Catecholamines potentiate amyloid β-peptide neurotoxicity: Involvement of oxidative stress, mitochondrial dysfunction, and perturbed calcium homeostasis

Oxidative stress and mitochondrial dysfunction are implicated in the neuronal cell death that occurs in physiological settings and in neurodegenerative disorders. In Alzheimer's disease (AD) degenerating neurons are associated with deposits of amyloid β-peptide (Aβ), and there is evidence for increased membrane lipid peroxidation and protein oxidation in the degenerating neurons. Cell culture studies have shown that Aβ can disrupt calcium homeostasis and induce apoptosis in neurons by a mechanism involving oxidative stress. We now report that catecholamines (norepinephrine, epinephrine, and dopamine) increase the vulnerability of cultured hippocampal neurons to Aβ toxicity. The catecholamines were effective in potentiating Aβ toxicity at concentrations of 10-200 μM, with the higher concentrations (100-200 μM) themselves inducing cell death. Serotonin and acetylcholine were not neurotoxic and did not modify Aβ toxicity. Levels of membrane lipid peroxidation, and cytoplasmic and mitochondrial reactive oxygen species, were increased following exposure to neurons to Aβ, and catecholamines exacerbated the oxidative stress. Subtoxic concentrations of catecholamines exacerbated decreases in mitochondrial energy charge and transmembrane potential caused by Aβ, and higher concentrations of catecholamines alone induced mitochondrial dysfunction. Antioxidants (vitamin E, glutathione, and propyl gallate) protected neurons against the damaging effects of Aβ and catecholamines, whereas the β- adrenergic receptor antagonist propanolol and the dopamine (D1) receptor antagonist SCH23390 were ineffective. Measurements of intracellular free Ca²⁺ ([Ca²⁺](i)) showed that Aβ induced a slow elevation of [Ca²⁺](i) which was greatly enhanced in cultures cotreated with catecholamines. Collectively, these data indicate a role for catecholamines in exacerbating Aβ-mediated neuronal degeneration in AD and, when taken together with previous findings, suggest roles for oxidative stress induced by catecholamines in several different neurodegenerative conditions.