M.Ira Thabrew

Changes in some rat hepatic microsomal components induced by prolonged administration of chloroquine.

Alterations in microsomal drug metabolizing enzymes and phospholipids following prolonged exposure to chloroquine have been investigated. The levels of microsomal aminopyrine-N-demethylase, aniline hydroxylase and both microsomal and cytosolic glutathione-S-transferase are reduced in treated rats. Microsomal epoxide hydrolase is unaffected by the treatment. An increase in the cholesterol-phospholipid ratio and a decrease in the phosphocholine-sphingomyelin ratio occur. There is a general reduction in the total microsomal phospholipid level though the percentage content of sphingomyelin is higher in all cases. The reduction in microsomal phospholipid level is probably due to a reduced incorporation of acetate into microsomal phospholipids as shown in this study using radioactive sodium acetate.

Structure-activity relationship in the toxicity of some naturally occuring coumarins-chalepin, imperatorin and oxypeucedanine

Imperatorin, oxypeucedanine and chalepin are furanocoumarins isolated from Clausena anisata a medicinal plant common in West Africa. Only chalepin is found to have anticoagulant activity when administered to rats at a single dose. Aniline hydroxylase activity was appreciably depressed by each of the substances. Ethylmorphine demethylase, hepatic DNA, reduced glutathione and glucose-6-phosphatase were unaffected by these compounds when administered at a dose of 50 mg/kg for 3 days prior to sacrifice. Under similar conditions only chalepin treatment resulted in alpha-1-globulin increase and a decrease in beta-globulin content of the serum. Intraperitoneal treatment with chalepin (100 mg/kg) for 2 days resulted in the death of 4 rats out of 10 within a 48 h of treatment. Livers of dead rats showed generalized necrosis of hepatocytes. No deaths were recorded for imperatorin and oxypeucedanine. Rats surviving after 8 weeks showed no changes in hepatic enzyme activity, reduced glutathione and DNA concentrations. However, chalepin and imperatorin induced alterations in the serum protein pattern within this period. Liver lesions were observed in chalepin treated animals and were characterized by very mild necrosis of hepatocytes. No lesions were observed in the livers of rats treated with imperatorin and oxypeucedanine.

The presence of aflatoxin and some polycyclic aromatic hydrocarbons in human foods

An analysis of several common food items (fish, meat, crops and spices) as sold in the Nigerian markets has shown the presence of (a) benzo[a]-pyrene and benz[a]anthracene in fish and meat samples, and (b) aflatoxin in crops and spices. These results are discussed in relation to the relatively high incidence of cancer in tropical Africa.

Effect of Liv-52 on carbon tetrachloride-induced changes in hepatic microsomal drug-metabolizing enzymes of the rat.

The effects of the hepatotonic Liv-52 on carbon tetrachloride (CCl4)-induced changes in the activities of the microsomal enzymes, aniline hydroxylase, p-aminopyrine N-demethylase and aryl hydrocarbon hydroxylase (AHH), have been investigated. Treatment with Liv-52 (before or after CCl4 administration) markedly decreased, the CCl4-mediated reduction in aniline hydrochloride and p-aminopyrine N-demethylase activities, although the decrease in AHH activity could not be prevented. Kinetic studies showed that the effect of Liv-52 was not due to an alteration in the Km values of the enzymes. The possible mechanism by which Liv-52 moderated the CCl4-induced changes in the microsomal drug-metabolizing enzymes is discussed.

Variations in induction of drug-metabolizing enzymes by trans-Stilbene oxide in rodent species

Trans-Stilbene oxide (400 mg/kg) produced a 500% increase in the microsomal epoxide hydratase activity in rat and mouse with little change in the soluble enzyme activity. However, in guinea pig, the soluble epoxide hydratase activity increased by about 33% with only a small increase (47.6%) in the microsomal enzyme activity. The soluble glutathione S-transferase activities were also induced in both rat and mouse, with little change in that of the guinea pig. Increasing dosage of trans-stilbene oxide from 400 mg/kg to 1000 mg/kg had little effect on the above enzyme activities. That the guinea pig was not relatively refractory to all inducing agents was shown by the fact that phenobarbital (100 mg/kg) and 3-methylcholanthrene (25 mg/kg) produced relatively similar increases in the activities of aniline hydroxylase and P-aminopyrine N-demethylase in rat, mouse and guinea pig. However, these inducers produced only a 15-20% stimulation in the soluble glutathione S-transferase and microsomal epoxide hydratase activities in guinea pig, when compared to a 50-80% increase in rat and mouse, suggesting a general resistance to induction by the phase II enzymes in guinea liver. In all three animal models, the inducer markedly increased the microsomal total phospholipid content, although the sphingomyelin content itself was decreased. In both rat and mouse, the microsomal cholesterol content was significantly decreased while that in guinea pig was unaffected. Possible factors responsible for the observed species differences are discussed.

