Vitamin D deficiency, inflammation, and albuminuria in chronic kidney disease: complex interactions

Assessing vitamin D as a biomarker in inflammatory bowel disease

Background and Aim

A reliable serum biomarker for inflammatory bowel disease (IBD) activity is needed. Vitamin D is involved in inflammation and has been demonstrated to be low in IBD patients with active disease. It is routinely measured in IBD patients. Therefore, vitamin D may have a role as a serum biomarker in IBD. This study aims to investigate whether serum vitamin D may be useful as a biomarker in IBD in a real-world IBD population.

Methods

Patients were identified by review of fecal calprotectin (FCP) results, and those who had a clinical review, vitamin D test, and FCP performed within 3 months were included. Clinical scores were calculated from chart review. Nonparametric tests were used to investigate vitamin D and FCP levels, serum biomarkers, and clinical scores.

Results

Of 616 patients identified, 325 episodes of matched vitamin D level and biomarker data were obtained. A statistically significant correlation was found between vitamin D levels and FCP levels for all patients (r = -0.19 [s -0.29 to -0.080], P < 0.001]. This remained true when patients were divided into IBD subsets. Low vitamin D was associated with partial Mayo scores and C-reactive protein (CRP) to albumin ratio in ulcerative colitis, and CRP and CRP/albumin ratio in Crohn's disease.

Conclusion

Vitamin D level is negatively correlated with FCP and it may be considered as an adjunct biomarker at this stage. A prospective study would be beneficial to investigate further correlations between vitamin D and existing biomarkers of inflammation in IBD.

Serum 25-hydroxyvitamin D as a predictive biomarker of clinical outcomes in patients with primary membranous nephropathy

Background

Primary membranous nephropathy (PMN) is an immune-related disease with increased morbidity and the most common cause of adult nephrotic syndrome (NS). The serum 25-hydroxyvitamin D [25(OH)D)], a biomarker of vitamin D (VD) status, tends to decline in patients with kidney disease. However, the relationship between 25(OH)D and PMN is still unclear. Therefore, this study aims to clarify the association between 25(OH)D and disease severity and therapy response of PMN.

Methods

A total of 490 participants diagnosed with PMN by biopsy from January 2017 to April 2022 were recruited at the First Affiliated Hospital of Nanjing Medical University. The correlations between baseline 25(OH)D and manifestations of nephrotic syndrome (NS) or seropositivity of anti-PLA2R Ab were confirmed by univariate and multivariate logistic analyses. Spearman's correlations were used to examine the associations between baseline 25(OH)D and other clinical parameters. In the follow-up cohort, Kaplan-Meier analysis was used to assess remission outcomes among groups with low, medium, and high levels of 25(OH)D. Furthermore, the independent risk factors for non-remission (NR) were explored by COX regression analysis.

Results

At baseline, 25(OH)D was negatively related to 24-h urinary protein and serum anti-PLA2R Ab. The lower level of baseline 25(OH)D was associated with an increased risk for the incidence of NS in PMN (model 2, OR 6.8, 95% CI 4.4, 10.7, P < 0.001) and seropositivity of anti-PLA2R Ab (model 2, OR 2.4, 95% CI 1.6, 3.7, P < 0.001). Furthermore, the lower level of 25(OH)D during follow-up was demonstrated as an independent risk factor for NR even after adjusting age, gender, MBP, 24 h UP, serum anti-PLA2R Ab, serum albumin, and serum C3 [25(OH)D (39.2-62.3 nmol/L): HR 4.90, 95% CI 1.02, 23.53 P = 0.047; 25(OH)D < 39.2 nmol/L: HR 17.52, 95% CI 4.04, 76.03 P < 0.001); vs. 25(OH)D ≥ 62.3 nmol/L]. The Kaplan-Meier survival analysis also demonstrated that the higher level of follow-up 25(OH)D had a higher possibility of remission than the lower one (log-rank test, P < 0.001).

Conclusion

Baseline 25(OH)D was significantly correlated with nephrotic proteinuria and seropositivity of anti-PLA2R Ab in PMN. As an independent risk factor for NR, a low level of 25(OH)D during follow-up might serve as a prognostic tool for sensitively identifying cases with a high probability of poor treatment response.

The clinical relevance of native vitamin D in pediatric kidney disease

Hypovitaminosis D has been reported to be common in chronic kidney disease (CKD) as well as in proteinuric disorders. We reviewed available evidence to assess clinically relevant effects of low vitamin D status and native vitamin D (NVD) therapy, in pediatric renal diseases. Online medical databases were searched for articles related to vitamin D status, associations of hypovitaminosis D and effects of NVD therapy in kidney disease. Hypovitaminosis D was associated with worse skeletal, cardiovascular, inflammatory, and renal survival outcomes in CKD. Low serum 25 hydroxy-vitamin D (25[OH]D) levels correlated positively with glomerular filtration rate and negatively with serum parathyroid (PTH) levels. However, to date, evidence of benefit of NVD supplementation is restricted mainly to improvements in serum PTH, and biochemical 25[OH]D targets form the basis of clinical practice recommendations for NVD therapy. In nephrotic syndrome (NS) relapse, studies indicate loss of 25[OH]D along with vitamin D binding protein in urine, and serum total 25[OH]D levels are low. Preliminary evidence indicates that free 25[OH]D may be a better guide to the biologically active fraction. NVD therapy in NS does not show consistent results in improving skeletal outcomes and hypercalciuria has been reported when total 25[OH]D levels were considered as indication for therapy. NVD formulations should be regularised, and therapy monitored adequately to avoid adverse effects.

Plasma 25-Hydroxyvitamin D3 Concentrations and Risk of New-Onset Proteinuria in Patients With Hypertension

OBJECTIVE

We aimed to evaluate the relationship of plasma 25-hydroxyvitamin D3 (25[OH]D3) with the risk of new-onset proteinuria and examine the possible effect modifiers in patients with hypertension and without chronic kidney disease at baseline.

METHODS

This is a post hoc analysis of the renal substudy of the China Stroke Primary Prevention Trial. A total of 1655 patients with hypertension, who had plasma 25(OH)D3 measurements, as well as without proteinuria and with an estimated glomerular filtration rate of ≥60 mL/min/1.73 m² at baseline, were included in the present study. The main outcome was new-onset proteinuria, defined as a urine dipstick reading of ≥1+ at the exit visit.

RESULTS

The mean (standard deviation) 25(OH)D3 level at baseline was 18.6 (7.5) ng/mL. The median follow-up duration was 4.4 years. Overall, there was a significant inverse association between plasma 25(OH)D3 and the risk of new-onset proteinuria (per standard deviation increment; [odds ratio] OR: 0.70; 95% confidence interval [CI]: 0.50, 0.97). Accordingly, when 25(OH)D3 was assessed as quartiles, a significantly lower risk of new-onset proteinuria was found in participants in quartiles 3-4 (≥17.8 ng/mL; OR: 0.45; 95% CI: 0.23, 0.87), compared with those in quartile 1 (<13.1 ng/mL). Furthermore, a stronger inverse relationship of plasma 25(OH)D3 and new-onset proteinuria was observed in nondiabetic participants (per standard deviation increment; OR: 0.57; 95% CI: 0.39, 0.83; vs. diabetics: OR: 1.48; 95% CI: 0.67, 3.28; P for interaction = 0.028).

CONCLUSION

There was a significant inverse association between plasma 25(OH)D3 and the risk of proteinuria in patients with hypertension, especially in those without diabetes.

Association between vitamin D metabolites, vitamin D binding protein, and proteinuria in dogs

BACKGROUND

Proteinuria has been associated with progression of renal disease and increased morbidity and mortality in dogs and people. In people, proteinuria also has been associated with hypovitaminosis D. Little is known about the relationship between vitamin D metabolism and proteinuria in dogs.

OBJECTIVES

To further elucidate vitamin D status in dogs with protein-losing nephropathy (PLN) and minimal to no azotemia. We hypothesized that vitamin D metabolites would be lower in dogs with PLN compared to healthy dogs.

ANIMALS

Twenty-three client-owned adult dogs with PLN and 10 healthy control dogs.

METHODS

Serum 25-hydroxyvitamin D (25[OH]D), 1,25-dihydroxyvitamin D (1,25[OH]₂ D), 24,25-dihydroxyvitamin D (24,25[OH]₂ D), serum vitamin D binding protein (VDBP), and urine 25(OH)D concentrations were measured.

RESULTS

Compared to healthy dogs, dogs with PLN had lower concentrations of all vitamin D metabolites (P < .01). Correlations (rho; 95% confidence interval [CI]) in dogs with PLN are reported. Serum 25(OH)D and 24,25(OH)₂ D concentrations were positively correlated with albumin (r = 0.47; 0.07-0.74), and 24,25(OH)₂ D was negatively correlated with urine protein-to-creatinine ratio (UPC; r = -0.54; -0.78 to -0.16). Urine 25(OH)D-to-creatinine ratio was negatively correlated with serum albumin concentration (r = -0.77; -0.91 to -0.50) and positively correlated with UPC (r = 0.79; 0.53-0.91). Serum VDBP concentration was positively correlated with serum albumin concentration (r = 0.53; 0.05-0.81).

