Pathophysiology of obesity-related renal dysfunction contributes to diabetic nephropathy

The Role of Resistin in Macrovascular and Microvascular Complications of Type 2 Diabetes

Resistin is an adipokine produced in adipose tissue with pro-inflammatory properties, whose elevation has been associated with insulin resistance and diabetes. Over the past years, significant research has explored the pathophysiological mechanisms involving resistin, utilizing various in vitro and in vivo models. Additionally, numerous clinical studies have aimed to establish a correlation between resistin and the development and progression of macrovascular and microvascular complications in type 2 diabetes. This narrative review summarizes in vitro, in vivo, and human studies published in English since the discovery of resistin in 2001 to the present, examining the role of this adipokine in the pathophysiology of macrovascular and microvascular complications in in vivo and in vitro T2D models, as well as the clinical evidence supporting its use as a biochemical marker in patients with these conditions. The results exhibit considerable heterogeneity and appear to be dependent on the experimental model or population studied. While experimental evidence supports resistin's involvement at the cellular and molecular levels in the pathogenesis of these complications, current clinical evidence remains insufficient to justify its use as a biochemical marker for either diagnosis or prognosis. Therefore, further well-designed studies are required to elucidate resistin's potential role in the clinical setting.

Prognostic value of preoperative nutritional status for postoperative moderate to severe acute kidney injury among older patients undergoing coronary artery bypass graft surgery: a retrospective study based on the MIMIC-IV database

OBJECTIVE

To investigate the association between preoperative nutritional scores and moderate-to-severe acute kidney injury (AKI) after coronary artery bypass graft (CABG) surgery and the predictive significance of nutritional indices for moderate to severe AKI.

METHODS

This study retrospectively included older patients underwent CABG surgery from the Medical Information Mart for Intensive Care (MIMIC) database. Nutritional scores were calculated by the Geriatric Nutritional Risk Index (GNRI) and the Prognostic Nutritional Index (PNI), respectively. Moderate-to-severe injury was determined by KDIGO criteria. Logistic regression, subgroup analysis, and restricted cubic splines were utilized to investigate the association. The predictive value was also assessed by the area under the curve (AUC), net reclassification index (NRI), and integrated discrimination improvement (IDI).

RESULTS

A total of 1,007 patients were retrospectively included, of which 100 (9.9%) and 380 (37.7%) had malnutrition calculated by GNRI and PNI scores. The incidence of moderate-to-severe AKI was 524 (52.0%). After adjustment for selected risk factors, worse nutritional scores were associated with a higher incidence of moderate-to-severe AKI (PGNRI<0.001; PPNI=0.001). Integrating these indices into different base models improves their performance, as manifested by significant improvements in AUCs and NRIs (p < 0.05).

CONCLUSION

Worse preoperative nutritional status was associated with an elevated risk of postoperative moderate-to-severe AKI. Integrating these indices into base models improve their predictive performance. These results highlight the importance of assessing nutritional status among older patients had CABG surgery.

USP19 Stabilizes TAK1 to Regulate High Glucose/Free Fatty Acid-induced Dysfunction in HK-2 Cells

OBJECTIVE

Obesity-induced kidney injury contributes to the development of diabetic nephropathy (DN). Here, we identified the functions of ubiquitin-specific peptidase 19 (USP19) in HK-2 cells exposed to a combination of high glucose (HG) and free fatty acid (FFA) and determined its association with TGF-beta-activated kinase 1 (TAK1).

METHODS

HK-2 cells were exposed to a combination of HG and FFA. USP19 mRNA expression was detected by quantitative RT-PCR (qRT-PCR), and protein analysis was performed by immunoblotting (IB). Cell growth was assessed by Cell Counting Kit-8 (CCK-8) viability and 5-ethynyl-2'-deoxyuridine (EdU) proliferation assays. Cell cycle distribution and apoptosis were detected by flow cytometry. The USP19/TAK1 interaction and ubiquitinated TAK1 levels were assayed by coimmunoprecipitation (Co-IP) assays and IB.

RESULTS

In HG+FFA-challenged HK-2 cells, USP19 was highly expressed. USP19 knockdown attenuated HG+FFA-triggered growth inhibition and apoptosis promotion in HK-2 cells. Moreover, USP19 knockdown alleviated HG+FFA-mediated PTEN-induced putative kinase 1 (PINK1)/Parkin pathway inactivation and increased mitochondrial reactive oxygen species (ROS) generation in HK-2 cells. Mechanistically, USP19 stabilized the TAK1 protein through deubiquitination. Importantly, increased TAK1 expression reversed the USP19 knockdown-mediated phenotypic changes and PINK1/Parkin pathway activation in HG+FFA-challenged HK-2 cells.

CONCLUSION

The findings revealed that USP19 plays a crucial role in promoting HK-2 cell dysfunction induced by combined stimulation with HG and FFAs by stabilizing TAK1, providing a potential therapeutic strategy for combating DN.

Population attributable fractions of modifiable risk factors for microvascular complications of type 2 diabetes in China: An analysis using national cross-sectional data

AIM

To assess the population attributable fractions (PAFs) for modifiable risk factors for microvascular complications of type 2 diabetes (T2D) in China.

