Abstract
α-ketoglutarate (KG), also referred to as 2-oxoglutarate, is a key intermediate of cellular metabolism with pleiotropic functions. Cell-permeable esterified analogs are widely used to study how KG fuels bioenergetic and amino acid metabolism and DNA, RNA, and protein hydroxylation reactions, as cellular membranes are thought to be impermeable to KG. Here we show that esterified KG analogs rapidly hydrolyze in aqueous media, yielding KG that, in contrast to prevailing assumptions, imports into many cell lines. Esterified KG analogs exhibit spurious KG-independent effects on cellular metabolism, including extracellular acidification, arising from rapid hydrolysis and de-protonation of α-ketoesters, and significant analog-specific inhibitory effects on glycolysis or mitochondrial respiration. We observe that imported KG decarboxylates to succinate in the cytosol and contributes minimally to mitochondrial metabolism in many cell lines cultured in normal conditions. These findings demonstrate that nuclear and cytosolic KG-dependent reactions may derive KG from functionally distinct subcellular pools and sources.
Highlights
Α-ketoglutarate (KG), referred to as 2-oxoglutarate, is a key intermediate of cellular metabolism with pleiotropic functions
Ester hydrolysis releases α-ketoglutaric acid and an alcohol, the latter of which is removed from cells by passive diffusion and evaporation or metabolism (Fig. 1a)[32]
KG derived from complete mono-hydrolysis of 1-octyl-KG was observed after 24 h, whereas a gradual increase in KG release from double hydrolysis of DMKG was observed over the 72-h time course (Fig. 1c)
Summary
Α-ketoglutarate (KG), referred to as 2-oxoglutarate, is a key intermediate of cellular metabolism with pleiotropic functions. Cell-permeable esterified analogs are widely used to study how KG fuels bioenergetic and amino acid metabolism and DNA, RNA, and protein hydroxylation reactions, as cellular membranes are thought to be impermeable to KG. We observe that imported KG decarboxylates to succinate in the cytosol and contributes minimally to mitochondrial metabolism in many cell lines cultured in normal conditions. These findings demonstrate that nuclear and cytosolic KG-dependent reactions may derive KG from functionally distinct subcellular pools and sources. Imported KG was used predominantly for cytosolic/nuclear dioxygenase activity and minimally contributed to mitochondrial TCA cycle metabolism, suggesting that mitochondrial KG is derived from a functionally distinct source. Our results highlight significant offtarget effects associated with esterified α-ketone metabolites, such as pyruvate and KG, and suggests that caution be used when interpreting metabolic phenotypes associated with these analogs
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