Can rodent models of diabetic kidney disease clarify the significance of early hyperfiltration?: recognizing clinical and experimental uncertainties

Glomerular hyperfiltration: part 2-clinical significance in children

Glomerular hyperfiltration (GHF) is a phenomenon that can occur in various clinical conditions affecting the kidneys such as sickle cell disease, diabetes mellitus, autosomal dominant polycystic kidney disease, and solitary functioning kidney. Yet, the pathophysiological mechanisms vary from one disease to another and are not well understood. More so, it has been demonstrated that GHF may occur at the single-nephron in some clinical conditions while in others at the whole-kidney level. In this review, we explore the pathophysiological mechanisms of GHF in relation to various clinical conditions in the pediatric population. In addition, we discuss the role and mechanism of action of important factors such as gender, low birth weight, and race in the pathogenesis of GHF. Finally, in this current review, we further highlight the consequences of GHF in the progression of kidney disease.

The Role of Macula Densa Nitric Oxide Synthase 1 Beta Splice Variant in Modulating Tubuloglomerular Feedback

Abnormalities in renal electrolyte and water excretion may result in inappropriate salt and water retention, which facilitates the development and maintenance of hypertension, as well as acid-base and electrolyte disorders. A key mechanism by which the kidney regulates renal hemodynamics and electrolyte excretion is via tubuloglomerular feedback (TGF), an intrarenal negative feedback between tubules and arterioles. TGF is initiated by an increase of NaCl delivery at the macula densa cells. The increased NaCl activates luminal Na-K-2Cl cotransporter (NKCC2) of the macula densa cells, which leads to activation of several intracellular processes followed by the production of paracrine signals that ultimately result in a constriction of the afferent arteriole and a tonic inhibition of single nephron glomerular filtration rate. Neuronal nitric oxide (NOS1) is highly expressed in the macula densa. NOS1β is the major splice variant and accounts for most of NO generation by the macula densa, which inhibits TGF response. Macula densa NOS1β-mediated modulation of TGF responses plays an essential role in control of sodium excretion, volume and electrolyte hemostasis, and blood pressure. In this article, we describe the mechanisms that regulate macula densa-derived NO and their effect on TGF response in physiologic and pathologic conditions. © 2023 American Physiological Society. Compr Physiol 13:4215-4229, 2023.

Role of the macula densa sodium glucose cotransporter type 1-neuronal nitric oxide synthase-tubuloglomerular feedback pathway in diabetic hyperfiltration

An increase of glomerular filtration rate (GFR) is a common observation in early diabetes and is considered a key risk factor for subsequent kidney injury. However, the mechanisms underlying diabetic hyperfiltration have not been fully clarified. Here, we tested the hypothesis that macula densa neuronal nitric oxide synthase (NOS1) is upregulated via sodium glucose cotransporter type 1 (SGLT1) in diabetes, which then inhibits tubuloglomerular feedback (TGF) promoting glomerular hyperfiltration. Therefore, we examined changes in cortical NOS1 expression and phosphorylation, nitric oxide production in the macula densa, TGF response, and GFR during the early stage of insulin-deficient (Akita) diabetes in wild-type and macula densa-specific NOS1 knockout mice. A set of sophisticated techniques including microperfusion of juxtaglomerular apparatus in vitro, micropuncture of kidney tubules in vivo, and clearance kinetics of plasma fluorescent-sinistrin were employed. Complementary studies tested the role of SGLT1 in SGLT1 knockout mice and explored NOS1 expression and phosphorylation in kidney biopsies of cadaveric donors. Diabetic mice had upregulated macula densa NOS1, inhibited TGF and elevated GFR. Macula densa-selective NOS1 knockout attenuated the diabetes-induced TGF inhibition and GFR elevation. Additionally, deletion of SGLT1 prevented the upregulation of macula densa NOS1 and attenuated inhibition of TGF in diabetic mice. Furthermore, the expression and phosphorylation levels of NOS1 were increased in cadaveric kidneys of diabetics and positively correlated with blood glucose as well as estimated GFR in the donors. Thus, our findings demonstrate that the macula densa SGLT1-NOS1-TGF pathway plays a crucial role in the control of GFR in diabetes.

Knockout of Macula Densa Neuronal Nitric Oxide Synthase Increases Blood Pressure in db/db Mice

[Figure: see text].

Kidney and vascular function in adult patients with hereditary fructose intolerance

Objective: Previous studies have shown that patients with hereditary fructose intolerance (HFI) are characterized by a greater intrahepatic triglyceride content, despite a fructose-restricted diet. The present study aimed to examine the long-term consequences of HFI on other aldolase-B-expressing organs, i.e. the kidney and vascular endothelium.

