Abstract
Fourteen saxicolous lichens from trans-Himalayan Ladakh region were identified by morpho-anatomical and chemical characteristics. The n-hexane, methanol and water extracts of the lichens were evaluated for their antioxidant capacities. The lichen extracts showing high antioxidant capacities and rich phenolic content were further investigated to determine their cytotoxic activity on human HepG2 and RKO carcinoma cell lines. The ferric reducing antioxidant power (FRAP), 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), 1,1-diphenyl-2-picrylhydrazyl (DPPH) and nitric oxide (NO) radical scavenging capacities and β-carotene-linoleic acid bleaching property exhibited analogous results where the lichen extracts showed high antioxidant action. The lichen extracts were also found to possess good amount of total proanthocyanidin, flavonoid and polyphenol. The methanolic extract of Lobothallia alphoplaca exhibited highest FRAP value. Methanolic extract of Xanthoparmelia stenophylla showed the highest ABTS radical scavenging capacity. The n-hexane extract of Rhizoplaca chrysoleuca exhibited highest DPPH radical scavenging capacity. Highest antioxidant capacity in terms of β-carotene linoleic acid bleaching property was observed in the water extract of Xanthoria elegans. Similarly, Melanelia disjuncta water extract showed highest NO scavenging capacity. Among n-hexane, methanol and water extracts of all lichens, the methanolic extract of Xanthoparmelia mexicana showed highest total proanthocyanidin, flavonoid and polyphenol content. From cytotoxic assay, it was observed that the methanolic extracts of L. alphoplaca and M. disjuncta were exhibiting high cytotoxic effects against cancer cell growth. Similarly, the water extract of Dermatocarpon vellereum, Umbilicaria vellea, X. elegans and M. disjuncta and the methanolic extract of M. disjuncta and X. stenophylla were found to possess high antioxidant capacities and were non-toxic and may be used as natural antioxidants for stress related problems. Our studies go on to prove that the unique trans-Himalayan lichens are a hitherto untapped bioresource with immense potential for discovery of new chemical entities, and this biodiversity needs to be tapped sustainably.
Highlights
Free radicals having one or more unpaired electrons are generated as a by-product in normal or pathological cell metabolism
We extend our present study towards the evaluation of cytotoxicity of eight lichen extracts out of the total fourty two extracts of fourteen lichen species those were taken for the initial screening based on antioxidant capacities and bioactive phytochemical constituents on human hepatocellular carcinoma HepG2 and colon carcinoma RKO cells
Fourteen saxicolous lichens from transHimalayan cold desert of Ladakh have been identified with their morpho-anatomical and chemical compositions and the antioxidant and free radical scavenging capacities of these lichen extratcts were reported for the first time
Summary
Free radicals having one or more unpaired electrons are generated as a by-product in normal or pathological cell metabolism. Reactive oxygen species (ROS) react swiftly with free radicals to become radicals themselves thereby starting free radical chain reaction. Superoxide anion (O2–), hydrogen peroxide (H2O2), hydroxyl radical (HON) and singlet oxygen (1O2) are the various forms of reactive oxygen species [1,2]. Excess ROS in our body damages biological molecules leading to the development of degenerative diseases such as premature aging, heart diseases, cancer, inflammation, diabetes, genotoxicity, arthritis and many more [3,4]. Trigger the process of generation of ROS within the body [5,6]. The most efficient way to exterminate free radicals that cause the oxidative stress is through antioxidant supplementation
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