Influence of bile acids on stimulated lipid peroxidation and hydrogen peroxide production in rat liver microsomes

In vitro investigation of a standardized dried extract of Citrullus colocynthis on liver toxicity in adult rats

A standardized extract of Citrullus colocynthis used as an oral natural laxative in folk medicine was tested for its influence on liver function parameters in vitro. Cytochrome P450 (CYP) dependent production of reactive oxygen species (ROS) under the influence of Citrullus colocynthis extract was investigated by means of stimulated lipid peroxidation (LPO), H2O2 formation and amplified chemiluminescence in rat liver microsomes. In rat liver 9000 x g supernatants 4 monooxygenase reactions mediated by different CYP forms were measured. Putative hepatotoxic effects of Citrullus colocynthis extract were measured by means of potassium and GSH concentrations in and LDH leakage from precision-cut rat liver slices. For possible hepatoprotective effects the influence of the extract on carbon tetrachloride-induced changes of these parameters was investigated. Citrullus colocynthis extract in concentrations higher than 10 microg/ml incubation mixture proved to inhibit lipid peroxidation and ROS-production as well as CYP1A-, 2B- and 3A-dependent reactions with typical substrates. In contrast, H2O2 production was not reduced under the influence of the extract, a slight but significant increase was seen. Citrullus colocynthis extract was found to be free of hepatotoxic effects in concentrations up to 100 microg/ml incubation mixture when liver slices were incubated in William's medium E for 22 hours. All viability parameters used were not influenced by the extract of Citrullus colocynthis. Carbon tetrachloride induced hepatotoxicity could not be prevented or alleviated. Moreover, the damage was sometimes enhanced by higher extract concentrations.

Estradiol, testosterone, dehydroepiandrosterone and androstenedione: novel derivatives and enantiomers. Interactions with rat liver microsomal cytochrome P450 and antioxidant/radical scavenger activities in vitro

Interactions of 27 steroids, among them 17 derivatives such as ethers, sulfates and amidosulfonates derived from 17 beta- and 17 alpha-estradiol, from testosterone and alpha- and beta-dihydrotesosterone and from dehydroepiandrosterone with rat liver microsomal cytochromes P450 (P450) were investigated in vitro by assessing binding to P450 and effects on P450 mediated monooxygenase functions as measured by different model reactions: ethoxyresorufin O-deethylation (EROD), ethoxycoumarin O-deethylation (ECOD) and ethylmorphine N-demethylation (EMND). With the exception of 17 alpha-estradiol-3-dimethylamidosulfonate, estrone, its -3-methylether and -3-amidosulfonate and testosterone, all other steroids displayed type I or reverse type I binding to P450. All steroids inhibited EROD activity in micromolar concentrations. An additional strong inhibition of ECOD and EMND activities was only demonstrated for the androgens and progestins. Estriol, estrone and mestranol displayed less inhibitory actions on the model reactions than estradiol. No major differences in comparison to the parent compounds were noted with the other derivatives. The only exceptions were 17 beta-(8,9-dehydro-14 alpha,15 alpha-methylene)estradiol, which displayed stronger effects than estradiol, and dehydroepiandrosterone-3-sulfate, which was less effective than dehydroepiandrosterone. Possible antioxidant properties of the steroids were examined by the stimulated lipid peroxidation (LPO), H2O2 production, and lucigenin (LC) and luminol (LM) amplified chemiluminescence (CL) using rat liver microsomes. Additionally, the influence on rat whole blood chemiluminescence (WB-CL) was assessed. All the estrogens, but not their methylethers and amidosulfonates inhibited LPO in micromolar concentrations. The effects on the other oxidase model reactions or on WB-CL were less distinct. Only ethinylestradiol and 17 beta-(8,9-dehydro-14 alpha,15 alpha-methylene)estradiol displayed a strong inhibitory action on all model reactions. With the exception of dehydroepiandrosterone-3-sulfate, which in general had only weak effects, the androgen and progestin derivatives, in contrast, strongly decreased H2O2 formation and LM- and LC-CL, but were mostly ineffective on LPO and WB-CL.

