X-ray diffraction evidence for myelin disorder in brain from humans with alzheimer's disease

Wide-angle X-ray diffraction studies revealed that the lipid phase transition temperature of myelin from brain tissue of humans with Alzheimer's disease was about 12°C lower than that of normal age-matched controls, indicating differences in the physical organization of the myelin lipid bilayer. Elevated levels of malondialdehyde and conjugated diene were found in brain tissue from humans with Alzheimer's disease, indicating an increased amount of lipid peroxidation over the controls. An increase in myelin disorder and in lipid peroxidation can both be correlated with aging in human brain, but the changes in myelin from humans with Alzheimer's disease are more pronounced than in normal aging. These changes might represent severe or accelerated aging.     

Vitamin E concentrations in human brain of patients with Alzheimer's disease,fetuses with Down's syndrome,centenarians, and controls

The concentration of vitamin E (alpha-tocopherol) was measured in samples of cortex from patients with Alzheimer's disease (AD), fetuses with Down's syndrome (DS), and also in a group of centenarians. The mean tocopherol concentrations in the two patient groups did not differ significantly from appropriate controls. When expressed per lipid the mean tocopherol concentration of the centenarians was greater than that of the controls but this reflected a significant decrease in the lipid concentration of the former group. These results indicate that neither the normal aging processes, Alzheimer's disease, nor the increased in vitro lipid peroxidation reported in fetuses with Down's syndrome result from a gross lack of alpha-tocopherol, or cause a significant depletion of the vitamin.     

The effects of aerobic exercise training on the age-related lipid peroxidation, Schwann cell apoptosis and ultrastructural changes in the sciatic nerve of rats

The potential role of exercise in preventing the age-related spontaneous peripheral neuropathy has not been studied. We examined the effects of long-term aerobic exercise training on lipid peroxidation, Schwann cell (SC) apoptosis and ultrastructural changes in the sciatic nerve of rats during aging. Three groups of 12-week old Wistar rats ran on a treadmill for 6, 9 and 12 months (exercise trained (ET) group, n=10 each) according to an exercise training program targeted at a speed of 22 m/min (at 7 degrees incline), 60 min/day, 6 days/week. Three corresponding groups of untrained rats were used as the controls (sedentary (SED) group). At the end of each period, sciatic nerve biopsies were performed, and processed for biochemical, immunohistochemical and ultrastructural analyses. The results showed that aging was associated with an increased level of nerve malondialdehyde (MDA, marker of lipid peroxidation) and a higher number of SC apoptosis in SED group. The SED group showed irregular nerve fibers with thin myelin sheaths and areas of myelin-axon detachment. However, the ET group had significantly diminished nerve lipid peroxidation and SC apoptosis. In the ET group, nerve fibers had a thick myelin sheath with frequent folding. These findings suggest that aerobic exercise training protects peripheral nerves by attenuating oxidative reactions, and preserving SCs and myelin sheath from pathologic changes, which occur during normal aging.     

Disorder in human myelin induced by superoxide radical: an in vitro investigation

Potassium superoxide (KO.2), applied as a source of superoxide radical directly in vitro to white matter from young adult human brain, caused the lipid phase of the myelin to change from a crystalline (ordered) state to a liquid crystalline (disordered) state. The myelin transition temperature decreased from 65 degrees C to 37 degrees C. This alteration was accompanied by a dramatic increase in the levels of lipid peroxidation products--malondialdehyde, a conjugated diene, and ethane. These changes in human myelin, induced by direct application of O2-. radical, simulated myelin deterioration that occurs in the course of natural aging, thus, providing further substantiation for the notion that O2-. might be a major toxic agent associated with the aging process.     

Lipid peroxidation in neurodegeneration: new insights into Alzheimer's disease

Imbalances of oxidative homeostasis and lipid peroxidation have been revealed as important factors involved in neurodegenerative disorders such as Alzheimer's disease. The brains of patients with Alzheimer's disease contain increased levels of lipid-peroxidation products such as 4-hydroxy-2-nonenal or acrolein, and enhanced lipid peroxidation can also be detected in cerebrospinal fluid and plasma from such patients. Recent research revealed that the interplay of transition metals, amyloid-beta peptide and lipid peroxidation might be responsible for increased oxidative stress and cell damage in this disease. In particular, the contrasting roles of amyloid-beta peptide, as a possible transition metal-chelating antioxidant for lipoproteins and a pro-oxidant when aggregated in brain tissue, has been the focus of discussion recently. In this context, lipid peroxidation has to be seen as an important part of the pathophysiological cascade in Alzheimer's disease, and its measurement in body fluids might serve as a therapy control for Alzheimer's disease and other neurodegenerative diseases.     

