Urinary Excretion of α- and β-Isomers of Biliverdin-IX in Humans

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The distribution and relative proportions of the four isomers of α-, β-, γ-and δ-biliverdin-IX were investigated using urinary samples from seven healthy adults. The biliverdins from samples were adsorbed on talc, and the adsorbed biliverdins were then soaked in a solution of methanol and concentrated sulfuric acid for derivation to the dimethyl esters. The esters were passed to a reversed-phase cartridge for clean-up, then quantitated by HPLC on a reversed-phase column. The analyses revealed that the biliverdins in 24-h urine were comprised of 6.4±2.5 nmol α- and 9.3±5.4 nmol β-isomers. The HPLC analyses suggested the presence of a δ-isomer in a much smaller amount, but no γ-isomer was detected. The identifications of α- and β-isomers were performed with co-chromatography and absorption spectra.