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Biomedical subjects

Helmut Sies

Publications and source records attributed to Helmut Sies.

At least 37 records · Page 2Linked to original sources
PubMed2005

Epicatechin protects endothelial cells against oxidized LDL and maintains NO synthase.

Intake of flavanol-rich food or beverages was previously shown to ameliorate endothelial function and to enhance bioactivity of nitric oxide with individuals at risk for cardiovascular disease. Here, we examined whether the major dietary flavanol, (-)-epicatechin, counteracts the action of oxidized LDL on endothelial cells, an action considered pivotal for endothelial dysfunction in the pathogenesis of atherosclerosis. Oxidation by myeloperoxidase plus nitrite rendered human LDL cytotoxic towards endothelial cells, more so than oxidation by Cu2+. Oxidized LDL also caused a marked loss of endothelial NO synthase protein which did not occur in the presence of a proteasome inhibitor, lactacystin. Both actions of oxidized LDL, which were not evoked by native LDL, were effectively counteracted by (-)-epicatechin. We conclude that dietary flavanols contribute to protection of the integrity of endothelial cells not only by scavenging free radicals but also by maintaining endothelial NO synthase.

Antioxidants↗
PubMed2005

Arginase-1 overexpression induces cationic amino acid transporter-1 in psoriasis.

Regulated uptake of extracellular l-arginine by cationic amino acid transporters (CATs) is required for inducible nitric oxide synthase and arginase activity. Both enzymes were recently recognized as important in the pathophysiology of psoriasis because of their contribution to epidermal hyperproliferation. We here characterize the expression pattern of CATs in psoriatic skin compared to healthy skin. CAT-1 mRNA expression was strongly upregulated in lesional and nonlesional areas of psoriatic skin compared to healthy skin, whereas expression of CAT-2A and the inducible isoform CAT-2B was unaltered in psoriatic skin. Furthermore, we tested the hypothesis that arginase-1 overexpression regulates CAT expression via intracellular l-arginine concentration. In in vitro experiments with arginase-1 overexpressing HaCaT cells, CAT-1 mRNA expression was increased. Likewise, this occurs in l-arginine-starved HaCaT cells. Both CAT-2 isoforms were not affected. Arginase-1 overexpression limits the synthesis of NO at physiological, but not supraphysiological, l-arginine levels. Plasma l-arginine concentration was diminished in psoriasis patients and the arginase product l-ornithine was significantly increased compared to healthy controls. In summary, arginase-1 overexpression leads to upregulated CAT-1 expression in psoriatic skin, which is due to lowered intracellular l-arginine levels and limits NO synthesis at physiological l-arginine concentrations.

Arginase↗
PubMed2005

Quinone-induced Cdc25A inhibition causes ERK-dependent connexin phosphorylation.

Gap junctional intercellular communication (GJC) varies during progression of the cell cycle. We propose here that Cdc25A, a dual specificity phosphatase crucial for cell cycle progression, is linked to connexin (Cx) phosphorylation and the modulation of GJC. Inhibition of Cdc25 phosphatases in rat liver epithelial cells employing a 1,4-naphthoquinone-based inhibitor, NSC95397, induced cell cycle arrest, tyrosine phosphorylation of the epidermal growth factor receptor (EGFR), and activation of extracellular signal-regulated kinases ERK-1 and -2. ERK activation was blocked by specific inhibitors of MAPK/ERK kinases 1/2 or of the EGFR tyrosine kinase. An EGFR-dephosphorylation assay suggested that Cdc25A interacts with the EGFR, with inhibition by NSC95397 resulting in activation of the receptor. As a consequence of ERK activation, Cx43 was phosphorylated, resulting in a downregulation of GJC. Loss of GJC was prevented by inhibition of ERK activation. In summary, cell cycle and GJC are connected via Cdc25A and the EGFR-ERK pathway.

Animals↗
PubMed2005

Loss of the tyrosyl radical in mouse ribonucleotide reductase by (-)-epicatechin.

