Multiple lipid oxidation products in low density lipoproteins induce interleukin-1 beta release from human blood mononuclear cells

Olfactory Receptors and Aortic Aneurysm: Review of Disease Pathways

Aortic aneurysm, the pathological dilatation of the aorta at distinct locations, can be attributed to many different genetic and environmental factors. The resulting pathobiological disturbances generate a complex interplay of processes affecting cells and extracellular molecules of the tunica interna, media and externa. In short, aortic aneurysm can affect processes involving the extracellular matrix, lipid trafficking/atherosclerosis, vascular smooth muscle cells, inflammation, platelets and intraluminal thrombus formation, as well as various endothelial functions. Many of these processes are interconnected, potentiating one another. Newer discoveries, including the involvement of odorant olfactory receptors in these processes, have further shed light on disease initiation and pathology. Olfactory receptors are a varied group of G protein coupled-receptors responsible for the recognition of chemosensory information. Although they comprise many different subgroups, some of which are not well-characterized or identified in humans, odorant olfactory receptors, in particular, are most commonly associated with recognition of olfactory information. They can also be ectopically localized and thus carry out additional functions relevant to the tissue in which they are identified. It is thus the purpose of this narrative review to summarize and present pathobiological processes relevant to the initiation and propagation of aortic aneurysm, while also incorporating evidence associating these ectopically functioning odorant olfactory receptors with the overall pathology.

"How to Release or Not Release, That Is the Question." A Review of Interleukin-1 Cellular Release Mechanisms in Vascular Inflammation

Cardiovascular disease remains the leading cause of death worldwide, characterized by atherosclerotic activity within large and medium-sized arteries. Inflammation has been shown to be a primary driver of atherosclerotic plaque formation, with interleukin-1 (IL-1) having a principal role. This review focuses on the current state of knowledge of molecular mechanisms of IL-1 release from cells in atherosclerotic plaques. A more in-depth understanding of the process of IL-1's release into the vascular environment is necessary for the treatment of inflammatory disease processes, as the current selection of medicines being used primarily target IL-1 after it has been released. IL-1 is secreted by several heterogenous mechanisms, some of which are cell type-specific and could provide further specialized targets for therapeutic intervention. A major unmet challenge is to understand the mechanism before and leading to IL-1 release, especially by cells in atherosclerotic plaques, including endothelial cells, vascular smooth muscle cells, and macrophages. Data so far indicate a heterogeneity of IL-1 release mechanisms that vary according to cell type and are stimulus-dependent. Unraveling this complexity may reveal new targets to block excess vascular inflammation.

Odorant receptors in macrophages: potential targets for atherosclerosis

In a recent report, Orecchioni et al. identify a role for the olfactory receptor (OR) Olfr2 and its human ortholog OR6A2 in atherosclerosis. Vascular macrophage Olfr2 binds octanal, a product of lipid peroxidation, activating the NLRP3 inflammasome and IL-1β secretion, and driving atherosclerosis pathology. Thus, OR6A2 inhibitors may represent a promising therapy for atherosclerosis.

The Combination of Cigarette Smoking and Alcohol Consumption Synergistically Increases Reactive Carbonyl Species in Human Male Plasma

Cigarette smoking and alcohol consumption are major risk factors for lifestyle-related diseases. Although it has been reported that the combination of these habits worsens risks, the underlying mechanism remains elusive. Reactive carbonyl species (RCS) cause chemical modifications of biological molecules, leading to alterations in cellular signaling pathways, and total RCS levels have been used as a lipid peroxidation marker linked to lifestyle-related diseases. In this study, at least 41 types of RCS were identified in the lipophilic fraction of plasma samples from 40 subjects using liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS). Higher levels of 10 alkanals, 5 trans-2-alkenals, 1 cis-4-alkenal, and 3 alkadienals were detected in the smoking/drinking group (N = 10) as compared to those with either habit (N = 10 each) or without both habits (N = 10) in the analysis of covariances adjusted for age and BMI. The levels of 3 alkanals, 1 trans-2-alkenal, 1 alkadienal, and 1 4-hydroxy-2-alkenal in the smoking/drinking group were significantly higher than those in the no-smoking/drinking and no-smoking/no-drinking groups. These results strongly indicate that the combination of cigarette smoking and alcohol drinking synergistically increases the level and variety of RCS in the circulating blood, and may further jeopardize cellular function.

Signaling Pathways Potentially Responsible for Foam Cell Formation: Cholesterol Accumulation or Inflammatory Response-What is First?

Accumulation of lipid-laden (foam) cells in the arterial wall is known to be the earliest step in the pathogenesis of atherosclerosis. There is almost no doubt that atherogenic modified low-density lipoproteins (LDL) are the main sources of accumulating lipids in foam cells. Atherogenic modified LDL are taken up by arterial cells, such as macrophages, pericytes, and smooth muscle cells in an unregulated manner bypassing the LDL receptor. The present study was conducted to reveal possible common mechanisms in the interaction of macrophages with associates of modified LDL and non-lipid latex particles of a similar size. To determine regulatory pathways that are potentially responsible for cholesterol accumulation in human macrophages after the exposure to naturally occurring atherogenic or artificially modified LDL, we used transcriptome analysis. Previous studies of our group demonstrated that any type of LDL modification facilitates the self-association of lipoprotein particles. The size of such self-associates hinders their interaction with a specific LDL receptor. As a result, self-associates are taken up by nonspecific phagocytosis bypassing the LDL receptor. That is why we used latex beads as a stimulator of macrophage phagocytotic activity. We revealed at least 12 signaling pathways that were regulated by the interaction of macrophages with the multiple-modified atherogenic naturally occurring LDL and with latex beads in a similar manner. Therefore, modified LDL was shown to stimulate phagocytosis through the upregulation of certain genes. We have identified at least three genes (F2RL1, EIF2AK3, and IL15) encoding inflammatory molecules and associated with signaling pathways that were upregulated in response to the interaction of modified LDL with macrophages. Knockdown of two of these genes, EIF2AK3 and IL15, completely suppressed cholesterol accumulation in macrophages. Correspondingly, the upregulation of EIF2AK3 and IL15 promoted cholesterol accumulation. These data confirmed our hypothesis of the following chain of events in atherosclerosis: LDL particles undergo atherogenic modification; this is accompanied by the formation of self-associates; large LDL associates stimulate phagocytosis; as a result of phagocytosis stimulation, pro-inflammatory molecules are secreted; these molecules cause or at least contribute to the accumulation of intracellular cholesterol. This chain of events may explain the relationship between cholesterol accumulation and inflammation. The primary sequence of events in this chain is related to inflammatory response rather than cholesterol accumulation.

The role of endothelial dysfunction and oxidative stress in cerebrovascular diseases

Cerebrovascular diseases (CBD) are one of the most dangerous complications of atherosclerosis. The clinical consequences of CBD deeply impact quality of life and the prognosis of patients. Atherosclerosis is the main cause of CBD development. Hypertension, dyslipidemia, diabetes, smoking, obesity, and other risk factors explain the higher CBD incidence in the general population, as they are able to anticipate the clinical expression of atherosclerosis. These risk factors are effectively able to promote endothelial dysfunction which is the premise for the early, clinical expression of atherosclerosis. The mechanisms by which risk factors can influence the occurrence of CBD are different and not fully understood. The inflammatory background of atherosclerosis can explain a great part of it. In particular, the oxidative stress may promote the development of vascular lesions by negatively influencing biochemical cellular processes of the endothelium, thus predisposing the vascular tree to morphological and functional damages. The aim of this narrative review is to evaluate the role of endothelial dysfunction and oxidative stress in CBD development.

