Molecular mechanisms of diabetic renal hypertrophy

Proximal tubule hypertrophy and hyperfunction: a novel pathophysiological feature in disease states

The role of proximal tubules (PTs), a major component of the renal tubular structure in the renal cortex, has been examined extensively. Along with its physiological role in the reabsorption of various molecules, including electrolytes, amino acids and monosaccharides, transcellular transport of different hormones and regulation of homeostasis, pathological events affecting PTs may underlie multiple disease states. PT hypertrophy or a hyperfunctioning state, despite being a compensatory mechanism at first in response to various stimuli or alterations at tubular transport proteins, have been shown to be critical pathophysiological events leading to multiple disorders, including diabetes mellitus, obesity, metabolic syndrome and congestive heart failure. Moreover, pharmacotherapeutic agents have primarily targeted PTs, including sodium-glucose cotransporter 2, urate transporters and carbonic anhydrase enzymes. In this narrative review, we focus on the physiological role of PTs in healthy states and the current understanding of the PT pathologies leading to disease states and potential therapeutic targets.

Non-enzymatic glycation and diabetic kidney disease

Chronic diabetes leads to various complications including diabetic kidney disease (DKD). DKD is a major microvascular complication and the leading cause of morbidity and mortality in diabetic patients. Varying degrees of proteinuria and reduced glomerular filtration rate are the cardinal clinical manifestations of DKD that eventually progress into end-stage renal disease. Histopathologically, DKD is characterized by renal hypertrophy, mesangial expansion, podocyte injury, glomerulosclerosis, and tubulointerstitial fibrosis, ultimately leading to renal replacement therapy. Amongst the many mechanisms, hyperglycemia contributes to the pathogenesis of DKD via a mechanism known as non-enzymatic glycation (NEG). NEG is the irreversible conjugation of reducing sugars onto a free amino group of proteins by a series of events, resulting in the formation of initial Schiff's base and an Amadori product and to a variety of advanced glycation end products (AGEs). AGEs interact with cognate receptors and evoke aberrant signaling cascades that execute adverse events such as oxidative stress, inflammation, phenotypic switch, complement activation, and cell death in different kidney cells. Elevated levels of AGEs and their receptors were associated with clinical and morphological manifestations of DKD. In this chapter, we discussed the mechanism of AGEs accumulation, AGEs-induced cellular and molecular events in the kidney and their impact on the pathogenesis of DKD. We have also reflected upon the possible options to curtail the AGEs accumulation and approaches to prevent AGEs mediated adverse renal outcomes.

The Combinational Effect of Inulin and Resveratrol on the Oxidative Stress and Inflammation Level in a Rat Model of Diabetic Nephropathy

Background

Using inulin can enhance resveratrol's effects by improving the intestinal microbiome and the stability of resveratrol.

Objectives

We aimed to investigate the effect of therapeutic intervention with combined inulin and resveratrol on kidney function in diabetic rats.

Methods

Diabetic model was induced by intraperitoneal injection of streptozotocin. Afterward, rats were divided into 6 groups: control, diabetic without treatment, diabetic treated with insulin, diabetic treated with resveratrol, diabetic treated with inulin, and diabetic treated with a combination of inulin and resveratrol. After 10 wk, the creatinine, urea, insulin, urinary proteins, and inflammatory and oxidative stress markers were evaluated. Pathologic changes were examined in kidney tissues.

Results

Renal dysfunction, accompanied by increased inflammation and oxidative stress, was observed. Our results showed that treatment with resveratrol and inulin had antidiabetic effects and was associated with reduced renal dysfunction, oxidative stress, and kidney inflammation. In addition, it was observed that combined treatment with inulin and resveratrol outperformed monotherapies in improving kidney function and reducing oxidative stress and inflammation.

Conclusions

Treatment with resveratrol and inulin can have renoprotective effects by improving oxidative stress and inflammation in kidney tissues. Therefore, employing these 2 compounds is suggested as an inexpensive and available method for diabetic nephropathy.

Pharmacological Targeting of Mitochondria in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD) in the United States and many other countries. DKD occurs through a variety of pathogenic processes that are in part driven by hyperglycemia and glomerular hypertension, leading to gradual loss of kidney function and eventually progressing to ESRD. In type 2 diabetes, chronic hyperglycemia and glomerular hyperfiltration leads to glomerular and proximal tubular dysfunction. Simultaneously, mitochondrial dysfunction occurs in the early stages of hyperglycemia and has been identified as a key event in the development of DKD. Clinical management for DKD relies primarily on blood pressure and glycemic control through the use of numerous therapeutics that slow disease progression. Because mitochondrial function is key for renal health over time, therapeutics that improve mitochondrial function could be of value in different renal diseases. Increasing evidence supports the idea that targeting aspects of mitochondrial dysfunction, such as mitochondrial biogenesis and dynamics, restores mitochondrial function and improves renal function in DKD. We will review mitochondrial function in DKD and the effects of current and experimental therapeutics on mitochondrial biogenesis and homeostasis in DKD over time. SIGNIFICANCE STATEMENT: Diabetic kidney disease (DKD) affects 20% to 40% of patients with diabetes and has limited treatment options. Mitochondrial dysfunction has been identified as a key event in the progression of DKD, and pharmacologically restoring mitochondrial function in the early stages of DKD may be a potential therapeutic strategy in preventing disease progression.

The UDPase ENTPD5 regulates ER stress-associated renal injury by mediating protein N-glycosylation

Impaired protein N-glycosylation leads to the endoplasmic reticulum (ER) stress, which triggers adaptive survival or maladaptive apoptosis in renal tubules in diabetic kidney disease (DKD). Therapeutic strategies targeting ER stress are promising for the treatment of DKD. Here, we report a previously unappreciated role played by ENTPD5 in alleviating renal injury by mediating ER stress. We found that ENTPD5 was highly expressed in normal renal tubules; however, ENTPD5 was dynamically expressed in the kidney and closely related to pathological DKD progression in both human patients and mouse models. Overexpression of ENTPD5 relieved ER stress in renal tubular cells, leading to compensatory cell proliferation that resulted in hypertrophy, while ENTPD5 knockdown aggravated ER stress to induce cell apoptosis, leading to renal tubular atrophy and interstitial fibrosis. Mechanistically, ENTPD5-regulated N-glycosylation of proteins in the ER to promote cell proliferation in the early stage of DKD, and continuous hyperglycemia activated the hexosamine biosynthesis pathway (HBP) to increase the level of UDP-GlcNAc, which driving a feedback mechanism that inhibited transcription factor SP1 activity to downregulate ENTPD5 expression in the late stage of DKD. This study was the first to demonstrate that ENTPD5 regulated renal tubule cell numbers through adaptive proliferation or apoptosis in the kidney by modulating the protein N-glycosylation rate in the ER, suggesting that ENTPD5 drives cell fate in response to metabolic stress and is a potential therapeutic target for renal diseases.

Recent advances in molecular mechanisms of acute kidney injury in patients with diabetes mellitus

Several insults can lead to acute kidney injury (AKI) in native kidney and transplant patients, with diabetes critically contributing as pivotal risk factor. High glucose per se can disrupt several signaling pathways within the kidney that, if not restored, can favor the instauration of mechanisms of maladaptive repair, altering kidney homeostasis and proper function. Diabetic kidneys frequently show reduced oxygenation, vascular damage and enhanced inflammatory response, features that increase the kidney vulnerability to hypoxia. Importantly, epidemiologic data shows that previous episodes of AKI increase susceptibility to diabetic kidney disease (DKD), and that patients with DKD and history of AKI have a generally worse prognosis compared to DKD patients without AKI; it is therefore crucial to monitor diabetic patients for AKI. In the present review, we will describe the causes that contribute to increased susceptibility to AKI in diabetes, with focus on the molecular mechanisms that occur during hyperglycemia and how these mechanisms expose the different types of resident renal cells to be more vulnerable to maladaptive repair during AKI (contrast- and drug-induced AKI). Finally, we will review the list of the existing candidate biomarkers of diagnosis and prognosis of AKI in patients with diabetes.

