetic nephropathy. Adequate assessment of the relationship between glycaemic control, GFR and AER therefore requires serial measurements of all three variables followed by multivariate analysis. A recent meta-analysis of ten type 1 diabetes studies concluded that the presence of hyperfiltration at baseline more than doubled the risk of developing micro- or macroalbuminuria at follow-up. However, not all studies allowed for confounding factors or regression dilution bias. Future studies will therefore need to address the independent role of hyperfiltration, not only in the evolution of albuminuria, but also in the subsequent decline of GFR.