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Biomedical subjects

A Columbano

Publications and source records attributed to A Columbano.

At least 55 records · Page 3Linked to original sources
PubMed1992

Stimulation of DNA synthesis by rat plasma following in vivo treatment with three liver mitogens.

The present study was undertaken to determine the effect of two different types of liver cell proliferative stimuli, namely compensatory regeneration and direct hyperplasia on DNA synthesis of normal and preneoplastic isolated hepatocytes. Platelet-poor plasma (PPP) isolated from male Wistar rats treated with three different hepato-mitogens, lead nitrate (LN), cyproterone acetate (CPA) and ethylene dibromide (EDB), or subjected to surgical partial hepatectomy (PH), was tested for its ability to stimulate DNA synthesis in normal and preneoplastic hepatocytes in primary cultures. Induction of DNA synthesis was detected as early as 30 min after CPA, EDB and PH administration and persisted up to 5 days after the LN administration. In addition, hepatocytes isolated from preneoplastic liver nodules were also able to respond in culture to the DNA synthesis stimulus induced by these factors.

Animals↗
PubMed1992

Mitogen-induced liver hyperplasia does not substitute for compensatory regeneration during promotion of chemical hepatocarcinogenesis.

Experiments were designed to determine the efficacy of different types of liver cell proliferative stimuli given during exposure to several liver tumor-promoting regimens, on the formation of foci of enzyme-altered hepatocytes. Male Wistar rats were initiated with diethylnitrosamine (150 mg/kg body wt). After a 2 week recovery period animals were subjected to promoting regimens, the resistant hepatocyte model, the phenobarbital model and the orotic acid model. While the rats were on these regimens they were given liver cell proliferative stimulus, either a compensatory type (two-thirds partial hepatectomy or a necrogenic dose of carbon tetrachloride) or a direct hyperplastic stimulus such as that induced by the primary mitogen, lead nitrate. Initiated cells so promoted by these regimens were monitored as foci of enzyme-altered hepatocytes positive for gamma-glutamyltransferase and placental glutathione S-transferase or deficient for adenosine triphosphatase. While carbon tetrachloride and partial hepatectomy-induced compensatory regeneration stimulated the promoting ability of the regimens used, direct hyperplasia could not stimulate the formation of foci and/or nodules from initiated hepatocytes. Evaluation of thymidine incorporation indicated that there was no significant difference in the extent of DNA synthesis in both the proliferative stimuli irrespective of the promoting procedure used.

2-Acetylaminofluorene↗
PubMed1992

Early ultrastructural changes during thioacetamide-induced apoptosis in rat liver.

An histological and ultrastructural study of the early changes in the liver following a single administration of thioacetamide (TH), was carried out in male Wistar rats. One hour after treatment, apoptosis was already present in the liver. By electron microscopy, the following sequential changes were observed: progressive detachment of hepatocytes from neighboring cells, formation of surface infolds with multiple blebs and, finally, release of several membrane-bounded apoptotic bodies in the extracellular space and into the sinusoidal lumen. Three hours after TH administration, the apoptotic cycle was almost entirely completed, as shown by the presence of phagocytosed apoptotic bodies inside the cytoplasm of intact liver cells. Our study evidences that TH induces apoptosis of liver cell as early as one hour after its administration. Moreover, our data show that the apoptotic cycle may be completed in 3-4 h. From the morphological point of view, apoptosis induced by TH appears indistinguishable from programmed cell death, occurring during embryogenesis or metamorphosis, and from apoptotic cell death seen during regression of mitogen-induced rat liver hyperplasia.

Animals↗
PubMed1992

Rapid induction of apoptosis in rat liver by cycloheximide.

