2044 GLYOXAL METABOLISM: A NOVEL PATHWAY IN ENDOGENOUS OXALATE SYNTHESIS

Abstract

You have accessJournal of UrologyStone Disease: Basic Research1 Apr 20112044 GLYOXAL METABOLISM: A NOVEL PATHWAY IN ENDOGENOUS OXALATE SYNTHESIS Kyle D. Wood, John Knight, Dean G. Assimos, and Ross P. Holmes Kyle D. WoodKyle D. Wood Winston-Salem, NC More articles by this author , John KnightJohn Knight Winston-Salem, NC More articles by this author , Dean G. AssimosDean G. Assimos Winston-Salem, NC More articles by this author , and Ross P. HolmesRoss P. Holmes Winston-Salem, NC More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2011.02.2275AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES The immediate precursor of the endogenous synthesis of oxalate is glyoxylate. The sources of glyoxylate are not well defined. Glyoxal, a reactive di-aldehyde, may be a significant source. Plasma glyoxal levels are higher in diabetics; a cohort with higher levels of urinary oxalate excretion. Glyoxal is detoxified through the glutathione dependent glyoxalase pathway to glycolate. We propose an alternative metabolism of glyoxal via aldehyde dehydrogenase yielding glyoxylate which may be accelerated by oxidative stress. METHODS The following 3 in-vitro model systems were employed: human liver lysates, HepG2 cells (hepatoma cell line), and human red blood cells. Incubations over time with varying concentrations of glyoxal (0.01 mM to 5 mM) were performed with liver lysates and HepG2 cells. HepG2 cells and erythrocytes were also incubated with 5mM and 50mM 13C labeled glucose. The effect of glutathione depletion on erythrocyte conversion of glyoxal to oxalate and glycolate was also studied. Liver lysates were incubated with disulfiram, an inhibitor of aldehyde dehydrogenase, NAD+, a known cofactor of this enzyme, and NADP+. Glyoxylate, glycolate and oxalate were measured using ion chromatography, ion chromatography coupled with mass spectroscopy, and high pressure liquid chromatography. RESULTS In human liver lysates treated with increasing concentrations of glyoxal, there was a linear increase in glyoxylate production. Human liver lysates only converted glyoxal to glyoxylate in the presence of NAD+ and this conversion was inhibited by disulfiram. As glyoxal concentrations were increased from 0 to 2.5 mM in HepG2 cells, there was a linear increase in both glycolate and oxalate production; significantly more glycolate produced than oxalate. Incubating red blood cells with both glyoxal and menadione, an agent which depletes glutathione, resulted in significantly more oxalate and decreased glycolate production. Human erythrocytes cultured with 50 mM 13C labeled glucose yielded both 13C labeled glycolate and oxalate whereas 5mM 13C labeled glucose did not yield oxalate or glycolate. CONCLUSIONS Glyoxal appears to be converted to glyoxylate via aldehyde dehydrogenase resulting in endogenous oxalate synthesis. Under conditions of oxidative stress there is an increased flux of glyoxal to oxalate formation. The exposure of cells to high levels of glucose results in its conversion to both glycolate and oxalate, likely via glyoxal. This novel pathway may be the major source of endogenous oxalate synthesis. © 2011 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 185Issue 4SApril 2011Page: e818 Advertisement Copyright & Permissions© 2011 by American Urological Association Education and Research, Inc.MetricsAuthor Information Kyle D. Wood Winston-Salem, NC More articles by this author John Knight Winston-Salem, NC More articles by this author Dean G. Assimos Winston-Salem, NC More articles by this author Ross P. Holmes Winston-Salem, NC More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...