Chemistry and analysis of HNE and other prominent carbonyl-containing lipid oxidation compounds

The process of lipid oxidation generates a diverse array of small aldehydes and carbonyl-containing compounds, which may occur in free form or esterified within phospholipids and cholesterol esters. These aldehydes mostly result from fragmentation of fatty acyl chains following radical oxidation, and the products can be subdivided into alkanals, alkenals (usually α,β-unsaturated), γ-substituted alkenals and bis-aldehydes. Isolevuglandins are non-fragmented di-carbonyl compounds derived from H₂-isoprostanes, and oxidation of the ω-3-fatty acid docosahexenoic acid yield analogous 22 carbon neuroketals. Non-radical oxidation by hypochlorous acid can generate α-chlorofatty aldehydes from plasmenyl phospholipids. Most of these compounds are reactive and have generally been considered as toxic products of a deleterious process. The reactivity is especially high for the α,β-unsaturated alkenals, such as acrolein and crotonaldehyde, and for γ-substituted alkenals, of which 4-hydroxy-2-nonenal and 4-oxo-2-nonenal are best known. Nevertheless, in recent years several previously neglected aldehydes have been investigated and also found to have significant reactivity and biological effects; notable examples are 4-hydroxy-2-hexenal and 4-hydroxy-dodecadienal. This has led to substantial interest in the biological effects of all of these lipid oxidation products and their roles in disease, including proposals that HNE is a second messenger or signalling molecule. However, it is becoming clear that many of the effects elicited by these compounds relate to their propensity for forming adducts with nucleophilic groups on proteins, DNA and specific phospholipids. This emphasizes the need for good analytical methods, not just for free lipid oxidation products but also for the resulting adducts with biomolecules. The most informative methods are those utilizing HPLC separations and mass spectrometry, although analysis of the wide variety of possible adducts is very challenging. Nevertheless, evidence for the occurrence of lipid-derived aldehyde adducts in biological and clinical samples is building, and offers an exciting area of future research.

Plasma IL-1Ra: linking hyperapoB to risk factors for type 2 diabetes independent of obesity in humans

Background/Objective:

Plasma apoB predicts the incidence of type 2 diabetes (T2D); however, the link between apoB-linpoproteins and risks for T2D remain unclear. Insulin resistance (IR) and compensatory hyperinsulinemia characterize prediabetes, and the involvement of an activated interleukin-1 (IL-1) family, mainly IL-1β and its receptor antagonist (IL-Ra), is well documented. ApoB-lipoproteins were reported to promote IL-1β secretion in immune cells; however, in vivo evidence is lacking. We hypothesized that obese subjects with hyperapoB have an activated IL-1 system that explains hyperinsulinemia and IR in these subjects.

Subjects/Methods:

We examined 81 well-characterized normoglycemic men and postmenopausal women (⩾27 kg m⁻², 45–74 years, non-smokers, sedentary, free of chronic disease). Insulin secretion and sensitivity were measured by the gold-standard Botnia clamp, which is a combination of a 1-h intravenous glucose tolerance test (IVGTT) followed by 3-h hyperinsulinemic euglycemic clamp.

Results:

Plasma IL-1β was near detection limit (0.071–0.216 pg ml⁻¹), while IL-1Ra accumulated at 1000-folds higher (77–1068 pg ml⁻¹). Plasma apoB (0.34–1.80 g l⁻¹) associated significantly with hypersinsulinemia (total_IVGTT: C-peptide r=0.27, insulin r=0.22), IR (M/I=−0.29) and plasma IL-1Ra (r=0.26) but not with IL-1β. Plasma IL-1Ra associated with plasma IL-1β (r=0.40), and more strongly with hyperinsulinemia and IR than apoB, while the association of plasma IL-1β was limited to second phase and total insulin secretion (r=0.23). Adjusting the association of plasma apoB to hyperinsulinemia and IR for IL-1Ra eliminated these associations. Furthermore, despite equivalent body composition, subjects with hyperapoB (⩾80th percentile, 1.14 g l⁻¹) had higher C-peptide secretion and lower insulin sensitivity than those with low plasma apoB (⩽20th percentile, 0.78 g l⁻¹). Adjustment for plasma IL-1 Ra eliminated all group differences.

Conclusion:

Plasma apoB is associated with hyperinsulinemia and IR in normoglycemic obese subjects, which is eliminated upon adjustment for plasma IL-1Ra. This may implicate the IL-1 family in elevated risks for T2D in obese subjects with hyperapoB.

Metabolomics pilot study to identify volatile organic compound markers of childhood asthma in exhaled breath

BACKGROUND

In-community non-invasive identification of asthma-specific volatile organic compounds (VOCs) in exhaled breath presents opportunities to characterize phenotypes, and monitor disease state and therapies. The feasibility of breath sampling with children and the preliminary identification of childhood asthma markers were studied.

METHOD

End-tidal exhaled breath was sampled (2.5 dm³) from 11 children with asthma and 12 healthy children with an adaptive breath sampler. VOCs were collected onto a Tenax®/Carbotrap hydrophobic adsorbent trap, and analyzed by GC-MS. Classification was by retention-index and mass spectra in a 'breath matrix' followed by multivariate analysis.

RESULTS

A panel of eight candidate markers (1-(methylsulfanyl)propane, ethylbenzene, 1,4-dichlorobenzene, 4-isopropenyl-1-methylcyclohexene, 2-octenal, octadecyne, 1-isopropyl-3-methylbenzene and 1,7-dimethylnaphtalene) were found to differentiate between the asthmatic and healthy children in the test cohort with complete separation by 2D principal components analysis (2D PCA). Furthermore, the breath sampling protocol was found to be acceptable to children and young people.

CONCLUSION

This method was found to be acceptable for children, and healthy and asthmatic individuals were distinguished on the basis of eight VOCs at elevated levels in the breath of asthmatic children.

Central immune overactivation in the presence of reduced plasma corticosterone contributes to swim stress-induced hyperalgesia

Although it is widely known that immunological, hormonal and nociceptive mechanisms are altered by exposure to repeated stress, the interplaying roles of each function in the development of post-stress hyperalgesia are not completely clear. Thus, we wanted to establish how interleukin 1-beta (IL-1β), corticosterone and microglia interact to contribute in the development of hyperalgesia following repeated forced swim. Rats were subjected to either forced swim, sham swim or non-conditioned. Each group was then treated with minocycline, ketoconazole, or saline. Thermal nociception was measured via the hot plate test, before and after the behavioral conditioning, whereas blood and lumbar spinal cord tissue samples were obtained at the end of the protocol. Serum levels of corticosterone, spinal tissue concentration of IL-1β and spinal OX-42 labeling (microglial marker) were determined. Rats exposed to forced swim stress developed thermal hyperalgesia along with elevated spinal tissue IL-1β, increased OX-42 labeling and relatively diminished serum corticosterone. Pre-treatment with minocycline and ketoconazole prevented the development of thermal hyperalgesia and the increase in IL-1β, without significantly modifying serum corticosterone. These results suggest that the development of forced swim-induced thermal hyperalgesia requires the simultaneous presence of increased spinal IL-1β, microglial activation, and relatively decreased serum corticosterone.

CD36 coordinates NLRP3 inflammasome activation by facilitating intracellular nucleation of soluble ligands into particulate ligands in sterile inflammation

Particulate ligands including cholesterol crystals and amyloid fibrils induce NLRP3-dependent production of interleukin-1β (IL-1β) in atherosclerosis, Alzheimer's disease and diabetes. Soluble endogenous ligands including oxidized-LDL, amyloid-β and amylin peptides accumulate in these diseases. Here we identify a CD36-mediated endocytic pathway that coordinates the intracellular conversion of these soluble ligands to crystals or fibrils, resulting in lysosomal disruption and NLRP3-inflammasome activation. Consequently, macrophages lacking CD36 failed to elicit IL-1β production in response to these ligands and targeting CD36 in atherosclerotic mice reduced serum IL-1β and plaque cholesterol crystal accumulation. Collectively, these findings highlight the importance of CD36 in the accrual and nucleation of NLRP3 ligands from within the macrophage and position CD36 as a central regulator of inflammasome activation in sterile inflammation.

