Mutagenesis, Vol. 18, No. 2, 211-216,
March 2003
© 2003 UK Environmental Mutagen Society/Oxford University Press
Infection of rats with Taenia taeniformis metacestodes increases hepatic CYP450, induces the activity of CYP1A1, CYP2B1 and COH isoforms and increases the genotoxicity of the procarcinogens benzo[a]pyrene, cyclophosphamide and aflatoxin B1
Instituto de Investigaciones Biomédicas and 1 Facultad de Medicina, UNAM, Apdo. Postal 70228, CP 04510, México DF, Mexico and 2 Parasitology Department, University of Asahikawa, Asahikawa, Japan
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Infection of rat liver by Taenia taeniformis metacestodes produced an increase in total CYP450 content and induced activity of the CYP1A1, CYP2B1 and COH isoforms. Variations in activity and P450 total content were found with increasing time of infection. During increased activity of P450 isoforms, rats were challenged with carcinogens metabolized by the mentioned isozymes and an increased amount of genotoxic damage was found when benzo[a] pyrene, cyclophosphamide and aflatoxin B1 were used. No change was seen in CYP2E1 activity. These results support previous findings regarding an increased susceptibility to genotoxic damage of infected organisms.
|
Introduction |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Several kinds of liver infection have been described as inducers of CYP2A isoform activity. Gentile and De Ruiter (1981)
described an increase in aflatoxin B1 (AFB1) activation in mice infected with Fasciola hepatica. In order to investigate whether this induction was due to the inflammatory reaction, Vandewaa et al. (1982) produced inflammation by hepatectomizing mice; they found that S9 from these mice activated AFB1, whereas control S9 did not.
Kirby et al. (1994a) showed that Opistorchis viverrini also increased the activity of CYP2A5 in hamster liver and increased the amount of AFB1 adducts in hepatocytes, demonstrating that procarcinogen activation is increased in infected liver. They further demonstrated this with an infection by hepatitis B virus (Kirby et al., 1994b). Montero et al. (1999) found induced expression of CYP2A5 in mouse liver infected with F.hepatica. All this evidence suggests that infections could induce an increased susceptibility to carcinogens and genotoxic agents by activating enzymes that participate in their metabolism. In fact, a study by Ross et al. (1992) supports this idea, since they found an association between an infectious disease (hepatitis B), exposure to AFB1 and hepatocarcinoma.
Other parasites are less specific about infecting liver, e.g. Taenia metacestodes infect several internal organs in humans and pigs, particularly the central nervous system and muscles, and yet increased genotoxicity in infected hosts has been described (Flisser et al., 1990; Herrera et al., 1994; Montero et al., 1994; Montero and Ostrosky, 1997; Serrano and Montero, 2001) and there is evidence of association with certain forms of cancer (Del Brutto, 1997; Herrera et al., 2000).
We were interested in exploring the possibility that Taenia metacestodes could modulate CYP450 enzymes in a manner similar to that described for O.viverrini and F.hepatica in liver. We chose a rat model, where infection with Taenia taeniformis cysts occurs in the liver. This infection takes place in a different manner to trematodes, since Taenia eggs delivered to the organ via circulation do not move as metacercariae do and, hence, they do not disrupt the tissue. Once the egg infects the liver, it develops into the metacestode form or cyst, which is sedentary and can grow up to 0.5 cm in diameter. We allowed the infection to progress for different periods in order to establish CYP450 modulation.
|
Materials and methods |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Animals
Sprague–Dawley rats (male and female), 6 weeks old, were used in groups of eight for controls and to be infected in each experiment. Every test was repeated once to confirm the results.
Chemicals
Benzo[a]pyrene (BaP), AFB1, cyclophosphamide (CP), N-nitrosodimethylamine (NDMA), coumarin, 7-hydroxycoumarin, ethoxyresorufin [to measure ethoxyresorufin dealkylase (EROD) activity], 7-pentoxyresorufin [to measure pentoxyresorufin dealkylase (PROD) activity], p-nitrophenol, resorufin, ß-NADPH. Wright and Giemsa dyes, secondary anti-goat IgG and 3,3-diaminobenzidine (DAB) were purchased from Sigma Chemical Co. (St Louis, MO). Goat polyclonal anti-rat CYP1A1/2, CYP2B1/2 and CYP2E1, along with microsome standards for each CYP, were manufactured by Daiichi Pure Chemicals Co. and purchased from Gentest Corp. Chemicals for electrophoresis and nitrocellulose membranes were purchased from Bio-Rad Laboratories (Richmond, CA).
