Comparison of microsomal drug-metabolizing enzymes in 14 rat inbred strains

Acute poisoning by chlorpyrifos differentially impacts survival and cardiorespiratory function in normotensive and hypertensive rats

Hypertension is the most important and well-known risk factor for cardiovascular disease (CVD). Recently, acute organophosphate (OP) poisoning has also been pointed as a CVD risk factor. Despite this evidence, no studies have contrasted the acute toxicosis and cardiovascular (CV) effects of OP poisoning under conditions of normotension and hypertension. In this work, adult male normotensive Wistar and Spontaneously Hypertensive rats (SHR) were intraperitoneally injected with saline or chlorpyrifos (CPF), an OP compound, monitored for acute toxicosis signs and 24-h survival. After poisoning, blood pressure, heart rate and ventilation were recorded, the Bezold-Jarisch Reflex (BJR), the Chemoreflex (CR) were chemically activated, as well as the cardiac autonomic tone (AUT) was assessed. Erythrocyte and brainstem acetylcholinesterase and plasmatic butyrylcholinesterase (BuChE) activities were measured as well as lipid peroxidation, advanced oxidation protein products (AOPP), nitrite/nitrate levels, expression of catalase, TNFα and angiotensin-I converting enzyme (ACE-1) within the brainstem. CPF induced a much more pronounced acute toxicosis and 33 % lethality in SHR. CPF poisoning impaired ventilation in SHR, the BJR reflex responses in Wistar rats, and the chemoreflex tachypneic response in both strains. CPF inhibited activity of cholinesterases in both strains, increased AOPP and nitrite/nitrate levels and expression of TNFα and ACE-1 in the brainstem of Wistar rats. Interestingly, SHR presented a reduced intrinsic BuChE activity, an important bioscavenger. Our findings show that, CPF at sublethal doses in normotensive rats lead to lethality and much more pronounced acute toxicity signs in the SHR. We also showed that cardiorespiratory reflexes were differentially impacted after CPF poisoning in both strains and that the cardiorespiratory disfunction seems to be associated with interference in cholinergic transmission, oxidative stress and inflammation. These results points to an increased susceptibility to acute toxicosis in hypertension, which may impose a significant risk to vulnerable populations.

Prevention of colon carcinogenesis by apple juice in vivo: impact of juice constituents and obesity

It is estimated that 75-85% of all chronic diseases are linked to lifestyle-related and environmental factors. The development of colon cancer is positively associated with obesity and inversely associated with the intake of dietary fibre, fruit and vegetable. Apple juice is the most widely consumed fruit beverage in Germany. It contains a specific spectrum of polyphenols and other components that may reduce the risk of colon cancer. Epidemiologic studies suggest an inverse correlation between apple consumption and colon cancer risk, although the mechanisms for these observations are not clear. The present review summarizes the preventive potential of apple juices and different apple constituents on biomarkers related to colon carcinogenesis with special focus on the in vivo evidence and the cancer promoting condition of obesity. However, under the cancer promoting condition of obesity, apple juice did not show cancer-preventive bioactivity. In our experiments a cancer-preventive bioactivity of apple juice is lacking in rats under the cancer-promoting condition of obesity. To further investigate, whether this lack of efficacy observed in obese rats might be representative for obese individuals human intervention studies on high risk groups such as obese or diabetic individuals are of interest and will be conducted.

