Functional characterization of 21 CYP2C19 allelic variants for clopidogrel 2-oxidation

Genetic variations in cytochrome P450 2C19 (CYP2C19) contribute to interindividual variability in the metabolism of therapeutic agents such as clopidogrel. Polymorphisms in CYP2C19 are associated with large interindividual variations in the therapeutic efficacy of clopidogrel. This study evaluated the in vitro oxidation of clopidogrel by 21 CYP2C19 variants harboring amino acid substitutions. These CYP2C19 variants were heterologously expressed in COS-7 cells, and the kinetic parameters of clopidogrel 2-oxidation were estimated. Among the 21 CYP2C19 variants, 12 (that is, CYP2C19.5A, CYP2C19.5B, CYP2C19.6, CYP2C19.8, CYP2C19.9, CYP2C19.10, CYP2C19.14, CYP2C19.16, CYP2C19.19, CYP2C19.22, CYP2C19.24 and CYP2C19.25) showed no or markedly low activity compared with the wild-type protein CYP2C19.1B. This comprehensive in vitro assessment provided insights into the specific metabolic activities of CYP2C19 proteins encoded by variant alleles, and this may to be valuable when interpreting the results of in vivo studies.

Functional characterization of 32 CYP2C9 allelic variants

Genetic variations in cytochrome P450 2C9 (CYP2C9) contribute to interindividual variability in the metabolism of clinically used drugs such as warfarin and tolbutamide. We functionally characterized 32 types of allelic variant CYP2C9 proteins. Recombinant CYP2C9 proteins generated using a heterologous expression system are useful for comparing functional changes in CYP2C9 variant proteins expressed from low-frequency alleles. Wild-type CYP2C9 and its 31 variants were found to be transiently expressed in COS-7 cells, and the enzymatic activity of the CYP2C9 variants was characterized using S-warfarin as a representative substrate. Among the 32 types of CYP2C9 allelic variants tested, CYP2C9.18, CYP2C9.21, CYP2C9.24, CYP2C9.26, CYP2C9.33 and CYP2C9.35 exhibited no enzyme activity, and 12 types showed significantly decreased enzyme activity. In vitro analysis of CYP2C9 variant proteins should be useful for predicting CYP2C9 phenotypes and for application to personalized drug therapy.

Abundance of unconventional CD8(+) natural killer T cells in the large intestine

Natural killer T (NKT) cells are mainly present in the liver and thymus, and the majority of these T cells express either a CD4(+) or a double-negative (DN) CD4(-)8(-) phenotype. In the present study, we examined whether such NKT cells were present in the intestine. NKT cells were rare in all sites of the small intestine, including an intraepithelial site. However, a considerable number of NKT cells were found at an intraepithelial site in the large intestine. This result was confirmed by both immunofluorescence and immunohistochemistry. In contrast to conventional NKT cells, NKT cells in the large intestine were CD8(+) or DN CD4(-)8(-). In the case of conventional NKT cells, their existence is known to depend on non-classical MHC class I-like antigens (i. e. CD1d) but not on classical MHC class I antigens. However, the NKT cells in the large intestine were independent of the presence of both CD1d and classical MHC class I antigens. These results were obtained using knockout mice lacking the corresponding genes and molecules. NKT cells in the large intestine were mainly alpha betaTCR(+) (> 75 %) but did not use an invariant chain of Valpha14Jalpha281, which is preferentially used by conventional NKT cells. These NKT cells did not bias the TCR-Vbeta usage toward Vbeta8. These findings suggest that the large intestine is a site in which unconventional NKT cells carrying the CD8(+) phenotype (or DN CD4(-)8(-)) are abundant and that these cells are independent of MHC and MHC-like antigens.