The genetic determinants of circulating C3-epimers of 25-hydroxyvitamin D

C3-epi-25(OH)D3 percentage, not level, may be a potential biomarker to reflect its pathological increase in multiple diseases: a cross-sectional case-control study

National surveys in developed countries have examined the presence of C3-epimer of 25-hydroxyvitamin D3 [C3-epi-25(OH)D3]. However, controversy remains regarding its association with disease occurrence due to its high correlation with 25-hydroxyvitamin D3 [25(OH)D3]. This study aims to investigate whether %C3-epi-25(OH)D3 can serve as an indicator for this relationship with various diseases. A total of 3086 healthy participants and 4120 patients were included in this study. We investigated the association between C3-epi-25(OH)D3 and %C3-epi-25(OH)D3 levels with gender, age, and season; compared the performance of C3-epi-25(OH)D3 and %C3-epi-25(OH)D3 across different disease conditions; and explored the correlation between %C3-epi-25(OH)D3 and various diseases. Results indicated that C3-epi-25(OH)D3 varied significantly by gender, age, and season (z/χ2 = 3.765, 10.163, and 150.975, all P < 0.01), while only season for %C3-epi-25(OH)D3 (χ2 = 233.098, P < 0.001). In contrast to the significant decrease in C3-epi-25(OH)D3, %C3-epi-25(OH)D3 showed a significant increase in 8 out of 11 disease categories (z = 3.464 ~ 11.543, all Padj < 0.05). Similar opposite changes were also observed in most of the investigated 32 specific diseases. Moreover, an elevation in %C3-epi-25(OH)D3 was found to be significantly associated with 29 specific diseases both in univariate analysis (OR = 1.16 ~ 2.10, all P < 0.05) and after adjusting for gender, age, and season (OR = 1.15 ~ 1.50, all P < 0.05). However, after further adjustment for 25(OH)D3 levels, the association remained significant only for 15 specific diseases (OR = 1.11 ~ 1.50, all P < 0.05). Seasonal stratification analysis further supports the consistent association of %C3-epi-25(OH)D3 with disease across all or nearly all four seasons. In conclusion, %C3-epi-25(OH)D3 may better reflect the production of C3-epi-25(OH)D3 in disease conditions, thereby offering a more applicable approach to investigate its association with diseases. However, the interpretation of this relationship may be confounded by 25(OH)D3 as a potential covariate.

C3-Epimer of 25-Hydroxyvitamin D3 as a Superior Marker for Predicting the Severity of Chronic Kidney Disease in Rheumatoid Arthritis Patients

Objective. 25-hydroxyvitamin D3 (25[OH]D3) is involved in oxidative stress regulation by upregulating the expression of antioxidant genes except for mineral homeostasis physiological role. C3-epimer of 25(OH)D3 (C3-epi-25[OH]D3) is a form of vitamin D metabolite with low bioaffinity in vivo, but little is known about the relationship between C3-epi-25(OH)D3 and diseases. This study was aimed at investigating the relationship between C3-epi-25(OH)D3 and the severity of chronic kidney disease (CKD) in patients with rheumatoid arthritis (RA). Method. A total of 318 RA inpatients were enrolled and divided into mild ( $n=247$ ), moderate ( $n=46$ ), and severe ( $n=25$ ) CKD groups according to the CKD prognosis criterion of the Kidney Disease Improving Global Outcomes guidelines. Serum levels of 25(OH)D2, 25(OH)D3, C3-epi-25(OH)D3, and free 25(OH)D (F25[OH]D) were measured, and the value of 25(OH)D was calculated. The relationship and changing trend of the indexes based on CKD severity were analyzed. Results. The serum levels of 25(OH)D, 25(OH)D3, and F25(OH)D showed a decreasing trend ( $z=-2.781–-3.996$ , $P<0.01$ ) in RA patients with CKD progression from mild to severe, while C3-epi-25(OH)D3 showed an increasing trend ( $z=6.741$ , $P<0.001$ ) and 25(OH)D2 showed no significant difference among the groups ( $z=0.976$ , $P=0.329$ ). Only levels of C3-epi-25(OH)D3 presented significant differences between adjacent CKD severity groups in RA patients (mild to moderate: $z=3.963$ , $Padj<0.001$ ; moderate to severe: $z=3.269$ , $Padj=0.002$ ). Multiple logistic regression analysis showed that 25(OH)D3 and C3-epi-25(OH)D3 were significant predictors for CKD progression in RA patients, and C3-epi-25(OH)D3 had a better predictive advantage (moderate vs. mild: $\text{OR}=4.79$ , $P<0.001$ ; severe vs. mild: $\text{OR}=17.85$ , $P<0.001$ ). Conclusions. To the best of our knowledge, this is the first study to reveal that C3-epi-25(OH)D3 is a dominant predictor of CKD severity in RA patients. Further studies are needed to explore the relationship between C3-epi-25(OH)D3 and other diseases.

