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 Table of Contents  
ORIGINAL ARTICLE
Year : 2021  |  Volume : 59  |  Issue : 1  |  Page : 5-9

Relationship between levels of vascular endothelial growth factor in blood and severity of diabetic retinopathy


1 Department of Ophthalmology, Aravind Eye Hospital, Udumalaipettai, Tamil Nadu, India
2 Department of Ophthalmology, PSG Institute of Medical Sciences and Research, Coimbatore, Tamil Nadu, India
3 Department of Cornea and VItreoretinal Services, Bejan Singh Eye Hospital, Nagercoil, Tamil Nadu, India
4 Department of Vitreo Retinal Services, Aravind Eye Hospital, Coimbatore, Tamil Nadu, India

Date of Submission27-Aug-2020
Date of Acceptance01-Jan-2021
Date of Web Publication27-Mar-2021

Correspondence Address:
Dr. Jebinth Brayan
Cassie Castle, Mathicode, Thickanamcode, Kanyakumari - 629 804, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/tjosr.tjosr_124_20

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  Abstract 


Aim: The aim of the study was to establish the relationship between levels of vascular endothelial growth factor (VEGF) in blood and severity of diabetic retinopathy (DR). Background: The importance of VEGF in the pathogenesis of DR is evident from numerous studies demonstrating a significant increase in VEGF levels in samples obtained from the eye. However, a correlation between blood levels of VEGF and DR has not been conclusively proven or disproven. In this article, we demonstrate the relationship between blood levels of VEGF and the severity of DR. Materials and Methods: This is a hospital-based descriptive analytic study. The study population consisted of 75 Type 2 diabetic patients attending outpatient department for routine DR screening. After obtaining informed consent, 5 ml of blood was drawn from each patient and estimated for the levels of serum VEGF. The data thus obtained were correlated with the grade of DR. Additional parameters studied were duration of diabetes mellitus (DM), hemoglobin levels, blood urea, serum creatinine, fasting blood sugar (FBS) and random blood sugar (RBS), and hemoglobin A1c (HBA1c) levels. Statistical analysis used in this study was Chi-square test, Student's t-test, independent one sample t-test, and analysis of variance using SPSS software version. 19. Results: Overall mean VEGF levels for the study population of 75 diabetic patients were 577.01 ± 291.13 pg/ml. The average duration of DM in the study population was 7.2 years. The average hemoglobin level in the study population was 11.53 ± 2.00 g/dl. The mean urea levels in mg/dl of the whole population were 35.47 ± 25.80 mg/dl. The mean creatinine levels for the population were 1.42 ± 1.55 mg/dL. The mean RBS levels for the whole population were 228.95 ± 74.499 mg/dL. The mean FBS levels for the 75 patients were 165.87 ± 59.04 mg/dl. The mean HBA1c levels were 9.49 ± 2.37%. Conclusion: Levels of blood VEGF are elevated in diabetic patients regardless of whether they have DR or not. There is no statistically significant relationship between blood levels of VEGF and the severity of DR. Even though severe grades of DR showed more anemia, there is no statistically significant relationship between anemia and DR. The levels of urea and creatinine were elevated in the more severe grade of DR. VEGF, therefore, could present a potential treatment and preventive strategy for not only DR but also DM and its complications in general.

Keywords: Diabetes mellitus, diabetic retinopathy, ELISA, ETDRS, vascular endothelial growth factor


How to cite this article:
Brayan J, Sundar D, Singh SB, Singh NB, Thomas M, Chandrakanth P. Relationship between levels of vascular endothelial growth factor in blood and severity of diabetic retinopathy. TNOA J Ophthalmic Sci Res 2021;59:5-9

How to cite this URL:
Brayan J, Sundar D, Singh SB, Singh NB, Thomas M, Chandrakanth P. Relationship between levels of vascular endothelial growth factor in blood and severity of diabetic retinopathy. TNOA J Ophthalmic Sci Res [serial online] 2021 [cited 2021 Jul 28];59:5-9. Available from: https://www.tnoajosr.com/text.asp?2021/59/1/5/312276