Influence of subchronic administration of catechol estrogens on the formation of reactive oxygen species in rat liver microsomes

Metabolic pathways of estrogens are the formation of catechol estrogens (CE; 2- and 4-hydroxy-estrogens), redox cycling of CE and free radical generation, mediated through cytochrome P450 (P450) oxidase/reductase activity. In previous investigations subchronic administration of estrogens showed prooxidative and antioxidative activities in rat liver microsomes (BARTH et al. 1999). To find out whether or not catechol metabolites are responsible for prooxidative activity, we checked 2- and 4-hydroxy-estradiol (2OH-E2 and 4OH-E2) and the non-catechol metabolite 6alpha-hydroxy-estradiol (6alpha-OH-E2) for formation of reactive oxygen species in liver microsomes of 30-day-old male Wistar rats after 5 days treatment (1, 10 mg/kg b. wt. orally, once a day). The results were compared with those after treatment of the rats with estradiol (E2), estradiol valerate (E2V) and ethinylestradiol (EE2). In liver homogenates glutathione and lipid peroxides were determined, in microsomes NADPH-Fe++-stimulated lipid peroxidation (LPO), H2O2 generation and lucigenin (LUC) and luminol (LUM) amplified chemiluminescence (CL) were investigated. In liver 9000 x g supernatants monooxygenase activities were measured. The two catechol estrogens did not show any antioxidative activity, whereas 6alpha-OH-E2 significantly diminished lipid peroxides in the liver as well as LPO and LUM-CL in liver microsomes. Among estrogens, only EE2 showed antioxidative activity. Both CE inhibited ethoxycoumarin O-deethylation. Peroxidative activity as enhanced LUC-CL was found after 2OH-E2 (1 mg/kg b.wt.) and E2, but 10 times higher doses of both CE did not change LUC-CL. Microsomal H2O2 generation was enhanced by E2, E2V and both CE, not by 6alpha-OH-E2. The lower level of H2O2 enhancement caused by CE in comparison to E2 and E2V together with unchanged LUC-CL after high CE doses did not unequivocally prove the CE to be mainly responsible for the prooxidative activities of E2 and E2V in liver microsomes, at least in 30-day-old male rats. Unchanged GSH in the liver after CE administration supports this hypothesis.

Influence of oestrogens on formation of reactive oxygen species in liver microsomes of differently aged male Wistar rats

Metabolic pathways of oestrogens are the formation of catechol oestrogens (CE; 2- and 4-hydroxy-oestrogens), redox cycling of CE and free radical generation, mediated through cytochrome P450 (P450) oxidase/reductase activity. We checked the oestrogens oestradiol (E2), oestradiol valerate (E2V) and ethinyloestradiol (EE2) for formation of reactive oxygen species in vitro and ex vivo in male Wistar rats in dependence on age. In liver microsomes of 10-, 30-, 60- and 270-day-old rats the influence of E2, E2V and EE2 (10(-7)-10(-3) M) on NADPH-Fe(++)-stimulated lipid peroxidation (LPO), H2O2 generation and lucigenin (LUC) and luminol (LUM) amplified chemiluminescence (CL) was investigated. The same parameters, additionally P450 content and monooxygenase activities were measured in liver 9000 x g supernatants after subchronic administration of the oestrogens (1, 10 mg/kg b. wt. orally). The most important results are the strong inhibitory capacities of the oestrogens in vitro on LPO in the order of E2V < E2 < EE2, most pronounced in 10-, 60- and 270-day-old animals. In microsomes of 30-day-old rats with the highest control LPO the antioxidative effect of the oestrogens was lower. Whereas the H2O2 generation was not changed by E2, enhanced by E2V, but diminished by EE2 in all age groups, CL(LUC) and CL(LUM) were inhibited in the order of E2 < E2V < EE2. Also after subchronical treatment of the rats the antioxidative action of the oestrogens was evident, microsomal LPO was inhibited in the order of E2 < E2V < EE2. All oestrogens inhibited ethylmorphine N-demethylation. But enhanced H2O2 generation and increased CL(LUC) also indicate a formation of reactive oxygen species by these oestrogens. Obviously in vitro the antioxidative phenolic structure of the oestrogens dominates, whereas after in vivo administration the dose- and age-dependent biotransformation produces prooxidative in addition to antioxidative structures.

