Cancer risk and oxidative DNA damage in man

In living cells reactive oxygen species (ROS) are formed continuously as a consequence of metabolic and other biochemical reactions as well as external factors. Some ROS have important physiological functions. Thus, antioxidant defense systems cannot provide complete protection from noxious effects of ROS. These include oxidative damage to DNA, which experimental studies in animals and in vitro have suggested are an important factor in carcinogenesis. Despite extensive repair oxidatively modified DNA is abundant in human tissues, in particular in tumors, i.e., in terms of 1-200 modified nucleosides per 10(5) intact nucleosides. The damaged nucleosides accumulate with age in both nuclear and mitochondrial DNA. The products of repair of these lesions are excreted into the urine in amounts corresponding to a damage rate of up to 10(4) modifications in each cell every day. The most abundant of these lesions, 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), is also the most mutagenic, resulting in GT transversions which are frequently found in tumor relevant genes. A series of other oxidative modifications of base and sugar residues occur frequently in DNA, but they are less well studied and their biological significance less apparent. The biomarkers for study of oxidative DNA damage in humans include urinary excretion of oxidized nucleosides and bases as repair products and modifications in DNA isolated from target tissue or surrogate cells, such as lymphocytes. These biomarkers reflect the rate of damage and the balance between the damage and repair rate, respectively. By means of biomarkers a number of important factors have been studied in humans. Ionizing radiation, a carcinogenic and pure source of ROS, induced both urinary and leukocyte biomarkers of oxidative DNA damage. Tobacco smoking, another carcinogenic source of ROS, increased the oxidative DNA damage rate by 35-50% estimated from the urinary excretion of 8-oxodG, and the level of 8-oxodG in leukocytes by 20-50%. The main endogenous source of ROS, the oxygen consumption, showed a close correlation with the 8-oxodG excretion rate although moderate exercise appeared to have no immediate effect. So far, cross-sectional study of diet composition and intervention studies, including energy restriction and antioxidant supplements, have generally failed to show an influence on the oxidative DNA modification. However, a diet rich of Brussels sprouts reduced the oxidative DNA damage rate, estimated by the urinary excretion of 8-oxodG, and the intake of vitamin C was a determinant for the level of 8-oxodG in sperm DNA. A low-fat diet reduced another marker of oxidative DNA damage in leukocytes. In patients with diseases associated with a mechanistically based increased risk of cancer, including Fanconi anemia, chronic hepatitis, cystic fibrosis, and various autoimmune diseases, the biomarker studies indicate an increased rate of oxidative DNA damage or in some instances deficient repair. Human studies support the experimentally based notion of oxidative DNA damage as an important mutagenic and apparently carcinogenic factor. However, the proof of a causal relationship in humans is still lacking. This could possibly be supported by demonstration of the rate of oxidative DNA damage as an independent risk factor for cancer in a prospective study of biobank material using a nested case control design. In addition, oxidative damage may be important for the aging process, particularly with respect to mitochondrial DNA and the pathogenesis of inflammatory diseases.

Paracetamol-induced spindle disturbances in V79 cells with and without expression of human CYP1A2

Spindle disturbing effects in terms of c-mitosis and cytotoxicity of paracetamol were investigated in two Chinese hamster V79 cell lines, one of which (V79MZh1A2) was transfected with human CYP1A2. This enzyme catalyses the oxidative formation of the reactive paracetamol metabolite, NAPQI, believed to initiate hepatoxicity by covalent binding to proteins after overdose. In the native V79 cell line paracetamol increased c-mitosis frequency in a concentration dependent manner from 8.7 + or - 3.5% (control) to 66 + or - 18% at 20 mM. A significant increase to 13.3 + or - 3.5% was first seen at 2.5 mM in the native cell line (P<0.05). In the V79MZh1A2 cells the concentration-effect curve was slightly shifted to the left (P<0.05) with c-mitosis frequency increased to 12.1 + or - 2.6% (P<0.05) at 1 mM paracetamol. At 5 mM paracetamol the c-mitosis frequency was 14.4 + or - 5.0% and 19.0 + or - 3.8% in the native and CYP1A2 expressing cell lines, respectively (P<0.05). At 20 mM paracetamol the c-mitosis frequency was 61 + or - 10% in the V79MZh1A2 cells. Cell survival was reduced to approximately 50% at 5-10 mM paracetamol in both cell lines. At 20 mM paracetamol survival was further decreased to 39 + or - 9% in V79MZh1A2 cells only (P<0.05). The present study demonstrated that paracetamol may disturb the spindle of dividing cells conveying a risk of aneuploidy. The spindle disturbing effect was only slightly enhanced by expression of CYP1A2, suggesting that metabolic activation plays only a minor role in this genotoxic effect. The reduction of survival mirrored the increase in c-mitosis frequency.

