Mileah Metcalf

N-(1,3-dimethylbutyl)-N′phenyl-p-phenylenediamine, more commonly known as 6PPD, is a tire antiozonant used to prevent rubber oxidation and degradation. When 6PPD reacts with ozone, it becomes 6PPD-Quinone (6PPD-Q). Stormwater road runoff facilitates the transport of phenylenediamines (PPDs) into the environment. In recent years, 6PPD-Q has been identified as an acute environmental toxicant causing major disruptions to aquatic life. To aid in the growing body of knowledge on the mechanism of action of PPD and potentially support environmental regulations, this study aims to elucidate the toxic effects of 6PPD and 6PPD-Q in Saccharomyces cerevisiae. To accomplish this, a growth assay, RNA sequencing, mitochondrial staining, and RT-qPCR were performed. The results suggest that 6PPD and 6PPD-Q impact growth and gene regulation by dysregulating Complex III, IV, and V of the oxidative phosphorylation pathway. Additionally, 6PPD and 6PPD-Q are, seemingly, agglomerated at different pHs and in various media. The agglomeration of 6PPD-Q may inhibit cellular uptake, leading to fewer discernible toxic effects. Taken together, we can posit that 6PPD and 6PPD-Q both induce oxidative stress upon exposure to budding yeast, but 6PPD seems to be more toxic than 6PPD-Q.

Quantum dots (QDs) are nanoparticles with intrinsic fluorescence. Recent studies have found that metal-based QDs often impart toxic effects on the biological systems they interact with. Their undefined limitations have offset their potential for biomedical application. Our study aimed to address the research gap regarding QDs’ impacts on the intracellular actin cytoskeleton and the associated structures. Our XTT viability assays revealed that QDs only reduced viability in transformed human liver epithelial (THLE-2) cells, whereas HeLa cells remained viable after QD treatment. We also used confocal microscopy to evaluate the morphological changes in THLE-2 induced by QDs. We further investigated cell protrusion morphology using phalloidin-Alexa488 which selectively labels F-actin. The fluorescent microscopy of this phalloidin label revealed that QD treatment resulted in the redistribution of actin filaments within both THLE-2 and HeLa cells. We also report that the average number of focal adhesions decreased in QD-treated cells. As actin filaments at the cell are peripherally linked to the extracellular matrix via talin and integrin and are thus a crucial component of cell motility, we conducted a migration assay. The migration assay revealed that cell motility was significantly reduced in both THLE-2 and HeLa cells following QD treatment. Our findings establish that the internalization of QDs reduces cell motility by rearranging actin filaments.