Biomedical subjects

R Fransson-Steen

Publications and source records attributed to R Fransson-Steen.

14 recordsLinked to original sources

PubMed2004

Metabolism of human cytochrome P450 marker substrates in mouse: a strain and gender comparison.

The aim was to characterize mouse gender and strain differences in the metabolism of commonly used human cytochrome (CYP) P450 probe substrates. Thirteen human CYP probe substrates (phenacetin, coumarin, 7-ethoxy-4-trifluoromethyl coumarin, amiodarone, paclitaxel, diclofenac, S-mephenytoin, bufuralol, dextromethorphan, chlorzoxazone, p-nitrophenol, testosterone and lauric acid) were used in activity measurements. The metabolism of the probe substrates was compared in liver microsomes from male and female NMRI, CBA, C57bl/6, 129/SvJ and CD1 strains. The expression of proteins identified on Western blots with commonly available antibodies selective for specific human and rat CYP enzymes were compared in the different mouse strains. Males had higher metabolism than corresponding females for phenacetin O-deethylation (human marker for CYP1A2 activity), and a high correlation was found between phenacetin activity and immunoreactivity in Western blots produced with rat CYP1A2 antibodies. Protein detected by antibodies cross-reacting with human CYP2B6 and rat CYP2B1/2 antibodies was female specific except for the 129/SvJ strain, where it was absent in both genders. Females generally had a higher metabolism of bufuralol 1'-hydroxylation and dextromethorphan O-demethylation (human markers for CYP2D activity). Bufuralol 1'-hydroxylation correlated with a female-dominant mouse CYP, which was detected with antibodies against rat CYP2D4. p-Nitrophenol 2-hydroxylation correlated better than chlorzoxazone 6-hydroxylation with the protein detected with antibodies against rat CYP2E1, indicating that p-nitrophenol is a more specific substrate for mouse CYP2E1.

Amiodarone↗

PubMed2001

Xpa and Xpa/p53+/- knockout mice: overview of available data.

DNA repair deficient Xpa-/- and Xpa-/-/p53+/- knock-out mice in a C57BL/6 genetic background, referred to as respectively the XPA and XPA/p53 model, were investigated in the international collaborative research program coordinated by International Life Sciences Institute (ILSI)/Health and Environmental Science Institute. From the selected list of 21 ILSI compounds, 13 were tested in the XPA model, and 10 in the XPA/p53 model. With one exception, all studies had a duration of 9 months (39 weeks). The observed spontaneous tumor incidence for the XPA model after 9 months was comparable to that of wild-type mice (total 6%). For the XPA/p53 model, this was somewhat higher (9%/13% for males/females). The 3 positive control compounds used, B[a]P, p-cresidine, and 2-AAF, gave positive and consistent tumor responses in both the XPA and XPA/p53 model, but no or lower responses in wild-type mice. From the 13 ILSI compounds tested, the single genotoxic carcinogen (phenacetin) was negative in both the XPA and XPA/p53 model. Positive tumor responses were observed for 4 compounds, the immunosuppressant cyclosporin A, the hormone carcinogens DES and estradiol, and the peroxisome proliferator WY-14,643. Negative results were obtained with 5 other nongenotoxic rodent carcinogens, and 2 noncarcinogens tested. As expected, both DNA repair deficient models respond to genotoxic carcinogens. Combined with previous results, 6 out of 7 (86%) of the genotoxic human and/or rodent carcinogens tested are positive in the XPA model. The positive results obtained with the 4 mentioned nongenotoxic ILSI compounds may point to other carcinogenic mechanisms involved, or may raise some doubts about their true nongenotoxic nature. In general. the XPA/p53 model appears to be more sensitive to carcinogens than the XPA model.

Academies and Institutes↗

PubMed2000

Analysis of rat liver foci growth with a quantitative two-cell model after treatment with 2,4,5,3',4'-pentachlorobiphenyl.

