The clinical significance of hyperfiltration in diabetes

Correlation of Microalbuminuria with Estimated GFR (eGFR) by Cockcroft-Gault and MDRD Formula in Type 2 Diabetics and Hypertensives

Increase in urine albumin excretion rate (AER) precede a fall in glomerular filtration rate in patients developing diabetic chronic kidney disease (CKD). Our results have shown that 7 (50 %) of diabetic and hypertensive individuals with decreased GFR do not have increased AER. In this cross-sectional study, we measured AER of 75 patients with type 2 diabetes and hypertension by immunoturbidimetric method. We correlated the results with eGFR values obtained by Cockcroft-Gault and MDRD method. The method used was not a compensated method. We measured serum creatinine by modified Jaffe's kinetic method in autoanalyzer XL-600. Analysis of data showed positive correlation between eGFR and microalbuminuria by both the methods with eGFR <60 mL/min/1.73 m(2). Pearson's correlation co-efficient (r) was 0.9 (p = 0.0001) by Cockcroft-Gault formula and 0.69 (p = 0.0063) by MDRD formula. Our results concluded that there was positive correlation between AER and eGFR <60 mL/min/1.73 m(2). We have recognized that these two parameters provide a complimentary benefit in management of cases with CKD.

Glomerular and tubular function in the diabetic kidney

Diabetes mellitus with its attendant complications is a significant cause of morbidity and mortality with diabetic nephropathy being the leading cause of end stage renal disease in the Western world. Characteristic structural and functional changes in the kidney early in the course of diabetes have been shown to have enduring effects on the progression of disease. A better understanding of the mechanisms underlying these changes is imperative to the development of new therapeutic strategies. Renal hypertrophy and hyperfiltration along with proximal tubular hyperreabsorption are among the distinctive features of early diabetic nephropathy. Additionally, there are particular alterations in the sensitivity of the glomerular and tubular function to dietary salt intake in early diabetes. Herein, we focus on these early physiologic changes and discuss some of the primary and secondary mechanisms discovered in recent years which lead to these alterations in kidney function.

Natural history and clinical characteristics of CKD in type 1 and type 2 diabetes mellitus

The nature of CKD in diabetes is changing. Diabetic glomerulosclerosis remains the cause of CKD in most type 1 diabetic individuals. However, the rate of progression of diabetic nephropathy has slowed because of improving glucose and blood pressure control. Most individuals with type 2 diabetes and 5% to 30% of those with type 1 diabetes with progressive CKD have normal urine albumin excretion or low-level microalbuminuria (albumin-to-creatinine ratio approximately <100 mg/g), which does not progress despite the decline in glomerular filtration. People with progressive CKD but normal albuminuria have predominantly interstitial or vascular changes with much less glomerular changes. It seems likely that these histological abnormalities relate to blood pressure, aging, obesity, and intrarenal vascular disease. Initial studies suggested that 85% to 100% of diabetic individuals with microalbuminuria (Kidney Disease Improving Global Outcomes [KDIGO] CKD albuminuria A2) progressed to proteinuria (KDIGO CKD albuminuria A3). Recent data demonstrate that even after 2 to 3 years of persistent microalbuminuria, most will revert to normal albumin excretion (KDIGO CKD albuminuria A1). Regression is more likely at lower levels of microalbuminuria and with improved glucose, blood pressure, and lipid control. Thus, low levels of microalbuminuria cannot be considered as established diabetic nephropathy.

A longitudinal assessment of the natural rate of decline in renal function with age

BACKGROUND

Cross-sectional studies have long suggested that renal function declines with age. Longitudinal studies regarding this issue are limited.

METHODS

We retrospectively analyzed a database of subjects attending a screening center in Israel between the years 2000-2012. Only subjects with normal estimated glomerular filtration rate (eGFR) were included. eGFR was assessed consequently at 5 or more yearly visits. The rate of decline in GFR with age was assessed in healthy subjects and in subjects with comorbidities.

RESULTS

The cohort included 2693 healthy subjects and 230 subjects with different comorbidities. Mean (±standard error) annual rate of decline in eGFR in healthy subjects was 0.97 ± 0.02 ml/min/year/1.73 m(2). This decline increased significantly from 0.82 ± 0.22 in age-group 20-30 years to 0.84 ± 0.08, 1.07 ± 0.08 and 1.15 ± 0.12 ml/min/year/1.73 m(2) in age groups 31-40, 41-50 and 50 years and older respectively (p < 0.001). No correlation was found between the annual decline in eGFR and body mass index. In subjects with hypertension, diabetes mellitus, impaired fasting glucose or combined comorbidity the decline in eGFR was 1.12 ± 0.12, 0.77 ± 0.16, 0.85 ± 0.17, and 1.18 ± 0.26 ml/min/year/1.73 m(2) respectively.

CONCLUSIONS

This large longitudinal study provides new data on the decrease in eGFR with age. Accurate prediction of the natural rate of GFR decline might be used to distinguish between normally aging kidneys and those with chronic disease. This approach could avoid unnecessary diagnostic procedures in the former and facilitate appropriate treatment in the latter.

Markers of and risk factors for the development and progression of diabetic kidney disease

Diabetic kidney disease (DKD) occurs in 25%-40% of patients with diabetes. Given the dual problems of a significant risk of progression from DKD to end-stage renal disease (ESRD) and increased cardiovascular morbidity and mortality, it is important to identify patients at risk of DKD and ESRD and initiate protective renal and cardiovascular therapies. The importance of preventive therapy is emphasized further by worldwide increases in the incidence of diabetes. This review summarizes the evidence regarding the prognostic value and benefits of targeting established and novel risk markers for DKD development and progression. Family history of DKD, smoking history, and glycemic, blood pressure, and plasma lipid level control are established factors for identifying people at greatest risk of DKD development and progression. Absolute albumin excretion rate (AER) and glomerular filtration rate (GFR) measurements also are important, although AER categorization generally lacks the necessary specificity and sensitivity, and estimates of declining GFR are compromised by methodological limitations for GFRs in the normal-to-high range. Emerging risk markers for progressive loss of kidney function include markers of oxidation and inflammation, profibrotic cytokines, uric acid, advanced glycation end products, functional and structural markers of vascular dysfunction, kidney structural changes, and tubular biomarkers. Among these, the most promising are serum uric acid and soluble tumor necrosis factor receptor (type 1 and type 2) levels, especially in relation to GFR changes. At present, these can only be considered as risk markers because they only identify an individual at increased risk of progressive DKD and not necessarily related to the causal pathway promoting kidney damage. Further work is needed to establish whether modulating these factors improves the prognosis in DKD. Although change in urinary peptidome levels also is a promising marker, there currently is neither a clinical assay nor adequate studies defining its prognostic value. Until these or other novel markers become available for clinical use, predictive accuracy often may be increased with greater attention to established markers.