Differential regulation of acid sphingomyelinase in macrophages stimulated with oxidized low-density lipoprotein (LDL) and oxidized LDL immune complexes: role in phagocytosis and cytokine release

Oxidized low-density lipoprotein (oxLDL) and oxLDL-containing immune complexes (oxLDL-IC) contribute to the formation of lipid-laden macrophages (foam cells). Fcγ receptors mediate uptake of oxLDL-IC, whereas scavenger receptors internalize oxLDL. We have previously reported that oxLDL-IC, but not free oxLDL, activate macrophages and prolong their survival. Sphingomyelin is a major constituent of cell membranes and lipoprotein particles and acid sphingomyelinase (ASMase) hydrolyses sphingomyelin to generate the bioactive lipid ceramide. ASMase exists in two forms: lysosomal (L-ASMase) and secretory (S-ASMase). In this study we examined whether oxLDL and oxLDL-IC regulate ASMase differently, and whether ASMase mediates monocyte/macrophage activation and cytokine release. The oxLDL-IC, but not oxLDL, induced early and consistent release of catalytically active S-ASMase. The oxLDL-IC also consistently stimulated L-ASMase activity, whereas oxLDL induced a rapid transient increase in L-ASMase activity before it steadily declined below baseline. Prolonged exposure to oxLDL increased L-ASMase activity; however, activity remained significantly lower than that induced by oxLDL-IC. Further studies were aimed at defining the function of the activated ASMase. In response to oxLDL-IC, heat-shock protein 70B' (HSP70B') was up-regulated and localized with redistributed ASMase in the endosomal compartment outside the lysosome. Treatment with oxLDL-IC induced the formation and release of HSP70-containing and IL-1β-containing exosomes via an ASMase-dependent mechanism. Taken together, the results suggest that oxLDL and oxLDL-IC differentially regulate ASMase activity, and the pro-inflammatory responses to oxLDL-IC are mediated by prolonged activation of ASMase. These findings may contribute to increased understanding of mechanisms mediating macrophage involvement in atherosclerosis.

Periodontal status and hyperlipidemia: statin users versus non-users

BACKGROUND

The association between serum lipids and periodontal disease has been studied predominantly in patients with chronic periodontitis with limited data available regarding periodontal status of patients with hyperlipidemia. Meanwhile, the impact of statins on the periodontal health of the population also remains largely underexplored. This study aims to assess the periodontal status among patients with hyperlipidemia and users of statins.

METHODS

In this cross-sectional study, 94 patients with hyperlipidemia (50 receiving statins and 44 receiving non-pharmacologic therapy) and 46 control individuals who were normolipidemic underwent periodontal examination (plaque index, gingival index [GI], probing depth [PD], and clinical attachment level [CAL]). Biochemical parameters measured included serum triglyceride (TG), total cholesterol (TC), low-density lipoprotein (LDL) cholesterol, and high-density lipoprotein cholesterol levels.

RESULTS

PD and GI were significantly higher in patients with hyperlipidemia who were non-statin users compared with the normolipidemic individuals (P <0.001 [PD] and P <0.05 [GI]) and the statin group (P = 0.001 [PD] and P <0.05 [GI]). Periodontal parameters between statin users and the normolipidemic group did not differ significantly. After adjusting for confounders, positive and significant correlations were observed between PD and TG, and TC and LDL, whereas CAL shared correlation with TC and LDL. GI was correlated with TG and TC. Regression analyses revealed that whereas TC was associated significantly with PD (P <0.001), LDL showed significant association with CAL (P = 0.013). TG showed significant association with GI (P = 0.020).

CONCLUSIONS

Our findings suggest that relative to the general population, patients with hyperlipidemia are more prone to periodontal disease. Also, within the limits of this study, statins have a positive impact on periodontal health.

Effects of aging and menopause on serum interleukin-6 levels and peripheral blood mononuclear cell cytokine production in healthy nonobese women

Inappropriate interleukin-6 production is thought to play a role in the development of several age-related conditions including atherosclerosis. This study aimed to determine whether aging affects circulating interleukin-6 (IL-6) levels. Healthy, nonobese women (n = 208, 44.5 ± 0.70 years, 22.4 ± 0.17 kg/m(2)) were categorized into four age groups (22-31, 32-41, 42-51, and 52-63 years; cross-sectional study). Cytokine levels in serum and those produced from peripheral blood mononuclear cell (PBMC) were measured. The oldest group had the highest circulating levels of IL-6 and oxidized low-density lipoprotein (ox-LDL) and higher PBMC production of IL-6, tumor necrosis factor-α (TNF-α), and interleukin-1 alpha (IL-1β). Additionally, significant interactions between age and menopause were found for serum IL-6 (P = 0.024), and TNF-α (P = 0.011) and IL-1β (P < 0.001) produced from PBMCs. Serum IL-6 levels positively correlated with age, waist-hip ratio (WHR), systolic blood pressure, circulating levels of TNF-α, IL-1β, and ox-LDL, and urinary 8-epi-prostaglandin F(2)α. Multiple stepwise regression models identified the following factors for contributing to serum IL-6 levels: serum IL-1β, menopause status, WHR, and serum TNF-α in mode I (R(2) = 0.302); serum IL-1β, age, serum TNF-α, and WHR (β = 0.197; P = 0.006) in model II (R(2) = 0.283). Sub-analysis was performed according to menopausal status. Serum IL-6 levels were positively associated with levels of IL-6, TNF-α, and IL-1β in PBMC supernatants (unstimulated) from postmenopausal women, whereas these were negatively associated in premenopausal women. In conclusion, circulating IL-6 levels may be interactively influenced by age and menopause. Additionally, estrogen deprivation after menopause may enhance PBMC cytokine production in postmenopausal women, resulting in increased IL-6 levels which are closely related to oxidative stress.

The influence of bioactive oxylipins from marine diatoms on invertebrate reproduction and development

Diatoms are one of the main primary producers in aquatic ecosystems and occupy a vital link in the transfer of photosynthetically-fixed carbon through aquatic food webs. Diatoms produce an array of biologically-active metabolites, many of which have been attributed as a form of chemical defence and may offer potential as candidate marine drugs. Of considerable interest are molecules belonging to the oxylipin family which are broadly disruptive to reproductive and developmental processes. The range of reproductive impacts includes; oocyte maturation; sperm motility; fertilization; embryogenesis and larval competence. Much of the observed bioactivity may be ascribed to disruption of intracellular calcium signalling, induction of cytoskeletal instability and promotion of apoptotic pathways. From an ecological perspective, the primary interest in diatom-oxylipins is in relation to the potential impact on energy flow in planktonic systems whereby the reproductive success of copepods (the main grazers of diatoms) is compromised. Much data exists providing evidence for and against diatom reproductive effects; however detailed knowledge of the physiological and molecular processes involved remains poor. This paper provides a review of the current state of knowledge of the mechanistic impacts of diatom-oxylipins on marine invertebrate reproduction and development.

Remnant lipoproteins as strong key particles to atherogenesis

Recent epidemiologic studies have revealed that hypertriglyceridemia is associated with atherosclerosis independent of other coronary risk factors. However, it is difficult to select patients at high risk for coronary artery disease using only serum triglyceride levels compared with low-density lipoprotein cholesterol levels since multiple factors are associated with elevating triglycerides. Atherosclerotic diseases with high triglyceride levels can be found in patients with familial combined hyperlipidemia, diabetes mellitus, and metabolic syndrome, in which remnant lipoproteins accumulate in the circulating blood. Recent researches have paid attention to remnant lipoproteins as atherogenic particles with the development of methods for measuring remnant cholesterol levels and apolipoprotein B-48 levels directly from human serum. Measurement of these parameters in addition to serum triglycerides may help to distinguish high-risk patients and enable us to prevent or suppress the progression of atherosclerotic diseases in those patients. However, questions remain to be answered to evaluate the significance of remnant lipoproteins. Here, we focus on three issues: the underlying problems in measuring remnant lipoprotein cholesterol, the assessment of postprandial hyperlipidemia as an atherogenic condition, and finally a review of our experimental and clinical findings about the mechanisms by which remnant lipoproteins induce atherosclerosis.

Periodontal status in subjects with hyperlipidemia

BACKGROUND

Hyperlipidemia is a major risk factor for cardiovascular disease. Recent reports showed a possible association between periodontal disease and an increased risk for cardiovascular disease. The aim of this study was to evaluate whether hyperlipidemia has any influence on periodontal status.

METHODS

Fifty-one subjects with hyperlipidemia and 47 normolipidemic subjects participated in this study. Biochemical parameters, including plasma triglyceride, total cholesterol, low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) levels, and periodontal parameters, including plaque index (PI), probing depth (PD), clinical attachment level (CAL), and percentage of sites with bleeding on probing (BOP [%]), were evaluated.

RESULTS

The mean values of PI, PD, CAL, and BOP (%) for the hyperlipidemic group were significantly higher than those for the control group. Plasma triglyceride, total cholesterol, and LDL-C levels were significantly and positively associated with PI, PD, BOP (%), and CAL. HDL-C was significantly, but negatively, associated with CAL. Plasma triglyceride level was significantly associated with PD and BOP (%) after further analyses.

