Quantitative aspects in the assessment of liver injury.
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Liver function data are usually difficult to use in their original form when one wishes to compare the hepatotoxic properties of several chemical substances. However, procedures are available for the conversion of liver function data into quantal responses. These permit the elaboration of dose-response lines for the substances in question, the calculation of median effective doses and the statistical analysis of differences in liver-damaging potency. These same procedures can be utilized for estimating the relative hazard involved if one compares the liver-damaging potency to the median effective dose for some other pharmacologie parameter. Alterations in hepatic triglycerides, lipid peroxidation, and the activities of various hepatic enzymes can also be quantitiated in a dose-related manner. This permits the selection of equitoxic doses required for certain comparative studies and the selection of doses in chemical interaction studies. The quantitative problems involved in low-frequency adverse reactions and the difficulty these present in the detection of liver injury in laboratory animals are discussed. (+info)
Molecular dynamics study of substance P peptides in a biphasic membrane mimic.
(2/931)
Two neuropeptides, substance P (SP) and SP-tyrosine-8 (SP-Y8), have been studied by molecular dynamics (MD) simulation in a TIP3P water/CCl4 biphasic solvent system as a mimic for the water-membrane system. Initially, distance restraints derived from NMR nuclear Overhauser enhancements (NOE) were incorporated in the restrained MD (RMD) in the equilibration stage of the simulation. The starting orientation/position of the peptides for the MD simulation was either parallel to the water/CCl4 interface or in a perpendicular/insertion mode. In both cases the peptides equilibrated and adopted a near-parallel orientation within approximately 250 ps. After equilibration, the conformation and orientation of the peptides, the solvation of both the backbone and the side chain of the residues, hydrogen bonding, and the dynamics of the peptides were analyzed from trajectories obtained in the RMD or the subsequent free MD (where the NOE restraints were removed). These analyses showed that the peptide backbone of nearly all residues are either solvated by water or are hydrogen-bonded. This is seen to be an important factor against the insertion mode of interaction. Most of the interactions with the hydrophobic phase come from the hydrophobic interactions of the side chains of Pro-4, Phe-7, Phe-8, Leu-10, and Met-11 for SP, and Phe-7, Leu-10, Met-11 and, to a lesser extent, Tyr-8 in SP-Y8. Concerted conformational transitions took place in the time frame of hundreds of picoseconds. The concertedness of the transition was due to the tendency of the peptide to maintain the necessary secondary structure to position the peptide properly with respect to the water/CCl4 interface. (+info)
Molecular dynamics study of substance P peptides partitioned in a sodium dodecylsulfate micelle.
(3/931)
Two neuropeptides, substance P (SP) and SP-tyrosine-8 (SP-Y8), have been studied by molecular dynamics (MD) simulation in an explicit sodium dodecylsulfate (SDS) micelle. Initially, distance restraints derived from NMR nuclear Overhauser enhancements (NOE) were incorporated in the restrained MD (RMD) during the equilibration stage of the simulation. It was shown that when SP-Y8 was initially placed in an insertion (perpendicular) configuration, the peptide equilibrated to a surface-bound (parallel) configuration in approximately 450 ps. After equilibration, the conformation and orientation of the peptides, the solvation of both the backbone and the side chain of the residues, hydrogen bonding, and the dynamics of the peptides were analyzed from trajectories obtained from the RMD or the subsequent free MD (where the NOE restraints were removed). These analyses showed that the peptide backbones of all residues are either solvated by water or are hydrogen-bonded. This is seen to be an important factor against the insertion mode of interaction. Most of the interactions come from the hydrophobic interaction between the side chains of Lys-3, Pro-4, Phe-7, Phe-8, Leu-10, and Met-11 for SP, from Lys-3, Phe-7, Leu-10, and Met-11 in SP-Y8, and the micellar interior. Significant interactions, electrostatic and hydrogen bonding, between the N-terminal residues, Arg-Pro-Lys, and the micellar headgroups were observed. These latter interactions served to affect both the structure and, especially, the flexibility, of the N-terminus. The results from simulation of the same peptides in a water/CCl4 biphasic cell were compared with the results of the present study, and the validity of using the biphasic system as an approximation for peptide-micelle or peptide-bilayer systems is discussed. (+info)
Effect of central corticotropin-releasing factor on carbon tetrachloride-induced acute liver injury in rats.
(4/931)
Central neuropeptides play important roles in many instances of physiological and pathophysiological regulation mediated through the autonomic nervous system. In regard to the hepatobiliary system, several neuropeptides act in the brain to regulate bile secretion, hepatic blood flow, and hepatic proliferation. Stressors and sympathetic nerve activation are reported to exacerbate experimental liver injury. Some stressors are known to stimulate corticotropin-releasing factor (CRF) synthesis in the central nervous system and induce activation of sympathetic nerves in animal models. The effect of intracisternal CRF on carbon tetrachloride (CCl4)-induced acute liver injury was examined in rats. Intracisternal injection of CRF dose dependently enhanced elevation of the serum alanine aminotransferase (ALT) level induced by CCl4. Elevations of serum aspartate aminotransferase, alkaline phosphatase, and total bilirubin levels by CCl4 were also enhanced by intracisternal CRF injection. Intracisternal injection of CRF also aggravated CCl4-induced hepatic histological changes. Intracisternal CRF injection alone did not modify the serum ALT level. Intravenous administration of CRF did not influence CCl4-induced acute liver injury. The aggravating effect of central CRF on CCl4-induced acute liver injury was abolished by denervation of hepatic plexus with phenol and by denervation of noradrenergic fibers with 6-hydroxydopamine treatment but not by hepatic branch vagotomy or atropine treatment. These results suggest that CRF acts in the brain to exacerbate acute liver injury through the sympathetic-noradrenergic pathways. (+info)
Transplanted hepatocytes proliferate differently after CCl4 treatment and hepatocyte growth factor infusion.
