<qa>  What is the association between PPD and circulating levels of Matrix MetalloproteinRecent clinical studies showed an association between Peripheral Artery Disease PAD and circulating levels of Matrix Metalloproteinases MMPs, especially MMP-2, MMP-9, MMP-8 and MMP-10, compared with healthy controls. A recent study showed the association between MMP-10 serum levels and severity and poor outcome in patients affected by Critical Limb Ischemia CLI. 