Role of altered insulin signaling pathways in the pathogenesis of podocyte malfunction and microalbuminuria

High-Density Lipoprotein in Patients with Diabetic Kidney Disease: Friend or Foe?

High-density lipoprotein (HDL) exhibits multiple metabolic protective functions, such as facilitating cellular cholesterol efflux, antioxidant, anti-inflammatory, anti-apoptotic and anti-thrombotic properties, showing antidiabetic and renoprotective potential. Diabetic kidney disease (DKD) is considered to be associated with high-density lipoprotein cholesterol (HDL-C). The hyperglycemic environment, non-enzymatic glycosylation, carbamylation, oxidative stress and systemic inflammation can cause changes in the quantity and quality of HDL, resulting in reduced HDL levels and abnormal function. Dysfunctional HDL can also have a negative impact on pancreatic β cells and kidney cells, leading to the progression of DKD. Based on these findings, new HDL-related DKD risk predictors have gradually been proposed. Interventions aiming to improve HDL levels and function, such as infusion of recombinant HDL (rHDL) or lipid-poor apolipoprotein A-I (apoA-I), can significantly improve glycemic control and also show renal protective effects. However, recent studies have revealed a U-shaped relationship between HDL-C levels and DKD, and the loss of protective properties of high levels of HDL may be related to changes in composition and the deposition of dysfunctional particles that exacerbate damage. Further research is needed to fully elucidate the complex role of HDL in DKD. Given the important role of HDL in metabolic health, developing HDL-based therapies that augment HDL function, rather than simply increasing its level, is a critical step in managing the development and progression of DKD.

A Population-Based Study of the Mediating Role of WBC, NEUT and PLT in the Relationship Between Triglyceride-Glucose Index and Urinary Albumin Excretion

Aim

To assess the potential association between the TyG index and the risk of abnormal UACR. Additionally, we aimed to determine the role and degree of influence of inflammatory biomarkers between the TyG index and abnormal UACR.

Materials and Methods

A cross-sectional study recruited 1021 participants from a health management center between 2021 and 2022. Logistic or linear regression models, as well as mediation analysis, were employed to investigate the associations between the TyG index, inflammatory biomarkers (total and differential white blood cell counts, platelet, mean platelet volume(MPV), C-reactive protein(CRP)), and the risk of abnormal UACR.

Results

The study included 1021 participants, of whom 55.0% were men. The median age (interquartile range [IQR]) was 61.0 (53, 70) years. In multivariable-adjusted logistic regression models, both with and without the inclusion of smoking, alcohol drinking, BMI, Lipid-lowering drugs using, TC, SUA, ALT, and AST as potential covariates, the TyG index was associated with the risk of UACR, both with the odds ratios (ORs) per 1-standard deviation (SD) increase were 1.32 (95% CI, 1.08-1.62) and 1.27 (95% CI, 1.05-1.52), respectively. This study also demonstrated a significant indirect effect of the TyG index on the risk of abnormal UACR through total white blood cell counts, neutrophil counts and platelet (P values < 0.05); The proportions mediated was 11.2%, 3.5% and 29.6% for each respective variable.

Conclusion

Insulin resistance and inflammation are associated with an increased risk of kidney insufficiency. And indicators of inflammation weakly mediate insulin resistance and risk of kidney insufficiency.

Associations of Insulin Resistance and High-Sensitivity C-Reactive Protein with Metabolic Abnormalities in Korean Patients with Type 2 Diabetes Mellitus: A Preliminary Study

We conducted this single-center, retrospective, cohort study to examine whether insulin resistance (IR) and high-sensitivity C-reactive protein (hsCRP) have a relationship with metabolic abnormalities in patients with type 2 diabetes mellitus (T2DM). In a total of 3758 patients (n = 3758) with T2DM, we analyzed medical records and thereby evaluated their baseline characteristics such as age, sex, duration of T2DM, systolic blood pressure (SBP), diastolic blood pressure (DBP), waist circumference, body mass index (BMI), visceral fat thickness (VFT), fasting plasma insulin levels, C-peptide levels, glycated hemoglobin (HbA1c), fasting plasma glucose (FPG), postprandial plasma glucose (PPG), homeostatic model assessment of insulin resistance (HOMA-IR), homeostatic model assessment of β-cell function (HOMA-β), aspartate aminotransferase (AST), alanine aminotransferase (ALT), total cholesterol (TC), triglyceride (TG), high-density lipoprotein (HDL), low-density lipoprotein (LDL), albuminuria, intima-media thickness (IMT) and hsCRP. The patients were stratified according to the tertile of the K index of the insulin tolerance test (KITT) or hsCRP. Thus, they were divided into the lowest (≥2.37), middle (1.54-2.36) and highest tertile (0-1.53) of KITT and the lowest (0.00-0.49), middle (0.50-1.21) and highest tertile (≥1.22) of hsCRP. Moreover, associations of KITT and hsCRP with metabolic abnormalities, such as steatotic liver disease (SLD), metabolic syndrome (MetS), albuminuria, diabetic retinopathy and carotid atherosclerosis, were also analyzed. There was a significant positive correlation between the prevalence of SLD, MetS, albuminuria and diabetic retinopathy and KITT (p < 0.001). Moreover, there was a significant positive association between the prevalence of SLD, MetS and albuminuria and hsCRP (p < 0.001). In conclusion, our results indicate that clinicians should consider the relationships of IR and hsCRP with metabolic abnormalities in the management of patients with T2DM. However, further large-scale, prospective, multi-center studies are warranted to confirm our results.

Dendrobium officinale polysaccharide decreases podocyte injury in diabetic nephropathy by regulating IRS-1/AKT signal and promoting mitophagy

BACKGROUNDS

High glucose (HG) caused oxidative stress and mitochondrial dysfunction, resulting in insulin resistance in podocytes, a key mechanism of diabetic nephropathy. Dendrobium officinale polysaccharide (DOP) was able to improve insulin resistance and antioxidant capability.

OBJECTIVE

The purpose of this study is to explore the mechanism by which DOP decreases the podocyte injury induced by HG.

METHODS

MPC5 cells were treated with HG, DOP, and IRS-1/2 inhibitor NT157. Afterwards, glucose consumption, generations of ROS and MDA were measured using the detection kits. Mitophagy was monitored using both MtphagTracyker and LysoTracker. The mitochondrial membrane potential was evaluated by JC-1 staining. DOP was also used in a mouse model of diabetes, with the measurements of urine albumin, blood creatinine and blood urea nitrogen.

RESULTS

Treatment with DOP suppressed the HG-induced reduction of glucose consumption, the phosphorylation of IRS-1 (phospho Y632), AKT (phospho Ser473 and Thr308) and Nephrin. In addition, HG-induced augment of ROS and MDA, formation of γ-H2A.X foci and translocation of AKT to nucleus were inhibited by DOP. DOP enhanced mitophagy, which was associated with decreased mitochondrial membrane potential and ROS production. DOP conferred protective effect on podocyte in the diabetic mouse by reducing the albumin/creatinine ratio and blood urea nitrogen, and restoring Nephrin expression in podocytes.

CONCLUSIONS

DOP alleviates HG-induced podocyte injuryby regulating IRS-1/AKT signal and promoting mitophagy.

The relationship between triglyceride-glucose index and albuminuria in United States adults

Purpose

Triglyceride-glucose (TyG) index is a simple and reliable indicator of metabolic dysfunction. We aimed to investigate a possible relationship between TyG index and albuminuria in the United States adult population.

Methods

This cross-sectional study was conducted among adults with complete TyG index and urinary albumin/urinary creatinine (UACR) from 2011-2018 National Health and Nutrition Examination Survey (NHANES). The independent relationship between TyG index and albuminuria (UACR>30mg/g) was evaluated. TyG index was compared with insulin resistance represented by homeostatic model assessment of insulin resistance (HOMA-IR), and metabolic syndrome. Subgroup analysis was also performed.

Results

A total of 9872 participants were included in this study, and the average TyG index was 8.53 ± 0.01. The proportion of albuminuria gradually increased with the increase of TyG index quartile interval. Elevated TyG index was independently associated with albuminuria, and this association persisted after additional adjustments for HOMA-IR or dichotomous metabolic syndrome. The area under the ROC curve (AUC) of TyG index was larger than that of log (HOMA-IR). Subgroup analysis suggested that the relationship between TyG index and albuminuria is of greater concern in age<60, overweight/obese, diabetic, and metabolic syndrome patients.

Conclusion

The TyG index may be a potential epidemiological tool to quantify the role of metabolic dysfunction, rather than just insulin resistance, in albuminuria in the United States adult population. Further large-scale prospective studies are needed to confirm our findings.

