The Emerging Role of Vitamin D and Vitamin D Receptor in Diabetic Nephropathy

Integrated analysis of blood DNA methylation, genetic variants, circulating proteins, microRNAs, and kidney failure in type 1 diabetes

Variation in DNA methylation (DNAmet) in white blood cells and other cells/tissues has been implicated in the etiology of progressive diabetic kidney disease (DKD). However, the specific mechanisms linking DNAmet variation in blood cells with risk of kidney failure (KF) and utility of measuring blood cell DNAmet in personalized medicine are not clear. We measured blood cell DNAmet in 277 individuals with type 1 diabetes and DKD using Illumina EPIC arrays; 51% of the cohort developed KF during 7 to 20 years of follow-up. Our epigenome-wide analysis identified DNAmet at 17 CpGs (5'-cytosine-phosphate-guanine-3' loci) associated with risk of KF independent of major clinical risk factors. DNAmet at these KF-associated CpGs remained stable over a median period of 4.7 years. Furthermore, DNAmet variations at seven KF-associated CpGs were strongly associated with multiple genetic variants at seven genomic regions, suggesting a strong genetic influence on DNAmet. The effects of DNAmet variations at the KF-associated CpGs on risk of KF were partially mediated by multiple KF-associated circulating proteins and KF-associated circulating miRNAs. A prediction model for risk of KF was developed by adding blood cell DNAmet at eight selected KF-associated CpGs to the clinical model. This updated model significantly improved prediction performance (c-statistic = 0.93) versus the clinical model (c-statistic = 0.85) at P = 6.62 × 10-14. In conclusion, our multiomics study provides insights into mechanisms through which variation of DNAmet may affect KF development and shows that blood cell DNAmet at certain CpGs can improve risk prediction for KF in T1D.

MYCT1 attenuates renal fibrosis and tubular injury in diabetic kidney disease

Tubulointerstitial abnormalities contribute to the progression of diabetic kidney disease (DKD). However, the underlying mechanism of the pathobiology of tubulointerstitial disease is largely unknown. Here, we showed that MYCT1 expression was downregulated in in vitro and in vivo DKD models. Adeno-associated virus (AAV)-Myct1 significantly attenuated renal dysfunction and tubulointerstitial fibrosis in diabetic db/db mice and downregulated Sp1 transcription and TGF-β1/SMAD3 pathway activation. In human proximal tubular epithelial cells, high glucose-induced high expression of SP1 and TGF-β1/SMAD3 pathway activation as well as overaccumulation of extracellular matrix (ECM) were abrogated by MYCT1 overexpression. Mechanistically, the binding of VDR to the MYCT1 promoter was predicted and confirmed using dual-luciferase reporter and ChIP analysis. VDR transcriptionally upregulates MYCT1. Our data reveal MYCT1 as a new and potential therapeutic target in treating DKD.

Effects of Vitamin D Supplementation in Diabetic Kidney Disease: An Systematic Review

Diabetes Mellitus is a highly prevalent condition in which Diabetes Mellitus type 2 is the most common. Diabetic Kidney Disease is one of the most relevant complications and affects approximately one-third of patients with Diabetes Mellitus. It is characterized by increased urinary protein excretion and a decrease in glomerular filtration rate, assessed by serum creatinine levels. Recent studies have shown that vitamin D levels are low in these patients. This study aimed to conduct a systematic review of the effects of vitamin D supplementation on proteinuria and creatinine, which are important markers for assessing the severity of kidney disease in patients with Diabetic Kidney Disease. PUBMED, EMBASE, and COCHRANE databases were consulted, Preferred Reporting Items for a Systematic Review and Meta-Analysis guidelines were followed, and the COCHRANE toll for bias assessment was applied. Six papers were quantitative studies and fulfilled the inclusion criteria for this review. The results showed that vitamin D supplementation of 50,000 I.U./week for 8 weeks effectively reduced proteinuria and creatinine in patients with Diabetic Kidney Disease, particularly in patients with Diabetes Mellitus type 2. Vitamin D supplementation is beneficial for patients with Diabetic Kidney Disease by having essential effects on disease-related inflammatory markers, such as the reduction of proteinuria and creatinine. However, more clinical trials must be conducted to evaluate the intervention among more significant numbers of patients.

The influence of calcitriol and methylprednisolone on podocytes function in minimal change disease in vitro model

Minimal change disease (MCD), considered one of the major causes of nephrotic syndrome, is a complex pathological condition with disturbances in podocytes' foot processes. Numerous studies suggested the essential role of vitamin D3 in maintaining proper glomerulus function. However, the data on direct potential of that compound in reference to podocytes are scarce. Thus, here we assessed the influence of calcitriol (active vitamin D3) on podocyte function, apart from commonly used steroids (methylprednisolone). CIHP-1 podocyte cell line was used to implement the LPS-PAN-induced MCD in vitro model. Viability, podocyte-related slit diaphragm proteins, morphology, function as a barrier was evaluated using flow cytometry, RT-PCR, confocal microscopy, and TEER analysis. Calcitriol or methylprednisolone did not affect cell viability. Podocyte-related proteins demonstrated different responses to in vitro treatment compared to previously reported changes in total glomeruli. Podocyte morphology was partially restored in the presence of the tested compounds. In addition, TEER analysis revealed improvement of LPS-PAN-induced cells' function as a barrier when vitamin D3 or steroid was used. In conclusion, a significant potential for modulation of MCD in vitro model podocytes with calcitriol or selected steroids was reported. Further studies on vitamin D3 in context of podocyte-related phenomenon accompanying MCD are of great importance.