A biologically based, quantitative foci-growth model was used to analyze the effect of 20 and 52 weeks treatment with 2,4,5,3', 4'-pentachlorobiphenyl (PCB118) on the development of enzyme-altered foci in rat liver initiated with partial hepatectomy and diethylnitrosamine. Hepatocyte proliferation was examined and the data were used in the selection of division rates for the computer simulations of foci growth. The bromodeoxyuridine-labeling index in foci was generally larger than in nonfocal tissue. A strong correlation was found between foci occurrence and proliferation in focal as well as nonfocal tissue, suggesting that cytotoxicity and regenerative proliferation are involved in the foci growth caused by PCB118. The foci growth model adequately simulated the foci data when certain assumptions were introduced. Given the general view that PCB118 is a nonmutagenic compound, the foci data could not be modeled assuming one homogeneous cell population, but was adequately fitted assuming two separate initiated cell populations that respond differently to the promotion stimulus. Other assumptions were a selective growth advantage for initiated cells during and shortly after the initiation treatment, and a transient increase of proliferation in focal hepatocytes at the first PCB administration in the higher dose groups. The model predicted an increased rate of focal cell death, at high doses, to adequately fit the foci data. These assumptions are supported by experimental data for other carcinogens, indicating the importance of studying cell kinetics in heterogeneous subpopulations of initiated cells in PCB-induced hepatocarcinogenesis.

Animals↗

PubMed1998

Interactive effects of three structurally different polychlorinated biphenyls in a rat liver tumor promotion bioassay.

Interactive effects between the non-ortho-substituted 3,3', 4,4', 5-pentachlorobiphenyl (PCB126), the mono-ortho-substituted 2,3,3',4, 4'-pentachlorobiphenyl (PCB105), and the di-ortho-substituted 2,2',4, 4',5,5'-hexachlorobiphenyl (PCB153) were studied in an initiation/promotion bioassay. Female Sprague-Dawley rats were injected with 30 mg/kg ip of N-nitrosodiethylamine 24 h after partial hepatectomy. Five weeks later, weekly sc administrations of the three PCBs in 15 systematically selected dose combinations started. After 20 weeks of administration, the animals were killed and the livers were analyzed for areas expressing placental glutathione-S-transferase as a marker of preneoplastic foci. In addition, concentration of liver and kidney retinoids and plasma retinol was analyzed, as well as body and organ weights, plasma transaminases, and induction of hepatic cytochrome P450 1A1/2 (CYP1A1/2) and CYP2B1/2 activities. Data were analyzed with a multivariate method. At the doses applied in this study, weak antagonism was observed between PCB126 and PCB153 for effects on volume fraction of foci, number of foci/cm3, concentration of plasma retinol and liver retinoids, relative liver weight, and induction of CYP2B1/2 activity. Weak antagonism was also observed between PCB126 and PCB105 for effects on volume fraction of foci, number of foci/cm3, and plasma retinol concentration. No interactions other than pure additivity were observed between PCB105 and PCB153. Synergism was not observed within the dose ranges investigated in this study. Knowledge of interactive effects is important for risk assessment of environmental mixtures of dioxin-like compounds. Antagonism between congeners generally results in risk assessments that overestimate human risk. The significance to human risk assessment of the relatively weak antagonism observed in this study is however unclear, considering many other uncertainties involved in the toxic equivalency factor (TEF) concept. A change of the TEF concept for risk assessments of dioxin-like substances is not motivated based on the results of this study.

Animals↗

PubMed1997

Furan-induced liver cell proliferation and apoptosis in female B6C3F1 mice.

Furan is a potent rodent hepatocarcinogen that probably acts through non-genotoxic mechanisms involving hepatotoxicity and regenerative hepatocyte proliferation. In addition to inducing necrosis, cytotoxicants like furan may also induce cytolethality through apoptosis which has been suggested to play a key role in carcinogenesis. Hepatocyte proliferation and apoptosis were studied in female B6C3F1 mice exposed to furan by oral gavage for 3 weeks at National Toxicology Program (NTP) bioassay doses (8 and 15 mg/kg body weight) and lower (4 mg/kg). Furan treatment led to a 2- to 3-fold significant increase in liver-related enzymes and bile acids in blood serum as compared to the control group. These changes were accompanied by minor subcapsular inflammation and minimal necrosis at 8 and 15 mg furan/kg. A dose-related increase in bromodeoxyuridine-labeling index (1.4- to 1.7-fold) and hematoxylin- and eosin-defined apoptotic index (6- to 15-fold) was observed at 8 and 15 mg/kg. Co-treatment of mice with aminobenzotriazole, an irreversible inhibitor of cytochromes P-450, prevented the observed hepatotoxic effects induced by furan. These results indicate that furan elicits hepatotoxicity in a dose-related manner through a toxic metabolite and, furthermore, suggest that apoptosis is an important form of cell death at hepatocarinogenic doses under short-term conditions.

