Liver cell necrosis and regeneration following injections of carbon tetrachloride. Effects of the thyrotropin-releasing hormone and somatostatin

Angiogenesis and experimental hepatic fibrosis

Angiogenesis is a basic change occurring during repair by granulation tissue. This process seems to precede fibrosis formation in most types of chronic liver disease. To examine its presence and significance in different types of hepatic insults, this paper sought to identify the presence, evolution and peculiarities of angiogenesis in the most common experimental models of hepatic fibrosis. The characterization of cells, vessels and extracellular matrix and the identification of factors associated with endothelium (factor VIII RA), vascular basement membrane, other components of the vascular walls (actin, elastin) and the presence of the vascular-endothelial growth factor were investigated. The models examined included Capillaria hepatica septal fibrosis, whole pig serum injections, carbon tetrachloride administration, main bile duct ligation and Schistosoma mansoni infection. The first four models were performed in rats, while the last used mice. All models studied exhibited prominent angiogenesis. The most evident relationship between angiogenesis and fibrosis occurred with the C. hepatica model due to circumstances to be discussed. Special attention was paid to the presence of pericytes and to their tendency to become detached from the vascular wall and be transformed into myofibroblasts, which is a sequence of events that explains the decisive role angiogenesis plays in fibrosis.

Secretion of inflammatory mediators by isolated rat Kupffer cells: the effect of octreotide

AIMS

We studied the production of inflammatory mediators by rat KC and the possible in vitro effect of the somatostatin analogue octreotide.

METHODS

Primary KC cultures were incubated with LPS added alone or with different concentrations of octreotide. The production of TNFalpha, IL-6, IL-10, IL-12 and IL-13 was assessed in culture supernatants by ELISA and that of nitric oxide (NO) by a modification of the Griess reaction.

RESULTS

Isolated KC produced a basal amount of TNFalpha, IL-6, IL-12, IL-13, and NO but not IL-10. LPS-stimulated KC secreted significantly increased amounts of TNFalpha (P < 0.001), IL-6 (P < 0.01), IL-10 (P < 0.001), IL-12 (P < 0.01), and NO (P < 0.001) whereas IL-13 production remained constant. Octreotide reduced IL-12 (P < 0.05) and increased IL-13 (P < 0.05) production by unstimulated KC. Furthermore, octreotide suppressed TNFalpha production (P < 0.05), without modifying TNFalpha mRNA expression and decreased iNOS expression and NO (P approximately 0.05) production by LPS-activated KC. These effects were reversed with Wortmannin pre-treatment suggesting that octreotide may act via interference with phosphatidylinositol 3-kinase pathways.

CONCLUSIONS

These data demonstrate that KC is a source of multiple inflammatory mediators, indicating a critical role in liver inflammatory disorders. Octreotide modulates inflammatory mediator production by isolated KC, suggesting that it might have immunoregulatory and anti-inflammatory effects in liver diseases.

Autoprotection: stimulated tissue repair permits recovery from injury

Autoprotection is a phenomenon whereby prior exposure to a small dose of a chemical results in protection against a subsequently administered lethal dose of the same compound. While CCl4 autoprotection has been studied the most, it has also been demonstrated for other chemicals. Recent studies indicate that the prevailing concept of decreased bioactivation of the normally lethal dose of CCl4 owing to decreased hepatic microsomal cytochrome P-450 content cannot be supported by direct end points of liver injury such as necrosis. These findings suggest a pivotal role for hepatocellular division and tissue healing processes stimulated by the protective dose in the mechanism of autoprotection. Augmentation of hepatocellular regeneration and tissue repair, stimulated by the protective dose, appears to permit timely recovery and restoration of hepatic structure and function. In the absence of the protective dose, hepatocellular division is substantially deficient and it occurs too late to tip the delicate balance between recovery from injury and progression of massive injury in favor of recovery. Abolition of autoprotection by colchicine antimitosis, under conditions where metabolism and disposition of CCl4 are not altered, is supportive of this concept. Selective colchicine antimitotic suppression of the early phase of hepatocellular division and tissue repair induced by a low dose of CCl4 results in progression of toxic liver injury, leading to hepatic failure and mortality. Studies have shown that pretreatment with phenobarbital results in postponed low-dose CCl4-stimulated cell division by 24 hours, which accordingly postpones the optimal autoprotection.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytoprotective effect of somatostatin in a rat model of hepatic ischemic reperfusion

