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R Schulte-Hermann

Publications and source records attributed to R Schulte-Hermann.

At least 91 records · Page 5Linked to original sources
PubMed1990

Effects of hypolipidemic drugs nafenopin and clofibrate on phenotypic expression and cell death (apoptosis) in altered foci of rat liver.

Phenotypically altered liver foci were produced in female Wistar rats by a single dose of N-nitrosomorpholine followed by promotion with phenobarbital (PB) for 20 or 28 weeks. Then treatment was changed to either hexachlorocyclohexane (HCH), or cyproterone acetate (CPA), or nafenopin (Naf) or clofibrate (Clof), two hypolipidemic drugs. Foci were identified by a positive reaction for gamma-glutamyl-transpeptidase (GGT) and other cytological markers. HCH and CPA could substitute for PB as foci promoters; in contrast, Naf and Clof decreased expression of GGT in foci resulting in a decline of number and area of detectable foci, effects particularly pronounced with Naf. Immunohistochemical investigations of serial sections revealed that Naf also reduced expression of the altered phenotype when cytochrome P450-PB and pyruvate kinase (type L) were used as foci markers, but not when glutathione-S-transferase B (GST-B) was used. Thus, the number of foci with enhanced GST-B did not decline significantly after the change from PB to Naf treatment. Furthermore, the reduction of GGT and the decrease of foci number during Naf treatment were not associated with increased evidence of cell death by apoptosis in foci, in contrast to the situation after PB withdrawal. These findings strongly suggest that the disappearance of GGT-positive foci after Naf is due to a phenotypic change resulting in a suppression of GGT expression rather than to physical elimination of foci.

Animals↗
PubMed1990

Determination of the length of the histological stages of apoptosis in normal liver and in altered hepatic foci of rats.

Apoptosis is a form of cell death involved in the regulation of cell number in various organs and tumors. Quantitative determination of cell loss through apoptosis in histological sections requires, in addition to counts of apoptotic cells, information on the duration of the histologically visible stages of apoptosis. Here we describe a method to determine the duration of apoptosis in (i) normal and (ii) putative preneoplastic tissue of the liver. (i) Female rats were treated with high doses of the hepatomitogen cyproterone acetate (CPA) to induce liver hyperplasia. After stopping CPA treatment, the hyperplasia partially regressed and excessive hepatocytes were eliminated by apoptosis. CPA was given to block the initiation of apoptosis, and thereafter the time course of elimination of apoptotic cell residues (apoptotic bodies, ABs) from the liver was studied. The mean duration of the histological stages of apoptosis was found to be approximately 3 h. (ii) Phenotypically altered cell foci in rat liver were produced by a single dose of N-nitrosomorpholine and subsequent promotion for 39 weeks with phenobarbital (PB). PB was withdrawn to stop foci growth and to stimulate apoptosis. Then rats were retreated with PB to block initiation of apoptosis in foci. The results indicate that the majority of apoptotic bodies in foci disappeared within 4 h after PB, suggesting that the stages of apoptosis are as short in foci as in normal liver. Finally a simple formula is given to calculate the cell loss rate by apoptosis. The method presented may provide data for quantitative cancer risk assessment from mathematical models of carcinogenesis.

Animals↗
PubMed1990

Hemoregulatory peptide pGlu-Glu-Asp-Cys-Lys: a new synthetic derivative for avoiding dimerization and loss of inhibitory activity.

