Diabetic Kidney Disease Associated with Chronic Exposure to Low Doses of Environmental Cadmium

Endoplasmic reticulum (ER) stress mediates kidney tubular epithelial cell injury in diabetic nephropathy (DN), although the underlying regulatory mechanisms remain poorly characterized. To examine this, human tubule epithelial cells (HK-2 cells), rat kidney tubular epithelial cells (NRK-52E cells), kidney tissues of patients with biopsy-proven DN and healthy controls along with db/db mice (spontaneous diabetic kidney injury) and their db/m littermates were subject to a variety of imaging and analytical techniques. Mechanistically, downregulation of protein UHRF1 induced by high glucose disrupts its regulatory functions on both promoter methylation and protein ubiquitination of GRP78. This dysregulation causes GRP78 accumulation in the cytoplasm subsequently facilitating its nuclear translocation via interactions with the nucleocytoplasmic transport machinery. Notably, GRP78 nuclear translocation enhances a gene network associated with ER stress and apoptosis, intensifying kidney tubular epithelial cell injury. Compound screening identified the phenolic glycoside Parishin as a specific inhibitor of GRP78 nuclear translocation, effectively mitigating ER stress and demonstrates kidney-protective efficacy in db/db mice. Overall, our findings establish the dual epigenetic regulatory mechanisms of GRP78 and demonstrate its role as a transcriptional regulator of ER stress-related gene expression, which drives tubular cells injury in DN. This suggests that targeting the nuclear translocation of GRP78 may serve as a novel therapeutic approach for DN.

This study investigates the relationship between kidney function and exposure to low-level cadmium (Cd) and lead (Pb) in individuals with and without diabetes. Specifically, it tests the hypothesis that the nephrotoxicity of Cd and Pb reduces the tubular degradation of filtered proteins, namely β2-microglobulin (β2M). Data were obtained from a Thai cohort of 137 people, of which 65 were diagnosed with diabetes. Blood Cd, blood Pb, and urinary excretion of Cd (ECd) were used as exposure indicators, while urinary N-acetylglucosaminidase (ENAG) and fractional tubular degradation of β2M (FrTDβ2M) reflected kidney tubular cell injury and the function of tubular cells, respectively. Spearman's rank correlation revealed that FrTDβ2M varied directly with the estimated glomerular filtration rate (eGFR; r = 0.434), and inversely with fasting plasma glucose (r = -0.215), ECd (r = -0.527), ENAG (r = -0.536), and Cd/Pb exposure (r = -0.249). In a multiple regression model analysis adjusting for potential confounders, the association between FrTDβ2M and eGFR in those with diabetes was particularly strong (β = 0.476) compared to controls (β = 0.360), whereas an inverse association of FrTDβ2M and ECd (β = -0.295) was found only in those with diabetes, along with a positive association of ENAG with ECd (R2 = 0.071). A mediation analysis has revealed that tubular injury (ENAG) mediated 26% of the FrTDβ2M decrease associated with Cd/Pb exposure. These findings suggested that tubular protein degradation pathways may be compromised under combined metabolic and environmental stressors, Cd, and Pb.

The aim of the present study was to investigate the effects of the iron chelator deferiprone in diabetic nephropathy (DN) rats and the mechanisms involved. Thirty-two male Wistar rats (180-220 g, 6 weeks old) were randomly divided into a control group, a DN group and two DN groups treated with either 50 or 100 mg/kg per day deferiprone. The DN group was established by feeding of a high-carbohydrate-fat diet and injection of 35 mg/kg streptozotocin into the vena caudalis. The duration of deferiprone treatment was 20 weeks. Histopathological changes were detected by hematoxylin-eosin and Masson staining, as well as transmission electron microscopy. Levels of nuclear factor (NF)-κB, monocyte chemotactic protein (MCP)-1, matrix metalloproteinase (MMP)-9, tissue-specific inhibitor of metalloproteinase (TIMP)-1, cyclo-oxygenase (COX)-2, and nitrotyrosine were determined in kidney tissues using reverse transcription-polymerase chain reaction (RT-PCR), western blotting, and immunohistochemistry. Histopathological observations showed that deferiprone treatment alleviated inflammation infiltrates and collagenous fibrosis in DN rats. Results from RT-PCR and western blotting indicated that deferiprone inhibited the expression of NF-κB, MCP-1, COX-2, and nitrotyrosine, which were overexpressed in DN rats. Immunohistochemistry showed that the mechanism of deferiprone action may involve regulation of MMP-9 and TIMP-1. Decreased MMP-9 expression and increased TIMP-1 expression in DN rats were significantly promoted and inhibited by deferiprone, respectively. Iron chelation by oral deferiprone has a renoprotective effect in DN rats by relieving oxidative stress, inflammation, and fibrosis, which is related to the cytokines NF-κB, MCP-1, MMP-9, TIMP-1, COX-2, and nitrotyrosine.

