Loss and Recovery of Glutaredoxin 5 Is Inducible by Diet in a Murine Model of Diabesity and Mediated by Free Fatty Acids In Vitro

Free fatty acids (FFA), hyperglycemia, and inflammatory cytokines are major mediators of β-cell toxicity in type 2 diabetes mellitus, impairing mitochondrial metabolism. Glutaredoxin 5 (Glrx5) is a mitochondrial protein involved in the assembly of iron–sulfur clusters required for complexes of the respiratory chain. We have provided evidence that islet cells are deprived of Glrx5, correlating with impaired insulin secretion during diabetes in genetically obese mice. In this study, we induced diabesity in C57BL/6J mice in vivo by feeding the mice a high-fat diet (HFD) and modelled the diabetic metabolism in MIN6 cells through exposure to FFA, glucose, or inflammatory cytokines in vitro. qRT-PCR, ELISA, immunohisto-/cytochemistry, bioluminescence, and respirometry were employed to study Glrx5, insulin secretion, and mitochondrial biomarkers. The HFD induced a depletion of islet Glrx5 concomitant with an obese phenotype, elevated FFA in serum and reactive oxygen species in islets, and impaired glucose tolerance. Exposure of MIN6 cells to FFA led to a loss of Glrx5 in vitro. The FFA-induced depletion of Glrx5 coincided with significantly altered mitochondrial biomarkers. In summary, we provide evidence that Glrx5 is regulated by FFA in type 2 diabetes mellitus and is linked to mitochondrial dysfunction and blunted insulin secretion.

Fucose as a Cleavage Product of 2'Fucosyllactose Does Not Cross the Blood-Brain Barrier in Mice

SCOPE

To further examine the role of the human milk oligosaccharide 2'fucosyllactose (2´FL) and fucose (Fuc) in cognition. Using ¹³ C-labeled 2'FL,thestudy previously showed in mice that ¹³ C-enrichment of the brain is not caused by ¹³ C₁ -2´FL itself, but rather by microbial metabolites. Here, the study applies ¹³ C₁ -Fuc in the same mouse model to investigate its uptake into the brain.

METHODS AND RESULTS

Mice received ¹³ C₁ -Fuc via oral gavage (2 mmol ¹³ C₁ -Fuc/kg^-1 body weight) or intravenously (0.4 mmol/kg^-1 body weight). ¹³ C-enrichment is measured in organs, including various brain regions, biological fluids and excrements. By EA-IRMS, the study observes an early rise of ¹³ C-enrichment in plasma, 30 min after oral dosing. However, ¹³ C-enrichment in the brain does not occur until 3-5 h post-dosing, when the ¹³ C-Fuc bolus has already reached the lower gut. Therefore, the researcher assume that ¹³ C-Fuc is absorbed in the upper small intestine but cannot cross the blood-brain barrier which is also observed after intravenous application of ¹³ C₁ -Fuc.

CONCLUSIONS

Late ¹³ C-enrichment in the rodent brain may be derived from ¹³ C₁ -Fuc metabolites derived from bacterial fermentation. The precise role that Fuc or 2´FL metabolites might play in gut-brain communication needs to be investigated in further studies.

Correlation of Early Nutritional Supply and Development of Bronchopulmonary Dysplasia in Preterm Infants <1,000 g

Background: Bronchopulmonary dysplasia (BPD) has multifactorial origins and is characterized by distorted physiological lung development. The impact of nutrition on the incidence of BPD is less studied so far. Methods: A retrospective single center analysis was performed on n = 207 preterm infants <1,000 g and <32 weeks of gestation without severe gastrointestinal complications to assess the impact of variations in nutritional supply during the first 2 weeks of life on the pulmonary outcome. Infants were grouped into no/mild and moderate/severe BPD to separate minor and major limitations in lung function. Results: After risk adjustment for gestational age, birth weight, sex, multiples, and antenatal steroids, a reduced total caloric intake and carbohydrate supply as the dominant energy source during the first 2 weeks of life prevailed statistically significant in infants developing moderate/severe BPD (p < 0.05). Enteral nutritional supply was increased at a slower rate with prolonged need for parenteral nutrition in the moderate/severe BPD group while breast milk provision and objective criteria of feeding intolerance were equally distributed in both groups. Conclusion: Early high caloric intake is correlated with a better pulmonary outcome in preterm infants <1,000 g. Our results are in line with the known strong impact of nutrient supply on somatic growth and psychomotor development. Our data encourage paying special attention to further decipher the ideal nutritional requirements for unrestricted lung development and promoting progressive enteral nutrition in the absence of objective criteria of feeding intolerance.