MATERIALS AND METHODS

Data collected from the China National HbA1c Surveillance System from 2009 to 2013 were used. The PAFs of four predefined risk factors, including an HbA1c of 7% or higher, blood pressure (BP) of 130/80 mmHg or higher, low-density lipoprotein-cholesterol (LDL-C) of 1.8 mmol/L or higher and body mass index (BMI) of 24 kg/m² or higher, were calculated for diabetic microvascular complications, including diabetic retinopathy (DR), diabetic kidney disease (DKD) and distal symmetric polyneuropathy (DSPN). PAFs were further adjusted for age, sex and duration of diabetes.

RESULTS

In total, there were 998 379 participants with T2D from nationwide mainland China included in this analysis. As for DR, an HbA1c of 7% or higher, BP of 130/80 mmHg or higher, LDL-C of 1.8 mmol/L or higher and BMI of 24 kg/m² or higher conferred PAFs of 16.2%, 15.2%, 5.8% and 2.8%, respectively. In the case of DKD, BP of 130/80 mmHg or higher provided a PAF of 25.2%, followed by an HbA1c of 7% or higher (13.9%), BMI of 24 kg/m² or higher (8.0%) and LDL-C of 1.8 mmol/L or higher (5.6%). As for DSPN, an HbA1c of 7% or higher, BP of 130/80 mmHg or higher, LDL-C of 1.8 mmol/L or higher and BMI of 24 kg/m² or higher contributed to PAFs of 14.2%, 11.7%, 5.9% and 5.8%, respectively. PAFs for diabetic microvascular complications were mildly to moderately reduced after adjusting for participants' age, sex and duration of diabetes.

CONCLUSIONS

Suboptimal glycaemic and BP control were the main contributors to diabetic microvascular complications, while the PAFs of unmet LDL-C and BMI control targets were quite limited for diabetic microvascular complications. In addition to glycaemic control, BP control should be especially prioritized in the management of diabetic microvascular complications to further reduce the disease burden.

RLIP: A necessary transporter protein for translating oxidative stress into pro-obesity and pro-carcinogenic signaling

Previously, we showed that knockout mice homozygous for deficiency of the mercapturic acid pathway (MAP) transporter protein, RLIP (RLIP^-/-), are resistant to chemical carcinogenesis, inflammation, and metabolic syndrome (MetS). We also found that RLIP^-/- mice are highly resistant to obesity caused by a high-fat diet (HFD). Interestingly, these studies showed that kinase, cytokine, and adipokine signaling that are characteristics of obesity were blocked despite the presence of increased oxidative stress in RLIP^-/- mice. The deficiencies in obesity-inducing kinase, cytokine, and adipokine signaling were attributable to a lack of clathrin-dependent endocytosis (CDE), a process that is severely deficient in RLIP^-/- mice. Because CDE is also necessary for carcinogenic signaling through EGF, WNT, TGFβ and other cancer-specific peptide hormones, and because RLIP^-/- mice are cancer-resistant, we reasoned that depletion of RLIP by an antisense approach should cause cancer regression in human cancer xenografts. This prediction has been confirmed in studies of xenografts from lung, kidney, prostate, breast, and pancreatic cancers and melanoma. Because these results suggested an essential role for RLIP in carcinogenesis, and because our studies have also revealed a direct interaction between p53 and RLIP, we reasoned that if RLIP played a central role in carcinogenesis, that development of lymphoma in p53^-/- mice, which normally occurs by the time these mice are 6 months old, could be delayed or prevented by depleting RLIP. Recent studies described herein have confirmed this hypothesis, showing complete suppression of lymphomagenesis in p53^-/- mice treated with anti-RLIP antisense until the age of 8 months. All control mice developed lymphoma in the thymus or testis as expected. These findings lead to a novel paradigm predicting that under conditions of increased oxidative stress, the consequent increased flux of metabolites in the MAP causes a proportional increase in the rate of CDE. Because CDE inhibits insulin and TNF signaling but promotes EGF, TGFβ, and Wnt signaling, our model predicts that chronic stress-induced increases in RLIP (and consequently CDE) will induce insulin-resistance and enhance predisposition to cancer. Alternatively, generalized depletion of RLIP would antagonize the growth of malignant cells, and concomitantly exert therapeutic insulin-sensitizing effects. Therefore, this review focuses on how targeted depletion or inhibition of RLIP could provide a novel target for treating both obesity and cancer.

The effect of Abelmoschus esculentus L. (Okra) extract supplementation on dietary intake, appetite, anthropometric measures, and body composition in patients with diabetic nephropathy

Background: Diabetes is a risk factor for chronic kidney disease because it induces nephropathy. Okra is a rich source of antioxidants, vitamins, minerals, and fibers, of which favorable effects in diabetes have been reported in many animal studies. The present trial aimed to investigate the effect of dried okra extract (DOE) supplementation on anthropometric measures, body composition, appetite, and dietary intake in diabetic nephropathy (DN) patients. Methods: In this triple-blind placebo-controlled randomized clinical trial, 64 DN patients were randomly allocated to receive a 125-mg capsule of DOE (n=32) or placebo (n=32) for 10 weeks. At baseline and endpoint of the trial, anthropometric variables, body composition indices, dietary intake, and appetite scores were evaluated. Results: The results showed that energy (P=0.047, CI: -425.87, -3.25, ES: 0.539) and carbohydrate (P=0.038, CI: -85.64, -2.53, ES: 0.555) intake as well as desire to eat salty food (P=0.023) were reduced in DOE group at the endpoint, compared to the baseline values. However, anthropometric measures, body composition, and appetite score were not significantly different between the two study groups. Conclusion: In conclusion, the present clinical trial showed that DOE could significantly decrease energy intake and carbohydrate consumption in the DN patients. Further clinical trials are needed to determine the effects of this supplement.