A Mendelian randomization study on causal effects of 25(OH) vitamin D levels on diabetic nephropathy

BACKGROUND

Vitamin D supplementation is associated with a lower incidence of diabetic nephropathy (DN); however, whether this association is causative is uncertain.

METHODS

We used two-sample Mendelian randomization to examine the causal influence of vitamin D on diabetic nephropathy in 7,751 individuals with type I diabetes-related nephropathy (T1DN) and 9,933 individuals with type II diabetes-related nephropathy (T2DN). Meanwhile, we repeated some previous studies on the influence of KIM-1 (kidney injury molecule 1) and body mass index (BMI) on DN. Additionally, to test the validity of the instruments variable for vitamin D, we conducted two negative controls Mendelian randomization (MR) on breast and prostate cancer, and a positive control MR on multiple sclerosis.

RESULTS

Results of the MR analysis showed that there was no causal association between 25(OH)D with the early/later stage of T1DN (early: OR = 0.903, 95%CI: 0.229 to 3.555; later: OR = 1.213, 95%CI: 0.367 to 4.010) and T2DN (early: OR = 0.588, 95%CI: 0.182 to 1.904; later: OR = 0.904, 95%CI: 0.376 to 2.173), nor with the kidney function of patients with diabetes mellitus: eGFRcyea (creatinine-based estimated GFR) (Beta = 0.007, 95%CI: -0.355 to 0.369)) or UACR (urinary albumin creatinine ratio) (Beta = 0.186, 95%CI: -0.961 to 1.333)).

CONCLUSIONS

We found no evidence that Vitamin D was causally associated with DN or kidney function in diabetic patients.

Serum homocysteine concentration as a marker for advanced diabetic nephropathy in a cohort of elderly patients

BACKGROUND

Hyperhomocysteinemia has been linked with chronic kidney disease (CKD). The present study investigated whether homocysteine (Hcy) serum levels might serve as a marker for the advancement of diabetic nephropathy (DN).

METHODS

Clinical and laboratory indicators including Hcy, vitamin D (VD), urine protein, estimated glomerular filtration rate (eGFR) and the urinary protein/creatinine ratio in subjects > 65 years with DN (n = 1,845), prediabetes (n = 1,180) and in a non-diabetes (control) group (n = 28,720) were analyzed.

RESULTS

DN patients had elevated Hcy concentrations, decreased VD and higher urinary protein levels, a reduced eGFR and a higher urinary protein/creatinine ratio compared with prediabetic and control subjects. After correcting for urinary protein quantitation, multivariate analysis revealed that both the Hcy concentration (P < 0.010) and urinary protein/creatinine ratio (P < 0.001) were risk factors, while the VD2 + VD3 serum concentration (P < 0.001) was a protective factor for DN. Moreover, Hcy > 12 µmol/L was a cut-off value for predicting advanced DN.

CONCLUSION

Hcy serum concentration is a potential marker for the advancement of CKD in DN but not prediabetes patients.

Vitamin D Ameliorates Podocyte Injury by Enhancing Autophagy Activity in Diabetic Kidney Disease

INTRODUCTION

Restoration of podocyte autophagy is considered as a feasible strategy for the treatment of diabetic kidney disease (DKD). This study aimed at investigating the protective effect and potential mechanism of vitamin D on podocyte injury of DKD.

METHODS

Type 2 diabetic db/db mice received intraperitoneal injections of vitamin D analog paricalcitol 400 ng/kg per day for 16 weeks. Immortalized mouse podocytes were cultured in high glucose (HG) medium with active vitamin D3 calcitriol or autophagy inhibitor 3-methyladenine. Renal function and urine albumin creatinine ratio were assessed at week 24. HE, PAS staining, and electron microscopy were used to evaluate renal histopathology and morphological changes. Immunohistochemistry, immunofluorescence, and Western blot were used to evaluate protein expression of nephrin and podocin in kidney tissue and podocytes. The expression of autophagy-related proteins (LC3, Beclin-1, Vps34) and apoptosis-related proteins (cleaved caspase-3, Bax) was determined by Western blotting. Podocyte apoptosis was further evaluated by using flow cytometer.

RESULTS

Albuminuria in a db/db mouse model was markedly attenuated after treatment with paricalcitol. This was accompanied by alleviation of mesangial matrix expansion and podocyte injury. Besides, the impaired autophagy in podocytes under diabetic conditions was also markedly enhanced after paricalcitol or calcitriol treatment, accompanied by restored decreased podocyte slit diaphragm proteins podocin and nephrin. Furthermore, the protective effect of calcitriol against HG-induced podocyte apoptosis could be abated by autophagy inhibitor 3-methyladenine.

CONCLUSION

Vitamin D ameliorates podocyte injury of DKD by enhancing podocyte autophagy activity, which may become a potential candidate autophagy activator for the therapeutic interventions for DKD.

Level of 25-hydroxyvitamin D and vitamin D receptor in diabetic foot ulcer and factor associated with diabetic foot ulcers

BACKGROUND

At present, there is no clinical study to elucidate the correlation between vitamin D deficiency and the incidence of diabetic foot osteomyelitis (DFO).This study aims to clarify levels of 25-hydroxyvitamin D [25(OH)VD] in peripheral blood and vitamin D receptor (VDR) expression in wound margin tissues (T-VDR) of patients with type 2 diabetes mellitus (T2DM) with diabetic foot ulcer (DFU) and DFO, and to determine its correlation with treatment outcomes of DFU and DFO, and and its value as a potential biomarker for the diagnosis of DFU and DFO.