HIV therapy, metabolic and cardiovascular health are associated with glomerular hyperfiltration among men with and without HIV infection

OBJECTIVE

Diabetes and hypertension, common conditions in antiretroviral-treated HIV-infected individuals, are associated with glomerular hyperfiltration, which precedes the onset of proteinuria and accelerated kidney function decline. In the Multicenter AIDS Cohort Study, we examined the extent to which hyperfiltration is present and associated with metabolic, cardiovascular, HIV and treatment risk factors among HIV-infected men.

DESIGN

Cross-sectional cohort using direct measurement of glomerular filtration rate by iohexol plasma clearance for 367 HIV-infected men and 241 HIV-uninfected men who were free of chronic kidney disease.

METHODS

Hyperfiltration was defined as glomerular filtration rate above 140-1 ml/min per 1.73 m per year over age 40. Multivariate logistic regression was used to estimate the odds ratios (ORs) of prevalent hyperfiltration for metabolic, cardiovascular, HIV and cumulative antiretroviral exposure factors.

RESULTS

Among individuals without chronic kidney disease, the prevalence of hyperfiltration was higher for HIV-infected participants (25%) compared to uninfected participants (17%; P = 0.01). After adjustment, HIV infection remained associated with hyperfiltration [OR 1.70, 95% confidence interval (CI) 1.11-2.61] and modified the association between diabetes and hyperfiltration, such that the association among HIV-uninfected men (OR 2.56, 95% CI 1.33-5.54) was not observed among HIV-infected men (OR 1.19, 95% CI 0.69-2.05). These associations were independent of known risk factors for hyperfiltration. Indicators of hyperglycemia and hypertension were also associated with hyperfiltration as was cumulative zidovudine exposure.

CONCLUSION

Hyperfiltration, a potential modifiable predictor of kidney disease progression, is significantly higher among antiretroviral-treated HIV-infected men. Furthermore, HIV-infection nullifies the association of diabetes and hyperfiltration present in HIV-uninfected men.

Pathophysiology of the diabetic kidney

Diabetes mellitus contributes greatly to morbidity, mortality, and overall health care costs. In major part, these outcomes derive from the high incidence of progressive kidney dysfunction in patients with diabetes making diabetic nephropathy a leading cause of end-stage renal disease. A better understanding of the molecular mechanism involved and of the early dysfunctions observed in the diabetic kidney may permit the development of new strategies to prevent diabetic nephropathy. Here we review the pathophysiological changes that occur in the kidney in response to hyperglycemia, including the cellular responses to high glucose and the responses in vascular, glomerular, podocyte, and tubular function. The molecular basis, characteristics, and consequences of the unique growth phenotypes observed in the diabetic kidney, including glomerular structures and tubular segments, are outlined. We delineate mechanisms of early diabetic glomerular hyperfiltration including primary vascular events as well as the primary role of tubular growth, hyperreabsorption, and tubuloglomerular communication as part of a "tubulocentric" concept of early diabetic kidney function. The latter also explains the "salt paradox" of the early diabetic kidney, that is, a unique and inverse relationship between glomerular filtration rate and dietary salt intake. The mechanisms and consequences of the intrarenal activation of the renin-angiotensin system and of diabetes-induced tubular glycogen accumulation are discussed. Moreover, we aim to link the changes that occur early in the diabetic kidney including the growth phenotype, oxidative stress, hypoxia, and formation of advanced glycation end products to mechanisms involved in progressive kidney disease.

Renal hemodynamic effect of sodium-glucose cotransporter 2 inhibition in patients with type 1 diabetes mellitus

BACKGROUND

The primary objective of this mechanistic open-label, stratified clinical trial was to determine the effect of 8 weeks' sodium glucose cotransporter 2 inhibition with empagliflozin 25 mg QD on renal hyperfiltration in subjects with type 1 diabetes mellitus (T1D).

METHODS AND RESULTS

Inulin (glomerular filtration rate; GFR) and paraaminohippurate (effective renal plasma flow) clearances were measured in individuals stratified based on having hyperfiltration (T1D-H, GFR ≥ 135 mL/min/1.73m(2), n=27) or normal GFR (T1D-N, GFR 90-134 mL/min/1.73m(2), n=13) at baseline. Renal function and circulating levels of renin-angiotensin-aldosterone system mediators and NO were measured under clamped euglycemic (4-6 mmol/L) and hyperglycemic (9-11 mmol/L) conditions at baseline and end of treatment. During clamped euglycemia, hyperfiltration was attenuated by -33 mL/min/1.73m(2) with empagliflozin in T1D-H, (GFR 172±23-139±25 mL/min/1.73 m(2), P<0.01). This effect was accompanied by declines in plasma NO and effective renal plasma flow and an increase in renal vascular resistance (all P<0.01). Similar significant effects on GFR and renal function parameters were observed during clamped hyperglycemia. In T1D-N, GFR, other renal function parameters, and plasma NO were not altered by empagliflozin. Empagliflozin reduced hemoglobin A1c significantly in both groups, despite lower insulin doses in each group (P≤0.04).

CONCLUSIONS

In conclusion, short-term treatment with the sodium glucose cotransporter 2 inhibitor empagliflozin attenuated renal hyperfiltration in subjects with T1D, likely by affecting tubular-glomerular feedback mechanisms.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov. Unique identifier: NCT01392560.