Infection
Adult T.taeniformis were grown in cats. Mature proglotids were expelled in feces from where they were extracted. Purified proglotids were macerated to release the eggs and these were obtained by filtration in metallic meshes (300 and 150 µm). Tissue debris was eliminated in a 2x Percoll gradient. The eggs were washed and resuspended in phosphate-buffered saline (PBS). Eggs were counted in a hemocytometer at the same time that viability was estimated. They were then resuspended in an adequate amount of PBS.
Sprague–Dawley rats, 6 weeks old, were inoculated with 100 viable eggs. Infection was allowed to develop for different times before enzymatic and genotoxicity determinations were made.
Coumarin hydroxylase (COH) activity determination (coumarin assay)
After an overnight fast, rats were injected with coumarin (0.5 mg/10 g body wt i.p.) at different times of infection. Animals were placed in metabolic cages and urine was collected over 5 h. Fluorescent hydroxycoumarin was obtained by digestion with ß-glucuronidase and extraction with chloroform and 1 M NaCl/0.01 M NaOH according to Rautio et al. (1992). The concentration of hydroxycoumarin was determined using a fluorometer, with an excitation filter of 365 nm and emision filter of 454 nm.
Concentrations were obtained by interpolation from a standard curve for hydroxycoumarin.
Preparation of liver S9 and microsomal fraction
Different groups of animals, 6 weeks old, were infected as already described (corresponding controls of the same age were used). The infection was allowed to progress for 40 and 120 days. Liver S9 fractions were prepared according to the procedure described by Maron and Ames (1983) from infected and non-infected rats. Animals were killed by cervical dislocation and their livers were freshly excised and washed in 150 mM KCl solution. Each sample was separately homogenized in the same solution (3 ml/g liver). The homogenate was centrifuged at 9000 g for 10 min and the supernatant was stored at –80°C. A portion of this supernatant fraction was centrifuged at 105 000 g for 1 h; the microsomal pellet was resuspended in phosphate buffer solution (67.5 mM K2HPO4 and 32.5 mM KH2PO4, pH 7.4) and centrifuged again. Finally, microsomes were stored in the same phosphate buffer solution containing 1 mM dithiothreitol, 1 mM EDTA and 20% glycerol. All the procedure was conducted aseptically at 4°C. Protein content was determined by the method of Bradford (1976).
CYP450 determination
The carbon monoxide difference spectra method was used (Omura and Sato, 1964).
A known concentration of protein in hepatic microsomes was reduced with sodium dithionite and associated with carbon monoxide, from which the characteristic absorption spectrum at 450 nm results.
The concentration of CYP450 was obtained by the differential reading between the reduced protein, non-associated with CO (reference sample) and the reading obtained with the reduced protein·CO complex. Wavelengths from 400 to 500 nm were used for the readings. The reference sample peaked at 490 nm and the reduced protein·CO complex peaked at 450 nm.
CYP1A1 and CYP2B1 activity determination
Microsomal EROD (CYP1A1) and PROD (CYP2B1) activities were measured spectrofluorometrically by monitoring the formation of resorufin according to Burke et al. (1994) with some modifications: excitation and emission wavelengths were set at 520 and 585 nm, respectively. Substrate (40 and 10 µl, respectively), 1.91 and 1.94 ml of buffer A (50 mM Tris–HCl, 25 mM MgCl2, pH 7.6) and 10 and 40 µl of microsomal sample were placed in a fluorimeter cuvette and incubated at 37°C for 3 min. Reactions were started by the addition of 500 µM NADPH (20 µl from a 50 mM solution in buffer A). With a total reaction volume of 2 ml, the cuvette was then placed in the fluorometer and the reactions followed for 3 min, recording the fluorescence reading every 15 s. Substrates were dissolved in dimethylsulfoxide as follows: 50 µM ethoxyresorufin and 1.0 mM pentoxyresorufin. Catalytic activities were calculated from a standard curve of resorufin (0–500 pmol/ml).