METHODS

156 T2DM patients with DFU (DFU group), 100 T2DM patients without DFU (T2DM group), and 100 healthy controls (NC group). The DFU group patients were subdivided into DFO (n = 80) and NDFO groups (n = 76). The level of serum 25(OH)VD was measured via chemiluminescence immunoassay, and T-VDR expression level was determined by quantitative real-time PCR.

RESULTS

The levels of serum 25(OH)VD in the DFU group were significantly lower than the T2DM group [(10.3 (5.8, 18.7) vs 15.7 (8.6, 24.6) ng/mL, P = 0.002)]. Similarly, the levels of serum 25(OH)VD and T-VDR expression in the DFO group were statistically lower than the NDFO group [9.2 (5.2, 20.5) vs 12.8 (6.9, 22.1) ng/mL, P = 0.006)], [1.96 (0.61, 3.97) vs 3.11 (1.36, 5.11), P = 0.004)], respectively. Furthermore, the levels of serum 25(OH)VD and T-VDR expression in DFU patients were positively correlated with the ulcer healing rate of foot ulcer after 8 weeks of treatment ( P = 0.031, P = 0.016, respectively). Multivariate logistic regression analysis showed that low level of serum 25(OH)VD was an independent risk factor for DFU and DFO (OR_DFU = 2.42, OR_DFO = 3.05, P = 0.008, 0.001, respectively), and decreased T-VDR expression level was an independent risk factor for DFO (OR = 2.83, P = 0.004). Meanwhile, the ROC curve analysis indicated that the AUC of serum 25(OH)VD level for the diagnosis of DFU and DFO was 0.821 (95% CI, 0.754-0.886, P < 0.001) and 0.786 (95%CI, 0.643-0.867, P < 0.001), respectively. When establishing a diagnosis of DFO, the AUC of T-VDR expression level was 0.703 (95%CI: 0.618-0.853, P < 0.001).

CONCLUSIONS

The levels of serum 25(OH)VD and T-VDR expression in DFU and DFO decreased. Serum 25(OH)VD and T-VDR are potentially valuable biomarkers for diagnosis and prognosis of DFU and DFO. .

Vitamin D and Diabetic Kidney Disease

Vitamin D is a hormone involved in many physiological processes. Its active form, 1,25(OH)₂D₃, modulates serum calcium-phosphate homeostasis and skeletal homeostasis. A growing body of evidence has demonstrated the renoprotective effects of vitamin D. Vitamin D modulates endothelial function, is associated with podocyte preservation, regulates the renin-angiotensin-aldosterone system, and has anti-inflammatory effects. Diabetic kidney disease (DKD) is a leading cause of end-stage kidney disease worldwide. There are numerous studies supporting vitamin D as a renoprotector, potentially delaying the onset of DKD. This review summarizes the findings of current research on vitamin D and its role in DKD.

Vitamin D Status, Vitamin D Receptor Polymorphisms, and Risk of Microvascular Complications Among Individuals With Type 2 Diabetes: A Prospective Study

OBJECTIVE

Evidence is limited regarding the associations between vitamin D status and microvascular complications in individuals with type 2 diabetes (T2D), among whom vitamin D deficiency or insufficiency is particularly common. In this study we aimed to prospectively investigate the associations of serum 25-hydroxyvitamin D [25(OH)D] and vitamin D receptor (VDR) polymorphisms with risk of diabetic microvascular complications.

RESEARCH DESIGN AND METHODS

This analysis included 14,709 participants with T2D who were free of microvascular complications from the UK Biobank. Incidence of diabetic microvascular complications was ascertained via electronic health records. Cox proportional hazards regression models were used to estimate hazard ratios (HRs) and 95% CIs.

RESULTS

Median serum 25(OH)D concentration was 40.7 nmol/L (interquartile range 27.5, 56.4). During a median of 11.2 years of follow-up, 1,370 people developed diabetic microvascular complications. Compared with participants with 25(OH)D <25 nmol/L, individuals with 25(OH)D ≥75 nmol/L had a multivariable-adjusted HR of 0.65 (95% CI 0.51, 0.84) for composite diabetic microvascular complications, 0.62 (0.40, 0.95) for diabetic retinopathy, 0.56 (0.40, 0.79) for diabetic nephropathy, and 0.48 (0.26, 0.89) for diabetic neuropathy. In addition, in comparisons with participants with 25(OH)D <25 nmol/L and minor allele homozygotes (TT of rs1544410 and GG of rs731236), the multivariable-adjusted HRs of composite diabetic microvascular complications were 0.54 (0.38, 0.78) and 0.55 (0.38, 0.80) for participants with serum 25(OH)D ≥50 nmol/L and major allele homozygotes (CC and AA), respectively, although no significant interaction was observed.

CONCLUSIONS

Higher serum 25(OH)D concentrations were significantly associated with lower risk of diabetic microvascular complications, including diabetic retinopathy, diabetic nephropathy, and diabetic neuropathy. Our findings suggest a potential beneficial role of maintaining adequate vitamin D status in the prevention of diabetic microvascular complications.

