Evaluation of Serum Vitamin D Level and its Receptor Gene Polymorphisms as Early Predictor Markers for Nephropathy and Cardiovascular Diseases in Type 2 Diabetes Mellitus Patients

Abstract

Background: Researchers proved the relation between insulin resistance, β-cells dysfunction, vitamin D (VD) deficiency and Vitamin D receptor (VDR) gene polymorphisms. Since they had been found to be linked to onset and progression of diabetes mellitus. Therefore, this study aimed to evaluate serum vitamin D level and its receptor gene polymorphisms (Taq1, Fok1 and Bsm1) in Sudanese type 2 DM patients and its association with diabetic nephropathy and CVD. Materials and methods: this a case control study conducted in military hospital at Khartoum state during period from 2015 to 2019. The study recruited 205 clinically diagnosed type 2 diabetic patients age ranged from (39 to 75) years and 100 apparently health matched control. Serum vitamin D level was estimated using ELISA competitive assay, levels of high sensitive C-reactive protein (hs-CRP), lipid profile, glycated hemoglobin (HbA1c) and microalbuminuria (MAU) were measured using Cobas C-311® fully automated analyzer. DNA was extracted using guanidine chloroform method, and genotypes of single nucleotide polymorphisms (SNPs) of vitamin D receptor gene (Taq1 [rs731236], Fok1 [rs2228570] and Bsm1 [rs1544410]) were analyzed by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) technique. Genotyping of some samples were confirmed by sequencing (Macrogen Company, Seoul, Korea). All statistical analyses was performed using the SPSS software (version 21.0; SPSS Inc.). Results: Compared to control group, Type 2 DM patients had significantly lower VD level p-value (0.007), while hs-CRP and MAU levels were significantly increased p-value (0.020 and 0.000) respectively. Diabetic females had significantly lower VD level than males p-value (0.000). Furthermore, Females had increased serum hs-CRP, total cholesterol (TC), high density lipoprotein cholesterol (HDL-C) and low density lipoprotein cholesterol (LDL-C) p-value (0.005, 0.000, 0.000 and 0.000) respectively. Patients received statin drugs showed decreases in hs-CRP, TC and LDL-C p-value (0.030, 0.000 and 0.000) respectively. In addition, diabetic patients with VD deficient had higher levels of hs-CRP and MAU than those with VD sufficient p-value (0.008 and 0.011) respectively. Patients exposed to sun-light had significantly higher VD and lower hs-CRP levels compared with less-exposed p-value (0.001 and 0.000) respectively. Moreover, exercise significantly increased VD and decreased MAU levels in DM patients p-value (0.046 and 0.002) respectively. VD was positively associated with age (r: 0.355 p-value 0.040) and negatively correlate with BMI (r: -0.502 p-value 0.009), duration of disease (r: -0.498 p-value 0.003), MAU (r: -0.384 p-value 0.015) and HbA1c (r: -0.327 p-value0.032). Positive correlation between MAU and duration (r: 0.280, P-value 0.00), BMI correlate positively with triglyceride (TG) (r: 0.37, P-value 0.017) and hs-CRP (r: 0.56, P-value 0.000), while it correlated negatively with HDL-C (r: -0.36, P-value 0.029). VDR-Taq1 polymorphism was significantly associated to reduce the risk of T2DM (OR=0.699, P-value 0.027) while no significant association was observed with Fok1 and Bsm1 VDR-polymorphism. Furthermore, patients with (Ff) dominant model had significant decrease in hs-CRP level compared with other patients groups had (FF) or (ff) models (p-value 0.048). In addition, there were insignificant differences in vitamin D and microalbuminuria levels according different genotypes of VDR (Taq1, Fok1 and Bsm1). Conclusion: The study concludes that, type 2 DM patients had lower vitamin D and higher MAU and hs-CRP levels. The levels of MAU and hs-CRP increased in patients with VD deficient. VD level was negatively correlate with BMI, duration of disease, MAU and HbA1c. Therefore, VD deficiency might be a risk factor for developing CVD and nephropathy in type 2 diabetic patients. Therefore, periodic monitoring and VD supplementation regimens is recommended especially for overweight and obese diabetic patients.VDR-Taq1 was associated to decrease risk of T2DM and VDR-Fok1 in dominant model was associated with CVD in Sudanese diabetic patients. .