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The levels of drug-metabolizing enzymes (DMEs) and transporter proteins in the human intestine are pertinent to determine oral drug bioavailability. Despite the paucity of reports on such measurements, it is well recognized that these values are essential for translating in vitro data on drug metabolism and transport to predict drug disposition in gut wall. In the current study, clinically relevant DMEs [cytochrome P450 (P450) and uridine 5'-diphospho-glucuronosyltransferase (UGT)] and drug transporters were quantified in total mucosal protein preparations from the human jejunum ( n = 4) and ileum ( n = 12) using quantification concatemer-based targeted proteomics. In contrast to previous reports, UGT2B15 and organic anion-transporting polypeptide 1 (OATP1A2) were quantifiable in all our samples. Overall, no significant disparities in protein expression were observed between jejunum and ileum. Relative mRNA expression for drug transporters did not correlate with the abundance of their cognate protein, except for P-glycoprotein 1 (P-gp) and organic solute transporter subunit alpha (OST- α ), highlighting the limitations of RNA as a surrogate for protein expression in dynamic tissues with high turnover. Intercorrelations were found within P450 [2C9-2C19 ( P = 0.002, R 2 = 0.63), 2C9-2J2 ( P = 0.004, R 2 = 0.40), 2D6-2J2 ( P = 0.002, R 2 = 0.50)] and UGT [1A1-2B7 ( P = 0.02, R 2 = 0.87)] family of enzymes. There were also correlations between P-gp and several other proteins [OST- α ( P < 0.0001, R 2 = 0.77), UGT1A6 ( P = 0.009, R 2 = 0.38), and CYP3A4 ( P = 0.007, R 2 = 0.30)]. Incorporating such correlations into building virtual populations is crucial for obtaining plausible characteristics of simulated individuals. SIGNIFICANCE STATEMENT: A number of drug transporters were quantified for the first time in this study. Several intercorrelations of protein abundance were reported. mRNA expression levels proved to be a poor reflection of differences between individuals regarding the level of protein expression in gut. The reported abundance of drug-metabolizing enzymes and transporters and their intercorrelations will contribute to better predictions of oral drug bioavailability and drug-drug interactions by linking in vitro observations to potential outcomes through physiologically based pharmacokinetic models., (Copyright © 2020 by The Author(s).)

The objective of this study was to determine the activity of steroid- and eicosanoid-metabolizing enzymes in horses with varying BCSs. The BCSs of twenty non-pregnant, anoestrous mares were determined prior to euthanasia, and tissue samples were collected from the liver, kidney, adrenal gland, ovary and endometrium. Cytochrome P450 1A (CYP1A), 2C (CYP2C), 3A (CYP3A) and uridine 5'-diphospho-glucuronosyltransferase (UGT) activities were determined using luminogenic substrates. The MIXED procedure of SAS was used to test the effect of BCS on enzyme activity and differences between tissues. Activity of CYP1A in adrenals was increased (p ≤ .05) in BCS 5 versus BCSs 4 and 6. Activity of CYP1A in the liver was increased (p = .05) in BCS 4 versus BCSs 5 and 6. Activity of CYP1A was 100-fold greater (p < .0001) in the liver than in the adrenal, ovary and kidney. Activity of CYP2C was 100-fold greater (p < .0001) in the liver than in the adrenal, ovary and endometrium. Activity of CYP3A was only detectable in the liver. Activity of UGT in the kidney was decreased (p = .02) in BCS 4 versus BCSs 5 and 6. Activity of UGT was threefold greater (p < .0001) in the liver than in the kidney, whereas activity of UGT was ninefold greater (p < .0001) in the kidney than in the ovary and endometrium. In general, BCS did not alter the activity of steroid- and eicosanoid-metabolizing enzymes in horses. However, tissue differences in these enzymes indicated abundant hepatic metabolism in horses, which is similar to other livestock species., (© 2017 Blackwell Verlag GmbH.)

