Species differences in drug metabolism

Effects of species of origin and mode of induction of microsomes on carbamazepine-induced cell toxicity

Standardization and validation of in vitro drug metabolism is essential for pre-clinical drug development as well as for in vitro toxicity assays including the lymphocyte toxicity assay (LTA) and the in vitro platelet toxicity assay (iPTA). Use of isolated liver microsomes (MIC) in in vitro testing has been utilized for a long time; however, the effect of species of origin and induction agents on the metabolic capacities of MIC is not adequately evaluated. In this study we investigated the impact of species of origin and induction agent on the capacity of MICs to bioactivate carbamazepine (CBZ) using cytotoxicity as a gross endpoint to measure the levels of cytotoxic metabolites generated by each type of MICs. Jurkat E6.1 cell line was used and MICs from human, rat, mouse, minipig and rabbit origin as well as rat MICs that is either non-induced or induced by phenobarbitone (PHB), dexamethasone (DEXA), 3-methylcholanthrene (3MC), clofibrate (CLOF) and isoniazid (INH) were investigated. MICs from minipig and rat MICs induced with 3MC exhibited the highest capacity to produce cytotoxic metabolites of CBZ. These findings will help optimize and standardize in vitro toxicity assays and provide guidance to pre-clinical investigation of drugs.

Recent advances in soluble decellularized extracellular matrix for heart tissue engineering and organ modeling

Despite the advent of tissue engineering (TE) for the remodeling, restoring, and replacing damaged cardiovascular tissues, the progress is hindered by the optimal mechanical and chemical properties required to induce cardiac tissue-specific cellular behaviors including migration, adhesion, proliferation, and differentiation. Cardiac extracellular matrix (ECM) consists of numerous structural and functional molecules and tissue-specific cells, therefore it plays an important role in stimulating cell proliferation and differentiation, guiding cell migration, and activating regulatory signaling pathways. With the improvement and modification of cell removal methods, decellularized ECM (dECM) preserves biochemical complexity, and bio-inductive properties of the native matrix and improves the process of generating functional tissue. In this review, we first provide an overview of the latest advancements in the utilization of dECM in in vitro model systems for disease and tissue modeling, as well as drug screening. Then, we explore the role of dECM-based biomaterials in cardiovascular regenerative medicine (RM), including both invasive and non-invasive methods. In the next step, we elucidate the engineering and material considerations in the preparation of dECM-based biomaterials, namely various decellularization techniques, dECM sources, modulation, characterizations, and fabrication approaches. Finally, we discuss the limitations and future directions in fabrication of dECM-based biomaterials for cardiovascular modeling, RM, and clinical translation.

Engineered tissues and strategies to overcome challenges in drug development

Current preclinical studies in drug development utilize high-throughput in vitro screens to identify drug leads, followed by both in vitro and in vivo models to predict lead candidates' pharmacokinetic and pharmacodynamic properties. The goal of these studies is to reduce the number of lead drug candidates down to the most likely to succeed in later human clinical trials. However, only 1 in 10 drug candidates that emerge from preclinical studies will succeed and become an approved therapeutic. Lack of efficacy or undetected toxicity represents roughly 75% of the causes for these failures, despite these parameters being the primary exclusion criteria in preclinical studies. Recently, advances in both biology and engineering have created new tools for constructing new preclinical models. These models can complement those used in current preclinical studies by helping to create more realistic representations of human tissues in vitro and in vivo. In this review, we describe current preclinical models to identify their value and limitations and then discuss select areas of research where improvements in preclinical models are particularly needed to advance drug development. Following this, we discuss design considerations for constructing preclinical models and then highlight recent advances in these efforts. Taken together, we aim to review the advances as of 2020 surrounding the prospect of biological and engineering tools for adding enhanced biological relevance to preclinical studies to aid in the challenges of failed drug candidates and the burden this poses on the drug development enterprise and thus healthcare.