Empagliflozin increases kidney weight due to increased cell size in the proximal tubule S3 segment and the collecting duct

The inhibition of renal SGLT2 glucose reabsorption has proven its therapeutic efficacy in chronic kidney disease. SGLT2 inhibitors (SGLTi) have been intensively studied in rodent models to identify the mechanisms of SGLT2i-mediated nephroprotection. So far, the overwhelming effects from clinical trials, could only partially be reproduced in rodent models of renal injury. However, a commonly disregarded observation from these studies, is the increase in kidney weight after SGLT2i administration. Increased kidney mass often relies on tubular growth in response to reabsorption overload during glomerular hyperfiltration. Since SGLT2i suppress hyperfiltration but concomitantly increase renal weight, it seems likely that SGLT2i have a growth promoting effect on the kidney itself, independent of GFR control. This study aimed to investigate the effect of SGLT2i on kidney growth in wildtype animals, to identify enlarged nephron segments and classify the size increase as hypertrophic/hyperplastic growth or cell swelling. SGLT2i empagliflozin increased kidney weight in wildtype mice by 13% compared to controls, while bodyweight and other organs were not affected. The enlarged nephron segments were identified as SGLT2-negative distal segments of proximal tubules and as collecting ducts by histological quantification of tubular cell area. In both segments protein/DNA ratio, a marker for hypertrophic growth, was increased by 6% and 12% respectively, while tubular nuclei number (hyperplasia) was unchanged by empagliflozin. SGLT2-inhibition in early proximal tubules induces a shift of NaCl resorption along the nephron causing compensatory NaCl and H₂O reabsorption and presumably cell growth in downstream segments. Consistently, in collecting ducts of empagliflozin-treated mice, mRNA expression of the Na⁺-channel ENaC and the H₂O-channels Aqp-2/Aqp-3 were increased. In addition, the hypoxia marker Hif1α was found increased in intercalated cells of the collecting duct together with evidence for increased proton secretion, as indicated by upregulation of carbonic anhydrases and acidified urine pH in empagliflozin-treated animals. In summary, these data show that SGLT2i induce cell enlargement by hypertrophic growth and possibly cell swelling in healthy kidneys, probably as a result of compensatory glucose, NaCl and H₂O hyperreabsorption of SGLT2-negative segments. Particularly affected are the SGLT2-negative proximal tubules (S3) and the collecting duct, areas of low O₂ availability.

Swinhoeic acid from Potentilla fragarioides ameliorates high glucose-induced oxidative stress and accumulation of ECM in mesangial cells via Keap1-dependent activation of Nrf2

OBJECTIVES

Diabetic nephropathy (DN) is one of the most common microvascular complications of diabetes mellitus. Oxidative stress resulting from high glucose promotes accumulation of ECM and development of DN. Activation of Nrf2 could attenuate oxidative stress and following accumulation of ECM. To find novel therapy for DN, we explored the effects of swinhoeic acid from Potentilla fragarioides on mesangial cells under high glucose and underlying mechanisms.

METHODS

CCK-8 and BrdU incorporation assays for survival of mesangial cells gave the concentration of swinhoeic acid in following investigations. ROS, MDA, SOD and CAT were determined. And ECM proteins and their upstream regulators TGF-β₁ and CTGF were detected using ELISA assays. Activation of Nrf2 was explored by immunofluorescence staining together with luciferase reporter assay. To demonstrate the role of Nrf2 activation, siRNA interference was performed. And co-immunoprecipitation assay was used to elucidate swinhoeic acid affects the interaction between Keap1 and Nrf2.

RESULTS

Swinhoeic acid at 10 and 20 μM attenuated oxidative stress and accumulation of ECM in mesangial cells under high glucose. Itactivated Nrf2 in a Keap1-dependent manner, which was involved in its effects.

CONCLUSION

Swinhoeic acid ameliorates oxidative stress and accumulation of ECM resulting from high glucose in mesangial cells via activating Nrf2 in Keap1-dependent manner.

Immune Modulation by Myeloid-Derived Suppressor Cells in Diabetic Kidney Disease

Diabetic kidney disease (DKD) frequently leads to end-stage renal disease and other life-threatening illnesses. The dysregulation of glomerular cell types, including mesangial cells, endothelial cells, and podocytes, appears to play a vital role in the development of DKD. Myeloid-derived suppressor cells (MDSCs) exhibit immunoregulatory and anti-inflammatory properties through the depletion of L-arginine that is required by T cells, through generation of oxidative stress, interference with T-cell recruitment and viability, proliferation of regulatory T cells, and through the promotion of pro-tumorigenic functions. Under hyperglycemic conditions, mouse mesangial cells reportedly produce higher levels of fibronectin and pro-inflammatory cytokines. Moreover, the number of MDSCs is noticeably decreased, weakening inhibitory immune activities, and creating an inflammatory environment. In diabetic mice, immunotherapy with MDSCs that were induced by a combination of granulocyte-macrophage colony-stimulating factor, interleukin (IL)-1β, and IL-6, reduced kidney to body weight ratio, fibronectin expression, and fibronectin accumulation in renal glomeruli, thus ameliorating DKD. In conclusion, MDSCs exhibit anti-inflammatory activities that help improve renal fibrosis in diabetic mice. The therapeutic targeting of the proliferative or immunomodulatory pathways of MDSCs may represent an alternative immunotherapeutic strategy for DKD.

The extract of Polygala fallax Hemsl. slows the progression of diabetic nephropathy by targeting TLR4 anti-inflammation and MMP-2/9-mediated anti-fibrosis in vitro

BACKGROUND

Polygala fallax Hemsl. is a plant that is commonly used as a folk medicine by Guangxi ethnic minorities, and it is also widely used in the clinical treatment of chronic diseases in China. The extract of P. fallax (EPF) contains key biologically active components from the roots and stems. However, the role of P. fallax or EPF in diabetic nephropathy (DN) is unclear.

PURPOSE

This study aimed to investigate the effects and mechanisms of EPF on high glucose (HG)-induced human glomerular mesangial cell (HMC) injury, inflammation, fibrosis, and apoptosis in vitro.

METHODS

For the in vitro study, MTT and ELISA assays were performed with HG-treated HMCs, as well as MMP, Hoechst, flow cytometry, qRT-PCR, and western blot analyses. The expression of the TLR4/NF-κB pathway, along with its downstream inflammatory, apoptosis, and fibrosis factors, was measured. The expression of the TLR4/NF-κB pathway and its downstream inflammatory factors were also measured after the addition of TLR4 inhibitors.

RESULTS

Our results suggest that EPF can reverse the hyperproliferation and apoptosis of HMCs induced by HG. In addition, the extract inhibited the increase in inflammatory factors IL-6, TNF-α, IL-1β, MCP-1, and IL-18 in cells treated with HG. The mRNA and protein expression of TLR4, MyD88, NF-κB, Col IV, FN, MMP-9, and MMP-2 were downregulated by EPF. In addition, EPF significantly reduced the loss of MMP and the upregulation of Bcl-2/Bax mRNA and protein levels after HG treatment.

CONCLUSION

These results demonstrated that EPF protects against diabetes-induced renal injury in vitro. EPF protected against HG-induced HMCs proliferation, apoptosis, fibrosis, and inflammation likely via inhibition of TLR4-dependent NF-κB signaling. This herbal extract may also be a novel treatment for DN.

Pathophysiology of mesangial expansion in diabetic nephropathy: mesangial structure, glomerular biomechanics, and biochemical signaling and regulation

Diabetic nephropathy, a kidney complication arising from diabetes, is the leading cause of death in diabetic patients. Unabated, the growing epidemic of diabetes is increasing instances of diabetic nephropathy. Although the main causes of diabetic nephropathy have been determined, the mechanisms of their combined effects on cellular and tissue function are not fully established. One of many damages of diabetic nephropathy is the development of fibrosis within the kidneys, termed mesangial expansion. Mesangial expansion is an important structural lesion that is characterized by the aberrant proliferation of mesangial cells and excess production of matrix proteins. Mesangial expansion is involved in the progression of kidney failure in diabetic nephropathy, yet its causes and mechanism of impact on kidney function are not well defined. Here, we review the literature on the causes of mesangial expansion and its impacts on cell and tissue function. We highlight the gaps that still remain and the potential areas where bioengineering studies can bring insight to mesangial expansion in diabetic nephropathy.

Sestrin2 attenuates renal damage by regulating Hippo pathway in diabetic nephropathy

Glomerular mesangial cell proliferation and extracellular matrix accumulation contribute to the progression of diabetic nephropathy (DN). As a conserved stress-inducible protein, sestrin2 (Sesn2) plays critical role in the regulation of oxidative stress, inflammation, autophagy, metabolism, and endoplasmic reticulum stress. In this study, we investigated the role of Sesn2 on renal damage in diabetic kidney using transgenic mice overexpressing Sesn2 and the effect of Sesn2 on mesangial cell proliferation and extracellular matrix accumulation in diabetic conditions and the possible molecular mechanisms involved. Sesn2 overexpression improved renal function and decreased glomerular hypertrophy, albuminuria, mesangial expansion, extracellular matrix accumulation, and TGF-β1 expression, as well as oxidative stress in diabetic mice. In vitro experiments, using human mesangial cells (HMCs), revealed that Sesn2 overexpression inhibited high glucose (HG)-induced proliferation, fibronectin and collagen IV production, and ROS generation. Meanwhile, Sesn2 overexpression restored phosphorylation levels of Lats1 and YAP and inhibited TEAD1 expression. Inhibition of Lats1 accelerated HG-induced proliferation and expression of fibronectin and collagen IV. Verteporfin, an inhibitor of YAP, suppressed HG-induced proliferation and expression of fibronectin and collagen IV. However, Sesn2 overexpression reversed Lats1 deficiency-induced Lats1 and YAP phosphorylation, nuclear expression levels of YAP and TEAD1, and proliferation and fibronectin and collagen IV expressions in HMCs exposed to HG. In addition, antioxidant NAC or tempol treatment promoted phosphorylation of Lats1 and YAP and inhibited TEAD1 expression, proliferation, and fibronectin and collagen IV accumulation in HG-treated HMCs. Taken together, Sesn2 overexpression inhibited mesangial cell proliferation and fibrosis via regulating Hippo pathway in diabetic nephropathy. Induction of Sesn2 may be a potential therapeutic target in diabetic nephropathy.

