Alpha-lipoic acid inhibits TNF-alpha-induced NF-kappaB activation and adhesion molecule expression in human aortic endothelial cells

Human guanylate binding protein-1 (hGBP-1) characterizes and establishes a non-angiogenic endothelial cell activation phenotype in inflammatory diseases

Blood vessel activation in inflammatory diseases is triggered by a myriad of different factors that partially reveal opposite activities on endothelial cells (EC). For example, inflammatory cytokines (IC) inhibit EC proliferation and induce cell adhesiveness for leukocytes. In contrast, angiogenic growth factors (AGF) activate EC proliferation and inhibit cell adhesiveness for leukocytes. In consequence, IC and AGF may induce two different activation phenotypes in EC that appear in a temporally and/or spatially coordinated manner in inflammatory tissues. Human guanylate binding protein-1 (hGBP-1) is a member of the large GTPase protein family. New results demonstrate that hGBP-1 is a specific marker of IC-activated EC that allows to differentiate the IC- and AGF-activated phenotype of EC at the single cell level, both in vitro and in vivo. In addition, hGBP-1 is the key mediator of the inhibitory effects of IC on EC proliferation and invasiveness. Both the expression pattern of hGBP-1 and its activity in EC supported the hypothesis that IC- and AGF-activation induce distinct adversely related phenotypes in EC. In future, hGBP-1 may be used as a marker to monitor the IC-induced phenotype of EC in inflammation and may also be exploited as a target to modulate EC activity in inflammatory diseases and tumor angiogenesis.

Manassantin a and b isolated fromSaururus chinensis inhibit TNF-α-induced Cell adhesion molecule expression of human umbilical vein endothelial cells

Leukocyte adhesion to the vascular endothelium is a critical initiating step in inflammation and atherosclerosis. We have herein studied the effect of manassantin A (1) and B (2), dineolignans, on interaction of THP-1 monocytic cells and human umbilical vein endothelial cells (HUVEC) and expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin in HUVEC. When HUVEC were pretreated with 1 and 2 followed by stimulation with TNF-alpha, adhesion of THP-1 cells to HUVEC decreased in dose-dependent manner with IC50 values of 5 ng/mL and 7 ng/mL, respectively, without cytotoxicity. Also, 1 and 2 inhibited TNF-alpha-induced up-regulation of ICAM-1, VCAM-1 and E-selectin. The present findings suggest that 1 and 2 prevent monocyte adhesion to HUVEC through the inhibition of ICAM-1, VCAM-1 and E-selectin expression stimulated by TNF-alpha, and may imply their usefulness for the prevention of atherosclerosis relevant to endothelial activation.

Chronic ethanol enhances ectodomain shedding in T cells and monocytes

BACKGROUND

Chronic ethanol (EtOH) has been shown to augment tumor necrosis factor (TNF)-alpha production, and this has been associated with EtOH-induced liver injury. We have recently described a chronic in vitro cell culture model where chronic ethanol exposure results in significantly augmented TNF production in Mono Mac 6 cells, a human monocytic cell line. This enhanced TNF production was redox regulated and associated with increased levels of TNF messenger RNA (mRNA) as well as increased processing of TNF by TNF converting enzyme (TACE), the enzymatic activity of which is regulated by the cellular redox state. We hypothesized that chronic ethanol through oxidative stress activates TACE-mediated ectodomain shedding of the preformed substrates p75 and p55 TNF receptors in Mono Mac 6 cells and L-selectin in Jurkat T cells.

METHODS

Mono Mac 6 or Jurkat T cells were treated with EtOH (0, 50, or 100 mM) for 4 to 6 days. Shedding of p75 and p55 TNF receptors (Mono Mac 6 cells) or L-selectin (Jurkat T cells) was induced by stimulation with lipopolysaccharide and phorbol myristate acetate for Mono Mac 6 cells and PMA alone for Jurkat T cells. Shedding was assessed by enzyme-linked immunosorbent assay for shed molecules in the cell supernatant as well as the cell-associated proteins recovered from cell pellets. Steady-state mRNA levels for p75 TNF receptor and L-selectin were determined by ribonuclease protection assay. Cell surface L-selectin and TACE were measured by flow cytometry, and cell associated p55 and p75 TNF receptors were measured by enzyme-linked immunosorbent assay.

