Efficacy of Ursolic Acid-Enriched Water-Soluble and Not Cytotoxic Nanoparticles against Enterococci

Abstract

Ursolic acid (UA), a pentacyclic triterpenoid acid found in many medicinal plants and aromas, is known for its antibacterial effects against multi-drug-resistant (MDR) Gram-positive bacteria, which seriously threaten human health. Unfortunately, UA water-insolubility, low bioavailability, and systemic toxicity limit the possibilities of its application in vivo. Consequently, the beneficial activities of UA observed in vitro lose their potential clinical relevance unless water-soluble, not cytotoxic UA formulations are developed. With a nano-technologic approach, we have recently prepared water-soluble UA-loaded dendrimer nanoparticles (UA-G4K NPs) non-cytotoxic on HeLa cells, with promising physicochemical properties for their clinical applications. In this work, with the aim of developing a new antibacterial agent based on UA, UA-G4K has been tested on different strains of the Enterococcus genus, including marine isolates, toward which UA-G4K has shown minimum inhibitory concentrations (MICs) very low (0.5–4.3 µM), regardless of their resistance to antibiotics. Time-kill experiments, in addition to confirming the previously reported bactericidal activity of UA against E. faecium, also established it for UA-G4K. Furthermore, cytotoxicity experiments on human keratinocytes revealed that nanomanipulation of UA significantly reduced the cytotoxicity of UA, providing UA-G4K NPs with very high LD50 (96.4 µM) and selectivity indices, which were in the range 22.4–192.8, depending on the enterococcal strain tested. Due to its physicochemical and biological properties, UA-G4K could be seriously evaluated as a novel oral-administrable therapeutic option for tackling difficult-to-treat enterococcal infections.

Pyrazole-Based Water-Soluble Dendrimer Nanoparticles as a Potential New Agent against Staphylococci

“…Let us first consider the two ingredients, G4K and BBB4. As expected, the cytotoxic profile of the empty dendrimer G4K conformed to that observed by us previously after both 4, 12, and 24 h [ 54 ]. Particularly, after 4 h of exposure, at concentrations of 5–100 µM, the G4K was the least toxic compound, with no significative difference in cell viability compared to the control, even at the maximum concentration tested (100 µM, cell viability 97.2%).…”

“…Moreover, as observed after 12 h of exposure, the cell viability did not change significantly for higher BBB4 concentrations. As for the BBB4-G4K NPs, the results obtained were very different from those observed for the NPs made of the same dendrimer G4K but loaded with ursolic acid (UA-G4 NPs) and those of the recently published [ 54 ]. In that study, the encapsulation of UA in G4K led to a reduction in the intrinsic cytotoxicity of the two ingredients, resulting in UA-loaded NPs significantly less cytotoxic than the two compounds when administered alone [ 54 ].…”

“…As for the BBB4-G4K NPs, the results obtained were very different from those observed for the NPs made of the same dendrimer G4K but loaded with ursolic acid (UA-G4 NPs) and those of the recently published [ 54 ]. In that study, the encapsulation of UA in G4K led to a reduction in the intrinsic cytotoxicity of the two ingredients, resulting in UA-loaded NPs significantly less cytotoxic than the two compounds when administered alone [ 54 ]. On the contrary, in this case, after 4, 12, and 24 h of exposure, and depending on the time of the experiments, a dramatic improvement in the cytotoxic effects of the BBB4-G4K NPs was observable starting from the 15 µM concentration, resulting in a reduction in cell viability below 50% [cell viability of 38.0% (4 h), 16.5% (12 h), and 13.7% (24 h)].…”

Antimicrobial Peptides and Cationic Nanoparticles: A Broad-Spectrum Weapon to Fight Multi-Drug Resistance Not Only in Bacteria

“…In this context, ursolic acid or pyrazole derivatives known to be endowed with several pharmacological activities have been successfully encapsulated in fourth- and fifth-generation cationic dendrimers modified with lysine, obtaining drug-loaded nanocomposites with proven high-water solubility and loading capacity [ 177 , 178 , 179 ]. When tested on bacteria, these nanocomposites displayed potent antibacterial activity, much higher than that of the encapsulated molecules, against Gram-positive MDR isolates of the Staphylococcus [ 180 ] and Enterococcus [ 181 ] genera, regardless of the intrinsic antibacterial effects of the dendrimers used as encapsulating agents. This achievement can be explained assuming that the cationic property of the NPs enveloping the bioactive molecules allowed their accumulation on the surfaces of bacteria and promoted their entry into the cells via pore formation.…”

Enhanced Antibacterial Activity of a Cationic Macromolecule by Its Complexation with a Weakly Active Pyrazole Derivative

“…Human keratinocytes (HaCaT), deriving from a generous gift of the Laboratory of Experimental Therapies in Oncology, IRCCS Istituto Giannina Gaslini (Genoa, Italy), were grown as previously described [ 6 , 22 , 35 , 36 ].…”