Participation of reactive oxygen metabolites in Clostridium difficile toxin A-induced enteritis in rats

Reactive oxygen metabolites (ROMs) contribute to the pathophysiology of intestinal inflammation. Our aim was to ascertain the involvement of ROMs in experimental ileitis in rats produced by toxin A of Clostridium difficile. Intraluminal toxin A caused a significant increase in hydroxyl radical and hydrogen peroxide production by ileal microsomes starting 1 h following toxin exposure and peaking at 2-3 h, and this was inhibited by pretreatment with DMSO, a ROM scavenger, or superoxide dismutase (SOD), which inactivates ROMs. In contrast, mucosal xanthine oxidase increased only slightly after toxin A exposure, and allopurinol, an inhibitor of xanthine oxidase, had no effect on toxin A-associated intestinal responses. Induction of neutropenia resulted in reduction of toxin-mediated free radical formation, fluid secretion, and permeability. The enterotoxic effects of C. difficile toxin A were associated with increased ROM release in ileal tissues, and the ROM inhibitors DMSO and SOD inhibited these effects. This suggests that ROMs released during toxin A enteritis are released primarily from neutrophils invading the inflamed bowel segment.

The role of ursodeoxycholic acid in bile acid-mediated kidney fragment toxicity

Elevated levels of bile acids are thought to play an important role in the renal failure of patients with obstructive jaundice undergoing surgery. In contrast, ursodeoxycholic acid (UDA) is widely used to improve cholestasis and has been proposed as protective bile acids and antioxidant. The present study employs kidney fragments to determine the role of reactive oxygen species (ROS) in the mechanism of toxicity of hydrophobic bile acids and to determine the nephroprotectant properties of UDA against the hydrophobic bile acids. The hydrophobic bile acids chenodeoxycholic (200 microM) and deoxycholic acid (200 microM) significantly (P<0.05) increased lactate dehydrogenase leakage (LDH) from glomerular fragments from 2.7+/-0.4 to 5.03+/-0.23 and 4.66+/-0.37 (micromol NADH consumed/min/mg protein) for chenodeoxycholic and deoxycholic acid respectively. Preincubating the fragments with UDA (500 microM) did not prevent the leakage of LDH caused by the bile acids. The level of lipid peroxidation was not increased in fragments exposed to either ursodeoxycholic (0-500 microM), lithocholic (0-100 microM), chenodeoxycholic (0-500 microM) or deoxycholic acid (0-500 microM). Furthermore UDA (500 microM) did not prevent the increase in lipid peroxidation caused by tert-butyl hydroperoxide (0-1000 microM) in the fragments. These results suggest that hydrophobic bile acids do not cause lipid peroxidation in kidney fragments and that UDA is neither capable of preventing the loss of membrane integrity induced by hydrophobic bile acids or acting as an antioxidant in kidney fragments.

