Prateeksha†
a,
B. S. Paliya†a,
R. Bajpaib,
V. Jadauna,
J. Kumara,
S. Kumara,
D. K. Upretib,
B. R. Singh‡
c,
S. Nayakab,
Y. Joshid and
Brahma N. Singh*a
aPharmacognosy & Ethnopharmacology Division, CSIR-National Botanical Research Institute, Lucknow – 226001, U.P., India. E-mail: bn.singh@nbri.res.in
bLichenology Laboratory, Plant Biodiversity and Conservation Biology Division, CSIR-National Botanical Research Institute, Lucknow – 226001, U.P., India
cCentre of Excellence in Materials Science (Nanomaterials), Z. H. College of Engineering & Technology, Aligarh Muslim University, Aligarh-202002, India
dDepartment of Botany, S. S. J. Campus Almora-263601, Uttarakhand, India
First published on 28th January 2016
The genus Usnea Adans. (Parmeliaceae; lichenized Ascomycetes) is a typical group of mostly pale grayish-green fruticoselichens that grow as leafless mini-shrubs. More than 360 species of Usnea are known in the world. Usnea has long been thought to have treat various illnesses in addition to its historical use as dyes, cosmetics, preservatives, and deodorants, particularly in eastern countries such as China, Japan, Taiwan, India and Europe. The current review focuses on the traditional uses and phytochemistry aspects of different Usnea species, and discusses the pharmacological findings and toxicology of their extracts and isolated compounds. The available compilation of data will provide a new base for future perspectives and highlight the need for further studies of this potent herbal source to harvest more beneficial therapeutic drugs. Nineteen species of the genus Usnea are found to be important folk medicines all over the world. It is evident from the comparative analysis of the searched literature that the genus Usnea has been used for various purposes for centuries and its long and traditional medicinal history was well documented in the past. As per ancient records and recent scientific literature, the species of genus Usnea have been used as promising traditional medicines, exerting an array of therapeutic properties to relieve sore throats, bronchitis, cold, flu, infection, and indigestion. Phytochemical analysis confirms the general presence of a wide range of metabolites, polysaccharides, fatty acids, phenolic acids, flavonoids, terpenes, sterols, depsides, depsidones, and benzofurans. As specific constituents, usnic acid, polyphenols, and depsides have been considered as main efficacy component for antibacterial and antifungal activities. In addition, pharmacological analysis also revealed that other pure compounds and crude extracts of Usnea species prove to be significant anti-cancer, anti-proliferative, anti-oxidant, anti-viral, anti-inflammatory, anti-ulcer, hepatoprotective, and anti-genotoxic agents. However, there is a need for more precise investigations to examine the clinical value of both isolated pure compounds and crude extracts and to elucidate their mechanisms of action. Apart from clinical validation and elucidation of their mechanism of action, biosafety studies of the compounds are also important to legitimately use the potential bioactive compounds for the further development of future lead drugs.
Lichens have been shown to produce a number of primary and secondary metabolites that may protect them against physical stresses or biological attack.5,6 Some lichen species and their metabolites have been used for medicinal and industrial purposes.7–10 Among the medicinal lichens, the genus Usnea Adans. (Parmeliaceae; lichenized Ascomycetes) is edible and is utilized in the preparation of traditional foods and medicines in both Eastern and Western countries.11,12 This genus is regarded as one of the taxonomically most difficult genera of macro-lichens.13 Most of the species are globally distributed with more than 350 species and highly variable in morphology. Many species are also very variable in chemistry, and may include several chemotypes.14 In India, 57 species of Usnea are known which grow luxuriantly in higher regions of Western Ghats and Himalaya.15,16 Many species are also very variable in chemistry, and may include several chemotypes. The species of Usnea are known to be used in traditional medicines, in dyeing and in spices in various parts of the country.15,17 The first recorded use of the Usnea species in traditional Chinese medicine dates to 101 B.C., when it was used as an antimicrobial agent under the Chinese name of Song Lo. Song Lo tea or its decoction has also been recorded for internal and external detoxification of the liver, treatment of malaria, wounds, snake bite, and cough.18 In Unani literature, the medicinal uses of Usnea species are mentioned as astringent, antidote, analgesic, cardiotonic, resolvent and stomachic.17,19–21