The hemoregulatory peptide (pGlu-Glu-Asp-Cys-Lys, pEEDCK) is a potent inhibitor of stem cell recruitment, which is a major source of hematological complications after cytostatic tumor therapy. By preventing recruitment, pEEDCK can keep hemopoietic stem cells in their normal nonproliferative state and in this way prevent damage by certain cell cycle-specific cytostatic drugs. pEEDCK could play a role as hemoprotector in tumor chemotherapy. As a thiol-containing peptide, pEEDCK is highly sensitive to oxidation, resulting in the formation of a dimer. Although monomeric pEEDCK is a strong inhibitor of colony-forming units-granulocyte/macrophage (CFU-GM) clonal growth, the dimer was previously found to enhance colony-stimulating factor-triggered CFU-GM colony formation. It seemed, thus, necessary to find methods that avoid undesired dimerization reactions. A solid phase strategy for pEEDCK synthesis is presented. The primary synthetic product, S-tert-butyl-sulfenyl-pEEDCK, was purified and stored with the thiol-protecting group remaining attached. Conversion to active monomeric pEEDCK was achieved by reductive treatment in situ before application and removal of tert-butyl-mercaptane in vacuo. The activation reagent (dithioerythritol) prevented reoxidation also in culture media, where unprotected peptide was oxidized rapidly (t1/2 less than 13 min). The purified synthetic peptide was found to be a potent inhibitor of CFU-GM colony formation (IC50 = 1.1 x 10(-12) M) in vitro. It was also found to inhibit colony formation of some leukemic cell lines (HL-60, RAJI) although at much higher concentrations (10(-8) to 10(-9) M). Friend leukemia cells were not inhibited in the dose range where CFU-GM were sensitive.

Amino Acid Sequence↗
PubMed1989

Histochemical and biochemical studies on the effect of the prostacyclin derivative iloprost on CCl4-induced lipid peroxidation in rat liver and its significance for hepatoprotection.

In the present study, it was investigated whether the prostacyclin derivative Iloprost would protect hepatocytes against CCl4-induced liver injury and which mechanism(s) of hepatocellular pathogenesis might be affected by it. Rats were treated with a single oral dose of CCl4 (2 ml per kg); Iloprost was infused continuously from 2 to 4 hr before intoxication until killing. The following results were obtained. The CCl4-induced release of AST, lactate dehydrogenase and alkaline phosphatase into the serum was reduced by 50 to 70% in rats treated with doses of 0.1 and 0.5 micrograms Iloprost per kg per min. Infusion of 0.02 and 0.004 micrograms Iloprost per kg per min did not affect the CCl4-induced enzyme release into the blood. CCl4 induced the occurrence of aldehydes (products of lipid peroxidation), which were detected by histochemical and biochemical means. At 12, 48 and 72 hr after CCl4, the aldehyde-positive liver section area was about 58, 69 and 16% in rats treated with CCl4 alone, but only about 18, 13 and less than 1% in rats treated additionally with Iloprost. The aldehyde-positive hepatocytes were located predominantly in the centrilobular zone of the liver. At 24 hr the extent of the aldehyde-positive section area was the same in rats with or without Iloprost treatment (about 90%). Biochemical determination, however, revealed that at this time point the malondialdehyde content after Iloprost in rats was about 70% lower than without Iloprost treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkaline Phosphatase↗
PubMed1989

Induction by cyproterone acetate of DNA synthesis and mitosis in primary cultures of adult rat hepatocytes in serum free medium.

The aim of this study was to elucidate whether serum-free conditions could be found in primary hepatocyte cultures under which the growth inducing properties of xenobiotics and hormones could be tested. Cyproterone acetate (CPA), a steroid with anti-androgenic and progestogenic activity, was chosen as a model compound because of its known strong mitogenic properties in rat liver in vivo. EGF served as a positive control. Induction of DNA synthesis was studied by [3H]-thymidine labeling and autoradiography. Mitoses were counted in hematoxylin stained specimens. The main steps which led to an efficient stimulation of DNA synthesis by CPA were (i) reduction of hormone concentrations to levels approaching (approx. 10x) physiological concentrations better than the previously used pharmacological ones (up to 2500x); (ii) supplementation with glucocorticoid (most effective at 10-100 nM dexamethasone); (iii) selection of the interval for cumulative labeling with thymidine at 44-68 h; (iv) lowering of cell density at seeding to 50,000 cells/cm2 (subconfluency); (v) treatment with concentrations of 10-100 microM CPA. With these conditions CPA labelling was 13-20% (increase 4- to 9-fold). Mitotic incidence was 0.56% (CPA) versus 0.08% in controls. From a dose response study (0.1-100 microM) a no-effect-level for induction of DNA synthesis was found in the range of 0.1-1 microM. None of the high concentrations of CPA did cause cytotoxicity as estimated by morphological observations or release of lactate dehydrogenase into the medium. This work demonstrates that CPA under appropriate, defined culture conditions induces DNA synthesis and mitosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Effects of non-genotoxic hepatocarcinogens phenobarbital and nafenopin on phenotype and growth of different populations of altered foci in rat liver.

