Vitamin D and diabetic nephropathy: A systematic review and meta-analysis

Vitamin D Supplementation: Shedding Light on the Role of the Sunshine Vitamin in the Prevention and Management of Type 2 Diabetes and Its Complications

As the incidence of type 2 diabetes mellitus (T2DM) continues to increase globally, researchers are keen to investigate various interventions to mitigate its impact. Among these, vitamin D supplementation has attracted significant attention due to its influence on insulin secretion from the pancreas and insulin receptors in body cells. A substantial body of evidence indicates that vitamin D supplementation can reduce low-grade inflammation, a critical factor in developing insulin resistance. In addition, vitamin D aids in sustaining low resting concentrations of reactive oxygen species and free radicals, normalizes Ca2+ signaling, diminishes the expression of cytokines that are pro-inflammatory, and enhances the production of cytokines that are anti-inflammatory. This review discusses the effects of vitamin D on the glycemic control of individuals with T2DM and evaluates the impact of vitamin D supplementation on glycemic markers in this population. The investigation employs a comprehensive analysis of the existing literature with a special focus on recent studies published in the past decade. Based on the findings in the literature, it can be concluded that vitamin D supplementation alongside anti-diabetic medications may enhance glycemic control and potentially reduce the risk of diabetic complications. The evidence supports the notion that vitamin D supplementation can be a valuable addition to pharmacological agents for the management of T2DM, potentially enhancing glycemic control and overall health outcomes in affected individuals.

Relationship between bone turnover markers and renal disease in elderly patients with type 2 diabetes: a cross-sectional study

OBJECTIVE

The prevalence of type 2 diabetes mellitus (T2DM) and bone metabolism disorders increase with age. Diabetic kidney disease (DKD) is one of the most serious microvascular complications of T2DM, and bone metabolism disorders are closely linked to the occurrence of DKD. The relationship between bone turnover markers(BTMs) and the kidney disease in elderly patients with T2DM remains unclear. Therefore, this study aims to investigate the association between common BTMs and DKD in a large sample of elderly patients. The goal is to provide a basis for early identification of high-risk individuals for DKD among elderly T2DM patients from a bone metabolism perspective.

METHODS

In this cross-sectional study, BTMs were collected from a cohort of 2,051 hospitalized Chinese patients. The relationships between 25-hydroxyvitamin D (25-OH-D), β-CrossLaps (β-CTX), osteocalcin (OSTEOC), intact parathyroid hormone (iPTH), and total type I collagen N-terminal propeptide (TP1NP), and DKD, as well as urinary albumin-to-creatinine ratio (UACR) and estimated glomerular filtration rate (eGFR) were analyzed using regression analysis and restrictive cubic spline (RCS) curves.

RESULTS

Higher 25-OH-D levels were independently linked to a lower incidence of DKD and decreased UACR. The RCS curves showed a linear association of 25-OH-D and DKD, approaching the L-shape. β-CTX was independently and positively correlated with UACR. There is an independent positive correlation between OSTEOC and UACR and a negative correlation with eGFR. iPTH is independently and positively correlated with DKD incidence and UACR, and negatively correlated with eGFR. Additionally, the RCS curves showed a non-linear association of OSTEOC and iPTH and DKD, approaching the J-shape, and the point of inflection is 10.875 ng/L and 34.15 pg/mL respectively. There is an independent positive correlation between TP1NP and UACR incidence, and a negative correlation with eGFR. Risk estimates significantly increase with higher TP1NP levels in the RCS model.

CONCLUSION

BTMs are closely associated with kidney disease in elderly patients with T2DM. These discoveries potentially assist clinicians in establishing more preventive measures and targeted treatment strategies for elderly patients with T2DM.

Association between lipoprotein-associated phospholipase A2 and 25-hydroxy-vitamin D on early stage diabetic kidney disease in patients with type-2 diabetes mellitus

Objective

This study aimed to analyse the association between lipoprotein-associated phospholipase A2 (Lp-PLA2) and 25-hydroxy-vitamin D (25[OH]D) and early diabetic kidney disease (DKD) in patients with type 2 diabetes mellitus (T2DM) and evaluate the potential roles of these two biomarkers in the clinical diagnosis of DKD.

Methods

A total of 422 inpatients with T2DM were retrospectively enrolled between January 2018 and March 2022 at the First Affiliated Hospital of Nanjing Medical University. The baseline clinical parameters of each patient were determined, and their demographic characteristics were extracted from the hospital information system. The patients were separated into groups according to serum Lp-PLA2 and 25(OH)D levels and binary logistic regression analysis was used to determine independent predictors of early DKD incidence.

Results

Levels of Lp-PLA2 significantly increased and those of 25(OH)D significantly decreased with DKD progression (both P < 0.001). Lp-PLA2 concentrations were positively correlated with albuminuria levels (r = 0.37, P < 0.001), whereas 25(OH)D levels were negatively correlation (r = -0.34, P < 0.001). The incidence of DKD was higher in the Lp-PLA2 elevated and 25(OH)D deficient groups (all P < 0.001). Body mass index, systemic immune-inflammatory index, serum uric acid, C-peptide, and triglyceride-glucose indices were positively associated with Lp-PLA2 levels (all P < 0.001) and negatively associated with 25(OH)D (all P < 0.05). Furthermore, Lp-PLA2 was an independent risk factor (OR = 1.003, P = 0.015), and 25(OH)D was an independent protective factor (OR = 0.937, P = 0.008) for early DKD occurrence in binary logistic regression analysis. The area under the curve for the combination of Lp-PLA2 and 25(OH)D for diagnosing DKD was 0.867, with a sensitivity of 70.4 % and a specificity of 89.5 %.

Conclusions

Increased serum Lp-PLA2 and decreased 25(OH)D levels are risk factors for early DKD in patients with T2DM. The combined detection of Lp-PLA2 and 25(OH)D may enhance the diagnostic efficacy of DKD.

Association of serum vitamin D and the risk of cardiovascular diseases among diabetic patients: A systematic review and meta-analysis

BACKGROUND

The emerging role of vitamin D has drawn the attention of researchers around the world, including its involvement in cardiovascular complications among individuals with diabetes.

AIM

This study aimed to obtain comprehensive evidence on the association between serum vitamin D level and the risk of cardiovascular disease among patients with diabetes.

METHODS

Systematic search was performed on July 1st, 2023, to identify and screen published literature reporting the association between vitamin D and cardiovascular disease among diabetic patients in six databases. Each eligible study was appraised for its quality using modified Newcastle Ottawa Scale for cross-sectional and cohort studies. Meta-analysis was performed using Dersimonian-Laird random effect model or fix-effect model. The heterogeneity and publication bias were judged based on percentage of I2 and the symmetry of Begg's funnel plot, respectively.

