Abstract
Fibulin-1, an extracellular matrix glycoprotein, is closely correlated with angiogenesis. The purpose of this investigation is to determine serum and vitreous fibulin-1 concentrations in diabetic retinopathy (DR). This cross-sectional investigation was carried out in a population of 154 diabetic patients (54 without DR, 42 with non-proliferative diabetic retinopathy (NPDR) and 58 with proliferative diabetic retinopathy (PDR)) and 49 control subjects. The diabetic group showed higher serum and vitreous fibulin-1 concentrations than the controls. Serum and vitreous fibulin-1 concentrations in PDR patients were significantly elevated compared with those in the other 3 groups. NPDR patients showed elevated levels of serum and vitreous fibulin-1 concentrations compared with patients without DR. Logistic regression analysis revealed that serum and vitreous fibulin-1 were risk factors for developing DR. Pearson correlation analysis showed that serum fibulin-1 was correlated with systolic blood pressure (SBP), diastolic blood pressure (DBP), fasting plasma glucose and vitreous fibulin-1. Furthermore, Pearson correlation analysis showed that vitreous fibulin-1 was correlated with SBP, DBP, high-density lipoprotein cholesterol and serum fibulin-1. Serum and vitreous fibulin-1 concentrations are elevated under DR condition.
Significance of this study
What is already known about this subject?
Angiogenesis is involved in the mechanism of diabetic retinopathy (DR).
Fibulin-1 plays an important role in angiogenesis.
Patients with diabetes displayed significantly higher fibulin-1 levels than those without diabetes.
What are the new findings?
The diabetic group showed higher serum and vitreous fibulin-1 concentrations than the controls.
Serum and vitreous fibulin-1 concentrations in PDR patients were significantly elevated compared with those in the other three groups. Non-proliferative diabetic retinopathy patients showed elevated levels of serum and vitreous fibulin-1 concentrations compared with patients without DR.
Logistic regression analysis revealed that serum and vitreous fibulin-1 were risk factors for developing DR.
How might these results change the focus of research or clinical practice?
Serum and vitreous fibulin-1 concentrations are elevated under DR condition.
Introduction
Diabetic retinopathy (DR), a common diabetic microvascular complication, contributes to ∼4.8% of blindness over the world.1 The pathogenesis of DR is complex and not quietly understood. A variety of evidence has focused on the key role of angiogenesis in the pathogenesis of DR, especially proliferative diabetic retinopathy (PDR).2 The imbalance between angiogenic stimulator and inhibitor results in the angiogenic process and at last PDR development.3
Fibulin-1, one member of extracellular matrix (ECM) family, interacts with other ECM family members such as fibronectin, elastin and basement membranes.4 Fibulin-1-deficient mice showed the destruction of endothelial lining in small vessels, massive hemorrhages in several tissues and ultimately early death.5 Recent studies have shown the important role of fibulin-1 in diabetes development. Diabetic patients had relatively higher serum fibulin-1 concentrations compared with non-diabetic patients.6 Fibulin-2 gene was found to be differentially expressed in the kidneys between streptozotocin-induced diabetic mice kidneys undergoing glomerulosclerosis and controls.7 In addition, serum fibulin-1 was correlated with plasma glucose levels which was evaluated by hemoglobin A(1c).6 Increased plasma fibulin-1 concentrations were found in diabetic participants with erectile dysfunction than in those without erectile dysfunction.8 Human coronary artery atherosclerotic lesions presented strong deposition of fibulin-1, which demonstrate the pathophysiological effects of fibulin-1 in atherosclerosis.9 Recently, fibulin-1 was found to inhibit angiogenesis and suppress tumor growth.10 Considering the correlation of angiogenesis with DR, it is hypothesized that fibulin-1 may be involved in DR development.
We performed this cross-sectional investigation to assess serum and vitreous fibulin-1 concentrations in DR patients.
Materials and methods
Patients
This study was performed in a consecutive population of 154 diabetic patients (54 patients without DR, 42 with non-PDR (NPDR) and 58 with PDR) who underwent vitreoretinal surgery in Department of Ophthalmology, Shandong Provincial Hospital Affiliated to Shandong University. Patients were excluded if they had vitrectomy history; other ocular disorders such as uveitis, glaucoma and corneal neovascularization; other systemic diseases including heart failure, renal failure, hematological, cardiological and metabolic disorders other than diabetes and obvious vitreal hemorrhage within the previous 3 months. Control participants included 49 subjects who matched with the cases by age and gender. Those subjects were enrolled from the subjects who underwent vitrectomy for retinal detachment in our hospital and had no systemic disease such as heart failure, renal failure, hematological, cardiological and metabolic disorders. They were confirmed having no diabetes by measuring fasting plasma glucose (<7.0 mmol/L) and 2-hour postprandial plasma glucose (<11.1 mmol/L). The study was planned according to the ethics guidelines of the Helsinki Declaration and was approved by the research ethics committee of our hospital. All subjects gave written informed consent regarding participation in this study.
Laboratory methods
Vitreous samples were abstracted by manual suction to a syringe through the aspiratin line of vitrectomy, before opening the infusion line. Serum and vitreous fibulin-1 concentrations were then measured by a commercially available ELISA kit (Cusabio Biotech Company).