Metabolic Fate and Distribution of 2´-Fucosyllactose: Direct Influence on Gut Microbial Activity but not on Brain

SCOPE

2´-Fucosyllactose (2´FL) is an abundant oligosaccharide in human milk. It is hypothesized that its brain enrichment is associated with improved learning. Accumulation of 2´FL in organs, biological fluids, and feces is assessed in wild-type and germ-free mice.

METHODS AND RESULTS

13 C-labelled 2´FL is applied to NMRI wild-type mice intravenously (0.2 g kg-1 ) or orally (1 g kg-1 ), while controls receive saline. Biological samples are collected (0.5-15 h) and 13 C-enrichment is measured by elemental analysis isotope ratio mass spectrometry (EA-IRMS). After oral application, 2´FL is primarily eliminated in the feces. 13 C-enrichment in organs including the brain follows the same pattern as in plasma with a maximum peak after 5 h. However, 13 C-enrichment is only detected when the 13 C-2´FL bolus reaches the colon. In contrast, in germ-free mice, the 13 C-bolus remains in the intestinal content and is expelled via the feces. Furthermore, intravenously applied 13 C-2´FL is eliminated via urine; no 13 C-enrichment of organs is observed, suggesting that intact 2´FL is not retained.

CONCLUSIONS

13 C-enrichment in brain and other organs after oral application of 13 C-2´FL in wild-type mice indicates cleaved fucose or other gut microbial 2´FL metabolites may be incorporated, as opposed to intact 2´FL.

A diet rich in omega-3 fatty acids enhances expression of soluble epoxide hydrolase in murine brain

Several studies suggest that intake of omega-3 polyunsaturated fatty acids (n3-PUFA) beneficially influences cognitive function. However, effects on the adult brain are not clear. Little is known about the impact of dietary intervention on the fatty acid profile in adult brain, the modulation in the expression of enzymes involved in fatty acid biosynthesis and metabolism as well as changes in resulting oxylipins. These questions were addressed in the present study in two independent n3-PUFA feeding experiments in mice. Supplementation of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA, 1% each in the diet) for 30days to adult NMRI and C57BL/6 mice led to a distinct shift in the brain PUFA pattern. While n3-PUFAs EPA, n3 docosapentaenoic acid and DHA were elevated, many n6-PUFAs were significantly decreased (except, e.g. C20:3 n6 which was increased). This shift in PUFAs was accompanied by immense differences in concentrations of oxidative metabolites derived from enzymatic conversion of PUFAs, esp. arachidonic acid whose products were uniformly decreased, and a modulation in the activity and expression pattern of delta-5 and delta-6 desaturases. In both mouse strains a remarkable increase in the soluble epoxide hydrolase (sEH) activity (decreased epoxy-FA concentrations and epoxy-FA to dihydroxy-FA-ratios) as well as sEH expression was observed. Taking the high biological activity of epoxy-FA, e.g. on blood flow and nociceptive signaling into account, this finding might be of relevance for the effects of n3-PUFAs in neurodegenerative diseases. On any account, our study suggests a new distinct regulation of brain PUFA and oxylipin pattern by supplementation of n3-PUFAs to adult rodents.

¹H- and ¹³C-NMR spectroscopy of Thy-1-APPSL mice brain extracts indicates metabolic changes in Alzheimer's disease

Biochemical alterations underlying the symptoms and pathomechanisms of Alzheimer's disease (AD) are not fully understood. However, alterations of glucose metabolism and mitochondrial dysfunction certainly play an important role. (1)H- and (13)C-NMR spectroscopy exhibits promising results in providing information about those alterations in vivo in patients and animals, especially regarding the mitochondrial tricarboxylic acid (TCA) cycle. Accordingly, transgenic mice expressing mutant human amyloid precursor protein (APP(SL))-serving as a model of neuropathological changes in AD-were examined with in vitro 1D (1)H- and 2D (1)H-(13)C-HSQC-NMR spectroscopy after oral administration of 1-(13)C-glucose and acquisition of brain material after 30 min. Perchloric acid extracts were measured using a 500 MHz spectrometer, providing more detailed information compared to in vivo spectra achievable nowadays. Area under curve (AUC) data of metabolite peaks were obtained and normalized in relation to the creatine signal, serving as internal reference. Besides confirming well-known metabolic alterations in AD like decreased N-acetylaspartate (NAA)/Creatine (Cr) ratio, new findings such as a decrease in phosphorylcholine (PC) are presented. Glutamate (Glu) and glutamine (Gln) concentrations were decreased while γ-aminobutyric acid (GABA) was elevated in Thy1-APP(SL) mice. (13)C-NMR spectroscopy revealed a shift in the Glx-2/Glx-4-ratio-where Glx represents a combined Glu/Gln-signal-towards Glx-2 in AD. These findings correlated well with the NAA/Cr-ratio. The Gln-4/Glu-4-ratio is altered in favor of Glu. Our findings suggest that glutamine synthetase (GS), which is predominantly present in glial cells may be impaired in the brain of Thy1-APP(SL) transgenic mice. Since GS is an ATP-dependent enzyme, mitochondrial dysfunction might contribute to reduced activity, which might also account for the increased metabolism of glutamate via the GABA shunt, a metabolic pathway to bypass intra-mitochondrial α-ketoglutarate-dehydrogenase, resulting in elevated GABA levels.

