Effects of the encapsulation of usnic acid into liposomes and interactions with antituberculous agents against multidrug-resistant tuberculosis clinical isolates

Abstract

Mycobacterium tuberculosis (Mtb) has acquired resistance and consequently the antibiotic therapeutic options available against this microorganism are limited. In this scenario, the use of usnic acid (UA), a natural compound, encapsulated into liposomes is proposed as a new approach in multidrug-resistant tuberculosis (MDR-TB) therapy. Thus the aim of this study was to evaluate the effect of the encapsulation of UA into liposomes, as well as its combination with antituberculous agents such as rifampicin (RIF) and isoniazid (INH) against MDR-TB clinical isolates. The in vitro antimycobacterial activity of UA-loaded liposomes (UA-Lipo) against MDR-TB was assessed by the microdilution method. The in vitro interaction of UA with antituberculous agents was carried out using checkerboard method. Minimal inhibitory concentration values were 31.25 and 0.98 µg/mL for UA and UA-Lipo, respectively. The results exhibited a synergistic interaction between RIF and UA [fractional inhibitory concentration index (FICI) = 0.31] or UA-Lipo (FICI = 0.28). Regarding INH, the combination of UA or UA-Lipo revealed no marked effect (FICI = 1.30-2.50). The UA-Lipo may be used as a dosage form to improve the antimycobacterial activity of RIF, a first-line drug for the treatment of infections caused by Mtb.

The Effect of Combining Natural Terpenes and Antituberculous Agents against Reference and Clinical Mycobacterium tuberculosis Strains

“…The literature data show synergistic interactions among antibiotics: isoniazid, rifampicin, and ethambutol (18.1% of combinations with FICI = 0.6) or ofloxacin, rifampicin, and ethambutol (91.3% of combinations with FICI = 0.31–0.62) against M. tuberculosis H37Rv [ 59 ] or between antibiotics and natural products: oleic acid (in combination with isoniazid, rifampicin and ethambutol, FICI in a range 0.09–0.36), 7-methyljuglone (in combination with isoniazid, FICI = 0.2 and with rifampicin, FICI = 0.5), usnic acid (with rifampicin, FICI = 0.25–0.38) against M. tuberculosis H37Rv strain and some Mtb drug-resistant clinical isolates [ 2 , 60 , 61 ], however little is known about their mechanism of action. Apart from positive results, the lack of synergy against different bacterial species was also documented.…”

Nano- and Microcarriers as Drug Delivery Systems for Usnic Acid: Review of Literature

“…In a recent study of the same research group [16], the antimicrobial effects of usnic acid encapsulated into liposomes against resistant strains of Mbt were investigated in combination with rifampicin and isoniazid as the first-line drugs in the treatment of tuberculosis. For this purpose, an in vitro microplate alamar blue assay test was employed for the evaluation of MIC values against several clinical isolates of Mbt, for which resistance to rifampicin and isoniazid was previously confirmed.…”

“…Encapsulation of usnic acid into liposomes led to 30-fold lower MIC values for all tested clinical isolates compared to free usnic acid (0.98:31.25, respectively). Such results were explained by possible electrostatic interactions between negatively charged carboxyl groups of mycolic acids in the Mtb cell wall and positively charged liposomal vesicles, or the direct interaction of liposomes and bacteria by the fusion processes, leading to the release of the encapsulated drug within the bacteria [16]. Also, both free and encapsulated usnic acid exhibited a synergistic effect with rifampicin in vitro using the checkerboard method (fractional inhibitory concentration index, FICI < 0.5), unlike the combinations with isoniazid that showed an indifferent effect (1 < FICI ≤ 4).…”

“…When it comes to the methodology used in the stated studies, three studies [15,16,31] included assessment of selected parameters at defined storage conditions and defined time points in both accelerated and long-term conditions, whereby in the accelerated stability, investigation formulations were subjected to (1) centrifugation, (2) horizontal mechanical stirring, and (3) freeze-thaw cycles. For instance, in the investigation of Lira et al [15], accelerated stability studies were used in the preformulation phase with the purpose of selecting optimal formulation with the highest amount of encapsulated usnic acid and concomitant good physico-chemical stability.…”

Usnic Acid Derivatives as Cytotoxic Agents Against Cancer Cells and the Mechanisms of Their Activity

“…Other types of encapsulation were used for antibacterial tests of UA, e.g. carboxylated poly(L-lactide) (cPLLA) microparticles [33], liposomes [29,34], hybrid core/shell iron oxide magnetic nanoparticles [35], manganese/iron oxide magnetic nanoparticles [36] and magnetic polylactic-co-glycolic acid-polyvinyl alcohol (PLGA-PVA) microsphere thin films [37].…”