Methods: Fifteen adult HFI patients were compared to healthy control individuals matched for age, sex and body mass index. Aortic stiffness was assessed by carotid-femoral pulse wave velocity (cf-PWV) and endothelial function by peripheral arterial tonometry, skin laser doppler flowmetry and the endothelial function biomarkers soluble E-selectin [sE-selectin] and von Willebrand factor. Serum creatinine and cystatin C were measured to estimate the glomerular filtration rate (eGFR). Urinary glucose and amino acid excretion and the ratio of tubular maximum reabsorption of phosphate to GFR (TmP/GFR) were determined as measures of proximal tubular function. Results: Median systolic blood pressure was significantly higher in HFI patients (127 versus 122 mmHg, p = .045). Pulse pressure and cf-PWV did not differ between the groups (p = .37 and p = .49, respectively). Of all endothelial function markers, only sE-selectin was significantly higher in HFI patients (p = .004). eGFR was significantly higher in HFI patients than healthy controls (119 versus 104 ml/min/1.73m², p = .001, respectively). All measurements of proximal tubular function did not differ significantly between the groups.

Conclusions: Adult HFI patients treated with a fructose-restricted diet are characterized by a higher sE-selectin level and slightly higher systolic blood pressure, which in time could contribute to a greater cardiovascular risk. The exact cause and, hence, clinical consequences of the higher eGFR in HFI patients, deserves further study.

Association Between Body Composition and Glomerular Hyperfiltration Among Chinese Adults

High body mass index (BMI) is the most common parameter to assess excess adiposity, and has been linked to glomerular hyperfiltration (GH). However, BMI may be misleading in the estimation of body fat content due to its inability to discriminate between body fat and lean mass. In recent years, the convenient biological impedance analysis has made prediction of certain diseases somewhat feasible and accessible using body composition (BC). Accordingly, we conducted a cross-sectional study to explore the association between BC and GH among Chinese adult population. A total of 6902 adults (aged 38.6 ± 8.3 years, 70.1% males) who consecutively visited the Health Checkup Clinic were enrolled. BC including fat mass and lean body mass (LBM) was evaluated by biological impedance analysis. The upper quartile of eGFR which exceeded 117.3 mL/min/1.73 m² was defined as GH, in comparison with the lower three quartiles (control group). As a categorical outcome, GH subjects had higher fat/LBM than the control group, which was 34.7 ± 10.9 (%) vs. 34.0 ± 10.5 (%), P = 0.01; however, the BMI in GH group was lower than in the control group, which was 24.5 ± 3.7 (%) vs. 24.9 ± 3.6 (%), P < 0.001. Fat/height and Fat/BSA were not significantly different between the two groups. Moreover, after adjusting for potential confounders, fat/LBM significantly correlated with GH (OR = 2.09, 95% CI, 1.11 to 3.93). The study revealed that fat/LBM significantly correlated with GH among Chinese adult population, which highlights that adiposity might be an important and potentially modifiable determinant of GH.

Macula Densa SGLT1-NOS1-Tubuloglomerular Feedback Pathway, a New Mechanism for Glomerular Hyperfiltration during Hyperglycemia

BACKGROUND

Glomerular hyperfiltration is common in early diabetes and is considered a risk factor for later diabetic nephropathy. We propose that sodium-glucose cotransporter 1 (SGLT1) senses increases in luminal glucose at the macula densa, enhancing generation of neuronal nitric oxide synthase 1 (NOS1)-dependent nitric oxide (NO) in the macula densa and blunting the tubuloglomerular feedback (TGF) response, thereby promoting the rise in GFR.

METHODS

We used microperfusion, micropuncture, and renal clearance of FITC-inulin to examine the effects of tubular glucose on NO generation at the macula densa, TGF, and GFR in wild-type and macula densa-specific NOS1 knockout mice.

RESULTS

Acute intravenous injection of glucose induced hyperglycemia and glucosuria with increased GFR in mice. We found that tubular glucose blunts the TGF response in vivo and in vitro and stimulates NO generation at the macula densa. We also showed that SGLT1 is expressed at the macula densa; in the presence of tubular glucose, SGLT1 inhibits TGF and NO generation, but this action is blocked when the SGLT1 inhibitor KGA-2727 is present. In addition, we demonstrated that glucose increases NOS1 expression and NOS1 phosphorylation at Ser1417 in mouse renal cortex and cultured human kidney tissue. In macula densa-specific NOS1 knockout mice, glucose had no effect on NO generation, TGF, and GFR.

CONCLUSIONS

We identified a novel mechanism of acute hyperglycemia-induced hyperfiltration wherein increases in luminal glucose at the macula densa upregulate the expression and activity of NOS1 via SGLT1, blunting the TGF response and promoting glomerular hyperfiltration.

