(+)-Usnic Acid as a Promising Candidate for a Safe and Stable Topical Photoprotective Agent

Oxidative DNA damage contributes to usnic acid-induced toxicity in human induced pluripotent stem cell-derived hepatocytes

Dietary supplements containing usnic acid have been increasingly marketed for weight loss over the past decades, even though incidences of severe hepatotoxicity and acute liver failure due to their overuse have been reported. To date, the toxic mechanism of usnic acid-induced liver injury at the molecular level still remains to be fully elucidated. Here, we conducted a transcriptomic study on usnic acid using a novel in vitro hepatotoxicity model employing human induced pluripotent stem cell (iPSC)-derived hepatocytes. Treatment with 20 μM usnic acid for 24 h caused 4272 differentially expressed genes (DEGs) in the cells. Ingenuity Pathway Analysis (IPA) based on the DEGs and gene set enrichment analysis (GSEA) using the whole transcriptome expression data concordantly revealed several signaling pathways and biological processes that, when taken together, suggest that usnic acid caused oxidative stress and DNA damage in the cells, which further led to cell cycle arrest and eventually resulted in cell death through apoptosis. These transcriptomic findings were subsequently corroborated by a variety of cellular assays, including reactive oxygen species (ROS) generation and glutathione (GSH) depletion, DNA damage (pH2AX detection and 8-hydroxy-2'-deoxyguanosine [8-OH-dg] assay), cell cycle analysis, and caspase 3/7 activity. Collectively, the results of the current study accord with previous in vivo and in vitro findings, provide further evidence that oxidative stress-caused DNA damage contributes to usnic acid-induced hepatotoxicity, shed new light on molecular mechanisms of usnic acid-induced hepatotoxicity, and demonstrate the usefulness of iPSC-derived hepatocytes as an in vitro model for hepatotoxicity testing and prediction.

Toxicity of Usnic Acid: A Narrative Review

Usnic acid (UA) is a dibenzofuran derivative naturally present in lichens, organisms resulting from the symbiosis between a fungus and a cyanobacterium, or an alga. UA shows antimicrobial, antitumor, antioxidant, analgesic, anti-inflammatory as well as UV-protective activities. Its use as pharmacological agent is widely described in traditional medicine, and in the past few years, the product has been marketed as a food supplement for the induction of weight loss. However, the development of severe hepatotoxicity in a limited number of subjects prompted the FDA to issue a warning letter, which led to the withdrawal of the product from the market in November 2001. Data published in literature on UA toxicology, genotoxicity, mutagenesis, and teratogenicity have been reviewed, as well as the case reports of subjects who developed hepatotoxicity following oral administration of UA as a slimming agent. Finally, we reviewed the most recent studies on the topical use of UA, as well as studies aimed at improving UA pharmacologic activity and reducing toxicity. Indeed, advancements in this field of research could open the possibility to reintroduce the use of UA as therapeutical agent.

Broccoli Sprouts and Their Influence on Thyroid Function in Different In Vitro and In Vivo Models

Broccoli sprouts are a super vegetable; however, they have possible negative effects on thyroid function, which is especially important for patients with hypothyroidism. As the data on this issue are scarce, this study aimed to determine the safety and possible beneficial effect of broccoli sprouts both in vitro and in vivo. The in vitro model comprised the evaluation of the impact of broccoli sprouts on normal and neoplastic thyroid cells and the determination of their anti-inflammatory and antioxidant (IL-6, TNF-alpha, NO, and SOD) potential in macrophages. The in vivo model concerned the histopathological analysis of thyroid glands in healthy rats and rats with hypothyroidism (induced by iodine deficiency or sulfadimethoxine ingestion) fed with broccoli sprouts. The results of our study indicated that broccoli sprouts decreased the viability of thyroid cancer cells and prevented inflammation. The results also confirmed the satisfactory safety profile of the sprouts, both in vitro and in vivo; however, a further in-depth evaluation of this problem is still needed. Information on the influence of brassica vegetables on thyroid function is of great importance in terms of public health, particularly when taking into account that the risk of iodine deficiency, hypothyroidism, and thyroid cancer in the global population is still increasing.

Usnic Acid Isolated from Usnea antarctica (Du Rietz) Reduced In Vitro Angiogenesis in VEGF- and bFGF-Stimulated HUVECs and Ex Ovo in Quail Chorioallantoic Membrane (CAM) Assay

Simple Summary

Anti-angiogenic therapy, a promising strategy against cancer progression, is limited by drug resistance. Natural plants, such as secondary metabolites of lichens, may represent an appropriate strategy to increase the effectiveness of conventional therapies and overcome resistance to anti-angiogenic therapy if combined with existing chemotherapy. Accordingly, our study was designed to determine the potential anti-angiogenic effect of usnic acid, a secondary metabolite of lichens, on VEGF- and bFGF-stimulated HUVECs as well as in quail chorioallantoic membrane assays, which were supplemented by histological sections of CAM-affected layers.

