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R Schulte-Hermann

Publications and source records attributed to R Schulte-Hermann.

At least 37 records · Page 2Linked to original sources
PubMed1999

Active cell death (apoptosis) and cellular proliferation as indicators of exposure to carcinogens.

An excess of cell multiplication over cell death is a crucial characteristic of preneoplastic and neoplastic cell populations. In many tumours, the rates of both cell birth and cell death are increased over those in the tissue of origin. Cell death may occur through active mechanisms: cellular suicide or active or programmed cell death, often referred to as apoptosis. The term 'apoptosis' was originally used on morphological grounds for a type of cell death characterized by condensation and fragmentation of cytoplasm and chromatin; however, other types of active cell death exist, in which cytoplasmic degradation by lysosomal, autophagic or proteasomal mechanisms may dominate, e.g. in some experimental mammary tumours and mammary tumour cell lines. Morphological and biochemical differences between the types of programmed cell death should be considered when selecting markers for identification and quantification of cell death. There is still a paucity of specific, efficient methods to assay active cell death, and unequivocal differentiation from degenerative necrosis, especially in tumours, may be difficult or impossible. Active cell death is regulated by a complex network of survival factors and death signals. Many mitogens of exogenous or endogenous origin not only stimulate cell birth but at the same time may inhibit cell death, i.e. increase survival. Endogenous factors also exist which induce active cell death; these include transforming growth factor beta1, CD95 or Fas ligand and tumour necrosis factor. Signal pathways leading to birth or death of cells appear to be interconnected to allow for the fine tuning of cell numbers in tissues. Active cell death can be triggered in two principal ways: by toxic chemicals or injury leading to damage of DNA or of other important cellular targets, and activation or inactivation of receptors by growth-regulating signal factors in the organism. Increases in cell proliferation or in cell survival induced by a chemical do not necessarily lead to cancer, but may indicate carcinogenic potential. Chemicals can affect the balance between replication and death of cells in a number of ways. Firstly, genotoxic carcinogens induce genetic damage which subsequently leads to activation of the suicide machinery, involving genes such as p53. As a result, cells with promutational lesions and mutations are eliminated, thereby providing protection from potentially initiated cells. Secondly, toxic doses of genotoxic or nongenotoxic agents induce acute or chronic injury, leading to cell death and subsequent regenerative proliferation. Thirdly, nongenotoxic carcinogens which are primary mitogens may increase the birth and/or inhibit the death of cells by direct interference with growth signalling pathways. This group of agents includes several trophic hormones; e.g. oestradiol stimulates both the replication and survival of mammary tumour cells. As demonstrated in the rat liver model, preneoplastic and neoplastic cells may be over-responsive to mitogenic or survival signals and thereby undergo selective growth. Conversely, preneoplastic clones and even malignant tumours may still depend on the survival effect of mitogens and regress upon withdrawal of the agent. This indicates that the mitogenic action of the agent is reversible and underlines the principal difference between genotoxic and nongenotoxic carcinogens. In conclusion, studies on cell proliferation and cell death are useful as adjuncts to carcinogenicity assays, and the results may facilitate the interpretation of effects. In conjunction with other biological data, this information may provide an indication of potential carcinogenicity.

Animals↗
PubMed1998

Investigations on genotoxic effects of groundwater from the Mitterndorfer Senke and from the vicinity of Wiener Neustadt.

