Anti-cancer and anti-inflammatory activities of apigenin nanoencapsulated in dairy proteins

Dietary polyphenols such as apigenin are the secondary plant metabolites reported to reduce incidence of many chronic diseases including cancers and chronic inflammation. However, the high hydrophobicity of lipophilic polyphenols results in low water solubility and bioavailability, which limits the therapeutic efficacy and impedes further applications in aqueous food systems. Nanoencapsulation is a potential approach to address the above problems. Thus, the objective of this dissertation was to develop nanodelivery systems of apigenin utilizing dairy proteins as carriers, followed by evaluating the in vitro and in vivo anticancer efficacy and anti-inflammatory effects. The first delivery system was fabricated by increasing mixtures with 0.6-2.0 mg/mL apigenin and 1% w/v whey protein isolate (WPI) to pH 13, followed by neutralization (the pH-cycle). The encapsulation efficiency was 93.44-98.38% and the loading capacity was 57.19-195.78 mg-apigenin/g-WPI. Nanodispersions maintained stable hydrodynamic diameters of 180-240 nm during 30-day ambient storage. Nanoencapsulation enhanced the cellular uptake of apigenin in human HCT-116 and HT-29 colorectal cancer cells, and the oral bioavailability in C57BL/6J mice. In vivo anti-colorectal cancer efficacy was evaluated in ApcMin+ mice. Results showed that neither free apigenin nor encapsulated apigenin positively suppressed colon carcinogenesis, by insignificantly affecting polyps numbers, tissue apoptosis, tumor marker expressions (COX-2，β-catenin, cyclin D1, and c-myc), and levels of inflammatory cytokines (TNF-α, IL-6, and IL-1β). The second nanodelivery system was fabricated by co-encapsulating apigenin and curcumin at various mass ratios in sodium caseinate using the pH cycle method. Curcumin enhanced the encapsulation efficiency and dispersion stability. When evaluated for anti-inflammatory activities in LPS-induced RAW 264.7 macrophages under non-toxic concentrations, unencapsulated polyphenol mixtures with an increased proportion of curcumin showed synergistic anti-inflammatory activities, evidenced by a combination index of smaller than 1, in inhibiting nitric oxide production, suppressing iNOS enzyme expression, decreasing pro-inflammatory cytokines (TNF-α and IL-6), and reducing ROS production. These synergistic anti-inflammatory effects of apigenin and curcumin were enhanced after coencapsulation. Findings from the present dissertation may provide insights to develop functional foods incorporated with lipophilic phytochemicals as potential strategies for disease prevention.