Cytochrome P450 (CYP) enzymes and uridine 5-diphospho-glucuronosyltransferase (UGT) enzymes are critical enzymes for drug metabolism. Both chemical drugs and traditional Chinese medicines are converted to more readily excreted compounds by drug metabolizing enzymes in human livers. Because of the disparate expression of CYP and UGT enzymes among different individuals, accurate quantification of these enzymes is essential for drug pharmacology, drug-drug interactions and drug clinical applications. The research progress in quantitative methods based on liquid chromatography-mass spectrometry for drug metabolizing enzymes in human liver microsomes in the recent decade is reviewed.

Purpose: To determine the liver expression of cytochrome P450 (CYPs) and uridine 5'-diphosphate-glucuronosyltransferases (UGTs), the major phase I and II metabolism enzymes responsible for clearance and detoxification of drugs, xenobiotic and endogenous substances., Methods: A validated isotope label-free method was established for absolute and simultaneous quantification of 9 CYPs (1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D, 2E1 and 3A4) and 5 UGTs (1A1, 1A4, 1A6, 1A9 and 2B7) in human liver microsomes using LC-MS/MS., Results: The LC-MS/MS method displayed excellent dynamic range (at least 250-fold) and high sensitivity for each of the signature peptides with acceptable recovery, accuracy and precision. The protein expression profile of CYP and UGT isoforms were then determined in match microsomes samples prepared from patients with HBV-positive human hepatocellular carcinoma (HCC). In the tumor microsomes, the average absolute amounts of 8 major CYP isoforms (except CYP2C19) and 3 UGT isoforms (UGT1A1, UGT1A4 and UGT2B7) were decreased significantly (p < 0.05), whereas UGT1A6 and UGT1A9 levels were unchanged (p > 0.05). In addition, among isoforms with altered expression, 6 of 8 CYP isoforms and all three UGT isoforms were much more variable in tumor microsomes. Lastly, the importance of CYP3A4 was greatly diminished whereas the importance of UGT1A6 was enhanced in tumor microsomes., Conclusion: The use of an isotope label-free absolute quantification method for the simultaneous determination of 9 CYPs and 5 UGTs in human liver microsomes reveals that expression levels of CYPs and UGTs in human liver are severely impact by HCC, which could impact drug metabolism, disposition and pharmacotherapy.

Purpose: Beagle dogs are used to study oral pharmacokinetics and guide development of drug formulations for human use. Since mechanistic insight into species differences is needed to translate findings in this species to human, abundances of cytochrome P450 (CYP) and uridine diphosphate glucuronosyltransferase (UGT) drug metabolizing enzymes have been quantified in dog liver and intestine., Methods: Abundances of enzymes were measured in Beagle dog intestine and liver using selected reaction monitoring mass spectrometry., Results: Seven and two CYPs were present in the liver and intestine, respectively. CYP3A12 was the most abundant CYP in both tissues. Seven UGT enzymes were quantified in the liver and seven in the intestine although UGT1A11 and UGT1A9 were present only in the intestine and UGT1A7 and UGT2B31 were found only in the liver. UGT1A11 and UGT1A2 were the most abundant UGTs in the intestine and UGT2B31 was the most abundant UGT in the liver. Summed abundance of UGT enzymes was similar to the sum of CYP enzymes in the liver whereas intestinal UGTs were up to four times more abundant than CYPs. The estimated coefficients of variation of abundance estimates in the livers of 14 donors were separated into biological and technical components which ranged from 14 to 49% and 20 to 39%, respectively., Conclusions: Abundances of canine CYP enzymes in liver and intestine have been confirmed in a larger number of dogs and UGT abundances have been quantified for the first time. The biological variability in hepatic CYPs and UGTs has also been estimated.

