Biomedical subjects

W Siems

Publications and source records attributed to W Siems.

At least 19 recordsLinked to original sources

PubMed2006

Beta-carotene breakdown products enhance genotoxic effects of oxidative stress in primary rat hepatocytes.

Since it has to be expected that individuals exposed to oxidative stress who take supplements of beta-carotene are simultaneously exposed to both beta-carotene cleavage products (CPs) and oxidative stress, and both exposures have been demonstrated to cause genotoxic effects in primary rat hepatocytes, cyto- and genotoxic effects on primary rat hepatocytes after supplementation of the medium with increasing concentrations of a CP mixture during exposure to oxidative stress by treatment with either DMNQ (2,3-dimethoxy-1,4-naphthoquinone) or hypoxia/reoxygenation (Hy/Reox) was investigated. The cytological endpoints analysed were the mitotic indices, the percentages of apoptotic and necrotic cells, the percentages of micronucleated (MN) cells and the number of chromosomal aberrations (CAs) and sister chromatid exchanges (SCE). The results obtained clearly demonstrate that the CP mixture enhances the genotoxic effects of oxidative stress exposure, whereas it had no effect at all on the endpoints of cytotoxicity studied. These results further support the hypothesis that CP might be responsible for the reported carcinogenic response in the beta-CArotene and Retinol Efficacy Trial (CARET) and Alpha-Tocopherol Beta-carotene Cancer prevention (ATBC) chemoprevention trials.

Animals↗

PubMed2005

Inhibition of defective adenylosuccinate lyase by HNE: a neurological disease that may be affected by oxidative stress.

Adenylosuccinate lyase is an enzyme of fumarase superfamily that participates in the purine biosynthetic pathway, catalysing the nonhydrolytic cleavage of succinyl groups from SAICA ribotide and adenylosuccinate. Enzyme defects are associated with a human inherited disease, which arises from single point mutations to the gene and results in mild to severe psychomotor retardation, epilepsy, muscle wasting, and autistic features. Adenylosuccinate lyase activity is lost to a different extent in the patients. Diminished levels of enzyme have been attributed to loss of catalytic activity, protein instability, or environmental factors. P100A/D422Y mutation represents a feasible model for studying the effect of cell milieu on the activity of the impaired enzyme. The defective enzyme is inhibited by micromolar concentrations of trans-4-hydroxy-2-nonenal (HNE), a major product of membrane peroxidation that has been found to accumulate in brain tissues of patients with neurodegenerative disorders. It is suggested that inactivation of defective adenylosuccinate lyase by HNE and other membrane peroxidation products may account, at least in part, for the impairment of neurological functions and recurrent worsening of the symptoms.

Adenylosuccinate Lyase↗

PubMed2005

Inhibition of ion transport ATPases by HNE.

4-Hydroxy-2,3-trans-nonenal (HNE), a major lipid peroxidation product, has been shown to react with specific amino acid residues of proteins and alter their function. In vitro exposure of erythrocyte ghosts and neutrophil membranes to HNE results in the inhibition of ion transport ATPases. Neutrophil membrane Ca2+-ATPase is strongly inhibited by micromolar concentrations of HNE, while HNE is considerably less effective against neutrophil Mg2+-ATPase and the erythrocyte ghost enzymes.

Adenosine Triphosphatases↗

PubMed2005

Cyto- and genotoxic potential of beta-carotene and cleavage products under oxidative stress.