Lipid peroxidation in aging brain and Alzheimer's disease

Lipid peroxidation is one of the major outcomes of free radical-mediated injury that directly damages membranes and generates a number of secondary products, both from fission and endocyclization of oxygenated fatty acids that possess neurotoxic activity. Numerous studies have demonstrated increased lipid peroxidation in brain of patients with Alzheimer's disease (AD) compared with age-matched controls. These data include quantification of fission and endocyclized products such as 4-hydroxy-2-nonenal, acrolein, isoprostanes, and neuroprostanes. Immunohistochemical and biochemical studies have localized the majority of lipid peroxidation products to neurons. A few studies have consistently demonstrated increased cerebrospinal fluid (CSF) levels of isoprostanes in AD patients early in the course of their dementia, and one study has suggested that CSF isoprostanes may improve the laboratory diagnostic accuracy for AD. Similar analyses of control individuals over a wide range of ages indicate that brain lipid peroxidation is not a significant feature of usual aging. Quantification of isoprostanes in plasma and urine of AD patients has yielded inconsistent results. These results indicate that brain lipid peroxidation is a potential therapeutic target in probable AD patients, and that CSF isoprostanes may aid in the assessment of antioxidant experimental therapeutics and the laboratory diagnosis of AD.     

Oxidative damage in cultured human olfactory neurons from Alzheimer's disease patients

Oxidative abnormalities precede clinical and pathological manifestations of Alzheimer's disease and are the earliest pathological changes reported in the disease. The olfactory pathways and mucosa also display the pathological features associated with Alzheimer's disease in the brain. Olfactory neurons are unique because they can undergo neurogenesis and are able to be readily maintained in cell culture. In this study, we examined neuronal cell cultures derived from olfactory mucosa of Alzheimer's disease and control patients for oxidative stress responses. Levels of lipid peroxidation (hydroxynonenal), N(epsilon)-(carboxymethyl)lysine (glycoxidative and lipid peroxidation), and oxidative stress response (heme oxygenase-1) were measured immunocytochemically. We found increased levels for all the oxidative stress markers examined in Alzheimer's disease neurons as compared to controls. Interestingly, in one case of Alzheimer's disease, we found hydroxynonenal adducts accumulated in cytoplasmic lysosome-like structures in about 20% of neurons cultured, but not in neurons from control patients. These lysosome-like structures are found in about 100% of the vulnerable neurons in brains of cases of Alzheimer's disease. This study suggests that manifestations of oxidative imbalance in Alzheimer's disease extend to cultured olfactory neurons. Primary culture of human olfactory neurons will be useful in understanding the mechanism of oxidative damage in Alzheimer's disease and can even be utilized in developing therapeutic strategies.     

Age-related changes in antioxidant enzymes and lipid peroxidation in brains of control and transgenic mice overexpressing copper-zinc superoxide dismutase.

The aim of our study was first to obtain a comprehensive profile of the brain antioxidant defense potential and peroxidative damage during aging. We investigated copper-zinc superoxide dismutase (CuZnSOD), manganese superoxide dismutase (MnSOD), seleno-dependent glutathione peroxidase (GSH-PX), glutathione reductase (GSSG-R) activities, endogenous and in vitro stimulated lipid peroxidation in 40 brains of control mice divided into 3 age groups: 2 months (young), 12 months (middle-aged) and 28 months (old). We found a positive correlation between age and activities of CuZnSOD (r = 0.47; P < 0.01) and GSH-PX (r = 0.72; P < 0.0001). CuZnSOD and GSH-PX activities are independently regulated during brain aging since temporal changes of these two enzymes do not correlate. No modification in MnSOD activity and basal lipid peroxidation was observed as a function of age. Nevertheless, stimulated lipid peroxidation was significantly higher at 12 months (6.53 +/- 0.71 mumole MDA/g tissue) than at 2 months (5.69 +/- 0.90) and significantly lower at 28 months (5.13 +/- 0.33) than at 12 months. Second, we used genetic manipulations to construct transgenic mice that specifically overexpress CuZnSOD to understand the role of CuZnSOD in neuronal aging. The human CuZnSOD transgene expression was stable during aging. The increased CuZnSOD activity in the brain (1.9-fold) of transgenic mice resulted in an enhanced rate of basal lipid peroxidation and in increased MnSOD activity in the 3 age groups. Other antioxidant enzymes did not exhibit modifications indicating the independence of the regulation between CuZnSOD and glutathione-related enzymes probably due to their different cellular localization in the brain.     