Vitamin D epimers are associated with circulating haemoglobin levels independently of C-reactive protein

Vitamin D deficiency has been shown to be associated with anaemia. Circulating 25(OH)D consists of both epimeric and nonepimeric forms. However, the relative roles of epimeric and nonepimeric vitamin D in regulating anaemia and haemoglobin levels remain unknown. Therefore, in this study, we examined the effect of vitamin D, including its epimers, on haemoglobin levels, independently of its effect on circulating high-sensitivity C-reactive protein (hsCRP). This was a cross-sectional study of 1655 subjects from a long-term follow-up cohort at the Electricity Generating Authority of Thailand. Venous blood sample were collected for determination of vitamin D [25(OH)D₂, 25(OH)D₃, 3'-epi-25(OH)D₂, and 3'-epi-25(OH)D₃], haemoglobin, and hsCRP levels. Data are presented as mean ± standard deviation. Age, sex, and body mass index (BMI) were significantly associated with circulating haemoglobin levels, while no association was found between total serum 25(OH)D and haemoglobin levels. However, when total 25(OH)D was separated into 3'-epimeric and non-3'-epimeric forms, 3'-epi-25(OH)D was significantly associated with haemoglobin levels, independently of age, sex, and BMI (P < 0.01). No association was found between non-3'-epi-25(OH)D and haemoglobin. When hsCRP was added to the model, the effect 3'-epi-25(OH)D on haemoglobin levels remained significant (P < 0.01). In conclusion, vitamin D epimers are associated with circulating haemoglobin levels, which supports the role of vitamin D in red blood cell and iron physiology.

Vitamin D Receptor Gene Polymorphism and Vitamin D Status in Population of Patients with Cardiovascular Disease-A Preliminary Study

The association between vitamin D receptor (VDR) polymorphism and the risk of cardiovascular diseases (CVD) remains unclear. This study aimed to assess a relationship between the VDR genotypes, plasma concentrations of vitamin D metabolites, and the occurrence of cardiovascular and metabolic disorders. Fifty-eight patients treated for various cardiological afflictions were included. Identification of VDR polymorphisms: ApaI, TaqI, BsmI, and FokI were carried out using the PCR-RFLP method. Plasma concentrations of 25-hydroxyvitamin-D2, 25-hydroxyvitamin-D3, and 3-epi-25-hydroxyvitamin D3 were assessed by the UPLC-MS/MS method. Lower incidence of BsmI AA genotype in the studied patients was observed compared with healthy controls, but the difference was insignificant. Among patients with the TT genotype, frequency of hypertension was higher than among carriers of other ApaI genotypes (p < 0.01). In addition, carriers of the TT ApaI, TC TaqI, and GA BsmI genotypes had an increased risk of obesity, while the presence of the FokI TT genotype was associated with a higher incidence of heart failure and hypertension. In conclusion, the BsmI AA genotype can be protective against CVD, but this observation needs study on a larger group of patients. Particular VDR genotypes were associated with 25-hydroxyvitamin-D levels, and the mechanism of this association should be further investigated.

Effect of Cytochrome P450 Family 2 Subfamily R Member 1 Variants on the Predisposition of Coronary Heart Disease in the Chinese Han Population

Propose: Cytochrome P450 family 2 subfamily R member 1 (CYP2R1) variations can affect the activity of 25-hydroxylase, resulting in the deficiency of 25(OH)D, which leads to an increased incidence and mortality of coronary heart disease (CHD). The purpose is to assess the influence of CYP2R1 variants on CHD risk among the Chinese Han population.

Methods: A total of 508 CHD patients and 510 healthy controls were enrolled. The MassARRAY platform completed genotyping of CYP2R1 variants. Odds ratios (ORs) with 95% confidence intervals (CI) were calculated using logistic regression analysis.