A single administration of the inhibitor of protein synthesis cycloheximide results in the occurrence of apoptosis in rat liver. The presence of intracellular apoptotic bodies was detected as early as 2 hours after treatment. No evidence of cell necrosis could be observed by histologic and biochemical analysis. Apoptosis was followed by an increased expression of testosterone-repressed prostate message-2 RNA, a gene whose activity has been associated to apoptotic cell death in involuting rat prostate. The finding of in vivo induction of apoptosis in nonproliferating cells by an inhibitor of protein synthesis, together with the rapidity and synchrony in the occurrence of cell death make this model potentially useful for the analysis of the kinetics of the apoptotic cycle and in exploring some of the mechanisms of regulation of genes possibly involved in this type of cell death.

Animals↗
PubMed1991

Induction of two different modes of cell death, apoptosis and necrosis, in rat liver after a single dose of thioacetamide.

A sequential study of the appearance of liver cell death after thioacetamide (TH) administration was performed in male Wistar rats. Within 3 hours of a single dose of TH, occurrence of cell death by apoptosis was evident around the centrilobular area. Light as well as electron microscopic examination demonstrated the presence of eosinophilic globules, often containing nuclear remnants (apoptotic bodies); they frequently were found within the cytoplasm of intact hepatocytes. The number of apoptotic bodies (ABs) was further enhanced at 6 hours, resulting in a 70-fold increase over the control values. Although necrosis or inflammation could not be observed at this time, as monitored by microscopic analysis as well as by determination of serum glutamate pyruvate transaminase levels, centrilobular necrosis accompanied by massive inflammatory reaction was evident at 12 hours and even more pronounced at 24 to 36 hours. Evidence of liver regeneration was found to occur at 48 hours, and the liver regained its normal architecture between 72 and 96 hours. Studies performed to analyze the activity of 'tissue' transglutaminase (tTG), a presumptive marker of apoptosis, showed that, 1 hour after treatment, TH caused a drastic dose-dependent inhibition of the enzyme activity. This early inhibition was followed by a rapid recovery in tTG activity that paralleled the induction of apoptosis in the liver. Treatment with cycloheximide (CH) 2 hours after TH partially inhibited the incidence of ABs at 6 hours (approximately 30% inhibition). The present study indicates that two different modes of cell death, apoptosis and necrosis, may be induced in a sequential fashion by a single dose of TH.

Alanine Transaminase↗
PubMed1990

Regulation of poly(ADP-ribose) polymerase mRNA levels during compensatory and mitogen-induced growth of rat liver.

Poly(ADP-ribose) polymerase mRNA levels were studied in hepatic regeneration following partial hepatectomy, and in hyperplasia induced by the mitogen lead nitrate. A significant increase in the level of poly(ADP-ribose) polymerase mRNA was found 8 h after partial hepatectomy when no detectable increase of DNA synthesis could be observed; the level of poly(ADP-ribose) polymerase transcripts increased up to six-fold within 1-2 days. A similar increase of the level of poly(ADP-ribose) polymerase mRNA was found 24 h after treatment with lead nitrate. A twofold increase in poly(ADP-ribose) polymerase activity was observed 2 days after (a) partial hepatectomy and (b) lead nitrate treatment. From these results an important role of poly(ADP-ribose) polymerase in cell proliferation could be suggested.

Animals↗
PubMed1990

Effect of lead nitrate on liver carbohydrate enzymes and glycogen content in the rat.