Along with its emerging position in the herbal market, primary as well as secondary metabolites (extrolites), the chemical constituents of Usnea species have been broadly investigated. Usnic acid, protocetraric acid, barbatic acid, norstictic acid, salazinic acid, and stictic acid were characterized as the main bioactive chemical constituents in Indian species.17,22,23 All the major secondary metabolites in Usnea belong to aromatic products formed from β-orcinol units, while ceparatic acid and protolichesterinic acid belong to higher aliphatic acids. Most of these metabolites are unique to Usnea lichens, being of great significance for systematics and phylogeny, and are employed at different taxonomic levels from species and subspecific to generic and higher ranks.24,25 Furthermore, these bioactive metabolites play important ecological roles in nature such as UV protection and defense against predators and pathogenic microorganisms.1,26
Significant research has been done on Usnea and its metabolites which confirm various biological activities including anti-microbial, anti-oxidant, anti-tumor, anti-viral, anti-inflammatory, cardiovascular protective, and hepatoprotective properties.17,20,22,27–33 These are closely correlated with the ethno-medicinal uses. Recent pharmacological studies have revealed significant anti-cancer, anti-genotoxic, anti-proliferative, and anti-neoplastic activities and these potentials have further put Usnea under the spotlight.29,34–36 The aim of this review is to summarize the recent advances in phytochemistry and pharmacology of the genus Usnea. Phylogenetic and toxicological aspects are also given in brief.
Usneasensu lato comprises of an assemblage of approximate 350 species worldwide.15 The species belonging to the genus Usnea contain usnic acid, a bioactive compound, which imparts a yellow colour to the thalli. Using modern concepts, the taxonomist divided Usnea into three genera, i.e., genus Dolichousnea, genus Eumitria and genus Usnea sensu stricto. The genus Dolichousnea is characterized by an annular pseudocyphellae between the segments, solid central axis and positive iodine reaction of central axis. The genus Eumitria is characterized by a fistulose central axis whereas genus Usnea sensu stricto is characterized by the absence of annular pseudocyphellae and a solid, I – central axis.
Usnea is a cosmopolitan genus occurring on all continents. Species diversity, however, is low in arid and arctic areas and is highest in humid regions of temperate latitudes. U. aciculifera is found in Eastern Asia and U. angulate is distributed in Australia, America and West Africa. U. baileyi is found in pantropical countries in world. U. compressa is widely distributed in India and Nepal. U. fragilis is known in the South-East Asian region. U. himalayana is from the Himalayas, Western Ghats and Africa. U. indica is endemic to North-West Himalayas and found in Uttarakhand in India. U. ghattensis is endemic to Western Ghats. U. luridorufa is found in North and South Asia. U. nepalensis is found in Himalayas and Western Ghats in India. Several species including U. orientalis, U. pangiana, U. sinensis, and U. perplexans are widely distributed in North-East Asia. U. pseudosinensis and U. robusta are restricted only to the Himalayas. U. subflorida is distributed in East Africa and North Asia, while U. subfloridana is found in Europe and North East Asia. U. undulata is found in South and East Africa.39–41
U. longissima is distributed throughout the Northern temperate zones, such as the sub-arctic and the coastal rainforests of Europe, Asia and North America.41,42 In India, the species is distributed in North-Eastern Himalayan regions between 1500–4000 m altitudes in moist old mixed forests of Quercus and Pinus. Seven chemosyndromes of U. longissima are reported from India which include barbatic acid, squamatic acid, diffractaic acid, evernic acid, fumaroprotocetraric acid and usnic acid strains. U. longissima is characterized by fruticose, a pendulous thallus of 60 cm long or more, of pale yellow-greyish green to light brown, a 0.5–1.0 mm diameter main branch, a 2–5 cm long, dense perpendicular usually decorticated or pulverulent to powdery lateral branches, sorediate or isidiate, with a colorless central lattice. Apothecia range from being rare to up to 5 mm in diameter, with ciliate margin. The species has more than seven chemotypes containing barbatic, squamatic, diffractiatic, evernic, fumarprotocetraric, and usnic acids.41
