Vitamin D and glucose metabolism in chronic kidney disease

Are There Any Pleiotropic Benefits of Vitamin D in Patients With Diabetic Kidney Disease? A Systematic Review of Randomized Controlled Trials

Background

Type 2 diabetes (T2D) and kidney disease are risk factors for vitamin D deficiency. Native forms of vitamin D have a lower risk of hypercalcemia than calcitriol, the active hormone. The enzyme responsible for activating native vitamin D is now known to be expressed throughout the body; therefore, native vitamin D may have clinically relevant effects in many body systems.

Objective

The objective of this systematic review was to examine the effect of native vitamin D supplementation on clinical outcomes and surrogate laboratory measures in patients with T2D and diabetic kidney disease (DKD).

Design

Systematic review.

Setting

Randomized controlled trials (RCTs) conducted in any country.

Patients

Adults with T2D and DKD receiving supplementation with any form of native vitamin D (eg, ergocalciferol, cholecalciferol, calcifediol).

Measurements

Clinical outcomes and surrogate clinical and laboratory measures reported in each of the trials were included in this review.

Methods

The following databases were searched from inception to January 31, 2023: Embase, MEDLINE, Cochrane CENTRAL, Web of Science, ProQuest Dissertations and Theses, and medRxiv. Only RCTs examining supplementation with a native vitamin D form with a control or placebo comparison group were included. We excluded studies reporting only vitamin D status or mineral metabolism parameters, without any other outcomes of clinical relevance or surrogate laboratory measures. Study quality was evaluated using the Cochrane risk-of-bias tool (RoB2). Results were synthesized in summary tables for each type of outcome with the P values from the original studies displayed.

Results

Nine publications were included, corresponding to 5 separate RCTs (377 participants total). Mean age ranged from 40 to 63. All trials administered vitamin D3. Intervention groups experienced improvements in vitamin D status and a reduction in proteinuria in 4 of the 5 included RCTs. There was a decrease in low-density lipoprotein and total cholesterol in the 2 trials in which they were measured. Improvements in bone mass, flow-mediated dilation, and inflammation were also reported, but each was only measured in 1 RCT. Effects on glucose metabolism, high-density lipoprotein, triglycerides, blood pressure, oxidative stress, and kidney function were mixed. No serious adverse effects were reported.

Limitations

Limitations include the small number of RCTs and lack of information on the use of drugs that affect measured outcomes (eg, proteinuria-lowering renin-angiotensin-aldosterone system inhibitors and lipid-lowering medication) in most studies. Our study is also limited by the absence of a prestudy protocol and registration.

Conclusions

Native vitamin D is a safe treatment that improves vitamin D status in patients with DKD. Vitamin D may modify proteinuria and lipid metabolism in DKD, but further well-designed trials that include well-established treatments are necessary. Overall, there is limited evidence for beneficial pleiotropic effects of vitamin D in patients with DKD.

The Interplay between Immune and Metabolic Pathways in Kidney Disease

Kidney disease is a significant health problem worldwide, affecting an estimated 10% of the global population. Kidney disease encompasses a diverse group of disorders that vary in their underlying pathophysiology, clinical presentation, and outcomes. These disorders include acute kidney injury (AKI), chronic kidney disease (CKD), glomerulonephritis, nephrotic syndrome, polycystic kidney disease, diabetic kidney disease, and many others. Despite their distinct etiologies, these disorders share a common feature of immune system dysregulation and metabolic disturbances. The immune system and metabolic pathways are intimately connected and interact to modulate the pathogenesis of kidney diseases. The dysregulation of immune responses in kidney diseases includes a complex interplay between various immune cell types, including resident and infiltrating immune cells, cytokines, chemokines, and complement factors. These immune factors can trigger and perpetuate kidney inflammation, causing renal tissue injury and progressive fibrosis. In addition, metabolic pathways play critical roles in the pathogenesis of kidney diseases, including glucose and lipid metabolism, oxidative stress, mitochondrial dysfunction, and altered nutrient sensing. Dysregulation of these metabolic pathways contributes to the progression of kidney disease by inducing renal tubular injury, apoptosis, and fibrosis. Recent studies have provided insights into the intricate interplay between immune and metabolic pathways in kidney diseases, revealing novel therapeutic targets for the prevention and treatment of kidney diseases. Potential therapeutic strategies include modulating immune responses through targeting key immune factors or inhibiting pro-inflammatory signaling pathways, improving mitochondrial function, and targeting nutrient-sensing pathways, such as mTOR, AMPK, and SIRT1. This review highlights the importance of the interplay between immune and metabolic pathways in kidney diseases and the potential therapeutic implications of targeting these pathways.

18F-FDG PET/MRI Imaging in a Preclinical Rat Model of Cardiorenal Syndrome-An Exploratory Study

Cardiorenal syndrome (CRS) denotes the bidirectional interaction of chronic kidney disease and heart failure with an adverse prognosis but with a limited understanding of its pathogenesis. This study correlates biochemical blood markers, histopathological and immunohistochemistry features, and 2-deoxy-2-fluoro-D-glucose positron emission tomography (¹⁸F-FDG PET) metabolic data in low-dose doxorubicin-induced heart failure, cardiorenal syndrome, and renocardiac syndrome induced on Wistar male rats. To our knowledge, this is the first study that investigates the underlying mechanisms for CRS progression in rats using ¹⁸F-FDG PET. Clinical, metabolic cage monitoring, biochemistry, histopathology, and immunohistochemistry combined with PET/MRI (magnetic resonance imaging) data acquisition at distinct points in the disease progression were employed for this study in order to elucidate the available evidence of organ crosstalk between the heart and kidneys. In our CRS model, we found that chronic treatment with low-dose doxorubicin followed by acute 5/6 nephrectomy incurred the highest mortality among the study groups, while the model for renocardiac syndrome resulted in moderate-to-high mortality. ¹⁸F-FDG PET imaging evidenced the doxorubicin cardiotoxicity with vascular alterations, normal kidney development damage, and impaired function. Given the fact that standard clinical markers were insensitive to early renal injury, we believe that the decreasing values of the ¹⁸F-FDG PET-derived renal marker across the groups and, compared with their age-matched controls, along with the uniform distribution seen in healthy developing rats, could have a potential diagnostic and prognostic yield in cardiorenal syndrome.