INTRODUCTION: This report describes the first study on genotoxic effects of Austrian ground- and drinking waters. Samples from the Mitterndorfer Senke (MS) and the vicinity of Wiener Neustadt were tested over a three years period. The MS is the largest aquifer in Austria. Due to deposition of industrial and community wastes, chemicals have polluted the groundwater in this area. Aim of the present study was to elucidate if consumption of these waters might pose a carcinogenic risk to humans. METHODS: 43 Water samples were tested in a test battery which consisted of bacterial gene mutation assays (Salmonella strains TA100 and TA98), micronucleus (MN) assays with cultures of primary rat hepatocytes and plant bioassays (MN tests with Tradescantia and Vicia faba). For the bacterial assays, the water samples were extracted with XAD resins. RESULTS: In total, 27.9% of the samples caused positive effects; 8 samples were active in Salmonella microsome assays, Strain TA100 was particularly sensitive upon addition of metabolic activation mix (6 positive samples). Four samples were positive exclusively in MN assays with cultures of primary rat hepatocytes; one sample gave positive results in all three bioassays. Finished waters from waterworks were consistently devoid of mutagenic activity under all experimental conditions. DISCUSSION: Overall, only a small fraction of the groundwaters caused mutagenic effects and in all cases the activities were moderate. Comparison of the results of the present study with data obtained in other investigations under similar experimental conditions shows that the genotoxicity of groundwaters of the MS area are lower than the effects caused by ground- and drinking waters from other countries. The fact that no genotoxic activity was detected in any of the finished drinking waters can be taken as an indication that consumption of these waters does not pose a health hazard arising from contamination with genotoxic carcinogens to humans.

Animals↗
PubMed1998

Expression of cytochrome P450 2A5 in preneoplastic and neoplastic mouse liver lesions.

Cytochrome P450 (CYP) 2A5 is involved in the metabolism of carcinogens like aflatoxin B1 and N-nitrosodiethylamine (NDEA), and CYP2A5 levels are increased in some pathological states of the liver (e.g., infectious hepatitis and porphyria). We analyzed the expression of CYP2A5 during experimental liver carcinogenesis in three different mouse strains (C3H/He, C57BL/6J, and B6C3F1) with immunohistochemical techniques and in situ hybridization. In normal liver, CYP2A5 protein and mRNA were detected in centrilobular hepatocytes only. Phenobarbital treatment increased the number of CYP2A5-positive centrilobular hepatocytes and the CYP2A5-positive areas were extended into the middle zone in all strains, but periportal hepatocytes remained negative. Fifty percent of the spontaneous foci in untreated mice, over 90% of the foci in mice treated with NDEA or phenobarbital and all of the hepatocellular adenomas and carcinomas displayed positive immunostaining and a strong CYP2A5 mRNA signal by in situ hybridization. In the liver tumors metastasized to the lung, expression of CYP2A5 had largely disappeared. CYP2A5 expression in neoplastic and putative preneoplastic lesions, although sometimes heterogeneous, was apparently independent of the typical zonal expression pattern in normal tissue. As expected, the C57BL/6J mice developed fewer foci and tumors than the C3H/He and B6C3F1 mice, but the phenotype of CYP2A5 overexpression was similar in all the strains. Our data suggest that the increased expression of CYP2A5 may play an important role in the development of liver cancer in mice and may be used as a novel marker for spontaneous and NDEA-induced mouse liver foci.

Animals↗
PubMed1998

Levels of transforming growth factor beta and transforming growth factor beta receptors in rat liver during growth, regression by apoptosis and neoplasia.