Pharmacokinetic properties of MH84, a γ-secretase modulator with PPARγ agonistic activity

Alzheimer's disease (AD) is the most common cause of dementia. Since no causative treatment is available, new therapeutic options are utmost needed. Several pirinixic acid derivatives, including MH84 (2-((4,6-bis(4-(trifluoromethyl)phenethoxy)pyrimidin-2-yl)thio)hexanoic acid), have shown promising in vitro results as γ-secretase modulators as well as PPARγ activators as potential pharmacological compounds against AD. Using a newly developed and validated sensitive LC-MS (APCI-qTOF mass analyzer) method, the pharmacokinetic and long-term accumulating properties as well as the blood-brain-barrier permeability of MH84 were evaluated in a preclinical animal study. MH84 was administered to mice by oral gavage with a dose of 12 mg/kg. Nine time points from 0.5 to 48 h with 6 animals per point were investigated. Additionally 6 animals were fed daily, for 21 days with an identical dose to determine possible long-term accumulation in plasma and brain tissue. The sample preparation was performed by a liquid-liquid extraction on Extrelut(®) columns whereas the LC separation was operated on a MulthoHigh 100 RP 18-5 μ column (125 × 4 mm) using an isocratic mobile phase of formic acid (0.1% (v/v))-methanol mixture (11:89 (v/v)) at a flow rate of 1 ml/min. The validation confirmed the new LC-MS method to be precise, accurate and reliable. After oral application, Cmax and Tmax of unmetabolized MH84 was determined to be 10.90 μg/ml and 3h in plasma. In brain tissue a constant level of 300 to maximum 320.64 ng/g was found after 1.5-6h. Daily gavage for 21 days did not lead to a long-term drug accumulation in the brain. The efficacy of the obtained MH84 levels needs to be investigated in further preclinical pharmacodynamic animal studies.

Alterations of brain membranes in schizophrenia: impact of phospholipase A(2)

Physiological enzymatic cleavage of membrane phospholipids by phospholipase A2 (PLA2) results in normal levels of phosphomonoester and phosphodiester, by which a normal dopamine neurotransmission is maintained. Data from postmortem tissue and in vivo imaging studies suggest that increased activity of intracellular calcium-independent PLA2 (iPLA2) in the brain of schizophrenic patients might accelerate the breakdown of membrane phospholipids and alter the properties of neuronal membranes, which in turn contributes to a hypodopaminergy. Alterations in PLA2 activity are probably genetically determined and represent a possible pharmacological target for Schizophrenia.

Simvastatin alters membrane cholesterol distribution and beta-amyloid levels in brains of female APP751SL mice

Statins (HMG-CoA reductase or CSE-inhibitors) strongly reduce the cellular amyloid-beta protein production by modulating the processing of amyloid precursor protein (APP) in vitro. Several in vivo studies have addressed this important issue in transgenic mouse models with inconsistent results. Recently, we showed that simvastatin alters cholesterol distribution in synaptosomal membranes (SPM) in vivo. In the present study, we tested whether these changes in cholesterol membrane distribution affect APP-processing in vivo. Female APP751SL mice were force-fed with simvastatin (50 mg/kg b.wt.) by oral gavage over a time period of 3 weeks. Our data show that chronic simvastatin treatment decreased cholesterol levels in the brain and affected cholesterol distribution within SPM. Simvastatin significantly increased the levels of insoluble Abeta1-40 and Abeta1-42 but reduced levels of soluble Abeta1-40 in the brain. The reduction of soluble Abeta1-40 levels in the brain was associated with an increase of plasma-levels of AP31.40 in simvastatin-treated animals that may indicate enhanced Abeta1-40-clearance from the brain. Although the observed alteration in transbilayer cholesterol is likely to be involved in changes of APP processing by alpha-, beta- and gamma-secretase, we cannot exclude other potential mechanisms of statins such as lipid and non-lipid related, pleiotropic effects. Our data were evaluated in reference to published studies and a possible gender effect was identified.

