The impairment of endothelium-dependent arterial relaxation by 7-ketocholesterol is associated with an early activation of protein kinase C

The current findings on the gut-liver axis and the molecular basis of NAFLD/NASH associated with gut microbiome dysbiosis

Recent research has highlighted the complex relationship between gut microbiota, metabolic pathways, and nonalcoholic fatty liver disease (NAFLD) progression. Gut dysbiosis, commonly observed in NAFLD patients, impairs intestinal permeability, leading to the translocation of bacterial products like lipopolysaccharides, short-chain fatty acids, and ethanol to the liver. These microbiome-associated mechanisms contribute to intestinal and hepatic inflammation, potentially advancing NAFLD to NASH. Dietary habits, particularly those rich in saturated fats and fructose, can modify the microbiome composition, leading to dysbiosis and fatty liver development. Metabolomic approaches have identified unique profiles in NASH patients, with specific metabolites like ethanol linked to disease progression. While bariatric surgery has shown promise in preventing NAFLD progression, the role of gut microbiome and metabolites in this improvement remains to be proven. Understanding these microbiome-related pathways may provide new diagnostic and therapeutic targets for NAFLD and NASH. A comprehensive review of current literature was conducted using multiple medical research databases, including PubMed, Scopus, Web of Science, Embase, Cochrane Library, ClinicalTrials.gov, ScienceDirect, Medline, ProQuest, and Google Scholar. The review focused on studies that examine the relationship between gut microbiota composition, metabolic pathways, and NAFLD progression. Key areas of interest included microbial dysbiosis, endotoxin production, and the influence of diet on gut microbiota. The analysis revealed that gut dysbiosis contributes to NAFLD through several mechanisms, diet significantly influences gut microbiota composition, which in turn affects liver function through the gut-liver axis. High-fat diets can lead to dysbiosis, altering microbial metabolic activities and promoting liver inflammation. Specifically, gut microbiota-mediated generation of saturated fatty acids, such as palmitic acid, can activate liver macrophages and increase TNF-α expression, contributing to NASH development. Different dietary components, including cholesterol, fiber, fat, and carbohydrates, can modulate the gut microbiome and influence NAFLD progression. This gut-liver axis plays a crucial role in maintaining immune homeostasis, with the liver responding to gut-derived bacteria by activating innate and adaptive immune responses. Microbial metabolites, such as bile acids, tryptophan catabolites, and branched-chain amino acids, regulate adipose tissue and intestinal homeostasis, contributing to NASH pathogenesis. Additionally, the microbiome of NASH patients shows an elevated capacity for alcohol production, suggesting similarities between alcoholic steatohepatitis and NASH. These findings indicate that targeting the gut microbiota may be a promising approach for NASH treatment and prevention. Recent research highlights the potential of targeting gut microbiota for managing nonalcoholic fatty liver disease (NAFLD). The gut-liver axis plays a crucial role in NAFLD pathophysiology, with dysbiosis contributing to disease progression. Various therapeutic approaches aimed at modulating gut microbiota have shown promise, including probiotics, prebiotics, synbiotics, fecal microbiota transplantation, and dietary interventions. Probiotics have demonstrated efficacy in human randomized controlled trials, while other interventions require further investigation in clinical settings. These microbiota-targeted therapies may improve NAFLD outcomes through multiple mechanisms, such as reducing inflammation and enhancing metabolic function. Although lifestyle modifications remain the primary recommendation for NAFLD management, microbiota-focused interventions offer a promising alternative for patients struggling to achieve weight loss targets.