Free radical attack on beta-carotene results in the formation of high amounts of cleavage products with prooxidant activities towards subcellular organelles such as mitochondria, a finding which could provide an explanation for the contradictory results obtained with beta-carotene in clinical efficacy and cancer prevention trials. Since primary hepatocytes proved to be very sensitive indicators for the genotoxic action of suspect mutagens/carcinogens we therefore investigated a beta-carotene cleavage products mixture (CP), apo-8'-beta-carotenal (apo-8') and beta-carotene in the primary rat hepatocyte assay in the presence and absence of oxidative stress provided by hypoxia/reoxygenation (Hy/re). The endpoints tested were: the mitotic indices, the percentages of necrotic and apoptotic cells, micronucleated cells (MN), chromosomal aberrations (CA) and sister chromatid exchanges (SCE). The results obtained indicate a genotoxic potential of both CP and apo-8' already in the concentration range of 100 nM and 1 microM, i.e. at physiologically relevant levels of beta-carotene and beta-carotene breakdown products. In contrast, no significant cytotoxic effects of these substances were observed, nor did beta-carotene induce significant cytotoxic or genotoxic effects at concentrations ranging from 0.01 up to 10 microM. However, when beta-carotene is supplemented during oxidative stress induced by hypoxia/reoxygenation, a dose-dependent increase of CP is observed accompanied by increasing genotoxicity. Furthermore, when beta-carotene cleavage products were supplied during oxidative stress significant additional increases of genotoxic effects were observed, the additional increases indicating an additive effect of both exposures. Summarizing, these results provide strong evidence that beta-carotene breakdown products are responsible for the occurrence of carcinogenic effects found in the Alpha-Tocopherol Beta-carotene-Cancer prevention (ATBC) study and the beta-CArotene and RETinol Efficacy (CARET) Trial.

Animals↗

PubMed2005

Effect of carotenoid oxidation products on neutrophil viability and function.

Human neutrophils are short-lived cells that play important roles in host defense and acute inflammation by releasing hydrolytic and cytotoxic proteins and reactive oxygen derivatives. Apoptosis, a physiological mechanism for cell death, regulates both production and survival of neutrophils, representing a basic biological mechanism for this type of cells. Carotenoids may react with toxic oxygen metabolites released by neutrophils to form a multitude of carotenoid cleavage products that exert, in turn, relevant prooxidative biological effects. Recent data suggest that carotenoid oxidation products may affect neutrophil viability and function by exerting proapoptotic activity and interfering with superoxide production by activated cells. The prooxidant and proapoptotic activities of carotenoid oxidation products could account, at least in some cases, for the procancerogenic properties of carotenoid rich diet.

Apoptosis↗

PubMed2003

Cytotoxic and genotoxic effects of beta-carotene breakdown products on primary rat hepatocytes.

According to Siems and colleagues, free radical attack on beta-carotene results in the formation of high amounts of cleavage products with prooxidant activities towards subcellular organelles such as mitochondria. This finding may be an explanation for the contradictory results obtained with beta-carotene in clinical efficacy and cancer prevention trials. Since primary hepatocytes proved to be very sensitive indicators of the genotoxic action of suspect mutagens/carcinogens we therefore investigated a beta-carotene cleavage products mixture (CP), apo8'- carotenal (apo8') and beta-carotene utilizing primary cultures of rat hepatocytes. The end-points tested were: the mitotic index, the percentage of necrotic and apoptotic cells, micronucleated cells, chromosomal aberrations and sister chromatid exchanges (SCE). Our results indicate a genotoxic potential of both CP and apo8' already at the concentrations 100 nM and 1 microM, i.e. at pathophysiologically relevant levels of beta-carotene and beta-carotene breakdown products. A 3 h treatment with CP induced statistically significant levels of micronuclei at concentrations of 0.1, 1 and 10 microM and chromosomal aberrations at concentrations of 1, 5 and 10 microM. Apo8' induced statistically significant levels of micronuclei at concentrations of 0.1, 1 and 5 microM and chromosomal aberrations at concentrations of 0.1, 1 and 10 microM. Statistically significant increases in SCE induction were only observed at a concentration of 10 microM CP and apo8'. In contrast, no significant cytotoxic effects of these substances were observed. Since beta-carotene induced neither significant cytotoxic nor genotoxic effects at concentrations ranging from 0.01 up to 10 microM, these observations indicate that most likely beta-carotene breakdown products are responsible for the occurrence of carcinogenic effects found in the Alpha-Tocopherol Beta-Carotene Cancer Prevention (ATBC) Study and the Beta-CArotene and RETinol Efficacy Trial (CARET).

Animals↗

PubMed2003

High sensitivity of plasma membrane ion transport ATPases from human neutrophils towards 4-hydroxy-2,3-trans-nonenal.

