Effect of interleukin (IL)-8 on benzo[a]pyrene metabolism and DNA damage in human lung epithelial cells.

It has been well established that inflammation and concurrent mutagenic exposures drive the carcinogenic process in a synergistic way. To elucidate the role of the inflammatory cytokine IL-8 in this process, we studied its effect on the activation and deactivation of the chemical mutagen benzo[a]pyrene B[a]P in the immortalized pulmonary BEAS-2B cell line. After 24h incubation with B[a]P in the presence or absence of IL-8, the B[a]P induced cytochrome P450 1A1 and 1B1 (CYP1A1 and CYP1B1) gene expression and CYP1A1 enzyme activity was significantly higher in the presence of the cytokine. Consistent with these findings, we observed higher concentration of the metabolite B[a]P-7,8-diol under concurrent IL-8 treatment conditions. Interestingly, we also found higher concentrations of unmetabolized B[a]P. To explain this, we examined the downstream effects of IL-8 on NADPH oxidases (NOXes). IL-8 lowered the intracellular NADPH level, but this effect could not explain the changes in B[a]P metabolism. IL-8 also significantly depleted intracellular glutathione (GSH), which also resulted in enhanced levels of unmetabolized B[a]P, but increased concentrations of the metabolite B[a]P-7,8-diol. No differences in B[a]P-DNA adducts level were found between B[a]P and B[a]P combined with IL-8, and this might be due to a 3-fold increase in nucleotide excision repair (NER) after IL-8 treatment. These findings suggest that IL-8 increased the formation of B[a]P-7,8-diol despite an overall delayed B[a]P metabolism via depletion of GSH, but DNA damage levels were unaffected due to an increase in NER capacity.

Inflammation-associated extracellular ß-glucuronidase alters cellular responses to the chemical carcinogen benzo[a]pyrene.

Neutrophils infiltrate tissues during inflammation, and when activated, they release ß-glucuronidase. Since inflammation is associated with carcinogenesis, we investigated how extracellular ß-glucuronidase changed the in vitro cellular response to the chemical carcinogen benzo(a)pyrene (B[a]P). For this we exposed human liver (HepG2) and lung (A549) cells to B[a]P in the presence or absence of ß-glucuronidase. ß-Glucuronidase reduced B[a]P-induced expression of CYP1A1 and CYP1B1 at 6 h after exposure, which did not depend on ß-glucuronidase activity, because the inhibitor D-saccharic acid 1,4-lactone monohydrate did not antagonize the effect of ß-glucuronidase. On the other hand, the inhibitory effect of ß-glucuronidase on CYP expression was dependent on signalling via the insulin-like growth factor receptor (IGF2R, a known receptor for ß-glucuronidase), because co-incubation with the IGF2R inhibitor mannose-6-phosphate completely abolished the effect of ß-glucuronidase. Extracellular ß-glucuronidase also reduced the formation of several B[a]P metabolites and B[a]P-DNA adducts. Interestingly, at 24 h of exposure, ß-glucuronidase significantly enhanced CYP expression, probably because ß-glucuronidase de-glucuronidated B[a]P metabolites, which continued to trigger the aryl hydrocarbon receptor (Ah receptor) and induced expression of CYP1A1 (in both cell lines) and CYP1B1 (in A549 only). Consequently, significantly higher concentrations of B[a]P metabolites and DNA adducts were found in ß-glucuronidase-treated cells at 24 h. DNA adduct levels peaked at 48 h in cells that were exposed to B[a]P and treated with ß-glucuronidase. Overall, these data show that ß-glucuronidase alters the cellular response to B[a]P and ultimately enhances B[a]P-induced DNA adduct levels.

Chemical characteristics for optimizing CYP2E1 inhibition.