Chimeric mice with humanized liver (PXB mice) have been generated by transplantation of urokinase-type plasminogen activator/severe combined immunodeficiency mice with human hepatocytes. The purpose of the present study was to clarify the protein expression levels of metabolizing enzymes and transporters in humanized liver of PXB mice transplanted with hepatocytes from three different donors, and to compare their protein expressions with those of human livers to validate this human liver model. The protein expression levels of metabolizing enzymes and transporters were quantified in microsomal fraction and plasma membrane fraction, respectively, by means of liquid chromatography-tandem mass spectrometry. Protein expression levels of 12 human P450 enzymes, two human UDP-glucuronosyltransferases, eight human ATP binding cassette (ABC) transporters, and eight human solute carrier transporters were determined. The variances of protein expression levels among samples from mice humanized with hepatocytes from all donors were significantly greater than those from samples obtained from mice derived from each individual donor. Compared with the protein expression levels in human livers, all of the quantified metabolizing enzymes and transporters were within a range of 4-fold difference, except for CYP2A6, CYP4A11, bile salt export pump (BSEP), and multidrug resistance protein 3 (MDR3), which showed 4- to 5-fold differences between PXB mouse and human livers. The present study indicates that humanized liver of PXB mice is a useful model of human liver from the viewpoint of protein expression of metabolizing enzymes and transporters, but the results are influenced by the characteristics of the human hepatocyte donor.

Cytochrome P450 (P450) and uridine 5'-diphospho-glucuronosyltransferase (UGT) enzymes mediate a major proportion of phase I and phase II metabolism of xenobiotics. In vitro-in vivo extrapolation (IVIVE) of hepatic clearance in conjunction with physiologically-based pharmacokinetics (PBPK) has become common practice in drug development. However, prediction of xenobiotic kinetics in virtual populations requires knowledge of both enzyme abundances and the extent to which these correlate. A multiplexed quantification concatemer (QconCAT) strategy was used in this study to quantify the expression of several P450 and UGT enzymes simultaneously and to establish correlations between various enzyme abundances in 24 individual liver samples (ages 27-66, 14 male). Abundances were comparable to previously reported values, including CYP2C9 (40.0 ± 26.0 pmol mg(-1)), CYP2D6 (11.9 ± 13.2 pmol mg(-1)), CYP3A4 (68.1 ± 52.3 pmol mg(-1)), UGT1A1 (33.6 ± 34.0 pmol mg(-1)), and UGT2B7 (82.9 ± 36.1 pmol mg(-1)), expressed as mean ± S.D. Previous reports of correlations in expression of various P450 (CYP3A4/CYP3A5*1/*3, CYP2C8/CYP2C9, and CYP3A4/CYP2B6) were confirmed. New correlations were demonstrated between UGTs [including UGT1A6/UGT1A9 (r(s) = 0.82, P < 0.0001) and UGT2B4/UGT2B15 (r(s) = 0.71, P < 0.0001)]. Expression of some P450 and UGT enzymes were shown to be correlated [including CYP1A2/UGT2B4 (r(s) = 0.67, P = 0.0002)]. The expression of CYP3A5 in individuals with *1/*3 genotype (n = 11) was higher than those with *3/*3 genotype (n = 10) (P < 0.0001). No significant effect of gender or history of smoking or alcohol use on enzyme expression was observed; however, expression of several enzymes declined with age. The correlation matrix produced for the first time by this study can be used to generate more realistic virtual populations with respect to abundance of various enzymes.