CONCLUSIONS

The results of our study showed that patients with mild or moderate hyperlipidemia manifested higher values of periodontal parameters compared to normolipidemic individuals. Further studies are needed to determine the effect of hyperlipidemia on periodontal disease.

Susceptibility of apolipoprotein B-containing lipoproteins to oxidation and antioxidant status in acute coronary syndromes

BACKGROUND

Oxidized lipoproteins may play an important role in the pathogenesis of atherosclerosis, and it has been shown that antioxidants have a protective effect against the progression of atherosclerosis.

HYPOTHESIS

The aim of this study was to investigate the oxidative susceptibility of apolipoprotein B-containing lipoproteins and antioxidant status in patients with acute coronary syndromes and chronic stable angina pectoris.

METHODS

The study population included 70 patients with acute coronary syndromes (14 with recent acute myocardial infarction and 56 with unstable angina pectoris), 105 patients with stable angina pectoris, and 75 control subjects. In addition to conventional lipid and lipoprotein analysis, the susceptibility of apolipoprotein B-containing lipoproteins to in vitro oxidation (lag phase) and plasma vitamin E and total carotene levels was measured.

RESULTS

The lag phase was significantly shorter in patients with acute coronary syndromes (45 +/- 12 min) than in patients with stable angina pectoris (51 +/- 10 min) and in control subjects (58 +/- 9 min) (p < 0.0001). Both plasma vitamin E and total carotene levels were lowest in patients with acute coronary syndromes (1.11 +/- 0.32 mg/dl and 119 +/- 32 micrograms/dl, respectively), followed by patients with stable angina pectoris (1.25 +/- 0.37 mg/dl and 132 +/- 37 micrograms/dl) and then controls (1.52 +/- 0.31 mg/dl and 167 +/- 41 micrograms/dl).

CONCLUSIONS

These data suggest that there is an intense oxidative process and a lower antioxidant status in acute coronary syndromes. This may lead to plaque instability due to the activation of the inflammatory response in coronary atherosclerotic lesions.

Effects of soy pinitol on the pro-inflammatory cytokines and scavenger receptors in oxidized low-density lipoprotein-treated THP-1 macrophages

Pinitol, a methylated form of D-chiro-inositol, acts as a insulin mediator. We investigated the effects of soy pinitol on the factors involved in foam cell formation using differentiated THP-1 macrophages. Pinitol slightly inhibited the lipid-laden foam cell formation by oxidized low-density lipoprotein (oxLDL) in a dose-dependent manner. Tumor necrosis factor-alpha and monocyte chemoattractant protein-1 releases were significantly reduced by pinitol treatment (0.05-0.5 mM), whereas interleukin-1beta and interleukin-8 secretions were significantly reduced in low-dose pinitol (0.05 or 0.1 mM) and 0.5 mM pinitol-treated cells, respectively, compared to no pinitol-treated cells. Gene expressions of CD36 and CD68 were significantly down-regulated by 0.05-0.5 mM pinitol compared to the oxLDL-treated control cells. Matrix metalloproteinase-9 gene expression was significantly decreased in 0.05-0.5 mM pinitol-treated cells compared to the no pinitol-treated macrophages. We conclude that pinitol has some inhibitory effects on foam cell formation by reducing lipid accumulation, secretion, and expression of some cytokines and macrophage scavenger receptor expression via its insulin-like action.

Antioxidants: the good, the bad and the ugly

Inflammation has a fundamental role in mediating all stages of atherosclerotic disease. The key role of oxidation in linking lipids and inflammation to atherosclerosis is compelling and is supported by experimental evidence. However, the relevance of the antioxidant hypothesis for the treatment of patients with atherosclerosis has not been definitively proven. Results of randomized trials with 'antioxidant' vitamins have been disappointing, and there are potentially important problems associated with their use, including their potential pro-oxidant effects. Probucol has reduced postpercutaneous coronary intervention (PCI)-restenosis and progression of carotid atherosclerosis in clinical trials. The antioxidant vascular protectant AGI-1067 has also been effective at preventing atherosclerosis in all tested animal models. The nonintervened reference coronary segments of the PCI vessel demonstrated improvements with AGI-1067 in the Canadian Antioxidant Restenosis Trial-1 (CART-1), evidence supportive of a clinical effect on slowing atherosclerosis progression. Two trials test the antioxidant/anti-inflammatory hypothesis with AGI-1067; CART-2 assesses its value for the reduction of both atherosclerosis progression and post-PCI restenosis, and Aggressive Reduction of Inflammation Stops Events (ARISE), which is evaluating its effects on hard cardiovascular outcomes.

Chylomicron remnants stimulate release of interleukin-1beta by THP-1 cells

Recent findings suggest that the oxidative modification of low-density lipoproteins (LDL) and an increase in triglyceride-rich lipoprotein particles including chylomicron remnants contribute to the progression of atherosclerosis, as does the inflammatory response. We therefore examined whether and how these lipoproteins affected interleukin (IL)-1beta release and mRNA expression for IL-1beta and IL-18 in THP-1 cells, a human monocyte cell line. Chylomicron remnants increased IL-1beta release into the conditioned medium by THP-1 in a dose- and time-dependent manner. At concentrations up to 1 microg/ml, chylomicron remnants increased IL-1beta release by 4-fold compared with the control. Neither native LDL nor oxidized LDL (OxLDL) significantly increased IL-1beta release. Chylomicron remnants increased IL-1beta mRNA expression by 3 times. Native LDL or OxLDL did not increase IL-1beta mRNA, while neither these lipoproteins nor chylomicron remnants increased IL-18 mRNA. Chylomicron remnants also increased the activities of caspase-1 and nuclear factor (NF)-kappaB significantly, while native LDL or OxLDL did not. In conclusion, chylomicron remnants stimulated IL-1beta mRNA expression and IL-1beta protein production probably via caspase-1 and NF-kappaB activation in THP-1 cells.

Plasma fibrinogen levels and cardiovascular risk factors in Japanese schoolchildren

BACKGROUND

Plasma fibrinogen level has been recognized as an independent risk factor for atherosclerosis and its thrombotic complications in adults. The present study aimed to clarify the association between plasma fibrinogen levels and cardiovascular risk factors in Japanese children.

METHODS

A total of 294 schoolchildren (145 boys and 149 girls) aged 10-13 years in a town in Nagano Prefecture, Japan, were surveyed in 2000 for body mass index (BMI), plasma fibrinogen, serum C-reactive protein (CRP), serum total cholesterol, serum high-density lipoprotein (HDL) cholesterol, hemoglobin (Hb) A1c, and ratio of serum total cholesterol to serum HDL cholesterol (TCHR).

RESULTS

The mean value and standard deviation of plasma fibrinogen level among the schoolchildren was 226.0+/-39.7 mg/dL for boys and 245.3+/-40.9 mg/dL for girls; significantly higher for girls. Among plasma fibrinogen tertiles, serum CRP tended to increase with plasma fibrinogen in both boys and girls. An increasing trend was also found in serum total cholesterol in boys, and in TCHR, HbA1c and BMI in girls. Multiple linear regression analysis revealed significant associations of plasma fibrinogen with serum CRP and HbA1c in both sexes, with TCHR in boys, and with BMI in girls.

CONCLUSIONS

Plasma fibrinogen levels were associated with cardiovascular risk factors such as serum CRP, TCHR, HbA1c, and BMI in Japanese schoolchildren.

Chylomicron remnants regulate early growth response factor-1 in vascular smooth muscle cells

Early growth response factor-1 (Egr-1) is a zinc-finger transcription factor that induces genes that promote atherosclerosis. The goal of the present study was to determine whether Egr-1 expression is modulated by atherogenic, triglyceride rich lipoproteins known as chylomicron remnants. Chylomicron remnants induced Egr-1 mRNA and protein expression in rat cultured vascular smooth muscle cells (VSMCs) and activated extracellular signal-regulated kinase (ERK) 1/2 in VSMCs. Further, chylomicron remnant-induced Egr-1 expression was inhibited by PD98059, a selective inhibitor of MAPK kinase (MEK), suggesting that the action of chylomicron remnants on Egr-1 was dependent on the ERK/MEK pathway. Chylomicron remnants also induced mRNA expression of the pro-inflammatory cytokines, IL-2 and IFN-gamma in VSMCs. We conclude that chylomicron remnants act as atherogenic lipoproteins via induction of Egr-1 expression and via cytokine-mediated inflammation.