Oxysterols in Central and Peripheral Synaptic Communication

Cholesterol is a key molecule for synaptic transmission, and both central and peripheral synapses are cholesterol rich. During intense neuronal activity, a substantial portion of synaptic cholesterol can be oxidized by either enzymatic or non-enzymatic pathways to form oxysterols, which in turn modulate the activities of neurotransmitter receptors (e.g., NMDA and adrenergic receptors), signaling molecules (nitric oxide synthases, protein kinase C, liver X receptors), and synaptic vesicle cycling involved in neurotransmitters release. 24-Hydroxycholesterol, produced by neurons in the brain, could directly affect neighboring synapses and change neurotransmission. 27-Hydroxycholesterol, which can cross the blood-brain barrier, can alter both synaptogenesis and synaptic plasticity. Increased generation of 25-hydroxycholesterol by activated microglia and macrophages could link inflammatory processes to learning and neuronal regulation. Amyloids and oxidative stress can lead to an increase in the levels of ring-oxidized sterols and some of these oxysterols (4-cholesten-3-one, 5α-cholestan-3-one, 7β-hydroxycholesterol, 7-ketocholesterol) have a high potency to disturb or modulate neurotransmission at both the presynaptic and postsynaptic levels. Overall, oxysterols could be used as "molecular prototypes" for therapeutic approaches. Analogs of 24-hydroxycholesterol (SGE-301, SGE-550, SAGE718) can be used for correction of NMDA receptor hypofunction-related states, whereas inhibitors of cholesterol 24-hydroxylase, cholestane-3β,5α,6β-triol, and cholest-4-en-3-one oxime (olesoxime) can be utilized as potential anti-epileptic drugs and (or) protectors from excitotoxicity.

Cholesterol Oxidation Products: Potential Adverse Effect and Prevention of Their Production in Foods

Cholesterol oxidation products (COPs) are a group of substances formed during food processing. COPs in diet is a health concern because they may affect human health in association with the risk of various diseases including atherosclerosis, Alzheimer's disease, age-related macular degeneration, diabetes, and chronic gastrointestinal inflammatory colitis. Production of COPs in foods can be affected by many factors such as temperature, pH, light, oxygen, water, carbohydrates, fatty acids, proteins, and metal cations. The key issue is preventing its generation in foods. Some COPs can also be produced in vivo by both nonenzymatic and enzymatic-catalyzed oxidation reactions. Currently, a number of natural antioxidants such as catechins, flavonoids, and other polyphenols have been proven to inhibit the generation of COPs. In addition, measures taken during food processing can also minimize the production of COPs, such as the Maillard reaction and marinating food with plant polyphenol-rich seasonings. In conclusion, a comprehensive approach encompassing the suppression on COPs generation and implementation of processing measures is imperative to safeguard human health against the production of COPs in the food chain.

Effect of Ergothioneine on 7-Ketocholesterol-Induced Endothelial Injury

Ergothioneine (ET) is a naturally occurring antioxidant that is synthesized by non-yeast fungi and certain bacteria. ET is not synthesized by animals, including humans, but is avidly taken up from the diet, especially from mushrooms. In the current study, we elucidated the effect of ET on the hCMEC/D3 human brain endothelial cell line. Endothelial cells are exposed to high levels of the cholesterol oxidation product, 7-ketocholesterol (7KC), in patients with cardiovascular disease and diabetes, and this process is thought to mediate pathological inflammation. 7KC induces a dose-dependent loss of cell viability and an increase in apoptosis and necrosis in the endothelial cells. A relocalization of the tight junction proteins, zonula occludens-1 (ZO-1) and claudin-5, towards the nucleus of the cells was also observed. These effects were significantly attenuated by ET. In addition, 7KC induces marked increases in the mRNA expression of pro-inflammatory cytokines, IL-1β IL-6, IL-8, TNF-α and cyclooxygenase-2 (COX2), as well as COX2 enzymatic activity, and these were significantly reduced by ET. Moreover, the cytoprotective and anti-inflammatory effects of ET were significantly reduced by co-incubation with an inhibitor of the ET transporter, OCTN1 (VHCL). This shows that ET needs to enter the endothelial cells to have a protective effect and is unlikely to act via extracellular neutralizing of 7KC. The protective effect on inflammation in brain endothelial cells suggests that ET might be useful as a nutraceutical for the prevention or management of neurovascular diseases, such as stroke and vascular dementia. Moreover, the ability of ET to cross the blood-brain barrier could point to its usefulness in combatting 7KC that is produced in the CNS during neuroinflammation, e.g. after excitotoxicity, in chronic neurodegenerative diseases, and possibly COVID-19-related neurologic complications.