RESULTS

As many as 22 studies were found eligible for the systematic review. A meta-analysis from 13 studies comprising of 3850 and 1797 (control and exposure groups, respectively) revealed that serum vitamin D level was significantly lower in patients with diabetes and cardiovascular diseases (Z = 4.89; p-total<0.001; SMD = 0.68 [95%CI: 0.41-0.95]), yet the heterogeneity was high. Following the adjustment of removing the potential outliers, the same results were still observed (Z = 6.19; p-total<0.001; SMD = 0.35 [95%CI: 0.24-0.46]). Though decreased, high heterogeneity could not be resolved, resulting in moderate level of this evidence. Another pooled analysis of 7 studies with 4211 patients in control group and 2381 patients in exposure group revealed that lower level of serum vitamin D is a risk factor for cardiovascular disease incidence among diabetic patients (Z = 4.89; p-total<0.001; OR: 1.76 [95%CI: 1.4-2.2]).

CONCLUSION

Serum vitamin D level status is a risk factor for developing cardiovascular diseases among diabetic patients, hence should be carefully monitored and maintained.

PROSPERO REGISTRATION

CRD42023437698.

Vitamin D is involved in the effects of the intestinal flora and its related metabolite TMAO on perirenal fat and kidneys in mice with DKD

BACKGROUND

Vitamin D was shown to directly exert a protective effect on diabetic kidney disease (DKD) in our previous study. However, whether it has an effect on perirenal adipose tissue (PRAT) or the intestinal flora and its metabolites (trimethylamine N-oxide, TMAO) is unclear.

METHODS

DKD mice were received different concentrations of 1,25-(OH)2D3 for 2 weeks. Serum TNF-α levels and TMAO levels were detected. 16S rRNA sequencing was used to analyze gut microbiota. qPCR was used to detect the expression of TLR4, NF-Κb, PGC1α, and UCP-1 in kidney and adipose tissue. Histological changes in kidney and perirenal adipose tissue were observed using HE, PAS, Masson and oil red staining. Immunofluorescence and immunohistochemistry were used to detect the expression of VDR, PGC1α, podocin, and UCP-1 in kidney and adipose tissue. Electron microscopy was used to observe the pathological changes in the kidney. VDR knockout mice were constructed to observe the changes in the gut and adipose tissue, and immunofluorescence and immunohistochemistry were used to detect the expression of UCP-1 and collagen IV in the kidney.

RESULTS

1,25-(OH)2D3 could improve the dysbiosis of the intestinal flora of mice with DKD, increase the abundance of beneficial bacteria, decrease the abundance of harmful bacteria, reduce the pathological changes in the kidney, reduce fat infiltration, and downregulate the expression of TLR4 and NF-κB in kidneys. The serum TMAO concentration in mice with DKD was significantly higher than that of the control group, and was significantly positively correlated with the urine ACR. In addition, vitamin D stimulated the expression of the surface markers PGC1α, UCP-1 and VDR in the PRAT in DKD mice, and TMAO downregulated the expression of PRAT and renal VDR.

CONCLUSIONS

The protective effect of 1,25-(OH)2D3 in DKD mice may affect the intestinal flora and its related metabolite TMAO on perirenal fat and kidneys.

Effects of dietary intervention on diabetic nephropathy: an umbrella review of systematic reviews and meta-analyses of randomized controlled trials

Objective

To evaluate the quality of evidence, potential biases, and validity of all available studies on dietary intervention and diabetic nephropathy (DN).

Methods

We conducted an umbrella review of existing meta-analyses of randomized controlled trials (RCTs) that focused on the effects of dietary intervention on DN incidence. The literature was searched via PubMed, Embase, Web of Science, and the Cochrane Database of Systematic Reviews. According to the Grading of Recommendations, Assessment, Development and Evaluation (GRADE), evidence of each outcome was evaluated and graded as "high", "moderate", "low" or "very low" quality to draw conclusions. Additionally, we classified evidence of outcomes into 4 categories.

Results

We identified 36 meta-analyses of RCTs and 55 clinical outcomes of DN from 395 unique articles. Moderate-quality evidence suggested that probiotic supplementation could significantly improve blood urea nitrogen (BUN), total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) levels in DN patients. Low-quality evidence indicated that probiotic supplementation significantly improved the serum creatinine concentration, urinary albumin-creatinine ratio (UACR), fasting blood glucose (FBG), HbA1c and high-density lipoprotein cholesterol (HDL-C) in DN patients. In addition, low-quality evidence suggested that a salt restriction diet could significantly improve the creatinine clearance rate (CrCl) in patients with DN. Low-quality evidence suggested that vitamin D supplementation could significantly improve the UACR in patients with DN. In addition, low-quality evidence has indicated that soy isoflavone supplementation could significantly improve BUN, FBG, total cholesterol (TC), triglyceride (TG) and LDL-C levels in patients with DN. Furthermore, low-quality evidence suggested that coenzyme Q10 supplementation could significantly improve HbA1c, TC and HDL-C in patients with DN, and dietary polyphenols also significantly improved HbA1c in patients with DN. Finally, low-quality evidence suggested that supplementation with antioxidant vitamins could significantly improve the serum creatinine concentration, systolic blood pressure, and HbA1c level in patients with DN. Given the small sample size, all significantly associated outcomes were evaluated as class IV evidence.

Conclusion

Moderate to low amounts of evidence suggest that supplementation with probiotics, vitamin D, soy isoflavones, coenzyme Q10, dietary polyphenols, antioxidant vitamins, or salt-restricted diets may significantly improve clinical outcomes in patients with DN.

Systematic Review Registration

https://www.crd.york.ac.uk/PROSPERO/, identifier CRD42024512670.

Progression of diabetic nephropathy and vitamin D serum levels: A pooled analysis of 7722 patients

BACKGROUND AND AIM

Low serum Vitamin D levels have been associated with diabetic nephropathy (DN). Our study aimed to analyse the serum levels of vitamin D in patients suffering from DN and the subsequent changes in serum vitamin D levels as the disease progresses.

METHODS

PubMed, Embase, SCOPUS and Web of Science were searched using keywords such as '25 hydroxyvitamin D' and 'diabetic nephropathy'. We included observational studies that reported the association between the serum 25 hydroxy vitamin D levels and diabetic nephropathy without restriction to age, gender, and location. R Version 4.1.2 was used to perform the meta-analysis. The continuous outcomes were represented as mean difference (MD) and standard deviation (SD) and dichotomous outcomes as risk ratios (RR) with their 95% confidence interval (CI).