Recent Progress in Hepatocyte Culture Models and Their Application to the Assessment of Drug Metabolism, Transport, and Toxicity in Drug Discovery: The Value of Tissue Engineering for the Successful Development of a Microphysiological System

Tissue engineering technology has provided many useful culture models. This article reviews the merits of this technology in a hepatocyte culture system and describes the applications of the sandwich-cultured hepatocyte model in drug discovery. In addition, we also review recent investigations of the utility of the 3-dimensional bioprinted human liver tissue model and spheroid model. Finally, we present the future direction and developmental challenges of a hepatocyte culture model for the successful establishment of a microphysiological system, represented as an organ-on-a-chip and even as a human-on-a-chip. A merit of advanced culture models is their potential use for detecting hepatotoxicity through repeated exposure to chemicals as they allow long-term culture while maintaining hepatocyte functionality. As a future direction, such advanced hepatocyte culture systems can be connected to other tissue models for evaluating tissue-to-tissue interaction beyond cell-to-cell interaction. This combination of culture models could represent parts of the human body in a microphysiological system.

Problems in Predicting Drug Effects across Species Lines

During the course of drug development, there are many instances where extrapolation of data from animals to man is difficult because the toxicologic and metabolic responses induced by drugs may be significantly different between the laboratory species. In cases where the drug in question has a potentially major therapeutic use in man, it is suggested that the data be evaluated on the basis of a pragmatic benefit-to-risk ratio, rather than zero-toxicity. In this way, we may provide drug therapy for those patients for whom adequate treatment does not exist, as well as protect those individuals who may be exposed to some hazard from the use of medicines.

Evaluation of the cytotoxicity of 10 chemicals in human and rat hepatocytes and in cell lines: Correlation between in vitro data and human lethal concentration

The cytotoxicity of 10 chemicals from the Multicentre Evaluation of In vitro Cytotoxicity (MEIC) list (nos 21-30) was evaluated in human and rat cultured hepatocytes and in two established cell lines (HepG2 and 3T3) according to the MEIC programme organized by the Scandinavian Society of Cell Toxicology. The MTT test was used as the endpoint of cytotoxicity after 24hr of exposure to the chemicals. Theophylline, phenobarbital and paraquat were the least cytotoxic compounds in the cellular systems (IC(50) = 450-17,000 mum) except for the 3T3 cells. The seven remaining chemicals (dextropropoxyphene, propranolol, arsenic trioxide, cupric sulfate, mercuric chloride, thioridazine and thallium sulfate) showed a similar relative cytotoxic ranking in the four in vitro systems in the lower range of concentrations (IC(50) = 2-350 mum). The data suggest that these 10 chemicals have a basal cytotoxic effect common to the four in vitro systems, and probably none of these compounds could be considered either hepatotoxic or species specific. The correlation between in vitro data and human lethal blood concentrations showed that the predictability of the in vitro systems was similar to that of in vivo rodent tests (LD(50)) only when low cytotoxic concentrations (IC(10)) were used for correlation.

Evaluation of the cytotoxicity of ten chemicals on human cultured hepatocytes: Predictability of human toxicity and comparison with rodent cell culture systems

The cytotoxic effect of the first 10 chemicals on the MEIC list (evaluated in the Multicentre Evaluation of In Vitro Cytotoxicity organized by the Scandinavian Society of Cell Toxicology) was evaluated on human and rat cultured hepatocytes and in the non-hepatic murine 3T3 cell line. The MTT test was used as an endpoint to evaluate cytotoxicity after 24 hr of exposure to the chemicals. The predictability of human toxicity using human hepatocytes was analysed and compared with the results using rodent cell culture systems and rat and mouse LD(50) tests. Ferrous sulphate, diazepam and isopropyl alcohol produced about the same toxicity in all three cell culture models; paracetamol and acetylsalicylic acid were more toxic to human and rat hepatocytes than to mouse 3T3 cells; amitriptyline, ethylene glycol, methanol and ethanol were more toxic to human hepatocytes than to rodent cells. Digoxin was the most cytotoxic chemical to human hepatocytes (IC(50), 4.9 nm), the alcoholic compounds (isopropanol, ethylene glycol, ethanol and methanol) were the least toxic (IC(50), 125-819 mm) and paracetamol, acetylsalicylic acid, ferrous sulphate, diazepam and amitriptyline showed intermediate cytotoxicities (IC(50), 0.05-6 mm). The data suggest that for these 10 chemicals, acute toxicity in humans was more accurately predicted using human hepatocytes than using rat hepatocytes or mouse non-hepatic 3T3 cells.

