Alzheimer's disease (AD) is a gradually debilitating disease that leads to dementia. The molecular mechanisms underlying AD are still not clear, and at present no reliable biomarkers are available for the early diagnosis. In the last several years, together with oxidative stress and neuroinflammation, altered cholesterol metabolism in the brain has become increasingly implicated in AD progression. A significant body of evidence indicates that oxidized cholesterol, in the form of oxysterols, is one of the main triggers of AD. The oxysterols potentially most closely involved in the pathogenesis of AD are 24-hydroxycholesterol and 27-hydroxycholesterol, respectively deriving from cholesterol oxidation by the enzymes CYP46A1 and CYP27A1. However, the possible involvement of oxysterols resulting from cholesterol autooxidation, including 7-ketocholesterol and 7β-hydroxycholesterol, is now emerging. In a systematic analysis of oxysterols in post-mortem human AD brains, classified by the Braak staging system of neurofibrillary pathology, alongside the two oxysterols of enzymatic origin, a variety of oxysterols deriving from cholesterol autoxidation were identified; these included 7-ketocholesterol, 7α-hydroxycholesterol, 4β-hydroxycholesterol, 5α,6α-epoxycholesterol, and 5β,6β-epoxycholesterol. Their levels were quantified and compared across the disease stages. Some inflammatory mediators, and the proteolytic enzyme matrix metalloprotease-9, were also found to be enhanced in the brains, depending on disease progression. This highlights the pathogenic association between the trends of inflammatory molecules and oxysterol levels during the evolution of AD. Conversely, sirtuin 1, an enzyme that regulates several pathways involved in the anti-inflammatory response, was reduced markedly with the progression of AD, supporting the hypothesis that the loss of sirtuin 1 might play a key role in AD. Taken together, these results strongly support the association between changes in oxysterol levels and AD progression.

Alzheimer’s disease (AD), the most common neurodegenerative disorder associated with dementia, is typified by the pathological accumulation of amyloid Aβ peptides and neurofibrillary tangles (NFT) within the brain. Considerable evidence indicates that many events contribute to AD progression, including oxidative stress, inflammation, and altered cholesterol metabolism. The brain’s high lipid content makes it particularly vulnerable to oxidative species, with the consequent enhancement of lipid peroxidation and cholesterol oxidation, and the subsequent formation of end products, mainly 4-hydroxynonenal and oxysterols, respectively from the two processes. The chronic inflammatory events observed in the AD brain include activation of microglia and astrocytes, together with enhancement of inflammatory molecule and free radical release. Along with glial cells, neurons themselves have been found to contribute to neuroinflammation in the AD brain, by serving as sources of inflammatory mediators. Oxidative stress is intimately associated with neuroinflammation, and a vicious circle has been found to connect oxidative stress and inflammation in AD. Alongside oxidative stress and inflammation, altered cholesterol metabolism and hypercholesterolemia also significantly contribute to neuronal damage and to progression of AD. Increasing evidence is now consolidating the hypothesis that oxidized cholesterol is the driving force behind the development of AD, and that oxysterols are the link connecting the disease to altered cholesterol metabolism in the brain and hypercholesterolemia; this is because of the ability of oxysterols, unlike cholesterol, to cross the blood brain barrier (BBB). The key role of oxysterols in AD pathogenesis has been strongly supported by research pointing to their involvement in modulating neuroinflammation, Aβ accumulation, and cell death. This review highlights the key role played by cholesterol and oxysterols in the brain in AD pathogenesis.

To date more than 4000 compounds are recognized to belong to the class of flavonoids. These natural phenolic drugs are poorly soluble in water and are rapidly degraded and metabolized in the human body, but nevertheless are very promising for their potential contribution to the prevention and therapy of major chronic diseases, including cardiovascular and neurodegenerative diseases and cancer. In recent years a number of flavanols (e.g. catechins), flavonols (e.g. quercetin, myricetin) and isoflavones (e.g. genistein, daidzein) have been confirmed to possess strong antioxidant, anti-inflammatory, anti-proliferative and anti-aging activities. Incorporation into lipidic or polymer-based nanoparticles appears to markedly help the oral delivery of flavonoids, as these particles can protect the drug from degradation in the gastrointestinal tract and, by virtue of their unique absorption mechanism through the lymphatic system, also from first-pass metabolism in the liver. In addition, both oral and parenteral administration of flavonoids exploits a pharmacologic delivery route that guarantees sustained release of the active principle at the desired site of action. A comprehensive review of studies currently available on the in vitro and in vivo experimental administration of flavonoids by means of nanovectors may be of use as a foundation for the development of advanced delivery systems for these powerful compounds, in view of their adoption in primary and secondary disease prevention.

