Kinetic Interactions of Dopamine and Dobutamine with Human Catechol-O-methyltransferase and Monoamine Oxidase in Vitro

Abstract

Dopamine and dobutamine are often infused together into acutely ill patients requiring temporary support of cardiac and renal function, but whether these catecholamines affect the metabolic clearance of each other is not established. We determined the kinetics of dopamine and dobutamine as substrates and inhibitors of each other, i.e., apparent V max , K m , and K i , with crude preparations of human blood mononuclear cell catechol-O-methyltransferase (COMT) and platelet monoamine oxidase (MAO) at pH 7.4 and 37°C. Values of V max for dopamine and dobutamine as substrates for COMT were 0.45 and 0.59 nmol of 3-O-methyl product formed per milligram of protein per minute, whereas those for K m were 0.44 and 0.05 mM, respectively. Dopamine and dobutamine were competitive inhibitors of each other in this reaction. The K i for dopamine as an inhibitor of dobutamine methylation was 1.5 mM, whereas that for dobutamine as an inhibitor of dopamine methylation was 0.015 mM. Dopamine but not dobutamine was a substrate for MAO. The V max for dihydroxyphenylacetaldehyde formation from dopamine was 0.29 nmol/mg protein/min and the K m for dopamine was 0.38 mM. Dobutamine was a noncompetitive inhibitor of dopamine oxidation in this reaction (K i Х 1.19 mM). The high apparent K m and K i values derived for dopamine and dobutamine when tested with these two human enzymes in vitro suggest that these catecholamines do not interfere with the metabolism of each other when both are infused together at therapeutic concentrations.Dopamine and dobutamine are catecholamines commonly infused together to treat critically ill patients with shock and/or heart failure. Dopamine is a biogenic amine given at low doses to maintain or enhance renal and splanchnic perfusion, whereas dobutamine is a chemically related synthetic inotrope employed to enhance cardiac output without increasing systemic vascular resistance (Latifi et al., 2000). Whether dopamine and dobutamine affect the systemic clearance of each other when both compounds are administered together is unclear from reports of three pharmacokinetic studies (Banner et al., 1989(Banner et al., , 1991Schwartz et al., 1991).Catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO) are the two enzymes primarily responsible for the initial metabolic disposition of infused catecholamines in the blood of mammals (Kopin, 1985). Moreover, formation of 3-O-methyldobutamine catalyzed by COMT appears to be the main route for dobutamine biodisposition in the dog (Murphy et al., 1976), and we have recently shown that 3-O-methyldobutamine is a major product of infused dobutamine metabolism in humans (Yan et al., 2002). To our knowledge there is no published information as to whether dobutamine serves as a substrate for MAO in humans.To evaluate the roles of COMT and MAO in the metabolic clearance of coinfused dopamine and dobutamine and in possible metabolic interactions between these two inotropes in humans, we now report kinetic studies of dopamine and dobutamine used both as substrates and...

East–West pathology agreement on precancerous liver lesions and early hepatocellular carcinoma #

“…There are significant differences in β‐adrenergic receptor density in different parts of the heart,23,28,29 distribution of degrading enzymes, and local metabolism. Catechol‐O‐methyltransferase (COMT), the primary enzyme responsible for dobutamine degradation,30,31 is 10‐fold less active in the right atrium than in the left ventricle 32. Other studies have shown a regional variation in COMT activity in different chambers of the heart 33.…”

3-O-Methyldobutamine, a Major Metabolite of Dobutamine in Humans

“…Those studies also provided evidence that COMT activity in human blood mononuclear cell preparations reflects that found in human red blood cells, which in turn have been used extensively to characterize the genetics of human COMT (Weinshilboum et al, 1999). Recent kinetic studies with the human mononuclear cell preparation reveal that dobutamine and dopamine act as competitive inhibitors of each other for COMT activity and that dobutamine serves as the better substrate, largely due to its lower apparent K m (0.05 versus 0.44 mM) (Yan et al, 2002). These observations are in accord with a recent structure-activity kinetic study that showed that both catecholamines serve as substrates for a human recombinant COMT enzyme (Lautala et al, 2001).…”

Effects of Donor Pre-Treatment With Dopamine on Survival After Heart Transplantation

“…Dopamine is inactivated by oxidative deamination by mitochondrial monoamine oxidase and by O-methylation by catechol-O-methyltransferase. This rapid enzymatic degradation accounts for a half-life of a few minutes when dopamine is circulating in the blood (32,33). Dopamine's ability to protect against cold preservation injury depends on its diffusion into cells (34).…”