Elevation of serum apelin-13 associated with proliferative diabetic retinopathy in type 2 diabetic patients

AIM: To compare apelin-13, a ligand of G-proteincoupled receptor which has been shown to be involved in retinal angiogenesis, and vascular endothelial growth factor(VEGF) serum levels in type 2 diabetes mellitus(T2DM) with or without retinopathy, and to investigate the relationship between the serum concentration of apelin-13 and diabetes retinopathy.METHODS: Sixty-nine patients with T2 DM were enrolled.Of the 69 patients, 16 had proliferative diabetic retinopathy(PDR group), 23 had non-PDR(NPDR group)and 30 had no retinopathy(T2DM group). Subjects’ information, including demographics, medical history,and use of medications were recorded. Their serum samples were collected for measuring the levels of C-reactive protein(CRP), serum lipid and glycosylated hemoglobin. Apelin-13 and VEGF serum levels were measured by enzyme-linked immunosorbent assay.Kruskal-Wallis test and one-way ANOVA were used to compare the differences among these groups. Chi-square test was used to assess categorical variables.Correlations between variables were investigated by Spearman rho correlation test and stepwise regression analysis. All statistical analyses were performed through SPSS 17.0 software.RESULTS: Sex, age, body mass index(BMI), blood pressure, CRP, hemoglobin A1c(Hb A1c) have no significantly difference in the three groups. Serum level of apelin-13 was significantly elevated in PDR group as compared with T2 DM group(P =0.041). Differences of VEGF serum concentration in the three groups were statistically significant(P =0.007, P =0.007 and P <0.001,respectively). Spearman rho correlation test showed that serum apelin-13 was positively correlated with BMI,serum triglycerides, VEGF, but not with age, duration of diabetes, blood pressure, CRP, Hb A1 c and total-cholesterol. Stepwise regression analysis showed that BMI also significantly associated with serum apelin-13(P =0.002), while VEGF and serum triglycerides were irrelevant. CONCLUSION: This study elucidated a positive association of apelin-13 serum level with PDR, but not with VEGF. Apelin-13 may influence the promotion of PDR but unrelated with VEGF.