|Year : 2019 | Volume
| Issue : 3 | Page : 1064-1070
Evaluation of urinary vitamin D-binding protein in type 1 diabetic children
Maha A Tawfik1, Soheir S Abou-El Ella1, Sally M El-Hefnawy2, Mai A El-Borai1
1 Department of Pediateric Medicine, Faculty of Medicine, Menoufia University, Menoufia, Egypt
2 Department of Biochemistry, Faculty of Medicine, Menoufia University, Menoufia, Egypt
|Date of Submission||06-Jan-2018|
|Date of Acceptance||03-Mar-2018|
|Date of Web Publication||17-Oct-2019|
Mai A El-Borai
Berket Elsabie, Menoufia Government
Source of Support: None, Conflict of Interest: None
The aim of the study was to measure the levels of vitamin D-binding protein (VDBP) and microalbumin in the urine of diabetic children (type 1) and to analyze the correlation of VDBP with other parameters.
Elevated urinary vitamin D-binding protein (UVDBP) level in patients with diabetes indicates that renal tubular damage may be involved in early stages of the development of diabetic nephropathy (DN).
Patients and methods
A total of 20 type 1 diabetic patients and 20 healthy controls were subjected to full history taken, thorough clinical examination, and laboratory investigation, which included complete blood count, blood glucose profile, glycosylated hemoglobin, parameters of kidney function, liver function, measurement of microalbuminurea, and VDBP in urine by enzyme-linked immunosorbent assay.
UVDBP level showed significant increases in type 1 diabetic patients with microalbuminuria and macroalbuminuria (mean: 562.990 ± 194.771) when compared with control group (mean: 172. 480 ± 41.856; P = 0.001). There was a positive correlation between UVDBP as a marker of DN and fasting blood glucose, 2-h postprandial blood glucose (2-h PP), glycosylated hemoglobin, duration of the disease, and albumin/creatinine ratio, but no significant correlation between UVDBP as a marker of DN and other laboratory data.
Our finding indicates that UVDBP level is a potential biomarker for early detection of DN.
Keywords: biomarkers, diabetes mellitus, diabetic nephropathy, vitamin D-binding protein
|How to cite this article:|
Tawfik MA, Abou-El Ella SS, El-Hefnawy SM, El-Borai MA. Evaluation of urinary vitamin D-binding protein in type 1 diabetic children. Menoufia Med J 2019;32:1064-70
|How to cite this URL:|
Tawfik MA, Abou-El Ella SS, El-Hefnawy SM, El-Borai MA. Evaluation of urinary vitamin D-binding protein in type 1 diabetic children. Menoufia Med J [serial online] 2019 [cited 2020 May 27];32:1064-70. Available from: http://www.mmj.eg.net/text.asp?2019/32/3/1064/268861
| Introduction|| |
Diabetes mellitus (DM) is a chronic disease that affects 6.4% of the adult population and is expected to rise to 552 million by 2030 .
This global increase in the prevalence of diabetes will inevitably lead to acceleration of microvascular and macrovascular complications of diabetes. Diabetic nephropathy (DN) is one of the common microvascular complications of DM. It is a leading cause of end-stage renal disease in developed and developing countries and a contributor to significant morbidity and mortality in patients with diabetes ,. Diabetes is now the major cause of end-stage kidney failure, in both developing and developed nations. It is the primary diagnosis causing kidney diseases in 20–40% of patients starting treatment for end-stage renal diseases worldwide. The aim of the study was to evaluate the urinary level of vitamin D-binding protein (UVDBP) as a new biomarker for DN .
