Failure to detoxify the intermediary metabolite
glyoxylate in human hepatocytes underlies the metabolic pathology of two potentially lethal hereditary
calcium oxalate kidney stone diseases, PH (
primary hyperoxaluria) types 1 and 2. In order to define more clearly the roles of
enzymes involved in the metabolism of
glyoxylate, we have established singly, doubly and triply transformed CHO (Chinese-hamster ovary) cell lines, expressing all combinations of normal human AGT (
alanine:glyoxylate aminotransferase; the
enzyme deficient in PH1), GR/HPR (
glyoxylate/
hydroxypyruvate reductase; the
enzyme deficient in PH2), and GO (
glycolate oxidase). We have embarked on the preliminary metabolic analysis of these transformants by studying the indirect toxicity of
glycolate as a simple measure of the net intracellular production of
glyoxylate. Our results show that
glycolate is toxic only to those cells expressing GO and that this toxicity is diminished when AGT and/or GR/HPR are expressed in addition to GO. This finding indicates that we have been able to reconstruct the
glycolate-->
glyoxylate,
glyoxylate-->
glycine, and
glyoxylate-->
glycolate metabolic pathways, catalysed by GO, AGT, and GR/HPR respectively, in cells that do not normally express them. These results are compatible with the findings in PH1 and PH2, in which AGT and GR/HPR deficiencies lead to increased
oxalate synthesis, due to the failure to detoxify its immediate precursor
glyoxylate. These CHO cell transformants have a potential use as a cell-based bioassay for screening small molecules that stabilize AGT or GR/HPR and might have use in the treatment of PH1 or PH2.