Antioxidant-Enriched Diet on Oxidative Stress and Inflammation Gene Expression: A Randomized Controlled Trial

The Mediterranean Diet (MedDiet) is associated with beneficial effects against chronic non-communicable diseases (CNCDs). In particular, the content of micronutrients leads to an improvement of the oxidative and inflammatory profiles. A randomized, parallel, controlled study, on 24 subjects, was conducted to evaluate if 2-week supplementation with a mixed apple and bergamot juice (MAB juice), had a positive impact on the body composition, the biochemical profile, and oxidative and inflammatory gene expression (Superoxide dismutase (SOD1), Peroxisome Proliferator-Activated Receptor γ (PPARγ), catalase (CAT), chemokine C-C motif ligand 5 (CCL5), Nuclear Factor Kappa B Subunit 1 (NFKB1), Vitamin D Receptor (VDR), and Macrophage Migration Inhibitory Factor (MIF)), respect to a MedDiet. Body composition evaluation analysis showed a gain in lean mass (p < 0.01). Moreover, a significant reduction in total cholesterol/HDL index (p < 0.01) was pointed out between the two groups. Gene expression analysis highlighted an increase in MIF (p ≤ 0.05), PPARγ (p < 0.001), SOD1 (p ≤ 0.05), and VDR (p ≤ 0.05) expressions when comparing MedDiet and MedDiet + MAB juice groups. These data based on the nutrigenomics approach demonstrated that supplementing 2 weeks of MAB juice to the MedDiet could contribute to a reduction in the risk of CNCDs.

Development and validation of short-term renal prognosis prediction model in diabetic patients with acute kidney injury

OBJECTIVE

Diabetes is a major cause of the progression of acute kidney injury (AKI). Few prediction models have been developed to predict the renal prognosis in diabetic patients with AKI so far. The aim of this study was to develop and validate a predictive model to identify high-risk individuals with non-recovery of renal function at 90 days in diabetic patients with AKI.

METHODS

Demographic data and related laboratory indicators of diabetic patients with AKI in the First Affiliated Hospital of Guangxi Medical University from January 31, 2012 to January 31, 2022 were retrospectively analysed, and patients were followed up to 90 days after AKI diagnosis. Based on the results of Logistic regression, a model predicting the risk of non-recovery of renal function at 90 days in diabetic patients with AKI was developed and internal validated. Consistency index (C-index), calibration curve, and decision curve analysis were used to evaluate the differentiation, accuracy, and clinical utility of the prediction model, respectively.

RESULTS

A total of 916 diabetic patients with AKI were enrolled, with a male to female ratio of 2.14:1. The rate of non-recovery of renal function at 90 days was 66.8% (612/916). There were 641 in development cohort and 275 in validation cohort (ration of 7:3). In the development cohort, a prediction model was developed based on the results of Logistic regression analysis. The variables included in the model were: diabetes duration (OR = 1.022, 95% CI  1.012-1.032), hypertension (OR = 1.574, 95% CI 1.043-2.377), chronic kidney disease (OR = 2.241, 95% CI 1.399-3.591), platelet (OR = 0.997, 95% CI 0.995-1.000), 25-hydroxyvitamin D3 (OR = 0.966, 95% CI  0.956-0.976), postprandial blood glucose (OR = 1.104, 95% CI 1.032-1.181), discharged serum creatinine (OR = 1.003, 95% CI 1.001-1.005). The C-indices of the prediction model were 0.807 (95% CI 0.738-0.875) and 0.803 (95% CI 0.713-0.893) in the development and validation cohorts, respectively. The calibration curves were all close to the straight line with slope 1. The decision curve analysis showed that in a wide range of threshold probabilities.

CONCLUSION

A prediction model was developed to help predict short-term renal prognosis of diabetic patients with AKI, which has been verified to have good differentiation, calibration degree and clinical practicability.

The Perspective of Vitamin D on suPAR-Related AKI in COVID-19

The coronavirus disease 2019 (COVID-19) pandemic has claimed the lives of millions of people around the world. Severe vitamin D deficiency can increase the risk of death in people with COVID-19. There is growing evidence that acute kidney injury (AKI) is common in COVID-19 patients and is associated with poorer clinical outcomes. The kidney effects of SARS-CoV-2 are directly mediated by angiotensin 2-converting enzyme (ACE2) receptors. AKI is also caused by indirect causes such as the hypercoagulable state and microvascular thrombosis. The increased release of soluble urokinase-type plasminogen activator receptor (suPAR) from immature myeloid cells reduces plasminogen activation by the competitive inhibition of urokinase-type plasminogen activator, which results in low plasmin levels and a fibrinolytic state in COVID-19. Frequent hypercoagulability in critically ill patients with COVID-19 may exacerbate the severity of thrombosis. Versican expression in proximal tubular cells leads to the proliferation of interstitial fibroblasts through the C3a and suPAR pathways. Vitamin D attenuates the local expression of podocyte uPAR and decreases elevated circulating suPAR levels caused by systemic inflammation. This decrease preserves the function and structure of the glomerular barrier, thereby maintaining renal function. The attenuated hyperinflammatory state reduces complement activation, resulting in lower serum C3a levels. Vitamin D can also protect against COVID-19 by modulating innate and adaptive immunity, increasing ACE2 expression, and inhibiting the renin–angiotensin–aldosterone system. We hypothesized that by reducing suPAR levels, appropriate vitamin D supplementation could prevent the progression and reduce the severity of AKI in COVID-19 patients, although the data available require further elucidation.