A simplified, rapid, and selective liquid chromatography-tandem mass spectrometry method for the determination of the activities of cytochrome P450 (CYP) enzymes and UDP-glucuronosyltransferases (UGTs) in two separate settings was developed and successfully applied to 8 CYP isoenzymes and UGT2B7 enzyme activities in rat liver microsomes. The triple-quadrupole mass spectrometric detection was operated in positive mode for the probe metabolites: CYP1A2 (resorufin), CYP2B6 (hydroxybupropion), CYP2C19 (5-hydroxyomeprazole), CYP2D6 (dextrophan), CYP3A4 (6β-hydroxytestosterone), and UGT2B7 (morphine-3-glucuronide); also in negative mode for CYP2C9 (4-hydroxytolbutamide), CYP2E1 (6-hydroxychloroxazone), and CYP4A (hydroxylauric acid). The metabolic reactions were terminated with acetonitrile, containing metoprolol and acetaminophen as the internal standard for positive and negative ion electrospray ionization, respectively. The method was validated over the concentration range of 25-2500 ng/mL for 5-hydroxyomeprazole, dextrophan, hydroxylauric acid, and morphine-3-glucuronide; 5-500 ng/mL for resorufin; 3-300 ng/mL for hydroxybupropion; 10-1000 ng/mL for 4-hydroxytolbutamide; 40-4000 ng/mL for 6-hydroxychloroxazone; and 63-6300 ng/mL for 6β-hydroxytestosterone. All of the extraction recoveries of these analytes were greater than 85%, except for hydroxylauric acid at mid-concentration with a recovery of 83.2% ± 3.2%. The matrix effects were between 85.8% and 119.9%; the respective within- and between-run precisions were 0.9-12.0% and 2.0-13.9%; and the within- and between-run accuracy levels were 0.6-17.2% and 0.1-15.1%, respectively, for all these analytes. All of the analytes were stable during the assay and storage in the liver microsomes of Sprague-Dawley rats. The measurement activity of multiple enzymes was feasible using a cocktail approach. This method proved to be a robust, fast, accurate, specific and sensitive assay, and was successfully used to investigate in vivo enzyme activities of 8 major CYP isoenzymes and UGT2B7 in Sprague-Dawley rats with fatty livers. By the end of the eighth week, the CD-fed induced fatty liver rats showed a significant decrease in the activities of CYP1A2 and UGT2B7 as compared to the standard diet group., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Comprehensive identification of cytochrome P450 enzymes (CYPs) and uridine diphosphoglucuronosyl transferases (UGTs) in human liver microsomes (HLMs) was performed with an SDS-PAGE-free protocol. HLMs were solubilized with 5% v/v ionic liquid, 1-butyl-3-methyl imidazolium tetrafluoroborate, followed by tryptic digestion, and 2D-SCX-RPLC-ESI-MS/MS (LTQ XL) analysis in triplicate. In total, 27 CYPs and 12 UGTs were confidently identified with average sequence coverage as 30.99 and 25.07%, average peptide number as 14 and 13, and average unique peptide number as 7 and 4, respectively. The highly similar isoforms of CYP3A, CYP2C, and CYP4F subfamilies could be unambiguously differentiated from each other, despite the fact that the sequence similarity of CYP2C9 and CYP2C19 is 91%. In addition, protein spectral count was used to approximately evaluate the relative abundance of identified CYPs and UGTs, and the results agreed with previous immunochemistry reports., (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Background: The strenuous procurement of cultured human hepatocytes and their short lives have constrained the cell culture model of cytochrome P450 (CYP450) induction, xenobiotic biotransformation, and hepatotoxicity. The development of continuous non-tumorous cell line steadily containing hepatocyte phenotypes would substitute the primary hepatocytes for these studies., Results: The hepatocyte-like cells have been developed from hTERT plus Bmi-1-immortalized human mesenchymal stem cells to substitute the primary hepatocytes. The hepatocyte-like cells had polygonal morphology and steadily produced albumin, glycogen, urea and UGT1A1 beyond 6 months while maintaining proliferative capacity. Although these hepatocyte-like cells had low basal expression of CYP450 isotypes, their expressions could be extensively up regulated to 80 folds upon the exposure to enzyme inducers. Their inducibility outperformed the classical HepG2 cells., Conclusion: The hepatocyte-like cells contained the markers of hepatocytes including CYP450 isotypes. The high inducibility of CYP450 transcripts could serve as a sensitive model for profiling xenobiotic-induced expression of CYP450.

Background: Bile acid synthesis, transport and metabolism are markedly altered in experimental cholestasis. Whether such coordinated regulation exists in human cholestatic diseases is unclear. We therefore investigated expression of genes for bile acid synthesis, detoxification and alternative basolateral export and regulatory nuclear factors in primary biliary cirrhosis (PBC)., Material/methods: Hepatic CYP7A1, CYP27A1, CYP8B1 (bile acid synthesis), CYP3A4 (hydroxylation), SULT2A1 (sulphation), UGT2B4/2B7 (glucuronidation), MRP4 (basolateral export), farnesoid X receptor (FXR), retinoid X receptor (RXR), short heterodimer partner (SHP), hepatocyte nuclear factor 1alpha (HNF1alpha) and HNF4alpha expression was determined in 11 patients with late-stage PBC and this was compared with non-cholestatic controls., Results: CYP7A1 mRNA was repressed in PBC to 10-20% of controls, while CYP27 and CYP8B1 mRNA remained unchanged. SULT2A1, UGT2B4/2B7 and CYP3A4 mRNA levels were unaltered or only mildly reduced in PBC. MRP4 protein levels were induced three-fold in PBC, whereas mRNA levels remained unchanged. Expression levels of FXR, RXR, SHP, PXR, CAR, HNF1alpha and HNF4alpha were moderately reduced in PBC without reaching statistical significance., Summary/conclusions: Repression of bile acid synthesis and induction of basolateral bile acid export may represent adaptive mechanisms to limit bile acid burden in chronic cholestasis. As these changes do not sufficiently counteract cholestatic liver damage, future therapeutic strategies should aim at stimulation of bile acid detoxification pathways.