Lipid peroxidation results in release of 4-hydroxy-2,3-trans-nonenal (HNE), which is known to conjugate to specific amino acids of proteins and may alter their function. The effect of HNE on the activities of Na(+)/K(+)-ATPase, Mg(2+)-ATPase, Ca(2+)-ATPase, and calmodulin-stimulated Ca(2+)-ATPase has been studied both in erythrocyte ghosts and in neutrophil membrane preparations. Neutrophil Ca(2+)-ATPase was strongly inhibited by micromolar concentrations of HNE (IC(50) = 12 microM), that means in the range of pathophysiologically relevant HNE levels. The IC(50) value for neutrophil Na(+)/K(+)-ATPase was about 40 microM. HNE was considerably less effective against neutrophil Mg(2+)-ATPase and the erythrocyte ghost enzymes (IC(50) values range from 91 to 240 microM). The data suggest that HNE may play a specific role in the regulation of neutrophil calcium homeostasis in response to oxidative stress.

Adenosine Triphosphatases↗

PubMed2003

Oxidative stress in cardio renal anemia syndrome: correlations and therapeutic possibilities.

Cardiovascular injury has been shown to be the most critical factor affecting quality of life and mortality in patients suffering from chronic renal failure. Oxidative stress has been thought to be an important risk factor for cardiovascular disorders. As oxidative stress parameters with high cardiovascular risk factor 4-hydroxynonenal and other aldehydic lipid peroxidation products, F2-isoprostanes, homocysteine, and cholesterol oxidation products were measured in chronic renal failure patients. 4-Hydroxynonenal and some cholesterol oxidation products correlated well with the degree of renal anemia. F2-isoprostane levels were related to inflammation, whereas homocysteine was increased due to malnutrition. Further, cholesterol oxidation products correlated well with the consumption of lipophilic antioxidants such as alpha-tocopherol. There was an almost linear correlation between the left ventricular mass index and 4-hydroxynonenal. Both parameters furthermore showed an inverse relationship to hemoglobin concentration. The correction of renal anemia by means of erythropoietin therapy led to an efficient strengthening of the antioxidative defence system. The improvement of the antioxidative capacity is of complex nature comprising both enzymatic pathways and low molecular antioxidants. The correction of renal anemia with its well documented reduction of the cardiovascular risk can be regarded as an antioxidative therapy, demonstrating the clinical efficiency of antioxidative protection in patients with chronic renal failure.

Anemia↗

PubMed2002

Oxidative stress in chronic renal failure as a cardiovascular risk factor.

Myocardial injury has been shown to be the most critical factor influencing quality of life and mortality in patients with chronic renal failure. Oxidative stress has been postulated to be an important risk factor for cardiovascular disorders. One reason for oxidative stress in patients with renal failure is the underlying disease itself. Renal toxicity, ischemia/reperfusion and immunological disorders of the kidney result in an elevated formation of reactive oxygen species active in the pathogenesis of kidney disease. However, treatment procedures were also shown to induce oxidative stress. Increased formation of free radicals leads to an accelerated lipid peroxidation (LPO). Furthermore, secondary aldehydic LPO products, e.g. malondialdehyde (MDA) and 4-hydroxynonenal (HNE), are formed which were shown to deplete antioxidants, inhibit protein syntheses, mitochondrial respiration, and enzyme functions. F2-isoprostanes, also metabolites of polyunsaturated fatty acids, represent an additional in vivo marker of oxidative stress. Both isoprostanes and aldehydic LPO products can be removed by hemodialysis, however, this suggests only in part their binding to other molecules which cause tissue damage. Protein carbonyls are end-products of such interventions. Oxysterols, another form of free-radical initiated oxidation products, were shown to initiate atherosclerosis and plaque formation increasing dramatically the risk of coronary heart disease. Today there is no doubt that the correction of the oxidant/antioxidant imbalance in patients with chronic renal failure is an important approach for the reduction of the risk of those patients to develop cardiovascular disorders. The complete correction of renal anemia represents an effective means of strengthening antioxidant capacity and, therefore, of reducting cardiovascular risk potential.