Neuroprotection by bilobalide in ischemia: improvement of mitochondrial function

Bilobalide, an active constituent of Ginkgo biloba, is known to have neuroprotective properties, but its mode of action remains unclear. In this study, bilobalide significantly reduced brain damage in mice (indicated by TTC staining) when given before transient middle cerebral artery occlusion (tMCAO). As measured by microdialysis in the ischemic striatum, local perfusion with bilobalide (10 microM) reduced ischemia-induced glutamate release by 70% while glucose levels were not affected. Mitochondria isolated from ischemic brain showed a decrease of respiration compared to non-ischemic controls. Treatment with bilobalide (10 mg/kg) before tMCAO improved respiratory capacity of complex I significantly when measured ex vivo. In addition, mitochondrial swelling induced ex vivo by calcium was used to estimate opening of the mitochondrial permeability transition pore. In this assay, the changes induced by tMCAO were completely reversed when mice had received pretreatment with bilobalide. We conclude that neuroprotection by bilobalide involves a mechanism in which the drug reverses ischemia-induced changes in mitochondria, leading to a reduction of glutamate release.

Isoquercitrin provides better bioavailability than quercetin: comparison of quercetin metabolites in body tissue and brain sections after six days administration of isoquercitrin and quercetin

In the present study, over a period of 8 days 12 mg/kg/d quercetin aglycone and 18 mg/kg/d isoquercitrin were orally given to rats, respectively. Four hours after administration, plasma samples were taken as well as tissue samples of liver, lung, heart, kidney and the brain sections hippocampus, cerebellum, striatum, cortex and the remaining brain. A HPLC-FD method with in-line post-column complexation was employed to quantify the quercetin metabolites (QM) in plasma and tissues. Compared to the quercetin gavage the isoquercitrin gavage consistently produced higher levels of QM in tissues (double to five-fold) as well as in plasma (double to three-fold). In body tissues, the highest amounts of QM were observed in the lung. In brain tissue, the highest levels of QM were found in the cerebellum, while the striatum contained the lowest levels of QM. In conclusion, this study clearly demonstrates that orally given isoquercitrin leads to higher levels in plasma and in all investigated tissue than quercetin aglycone.

Increased brain membrane fluidity in schizophrenia

Recent findings showing significant correlations between phospholipase A2 (PLA2) activity and structural changes in schizophrenic brains contribute to the membrane hypothesis of schizophrenia, which was hampered because a clean functional link between elevated PLA2 activity and brain structure was missing (Neuroimage, 2010; 52: 1314-1327). We measured membrane fluidity parameters and found that brain membranes isolated from the prefrontal cortex of schizophrenic patients showed significantly increased flexibility of fatty acid chains. Our findings support a possible link between elevated PLA2 activity in cortical areas of schizophrenic patients and subsequent alterations of the biophysical parameters of neuronal membranes leading to structural changes in these areas.

Lipid membranes and beta-amyloid: a harmful connection

Gradual changes in steady-state levels of beta amyloid peptides (Abeta) in the brain are considered as initial step in the amyloid cascade hypothesis of Alzheimer's disease (AD). Abeta is a product of the secretase cleavage of the amyloid precursor protein and there is evidence that the membrane lipid environment may modulate secretase activity and alters its function. Abeta disturbs membrane properties of artificial and isolated biological membranes and of plasma membranes in living cells. Abeta induced changes in membrane fluidity could be explained by physico-chemical interactions of the peptide with membrane components such as cholesterol, phospholipids and gangliosides. Thus, cell membranes may be the location where the neurotoxic cascade of Abeta is initiated. Perturbation of membranes, binding to lipids and alteration of cellular calcium signaling by Abeta have been reported by several studies and these topics are examined in this review.

