Cytochromes P450 mediating the <i>N</i>‐demethylation of amitriptyline

Ghahramani, Parviz; Ellis, S. W.; Lennard, M. S.; Ramsay, Lawrence E.; Tucker, Geoffrey T.

doi:10.1046/j.1365-2125.1997.05382.x

Cited by 66 publications

(18 citation statements)

References 4 publications

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“…However, our study suggests that the affinity of amitripty line for CYP 2C 19 is more than 10 times high er than that of mephenytoin (Km 13 pmol/1 compared to Km values in the range of 200-300 pmol/1 for mephenytoin as reported by Hall et al [14]). Thus, no measurable inhibi tion is expected to take place in the experi ment designed by Ghahramani et al [9]. An analogous problem has occurred with regard to in vitro studies on imipramine N-demethylation.…”

Section: Discussionmentioning

confidence: 94%

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Metabolism of the Tricyclic Antidepressant Amitriptyline by cDNA-Expressed Human Cytochrome P450 Enzymes

Olesen

Línnet

1997

Pharmacology

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The metabolism of amitriptyline was studied in vitro using cDNA-expressed human cytochrome P450 (CYP) enzymes 1A2, 3A4, 2C9, 2C19, 2D6 and 2E1. CYP 2C19 was the most important enzyme with regard to the demethylation of amitriptyline, the quantitatively most important metabolic pathway. CYP 1A2, 3A4, 2C9 and CYP 2D6 also participated in the demethylation of amitriptyline. CYP 2D6 was the sole enzyme mediating the hydroxylation of amitriptyline, and (E)-10-OH-amitriptyline was exclusively produced. CYP 2E1 did not metabolize amitriptyline. Concerning the quantitative relations, CYP 2C19 and 2D6 exhibited high affinities with K_m values in the range of 5-13 µmol/l, whereas the affinities of 1 A2, 3A4 and 2C9 were somewhat lower with K_m values ranging from 74 to 92 µmol/l. CYP 2C19 displayed the highest reaction capacity per mole with V_max equal to 475 mol h^–1 (mol CYP)^–1. The other enzymes had V_max values in the range of 90–145 mol h^–1 (mol CYP)^–1. Allowing for the typical relative distribution of amounts of CYP enzymes in the liver, a simulation study suggested that, at therapeutic doses, on average about 60% of the metabolism depended on CYP 2C19. At toxic doses, CYP 2C19 is expected to be saturated, and CYP 3A4 may now play a dominant role in the metabolism.

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Section: Discussionmentioning

confidence: 94%

“…Ghahramani et al [9] found support for involvement of CYP 3A4. 2C9 and 2D6 on the basis of hepatic microsomal studies with selective inhibition of CYP isoforms, but were unable to establish a role for 2C19, which one should have ex pected from the cited in vivo study.…”

Section: Discussionmentioning

confidence: 99%

Metabolism of the Tricyclic Antidepressant Amitriptyline by cDNA-Expressed Human Cytochrome P450 Enzymes

Olesen

Línnet

1997

Pharmacology

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“…For example, CYP2D6 can metabolizes progesterone (8) and pregnenolone (9), and Guengerich et al have recently described a spirosulphonamide as a high affinity substrate of CYP2D6, which lacks a basic nitrogen (10). Furthermore, the enzyme can catalyze N-dealkylation reactions of substrates such as deprenyl (11), amitriptyline (12), methamphetamine (13), the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (14), and dextromethorphan (15), a commonly used antitussive.…”

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confidence: 99%

Residues Glutamate 216 and Aspartate 301 Are Key Determinants of Substrate Specificity and Product Regioselectivity in Cytochrome P450 2D6

