Oxidative injury in diseases of the central nervous system: focus on Alzheimer's disease

Beta-amyloid inhibits integrated mitochondrial respiration and key enzyme activities

Disrupted energy metabolism, in particular reduced activity of cytochrome oxidase (EC 1.9.3.1), alpha-ketoglutarate dehydrogenase (EC 1.2.4.2) and pyruvate dehydrogenase (EC 1.2.4.1) have been reported in post-mortem Alzheimer's disease brain. beta-Amyloid is strongly implicated in Alzheimer's pathology and can be formed intracellularly in neurones. We have investigated the possibility that beta-amyloid itself disrupts mitochondrial function. Isolated rat brain mitochondria have been incubated with the beta-amyloid alone or together with nitric oxide, which is known to be elevated in Alzheimer's brain. Mitochondrial respiration, electron transport chain complex activities, alpha-ketoglutarate dehydrogenase activity and pyruvate dehydrogenase activity have been measured. Beta-amyloid caused a significant reduction in state 3 and state 4 mitochondrial respiration that was further diminished by the addition of nitric oxide. Cytochrome oxidase, alpha-ketoglutarate dehydrogenase and pyruvate dehydrogenase activities were inhibited by beta-amyloid. The K(m) of cytochrome oxidase for reduced cytochrome c was raised by beta-amyloid. We conclude that beta-amyloid can directly disrupt mitochondrial function, inhibits key enzymes and may contribute to the deficiency of energy metabolism seen in Alzheimer's disease.

Dementia: a neuroendocrine perspective

The etiology of Alzheimer's disease (AD) has not been as yet completely defined. Genetic, environmental and neurophysiological aspects should all be taken into account. The disease has also neuroendocrine implications, some of which are discussed in this review. It is known that stress and glucocorticoids may affect neurone survival. On the contrary, some data indicate that DHEA and DHEAS exert a neuroprotective action. In AD, changes in hypothalamic-pituitary-adrenal axis function have been reported. Experimental and clinical evidence indicates that glucocorticoid hypersecretion and DHEAS levels decrement may add to hippocampal dysfunction in aging and in AD. Glucocorticoid and beta-amyloid concur in the mechanism of neurone damage, as well as excitatory amino acids (EAA), Ca++ and reactive oxygen species (ROS). The neuroprotective effects exerted by IGFs are also hindered in aging and even more in AD. Production and biological actions of IGFs are negatively influenced by cortisol hypersecretion and DHEAS decrease in patients with AD.

The curry spice curcumin reduces oxidative damage and amyloid pathology in an Alzheimer transgenic mouse

Inflammation in Alzheimer's disease (AD) patients is characterized by increased cytokines and activated microglia. Epidemiological studies suggest reduced AD risk associates with long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs). Whereas chronic ibuprofen suppressed inflammation and plaque-related pathology in an Alzheimer transgenic APPSw mouse model (Tg2576), excessive use of NSAIDs targeting cyclooxygenase I can cause gastrointestinal, liver, and renal toxicity. One alternative NSAID is curcumin, derived from the curry spice turmeric. Curcumin has an extensive history as a food additive and herbal medicine in India and is also a potent polyphenolic antioxidant. To evaluate whether it could affect Alzheimer-like pathology in the APPSw mice, we tested a low (160 ppm) and a high dose of dietary curcumin (5000 ppm) on inflammation, oxidative damage, and plaque pathology. Low and high doses of curcumin significantly lowered oxidized proteins and interleukin-1beta, a proinflammatory cytokine elevated in the brains of these mice. With low-dose but not high-dose curcumin treatment, the astrocytic marker GFAP was reduced, and insoluble beta-amyloid (Abeta), soluble Abeta, and plaque burden were significantly decreased by 43-50%. However, levels of amyloid precursor (APP) in the membrane fraction were not reduced. Microgliosis was also suppressed in neuronal layers but not adjacent to plaques. In view of its efficacy and apparent low toxicity, this Indian spice component shows promise for the prevention of Alzheimer's disease.

In-vitro activity of S. lavandulaefolia (Spanish sage) relevant to treatment of Alzheimer's disease

Salvia lavandulaefolia Vahl. (Spanish sage) essential oil and individual monoterpenoid constituents have been shown to inhibit the enzyme acetylcholinesterase in-vitro and in-vivo. This activity is relevant to the treatment of Alzheimer's disease, since anticholinesterase drugs are currently the only drugs available to treat Alzheimer's disease. Other activities relevant to Alzheimer's disease include antioxidant, anti-inflammatory and estrogenic effects. Results of in-vitro tests for these activities are reported here for S. lavandulaefolia extracts, the essential oil and its major constituents. Antioxidant activity (inhibition of bovine brain liposome peroxidation) was found in the EtOH extract of the dried herb (5 mg mL(-1)) and the monoterpenoids (0.1 M) alpha- and beta-pinene and 1,8-cineole. Thujone and geraniol had lower antioxidant effects, while camphor had no antioxidant effects. Possible anti-inflammatory activity (eicosanoid inhibition in rat leucocytes) was found in the EtOH extract (50 microg mL(-1)) and was shown by the monoterpenoids alpha-pinene and geraniol (0.2 mM), but not 1,8-cineole, thujone or camphor. Possible estrogenic activity (via induction of beta-galactosidase activity in yeast cells) was found in the essential oil (0.01 mg mL(-1)) and the monoterpenoid geraniol (0.1-2 mM). 1,8-Cineole, alpha- and beta-pinene and thujone did not exhibit estrogenic activity in this analysis. These results demonstrate that S. lavandulaefolia, its essential oil and some chemical constituents have properties relevant to the treatment of Alzheimer's disease and provide further data supporting the value of carrying out clinical studies in patients with Alzheimer's disease using this plant species.

Increased lipid peroxidation precedes amyloid plaque formation in an animal model of Alzheimer amyloidosis

Oxidative stress is a key feature in the Alzheimer's disease (AD) brain and manifests as lipid peroxidation (LPO). Isoprostanes (iPs) are specific and sensitive markers of in vivo LPO. To determine whether amyloid beta (Abeta) deposition in vivo is associated with increased LPO, we examined iP levels in a transgenic mouse model (Tg2576) of AD amyloidosis. Urine, plasma, and brain tissues were collected from Tg2576 and littermate wild-type (WT) animals at different time points starting at 4 months of age and continuing until 18 months of age. Levels of urinary 8,12-iso-iPF(2alpha)-VI were higher in Tg2576 than in WT animals as early as 8 months of age and remained this high for the rest of the study. A similar pattern was observed for plasma levels of 8,12-iso-iPF(2alpha)-VI. Homogenates from the cerebral cortex and hippocampus of Tg2576 mice had higher levels of 8,12-iso-iPF(2alpha)-VI than those from WT mice starting at 8 months of age. In contrast, a surge of Abeta 1-40 and 1-42 levels as well as Abeta deposits in Tg2576 mouse brains occurred later, at 12 months of age. A direct correlation was observed between brain 8,12-iso-iPF(2alpha)-VI and Abeta 1-40 and 1-42. Because LPO precedes amyloid plaque formation in Tg2576 mice, this suggests that brain oxidative damage contributes to AD pathogenesis before Abeta accumulation in the AD brain.