Correlation of DHEA with diabetic nephropathy and its clinical value in early detection

Aims/Introduction

This study was carried out to assess the association of dehydroepiandrosterone (DHEA) with diabetic nephropathy (DN) in patients with type 2 diabetes mellitus to better predict the progression of diabetic nephropathy.

Materials and Methods

A total of 1,082 patients with type 2 diabetes mellitus in the Department of Endocrinology and Metabolism of Tianjin Medical University General Hospital were enrolled in this study, and grouped for comparison. The effect of serum DHEA on DN was evaluated by multivariate logistic regression analysis, and receiver operating characteristic curves were established to explore the optimal concentration of DHEA in patients with DN and non‐DN.

Results

DHEA was significantly decreased in patients with DN (P < 0.001). The prevalence of DN was significantly higher in the low DHEA quartile than in the other quartiles (P < 0.001). Spearman‐related analysis showed that DHEA levels were negatively correlated with patient age, course of diabetes, systolic blood pressure, blood creatinine, uric acid, urine albumin‐to‐creatinine ratio, 24‐h urine microalbumin, 24‐h urine protein quantification and glomerular filtration rate, and positively correlated with body mass index, total cholesterol and low density lipoprotein. Logistic regression analysis showed that the effect of DHEA on DN was statistically significant (P < 0.001). The receiver operating characteristic curve showed that the sensitivity was 81.4%, the specificity was 70% and the area under the curve was 0.812 when the optimal cut‐off value was 1,640 (pg/mL).

Conclusion

DHEA is significantly associated with DN and might be a protective factor for DN, and is important for the prediction of DN.

Nuclear receptors in renal health and disease

As a major social and economic burden for the healthcare system, kidney diseases contribute to the constant increase of worldwide deaths. A deeper understanding of the underlying mechanisms governing the etiology, development and progression of kidney diseases may help to identify potential therapeutic targets. As a superfamily of ligand-dependent transcription factors, nuclear receptors (NRs) are critical for the maintenance of normal renal function and their dysfunction is associated with a variety of kidney diseases. Increasing evidence suggests that ligands for NRs protect patients from renal ischemia/reperfusion (I/R) injury, drug-induced acute kidney injury (AKI), diabetic nephropathy (DN), renal fibrosis and kidney cancers. In the past decade, some breakthroughs have been made for the translation of NR ligands into clinical use. This review summarizes the current understanding of several important NRs in renal physiology and pathophysiology and discusses recent findings and applications of NR ligands in the management of kidney diseases.

The Role of Vitamin D in Diabetic Nephropathy: A Translational Approach

According to several animal and human studies, vitamin D appears to play a significant role in the development of diabetic nephropathy. However, the possible renoprotective effect of vitamin D and its influence on the reversal of already existing renal damage remains doubtful. At this moment, there are a few hypotheses concerning the underlying molecular and genetic mechanisms including the link between vitamin D and inflammation, oxidative stress, and extracellular matrix accumulation. The present review aims to investigate the potential role of vitamin D in the development of diabetic kidney disease from a translational approach.

Association of Serum 25 (OH) Vitamin D With Chronic Kidney Disease Progression in Type 2 Diabetes

OBJECTIVES

Growing evidence demonstrated that vitamin D levels had been linked to type 2 diabetes mellitus (T2DM) and chronic kidney disease (CKD) in light of various extraskeletal effects. Therefore, the present study aimed to evaluate the association of 25-hydroxyvitamin D [25(OH)D] level with the clinicopathological features and CKD progression in T2DM.

METHODS

A total of 182 patients with T2DM with CKD stages 1 through 4 (G1-G4) were retrospectively included. Identification of the serum 25(OH)D level associated with CKD progression was executed by Kaplan-Meier survival analysis and Cox proportional hazards models. We further performed sensitivity analyses with a time-weighted average (TWA) of the serum 25(OH)D level in 75 participants to reinforce the findings.

RESULTS

The median serum 25(OH)D level was 26 (IQR, 14; 39) nmol/L in the study participants. Median follow-up time was 42 months, during which 70 (38%) patients confronted CKD progression. Cumulative kidney outcomes were significantly higher in the lowest tertile of the serum 25(OH)D level in Kaplan-Meier analyses (P < 0.001). Consistently, the analyses of Cox proportional hazards regression models indicated a significantly greater risk for CKD progression in the lowest tertile of the serum 25(OH)D level compared with the highest tertile of the serum 25(OH)D level (P = 0.03). These relationships remained robust with further sensitivity analysis of data with TWA of the serum 25(OH)D level, showing an independent association between lower TWA of the serum 25(OH)D level and an unfavorable renal outcome in patients with T2DM with CKD.

CONCLUSIONS

Our findings demonstrated that patients with T2DM with a decreased 25(OH)D level had deteriorated renal function. Both lower levels of baseline and TWA of serum 25(OH)D were associated with an increased risk of CKD progression in patients with T2DM, which suggested that the long-term maintenance of optimal vitamin D levels from early in life might be associated with reduced future risk of CKD development in T2DM.

Correlation Between Serum 25-Hydroxyvitamin D Levels in Albuminuria Progression of Diabetic Kidney Disease and Underlying Mechanisms By Bioinformatics Analysis

AIM

This study aimed to assess the correlation between serum concentration of 25-hydroxyvitamin D and albuminuria progression of diabetic kidney disease (DKD) and to use bioinformatics methods to determine the potential mechanism in the pathological process of advanced DKD.

