| Abstract|| |
The status of vitamin A, α-tocopherol and retinol binding protein (RBP) was investigated in 34 type 2 diabetic patients with renal impairment (mean serum creatinine 176 µmol/L), 26 type 2 diabetic patients with chronic renal failure (CRF) (mean serum creatinine 629 µmol/L) and 19 non-diabetic patients with CRF. In renal failure patients, the change in response to the dialysis procedure over the time for all the measured parameters was evaluated. Fasting plasma retinol, α-carotene, β-carotene and α-tocopherol were determined by high-pressure liquid chromatography. The concentrations of RBP in plasma were determined by a double antibody sandwich enzyme linked immunosorbent assay. Concentrations of retinol, RBP and β-carotene were significantly higher in diabetic patients with CRF than in diabetic patients with renal impairment or in non-diabetic patients with CRF. A significant decrease was found for the concentrations of β-carotene (p<0.003) and RBP (p<0.003) in response to the dialysis procedure. Retinol/RBP ratio significantly increased with time (p<0.0004). Serum creatinine concentrations were associated with the increased plasma RBP indicating that RBP may be dependent on renal function and changes in levels of RBP in serum may be used in the assessment of renal function.
Keywords: Diabetes, Nephropathy, Human plasma, Vitamin A, α-tocopherol, Renal failure.
|How to cite this article:|
Abahusain MA, Al-Nahedh NN. The Biochemical Status of Vitamin A and Alpha-tocopherol during Different Stages of Renal Disease and its Relationship to Diabetes. Saudi J Kidney Dis Transpl 2002;13:18-23
|How to cite this URL:|
Abahusain MA, Al-Nahedh NN. The Biochemical Status of Vitamin A and Alpha-tocopherol during Different Stages of Renal Disease and its Relationship to Diabetes. Saudi J Kidney Dis Transpl [serial online] 2002 [cited 2020 Jan 26];13:18-23. Available from: http://www.sjkdt.org/text.asp?2002/13/1/18/33197
| Introduction|| |
Patients with chronic renal failure (CRF) have markedly increased plasma concentrations of retinol and retinol binding protein (RBP),,, and slightly elevated β-carotene. 
The serum RNP of patients on continuous ambulatory peritoneal dialysis (CAPD) declined with the duration on dialysis. 
The small molecular size of the free RBP (MW=21,000 Daltons) allows it to cross the glomerular barrier more easily than the RBP bound to pre-albumin (MW=75,000 Daltons). , In the normal state, small proteins are filtered through the glomeruli, and taken up and catabolized in the tubular cells. However, The glomerular clearance decreases as the MW increases; the glomerular membrane is nearly impermeable to molecules with MW>60,000 Daltons. 
In chronic renal failure, high serum creatinine level is associated with high concentrations of RBP. , The RBP and creatinine increase significantly during the acute renal failure, but decrease to baseline after recovery. 
The aim of the present study is to answer two questions: Whether the rise in serum retinol, α-tocopherol, α- and β-carotene, and RBP differs in the different stages of the renal disease and whether any differences are due to diabetes.
| Subjects and Methods|| |
Sixty diabetic patients (aged 39-78 years) attending King Khalid University Hospital in Riyadh, Saudi Arabia were classified into two subgroups: diabetics with renal impairment (mean serum creatinine 176 µmol/L) (n=34; male/female (M/F) 20/14), diabetics with chronic renal failure (DCRF) (mean serum creatinine 629 µmol/L) (n=26, M/F 3/23). Nineteen Non-diabetic patients with renal failure (NDCRF) (M/F 3/16) were matched in age and sex with the diabetic patients with chronic renal failure. Both groups of patients with CRF were supplemented with multivitamin tablets containing 200 mg vitamin A.
Plasma for the determination of retinol, α-tocopherol, α-carotene, β-carotene and RBP levels was frozen in aliquots and stored at - 70 o C until the time of analysis. Serum creatinine and total urine protein concentrations were obtained from the patients' files. Blood samples for the diabetic and non-diabetic patients with renal failure were obtained at different times during dialysis (pre-, during and post-dialysis).
The levels of retinol, α-carotene, β-carotene and a-tocopherol were determined by high pressure liquid chromatography (HPLC)  with some modification.  The concentration of RBP in plasma was determined by a double antibody sandwich enzyme linked immunosorbent assay (ELISA). 
| Statistical Analysis|| |
Two-way analysis of variance (ANOVA) and the t-test were used to evaluate differences between groups. Correlations were computed using Spearman's rank coefficient for nonparametric data. Differences were judged to be significant when P values were less than 0.01. The significance of change in plasma parameter concentrations over time (pre-, during, and post-dialysis) were measured using Wilk's Lambda for the two groups combined and Roy's Max root for the two groups separate. Statistical analyses were done using Mini Tab, version 10, 1996; State College, PA, USA.
| Results|| |
[Table - 1] shows the values of the various parameters measured. The mean plasma concentrations of retinol and RBP were significantly higher in both DCRF and NDCRF than in the diabetic patients with renal impairment (P<0.0001, P<0.0001 respectively). The plasma β-carotene level was significantly higher in the DCRF than the NDCRF (P<0.0001) or diabetic patients with renal impairment. The DCRF and NDCRF patients had significantly higher serum creatinine than the diabetic patients with renal impairment (P<0.0001). There was no significant difference of the serum creatinine and plasma RBP in the two CRF groups [Table - 1].
[Table - 2] shows the mean plasma concentration of the studied parameters at pre-, during, and post dialysis for the diabetics and non-diabetic patients with CRF. A significant decrease was found for β-carotene (P<0.003) and RBP (P<0.003) and a modest decrease was found for α-tocopherol (P<0.02) and α-carotene (P<0.03). Retinol/ RBP ratio significantly increased with time (p<0.0004).
