Summary
Human hepatic microsomes were isolated from wedge biopsies of the liver from 13 patients undergoing abdominal surgery. Ultrasonic homogenisation was used to increase the yield of microsomal monooxygenase activity (7-ethoxycoumarin O-deethylase, NADPH-cytochrome c reductase), resulting in a 30% higher total enzyme activity per g liver than preparation by other techniques. In 4 individual microsomal preparations the influence of cimetidine and ranitidine on Michaelis-Menten kinetics of O-deethylation and of reductase activity were studied. Without the H2-receptor blocking drugs, enzyme kinetics of O-deethylation with a Km of 51.0±16.4 µM (n=3) were obtained using Lineweaver-Burke plots. Both, cimetidine and ranitidine inhibited the O-deethylation; cimetidine had a five-fold higher inhibitory affinity (Ki 1.01 and 3.94 mM) to the monooxygenase than ranitidine (Ki 4.96 and 17.70 mM) in the uninduced liver. However, in liver from a patient with induced enzyme activity (Km=478.0 µM), the Ki of ranitidine was similar to that of cimetidine (Ki ran 3.57 versus Ki cim 2.49 mM). The reductase activity was not inhibited by ranitidine and only marginally so by cimetidine.
The results suggest that in human hepatic microsomes oxidative drug metabolism is inhibited by both H2-receptor antagonists. However, the inhibitory potency of the compounds seems to depend on the individual isozyme pattern of the hepatic microsomes. Thus, while cimetidine is an relatively nonspecific enzyme inhibitor, ranitidine might more selectively inhibit induced drug metabolizing enzymes.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Ahmad N, Black M (1977) The hepatic microsomal mixed function oxidase system in man: Cofactor effects and the influence of cholestasis. J Pharmacol Exp Ther 203: 397–408
Bahr VC, Groth C-G, Jansson H, Lundren G, Lind M, Glaumann H (1980) Drug metabolism in human liver in vitro: Establishment of human liver bank. Clin Pharmacol Ther 27: 711–725
Bell JA, Gower AJ, Martin LE, Millis ENC, Smith WP (1981) Interaction of H2-receptor antagonists with drug metabolizing enzymes. Biochem Soc Trans 9: 113–114
Bisswanger H (1979) Theorie und Methoden der Enzymkinetik. Verlag Chemie, Weinheim Deerfield Beach Basel, pp 55–102, 125–131, 152–168, 177–183
Boobis AR, Kahn GC, Whyte C, Brodie MJ, Davies DS (1981) Biphasic O-deethylation of phenacetin and 7-ethoxycoumarin by human and rat liver microsomal fractions. Biochem Pharmacol 30: 2451–2456
Boobis AR, Brodie MJ, Kahn GC, Fletcher DR, Saunders JH, Davies DS (1980) Monooxygenase activity of human liver in microsomal fractions of needle biopsy specimens. Br J Clin Pharmacol 9: 11–19
Breen KJ, Bury R, Desmond PV, Mashford ML, Morphett B, Westwood B, Shaw RG (1982) Effects of cimetidine and ranitidine on hepatic drug metabolism. Clin Pharmacol Ther 31: 297–300
Farrell GC, Looksley WGE, Powell LW (1979) Drug metabolism in liver disease: Activity of hepatic microsomal metabolizing system. Clin Pharmacol Ther 26: 483–492
Garg DC, Weidler DJ, Eshelman FN (1983) Ranitidine bioavailability and kinetics in normal male subjects. Clin Pharmacol Ther 33 [4]: 445–452
Haegerty AM, Castleden CM, Patel L (1982) Failure of ranitidine to interact with propranolol. Br Med J 284: 1304
Hajek KK, Cook NI, Novak RF (1982) Mechanism of inhibition of microsomal drug metabolism by imidazol. J Pharmacol Exper Ther 223: 97–104
Henry BA, Mac Conald IA, Kichingman G, Bell GD, Langmann MJS (1980) Cimetidine or ranitidine: Comparison of effects on hepatic drug metabolism. Br Med J 281: 775–778
Hoensch H, Hartmann F, Schomerus H, Bieck P, Dölle W (1979) Monooxygenase enzyme activity in alcoholics with varying degrees of liver damage. Gut 20: 666–672
Hoensch HP, Hutzel H (1982) Hemmung der fremdstoffabbauenden Enzymaktivität in der menschlichen Leber durch Ranitidine und Cimetidine. Verh Dtsch Ges Inn Med 88: 653–657
