Bilirubin-Albumin Binding At Varying Conditions Of Hematocrit, Sodium Benzoate Concentration, And Bilirubin/Albumin Molar Ratios

Abstract

Hyperbilirubinemia, which causes jaundice, is quite common in newborns. Typically bilirubin is bound to its carrier protein albumin and very little unbound bilirubin is present in the blood. However, in cases of hyperbilirubinemia there is a marked increase in unbound bilirubin, which can be toxic. The two methods traditionally used to treat hyperbilirubinemia are exchange transfusion and phototherapy. Each of these methods have drawbacks. The Department of Chemical, Bio, and Materials Engineering at Arizona State University is currently developing an extra-corporeal hemoperfusion column that will remove the unbound bilirubin fraction from the blood of jaundiced patients. This column utilizes coated activated charcoal beads, which serves as the sorbent for unbound bilirubin, and sodium benzoate, which serves as the solutizer for unbinding bilirubin from albumin. The effect of varying hematocrit, sodium benzoate concentration, and bilirubin to albumin molar ratios were studied in relation to bilirubin-albumin unbinding. Specific attention was given to unbound bilirubin concentration. The results showed increasing hematocrits reduced both total bilirubin concentration ([TB]) and unbound bilirubin concentration ([UB]). In fact, a hematocrit of 60 resulted in a [UB] that was less than 10 ug% at any sodium benzoate concentration ([SB]) or bilirubin to albumin molar ratio (B/A). Sodium benzoate was shown to unbind bilirubin from albumin at low bilirubin to albumin molar ratios and at low to moderate hematocrit levels. Therefore, sodium benzoate is capable of increasing the unbound bilirubin fraction, thereby increasing the hemoperfusion columns efficiency. The results also indicate that an increase in [SB] from 50 to 100 mM did not significantly increase the [UB]. The data suggests as the B/A approaches unity, sodium benzoate in any concentration was not effective in increasing the [UB] when red blood cells were present. Because of its low concentration, the measurement of unbound bilirubin is difficult. The most accepted method of determining [UB] is the peroxidase method. Also, the automated Labo UB Analyzer UA-1, is used in clinical situations to measure both [TB] and [UB]. The Labo is based on the manual peroxidase test. Both of these methods were compared prior to analyzing serum samples. Results showed that the Labo read [UB] with a much smaller coefficient of variation (8.4%) than the manual peroxidase method (23.1%). Because of this, the Labo was used in analyzing the serum samples that were prepared in order to study bilirubin-albumin binding.