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Biomedical subjects

P O Seglen

Publications and source records attributed to P O Seglen.

At least 73 records · Page 4Linked to original sources
PubMed1990

Effects of the tumor promoter 2-acetylaminofluorene and of 4-acetylaminofluorene on rat liver growth.

2-Acetylaminofluorene (2-AAF) is a moderately cytotoxic drug which is nevertheless capable of promoting diethylnitrosamine-initiated rat liver carcinogenesis in the absence of detectable hepatotoxicity. 2-AAF does not stimulate net growth of the normal liver, but alters hepatocellular ploidy distributions (fewer binucleated and more diploid cells) in a manner indicative of altered growth control. The non-cytotoxic analogue 4-AAF induces a similar ploidy change, and also stimulates liver growth. The possibility should therefore be considered that both agents may specifically elicit a mononucleating growth response in normal liver, which in the case of 2-AAF is antagonized by a general (cytotoxic) growth inhibition. In the promotion of liver carcinogenesis, 2-AAF may act as a growth stimulant upon cytotoxicity-resistant initiated cells; cytotoxicity per se playing no causative role.

2-Acetylaminofluorene↗
PubMed1989

[Use of citation analysis and other bibliometric methods in evaluation of the quality of research].

Bibliometric methods for scientific evaluation have been critically examined. The citation frequency for scientific publications, as given in the Science Citation Index, is influenced by various forms of citation bias as well as by the characteristic dynamics and citation practices of the various scientific fields, and therefore cannot be taken as an unequivocal measure of scientific quality. Even for single authors the citation frequency is very variable; therefore this parameter should not be used for graded evaluation of individual scientists or research groups. At higher aggregate levels (large institutes etc.) bibliometric indicators may, as part of a more general evaluation, give relevant information about research activity, provided due corrections are made for variable research field effects. The journal impact factor, i.e. the mean citation frequency of all articles in a journal, has been suggested as a rapid indicator of article quality. However, the distribution of citation frequency values within a journal is extremely broad and skewed; therefore, assigning the same value to all articles would not seem to serve the purpose of evaluation particularly well. Furthermore, the citation frequencies of articles published by individual authors or research groups are found to correlate extremely poorly with the corresponding journal impact factors. The latter parameter would thus appear to be unsuitable as an indicator of scientific quality.

Bibliometrics↗
PubMed1989

Energy dependence of different steps in the autophagic-lysosomal pathway.

The energy dependence of the autophagic-lysosomal pathway was investigated in isolated rat hepatocytes, using electroinjected [14C]lactose as an autophagy probe and atractyloside to alter intracellular ATP levels. Since autophagocytosed lactose is hydrolyzed in lysosomes, several steps in the pathway could be analyzed. The following observations were made. 1) The overall autophagic degradation of electroinjected [14C]lactose was strongly energy-dependent. More than 85% inhibition was obtained when the ATP content decreased from the control value of 10 mumol/g dry weight to 4 mumol/g dry weight. 2) The initial step, i.e. the autophagic sequestration of [14C]lactose, measured in the presence of vinblastine to prevent transfer of lactose to lysosomes, was as sensitive to small changes in ATP as was the overall lactose degradation. 3) The steady state level of sequestered [14C]lactose remained constant as ATP decreased from 10 to 4 mumol/g dry weight, indicating that the sequestration step and some postsequestrational process were inhibited to a similar extent by ATP depletion. 4) The final step in the pathway, intralysosomal hydrolysis, was measured by allowing [14C]lactose to preaccumulate intralysosomally in the presence of the reversible lysosome inhibitor propylamine. Following propylamine removal and inhibition of further sequestration by 3-methyladenine, ATP-dependent hydrolysis of the intralysosomal [14C]lactose could be demonstrated. However, this hydrolysis step was not as sensitive to small changes in ATP as was the sequestration step or the overall autophagic lactose degradation. Control of the autophagic-lysosomal pathway in response to energy deprivation would therefore not seem to occur at the lysosomal level, but may be exerted both at the sequestration step and at a postsequestrational, prelysosomal step.

Adenine↗
PubMed1989

Diploid nature of hepatocellular tumours developing from transplanted preneoplastic liver cells.

Hepatocyte suspensions were transplanted to the livers of syngeneic Wistar Kyoto rats by means of intraportal injection. Labelling of the donor cells with 51Cr or tritiated thymidine showed that 20% of the cells survived the transplantation procedure and were permanently retained by the recipient liver. Hepatocytes transplanted from normal livers produced no tumours, whereas donor cells from preneoplastic livers of rats treated with the carcinogens diethylnitrosamine and 2-acetylaminofluorene produced neoplastic nodules and hepatocellular carcinomas in the recipients. The number of tumours per host liver was proportional to the number of hepatocytes transplanted. Treatment of the host rats with phenobarbitone accelerated tumour development, causing liver cancer in the majority of the animals within three months. As opposed to the polyploid surrounding liver, both phenobarbitone-promoted and unpromoted host tumours contained predominantly (70-90%) diploid cells, regardless of the wide range of transplant ploidies (10-80% diploid cells) achieved by means of centrifugal elutriation. The results indicate that all host tumours arise from diploid donor hepatocytes and that the acquisition of a constitutive, predominantly non-polyploidising growth pattern may be a characteristic property of hepatocellular tumours.

