ABSTRACT
Hydroxylation activity at the 6ß-position of steroid hormones (testosterone, progesterone, and cortisol) by human cytochromes P450 (CYP) 3A4, polymorphic CYP3A5, and fetal CYP3A7 were compared to understand the catalytic properties of the major forms of human CYP3A subfamily. Testosterone, progesterone, and cortisol 6ß-hydroxylation activities of recombinant CYP3A4, CYP3A5, and CYP3A7 were determined by liquid chromatography. Michaelis constants (Km) for CYP3A7-mediated 6ß-hydroxylation of testosterone, progesterone, and cortisol were similar to those of CYP3A4 and CYP3A5. The maximal velocity (kcat) and kcat/Km values for CYP3A4 were the highest, followed by CYP3A5 and those for CYP3A7 were the lowest among three CYP3A subfamily members. A decrease in Km values for progesterone 6ß-hydroxylation by CYP3A4, CYP3A5, and CYP3A7 in the presence of testosterone was observed, and the kcat values for CYP3A5 gradually increased with increasing testosterone. This indicated that testosterone stimulated progesterone 6ß-hydroxylation by all three CYP3A subfamily members. However, progesterone inhibited testosterone 6ß-hydroxylation mediated by CYP3A4, CYP3A5, and CYP3A7. In conclusion, the kcat values, rather than Km values, for 6ß-hydroxylation of three steroid hormones mediated by CYP3A7 were different from those for CYP3A4 and CYP3A5. In addition, the inhibitory/stimulatory pattern of steroid-steroid interactions would be different among CYP3A subfamily members.
Subject(s)
Cytochrome P-450 CYP3A/metabolism , Hormones/metabolism , Steroids/metabolism , Catalysis , Humans , Hydrocortisone/metabolism , Hydroxylation , Kinetics , Microsomes, Liver/metabolism , Progesterone/metabolism , Recombinant Proteins/metabolism , Testosterone/metabolismABSTRACT
PURPOSE: Hydroxylation activity at the 6ß-position of steroid hormones (testosterone, progesterone, and cortisol) by human cytochromes P450 (P450 or CYP) 3A4 and CYP3A5 and their molecular docking energy values were compared to understand the catalytic properties of the major forms of human CYP3A, namely, CYP3A4 and CYP3A5. METHODS: Testosterone, progesterone, and cortisol 6ß-hydroxylation activities of recombinant CYP3A4 and CYP3A5 were determined by liquid chromatography. Docking simulations of these substrates to the heme moiety of reported crystal structures of CYP3A4 (Protein Data Bank code ITQN) and CYP3A5 (6MJM) were conducted. RESULTS: Michaelis constants (Km) for CYP3A5- mediated 6ß-hydroxylation of testosterone and progesterone were approximately twice those for CYP3A4, whereas the value for cortisol 6ß-hydroxylation mediated by CYP3A5 was similar to the value for that by CYP3A4. Maximal velocities (Vmax) of the three steroid hormones 6ß-hydroxylation catalyzed by CYP3A5 were 30%-63% of those by CYP3A4. Thus, Vmax/ Km values of these hormones for CYP3A5 resulted in 22%- 31% of those for CYP3A4. The differences in the docking energies between CYP3A4 and CYP3A5 for steroid hormones were slightly correlated to the logarithm of CYP3A5/CYP3A4 ratios for Km values (substrate affinity). CONCLUSIONS: The Vmax, rather than Km values, for CYP3A5-mediated 6ß-hydroxylation of three steroid hormones were different from those for CYP3A4. Molecular docking simulations could partially explain the differences in the accessibility of substrates to the heme moiety of human CYP3A molecules, resulting in the enzymatic affinity of CYP3A4 and CYP3A5.
Subject(s)
Cytochrome P-450 CYP3A/metabolism , Hydrocortisone/metabolism , Molecular Docking Simulation , Progesterone/metabolism , Testosterone/metabolism , Cytochrome P-450 CYP3A/chemistry , Humans , Hydrocortisone/chemistry , Hydroxylation , Kinetics , Progesterone/chemistry , Testosterone/chemistrySubject(s)
Aneurysm/therapy , Embolization, Therapeutic , Hepatic Artery , Aged , Aged, 80 and over , Humans , MaleABSTRACT
A patient who received antithymocyte globulin therapy for aplastic anemia due to D-penicillamine therapy is described. Bone marrow recovery and peripheral blood recovery were complete 1 month and 3 months, respectively, after treatment, and blood transfusion or other therapies were not necessary in a follow-up period of more than 2 years. Use of antithymocyte globulin may be the optimal treatment of D-penicillamine-induced aplastic anemia.