Cardiovascular Diseases↗

PubMed2002

Elevated serum concentration of cardiotoxic lipid peroxidation products in chronic renal failure in relation to severity of renal anemia.

Patients with end-stage renal disease undergoing hemodialysis (HD) are exposed to oxidative stress. Increased levels of malondialdehyde (MDA) and 4-hydroxylnonenal (HNE) were found in plasma of uremic patients indicating accelerated lipid peroxidation (LPO) as a consequence of multiple pathogenetic factors. The catabolism and action of those products was already intensively studied. As highly reactive metabolites they are able to bind to proteins, nucleic acids, and other molecules. Doing so, they exert molecular signal effects in cells and are able to exacerbate tissue and organ damage, e.g. cardiotoxic effects. Since renal anemia was shown to promote oxidative stress as well, the aim of our investigation was to examine its role in HD patients. Therefore, two groups of HD patients were investigated (group I Hb < 10 g/dl, group II Hb > 10 g/dl) and serum concentrations of MDA, HNE, and of protein carbonyls, a marker for protein oxidation, were determined. All HD patients had significantly higher levels of the LPO products MDA and HNE compared with controls. However, group I patients showed higher MDA and HNE concentrations compared to group II patients. The same result could be seen for protein carbonyls. During HD concentration of both LPO products decreased. However, this was not the case for protein carbonyls. These results lead to the conclusion that optimized correction of the renal anemia may result in a significant reduction of oxidative stress and therefore in the reduction of organ tissue damage. In this way correction of renal anemia will reduce the cardiovascular risk and comorbidity of HD patients improving their prognosis.

Aldehydes↗

PubMed2002

Homocysteine in chronic renal failure in relation to renal anemia and to oxidative stress parameters 4-hydroxynonenal and malondialdehyde.

Homocysteine serum levels were measured in patients with end-stage renal disease in relation to severity of renal anemia and oxidative stress parameters such as 4-hydroxynonenal (HNE) and malondialdehyde (MDA). The predialytic homocysteine serum levels of the patients are five times as high as in healthy controls. It was found that homocysteine does not correlate to hemoglobin concentration and to oxidative stress, but rather to parameters of nutrition status such as albumine concentration and protein catabolic rate. The homocysteine accumulation represents a cardiovascular risk factor which is statistically independent of oxidative stress, but dependent on nutrition or energy status in patients with chronic renal failure.

Aldehydes↗

PubMed2001

Enrichment of eggs with n-3 polyunsaturated fatty acids: effects of vitamin E supplementation.

Eggs enriched with n-3 polyunsaturated fatty acids (PUFA) could contribute to dietary intake of these healthful fatty acids (FA). Because n-3 PUFA are highly susceptible to peroxidation, a first part of the study with Leghorn laying hens was carried out to investigate the influence of different levels of fish oil (0, 0.7, 1.4, 2.8, or 5.6%, respectively) in the diet on n-3 PUFA, cholesterol, vitamin E, and lipid peroxidation product contents in eggs. Addition of fish oil to a complete diet based on wheat, rye, tapioca, and soybean constituents containing 11 IU vitamin E/kg resulted in increased n-3 PUFA content in egg yolk, mainly due to accumulation of docosahexaenoic acid. Cholesterol was not altered up to 2.8% fish oil in the diet. The vitamin E content of the yolk was insufficient for the protection of PUFA from peroxidation. Addition of up to 2.8% fish oil to laying hen diets increased the n-3 PUFA content of yolks with a concomitant imbalance between vitamin E and PUFA, leading to increased levels of cytotoxic aldehydic lipid peroxidation products such as malondialdehyde (MDA). In a second part of the studies, the balance between vitamin E, PUFA, and lipid peroxidation was analyzed during the period of storage of n-3 PUFA-enriched eggs produced after feeding the laying hens with 1.5% fish oil diets with different concentrations of vitamin E (0, 5, 10, 20, 40, 80, 160 IU/kg). Storage of eggs resulted in a marked loss of vitamin E in yolk. In stored eggs, the cytotoxic lipid peroxidation products MDA, 4-hydroxynonenal, and 4-hydroxyhexenal were reduced in response to vitamin E supplementation. To prevent the increase of cytotoxic aldehydic lipid peroxidation during production and storage of n-3 PUFA-enriched eggs, a high vitamin E supplementation with at least 80 IU vitamin E/kg is needed.

