Multidrug Resistance Protein 1 (MRP1/ABCC1)-Mediated Cellular Protection and Transport of Methylated Arsenic Metabolites Differs between Human Cell Lines.

The ATP-binding cassette (ABC) transporter multidrug resistance protein 1 (MRP1/ABCC1) protects cells from arsenic (a proven human carcinogen) through the cellular efflux of arsenic triglutathione [As(GS)3] and the diglutathione conjugate of monomethylarsonous acid [MMA(GS)2]. Previously, differences in MRP1 phosphorylation (at Y920/S921) and N-glycosylation (at N19/N23) were associated with marked differences in As(GS)3 transport kinetics between HEK293 and HeLa cell lines. In the current study, cell line differences in MRP1-mediated cellular protection and transport of other arsenic metabolites were explored. MRP1 expressed in HEK293 cells reduced the toxicity of the major urinary arsenic metabolite dimethylarsinic acid (DMAV), and HEK-WT-MRP1-enriched vesicles transported DMAV with high apparent affinity and capacity (Km 0.19 µM, Vmax 342 pmol⋅mg-1protein⋅min-1). This is the first report that MRP1 is capable of exporting DMAV, critical for preventing highly toxic dimethylarsinous acid formation. In contrast, DMAV transport was not detected using HeLa-WT-MRP1 membrane vesicles. MMA(GS)2 transport by HeLa-WT-MRP1 vesicles had a greater than threefold higher Vmax compared with HEK-WT-MRP1 vesicles. Cell line differences in DMAV and MMA(GS)2 transport were not explained by differences in phosphorylation at Y920/S921. DMAV did not inhibit, whereas MMA(GS)2 was an uncompetitive inhibitor of As(GS)3 transport, suggesting that DMAV and MMA(GS)2 have nonidentical binding sites to As(GS)3 on MRP1. Efflux of different arsenic metabolites by MRP1 is likely influenced by multiple factors, including cell and tissue type. This could have implications for the impact of MRP1 on both tissue-specific susceptibility to arsenic-induced disease and tumor sensitivity to arsenic-based therapeutics.

A novel pathway for arsenic elimination: human multidrug resistance protein 4 (MRP4/ABCC4) mediates cellular export of dimethylarsinic acid (DMAV) and the diglutathione conjugate of monomethylarsonous acid (MMAIII).

Hundreds of millions of people worldwide are exposed to unacceptable levels of arsenic in drinking water. This is a public health crisis because arsenic is a Group I (proven) human carcinogen. Human cells methylate arsenic to monomethylarsonous acid (MMA(III)), monomethylarsonic acid (MMA(V)), dimethylarsinous acid (DMA(III)), and dimethylarsinic acid (DMA(V)). Although the liver is the predominant site for arsenic methylation, elimination occurs mostly in urine. The protein(s) responsible for transport of arsenic from the liver (into blood), ultimately for urinary elimination, are unknown. Human multidrug resistance protein 1 (MRP1/ABCC1) and MRP2 (ABCC2) are established arsenic efflux pumps, but unlike the related MRP4 (ABCC4) are not present at the basolateral membrane of hepatocytes. MRP4 is also found at the apical membrane of renal proximal tubule cells, making it an ideal candidate for urinary arsenic elimination. In the current study, human MRP4 expressed in HEK293 cells reduced the cytotoxicity and cellular accumulation of arsenate, MMA(III), MMA(V), DMA(III), and DMA(V) while two other hepatic basolateral MRPs (MRP3 and MRP5) did not. Transport studies with MRP4-enriched membrane vesicles revealed that the diglutathione conjugate of MMA(III), monomethylarsenic diglutathione [MMA(GS)(2)], and DMA(V) were the transported species. MMA(GS)(2) and DMA(V) transport was osmotically sensitive, allosteric (Hill coefficients of 1.4 ± 0.2 and 2.9 ± 1.2, respectively), and high affinity (K0.5 of 0.70 ± 0.16 and 0.22 ± 0.15 µM, respectively). DMA(V) transport was pH-dependent, with highest affinity and capacity at pH 5.5. These results suggest that human MRP4 could be a major player in the elimination of arsenic.

Efficacy of compressed sodium chloride (CSC) against E. coli and Candida auris in minutes and methods improvement for testing.

Controlling infections has become one of the biggest problems in the world, whether measured in lives lost or money spent. This is worsening as pathogens continue becoming resistant to therapeutics. Antimicrobial surfaces are one strategy being investigated in an attempt to decrease the spread of infections through the most common route of transmission: surfaces, including hands. Regulators have chosen two hours as the time point at which efficacy should be measured. The objectives of this study were to characterize the new antimicrobial surface compressed sodium chloride (CSC) so that its action may be understood at timepoints more relevant to real-time infection control, under two minutes; to develop a sensitive method to test efficacy at short time points; and to investigate antifungal properties for the first time. E. coli and Candida auris are added to surfaces, and the surfaces are monitored by contact plate, or by washing into collection vats. An improved method of testing antimicrobial efficacy is reported. Antimicrobial CSC achieves at least 99.9% reduction of E. coli in the first two minutes of contact, and at least 99% reduction of C. auris in one minute.