RESULTS

Chronic EtOH exposure for 6 days resulted in a significant dose-dependent increase in shedding of p75 and p55 TNF receptors from Mono Mac 6 cells and L-selectin from Jurkat T-cells. The enhanced shedding was correlated with an alcohol-induced increase in mRNA levels and cell surface protein levels for these TACE substrates. Although chronic EtOH exposure increased the total amount of p75 and p55 TNF receptor and L-selectin shed into the media, the efficiency of shedding was suppressed by EtOH. In the case of Mono Mac 6 cells, the EtOH exposure increased superoxide production. Inhibition of nicotinamide adenine dinucleotide phosphate (reduced form) oxidase and hydrogen peroxide partially prevented the increased production of p75 TNF receptor in these cells.

CONCLUSIONS

These results suggest that chronic EtOH up-regulates p75 and p55 TNF receptors on monocytes and L-selectin on T-cells. However, the TACE-mediated shedding efficiency of these substrates may be inhibited in the presence of EtOH. These results may have implications in monocyte signaling and T-cell trafficking, which may, in part, contribute to immune dysregulation associated with chronic ethanol.

Effective treatments for insulin resistance: trim the fat and douse the fire

Currently, only limited treatments are available for insulin resistance, a major cause of type 2 diabetes (T2D) and the metabolic syndrome. Combined innovative pharmaceutical and non-pharmaceutical strategies are needed. Obesity, a major cause of insulin resistance in T2D, can be treated relatively safely with modern bariatric surgery. Exercise training to increase VO(2max) is an important non-pharmaceutical approach to decrease insulin resistance. The thiazolidinediones are useful in treating insulin resistance, but newer agents with broader specificity might be more efficacious without deleterious side effects. Recently oxidative stress has been implicated in insulin resistance. One antioxidant that is safe and appears effective is alpha-lipoic acid. Thus, combinations of surgery, exercise training, insulin sensitizers and antioxidants will probably constitute future insulin resistance management.

? lipoic acid inhibits human T-cell migration: Implications for multiple sclerosis

We have demonstrated previously the ability of the antioxidant alpha lipoic acid (ALA) to suppress and treat a model of multiple sclerosis (MS), relapsing experimental autoimmune encephalomyelitis (EAE). We describe the effects of ALA and its reduced form, dihydrolipoic acid (DHLA), on the transmigration of human Jurkat T cells across a fibronectin barrier in a transwell system. ALA and DHLA inhibited migration of Jurkat cells in a dose-dependent fashion by 16-75%. ALA and DHLA reduced matrix metalloproteinase-9 (MMP-9) activity by 18-90% in Jurkat cell supernatants. GM6001, a synthetic inhibitor of MMP, reduced Jurkat cell migration, but not as effectively as ALA and DHLA did. Both ALA and DHLA downmodulated the surface expression of the alpha4beta1 integrin (very late activation-4 antigen; VLA-4), which binds fibronectin and its endothelial cell ligand vascular cell adhesion molecule-1 (VCAM-1). Moreover, ALA, but not DHLA, reduced MMP-9-specific mRNA and extracellular MMP-9 from Jurkat cells and their culture supernatants as detected by relative reverse transcriptase-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA), respectively. ALA and DHLA inhibited Jurkat cell migration and have different mechanisms for inhibiting MMP-9 activity. These data, coupled with its ability to treat relapsing EAE, suggest that ALA warrants investigation as a therapy for MS.