Recent studies have demonstrated that the onset and course of DN can be ameliorated significantly by several interventions, but these interventions have their greatest effect if instituted at a very early stage in the course of the development of DN ,. Other aspects of glucometabolic derangements than diabetes have also been suggested to be of importance for the development of kidney damage. In particular, insulin resistance has been shown to be closely associated with the two major indices of kidney damage and dysfunction used in clinical practice, glomerular filtration rate (GFR) and urinary albumin/creatinine ratio (ACR), even before the development of diabetes. Both GFR and ACR have limitations as biomarkers as they both mainly reflect an underlying disease process that already is well established ,. The loss of UVDBP is likely to be elevated in diabetic patients, and particularly to better identify individuals with an increased risk for chronic kidney disease, there is a need for biomarkers that may detect early signs of kidney damage ,. A recent study reported elevated UVDBP levels in diabetes patients with normoalbuminuria indicating that renal tubular damage may be involved in early stages of the development of DN . Vitamin D-binding protein (VDBP), originally known as the group-specific component (GC-globulin), is a 51–58 kD multifunctional serum glycoprotein that is synthesized in large quantities by hepatic parenchymal cells and secreted into the circulation as a monomer accentuated in those patients with DN. The B cells of the pancreas contain a receptor for the 1,25-dihydroxy vitamin D3 and the concentration of this steroid in serum may have an effect on insulin secretion .
VDBP is essential for vitamin D cellular endocytosis and metabolism. Thus, variants of the VDBP may affect the amount of active vitamin D in B cells and, subsequently, insulin secretion. There is circumstantial evidence that vitamin D pathway is involved in the development of diabetes .
The aim of the study was to measure the level of VDBP and microalbumin in the urine of diabetic children (type 1).
| Patients and Methods|| |
This prospective study was conducted on 40 children: 20 children who were already diagnosed with DM according to the criteria of WHO and selected from Pediateric Medicine Department, Faculty of Medicine, Menoufia University, in the duration between April 2017 and October 2017 and 20 healthy children as controls. Inclusion criteria included duration of illness of the child with diabetes to be not less than 5 years, age of the children to be between 7 and 15 years, and children of both sexes. Exclusion criteria were urinary tract infection, collagen disease, decompensated heart failure, liver diseases, renal diseases other than DN, cancer, and type 2 DM.
Patients and controls signed informed consent forms before participation, and study approval was obtained from the ethical committee of the Faculty of Medicine, Menoufia University.
Complete history taking, clinical examination, and certain laboratory investigations were done for both cases and controls.
Selection criteria of blood sample
After 12 h of overnight fasting, 10 ml of venous blood was withdrawn from every child by sterile venipuncture and divided into three samples for estimation of glycated hemoglobin (HbA1c), blood glucose, serum alanine transaminase and aspartate aminotransferase (liver function tests), serum urea, and creatinine.
Selection criteria of urine sample
A volume of 50 ml of fresh morning urine sample was collected in a sterile container from every child and centrifuged for 20 min at the speed of 2000–3000 rpm. The supernatant obtained was used for measurement of albumin and VDBP.
The laboratory tests included complete blood count, which was performed using automated CELL-DYN Ruby hematology analyzer (Abbott, Illinois, USA), and liver and renal function tests, which were performed using AU480 Beckman Coulter analyzer (Beckman Coulter Inc., California, USA).
Quantitative colorimetric determination of HbA1c as percentage of total hemoglobin was done using kits supplied by Teco Diagnostics (California, USA). Determination of blood glucose was done by enzymatic colorimetric method using Spinreact kit (Trinder, Spain). Quantitative measurement of microalbuminuria was done using enzyme-linked immunosorbent assay (ELISA) kit supplied by DRG Diagnostics (USA). Determination of the level of VDBP was done by double-antibody sandwich ELISA.
Data were expressed in the form of range, mean, and SD for continuous quantitative variables, whereas number and percentage were used for description of qualitative variables. Categorical data were compared by χ2-test. Analysis of variance test was used for comparing multiple groups of normally distributed quantitative data. In the comparison of two groups for normally distributed quantitative data, Student's t-test was used. Pearson's correlation test was used to examine possible correlations between variables. All data were collected, tabulated, and statistically analyzed using SPSS 19.0 for windows (SPSS Inc., Chicago, Illinois, USA) and MedCalc 13 for windows (MedCalc Software BVBA, Ostend, Belgium).
| Results|| |
The study populations were divided into two groups. Group 1 included 20 diabetic patients with type 1 diabetes and their ages at the time of the study ranged between 7 and 15 years. There were 11 (65%) female and nine (45%) male patients. Group 2 included 20 healthy controls matched with diabetic children in age and sex.