Species differences in the biotransformation of an alpha 4 beta 2 nicotinic acetylcholine receptor partial agonist: the effects of distinct glucuronide metabolites on overall compound disposition

The metabolism and disposition of (1R,5S)-2,3,4,5-tetrahydro-7-(trifluoromethyl)-1,5-methano-1H-3-benzazepine (1), an alpha(4)beta(2) nicotinic acetylcholine receptor partial agonist, was investigated in Sprague-Dawley rats and cynomolgus monkeys receiving (1R,5S)-2,3,4,5-tetrahydro-7-(trifluoromethyl)-1,5-methano-1H-4[(14)C]-3- benzazepine hydrochloride ([(14)C]1) orally. Although both species chiefly (>or=62%) cleared 1 metabolically, species-specific dispositional profiles were observed for both 1 and total radioactivity. Radioactivity was excreted equally in the urine and feces of intact rats but largely (72%) in bile in bile duct-cannulated animals. In monkeys, radioactivity recoveries were 50-fold greater in urine than feces and minimal (<5%) in bile. Both species metabolized 1 similarly: four-electron oxidation to one of four amino acids or two lactams (minor) and glucuronide formation (major). In rats, the latter pathway predominantly formed an N-carbamoyl glucuronide (M6), exclusively present in bile (69% of dose), whereas in monkeys it afforded an N-O-glucuronide (M5), a minor biliary component (4%) but the major plasma (62%) and urinary (42%) entity. In rats, first-pass hepatic conversion of 1 to M6, which was confirmed in rat hepatocytes, and its biliary secretion resulted in the indirect enterohepatic cycling of 1 via M6 and manifested in double-humped plasma concentration-time curves and long t(1/2) for both 1 and total radioactivity. In monkeys, in which only M5 was formed, double-humped plasma concentration-time curves were absent, and moderate t(1/2) for both 1 and total radioactivity were observed. A seemingly subtle, yet critical, difference in the chemical structures of these two glucuronide metabolites considerably affected the overall disposition of 1 in rats versus monkeys.

In vivo metabolism of norbormide in rats and mice

Norbormide's species-selective lethality displays 150-fold and 40-fold more sensitivity to rats than mice and guinea pigs, respectively. Our previous study revealed marked inter-species differences in rate and route of metabolism in liver preparations from different species, with hydroxylation the major route. To examine whether rapid metabolic clearance or species-dependent formation of a toxic metabolite play a role in the marked species-sensitivity, we initiated in vivo metabolic studies in rats and mice. After oral dosing, norbormide was detected in mouse but not rat blood. In contrast, liver analysis revealed that norbormide concentration was significantly higher in rat compared with mouse, and that it underwent extensive metabolism tentatively identified via hydroxylation in rat, whilst none was detected in mouse. Although an unidentified metabolite (M3) was detected in rat blood after oral dosing, no metabolites were detected 1min after intravenous dosing, which proved lethal at 0.5mg/kg. Taken together, the data indicate that the toxicity resides with the parent compound, rather species-dependent formation of a potent metabolite and that species sensitivity may be controlled at the pharmacodynamic level.

In vitro metabolism of norbormide in rat, mouse and guinea pig liver preparations

Differences between species in response to norbormide (NRB) may arise through differential pharmacodynamic and/or pharmacokinetic properties. We hypothesise that species-selectivity is at least partly determined by differences in metabolism based on in vitro data generated in liver preparations from rats, mice and guinea pigs. HPLC separation and LC/MS identification revealed that NRB undergoes metabolism primarily to hydroxylated form that was tentatively identified in both rat and non-rat species with NADPH as the preferred cofactor. However, the metabolic profile and the rate are different between species. Gender differences are also reported in the metabolic rate in rats and we postulate that this may be responsible for different toxic sensitivities seen between sexes. Using this knowledge, we aim to develop pharmacological tool(s) for use in designing a new class of drugs that can be targeted in a tissue-selective manner. Further in vivo pharmacokinetic with receptor affinity studies are warranted.

