Functional Characterization of 29 Cytochrome P450 4F2 Variants Identified in a Population of 8380 Japanese Subjects and Assessment of Arachidonic Acid ω-Hydroxylation.

Cytochrome P450 4F2 (CYP4F2) is an enzyme that is involved in the metabolism of arachidonic acid (AA), vitamin E and K, and xenobiotics including drugs. CYP4F2*3 polymorphism (rs2108622; c.1297G>A; p.Val433Met) has been associated with hypertension, ischemic stroke, and variation in the effectiveness of the anticoagulant drug warfarin. In this study, we characterized wild-type CYP4F2 and 28 CYP4F2 variants, including a Val433Met substitution, detected in 8380 Japanese subjects. The CYP4F2 variants were heterologously expressed in 293FT cells to measure the concentrations of CYP4F2 variant holoenzymes using carbon monoxide-reduced difference spectroscopy, where the wild type and 18 holoenzyme variants showed a peak at 450 nm. Kinetic parameters [Vmax , substrate concentration producing half of Vmax (S50 ), and intrinsic clearance (CL int ) as Vmax /S50 ] of AA ω-hydroxylation were determined for the wild type and 21 variants with enzyme activity. Compared with the wild type, two variants showed significantly decreased CL int values for AA ω-hydroxylation. The values for seven variants could not be determined because no enzymatic activity was detected at the highest substrate concentration used. Three-dimensional structural modeling was performed to determine the reason for reduced enzymatic activity of the CYP4F2 variants. Our findings contribute to a better understanding of CYP4F2 variant-associated diseases and possible future therapeutic strategies. SIGNIFICANCE STATEMENT: CYP4F2 is involved in the metabolism of arachidonic acid and vitamin K, and CYP4F2*3 polymorphisms have been associated with hypertension and variation in the effectiveness of the anticoagulant drug warfarin. This study presents a functional analysis of 28 CYP4F2 variants identified in Japanese subjects, demonstrating that seven gene polymorphisms cause loss of CYP4F2 function, and proposes structural changes that lead to altered function.

Functional Assessment of 12 Rare Allelic CYP2C9 Variants Identified in a Population of 4773 Japanese Individuals.

Cytochrome P450 2C9 (CYP2C9) is an important drug-metabolizing enzyme that contributes to the metabolism of approximately 15% of clinically used drugs, including warfarin, which is known for its narrow therapeutic window. Interindividual differences in CYP2C9 enzymatic activity caused by CYP2C9 genetic polymorphisms lead to inconsistent treatment responses in patients. Thus, in this study, we characterized the functional differences in CYP2C9 wild-type (CYP2C9.1), CYP2C9.2, CYP2C9.3, and 12 rare novel variants identified in 4773 Japanese individuals. These CYP2C9 variants were heterologously expressed in 293FT cells, and the kinetic parameters (Km, kcat, Vmax, catalytic efficiency, and CLint) of (S)-warfarin 7-hydroxylation and tolbutamide 4-hydroxylation were estimated. From this analysis, almost all novel CYP2C9 variants showed significantly reduced or null enzymatic activity compared with that of the CYP2C9 wild-type. A strong correlation was found in catalytic efficiencies between (S)-warfarin 7-hydroxylation and tolbutamide 4-hydroxylation among all studied CYP2C9 variants. The causes of the observed perturbation in enzyme activity were evaluated by three-dimensional structural modeling. Our findings could clarify a part of discrepancies among genotype-phenotype associations based on the novel CYP2C9 rare allelic variants and could, therefore, improve personalized medicine, including the selection of the appropriate warfarin dose.

Anatomic assessment of variations in myocardial approaches to the atrioventricular node.

INTRODUCTION: The tissues in the posteroinferior atrioventricular (AV) junction around the AV node are important in procedures for ablating and manipulation of catheters in and around the coronary sinus (CS). However, information with regard to the histological arrangement of perinodal myocardium relative to the CS is lacking. METHODS AND RESULTS: We examined 21 postmortem human hearts without any abnormalities (9 women; mean age 68.8 ± 14.3 years). After making measurements, the posteroinferior AV junction was removed and processed for histology. Sections were cut parallel to the septum. We assessed the myocardial arrangements from the atrial septum and the CS toward the AV nodal tissue, including the transitional cell zone, and measured the dimensions between the compact AV node and the CS, and the circumference of the CS. We observed 3 patterns of myocardial approaches to the AV node: extension of myocardium from the atrial septum (Group A; n = 6); extension of CS musculature (Group B; n = 6); and both septal and CS musculature (Group C; n = 9). The distance between the AV node and the CS in Group A was significantly longer than in the other groups (mean 11.5 ± 3.1 mm, 1.7 ± 0.6 mm, 3.8 ± 1.5 mm, respectively; P < 0.0001), and the circumference of the CS in Group B was longer than in Group A (mean 31.1 ± 7.9 mm*, 44.4 ± 8.4 mm*, 33.7 ± 6.9 mm, respectively; P < 0.05). CONCLUSION: The myocardial approaches including the transitional cell zone toward the AV node are variable in normal hearts. The location and size of the CS can affect the myocardial arrangements and the area of transitional cells around the AV node.