2-Acetylaminofluorene↗
PubMed1989

Neuroendocrine dysdifferentiation and bombesin production in carcinogen-induced hepatocellular rat tumours.

Primary rat hepatocellular tumours, induced by a combination of diethylnitrosamine and 2-acetylaminofluorene, were examined for the presence of neuroendocrine peptides by immunocytochemical methods. Two-thirds of the tumours showed positive immunostaining for either neuron-specific enolase (NSE), protein S-100 or bombesin. NSE was commonly observed both in hepatocarcinomas and in neoplastic nodules, whereas protein S-100 was more frequently seen in carcinomas (49% positive) than in nodules (13% positive). Bombesin, previously shown to function as an autocrine growth factor in small-cell carcinoma of the lung, was present in neurosecretory granules in 13% of the nodules and 29% of the carcinomas. Normal, preneoplastic and peritumorous liver tissue, including the frequent atypical foci present in the latter two categories, was uniformly negative for all neuroendocrine markers. The foci, like the nodules and carcinomas, generally stained positively for the liver tumour marker glutathione S-transferase type P (GSTP). The results suggest that dysdifferentiation of altered hepatocytes in a neuroendocrine direction may be a common, late event in liver carcinogenesis which could possibly contribute to tumour formation, e.g. by establishing autocrine or paracrine circuits.

Animals↗
PubMed1989

[Evaluation of scientific quality using citation analysis and other bibliometric methods].

Bibliometric methods for scientific evaluation are examined. The citation frequency for scientific publications, as given in the Science Citation Index, is influenced by various forms of citation bias as well as by the characteristic dynamics and citation practices of the various scientific fields, and therefore cannot be taken as an unequivocal measure of scientific quality. Even for single authors the citation frequency is very variable; therefore this parameter should not be used for graded evaluation of individual scientists or research groups. At higher aggregate levels (large institutes etc) bibliometric indicators may, as part of a more general evaluation, give relevant information about research activity, provided due corrections are made for variable research field effects. The journal impact factor, i e the mean citation frequency of all articles in a journal, has been suggested as a rapid indicator of article quality. However, the distribution of citation frequency values within a journal is extremely broad and skewed; therefore assigning the same value to all articles would not seem to serve the purpose of evaluation particularly well. Furthermore the citation frequencies of articles published by individual authors or research groups are found to correlate extremely poorly with the corresponding journal impact factors. The latter parameter would thus appear to be unsuitable as an indicator of scientific quality.

Bibliometrics↗
PubMed1989

Experimental characterization of the autophagic-lysosomal pathway in isolated rat hepatocytes.

When isolated rat hepatocytes are incubated under amino-acid-free conditions autophagy is maximally activated and overall lysosomal proteolysis is greatly enhanced. To facilitate this, cytoplasmic material is sequestered by autophagic membranes, and the resulting autophagosomes enter the lysosomes by a fusion process to have their contents degraded. The various steps in the autophagic-lysosomal pathway have been investigated by utilizing reversible electropermeabilization to introduce radioactive sugar probes into the hepatocyte cytosol. The inert disaccharide sucrose and the inert trisaccharide raffinose have been used as sequestration probes to study the sequestrational step of autophagy, while the hydrolysable disaccharide lactose has been used to study the fusion and intralysosomal hydrolysis steps. Sucrose and lactose have been used to map the extent of convergence between the autophagic and endocytic (heterophagic) pathways. Sequestration of native cytosolic enzymes has been measured to investigate the question of selectivity in the autophagic process. Finally, the effect of insulin on the sequestrational step has been evaluated.

Adenine↗
PubMed1988

Changes in ploidy distributions in human liver carcinogenesis.

Cellular and nuclear DNA content was measured by flow cytometry and the fraction of binucleated cells by fluorescence microscopy in normal adult human livers, hepatocellular carcinomas, cirrhotic livers surrounding tumors, and in some benign liver conditions. In five normal livers about one-half of the hepatocytes were polyploid; the majority of these were binucleated tetraploids containing two diploid nuclei. Thus, polyploidization in human liver does not progress as far as, for example, in the rat, where 80%-90% of adult hepatocytes are polyploid, mostly with tetraploid or octoploid nuclei. In five human euploid hepatocellular carcinomas and one investigated case of focal nodular hyperplasia, the percentage of polyploid cells was significantly reduced. Four other carcinomas exhibited a prominent aneuploid (hypotetraploid) peak in addition to the diploid peak. An abnormally low fraction of binucleated cells was also indicated in these tumors. Liver tissue surrounding the tumors had a ploidy distribution similar to that of normal liver. The results suggest that, like in several models of experimental hepatocarcinogenesis, human hepatocellular tumor growth is associated with a decreased polyploidization tendency and a corresponding increase in diploid, divisional growth, which may give the tumors a growth advantage relative to the surrounding liver.

