Vitamin D resistance in chronic kidney disease (CKD)

Population Pharmacokinetic Model of Vitamin D3 and Metabolites in Chronic Kidney Disease Patients with Vitamin D Insufficiency and Deficiency

Vitamin D insufficiency and deficiency are highly prevalent in patients with chronic kidney disease (CKD), and their pharmacokinetics are not well described. The primary study objective was to develop a population pharmacokinetic model of oral cholecalciferol (VitD3) and its three major metabolites, 25-hydroxyvitamin D3 (25D3), 1,25-dihydroxyvitamin D3 (1,25D3), and 24,25-dihydroxyvitamin D3 (24,25D3), in CKD patients with vitamin D insufficiency and deficiency. CKD subjects (n = 29) were administered one dose of oral VitD3 (5000 I.U.), and nonlinear mixed effects modeling was used to describe the pharmacokinetics of VitD3 and its metabolites. The simultaneous fit of a two-compartment model for VitD3 and a one-compartment model for each metabolite represented the observed data. A proportional error model explained the residual variability for each compound. No assessed covariate significantly affected the pharmacokinetics of VitD3 and metabolites. Visual predictive plots demonstrated the adequate fit of the pharmacokinetic data of VitD3 and metabolites. This is the first reported population pharmacokinetic modeling of VitD3 and metabolites and has the potential to inform targeted dose individualization strategies for therapy in the CKD population. Based on the simulation, doses of 600 International Unit (I.U.)/day to 1000 I.U./day for 6 months are recommended to obtain the target 25D3 concentration of between 30 and 60 ng/mL. These simulation findings could potentially contribute to the development of personalized dosage regimens for vitamin D treatment in patients with CKD.

Non-alcoholic fatty liver and chronic kidney disease: Retrospect, introspect, and prospect

With the growing prevalence of obesity and diabetes in the United States and across the world, a rise in the overall incidence and prevalence of non-alcoholic fatty liver disease (NAFLD) is expected. The risk factors for NAFLD are also associated with the development of chronic kidney disease (CKD). We review the epidemiology, risk factors, genetics, implications of gut dysbiosis, and specific pathogenic mechanisms linking NAFLD to CKD. Mechanisms such as ectopic lipid accumulation, cellular signaling abnormalities, and the interplay between fructose consumption and uric acid accumulation have led to the emergence of potential therapeutic implications for this patient population. Transplant evaluation in the setting of both NAFLD and CKD is also reviewed. Potential strategies for surveillance and management include the monitoring of comorbidities, the use of non-invasive fibrosis scoring systems, and the measurement of laboratory markers. Lastly, we discuss the management of patients with NAFLD and CKD, from preventative measures to experimental interventions.

[Nutrition in chronic kidney disease]

INTRODUCTION

Chronic kidney disease patients often also present protein-calorie malnutrition, and it is a powerful predictor of morbidity and mortality. In this article, causes and management are shown, highlighting oral and parenteral nutritional supplementation, especially during dialysis process.

The Effect of Long-Term Cholecalciferol Supplementation on Vascular Calcification in Chronic Kidney Disease Patients With Hypovitaminosis D

OBJECTIVE

The role of vitamin D supplementation on vascular calcification (VC) in patients with chronic kidney disease (CKD) is controversial. The objective of this study was to evaluate the effects of long-term cholecalciferol supplementation on VC in nondialysis patients with CKD stages 3-4 with hypovitaminosis D.

DESIGN AND METHODS

Eighty patients aged 18-85 years with creatinine clearance between 15 and 60 mL/min/1.73 m² and serum 25(OH)D level < 30 ng/mL were enrolled in a 18-month prospective study. Individuals with vitamin D insufficiency (25-hydroxyvitamin D [25(OH)D] level between 16 and 29 ng/mL) were included in a randomized, double-blind, two-arm study to receive cholecalciferol or placebo. Patients with vitamin D deficiency [25(OH)D < 15 ng/mL] were included in an observational study and mandatorily received cholecalciferol. The coronary artery calcium score was obtained by multislice computed tomography at baseline and the 18th month.