Traditional used Plants against Cognitive Decline and Alzheimer Disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized clinically by progressive memory deficits, impaired cognitive function, and altered and inappropriate behavior. Aging represents the most important risk factor for AD and the global trend in the phenomenon of population aging has dramatic consequences for public health, healthcare financing, and delivery systems in the word and, especially in developing countries. Mounting evidence obtained in in vitro and in vivo studies, suggests that various traditionally used plants in Asia, India, and Europe significantly affect key metabolic alterations culminating in AD-typical neurodegeneration. The present article aims to bring the reader up-to-date on the most recent studies and advances describing the direct and indirect activities of traditional used plants and its constituents possibly relieving features of AD. A variety of traditional used plants and its extracts exerted activities on AD related drug targets including AChE activity, antioxidative activity, modulation of Aβ-producing secretase activities, Aβ-degradation, heavy metal chelating, induction of neurotrophic factors, and cell death mechanisms. Although pre-clinical investigations identified promising drug candidates for AD, clinical evidences are still pending.

Mitochondrial dysfunction: common final pathway in brain aging and Alzheimer's disease--therapeutic aspects

As a fully differentiated organ, our brain is very sensitive to cumulative oxidative damage of proteins, lipids, and DNA occurring during normal aging because of its high energy metabolism and the relative low activity of antioxidative defense mechanisms. As a major consequence, perturbations of energy metabolism including mitochondrial dysfunction, alterations of signaling mechanisms and of gene expression culminate in functional deficits. With the increasing average life span of humans, age-related cognitive disorders such as Alzheimer's disease (AD) are a major health concern in our society. Age-related mitochondrial dysfunction underlies most neurodegenerative diseases, where it is potentiated by disease-specific factors. AD is characterized by two major histopathological hallmarks, initially intracellular and with the progression of the disease extracellular accumulation of oligomeric and fibrillar beta-amyloid peptides and intracellular neurofibrillary tangles composed of hyperphosphorylated tau protein. In this review, we focus on findings in AD animal and cell models indicating that these histopathological alterations induce functional deficits of the respiratory chain complexes and therefore consecutively result in mitochondrial dysfunction and oxidative stress. These parameters lead synergistically with the alterations of the brain aging process to typical signs of neurodegeneration in the later state of the disease, including synaptic dysfunction, loss of synapses and neurites, and finally neuronal loss. We suggest that mitochondrial protection and subsequent reduction of oxidative stress are important targets for prevention and long-term treatment of early stages of AD.

Plant foods and brain aging: a critical appraisal

In the 21st century, human aging will be one of the biggest challenges for most societies throughout the world. The decline in human fitness is a typical hallmark of the aging process. Aside from the cardiovascular system, the brain most often suffers significantly from the life-long impact of stressors, such as reactive oxygen and nitrogen species. Oxytosis, i.e. oxidative stress-induced cell death, has been identified to play a major role in the development and onset of chronic diseases. Foods, especially of plant origin, are rich in antioxidants and numerous in vivo data suggest that a diet rich in fruits and vegetables supports the maintenance of animal and human health. These beneficial effects also extend to the central nervous system, which, due to the presence of the blood-brain barrier, tightly controls the influx of metabolites and nutrients. In earlier studies the impact of antioxidant vitamins, such as alpha-tocopherol and ascorbic acid, on brain health has been of interest. Recently, the focus moved to assessing the potential of unsaturated fatty acids and secondary plant metabolites, particularly of polyphenols, to act as neuroprotectants. Considerable experimental evidence suggests that polyphenols and other plant-derived bioactivities affect animal and human brain function not only by directly lowering oxidative stress load but also by modulating various signal transduction pathways.

Flavonoids and the aging brain

Like in all other organs, the functional capacity of the human brain deteriorates over time. Pathological events such as oxidative stress, due to the elevated release of free radicals and reactive oxygen or nitrogen species, the subsequently enhanced oxidative modification of lipids, protein, and nucleic acids, and the modulation of apoptotic signaling pathways contribute to loss of brain function. The identification of neuroprotective food components is one strategy to facilitate healthy brain aging. Flavonoids were shown to activate key enzymes in mitochondrial respiration and to protect neuronal cells by acting as antioxidants, thus breaking the vicious cycle of oxidative stress and tissue damage. Furthermore, recent data indicate a favorable effect of flavonoids on neuro-inflammatory events. Whereas most of these effects have been shown in vitro, limited data in vivo are available, suggesting a rather low penetration of flavonoids into the brain. Nevertheless, several reports support the concept that flavonoid intake inhibits certain biochemical processes of brain aging, and might thus prevent to some extent the decline of cognitive functions with aging as well as the development or the course of neurodegenerative diseases. However, more data are needed to assess the true impact of flavonoids on brain aging.