METHODS

A total of 178 type 1 diabetes mellitus (T1DM) patients with microalbuminuria complications who were hospitalized at least twice (with an interval > 24 months) in the Department of Endocrinology of The First Affiliated Hospital of USTC were included in this study. According to the urinary albumin creatinine ratio (UACR), we classified DKD stages as follows: microalbuminuria (UACR, 30-300 mg/g), and macroalbuminuria (UACR, >300 mg/g). We divided the patients into DKD progression (N=44) and stable group (N=134) on account of urinary albumin-to-creatinine ratio (UACR) by at least two randomized measurements. Stable group was defined as UACR between 30 and 300 mg/g, whereas progression group was defined as UACR >300 mg/g at the end of follow-up. Data were obtained from participants' medical records, and the 25-hydroxyvitamin D level was categorized into three groups as follows: G1 (N=45), <10 ng/mL; G2 (N=80), 10-20 ng/ml; and G3 (N=53), ≥20 ng/mL. The Nephroseq database (http://v5.nephroseq.org) was used to identify VDR expression in diabetic nephropathy. The dataset GSE142025 from GEO (http://www.ncbi.nlm.nih.gov/geo) was downloaded. After stratification by the median-centered log2 VDR expression value, the 21 advanced DKD samples were divided into two groups (low VDR expression group and high VDR expression group). Gene set enrichment analysis (GSEA) (http://software.broadinstitute.org/gsea/index.jsp). Differentially expressed genes (DEGs) were screened by the limma package (adjusted p < 0.05, |logFC| > 1). The Gene Ontology (GO; http://www.geneontology.org/) database and pathway analysis within the Kyoto Encyclopedia of Genes and Genomes (KEGG; https://www.kegg.jp/) were performed using the R package ClusterProfile. The CIBERSORT (Cell type Identification By Estimating Relative Subsets Of known RNA Transcripts) algorithm was utilized for calculating the infiltrated immune cells in advanced kidney tissues.

RESULTS

1) A multivariate Cox regression analysis revealed that DR (diabetic retinopathy), eGFR (estimated glomerular filtration rate), and 25-hydroxyvitamin D were significant independent predictors of DKD progression (HR: 2.57, 95% CI: 1.44.4.24, p=0.007; HR: 2.13, 95% CI: 1.58.3.79, p = 0.011; HR: 0.732, 95% CI: 0.232-0.816, p = 0.023, respectively). 2) Kaplan-Meier survival curves of DKD progression by serum 25-hydroxyvitamin D stratification showed that the G2 and G3 groups were significantly different when compared with the G1 group (log-rank χ2 = 14.69, p <0.001; χ2 = 28.26, p <0.001, respectively). 3) There was a weak negative correlation between 25-hydroxyvitamin D level and UACR at baseline,and the overall mean rate of change in eGFR was 1.121 ± 0.19 ml/min/1.73 m2/year. Neither crude nor adjusted rate of decline in eGFR was significantly different among patients classified according to baseline serum 25-hydroxyvitamin D levels (all p<0.05). 4) The high expression of VDR group was most positively correlated with enriched gene sets like reactome innate immune system and reactome G alpha I signaling events when compared with the low expression of VDR group. 5) The CIBERSORT algorithm showed decreased M2 macrophage infiltration in advanced kidneys in comparison to low VDR expression and high VDR expression.

CONCLUSION

This study concluded that low 25-hydroxyvitamin D levels can predict an increased risk of DKD albuminuria progression and eGFR decline. Decreased M2 macrophage infiltration may be a potential mechanism involved in this pathogenesis.

Metformin Ameliorates Epithelial-Mesenchymal Transition of Renal Tubular Epithelial Cells in Diabetes by Increasing Vitamin D Receptor Expression

BACKGROUND

Metformin is used as a first-line drug for the treatment of type 2 diabetes. Epithelial-mesenchymal transition (EMT) plays a significant role in the development of renal tubular damage in diabetic kidney disease. However, the underlying mechanisms of EMT in diabetic kidney disease are unclear and how to inhibit this process remains to be explored.

METHODS

C57 mice were randomly divided into four groups, including the normal control group (NC group), the Type 2 diabetes group (T2DM group), the metformin group (MET group), and glibenclamide group (GLIB). Fasting blood glucose (FBG), glycated hemoglobin (HbA1c), urinary albumin, RBP, PCX, and creatinine were measured. Renal pathology was observed with HE staining. Molecular mechanism of VDR expression are regulated by metformin through wound healing assay, and Western blot analysis of VDR, Ecad, and SMA in HK2 cells.

RESULTS

In animal experiments, compared with the NC group, the T2DM group showed decreased body weight, increased levels of FBG, HbA1c, UAlb/UCR, URBP/UCR, and UPCX/UCR, decreased levels of VDR protein and mRNA expression in renal tissues (P < 0.05), and significantly increased renal pathological damage in mice in the T2DM group. Compared with the T2DM group, mice in the GLIB and MET groups had higher body weight and lower FBG, HbA1c, UAlb/UCR, URBP/UCR, and UPCX/UCR (P < 0.05). In addition, renal pathological damage was significantly reduced in the MET group compared to the GLIB group. In HK2 cells, high glucose promoted the reduction of VDR and the development of EMT compared to the NC group. In addition, we found that Metformin can up-regulate VDR and inhibit EMT.

