Regulation of Cytochrome P450 2a5 by Artemisia capillaris and 6,7-Dimethylesculetin in Mouse Hepatocytes.

Jaundice is a potentially fatal condition resulting from elevated serum bilirubin levels. For centuries, herbal remedies containing Artemisia capillaris Thunb. including the compound 6,7-dimethylesculetin (DE) have been used in Asia to prevent and treat jaundice in neonates. DE activates an important regulator of bilirubin metabolism, the constitutive androstane receptor (CAR), and increases bilirubin clearance. In addition, murine cytochrome P450 2a5 (Cyp2a5) is known to be involved in the oxidative metabolism of bilirubin. Moreover, treatment of mice with phenobarbital, a known inducer of both CAR and Cyp2a5, increases expression of Cyp2a5 suggesting a potential relationship between CAR and Cyp2a5 expression. The aim of this study is to investigate the influence of Artemisia capillaris and DE on the expression and regulatory control of Cyp2a5 and the potential involvement of CAR. Treatment of mouse hepatocytes in primary culture with DE (50 µM) significant increased Cyp2a5 mRNA and protein levels. In mice, Artemisia capillaris and DE treatment also increased levels of hepatic Cyp2a5 protein. Luciferase reporter assays showed that CAR increases Cyp2a5 gene transcription through a CAR response element in the Cyp2a5 gene promoter. Moreover, DE caused nuclear translocation of CAR in primary mouse hepatocytes and increased Cyp2a5 transcription in the presence of CAR. These results identify a potential CAR-mediated mechanism by which DE regulates Cyp2a5 gene expression and suggests that DE may enhance bilirubin clearance by increasing Cyp2a5 levels. Understanding this process could provide an opportunity for the development of novel therapies for neonatal and other forms of jaundice.

An unusual case of peripheral vestibular disease in a cat following ear cleaning.

The occurrence of vestibular disease in a cat following a wellness/vaccination visit which included routine ear cleaning is described. The cat recovered in 10 days following supportive therapy. The cause of vestibular disease was not identified but sensitivity to an ear cleaning solution or subclinical ear disease may have played a role.

Maladie vestibulaire périphérique inhabituelle chez un chat après un nettoyage d'oreilles. Le présent rapport de cas décrit l'occurrence d'une maladie vestibulaire chez un chat après une visite pour examen de santé et vaccination qui incluait le nettoyage routinier des oreilles. Le chat s'est rétabli dans un délai de 10 jours après une thérapie de soutien. La cause de la maladie vestibulaire n'a pas été identifiée, mais la sensibilité à une solution de nettoyage des oreilles ou une maladie subclinique de l'oreille peut avoir joué un rôle.(Traduit par Isabelle Vallières).

Cytochrome P450 2A5 and bilirubin: mechanisms of gene regulation and cytoprotection.

Bilirubin (BR) has recently been identified as the first endogenous substrate for cytochrome P450 2A5 (CYP2A5) and it has been suggested that CYP2A5 plays a major role in BR clearance as an alternative mechanism to BR conjugation by uridine-diphosphate glucuronyltransferase 1A1. This study investigated the mechanisms of Cyp2a5 gene regulation by BR and the cytoprotective role of CYP2A5 in BR hepatotoxicity. BR induced CYP2A5 expression at the mRNA and protein levels in a dose-dependent manner in primary mouse hepatocytes. BR treatment also caused nuclear translocation of Nuclear factor-E2 p45-related factor 2 (Nrf2) in hepatocytes. In reporter assays, BR treatment of primary hepatocytes transfected with a Cyp2a5 promoter-luciferase reporter construct resulted in a 2-fold induction of Cyp2a5 reporter activity. Furthermore, cotransfection of the hepatocytes with a Nrf2 expression vector without BR treatment resulted in an increase in Cyp2a5 reporter activity of approximately 2-fold and BR treatment of Nrf2 cotransfectants further increased reporter activity by 4-fold. In addition, site-directed mutation of the ARE in the reporter construct completely abolished both the BR- and Nrf2-mediated increases in reporter activity. The cytoprotective role of CYP2A5 against BR-mediated apoptosis was also examined in Hepa 1-6 cells that lack endogenous CYP2A5. Transient overexpression of CYP2A5 partially blocked BR-induced caspase-3 cleavage in Hepa 1-6 cells. Furthermore, in vitro degradation of BR was increased by microsomes from Hepa 1-6 cells overexpressing CYP2A5 compared to control cells transfected with an empty vector. Collectively, these results suggest that Nrf2-mediated CYP2A5 transactivation in response to BR may provide an additional mechanism for adaptive cytoprotection against BR hepatotoxicity.