The effect of arteriosclerosis on new-onset renal damage in diabetic patients

The aim of this study was to investigate the effect of arteriosclerosis on new-onset renal damage in a Chinese community population with diabetes. Patients with diabetes who had attended at least one physical examination after the Brachial-ankle pulse wave velocity (BaPWV) test from 2010 to 2018 were selected as subjects. A total of 4,462 patients were included in the study cohort. BaPWV levels <1,400 cm/s, 1,400-1,799 cm/s, and ≥1,800 cm/s were applied to divide the subjects into a normal arterial stiffness group, borderline atherosclerosis group and atherosclerosis group. Renal damage was defined by isolated proteinuria, isolated eGFR <60 mL/min/1.73 m², proteinuria and eGFR <60 mL/min/1.73 m². A Cox proportional risk model was used to analyze the effect of different groups on new-onset renal damage. After a median follow-up of 2.85 (1.88-4.90) years, Cox proportional risk models showed that after adjusting for risk factors, compared with the normal group, the HR and 95% CI of the risk of new-onset renal damage were 1.29 (95% CI: 0.95-1.76) and 1.59 (95% CI: 1.14-2.22) in the borderline atherosclerosis group and the atherosclerosis group, respectively. Atherosclerosis is a risk factor for new-onset renal damage, especially new-onset proteinuria, in diabetic patients.

Association of parental cardiovascular risk factors with offspring type 1 diabetes mellitus insulin sensitivity

AIM

This study aimed to determine whether the insulin resistance (IR) and lipid profiles in Type 1 Diabetes (T1D) offspring are associated with IR and other cardiovascular risk factors in their parents.

METHODS

This study included 99 T1D patients (19.6 ± 4.0 yrs.), 85 mothers and 60 fathers. Parents' IR was assessed by HOMA-IR, and the insulin sensitivity in T1D patients was assessed by the estimated Glucose Disposal Rate (eGDR).

RESULTS

The eGDR in the T1D offspring was negatively related to age (p = 0.023), weight (p = 0.004), LDL (p = 0.026), and microalbuminuria (p = 0.019). Maternal Type 2 Diabetes (p < 0.001) and HOMA-IR (p = 0.029) were negatively related to eGDR in their T1D offspring. The maternal HOMA-IR and the proband's eGDR were positively (p = 0.012) and negatively (p = 0.042) associated with the birth weight of the T1D offspring, respectively. We didn't find an association with the fathers' profiles.

CONCLUSIONS

In a cohort of offspring with T1D the insulin sensitivity was related to the IR, lipid profile, and the presence of T2D only in their mothers. Precocious screening and treatment of these risk factors beyond glycemic control will benefit T1D with this background.

Impact of Weight Loss on the Severity of Albuminuria in Obese Diabetic Patients Undergoing Laparoscopic Sleeve Gastrectomy and One-Anastomosis Gastric Bypass

AIM

To examine the effect of weight-loss induced bariatric procedures on albuminuria levels among diabetic patients suffering from obesity.

METHODS

Adults patients who suffer from morbid obesity and type 2 diabetes mellitus (T2DM) were included in a prospective cohort study. Subjects were scheduled to undergo laparoscopic sleeve gastrectomy (LSG) or one-anastomosis gastric bypass (OAGB). The albumin-to-creatinine ratio (ACR) was adopted to assess the degree of albuminuria. Microalbuminuria was determined as a ratio of >2.5-30 mg/mmol and >3.5-30 mg/mmol for males and females, respectively, while macroalbuminuria was diagnosed when the ACR exceeded >30 mg/mmol.

RESULTS

The mean uACR decreased significantly from 20.95±16.89 to 9.92±12.69mg/mmol in LSG cohort (p <0.001), and from 19.52±16.65 to 9.34±11.77mg/mmol in the OAGB cohort, with no statistically considerable differences between both cohorts at the end of follow-up (p = 0.78). Twelve months after the procedures, the percentages of cases with microalbuminuria decreased significantly to 23.8% and 23.9%, respectively (p < 0.001); likewise, the percentages of cases with macroalbuminuria significantly decreased to 7.9% and 7.5% in the LSG and OAGB groups, respectively (p < 0.001). There were no statistically considerable differences between LSG and OAGB regarding the percentages of patients with micro or macroalbuminuria at the end of follow-up. Besides, there were no significant associations between the degree of weight loss and improvement (p = 0.959) or remission (p = 0.73) of microalbuminuria.

CONCLUSION

Bariatric surgery significantly reduced the severity of albuminuria 1-year after the procedure, with no preference for one procedure over the other.

Spatial localization of β-unsaturated aldehyde markers in murine diabetic kidney tissue by mass spectrometry imaging

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease. Limitations in current diagnosis and screening methods have sparked a search for more specific and conclusive biomarkers. Hyperglycemic conditions generate a plethora of harmful molecules in circulation and within tissues. Oxidative stress generates reactive α-dicarbonyls and β-unsaturated hydroxyhexenals, which react with proteins to form advanced glycation end products. Mass spectrometry imaging (MSI) enables the detection and spatial localization of molecules in biological tissue sections. Here, for the first time, the localization and semiquantitative analysis of “reactive aldehydes” (RAs) 4-hydroxyhexenal (4-HHE), 4-hydroxynonenal (4-HNE), and 4-oxo-2-nonenal (4-ONE) in the kidney tissues of a diabetic mouse model is presented. Ionization efficiency was enhanced through on-tissue chemical derivatization (OTCD) using Girard’s reagent T (GT), forming positively charged hydrazone derivatives. MSI analysis was performed using matrix-assisted laser desorption ionization (MALDI) coupled with Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR). RA levels were elevated in diabetic kidney tissues compared to lean controls and localized throughout the kidney sections at a spatial resolution of 100 µm. This was confirmed by liquid extraction surface analysis–MSI (LESA-MSI) and liquid chromatography–mass spectrometry (LC–MS). This method identified β-unsaturated aldehydes as “potential” biomarkers of DN and demonstrated the capability of OTCD-MSI for detection and localization of poorly ionizable molecules by adapting existing chemical derivatization methods. Untargeted exploratory distribution analysis of some precursor lipids was also assessed using MALDI-FT-ICR-MSI.

Hypertriglyceridemia and Other Risk Factors of Chronic Kidney Disease in Type 2 Diabetes: A Hospital-Based Clinic Population in Greece

AIMS/INTRODUCTION

Several reports indicate an increasing prevalence of chronic kidney disease (CKD) in type 2 diabetes mellitus (T2DM). Hyperglycemia and hypertension are the main risk factors for CKD development and progression. However, despite the achievement of recommended targets for blood glucose and blood pressure (BP), the residual risk of diabetic chronic kidney disease (DCKD) remains relatively high. The aim of this study is to examine dyslipidemia and other major risk factors to provide support for the prevention and treatment of DCKD.

MATERIALS AND METHODS

Participants are from the Redit-2-Diag study that examines 1759 subjects within a period of 6 months. DCKD severity is staged according to KDIGO criteria.

RESULTS

An increase in hemoglobin A1c (1 unit) and systolic blood pressure (1 mm Hg) increases the probability of being classified into a higher CKD stage by 14% and 26%, respectively. Moreover, an increase of triglycerides by 88.5 mg/dL increases the risk of classification to a worse CKD stage by 24%.

CONCLUSIONS

Elevated triglycerides, systolic blood pressure, and poor glycemic control increase the risk of CKD in T2DM and should be addressed in the treatment strategies.

Insulin resistance-related differences in the relationship between left ventricular hypertrophy and cardiorespiratory fitness in hypertensive Black sub-Saharan Africans

BACKGROUND

Left ventricular hypertrophy (LVH) is associated with impaired cardiorespiratory fitness (CRF), a surrogate marker of poor outcome. Insulin resistance (IR) plays a central role in all stages of cardiovascular disease continuum. This study evaluates IR-related differences in the relationship between left ventricular mass (LVM) and CRF in asymptomatic newly diagnosed hypertensive Black sub-Saharan Africans.

METHODS

In this cross-sectional observational study, 126 asymptomatic newly diagnosed hypertensive participants (50.5 ± 9.5 years) underwent comprehensive resting transthoracic echocardiographic examination and maximal incremental cardiopulmonary exercise test (CPET). CRF was estimated in maximal oxygen uptake (VO2max). CPET results were compared between participants with and without LVH. Multivariate analysis examined the influence of IR on the observed differences.

RESULTS

Those with LVH had lower VO2max (15.7 ± 5.5 mL min^-1 kg^-1 vs. 18.4 ± 3.7 mL min^-1 kg^-1; P = 0.001) than those without LVH. In patients with IR, LVM (r = -0.261, P = 0.012), LVM indexed to body surface area (LVMIbsa; r = -0.229, P = 0.027), and LVM indexed to height to an allometric power of 2.7 (LVMIh^2.7; r = -0.351, P = 0.001), and VO2max were negatively correlated. In hypertensive patients without IR, these same parameters and VO2max have no significant correlation. Body mass index (BMI), LVM, and LVMIbsa emerged as independent determinants of VO2max, explaining 46.9% of its variability (overall P = 0.001) in IR participants, a relationship not found in participants without IR.