CYP2E1 activity determination
Hydroxylation of 4-nitrophenol to 4-nitrocatechol was determined by a modification of the method described by Koop (1986). 4-Nitrophenol (0.2 mM) was dissolved in 50 mM Tris–HCl, 25 mM MgCl2, pH 7.4. An aliquot of 930 µl of this solution and 50 µl of microsomal sample were incubated at 37°C for 5 min. Reactions were started by adding 20 µl of 50 mM NADPH and incubation continued for 10 min more. Reaction mixtures were stopped by adding 0.5 ml of 0.6 N perchloric acid followed by centrifugation. 4-Nitrocatechol formation was then spectrophotometrically determined in 1 ml of supernatant plus 0.1 ml of 10 N NaOH at 510 nm. A standard curve with 4-nitrocatechol (5–50 nmol/ml) was used to calculate microsomal activity.
Immunoblots for CYP1A1/2, CYP2B1 and CYP2E1
The same samples used for P450 isoform activity were used for these determinations. Aliquots of 5 µg of microsomal protein from individual animals were separated by 10% SDS–PAGE (Laemmli, 1970) and transferred to 0.45 µm nitrocellulose sheets (Towbin et al., 1979). Nitrocellulose membranes were blocked overnight with 5% non-fat dry milk dissolved in saline (20 mM NaCl, 2.5 mM Tris–HCl, pH 7.4, and 0.05 Tween 20). After a 10 min wash with PBS containing 0.3% Tween 20, the blots were probed with the corresponding anti-rat primary antibody: anti-CYP1A1/2, anti-CYP2B1/2 or anti-CYPE1 (1:400 dilution). After incubation with peroxidase-conjugated anti-goat IgG secondary antibody, CYP proteins were revealed with DAB (10 mg/ml) and hydrogen peroxide. Relative increases in band intensity over controls for each CYP isoform were determined with a microcomputer program (Kodak Digital Science 1D v.3.0.0; Eastman Kodak, USA).
Reticulocyte micronucleus assays
Procarcinogens like BaP, CP, NDMA and AFB1 are metabolized by several CYP450 isoforms each, however, isoforms responsible for the formation of the main mutagenic metabolites have been identified. In this way, BaP is used to study CYP1A1 activity, CP is used as a probe for CYP2B1 and NDMA is used for CYP2E1. AFB1 is a substrate for several CYP450 isoforms, including COH, as has been determined in several rodent species and in humans (Forrester et al., 1990; Béréziat et al., 1995); for this reason we used it as a probe for COH activity, so we could make a comparison with other infection models.
Separated groups of infected and non-infected animals were administered NDMA (17 mg/kg i.p., H2O as solvent), CP (25 mg/kg i.p., DMSO as solvent) or BaP (200 mg/kg i.p., DMSO as solvent) at day 60 after infection. AFB1 (1 mg/kg i.p., DMSO as solvent) was tested at day 20 after infection. Blood drops were obtained from the tail before treatment and at 24, 48 and 72 h after treatment; three smears were made per animal per day. Slides were stained with Wright and Giemsa, according to the method described by Romagna and Staniforth (1989). A total of 4000 blue stained reticulocytes were scored for each animal and micronuclei (MN) were counted in them. MN frequency was calculated as: (no. of MN in reticulocytes/4000)x1000 and is expressed as MN freq (
). Tests with each chemical were repeated for a second time under the same experimental conditions. Results of two experiments are presented.
Statistical analysis
Differences between P450 activity, MN induction and band intensity between control and infected animals were calculated by Student’s t-test, with a P value of 0.05.
|
Results |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
COH activity
COH activity or CYP2A5 induction has been found with O.viverrini and with F.hepatica infections, as already stated in the Introduction. We determined coumarin metabolism in the first place with the purpose of determining if a Taenia infection would induce a response similar to that found with trematodes.
Determinations were made at different times of infection in the same group of rats, as the metabolite 7-hydroxycoumarin was measured in urine. Determinations were made before and at 18, 30, 60, 80 and 140 days after the inoculation of eggs. At days 18 and 30 a 3-fold increase in COH activity was observed over the control (P < 0.05). From there on, the activity began to decline and at day 60 it was only increased 2-fold over the control, but still significantly different (P < 0.05). A longer time of infection produced an inhibition of COH activity, reaching values of half of those found in controls at days 80 and 140 of infection (P < 0.05) (Figure 1a).
|
CYP450 determination
Total content of CYP450 was determined in liver microsomal preparations from control and infected rats at 40 and 120 days after infection. It was found that at 40 days the content of CYP450 showed a 2-fold increase over non-infected animals (P < 0.05). However, in an older infection CYP450 content returned to normal values (Figure 2
).
|
The same microsomal samples were used for isoform activity determination and immunoblots.
