Lack of efflux of diglycolic acid from proximal tubule cells leads to its accumulation and to toxicity of diethylene glycol

Abstract

Diethylene glycol (DEG) mass poisonings have resulted from ingestion of adulterated pharmaceuticals, leading to proximal tubular necrosis and acute kidney injury. Diglycolic acid (DGA), one of the primary metabolites, accumulates greatly in kidney tissue and its direct administration results in toxicity identical to that in DEG-treated rats. DGA is a dicarboxylic acid, similar in structure to Krebs cycle intermediates such as succinate. Previous studies have shown that DGA is taken into kidney cells via the succinate-related dicarboxylate transporters. These studies have assessed whether the DGA that is taken up by primary cultures of human proximal tubule (HPT) cells is effluxed. In addition, a possible mechanism for efflux, via organic anion transporters (OATs) that exchange external organic anions for dicarboxylates inside the cell, was assessed using transformed cell lines that actively express OAT activities. When HPT cells were cultured on membrane inserts, then loaded with DGA and treated with the OAT4/5 substrate estrone sulfate or the OAT1/3 substrate para-aminohippurate, no DGA efflux was seen. A repeat of this experiment utilizing RPTEC/TERT1 cells with overexpressed OAT1 and OAT3 had similar results. In these cells, but not in HPT cells, co-incubation with succinate increased the uptake of PAH, confirming the presence of OAT activity in the RPTEC/TERT1 cells. Thus, despite OATs stimulation in cells with OAT activity, there was little to no efflux of DGA from the cells. This study concluded that DGA is poorly transported out of cells and that stimulation of OAT transporters is not a viable target for reducing DGA accumulation in cells.