Antioxidant properties of Mediterranean food plant extracts: geographical differences

Locally grown, wild food plants seasonally contribute a considerable portion of the daily diet in certain Mediterranean areas and it has been suggested that the beneficial effects of the Mediterranean diet on human health partly originate from the antioxidant effect of flavonoid-rich food plants. The nutrient content of most wild plants is higher than that of cultivated ones and may vary depending on the prevailing environmental conditions. Accordingly, three local Mediterranean plant foods (i.e. Cichorium intybus, Sonchus oleraceus, Papaver rhoeas) were collected in Greece (Crete), southern Italy, and southern Spain in order to assess possible differences in their in vitro antioxidant potential. The biological assays revealed diverse intra-plant specific antioxidant effects for the tested extracts ranging from no activity to almost complete protection. Furthermore, substantial differences in the polyphenol content were found for the nutritionally used part of the same plant originating from different locations. However, no clear correlations between the polyphenol content and the extracts' antioxidant activities were found. Taken together, the data suggest that certain local Mediterranean plant foods possess promising antioxidant activity and that the observed biological effects are possibly influenced by the geographically-dependent environmental conditions prevailing during plant growth.

Statins: drugs for Alzheimer’s disease?

Evidences from cell culture experiments and animal studies suggest a strong link between cholesterol and Alzheimer's disease (AD). This relationship is supported by retrospective epidemiological studies demonstrating that statin treatment reduced the prevalence of AD in patients suffering from hypercholesterolaemia. The alternative processing of the amyloid-precursor protein (APP) in the brain of AD patients leads to the production of the neurotoxic amyloid-beta protein (Abeta), a causative factor for AD pathology. In vitro, this mechanism is modulated by alterations in cellular cholesterol levels. Moreover, lowering cholesterol in animal experiments reduced the production of Abeta in most but not all studies. These findings led to prospective clinical trials of cholesterol-lowering statins in AD patients, even if many studies do not support elevated cholesterol levels in serum and brain as a risk factor for Alzheimer's disease. Most of these studies were negative. Thus, up to date there is insufficient evidence to suggest the use of statins for treatment in patients with AD.

Murine synaptosomal lipid raft protein and lipid composition are altered by expression of human apoE 3 and 4 and by increasing age

Apolipoprotein E (apoE) 4 and aging are risk factors for Alzheimer's disease (AD). Mice expressing human apoE4 and aged wild-type mice show a similarity in the transbilayer distribution of cholesterol in synaptic plasma membranes (SPMs) but differ markedly compared with apoE3 mice and young mice. The largest changes in cholesterol distribution were observed in the SPM exofacial leaflet where there was a doubling of cholesterol. Lipid rafts are thought to be associated with the exofacial leaflet, and we proposed that lipid raft protein and lipid composition would be associated with apoE genotype and age. Lipid rafts were isolated from synaptosomes of different age groups (2, 12, 24 months) of mice expressing human apoE3 and apoE4. Lipid raft markers, alkaline phosphatase (ALP), flotillin-1, cholesterol and sphingomyelin (SM) were examined. Lipid rafts of young apoE4 mice were more similar to older mice as compared with young apoE3 mice in reductions in alkaline phosphatase activity and flotillin-1 abundance. Lipid raft cholesterol and sphingomyelin levels were not significantly different between the young apoE3 and apoE4 mice but cholesterol levels of lipid rafts did increase with age in both genotypes. Results of the present study demonstrate that the two risk factors for Alzheimer's disease, apoE4 genotype and increasing age have similar effects on brain lipid raft protein markers and these findings support the notion that the transbilayer distribution of cholesterol is associated with lipid raft function.

Brain Cholesterol, Statins and Alzheimer’s Disease

Growing evidence suggests that cellular cholesterol homeostasis is causally involved in different steps leading to pathological events in the brain of Alzheimer's Disease (AD) patients. It was previously demonstrated that the processing of the amyloid beta-peptide precursor protein (APP) is modulated by pronounced alterations in cellular cholesterol levels using statins or cholesterol extracting agents. However, a cholesterol-rich diet was found to enhance amyloid beta-peptide (Abeta) burden in the brain of transgenic mice without clearly affecting total brain cholesterol levels. Recent retrospective epidemiological studies have reported that the use of statins potentially suppresses the development of AD. Although some HMG-CoA reductase inhibitors seem to influence the central cholesterol pool in vivo, the above epidemiological findings are probably not linked to statin-induced changes in brain membrane cholesterol levels per se since not all statins active in preventing AD enter the central nervous system (CNS). Recently, we reported that different statins, regardless of their brain availability, induce alterations in cellular cholesterol distribution in the brain. Such pleiotropic, cholesterol-synthesis independent statin effects might be indirect and are possibly mediated at the blood-brain barrier (BBB) via nitric oxide (NO) or apolipoprotein E (ApoE).

