Search PubMed⌕ Search

Biomedical subjects

H E Poulsen

Publications and source records attributed to H E Poulsen.

At least 19 recordsLinked to original sources
PubMed1995

Determination of ascorbic acid and dehydroascorbic acid in plasma by high-performance liquid chromatography with coulometric detection--are they reliable biomarkers of oxidative stress?

The concentrations of the hydrophilic antioxidants ascorbic acid and dehydroascorbic acid in plasma for some time have been considered possible biomarkers of oxidative stress. However, several problems are associated with the accurate measurement of these two compounds. We have developed and validated a selective and reproducible high-performance liquid chromatographic method for the quantification of ascorbic acid and dehydroascorbic acid in plasma. The method meets the requirements of a reliable routine analysis. The plasma samples are stabilized with 5 mM metaphosphoric acid, centrifugated at 4 degrees C before HPLC analysis. For ascorbic acid analysis, the sample pH is adjusted to 2.6, whereas for total ascorbic acid measurement dehydroascorbic acid is reduced to ascorbic acid using dithiothreitol for 5 min at pH 6.2 after which the sample pH is adjusted to 2.6. The samples are analyzed on a reversed-phase system using coulometric detection. Dehydroascorbic acid concentrations ae calculated by subtraction. Within- and between-day coefficients of variation for the complete assay were in the range of 4-8 and 3-6% for ascorbic acid and total ascorbic acid, respectively. The stability of ascorbic acid was monitored under various conditions including storage and the implications as well as the reliability of ascorbic acid as a biomarker are discussed.

Ascorbic Acid↗
PubMed1995

Early biochemical markers of effects: enzyme induction, oncogene activation and markers of oxidative damage.

Experimental carcinogenicity studies focus on identification of single carcinogens. Humans, however, appear exposed to a variety of low doses of carcinogens. Furthermore, few chemical entities are carcinogenic or toxic per se, but require metabolic activation to form ultimate carcinogens or toxins. In contrast to experimental animals, humans show considerable difference in genetic properties. In that situation it is particularly important to estimate individual capability for metabolic activation. To an increasing extent, activation includes formation of toxic oxygen metabolites. Particular targets for activated species are DNA and lipids; in particular low-density lipoproteins (LDL). Modifications of DNA are important for initiating the multistep process of carcinogenesis, in particular if oncogenes are activated or if tumor supressor genes are inactivated. Such DNA modification can be identical regardless of the reactive specimens being a xenobiotic or an oxygen species. Modification of LDL can start the process of atherosclerosis by transforming macrophages into foam cells, deposited as fatty streaks in the arterial wall. Biomarkers for activation capacity of xenobiotics include the use of prototype substrates and molecular techniques to determine genetic polymorphisms. Oxidative DNA modification can be measured from urinary excretion of oxidatively modified deoxynucleosides, particularly guanosine. Future efforts have to include individual measurements in order to improve the 'resolution' of molecular epidemiological approaches.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1995

Menadione-induced DNA fragmentation without 8-oxo-2'-deoxyguanosine formation in isolated rat hepatocytes.

Menadione (2-methyl-1,4-naphthoquinone) induces oxidative stress in cells causing perturbations in the cytoplasm as well as nicking of DNA. The mechanisms by which DNA damage occurs are still unclear, but a widely discussed issue is whether menadione-generated reactive oxygen species (ROS) directly damage DNA. In the present study, we measured the effect of menadione on formation of 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxodG), an index of oxidative DNA base modifications, and on DNA fragmentation. Isolated hepatocytes from phenobarbital-pretreated rats were exposed to menadione, 25-400 microM, for 15, 90 or 180 min with or without prior depletion of reduced glutathione (GSH) by diethyl maleate. Menadione caused profound GSH depletion and internucleosomal DNA fragmentation, which was demonstrated by a prominent fragmentation ladder on agarose gel electrophoresis. We found no oxidative modification of DNA in terms of increased 8-oxodG formation. In contrast, the positive control of sunlamp light increased 8-oxodG 5-fold in rat hepatocytes. We conclude that oxidative modification of DNA bases is unlikely to be important in menadione-induced DNA damage.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1995

Restricted pulmonary diffusion capacity after exercise is not an ARDS-like injury.