Association of kidney disease measures with risk of renal function worsening in patients with type 1 diabetes

BACKGROUND

Albuminuria has been classically considered a marker of kidney damage progression in diabetic patients and it is routinely assessed to monitor kidney function. However, the role of a mild GFR reduction on the development of stage ≥3 CKD has been less explored in type 1 diabetes mellitus (T1DM) patients. Aim of the present study was to evaluate the prognostic role of kidney disease measures, namely albuminuria and reduced GFR, on the development of stage ≥3 CKD in a large cohort of patients affected by T1DM.

METHODS

A total of 4284 patients affected by T1DM followed-up at 76 diabetes centers participating to the Italian Association of Clinical Diabetologists (Associazione Medici Diabetologi, AMD) initiative constitutes the study population. Urinary albumin excretion (ACR) and estimated GFR (eGFR) were retrieved and analyzed. The incidence of stage ≥3 CKD (eGFR < 60 mL/min/1.73 m2) or eGFR reduction > 30% from baseline was evaluated.

RESULTS

The mean estimated GFR was 98 ± 17 mL/min/1.73m² and the proportion of patients with albuminuria was 15.3% (n = 654) at baseline. About 8% (n = 337) of patients developed one of the two renal endpoints during the 4-year follow-up period. Age, albuminuria (micro or macro) and baseline eGFR < 90 ml/min/m² were independent risk factors for stage ≥3 CKD and renal function worsening. When compared to patients with eGFR > 90 ml/min/1.73m² and normoalbuminuria, those with albuminuria at baseline had a 1.69 greater risk of reaching stage 3 CKD, while patients with mild eGFR reduction (i.e. eGFR between 90 and 60 mL/min/1.73 m2) show a 3.81 greater risk that rose to 8.24 for those patients with albuminuria and mild eGFR reduction at baseline.

CONCLUSIONS

Albuminuria and eGFR reduction represent independent risk factors for incident stage ≥3 CKD in T1DM patients. The simultaneous occurrence of reduced eGFR and albuminuria have a synergistic effect on renal function worsening.

A Novel Method for the Determination of Vancomycin in Serum by High-Performance Liquid Chromatography-Tandem Mass Spectrometry and Its Application in Patients with Diabetic Foot Infections

A novel, precise, and accurate high-performance liquid chromatography-tandem mass spectrometry (Q-trap-MS) method was developed, optimized, and validated for determination of vancomycin in human serum using norvancomycin as an internal standard. Effect of different parameters on the analysis was evaluated. ZORBAX SB-C18 column (150 × 4.6 mm, 5 μm) using water (containing 0.1% formic acid, v/v)⁻acetonitrile (containing 0.1% formic acid, v/v) as a mobile phase was chosen. The calibration curve was linear over the concentration ranges of 1 to 2000 ng/mL for vancomycin. The limit of detection (LOD) and limit of quantification (LOQ) for vancomycin were 0.3 and 1.0 ng/mL. Recoveries were between 87.2 and 102.3%, which gave satisfactory precision. A total of 100 serum samples (from 50 patients with diabetic foot proven Gram-positive infection and 50 nondiabetic patients with pneumonia requiring hospitalization and antibiotic therapy) were analyzed by this method. The trough vancomycin concentrations of diabetic foot infection (DFI) patients and nondiabetic patients were 8.20 ± 2.83 μg/mL (range: 4.80⁻14.2 μg/mL) and 15.80 ± 5.43 μg/mL (range: 8.60⁻19.5 μg/mL), respectively. The method is sensitive, precise, and reproducible, it could be applied for routine laboratory analysis of vancomycin in serum samples.

Association of elevated blood serum high-sensitivity C-reactive protein levels and body composition with chronic kidney disease: A population-based study in Taiwan

Chronic kidney disease (CKD) is a risk factor for cardiovascular diseases and is associated with an increase in all-cause mortality. Studies regarding association among various body compositions in different inflamed states and the risk of CKD were rare. We aimed to evaluate the relationship among body composition, high-sensitivity C-reactive protein (hsCRP) level, and the risk of CKD.This was a retrospective cross-sectional study using annual health examination data from 2 medical centers in northern and southern Taiwan between January and December 2015. We performed a variance analysis of the estimated glomerular filtration rate (eGFR) distribution in groups based on hsCRP and body fat percentage (BFP), and a multivariate logistic regression model was used to assess the relationship among BFP, hsCRP levels, and CKD.A total of 10,267 subjects aged ≥18 years undergoing health examination were analyzed. In our study, overweight/obese patients were associated with increased risk of CKD. Nevertheless, in subjects with elevated hsCRP level, overweight/obese group with a higher BFP had a lower risk of CKD as compared with overweight/obese with normal BFP group (for BMI ≧ 23 kg/m, high BFP/high hsCRP: odds ratio [OR] for CKD 1.86, 95% confidence interval [CI] = 1.10-3.17, P = .02; normal BFP/high hsCRP group: OR 2.32, 95% CI = 1.23-4.37, P = .01) after adjusting for various confounders.Our findings suggest that various body compositions in different inflamed states may interfere with the risk of CKD. These results provide an important method for the early detection of impaired renal function by identifying various body compositions and inflammation states to detect CKD at an earlier stage.

