Early increase in the phosphorylation of liver chromatin non-histone proteins from thyroidectomized rats treated with triiodothyronine.
Explore the source record for details and available documents.
Adenosine Triphosphate↗
Biomedical subjects
C F Cesarone
Publications and source records attributed to C F Cesarone.
Influence of the culture time on DNA damage and repair in isolated rat hepatocytes exposed to nitrochlorobenzene derivatives.
The induction of DNA damage on 1.5- and 24-h cultured hepatocytes was tested after a 3-h exposure to 5 and 50 microM mono-, di-, and trinitrochlorobenzene (100-00-5; 97-00-7; 88-88-0). DNA-repair synthesis, elicited by nitrochlorobenzene treatment, was also estimated 24 and 48 h after the withdrawal of the nitro-aryl halides. DNA damage and repair were evaluated by determining the DNA elution rate in alkali. A dose-related rate of DNA damage was obtained by exposure of 1.5-h-cultured hepatocytes to 5 and 50 microM nitrochlorobenzenes . DNA of 24-h-cultured cells was not affected by nitrochlorobenzene treatment. The data obtained by exposure to 5 microM methyl methanesulfonate (66-27-3) and nitrosodimethylamine (62-75-9), direct and indirect methylating agents, suggest that 24-h-cultured liver cells are still able to transform nitrosodimethylamine but not nitrochlorobenzenes . Isolated hepatocytes maintain their capability of repairing the induced DNA damage when cultured for 24 and 48 h in fresh medium. The system offers an interesting model to investigate the perturbations related to the metabolism of xenobiotics.
Animals↗
DNA topoisomerase I activity in regenerating liver of hypothyroid rats.
DNA topoisomerase I activity is known to be inhibited by poly(ADP-ribosyl)ation. Both poly(ADP-ribose)polymerase and DNA topoisomerase I participate to major biological events, such as DNA transcription, repair and synthesis. Previously, a 2-fold increase in PARP activity has been shown in hypothyroid animals. Using the regenerating rat liver model, we have studied the behaviour of DNA topoisomerase I activity in hypothyroid rats. PARP activity, was also studied in another set of experiments. DNA topoisomerase I relaxing activity was determined on supercoiled plasmid DNA, and topoisomers separated by agarose gel electrophoresis. An increase in the relaxing activity of Topo I was observed early after hepatectomy. This enhancement well correlates with the reported inhibition of PARP activity at the scheduled times. The data from hypothyroid animals support an inverse relationship between PARP and Topo I. These results are completely reversed with respect to those obtained during liver regeneration in euthyroids.
Animals↗
Poly(ADP-ribose) polymerase activity in regenerating liver of hypothyroid rats.
The role of PARP, a nuclear enzyme involved in DNA synthesis, repair and cell transformation, was studies during liver regeneration in hypothyroid animals. Hypothyroidism was induced by in vivo administration of propylthiouracil. In regenerating euthyroid animals PARP activity is stimulated showing an early and significant increase at 1.5 h with a maximum at 6 h after partial hepatectomy. Such an increase returns to control values within 18 h preceding the onset of DNA synthesis. A markedly different behavior, with respect to euthyroids, has been evidenced in hypothyroid rats. At first, liver PARP level was about 2-fold higher in non regenerating hypothyroid rats with respect to control euthyroids. During regeneration, PTU-treated animals show a net decrease in PARP activity, with a minimum at 6-9 h after partial hepatectomy. The activity returns to control levels within 24 days. The minimum in PARP activity anticipates, also in this case, the onset of DNA synthesis, which exhibits a maximum at 15-18 h. During liver regeneration PARP activity shows modifications related to the beginning of de novo DNA synthesis. Furthermore, these variations in turn undergo the effects of hypothyroidism.
Animals↗
Effect of glutathione on alterations of liver DNA structure and metabolic activities induced in vivo by 2-acetylaminofluorene.
The effect on liver tissue of glutathione administration to rats treated for 7-14 days with 2-acetylaminofluorene was investigated. The DNA damage induced by the hepatotoxic agent and evaluated by the alkaline elution technique was significantly reduced by glutathione. Furthermore, GSH administration maintained liver GSH level, prevented the increase in alkaline phosphatase and reduced the decrease in glucose-6-phosphatase activity. GSH did not significantly influence the increase in gamma-glutamyl-transpeptidase and glutathione-S-transferase activities.
2-Acetylaminofluorene↗
Effects of aminothiols in 2-acetylaminofluorene-treated rats. I. Damage and repair of liver DNA, hyperplastic foci, and Zymbal gland tumors.
One hundred and seventy-nine male Wistar rats were divided into 6 groups and fed with a standard diet supplemented with 0.05% 2-acetylaminofluorene (2AAF) and/or 0.1% glutathione (GSH) or N-acetyl-L-cysteine (NAC). Each treatment cycle lasted for 3 weeks, followed by 1 week of standard meal. After 4 cycles, survival was 100% in the 3 control groups, and 86.0, 100 and 91.7%, in the groups receiving 2AAF, 2AAF plus GSH, and 2AAF plus NAC, respectively. After an additional 4-8 weeks, all the 5 surviving rats fed with 2AAF exhibited deforming ear tumors, which on histological examination were classified as sebaceous squamocellular carcinomas of Zymbal glands. No such tumors were detectable in control groups, nor in the 16 surviving rats fed with 2AAF plus GSH or NAC. In the liver, 2AAF produced significant DNA damage at the 3rd week of each cycle, which was partially repaired during the week of standard meal feeding. Moreover, 2AAF determined the appearance of gamma-glutamyl transpeptidase-positive foci, which tended to increase with time both in number and in size. GSH and NAC exerted similar protective effects on these phenomena, but only at early stages of the experimental model used.