Transforming growth factor beta1 (TGF-beta1) has been implicated as inhibitor of cell proliferation and a potent inducer of apoptosis in vitro and in vivo after the administration of high doses. To assess the role of endogenous TGF-beta1, we quantitated the cytokine and its receptors in rat liver during regenerative and hyperplastic growth, regression by apoptosis, and in hepatocellular carcinoma (HCC). This was accomplished by Northern blot analysis and by RNase protection assay of the messenger RNA (mRNA) of TGF-beta1 and TGF-beta receptors (TbetaR) types I to III and by an activity bioassay of the TGF-beta proteins. Untreated rat livers were found to contain 15.6 +/- 4.8 ng TGF-beta1 protein/g tissue; TGF-beta2 protein was not detected. To induce toxic cell death and subsequent regenerative DNA synthesis in the liver, rats were treated with a necrogenic dose of carbon tetrachloride (CCl4). After 24 and 48 hours, there was an upregulation of TGF-beta1 (mRNA, up to tenfold; protein, about twofold) and of TbetaRs (mRNA: two- to fourfold); that indicates an overall enhanced production of and sensitivity to TGF-beta1, which may serve to confine the regenerative response. Hyperplastic liver growth and regression of the hyperplasia were induced by treatment with cyproterone acetate (CPA) or nafenopin (NAF) followed by withdrawal; neither mRNAs of TGF-beta1 and TbetaR types I to III nor TGF-beta1 protein exhibited significant changes during the growth phase or during regression by apoptosis. We also studied neoplastic growth. HCC, obtained after long-term treatment with NAF, exhibited high rates of cell replication and apoptosis. The majority of lesions contained mRNA and protein of TGF-beta1 and mRNA of TbetaR types I to III at concentrations similar to those of the surrounding tissue. In conclusion, during liver regeneration there is a pronounced upregulation of expression of both TGF-beta1 and TbetaRs I to III, but not during mitogen-induced liver growth or regression. It appears that apoptosis is induced via altered local concentration of TGF-beta1, in a paracrine and/or autocrine way. By this mechanism the lethal effects of TGF-beta1 may be locally confined, and overshoots of apoptosis in the liver may be prevented.

Animals↗
PubMed1998

Survival of normal colonic epithelial cells from both rats and humans is prolonged by coculture with rat embryo colonic fibroblasts.

Primary cultures of normal colonic epithelial cells from both humans (HCEC) and rats (RCEC) have been established using coculture with colon fibroblasts isolated from rat term embryos. While no other factors we have analyzed had any effect on the survival of epithelial cells, which is normally 3-4 days, coculture with viable fibroblasts extended this period to at least 2 weeks. The effects depended on early passages and low seeding densities of the fibroblasts and on direct cell-cell contact. We have obtained cultures of epithelial cells expressing keratin, laminin, and uvomorulin, displaying a polygonal, epithelial morphology and forming microvilli. DNA synthesis as measured by BrdU uptake into DNA varied widely between colonies of the same culture depending on cell morphology: flat colonies of RCECs contained 5.7% +/- 0.56% BrdU-positive cells, while the proportion in dense three-dimensional colonies reached 50.3% +/- 2.6%. In HCECs the growth fraction was lower, but showed the same distribution between classes of colonies. In the presence of rat embryonic colon fibroblasts, growth factors exerted survival activity on colonic epithelial cells. Consecutive addition of insulin and epidermal growth factor/fibroblast growth factor (EGF/FGF) increased colony number (15.0 +/- 1.0 and 23.0 +/- 2.0 colonies/well respectively; p < or = 0.05 increased above control) and size (1022 +/- 155 and 1207 +/- 158 cells/colony respectively; p < or = 0.05 increased above control) compared to serum-free control medium and basic MEM without growth factors. BrdU labeling index was not increased, however: EGF/FGF actually decreased BrdU labeling from 33.2% +/- 3.9% in controls to 21.3% +/- 3.8% in the EGF/FGF group (p < or = 0.05) owing to the high proportion of flat colonies consisting of resting cells. The newly established culture model can now be used to investigate growth control mechanisms in colonic mucosa and the effects of toxic and/or tumor-promoting substances on these mechanisms.

Animals↗
PubMed1998

Activated granulocytes oxidize the endogenous stem cell inhibitory peptide pGlu-Glu-Asp-Cys-Lys (pEEDCK) to the stimulatory dimer: a redox-mediated mechanism for demand-induced hematopoietic regulation.