  Introduction Top


Diabetic retinopathy (DR) is one of the most debilitating complications of diabetes mellitus (DM). It can either be a nonproliferative or proliferative pathology of the retina. It is probably the most significant complication of a systemic disease in the eye. Over a period of half a century, the world has witnessed remarkable progress in the field of DR and its management. From the early days of the Arlie house classification for staging of DR, we have now entered firmly into the realm of antivascular endothelial growth factor (anti-VEGF) therapy. Literature review shows five major points of change in the field of DR. First, diabetes and its complications have become a global problem; to the extent that DR has assumed the status of a global epidemic. DR has thus become the leading cause of blindness in the middle-aged population.[1] Second, a number of randomized control trials, strict control of blood sugars, and additional systemic comorbidities play a major role in the disease progression.[2],[3] Third, optical coherence tomography has become a major component in DR staging and management. With the improved resolution of images, ophthalmologists can cut down on the use of fundus fluorescein angiography. Fourth, timely retinal photocoagulation can protect the retina from developing end-stage disease. And Finally, the role of VEGF appears to be central to the pathogenesis of DR. Thus, anti-VEGF therapy has become one of the first lines of treatment, especially of diabetic macular edema.

The importance of VEGF in the disease pathogenesis was realized when the vitreous cavity of patients with DR had higher levels of VEGF than those of controls. To the best of our knowledge, previous studies were mainly based on measurements of VEGF in the vitreous cavity.[4],[5],[6],[7],[8] We aim to study the serum levels of VEGF in diabetic patients with DR and also the correlation, if any, between serum VEGF and the grading of DR.


  Materials and Methods Top


This was a hospital-based descriptive analytic study performed at a tertiary health-care institution and hospital in the department of ophthalmology over a period of 12 months after obtaining institutional ethical committee approval. A total of 75 Type 2 DM patients with or without DR were included in the study. Patients with Type 1 DM, with other retinal pathologies, terminally ill and those who have previously received anti-VEGF therapy were excluded from the study.

A written informed consent in patient's own language was obtained. A detailed history and a thorough ocular examination were performed. The 75 patients were divided into five groups consisting of 15 patients each according to the ETDR classification of DR – no DR, mild nonproliferative DR (mild NPDR), moderate nonproliferative DR (moderate NPDR), severe nonproliferative DR (severe NPDR), and proliferative DR (PDR). Fundus examination through 90D slit-lamp biomicroscopy and 20D indirect ophthalmoscopy was done followed by fundus photographs with a field of 50°. 5 ml blood samples were then withdrawn to measure the concentration of serum VEGF levels quantitatively using ELISA kit for human VEGF (Neogen USA Human VEGF Product #452610).

Statistical analysis of data was done using SPSS (IBM SPSS Statistics for Windows, Version 23.0. Armonk, NY: IBM Corp.). Correlation of data between the study variables were done by Chi-square test, Student's t-test, independent one sample t-test, and analysis of variance.


  Results Top


In this study, of 75 patients, 15 patients were grouped each on the basic of the ETDRS classification of DR into no DR, mild NPDR, moderate NPDR, severe NPDR, and PDR. The age of the patients ranged from 41 to 82 years, and the mean age of the patients was 58.16 ± 8.6 years and the mean age in each group is as listed in [Table 1]. The gender distribution of population was 56 males and 19 females. The average male-to-female ratio was 2.75:1 and for each group is listed in [Table 1].
Table 1: Demographic characteristics of the population under study

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Primary outcome measures

Vascular endothelial growth factor levels

Overall mean VEGF levels for the study population of 75 diabetic patients were 577.01 ± 291.13 pg/ml. The lowest value of VEGF was seen in the no DR group (34 pg/ml). The highest value was seen in the mild DR group (1296 pg/ml). Overall, there was no statistical significance in the variation of VEGF and the grade of DR (P = 0.544) [Table 2].
Table 2: Relationship of grades of diabetic retinopathy and mean vascular endothelial growth factor, haemoglobin, urea, creatinine, random blood sugar, fasting blood sugar, and hemoglobin A1c

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Secondary outcome measures

Duration of diabetes mellitus

The average duration of DM in the study population was 7.2 years. The subpopulation without any DR had the minimum duration of 6.53 years. The population with mild NPDR had the maximum duration of 12.80 years. There was no statistically significant difference in the duration of DM and the grade of DR (P = 0.137) [Table 2].