Pulmonary diffusion capacity (DLCO) is reduced 2 h after various types of exercise, such as rowing, treadmill running, arm cranking and marathon running. The decrease in DLCO may involve alterations in the alveolar-capillary membrane as well as depletion of the central blood volume. We hypothesized that the reduction in DLCO might also be influenced by oxygen free radicals, acute phase proteins and endotoxin, which are also involved in the adult respiratory distress syndrome (ARDS). Ten competitive male oarsmen performed a 6 min 'all-out' ergometer row. Single breath DLCO was determined before and 2 h after rowing and venous blood samples were also obtained during the row. Absolute DLCO decreased by 11% (range 0-20%) 2 h after rowing, whereas the concentration of endotoxin did not change significantly and interleukin (IL)-1-alpha, IL-8 and tumour necrosis factor (TNF)-alpha were below the levels of detection before, during and 2 h after rowing. Oxygen free radicals were evaluated by oxidative modification of amino acids and DNA. Corrected for creatinine in urine voided 3 h post-exercise, the DNA repair product 8-oxo-7,8-dehydro-2-deoxyguanosine (8-oxodG) did not change significantly. The ratio of fluorescence due to dityrosine to that due to tryptophan in plasma proteins increased after exercise. This might reflect an effect of oxygen free radicals, but it might also indicate an altered relative composition of plasma proteins. These results suggest that the reduced pulmonary diffusion capacity following exercise is unrelated to factors typically associated with ARDS.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1995

Reduction of oxidative DNA-damage in humans by brussels sprouts.

The effect of consumption of Brussels sprouts on levels of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in human urine was investigated in 10 healthy, male, non-smoking volunteers. Following a 3 week run-in period, five volunteers continued on a diet free of cruciferous vegetables for a subsequent 3 week intervention period (control group), while the other five (sprouts group) consumed 300 g of cooked Brussels sprouts per day, at the expense of 300 g of a glucosinolate-free vegetable. Levels of 8-oxodG in 24 h urine samples were measured by HPLC. In the control group there was no difference between the two periods in levels of 8-oxodG (P = 0.72). In contrast, in the sprouts group the levels of 8-oxodG were decreased by 28% during the intervention period (P = 0.039). The present findings support the results of epidemiologic studies that consumption of cruciferous vegetables may result in a decreased cancer risk.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1995

Short-term moderate energy restriction does not affect indicators of oxidative stress and genotoxicity in humans.

Restriction of energy intake (ER), without malnutrition of essential nutrients, has repeatedly been demonstrated to increase longevity in rodents. In the antioxidant theory of aging the lack of balance between the generation of free radicals and free radical scavenging was thought to be a main causal agent, in the aging process. From this point of view the antiaging effect induced by ER might be due to the lower rate of free-radical production and related damage induced by a lower metabolic rate. The antiaging effects of ER might also occur in humans. This study explored the effects of a 10-week moderately energy-restricted diet (80% of habitual) in 24 non-obese middle-aged men (16 ER subjects, 8 controls) on resting metabolic rate (RMR) and indicators of the primary antioxidant defense system, oxidative stress and genotoxicity. RMR decreased significantly in both groups, even when adjustments were made for the change in body composition. The increase in blood vitamin C concentration correlated with the increase in urinary 8-hydroxydeoxyguanosine (80HdG) excretion. The change in urinary 80HdG excretion also correlated with the change in RMR per kg fat-free mass. No differences between groups were found for changes in indicators of genotoxicity, erythrocyte catalase, glutathione peroxidase and superoxide dismutase activity and in plasma vitamin E, A or beta-carotene concentrations. We conclude that 10 weeks of moderate ER did not affect indicators of antioxidative capacity, oxidative stress and genotoxicity of humans. Since subjects were not in energy balance at the end of the study, no conclusions can be made with respect to long-term effects.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1995

Selective serotonin reuptake inhibitors and theophylline metabolism in human liver microsomes: potent inhibition by fluvoxamine.