Non-genotoxic hepatocarcinogens share the ability to induce liver growth in rodents. Phenobarbital (PB), as one prototype compound, promotes the development of liver tumors; altered cell foci of the clear-eosinophilic phenotype, also identified by gamma-glutamyltransferase expression, appear to be precursor lesions. These foci seem to over-respond to the growth-inducing effect of PB. In contrast, the question as to whether peroxisome inducers are also tumor promoters is still unsettled. We will present evidence which strongly suggests that the peroxisome inducer, nafenopin (Naf), promotes tumor development in rat livers by stimulating selective growth of a hitherto undescribed subtype of altered foci. This subtype is characterized by weak diffuse cytoplasmic basophilia of its hepatocytes. Initiation in rats by aflatoxin B1 followed by promotion with Naf produced numerous adenomas and carcinomas; their morphology resembled that of the weakly basophilic foci. Both clear-eosinophilic and weakly basophilic foci appear "spontaneously" in the liver of aging rats. Promotion of such lesions by PB-type compounds or peroxisome inducers may explain cancer formation by these non-genotoxic agents.

Aging↗
PubMed1988

Quantitative structure-activity studies on effects of sixteen different steroids on growth and monooxygenases of rat liver.

Sixteen steroids with different endocrine activities were administered to female rats for 6 or 7 days, in a broad range of doses. Liver growth was recorded by measuring weight and DNA contents and monooxygenase activity by assaying the turnover of five different substrates. According to their effects on these parameters steroids were assigned into one of the following three groups: (a) Estrogens estradiol and ethinylestradiol, as well as the progestins norethynodrel and norethisterone (norethindrone) which have estrogenic activity in rats. These agents induced pronounced liver growth and excessive DNA increase which was not associated with major monooxygenase induction. (b) A different type of response consisted of liver growth and DNA increase associated with a pronounced induction of monooxygenase(s) in a characteristic pattern. This response was elicited by pregnenolone-16 alpha-carbonitril, by progestins progesterone, cyproterone acetate, and medroxyprogesterone (but not gestoden and levonorgestrel), by the antimineralocorticoid spironolactone and by the glucocorticoids cortisol and dexamethasone. Apparently, this response pattern was not related to any specific endocrine action but to certain structural features, in particular to the presence of a saturated, at least two-membered alkyl substituent at C17 of the steroid ring system. (c) No or small effects were observed after gestoden, levonorgestrel and the androgens testosterone and methyltestosterone. Dose-response stuides revealed that estrogens estradiol and EE2 induced hepatic effects more potently by four orders of magnitude than progestins. The response patterns observed may be relevant to the tumor-promoting activity of some of the steroids tested.

Animals↗
PubMed1987

Dose-response studies on the effects of alpha-, beta-, and gamma-hexachlorocyclohexane on putative preneoplastic foci, monooxygenases, and growth in rat liver.

Alpha-, beta-, and gamma-hexachlorocyclohexane (alpha-, beta-, gamma-HCH) isomers are widespread environmental pollutants; alpha-HCH can cause liver tumors in rats and mice. In the present study we have checked first the tumor-initiating activity of HCH using the appearance of phenotypically altered foci in female rat liver as an end point. Foci were identified by means of the gamma-glutamyltransferase (GGT) reaction and by morphological alterations. No evidence of initiating activity was found. Secondly, we have attempted to determine quantitatively the ability of HCH isomers to promote tumor development. For this purpose growth and phenotypic changes of foci were used as an end point. Rats received a single dose of N-nitrosomorpholine. Then five different doses of each HCH isomer or phenobarbital (PB) (as a positive control) were administered continuously via the diet for 4, 15, and 20 weeks. Both number and size of altered foci were enhanced by doses of 2 to 3 mg/kg or more of the three isomers; in addition, foci phenotypes showed a pronounced shift towards strong expression of GGT and sharp demarcation from the surrounding liver. Based on daily doses the three HCH isomers were approximately equipotent; based on concentrations in liver or adipose tissue, gamma-HCH was severalfold more effective than alpha- and beta-HCH. Thirdly, size and DNA and monooxygenase activities of the liver were determined. All three parameters were enhanced by HCH isomers and PB. However, no strict correlations were found. Rather, at the highest doses tested PB was the most effective inducer of monooxygenases, alpha-HCH was the most potent inducer of liver growth, and all three HCHs were more potent than PB as inducers of focal expansion. Thus, induction of liver growth appears to be associated with foci expansion (tumor promotion); however, neither liver growth nor monooxygenase induction can be used for quantitative predictions of foci expansion by chemical compounds. Finally, no-observed-effect levels were estimated for the parameters studied and are discussed in relation to human exposure.