Effects of Calcium Fortified Beverage Intake on Insulin Sensitivity and Antioxidant Metabolism in Healthy Elderly

Calcium, one of the most important nutrients, determines the quality of life of the elderly. It has been reported that 7 out of 10 people over the age of 60 have insufficient calcium intake. The purpose of this study was to evaluate the effect of calcium fortified beverage (CFB) intake on insulin sensitivity and antioxidant metabolism in healthy elderly. A crossover clinical trial was performed and antioxidant status of healthy elderly (age above 65 years, n = 8) was analyzed. Subjects did not take CFB for 0–3 weeks. They then took it for 3–6 weeks. CFB supplementation decreased insulin levels (Δ3–6 weeks: 1.19 ± 0.65 μ IU/mL → Δ0–3 weeks: −0.58 ± 0.38 μ IU/mL). Increasing degree of fasting blood glucose level was suppressed by intake of CFB, although the suppression was not statistically significant. Except for insulin, there were no significant differences in results of biochemical analysis between 0–3 weeks and 3–6 weeks. Catalase activity was significantly increased by CFB supplementation (Δ3–6 weeks: 3.50 ± 5.30 K g/Hb) compared to the no CFB supplementation period (Δ0–3 weeks: −12.48 ± 4.37 K g/Hb). However, the activity of superoxide dismutase and glutathione-peroxidase were not significantly different between 0–3 weeks and 3–6 weeks. H₂O₂-induced DNA oxidative damage was also decreased significantly by CFB supplementation. Taken together, these results indicate that CFB has beneficial effect on insulin sensitivity and some antioxidant enzymes in healthy elderly.

The Impact of Comorbidities on the Pharmacological Management of Type 2 Diabetes Mellitus

Diabetes mellitus affects over 20% of people aged > 65 years. With the population of older people living with diabetes growing, the condition may be only one of a number of significant comorbidities that increases the complexity of their care, reduces functional status and inhibits their ability to self-care. Coexisting comorbidities may compete for the attention of the patient and their healthcare team, and therapies to manage comorbidities may adversely affect a person's diabetes. The presence of renal or liver disease reduces the types of antihyperglycemic therapies available for use. As a result, insulin and sulfonylurea-based therapies may have to be used, but with caution. There may be a growing role for sodium-glucose co-transporter 2 (SGLT-2) inhibitors in diabetic renal disease and for glucagon-like peptide (GLP)-1 therapy in renal and liver disease (nonalcoholic steatohepatitis). Cancer treatments pose considerable challenges in glucose therapy, especially the use of cyclical chemotherapy or glucocorticoids, and cyclical antihyperglycemic regimens may be required. Clinical trials of glucose lowering show reductions in microvascular and, to a lesser extent, cardiovascular complications of diabetes, but these benefits take many years to accrue, and evidence specifically in older people is lacking. Guidelines recognize that clinicians managing patients with type 2 diabetes mellitus need to be mindful of comorbidity, particularly the risks of hypoglycemia, and ensure that patient-centered therapeutic management of diabetes is offered. Targets for glucose control need to be carefully considered in the context of comorbidity, life expectancy, quality of life, and patient wishes and expectations. This review discusses the role of chronic kidney disease, chronic liver disease, cancer, severe mental illness, ischemic heart disease, and frailty as comorbidities in the therapeutic management of hyperglycemia in patients with type 2 diabetes mellitus.

Diabetic Hemodialysis: Vitamin D Supplementation and its Related Signaling Pathways Involved in Insulin and Lipid Metabolism

BACKGROUND

This study was conducted to determine the effects of vitamin D supplementation on some of the gene expressions related to insulin and lipid metabolism in diabetic hemodialysis (HD) patients.

METHODS

A double-blind, randomized, placebo-controlled clinical trial was carried out in 55 patients with diabetic HD. The current project used two groups in which each subject received vitamin D supplements (50,000 IU, n=28) or placebo (50,000 IU, n=27) every 2 weeks for 12 weeks. Gene expression analyses (RT-PCR) were included to obtain the rate of gene expression of the related insulin and lipid metabolism genes in peripheral blood mononuclear cells (PBMCs) of patients with diabetic HD.

RESULTS

Our data revealed that consumption of vitamin D supplementation enables to overexpress the peroxisome proliferation-activated receptor gamma (PPAR-γ) (P=0.001), AKT (P=0.04), PI3K (P=0.02), insulin receptor substrate-1 (IRS1) (P0.008) and glucose transporter type 4 (GLUT-4) (P=0.01) and downregulate the expression of protein kinase C (PKC) (P=0.001) in patients with diabetic HD than control group following the 12-week intervention. In addition, vitamin D supplementation downregulated low-density lipoprotein receptor (LDLR) (P=0.03) expression in the subjects with diabetic HD than the control group. Vitamin D supplementation did not show any effects on the expression of pyruvate dehydrogenase kinase 1 (PDK1) (P=0.37), IRS2 (P=0.90) and lipoprotein (a) [Lp(a)] (P=0.05).

CONCLUSION

Our findings confirmed that diabetic HD subjects who received the vitamin D supplementation (for 12 weeks), showed a significant overexpression in the PPAR-γ, AKT, PI3K, IRS1 and GLUT4 genes, and also showed a significant downregulation in the PKC and LDLR genes. Moreover, no effects on PDK1, IRS2 and Lp(a) expression were observed.

Serum Vitamin D and Its Upregulated Protein, Thioredoxin Interacting Protein, Are Associated With Beta-Cell Dysfunction in Adult Patients With Type 1 and Type 2 Diabetes

OBJECTIVES

Diabetes mellitus is characterized by either complete deficiency of insulin secretion, as in type 1 diabetes, or decompensation of the pancreatic beta cells in type 2 diabetes. Both vitamin D (vitD) and thioredoxin interacting protein (TXNIP) have been shown to be involved in beta-cell dysfunction. Therefore, this study was designed to examine vitD and TXNIP serum levels in patients with diabetes and to correlate these levels with beta-cell function markers in both types of diabetes.

METHODS

The routine biochemical parameters and the serum levels of vitD and TXNIP were measured in 20 patients with type 1 diabetes and 20 patients with type 2 diabetes. The levels were then compared to those of 15 healthy control volunteers. Insulin, C-peptide and proinsulin (PI), vitD and TXNIP were measured by ELISA. Beta-cell dysfunction was assessed by homeostatic model assessment (HOMA-beta), proinsulin-to-C-peptide (PI/C) and proinsulin-to-insulin (PI/I) ratios. Correlations among various parameters were studied.

