Disease relevance of Bufuralol

• Hydroxylation of the low-extraction drug bufuralol resulted in the formation of 251 +/- 25 nmol 1'OH-bufuralol/gm wet wt/hr in mildly diseased liver tissue and was significantly (p less than 0.01) reduced in liver tissue exhibiting chronic active hepatitis (166 +/- 23 nmol/gm wet wt/hr) and cirrhosis (124 +/- 21 nmol/gm wet wt/hr) [1].
• Purified recombinant P450 1A2 (expressed in E. coli) produced 1'-, 4-, and 6-hydroxybufuralol in a reconstituted system, although P450 2D6 (expressed in human lymphoblast cell lines) was found to catalyze only bufuralol 1'-hydroxylation.(ABSTRACT TRUNCATED AT 400 WORDS)[2]
• A rat liver cDNA library was prepared using the expression vector bacteriophage lambda gt11 and plaques were screened using polyclonal antibodies raised to purified rat liver cytochrome P-450UT-H, the major enzyme involved in debrisoquine 4-hydroxylation, bufuralol 1'-hydroxylation, and sparteine delta 5-oxidation [3].
• All three beta-adrenoceptor antagonists reduced exercise tachycardia, but at the doses chosen the effects of bufuralol were less than those of propranolol [4].
• Simultaneous hemodynamic and equilibrium radionuclide function measurements were performed at rest and during exercise before and 75 min after oral administration of 30 mg bufuralol, a nonselective beta-adrenoceptor blocking drug, in 10 patients with stable angina pectoris [5].

High impact information on Bufuralol

• We demonstrate that anti-LKM1 IgGs specifically inhibit the hydroxylation of bufuralol in human liver microsomes [6].
• Using two assay systems with different selectivity for the two cytochrome P-450 isozymes catalyzing bufuralol metabolism in human liver, we show that anti-LKM1 exclusively recognizes cytochrome P-450db1 [6].
• Cigarette smoke condensate strongly inhibited the activation of several potent procarcinogens by human liver microsomes, particularly the reactions catalyzed by P-450 1A2, but was not so inhibitory of the activation reactions catalyzed by P-450 3A4 and of P-450 2D6-catalyzed bufuralol 1'-hydroxylation [7].
• The only agent to inhibit bufuralol hydroxylation was vinblastine, which did so with a Ki of 90 microM (Km of the enzyme for the substrate = 12 microM) [8].
• A cDNA coding for an allelic variant of rat IID1, designated IID1v, was isolated that produced a P-450 having a 10-fold lower catalytic activity toward the substrate bufuralol when expressed in COS-1 cells (Matsunaga, E., Zanger, U. M., Hardwick, J. P., Gelboin, H. V., Meyer, U. A., and Gonzalez, F. J. (1989) Biochemistry, 28, 7349-7355) [9].

Chemical compound and disease context of Bufuralol

• Of greater significance however, was the finding that intact E. coli cells, even in the absence of exogenous NADPH, were able to metabolize bufuralol at rates almost as high as those measured in membranes (4.6 +/- 0.4 min-1 versus 5.7 +/- 0.2 min-1 at 50 microM substrate) [10].
• CYP2D6, Cyp2d-9 and both mutant CYP2D6 proteins were co-expressed with NADPH cytochrome P-450 reductase as a functional mono-oxygenase system in Escherichia coli and their relative catalytic activities towards bufuralol and testosterone were determined [11].

Biological context of Bufuralol

• Twenty-four genetic polymorphisms in the CYP2D6 gene were analysed in liver DNA samples of 39 Japanese and 44 Caucasians and compared with CYP2D6 protein levels and bufuralol 1'- and 6-hydroxylation activities in liver microsomes of these human samples [12].
• The kinetics of bufuralol 1'-hydroxylase activity of hepatic microsomal fractions have been determined in female DA and Fischer 344 rats, strains between which there is a large difference in debrisoquine 4-hydroxylase activity [13].
• This may mean that the competing drug also is metabolized by P-450dbl and that its metabolism is subject to the same genetic variation as the oxidation of bufuralol [14].
• Quinidine was a potent inhibitor of the 4-hydroxylation of debrisoquine and the 1'-hydroxylation of bufuralol, with IC50 values of 0.7 and 0.2 microM, being around 100 times more potent in this respect than quinine [15].
• Finally, a similar prediction using literature bufuralol data, coupled with the observed protein binding data, was used to illustrate that the most accurate predictions of bufuralol clearance are obtained when the amount of protein in the incubation is kept to a minimum and the overall incubation time is less than 20 min [16].