We have previously shown that the pentapeptide pGlu-Glu-Asp-Cys-Lys (pEEDCK), which is associated with mature leukocytes, maintains pluripotent hematopoietic stem cells (colony-forming units-spleen [CFU-S]) in a quiescent state under physiological conditions. It is also known that its oxidation product, the disulfide-bonded homodimer (pEEDCK)2, is a growth factor for CFU-S in vivo. In this paper we report on the combined actions of the monomer and dimer in inducing rapid changes in stem cell proliferation in vivo. A single injection of 20 microg/kg synthetic dimer into mice stimulated CFU-S proliferation (60% in S-phase after 9-11 hours) and population expansion. Stimulated CFU-S traversed one cell cycle, with an estimated S-phase time of 5.5 hours, and then become quiescent again. Proliferation of CFU-S in response to dimer showed no sensitivity to the inhibitory effects of monomeric pEEDCK, whereas CFU-S proliferation did display sensitivity to inhibition after injection of cytosine arabinoside or doxorubicin. Products of mature granulocytes undergoing an oxidative burst reaction rapidly oxidized monomeric pEEDCK to the dimer. The suppressive effect of endogenous pEEDCK monomer on stem cell proliferation was thus converted within minutes to a stimulatory signal (dimer). Because many in vivo situations (e.g., infection) requiring increased hematopoiesis involve granulocyte and macrophage activation, the formation of dimer from endogenous pEEDCK monomer may provide an almost instantaneous demand-induced emergency signal for increasing stem cell proliferation and blood cell production.

Animals↗
PubMed1997

Inherent increase of apoptosis in liver tumors: implications for carcinogenesis and tumor regression.

We quantitatively assessed rates of cell replication and of apoptosis during the development and regression of liver cancer. In rats, apoptotic activity gradually increased from normal liver to putative preneoplastic foci (PPF), to hepatocellular adenoma (HCA), and to hepatocellular carcinoma (HCC). At all stages, rates of cell replication were higher than of apoptosis, allowing a preferential net gain of (pre)neoplastic cells. As in rats, in human HCC, birth and death rates were increased manifold, indicating a species-independent phenomenon. Implications of the increasing cell turnover were studied in rats using the administration and withdrawal of nafenopin (NAF), a liver mitogen and nongenotoxic carcinogen. Prolonged NAF treatment enhanced cell number in normal liver by 25%, while PPF and liver tumors were amplified at least 100-fold. After stopping NAF treatment, cell replication ceased, while cell elimination by apoptosis was increased in normal and (pre)neoplastic liver. HCA and HCC showed the most pronounced shifts from replication toward apoptosis. As a result, 5 weeks after halting NAF, 20% of cells in normal liver, but about 85% of (pre)neoplastic lesions including HCC, were eliminated. The implications of these findings include that nongenotoxic carcinogens can act as survival factors even for malignant cells. Furthermore, tumor cells not only exhibit excessive proliferation, but also undergo apoptosis at rates that far exceed those in normal tissue. Therefore, inhibition of cell death by the survival activity of nongenotoxic carcinogens results in selective growth of (pre)neoplastic lesions. On the other hand, blockade of survival effects leads to excessive apoptosis in (pre)neoplasia and seems promising as a therapeutic concept for the selective elimination of (liver) cancer.

Adenoma, Liver Cell↗
PubMed1997

Inhibition instead of enhancement of lipid peroxidation by pretreatment with the carcinogenic peroxisome proliferator nafenopin in rat liver exposed to a high single dose of corn oil.