RESULTS

Patients with type 1 diabetes had significantly lower HOMA-beta, vitD and TXNIP levels; however, they had higher PI/C levels than the control group. Meanwhile, patients with type 2 diabetes had significantly higher C-peptide, proinsulin, PI/C, HOMA-insulin resistance (HOMA-IR) and lower HOMA-beta and vitD levels, with no significant difference in TXNIP levels as compared to the control group. In addition, vitD was significantly correlated positively with HOMA-beta and TXNIP and negatively with PI, PI/C, PI/I and HOMA-IR. TXNIP correlated positively with HOMA-beta and negatively with PI/C.

CONCLUSIONS

Our data showed that vitD and TXNIP were associated with different beta-cell dysfunction markers, indicating their potential abilities to predict the beta-cell status in people with diabetes.

The Effects of Vitamin D Supplementation on Signaling Pathway of Inflammation and Oxidative Stress in Diabetic Hemodialysis: A Randomized, Double-Blind, Placebo-Controlled Trial

Objective: This study was carried out to determine the effects of vitamin D supplementation on signaling pathway of inflammation and oxidative stress in diabetic hemodialysis (HD) patients.

Methods: This randomized double-blind placebo-controlled clinical trial was conducted among 60 diabetic HD patients. Subjects were randomly allocated into two groups to intake either vitamin D supplements at a dosage of 50,000 IU (n = 30) or placebo (n = 30) every 2 weeks for 12 weeks. Gene expression of inflammatory cytokines and biomarkers of oxidative stress were assessed in peripheral blood mononuclear cells (PBMCs) of diabetic HD patients with RT-PCR method.

Results: Results of RT-PCR indicated that after the 12-week intervention, compared to the placebo, vitamin D supplementation downregulated gene expression of interleukin (IL)-1β (P = 0.02), tumor necrosis factor alpha (TNF-α) (P = 0.02) and interferon gamma (IFN-γ) (P = 0.03) in PBMCs of diabetic HD patients. Additionally, vitamin D supplementation, compared to the placebo, downregulated gene expression of transforming growth factor beta (TGF-β) (P = 0.04), protein kinase C (PKC) (P = 0.001), and mitogen-activated protein kinases 1 (MAPK1) (P = 0.02) in PBMCs of diabetic HD patients. Although not significant, vitamin D supplementation let to a reduction of nuclear factor kappa B (NF-kB) (p = 0.75) expression in PBMCs isolated from diabetic patients compared to the placebo group. There was no statistically significant change following supplementation with vitamin D on gene expression of interleukin (IL)-4, IL-6, and vascular endothelial growth factor (VEGF) in PBMCs of diabetic HD patients.

Conclusions: Overall, we found that vitamin D supplementation for 12 weeks among diabetic HD patients had beneficial effects on few gene expression related to inflammation and oxidative stress.

Clinical trial registration: IRCT201701035623N101. Registered on January 8, 2017.

Clinical Trial on the Effects of Vitamin D Supplementation on Metabolic Profiles in Diabetic Hemodialysis

The current study was conducted to assess the effects of vitamin D supplementation on insulin metabolism, lipid fractions, biomarkers of inflammation, and oxidative stress in diabetic hemodialysis (HD) patients. This randomized double-blind placebo-controlled clinical trial was carried out among 60 diabetic HD patients. Subjects were randomly allocated into two groups to intake either oral vitamin D3 supplements at a dosage of 50 000 IU (n=30) or placebo (n=30) every 2 weeks for 12 weeks. After 12 weeks of intervention, subjects who received vitamin D supplements compared with the placebo had significantly decreased serum insulin concentrations (-3.4±3.7 vs. +2.0±4.2 μIU/ml, p<0.001), homeostasis model of assessment-estimated insulin resistance (HOMA-IR) (-1.2±1.8 vs. +0.9±2.3, p<0.001), and improved quantitative insulin sensitivity check index (QUICKI) (+0.02±0.03 vs. -0.01±0.02, p<0.001). In addition, compared with the placebo, vitamin D supplementation led to significant reductions in serum high-sensitivity C-reactive protein (hs-CRP) (-1.4±2.5 vs. +1.4±4.8 mg/l, p=0.007), plasma malondialdehyde (MDA) (-0.1±0.2 vs. +0.1±0.2 μmol/l, p=0.009) and a significant increase in plasma total antioxidant capacity (TAC) concentrations (+33.8±56.7 vs. -2.0±74.5 mmol/l, p=0.04). We did not see any significant effect of vitamin D supplementation on lipid profiles and other biomarkers of inflammation and oxidative stress compared with the placebo. Overall, we found that vitamin D supplementation had beneficial effects on serum insulin, HOMA-IR, QUICKI, serum hs-CRP, plasma MDA, and TAC levels among diabetic HD patients for 12 weeks. CLINICAL REGISTRATION:: http://www.irct.ir: IRCT201611155623N92.

Metabolic profiling of a chronic kidney disease cohort reveals metabolic phenotype more likely to benefit from a probiotic

SCOPE

Persistent reduction in Glomerular Filtration Rate (GFR) is a hallmark of Chronic Kidney Disease (CKD) and is associated with an elevation of Blood Urea Nitrogen (BUN). This metabolomics pilot study sought to identify metabolites that differentiated patients with CKD whose BUN decreased on a probiotic and possible mechanisms.

METHODS AND RESULTS

Metabolomics was used to analyze baseline plasma samples previously diagnosed with CKD Stage III-IV. Patients had participated in a dose escalation study of the probiotic Renadyl™. A total of 24 samples were categorized depending on whether BUN increased or decreased from baseline after 4 months of probiotic use. Multivariate analysis was used to analyze the data and determine the metabolites that best differentiated the phenotypic groups. The sixteen patients who had a decrease in BUN were not significantly different based on demographic and clinical measures from those whose BUN increased or did not change with the exception of age. Eleven of the fourteen metabolites that differentiated the groups were known to be modulated by gut microflora, which may eventually provide a mechanistic link between probiotic and outcomes.

CONCLUSIONS

Metabolomics revealed metabolites at baseline that may predict individuals with CKD that would most benefit from a probiotics.