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.

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.

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.

Energy restriction and oxidative DNA damage in humans

The cancer-preventive effect of energy restriction in rodents has been related to a decrease in oxidative damage to DNA. We have investigated the effect of energy restriction on the rate of oxidative DNA modification estimated from the urinary excretion of the repair product, 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), in healthy, normal weight men. Before and after 10 weeks on a diet containing 80 (n = 16) or 100% (n = 8) of the estimated weight-maintaining energy, resting metabolic rate (RMR) was measured and 24-h urine was collected for 8-oxodG determination by HPLC. During the study, the weight loss was 10 and 2.5% of the initial weight, mostly in terms of fat, and the RMR decreased by 13 and 8% in the energy-restricted and control groups, respectively. With the use of t tests there was no significant difference within or between groups with respect to 8-oxodG excretion. However, if RMR was included as a covariate in multifactorial ANOVA, an average relative 17% (2-31%; 95% confidence interval) increase in 8-oxodG excretion in the energy-restricted group was significantly different from the corresponding value of the control group (P < 0.02). In the energy-restricted group the change in 8-oxodG excretion was correlated closely with the decrease in RMR (r = 0.63; P = 0.013). In the present study, 20% energy restriction for 10 weeks did not reduce oxidative DNA damage; we question a beneficial effect on cancer risk in normal weight humans.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

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.

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.

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.

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.

Oxidative DNA damage after transplantation of the liver and small intestine in pigs

Oxidative damage is thought to play an important role in ischemia/reperfusion injury, including the outcome of transplantation of the liver and intestine. We have investigated oxidative DNA damage after combined transplantation of the liver and small intestine in 5 pigs. DNA damage was estimated from the urinary excretion of the repair product 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG). In the first 1-3 hr after reperfusion of the grafts, 8-oxodG excretion was increased 2.9-fold (1.7-4.1; 95% confidence intervals; P < 0.05). A control experiment included sham surgery with clamping of the suprarenal inferior caval vein in 2 pigs during steady state infusion of 8-oxodG. While the caval vein was clamped, the urinary excretion of 8-oxodG was almost blocked, whereas after removal of the clamp, the excretion returned to and did not exceed the preclamp levels. In a separate experiment with 2 pigs, the elimination of injected 8-oxodG was shown to adhere to first-order kinetics with a clearance and a terminal elimination half-life of approximately 4 ml min-1 kg-1 and 2 1/2 hr, respectively. The injected dose was completely excreted into the urine within 4 hr. It is concluded that substantial oxidative damage to DNA results from reperfusion of transplanted small intestine and liver in pigs, as estimated from the readily excreted repair product 8-oxodG.

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.

Radiation-induced formation of 8-hydroxy-2'-deoxyguanosine and its prevention by scavengers