Administration, Oral↗

PubMed1997

Reverse transcription-polymerase chain reaction-based methodology to quantify differential gene expression directly from microdissected regions of frozen tissue sections.

Quantitative differences in the expression of oncogenes are a critical feature of the cancer process. Several methods are currently available for assessing differential gene expression, but none can be used to determine quantitative changes in gene expression from small numbers of cells. The ability to conduct this type of quantitative analysis would be useful in the study of definable, early stages of carcinogenesis when very few cells are involved. We therefore developed a highly sensitive, slide-based technique that incorporates the benefits of in situ polymerase chain reaction (PCR) and reverse transcription-PCR (RT-PCR) to quantify differential c-myc gene expression from liver tissue sections having either low or high levels of proliferating hepatocytes. To eliminate the need for isolating and quantifying mRNA, cells of interest were microdissected from frozen histological sections and their RNA directly subjected to RT-PCR amplification. These reactions were conducted in the presence of an internal RNA standard that was specifically designed to normalize differential RT and PCR efficiencies between samples. GENESCAN software analysis was used to determine the ratios of the RT-PCR products of the target gene to the RNA standard. These ratios were then normalized to the numbers of cells isolated, as quantified by image analysis, and comparative gene expression values were determined between sample groups. We conclude that this technology can be adapted to study any gene of interest in any type of frozen tissue or isolated cells. This methodology is particularly applicable to the molecular analysis of histopathologically distinct preneoplastic and neoplastic lesions identified on tissue sections.

Animals↗

PubMed1997

Promotion of enzyme altered foci in female rat 2,3,3',4,4',5-hexachlorobiphenyl.

The tumor promoting activity of 2,3,3',4,4',5-hexachlorobiphenyl (PCB 156) was studied in an initiation/promotion bioassay in female Sprague-Dawley rats initiated with N-nitrosodiethylamine after partial hepatectomy. PCB 156 (50, 300, 1500, or 7500 microg/kg body weight/week) was administered by once-weekly subcutaneous injections for 20 weeks. Some high dose animals were left without treatment for an additional 20 weeks to study posttreatment effects. The volume fraction of the liver occupied by glutathione S-transferase P-positive foci was significantly increased to 2.9, 3.3, and 12% at 300, 1500, and 7500 microg/kg body weight/week, respectively, compared to 1.2% in the controls. The volume fraction was 43% in the high dose group 20 weeks after treatment was stopped, probably reflecting the slow body clearance of PCB 156 as indicated by the sustained liver and adipose tissue concentrations. Treatment with PCB 156 following initiation caused decreased body weight gain, thymic atrophy, liver enlargement, induction of hepatic cytochrome P450 1A1/2 (CYP1A1/2) and CYP2B1/2 activities, histopathological effects, and increased activities of aspartate aminotransferase and gamma-glutamyltransferase in plasma. These results show that PCB 156 can enhance the growth of altered foci in rat liver and probably act as a tumor promoter of hepatocarcinogenesis. Based on promotional activity a relative potency of PCB 156 to 2,3,7, 8-tetrachlorodibenzo-p-dioxin of 0.0001-0.001 is proposed.

Adipose Tissue↗

PubMed1997

Promotion of altered hepatic foci by 2,3',4,4',5-pentachlorobiphenyl in Sprague-Dawley female rats.

The tumor promotion potential of 2,3',4,4',5-pentachlorobiphenyl (PCB-118) was studied in a two-stage initiation/promotion bioassay in female Sprague-Dawley rats. The animals were initiated by intraperitoneal administration of N-nitrosodiethylamine after partial hepatectomy. After 5 weeks of recovery, the promotion period commenced by once-weekly subcutaneous administrations of PCB-118 at six dose levels (10, 40, 160, 640, 2500, and 10,000 microg/kg body weight/week) for 20 weeks. In addition, three of these dose levels (40, 640, and 10,000 microg/kg body weight/week) were administered for 52 weeks. Evaluation of hepatic foci positive for glutathione S-transferase P demonstrated that the mono-ortho chlorine substituted congener PCB-118 significantly increased the number of foci/cm3 of liver in the two highest dose groups after 20 weeks, but did not significantly increase the percentage of the liver occupied by foci. After 52 weeks of treatment, both the percentage and the number of foci/cm3 were significantly increased in the highest dose group. A toxic equivalency factor based on foci development during 20 weeks of treatment would be less than 0.00002. Altered relative liver and thymus weights were observed after treatment with both substances as well as an induction of methyl cholanthrene- and phenobarbital-inducible isoenzymes of cytochrome P450 monooxygenase. These results show that PCB-118 has a potency to enhance foci growth in rat liver, although the potency is low compared to that of structurally related compounds.