Comparative Morphological, Metabolic and Transcriptome Analyses in elmo1−/−, elmo2−/−, and elmo3−/− Zebrafish Mutants Identified a Functional Non-Redundancy of the Elmo Proteins

The ELMO protein family consists of the homologues ELMO1, ELMO2 and ELMO3. Several studies have shown that the individual ELMO proteins are involved in a variety of cellular and developmental processes. However, it has poorly been understood whether the Elmo proteins show similar functions and act redundantly. To address this question, elmo1−/−, elmo2−/− and elmo3−/− zebrafish were generated and a comprehensive comparison of the phenotypic changes in organ morphology, transcriptome and metabolome was performed in these mutants. The results showed decreased fasting and increased postprandial blood glucose levels in adult elmo1−/−, as well as a decreased vascular formation in the adult retina in elmo1−/−, but an increased vascular formation in the adult elmo3−/− retina. The phenotypical comparison provided few similarities, as increased Bowman space areas in adult elmo1−/− and elmo2−/− kidneys, an increased hyaloid vessel diameter in elmo1−/− and elmo3−/− and a transcriptional downregulation of the vascular development in elmo1−/−, elmo2−/−, and elmo3−/− zebrafish larvae. Besides this, elmo1−/−, elmo2−/−, and elmo3−/− zebrafish exhibited several distinct changes in the vascular and glomerular structure and in the metabolome and the transcriptome. Especially, elmo3−/− zebrafish showed extensive differences in the larval transcriptome and an impaired survivability. Together, the data demonstrated that the three zebrafish Elmo proteins regulate not only similar but also divergent biological processes and mechanisms and show a low functional redundancy.

Increased activity of the metalloproteinase PAPP-A promotes diabetes-induced glomerular hypertrophy

BACKGROUND

Diabetic nephropathy (DN) is a serious complication of diabetes and a common cause of end stage renal failure. Insulin-like growth factor (IGF)-signaling has been implicated in DN, but is mechanistically poorly understood. Here, we assessed the activity of the metalloproteinase PAPP-A, an activator of IGF activity, and its possible interaction with the endogenous PAPP-A inhibitors stanniocalcin (STC)-1 and -2 in the mammalian kidney under normal and hyperglycemic conditions.

METHODS AND RESULTS

Immunohistochemistry demonstrated that PAPP-A, its proteolytic substrate IGF binding protein-4, STC1 and STC2 are present in the human kidney. Endogenous inhibited complexes of PAPP-A (PAPP-A:STC1 and PAPP-A:STC2) were demonstrated in media conditioned by human mesangial cells (HMCs), suggesting that PAPP-A activity is regulated by the STCs in kidney tissue. A method for the selective detection of active PAPP-A in tissue was developed and a significant increase in glomerular active PAPP-A in human diabetic kidney relative to normal was observed. In DN patients, the estimated glomerular filtration rate correlated with PAPP-A activity. In diabetic mice, glomerular growth was reduced when PAPP-A activity was antagonized by adeno-associated virus-mediated overexpression of STC2.

CONCLUSION

We propose that PAPP-A activity in renal tissue is precisely balanced by STC1 and STC2. An imbalance in this equilibrium causing increased PAPP-A enzymatic activity potentially contributes to the development of DN, and thus, therapeutic targeting of PAPP-A activity may represent a novel strategy for its treatment.

Changes in Serum Intact Fibroblast Growth Factor 23 Concentrations From Midlife to Late Life and Their Predictors in the Community: The ARIC Study

Objective

To investigate longitudinal changes in the blood concentration of fibroblast growth factor 23 (FGF23) from midlife to late life and their major predictors in the general population.

Patients and Methods

In 14,444 participants of the Atherosclerosis Risk in Communities Study, we analyzed the association of 31,095 measurements of serum intact FGF23 with age using data from 3 visits (visit 2 [N=13,460; mean age, 57 years]; visit 3 [N=12,323; mean age, 60 years]; and visit 5 [N=6122; mean age, 76 years]) and a linear mixed-effects model. Among 5804 participants who had FGF23 measurements at both visits 3 and 5, we explored predictors of FGF23 change from midlife to late life using linear regression models. Prespecified risk factors were estimated glomerular filtration rate, body mass index, ever smoking, ever drinker, diabetes, hypertension, history of cardiovascular disease, total cholesterol, and high-density lipoprotein cholesterol.

Results

Median FGF23 concentrations were 41.9 pg/mL (interquartile interval [IQI], 33.9 to 51.8 pg/mL) at visit 2, 38.3 pg/mL (IQI, 30.6 to 48.3 pg/mL) at visit 3, and 55.0 pg/mL (IQI, 44.4 to 70.3 pg/mL) at visit 5. A linear mixed-effects model showed that the association of FGF23 with age was nonlinear, with a slight decline or no change in age 45-60 years and a monotonic increase in age greater than or equal to 65 years (FGF23, +10 to 15 pg/mL per 10 years of age). In a multivariable linear regression model, significantly greater increases in FGF23 were noted, with midlife estimated glomerular filtration rate less than 60 mL/min per 1.73 m2 vs more than or equal to 60 mL/min per 1.73 m2 (ΔFGF23, +4.4 pg/mL [95% CI, 0.9 to 8.0]), diabetes vs no diabetes (ΔFGF23, +6.2 pg/mL [95% CI, 4.1 to 8.3]), and hypertension vs no hypertension (ΔFGF23, +4.1 pg/mL [95% CI, 2.7 to 5.4]).

Conclusion

FGF23 did not show any major changes in midlife but increased linearly in late life. Reduced kidney function, diabetes, and hypertension were robustly associated with a greater increase in FGF23. Further investigations are needed to understand the potential mechanisms linking these conditions to an increase in FGF23 concentrations.

d-allulose protects against diabetic nephropathy progression in Otsuka Long-Evans Tokushima Fatty rats with type 2 diabetes

d-allulose is a rare sugar that has been reported to possess anti-hyperglycemic effects. In the present study, we hypothesized that d-allulose is effective in attenuating the progression of diabetic nephropathy in the Otsuka Long-Evans Tokushima Fatty (OLETF) rat model of type 2 diabetes mellitus. Drinking water with or without 3% d-allulose was administered to OLETF rats for 13 weeks. Long-Evans Tokushima Otsuka rats that received drinking water without d-allulose were used as non-diabetic control rats. d-allulose significantly attenuated the increase in blood glucose levels and progressive mesangial expansion in the glomerulus, which is regarded as a characteristic of diabetic nephropathy, in OLETF rats. d-allulose also attenuated the significant increases in renal IL-6 and tumor necrosis factor-α mRNA levels in OLETF rats, which is a proinflammatory parameter. Additionally, we showed that d-allulose suppresses mesangial matrix expansion, but its correlation with suppressing renal inflammation in OLETF rats should be investigated further. Collectively, our results support the hypothesis that d-allulose can prevent diabetic nephropathy in rats.

Direct evidence of proximal tubular proliferation in early diabetic nephropathy

Kidney hypertrophy is a common clinical feature in patients with diabetes and is associated with poor renal outcomes. Initial cell proliferation followed by cellular hypertrophy are considered the responsible mechanisms for diabetic kidney hypertrophy. However, whether similar responses against hyperglycemia continue in the chronic phase in diabetes is unclear. We performed lineage tracing analysis of proximal tubular epithelia using novel type 2 diabetic mice with a tamoxifen-inducible proximal tubule-specific fluorescent reporter. Clonal analysis of proximal tubular epithelia demonstrated that the labeled epithelia proliferated in type 2 diabetic mice. Based on the histological analysis and protein/DNA ratio of sorted labeled tubular epithelia, there was no evidence of cellular hypertrophy in type 2 diabetic mice. Lineage tracing and histological analyses of streptozocin-induced type 1 diabetes also revealed that cellular proliferation occurs in the chronic phase of type 1 diabetes induction. According to our study, epithelial proliferation accompanied by SGLT2 upregulation, rather than cellular hypertrophy, predominantly occurs in the hypertrophic kidney in both type 1 and type 2 diabetes. An increased number of SGLT2+ tubular epithelia may be an adaptive response against hyperglycemia, and linked to the hyper-reabsorption of sodium and glucose observed in type 2 diabetes patients.

Update on Pathogenesis of Glomerular Hyperfiltration in Early Diabetic Kidney Disease

In the existing stages of diabetic kidney disease (DKD), the first stage of DKD is called the preclinical stage, characterized by glomerular hyperfiltration, an abnormally elevated glomerular filtration rate. Glomerular hyperfiltration is an independent risk factor for accelerated deterioration of renal function and progression of nephropathy, which is associated with a high risk for metabolic and cardiovascular disease. It is imperative to understand hyperfiltration and identify potential treatments to delay DKD progress. This paper summarizes the current mechanisms of hyperfiltration in early DKD. We pay close attention to the effect of glucose reabsorption mediated by sodium-glucose cotransporters and renal growth on hyperfiltration in DKD patients, as well as the mechanisms of nitric oxide and adenosine actions on renal afferent arterioles via tubuloglomerular feedback. Furthermore, we also focus on the contribution of the atrial natriuretic peptide, cyclooxygenase, renin-angiotensin-aldosterone system, and endothelin on hyperfiltration. Proposing potential treatments based on these mechanisms may offer new therapeutic opportunities to reduce the renal burden in this population.