CONCLUSION

Our study shows that the renoprotective effect of metformin is independent of glycemic control and metformin is involved in the progression of EMT by regulating VDR expression.

Vitamin D Supplementation Could Enhance the Effectiveness of Glibenclamide in Treating Diabetes and Preventing Diabetic Nephropathy: A Biochemical, Histological and Immunohistochemical Study

Diabetes mellitus is an oxidative stress-related disease characterized by hyperglycemia and a variety of complications, including nephropathy. Vitamin D has variable functions extending beyond the calcium metabolism to prevent oxidative tissue damage. We aimed to investigate whether vitamin D supplements could enhance Glibenclamide's effectiveness in treating diabetes and minimize the risk of associated pathology. Wistar rats were divided into normal control (n = 10) and diabetic (n = 30), where animals received two low doses of Streptozotocin 30 mg/kg/BW intraperitoneally to develop diabetes. The diabetic rats were then randomly divided into three equal groups: untreated, treated with Glibenclamide (0.6 mg/kg), and treated with Glibenclamide and Vitamin D3 (500 IU/kg). After eight weeks, the animals were sacrificed, and blood samples and kidney tissues were collected to evaluate biochemical, anti-oxidant, and pro-inflammatory cytokine levels and histological and immunohistochemical changes. Diabetic animals had significantly increased fasting blood glucose, lipid profile, blood urea, serum creatinine, and Malondialdehyde levels, whereas serum insulin, albumin, and the anti-oxidant enzymes superoxide dismutase and catalase were significantly decreased compared to normal control (p < 0.01). Furthermore, some renal histological changes were observed together with significantly increased immunoreactivity of anti-p53, anti-TNF-α, and anti-IL-6 antibodies when compared to the normal control. All abnormal parameters improved significantly with Glibenclamide therapy (p < 0.01), but combination therapy with vitamin D produced a much better result. In conclusion, vitamin D supplementation along with anti-diabetic medication can help prevent or reduce the severity of diabetic nephropathy due to its potent antioxidant, anti-inflammatory, and anti-apoptotic properties.

Bioinformatics analysis of genes related to iron death in diabetic nephropathy through network and pathway levels based approaches

Diabetic nephropathy is one of the common microvascular complications of diabetes. Iron death is a recently reported way of cell death. To explore the effects of iron death on diabetic nephropathy, iron death score of diabetic nephropathy was analyzed based on the network and pathway levels. Furthermore, markers related to iron death were screened. Using RNA-seq data of diabetic nephropathy, samples were clustered uniformly and the disease was classified. Differentially expressed gene analysis was conducted on the typed disease samples, and the WGCNA algorithm was used to obtain key modules. String database was used to perform protein interaction analysis on key module genes for the selection of Hub genes. Moreover, principal component analysis method was applied to get transcription factors and non-coding genes, which interact with the Hub gene. All samples can be divided into two categories and principal component analysis shows that the two categories are significantly different. Hub genes (FPR3, C3AR1, CD14, ITGB2, RAC2 and ITGAM) related to iron death in diabetic nephropathy were obtained through gene expression differential analysis between different subtypes. Non-coding genes that interact with Hub genes, including hsa-miR-572, hsa-miR-29a-3p, hsa-miR-29b-3p, hsa-miR-208a-3p, hsa-miR-153-3p and hsa-miR-29c-3p, may be related to diabetic nephropathy. Transcription factors HIF1α, KLF4, KLF5, RUNX1, SP1, VDR and WT1 may be related to diabetic nephropathy. The above factors and Hub genes are collectively involved in the occurrence and development of diabetic nephropathy, which can be further studied in the future. Moreover, these factors and genes may be potential target for therapeutic drugs.

The Role of Vitamin D Intake on the Prognosis and Incidence of Lung Cancer: A Systematic Review and Meta-Analysis

The correlation between vitamin D intake and lung cancer development is controversial. This meta-analysis aims to evaluate the relationship between vitamin D and the prognosis and incidence of lung cancer. A comprehensive database search on PubMed, Web of Science, EBSCO, and Cochrane Library was carried out from the beginning to November 2020. Long-term survival and the incidence rate of patients with lung cancer were the primary outcomes of the study. Ten eligible studies were selected for the meta-analysis following specific inclusion and exclusion criteria. Four included studies, covering 5,007 patients, compared the overall survival (OS) and relapse-free survival (RFS) of lung cancer patients among total vitamin D users with non-users. Significantly, the estimated pooled hazard ratio (HR) revealed that vitamin D could improve OS and RFS of lung cancer patients [HR=0.83, 95% CI (0.72-0.95); HR=0.79, 95% CI (0.61-0.97), respectively]. Vitamin D intake was inversely associated with lung cancer incidence in six studies [OR=0.90, 95% CI (0.83-0.97)]. The present meta-analysis shows vitamin D not only improves the long-term survival of lung cancer patients but has a beneficial effect on the incidence of lung cancer. Notwithstanding, more studies are needed to confirm the study results.

