Metabolism human liver microsome

In efforts designed to replace the imidazopyridine ring system, indolizi-dines such as (32) [101] (human H3 if = 13 nM), and related heterocycles [102-104] were identified as potent H3 antagonists. Indolizidine (32) suffered from rapid metabolism in human liver microsomes, however, substitution on the indolizidine ring suppresses this liability. 

Fisher, M.B., Campanale, K., Ackermann, B.L. et al. (2000) In vitro glucuronidation using human liver microsomes and the pore-forming peptide alamethicin. Drug Metabolism and Disposition The Biological Fate of Chemicals, 28, 560-566. 

Chauret, N., Gauthier, A. and Nicoll-Griffth, D.A. (1998) Effect of common solvents on in vitro cytochrome P450 mediated metabolic activities in human liver microsomes. Drug Metabolism and Disposition The Biological Fate of Chemicals, 26, 1-4. 

Overall, the human intestine is capable of metabolizing UDP-glucuronyltransferase substrates, although the rates of metabolism are between 5- and 10-fold lower than those observed in human liver microsomes. However, the presence of a metabolic capacity towards UDP-glucuronyltransferase substrates at the level of the enterocyte can exert a significant gut wall first-pass extraction on oral administration. 

The metabolism of several CYP3A4 substrates in microsomes from the upper small intestine has been compared with liver microsomal metabolism. The results are summarized in Table 13.3. Thus, microsomes from the human upper small intestine can metabolize CYP3A4 substrates at rates approaching those found in human liver microsomes. However, the rate of metabolism in intestinal microsomes can be highly variable (8-fold for sirolimus [17] and 18- to 29-fold for midazolam [19]). 

Bangchang et al. [142] studied a number of antimalarial drugs for their effect on the metabolism of primaquine by human liver microsomes (N = 4) in vitro. The only metabolite generated was identified as carboxyprimaquine by cochromatography with the authentic standard. 

Iyer L, King CD, Whitington PF et al. Genetic predisposition to the metabolism of irinotecan (CPT-11). Role of uridine diphosphate glucuronosyltransferase isoform 1A1 in the glucuronidation of its active metabolite (SN-38) in human liver microsomes. J Clin Invest 1998 101 847-854. 

Two papers described the optimization of LLE and physicochemical properties in a series of pyrazole HTV nonnucleoside reverse transcriptase inhibitors (NNRTIs) and the selection of lersivirine (6) as a development candidate [15,16]. The early lead (7) was relatively lipophilic (clogP = 4.3), rapidly metabolized in human liver microsomes and had an LLE of only 1.9 [pIC50 (HIV RT) - clogP] [15]. An optimization program targeting increased LLE in less lipophilic compounds of low MW (to... 

The species differences in biotransformation pathways, rates of elimination, and intrinsic hepatic clearance of esfenvalerate and deltamethrin using rat and human liver microsomes were examined [33]. Esfenvalerate was eliminated primarily via NADPH-dependent oxidative metabolism in both rat and human liver microsomes. The CLint of esfenvalerate was estimated to be threefold greater in rodents than in humans on a per kg body weight basis. Deltamethrin was also eliminated primarily via NADPH-dependent oxidative metabolism in rat liver microsomes however, in human liver microsomes, deltamethrin was eliminated almost entirely via... 

NADPH-independent hydrolytic metabolism. The CLint for deltamethrin was estimated to be twice as rapid in humans as in rats on a per kg body weight basis. Metabolism by purified rat and human CESs was used to examine further the species differences in hydrolysis of deltamethrin and esfenvalerate. Results of CES metabolism revealed that hCEl was markedly more active toward deltamethrin than the Class I rat CESs, hydrolase A and B, and the Class II human CES, hCE2 however, hydrolase A metabolized esfenvalerate twice as fast as hCEl, whereas hydrolase B and hCEl hydrolyzed esfenvalerate at equal rates. These studies demonstrated a significant species difference in the in vitro pathways of biotransformation of deltamethrin in rat and human liver microsomes, which was due in part to differences in the intrinsic activities of rat and human CESs. 

He M, Rettie AE, Neal J, et al. Metabolism of sulfinpyrazone sulfide and sulfinpyrazone by human liver microsomes and cDNA-expressed cytochrome P450s. Drug Metab Dispos 2001 29(5) 701-711. 

Reid JM, Walker DL, Miller JK, et al. The metabolism of pyrazoloacridine (NSC 366140) by cytochromes p450 and flavin monooxygenase in human liver microsomes. Clin Cancer Res 2004 10(4) 1471-1480. 