Discovery of caffeoylisocitric acid as a Keap1-dependent Nrf2 activator and its effects in mesangial cells under high glucose

Diabetic nephropathy (DN) is one of the severe microvascular complications of diabetes mellitus. Oxidative stress resulting from aberrant metabolism of glucose mediates renal inflammation and fibrosis in the progression of DN. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor regulating the expression of antioxidant enzymes. Activating Nrf2 will give a promising therapy for DN. To discover novel Nrf2 activators, we have investigated caffeoylisocitric acid using mesangial cells under high glucose. The results showed at 10 μM, caffeoylisocitric acid significantly inhibited the self-limited proliferation of mesangial cells induced by high glucose. Further assessments have disclosed caffeoylisocitric acid mitigated oxidative stress, inflammation and accumulation of extracellular matrix resulting from high glucose via inactivating MAPK signalling. Meanwhile activation of Nrf2 was observed and involved in these effects through the interaction between Keap1 and caffeoylisocitric acid to disrupt Keap1-Nrf2 complex. Therefore, caffeoylisocitric acid is a promising Nrf2 activator targeting DN.

Nailfold capillaroscopy and microvascular involvement in Diabetes Mellitus

Objective: to study the relationship between microvascular lesions of Diabetes Mellitus and alterations in the nailfold capillaroscopy. Subjects and Methods: cross-sectional study including 140 individuals (70 with Diabetes Mellitus and 70 controls). Epidemiological and clinical variables were collected from patient’s charts. Fundus ophthalmoscopy, nailfold capillaroscopy, analysis of microalbuminuria and renal clearance as well as fasting glycaemia and HbA1c values were studied simultaneously.Results: capillary density was reduced, and vascular dilatation was increased in Diabetes Mellitus patients when compared to controls (both with p<0.0001). In diabetic individuals the number of dermal papillary capillaries/mm3 correlated negatively with microalbuminuria (p=0.02), patient’s age (p=0.03), values of HbA1c (p=0.03). Patients with diabetic retinopathy and using antiplatelet agents had lower capillary density (p<0.0001 and 0.04 respectively). Capillary dilatation was associated with disease duration (p=0.04).Conclusion: microvascular disease in Diabetes Mellitus is reflected in nailfold capillaroscopy. Decreased capillary density, increased number of ectasias and increased presence of avascular areas were observed in patients with diabetes when compared to controls. In the present study, capillary density correlated/ associate with age, retinopathy, use of antiplatelet medication, HbA1c, microalbuminuria and diabetes duration. Ectasias or dilatations were related to retinopathy, glomerular filtration rate and longer disease duration.

Role of small leucine zipper protein in hepatic gluconeogenesis and metabolic disorder

Hepatic gluconeogenesis is the central pathway for glucose generation in the body. The imbalance between glucose synthesis and uptake leads to metabolic diseases such as obesity, diabetes, and cardiovascular diseases. Small leucine zipper protein (sLZIP) is an isoform of LZIP and it mainly functions as a transcription factor. Although sLZIP is known to regulate the transcription of genes involved in various cellular processes, the role of sLZIP in hepatic glucose metabolism is not known. In this study, we investigated the regulatory role of sLZIP in hepatic gluconeogenesis and its involvement in metabolic disorder. We found that sLZIP expression was elevated during glucose starvation, leading to the promotion of phosphoenolpyruvate carboxylase and glucose-6-phosphatase expression in hepatocytes. However, sLZIP knockdown suppressed the expression of the gluconeogenic enzymes under low glucose conditions. sLZIP also enhanced glucose production in the human liver cells and mouse primary hepatic cells. Fasting-induced cyclic adenosine monophosphate impeded sLZIP degradation. Results of glucose and pyruvate tolerance tests showed that sLZIP transgenic mice exhibited abnormal blood glucose metabolism. These findings suggest that sLZIP is a novel regulator of gluconeogenic enzyme expression and plays a role in blood glucose homeostasis during starvation.

Circulating Proprotein Convertase Subtilisin/Kexin Type 9 Levels Predict Future Cardiovascular Event Risks in Hemodialyzed Black African Patients

CONTEXT AND OBJECTIVE

Cardiovascular diseases are the leading cause of mortality in patients. In this context, proprotein convertase subtilisin/kexin type 9 (PCSK9) appears to be the new biomarker identified as interfering in lipid homeostasis. This study aimed to investigate the association between PCSK9, dyslipidemia, and future risk of cardiovascular events in a population of black Africans.

METHODS

A cross-sectional study was conducted between August 2016 and July 2020 in six hemodialysis centers in the city of Kinshasa, Democratic Republic of the Congo. Serum PCSK9 was measured by ELISA; lipid levels of 251 chronic kidney disease grade 5 (CKD G5) hemodialysis patients and the Framingham predictive instrument were used for predicting cardiac events.

RESULTS

Total cholesterol (TC), low-density lipoprotein cholesterol (LDL-c), and triglycerides (TG) were significantly increased in the tertile with the highest PCSK9. By contrast, high-density lipoprotein cholesterol (HDL-c) was significantly decreased in the same tertile. A strong positive and significant correlation was found between PCSK9 and TC, TG, and LDL-c. Negative and significant correlation was observed between PCSK9 and HDL-c. The levels of PCSK9, smoking, overweight, and atherogenic dyslipidemia were associated with future risks for cardiovascular events in univariate analysis. After adjustment, all these variables persisted as independent determinants of future risk for cardiovascular events. The probability of having a cardiovascular event in this population was independently associated with PCSK9 levels. Compared to the patients in the lowest PCSK9 tertile, patients with PCSK9 levels in the middle (aOR 5.9, 95% CI 2.06-17.3, P<0.001) and highest tertiles (aOR 8.9, 95% CI 3.02-25.08, P<0.001) presented a greater risk of cardiac event.

CONCLUSION

Increased PCSK9 serum levels are associated with higher levels of TC, LDL-c, and TG and lower levels of HDL-c in black African hemodialysis patients. Serum PCSK9 levels in these patients predict increased risk of cardiovascular events, independent of traditional potential confounders.

A natural product of acteoside ameliorate kidney injury in diabetes db/db mice and HK-2 cells via regulating NADPH/oxidase-TGF-β/Smad signaling pathway

This study was designed to investigate the protective effects and mechanisms of acteoside on DKD in diabetes male db/db mice and high glucose-induced HK-2 cells. The diabetes db/db mice were divided randomly into model group, metformin group, irbesartan group, and acteoside group. We observed the natural product of acteoside exhibiting a significant effect in renal protection through analyzing of biochemical indicators and endogenous metabolites, histopathological observations, and western blotting. HK-2 cells subjected to high glucose were used in invitro experiments. The molecular mechanisms of them were investigated by RT-PCR and western blot. Acteoside prevents high glucose-induced HK-2 cells and diabetes db/db mice by inhibiting NADPH/oxidase-TGF-β/Smad signaling pathway. Acteoside regulated the disturbed metabolic pathway of lipid metabolism, glyoxylate and dicarboxylate metabolism, and arachidonic acid metabolism. We discovered the natural product of acteoside exhibiting a significant effect in renal protection. This study paved the way for further exploration of pathogenesis, early diagnosis, and development of a new therapeutic agent for DKD.

Nephroprotective Effects of Tetramethylpyrazine Nitrone TBN in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal failure, but therapeutic options for nephroprotection are limited. Oxidative stress plays a key role in the pathogenesis of DKD. Our previous studies demonstrated that tetramethylpyrazine nitrone (TBN), a novel nitrone derivative of tetramethylpyrazine with potent free radical-scavenging activity, exerted multifunctional neuroprotection in neurological diseases. However, the effect of TBN on DKD and its underlying mechanisms of action are not yet clear. Herein, we performed streptozotocin-induced rat models of DKD and found that TBN administrated orally twice daily for 6 weeks significantly lowered urinary albumin, N-acetyl-β-D-glycosaminidase, cystatin C, malonaldehyde, and 8-hydroxy-2′-deoxyguanosine levels. TBN also ameliorated renal histopathological changes. More importantly, in a nonhuman primate model of spontaneous stage III DKD, TBN increased the estimated glomerular filtration rate, decreased serum 3-nitrotyrosine, malonaldehyde and 8-hydroxy-2′-deoxyguanosine levels, and improved metabolic abnormalities. In HK-2 cells, TBN increased glycolytic and mitochondrial functions. The protective mechanism of TBN might involve the activation of AMPK/PGC-1α-mediated downstream signaling pathways, thereby improving mitochondrial function and reducing oxidative stress in the kidneys of DKD rodent models. These results support the clinical development of TBN for the treatment of DKD.

