Bojan Flaks

Modification of toxic liver injury in the rat. I. Effect of inhibition of protein synthesis on the action of 2-acetylaminofluorene, carbon tetrachloride, 3'-methyl-4-dimethylaminoazobenzene and diethylnitrosamine.

Summary Rats were treated with single doses of varying amounts of diethylnitrosamine (DEN), 2-acetylaminofluorene (2-AAF), 3′-methyl-4-dimethylaminoazobenzene (3′-MeDAB) or carbon tetrachloride (CCl 4 ), with or without simultaneous single doses of cycloheximide (CHM) of 1.5 mg/kg body weight. The rats were killed 24 and 48 h after treatment and their hepatic and other tissues examined histologically. CHM treatment was found to give almost complete protection to the rat liver against the necrogenic action of 2-AAF and 3′-MeDAB and partial, but considerable, protection against CCl 4 and DEN. The findings are discussed in relation to the role of protein synthesis in cell death.

Immunotoxic effects of prolonged dietary exposure of male rats to 2,3,7,8-tetrachlorodibenzo-p-dioxin

The effects of low level exposure of rats to 2,3,7,8-tetrachlorodibenzo-p- dioxin (TCDD) on their immune system was investigated Dietary administration to young adult male Leeds strain rats of a total dose of 3 micrograms/kg body weight of TCDD resulted in an exposure duration-dependent reduction of in vitro lipopolysaccharide-induced production of interleukin (IL)-1 in cultures of their splenic macrophages. A 30-day exposure produced approximately 30% suppression and 180-day exposure produced approximately 52% suppression. This reduction did not negatively influence lipopolysaccharide- induced proliferation of B cells, instead an enhancement of B cell proliferation was observed after 30 days exposure. A 180 day exposure significantly suppressed the generation of IL-2 by either concanavalin A or phorbol myristate acetate/calcium ionophore stimulation, and reduced the lectin-induced proliferation of splenic T cells. The 30-day TCDD exposure showed no such immunotoxicity. TCDD at both exposure durations suppressed the expression of the alpha chain of the IL-2 receptor in concanavalin A-activated T cells, without affecting the CD4+/CD8+ ratio. The results suggest that exposure to a low dietary dose of TCDD suppresses the functions of several T cell subsets, some of the immunotoxic effects being produced early, while others require a longer exposure also down-regulates the IL-1 production function of macrophages. A common mechanism of TCDD immunotoxicity may be on the multifunctional signal transduction pathways downstream to the activation of protein kinase C and Ca2+ flux.

The effect of prolonged dietary administration of the non-carcinogen, 4-acetylaminofluorene on the liver of the rat an electron microscope study

Abstract A diet containing 0.05 % of the non-carcinogen 4-acetylaminofluorene (4-AAF) was fed to male Leeds strain rats for periods of up to 10 months. Some animals were killed after 8–12 weeks, 6 months and 8–10 months of 4-AAF feeding, while further groups were returned to a normal diet after 10 months of treatment and then killed 2, 5, 9 and 12 months later. The hepatic tissues were removed and prepared for electron microscopy. The main fine structural changes induced by 4-AAF were a prominent hypertrophy of the agranular endoplasmic reticulum, glycogen depletion and lipid accumulation. It was noted that these changes persisted following withdrawal of dietary 4-AAF, for the duration of the experiment. The effects of 4-AAF are compared with those of its carcinogenic isomer, 2-acetylaminofluorene (2-AAF) and the possibility is discussed that the clear differences revealed in this study may be directly related to the relative carcinogenicities of these two compounds.

Early changes in the fine structure of rat hepatocytes, induced by the non-carcinogen 4-acetylaminofluorene

Abstract The non-carcinogen, 4-acetylaminofluorene (4-AAF) was fed to male Leeds strain rats at a level of 0.05% of the diet. The animals were killed after 7–10 days and 3–4 weeks of treatment and their hepatic tissue was examined by electron microscopy. The main changes produced by 4-AAF in the hepatocytes were proliferation of the agranular endoplasmic reticulum and glycogen depletion. No other changes were observed, apart from a minor degree of intracellular lipid accumulation. Comparison of the effects produced by 4-AAF with those previously shown to be produced by the carcinogenic isomer 2-acetylaminofluorene (2-AAF) revealed striking differences, which may possibly be related to the difference in the carcinogenic activities of these compounds.

Acute fine structural changes in rat hepatocytes induced by a single large dose of 2-acetylaminofluorene.