In patients with renal impairment, there was a significant positive correlation between retinol and RBP (r=0.35, p=0.0001), retinol and serum creatinine (r=0.29, p=0.001), retinol and α-tocopherol (r=0.28, p=0.0002), retinol and urine protein (r=0.56, p=0.0001). Serum creatinine was significantly associated with RBP (r=0.4, p=0.0001), and urine protein (r=0.70, p=0.0001). Beta-carotene had a significant positive correlation with a-carotene (r=0.33, p=0.0001). a-carotene correlated positively with a-tocopherol (r=0.28, p=0.004). There was a significant positive correlation between age and retinol (r=0.21, p=0.006), age and RBP (r=0.33, p=0.0001), and age and creatinine (r=0.4, p=0.0001). There was a significant inverse relationship between creatinine clearance and retinol (r=-0.63, p=0.003), creatinine clearance and urine protein (r=-0.55, p=0.01), creatinine clearance and serum creatinine (r=-0.55, p=0.0001) in male patients only, creatinine clearance and age (r=-0.50, p=0.0006) in both males and females.
In CRF patients, all significant correlations were lost with the exception of those of retinol and RBP (p=0.02), serum creatinine and RBP (p=0.02) and serum creatinine and retinol (p=0.04).
| Discussion|| |
Retinol, RBP, α-tocopherol and carotenoids status in type 2 diabetic patients with renal impairment, type 2 diabetic patients with CRF and non-diabetic patients with CRF were evaluated.
The plasma β-carotene concentration was significantly higher in the DCRF than the NDCRF or diabetic patients with renal impairment. This rise of β-carotene in the DCRF patients is not due to vitamin A supplementation as both groups of patients with CRF received it. The increased level of β-carotene in the DCRF patients may be related to the disturbed metabolism of lipoproteins due to diabetes. 
In this study, the two groups of patients with renal failure whether diabetics or non-diabetics had markedly increased concentrations of retinol and RBP when compared to the diabetic patients with renal impairment.
The highly increased levels of retinol and RBP were in agreement with previous reports. , In the CRF patients, the plasma retinol and RBP concentrations were on the average three times the normal, similar to the levels reported by others.  The retinol level was also elevated among diabetic patients with renal impairment and this is in agreement with previously reported data. ,
There was a strong correlation between the retinol and RBP levels (p=0.0001). This was consistent with the data of others ,, and to the fact that RBP is the carrier protein for the vitamin. In renal dysfunction, both the excretion and tubular catabolism of RNP are reduced, which result in the accumulation of these proteins in the blood. ,
The elevated plasma retinol in renal impairment or failure may be due to the increased RBP levels, ,,, reduced vitamin excretion and decreased conversion of retinol to retinoic acid. 
Patients with CRF have been reported to have high liver retinol content, which suggests an excess of retinol in the whole body.  The observed increase of serum retinol in the nephrectomized rats was suggested to be due to the increase in retinol associated with RBP, coupled with the thyroxin binding protein (transthyretin-TTR), besides the upregulation of the hepatic release mechanism in renal disease.  It was suggested that renal failure resulted in a change in the signal for release of retinol RBP into the circulation. 
In our study, there was a positive correlation between serum creatinine and both plasma RBP and retinol, which was consistent with previous reports. ,, Also, there was a significant positive correlation between urine protein and plasma RBP and retinol. Since serum creatinine and urine protein levels usually indicate the renal functional status, this positive correlation indicates that serum retinol and RBP may be dependent on renal function. Accordingly, the changes of the level of RBP in serum and urine may be valuable in assessing the alterations of renal function. It was reported that the serum RBP level was increased with the decrease in glomerular filtration and creatinine clearance.  The current study did not confirm these results although there was a significant negative correlation between retinol and creatinine clearance in male diabetic patients.
All the CRF patients in our study, whether diabetic or not, had a decline of the plasma level of all the parameters in response to dialysis; only retinol was not affected. The retinol/RBP ratio significantly increased during dialysis indicating the loss of RBP, probably due to its small size; this was consistent with earlier reports.  Others found higher plasma retinol in samples taken immediately post-dialysis in comparison with the pre-dialysis levels. 
In conclusion, our study suggests that patients with CRF (diabetic and nondiabetic) had high concentrations of retinol and RBP. Thus, supplementation of vitamin A may not be necessary for these patients. Diabetic patients with CRF had higher plasma β-carotene concentrations than nondiabetic patients with CRF, which may be due to the disturbed metabolism of lipoproteins in the diabetic state. Moreover, there was correlation between serum creatinine and urine protein concentration, and the plasma RBP indicating the possibility of using it in the assessment of renal function.
| Acknowledgement|| |
We would like to express our gratitude and appreciation to the administration of the King Faisal Specialist Hospital and Research Centre, for allowing us to use their excellent facilities. We are grateful to the Biological and Medical Research Department staff (King Faisal Specialist Hospital and Research Center) for their technical assistance in the HPLC analysis. We are also grateful to Dr. Devol, E for his help with data analysis. We express our appreciation to the doctors and nurses at the dialysis unit at King Khalid Hospital for their valuable assistance. We would like to acknowledge the valuable support of the staff at the Research Center, College of Medicine and Clinical Biochemistry, College of Medicine.
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Nora N Al-Nahedh
Department of Family and Community Medicine, College of Medicine, King Saud University, P.O. Box 2925, Riyadh 11461
[Table - 1], [Table - 2]