Human Herpesvirus 8 infection may contribute to oxidative stress in diabetes type 2 patients

OBJECTIVE

To investigate the link between Human Herpesvirus 8 (HHV8) infection and plasma oxidative stress in patients with diabetes mellitus type 2 (DM2).

RESULTS

Blood samples collected from DM2 and control subjects were screened for the presence of antibodies against HHV8 and for biomarkers of oxidative stress. We determined the products of radical damage on the plasma lipid fraction, such as malondialdehyde (MDA), fatty acid hydroperoxides (HP) and 7-ketocholesterol (7-keto), the oxidation products of unsaturated fatty acids (UFA) and cholesterol, respectively. The level of plasma antioxidant α-tocopherol (α-toc) was also assessed. Relevant differences were observed in the redox status in DM2 and either HHV8-positive or -negative control subjects. The level of α-toc significantly decreased in both DM2 and HHV8-positive subjects. Levels of MDA, HP and 7-keto were much higher in HHV8-positive and DM2 subjects, indicating that plasma oxidative stress is a common feature in both DM2 and HHV8-infection. In addition, 7-keto was further increased in HHV8-positive DM2 patients. We hypothesized that the HHV8-infection may contribute to the production of ROS, and hence to the oxidative stress closely related to the pathogenesis and development of DM2.

7-Ketocholesterol enhances leukocyte adhesion to endothelial cells via p38MAPK pathway

7-Ketocholesterol is a major dietary cholesterol oxidation product found in high concentrations in atherosclerotic plaques, which contribute to the development of atherosclerosis. This study aimed to investigate the effects of 7-ketocholesterol on endothelial inflammation, as well as the underlying mechanisms. Pretreatment of human umbilical vein endothelial cells (HUVEC) with 7-ketocholesterol significantly enhanced the total interactions between human monocytic cells (THP-1 cell line) and TNFα-activated HUVECs under physiological flow conditions, compared to pretreatment with cholesterol (TNFα+50 μM cholesterol: 13.1 ± 0.54 cells/CPF, TNFα+50 μM 7-ketocholesterol: 18.9 ± 0.35 cells/CPF, p < 0.01). 7-Ketocholesterol enhanced the expression of E-selectin, ICAM-1, and VCAM-1 proteins. It also activated p38 mitogen-activated protein kinase (MAPK), and treatment with a p38 MAPK inhibitor inhibited both E-selectin expression via ATF-2 activation and 7-ketocholesterol-induced THP-1 adhesion to HUVECs. These findings suggest that 7-ketocholesterol enhances leukocyte–endothelial interactions by upregulating the expression of adhesion molecules, presumably via the p38 MAPK-dependent pathway.

Dietary docosahexaenoic acid supplementation prevents the formation of cholesterol oxidation products in arteries from orchidectomized rats

Testosterone deficiency has been correlated with increased cardiovascular diseases, which in turn has been associated with increased oxidative stress. Several studies have considered cholesterol oxidation products (COPs) as oxidative stress biomarkers, since some of them play pro-oxidant and pro-inflammatory roles. We have previously described the cardioprotective effects of a dosahexaenoic acid (DHA) supplemented diet on the aortic and mesenteric artery function of orchidectomized rats. The aim of this study was to investigate whether impaired gonadal function alters the formation of COPs, as well as the potential preventive role of a DHA-supplemented diet on that effect. For this purpose, aortic and mesenteric artery segments obtained from control and orchidectomized rats, fed with a standard or supplemented with DHA, were used. The content of the following COPs: 7α-hydroxycholesterol, 7β-hydroxycholesterol, 7-ketocholesterol, 5,6α-epoxycholesterol, 5,6β-epoxycholesterol, cholestanetriol and 25-hydroxycholesterol, were analyzed by gas chromatography. The results showed that orchidectomy increased the formation of COPs in arteries from orchidectomized rats, which may participate in the orchidectomy-induced structural and functional vascular alterations already reported. The fact that the DHA-supplemented diet prevented the orchidectomy-induced COPs increase confirms the cardiovascular protective actions of DHA, which could be of special relevance in mesenteric arterial bed, since it importantly controls the systemic vascular resistance.