CONCLUSIONS

IR may participate in the deterioration of CRF associated with LVH. Measures to improve insulin sensitivity should be considered for improving CRF and therefore the prognosis of insulin-resistant hypertensive patients. Targeting IR in hypertensive patients with LVH could improve prognosis.

Tetrahydrocurcumin Ameliorates Kidney Injury and High Systolic Blood Pressure in High-Fat Diet-Induced Type 2 Diabetic Mice

BACKGROUND

Activation of the intrarenal renin-angiotensin system (RAS) is implicated in the pathogenesis of kidney injury and hypertension. We aimed to investigate the protective effect of tetrahydrocurcumin (THU) on intrarenal RAS expression, kidney injury, and systolic blood pressure (SBP) in high-fat diet (HFD)-induced type 2 diabetic mice.

METHODS

Eight-week-old male mice were fed a regular diet (RD) or HFD for 12 weeks, and THU (50 or 100 mg/kg/day) was intragastrically administered with HFD. Physiological and metabolic changes were monitored and the expression of RAS components and markers of kidney injury were assessed.

RESULTS

HFD-fed mice exhibited hyperglycemia, insulin resistance, and dyslipidemia compared to those in the RD group (P<0.05). Kidney injury in these mice was indicated by an increase in the ratio of albumin to creatinine, glomerular hypertrophy, and the effacement of podocyte foot processes. Expression of intrarenal angiotensin-converting enzyme, angiotensin II type I receptor, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-4, and monocyte chemoattractant protein-1 was also markedly increased in HFD-fed mice. HFD-fed mice exhibited elevated SBP that was accompanied by an increase in the wall thickness and vascular cross-sectional area (P<0.05), 12 weeks post-HFD consumption. Treatment with THU (100 mg/kg/day) suppressed intrarenal RAS activation, improved insulin sensitivity, and reduced SBP, thus, attenuating kidney injury in these mice.

CONCLUSION

THU alleviated kidney injury in mice with HFD-induced type 2 diabetes, possibly by blunting the activation of the intrarenal RAS/nicotinamide adenine dinucleotide phosphate oxidase IV (NOX4)/monocyte chemoattractant protein 1 (MCP-1) axis and by lowering the high SBP.

Faster lipid β-oxidation rate by acetyl-CoA carboxylase 2 inhibition alleviates high-glucose-induced insulin resistance via SIRT1/PGC-1α in human podocytes

Diabetic nephropathy (DN) is becoming a research hotspot in recent years because the prevalence is high and the prognosis is poor. Lipid accumulation in podocytes induced by hyperglycemia has been shown to be a driving mechanism underlying the development of DN. However, the mechanism of lipotoxicity remains unclear. Increasing evidence shows that acetyl-CoA carboxylase 2 (ACC2) plays a crucial role in the metabolism of fatty acid, but its effect in podocyte injury of DN is still unclear. In this study, we investigated whether ACC2 could be a therapeutic target of lipid deposition induced by hyperglycemia in the human podocytes. Our results showed that high glucose (HG) triggered significant lipid deposition with a reduced β-oxidation rate. It also contributed to the downregulation of phosphorylated ACC2 (p-ACC2), which is an inactive form of ACC2. Knockdown of ACC2 by sh-RNA reduced lipid deposition induced by HG. Additionally, ACC2-shRNA restored the expression of glucose transporter 4 (GLUT4) on the cell surface, which was downregulated in HG and normalized in the insulin signaling pathway. We verified that ACC2-shRNA alleviated cell injury, apoptosis, and restored the cytoskeleton disturbed by HG. Mechanistically, SIRT1/PGC-1α is close related to the insulin metabolism pathway. ACC2-shRNA could restore the expression of SIRT1/PGC-1α, which was downregulated in HG. Rescue experiment revealed that inhibition of SIRT1 by EX-527 counteracted the effect of ACC2-shRNA. Taken together, our data suggest that podocyte injury mediated by HG-induced insulin resistance and lipotoxicity could be alleviated by ACC2 inhibition via SIRT1/PGC-1α.

Melanocortin System in Kidney Homeostasis and Disease: Novel Therapeutic Opportunities

Melanocortin peptides, melanocortin receptors, melanocortin receptor accessory proteins, and endogenous antagonists of melanocortin receptors are the key components constituting the melanocortin hormone system, one of the most complex and important hormonal systems in our body. A plethora of evidence suggests that melanocortins possess a protective activity in a variety of kidney diseases in both rodent models and human patients. In particular, the steroidogenic melanocortin peptide adrenocorticotropic hormone (ACTH), has been shown to exert a beneficial effect in a number of kidney diseases, possibly via a mechanism independent of its steroidogenic activity. In patients with steroid-resistant nephrotic glomerulopathy, ACTH monotherapy is still effective in inducing proteinuria remission. This has inspired research on potential implications of the melanocortin system in glomerular diseases. However, our understanding of the role of the melanocortinergic pathway in kidney disease is very limited, and there are still huge unknowns to be explored. The most controversial among these is the identification of effector cells in the kidney as well as the melanocortin receptors responsible for conveying the renoprotective action. This review article introduces the melanocortin hormone system, summarizes the existing evidence for the expression of melanocortin receptors in the kidney, and evaluates the potential strategy of melanocortin therapy for kidney disease.

Characteristics of nephropathy in severely obese Japanese patients complicated with type 2 diabetes mellitus: a cross-sectional cohort study

PURPOSE

We aimed to investigate the characteristics of kidney disease in severely obese Japanese patients with type 2 diabetes mellitus (T2DM).

METHODS

This was a cross-sectional study of severely obese patients (body mass index ≥35 kg/m²) with T2DM treated at Jinnouchi Hospital, Kumamoto, Japan.

RESULTS

A total of 3128 T2DM patients visited the hospital during the survey period, of whom 55 patients (1.7%) were severely obese and 50 patients were enrolled. In terms of diabetic nephropathy (DN), twenty-five patients were stage 1 (non-DN, 50.0%), sixteen were stage 2 (32.0%), five were stage 3 (10.0%), and four were stage 4 (8.0%). There were significant differences in the presence of urinary occult blood (P = 0.01) and history of cardiovascular disease (CVD) (P = 0.04) between patients with DN (stages 2-4) and those without DN (stage 1). The presence of urinary occult blood (odds ratio [OR], 4.96; 95% confidence interval, 1.32-18.6; P = 0.02) was significantly associated with the presence of DN according to multivariate logistic regression analysis with forced inclusion of age, sex, and CVD history.

CONCLUSIONS

Urinary occult blood may be a significant independent factor associated with the presence of nephropathy in severely obese Japanese patients with T2DM. The presence of urinary occult blood could thus be an important pathogenic factor in obesity-related nephropathy in patients with T2DM.

Atherogenic dyslipidemia and diabetic nephropathy

Chronic kidney disease is associated with altered lipid metabolism and lipid accumulation. Although it is though that hyperlipemia is a consequence of kidney dysfunction, several lines of evidence support that hyperlipidemia may contribute to the onset and progression of kidney disease, also in diabetes. This review describes the results of recent observational studies supporting the concept that glucose is only partly responsible for kidney damage onset, while a cluster of factors, including hypertriglyceridemia and low HDL-cholesterol, could play a relevant role in inducing onset and progression of DKD. We also report the results of randomized clinical trials investigating in type 2 diabetic patients the role of drug improvement of hypertriglyceridemia on renal outcomes. Finally, we discuss putative mechanisms linking hyperlipidemia (i.e. hypertriglyceridemia or low HDL cholesterol) with kidney disease.

A Novel Indoline Derivative Ameliorates Diabesity-Induced Chronic Kidney Disease by Reducing Metabolic Abnormalities

Both diabetes and obesity (diabesity) contribute significantly to the development of chronic kidney disease (CKD). In search of new remedies to reverse or arrest the progression of CKD, we examined the therapeutic potential of a novel compound, AN1284, in a mouse model of CKD induced by type 2 diabetes with obesity. Six-week-old BKS Cg-Dock 7^m+/+ Lepr^db/J mice with type 2 diabetes and obesity were treated with AN1284 (2.5 or 5 mg kg^-1 per day) via micro-osmotic pumps implanted subcutaneously for 3 months. Measures included renal, pancreatic, and liver assessment as well as energy utilization. AN1284 improved kidney function in BSK-db/db animals by reducing albumin and creatinine and preventing renal inflammation and morphological changes. The treatment was associated with weight loss, decreased body fat mass, increased utilization of body fat toward energy, preservation of insulin sensitivity and pancreatic β cell mass, and reduction of dyslipidemia, hepatic steatosis, and liver injury. This indoline derivative protected the kidney from the deleterious effects of hyperglycemia by ameliorating the metabolic abnormalities of diabetes. It could have therapeutic potential for preventing CKD in human subjects with diabesity.