RESULTS

Twenty-three studies were included in our analysis with 7722 patients. Our analysis revealed that vitamin D was significantly lower in diabetic patients with nephropathy than those without nephropathy (MD: -4.32, 95% CI: 7.91-0.74, p-value = .0228). On comparing diabetic patients suffering from normoalbuminuria, microalbuminuria, or macroalbuminuria, we found a significant difference in serum vitamin D levels across different groups. Normoalbuminuria versus microalbuminuria showed a MD of -1.69 (95% CI: -2.28 to -1.10, p-value = .0002), while microalbuminuria versus macroalbuminuria showed a MD of (3.75, 95% CI: 1.43-6.06, p-value = .0058), proving that serum vitamin D levels keep declining as the disease progresses. Notwithstanding, we detected an insignificant association between Grade 4 and Grade 5 DN (MD: 2.29, 95% CI: -2.69-7.28, p-value = .1862).

CONCLUSION

Serum Vitamin D levels are lower among DN patients and keep declining as the disease progresses, suggesting its potential benefit as a prognostic marker. However, on reaching the macroalbuminuria stage (Grades 4 and 5), vitamin D is no longer a discriminating factor.

Effects of Vitamin D Supplementation in Diabetic Kidney Disease: A 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 Impact of Vitamin D Deficiency and Insufficiency on the Outcome of Type 2 Diabetes Mellitus Patients: A Systematic Review

Vitamin D deficiency and insufficiency are public health concerns that have contributed to multiple negative health outcomes. Recent studies have revealed that vitamin D deficiency and insufficiency influence glycaemic control and the development of diabetes complications. The goal of this systematic review is to summarise the latest evidence on the impact of vitamin D deficiency and insufficiency on the outcome of Type 2 Diabetes Mellitus (T2DM) patients. In this PRISMA-guided systematic review, articles were sourced from three databases, namely, PubMed, Scopus, and Web of Science. The review only included literature published from 2012 until 2022, and 33 eligible studies met the inclusion criteria for this review. The included articles were critically appraised using the Mixed Method Appraisal Tool (MMAT). According to our findings, vitamin D deficiency or insufficiency is associated with mental health status, macrovascular and microvascular complications of T2DM, metabolic syndrome, increased risk of obesity, increased blood pressure, dyslipidaemia, glycaemic control, nerve-related disease, musculoskeletal-related complications, and reduced quality of life. Due to the diverse implications of vitamin D deficiency and insufficiency, screening for vitamin D levels in T2DM patients may be beneficial.

Inverse Association Between Baseline Plasma Selenium Concentrations and Risks of Renal Function Decline in Hypertensive Adults

BACKGROUND

The kidney has the highest level of selenium (Se) in the body, but the role of plasma Se in chronic kidney disease is uncertain.

OBJECTIVE

We aimed to investigate the longitudinal association between baseline plasma Se and renal function decline in adults with hypertension and to explore possible effect modifiers.

METHODS

This was a post hoc analysis of 935 men and women with hypertension aged 40 to 75 years from a folic-acid intervention trial (the China Stroke Primary Prevention Trial) in China. The baseline plasma Se was analyzed both as a continuous variable and as tertiles. The primary outcome was a rapid decline in renal function, defined as a mean decline in the estimated glomerular filtration rate of ≥ 5 mL/(min × 1.73 m2) per year.

RESULTS

The median follow-up duration from baseline to outcome was 4.4 years. After multivariate adjustment, there was an inverse association between plasma Se and a rapid decline in renal function (per 10-unit increment; OR: 0.85; 95% CI: 0.73, 0.99). When the baseline plasma Se was assessed as tertiles, compared to the lowest tertile (<74.5 μg/L), a lower trend of the primary outcome was found in the second tertile (74.5 to < 89.4 μg/L; OR: 0.60; 95% CI: 0.34, 1.07) and the highest tertile (89.4 to <150 μg/L; OR: 0.42; 95% CI: 0.22, 0.80; Ptrend = 0.006). Furthermore, the Se-renal association was more pronounced among participants with folic acid treatment or with a higher baseline folate concentration (both Pinteraction values < 0.05).

CONCLUSIONS

In this sample of Chinese adults with hypertension, baseline plasma Se concentrations were inversely associated with the risk of renal function decline. The China Stroke Primary Prevention Trial was registered at clinicaltrials.gov as NCT00794885.

Vitamin D and Multiple Health Outcomes: An Umbrella Review of Observational Studies, Randomized Controlled Trials, and Mendelian Randomization Studies

Observational studies, randomized controlled trials (RCTs), and Mendelian randomization (MR) studies have yielded inconsistent results on the associations of vitamin D concentrations with multiple health outcomes. In the present umbrella review we aimed to evaluate the effects of low vitamin D concentrations and vitamin D supplementation on multiple health outcomes. We summarized current evidence obtained from meta-analyses of observational studies that examined associations between vitamin D concentrations and multiple health outcomes, meta-analyses of RCTs that investigated the effect of vitamin D supplementation on multiple health outcomes, and MR studies that explored the causal associations of vitamin D concentrations with various diseases (international prospective register of systematic reviews PROSPERO registration number CRD42018091434). A total of 296 meta-analyses of observational studies comprising 111 unique outcomes, 139 meta-analyses of RCTs comprising 46 unique outcomes, and 73 MR studies comprising 43 unique outcomes were included in the present umbrella review. Twenty-eight disease outcomes were identified by both meta-analyses of observational studies and MR studies. Seventeen of these reported disease outcomes had consistent results, demonstrating that lower concentrations of vitamin D were associated with a higher risk for all-cause mortality, Alzheimer's disease, hypertension, schizophrenia, and type 2 diabetes. The combinations of consistent evidence obtained by meta-analyses of observational studies and MR studies together with meta-analyses of RCTs showed that vitamin D supplementation was associated with a decreased risk for all-cause mortality but not associated with the risk for Alzheimer's disease, hypertension, schizophrenia, or type 2 diabetes. The results indicated that vitamin D supplementation is a promising strategy with long-term preventive effects on multiple chronic diseases and thus has the potential to decrease all-cause mortality. However, the current vitamin D supplementation strategy might not be an efficient intervention approach for these diseases, suggesting that new strategies are highly needed to improve the intervention outcomes.