Endothelial cells, endoplasmic reticulum stress and oxysterols

Oxysterols are bioactive lipids that act as regulators of lipid metabolism, inflammation, cell viability and are involved in several diseases, including atherosclerosis. Mounting evidence linked the atherosclerosis to endothelium dysfunction; in fact, the endothelium regulates the vascular system with roles in processes such as hemostasis, cell cholesterol, hormone trafficking, signal transduction and inflammation. Several papers shed light the ability of oxysterols to induce apoptosis in different cell lines including endothelial cells. Apoptotic endothelial cell and endothelial denudation may constitute a critical step in the transition to plaque erosion and vessel thrombosis, so preventing the endothelial damaged has garnered considerable attention as a novel means of treating atherosclerosis. Endoplasmic reticulum (ER) is the site where the proteins are synthetized and folded and is necessary for most cellular activity; perturbations of ER homeostasis leads to a condition known as endoplasmic reticulum stress. This condition evokes the unfolded protein response (UPR) an adaptive pathway that aims to restore ER homeostasis. Mounting evidence suggests that chronic activation of UPR leads to cell dysfunction and death and recently has been implicated in pathogenesis of endothelial dysfunction. Autophagy is an essential catabolic mechanism that delivers misfolded proteins and damaged organelles to the lysosome for degradation, maintaining basal levels of autophagic activity it is critical for cell survival. Several evidence suggests that persistent ER stress often results in stimulation of autophagic activities, likely as a compensatory mechanism to relieve ER stress and consequently cell death. In this review, we summarize evidence for the effect of oxysterols on endothelial cells, especially focusing on oxysterols-mediated induction of endoplasmic reticulum stress.

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Endothelial cells dysfunction is critical in the process of atherothrombosis.

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Endoplasmic reticulum stress is a key component in endothelial cell dysfunction.

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Oxysterols are oxidation products of cholesterol found in atherosclerosis lesions.

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Oxysterols are potential modulators of endoplasmic reticulum stress.

7-Ketocholesterol and 5,6-secosterol induce human endothelial cell dysfunction by differential mechanisms

7-Ketocholesterol and 5,6-secosterol are cholesterol autoxidation products generated under oxidative stress by two distinct mechanisms. They are present in atherosclerotic plaques and are candidate players in the disease initiation and progression. While 7-ketocholesterol affects at cellular level, in particular apoptosis, are well known and reported on diverse cell lines, 5,6-secosterol is a recently discovered oxysterol with relatively few reports on the potential to affect endothelial cell functions. Endothelial cells have a central role in cardiovascular disease as they provide the barrier between blood and the vessel wall where atherosclerosis starts and progresses. Insults to endothelial cells provoke their dysfunction favoring pro-atherogenic and pro-thrombotic effects. In the present work, we tested 7-ketocholesterol and 5,6-secosterol on endothelial cells - focusing on apoptosis and the associated mitochondrial/lysosome alterations - and on endothelial function using the in vitro model of arterial relaxation of aortic rings. Our data provide evidence that 7-ketocholesterol and 5,6-secosterol are efficient instigators of apoptosis, which for 5,6-secosterol is associated to PKC and p53 up-regulation. In addition 5,6-secosterol is a potent inhibitor of endothelial-dependent arterial relaxation through PKC-dependent mechanisms. This may contribute to pro-atherogenic and pro-thrombotic mechanisms of 5,6-secosterol and highlights the role of cholesterol autoxidation in cardiovascular disease.

Involvement of oxysterols in age-related diseases and ageing processes

Ageing is accompanied by increasing vulnerability to major pathologies (atherosclerosis, Alzheimer's disease, age-related macular degeneration, cataract, and osteoporosis) which can have similar underlying pathoetiologies. All of these diseases involve oxidative stress, inflammation and/or cell death processes, which are triggered by cholesterol oxide derivatives, also named oxysterols. These oxidized lipids result either from spontaneous and/or enzymatic oxidation of cholesterol on the steroid nucleus or on the side chain. The ability of oxysterols to induce severe dysfunctions in organelles (especially mitochondria) plays key roles in RedOx homeostasis, inflammatory status, lipid metabolism, and in the control of cell death induction, which may at least in part contribute to explain the potential participation of these molecules in ageing processes and in age related diseases. As no efficient treatments are currently available for most of these diseases, which are predicted to become more prevalent due to the increasing life expectancy and average age, a better knowledge of the biological activities of the different oxysterols is of interest, and constitutes an important step toward identification of pharmacological targets for the development of new therapeutic strategies.

