Species difference in intestinal drug metabolising enzymes in mouse, rat and hamster and their inducibility by masheri, a pyrolysed tobacco product

Activities of several drug metabolising enzymes in the small intestine were investigated in Swiss mice, Sprague Dawley rats and Syrian Golden Hamsters fed 10% masheri, a pyrolysed tobacco product, in diet, for 20 months. The basal levels of enzymes in proximal (PI), medium (MI) and distal (DI) parts of the intestine in the three species were similar. However, the levels of cytochrome P-450, benzo(a) pyrene hydroxylase (B(a)OH) and glutathione S-transferase (GST) were highest in hamsters followed by rat and mice. Upon treatment with masheri, significant induction of cytochrome P-450 and B(a)PH was observed in PI and DI of all the three species. However, GSH and GST was depleted upon masheri treatment in all the three species again only in proximal and distal parts of the intestine. Thus increase in activating enzymes together with depletion in GSH-GST system upon exposure could be an important factor in the susceptibility of the small intestine to hazardous xenobiotic exposure.     

Short-term and long-term effects of brown and black masheri (pyrolysed tobacco product) on vitamin A and vitamin C levels in mice and hamsters

The short-term and long-term effects of two most commonly used brown and black masheri were studied in Swiss mice and Syrian golden hamsters. In short-term studies, both the types of masheri extracts (ME) at 3/4 LD50 dose given ip did not have any effect on either liver or plasma vitamin C levels (both species). However, a decrease in liver vitamin A was observed only in hamsters injected with black ME. Similar effect was not observed in mice injected with both the types of masheri extracts. In long-term studies, when both the types of masheri were fed through diet at 10% level for 20 months, no effect was observed on hepatic or plasma vitamin C levels in mice (both sexes), while an increase in vitamin C levels was observed in black masheri diet fed hamsters. A depletion in liver vitamin A was observed in hamsters fed both the types of masheri. Such an effect was observed only in black masheri diet fed Swiss mice (both sexes) and brown masheri diet fed Swiss females.     

Effect of Siamese cassia leaves on the activities of chemical carcinogen metabolizing enzymes and on mammary gland carcinogenesis in the rat.

Male Wistar rats were fed AIN-76 semipurified diet or diet containing 5% ground lyophilized Siamese cassia leaves for 2 weeks before sacrifice. Hepatic S9 fractions were prepared and assayed for the level of cytochrome P450 (P450), the activities of monooxygenase, i.e., aniline hydroxylase (ANH), aminopyrine-N-demethylase (AMD) as well as the capacity to metabolically activate the mutagenicities of aflatoxin B(1) (AFB(1)) and benzo(a)pyrene (B(a)P). In addition, the activities of detoxificating enzymes such as glutathione-S-transferase (GST) and UDP-glucuronyltransferase (UGT) were also measured. It was found that feeding of Siamese cassia leaves significantly reduced the activities of hepatic ANH and AMD as well as the capacity to activate the mutagenicity of AFB(1) towards Salmonella typhimurium TA100, being 31, 73 and 41% of control group, respectively. It also slightly decreased, but not significantly, the capacity to activate the mutagenicity of B(a)P towards S. typhimurium YG1029. On the other hand, however, the activities of both GST and UGT were markedly increased in those animals, being 250 and 220% of control animals. The anticarcinogenic potential of Siamese cassia leaves was also investigated in female Sprague Dawley rats treated with 9,10-dimethyl-1,2-benzanthracene (DMBA). The animals were fed control diet or diet containing ground lyophilized Siamese cassia leaves 2 weeks prior to and 1 week after intragastrically administration of DMBA, and then they were placed on a pellet diet for additional 25 weeks. Interestingly, it was found that feeding of diet containing 2.5 and 4% Siamese cassia leaves resulted in a significant decrease in the multiplicity of mammary gland tumors as well as a slight delay of the onset of tumor development. The incidence of tumors in the group fed 4% Siamese cassia leaves, but not in the 2.5% group, was lowered, although not significantly, than that of control group. The results in the present study therefore demonstrated that Siamese cassia leaves possess phase II enzyme inducing property as well as the ability to reduce some phase I enzyme activities in rat liver. This Thai vegetable also exhibit cancer chemopreventive potential, at least against DMBA-induced mammary gland carcinogenesis which may be partly due to phase II inducing capacity as well as phase I inhibitory activity.     