Clinical Challenges in Diagnosis and Management of Diabetic Kidney Disease

To search for biomarkers of IgA nephropathy, protein profiles of urine samples from patients with IgA nephropathy and normal volunteers were compared using two-dimensional DIGE. Most of the 172 spots identified in the urine were serum proteins, and their amounts in IgA nephropathy urine were much higher than those in normal urine; this can be explained as proteinuria caused by glomerular dysfunction. However, only alpha(1)-microglobulin, also one of the major serum proteins, in IgA nephropathy urine was not higher in amount than that in normal urine. We confirmed using ELISA analysis that the amounts of transferrin and albumin in IgA nephropathy and diabetic nephropathy urine were much higher than those in normal urine, whereas the amount of alpha(1)-microglobulin in IgA nephropathy urine was not higher than that in normal urine and was much lower than that in diabetic nephropathy urine. Approximately 50% of alpha(1)-microglobulin forms a complex with IgA in serum. These results suggest that alpha(1)-microglobulin in IgA nephropathy urine is a characteristic protein and might be a biomarker for IgA nephropathy and that alpha(1)-microglobulin might have a relationship with IgA nephropathy pathology.

Pigment epithelium-derived factor (PEDF) inhibits proximal tubular cell injury in early diabetic nephropathy by suppressing advanced glycation end products (AGEs)-receptor (RAGE) axis

Dear Editor, Recently, we conducted a preclinical investigation to find the ameliorative properties of metformin on renal biochemical and histologic alterations of gentamicin-induced kidney damage in male Wistar rats (1). In this investigation, attenuation of gentamicin-induced acute kidney injury was found. Likewise, Taheri et al. conducted a study on the effects of metformin on renal tubular cells after unilateral ischemia reperfusion in rats’ kidney. They observed that metformin provided kidney protection against ischemia and reperfusion-induced injury (2). They concluded that metformin has tissue-protective effect through activation of adenosine monophosphate-activated protein kinase (AMPK) and endothelial nitric oxide synthase (2). More recently we conducted a study on 70 male Wistar rats to test the efficacy of coadministrating garlic extract and metformin in prevention of gentamicin-induced renal tubular damage in Wistar rats (3). The result of this study showed that metformin, garlic juice, or their combination had both curative and protective effects on gentamicin-induced kidney injury. In addition, Kim et al. conducted a study using metformin for diabetic rats for 17 weeks and found that treatment of diabetic rats with metformin had restored podocyte loss. They suggested that diabetes-induced podocyte loss in diabetic nephropathy could be suppressed by metformin through the repression of oxidative injury. They proposed that diabetes-induced podocyte loss in diabetic nephropathy could be reduced by metformin (4). Kim et al. found that the phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) was decreased in the kidney of diabetic rats and metformin could restore its modification (4). Diabetic nephropathy is one of the most important complications of diabetes mellitus (5-11) and metformin has been broadly used for the treatment of type 2 diabetes (12). Thus, the suggestion of Baradaran et al. further attests our results and those by Taheri et al., which stated metformin protects against tubular injury by restoring the biochemical alterations and modulation of oxidative stress on the tubules (2, 3). Furthermore, according to the study of Kim et al. metformin protects podocytes in diabetic nephropathy (4). On the other hand, there is also tubular cell injury in diabetic nephropathy due to glycosuria (12-18). These findings can more potentiate the clinical use of metformin in the prevention of diabetic nephropathy. Previously, Morales et al. showed that gentamicin-induced renal tubular damage was attenuated by metformin (17). It is evident that metformin treatment significantly attenuates the increase in malondialdehyde and total reactive oxygen species generation and restores both enzymatic and nonenzymatic antioxidants to their physiologic levels (18, 19). These findings advocate the use of metformin in diabetes due to its protective effect on kidney beyond its blood regulatory effects. In fact, it is reasonable to illuminate three different actions of metformin including blood sugar regulatory property, renal tubular cell protection by acting as an effective antioxidant, and finally, protective effect on diabetic nephropathy through saving the podocytes (4, 18, 19). Hence, patients with diabetes might benefit from all of these three distinct protective properties (4, 18, 19). In this regard, more experimental or clinical studies are recommended to improve our knowledge regarding the kidney protective properties of metformin.

