Effect of retinal laser photocoagulation on the activity of metalloproteinases and the α2-Macroglobulin proteolytic state in the vitreous of eyes with proliferative diabetic retinopathy

Panretinal photocoagulation (PRP) reduces the incidence of severe visual loss in proliferative diabetic retinopathy (PDR). The aim of the study was to determine the effect of PRP on the activity of matrix metalloproteinase-2 (MMP-2) and MMP-9, and also on the α2-Macroglobulin (α2M) proteolytic state in the vitreous of eyes with PDR. Vitreous samples were obtained from patients undergoing vitrectomy for the treatment of retinal diseases: 17 with PDR and eight with idiopathic macular hole (MH). Qualitative evaluation of the MMP-2 and MMP-9 activation status was performed by gelatin zymography and quantitative assay was carried out for vitreous total protein content and α2M. The proteolytic state of α2M was evaluated by Western blotting. Although all vitreous samples contained proMMP-2, increased proMMP-9 and active MMP-9 were detected in PDR samples without PRP. In addition, after PRP the proMMP-9 activity was significantly decreased, whereas the proMMP-2 activity was not affected. Enhanced total protein and α2M concentrations were observed in all vitreous samples from PDR patients with and without previous PRP compared with samples from patients with MH. However, a differential proteolytic state of α2M, expressed as 180/85–90 kDa ratio, was detected among PDR patients with and without PRP treatment. Whereas a low 180/85–90 kDa ratio of α2M in vitreous of PDR patients without PRP was observed, a high proportion of 180 kDa subunit was principally detected in PDR with PRP. These results demonstrate that PDR occurs with an enhanced activity of MMP-9 and activation of α2M by proteinases, which is reversed after PRP. In addition, we suggest that α2M plays a key role in the control and regulation of the ocular neovascularization involved in the pathogenesis of ischemic retinal diseases such as PDR.