Changes in biochemical parameters in rabbits blood after oral exposure to diphenyl diselenide for long periods

The concept that selenium-containing molecules may be better antioxidants than classical antioxidants, has led to the design of synthetic organoselenium compounds. The present study was conducted to evaluate the potential toxicity of long time oral exposure to diphenyl diselenide (PhSe)2 in rabbits. Male adult New Zealand rabbits were divided into four groups, group I served as control; groups II, III and IV received 0.3, 3.0 and 30 ppm of (PhSe)2 pulverized in the chow for 8 months. A number of parameters were examined in blood as indicators of toxicity, including delta-aminolevulinate dehydratase (delta-ALA-D), catalase, glutathione peroxidase (GPx), alanine aminotransferase (ALT), aspartate aminotransferase (AST), urea, creatinine, TBARS, non-protein-SH, ascorbic acid and selenium. The results demonstrated that 6 and 8 months of 30 ppm (PhSe)2 intake caused a significant increase in blood delta-ALA-D activity. Erythrocyte non-protein thiol levels were significantly increased after 2 months of 30 ppm (PhSe)2 intake and then return to control levels after prolonged periods of intake. Ingestion of 3.0 ppm of (PhSe)2 for 8 months significantly increased catalase activity in erythrocytes. Conversely, no alterations in GPx, ALT, AST, TBARS and selenium levels were observed in rabbit serum, conversely, selenium levels in peri-renal adipose tissue were significantly increased after 8 months of 30 ppm (PhSe)2 intake, indicating its great lipophylicity. The present results suggest that diphenyl diselenide was not hepato- or renotoxic for rabbits, but caused some biochemical alterations that can be related to some pro-oxidant activity of the compound (particularly the reduction in Vitamin C).

Can in vitro drug metabolism studies with human tissue replace in vivo animal studies?

Animals provide a physiologically relevant system for evaluation of drug metabolism, but marked inter-species differences limit extrapolation to humans. Liver microsomes are used extensively as an in vitro human drug metabolising system, and with appropriate selection of parameters, such as substrate and enzyme concentrations, may predict both routes and rate of metabolism. However, variable enzyme expression between donors and overlapping substrate specificity influence reproducibility, hence recombinant human CYP enzymes expressed in human, yeast or insect cells have been developed. For complex metabolic profiles involving sequential or competing pathways, isolated hepatocytes and liver slices are of value. Altered enzyme activity and restricted availability constrain their use. Cryopreservation or culture increase availability, but changes in enzyme activity remain a constraint. To date, human in vitro systems do not predict all aspects of drug metabolism, thus a combination of in vivo animal and in vitro human studies will be required for the foreseeable future.

Investigations into the potential neurotoxicity induced by diselenides in mice and rats

It is well known that selenium is highly toxic to several species of mammals. Here we report the potential neurotoxicity of diselenides, as measured by the manifestation of seizures. The modulation of various neurotransmitter systems potentially involved in seizure episodes and death was also evaluated. The results of the present investigation suggest that toxicity of diselenides depends on the route of administration as well the species (rats or mice). These data show that modulation of more than one neuronal system can account for diselenide-induced seizures in mice. Additionally, changes in structure of diselenides, such as to introduce a functional group, influence the appearance of seizure episode. Conversely, all allosteric modulators tested did not protect dipropyl diselenide-induced seizures, indicating that aliphatic is more toxic than aromatic diselenides. Acute treatment with dipropyl diselenide inhibited [3H]-glutamate uptake to the crude synaptosomes. In contrast animals injected with diphenyl diselenide did not inhibit [3H]-glutamate uptake.

