An ion metathesis strategy for overcoming therapeutic limitations of rose bengal

Abstract

The therapeutic use of rose bengal (RB) has been limited by its anionic nature, high water solubility, and short half-life. Herein, RB was converted into a group of uniform materials based on organic salts (GUMBOS) via ion metathesis reactions to replace its sodium counterions with distinct cationic antiseptics (i.e., benzyldimethylhexadecylammonium, BZK; cetylpyridinium, C16Py; and chlorhexidine, CHX). The potential use of RB-based GUMBOS as antibacterial agents was investigated against a panel of Gram-positive and Gram-negative bacteria, namely Staphylococcus aureus (S. aureus), methicillin-resistant S. aureus (MRSA), Enterococcus faecalis (E. faecalis), Pseudomonas aeruginosa (P. aeruginosa), and Escherichia coli (E. coli). The micro-broth dilution method was used to determine the minimum inhibitory concentration (MIC) of synthesized GUMBOS as well as their parent compounds and unreacted stoichiometric mixtures. Hemolytic effects were further studied using human red blood cells. When compared to parent compounds and unreacted mixtures, GUMBOS showed equal or improved activity towards the non-resistant strain of S. aureus (i.e., DSM 2569) and E. faecalis. Additionally, [CHX][RB] was found to be active against E. coli with a MIC of 6.4–0.8 nmol mL−1, being 79 and 48 times more potent than RB and the corresponding unreacted mixture. The [CHX][RB] GUMBOS also showed the lowest hemolytic activity among all tested compounds and mixtures (percentage of hemolysis <5%). Overall, these results demonstrated that this ion metathesis strategy can improve the antibacterial activity of RB against Gram-positive bacteria and extend its spectrum of action towards E. coli, which could further contribute to safety improvements in multiple industries.