Eicosapentaenoic acid protects endothelial cells against anoikis through restoration of cFLIP

Protective effects of a unique combination of nutritionally active ingredients on risk factors and gene expression associated with atherosclerosis in C57BL/6J mice fed a high fat diet

Atherosclerosis, an inflammatory disorder of the vasculature and the underlying cause of cardiovascular disease, is responsible for one in three global deaths. Consumption of active food ingredients such as omega-3 polyunsaturated fatty acids, flavanols and phytosterols has many beneficial effects on cardiovascular disease. However, their combined actions on the risk factors for atherosclerosis remains poorly understood. We have previously shown that a formulation containing each of these active components at physiologically relevant doses modulated several monocyte/macrophage processes associated with atherosclerosis in vitro, including inhibition of cytokine-induced pro-inflammatory gene expression, chemokine-driven monocyte migration, expression of M1 phenotype markers, and promotion of cholesterol efflux. The objectives of the present study were to investigate whether the protective actions of the formulation extended in vivo and to delineate the potential underlying mechanisms. The formulation produced several favourable changes, including higher plasma levels of HDL and reduced levels of macrophages and myeloid-derived suppressor cells in the bone marrow. The mRNA expression of liver-X-receptor-α, peroxisome proliferator-activated receptor-γ and superoxide dismutase-1 was induced in the liver and that of interferon-γ and the chemokine (C-X-C motif) ligand 1 decreased, thereby suggesting the potential mechanisms for many beneficial effects. Other changes were also observed such as increased plasma levels of triglycerides and lipid peroxidation that may reflect potential activation of brown fat. This study provides new insights into the protective actions and the potential underlying mechanisms of the formulation in vivo, particularly in relation to risk factors together with changes in systemic inflammation and hepatic lipid alterations associated with atherosclerosis and metabolic syndrome, and supports further assessments in human trials.

Extracellular proteolytic pathophysiology in the neurovascular unit after stroke

The NINDS Stroke Progress Review Group recommended a shift in emphasis from a purely neurocentric view of cell death towards a more integrative approach whereby responses in all brain cells and matrix are considered. The neurovascular unit (fundamentally comprising endothelium, astrocyte, and neuron) provides a conceptual framework where cell-cell and cell-matrix signaling underlies the overall tissue response to stroke and its treatments. Here, we briefly review recent data on extracellular proteolytic dysfunction in the neurovascular unit after a stroke. The breakdown of neurovascular matrix initiates blood-brain barrier disruption with edema and/or hemorrhage. Endothelial dysfunction amplifies inflammatory responses. Perturbation of cell-matrix homeostasis triggers multiple cell death pathways. Interactions between the major classes of extracellular proteases from the plasminogen and matrix metalloprotease families may underlie processes responsible for some of the hemorrhagic complications of thrombolytic stroke therapy. Targeting the proteolytic imbalance within the neurovascular unit may provide new approaches for improving the safety and efficacy of thrombolytic reperfusion therapy for stroke.

Screening of therapeutic strategies for Huntington's disease in YAC128 transgenic mice

Huntington’s disease (HD) is a hereditary neurodegenerative disorder caused by an unstable expansion of cytosine-adenine-guanine (CAG) repeats in the HD gene. The symptoms include cognitive dysfunction and severe motor impairment with loss of voluntary movement coordination that is later replaced by bradykinesia and rigidity. The neuropathology is characterized by neuronal loss mainly in the striatum and cortex, and the appearance of neuronal intranuclear inclusions of mutant huntingtin. The mechanisms responsible for neurodegeneration are still not fully understood although excitotoxicity and a consequent increase in intracellular calcium concentration as well as the activation of caspases and calapins are known to play a key role. There is currently no satisfactory treatment or cure for this disease. The YAC128 transgenic mice express the full-length human HD gene with 128 CAG repeats and constitute a unique model for the study of HD as they replicate the slow and biphasic progression of behavioral deficits characteristic of the human condition and show striatal neuronal loss. As such, these transgenic mice have been an invaluable model not only for the elucidation of the neurodegenerative pathways in HD, but also for the screening and development of new therapeutic approaches. Here, I will review the unique characteristics of this transgenic HD model and will provide a summary of the therapies that have been tested in these mice, namely: potentiation of the protective roles of wild-type huntingtin and mutant huntingtin aggregation, transglutaminase inhibition, inhibition of glutamate- and dopamine-induced toxicity, apoptosis inhibition, use of essential fatty acids, and the novel approach of intrabody gene therapy. The insights obtained from these and future studies will help identify potential candidates for clinical trials and will ultimately contribute to the discovery of a successful treatment for this devastating neurodegenerative disorder.