A study based on the ITS sequence data supported the subgenera Eumitria and Usnea, and revealed a new subgenus, Dolichousnea.46 The authors also concluded that Usnea contains at least three taxa at subgeneric level, Usnea, Eumitria, and Dolichousnea. Neuropogon was not included in this study and the position remained unclear. Molecular phylogenies based on the ITS-LSU nrDNA and part of the β-tubulin region have been used to examine the position of Neuropogon in Usnea s. lat.43 Bayesian inference and maximum parsimony strongly supported the monophyly of Neuropogon. Subgenus Usnea and Neuropogon form a strongly supported group with subg. Eumitria and subg. Dolichousnea is a consecutive monophyletic sister group. The following generic classification was proposed: Usnea (subgenus Usnea only), Neuropogon, Eumitria, and Dolichousnea. Dolichousnea is elevated to generic rank. The following new combinations are made: Dolichousnea Articus, D. longissima (Ach.) Articus, D. trichodeoides (Vain.) Articus, D. diffracta (Vain.) Articus, and Eumitria pectinata (Taylor) Articus.43 Recently, the phylogenetic relationships of 52 Usnea species from across the genus, based on ITS rDNA, nuLSU, and two protein-coding genes RPB1 and MCM7 have been investigated. The phylogeny based on the concatenated dataset revealed that the genus Usnea is subdivided into four highly-supported clades, corresponding to the traditionally circumscribed subgenera Eumitria, Dolichousnea, Neuropogon and Usnea.47 However, characteristics that have been used to describe these clades are often homoplasious within the phylogeny and their parallel evolution is suggested. The study has suggested that combinations of phenotypic characters are suitable discriminators for delimitating species, but are inadequate to describe generic subdivisions.
Species/folk name | Country | Uses | References |
---|---|---|---|
Usnea spp. Dill. ex Adans. ushna | Unani medicine of India | Used for heart troubles, for reducing inflammation, for promoting digestion and improving appetite, as an antidote, as an astringent, and as an analgesic. It also helps wounds heal and lactation in women if applied as a paste on breast | 157 |
U. aciculifera Vain. | China | Used for bladder infection, painful urination, urinary retention, swelling, and edema in heart and kidneys | 76 |
U. articulata (L.) Hoffm. hewas | Tanzania | Used to treat stomachache. A handful of hewasis chewed fresh and the juice swallowed, it is bitter but relieves the pain | 158 |
U. atlantica Vain. barbas | Canary Islands | Used as a disinfectant | 159 |
U. baileyi (Stirt.) Zahlbr. | India | Mixed with other aromatic herbs, such as Valeriana jatamansi for favoring and curing tobacco | 160 |
U. barbata (L.) Weber ex F.H. Wigg. | USA | Used to treat fungal infections of the mouth, stomach, intestines, anus, vagina, nose, ear, skin as well as “systematic fungal infection” | 11 |
South Africa | Applied to treat mammary infections in cattle, the udder is washed several times with decoction of lichen. Also used for indigestion in humans | 65 | |
Nepal | Endangered medicinal lichen banned from raw export | 161 | |
Philippines | Used for wounds, chopped and mixed with coconut oil, spread over wound. Also utilized for abdominal pain, it used as drink decoction | 162 | |
tagahumok puti | West Malaysia | Used for colds and strengthening after confinement | 163 |
Europe | Used to treat insomnia, nausea, and the uterus, also used for internal and external bleeding, whooping cough, jaundice, and growing hair | 82 | |
memby rakúíja | Spain | Utilized as drying agent and antiseptic for cracks and irritations of the feet | 164 |
Brazil | Liquid made from it is given to women to cure sterility | 165 | |
U. campestris R. Sant barba de piedra | Argentina | Unspecified medicine | 166 |
U. ceratina Ach. | China | Adopted to treat coughs, inflamed lungs, pulmonary tuberculosis, hepatitis, and headache due to heat, infection due to injury, inflamed lymph channels, mastitis, and snakebites | 100 |
U. densirostra Taylor, U. durietzii Mot. yerba de la piedra; barba de piedra | Argentina | Tea applied externally as astringent, antiseptic, and anti-inflammatory | 167 |