Translocation of phospholipase A2 to membranes by oxidized LDL and hydroxyoctadecadienoic acid to contribute to cholesteryl ester formation

We examined the mechanisms underlying the activation of group IVA cytosolic phospholipase A(2) (cPLA(2)alpha) contributing to the supply of fatty acids required for the formation of cholesteryl ester in oxidized low-density lipoprotein (oxLDL)-stimulated macrophages. The possible involvement of oxidized lipids was also examined. In [(3)H]arachidonic acid-labeled mouse peritoneal macrophages, oxLDL stimulated the release of arachidonic acid, which was suppressed by methyl arachidonyl fluorophosphonate (MAFP), a cPLA(2)alpha inhibitor. oxLDL induced an increase in PLA(2)alpha levels in the membrane fraction without affecting those in whole cells or the activity in the lysate. Among 13-hydroxyoctadecadienoic acid (13-HODE), 7-ketocholesterol, and 25-hydroxycholesterol, oxidized lipids present in oxLDL particles, only 13-HODE induced the release of arachidonic acid, which was also sensitive to MAFP. Under conditions where addition of Ca(2+) to the cell lysate induced an increase in cPLA(2)alpha protein in the membrane fraction, preincubation with 13-HODE facilitated the Ca(2+)-dependent translocation of cPLA(2)alpha. Furthermore, 13-HODE increased cholesteryl ester formation in the presence of [(3)H]cholesterol. These results suggest that 13-HODE mediates the oxLDL-induced activation of cPLA(2)alpha through an increase in cPLA(2)alpha protein in the membranes, thus contributing, in part, to the supply of fatty acids required for the esterification of cholesterol in macrophages.

Antioxidants and atherosclerosis: Emerging drug therapies

Inflammation has a fundamental role in mediating all stages of atherosclerotic disease. The key role of oxidation in linking lipids and inflammation to atherosclerosis is compelling and supported by experimental evidence. However, the relevance of the antioxidant hypothesis for the treatment of patients with atherosclerosis has not been definitively proven. Probucol has reduced post-percutaneous coronary intervention (PCI) restenosis and progression of carotid atherosclerosis in clinical trials. The antioxidant/vascular protectant AGI-1067 has also been effective at preventing atherosclerosis in all tested animal models. The nonintervened reference coronary segments of the PCI vessel demonstrated improvements with AGI-1067 in the Canadian Antioxidant Restenosis Trial-1 (CART-1), evidence supportive of a clinical effect on slowing atherosclerosis progression. Results of randomized trials with the "antioxidant" vitamins have been disappointing, but there are potentially important problems associated with their use, including their potential pro-oxidant effects. Two important trials that test the antioxidant/anti-inflammatory hypothesis are ongoing with AGI-1067: CART-2, which assesses its value for the reduction of both atherosclerosis progression in non-PCI vessels and post-PCI restenosis; and Aggressive Reduction of Inflammation Stops Events (ARISE), which is evaluating the effects of AGI-1067 on hard cardiovascular outcomes.

Vitamin E–loaded dialyzer resets PBMC-operated cytokine network in dialysis patients

BACKGROUND

In hemodialysis patients the activity of stimulated Th1 lymphocytes is depressed, while Th2 cells are constitutively primed. Such phenomena may depend on monocyte activation and altered release of interleukin (IL)-12 and IL-18, which regulate Th cell differentiation. Reactive oxygen species (ROS) activate monocytes; therefore, a hemodialyzer with antioxidant activity would contrast ROS, prevent monocyte activation, reset IL-12 and IL-18 release, and restore Th1/Th2 balance.

METHODS

Ten patients on regular dialysis treatment (RDT) with cellulosic membrane (CM) were shifted to vitamin E-coated dialyzer (VE). During treatment with CM and after 3, 6, and 12 months of treatment with VE, peripheral blood mononuclear cells (PBMC) and purified CD4+ cells were isolated, and cultured, resting, mitogen-stimulated, and interferon gamma (IFNgamma), IL-4, IL-10, IL-12, and IL-18 release was measured. Vitamin E and A plasma levels and the effects of a single dialysis session on peripheral blood NO levels were assayed.

RESULTS

The constitutive release of IL-4 and IL-10 by CD4+ cells was abated significantly by treatment with VE (nadir -77.8% and -55.3%, respectively, at 12 months). INFgamma release by mitogen-stimulated CD4+ recovered with VE (zenith +501% at 12 months). PBMC constitutive production of IL-12 and IL-18 was significantly reduced by VE (nadir at 12 months -64.7% and -51.3%, respectively). VE increased plasma levels of vitamins E and A. NO plasma levels fell after a single dialysis treatment with VE (-17%, P < 0.05) in contrast with CU (+27.1%, P < 0.05).

CONCLUSION

The network of cytokines released by monocytes and Th cells is reset toward normality by treatment with vitamin E-coated dialyzer.

Oxidized LDL activates phospholipase A2 to supply fatty acids required for cholesterol esterification

We examined the roles of phospholipase A2 (PLA2) in oxidized LDL (oxLDL)-induced cholesteryl ester formation in macrophages. In [3H]oleic acid-labeled RAW264.7 cells and mouse peritoneal macrophages, oxLDL induced [3H]cholesteryl oleate formation with an increase in free [3H]oleic acid and a decrease in [3H]phosphatidylcholine. The changes in these lipids were suppressed by methyl arachidonyl fluorophosphonate (MAFP), a cytosolic PLA2 (cPLA2) inhibitor. However, MAFP had no effect on the ACAT activity or the binding and/or uptake of oxLDL. Stimulation with oxLDL in the presence of [3H]cholesterol increased [3H]cholesteryl ester bearing fatty acyl chains derived from cellular and/or exogenous (oxLDL) lipids. The formation of cholesteryl ester under this condition was also inhibited by MAFP, and the inhibitory effect was reversed by adding oleic acid. While oxLDL did not affect the activity or amounts of cPLA2, preincubation with oxLDL enhanced the release of oleic acid and arachidonic acid induced by ionomycin in RAW264.7 cells. 13(S)-hydroxyoctadecadienoic acid, but not 7-ketocholesterol, also enhanced ionomycin-induced oleic acid release. These results suggest that oxLDL induces cPLA2 activation, which contributes, at least in part, to the supply of fatty acids required for the cholesteryl esterification, probably through the acceleration by oxidized lipids of the catalytic action of cPLA2 in macrophages.

Galectin-3 expression in macrophages is signaled by Ras/MAP kinase pathway and up-regulated by modified lipoproteins

To study the signaling pathway involved in the regulation of galectin-3 expression we used phorbol ester to stimulate macrophage differentiation of THP-1 cells. Treatment with phorbol 12-myristate 13-acetate (PMA) increased significantly the level of expression of galectin-3 in THP-1 cells. PMA-induced galectin-3 overexpression was blocked by: protein kinase C inhibitors staurosporine, calphostin C, and apigenin; tyrosine-specific protein kinase inhibitors genistein and tyrphostin A25; PD 98059, a selective inhibitor of mitogen-activated protein kinase (MAPK) kinase 1 (MEK1 or MKK1); and SB 203580, a specific inhibitor of p38 MAPK. Galectin-3 up-regulation was not affected by exposure to two inhibitors of cAMP-dependent protein kinase (PKA), H-89 and KT5720. Co-transfection of pPG3.5, a plasmid vector containing the rabbit galectin-3 promoter and the constructs pMCL-MKK1 N3 or pRC-RSV-MKK3Glu that constitutively express MKK1 and MKK3, raised the activity of galectin-3 promoter by 185% and 110%, respectively. Co-transfection with a Ha-Ras expression vector stimulated galectin-3 promoter activity approximately 10-fold. Expression of c-Jun or v-Jun raised the level of galectin-3 promoter activity more the three- and fourfold, respectively. Co-transfection of c-Jun and pPG3.5 5'-upstream deletion mutants resulted in a reduction of the galectin-3 promoter activity by 50% to 80%. Transfection of c-Jun, v-Jun or Ha-Ras increased significantly galectin-3 protein in THP-1 cells. These findings indicated that Ras/MEKK1/MKK1-dependent/AP-1 signal transduction pathway plays an important role in the expression of galectin-3 in PMA-stimulated macrophages. We further investigated the effect of modified lipoproteins on galectin-3 expression in macrophages. Murine resident peritoneal macrophages loaded with acetylated low-density lipoprotein (AcLDL) or oxidized LDL (OxLDL) showed increased galectin-3 protein and mRNA. These results showed that treatment of macrophages with PMA or modified lipoproteins results in galectin-3 overexpression. These findings may explain the enhanced expression of galectin-3 in atherosclerotic foam cells and suggest that Ras/MAPK signal transduction pathway is involved in controlling this gene.