Nutritional Vitamin D in Renal Transplant Patients: Speculations and Reality

Reduced levels of nutritional vitamin D are commonly observed in most chronic kidney disease (CKD) patients and particularly in patients who have received a kidney transplant (KTx). In the complex clinical scenario characterizing the recipients of a renal graft, nutritional vitamin D deficiency has been put in relation not only to the changes of mineral and bone metabolism (MBM) after KTx, but also to most of the medical complications which burden KTx patients. In fact, referring to its alleged pleiotropic (non-MBM related) activities, vitamin D has been claimed to play some role in the occurrence of cardiovascular, metabolic, immunologic, neoplastic and infectious complications commonly observed in KTx recipients. Furthermore, low nutritional vitamin D levels have also been connected with graft dysfunction occurrence and progression. In this review, we will discuss the purported and the demonstrated effects of native vitamin D deficiency/insufficiency in most of the above mentioned fields, dealing separately with the MBM-related and the pleiotropic effects.

Study of the effect of vitamin D supplementation on glycemic control in type 2 diabetic prevalent hemodialysis patients

Vitamin D is claimed to have an adjuvant effect on glycemic control by dual action on pancreatic β-cells and insulin resistance. The aim of this study was to assess the possible effect of short-term alfacalcidol supply on glycemic control in type 2 diabetic hemodialysis (HD) patients. Twenty type 2 diabetic HD patients (using diet and oral drugs but not insulin) were randomly selected from our dialysis unit as well as 20 non-diabetic HD patients as control. A third group of 12 healthy subjects were studied as well. All three groups were similar in age, sex, and body mass index. Oral alfacalcidol therapy was administrated daily as recommended by Kidney Disease Outcomes Quality Initiative (K/DOQI) guidelines for 12 weeks guided by monthly serum phosphorus and Cax PO4 product. Corrected total calcium, phosphorus, intact parathyroid hormone, 25-hydroxy vitamin D (25[OH]D), and glucoparameters (fasting blood glucose, glycated hemoglobin [HbA1c%], insulin resistance by homeostatic model assessment, and β-cell function by HOMA-β%) were measured under basal conditions and after 3 months of therapy. 25(OH)D was non-significantly lower in diabetic than non-diabetic HD patients, but significantly lower than healthy subjects at the start of the study. However, vitamin D level increased significantly after 3 months of trial, although the levels did not reach normal values. This vitamin D rise was associated with highly significant improvement in concentrations of fasting blood sugar (FBS), fasting insulin, HbA1c%, and HOMA-β-cell function in diabetic and non-diabetic controls. However, there was a significant rise in insulin resistance after treatment. The percentage of change was evident more in diabetics regarding FBS and 25(OH)D concentration. Adjustment of 25(OH)D level in type 2 diabetic prevalent HD patients may improve, at least with short-term therapy, glycemic control mainly through improving β-cell function.

Effect of Vitamin D Receptor Activators on Glomerular Filtration Rate: A Meta-Analysis and Systematic Review

Background

Vitamin D receptor activators (VDRAs) can protect against mineral bone disease, but they are reported to elevate serum creatinine (SCr) and may also reduce glomerular filtration rate (GFR).

Methods

We conducted a systematic review and meta-analysis of randomized clinical trials (RCTs) to evaluate the effect of VDRAs on kidney function and adverse events. MEDLINE, EMBASE, the Cochrane Controlled Trials Register were searched for RCTs that evaluate vitamin D receptor activators (alfacalcidol, calcitriol, doxercalciferol, falecalcitriol, maxacalcitol and paricalcitol) up to March 2015.

Results

We included 31 studies, all of which were performed between 1976 and 2015, which enrolled 2621 patients. Patients receiving VDRAs had lower eGFR (weighted mean difference WMD -1.29 mL/min /1.73 m², 95% CI -2.42 to -0.17) and elevated serum creatinine (WMD 7.03 μmol/L, 95% CI 0.61 to 13.46) in sensitivity analysis excluding studies with dropout rate more than 30%. Subgroup analysis of the 5 studies that not use SCr-based measures did not indicated lower GFR in the VDRAs group(WMD -0.97 mL/min/1.73 m2, 95% CI -4.85 to 2.92). Compared with control groups, there was no difference in all-cause mortality (relative risk RR 1.41, 95% CI 0.58 to 3.80), cardiovascular disease (RR 0.84, 95% CI 0.42 to 1.71), and severe adverse events (RR 1.15, 95% CI 0.75 to 1.77) for the VDRAs groups. Episodes of hypercalcemia (RR 3.29, 95% CI 2.02 to 5.38) were more common in the VDRAs group than in the control group.

Conclusions

Administration of VDRAs increased serum creatinine levels. Subgroup analysis of studies that did not use SCr-based measures did not indicate a lower GFR in the VDRA group. Future studies with non-SCr-based measures are needed to assess whether the mild elevations of serum creatinine are of clinical significance.

Vitamin D and Clinical Outcomes in Dialysis

Most dialysis patients are vitamin D deficient, including deficiencies in both activated vitamin D (1, 25-dihydroxyvitamin D) and the less active 25-hydroxyvitamin D. These and other abnormalities associated with chronic kidney disease (CKD), if they remain untreated, lead to secondary hyperparathyroidism and bone changes, such as osteitis fibrosa cystica. Activated vitamin D has been proven to decrease parathyroid hormone (PTH) levels in dialysis patients and is currently used for this indication. There are multiple other potential "pleotrophic" effects associated with vitamin D therapy. These include associations with lower all-cause and cardiovascular mortality, lower rates of infections and improved glycemic indexes. Meta-analyses of multiple observational studies have shown activated vitamin D therapy to be associated with improved survival. Observational data also suggest fewer infections and better glucose control. There have been no randomized clinical trials powered to evaluate mortality or other clinical outcomes. Small trials of nutritional vitamin D (ergocalciferol and cholecalciferol) showed increases in 25-hydroxyvitamin D levels without hypercalcemia or hyperphosphatemia, even when given in addition to activated vitamin D therapy. While activated vitamin D therapy is associated with improved outcomes, it also leads to higher fibroblast growth factor 23 (FGF-23) levels, which may be detrimental in dialysis patients. Further research is needed to evaluate whether activated or nutritional vitamin D therapy are beneficial in dialysis patients for outcomes other than secondary hyperparathyroidism.

