Daniela Rossin

Relation between TLR4/NF-κB signaling pathway activation by 27-hydroxycholesterol and 4-hydroxynonenal, and atherosclerotic plaque instability.

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.

HNE and cholesterol oxidation products in colorectal inflammation and carcinogenesis

Abstract Consistent experimental data suggest the importance of inflammation‐associated oxidative stress in colorectal cancer (CRC) pathogenesis. Inflammatory bowel disease with chronic intestinal inflammation is now considered a precancerous condition. Oxidative stress is an essential feature of inflammation. Activation of redox‐sensitive pro‐inflammatory cell signals and inflammatory mediators concur to establish a pro‐tumoral environment. In this frame, lipid oxidation products, namely 4‐hydroxynonenal and oxysterols, can be produced in big quantity so as to be able to exert their function as inducers of cell signaling pathways of proliferation and survival. Notably, an important source of these two compounds is represented by a high fat diet, which is undoubtedly a risk factor for inflammation and CRC development. Current evidence for the emerging implication of these two oxidized lipids in inflammation and CRC development is discussed in this review. Graphical abstract Figure. No Caption available. HighlightsInflammation is a major driving force in colorectal cancer (CRC) development.Oxysterols and HNE are overproduced by colitis‐associated oxidative reactions.They also originate from a high fat diet, which is a risk factor for inflammation/CRC.Accumulation of oxysterols and HNE in intestinal mucosa favor tumor growth.These oxidation compounds behave as signaling molecules in survival and proliferation.

Lipid oxidation products in the pathogenesis of inflammation-related gut diseases

BACKGROUND A defective mucosal barrier function is the principal cause of the uncontrolled onset and progression of a number of human inflammatory gut diseases, most of which are characterized by chronic intermittent immune and inflammatory responses leading to structural intestinal damage, which can represent a potential risk for colorectal cancer development. During the active disease phase the production of pro-inflammatory cytokines and chemokines, and the induction of oxidative reactions by activated leukocytes and epithelial cells represent the main event in the intestinal inflammation. OBJECTIVE Oxidative stress plays a key role in the development of intestinal damage. Indeed reactive oxygen species and their oxidized by-products regulate redox-sensitive signaling pathways and transcription factors, which sustain inflammation within the intestinal layer. METHODS Polyunsaturated fatty acids and cholesterol are the principal targets of oxidative modifications. These lipids, which are cell membrane constituents or are present in food, readily undergo non-enzymatic oxidation to form chemically-reactive species that can induce a wide range of biological effects including inflammation, programmed cell death, and proliferation. RESULTS AND CONCLUSIONS In this review we summarize the current knowledge on the role of lipid oxidation products in regulating redox pathways involved in the pathogenesis of inflammation- related gut diseases. In particular, lipid peroxidation end products, such as isoprostanes and aldehydes, and cholesterol oxidation-derived oxysterols are taken into consideration. The control of oxidative damage and consequently tissue local over-production of lipid oxidation products by using specific antioxidant and anti-inflammatory molecules in the diet may have clinical and therapeutic benefits.

Inhibition of herpes simplex-1 virus replication by 25-hydroxycholesterol and 27-hydroxycholesterol

Oxysterols are known pleiotropic molecules whose antiviral action has been recently discovered. Here reported is the activity of a panel of oxysterols against HSV-1 with the identification of a new mechanism of action. A marked antiviral activity not only of 25HC but also of 27HC against HSV-1 was observed either if the oxysterols were added before or after infection, suggesting an activity unrelated to the viral entry inhibition as proposed by previous literature. Therefore, the relation between the pro-inflammatory activity of oxysterols and the activation of NF-kB and IL-6 induced by HSV-1 in the host cell was investigated. Indeed, cell pre-incubation with oxysterols further potentiated IL-6 production as induced by HSV-1 infection with a consequent boost of the interleukins total cell secretion. Further, a direct antiviral effect of IL-6 administration to HSV-1 infected cells was demonstrated, disclosing an additional mechanism of antiviral action by both 25HC and 27HC.