Oxidative stress is discussed as a possible hepatocarcinogenic mechanism of peroxisome proliferators (PP) in rodents and is suggested to result from the induction of peroxisomal beta-oxidation (PBOX) by PP. The induced PBOX is assumed to produce excessive H2O2 from the degradation of fatty acids, ultimately leading to oxidative stress and lipid peroxidation. In the present short term-study, we attempted to stimulate lipid peroxidation in male Wistar rats by (1) inducing PBOX enzymes with the peroxisome proliferator nafenopin at 90 mg/kg body weight per day in the diet for 10-11 days, and (2) by supplying the induced PBOX with an abundant amount of fatty acid as substrate, using a corn oil gavage at 20 ml/kg body weight. The corn-oil gavage alone, i.e. without preceding nafenopin treatment, enhanced liver triacylglycerol nine- to tenfold and hepatic lipid peroxidation, measured as thiobarbituric acid reactive substances (TBARS), was increased 50% compared with controls. Both observations were made after 18 h when the peak elevations occurred. Upon pretreatment with nafenopin, associated with a sevenfold induction of PBOX, the corn oil gavage however caused only a threefold maximal increase in hepatic triacylglycerol, also at the 18 h time-point; TBARS remained almost at control levels, as monitored at seven time points over 24-25 h. These results suggest that nafenopin reduces rather than enhances lipid peroxidation, despite the provision, in a short term study, of high doses of substrate to the induced enzyme system that is hypothetically causing oxidative stress in the liver.

Animals↗
PubMed1997

Apoptosis in the liver and its role in hepatocarcinogenesis.

Apoptosis seems to be the predominant type of active cell death in the liver (type I), while in other tissues cells may die via biochemically and morphologically different pathways (type II, type III). Active cell death is under the control of growth factors and death signals. In the liver, endogenous factors, such as transforming growth factor beta 1 (TGF-beta 1), activin A, CD95 ligand, and tumor necrosis factor (TNF) may be involved in induction of apoptosis. Release and action of these death factors seems to be triggered by exogenous signals such as withdrawal of hepato-mitogens, food restriction, etc. During stages of hepatocarcinogenesis, not only DNA synthesis but also apoptosis gradually increase from normal to preneoplastic to adenoma and carcinoma tissue. Also, in human carcinomas, birth and death rates of cells are several times higher than in surrounding liver. (Pre)neoplastic liver cells are more susceptible than normal hepatocytes to stimulation of cell replication and of cell death. Consequently, tumor promoters may act as survival factors, i.e., inhibit apoptosis preferentially in preneoplastic and even in malignant liver cells, thereby stimulating selective growth of (pre)neoplastic lesions. On the other hand, regimens favoring apoptosis and lowering cell replication may result in selective elimination of (pre)neoplastic cell clones from the liver. Finally, we have studied the first stage of carcinogenesis, namely the appearance of putatively initiated cells after a single dose of the genotoxic carcinogen N-nitrosomorpholine (NNM). Most of these cells were found to be eliminated by apoptosis, suggesting that initiation, at the organ level, can be reversed at least partially by preferential elimination of initiated cells. These events may be regulated by autocrine or paracrine actions of survival factors.

Apoptosis↗
PubMed1997

Toxic effects of griseofulvin: disease models, mechanisms, and risk assessment.

Griseofulvin (GF) has been in use for more than 30 years as a pharmaceutical drug in humans for the treatment of dermatomycoses. Animal studies give clear evidence that it causes a variety of acute and chronic toxic effects, including liver and thyroid cancer in rodents, abnormal germ cell maturation, teratogenicity, and embroyotoxicity in various species. No sufficient data from human studies are available at present to exclude a risk in humans: therefore, attempts were made to elucidate the mechanisms responsible for the toxic effects of GF and to address the question whether such effects might occur in humans undergoing GF therapy. It is well documented that GF acts as a spindle poison and its reproductive toxicity as well as the induction of numerical chromosome aberrations and of micronuclei in somatic cells possibly may result from disturbance of microtubuli formation. Likewise, a causal relationship between aneuploidy and cancer has been repeatedly postulated. However, a critical survey of the data available on aneuploidogenic chemicals revealed insufficient evidence for such an association. Conceivably, other mechanisms may be responsible for the carcinogenic effects of the drug. The induction of thyroid tumors in rats by GF is apparently a consequence of the decrease of thyroxin levels and it is unlikely that such effects occur in GF-exposed humans. The appearance of hepatocellular carcinomas (HCC) in mice on GF-supplemented diet is preceded by various biochemical and morphological changes in the liver. Among these, hepatic porphyria is prominent, it may result from inhibition of ferrochelatase and (compensatory) induction of ALA synthetase. GF-induced accumulation of porphyrins in mouse liver is followed by cell damage and necrotic and inflammatory processes. Similar changes are known from certain human porphyrias which are also associated with an increased risk for HCC. However, the porphyrogenic effect of GF therapy in humans is moderate compared with that in the mouse model, although more detailed studies should be performed in order to clarify this relationship on a quantitative basis. A further important effect of GF-feeding in mice is the formation of Mallory bodies (MBs) in hepatocytes. These cytoskeletal abnormalities occur also in humans, although under different conditions; their appearance is associated with the induction of liver disease and HCC. Chronic liver damage associated with porphyria and MB formation, enhanced cell proliferation, liver enlargement, and enzyme induction all may contribute to the hepatocarcinogenic effect of GF in mice. In conclusion, further investigation is required for adequate assessment of health risks to humans under GF therapy.

