APLN and diabetes mellitus: As Table 5 presented, Pearson correlation analysis showed that serum VEGF, apelin, and HO-1 in patients with PDR was related to the time course of DM, FPG and HbAlc (all p < 0.05), and the serum VEGF, apelin, and HO-1 in patients with PDR was not related to the age, gender, BMI, hypertension, HDL-c, LDL-c, TG and TC (all p > 0.05).