Safety and efficacy of antihyperglycaemic agents in diabetic kidney disease

Diabetic kidney disease (DKD) is the major contributor to the mortality and the financial burden of diabetes, accounting for approximately 50% of the cases of end-stage renal disease (ESRD) in the developed world. Several studies have already demonstrated that achieving blood pressure targets in DKD with agents blocking the renin-angiotensin system confer superior renoprotection when compared to other agents. However, the effects on renal outcomes of antihyperglycaemic agents in these patients have not been reported or studied broadly until recent years. The intent of this article is to review the available data on safety, efficacy, impact on renal outcomes and pathophysiology implications of the most utilized antihyperglycaemic agents in DKD/ESRD.

Role of mTOR signaling in the regulation of high glucose-induced podocyte injury

Podocyte injury, which promotes progressive nephropathy, is considered a key factor in the progression of diabetic nephropathy. The mammalian target of rapamycin (mTOR) signaling cascade controls cell growth, survival and metabolism. The present study investigated the role of mTOR signaling in regulating high glucose (HG)-induced podocyte injury. MTT assay and flow cytometry assay results indicated that HG significantly increased podocyte viability and apoptosis. HG effects on podocytes were suppressed by mTOR complex 1 (mTORC1) inhibitor, rapamycin, and further suppressed by dual mTORC1 and mTORC2 inhibitor, KU0063794, when compared with podocytes that received mannitol treatment. In addition, western blot analysis revealed that the expression levels of Thr-389-phosphorylated p70S6 kinase (p-p70S6K) and phosphorylated Akt (p-Akt) were significantly increased by HG when compared with mannitol treatment. Notably, rapamycin significantly inhibited HG-induced p-p70S6K expression, but did not significantly impact p-Akt expression. However, KU0063794 significantly inhibited the HG-induced p-p70S6K and p-Akt expression levels. Furthermore, the expression of ezrin was significantly reduced by HG when compared with mannitol treatment; however, α-smooth muscle actin (α-SMA) expression was significantly increased. Immunofluorescence analysis on ezrin and α-SMA supported the results of western blot analysis. KU0063794, but not rapamycin, suppressed the effect of HG on the expression levels of ezrin and α-SMA. Thus, it was suggested that the increased activation of mTOR signaling mediated HG-induced podocyte injury. In addition, the present findings suggest that the mTORC1 and mTORC2 signaling pathways may be responsible for the cell viability and apoptosis, and that the mTORC2 pathway could be primarily responsible for the regulation of cytoskeleton-associated proteins.

Hyperinsulinemia Can Cause Kidney Disease in the IGT Stage of OLETF Rats via the INS/IRS-1/PI3-K/Akt Signaling Pathway

AIMS

We investigated the changes of renal structure and its function in normal glucose tolerance (NGT), impaired glucose tolerance (IGT), diabetes mellitus (DM), and diabetic kidney disease (DKD) stages in OLETF rats and explored the role of the INS/IRS-1/PI3-K/Akt signaling pathway.

METHODS

OLETF rats were assigned into four groups on the basis of OGTT results and 24 h urinary microalbumin: NGT, IGT, DM, and DKD groups. The changes of renal structure and function and the corresponding pathological changes were observed. The absorption of albumin and the expression of megalin, cubilin, IRS-1, PI3-K, and Akt in NRK-52E cells were measured after being stimulated by different concentrations of insulin.

RESULTS

In the IGT group, the index which reflects the function of renal tubule-like N-acetyl-β-glucosaminidase, neutrophil gelatinase-associated lipocalin, retinol-binding protein, and cystatin C was higher than those in the control group and the NGT group (P < 0.05). Significant renal structure damages, especially in renal tubules, were observed in the IGT group. In the presence of insulin at a high concentration, the IRS-1/PI3-K/Akt signaling pathway in renal tubular epithelial cells was inhibited, and the expression of megalin and cubilin was significantly downregulated which was accompanied by a minimum uptake of albumin.

CONCLUSIONS

In contrast to DKD, the renal structural damage and functional changes in the IGT stage, in which we propose the term "IGT kidney disease," mainly manifest as renal tubular injury. Insulin resistance and compensatory hyperinsulinemia may be involved in its pathogenesis.

Dapagliflozin, a sodium-glucose co-transporter-2 inhibitor, slows the progression of renal complications through the suppression of renal inflammation, endoplasmic reticulum stress and apoptosis in prediabetic rats

AIM

To evaluate the renoprotective roles of dapagliflozin in prediabetic rats in order to elucidate the effects of this sodium-glucose co-transporter-2 (SGLT2) inhibitor on the renal complications associated with metabolic dysfunction in diet-induced obesity.

METHODS

Obesity was induced by feeding a high-fat diet (HFD) to male Wistar rats for 16 weeks. HFD-fed rats were treated with dapagliflozin (1 mg/kg/d) or metformin (30 mg/kg/d) by oral gavage for 4 weeks after insulin resistance had been established. The metabolic characteristics and renal function associated with lipid accumulation, inflammation, fibrosis, endoplasmic reticulum (ER) stress and apoptosis in the renal tissue were examined.

RESULTS

The results showed that HFD-fed rats developed both obesity and impaired renal function, along with increased renal triglyceride accumulation. Importantly, dapagliflozin had greater efficacy in improving renal function and reducing both body weight and visceral fat accumulation than metformin treatment. Dapagliflozin and metformin were found to have similar effects regarding the suppression of renal triglycerides, superoxide dismutase (SOD) expression and malondialdehyde (MDA) levels, subsequently leading to a decrease in renal inflammation and fibrosis. Renal ER stress and apoptosis were increased in HFD-fed rats and were effectively reduced after administration of dapagliflozin. The expression of renal SGLT2 was not affected by administration of dapagliflozin or metformin.

CONCLUSION

Collectively, these findings indicate that dapagliflozin exerts renoprotective effects by alleviating obesity-induced renal inflammation, fibrosis, ER stress, apoptosis and lipid accumulation in the prediabetic condition.

Narrative review of the effects of antidiabetic drugs on albuminuria

Diabetes mellitus is the most prevalent metabolic disorder worldwide. Glycemic control is the main focus of antidiabetic therapy. However, there are data suggesting that some antidiabetic drugs may have intrinsic beneficial renal effects and protect against the development and progression of albuminuria, thus minimizing the risk of diabetic nephropathy. These pharmacological agents can suppress upstream molecular pathways involved in the pathophysiology of diabetes-induced renal dysfunction such as oxidative stress, inflammatory responses, and apoptosis. In this narrative review, the pathophysiology of albuminuria in patients with diabetic nephropathy is discussed. Furthermore, the renoprotective effects of antidiabetic drugs, focusing on albuminuria, are reviewed.

The podocyte protease web: uncovering the gatekeepers of glomerular disease

Proteases regulate glomerular physiology. The last decade has revealed a multitude of podocyte proteases that govern the glomerular response to numerous chemical, mechanical, and metabolic cues. These proteases form a protein signaling web that integrates stress stimuli and serves as a key controller of the glomerular microenvironment. Both the extracellular and intracellular proteolytic networks are perturbed in focal segmental glomerulosclerosis, as well as hypertensive and diabetic nephropathy. Accordingly, the highly intertwined podocyte protease web is an integrative part of the podocyte's damage response. Novel mass spectrometry-based technologies will help to untangle this proteolytic network: functional readouts acquired from deep podocyte proteomics, single glomerular proteomics, and degradomics have exposed unanticipated protease activity in podocytes. Future efforts should characterize the interdependency and upstream regulation of key proteases, along with their role in promoting tissue heterogeneity in glomerular diseases. These efforts will not only illuminate the machinery of podocyte proteostasis but also reveal avenues for therapeutic intervention in the podocyte protease web.

Mitochondrial dysfunction in diabetic kidney disease

Globally, diabetes is the leading cause of chronic kidney disease and end-stage renal disease, which are major risk factors for cardiovascular disease and death. Despite this burden, the factors that precipitate the development and progression of diabetic kidney disease (DKD) remain to be fully elucidated. Mitochondrial dysfunction is associated with kidney disease in nondiabetic contexts, and increasing evidence suggests that dysfunctional renal mitochondria are pathological mediators of DKD. These complex organelles have a broad range of functions, including the generation of ATP. The kidneys are mitochondrially rich, highly metabolic organs that require vast amounts of ATP for their normal function. The delivery of metabolic substrates for ATP production, such as fatty acids and oxygen, is altered by diabetes. Changes in metabolic fuel sources in diabetes to meet ATP demands result in increased oxygen consumption, which contributes to renal hypoxia. Inherited factors including mutations in genes that impact mitochondrial function and/or substrate delivery may also be important risk factors for DKD. Hence, we postulate that the diabetic milieu and inherited factors that underlie abnormalities in mitochondrial function synergistically drive the development and progression of DKD.