CD36-dependent 7-ketocholesterol accumulation in macrophages mediates progression of atherosclerosis in response to chronic air pollution exposure

RATIONALE

Air pollution exposure has been shown to potentiate plaque progression in humans and animals. Our previous studies have suggested a role for oxidized lipids in mediating adverse vascular effect of air pollution. However, the types of oxidized lipids formed in response to air pollutants and how this occurs and their relevance to atherosclerosis are not fully understood.

OBJECTIVE

To investigate the mechanisms by which particulate matter <2.5 μm (PM2.5) induces progression of atherosclerosis.

METHODS AND RESULTS

Atherosclerosis-prone ApoE(-/-) or LDLR(-/-) mice were exposed to filtered air or concentrated ambient PM2.5 using a versatile aerosol concentrator enrichment system for 6 months. PM2.5 increased 7-ketocholesterol (7-KCh), an oxidatively modified form of cholesterol, in plasma intermediate density lipoprotein/low-density lipoprotein fraction and in aortic plaque concomitant with progression of atherosclerosis and increased CD36 expression in plaque macrophages from PM2.5-exposed mice. Macrophages isolated from PM2.5-exposed mice displayed increased uptake of oxidized lipids without alterations in their efflux capacity. Consistent with these finding, CD36-positive macrophages displayed a heightened capacity for oxidized lipid uptake. Deficiency of CD36 on hematopoietic cells diminished the effect of air pollution on 7-KCh accumulation, foam cell formation, and atherosclerosis.

CONCLUSIONS

Our results suggest a potential role for CD36-mediated abnormal accumulations of oxidized lipids, such as 7-KCh, in air pollution-induced atherosclerosis progression.

11β-Hydroxysteroid dehydrogenase type 1 contributes to the regulation of 7-oxysterol levels in the arterial wall through the inter-conversion of 7-ketocholesterol and 7β-hydroxycholesterol

The atherogenic 7-oxysterols, 7-ketocholesterol (7-KC) and 7β-hydroxycholesterol (7βOHC), can directly impair arterial function. Inter-conversion of 7-KC and 7βOHC has recently been shown as a novel role for the glucocorticoid-metabolizing enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). Since this enzyme is expressed in vascular smooth muscle cells, we addressed the hypothesis that inter-conversion of 7-KC and 7βOHC by 11β-HSD1 may contribute to regulation of arterial function.

Incubation (4–24 h) of aortic rings with either 7-KC (25 μM) or 7βOHC (20 μM) had no effect on endothelium-dependent (acetylcholine) or -independent (sodium nitroprusside) relaxation. In contrast, exposure to 7-KC (but not to 7βOHC) attenuated noradrenaline-induced contraction (E_max) after 4 h (0.78 ± 0.28 vs 0.40 ± 0.08 mN/mm; p < 0.05) and 24 h (2.28 ± 0.34 vs 1.56 ± 0.48 mN/mm; p < 0.05). Both 7-oxysterols were detected by GCMS in the aortic wall of chow-fed C57Bl6/J mice, with concentrations of 7-KC (1.41 ± 0.81 ng/mg) higher (p = 0.05) than 7βOHC (0.16 ± 0.06 ng/mg). In isolated mouse aortic rings 11β-HSD1 was shown to act as an oxo-reductase, inter-converting 7-KC and 7βOHC. This activity was lost in aorta from 11β-HSD1^−/− mice, which had low oxysterol levels. Renal homogenates from 11β-HSD1^−/− mice were used to confirm that the type 2 isozyme of 11β-HSD does not inter-convert 7-KC and 7βOHC.

