Glycolate and glyoxylate metabolism in HepG2 cells

Abstract

alate synthesis in human hepatocytes is not well defined despite the clinical significance of its overproduction in diseases such as the primary hyperoxalurias. To further define these steps, the metabolism to oxalate of the oxalate precursors glycolate and glyoxylate and the possible pathways involved were examined in HepG2 cells. These cells were found to contain oxalate, glyoxylate, and glycolate as intracellular metabolites and to excrete oxalate and glycolate into the medium. Glycolate was taken up more effectively by cells than glyoxylate, but glyoxylate was more efficiently converted to oxalate. Oxalate was formed from exogenous glycolate only when cells were exposed to high concentrations. Peroxisomes in HepG2 cells, in contrast to those in human hepatocytes, were not involved in glycolate metabolism. Incubations with purified lactate dehydrogenase suggested that this enzyme was responsible for the metabolism of glycolate to oxalate in HepG2 cells. The formation of 14 C-labeled glycine from 14 C-labeled glycolate was observed only when cell membranes were permeabilized with Triton X-100. These results imply that peroxisome permeability to glycolate is restricted in these cells. Mitochondria, which produce glyoxylate from hydroxyproline metabolism, contained both alanine:glyoxylate aminotransferase (AGT)2 and glyoxylate reductase activities, which can convert glyoxylate to glycine and glycolate, respectively. Expression of AGT2 mRNA in HepG2 cells was confirmed by RT-PCR. These results indicate that HepG2 cells will be useful in clarifying the nonperoxisomal metabolism associated with oxalate synthesis in human hepatocytes.

Metabolism of [13C5]hydroxyproline in vitro and in vivo: implications for primary hyperoxaluria

“…HepG2 cells have previously been shown to retain several hepatic functions, including the ability to synthesize glycolate and oxalate (5). The present results indicate that these cells express all the genes in the Hyp catabolic pathway (Fig.…”

“…HepG2 cells retain many of the functional properties of liver cells, including the capacity to synthesize oxalate and glycolate (5). Figure 3A shows that these cells express mRNA for all enzymes in the pathway at levels similar to those in human liver, except for a lower expression of HPOX and 1P5CDH.…”

Bacterial quorum sensing, cooperativity, and anticipation of stationary-phase stress

“…Much of the literature on biological oxalate synthesis focuses on the formation of oxalate crystals that cause kidney stones in humans and crystal formation in plants (30)(31)(32). Oxalate production by certain plant pathogenic fungi is important for virulence (33,34).…”

Stabilization of LKB1 and Akt by neddylation regulates energy metabolism in liver cancer

“…Importantly, glycine, a metabolite that reflects proliferation rate across cancer cells [23], was attenuated (21%, p< 0.05) after NAE1 inhibition. Finally, glycolic acid, the classical inhibitor of the aerobic glycolysis through lactate dehydrogenase (LDH) activity [24], was increased in the liver of …”