Diabetic Nephropathy and COVID-19: The Potential Role of Immune Actors

Nowadays, type II diabetes mellitus, more specifically ensuing diabetic nephropathy, and severe COVID-19 disease are known to be closely associated. The exact mechanisms behind this association are less known. An implication for the angiotensin-converting enzyme 2 remains controversial. Some researchers have started looking into other potential actors, such as neuropilin-1, mitochondrial glutathione, vitamin D, and DPP4. In particular, neuropilin-1 seems to play an important role in the underlying mechanism linking COVID-19 and diabetic nephropathy. We suggest, based on the findings in this review, that its up-regulation in the diabetic kidney facilitates viral entry in this tissue, and that the engagement of both processes leads to a depletion of neuropilin-1, which was demonstrated to be strongly associated with the pathogenesis of DN. More studies are needed to confirm this hypothesis, and research should be directed towards elucidating the potential roles of all these suggested actors and eventually discovering new therapeutic strategies that could reduce the burden of COVID-19 in patients with diabetic nephropathy.

Diabetic Nephropathy: Challenges in Pathogenesis, Diagnosis, and Treatment

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease worldwide. Chronic hyperglycemia and high blood pressure are the main risk factors for the development of DN. In general, screening for microalbuminuria should be performed annually, starting 5 years after diagnosis in type 1 diabetes and at diagnosis and annually thereafter in type 2 diabetes. Standard therapy is blood glucose and blood pressure control using the renin-angiotensin system blockade, targeting A1c < 7%, and <130/80 mmHg. Regression of albuminuria remains an important therapeutic goal. However, there are problems in diagnosis and treatment of nonproteinuric DN (NP-DN), which does not follow the classic pattern of DN. In fact, the prevalence of DN continues to increase, and additional therapy is needed to prevent or ameliorate the condition. In addition to conventional therapies, vitamin D receptor activators, incretin-related drugs, and therapies that target inflammation may also be promising for the prevention of DN progression. This review focuses on the role of inflammation and oxidative stress in the pathogenesis of DN, approaches to diagnosis in classic and NP-DN, and current and emerging therapeutic interventions.

Association Between 25(OH)Vitamin D, HbA1c and Albuminuria in Diabetes Mellitus: Data From a Population-Based Study (VIDAMAZON)

BACKGROUND

The effect of glycemic control on diabetic kidney disease (DKD) is well known. Recent evidence has suggested that Vitamin D (VD) may have a nephroprotective effect in diabetes, but the relationship between VD, glycemic control, and albuminuria has yet to be clarified.

OBJECTIVE

Evaluate the relationship between 25-hydroxy-vitamin D [25(OH)D], HbA1c, and albuminuria in Diabetes Mellitus (DM).

PATIENTS AND METHODS

Cross-sectional study with 1576 individuals with DM who had 25(OH)D, HbA1c, and albuminuria levels measured. Patients with abnormal creatinine levels were excluded, in order to avoid interference on VD levels by impaired kidney function.

RESULTS

Patients with HbA1c ≥7% had lower 25(OH)D when compared to patients with HbA1c <7% (29.7 ± 10.2 vs 28.1 ± 9.9 ng/ml, p = 0.003) and 25(OH)D levels seems to predict 1.5% of HbA1c behavior. The 25(OH)D concentrations in patients with normoalbuminuria were higher than the levels observed in those with micro or macroalbuminuria (29.8 ± 9.0 vs 26.8 ± 8.6 and 25.1 ± 7.6, respectively, p = 0.001), patients who had 25(OH)D <20 ng/ml and 25(OH)D <30 ng/ml were at a higher risk of presenting albuminuria [OR = 2.8 (95% CI = 1.6 - 4.9), p<0.001, and OR = 2.1 (95% CI = 1.3 - 4.6), p<0.001, respectively]. In our regression model, albuminuria was influenced by HbA1c (r² = 0.076, p<0.00001) and 25(OH)D (r² = 0.018, p = 0.002) independently.

CONCLUSION

Our study found an association between vitamin D levels, HbA1c and DKD. Additionally, our data suggest that the association between urinary albumin excretion and vitamin D levels is independent of glycemic control in patients with diabetes. Even though our patients presented normal creatinine levels, it is necessary further prospective studies to confirm if this association precedes or not the loss of renal function.

Nuclear receptors in the kidney during health and disease

Over the last 30 years, nuclear receptors (NRs) have been increasingly recognized as key modulators of systemic homeostasis and as contributing factors in many diseases. In the kidney, NRs play numerous important roles in maintaining homeostasis-many of which continue to be unraveled. As "master regulators", these important transcription factors integrate and coordinate many renal processes such as circadian responses, lipid metabolism, fatty acid oxidation, glucose handling, and inflammatory responses. The use of recently-developed genetic tools and small molecule modulators have allowed for detailed studies of how renal NRs contribute to kidney homeostasis. Importantly, while NRs are intimately involved in proper kidney function, they are also implicated in a variety of renal diseases such as diabetes, acute kidney injury, and other conditions such as aging. In the last 10 years, our understanding of renal disease etiology and progression has been greatly shaped by knowledge regarding how NRs are dysregulated in these conditions. Importantly, NRs have also become attractive therapeutic targets for attenuation of renal diseases, and their modulation for this purpose has been the subject of intense investigation. Here, we review the role in health and disease of six key renal NRs including the peroxisome proliferator-activated receptors (PPAR), estrogen-related receptors (ERR), the farnesoid X receptors (FXR), estrogen receptors (ER), liver X receptors (LXR), and vitamin D receptors (VDR) with an emphasis on recent findings over the last decade. These NRs have generated a wealth of data over the last 10 years that demonstrate their crucial role in maintaining normal renal homeostasis as well as their capacity to modulate disease progression.