The metabolic fate of [14C] benzoic acid in protein-energy deficient rats

The metabolic fate of [14C] benzoic acid administered i.p. to marasmic-kwashiorkor rats has been investigated. Rats fed a normal diet with benzoic acid administered i.p. at 200 mg/kg, excreted the benzoic acid mainly as hippuric acid (99% of 24 h excretion), while marasmic-kwashiorkor rats excreted 62--85% as hippuric acid and 14--37% as the glucuronide conjugate. 2 weeks after repletion metabolism of benzoic acid by the marasmic-kwashiorkor rats on the stock diet had returned to normal; most of the benzoate was excreted as hippuric acid.

Effect of dietary vitamin E (α-tocopherol) on aflatoxin B metabolism

SummaryIntraperitoneal injection of rats with 2 mg/kg ring labelled14C AFB1 (spec. act. 110 mCi/mM/nmole) showed a higher level of radioactivity in the urine of test animals on diets containing 600 mg/kg vit. E 24 h after pretreatment. Analysis of the urine by chloroform extraction, thin layer chromatography and liquid scintillation counting of the various fractions showed less aflatoxin M1 (AFM1) and less unmetabolized AFB1 in test samples than in controls.Incubation of ring labelled14C AFB1 with hepatic 10,000 g supernatant fractions, however, showed increased metabolism of AFB1 by fractions from test animals as compared with the controls. Rate of disappearance of14C AFB1 and the consequent formation of AFM1 was greater in the test fractions than in the controls (4). At 30 days all test animals showed higher levels of serum vitamin E than the controls. Hepatic aniline hydroxylase and ethyl morphine N-demethylase activities of the liver fractions and blood glutathione reductase activity were greater in the tests. P-nitroanisole-O-demethylase activity was reduced while hepatic and serum reduced glutathione levels remained basically unaltered.

Inhibition of mitochondrial respiration by chalepin, a naturally occurring furocoumarin

Polarographic measurements of the rates of oxygen consumption by isolated rat liver mitochondria respiring on pyruvate/malate in metabolic state 4 revealed that additions of micromolar amounts of chalepin, a naturally occurring furocoumarin resulted in significant decreases in respiratory rates. At 16 microM chalepin, respiration was inhibited by at least 40%. A maximum inhibition of 60% was obtained at 80 microM chalepin. Whereas 16 microM chalepin gave 76% reduction of respiratory control ratio, at most 80% reduction was obtained at greater than or equal to 80 microM chalepin. There was no significant effect on either metabolic state 4 respiration or respiratory control ratio when succinate was used as electron donor. A comparison with the effects of rotenone indicates that chalepin is probably only one-tenth as potent as this classical inhibitor of respiration. These results show that chalepin-like rotenone is an inhibitor of energy coupling site 1.

Liver microsomal membrane lipid composition in marasmic-kwashiorkor

Abstract The microsomal membrane cholesterol and phospholipid content and phospholipid composition of marasmic kwashiorkor rats have been compared with those of normal rats. A Significant increase in the cholesterol/phospholipid ratio, as well as in the sphingomyelin/phosphatidyl-choline ratio was observed in the marasmic-kwashiorkor rat. These effects would tend to decrease the fluidity of the phospholipid bilayer of the endoplasmic reticulum membrane and may thus affect drug metabolism. It is well known that a change in the quality or quantity of dietary protein causes an alteration in the rates of metabolism of many xenobiotics by the mammalian liver (1–3). These metabolic alteration have been attributed mainly to changes in the levels of microsomal membrane proteins themselves, especially that of cytochrome P-450 (4–6). However, a recent report by Suzuki et al. (7) indicates that the more subtle features of drug metabolism such as interactions between NADPH-cytochrome P-450 reductase, cytochrome P-450, cytochrome b and other specific drug metabolzing enzymes in the membrane of the endoplasmic reticulum might well be affected by the fluidity of the phospholipid bilayer. There is still a high incidence of protein-energy malnutrition (PEM) diseases such as kwashiorkor in many part of the world (8). The membrane lipid composition from microsomes of marasmic-kwashiorkor rats have therefore been investigated with a view to finding out if there are any changes in these components due to protein deficiency which could contribute to the decreased metabolism of xenobiotics in this condition.

Levels of microsomal drug-metabolizing enzymes in animals which are highly susceptible to aflatoxin carcinogenicity: The case of the duck

A comparative study of the microsomal fractions of the duck and rat has shown significant differences in the total protein contents in these fractions and also in the activities of 2 phase I drug-metabolizing enzymes, ethylmorphine N-demethylase and aniline hydroxylase. These results are discussed in relation to the high susceptibility of birds (especially ducks) to toxic or carcinogenic substances.