AFB1 genotoxicity
AFB1 was used as a probe for the functional consequences of alterations in activity of COH at 20 days of infection (when we found the maximal COH activity by the coumarin assay). Only infected males showed a significant MN induction (Figure 3). The difference between infected and control animals was statistically significant (P < 0.05). Infected females showed only a slight, non-significant increase in MN frequency, compared with non-infected controls, which showed a significant MN increase at 24 h (0.33 ± 0.38 compared with 3.0 ± 1.59 at 24 h). It should be noted that increased MN frequencies are also coincident with the increase in total CYP450 spectrophotometric activity (Figures 2 and 3
).
|
CYP1A1 activity, immunological determination and BaP genotoxicity
EROD activity in infected animals at 40 days of infection occurred at a slightly higher rate than in controls, but the difference was not significant. In an older infection (120 days), however, the activity of the enzyme was significantly higher (2.5-fold increase, P < 0.05) (Figure 4a
). This pattern of activity induction is not comparable with total CYP450 increments (Figure 2), however, induction of individual isoforms can occur independently. This result is interesting if we consider that CYP1A1 is not a constitutive isoform in rat liver.
|
Immunoblots were made using the same liver microsomal samples that were used for determining isoform activity. A significant increase in CYP1A1/2 was found in infected animals at 120 days after infection (Figure 4b
) (P < 0.05). Not only CYP1A1 was induced, but CYP1A2, which is constitutive in rat liver, also showed a significantly increased concentration (P < 0.05).
BaP was used to determine the functional consequences of alterations in CYP1A1 activity. It was administered to rats at 60 days of infection. A different MN yield was found between non-infected and infected animals, being 2-fold greater at 72 h in infected rats (P < 0.05) (Figure 4c) than in non-infected, in which CYP1A1 hepatic activity and protein concentration were very low.
CYP2B1 activity, immunological determination in liver microsomes and CP genotoxicity
PRO dealkylation was used to measure the activity of this isoform. Microsome samples of animals at 120 days of infection were used to determine induction of activity, which showed a significant 1.6-fold increase (P < 0.05) (Figure 5a).
|
CYP2B1 protein concentration showed a non-significant increase in infected animals (Figure 5b
), in spite of the induction found in the PRO dealkylation determination, thus suggesting that the greater activity found is not due to increased transcription of the enzyme, but rather to some other mechanism, possibly related to the regulation of the holoenzyme level, as has been described for other P450 isozymes (Ding et al., 1997, 2001). CYP2B2 was detected in some of the infected and non-infected rats.
CP was used to study the effect of CYP2B1 induction. It was injected into rats with a 60 day infection. The effect was noticed at 48 h in infected animals, in which MN frequency was significantly higher (2-fold) than in non-infected (P < 0.05) (Figure 5c). In non-infected animals an effect was found only in male rats at 48 h, which could be explained by the fact that CYP2B1 is male dominant, whereas activity in female rats is lower (Lewis, 2001).
CYP2E1 activity, immunological determination in hepatic microsomes and NDMA genotoxicity
p-Nitrophenol hydroxylation was used to estimate the activity levels of this enzyme in our study. No difference was found between control and infected animals in the metabolism of this chemical (Figure 6a).
|
In immunoblots, CYP2E1, which is constitutive in liver, was as concentrated in controls as it was in infected animals (Figure 6b
).
NDMA induced MN in both controls and rats with a 60 day infection at the same rate, which was to be expected from the results obtained for the enzyme activity (CYP2E1) at different times of infection and in the immunoblot results, where no induction due to infection was found (Figure 6c).
MN frequency without chemical treatment
It should be noted that infected animals showed an increased MN frequency compared with non-infected, without any chemical treatment. The average MN yield was 0.57 ± 0.4 for non-infected, whereas for infected animals it was 1.11 ± 0.7 (P < 0.05) (Figure 7).
|
|
Discussion |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
COH alterations due to parasitic infections in mouse and hamster have been described before (Kirby et al., 1994a
,b; Montero et al., 1999) at early steps of induced infections and they have been correlated with an increase in AFB1 metabolism. In our rat model we found that early stages of the infection with T.taeniformis also induced the activity of COH, however, later on in the process, when the parasites were established, COH activity declined to levels lower than that found in control, non-infected rats. In humans COH has been identified as CYP2A6 and its ortholog in mice is CYP2A5. The structural ortholog in rat liver is CYP2A1/2 (Ribeiro et al., 2001), however, this enzyme does not 7-hydroxylate coumarin to the same extent as does human CYP2A6. In fact, in rat and mouse other positions in the coumarin molecule seem to be preferred for the reaction with CYP2A (Pearce et al., 1992). In spite of this, we found an increase in COH activity measured as the formation of the 7-hydroxylated metabolite due to infection with T.taeniformis metacestodes.