Vitamin D Analogs Can Retard the Onset or Progression of Diabetic Kidney Disease: A Systematic Review

Introduction

Previous studies have shown that vitamin D analogs (such as paricalcitol) can reduce albuminuria in patients with diabetes mellitus and retard the progression of diabetic kidney disease (DKD). A recent systematic review reported significant improvement of renal function in patients with DKD who received vitamin D or its analogs. Study-driven data about their use in improving DKD outcomes have continued to accumulate over the years.

Aim

This paper aims to systematically review the contemporary evidence about the effectiveness of vitamin D analogs in retarding the onset or progression of DKD.

Methods

With appropriate descriptors, two electronic databases (PubMed and Google Scholar) were searched for articles published between 2015 and 2021 in the English language. Primary studies that fulfilled the inclusion criteria were selected; their titles and abstracts were screened, and duplicates were removed. Relevant data were retrieved from the final selected studies using a preconceived data-extraction form.

Results

A total of eight studies (three randomized-controlled trials, one prospective study, and four cross-sectional studies) were reviewed. A total of 6,243 participants were investigated in the eight studies and comprised young adults, middle-aged adults, and the elderly with a male-gender predominance. One randomized controlled trial reported that paricalcitol significantly improved renal function in type 1 diabetes patients with renal impairment when combined with renin-angiotensin-aldosterone system (RAAS) blockers. A strong correlation between vitamin D deficiency and DKD risk was noted in the majority of the cross-sectional studies. High doses of cholecalciferol (4,000 or 10,000 IU/day), given early in DKD, significantly reduced disease prevalence.

Conclusion

Paricalcitol may retard the onset or progression of DKD, especially if administered in combination with RAAS blockers. The association of vitamin D deficiency with DKD risk also supports this therapeutic effect. Future systematic reviews are still needed to strengthen the current evidence on therapeutic benefit of vitamin D or its analogs in DKD.

A Randomized Double-Blind Placebo-Controlled Trial Evaluating the Efficacy of Oral Cholecalciferol in Improving Renal and Vascular Functions in Vitamin D-Deficient Patients With Type 2 Diabetes Mellitus

This study was performed to evaluate the efficacy of cholecalciferol in improving renal and vascular functions in vitamin D-deficient patients with type 2 diabetes mellitus (T2DM) along with chronic kidney disease (CKD). One hundred patients (18 - 65 years), having T2DM along with CKD (stage IIIA and IIIB) and hypovitaminosis D were randomized (1:1) to receive either oral cholecalciferol 60,000 IU (Group A) or placebo (Group B) weekly for 8 weeks along with standard background treatment. They were followed up for another 24 weeks. Various parameters of renal and vascular functions were compared. Except for serum calcium and phosphate levels which were significantly higher in Group A (p < 0.001), there was no significant difference in any of the biochemical or vascular parameters between the two groups at 8 weeks. There were comparable changes in urinary albumin-creatinine ratio and carotid-femoral pulse wave velocity in the two groups at 8 and 24 weeks. There was no improvement in any of the vascular parameters from the corresponding baseline values in the two groups at 8 and 32 weeks. No improvement in renal and vascular functions was observed following treatment with oral cholecalciferol in patients with T2DM and CKD.

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.

Pathophysiological Implication of Vitamin D in Diabetic Kidney Disease

BACKGROUND

Vitamin D is a hormone regulating not only calcium and phosphate homeostasis but also, at the same time, exerting many other extraskeletal functions via genomic effects (gene transcription) and probably by non-genomic effects as well. Availability is ensured by dietary intake of its precursors and by de novo production via sunlight. Yet, vitamin D deficiency and insufficiency are very common across the globe and are connected to many pathophysiological states, for example, diabetes mellitus, allergies, autoimmune diseases, pregnancy complications, and recently have also been associated with worse COVID-19 clinical outcomes.

SUMMARY

In this review, we summarize current knowledge about vitamin D metabolism in general, its role in diabetes mellitus (mainly type 2) and diabetic complications (mainly diabetic kidney disease), and potential therapeutic perspectives including vitamin D signalling as a druggable target. Key Messages: Vitamin D is not only a vitamin but also a hormone involved in many physiological processes. Its insufficiency or deficiency can lead to many pathological states.

Relationship of serum vitamin D levels with diabetic microvascular complications in patients with type 2 diabetes mellitus

Background:

Vitamin D deficiency has been reported to be associated with diabetic microvascular complications, but previous studies have only focused on the relationship between vitamin D and specific complications. Therefore, we aimed to explore the relationship between vitamin D level and diabetic microvascular complications in general, including diabetic retinopathy (DR), diabetic nephropathy (DN), and diabetic peripheral neuropathy (DPN).

Methods:

This was a cross-sectional study of 815 patients with type 2 diabetes mellitus (T2DM). Clinical information and laboratory results were collected from the medical records. The relationship between vitamin D and the three diabetic microvascular complications was investigated.

Results:

The serum 25-hydroxyvitamin D (25 [OH] D) level of patients with DPN and/or DN was significantly lower than that of T2DM patients without any microvascular complications (P < 0.01). Univariate analysis showed that the 25 (OH) D level was related to DPN and DN, but not DR. After adjustment, the 25 (OH) D level was confirmed to be an independent protective factor for DPN (odds ratio [OR]: 0.968, P = 0.004]) and DN (OR: 0.962, P = 0.006). The prevalence of DPN and DN increased significantly as the serum 25 (OH) D levels decreased. Furthermore, patients with both DPN and DN had the lowest concentration of serum 25 (OH) D (P < 0.001), and the prevalence of macroalbuminuria increased more abruptly than that of microalbuminuria across the 25 (OH) D tertiles. Among the patients with vitamin D insufficiency, those with DPN presented more comorbid macroalbuminuria than those without DPN (15.32% vs. 4.91%; P = 0.001).

Conclusions:

Vitamin D deficiency is independently associated with higher risk of DPN and DN, but not DR, in T2DM patients. Further, it may be a potential predictor for both the occurrence and severity of DPN and DN.

Systematic Review of Nutrition Supplements in Chronic Kidney Diseases: A GRADE Approach

Chronic kidney disease (CKD) is cumulative worldwide and an increasing public health issue. Aside from the widely known protein restriction and medical therapy, less evident is the renal protection of nutrition supplements in CKD patients. This systematic review (SR), using a Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach, aims to summarize and quantify evidence about the prevention effects of vitamin D and analogues, omega-3 polyunsaturated fatty acid (omega-3 PUFA), dietary fiber, coenzyme Q10 (CoQ10), and biotics on CKD progression. This study was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement to examine SRs and/or meta-analysis of clinical controlled trials identified from PubMed, Embase, and the Cochrane Library. Finally, seventeen SRs were included in the qualitative analysis. The beneficial effects of these nutrition supplements in CKD patients mostly seem to be at low to very low evidence on proteinuria, kidney function, and inflammations and did not appear to improve CKD prognosis. The recommendation of nutrition supplements in CKD patients needs to discuss with physicians and consider the benefits over the adverse effects. Longer follow-up of larger randomized trials is necessary to clarify the benefits of nutrition supplements in CKD patients.

