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Biomedical subjects

G E Neal

Publications and source records attributed to G E Neal.

At least 91 records · Page 5Linked to original sources
PubMed1983

The production of carcinomas in vivo by the intravenous or subcutaneous injection of a hepatocellular tumour cell line.

Suspensions of cells of an aflatoxin-induced hepatocellular carcinoma cell line, which grow rapidly as tumours when injected subcutaneously into nude mice, have been injected subcutaneously and also intravenously via the hepatic portal or tail vein into syngeneic host animals. Efficiency of the injections was checked histologically and histochemically in parallel experimental animals. Subcutaneous injections consistently resulted in the appearance of solid tumours at the site of injection within 1 month. However, despite the apparent importance of the establishment of a blood supply when tumours are grown subcutaneously, only a low incidence of tumours (less than 20%) was detected in animals receiving intravenous injections. These results suggest that the proposed use of injection of liver cell suspensions into the portal tract as a sensitive means of detecting transformation may only be of limited value.

Acyltransferases↗
PubMed1983

The inhibitory effects of ethoxyquin on the carcinogenic action of aflatoxin B1 in rats.

Ethoxyquin (EQ), a widely used antioxidant, inhibits the carcinogenic effects of polycyclic aromatic hydrocarbons. The aim of the present study was to determine whether EQ modifies the hepatocarcinogenic effects of aflatoxin B1 (AFB1) in rats. Both compounds were administered in the diet. Rats were fed either EQ for 2 weeks and then AFB1 for 6 weeks, EQ and AFB1 simultaneously or EQ following the cessation of AFB1 treatment. The results indicate that EQ can inhibit the hepatocarcinogenic effects of AFB1 and that the most effective inhibition is obtained when EQ and AFB1 are given simultaneously.

Aflatoxin B1↗
PubMed1983

The metabolism of aflatoxin B1 by hepatocytes isolated from rats following the in vivo administration of some xenobiotics.

Isolated rat hepatocytes, an intact cellular system capable of performing phase I and phase II metabolism, have been used to investigate metabolism of aflatoxin B1. These cells were found to metabolise [14C]aflatoxin B1 to aflatoxins M1 and Q1, and to radiolabelled polar material, presumably conjugates, as analysed by h.p.l.c., t.l.c. and radioactive determination. In vivo administration of the mixed function oxidase inducers, phenobarbitone and 3-methylcholanthrene, resulted in enhanced hepatocyte phase I (microsomal) metabolism of aflatoxin B1. In contrast to metabolism of AFB1 by in vitro subcellular systems increased production of polar material (conjugated metabolites) derived from [14C]aflatoxin B1 was also detected in hepatocytes isolated from these pretreated animals. Formation of aflatoxin Q1 by isolated hepatocytes appeared to be mediated by cytochrome P450-linked enzymes whereas cytochrome P448-linked enzymes were apparently involved in aflatoxin M1 production. Chronic feeding of aflatoxin B1 to rats enhanced hepatocyte production of conjugated material only and did not elevate cellular cytochrome P450 levels, thus suggesting that aflatoxin B1 is not an inducer of its own primary metabolism.

Aflatoxin B1↗
PubMed1983

Some studies on the relationship between the cytotoxicity of aflatoxin B1 to rat hepatocytes and metabolism of the toxin.

Aflatoxin B1 (AFB1) caused marked, rapid (1 h) inhibition of RNA synthesis and subsequent cytotoxic response in isolated and primary cultured hepatocytes, from control rats, which are known to metabolise AFB1. A rat liver-derived cell line, BL8L, was much less susceptible to these effects of AFB1. These cells have no detectable AFB1 metabolising capacity, but a less potent, anti-mitotic action of AFB1 was observed in the BL8L cell line. Thus AFB1 would seem to require metabolism to exert its acute cytotoxic action which is found at very low AFB1 concentrations, although a direct antimitotic effect, independent of metabolism, is seen in dividing cells. Phenobarbitone and 3-methylcholanthrene in vivo pretreatments, known inducers of AFB1 metabolism, resulted in reduced AFB1 inhibition of RNA synthesis and cytotoxicity in hepatocytes, but only at lower concentrations of AFB1 used, whereas cells from AFB1 fed rats were much less susceptible to AFB1 toxicity at all concentrations used. This resistance to cytotoxicity of AFB1 would appear to involve detoxification mechanisms, primarily the formation of polar conjugates of AFB1 metabolites, particularly glutathione conjugates. These cell culture systems are useful for studying association between metabolism and cytotoxicity of AFB1, and other xenobiotics.

Aflatoxin B1↗
PubMed1981

A comparison of the effects of pretreatment with phenobarbitone and 3-methylcholanthrene on the metabolism of aflatoxin B1 by rat liver microsomes and isolated hepatocytes in vitro.