Interaction of chlormezanone enantiomers with rat liver microsomes

Both chlormezanone enantiomers, for the first time obtained by enantiospecific HPLC with a 100% yield, bind to oxidized cytochrome P-450 in rat liver microsomes with a binding curve according to type I, similar to hexobarbital but less pronounced. There are no differences between the binding curves of the two enantiomers. Ethylmorphine N-demethylation, ethoxycoumarin and ethoxyresorufin O-deethylation are inhibited by both chlormezanone enantiomers at 0.1-1 mM concentrations: no differences could be found. Luminol and lucigenin amplified chemiluminescence indicating the formation of reactive oxygen species was not influenced by either enantiomer in concentration ranges between millimolar and micromolar, whereas hydrogen peroxide formation was inhibited. NADPH/Fe stimulated lipid peroxidation was not influenced. Scavenger activity could not be demonstrated: the zymosan stimulated whole blood chemiluminescence was not influenced significantly.

Chromatographic resolution of ciprofibrate and interaction of the racemate and both enantiomers with rat liver microsomes in vitro

The enantiomers of ciprofibrate may be achieved by enantioselective HPLC separation of its methylesters using a OD - Daicel column. Ciprofibrates (racemate and both enantiomers) bind to oxidized cytochrome P-450 in rat liver microsomes according type II like aniline or most probably as inversed type I, but less pronounced and with a general shift to the left. Ethylmorphine N-demethylation, ethoxycoumarin and ethoxyresorufin O-deethylation are all inhibited by the ciprofibrates, most effectively ethoxyresorufin O-deethylation by S(-)-ciprofibrate even in microM concentrations. Microsomal luminol and lucigenin amplified chemiluminescence indicating the formation of reactive oxygen species, microsomal hydrogen peroxide formation and NADPH/Fe stimulated lipid peroxidation were inhibited in a concentration dependent manner in concentration ranges between mM and microM. This might be due to distinct scavenger activities of all 3 compounds: the zymosan stimulated chemiluminescence of whole blood was completely inhibited in mM concentrations and influenced significantly down to concentrations of 10 microM, whereas burst and phagocytosis tests with human polynuclear leucocytes were not influenced.

Ciprofibrate--racemate and enantiomers: effects of a four-week treatment on male inbred Fischer rats. A biochemical and morphological study

Ciprofibrates (racemate and both enantiomers, Raccip, R- and Scip) were administered orally in doses of 1 and 10 mg/kg once daily over 28 days to male inbred Fischer 344 rats, age 90-110 days at the beginning of the experiment. Body mass gain was observed in all groups. The 1 mg groups showed almost no difference to the control group. The 10 mg groups exhibited less body mass gain, most pronounced in the Scip group. Liver masses were increased in a dose dependent manner up to more than 200%, only the 10 mg Scip group was not significantly different from the 1 mg group which exhibited an increase in liver weight to about 175%. Also the kidney weights increased to 130%, whereas thymus and spleen weights were decreased in the high dose groups. Liver microsomal cytochromes P450 (P450) concentrations were not altered in the 1 mg groups and distinctly lowered in the 10 mg groups. Ethoxyresorufin and ethoxycoumarin O-deethylations were lowered in all experimental groups in a dose dependent manner, after administration of the high doses down to 30% of the control levels or less. Pentoxyresorufin O-depentylation, however, was increased in all 1 mg groups. In the high dose groups it was not altered. Ethylmorphine N-demethylation was decreased after administration of the high doses by about 50%, but only Scip decreased this reaction also after administration of the low dose. NADPH/Fe2+-stimulated microsomal luminol and lucigenin amplified chemiluminescence was increased, whereas hydrogen peroxide formation was depressed even by the low doses to 50% of the normal values, to about 25% by the high doses. Microsomal lipid peroxidation, however, was only slightly or not influenced. Glutathion concentrations (in the reduced and the oxidized form) were increased in a dose dependent manner by about 20 to 30%, the concentration of lipid peroxides was not significantly influenced. Thus, the effects of the enantiomers were not different and were similar to those of the racemate. In serum, cholesterol and triglycerides were only moderately lowered. Albumin concentrations were significantly enhanced in all groups, total proteins after 1 mg/kg Raccip only. Serum bilirubins were not altered, and among the indicator enzymes for liver damage only ALAT, alkaline phosphatase and the dehydrogenases were increased, in no case higher than twofold. Histologically distinct effects were seen after administration of both doses, more pronounced after 10 mg/kg, but with no differences between the enantiomers and Raccip: marked hypertrophy of the hepatocytes, reduced staining of the nuclei, strongly acidophilic granulated cytoplama, no basophilia of the cell bodies, loss of glycogen. These changes were most pronounced around the central veins. Hepatocyte apoptoses also were observed. By immunohistochemistry an increased staining was seen for all P450 isoforms tested (1A1, 2B1, 2E1, 3A2 and 4A1), predominantly perivenously and most pronounced after administration of the high doses without differences between Rcip, Scip or Raccip (preliminary results). By electron microscopy a moderate proliferation of peroxisomes after treatment with 1 mg/kg Cips with a ratio between mitochondria and peroxisomes of about 1:1 (controls: 10:1) was observed, and the peroxisomes were a more heterogeneous population. The relative portions of glycogen and both forms of the ER decreased. Treatment with 10 mg/kg Rcip, Scip or Raccip led to a strong increase in the number of peroxisomes, in some hepatocytes the ratio between mitochondria and peroxisomes was 1:3 with an increased heterogeneity among the peroxisomes evidenced by a broad range of electron densities. Most peroxisomes lacked a nucleoid. Thus, the biochemical effects differed only slightly and the morphological effects of the enantiomers were not different and were similar to those of the racemate.