Brain-membrane cholesterol in Alzheimer's disease

Cholesterol represents an important determinant of the physical state of biological membranes. Growing evidence indicate that changes in brain cholesterol and variations in neuronal membrane structure are involved in the development of Alzheimer's disease (AD). Cholesterol modulates the cleavage of the amyloid precursor protein and thus affect cellular production of beta-amyloid peptides (Ab). On the other hand, cholesterol seems to be protective against the neurotoxic and membrane disordering properties of Ab. Present review summarizes reports focusing on brain membrane changes in AD and the effects of Ab on these structures. Since it has been shown that these Ab effects are cholesterol dependent, recent findings are presented indicating that the modulation of membrane cholesterol refers to different cholesterol pools within the membranes. Further, consequences thereof for possible pharmacological strategies are discussed.

Effects of aging and beta-amyloid on the properties of brain synaptic and mitochondrial membranes

The effects of aging and of different amyloid beta-peptides (A beta) on the properties of purified synaptosomal plasma and mitochondrial membranes were studied using different fluorescent dyes. Aging led to opposite membrane alterations in both mouse brain fractions. Cholesterol levels were significantly enhanced in synaptosomal plasma membranes (SPM) from aged mice only. Flexibility of membrane fatty acids was decreased in synaptosomal plasma and mitochondrial membranes, mobility of pyrene was enhanced, but in SPM only. With regard to acyl chain flexibility in aged brain membranes, both membrane preparations were less sensitive to A beta. By contrast, effects of A beta on the mobility of pyrene were not reduced for aged synaptic membranes, but even seemed to be enhanced in the case of aged mitochondrial membranes. The data presented significantly enhance our understanding of the mechanism of the A beta's disordering effects on synaptosomal membranes that are also detectable for mitochondrial membranes and show for the first time that A beta effects are modified by brain aging. This is of special interest since membrane alterations and in particular modifications of membrane cholesterol were recently linked to Alzheimer's Disease.

Membrane-disordering effects of beta-amyloid peptides

beta-Amyloid (Abeta) protein is the major constituent of senile plaques and cerebrovascular deposits characteristic of Alzheimer's disease (AD). The causal relationship between Abeta and AD-specific lesions like neurodegeneration and atrophy is still not known. The present article summarizes our studies indicating that rather low concentrations of Abeta significantly alter the fluidity of cell membranes and subcellular fractions from different tissues and different species including humans, as a possible initial step of its biological effects. Using different fluorescent probes our data show clearly that Abeta peptides specifically disturb the acyl-chain layer of cell membranes in a very distinct fashion. By contrast, membrane properties at the level of the polar heads of the phospholipid bilayer at the interface with membrane proteins are much less affected.

Effects of hyperforin on the fluidity of brain membranes

Hyperforin, an acylphloroglucinol derivative isolated from Hypericum perforatum (St. John's wort, SJW), affects several ionic conductance mechanisms in brain cells by an as yet unknown mechanism. We tested the effects of hyperforin on the fluidity of crude brain membranes from young guinea pigs. We performed fluidity measurements with three different fluorescent probes. Diphenylhexatriene (DPH) and trimethylammonium-diphenylhexatriene (TMA-DPH) anisotropy measurements were inversely correlated with the flexibility of fatty acids in the membrane hydrocarbon core and in the hydrophilic area of membrane phospholipids, respectively. The ratio of pyrene excimer to monomer fluorescence intensities was used as an indicator of membrane annular and bulk fluidity. Incubation of brain membranes with relatively high concentrations of hyperforin sodium salt (10 micromol/l) resulted in increased DPH and decreased TMA-DPH anisotropy, respectively, indicating that hyperforin modifies specific membrane structures in different ways. It decreases the flexibility of fatty acids in the membrane hydrocarbon core, but fluidizes the hydrophilic region of membrane phospholipids. Interestingly, relatively low concentrations of hyperforin (0.3 micromol/l) significantly decreased the annular fluidity of lipids close to membrane proteins. These findings are remarkable, as inhibition of several neurotransmitter-uptake systems and modulation of several ionic conductance mechanisms by hyperforin occur in the same concentration range. However, bulk fluidity was unchanged by this low hyperforin concentration. The results emphasise a physicochemical interaction of hyperforin with specific membrane structures that probably contribute to its novel pharmacological properties.