Helsby, N.A., Ward, S.A., Howells, R.E. and Breckenridge, A.M. (1990) in vitro metabolism of the biguanide antimalarials in human liver microsomes evidence for a role of the mephenytoin hydroxylase (P450 MP)... 

Wienkers, L.C., Allievi, C., Hauer, M.J. and Wynalda, M.A. (1999) Cytochrome P-450-mediated metabolism of the individual enantiomers of the antidepressant agent reboxetine in human liver microsomes. Drug Metabolism and Disposition, 27 (11), 1334-1340. 

Ahmed, S.S., Napoli, K.L. and Strobel, H. W. (1995) Oxygen radical formation during cytochrome P450-catalyzed cyclosporine metabolism in rat and human liver microsomes at varying hydrogen ion concentrations. Molecular and Cellular Biochemistry, 151 (2),... 

Venkatakrishnan, K., von Molfke, L.L., Court, M.H., Harmatz, J.S., Crespi, C.L. and Greenblatt, D.J. (2000) Comparison between cytochrome P450 (CYP) content and relative activity approaches to scaling from cDNA-expressed CYPs to human liver microsomes ratios of accessory proteins as sources of discrepancies between the approaches. Drug Metabolism and Disposition, 28 (12), 1493-1504. 

Substrate-dependent effect of acetonitrile on human liver microsomal cytochrome P450 2C9 (CYP2C9) activity. Drug Metabolism and Disposition, 28 (5), 567-572. 

Palamanda, J., Feng, W.W., Lin, C.C. and Nomeir, A.A. (2000) Stimulation of tolbutamide hydroxylation by acetone and acetonitrile in human liver microsomes and in a cytochrome P-450 2C9-reconstituted system. Drug Metabolism and Disposition, 28 (1), 38-43. 

Several kinetic parameters can be measured on different experimental systems to account for the interaction of a compound with CYPs. For example when studying the metabolic stability of a compound, it could be measured in a recombinant CYP system, in human liver microsomes, in hepatocytes and so on. Each system increases in biological complexity. Although in the recombinant CYP system only the cytochrome under consideration is studied, in the case of the human liver microsomes, there is a pool of enzyme present that includes several CYPs, and finally in the hepatocyte cell system, metabolizing enzymes play an important role in the metabolic compound stability. In addition, transport systems are also present that could involve recirculation or other transport phenomena. The more complex the experimental system, the more difficult it is to extract information on the protein/ligand interaction, albeit it is closer to the in vivo real situation and therefore to the mechanism that is actually working in the body. 

In addition, compound 15 also had good metabolic stability in human liver microsome in vitro assay (hLM ti/2 = 39min) and in rat in vivo pharmacokinetic studies (ty2 = 3.3 h, po), with a rat oral bioavailability of 15%, showing a significant improvement in these PK parameters over the lead compound 1. The observed improvement in PK during the optimization was another validation of the strategy discussed above. This part of the optimization process is summarized in Scheme 19.2. 

K. M. Knights, R. Gasser, W. Klemisch, In vitro Metabolism of Acitretin by Human Liver Microsomes Evidence for an Acitretinoyl-Coenzyme A Thioester Conjugate in the Transesterification to Etretinate , Biochem. Pharmacol. 2000, 60, 507-516. 

Masubuchi Y, Hosokawa S, Horie T, Suzuki T, Ohmori S, et al. 1994. Cytochrome P450 isozymes involved in propranolol metabolism in human liver microsomes. The role of CYP2D6 as ring-hydroxylase and CYP1A2 as N-desisopro-pylase. Drug Metab Dispos 22 909-915. 

The major fecal metabolites in male rats administered a single oral dose of "C-heptachlor are heptachlor epoxide, 1-exo-hydroxychlordene, 1-exo-hydroxy-2,3-exo-epoxychlordene, and 1,2-dihydroxydihydrochlordene, as well as two unidentified products (Figure 2-2) (Tashiro and Matsumura 1978). By day 3, 50% of the dose was excreted in the feces. About 72% of the radioactivity was eliminated in the feces in the form of metabolites and 26.2% as parent compound by day 10. The same metabolites were identified in the comparative in vitro study using rat and human microsomal preparations (Tashiro and Matsumura 1978). Heptachlor epoxide is metabolized one step further to a dehydrogenated derivative of 1-exo-hydroxy-2,3-exo-epoxychlordene. Less than 0.1 % of radiolabel was seen of this compound in an in vitro study using human liver microsomes (Tashiro and Matsumura 1978). 

Cashman JR, Park SB, Yang ZC, Wrighton SA, Jacob P, 3rd, Benowitz NL (1992) Metabolism of nicotine by human liver microsomes stereoselective formation of trans-nicotine N -oxide. Chem Res Toxicol 5(5) 639-646... 

---