Early chronic low-level lead exposure produces glomerular hypertrophy in young C57BL/6J mice

Early chronic lead exposure continues to pose serious health risks for children, particularly those living in lower socioeconomic environments. This study examined effects on developing glomeruli in young C57BL/6J mice exposed to low (30 ppm), higher (330 ppm) or no lead via dams' drinking water from birth to sacrifice on post-natal day 28. Low-level lead exposed mice [BLL mean (SD); 3.19 (0.70) μg/dL] had an increase in glomerular volume but no change in podocyte number compared to control mice [0.03 (0.01) μg/dL]. Higher-level lead exposed mice [14.68 (2.74) μg/dL] had no change in either glomerular volume or podocyte number. The increase in glomerular volume was explained by increases in glomerular capillary and mesangial volumes with no change in podocyte volume. Early chronic lead exposure yielding very low blood lead levels alters glomerular development in pre-adolescent animals.

Diabetic ketoacidosis and hyperglycemic hyperosmolar state

Diabetic ketoacidosis (DKA) and the hyperglycemic hyperosmolar state (HHS) are potentially fatal hyperglycemic crises that occur as acute complications of uncontrolled diabetes mellitus. The authors provide a review of the current epidemiology, precipitating factors, pathogenesis, clinical presentation, evaluation, and treatment of DKA and HHS. The discovery of insulin in 1921 changed the life expectancy of patients with diabetes mellitus dramatically. Today, almost a century later, DKA and HHS remain significant causes of morbidity and mortality across different countries, ages, races, and socioeconomic groups and a significant economic burden for society.

Targeted glomerular angiopoietin-1 therapy for early diabetic kidney disease

Vascular growth factors play an important role in maintaining the structure and integrity of the glomerular filtration barrier. In healthy adult glomeruli, the proendothelial survival factors vascular endothelial growth factor-A (VEGF-A) and angiopoietin-1 are constitutively expressed in glomerular podocyte epithelia. We demonstrate that this milieu of vascular growth factors is altered in streptozotocin-induced type 1 diabetic mice, with decreased angiopoietin-1 levels, VEGF-A upregulation, decreased soluble VEGF receptor-1 (VEGFR1), and increased VEGFR2 phosphorylation. This was accompanied by marked albuminuria, nephromegaly, hyperfiltration, glomerular ultrastructural alterations, and aberrant angiogenesis. We subsequently hypothesized that restoration of angiopoietin-1 expression within glomeruli might ameliorate manifestations of early diabetic glomerulopathy. Podocyte-specific inducible repletion of angiopoietin-1 in diabetic mice caused a 70% reduction of albuminuria and prevented diabetes-induced glomerular endothelial cell proliferation; hyperfiltration and renal morphology were unchanged. Furthermore, angiopoietin-1 repletion in diabetic mice increased Tie-2 phosphorylation, elevated soluble VEGFR1, and was paralleled by a decrease in VEGFR2 phosphorylation and increased endothelial nitric oxide synthase Ser(1177) phosphorylation. Diabetes-induced nephrin phosphorylation was also reduced in mice with angiopoietin-1 repletion. In conclusion, targeted angiopoietin-1 therapy shows promise as a renoprotective tool in the early stages of diabetic kidney disease.

Weight-loss diets in people with type 2 diabetes and renal disease: a randomized controlled trial of the effect of different dietary protein amounts

BACKGROUND

Higher-protein weight-loss diets (defined as >25% of energy as protein) are not recommended for individuals with type 2 diabetes because of their potential adverse effect on renal function.

OBJECTIVE

We aimed to examine the effect of such diets on renal function over 12 mo in people with type 2 diabetes and early renal disease.

DESIGN

Overweight and obese people with type 2 diabetes were screened to identify those with an albumin:creatinine ratio from 3 to 30 mg/mmol. Seventy-six subjects were randomly assigned to either a moderate-protein weight-loss diet or a standard-protein weight-loss diet for 12 mo. The primary endpoint was the change in renal function as assessed by the isotope glomerular filtration rate (GFR), estimated GFR, and cystatin C. Forty-five subjects (moderate protein: n = 21; standard protein: n = 24) completed the study.

RESULTS

The mean (±SE) weight loss was not different between diets at 9.7 ± 13.4 kg for the moderate-protein diet and 6.6 ± 7.1 kg for the standard-protein diet. There were no changes in renal function or albuminuria or blood pressure, although glycated hemoglobin was lowered with both diets. Changes in renal function were related to the baseline estimated GFR. Patients with stage 1-3 renal disease (<120 mL · min(-1) · 1.73 m(-2); n = 33) had an improvement in renal function, whereas patients with hyperfiltration (>120 mL · min(-1) · 1.73 m(-2); n = 12) had a decrease in the GFR. After adjustment for weight loss, the baseline GFR remained a significant predictor of outcomes with no effect of dietary treatment. An average difference in protein intake between diets of 19 ± 6 g/d was achieved.

CONCLUSION

Weight loss improved renal function, but differences in dietary protein had no effect. This trial was registered at the Australian and New Zealand Clinical Trial Register as ACTRN12608000045314.

Renal hyperfiltration and systemic blood pressure in patients with uncomplicated type 1 diabetes mellitus

BACKGROUND

Patients with type 1 diabetes mellitus (DM) and renal hyperfiltration also exhibit systemic microvascular abnormalities, including endothelial dysfunction. The effect of renal hyperfiltration on systemic blood pressure (BP) is less clear. We therefore measured BP, renal hemodynamic function and circulating renin angiotensin aldosterone system (RAAS) mediators in type 1 DM patients with hyperfiltration (n = 36, DM-H, GFR≥135 ml/min/1.73 m(2)) or normofiltration (n = 40, DM-N), and 56 healthy controls (HC). Since renal hyperfiltration represents a state of intrarenal RAAS activation, we hypothesized that hyperfiltration would be associated with higher BP and elevated levels of circulating RAAS mediators.

METHODS

BP, glomerular filtration rate (GFR - inulin), effective renal plasma flow (paraaminohippurate) and circulating RAAS components were measured in DM-H, DM-N and HC during clamped euglycemia (4-6 mmol/L). Studies were repeated in DM-H and DM-N during clamped hyperglycemia (9-11 mmol/L).