Analysis of proteome and transcriptome of tumor necrosis factor ? stimulated vascular smooth muscle cells with or without alpha lipoic acid

Vascular smooth muscle cells (VSMCs) play an important role in the development and progression of atherosclerosis. Tumor necrosis factor alpha (TNFalpha), a cytokine secreted by VSMCs and macrophages in atherosclerotic lesions, regulates a variety of cellular functions of inflammatory cells and VSMCs by promoting cell growth and motility, which are critical for the initiation and progression of vascularlesions. Alpha lipoic acid (ALA), a well known antioxidant, acts as a pyruvate dehydrogenase cofactor in mitochondrial metabolism. Recently, we reported that ALA has many beneficial effects on vascular cells in atherosclerosis. The aim of the current study was to examine VSMCs, treated for 24 hours with TNFalpha (10 ng/mL) in the presence or absence of ALA (2 mM), for differential protein and genes expression using two-dimensional gel electrophoresis (2-DE) and DNA microarray analysis, respectively. Using 2-DE, we identified proteins whose expression changed by at least 2.5-fold after TNFalpha stimulation. Proteins up-regulated by TNFalpha that were subsequently down-regulated in the presence of ALA were identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry as plasminogen activator inhibitor-2, fetal liver LKB-interacting protein, osteoblast-specific factor 2, glucosidase II, cyclin-dependent kinase 3, endoplasmin precursor and glutathione synthetase. TNFalpha down-regulated proteins that were up-regulated in the presence of ALA were keratin 19, eukaryotic translation elongation factor and Rho GDP dissociation inhibitor alpha. Gene expression analysis using DNA microarray tools confirmed the up-regulation or down-regulation of some, but not all, of the proteins observed in ALA challenged, TNFalpha-treated cells. This data should provide valuable information about the underlying mechanisms of atherosclerosis.

Antioxidative treatment reverses imbalances of nitric oxide synthase isoform expression and attenuates tissue-cGMP activation in diabetic rats

Oxidative stress and impaired bioactivity of vascular nitric oxide (NO) play an important role in the pathogenesis of macro- as well as microangiopathic complications in diabetes mellitus. To determine the cause of this impaired bioactivity, we tested the effect of long-term hyperglycemia and antioxidative treatment on tissue-specific endothelial (e)NOS- and inducible (i)NOS-expression and the main target of NO action, cGMP, in diabetic rats. After 4 weeks of hyperglycemia, eNOS-mRNA expression was significantly down-regulated in all tissues tested. In contrast, iNOS-mRNA was significantly up-regulated and tissue generation of cGMP significantly increased. Treatment with alpha-lipoicacid reversed changes of NOS-isoform expression as well as cGMP-concentration without changing blood glucose levels. In addition, oxidative stress significantly decreased in diabetic rats treated with alpha-lipoicacid. Together, diabetes regulates NOS-isoforms differentially by down-regulating eNOS and up-regulating iNOS. In addition, our data suggest that the cause of impaired endothelial vasodilatation in experimental diabetes is not degradation or inactivation of NO. On the contrary, these results support the concept of decreased reactivity of the vascular smooth muscle to NO or increased NO activity as a possible vascular damaging agent, e.g., by inducing apoptosis in vascular cells. Furthermore, our data show that antioxidative treatment is capable of reversing changes in the NO-cGMP system and may therefore be an important therapeutic option for preventing vascular damage in diabetes mellitus.