Phelligridin D from Inonotus obliquus attenuates oxidative stress and accumulation of ECM in mesangial cells under high glucose via activating Nrf2

Diabetic nephropathy (DN) is one of the most common microvascular complications of diabetes mellitus and becomes the financial burden and health problem. Pathogenesis of DN has revealed that high glucose has resulted in the oxidative stress and accumulation of extracellular matrix (ECM). Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor regulating the expression of anti-oxidant enzymes. Therefore, activating Nrf2 gives a promising approach for the treatment of DN. In the discovery of bioactive phytochemicals targeting DN, we have identified phelligridin D from Inonotus obliquus and explored its protective effects against oxidative stress and accumulation of ECM using mesangial cells under high glucose and potential mechanisms. In addition to inhibiting the self-limited proliferation of mesangial cells cultured in high glucose, phelligridin D can attenuate oxidative stress through reducing reactive oxygen species (ROS) and malondialdehyde (MDA) as well as elevating the activity of superoxide dismutase (SOD) and catalase (CAT). Meanwhile, the major components of ECM including collagen IV, fibronectin and laminin were decreased by phelligridin D via inhibiting the secretion of transforming growth factor-β₁ (TGF-β₁) and downstream connective tissue growth factor (CTGF). Further investigations have revealed phelligridin D activated Nrf2 in mesangial cells under high glucose, which was involved in its protective effects. These findings can provide evidences for the discovery of novel therapy targeting DN and application of I. obliquus in practice.

Deciphering the Efficacy and Mechanisms of Chinese Herbal Medicine for Diabetic Kidney Disease by Integrating Web-Based Biochemical Databases and Real-World Clinical Data: Retrospective Cohort Study

Background

Diabetic kidney disease (DKD) is one of the most crucial causes of chronic kidney disease (CKD). However, the efficacy and biomedical mechanisms of Chinese herbal medicine (CHM) for DKD in clinical settings remain unclear.

Objective

This study aimed to analyze the outcomes of DKD patients with CHM-only management and the possible molecular pathways of CHM by integrating web-based biomedical databases and real-world clinical data.

Methods

A total of 152,357 patients with incident DKD from 2004 to 2012 were identified from the National Health Insurance Research Database (NHIRD) in Taiwan. The risk of mortality was estimated with the Kaplan-Meier method and Cox regression considering demographic covariates. The inverse probability of treatment weighting was used for confounding bias between CHM users and nonusers. Furthermore, to decipher the CHM used for DKD, we analyzed all CHM prescriptions using the Chinese Herbal Medicine Network (CMN), which combined association rule mining and social network analysis for all CHM prescriptions. Further, web-based biomedical databases, including STITCH, STRING, BindingDB, TCMSP, TCM@Taiwan, and DisGeNET, were integrated with the CMN and commonly used Western medicine (WM) to explore the differences in possible target proteins and molecular pathways between CHM and WM. An application programming interface was used to assess these online databases to obtain the latest biomedical information.

Results

About 13.7% (20,947/131,410) of patients were classified as CHM users among eligible DKD patients. The median follow-up duration of all patients was 2.49 years. The cumulative mortality rate in the CHM cohort was significantly lower than that in the WM cohort (28% vs 48%, P<.001). The risk of mortality was 0.41 in the CHM cohort with covariate adjustment (99% CI 0.38-0.43; P<.001). A total of 173,525 CHM prescriptions were used to construct the CMN with 11 CHM clusters. CHM covered more DKD-related proteins and pathways than WM; nevertheless, WM aimed at managing DKD more specifically. From the overrepresentation tests carried out by the online website Reactome, the molecular pathways covered by the CHM clusters in the CMN and WM seemed distinctive but complementary. Complementary effects were also found among DKD patients with concurrent WM and CHM use. The risk of mortality for CHM users under renin-angiotensin-aldosterone system (RAAS) inhibition therapy was lower than that for CHM nonusers among DKD patients with hypertension (adjusted hazard ratio [aHR] 0.47, 99% CI 0.45-0.51; P<.001), chronic heart failure (aHR 0.43, 99% CI 0.37-0.51; P<.001), and ischemic heart disease (aHR 0.46, 99% CI 0.41-0.51; P<.001).

Conclusions

CHM users among DKD patients seemed to have a lower risk of mortality, which may benefit from potentially synergistic renoprotection effects. The framework of integrating real-world clinical databases and web-based biomedical databases could help in exploring the roles of treatments for diseases.

p53/microRNA-214/ULK1 axis impairs renal tubular autophagy in diabetic kidney disease

Dysregulation of autophagy in diabetic kidney disease (DKD) has been reported, but the underlying mechanism and its pathogenic role remain elusive. We show that autophagy was inhibited in DKD models and in human diabetic kidneys. Ablation of autophagy-related gene 7 (Atg7) from kidney proximal tubules led to autophagy deficiency and worse renal hypertrophy, tubular damage, inflammation, fibrosis, and albuminuria in diabetic mice, indicating a protective role of autophagy in DKD. Autophagy impairment in DKD was associated with the downregulation of unc-51-like autophagy-activating kinase 1 (ULK1), which was mediated by the upregulation of microRNA-214 (miR-214) in diabetic kidney cells and tissues. Ablation of miR-214 from kidney proximal tubules prevented a decrease in ULK1 expression and autophagy impairment in diabetic kidneys, resulting in less renal hypertrophy and albuminuria. Furthermore, blockade of p53 attenuated miR-214 induction in DKD, leading to higher levels of ULK1 and autophagy, accompanied by an amelioration of DKD. Compared with nondiabetic samples, renal biopsies from patients with diabetes showed induction of p53 and miR-214, associated with downregulation of ULK1 and autophagy. We found a positive correlation between p53/miR-214 and renal fibrosis, but a negative correlation between ULK1/LC3 and renal fibrosis in patients with diabetes. Together, these results identify the p53/miR-214/ULK1 axis in autophagy impairment in diabetic kidneys, pinpointing possible therapeutic targets for DKD.

Mefunidone ameliorates diabetic kidney disease in STZ and db/db mice

Diabetic kidney disease (DKD) is a major cause of end stage renal diseases worldwide. Despite successive interventions for delaying the progression of DKD, current treatments cannot reverse the pathological progression. Mefunidone (MFD) is a new compound with potent antifibrotic properties, but the effect of MFD on DKD remains unknown. Therefore, we investigated the protective effects of MFD in both models of the db/db type 2 diabetes (T2D) and streptozotocin (STZ)-induced type 1 diabetes (T1D) models. Compared with the model group, MFD treatment significantly reduced pathological changes observed by PAS staining, PASM staining, and Masson staining in vivo. To further elucidate the potential mechanisms, we discovered MFD treatment notably restored podocyte function, alleviated inflammation, abated ROS generation, inhibited the TGF-β1/SAMD2/3 pathway, suppressed the phosphorylation levels of MAPKs (ERK1/2, JNK, and P38), and reduced epithelial-to-mesenchymal transition(EMT). In conclusion, these findings demonstrate the effectiveness of MFD in diabetic nephropathy and elucidate its possible mechanism.

Discovery of polypodiside as a Keap1-dependent Nrf2 activator attenuating oxidative stress and accumulation of extracellular matrix in glomerular mesangial cells under high glucose

Diabetic nephropathy (DN) is a severe microvascular complication of diabetes mellitus. High glucose has resulted in oxidative stress and following renal fibrosis as the crucial nodes of this disease. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor regulating transcription of many antioxidant genes and suppressing synthesis of extracellular matrix. To discover Nrf2 activators targeting DN, we have evaluated polypodiside using cell-based assays. The results showed polypodiside inhibited the high glucose-induced self-limited proliferation of glomerular meangial cells. Activation of Nrf2 and enhanced transcription to antioxidant response elements were observed in the presence of polypodiside. Oxidative stress and accumulation of extracellular matrix induced by high glucose in glomerular meangial cells have been ameliorated by polypodiside. Further investigations revealed the effects of polypodiside on glomerular meangial cells were associated with activation of Nrf2. Co-immunoprecipitation of Nrf2 disclosed polypodiside disrupted the Kelch-like ECH-associated protein-1 (Keap1)-Nrf2 interaction. Molecular docking elucidated polypodiside could enter the Nrf2 binding cavity of Keap1 via interacting with the residues encompassing that cavity. These findings indicate polypodiside is a Keap1-dependent Nrf2 activator affording the catabatic effects against oxidative stress and accumulation of extracellular matrix in glomerular meangial cells under high glucose.