Metformin Is Associated with the Inhibition of Renal Artery AT1R/ET-1/iNOS Axis in a Rat Model of Diabetic Nephropathy with Suppression of Inflammation and Oxidative Stress and Kidney Injury

Diabetes is the most common cause of end-stage renal disease, also called kidney failure. The link between the renal artery receptor angiotensin II type I (AT1R) and endothelin-1 (ET-1), involved in vasoconstriction, oxidative stress, inflammation and kidney fibrosis (collagen) in diabetes-induced nephropathy with and without metformin incorporation has not been previously studied. Diabetes (type 2) was induced in rats and another group started metformin (200 mg/kg) treatment 2 weeks prior to the induction of diabetes and continued on metformin until being culled at week 12. Diabetes significantly (p < 0.0001) modulated renal artery tissue levels of AT1R, ET-1, inducible nitric oxide synthase (iNOS), endothelial NOS (eNOS), and the advanced glycation end products that were protected by metformin. In addition, diabetes-induced inflammation, oxidative stress, hypertension, ketonuria, mesangial matrix expansion, and kidney collagen were significantly reduced by metformin. A significant correlation between the AT1R/ET-1/iNOS axis, inflammation, fibrosis and glycemia was observed. Thus, diabetes is associated with the augmentation of the renal artery AT1R/ET-1/iNOS axis as well as renal injury and hypertension while being protected by metformin.

Glomerular Diseases in Diabetic Patients: Implications for Diagnosis and Management

The prevalence of diabetes continues to rise worldwide. In addition to rising rates of diabetic kidney disease, we are also seeing a parallel rise in nondiabetic kidney disease among patients with diabetes. These nondiabetic lesions include focal segmental glomerulosclerosis, IgA nephropathy, membranous nephropathy, and other glomerular diseases. The management of diabetic kidney disease is rapidly evolving to include, beyond glycemic control and renin angiotensin inhibition, the use of sodium-glucose cotransporter 2 (SGLT2) inhibitors and mineralocorticoid receptor antagonists. These and other new treatment strategies should be applicable to managing glomerular disease in diabetic patients to reduce toxicities associated with immunosuppression and, in particular, corticosteroids. The prevalence of glomerular disease in diabetic patients is underappreciated. Diagnosis and appropriately treating these diseases remain an important avenue to modify kidney outcomes in diabetic patients.

Diabetic nephropathy in mice is aggravated by the absence of podocyte IRE1 and is correlated with reduced kidney ADH1 expression

Background

Inositol-requiring enzyme 1 (IRE1) plays a critical role in attenuating endoplasmic reticulum (ER) stress associated with renal injury which may also be a factor in diabetic nephropathy (DN). Alcohol dehydrogenase type I (ADH1) activity is prominent in the kidney, ADH1 activity is also reported to exert protective effects against ER stress that are not caused by alcohol consumption. However, the role of IRE1 in DN and the correlation between IRE1 and ADH1 activity remain unclear.

Methods

IRE1α floxed mice (Ire1^f/f ) of C57BL/6J background were established and crossbred with Ire1α^f/f mice to produce podocyte-specific IRE1α knockout mice. Male db/db mice (C57BLKS/J-leprdb/leprdb mice) were used as a DN model. Male mice were made diabetic by injection of streptozotocin. pLKO.1-based vectors encoding short hairpin RNA (shRNA) specific to the IRE1α gene were transfected into HEK293T cells to knockdown IRE1α in mouse podocytes. ELISA, Masson's staining, and electron microscopy were performed to analyze the development of DN. The ADH1 expression was assayed by qPCR and western blot.

Results

We found that IRE activity was increased in the glomeruli of DN mouse models. In contrast, ADH1 expression was decreased in these models and mice with podocyte-specific disruption of IRE1 (PKO mice). PKO mice that were made diabetic using strepto-zotocin exhibited accelerated proteinuria, enhanced glomerular fibrosis, and podocyte cell death. In addition, in cultured podocytes, the knockdown of IRE1 downregulated the ADH1 mRNA expression and induced ER stress, consistent with the result of PKO mice, while its detrimental effects were reversed by ADH1 overexpression.

Conclusions

Activation of IRE1 in podocytes serves to limit the progress of DN. The dependence of kidney ADH1 expression on podocyte IRE1 further suggests that ADH1 activity may play an important role downstream of IRE1 in protecting against DN.