Reactive oxygen species (ROS) induce 8-hydroxy-2'-deoxyguanosine (8-OHdG) formation, which has been proposed as a key biomarker relevant to carcinogenesis. 8-OHdG has been induced in a number of different ways, most often without knowledge of the specific type and amount of ROS generated. We have measured 8-OHdG formation in calf thymus DNA exposed to ionizing radiation under conditions generating either hydroxyl radicals (OH.), superoxide anions (O2-) or both. Additionally, we investigated the relationship between the scavenger effect of the drug 5-aminosalicylic acid (5-ASA) and increasing OH. exposure toward 8-OHdG formation. The effect of this drug was compared to those of the physiological scavengers ascorbate and reduced glutathione (GSH). We found that OH. generated 8-OHdG in a dose-dependent manner, whereas O2- did not cause 8-OHdG formation. 5-ASA, ascorbate and GSH all acted as hydroxyl radical scavengers, although with different concentration-effect curves, emphasizing the importance of using relevant pharmaco-/physiological concentrations in studies focusing on therapeutic applications of scavengers. The scavenger effect of 5-ASA at concentrations > or = 0.1 mM was similar at 30 and 100 Gy radiation, i.e. within a wide range of OH. exposure, which is useful information considering clinical applications where the exact amount of ROS formed is unknown. Both 5-ASA and ascorbate at low concentrations (< or = 0.1 mM) were less efficient in preventing 8-OHdG formation from X-ray generated OH. than was shown in a previous comparable study using light as the source of ROS. This differentiation probably reflects variations in both number and type of ROS formed in the two systems.

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.

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)

Effect of ascorbate and 5-aminosalicylic acid on light-induced 8-hydroxydeoxyguanosine formation in V79 Chinese hamster cells

Recently we showed that ascorbate and 5-aminosalicylic acid (5-ASA) prevented 8-hydroxydeoxyguanosine (8-OHdG) formation in calf thymus DNA exposed to UV-visible light. However, the ultimate defense against oxidative DNA damage depends on an intracellular/intranuclear effect of the compounds. In the present study we investigated the effect of ascorbate and 5-ASA on 8-OHdG formation in V79 Chinese hamster cells exposed to light from a sun-lamp. Exposure for 1 min (4560 mJ/cm2) increased 8-OHdG formation in cellular DNA to 30-40 times background level. Preincubation of the cells with ascorbate or 5-ASA at concentrations of 0.1, 1 and 10 mM diminished the 8-OHdG formation to 0.67, 0.74 and 0.49 times controls (P < 0.05) for ascorbate respectively, and to 0.82, 0.66 and 0.33 times controls (P < 0.05), for 5-ASA. These findings demonstrate that both ascorbate and 5-ASA prevent oxidative DNA damage in cells by acting as intracellular/intranuclear antioxidants.

8-Hydroxydeoxyguanosine as a urinary biomarker of oxidative DNA damage

Living organisms are continuously exposed to reactive oxygen species as a consequence of biochemical reactions as well as external factors. Oxidative DNA damage has been implicated in aging, carcinogenesis and other degenerative diseases. The urinary excretion of the DNA repair product 8-hydroxydeoxyguanosine (8OHdG) has been proposed as a noninvasive biomarker of oxidative DNA damage in humans in vivo. We have developed a three-dimensional HPLC analysis with electrochemical detection for the analysis of 8OHdG in urine and studied factors affecting the excretion of this biomarker in 83 healthy humans and in various laboratory animals, including dog, pig, and rat. Previously, other groups have used comparable HPLC methods or gas chromatography-mass spectrometry with selective ion monitoring for measuring the excretion of 8OHdG in humans, rats, mice, and monkeys. In the 169 humans studied so far, the average 8OHdG excretion was 200-300 pmol/kg per 24 h with a sevenfold range, and the coefficient of variation was 30-40%. This excretion corresponds 140-200 oxidative modification of guanine bases per cell per day. Thirty-two smokers from our study population excreted 50% (31-69%; 95% confidence interval) more 8OHdG than 53 nonsmokers. This indicates a 50% increased rate of oxidative DNA damage from smoking, adding to the other well-known health hazards of smoking. The biochemical-physiological basis is unknown but may be related to smoke constituents including or generating reactive oxygen species and/or consuming antioxidants and/or the well-known enhancing effect of smoking on the metabolic rate. In our 83 healthy subjects the 8OHdG excretion correlated with body composition. Thus, lean and/or male subjects excreted more than obese and/or female subjects, possibly related to differences in metabolic rate. In accordance, the excretion of 8OHdG decreased after calorie restriction, which will cause a decline in the metabolic rate. Across the investigated species, humans, dogs, pigs, and rats, the excretion of 8OHdG correlated with the specific metabolic rate, confirming data from other groups on humans, monkeys, rats, and mice. The excretion of 8OHdG decreased with age in rats in parallel with the decline in metabolic rate with advancing age. The excretion of 8OHdG reflects the formation and repair of only one out of approximately 20 described oxidative DNA modifications. So far, methods are not available for the determination of the corresponding repair products, except 8OHdG and thymidine glycol, in urine. Moreover, the importance in terms of mutagenicity, particularly regarding tumour suppressor genes and oncogenes, is mainly documented for 8OHdG in DNA.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of benzo[a]pyrene and (+-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene on mitosis in Chinese hamster V79 cells with stable expression of rat cytochrome P4501A1 or 1A2