Bioanalytical applications of tandem mass spectrometry in the in vitro metabolism of the anticholinergic drug cimetropium bromide to detect differences in species metabolism

1. In vitro metabolism of the anticholinergic drug, cimetropium bromide, was investigated using four different animal hepatic microsomal incubates derived from rat, hamster, guinea pig, and mouse livers. 2. Constant neutral loss (CNL) tandem mass spectrometry was used to detect the presence of the N-methylenecyclopropyl-scopine functionality by monitoring loss of 54 daltons (corresponding to loss of methylenecyclopropane) in microsomal incubates. 3. A CNL loss of 46 daltons was used to screen for the presence of ester hydrolysis products. 4. A comparison of the daughter ion spectra obtained on ions detected by CNL scanning, with daughter ion spectra of synthetic standards, determined the presence of ten metabolites of cimetropium bromide. 5. Hydroxylation of the aromatic ring in the ester side-chain was found to be the major metabolic pathway, and ester bond hydrolysis was a minor metabolic pathway. 6. N-Demethylation of the bridgehead nitrogen was observed only in rat and hamster incubates. 7. Using the method of CNL scanning it was possible to screen different animal microsomal incubates without resorting to any major purification procedures such as h.p.l.c. 8. This scanning method revealed differences between species in the metabolic pathways of cimetropium bromide.

Liver slices in dynamic organ culture. II. An in vitro cellular technique for the study of integrated drug metabolism using human tissue

1. Precision cut human liver slices in dynamic organ culture have been used to study the integrated metabolism of 7-ethoxycoumarin and the conjugation of 7-hydroxycoumarin. 2. The metabolism of 7-ethoxycoumarin and 7-hydroxycoumarin was monitored for 6 h. For both substrates there was a time-dependent increase in metabolites present in the incubation medium. The low levels of free 7-hydroxycoumarin found in the medium when 7-ethoxycoumarin was the substrate suggests good coupling of phase I and phase II metabolism. 3. With suitable incubation conditions, i.e. change of medium containing new substrate every 2 h, the metabolism of both 7-ethoxycoumarin and 7-hydroxycoumarin by human liver slices was found to proceed at similar rates for up to 24 h. This was demonstrated using five separate human liver preparations. 4. Human liver slices also metabolized mono-chlorobenzene and o-, m- and p-dichlorobenzene to aqueous soluble metabolites. There was a time-dependent increase in the appearance of aqueous soluble metabolites present in the incubation medium. Metabolites were not retained by the liver slices. 5. A cold-storage transit buffer has been described and used to maintain the levels of drug metabolism in both rat and human tissue for periods of up to 6 h. 6. The use of human liver slices in dynamic organ culture as a suitable method for the direct assessment of integrated hepatic drug metabolism is proposed.

Drug metabolising activity of freshly isolated human hepatocytes

Hepatocytes have been isolated from samples of adult human liver by removal of extracellular calcium followed by perfusion with collagenase. The hepatocytes were isolated with a yield of up to 39 X 10(6) cells/g and with a viability of up to 74%. The cells were active in the oxidation of aldrin and 7-ethoxycoumarin. They also catalysed the conjugation of 7-hydroxycoumarin. Monooxygenase activity of the hepatocytes was linear for at least 60 min. Maintenance of the hepatocytes in suspension at 4 degrees C for 19 h resulted in a 15% loss in viability. This was accompanied by a 50% decrease in monooxygenase activity expressed per viable cell. It is concluded that human hepatocytes can be isolated in sufficient yield and with satisfactory viability for use in a range of studies on drug metabolism and toxicity.

Comparative metabolism of 3,5-di-tert-butyl-4-hydroxytoluene (BHT) in mice and rats