Statistical analysis
The results were expressed as means±SEs or median (IQR). Kolmogorov-Smirnov test was performed to analyze the data normality. The differences in variables between the four groups were performed by χ2 tests, one-way analysis of variance or Kruskal-Wallis test. Logistic regression analysis was used to determine the risk factors for developing DR. The correlation of fibulin-1 with other parameters was analyzed by Pearson correlation analysis and multiple linear regression analysis. Statistical analysis was carried out using the SPSS V.16.0 software program (SPSS, Chicago, Illinois, USA). All analyses reported significance at the p<0.05 level.
Results
Clinical parameters of the case and control group
Diabetic patients showed higher systolic blood pressure (SBP), diastolic blood pressure (DBP), fasting plasma glucose (FPG) and triglycerides (TG) compared with the controls (table 1).
Serum and vitreous fibulin-1 concentrations
As shown in table 1, the diabetic group showed higher serum and vitreous fibulin-1 concentrations than the controls. Serum and vitreous fibulin-1 concentrations in PDR patients were significantly elevated compared with those in the other three groups. NPDR patients showed elevated levels of serum and vitreous fibulin-1 concentrations compared with patients without DR.
The association of fibulin-1 concentrations with DR
Serum and vitreous fibulin-1 concentrations were higher in T2DM patients with DR than in those without DR (8.96 (7.22–10.69) vs 6.74 (5.59–8.60) ng/mL, p<0.001 and 4.43 (3.49–5.87) vs 3.28 (2.70–4.03) ng/mL, p<0.001, respectively). As shown in table 2, simple logistic regression analysis and multivariate logistic regression revealed that serum and vitreous fibulin-1 were risk factors of developing DR.
The correlation of fibulin-1 concentrations with other parameters
As shown in table 3, Pearson correlation analysis showed that serum fibulin-1 was correlated with SBP, DBP, FPG and vitreous fibulin-1. Multiple regression analysis still revealed a correlation of serum fibulin-1 with SBP, FPG and vitreous fibulin-1. Furthermore, Pearson correlation analysis showed that vitreous fibulin-1 was correlated with SBP, DBP, high-density lipoprotein cholesterol (HDL-C) and serum fibulin-1 (table 4). Multiple regression analysis indicated that vitreous fibulin-1 was associated with HDL-C and serum fibulin-1 (table 4).
Discussion
Fibulin-1 is one of the ECM proteins highly expressed in circulation. Recent studies have showed that fibulin-1 is demonstrated to be a biomarker for assessing the condition of diabetes.6 ,11–13 Patients with diabetes displayed significantly higher fibulin-1 levels than those without diabetes.6 ,11 Furthermore, higher fibulin-1 protein concentrations were found in artery extracts from patients with diabetes than those in controls.6 Plasma fibulin-1 concentrations were found to be positively correlated with glycated hemoglobin.6 ,12 In addition, our study also demonstrated that serum fibulin-1 was correlated with FPG. Scholze et al's investigation indicated that diabetes was an independent predictor of plasma fibulin-1 after a multivariable regression model. Skov et al13 reported that plasma fibulin-1 was elevated in diabetic patients during the 2-year follow-up. And metformin treatment markedly reduced plasma fibulin-1 concentrations in those diabetic patients.13 It seems that serum fibulin-1 was correlated with plasma glucose. And higher serum fibulin-1 may be responsive to diabetes disease condition. Therefore, further investigation on animals should be performed to determine the pathogenesis of fibulin-1 involved in diabetes.
Fibulin-1 is also a new factor in cardiovascular disease. It was found that plasma concentration of fibulin-1 predicted all-cause and cardiovascular mortality in diabetic patients.6 Recent study showed a correlation between plasma fibulin-1 concentrations and cardiovascular risk markers in diabetic patients.12 Patients with peripheral arterial disease and coronary artery disease had higher fibulin-1 concentrations than the controls.14 This indicates that fibulin-1 was correlated with diabetic macrovascular complication. However, no investigation has been performed about the association between fibulin-1 and diabetic microvascular complication. DR is an important diabetic microvascular complication. Then our results showed that serum and vitreous fibulin-1 were elevated under DR condition.
Angiogenesis is a potential mechanism of DR. Fibulin-1 was found to serve as an angiogenesis inhibitor. It was found that fibulin-1 overexpression contributed to suppressed tumor growth, induced tumor cell apoptosis and inhibited angiogenesis in the bladder cancer and renal cell carcinoma condition.15 ,16 ADAMTS-1 is a metalloprotease which is involved in the inhibition of angiogenesis. Lee et al17 reported that fibulin-1 could enhance the binding of ADAMTS-1 to cleave aggrecan when colocalized with ADAMTS-1. This indicates that fibulin-1 could inhibit the angiogenesis by promoting ADAMTS-1 activity. Therefore, fibulin-1 is hypothesized to play a role in DR development through an antiangiogenesis effect. However, this role is controversy with relatively higher serum and vitreous fibulin-1 concentrations in DR. This may be explained that as angiogenesis is an important mechanism of DR development and progression, more fibulin-1 concentrations were released to inhibit angiogenesis process through its anti-inflammatory role under the condition of DR disease.
In conclusion, serum and vitreous fibulin-1 concentrations are elevated under DR condition.
Footnotes
Contributors BH researched literature and conceived the study. MT and JW were involved in protocol development and data analysis. YW and QL wrote the first draft of the manuscript.
Competing interests None declared.
Patient consent Obtained.
Ethics approval The research ethics committee of Yuhuangding Hospital.
Provenance and peer review Not commissioned; externally peer reviewed.