RESULTS

Baseline GFR was elevated in DM-H vs. DM-N and HC (167±6 vs. 115±2 and 115±2 ml/min/1.73 m(2), p<0.0001). Baseline systolic BP (SBP, 117±2 vs. 111±2 vs. 109±1, p = 0.004) and heart rate (76±1 vs. 67±1 vs. 61±1, p<0.0001) were higher in DM-H vs. DM-N and HC. Despite higher SBP in DM-H, plasma aldosterone was lower in DM-H vs. DM-N and HC (42±5 vs. 86±14 vs. 276±41 ng/dl, p = 0.01). GFR (p<0.0001) and SBP (p<0.0001) increased during hyperglycemia in DM-N but not in DM-H.

CONCLUSIONS

DM-H was associated with higher heart rate and SBP values and an exaggerated suppression of systemic aldosterone. Future work should focus on the mechanisms that explain this paradox in diabetes of renal hyperfiltration coupled with systemic RAAS suppression.

Effects of renal denervation on insulin resistance

Hypertension and diabetes are recognized as two major comorbidities accounting for the greatest proportion of cardiovascular morbidity and mortality. Despite the availability of safe and effective pharmacological therapies, the percentage of patients achieving optimal blood pressure and glycemic control remains unsatisfactory. The contribution of sympathetic activation to the development and maintenance of systemic hypertension and comorbidities is well recognized. Aside from several novel pharmacological approaches, catheter-based sympathetic renal denervation (RDN) has gained a significant role in treatment-resistant hypertension and has recently been introduced to clinical practice. Preliminary data indicate that aside from better blood pressure control, RDN may also be associated with a reduction in fasting glucose and insulin levels, as well as improvements in the Homeostasis Model Assessment (HOMA) index. If these observations are confirmed in larger controlled clinical trials, RDN may emerge as a preferred treatment option for patients with resistant hypertension and concomitant alterations of glucose metabolism.

Comparison of serum cystatin C, serum creatinine, measured GFR, and estimated GFR to assess the risk of kidney failure in American Indians with diabetic nephropathy

BACKGROUND

We compared values of baseline serum cystatin C (SCysC), serum creatinine (SCr), and measured glomerular filtration rate (mGFR) for predicting end-stage renal disease (ESRD) in patients with type 2 diabetes and elevated albuminuria.

STUDY DESIGN

Observational longitudinal study.

SETTING & PARTICIPANTS

Pima Indians with type 2 diabetes and elevated albumin-creatinine ratio (ACR ≥30 mg/g).

PREDICTORS

Baseline SCysC, SCr, and mGFR.

OUTCOMES & MEASUREMENTS

Individuals were followed up from their first examination with diabetes and ACR ≥30 mg/g until December 2010, onset of ESRD, or death, whichever came first. Incidence rates adjusted for age and sex were computed by Mantel-Haenszel stratification. The abilities of SCysC, SCr, and mGFR values to predict ESRD were compared with receiver operating characteristic curves.

RESULTS

Of 234 Pima Indians with a mean age of 42.8 years who were followed up for a median of 10.7 (range, 0.6-21.3) years, 68 (29%) developed ESRD. The incidence of ESRD was significantly higher in patients in the lowest versus highest tertile of 1/SCysC (incidence rate ratio, 2.43; 95% CI, 1.31-4.50). By contrast, mGFR and 1/SCr had J-shaped associations with ESRD. In unadjusted analyses, 1/SCysC had the highest area under the receiver operating characteristic curve (AUROC; 0.719 ± 0.035) and mGFR had the lowest (0.585 ± 0.042; P < 0.001); the AUROC for 1/SCr was intermediate (0.672 ± 0.040; P = 0.1 and P = 0.03 vs 1/SCysC and mGFR, respectively). In analyses adjusted for age, sex, diabetes duration, height, weight, hemoglobin A1c level, and ACR, 1/SCysC had the highest AUROC (0.845 ± 0.026). Models with mGFR or 1/SCr alone had similar AUROCs (P = 0.9) and both were lower than the model with 1/SCysC alone (P = 0.02 and P = 0.03, respectively).

LIMITATIONS

The predictive values of the filtration markers are limited to the extent that their precision is based on a single measurement.

CONCLUSIONS

SCysC level was a better predictor of ESRD than mGFR or SCr level in Pima Indians with type 2 diabetes and elevated albuminuria.

Relationship between BNP level and renal function in diabetic nephropathy with microalbuminuria

AIMS

We examined the relationship between the brain natriuretic peptide (BNP) level and renal function in diabetic nephropathy with microalbuminuria.

METHODS

The subjects were 97 Japanese type 2 diabetes mellitus outpatients with microalbuminuria. Associations between the annual rate of decline in estimated glomerular filtration rate (eGFR) and various metabolic parameters at baseline (BMI, systolic blood pressure, HbA1c, LDL cholesterol, urine albumin-creatinine ratio, BNP and eGFR) were examined.

RESULTS

Among the baseline factors, eGFR and BNP had significant associations with the annual rate of decline in eGFR in Pearson correlation analysis (r=0.295, p=0.003; r=0.223, p=0.028, respectively). Multiple linear regression analysis also showed the significance of baseline eGFR and BNP as independent predictors of renal function (β=0.340, p=0.001; β=0.278, p=0.005, respectively). In multivariate logistic regression analysis, eGFR and BNP were independently associated with the risk of a decline in GFR (p=0.003, p=0.011, respectively). ROC curve analysis showed a cutoff value of BNP is 17.0 pg/mL for predicting a decline in GFR.

CONCLUSIONS

The BNP level at baseline is an independent predictor of the annual rate of decline in eGFR. Therefore, monitoring of BNP can play an important role in management of diabetic nephropathy.

