Characterization of physicochemical properties of pan-frying bacon fat and its potential effects on breast cancer progression

Breast cancer (BC) is the most commonly diagnosed cancer among women in the US. Approximately 1 in 8 women would be diagnosed with BC in their lifetime. The incidence of BC varies around the world, and the age-standardized rate doubles in some developed countries like the US, Canada, Australia, when compared with countries in East Asia. Epidemiology studies demonstrated that environmental factors play an important role in the risk of the onset and progression of BC. Among environmental factors, diet is considered one of the most important and most modifiable risk factors. It is intriguing to investigate the differences between dietary intake in the western world and other parts of the world and to find the correlation between diet and the incidence and development of BC. A Western pattern diet is generally characterized by high intake of red meat, processed meat, high-fat dairy products, and high-sugar drinks. Fats account for approximately 35% of the average American’s caloric intake. Therefore, it is important to address the relationship between fat consumption and health.\nThe overall objective of this project was to characterize bacon fat chemically and to investigate the impact of a bacon fat diet on breast cancer progression in vivo. Our central hypothesis was that consumption of bacon fat would impact breast cancer pathophysiology, and it may accelerate the progression of breast cancer.\nThe first specific aim was to characterize bacon fat (BF) and compare it with lard and fat extracted from bacon. Bacon was pan-fried under controlled conditions, and BF was collected for chemical analysis and animal feed. Soxhlet extraction was used to extract lipid from fried bacon, and the lipid content was calculated. Fatty acid composition and cholesterol concentration were determined by GC-MS and UPLC-ESI-MSMS, respectively. Lard was utilized as a control because bacon fat and lard are both lipids from pig; however, during processing of bacon, the meat undergoes curing and salting, whereas lard is rendered from the fatty tissue of the pig.\nThe second specific aim was to evaluate the effects of a low-fat bacon fat diet on breast cancer progression in preclinical (murine) models, including the impact on primary tumor growth and metastatic potential. The syngeneic allograft mouse model BALB/c mouse strain and FVB mouse strain were selected. In each preclinical study, mice were randomly placed on diets with lard (5% fat from lard, 5% lipid from soybean oil), bacon fat (5% BF, 5% lipid from soybean oil), or a control diet with no expected cholesterol, where lipid content was matched with soybean oil (10% soybean oil). The completed preclinical study includes five parts: 1) Dietary effect of BF on orthotopic primary tumor growth. 2) Dietary effect of BF on breast cancer metastasis and survival on syngeneic BALB/c mice. 3) Dietary effect of BF on breast cancer metastasis on FVB mice and the effect of cholesterol uptake inhibitor. 4) Short-term dietary effect of BF on breast cancer metastasis in BALB/c mice. The mice were euthanized three days after breast cancer cell engraftment to measure the acute response in the tumor microenvironment, including macrophages, neutrophils, and T cells in the pre-metastatic lung. 5) Long term effect of BF on breast cancer metastasis on BALB/c mice.\nThe major findings of this dissertation were:\n(1) Pan-fried BF has an altered fatty acid profile and increased oxysterol 7a/b-\nhydroxycholesterol compared with uncooked lard. High temperature pan-frying induced\nlipid oxidation, including fatty acid oxidation and cholesterol oxidation in bacon fat.\n(2) Consumption of bacon fat increased breast tumor growth and increased distal metastasis.\nThus, it is associated with shorter survival in breast cancer-bearing mice. (3) Consumption of lard increased metastasis compared with a cholesterol-free diet, and the metastatic burden was further increased by the bacon diet. The cholesterol uptake inhibitor Ezetimibe attenuated metastasis increased by the bacon fat-containing diet.\n(4) Myeloid infiltration increases in premetastatic lungs in bacon diet compared to control diet; T cell infiltration in metastatic lungs is altered in mice fed a bacon fat-containing diet compared to control diet. Distal metastasis was observed in both lung and bone, and metastasis increased in mice fed a bacon fat-containing diet.\nIn conclusion, this dissertation demonstrated the lipid composition differences between BF and uncooked lard; and that consumption of bacon fat increased breast cancer tumor growth and metastasis in preclinical models.

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