Hemoglobin levels

The average hemoglobin level in the study population was 11.53 ± 2.00 g/dl. There was no significant difference in the hemoglobin levels and the severity of DR (P = 0.791) [Table 2].

Urea levels

The mean urea levels in mg/dl of the whole population were 35.47 ± 25.80 mg/dl. There was no significant difference in the levels of urea and the severity of DR (P = 0.138) [Table 2].

Serum creatinine levels

The mean creatinine levels for the population were 1.42 mg/dL ± 1.55. The minimum value was seen in the patients with no DR (0.91 mg/dL). The highest values were seen in the group with PDR (2.26 mg/dL). However, any intergroup variation of creatinine was not statistically significant (P = 0.11) [Table 2].

Random blood sugar levels

The mean random blood sugar (RBS) levels for the whole population were 228.95 ± 74.499 mg/dL. The normal RBS was taken to be 70–140 mg/dL. After statistical analysis, the rise in the mean RBS was found to be significant. However, there was no statistically significant change in the RBS levels and the severity of DR (P = 0.430) [Table 2].

Fasting blood sugar levels

The mean fasting blood sugar (FBS) levels for the 75 patients were 165.87 ± 59.04 mg/dl. However, there was no significant difference in the FBS levels and the severity of DR (P = 0.408) [Table 2].

Haemoglobin A1c levels

The mean hemoglobin A1c (HBA1c) levels were 9.49% ± 2.37%. The lowest HBA1c levels were seen in the group with no DR (8.45%) and the highest was seen with the group with severe NPDR (10.46%). However, the difference was not statistically different (P = −0.230) [Table 2].


  Discussion Top


DR is without doubt one of the most significant ocular complications of a systemic disease. Several studies have showed that the VEGF plays a prime role in the pathogenesis of DR. The vitreous levels of VEGF are elevated in patients with DR in particular active, advanced stages of DR is an undisputable fact. However, previous studies show conflicting data with the association of blood VEGF and DR.

The aim was to study the comparison between the serum VEGF levels of DM patients with and without DR, and if there was any association between serum VEGF levels with the severity of DR.

Demography

The average age of the patients in the study population was 58.16 years, of which only Type 2 diabetics was included in the study. Any patient with Type 1 diabetes was excluded from the study.

Earlier studies done in similar populations from South India report age and longer duration of DM as risk factors for DR.[9],[10],[11] However, in our study, further analysis of the age and the severity of diabetes showed no statistical significance. Regarding the association with gender, majority of the patients were male, with an overall male-to-female ratio of 2.75:1. A similar result was reported by Raman et al., where they report an increased risk of DR among male patients (odds ratio = 1.41).[11]

Primary outcome measures

The serum VEGF level in the 75 patients was taken as our primary outcome. The average serum VEGF levels were 577.01 g/ml. On comparing this value with the known normal serum VEGF levels, our result was proven to be very significant. This result has been reported in a number of other studies as well.[12],[13]

We then analyzed the elevation between the group with no DR and the normal population values. This too was significantly elevated (P = 0.0076). Therefore, it appears that VEGF is elevated in diabetics per se and not specifically in patients with DR. This can be explained by the fact that VEGF is a systemic factor and not confined to the eye. VEGF has been implicated in the pathogenesis of not only DR but also in diabetic nephropathy, neuropathy, and even diabetic macrovascular disease.[14],[15],[16]

Paradoxically, the group with PDR had the minimum mean value of VEGF. The group with mild NPDR had the maximum mean VEGF value. On testing the relation between VEGF and the severity of DR, there was no statistical significance detected. Similar results have been obtained in other studies.[17] Hence, serum VEGF levels are elevated in diabetics when compared with the normal population. However, there is no relationship with the severity of DR.

