Bounded polyphenols from persimmon by-products: modulatory, anti-virulence and cytoprotective effects against bacterial pathogens
- Autores: Bryan Mauricio Moreno Chamba
- Directores de la Tesis: Manuel Valero Roche (dir. tes.), Nuria Martí Bruñá (codir. tes.)
- Lectura: En la Universidad Miguel Hernández de Elche ( España ) en 2024
- Idioma: inglés
- Tribunal Calificador de la Tesis: Cristina García Viguera (presid.), Luis Pérez García-Estañ (secret.), Sylvia Duncan (voc.)
- Materias:
- Enlaces
- Tesis en acceso abierto en: RediUMH
- Resumen
Food by-products are a valuable source of bioactive compounds with therapeutic properties. Particularly, polyphenols have garnered attention not only for their antioxidant activity but also for their structural diversity, which enables them to participate in various biological processes. They are potential candidates for targeting different diseases that affect human health. Among their numerous properties, the antibacterial activity of polyphenols is one of the most documented. This is of importance in an era where antimicrobial resistance to current antibiotics is alarmingly raising, making the search for new antibacterials crucial. However, many studies on the antibacterial activity of polyphenols primarily focus on their ability to inhibit bacterial proliferation, often overlooking other antibacterial properties that could support their potential applications. Furthermore, most polyphenolic studies concentrate on evaluating available polyphenols, which are easily extractable from their matrix, such as by-products, and often disregard bound polyphenols. Bound polyphenols, which provide structural functions within polysaccharides, may offer higher therapeutic potential, especially against bacterial infections and related diseases. This Thesis aims to explore the antibacterial potential of bound polyphenols from persimmon by-products, investigating applications beyond their inhibitory effects, which could facilitate the reintegration of persimmon by-products into the value chain for nutraceutical and therapeutic uses.
The present Thesis is divided into three chapters. Chapter 1 examines the effect of polysaccharides from persimmon by-products on bacterial strains related to human health. Polysaccharides were purified using solvent-assisted extraction treatments and subjected to in vitro digestion to determine their potential prebiotic effects. Results indicated that persimmon dietary fibre (DF), particularly the digested fraction treated with acetone, promoted the growth of beneficial strains such as Lactobacillus casei, Lactococcus lactis, and Bifidobacterium bifidum while selectively limiting the proliferation of Escherichia coli, indicating a potential prebiotic effect. Additionally, the results suggested a modest antibacterial activity, notably against Staphylococcus aureus, when tested on foodborne pathogens. To further explore the antibacterial potential of persimmon DF, other properties related to bacterial resistance were assessed, including antibiofilm activity. Promising results were observed, with inhibition of initial cell attachment of pathogens. Furthermore, when combined with gentamycin, the digested persimmon DF treated with acetone exhibited a synergistic and bactericidal effect against S. aureus. The study also identified that polysaccharides from fruit by-products contain bound polyphenols, which were extracted and found to include galloylated compounds (mainly gallic acid) responsible for the recorded antibacterial activity.
The previous study highlighted the effect of the bound polyphenols from persimmon by-product as significant antibacterial agents. To compare their efficacy, Chapter 2 explored the anti-virulence activity of bound polyphenolic extracts from persimmon with available polyphenols from pomegranate and grape by-products. The study focused on the effects of these extracts, at sub-inhibitory concentrations, on bacterial quorum sensing (QS), which governs bacterial behaviour. Results showed that all three extracts, particularly pomegranate, inhibited virulence factors violacein and pyocyanin in Chromobacterium violaceum and Pseudomonas aeruginosa, respectively, indicating quorum quenching (QQ) effects. Metabolic analysis confirmed the reduction of autoinducers, suggesting potential impacts on biofilms, bacterial motility, and resistance factors. The grape extract notably disrupted biofilms and swarming motility, while all extracts reduced efflux pump activity in P. aeruginosa and ß-lactamase activity in Klebsiella pneumoniae. The antibacterial mode of action involved cell membrane damage (CMD), with the grape extract having a minor effect.
The results indicated that bound polyphenols from persimmon by-products had antibacterial effects comparable to pomegranate and grape extracts, targeting bacterial virulence through quorum sensing autoinducers. Chapter 3 explored the effect of these extracts in cell host environment, particularly intestinal and skin epithelium. The extracts reduced the adhesion of Salmonella enterica and K. pneumoniae to adenocarcinoma colon cells (Caco-2) and S. aureus and E. coli to keratinocyte cells (HaCaT). They also enhanced the competitive exclusion of pathogens by L. lactis and Cutibacterium acnes on Caco-2 and HaCaT cells, respectively. Pomegranate extract showed a notable anti-invasion effect against S. enterica on Caco-2 cells. The extracts maintained the barrier function of lipopolysaccharides from E. coli (LPS)-challenged cells, reduced pro-inflammatory cytokines IL-6 and IL-8, and decreased intracellular reactive oxygen species (ROS) levels. Cytoprotection by persimmon and grape extracts was dependent of nuclear factor erythroid 2-related factor 2 (Nrf2) pathway, which is a transcription factor implicated in the activation of cell defence mechanisms. Contrary, pomegranate extract had a Nrf2-independent effect. Characterization identified significant gallic acid in persimmon extract and punicalagin, delphinidin, and cyanidin 3-O-glucoside in pomegranate and grape extracts, respectively, attributing the observed effects to these compounds.
Overall, the results support the antibacterial potential of bound polyphenols from persimmon by-products, showing effects equivalent to other polyphenolic extracts. The findings also highlight the potential of persimmon DF as a prebiotic substrate and the bound polyphenolic extract as a nutraceutical or functional ingredient, promoting the revalorisation of persimmon by-product. These components could attenuate pathogen virulence and provide cytoprotective properties, potentially reducing bacterial infection risks. However, these effects need confirmation in in vivo models.