The flavonoid (-)-epicatechin was previously demonstrated to interfere with tyrosine nitration by peroxynitrite [Biochem. Biophys. Res. Commun. 285 (2001) 782]. This effect was hypothesized to be based upon an interaction of epicatechin with a transiently generated tyrosyl radical. In the present study, using electron paramagnetic resonance, we demonstrate that (-)-epicatechin is capable of destabilizing the tyrosyl radical of the mouse ribonucleotide reductase R2 component. First-order rate constants for the disappearance of tyrosyl radical signals were 1 x 10(-4) and 2 x 10(-4)s(-1)for epicatechin and hydroxyurea, a well-known tyrosyl radical scavenger, respectively. In keeping with scavenging the ribonucleotide reductase tyrosyl radical, cellular production of deoxyribonucleotides and DNA synthesis were impaired by (-)-epicatechin in normal human keratinocytes and in human squamous carcinoma cells.

Animals↗
PubMed2005

Myeloperoxidase-induced lipid peroxidation of LDL in the presence of nitrite. Protection by cocoa flavanols.

Lipid peroxidation (LPO) of low-density lipoprotein (LDL) is believed to be a pivotal process rendering this plasma lipoprotein atherogenic. Several endogenous factors have been proposed to mediate LPO of LDL, among them myeloperoxidase (MPO), which is active in atherosclerotic lesions, and the plasma level of which has been proposed to be a prognostic parameter for cardiac events. Nitrite, a major oxidation product of nitric oxide, is substrate of MPO and a cofactor of MPO-mediated LPO under physiological conditions. Dietary flavonoids including (-)-epicatechin, a major flavan-3-ol in cocoa products, grapes and wine, are substrates of MPO as well as potent inhibitors of LPO in LDL at micromolar concentrations. Moreover, they strongly suppress protein tyrosine nitration of LDL by MPO/nitrite or peroxynitrite. By blunting undesirable MPO-mediated actions of nitrite, presumably via scavenging of the strong prooxidant and nitrating *NO2 radical, dietary flavonoids modulate NO metabolism in a favorable direction and thus counteract endothelial dysfunction. This article gives a survey on recent progress in this field with special reference to own recently published work.

Atherosclerosis↗
PubMed2005

Effects of vitamin C and aspirin in ischemic stroke-related lipid peroxidation: results of the AVASAS (Aspirin Versus Ascorbic acid plus Aspirin in Stroke) Study.

A condition of oxidative stress is known to occur in ischemic stroke, the current therapeutic intervention of which is largely limited to thrombolysis. To assess the effect of vitamin C - in conjunction to aspirin - in ischemic stroke-related lipid peroxidation, we measured plasma levels of ascorbate, of 8,12-isoprostanes F2alpha-VI (8,12-iPF2alpha-VI) and activities and levels of a broad spectrum of antioxidant enzymes and micronutrients in stroke patients randomized to receive, from stroke onset and up to three months, either vitamin C (200 mg/day) plus aspirin (300 mg/day) or only aspirin (300 mg/day). By the end of the first week, patients treated with vitamin C plus aspirin had higher vitamin C levels (p = 0.02) and lower 8,12-iPF2alpha-VI levels (p = 0.01) than patients treated with aspirin alone. The significance was maintained for the increase of vitamin C after three months of therapy (p < 0.01). The clinical functional outcome for both groups of patients similarly ameliorated after three months of treatment. We conclude that vitamin C, at the dose of 200 mg/day and in conjunction with aspirin, significantly decreases ischemic stroke-related lipid peroxidation in humans. Further studies are warranted to clarify whether the use of vitamin C may add clinical long-term beneficial effects in patients with stroke.

Ascorbic Acid↗
PubMed2005

Supplementation with tomato-based products increases lycopene, phytofluene, and phytoene levels in human serum and protects against UV-light-induced erythema.

