Possible Influence of Vitamin D Receptor Gene Polymorphisms on Recombinant Human Erythropoietin Requirements in Dialysis Patients

Association between vitamin D receptor (FokI) genetic variant rs2228570 and iron profile in hemodialysis patients

Iron deficiency is a common etiology of anemia that causes suboptimal response to erythropoietin therapy in hemodialysis (HD) patients. This study investigated the association between vitamin D receptor (VDR) genetic variant (FokI) rs2228570 with iron indices (serum iron, transferrin, transferrin saturation, and ferritin). Sixty adequately hemodialyzed patients subdivided into two groups; 31 patients with transferrin saturation (TSAT) < 20% and 29 with TSAT > 20% who received I.V sodium ferric gluconate, calcium, and vitamin D. Sixty normal healthy were selected as the control group.. VDR genetic variant (SNP rs2228570) was genotyped in all subjects using PCR/RFLP. HD patients showed a higher frequency of rs2228570 FF genotype (38.3%) than controls (31.7%). The frequency of ff genotype and f allele in patients (8.4 and 35% respectively) were significantly lower than controls (25 and 46.7% respectively). Allele model (f vs. F): OR 0.721, 95% CI 0.521-0.998, P = 0.049. While (ff vs. FF): OR 0.452, 95% CI 0.223-0.917, P = 0.028. The distribution of Ff + ff genotypes in HD cases with TSAT > 20% was higher than in HD cases with TSAT < 20%, Dominant model (Ff +ff vs FF): OR 2.753, 95% CI 1.902-3.409, P = 0.048. f allele showed lower frequency in low TSAT group than high TSAT group (27.4 vs. 43.1%) with significant P value (P = 0.042) with allele model (f vs. F): OR 2.012, 95% CI 1.923-4.226, P = 0.042. Fok-1 ff, Ff + ff genotypes were significantly associated with TSAT > 20% with a protective effect against low TSAT in HD patients.

Relationship between vitamin D receptor gene polymorphisms and anemia in postmenopausal Vietnamese women

Background: Both in vitro and in vivo studies have shown that calcitriol, the active form of vitamin D, is involved in hematopoiesis. Vitamin D receptor (VDR) gene has been suggested as one of the candidate genes for anemia. Objective: Investigate relationship between anemia and the commonly studied polymorphisms of VDR gene (FokI, BsmI, ApaI and TaqI) in terms of genotype and haplotype in Vietnamese. Methods: A case-control study including 132 postmenopausal women without chronic kidney diseases was designed to investigate the relationship between VDR polymorphism and anemia. Four single nucleotide polymorphisms (SNPs) FokI (rs2228570), BsmI (rs1544410), ApaI (rs7975232), and TaqI (rs731236) were typed by polymerase chain reaction and restriction fragment length polymorphism method. Results: Genotype distributions of four SNPs were in Hardy-Weinberg equilibrium in both anemia and control groups. The SNPs at the 3’end of the VDR gene (BsmI, ApaI and TaqI) exhibited a strong linkage disequilibrium. There was no significant association between anemia and VDR polymorphism in terms of allele, genotype, and haplotype in the analyses unadjusted or adjusted for the covariates (age, body mass index, educational level, serum ferritin, iron and albumin). Conclusion: VDR gene did not influence anemia in postmenopausal women without chronic kidney disease. For further study on the association between VDR gene and anemia, the use of larger sample size, a prospective study design, and additional markers would enhance the reliability and validity of findings.

Association between hematological profile and serum 25-hydroxyvitamin D levels and FokI polymorphism in individuals with cystic fibrosis

