Abstract

Introduction

Lichens have a very important role in both human and animal nutrition, as well as in the pharmaceutical industry and traditional medicine (1). Lichens synthesize a large number of secondary metabolites and most of these metabolites are unique to the lichen. The extracts of the lichens and their secondary metabolites exhibit a broad spectrum of biological activity (2).

Material and methods

Lichens were collected at the site of the eastern slope of the mountain Kopaonik on the territory of the Republic of Serbia. Extraction was performed with methanol using the Soxhlet apparatus. The phytochemical analysis of the methanol extract of lichen Pleurosticta acetabulum was carried out by high-performance liquid chromatography (HPLC). The antioxidant activity of the lichen extract was evaluated by measuring the total anti-oxidative capacity, reducing capacity, inhibition lipid peroxidation and scavenging capacity on 2,2-diphenyl-1-picrylhydrazyl (DPPH) and hydroxyl (OH) radicals. To determine total phenols and flavonoids, we used spectrophotometric methods (3). In vitro anticancer activity on HeLa S3 adenocarcinoma cervix and LS174 human colon adenocarcinoma cells line was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay (4).

Results

Salazinic acid (retention time± standard deviation: t_R =1.56 ± 0.20), norstictic acid (t_R=2.70 ± 0.10), protocetraric (t_R=3.24 ± 0.20) acid and evernic acid (t_R=5.08 ± 0.10) were identified from methanol extract of lichen P. acetabulum. As a result of the antioxidant activity, methanol extract of P. acetabulum had moderate free radical DPPH scavenging activity (half-maximum inhibitory concentration IC₅₀ = 48.52 µg/mL), OH radical scavenging activity ( IC₅₀ = 163.83 µg/mL) and inhibition lipid peroxidation (IC₅₀= 74.30±1.48). Measured values of absorbance for reducing power varied from 0.25 to 0.018. The value of total antioxidant capacity was 74.29 mg AA/g (equivalents of ascorbic acid per g of dry extract). The contents of total phenols and flavonoids in the lichen extract were 73.45 mg GA/g (mg equivalents of gallic acid per g of dry extract) and 15.42 mg RU/g (mg equivalents of routine per g of dry extract), respectively. Cytotoxic activity (based on the IC₅₀ values) ranged from 39.17±5.54 µg/mL to >200 µg/mL after 24 h and 72 h treatment of extract.

Conclusion

The present study provides data for supporting the use of P. acetabulum extract as natural antioxidant agents and confirms that this extract represents a significant source of phenolic compounds.

REFERENCES

1. Romagni JG., Dayan F. (2002). Structural diversity of lichen metabolites and their potential use. Advances in Microbial Toxin Research and Its Biotechnological Exploitation, 12:151-169.
2. Müller K. (2001). Pharmaceutically relevant metabolites from lichens. Applied Microbiology and Biotechnology, 56(1-2):9-16.
3. Manojlovic N. T., Vasiljevic PJ., Maskovic PZ., Juskovic M., & Bogdanovic-Dusanovic, G. (2012). Chemical composition, antioxidant, and antimicrobial activities of lichen Umbilicaria cylindrica (L.) Delise (Umbilicariaceae). Evidence-based Complementary and Alternative Medicine, Article ID 452431.
4. Mosmann, T. (1983). Rapid colorimetric assay for cellular growth and survival: application to proliferation and cytotoxicity assays. Journal of Immunological Methods, 65(1-2), 55-63.