UVDBP level showed significant increases in type 1 diabetic patients with microalbuminuria and macroalbuminuria (mean: 562.990 ± 194.771) when compared with control group (mean: 172. 480 ± 41.856; P = 0.001; [Table 1]).
|Table 1: Comparison between cases and control groups regarding all quantitative parameters of the study|
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Statistically, there was no significant difference between diabetic children regarding family history (P = 0.07; [Table 2]).
|Table 2: Comparison between positive and negative family history of cases group|
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There was no significant difference between group 1 (diabetic children) and group 2 (healthy controls) regarding sex (P = 0.08; [Table 3]).
Duration of diabetes is positively correlated with the level of UVDBP and microalbumin in urine [Table 4].
|Table 4: Correlations between VDBP and microalbumin with all quantitative parameters among study group|
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Fasting and postprandial blood glucose levels and HbA1c showed a significant increase in the patient group compared with the control group (P = 0.001). UVDBP level showed significant increase in group 1 compared with group 2 (P = 0.012). Urinary microalbumin level showed significant increase in group 1 in comparison with group 2 (P = 0.017). Blood urea and creatinine levels showed a significant increase in patient group compared with controls (P = 0.002; [Table 1]).
Spearman's correlation coefficients were used to assess the significant correlation between UVDBP and other laboratory data. We demonstrated that there is a positive correlation between UVDBP as a marker of DN and fasting blood glucose, 2-h PP, HbA1c, duration of the disease, and ACR, but no significant correlation between UVDBP as a marker of DN and other laboratory data. We found a positive correlation between UVDBP and urinary microalbumin in type 1 diabetic patients [Table 4].
Age, duration of the disease, fasting blood glucose, 2-h PP, HbA1c, and microalbumin were statistically significant predictors for VDBP (P = 0.001). On the contrary, sex, family history, alanine transaminase, hemoglobin, urea, creatinine, and aspartate aminotransferase were not statistically significant predictors for VDBP (P = 0.05; [Table 5]).
|Table 5: Multiple regression analysis to predict vitamin D-binding protein by all study parameters|
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No statistically significant predictors for microalbumin were found (P = 0.05; [Table 6]).
|Table 6: Multiple regression analysis to predict microalbumin by all study parameters|
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| Discussion|| |
Studies concerning the action of VDBP in the kidney have received increased attention and have suggested that VDBP is vital in the endocrine biosynthetic process of 1,25(OH) 2D within renal proximal tubules. In this process, 1,25(OH) 2D binds to VDBP, and the complex is actively reabsorbed from the glomerular filtrate through megalin-mediated endocytosis. As receptor-mediated uptake of proteins such as VDBP is energy consuming, tubular injury would be expected to result in UVDBP loss ,.
In the present study, following quantitative measurements of 40 urine samples with ELISA, a statistical comparison was done between the various studied parameters in diabetic patients at various stages of the disease versus healthy control children.
It revealed a significant decrease of GFR and significant increase of blood urea nitrogen (BUN), serum creatinine, and UVDBP at various stages of DN. Furthermore, statistically significant progressive increase was recorded in UVDBP levels throughout normoalbuminuria, microalbuminuria, and macroalbuminuria.
The reasons underlying the enhanced excretion of urinary UVDBP in patients with DN may be associated with renal tubular damage in patients with DN. It has been increasingly documented that the renal tubular injury plays an integral role in the pathogenesis of diabetic kidney disease. In addition, tubulointerstitial lesions are found to be the early and independent features of diabetic kidney disease .
Liu et al.  indicated that the urinary excretion of VDBP may be a novel biomarker of tubulointerstitial damage. Damaged tubular epithelial cells in areas of tubulointerstitial fibrosis may no longer be able to handle VDBP, resulting in gross VDBP loss in urine. In humans, UVDBP increased with increasing severity of renal damage, and responded to renoprotective therapy. Yet, persisting UVDBP above normal suggested persistent tubulointerstitial damage .
It has been demonstrated that the presence of vitamin D deficiency or insufficiency in patient with diabetes is independently associated with the development of DN, and this can be explained by decreased UVDBP secondary to tubular damage ,.
