Please use this identifier to cite or link to this item:
Title: Vitamin D Binding Protein (VDBP) Gene Polymorphism and Diabetes Mellitus in a Pakistani Population
Authors: Iqbal, Khalida
Keywords: Chemistry
Issue Date: 2018
Publisher: University of Karachi, Karachi.
Abstract: Introduction: Type 2 diabetes mellitus (T2DM) is a multifaceted metabolic syndrome characterized via insulin resistance (IR), impairment of beta-cell function and perturbed immune function. Complex interrelation of several genetic and environmental risk factors develops this ailment. Recent emerging evidences have pointed out that vitamin D deficiency (hypovitaminosis D) and vitamin D related polymorphic genes has substantial contribution in the etiology of T2DM, one such gene is VDBP gene. Vitamin D deficiency and T2DM are endemic throughout the world and both are commonly observed together. Pakistan is a tropical region and receives abundant sunlight throughout the year. Despite this, long term vitamin D deficiency is widespread in this populace. The genesis and epidemiology of this deficiency in the population require awareness, in particular to non insulin diabetes mellitus. Our research focused on two parameters of this problem i.e., nutrition and genetic aspects of vitamin D deficiency in patients suffering from T2DM. In a representative Pakistani population, a case-control study was conducted to answer a multitude of questions concerning hypovitaminosis D and VDBP gene variants in T2DM cases and normal subjects. Study objectives involved: our first objective included estimation of extent of vitamin D deficiency as well as interrelation with T2DM; our second objective involved determination of frequency distributions of VDBP gene variants (rs7041 and rs4588) and their association with T2DM; our third objective was to investigate the interrelation between VDBP(GC) gene variants and glycemic indices and; our fourth objective included evaluation of VDBP expression in patients suffering with T2DM and its comparison to non-diabetic normal subjects. Methodology: A case-control approach was incorporated comprising of 165 T2DM and 165 age and gender-matched healthy controls satisfying the inclusion criteria. A pre-coded structured questionnaire was applied to determine demographic features. Blood sample was obtained and assessed for 25(OH)D, PTH, Calcium, ALP, Phosphate, Albumin, ALT, creatinine, lipid profile, FPG and fasting insulin. DNA was extracted and VDBP[GC] gene variants (rs7041 and rs4588) were detected by PCR-RFLP technique. 2-Dimensional Gel Electrophoresis (2-DE) was performed to evaluate VDBP expression which was validated by western blotting. In silico protein-protein interaction (PPI) analysis of VDBP was performed using String database to identify VDBP interacting proteins. Mean 25-OH-D3iii levels were equated amongst T2DM patients and healthy controls via independent-samples t-test. Proportions of hypovitaminosis D were compared between patients with poor glycemic control and good glycemic control via Chi-Square test. Interrelation of 25-OH D3 concentrations with FBG as well as RBG was examined using Pearson’s correlation analysis. Association between monthly house hold income (MMHI) and poor glycemic control with hypovitaminosis D was estimated using binomial logistic regression analysis. Effect of statin usage on 25-OH-D3 extents was assessed using multiple liner regression analysis. Mean 25(OH)D levels across VDBP genotypes and diplotypes were assessed using One-Way ANOVA. Association of VDBP gene variants with T2DM was determined using conditional logistic regression analysis. VDBP gene variants were assessed across glycemic indices (FPG, RBG, HbA1C, insulin, HOMA-IR) via One-Way ANOVA. Mean normalized volume of VDBP spots and intensities of VDBP band were equated by means of independent-samples t-test. Results: Immensely prevalent vitamin D deficiency was detected in study population (61.2%), more than half of T2DM patients (52.7%) and healthy controls (69.7%) were vitamin D deficient and thus, no relationship could have been established with T2DM. Mean levels of 25-OH-D3 were substantially varied across MMHI groups (p<0.013) in healthy controls. Moreover, 2.24 folds higher risk of hypovitaminosis D was identified in normal subjects with MMHI <50,000 PKR. Sedentary life style and smoking emerged as significant predictor of sub-optimal vitamin D levels in patients of T2DM. FBG (r = - 0.137, p = 0.15), RBG (r = - 0.238, p = 0.025) and HbA1C (r = -0.203; p = 0.016) were negatively interrelated with vitamin D levels in T2DM patients. Poor glycemic controlled T2DM patients were having 4-folds higher odds of vitamin D deficiency. Use of statins was lacking any relationship with vitamin D levels in T2DM patients (p>0.05). Mean vitamin D levels in GC 1-1 genotype carrying individuals were highest, GC 1-2 genotype had intermediate range, GC 2-2 genotype carriers were having lowest levels and were not linked with 25-OH-D3 levels and VDBP variants both in T2DM cases and healthy controls. Higher prevalence’s of GC 1-2 genotype and GC 1s-2 diplotype were detected in T2DM patients than healthy subjects. GC 1-2 genotype carriers were represented with 3-fold increased odds of developing T2DM. There was lack of an association between VDBP genotypes and diplotypes with glycemic indices in T2DM patients and healthy controls.iv VDBP expression was substantially upregulated in T2DM patients (Fold change >1.7, *p<0.05). Conclusion: Hypovitaminosis D is widespread in a Pakistani population. Correlation of vitamin D deficiency with glycemic indices (FBG, RBG and HbA1C) reflects substantial contribution of vitamin D in regulating glucose-homeostatis related mechanisms in T2DM cases. Our facts suggest that lifelong sub-optimal levels of vitamin D in VDBP variants allele carriers make them more susceptible to classical risk factors of T2DM. Altered expression of VDBP in T2DM patients indicates that 25(OH)D, 1,25(OH)D and VDBP ought to be measured concomitantly to evaluate functional vitamin D status. We suggest that intake of vitamin D3 supplements, prolonged exposure of skin to sunbeams and ingestion of vitamin D rich diets would be highly beneficial in correcting widespread vitamin D deficiency which in turn will restore mechanistic effects of vitamin D in glucose homeostatis.
Gov't Doc #: 22946
Appears in Collections:PhD Thesis of All Public / Private Sector Universities / DAIs.

Files in This Item:
File Description SizeFormat 
Khalida iqbal Biochemistry 2018 uok karachi.pdfphd.Thesis1.58 MBAdobe PDFView/Open

Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.