Enzyme-catalyzed processes of first-pass hepatic and intestinal drug extraction

Dd, Shen; Kl, Kunze; Thummel, KE

doi:10.1016/s0169-409x(97)00039-2

Cited by 258 publications

(132 citation statements)

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“…This finding is consistent with data published by Matsubara et al (2004), Takara et al (2003), and Takemoto et al (2003) showing decreasing expression of CYP3A mRNA and decreasing activity along the whole intestine. Even for the human equivalent CYP3A4 declining mRNA expression and activity profile along the human intestine could be demonstrated (Thummel et al, 1997). The same holds true for CYP2B1, which was also found to be less expressed at lower intestinal regions (Rosenberg, 1991;Takemoto et al, 2003).…”

Section: Mitschke Et Almentioning

confidence: 78%

Characterization of Cytochrome P450 Protein Expression along the Entire Length of the Intestine of Male and Female Rats

Mitschke

Reichel²,

Fricker³

et al. 2008

Drug Metab Dispos

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ABSTRACT:Intestinal cytochrome P450 (P450) proteins play an important role in the biotransformation of drugs and may significantly limit their oral absorption and bioavailability. Therefore, we have investigated the amount of P450 proteins via Western blot analysis along the entire intestine of male and female rats. Despite of the use of an inbred rat strain, controlled housing conditions for the animals, and a timed sample preparation, high interindividual differences in the expression of all P450 proteins was observed. CYP3A (135-243 fmol/mg of protein) and CYP2B1 (107-645 fmol/mg of protein) were the most abundant P450 isoforms in the duodenum and jejunum of rat intestine but were present in neither the ileum nor the colon. Compared with CYP2B1 and CYP3A, CYP2D1 (25-71 fmol/mg of protein) and CYP2C6 (3-10 fmol/mg of protein) were only expressed in minor amounts. CYP2C11 could not be identified in the entire rat intestine. In conclusion, this is the first systematic evaluation and quantification of the expression of P450 proteins along the entire length of the intestine in both male and female rats. These data will provide a basis for a better understanding of the extent of intestinal metabolism along the gastrointestinal tract.Absorption through the gut is a key step in the oral delivery of drugs. The main interface between gut lumen and the bloodstream is an epithelial cell layer consisting of polarized enterocytes controlling the passage of exogenous substances into the portal circulation. Enterocytes have a variety of structural features, including tight junctions reducing paracellular permeability, numerous drug transporters, and a set of metabolic enzymes that may all affect the entry of drugs into the body. The extent to which a drug is absorbed also depends on the intrinsic properties of the compound such as solubility, permeability, efflux or uptake transport properties, and susceptibility to metabolic degradation (Martinez and Amidon, 2002;Benet et al., 2004).Although the liver is known as the major site of first-pass extraction, recent studies have indicated that the small intestine also contributes significantly to the first-pass metabolism of many drugs, e.g., cyclosporine (Wu et al., 1995), nifedipine (Iwao et al., 2002), midazolam (Paine et al., 1996, and diltiazem (Iwao et al., 2004). It is known that several uptake and efflux transporter and P450 isoforms are expressed in the human and rat intestine (van de Kerkhof et al., 2007). If a drug is a substrate of efflux transporters, it may enter and exit the enterocytes several times, and, with each cycle, small quantities may be metabolized by cytochrome P450 (P450) enzymes localized in the endoplasmic reticulum. The P450 enzymes belong to a superfamily of heme proteins that show a broad substrate specificity, with substrates ranging in size from ethylene (M r 28) to cyclosporine (M r 1201) (Isin and Guengerich, 2007). Although the liver is regarded as the main organ of drug metabolism, P450 proteins are also expressed in other tissues, e.g., kidn...

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Section: Mitschke Et Almentioning

confidence: 78%

Characterization of Cytochrome P450 Protein Expression along the Entire Length of the Intestine of Male and Female Rats

Mitschke

Reichel²,

Fricker³

et al. 2008

Drug Metab Dispos

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“…The "true" E i would thus have ranged from ϳ20 to 60% (assuming the 6% estimate) or from 7 to 30% (assuming the 20% estimate). These values are considerably less than the extraction ratio predicted for the human intestine in vivo (ϳ99%) by Thummel et al (1997). One potential explanation for this discrepancy is that the modified Caco-2 cells have been shown to contain only 16 to 30% of the CYP3A4 present in human intestinal mucosal homogenates (Paine et al, 2002).…”

Section: Downloaded Frommentioning

confidence: 87%

“…Human intestinal microsomes exhibited a high and variable intrinsic clearance (V max /K m ) for saquinavir metabolism (0.6 -8.8 ml/min/mg), suggesting that intestinal CYP3A4 could play a major role (Fitzsimmons and Collins, 1997;Eagling et al, 2002). Indeed, based on estimates of the total amount of immunoreactive CYP3A protein in the entire small intestine (70 nmol) , the turnover of saquinavir by CYP3A4, and the average duration of saquinavir absorption (T max ), Thummel et al (1997) predicted that the high extraction ratio of saquinavir observed in vivo (0.96) (Williams et al, 1992) could be entirely attributed to first-pass metabolism in the intestine (i.e., the contribution by the liver need not be considered).…”

mentioning

confidence: 99%

Contributions of CYP3A4, P-glycoprotein, and Serum Protein Binding to the Intestinal First-Pass Extraction of Saquinavir