Cytochrome P450 2E1 (CYP2E1) expression and activity in the liver is associated with the degree of liver damage in patients with alcoholic steatohepatitis (ASH) as well as non-alcoholic steatohepatitis (NASH). CYP2E1 is known to generate reactive oxygen species, which leads to oxidative stress, one of the hallmarks of both diseases. Apart from ROS, toxic metabolites can be formed by CYP2E1 metabolism, further potentiating liver injury. Therefore, CYP2E1 is implicated in the pathogenesis of ASH and NASH. The aim of this study was to determine the chemical characteristics of compounds that are important to inhibit CYP2E1. To this end, structurally related analogs that differed in their lipophilic, steric and electronic properties were tested. In addition, homologues series of aliphatic primary alcohols, secondary alcohols, aldehydes, ketones and carboxylic acids were tested. It was found that inhibition of the CYP2E1 activity is primarily governed by lipophilicity. The optimal log D7.4 (octanol/water distribution coefficient at pH 7.4) value for inhibition of CYP2E1 was approximately 2.4. In the carboxylic acids series the interaction of the carboxylate group with polar residues lining the CYP2E1 active site also has to be considered. This study sketches the basic prerequisites in the search for inhibitors of CYP2E1, which would strengthen our therapeutic armamentarium against CYP2E1 associated diseases, such as ASH and NASH.

Paracetamol as a Post Prandial Marker for Gastric Emptying, A Food-Drug Interaction on Absorption.

UNLABELLED: The use of paracetamol as tool to determine gastric emptying was evaluated in a cross over study. Twelve healthy volunteers were included and each of them consumed two low and two high caloric meals. Paracetamol was mixed with a liquid meal and administered by a nasogastric feeding tube. The post prandial paracetamol plasma concentration time curve in all participants and the paracetamol concentration in the stomach content in six participants were determined. It was found that after paracetamol has left the stomach, based on analysis of the stomach content, there was still a substantial rise in the plasma paracetamol concentration time curve. Moreover, the difference in gastric emptying between high and low caloric meals was missed using the plasma paracetamol concentration time curve. The latter curves indicate that (i) part of the paracetamol may leave the stomach much quicker than the meal and (ii) part of the paracetamol may be relatively slowly absorbed in the duodenum. This can be explained by the partition of the homogenous paracetamol-meal mixture in the stomach in an aqueous phase and a solid bolus. The aqueous phase leaves the stomach quickly and the paracetamol in this phase is quickly absorbed in the duodenum, giving rise to the relatively steep increase of the paracetamol concentration in the plasma. The bolus leaves the stomach relatively slowly, and encapsulation by the bolus results in relatively slow uptake of paracetamol from the bolus in the duodenum. These findings implicate that paracetamol is not an accurate post prandial marker for gastric emptying. The paracetamol concentration time curve rather illustrates the food-drug interaction on absorption, which is not only governed by gastric emptying. TRIAL REGISTRATION: ClinicalTrials.gov NCT01335503 Nederlands Trial Register NTR2780.

Randomised clinical study: Aspergillus niger-derived enzyme digests gluten in the stomach of healthy volunteers.

BACKGROUND: Aspergillus niger prolyl endoprotease (AN-PEP) efficiently degrades gluten molecules into non-immunogenic peptides in vitro. AIM: To assess the efficacy of AN-PEP on gluten degradation in a low and high calorie meal in healthy subjects. METHODS: In this randomised, double-blind, placebo-controlled, cross-over study 12 healthy volunteers attended to four test days. A liquid low or high calorie meal (4 g gluten) with AN-PEP or placebo was administered into the stomach. Via a triple-lumen catheter gastric and duodenal aspirates were sampled, and polyethylene glycol (PEG)-3350 was continuously infused. Acetaminophen in the meals tracked gastric emptying time. Gastric and duodenal samples were used to calculate 240-min area under the curve (AUC0-240 min ) of ?-gliadin concentrations. Absolute ?-gliadin AUC0-240 min was calculated using duodenal PEG-3350 concentrations. RESULTS: AN-PEP lowered α-gliadin concentration AUC0-240 min, compared to placebo, from low and high calorie meals in stomach (low: 35 vs. 389 µg × min/mL; high: 53 vs. 386 µg × min/mL; P < 0.001) and duodenum (low: 7 vs. 168 µg × min/mL; high: 4 vs. 32 µg × min/mL; P < 0.001) and absolute α-gliadin AUC0-240 min in the duodenum from low (2813 vs. 31 952 µg × min; P < 0.001) and high (2553 vs. 13 095 µg × min; P = 0.013) calorie meals. In the placebo group, the high compared to low calorie meal slowed gastric emptying and lowered the duodenal α-gliadin concentration AUC0-240 min (32 vs. 168 µg × min/mL; P = 0.001). CONCLUSIONS: AN-PEP significantly enhanced gluten digestion in the stomach of healthy volunteers. Increasing caloric density prolonged gastric residence time of the meal. Since AN-PEP already degraded most gluten from low calorie meals, no incremental effect was observed by increasing meal caloric density. ClinicalTrials.gov, Number: NCT01335503; www.trialregister.nl, Number: NTR2780.