AFB1 is a substrate for COH in several rodent species. This activity has been attributed to CYP2A enzymes: CYP2A5 in hamster and mouse and CYP2A3 in rat nasal epithelium (Béréziat et al., 1995), with CYP2A6 (Forrester et al., 1990) also participating to a certain extent in AFB1 activation in human liver. In rat liver, however, the role of CYP2A in AFB1 metabolism seems to be less important, given the fact that COH activity is normally very low. Hence, the increased genotoxicity due to AFB1 could be attributed to the induced COH activity found in infected animals, if it were not that total CYP450 spectrographic activity was increased at the same time that AFB1 was administered to the animals, coinciding with the time that COH was also induced, which raises the possibility that increased genotoxicity could be due to other CYP450 isoforms induced at the same time and that we did not measure e.g. CYP3A4.
CYP1A1 and/or CYP1A2, which also seem to participate in AFB1 activation, were not induced at that time.
The induction of total CYP450 activity found differs from others reported in the literature, where P450 activity was decreased by several parasitic infections, like Plasmodium berghei, Ancylostoma ceylanicum and F.hepatica in rats. However, variations in time were also found in those studies, as well as specific drug metabolism alterations. Other infections, by bacteria or viruses, suppress P450 hepatic activity, but, as has been reported with parasites, within a certain study there is usually evidence for some selectivity, affecting different subsets of P450 isoforms (Morgan, 1997). This could be compared with the action of xenobiotics that are capable of inducing specific P450 isoforms while leaving others unaffected. Of the isoforms investigated, CYP2E1 was the only one that was not altered at any point under the conditions of our study.
Induction of the CYP4A and CYP3A families has been reported on the administration of lipopolysaccharide to rats (Morgan, 1997). These findings suggest that the inflammatory and immunological reactions are of different quality with respect to the infecting agent. Trematodes have been shown to induce COH (CYP2A) in mammals (Kirby et al., 1994a,b; Montero et al., 1999); this induction could be due to liver damage, as was suggested by Vandewaa et al. (1982), who showed that inflammation alone could increment AFB1 metabolism in partially hepatectomized mice, and by Camus-Randon et al. (1996), even though the specific factor responsible for it has not been identified. Cytokines produced during an inflammatory response are the logical suspects to explain P450 induction. However, TNF, IFN
, IL-6 and IL-1, which are produced in large amounts and are the first mediators of the host response, have been proved to inhibit P450 content and activity (Morgan, 1997), hence, there should be other mediators. Recent advances made by LaBella and Brandes (2000) demonstrated that histamine (which is released by mast cells under stimulation by a histamine releasing factor produced by eosinophils and neutrophils in an inflammatory reaction) could be involved in the regulation of some P450 isoforms, since histamine has been shown to bind the P450 heme moiety, regulating the catalytic activity of P450 enzymes (Brandes et al., 1998; LaBella and Brandes, 2000) and evidence suggests that several P450 families could be regulated this way, not only CYP3A, which is mentioned by LaBella and Brandes (2000), but also those involved with CP, arylalkylamine and imidazole metabolism. Furthermore, Delescluse et al. (2000) have suggested that CYP1A1 could be induced by mechanisms different to the classical AhR, but related to other nuclear receptors, like hormone receptors, which were shown to be related to histamine action on P450.
Phase II metabolism enzymes could also be induced by T.taeniformis and the other infections cited here. We did not measure them because we wanted to evaluate the activation of procarcinogens such as BaP, AFB1 and CP, which are known to be transformed by CYP450 isoforms into their carcinogenic metabolites, which are the ones that form adducts in the DNA (Eaton and Gallagher, 1994; Bethizy and Hayes, 1994). Phase II metabolism by glutathione S-transferase, for example, would in these cases be detoxifying, thus establishing an equilibrium which would be reflected in a negative genotoxic response; this was not the case, as was observed in Results. Reticulocytes, on the other hand, are known to metabolize and activate some chemicals, but they lack CYP450 activity, so it is reasonable to assume that the increased frequency of MN in these cells was related to the induced liver metabolism activating the procarcinogens. There could be an effect of reticulocyte metabolism in the MN yield, however, due to some form of oxidative stress related to the inflammatory response and this could explain the increased MN frequency seen in infected animals before treatment with procarcinogens and in comparison with the MN frequency in non-infected rats (see Results).