Lower serum 25-hydroxyvitamin D levels are associated with impaired glomerular filtration rate in type 2 diabetes patients

BACKGROUND

25-Hydroxyvitamin D [25(OH)D] deficiency has been implicated as a possible risk factor for the onset and progression of diabetes kidney disease (DKD). The aim of this study was to evaluate the interaction between levels of 25(OH)D and DKD in type 2 diabetes mellitus (DM) patients.

METHODS

Cross-sectional design, outpatient type 2 DM. Glomerular filtration rate (GFR) was measured by 51Cr-EDTA and estimated by Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI), urinary albumin excretion (UAE) by immunoturbidimetry, and 25(OH)D by chemiluminescence. Receiver operating characteristic (ROC) curve analysis and generalized linear model (Poisson robust regression estimator) were used to assess the interaction between 25(OH)D levels and renal function.

RESULTS

A total of 114 type 2 DM patients aged 60 ± 10 years, 49 males (43%), DM duration 22 ± 10 years, with GFR > 60 ml/min/1.73 m2 were evaluated. Patients with GFRs 60-90 (n = 50) had significantly lower 25(OH)D levels than individuals with GFRs > 90 ml/min/1.73 m2 (n = 64), respectively 40 ± 20 versus 48 ± 20 nmol/l, p = 0.027. This difference was more pronounced for older individuals (39 ± 20 versus 54 ± 23 nmol/l, respectively), and Poisson robust regression disclosed that lower 25(OH)D [Poisson regression (PR) = 0.989, confidence interval (CI): 0.978-0.999, p = 0.034], and advanced age (PR = 1.050, CI: 1.007-1.096, p = 0.023) were significantly associated with the lower GFR category, adjusted for seasons. ROC curve analysis showed that the cutoff point of 25(OH)D of 41 nmol/l was associated with lower GFR [area under the curve (AUC) = 0.694, p = 0.009]. CKD-EPI estimated GFR (eGFR) was not associated with 25(OH)D in any analysis. There was no difference in 25(OH)D levels between patients with elevated UAE as compared with normoalbuminuric ones (44 ± 21 versus 46 ± 19 nmol/l, p = 0.587).

CONCLUSION

Lower levels of 25(OH)D are associated with decreased GFR in patients with type 2 DM, especially in older patients, with no evidence of interaction with UAE levels.

Vitamin D-mitochondria cross-talk could modulate the signaling pathway involved in hypertension development: a translational integrative overview

Vitamin D deficiency is a worldwide pandemic and results in osteoporosis, hypertension, and other cardiovascular diseases. At the cellular level, it produces significant oxidative stress, inflammatory markers, and mitochondrial damage. There is increasing evidence about the role of vitamin D in the regulation of the renin-angiotensin-aldosterone system (RAAS). Moreover, there is evidence of involvement in cardiovascular complications, as well as in the immune system disorders. Vitamin D values below 25ng/mL are related to an increase in vascular tone mediated by smooth muscle contraction. Furthermore, it can produce direct effects on vascular smooth muscle cells, RAAS over-regulation, modulation of calcium metabolism, and secondary hyperparathyroidism. All this predisposes patients to develop hypertrophy of the left ventricle and vascular wall, causing hypertension. In this work, a review is presented of the main mechanisms involved in the development of hypertension due to vitamin D deficiency. Among them are the link established between the levels of extra-mitochondrial inorganic phosphate, its main regulatory hormones -such as vitamin D-, the cardiovascular system, reactive oxygen species, and mitochondrial metabolism. The role of the mitochondrial vitamin D receptor and the regulation of the respiratory chain could influence arterial remodelling since its activation would reduce oxidative damage and preserve cell life. However, there are aspects not yet understood about the intricate signalling network that appeared simple in experimental trials, but complex in clinical studies. In this way, the completion of new studies as VITAL, could clarify, and thus support or refute the possible benefits of vitamin D in hypertensive cardiovascular disease.

1α,25-Dihydroxyvitamin D3 prevents renal oxidative damage via the PARP1/SIRT1/NOX4 pathway in Zucker diabetic fatty rats

Diabetic nephropathy (DN) is one of the most important renal complications associated with diabetes, and the mechanisms are yet to be fully understood. To date, few studies have shown the antioxidant effects of 1α,25-dihydroxyvitamin-D₃ [1,25(OH)₂D₃] on hyperglycemia-induced renal injury. The aim of the present study was to explore the potential mechanism by which 1,25(OH)₂D₃ reduced oxidative stress in diabetic rat kidneys. In this study, we established a vitamin D-deficient spontaneous diabetes model: 5-6 wk of age Zucker diabetic fatty (ZDF) rats were treated with or without 1,25(OH)₂D₃ for 7 wk, age-matched Zucker lean rats served as control. Results showed that ZDF rats treated with 1,25(OH)₂D₃ had decreased body mass, food intake, water intake, and urine volume. 1,25(OH)₂D₃ ameliorated urine glucose, blood glucose and abnormal glucose tolerance. Additionally, 1,25(OH)₂D₃ significantly lowered microalbuminuria, decreased the glomerular basement membrane thickness, and in some degree inhibited glomerular hypertrophy, mesangial expansion, and tubular dilatation. Furthermore, 1,25(OH)₂D₃ attenuated renal oxidative damage, as reflected by the levels of malondialdehyde, reduced glutathione, 4-hydroxynonenal, 8-hydroxy-2'-deoxyguanosine, and reactive oxygen species production, and notably inhibited poly(ADP-ribose) polymerase-1 (PARP1), activated sirtuin 1 (SIRT1), and decreased the expression of NADPH oxidase 4 (NOX4). Of interest, the abovementioned proteins could be involved in the antioxidant mechanism of 1,25(OH)₂D₃ in diabetic rat kidneys. Our study showed that oxidative stress might be a major contributor to DN pathogenesis and uncovered the antioxidant role of 1,25(OH)₂D₃ in diabetic nephropathy that was associated with the PARP1/SIRT1/ NOX4 pathway.

Type 2 Diabetes Mellitus, Insulin Resistance, and Vitamin D

PURPOSE OF REVIEW

There is a growing, largely inconsistent, literature on the role of vitamin D in association with type 2 diabetes, insulin resistance/insulin secretion, glycemic indices, and complications of type 2 diabetes. Pathophysiologic, bystander, preventive, and treatment roles of vitamin D have all been proposed. In this focused review, we attempt to organize and clarify our current information in this area.