Adipose Tissue↗
PubMed1987

Initiation and promotion in hepatocarcinogenesis.

Initiation and promotion have been recognized as essential parts of the multi-stage concept of chemical carcinogenesis. In the liver, initiation by genotoxic carcinogens results in appearance of foci of phenotypically altered hepatocytes. Accelerated growth and phenotypic changes of these foci during tumor promotion by phenobarbital are described, and possible mechanisms of initiation and promotion considered.

Animals↗
PubMed1987

Biochemical events in nitrosamine-induced hepatocarcinogenesis: relevance of animal data to human carcinogenesis.

Administration of carcinogens to experimental animals results in the early formation of phenotypically altered cell foci. Evidence suggesting their intermediary role in hepatocarcinogenesis, and some of their biological properties are reviewed. Two concepts relating to the mechanism of tumour promotion are described briefly, i.e., the 'resistant cell' hypothesis and that of 'overexpression of adaptive growth'. It is concluded that studies on liver foci may be helpful in elucidating the nature of the events involved in the initiation of carcinogenesis. Some aspects relating to human hepatocarcinogenesis are also considered briefly.

Animals↗
PubMed1986

Growth, regression and cell death in rat liver as related to tissue levels of the hepatomitogen cyproterone acetate.

Previous studies have shown that "xenobiotic" compounds such as the environmental pollutant alpha-hexachlorocyclohexane (alpha-HCH) and the synthetic sex steroid cyproterone acetate (CPA) induce growth of rat liver by hypertrophy and hyperplasia. After withdrawal of the growth stimuli, liver hypertrophy was usually found to be readily reversible. Conflicting observations were made concerning the fate of liver hyperplasia: hepatic hyperplasia persisted when induced by alpha-HCH but was found to be partially reversible when induced by CPA. The present study confirms the reversibility of hepatic hyperplasia induced by CPA in rats: about 30% of liver DNA present at maximal liver enlargement disappeared within 6 days after cessation of CPA treatment. Simultaneously, a dramatic increase in the rate of cell elimination by apoptosis was found. Glutamate-pyruvate transaminase and alkaline phosphatase in serum did not show major increases, suggesting that cell death was not due to lytic membrane damage. Furthermore, if treatment with CPA was continued or resumed, the enhanced DNA content persisted and the number of apoptotic bodies was greatly reduced. These observations suggest that the occurrence of cell death is due to withdrawal of the growth stimulus CPA. It may reflect a regulatory phenomenon serving to maintain homeostasis of cell number. Further studies showed that CPA is rapidly eliminated from rat liver and serum: t 1/2 in the liver is about 11 h. In contrast, alpha-HCH was previously found to be eliminated more slowly: t 1/2 approximately 144 h. The present study revealed that alpha-HCH, CPA and nafenopin lower the number of apoptotic bodies. This suggests that inducers of liver growth can inhibit hepatocellular death by apoptosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Alanine Transaminase↗
PubMed1986

Induction of monooxygenases and growth in rat liver by progesterone.