Epidemiology of diabetic kidney disease

The increasing prevalence of diabetes has led to DKD becoming the leading cause of ESRD in many regions. The economic cost of DKD will grow to prohibitive amounts unless strategies to prevent its onset or progression are urgently implemented. In type 1 and type 2 diabetes, the presence of microalbuminuria and macroalbuminuria confers increased risk of developing ESRD and of death. Comparison of recent studies with earlier historical studies shows that the incidence of ESRD and death has decreased in DKD. Increased risk of albuminuria has been identified in certain non-European ethnic groups. However, the initial concept of progression of DKD as an albuminuric phenotype involving development of microalbuminuria, macroalbuminuria, and then ESRD has had to be modified. Albumin excretion frequently regresses, and GFR can decline without abnormality in albumin excretion. There is emerging evidence that changes in renal function occurring early in the course of diabetes predict future outcomes. The major challenges are to prevent DKD onset, to detect it early, and to improve DKD outcomes globally.

Evaluation of the association between arsenic and diabetes: a National Toxicology Program workshop review

BACKGROUND

Diabetes affects an estimated 346 million persons globally, and total deaths from diabetes are projected to increase > 50% in the next decade. Understanding the role of environmental chemicals in the development or progression of diabetes is an emerging issue in environmental health. In 2011, the National Toxicology Program (NTP) organized a workshop to assess the literature for evidence of associations between certain chemicals, including inorganic arsenic, and diabetes and/or obesity to help develop a focused research agenda. This review is derived from discussions at that workshop.

OBJECTIVES

Our objectives were to assess the consistency, strength/weaknesses, and biological plausibility of findings in the scientific literature regarding arsenic and diabetes and to identify data gaps and areas for future evaluation or research. The extent of the existing literature was insufficient to consider obesity as an outcome.

DATA SOURCES, EXTRACTION, AND SYNTHESIS

Studies related to arsenic and diabetes or obesity were identified through PubMed and supplemented with relevant studies identified by reviewing the reference lists in the primary literature or review articles.

CONCLUSIONS

Existing human data provide limited to sufficient support for an association between arsenic and diabetes in populations with relatively high exposure levels (≥ 150 µg arsenic/L in drinking water). The evidence is insufficient to conclude that arsenic is associated with diabetes in lower exposure (< 150 µg arsenic/L drinking water), although recent studies with better measures of outcome and exposure support an association. The animal literature as a whole was inconclusive; however, studies using better measures of diabetes-relevant end points support a link between arsenic and diabetes.

Arsenic exposure, diabetes prevalence, and diabetes control in the Strong Heart Study

This study evaluated the association of arsenic exposure, as measured in urine, with diabetes prevalence, glycated hemoglobin, and insulin resistance in American Indian adults from Arizona, Oklahoma, and North and South Dakota (1989-1991). We studied 3,925 men and women 45-74 years of age with available urine arsenic measures. Diabetes was defined as a fasting glucose level of 126 mg/dL or higher, a 2-hour glucose level of 200 mg/dL or higher, a hemoglobin A1c (HbA1c) of 6.5% or higher, or diabetes treatment. Median urine arsenic concentration was 14.1 µg/L (interquartile range, 7.9-24.2). Diabetes prevalence was 49.4%. After adjustment for sociodemographic factors, diabetes risk factors, and urine creatinine, the prevalence ratio of diabetes comparing the 75th versus 25th percentiles of total arsenic concentrations was 1.14 (95% confidence interval: 1.08, 1.21). The association between arsenic and diabetes was restricted to participants with poor diabetes control (HbA1c ≥8%). Arsenic was positively associated with HbA1c levels in participants with diabetes. Arsenic was not associated with HbA1c or with insulin resistance (assessed by homeostatic model assessment to quantify insulin resistance) in participants without diabetes. Urine arsenic was associated with diabetes control in a population from rural communities in the United States with a high burden of diabetes. Prospective studies that evaluate the direction of the relation between poor diabetes control and arsenic exposure are needed.

Glomerular hyperfiltration and renal disease progression in type 2 diabetes

OBJECTIVE

To describe the prevalence and determinants of hyperfiltration (glomerular filtration rate [GFR] ≥120 mL/min/1.73 m(2)), GFR decline, and nephropathy onset or progression in type 2 diabetic patients with normo- or microalbuminuria.

RESEARCH DESIGN AND METHODS

We longitudinally studied 600 hypertensive type 2 diabetic patients with albuminuria <200 μg/min and who were retrieved from two randomized trials testing the renal effect of trandolapril and delapril. Target blood pressure (BP) was <120/80 mmHg, and HbA(1c) was <7%. GFR, albuminuria, and glucose disposal rate (GDR) were centrally measured by iohexol plasma clearance, nephelometry in three consecutive overnight urine collections, and hyperinsulinemic euglycemic clamp, respectively.

RESULTS

Over a median (range) follow-up of 4.0 (1.7-8.1) years, GFR declined by 3.37 (5.71-1.31) mL/min/1.73 m(2) per year. GFR change was bimodal over time: a larger reduction at 6 months significantly predicted slower subsequent decline (coefficient: -0.0054; SE: 0.0009), particularly among hyperfiltering patients. A total of 90 subjects (15%) were hyperfiltering at inclusion, and 11 of 47 (23.4%) patients with persistent hyperfiltration progressed to micro- or macroalbuminuria versus 53 (10.6%) of the 502 who had their hyperfiltration ameliorated at 6 months or were nonhyperfiltering since inclusion (hazard ratio 2.16 [95% CI 1.13-4.14]). Amelioration of hyperfiltration was independent of baseline characteristics or ACE inhibition. It was significantly associated with improved BP and metabolic control, amelioration of GDR, and slower long-term GFR decline on follow-up.

CONCLUSIONS

Despite intensified treatment, patients with type 2 diabetes have a fast GFR decline. Hyperfiltration affects a subgroup of patients and may contribute to renal function loss and nephropathy onset or progression. Whether amelioration of hyperfiltration is renoprotective is worth investigating.