RECENT FINDINGS

Clinical study interpretation is difficult because of variability in dosage, dosage form, study duration, and populations studied, as well as recently reported normal human polymorphisms in vitamin D synthesis and catabolism, vitamin D-binding protein, and vitamin D receptors in addition to a host of potential epigenetic confounders. Low vitamin D status appears to be associated with type 2 diabetes and most other insulin resistance disorders reported to date. The extraskeletal benefits of supplementation/repletion in these disorders in our species, with a few highlighted exceptions, remain to be established. This focused review attempts to summarize our current knowledge in this burgeoning area through a review of key meta-analyses, observational studies, randomized control trials, and Mendelian randomization studies and will hopefully serve as a guide to indicate future research directions and current best practice.

ASSOCIATIONS BETWEEN VITAMIN D AND MICROVASCULAR COMPLICATIONS IN MIDDLE-AGED AND ELDERLY DIABETIC PATIENTS

Objective: The objective of this cross-sectional study was to investigate the association of serum 25-hydroxyvitamin D (25[OH]D) levels with estimated glomerular filtration rate (eGFR), albumin/creatinine ratio (ACR), and the prevalence of diabetic retinopathy (DR) in Chinese diabetic adults. Methods: A total of 4,767 diabetic participants were enrolled from seven communities in Shanghai, China, in 2018. Participants underwent several examinations, which included the measurement of anthropometric parameters, blood pressure, glucose, lipid profiles, 25(OH)D, and ACR. DR was detected based on high-quality fundus photographs and remotely read by ophthalmologists. Results: Compared with the first 25(OH)D quartile, participants in the fourth quartile had a lower prevalence of high ACR (odds ratio [OR], 0.77; 95% confidence interval [CI], 0.61 to 0.96) (P for trend <.01). No association was found between 25(OH)D levels and eGFR. For DR, the OR (95% CI) for DR ranging from 0 to 4 in ordinal logistic regression associated with 25(OH)D was 0.62 (0.47 to 0.82) for the fourth 25(OH)D quartile (P for trend <.01) compared with the first quartile. These associations were all fully adjusted for confounding factors. Conclusion: Lower serum 25(OH)D concentration is significantly associated with increased ACR and higher prevalence of DR in middle-aged and elderly diabetic adults. However, the possibility of a causal relationship between 25(OH)D deficiency and diabetic microvascular complications remains to be demonstrated. Abbreviations: 25(OH)D = 25-hydroxyvitamin D; ACR = albumin/creatinine ratio; BMI = body mass index; CI = confidence interval; DKD = diabetic kidney disease; DR = diabetic retinopathy; eGFR = estimated glomerular filtration rate; HbA1c = glycated hemoglobin; HDL = high-density lipoprotein; LDL = low-density lipoprotein; OR = odds ratio; T2DM = type 2 diabetes mellitus.

Effects of Vitamin D Supplementation on Renal Function, Inflammation and Glycemic Control in Patients with Diabetic Nephropathy: a Systematic Review and Meta-Analysis

BACKGROUND/AIMS

Vitamin D (VD) is widely recognized as renal protective. However, whether VD supplementation provides benefit to patients with diabetic nephropathy (DN) remains controversial. Here, we performed a meta-analysis to systematically evaluate the impact of VD supplementation on indexes of renal function, inflammation and glycemic control in DN patients, and to explore the potential renal protective mechanism of VD.

METHODS

We searched Pubmed, Embase, Cochrane Library, and three major Chinese biomedical databases (CNKI, WANGFANG and VIP) for randomized controlled trials (RCTs) examining the effects of VD or its analogs in DN patients, published between September 2007 and July 2018. Quality assessment and data extraction were performed independently by two authors, according to the Cochrane systematic review methods. Meta-analysis based on the extracted results were performed via Revman 5.2 software.

RESULTS

We included 20 RCTs representing 1,464 patients with DN in this meta-analysis. VD supplementation significantly reduced 24-hour urine protein [MD = -0.26; 95% CI (-0.34, -0.17); P < 0.00001; I2 = 95%], UAER [MD = -67.36; 95% CI (-91.96, -42.76); P < 0.00001; I2 = 97%], hs-CRP [MD = -0.69; 95% CI (-0.86,-0.53); P < 0.00001; I2 = 0%], TNF-α [MD = -56.79; 95% CI (-77.05, -36.52); P < 0.00001; I2 = 89%] and IL-6 [MD = -0.73; 95% CI(-1.03, -0.44); P < 0.00001; I2 = 0%]. However, VD supplementation failed to decrease SCr [MD = -0.83; 95% CI (-3.67,2.02); P = 0.57; I2 = 0%] or increase eGFR [MD = 2.13; 95% CI (-2.06, 6.32); P = 0.32; I2 = 0%]. In addition, VD supplementation showed no impact on indexes of glycemic control, such as HbA1c [MD = 0.01; 95% CI (-0.09, 0.11); P = 0.84; I2 = 0%] and FBG [MD = -0.05; 95% CI (-0.29, 0.20); P = 0.70; I2 = 0%]. Analysis of 24-hour urine protein, SCr, eGFR, hs-CRP or HbA1c revealed no difference between subgroups based on the type of VD supplementation, including calcitriol, alfacalcidol and vitamin D3, and the dose or duration of calcitriol usage.

CONCLUSION

In patients with DN, VD supplementation provides beneficial effects on 24-hour urine protein and inflammation indexes, but not on SCr, eGFR or glycemic control indexes. More RCTs that comprehensively evaluate the impact of VD supplementation on indexes of renal function, inflammation and glycemic control in DN atients are required in order to reach conclusive results.

Haplotypes in vitamin D receptor gene encode risk in diabetic nephropathy

BACKGROUND

Diabetic Nephropathy (DN) is one of the microvascular complications of diabetes and its early diagnosis can improve patient's quality of life. Genetic factors may increase the risk of DN development. This study aimed to evaluate the association of vitamin D receptor (VDR) gene polymorphisms and DN.

METHOD

A total of 313 Iranian participants including 104 diabetic patients with nephropathy (DN), 100 diabetic patients without nephropathy (D) and 109 healthy people (HC) were studied. The frequencies of rs7975232, rs731236 and rs4516035 variants of VDR gene were determined and compared between three groups. Estimated haplotype frequencies between polymorphisms in the cases and controls were also calculated.