ABSTRACT Objective The present study aimed at investigating the association between hematological profile and serum 25-hydroxyvitamin D (25[OH]D) levels and Fokl polymorphism of the vitamin D receptor gene in individuals with Cystic Fibrosis. Methods A cross-sectional study that involved 18 men and women aged 0-25 years with Cystic Fibrosis. Socio-demographic information and the factors associated with sun exposure were obtained. Weight, height, and arm circumference were also measured. Blood sample was collected for the analysis of biochemical parameters (25[OH]D, parathyroid hormone, and calcium levels and blood count) and for the validation of the presence of FokI polymorphism in the vitamin D receptor gene. Results Among the participants, 33.33% (n=6) had vitamin D deficiency (19.60±6.180 ng/mL), and 27.8% (n=5) presented with anemia and low weight for age. In terms of genotype, 5.6% (n=1) presented with the FF genotype, 72.3% (n=13) had the Ff genotype, and 22.2% (n=4) had the ff genotype. Serum 25(OH)D levels were associated with hemoglobin (p=0.008) and hematocrit (p=0.019) levels and leukocyte count (p=0.0114). No association was observed between 25(OH)D levels and the genotypes (FF, Ff, and ff) (p=0.2451). In addition, an association was observed between FokI polymorphism and the total leukocyte count (p=0.01). Conclusion An association was observed between serum 25(OH)D levels and hemoglobin and hematocrit levels and leukocyte count in individuals with Cystic Fibrosis. Moreover, FokI polymorphism was associated with total leukocyte count.

Vitamin D Receptor: A Novel Therapeutic Target for Kidney Diseases

BACKGROUND

Kidney disease is a serious problem that adversely affects human health, but critical knowledge is lacking on how to effectively treat established chronic kidney disease. Mounting evidence from animal and clinical studies has suggested that Vitamin D Receptor (VDR) activation has beneficial effects on various renal diseases.

METHODS

A structured search of published research literature regarding VDR structure and function, VDR in various renal diseases (e.g., IgA nephropathy, idiopathic nephrotic syndrome, renal cell carcinoma, diabetic nephropathy, lupus nephritis) and therapies targeting VDR was performed for several databases.

RESULT

Included in this study are the results from 177 published research articles. Evidence from these papers indicates that VDR activation is involved in the protection against renal injury in kidney diseases by a variety of mechanisms, including suppression of RAS activation, anti-inflammation, inhibiting renal fibrogenesis, restoring mitochondrial function, suppression of autoimmunity and renal cell apoptosis.

CONCLUSION

VDR offers an attractive druggable target for renal diseases. Increasing our understanding of VDR in the kidney is a fertile area of research and may provide effective weapons in the fight against kidney diseases.

Association of hematology profile with serum 25-hydroxy vitamin D and Bsml polimorphism in community-dwelling older adults

ABSTRACT Objective: To investigate the association between serum level of 25-hydroxy vitamin D and the Vitamin D Receptos gene BsmI polymorphism in the blood profile of community-dwelling older adults. Methods: This cross-sectional study included 142 older males and females. A questionnaire collected socio demographic information, medical history, and factors associated with sun exposure. Weight, height, and waist circumference were measured. Biological material was collected to analyze biochemical parameters 25-hydroxy vitamin D, parathormone, serum calcium, urea, creatinine, liver enzymes, and blood profile) and to verify the presence of the vitamin D receptos gene BsmI polymorphism. Results: Most participants were female (80.3%). The mean levels of 25-hydroxy vitamin D, hemoglobin, and hematocrit were 32.1±7.3 ng/dL, 13.5±1.5 d/dL, and 40.0±4.4%, respectively. Fifty-eight (40.8%) participants had vitamin D insufficiency/deficiency (25.7±3.3 ng/mL), and 18 (12.6%) had anemia. Serum vitamin D was associated with hemoglobin (p=0.030) and hematocrit (p=0.032). However, when subjects were categorized as anemic or not anemic, said association was not maintained (p=0.270). Moreover, the BsmI polymorphism was not associated with hemoglobin and hematocrit levels, regardless of vitamin D status. Conclusion: The serum level of vitamin D is associated with hematocrit and hemoglobin levels in older adults. However, these blood parameters were not associated with the vitamin D receptor gene BsmI polymorphism.

Vitamin D receptor polymorphism in chronic kidney disease patients with complicated cardiovascular disease

Several studies indicate a relationship between vitamin D and cardiovascular disease. Pleiotropic actions of vitamin D and its analogs are mediated by vitamin D receptor (VDR). VDRs have been identified in almost all tissues, including vascular smooth muscle cells, cardiomyocytes, and endothelial cells. The FokI and BsmI polymorphisms of the VDR gene are regarded as strong markers of disturbed vitamin D signaling pathway. Studies investigating the relationship between VDR genotypes and left ventricular hypertrophy revealed a highly significant association with the BsmI Bb heterozygous genotype. There are conflicting data on the action of vitamin D in left ventricular hypertrophy. Experimental as well as observational studies and small clinical trials have suggested that vitamin D administration may favorably influence left ventricular hypertrophy, whereas large randomized clinical trials have shown negative results. However, a beneficial effect on the left atrial volume index and the duration of hospitalization were observed in patients treated with vitamin D analogs. Larger clinical trials with robust clinical end points are needed to confirm that vitamin D is effective in preventing cardiovascular disease in chronic kidney disease patients and in general population.