These results demonstrate that 7-KC has greater effects than 7βOHC on vascular function, and that 11β-HSD1 can inter-convert 7-KC and 7βOHC in the arterial wall, contributing to the regulation of 7-oxysterol levels and potentially influencing vascular function. This mechanism may be important in the cardioprotective effects of 11β-HSD1 inhibitors.

An effective method for allylic oxidation of Delta5-steroids using tert-butyl hydroperoxide

An allylic oxidation method for Delta(5)-steroids using TBHP as oxidant with a 2-quinoxalinol salen Cu(II) complex as catalyst is reported. A variety of Delta(5)-steroidal substrates are selectively oxidized to the corresponding enones. Excellent yields are achieved (up to 99% under optimized conditions) while significantly reducing reaction times required as compared to other current methods.

Optimal TBHP allylic oxidation of Delta5-steroids catalyzed by dirhodium caprolactamate

Dirhodium caprolactamate is the most efficient catalyst for the oxidation of Delta5-steroids to 7-keto-Delta5-steroids by 70% tert-butyl hydroperoxide in water (T-HYDRO). Isolated product yields range from 38 to 87%.

S-nitrosoglutathione incorporated in poly(ethylene glycol) matrix: potential use for topical nitric oxide delivery

Incorporation of nitric oxide (NO) donors in non-toxic polymeric matrices can be a useful strategy for allowing topical NO delivery. We have incorporated the NO-donor S-nitrosoglutathione (GSNO) into a liquid poly(ethylene glycol) (PEG)/H2O matrix through the S-nitrosation of GSH by a NO/O2 gas mixture. Kinetic measurements of GSNO decomposition associated with NO release were performed at 25, 35, and 45 degrees C in the dark and under irradiation with UV/Vis light, lambda>480 nm and lambda=333 nm. NO release from the liquid matrix to the gas phase was confirmed by mass spectrometry. The PEG/H2O matrix stabilizes GSNO leading to expressive reductions in the initial rates of thermal and photochemical NO release, compared to aqueous GSNO solution. This matrix effect is assigned to diffusional constrains imposed on the escape of the NO and GS radicals formed in the solvent cage. This effect allows the storage of PEG-GSNO formulations for extended periods (more than 65 days at freezer) with negligible decomposition. PEG-GSNO formulation seems therefore to be applicable in topical NO delivery and GSNO displays potential as a percutaneous absorption enhancer. Moreover, the rate of NO release can be locally increased by irradiation with visible light.

Lysophosphatidylcholine and 7-oxocholesterol modulate Ca2+ signals and inhibit the phosphorylation of endothelial NO synthase and cytosolic phospholipase A2

The oxidation of plasma LDLs (low-density lipoproteins) is a key event in the pathogenesis of atherosclerosis. LPC (lysophosphatidylcholine) and oxysterols are major lipid constitutents of oxidized LDLs. In particular, 7-oxocholesterol has been found in plasma from cardiac patients and atherosclerotic plaque. In the present study, we investigated the ability of 7-oxocholesterol and LPC to regulate the activation of eNOS (endothelial nitric oxide synthase) and cPLA2 (cytosolic phospholipase A2) that synthesize two essential factors for vascular wall integrity, NO (nitric oxide) and arachidonic acid. In endothelial cells from human umbilical vein cords, both 7-oxocholesterol (150 microM) and LPC (20 microM) decreased histamine-induced NO release, but not the release activated by thapsigargin. The two lipids decreased NO release through a PI3K (phosphoinositide 3-kinase)-dependent pathway, and decreased eNOS phosphorylation. Their mechanisms of action were, however, different. The NO release reduction was dependent on superoxide anions in LPC-treated cells and not in 7-oxocholesterol-treated ones. The Ca2+ signals induced by histamine were abolished by LPC, but not by 7-oxocholesterol. The oxysterol also inhibited (i) the histamine- and thapsigargin-induced arachidonic acid release, and (ii) the phosphorylation of both cPLA2 and ERK1/2 (extracellular-signal-regulated kinases 1/2). The results show that 7-oxocholesterol inhibits eNOS and cPLA2 activation by altering a Ca2+-independent upstream step of PI3K and ERK1/2 cascades, whereas LPC desensitizes eNOS by interfering with receptor-activated signalling pathways. This suggests that 7-oxocholesterol and LPC generate signals which cross-talk with heterologous receptors, effects which could appear at early stage of atherosclerosis.

