I recommend this paper
Excellent summary of current knowledge. As to the initiating factors, I believe there is evidence for an entero-hepatic-immunological axis as the major generator of both nitrosative/oxidative stress and mitoenergetic stress in peripheral tissues, which effects distal tissues including neurons, especially when there is aberrant food ligand stimulation of nuclear receptors and an oxidative diet (1) with high glycemic stress (2).
1. Halvorsen BL, Carlsen MH, Phillips KM, Bohn SK, Holte K, Jacobs DR Jr, Blomhoff R. Content of redox-active compounds (ie, antioxidants) in foods consumed in the United States.
Am J Clin Nutr. 2006 Jul;84(1):95-135.
2. Hu Y, Block G, Norkus EP, Morrow JD, Dietrich M, Hudes M. Relations of glycemic index and glycemic load with plasma oxidative stress markers. Am J Clin Nutr. 2006 Jul;84(1):70-6. Abstract
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