Autopsy Samples of Alzheimer''s Cortex Show Increased Peroxidation In Vitro

The formation of thiobarbituric acid-reactive products was measured as an index of peroxidation by oxygen free radicals in homogenates of frontal cortex and cerebellum from brains taken at autopsy and verified histologically as being Alzheimer's (n = 6) or normal (n = 6). Compared with controls, basal peroxidation is significantly higher in Alzheimer's cortex, and this difference is also evident in the presence of exogenous iron. Peroxidation in cerebellum and levels of total glutathione, RNA, and DNA in cortex and cerebellum do not differ significantly between Alzheimer's brain and controls. Iron-induced peroxidation in cortex is reduced by the lazaroid U-74500A, with calculated IC50 values that are significantly higher in Alzheimer's samples (10 microM) than in controls (2.5 microM). These observations suggest that cerebral cortex from Alzheimer's patients differs from controls with respect to in vitro peroxidation.     

Myelin Membranes Isolated from Rats Intracranially Injected with apoTransferrin Are More Susceptible to in Vitro Peroxidation

Purified myelin obtained from 17 day old rats intracranially injected with aTf at 3 days of age was submitted to in vitro peroxidation using Fe + ascorbic acid (FeA) or Cu + H₂O₂ (CuH), to investigate the susceptibility of this membrane to in vitro metal catalyzed peroxidation. There was an increase in thiobarbituric acid-reactive-substances (TBARS) (60%) and in protein-associated carbonyls (PAC) (20%) in the myelin from aTf injected rats in comparison to myelin from controls, indicating a higher susceptibility to peroxidation. Desferoxamine (DFX) injected simultaneously with aTf did not change the response of myelin to aTf. CNS myelin is highly vulnerable to oxidative stress, and its susceptibility to peroxidation increases in myelin isolated from aTf injected rats. This increased liability to peroxidation as well as the previously reported aTf-dependent increment in certain myelin proteins and lipids and in the expression of specific myelin mRNAS, does not appear to be due to an increased amount of iron bound to the injected aTf. The changes in composition that we have previously reported could result in an abnormal myelin, allowing the peroxidative system to act upon the membrane more easily than in normal circumstances.     

Ubiquinone, dolichol, and cholesterol metabolism in aging and Alzheimer's disease.

The lipid compositions of various regions of the human brain were investigated during aging and in Alzheimer's disease. The phospholipid amounts and compositions remained unchanged during aging. There were, however, considerable differences both in phospholipid composition and amount when the various regions were compared. The level of dolichol increased severalfold in all regions up to the age of 70, but there was no further elevation thereafter. The ubiquinone level decreased significantly in all parts of the brain upon aging. In Alzheimer's disease, the dolichol level was decreased in all regions, and particularly, in those affected by the disease. In contrast, the dolichyl-P concentration increased in those regions that exhibited morphological changes. There was no modification in cholesterol distribution, but a significant elevation in ubiquinone content was observed in most regions. The only phospholipid whose level was elevated was phosphatidylinositol, and only in those parts of the brain that were affected. The content of polyunsaturated fatty acids in phosphatidylethanolamine was greatly decreased in connection with the disease, with a parallel increase in the saturated portion. The results indicate that Alzheimer's disease results in specific and significant changes in the levels of lipid products of the mevalonate pathway in the brain.     