Our results revealed that GFR, based on the Modification of Diet in Renal Disease (MDRD) Study equation, was significantly lower in diabetic patients than that of the healthy control group, and also serum creatinine and BUN were significantly higher in microalbuminuria and macroalbuminuria patients when compared with healthy control groups. This is agreement with the findings of Liang & Deng  who reported that high levels of BUN and creatinine indicate a falling of GFR as a result of decrease kidney capacity to excrete waste products.
Microalbuminuria is a predictor of outcome in patients with renal diseases. Additionally, it is a predictor of morbidity and mortality in patients who do not have evidence of renal diseases. Although 24-h urine excretion analysis has traditionally been preferred, the ACR has been shown to be a similarly valid screening tool for DN .
Albuminuria can be reduced effectively by inhibition of renin-angiotensin system, and maximum reduction of albuminuria to the lowest possible level should be the goal of renoprotective therapy .
Duration of diabetes is a very important factor in the development of DN as demonstrated in several studies. Gonen et al.  reported that longer the duration of diabetes, higher the frequency of DN in a study of adolescents with a mean duration of disease of 9 years, and they found that the duration of disease was an important factor in the overall severity of glomerulopathy. Overt nephropathy caused by glomerulosclerosis first appears 5–10 years after the onset of IDDM .
In agreement with our results, Boer et al.  found that the duration of diabetes was longer in the microalbuminuria and macroalbuminuria patients.
The current study showed a significant increase in fasting and postprandial blood glucose levels and HbA1c in type 1 diabetic patients with macroalbuminuria and microalbuminuria. This correlates with Gallego et al.  who studied the correlation of DN and HbA1C in newly diagnosed type 1 diabetic patients and found that mean fasting plasma glucose levels and HbA1C of population with macroalbuminuria and microalbuminuria were higher as compared with population without albuminuria, and correlation was found extremely significant. This shows that fasting plasma glucose and HbA1C are positively associated with the incidence of DN in population.
Such findings support that the lack of tight glycemic control is a risk factor for developing diabetic complications .
Blood urea levels showed a significant increase in all patients groups when compared with control group. Moreover, blood urea levels were significantly higher in macroalbuminuria patients when compared with other study group. In agreement with our results, Jacobson , founded that blood urea levels were significantly higher in all patients groups when compared with control group. However, unlike our results, Huda J. Waheed found that blood urea levels were significantly higher in microalbuminuria patients when compared with other study group.
Our results showed a significant decrease of estimated GFR in type 1 diabetic patients with microalbuminuria when compared with the control groups. Similar to our results, Jacobson et al.  found that patients in the microalbuminuric and macroalbuminuric groups had a lower eGFR when compared with normoalbuminuric diabetic patients. Such findings support that in most cases, proteinuria and decreased GFR occur in parallel. However, approximately 10% of participants with type 1 DM will have low GFR without microalbuminuria or macroalbuminuria .
In the present study, UVDBP level showed significant increases when type 1 diabetic patients with microalbuminuria and macroalbuminuria were compared with control group. Similar to our results, Sandholm et al.  showed urinary levels of VDBP were significantly higher in macroalbuminuria group when compared with control, normoalbuminuria, and microalbuminuria groups. After adjusting for several clinical parameters, UVDBP was significantly associated with albuminuria. In agreement with our results, Gariani et al.  found that UVDBP level was not different between the microalbumin and macroalbuminuria groups in comparison with the control group.
In the present study, there was a significant correlation between UVDBP as a marker of DN and HbA1c, ACR, and urea and no significant correlation between UVDBP as a marker of DN and other laboratory data. This is in agreement with the idea that VDBP only reflects tubular damage in early stages of renal disease. In agree with our results, Liang & Deng et al.  found that the urinary ACR positively correlated with the UVDBP, and also Ziegler et al.  found that baseline urinary albumin excretion was related to UVDBP, but unlike our results, they found that UVDBP was not associated with HbA1c.
| Conclusion|| |
Our finding indicated that UVDBP level is a potential biomarker for early detection of DN.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]