Natural Ellagic Acid-Polyphenol ″Sandwich Biscuit″ Self-Assembled Solubilizing System for Formation Mechanism and Antibacterial Synergia

Ellagic acid (EA) has limited utility due to its extremely low solubility. Inspired by the naturally high content of EA in Triphala, the research group discovered that there might be noncovalent self-assembled nanoaggregates centered on EA in natural polyphenols that could significantly improve EA's solubility and enhance its antibacterial activity. Therefore, seven polyphenols that we found were potentially involved in EA self-assembly were separated and identified from Triphala, and 18 binary, ternary, and quaternary self-assembly systems were constructed by combining them with EA. Finally, a ternary self-assembled solubilizing system centered on ellagic acid-gallic acid-catechin (EA-GA-CA) was established. The system could improve the solubility of EA from 0.95 to 171.345 μg·mL-1, leading to a notable 180-fold increase, and the stability of EA in water was increased 3 times compared with the mixture of EA, GA, and CA, which is currently the most effective carrier-free hydrotropic solubilizing method of EA. The in vitro release rate reached about 61%, which was about 60 times higher than that of EA. Exploring the formation mechanism of the self-assembled complex revealed that EA, GA, and CA were induced by hydrogen bonding and π-π stacking to form a solubilizing structure resembling a sandwich biscuit. In addition, in vitro antibacterial experiments, biofilm clearance experiments, and infected wound healing experiments demonstrated that the EA-GA-CA complex has a better inhibitory effect on Staphylococcus aureus (S. aureus) and methicillin-resistant S. aureus (MRSA) than EA, GA, CA, benzylpenicillin potassium, and the mixture of EA, GA, and CA (MIC = 12.5 mM). The inhibition rate of the EA-GA-CA complex against S. aureus reaches 82.68%, and it can rapidly promote the healing of infected wounds caused by S. aureus within 4-6 days (the healing rate increased from 15 to 75%). This study aims to provide new ideas for EA's natural small molecule carrier-free self-assembly solubilization and synergistic applications.