CONCLUSIONS AND CLINICAL IMPORTANCE

Dogs with PLN have decreased serum concentrations of vitamin D metabolites. Urine 25(OH)D-to-creatinine ratio and UPC are correlated in PLN dogs. Future studies are needed to assess additional management strategies for dogs with PLN.

Serum 25-Hydroxyvitamin D, Albumin, and Mortality Among Chinese Older Adults: A Population-based Longitudinal Study

CONTEXT

The associations between serum 25-hydroxyvitamin D concentrations [25(OH)D] and all-cause mortality have been inconsistent in existing literatures. One plausible reason is the interaction of intrinsic vitamin D with other biological conditions such as malnutrition and chronic inflammation.

OBJECTIVE

To explore the associations between serum levels of 25(OH)D, albumin, and all-cause mortality and further evaluate their interactions in elderly people.

DESIGN

Population-based longitudinal study.

SETTING AND PARTICIPANTS

Data were obtained from 1834 people aged 65 to 112 who had their serum 25(OH)D and albumin assayed at baseline in 2011. Participants' survival status was ascertained at the 2014 and 2018 follow-up survey waves.

MAIN OUTCOME MEASURES

All-cause mortality.

RESULTS

Among the 1834 participants, both serum 25(OH)D and albumin concentrations were inversely associated with all-cause mortality (Ps < 0.001). In addition, the interaction effect of 25(OH)D and albumin on all-cause mortality was observed among the participants (P = 0.001). In the group with a higher albumin level (≥40 g/L), participants with a lower level of 25(OH)D (<50 nmol/L) had higher risk of mortality than their counterparts (hazard ratio, 1.92; 95% confidence interval, 1.45-2.56), and the association was more pronounced in women. In the group with a lower albumin level (<40 g/L), the associations failed to reach statistical significance in all participants as well as in women and in men.

CONCLUSIONS

Serum 25(OH)D and albumin levels were inversely associated with all-cause mortality in Chinese older adults. The association between 25(OH)D and mortality was more pronounced in participants with higher albumin levels.

Associations Between Complement Components and Vitamin D and the Physical Activities of Daily Living Among a Longevous Population in Hainan, China

Background: Vitamin D and complement components shared some common pathophysiological pathways in the musculoskeletal system, circulation, and metabolism, which were linked to physical function. It is hypothesized that serum complement components may interact with vitamin D in respect of the physical activities of daily living (PADLs). Objective: To investigate if serum complement components 3 (C3), complement components 4 (C4), and 25-hydroxyvitamin D [25(OH)D] associate with PADLs, and to examine whether the association between 25(OH)D levels and PADLs varies at different complement component levels among Chinese centenarians. Methods: This study was conducted in a group of population-based centenarians. PADLs were evaluated using the Barthel Index. Multiple regressions were used to analyze the associations among 25(OH)D, complements C3 and C4, and PADLs. Results: Among 943 participants, 672 (71.3%) had physical dependence (PD). After adjusting for potential confounders, serum 25(OH)D and C3 levels were positively correlated with PADLs, while C4 levels were negatively correlated with PADLs (Ps < 0.05). Serum 25(OH)D levels significantly interacted with both C3 (P for interaction = 0.033) and C4 (P for interaction = 0.006) levels on PADLs. At lower complement component levels, the multivariate odds ratios (ORs) of the upper tertile of vitamin D for PD were 0.32 (95% CI: 0.18-0.55) in the C3 group and 0.29 (95% CI: 0.16-0.50) in the C4 group. At higher complement component levels, the ORs in the C3 and C4 groups were not statistically significant. Conclusions: In a group of population-based Chinese centenarians, we observed that serum complement C3 and 25(OH)D levels were positively associated with PADLs, while C4 was negatively associated with PADLs. The associations between 25(OH)D levels and PADLs were more pronounced in groups with lower serum complement component levels.

Seasonal variation of serum 25-hydroxyvitamin D and parameters of bone and mineral disorder in dialysis patients

BACKGROUND

Vitamin D deficiency is common among dialysis patients and may impact blood concentrations of calcium, phosphorus, intact parathyroid hormone (iPTH), and alkaline phosphatase (ALP). Seasonal variation of serum 25-hydroxyvitamin D [25(OH)D] concentrations has been well established for the general population; however, less is known about circannual variation in 25(OH)D as well as other parameters of mineral and bone disorder among dialysis patients.

METHOD

Based on 57,500 serum 25(OH)D measurements collected over two years from January 2009 to December 2010 among 25,025 dialysis patients, we evaluated the circannual variations in serum concentrations of 25(OH)D, calcium, phosphorus, iPTH, and ALP by a linear regression model with a cosinor function for the time period (month). We adjusted for potential confounders including case-mix variables, and ultraviolet index.

RESULTS

Serum 25(OH)D concentrations showed significant circannual variation and mean serum 25(OH)D was 3.2 ng/mL higher in summer than in winter. Furthermore, 25(OH)D concentration increased steadily by 1.3 ng/mL per year. While serum calcium concentrations showed statistically significant but clinically negligible seasonal variation (0.02 mg/dL in peak-trough difference), serum phosphorus did not follow such a pattern. Serum iPTH concentrations also showed a modest seasonal variation with 9% higher values in winter than in summer. Concordantly, ALP concentrations in the winter were 2% higher than in the summer time. Seasonal variation of 25(OH)D was greater in male (vs. female), African-American (vs. non-African-American), and younger (vs. older) dialysis patients.

CONCLUSION

Serum 25(OH)D and iPTH concentrations show seasonal variation among dialysis patients while the variation in other parameters of mineral and bone disorder was clinically irrelevant, if any. Serum 25(OH)D also showed a gradual increase over time. Clinicians and researchers should be aware of these changes when interpreting laboratory results in dialysis patients.

Urine albumin and serum uric acid are important determinants of serum 25 hydroxyvitamin D level in pre-dialysis chronic kidney disease patients

Low serum 25 hydroxyvitamin D (25 OH D) is common among chronic kidney disease (CKD) patients. This cross-sectional study is looking for the different factors associated with serum 25 OH D among pre-dialysis CKD. 1624 adult stage 3–5 CKD patients were studied beside 200 normal control subjects. All candidates were tested for body mass index (BMI), estimated glomerular filtration rate (eGFR), calcium (Ca), phosphorus (P), parathormone (PTH), 25 OH D, albumin, and uric acid (UA), and urine albumin/creatinine ratio (ACR). Multivariate linear regression analysis was done to determine predictors of 25 OH D. 98.6% of CKD patients have inadequate level of 25 OH D vs 48% of normal subjects. Serum 25 OH D was significantly lower in CKD patients (mean ± S.D = 16.54 ± 5.8 vs 37.79 ± 3.58 ng/mL for CKD vs control group respectively, p < .001). Serum level of 25 OH D has significant positive correlation with Ca (r = 0.337, p < .001), and significant negative correlation with P, PTH, UA, and ACR (r = −0.440, −0. 679, −0.724, and −0.781respectively, p < .001 in all). The independent predictors of 25 OH D were Ca, P, UA, PTH, and ACR (R square = 0.7, β = −0.087, −0.226, −0.313, −0.253, and −0.33 respectively, p < .001 in all). In conclusion, pre-dialysis CKD patients frequently suffer low 25 OH D. Among the different abnormalities related to CKD, urine albumin excretion rate and UA are the most important predictors of 25 OH D in these patients.

Cross-sectional evaluation of the relationship between vitamin D status and supplement use across levels of kidney function in adults

OBJECTIVES

The objective of this study was to assess vitamin D status of US non-pregnant adults using a standardised assay across 15 mL/min/1.73 m2 increments of kidney function, report the use of dietary supplements containing vitamin D and assess relationships between vitamin D and markers of bone resorption.

DESIGN

This study is a cross-sectional evaluation.

SETTING

The study is from the US National Health and Nutrition Evaluation Survey in 2001-2012.

PARTICIPANTS

The participants were non-institutionalised, non-pregnant adults, age ≥20 years.

PRIMARY AND SECONDARY OUTCOME MEASURES

The primary outcome measure was serum 25OHD evaluated using liquid chromatography-tandem mass spectroscopy traceable to international reference standards. Secondary outcome measures were use of dietary supplements containing vitamin D and the serum intact parathyroid hormone and bone-specific alkaline phosphatase in a subset of participants.