Abstract

Natural products include a diverse set of compounds of drug discovery that are currently being actively used to target tumor angiogenesis. In the present study, we evaluated the anti-angiogenic activities of secondary metabolite usnic acid isolated from Usena antarctica. We investigated the in vitro effects on proliferation, migration, and tube formation of VEGF- and bFGF-stimulated HUVECs. Ex ovo anti-angiogenic activity was evaluated using the CAM assay. Our findings demonstrated that usnic acid in the concentration of 33.57 µM inhibited VEGF (25 ng/mL) and bFGF (30 ng/mL)-induced HUVECs proliferation, migration, and tube formation. The ex ovo CAM model was used to confirm the results obtained from in vitro studies. VEGF- and bFGF-induced vessel formation was inhibited by usnic acid after 72 h in over 2-fold higher concentrations compared to in vitro. Subsequently, histological sections of affected chorioallantoic membranes were stained with hematoxylin–eosin and alcian blue to determine the number and diameter of vessels as well as the thickness of the individual CAM layers (ectoderm, mesoderm, endoderm). Usnic acid was able to suppress the formation of VEGF- and bFGF-induced vessels with a diameter of less than 100 μm, which was demonstrated by the reduction of mesoderm thickness as well.

Assessment of safety and health-benefits of Citrus hystrix DC. peel essential oil, with regard to its bioactive constituents in an in vitro model of physiological and pathological skin conditions

Citrus hystrix DC. peel essential oil (ChEO) has been reported to have many biological activities and is promoted for topical application. However, its effect on skin functioning has not yet been studied. This study aimed to evaluate its safety for normal skin cells as well as its potential activity against human melanoma. In addition, pro-inflammatory and anti-inflammatory activity was assessed, as well as inhibitory effects on important skin enzymes: tyrosinase and hyaluronidase. To better understand the complexity of the action of ChEO and the role of individual components, the study also included an evaluation of the activity of its main constituents: limonene, β-pinene, and terpinen-4-ol as well as two mixtures of these compounds, specially designed for this purpose: M1 in equal proportions (1:1:1) and M2 in proportions mimicking those found in the ChEO (2.6:1.7:1). The results showed that the essential oil of the C. hystrix peel, as well as its major components, was not cytotoxic to normal human skin cells representing various skin layers, namely keratinocytes (HaCaT), melanocytes (HEM), and fibroblasts (HDF), even after prolonged exposure of 72 h. The pro-inflammatory effect of ChEO, tested by caspase-1 activation in HaCaT cells, was less pronounced compared to limonene, β-pinene and terpinen-4-ol, and generally very low. On the other hand, its anti-inflammatory effect was noticeable and was half the potency of diclofenac sodium used as the reference drug. Although the anti-hyaluronidase activity of C. hystrix peel essential oil was lower compared to β-pinene and terpinen-4-ol, ChEO revealed fairly high anti-tyrosinase activity, with an enzyme inhibition level of over 80% at a concentration of 150-220 μg/ml. Studies on the potential anti-melanoma effect were performed using the LDH assay on three human cell lines of varying degrees of malignancy, namely WM793, A375, and HTB140. ChEO was more active than the tested single compounds or their mixtures. WM793 cells were found to be most susceptible, while HTB140 and A375 cells were slightly more resistant (IC₅₀ 59, 88 and 70 μg/ml, respectively). Our data indicate that ChEO is safe for the skin and has a perspective as an anti-melanoma agent.

Antimelanoma Potential of Cladonia mitis Acetone Extracts - Comparative in Vitro Studies in Relation to Usnic Acid Content

In this study, the cytotoxic activity of acetone extracts of Cladonia mitis was assessed with respect to the content of usnic acid, a secondary metabolite commonly present in this species. Following quantitative HPLC analysis of the extracts, usnic acid was isolated by preparative chromatography. The study of cytotoxic activity was performed using the MTT test on three melanoma cell lines - HTB140, A375 and WM793. The selectivity of action was also assessed by comparing the effect towards normal human keratinocytes HaCaT. The results showed a dose-dependent cytotoxic activity of the extracts tested and usnic acid itself, but no relationship was found between the content of usnic acid and the activity of the extracts. Furthermore, the extracts showed varied, but rather low anti-tyrosinase activity. Other in vitro and in vivo studies are necessary to demonstrate that C. mitis extracts may be useful in the adjuvant external treatment of skin melanoma.

A Comparative Survey of Anti-Melanoma and Anti-Inflammatory Potential of Usnic Acid Enantiomers-A Comprehensive In Vitro Approach

Usnic acid (UA) is a chiral lichen metabolite with an interesting pharmacological profile. The aim of this study was to compare the anti-melanoma effect of (+)-UA and (−)-UA in an in vitro model by studying their impact on the cells as well as the processes associated with cancer progression. The effect of UA enantiomers on the viability, proliferation, and invasive potential of three melanoma cell lines (HTB140, A375, WM793) was evaluated. Their interaction with a chemotherapeutic drug—doxorubicin was assessed by isobolographic analysis. Anti-inflammatory and anti-tyrosinase properties of (+)-UA and (−)-UA were also examined. Both UA enantiomers dose- and time-dependently decreased the viability of all three melanoma cell lines. Their synergistic effect with doxorubicin was observed on A375 cells. (+)-Usnic acid at a sub-cytotoxic dose strongly inhibited melanoma cells migration. Both UA enantiomers decreased the release of pro-inflammatory mediators. The cytotoxic effect of (+)-UA and (−)-UA depends greatly on the melanoma cell type; however, the overall anti-melanoma potential is perspective. Our results indicate that the strategy of combining usnic acid enantiomers with cytostatic drugs may be an interesting option to consider in combating melanoma; however, further studies are required.