Focal adhesion kinase and endothelial cell apoptosis

Focal adhesion kinase (FAK) is a key component of cell-substratum adhesions, known as focal adhesion complexes. Growing evidence indicates that FAK is important in maintenance of normal cell survival and that disruption of FAK signaling results in loss of substrate adhesion and anoikis (apoptosis) of anchorage-dependent cells, such as endothelial cells. Basal FAK activity in non-stimulated endothelial cells is important in maintaining cell adhesion to integrins via PI3 kinase/Akt signaling. FAK activity is dependent upon small GTPase signaling. FAK also appears to be important in cardiomyocyte hypertrophy and hypoxia/reoxygenation-induced cell death. This review summarizes the signaling pathways of FAK in prevention of apoptosis and the role of FAK in mediating adenosine and homocysteine-induced endothelial cell apoptosis and in cardiovascular diseases.

IGF-1 and atherothrombosis: relevance to pathophysiology and therapy

IGF-1 (insulin-like growth factor-1) plays a unique role in the cell protection of multiple systems, where its fine-tuned signal transduction helps to preserve tissues from hypoxia, ischaemia and oxidative stress, thus mediating functional homoeostatic adjustments. In contrast, its deprivation results in apoptosis and dysfunction. Many prospective epidemiological surveys have associated low IGF-1 levels with late mortality, MI (myocardial infarction), HF (heart failure) and diabetes. Interventional studies suggest that IGF-1 has anti-atherogenic actions, owing to its multifaceted impact on cardiovascular risk factors and diseases. The metabolic ability of IGF-1 in coupling vasodilation with improved function plays a key role in these actions. The endothelial-protective, anti-platelet and anti-thrombotic activities of IGF-1 exert critical effects in preventing both vascular damage and mechanisms that lead to unstable coronary plaques and syndromes. The pro-survival and anti-inflammatory short-term properties of IGF-1 appear to reduce infarct size and improve LV (left ventricular) remodelling after MI. An immune-modulatory ability, which is able to suppress 'friendly fire' and autoreactivity, is a proposed important additional mechanism explaining the anti-thrombotic and anti-remodelling activities of IGF-1. The concern of cancer risk raised by long-term therapy with IGF-1, however, deserves further study. In the present review, we discuss the large body of published evidence and review data on rhIGF-1 (recombinant human IGF-1) administration in cardiovascular disease and diabetes, with a focus on dosage and safety issues. Perhaps the time has come for the regenerative properties of IGF-1 to be assessed as a new pharmacological tool in cardiovascular medicine.

Deletion of the dual specific phosphatase-4 (DUSP-4) gene reveals an essential non-redundant role for MAP kinase phosphatase-2 (MKP-2) in proliferation and cell survival