Carotenoids are suitable photoprotectants, and beta-carotene supplements are used for protection against ultraviolet (UV) light-induced erythema. Protective effects are also observed when carotenoids are provided with the diet. Here, we investigated the photoprotective effects of synthetic lycopene in comparison with a tomato extract (Lyc-o-Mato) and a drink containing solubilized Lyc-o-Mato (Lyc-o-Guard-Drink). With these different sources, the volunteers ingested similar amounts of lycopene (about 10 mg/day). After 12 weeks of supplementation, significant increases in lycopene serum levels and total skin carotenoids were observed in all groups. Significant increases in the serum levels of phytofluene and phytoene occurred in the Lyc-o-Mato and the Lyc-o-Guard-Drink group. At weeks 0, 4, and 12 an erythema was induced with a solar light simulator. Dorsal skin of each subject was irradiated with 1.25 minimal erythemal dose (MED). Reddening of the skin was evaluated before and 24 hours after irradiation by chromametry and expressed as positive a-values (red/green-axis). delta a-values (difference of a-value before irradiation and after 24 hours) were used as an index of erythema intensity. A decrease in the delta a-value from week 0 to week 12, indicating prevention of erythema formation, was observed in all groups. Compared to week 0, the delta a-value at week 12 was 25% lower in the synthetic lycopene group. The protective effect was more pronounced in the Lyc-o-Mato (38%) and Lyc-o-Guard-Drink (48%) groups. In the two latter groups, phytofluene and phytoene may have contributed to protection. Both of these carotenoids exhibit absorption maxima at wavelengths of UV light. Absorption of UV light protects skin from photodamage and might explain the differences observed between groups.

Adult↗
PubMed2005

Dietary habits are major determinants of the plasma antioxidant status in healthy elderly subjects.

Previous studies indicate that regular consumption of a diet rich in fruits and vegetables is associated with a lower risk for age-related diseases. The aim of the present study was to evaluate whether the often-reported age-related decrease of plasma antioxidants in man depends on differences in dietary intake or on other age- and gender-related factors. In this observational case-control study, thirty-nine community-dwelling healthy subjects aged 65 years and older consuming high intakes of fruits and vegetables daily (HI) and forty-eight healthy subjects aged 65 and older consuming low intakes of fruit and vegetables daily (LI) were enrolled. Plasma levels of retinol, tocopherols, carotenoids and malondialdehyde (MDA) as well as content of protein carbonyls in Ig G were measured. Plasma levels of retinol, tocopherols and carotenoids were significantly higher in group HI than in group LI subjects independent of age and gender. MDA levels were inversely correlated with vitamin A and alpha-carotene. Protein carbonyls were inversely correlated with gamma-tocopherol. In the elderly, a higher daily intake of fruits and vegetables is associated with an improved antioxidant status in comparison to subjects consuming diets poor in fruits and vegetables. Modification of nutritional habits among other lifestyle changes should be encouraged to lower prevalence of disease risk factors in later life.

Age Factors↗
PubMed2005

Tumor promoter TPA stimulates MMP-9 secretion from human keratinocytes by activation of superoxide-producing NADPH oxidase.

Matrix metalloproteinase-9 (MMP-9) is involved in physiological tissue remodelling processes as well as in tumor invasion and metastasis. The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) increases MMP-9 secretion from normal human epidermal keratinocytes (NHEK) in vivo and in vitro. Here we show that the flavoprotein inhibitor diphenyleneiodinium (DPI) and the NADPH oxidase inhibitor apocynin block TPA-induced MMP-9 secretion of NHEK in vitro. Furthermore, N-acetyl-L-cysteine and L-cysteine lowered TPA-induced MMP-9 secretion, suggesting an involvement of reactive oxygen species(ROS). TPA exerts its effect on MMP-9 gene expression and secretion via the superoxide-producing enzyme NADPH oxidase: TPA rapidly stimulates generation of superoxide anion as well as gene expression of two cytosolic NADPH oxidase subunits (p47-phox and p67-phox) after 2 h, which is followed by induction of MMP-9 gene expression after 4 h. Taken together, the novel finding herein is the TPA-induced MMP-9 secretion from normal human epidermal keratinocytes through a NADPH oxidase dependent pathway.