RESULTS

The median 25OHD concentration in 27 543 US non-pregnant adults was 25.7 ng/mL (range, 2.2-150.0 ng/mL). Vitamin D supplements were used by 38.0%; mean (SE)=757 (43) international units/day. The range of 25OHD concentration across groups, stratified by kidney function, was 23.0-28.1 ng/mL. The lowest concentration of 25OHD observed was in people with higher kidney function (23.0 ng/mL for estimated glomerular filtration rate >105 mL/min/1.73 m2). Only 24% of people not taking a dietary supplement had a 25OHD concentration >30 ng/mL. Serum intact parathyroid hormone inversely correlated with 25OHD within all kidney function groups. Bone-specific alkaline phosphatase was also negatively associated with 25OHD concentration.

CONCLUSIONS

These data indicate that 25OHD concentrations and supplement use may be suboptimal in a significant proportion of the population, across all kidney function levels. The response of bone resorption markers further suggests that 25OHD levels could be improved. Together, these data support a re-evaluation of the 25OHD concentration associated with health in adults.

Serum 25-Hydroxyvitamin D were associated with higher risk of both albuminuria and impaired GFR incidence: a cohort study based on CLHLS study

BACKGROUND

This study aimed to examine the relationship between 25-hyfromxyvitamin D (25OHD) and chronic kidney disease (CKD) incidence.

METHODS

All the elderly who had participated both in the 2011-2012 survey and 2014 survey in the Chinese Longitudinal Healthy Longevity Survey (CLHLS), and have biomarker data were included in the analysis. We studied those without CKD with complete data at 2011-2012 waves. Serum 25-Hydroxyvitamin D was assessed at baseline. Cox proportional risk model was used to evaluate associations between serum 25-Hydroxyvitamin D and CKD (including both albuminuria and impaired eGFR) incidence after adjusted for potential confounding..

RESULTS

During the follow-up years, 255 incident cases of CKD were diagnosed. Those who developed CKD had relatively lower serum 25(OH)D (mean 37.63 vs.51.36 nmol/L, p < 0.001) compared with those who remained free of CKD. Each 1 nmol/L increase in 25(OH)D was associated with 3.4% reduced risk of CKD (HR = 0.966, 95%CI: 0.959-0.973) after adjusted for related covariates. The HRs of each 1 nmol/L increase in 25(OH)D for albuminuria and impaired eGFR were 0.952(95%CI: 0.941-0.963) and 0.975(95%CI: 0.966-0.983) respectively. When use the classifications (sufficiency, insufficiency, deficiency) or quintiles of baseline 25(OH)D levels in the Cox model, the corresponding HRs showed an increasing trend along with the decrease of baseline 25(OH)D levels (p for trend < 0.001).

CONCLUSIONS

Higher 25(OH)D levels were inversely and independently associated with CKD incidence among Chinese elderly. The trend for the observed linear relationship b was most pronounced among the lowest quintile.

Differential Association of Vitamin D Deficiency With Albuminuria by Sex in the Korean General Population: A Cross-sectional Study of the Korea National Health and Nutrition Examination Survey 2011-2012

Objectives

Albuminuria has emerged as a biomarker for several medical conditions, and vitamin D has received attention due to its associations with various disorders. We evaluated the association between low serum vitamin D levels and prevalent albuminuria by sex in the Korean general population.

Methods

We analyzed 9823 participants (4401 males, 5422 females) from the Korea National Health and Nutrition Examination Survey 2011-2012 (KNHANES V-2), and categorized them as having a normal range of vitamin D levels, vitamin D insufficiency, or vitamin D deficiency. A multivariable logistic regression model was used to compare the risk of albuminuria across these groups. Stratified analyses were conducted by smoking status, obesity, and renal function.

Results

Albuminuria was found in 325 of the 4401 male participants (7.4%) and in 455 of the 5422 female participants (8.4%). Among the males, vitamin D deficiency was associated with an odds ratio (OR) for albuminuria of 1.78 (95% confidence interval [CI], 1.07 to 2.97, p<0.05). However, such an association was not found in females. The association was stronger in male current smokers (OR, 3.54; 95% CI, 1.47 to 8.50; p=0.005).

Conclusions

The findings of this study suggest that sex differences exist in the association between serum vitamin D deficiency and albuminuria. Additionally, we observed that the association was stronger in current smokers than in the overall male population, but was not seen in non-smokers. Therefore, different approaches by sex and smoking status might be needed when considering using vitamin D as a biomarker for renal function.

Correlation between serum 25-hydroxyvitamin D levels and carotid intima-media thickness in a Brazilian population descended from African slaves

Hypovitaminosis D has been identified as a possible new cardiovascular risk factor. However, the results of studies correlating serum vitamin D levels with markers of subclinical atherosclerosis have been conflicting. The aim of this study was to correlate serum levels of 25-hydroxyvitamin D [25(OH)D] with carotid intima-media thickness (C-IMT) and conventional cardiovascular risk factors in Afro-descendants. A cross-sectional analysis was performed on a sample of 382 individuals from a cohort of descendants of African slaves, inhabitants of “Quilombola” communities, with a mean age of 57.79 ±15.3 years, 54.5% of whom were women. Socio-demographic and clinical data were collected and biochemical tests were performed, including serum levels of 25(OH)D by electrochemiluminescence and urinary albumin excretion, evaluated by the albumin/creatinine ratio (ACR) in a spot urine sample. All participants underwent high-resolution ultrasonography for C-IMT measurement. Hypovitaminosis D was defined as serum 25(OH)D levels <30 ng/mL. The mean serum 25(OH)D levels were 50.4±13.5 ng/mL, with a low prevalence of hypovitaminosis D (4.86%). By simple linear correlation, a significant inverse association between 25(OH)D levels and C-IMT (r=-0.174, P=0.001) was observed. However, after multiple linear regression analysis, the significance of the association between serum levels of 25(OH)D and C-IMT measurement was lost (β=-0.039, P=0.318) and only male gender, age, smoking, systolic blood pressure, glucose and low density lipoprotein (LDL)-cholesterol remained significantly associated with C-IMT. Levels of 25(OH)D were independently and positively associated with HDL-cholesterol and inversely associated with age and ACR. In conclusion, no independent association between 25(OH)D levels and C-IMT was observed in this population. On the other hand, there was an inverse association with albuminuria, a marker of endothelial lesion.

Randomized Controlled Trial for the Effect of Vitamin D Supplementation on Vascular Stiffness in CKD

BACKGROUND AND OBJECTIVES

Vitamin D is implicated in vascular health in CKD. This study compared placebo, calcifediol, and calcitriol treatment with changes in vascular stiffness, BP, proteinuria, mineral metabolism parameters, C-reactive protein, and fibroblast growth factor 23 in patients with stable CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We conducted a double-blind, randomized controlled trial in out-patient CKD clinics in Vancouver, Canada, from February of 2011 to August of 2014, enrolling 119 patients with an eGFR of 15-45 ml/min per 1.73 m2. Change in pulse wave velocity (PWV) was measured after 6 months of treatment with a fixed dose of oral calcifediol (5000 IU 25-hydroxyvitamin D3), calcitriol (0.5 µg 1,25-dihydroxyvitamin D3), or placebo, thrice weekly.

RESULTS

Eighty-seven participants were evaluated. Mean age was 66 years, 71% were men, 40% were diabetic, and mean baseline PWV was 11.5 m/s (SD=3.9 m/s). After 6 months, the PWV decreased in the calcifediol group (mean change, -1.1; 95% confidence interval [95% CI], -2.2 to 0.1 m/s), remained unchanged in the calcitriol group (mean change, 0.2; 95% CI, -0.9 to 1.4 m/s), and increased in the placebo group (mean change, 1.1; 95% CI, -0.1 to 2.2 m/s). The overall P value for between-arm changes was 0.03. Absolute PWV change was significantly different between groups (P=0.04): the combined vitamin D treatment group saw decreased PWV (mean change, -0.4; 95% CI, -1.2 to 0.4 m/s) whereas the placebo group saw increased PWV (mean change, +1.1; 95% CI, -0.1 to 2.2 m/s). The treatment group demonstrated significantly decreased serum parathyroid hormone (mean difference, -0.5; 95% CI, -0.7 to -0.3 ln[pg/ml]; P<0.001) and increased calcium (mean difference, 0.4; 95% CI, -0.1 to 0.7 mg/dl; P=0.02). In observational analysis, participants in the highest 25-hydroxyvitamin D tertile at trial end had significant decreases in PWV (mean change, -1.0; 95% CI, -2.0 to 0.0 m/s) compared with the middle and lowest tertiles (P<0.01). Side effects were minor and rare.

CONCLUSIONS

Six months of supplemental vitamin D analogs at fixed doses may achieve a reduction of PWV in patients with advanced CKD. Because the treatment effect was attenuated when baseline PWV was included as a covariate, these findings should be replicated in larger populations and further studied.