U. diffracta Vain. lao-jun-xu, Lao Tzu’s beard, pine gauze, or female gauze | China | Utilized to cure cough, tuberculosis of neck or lungs, headache, dizziness, sweating, dim vision, swelling, pus oozing from breasts or sores, burns and scalds, snakebite, traumatic injuries, bone fracture, bleeding from external injuries, vomiting, blood in feces, bleeding from uterus, menstrual disorders, vaginal discharge, swelling of female genitalia, urinary tract afflictions, parasitic infections, when it used as a drink decoction; or apply decoction or powdered lichen to affected area | 100 |
song-nag | Korea | Used to induce menstruation and treated tuberculosis of the neck | 11 |
gser.skud | Tibet | Cured fevers of the lungs, liver, and channels and fever caused by poisoning | 74 |
U.durietzii Mot. [syn. Neuropogon durietzii] | Argentina | Same as Argentine use of U. densirostra | 168 |
Usnea filipendula Stirt. [syn. Usnea dasypoga] | Russia | Powdered form used to treat wounds and some infections | 48 |
U. florida (L.) F. H. Wigg. | China | Used for aching in sinews and bones, stopping bleeding or infection from external injuries, skin diseases, painful urination, coughs, tuberculosis of lungs or neck, heart palpitations, and edema. Drink decoction; or apply decoction or powdered lichen to affected area | 57 and 169 |
South central Chile | Infusion taken for management of diarrhea | 49 | |
Europe | Decoction used for colds and coughs | 51 | |
Chile | Infusion used for diarrhea | 49 | |
U. himalayana C. Bab. nayonayo saruogase | Japan | Burned as a “lichen cigarette” | 3 |
U. hirta (L.) F. H. Wigg. | Europe | Used for heal wounds and to prevent hair loss | 51 |
U. laevis (Eschw.) Nyl. barba de piedra or tusinya | USA | Utilized to treat dermatosis, fungal infections, tuberculosis, and pneumonia | 170 |
U. longissima Ach. | India | Used as a simple drug to stimulate menstruation or induce abortion, taken orally and inserted into the vagina | 171 |
China | Used in Chinese medicine especially as an expectorant and in the treatment of ulcers, stop sweating, dizziness cold, pain, phlegm, and stop swelling in female genitalia. Also applied as a decongestant for treatment of ulcers and tuberculosis | 57,99 and 102 | |
sun-lo | Mongolia | Used medicinally | 7 |
Madhya Pradesh, India | Used to treat bone fractures, along with other ingredients | 63 | |
Turkey | Applied for treating cancer, tuberculosis, and ulcers | 52 and 53 | |
Indo-Tibetan Himalayas | Used to heal bone fractures. Washed, air-dried, soaked overnight in salted water, and placed over affected part | 172 | |
urmil | Canada | Used to strain impurities out of hot pitch when making medicine, and for other unspecified medicines | 173 |
U. nidifica Taylor uru nū | Rarotongan | Thallus chewed and applied to cuts (to stop bleeding) and stings | 174 |
U. pectinata Taylor | China | Used for stopping bleeding from external injuries, relieving pain, bloody feces, and swelling | 100 |
U. plicata (L.) Weber | Libya | Used as an ingredient in medicinal decoction called scıba | 54 and 55 |
scíba | Europe | An astringent for internal and external use for whooping cough, jaundice, strengthening stomach and abdominal cavity, and restraining abortion | 56 |
U. strigosa (Ach.) Eaton | Papua New Guinea | Concoction taken orally for headaches | 58 |
U. sikkimensis Biswas sp. nov. darimataghosa | India | Used for lung troubles, hemorrhages, and asthma; powdered and used to strengthen hair. Also used to bandage surface wounds, skin eruptions, and boils, when it inserted into nostril to stop nose bleeds; put in shoes to prevent or treat blisters | 83 and 84 |
U. strigosa (Ach.) Eaton oleazu | Kimi | Concoction taken orally for curing headaches | 58 |
U. subfloridana Stirt. | Ireland | Applied for treating sore eyes, mixed with tobacco and butter, boiled, cooled, and applied as lotion to eyes | 59 |
China | Used for painful and reddened eyes, bleeding from external injuries, and swelling | 57 | |
U.subsordida Stirt. ayurvedic medicine | India | Same as ayurvedic use of U. baileyi | 160 |
U. trichodeoides Vain. | China | Used for coughs, pulmonary tuberculosis, headaches, blurred vision, inflamed cornea, swellings, sores, uterine bleeding, menstrual disorders, and vaginal discharge | 57 |
Africa, Mt. Kilmanjaro | Used as an ingredient in herbal tea given by African guide to relieve altitude sickness | 60 |