Arterial stiffness is an independent predictor for albuminuria progression among Asians with type 2 diabetes-A prospective cohort study

AIM

Albuminuria progression has been associated with renal deterioration in type 2 diabetes (T2DM). Central arterial stiffness can aggravate systemic vasculopathy by propagating elevated systolic and pulse pressures forward, thereby accentuating global vascular injury. We aim to investigate whether central arterial stiffness is an independent predictor for albuminuria progression in a multi-ethnic T2DM Asian cohort in Singapore.

METHODS

In a prospective cohort, 1012 T2DM patients were assessed at baseline and after a median follow-up of 3.1years. 880 patients with baseline normo- (urinary albumin-to-creatinine ratio (ACR)<30mg/g, n=579) and microalbuminuria (ACR=30-299mg/g, n=301) were divided into progression and non-progression groups according to ACR changes. Progression was defined as transition from normo- to microalbuminuria, micro- to macroalbuminuria, or normo- to macroalbuminuria. Central arterial stiffness was estimated by carotid-femoral pulse wave velocity (PWV) using applanation tonometry method. Stepwise multiple regression analysis was used to determine the predictor(s) for albuminuria progression.

RESULTS

Albuminuria progression occurred in 178 patients (20.2%). Baseline PWV was higher in progression (10.1±2.9m/s) than non-progression group (9.2±2.4m/s, p<0.001). 1-SD increase in baseline PWV was associated with albuminuria progression (OR=1.457, 95% CI, 1.236-1.718, p<0.001). Stepwise regression analysis identified that baseline PWV (OR=1.241, 95% CI, 1.033-1.490, p=0.021), BMI (OR=1.046, 95% CI, 1.012-1.080, p=0.008), nature log-transformed estimated glomerular filtration rate (LneGFR) (OR=0.320, 95% CI, 0.192-0.530, p=0.010) and LnACR (OR=1.344, 95% CI, 1.187-1.522, p=0.008) are predictors for albuminuria progression.

CONCLUSION

Increased central arterial stiffness at baseline predicted future progression of albuminuria. Our results suggest the potential benefit of ameliorating central arterial stiffness to retard albuminuria progression in T2DM.

Viability of primary cultured podocytes is associated with extracellular high glucose-dependent autophagy downregulation

Structural and functional impairment of podocytes plays an important role in the development of diabetic nephropathy, a chronic complication of diabetes mellitus and leading cause of renal failure requiring renal replacement therapy. Autophagy plays a crucial role in podocyte viability and function, and its activity is modulated by a variety of pathophysiological factors found in diabetic milieu. Here we show that downregulation of autophagy is critical for podocyte survival in hyperglycemic environment. Moreover, long-term exposure to high glucose leads to inhibition of autophagy as well as to the development of insulin resistance in podocytes. Furthermore, impairment of autophagy is involved in alteration of insulin-dependent glucose uptake in podocytes, suggesting a relationship between these two processes. Taken together, our findings suggest that downregulation of podocyte autophagy, observed after long-term exposure to high glucose, results from their suppressed sensitivity to insulin, and may therefore lead to diminished podocyte cell viability as well as their reduced number in glomerulus.

Septin 7 reduces nonmuscle myosin IIA activity in the SNAP23 complex and hinders GLUT4 storage vesicle docking and fusion

Glomerular epithelial cells, podocytes, are insulin responsive and can develop insulin resistance. Here, we demonstrate that the small GTPase septin 7 forms a complex with nonmuscle myosin heavy chain IIA (NMHC-IIA; encoded by MYH9), a component of the nonmuscle myosin IIA (NM-IIA) hexameric complex. We observed that knockdown of NMHC-IIA decreases insulin-stimulated glucose uptake into podocytes. Both septin 7 and NM-IIA associate with SNAP23, a SNARE protein involved in GLUT4 storage vesicle (GSV) docking and fusion with the plasma membrane. We observed that insulin decreases the level of septin 7 and increases the activity of NM-IIA in the SNAP23 complex, as visualized by increased phosphorylation of myosin regulatory light chain. Also knockdown of septin 7 increases the activity of NM-IIA in the complex. The activity of NM-IIA is increased in diabetic rat glomeruli and cultured human podocytes exposed to macroalbuminuric sera from patients with type 1 diabetes. Collectively, the data suggest that the activity of NM-IIA in the SNAP23 complex plays a key role in insulin-stimulated glucose uptake into podocytes. Furthermore, we observed that septin 7 reduces the activity of NM-IIA in the SNAP23 complex and thereby hinders GSV docking and fusion with the plasma membrane.

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Septin 7, nonmuscle myosin heavy chain IIA (NMHC-IIA) and SNAP23 form a complex.

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Knockdown of septin 7 increases NM-IIA activity in the SNAP23 complex.

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Insulin decreases septin 7 level and increases NM-IIA activity in the SNAP23 complex.

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Septin 7 hinders GSV docking/fusion by reducing NM-IIA activity in the SNAP23 complex.

Plasma Triglycerides and HDL-C Levels Predict the Development of Diabetic Kidney Disease in Subjects With Type 2 Diabetes: The AMD Annals Initiative

OBJECTIVE

Despite the achievement of blood glucose, blood pressure, and LDL cholesterol (LDL-C) targets, the risk for diabetic kidney disease (DKD) remains high among patients with type 2 diabetes. This observational retrospective study investigated whether diabetic dyslipidemia-that is, high triglyceride (TG) and/or low HDL cholesterol (HDL-C) levels-contributes to this high residual risk for DKD.

RESEARCH DESIGN AND METHODS

Among a total of 47,177 patients attending Italian diabetes centers, 15,362 patients with a baseline estimated glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m², normoalbuminuria, and LDL-C ≤130 mg/dL completing a 4-year follow-up were analyzed. The primary outcome was the incidence of DKD, defined as either low eGFR (<60 mL/min/1.73 m²) or an eGFR reduction >30% and/or albuminuria.

RESULTS

Overall, 12.8% developed low eGFR, 7.6% an eGFR reduction >30%, 23.2% albuminuria, and 4% albuminuria and either eGFR <60 mL/min/1.73 m² or an eGFR reduction >30%. TG ≥150 mg/dL increased the risk of low eGFR by 26%, of an eGFR reduction >30% by 29%, of albuminuria by 19%, and of developing one abnormality by 35%. HDL-C <40 mg/dL in men and <50 mg/dL in women were associated with a 27% higher risk of low eGFR and a 28% risk of an eGFR reduction >30%, with a 24% higher risk of developing albuminuria and a 44% risk of developing one abnormality. These associations remained significant when TG and HDL-C concentrations were examined as continuous variables and were only attenuated by multivariate adjustment for numerous confounders.

CONCLUSIONS

In a large population of outpatients with diabetes, low HDL-C and high TG levels were independent risk factors for the development of DKD over 4 years.

Persistent Insulin Resistance in Podocytes Caused by Epigenetic Changes of SHP-1 in Diabetes

Poor glycemic control profoundly affects protein expression and the cell signaling action that contributes to glycemic memory and irreversible progression of diabetic nephropathy (DN). We demonstrate that SHP-1 is elevated in podocytes of diabetic mice, causing insulin unresponsiveness and DN. Thus, sustained SHP-1 expression caused by hyperglycemia despite systemic glucose normalization could contribute to the glycemic memory effect in DN. Microalbuminuria, glomerular filtration rate, mesangial cell expansion, and collagen type IV and transforming growth factor-β expression were significantly increased in diabetic Ins2^+/C96Y mice compared with nondiabetic Ins2^+/+ mice and remained elevated despite glucose normalization with insulin implants. A persistent increase of SHP-1 expression in podocytes despite normalization of systemic glucose levels was associated with sustained inhibition of the insulin signaling pathways. In cultured podocytes, high glucose levels increased mRNA, protein expression, and phosphatase activity of SHP-1, which remained elevated despite glucose concentration returning to normal, causing persistent insulin receptor-β inhibition. Histone posttranslational modification analysis showed that the promoter region of SHP-1 was enriched with H3K4me1 and H3K9/14ac in diabetic glomeruli and podocytes, which remained elevated despite glucose level normalization. Hyperglycemia induces SHP-1 promoter epigenetic modifications, causing its persistent expression and activity and leading to insulin resistance, podocyte dysfunction, and DN.