Oxidative stress, alpha-tocopherol therapy, and atherosclerosis

Atherosclerosis is the leading cause of morbidity and mortality in the United States. Evidence suggests that antioxidants, especially alpha-tocopherol (AT), have potential benefits with respect to cardiovascular disease. AT has been shown to decrease lipid peroxidation, to inhibit platelet adhesion, aggregation, and smooth muscle cell proliferation, to exert anti-inflammatory effects on monocytes, and to improve endothelial function. Low levels of AT are related to a higher incidence of cardiovascular disease and increased intakes appear to afford protection against cardiovascular disease. Although clinical trials with AT supplementation to date have been conflicting, the majority of evidence supports a benefit for AT supplementation in patients with pre-existing cardiovascular disease. Clearly, more clinical trials are required in individuals with increased oxidative stress before a definitive recommendation can be made with respect to AT supplementation in atherosclerosis.

Do changes in the cell membrane structure induce the generation of lipid peroxidation products which serve as first signalling molecules in cell to cell communication?

Evidence is presented that mammalian and plant cells respond equally to any event which changes their cell membrane structure. Proliferation, wounding or aging induces generation of lipidhydroperoxides from cell wall phospholipids. These are transformed to signalling compounds, some of these induce apoptosis. If the exerted impact exceeds a certain level, the original enzymic reaction switches to a non-enzymic one which produces peroxylradicals. The latter are not liberated enzymically. Peroxylradicals generate a second set of signalling compounds, but cause also severe damage: they epoxidize double bonds, and oxidize proteins, sugars and nucleic acids. Such reactions occur in all inflammatory diseases. Lipidhydoperoxides and their degradation products are incorporated in fat. Apparently, these compounds are transferred partly to LDL. Such LDL is still recognized by the cell LDL receptor. Toxic lipid peroxidation products are therefore introduced into cells and might be able to damage cells from inside long before the typical signs of atherosclerosis and other chronic diseases become visible.

Circulating oxidized LDL is associated with subclinical atherosclerosis development and inflammatory cytokines (AIR Study)

OBJECTIVE

Circulating oxidized LDL (Ox-LDL) is associated with clinical manifestations of atherosclerosis. However, no previous study has examined the relationship between subclinical atherosclerosis and Ox-LDL. The aims of the present study were to investigate the relationship between clinically silent ultrasound-assessed atherosclerotic changes in the carotid and femoral arteries and Ox-LDL and to explore the relationship between Ox-LDL, C-reactive protein, and the inflammatory cytokines interleukin-6 and tumor necrosis factor-alpha.

METHODS AND RESULTS

The study group (n=391) consisted of clinically healthy, 58-year-old men recruited from the general population. Ox-LDL was measured by using a specific monoclonal antibody, mAb-4E6. The results showed that Ox-LDL was related to intima-media thickness and plaque occurrence in the carotid and femoral arteries. In addition, Ox-LDL was associated with tumor necrosis factor-alpha and C-reactive protein. Circulating Ox-LDL was also associated with LDL cholesterol but not with blood pressure or smoking. When adjusting for other risk factors, both LDL cholesterol and Ox-LDL seemed to be independent predictors of plaque occurrence in the carotid and femoral arteries (odds ratios for quintile 5 versus quintile 1 were 2.17, P=0.049 and 2.25, P=0.050, for LDL cholesterol and Ox-LDL, respectively).

CONCLUSIONS

Ox-LDL was associated with both subclinical atherosclerosis and inflammatory variables, supporting the concept that oxidatively modified LDL may play a major role in atherosclerosis development, although no causality can be shown in this cross-sectional study.

Are changes of the cell membrane structure causally involved in the aging process?

Lipid peroxidation is recognized by proliferation, wounding, and aging. The connecting link between these different events is a change in cell wall structure, which activates membrane bound phospholipases. These cleave phospholipids. Thus liberated polyunsaturated fatty acids (PUFAs) are substrates for lipoxygenases, which accept equally well linoleic acid and arachidonic acid and generate lipid hydroperoxides (LOOHs). If the amount of free PUFAs exceeds a certain amount, lipoxygenases commit suicide. The consequence is liberation of free iron ions that react with LOOHs by formation of radicals. These start a chain reaction. LOO* radicals produced in the course of this process attack proteins, nucleic acids, and also double bonds of all unsaturated compounds by epoxidation. Morever LOOHs are decomposed to toxic epoxy acids and alphabetagammadelta-unsaturated aldehydes. Both species react with glutathione. The resulting products seem to induce apoptosis. Since the products generated by wounding or aging are formed by decomposition of LOOHs the investigation of the aging processes can be simplified by studying the physiological action of artificially generated lipid peroxidation products derived from pure PUFAs. Degradation products of LOOHs are generated by thermal decomposition of fat-containing PUFAs. These products are induced into the body by adsorption in the intestine. They are at least partly incorporated in low density lipoproteins (LDLs). Primarily investigations seem to indicate that an overload of a diet rich in PUFAs induces only after two days an increase in oxidized LDL/PUFAs for a factor up to two in young people and for a factor of more than two in old individuals.

Prevention of restenosis with antioxidants: mechanisms and implications

The aim of this review is to give an overview of the field of restenosis prevention with antioxidants, put in the perspective of their potential use for the prevention of atherosclerosis progression. Compelling evidence points to oxidative stress as an important trigger in the complex chain of events leading to atherosclerosis. There is also evidence that oxidative stress occurs early after angioplasty. Reactive oxygen species (ROS) can induce endothelial dysfunction and macrophage activation, resulting in the release of cytokines and growth factors that stimulate matrix remodeling and smooth muscle cell proliferation. The accumulation of new extracellular matrix and smooth muscle cells will result in the neointimal formation responsible for lumen narrowing after stent deployment and which contributes to that after balloon angioplasty. In addition, oxidation processes are involved in the cross-linking of collagen fibers, and this coupled with smooth muscle cell contraction and endothelial dysfunction may result in long-term vascular constriction or lack of adaptive vascular remodeling after balloon angioplasty. The powerful antioxidant probucol has been shown to prevent coronary restenosis after balloon angioplasty in the Multivitamins and Probucol (MVP) trial and other clinical studies. However, prolongation of the QT interval with probucol remains a long-term safety concern. AGI-1067, a metabolically stable analog of probucol, is a vascular protectant with strong antioxidant properties as potent to those of probucol. There has been no evidence of prolongation of the QT interval with AGI-1067 in initial clinical studies. The anti-restenosis properties of AGI-1067 are being assessed in the Canadian Antioxidant Restenosis Trial (CART)-1. Considering that oxidative stress and inflammation may persist for a prolonged period after stent placement, treatment with AGI-1067 for the entire period of risk after percutaneous coronary intervention (PCI) [instead of only 4 weeks in CART-1] may result in enhanced protection against luminal renarrowing. This hypothesis will be tested in the randomized, multicenter CART-2 trial. AGI-1067 has been effective at preventing atherosclerosis in all tested animal models, including the low density lipoprotein receptor-deficient and apo-E knockout mice. This has potentially important implications, as PCI and local approaches to prevent restenosis such as coated stents are not expected to prevent atherosclerosis progression, myocardial infarction and cardiovascular death. As the ultimate goal of therapy for patients with coronary artery disease must remain prevention of disease progression and atherosclerosis-related events, CART-2 will test the value of AGI-1067 for the reduction of both post-PCI restenosis and atherosclerosis progression.