Aldehydes↗

PubMed2000

Neutral endopeptidase and alcohol consumption, experiments in neutral endopeptidase-deficient mice.

Alcohol consumption was investigated in mice which were rendered deficient in the peptide-degrading enzyme neutral endopeptidase (EC 3.4.24.11) (NEP-/-) by gene targeting and compared to alcohol consumption in corresponding wild type mice (NEP+/+). Mice were offered a free choice to drink tap water or 10% alcohol. The NEP-/- mice consumed significantly more alcohol ( approximately 42%) than the NEP+/+ mice, whereas no significant differences were observed in the total fluid consumption. The daily food consumption of alcohol naive NEP-/- animals was elevated ( approximately 29%). Furthermore, the activities of peptidases closely related to neutral endopeptidase were analysed ex vivo in several brain regions from NEP-/- and NEP+/+ mice not treated with alcohol. There was no obvious compensation for the total loss of neutral endopeptidase by the functionally related peptidases angiotensin-converting enzyme and aminopeptidase N. In vitro, the degradation of exogenously applied [Leu(5)]enkephalin was not reduced in membrane preparations of those brain regions assayed in NEP-/- mice. A small reduction in [Leu(5)]enkephalin degradation was detected in striatal membrane preparations of NEP-/- mice, if aminopeptidase N was additionally blocked by bestatin or amastatin.

Alcohol Drinking↗

PubMed1998

Dose- and wavelength-dependent oxidation of crystallins by UV light--selective recognition and degradation by the 20S proteasome.

The lens of the human eye is a suitable model for age-related alterations at the molecular level. Age-related cataract formation is closely related to the accumulation of oxidatively altered proteins. In this study the influence of UV-A, UV-B, and UV-C irradiation on the proteolytic susceptibility of alpha-, betaL-, and betaH-crystallins by the isolated 20S proteasome was investigated. The proteins were irradiated with 280, 300, and 350 nm monochromatic light. Changes of the physical properties of the crystallins were characterized by absorbance measurements at 280 nm, fluorescence spectra, and SDS-PAGE-electrophoresis. The proteolytic susceptibility of crystallins was maximal after irradiation at 280 nm and three- to fivefold lower at 300 nm. Irradiation at 350 nm was not able to initiate proteolysis, probably due to protein-aggregate formation of higher molecular weight, as shown by SDS-PAGE. The damage of crystallins by UV-C light might be a signal for its proteolytic degradation by the 20S proteasome, whereas UV-B and UV-A do not increase the proteolytic susceptibility to the same extent but promote the formation of crosslinked proteins. Therefore, irradiation with UV, which is not followed by an increase in the proteolytic susceptibility, is accompanied by the formation of crosslinked proteins. It was concluded, that also long UV-B and UV-A may be involved in age-related alterations of the human lens and cataract formation.

Crystallins↗

PubMed1997

Evaluation of purine nucleotide loss, lipid peroxidation and ultrastructural alterations in post-hypoxic hepatocytes.

1. Hypoxic alterations in isolated rat hepatocytes were demonstrated by a 90% ATP loss during 60 min of ischaemia and temporary increases of nucleotide degradation products. 2. The oxidative stress during reoxygenation was demonstrated in these cells by a decrease in reduced glutathione (GSH) concentration (30%) and a threefold increase in lipid peroxidation products such as 4-hydroxynonenal and thiobarbituric acid-reactive substances (TBA-RSs). The tremendous GSH loss could not be balanced by the slight oxidized glutathione (GSSG) increase during reoxygenation. 3. For the first time the involvement of free radicals was directly demonstrated using electron spin resonance (ESR) spectroscopy in reoxygenated liver cells. Using the spin trap 5,5-dimethylpyrroline-1-oxide (DMPO), a carbon-centred radical and the adduct of the hydroxyl radical could be detected during early reoxygenation. 4. Morphological alteration of cells was observed, beginning during hypoxia and increasing during post-hypoxic reoxygenation. Electron microscopic findings of hypoxic and post-hypoxic cell damage included pyknosis of nuclei, spherical transformation of mitochondria and increased number of vesicles.