Soluble LDL-R are formed by cell surface cleavage in response to phorbol esters

A 140-kDa soluble form of the low density lipoprotein (LDL) receptor has been isolated from the culture medium of HepG2 cells and a number of other cell types. It is produced from the 160-kDa mature LDL receptor by a proteolytic cleavage, which is stimulated in the presence of 4beta-phorbol 12-myristate 13-acetate (PMA), leading to the release of a soluble fragment that constitutes the bulk of the extracellular domain of the LDL receptor. By labeling HepG2 cells with [35S]methionine and chasing in the presence of PMA, we demonstrated that up to 20% of LDL-receptors were released into the medium in a 2-h period. Simultaneously, the level of labeled cellular receptors was reduced by 30% in those cells treated with PMA compared to untreated cells, as was the total number of cell surface LDL-receptors assayed by the binding of 125I-labeled antibody to whole cells. To determine if endocytosis was required for cleavage, internalization-defective LDL-receptors were created by mutagenesis or deletion of the NPXY internalization signal, transfected into Chinese hamster ovary cells, and assayed for cleavage in the presence and absence of PMA. Cleavage was significantly greater in the case of the mutant receptors than for wild-type receptors, both in the absence and presence of PMA. Similar results were seen in human skin fibroblasts homozygous for each of the internalization-defective LDL receptor phenotypes. LDL receptor cleavage was inhibited by the hydoxamate-based inhibitor TAPI, indicating the resemblance of the LDL receptor cleavage mechanism to that of other surface released membrane proteins.

Palmitate, but not unsaturated fatty acids, induces the expression of interleukin-6 in human myotubes through proteasome-dependent activation of nuclear factor-kappaB

Circulating interleukin-6 (IL-6), insulin, and free fatty acid (FFA) concentrations are associated with impaired insulin action in obese and type 2 diabetic individuals. However, a causal relationship between elevated plasma FFAs and IL-6 has not been shown. Because skeletal muscle represents a major target of impaired insulin action, we studied whether FFAs may affect IL-6 expression in human myotubes. We demonstrate that specifically saturated FFAs, e.g. palmitate (0.25 mm), induce IL-6 mRNA expression and protein secretion by a proteasome-dependent mechanism that leads to a rapid and chronic activation of nuclear factor-kappaB. Insulin, high glucose concentrations, or unsaturated FFAs did not activate IL-6 expression. In fact, the unsaturated FFA linoleate inhibited palmitate-induced IL-6 production. Because inhibition of palmitate metabolism by the acyl-CoA synthetase inhibitor triacsin C did not abolish IL-6 expression, it appears that the palmitate molecule per se exerts the observed effects. Furthermore, we show that in human myotubes, IL-6 activates the phosphorylation of signal transducer and activator of transcription 3 in concentrations similar to hepatocytes. However, no inhibitory effect of IL-6 on insulin action, determined as phosphatidylinositol 3-kinase association with insulin receptor substrate-1, Akt phosphorylation, and glycogen synthesis, was detected. We conclude that IL-6 expression may be modulated by the composition of circulating FFA, e.g. by diet, and that skeletal muscle cells could be target cells for IL-6.

Advanced glycation end-products increase monocyte adhesion to retinal endothelial cells through vascular endothelial growth factor-induced ICAM-1 expression: inhibitory effect of antioxidants

Accumulating evidence indicates a role for advanced glycation end-products (AGEs) in the development of diabetic retinopathy. In the present study, we examined the in vitro effect of AGEs on human monocyte adhesion to bovine retinal endothelial cells (BRECs) and the molecular mechanisms involved in this effect. Treatment of cultured BRECs with AGEs led to a significant increase in monocyte adhesion and intercellular cell adhesion molecule-1 (ICAM-1) expression. These effects were inhibited by antioxidants including gliclazide and vitamins C and E. On the basis of the stimulatory effect of AGEs on vascular endothelial growth factor (VEGF) secretion by retinal endothelial cells, the role of this growth factor as mediator of AGE-induced monocyte adhesion to BRECs was next investigated. Incubation of BRECs with VEGF increased monocyte adhesion to these cells and enhanced ICAM-1 expression. Treatment of BRECs with an anti-VEGF antibody abrogated AGE-induced monocyte adhesion and ICAM-1 expression. Finally, incubation of BRECs with protein kinase C (PKC) and nuclear factor (NF)-kappaB inhibitors suppressed monocyte adhesion and ICAM-1 expression elicited by AGEs and VEGF. Taken together, these data indicate that AGEs increase monocyte adhesion to BRECs and that this effect is mediated through VEGF-induced ICAM-1 expression. They also demonstrate that this effect is oxidative stress-sensitive and involves PKC and NF-kappaB-dependent signaling pathways.