Adolescent↗
PubMed1988

Prelysosomal convergence of autophagic and endocytic pathways.

[14C]Lactose, electroinjected into the cytosol of isolated rat hepatocytes, was sequestered by autophagy, transferred to lysosomes and eventually hydrolysed. Asparagine prevented the fusion between prelysosomal autophagic vacuoles and lysosomes, and caused lactose to accumulate in the former. However, if the hepatocytes were simultaneously allowed to endocytose added beta-galactosidase, no lactose accumulation occurred. These results suggest that autophagically sequestered lactose and endocytosed beta-galactosidase were delivered to the same prelysosomal vacuole, where the lactose was hydrolysed by the enzyme. The name amphisome is suggested for this new functional compartment, common to the autophagic and endocytic pathways.

Animals↗
PubMed1988

2-Acetylaminofluorene promotion of liver carcinogenesis by a non-cytotoxic mechanism.

2-Acetylaminofluorene (AAF), given in the diet at 0.02% for 4 weeks, is an effective promoter of liver carcinogenesis initiated by partial hepatectomy (PH) plus diethylnitrosamine (DEN) in the inbred rat strain Wistar Kyoto. AAF promotes the early (6 week) appearance of phenotypically altered (gamma-glutamyltranspeptidase-positive) cells as well as the later appearance of neoplastic nodules (2-4 months) and hepatocarcinomas (4-8 months). Promotion does not seem to involve selective cytotoxicity (selection of AAF-resistant hepatocytes), since neither AAF alone nor DEN + AAF has any inhibitory effect on overall liver growth.

2-Acetylaminofluorene↗
PubMed1988

The polyploidizing growth pattern of normal rat liver is replaced by divisional, diploid growth in hepatocellular nodules and carcinomas.

DNA content was measured by flow cytometry in isolated nuclei from 71 neoplastic nodules and 15 hepatocellular carcinomas isolated from rat liver at various times after treatment with an initiation--promotion regimen employing diethylnitrosamine and 2-acetylaminofluorene. Nodules and carcinomas contained mostly diploid nuclei as compared with both surrounding and normal hepatocytes which were predominantly polyploid. There appears to be a positive correlation between the degree of diploidy in nodules and their rate of proliferation. No aneuploid populations were identified in any neoplasm despite good peak resolution. These results show that an alteration in proliferation pattern from normal polyploidizing growth to diploid--diploid divisional growth is a consistent characteristic throughout the carcinogenic process in our experimental model.

2-Acetylaminofluorene↗
PubMed1987

Temperature dependence of protein degradation, autophagic sequestration and mitochondrial sugar uptake in rat hepatocytes.

Lysosomal (propylamine-sensitive) protein degradation as well as the energy-dependent (chymostatin-sensitive) part of the non-lysosomal protein degradation was found to be strongly affected by temperature in isolated rat hepatocytes, the activation energy (Ea) being about 25 kcal/mol for both processes. In contrast, the energy-independent (chymostatin-resistant) part of the non-lysosomal degradation had an Ea of approx. 10 kcal/mol only. Sequestration of electroinjected [14C]sucrose into sedimentable organelles showed a pronounced temperature dependence. By means of digitonin extraction it was possible to distinguish between a moderately temperature-sensitive mitochondrial sugar uptake (Ea approx. 12 kcal/mol) and a strongly temperature-dependent autophagic sequestration (Ea approx. 22 kcal/mol). There was no significant autophagic sequestration below 20 degrees C. The sequestration process is more temperature-sensitive than, for example, the early steps of endocytosis, and is likely to represent the major controlling step in the overall autophagic-lysosomal pathway.

Animals↗
PubMed1987

Sugar uptake by fluid-phase pinocytosis and diffusion in isolated rat hepatocytes.