KCNQ1OT1/miR-18b/HMGA2 axis regulates high glucose-induced proliferation, oxidative stress, and extracellular matrix accumulation in mesangial cells

The dysregulated long noncoding RNAs (lncRNAs) are associated with the pathogenesis of diabetic nephropathy (DN). LncRNA potassium voltage-gated channel subfamily Q member 1 overlapping transcript 1 (KCNQ1OT1) plays an important role in diabetes, but the role and mechanism of KCNQ1OT1 in DN are largely unknown. Serum samples were collected from 30 DN patients and normal volunteers. High glucose (HG)-challenged human mesangial cells (HMCs) were used as a cell model of DN. KCNQ1OT1, microRNA-18b (miR-18b), and high mobility group protein A2 (HMGA2) abundances were examined via quantitative reverse transcription polymerase chain reaction or western blot. Cell proliferation was assessed via 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide. Oxidative stress was assessed via the levels of reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD), and SOD2. Extracellular matrix (ECM) accumulation was investigated by the levels of fibronectin (FN), collagen I (Col I), and Col IV. The relationship between miR-18b and KCNQ1OT1 or HMGA2 was determined via dual-luciferase reporter analysis, RNA immunoprecipitation, and pull-down. KCNQ1OT1 expression was increased and miR-18b expression was decreased in DN patients and HG-challenged HMCs. miR-18b was targeted via KCNQ1OT1. Knockdown of KCNQ1OT1 weakened HG-caused proliferation, oxidative stress, and ECM accumulation of HMCs by increasing miR-18b. HMGA2 was targeted via miR-18b. miR-18b alleviated HG-induced cell proliferation, oxidative stress, and ECM accumulation by decreasing HMGA2. Silence of KCNQ1OT1 reduced HMGA2 expression via miR-18b. KCNQ1OT1 knockdown attenuated HG-induced proliferation, oxidative stress, and ECM accumulation of HMCs by regulating miR-18b/HMGA2 axis.

Temporal Alterations in Mitochondrial β-Oxidation and Oxidative Stress Aggravate Chronic Kidney Disease Development in 5/6 Nephrectomy Induced Renal Damage

Five-sixths nephrectomy (5/6Nx) model is widely used for studying the mechanisms involved in chronic kidney disease (CKD) progression, a kidney pathology that has increased dramatically in recent years. Mitochondrial impairment is a key mechanism that aggravates CKD progression; however, the information on mitochondrial bioenergetics and redox alterations along a time course in a 5/6Nx model is still limited and in some cases contradictory. Therefore, we performed for the first time a time-course study of mitochondrial alterations by high-resolution respirometry in the 5/6Nx model. Our results show a decrease in mitochondrial β-oxidation at early times, as well as a permanent impairment in adenosine triphosphate (ATP) production in CI-linked respiration, a permanent oxidative state in mitochondria and decoupling of these organelles. These pathological alterations are linked to the early decrease in complex I and ATP synthase activities and to the further decrease in complex III activity. Therefore, our results may suggest that mitochondrial bioenergetics impairment is an early event in renal damage, whose persistence in time aggravates CKD development in the 5/6Nx model.

Cilostazol ameliorates diabetic nephropathy by inhibiting highglucose- induced apoptosis

Diabetic nephropathy (DN) is a hyperglycemia-induced progressive development of renal insufficiency. Excessive glucose can increase mitochondrial reactive oxygen species (ROS) and induce cell damage, causing mitochondrial dysfunction. Our previous study indicated that cilostazol (CTZ) can reduce ROS levels and decelerate DN progression in streptozotocin (STZ)-induced type 1 diabetes. This study investigated the potential mechanisms of CTZ in rats with DN and in high glucose-treated mesangial cells. Male Sprague-Dawley rats were fed 5 mg/kg/day of CTZ after developing STZ-induced diabetes mellitus. Electron microscopy revealed that CTZ reduced the thickness of the glomerular basement membrane and improved mitochondrial morphology in mesangial cells of diabetic kidney. CTZ treatment reduced excessive kidney mitochondrial DNA copy numbers induced by hyperglycemia and interacted with the intrinsic pathway for regulating cell apoptosis as an antiapoptotic mechanism. In high-glucose-treated mesangial cells, CTZ reduced ROS production, altered the apoptotic status, and down-regulated transforming growth factor beta (TGF-β) and nuclear factor kappa light chain enhancer of activated B cells (NF-κB). Base on the results of our previous and current studies, CTZ deceleration of hyperglycemia-induced DN is attributable to ROS reduction and thereby maintenance of the mitochondrial function and reduction in TGF-β and NF-κB levels.

Discovery of a coumarin derivative as Nrf2 activator mitigating oxidative stress and fibrosis in mesangial cells under high glucose

Diabetic nephropathy (DN) is a severe microvascular complication of diabetes mellitus. Oxidative stress and fibrosis largely contribute to the progression of DN. Recently, Nrf2 was found to be a potential target preventing DN. In the discovery of novel Nrf2 activators for the treatment of DN, we have evaluated coumarin derivatives from Wikstroemi indiaca. Molecular docking results have shown compound 4 could bind to Keap1 and activate Nrf2 significantly. Cell-based assays have revealed compound 4 activated Nrf2 and attenuated oxidative stress and fibrosis induced by high glucose in mesangial cells. Meanwhile, it was validated that disruption of the interaction between Keap1 and Nrf2 was involved in the activation of Nrf2 by compound 4 in mesangial cells under high glucose.

Protective effects of Vitex pseudo-negundo leaves on diabetic-induced nephropathy in rats

Objectives The belief of therapeutic effects of herbal remedies in diseases such as diabetes is rooted in medical history. The present study evaluated protective efficacy of the hydroalcoholic extract of Vitex pseudo-negundo leaves (VLHE) on the renal disorders in streptozotocin-induced diabetic rats. Methods Fifty Wistar male rats were recruited and divided into five groups of 10, including healthy controls and diabetic controls: three diabetic groups of which first group was treated with glibenclamide, and two groups treated with 250 and 500 mg/kg of VLHE, respectively, for six weeks. Renal biochemical tests and tissue histopathological evaluation were performed and the antioxidant status was examined. Results There were significant decreases in superoxide dismutase and glutathione peroxidase activities and increases in malondialdehyde levels in renal tissue of diabetic groups compared with healthy controls. In the VLHE-treated rats, fasting blood sugar, blood urea nitrogen and creatinine were declined, serum albumin elevated, kidney weight lowered, lipid peroxidation and reinforcement of the activities of antioxidant enzymes decreased compared with healthy groups. Histological assessments revealed that the vacuolar degeneration of tubules and shrinkage of glomeruli in VLHE-treated rats was decreased compared with diabetic rats. Conclusions The study suggested that administrating of VLHE in nephropathic rats ameliorated the disease by reduction of oxidative stress and increase in renal antioxidant enzyme activities.

Icariin Prevents Extracellular Matrix Accumulation and Ameliorates Experimental Diabetic Kidney Disease by Inhibiting Oxidative Stress via GPER Mediated p62-Dependent Keap1 Degradation and Nrf2 Activation

The present study aimed to determine whether icariin could attenuate type 1 diabetic nephropathy (T1DN) induced by streptozotocin (STZ) after 4 weeks or not. Therefore, its therapeutic effect on diabetic kidney disease was investigated in view of reactive oxygen (ROS) and extracellular matrix (ECM) generation in human glomerular mesangial cells under high glucose. To establish the participation and the key role of GPER and Nrf2 in ECM deposition, a combination of G15 (antagonist of GPER) or siGPER and siNrf2 were performed, respectively. The results showed that T1DN can be significantly inhibited by oral icariin, evidenced by improvement of 24 h urinary volume, 24 h proteinuria, microalbuminuria, and histopathological changes of kidney. Icariin decreased the levels of intracellular superoxide anion, impeded the generation of fibronectin and increased the expression and activity of antioxidant enzymes in the human glomerular mesangial cells treated with high glucose. It acted as a GPER activator, increased dissociation of Nrf2/Keap1 complexes, combination of Keap1/p62 complexes, Nrf2 translocation to nuclear, Nrf2/ARE DNA binding activity, and ARE luciferase reporter gene activity in glomerular mesangial cells. The Nrf2 inhibitor ML385 or siNrf2 obviously abolished extracellular matrix (ECM) generation inhibited by icariin. Furthermore, icariin-induced Nrf2 activation was mainly dependent on p62-mediated Keap1 degradation, which functions as an adaptor protein during autophagy. The GPER antagonist G15 and siGPER obviously abolished the above effects by icariin. Taken together, the present study demonstrated that the therapeutic effects of icariin on type 1 diabetic nephropathy in rats via GPER mediated p62-dependent Keap1 degradation and Nrf2 activation.

Triphala Ameliorates Nephropathy via Inhibition of TGF-β1 and Oxidative Stress in Diabetic Rats

INTRODUCTION

Advanced glycation end products, oxidative stress, and TGF-β expression play a crucial role in pathophysiology of diabetic nephropathy. Inhibition of oxidative stress and TGF-β expression by natural traditional medicines may give an economic and safe alternative treatment option. Triphala churna, a traditional medicine, has been proved to have potent antioxidant activity, and individual components of it have shown significant antidiabetic activity. Hence, the present study was designed to study the effect of Triphala churna in diabetic nephropathy in rats.

METHODS

Diabetes was induced in rats by administration of streptozotocin (55 mg/kg i.p.). Four weeks after induction of diabetes, the animals were treated with Triphala churna at the doses of 250, 500, and 1,000 mg/kg for next 4 weeks. Various biochemical and urine parameters such as glucose, creatinine, blood urea nitrogen (BUN), total protein, and albumin were assessed at the end of study. Creatinine clearance, BUN clearance, and glomerular filtration rate were determined. Oxidative stress parameters such as malondialdehyde, catalase, reduced glutathione, and superoxide dismutase were determined in kidney tissues. TGF-β1 expression was measured with ELISA, immunohistochemistry, and western blot techniques. Histopathology study was carried out with haemotoxylin and eosin, periodic acid-Schiff, and Masson's trichrome staining to determine histological changes.

