Date of Award

2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Pharmaceutical Sciences

Specialization

Pharmacology and Toxicology

Department

Biomedical and Pharmaceutical Sciences

First Advisor

Jaime Ross

Second Advisor

Giuseppe Coppotelli

Abstract

Plastics can broadly be defined as semi- or fully synthetic organic polymers and are one of the most widely used commercial materials to support a variety of industries including technology, fashion, agriculture, and medicine. Plastics became popularized during World War II due to their low cost, lightweight, and quick production which made them suitable to support the war effort. Since that time, global annual plastic production has grown at a nearly exponential rate with our current production at nearly 500 million tons per year and a projected growth to over 1 billion tons per year by 2050. Despite the societal advancements plastics have supported, this mass production has led to a global plastic pollution crisis. Of the plastic produced, an estimated 70-80% ends up as mismanaged environmental waste or in landfills, and the United Nations estimates that 19-23 million tons of plastic waste enter earth’s water systems each year.

Once in the environment, plastics do not biodegrade but rather fragment into micro- (< 5 mm) and nano- (< 100-1000 nm) plastics through processes such as UV radiation, physical abrasion, and oxidation. Because of their small size and high surface area, nano- and microplastics (NMPs) are able to move rapidly across the environment and be easily ingested/inhaled which can result in bioaccumulation within organisms and transfer across different trophic levels. While NMPs have only recently been identified as an environmental pollutant, they have already been shown to accumulate in water, soil, air, wildlife, and even human tissues where they may exert adverse effects such as mediating transfer of viruses and bacteria, leaching harmful chemicals, inducing inflammation, altering metabolic pathways, and increasing oxidative stress. It still remains largely unknown, however, exactly how NMPs exposure can impact human health. In particular, research on NMPs below 5 µm in size is severely limited due to the difficulty of monitoring NMPs in this size range. As a result, there is a distinct lack of knowledge on the effect of NMPs in this size range on general human health, their potential role in disease, and methodologies for their evaluation.

To begin addressing these gaps, we first conducted a study in which we exposed female 4 and 21 month old C57BL/6J mice to a 1:1 volume mixture of 0.1 and 2 µm fluorescently-labeled pristine spherical polystyrene nano- and microplastics (PS-NMPs) for 3 weeks via drinking water. Following this exposure, we then conducted a series of behavioral assays to assess cognitive function, as well as using biochemical analyses to analyze inflammatory markers in tissue. We found that a short-term exposure to 0.1 and 2 µm PS-NMPs induced significant behavioral changes, as well as altered immune markers in both liver and brain tissue, and that these effects seemed to be age-dependent.

Following the discovery of these exposure outcomes in a “healthy” C57BL/6J mouse model, we further aimed to explore how these effects may be exacerbated when combined with a genetic risk factor for disease. Apolipoprotein E (APOE) is a protein with many functions including lipid metabolism, cytoskeletal structure/assembly, and mitochondrial functioning and has been identified to have 3 major isoforms in humans: APOE2, APOE3, and APOE4. APOE4 in particular has been identified as one of the strongest genetic risk factors for the development of Alzheimer’s disease (AD). To understand how NMPs exposure may interact with the APOE4 allele to increase disease risk, we designed a study in which we exposed 3-6 month old male and female APOE3 and APOE4 humanized knock-in mice (APOE3/4 h-KI) to a high concentration (0.125 mg/mL) of 0.1 and 2 µm PS-NMPs for 3 weeks via drinking water. Results from this study have shown that exposure to 0.1 and 2 µm PS-NMPs predominantly altered behavior in APOE4 mice as compared to their APOE3 counterparts, and that this effect seems to be sex-dependent. Additionally, we found significant sex-dependent alterations to immune and metabolic markers in brain and liver tissue in both APOE3 and APOE4 mice following PS-NMPs exposure.

Following each of these exposure studies, it became clear that NMPs were capable of crossing biological barriers and exerting toxic effects, but it remains difficult to assess NMPs accumulation in mammalian systems. It is critical to evaluate overall particle accumulation, as this may help reveal correlations between NMPs burden and disease severity. This challenge is even further complicated for NMPs < 5 µm, which often evade most sampling and detection techniques. To address this, we developed a novel workflow to extract, isolate, and quantify 2 and 0.1 µm PS-NMPs from mammalian tissue. Using this methodology, we were able to successfully recover 85% and 30% of our 2 and 0.1 µm PS-NMPs, respectively. We were further able to use this methodology on kidney tissue collected from our C57BL/6J study where mice were exposed to a 1:1 volume mixture of 0.1 and 2 µm PS-NMPs and found that this methodology can be applied to actual laboratory studies to detect dose-dependent changes in NMPs accumulation.

Results from each of these studies, independently and together, suggest that NMPs are capable of exerting toxic effects on mammalian organisms. These effects include, but are not limited to, alterations in immune and metabolic markers, changes in behavior, potential interactions with specific disease risk factors, and bioaccumulation of NMPs in every major organ examined. Although NMPs research is still largely in its infancy, these findings highlight the urgent need for more work to better understand the extent of NMPs toxicity and the risks these pollutants pose to overall human health.

Download

Available for download on Tuesday, August 08, 2028

Share

COinS