Renal function in diabetic disease models: the tubular system in the pathophysiology of the diabetic kidney

Diabetes mellitus affects the kidney in stages. At the onset of diabetes mellitus, in a subset of diabetic patients the kidneys grow large, and glomerular filtration rate (GFR) becomes supranormal, which are risk factors for developing diabetic nephropathy later in life. This review outlines a pathophysiological concept that focuses on the tubular system to explain these changes. The concept includes the tubular hypothesis of glomerular filtration, which states that early tubular growth and sodium-glucose cotransport enhance proximal tubule reabsorption and make the GFR supranormal through the physiology of tubuloglomerular feedback. The diabetic milieu triggers early tubular cell proliferation, but the induction of TGF-β and cyclin-dependent kinase inhibitors causes a cell cycle arrest and a switch to tubular hypertrophy and a senescence-like phenotype. Although this growth phenotype explains unusual responses like the salt paradox of the early diabetic kidney, the activated molecular pathways may set the stage for tubulointerstitial injury and diabetic nephropathy.

Renal function and incidence of chronic kidney disease in HIV patients: a Danish cohort study

BACKGROUND

Impaired renal function is of major concern in human immunodeficiency virus (HIV)-infected patients.

METHODS

We used a mixed effects linear regression model to determine estimated glomerular filtration rates (eGFRs) in a population-based cohort of incident Danish HIV patients and stratified on baseline eGFR (eGFR(B)) < 90 and ≥ 90 ml/min per 1.73 m(2). Incidence rate ratios (IRRs) for chronic kidney disease (CKD) - 2 consecutive eGFR values < 60 ml/min per 1.73 m(2) measured > 3 months apart - were estimated (time-updated Cox-regression model).

RESULTS

The effect of time with HIV on eGFR was small in both strata (- 0.09 (95% confidence interval (CI) - 0.27, 0.09) and - 0.46 (95% CI - 0.64, - 0.27) ml/min per 1.73 m(2) per y). Treatment with tenofovir and indinavir was associated with lower eGFR in both strata: tenofovir - 2.00 (95% CI - 3.45, - 0.56) and - 1.94 (95% CI - 3.43, - 0.44) ml/min per 1.73 m(2) and indinavir - 2.14 (95% CI - 3.63, - 0.64) and - 3.29 (95% CI - 5.25, - 1.32) ml/min per 1.73 m(2). Nevirapine, atazanavir, and the combination of tenofovir and atazanavir were associated with lower eGFR in patients with eGFR(B) < 90 ml/min per 1.73 m(2). Highly active antiretroviral therapy (HAART) and exposure to tenofovir and atazanavir in combination were associated with CKD in patients with eGFR(B) < 90 ml/min per 1.73 m(2) (adjusted IRRs 6.08 (95% CI 2.76-13.41) and 26.75 (95% CI 9.54-75.05)).

CONCLUSION

Tenofovir and indinavir reduce eGFR, while time with HIV only has a modest effect on this parameter. Low eGFR(B) is associated with an increased risk of CKD, especially when receiving HAART regimens containing the combination tenofovir/atazanavir.

Hyperfiltration in type 1 diabetes: does it exist and does it matter for nephropathy?

AIMS/HYPOTHESIS

Hyperfiltration is widely regarded as a contributing factor to the development of microalbuminuria and progressive nephropathy in type 1 diabetes. However, recent studies have questioned this conclusion.

METHODS

To address this conflicting evidence, we examined the association between hyperfiltration and progression to microalbuminuria in 2,318 adults with type 1 diabetes. We also compared the estimated GFR in our diabetic patients with rates observed in 6,247 adults from the Finnish general population, using age- and sex-specific z scores.

RESULTS

The distribution of estimated GFR in adults with type 1 diabetes and normoalbuminuria was not significantly different from that expected in the general population (p = 0.51, Mann-Whitney test). Type 1 diabetic patients with a higher estimated GFR were also no more likely to develop microalbuminuria over a median of 5.2 years of follow-up than those with normal estimated GFR. This was the case regardless of whether hyperfiltration was defined by an absolute threshold, deciles of estimated GFR or a z score, using creatinine- or cystatin-based clearance formulas in men or in women.

CONCLUSIONS/INTERPRETATION

Together with other studies, these data suggest that creatinine- or cystatin-based estimates of GFR do not predict the development of microalbuminuria in patients with type 1 diabetes. Moreover, in the absence of incipient or overt nephropathy, conventionally determined renal function in patients with type 1 diabetes appears no different from that in the general population. This is hardly surprising, given that these individuals, by all definitions, do not have kidney disease.

Integrin α1/Akita double-knockout mice on a Balb/c background develop advanced features of human diabetic nephropathy

Animal models that mimic human diabetic nephropathy are useful to identify key factors in pathogenesis of this disease, as well as the development of new therapies. Several mouse models of diabetes have features of human diabetic nephropathy, yet none of these completely fulfill the Animal Models of Diabetes Complications Consortium criteria and completely reproduce pathological and functional features of the human disease. The Akita mouse carries a mutation in the insulin-2 gene and, to date, only survives as heterozygotes that develop spontaneous type 1 diabetes. Here we show that Akita mice with mutation of both insulin-2 alleles (Akita knockout (KO)) survive if crossed onto the Balb/c background. These mice develop hyperglycemia, more severe albuminuria, and mesangial sclerosis compared with heterozygous mice on the same genetic background. Interestingly, crossing these AkitaKO mice with integrin α1KO mice, a model of exacerbated glomerulosclerosis after injury and also on the Balb/c background, resulted in a 16-fold increase in albuminuria, significant mesangial matrix expansion, nodular and diffuse glomerulosclerosis, and a 2-fold increase in glomerular basement membrane thickening when compared with nondiabetic mice. Moreover, a significant decline in glomerular filtration was evident in the α1KOAkitaKO mice at 6 months of age. Thus, the integrin α1KOAkitaKO Balb/c mouse represents a promising model presenting with most features of human diabetic nephropathy.

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.

Changes of the tubular markers in type 2 diabetes mellitus with glomerular hyperfiltration

AIM

To assess whether glomerular hyperfiltration (GHF) could result in renal tubular damage in type 2 diabetes mellitus (T2DM) patients.

