MPO and Alzheimer disease: In addition, the contribution of OS in different AD models has been evaluated; for example, intracerebroventricular administration of Aβ molecules of various lengths, such as Aβ25–35, in rats results in oxidative stress, a significant increase in the levels of the malondialdehyde (MDA) and Mpo genes, and a decrease in superoxide dismutase (SOD) levels.