Glucose dilates renal afferent arterioles via glucose transporter-1

Glomerular hyperfiltration occurs during the early stage of diabetes. An acute glucose infusion increases glomerular filtration rate. The involvement of tubuloglomerular feedback response and direct effect of glucose on the afferent arterioles (Af-Arts) have been suggested. However, the signaling pathways to trigger Af-Art dilatation have not been fully identified. Therefore, in the present study we tested our hypothesis that an increase in glucose concentration enhances endothelial nitric oxide synthesis activity and dilates the Af-Arts via glucose transporter-1 (GLUT1) using isolated mouse Af-Arts with perfusion. We isolated and microperfused the Af-Arts from nondiabetic C57BL/6 mice. The Af-Arts were preconstricted with norepinephrine (1 µM). When we switched the d-glucose concentration from low (5 mM) to high (30 mM) in the perfusate, the preconstricted Af-Arts significantly dilated by 37.8 ± 7.1%, but L-glucose did not trigger the dilation. GLUT1 mRNA was identified in microdisserted Af-Arts measured by RT-PCR. Changes in nitric oxide (NO) production in Af-Art were also measured using fluorescent probe when ambient glucose concentration was increased. When the d-glucose concentration was switched from 5 to 30 mM, NO generation in Af-Art was significantly increased by 19.2 ± 6.2% (84.7 ± 4.1 to 101.0 ± 9.3 U/min). l-Glucose had no effect on the NO generation. The GLUT1-selective antagonist 4-[({[4-(1,1-Dimethylethyl)phenyl]sulfonyl}amino)methyl]- N-3-pyridinylbenzamide and the nitric oxide synthase inhibitor N^G-nitro-l-arginine methyl ester blocked the high glucose-induced NO generation and vasodilation. In conclusion, we demonstrated that an increase in glucose concentration dilates the Af-Art by stimulation of the endothelium-derived NO production mediated by GLUT1.

B cells in type 1 diabetes mellitus and diabetic kidney disease

Type 1 diabetes mellitus (T1DM) is an autoimmune disorder that affects an estimated 30 million people worldwide. It is characterized by the destruction of pancreatic β cells by the immune system, which leads to lifelong dependency on exogenous insulin and imposes an enormous burden on patients and health-care resources. T1DM is also associated with an increased risk of comorbidities, such as cardiovascular disease, retinopathy, and diabetic kidney disease (DKD), further contributing to the burden of this disease. Although T cells are largely considered to be responsible for β-cell destruction in T1DM, increasing evidence points towards a role for B cells in disease pathogenesis. B cell-depletion, for example, delays disease progression in patients with newly diagnosed T1DM. Loss of tolerance of islet antigen-reactive B cells occurs early in disease and numbers of pancreatic CD20⁺ B cells correlate with β-cell loss. Although the importance of B cells in T1DM is increasingly apparent, exactly how these cells contribute to disease and its comorbidities, such as DKD, is not well understood. Here we discuss the role of B cells in the pathogenesis of T1DM and how these cells are activated during disease development. Finally, we speculate on how B cells might contribute to the development of DKD.

High-Normal Estimated Glomerular Filtration Rate in Early-Onset Preeclamptic Women 10 Years Postpartum

Women with a history of preeclampsia have a 5- to 12-fold increased risk to develop end-stage kidney disease. Previous observations in small cohorts suggest that former preeclamptic (fPE) women have subtle abnormalities in renal hemodynamics and renal function, which might predispose them to renal failure in later life. In this study, we analyzed renal function in a cross-sectional cohort consisting of former early-onset preeclamptic (fPE, n=339) and former healthy pregnant women (fHP, n=332), overall with a mean age of 39 years at 10 years postpartum. Estimated glomerular filtration rate (eGFR), assessed by the modification of diet in renal disease (MDRD) and chronic kidney disease–epidemiology (CKD-epi) equations, and urinary protein:creatinine ratios were assessed 10 years postpartum. Median MDRD and CKD-epi eGFR did not significantly differ between fHP and fPE groups, whereas a comparison of distribution of eGFR revealed a shift toward a high-normal MDRD eGFR in the fPE group (χ 2 , P =0.02) with the same trend for CKD-epi eGFR (χ 2 , P =0.18). The odds ratio for fPE women having MDRD eGFR >110 mL/min per 1.73 m 2 was 1.6 (1.1–2.4). In addition, the median urinary protein:creatinine ratio was slightly higher in fPE (8.5 versus 7.1 mg/mmol; P <0.01) and correlated positively with both MDRD and CKD-epi eGFR in fPE women. No increased incidence of CKD in fPE women was observed. In conclusion, we demonstrate subtle changes in renal function in former early-onset preeclamptic women 10 years postpartum, characterized by a high-normal eGFR and a slightly higher protein excretion. Whether these subtle differences predispose to or predict long-term renal function loss in fPE women remains to be investigated.