RESULTS

During the study, VC did not change in the treated insufficient group (418 [81-611] to 364 [232-817] AU, P = 0.25) but increased in the placebo group (118 [37-421] to 199 [49-490] AU, P = 0.01). The calcium score change was inversely correlated with 25(OH)D change (r = -0.45; P = 0.037) in the treated insufficient group but not in the placebo group. Renal function did not change in the insufficient, treated, and placebo groups. In multivariate analysis, there was no difference in VC progression between the treated and placebo insufficient groups (interaction P = 0.92). In the deficient group, VC progressed (265 [84-733] to 333 [157-745] AU; P = 0.006) and renal function declined (33 [26-43] to 23 [17-49] mL/min/1.73 m²; P = 0.04). The calcium score change was inversely correlated with cholecalciferol cumulative doses (r = -0.41; P = 0.048) and kidney function change (r = -0.43; P = 0.033) but not with 25(OH)D change (r = -0.08; P = 0.69).

CONCLUSION

Vitamin D supplementation did not attenuate VC progression in CKD patients with hypovitaminosis D.

CONCLUSION

Vitamin D supplementation did not attenuate VC progression in CKD patients with hypovitaminosis D.

Determination of vitamin D in tears of healthy individuals by the electrochemiluminescence method

BACKGROUND

Vitamin D is a fat-soluble steroid hormone which can be converted into various forms and is of extreme physiological importance to our body. However, its functions and local metabolic pathways in some organs, such as the eye, have not yet been well studied. We aimed to verify the correlation between vitamin D levels in blood and tear fluid and the possibility of using tear fluid as a biological material for monitoring eye disorders in the future.

METHODS

The electrochemiluminescence method was used to examine blood and tear samples collected with Schirmer test strips from 21 individuals without ocular disease.

RESULTS

At the 95% confidence interval, mean tear fluid vitamin D = 37.8 ± 3.6 ng/mL, which is higher than the serum level, with a mean of 30.3 ± 7.7 ng/mL; Lin's concordance correlation coefficient = -0.018 (-0.174; 0.139), Pearson's coefficient = -0.070, and the Bland-Altman coefficient = -11.12 (-30.40; 8.16). Results were obtained using the program Stata version 11.0.

CONCLUSION

It is possible to determine vitamin D levels in tear fluid using the electrochemiluminescence method, and as the results do not correlate with blood, there is possibility of using tear fluid as a biological matrix for detection of vitamin D, which may increase the possibilities of new studies in eye disorders.

Gonadal Hormones in the Pathogenesis and Treatment of Bone Health in Patients with Chronic Kidney Disease: a Systematic Review and Meta-Analysis

PURPOSE OF REVIEW

Patients with chronic kidney disease (CKD) have a greatly increased fracture risk compared with the general population. Gonadal hormones have an important influence on bone mineral density (BMD) and fracture risk, and hormone therapies can significantly improve these outcomes. Gonadal dysfunction is a frequent finding in patients with CKD; yet, little is known about the impact of gonadal hormones in the pathogenesis and treatment of bone health in patients with CKD. This systematic review and meta-analysis aimed to examine the effects of gonadal hormones and hormone therapies on bone outcomes in men and women with CKD.

METHODS

EMBASE, MEDLINE, SCOPUS, and clinical trial registries were systematically searched from inception to February 14, 2018 for studies that assessed gonadal hormones or hormone treatments with bone outcomes in patients with CKD stage 3-5D. Two independent reviewers screened the titles and abstracts of search results according to inclusion criteria and assessed study quality and risk of bias using validated assessment tools.

