Biological behavior of prestages of cancer cells: an introduction.
Explore the source record for details and available documents.
Animals↗
Biomedical subjects
R Schulte-Hermann
Publications and source records attributed to R Schulte-Hermann.
Apoptosis and multistage carcinogenesis in rat liver.
Apoptosis is a type of active cell death. It is involved in the homeostasis of cell number in tissues and is controlled by the growth regulatory network in the organism. It is also involved in the active removal of damaged cells. We have studied the role of apoptosis in cancer pre-stages and overt cancer in vivo, using rat liver as our main model system. Quantitative determination of apoptosis in histological specimens revealed that the rate of apoptosis tends to increase from normal to (pre)neoplastic to malignant cells. Thereby active cell death largely counterbalances the increasing replicative activity in developing malignancy. Tumor promoters shift the balance in favor of cell replication, whereas promoter withdrawal, fasting or TGF-beta 1 favor apoptosis (anti-promotion). Preneoplastic cells are more susceptible than normal liver cells to stimulation of both cell replication or cell death. Consequentially (pre)neoplastic tissue may preferentially grow or die during the appropriate treatment. Regimens that favor apoptosis and lower cell replication are shown to result in the elimination of preneoplastic cell clones from the liver (anti-initiation) and to reduce the cancer risk of the animal.
Animals↗
Role of active cell death (apoptosis) in multi-stage carcinogenesis.
Active cell death is a genetically encoded self-destruction of a cell. There occur morphologically different types of active cell death, e.g. apoptosis in the liver or autophagic cell death in human mammary carcinoma cells after tamoxifen treatment (Pre)neoplastic lesions in rat liver exhibit enhanced rates of apoptosis, which tend to increase with increasing malignancy. Tumor promoters and non-genotoxic carcinogens inhibit active cell death, thereby increasing the accumulation of (pre)neoplastic cells and accelerating the development of cancer. On the other hand promoter withdrawal, fasting or application of negative growth signals such as transforming growth factor beta 1 (TGF beta 1) enhance apoptosis and can lead to selective regression of preneoplastic lesions or tumors.
Animals↗
Active cell death (apoptosis) in liver biology and disease.
Explore the source record for details and available documents.
Animals↗
Food restriction eliminates preneoplastic cells through apoptosis and antagonizes carcinogenesis in rat liver.
Restriction of dietary calories reduces cancer formation in experimental animals and probably also in humans. This effect is generally attributed to the inhibitory effect of fasting on cell proliferation. Here we studied the effect of fasting on physiological cell death through apoptosis by using rat liver as a model. (i) In normal liver, involution of hyperplasia by apoptosis was reinforced by food withdrawal and suppressed by feeding. Complete food withdrawal for 8 days or food reduction by 40% for 3 months eliminated 20-30% of normal liver cells through apoptosis. (ii) Putative preneoplastic liver foci exhibited severalfold higher rates of DNA replication and apoptosis than unaltered liver. Food restriction lowered DNA replication but increased apoptosis, which reduced the number and volume of putative preneoplastic liver foci by 85% within 3 months. Subsequent return to ad libitum feeding normalized cell replication and apoptosis but clear differences in the volume and number of putative preneoplastic liver foci persisted throughout the following 17 months. Treatment of animals after food restriction with nafenopin, a peroxisome proliferator and potent tumor promoter, produced only half as many hepatocellular adenomas and carcinomas as in animals fed unrestrictedly throughout their lifetime. This indicates that food restriction had actually eliminated a part of the initiated cells. This study demonstrates that food restriction preferentially enhances apoptosis of preneoplastic cells. This effect in combination with lowered cell replication provides protection from carcinogenesis.
Animals↗
Induction of genotoxic effects by chlorohydroxyfuranones, byproducts of water disinfection, in E. coli K-12 cells recovered from various organs of mice.