(5/931)
To understand regulation of transplanted hepatocyte proliferation in the normal liver, we used genetically marked rat or mouse cells. Hosts were subjected to liver injury by carbon tetrachloride (CCl4), to liver regeneration by a two-thirds partial hepatectomy, and to hepatocellular DNA synthesis by infusion of hepatocyte growth factor for comparative analysis. Transplanted hepatocytes were documented to integrate in periportal areas of the liver. In response to CCl4 treatments after cell transplantation, the transplanted hepatocyte mass increased incrementally, with the kinetics and magnitude of DNA synthesis being similar to those of host hepatocytes. In contrast, when cells were transplanted 24 h after CCl4 administration, transplanted hepatocytes appeared to be injured and most cells were rapidly cleared. When hepatocyte growth factor was infused into the portal circulation either subsequent to or before cell transplantation and engraftment, transplanted cell mass did not increase, although DNA synthesis rates increased in cultured primary hepatocytes as well as in intact mouse and rat livers. These data suggested that procedures causing selective ablation of host hepatocytes will be most effective in inducing transplanted cell proliferation in the normal liver. The number of transplanted hepatocytes was not increased in the liver by hepatocyte growth factor administration. Repopulation of the liver with genetically marked hepatocytes can provide effective reporters for studying liver growth control in the intact animal. (+info)
Bone marrow as a potential source of hepatic oval cells.
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Bone marrow stem cells develop into hematopoietic and mesenchymal lineages but have not been known to participate in production of hepatocytes, biliary cells, or oval cells during liver regeneration. Cross-sex or cross-strain bone marrow and whole liver transplantation were used to trace the origin of the repopulating liver cells. Transplanted rats were treated with 2-acetylaminofluorene, to block hepatocyte proliferation, and then hepatic injury, to induce oval cell proliferation. Markers for Y chromosome, dipeptidyl peptidase IV enzyme, and L21-6 antigen were used to identify liver cells of bone marrow origin. From these cells, a proportion of the regenerated hepatic cells were shown to be donor-derived. Thus, a stem cell associated with the bone marrow has epithelial cell lineage capability. (+info)
Acute carbon tetrachloride feeding induces damage of large but not small cholangiocytes from BDL rat liver.
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Bile duct damage and/or loss is limited to a range of duct sizes in cholangiopathies. We tested the hypothesis that CCl4 damages only large ducts. CCl4 or mineral oil was given to bile duct-ligated (BDL) rats, and 1, 2, and 7 days later small and large cholangiocytes were purified and evaluated for apoptosis, proliferation, and secretion. In situ, we measured apoptosis by morphometric and TUNEL analysis and the number of small and large ducts by morphometry. Two days after CCl4 administration, we found an increased number of small ducts and reduced number of large ducts. In vitro apoptosis was observed only in large cholangiocytes, and this was accompanied by loss of proliferation and secretion in large cholangiocytes and loss of choleretic effect of secretin. Small cholangiocytes de novo express the secretin receptor gene and secretin-induced cAMP response. Consistent with damage of large ducts, we detected cytochrome P-4502E1 (which CCl4 converts to its radicals) only in large cholangiocytes. CCl4 induces selective apoptosis of large ducts associated with loss of large cholangiocyte proliferation and secretion. (+info)
Effect of mitogenic or regenerative cell proliferation on lacz mutant frequency in the liver of MutaTMMice treated with 5, 9-dimethyldibenzo[c,g]carbazole.
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The purpose of this work was to investigate the impact of cell proliferation on liver mutagenesis. The genotoxic hepatocarcinogen 5, 9-dimethyldibenzo[c,g]carbazole (DMDBC) was administered to lacZ transgenic MutaTMMice at a non-hepatotoxic dose of 10 mg/kg, which induces only a slight increase in the liver lacZ mutant frequency (MF). To determine if cell proliferation stimuli enhanced DMDBC mutagenicity, MF was analyzed in mice first receiving DMDBC 10 mg/kg, then approximately 2 weeks later, either carbon tetrachloride (CCl4, a cytotoxic agent inducing regenerative cell proliferation) or phenobarbital (PB, a mitogenic agent inducing direct hyperplasia). In preliminary studies, the extent of cell proliferation induced by CCl4, PB and DMDBC was determined in non-transgenic CD2F1 mice by means of 5-bromodeoxyuridine labeling. The labeling index was significantly increased after CCl4 and PB, while no change was detected with DMDBC. MF was then determined in MutaTMMice 28 days after initial DMDBC treatment. No increase in MF was detected in mice receiving CCl4 or PB alone. A 2- to 3-fold increase in MF was detected in mice treated with 10 mg/kg DMDBC alone. In contrast, MF was markedly increased in mice receiving DMDBC followed by proliferative treatment (15-fold with CCl4 and 25-fold with PB). These results demonstrate that expression of DMDBC-induced mutations in mouse liver largely depends on the induction of cell proliferation (by a cytotoxic or mitogenic stimulus) and illustrate that MutaTMMouse is a valuable tool to investigate the early events of liver carcinogenesis. (+info)