Measurements of sugar pinocytosis (fluid-phase endocytosis of radiolabelled sucrose, lactose and raffinose) in freshly isolated rat hepatocytes are disturbed by sugar diffusing into the cells through plasma-membrane blebs. Non-pinocytic entry may be even more pronounced at 0 degrees C, and is a major contributor to 'background' radioactivity. By electrodisruption of the plasma membrane, a distinction can be made between pinocytotically sequestered sugar and free sugar that has entered the cytosol by diffusion. Pinocytosis proceeds at a rate of 2%/h (relative to the intracellular fluid volume), whereas the rate of sucrose entry by diffusion is more than twice as high. Three pinocytotic compartments are distinguishable in isolated hepatocytes: (1) a rapidly recycling compartment, which is completely destroyed by electrodisruption, and which may represent pinocytic channels continuous with the plasma membrane; (2) a non-recycling (or very slowly recycling) electrodisruption-resistant compartment, which allows accumulation of the lysosomally hydrolysable sugar lactose, and which therefore must represent non-lysosomal vacuoles (endosomes?); (3) a lysosomal compartment (non-recycling, electrodisruption-resistant), which accumulates raffinose and sucrose, but which hydrolyses lactose. The last two compartments can be partially resolved in metrizamide/sucrose density gradients by the use of different sugar probes.

Animals↗
PubMed1987

Energy dependence of autophagic protein degradation in isolated rat hepatocytes.

The effect of small changes in intracellular ATP on autophagic flux was studied in isolated rat hepatocytes by using inhibitors of ATP production or by varying the metabolic conditions. The following observations were made. There was a linear relationship between endogenous protein degradation and intracellular ATP, the rate of proteolysis declining with decreasing ATP concentrations. 15% of the maximal proteolysis is either independent of ATP or has a very high affinity for this metabolite. There was a linear relationship between the autophagic sequestration of cytosolic [14C]sucrose and intracellular ATP, the sequestration rate decreasing with decreasing ATP concentrations. ATP depletion did not cause release of [14C]sucrose previously sequestered in autophagosomes and lysosomes at high ATP levels. Intracellular accumulation of chloroquine, used as an indicator of the pH inside lysosomes and other acidic cell compartments, diminished with decreasing cellular ATP content. Amino acids inhibited proteolysis without affecting ATP levels or chloroquine accumulation. We conclude from the high sensitivity of autophagy towards relatively small changes in the concentration of intracellular ATP that, besides amino acids, ATP is a very important factor in controlling the rate of autophagy in rat hepatocytes.

Adenosine Triphosphate↗
PubMed1987

Transplantation of preneoplastic rat hepatocytes by intraportal injection.

Hepatocyte suspensions prepared from inbred male Wistar-Kyoto rats were transplanted to the livers of syngeneic recipients by injection into the portal venous system immediately after partial hepatectomy. Donor cells were labelled with 51Cr in vitro before transplantation. Animals were sacrificed 1 hr, 10 hr, 48 hr, or 1 week later and the liver radioactivity was measured in a gamma counter. Total liver radioactivity declined rapidly during the first 10 hr after transplantation, and then stabilized. After 1 week, 15-20% of the injected radioactivity still remained, indicating that this fraction of the injected cells was retained by the liver. The percentage was unaffected by the number of cells injected. In another experiment, 10(6) hepatocytes from a carcinogen-treated rat were transplanted to syngeneic rats fed 0.05% phenobarbital in the diet. Recipients developed liver carcinomas from 7 weeks after transplantation, and at 5 months 4 out of 5 animals showed severe debility and had large hepatocellular carcinomas. This model generates tumors considerably faster than those previously described, and is well suited for the study of the tumorigenic potential of subclasses of cells in liver carcinogenesis.

Animals↗
PubMed1987

Endocytosis of asialo-glycoproteins and attachment to asialo-glycoproteins of hepatocytes from carcinogen-treated rats.

Endocytosis and degradation of asialo-glycoprotein were investigated in hepatocytes from carcinogen-treated rats. The cells were isolated at an early stage of carcinogenesis after a sequential treatment with diethylnitrosamine and 2-acetylaminofluorene. Hepatocytes at this pre-nodular stage take up asialo-orosomucoid at a lower rate than hepatocytes from normal rats, whereas degradation of the protein occurs at a similar rate in the two populations. The lower rate of uptake appears to result from a decreased binding capacity in treated hepatocytes. The reduced binding capacity leads to slower kinetics of cell attachment to a substratum of asialo-glycoprotein. The lower number of receptors did not seem to be confined to a particular subpopulation of hepatocytes. Diploid and tetraploid hepatocytes, isolated by centrifugal elutriation, displayed the same reduction in binding capacity.

Animals↗
PubMed1986

Use of [3H]raffinose as a specific probe of autophagic sequestration.

The trisaccharide [3H]raffinose, introduced into the cytosol of isolated rat hepatocytes by means of electropermeabilization, was sequestered autophagically and accumulated in lysosomes and pre-lysosomal vacuoles. In contrast to the disaccharide [14C]sucrose previously used as a sequestration probe, raffinose was not taken up by the mitochondria. The sequestration of raffinose was completely inhibited by the autophagy suppressor 3-methyladenine, stressing its potential utility as a specific probe of hepatocytic autophagy.

Adenine↗