Results: Rs6486205 (OR = 1.25, 95% CI: 1.05–1.50, p = 0.014), rs10741657 (OR = 1.29, 95% CI: 1.08–1.54, p = 0.005), and rs2060793 (OR = 1.27, 95% CI: 1.06–1.51, p = 0.009) were associated with the increased susceptibility to CHD in the whole subjects. Interestingly, the relationships between these variants and CHD risk were observed in the subjects with age >60 years, males or non-smoker. Additionally, the haplotypes A_rs10741657A_rs2060793 and G_rs10741657G_rs2060793 had the higher risk of CHD, and the combination (rs6486205 and rs10741657) was the best multi-locus model.

Conclusion: Our study suggested the contribution of CYP2R1 polymorphisms to the increased CHD predisposition in the Chinese Han population. Furthermore, the risk association was related to confounding factors for CHD, including age, sex, and smoking. These findings might help to strengthen the understanding of the CYP2R1 gene in the occurrence of CHD.

Vitamin D Metabolism and Guidelines for Vitamin D Supplementation

Vitamin D is essential for bone health and is known to be involved in immunomodulation and cell proliferation. Vitamin D status remains a significant health issue worldwide. However, there has been no clear consensus on vitamin D deficiency and its measurement in serum, and clinical practice of vitamin D deficiency treatment remains inconsistent. The major circulating metabolite of vitamin D, 25-hydroxyvitamin D (25(OH)D), is widely used as a biomarker of vitamin D status. Other metabolic pathways are recognised as important to vitamin D function and measurement of other metabolites may become important in the future. The utility of free 25(OH)D rather than total 25(OH)D needs further assessment. Data used to estimate the vitamin D intake required to achieve a serum 25(OH)D concentration were drawn from individual studies which reported dose-response data. The studies differ in their choice of subjects, dose of vitamin D, frequency of dosing regimen and methods used for the measurement of 25(OH)D concentration. Baseline 25(OH)D, body mass index, ethnicity, type of vitamin D (D₂ or D₃) and genetics affect the response of serum 25(OH)D to vitamin D supplementation. The diversity of opinions that exist on this topic are reflected in the guidelines. Government and scientific societies have published their recommendations for vitamin D intake which vary from 400-1000 IU/d (10-25 μg/d) for an average adult. It was not possible to establish a range of serum 25(OH)D concentrations associated with selected non-musculoskeletal health outcomes. To recommend treatment targets, future studies need to be on infants, children, pregnant and lactating women.

Epimers of Vitamin D: A Review

In this review, we discuss the sources, formation, metabolism, function, biological activity, and potency of C3-epimers (epimers of vitamin D). We also determine the role of epimerase in vitamin D-binding protein (DBP) and vitamin D receptors (VDR) according to different subcellular localizations. The importance of C3 epimerization and the metabolic pathway of vitamin D at the hydroxyl group have recently been recognized. Here, the hydroxyl group at the C3 position is orientated differently from the alpha to beta orientation in space. However, the details of this epimerization pathway are not yet clearly understood. Even the gene encoding for the enzyme involved in epimerization has not yet been identified. Many published research articles have illustrated the biological activity of C3 epimeric metabolites using an in vitro model, but the studies on in vivo models are substantially inadequate. The metabolic stability of 3-epi-1α,25(OH)₂D3 has been demonstrated to be higher than its primary metabolites. 3-epi-1 alpha, 25 dihydroxyvitamin D3 (3-epi-1α,25(OH)₂D3) is thought to have fewer calcemic effects than non-epimeric forms of vitamin D. Some researchers have observed a larger proportion of total vitamin D as C3-epimers in infants than in adults. Insufficient levels of vitamin D were found in mothers and their newborns when the epimers were not included in the measurement of vitamin D. Oral supplementation of vitamin D has also been found to potentially cause increased production of epimers in mice but not humans. Moreover, routine vitamin D blood tests for healthy adults will not be significantly affected by epimeric interference using LC-MS/MS assays. Recent genetic models also show that the genetic determinants and the potential factors of C3-epimers differ from those of non-C3-epimers.Most commercial immunoassays techniques can lead to inaccurate vitamin D results due to epimeric interference, especially in infants and pregnant women. It is also known that the LC-MS/MS technique can chromatographically separate epimeric and isobaric interference and detect vitamin D metabolites sensitively and accurately. Unfortunately, many labs around the world do not take into account the interference caused by epimers. In this review, various methods and techniques for the analysis of C3-epimers are also discussed. The authors believe that C3-epimers may have an important role to play in clinical research, and further research is warranted.