Male Wistar rats were given a single i.v. injection of lead nitrate (10 mumol/100 g body wt) and were killed with matched controls 24, 48, 72 h and 20 days after the treatment. Changes of liver carbohydrate metabolism were studied histochemically testing the following parameters: glycogen content, activities of glycogen synthase (SYN), glycogen phosphorylase (PHO), glucose-6-phosphatase (G6PASE), glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), glyceraldehyde-3-phosphate dehydrogenase (GAPDH). In addition, gammaglutamyltransferase (GGT) activity was demonstrated. Between 24 and 48 h after lead nitrate injection there was a nearly complete loss of liver glycogen. Seventy-two hours later the polysaccharide reappeared in single hepatocytes and after 20 days the livers of the lead-treated animals not only had replenished their glycogen stores but contained even more glycogen than the matched controls. SYN and PHO activities were diminished from 24 to 72 h, but returned to control values after 20 days. G6PASE and GGT remained elevated up to 72 h before dropping to normal at 20 days after treatment. The pentose phosphate pathway enzymes G6PDH and 6PGDH showed the most remarkable changes in livers treated with lead nitrate. G6PDH was already elevated at 24 h, but only in Kupffer cells. At 48 and 72 h, when hepatocytes exhibited a highly increased mitotic rate, the levels of G6PDH, 6PGDH and GAPDH were elevated. After 20 days dehydrogenase activities were comparable to those of controls. The results of this study suggest that a single dose of lead nitrate not only stimulates proliferation of hepatocytes but also induces considerable changes in rat liver carbohydrate metabolism, especially between 24 and 72 h after administration. During that period glycogen metabolism undergoes a strong reduction, whereas gluconeogenesis and particularly the pentose phosphate pathway respond with a remarkable increase. This metabolic profile is most likely associated with lead biotransformation as well as with liver cell proliferation. It corresponds only partially to that found in preneoplastic and neoplastic liver lesions observed in chemical carcinogenesis, and is reversible, in contrast to the persistent alterations associated with neoplastic transformation.

Animals↗
PubMed1990

Cell proliferation and promotion of rat liver carcinogenesis: different effect of hepatic regeneration and mitogen induced hyperplasia on the development of enzyme-altered foci.

A series of experiments was performed to investigate the effect of different types of cell proliferation on the development of enzyme-altered preneoplastic hepatic foci in male Wistar rats. Animals were given a single dose of diethylnitrosamine (100 mg/kg body weight). After a 2-week recovery period liver cell proliferation was repeatedly induced by four or eight necrogenic doses of carbon tetrachloride (compensatory cell proliferation), or by four or eight treatments with three different liver mitogens, namely lead nitrate, ethylene dibromide and nafenopin (direct hyperplasia). The carcinogen altered hepatocytes were monitored as gamma-glutamyltransferase positive or adenosine triphosphatase negative foci. The results indicate that compensatory cell proliferation induced by both four and eight carbon tetrachloride treatments enhanced the growth of diethylnitrosamine-initiated hepatocytes to enzyme-altered foci. On the contrary, repeated waves of cell proliferation induced by liver mitogens did not result in any significant number of enzyme-altered foci.

Adenosine Triphosphatases↗
PubMed1990

Liver hyperplasia is not necessarily associated with increased expression of c-fos and c-myc mRNA.

Experiments were designed to investigate the expression of three cell-cycle-dependent proto-oncogenes in response to two different types of proliferative stimuli: compensatory cell proliferation after partial hepatectomy (PH) or CCl4 and liver hyperplasia induced by the mitogens ethylene dibromide (EDB) and cyproterone acetate (CPA). Steady-state levels of messenger RNAs for c-fos and c-myc were found to be elevated after PH or CCl4 with a maximum increase between 0.5 and 2 h for c-fos and at 2-3 h for c-myc and a rapid decline after 3 h. However, when liver cell proliferation was induced by mitogens, no increase in the expression of c-fos mRNA was observed with both EDB or CPA during the first 24 h. In addition, elevated expression of c-myc was found only in liver hyperplasia induced by EDB, but not with CPA. While the expression of c-myc mRNA and c-fos mRNA was different in the two types of proliferative stimuli, that of c-Ha-ras and c-Ki-ras was similar in all the experimental groups. Cell proliferation monitored by means of incorporation of labelled thymidine into DNA or mitotic index at 24 h following PH, EDB and CPA occurred at a similar extent in all the experimental groups. Our data indicate that the transient and sequential expression of cell-cycle-related genes may vary in response to proliferative stimuli of different nature and suggest that increased expression of cell-cycle-related genes may not be a necessary prerequisite for the entry of the cells into the cell cycle.

