title: Elevation of serum apelin-13 associated with proliferative diabetic retinopathy in type 2 diabetic patients.
abstract: OBJECTIVE
  To compare apelin-13, a ligand of G-protein-coupled 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 T2DM 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 (HbA1c) have no significantly difference in the three groups. Serum level of apelin-13 was significantly elevated in PDR group as compared with T2DM 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, HbA1c 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Ophthalmology, Xi'an Ninth Hospital Affiliated to Medical College of Xi'an Jiaotong University, Xi'an 710054, Shaanxi Province, China ; Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education, School of Medicine, Xi'an Jiaotong University, Xi'an 710061, Shaanxi Province, China.
authors.forename: Jun-Hui
authors.initials: JH
authors.lastname: Du
authors.affiliation: Outpatient Department, Guangzhou Sanitorium of PLA, Guangzhou 510515, Guangdong Province, China.
authors.forename: Xia
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Ophthalmology, the Affiliated Hospital of Xi'an Medical University, West Fenghao Road 48, Xi'an 710077, Shaanxi Province, China.
authors.forename: Rong
authors.initials: R
authors.lastname: Li
authors.affiliation: Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education, School of Medicine, Xi'an Jiaotong University, Xi'an 710061, Shaanxi Province, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Xu
authors.affiliation: Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education, School of Medicine, Xi'an Jiaotong University, Xi'an 710061, Shaanxi Province, China.
authors.forename: Ran-Ran
authors.initials: RR
authors.lastname: Ma
authors.affiliation: Department of Endocrinology, Xi'an Ninth Hospital Affiliated to Medical College of Xi'an Jiaotong University, Xi'an 710054, Shaanxi Province, China.
authors.forename: Song-Fang
authors.initials: SF
authors.lastname: Liu
authors.affiliation: Department of Ophthalmology, Xi'an Ninth Hospital Affiliated to Medical College of Xi'an Jiaotong University, Xi'an 710054, Shaanxi Province, China.
authors.forename: Zhong
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education, School of Medicine, Xi'an Jiaotong University, Xi'an 710061, Shaanxi Province, China.
authors.forename: Hong-Zhi
authors.initials: HZ
authors.lastname: Sun
keywords: apelin-13; diabetic retinopathy; vascular endothelial growth factor