The role of antioxidants in ischaemia-reperfusion in a human DIEP flap model.

BACKGROUND: A better understanding of the pathophysiology of ischaemia-reperfusion injury and a possible treatment for it, is of great importance. The deep inferior epigastric perforator (DIEP) flap is an innovative, clinical model of ischaemia-reperfusion. There has been an ongoing interest in the health benefits and medical applications of antioxidants. We hypothesised that during ischaemia-reperfusion, specific antioxidants are depleted. METHODS: Seventeen DIEP flaps were performed in 15 patients undergoing breast reconstruction. In each free flap, 3-mm skin biopsies were taken from the DIEP flap at four different time points during and after surgery. In those tissue biopsies, concentrations of the antioxidants vitamin E, glutathione (GSH) and uric acid and total antioxidant capacity (TEAC) were measured. RESULTS: Unexpectedly, no immediate change was observed in GSH concentrations during ischaemia-reperfusion. Uric acid concentrations were significantly increased at all time points following reperfusion. Vitamin E concentrations also showed a significant incline 30min and 1h after reperfusion. However, 1h after reperfusion, a significant decrease in total hydrophilic antioxidant capacity (TEAC) was seen. In the next hour, this capacity recovered. CONCLUSIONS: During ischaemia-reperfusion, a deficiency in hydrophilic antioxidant capacity develops. This is a potential cause for the development of ischaemia-reperfusion injury by reactive oxygen species. This clinical trial is registered on Clinical Trials: http://www.clinicaltrials.gov/. Trial registry name: The DIEP-flap as a model of ischaemia-reperfusion. Registration identification number (NCT): 00482469.

Differences in pharmacological activities of the antioxidant flavonoid monoHER in humans and mice are caused by variations in its metabolic profile.

Despite its well-known cardiotoxicity, the anthracycline doxorubicin continues to be a widely used chemotherapeutic agent. The flavonoid 7-mono-O-(ß-hydroxyethyl)-rutoside (monoHER) has shown protection against doxorubicin-induced cardiotoxicity in mice. However, this protection has not been observed in humans. This prompted us to investigate monoHER metabolism in humans and compare it with that in mice. Five healthy volunteers received monoHER by intravenous infusion. After infusion, bile fluid was collected, and the monoHER metabolites were identified by liquid chromatography-diode-array detection (LC-DAD), time-of-flight mass spectrometry (TOF-MS), and (1)H-nuclear magnetic resonance (NMR). Thirteen different metabolites were identified. MonoHER was predominantly converted into inactive glucuronidated metabolites. In mice, the major metabolic route is methylation, which forms bioactive metabolites that are implicated in the cardioprotective effect of monoHER. This indicates that the different pharmacological effects of monoHER in mice and humans might be explained by a difference in monoHER metabolism. This study adds to the growing appreciation of flavonoid metabolites as bioactive compounds.

The semisynthetic flavonoid monoHER sensitises human soft tissue sarcoma cells to doxorubicin-induced apoptosis via inhibition of nuclear factor-κB.