Induced activity of isoforms CYP2A, CYP1A and CYP2B is of toxicological relevance since these isoforms are involved in the biotransformation of important procarcinogens present in the environment, such as polycyclic aromatic hydrocarbons (CYP1A1), barbital drugs, anticancer drugs and some pesticides that are still in commercial use in third-world countries (CYP2B1) and nitrosamines in food and AFB1 (CYP2A), which is a persistent problem in seed storage around the world.
The exposure of infected animals to genotoxic probe drugs for each of these isoforms resulted in an increased sensitivity of the infected individuals, which suffered more genotoxic damage than the controls. It is a demonstration that infections contribute to increase the risk for carcinogenicity in individuals exposed to carcinogens for occupational, accidental or medical reasons, since parasitic infections are chronic diseases and re-infection is common in areas with a high prevalence. This risk adds to that represented by the increased genotoxic damage that has been found in infected organisms, probably attributable to the oxidative damage produced by chronic inflammation, as already stated. However, evidence suggests that not only the oxidative damage, but a more complex interaction stemming from the parasite’s strategies to survive the host response might be responsible for the unique mutations found in transgenic mice infected with F.hepatica (Motorna et al., 2001) and possibly for the increased genotoxic damage that was found in this study and in others before, where aneuploidy and specific chromosomal translocations were described (Montero and Ostrosky, 1997; Herrera et al., 2001; Serrano and Montero, 2001). It should also be underlined that this genotoxic action affects not only the infected organ, but also reaches peripheral blood, as has been abundantly documented (Flisser et al., 1990; Anwar and Rosin, 1993; Herrera et al., 1994; Montero et al., 1994; Montero and Ostrosky, 1997; Serrano and Montero, 2001).
|
Acknowledgments |
|---|
We are grateful to the laboratory of Dr Javier Espinosa, particularly to Diana María Escobar García for her technical support in determining CYP450 isoform activity and Gerardo Cono for teaching us the S9 and microsome preparation. We also want to express our gratitude to Dr James Gentile for his valuable suggestions.
|
Notes |
|---|
3 To whom correspondence should be addressed. Tel: +52 5 622 3158; Fax: +52 5 550 0048; Email: dorinda{at}servidor.unam.mx
|
References |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
-
Anwar,W. and Rosin,M. (1993) Reduction in chromosomal damage in schistosomiasis patients after treatment with Praziquantel. Mutat. Res., 298, 179–185.[CrossRef][Web of Science][Medline]
Béréziat,J.C., Raffalli,F., Schmezer,P., Frei,E., Genste,O. and Lang,M.A. (1995) Cytochrome P450 2A of nasal epithelium: regulation and role in carcinogen metabolism. Mol. Carcinog., 14, 130–139.[Web of Science][Medline]
Bethizy,J.D. and Hayes,J.R. (1994) Metabolism. A determinant of toxicity. In Hayes,A.W. (ed.), Principles and Methods of Toxicology, 3rd Edn. Raven Press, New York, NY, pp. 59–97.
Bradford,M. (1976) A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal. Biochem., 72, 248–254.[CrossRef][Web of Science][Medline]
Brandes,L.J., Queen,G.M. and LaBella,F.S. (1998) Potent interaction of histamine and polyamines at microsomal cytochrome P450, nuclei, and chromatin from rat hepatocyes. J. Cell Biochem., 69, 233–243.[CrossRef][Web of Science][Medline]
Burke,M.D., Thompson,S., Weavwer,R.J., Wolf,C.R. and Mayer,R.T. (1994) Cytochrome P450 specificities of alkoxyresorufin O-dealkylation in human and rat liver. Biochem. Pharmacol., 48, 923–936.[CrossRef][Web of Science][Medline]
Camus-Randon,A.M., Raffalli,F., Béréziat,J.C., McGregor,D., Konstandi,M. and Lang,M. (1996) Liver injury and expression of cytochromes P450: evidence that regulation of CYP2A5 is different from that of other major xenobiotic metabolizing CYP enzymes. Toxicol. Appl. Pharmacol., 138, 140–148.[CrossRef][Web of Science][Medline]
Del Bruto,O., Castillo,P., Mena,I. and Freire,A. (1997) Neurocysticercosis among patients with cerebral gliomas. Arch. Neurol., 54, 1125–1128.