Secondary outcome measures

Duration of diabetes mellitus

In our study, the average duration of DM was 7.2 years. There was no statistically significant relationship between the duration of DM and severity of DR. However, the group with the minimum duration of DM was the group with no DR. This is in keeping with the established fact that the duration of DM is an important risk factor for the development of DR.

Hemoglobin level

The mean hemoglobin level was 11.53 g/dL. Taking the normal range of hemoglobin to be 12–15 g/dL, our population appears to be on the anemic side. In addition, the group with PDR had the lowest mean hemoglobin of 11.29; the group with the highest hemoglobin was the group with no DR. Although this is not statistically significant, this trend is in keeping with the fact that anemia worsens the retinopathy status. In addition, treating anemia has been proven to improve retinopathy and delay its progression.[18]

Urea and creatinine levels

The average urea level for our population was 35.47 mg/dL. Taking the normal range of serum urea to be from 14 to 40 mg/dL, this value falls into the high normal range. The mean creatinine levels were 1.42 mg/dL. As the normal range of creatinine is 0.66–1.09 mg/dL, this definitely falls into the high range. There was no statistically significant relationship between the creatinine levels or urea levels and the severity of diabetes. Even though the group with PDR had the highest urea levels and creatinine levels, this is very much in keeping with the fact that both nephropathy and retinopathy are microvascular disease and often the presence of one indicates the presence of the other. However, there is also a good chance of this renal disease being nondiabetic in origin. As highlighted in an earlier study by Prakash et al., nondiabetic renal disease versus diabetic disease was 22.6% versus 3.2% when the duration of DM was between 5 and 10 years. It is only after 10 years of DM that diabetic renal disease jumped ahead to 32.2% versus 6.5% for nondiabetic renal disease.[19] As our population, mean duration of diabetes was 7.2 years, it is likely that any renal impairment is more of a nondiabetic origin.

Random blood sugar and fasting blood sugar levels

The average RBS levels for the whole population were 228.95 mg/dL and the mean FBS was 165.87 mg/dL. Both these values are elevated when compared with normal values. This fact has important long-term prognostic value as it has been proved in numerous studies that control of blood sugar and other comorbidities play a major role in the control of diabetic complications. There was no statistically significant association between the levels of RBS and FBS and the severity of diabetes.

Hemoglobin A1c levels

The mean HBA1c level for our study population was 9.49%. The normal upper limit is taken to be 6.3%. As the HBA1c level indicates the state of blood sugar control for a prior 3 months, this indicates a very poor control. However, there was no significant relationship between HBA1c levels and the severity of DR. Moreover, no general trends were observed.

Limitation of this study

Many of the parameters studied showed wide standard deviations. This could be because of a small sample size. Possibly due to this same reason, many of the outcome measures did not show a statistically significant relationship with the severity of DR. Therefore, by increasing the sample size, it is possible that we could have obtained more significant results.

We did not have a population of healthy controls. Hence, we could only compare our study population with known normal ranges. Having a group of age- and sex-matched healthy control could have eliminated any confounders which might have arisen.

We did not study other comorbid conditions such as blood pressure, obesity, and hypercholesterolemia. All these factors have been proven to affect the complications of diabetes and they would have been useful in this study.


  Conclusion Top


Serum VEGF levels were found to be significantly elevated in our study population when compared with the normal VEGF levels. This elevation of VEGF was observed in the entire diabetic population irrespective of whether they had retinopathy or not. There was no significant relationship between the serum VEGF levels and the severity of DR. Anemia was associated with severe grades of retinopathy. There was an elevation of urea and creatinine levels in the study population; this elevation was higher in the more severe grades of DR. RBS and FBS levels were high in the study population indicating a state of chronic hyperglycemia and also suboptimal control of blood sugars. The trend in HbA1c levels mirrored that of RBS and FBS again highlighting a poor control of sugars. In conclusion, an elevated serum VEGF level is significantly associated with DM and is linked to many of its complications. Although we are yet to discover about VEGF and its exact role in the pathogenesis of DR, one thing is certain, levels of VEGF lie a potential treatment and preventive strategy of not only DR but also of many of the complications of DM.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

This study was financially supported by PRIME, PSG IMSR.

Conflicts of interest

There are no conflicts of interest.



 
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