Animals↗

PubMed1996

Apoptosis and cancer risk assessment.

Apoptosis is one form of physiological or active cell death. The balance between cell proliferation and cell death or apoptosis not only effects organ growth but also has a profound impact on the net increase and growth of initiated cells and preneoplastic and tumor cell populations. With respect to cancer development apoptosis is becoming widely recognized as being an innate tissue defense against carcinogens by inhibiting survival and controlling growth of precancerous cell populations and tumors at different stages of carcinogenesis. Experimental data on cell birth and cell death rates help identify the mode of action of a chemical and can be incorporated into biologically based cancer models. This article describes the quantitation and regulation of apoptosis in rodent liver and how loss of regulation can have a role in hepatocarcinogenesis. A biologically-based mouse liver cancer model is presented and utilized to describe how treatment related growth effects affect the process of carcinogenesis. Advantages and limitations of biologically based cancer models in cancer research and risk assessment are discussed.

Animals↗

PubMed1995

Application of the benchmark method to risk assessment of trichloroethene.

An alternative approach for risk assessment of nongenotoxic substances, the benchmark method, has been evaluated and applied to trichloroethene as a test case. The benchmark dose is the dose that corresponds to a specific increase in risk, normally 1 or 10%. Experimental data from the literature on trichloroethene were used for these calculations. Eighty sets of data on effects on liver, kidney, the central nervous system, and tumors were analyzed. All non-observed-effect levels (NOELs) were higher than the benchmark dose corresponding to 1% extra risk, and 42% of the NOELs and 93% of the lowest-observed-effect levels (LOELs) were higher than the benchmark dose corresponding to 10% extra risk. The present study confirms that the benchmark methodology gives a more detailed picture of dose-response relationships than risk assessment using the NOEL/LOEL approach and facilitates comparison between various toxicity studies. However, the polynomial regression models used in the present study quite often failed to fit the experimental data. Despite the advantages with the benchmark approach, several factors must be considered in the risk assessment process. In the case of trichloroethene, a revised risk assessment using the benchmark approach would lead to a similar guideline value as the traditional NOEL/LOEL approach.

Animals↗

PubMed1994

Two inhibitors of gap junctional intercellular communication, TPA and endosulfan: different effects on phosphorylation of connexin 43 in the rat liver epithelial cell line, IAR 20.

The skin tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) and the chlorinated insecticide, endosulfan, are two potent inhibitors of gap junctional intercellular communication. In the present study the effects of TPA and endosulfan on cell communication have been investigated in IAR 20 rat liver epithelial cells, as well as the effects of these compounds on connexin 43 (cx43), the main gap junction protein in this cell line. The results clearly demonstrate that at non-toxic doses both compounds inhibited the cell communication by at least 90% within 5 min. The communication was partially restored after 4 h of TPA exposure and almost fully restored by 24 h, whereas in endosulfan-exposed cells the communication was completely down-regulated for the whole exposure-period of 24 h. Immunoblots of IAR 20 cell extracts indicated that TPA initially caused an increased phosphorylation of cx43. A normal phosphorylation pattern was observed after 4 h when the cell communication was restored. Immunoblot analysis after endosulfan-exposure showed a slightly increased phosphorylation of cx43 after 10 min treatment, gradually followed by dephosphorylation during the rest of the 24 h treatment period. Immunostaining of IAR 20 cells showed that both compounds caused a rapid disappearance of cx43 from the cell membrane. After 4 h of exposure immunofluorescent cx43-plaques started to reappear in the cell membrane, although less pronounced in endosulfan-treated cells. However, after 24 h of endosulfan-exposure a high number of cx43-spots was demonstrated. These results indicate that different mechanisms are responsible for the inhibition of gap junctional intercellular communication induced by TPA and by endosulfan, at least during the later part of the 24 h exposure-period. TPA causes a marked hyperphosphorylation of cx43, whereas endosulfan increases phosphorylation initially only slightly but longer exposure-periods lead to hypophosphorylation. Thus, phosphorylation as well as dephosphorylation seem to be important factors involved in the regulation of the function of cx43 in this cell line.