Paine¹,

McLaughlin²,

Flanagan³

et al. 2003

Journal of Biological Chemistry

107

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Cytochrome P450 2D6 (CYP2D6) metabolizes a wide range of therapeutic drugs. CYP2D6 substrates typically contain a basic nitrogen atom, and the active-site residue Asp-301 has been implicated in substrate recognition through electrostatic interactions. Our recent computational models point to a predominantly structural role for Asp-301 in loop positioning (Kirton, S. B., Kemp, C. A., Tomkinson, N. P., St.-Gallay, S., and Sutcliffe, M. J. (2002) Proteins 49, 216 -231) and suggest a second acidic residue, Glu-216, as a key determinant in the binding of basic substrates. We have evaluated the role of Glu-216 in substrate recognition, along with Asp-301, by sitedirected mutagenesis. Reversal of the Glu-216 charge to Lys or substitution with neutral residues (Gln, Phe, or Leu) greatly decreased the affinity (K m values increased 10 -100-fold) for the classical basic nitrogen-containing substrates bufuralol and dextromethorphan. Altered binding was also manifested in significant differences in regiospecificity with respect to dextromethorphan, producing enzymes with no preference for N-demethylation versus O-demethylation (E216K and E216F). Neutralization of Asp-301 to Gln and Asn had similarly profound effects on substrate binding and regioselectivity. Intriguingly, removal of the negative charge from either 216 or 301 produced enzymes (E216A, E216K, and D301Q) with elevated levels (50 -75-fold) of catalytic activity toward diclofenac, a carboxylate-containing CYP2C9 substrate that lacks a basic nitrogen atom. Activity was increased still further (>1000-fold) upon neutralization of both residues (E216Q/D301Q). The kinetic parameters for diclofenac (K m 108 M, k cat 5 min ؊1 ) along with nifedipine (K m 28 M, k cat 2 min ؊1) and tolbutamide (K m 315 M, k cat 1 min ؊1 ), which are not normally substrates for CYP2D6, were within an order of magnitude of those observed with CYP3A4 or CYP2C9. Neutralizing both Glu-216 and Asp-301 thus effectively alters substrate recognition illustrating the central role of the negative charges provided by both residues in defining the specificity of CYP2D6 toward substrates containing a basic nitrogen.Cytochromes P450 are a superfamily of heme-containing enzymes responsible for the oxidative metabolism of an extremely wide variety of substrates. Human cytochrome P450 2D6 (CYP2D6) 1 is one of the most important members of this family due to its central role in the metabolism of many drugs in common clinical use (1), such as opioids, antidepressants, neuroleptics, and various cardiac medications. CYP2D6 is polymorphic, giving rise to wide interindividual and ethnic differences in drug metabolism (2, 3). Inheritance of the defective gene results in the "poor metabolizer" phenotype that results in impaired drug oxidation reactions (4) and may be linked to altered disease susceptibility (5, 6). P450-drug and drug-drug interactions involving CYP2D6 ligands are a prime consideration in the development of new drugs, emphasizing the importance of a detailed understanding of the factors that gover...

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“…The liver metabolism considered amitriptyline biotransformation by CYP isoforms 1A2, 2B6, 2C8, 2C9, 2C19, 2D6, and 3A43435. The values of the maximal rate of saturating substrate concentrations (Vmax), Michaelis constants (Km) and Inter System Extapolation Factors (ISEF) used in the model are reported in the Table (4).…”

Section: Methodsmentioning

confidence: 99%

“…Values are after34. † Denotes another source of data i.e.,35.ISEF values correspond to B-Cell Lymphoma model and are taken from Simcyp Simulator.…”

Section: Figurementioning

confidence: 99%

A four-compartment PBPK heart model accounting for cardiac metabolism - model development and application

Tylutki

Polak

2017

Sci Rep

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In the field of cardiac drug efficacy and safety assessment, information on drug concentration in heart tissue is desirable. Because measuring drug concentrations in human cardiac tissue is challenging in healthy volunteers, mathematical models are used to cope with such limitations. With a goal of predicting drug concentration in cardiac tissue, we have developed a whole-body PBPK model consisting of seventeen perfusion-limited compartments. The proposed PBPK heart model consisted of four compartments: the epicardium, midmyocardium, endocardium, and pericardial fluid, and accounted for cardiac metabolism using CYP450. The model was written in R. The plasma:tissues partition coefficients (Kp) were calculated in Simcyp Simulator. The model was fitted to the concentrations of amitriptyline in plasma and the heart. The estimated parameters were as follows: 0.80 for the absorption rate [h−1], 52.6 for Kprest, 0.01 for the blood flow through the pericardial fluid [L/h], and 0.78 for the P-parameter describing the diffusion between the pericardial fluid and epicardium [L/h]. The total cardiac clearance of amitriptyline was calculated as 0.316 L/h. Although the model needs further improvement, the results support its feasibility, and it is a first attempt to provide an active drug concentration in various locations within heart tissue using a PBPK approach.

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Cytochromes P450 mediating the N‐demethylation of amitriptyline

Cited by 66 publications

References 4 publications

Metabolism of the Tricyclic Antidepressant Amitriptyline by cDNA-Expressed Human Cytochrome P450 Enzymes

Metabolism of the Tricyclic Antidepressant Amitriptyline by cDNA-Expressed Human Cytochrome P450 Enzymes

Residues Glutamate 216 and Aspartate 301 Are Key Determinants of Substrate Specificity and Product Regioselectivity in Cytochrome P450 2D6

A four-compartment PBPK heart model accounting for cardiac metabolism - model development and application

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