Characterization of Arsenic Hepatobiliary Transport Using Sandwich-Cultured Human Hepatocytes

Abstract

Arsenic is a proven human carcinogen and is associated with a myriad of other adverse health effects. This metalloid is methylated in human liver to monomethylarsonic acid (MMA(V)), monomethylarsonous acid (MMA(III)), dimethylarsinic acid (DMA(V)), and dimethylarsinous acid (DMA(III)) and eliminated predominantly in urine. Hepatic basolateral transport of arsenic species is ultimately critical for urinary elimination; however, these pathways are not fully elucidated in humans. A potentially important human hepatic basolateral transporter is the ATP-binding cassette (ABC) transporter multidrug resistance protein 4 (MRP4/ABCC4) that in vitro is a high-affinity transporter of DMA(V) and the diglutathione conjugate of MMA(III) [MMA(GS)(2)]. In rats, the related canalicular transporter Mrp2/Abcc2 is required for biliary excretion of arsenic as As(GS)(3) and MMA(GS)(2). The current study used sandwich cultured human hepatocytes (SCHH) as a physiological model of human arsenic hepatobiliary transport. Arsenic efflux was detected only across the basolateral membrane for 9 out of 14 SCHH preparations, 5 had both basolateral and canalicular efflux. Basolateral transport of arsenic was temperature- and GSH-dependent and inhibited by the MRP inhibitor MK-571. Canalicular efflux was completely lost after GSH depletion suggesting MRP2-dependence. Treatment of SCHH with As(III) (0.1-1 µM) dose-dependently increased MRP2 and MRP4 levels, but not MRP1, MRP6, or aquaglyceroporin 9. Treatment of SCHH with oltipraz (Nrf2 activator) increased MRP4 levels and basolateral efflux of arsenic. In contrast, oltipraz increased MRP2 levels without increasing biliary excretion. These results suggest arsenic basolateral transport prevails over biliary excretion and is mediated at least in part by MRPs, most likely including MRP4.

Chronic Kidney Disease and Exposure to Nephrotoxic Metals

“…In vivo and in vitro studies suggest that transport of iAs into cells may lead to alterations in intracellular signaling processes. Exposure of mice to iAs reduced the expression of raf kinase inhibitor protein (RKIP) [ 63 ], which is involved in the regulation of multiple cell signaling cascades [ 64 , 65 , 66 ]. RKIP is thought to play an important role in the regulation of growth and the survival of cells, suggesting that downregulation of its expression may lead to uncontrolled growth of cells and cancer [ 66 ].…”

Strain differences in arsenic-induced oxidative lesion via arsenic biomethylation between C57BL/6J and 129X1/SvJ mice

“…MRP3 was predominantly expressed at mRNA levels in the liver, but might not mediate efflux of inorganic or methylated arsenicals46. MRP4 is suggested to play a vital role in elimination of methylated arsenicals465152, but its transcription was not consistent with the results of hepatic arsenic excretion of the two mouse strains. Thus, strain difference in response to arsenic is not likely to be caused by arsenic transporters in the liver.…”

Navigating a Two-Way Street: Metal Toxicity and the Human Gut Microbiome

“… 51 After passing through the kidneys, about 90% of ingested iAs eventually leaves the body in urine and less than 10% in feces, although this varies across species and may depend on whether exposure comes from water or food. 52 , 53 , 54 The liver also releases some arsenicals into bile, which flows into the small intestine to help digest dietary fats. 55 Arsenicals may accumulate in tissues, particularly the kidneys.…”

“… 49 Because both iAs and MeHg are transported across the gut epithelium into the bloodstream and from the liver into the blood or bile, any host or microbial effects on transport efficiency, gut barrier function, and tissue absorption rates also modulate metabolism and body burden. 54 , 68 , 69 , 70 , 71 …”