Beneficial effects of calcitriol on hypertension, glucose intolerance, impairment of endothelium-dependent vascular relaxation, and visceral adiposity in fructose-fed hypertensive rats

Besides regulating calcium homeostasis, the effects of vitamin D on vascular tone and metabolic disturbances remain scarce in the literature despite an increase intake with high-fructose corn syrup worldwide. We investigated the effects of calcitriol, an active form of vitamin D, on vascular relaxation, glucose tolerance, and visceral fat pads in fructose-fed rats. Male Wistar-Kyoto rats were divided into 4 groups (n = 6 per group). Group Con: standard chow diet for 8 weeks; Group Fru: high-fructose diet (60% fructose) for 8 weeks; Group Fru-HVD: high-fructose diet as Group Fru, high-dose calcitriol treatment (20 ng / 100 g body weight per day) 4 weeks after the beginning of fructose feeding; and Group Fru-LVD: high-fructose diet as Group Fru, low-dose calcitriol treatment (10 ng / 100 g body weight per day) 4 weeks after the beginning of fructose feeding. Systolic blood pressure was measured twice a week by the tail-cuff method. Blood was examined for serum ionized calcium, phosphate, creatinine, glucose, triglycerides, and total cholesterol. Intra-peritoneal glucose intolerance test, aortic vascular reactivity, the weight of visceral fat pads, adipose size, and adipose angiotensin II levels were analyzed at the end of the study. The results showed that the fructose-fed rats significantly developed hypertension, impaired glucose tolerance, heavier weight and larger adipose size of visceral fat pads, and raised adipose angiotensin II expressions compared with the control rats. High- and low-dose calcitriol reduced modestly systolic blood pressure, increased endothelium-dependent aortic relaxation, ameliorated glucose intolerance, reduced the weight and adipose size of visceral fat pads, and lowered adipose angiotensin II expressions in the fructose-fed rats. However, high-dose calcitriol treatment mildly increased serum ionized calcium levels (1.44 ± 0.05 mmol/L). These results suggest a protective role of calcitriol treatment on endothelial function, glucose tolerance, and visceral adiposity in fructose-fed rats.

Vitamin D receptor activator and dietary sodium restriction to reduce residual urinary albumin excretion in chronic kidney disease (ViRTUE study): rationale and study protocol

Optimal albuminuria reduction is considered essential to halting chronic kidney disease (CKD) progression. Both vitamin D receptor activator (VDRA) treatment and dietary sodium restriction potentiate the efficacy of renin-angiotensin-aldosterone-system (RAAS) blockade to reduce albuminuria. The ViRTUE study addresses whether a VDRA in combination with dietary sodium restriction provides further albuminuria reduction in non-diabetic CKD patients on top of RAAS blockade. The ViRTUE study is an investigator-initiated, prospective, multi-centre, randomized, double-blind (paricalcitol versus placebo), placebo-controlled trial targeting stage 1-3 CKD patients with residual albuminuria of >300 mg/day due to non-diabetic glomerular disease, despite angiotensin-converting enzyme inhibitor or angiotensin receptor blocker use. During run-in, all subjects switched to standardized RAAS blockade (ramipril 10 mg/day) and blood pressure titrated to <140/90 mmHg according to a standardized protocol. Eligible patients are subsequently enrolled and undergo four consecutive study periods in random order of 8 weeks each: (i) paricalcitol (2 µg/day) combined with a liberal sodium diet (∼200 mmol Na(+)/day, i.e. mean sodium intake in the general population), (ii) paricalcitol (2 µg/day) combined with dietary sodium restriction (target: 50 mmol Na(+)/day), (iii) placebo combined with a liberal sodium diet and (iv) placebo combined with dietary sodium restriction. Data are collected at the end of each study period. The primary outcome is 24-h urinary albumin excretion. Secondary study outcomes are blood pressure, renal function (estimated glomerular filtration rate), plasma renin activity and, in a sub-population (N = 9), renal haemodynamics (measured glomerular filtration rate and effective renal plasma flow). A sample size of 50 patients provides 90% power to detect a 23% reduction in albuminuria, assuming a 25% dropout rate. Further reduction of residual albuminuria by combination of VDRA treatment and sodium restriction during single-agent RAAS-blockade will justify long-term studies on cardiorenal outcomes and safety.

CLINICAL TRIAL REGISTRATION

NTR2898 (Dutch trial register).

The effects of short-term vitamin D supplementation on glucose metabolism in dialysis patients: a systematic review and meta-analysis

PURPOSE

We tested whether short-term vitamin D supplementation improves insulin resistance in patients with kidney disease, a condition with little intrinsic vitamin D activity.

METHODS

PubMed, EMBASE and CENTRAL were searched for relevant observational studies and randomized clinical trials (RCTs). Random-effects models were employed for meta-analysis, and effect sizes were summarized as standardized mean difference (SMD) with 95% confidence intervals. Separate analyses were done for RCTs and non-randomized intervention studies (NRIS).

RESULTS

Seventeen studies (5 RCTs and 12 NRIS) were included. The meta-analysis population (n = 131) was mostly middle aged (40-50 years), male and non-diabetic, and on hemodialysis. The duration (4-12 weeks) and type of supplementation varied between studies. Among RCTs, compared to placebo, vitamin D supplementation was associated with significant decrease in fasting glucose [SMD -1.13, (-2.11 to -0.11)] and PTH levels [SMD -1.50, (-2.95 to -0.04)] but no difference in fasting insulin levels [SMD 1.32, (-0.15 to 2.79)]. Among NRIS, there was only a significant decrease in PTH levels [SMD -1.68, (-2.55 to -0.82)] between pre- and post-vitamin D treatment levels.

CONCLUSIONS

Short-term (4-12 weeks) supplementation with vitamin D is associated with lower fasting glucose levels in ESRD with no change in fasting insulin levels. However, the findings from this study are limited by the studies that were used in the meta-analysis, which were mostly small, used multiple different vitamin D compounds and dosing regimens, and had large heterogeneity, and funnel plots showed that there was a dearth of studies with null or negative finding. Therefore, larger RCTs need to be performed to answer this important clinical question.

Uric acid suppresses 1 alpha hydroxylase in vitro and in vivo

OBJECTIVE

Patients with gout have lower calcitriol levels that improve when uric acid is lowered. The mechanism of these observations is unknown. We hypothesized that uric acid inhibits 1-αhydroxylase.

MATERIALS AND METHODS

In vivo, Sprague Dawley rats were randomized to control (n = 5), allantoxanamide (n=8), febuxostat (n=5), or allantoxanamide+febuxostat (n = 7). Vitamin D, PTH, and 1-αhydroxylase protein were evaluated. In order to directly evaluate the effect of uric acid on 1-αhydroxylase, we conducted a series of dose response and time course experiments in vitro. Nuclear factor κ-B (NFκB) was inhibited pharmacologically. Finally, to evaluate the potential implications of these findings in humans, the association between uric acid and PTH in humans was evaluated in a cross-sectional analysis of data from the NHANES (2003-2006); n = 9773.