Clinical Trial Registration—

URL: http://www.trialregister.nl . Unique identifier: NTR2668.

Combined body mass index with high-sensitivity C-reactive protein as independent predictors for chronic kidney disease in a relatively healthy population in Taiwan

BACKGROUND/OBJECTIVES

Obesity, a chronic inflammatory state, increases risk of cardiovascular disease and insulin resistance, which are the leading cause of end-stage renal disease (ESRD). We evaluated the relationship between body mass index (BMI) and high-sensitivity C-reactive protein (hsCRP) level and impaired kidney function to determine the predictive value of both markers for estimating chronic kidney disease (CKD) risk in a healthy adult population in Taiwan.

SUBJECTS/METHODS

In a retrospective cross-sectional study of 4100 subjects ⩾18 years, a multivariate logistic regression model was used to assess the relationship among BMI, high hsCRP levels and CKD. Receiver-operating characteristic curve and Youden index were developed to define the discrimination power of combining BMI with hsCRP for CKD prediction and to determine the best predictive index.

RESULTS

Overweight/obese subjects with high hsCRP levels had the highest odds ratio for CKD (P=0.048). In females, combining BMI with hsCRP for CKD prediction was superior to that of males (0.890 vs 0.623, respectively; both P<0.001). For females, the Youden index was 25.65 kg/m(2) for BMI and 1.04 μg/ml for hsCRP.

CONCLUSIONS

Overweight/obesity with higher hsCRP levels is associated with reduced renal function and increased risk for CKD. BMI and hsCRP levels can be used as surrogate markers for CKD risk, especially for females.

Abdominal Adipose Tissue was Associated with Glomerular Hyperfiltration among Non- Diabetic and Normotensive Adults with a Normal Body Mass Index

Glomerular hyperfiltration is recognized as an early marker of progressive kidney dysfunction in the obese population. This study aimed to identify the relationship between glomerular hyperfiltration and body fat distribution measured by computed tomography (CT) in healthy Korean adults. The study population included individuals aged 20-64 years who went a routine health check-up including an abdominal CT scan. We selected 4,378 individuals without diabetes and hypertension. Glomerular filtration rate was estimated using the CKD-EPI equation, and glomerular hyperfiltration was defined as the highest quintile of glomerular filtration rate. Abdominal adipose tissue areas were measured at the level of the umbilicus using a 16-detector CT scanner, and the cross-sectional area was calculated using Rapidia 2.8 CT software. The prevalence of glomerular hyperfiltration increased significantly according to the subcutaneous adipose tissue area in men (OR = 1.74 (1.16-2.61), P for trend 0.016, for the comparisons of lowest vs. highest quartile) and visceral adipose tissue area in women (OR = 2.34 (1.46-3.75), P for trend < 0.001) in multivariate analysis. After stratification by body mass index (normal < 23 kg/m2, overweight ≥ 23 kg/m2), male subjects with greater subcutaneous adipose tissue, even those in the normal BMI group, had a higher prevalence of glomerular hyperfiltration (OR = 2.11 (1.17-3.80), P for trend = 0.009). Among women, the significance of visceral adipose tissue area on glomerular hyperfiltration resulted from the normal BMI group (OR = 2.14 (1.31-3.49), P for trend = 0.002). After menopause, the odds ratio of the association of glomerular hyperfiltration with subcutaneous abdominal adipose tissue increased (OR = 2.96 (1.21-7.25), P for trend = 0.013). Subcutaneous adipose tissue areas and visceral adipose tissue areas are positively associated with glomerular hyperfiltration in healthy Korean adult men and women, respectively. In post-menopausal women, visceral adipose tissue area shows significant positive association with glomerular hyperfiltration as in men.

1H NMR-based metabonomic analysis of serum and urine in a nonhuman primate model of diabetic nephropathy

Diabetic nephropathy (DN) is a serious metabolic disease, and comprehensive understanding of its complex mechanism will help in preventing the onset and progression of DN. To reveal the systemic metabolic changes associated with renal injury, we performed 1H NMR-based metabonomic and multivariate analyses to analyze serum and urine obtained from a nonhuman primate model of DN. Our results indicated that DN monkeys exhibited a distinct metabolic profile, including higher levels of VLDL/LDL, lipids, unsaturated lipids, uric acid, allantoin, fumarate and hippurate, as well as lower levels of HDL, alanine, glutamate, pyruvate, formate, tyrosine, histidine and NAD+. The disturbed metabolic pathways were further identified, including NAD+ metabolism, purine metabolism, oxidative stress, lipid metabolism, and renal tubular reabsorption. This study highlights that NMR-based metabonomics provides insight into the underlying pathways in the pathogenesis and progression of DN at the metabolic level.