The Effect of Bariatric Surgery versus Intensive Medical Care on Prevention of Microalbuminuria in Patients with Type 2 Diabetes: 3 Year Experience of a Prospective Study

BACKGROUND: Bariatric surgery could improve diabetic kidney disease; however, the effect of surgery versus medical therapy on renal out comes needs further evaluation. AIM: The aim of the study was to investigate the effect of sleeve-gastrectomy versus intensive medical therapy on the prevention of albuminuria in patients with Type 2 diabetes mellitus (T2DM). METHODS: This is a prospective study of 33 patients with T2DM undergoing sleeve gastrectomy matched for age, sex, and duration of diabetes to 64 medically treated patients. Urinary albumin/creatinine ratio (uACR) was assessed before and 3–year after intervention. RESULTS: At baseline, there was no significant difference between surgical and medical group regarding body mass index (BMI), blood pressure, Hemoglobin A1c (HbA1c), or uACR. After 3 years of interventions the mean BMI (kg/m2) and HbA1c (%) became significantly lower in the surgical group compared to medical group. Although mean uACR (g/mg) increased after interventions compared to its levels before interventions in both surgical (11.7 ± 4.8 vs.18.2 ± 5.9) g/mg and medical (13.4 ± 4.5 vs.17.1 ± 6) g/mg groups, albuminuria developed in only three surgical patients and two medical patients (p > 0.05). CONCLUSION: Although bariatric surgery is associated with more reduction in body weight and better glycemic control than intensive medical therapy, sleeve-gastrectomy may not be superior to intensive medical care in prevention of microalbuminuria in patients with T2DM.

Combined effect of obesity and metabolic profile on glomerular dysfunction in hypertensive subjects

AIM

The aim of this study is to explore the individual and combined effects of obesity and metabolic profile on the impairment of glomerular function among hypertensive subjects.

METHODS

This is a cross-sectional study enrolling 499 hypertensive subjects. Based on body mass index values and metabolic profile, they were assigned to one of four metabolic phenotype groups: MHNO: metabolically healthy non-obese, MHO: metabolically healthy but obese, MUHNO: metabolically unhealthy but non-obese, and MUHO: metabolically unhealthy and obese. The effect of the interaction between obesity and metabolic profile was tested on an additive scale, for both microalbuminuria and reduced estimated glomerular filtration rate (eGFR).

RESULTS

After adjustment for confounding factors, the highest risk of both microalbuminuria and decreased eGFR was found among patients of the MUHO group (OR = 6.0 [2.13], p < 0.0001, OR = 5.4 [1.26], p = 0.03, respectively). Analysis of the additive interaction indicates that 51% and 53% of the risk of microalbuminuria and its combination with low eGFR respectively is explained by the co-occurrence of obesity and metabolic disorder. The mechanism of this interaction is synergistic (synergy index = 2.6, [1.5.3]).

CONCLUSION

The decline of glomerular function in hypertensive subjects is significantly exacerbated by the interaction between obesity and metabolic disorders. The management of such high-risk subjects requires, in addition to the therapeutic regimen, an adequate dietary and physical program in order to preserve glomerular function.

Antiangiogenic therapy in diabetic nephropathy: A double‑edged sword (Review)

Diabetes and the associated complications are becoming a serious global threat and an increasing burden to human health and the healthcare systems. Diabetic nephropathy (DN) is the primary cause of end-stage kidney disease. Abnormal angiogenesis is well established to be implicated in the morphology and pathophysiology of DN. Factors that promote or inhibit angiogenesis serve an important role in DN. In the present review, the current issues associated with the vascular disease in DN are highlighted, and the challenges in the development of treatments are discussed.

MicroRNA-155 Mediates Obesity-Induced Renal Inflammation and Dysfunction

Chronic inflammation is a major contributor to obesity-related renal damage. Recent studies have demonstrated that microRNA (miR)-155 is closely associated with hyperglycemia-induced nephropathy, but whether renal miR-155 participates in the inflammatory response and development of obesity-related nephropathy is unknown. In present study, we investigated the pathophysiological role of renal miR-155 in palmitic acid (PA)-treated endothelial cell and high-fat-diet (HFD)-fed mouse models by specific miR-155 sponge. Mice fed with HFD exhibited higher levels of renal miR-155, which positively correlated with urine microalbumin and blood urea nitrogen. In vitro study, mouse renal vascular endothelial cells stimulated with PA also showed higher miR-155 levels, accompanied with increased inflammatory response. Suppression of renal miR-155 effectively attenuated HFD-induced renal structural damages and dysfunction. MiR-155 sponge treatment also significantly decreased NF-κB signaling and downstream gene expression in vitro and in vivo. The obesity-increased macrophage infiltration and lipotoxicity was decreased in mouse kidney after miR-155 sponge treatment. Mechanistically, miR-155 directly targeted 3'-UTR of SHIP1/INPP5D and suppressed its expression in vitro and in vivo, whereas silence of SHIP1/INPP5D abolished the renal protective benefits of miR-155 sponge in obese mice. Taken together, present findings for the first time provided evidence for the potential role of miR-155 in obesity-related nephropathy and clarified that SHIP1/NF-κB signaling was a potential molecular mechanism.