Modulatory influence of Brassica compestris Linn var sarson on phase-II carcinogen metabolizing enzymes and glutathione levels in mice

The present study reports the modulatory influence of 95% ethanolic extract from the seeds of B. compestris on the activity of phase-II enzymes such as glutathione S-transferase (GST), DT-diaphorase (DTD) and reduced glutathione (GSH) level in the skin, lung, kidney and forestomach of the mouse. Oral treatment with the seed extract at 800 mg/kg body wt. for 15 days significantly elevated GST in lung and forestomach and DT-diaphorase in forestomach and skin and GSH level in lung, kidney forestomach and skin. The lower dose 400 mg/kg body wt was effective only in inducing GST and DT-diaphorase activity in forestomach and reduced glutathione level in lung. The findings suggest that B. compestris seed extract may block or suppress the events associated with chemical carcinogenesis at least in part, by inducing metabolic detoxification of the carcinogen.     

Effect of a high cholesterol diet on lipid metabolizing enzymes in spontaneously hypertensive rats

A high cholesterol diet induced a fatty liver and an increase in cholesterol oleate in spontaneously hypertensive rats. The activity of microsomal glycerophosphate acyltransferase in liver increased 2-3-fold to meet the increased supply of oleate, the synthesis of which was stimulated by a 10-fold increase in microsomal delta 9-desaturase activity. Hepatic fatty acid synthetase and diacylglycerol acyltransferase activities were decreased somewhat. These results, together with the fact that the large increases in hepatic cholesterol ester and triacylglycerol were not correspondingly reflected in plasma, indicated that the fatty liver resulted from decreased secretion of lipoprotein rather than increased lipogenesis. Endogenous cholesterol in liver microsomes increased 2-fold and hepatic acyl-CoA:cholesterol acyltransferase activity increased 3-fold, whereas plasma lecithin:cholesterol acyltransferase activity was unchanged. Thus, the increase in cholesterol oleate seen in spontaneously hypertensive rats fed a high cholesterol diet is due mainly to increases in acyl-CoA:cholesterol acyltransferase and delta 9-desaturase activities.     

Chemoprotective influence of Zanthoxylum sps. on hepatic carcinogen metabolizing and antioxidant enzymes and skin papillomagenesis in murine model

In the present study, the putative potential of pericarp of dried fruit of Zanthoxylum (Rutaceae Family), a common spice additive in India's west coast cuisines, in protecting against carcinogenesis has been reported. Extract from dried fruit of Zanthoxylum was orally administered to mice at two dose levels: 100 and 200 mg/kg body wt. for 14 days. Results reveal bifunctional nature of Zanthoxylum species as deduced from its potential to induce phase-I and phase-II enzyme activities associated with carcinogen activation and detoxification in the liver of mice. Hepatic glutathione S-transferase and DT-diaphorase were found significantly elevated by the treatment. Zanthoxylum was also effective in augmenting the antioxidant enzyme activities of glutathione peroxidase, superoxide dismutase and catalase albeit significantly by high dose of the extract (P < 0.05; P < 0.01). Reduced glutathione was also significantly elevated in the liver of treated animals (P < 0.05). The present study also investigated peri-initiation application of acetone extract of Zanthoxylum on initiated mouse skin. Results showed a significant reduction in tumor incidence from 68% to 36% (P < 0.05); as well as, a reduction in tumor burden per effective mouse from 3.87 to 0.72 (P < 0.01). Cumulatively, the findings strongly suggest cancer chemopreventive potential of Zanthoxylum sps.     

Effect of geraniol,a plant derived monoterpene on lipids and lipid metabolizing enzymes in experimental hyperlipidemic hamsters

Hyperlipidemia is a major, modifiable risk factor for atherosclerosis and cardiovascular disease. In the present study, we have focused on the effect of different doses of geraniol (GOH) on the lipid profile and lipid metabolizing enzymes in atherogenic diet (AD) fed hamsters. Male Syrian hamsters were grouped into seven: group 1 were control animals; group 2 were animals fed GOH alone (200 mg/kg b.w); group 3 were animals fed AD (10 % coconut oil, 0.25 % cholesterol, and 0.25 % cholic acid); group 4 were animals fed AD + corn oil (2.5 ml/kg b.w); and groups 5, 6, and 7 were fed AD as in group 3 + different doses of GOH (50, 100, and 200 mg/kg b.w), respectively, for 12 weeks. At the end of the experimental period, animals were sacrificed by cervical dislocation and various assays were performed in the plasma and tissues. The AD hamsters showed marked changes in lipid profile and lipid metabolizing enzymes. However, supplementation with GOH counteracted the hyperlipidemia by inhibiting HMG CoA reductase and suppressing lipogenesis. The antihyperlipidemic efficacy of GOH was found to be effective at the dose of 100 mg/kg b.w. This study illustrates that GOH is effective in lowering the risk of hyperlipidemia in AD fed hamsters.     