1. Fluvoxamine and seven other selective serotonin reuptake inhibitors (SRRI) were tested for their ability to inhibit a number of human cytochrome P450 isoforms (CYPs). 2. None of the drugs showed potent inhibition of CYP2A6 (coumarin 7-hydroxylase) or CYP2E1 (chlorzoxazone 6-hydroxylase), while norfluoxetine was the only potent inhibitor of CYP3A having IC50 values of 11 microM and 19 microM for testosterone 6 beta-hydroxylase and cortisol 6 beta-hydroxylase, respectively. 3. Norfluoxetine, sertraline and fluvoxamine inhibited CYP1A1 (7-ethoxyresorufin O-deethylase) in microsomes from human placenta (IC50 values 29 microM, 35 microM and 80 microM, respectively). Fluvoxamine was a potent inhibitor of CYP1A2-mediated 7-ethoxyresorufin O-deethylase activity (IC50 = 0.3 microM) in human liver. 4. In microsomes from three human livers fluvoxamine potently inhibited all pathways of theophylline biotransformation, the apparent inhibitor constant, Ki, was 0.07-0.13 microM, 0.05-0.10 microM and 0.16-0.29 microM for inhibition of 1-methylxanthine, 3-methylxanthine and 1,3-dimethyluric acid formation, respectively. Seven other SSRIs showed either weak or no inhibition of theophylline metabolism. 5. Ethanol inhibited the formation of 1,3-dimethyluric acid with K(i) value of 300 microM, a value which is consistent with inhibition of CYP2E1. Ethanol and fluvoxamine both inhibited 8-hydroxylation by about 45% and, in combination, the compounds decreased the formation of 1,3-dimethyluric acid by 90%, indicating that CYP1A2 and CYP2E1 are equally important isoforms for the 8-hydroxylation of theophylline. 6. It is concluded that pharmacokinetic interaction between fluvoxamine and theophylline is due to potent inhibition of CYP1A2.

Antidepressive Agents↗
PubMed1995

Kinetics and inhibition by fluvoxamine of phenacetin O-deethylation in V79 cells expressing human CYP1A2.

The kinetics of phenacetin O-deethylation and its inhibition by fluvoxamine was investigated in a V79 cell line (V79MZh1A2) transfected with human CYP1A2. In four sets of experiments the apparent Km values for phenacetin O-deethylation ranged from 35 to 95 microM and the Ki for fluvoxamine-mediated inhibition of the reaction ranged from 2.7 to 14.5 nM, i.e. comparable to values obtained in human liver microsomes. The kinetic performance of the V79MZh1A2 cell line demonstrates its usefulness as an analytical tool in a variety of toxicological and drug metabolism studies involving CYP1A2.

Acetaminophen↗
PubMed1995

Cytochrome P4502E1 inhibition by propylene glycol prevents acetaminophen (paracetamol) hepatotoxicity in mice without cytochrome P4501A2 inhibition.

Acetaminophen hepatotoxicity is associated with its biotransformation to the reactive metabolite N-acetyl-p-benzoquinone imine that binds to protein. Two forms of cytochrome P450, CYP2E1 and CYP1A2, have been implicated as primarily responsible for the bioactivation. To determine the relative contributions of these P450's, overnight fasted male NMRI mice were pretreated with 10 ml of 50% v/w propylene glycol/kg or fluvoxamine (10 mg/kg) at -80 and -20 min. relative to acetaminophen dosing to inhibit CYP2E1 and CYP1A2, respectively. Mice were sacrificed at 0.5 or 4 hr after a hepatotoxic dose of acetaminophen (300 mg/kg). Propylene glycol or propylene glycol plus fluvoxamine, but not fluvoxamine alone protected against acetaminophen hepatotoxicity as indicated by abolished increase in serum alanine aminotransferase activity, less depletion of hepatic glutathione and lower liver:body weight ratios. Propylene glycol inhibited the activity of CYP2E1 as indicated by 84% reduction in the clearance of 3 mg/kg dose of chlorzoxazone, whereas fluvoxamine inhibited the activity of CYP1A2 as indicated by 40% reduction in the clearance of a 10 mg/kg dose of caffeine. For this animal model, the data are consistent with the notion that hepatoxicity is associated with bioactivation of acetaminophen by CYP2E1 but not by CYP1A2.

Acetaminophen↗
PubMed1994

[The effect on health of dietary antioxidants and antioxidant supplements].