RESULTS

1,25(OH)2D and 1-αhydroxylase protein were reduced in hyperuricemic rats and improved with febuxostat treatment. Uric acid suppressed 1-αhydroxylase protein and mRNA expression in proximal tubular cells. This was prevented by NFκB inhibition. In humans, for every 1mg/dL increase in uric acid, the adjusted odds ratio for an elevated PTH (>65 pg/mL) was 1.21 (95% C.I. 1.14, 1.28; P<0.0001), 1.15 (95% C.I. 1.08, 1.22; P<0.0001), and 1.16 (95% C.I. 1.03, 1.31; P = 0.02) for all subjects, subjects with estimated GFR ≥ 60, and subjects with estimated GFR <60 mL/min/1.73 m(2) respectively.

CONCLUSION

Hyperuricemia suppresses 1-αhydroxylase leading to lower 1,25(OH)2D and higher PTH in rats. Our results suggest this is mediated by NFκB. The association between uric acid and PTH in NHANES suggests potential implications for human disease.

Defective bone microstructure in hydronephrotic mice: a histomorphometric study in ICR/Mlac-hydro mice

Chronic renal impairment can lead to bone deterioration and abnormal bone morphology, but whether hydronephrosis is associated with bone loss remains unclear. Herein, we aimed to use computer-assisted bone histomorphometric technique to investigate microstructural bone changes in Imprinting Control Region (ICR) mice with a spontaneous mutation that was associated with bilateral nonobstructive hydronephrosis (ICR/Mlac-hydro). The results showed that 8-week-old ICR/Mlac-hydro mice manifested decreases in trabecular bone number and thickness, and an increased trabecular separation, thereby leading to a reduction in trabecular bone volume compared with the wild-type mice. Furthermore, histomorphometric parameters related to both bone resorption and formation, that is, eroded surface, osteoclast surface, and osteoblast surface, were much lower in ICR/Mlac-hydro mice than in the wild type. A decrease in moment of inertia was found in ICR/Mlac-hydro mice, indicating a decrease in bone strength. In conclusion, ICR/Mlac-hydro mice exhibited trabecular bone loss, presumably caused by marked decreases in both osteoblast and osteoclast activities, which together reflected abnormally low bone turnover. Thus, this mouse strain appeared to be a valuable model for studying the hydronephrosis-associated bone disease.

Can vitamin D slow down the progression of chronic kidney disease?

Pharmacological blockade of the renin-angiotensin-aldosterone system (RAAS) is the cornerstone of renoprotective therapy, and the reduction of persistent RAAS activation is considered to be an important target in the treatment of chronic kidney disease (CKD). Vitamin D is a steroid hormone that controls a broad range of metabolic and cell regulatory functions. It acts as a transcription factor and can suppress the renin gene, thereby acting as a negative endocrine regulator of RAAS. RAAS activation can reduce renal Klotho expression, and the Klotho-fibroblast growth factor 23 interaction may further reduce the production of active vitamin D. Results from both clinical and experimental studies suggest that vitamin D therapy is associated with a reduction in blood pressure and left ventricular hypertrophy and improves cardiovascular outcomes. In addition, a reduction in angiotensin II through RAAS blockade may have anti-proteinuric and anti-fibrotic effects. Vitamin D has also been shown to modulate the immune system, regulate inflammatory responses, improve insulin sensitivity and reduce high-density lipoprotein cholesterol. Taken together, these pleiotropic effects of vitamin D may slow down the progression of CKD. In this review, we discuss the experimental and early clinical findings that suggest a renoprotective effect of vitamin D, thereby providing an additional rationale beyond mineral metabolism for the close monitoring of, and supplementation with vitamin D from the earliest stages of CKD.

A pilot study of active vitamin D administration and insulin resistance in African American patients undergoing chronic hemodialysis

OBJECTIVE

Insulin resistance (IR) is associated with increased cardiovascular risk in multiple patient populations, including those undergoing chronic hemodialysis (CHD). Active vitamin D deficiency has been proposed to play a role in the extent of IR observed in patients with CHD. We postulated that administration of paracalcitol, an active vitamin D medication, influences IR in patients with CHD.

DESIGN AND METHODS

This was a pilot randomized controlled trial. Ten prevalent CHD patients receiving a stable dose of paracalcitol were recruited. Paracalcitol was withheld for 8 weeks in all patients (phase I). Parathyroid hormone levels were managed with the calcium-sensing receptor agonist cinacalcet. At week 8, patients were randomized to continue cinacalcet or to restart paracalcitol for 8 weeks (phase II). The primary outcome was the change in IR measured by the glucose disposal rate (GDR) using hyperinsulinemic euglycemic clamp (HEGC) method. Secondary outcomes included changes in IR between groups in indirect indices of IR, biomarkers of inflammation, and adipokine levels.

RESULTS

The mean age was 49 years (range, 46-57 years) and 40% of patients were women. There was no detectable change in the GDR at the end of phase I (P = .7) when compared with baseline values. There was also no statistically significant difference in GDR between groups at the end of phase II (P = .9). No changes were observed in indirect indices of IR, adipokine levels, or biomarkers of inflammation in either phase.

CONCLUSION

The results of this pilot study suggest that withdrawal of paracalcitol over 8 to 16 weeks and replacement for 8 weeks after withdrawal does not influence IR measured by HEGC in patients receiving CHD.

Paricalcitol does not improve glucose metabolism in patients with stage 3-4 chronic kidney disease

Patients with chronic kidney disease are often insulin resistant and glucose intolerant--abnormalities that promote cardiovascular disease. Administration of 1,25-dihydroxyvitamin D (calcitriol) has improved glucose metabolism in patients with end-stage renal disease. We conducted a randomized, placebo-controlled clinical trial to test whether paricalcitol, a 1,25-dihydroxyvitamin D analog, changes glucose tolerance in earlier stages of chronic kidney disease. In a crossover design, 22 nondiabetic patients with estimated glomerular filtration rates of stage 3-4 chronic kidney disease and fasting plasma glucose of 100-125 mg/dl were given daily oral paricalcitol for 8 weeks and matching placebo for 8 weeks, separated by an 8-week washout period. The order of interventions was random and blinded to both participants and investigators. Paricalcitol significantly reduced serum concentrations of parathyroid hormone, 1,25-dihydroxyvitamin D, and 25-hydroxyvitamin D while significantly increasing serum concentrations of fibroblast growth factor-23 and 24,25-dihydroxyvitamin D. Paricalcitol, however, had no significant effect on glucose tolerance (the primary outcome measure), insulin sensitivity, beta-cell insulin response, plasma free fatty acid suppression, or urinary F2-isoprostane excretion. Thus, despite substantial effects on vitamin D metabolism, paricalcitol did not improve glucose metabolism in nondiabetic patients with stage 3-4 chronic kidney disease.