Imai Y (1979) Reconstituted O-dealkylase systems containing various forms of liver microsomal cytochrome P-450. J Biochem 86: 1697–1707
Kapitulnik J, Poppers PJ, Conney AH (1977) Comparative metabolism of benzo(a)pyrene and drugs in human liver. Clin Pharmacol Ther 21: 166–176
Kirch W, Hoensch H, Janisch HD (1984) Interactions and noninteractions with ranitidine. Clin Pharmacokinet 9: 493–510
Klotz U, Reimann IW, Ohnhaus EE (1983) Effect of ranitidine on the steady state pharmacokinetics of diazepam. Eur J Clin Pharmacol 24: 357–360
Knodell RG, Holtzmann JL, Crankshaw DL, Steele NM, Stanley LN (1982) Drug metabolism by rat and human hepatic microsomes in response to interaction with H2-receptor antagonists. Gastroenterology 82: 84–88
Lowry OH, Rosebrough NJ, Farr AL, Randall RJ (1951) Protein measurement with folin phenol reagent. J Biol Chem 193: 265–275
McCarthy DM (1983) Ranitidine or cimetidine. Ann Int Med 4: 551–553
Nebert DW, Negeshi M (1982) Multiple forms of cytochrome P-450 and the importance of molecular biology and evolution. Biochem Pharmacol 31: 2311–2317
Netter KJ, Seidel G (1964) An adaptively stimulated O-demethylating system in rat liver microsomes and its kinetic properties. J Pharmacol Exp Ther 146: 61–65
Park BK, Breckenridge AM (1981) Clinical implications of enzyme induction and enzyme inhibition. Clin Pharmacokinet 6: 1–24
Pelkonen O, Kaltiala EH, Larmi KI, Kärki NT (1974) Cytochrome P-450 linked monooxygenase system and drug induced spectral interactions in human liver microsomes. Chem Biol Interact 9: 205–216
Pelkonen O, Puurunen J (1980) The effect of cimetidine on in vitro and in vivo microsomal drug metabolism in the rat. Biochem Pharmacol 29: 3075–3080
Puurunen J, Sotaniemi E, Pelkonen O (1980) Effect of cimetidine on microsomal drug metabolism in man. Eur J Clin Pharmacol 18: 185–187
Rendic S, Kajfez F, Ruf HH (1983) Characterization of cimetidine, ranitidine and related structures: Interaction with cytochrome P-450. Drug Metab Dispos 11: 137–142
Rendic S, Sinjic V, Toso R, Kajfez F, Ruf HH (1979) Interaction of cimetidine with liver microsomes. Xenobiotica 9: 555–564
Rendic S, Alebic-Kolbah T, Kajfez F (1982) Interaction of ranitidine with liver microsomes. Xenobiotica 12: 9–17
Schöne B, Fleischmann A, Remmer H, Oldershausen HF von (1972) Determination of drug metabolizing enzymes in needle biopsies of human liver. Eur J Clin Pharmacol 4: 65–73
Somogyi A, Gugler R (1982) Drug interactions with cimetidine. Clin Pharmacokinet 7: 23–41
Spahn H, Mutschler E, Kirch W, Ohnhaus EE, Janisch HD (1983) Influence of ranitidine on plasma metoprolol and atenolol concentrations. Br Med J 286: 1546–1547
Speeg KV, Patwardhan RV, Avynt GR, Mitchell MC, Schenker S (1982) Inhibition of microsomal drug metabolism by histamin H2-receptor antagonists studied in vivo and in vitro in rodents. Gastroenterology 82: 89–96
Ulrich V, Weber P (1972) The O-dealkylation of 7-ethoxycoumarin by liver microsomes. Hoppe-Seylers Z Physiol Chem 353: 1171–1177
Vesell ES, Passananti GT (1973) Inhibition of drug metabolism in man. Drug Metab Dispos 1: 402–410
Williams CH, Kamin H (1962) Microsomal triphoshopyridine nucleotidecytochrome c reductase of liver. J Biol Chem 237: 587–595
Woodhouse KW, Williams FM, Mutch E, Wright P, James OFW, Rawlins MD (1984) The effect of alcoholic cirrhosis on the two kinetic components (high and low affinity of microsomal O-deethylation of 7-ethoxycoumarin in human liver. Eur J Clin Pharmacol 26: 61–64
Zeldis JB, Friedman LS, Isselbacher KJ (1983) Ranitidine: A new H2-receptor antagonist. N Engl J Med 309: 1368–1374
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Hoensch, H.P., Hutzel, H., Kirch, W. et al. Isolation of human hepatic microsomes and their inhibition by cimetidine and ranitidine. Eur J Clin Pharmacol 29, 199–206 (1985). https://doi.org/10.1007/BF00547422
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00547422