Mitogen-activated protein kinase phosphatase-2 (MKP-2) is a type 1 nuclear dual specific phosphatase (DUSP) implicated in a number of cancers. We examined the role of MKP-2 in the regulation of MAP kinase phosphorylation, cell proliferation, and survival responses in mouse embryonic fibroblasts (MEFs) derived from a novel MKP-2 (DUSP-4) deletion mouse. We show that serum and PDGF induced ERK-dependent MKP-2 expression in wild type MEFs but not in MKP-2(-/-) MEFs. PDGF stimulation of sustained ERK phosphorylation was enhanced in MKP-2(-/-) MEFs, whereas anisomycin-induced JNK was only marginally increased. However, marked effects upon cell growth parameters were observed. Cellular proliferation rates were significantly reduced in MKP-2(-/-) MEFs and associated with a significant increase in cell doubling time. Infection with adenoviral MKP-2 reversed the decrease in proliferation. Cell cycle analysis revealed a block in G(2)/M phase transition associated with cyclin B accumulation and enhanced cdc2 phosphorylation. MEFs from MKP-2(-/-) mice also showed enhanced apoptosis when stimulated with anisomycin correlated with increased caspase-3 cleavage and γH2AX phosphorylation. Increased apoptosis was reversed by adenoviral MKP-2 infection and correlated with selective inhibition of JNK signaling. Collectively, these data demonstrate for the first time a critical non-redundant role for MKP-2 in regulating cell cycle progression and apoptosis.

Over-expression of mitogen-activated protein kinase phosphatase-2 enhances adhesion molecule expression and protects against apoptosis in human endothelial cells

BACKGROUND AND PURPOSE

We assessed the effects of over-expressing the dual-specific phosphatase, mitogen-activated protein (MAP) kinase phosphatase-2 (MKP-2), in human umbilical vein endothelial cells (HUVECs) on inflammatory protein expression and apoptosis, two key features of endothelial dysfunction in disease.

EXPERIMENTAL APPROACHES

We infected HUVECs for 40 h with an adenoviral version of MKP-2 (Adv.MKP-2). Tumour necrosis factor (TNF)-α-stimulated phosphorylation of MAP kinase and protein expression was measured by Western blotting. Cellular apoptosis was assayed by FACS.

KEY RESULTS

Infection with Adv.MKP-2 selectively abolished TNF-α-mediated c-Jun-N-terminal kinase (JNK) activation and had little effect upon extracellular signal-regulated kinase or p38 MAP kinase. Adv.MKP-2 abolished COX-2 expression, while induction of the endothelial cell adhesion molecules, intercellular adhesion molecule (ICAM) and vascular cell adhesion molecule (VCAM), two NFκB-dependent proteins, was not affected. However, when ICAM and VCAM expression was partly reduced by blockade of the NFκB pathway, Adv.MKP-2 was able to reverse this inhibition. This correlated with enhanced TNF-α-induced loss of the inhibitor of κB (IκB)α loss, a marker of NFκB activation. TNF-α in combination with NFκB blockade also increased HUVEC apoptosis; this was significantly reversed by Adv.MKP-2. Protein markers of cellular damage and apoptosis, H2AX phosphorylation and caspase-3 cleavage, were also reversed by MKP-2 over-expression.

CONCLUSIONS AND IMPLICATIONS

Over-expression of MKP-2 had different effects upon the expression of inflammatory proteins due to a reciprocal effect upon JNK and NFκB signalling, and also prevented TNF-α-mediated endothelial cell death. These properties may make Adv.MKP-2 a potentially useful future therapy in cardiovascular diseases where endothelial dysfunction is a feature.

Effects of eicosapentaenoic acid on endothelial cell-derived microparticles, angiopoietins and adiponectin in patients with type 2 diabetes

AIM

The aim of this study was to evaluate the significance of endothelial cell-derived microparticles (EDMP), angiopoietin-2 (Ang-2) and adiponectin in hyperlipidemic patients with and without type 2 diabetes mellitus, and to compare the two for the effects of eicosapentaenoic acid (EPA) on these markers.

METHODS

One hundred and twenty-six hyperlipidemic patients with and without type 2 diabetes mellitus received EPA 1,800 mg daily, and 50 of the patients were non-diabetic.

RESULTS

EDMP and Ang-2 levels prior to treatment were higher in diabetic patients than in non-diabetic patients, whereas adiponectin levels were lower in diabetics. When diabetic patients were classified into two groups on the basis of Ang-2 levels, the levels of all markers remained unchanged in those without a high Ang-2 level after EPA treatment. In contrast, all markers except for adiponectin were decreased significantly in diabetic patients with high Ang-2 levels after 6 months of EPA treatment. These diabetic patients with high Ang-2 levels displayed a more significant increase in adiponectin levels after EPA treatment than those who did not.

