Consistently with MMP-9, the activation of MMP-2 is also an early event in the pathogenesis of diabetic retinopathy, which precedes mitochondrial damage [4,42], and we cannot rule out the role of homocysteine in functional and transcriptional regulation of MMP-2 in diabetic retinopathy, but this is beyond the scope of the present study. Here, MMP9 is linked to diabetic retinopathy.