Pharmacologic rescue of an enzyme-trafficking defect in primary hyperoxaluria 1

Primary hyperoxaluria 1 (PH1; Online Mendelian Inheritance in Man no. 259900), a typically lethal biochemical disorder, may be caused by the AGT^P11LG170R allele in which the alanine:glyoxylate aminotransferase (AGT) enzyme is mistargeted from peroxisomes to mitochondria. AGT contains a C-terminal peroxisomal targeting sequence, but mutations generate an N-terminal mitochondrial targeting sequence that directs AGT from peroxisomes to mitochondria. Although AGT^P11LG170R is functional, the enzyme must be in the peroxisome to detoxify glyoxylate by conversion to alanine; in disease, amassed glyoxylate in the peroxisome is transported to the cytosol and converted to oxalate by lactate dehydrogenase, leading to kidney failure. From a chemical genetic screen, we have identified small molecules that inhibit mitochondrial protein import. We tested whether one promising candidate. Food and Drug Administration (FDA)-approved dequalinium chloride (DECA), could restore proper peroxisomal trafficking of AGT^P11LG170R. Indeed treatment with DECA inhibited AGT^P11LG170R translocation into mitochondria and subsequently restored trafficking to peroxisomes. Previous studies have suggested that a mitochondrial uncoupler might work in a similar manner. Although the uncoupler carbonyl cyanide m-chlorophenyl hydrazone inhibited AGT^P11LG170R import into mitochondria, AGT^P11LG170R aggregated in the cytosol, and cells subsequently died. In a cellular model system that recapitulated oxalate accumulation, exposure to DECA reduced oxalate accumulation, similar to pyridoxine treatment that works in a small subset of PH1 patients. Moreover, treatment with both DECA and pyridoxine was additive in reducing oxalate levels. Thus, repurposing the FDA-approved DECA may be a pharmacologic strategy to treat PH1 patients with mutations in AGT because an additional 75 missense mutations in AGT may also result in mistrafficking.