Identification of differentially expressed miRNAs associated with chronic kidney disease-mineral bone disorder

The purpose of this study is to characterize a meta-signature of differentially expressed mRNA in chronic kidney disease (CKD) to predict putative microRNA (miRNA) in CKD-mineral bone disorder (CKD-MBD) and confirm the changes in these genes and miRNA expression under uremic conditions by using a cell culture system. PubMed searches using MeSH terms and keywords related to CKD, uremia, and mRNA arrays were conducted. Through a computational analysis, a meta-signature that characterizes the significant intersection of differentially expressed mRNA and expected miRNAs associated with CKD-MBD was determined. Additionally, changes in gene and miRNA expressions under uremic conditions were confirmed with human Saos-2 osteoblast-like cells. A statistically significant mRNA meta-signature of upregulated and downregulated mRNA levels was identified. Furthermore, miRNA expression profiles were inferred, and computational analyses were performed with the imputed microRNA regulation based on weighted ranked expression and putative microRNA targets (IMRE) method to identify miRNAs associated with CKD occurrence. TLR4 and miR-146b levels were significantly associated with CKD-MBD. TLR4 levels were significantly downregulated, whereas primiR- 146b and miR-146b were upregulated in the presence of uremic toxins in human Saos-2 osteoblast-like cells. Differentially expressed miRNAs associated with CKD-MBD were identified through a computational analysis, and changes in gene and miRNA expressions were confirmed with an in vitro cell culture system.

Vitamin D status in renal transplant recipients living in a low-latitude city: association with body fat, cardiovascular risk factors, estimated glomerular filtration rate and proteinuria

Recent evidence suggests that vitamin D deficiency is associated with CVD, impaired kidney function and proteinuria. To date, no study has evaluated these associations in renal transplant recipients (RTR) adjusting for body adiposity assessed by a ‘gold standard’ method. This study aimed to evaluate the vitamin D status and its association with body adiposity, CVD risk factors, estimated glomerular filtration rate (eGFR) and proteinuria in RTR, living in Rio de Janeiro, Brazil (a low-latitude city (22°54'10"S)), taking into account body adiposity evaluated by dual-energy X-ray absorptiometry (DXA). This cross-sectional study included 195 RTR (114 men) aged 47·6 (sd11·2) years. Nutritional evaluation included anthropometry and DXA. Risk factors for CVD were hypertension, diabetes mellitus, dyslipidaemia and the metabolic syndrome. eGFR was evaluated using the Chronic Kidney Disease Epidemiology Collaboration equation. Serum 25-hydroxyvitamin D (25(OH)D) concentration was used to define vitamin D status as follows: 10 % (n19) had vitamin D deficiency (<16 ng/ml), 43 % (n85) had insufficiency (16–30 ng/ml) and 47 % (n91) had sufficiency (>30 ng/ml). Percentage of body fat (DXA) was significantly associated with vitamin D deficiency independently of age, sex and eGFR. Lower 25(OH)D was associated with higher odds of the metabolic syndrome and dyslipidaemia after adjustment for age, sex and eGFR, but not after additional adjustment for body fat. Hypertension and diabetes were not related to 25(OH)D. Lower serum 25(OH)D was associated with increasing proteinuria and decreasing eGFR even after adjustments for age, sex and percentage of body fat. This study suggests that in RTR of a low-latitude city hypovitaminosis D is common, and is associated with excessive body fat, decreased eGFR and increased proteinuria.

The Association of Vitamin D With Estimated Glomerular Filtration Rate and Albuminuria: 5th Korean National Health and Nutritional Examination Survey 2011-2012

OBJECTIVES

The kidney plays a key role in the metabolism of vitamin D. However, the relationship between GFR and 25(OH)D is not well understood. Moreover, few studies have investigated the effect of albuminuria, a known mediator of kidney function, on vitamin D levels. Our aim was to investigate the associations among estimated GFR (eGFR), albumin-creatinine ratio (ACR), and 25(OH)D.

METHODS

We investigated the relationship of 25-hydroxyvitamin D (25[OH]D) with eGFR and albuminuria in 11,336 adults who participated in the 5th Korea National Health and Nutrition Examination Survey (KNHANES) 2011-2012. The eGFR, ACR, and serum 25(OH)D were measured in participants who met the detailed inclusion criteria.

RESULTS

We found that after adjusting for covariates and log-ACR values, the mean (95% CI) eGFR decreased significantly with increasing 25(OH)D levels (Q1: 93.4 [92.7-94.0]; Q2: 91.9 [91.2-92.5]; Q3: 90.9 [90.3-91.6]; and Q4: 90.2 [89.5-90.8] mL/min/1.73m²; P < .001). However, the mean 25(OH)D value was highest at eGFR 61-90 mL/min per 1.73 m² and decreased significantly with decreasing eGFR levels (>90: 17.3 [17.1-17.5]; 61-90: 17.6 [17.4-17.8]; 46-60: 17.1 [16.2-18.0]; 31-45: 16.2 [14.2-18.2]; ≤30: 13.8 [17.0-10.7] ng/mL; P = .008). After adjusting for covariates and log-eGFR, the mean ACR decreased significantly with increasing 25(OH)D quartiles (Q1: 22.0 [18.1-25.9]; Q2: 20.4 [16.6-24.2]; Q3: 16.3 [12.5-20.0]; Q4: 15.0 [11.2-18.8] μg/mg; P = .043).

CONCLUSIONS

The mean eGFR values were negatively associated with 25(OH)D levels independently of ACR. However, the mean 25(OH)D values were decreased significantly with decreasing eGFR levels in moderate and severe chronic kidney disease stages. Also, the mean ACR values were negatively associated with 25(OH)D levels independently of eGFR in an Korean adult population.

Prevalence and correlates of 25-hydroxyvitamin D deficiency in the Chronic Kidney Disease in Children (CKiD) cohort

BACKGROUND

Vitamin D plays an important role in the mineral and bone disorder seen in chronic kidney disease (CKD). Deficiency of 25-hydroxyvitamin D (25OHD) is highly prevalent in the adult CKD population.

METHODS

The prevalence and determinants of 25OHD deficiency (defined as a level <20 ng/ml) were examined longitudinally in 506 children in the CKiD cohort. Predictors of secondary hyperparathyroidism and the determinants of 1,25-dihydroxyvitamin D (1,25(OH)2D) levels were also evaluated.

RESULTS

Deficiency of 25OHD was observed in 28 % of the cohort at enrollment. Significant predictors of 25OHD deficiency were older age, non-white race, higher body mass index, assessment during winter, less often than daily milk intake, non-use of nutritional vitamin D supplement and proteinuria. Lower values of glomerular filtration rate (GFR), serum 25OHD, calcium and higher levels of FGF23 were significant determinants of secondary hyperparathyroidism. Lower GFR, low serum 25OHD, nephrotic-range proteinuria, and high FGF23 levels were significant determinants of serum 1,25(OH)2 D levels.

CONCLUSIONS

Deficiency of 25OHD is prevalent in children with CKD and is associated with potentially modifiable risk factors such as milk intake, nutritional vitamin D supplement use, and proteinuria. 25OHD deficiency is a risk factor for secondary hyperparathyroidism and decreased serum 1,25(OH)2D in children with CKD.

The effect of some medications given to CKD patients on vitamin D levels

BACKGROUND

Vitamin D deficiency and polypharmacy is a common problem over chronic kidney disease (CKD) population.

OBJECTIVES

To assess the clinical and analytical characteristics of CKD patients with 25-OH-D3 deficiency (<15 ng/mL), including the possible role of associated drugs.

METHODS

A single center observational review of 137 incident patients referred to our outpatient clinic with different stages of CKD and 25-OH-D3<15ng/mL (male gender 53.3%, mean age 70.8 [±16.1] years, mean GFR (MDRD-4) 43.6 [±25.5] ml/min/1.73 m²). 25-OH-D3 levels were collected in spring. Clinical and biochemical data and associated medications were recorded.

RESULTS

Mean 25-OH-D3 levels were 8.23 [±4.03] ng/ml. Eighty-eight patients (64.7%) had 3 or more concomitant drugs. Only 7 patients (5.1%) were not receiving any medication. Patients were divided in three groups according the therapies into none (n=26), RAS inhibitors or allopurinol (n=81), and RAS inhibitors plus allopurinol (n=30); with the aim to study the influence of statin therapy. Patients under renin angiotensin (RAS) inhibitors or Allopurinol treatment presented significantly higher 25-OH-D3 levels (p=0.001 and p=0.01 respectively), however patients with Statins treatment had lower 25-OH-D3 level (p=0.039). Personal history of diabetes, cardiovascular events or other therapies did not modify 25-OH-D3 levels, adjusted by age and eGFR.

CONCLUSIONS

CKD patients with vitamin D deficiency who received RAS inhibitors or Allopurinol treatment had higher 25-OH-D3 levels, however those with statins treatment had lower vitamin D levels. Randomized controlled trials are required to confirm these findings.