BACKGROUND: Despite therapeutic advances, the prognosis of patients with metastatic soft tissue sarcoma (STS) remains extremely poor. The results of a recent clinical phase II study, evaluating the protective effects of the semisynthetic flavonoid 7-mono-O-(ß-hydroxyethyl)-rutoside (monoHER) on doxorubicin-induced cardiotoxicity, suggest that monoHER enhances the antitumour activity of doxorubicin in STSs. METHODS: To molecularly explain this unexpected finding, we investigated the effect of monoHER on the cytotoxicity of doxorubicin, and the potential involvement of glutathione (GSH) depletion and nuclear factor-κB (NF-κB) inactivation in the chemosensitising effect of monoHER. RESULTS: MonoHER potentiated the antitumour activity of doxorubicin in the human liposarcoma cell line WLS-160. Moreover, the combination of monoHER with doxorubicin induced more apoptosis in WLS-160 cells compared with doxorubicin alone. MonoHER did not reduce intracellular GSH levels. On the other hand, monoHER pretreatment significantly reduced doxorubicin-induced NF-κB activation. CONCLUSION: These results suggest that reduction of doxorubicin-induced NF-κB activation by monoHER, which sensitises cancer cells to apoptosis, is involved in the chemosensitising effect of monoHER in human liposarcoma cells.

The olive oil antioxidant hydroxytyrosol efficiently protects against the oxidative stress-induced impairment of the NObullet response of isolated rat aorta.

The Mediterranean diet, which is abundant in antioxidants, is associated with a relatively low incidence of coronary heart disease. Olive oil and olives, which contain the antioxidants hydroxytyrosol, oleuropein, and tyrosol, are important components of this diet. In this study, the effects of oxidative stress on the nitric oxide radical (NO(*))-mediated relaxation of rat aorta and the protection by these antioxidants were determined. Cumene hydroperoxide (CHP) was used to mimic oxidative stress induced by lipid hydroperoxides, which is mediated by the formation of hydroxyl radicals (OH(*)). CHP (300 microM) impaired the NO(*)-mediated relaxation of rat aorta by the acetylcholine receptor agonist carbachol (P < 0.05). This was due to a reduction in NO(*) production. A diminished NO(*)-mediated relaxation disturbs the vascular tone and leads to a rise in blood pressure, which is a well-established risk factor for coronary heart disease. Hydroxytyrosol (10 microM) efficiently protected the aorta against the CHP-induced impairment of the NO(*)-mediated relaxation (P < 0.05). Oleuropein, tyrosol, and homovanillic alcohol, a major metabolite of hydroxytyrosol, did not show protection. Moreover, hydroxytyrosol was found to be a potent OH(*) scavenger, which can be attributed to its catechol moiety. Because of its amphiphilic characteristics (octanol-water partitioning coefficient = 1.1), hydroxytyrosol will readily cross membranes and provide protection in the cytosol and membranes, including the water-lipid interface. The present study provides a molecular basis for the contribution of hydroxytyrosol to the benefits of the Mediterranean diet.

Protectors against doxorubicin-induced cardiotoxicity: flavonoids.

Doxorubicin is a widely used anthracycline anticancer agent. Its use may cause cardiomyopathy: in fact, the development of cumulative dose-related cardiotoxicity forms the major limitation of clinical doxorubicin use. We therefore searched for protective agents that combine iron-chelating and oxygen radical-scavenging properties. Moreover, any novel protector should not interfere with the cytostatic activity of doxorubicin. After extensive in vitro screening we found that flavonoids could serve this purpose. In particular 7-monohydroxyethylrutoside almost completely protected against the negative inotropic action of doxorubicin in the electrically paced mouse left atrium model. In vivo it gave full protection at 500 mg/kg intraperitoneally against the doxorubicin-induced ST-interval lengthening in the ECG. Moreover, this protector did not influence the antitumor effect of doxorubicin either in vitro using the human ovarian cell lines A2780 and OVCAR-3 and the human breast cancer cell line MCF-7 or in vivo in A2780 and OVCAR-3 subcutaneous xenografts in nude mice. Comparison of various iron chelators suggest that iron, in contrast to the general assumption, might not play a crucial role in the oxidative stress-induced toxicity of doxorubicin. Moreover, incubation of vascular endothelial cells with doxorubicin produced overexpression of adhesion molecules, which could be inhibited by 7-monohydroxyethylrutoside. From a study in human volunteers, we conclude that an intravenous dose of 1500 mg/m(2) of 7-monohydroxyethylrutoside is feasible and is safe to be investigated as protection against doxorubicin-induced cardiotoxicity.