α-Lipoic acid is effective in prevention and treatment of experimental autoimmune encephalomyelitis

Alpha-lipoic acid (alpha-LA) is a neuroprotective metabolic antioxidant that has been shown to cross the blood brain barrier. We tested whether alpha-LA is capable to prevent MOG35-55-induced experimental autoimmune encephalomyelitis (EAE), an established model of multiple sclerosis (MS). Daily oral administration of alpha-LA, starting at the time of immunization, significantly prevented EAE progression as compared to control mice. This was associated with a reduction of CNS infiltrating T cells and macrophages as well as decreased demyelination. We then tested alpha-LA in a therapeutic protocol aimed at suppressing EAE after its onset. Intraperitoneal (i.p.), but not oral, administration of alpha-LA significantly prevented disease progression when compared to vehicle-treated controls. Similarly, we observed significant reduction of demyelination and inflammatory infiltration. This clinical effect was not due to an impairment of MOG35-55 recognition by encephalitogenic T cells. In contrast, MOG-specific T cells showed a decreased production of IFNgamma and IL-4, suggesting an immunosuppressive activity on both Th1 and Th2 cytokines. In addition, alpha-LA inhibited the proteolytic activity of MMP2 and MMP9 only at very high doses. Our data indicate that alpha-LA can effectively interfere with the autoimmune reaction associated with EAE through mechanisms other than its antioxidant activity and supports further studies on the use of alpha-LA as a potential therapy for MS.

Effect of R(+)alpha-lipoic acid on pyruvate metabolism and fatty acid oxidation in rat hepatocytes

R-(+)-alpha-lipoic acid (R-LA) is the naturally occurring enantiomer of LA. It is a strong antioxidant and cofactor of key metabolic enzyme complexes catalyzing the decarboxylation of alpha-keto acids. Racemic LA (rac-LA) has shown promise in treating diabetic polyneuropathy, and some studies suggest that it improves glucose homeostasis in patients with type 2 diabetes. We examined the effects of R-LA on pyruvate metabolism and free fatty acid (FFA) oxidation in primary cultured hepatocytes isolated from 24-hour fasted rats. After overnight culture in serum-free medium, cells were pre-exposed to R-LA for 3 hours before assays. R-LA (25 to 200 micromol/L) significantly increased pyruvate oxidation ( approximately 2-fold at the highest dose tested) measured as (14)CO(2) production from [1-(14)C]pyruvate by the cells over 1 hour post-treatment. These effects correlated with proportional, significant increases in the activation state of the pyruvate dehydrogenase (PDH) complex. R-LA treatment inhibited glucose production from pyruvate by approximately 50% at 50 micromol/L R-LA and approximately 90% at 200 micromol/L. Palmitate oxidation was measured in hepatocytes cultured in the presence of albumin and physiological (0.1 mmol/L) or high (1.5 mmol/L) concentrations of FFA. The latter markedly enhanced FFA oxidation. R-LA treatment significantly inhibited FFA oxidation in both media, but was more effective in high FFA, where it reduced FFA oxidation by 48% to 82% at 25 to 200 micromol/L, respectively. Identical doses of R-LA did not affect FFA oxidation by L6 myotubes (a cell culture model for skeletal muscle) in either high or low FFA medium, but enhanced pyruvate oxidation. In conclusion, 3-hour exposure of primary cultured rat hepatocytes to R-LA at therapeutically relevant concentrations increased pyruvate oxidation, apparently by activation of the PDH complex, and decreased gluconeogenesis and FFA oxidation. These features may prove useful in the control of type 2 diabetes.