Normal 25-Hydroxyvitamin D Levels Are Associated with Less Proteinuria and Attenuate Renal Failure Progression in Children with CKD

Angiotensin-converting enzyme inhibitors (ACEi) for renin-angiotensin-aldosterone system (RAAS) blockade are routinely used to slow CKD progression. However, vitamin D may also promote renoprotection by suppressing renin transcription through cross-talk between RAAS and vitamin D-fibroblast growth factor-23 (FGF-23)-Klotho pathways. To determine whether vitamin D levels influence proteinuria and CKD progression in children, we performed a post hoc analysis of the Effect of Strict Blood Pressure Control and ACE Inhibition on Progression of CKD in Pediatric Patients (ESCAPE) cohort. In 167 children (median eGFR 51 ml/min per 1.73 m(2)), serum 25-hydroxyvitamin D (25(OH)D), FGF-23, and Klotho levels were measured at baseline and after a median 8 months on ACEi. Children with lower 25(OH)D levels had higher urinary protein/creatinine ratios at baseline (P=0.03) and at follow-up (P=0.006). Levels of 25(OH)D and serum vitamin D-binding protein were not associated, but 25(OH)D ≤50 nmol/L associated with higher diastolic BP (P=0.004). ACEi therapy also associated with increased Klotho levels (P<0.001). The annualized loss of eGFR was inversely associated with baseline 25(OH)D level (P<0.001, r=0.32). Five-year renal survival was 75% in patients with baseline 25(OH)D ≥50 nmol/L and 50% in those with lower 25(OH)D levels (P<0.001). This renoprotective effect remained significant but attenuated with ACEi therapy (P=0.05). Renal survival increased 8.2% per 10 nmol/L increase in 25(OH)D (P=0.03), independent of eGFR; proteinuria, BP, and FGF-23 levels; and underlying renal diagnosis. In children with CKD, 25(OH)D ≥50 nmol/L was associated with greater preservation of renal function. This effect was present but attenuated with concomitant ACEi therapy.

Serum 25-hydroxyvitamin D level and kidney function decline in a Swiss general adult population

BACKGROUND AND OBJECTIVES

Molecular evidence suggests that levels of vitamin D are associated with kidney function loss. Still, population-based studies are limited and few have considered the potential confounding effect of baseline kidney function. This study evaluated the association of serum 25-hydroxyvitamin D with change in eGFR, rapid eGFR decline, and incidence of CKD and albuminuria.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Baseline (2003-2006) and 5.5-year follow-up data from a Swiss adult general population were used to evaluate the association of serum 25-hydroxyvitamin D with change in eGFR, rapid eGFR decline (annual loss >3 ml/min per 1.73 m(2)), and incidence of CKD and albuminuria. Serum 25-hydroxyvitamin D was measured at baseline using liquid chromatography-tandem mass spectrometry. eGFR and albuminuria were collected at baseline and follow-up. Multivariate linear and logistic regression models were used considering potential confounding factors.

RESULTS

Among the 4280 people included in the analysis, the mean±SD annual eGFR change was -0.57±1.78 ml/min per 1.73 m(2), and 287 (6.7%) participants presented rapid eGFR decline. Before adjustment for baseline eGFR, baseline 25-hydroxyvitamin D level was associated with both mean annual eGFR change and risk of rapid eGFR decline, independently of baseline albuminuria. Once adjusted for baseline eGFR, associations were no longer significant. For every 10 ng/ml higher baseline 25-hydroxyvitamin D, the adjusted mean annual eGFR change was -0.005 ml/min per 1.73 m(2) (95% confidence interval, -0.063 to 0.053; P=0.87) and the risk of rapid eGFR decline was null (odds ratio, 0.93; 95% confidence interval, 0.79 to 1.08; P=0.33). Baseline 25-hydroxyvitamin D level was not associated with incidence of CKD or albuminuria.

CONCLUSIONS

The association of 25-hydroxyvitamin D with eGFR decline is confounded by baseline eGFR. Sufficient 25-hydroxyvitamin D levels do not seem to protect from eGFR decline independently from baseline eGFR.

Circulating fibroblast growth factor 23 (FGF23) levels are associated with metabolic disturbances and fat distribution but not cardiovascular risk in HIV-infected patients

OBJECTIVES

Dyslipidaemia, insulin resistance, metabolic syndrome and HIV/HAART-associated lipodystrophy syndrome (HALS) are common comorbidities in HIV-1-infected patients, which may increase cardiovascular risk. Fibroblast growth factor 23 (FGF23) is a bone-derived hormone with effects on metabolism and phosphate homeostasis. The aim of this study was to determine the relationship between FGF23 levels, metabolic alterations, fat distribution and cardiovascular risk.

METHODS

This was a cross-sectional study. Serum FGF23 levels were analysed in 152 patients and 34 healthy control individuals. Patients belonged to three groups: HIV-1-infected, antiretroviral-treated patients who have developed HALS (n = 60); HIV-1-infected, antiretroviral-treated patients without HALS (n = 43); and untreated (naive) HIV-1-infected patients (n = 49). Serum FGF23 levels were compared with lipid and glucose homeostasis parameters, fat distribution and cardiovascular risk.

RESULTS

Serum FGF23 levels were increased in HIV-1-infected patients, but the increase was most marked in those with HALS. FGF23 levels showed a strong positive correlation with age, indicators of dyslipidaemia (LDL cholesterol, polyunsaturated fatty acids and monounsaturated fatty acids), HALS parameters (trunk/appendicular fat ratio), insulin resistance (fasting insulin and homeostasis model assessment of insulin resistance) and C-reactive protein. FGF23 levels correlated with cardiovascular risk but correlation was lost after age adjustment.

CONCLUSIONS

FGF23 levels are increased in HIV-1-infected patients, especially in those with HALS, and this increase is associated with dyslipidaemia, insulin resistance, metabolic syndrome, fat distribution and parameters of inflammation. FGF23 is not associated with cardiovascular risk when age is taken into account.

Vitamin D and chronic kidney disease

Chronic kidney disease (CKD) has been recognized as a significant global health problem because of the increased risk of total and cardiovascular morbidity and mortality. Vitamin D deficiency or insufficiency is common in patients with CKD, and serum levels of vitamin D appear to have an inverse correlation with kidney function. Growing evidence has indicated that vitamin D deficiency may contribute to deteriorating renal function, as well as increased morbidity and mortality in patients with CKD. Recent studies have suggested that treatment with active vitamin D or its analogues can ameliorate renal injury by reducing fibrosis, apoptosis, and inflammation in animal models; this treatment also decreases proteinuria and mortality in patients with CKD. These renoprotective effects of vitamin D treatment are far beyond its classical role in the maintenance of bone and mineral metabolism, in addition to its pleiotropic effects on extra-mineral metabolism. In this review, we discuss the altered metabolism of vitamin D in kidney disease, and the potential renoprotective mechanisms of vitamin D in experimental and clinical studies. In addition, issues regarding the effects of vitamin D treatment on clinical outcomes are discussed.

Non-linear association of serum 25-hydroxyvitamin D with urinary albumin excretion rate in normoalbuminuric subjects

Background

Vitamin D deficiencies and increases in urinary albumin excretion (UAE) are both important and potentially related health problems; however, the nature of their relationship has not been established in normoalbuminuric subjects.

Methods

We obtained data from 14,594 normoalbuminuric Korean adults who underwent voluntary health screenings. We used a generalized additive model to examine the threshold level for relationship between serum 25-hydroxyvitamin D [25(OH)D] and urinary-albumin creatinine ratio (UACR) levels. We conducted multivariate logistic regression for high-normal UAE (UACR, 10–29 mg/g), according to various categories of vitamin D status.

Results

The generalized additive model confirmed a non-linear relationship between serum 25(OH)D and UACR levels, and the threshold concentration of 25(OH)D was 8.0 ng/mL after multivariate adjustment. Comparing subjects who fell into the lowest category of serum 25(OH)D levels with subjects who were in the reference range (the highest category), we observed that the multivariate adjusted odds ratio (OR) for high-normal UAE was significantly increased, regardless of the criteria used to categorize vitamin D levels: OR of the 1^st quartile over the 4^th quartile, 1.20 (95% CI, 1.04-1.39); OR of the 1.0-4.9^th percentile over the 50-100^th percentile, 1.56 (95% CI, 1.25-1.93); and OR of vitamin D deficiency group over vitamin D sufficiency group, 1.28 (95% CI, 1.08-1.52).

Conclusions

We demonstrated that there was an inverse relationship between serum 25(OH)D less than 8.0 ng/mL and UACR in normoalbuminuric subjects, suggesting that severe vitamin D deficiency could cause an increase in UAE in subjects with normoalbuminuria.

Vitamin D and inflammatory diseases

Beyond its critical function in calcium homeostasis, vitamin D has recently been found to play an important role in the modulation of the immune/inflammation system via regulating the production of inflammatory cytokines and inhibiting the proliferation of proinflammatory cells, both of which are crucial for the pathogenesis of inflammatory diseases. Several studies have associated lower vitamin D status with increased risk and unfavorable outcome of acute infections. Vitamin D supplementation bolsters clinical responses to acute infection. Moreover, chronic inflammatory diseases, such as atherosclerosis-related cardiovascular disease, asthma, inflammatory bowel disease, chronic kidney disease, nonalcoholic fatty liver disease, and others, tend to have lower vitamin D status, which may play a pleiotropic role in the pathogenesis of the diseases. In this article, we review recent epidemiological and interventional studies of vitamin D in various inflammatory diseases. The potential mechanisms of vitamin D in regulating immune/inflammatory responses in inflammatory diseases are also discussed.

