The genes of all seven CYP 3A isoenzymes identified in the equine genome are expressed in the airways of horses

In the present study, we examined the gene expression of cytochrome P450 3A ( CYP 3A) isoenzymes in the tracheal and bronchial mucosa and in the lung of equines using TaqMan probes. The results show that all seven CYP 3A isoforms identified in the equine genome, that is, CYP 3A89, CYP 3A93, CYP 3A94, CYP 3A95, CYP 3A96, CYP 3A97 and CYP 3A129, are expressed in the airways of the investigated horses. Though in previous studies, CYP 3A129 was found to be absent in equine intestinal mucosa and liver, this CYP 3A isoform is expressed in the airways of horses. The gene expression of the CYP 3A isoenzymes varied considerably between the individual horses studied. However, in most of the horses CYP 3A89, CYP 3A93, CYP 3A96, CYP 3A97 and CYP 3A129 were expressed to a high extent, while CYP 3A94 and CYP 3A95 were expressed to a low extent in the different parts of the airways. The CYP 3A isoenzymes present in the airways may play a role in the metabolic degradation of inhaled xenobiotics. In some instances, the metabolism may, however, result in bioactivation of the xenobiotics and subsequent tissue injury.