Activation of tyrosine kinases by reactive oxygen species in vascular smooth muscle cells: significance and involvement of EGF receptor transactivation by angiotensin II

Enhanced production of reactive oxygen species (ROS) such as H(2)O(2) and a failure in ROS removal by scavenging systems are hallmarks of several cardiovascular diseases such as atherosclerosis and hypertension. ROS act as second messengers that play a prominent role in intracellular signaling and cellular function. In vascular smooth muscle cells (VSMCs), a vascular pathogen, angiotensin II, appears to initiate growth-promoting signal transduction through ROS-sensitive tyrosine kinases. However, the precise mechanisms by which tyrosine kinases are activated by ROS remain unclear. In this review, the current knowledge that suggests how certain tyrosine kinases are activated by ROS, along with their functional significance in VSMCs, will be discussed. Recent findings suggest that transactivation of the epidermal growth factor receptor by ROS requires metalloprotease-dependent heparin-binding epidermal growth factor-like growth factor production, whereas other ROS-sensitive tyrosine kinases such as PYK2, JAK2, and platelet-derived growth factor receptor require activation of protein kinase C-delta. Each of these ROS-sensitive kinases could mediate specific signaling critical for pathophysiological responses. Detailed analysis of the mechanism of cross-talk and the downstream function of these various tyrosine kinases will yield new therapeutic interventions for cardiovascular disease.

An alpha-lipoic acid–vitamin E mixture reduces post-embolism lipid peroxidation, cerebral infarction, and neurological deficit in rats

Oxidative stress increases delayed neuronal death in the brain following ischemia. As a consequence, many attempts to reduce the damage resulting from cerebral ischemia under more highly oxidized conditions have focused on treatments aimed at maintaining the redox equilibrium of the local environment. This study demonstrates the synergistic effects of combining treatments with alpha-lipoic acid (LA) and vitamin E (VE) as an efficient measure to reduce the damage caused by cerebral ischemia. Two oral therapeutic protocols were examined: intensive treatment (100 mg/kg LA and 140 mg/kg VE for 7 days after ischemia) and prophylactic treatment (20 mg/kg LA and 50 mg/kg VE from 30 days before infarction up to the day of sacrifice). The prophylactic treatment reduced serum lipid peroxidation, and diminished brain infarct volume by approximately 50%. Furthermore, prophylactically treated rats showed a reduction in post-ischemia neurological scores. No significant differences were found in the intensively treated group. Our data indicate that pre-ischemia administration of the LA-VE antioxidant mixture reduced the volume of brain damaged and the functional consequences of embolic infarction. These findings suggest that prophylaxis with an LA-VE mixture may be valuable in reducing cerebral damage levels in patients with a high risk of stroke.

Ascorbic acid blocks the growth inhibitory effect of tumor necrosis factor-alpha on endothelial cells

Impaired endothelial cell proliferation has been proposed to be an early, critical defect contributing to the development of atherosclerosis. Recent studies show that high plasma tumor necrosis factor (TNF)-alpha levels and low serum ascorbic acid (AA) levels correlate with atherosclerosis severity. Additionally, AA has been reported to have potential beneficial effects in preventing atherosclerosis. Based on these studies, we investigated the role of AA (< or =1mM) on TNF-alpha-mediated vascular endothelial cell growth inhibition in vitro. In accordance with previous reports, we found that TNF-alpha alone inhibited endothelial cell proliferation. Further studies revealed that AA alone enhanced endothelial cell proliferation and that AA blocked endothelial cell growth inhibition induced by TNF-alpha. By contrast, we observed no effect of AA on endothelial cell activation or nuclear entry of nuclear factor-kappaB in response to TNF-alpha. The protective effect of AA on endothelial cell proliferation was not simply the result of its antioxidant activity but did correlate with collagen IV expression by endothelial cells. AA pre-treatment of proliferating endothelial cells promoted retinoblastoma protein (Rb) phosphorylation and decreased p53 levels when compared to untreated cells. Furthermore, the addition of AA to TNF-alpha-treated proliferating endothelial cells blocked both the inhibition of retinoblastoma protein phosphorylation and enhanced p53 expression induced by TNF-alpha. Consistent with these results, we found that AA protects endothelial cells against TNF-alpha-induced apoptosis. These studies highlight the potential therapeutic role of AA in promoting endothelial cell proliferation during inflammatory conditions, such as atherosclerosis and cardiovascular disease.