To evaluate the possible cytoprotective effect of somatostatin in hepatic ischemic reperfusion injury we used 75 adult male Wistar rats randomly separated into four groups. The rats in group 1 underwent sham operations, and those in group 2 underwent resection of the median and left lateral lobes. The rats in group 3 underwent a 90-min period of ischemia of the right lateral lobe, which we induced by temporarily occluding the right portal vein and the hepatic artery. On restoration of flow to the right lateral lobe, the median and left lateral lobes (about 80% of total liver mass) were excised (and later assayed for thymidine kinase basal activity). The rats in group 4 were given the same treatment as group 3 rats except that a saline solution of somatostatin was infused at a rate of 2 micrograms/min starting at laparotomy and lasting 24 hr. The rats in groups 1, 2 and 3 were infused with saline. Rats in groups 2, 3 and 4 were randomly assigned to two subgroups; one of these subgroups was observed until spontaneous death, and rats in the other group were killed 24 hr after the procedure for obtaining peripheral blood and liver samples. Somatostatin infusion improved the animals' survival rates from 0% (group 3) to 60% (group 4) (p < 0.05) and decreased bilirubin levels (0.78 +/- 0.17 mg/dl, n = 15 [group 4] vs. 1.69 +/- 0.04 mg/dl, n = 15 [group 3]; p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of the prostaglandin E2 analogue enprostil on the carbon tetrachloride-induced necrosis of liver cells in mice

Female mice, eight weeks old, were injected with carbon tetrachloride (CCl4) (10 mg subcutaneously). Groups of mice (n = 10-30) were then injected with enprostil (E) 2, 20 or 50 micrograms/kg body weight (bw) intraperitoneally 15 min and two h after, or E 100 micrograms/kg bw two h after the CCl4 injection. The mice were killed after 24, 48 or 72 h. Plasma activity concentrations of alanine aminotransferase (ALAT) were determined in blood specimens from the iliac veins. The extent of liver cell necrosis in histological sections was recorded on a 100 mm Visual Analogue Scale (VAS) and measured using the electronic Mini Mop method. In the group given the highest single dose of E (100 micrograms/kg) a significant lowering of the CCl4-induced liver cell necrosis was found after 24 h. No significant differences were found after 48 and 72 h. In the other groups injected with lower doses of E after CCl4, no significant differences were found compared to groups injected with CCl4 alone.