The genotoxic effects of three chlorohydroxyfuranones (CHFs), 3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-furanone (MX), 3-chloro-4-(chloromethyl)-5-hydroxy-2[5H]furanone (CMCF) and 3,4,-dichloro-5-hydroxy-2[5H]furanone (MCA), which are formed as byproducts of water disinfection with chlorine, were investigated in bacterial differential DNA repair assays in vitro and in animal-mediated assays in vivo. As indicators of DNA damage, E. coli K-12 strains were used that differ in their repair capacity (uvrB/recA vs. uvr+/rec+). Liquid incubation of the compounds without metabolic activation caused a pronounced reduction of the viability of the repair-deficient strain relative to the repair-proficient wild-type strain. The order of potency of genotoxic activity in vitro (dose range 0.004-10 micrograms/ml) was MX > CMCF > MCA. Addition of mouse S-9 mix or bovine serum albumin to the incubation mixtures resulted in an almost complete loss of the activity of all three test compounds. In the animal-mediated assays, mixtures of the indicator bacteria were injected intravenously into mice which were subsequently treated with the test compounds (200 mg/kg b.w.). Two hours later, the cells were recovered from various organs and the relative survival frequencies determined. Under these conditions, all three compounds caused pronounced genotoxic effects, MX and CMCF being stronger genotoxins than MCA. The strongest effects were consistently found in the gastrointestinal tract, but statistically significant DNA damage was also observed in indicator cells recovered from lungs, liver, spleen and kidneys. In a further experiment, the effects of lower doses of MX (4.3, 13 and 40 mg/kg) were investigated. In these experiments dose-dependent effects were measured in all organs. CMCF and MA caused only marginal effects at 40 mg/kg except in the stomach where approximately a 50% reduction of relative survival frequency was observed with CMCF. The results of these animal-mediated assays indicate that (i) all three CHFs cause genotoxic effects in the living animal, and (ii) the potencies of the three compounds observed under in vivo conditions are not commensurate with their extremely high activities measured in vitro. One possible explanation for the weaker responses observed in the animal-mediated assays might be that CHFs are inactivated by non-specific protein binding.
Analysis of Variance↗
Enhanced clastogenicity of contaminated groundwater following UV irradiation detected by the Tradescantia micronucleus assay.
The Tradescantia micronucleus (Trad-MCN) assay was used to determine clastogenic effects of contaminated groundwater collected near a hazardous waste landfill. Water samples were taken from a purification plant (activated charcoal filtration, UV irradiation) which was built to avoid groundwater contamination by this landfill. Five series of experiments were conducted during approximately 4 months. In addition, water samples were irradiated under laboratory conditions with increasing doses of UV light. Several field water samples gave positive, dose-dependent effects before filtration and irradiation. Maximal values (6.1 +/- 4.7 micronuclei (MCN)/100 tetrads) were six-fold above controls. UV irradiation of activated charcoal-filtered water resulted in an enhancement of MCN frequencies. Exposure of groundwater to UV irradiation in the laboratory led to a dose-dependent increase of micronuclei. At the highest dose (1500 J/m2) the MCN frequency was more than six times higher than in the unirradiated sample (5.4 +/- 1.0 vs. 0.8 +/- 0.4 MCN/100 tetrads). The clastogenicity of UV-irradiated samples decreased with a half-life of approximately 1 day. Irradiation of tap water did not increase the MCN frequency. Our results indicate that irradiation of water with UV light for disinfection purposes might lead to a transiently increased genotoxicity of chemically polluted water samples.
Hydrocarbons, Halogenated↗
Effects of ethanol treatment on DNA damage induced in Escherichia coli K-12 in various organs of mice by N-nitro-sonornicotine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and N-nitrosopyrrolidine.