Effect of sodium molybdate on carbohydrate metabolizing enzymes in alloxan-induced diabetic rats

We evaluated the effect of sodium molybdate on carbohydrate metabolizing enzymes and mitochondrial enzymes in diabetic rats. Diabetic rats showed a significant reduction in the activities of glucose metabolising enzymes like hexokinase, glucose-6-phosphate dehydrogenase, glycogen synthase and in the level of glycogen. An elevation in the activities of aldolase, glucose-6-phosphatase, fructose 1,6- bisphosphatase, glycogen phosphorylase and in the level of blood glucose were also observed in diabetic rats when compared to control rats. The activities of mitochondrial enzymes isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, succinate dehydrogenase, malate dehydrogenase, NADH-dehydrogenase and cytochrome-C-oxidase were also significantly lowered in diabetic rats. Molybdate administration to diabetic rats reversed the above changes in a significant manner. From our observations, we conclude that administration of sodium molybdate regulated the blood sugar levels in alloxan-induced diabetic rats. Sodium molybdate therapy not only maintained the blood glucose homeostasis but also altered the activities of carbohydrate metabolising enzymes. Molybdate therapy also considerably improved the activities of mitochondrial enzymes, thereby suggesting its role in mitochondrial energy production.     

Effect of thyroid hormones on the activities of hepatic alcohol metabolizing enzymes.

Treatment with thyroxine or triiodothyronine for 7 days in order to simulate a hyperthyroid state results in an enhanced activity of the microsomal ethanol oxidizing system. Conversely, a decrease of hepatic alcohol dehydrogenase activity was observed under these experimental conditions, whereas hepatic catalase activity remained unchanged. These findings suggest that if chronic ethanol consumption simulates a “hyperthyroid hepatic state”, increased rates of ethanol metabolism observed following prolonged alcohol intake might therefore be attributed at least in part to an induction of microsomal ethanol oxidizing system activity in the liver.     

Effect of cadmium on pulmonary and renal microsomal drug metabolizing enzymes of the guinea-pig

1. The effect of acute cadmium (Cd) treatment on pulmonary and renal microsomal aniline 4-hydroxylase and ethylmorphine N-demethylase enzyme activities of adult male guinea-pigs were assessed 72 hr following a single dose of Cd ion (2 mg Cd2+/kg i.p.). Tissue and microsomal Cd levels were also determined. 2. There were no significant differences between either lung or kidney tissue weights, microsomal protein contents or enzyme activities of Cd treated and control animals. 3. The tissues and microsomes of Cd-treated animals were found to have significantly higher levels of Cd than those of control animals. In Cd treated animals, tissue and microsomal Cd levels of kidney were found to be higher than that of lung. 4. In vitro addition of cadmium chloride (CdCl2) to incubation mixtures produced concentration related inhibitions of microsomal drug metabolizing enzymes in each tissue. However, in vitro effect of CdCl2 was found to be stronger on drug metabolizing enzymes of kidney than those of lung. In addition, while the strength of Cd effect was more pronounced on the activity of ethylmorphine N-demethylase than that of aniline 4-hydroxylase in the lung, the opposite was observed in the kidney.     

Effect of vitamin A deficiency on hepatic and intestinal drug metabolizing enzymes in rats

Feeding of vitamin A-deficient diet to male weanling rats for 10 weeks caused significant reduction in the hepatic cytochrome P-450, cytochrome b5, aminopyrine N-demethylase and arylhydrocarbon hydroxylase activities. Contrary to this, the levels of these Phase I enzymes were found to be significantly elevated in all the 3 portions (proximal, middle and distal) of the intestine in deficient animals as compared to corresponding pair-fed controls. Of the Phase II enzymes studied, UDP-glucuronyltransferase showed a significant decrease whereas glutathione S-transferase showed a significant increase in vitamin A-deficient rat liver and small intestine. The study suggests that vitamin A deficiency causes an imbalance between the Phase I and phase II drug metabolizing enzyme systems which may decrease the capacity of the organism to withstand the neoplastic effects of chemical carcinogens in vitamin A deficiency.     