Mouly¹,

Paine²,

Watkins³

2004

J Pharmacol Exp Ther

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Using CYP3A4-expressing Caco-2 cell monolayers, we assessed the roles of CYP3A4-mediated metabolism, P-glycoprotein (P-gp)-mediated efflux, and serum protein binding in determining the extent of the intestinal first-pass extraction (E i ) of saquinavir. Saquinavir (5-40 M) was added to the apical compartment of culture inserts. After 3 h, apical and basolateral media and cell scrapings were analyzed for saquinavir and a major CYP3A4-mediated metabolite (M7). The intracellular concentration of saquinavir was estimated from the degree of inhibition of CYP3A4 catalytic activity (midazolam 1Ј-hydroxylation). Compared with vehicle, the P-gp inhibitor LY335979 (zosuquidar trihydrochloride) (0.5 M, apical) increased saquinavir cell content and M7 formation rate, but decreased the E i by ϳ50% due to a Ͼ90% increase in the amount of saquinavir recovered in the basolateral compartment. Compared with LY335779, physiological concentrations of basolateral serum proteins [human serum albumin and ␣1-acid glycoprotein (AAG)] increased saquinavir permeability by a similar degree but decreased the E i by ϳ50% due to a marked reduction in M7 formation. Increasing AAG concentration (1.0 -2.5 g/l) had no additional effect on permeability or E i . An estimate of the range of the E i of saquinavir (7-60%) was less than has been predicted based on in vitro data (Ͼ99%) but was consistent with a clinical study involving grapefruit juice. The incidental finding of greater M7 formation after basolateral compared with apical dosing could not be explained by differences in saquinavir cell content. We conclude that variable intestinal first-pass extraction of saquinavir in human immunodeficiency virus-infected patients could reflect variation in P-gp-mediated efflux and/or CYP3A4-catalyzed metabolism, but not in blood AAG levels.

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“…Cytochrome P450 (P450)-mediated drug metabolism in the small intestine could have a major impact on the bioavailability and, consequently, the therapeutic efficacy or toxicity of a given drug (Thummel et al, 1997;Lin et al, 1999;Suzuki and Sugiyama, 2000;Kaminsky and Zhang, 2003). Orally administered drugs are potentially subject to first-pass metabolism, initially in the small intestine, and then in the liver, before they reach systemic circulation.…”

Section: Introductionmentioning

confidence: 99%

Role of Intestinal Cytochrome P450 (P450) in Modulating the Bioavailability of Oral Lovastatin: Insights from Studies on the Intestinal Epithelium-Specific P450 Reductase Knockout Mouse

Zhu

D’Agostino²

2011

Drug Metab Dispos

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ABSTRACT:The extents to which small intestinal (SI) cytochrome P450 (P450) enzymes control the bioavailability of oral drugs are not well defined, particularly for drugs that are substrates for both P450 and the P-glycoprotein (P-gp). In this study, we have determined the role of SI P450 in the clearance of orally administered lovastatin (LVS), an anti-hypercholesterolemia drug, using an intestinal epithelium (IE)-specific P450 reductase knockout (IE-Cpr-null) mouse model. In the IE-Cpr-null mouse, which has little P450 activities in the IE, the oral bioavailability of LVS was substantially higher than that in wild-type (WT) mice (15 and 5%, respectively). In control experiments, the clearance rates were not different between the two strains, either for intraperitoneally dosed LVS, which bypasses SI metabolism, or for orally administered pravastatin, which is known to be poorly metabolized by P450. Thus, our results demonstrate a predominant role of SI P450 enzymes in the first-pass clearance of oral LVS. The absence of IE P450 activities in the IE-Cpr-null mice also facilitated the identification of the molecular targets for orally administered grapefruit juice (GFJ), which is known to inhibit LVS clearance in humans. We found that pretreatment of mice with oral GFJ enhanced the systemic exposure of LVS in WT, but not in IE-Cpr-null mice, a result suggesting that the main target of GFJ action in the small intestine is P450, but not P-gp.

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Enzyme-catalyzed processes of first-pass hepatic and intestinal drug extraction

Cited by 258 publications

References 145 publications

Characterization of Cytochrome P450 Protein Expression along the Entire Length of the Intestine of Male and Female Rats

Characterization of Cytochrome P450 Protein Expression along the Entire Length of the Intestine of Male and Female Rats

Contributions of CYP3A4, P-glycoprotein, and Serum Protein Binding to the Intestinal First-Pass Extraction of Saquinavir

Role of Intestinal Cytochrome P450 (P450) in Modulating the Bioavailability of Oral Lovastatin: Insights from Studies on the Intestinal Epithelium-Specific P450 Reductase Knockout Mouse

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