RESULTS

Treatment with Triphala churna significantly improved urine parameters. Triphala churna treatment also improved plasma proteins, albumin, creatinine, and BUN levels. The oxidative stress was reduced in the kidney with the treatment of Triphala churna. Histopathological studies revealed that Triphala churna reduced kidney damage. Immunohistochemistry, ELISA, and western blotting study revealed that treatment with Triphala decreased the expression of TGF-β in kidney tissues.

CONCLUSION

From the results, it can be concluded that Triphala churna has a significant nephroprotective effect because of its capability of inhibiting oxidative stress and TGF-β in diabetes.

AMPK in microvascular complications of diabetes and the beneficial effects of AMPK activators from plants

BACKGROUND

Diabetes mellitus is a multifactorial disorder with the risk of micro- and macro-vascular complications. High glucose-induced derangements in metabolic pathways are primarily associated with the initiation and progression of secondary complications namely, diabetic nephropathy, neuropathy, and retinopathy. Adenosine monophosphate-activated protein kinase (AMPK) has emerged as an attractive therapeutic target to treat various metabolic disorders including diabetes mellitus. It is a master metabolic regulator that helps in maintaining cellular energy homeostasis by promoting ATP-generating catabolic pathways and inhibiting ATP-consuming anabolic pathways. Numerous pharmacological and plant-derived bioactive compounds that increase AMP-activated protein kinase activation has shown beneficial effects by mitigating secondary complications namely retinopathy, nephropathy, and neuropathy.

PURPOSE

The purpose of this review is to highlight current knowledge on the role of AMPK and its activators from plant origin in diabetic microvascular complications.

METHODS

Search engines such as Google Scholar, PubMed, Science Direct and Web of Science are used to extract papers using relevant key words. Papers mainly focusing on the role of AMPK and AMPK activators from plant origin in diabetic nephropathy, retinopathy, and neuropathy was chosen to be highlighted.

RESULTS

According to results, decrease in AMPK activation during diabetes play a causative role in the pathogenesis of diabetic microvascular complications. Some of the plant-derived bioactive compounds were beneficial in restoring AMPK activity and ameliorating diabetic microvascular complications.

CONCLUSION

AMPK activators from plant origin are beneficial in mitigating diabetic microvascular complications. These pieces of evidence will be helpful in the development of AMPK-centric therapies to mitigate diabetic microvascular complications.

A protective role of renalase in diabetic nephropathy

Renalase, a recently discovered secreted flavoprotein, exerts anti-apoptotic and anti-inflammatory effects against renal injury in acute and chronic animal models. However, whether Renalase elicits similar effects in the development of diabetic nephropathy (DN) remains unclear. The studies presented here tested the hypothesis that Renalase may play a key role in the development of DN and may have therapeutic potential for DN. Renalase expression was measured in human kidney biopsies with DN and in kidneys of db/db mice. The role of Renalase in the development of DN was examined using a genetically engineered mouse model: Renalase knockout mice with db/db background. The renoprotective effects of Renalase in DN was evaluated in db/db mice with Renalase overexpression. In addition, the effects of Renalase on high glucose-induced mesangial cells were investigated. Renalase was down-regulated in human diabetic kidneys and in kidneys of db/db mice compared with healthy controls or db/m mice. Renalase homozygous knockout increased arterial blood pressure significantly in db/db mice while heterozygous knockout did not. Renalase heterozygous knockout resulted in elevated albuminuria and increased renal mesangial expansion in db/db mice. Mesangial hypertrophy, renal inflammation, and pathological injury in diabetic Renalase heterozygous knockout mice were significantly exacerbated compared with wild-type littermates. Moreover, Renalase overexpression significantly ameliorated renal injury in db/db mice. Mechanistically, Renalase attenuated high glucose-induced profibrotic gene expression and p21 expression through inhibiting extracellular regulated protein kinases (ERK1/2). The present study suggested that Renalase protected against the progression of DN and might be a novel therapeutic target for the treatment of DN.

Combination of Naringenin and Lisinopril Ameliorates Nephropathy in Type-1 Diabetic Rats

BACKGROUND

Diabetes is a metabolic disorder affecting a large percentage of the population worldwide. The chronic hyperglycemic condition leads to the generation of advanced glycation end products, reactive oxygen species and inflammatory cytokines, which worsen the functioning of the kidney. Clinical management of diabetic nephropathy is difficult as it requires a multi-focused approach. Hence, a combination of lisinopril a drug used in clinical practice for nephropathy, and naringenin, a flavonoid reported to have a significant effect in nephropathy, may show additive or synergistic effect with less side effects.

OBJECTIVE

The objective of the present study was to evaluate the effect of a combination of lisinopril with naringenin in diabetic nephropathy.

METHODS

Diabetes was induced in male Sprague Dawley rats by streptozotocin (55 mg/kg, i.p.). After four weeks of diabetes induction animals were treated with naringenin alone and a combination of Lisinopril and naringenin for the next four weeks. At the end of the study, various urine and biochemical parameters were evaluated. Oxidative stress parameters like malondialdehyde, reduced glutathione; catalase and superoxide dismutase for kidney tissues were estimated and histopathology studies of kidneys were carried out.

RESULTS

The combination of lisinopril (10 mg/kg) and naringenin (25 and 50 mg/kg) treatment showed significant improvement in the biochemical and urine parameters. Combination treatment also attenuated renal oxidative stress and renal damage as observed in histopathological studies.

CONCLUSION

Treatment with a combination of lisinopril and naringenin showed a promising effect on diabetic nephropathy in rats.

Olinciguat, an Oral sGC Stimulator, Exhibits Diverse Pharmacology Across Preclinical Models of Cardiovascular, Metabolic, Renal, and Inflammatory Disease

Nitric oxide (NO)-soluble guanylate cyclase (sGC)-cyclic 3',5' GMP (cGMP) signaling plays a central role in regulation of diverse processes including smooth muscle relaxation, inflammation, and fibrosis. sGC is activated by the short-lived physiologic mediator NO. sGC stimulators are small-molecule compounds that directly bind to sGC to enhance NO-mediated cGMP signaling. Olinciguat, (R)-3,3,3-trifluoro-2-(((5-fluoro-2-(1-(2-fluorobenzyl)-5-(isoxazol-3-yl)-1H-pyrazol-3-yl)pyrimidin-4-yl)amino)methyl)-2-hydroxypropanamide, is a new sGC stimulator currently in Phase 2 clinical development. To understand the potential clinical utility of olinciguat, we studied its pharmacokinetics, tissue distribution, and pharmacologic effects in preclinical models. Olinciguat relaxed human vascular smooth muscle and was a potent inhibitor of vascular smooth muscle proliferation in vitro. These antiproliferative effects were potentiated by the phosphodiesterase 5 inhibitor tadalafil, which did not inhibit vascular smooth muscle proliferation on its own. Olinciguat was orally bioavailable and predominantly cleared by the liver in rats. In a rat whole body autoradiography study, olinciguat-derived radioactivity in most tissues was comparable to plasma levels, indicating a balanced distribution between vascular and extravascular compartments. Olinciguat was explored in rodent models to study its effects on the vasculature, the heart, the kidneys, metabolism, and inflammation. Olinciguat reduced blood pressure in normotensive and hypertensive rats. Olinciguat was cardioprotective in the Dahl rat salt-sensitive hypertensive heart failure model. In the rat ZSF1 model of diabetic nephropathy and metabolic syndrome, olinciguat was renoprotective and associated with lower circulating glucose, cholesterol, and triglycerides. In a mouse TNFα-induced inflammation model, olinciguat treatment was associated with lower levels of endothelial and leukocyte-derived soluble adhesion molecules. The pharmacological features of olinciguat suggest that it may have broad therapeutic potential and that it may be suited for diseases that have both vascular and extravascular pathologies.

Bile cast nephropathy: when the kidneys turn yellow

Kidney injury is a common finding in patients with liver disease. Bile cast nephropathy (also known as cholemic nephropathy) is an overlooked cause of renal injury in patients with hyperbilirubinemia. It can occur as a result of the toxic effects of bilirubin and bile acids on the renal tubules via several mechanisms. Bile cast nephropathy has characteristic histopathological changes consisting of bilirubin cast deposition in the distal nephron along with tubular epithelial cell injury. Treatment is based on the reversal of liver injury. This review aims to describe bile cast nephropathy in terms of its clinical and morphological features and to shed light on diagnostic techniques. In addition, we present data on management of such nephropathy while reviewing all the reported cases of bile cast nephropathy.

