Identification of an Ascorbic Acid Metabolite among “Uremic Middle

Among uremic toxins in the middle molecular mass range, 3C-nuclear magnetic resonance, ultraviolet spectrome-try, and chromatographic analyses allow identification of the main component of the so-called “2-5-3 fraction ” as ascorbic acid 2-sulfate, a conjugated metabolite of ascorbic acid. We previously (Clin Nephrol 1986;25:21 2-8) showed an inhibi-tory effect of the 2-5-3 fraction on microtubule formation. Therefore, we tested the action of ascorbic acid 2-sulfate and its synthetized enantiomers on tubulin polymerization. Be-cause these molecules did not exert any inhibitory effect, we hypothesize that the 2-5-3 fraction is a mixture of compounds in which only a very low quantity of the inhibitory factor is present. AddItional Keyphrases: kidney function inhibition of tubulin polymerization. chromatography, ion-pair Since postulation of the “middle molecules ” hypothesis by Babb et al. (1), numerous attempts have been made to separate and identify substances in the molecular mass range of 300-2000 Da that accumulate in uremic fluids and exert toxic effects (2). The chemical nature of these sub-stances appears to be highly diverse, being reported as (e.g.) peptidic substances (3-7), carbohydrates (8, 9), or a double conjugate of glucuronidate-O-hydroxyhippuric acid (10). Later we identified the same double conjugate mole-cule (11) and three others that were also glucurono-conju-gates of phenolic acids (12, 13). Among the middle molecular mass compounds, we pre-viously reported that a particular chromatographic frac-tion, the so-called “2-5-3 fraction, ” inhibits microtubule formation (14, 15) and speculated that these results might be correlated with the occurrence of uremic neuropathy. We report here the identification of one of these compo-nents