CONCLUSION

These results suggest that EPA possesses an adiponectin-dependent anti-atherosclerotic effect and may be beneficial for the prevention of vascular complications in diabetic patients with high Ang-2 levels.

Different mechanisms of saturated versus polyunsaturated FFA-induced apoptosis in human endothelial cells

Apoptosis and underlying mechanisms were evaluated in human umbilical vein endothelial cells (HUVECs), in target tissues of late diabetic vascular complications [human aortic endothelial cells (HAECs) and human retinal endothelial cells (HRECs)], and in endothelial progenitor cells (EPCs) exposed to FFAs, which are elevated in obesity and diabetes. Saturated stearic acid concentration dependently induced apoptosis that could be mediated via reduced membrane fluidity, because both apoptosis and membrane rigidity are counteracted by eicosapentaenoic acid. PUFAs triggered apoptosis at a concentration of 300 micromol/l in HUVECs, HAECs, and EPCs, but not HRECs, and, in contrast to stearic acid, involved caspase-8 activation. PUFA-induced apoptosis, but not stearic acid-induced apoptosis, strictly correlated (P < 0.01) with protein expression of E2F-1 (r = 0.878) and c-myc (r = 0.966). Lack of c-myc expression and activity owing to quiescence or transfection with dominant negative In373-Myc, respectively, renders HUVECs resistant to PUFA-induced apoptosis. Because c-myc is abundant in growing cells only, apoptosis triggered by PUFAs, but not by saturated stearic acid, obviously depends on the growth/proliferation status of the cells. Finally, this study shows that FFA-induced apoptosis depends on the vascular origin and growth/proliferation status of endothelial cells, and that saturated stearic acid-induced apoptosis and PUFA-induced apoptosis are mediated via different mechanisms.

The death of ouabain-treated renal epithelial cells: evidence against anoikis occurrence

The mechanisms of cell death signaling triggered by cardiotonic steroids are poorly understood. Based on massive detachment of ouabain-treated Madin-Darby canine kidney (MDCK) cells, it may be proposed that the cytotoxic action of these compounds is mediated by anoikis, i.e. a particular mode of death occurring in cells lacking cell-to-extracellular matrix interactions. We tested this hypothesis. Six hour incubation of MDCK cells with ouabain, marinobufagenin or K+-free medium almost completely blocked Na+,K+-ATPase, increased Na (i) + content by approximately 10-fold and suppressed cell attachment to regular-plastic-plates by up to 5-fold. In contrast, the death of attached cells was observed after 24-h incubation with ouabain but not in the presence of marinobufagenin or K+-free medium. Cells treated with ouabain and undergoing anoikis on ultra-low attachment plates exhibited different cell volume behaviour, i.e. swelling and shrinkage, respectively. The pan-caspase inhibitor z-VAD.fmk and the protein kinase C activator PMA rescued MDCK cells from anoikis but did not influence the survival of ouabain-treated cells, whereas medium acidification from pH 7.2 to 6.7 almost completely abolished the cytotoxic action of ouabain, but did not significantly affect anoikis. Our results show that the Na (i) + ,K (i) + -independent mode of MDCK cell death evoked by ouabain is not mediated by anoikis.

Eicosapentaenoic acid inhibits TNF-α-induced Lnk expression in human umbilical vein endothelial cells: involvement of the PI3K/Akt pathway

