Preparation of novel antimicrobial polymer colloids based on (+)-usnic acid and poly(vinylbenzyl chloride)

Inhibition of Autophagy Increases Cell Death in HeLa Cells through Usnic Acid Isolated from Lichens

The Western Ghats, India, is a hotspot for lichen diversity. However, the pharmacological importance of lichen-associated metabolites remains untapped. This study aimed to evaluate the cytotoxic potential of lichens of this region. For this, sixteen macrolichens were collected and identified from two locations in the Western Ghats. The acetone extract of Usnea cornuta (UC2A) showed significant cytotoxicity towards multiple human cancer cell lines. Interestingly, co-treatment with chloroquine (CQ), an autophagy inhibitor, increased the cytotoxic potential of the UC2A extract. A gas chromatography mass spectrometry (GCMS) study revealed usnic acid (UA), atraric acid and barbatic acid as the dominant cytotoxic compounds in the UC2A extract. Further, UA was purified and identified from the UC2A extract and evaluated for cytotoxicity in HeLa cells. The monodansyl cadaverine and mitotracker red double staining revealed the autophagy-inducing activities of UA, and the inhibition of autophagy was confirmed via CQ treatment. Autophagy inhibition increased the cytotoxicity of UA by 12-16% in a concentration-dependent manner. It also increased lipid peroxidation, ROS levels and mitochondrial depolarization and decreased glutathione availability. A decrease in zeta potential and a 40% increase in caspase 3/7 activity were also noted after CQ treatment of UA-treated cells. Thus, cytotoxicity of UA can be increased by inhibiting autophagy.

Enhanced wound-healing capability with inherent antimicrobial activities of usnic acid incorporated poly(ε-caprolactone)/decellularized extracellular matrix nanofibrous scaffold

An extracellular matrix-mimicking, biodegradable tissue-engineered skin substitute with improved antibacterial, antibiofilm, and wound healing capabilities is essential in skin tissue regeneration applications. The purpose of this study was to develop a novel biodegradable composite nanofibrous poly(ε-caprolactone) (PCL)/decellularized extracellular matrix (dECM) scaffolds loaded with usnic acid (UA); (PEU), where UA is employed as an antibacterial agent as well as a wound-healing accelerator. The architecture and fiber structure of the scaffolds were examined using scanning electron microscopy, and the results revealed that the average diameters decreased as the dECM content increased. The chemical composition, changes in the crystalline structure, homogeneity, and thermal stability of the nanofiber scaffolds with different material compositions were determined using Fourier-transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, and thermogravimetric analysis, respectively. The composite nanofibrous scaffolds exhibited strong antibacterial activity against various bacterial species, such as Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus mutans, and Cutibactrium acnes, and fungal pathogens (such as Candida albicans). Additionally, the composite nanofibrous scaffolds exhibited biofilm inhibition properties against Klebsiella pneumoniae and Pseudomonas aeruginosa. An evaluation of the appearance of in vivo full-thickness excisional wounds treated with the composite nanofiber scaffolds, as well as a histological analysis of the wounds 21 days after surgery, revealed that treatment with nanofibrous PEU scaffolds enhanced wound healing. This study reveals that the proposed composite nanofibrous PEU scaffold has substantial potential for treating infectious full-thickness wounds.

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

Usnic acid is one of the most investigated lichen secondary metabolites, with several proven biological properties with potential medical relevance. However, its unfavorable physico-chemical properties, as well as observed hepatotoxicity, have discouraged wide-range utilization of usnic acid as a promising therapeutic agent. In accordance with the growing research interest in the development of nanotechnology, especially in the arena of preparations based on natural sources of medicinal compounds, usnic acid incorporated into nano- and microsized colloidal carriers has been a subject of a large number of publications. Therefore, this review discusses the overall results of the studies dealing with usnic acid encapsulated into lipid-based, polymeric and nonorganic micro- and/or nanocarriers, as potential drug delivery systems for this natural compound, in an attempt to introduce its usage as a potential antitumor, antimicrobial, wound-healing, antioxidative and anti-inflammatory drug.