Animals↗
PubMed1989

Studies on the kinetics of expression of cell cycle dependent proto-oncogenes during mitogen-induced liver cell proliferation.

The present study was undertaken to determine the kinetics of DNA synthesis and expression of cell cycle dependent proto-oncogenes in response to two types of cell proliferative stimuli in male Wistar rat liver. The peak of DNA synthesis was approximately 24 h after a compensatory cell proliferative stimulus induced by 2/3 partial hepatectomy and approximately 36 h following a mitogenic stimulus obtained with a single dose of lead nitrate (10 micromol/100 g body wt, through femoral vein). Even though both proliferative stimuli induced the expression of c-fos, c-myc and c-Ha-ras, the extent of the increase in c-fos expression was 4- to 5-fold less in mitogen-induced cell proliferation. In addition, while the expression of c-myc, following partial hepatectomy returned to basal level by 4 h, the induced expression of c-myc persisted for up to 40 h during the lead nitrate-induced liver cell proliferation.

Animals↗
PubMed1989

Induction of rat liver glutathione transferase subunit 7 by lead nitrate.

The effect of a single dose of lead nitrate (10 microM/100 g body wt), a hepatic mitogen, on rat liver glutathione transferase (GST) subunit expression was investigated. Using SDS-polyacrylamide gel electrophoresis and Western blot technique evidence for the induction of GST 7-7 is shown. This occurrence is identical to that observed in preneoplastic nodules generated in rat liver by different models of chemical carcinogenesis, suggesting that lead nitrate may be a very simple model for investigation of the mechanism of glutathione transferase 7-7 gene expression in chemical hepatocarcinogenesis.

Animals↗
PubMed1989

Further evidence that mitogen-induced cell proliferation does not support the formation of enzyme-altered islands in rat liver by carcinogens.

Our earlier studies have revealed that direct hyperplasia induced by liver mitogens such as lead nitrate, ethylene dibromide, nafenopin and cyproterone acetate, unlike compensatory cell proliferation induced by partial hepatectomy and CCl4, does not support the formation of enzyme-altered islands induced by chemical carcinogens in the liver. In the previous studies carcinogens were given at the peak of DNA synthesis induced by the liver mitogens. If the mitogens have altered the sensitive phase of the hepatocyte to the carcinogenic attack, administering the carcinogen at one time point following the mitogenic stimulus might have missed the sensitive phase. In order to overcome this possibility in the present study male Wistar rats weighing 200-250 g were given N-methyl-N-nitrosourea (MNU; 60 mg/kg, i.p.) at three points representing G1, S and G2/M phases of the cell cycle following different types of liver cell proliferative stimuli. In another experiment MNU (60 mg/kg, i.p.) and diethylnitrosamine (15 mg/kg, i.p.) were given prior to the administration of proliferative stimuli. The initiated hepatocytes were also assayed following promotion by two different promoting regimens, namely phenobarbital and the resistant-hepatocyte model. Further, the initiated hepatocytes were monitored not only by using the appearance of islands of enzyme-altered hepatocytes but also using the incidence of hepatocellular carcinoma. The results of this study clearly revealed that irrespective of the protocol used, only the compensatory liver cell proliferation but not the mitogen-induced direct hyperplasia supported the formation and the growth of enzyme-altered islands in the liver induced by chemical carcinogens.

Adenosine Triphosphatases↗
PubMed1989

Cell deletion by apoptosis during regression of renal hyperplasia.

