Table 3.

Recent studies examining the relationship between miRNAs and arsenic exposure

Type of study (in vitro, in vivo, human subjects)	Arsenical exposure	Cell type analyzed	Type of miRNA analysis and method used	Major findings	Reference
In vitro exposure to arsenite (immortalized human bronchial epithelial cell line)	0, 10, 15, 20 μM arsenic chloride for 24 h	Human immortalized bronchial epithelial cell line BEAS-2B	Total RNA analyzed for levels of 95 cancer-related miRNAs using a miRNA qPCR array. Subsequent analysis of miR-190 levels using real-time qPCR.	Arsenite exposure correlated with dose-dependent increase in miR-190. miR-190 overexpression alone sufficient for acquisition of malignant characteristics in BEAS-2B.	Beezold et al., 2011 [77]
In vitro exposure to ATO (human hepatocellular carcinoma cell line)	4 μM ATO (As2O3) for 24 h	Human hepatocellular carcinoma cell line Hep-G2	Total RNA analyzed for levels of 677 human miRNAs using a miRNA PCR array. Levels of selected miRNAs analyzed using real-time qPCR.	Identified miR-29a as a likely critical mediator of ATO-mediated apoptosis and inhibition of cell growth.	Meng et al., 2011 [73]
In vitro exposure to arsenite (immortalized human bronchial epithelial cell line)	2.5 μM arsenite (NaAsO2) for 16 weeks, resulting in malignant transformation	Immortalized human bronchial epithelial cell line p53low HBEC, which contains stable shRNA knockdown of TP53	Total RNA analyzed for levels of 856 human miRNAs using a miRNA PCR array. Levels of selected miRNAs also analyzed using real-time qPCR.	Malignant transformation associated with reduction of miR-200 family members; downregulation of miR-200b shown to be essential for malignant transformation.	Wang et al., 2011 [76]
In vivo exposure to arsenite (chick embryos); in vitro exposure to arsenite (human umbilical cord vein cell line)	100 nM arsenite (NaAsO2) injected in yolk sac of chick embryos at HH stages 6, 9, and 12; embryos harvested at HH stage 18. EA.hy926 cells exposed to 100 nM arsenite (NaAsO2) for 72 h	White Leghorn chick (Bovan strain) whole embryos; human umbilical cord vein cell line EA.hy926	Total RNA analyzed for miRNA levels using several methods including miRNA PCR arrays and real-time qPCR and Northern blots of selected targets.	miR-9 and miR-181b implicated as potential mediators of the toxic developmental effects of arsenic, specifically abnormal angiogenesis.	Cui et al., 2012 [75]
In vitro exposure to ATO (APL cell line)	Therapeutic dose of 2 μM ATO (As2O3) for 24 h	human APL cell line NB4	Total RNA analyzed for levels of 88 cancer-associated human miRNAs using a miRNA PCR array.	Exposure modulated 88 cancer-associated miRNAs, including those predicted to bind mRNAs of genes involved in cell cycle and apoptosis.	Ghaffari et al., 2012 [72]
In vitro exposure to arsenite (immortalized human embryonic lung fibroblasts)	1.0 μM arsenite (NaAsO2) for ~15 weeks, resulting in acquisition of malignant characteristics	Immortalized human embryonic lung fibroblast cell line HELF	Total RNA analyzed for miR-21 levels using real-time qPCR.	Identified ROS-sensitive pathways as inducers of miR-21. MiR-21 upregulation implicated as important event in the acquisition of malignant characteristics.	Ling et al., 2012 [78•]

APL: acute myelocytic leukemia

ATO: arsenic trioxide

HH: Hamburger-Hamilton

qPCR: quantitative polymerase chain reaction

ROS: reactive oxygen species