Attenuation of cadmium-induced liver injury in senescent male fischer 344 rats: role of Kupffer cells and inflammatory cytokines.

In the previous study we showed that senescent male Fischer 344 rats were resistant to Cd-induced hepatotoxicity compared with young-adult rats. In the present study we investigated the role of Kupffer cells and inflammatory cytokines in this effect of aging. The phagocytic activity of Kupffer cells, determined as the removal of carbon from blood, was stimulated by the administration of a hepatotoxic dose of Cd (3 mg/kg sc) in young-adult (5 months) rats but not in old (28 months) rats. Hepatic concentrations of interleukin (IL)-1beta and cytokine-induced neutrophil chemoattractant (CINC), but not of tumor necrosis factor-alpha or IL-6, were elevated in young rats treated with Cd. In old rats, however, the increase in IL-1beta produced by Cd was not statistically significant and the increase in CINC was much lower than in young-adult rats. Pretreatment with gadolinium chloride or cyclosporin A inhibited the elevations in hepatic cytokines and attenuated Cd-induced liver damage, assessed on the basis of serum alanine aminotransferase and sorbitol dehydrogenase activities. Cd-induced hepatotoxicity in the different treatment groups correlated well with hepatic levels of CINC (r = 0.98, p < 0.001) but not with those of IL-1beta. The results suggest that (1) Kupffer cell activation is essential for inflammatory liver damage from Cd, (2) IL-1beta and CINC are important mediators of the inflammatory response induced by Cd, and (3) the attenuation of Cd-induced liver injury in senescent rats is caused by an impairment in Kupffer cell activation, leading to a lower production of CINC and less inflammatory liver injury.

Effect of age and carbon tetrachloride on cytokine concentrations in rat liver.

Interleukin-1beta (IL-1beta), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha) concentrations were measured in livers of young-adult and old rats administered carbon tetrachloride or vehicle. IL-1beta levels were higher and IL-6 levels were lower in old rats than in young-adult rats. Carbon tetrachloride treatment increased IL-1beta and decreased TNF-alpha and IL-6. The elevation in IL-1beta was diminished by aging. These results indicate that the increase in carbon tetrachloride hepatotoxicity that occurs in old age could be related to a dysregulation of inflammatory cytokines.

Serum and liver concentrations of tumor necrosis factor alpha and interleukin-1beta following administration of carbon tetrachloride to male rats.

Inflammatory cytokines are recognized as early mediators of tissue damage and repair. The purpose of this study was to determine the effects of carbon tetrachloride administration on tumor necrosis factor-alpha (TNF-alpha) and interleukin 1beta (IL-1beta) concentrations in serum and liver of rats. Administration of 0.2 ml/kg, i.p., of CCl4 to male Fischer 344 rats caused modest increases in serum levels of both cytokines; elevations of TNF-alpha were statistically significant at 4 and 12 h, and elevations of IL-1beta were statistically significant at 24 h. Although CCl4 produced substantial increases in liver IL-1beta concentrations (more than 3-fold), levels of TNF-alpha were not affected. Treatment with 0.1, 0.32 or 1.0 ml/kg of CCl4 produced dose-dependent increases in serum alanine aminotransferase (ALT) and sorbitol dehydrogenase (SDH) activities, but serum cytokine concentrations were not dose-dependent and did correspond with serum ALT and SDH activities. The results suggest that IL-1beta production in rat liver is stimulated by hepatotoxic doses of CCl4. Production of TNF-alpha may also be induced, but the source of TNF-alpha in serum could be a tissue or organ other than liver.

Alterations in epidermal growth factor binding to hepatic membranes following dietary exposure of rats to known hepatocarcinogens.