Proteomic and phosphoproteomic analysis of renal cortex in a salt-load rat model of advanced kidney damage

Salt plays an essential role in the progression of chronic kidney disease and hypertension. However, the mechanisms underlying pathogenesis of salt-induced kidney damage remain largely unknown. Here, Sprague-Dawley rats, that underwent 5/6 nephrectomy (5/6Nx, a model of advanced kidney damage) or sham operation, were treated for 2 weeks with a normal or high-salt diet. We employed aTiO₂ enrichment, iTRAQ labeling and liquid-chromatography tandem mass spectrometry strategy for proteomic and phosphoproteomic profiling of the renal cortex. We found 318 proteins differentially expressed in 5/6Nx group relative to sham group, and 310 proteins significantly changed in response to salt load in 5/6Nx animals. Totally, 1810 unique phosphopeptides corresponding to 550 phosphoproteins were identified. We identified 113 upregulated and 84 downregulated phosphopeptides in 5/6Nx animals relative to sham animals. Salt load induced 78 upregulated and 91 downregulated phosphopeptides in 5/6Nx rats. The differentially expressed phospholproteins are important transporters, structural molecules, and receptors. Protein-protein interaction analysis revealed that the differentially phosphorylated proteins in 5/6Nx group, Polr2a, Srrm1, Gsta2 and Pxn were the most linked. Salt-induced differential phosphoproteins, Myh6, Lmna and Des were the most linked. Altered phosphorylation levels of lamin A and phospholamban were validated. This study will provide new insight into pathogenetic mechanisms of chronic kidney disease and salt sensitivity.

The dose-response effect of insulin sensitivity on albuminuria in children according to diabetes type

BACKGROUND

Insulin resistance is associated with microalbuminuria among youth with diabetes mellitus. We sought to determine the dose-response effect of insulin sensitivity (IS) on the magnitude of albuminuria and whether there is a threshold below which urine albumin excretion increases.

METHODS

These analyses included participants from the SEARCH for Diabetes in Youth Study with incident diabetes who completed a baseline study visit (n = 2988). We estimated IS using a validated equation incorporating waist circumference, HbA1C, and fasting serum triglycerides. Multivariate regression analyses were performed to assess the effect of IS on urine albumin creatinine ratio (UACR), stratified by diabetes type. The IS threshold was then determined using segmented regressions within each diabetes type and incorporated into the multivariate model.

RESULTS

There was an association between IS and UACR in type 2 diabetes only (beta = -0.39; p < 0.001). There was strong statistical evidence for a threshold effect of IS score on UACR in the group of youth with type 2 (beta = 0.40; p < 0.001) but not type 1 diabetes (p = 0.3).

CONCLUSIONS

In cross-sectional analyses, there is a negative association between IS and UACR in youth with type 2 but not type 1 diabetes, and this association likely includes a threshold effect of IS on UACR.

Inhibition of TRPC6 by protein kinase C isoforms in cultured human podocytes

Transient receptor potential canonical‐6 (TRPC6) ion channels, expressed at high levels in podocytes of the filtration barrier, are recently implicated in the pathogenesis of various forms of proteinuric kidney diseases. Indeed, inherited or acquired up‐regulation of TRPC6 activities are suggested to play a role in podocytopathies. Yet, we possess limited information about the regulation of TRPC6 in human podocytes. Therefore, in this study, we aimed at defining how the protein kinase C (PKC) system, one of the key intracellular signalling pathways, regulates TRPC6 function and expression. On human differentiated podocytes, we identified the molecular expressions of both TRPC6 and several PKC isoforms. We also showed that TRPC6 channels are functional since the TRPC6 activator 1‐oleoyl‐2‐acetyl‐sn‐glycerol (OAG) induced Ca²⁺‐influx to the cells. By assessing the regulatory roles of the PKCs, we found that inhibitors of the endogenous activities of classical and novel PKC isoforms markedly augmented TRPC6 activities. In contrast, activation of the PKC system by phorbol 12‐myristate 13‐acetate (PMA) exerted inhibitory actions on TRPC6 and suppressed its expression. Importantly, PMA treatment markedly down‐regulated the expression levels of PKCα, PKCβ, and PKCη reflecting their activation. Taken together, these results indicate that the PKC system exhibits a ‘tonic’ inhibition on TRPC6 activity in human podocytes suggesting that pathological conditions altering the expression and/or activation patterns of podocyte‐expressed PKCs may influence TRPC6 activity and hence podocyte functions. Therefore, it is proposed that targeted manipulation of certain PKC isoforms might be beneficial in certain proteinuric kidney diseases with altered TRPC6 functions.

Hydrochloride pioglitazone protects diabetic rats against podocyte injury through preserving glomerular podocalyxin expression

OBJECTIVE

We sought to test the effect of different dosages of pioglitazone (PIO) on the glomerular expression of podocalyxin and urinary sediment podocalyxin excretion and to explore the potential renoprotective mechanism.

MATERIALS AND METHODS

Type 1 diabetes induced with streptozotocin (65 mg/kg) in 36 male Sprague-Dawley rats were randomly allocated to be treated with vehicle or 10, 20, 30 mg/kg/d PIO respectively for 8 weeks. Eight rats were enrolled in the normal control group.

RESULTS

At 8th week, rats were sacrificed for the observation of kidney injury through electron microscope. Glomerular podocalyxin production including mRNA and protein were determined by RT-PCR and immunohistochemistry respectively. Levels of urinary albumin excretion and urinary sediment podocalyxin, kidney injury index were all significantly increased, whereas expression of glomerular podocalyxin protein and mRNA were decreased significantly in diabetic rats compared to normal control. Dosages-dependent analysis revealed that protective effect of PIO ameliorated the physiopathological changes and reached a peak at dosage of 20 mg/kg/d.

CONCLUSION

PIO could alleviate diabetic kidney injury in a dose-dependent pattern and the role may be associated with restraining urinary sediment podocalyxin excretion and preserving the glomerular podocalyxin expression.

Insulin resistance is associated with the development of albuminuria in Korean subjects without diabetes

Previous studies have shown that insulin resistance is associated with the development of albuminuria. However, most studies are done on a background of diabetes or metabolic syndrome and there is little data from general population. The aim of this study is to define the effect of insulin resistance on the development of albuminuria in healthy individuals without diabetes. We analyzed 60,047 participants without baseline diabetes or chronic kidney disease, who underwent at least two health maintenance visits at a 2-year interval between 2002 and 2009 at a tertiary hospital in Korea. We measured the incidence of albuminuria at the second examination and calculated the odds ratio for the development of albuminuria according to the quintile of the homeostasis model assessment of insulin resistance (HOMA-IR). After 2 years, 880 cases of incident albuminuria were observed. The cumulative incidences of albuminuria were 1.08, 1.50, 1.35, 1.47, and 1.92% for the 1st to 5th quintiles of HOMA-IR. On multivariate logistic analysis, the odds ratios for incident albuminuria compared to those in the 1st quintile were 1.38 (95% CI 1.10-1.73; P=0.006), 1.23 (95% CI 0.97-1.55; P=0.087), 1.32 (95% CI 1.04-1.67; P=0.020), and 1.66 (95% CI 1.31-2.09; P<0.001) in the 2nd, 3rd, 4th, and 5th quintiles, respectively. A high level of insulin resistance assessed with HOMA-IR was associated with the development of albuminuria in relatively healthy subjects without diabetes. Further research is needed to verify the role of insulin resistance in the development of albuminuria and renal injury.

Insulin sensitivity and albuminuria: the RISC study

OBJECTIVE

Accumulating evidence suggests an association between insulin sensitivity and albuminuria, which, even in the normal range, is a risk factor for cardiovascular diseases. We evaluated whether insulin sensitivity is associated with albuminuria in healthy subjects.

RESEARCH DESIGN AND METHODS

We investigated 1,415 healthy, nondiabetic participants (mean age 43.9 ± 8.3 years; 54.3% women) from the RISC (Relationship between Insulin Sensitivity and Cardiovascular Disease) study, of whom 852 participated in a follow-up examination after 3 years. At baseline, insulin sensitivity was assessed by hyperinsulinemic-euglycemic clamps, expressed as the M/I value. Oral glucose tolerance test-based insulin sensitivity (OGIS), homeostasis model assessment of insulin resistance (HOMA-IR), and urinary albumin-to-creatinine ratio (UACR) were determined at baseline and follow-up.

RESULTS

Microalbuminuria (UACR ≥30 mg/g) was present in fewer than 2% at either study visit. After multivariate adjustments, there was no cross-sectional association between UACR and any measure of insulin sensitivity. Neither OGIS nor HOMA-IR was significantly associated with follow-up UACR, but in a multivariate regression analysis, baseline M/I emerged as an independent predictor of UACR at follow-up (β-coefficient -0.14; P = 0.001).

