Absolute quantification and modulation of cytochrome P450 3A isoforms in cattle liver

The cytochrome P450 3A (CYP3A) is the most important CYP in human liver, and extensive data about its regulation and function have been published. However, data referring to CYP3A in veterinary species are still incomplete. This is peculiar for cattle: four CYP3A isoforms have been identified so far, but their individual contribution to the overall CYP3A expression and function has not been characterized yet. Thus, CYP3A28, 3A38 and 3A48 mRNA levels were measured in cattle liver by using quantitative real-time RT-PCR assays and an absolute quantification approach. The fourth CYP3A isoform (CYP3A24) was not considered as it is only a predicted coding sequence. Possible breed-differences in the expression of individual CYP3A isoforms were investigated in five meat cattle breeds (Charolais, CH; Piedmontese, PM; Blonde d’Aquitaine, BA; Marchigiana, MA; Valdostana, VALD); the likely transcriptional effect of the prototypical inducer phenobarbital (PB) was evaluated, too. Results suggest CYP3A38 (before identified as CYP3A5) as the main CYP3A isoform in cattle liver (~68-90% of total CYP3A), followed by CYP3A48 (~7%-31%) and CYP3A28 (≤1%). Significant breed-differences in CYP3A gene abundances were noticed. CYP3A28 higher amounts were found in BA, while MA and VALD showed the largest amount of CYP3A38 and CYP3A48 copy numbers, respectively. Finally, PB significantly up-regulated all CYP3A isoforms. Presented data provide new information about hepatic cattle CYP3As; particularly, a heterogeneity in the expression of distinct CYP3A isoforms (CYP3A38>3A48>>3A28), the presence of breed-differences as well as a common up-regulation following PB exposure, although with different orders of magnitude. Grants: 2009ZE5HJP (MIUR); 60A08-7517/13 (University of Padua).