Date of Graduation

2016

Document Type

Dissertation

Degree Type

PhD

College

School of Public Health

Department

Epidemiology

Committee Chair

Linda M Sargent

Committee Co-Chair

Michael A McCawley

Committee Member

Nancy L Guo

Committee Member

Travis L Knuckles

Committee Member

Daniel G Panaccione

Committee Member

Dale W Porter

Abstract

Multiwalled carbon nanotubes (MWCNT) are one of the most exciting industrial materials of our time. They are used in life-saving medical therapeutics and many commercial products that could make day-to-day life seem effortless. However, previous toxicological research has demonstrated this material to be significantly genotoxic in both in vitro and in vivo models and potentially carcinogenic in the lung. The unique physiochemical properties of MWCNT make respiratory exposures likely in workers. Combining the genotoxic effects with the potential for lung deposition in the workplace, MWCNT should be considered as a potential health hazard. Altering the physiochemical properties of MWCNT has been shown to effect toxicity, however there has been limited research on how this effects the mechanism of genotoxicity and carcinogenicity.;Therefore, the aim of the first study was to determine the effect of MWCNT diameter on the mechanism of genotoxicity. Previous research has demonstrated that exposure to MWCNT material both in vitro and in vivo induces DNA damage leading to significant aneuploidy. It is known that the microtubules that make up the mitotic spindle are 20 nm in diameter. Therefore, human lung epithelial cells were exposed to MWCNT material 10-20 nm in diameter at occupationally-relevant doses. Significant genotoxicity was observed as arrests in the G1/S phase of the cell cycle. Exposure to MWCNT led to significantly increased mitotic spindle aberrations that were predominately monopolar in morphology and fragmented centrosomes. Exposure to the highest dose produced 62% aneuploidy cells that was significantly greater than control. Aneuploidy was the result of both gains and losses of chromosomes 1 and 4.;The aim of the second study was to determine the effect of MWCNT chemical composition on the mechanism of genotoxicity. Previous research has demonstrated that eliminating metal contaminates in the MWCNT through high-temperature treatment post-synthesis (MWCNT-HT) or incorporating nitrogen into the lattice structure of the walls of MWCNT structure during synthesis (MWCNT-ND) can potentially reduce the toxicity of the pristine material (MWCNT-7). Therefore, two types of human lung epithelial cells were exposed to MWCNT-7, MWCNT-HT, and MWCNT-ND in a dose-response. Significant genotoxicity was observed in two cell types through arrests in the cell cycle that indicate centrosomal damage after exposure to each MWCNT material. Exposure to each MWCNT material also led to significantly increased mitotic spindle aberrations and fragmented centrosomes. Exposure to the highest dose of MWCNT-7, HT and ND material produced 65, 58, and 53% aneuploidy cells, respectively. Detailed chromosome analysis demonstrated significantly increased frequency of fragmented centromeres and translocations between chromosomes 1 and 4.;The aim of the third study was to determine the mechanism of carcinogenicity of inhaling MWCNT-7 material via a two-stage initiation-promotion protocol. Previous research demonstrated the MWCNT-7 material to be significantly genotoxic and the potential for MWCNT material to be a tumor promoter. At 17 months post-exposure, 23.2, 51.9, 26.5, and 90.5% of mice from the control, initiating agent only, MWCNT-7 only, or initiating agent and MWCNT-7 group, respectively, had lung tumors. The tumor multiplicity, potency, and volume in the latter group was significantly greater than control indicating that MWCNT-7 material is a strong tumor promoter. Additionally, mice that received both initiating agent and MWCNT-7 demonstrated evidence of serosal tumors morphologically consistent with sarcomatous mesotheliomas.;In conclusion, these studies indicate that MWCNT material, regardless of physicochemical modification, is significantly genotoxic by disrupting the mitotic spindle and fragmenting centrosomes leading to significant aneuploidy. The MWCNT-7 material produced the greatest amount of aneuploidy. Inhalation exposure to this material was significantly carcinogenic and shown to work through the mechanism of tumor promotion rather than initiation.

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