Evidence of an oxidative challenge in the Alzheimer's brain

Alzheimer's disease may arise from or produce oxidative damage in the brain. To assess the responses of the Alzheimer's brain to possible oxidative challenges, we assayed for glutathione, glucose-6-phosphate dehydrogenase, catalase and superoxide dismutase in twelve regions of Alzheimer's disease and aged control brains. In addition, we determined levels of malondialdehyde to evaluate lipid peroxidation in these brain regions. Most brain regions showed evidence of a response to an oxidative challenge, but the cellular response to this challenge differed among brain regions. These data suggest that the entire Alzheimer's brain may be subject to an oxidative challenge, but that some brain areas may be more vulnerable than others to the consequent neural damage that characterizes the disease.     

Lipid Composition in Different Regions of the Brain in Alzheimer''s Disease/Senile Dementia of Alzheimer''s Type

The lipid compositions of 10 different brain regions from patients affected by Alzheimer's disease/senile dementia of Alzheimer's type were analyzed. The total phospholipid amount decreased somewhat in nucleus caudatus and in white matter. The cortical areas that are morphologically affected by Alzheimer's disease, i.e., frontal and temporal cortex and the hippocampus, showed elevated contents of lipid solvent-extractable phosphatidylinositol. Sphingomyelin content was decreased in regions rich in myelin. There was a 20-50% decrease in dolichol amount in all investigated parts of the brain, but no change was seen in the polyisoprenoid pattern. Levels of alpha-unsaturated polyprenes were decreased in Alzheimer brains. Dolichyl-phosphate content increased in most regions, up to 100%. In both control and Alzheimer tissue almost all of the dolichyl-phosphate was covalently bound, apparently through glycosylation. Cholesterol amounts were highly variable but mostly unchanged, whereas ubiquinone concentrations increased by 30-100% in most regions in brains affected by Alzheimer's disease. These results demonstrate that both phospholipids and neutral lipids are modified in brains affected by Alzheimer's disease/senile dementia of Alzheimer's type.     

Oxidative damage in brain from human mutant APP/PS-1 double knock-in mice as a function of age

Oxidative stress is strongly implicated in the progressive decline of cognition associated with aging and neurodegenerative disorders. In the brain, free radical-mediated oxidative stress plays a critical role in the age-related decline of cellular function as a result of the oxidation of proteins, lipids, and nucleic acids. A number of studies indicate that an increase in protein oxidation and lipid peroxidation is associated with age-related neurodegenerative diseases and cellular dysfunction observed in aging brains. Oxidative stress is one of the important factors contributing to Alzheimer's disease (AD), one of whose major hallmarks includes brain depositions of amyloid beta-peptide (Abeta) derived from amyloid precursor protein (APP). Mutation in APP and PS-1 genes, which increases production of the highly amyloidogenic amyloid beta-peptide (Abeta42), is the major cause of familial AD. In the present study, protein oxidation and lipid peroxidation in the brain from knock-in mice expressing human mutant APP and PS-1 were compared with brain from wild type, as a function of age. The results suggest that there is an increased oxidative stress in the brain of wild-type mice as a function of age. In APP/PS-1 mouse brain, there is a basal increase (at 1 month) in oxidative stress compared to the wild type (1 month), as measured by protein oxidation and lipid peroxidation. In addition, age-related elevation of oxidative damage was observed in APP/PS-1 mice brain compared to that of wild-type mice brain. These results are discussed with reference to the importance of Abeta42-associated oxidative stress in the pathogenesis of AD.     

F4 - Isoprostanes as Specific Marker of Docosahexaenoic Acid Peroxidation in Alzheimer's Disease

Abstract : F₂-isoprostanes are prostaglandin-like compounds derived from free radical-catalysed peroxidation of arachidonic acid. Peroxidation of eicosapentaenoic acid produces F₃-isoprostanes, whereas peroxidation of docosahexaenoic acid would give F₄-isoprostanes. This study demonstrates the presence of esterified F₄-isoprostanes in human brain and shows that levels are elevated in certain brain cortex regions in Alzheimer's disease. Our data with Alzheimer's disease suggest that analysis of F₄-isoprostanes will provide new opportunities to study lipid peroxidation in the neurodegenerative diseases.     

In vitro and in vivo studies investigating possible antioxidant actions of nicotine: relevance to Parkinson's and Alzheimer's diseases.