Increasing use of vitamin D supplementation in the chronic renal insufficiency cohort study

OBJECTIVE

This study examined rates and determinants of vitamin D supplementation among Chronic Renal Insufficiency Cohort (CRIC) participants and determined the association between dose and 25-hydroxyvitamin D (25(OH)D) level. The 2010 Institute of Medicine Report noted a significant increase in vitamin D supplementation in the general population, but use in chronic kidney disease (CKD) is unknown.

METHODS

CRIC is a multicenter prospective observational cohort study of 3,939 participants with a median baseline age of 60 and an estimated glomerular filtration rate (eGFR) of 42.1 mL/minute per 1.73 m2. Of the cohort, 54.9% was male, 42.1% were Black, and 48.4% were diabetic. Multivariable logistic generalized estimating equations were used to examine determinants of supplementation use assessed annually between 2003 and 2011. Cross-sectional linear regression models, based on a subset of 1,155 participants, assessed associations between supplement dose and 25(OH)D level, measured by high-performance liquid chromatography coupled with tandem mass spectrometry.

RESULTS

The proportion of participants reporting supplement use increased (P < .0001), from 10% at baseline to 44% at 7-year follow-up visits. This was largely due to initiation of products containing only ergocalciferol or cholecalciferol. The odds of supplementation were greater in older, female, non-Black, married participants with greater education and lower body mass index. Among participants taking supplementation, dose was positively associated with 25(OH)D level, adjusted for race, season, diabetes, dietary intake, eGFR, and proteinuria. Only 3.8% of non-Black and 16.5% of Black participants taking a supplement were deficient (<20 ng/mL), whereas 22.7% of non-Black and 62.4% of black participants not reporting supplement use were deficient.

CONCLUSIONS

Vitamin D supplementation rates rose significantly among CRIC participants over 7 years of follow-up and were associated with greater serum 25(OH)D levels. Studies of vitamin D levels on clinical outcomes in CKD and future vitamin D interventional studies should consider these changes in supplementation practices.

Vitamin D insufficiency and deficiency with stages of chronic kidney disease in an Asian population

Background

Vitamin D insufficiency is associated with proteinuria and could be a risk factor for end-stage renal disease (ESRD). However, few studies have examined the significance of vitamin D insufficiency as a contributing factor for the development of ESRD in the Asian chronic kidney disease (CKD) population.

Methods

Authors examined the relationship between vitamin D status and the staging of CKD using data from an outpatient clinic-based screening in 2,895 Thai CKD patients. Serum levels of 25-hydroxyvitamin D were analyzed according to CKD stages. Vitamin D deficiency and insufficiency were defined as a serum 25-hydroxyvitamin D concentration < 10 ng/mL and 10–30 ng/mL, respectively.

Results

The mean (SD) 25-hydroxyvitamin D levels were significantly lower according to severity of renal impairment (CKD stage 3a: 27.84±14.03 ng/mL, CKD stage 3b: 25.86±11.14 ng/mL, CKD stage 4: 24.09±11.65 and CKD stage 5: 20.82±9.86 ng/mL, p<0.001). The prevalence of vitamin D deficiency/insufficiency was from CKD stage 3a, 3b, 4 to 5, 66.6%, 70.9%, 74.6%, and 84.7% (p<0.001). The odds ratio (95% CI) of vitamin D insufficiency/deficiency (serum 25-hydroxyvitamin D ≤ 30 ng/mL) and vitamin D deficiency (serum 25-hydroxyvitamin D < 10 ng/mL) for developing ESRD, after adjustment for age, gender, hemoglobin, serum albumin, calcium, phosphate and alkaline phosphatase were 2.19 (95% CI 1.07 to 4.48) and 16.76 (95% CI 4.89 to 57.49), respectively.

Conclusion

This study demonstrates that 25-hydroxyvitamin D insufficiency and deficiency are more common and associated with the level of kidney function in the Thai CKD population especially advanced stage of CKD.

Comparison of mineral metabolites as risk factors for adverse clinical outcomes in CKD

Patients with chronic kidney disease are at increased risk for progressing to end-stage renal disease, developing cardiovascular disease, and dying prematurely. Recent evidence has suggested that disordered mineral metabolism, which includes hyperphosphatemia, secondary hyperparathyroidism, vitamin D deficiency, and fibroblast growth factor 23 excess, may contribute to the high rates of adverse outcomes in this population. However, marked within-subject variability for some of these biochemical parameters exists, potentially detracting from the utility of certain metabolites as prognostic tools. This review summarizes the available data on the epidemiology of phosphate, parathyroid hormone, vitamin D, and fibroblast growth factor 23, and their relationships with adverse clinical outcomes in chronic kidney disease, compares the performance of each as a biomarker of risk and introduces recent insights into the pathophysiology behind some of the observed relationships.

Vitamin D and inflammation

Recent studies have provided evidence for an important role of vitamin D deficiency in the pathogenesis of cardiovascular disease (CVD) in the general population, and of an association with markers of inflammation. Vitamin D deficiency, defined by low serum levels of 25-hydroxyvitamin D, is especially prevalent in patients with chronic kidney disease (CKD). Chronic low-grade inflammation is a hallmark of CKD and has been disclosed as one important factor contributing to the progression of CKD and a high cardiovascular comorbidity. This review highlights clinical and experimental studies that could potentially explain a link between vitamin D and inflammation. Whether correction of vitamin D deficiency has beneficial effects on markers of inflammation and cardiovascular outcome should be investigated by controlled clinical trials.

Targets, trends, excesses, and deficiencies: refocusing clinical investigation to improve patient outcomes

Clinical trials in nephrology have focused on achieving targets, supplementing deficiencies, and correcting excesses in order to improve patient outcomes. The majority of interventions have failed to demonstrate benefit and some have caused harm. It may be that therapies aiming to 'normalize' parameters may actually disturb evolutionary adaptation, thus causing harm. By refocusing on the physiology of disease, and complexity of adaptation, we may design better trials. We review successful and unsuccessful trials in nephrology and other disciplines and suggest a set of principles by which to design future clinical trials:(1) acknowledge heterogeneity of chronic kidney disease populations and appropriately characterize populations for studies; (2) develop better validated biomarkers (through proteomics, genomics, and metabolomics) to identify responders and nonresponders to interventions; (3) design interventions that mimic physiological processes without collateral detrimental effects; (4) reconsider the status of the randomized-controlled trial as the only 'gold standard' and perform large-scale pragmatic trials comparing current care with the intervention(s) of interest, and (5) broaden nephrology research culture so that the majority of patients are enrolled into observational cohorts and intervention studies, which foster greater knowledge acquisition and dissemination. Improved understanding of pathophysiological mechanisms, in conjunction with more innovative but stringent clinical trial design, will ultimately lead to improved patient outcomes.

Nutritional vitamin D use in chronic kidney disease: a survey of pediatric nephrologists

BACKGROUND

Vitamin D deficiency may contribute to risk of cardiovascular disease, diabetes, and infections, in addition to known effects on mineral metabolism. Controversy remains regarding the use of nutritional vitamin D supplementation in chronic kidney disease (CKD), and the supplementation practices of pediatric nephrologists are unknown.

METHODS

An electronic survey containing eight vignettes was sent to physician members of the International Pediatric Nephrology Association in 2011 to identify physician and patient characteristics that influence nephrologists to supplement CKD patients with nutritional vitamin D. Vignettes contained patient characteristics including light vs dark skin, CKD stage, cause of renal disease, parathyroid hormone (PTH), and 25(OH) vitamin D levels. Multivariate logistic generalized estimating equation regression was used to identify predictors of supplementation.

RESULTS

Of 1,084 eligible physicians, 504 (46%) completed the survey. Supplementation was recommended in 73% of cases overall (ranging from 91% of those with vitamin D levels <10 ng/mL to 35% with levels >30). Greater CKD severity was associated with greater recommendation of supplementation, especially for patients with higher vitamin D levels (test for interaction p < 0.0001). PTH level above target for CKD stage was associated with greater recommendation to supplement in pre-dialysis CKD, but did not have an impact on recommendations in dialysis patients (test for interaction p < 0.0001). Skin color, cause of CKD, and albumin levels were not associated with supplementation recommendation.

CONCLUSIONS

Recommending nutritional vitamin D is common worldwide, driven by CKD stage and vitamin D and PTH levels. Future studies are needed to establish the risks and benefits of supplementation.