CONCLUSIONS

In healthy middle-aged adults, reduced insulin sensitivity, assessed by hyperinsulinemic-euglycemic clamp, is continuously associated with a greater risk of increasing albuminuria. This finding suggests that reduced insulin sensitivity either is simply related to or might causally contribute to the initial pathogenesis of albuminuria.

Signal transduction in podocytes--spotlight on receptor tyrosine kinases

The mammalian kidney filtration barrier is a complex multicellular, multicomponent structure that maintains homeostasis by regulating electrolytes, acid-base balance, and blood pressure (via maintenance of salt and water balance). To perform these multiple functions, podocytes--an important component of the filtration apparatus--must process a series of intercellular signals. Integrating these signals with diverse cellular responses enables a coordinated response to various conditions. Although mature podocytes are terminally differentiated and cannot proliferate, they are able to respond to growth factors. It is possible that the initial response of podocytes to growth factors is beneficial and protective, and might include the induction of hypertrophic cell growth. However, extended and/or uncontrolled growth factor signalling might be maladaptive and could result in the induction of apoptosis and podocyte loss. Growth factors signal via the activation of receptor tyrosine kinases (RTKs) on their target cells and around a quarter of the 58 RTK family members that are encoded in the human genome have been identified in podocytes. Pharmacological inhibitors of many RTKs exist and are currently used in experimental and clinical cancer therapy. The identification of pathological RTK-mediated signal transduction pathways in podocytes could provide a starting point for the development of novel therapies for glomerular disorders.

Advanced diabetic nephropathy with nephrotic range proteinuria: a pilot study of the long-term efficacy of subcutaneous ACTH gel on proteinuria, progression of CKD, and urinary levels of VEGF and MCP-1

BACKGROUND AND OBJECTIVE

Adrenocorticotropic hormone (ACTH) is able to reduce proteinuria in nondiabetic glomerulopathies through activation of melanocortin receptors (MCR) expressed in the podocyte. To determine the efficacy of ACTH, we conducted a randomized, open-label pilot trial of ACTH gel in patients with advanced diabetic nephropathy.

STUDY DESIGN

Twenty-three (23) patients with diabetic nephropathy were randomized to daily subcutaneous (SQ) injections of 16 or 32 units of ACTH gel for six months. Outcome. The primary endpoint was the percentage of patients achieving a complete remission (<300 mg/24 hours) within 6 months. Exploratory endpoints included the percentage of partial (50% reduction) remissions, changes in Cr, and urinary cytokine markers.

RESULTS

After 6 months of ACTH gel therapy, 8 of 14 (57%) patients achieved a complete (n = 1) or partial (n = 7) remission. In the low-dose ACTH gel group (16 units), urinary protein fell from 6709 + 953 to 2224 + 489 mg/24 hrs (P < 0.001). In contrast, 2 of 6 patients in the 32-unit group achieved partial remission, but aggregate proteinuria (5324 + 751 to 5154 + 853 mg/24 hours) did not change. Urinary VEGF increased from 388 to 1346 pg/mg urinary creatinine (P < 0.02) in the low-dose group but remained unchanged in the high-dose group.

CONCLUSION

ACTH gel stabilizes renal function and reduces urinary protein for up to 6 months after treatment. The ClinTrials.gov identifier is NCT01028287.

Renal function following three distinct weight loss dietary strategies during 2 years of a randomized controlled trial

OBJECTIVE

This study addressed the long-term effect of various diets, particularly low-carbohydrate high-protein, on renal function on participants with or without type 2 diabetes.

RESEARCH DESIGN AND METHODS

In the 2-year Dietary Intervention Randomized Controlled Trial (DIRECT), 318 participants (age, 51 years; 86% men; BMI, 31 kg/m(2); mean estimated glomerular filtration rate [eGFR], 70.5 mL/min/1.73 m(2); mean urine microalbumin-to-creatinine ratio, 12:12) with serum creatinine <176 μmol/L (eGFR ≥ 30 mL/min/1.73 m(2)) were randomized to low-fat, Mediterranean, or low-carbohydrate diets. The 2-year compliance was 85%, and the proportion of protein intake significantly increased to 22% of energy only in the low-carbohydrate diet (P < 0.05 vs. low-fat and Mediterranean). We examined changes in urinary microalbumin and eGFR, estimated by Modification of Diet in Renal Disease and Chronic Kidney Disease Epidemiology Collaboration formulas.

RESULTS

Significant (P < 0.05 within groups) improvements in eGFR were achieved in low-carbohydrate (+5.3% [95% CI 2.1-8.5]), Mediterranean (+5.2% [3.0-7.4]), and low-fat diets (+4.0% [0.9-7.1]) with similar magnitude (P > 0.05) across diet groups. The increased eGFR was at least as prominent in participants with (+6.7%) or without (+4.5%) type 2 diabetes or those with lower baseline renal function of eGFR <60 mL/min/1.73 m(2) (+7.1%) versus eGFR ≥ 60 mL/min/1.73 m(2) (+3.7%). In a multivariable model adjusted for age, sex, diet group, type 2 diabetes, use of ACE inhibitors, 2-year weight loss, and change in protein intake (confounders and univariate predictors), only a decrease in fasting insulin (β = -0.211; P = 0.004) and systolic blood pressure (β = -0.25; P < 0.001) were independently associated with increased eGFR. The urine microalbumin-to-creatinine ratio improved similarly across the diets, particularly among participants with baseline sex-adjusted microalbuminuria, with a mean change of -24.8 (P < 0.05).

CONCLUSIONS

A low-carbohydrate diet is as safe as Mediterranean or low-fat diets in preserving/improving renal function among moderately obese participants with or without type 2 diabetes, with baseline serum creatinine <176 μmol/L. Potential improvement is likely to be mediated by weight loss-induced improvements in insulin sensitivity and blood pressure.

Ectopic lipid accumulation: A potential cause for metabolic disturbances and a contributor to the alteration of kidney function

Ectopic lipid accumulation is now known to be a mechanism that contributes to organ injury in the context of metabolic diseases. In muscle and liver, accumulation of lipids impairs insulin signaling. This hypothesis accounts for the mechanism of insulin resistance in obesity, type 2 diabetes, aging and lipodystrophy. Increasing data suggest that lipid accumulation in the kidneys could also contribute to the alteration of kidney function in the context of metabolic syndrome and obesity. Furthermore and more unexpectedly, animal models of kidney disease exhibit a decreased adiposity and ectopic lipid redistribution suggesting that kidney disease may be a state of lipodystrophy. However, whether this abnormal lipid partitioning during chronic kidney disease (CKD) may have any functional impact in these tissues needs to be investigated. Here, we provide a perspective by defining the problem and analyzing the possible causes and consequences. Further human studies are required to strengthen these observations, and provide novel therapeutic approaches.

Structural renal changes in obesity and diabetes

Overweight, obesity, and associated diseases represent an emerging problem, not only in Western countries but also in the developing world. They are now characterized as epidemic diseases. Obesity is particularly serious because its incidence in children and adolescents increased dramatically: it is estimated that in the United States every eighth adolescent suffers from obesity, which in the long run may reduce life expectancy in the population. Apart from cardiovascular disease (ie, blood pressure, stroke, and coronary heart disease), kidney diseases also have been shown to be associated with obesity. Epidemiologic studies have indicated that obesity can be a risk factor of chronic kidney disease irrespective of the presence or absence of diabetes, arterial hypertension, and other comorbidities. More evidence is accumulated on the link between chronic kidney disease in obesity and abnormalities in adipokine secretion (hyperleptinemia, lack of adiponectin), activation of the renin-angiotensin system, chronic inflammation, endothelial dysfunction, lipid accumulation, impaired renal hemodynamics, and diminished nephron number related to body mass. In general, obesity is known to aggravate the course of many primary renal diseases such as glomerulonephritides, but also impairs renal function after kidney transplantation. Microalbuminuria, proteinuria, hyperfiltration, and impaired renal function are associated with obesity. Histologically, secondary focal segmental sclerosis has been shown to be caused particularly by obesity. Of practical purpose for clinical nephrology, loss of body weight either by lifestyle modification or bariatric surgery improves albuminuria and hyperfiltration in obese patients, making renal disease in obesity accessible for prevention programs. This review specifically addresses the pathogenesis and morphology of renal functional and particularly structural changes in obesity and associated renal disease such as diabetic nephropathy.