7-Ketocholesterol modulates intercellular communication through gap-junction in bovine lens epithelial cells

Background

Connexin43 (Cx43) is an integral membrane protein that forms intercellular channels called gap junctions. Intercellular communication in the eye lens relies on an extensive network of gap junctions essential for the maintenance of lens transparency. The association of Cx43 with cholesterol enriched lipid raft domains was recently demonstrated. The objective of this study is to assess if products of cholesterol oxidation (oxysterols) affect gap junction intercellular communication (GJIC).

Results

Primary cultures of lens epithelial cells (LEC) were incubated with 7-ketocholesterol (7-Keto), 25-hydroxycholesterol (25-OH) or cholesterol and the subcellular distribution of Cx43 was evaluated by immunofluorescence confocal microscopy. The levels of Cx43 present in gap junction plaques were assessed by its insolubility in Triton X-100 and quantified by western blotting. The stability of Cx43 at the plasma membrane following incubation with oxysterols was evaluated by biotinylation of cell surface proteins. Gap junction intercellular communication was evaluated by transfer of the dye Lucifer yellow. The results obtained showed that 7-keto induces an accumulation of Cx43 at the plasma membrane and an increase in intercellular communication through gap junction. However, incubation with cholesterol or 25-OH did not lead to significant alterations on subcellular distribution of Cx43 nor in intercellular communication. Data further suggests that increased intercellular communication results from increased stability of Cx43 at the plasma membrane, presumably forming functional gap-junctions, as suggested by decreased solubility of Cx43 in 1% Triton X-100. The increased stability of Cx43 at the plasma membrane seems to be specific and not related to disruption of endocytic pathway, as demonstrated by dextran uptake.

Conclusions

Results demonstrate, for the first time, that 7-keto induces an increase in gap junction intercellular communication, that is most likely due to an increased stability of protein at the plasma membrane and to increased abundance of Cx43 assembled in gap junction plaques.

Impairment of the cytotoxic and oxidative activities of 7 beta-hydroxycholesterol and 7-ketocholesterol by esterification with oleate

Atherosclerosis involves inflammatory processes, as well as cytotoxic and oxidative reactions. In atherosclerotic plaques, these phenomena are revealed by the presence of dead cells, oxidized lipids, and oxidative DNA damage, but the molecules triggering these events are still unknown. As 7 beta-hydroxycholesterol and 7-ketocholesterol, which are present at elevated concentrations in atherosclerotic lesions, are strongly cytotoxic and pro-oxidative, their effects were determined on cell death, superoxide anion and nitric oxide production, lipid peroxidation, and oxidative DNA damage. 7-Ketocholesterol- and 7 beta-hydroxycholesterol-induced cell death leads to a loss of mitochondrial potential, to increased permeability to propidium iodide, and to morphological nuclear changes (swelling, fragmentation, and/or condensation of nuclei). These effects are preceded by the formation of cytoplasmic monodansylcadaverine-positive structures and are associated with a rapid enhancement of cells overproducing superoxide anions, a decrease in cells producing nitric oxide, lipid peroxidation (formation of malondialdehyde and 4-hydroxynonenal adducts, low ratio of [unsaturated fatty acids]/[saturated fatty acids]) as well as oxidative DNA damage (8-oxoguanine formation). Noteworthy, none of the cytotoxic features previously observed with 7 beta-hydroxycholesterol and 7-ketocholesterol were noted with cholesterol, 7 beta-hydroxycholesteryl-3-oleate and 7-ketocholesteryl-3-oleate, with the exception of a slight increase in superoxide anion production with 7 beta-hydroxycholesteryl-3-oleate. This finding supports the theory that 7 beta-hydroxycholesterol and 7-ketocholesterol could induce cytotoxic and oxidative processes observed in atherosclerotic lesions and that esterification of these compounds may contribute to reducing atherosclerosis progression.