174 - Chronic low level oxidative stress in primary hyperoxaluria type 1

Abstract

The Primary Hyperoxalurias (PH’s) are a family of inborn errors of glyoxylate metabolism resulting in excessive production of endogenous oxalate and PH1 is the most severe form of this disorder. There is no cure and treatment options are limited due to a poor understanding of the underlying pathology. Based on previously published reports we hypothesize that oxidative stress may play a unique role in PH1. In the absence of alanine-glyoxylate aminotransferase (AGT), the liver specific enzyme deficient in PH1, a futile redox cycle can occur between glycolate oxidase (GO) and glyoxylate reductase (GR). GO produces hydrogen peroxide and GR consumes NADPH. This mechanism points to a potential alteration in redox environment that has not yet been studied. Therefore, we performed a comprehensive global proteomics study comparing livers of PH1 mice to WT mice. In this study we found 155 significantly altered proteins, including 36 redox related proteins. PH1 model mice at experimental age show no phenotypic difference except for increased oxalate excretion. This data, combined with the use of Systems/ Pathway analysis, strongly suggests that PH1 mice are experiencing oxidative stress. Interestingly, functional data did not fully reflect these findings. mtDNA damage was not significantly changed in PH1 vs. WT using an XLPCR technique, nor was urinary 8-oxodG using an ELISA kit. However, GSH levels were significantly lower in PH1 mice measured by HPLC-ECD. All together this evidence suggests that the PH1 mouse is experiencing chronic low levels of oxidative stress that the mouse is compensating for at the proteomic level. Therefore, we have concluded that the redox related proteins have been modified in order to cope with an otherwise undetectable change in oxidative stress. We believe this is a highly unusual multi-tool approach and finding that the standard oxidative stress related tools would have missed if carried out alone.