Differences in apoptotic signaling and toxicity between dimethylmonothioarsinic acid (DMMTAV) and its active metabolite, dimethylarsinous acid (DMAIII), in HepaRG cells: Possibility of apoptosis cascade based on diversity of active metabolites of DMMTAV.

Dimethylmonothioarsinical acid (DMMTAV), a metabolite of arsenosugars (AsSug) and arsenolipids (AsLP), which are major organoarsenicals contained in seafoods, has been a focus of our attention due to its toxicity. It has been reported that the toxicity of DMMTAV differs according to the host cell type and that dimethylarsinous acid (DMAIII), which is a higher active metabolite of inorganic and organo arsenic compounds, may be the ultimate substance. To further elucidate the details of the mechanisms of DMMTAV, we carried out toxicological characterization by comparing DMMTAV and DMAIII using HepaRG cells, which are terminally differentiated hepatic cells derived from a human hepatic progenitor cell line that retains many characteristics, e.g, primary human hepatocytes including the morphology and expression of key metabolic enzymes (P450 s and GSTs, etc.) and complete expression of all nuclear receptors. HepaRG cells were induced to undergo differentiation by DMSO, which result red in increased levels of metabolic enzymes such as P450 and GST, in non-differentiated cells the cellular toxicities of DMMTAV and DMAIII were reduced and the induction of toxicity by DMMTAV was increased by GSH but not by DMAIII. Both DMAIII and DMMTAV induce apoptosis and increase caspase 3/7 activity. DMAIII exposure increased the activity of caspase-9. On the contrary, DMMTAV exposure resulted in markedly elevated activity of caspase-8 as well as caspase-9. These results suggest there are differences between the signaling pathways of apoptosis in DMAIII and DMMTAV and that between their active metabolites. Consequently, the ultimate metabolic substance of toxicity induction of DMMTAV may not only be DMAIII, but may also be partly due to other metabolic substances produced through the activation mechanism by GSH.

A biological indicator of inorganic arsenic exposure using the sum of urinary inorganic arsenic and monomethylarsonic acid concentrations.

OBJECTIVES: The sum of urinary inorganic arsenic (iAs), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) concentrations is used for the biological monitoring of occupational iAs exposure. Although DMA is a major metabolite of iAs, it is an inadequate index because high DMA levels are present in urine after seafood consumption. We estimated the urinary iAs+MMA concentration corresponding to iAs exposure. METHODS: We used data from two arsenic speciation analyses of urine samples from 330 Bangladeshi with oral iAs exposure and 172 Japanese workers without occupational iAs exposure using high-performance liquid chromatography with inductively coupled plasma mass spectrometry. RESULTS: iAs, MMA, and DMA, but not arsenobetaine (AsBe), were detected in the urine of the Bangladeshi subjects. The correlation between iAs+MMA+DMA and iAs+MMA was obtained as log (iAs+MMA) = 1.038 log (iAs+MMA+DMA) -0.658. Using the regression formula, the iAs+MMA value was calculated as 2.15 and 7.5 µg As/l, corresponding to 3 and 10 µg As/m(3) of exposures, respectively. In the urine of the Japanese workers, arsenic was mostly excreted as AsBe. We used the 95th percentile of iAs+MMA (12.6 µg As/l) as the background value. The sum of the calculated and background values can be used as a biological indicator of iAs exposure. CONCLUSION: We propose 14.8 and 20.1 µg As/l of urinary iAs+MMA as the biological indicators of 3 and 10 µg As/m(3) iAs exposure, respectively.

A novel metabolic activation associated with glutathione in dimethylmonothioarsinic acid (DMMTA(V))-induced toxicity obtained from in vitro reaction of DMMTA(V) with glutathione.

The purpose of the present study was to elucidate the metabolic processing of dimethylmonothioarsinic acid (DMMTA(V)), which is a metabolite of inorganic arsenic and has received a great deal of attention recently due to its high toxicity. The metabolites produced from an in vitro reaction with GSH were analyzed by high performance liquid chromatography-time of flight mass spectrometer (HPLC-TOFMS), HPLC with a photodiode array detector (PDA), and also gas chromatography-mass spectrometry (GC-MS) and GC with a flame photometric detector (FPD). The reaction of dimethylarsinic acid (DMA(V)) with GSH did not generate DMA(V)-SG but did generate dimethylarsinous acid (DMA(III)) or DMA(III)-SG. On the contrary, we confirmed that the reaction of DMMTA(V) with GSH directly produced the stable complex of DMMTA(V)-SG without reduction through a trivalent dimethylated arsenic such as DMA(III) and DMA(III)-SG. Furthermore, the present study suggests the production of hydrogen sulfide (H2S) and dimethylmercaptoarsine (DMA(III)-SH), a trivalent dimethylated arsenic, as well as DMA(III) and DMA(III)-SG in the decomposition process of DMMTA(V)-SG. These results indicate that the toxicity of DMMTA(V) depends not only on the formation of DMA(III) but also on at least those of H2S and DMA(III)-SH.

Proposal for novel metabolic pathway of highly toxic dimethylated arsenics accompanied by enzymatic sulfuration, desulfuration and oxidation.

The International Agency for Research on Cancer (IARC) has concluded that dimethylarsinic acid [(CH3)2AsO(OH), DMA(V)], a main metabolite of inorganic arsenic, is responsible for carcinogenesis in urinary bladder and lung in rodents, and various modes of carcinogenic action have been proposed. One theory concerning the mode of action is that the biotransformation of dimethylarsinous acid [(CH3)2AsOH, DMA(III)] from DMA(V) plays an important role in the carcinogenesis by way of reactive oxygen species (ROS) production. Furthermore, dimethylmonothioarsinic acid [(CH3)2AsS(OH), DMMTA(V)], a metabolite of DMA(V), has also been noted because of its higher toxicity. However, the metabolic mechanisms of formation and disappearance of DMA(III) and DMMTA(V), and their toxicity are not fully understood. Thus, the purpose of the present study was to clarify the mechanism of metabolic formation of DMMTA(V) and DMA(V) from DMA(III). The in vitro transformation of arsenicals by treatment with liver homogenate from rodents and sulfur transferase was detected by HPLC-ICP-MS and HPLC-tandem MS. DMMTA(V) is produced from DMA(III) but not DMA(V) by cellular fractions from mouse liver homogenates and by rhodanese from bovine liver in the presence of thiosulfate, a sulfur donor. Not only DMMTA(V) thus produced but also DMA(III) are re-converted into DMA(V) by an in vitro addition of S9 mix. These findings indicate that the metabolic process not only of DMA(III) to DMA(V) or DMMTA(V) but also of DMMTA(V) to DMA(V) consists of a complicated mode of interaction between monooxygenase including cytochrome P450 (CYP) and/or sulfur transferase.