Aldehydes↗

PubMed1997

Differential response of oxygen radical metabolism in rat heart, liver and kidney to cyclosporine A treatment.

OBJECTIVE AND DESIGN: The study was designed to elucidate whether cyclosporine A (Cy A) induces oxidative stress in heart, liver and kidney. MATERIAL AND TREATMENT: Male Wistar rats were treated with NaCl (n = 7), cremophor (vehicle for Cy A: n = 7) and 30 mg/kg b.w. Cy A in cremophor (n = 7) daily for 4 weeks. METHODS: Oxidized (GSSG) and reduced (GSH) glutathione, lipid peroxides and superoxide dismutase were measured in the organs. RESULTS: Increases in GSSG [nmol/mg prot.] and a compensatory rise in total GSH [nmol/mg prot.] indicating Cy A-induced oxidative stress were found in kidney (0.39 +/- 0.09 vs. 0.47 +/- 0.14 vs. 0.64 +/- 0.18; 20.71 +/- 3.86 vs. 21.07 +/- 3.86 vs. 28.14 +/- 3.37) and liver (0.51 +/- 0.11 vs. 0.51 +/- 0.09 vs. 0.65 +/- 0.25; 33.35 +/- 5.06 vs. 32.88 +/- 5.12 vs. 44.12 +/- 6.06) but not in heart. CONCLUSION: Cy A-induced oxidative stress may contribute to the hepatotoxicity and nephrotoxicity of this drug. After heart transplantation, accelerated allograft atherosclerosis limits transplantation success. We did not find any evidence that Cy A induces oxidative stress in the heart which might favour atherogenesis.

Animals↗

PubMed1996

[Adjuvant therapy in lymphedema].

Therapy of first choice in chronic lymphedema is the complex physical drainage therapy. Complementary measures serve the prevention of erysipelas, the treatment of secondary tissue damage and additionally existing diseases in the lymphedematous area. Some measures of physical medicine and drugs are discussed. Antioxidative therapy as a new principle is presented. It is used to decrease secondary tissue damage by free radicals and to prevent possible damage far from the lymphedematous area.

Antioxidants↗

PubMed1995

Perioperative vascular flushing perfusion in acute mesenteric artery occlusion.

AIM: To evaluate in animals and patients a perioperative vascular flushing perfusion with antioxidants in order to improve postischaemic condition of the bowel and hence, to prolong the warm ischaemia tolerance time. MATERIALS: 40 rats and 10 patients with acute mesenteric artery occlusion. METHODS: Intestinal ischaemia was induced in 40 rats by clipping the superior mesenteric artery for 1 h. Thirty animals received a vascular flushing perfusion with oxygen radical scavengers (ascorbate, tocopherol or oxypurinol). Histology, ATP, ADP levels were examined in tissue biopsies and malondialdehyde, lactate dehydrogenase, alkaline phosphatase levels were measured in blood during ischaemia and 60 min after reperfusion. RESULTS: ATP restoration was particularly improved in the oxypurinol group (ATP/ADP-ratio = 2 vs. 1.2 in the control group). Malondialdehyde increase observed after reperfusion as a marker of radical induced lipid destruction was significantly attenuated (control group 160% of base level vs. 127% in the ascorbate group, 133% in the tocopherol group, 121% in the oxypurinol group). Histological alterations during ischaemia/reperfusion were markedly less extensive in the perfusion groups than in control. The patients treated perioperatively with arterial flushing perfusion had an overall mortality of 10%. CONCLUSION: Vascular flushing perfusion with oxygen radical scavengers prevents radical induced ischaemic damage and may prolong the warm ischaemic tolerance time of the intestine.

Acute Disease↗