MMP9 and Cognitive impairment: The proteolytic activities of MMP-2 and MMP-9 in postmortem human frontal and parietal cortical tissues obtained from subjects with a clinical diagnosis of AD, mild cognitive impairment (MCI), or no cognitive impairment were compared using gelatin zymography in the research, which demonstrated higher activity of MMP-9, but not MMP-2, in AD and MCI brains when compared to cognitively healthy brain samples.