Modulation of extracellular homocysteine concentration in human cell lines

BACKGROUND

Despite the growing evidence that plasma homocysteine is a cardiovascular risk factor, the mechanism behind the vascular injuries is still unknown. Information about the metabolism of homocysteine is, therefore, essential for an understanding of its role in atherogenesis, thereby enabling a modulation of that risk.

METHODS

In the present study, we have examined the modulation of extracellular homocysteine in HeLa and hepatoma cell cultures in relation to a changed extracellular thiol redox status and in the presence of specific inhibitors of amino acid transporters.

RESULTS

The findings in the present study show that a changed thiol redox status by copper ions, copper chelator or the monothiol, N-acetylcysteine (NAC), affects extracellular homocysteine in the same way in hepatoma cell cultures, but not to the same extent as observed in HeLa cell cultures. However, the dithiols, dithiothreitol (DTT) and alpha-lipoic acid (LA), which lowered extracellular homocysteine concentration in HeLa cell cultures, increased the extracellular total homocysteine concentration in hepatoma cell cultures, probably mainly as a result of increased release of homocysteine extracellularly. Studies with specific inhibitors of amino acid transporters in HeLa cell cultures showed that homocysteine uptake occurred mainly by system A and glutamate transporters. Hepatoma cells seemed to have a much smaller uptake capacity of homocysteine compared to HeLa cells.

CONCLUSION

The lack of uptake capacity of homocysteine in hepatoma cells indicates that hepatocytes only play a small role in the elimination of homocysteine from circulation. Intracellular metabolism, cellular export and the complex pattern of homocysteine uptake in different cells are important to examine further in order to possibly be able to lower plasma homocysteine levels.

Olive oil and red wine antioxidant polyphenols inhibit endothelial activation: antiatherogenic properties of Mediterranean diet phytochemicals

OBJECTIVE

Epidemiology suggests that Mediterranean diets are associated with reduced risk of cardiovascular disease. Because monocyte adhesion to the endothelium is crucial in early atherogenesis, we evaluated whether typical olive oil and red wine polyphenols affect endothelial-leukocyte adhesion molecule expression and monocyte adhesion.

METHODS AND RESULTS

Phytochemicals in olive oil and red wine, including oleuropein, hydroxytyrosol, tyrosol, elenolic acid, and resveratrol, with or without antioxidant activity, were incubated with human umbilical vein endothelial cells for 30 minutes, followed by co-incubation with bacterial lipopolysaccharide or cytokines to trigger adhesion molecule expression. At nutritionally relevant concentrations, only oleuropein, hydroxytyrosol, and resveratrol, possessing a marked antioxidant activity, reduced monocytoid cell adhesion to stimulated endothelium, as well as vascular cell adhesion molecule-1 (VCAM-1) mRNA and protein by Northern analysis and cell surface enzyme immunoassay. Reporter gene assays with deletional VCAM-1 promoter constructs indicated the relevance of nuclear factor-kappaB, activator protein-1, and possibly GATA binding sites in mediating VCAM-1 transcriptional inhibition. The involvement of nuclear factor-kappaB and activator protein-1 was finally demonstrated at electrophoretic mobility shift assays.

CONCLUSIONS

Olive oil and red wine antioxidant polyphenols at nutritionally relevant concentrations transcriptionally inhibit endothelial adhesion molecule expression, thus partially explaining atheroprotection from Mediterranean diets.

