Investigating the impact of hyperbilirubinemia on cognitive dysfunction in adult zebrafish: an in vivo model.

Background: Despite the well-known effects of elevated bilirubin in neonates, its neurotoxic potential in adults remains uncertain. In perioperative and hepatic disease contexts, transient bilirubin elevations are common; however, their direct contribution to cognitive dysfunction has not been clearly established. This study aimed to determine whether transient bilirubin elevation alone can impair cognition and disrupt blood-brain barrier (BBB) function in adult zebrafish, and to compare these effects with those of liver injury.

Methods: Adult zebrafish were assigned to either a bilirubin-injected group (retro-orbital injection of bilirubin) or a liver injury group (hepatocyte-specific ablation using a nitroreductase/metronidazole system). Cognitive performance was assessed using the T-maze test, and BBB integrity was evaluated using Evans blue staining. Expression of inflammatory genes (il1b, stat1b, ifng1) in brain tissue was analyzed via reverse transcription quantitative polymerase chain reaction.

Results: Zebrafish injected with bilirubin exhibited impaired spatial learning without locomotor deficits, accompanied by marked Evans blue accumulation, indicating BBB disruption. Zebrafish in the liver injury group exhibited similar cognitive impairment and a modest increase in BBB permeability, yet displayed significantly higher expression of inflammatory genes. These findings suggest that, although both models induce behavioral deficits, their underlying mechanisms may differ.

Conclusion: Transient bilirubin elevation alone was sufficient to impair cognition and disrupt BBB function in adult zebrafish, even in the absence of overt liver damage or systemic inflammation. Although inflammation is more pronounced during liver injury, bilirubin itself may exert direct neurovascular effects. These results support considering bilirubin levels as a modifiable risk factor for perioperative neurocognitive dysfunction.