2-Acetylaminofluorene↗
Effects of aminothiols in 2-acetylaminofluorene-treated rats. III. Metabolic activation of aromatic amines.
Six groups of Wistar rats received a standard diet supplemented with 0.05% 2-acetylaminofluorene and/or 0.1% natural (reduced glutathione) or synthetic (N-acetyl-L-cysteine) aminothiols. The discontinuous feeding regimen consisted of 4 cycles, each composed of 3 weeks of treatment followed by withdrawal for 1 week. At the 3rd and 4th week of each cycle, the liver was removed from 4-5 rats within each group, and pools of S-12 fractions were assayed for the ability to activate 2-acetylaminofluorene and other aromatic amines, either structurally related (i.e. 4-acetylaminofluorene and 2-aminofluorene) or unrelated (i.e. 2-naphtylamine and benzidine) to mutagenic metabolites in strain TA98 of S. typhimurium. In untreated rats, there was a consistent and marked trend to an age-dependent loss of metabolic activation of all test compounds during the 16 weeks of the experiment. Feeding of 2-acetylaminofluorene resulted in an evident autoinduction of metabolism which was continuously amplified with time, even during the withdrawal weeks. In the same animals, activation of the other amines was initially inhibited but then progressively shifted to a mild cross-induction which, in the case of the structurally related compounds, became significant at the end of the 4-cycle treatment with 2-acetylaminofluorene. The metabolic effects of the two aminothiols were broadly variable, depending on the thiol, on its co-administration with 2AAF, on the week and cycle of treatment, and on promutagens tested.
2-Acetylaminofluorene↗
Effects of aminothiols in 2-acetylaminofluorene-treated rats. II. Glutathione cycle and liver cytosolic activities.
Reduced glutathione, enzymes involved in its metabolism and other cytosolic activities were evaluated in liver preparations of Wistar rats fed with a diet supplemented with 2-acetylaminofluorene (0.05%) and/or with glutathione or N-acetyl-L-cysteine (0.1%). The treatment lasted 4 cycles, each composed of 3 weeks of special diet followed by 1 week of standard diet. The carcinogen produced a considerable increase in gamma-glutamyl transpeptidase in liver homogenates at cycles III and IV, with an irreversible trend which was not discontinued even during the weeks of standard diet. Moreover, generally from cycle I, 2-acetylaminofluorene stimulated several enzyme activities in the liver cytosol, such as glutathione S-transferase, glutathione reductase, glucose 6-phosphate dehydrogenase, NADH- and NADPH-dependent diaphorases. Administration of the two aminothiols to untreated rats resulted in a significant enhancement of glutathione peroxidase, glucose 6-phosphate dehydrogenase and diaphorases. In 2-acetylaminofluorene-treated rats, both thiols further stimulated glutathione S-transferase during the last treatment cycles and attenuated gamma-glutamyl transpeptidase activity, which however was not sufficient to thoroughly counteract the liver lesions due to the massive feeding of the carcinogen. Hepatocellular glutathione was enhanced during the last cycle of treatment with 2-acetylaminofluorene, and was further increased by co-administration of exogenous glutathione.
2-Acetylaminofluorene↗
Detoxifying activities in alveolar macrophages of rats treated with acetylcysteine, diethyl maleate and/or aroclor.
Single or sequential treatment of rats with the thiol N-acetyl-L-cysteine (NAC), the glutathione depletor diethyl maleate (DEM) and the enzyme inducer Aroclor 1254 (AR) produced several significant variations on metabolic activities of pulmonary alveolar macrophages (PAM). Specifically, all three compounds elicited an increase in some oxidoreductase activities, including the two dehydrogenases involved in the hexose monophosphate shunt (G6PD and 6PGD) and NADH- or NADPH-dependent diaphorases. Diaphorase activities were especially increased by sequential treatments with AR and DEM or with DEM and NAC. Both NAC and AR also stimulated other detoxifying mechanisms, such as those related to GSH S-transferase activity and to the NADPH-dependent reduction of hexavalent chromium. Therefore, all the monitored parameters were significantly enhanced not only by the enzyme inducer, but also by the thiol, demonstrating its protective role in the biotransformation of mutagenic/carcinogenic compounds.
Acetylcysteine↗
In vitro effect of 3,5,3'-triiodothyronine on poly(ADP-ribosyl)ation of DNA topoisomerase I.
DNA topoisomerase I activity (topo I) is known to be inhibited by poly(ADP-ribosyl)ation. Both poly(ADP-ribose)polymerase (pADPRP) and DNA topoisomerase I participate to major biological events, such as DNA transcription, repair and synthesis. It has been shown that thyroid hormones, such as 3,5,3'-triiodothyronine (T3), stimulate DNA transcription and down-regulate pADPRP activity. Using an in vitro model, we have studied the poly(ADP-ribosyl)ation of topo I, in vitro, in the presence of T3. T3 treatment of pADPRP inhibits the enzyme up to 75-80% of control activity. DNA topoisomerase I relaxing activity was determined on supercoiled plasmid DNA, and topoisomers were separated by agarose gel electrophoresis. Poly(ADP-ribosyl)ation completely inhibits the relaxing activity of topo I, with respect to non-ribosylated controls, but the activity remains unaffected when pADPRP is inactivated by heat or treated with specific inhibitors, such as 3-aminobenzamide (3ABA). In this study we show that treatment of pADPRP with T3 reduces the inhibition on topo I. In this system 10(-8) M T3 was effective in maintaining almost all topo I activity, even though modifications in processivity and distributivity of the reaction were noted. These data support a close relationship between pADPRP and topo I in hormone-stimulated DNA transcription.
DNA Topoisomerases, Type I↗