DNA damage induced by tobacco-related nitrosamines was quantitatively determined in animal-mediated DNA-repair assays with Escherichia coli K-12 strains. Intraperitoneal administration of N-nitrosonornicotine (NNN), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N-nitrosopyrrolidine (NPYR) caused dose-dependent genotoxic effects in indicator bacteria recovered from various organs of nitrosamine-pretreated mice. Oral administration of ethanol (6.3 g/kg body wt) 1 h prior to administration of NNN, NNK or NPYR resulted in a substantial reduction of genotoxicity that was more pronounced in the liver as compared to lungs, spleen, kidneys and blood. However, when the same ethanol dose was given 26 h before NNN or NPYR, an increase of DNA damage was found, that was, in most cases, higher in the kidneys than in the liver. Significant enhancement of genotoxic activity was also measured in lungs and spleen, whereas only a marginal increase was detectable in the blood. Repeated administration of smaller ethanol doses (2.0 g/kg body wt at 12 h intervals) for 4 days caused a comparable increase. Similar enhancement of genotoxicity was also measured when acetone (3.5 g/kg) was given orally 15 h before the nitrosamine administration. The stimulating effect of ethanol was dose dependent and was absent when the alcohol was administered 60 h prior to the nitrosamine. Neither ethanol nor acetone had an effect on the genotoxicity of NNK under identical experimental conditions. The same E. coli K-12 strains were used to test NNN, NNK and NPYR in in vitro assays. The ranking order of activation capacity was liver S-9 > kidney S-9 > lung S-9 for all three nitrosamines. Blood S-9 did not markedly activate the nitrosamines. S-9 mixtures prepared from mice that had been treated with ethanol (6.3 g/kg body wt) for 26 h before death activated NNN and NPYR more efficiently than those S-9s from untreated animals. The increase of genotoxic activity was more pronounced with S-9 from kidneys and lungs than from liver. No difference was seen with S-9 from ethanol-treated and untreated mice with NNK.
Animals↗
Tumor development and apoptosis.
Apoptosis or other types of active cell death may play a major role at various stages of carcinogenesis. Active cell death can be induced, by internal and exogenous signals, in preneoplastic, neoplastic and even malignant cells. It may reverse the effects of initiation and promotion and may lead to tumor regression. Conversely tumor promoters may inhibit active cell death in preneoplastic cells and thereby accelerate cancer development.
Animals↗
[Relevance of apoptosis for carcinogenesis].
Apoptosis is a type of active, genetically programmed cell death. It occurs under specific conditions and is characterized by it's morphology. It is controlled by genes, hormones and other factors regulating the growth of organs and cells in the organism. In the liver and some other epithelial tissues transforming growth factor beta 1 and related peptides seem to be involved in the homeostasis of cell multiplication and cell death. In the course of carcinogenesis, initiated, preneoplastic and neoplastic cells and cell foci in the liver show enhanced DNA synthesis and also enhanced apoptosis. Tumor promoters inhibit apoptosis and increase cell replication and can thereby shift the balance between birth and death of cells accelerating tumor development. Fasting can have the opposite effect.
Animals↗
Prevention of genotoxic effects by dietary constituents in various organs of mice treated with nitrosamines.
Explore the source record for details and available documents.
Animals↗
Detection of mutagenic activity in textiles with Salmonella typhimurium.
A hundred and ninety-six textile samples were tested in a modified version of the Salmonella/microsome assay for release of mutagenic contaminants. As heat sterilization of the samples can result in reduction of mutagenic activity, tests were performed with streptomycin resistant derivatives of Salmonella tester strains TA98 and TA100. Textile samples were preincubated in buffered saline (PBS), DMSO or ethanol. Subsequently, the fabrics were placed on streptomycin supplemented selective agar plates. In total, 18 samples (9.2%) exerted mutagenic activity. DMSO was the most effective solvent (15 positives) followed by ethanol (9 positive samples) and PBS (7 positives). Most fabrics (16) caused mutagenic effects only upon metabolic activation with liver S9 mix. Chemical analysis indicates that the positive results obtained with PBS are not due to release of histidine or formaldehyde. Three directly active samples gave negative results in strain TA98NR which is devoid of classical nitroreductase. With one exception all other textiles were negative in strain TA98/1,8-DNP6 (which lacks O-acetyltransferase). These findings indicate that nitroaromatics and amines might be responsible for the mutagenic effects of the textiles.
Buffers↗
Transforming growth factor-beta 1 as a signal for induction of cell death by apoptosis.
Cell death by apoptosis is a major determinant of growth of normal tissues and tumours. The present study aimed to elucidate signal factors involved in its regulation. Epithelial cells in control liver, during regression of cyproterone acetate induced liver hyperplasia, in liver (pre)neoplasia and in uterus undergoing apoptosis in vivo show immunostaining for transforming growth factor beta 1 (TGF-beta 1) as detected by anti-pre(266-278) TGF-beta 1 antibodies. Positive immunostaining is also seen in a few intact cells of hyperplastic, regressing liver apparently preparing for apoptosis, but is virtually not found in hepatocytes of normal or growing liver nor in cells undergoing death by necrosis. Recombinant latency associated protein (rLAP, dimer of the pro-region non-covalently associated with the mature region) complex and mature TGF-beta 1 induce apoptosis in isolated hepatocytes cultured in vitro. These findings suggest an involvement of TGF-beta 1 in the induction of apoptosis in certain epithelia in vivo.
