Albumin domain II mutant with high bilirubin binding affinity has a great potential as serum bilirubin excretion enhancer for hyperbilirubinemia treatment

Abstract Background 4Z,15Z-bilirubin-IXα (BR), an endogenous toxic compound that is sparingly soluble in water, binds human serum albumin (HSA) with high affinity in a flexible manner. Our previous findings suggest that both Lys195 and Lys199 in subdomain IIA are important for the high-affinity binding of BR, and especially Lys199 in stand-alone domain II plays a prominent role in the renal elimination of BR. Our hypothesis is that HSA-domain II with high BR binding would be a useful therapeutic agent to treat hyperbilirubinemia in patients with impaired liver function. Methods Unbound BR concentrations were determined using a modified HRP assay. To evaluate the effect of pan3_3-13 domain II mutant in promoting urinary BR excretion, the serum concentration and urinary excretion amount of BR were determined using bile duct ligation mice. Results After three or six rounds of panning, pan3_3-13 and pan6_4 were found to have a significantly higher affinity for BR than wild-type domain II. Administration of pan3_3-13 significantly reduced serum BR level and increased its urinary excretion in the disease model mice as compared to wild-type domain II treatment. Conclusions These results suggest that pan3_3-13 has great potential as a therapeutic agent that promotes urinary BR excretion in hyperbilirubinemia. General significance This is the first study to be applied to other HSA bound toxic compounds that are responsible for the progression of disease, thereby paving the way for the development of non-invasive and cost effective blood purification treatment methods.