In male and female DDY/Slc mice given single oral doses (20 or 500 mg/kg body weight) of 3,5-di-tert-butyl-4-hydroxytoluene (BHT) labelled with 14C at the p-methyl group, 14C was distributed mainly in the stomach, intestines, liver and kidney, and then excreted in the urine, faeces and expired air. During the 7 days after treatment, 41-65, 26-50 and 6-9% of the 14C dose was excreted in faeces, urine and expired air, respectively, and the total recovery was 96-98%. Levels of 14C in 21 male and 22 female tissues 7 days after treatment were less than 1 microgram BHT equivalents/g tissue (ppm) in mice given 20 mg/kg and less than 11 ppm in mice given 500 mg/kg. When [14C]BHT was given orally to male mice at 20 mg/kg/day for 10 days, 14C was rapidly excreted and did not exhibit any tendency to accumulate in any tissues. Thin-layer chromatography and high-performance liquid chromatography analyses showed that more than 43 metabolites were present in the urine and faeces of both species, and all of these were identified to determine metabolic pathways for BHT in mice and rats. Major metabolic reactions of [14C]BHT in mice were the oxidation of the p-methyl group attached to the benzene ring and of the tert-butyl groups. The products from the latter reaction were cyclized to some extent by reacting with the adjacent phenolic OH group to give hemiacetals or lactones. The carboxyl derivatives from the p-methyl oxidation were conjugated with glucuronic acid. When single oral doses of 20 or 500 mg [14C]BHT/kg were given to male Sprague-Dawley rats, metabolites similar to those in mice were found. However, the major biotransformation was oxidation of the p-methyl group, and oxidation of the tert-butyl groups was a minor reaction in rats.

Metabolism of flecainide

After oral administration in healthy human subjects, flecainide absorption is prompt (average peak level at 3 to 4 hours) and nearly complete (at least 90%); flecainide does not appear to undergo consequential presystemic biotransformation. Oral absorption in patients with cardiac arrhythmias, renal disease and congestive heart failure (CHF) is also good. Plasma levels of flecainide are proportional to dose within the therapeutic range. Neither food nor antacid affect the extent of flecainide absorption. In healthy subjects, the plasma half-life of unchanged flecainide is relatively long (mean 13 hours after single doses and 16 hours after multiple dosage). For patients with ventricular premature complexes, the half-life is longer (mean 20 hours), and twice-daily oral dosage is effective. The rate of flecainide elimination from plasma may possibly be reduced in older patients. Overall, the plasma pharmacokinetics of flecainide appear to be reasonably linear (not dose- or concentration-dependent). In humans, most (mean 86%) of a single oral dose is excreted in urine as flecainide and its metabolites; only a small portion (mean 5%) is found in feces. Thus, flecainide does not appear to undergo extensive biliary excretion. A substantial portion (mean 27%) of a dose is excreted in urine as unchanged flecainide. Under alkaline urinary conditions, flecainide elimination may be decreased. Only 2 major and 2 or 3 minor metabolites are found in human urine. The 2 major urinary metabolites possess little or no detectable antiarrhythmic activity and are also the major metabolites present in human plasma (primarily conjugated); since free metabolite levels are very low in plasma, metabolites are not likely to contribute any consequential pharmacologic activity. The rate of flecainide elimination from plasma is somewhat slower in patients with moderate renal failure and in patients with CHF than that for healthy persons, and is markedly slower in some patients with end-stage renal disease. Urinary excretion of unchanged flecainide is somewhat less in moderate renal patients and is markedly less in end-stage renal patients, but is not altered in CHF patients. Dosage should be reduced in patients with more severe renal disease and, if indicated, in some CHF patients. Hemodialysis is not an effective means for removal of unchanged flecainide, but does provide more substantial removal of metabolites. Flecainide is not extensively bound (mean 40%) to human plasma proteins in vitro and binding is independent of total drug level.(ABSTRACT TRUNCATED AT 400 WORDS)

Induction of hepatic long-chain acyl-CoA hydrolase by clofibric acid administration

The induction of hepatic long-chain acyl-CoA hydrolase in the cytosolic fraction by administration of clofibric acid (p-chlorophenoxyisobutyric acid) was compared in rats, mice and guinea-pigs. In rats, two long-chain acyl-CoA hydrolases were induced by the administration of clofibric acid. In mice, only one long-chain acyl-CoA hydrolase was induced, and this hydrolase had properties similar to those of the lower-molecular-weight hydrolase induced in the hepatic cytosol of rats. In hepatic cytosol of guinea-pig, no hydrolase was induced by the administration of clofibric acid.