RESULTS

No significant differences were identified for allele /genotype frequencies in HC, D and DN groups. However haplotype analysis showed that haplotype encompassing CCC alleles for rs7975232, rs731236 and rs4516035 variants, respectively was more frequent in DN subjects compared to HC (p-value = 0.01) and also, haplotype comprising TCC alleles was more frequent in DN group compared to both HC and D groups (p-value = 0.004 and 0.007, respectively).

CONCLUSION

Our study identified that CCC and TCC VDR haplotypes are risk factors for DN in patients with diabetes type 2.

The cellular selection between apoptosis and autophagy: roles of vitamin D, glucose and immune response in diabetic nephropathy

BACKGROUND AND AIMS

Apoptosis, autophagy and cell cycle arrest are cellular responses to injury which are supposed to play fundamental roles in initiation and progression of diabetic nephropathy (DN). The aims of the present study is to shed light on the potential effects of vitamin D analog 22-oxacalcitriol (OCT) on different cell responses during DN, and the possible interplay between both glucose, immune system and vitamin D in determining the cell fate.

METHOD

All rats were randomly allocated into one of three groups: control, vehicle-treated DN group and OCT-treated DN group. Eight weeks after induction of diabetes, the rats were killed. Fasting blood glucose levels, serum 25 (OH) D, renal functions, cytokines and gene expression of autophagy, apoptotic and cell cycle arrest markers were assessed. In addition, the histological assessment of renal architecture was done.

RESULTS

OCT treatment remarkably improved the renal functions and albuminuria. The reductions in mesangial cell hypertrophy, extracellular matrix as well as cell loss were significantly associated with upregulation of pro-autophagy gene expressions and downregulation of both pro-apoptotic and G1-cell cycle arrest genes expression. The reno-protective effects of OCT treatment were associated with significant attenuation of the fasting blood glucose, serum IL-6, renal TLR-4 and IFN-g gene expression.

CONCLUSION

Modulator effects of OCT on glucose and immune system play important roles in renal cell fate decision and chronic kidney disease progression.

Vitamin-D concentrations, cardiovascular risk and events - a review of epidemiological evidence

Vitamin D has long been established as an elemental factor of bone physiology. Beyond mineral metabolism, the expression of the vitamin D receptor has been identified throughout the cardiovascular (CV) system. Experimental studies showed beneficial effects of vitamin D on heart and vessels, but vitamin D intoxication in animals also led to hypercalcemia and vascular calcification. Our knowledge has been extended by epidemiological studies that showed that 25-hydroxyvitamin D (25(OH)D) levels are inversely associated with an increased CV risk itself, but also with established CV risk factors, such as arterial hypertension, endothelial dysfunction and atherosclerosis. Conversely, randomized controlled trials could not document significant and consistent effects of vitamin D supplementation on CV risk or events. Potential explanations may lie in differences in reference ranges or the possibility that low vitamin D in CV disease is only an epiphenomenon. In the latter case, the key question is why low 25(OH)D levels are such a strong predictor of health. While we wait for new data, the current conclusion is that vitamin D is a strong risk marker for CV risk factors and for CV diseases itself.

Vitamin D and diabetes mellitus: Causal or casual association?

The incidence of both type 2 and type 1 diabetes mellitus has been increasing worldwide. Vitamin D deficiency, or the awareness of its prevalence, has also been increasing. Vitamin D may have a role in the pathogenic mechanisms predisposing to type 2 diabetes by modulating insulin resistance and/or pancreatic β-cell function. Vitamin D status or elements involved in its activation or transport may also be involved in the development of type 1 diabetes mellitus through immunomodulatory role . Based on these observations a potential association between vitamin D and diabetes has been hypothesized. In this review we discuss up to date evidence linking vitamin D with the development of diabetes. Moreover, the role of vitamin D supplementation in the prevention of both types of diabetes is analysed together with its role in improving glycemic control in diabetic patients. We also address the potential role of vitamin D deficiency in the development of macro- and microvascular complications in diabetes. Finally, we provide recommendation for Vitamin D therapy in diabetes in view of current evidence and highlight areas for potential future research in this area.

Albuminuria Reduction after High Dose of Vitamin D in Patients with Type 1 Diabetes Mellitus: A Pilot Study

BACKGROUND

Some studies suggest an association between diabetic kidney disease (DKD) and vitamin D (VD), but there is no data about the effect of high dose of VD on DKD in type 1 diabetes mellitus (T1DM). Our pilot study aims to evaluate albuminuria reduction in patients with T1DM supplemented with high dose of VD.

METHODS

22 patients received doses of 4,000 and 10,000 IU/day of cholecalciferol for 12 weeks according to patient's previous VD levels. They were submitted to continuous glucose monitoring system, 24 hours ambulatory blood pressure monitoring and urine albumin-to-creatinine ratio before and after VD supplementation.

RESULTS

There was a reduction of DKD prevalence at the end of the study (68 vs 32%; p = 0.05), with no changes on insulin doses, glycated hemoglobin, glycemic variability and blood pressure values. A correlation between percentage variation of VD levels (ΔVD) and albuminuria at the end of the study was presented (r = -0.5; p < 0.05). Among T1DM patients with DKD at the beginning of the study, 8/13 (62%) had their DKD stage improved, while the other five ones (38%) showed no changes (p < 0.05).

CONCLUSION

Our pilot study suggests an association between VD high dose supplementation, lower prevalence and improvement in stages of DKD in T1DM.

In vitro and in vivo inhibition of mTOR by 1,25-dihydroxyvitamin D3 to improve early diabetic nephropathy via the DDIT4/TSC2/mTOR pathway

We investigated whether 1,25-dihydroxy-vitamin D₃ (1,25(OH)₂D₃) could improve early diabetic nephropathy through the DNA-damage-inducible transcript 4/tuberous sclerosis 2/mammalian target of rapamycin pathway. Rat mesangial cells were cultured in media containing normal glucose or high glucose and were treated with or without 1,25(OH)₂D₃. Mesangial cells proliferation was measured. Streptozotocin-induced diabetic rats were injected intravenously with a recombinant lentivirus against the rat vitamin D receptor gene. Urinary and serum albumin, fasting plasma glucose, serum triglyceride, total cholesterol, calcium, parathyroid hormone and serum 25-dihydroxy-vitamin D (25(OH)D) levels, mean glomerular volume, glomerular basement membrane thickness and total kidney volume were determined. The expressions of vitamin D receptor, DNA-damage-inducible transcript 4, and mammalian target of rapamycin were measured. 1,25(OH)₂D₃ inhibited the proliferation of mesangial cells induced by hyperglycemia. 1,25(OH)₂D₃ also significantly reduced albumin excretion, mean glomerular volume, glomerular basement membrane, and total kidney volume in rats with diabetic nephropathy. The expression of DNA-damage-inducible transcript 4 was elevated by 1,25(OH)₂D₃ treatment. The phosphorylation of mammalian target of rapamycin was reduced by 1,25(OH)₂D₃ treatment. Vitamin D receptor gene silencing blocked all of the above results. The current study demonstrates that 1,25(OH)₂D₃ can effectively inhibit mesangial cells proliferation induced by hyperglycemia, thus suppressing the development of diabetic nephropathy. This study also shows that the nephron-protective effect of 1,25(OH)₂D₃ occurs partly through the DDIT4/TSC2/mTOR pathway.