Expression of SHP-1 induced by hyperglycemia prevents insulin actions in podocytes

Renal podocyte apoptosis is an early event of diabetic nephropathy progression. Insulin action is critical for podocyte survival. Previous studies demonstrated that Src homology-2 domain-containing phosphatase-1 (SHP-1) is elevated in renal cortex of type 1 diabetic mice; we hypothesized that hyperglycemia-induced SHP-1 expression may affect insulin actions in podocytes. Type 1 diabetic Akita mice (Ins2(+/C96Y)) developed elevated foot process effacement and podocyte apoptosis compared with control littermate mice (Ins2(+/+)). In contrast to Ins2(+/+) mice, insulin-stimulated protein kinase B (Akt) and extracellular signal-regulated kinase (ERK) phosphorylation were remarkably reduced in renal podocytes of Akita mice. This renal insulin resistance was associated with elevated SHP-1 expression in the glomeruli. Cultured podocytes exposed to high glucose concentration (HG; 25 mM) for 96 h exhibited high levels of apoptotic markers and caspase-3/7 enzymatic activity. HG exposure raised mRNA and protein levels of SHP-1 and reduced the insulin-signaling pathway in podocytes. Overexpression of dominant-negative SHP-1 in podocytes prevented HG effects and restored insulin actions. Elevated SHP-1 expression induced by high glucose levels was directly associated with insulin receptor-β in vitro and in vivo to prevent insulin-stimulated Akt and ERK phosphorylation. In conclusion, our results showed that high levels of SHP-1 expression in glomeruli cause insulin resistance and podocyte loss, thereby contributing to diabetic nephropathy.

Podocyte as a potential target of inflammation: role of pioglitazone hydrochloride in patients with type 2 diabetes

OBJECTIVE

To observe the effects of pioglitazone hydrochloride on urinary sediment podocalyxin and monocyte chemoattractant protein-1 (MCP-1) excretion in patients with type 2 diabetes and to explore its possible renoprotective mechanisms.

METHODS

Ninety-eight patients with uncontrolled type 2 diabetes, who were previously prescribed metformin, acarbose, or both, were randomly assigned to a DP group (add-on pioglitazone; n = 49) or a DS group (add-on sulfonylurea; n = 49).

RESULTS

After 12 weeks of treatment, both add-on pioglitazone therapy (the DP group) and add-on sulfonylurea therapy (the DS group) demonstrated a similar improvement in fasting blood glucose and hemoglobin A1c, but systolic and diastolic blood pressure declined significantly in only the DP group. Moreover, the DP group showed significantly better efficacy in reducing urinary MCP-1 excretion in comparison with the DS group. Furthermore, both urinary albumin and urinary sediment podocalyxin excretion decreased significantly in the DP group but not in the DS group. The urinary sediment podocalyxin to creatinine ratio had a positive correlation with urinary albumin to creatinine ratio (r = 0.624; P<.01) and urinary MCP-1 to creatinine ratio (r = 0.346; P<.01).

CONCLUSION

Pioglitazone treatment revealed a podocyte-protective capacity in patients with type 2 diabetes, and the underlying mechanisms may be partly attributed to its effective suppression of excessive local renal inflammation.

Obesity and diabetic kidney disease

Obesity and diabetes are major causes of CKD and ESRD, and are thus enormous health concerns worldwide. Both obesity and diabetes, along with other elements of the metabolic syndrome including hypertension, are highly interrelated and contribute to the development and progression of renal disease. Studies show that multiple factors act in concert to initially cause renal vasodilation, glomerular hyperfiltration, and albuminuria, leading to the development of glomerulopathy. The coexistence of hypertension contributes to the disease progression, which, if not treated, may lead to ESRD. Although early intervention and management of body weight, hyperglycemia, and hypertension are imperative, novel therapeutic approaches are also necessary to reduce the high morbidity and mortality associated with both obesity-related and diabetes-related renal disease.

Role of insulin resistance in kidney dysfunction: insights into the mechanism and epidemiological evidence

Several lines of evidence suggest a pathogenic role of insulin resistance on kidney dysfunction. Potential mechanisms are mostly due to the effect of single abnormalities related to insulin resistance and clustering into the metabolic syndrome. Hyperinsulinemia, which is inevitably associated to insulin resistance in non diabetic states, also appears to play a role on kidney function by inducing glomerular hyperfiltration and increased vascular permeability. More recently, adipocytokine which are linked to insulin resistance, low grade inflammation, endothelial dysfunction and vascular damage have been proposed as additional molecules able to modulate kidney function. In addition, recent evidences point also to a role of insulin resistance at the level of the podocyte, an important player in early phases of diabetic kidney damage, thus suggesting a new mechanism through which a reduction of insulin action can affect kidney function. In fact, mouse models not expressing the podocyte insulin receptor develop podocytes apoptosis, effacement of its foot processes along with thickening of the glomerular basement membrane, increased glomerulosclerosis and albuminuria. A great number of epidemiological studies have repeatedly reported the association between insulin resistance and kidney dysfunction in both non diabetic and diabetic subjects. Among these, studies addressing the impact of insulin resistance genes on kidney dysfunction have played the important role to help establish a cause-effect relationship between these two traits. Finally, numerous independent intervention studies have shown that a favourable modulation of insulin resistance has a positive effect also on urinary albumin and total protein excretion. In conclusion, several data of different nature consistently support the role of insulin resistance and related abnormalities on kidney dysfunction. Intervention trials designed to investigate whether treating insulin resistance ameliorates also hard renal end-points are both timely and needed.

Deciphering the mechanisms of the Na+/H+ exchanger-3 regulation in organ dysfunction

The Na+/H+ exchanger-3 (NHE3) belongs to the mammalian NHE protein family and catalyzes the electro-neutral exchange of extracellular sodium for intracellular proton across cellular membranes. Its transport function is of essential importance for the maintenance of the body's salt and water homeostasis as well as acid-base balance. Indeed, NHE3 activity is finely regulated by a variety of stimuli, both acutely and chronically, and its transport function is fundamental for a multiplicity of severe and world-wide infection-pathological conditions. This review aims to provide a concise overview of NHE3 physiology and discusses the role of NHE3 in clinical conditions of prominent importance, specifically in hypertension, diabetic nephropathy, heart failure, acute kidney injury, and diarrhea. Study of NHE3 function in models of these diseases has contributed to the deciphering of mechanisms that control the delicate ion balance disrupted in these disorders. The majority of the findings indicate that NHE3 transport function is activated before the onset of hypertension and inhibited thereafter; NHE3 transport function is also upregulated in diabetic nephropathy and heart failure, while it is reported to be downregulated in acute kidney injury and in diarrhea. The molecular mechanisms activated during these pathological conditions to regulate NHE3 transport function are examined with the aim of linking NHE3 dysfunction to the analyzed clinical disorders.

Ezetimibe ameliorates early diabetic nephropathy in db/db mice

AIM

Lipid-lowering medications have been suggested to have a potential benefit in the treatment of chronic kidney disease (CKD) such as diabetic nephropathy. Although ezetimibe has been widely used to lower serum cholesterol levels, the effect of this drug on diabetic nephropathy remains unclear. In the present study, therefore, we examined the protective effect of ezetimibe on diabetic nephropathy in db/db mice.

METHOD

Db/db mice were fed a standard diet with 0.01% (w/w) of ezetimibe for 8 weeks from 8 weeks of age.

RESULTS

Treatment with ezetimibe did not affect food intake, body weight gain, adiposity, or blood pressure in db/db mice. Ezetimibe also had no effect on glucose metabolism such as fasting plasma glucose and insulin; however, it markedly reduced plasma lipid levels and hepatic lipid contents and reduced the urinary excretion of albumin by 50% in db/db mice, suggesting the effect of ezetimibe on diabetic nephropathy. Furthermore, ezetimibe improved glomerular hypertrophy. Although ezetimibe had no effect on oxidative stress measured by urinary 8-OHdG in db/db mice, the plasma adiponectin level was normalized, and the expression of adiponectin receptor 1 in the kidney was increased by ezetimibe treatment.

CONCLUSION

Our data suggest that ezetimibe can improve early diabetic nephropathy through its hypolipidemic effect, and the amelioration of adiponectin resistance may also be responsible for the renoprotective effect of ezetimibe as its underlying mechanism.

Anion exchanger 1 in red blood cells and kidney: Band 3's in a pod

The bicarbonate/chloride exchanger 1 (AE1, Band 3) is abundantly expressed in the red blood cell membrane, where it is involved in gas exchange and functions as a major site of cytoskeletal attachment to the erythrocyte membrane. A truncated kidney isoform (kAE1) is highly expressed in type A intercalated cells of the distal tubules, where it is vital for urinary acidification. Recently, kAE1 has emerged as a novel physiologically significant protein in the kidney glomerulus. This minireview will discuss the known interactions of kAE1 in the podocytes and the possible mechanisms whereby this important multispanning membrane protein may contribute to the function of the glomerular filtration barrier and prevent proteinuria.