Aneuploidy↗
PubMed1996

Mutational spectra of Salmonella typhimurium revertants induced by chlorohydroxyfuranones, byproducts of chlorine disinfection of drinking water.

The base substitution specificities of 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), 3-chloro-4-(chloromethyl)-5-hydroxy-2(5H)-furanone (CMCF), 3,4-dichloro-5-hydroxy-2(5H)-furanone (MCA), and chloromalonaldehyde (CMA), a putative breakdown product of MCA, were examined in the hisG46 gene and in the hisG428 gene of Salmonella typhimurium using allele specific oligonucleotide hybridization. Although the compounds are structurally closely related, they induced substantially different mutation spectra: MCA and CMA caused primarily GC-->AT transitions in the hisG46 allele (target sequence CCC), in particular, at the second position of the codon in strain TA100. In TA100 the mutation spectrum of MCA was similar to that of CMA. The mutational specificity of MCA can be explained as a consequence of misincorporation opposite to cyclic etheno adducts identical to those formed by the carcinogen vinyl chloride. The spectra induced by MX and CMCF in TA100 were almost identical but distinctively different from the spectra of MCA and CMA. Both compounds induced primarily GC-->TA transversions, in particular, at the second position of the codon, and to a lesser extent in the first position of the codon. An identical site bias is induced by carcinogens such as polycyclic aromatic hydrocarbons and heterocyclic amines as a consequence of formation of (noncyclic) guanosine adducts. In hisG428 (target sequence TAA) MX induced again primarily GC-->TA transversions in Tyr tRNA genes (supC/M) and, to a lesser extent, intragenic AT-->TA transversions (TAA-->AAA). The possible involvement of guanosine and adenosine adducts in the mutational specificity of MX is addressed.

Chlorine↗
PubMed1996

Transforming growth factor beta 1-induced cell death in preneoplastic foci of rat liver and sensitization by the antiestrogen tamoxifen.

Previous studies have shown 5- to 10-fold higher rates of apoptosis in prestages of liver cancer (putative preneoplastic cell foci [PPF]) than in unaltered liver; fasting or withdrawal of tumor promoters enhanced apoptosis even further. We studied whether transforming growth factor beta 1 (TGF-beta 1), an inducer of apoptosis in normal liver, might be involved in induction of apoptosis in PPF. PPF were produced in 7-week-old female Sprague-Dawley rats with a single oral dose of the genotoxic carcinogen 7,12-dimethylbenz(a)anthracene (DMBA). At 24 weeks of age, TGF-beta 1 was injected into animals (40 micro g/kg intravenously) either once and they were killed 4 hours later (single-dose experiment) or eight times at 24-hour intervals and they were killed 24 hours after the last administration (multiple-dose experiment). Further subgroups received daily subcutaneous injections of tamoxifen (TAM) (8 mg/kg) for 4 consecutive weeks before TGF-beta 1 treatment. In normal liver, the apoptosis incidence was low in solvent- and TAM-only-treated animals, in the single- as well as the multiple-dose experiment. TGF-beta 1, increased the apoptosis incidence severalfold, and the combined administration of TGF-beta 1 with TAM caused a further strong increase. The already-elevated basal apoptotic incidence in PPF was further increased by TGF-beta 1, and particularly by TGF-beta 1 plus TAM treatments, which resulted in a reduction of foci number and size. In summary, these results show that TGF-beta 1 can induce apoptosis in PPF. This apoptosis-inducing activity is strongly enhanced by the additional treatment with the antiestrogen TAM, which by itself does not have any cell death-inducing effect in the liver or PPF. The elevated apoptotic activity of PPF in response to TGF-beta 1 can lead to a selective reduction of the liver load with preneoplastic cells.