Female Wistar rats were treated with various doses of progesterone orally via the diet or via the SC route. Oral treatment resulted in enhanced progesterone levels in the liver as measured by radioimmunoassay. There were up to 3-fold increases in activity of ethylmorphine demethylation by isolated microsomes; metabolism of aminopyrine and benzphetamine was less enhanced, that of aniline and p-nitroanisol showed no distinct increases. Progesterone also caused increases in liver size and total liver protein by up to 50%; total liver DNA showed only slight, insignificant increments. These studies suggest that hepatic effects of progesterone are similar to those previously described with synthetic steroids such as pregnenolone-16 alpha-carbonitrile (PCN) and cyproterone acetate.

Animals↗
PubMed1986

Facilitated expression of adaptive responses to phenobarbital in putative pre-stages of liver cancer.

Female rats received N-nitrosomorpholine to produce altered cell foci (potential cancer pre-stages) in the liver, followed by phenobarbital (PB) for 2 weeks. As indicators of adaptive responses we measured DNA synthesis cumulatively by infusion of [3H]thymidine for the entire period of PB treatment, and cytochrome P450-PB by immunocytochemistry on histological liver sections. Altered cell foci were identified by expression of gamma-glutamyltransferase (gamma-GT), and/or altered morphology. The following results were obtained. In normal parts of the liver PB induced DNA replication only in association with expression of P450-PB; both responses were restricted to the pericentral area of the liver lobule. In foci, PB treatment led to enhanced DNA synthesis. Furthermore, PB caused a 3-fold increase in the number of foci expressing cytochrome P450-PB, gamma-GT or both. Cumulative determination of DNA synthesis showed that this increase did not result from selective proliferation of single initiated cells. It is concluded that in foci also PB can induce expression of the adaptive increases in cytochrome P450-PB and DNA synthesis. Foci show the responses to PB more readily than normal hepatocytes, and irrespective of their position within the liver lobule. These findings suggest that expression of adaptive responses to inducing tumor promoters is facilitated in altered foci.

Adaptation, Physiological↗
PubMed1986

Pyruvate kinase isoenzymes in altered foci and carcinoma of rat liver.

Pyruvate kinase (PK) isoenzymes, rate limiting for the last steps of glycolysis, were studied in normal rat liver, putative preneoplastic foci, neoplastic nodules and hepatocellular carcinoma. These lesions were produced by an initiation-promotion protocol: treatment with a single dose of N-nitrosomorpholine (NNM) was followed by feeding diets containing phenobarbital (PB) or alpha-hexachlorocyclohexane (alpha-HCH), or basal diet. PK was demonstrated (i) by immunocytochemistry on histological sections with antibodies specifically directed against the L and M2 isoenzymes, (ii) by electrophoretic separation of isoenzymes in homogenates from liver and larger tumors, and (iii) by electrophoretic separation of isoenzymes in parenchymal and stromal cells isolated from liver and tumors. Immunocytochemistry showed decreases of L-PK (L-PK-) in hepatocytes of most of the foci, nodules and carcinomas. Most L-PK- foci showed increases in gamma-glutamyltransferase (gamma-GT) and epoxide hydrolase (EH). PB or alpha-HCH treatment further decreased expression of L-PK in foci, but not in normal liver. Cells and foci with enhanced L-PK (L-PK+) were also found after carcinogen treatment. These did not show increases of gamma-GT or EH or any distinct morphological alterations with the exception of some which were basophilic ('tigroid') in H and E stained sections. No L-PK+ tumors were found. We could not demonstrate the M2-type PK in parenchymal cells of liver or any of the lesions described above. This isoenzyme was restricted to stromal cells in normal rat liver and in all stages of carcinogenesis as shown by immunohistology and by electrophoresis of preparations from isolated cell populations. However, stromal cells from hepatocellular carcinomas exhibited a 3-fold increase of M2-PK compared with stromal cells from normal liver. These results do not support an isoenzyme shift from L to M2-PK in the course of malignant transformation of hepatocytes as suggested previously.

Animals↗
PubMed1986

Cytoprotective effect of the prostacyclin derivative iloprost against liver cell death induced by the hepatotoxins carbon tetrachloride and bromobenzene.