Luminol and lucigenin amplified chemiluminescence and lipidperoxidation with brain microsomes from rats during ontogenetic development

The chemiluminescence (CL) amplifiers luminol (LM) and lucigenin (LC) react with different reactive oxygen species (ROS) in dependence on the ROS generating system used. With liver microsomes LMCL indicates predominantly superoxide anion radicals, whereas LCCL is mainly a measure for hydroxyl radical formation or of reactive organic radicals. With brain microsomes only LCCL, but not LMCL could be measured. For both brain microsomes from newborn (both sexes) and 60 day-old (male) rats LCCL is dependent on protein and NADPH concentration, activity in newborns being only 15% compared with young adult rats. As compared with liver microsomes 10-fold higher protein concentrations are needed to obtain comparable LCCL, whereas the NADPH demand is the same as with liver. A distinct ontogenetic development was demonstrated: low activities in the fetus, in newborn and 10-day-old rat are followed by higher activities with increasing age, after a maximum at an age of 60 days a decline was observed. Microsomal lipidperoxidation (LPO) was measured as formation of thiobarbituric acid reactive substances (TBARS) and was also dependent on protein and NADPH concentration. Unexpectedly, LPO with brain microsomes from newborn rats did not show any developmental variation.

Peroxidative and glutathione status in uterus and placenta after normal and pathological pregnancy

In 10 women with disturbed pregnancies without hypertension, reduced (GSH) and oxidized glutathione (GSSG) as well as lipid peroxides as thiobarbituric acid reactive substances (TBARS) were determined in the placenta and in the uterine tissue after unexpected stress-induced Caesarian section (group II). Production of TBARS was also measured in vitro in the 9000 x g supernatant of both tissues. The results were compared with those from women after normal pregnancy and expected Caesarian section (group I). After normal pregnancy higher TBARS and lower GSH with higher GSSG/GSH ratio were found in the placenta in comparison to the uterine tissue, indicating an oxidant/antioxidant imbalance in the placenta. No statistically significant differences were shown between the parameters of groups I and II. The possible oxidant stress associated with disturbed pregnancy and subsequent unexpected Caesarian section in this study was insufficient to alter tissue levels of glutathione nor the peroxidative status of placenta and uterus.