Derangement of intestinal epithelial cell monolayer by dietary cholesterol oxidation products

Abstract The emerging role of the diet in the incidence of intestinal inflammatory diseases has stimulated research on the influence of eating habits with pro‐inflammatory properties in inducing epithelial barrier disturbance. Cholesterol oxidation products, namely oxysterols, have been shown to promote and sustain oxidative/inflammatory reactions in human digestive tract. This work investigated in an in vitro model the potential ability of a combination of dietary oxysterols representative of a hyper‐cholesterol diet to induce the loss of intestinal epithelial layer integrity. The components of the experimental mixture were the main oxysterols stemming from heat‐induced cholesterol auto‐oxidation, namely 7‐ketocholesterol, 5&agr;,6&agr;‐and 5&bgr;,6&bgr;‐epoxycholesterol, 7&agr;‐ and 7&bgr;‐hydroxycholesterol. These compounds added to monolayers of differentiated CaCo‐2 cells in combination or singularly, caused a time‐dependent induction of matrix metalloproteinases (MMP)‐2 and ‐9, also known as gelatinases. The hyperactivation of MMP‐2 and ‐9 was found to be associated with decreased levels of the tight junctions zonula occludens‐1 (ZO‐1), occludin and Junction Adhesion Molecule‐A (JAM‐A). Together with such a protein loss, particularly evident for ZO‐1, a net perturbation of spatial localization of the three tight junctions was observed. Cell monolayer pre‐treatment with the selective inhibitor of MMPs ARP100 or polyphenol (‐)‐epicathechin, previously shown to inhibit NADPH oxidase in the same model system, demonstrated that the decrease of the three tight junction proteins was mainly a consequence of MMPs induction, which was in turn dependent on the pro‐oxidant property of the oxysterols investigated. Although further investigation on oxysterols intestinal layer damage mechanism is to be carried on, the consequent ‐ but incomplete ‐ prevention of oxysterols‐dependent TJs alteration due to MMPs inhibition, avoided the loss of scaffold protein ZO‐1, with possible significant recovery of intestinal monolayer integrity. Graphical abstract No caption available. HighlightsOxysterols produced in cholesterol‐rich foods alter intestinal epithelial layer.Matrix metalloproteinases (MMPs)‐2 and ‐9 are activated by dietary oxysterols.Oxysterols affect MMP‐2 and ‐9 when used in combination as they are in food.Oxy‐mix disrupts intestinal tight junctions mainly through MMP‐2 and‐9 induction.These effects depend on the pro‐oxidant/inflammatory properties of dietary oxysterols.

Modulation of cell signaling pathways by oxysterols in age-related human diseases.

Cholesterol oxidation products, named oxysterols, may derive from the diet or originate endogenously by autoxidative nonenzymatic modification of cholesterol as well as through enxymatic pathways involved in lipid metabolism and maintenance of cholesterol homeostasis. Oxysterols have been shown to exert several in vitro and in vivo biochemical activities of both physiologic and pathologic relevance and they appear to be implicated in the pathogenesis of various age-related chronic diseases, including atherosclerosis and Alzheimers disease (AD), where hypercholesterolemia represents a primary risk factor, and a redox state impairment and inflammation seem to play a central role. Our recent studies show that, in cells of the macrophage lineage or in human neuronal cells (differentiated or not), respectively in the contest of atherosclerosis or AD, oxysterols can initiate specific signal transduction pathways that are relevant to the development of these diseases. Regarding atherosclerosis, we have observed that oxysterols can contribute to plaque instability and rupture by enhancing inflammatory responses and matrix turnover through an unbalanced up-regulation of MMP-9. Concerning AD, we have demonstrated that oxysterols may promote neuroinflammatory changes and accelerate APP processing toward β-amyloid production by up-regulating APP and BACE1 protein levels. In addition, TLR4, a key player of immune and inflammatory signaling responses, seems to have an important role in the pathogenesis of both atherosclerosis and AD.