SummaryMale rats were given a single intragastric dose of 2-acetylaminofluorene, 600 mg/kg body weight, killed at intervals up to 14 days after treatment, and their hepatic tissue examined by electron microscopy. The early cytoplasmic lesion produced in hepatocytes by lower doses, consisting of perinuclear glycogen pooling, peripheral displacement of organelles and pyknosis, was delayed for several days. Among the changes which appeared to be independent of this lesion were disorganization and decrease of the granular endoplasmic reticulum and abnormalities of the bile canaliculi. These changes were similar to those which are seen during chronic exposure to 2-AAF and other hepatocarcinogens and in hepatic cell tumours.

Modification of toxic liver injury in the rat II. Protective effect of cycloheximide on ethionine-induced damage and autoprotective effects of high doses of ethionine, 3′-methyl-4-dimethylaminoazobenzene, and 2-acetylaminofluorene

Abstract Male and female rats were given various single oral doses of dl -ethionine, with and without accompanying doses of cycloheximide. It was found that a single dose of cycloheximide prevented the appearance of hepatic cell damage in dl -ethionine-treated female rats, up to 48 hr. In the male rat, two consecutive doses of cycloheximide, with an interval of 5.5 hr, were necessary to achieve protection. However, very large doses of dl -ethionine alone failed to produce the early liver injury which resulted from lower doses, although delayed damage did appear after several days. Similar results were obtained with high doses of 2-acetylamino-fluorene. Very high doses of 3′-methyl-4-dimethylaminoazobenzene failed entirely to induce the periportal hepatic cell lesion which is characteristic of this agent, instead giving rise to minimal centrilobular necrosis and leading to a massive proliferation of bile duct cells within a week.

Modification of toxic liver injury in the rat. III. Fine structure of hepatocytes during cycloheximide protection and autoprotection in acute ethionine intoxication.

Abstract Male rats were treated with single oral doses of 800 or 1200 mg/kg of dl -ethionine, with and without additional subcutaneous injections of cycloheximide (CHM), and were killed after 24 and 48 hr. Other rats were given oral dl -ethionine at the level of 8000 mg/kg and killed 24 or 48 hr or 10 days after treatment. It is known that this dose does not produce the early histopathological changes which result from treatment with the lower doses and it has therefore been termed “autoprotective,” owing to the apparent similarity of its effects to those of combined treatment with CHM and dl -ethionine. The hepatic tissues were examined by electron microscopy. dl -Ethionine induced a characteristic lesion involving perinuclear glycogen pooling, with peripheral displacement of the cytoplasmic organelles, and rarefaction of the glycogen. This was prevented by CHM which, however, greatly enhanced changes in the granular endoplasmic reticulum and Golgi apparatus. Autoprotective doses of dl -ethionine also failed to induce this lesion but resulted in marked changes in the endoplasmic reticulum. By 10 days after 8000 mg/kg of dl -ethionine, delayed damage occurred, apparently identical to that produced within 24 hr by lower doses. Because of the similar fine structural effects induced by CHM protection and autoprotection, it is concluded that both may have a common mechanistic basis, which may be related to inhibition of protein synthesis in the hepatocyte.

Persistent ultrastructural changes in pancreatic acinar cells induced by 4-acetylaminofluorene

Abstract Male Leeds rats were fed a diet containing 0.05% of the non-carcinogen 4-acetylaminofluorene (4-AAF) for 8–10 months. They were then returned to a normal diet and their pancreatic tissues examined by electron microscopy at intervals between 2 and 12 months after the end of 4-AAF treatment. 4-AAF was found to induce a persistent alteration in the morphology of the granular endoplasmic reticulum, involving distortion and dilatation of the cisternae. In some respects this lesion resembles that which is induced by the carcinogenic isomer, 2-acetylaminofluorene (2-AAF).

Fine structural changes in rat pancreatic cells during prolonged treatment with 4-acetylaminofluorene

Abstract The non-carcinogen 4-acetylaminofluorene (4-AAF) was fed to male Leeds strain rats at a concentration of 0.05% of the diet. The animals were killed after 7–10 days, 3–4 weeks, 8–12 weeks and 8–10 months of treatment and their pancreatic acinar cells were examined by electron microscopy. Although 4-AAF did not appear to produce any significant inhibition of secretory protein synthesis, it did produce conspicuous morphological alterations in the granular endoplasmic reticulum, together with some mitochondrial damage and focal cytoplasmic degradation. These changes are discussed in relation to those produced in this tissue by the carcinogenic isomer, 2-acetylaminofluorene (2-AAF).