Animals↗
PubMed1996

Hepatocarcinogenic potential of di(2-ethylhexyl)phthalate in rodents and its implications on human risk.

The plasticizer di(2-ethylhexyl) phthalate (DEHP), to which humans are extensively exposed, was found to be hepatocarcinogenic in rats and mice. DEHP is potentially set free from objects made of synthetic materials (e.g., those used in medicine). Chronically, the greatest amounts are transferred to persons undergoing hemodialysis (up to 3.1 mg/kg b.w. per day) who would thus be considered the individuals most endangered by tumorigenesis. Although toxicokinetics seem to play a certain unclear role in the course of DEHP-related toxicity, toxicodynamic factors appear more decisive. DEHP is a representative of "peroxisome proliferators" (PP), a distinct group of substances that, in rodents, do not only induce peroxisomes but also specific enzymes in other organelles, organ growth, and DNA synthesis. The cluster of the characteristic effects of PP is generally, although perhaps not quite appropriately summarized as "peroxisome proliferation," and is strongest in the liver. The lowest observed effect level (LOEL) and the no observed effect level (NOEL) of peroxisome proliferation in the rat, as determined by the induction of specific enzymes (peroxisomal beta-oxidation, carnitine-acetyl-transferase, cytochrome P-452), DNA synthesis, and hepatomegaly, may be assumed as 50 and 25 mg/kg b.w. per day, respectively. DEHP and other carcinogenic PP are neither genotoxic nor tumor initiators, but they appear to be tumor promoters, also implicating a threshold level for the carcinogenic effect. Although a causal relationship between a particular effect of peroxisome proliferation and hepatocarcinogenesis is as yet unknown, peroxisome proliferation as a whole phenomenon appears to be associated with the potential of tumor induction, as shown by comparison of the relative strength of individual PP and by comparison of species and organ specificities. Likewise, LOEL and NOEL of rodent carcinogenesis, that is, 300 and 50 to 100 mg/kg b.w. per day, respectively, are above but not too far from the corresponding values for the investigated parameters of peroxisome proliferation. Thus, with respect to dose alone, worst-case exposure in hemodialysis patients is at least 16-fold below the LOEL of any characterized PP-specific effect of DEHP and approximately 100-fold below that of DEHP-related tumorigenesis. Also, primates are less responsive to PP than rats with respect to the investigated biochemical and morphological parameters. If this lower primate responsiveness is extrapolated to estimate carcinogenicity in humans, we might thus arrive at an even larger safety margin than when based on exposure alone. Doses of PP hypolipidemics that had clearly induced several indicators of peroxisome proliferation in rats did not cause any clear-cut enhancements in the peroxisomes of patients, even though most of these hypolipidemics were considerably stronger PP than DEHP. Thus, an actual threat to humans by DEHP seems rather unlikely. Accordingly, hepatocarcinogenesis was neither enhanced in workers exposed to DEHP nor in patients treated with hypolipidemics.

Animals↗
PubMed1996

[Molecular biology of tobacco smoke associated neoplasia].