Periodontitis and diabetes interrelationships: role of inflammation

Diabetes mellitus is a systemic disease with several major complications affecting both the quality and length of life. One of these complications is periodontal disease (periodontitis). Periodontitis is much more than a localized oral infection. Recent data indicate that periodontitis may cause changes in systemic physiology. The interrelationships between periodontitis and diabetes provide an example of systemic disease predisposing to oral infection, and once that infection is established, the oral infection exacerbates systemic disease. In this case, it may also be possible for the oral infection to predispose to systemic disease. In order to understand the cellular/molecular mechanisms responsible for such a cyclical association, one must identify common physiological changes associated with diabetes and periodontitis that produce a synergy when the conditions coexist. A potential mechanistic link involves the broad axis of inflammation, specifically immune cell phenotype, serum lipid levels, and tissue homeostasis. Diabetes-induced changes in immune cell function produce an inflammatory immune cell phenotype (upregulation of proinflammatory cytokines from monocytes/polymorphonuclear leukocytes and downregulation of growth factors from macrophages). This predisposes to chronic inflammation, progressive tissue breakdown, and diminished tissue repair capacity. Periodontal tissues frequently manifest these changes because they are constantly wounded by substances emanating from bacterial biofilms. Diabetic patients are prone to elevated low density lipoprotein cholesterol and triglycerides (LDL/TRG) even when blood glucose levels are well controlled. This is significant, as recent studies demonstrate that hyperlipidemia may be one of the factors associated with diabetes-induced immune cell alterations. Recent human studies have established a relationship between high serum lipid levels and periodontitis. Some evidence now suggests that periodontitis itself may lead to elevated LDL/TRG. Periodontitis-induced bacteremia/endotoxemia has been shown to cause elevations of serum proinflammatory cytokines such as interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha), which have been demonstrated to produce alterations in lipid metabolism leading to hyperlipidemia. Within this context, periodontitis may contribute to elevated proinflammatory cytokines/serum lipids and potentially to systemic disease arising from chronic hyperlipidemia and/or increased inflammatory mediators. These cytokines can produce an insulin resistance syndrome similar to that observed in diabetes and initiate destruction of pancreatic beta cells leading to development of diabetes. Thus, there is potential for periodontitis to exacerbate diabetes-induced hyperlipidemia, immune cell alterations, and diminished tissue repair capacity. It may also be possible for chronic periodontitis to induce diabetes.

Signaling mechanisms of nuclear factor-kappab-mediated activation of inflammatory genes by 13-hydroperoxyoctadecadienoic acid in cultured vascular smooth muscle cells

Oxidatively modified low density lipoprotein (LDL) has been implicated in the pathogenesis of atherosclerosis. LDL oxidation may be mediated by several factors, including cellular lipoxygenases. The lipoxygenase product of linoleic acid, 13-hydroperoxyoctadecadienoic acid (13-HPODE), is a significant component of oxidized LDL and has been shown to be present in atherosclerotic lesions. However, the mechanism of action of these oxidized lipids in vascular smooth muscle cells (VSMCs) is not clear. In the present study, we show that 13-HPODE leads to the activation of Ras as well as the mitogen-activated protein kinases, extracellular signal-regulated kinase 1/2, p38, and c-Jun amino-terminal kinase, in porcine VSMCs. 13-HPODE also specifically activated the oxidant stress-responsive transcription factor, nuclear factor-kappaB, but not activator protein-1 or activator protein-2. 13-HPODE-induced nuclear factor-kappaB DNA binding activity was blocked by an antioxidant, N-acetylcysteine, as well as an inhibitor of protein kinase C. 13-HPODE, but not the hydroxy product, 13-(S)-hydroxyoctadecadienoic acid, also dose-dependently increased vascular cell adhesion molecule-1 promoter activation. This was inhibited by an antioxidant as well as by inhibitors of Ras p38 mitogen-activated protein kinase and protein kinase C. Our results suggest that oxidized lipid components of oxidized LDL, such as 13-HPODE, may play a key role in the atherogenic process by inducing the transcriptional regulation of inflammatory genes in VSMCs via the activation of key signaling kinases.

2,4-Decadienal downregulates TNF-alpha gene expression in THP-1 human macrophages

Oxidized lipoproteins inhibit TNF-alpha secretion by human THP-1 macrophages due, at least in part, to aldehydes derived from the oxidation of polyunsaturated fatty acids. This study extends these findings by investigating the effect of three aldehydes (2,4-decadienal (2,4-DDE), hexanal and 4-hydroxynonenal (4-HNE)) on TNF-alpha and IL-1beta mRNA expression. The 2,4-DDE and 4-HNE showed considerable biological activity which induced cytotoxicity on THP-1 macrophages at concentration of 50 microM. Hexanal, on the other hand, had a lower cytotoxic capacity and concentration of 1000 microM was needed for the effect to be observed. Exposure of THP-1 macrophages to aldehydes for 24 h inhibited TNF-alpha mRNA expression but increased or did not affect IL-1beta mRNA levels. The inhibitory action of 2,4-DDE was dose dependent and began at 5 microM (46%, P<0.001). The effect of 4-HNE was less inhibitory than 4-DDE but only when cytotoxic concentrations were used (50 microM). Very high concentrations of hexanal (200 microM) were needed to inhibit TNF-alpha expression (23%, P<0.001). This downregulation of TNF-alpha gene expression by 2,4-DDE was parallel to a lower protein production. These data indicate that low levels of 2,4-DDE may modulate inflammatory action by inhibiting TNF-alpha mRNA gene expression and that the biological activity of 2,4-DDE may be involved in the development of atherosclerosis.

Lipid peroxidation in aging and age-dependent diseases

Aging is related with an increase in oxidation products derived from nucleic acids, sugars, sterols and lipids. Evidence will be presented that these different oxidation products are generated by processes induced by changes in the cell membrane structure (CMS), and not by superoxide, as commonly assumed. CMS activate apparently membrane bound phospholipases A2 in mammals and plants. Such changes occur by proliferation, aging and especially by wounding. After activation of phospholipases, influx of Ca2+ ions and activation of lipoxygenases (LOX) is induced. The LOX transform polyunsaturated fatty acids (PUFAs) into lipid hydroperoxides (LOOHs), which seem to be decomposed by action of enzymes to signalling compounds. Following severe cell injury, LOX commit suicide. Their suicide liberates iron ions that induce nonenzymic lipid peroxidation (LPO) processes by generation of radicals. Radicals attack all compounds with the structural element -CH=CH-CH(2)-CH=CH-. Thus, they act on all PUFAs independently either in free or conjugated form. The most abundant LPO products are derived from linoleic acid. Radicals induce generation of peroxyl radicals, which oxidise a great variety of biological compounds including proteins and nucleic acids. Nonenzymic LPO processes are induced artificially by the treatment of pure PUFAs with bivalent metal ions. The products are separable after appropriate derivatisation by gas chromatography (GC). They are identified by electron impact mass spectrometry (EI/MS). The complete spectrum of LPO products obtained by artificial LPO of linoleic acid is detectable after wounding of tissue, in aged individuals and in patients suffering from age-dependent diseases. Genesis of different LPO products derived from linoleic acid will be discussed in detail. Some of the LPO products are of high chemical reactivity and therefore escape detection in biological surrounding. For instance, epoxides and highly unsaturated aldehydic compounds that apparently induce apoptosis.