Impact of body composition on estimated glomerular filtration rate in relatively healthy adults in Taiwan

BACKGROUND/OBJECTIVES

Chronic kidney diseases are associated with changes in cardiometabolic risk (CMR) factors in which body composition parameters have been used as sensitive predictors. This study aimed to explore the associations of anthropometric indicators, body fat (BF), body mass index (BMI) and waist circumference (WC) with estimated glomerular filtration rate (eGFR) in an adult healthy Chinese population.

SUBJECTS/METHODS

A cross-sectional study was conducted for the subjects undergoing annual health examinations. The associations of subjects with body composition parameters were analyzed using the cutoff values of BMI, BF and WC in accordance with the criteria for Asian or Taiwanese population by gender.

RESULTS

A total of 3473 subjects, aged 30-45 years, who received physical examinations in 2007 were analyzed. The levels of CMR factors were significantly higher in males than in females. eGFR was negatively associated with BMI but positively related to BF. The additional roles of BMI and WC were observed in the subjects who were categorized according to BF. Females with normal weight obese were associated with increased eGFR, whereas a higher eGFR was found in males with low/normal BF and BMI or normal WC.

CONCLUSIONS

Our data provided evidence that anthropometric parameters were associated with changes of eGFR in relatively healthy adults. Higher eGFR was observed in females with normal weight obese in whom hyperfiltration may be suspected, and this finding deserves further studies.

Nephron filtration rate and proximal tubular fluid reabsorption in the Akita mouse model of type I diabetes mellitus

An increase of glomerular filtration rate (hyperfiltration) is an early functional change associated with type I or type II diabetes mellitus in patients and animal models. The causes underlying glomerular hyperfiltration are not entirely clear. There is evidence from studies in the streptozotocin model of diabetes in rats that an increase of proximal tubular reabsorption results in the withdrawal of a vasoconstrictor input exerted by the tubuloglomerular feedback (TGF) mechanism. In the present study, we have used micropuncture to assess single nephron function in wild type (WT) mice and in two strains of type I diabetic Ins2+/- mice in either a C57Bl/6 (Akita) or an A1AR-/- background (Akita/A1AR-/-) in which TGF is non-functional. Kidney glomerular filtration rate (GFR) of anesthetized mice was increased by 25% in Akita mice and by 52% in Akita/A1AR-/-, but did not differ between genotypes when corrected for kidney weight. Single nephron GFR (SNGFR) measured by end-proximal fluid collections averaged 11.8 ± 1 nl/min (n=17), 13.05 ± 1.1 nl/min (n=23; p=0.27), and 15.4 ± 0.84 nl/min (n=26; p=0.009 compared to WT; p=0.09 compared to Akita) in WT, Akita, and Akita/A1AR-/- mice respectively. Proximal tubular fluid reabsorption was not different between WT and diabetic mice and correlated with SNGFR in all genotypes. We conclude that glomerular hyperfiltration is a primary event in the Akita model of type I diabetes, perhaps driven by an increased filtering surface area, and that it is ameliorated by TGF to the extent that this regulatory system is functional.

Effects of aging and uninephrectomy on renal changes in Tsukuba hypertensive mice

Renal dysfunction is accelerated by various factors such as hypertension, aging and diabetes. Glomerular hyper-filtration, considered one of the major risk factors leading to diabetic nephropathy, is often encountered in diabetic patients. However, the interrelationship of these risk factors during the course and development of renal dysfunction has not been fully elucidated. In this study, the effects of aging and uninephrectomy (UNx)-induced hyperfiltration on renal changes were investigated in Tsukuba hypertensive mice (THM) carrying both human renin and angiotensinogen genes. In THM, the urinary albumin/creatinine (Alb/Cr) ratio was elevated with age without a concomitant increase in the plasma Cr concentration. Moreover, the urinary neutrophil gelatinase-associated lipocalin/Cr (NGAL/Cr) ratio, the renal monocyte chemoattractant protein-1 (MCP-1) mRNA expression and the renal collagen type I α 2 (COL1A2) mRNA expression were also increased with age. Age-related albuminuria in THM is likely caused by renal tubular damage, enhanced inflammatory response and tubulointerstitial fibrosis. Furthermore, following UNx, the urinary Alb/Cr ratio and the plasma Cr concentration were increased in THM. The urinary NGAL/Cr ratio and the renal MCP-1 and COL1A2 mRNA expression were not affected by UNx. These results suggested that UNx-induced albuminuria in THM was caused by glomerular dysfunction, rather than renal tubular injury. In conclusion, this study demonstrated for the first time the effects of aging and UNx on renal changes in THM. These findings strongly reinforce the significance of applying a diversity of therapeutic approaches to the management of renal dysfunction.