Thrombospondin-1 regulation of latent TGF-β activation: A therapeutic target for fibrotic disease

Transforming growth factor-β (TGF-β) is a central player in fibrotic disease. Clinical trials with global inhibitors of TGF-β have been disappointing, suggesting that a more targeted approach is warranted. Conversion of the latent precursor to the biologically active form of TGF-β represents a novel approach to selectively modulating TGF-β in disease, as mechanisms employed to activate latent TGF-β are typically cell, tissue, and/or disease specific. In this review, we will discuss the role of the matricellular protein, thrombospondin 1 (TSP-1), in regulation of latent TGF-β activation and the use of an antagonist of TSP-1 mediated TGF-β activation in a number of diverse fibrotic diseases. In particular, we will discuss the TSP-1/TGF-β pathway in fibrotic complications of diabetes, liver fibrosis, and in multiple myeloma. We will also discuss emerging evidence for a role for TSP-1 in arterial remodeling, biomechanical modulation of TGF-β activity, and in immune dysfunction. As TSP-1 expression is upregulated by factors induced in fibrotic disease, targeting the TSP-1/TGF-β pathway potentially represents a more selective approach to controlling TGF-β activity in disease.

Disparate phospho-Smad2 levels in advanced type 2 diabetes patients with diabetic nephropathy and early experimental db/db mouse model

Uncontrolled activation of transforming growth factor beta (TGF-β) family members is hypothesized to participate in type 2 diabetes (T2D) dependent diabetic nephropathy (DN). We evaluated and compared downstream activation of the Smad2-signaling pathway in kidney samples from T2D patients to kidneys from the T2D model of leptin receptor deficient db/db mouse. Furthermore, expression of TGF-β family members was evaluated to elucidate molecular mechanisms in the mouse model. Kidney samples from patients with advanced stages of DN showed elevated pSmad2 staining whereas db/db mouse kidneys surprisingly showed a decrease in pSmad2 in the tubular compartment. Structurally, kidney tissue showed dilated tubules and expanded glomeruli, but no clear fibrotic pattern was found in the diabetic mice. Selective TGF-β family members were up-regulated at the mRNA level. Antagonists of bone morphogenetic protein (BMP) ligands, such as Gremlin1, USAG1 and Sclerostin, were strongly up-regulated suggesting a dampening effect on BMP pathways. Together, these results indicate a lack of translation from T2D patient kidneys to the db/db model with regards to Smad signaling pathway. It is plausible that a strong up-regulation of BMP antagonizing factors account for the lack of Smad1/5/8 activation, in spite of increased expression of several BMP members.

Resistin-Like Molecule Beta (RELM-β) Regulates Proliferation of Human Diabetic Nephropathy Mesangial Cells via Mitogen-Activated Protein Kinases (MAPK) Signaling Pathway

BACKGROUND Resistin-like molecule beta (RELM-β) has been reported to be associated with diabetic nephropathy (DN). However, the role of RELM-β in DN is poorly understood. This study was conducted to delineate the underlying mechanisms of action and to investigate the role of RELM-β in the primitive development of DN via MAPK signaling pathways. MATERIAL AND METHODS Lentivirus-mediated vectors and RNAi technology were used to establish the model of RELM-β up-regulated and down-regulated expression in human mesangial cells (HMCs). The proliferation of HMCs was detected through CCK-8 method. The cell cycle and cell proliferation of HMCs was detected through flow cytometry. The MAPKs pathway protein activity was detected through Western blotting. RESULTS The HMCs with up-regulated and down-regulated expression of RELM-β increased or decreased significantly at 2-3 days. The HMCs with high glucose intervention reversed the proliferation inhibition. The HMCs with exogenous glucose or RELM-β protein intervention partially reversed the cell cycle inhibition. Among the MAPKs pathway, the phosphorylation activity of p38MAPK and JNK increased or decreased and ERK1/2 did not change in the overexpression or inhibition of RELM-β. The p38 MAPK pathway inhibitor SB202190 significantly inhibited the proliferation of HMCs caused by overexpression of RELM-β. Up-regulated expression of RELM-b induced the phosphorylation of p38 MAPK, JNK in HMCs and promoted HMCs proliferation and participated in early DN through the MAPKs pathway. CONCLUSIONS The results provide evidence that RELM-b is a potential molecular target for the treatment of DN.

Transcriptional and Translational Modulation of myo-Inositol Oxygenase (Miox) by Fatty Acids: IMPLICATIONS IN RENAL TUBULAR INJURY INDUCED IN OBESITY AND DIABETES

The kidney is one of the target organs for various metabolic diseases, including diabetes, metabolic syndrome, and obesity. Most of the metabolic studies underscore glomerular pathobiology, although the tubulo-interstitial compartment has been underemphasized. This study highlights mechanisms concerning the pathobiology of tubular injury in the context of myo-inositol oxygenase (Miox), a tubular enzyme. The kidneys of mice fed a high fat diet (HFD) had increased Miox expression and activity, and the latter was related to phosphorylation of serine/threonine residues. Also, expression of sterol regulatory element-binding protein1 (Srebp1) and markers of cellular/nuclear damage was increased along with accentuated apoptosis and loss of tubular brush border. Similar results were observed in cells treated with palmitate/BSA. Multiple sterol-response elements and E-box motifs were found in the miox promoter, and its activity was modulated by palmitate/BSA. Electrophoretic mobility and ChIP assays confirmed binding of Srebp to consensus sequences of the miox promoter. Exposure of palmitate/BSA-treated cells to rapamycin normalized Miox expression and prevented Srebp1 nuclear translocation. In addition, rapamycin treatment reduced p53 expression and apoptosis. Like rapamycin, srebp siRNA reduced Miox expression. Increased expression of Miox was associated with the generation of reactive oxygen species (ROS) in kidney tubules of mice fed an HFD and cell exposed to palmitate/BSA. Both miox and srebp1 siRNAs reduced generation of ROS. Collectively, these findings suggest that HFD or fatty acids modulate transcriptional, translational, and post-translational regulation of Miox expression/activity and underscore Miox being a novel target of the transcription factor Srebp1. Conceivably, activation of the mTORC1/Srebp1/Miox pathway leads to the generation of ROS culminating into tubulo-interstitial injury in states of obesity.