Insulin resistance in patients with chronic kidney disease

Metabolic syndrome and its components are associated with chronic kidney disease (CKD) development. Insulin resistance (IR) plays a central role in the metabolic syndrome and is associated with increased risk for CKD in nondiabetic patients. IR is common in patients with mild-to-moderate stage CKD, even when the glomerular filtration rate is within the normal range. IR, along with oxidative stress and inflammation, also promotes kidney disease. In patients with end stage renal disease, IR is an independent predictor of cardiovascular disease and is linked to protein energy wasting and malnutrition. Systemic inflammation, oxidative stress, elevated serum adipokines and fetuin-A, metabolic acidosis, vitamin D deficiency, depressed serum erythropoietin, endoplasmic reticulum stress, and suppressors of cytokine signaling all cause IR by suppressing insulin receptor-PI3K-Akt pathways in CKD. In addition to adequate renal replacement therapy and correction of uremia-associated factors, thiazolidinedione, ghrelin, protein restriction, and keto-acid supplementation are therapeutic options. Weight control, reduced daily prednisolone dosage, and the use of cyclosporin decrease the risk of developing new-onset diabetes after kidney transplantation. Improved understanding of the pathogenic mechanisms underlying IR in CKD may lead to more effective therapeutic strategies to reduce uremia-associated morbidity and mortality.

Vitamin D deficiency in hemodialysis patients

BACKGROUND

Vitamin D [(25(OH)D] deficiency and insufficiency is common in patients with chronic kidney disease (CKD). 25(OH)D has been found to have beneficial effects on bone, cardiovascular and immune functions. There are little data about vitamin D levels in Indian patients on dialysis. This study was undertaken to determine the vitamin D status of Indian CKD patients on hemodialysis.

MATERIALS AND METHODS

We included 45 patients on maintenance hemodialysis coming to Medanta, Medicity, Gurgaon. 25(OH)D levels were measured with radioimmunoassay (Diasorin) method and parathyroid hormone (PTH) was measured using electrochemiluminiscence immunoassay (ECLIA).

RESULTS

The mean age of patients was 55 ± 13 years. 32/45 (71%) were males. 23/45 (51%) were diabetics. The median duration of hemodialysis was 5.5 months (range 1-74 months). 33/45 (74%) patients were on thrice weekly hemodialysis. The mean level of vitamin D was 10.14 ± 8.7 ng/ml. Majority of the patients [43/45 (95.5%)] were either vitamin D deficient or had insufficient levels. 40/45 (88.9%) were vitamin D deficient (levels <20 ng/ml); of these, 29/40 (64.4%) had severe vitamin D deficiency (levels <10 ng/ml) and 3/45 (6.7%) had insufficient levels (20-30 ng/ml) of vitamin D. Only 2/45 (4.4%) patients had normal levels of vitamin D. 23/45 (51%) of patients were receiving calcitriol. The mean levels of serum calcium, phosphorus, alkaline phosphatase, and albumin were 8.8 ± 0.64 mg/dl, 5.0 ± 0.7 mg/dl, 126 ± 10.3 IU/l and 3.6 ± 0.62 g/dl, respectively. PTH levels ranged from 37 to 1066 pg/ml, and the median was 195.8 pg/ml. There was a weak correlation between 25(OH)D levels and weight, sex, hemoglobin, albumin, alkaline phosphatase, and presence of diabetes. There was, however, no correlation with duration of dialysis or PTH levels.

CONCLUSION

Vitamin D deficiency and insufficiency are universal in our hemodialysis patients, with severe vitamin D deficiency in two-third of patients.

Chronic kidney disease, insulin resistance, and incident diabetes in older adults

BACKGROUND AND OBJECTIVES

Insulin resistance is a complication of advanced CKD. Insulin resistance is less well characterized in earlier stages of CKD. The response of the pancreatic β cell, effects on glucose tolerance, and risk of diabetes are not clear.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The Cardiovascular Health Study included 4680 adults without baseline diabetes. The Chronic Kidney Disease Epidemiology Collaboration creatinine equation was used to obtain the estimated GFR (eGFR). Insulin resistance was evaluated as fasting insulin concentration. The insulin sensitivity index, β cell function, and glucose tolerance were assessed by oral glucose tolerance testing. Incident diabetes was defined as fasting glucose ≥126 mg/dl, nonfasting glucose ≥200 mg/dl, or use of glucose-lowering medications.

RESULTS

Mean age was 72.5 years (range, 65-98 years). Mean eGFR was 72.2 (SD 17.1) ml/min per 1.73 m(2). After adjustment, each 10 ml/min per 1.73 m(2) lower eGFR was associated with a 2.2% higher fasting insulin concentration (95% confidence interval [CI], 1.4%, 2.9%; P<0.001) and a 1.1% lower insulin sensitivity index (95% CI, 0.03%, 2.2%; P=0.04). Surprisingly, eGFR was associated with an augmented β cell function index (P<0.001), lower 2-hour glucose concentration (P=0.002), and decreased risk of glucose intolerance (P=0.006). Over a median 12 years' follow-up, 437 participants (9.3%) developed diabetes. eGFR was not associated with the risk of incident diabetes.

CONCLUSIONS

Among older adults, lower eGFR was associated with insulin resistance. However, with lower eGFR, β cell function was appropriately augmented and risks of impaired glucose tolerance and incident diabetes were not increased.

Measurement of insulin resistance in chronic kidney disease

PURPOSE OF REVIEW

Insulin resistance is a known complication of end-stage renal disease that also appears to be present in earlier stages of chronic kidney disease (CKD). It is a risk factor for cardiovascular disease and an important potential therapeutic target in this population. Measurement of insulin resistance is reviewed in the context of known pathophysiologic abnormalities in CKD.

RECENT FINDINGS

Insulin resistance in CKD is due to a high prevalence of known risk factors (e.g. obesity) and to unique metabolic abnormalities. The site of insulin resistance in CKD is localized to skeletal muscle. Estimates based on fasting insulin concentration may not adequately capture insulin resistance in CKD because they largely reflect hepatic defects and because CKD impairs insulin catabolism. A variety of dynamic tests are available to directly measure insulin-mediated glucose uptake.

