Toxicity Assessment of 4-Methyl-1-cyclohexanemethanol and Its Metabolites in Response to a Recent Chemical Spill in West Virginia, USA

Abstract

The large-scale chemical spill on January 9, 2014 from coal processing and cleaning storage tanks of Freedom Industries in Charleston affected the drinking water supply to 300,000 people in Charleston, West Virginia metropolitan, while the short-term and long-term health impacts remain largely unknown and need to be assessed and monitored. There is a lack of publically available toxicological information for the main contaminant 4-methyl-1-cyclohexanemethanol (4-MCHM). Particularly, little is known about 4-MCHM metabolites and their toxicity. This study reports timely and original results of the mechanistic toxicity assessment of 4-MCHM and its metabolites via a newly developed quantitative toxicogenomics approach, employing proteomics analysis in yeast cells and transcriptional analysis in human cells. These results suggested that, although 4-MCHM is considered only moderately toxic based on the previous limited acute toxicity evaluation, 4-MCHM metabolites were likely more toxic than 4-MCHM in both yeast and human cells, with different toxicity profiles and potential mechanisms. In the yeast library, 4-MCHM mainly induced chemical stress related to transmembrane transport and transporter activity, while 4-MCHM metabolites of S9 mainly induced oxidative stress related to antioxidant activity and oxidoreductase activity. With human A549 cells, 4-MCHM mainly induced DNA damage-related biomarkers, which indicates that 4-MCHM is related to genotoxicity due to its DNA damage effect on human cells and therefore warrants further chronic carcinogenesis evaluation.

Effects of MCHM on yeast metabolism

“…From these genes, particularly from AHA1, ENO1, GRE2, PDR3 and PDR16, we can infer that MCHM is affecting DNA replication (Tkach et al, 2012) . This is in correspondence with the previously described DNA damage effect (particularly double strand break) of MCHM in human cells (Lan et al, 2015) . From the other stress-related upregulated genes: SNQ2 and QDR3 encode multidrug transporters involved in multidrug resistance (Rogers et al, 2001;Tenreiro et al, 2005); ENB1 encodes for an endosomal ferric enterobactin transporter, which is expressed under conditions of iron deprivation (Philpott et al, 2002) ; TPO1 codes for a polyamine transporter which exports spermine and spermidine from the cell during oxidative stress, controlling the timing of expression of stress-responsive genes (Krüger et al, 2013) ; ICT1 codes the lysophosphatidic acid acyltransferase responsible for enhanced phospholipid synthesis during organic solvent stress (Ghosh et al, 2008) .…”

“…It is of note that the other protective metabolite against representative inhibitors found by Wang et al (Wang et al, 2015) , myo-inositol, also has a lower level due to MCHM. It is also interesting the higher levels after MCHM treatment of glutathione, a critical protector against oxidative stress, in contrast to the previously reported oxidative stress in MCHM treated cells (Lan et al, 2015) . On the other hand, the level of acetyl-L-carnitine, which protects yeast cells from apoptosis and aging and inhibits mitochondrial fission (Palermo et al, 2010) , is increased due to MCHM.…”

“…In the evaluation of different cell lines, HEK-293, HepG2, H9c2 and GT1-7 only the highest dose of MCHM (1 mM) elicited a statistically significant decrease in cell viability, when compared to the control (1% DMSO) (Han et al, 2017) . MCHM induced DNA damage-related biomarkers in human A549 cells, indicating that it is related to genotoxicity (Lan et al, 2015) . MCHM affected larval visual motor response in an acute developmental toxicity assay with zebrafish embryos (Horzmann et al, 2017) .…”

“…MCHM affected larval visual motor response in an acute developmental toxicity assay with zebrafish embryos (Horzmann et al, 2017) . MCHM mainly induced chemical stress related to transmembrane transport activity and oxidative stress in yeast (Lan et al, 2015) .…”

Assessing human exposure and odor detection during showering with crude 4-(methylcyclohexyl)methanol (MCHM) contaminated drinking water

“…These health effects are consistent with the material safety data sheet for crude MCHM which cautions that it is "harmful if swallowed", "causes skin and eye irritation", and "at elevated temperatures, vapor may cause irritation of eyes and respiratory tract" and recommends medical attention be sought following inhalation, contact, or ingestion exposures (Eastman Chemical Company 2011). Recent studies indicate 4-MCHM is moderately toxic in human and yeast cells; 4-MCHM metabolites are more toxic than 4-MCHM and both 4-MCHM and its metabolites should be considered potential carcinogens (Lan et al 2015).…”