METHODS

Reference value of estimated glomerular filtration rate (eGFR) was determined in 248 healthy individuals based on serum CysC levels. GHF was defined as an eGFR exceeding the sex-specific 97.5th percentile in non-diabetic individuals. In the present study, 30 with GHF, 58 with norm-GFR T2DM, and 24 healthy controls were recruited. Tubular markers, such as urinary N-acetyl-β-D-glucosaminidase (NAG) and kidney injury molecule 1 (KIM-1), as well as serum and urinary neutrophil gelatinase-associated lipocalin (NGAL), were measured and compared. The correlation of these markers with eGFR was analyzed in the GHF group.

RESULTS

The GHF group had higher urinary NGAL and KIM-1 levels but lower serum NGAL level than the norm-GFR and control groups. Slightly decreased serum NGAL and increased urinary NGAL levels were also noted in the norm-GFR group compared with those of the controls. There was no statistical difference in the urinary NAG values among the three groups. Correlation analysis showed that eGFR was positively related to fasting blood glucose (FBG), HbA1c, urinary NGAL, and KIM-1, but negatively with serum NGAL in the GHF group.

CONCLUSION

Higher urinary tubular damage markers were found in T2DM patients with GHF than the norm-GFR and control groups, probably a direct proof that GHF is a deleterious factor for diabetic nephropathy.

Microvascular disease precedes the decline in renal function in the streptozotocin-induced diabetic rat

Diabetic nephropathy is a progressive and generalized vasculopathic condition associated with abnormal angiogenesis. We aim to determine whether changes in renal microvascular (MV) density correlate with and play a role in the progressive deterioration of renal function in diabetes. We hypothesize that MV changes represent the early steps of renal injury that worsen as diabetes progresses, initiating a vicious circle that leads to irreversible renal injury. Male nondiabetic (ND) or streptozotocin-induced diabetic (D) Sprague-Dawley rats were followed for 4 or 12 wk. Renal blood flow and glomerular filtration rate (GFR) were measured by PAH and (125)I-[iothalamate], respectively. Renal MV density was quantified ex vivo using three-dimensional micro computed tomography and JG-12 immunoreactivity. Vascular endothelial growth factor (VEGF) levels (ELISA) and expression of VEGF receptors and factors involved in MV remodeling were quantified in renal tissue by Western blotting. Finally, renal morphology was investigated by histology. Four weeks of diabetes was associated with increased GFR, accompanied by a 34% reduction in renal MV density and augmented renal VEGF levels. However, at 12 wk, while GFR remained similarly elevated, reduction of MV density was more pronounced (75%) and associated with increased MV remodeling, renal fibrosis, but unchanged renal VEGF compared with ND at 12 wk. The damage, loss, and subsequent remodeling of the renal MV architecture in the diabetic kidney may represent the initiating events of progressive renal injury. This study suggests a novel concept of MV disease as an early instigator of diabetic kidney disease that may precede and likely promote the decline in renal function.

Lower urinary tract symptoms have negative associations with glomerular filtration rate irrespective of prostate volume in Korean men

OBJECTIVE

To understand the relationship between lower urinary tract symptoms (LUTS) and renal function by prostate volume (PV) in Korean men. LUTS can be related to early renal dysfunction, irrespective of bladder outlet obstructive lesions, few studies have been conducted.

METHODS

We conducted a cross-sectional survey of 3713 men, aged≥40 years, who received routine comprehensive health evaluations, including transrectal ultrasonography and the International Prostate Symptom Score questionnaire. We used the estimated glomerular filtration rate (GFR) for the assessment of renal function and the IPSS for LUTS severity. We compared LUTS and GFR using multivariate regression analysis after adjusting for age and/or PV.

RESULTS

An increasing severity of LUTS, especially voiding LUTS, was associated with a decreasing GFR in the older age group (≥55 years). In a stratified analysis by PV of 30 cm3, voiding LUTS showed a negative association with GFR, irrespective of the PV (P for trend<.01 and P for trend<.02), but total LUTS did so only in the small PV group.

CONCLUSION

In men without known urinary tract disease, LUTS and renal function had a negative association, especially in older men with a normal PV. Although the underlying mechanism is uncertain, physicians who treat patients with moderate or severe LUTS should monitor renal function, even in patients with a normal PV.

Glomerular hyperfiltration and renal progression in children with autosomal dominant polycystic kidney disease

BACKGROUND AND OBJECTIVES

The purpose of this study was to determine whether glomerular hyperfiltration (GH) occurring early in autosomal dominant polycystic kidney disease (ADPKD) is indicative of more rapid disease progression in children.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

One hundred eighty children with ADPKD (ages 4 to 18 years) with normal renal function were examined by renal ultrasound. Renal volume was calculated using a standard formula for a modified ellipsoid. Creatinine clearance was calculated from serum creatinine and 24-hour urine creatinine. GH was defined as creatinine clearance ≥140 ml/min per 1.73 m(2).

RESULTS

Thirty-two children had GH (mean age 11.4 ± 3.6 years) and 148 had normal renal function (mean age 10.8 ± 3.9 years). Patients with GH at baseline demonstrated an increased rate of total renal volume growth (β: rate of change = +19.3 ± 10.8 cm(3)/year) over 5 years compared with those without GH at baseline (β = -4.3 ± 7.7 cm(3)/year), P = 0.008. Those with GH at baseline experienced a faster decline in creatinine clearance in subsequent years (β = -5.0 ± 0.8 ml/min per 1.73 m(2) per year) compared with those without GH at baseline (β = +1.0 ± 0.4 ml/min per 1.73 m(2) per year), P < 0.0001.

CONCLUSIONS

This study revealed that occurrence of GH in ADPKD children is associated with a significantly faster decline in renal function and higher rate of kidney enlargement over time. GH combined with the increased renal volume may therefore be used as an early marker for a more severe progression of ADPKD in children.

Estimated glomerular filtration rate and its association with the retinol-binding protein 4 (RBP4) locus on human chromosome 10q23

BACKGROUND

We tested for associations between estimated glomerular filtration rate (eGFR) and retinol-binding protein 4 (RBP4) haplotypes found on human chromosome 10q23. This locus had been linked to eGFR in a previous linkage scan in patients with Type 2 diabetes mellitus.