Delescluse,C., Lemaire,G., de Sousa,G. and Rahmani,R. (2000) Is CYP1A1 induction always related to AHR signaling pathway? Toxicology, 153, 73–82.[CrossRef][Web of Science][Medline]
Ding,S., Yao,D., Burchell,B., Wolf,C.R. and Friedberg,T. (1997) High levels of recombinant CYP3A4 expression in Chinese hamster ovary cells are modulated by coexpressed human P450 reductase and hemin supplementation. Arch. Biochem. Biophys., 348, 403–410.[CrossRef][Web of Science][Medline]
Ding,S., Yao,D., Deeni,Y.Y., Burchell,B., Wolf,C.R. and Friedberg,T. (2001) Human NADPH-P450 oxidoreductase modulates the level of cytochrome P450 CYP2D6 holoprotein via haem oxygenase-dependent and -independent pathways. Biochem. J., 356, 613–619.[CrossRef][Web of Science][Medline]
Eaton,D. and Gallagher,E. (1994) Mechanisms of aflatoxin carcinogenesis. Annu. Rev. Pharmacol. Toxicol., 34, 135–172.[CrossRef][Web of Science][Medline]
Flisser,A., González,D., Plancarte,A., Ostrosky,P., Montero,R., Stephano,A. and Correa,D. (1990) Praziquantel treatment of brain and muscle porcine Taenia solium cisticercosis. Parasitol. Res., 76, 640–642.[CrossRef][Web of Science][Medline]
Forrester,L.M., Neal,G.E., Judah,D.J., Glancey,M.J. and Wolf,C.R. (1990) Evidence for involvement of multiple forms of cytochrome P-450 in aflatoxin B1 metabolism in human liver. Proc. Natl Acad. Sci. USA, 87, 8306–8310.
Gentile,J.M. and De Ruiter,E. (1981) Promutagen activation in parasite-infected organisms: preliminary observations with Fasciola hepatica-infected mice and aflatoxin B1. Toxicol. Lett., 8, 273–282.[CrossRef][Web of Science][Medline]
Herrera,L.A., Santiago,P., Rojas,G., Salazar,P.M., Tato,P., Molinari,J.L., Schiffmann,D. and Ostrosky,P. (1994) Immune response impairment, genotoxicity and morphological transformation induced by Taenia solium metacestode. Mutat. Res., 305, 223–228.[CrossRef][Web of Science][Medline]
Herrera,L.A., Ramírez,T., Rodríguez,U., Corona,T., Sotelo,J., Lorenzo,M., Ramos,F., Verdorfer,I., Gebhart,E. and Ostrosky,P. (2000) Posible association between Taenia solium cisticercosis and cancer: increased frequency of DNA damage in peripheral lymphocytes from neurocysticercosis patients. Trans. R. Soc. Trop. Med. Hyg., 94, 61–65.[CrossRef][Web of Science][Medline]
Herrera,L.A., Rodriguez,U., Gebhart,E. and Ostrosky-Wegman,P. (2001) Increased translocation frequency of chromosomes 7, 11 and 14 in lymphocytes from patients with neurocysticercosis. Mutagenesis, 16, 495–497.
Kirby,G.M., Pelkonen,P., Vatanasapt,V., Camus,A.M., Wild,C.P. and Lang,M. (1994a) Association of liver fluke (Opisthorchis viverrini) infestation with increased expression of cytochrome P450 and carcinogen metabolism in male hamster liver. Mol. Carcinog., 11, 81–89.[Web of Science][Medline]
Kirby,G.M., Chemin,Y., Montesano,R., Chisari,F.V., Lang,M.A. and Wild,C.P. (1994b) Induction of specific cytochrome P450s involved in aflatoxin B1 metabolism in hepatitis B virus transgenic mice. Mol. Carcinog., 11, 74–80.[Web of Science][Medline]
Koop,D.R. (1986) Hydroxylation of p-nitrophenol by rabbit ethanol-inducible cytochrome P-450 isozyme 3a. Mol. Pharmacol., 29, 399–404.[Abstract]
Laemmli,U.K. (1970) Maturation of the head of bacteriophage T4 I DNA packaging events. Nature, 227, 280.[Medline]
LaBella,F.S. and Brandes,L.J. (2000) Interaction of histamine and other bioamines with cytochromes P450: implications for cell growth modulation and chemopotentiation by drugs. Semin. Cancer Biol., 10, 47–53.[CrossRef][Web of Science][Medline]
Lewis,D. (2001) Substrate selectivity and metabolism. In Guide to Cytochromes P450. Structure and Function, Ch. 4. Taylor and Francis, London, UK.