The world pandemic of vitamin D deficiency could possibly be explained by cellular inflammatory response activity induced by the renin-angiotensin system

This review attempts to show that there may be a relationship between inflammatory processes induced by chronic overstimulation of the renin-angiotensin system (RAS) and the worldwide deficiency of vitamin D (VitD) and that both disorders are probably associated with environmental factors. Low VitD levels represent a risk factor for several apparently different diseases, such as infectious, autoimmune, neurodegenerative, and cardiovascular diseases, as well as diabetes, osteoporosis, and cancer. Moreover, VitD insufficiency seems to predispose to hypertension, metabolic syndrome, left ventricular hypertrophy, heart failure, and chronic vascular inflammation. On the other hand, inappropriate stimulation of the RAS has also been associated with the pathogenesis of hypertension, heart attack, stroke, and hypertrophy of the left ventricle and vascular smooth muscle cells. Because VitD receptors (VDRs) and RAS receptors are almost distributed in the same tissues, a possible link between VitD and the RAS is even more plausible. Furthermore, from an evolutionary point of view, both systems were developed simultaneously, actively participating in the regulation of inflammatory and immunological mechanisms. Changes in RAS activity and activation of the VDR seem to be inversely related; thus any changes in one of these systems would have a completely opposite effect on the other, making it possible to speculate that the two systems could have a feedback relationship. In fact, the pandemic of VitD deficiency could be the other face of increased RAS activity, which probably causes lower activity or lower levels of VitD. Finally, from a therapeutic point of view, the combination of RAS blockade and VDR stimulation appears to be more effective than either RAS blockade or VDR stimulation individually.

Factors related to nephrotic-range proteinuria in late-stage chronic kidney disease patients with diabetes mellitus

PURPOSE

Diabetic nephropathy and proteinuria are important risk factors for both end-stage renal disease and cardiovascular events. The present study aimed to identify the factors associated with nephrotic-range proteinuria in patients with advanced diabetic nephropathy.

METHODS

This cross-sectional study enrolled 386 diabetic patients with chronic kidney disease (CKD) stages 3-5, from our outpatient Department of Nephrology. Urinary protein-to-creatinine ratio was recorded. Additionally, other laboratory parameters, body mass index, blood pressure, comorbidities, and medications were also reviewed.

RESULTS

The mean age of the patients was 65.1 ± 11.6 years. Among patients with CKD stage 3 and 4, the odds ratio (OR) for nephrotic-range proteinuria in relation with systolic blood pressure significantly increased starting from 121 mmHg (OR 7.04 and 11.79 for systolic blood pressure of 121-140 and ≥141 mmHg, respectively, in comparison with systolic blood pressure below 121 mmHg). In addition, serum phosphorus ≥4.7 mg/dl was associated with significantly higher risk (OR 15.45) for severe proteinuria, compared with a phosphorus level ≤2.6 mg/dl. Finally, hypertriglyceridemia ≥241 mg/dl was also associated with higher OR for severe proteinuria, compared with a triglyceride level ≤200 mg/dl. Similar associations were found in patients with CKD stage 5.

CONCLUSIONS

Higher systolic blood pressure, serum phosphorus, and triglyceride levels are associated with nephrotic-range proteinuria in patients with diabetic nephropathy and CKD stage 3-5. Further studies should clarify whether a reduction in serum phosphorus would lead to a decrease in proteinuria in these patients.

Lanthanum Carbonate Modulates Inflammatory Profile in Hemodialysis Patients: Relationship with Fibroblast Growth Factor-23

Elevated fibroblast growth factor 23 (FGF-23) is independently associated with increased inflammatory markers in chronic kidney disease. Lanthanum carbonate (LaCa) reduces FGF-23. We studied the effects of LaCa on inflammatory profile of hemodialysis patients, and the relationship with changes in FGF-23. This prospective study was performed under habitual clinical practice conditions. Twenty-six hemodialysis patients with serum phosphate > 5 mg/dl receiving calcium-based phosphate binders were switched to LaCa. Ten patients with phosphate ≤ 5 mg/dl under calcium-based phosphate binders were enrolled as a control group for comparison. Serum calcium, phosphorus, calcium-phosphate product (CaxP), intact parathyroid hormone and the inflammatory profile [including serum high-sensitivity C-reactive protein (hs-CRP), tumor necrosis factor-α (TNF-α), interleukin (IL)-6 and IL-10, as well as mRNA expression levels of TNF-α and IL-6 in peripheral blood mononuclear cells] were analyzed. Serum FGF-23 significantly decreased in patients switched to LaCa (P< 0.01), with a concomitant reduction in serum hsCRP (-10.9%, P < 0.01), TNF-α (-6.7%, P < 0.05) and IL-6 (-8.1%, P < 0.01). mRNA expression levels of TNF-α and IL-6 in PBMC also decreased by 7.8% (P< 0.05) and 10.3% (P< 0.01), respectively. Multivariate regression analysis demonstrated that variations in FGF-23 were the only independent determinant of the changes in serum and mRNA expression levels of inflammatory parameters. In conclusion, LaCa posses anti-inflammatory actions, which are significant and independently associated with the reduction of FGF-23. FGF-23 may regulate inflammatory cytokine gene expression at the transcriptional level. Whether these effects have influence on clinical outcomes warrants consideration.

CYP24A1 exacerbated activity during diabetes contributes to kidney tubular apoptosis via caspase-3 increased expression and activation

Decreases in circulating 25,hydroxyl-vitamin D3 (25 OH D3) and 1,25,dihydroxyl-vitamin D3 (1,25 (OH)2 D3) have been extensively documented in patients with type 2 diabetes. Nevertheless, the molecular reasons behind this drop, and whether it is a cause or an effect of disease progression is still poorly understood. With the skin and the liver, the kidney is one of the most important sites for vitamin D metabolism. Previous studies have also shown that CYP24A1 (an enzyme implicated in vitamin D metabolism), might play an important role in furthering the progression of kidney lesions during diabetic nephropathy. In this study we show a link between CYP24A1 increase and senescence followed by apoptosis induction in the renal proximal tubules of diabetic kidneys. We show that CYP24A1 expression was increased during diabetic nephropathy progression. This increase derived from protein kinase C activation and increased H₂O₂ cellular production. CYP24A1 increase had a major impact on cellular phenotype, by pushing cells into senescence, and later into apoptosis. Our data suggest that control of CYP24A1 increase during diabetes has a beneficial effect on senescence induction and caspase-3 increased expression. We concluded that diabetes induces an increase in CYP24A1 expression, destabilizing vitamin D metabolism in the renal proximal tubules, leading to cellular instability and apoptosis, and thereby accelerating tubular injury progression during diabetic nephropathy.

Vitamin D supplementation in pre-dialysis chronic kidney disease: A systematic review

Vitamin D deficiency is associated with a variety of skeletal, cardiometabolic, and immunologic co-morbidities that are present in chronic kidney disease (CKD). We performed a systematic review to investigate the effects of vitamin D supplementation, in the form of ergocalciferol or cholecalciferol, on various health outcomes in early CKD. Seventeen clinical trials were identified, only two of which were randomized, placebo controlled trials. The majority of studies supplementing with > 2,000 IU/day of cholecalciferol achieved optimal vitamin D status, whereas studies supplementing with ergocalciferol were less consistent. Studies varied widely in their effects on lowering serum parathyroid hormone concentrations. Few studies investigated effects of vitamin D treatment on other clinical health indicators in early CKD. Rigorous studies are necessary to investigate optimal vitamin D dosing strategies in early CKD for the maintenance of adequate vitamin D status, management of secondary hyperparathyroidism and improvement of non-skeletal related clinical outcomes.

High-dose cholecalciferol reduces parathyroid hormone in patients with early chronic kidney disease: a pilot, randomized, double-blind, placebo-controlled trial

BACKGROUND

Vitamin D deficiency contributes to secondary hyperparathyroidism, which occurs early in chronic kidney disease (CKD).

OBJECTIVES

We aimed to determine whether high-dose cholecalciferol supplementation for 1 y in early CKD is sufficient to maintain optimal vitamin D status (serum 25-hydroxyvitamin D [25(OH)D] concentration ≥30 ng/mL) and decrease serum parathyroid hormone (PTH). A secondary aim was to determine the effect of cholecalciferol on blood pressure and serum fibroblast growth factor-23 (FGF23).

DESIGN

This was a double-blind, randomized, placebo-controlled trial. Forty-six subjects with early CKD (stages 2-3) were supplemented with oral cholecalciferol (vitamin D group; 50,000 IU/wk for 12 wk followed by 50,000 IU every other week for 40 wk) or a matching placebo for 1 y.

RESULTS

By 12 wk, serum 25(OH)D increased in the vitamin D group only [baseline (mean ± SD): 26.7 ± 6.8 to 42.8 ± 16.9 ng/mL; P < 0.05] and remained elevated at 1 y (group-by-time interaction: P < 0.001). PTH decreased from baseline only in the vitamin D group (baseline: 89.1 ± 49.3 to 70.1 ± 24.8 pg/mL; P = 0.01) at 12 wk, but values were not significantly different from baseline at 1 y (75.4 ± 29.5 pg/mL; P = 0.16; group-by-time interaction: P = 0.09). Group differences were more pronounced in participants with secondary hyperparathyroidism (group-by-time interaction: P = 0.004). Blood pressure and FGF23 did not change in either group.