The effect of Sudan III on drug metabolizing enzymes

We have examined the induction of drug metabolizing enzymes in rat liver microsomes by azo dye, 1-(p-phenylazophenylazo)-2-naphthol (Sudan III). Marked increases were observed in the levels of cytochrome P-448 as well as in p-nitroanisole O-demethylase (p-NAD), amaranth (AR) and neoprontosil reductases (NPR) and 7-ethoxycoumarin O-deethylase (ECD) activities. On the other hand, aminopyrene N-demethylase activity was not significantly increased. Further, induced ECD activity was inhibited 90% by a specific antibody against cytochrome P-448 while the inhibition observed with an antibody against cytochrome P-450 was less than 25%. Simultaneous administration of Sudan III and 3-methylcholanthene (3-MC) induced cytochrome P-448 up to a level brought about by either Sudan III or 3-MC treatment alone. In contrast, Sudan III did not induce cytochrome P-448 in the 3-MC insensitive DBA/2 mouse. Solubilized microsomes from Sudan III-treated rats showed an identical sodium dodecyl sulfate polyacrylamide gel electrophoretic (SDS-PAGE) pattern with those from 3-MC-treated animals. It is concluded that the cytochrome P-448 induced in liver by Sudan III is very similar to that induced by 3-MC. Sudan III also induced UDP-glucuronyltransferase activity towards 1-naphthol and estradiol. It did not induce NADPH-cytochrome c reductase, nor any of the enzymes which constitute the microsomal electron transport chain except for cytochrome P-448.     

Caffeine: its action on purine metabolizing enzymes.

The many pharmacological and biochemical effects of caffeine may be explained in part by its inhibitory action in vivo and in vitro upon enzymes which metabolize purines. We have demonstrated that in $\text{Crithidia}\text{fasciculata}$ this methylxanthine (as well as theophylline) is a rather weak competitive inhibitor of adenine aminohydrolase, ribonucleoside hydrolase, hypoxanthine and guanine phosphoribosyltransferases. Caffeine does not interfere with purine base transport in Crithidia, however in leucocytes purine uptake is reduced. While the methylxanthines are weak purine enzyme inhibitors, the large number of enzymes affected accounts for their physiological importance in these cells.     

脱氧鬼臼毒素对粘虫几种代谢酶系的影响

脱氧鬼臼毒素是砂地柏Sabina vulgaris Ant.中的主要杀虫活性成分之一。为探讨其作用机理,以叶碟饲喂法处理粘虫Mythimna separata Walker 4龄幼虫,测定了饲喂处理12h、24 h、36 h、48 h和72 h后试虫的羧酸酯酶（CarE）、酸性磷酸酯酶(ACP)、碱性磷酸酯酶(AKP)、谷胱甘肽S-转移酶（GSTs）和多功能氧化酶(MFO)的活性。结果表明：脱氧鬼臼毒素对粘虫羧酸酯酶的活性无明显影响;对酸性磷酸酯酶具有明显的抑制作用,且随着处理时间的延长,抑制作用增强;对碱性磷酸酯酶的影响较为复杂,表现为先抑制,后有所恢复,再被抑制的变化过程;对谷胱甘肽S-转移酶处理12 h后活性变化不明显,24 h后被抑制,36 h后逐渐激活,与对照差异极显著;对细胞色素P450酶系的O-脱甲基酶活性具有明显的抑制作用。     

Effect of chlorinated naphthalenes and terphenyls on the activities of drug metabolizing enzymes in rat liver

γ-Aminobutyric acid-α-ketoglutarate transaminase from pig brain is irreversibly inactivated by 4-amino-5-halopentanoic acids. Protection from inactivation by the natural substrates, the pH dependence of inactivation and the incorporation of 1.7 moles of radioactive inhibitor per mole of enzyme from (S)-[U-¹⁴C]-4-amino-5-chloropentanoic acid suggest a covalent adduct at the active site of the enzyme. A mechanism-based inactivation is proposed.     

Different inhibition of enalaprilat and imidaprilat on bradykinin metabolizing enzymes

Effects of angiotensin-converting enzyme (ACE) inhibitors, enalaprilat and imidaprilat, on bradykinin (BK) metabolizing enzymes, aminopeptidase P (APP), neutral endopeptidase (NEP) and carboxypeptidase N (CPN), were examined. APP activity in the mouse lung was inhibited by enalaprilat in a concentration-dependent manner while imidaprilat did not influence the enzyme activity. The inhibitory effects of these ACE inhibitors on the NEP activity in the mouse lung and the CPN activity in the mouse serum were negligible. These data suggested that the influence of enalaprilat on the APP activity and subsequent BK metabolism are different from those of imidaprilat.