Maron,D. and Ames,B. (1983) Revised methods for the Salmonella mutagenicity test. Mutat. Res., 113, 173–215.[CrossRef][Web of Science][Medline]
Montero,R. and Ostrosky,P. (1997) Genotoxic activity of Praziquantel. Mutat. Res., 387, 123–139.[CrossRef][Web of Science][Medline]
Montero,R., Flisser,A., Madrazo,I., Cuevas,C. and Ostrosky,P. (1994) Mutation at the HPRT locus in patients with neurocysticercosis treated with praziquantel. Mutat. Res., 305, 181–188.[CrossRef][Web of Science][Medline]
Montero,R., Gentile,G.J., Frederick,L., McMannis,J., Murphy,T., Silva,G., Blankespoor,H. and Gentile,J.M. (1999) Induced expression of CYP2A5 in inflamed trematode-infested mouse liver. Mutagenesis, 14, 217–220.
Morgan,E.T. (1997) Regulation of cytochromes P450 during inflammation and infection. Drug Metab. Rev., 29, 1129–1188.[Web of Science][Medline]
Motorna,O.O., Martin,H., Gentile,G.J. and Gentile,J.M. (2001) Analysis of lacI mutations in Big Blue® transgenic mice subjected to parasite-induced inflammation. Mutat. Res., 484, 69–76.[Web of Science][Medline]
Omura,T. and Sato,R. (1964) The carbon monoxide-binding pigment of liver microsomes. J. Biol. Chem., 239, 2370–2378.
Pearce,R., Greenway,D. and Parkinson,A. (1992) Species differences and interindividual variation in liver microsomal cytochrome P450 2A enzymes: effects on coumarin, dicumarol, and testosterone oxidation. Arch. Biochem. Biophys., 298, 211–225.[CrossRef][Web of Science][Medline]
Rautio,A., Kraul,H., Kojo,A., Salmela,E. and Pelkonen,O. (1992) Interindividual variability of coumarin 7-hydroxylation in healthy volunteers. Pharmacogenetics, 2, 227–233.[CrossRef][Web of Science][Medline]
Ribeiro,L.F., Moraes,E., Albano,R.M., Silva,M.C., Godoy,W., Glisovic,T. and Lang,M.A. (2001) Rat oesophageal cytochrome P450 (CYP) monooxygenase system: comparison to the liver and relevance in N-nitrosodiethylamine carciongenesis. Carcinogenesis, 22, 1877–1883.
Romagna,F. and Staniforth,C.D. (1989) The automated bone marrow micronucleus test. Mutat. Res., 213, 91–104.[Web of Science][Medline]
Ross,R., Yuan,J.M., Yu,M., Wogan,G., Qian,G.S., Tu,J.T., Groopman,J.D., Gao,Y.T. and Henderson,B.E. (1992) Urinary aflatoxin biomarkers and risk of hepatocellular carcinoma. Lancet, 339, 943–946.[CrossRef][Web of Science][Medline]
Serrano,L. and Montero,R. (2001) Micronuclei and chromatin buds are the result of related genotoxic events. Environ. Mol. Mutagen., 38, 38–45.[CrossRef][Web of Science][Medline]
Towbin,H., Staehelin,T. and Gordon,J. (1979) Electrophoretic transfer of protein from polyacrylamide gels to nitrocellulose-sheets: procedure and same applications. Proc. Natl Acad. Sci. USA, 76, 4350–4354.
Vandewaa,E.A., Barney,C.C. and Gentile,J.M. (1982) Promutagen activation in partially hepatectomized mice. Toxicol. Lett., 14, 253–260.[CrossRef][Web of Science][Medline]
Received on July 20, 2002; revised on August 11, 2002; accepted on November 12, 2002.
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||