Interaction of chlormezanone with rat liver microsomes and its degradation

Chlormezanone binds to oxidized cytochrome P450 in rat liver microsomes with a binding curve according to type I like hexobarbital but less pronounced and with a general shift to the left. Ethylmorphine N-demethylation, ethoxycoumarin and ethoxyresorufin O-deethylation are inhibited by chlormezanone in mM concentrations only whereas pentoxyresorufin O-depentylation is inhibited by about 50% in microM concentrations. Luminol and lucigenin amplified chemiluminescence indicating the formation of reactive oxygen species was not influenced in concentration ranges between mM and microM, whereas NADPH/Fe stimulated lipid peroxidation showed a tendency of inhibition. But scavenger activity could not be demonstrated: the zymosan stimulated chemiluminescence of whole blood was not influenced significantly. The degradation process of chlormezanone was elucidated. The first step involves ring opening by chemical hydrolysis with subsequent formation of an unstable acylhalfaminal which is the source of 4-chlorobenzaldehyde. This aldehyde undergoes enzymatically controlled oxidation to 4-chlorobenzoic acid which is the parent compound of following phase II reactions. The second degradation product is 2-carboxyethane-sulfinic-acid-N-methylamide, which is hydrolyzed very quickly. Neither oxidation of the sulfinic acid or its N-methylamide derivative could be observed nor N-demethylation of chlormezanone.

Review of progress in sterol oxidations: 1987-1995

Material dealing with the chemistry, biochemistry, and biological activities of oxysterols is reviewed for the period 1987-1995. Particular attention is paid to the presence of oxysterols in tissues and foods and to their physiological relevance.

Influence of the xanthine derivative denbufylline and the anti-inflammatory agent nabumetone on microsomal free radical production and lipid peroxidation in rat liver

The influence of denbufylline, nabumetone and its main metabolite BRL 10,720 on iron stimulated lipid peroxidation (LPO), cytochrome P 450 dependent H2O2 and chemiluminescence (CL) production was investigated in rat liver microsomes in vitro (10(-5)-10(-3) M) and in vivo after treatment of rats (5-300 mg/kg b.m. orally on three consecutive days). In rat liver slices the release of thiobarbituric acid reactants (TBAR) was measured after 1 hour of incubation with the drugs. Denbufylline, nabumetone and BRL 10,720 exerted a significant inhibition of iron stimulated LPO in vitro. Nabumetone showed the strongest antioxidative activity, which was also seen in liver slices. These antioxidative effects were not found after in vivo treatment of rats. Denbufylline (10(-3) M) additionally inhibited H2O2 formation and the luminol and lucigenin amplified CL in vitro. Unexpectedly, nabumetone increased H2O2 formation both in vitro and in vivo, but in vitro only lucigenin amplified CL. BRL 10,720 increased microsomal H2O2 production in vivo. Moreover, BRL 10,720 enhanced CL in vitro and in vivo significantly, which is interpreted as an increase of the production of superoxide anion radicals and other reactive oxygen species such as H2O2, but lipid peroxidation in liver microsomes was not enhanced. These results suggest that denbufylline, nabumetone and BRL 10,720 in contrast to the in vitro effects did not exert antioxidative activities after treatment of rats. On the contrary, BRL 10,720 was found to support the formation of reactive oxygen species in liver microsomes.

Peroxidative status and glutathione content of the brain in normal weight and intra-uterine growth-retarded newborn piglets

The peroxidative and glutathione status as well as the production of reactive oxygen species were studied in the brain of normal weight (NW) and intra-uterine growth-retarded (IUGR) newborn piglets. In NW as well as IUGR newborn piglets reduced (GSH) and oxidized (GSSG) glutathione, lipid peroxides, iron stimulated lipid peroxidation, H2O2 production and lucigenin and luminol amplified chemiluminescence are very similar in the different brain regions, with one exception. In the cerebellum, higher GSH concentration, higher superoxide anion generation, lower levels of lipid peroxides and a tendency toward a lower capacity of H2O2 production were seen. But the intra-uterine growth retardation to body weights of half the average body weights of the respective litter did not influence the peroxidative status and the GSH/GSSG equilibrium in the brain of newborn piglets.