Animals↗
Glutathione S-transferase isoenzyme patterns in different subtypes of enzyme-altered rat liver foci treated with the peroxisome proliferator nafenopin or with phenobarbital.
It is known that phenobarbital (PB) and the peroxisome proliferator (PP) nafenopin (NAF) promote tumor formation by stimulating selective growth of different subtypes of liver foci. While PB enhanced the gamma-glutamyltranspeptidase (GGT)-positive eosinophilic-clear cell foci (ECF), NAF amplified the GGT-negative weakly basophilic foci (WBF). These findings provide the possibility of using the occurrence of these foci subtypes as early indicators for the carcinogenic potential of PB- and PP-type promoters. In order to improve the methods for the discrimination between ECF and WBF we studied further differences in their phenotype, as determined by the expression pattern of glutathione S-transferase (GST) subunits. GST subunits of the alpha (Ya, Yc), mu (Yb1, Yb2) and pi family (Yp), which compose different GST isoenzymes, were demonstrated by immunohistochemical methods. ECF were the only foci subpopulation that expressed GST subunit Yp, while this subunit was always absent in WBF and in another focus subtype, the tigroid foci (TF). Neither PB nor NAF changed this pattern. Thus Yp expression was rather a function of the focus type than of the promoter used. Upon PB treatment expression of the GST subunits Yb1 and Yb2 was frequently elevated in ECF, while Ya and Yc remained more or less unchanged. In NAF-treated livers large WBF, however, showed diminished expression of all investigated GST subunits of the alpha and mu family. In conclusion, PB seems to promote mostly ECF with elevated levels of mu and pi class GSTs, while low levels or absence of all GSTs tested may be associated with growth selection of WBF through the PP NAF.
Adenoma↗
Peroxisomal enzyme induction uncoupled from enhanced DNA synthesis in putative preneoplastic liver foci of rats treated with a single dose of the peroxisome proliferator nafenopin.
Putative preneoplastic foci of spontaneous origin could be detected in the livers of 2 year old, untreated male Wistar rats. The unaltered and preneoplastic hepatocytes showed an identical expression of the peroxisomal marker enzyme acyl-CoA oxidase, as determined by immunohistochemical staining. A single dose of the peroxisome proliferator (PP) nafenopin (NAF) induced the enzyme predominantly in hepatocytes around the central venules and cell replication mainly in the periportal areas. However, upon one NAF application almost all of the preneoplastic foci showed a considerably weaker immunoreaction for peroxisomal acyl-CoA oxidase than the surrounding tissue. Concomitantly NAF elevated replicative DNA synthesis index in foci up to approximately 40%, while replication of hepatocytes in the unaltered portion of the livers increased only slightly to moderately. In conclusion, NAF-induced peroxisomal acyl-CoA oxidase and replicative DNA synthesis seem not to be necessarily coupled within the same liver cell. Furthermore, preneoplastic foci responded rather to the cell replicative than to the peroxisomal effects of NAF, suggesting that the PP-induced growth stimulus is of particular significance for the carcinogenic action of this class of compounds.
Acyl-CoA Oxidase↗
Enhancement of peroxisomal enzymes, cytochrome P-452 and DNA synthesis in putative preneoplastic foci of rat liver treated with the peroxisome proliferator nafenopin.