Adducts, formed by carcinogens of tobacco smoke with DNA, can be detected by means of molecular techniques and are used as marker of internal exposure. Carcinogen-DNA adducts produce specific mutations in tumor-suppressor genes (e.g. p53) and oncogenes (e.g. ras), which can be involved in tumor initiation or in later stages of tumor progression (e.g. evolution of an invasive phenotype). Benzo(a)-pyrene, an important carcinogen of tobacco smoke, induces GT transversions, as demonstrated in in vitro systems and animal models. Mutations in the p53- or ras-gene are more common in human tumors of the lung, head and neck, bladder and pancreas in smokers than in non-smokers. Molecular biology of cancer gains increasing significance in clinical practice since 1.) the presence of certain mutations confers an unfavorable prognosis to malignant disease (e.g. ras mutations in lung cancer), 2.) ras and p53 mutations often occur early during tumor development and can thus facilitate diagnosis of malignant disease, and 3.) minimal residual disease can be detected using molecular techniques. After resection of cancer of the head and neck, tumor recurred more frequently in patients with no evidence of residual disease as assessed by pathohistologic criteria than in patients with no evidence of residual disease as evaluated by p53 immunostaining.

Carcinogens↗
PubMed1995

In situ detection of fragmented DNA (TUNEL assay) fails to discriminate among apoptosis, necrosis, and autolytic cell death: a cautionary note.

Detection of DNA fragments in situ using the terminal deoxyribonucleotidyl transferase (TDT)-mediated dUTP-digoxigenin nick end labeling (TUNEL) assay is increasingly applied to investigate active cell death (apoptosis). We studied the specificity of the assay in well-defined models of apoptosis and necrosis as well as in postmortem autolysis in rat liver. During involution of liver hyperplasia, which follows stopping treatment with the hepatomitogens cyproterone acetate (CPA) or nafenopin (NAF), numerous apoptotic hepatocytes could be observed with TUNEL-positive chromatin residues. A similar TUNEL-positive reaction appeared in necrotic hepatocytes after a cytotoxic dose of carbon tetrachloride (CCl4) or N-nitrosomorpholine (NNM). Also, in insufficiently fixed, autolytic livers TUNEL-positive nuclei were observed. Thus, DNA fragmentation is common to different kinds of cell death; its detection in situ should not be considered a specific marker of apoptosis.

Animals↗
PubMed1995

Growth kinetics of enzyme-altered liver foci in rats treated with phenobarbital or alpha-hexachlorocyclohexane.

A quantitative method based upon a stochastic model for the appearance of initiated cells and their clonal growth was used to estimate cell birth and death rates in enzyme-altered liver foci (EAF). gamma-Glutamyltranspeptidase (gamma-GT)-positive foci were initiated in livers of female SPF Wistar rats by a single application of N-nitrosomorpholine. Serial terminations during and after stop of promoter treatment with either phenobarbital (PB) or alpha-hexachlorocyclohexane (alpha-HCH) provided information on the growth and regression of the EAF. Simultaneous labeling index (LI) measurements were obtained via single injections with [3H]thymidine. No significant increases of the LI were observed with PB or alpha-HCH treatment. Since both agents are strong liver promoters we conclude that the growth of gamma-GT-positive foci is mainly due to a decrease in the rate of apoptosis. Indeed, our analysis supports this conclusion but determines that the abrogation of homeostatic control during promoter treatment is subtle. The ratio of cell death and cell birth rate is found to be decreased only slightly during promoter treatment and slightly increased after stop of promotion. For the mathematical analysis, two distinct focal growth scenarios were employed: (i) volume growth, i.e., all cells within individual foci cycle actively with the same rate, and (ii) surface growth where only cells on the surface of foci cycle actively while interior cells are resting. The model based upon scenario (ii) provides a better fit to the data and is more consistent with the experimental observations indicating heterogeneity of cell division rates within individual foci.

Animals↗