Arpamas Vachiraarunwong

Occupational cholangiocarcinoma among printing workers in Japan has raised concern regarding the carcinogenic hazards of chlorinated organic solvents, particularly 1,2-dichloropropane (1,2-DCP) and dichloromethane (DCM). Because workers were often exposed to multiple solvents, this study examined whether DCM modifies 1,2-DCP-associated hepatocellular tumor development in mice. Male C3H/HeN mice were administered corn oil vehicle, 1,2-DCP alone at 500 mg/kg bw, or 1,2-DCP and DCM at 500 mg/kg bw each by oral gavage twice weekly for 52 weeks. Combined exposure significantly increased the incidence of hepatocellular adenomas (HCAs) compared with both the vehicle control and 1,2-DCP-alone groups. Tumor multiplicity was also significantly higher in the 1,2-DCP + DCM group than in the 1,2-DCP-alone group. HCAs from the 1,2-DCP + DCM group showed increased cell proliferative activity, 29 uniquely altered differentially expressed genes, significant upregulation of Gpc3 and Igfbp1, and downregulation of Dcn, consistent with altered tumor-associated molecular features. Canonical pathway analysis indicated suppression of xenobiotic metabolism, bile acid metabolism, and peroxisomal function in treatment-associated HCAs. These findings indicate that DCM co-exposure enhanced 1,2-DCP-associated hepatocellular tumor development and altered tumor-associated molecular features in mice, highlighting the importance of considering combined solvent exposure in chemical carcinogenic risk assessment.

Although numerous experimental studies have demonstrated the carcinogenic potential of multi-walled carbon nanotubes (MWCNTs) in lungs, the underlying molecular mechanisms—especially gene expression changes associated with different tumor types—remain poorly characterized. To elucidate the molecular signatures associated with MWCNT-induced carcinogenesis, we performed microarray-based gene expression profiling of rat lung tumors induced by MWCNT-7, including both adenocarcinoma (ADC) and malignant mesothelioma (MM), as well as ADCs induced by two types of double-walled CNTs (DWCNTs) differing in fiber length (1.5 µm and 7 µm). Hierarchical clustering revealed that the MWCNT-7-induced MM exhibited a gene expression profile distinct from the ADCs. The ADCs induced by the DWCNTs and the ADC induced by MWCNT-7 shared several pathways that were distinct from those of the MWCNT-7 induced MM. The distinct pathways upregulated in the ADCs versus the MM support the conclusion that MWCNT-induced ADCs arise through distinct biological mechanisms compared to MWCNT-induced MMs and identified tumor-type-specific biomarker candidates: complement factor I (CFI) and secreted phosphoprotein 1 (SPP1) for ADCs, and fibronectin 1 (FN1) for MM. In addition, the gene expression profiles of the ADCs induced by the three fiber types indicate that both types of thin flexible DWCNTs used in the present study promoted a number of carcinogenic pathways in the rat lung that were also promoted by MWCNT-7, which is a class 2B carcinogen. These results support the conclusion that DWCNTs are carcinogenic in the rat lung and highlight the importance of further assessments of the potential lung carcinogenicity of inhaled thin flexible CNTs.