The thiol reactivity of the oxidation product of 3,5,7-trihydroxy-4H-chromen-4-one containing flavonoids.

Flavonoids are assumed to have beneficial effects due to their antioxidant properties. The catechol moiety present in numerous flavonoids is oxidized during the antioxidative reaction yielding a quinone. Quinones are toxic due to their ability to react, e.g. with thiol groups. The 3,5,7-trihydroxy-4H-chromen-4-one group is another antioxidant pharmacophor in certain flavonoids. During the antioxidative reaction this group is also oxidized. The aim of the present study is to determine the thiol reactivity of this oxidized group. Galangin is a flavonoid that only contains the 3,5,7-trihydroxy-4H-chromen-4-one group as the antioxidant pharmacophor. Incubation of galangin with horseradish peroxidase/H(2)O(2) leads to an oxidation product which after addition of glutathione is instantaneously converted to an adduct. Based on these results it is expected that--similar to the catechol containing antioxidants--the 3,5,7-trihydroxy-4H-chromen-4-one containing antioxidants shift the damage provoked by oxidative stress from lipid peroxidation to thiol arylation. This should be considered in application of these types of antioxidants.

Oxidant metabolism in chronic obstructive pulmonary disease.

The development and progression of chronic obstructive pulmonary disease (COPD) have been associated with increased oxidative stress or reduced antioxidant resources. Several indicators of oxidative stress, such as hydrogen peroxide exhalation, lipid peroxidation products and degraded proteins, are indeed elevated in COPD patients. As a result, the antioxidant capacity decreases in COPD patients. The fall in antioxidant capacity of blood from COPD patients should not only be regarded as a reflection of the occurrence of oxidative stress but also as evidence that oxidative stress spreads out to the circulation and can therefore generate a systemic effect. COPD is linked to weight loss and in particular to loss in fat-free mass by skeletal muscle wasting. This systemic effect can be mediated by both oxidative stress and oxidative stress-mediated processes like apoptosis and inflammation. Furthermore, COPD is a predisposition for lung cancer through several mechanisms including oxidative stress and oxidative stress-mediated processes such as inflammation and disruption of genomic integrity. Current therapeutic interventions against the far-reaching consequences of the systemic oxidative stress in chronic obstructive pulmonary disease are not yet optimised. A diet designed to reduce chronic metabolic stress might form an effective therapeutic strategy in chronic obstructive pulmonary disease.

Lack of inhibition of endothelial nitric oxide synthase in the isolated rat aorta by doxorubicin.

Besides inducing cardiotoxicity, doxorubicin also affects the vasculature. Recent observations in cultured endothelial cells indicated that the endothelial form of nitric oxide synthase might be inhibited by doxorubicin thereby seriously interfering with vascular function. We have investigated the effect of doxorubicin on the relaxation induced by the muscarinic agonist carbachol in the isolated rat aorta. It was found that doxorubicin at concentrations up to 50 microM does not alter the relaxant response to carbachol. Direct measurement of nitrite, the metabolite of NO*, by the Griess assay confirmed our observation that NO*)production is not inhibited by doxorubicin.

Analysis of oxidative DNA damage after human dietary supplementation with linoleic acid.

It has been hypothesized that oxygen radicals generated by peroxidation of dietary linoleic acid may induce genetic damage and thereby increase cancer risk. We examined the effect of dietary supplementation with linoleic acid on the levels of oxidative DNA damage in peripheral lymphocytes and on the blood plasma antioxidant potential. Thirty volunteers received during 6 weeks either a high dose of linoleic acid (15 g/day), an intermediate dose of linoleic acid (7.5 g/day) or an isocaloric supplement without linoleic acid (15 g palmitic acid/day). After the intervention, no significant increase in oxidative DNA damage, measured as relative amounts of 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxodG) in DNA from peripheral lymphocytes, was observed in both high and intermediate linoleic acid-supplemented groups (increase of respectively 13 and 21%; P>0.05). Also, the differences between levels of oxidative DNA damage in the high or intermediate linoleic acid-supplemented group and the control group receiving palmitic acid (23% decrease) were not significant. Furthermore, no statistically significant differences were found between the total antioxidant capacities of blood plasma from the different experimental groups. Plasma levels of malondialdehyde, an important end-product of lipid peroxidation, were not increased after supplementation, nor were effects found on the plasma concentrations of retinol, alpha-tocopherol and beta-carotene. Despite the experimental design that excludes several forms of bias introduced in studies based on modulation of dietary composition, our results provide no indication of increased oxidative stress or genetic damage as a result of increased dietary intake of linoleic acid. Therefore, we see no scientific basis to reconsider the public health policy to stimulate the intake of polyunsaturated fatty acids aimed at the reduction of coronary heart diseases.