Comparative pharmacokinetics of benzodiazepines in dog and man

The pharmacokinetic parameters disposition half-life, metabolic clearance, volume of distribution, intrinsic clearance of unbound drug, and (distributive tissue volume/unbound fraction in tissue) were compared for 12 benzodiazepines in dog and man. With the exception of volume of distribution, statistically significant correlations were obtained when parameters were plotted on a double logarithmic grid. In general, benzodiazepines were metabolized more rapidly and exhibited greater tissue distribution in dog than in man. The variability in parameters was such, however, as to make extrapolations from one species to another subject to considerable error.

Toxicology investigations with cell culture systems

This review concerns some of the cell culture systems that are most frequently used in toxicology investigations. In particular, it sets out to evaluate the effectiveness of these cell culture systems in assessing the toxic potential of chemicals. Metabolic studies and general and specific toxicology investigations are highlighted. Specific toxicology investigations relate to the effects of the tests substances on the highly specialized functions typical of the cell systems chosen. The general toxicology investigations include most of the other studies where differentiated or undifferentiated cells have been used to evaluate the effects of the tested substances on common basic biochemical processes essential for life. Lastly, we have attempted to focus attention on the most promising applications of cell cultures in toxicology studies for the near future and to identify those areas where further research is needed. Because of the several excellent reviews that already exist, we have decided not to consider cell cultures utilized in screening potential mutagens and carcinogens. We have also excluded investigations of drug therapeutic effects and action mechanisms of drugs.

Species difference and characterization of intestinal esterase on the hydrolizing activity of ester-type drugs

The ability of the esterase from intestine was studied for hydrolysis of ester-type drugs during absorption. The intestinal esterase is present in the absorption sites in the intestine and hydrolyzes to a large extent during the absorption. In a study of the dietary effect on intestinal esterase, the esterase activity increased in rats fed a high-fat diet, decreased in those fasted or fed a fat-free diet, whereas the esterase activity in the rat treated with phenobarbital showed no marked change. Thus the esterase from intestinal mucosa appears to be characteristically quite different from hepatic esterase. The esterase from human intestine was characterized and compared with esterase from rats, mice, rabbits, guinea pigs and dogs. There was a difference in the substrate specificity of the esterase and there were significant species differences in the electrophoretic behavior of the enzyme among the species tested. These results indicate that intestinal esterase from humans differs characteristically from esterases in experimental animals.

Effect of lyophilization and storage of liver 9,000xg supernatant fraction on the metabolism of imipramine in several species of animals

Effects of lyophilization and storage of liver 9,000xg supernatant fraction on the activity of drug metabolizing enzymes in some species of animals were studied. Imipramine metabolizing enzyme activity and the content of cytochrome P-450 were stable for, at least, one month without any loss of the activity when lyophilized liver 9,000xg supernatant fraction of some animal species, i.e., rat, mouse, guinea pig, rabbit and dog, was stored under reduced pressure in a deep freezer (-20 degrees C). There were no differences of imipramine metabolism between lyophilized liver 9,000xg supernatant fraction which was kept in a deep freezer for one month and a fresh fraction which was prepared immediately before determinations of the enzyme activity and cytochrome P-450. The data presented here indicated that the lyophilized preparation of the liver 9,000xg supernatant as well as the fresh preparation can be used for the determination of the drug metabolizing enzyme activity.

The liver parenchyma and foreign compound metabolism in red-winged blackbird compared with rat

1. Aniline p-hydroxylase, aminopyrine N-demethylase, and p-nitroanisole O-demethylase activities were measured in liver microsomes prepared from the red-winged blackbird (Agelaius phoeniceus) and compared with analogous preparations from rat. All had lower activities in birds than in rats, when expressed in terms of microsomal protein. 2. Hepatic parenchyma of the bird was observed by electron microscopy to contain less endoplasmic reticulum than that of rat. This morphological difference may partially explain the species difference in enzyme activities. 3. Cytochrome P-450 levels were not sex-dependent in the red-winged blackbird, unlike rat, but the opposite was true for the rate of hydroxylation of aniline. 4. There was no species difference in the activity of aniline p-hydroxylase when expressed in terms of activities per unit of cytochrome P-450, but the activity of p-nitroanisole O-demethylase was higher in red-winged blackbird than in rat; the reverse may be true for the activity of aminopyrin N-demethylase.