Plasma from hemodialysis patients evoked weak photon emissions (chemiluminescence) in a characteristic emission spectrum with a peak at 430 nm, attributed to attack by hydroxyl radicals generated from the iron-catalyzed breakdown of hydrogen peroxide (Fenton reaction), whereas plasma from normal healthy subjects showed a rather weak red chemiluminescence peak at around 680 nm, similar to that resulting from attack by hydroxyl radicals. However, the addition of hydrogen peroxide in the absence of divalent irons induced almost the same red chemiluminescent emission spectrum in both plasmas. The HPLC-gel-filtration chromatography carried out with both plasmas revealed that a primary emitter evoking a peak emission at 430 nm was located in the fraction of lower-molecular-mass substances in fractionated plasma from hemodialysis patients. In contrast, the elution peaks evoking red chemiluminescence with the addition of hydrogen peroxide were mainly observed for the higher-molecular-mass fraction, as determined by gel chromatography of both plasmas. Therefore, the observation of a chemiluminescence peak at 430 nm, induced by the generation of hydroxyl radicals, correlated well with chemiluminescent emissions in plasma samples from patients with chronic renal failure. Spectral analyses of clinical samples that show weak chemiluminescence by forced oxidation by such an active oxygen may provide a new and more sensitive method for diagnosing metabolic disorders.
Characteristic light emission induced by the oxidation of hydroxyl radicals has been found in plasma of hemodialysis patients (Agatsuma et al., Clin Chem 1992;38:48-55). We purified a primary emitter, a chemiluminescent component peaking at 430 nm, by anion-exchange chromatography and reversed-phase HPLC. By using proton nuclear magnetic resonance and authentic indoxyl compounds, we determined the primary emitter to be indoxyl-beta-D-glucuronide. Absorption and fluorescence spectra of the purified sample coincided well with those of authentic indoxyl-beta-D-glucuronide, as did the peak in the chemiluminescence emission spectrum. Retention time of the purified sample on reversed-phase HPLC, measured by fluorescence, was also in accordance with that of indoxyl-beta-D-glucuronide. To our knowledge, this is the first identification of a primary emitter of low-level chemiluminescence from a biological source.
Ultraweak chemiluminescence (CL) from bilirubin occurs in the presence of triplet oxygen and is stimulated by the addition of aldehydes. Active oxygen species also enhance bilirubin CL, in the absence of aldehydes. An inhibitory effect of active oxygen scavengers on the CL indicated that active oxygens generated from the decomposition of added hydrogen peroxide or from the xanthine-xanthine oxidase reaction contributed to the CL from bilirubin molecules. However, the contribution of singlet oxygen to the CL disappeared in the presence of formaldehyde. This suggested that the scission of tetrapyrrole bonds via a dioxetane intermediate or the production of triplet carbonyls from the oxidation of aldehydes by singlet oxygen was not involved in the CL, at least in the presence of formaldehyde. The spectrum of CL induced by the generation of active oxygen was the same as that from the aldehyde-enhanced CL reaction. We propose that the formation of a hydroperoxide (and/or hydroxide) bilirubin intermediate, but not a dioxetane, may be involved in the excitation of bilirubin molecules for CL.
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