Overexpression of transcription factor FOXC2 in cultured human podocytes upregulates injury markers and increases motility

Obesity and diabetes-related kidney diseases associate with renal failure and cardiovascular morbidity, and represent a major health issue worldwide. However, the molecular mechanisms leading to their development remain poorly understood. We observed increased expression of transcription factor FoxC2 in the podocytes of obese Zucker rats that are insulin resistant and albuminuric. We also found that depletion of adiponectin, an adipocyte-derived hormone whose secretion is decreased in obesity, upregulated FOXC2 in differentiated human podocytes in vitro. Overexpression of FOXC2 in cultured human podocytes led to increased nuclear expression of FOXC2 associated with a change of cellular morphology. This was accompanied by upregulation of vimentin, a key mesenchymal marker, and active beta-catenin, associated with podocyte injury. We also observed re-organization of the actin cytoskeleton, disrupted localization of the tight junction protein ZO-1, and increased motility of podocytes overexpressing FOXC2. These data indicate that the expression of FOXC2 in podocytes needs to be tightly regulated, and that its overexpression induces a chain of cellular events leading to podocyte dysfunction. These changes may lead to podocyte detachment and depletion ultimately contributing to albuminuria. We also suggest a novel molecular mechanism linking obesity-induced decrease in adiponectin to podocyte dysfunction via upregulation of FOXC2.

Effect of Acetazolamide on Obesity-Induced Glomerular Hyperfiltration: A Randomized Controlled Trial

AIMS

Obesity is an important risk factor for the development of chronic kidney disease. One of the major factors involved in the pathogenesis of obesity-associated kidney disease is glomerular hyperfiltration. Increasing salt-delivery to the macula densa is expected to decrease glomerular filtration rate (GFR) by activating tubuloglomerular feedback. Acetazolamide, a carbonic anhydrase inhibitor which inhibits salt reabsorption in the proximal tubule, increases distal salt delivery. Its effects on obesity-related glomerular hyperfiltration have not previously been studied. The aim of this investigation was to evaluate whether administration of acetazolamide to obese non diabetic subjects reduces glomerular hyperfiltration.

MATERIALS AND METHODS

The study was performed using a randomized double-blind crossover design. Obese non-diabetic men with glomerular hyperfiltration were randomized to receive intravenously either acetazolamide or furosemide at equipotent doses. Twelve subjects received the allocated medications. Two weeks later, the same subjects received the drug which they had not received during the first study. Inulin clearance, p-aminohippuric acid clearance and fractional lithium excretion were measured before and after medications administration. The primary end point was a decrease in GFR, measured as inulin clearance.

RESULTS

GFR decreased by 21% following acetazolamide and did not decrease following furosemide. Renal vascular resistance increased by 12% following acetazolamide, while it remained unchanged following furosemide administration. Natriuresis increased similarly following acetazolamide and furosemide administration. Sodium balance was similar in both groups.

CONCLUSIONS

Intravenous acetazolamide decreased GFR in obese non-diabetic men with glomerular hyperfiltration. Furosemide, administered at equipotent dose, did not affect GFR, suggesting that acetazolamide reduced glomerular hyperfiltration by activating tubuloglomerular feedback.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01146288.

Disease severity and staging of obesity: a rational approach to patient selection

The increasing prevalence of obesity places ever-increasing cost demands on healthcare systems. One million individuals are eligible for bariatric surgery in the UK, and yet less than 6000 bariatric procedures are performed annually. Bariatric surgery reverses or improves almost all the medical and psychosocial co-morbidities associated with obesity. Although the BMI is a simple method to estimate adiposity at a population level, it is relatively inaccurate within an individual and provides little-to-no indication of overall health status or disease severity. Staging systems overcome the inherent limitations of BMI and allow highly informed decision-making for an individual. At a societal level, this helps to identify those most likely to gain and maximise economic benefit. This review summarises the co-morbidities associated with obesity and the evidence for their improvement following surgery. The rationale for new staging criteria and appropriate patient selection are discussed.

Chaperonin-containing t-complex protein-1 subunit β as a possible biomarker for the phase of glomerular hyperfiltration of diabetic nephropathy

In cell model, we discovered the association between chaperonin-containing t-complex polypeptide 1 subunit β (TCP-1β) and early diabetic nephropathy (DN). In this study, we further explored the relationships between TCP-1β and type 2 diabetic mellitus (DM). To mimic the clinical hyperfiltration state, a type 2 DM mice model was established by feeding a high-fat diet in combination with treatment of streptozotocin and nicotinamide. Blood and urine were collected to determine creatinine clearance (C_cr), and kidney tissues were harvested for evaluation of TCP-1β expression by immunohistochemistry and Western blot. Meanwhile, clinical subjects of healthy controls and type 2 DM were recruited to strengthen the evidence with urine TCP-1β. Results showed that C_cr and the expression of TCP-1β in kidney were significantly higher one week after hyperglycemia development, suggesting that the hyperfiltration state was successfully established in the mice model. TCP-1β was expressed predominantly on renal tubules. By using the estimated glomerular filtration rate to index progression in clinical investigation, urine TCP-1β level was associated with the hyperfiltration phase in type 2 DM patients. Conclusively, we confirmed that TCP-1β is a possible biomarker for early nephropathy of type 2 DM, but further mechanistic study to elucidate its cause and pathway is needed.

