RESUMO
Crude sophorolipids (SLs) have been proven to perform varying degrees of inhibitory effects on different pathogenic bacteria. However, systematic comparative studies of pure lactonic sophorolipid (LSL) among different types of bacteria are few. In this study, the antibacterial effects and mechanisms of LSL on pathogenic bacteria of Staphylococcus aureus, Lactobacillus sp., Pseudomonas aeruginosa, and Escherichia coli were investigated. Bacteriostatic circle, antibacterial rate, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) of LSL on different pathogenic bacteria were measured. Then, the antibacterial mechanisms of LSL on S. aureus and P. aeruginosa were explored using ultrastructural observation, cell membrane permeability analysis, intracellular ATP content determination, and extracellular UV absorption detection. With the minimum MIC and MBC values of 0.05 and 0.20 mg/ml, LSL exhibited the best inhibitory effect against S. aureus, followed by P. aeruginosa. LSL showed no significant inhibitory effect on E. coli and Lactobacillus sp. For both S. aureus and P. aeruginosa, LSL achieved bacteriostatic and bactericidal effects by destroying the cell wall, increasing the permeability of the cell membrane and leading to the flow out of intracellular contents. However, the action mode and action intensity of LSL on the cell wall and membrane of these two bacteria were significantly different. LSL had a greater influence on the cell membrane of S. aureus by "leaking," while it exhibited a stronger effect on the cell wall of P. aeruginosa by "blasting." These results contributed to a better understanding of the relationship between LSL and different bacterial cell structures, further suggesting the conclusion that LSL might be used for the targeted treatment of special pathogenic bacteria.
RESUMO
Etoposide (ETO), a traditional anticancer chemotherapeutic agent, is commercialized in oral soft gelatin capsules and non-aqueous parenteral solutions form. Novel formulation application and new excipients exploration are needed to improve the water-solubility and comfort of the drug administration. In the present study, novel etoposide-loaded submicron emulsions (ESE) with the biosurfactants of acidic sophorolipid (ASL) and lactonic sophorolipid (LSL) instead of the chemical surfactant of Tween-80 were prepared and characterized. Firstly, parameters of medium-chain triglyceride: long-chain triglyceride (MCT:LCT), lecithin concentration, homogenization pressure and cycle, and type and concentration of surfactants were investigated to optimize the formation of ESEs. Then the physicochemical properties, antitumor activity, stability, and security of ESEs were compared. The results showed that ASL performed the best properties and activities than Tween-80 and LSL in ESE formation. ASL-ESE showed higher drug loading capacity, slower release rate, and significantly increased antitumor activity against ovarian cancer cell line A2780 via apoptosis than Tween-ESE and commercial ETO injection. Besides, both ASL-ESE and Tween-ESE caused no hemolysis, and the safe dose of ASL was 2.14-fold that of Tween-80 in the hemolysis test, making ASL more reliable for drug delivery applications. Furthermore, ASL-ESE exhibited equivalent long-term and autoclaving stability to Tween-ESE. These results thus suggested the excellent competences of ASL in ESE formation, efficacy enhancement, and safety improvement.