Regression of renal hyperplasia after withdrawal of the mitogenic stimulus induced by a single injection of lead nitrate was studied in male Wistar rats. Lead nitrate administration (10 mumol/100 g body weight) resulted in a ninefold increase in the incorporation of labeled thymidine into renal DNA and in an enhancement in the mitotic index; these changes were accompanied by an increase in the organ weight and DNA content that reached a maximum at 2 days. Regression of the renal hyperplasia was observed as early as 3 days after treatment and was completed within 2 weeks. Although lytic necrosis was not responsible for cell loss, the elimination of the excess renal cells took the form of apoptosis. This distinctive mode of cell death, which has been implicated in the involution of hyperplasia in other tissues and organs, was characterized by the occurrence of intracellular and extracellular membrane-bounded eosinophilic globules that often contained nuclear fragments. It affected mainly cells of the proximal tubules, and it was not detected once the kidney had regressed to its original mass. These results support the hypothesis that apoptosis is involved in the regulation of organ size.

Animals↗
PubMed1988

Modulation of the activity of hepatic gamma-glutamyl transpeptidase, adenosine triphosphatase, placental glutathione S-transferase and adenylate cyclase by acute administration of lead nitrate.

The effect of a single administration of lead nitrate on the activity of gamma-glutamyltranspeptidase (gamma-GT), adenosine triphosphatase (ATPase), the placental form of glutathione S-transferase (GST-P) and adenylate cyclase (AC), four enzymes widely used as phenotypic markers for preneoplasia, was investigated in the liver of male Wistar rats. The results of the histochemical enzymatic staining indicated that an acute treatment with lead nitrate induces the activity of gamma-GT, mainly in the hepatocytes located around zone I of the liver acinus, with a maximum seen between 72-96 hours. On the other hand, the activity of ATPase was found to be severely inhibited at 2-3 days after treatment, as shown by a strong decrease in the staining of the bile canaliculi of zones II and III. Immunohistochemical analysis revealed that lead nitrate administration also resulted in the appearance in most of the hepatocytes of GST-P, an enzyme whose activity is almost undetectable in normal rat liver, but is elevated in preneoplastic liver lesions. Finally, lead nitrate treatment resulted in an inhibition of AC activity which was maximal after 24 hours.

Adenosine Triphosphatases↗
PubMed1987

Inability of mitogen-induced liver hyperplasia to support the induction of enzyme-altered islands induced by liver carcinogens.

Experiments were designed to determine whether liver cell proliferation induced by direct mitogens is as effective as compensatory cell proliferation consequent to previous cell loss, in supporting the growth of enzyme-altered islands in the liver induced by chemical carcinogens. Male Wistar rats were given injections of a single nonnecrogenic dose of N-methyl-N-nitrosourea or benzo(a)pyrene during the S phase following the administration of four different liver mitogens, namely, lead nitrate, ethylene dibromide, nafenopin, and cyproterone acetate, or during compensatory cell proliferation following partial hepatectomy or a necrogenic dose of CCl4. The carcinogen-altered hepatocytes were monitored as gamma-glutamyltransferase- or placental glutathione S-transferase-positive foci using a 2-wk promoting regimen consisting of 0.03% 2-acetylaminofluorene coupled with a necrogenic dose of CCl4. The results indicate that, unlike compensatory cell proliferation induced by partial hepatectomy or CCl4, the mitogen-induced cell proliferation did not result in a significant number of enzyme-altered islands, despite the fact that the extent of cell proliferation at the time of carcinogen administration, as monitored by the examination of labeled cells, is similar with both types of proliferative stimuli.

Animals↗
PubMed1987

Hexose monophosphate shunt and cholesterogenesis in lead-induced kidney hyperplasia.

De novo cholesterol synthesis and hexose monophosphate (HMP) shunt were studied in rat kidney stimulated to proliferate by a single administration of lead nitrate. Lead-treated rat kidneys showed an increase in DNA synthesis, as measured by [3H]thymidine incorporation starting at 18 h and with a maximum at 24 h. Renal DNA synthesis was preceded by an increase in de novo cholesterol synthesis and an enhancement in the activity of the HMP shunt, as indicated by increased activity of G6PDH and 6PGDH. These findings indicate that enhancement of cholesterol synthesis and of the HMP shunt is closely associated with the active proliferative process induced in the kidney by treatment with lead nitrate.

Animals↗