Blood Proteins↗
PubMed2005

Cocoa polyphenols and inflammatory mediators.

Cocoa products are sources of flavan-3-ols, which have attracted interest regarding cardiovascular health. This review provides a survey of our research on the effects of cocoa polyphenols on leukotriene and nitric oxide (NO) metabolism and on myeloperoxidase-induced modification of LDL. Because intake of flavonoid-rich chocolate by human subjects was reported to decrease the plasma concentrations of proinflammatory cysteinyl leukotrienes, we assessed whether cocoa polyphenols inhibited human 5-lipoxygenase, the key enzyme of leukotriene synthesis. (-)-Epicatechin and other cocoa flavan-3-ols proved to be inhibitory at the enzyme level. This action may confer antileukotriene action in vivo. In a double-blind crossover study, 20 individuals at risk for cardiovascular diseases received cocoa beverages with high or low contents of flavan-3-ols. NO-dependent, flow-mediated dilation of the brachial artery and concentrations of nitroso compounds in plasma were measured, and it was shown that ingestion of the high-flavanol coca drink but not the low-flavanol cocoa drink significantly increased plasma concentrations of nitroso compounds and flow-mediated dilation of the brachial artery. Therefore, ingested flavonoids may reverse endothelial dysfunction through enhancement of NO bioactivity. Oxidative modification of LDL appears to be crucial for atherogenesis, and one of the mediators is the proinflammatory proatherogenic enzyme myeloperoxidase. Micromolar concentrations of (-)-epicatechin or other flavonoids were found to suppress lipid peroxidation in LDL induced by myeloperoxidase in the presence of physiologically relevant concentrations of nitrite, an NO metabolite. Adverse effects of NO metabolites, such as nitrite and peroxynitrite, were thus attenuated.

Animals↗
PubMed2005

Vitamins E and C are safe across a broad range of intakes.

A robust database shows that dietary supplements of vitamins E and C are safe for the general population. Because these nutrients supply antioxidant and other functions for homeostasis and protection against free radical damage, supplementation has been intensively studied. Because of perceived benefits, many persons consume quantities of vitamins E and C well above the recommended dietary allowances. As safety guidance, tolerable upper intake levels have been established by the Food and Nutrition Board, Institute of Medicine, at 1000 mg for vitamin E and 2000 mg for vitamin C in adults. Many clinical trials with these vitamins have involved subjects with various diseases, and no consistent pattern of adverse effects has occurred at any intake. Numerous studies of vitamin C supplementation have provided no pattern of evidence to support concerns about safety other than occasional gastrointestinal upset or mild diarrhea resulting from the osmotic effects of unabsorbed quantities of vitamin C. Evidence of bleeding effects and other potential adverse effects of high vitamin E intakes in humans is not convincing. Evidence of adverse effects of vitamin C that result from its effects on iron absorption and metabolism has not been confirmed in clinical trials. Thus, we conclude from clinical trial evidence that vitamin E supplements appear safe for most adults in amounts </=1600 IU (1073 mg RRR-alpha-tocopherol or the molar equivalent of its esters) and that vitamin C supplements of </=2000 mg/d are safe for most adults.

Antioxidants↗
PubMed2005

Cocoa-related flavonoids inhibit CFTR-mediated chloride transport across T84 human colon epithelia.