Reactive free oxygen radicals are formed in the reactions involved in normal cell metabolism. This formation is closely regulated e.g. by dietary antioxidants. Present knowledge suggests that an imbalance, with surplus of free radicals, can play a role in the pathogenesis of certain types of cancer, atherosclerosis, and cataract. A number of epidemiological studies have demonstrated a reduced risk of developing these diseases in persons who consume a diet with a high content of vegetables and fruit, which contains large quantities of the antioxidants: beta-carotene, vitamins C and E. Intervention studies, using supplements of these antioxidants, have so far not been able to show a beneficial effect. The apparently protective effect of fruit and vegetables may be due to other active ingredients. In Denmark the average intake of vegetables and fruit is low, and it is estimated that an increased consumption of these foods could reduce the occurrence of certain cancer types and atherosclerosis. In contrast, there is no evidence that antioxidant supplements would provide protection against disease, and their safety remains to be established.

Antioxidants↗
PubMed1994

Simultaneous determination of urinary free cortisol and 6 beta-hydroxycortisol by high-performance liquid chromatography to measure human CYP3A activity.

The ratio of the hydrophilic metabolite 6 beta-hydroxycortisol to its parent compound cortisol has recently been demonstrated to be a specific marker for human CYP3A oxygenase activity. We have developed a sensitive and simple single-run high-performance liquid chromatographic method for the quantification of urinary free cortisol and 6 beta-hydroxycortisol using dexamethasone as internal standard. The urine samples (1 ml) are applied to Sep-Pak cartridges, which are washed with water and eluted with ethyl acetate-diethyl ether (4:1, v/v). The organic extracts are washed sequentially with alkaline and acidic solutions saturated with sodium sulfate and subsequently concentrated to dryness. After reconstitution in ethanolic water, the samples are analyzed on a reversed-phase gradient system using ultraviolet absorbance detection at 254 nm. The within- and between-day coefficients of variation (C.V.) for the assay where both in the range of 5-10%. The reference interval for the 6 beta-hydroxycortisol/cortisol ratio of eleven healthy non-smoking subjects was 2.77-26.88 with an average of 10.09 +/- 6.89 (S.D.). The method constitutes an improvement over previous methods and is suitable for routine assessment of the 6 beta-hydroxycortisol/cortisol ratio requiring only 1 ml of urine or less.

Biomarkers↗
PubMed1994

[Endothelium-derived relaxing factor/nitrogen oxide. Pharmacological and clinical cardiovascular aspects].

The potent vasodilator endothelium derived relaxing factor (EDRF) is released by the vascular endothelium both under basal conditions and upon stimulation by acetylcholine and other endothelium dependent vasodilators. EDRF has been identified as nitric oxide (NO) and provides communication between endothelial and smooth muscle cells in the vascular wall. Injured and/or dysfunctional endothelium as seen in a variety of cardiovascular diseases may result in decreased production of NO leading to unfavorable vasoconstriction and vasospasm whereas its overproduction may cause pathological vasodilation. Understanding the role of nitric oxide in regulation of vascular tone may facilitate novel strategies for prevention and treatment of cardiovascular disorders.

Cardiovascular Diseases↗
PubMed1994

[Nitroglycerin preparations. Effect and tolerance].

Nitroglycerin and other organic nitrates are beneficial in ischaemic heart disease and myocardial infarction and as adjunctive therapy in congestive heart failure. The nitrates are inactive prodrugs, and their vascular effects depend on metabolic conversion to vasoactive intermediates like nitric oxide and/or nitrosothiols with subsequent stimulation of guanylate cyclase causing increased formation of cyclic GMP. The compounds relax vascular smooth muscle producing venous dilatation at low concentrations and at higher concentrations dilation of coronary arteries and collaterals and systemic arterial vessels. Nitrate tolerance is, however, a problem with continuous nitrate therapy. Tolerance is most likely to occur with frequent dosing or with the use of long-acting nitrates or transdermal applications resulting in constant plasma concentrations. Therapeutic strategies should be designed to provide a daily low-nitrate period or nitrate-free period to obviate the development of tolerance and thus maintain the antianginal effects.

Drug Tolerance↗
PubMed1994

Altered peripheral vasodilator profile of nitroglycerin during long-term infusion of N-acetylcysteine.