SUMMARY

Insulin resistance may be an important therapeutic target in CKD. Complementary methods are available to assess insulin resistance, and each method has unique advantages, disadvantages, and levels of complexity. These characteristics, and the likelihood that CKD alters the performance of some insulin resistance measurements, must be considered when designing and interpreting clinical studies.

Modulation of vitamin D signaling is a potential therapeutic target to lower cardiovascular risk in chronic kidney disease

While it is true that many traditional cardiovascular risk factors are amenable to intervention in chronic kidney disease (CKD), the results of intervention may not be as efficacious as those obtained in the general population. Thus, there may also be a unique milieu established in CKD, which causes excess cardiovascular disease (CVD) burden by mechanisms that are as yet not fully recognized. Recently, vitamin D has sparked widespread interest because of its potential favorable benefits on CVD. However, the mechanisms for how vitamin D may improve CVD risk markers and outcomes have not been fully elucidated. Furthermore, hypovitaminosis D is highly prevalent in the CKD cohort. Given this background, we hypothesize that low vitamin D status may act as a new CVD risk marker, and modulation of vitamin D signaling may be a potential therapeutic target to lower cardiovascular risk in CKD. The data presented in this review support that the low vitamin D status may be linked with the high cardiovascular risk in CKD, based on both the biological effects of vitamin D itself on the cardiovascular system, and the cross-actions between vitamin D signaling and the multiple metabolic pathways. Considering the high prevalence of hypovitaminosis D, limited natural vitamin D food sources, and reduced sun exposure in CKD patients, recommendations for treatment of hypovitaminosis D mainly focus on exogenous supplementation with vitamin D and its analogues. Although promising, when to start therapy, the route of administration, the dose, and the duration remain need to be discussed.

Risk factors for hypovitaminosis D in nondialyzed chronic kidney disease patients

BACKGROUND

Hypovitaminosis D is highly prevalent among patients with chronic kidney disease and has been associated with worse outcome even in the earlier stages of the disease.

OBJECTIVE

This study aimed to investigate the risk factors for hypovitaminosis D in nondialyzed patients with chronic kidney disease.

DESIGN

This cross-sectional study included 120 patients with chronic kidney disease at stages 2 to 5 (62% male, age: 55.4 ± 11.3 year, estimated glomerular filtration rate: 35.1 ± 15 mL/minute, body mass index [BMI]: 27.1 ± 5.2 kg/m(2), 31% diabetics). Serum 25-hydroxivitamin D [25(OH)D] was measured by chemiluminescence. Subjective global assessment, total body fat (dual-energy X-ray absorptiometry), visceral and subcutaneous abdominal fat (computed tomography), and several laboratory parameters were assessed.

RESULTS

Insufficiency of 25(OH)D (15 to 30 ng/mL) was observed in 55% and deficiency (<15 ng/mL) in 20% of the patients. Patients with diabetes, BMI ≥30 kg/m(2), and who had the blood collection during the winter or spring had lower levels of 25(OH)D. Serum 25(OH)D correlated inversely with parathyroid hormone, proteinuria, insulin resistance, leptin, and subcutaneous abdominal fat. The risk factors for hypovitaminosis D were diabetes (odds ratio: 3.8; 95% CI: 1.2 to 11.7; P = .022) and BMI ≥30 kg/m(2) (odds ratio: 4.3; 95% CI: 1.2 to 15.3; P = .018). In the logistic regression analysis adjusting for gender, skin color, and season of the year, diabetes and BMI ≥30 kg/m(2) were independently associated with hypovitaminosis D.

CONCLUSIONS

Diabetes and obesity were the risk factors for hypovitaminosis D in nondialyzed patients with chronic kidney disease. Effective interventional protocols of vitamin D supplementation taking into account these risk factors are warranted for this population.

Management of diabetes in dialysis patients

Diabetes mellitus is the most common cause of kidney disease worldwide, and of end-stage renal disease (ESRD) in the United States and elsewhere. Mortality rates of patients with diabetes mellitus (DM) on chronic dialysis exceed those of non-DM patients. ESRD and dialysis add to the complexity of glycemic management in this population. Abnormal glucoregulation includes reduced insulin sensitivity and renal clearance of the hormone. Implementation of dialysis affects glucose and insulin levels, while increasing insulin sensitivity. Tight glycemic control carries an increased risk of hypoglycemia in ESRD. Monitoring glycemic control with hemoglobin A(1c) (HbA(1c)) levels may be suboptimal because of analytical and clinical variability of the test. Recent studies on HbA(1c) and clinical outcomes in this population present complementary results on the role of glycemic control in patients with DM with ESRD.

Vitamin D, proteinuria, diabetic nephropathy, and progression of CKD

Although the endocrine effects of vitamin D are widely recognized, somewhat less appreciated is that vitamin D may serve paracrine functions through local activation by 1-alpha-hydroxylase and thus maintain immunity, vascular function, cardiomyocyte health, and abrogate inflammation and insulin resistance. In the kidney, vitamin D may be important for maintaining podocyte health, preventing epithelial-to-mesenchymal transformation, and suppressing renin gene expression and inflammation. Replacement with pharmacologic dosages of vitamin D receptor agonists (VDRA) in animal models of kidney disease consistently show reduction in albuminuria, abrogation of glomerulosclerosis, glomerulomegaly, and glomerular inflammation, effects that may be independent of BP and parathyroid hormone, but the effects of VDRA in preventing tubulointerstitial fibrosis and preventing the progression of kidney failure in these animal models are less clear. Emerging evidence in patients with chronic kidney disease (CKD) show that vitamin D can reduce proteinuria or albuminuria even in the presence of angiotensin-converting enzyme inhibition. In addition to reducing proteinuria, VDRA may reduce insulin resistance, BP, and inflammation and preserve podocyte loss providing biologic plausibility to the notion that the use of VDRA may be associated with salubrious outcomes in patients with diabetic nephropathy. Patients with CKD have a very high prevalence of deficiency of 25-hydroxyvitamin D. Whether pharmacologic dosages of vitamin D instead of VDRA in patients with CKD can overcome the paracrine and endocrine functions of this vitamin remains unknown. To demonstrate the putative benefits of native vitamin D and VDRA among patients with CKD, randomized, controlled trials are needed.