Cocoa beans have historically been used as a treatment for diarrhea, leading us to hypothesize that polyphenols contained in cocoa inhibit intestinal Cl- secretion. In this study, the dose-dependent effects of flavonoid compounds present in cocoa, or molecularly closely related compounds, were tested on forskolin-stimulated cystic fibrosis transmembrane conductance regulator (CFTR)-mediated Cl- secretion across T84 colonic epithelia in Ussing chambers. Addition of cocoa extract or cocoa flavanols to the mucosal side of tissues caused partial inhibition following Michaelis-Menten kinetics and resulted in a rank order of maximum blocker effects as follows: epicatechin > catechin > or = standardized cocoa preparation > or = procyanidin B2. Half-maximal blocker concentrations (Ki) were not substantially different between the tested preparations and were in the range of 100 micromol/L. For comparison, the structurally related flavonoids, quercetin and luteolin, caused a total block of Cl- currents with Ki values similar to the cocoa flavanols tested. Morin and baicalein were less effective blockers. Effects of test compounds on mucosal redox potential did not correlate with blocker activity. These data indicate that cocoa flavanols target intestinal CFTR Cl- transport and may serve as mild inhibitors of cAMP-stimulated Cl- secretion in the intestine.

Cacao↗
PubMed2005

Astaxanthin diminishes gap junctional intercellular communication in primary human fibroblasts.

Astaxanthin is a carotenoid found in plants and algae; it provides the color of marine seafood such as salmon, lobster, or shrimp. Carotenoids are antioxidants and exhibit other biological functions, including effects on gap junctional communication important for homeostasis, growth control, and development of cells. Cancer cells have an impaired gap junctional intercellular communication. The objective of the present study was to determine the effects of astaxanthin and canthaxanthin on gap junctional intercellular communication in vitro. Primary human skin fibroblasts were exposed to carotenoids from 0.001 to 10 micromol/L, and gap junctional communication was measured with a dye transfer assay. After incubation with canthaxanthin for 24 and 72 h, intercellular communication increased, whereas it was strongly diminished by astaxanthin at levels > 0.1 micromol/L. Inhibition was reversed when astaxanthin was withdrawn. Western blot analysis showed that after exposure to canthaxanthin, the amount of the gap junction protein connexin43 was increased. Incubation with astaxanthin led to a change in the phosphorylation pattern of connexin43, shifting from higher to lower phosphorylation states. We suggest that astaxanthin affects channel function by changing the phosphorylation pattern of connexin43.

Anticarcinogenic Agents↗
PubMed2005

Nutritional, dietary and postprandial oxidative stress.

Nutritional, or dietary oxidative stress denotes a disturbance of the redox state resulting from excess oxidative load or from inadequate nutrient supply favoring prooxidant reactions. Low intake or impaired availability of dietary antioxidants including vitamins E and C, carotenoids, polyphenols, and other micronutrients (e.g., selenium) weakens the antioxidant network. Postprandial oxidative stress, as a subform of nutritional oxidative stress, ensues from sustained postprandial hyperlipidemia and/or hyperglycemia and is associated with a higher risk for atherosclerosis, diabetes, and obesity. In Western societies, a significant part of the day is spent in the postprandial state. Unsaturated fatty acids incorporated into LDL and oxidized LDL are an atherogenic factor. Lipid hydroperoxides present in the diet are absorbed, contributing to the prooxidant load. In hyperlipidemic and hyperglycemic subjects, endothelium-dependent vasodilation is impaired in the postprandial state, making postprandial oxidative stress an important factor modulating cardiovascular risk. Postprandial oxidative stress is attenuated when dietary antioxidants are supplied together with a meal rich in oxidized or oxidizable lipids. Ingestion of dietary polyphenols, e.g., from wine, cocoa, or tea, improves endothelial dysfunction and lowers the susceptibility of LDL lipids to oxidation. Polyphenols affect endothelial function not solely as antioxidants but also as modulatory signaling molecules.

Antioxidants↗
PubMed2005

Doxorubicin induces EGF receptor-dependent downregulation of gap junctional intercellular communication in rat liver epithelial cells.

