Does Pattern Scan Laser (PASCAL) photocoagulation really induce less VEGF expression in murine retina than conventional laser treatment?

Abstract

To investigate the differences in the mRNA and protein expression levels of vascular endothelial growth factor (VEGF) in murine retina between mice subjected to conventional laser (AG) and those subjected to Pattern Scan Laser (PASCAL) system. Male C57BL/6 mice were randomly assigned to one of three groups: Group 1 (G1) receiving retinal scatter laser photocoagulation using with AG photocoagulator (n=16), Group 2 (G2) receiving retinal scatter laser photocoagulation using with PASCAL (n=16) and Group 3 (G3) served as an untreated control group (n=6). Molecular and morphological analyses of VEGF were performed on days 1, 2 and 5 by ELISA, real-time PCR and immuno-histochemical analysis. In samples which underwent AG (G1), when compared with the control group (G3), VEGF mRNA level increased 2.4 folds on day 2, whereas it decreased on day 5 (p□0.001). In samples which underwent PASCAL (G2), on the other hand, VEGF mRNA level increased 1.8 folds on day 1 and 2.2 folds on day 5 when compared with the control group (G3). In samples which underwent AG (G1), when compared with the control group (G3), VEGF protein level increased significantly on day 2, whereas it decreased on day 5 (p□0.001). In group G2, the VEGF levels in the sensory retina significantly increased as compared to control groups at both 2 and 5days after laser photocoagulation using PASCAL laser (p=0.012, both time points). The peak expressions of VEGF protein in samples which underwent PASCAL and conventional laser were found on day 5 and day 2 respectively. In retinas of PASCAL-treated mice, VEGF immunoreactivity gradually increased during the 5-day follow-up. However, in argon laser group, the strongest VEGF immunoreactivity was detected on day 2, then started to decrease on day 5. In summary, the expression of VEGF protein and mRNA gradually increase during a 5-day follow-up period in PASCAL-treated mouse eyes, whereas in AG group they reach their peak levels on the second day of follow-up and started decreasing after then. These results may also explain why the PASCAL system is less effective in regressing neovascularization in the clinic.