A new enzymatic assay for selectively measuring conjugated bilirubin concentration in serum with use of bilirubin oxidase

Binding specificity of alpha-bilirubin-imprinted poly(methacrylic acid-co-ethylene glycol dimethylacrylate) toward alpha-bilirubin

alpha-Bilirubin is an important index to determine the liver's functions. Poly(methacrylic acid-co-ethylene glycol dimethylacrylate) (poly(MAA-co-EGDMA)) imprinted with alpha-bilirubin was proposed and shown to be able to bind alpha-bilirubin specifically. The extraction condition was also discussed. Polymers prepared by imprinting bilirubin in poly(MAA-co-EGDMA) and in poly(beta-cyclodextrin-co-EGDMA) were compared. In this work, binding specificity of molecularly imprinted polymer (MIP) toward the target template, alpha-bilirubin, is discussed. Adsorption profile of alpha-bilirubin by bilirubin-imprinted poly(MAA-co-EGDMA) was measured as a function of time, from where the equilibrium could be determined. Two hours was determined to be the proper time for adsorption. Biliverdin as a rather similar analog compound of bilirubin was chosen for comparison of binding specificity in this study. Progesterone as well as testosterone was also chosen for study because they both co-exist in serum with bilirubin and might interfere with binding capacity of imprinted poly(MAA-co-EGDMA) toward alpha-bilirubin. Specificity of this polymer for bilirubin was thus confirmed by tasks carried out in mixture solutions comprised of compounds above. It is true that biliverdin contained in the binary mixture did affect the binding capacity of bilirubin. Nevertheless, polymer's binding specificity for bilirubin was essentially sufficient for recognition of alpha-bilirubin in the presence of other compounds. How MIP identified the target template molecule, alpha-bilirubin, is also elucidated.

Effects of bilirubin and its photoisomers on direct bilirubin measurement using bilirubin oxidase

We examined the reactivity of human serum albumin-bound bilirubin and its photoisomers as substrates for a direct bilirubin assay using bilirubin oxidase. The reduction of (EZ)-cyclobilirubin reached 100% 5 min after addition of the enzyme at any pH tested (3.5-7.4) in 0.1 mol/L phosphate buffer, whereas the reduction of (ZE)-bilirubin or (ZZ)-bilirubin reached 100% only below pH 4.5 or 5.5, respectively. (ZZ)-Bilirubin and its photoisomers did not react in citrate-lactate buffer at pH 3.7. The circular dichroism spectrum of (ZZ)-bilirubin in this buffer did not show a positive Cotton effect. These results indicate that a three-dimensional structure surrounding the reaction site of bilirubin is important for the reactivity with bilirubin oxidase.

Enzymatic assay for conjugated bilirubin (Bc) in serum using bilirubin oxidase (BOD)

We described an automated enzymatic assay for conjugated bilirubin (Bc) in serum using the Iatro D-Bil kit, with bilirubin oxidase (EC 1.3.3.5 BOD) from Myrothecium species. The specificity of the enzyme in the Iatro D-Bil kit was examined by analyzing unconjugated bilirubin (Bu), delta bilirubin (Bdelta), and Bc with high-performance liquid chromatography (HPLC), before and after the enzymatic reaction using BOD. The within-assay coefficients of variation (CV) of this method were 0.58 to 5.00% (n = 20) at 1.4 to 155.8 micromol/L. Day-to-day Cvs ranged from 1.61 to 7.14% at 1.2 to 182.1 micromol/L. The analytical recovery was 96 to 101%. The presence of ascorbic acid, reduced glutathione, L-cysteine, uric acid, urea, creatinine, glucose, lipemic material, anticoagulants, hemoglobin, or human serum albumin did not affect this assay system. The correlation coefficient between values obtained with the Iatro D-Bil kit (y) and HPLC method as reference for conjugated fractions (x) was; r = 0.983, y = 0.952x + 8.851 micromol/L, Sy/x = 11.97 (n = 56). We studied serum Bc levels, not including Bu and Bdelta, in patients with hepatic diseases or autoimmune hemolytic anemia. Levels of Bc obtained by the proposed method changed more rapidly than did those of direct bilirubin (D-Bil) obtained by diazo-dye method during the course of the diseases.