Exposure of rat liver epithelial cells to doxorubicin, an anthraquinone derivative widely employed in cancer chemotherapy, led to a dose-dependent decrease in gap junctional intercellular communication (GJC). Gap junctions are clusters of inter-cellular channels consisting of connexins, the major connexin in the cells used being connexin-43 (Cx43). Doxorubicin-induced loss of GJC was mediated by activation of extracellular signal-regulated kinase (ERK)-1 and ERK-2, as demonstrated using inhibitors of ERK activation. Furthermore, activation of the epidermal growth factor (EGF) receptor by doxorubicin was responsible for ERK activation and the subsequent attenuation of GJC. Inhibition of GJC, however, was not by direct phosphorylation of Cx43 by ERK-1/2, whereas menadione, a 1,4-naphthoquinone derivative that was previously demonstrated to activate the same EGF receptor-dependent pathway as doxorubicin, resulting in downregulation of GJC, caused strong phos-phorylation of Cx43 at serines 279 and 282. Thus, ERK-dependent downregulation of GJC upon exposure to quinones may occur both by direct phosphorylation of Cx43 and in a phosphorylation-independent manner.

Animals↗
PubMed2004

Bioactivity and protective effects of natural carotenoids.

Carotenoids comprise a class of natural fat-soluble pigments which are found in numerous fruits and vegetables. The consumption of a diet rich in carotenoids has been epidemiologically correlated with a lower risk for several diseases. The antioxidant activity of carotenoids and biochemical properties influencing signaling pathways have been discussed as basic mechanisms of prevention. Conflicting data from intervention studies with beta-carotene to prevent cancers and cardiovascular disorders have challenged the concept. However, there is convincing evidence that carotenoids are important components of the antioxidant network. Photooxidative damage is suggested to be involved in the pathobiochemistry of several diseases affecting the skin and the eye, and carotenoids may protect light-exposed tissues. Lutein and zeaxanthin are the predominant carotenoids of the retina and are considered to act as photoprotectants preventing retinal degeneration. The unique distribution, localization and high levels of both carotenoids within the macula lutea as well as their physicochemical properties make them suitable candidates for photoprotection. beta-Carotene is used as an oral sun protectant for the prevention of sunburn and has been shown to be effective either alone or in combination with other carotenoids or antioxidant vitamins. Protective effects are also achieved with a diet rich in lycopene.

Animals↗
PubMed2004

Flavanol-rich cocoa drink lowers plasma F(2)-isoprostane concentrations in humans.

Flavan-3-ols are potent antioxidants in vitro, but convincing evidence for antioxidant action in vivo is lacking. We examined whether an oxidative stress-mediated increase in plasma F(2)-isoprostanes is counteracted by a flavanol-rich cocoa beverage. Twenty volunteers were examined in a comparative randomized double-blind crossover design with respect to ingestion of high-flavanol cocoa drink (HFCD; 187 mg flavan-3-ols/100 ml) vs. low-flavanol cocoa drink (LFCD; 14 mg/100 ml). With 10 individuals, the treatment was combined with strenuous physical exercise. Total (esterified plus nonesterified) F(2)-isoprostanes were analyzed by GC/MS. LFCD caused a slight increase in the mean (+/- SEM) plasma concentrations of F(2)-isoprostanes 2 and 4 h after intake (2.16 +/- 0.19 nM at 4 h vs. 1.76 +/- 0.11 nM at 0 h, n = 10), which may be attributable to postprandial oxidative stress. This increase did not occur with HFCD (1.57 +/- 0.06 nM at 4 h vs. 1.65 +/- 0.10 nM at 0 h, n = 10). The difference in F(2)-isoprostanes 2 and 4 h after intake of HFCD vs. LFCD became statistically significant when the intake was combined with physical exercise (P < 0.01, ANOVA). We conclude that dietary flavanols, using cocoa drink as example, can lower the plasma level of F(2)-isoprostanes, indicators of in vivo lipid peroxidation.

Adult↗