The use of vitamin supplements in self-medication.

Supplements, frequently containing vitamins, are often taken to try to compensate for an unhealthy life style or in an attempt to maximise health or performance. As illustrated by vitamin E, fundamental issues on both the efficacy and safety of the chronic use of relatively high dosages of vitamins still need to be resolved. To recommend the application of vitamin supplements, firstly the gaps in our knowledge on these fundamental issues should be filled. Secondly, objective and scientifically sound information should be given to the public. Via diverse sources there is an uncontrolled supply of vitamins. Educating the consumer on vitamins is therefore the only way to come to a rational use of vitamin supplements in self medication.

Hypochlorous acid is a potent inhibitor of GST P1-1.

Glutathione S-transferase is a phase II detoxification enzyme that can be inactivated by H(2)O(2). During oxidative stress various other reactive oxygen species are generated that are more reactive than the relatively stable H(2)O(2). Hypochlorous acid (HOCl) is a powerful oxidant which is highly reactive towards a range of biological substrates. We studied the influence of HOCl on the activity of GST P1-1. HOCl inhibits purified glutathione S-transferase P1-1 in a concentration dependent manner with an IC(50)-value of 0.6 microM, which is more than 1000 times as low as IC(50) reported for H(2)O(2). HOCl lowered the V(max) value, but did not affect the K(m) for CDNB. Our results show that HOCl is a potent, non-competitive inhibitor of GST P1-1. The relevance of this effect is discussed.

Transcription factor NF-kappaB as a potential biomarker for oxidative stress.

There is increasing interest in the involvement of transcription factors, such as of the transcription factor NF-kappaB (nuclear factor-kappaB), in the pathogenesis of various diseases. NF-kappaB is involved in the control of the transcription of a variety of cellular genes that regulate the inflammatory response by the production of cytokines, chemokines, cell adhesion molecules and acute phase proteins. The involvement of NF-kappaB is especially of interest as it is activated by oxidative stress and its activation can be modulated by antioxidant compounds. The activation of NF-kappaB can be determined by the electromobility shift assay (EMSA) with a NF-kappaB binding-site-specific probe. EMSA can also be used on human mononuclear cells isolated from peripheral blood, which could make the assay applicable for clinical trials. The critical steps of the EMSA are discussed, addressing some pitfalls of the assay. The procedure that can be used to express NF-kappaB activity in human subjects is evaluated. This offers the possibility to use NF-kappaB as a functional biomarker of oxidative stress as illustrated by several examples of in vitro and in vivo studies.

Masking of antioxidant capacity by the interaction of flavonoids with protein.

The effect of antioxidants is often executed in complex biological mixtures where various interactions may take place. Therefore, the antioxidant capacity of antioxidants in blood plasma is examined. The assay used is the trolox equivalent antioxidant capacity (TEAC). This method gives the antioxidant capacity of a compound by measuring spectrophotometrically the disappearance of the blue/green stable ABTS [2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)] radical, caused by scavenging. The results show that the antioxidant capacity of quercetin, rutin, catechin or 7-monohydroxyethylrutoside (monoHER) and blood plasma is not additive. This is partly due to interactions between the antioxidant and plasma proteins. However, the antioxidant capacity of alpha-tocopherol, which also binds to protein, is not affected by the interaction. This means that besides the antioxidant capacity of the compound itself, the environment in which the antioxidant has to execute his function is important.