n-3 Polyunsaturated fatty acids (PUFAs) exert anti-inflammatory properties by influencing inflammatory cell activation processes. Lnk is an adaptor protein involving endothelial cell (EC) activation because it is induced by tumor necrosis factor-alpha (TNF-alpha). This study was conducted to evaluate the role of eicosapentaenoic acid (EPA), an n-3 PUFA, in the regulation of Lnk expression in human umbilical vein endothelial cells (HUVECs). Primary HUVECs were pretreated with EPA for 12 h at various concentrations (0-40 muM) and then exposed for another 12 h in the presence or absence of TNF-alpha (10 ng/ml). Lnk mRNA and protein were detected using reverse transcriptase polymerase chain reaction, immunoprecipitation and Western blot analysis. Results showed that pretreatment of HUVEC with EPA inhibited TNF-alpha-induced expression of Lnk in a dose-dependent manner. TNF-alpha-induced Lnk was also inhibited by a phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002. Thus, we investigated the role of PI3K/Akt signaling pathway in this process. Phosphorylation of Akt was assessed by Western blot analysis. We found that EPA treatment decreased the amount of activated Akt. These results showed that EPA inhibited TNF-alpha-induced Lnk expression in HUVECs through the PI3K/Akt pathway. This may be a potential mechanism by which EPA protects ECs under inflammatory conditions.

Oxidative stress at the vascular wall. Mechanistic and pharmacological aspects

During the process of energy production in aerobic respiration, vascular cells produce reactive oxygen species (ROS). A growing body of evidence indicates that oxidative stress refers to a condition in which cells are subjected to excessive levels of ROS. Overall vascular function is dependent upon a fine balance of oxidant and antioxidant mechanisms, which determine endothelial functions. Considerable experimental and clinical data indicate that intracellular oxidant milieu is also involved in several redox-sensitive cellular signaling pathways such as ion transport systems, protein phosphorylation, and gene expression and thus also plays important roles as modulator of vascular cell functions such as cell growth, apoptosis, migration, angiogenesis and cell adhesion. Overproduction of ROS under pathophysiologic conditions is integral in the development of cardiovascular diseases. This fact has raised an intensive search of new pharmacological approaches to improve vascular hemostasis and particularly those intended to decrease oxidative stress or augment the antioxidant defense mechanisms.

Ethyl-EPA treatment improves motor dysfunction, but not neurodegeneration in the YAC128 mouse model of Huntington disease

Huntington disease (HD) is an adult-onset neurodegenerative disorder that is characterized by selective degeneration in the striatum. There are currently no treatments that can prevent the progressive decline of motor and cognitive function in HD. In parallel with a human clinical trial, we examined the efficacy of ethyl-EPA treatment in the YAC128 mouse model of HD. Oral delivery of ethyl-EPA to symptomatic YAC128 mice beginning at 7 months of age increased membrane EPA levels 3-fold (P < 0.001) and resulted in a modest but significant improvement in motor dysfunction by 12 months of age as measured by open-field activity (P = 0.01) and performance on the rotarod (P = 0.05). At this age, ethyl-EPA-treated YAC128 mice showed no improvement in striatal volume, striatal neuron counts, striatal neuronal cross-sectional area, or striatal DARPP-32 expression compared to untreated YAC128 mice, thereby indicating no reduction of striatal neuropathology. This result is congruent with modest motor benefits observed in HD patients treated with ethyl-EPA. Overall, this work demonstrates the feasibility of experimental therapeutics in the YAC128 mouse model and suggests that experiments in these mice may be predictive for future human clinical trials.

Akt inhibition upregulates FasL, downregulates c-FLIPs and induces caspase-8-dependent cell death in Jurkat T lymphocytes

In T lymphocytes, the role of Akt in regulating Fas/Fas ligand (FasL)-mediated apoptotic signaling and death is not clearly understood. In this study, we observed that inhibition of Akt causes enhanced expression of FasL mRNA and protein and increased death-inducing signaling complex (DISC) formation with Fas-associated death domain (FADD) and procaspase-8 recruitment. Also, caspase-8 was activated at the DISC with accompanying decrease in c-FLIPs expression. FasL neutralizing antibody significantly decreased apoptotic death in the Akt-inhibited T cells. Additionally, Akt inhibition-induced Fas signaling was observed to link to the mitochondrial pathway via Bid cleavage. Further, inhibition of caspase-8 activity effectively blocked the loss of mitochondrial membrane potential and DNA fragmentation, suggesting that DISC formation and subsequent caspase-8 activation are critical initiating events in Akt inhibition-induced apoptotic death in T lymphocytes. These data demonstrate yet another important survival function governed by Akt kinase in T lymphocytes, which involves the regulation of FasL expression and consequent apoptotic signaling.