Effect of vitamin D on proteinuria in type 2 diabetic patients

Background

Vitamin D (Vit D) deficiency is a common disorder in diabetic patients and may be a risk factor for ischemic heart disease and exacerbation of diabetic nephropathy(DN).

Objectives

The aim of this study was to evaluate the effect of Vit D3 therapy on protein uriain type 2 diabetic patients with deficient or insufficient serum Vit D.

Patients and Methods

In a double blind clinical trial, 60 type 2 diabetic patients with proteinuria greater than 150 mg/day who had Vit D deficiency or insufficiency were randomly enrolled in two equal groups. Pearl of Vit D as 50 000 IU/week and placebo (1 tablet per week) were prescribed in patients of case and control groups respectively for 8 weeks. At the beginning and 2 months later, 24 hours urine protein was checked in all patients.

Results

There is no difference between serums Vit D level in case and control group at the beginning of the study, however at the end of the study serum Vit D level was significantly higher in the case group. There is no difference in proteinuria between case and control group at the beginning and the end of the study, while a significant difference between the changes of proteinuria before and after the study was seen in two groups (P = 0.028).

Conclusions

Vit D deficiency may exacerbate protein uric and DN, hence correction of Vit D deficiency may decrease proteinuria in diabetic patients with nephropathy.

Vitamin D3 Partly Antagonizes Advanced-Glycation Endproducts-Induced NFκB Activation in Mouse Podocytes

BACKGROUND/AIMS

We have previously shown that advanced glycation-endproducts (AGEs) induced NFκB activation in differentiated mouse podocytes. This NFκB activation may contribute to the progression of renal disease and mediation of fibrosis by various mechanisms. This study was undertaken to test whether this detrimental response may be reversed by vitamin D3 or its analogue paricalcitol.

METHODS

Differentiated mouse podocytes were challenged with glycated bovine serum albumin (AGE-BSA), or non-glycated control BSA (in the presence or absence of various concentrations of vitamin D3 (decostriol, 1α,25-dihydroxyvitamin D3)) or its active analog paricalcitol. Quantitative mRNA expressions were measured by real-time PCR, whereas protein expressions were determined by Western blotting followed by densitometry. Cytoplasmic and nuclear protein expression of the NFκB subunit p65 (Rel A) were determined by Western blotting. Furthermore, the ratio of phosphorylated to non-phosphorylated IκB-α was measured using specific antibodies. Electrophoretic mobility shift assays and a capture ELISA assay were used to assess NFκB transactivation in vitro. In addition, NFκB transactivation was also monitored in HEK-NFκBIA reporter cells using live cell luminometry.

RESULTS

Podocytes expressed the receptor for vitamin D. The vitamins did not suppress receptor for AGEs (RAGE) expression; instead, they rather upregulated RAGE. Although vitamin D3 and paricalcitol partly and differentially modified some of the studied parameters, both hormones inhibited AGE-BSA-induced NFκB transactivation, presumably by various mechanisms including the upregulation of IκB-α protein, keeping NFκB sequestered in an inactive state in the cytoplasm.

CONCLUSION

Vitamin D3 or its analog paricalcitol partly prevented AGE-mediated NFκB activation, an important feature of diabetic nephropathy (DN). Whether this in vitro finding is of clinical relevance to prevent/treat DN requires further studies.

Vitamin D and cardiovascular disease prevention

Vitamin D is a precursor of the steroid hormone calcitriol that is crucial for bone and mineral metabolism. Both the high prevalence of vitamin D deficiency in the general population and the identification of the vitamin D receptor in the heart and blood vessels raised interest in the potential cardiovascular effects of vitamin D. Experimental studies have demonstrated various cardiovascular protective actions of vitamin D, but vitamin D intoxication in animals is known to induce vascular calcification. In meta-analyses of epidemiological studies, vitamin D deficiency is associated with an increased cardiovascular risk. Findings from Mendelian randomization studies and randomized, controlled trials (RCTs) do not indicate significant effects of a general vitamin D supplementation on cardiovascular outcomes. Previous RCTs, however, were not adequately designed to address extraskeletal events, and did not focus on vitamin D-deficient individuals. Therefore, currently available evidence does not support cardiovascular benefits or harms of vitamin D supplementation with the commonly used doses, and whether vitamin D has cardiovascular effects in individuals with overt vitamin D deficiency remains to be evaluated. Here, we provide an update on clinical studies on vitamin D and cardiovascular risk, discuss ongoing vitamin D research, and consider the management of vitamin D deficiency from a cardiovascular health perspective.

Vitamin D and Diabetic Complications: True or False Prophet?

Vitamin D deficiency is now recognized as a condition of increasing prevalence worldwide. Vitamin D has an established role in calcium and bone metabolism; however, more recently associations with vitamin D deficiency and risk of developing diabetes, diabetes complications, and cardiovascular disease have all been acknowledged. The vitamin D receptor is ubiquitously expressed, and experimental, in vitro, and in vivo studies strongly suggest a role in regulating the transcription of multiple genes beyond calcium homeostasis. These include antiproliferative, immunomodulatory, angiogenic, inhibition of the renin-angiotensin-aldosterone system, and neurotrophic factor expression. Observational studies report a strong association between vitamin D deficiency and cardiovascular and metabolic disorders; however, there remains a paucity of large long-term randomized clinical trials showing a benefit with treatment. An increasing body of literature suggests a possible pathogenetic role of vitamin D in the long-term complications of diabetes and vitamin D deficiency may also exacerbate symptoms of painful diabetic peripheral neuropathy. It remains unknown if supplementation of vitamin D to normal or non-deficient levels alters pathogenetic processes related to diabetic microvascular complications. With the high prevalence of vitamin D deficiency in patients with diabetes and putative mechanisms linking vitamin D deficiency to diabetic complications, there is a compelling argument for undertaking large well-designed randomized controlled trials of vitamin D supplementation.