RECENT FINDINGS

Thirteen studies met the inclusion criteria. Six moderate-to-high quality observational studies showed inconsistent association between any gonadal hormone and bone outcomes, limited by significant study heterogeneity. Five moderate-high risk of bias interventional studies examined treatment with selective oestrogen receptor modulators in post-menopausal women (four using raloxifene and one bazedoxifene) and demonstrated variable effects on BMD and fracture outcomes. Meta-analysis of raloxifene treatment in post-menopausal women demonstrated improvement in lumbar spine (SMD 3.30; 95% CI 3.21-3.38) and femoral neck (SMD 3.29; 95% CI 3.21-3.36) BMD compared with placebo. Transdermal oestradiol/norethisterone in pre-menopausal women receiving dialysis (n = 1 study), demonstrated BMD improvement over 12 months. Testosterone treatment for 6 months in dialysis-dependant men (n = 1 study) did not improve BMD. There is evidence that raloxifene treatment may be beneficial in improving BMD in post-menopausal women with CKD. There is insufficient evidence for other hormone treatments in men or women. Despite high fracture rates and frequent gonadal dysfunction in patients with CKD, significant evidence gaps exist, and well-designed studies are required to specifically assess the impact of gonadal status in the pathogenesis of CKD-related bone fragility and its treatment.

Vitamin D (25(OH)D) in patients with chronic kidney disease stages 2-5

OBJECTIVE

To establish the impact the chronic kidney disease stage has in the native vitamin D levels in patients not undergoing dialysis treatment.

METHODS

A study performed in Manizales, Colombia, a city located 2,200 meters above sea level, without important stational variations. Patients with 18 years of age or more, with chronic kidney disease stages 2 to 5 and not undergoing dialysis treatment were recruited for this study. Demographic and anthropometric variations were evaluated as well as solar exposure, CKD etiology and laboratory variables related to bone and mineral diseases. For each CKD clinical stage, correlations were evaluated for vitamin D levels, laboratory results for bone and mineral diseases, solar exposure and ethnicity.

RESULTS

Three hundred thirty-three patients were evaluated with a median age of 71 years, most of them mestizo (71%), 173 were women. The main CKD etiology was hypertensive nephropathy (32.2%). 21.1% of patients had normal vitamin D levels, 70.1% were within insufficient range and 8.8% were in deficit. A negative correlation was found between the levels of vitamin 25 (OH) D and the values for: creatinine, phosphorous, calcium x phosphorous product, PTH, 24 hours urine protein and BMI. A positive relationship was found for calcium and albumin. Positive significant statistical correlation was found for vitamin 25(OH) D levels and solar exposure for stages 3b and 4 of CKD.

CONCLUSIONS

It is common to find low levels of vitamin 25(OH) D in patients with CKD; these can contribute to the appearance of secondary hyperparathyroidism.

OBJETIVO

Establecer el impacto del estadio clínico en los niveles de vitamina D nativa en pacientes con enfermedad renal crónica (ERC) sin diálisis.

MÉTODOS

Estudio realizado en Manizales, Colombia, una ciudad tropical ubicada a 2,200 metros de altura sobre el nivel del mar, sin variaciones estacionales importantes a lo largo del año. Se incluyeron pacientes mayores de 18 años, con enfermedad renal crónica estadio 2 a 5 sin tratamiento dialítico. En ellos se evaluaron variables demográficas, antropométricas, grado de exposición solar, etiología de la enfermedad, y variables de laboratorio relacionadas con desórdenes óseos y minerales. Para cada estadío clínico se evaluó la correlación entre los niveles de vitamina D y los resultados de las pruebas de laboratorio relacionadas con desordenes óseos y minerales, exposición solar y etnia.

RESULTADOS

Se evaluaron 331 pacientes, con una edad media de 71 años, la mayoría mestizos (71%), 173 mujeres. La principal etiología de ERC fue nefropatía hipertensiva (33.2%). El 21.1% de los pacientes tenían niveles normales de vitamina D, fueron insuficientes en 70.1% y 8.8% en déficit. Se detectó correlación negativa, entre los niveles de vitamina 25(OH)D y los valores de creatinina, fósforo, producto calcio x fósforo, PTH, proteínas en orina de 24 horas e IMC. Correlación positiva para el calcio y la albumina. Se encontró significancia estadística positiva entre los niveles de vitamina 25(OH)D y la exposición solar para los estadios 3b y 4.