Animals↗

PubMed1992

The insecticide endosulfan and its two stereoisomers promote the growth of altered hepatic foci in rats.

The non-genotoxic, chlorinated cyclodiene insecticide endosulfan was studied for its ability to act as a tumour promoter in a two-stage, altered hepatic foci bioassay in male Sprague-Dawley rats. Two stereoisomers of endosulfan, alpha-endosulfan (ENDO alpha) and beta-endosulfan (ENDO beta) were used, as well as a commercially-occurring mixture of the alpha- and beta-isomers (ENDO alpha beta). The animals were initiated by intraperitoneal injection of nitrosodiethylamine 24 h after a two-thirds-partial hepatectomy. Five weeks later the animals were transferred to diets containing 30, 100 and 300 p.p.m. of either ENDO alpha beta, ENDO alpha or ENDO beta. The study was terminated 25 weeks after initiation and the development of foci of gamma-glutamyltranspeptidase-positive hepatocytes was evaluated by stereological methods. The results show that endosulfan and its two stereoisomers promote the development of altered hepatic foci, suggesting that endosulfan is a tumour-promoting agent acting by clonal expansion of initiated cells.

Animals↗

PubMed1992

Inhibitory effects of endosulfan on gap junctional intercellular communication in WB-F344 rat liver cells and primary rat hepatocytes.

The chlorinated cyclodiene insecticide endosulfan is a potent inhibitor of gap junctional intercellular communication (GJIC) in vitro, a property shared by many tumour promoters and suggested to indicate an intrinsic tumour-promoting potential. However, endosulfan did not act as a tumour promoter in an altered hepatic foci assay in the rat in vivo, and ambiguous results regarding the carcinogenic potential of endosulfan have emerged from long-term studies in rodents. In the present study the GJIC-inhibitory potentials of the two isomers of endosulfan were investigated in WB-F344 rat liver epithelial cells and primary rat hepatocytes. The results show that both isomers are inhibitors of GJIC. However, beta-endosulfan (ENDO beta) is a more potent inhibitor of GJIC in primary rat hepatocytes than alpha-endosulfan (ENDO alpha), whereas the two isomers were equally potent as inhibitors of GJIC in WB-F344 rat liver cells. In primary rat hepatocytes membrane-permeant dibutyryl cyclic AMP (dB-cAMP) counteracts the inhibitory effect of ENDO beta without affecting the effect of ENDO alpha. However, in WB-F344 rat liver cells dB-cAMP failed to prevent the inhibitory effects of either ENDO alpha or ENDO beta. In addition, studies in WB-F344 rat liver cells show that ENDO alpha beta does not decrease the intracellular cAMP concentration. Thus, it is unlikely that ENDO alpha beta or its isomers and metabolites inhibit GJIC by lowering the intracellular cAMP concentration. Furthermore, comparison of the effective doses and recovery times imply that GJIC in WB-F344 rat liver cells is more sensitive to treatment by ENDO alpha beta, its isomers and metabolites than GJIC in primary rat hepatocytes. Thus, the present results demonstrate significant differences between primary rat hepatocytes and WB-F344 rat liver cells in the response of their GJIC to endosulfan.

1-Methyl-3-isobutylxanthine↗

PubMedDate not supplied

Importance of and approaches to quantification of hepatocyte apoptosis.

Abnormal regulation of the life cycle of cells is a key feature of neoplasia. The net increase and growth of initiated cells, preneoplastic lesions, and tumors is highly dependent on rates of both cell proliferation and cell death. Studies of mechanisms involved in regulation of cell death and the development of methods to detect dying and dead cells thus appear to be as important as measurements of cell proliferation in understanding the growth of both normal, preneoplastic and neoplastic lesions. This article describes apoptosis in the mouse liver and its potential role in liver carcinogenesis. Quantitation of hepatocyte apoptosis is a emerging and evolving research area that will require evaluations as thoroughly as those performed with cell proliferation in order to understand all the variables that might influence its occurrence, measurement, and interpretations. Utilizing available data, various methodologies for identifying hepatocyte apoptosis are presented and compared. Aspects important for the quantitation of apoptosis in liver are emphasized. Accurate quantitation of apoptosis, in conjunction with proliferation measurements, is critical for investigations of the mechanisms of chemically induced carcinogenesis and the development of assays for growth alterations and can be applied to biologically based cancer models.

Animals↗