Date of Award

2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Pharmaceutical Sciences

Specialization

Pharmacology and Toxicology

Department

Biomedical and Pharmaceutical Sciences

First Advisor

Angela Slitt

Abstract

Per- and poly-fluoroalkyl substances (PFAS) are a class of synthetic chemicals that have been released into the environment over the past six decades. Some perfluoroalkyl acids (PFAA), such as perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), have been associated with hepatic steatosis in rodents and monkeys, however it is unclear if lipid accumulation occurs in humans. This thesis explores the liver effects of PFAS on non-alcoholic fatty liver disease, or NAFLD, using mouse and primary human hepatocytes. The central hypotheses are that diet and liver lipid composition alter PFAS-induced outcomes, and PFAS structure (i.e. functional groups and chain length) will also dictate outcomes in hepatocytes regarding lipid metabolism, gene activation, and lipid accumulation.

In manuscript 1, PFOS was evaluated for augmentation of HFD-induced hepatic steatosis and the potential to interfere with lipid loss after switching from a high fat diet (HFD) to a standard diet (SD). 5-week-old male C57BL/6J mice were fed HFD for 4 weeks to increase body weight and induce liver lipid accumulation. Then, some HFD mice were switched to SD to mimic weight loss induced improvement of NAFLD. At that time, mice were also given diet only or diet containing 0.0003% PFOS. After 10 weeks on study, hepatic lipids, serum and liver PFOS levels, and gene and protein expression were evaluated.

In manuscript 2, critical members of the PFAS family were screened for gene expression changes and lipid accumulation in a five-donor pool of cryopreserved human hepatocytes. Hepatocytes were cultured and treated with vehicle or various PFAS at concentrations of 0.25 to 25 μM in media. After 48-hr or 72-hr treatments, mRNA transcripts related to lipid transport, metabolism, and synthesis were measured or cells were stained with Nile Red dye to quantify intracellular lipids.

In manuscript 3, to complement manuscript 1, the impact of maternal diet and PFAS exposure on the risk to mouse pup liver and diet related PFAS partitioning to pups was evaluated. Timed-pregnant dams received at gestation day 1 (GD1) were fed a standard chow diet (SD) or 60% Kcal high fat diet (HFD) and dosed with either vehicle (0.5% Tween 20 in water), 1 mg/kg PFOS, 1 mg/kg PFOA, 1mg/kg PFHxS, or PFAS mix (1 mg/kg of each PFOS, PFOA, and PFHxS) via oral gavage (10 mL/kg). At PND 21, dam and pup liver were collected, weighed, and liver lipids were isolated in dams and pups. Pup serum was also evaluated for PFAS concentration, alanine aminotransferase (ALT), leptin and adiponectin measurements.

Both in vivo mouse studies revealed that diet composition can exert significant influence on PFAS related partitioning to liver and pups, and PFAS liver lipid accumulation. These studies also highlight novel results with short chain PFAA and replacement PFAS, and mixtures, and suggest that different PFAS structures and PFAS in combination may behave differently and should be evaluated carefully for potential human health effects.

Master_gene_expression_data.csv (45 kB)
Master Gene Expression Data

Available for download on Saturday, May 14, 2022

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