Bilirubin and the ABCc1 expression in the brain of the Gunn rat

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

Vancouver

Encuentro; Pediatric Academic Societies' Annual Meeting (PAS); 2010

Pediatric Academic Societies

Bilirubin and the ABCc1 expression in the brain of the Gunn rat 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 enters and accumulate in brain selective regions leading to neurological damage (Kernicterus). A modulation of the expression of ABC protein ABCc1, (Mrp1) involved in UCB transport has been reported at the choroid plexus on Blood Cerebrospinal Fluid Barrier (BCSFB) of the jaundiced Gunn rats (Gazzin et al., PAS 2009, Abstract 752671). In vitro, Mrp1 protects cells from UCB toxicity. Aim: To evaluate the effect of increased levels of UCB on the Mrp1 protein expression on cerebral cortex (Cx). Methods: Homozygous hyperbilirubinemic (jj) Gunn rats, the animal model for kernicterus, were examined 2, 9, 17 and 60 days after birth. Heterozygous (Jj) and the homozygous (JJ) animals served as controls. Mrp1 relative expression was assessed by quantitative Western blot, as respect to the transporter amount in reference sample (Pool P60 Jj cortices). Total tissue UCB (TUCB) content was measured by HPLC. Results: Mrp1 expression was comparable among normal (JJ, Jj) and hyperbilirubinemic (jj) animals for all ages analyzed, and a similar developmental increase of Mrp1 relative expression was detected in all genotypes. As example, Mrp1 expression on JJ animals was 0.49; 1.16; 0.90 and 0.65 at 2, 9, 17 and 60 d-old rats, respectively ( p≤ 0.005 between P2-P9 and P9-P60; p≤ 0.01 between P2-P60, and P9-P17; p≤ 0.05 between P17-P60) as respect the reference sample. The lower Mrp1 expression at P2 matches with the more vulnerable period for UCB neurotoxicity. In 9 days old animals, the Tissue UCB (TUCB) content on Cx was 100 fold higher in jj Gunn rats (4.5 ± 1.3 nmol/g) as compared to JJ and Jj animals (0.05 ± 0.008 and 0.054 ± 0.006 nmol/g, respectively), whose values were similar. No significant differences in TUCB level was found between Cx (4.5 ± 1.3 nmol/g) and others regions known to be damaged by UCB (cerebellum, 5.23 ± 1.67 nmol/g). Conclusions: Bilirubin does not modulate the Mrp1 expression in Gunn cerebral cortex. The expression of this transporter in the hypoplasic cerebellum of jj Gunn rats, despite TUCB levels similar to cerebral cortex, needs to be investigated.