It was investigated whether the prostacyclin derivative Iloprost (Schering, Berlin) protects rat hepatocytes against lethal damage induced by carbon tetrachloride (CCl4) and bromobenzene (BB). Iloprost was tested in whole animal experiments (intoxication with 2 ml CCl4/kg) and with primary hepatocyte cultures (intoxication with 1.6 mM BB). Cell damage was estimated by light microscopic examination of hepatocellular morphology and by the release of hepatocellular enzymes (glutamic-pyruvic transaminase, GPT; glutamic-oxalacetic transaminase, GOT; lactic dehydrogenase, LDH) into the blood or culture medium. In both experimental set-ups, Iloprost (0.1 micrograms/kg/min in whole animal experiments and 10(-9)-10(-12) M in primary hepatocyte cultures) largely preserved normal hepatocellular morphology after intoxication. Furthermore, the toxin-induced release of hepatocellular enzymes into the blood (GOT, GPT) or into the culture medium (LDH) was reduced by 50%-70% in the presence of Iloprost. It is concluded that the prostacyclin derivative Iloprost possesses cytoprotective activity on rat hepatocytes against lethal injury by CCl4 or BB.

Alanine Transaminase↗
PubMed1986

Effect of tumor promoting contraceptive steroids on growth and drug metabolizing enzymes in rat liver.

Liver tumor formation in rats treated with oral contraceptive steroids for long periods has been associated with the tumor promoting potential of these agents. As other known liver tumor promoters, e.g., phenobarbital and hexachlorocyclohexane, induce liver growth and hepatic monooxygenases, we investigated whether or not estrogens have similar effects. Female rats were treated with a wide range of doses of ethinylestradiol, including human contraceptive doses, which are approximately 1 microgram/kg. The physiological estrogen estradiol was studied for comparison. Also included were norethynodrel and norethisteron and its acetate and enanthate because these human progestins act predominantly estrogenic in rats. Daily s.c. doses of ethinylestradiol (0.5 mg/kg) produced a rapid increase of liver mass, DNA, RNA, and protein which was almost maximal after 7 days. The percentages of parenchymal cells involved in DNA synthesis and mitosis were enhanced up to 20-fold, suggesting parenchymal hyperplasia as the main cause of liver growth. Sinus wall cells showed a proportionate increase of number and DNA synthesis. Likewise, all other steroids tested produced significant increases of liver mass and DNA. For ethinylestradiol and estradiol extrapolated threshold doses were in the range of 1 microgram/kg. These doses are below those used in previous tumor promotion studies in rats. Using 5 different substrates to check monooxygenase activities of isolated liver microsomes, no induction or only very weak induction by estrogens was found. These studies suggest that induction of liver growth may be a property relevant for the tumor promoting activity of estrogens; in contrast, induction of hepatic monooxygenases does not appear to be necessary for liver tumor promotion in the rat.

Adipose Tissue↗
PubMed1985

Effect of calf and rat serum on the induction of DNA synthesis and mitosis in primary cultures of adult rat hepatocytes by cyproterone acetate and epidermal growth factor.

Induction of hepatocyte DNA synthesis in culture by cyproterone acetate (CPA), a potent hepatomitogen in vivo, was studied. Adult rat hepatocytes were grown on collagen gels in primary culture for 3 to 10 d. Epidermal growth factor (EGF) was used as a model inducer to establish appropriate culture conditions. (a) In serum-free medium EGF stimulated a wave of DNA synthesis in 10 to 30% of the hepatocytes. CPA had only a weak effect. (b) Increasing concentrations of newborn bovine serum (NBS) at 5 to 95% progressively inhibited the stimulatory effect of EGF. A similar inhibition was obtained by adding bovine serum albumin; 20% NBS, however, had a slightly stimulatory effect on the induction of DNA synthesis by CPA. (c) Portal rat serum (RS) at concentration of 5 to 95% markedly stimulated DNA synthesis, a plateau being reached between 20 and 95%. EGF had a distinct enhancing effect on DNA synthesis in the presence of 5 and 20% RS but not at 50 and 95%. CPA stimulated DNA synthesis in the presence of 20, 50, and 95% RS in a synergistic way. (d) Mitoses were found after treatment with EGF or with CPA. These results show that CPA can induce DNA synthesis in cultured hepatocytes and that RS contains factors facilitating the response to CPA.

Animals↗