The effect of bioactivation of benzo[a]pyrene (B[a]P) and (+-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (B[a]P-7,8-diol) on spindle disturbances and toxicity has been investigated in V79 Chinese hamster cells genetically engineered to express cytochrome P4501A1 (CYP1A1) and cytochrome P4501A2 (CYP1A2). B[a]P induces spindle disturbances in native V79 Chinese hamster cells. This effect was enhanced by the expression of CYP1A1 but not CYP1A2. The increased effect seen in the CYP1A1-expressing cell line could be brought back to the level seen in the native cell line by alpha-naphthoflavone in a dose-dependent manner. This strongly suggests that a CYP1A1-dependent metabolite, conceivably (+-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (BPDE) accounts for the increased spindle disturbing effect. B[a]P-7,8-diol induced spindle disturbances at remarkably low concentrations, 10(-8) M, irrespective of expression of the two CYPs. Our data suggest that B[a]P-7,8-diol is the most potent spindle-disturbing metabolite, whereas BPDE is the most important metabolite concerning mutagenesis. The concentrations inducing spindle disturbances correspond to those that are positive in mutation assays. We hypothesize that B[a]P is a complete carcinogen because of its ability to induce both aneuploidy and mutations after metabolic conversion of low non-cytotoxic concentrations.

Drug metabolism and genetic polymorphism in subjects with previous halothane hepatitis

To test the hypothesis that halothane hepatitis is caused by a combination of altered drug metabolism and an immunoallergic disposition, the metabolism of antipyrine, metronidazole, sparteine, phenytoin, and racemic R- and S-mephenytoin was investigated in seven subjects with previous halothane hepatitis. The HLA tissue types and the complement C3 phenotypes were also determined. The metabolism of antipyrine and metronidazole was within normal range in all subjects, and they were all fast or extensive metabolizers of sparteine, mephenytoin, and phenytoin. HLA tissue types were unremarkable. Five of the seven subjects had complement C3 phenotypes F or FS. In the general population phenotype S is the most common, but the difference in complement C3 phenotypes is not statistically significant (p = 0.07). We conclude, although in a limited number of patients, that subjects with previous halothane hepatitis do not appear to be different from controls with regard to drug metabolism and HLA tissue type. The possibility of a higher frequency of complement C3 phenotype F and FS needs further investigation.

Non-induction of extrahepatic antipyrine and metronidazole metabolism evaluated from partially hepatectomized rats

1. The effect of beta-naphthoflavone (BNF), given i.p. (n = 9) and orally (n = 9), on the metabolism of antipyrine and metronidazole was investigated in rats. 2. The clearances of antipyrine and metronidazole were determined on a single saliva sample. The rates of formation of antipyrine and metronidazole metabolites were determined from a 20 h urine sample and saliva clearance. 3. Administration of beta-naphthoflavone i.p. was significantly more effective than oral dosage on the induction of antipyrine and metronidazole metabolism (p < 0.05). 4. The capacity of extrahepatic tissues to metabolize antipyrine and metronidazole was quantitatively assessed in rats with and without pretreatment with beta-naphthoflavone immediately after sham operation or 70% partial hepatectomy (n = 40). 5. Antipyrine and metronidazole clearances correlated with liver weight in induced and non-induced rats. Linear regression of antipyrine and metronidazole clearances did show a non-significant Y-intercept (p > 0.05), indicating a negligible extrahepatic metabolism in both induced and in non-induced rats. 6. From a quantitative point of view this study indicates that induction of extrahepatic cytochrome P450 metabolism of antipyrine and metronidazole is negligible.