In agreement with previous reports (Neal and Colley, Biochem. J., 174 (1978) 839; Gurtoo and Dave, Cancer Res., 35 (1975) 382) the capacity of isolated hepatic microsomes to metabolise aflatoxin B1 (AFB1) is enhanced by pretreatment in vivo with phenobarbitone. Microsomes isolated from rats pretreated with 3-methylcholanthrene also exhibit increased metabolism of AFB1. The levels of metabolism are increased in proportion to the increased levels of cytochromes P-450 and P-448 indicating similar overall efficiencies of the two cytochromes to metabolise AFB1. However, the qualitative aspects of the metabolism induced by the two compounds are very different. In agreement with the previous data (Neal and Colley, Biochem J., 174 (1978) 839) the formation of aflatoxins Q1, M1 and B1-dihydrodiol are enhanced by pretreatment with phenobarbitone whereas pretreatment with 3-methylcholanthrene, while not affecting the production of aflatoxin Q1 and slightly lowering AFB1-dihydrodiol formation, increases the production of aflatoxin M1 greater than 10-fold. Covalent binding of AFB1 to microsomal protein in vitro is increased by pretreatment in vivo with phenobarbitone, but decreased by pretreatment with 3-methylcholanthrene. The changes in the level of protein binding in vitro brought about by these pretreatments are quantitatively similar to the relative changes in AFB1-dihydrodiol tris complex production induced by the two compounds indicating a role for this metabolite in protein binding. Covalent binding of AFB1 to DNA in vitro is also increased by pretreatment in vivo with phenobarbitone, but not by 3-methylcholanthrene and the total level of binding of AFB1 to DNA in the in vitro system is greater than binding to microsomal protein. The possible mechanisms for binding AFB1 to microsomal protein and DNA are discussed. In contrast to the microsomal incubations, only low levels of aflatoxins Q1 and M1 are present after 2 h incubation AFB1 with intact hepatocytes isolated from control, methylcholanthrene or phenobarbitone pretreated rats. Pretreatment with either phenobarbitone or 3-methylcholanthrene induces the formation of polar metabolites, presumably conjugates, emphasising the predominant role of phase 2 metabolism in intact cellular systems.

Aflatoxin B1↗
PubMed1981

An examination of the relative resistances to aflatoxin B1 and susceptibilities to gamma-glutamyl p-phenylene diamine mustard of gamma-glutamyl transferase negative and positive cell lines.

Two epithelial cell lines have been derived from rat liver. One, containing only low levels of gamma-glutamyl transferase (GGT) was obtained from normal liver and the other, containing high levels of the enzyme was isolated from an aflatoxin B1-induced hepatoma. The GGT levels present in the two cell lines have been examined by histochemical staining, by a fluorescence assay using disrupted cells, and also by intact fluorescence-labelled cells in a laser flow cytofluorimeter. The cells containing high levels of GGT have been found to be less sensitive to microsomally-activated aflatoxin B1 than are the GGT negative cells, a feature of the in vivo situation. Evidence for activation of the gamma-glutamyl derivative of an alkylating mustard analogue of p-phenylene diamine by the GGT positive cells is presented. This finding could be of relevance to the possible chemotherapy of GGT-rich lesions in vivo.

Aflatoxin B1↗
PubMed1980

Effect of partial hepatectomy on the response of rat liver to aflatoxin B1.

The effect of partial hepatectomy (PH) on aflatoxin B1 (AFB1) action in rat liver has been examined using adult male Fischer 344 rats. The elevated levels of hepatic DNA synthesis, present 26 hr after PH (> 15 times the control level) and 33 hr after PH, are rapidly inhibited by i.p. administration of AFB1. The percentage inhibitions are greater than those observed using intact or sham-operated animals. However, it was possible to demonstrate elevation of DNA synthesis in PH rats treated with AFB1. Rats 2 hr after being treated with AFB1 (0.075 mg/kg) at 24 and 31 hr after PH exhibited levels of DNA synthesis 380 to 400% of those present in sham-operated uninjected controls. After 62 weeks, the livers of the PH rats treated with AFB1 displayed no hepatocellular carcinoma. There was present, however, an increased incidence of lesions believed to be preneoplastic. The differences between the long-term effects of AFB1 and other hepatocarcinogens on the livers of PH rats are discussed in terms of their relative capacities and modes of action in inhibiting DNA synthesis.

Aflatoxins↗
PubMed1978

Some high-performance liquid-chromatographic studies of the metabolism of aflatoxins by rat liver microsomal preparations.

