| Investigator: | Daniel T. O'Connor, MD |
|---|---|
| Group: | APP |
| Genes Studied: | CYP2D6, CYP3A4, CYP3A5 |
| Drugs Studied: | yohimbine |
| Diseases Studied: | Hypertension |
| Number of columns (phenotypes): | 12 |
| Number of rows (proteins): | 3 |
Details
a2-adrenergic blockade has been used to investigate adrenergic dysfunction in human hypertension, suggesting a discrete subset of individuals at genetic risk of hypertension with exaggerated sympathetic responses to the a2-antagonist yohimbine. a2-blockade may also be useful in the treatment of impotence/erectile dysfunction, orthostatic hypotension in autonomic failure, xerostomia (dry mouth), narcolepsy, sensorineural deafness, and depression. However, the role of pharmacokinetic determinants of yohimbine disposition is not completely understood in these settings, particularly in diverse human populations.
This phenotype file investigates the in vitro metabolism of yohimbine. Yohimbine, at a substrate concentration from 1 to 250 uM, was incubated in the presence of microsomes from cells containing heterologously expressed CYP (cytochrome P-450) isoforms co-expressed with CYP/NADPH reductase. CYP2D6, CYP3A4 and CYP3A5, expressed in a baculovirus system (Gentest Corp., Woburn, MA), were aliquotted and stored at -80 degrees C, and thawed on ice before use. Microsomes were used at various protein concentrations (0.120, 0.116 and 0.118 mg/ml for CYP2D6, CYP3A4 and CYP3A5, respectively) in the presence of NADP (1.3 mM), glucose-6-phosphate (3.3 mM), MgCl2 (3.3 mM), and glucose 6-phosphate dehydrogenase (0.2 U) in a total volume of 0.5 ml of 100 mM potassium phosphate (pH 7.4). In preliminary experiments, the time courses of metabolite formation were checked to define conditions of reaction linearity (5 to 40 minutes) and to assure an overall substrate consumption lower than 10%. Reactions, performed in triplicate, were initiated by addition of cofactors, followed by incubation for 10 minutes at 37 degrees C in a shaking water bath open to the atmosphere. Reactions were stopped by addition of CH2Cl2 (4 ml) and the mixture was immediately shaken for 5 minutes and then centrifuged. The organic layer (3.5 ml) was evaporated to dryness under a nitrogen stream.
Categories of Pharmacogenetic Knowledge
FA
Molecular and Cellular Functional Assays
Publications
Primary phenotype data has been submitted and is available
Primary genotype data has been submitted and is available
Literature annotations available
| Relationship | Reference |
|---|---|
|
Human sympathetic activation by alpha2-adrenergic blockade with yohimbine: Bimodal, epistatic influence of cytochrome P450-mediated drug metabolism. Clin Pharmacol Ther. 2004. Le Corre Pascal, Parmer Robert J, Kailasam Mala T, Kennedy Brian P, Skaar Todd P, Ho Herbert, Leverge Roger, Smith Douglas W, Ziegler Michael G, Insel Paul A, Schork Nicholas J, Flockhart David A, O'connor Daniel T. PMID: 15289791. |
|
Expression of altered alpha2-adrenergic phenotypic traits in normotensive humans at genetic risk of hereditary (essential) hypertension. J Hypertens. 1998. Dao T T, Kailasam M T, Parmer R J, Le H V, Le Verge R, Kennedy B P, Ziegler G, Insel P A, Wright F A, O'Connor D T. PMID: 9663918. |
| Protein | The name assigned to the protein being studied. |
|---|---|
| Vmax for 10-OH-yohimbine (pmol/min/mg microsomal protein) | Maximal rate of conversion of yohimbine to 10-OH-yohimbine at saturating concentration of yohimbine (pmol/min/mg microsomal protein) . Values shown are the mean of 3 experiments. |
| SEM of Vmax for 10-OH-yohimbine | Standard error of mean maximal rate of conversion of yohimbine to 10-OH-yohimbine at saturating concentration of yohimbine. |
| Km for 10-OH-yohimbine (micromolar) | Concentration of yohimbine for half-maximal conversion to 10-OH-yohimbine (micromolar). Values shown are the mean of 3 experiments. |
| SEM of Km for 10-OH-yohimbine | Standard error of mean Km for 10-OH-yohimbine. |
| Vmax for 11-OH-yohimbine (pmol/min/mg microsomal protein) | Maximal rate of conversion of yohimbine to 11-OH-yohimbine at saturating concentration of yohimbine (pmol/min/mg microsomal protein) . Values shown are the mean of 3 experiments. |
| SEM of Vmax for 10-OH-yohimbine | Standard error of mean maximal rate of conversion of yohimbine to 10-OH-yohimbine at saturating concentration of yohimbine. |
| Km for 10-OH-yohimbine (micromolar) | Concentration of yohimbine for half-maximal conversion to 10-OH-yohimbine (micromolar). Values shown are the mean of 3 experiments. |
| SEM of Km for 11-OH-yohimbine | Standard error of mean Km for 11-OH-yohimbine. |
| CL int 10-OH-yohimbine (microliter/min/mg microsomal protein) | Intrinsic clearance of 10-OH-yohimbine (microliter/min/mg microsomal protein), Vmax divided by Km. |
| CL int 11-OH-yohimbine (microliterl/min/mg microsomal protein) | Intrinsic clearance of 11-OH-yohimbine (microliter/min/mg microsomal protein), Vmax divided by Km. |
| Ratio CL int 10-OH/11-OH | Ratio of intrinsic clearance of 10-OH-yohimbine to intrinsic clearance of 11-OH-yohimbine. |
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