Intracellular, time-resolved speciation and quantification of arsenic compounds in human urothelial and hepatoma cells

Abstract

In contrast to the temporary administration of arsenic in cancer therapy (e.g. in the form of arsenic trioxide), chronic exposure to low doses can cause bladder cancer and other cancers. Especially the trivalent arsenic species MMA(III) (monomethylarsonous acid) and DMA(III) (dimethylarsinous acid) are known to be highly toxic. In the present study we analysed the soluble, intracellular biotransformation products of MMA(III) in methylating HepG2 (hepatocytes) and non-methylating UROtsa cells (urothelial cells) after various times of exposure. As most of the intracellular arsenic is bound to cellular structures and proteins the soluble arsenic metabolites can hardly be speciated and even less quantified. Using an improved isolation procedure and HPLC-ICP/MS, we investigated the time-resolved biotransformation of MMA(III) and detected and quantified MMA(V) (monomethylarsonic acid) as an oxidation product of MMA(III) and, to a minor degree, DMA(V) (dimethylarsenic acid) as a methylation and oxidation product of MMA(III) in the lysates of HepG2 cells. In contrast, only MMA(V) but no DMA(V) was detected in the lysates of UROtsa cells. We conclude from our study that MMA(III) is taken up by HepG2 and UROtsa cells and immediately oxidized to MMA(V). Only in HepG2 cells MMA(V) is finally methylated to DMA(V) over time. The new method might help to advance the analysis of metabolic pathways of arsenic in mammalian cells.