Understanding, and Reversing, Metabolic Memory Is Within Reach

Mitochondrial abnormalities play critical roles in diabetic tubular injury progression. Dipeptidyl peptidase-4 (DPP4) inhibitors are widely used antihyperglycemicagents that exert renal protective and positive effects against mitochondrial dysfunction in diabetic kidney disease (DKD). However, their underlying mechanism remains unclear. In this study, DPP4 upregulation, mitochondrial fragmentation, and altered mitochondrial dynamics-associated protein expression were observed in the tubules ofDBA2/J (D2) diabetic mice with unilateral nephrectomy and in albumin-stimulated tubular cells. The inhibition of DPP4 by sitagliptin(Sita) ameliorated these mitochondrial perturbations bothin vivoandin vitro, whereas DPP4 overexpression aggravated mitochondrial fusion-fission disorder and tubular cell injury in albumin-treated HK-2 cells. Downstream of DPP4,the SDF-1α/CXCR4 pathway was significantly suppressed in diabetic tubules. After Sitatreatment, this signaling pathway was restored, and themitochondrial dynamics was improved. Furthermore, a direct interaction between STAT3 and OPA1 was found inthe mitochondria oftubular cells, and this effect was weakened by overloading albumin andby CXCR4 siRNA treatment, suggesting a possible link between DPP4-mediated SDF-1α/CXCR4/STAT3 signaling and mitochondrial dysfunction in diabetic tubular cells. The results suggest that a novel mechanism links the DPP4 enzyme to impaired mitochondrial dynamics homeostasis during tubular injury in DKD and highlight that the SDF-1α/CXCR4/STAT3 signaling pathway could become a potential target for managing DKD.

The risk of developing chronic kidney disease (CKD), signified by a decrease in the estimated glomerular filtration rate (eGFR), has been linked to long-term exposure to low levels of the metal pollutant cadmium (Cd). Proteinuria is a hallmark of CKD and predicts continued progressive functional decline of the kidney. The aim of this study was to use the extent of proteinuria for Cd health risk assessment. Data were from 405 apparently healthy Thai nationals, of whom 12.6% had an eGFR below 60 mL/min/1.73 m2 (low eGFR), and 16.3% and 13.5% had moderate and severe proteinuria. Urinary excretion of Cd (ECd) and urinary total protein (Epro) were measured and normalized to both creatinine clearance (Ccr) and creatinine excretion (Ecr). We found that the risk of having a low eGFR [prevalence odds ratio (POR) = 12.2, P < 0.001] and severe proteinuria [POR = 10.4, P = 0.001) were increased markedly for every ten-fold increase in ECd/Ccr. However, when ECd was normalized to Ecr, the association between eGFR and ECd was found to be insignificant due to non-differential errors introduced by the Ecr-normalization. Respective benchmark dose limit (BMDL) values of ECd/Ecr that increased protein excretion by 5% and 10% were 0.0536 and 0.1140 µg/g creatinine. The ECd/Ecr at which 5% of the population had Cd-related proteinuria was 1.86 µg/g creatinine, respectively. For the first time, a urinary Cd excretion rate of 0.0536 µg/g creatinine has been derived as a Cd exposure level that produces negligible kidney damage.

Markers of and Risk Factors for the Development and Progression of Diabetic Kidney Disease

The impact of parental overweight/obese on cumulative live birth rate in in vitro fertilization/intracytoplasmic sperm injection using a freeze-all strategy is still unknown. To explore the effect of parental body mass index (BMI) on cumulative live birth rate (CLBR) in a freeze-all strategy over 1.5 years. This was a retrospective study in a tertiary care academic medical center; 23 482 patients (35 289 frozen-thawed embryo transfer cycles) were divided into 4 groups according to Asian BMI classification. The main outcome measure was CLBR. Female overweight/obesity had a lower tendency in CLBR (groups 1-4: optimistic: 69.4%, 67.9%, 62.3%, and 65.7%; conservative: 62.9%, 61.1%, 55.4%, and 57.6%) and prolonged time (groups 1-4: 11.0, 12.2, 15.9, and 13.8 months for 60% CLBR in the optimistic method; 8.7, 9.5, 11.7, 11.0 months for 50% CLBR in the conservative method). The same trend to a lesser extent was also observed in male BMI groups. When combining parental BMI, "parental overweight/obesity" had lower CLBR and longer time for reaching CLBR >50% (optimistic: 4.5 months for 60% CLBR; conservative: 3 months for 50% CLBR), followed by "only female high BMI" (optimistic: 2.1 months for 60% CLBR; conservative: 1.7 months for 50% CLBR), while "only male high BMI" had no influence. Our results showed the importance of parental BMI, female BMI, and male BMI on the 1.5-year CLBR using a freeze-all strategy; the time to reach the CLBR (60% in optimistic, 50% in conservative) for overweight and obese patients was several months, but it is not as long as losing weight.

The influence of female and male body mass index on live births after assisted reproductive technology treatment: a nationwide register-based cohort study

Beneficial effects of metformin and irbesartan on advanced glycation end products (AGEs)–RAGE-induced proximal tubular cell injury

Irbesartan inhibits advanced glycation end product (AGE)-induced proximal tubular cell injury in vitro by suppressing receptor for AGEs (RAGE) expression