The effect of cigarette smoke on the expression of several cytochromes P450 (CYP) and UDP-glucuronosyl-transferases (UGT) was studied in mice. The animals were exposed to cigarette smoke for 4 to 30 days. Enzymatic activities supported by CYP1A1, 1A2, 2B, 2E1 and the glucuronidation activity toward phenols were measured in lung, liver and kidney microsomes. Cigarette smoke induced several CYPs, especially in lung. CYP2E1 was more induced than CYP1A1 in this organ. The expression of CYP2E1 was also increased in kidney (5.6 times after 30 days). The glucuronidation in kidney was non-sensitive to the treatment whatever substrate used. In contrast, this activity was enhanced in liver and particularly in lung, in which the glucuronidation of 1-naphthol and 2-hydroxybiphenyl was increased by 122 and 180%, respectively. Interestingly, the times of induction differed according to the substrate used, thus suggesting the presence of different UGTs active toward phenols that were differentially affected by cigarette smoke. The UGT activities toward phenols were low in lung, when compared with those measured in liver or kidney. In conclusion, cigarette smoke greatly affected both glucuronidation activity and the hydroxylation reactions supported by CYPs in mouse liver and lung.

The influence of dietary fiber on xenobiotic-metabolizing enzymes (XME) was assessed using germ-free rats fed inulin and other sources of fiber (wheat bran, carrot, cocoa and oat). The consumption of cocoa fiber greatly modified the hepatic cytochrome P450 isoenzymatic profile, causing a strong enhancement of 1A2 and 2B1/B2 forms, concomitant with a significant decrease of the constitutive form 2C11, compared with all of the other types of fiber. Moreover, rats fed the cocoa fiber diet had a higher specific activity of hepatic UDP-glucuronosyl transferase than their carrot fiber- and wheat bran-fed counterparts. Intestinal UDP-glucuronosyl transferase was unaffected by the type of ingested fiber. Diet composition also did not alter the specific activity of glutathione-S-transferase in the liver, small intestine, or colon. Using earlier results obtained in heteroxenic rats, we show that intestinal microflora plays a key role in some of the effects of fiber on XME, although this is not a necessary prerequisite for all of the liver alterations.

The activities of the conjugative enzymes, glutathione S-transferase and UDP-glucuronyl-transferase, have been measured in vitro in the livers of camels, guinea-pigs and rats. Some sex differences were observed in the levels of these conjugative enzymes. In rats and guinea-pigs, females had higher UDP-glucuronyltransferase activity than males. In camels, females had higher glutathione S-transferase activity than males. In these species, the cytochrome P-450 isozymes observed between the 50,000 and 60,000 mol. wt regions have been separated and characterized by SDS-polyacrylamide gel electrophoresis. Camels showed lower levels of all types of cytochrome P-450 isozymes, while guinea-pigs showed higher levels of most of these isozymes. In general, camels seemed to have the lowest drug-metabolizing enzyme activity when compared to rats and guinea-pigs.