The peroxisome proliferator (PP) nafenopin (NAF) enhanced tumor development in rat liver through promotion of a subtype of putative preneoplastic cell foci, characterized by weak cytoplasmic basophilia. In order to elucidate the selective growth advantage of these weakly basophilic foci (WBF) we investigated the effects of NAF on their metabolic phenotype and DNA synthesis. In WBF, as well as in other foci subpopulations and in hepatocellular carcinomas the occurrence of five NAF-inducible enzymes, i.e. of peroxisomal beta-oxidation (acyl-CoA oxidase, bifunctional protein and thiolase), catalase and cytochrome P-452 was studied by immunohistochemical methods. In untreated livers almost all foci were stained with the same intensity as the surrounding tissue. When NAF was applied, most of the liver foci showed considerably less staining than the non-focal parenchyma in which pronounced enzyme induction had occurred. However, the subpopulation of WBF showed a more heterogeneous pattern of enzyme expression varying from less to even more than in the adjacent tissue. A similarly broad range of expression of peroxisomal enzymes was found in hepatocellular carcinomas. On average, however, the tumors exhibited less staining and lower activity of peroxisomal beta-oxidation than the surrounding parenchyma. WBF always showed higher rates of DNA synthesis than other foci subtypes and unaltered liver. In approximately one-third of these foci DNA synthesis was found to be enhanced concomitantly with elevated expression of peroxisomal beta-oxidation enzymes. In conclusion, WBF may have a selective growth advantage as they 'overrespond' to the inducing effects of NAF on DNA synthesis and peroxisomal enzymes.
3-Hydroxyacyl CoA Dehydrogenases↗
Condensation of the chromatin at the membrane of an apoptotic nucleus is not associated with activation of an endonuclease.
A current hypothesis holds that chromatin fragmentation into oligonucleosomal patterns is an early event during apoptosis. In contrast, induction of apoptosis in cultured hepatocytes by TGF-beta 1 was not associated with DNA fragmentation into oligonucleosomes in hepatocyte monolayers and apoptotic fragments. For a more rigorous test of the hypothesis we performed a number of experiments. We compared nuclear changes resulting from TGF-beta 1 with those induced by Ca2+, a known activator of endonuclease. The morphology of apoptotic and Ca(2+)-treated nuclei was different as judged by DNA staining with Hoechst 33258. Likewise, electron microscopy of apoptotic nuclei showed characteristic condensation of the chromatin as well as dissolution of the nucleolar structure and nuclear fragmentation, changes not seen after Ca2+ treatment, after three hours of incubation. Analysis of DNA fluorescence of nuclei by FACS revealed that treatment with Ca2+ reduced the signal by 20%. In contrast, nuclei from TGF-beta 1-treated hepatocytes did not exhibit a reduced signal and after sorting by FACS, apoptotic nuclei remained in the 2N and 4N fractions. The absence of detectable DNA fragmentation in apoptotic nuclei was further verified by in situ nick translation, not only in hepatocytes but also in a mouse lymphoma cell line. From these findings we conclude that activation of an endonuclease is not an early event on the pathway to morphologically recognizable apoptosis.
Animals↗
Cell proliferation and apoptosis in normal liver and preneoplastic foci.
The growth rate of tissues including tumors is determined by the difference between cell replication and cell death. Among different types of cell death, apoptosis, a form of programmed cell death, is of particular importance. Nongenotoxic carcinogens exert their carcinogenic effects not only via stimulation of cell replication but also by modulating the incidence of apoptosis. This can be seen at different stages of carcinogenesis: a) After initiation in the liver, many initiated cells may undergo apoptosis and never develop into preneoplastic foci, as suggested by both biological and mathematical studies. Thus, apoptosis appears to determine the efficiency of initiation. b) In the promotion stage, early preneoplastic hepatic foci originate either from treatment with a genotoxic carcinogen or spontaneously exhibit much higher rates of cell replication than normal cells, but nevertheless show little preferential growth. This is due to enhanced rates of apoptosis. Some tumor promoters were found to inhibit apoptosis and thereby accelerate foci growth and carcinogenesis. c) In neoplastic nodules and tumors, apoptosis has been shown to be an important growth determinant and to be regulated by growth regulatory hormones, which thereby may decrease or accelerate tumor growth. Studies on the regulation of apoptosis revealed that in the liver, transforming growth factor TGF-beta 1 is involved in the initiation of apoptosis. This was based on three lines of evidence: TGF-beta 1 induced apoptosis in isolated hepatocytes, b) in vivo hepatocytes undergoing apoptosis showed positive immunostaining with antibodies against a precursor of TGF-beta 1.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