Proximal tubular hypertrophy and enlarged glomerular and proximal tubular urinary space in obese subjects with proteinuria

Background

Obesity is associated with glomerular hyperfiltration, increased proximal tubular sodium reabsorption, glomerular enlargement and renal hypertrophy. A single experimental study reported an increased glomerular urinary space in obese dogs. Whether proximal tubular volume is increased in obese subjects and whether their glomerular and tubular urinary spaces are enlarged is unknown.

Objective

To determine whether proximal tubules and glomerular and tubular urinary space are enlarged in obese subjects with proteinuria and glomerular hyperfiltration.

Methods

Kidney biopsies from 11 non-diabetic obese with proteinuria and 14 non-diabetic lean patients with a creatinine clearance above 50 ml/min and with mild or no interstitial fibrosis were retrospectively analyzed using morphometric methods. The cross-sectional area of the proximal tubular epithelium and lumen, the volume of the glomerular tuft and of Bowman’s space and the nuclei number per tubular profile were estimated.

Results

Creatinine clearance was higher in the obese than in the lean group (P=0.03). Proteinuria was similarly increased in both groups. Compared to the lean group, the obese group displayed a 104% higher glomerular tuft volume (P=0.001), a 94% higher Bowman’s space volume (P=0.003), a 33% higher cross-sectional area of the proximal tubular epithelium (P=0.02) and a 54% higher cross-sectional area of the proximal tubular lumen (P=0.01). The nuclei number per proximal tubular profile was similar in both groups, suggesting that the increase in tubular volume is due to hypertrophy and not to hyperplasia.

Conclusions

Obesity-related glomerular hyperfiltration is associated with proximal tubular epithelial hypertrophy and increased glomerular and tubular urinary space volume in subjects with proteinuria. The expanded glomerular and urinary space is probably a direct consequence of glomerular hyperfiltration. These effects may be involved in the pathogenesis of obesity-related renal disease.

Role of p66shc in renal toxicity of oleic acid

BACKGROUND/AIMS

Adult and childhood obesity is an independent risk factor in development of chronic kidney disease (CKD) and its progression to end-stage kidney disease. Pathologic consequences of obesity include non-esterified fatty acid-induced oxidative stress and consequent injury. Since the serine36-phosphorylated p66shc is a newly recognized mediator of oxidative stress and kidney injury, we studied its role in oleic acid (OA)-induced production of reactive oxygen species (ROS), mitochondrial depolarization and injury in cultured renal proximal tubule cells.

METHODS

Renal proximal tubule cells were used and treated with OA: ROS production, mitochondrial depolarization as well as injury were determined. Transcriptional effects of OA on the p66shc gene were determined in a reporter luciferase assay. The role of p66shc in adverse effects of OA was determined using knockdown, p66shc serine36 phosphorylation and cytochrome c binding-deficient cells.

RESULTS

We found that OA increased ROS production via the mitochondria - and to a less extent via the NADPH oxidase - resulting in ROS-dependent mitochondrial depolarization and consequent injury. Interestingly, OA also stimulated the promoter of p66shc. Hence, knockdown of p66shc, impairment its Ser36 phosphorylation (mutation of Ser36 residue to alanine) or cytochrome c binding (W134F mutation) significantly attenuated OA-dependent lipotoxicity.

CONCLUSION

These results offer a novel mechanism by which obesity may lead to renal tubular injury and consequently development of CKD. Manipulation of this pathway may offer therapeutic means to ameliorate obesity-dependent renal lipotoxicity.

Short-term changes after a weight reduction intervention in advanced diabetic nephropathy

BACKGROUND AND OBJECTIVES

Obesity precedes and is strongly linked to the development of type 2 diabetic nephropathy in most patients, yet little is known about the effects of weight reduction on this disease. This study aimed to establish proof of concept for the hypothesis that weight reduction ameliorates diabetic nephropathy.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Six obese individuals with advanced diabetic nephropathy (estimated GFR <40 ml/min per 1.73 m(2), urine albumin excretion >30 mg/d) currently taking a renin-aldosterone axis inhibitor underwent a 12-week very low calorie ketogenic weight reduction diet with encouragement of exercise between March and September 2012. Albuminuria and other parameters of kidney health were the main outcome measures.

RESULTS

There was a 12% reduction in weight (median 118.5 versus 104.3 kg, P=0.03). The intervention was associated with a 36% reduction in albuminuria that did not reach statistical significance (2124 versus 1366 mg/24 h, P=0.08) and significant reductions in the filtration markers serum creatinine (3.54 versus 3.13 mg/dl, P<0.05) and cystatin C (2.79 versus 2.46 mg/l, P<0.05). Improvements were also noted for the diabetes markers fasting glucose (166 versus 131 mg/dl, P<0.05), fasting insulin (26.9 versus 10.4 μU/ml, P<0.05), and insulin resistance (9.6 versus 4.2, P=0.03). Physical function, general health, and the number of diabetes medications also showed statistically significant signs of improvement.