Administration of the chemical carcinogen 2-acetylaminofluorene (2-AAF) has previously been shown to lower hepatic epidermal growth factor (EGF) binding levels during chemically induced hepatocarcinogenesis. To further characterize the specificity of this response, EGF binding levels for liver microsomes were determined after a 3-week administration of subacute doses of 2-AAF and five other known hepatocarcinogens: 3'-methyl-4-dimethylaminoazobenzene (3'Me-DAB), 2-AAF, aflatoxin B1 (AFB1), thioacetamide (TA), ethionine, benzidine (Benz), as well as four non-hepatocarcinogens: fluorene, p-aminoazobenzene, 4-acetylaminofluorene (4-AAF), and 3-methylcholanthrene. Five of six of the hepatocarcinogens tested (3'Me-DAB, 2-AAF, TA, AFB1 and Benz) caused significant lowering of EGF binding levels, and one of the four non-hepatocarcinogens (4-AAF) caused significant lowering of EGF binding levels. Paired feeding studies indicated that the decreases in EGF binding levels were not a result of differences in net diet consumption. These findings show that decreases in EGF binding capacity are caused by a diverse group of known hepatocarcinogenic compounds at an early stage in the carcinogenesis process.

Carcinogen-induced alteration in liver epidermal growth factor receptor distribution during the promotion stage of hepatocarcinogenesis in rat.

Changes in hepatic membrane binding capacity for epidermal growth factor (EGF) were assessed during 2-acetylaminofluorine (2-AAF)-induced hepatocarcinogenesis. An overall decrease in membrane EGF binding levels was observed throughout the period of 2-AAF administration. Immunochemical studies indicated the decreases in EGF binding levels were paralleled by decreases in tissue EGF receptor levels. Immunohistochemical studies showed that the losses in hepatic EGF receptor levels were not uniform throughout the liver during the early, promotion stage of cancer development. During the promotion stage, preneoplastic liver nodules were found to display a higher level of EGF receptor than surrounding hepatic tissue. This resistance to 2-AAF-mediated down-regulation of EGF receptor may confer a proliferative advantage to the developing nodule relative to the surrounding liver tissue. Similar immunochemical and immunohistochemical analysis of hepatocarcinomas at late stages of 2-AAF-induced hepatocarcinogenesis indicated a uniform loss of EGF receptor in tumor and surrounding tissue. These studies indicate that carcinogen-mediated changes in EGF binding levels are different during the multistage process of hepatocarcinogenesis, and that resistance to down-regulation of EGF receptor among preneoplastic nodules may have a role in providing a selective growth advantage to initiated cell populations. EGF receptor may be useful as a dynamic marker assessing the development of hepatic tumors.

Changes in the binding capacity of hepatic membranes for epidermal growth factor during multistage hepatocarcinogenesis in rats.

To study changes in hepatic capacity for binding epidermal growth factor (EGF) during 2-acetylaminofluorene (2-AAF)-induced, multistage hepatocarcinogenesis, a 5 cycle protocol of discontinuous 2-AAF administration was used to produce hepatocarcinogenesis in rats. The hallmark of the 5 cycle protocol is that rats fed 1 to 3 cycles of 2-AAF are at low risk for cancer, while rats fed 2-AAF for 4 or 5 cycles are at high risk for cancer. EGF binding by liver membranes was found to be lowered to 20-25% of control throughout the 5 cycle regimen. When the persistence of lowered EGF binding was tested by returning rats fed 2-AAF for 1 to 3 cycles to diet without 2-AAF for 3 weeks, binding was found to recover to 80 to 90% of values for control rats. In contrast, for rats fed 2-AAF for 4 or 5 cycles, EGF binding capacity remained low, 30 to 40% of control, following placement of rats on diet without 2-AAF for 3 weeks. Immunochemical analysis indicated a close correspondence between changes in EGF receptor levels and changes in the above EGF binding levels. These studies show that during the 2-AAF protocol, the 2-AAF-mediated loss in hepatic EGF binding capacity and EGF receptor protein undergo a transition from a reversible loss to a persistent loss in binding capacity, and EGF receptor protein, as rats underwent a change from low to high risk for developing hepatocarcinomas. The persistent decrease in hepatic EGF binding level may be associated with the progression stage of hepatocarcinogenesis.