Extrahepatic Drug Metabolism Research Articles

Drug Disposition Protein Quantification in Matched Human Jejunum and Liver From Donors With Obesity.

Mathematical models, such as physiologically‐based pharmacokinetic models, are used to predict, for example, drug disposition and toxicity. However, populations differ in the abundance of proteins involved in these processes. To improve the building and refinement of such models, they must take into account these interindividual variabilities. In this study, we used global proteomics to characterize the protein composition of jejunum and liver from 37 donors with obesity enrolled in the COCKTAIL study. Liver protein levels from the 37 donors were further compared with those from donors without obesity. We quantified thousands of proteins and could present the expression of several drug‐metabolizing enzymes, for the first time, in jejunum, many of which belong to the cytochrome P450 (CYP) (e.g., CYP2U1) and the amine oxidase (flavin‐containing) (e.g., monoamine oxidase A (MAOA)) families. Although we show that many metabolizing enzymes had greater expression in liver, others had higher expression in jejunum (such as, MAOA and CES2), indicating the role of the small intestine in extrahepatic drug metabolism. We further show that proteins involved in drug disposition are not correlated in the two donor‐matched tissues. These proteins also do not correlate with physiological factors such as body mass index, age, and inflammation status in either tissue. Furthermore, the majority of these proteins are not differently expressed in donors with or without obesity. Nonetheless, interindividual differences were considerable, with implications for personalized prediction models and systems pharmacology.

Correction to “Deletion of Microsomal Cytochrome b5 Profoundly Affects Hepatic and Extrahepatic Drug Metabolism”

Correction to “Deletion of Microsomal Cytochrome <i>b</i>₅ Profoundly Affects Hepatic and Extrahepatic Drug Metabolism”

Investigation of drug metabolism in various segments of small intestine in the rat

In the extrahepatic drug metabolism the intestinal tract can play an important role. These experiments were designed to study the biotransformation of p-nitrophenol (PNP) in the small intestine in the rat. Various segments of the small intestine (proximal and distal jejunum, terminal ileum) were perfused with isotonic solution in vivo containing different concentrations of PNP (20-100-500-1000 μM) and the concentrations of metabolites (PNP-G: p-nitrophenol glucuronide, PNP-S: p-nitrophenol sulfate) were determined in the perfusion medium. It was found a decreasing tendency in the glucuronidation from the proximal to distal segment of the small intestine: e.g. 430 nmol, 240 nmol, and 100 nmol PNP-G appeared in the perfusion medium in the proximal, distal jejunum and in the terminal ileum, respectively, when 500 μM PNP was luminally perfused for 90 minutes. Similar ratio was found at the luminal perfusion of other PNP-concentrations, too. Luminal appearance of sulfoconjugate of PNP was considerably lower and no clear gradient tendency in the formation of PNP-S could be detected in the small intestine from the proximal to distal segment. Our results show that there are considerable differences in drug metabolism in various segments of the small intestine. We have found a gradient conjugating activity from proximal to distal segment of small intestine in the glucuronidation of PNP.

Deletion of Microsomal Cytochromeb5Profoundly Affects Hepatic and Extrahepatic Drug Metabolism

We demonstrated recently that cytochrome b(5) plays an important in vivo role in hepatic cytochrome P450 (P450) function [J Biol Chem 283:31385-31393, 2008]. We have now generated a model in which cytochrome b(5) has been deleted in all tissues [cytochrome b(5) complete null (BCN)], which surprisingly results in a viable mouse despite the putative in vivo roles of this protein in lipid and steroid hormone metabolism and the reduction of methemoglobin. In contrast to the liver-specific deletion, complete deletion of cytochrome b(5) leads to a neonatal increase in the expression of many hepatic P450s at both the protein and mRNA level. In extrahepatic tissues, some changes in P450 expression were also observed that were isoform-dependent. In vitro cytochrome P450 activities in liver, kidney, lung, and small intestine of BCN mice were determined for a range of model substrates and probe drugs; a profound reduction in the metabolism of some substrates, particularly in lung, kidney, and small intestine, was observed. In vivo, the metabolism of metoprolol was significantly altered in BCN mice, in contrast to the previous finding in the liver-specific cytochrome b(5) deletion, suggesting that extrahepatic cytochrome b(5) plays a significant role in its disposition. Testicular Cyp17 hydroxylase and lyase activities were also significantly reduced by cytochrome b(5) deletion, leading to significantly lower levels of testicular testosterone. The BCN mouse provides an additional model system with which to further investigate the functions of cytochrome b(5), particularly in extrahepatic tissues.