Interleukin-1 beta (IL-1) is one of the major inflammation mediators, commonly reported to be an inhibitor of hepatic drug metabolism. We studied the effect of IL-1 treatment on various drug-metabolizing enzymes in male and female rats. IL-1 induced both cytochrome P450 (P450) 3A1 activity and protein in females, but in males, IL-1 repressed P450 3A2 activity, without decreasing the protein. P450 1A1 was impaired in males, but was retained after dexamethasone pretreatment. IL-1 did not change P450 2B1/2 activity and protein, but counteracted their induction by dexamethasone. Uridine diphospho-glucuronosyltransferase (UGT) 1A2 (bilirubin) activity and its induction by dexamethasone were not affected by IL-1 treatment. Both P450 2C11 and epoxide hydrolase activities were repressed by IL-1 treatment, and both activities were impaired after dexamethasone treatment. These results clearly demonstrate that IL-1 acts at different steps of protein synthesis and gene expression. The effect of IL-1 on P450 was isoform-dependent, indicating that IL-1 can act on pretranscriptional events. The discrepancy between the variations of the activities and the protein of P450 3A2 suggests a post-translational regulation. For P450 2C11, 3A1, and for microsomal epoxide hydrolase, but not for P450 1A1 and 2B1/2, IL-1 mimics the glucocorticoid effects. These differential effects can affect the kinetics and the bioavailability of drugs used in pathologies in which IL-1 is increased.

Resistance to chemotherapy is a significant problem in the treatment of colorectal carcinomas. To obtain insight into the mechanism of drug resistance, the expression of P-170 glycoprotein and biotransformation enzymes that are potentially able to contribute to drug resistance were investigated in paired samples of normal mucosa and tumors from 24 patients with colorectal cancer. In the tumors, glutathione S-transferase (GST) enzyme activity and content of GST-pi and P-170 glycoprotein were increased significantly compared with normal mucosa (P less than 0.03, P less than 0.003, and P less than 0.02, respectively). In contrast, GST-alpha and -mu, present in minor amounts compared with GST-pi, were downregulated in the tumor. Cytochrome P-450(4,5,6) and UDP-glucuronyltransferase (towards 4-nitrophenol and bilirubin) levels were significantly lower in the tumors (P less than 0.0001 and P less than 0.0002, respectively). Because decreased expression of cytochrome P-450 and increased levels of GST-pi and the P-170 glycoprotein have been implicated in (multi)drug resistance, these findings strongly suggest that in colorectal tumors the inherent resistance is multifactorial. Research to overcome this resistance should therefore be directed toward a combined treatment that eliminates all of these different mechanisms.

Biotransformation or drug-metabolising enzymes have an important function in the detoxication of ingested toxic, carcinogenic, or tumour promoting compounds. Enzyme activity and isoenzyme composition of three biotransformation systems: glutathione S-transferase, uridine diphosphate-glucuronosyltransferase, and cytochrome P-450 were studied in normal small and large intestinal mucosa from three kidney donors. The activity of most drug-metabolising enzymes decreases slightly from proximal to distal small intestine, whereas in the mucosa of the large intestine a sharp fall in activity was observed. The isoenzyme composition for each of the three biotransformation systems changed from the small to the large intestine. Class Alpha glutathione S-transferases were not expressed in the colon, in contrast to the small intestine where both Alpha and Pi class isoenzymes are present. In addition, with monoclonal antibodies fewer protein bands for UDP-glucuronosyltransferases and cytochrome P-450 were detected in the colon. In the small intestine both isoforms P-450(4) and P-450(5) were present, whereas in the colon only reduced amounts of cytochrome P-450(4) could be visualised. For UDP-glucuronosyltransferase, 53 and 54 kDa proteins could be detected in the small intestine, but in the colon there was only weak staining of the 54 kDa band. In the normal human colon enzymes are less active and there are fewer isoenzymes present in the mucosa than in the small intestine. This implies a lower level of the detoxifying potential in the colon, which might be important in regard to the high rates of carcinogenesis in the colon.