Glomerular hyperfiltration: definitions, mechanisms and clinical implications

Glomerular hyperfiltration is a phenomenon that can occur in various clinical conditions including kidney disease. No single definition of glomerular hyperfiltration has been agreed upon, and the pathophysiological mechanisms, which are likely to vary with the underlying disease, are not well explored. Glomerular hyperfiltration can be caused by afferent arteriolar vasodilation as seen in patients with diabetes or after a high-protein meal, and/or by efferent arteriolar vasoconstriction owing to activation of the renin-angiotensin-aldosterone system, thus leading to glomerular hypertension. Glomerular hypertrophy and increased glomerular pressure might be both a cause and a consequence of renal injury; understanding the renal adaptations to injury is therefore important to prevent further damage. In this Review, we discuss the current concepts of glomerular hyperfiltration and the renal hemodynamic changes associated with this condition. A physiological state of glomerular hyperfiltration occurs during pregnancy and after consumption of high-protein meals. The various diseases that have been associated with glomerular hyperfiltration, either per nephron or per total kidney, include diabetes mellitus, polycystic kidney disease, secondary focal segmental glomerulosclerosis caused by a reduction in renal mass, sickle cell anemia, high altitude renal syndrome and obesity. A better understanding of the mechanisms involved in glomerular hyperfiltration could enable the development of new strategies to prevent progression of kidney disease.

Sympathetic nervous system activity is associated with obesity-induced subclinical organ damage in young adults

Excess weight is established as a major risk factor for cardiovascular diseases, particularly in young individuals. To get a better understanding of the pathophysiology underlying increased cardiovascular disease risk, we evaluated early signs of organ damage and their possible relationship to sympathetic nervous activity. Eighteen lean (body mass index <25 kg/m(2)) and 25 overweight or obese (body mass index >25 kg/m(2)) healthy university students were included in the study. We comprehensively assessed subclinical target organ damage, including the following: (1) assessment of renal function; (2) left ventricular structure and systolic and diastolic function; and (3) endothelial function. Muscle sympathetic nervous activity was assessed by microneurography. Participants with excess weight had decreased endothelial function (P<0.01), elevated creatinine clearance (P<0.05), increased left ventricular mass index (P<0.05), increased left ventricular wall thickness (P<0.01), lower systolic and diastolic function (P<0.01), and elevated muscle sympathetic nervous activity (P<0.001) compared with lean individuals. In multiple regression analysis, endothelial function was inversely related to muscle sympathetic nervous activity (R(2)=0.244; P<0.05), whereas creatinine clearance and left ventricular mass index were positively related to muscle sympathetic nervous activity, after adjustment for body mass index, sex, and blood pressure (R(2)=0.318, P<0.01 and R(2)=0.312, P<0.05, respectively). Excess weight in young individuals is associated with subclinical alterations in renal and endothelial function, as well as in the structure of the heart, even in the absence of hypertension. Sympathetic activity is closely associated with cardiovascular and renal alterations observed in these subjects.

The renal vascular response to diabetes

PURPOSE OF REVIEW

Diabetes mellitus is the primary cause of end-stage renal disease, yet the mechanisms underlying diabetic nephropathy remain ill-defined. The widely accepted opinion holds that events occurring early during the course of diabetes engender the eventual decline in renal function. This review will summarize recent advances (published January 2008 through June 2009) regarding the renal vascular and glomerular functional changes that occur during the early stage of diabetes.

RECENT FINDINGS

Reduced C-peptide levels and increased cyclooxygenase-2 activity both seem to promote diabetic hyperfiltration, presumably via effects on afferent arteriolar tone. In addition, exaggerated tonic influences of K+ channels on afferent arteriolar function likely act in concert with impaired Ca2+ influx responses to changes in membrane potential to promote vasodilation. Mechanisms underlying these changes remain largely speculative. Diabetes may also alter autoregulation of renal blood flow and glomerular filtration rate, as well as provoke afferent arteriolar dilation secondary to alterations in proximal tubular reabsorption; however, conflicting evidence continues to flood the literature concerning these events.

SUMMARY

New evidence has expanded our appreciation of the complexity of events that promote preglomerular vasodilation during the early stage of diabetes; however, it seems that the more we know, the less we understand.

Renal hyperfiltration and the development of microalbuminuria in type 1 diabetes

OBJECTIVE

The purpose of this study was to examine prospectively whether renal hyperfiltration is associated with the development of microalbuminuria in patients with type 1 diabetes, after taking into account known risk factors.

RESEARCH DESIGN AND METHODS

The study group comprised 426 participants with normoalbuminuria from the First Joslin Kidney Study, followed for 15 years. Glomerular filtration rate was estimated by serum cystatin C, and hyperfiltration was defined as exceeding the 97.5th percentile of the sex-specific distribution of a similarly aged, nondiabetic population (134 and 149 ml/min per 1.73 m(2) for men and women, respectively). The outcome was time to microalbuminuria development (multiple albumin excretion rate >30 microg/min). Hazard ratios (HRs) for microalbuminuria were calculated at 5, 10, and 15 years.

