Constictic acid

Neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease are multifactorial disorders which are increasing in incidence and prevalence over the world without existing effective therapies. The search for new multitarget compounds is the latter therapeutic strategy to address these pathological conditions. Lichens have an important and unknown therapeutic value attributed to their unique secondary metabolites. The aim of this study is to evaluate for the first time the in vitro neuroprotective activities and molecular mechanisms underlying methanol extracts of lichens of the parmelioid clade and to characterize major bioactive secondary metabolites responsible for their pharmacological actions. Of the 15 parmelioid lichen species, our results showed that Parmotrema perlatum and Hypotrachyna formosana methanol extracts exhibited high antioxidant activity as evidenced in ORAC, DPPH, and FRAP assays. Then, SH-SY5Y cells were pretreated with methanol extracts (24 h) followed by Fenton reagent exposure (2 h). Pretreatments with these two more antioxidant methanol lichen extracts increased cell viability, reduced intracellular ROS, prevented oxidative stress biomarkers accumulation, and upregulated antioxidant enzyme (CAT, SOD, GR, and GPx) activity compared to Fenton reagent cells. The neuroprotective activity was much higher for H. formosana than for P. perlatum, even equal to or higher than Trolox (reference compound). Moreover, H. formosana extracts inhibited both AChE and BuChE activities in a concentration dependent manner, and P. perlatum only showed concentration dependent activity against AChE. Finally, chemical composition analysis using TLC and HPLC methods revealed that physodic acid, lividic acid, and lichexanthone are major secondary metabolites in H. formosana and stictic acid and constictic acid are in P. perlatum. These results demonstrated that P. perlatum and, specially, H. formosana are promising multitargeted neuroprotective agents due to their antioxidant and AChE and BuChE inhibition activities.

Cancer is the second leading cause of human deaths in the USA. Despite continuous efforts to treat cancer over the past 50 years, human mortality rates have not decreased significantly. Natural products, such as lichens, have been good sources of anticancer drugs. This study reports the cytotoxic activity of crude extracts of 17 lichen species against Burkitt's lymphoma (Raji) cells. Out of the 17 lichen species, extracts from 14 species showed cytotoxicity against Raji cells. On the basis of IC50 values, we selected Xanthoparmelia chlorochroa and Tuckermannopsis ciliaris to study the mechanism of cell death. Viability of normal lymphocytes was not affected by the extracts of X. chlorochroa and T. ciliaris. We found that extracts from both lichens decreased proliferation, accumulated cells at the G0 /G1 stage, and caused apoptosis in a dose-dependent manner. Both lichen extracts also caused upregulation of p53. The T. ciliaris extract upregulated the expression of TK1 but X. chlorochroa did not. We also found that usnic, salazinic, constictic, and norstictic acids were present in the extract of X. chlorochroa, whereas protolichesterinic acid in T. ciliaris extracts. Our data demonstrate that lichen extracts merit further research as a potential source of anticancer drugs.

In this work, we carried out studies of the chemical composition of hexane, chloroform and ethanol extracts from two samples of the lichen Parmotrema hypoleucinum collected in Algeria. Each sample of the lichen P. hypoleucinum was collected on two different supports: Olea europaea and Quercus coccifera. Hexane extracts were prepared, in Soxhlet; each hexane extract was fractionated by its solubility in methanol; the products soluble in methanol were separated (cold): 1-Hexane, 2-Hexane; and the products insoluble in methanol (cold): 1-Cires, 2-Cires. A diazomethane esterified sample of 1-Hexane, 2-Hexane, 1-Cires and 2-Cires was analyzed by GC-MS, and the components were identified as methyl esters. In the 1-Hexane and 2-Hexane fractions, the methyl esters of the predominant fatty acids in the lichen were identified: palmitic acid, linoleic acid, oleic acid and stearic acid; a hydrocarbon was also identified: 13-methyl-17-norkaur-15-ene and several derivatives of orsellinic acid. In the 1-Cires and 2-Cires fractions, the previous fatty acids were no longer observed, and only the derivatives of orsellinic acid were found. The analysis of the 1-Hexane, 2-Hexane fractions by HPLC-MS/MS allows us to identify different chemical components, and the most characteristic products of the lichen were identified, such as Atranol, Chloroatranol, Atranorin and Chloroatranorin. In the fractions of 1-Cires and 2-Cires, the HPLC-MS/MS analysis reveals that they are very similar in their chemical components; the characteristic products of this lichen in this fraction are Atranorin and Chloroatranorin. In the extracts of chloroform, 1-Chloroform and 2-Chloroform, the analysis carried out by HPLC-MS/MS shows small differences in their chemical composition at the level of secondary products; among the products to be highlighted for this work, we have chloroatranorin, the stictic acid, norstictic acid and other derivatives. In the analysis of the most polar extracts carried out in ethanol: 1-Ethanol and 2-Ethanol, HPLC-MS/MS analysis shows very similar chemical compositions in these two extracts with small differences. In these extracts, the following acids were identified as characteristic compounds of this lichen: constictic acid, stictic acid, substictic acid and methylstictic acid. In the HPLC-MS/MS analysis of all these extracts, alectoronic acid was not found.