Two major transmembranal polypeptides of bovine olfactory epithelium were identified by SDS electrophoretic analysis of Triton X-114 solubilized membranes. Both polypeptides were present in large amounts in membranes of the olfactory epithelium but were barely detectable in membranes of the nasal respiratory epithelium. Both polypeptides are enriched in the deciliated epithelium as compared with isolated cilia. One of them is a glycoprotein with an apparent molecular mass of 56 kDa (gp56); the other is an unglycosylated protein with an apparent molecular mass of 52 kDa (p52). Sequence analysis of peptides obtained by CNBr cleavage of purified gp56 indicates that it is highly homologous to UDP-glucuronosyl transferase (UDPGT). Parallel analysis shows that p52 is highly homologous to cytochrome P-450 sequences of the IIA subfamily. This protein is assigned the name P-450olf2. Polyclonal antibodies were raised against synthetic peptides corresponding to gp56 and p52 peptide sequences. Immunoblots with these antibodies reveal the following properties of gp56 and p52: (1) they are enriched in the microsomal fraction of the bovine olfactory epithelium; (2) they are possibly specific to the olfactory epithelium, as we could not detect reactivity in microsomes derived from respiratory epithelium or lung, and only a very small amount of basal reactivity was seen with liver microsomes; (3) cross-reacting proteins exist in microsomes derived from the rat olfactory epithelium. These results are consistent with a mechanism whereby the microsomal enzymes are involved in odorant modification and clearance from the nasal tissue.

In humans, data on biotransformation enzymes in the intestine, and to a lesser extent in the liver, are rather scarce. Much knowledge about these enzymes is, therefore, obtained from animal studies. We were able to examine both small intestinal and hepatic tissue from a kidney donor and performed a systematic study on enzyme contents and distribution in these organs. In the small intestine the longitudinal distribution of cytochrome P450, glutathione S-transferase, and bilirubin uridine 5'-diphosphate (UDP)-glucuronosyltransferase declined from duodenum to ileum. Activity of 4-nitrophenol- and 4-methylumbelliferone UDP-glucuronosyltransferase increased or remained constant, respectively. Total and specific activity of most enzymes was much higher in the liver, except for bilirubin UDP-glucuronosyltransferase and glutathione S-transferase, where the small intestine contained 28.6% and 7.4% of total hepatic activity, respectively. The relatively great amount of bilirubin UDP-glucuronosyltransferase activity in the small intestinal mucosa of this patient, who probably suffered from Gilbert's syndrome, could indicate that under pathological conditions intestinal metabolism may contribute significantly to the clearance of bilirubin. With a monoclonal antibody, UDP-glucuronosyltransferase isoforms were immunodetectable in microsomes. In the liver, two bands, one of 57 kilodaltons and one in between 53 and 54 kilodaltons, were seen. In the proximal small intestine two isoforms (53 and 54 kilodaltons) were detected. However, in the distal small intestine where bilirubin UDP-glucuronosyltransferase activity was low, only one isoform (54 kilodaltons) was seen. This may indicate that bilirubin UDP-glucuronosyltransferase activity is correlated with the 53-kilodalton isoform. The presence of multiple UDP-glucuronosyltransferase isoforms in humans, similar to that described before in the rat, is further established by this study.

The protective effect of SKF 525-A on the suppression of cytochrome P-450 content and monooxygenase activities by treatment with CoCl2 and polyriboinosinic acid-polyribocytidylic acid [poly(I.C] was compared as a part of studies of suppression of drug metabolizing enzymes by interferon inducers. Induction of heme oxygenase activity by CoCl2 and poly (I.C) was not altered by simultaneous treatment with SKF 525-A. Depression of cytochrome P-450 content and benzphetamine N-demethylase activity by treatment with CoCl2 was prevented by co-treatment with SKF 525-A. This effect was explained by the prevention of release of heme from cytochrome P-450 by forming metabolic intermediate complexes with metabolites of SKF 525-A. On the other hand, poly(I.C) significantly suppressed P-450 content and benzphetamine N-demethylase and benzo [a] pyrene hydroxylase activities, even under simultaneous treatment with SKF 525-A. This inhibition by poly (I.C) was accompanied by weak staining of proteins corresponding to cytochrome P-450 in SDS gel electrophoresis. In addition, the activity of non-heme enzyme, 4-hydroxybiphenyl glucuronyltransferase, was suppressed by treatment with poly (I.C) but not by CoCl2-treatment. These findings strongly suggested that, unlike CoCl2, poly (I.C) suppressed cytochrome P-450 content and monooxygenase activities due to decreased synthesis or increased degradation of the apoprotein of cytochrome P-450 with slight contribution of the induced heme oxygenase.