Renal anaemia and EPO hyporesponsiveness associated with vitamin D deficiency: the potential role of inflammation

Resistance to erythropoiesis-stimulating agents (ESAs) has been observed in a considerable proportion of patients with chronic kidney disease (CKD) and it is reportedly associated with adverse outcomes, such as increased cardiovascular morbidity, faster progression to end-stage renal disease (ESRD) and all-cause mortality. The major causes of ESA resistance include chronic inflammation producing suppressive cytokines of early erythroid progenitor proliferation. In addition, pro-inflammatory cytokines stimulate hepcidin synthesis thus reducing iron availability for late erythropoiesis. Recent studies showing an association in deficiencies of the vitamin D axis with low haemoglobin (Hb) levels and ESA resistance suggest a new pathophysiological co-factor of renal anaemia. The administration of either native or active vitamin D has been associated with an improvement of anaemia and reduction in ESA requirements. Notably, these effects are not related to parathyroid hormone (PTH) values and seem to be independent on PTH suppression. Another possible explanation may be that calcitriol directly stimulates erythroid progenitors; however, this proliferative effect by extra-renal activation of 1α-hydroxylase enzyme is only a hypothesis. The majority of studies concerning vitamin D deficiency or supplementation, and degree of renal anaemia, point out the prevalent role of inflammation in the mechanism underlying these associations. Immune cells express the vitamin D receptor (VDR) which in turn is involved in the modulation of innate and adaptive immunity. VDR activation inhibits the expression of inflammatory cytokines in stromal and accessory cells and up-regulates the lymphocytic release of interleukin-10 (IL-10) exerting both anti-inflammatory activity and proliferative effects on erythroid progenitors. In CKD patients, vitamin D deficiency may stimulate immune cells within the bone marrow micro-environment to produce cytokines, inducing impaired erythropoiesis. Immune activation involves the reticuloendothelial system, increasing hepcidin synthesis and functional iron deficiency. Consequences of this inflammatory cascade are erythropoietin (EPO) resistance and anaemia. Given the key role of inflammation in the response to EPO, the therapeutic use of agents with anti-cytokines properties, such as vitamin D and paricalcitol, may provide benefit in the prevention/treatment of ESA hyporesponsiveness.

Association between vitamin D receptor gene haplotypes and chronic periodontitis among Japanese men

BACKGROUND

The vitamin D receptor (VDR) is involved in a variety of biological processes, such as bone metabolism and modulation of the immune response. Recent findings suggest that the pathway involving bone mineral density-mediated effects is important for the development of periodontitis, but their effects of combined VDR gene polymorphisms have not been confirmed on periodontitis. We assessed the relationship between ApaI, BsmI, and FokI VDR polymorphisms and the risk of severe chronic periodontitis among Japanese adult men.

MATERIALS AND METHODS

In a cross-sectional study, we examined 97 unrelated healthy Japanese men (mean age: 45.6 years, range: 22-59). A clinical examination was performed at a worksite health checkup, and information was obtained using a self-reported questionnaire. DNA was extracted from whole blood, and the VDR ApaI, BsmI, and FokI polymorphisms were genotyped using polymerase chain reaction.

RESULTS

F-carriers of FokI VDR polymorphisms were less likely to develop severe chronic periodontitis than non-F-carriers (p = 0.09). The ApaI and BsmI VDR polymorphisms did not show significant differences in the alleles or genotypes between the subjects with or without severe chronic periodontitis. The haplotype analysis of the three combined VDR polymorphisms revealed that the Abf homozygote had a notably higher prevalence of severe chronic periodontitis than the others, and adjustments for age, smoking status, number of teeth present, and prevalence of diabetes did not change this association (OR = 7.5; 95% CI = 1.6-34.4; p = 0.01).

CONCLUSION

The VDR haplotype constructed from the ApaI, BsmI, and FokI polymorphisms is related to the risk of severe chronic periodontitis in Japanese men.