The tubular hypothesis of nephron filtration and diabetic kidney disease

Kidney size and glomerular filtration rate (GFR) often increase with the onset of diabetes, and elevated GFR is a risk factor for the development of diabetic kidney disease. Hyperfiltration mainly occurs in response to signals passed from the tubule to the glomerulus: high levels of glucose in the glomerular filtrate drive increased reabsorption of glucose and sodium by the sodium-glucose cotransporters SGLT2 and SGLT1 in the proximal tubule. Passive reabsorption of chloride and water also increases. The overall capacity for proximal reabsorption is augmented by growth of the proximal tubule, which (alongside sodium-glucose cotransport) further limits urinary glucose loss. Hyperreabsorption of sodium and chloride induces tubuloglomerular feedback from the macula densa to increase GFR. In addition, sodium-glucose cotransport by SGLT1 on macula densa cells triggers the production of nitric oxide, which also contributes to glomerular hyperfiltration. Although hyperfiltration restores sodium and chloride excretion it imposes added physical stress on the filtration barrier and increases the oxygen demand to drive reabsorption. Tubular growth is associated with the development of a senescence-like molecular signature that sets the stage for inflammation and fibrosis. SGLT2 inhibitors attenuate the proximal reabsorption of sodium and glucose, normalize tubuloglomerular feedback signals and mitigate hyperfiltration. This tubule-centred model of diabetic kidney physiology predicts the salutary effect of SGLT2 inhibitors on hard renal outcomes, as shown in large-scale clinical trials.

Inhibitor of myogenic differentiation family isoform a, a new positive regulator of fibronectin production by glomerular mesangial cells

Overproduction of extracellular matrix proteins, including fibronectin by mesangial cells (MCs), contributes to diabetic nephropathy. Inhibitor of myogenic differentiation family isoform a (I-mfa) is a multifunctional cytosolic protein functioning as a transcriptional modulator or plasma channel protein regulator. However, its renal effects are unknown. The present study was conducted to determine whether I-mfa regulated fibronectin production by glomerular MCs. In human MCs, overexpression of I-mfa significantly increased fibronectin abundance. Silencing I-mfa significantly reduced the level of fibronectin mRNA and blunted transforming growth factor-β1-stimulated production of fibronectin. We further found that high glucose increased I-mfa protein content in a time course (≥48 h) and concentration (≥25 mM)-dependent manner. Although high glucose exposure increased I-mfa at the protein level, it did not significantly alter transcripts of I-mfa in MCs. Furthermore, the abundance of I-mfa protein was significantly increased in the renal cortex of rats with diabetic nephropathy. The I-mfa protein level was also elevated in the glomerulus of mice with diabetic kidney disease. However, there was no significant difference in glomerular I-mfa mRNA levels between mice with and without diabetic nephropathy. Moreover, H2O2 significantly increased I-mfa protein abundance in a dose-dependent manner in cultured human MCs. The antioxidants polyethylene glycol-catalase, ammonium pyrrolidithiocarbamate, and N-acetylcysteine significantly blocked the high glucose-induced increase of I-mfa protein. Taken together, our results suggest that I-mfa, increased by high glucose/diabetes through the production of reactive oxygen species, stimulates fibronectin production by MCs.

Glucose Dialysate Induces Mitochondrial DNA Damage in Peritoneal Mesothelial Cells

Background

It is known that peritoneal mesothelial cells (PMCs) are denuded in patients undergoing long-term continuous ambulatory peritoneal dialysis (CAPD); the mechanism of damage is not well known. A high quantity of glucose loaded onto PMCs in these patients may generate toxic radicals during the mitochondrial metabolism, leading to mitochondrial DNA damage that accumulates due to the incomplete repair system of this DNA.

Objective

To study damage to the PMCs of long-term CAPD patients, and to examine whether glucose overload accelerates this damage in vitro.

Design

Descriptive clinical and in vitro study.

Participants

Stable CAPD patients and nonuremic patients undergoing elective abdominal surgery.

Methods

( 1 ) Clinical Samples: 13 peritoneal tissue samples from CAPD patients and 5 omental tissue samples from patients with normal renal function were investigated. PMCs in dialysate effluent were collected from another 13 stable CAPD patients. ( 2 ) In Vitro Samples: Primary cultured PMCs were incubated for up to 144 hours in medium containing one of the following: 5.6 mmol/L glucose (control), 56 mmol/L glucose (G), 222 mmol/L glucose (high G), or 222 mmol/L mannitol (high M; osmolar control for high G). The tissues and cells of clinical and in vitro samples were stained for light and immunoelectron microscopy with anti–8-hydroxy-2'-deoxyguanosine (anti–8-OH-dG) antibody, a marker of oxidative DNA damage. In vitro cells were also studied using transmission electron microscopy. Cellular ATP content, mitochondrial membrane potential, and intracellular generation of reactive oxygen species (ROS) were analyzed by luciferase–luciferin system, or by flow cytometry using rhodamine 123 and 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA).

Results

Biopsy specimens showed strong cytoplasmic staining with 8-OH-dG in patients on long-term CAPD, but only faint staining in patients with end-stage renal disease before the initiation of CAPD, and no staining in patients with normal renal function. Dialysate effluent showed strong granular staining with 8-OH-dG in most PMCs in all long-term CAPD patients, but only faint and focal staining in patients at the start and after 3 – 5 months of CAPD. In vitro experiments also showed strong granular staining by 8-OH-dG in most PMCs cultured in high G, weak staining in G and high M, and no staining in the control. Immunoelectron microscopy revealed the localization of 8-OH-dG to mitochondria. Transmission electron microscopy showed swelling of mitochondria, with decreased cristae, in PMCs cultured in high G. However, only partial expansion of mitochondria was seen in G and high M, and no changes were seen in the control. Cellular ATP content and mitochondrial membrane potential were reduced early, followed by an increase when cultured in high G. Intracellular ROS production was also increased in PMCs cultured in high G and high M.

Conclusions

These data suggest that high-glucose peritoneal dialysate may promote oxidative mitochondrial DNA damage in PMCs in CAPD patients.

A light microscopic investigation of the renoprotective effects of α-lipoic acid and α-tocopherol in an experimental diabetic rat model

We investigated the effects of α-lipoic acid (AL) and α-tocopherol (AT) on renal histopathology in a streptozotocin (STZ) induced diabetic rat model. Adult male rats were divided into six groups: group 1, saline only; group 2, AL only; group 3, AT only; group 4, STZ only; group 5, STZ + AL; group 6 STZ + AT. Experimental diabetes was induced by STZ. AL and AT were administered for 15 days. Kidney sections were examined using a light microscope after hematoxylin and eosin (H & E), periodic acid-Schiff (PAS) and caspase-3 staining. Histological damage to glomeruli, tubule epithelial cells and basement membrane was observed in group 4. Administration of AT and AL reduced renal injury in the diabetic rats. Group 5 exhibited a greater curative effect on diabetic rats than group 6. AT and AL may be useful for preventing diabetic renal damage.

Late-onset renal hypertrophy and dysfunction in mice lacking CTRP1

Local and systemic factors that influence renal structure and function in aging are not well understood. The secretory protein C1q/TNF-related protein 1 (CTRP1) regulates systemic metabolism and cardiovascular function. We provide evidence here that CTRP1 also modulates renal physiology in an age- and sex-dependent manner. In mice lacking CTRP1, we observed significantly increased kidney weight and glomerular hypertrophy in aged male but not female or young mice. Although glomerular filtration rate, plasma renin and aldosterone levels, and renal response to water restriction did not differ between genotypes, CTRP1-deficient male mice had elevated blood pressure. Echocardiogram and pulse wave velocity measurements indicated normal heart function and vascular stiffness in CTRP1-deficient animals, and increased blood pressure was not due to greater salt retention. Paradoxically, CTRP1-deficient mice had elevated urinary sodium and potassium excretion, partially resulting from reduced expression of genes involved in renal sodium and potassium reabsorption. Despite renal hypertrophy, markers of inflammation, fibrosis, and oxidative stress were reduced in CTRP1-deficient mice. RNA sequencing revealed alterations and enrichments of genes in metabolic processes in CTRP1-deficient animals. These results highlight novel contributions of CTRP1 to aging-associated changes in renal physiology.

Amelioration of Hyperglycemia-Induced Nephropathy by 3,3'-Diindolylmethane in Diabetic Mice

Type 1 diabetes mellitus (insulin-dependent diabetes) is characterized by hyperglycemia caused by an insulin deficiency. Diabetic nephropathy is a major complication of hyperglycemia. 3,3′-diindolylmethane (DIM)-a natural compound produced from indole-3-carbinol, found in cruciferous vegetables-enhances glucose uptake by increasing the activation of the insulin signaling pathway in 3T3-L1 adipocytes. In this study, we investigated whether DIM could improve insulin-dependent diabetes and nephropathy in streptozotocin (STZ)-induced diabetic mice. In mice, STZ induced hyperglycemia, hunger, thirst, and abnormally increased kidney weight and serum creatinine, which is a renal functional parameter. DIM decreased STZ-increased high blood glucose levels and food and water intake in diabetic mice. DIM also improved diabetic nephropathy by inhibiting the expression of PKC-α, the marker of albuminuria, and TGF-β1, an indicator of renal hypertrophy, in diabetic mice. Our findings suggest that DIM may ameliorate hyperglycemia and diabetic nephropathy through the inhibition of PKC-α and TGF-β1 signaling.