Oxidized LDL-mediated monocyte adhesion to endothelial cells does not involve NFkappaB

Oxidised LDL (oxLDL) is a key pathogenic mediator of atherogenesis, exhibiting many proatherogenic properties. We have examined the effect of oxLDL on monocyte adhesion in the endothelial cell line, EA.hy 926. This has included the role of endothelial cell adhesion molecule expression (ICAM-1 and VCAM-1), monocyte chemoattractant protein-1 (MCP-1), and the transcription factor NFkappaB in this interaction. In response to oxLDL (10-100 microg/ml), monocyte adhesion to cells increased dose-dependently. Adhesion of oxLDL at 100 microg/ml was equivalent to that seen with TNFalpha (10 ng/ml). Unmodified LDL (nLDL, 100 microg/ml) had no effect. Both oxLDL and nLDL increased MCP-1 mRNA levels. Interestingly, oxLDL had no effect on the expression of ICAM-1 and VCAM-1. In addition NFkappaB was not activated as shown by western blots of IkappaB-alpha degradation and electrophoretic mobility shift assay. In summary these data show that increased monocyte adhesion to EA.hy 926 cells occurs independently of ICAM-1, VCAM-1, and NFkappaB activation and may involve novel adhesive mechanisms.

t-Butyl hydroperoxide and oxidized low density lipoprotein enhance phospholipid hydrolysis in lipopolysaccharide-stimulated retinal pericytes

Free radicals induced by organic peroxides or oxidized low density lipoprotein (oxLDL) play a critical role in the development of atherosclerosis. In investigating this process, and the concomitant inflammatory response, the role of pericytes, cells supporting the endothelial ones in blood vessels, has received little attention. In this study we tested the hypothesis that tert-butyl hydroperoxide (t-BuOOH) and oxLDL, administered in sublethal doses to the culture medium of retinal pericytes, function as prooxidant signals to increase the stimulation of the peroxidation process induced by lipopolysaccharide (LPS). Confluent cell monolayers were exposed to t-BuOOH (25-400 microM), native LDL or oxLDL (3.4-340 nmol hydroperoxides/mg protein, 1-100 micro). LPS (1 microg/ml), t-BuOOH (200 microM), and oxLDL (100 microM), but not native LDL, incubated for 24 h with cells, markedly increased lipid peroxidation, cytosolic phospholipase A2 (cPLA2) activity and arachidonic acid (AA) release in a time- and dose-dependent manner. AACOCF(3), a potent cPLA2 inhibitor, and the antioxidant alpha-tocopherol strongly inhibited the prooxidant-stimulated AA release. Long-term exposure to maximal concentrations of t-BuOOH (400 microM) or oxLDL (100 microM) had a sharp cytotoxic effect on the cells, described by morphological and biochemical indices. The presence of t-BuOOH or oxLDL at the same time, synergistically increased phospholipid hydrolysis induced by LPS alone. 400 microM t-BuOOH or 100 microM oxLDL had no significant effect on the stimulation of an apoptosis process estimated by DNA laddering and light and electron microscopy. The results indicate that (i) pericytes may be the target of extensive oxidative damage; (ii) activation of cPLA2 mediates AA liberation; (iii) as long-term regulatory signals, organic peroxide and specific constituents of oxLDL increase the pericyte ability to degrade membrane phospholipids mediated by LPS which was used, in the present study, to simulate in vitro an inflammatory burst in the retinal capillaries.

Oxidized low density lipoprotein inhibits interleukin-12 production in lipopolysaccharide-activated mouse macrophages via direct interactions between peroxisome proliferator-activated receptor-gamma and nuclear factor-kappa B

Lipopolysaccharide (LPS) increases the production of interleukin-12 (IL-12) from mouse macrophages via a kappaB site within the IL-12 p40 promoter. In this study, we found that oxidized low density lipoprotein (oxLDL) inhibited this LPS-stimulated production of IL-12 in a dose-dependent manner while native LDL did not. OxLDL inhibited p40 promoter activation in monocytic RAW264.7 cells transiently transfected with p40 promoter/reporter constructs, and the repressive effect mapped to a region in the p40 promoter containing a binding site for nuclear factor-kappaB (NF-kappaB) (p40-kappaB). Activation of macrophages by LPS in the presence of oxLDL resulted in markedly reduced binding to the kappaB site, as demonstrated by the electrophoretic mobility shift assays. In contrast, native LDL did not inhibit the IL-12 p40 promoter activation and NF-kappaB binding to the kappaB sites, suggesting that oxidative modification of LDL was crucial for the inhibition of NF-kappaB-mediated IL-12 production. 9-Hydroxyoctadecadienoic acid, a major oxidized lipid component of oxLDL, significantly inhibited IL-12 production in LPS-stimulated mouse macrophages and also suppressed NF-kappaB-mediated activation in IL-12 p40 promoter. The NF-kappaB components p50 and p65 directly bound peroxisome proliferator-activated receptor-gamma (PPAR-gamma) in vitro. In cotransfections of CV-1 and HeLa cells, PPAR-gamma inhibited the NF-kappaB transactivation in an oxLDL-dependent manner. From these results, we propose that oxLDL-mediated suppression of the IL-12 production from LPS-activated mouse macrophages may, at least in part, involve both inhibition of the NF-kappaB-DNA interactions and physical interactions between NF-kappaB and PPAR-gamma.

Pathophysiological relationships between periodontitis and systemic disease: recent concepts involving serum lipids

Periodontitis has been traditionally regarded as a chronic inflammatory oral infection. However, recent studies indicate that this oral disease may have profound effects on systemic health. The search for cellular/molecular mechanisms linking periodontitis to changes in systemic health and systemic physiology has resulted in the evolution of a new area of lipid research establishing linkages between existing multidisciplinary biomedical literature, recent observations concerning the effects of serum lipids on immune cell phenotype/function, and a heightened interest in systemic responses to chronic localized infections. There appears to be more than a casual relationship between serum lipid levels and systemic health (particularly cardiovascular disease, diabetes, tissue repair capacity, and immune cell function), susceptibility to periodontitis, and serum levels of pro-inflammatory cytokines. In terms of the potential relationship between periodontitis and systemic disease, it is possible that periodontitis-induced changes in immune cell function cause metabolic dysregulation of lipid metabolism through mechanisms involving proinflammatory cytokines. Sustained elevations of serum lipids and/or pro-inflammatory cytokines may have a serious negative impact on systemic health. The purpose of this paper is to present the background, supporting data, and hypotheses related to this concept. As active participants in this emerging and exciting area of investigation, we hope to stimulate interest and awareness among biomedical scientists and practitioners.

Regulation of cell growth by oxidized LDL

The first reports of the influences of oxidized LDL (oxLDL) on cell function pertained to negative effects on cell growth-growth arrest, injury, and toxicity. Since these studies, it has become apparent that sublethal levels of oxLDL cause some, but not all, cells to proliferate. This review highlights the growth-promoting effects of oxLDL rather than its inhibitory or injurious effects. Smooth muscle cells (SMCs) and monocyte-macrophages proliferate after exposure to oxLDL; endothelial cells do not. Scavenger receptors are involved in the proliferative effects on monocyte-macrophages, whereas the effects of oxLDL on SMCs appear to be receptor independent. Lysophosphatidylcholine (lysoPC), and structurally related lipids are among the growth-promoting constituents of oxLDL. OxLDL exerts at least a part of its effects by inducing expression or causing the release of growth factors. OxLDL (or lysoPC) can cause the release of basic fibroblast growth factor (bFGF) from SMCs; oxLDL (or lysoPC) can induce heparin binding EGF-like growth factor (HB-EGF) synthesis and release from macrophages. An imposing array of changes in cytokine and growth factor expression and/or release can be imposed by oxLDL on a wide variety of cell types. These effects and the studies probing the cell signaling events leading to them are described.

Stimulating effect of biologically modified low density lipoproteins on ADP-induced aggregation of washed platelets persists in absence of specific binding

Oxidized low density lipoproteins are closely associated with atherosclerosis and also might be directly involved in thrombosis because they have been shown to mediate a stimulating effect on human platelets. In this work, we used biologically modified low density lipoproteins (i.e., low density lipoproteins sufficiently oxidized to show specificity for the macrophage scavenger receptor system) to examine if specific binding of the oxidized apolipoprotein moiety to the platelet surface is a prerequisite for the platelet-stimulating effects reported by other authors. We find that biologically modified low density lipoproteins show specific binding to human platelets (K(d)=5.83+/-0.4 microg/mL, 3850+/-620 sites/platelet) and strongly augment both ADP- and thrombin-induced aggregation of washed platelets. Maleylated albumin, an antagonist of oxidized low density lipoproteins binding to all currently classified scavenger receptors, is able to reduce platelet oxidized low density lipoproteins binding to background levels. Nevertheless, maleylated albumin is not able to exert any kind of normalizing effect on the augmented ADP-induced aggregation response observed in the presence of biologically modified low density lipoproteins. From these data, we conclude that specific binding of oxidatively modified apolipoprotein B to the platelet surface is not essential to the process of platelet stimulation. Therefore, we conclude that these stimulating effects may be mediated by unidentified compounds formed in the lipid phase of the lipoproteins.