An inverse relationship appears to exist between cigarette smoking and the risk of Parkinson's and Alzheimer's diseases. Since both diseases are characterized by enhanced oxidative stress, we investigated the antioxidant potential of nicotine, a primary component of cigarette smoke. Initial chromatographic studies suggest that nicotine can affect the formation of the neurotoxin 6-hydroxydopamine resulting from the addition of dopamine to Fenton's reagent (i.e., Fe2+ and H2O2). Thus, under certain circumstances, nicotine can strongly affect the course of the Fenton reaction. In in vivo studies, adult male rats being treated with nicotine showed greater memory retention than controls in a water maze task. However, neurochemical analysis of neocortex, hippocampus, and neostriatum from these same animals revealed that nicotine treatment had no effect on the formation of reactive oxygen species or on lipid peroxidation for any brain region studied. In an in vitro study, addition of various concentrations of nicotine to rat neocortical homogenates had no effect on lipid peroxidation compared to saline controls. The results of these studies suggest that the beneficial/protective effects of nicotine in both Parkinson's disease and Alzheimer's disease may be, at least partly, due to antioxidant mechanisms.     

No evidence for increased oxidative damage to lipids, proteins, or DNA in Huntington's disease

It has been proposed that mitochondrial dysfunction and excitotoxic mechanisms lead to oxidative damage in the brain of Huntington;s disease patients. We sought evidence that increased oxidative damage occurs by examining postmortem brain material from patients who had died with clinically and pathologically diagnosed Huntington's disease. Oxidative damage was measured using methods that have already demonstrated the presence of increased oxidative damage in Parkinson's disease, Alzheimer's disease, and senile dementia of the Lewy body type. No alterations in the levels of lipid peroxidation (as measured by lipid peroxides and thiobarbituric acid-malondialdehyde adducts) were found in the caudate nucleus, putamen, or frontal cortex of patients with Huntington's disease compared with normal controls. Similarly, there were no elevations in the levels of 8-hydroxyguanine or of a wide range of other markers of oxidative DNA damage. Levels of protein carbonyls in these tissues were also unaltered. Our data suggest that oxidative stress is not a major component of the degenerative processes occurring in Huntington's disease, or at least not to the extent that occurs in other neurodegenerative disorders.     

End products of lipid peroxidation in erythrocyte membranes in Alzheimer's disease

Alzheimer's disease (AD) is accompanied by oxidative stress in the brain. Because the brain tissue is rich in polyunsaturated fatty acids, it is prone to the free radical attack resulting in lipid peroxidation. Intermediates of lipid peroxidation may diffuse from the primary site, cross the blood-brain barrier and modify erythrocyte membranes in the bloodstream. We exposed isolated erythrocyte membranes from patients with AD and the control group to in vitro free radical damage and monitored the accumulation of the end products of lipid peroxidation, lipofuscin-like pigments (LFPs), by fluorescence spectroscopy. LFPs were analyzed by means of tridimensional and synchronous fluorescence spectroscopy. The levels of LFP formed during in vitro peroxidation were significantly higher in erythrocyte membranes from patients with AD compared with the control group. Furthermore, the chemical composition of LFP in AD was different from the control group. The analysis of the specific modifications of erythrocyte membranes in AD is of great medical importance regarding the need of a diagnostic blood biomarker.     

Metabolic Processes in Alzheimer''s Disease: Adenine Nucleotide Content and Production of 14CO2 from [U-14C]Glucose In Vitro in Human Neocortex

Samples of neocortex removed at diagnostic craniotomy from patients with Alzheimer's disease and incubated in vitro showed an increased production of 14CO2 from [U-14C]glucose compared with neurosurgical controls. This was a feature of incubations in the presence of both 5 mM K+ (142% control) and 31 mM K+ (126%). Specific labelling of the amino acid pool was unaltered, suggesting that the apparent increase of CO2 production was not merely a reflection of changes in dilution of the radiolabel from glucose. The content of adenine nucleotides was significantly less than control values in the tissue from patients with Alzheimer's disease after in vitro incubations but the adenylate energy charge was unchanged, indicating that normal energy metabolism was not grossly impaired in these preparations.