Application of peptides containing the cleavage sequence of pro-TNFalpha in assessing TACE activity of whole cells

Tumor necrosis factor-alpha (TNFalpha) is presumably shed from cell membranes by TNFalpha-cleaving enzyme (TACE). The peptides SPLAQAVRSSSR and Dabcyl-LAQAVRSSSR-Edans, each encompassing the cleavage sequence of pro-TNFalpha recognized by TACE, were applied to intact umbilical vein endothelium (HUVEC), peripheral blood leukocytes (PBL) and the mast cell line HMC-1, which express TACE, to homogenates of rat heart tissue and to membrane and cytoplasmic extracts of PBL. Formation of SPLAQA (specific cleavage) was determined by HPLC, while cleavage (specific plus non-specific) of Dabcyl-TNFalpha-Edans was followed over time by measuring fluorescence. Participation of TACE was assessed from inhibition due to the drug TAPI-2. Incubation with recombinant human TACE gave specific cleavage, fully inhibitable by TAPI-2 (IC50 < 0.1 microM). HUVEC rapidly degraded TNFalpha-peptide, but in a non-specific manner (no SPLAQA detectable) and 50 microM TAPI-2 was without effect. Fluorescence was evoked when Dabcyl-LAQAVRSSSR-Edans was incubated with HMC-1 or PBL and also with cytoplasmic and membrane fractions of lysed PBL, but in no case was there significant inhibition by TAPI-2. However, marginal (10%) inhibition of fluorescence by 50 microM TAPI-2 was observed with homogenized heart tissue. This contained TACE, about 75% of which was without the inhibitory cysteine switch (Western blot). In conclusion, simple peptide analogs of pro-TNFalpha cannot be employed as substrates for measuring membrane TACE activity, largely due to extensive non-specific proteolytic cleavage by whole cells and cell extracts.

Oxidative stress and stress-activated signaling pathways: a unifying hypothesis of type 2 diabetes

In both type 1 and type 2 diabetes, the late diabetic complications in nerve, vascular endothelium, and kidney arise from chronic elevations of glucose and possibly other metabolites including free fatty acids (FFA). Recent evidence suggests that common stress-activated signaling pathways such as nuclear factor-kappaB, p38 MAPK, and NH2-terminal Jun kinases/stress-activated protein kinases underlie the development of these late diabetic complications. In addition, in type 2 diabetes, there is evidence that the activation of these same stress pathways by glucose and possibly FFA leads to both insulin resistance and impaired insulin secretion. Thus, we propose a unifying hypothesis whereby hyperglycemia and FFA-induced activation of the nuclear factor-kappaB, p38 MAPK, and NH2-terminal Jun kinases/stress-activated protein kinases stress pathways, along with the activation of the advanced glycosylation end-products/receptor for advanced glycosylation end-products, protein kinase C, and sorbitol stress pathways, plays a key role in causing late complications in type 1 and type 2 diabetes, along with insulin resistance and impaired insulin secretion in type 2 diabetes. Studies with antioxidants such as vitamin E, alpha-lipoic acid, and N-acetylcysteine suggest that new strategies may become available to treat these conditions.

Ascorbate inhibits iNOS expression in endotoxin- and IFN gamma-stimulated rat skeletal muscle endothelial cells

Lipopolysaccharide endotoxin and interferon-gamma induced inducible nitric oxide synthase (iNOS) protein expression and nitrite/nitrate formation in microvascular endothelial cell cultures (ECs) derived from rat skeletal muscle. Pretreatment of ECs with ascorbate accumulated a large amount of ascorbate inside the cells and consequently decreased both intracellular oxidant level and iNOS induction. These effects of ascorbate were abolished in the presence of exogenous superoxide generated by xanthine oxidase/xanthine plus catalase but were not altered when N-nitro-L-arginine methyl ester was applied to inhibit nitric oxide synthesis. Ascorbate also attenuated the activation of transcription factor IRF-1 but not NF kappa B. These results indicate that ascorbate inhibits iNOS expression in ECs by an antioxidant mechanism independent of both NF kappa B activation and the reported negative feedback effect of nitric oxide.