Differential metabolism of the pyrrolizidine alkaloid, senecionine, in fischer 344 and sprague-dawley Rats

The pyrrolizidine alkaloids (PAs), contained in a number of traditional remedies in Africa and Asia, show wide variations in metabolism between animal species but little work has been done to investigate differences between animal strains. The metabolism of the PA senecionine (SN) in Fischer 344 (F344) rats has been studied in order to compare to that found in the previously investigated Sprague-Dawley (SD) rats (Drug Metab. Dispos. 17: 387, 1989). There was no difference in the formation of (+/-) 6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP, bioactivation) by hepatic microsomes from either sex of SD and F344 rats. However, hepatic microsomes from male and female F344 rats had greater activity in the N-oxidation (detoxication) of SN by 88% and 180%, respectively, when compared to that of male and female SD rats. Experiments conducted at various pH showed an optimum pH of 8.5, the optimal pH for flavin-containing monooxygenase (FMO), for SN N-oxidation by hepatic microsomes from F344 females. In F344 males, however, a bimodal pattern was obtained with activity peaks at pH 7.6 and 8.5 reflecting the possible involvement of both cytochrome P450 (CYP) and FMO. Use of specific inhibitors (SKF525A, 1-benzylimidazole and methimazole) showed that the N-oxide of SN was primarily produced by FMO in both sexes of F344 rats. In contrast, SN N-oxide formation is known to be catalyzed mainly by CYP2C11 rather than FMO in SD rats. This study, therefore, demonstrated that there were substantial differences in the formation of SN N-oxide by hepatic microsomes from F344 and SD rats and that this detoxification is catalyzed primarily by two different enzymes in the two rat strains. These findings suggest that significant variations in PA biotransformation can exist between different animal strains.

N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) has differential efficacy for causing central noradrenergic lesions in two different rat strains: comparison between Long-Evans and Sprague-Dawley rats

We tested the hypothesis that Long-Evans (LE) and Sprague-Dawley (SD) rat strains were equally sensitive to the noradrenergic neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) with respect to central lesions of locus coeruleus (LC) terminals as measured by immunohistochemical localization of dopamine-beta-hydroxylase (D beta H). Analysis of D beta H immunoreactivity was made by both qualitative and quantitative methods. Intraperitoneal injections of 50 mg/kg DSP-4 caused a dramatic reduction of noradrenergic terminals in the neocortex, hippocampus and cerebellum of SD, but not LE rats as compared to saline-injected controls. This finding indicates that LE rats are less sensitive than SD rats to the neurotoxic effects of DSP-4 in the central nervous system.

Dextromethorphan metabolism in rat: interstrain differences and the fate of individually administered oxidative metabolites

1. Dextromethorphan undergoes O- and N-demethylation, with the resultant metabolites being further N- and O-demethylated respectively to 3-hydroxymorphinan. The polymorphically expressed O-demethylation reaction is catalysed by P4502D1 in the Sprague-Dawley (SD) rat. The Dark-Agouti (DA) rat lacks this enzyme. 2. The aims were: (1) to determine if there were strain differences also in the Hooded Wistar (HW) and Albino Wistar (AW) rats with respect to the four demethylation reactions after dextromethorphan 20 mg/kg intraperitoneally; (2) to investigate the inhibition of the demethylation reactions by quinine and quinidine (each 40 mg/kg i.p.) in the above strains; and (3) to investigate the fate of separately administered metabolites (5 mg/kg i.p.) of dextromethorphan in the SD strain. 3. The total recovery of dextromethorphan and metabolites in the four strains ranged from 38 to 64% of the dose. The O-demethylation ratios (expressed as the ratio of urinary total dextrorphan divided by dextromethorphan) in the AW and DA strains were similar but less than in the SD/HW strains; the N-demethylation ratios (expressed as the ratio of urinary total 3-hydroxymorphinan plus 3-methoxymorphinan divided by dextromethorphan) in the DA and SD strains were similar but greater than in the AW and HW strains. Quinine and quinidine significantly reduced the O-demethylation ratio in the SD and DA rat strains, and the N-demethylation ratio in the SD strain. 4. In the SD rat the major metabolic route was via O-demethylation to dextrorphan. The source of 3-hydroxymorphinan is primarily from N-demethylation of dextromethorphan to 3-methoxymorphinan and its subsequent O-demethylation to 3-hydroxymorphinan. The O-demethylation metabolic ratio for dextromethorphan should be calculated as the quotient of urinary total dextrorphan divided by dextromethorphan.

