Date of Graduation

8-2025

Document Type

Thesis

Degree Name

Master of Science in Human Environmental Science (MS)

Degree Level

Graduate

Department

General Human Environmental Sciences

Advisor/Mentor

Trudo, Sabrina

Committee Member

Fiddler, Joanna

Second Committee Member

Roberts, Mallori

Keywords

apigenin; cancer; flavonoids; macrophages; vegetables

Abstract

Colorectal cancer is one of the most fatal diseases in the United States. Chronic tissue inflammation can cause cell proliferation, which leads to tumor formation and cancer development. Macrophages are responsible for maintaining tissue homeostasis and for inflammatory responses. M1 macrophages exhibit proinflammatory responses while M2 macrophages exhibit anti-inflammatory responses. Imbalance between M1 and M2 macrophages is closely related to inflammation-associated disease development. The anti-inflammatory effects of apiaceous vegetable constituents, specifically flavonoids, have been studied for their preventative effects towards reducing disease risk. However, sufficient evidence is lacking on the mechanisms by which flavonoids impact M1/M2 macrophage polarization. RAW 264.7 cells were pre-treated with apigenin for 2 hr prior to applying lipopolysaccharide (LPS) and interferon γ (IFNγ) for M1 macrophage polarization or interleukin-4- 4 (IL-4) for M2 macrophage polarization. After 22-hr incubation, culture media was used for nitric oxide (NO) quantification, and the cells were used to quantify gene expression, and the expression and nuclear translocation of proteins. We screened nine polyphenols for their effect on NO production in M1 macrophages. Among them, apigenin was the most effective in reducing NO production in LPS/IFNγ-induced M1 macrophages. Apigenin downregulated mRNA expression of M1-related genes, including TNFα, CD86, and IL-6 in M1 macrophages but had no effect on IL-1β and iNOS. Apigenin reduced IL-6 and IL-10 cytokine production in LPS/IFNγ-induced macrophages but had no effect on IL-1β and TNFα. Apigenin did not induce M2 marker genes such as CD163, CD206, and IL-10 in M1 macrophages, which indicates apigenin does not repolarize M1 macrophages toward M2 macrophages. Apigenin also suppressed M2 macrophage polarization by downregulating M2 gene expression of Arg-1, CD206, and IL-13 in IL-4-induced M2 macrophages. Apigenin suppressed M1 macrophage polarization by inhibiting phosphorylation of p65 and STAT1, downstream targets of LPS and IFNγ, respectively. These are major transcription factors regulating M1 macrophage polarization. Although nuclear translocation of p65 was not influenced, apigenin inhibited NF-κB transcriptional activity. Taken together, apigenin inhibited M1 macrophage polarization through suppression of LPS/IFNγ signal transduction, implying that apigenin could be a promising anti-inflammatory polyphenol for preventing inflammation-associated diseases and might play a critical role in colon cancer development.

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