Omega-3 fatty acids and inflammation

Dietary omega-3 (n-3) fatty acids have a variety of anti-inflammatory and immune-modulating effects that may be of relevance to atherosclerosis and its clinical manifestations of myocardial infarction, sudden death, and stroke. The n-3 fatty acids that appear to be most potent in this respect are the long-chain polyunsaturates derived from marine oils, namely eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), and this review is restricted to these substances. A variety of biologic effects of EPA and DHA have been demonstrated from feeding studies with fish or fish oil supplements in humans and animals. These include effects on triglycerides, high-density lipoprotein cholesterol, platelet function, endothelial and vascular function, blood pressure, cardiac excitability, measures of oxidative stress, pro- and anti-inflammatory cytokines, and immune function. Epidemiologic studies provide evidence for a beneficial effect of n-3 fatty acids on manifestations of coronary heart disease and ischemic stroke, whereas randomized, controlled, clinical feeding trials support this, particularly with respect to sudden cardiac death in patients with established disease. Clinically important anti-inflammatory effects in man are further suggested by trials demonstrating benefits of n-3 fatty acids in rheumatoid arthritis, psoriasis, asthma, and inflammatory bowel disorders. Given the evidence relating progression of atherosclerosis to chronic inflammation, the n-3 fatty acids may play an important role via modulation of the inflammatory processes.

Homocysteine enhances endothelial apoptosis via upregulation of Fas-mediated pathways

Hyperhomocysteinemia is an independent risk factor for the development of atherosclerosis. However, the underlying mechanism of endothelial cell injury in hyperhomocysteinemia has not been elucidated. In this study, we examined the effect of homocysteine (Hcy) on Fas-mediated apoptosis in endothelial cells. Hcy-induced upregulation of Fas in endothelial cells (ECs) in a dose-dependent manner. At the same time, Hcy increased intracellular peroxide in ECs. Hcy-induced Fas expression was inhibited by the treatment with catalase. Hcy increased NF-kappaB DNA binding activity, and adenovirus-mediated transfection of a Ikappa-B mutant (Ikappa-B mt) gene inhibited Hcy-induced Fas expression. ECs were sensitive to Fas-mediated apoptosis when exposed to Hcy. Under these condition, Ikappa-B mt protected ECs from Fas-mediated apoptosis. In addition, Hcy inhibited expression of the caspase-8 inhibitor FLICE-inhibitory protein (FLIP). Adenovirus-mediated transfection of constitutively active Akt gene abolished the Hcy-mediated downregulation of FLIP. These data suggest that upregulation of Fas expression and downregulation of FLIP is a mechanism through which Hcy induces EC apoptosis.

Fas Signaling Induces Akt Activation and Upregulation of Endothelial Nitric Oxide Synthase Expression

A growing body of evidence has shown that Fas, a death receptor, mediates apoptosis-unrelated biological effects. Here, we report that Fas engagement with Fas ligand induced activation of Akt and upregulation of endothelial nitric oxide synthase expression without induction of apoptosis. In the presence of the phosphatidylinositol 3-kinase inhibitor wortmannin, Fas ligand, however, induced apoptosis instead of upregulation of endothelial nitric oxide synthase expression. In vivo, systolic blood pressure was slightly higher in mutant mice with decreased cell surface Fas expression ( lpr mice) compared with wild-type mice. In addition, chronic inhibition of nitric oxide synthesis by N G -nitro-l-arginine induced a progressive increase in the levels of blood pressure in wild-type mice, whereas no further increase in the levels of blood pressure was observed in lpr mice. Furthermore, acetylcholine caused a lesser endothelium-dependent relaxation of the strips from lpr mice compared with wild-type mice, although the vasoconstrictor potency of phenylephrine was not different between the two groups. These findings indicate that Fas signaling may have a role in the regulation of endothelial function and blood pressure through modulating endothelial nitric oxide synthase expression in the Akt signal-dependent manner.