CONCLUSIONES

En pacientes con ERC es comun detectar bajos niveles de 25(OH)D, los cuales pueden contribuir a la generación de hiperparatiroidismo secundario.

Vitamin D in Tear Fluid

PURPOSE

To determine the source(s) of vitamin D in tear fluid and examine the expression of the endocytic proteins and putative vitamin D transporters megalin and cubilin in lacrimal and Harderian glands.

METHODS

Wild-type, heterozygous, and vitamin D receptor (VDR) knockout C57BL/6 mice were used, with a subset of knockout mice fed a replenishment diet for some studies. Mouse lacrimal and Harderian glands from each group were used to measure megalin and cubilin by RT-PCR, Western blot, and immunohistochemistry. New Zealand white rabbits were used to collect lacrimal and accessory gland fluid for vitamin D mass spectroscopy measurements.

RESULTS

Ten-week-old knockout mice were significantly (P < 0.05) smaller than wild-type mice. Real-time PCR and Western blot showed decreased expression of megalin and cubilin in select VDR knockout mouse groups. Immunohistochemistry showed apical duct cell megalin staining and weaker megalin staining in VDR knockout mice compared with controls. Vitamin D2 was more prevalent in rabbit lacrimal and accessory gland fluid than vitamin D3, and greater amounts of Vitamin D2 were found in in tear fluid obtained directly from lacrimal and accessory glands as compared with plasma concentrations.

CONCLUSIONS

This is the first study to demonstrate the presence of megalin and cubilin in lacrimal and accessory glands responsible for producing tear fluid. The results strengthen the hypothesis that megalin and cubilin are likely involved in the secretory pathway of vitamin D into tear fluid by the duct cells.

The Prognostic Role of Red Blood Cell Distribution Width in Coronary Artery Disease: A Review of the Pathophysiology

Red blood cell distribution width (RDW) is a measure of red blood cell volume variations (anisocytosis) and is reported as part of a standard complete blood count. In recent years, numerous studies have noted the importance of RDW as a predictor of poor clinical outcomes in the settings of various diseases, including coronary artery disease (CAD). In this paper, we discuss the prognostic value of RDW in CAD and describe the pathophysiological connection between RDW and acute coronary syndrome. In our opinion, the negative prognostic effects of elevated RDW levels may be attributed to the adverse effects of independent risk factors such as inflammation, oxidative stress, and vitamin D₃ and iron deficiency on bone marrow function (erythropoiesis). Elevated RDW values may reflect the intensity of these phenomena and their unfavorable impacts on bone marrow erythropoiesis. Furthermore, decreased red blood cell deformability among patients with higher RDW values impairs blood flow through the microcirculation, resulting in the diminution of oxygen supply at the tissue level, particularly among patients suffering from myocardial infarction treated with urgent revascularization.

Prevalence and prognostic implications of vitamin D deficiency in chronic kidney disease

Vitamin D is an important nutrient involved in bone mineral metabolism, and vitamin D status is reflected by serum total 25-hydroxyvitamin D (25[OH]D) concentrations. Vitamin D deficiency is highly prevalent in patients with chronic kidney disease (CKD), and nutritional vitamin D supplementation decreases elevated parathyroid hormone concentrations in subgroups of these patients. Furthermore, vitamin D is supposed to have pleiotropic effects on various diseases such as cardiovascular diseases, malignancies, infectious diseases, diabetes, and autoimmune diseases. Indeed, there is cumulative evidence showing the associations of low vitamin D with the development and progression of CKD, cardiovascular complication, and high mortality. Recently, genetic polymorphisms in vitamin D-binding protein have received great attention because they largely affect bioavailable 25(OH)D concentrations. This finding suggests that the serum total 25(OH)D concentrations would not be comparable among different gene polymorphisms and thus may be inappropriate as an index of vitamin D status. This finding may refute the conventional definition of vitamin D status based solely on serum total 25(OH)D concentrations.