CONCLUSIONS

After 1 y, this oral cholecalciferol regimen was safe and sufficient to maintain serum 25(OH)D concentrations and prevent vitamin D insufficiency in early CKD. Furthermore, serum PTH improved after cholecalciferol treatment, particularly in patients who had secondary hyperparathyroidism.

25-Hydroxyvitamin D levels and chronic kidney disease in the AusDiab (Australian Diabetes, Obesity and Lifestyle) study

Background

Low 25-hydroxy vitamin D (25(OH)D) levels have been associated with an increased risk of albuminuria, however an association with glomerular filtration rate (GFR) is not clear. We explored the relationship between 25(OH)D levels and prevalent chronic kidney disease (CKD), albuminuria and impaired GFR, in a national, population-based cohort of Australian adults (AusDiab Study).

Methods

10,732 adults ≥25 years of age participating in the baseline survey of the AusDiab study (1999–2000) were included. The GFR was estimated using an enzymatic creatinine assay and the CKD-EPI equation, with CKD defined as eGFR <60 ml/min/1.73 m². Albuminuria was defined as a spot urine albumin to creatinine ratio (ACR) of ≥2.5 mg/mmol for men and ≥3.5 for women. Serum 25(OH)D levels of <50 nmol/L were considered vitamin D deficient. The associations between 25(OH)D level, albuminuria and impaired eGFR were estimated using multivariate regression models.

Results

30.7% of the study population had a 25(OH)D level <50 nmol/L (95% CI 25.6-35.8). 25(OH)D deficiency was significantly associated with an impaired eGFR in the univariate model (OR 1.52, 95% CI 1.07-2.17), but not in the multivariate model (OR 0.95, 95% CI 0.67-1.35). 25(OH)D deficiency was significantly associated with albuminuria in the univariate (OR 2.05, 95% CI 1.58-2.67) and multivariate models (OR 1.54, 95% CI 1.14-2.07).

Conclusions

Vitamin D deficiency is common in this population, and 25(OH)D levels of <50 nmol/L were independently associated with albuminuria, but not with impaired eGFR. These associations warrant further exploration in prospective and interventional studies.

Fibroblast growth factor 23 and Inflammation in CKD

BACKGROUND AND OBJECTIVES

Levels of fibroblast growth factor 23 (FGF23) and inflammatory markers are commonly elevated in CKD, and each is associated with adverse clinical outcomes. This study tested the hypothesis that FGF23 is independently associated with inflammation in CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The association between levels of FGF23 and the inflammatory markers IL-6, C-reactive protein (CRP), TNF-α, and fibrinogen was assessed in a cross-sectional analysis of 3879 participants enrolled in the Chronic Renal Insufficiency Cohort (CRIC) study between June 2003 and September 2008.

RESULTS

FGF23 correlated directly with IL-6 (r=0.4), CRP (r=0.2), TNF-α (r=0.4), and fibrinogen (r=0.3; P<0.001 for each). In univariate and multivariable-adjusted linear regression analyses, natural log (ln) transformed FGF23 was significantly associated with lnIL-6, lnCRP, lnTNF-α, and fibrinogen (P<0.001 for each). Each unit higher lnFGF23 was associated with severe inflammation, defined as levels of all inflammatory markers in the highest 25th percentile, in univariate (odds ratio [OR], 2.4 [95% confidence interval (CI), 2.0-2.9]) and multivariable-adjusted (OR, 2.0 [95% CI, 1.6-2.5]) logistic regression analyses. Ascending FGF23 quartiles were independently associated with severe inflammation (OR, 5.6 for the highest versus lowest FGF23 quartile [95% CI, 2.3-13.9]; P for trend < 0.001).

CONCLUSIONS

Higher FGF23 levels are independently associated with higher levels of inflammatory markers in patients with CKD and with significantly greater odds of severe inflammation. Future studies should evaluate whether inflammation modifies the association between FGF23 and adverse outcomes in CKD.

Fibroblast growth factor 23 is associated with proteinuria and smoking in chronic kidney disease: an analysis of the MASTERPLAN cohort

BACKGROUND

Fibroblast growth factor 23 (FGF23) has emerged as a risk factor for cardiovascular disease and mortality throughout all stages of chronic kidney disease (CKD), independent from established risk factors and markers of mineral homeostasis. The relation of FGF23 with other renal and non-renal cardiovascular risk factors is not well established.

METHODS

Using stored samples, plasma FGF23 was determined in 604 patients with moderate to severe kidney disease that participated in the MASTERPLAN study (ISRCTN73187232). The association of FGF23 with demographic and clinical parameters was evaluated using multivariable regression models.

RESULTS

Mean age in the study population was 60 years and eGFR was 37 (± 14) ml/min/1.73 m(2). Median proteinuria was 0.3 g/24 hours [IQR 0.1-0.9]. FGF23 level was 116 RU/ml [67-203] median and IQR. Using multivariable analysis the natural logarithm of FGF23 was positively associated with history of cardiovascular disease (B = 0.224 RU/ml; p = 0.002), presence of diabetes (B = 0.159 RU/ml; p = 0.035), smoking (B = 0.313 RU/ml; p < 0.001), phosphate level (B = 0.297 per mmol/l; p = 0.0024), lnPTH (B = 0.244 per pmol/l; p < 0.001) and proteinuria (B = 0.064 per gram/24 hrs; p = 0.002) and negatively associated with eGFR (B = -0.022 per ml/min/1.73 m(2); p < 0.001).

CONCLUSIONS

Our study demonstrates that in patients with CKD, FGF23 is related to proteinuria and smoking. We confirm the relation between FGF23 and other cardiovascular risk factors.

Vitamin D deficiency and persistent proteinuria among HIV-infected and uninfected injection drug users

OBJECTIVE

Proteinuria occurs commonly among HIV-infected and uninfected injection drug users (IDUs) and is associated with increased mortality risk. Vitamin D deficiency, highly prevalent among IDUs and potentially modifiable, may contribute to proteinuria. To determine whether vitamin D is associated with proteinuria in this population, we conducted a cross-sectional study in the AIDS Linked to the IntraVenous Experience (ALIVE) Study.

METHODS

25(OH)-vitamin D levels were measured in 268 HIV-infected and 614 HIV-uninfected participants. The association between vitamin D deficiency (<10  ng/ml) and urinary protein excretion was evaluated by linear regression. The odds of persistent proteinuria (urine protein-to-creatinine ratio >200  mg/g on two occasions) associated with vitamin D deficiency was examined using logistic regression.

RESULTS

One-third of participants were vitamin D-deficient. Vitamin D deficiency was independently associated with higher urinary protein excretion (P < 0.05) among HIV-infected and diabetic IDUs (P-interaction < 0.05 for all). Persistent proteinuria occurred in 18% of participants. Vitamin D deficiency was associated with greater than six-fold odds of persistent proteinuria among diabetic IDUs [odds ratio (OR) 6.29, 95% confidence interval (CI) 1.54, 25.69] independent of sociodemographic characteristics, comorbid conditions, body mass index, and impaired kidney function [estimated glomerular filtration rate (eGFR) <60  ml/min per 1.73  m(2)]; no association, however, was observed among nondiabetic IDUs (OR 1.06, 95% CI 0.64, 1.76) (P-interaction <0.05).

CONCLUSIONS

Vitamin D deficiency was associated with higher urinary protein excretion among those with HIV infection and diabetes. Vitamin D deficiency was independently associated with persistent proteinuria among diabetic IDUs, although not in nondiabetic persons. Whether vitamin D repletion ameliorates proteinuria in these patients requires further study.

Vitamin D deficiency is common in children and adolescents with chronic kidney disease

Here we determined if vitamin D deficiency is more common in children with chronic kidney disease compared to healthy children. In addition, we sought to identify disease-specific risk factors for this deficiency, as well as its metabolic consequences. We found that nearly half of 182 patients (ages 5 to 21) with kidney disease (stages 2 to 5) and a third of age-matched 276 healthy children were 25-hydroxyvitamin D deficient (<20 ng/ml). The risk of deficiency was significantly greater in advanced disease. Focal segmental glomerulosclerosis and low albumin were significantly associated with lower 25-hydroxyvitamin D, which, in turn, was associated with significantly higher intact parathyroid hormone levels. We found that 25-hydroxyvitamin D levels were positively associated with 1,25-dihydroxyvitamin D, the relationship being greatest in advanced disease (significant interaction), and inversely related to those of inflammatory markers C-reactive protein and IL-6. The association with C-reactive protein persisted when adjusted for the severity of kidney disease. Thus, lower 25-hydroxyvitamin D may contribute to hyperparathyroidism, inflammation, and lower 1,25-dihydroxyvitamin D in children and adolescents, especially those with advanced kidney disease.