Genetic variation in rates of antipyrine metabolite formation: a study in uninduced twins.

Abstract

Adult, male, unmedicated twins received antipyrine orally under carefully controlled environmental conditions. Relative contributions of genetic and environmental factors to 2-fold interindividual variations in rate constants for formation of the three main antipyrine metabolites were compared. Heritabilities for rate constants for formation of4-hydroxyantipyrine, Ndemethylantipyrine, and 3-hydroxymethylantipyrine were 0.88, 0.85, and 0.70, respectively. These results suggest that each molecular form of cytochrome P-450 that converts antipyrine to a different metabolite exhibits genetically controlled interindividual variations in activity. Unrelated adult male subjects whose environments were also carefully controlled exhibited highly reproducible rate constants for formation of antipyrine metabolites. Because the rate constant for metabolite formation sensitively detects certain variations in the gene product, it should be used in future pharmacogenetic studies on rates of production of multiple metabolites from a single parent drug.In 1968, causes of large interindividual variations in rates of antipyrine (AP) decay in normal adults were identified in monozygotic (MZ) and dizygotic (DZ) twins (1). Interindividual variations in AP clearance were maintained mainly by genetic factors. The twins lived in different households under nearly basal conditions with respect to multiple environmental factors capable of altering rates of AP clearance. In contrast to large interindividual variations, AP clearance in a given subject was highly reproducible, provided that no significant environmental perturbations occurred.The twin study reported 13 years ago measured only plasma AP kinetics (1). Because AP is degraded through multiple reactions catalyzed by enzymes independently influenced by numerous genetic and environmental factors, each metabolic pathway needs to be investigated separately. This approach, which was the objective of the present study, permitted a more specific estimate of gene activity than did the earlier study.In several species, including man, three primary metabolites ofAP have been identified: 3-hydroxymethyl-AP, N-demethyl-AP, and 4-hydroxy-AP (2-5). Each metabolite is formed by a separate hepatic cytochrome P450-mediated monooxygenase (6, 7). Conjugation then occurs to varying extents with glucuronide, rendering products even more water soluble and hence more easily excreted in urine where metabolites are identified (2-8). In the present study, under carefully controlled environmental conditions, the relative roles of heredity and environment in controlling large interindividual variations in rates of hepatic formation of each AP metabolite were assessed in twins by using new sensitive techniques for metabolite detection. These data were used to test different pharmacokinetic models of AP elimination. MATERIALS AND METHODSSelection of Subjects. Ten unrelated subjects, 10 pairs of MZ twins, and 10 pairs of DZ twins between the ages of 16 and 35 yr without previous serious illness were obta...

Polymorphism of theophylline metabolism in man.

“…They were carefully selected to be under near basal environmental conditions so that their rate of theophylline metabolism would be neither markedly induced nor inhibited. 15 of the 27 family members and several twins and unrelated subjects had previously participated in the AP studies performed in this laboratory (12,16). No subject had a history of serious illness or drug allergy, consumed any medications or ethanol regularly, smoked tobacco, or was chronically exposed to inducing or inhibiting chemicals.…”

“…In addition to providing blood, three subjects collected saliva samples, which were stimulated by chewing parafilm, at 4,8,12,16,20,24,28,32, and 36 h after drug administration. These three subjects did not take theophylline again.…”

“…Theophylline, when administered at a sub-therapeutic dose (5 mg/kg), and its three main metabolites, conform to an open one-compartment model with parallel, simultaneously occurring, first-order reactions in which excretion is faster than metabolite formation (23)(24)(25)(26)(27). Kinetic data on theophylline elimination were analyzed by two different methods, the Rate method and the SigmaMinus method described in detail elsewhere (16,26,27).…”

“…At 0800, after an 8-h fast, all subjects received an oral dose (5 mg/kg) of theophylline (Elixicon, by Berlex Laboratories). Saliva samples, stimulated by chewing parafilm, were collected at 2, 4, 6, 10, 16,20,24, and 28 h after theophylline.…”

Monogenic control of variations in antipyrine metabolite formation. New polymorphism of hepatic drug oxidation.

“…The results reflected not only the design of the particular study but also the criteria used to select subjects (1). The conclusion that genetic factors are primarily responsible for such variations Received for publication 24 September 1982 and in revised form 4 January 1983. among normal subjects under carefully controlled, relatively noninducing environmental conditions derived from studies using antipyrine (AP) (2)(3)(4),' amobarbital (5), dicoumarol (6), ethanol (7), halothane (8), phenylbutazone (9), phenytoin (10), and salicylate (11). Nevertheless, it is also well recognized that numerous other host factors, including many disease states, can alter the genetically controlled capacity of a subject to eliminate certain drugs (1).…”