Overview of extracellular microvesicles in drug metabolism

Importance of the field: Liver is the major body reservoir for enzymes involved in the metabolism of endogenous and xenobiotic compounds. Recently, it has been shown that hepatocytes release exosome-like vesicles to the extracellular medium, and the proteomic characterization of these hepatocyte-secreted exosomes has revealed the presence of several of these enzymes on them.Areas covered in this review: A systematic bibliographic search focused on two related aspects: i) xenobiotic-metabolizing enzymes that have been detected in microvesicles (MVs); and ii) MVs that are in the blood stream or secreted by cell types with clear interactions with this fluid.What the reader will gain: A discussion of these hepatocyte-secreted vesicles along with other MVs as enzymatic carriers in the context of extrahepatic drug-metabolizing systems.Take home message: The contribution of many tissues including the liver to the MV plasma population is supported by several reports. On the other hand, many enzymes involved in the metabolism of drugs have been detected in MVs. Together, these observations support a role of hepatic-MVs in spreading the liver metabolizing activities through the body contributing in this manner to extrahepatic drug metabolism systems what could be relevant for body homeostasis and pharmaceutical interests.

A new technique of one-stage total hepatectomy in the rat

Background. A small animal model of one-stage total hepatectomy is needed for the study of the consequences of fulminant liver failure and to investigate the extrahepatic metabolism of drugs metabolized by the liver. The models of hepatectomy described previously in the rat have the disadvantage of multiple stages, technical difficulty, or achievement of only an incomplete removal of the liver tissue. Methods. A Y-shaped graft was prepared from the inferior vena cava and the left renal vein of a donor rat. A total hepatectomy was performed in a recipient rat. The graft was placed and the portorenal and lower cavocaval anastomoses were performed by means of the polyethylene cuff technique. The upper cavocaval anastomosis was fashioned with a continuous suture. The procedure was performed on 49 rats, and the animals were studied for survival and biochemical profiles. Results. The surgical procedure took a mean of 40 ± 5 minutes and was not associated with any operative deaths. The portal clamping time did not exceed 15 minutes. Spontaneous mean survival of the anhepatic rats was 360 ± 30 minutes, and glucose supplemented animals had a mean survival time of 20 ± 5 hours. The anhepatic state was associated with significant metabolic and biochemical alterations. Conclusions. This procedure is quick to perform and does not require considerable microsurgical expertise. It provides a reproducible small animal model of total hepatectomy that is particularly useful for metabolic studies.

Extrahepatic metabolism of drugs in humans.

Although the liver plays the major role in drug metabolism [e.g. by oxidative cytochrome P450 (CYP)-dependent phase I and conjugation or phase II reactions], drug metabolising enzymes are also present at other sites. Depending on the particular drug and enzymes involved, these extrahepatic organs and/or tissues can contribute to the elimination of drugs and, thus, should be considered in any discussion of drug disposition. By the use of relatively new techniques in molecular biology, e.g. immunoblotting with antibodies directed to various CYP isoenzymes, the tissue and organ distribution of these drug metabolising enzymes can be determined. In addition, microsomal and cytosolic enzyme activity and capacity can be directly assessed in vitro by incubation of the enzymes with the drugs of interest. Both approaches have demonstrated the presence of 3 CYP families at different extrahepatic sites, such as the mucosa of the gastrointestinal tract, kidney, lung, brain or skin. Enzymes including epoxide hydrolases, hydrolysing enzymes, glutathione S-transferases, UDP-glucuronosyltransferases, sulphotransferases, N-acetyltransferases, and methyltransferases are discussed. Indirect evidence of extrahepatic drug metabolism can be generated from pharmacokinetic studies whenever total body clearance exceeds liver blood flow, or when severe liver dysfunction or anhepatic conditions do not affect metabolic clearance. Indeed, extrahepatic metabolism has been demonstrated for numerous drugs. Therefore, the metabolic profile and sites of enzymatic reactions for each drug should be determined.

Effects of some inducers on hepatic and extrahepatic drug metabolism in the mallard duck ( Anas platyrhynchos)

1. Cytochrome P-450-dependent activities were measured in the liver, duodenum and kidney of mallard ducks ( Anas platyrhynchos) after pretreatment with known inducers of these enzymes (phenobarbital, β-naphthoflavone, polychlorobiphenyls, and two imidazole fungicides, prochloraz and imazalil). 2. Liver enzymes were highly induced by phenobarbital, and to a lesser extent by β-naphthoflavone. Considerable differences were found between ducks and rodents in the nature of monooxygenase acivities expressed after pretreatment with these two compounds. PCBs and fungicides caused only minor modifications in cytochrome P-450 level and enzymatic activities. 3. Extrahepatic enzyme activities were induced by phenobarbital, and were modified only slightly by other compounds.

