In Vitro and In Vivo Activation of Astrocytes by Amyloid-β is Potentiated by Pro-Oxidant Agents

Alzheimer's disease (AD) is a devastating age-related neurodegenerative disease. Age is the main risk factor for sporadic AD, which is the most prevalent type. Amyloid-beta peptide (A beta) neurotoxicity is the proposed first step in a cascade of deleterious events leading to AD pathology and dementia. Glial cells play an important role in these changes. Astrocytes provide vital support to neurons and modulate functional synapses. Therefore, the toxic effects of A beta on astrocytes might promote neurodegenerative changes that lead to AD. Aging reduces astrocyte antioxidant defenses and induces oxidative stress. We studied the effects of A beta(42) on cultures of human astrocytes in the presence or absence of the following pro-oxidant agents: buthionine sulfoximine (BSO), a glutathione synthesis inhibitor, and FeSO4, which liberates redox active iron. Pro-oxidant conditions potentiated A beta toxicity, as shown by the generation of free radicals, inflammatory changes, and apoptosis. Similar treatments were assessed in rats in vivo. A combination of A beta(40) and A beta(42) or A beta(42) alone was infused intracerebroventricularly for 4 weeks. Other animal groups were also infused with BSO and FeSO4. A long-term analysis that ended 4 months later showed greater cognitive impairment in the Morris water maze task, which was induced by A beta plus pro-oxidant agent treatments. Pro-oxidant agents also potentiated brain tissue pathology. This was demonstrated in histological studies that showed highly increased astrocyte reactivity in AD-vulnerable areas, A beta deposits, and oxidative damage of AD-sensitive hippocampal neurons. To increase our understanding of AD, experimental models should be used that mimic age-related brain changes, in which age-related oxidative stress potentiates the effects of A beta.