Variables affecting nicotine metabolism

Nicotine metabolism is exceedingly sensitive to perturbation by numerous host factors. To reduce the large variations and discrepancies in the literature pertaining to nicotine metabolism, investigators in future studies need to recognize and better control these host factors. Recent advances in the understanding of nicotine metabolism have suggested new approaches to elucidating underlying mechanisms of certain toxic effects associated with cigarette smoking.

Pharmacokinetic differences of desmethyldiazepam in three outbred Wistar strains related to differences in liver enzyme activities

Various strains of rats differ in their sensitivities towards benzodiazepines suggesting that variations in biological features are responsible for these differences. All reports concern inbred strains. We have studied male rats of three outbred Wistar strains with regard to the pharmacokinetics of desmethyldiazepam given as a single intravenous dose. The elimination half-life of desmethyldiazepam was longer in the Riv:TOX(M) (from the National Institute of Public Health and Environmental Protection) and in the Cpb:WU strain than in the Crl:(WI)BR strain. This strain difference in elimination of desmethyldiazepam may be related to differences in liver enzyme activities.

Inhibition of hepatic microsomal drug metabolism by atracurium administration in the rat

The muscle relaxant atracurium is known to undergo extrahepatic degradation via Hofmann elimination and ester hydrolysis. The purpose of the present study was to evaluate the effects of atracurium on hepatic P450-dependent enzyme activities. Thirty-two male Sprague-Dawley rats were anaesthetized, mechanically ventilated, and randomly allocated to one of four study groups: group 1 received saline, group 2 atracurium, group 3 vecuronium, and group 4 pancuronium intravenously for a period of 3 hr. Equipotent doses of the muscle relaxants were applied; the doses had been obtained in a pilot study using evoked electromyography. At the end of the study period, the livers were removed and analyzed. All three muscle relaxants may lead to inhibition of hepatic drug metabolism. Atracurium influences hepatic P450, although it is predominantly degraded in extrahepatic tissues. Further studies are needed to evaluate the contribution of the major metabolite laudanosine to this inhibitory action.

Substrate specificity of purified rabbit liver esterase ES-1

1. Substrate hydrolysis by two purified rabbit liver esterase-1 allozymes (ES-1A and ES-1B) was compared under conditions differing in substrate, pH and temperature. ES-1A and ES-1B activities had a similar pH and temperature dependency and similar thermal stability profile. 2. There were marked differences in specific activity of ES-1A and ES-1B. ES-1A hydrolysed procaine more rapidly than ES-1B, but was less active towards aspirin. The acetate and propionate esters of p-nitrophenyl were hydrolysed slower by ES-1A than by ES-1B. 3. The effect of substrate concentration on ES-1A activity did not comply with the Michaelis-Menten kinetics, which may be due to so-called substrate activation. 4. At identical substrate concentration, pH and temperature, selected artificial esters were better substrates for ES-1A than selected physiological substrates. Beta-Naphthyloctanoate was found to be a suitable substrate for ES-1A. 1,3-Dioctanoylglycerol was hydrolysed at a rate of only 2% of that of beta-naphthyloctanoate. 5. With methyl, p-nitrophenyl, beta-naphthyl and 4-methylumbelliferyl esters as substrates, ES-1A activity is influenced by length and structure of the acyl moiety. Likewise, ES-1A activity is influenced by the nature of the alkyl moiety of acetate esters. With acetate and methyl esters, branched chains when compared with unbranched chains reduced the esterase activity of ES-1A. Elongation of the acyl moiety up to four or five C atoms gradually raised the velocity of methyl, p-nitrophenyl, and 4-methylumbelliferyl ester hydrolysis by ES-1A. A similar pattern was found for the length of the alkyl moiety of acetate esters. 6. The high degree of similarity between the observed substrate specificity of rabbit ES-1A and that reported earlier for rat ES-10, suggests that these two esterases have a common evolutionary origin.