The metabolism of aflatoxin B1 in vitro was examined in rat liver microsomal preparations. 2. H.p.l.c. (high-performance liquid-chromatographic) systems were used. A silica column was used to separate non-polar metabolites. A system utilizing a reversed-phase column which separates both poar and non-polar metabolites was also developed. 3. The principal metabolites of aflatoxin B1 found were aflatoxin M1, aflatoxin Q1 and a compound which co-chromatographed with a degradation product of aflatoxin B1 2,3-dihydrodiol. 4. The time course of metabolism of aflatoxin B1 by microsomal preparations isolated from control and phenobarbitone-pretreated rats was examined. The rate and extent of metabolism was greater with microsomal preparations from the latter. The formation of aflatoxin Q1 was enhanced 4--5-fold by phenobarbitone pretreatment, whereas the production of aflatoxin M1 was only increased 1--2-fold. The formation of the degradation product of aflatoxin B1 2,3-dihydrodiol was increased 4--5-fold by the pretreatment with phenobarbitone. 5. The microsomal metabolism of aflatoxins M1, P1 and Q1 was examined. Aflatoxin M1 apparently underwent very limited microsomal metabolism to more polar compounds. Aflatoxin P1 was not metabolized. The situation with aflatoxin Q1 was complicated in that it was metabolized in the absence of NADPH to an unidentified metabolite. Aflatoxin B1 appeared as a metabolite of aflatoxin Q1 only when NADPH was present, and the formation of more polar metabolites was also then observed.

Aflatoxins↗
PubMed1978

A comparison of the changes induced in rat liver by feeding low levels of aflatoxin B1 or an azo dye.

(1) Rats have been given 6 weeks' feeding with low levels of the hepatocarcinogens aflatoxin B1 and 2-methyl dimethyl aminoazobenzene (2-Me-DAB). (2) It has been confirmed that 3 weeks' feeding with either toxin is sub-carcinogenic, whereas 6 weeks' feeding results in a high incidence of hepatocarcinoma. (3) The changes occurring in the liver during this feeding have been monitored by histological examination and zonal rotor centrifugation. (4) Marked similarities have been observed between the time courses of development of changes induced in the liver by the two carcinogens. Little change is observed after 2 weeks' feeding with the toxins. The greatest change occurs after 3 weeks' feeding, which results in tissue necrosis and the loss of a large proportion of the tetraploid hepatocyte nuclei. (5) A compensatory proliferation of predominantly diploid hepatocytes takes place in the presence of a continuing supply of either of the carcinogens. This indicates that not only does feeding each carcinogen induce the production of a population of hepatocytes resistant to the cytotoxicity of the inducing agent, but that the population is also resistant to the cytotoxicity of the other carcinogen.

Aflatoxins↗
PubMed1977

Mode of action and human health aspects of aflatoxin carcinogenesis.

The toxicity and carcinogenicity of the aflatoxins have been studied extensively in the rat. In this species these compounds are recognized as some of the most active hepatocarcinogens. The early lesions induced by the aflatoxins have been studied in an attempt to recognize the developing malignant neoplasm prior to the presence of metastasis. The relationship of focal hyperplasia to neoplasia will be discussed in comparison with other recognized carcinogens. The pattern of human hepatic neoplasia will be compared with that of neoplasia induced by the aflatoxins in order to add weight to the "mycotoxin hypothesis" of the aetiology of hepatic neoplasia. The role of dietary modification will also be discussed.

Aflatoxins↗
PubMed1976

Some studies of the effects of aflatoxin B1 in vivo and in vitro on nucleic acid synthesis in rat and mouse.

The mouse compared with the rat, is more resistent to the acute toxic action of aflatoxin B1 and is refractory to its hepatocarcinogenic properties. Aflatoxin B1 inhibits DNA synthesis more strongly than RNA synthesis in the rat, and both nucleic acid syntheses more strongly in rat than in the mouse. Mouse hepatic microsomes, like those of the rat, are capable of metabolizing aflatoxin B1 in vitro in the presence of NADPH, to an active form which binds to DNA both in solution and in intact nuclei and also inhibits nuclear RNA synthesis. Non NADPH-dependent binding of aflatoxin B1 to nuclei is not effective in inhibiting RNA polymerase and is largely removed by washing with lipid solvents. Mouse nuclear RNA polymerases particularly Mn 2+ (NH4)2SO4 primed acitivity are more resistant to inhibition in vitro by activated aflatoxin B1 than are the corresponding enzyme activities in rat liver nuclei. This would appear to be due to the bound aflatoxin B1 being less efficient in the case of the mouse nucleus, in inhibiting RNA synthesis. Mouse liver slices exhibit a much lesser degree of inhibition of RNA synthesis by aflatoxin B1 than do rat liver slices. Accompanying this is a lower level of binding of aflatoxin B1 to subcellular particulate fractions in the mouse liver slice compared to the rat, this disparity being most marked in the case of the nuclear fraction. The suggestion is made that the resistance of RNA synthesis in the mouse liver, to aflatoxin B1, and perhaps also resistance to its toxicity, is dependent, not on a lower capacity to activate the toxin, but (a) on a less efficient inhibition of RNA synthesis by nuclear bound toxin, and (b) a detoxifying mechanism at least partially situated in the cytosol fraction.

Aflatoxins↗