Impact of Bilirubin on the ABCc1 expression on brain parenchyma in Gunn rats

ANDREA L. BERENGENO; SILVIA GAZZIN; JAROSLAV ZELENKA; LUCIE ZDRAHALOVA; M. CELESTE ROBERT; ALAN RASENI; LIBOR VITEK; CLAUDIO TIRIBELLI

Frederick

Encuentro; 6th Annual North American ABC Meeting; 2009

Impact of Bilirubin on the ABCc1 expression on brain parenchyma in Gunn rats Berengeno Andrea, Gazzin Silvia, Zelenka Jaroslav, Zdrahalova Lucie, Robert M. Celeste, Raseni Alan, Vitek Libor, Tiribelli Claudio. Background: In newborns with high blood levels of unconjugated bilirubin (UCB), the pigment may enter and accumulate in brain selective regions leading to neurological damage (Kernicterus). In vivo, a modulation of UCB transporters (ABCb1, Pgp and ABCc1, Mrp1) expression at the Blood Brain Interfaces (BBI) of jaundice Gunn rats has been reported, in the absence of macroscopic evidence of damage. Aim: Since Mrp1 has been related with a major protection against UCB toxicity in vitro and this transporter is expressed on brain parenchyma, the aim was to evaluate in vivo the effect of increased levels of UCB on the Mrp1 protein expression on brain cortex (Cx). Methods: Homozygous hyperbilirubinemic (jj) Gunn rats, the animal model for kernicterus and Crigler-Najjar syndrome, at 2, 9, 17 and 60 days after birth were used. Heterozygous (Jj) and the homozygous (JJ) animals were used as controls. Mrp1 relative expression was assessed by quantitative Western blot. Total tissue UCB (TUCB) content was measured by HPLC. Results: Mrp1 expression was unchanged among normal (JJ, Jj) and hyperbilirubinemic (jj) animals. Interestingly a developmental increase of the Mrp1 relative expression (P2:0.46; P9:1.05; P17:1.11 and P60: 0.67; P≤ 0.005) for all post-natal ages respect to P2 was detected. The lower Mrp1 expression matches with the more vulnerable period for UCB neurotoxicity. The tissue UCB (TUCB) content on Cx was 80 fold higher in jj Gunn rats as compared to JJ and Jj animals, whose values were similar. No differences in TUCB content was found between Cx and others regions know to be damaged by UCB (cerebellum, mid-brain). Conclusions: Bilirubin seems to be unable to modulate the Mrp1 expression on cerebral cortex, in agreement with the absence of macroscopical evidence of UCB toxicity. The expression of this transporter in the hypoplasic cerebellum of jj Gunn rats, despite TUCB levels equal to Cx, needs to be investigated.