Prior studies in animals have shown that in the brain, MMP-9 is directly involved in the degradation and clearance of Aβ, suggesting a more protective rather than destructive role of MMP-9 in AD [6, 17, 18], while others have demonstrated that MMP-9 increases lipoprotein receptor shedding in endothelial cells, leading to reduced Aβ transport across the blood-brain barrier [19]. This evidence concerns the gene MMP9 and Alzheimer disease.