SummaryAll three cholesterol oxidation products implicated thus far in the pathogenesis of Alzheimer's disease, 7b-hydroxycholesterol, 24-hydroxycholesterol, and 27-hydroxycholesterol, markedly enhance the binding of amyloidbeta (Ab) to human differentiated neuronal cell lines (SK-N-BE and NT-2) by up-regulating net expression and synthesis of CD36 and b1-integrin receptors. However, only 24-hydroxycholesterol markedly potentiates the proapoptotic and pro-necrogenic effects of Ab 1-42 peptide on these cells: 7b-hydroxycholesterol and 27-hydroxycholesterol, like unoxidized cholesterol, show no potentiating effect. This peculiar behavior of 24-hydroxycholesterol at physiologic concentrations (1 lM) depends on its strong enhancement of the intracellular generation of NADPH oxidase-dependent reactive oxygen species (ROS), mainly H 2 O 2 , and the consequent impairment of neuronal cell redox equilibrium, measured in terms of the GSSG ⁄ GSH ratio. Cell incubation with antioxidants quercetin or genistein prevents 24-hydroxycholesterol's pro-oxidant effect and potentiation of Ab-induced necrosis and apoptosis. Thus, the presence of 24-hydroxycholesterol in the close vicinity of amyloid plaques appears to enhance the adhesion of large amounts of Ab to the plasma membrane of neurons and then to amplify the neurotoxic action of Ab by locally increasing ROS steady-state levels. This report further supports a primary involvement of altered brain cholesterol metabolism in the complex pathogenesis of Alzheimer's disease.

Oxysterols are a family of 27-carbon cholesterol oxidation derivatives that may be absorbed with the diet or originated endogenously. These cholesterol metabolites are now considered to be potentially involved in the initiation and progression of major chronic diseases including atherosclerosis, neurodegenerative processes, diabetes, kidney failure, and ethanol intoxication. Thus we deemed it of interest to comprehensively analyze the actual relevance of oxysterols, acting through up-regulation of inflammation, apoptosis and fibrosis, to human pathology from cell signaling to disease expression; we also review the available literature on related therapeutic prospects. Oxysterols of pathophysiologic relevance generally possess a strong pro-oxidant effect, chiefly since they activate NAD(P)H oxidases. Further, stimulation of the MEK/ERK signaling pathway appears to be a common feature of the biochemical effects of this class of compounds. Selective metabolic inhibitors of NAD(P)H oxidase and the MAPK pathway might quench or even prevent the cytotoxic effects of pathological accumulation of cholesterol oxides in cells and tissues. The marked reduction of plasma oxysterols reported for statin-based therapy is interesting: it has been associated with a lower incidence and prevalence of Alzheimer's disease (AD) and vascular dementia. Quenching reactive oxygen species' generation seems the likely mechanism exploited by statins against AD incidence and development; intervention with antioxidants might thus also be re-considered as regards molecular "integrated" prevention and possible therapy of human "multifactorial" disease processes.

Alzheimer's disease (AD), a neurodegenerative disorder, is the most common form of dementia in developed countries. It is a complex and genetically heterogeneous disease, characterized by progressive memory deficit, cognitive impairment and personality changes, accompanied by specific structural abnormalities in the brain. The main histological features of AD are extracellular deposits of amyloid-β (A ) in the form of senile plaques, A deposits in the cerebral blood vessels, and intracellular inclusions of hyperphosphorylated tau in the form of neurofibrillary tangles (NFT).The loss of neurons and synapses in the neocortex, hippocampus and other subcortical regions of the brain is also a common feature of AD. 1,2 AD begins with the abnormal processing of amyloid precursor protein (APP) by the sequential enzymatic actions of two enzymes of the amyloidogenic pathway: beta-site amyloid precursor protein-cleaving enzyme 1 (BACE1), a -secretase, and -secretase; these actions lead to excess of production and/or reduced clearance of A peptides, which comprise 39-43 amino acids.An imbalance between production and clearance of A in the brain, and their aggregation, causes A to accumulate, and this excess may be the initiating factor in AD. Monomers of A 40 are usually much more prevalent than the aggregation-prone and damaging A 42 species, but an increased proportion of A 42 appears sufficient to cause early onset of AD. Additionally, insoluble oligomers and intermediate amyloids are the most neurotoxic forms of A 42 . 3Several mechanisms (e.g. perturbation of brain metabolism, oxidative stress, inflammation, presence of the apolipoprotein E (ApoE) 4 allele, impaired cholesterol metabolism) contribute to the development and progression of AD. Among these, a growing body of epidemiological and molecular evidence suggests a mechanistic link between cholesterol and AD progression. A number of genes involved in cholesterol homeostasis have been identified as susceptibility loci for sporadic or late-onset AD, 4-6 and altered cholesterol metabolism seems to play a fundamental role in the formation of amyloid plaques and in tau hyperphosphorylation. 7,8 In addition, hypercholesterolemia is unanimously recognized to be a risk factor for sporadic AD, a form that accounts for the great majority of cases. 4,[9][10][11] Finally, this evidence is supported by epidemiological studies indicating that cholesterol-lowering agents belonging to the family of statins reduce the prevalence of AD, 12-14 aconclusion not yet fully accepted because of the contradictory results reported by prospective clinical studies. 15-17Apolipoprotein E and its receptors in AD Role of cholesterol in ADThe brain is the organ with the highest concentration of cholesterol, which is essential for its normal function, being a major component of neuronal cell membranes and a determinant of membrane fluidity. 29 In the brain, cholesterol is mostly present in the free form and is derived from de novo biosynthesis from acetyl-coenzyme A mediated by 3-hydroxy-3-meth...