CONCLUSIONS

After a short-term intensive weight reduction intervention in patients with advanced diabetic nephropathy, improvements were observed in markers of glomerular filtration, diabetes status, and risk factors for kidney disease progression, as well as other general indicators of health and well-being.

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.

RLIP76 protein knockdown attenuates obesity due to a high-fat diet

Feeding a Western high-fat diet (HFD) to C57BL/6 mice induces obesity, associated with a chronic inflammatory state, lipid transport, and metabolic derangements, and organ system effects that particularly prominent in the kidneys. Here, we report that RLIP76 homozygous knock-out (RLIP76(-/-)) mice are highly resistant to obesity as well as these other features of metabolic syndrome caused by HFD. The normal increase in pro-inflammatory and fibrotic markers associated with HFD induced obesity in wild-type C57B mice was broadly and nearly completely abrogated in RLIP76(-/-) mice. This is a particularly striking finding because chemical markers of oxidative stress including lipid hydroperoxides and alkenals were significantly higher in RLIP76(-/-) mice. Whereas HFD caused marked suppression of AMPK in wild-type C57B mice, RLIP76(-/-) mice had baseline activation of AMP-activated protein kinase, which was not further affected by HFD. The baseline renal function was reduced in RLIP76(-/-) mice as compared with wild-type, but was unaffected by HFD, in marked contrast to severe renal impairment and glomerulopathy in the wild-type mice given HFD. Our findings confirm a fundamental role of RLIP76 in regulating the function of obesity-promoting pro-inflammatory cytokines, and provide a novel mechanism for targeted therapy of obesity and metabolic syndrome.

Rapid rise in hypertension and nephropathy in youth with type 2 diabetes: the TODAY clinical trial

OBJECTIVE

Among adolescents with type 2 diabetes, there is limited information regarding incidence and progression of hypertension and microalbuminuria. Hypertension and microalbuminuria assessments made during the TODAY clinical trial were analyzed for effect of treatment, glycemic control, sex, and race/ethnicity.

RESEARCH DESIGN AND METHODS

A cohort of 699 adolescents, 10-17 years of age, <2 years duration of type 2 diabetes, BMI ≥ 85%, HbA1c ≤ 8% on metformin therapy, controlled blood pressure (BP), and calculated creatinine clearance >70 mL/min, were randomized to metformin, metformin plus rosiglitazone, or metformin plus intensive lifestyle intervention. Primary study outcome was loss of glycemic control for 6 months or sustained metabolic decompensation requiring insulin. Hypertension and microalbuminuria were managed aggressively with standardized therapy to maintain BP <130/80 or <95th percentile for age, sex, and height and microalbuminuria <30 μg/mg.

RESULTS

In this cohort, 319 (45.6%) reached primary study outcome, and 11.6% were hypertensive at baseline and 33.8% by end of study (average follow-up 3.9 years). Male sex and higher BMI significantly increased the risk for hypertension. Microalbuminuria was found in 6.3% at baseline and rose to 16.6% by end of study. Diagnosis of microalbuminuria was not significantly different between treatment arms, sex, or race/ethnicity, but higher levels of HbA1c were significantly related to risk of developing microalbuminuria.

CONCLUSIONS

Prevalence of hypertension and microalbuminuria increased over time among adolescents with type 2 diabetes regardless of diabetes treatment. The greatest risk for hypertension was male sex and higher BMI. The risk for microalbuminuria was more closely related to glycemic control.

Obesity, adiposity, and dyslipidemia: a consensus statement from the National Lipid Association

The term "fat" may refer to lipids as well as the cells and tissue that store lipid (ie, adipocytes and adipose tissue). "Lipid" is derived from "lipos," which refers to animal fat or vegetable oil. Adiposity refers to body fat and is derived from "adipo," referring to fat. Adipocytes and adipose tissue store the greatest amount of body lipids, including triglycerides and free cholesterol. Adipocytes and adipose tissue are active from an endocrine and immune standpoint. Adipocyte hypertrophy and excessive adipose tissue accumulation can promote pathogenic adipocyte and adipose tissue effects (adiposopathy), resulting in abnormal levels of circulating lipids, with dyslipidemia being a major atherosclerotic coronary heart disease risk factor. It is therefore incumbent upon lipidologists to be among the most knowledgeable in the understanding of the relationship between excessive body fat and dyslipidemia. On September 16, 2012, the National Lipid Association held a Consensus Conference with the goal of better defining the effect of adiposity on lipoproteins, how the pathos of excessive body fat (adiposopathy) contributes to dyslipidemia, and how therapies such as appropriate nutrition, increased physical activity, weight-management drugs, and bariatric surgery might be expected to impact dyslipidemia. It is hoped that the information derived from these proceedings will promote a greater appreciation among clinicians of the impact of excess adiposity and its treatment on dyslipidemia and prompt more research on the effects of interventions for improving dyslipidemia and reducing cardiovascular disease risk in overweight and obese patients.