Improving absorption and bioactivities of phytochemicals using protein/polysaccharide nanoparticle delivery systems
Creators: name: Zheng, Ting
Publisher: name: No Publisher Supplied
Year: 2022

description: Phytochemicals have gained increasing attention due to their potential health benefits, while their applications to the functional food industry have encountered multiple hurdles. It was found that many phytochemicals are susceptible to temperature, pH, oxygen abuse, and present low intestinal absorption rates, leading to compromised bioactivities in the human body. Protein/polysaccharide nanoparticle delivery systems have been proposed as a potential solution for potentiating the bioavailability and bioefficacy of phytochemicals. Nanoparticles assembled with protein and polysaccharides rise above synthetic materials with advantages such as vast abundance, biodegradable and biocompatible, and flexible with modification. However, there are no universal delivery systems for phytochemicals with distinctive chemical and physical properties. Therefore, this research aims to evaluate the suitability and efficiency of delivery systems developed for different encapsulating purposes. In this dissertation, two representative phytochemicals, one with low permeability and one with low solubility, were selected, protein/polysaccharide nanoparticle systems designed for each phytochemical were developed, and the feasibility and efficiency of encapsulation were evaluated using in vitro and cell models. In the first part, a black tea polyphenol, theaflavin-3,3’-digallate (TF3), was encapsulated in nanoparticles comprising chitosan (CS) and caseinophosphopeptides (CPPs) to improve its stability and intestinal absorption. Genipin, a natural crosslinker, was used to prevent pH-induced disassociation of nanoparticles by covalent crosslinking. The effect of genipin-crosslinked nanoparticle (GnNPs) encapsulation on the stability, intestinal absorption, bioactivities, and colonic metabolism of TF3 were then evaluated using in vitro models. Our results showed that the GnNPs system could effectively enhance the chemical stability of TF3 with significantly higher retention during cell culture incubation. Intestinal uptake and absorption of TF3 were also greatly enhanced, as indicated by accumulated intracellular distribution in Caco-2 cells and four-fold higher diffusion through porcine jejunum. However, the anti-liver cancer activity of TF3 seemed to be lessened after encapsulation, and this higher absorption but lower bioactivity paradox suggested that the anti-cancer activity such as induction of cell apoptosis might not require cellular entry and was likely due to TF3-generated oxidative stress in the cell culture medium. Further fermentation study showed that TF3 was quickly metabolized to degalloylated TF3 and phenolic acid with lower molecular weight, such as pyrogallol and 3-(4-hydroxyphenyl) propionic acid. In contrast, encapsulated TF3 delayed the microbial catabolism with minor degalloylation and biotransformation. In the second part, carnosic acid (CA), a phenolic diterpene found in leaves of sage and rosemary, was encapsulated in zein-based nanoparticles to improve its gastrointestinal solubility using the antisolvent method. Additionally, carboxymethyldextran (CMD) and sodium caseinate (SC) were used for surface coating to address the poor colloidal stability innate with zein nanoparticles. Characterization of CA in Zein/CMD/SC nanoparticles was performed by investigating the interactions between different components, defining the particle sizes, surface charges, and morphology. Then, the release and digestion profiles of CA in Zein/CMD/SC nanoparticles and free form were evaluated in the simulated gastrointestinal medium and the TIM-1 dynamic digestion model. Further cellular uptake and mechanisms were clarified in cells under confocal. Lastly, the influence of encapsulation on the bioactivities of CA was compared using the 3T3-L1 adipocyte model and liver cancer cells HepG2. The results showed that CA encapsulated in Zein/CMD/SC nanoparticles demonstrated substantially higher dissolution and intestinal absorption than CA in water. Cell studies indicated that nanoparticle encapsulation could achieve equivalent efficacy in lipid accumulation inhibition, cell cycle arrestment, apoptosis induction, and caspase-3 expression compared to CA fully dissolved in DMSO. This work could provide a systemic screening framework for evaluating the cargo delivery efficiency of protein/polysaccharide nanoparticle systems and greatly facilitate applications of phytochemicals in the functional food industry.