It is now thought that atherosclerosis, although due to increased plasma lipids, is mainly the consequence of a complicated inflammatory process, with immune responses at the different stages of plaque development. Increasing evidence points to a significant role of Toll-like receptor 4 (TLR4), a key player in innate immunity, in the pathogenesis of atherosclerosis. This study aimed to determine the effects on TLR4 activation of two reactive oxidized lipids carried by oxidized low-density lipoproteins, the oxysterol 27-hydroxycholesterol (27-OH) and the aldehyde 4-hydroxynonenal (HNE), both of which accumulate in atherosclerotic plaques and play a key role in the pathogenesis of atherosclerosis. Secondarily, it examined their potential involvement in mediating inflammation and extracellular matrix degradation, the hallmarks of high-risk atherosclerotic unstable plaques. In human promonocytic U937 cells, both 27-OH and HNE were found to enhance cell release of IL-8, IL-1β, and TNF-α and to upregulate matrix metalloproteinase-9 (MMP-9) via TLR4/NF-κB-dependent pathway; these actions may sustain the inflammatory response and matrix degradation that lead to atherosclerotic plaque instability and to their rupture. Using specific antibodies, it was also demonstrated that these inflammatory cytokines increase MMP-9 upregulation, thus enhancing the release of this matrix-degrading enzyme by macrophage cells and contributing to plaque instability. These innovative results suggest that, by accumulating in atherosclerotic plaques, the two oxidized lipids may contribute to plaque instability and rupture. They appear to do so by sustaining the release of inflammatory molecules and MMP-9 by inflammatory and immune cells, for example, macrophages, through activation of TLR4 and its NF-κB downstream signaling.

The ageing endothelium progressively loses its remarkable and crucial ability to maintain homeostasis of the vasculature, as it acquires a proinflammatory phenotype. Cellular and structural changes gradually accumulate in the blood vessels, and markedly in artery walls. Most changes in aged arteries are comparable to those occurring during the atherogenic process, the latter being more marked: pro-oxidant and proinflammatory molecules, mainly deriving from or triggered by oxidized low density lipoproteins (oxLDLs), are undoubtedly a major driving force of this process. Oxysterols, quantitatively relevant components of oxLDLs, are likely candidate molecules in the pathogenesis of vascular ageing, because of their marked pro-oxidant, proinflammatory and proapoptotic properties. An increasing bulk of experimental Giuseppe Poli is Professor of General Pathology and Pathophysiology at the School of Medicine, University of Torino. For more than 40 years he has been involved in elucidating the role of lipid peroxidation, and then the roles of a variety of lipid oxidation products, in the pathogenesis of major chronic diseases. More recently, he focused his research interest on the pathophysiology of cholesterol oxidation products. Simona Gargiulo is a molecular biologist with expertise in the role of oxidized lipids in the pathogenesis of age-related diseases such as atherosclerosis. In particular, she has been studying the involvement of compounds derived from cholesterol oxidation in inflammation and oxidative stress processes. She is a postdoctoral fellow at the University of Torino, School of Medicine. data point to the contribution of a variety of oxysterols of pathophysiological interest, also in the age-related genesis of endothelium dysfunction, intimal thickening due to lipid accumulation, and smooth muscle cell migration and arterial stiffness due to increasing collagen deposition and calcification. This review provides an updated analysis of the molecular mechanisms whereby oxysterols accumulating in the wall of ageing blood vessels may 'activate' endothelial and monocytic cells, through expression of an inflammatory phenotype, and 'convince' smooth muscle cells to proliferate, migrate and, above all, to act as fibroblast-like cells. Abstract figure legend Oxysterol-driven anticipation and/or amplification of the main features of ageing blood vessels. Abbreviations