Olive oil polyphenols reduce oxysterols -induced redox imbalance and pro-inflammatory response in intestinal cells

Dietary habits may strongly influence intestinal homeostasis. Oxysterols, the oxidized products of cholesterol present in cholesterol-containing foodstuffs, have been shown to exert pro-oxidant and pro-inflammatory effects, altering intestinal epithelial layer and thus contributing to the pathogenesis of human inflammatory bowel diseases and colon cancer. Extra virgin olive oil polyphenols possess antioxidant and anti-inflammatory properties, and concentrate in the intestinal lumen, where may help in preventing intestinal diseases. In the present study we evaluated the ability of an extra virgin olive oil phenolic extract to counteract the pro-oxidant and pro-inflammatory action of a representative mixture of dietary oxysterols in the human colon adenocarcinoma cell line (Caco-2) undergoing full differentiation into enterocyte-like cells. Oxysterols treatment significantly altered differentiated Caco-2 cells redox status, leading to oxidant species production and a decrease of GSH levels, after 1 h exposure, followed by an increase of cytokines production, IL-6 and IL-8, after 24 h. Oxysterol cell treatment also induced after 48 h an increase of NO release, due to the induction of iNOS. Pretreatment with the phenolic extract counteracted oxysterols effects, at least in part by modulating one of the main pathways activated in the cellular response to the action of oxysterols, the MAPK-NF-kB pathway. We demonstrated the ability of the phenolic extract to directly modulate p38 and JNK1/2 phosphorylation and activation of NF-kB, following its inhibitor IkB phosphorylation. The phenolic extract also inhibited iNOS induction, keeping NO concentration at the control level. Our results suggest a protective effect at intestinal level of extra virgin olive oil polyphenols, able to prevent or limit redox unbalance and the onset and progression of chronic intestinal inflammation.

Implication of oxysterols in chronic inflammatory human diseases

A growing bulk of evidence suggests that cholesterol oxidation products, known as oxysterols, are potentially involved in the pathogenesis of major chronic diseases, including atherosclerosis, Alzheimers disease, and inflammatory bowel disease. Oxysterols are involved in various key steps of these complex processes, mainly thanks to their ability to act through up-regulation of oxidative stress, inflammation, and cell toxicity. This review summarizes the current knowledge of the effects induced by these compounds on cells, after their accumulation in the arterial wall, brain, and intestine. This evidence might help to develop innovative strategies to counteract the progression of these chronic inflammatory human diseases.

Up-regulation of COX-2 and mPGES-1 by 27-hydroxycholesterol and 4-hydroxynonenal: A crucial role in atherosclerotic plaque instability

&NA; Atherosclerosis is currently understood to be mainly the consequence of a complicated inflammatory process at the different stages of plaque development. Among the several inflammatory molecules involved, up‐regulation of the functional cyclooxygenase 2/membrane‐bound prostaglandin E synthase 1 (COX‐2/mPGES‐1) axis plays a key role in plaque development. Excessive production of oxidized lipids, following low‐density lipoprotein (LDL) oxidation, is a characteristic feature of atherosclerosis. Among the oxidized lipids of LDLs, the oxysterol 27‐hydroxycholesterol (27‐OH) and the aldehyde 4‐hydroxynonenal (HNE) substantially accumulate in the atherosclerotic plaque, contributing to its progression and instability through a variety of processes. This study shows that 27‐OH and HNE promote up‐regulation of both the inducible enzymes COX‐2 and mPGES‐1, leading to increased production of prostaglandin (PG) E2 and inducible nitric oxide synthase, and the subsequent release of nitric oxide in human promonocytic U937 cells. The study also examined the potential involvement of the functionally coupled COX‐2/mPGES‐1 in enhancing the production of certain pro‐inflammatory cytokines and of matrix metalloproteinase 9 by U937 cells. This enhancement is presumably due to the induction of PGE2 synthesis, as a result of the up‐regulation of the COX‐2/mPGES‐1, stimulated by the two oxidized lipids, 27‐OH and HNE. Induction of PGE2 synthesis might thus be a mechanism of plaque instability and eventual rupture, contributing to matrix metalloproteinase production by activated macrophages. Graphical abstract Figure. No caption available. Highlights27‐OH and HNE stimulate inflammation by COX‐2/mPGES‐1 axis and PGE2 release.27‐OH and HNE induce NO production through iNOS up‐regulation.Inflammation promoted by 27‐OH and HNE may be involved in plaque instability.Inhibition of inflammation induced by 27‐OH and HNE reduces MMP‐9 up‐regulation.