OBJECTIVES: The aim of this study was to compare the short- and long-term effects of intravenous nitroglycerin plus placebo and nitroglycerin plus N-acetylcysteine on peripheral arteries, veins and microcirculation in humans. BACKGROUND: The thiol donor N-acetylcysteine may potentiate the hemodynamic response to nitrates in nitrate-tolerant and nontolerant patients. The vascular changes responsible for this effect are not clear. METHODS: Eight male volunteers were treated with nitroglycerin (0.1 microgram/kg per min) combined with N-acetylcysteine (2 g intravenously, followed by 5 mg/kg per h) or placebo for 23 h in a double-blind, randomized, crossover study. Venous volume, the diameter of the radial and temporal arteries, calf blood flow and subcutaneous blood flow were measured at baseline and repeated after 1 and 23 h of infusion. RESULTS: Prolonged coadministration of N-acetylcysteine and nitroglycerin potentiated the acute venodilator effect of nitroglycerin as estimated by changes in venous volume (nitroglycerin plus N-acetylcysteine, 4.45 +/- 0.36 ml/100 g; nitroglycerin plus placebo, 3.65 +/- 0.46 ml/100 g, mean +/- SEM, p < 0.05) and prevented development of tolerance as seen after 23 h of treatment with nitroglycerin plus placebo (4.35 +/- 0.25 vs. 3.47 +/- 0.41 ml/100 g, p < 0.05). N-acetylcysteine had no effect on nitroglycerin-induced changes in arterial diameters (p > 0.05) but significantly increased microcirculatory subcutaneous blood flow after 1 h (nitroglycerin plus N-acetylcysteine: 6.3 +/- 1.3 ml/100 g per min vs. nitroglycerin plus placebo: 3.5 +/- 0.3 ml/100 g per min, p < 0.05) and after 23 h (4.4 +/- 0.6 vs. 3.1 +/- 0.5 ml/100 g per min, p < 0.05). CONCLUSIONS: The results suggest that coadministration of nitroglycerin and N-acetylcysteine in humans 1) potentiates and preserves nitroglycerin-induced venodilation and 2) augments the effect of nitroglycerin on small resistance vessels (regulating subcutaneous blood flow) without affecting the response to nitroglycerin in middle-sized arteries. Both the development of nitrate tolerance and the administration of N-acetylcysteine significantly change the normal vasodilator profile of nitroglycerin in humans.

Acetylcysteine↗
PubMed1994

Oxidative DNA damage correlates with oxygen consumption in humans.

Generation of reactive oxygen species from mitochondrial respiration has been proposed as an important determinant of longevity and cumulative cancer risk. Interspecies correlations and animal calorie restriction studies of metabolic rate and oxidative DNA damage support this notion. In the present study we have demonstrated a close association between oxidative DNA damage as assessed by the urinary excretion of 8-oxo-7,8-dihdro-2'-deoxyguanosine (8-oxodG) and oxygen consumption in 33 healthy premenopausal women (r = 0.64; p = 0.00007). In the 12 women who smoked, 8-oxodG excretion was increased by 35%, although oxygen consumption increased only 10% compared with the 21 nonsmoking women. Apparently, the rate of oxidative DNA damage relates to mitochondrial respiration in humans and is aggravated by smoking.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1994

Nitrate tolerance in vivo is not associated with depletion of arterial or venous thiol levels.

Results from in vitro experiments suggest that development of nitrate tolerance is due to a depletion of vascular thiol compounds (ie, cysteine and glutathione [GSH]) necessary for the bioconversion of organic nitrates. However, it is unknown whether in vivo tolerance development is associated with changes in thiol levels. This study measures plasma and vessel tissue GSH and cysteine levels in nontolerant rats, nitrate-tolerant rats, and rats treated with the two characteristically different thiol donors N-acetyl-L-cysteine and L-2-oxothiazolidine-4-carboxylic acid (OXO). Chronically catheterized conscious rats received an intravenous infusion of either nitroglycerin (NTG, 0.2 mg/h) or matching placebo for 3 days. At day 3, the hypotensive effect of 2.5 mg NTG/kg was decreased by 74 +/- 6% (mean +/- SEM, P < .05) in the NTG-treated group (n = 7), indicating the development of tolerance. No change in the hypotensive effect of NTG was seen in the placebo group (n = 6, P > .05). Hemodynamic tolerance is not associated with changes in aorta cysteine or GSH levels as compared with the placebo group (cysteine, 77 +/- 14 versus 57 +/- 11 [mean + SEM] nmol/g; GSH, 414 +/- 62 versus 399 +/- 89 nmol/g; P > .05). However, the increase in vascular thiol levels seen after OXO treatment in nontolerant rats is completely absent in nitrate-tolerant animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcysteine↗