Effect of Erythromycin on Tricyclic Antidepressant Metabolism

Macrolide antibiotics such as erythromycin have been found to impair the hepatic metabolism of carbamazepine. In addition, recent studies have shown that intestinal flora can N-demethylate tricyclic antidepressants, suggesting that the human gut may be a possible site of extrahepatic drug metabolism. Therefore, we conducted a study to determine whether the concurrent use of erythromycin might influence the metabolism and steady-state plasma concentrations of tricyclic antidepressants. Six days of erythromycin administration caused no systematic change in either the parent tricyclic or its metabolite(s). Thus, the short term concurrent use of erythromycin does not appear to alter hepatic or gut flora tricyclic metabolism to an appreciable extent. Nevertheless, prior reports of altered carbamazepine kinetics by erythromycin should increase the physician's awareness of a possible drug interaction when erythromycin is used concurrently with a tricyclic antidepressant.

Extrahepatic Metabolism of Drugs and other Foreign Compounds

Extrahepatic Metabolism of Drugs and other Foreign Compounds

Book Review: Extrahepatic Metabolism of Drugs and Other Foreign Compounds

Book Review: Extrahepatic Metabolism of Drugs and Other Foreign Compounds

Alterations of drug metabolism in rats exposed to cigarette smoke.

In male rats exposed to cigarette smoke, antipyrine clearance was enhanced to the same extent as has been observed in human cigarette smokers. The activity of aryl hydrocarbon hydroxylase, a representative microsomal mixed function oxidase, was increased significantly in lung and kidney of smoke-exposed rats compared with controls. The activity of this enzyme in the liver, however, was not altered by cigarette smoke. Although aryl hydrocarbon hydroxylase activity in extrahepatic tissues was significantly enhanced after cigarette smoke exposures, the total drug metabolizing capacity of these tissues remained trivial compared with that of the liver. Hence, extrahepatic drug metabolism is unlikely to account for enhanced antipyrine elimination in cigarette smokers. The present study has established an animal model for studying the changes produced by cigarette smoke which result in enhanced drug metabolism in man.

Comparative alterations in extrahepatic drug metabolism by factors known to affect hepatic activity

Various factors known to alter hepatic drug metabolism were examined for their effects on drug metabolism in certain extrahepatic organs, viz. lung and kidney. The prominent sex-related differences in drug metabolism in rat liver were not seen in either lung or kidney. Pretreatment of rats with phenobarbital produced the expected large increases in hepatic NADPH cytochrome c reductase, cytochrome P-450. aminopyrine demethylase and biphenyl hydroxylase activities without concomitant changes in any of these parameters in lung, and only scattered and smaller changes in kidney. 3-Methylcholanthrene (3-MC) pretreatment significantly increased cytochrome P-450 levels in all three organs. Pretreatment of rats with carbon tetrachloride (CCl 4) produced consistent inhibition of mixedfunction oxidation in hepatic microsomes. but the extrahepatic effects were less predictable and were both organ- and enzyme-specific. An increase in renal UDP-glucuronyltransferase activity was observed after CCl 4 treatment that paralleled a similar but larger increase observed in liver. Extrahepatic NADPH cytochrome c reductase and N-methyl- p-chloroaniline demethylase values were unaffected by CCl 4. Lung and kidney responded in a like manner to liver to the additions in vitro of β-diethylaminoethyl diphenylpropylacetate (SKF-525A). Losses in enzyme activities in lung and kidney microsomes roughly paralleled those of liver when stored as pellets for up to 14 days at −70°. Two or 4 days of starvation produced substrate-specific changes in enzyme-specific activity in liver and kidney, with lung appearing resistant to the effect. When enzyme activity was expressed on a whole organ basis, however, lung cytochrome P-450 values decreased significantly and parameters from liver and kidney increased or decreased in a substrate-specific manner. It is concluded that some physiological and pharmacological factors that influence hepatic drug metabolism produce similar effects in lung and kidney, while other factors produce organ-specific effects.

Drugs and fetal metabolism.

Biochemical mechanisms related to oxidative and conjugative drug biotransformation are outlined, and the present knowledge about the development of the capacity of the human fetal liver to catalyze these reactions is summarized. The possible importance of extrahepatic drug metabolism in the human fetus is also discussed.