Colchicine antimitosis abolishes CCl4 autoprotection

A subtoxic dose of CCl4 is known to destroy liver microsomal cytochrome P-450 and this is widely accepted as the mechanism of CCl4 autoprotection. Circumstantial evidence suggests that while cytochrome P-450 is significantly decreased, this mechanism alone cannot explain the phenomenon of autoprotection. Previous studies have established that hepatocellular regeneration is stimulated as early as 6 hr after the administration of a low dose of CCl4. If the early phase stimulation of hepatocellular regeneration by the protective dose is indeed the mechanism of autoprotection, then ablation of this early phase of tissue healing by colchicine should result in an abolishment of autoprotection. Present studies were conducted to test this conceptual premise. The protection afforded by a low dose of CCl4 (LCCl4, 100 microliter/kg, ip) on the toxic effects of a subsequently administered moderately toxic dose of CCl4 (HCCL4, 2.5 ml/kg, ip) was established in male Sprague-Dawley rats. The protective dose provided 100% protection, whereas only 62.5% survival was observed when the corn oil vehicle was administered instead of the protective dose of LCCl4. Colchicine administration (1 mg/kg, ip in saline) 2 hr prior to the injection of LCCl4 led to a complete loss of autoprotection resulting in 100% mortality in rats given the HCCl4. Earlier studies have established that colchicine selectively suppresses the early phase of hepatocellular regeneration at 6 hr without influencing the second phase at 36-48 hr. The consequence of colchicine antimitosis on the toxicological endpoints of liver injury was evaluated by serum enzyme elevations and by histopathological examination of the liver during a time course of 6, 24, 48, 72, and 96 hr after the administration of HCCl4. In the autoprotection regime, after only a transient and modest elevation of serum alanine and aspartate transaminases, complete recovery occurred by 96 hr. Hepatocellular necrosis was consistently lower compared to all other groups. Colchicine preadministration in the autoprotection regime resulted in significantly greater and progressive elevation of the serum enzymes and a correspondingly commensurate progression of hepatic lesion. Toxic effects of HCCl4 alone were more rapidly and maximally augmented by colchicine preadministration. The role of hepatocellular regeneration in autoprotection was evaluated by 3H-thymidine incorporation in hepatocellular nuclear DNA and by morphometric estimation of mitotic index. While HCCl4 alone resulted in some stimulation of 3H-thymidine incorporation and mitosis, the regenerative activity observed with prior LCCl4 administration was remarkably greater, particularly at 48 hr. Colchicine preadministration in either of these 2 protocols decisively obtunded the stimulated regenerative activities essentially abolishing the tissue healing mechanisms.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of hepatocellular regeneration in CCl4 autoprotection

The destruction of liver microsomal cytochromes P450 by a previously administered low dose of CCl4 has been widely accepted as the mechanism of CCl4 autoprotection. However, circumstantial evidence suggests that this mechanism cannot completely explain the phenomenon of autoprotection. The protective effect of a low dose of CCl4 (0.3 ml/kg, po) on the lethal effect of a subsequently administered high dose (5 ml/kg, po) was established in male Sprague Dawley rats. The protective dose permitted 100% survival, whereas only 15% survival was observed without it. Hepatotoxicity, measured by serum enzyme elevations (aspartate transaminase, alanine transaminase, and sorbitol dehydrogenase) and histopathological changes 24 hr after the treatment with high dose, was similar in both the groups, even though the protective dose had significantly decreased liver microsomal cytochromes P450 (to 62% of normal) and associated enzymes, aminopyrine demethylase and aniline hydroxylase. Rats pretreated with CoCl2 to decrease hepatic microsomal cytochrome P450 to 44% of normal levels did not show a significant protection from the hepatotoxicity of high dose of CCl4. Previous studies have established that hepatocellular regeneration is stimulated within 6 hr after the administration of a low dose of CCl4. Based on this observation, a premise that autoprotection results from augmented recovery from injury rather than decreased injury appears likely. Hence, the role of hepatocellular regeneration was evaluated by following 3H-thymidine incorporation in hepatocellular nuclear DNA, labelling index by autoradiography, and by morphometric estimation of mitotic index. After administration of the protective dose of CCl4, stimulated nuclear DNA synthesis measured by 3H-thymidine incorporation into nuclear DNA was increased and this remained high even after subsequent administration of high dose of CCl4. Forty-eight hr after the administration of a lethal dose of CCl4 alone (5 ml/kg, po), labelling index was slightly increased, but mitotic index was not increased. In the surviving rats (15%), both labelling index and mitotic index were significantly elevated after an additional 24 hr. In rats receiving the protective dose, a significantly greater elevation of labelling index as well as mitotic index occurred 48 hr after the administration of the same lethal dose of CCl4. These results suggest that hepatocellular regeneration stimulated by the protective dose, as a biological response recruited to overcome the accompanying limited injury, may augment and sustain tissue repair processes to permit tissue restoration even after the massive liver injury elicited by the subsequent large dose of CC14.