Differential effects of lovastatin treatment on brain cholesterol levels in normal and apoE-deficient mice

Growing evidence indicates that membrane cholesterol is involved in the development of Alzheimer's disease. Therefore, the availability of pharmacological strategies to modify brain cholesterol is of increasing importance. Accordingly, we investigated the effects of the HMG-CoA reductase inhibitor lovastatin on brain cholesterol levels in vivo. Brain cholesterol was significantly decreased by lovastatin treatment (100 mg/kg/day) in 1- and 12-month-old C57BL/6J mice. Reduced brain cholesterol was associated with decreased pyrene-excimer fluorescence, indicating altered membrane function. Lovastatin had no effect on brain cholesterol ApoE-/- mice. Peripheral cholesterol levels were not affected by lovastatin in all three groups of mice. We demonstrate for the first time that lovastatin represents a valid pharmacological tool to significantly modulate brain cholesterol levels.

Piracetam reverses hippocampal membrane alterations in Alzheimer's disease

The in vitro effects of piracetam treatment on the fluidity of membranes from the hippocampus of Alzheimer's Disease patients (AD) and non-demented controls were studied. Hippocampal membranes of AD patients showed a significant lower hydrocarbon core fluidity compared with membranes from elderly non-demented controls. Preincubation with piracetam enhanced the hydrocarbon core fluidity of hippocampal membranes from AD-patients as well as elderly controls in a concentration depending fashion, although the effect was more pronounced for the AD membranes. In the presence of piracetam, the difference of the membrane fluidity between AD and control membranes was not longer apparent.

Cholesterol modulates the membrane-disordering effects of beta-amyloid peptides in the hippocampus: specific changes in Alzheimer's disease

Cholesterol represents an important determinant of the physical state of biological membranes. In Alzheimer's disease (AD) brains, specific changes in the distribution of cholesterol and its membrane-ordering effects take place. In the present study, membrane fluidity was investigated at the level of the hydrocarbon core and of the heads of the phospholipid bilayers using two different fluorescent probes. Hippocampal membranes of AD brains showed a reduced fluidity in the hydrocarbon core region only. Fluidity was correlated with the cholesterol content in AD and control membranes. Aggregated beta-amyloid peptides (Abeta) disrupted brain membrane structure in AD patients and controls in the same fashion. However, this effect was correlated with the cholesterol content in AD membranes only. It is suggested that in AD the brain becomes specifically sensitive for the modulation by membrane-bound cholesterol of the membrane-disturbing and ultimately neurotoxic properties of Abeta.

Piracetam: novelty in a unique mode of action

Extensive research of the recent years has demonstrated that piracetam is effective in the treatment of cognitive decline in aging and dementia. It is usually much more active in situations of impaired brain function. Accordingly, its mechanism of action has been associated with neurochemical deficits of the aged brain relevant to cognitive dysfunctions. Since many of these neurochemical deficits depend on changes of membrane properties, including fluidity, it is of special importance that piracetam not only modifies membrane properties by interacting with the polar head moieties of the phospholipid bilayer, but also that this effect is more pronounced in membranes of aged as opposed to young animal and human brains, and that this mechanism also has specific relevance for brain membranes of Alzheimer's disease patients. Altering membrane properties might also be involved in vascular effects of piracetam such as improved erythrocyte deformability and normalization of hyperactive platelet aggregation. This novel mechanism of piracetam thus combines a rather non-specific physico-chemical mode of action with the pharmacological and clinical experience with this unique drug - effects are always much more pronounced when function is impaired.

Effects of beta-amyloid peptides on the fluidity of membranes from frontal and parietal lobes of human brain. High potencies of A beta 1-42 and A beta 1-43

beta-amyloid peptide (A beta) and several A beta-fragments decrease the fluidity of human cortex membranes in a concentration dependent fashion. The effect of A beta on membrane fluidity increases with peptide length, is most pronounced for A beta 1-43 and can be seen at concentrations as low as 100 nmol/l. While the fragment A beta 25-35 is active, scrambled peptide (A beta 35-25) when investigated under similar conditions shows no effects on membrane fluidity. The effect of A beta peptides on fluidity of the phospholipid bilayer is more pronounced in the hydrocarbon core (labeled with the fluorescence probe 1,6-diphenylhexa-1,3,5-triene) than in the region of the hydrophilic heads (labeled with the fluorescence probe 1-[4'-(trimethylamino)phenyl]-6-phenylhexa-1,3,5-triene). It is suggested that the effect of A beta on neuronal membranes is probably a major initial mechanism in a cascade of events finally leading to neurotoxicity and cell death in Alzheimer's disease.