METHODS

We analysed 469 patients with Type 2 diabetes and 174 normoalbuminuric controls for associations between RBP4 haplotypes and eGFR. For comparison with controls, 295 cases with proteinuria/end-stage renal disease were tested for associations with advanced diabetic nephropathy. Genotyping was performed using high-resolution DNA melting assays. Data analysis was performed using the haplo.stats package.

RESULTS

Genetic variations in RBP4 were not associated with advanced diabetic nephropathy. Compared with the common A/G/G/C haplotype, C/A/A/C carriers among the normoalbuminuric controls had higher eGFR values among younger patients but lower eGFRs among the older patients (effect size=2.2, P=3.3×10(-7)). Furthermore, while eGFR values were fairly consistent over the range of systolic blood pressure (SBP) values for the common haplotype, eGFR in C/A/A/C carriers increased with SBP (effect size=3.6, P=1.5×10(-2)). There was a significant interaction between the C/A/A/C haplotype and HbA1c as they affect eGFR compared to the common haplotype (effect size=2.1, P=2.1×10(-3)). Power calculations demonstrated that our study had >90% power to detect the observed interactions even while performing multiple hypotheses testing. The interaction between SBP and the C/A/A/C haplotype remained significant (P=2.8×10(-2)) even when these three haplotype-environment interactions were simultaneously estimated.

CONCLUSION

RBP4 haplotypes may be important in genetically modulating renal function in response to environmental challenges among patients with Type 2 diabetes.

Estimation of renal function in patients with diabetes

Diabetes is the leading cause of chronic kidney disease (CKD), which makes estimation of renal function crucial. Serum creatinine is not an ideal marker of glomerular filtration rate (GFR), which also depends on digestive absorption, and the production of creatinine in muscle and its tubular secretion. Formulas have been devised to estimate GFR from serum creatinine but, given the wide range of GFR, proteinuria, body mass index and specific influence of glycaemia on GFR, the uncertainty of these estimations is a particular concern for patients with diabetes. The most popular recommended formulas are the simple Cockcroft-Gault equation, which is inaccurate and biased, as it calculates clearance of creatinine in proportion to body weight, and the MDRD equation, which is more accurate, but systematically underestimates normal and high GFR, being established by a statistical analysis of results from renal-insufficient patients. This underestimation explains why the MDRD equation is repeatedly found to give a poor estimation of GFR in patients with recently diagnosed diabetes and is a poor tool for reflecting GFR decline when started from normal, as well as the source of unexpected results when applied to epidemiological studies with a 60mL/min/1.73m(2) threshold as the definition of CKD. The more recent creatinine-based formula, the Mayo Clinic Quadratic (MCQ) equation, and the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) improve such underestimation, as both were derived from populations that included subjects with normal renal function. Determination of cystatin C is also promising, but needs standardisation.

The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation is less accurate in patients with Type 2 diabetes when compared with healthy individuals

AIMS

To analyse the performances of Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and of Modification of Diet in Renal Disease (MDRD) study equations to estimate glomerular filtration rate (GFR) in patients with Type 2 diabetes mellitus with GFRs >60 ml/min and in healthy volunteers.

METHODS

This cross-sectional study included 111 individuals (56 patients with Type 2 diabetes and 55 healthy volunteers), aged 58 ± 9 years; 54 individuals were men (49%) and ninety-eight (88%) were white. Glomerular filtration rate was measured by the (51) Cr-EDTA single-injection method ((51) Cr-GFR) and estimated according to the standardized MDRD and CKD-EPI equations. Serum creatinine was measured by a traceable Jaffe method. Bland-Altman analysis was used to examine the agreement between measured and estimated GFR. Bias, accuracy and precision were evaluated.

RESULTS

In diabetic individuals, (51) Cr-GFR was 106 ± 27 ml/min/1.73 m(2) , CKD-EPI-estimated GFR 82 ± 18 ml/min/1.73 m(2) and MDRD-estimated GFR 80 ± 21 ml/min/1.73 m(2) (P < 0.001). In healthy volunteers, the corresponding values were 98 ± 20, 89 ± 13 and 84 ± 14 ml/min/1.73 m(2) (P < 0.001). The accuracy of CKD-EPI (P30) was higher in healthy volunteers than in diabetic patients (90 vs. 66%, respectively, P < 0.001). The MDRD equation performed as poorly as the CKD-EPI equation in individuals with Type 2 diabetes.

CONCLUSIONS

The CKD-EPI equation is less accurate in patients with Type 2 diabetes when compared with healthy individuals, with a 2.5-fold greater bias.

Nephrinuria associates with multiple renal traits in type 2 diabetes

BACKGROUND

The involvement of nephrin in controlling renal function is unclear with the literature only emphasizing its role in albuminuria. We therefore investigated the potential association between nephrinuria as evidenced by the appearance of urinary immunopositive nephrin fragments, with multiple renal traits.

METHODS

Western blot analysis of the urine samples from a cross-sectional study of 381 Chinese type 2 diabetic patients revealed four distinct protein fragments, indicative of nephrinuria. Albuminuria was measured in random spot urine samples using the albumin/creatinine ratio (ACR), while estimated glomerular filtration rate (eGFR) was calculated using the creatinine-based Modification of Diet in Renal Disease formula.

RESULTS

Each nephrin fragment was associated with a decline in eGFR (smallest P = 0.001). Even with the inclusion of logarithmic form of ACR (ln ACR) in the multivariate model, nephrinuria still remained significantly associated with lower eGFR (smallest P < 0.05). Nephrinuria was also strongly associated with lnACR and this finding was independent of eGFR (smallest P < 0.001). Thus, nephrinuria was independently associated with both renal traits in the form of lnACR and eGFR. Furthermore, nephrinuria was significantly associated with lower eGFR even among normoalbuminuric patients (ACR ≤ 30 mg/g) (smallest P = 0.002), potentially implicating nephrinuria in the development of normoalbuminuric renal insufficiency. Apart from the renal traits under investigation, the presence of nephrinuria did not associate with other patient clinical characteristics.

CONCLUSIONS

Nephrinuria was associated with multiple renal traits in type 2 diabetes even in normoalbuminuric patients who are traditionally perceived as having a low risk of chronic kidney disease.