Genotype???phenotype associations for common CYP3A4 and CYP3A5 variants in the basal and induced metabolism of midazolam in European- and African-American men and women

Abstract

CYP3A activity in adults varies between individuals and it has been suggested that this has a genetic basis, possibly related to variant alleles in CYP3A4 and CYP3A5 genes. Accordingly, genotype-phenotype associations were investigated under constitutive and induced conditions. Midazolam's systemic and oral clearances, and the erythromycin breath test (ERBT) were determined in 57 healthy subjects: 23 (11 men, 12 women) European- and 34 (14 men, 20 women) African-Americans. Studies were undertaken in the basal state and after 14-15 days pretreatment with rifampin. DNA was characterized for the common polymorphisms CYP3A4*1B, CYP3A5*3, CYP3A5*6 and CYP3A5*7 by direct sequencing, and for exon 21 and exon 26 variants of MDR1 by allele-specific, real-time polymerase chain reaction. In 95% of subjects, the basal systemic clearance of midazolam was unimodally distributed and variability was less than four-fold whereas, in 98% of the study population, oral clearance varied five-fold. No population or sex-related differences were apparent. Similar findings were observed with the ERBT. Rifampin pretreatment markedly increased the systemic (two-fold) and oral clearance (16-fold) of midazolam, and the ERBT (two-fold) but the variabilities were unchanged. No associations were noted between these phenotypic measures and any of the studied genotypes, except for oral clearance and its fold-increase after rifampin. These were related to the presence of CYP3A4*1B and the inversely linked CYP3A5*3 polymorphism, with the extent of induction being approximately 50% greater in CYP3A5*3 homozygotes compared to wild-type subjects. In most healthy subjects, variability in intestinal and hepatic CYP3A activity, using midazolam as an in-vivo probe, is modest and common polymorphisms in CYP3A4 and CYP3A5 do not appear to have important functional significance.

Frequency of common CYP3A5 gene variants in healthy Polish newborn infants

“…These CYP3A5 genotypes have been associated with the lower mean clearances of benzodiazepines and etopo- USA/(Afro-Americans) Healthy adults, (34) 0.721 0.279 [9] Finnish/(Caucasians) Healthy adults, (754) 0.070 0.930 [22] USA/(Afro-Americans) Healthy adults, (25) 0.540 0.460 [11] side, which might increase the probability of drugrelated adverse reactions, such as peripheral neuropathy [16]. Additionally, a strong association between the CYP3A5*1 genotype and tacrolimus dose requirement was observed.…”

“…This is especially important because the most effective immunosuppressive therapy is required for adequate protection against transplant rejection, in the case of chemotherapy in bone marrow recipients and lymphoproliferative disease treatment [6,13]. This allele is infrequent in Poland and other European populations [9]. The exact correlation between CYP3A5 genotypes and drug metabolism needs to be further analyzed, and clear relationships between genetic variants and type of CYP expression needs to be confirmed.…”

“…It must be noted that data from various pharmacogenetic studies are often conflicting, especially in the case of midazolam. Some studies do not confirm that CYPA5*1 allele carriers metabolize the drug better than individuals with other variants [9]. The frequency of the CYP3A5*3 variant differs among populations and races, ranging from 27-50% in the Afro-American population, 60-70% among Asians, and up to 85-95% in individuals of Caucasian ancestry, in which the expresser variant is uncommon.…”

“…Conversely, the presence of the wild-type, expresser-related A6986 allele (CYP3A5*1) leads to the phenotype of high CYP3A5 catalytic activity. In CYP3A5 expressers, dose requirements for certain immunosuppressants, such as tacrolimus, tend to be higher, while clearance of the anxiolytic midazolam is slower among individuals with a *3 genotype [5,9]. It must be noted that data from various pharmacogenetic studies are often conflicting, especially in the case of midazolam.…”

A Novel Polymorphic Cytochrome P450 Formed by Splicing of CYP3A7 and the Pseudogene CYP3AP1

“…The Caucasian most common haplotype consists, among other polymorphisms, of CYP3A4*1A, CYP3A7*1, CYP3A7_39256 T, and CYP3A5*3, whereas the African most common haplotype contains CYP3A4*1B, CYP3A7*2, CYP3A7_39256 A, and CYP3A5*1. An altered expression of CYP3A4*1B is controversial (19,37), and CYP3A7.1 and CYP3A7.2 have differences in catalytic activity but are both functional enzymes (18). Therefore, it is unlikely that these alleles could have provided a significant adaptation advantage.…”