Anatomical context of Bufuralol

• Antibodies against P-450 buf I and P-450 buf II inhibited bufuralol 1'-hydroxylation in microsomes of in vivo and in vitro phenotyped poor metabolizer individuals demonstrating that the residual activities are immunochemically related to the activities in extensive metabolizers [17].
• Baculovirus-expressed 2D6 was used to immunize mice for hybridoma production and two clones yielded monoclonal antibodies, that were positive against 2D6 by ELISA and inhibited 2D6 catalysed metabolism of bufuralol, dextromethorphan and phenanthrene by more than 90% [18].
• The bufuralol/debrisoquine monooxygenase activity ratios were higher in kidney and lung, and lower in cerebral cortex and spleen than in liver [19].
• Debrisoquine 4-monooxygenase and bufuralol 1'-monooxygenase activities were found in liver, and at low levels in cerebral cortex, kidney cortex, lung, small intestine and spleen [19].
• Hepatic subcellular fractions from cynomolgus and rhesus monkeys showed significantly higher activities than those from humans for ethoxyresorufin O-deethylase, bufuralol 1'-hydroxylase, midazolam 1'-hydroxylase, erythromycin N-demethylase, acetaminophen UDP-glucuronosyltransferase, acetaminophen sulfotransferase, and tolbutamide 4-hydroxylase [20].

Associations of Bufuralol with other chemical compounds

• The capacity of human liver microsomes from 28 individuals to metabolize debrisoquine and bufuralol, two drugs oxidized polymorphically in humans, as well as the carcinogen 2-acetylaminofluorene (AAF), was determined [21].
• Using the inhibitor quinidine, a Ki of 0.06 microM was observed with P-450 buf I as opposed to 80 microM with P-450 buf II for bufuralol 1'-hydroxylation [17].
• These observations might suggest that quinidine oxidation is catalyzed by the same P-450 forms that oxidize debrisoquine, bufuralol, and sparteine; i.e., rat P-450UT-H and P-450DB [22].
• At least five other, minor, bufuralol products were formed by human liver microsomes, in addition to 1'-hydroxybufuralol [2].
• In both applied orthogonal HPLC modes we observed that use of TCPB containing electrodes (no addition of neutral macrocyclic ionophores) gives more than five fold improvement in limit of detection down to 10(-7) M for mabuterol, bufuralol, alprenolol and tertatolol in comparison with UV detection [23].

Gene context of Bufuralol

• This cell line exhibits bufuralol 1'-hydroxylase activity and immunologically detectable CYP2D6 protein [24].
• Neither apo- nor holo-b5 increased bufuralol 1'-hydroxylation activity by CYP1A1 or 2D6 or theophylline 8-hydroxylation by CYP1A2 [25].
• All six compounds reversibly inhibited CYP2D6 (bufuralol 1'-hydroxylation) and CYP2C9 (tolbutamide methyl hydroxylation) activities [26].
• Based on the intrinsic formation clearances and the results of inhibition experiments (CYP2D6, 50 microM bufuralol; FMO3 mediated, 100 mM methionine) using human liver microsomes, it was estimated that CYP3A contributes to >80% of K11777 metabolite formation [27].
• Microsomes prepared from CYP1B1 cDNA expressing cells exhibit elevated levels of 7-ethoxy-resorufin deethylase (EROD), 7-ethoxy-4-trifluoromethyl-coumarin deethylase (EFCD), benzo(alpha)pyrene hydroxylase (BPH), bufuralol 1'-hydroxylase, testosterone hydroxylase activities and spectrally quantifiable cytochrome P450 [28].

Analytical, diagnostic and therapeutic context of Bufuralol

• The DA rat has been proposed as an animal model for the human debrisoquine 4-hydroxylase/bufuralol 1'-hydroxylase genetic deficiency [29].
• A Caucasian having CYP2D6*3/*5 had a protein with slower gel mobility (immunoblotting with anti-CYP2D6 antibody) and very low activity for bufuralol 1'-hydroxylation [12].
• Determination of bufuralol and its major metabolites in plasma by high-performance liquid chromatography [30].
• Binding of bufuralol, dextromethorphan, and 3,4-methylenedioxymethylamphetamine to wild-type and F120A mutant cytochrome P450 2D6 studied by resonance Raman spectroscopy [31].
• After oral administration of bufuralol non-linear kinetics may occur [32].

References