RESULTS

Renal hyperfiltration was present in 24% of the study group and did not increase the risk of developing microalbuminuria. The unadjusted HR for microalbuminuria comparing those with and without hyperfiltration at baseline was 0.8 (95% CI 0.4-1.7) during the first 5 years, 1.0 (0.6-1.7) during the first 10 years, and 0.8 (0.5-1.4) during 15 years of follow-up. The model adjusted for baseline known risk factors including A1C, age at diagnosis of diabetes, diabetes duration, and cigarette smoking resulted in similar HRs. In addition, incorporating changes in hyperfiltration status during follow-up had minimal impact on the HRs for microalbuminuria.

CONCLUSIONS

Renal hyperfiltration does not have an impact on the development of microalbuminuria in type 1 diabetes during 5, 10, or 15 years of follow-up.

Oxidant/antioxidant status and hyperfiltration in young patients with type 1 diabetes mellitus

Diabetic nephropathy (DN), a major cause of morbidity and mortality in diabetes, will develop within a subset of type 1 diabetes mellitus (T1DM) patients, and oxidative stress has been implicated in its pathogenesis. To investigate the relationship between indicators of early DN stages (hyperfiltration estimated by creatinine clearance > or =150 ml/min per 1.73 m(2), microalbuminuria) and oxidative stress, a prospective study was conducted in 29 T1DM patients (age 13.89 +/- 4.61 years) and 18 control subjects (age 13.23 +/- 3.99 years). Blood samples were collected to assay for biomarkers of oxidative stress (malondialdehyde and carbonyl groups) and antioxidants (glutathione peroxidase, reduced glutathione, alpha-tocopherol, and beta-carotene). With respect to control subjects, in T1DM patients, an increase was found in biomarkers of oxidative stress (p < 0.05), mainly due to the group of subjects with hyperfiltration, and a decrease in the ratio alpha-tocopherol/lipids (p < 0.05). In multiple regression analyses, age at disease onset, glycated hemoglobin, microalbuminuria, and oxidative stress biomarkers remained as explicative variables of hyperfiltration (R (2) adjusted = 0.731, p = 0.000). These findings support the importance of the oxidative damage to lipids and proteins, which is linked to hyperfiltration and which could contribute to the development of DN in patients with T1DM.

New insights into the mechanisms of fibrosis and sclerosis in diabetic nephropathy

Progression of diabetic nephropathy (DN) is manifested by gradual scarring of both the renal glomerulus and tubulointerstitial region. Over the past several years, the general understanding of the pathogenic factors that lead to renal fibrosis in DN has expanded considerably. In this review, some of the important factors that appear to be involved in driving this fibrosing process are discussed, with special emphasis on newer findings and insights. It is now clear that multiple cell types in the kidney contribute to progressive fibrosis in DN. New concepts about bradykinin, TGF-beta and eNOS signaling as well as JAK/STAT activation and the central role of inflammation in both glomerular and tubulointerstitial fibrosis are discussed.

Modulation of single-nephron GFR in thedb/dbmouse model of type 2 diabetes mellitus. II. Effects of renal mass reduction

This study examines for the first time the effects of uninephrectomy (Nx) on modulation of whole kidney glomerular filtration rate (GFR), single-nephron GFR (SNGFR), and progression of diabetic nephropathy in the db/db mouse model of type 2 diabetes mellitus. To characterize SNGFR and tubuloglomerular feedback (TGF) responses to Nx and chronic neuronal nitric oxide synthase inhibition in the db/db mouse, we studied the effects of Nx on whole kidney GFR, SNGFR, and TGF characteristics in db/db and wild-type (WT) mice after Nx or sham Nx. We also documented progression of glomerular changes over a 6-mo period. Whole kidney GFR and SNGFR were significantly higher in db/db Nx than db/db sham mice, without change in proximal tubule reabsorptive rates. The TGF responses, determined as proximal-distal SNGFR differences, were brisk: 12.1 ± 1.0 vs. 8.4 ± 0.6 nl/min in WT sham ( P < 0.05), 15.7 ± 1.0 vs. 12.0 ± 1.0 nl/min in WT Nx ( P < 0.05), and 17.8 ± 1.3 vs. 14.3 ± 1.0 nl/min in db/db Nx ( P < 0.05) mice. Chronic ingestion of the neuronal nitric oxide synthase inhibitor S-methylthiocitrulline for 2–3 wk after Nx had no effect on SNGFR or the TGF response. These studies show further elevations in whole kidney GFR and SNGFR in these hyperglycemic morbidly obese db/db mice, with an intact TGF system after Nx. In addition, in the db/db Nx mice, 4–6 mo after Nx, there was an exacerbation of the lesions of diabetic nephropathy, as quantified by a significant increase in the ratio of mesangial surface area to total glomerular surface area.