U. longissima grows commonly on bark, mostly on the twigs of trees, bushes and over soil and rock in temperate and alpine regions of India, it is known locally as “Syara” by the Bhotia and Garhwalis of remote areas of Uttarkashi district of Uttarakhand, India and is used for making pillows. The Baiga tribes of Madhya Pradesh, India used the species along with other ingredients for treating bone fractures.62,63 Likewise the ancient Greeks used lichen as medicines. Hippocrates recommended a lichen, perhaps U. barbata, for uterine complaints. The Chinese used U. longissima as an expectorant and as a powder application to heal external ulcers in the name “Sun-Lo”.1 It is also a major ingredient of Chinese medicine.57 In China, this species of Usnea is also called as “Lao-tzu’s” beard, “Pine gauze” and used for stopping sweating dizziness cold, pain and phlegm. U. longissima is still utilizing today as a tincture to treat tuberculosis lymphadenitis. In the Bolivian Andes, U. longissima is commercially sold as a folk medicine for cough and hoarseness.7,12 The Nitinaht Indians of Vancouver also used the species for wound dressing in Turkey.63 U. longissima is used in the treatment of gastric ulcers by the Anatolians as a folk medicine. This species is also used as to strain impurities from hot pitch before the pitch was used as medicine. In Unani medicine, it has been described to stimulate menstruation or induce abortion, taken orally and inserted into the vagina.63 However, it was used for treating cancer, tuberculosis, and ulcers in Turkey.64 It has also been used as a decongestant and for the local treatment of ulcers and tuberculosis by Chinese people.57
U. barbata is used to treat mammary infections in cattle. The udder is washed several times with a decoction of lichen and used for indigestion in humans, where the tincture or decoction taken orally several times daily.65 In the Philippines, it has been used for wounds, chopped, and mixed with coconut oil, spread over the wound and for abdominal pain where the decoction is used as a drink.66 However, in Europe it was used for internal and external bleeding, whooping cough, jaundice, and growing hair.67 Spanish people used it as drying agent and an antiseptic for cracks and irritations of the feet.68 In China U. aciculifera was used to treat bladder infection, painful urination, urinary retention, swelling, and edema in the heart and kidneys.57 In Tanzania, U. articulate was used for the treatment of stomachache.69 A handful of U. articulate and U. gigas are chewed fresh and the bitter juice swallowed, relieving pain after a time. In China, U. ceratina was used for coughs, inflamed lungs, pulmonary tuberculosis, hepatitis, heat related headaches, infection due to injury, inflamed lymph channels, mastitis, and snakebites.57
In traditional Argentinian medicine, teas of U. densirostra and U. durietzii were used externally as astringents, antiseptics, and anti-inflammatory agents.70,71 In China, U. diffracta has been applied to treat a range of problems such as cough, tuberculosis of neck or lungs, headache, dizziness, sweating, dim vision, swelling, pus oozing from breasts or sores, burns and scalds, snakebite, traumatic injuries, bone fracture, bleeding from external injuries, vomiting blood, blood in feces, bleeding from uterus, menstrual disorders, vaginal discharge, swelling of female genitalia, urinary tract afflictions, and ascarid or schistosoma parasitic infections.72,73 The same species of Usnea were used to cure fevers of the lungs, liver, and heart and fever caused by poisoning in Tibet74 while in Korea, the species was used to induce menstruation (Pusan) and treat tuberculosis of the neck.75
The traditional Chinese herbal medicine, U. florida has been used for aching in sinews and bones, stopping bleeding or infection from external injuries, skin diseases, painful urination, coughs, tuberculosis of lungs or neck, heart palpitations, and edema.76 The decoction of U. florida was also used for colds and coughs in Europe,77 while in Chile, its infusion is used for diarrhea.49 U. himalayana is burned as a “lichen cigarette” in Japan.78 U. hirta has been used by European people to heal wounds and to prevent hair loss.77 U. laevis has been widely used to treat different kind of microbial infections including dermatosis, fungal infections, tuberculosis, and pneumonia.50 In Canada, most of the Usnea species were used for wound dressing, but U. longissima is preferred by wrapping around the wound.79 It was recorded that U. pectinata had been used in China for stopping bleeding from external injuries, relieving pain, bloody feces, and swelling.76
U. plicata used as an astringent for internal and external use,80 also for whooping cough,81 jaundice, strengthening stomach and abdominal cavity, and restraining abortion in Europe.82 As the traditional Indian herbal medicine, U. sikkimensis has been used for treating lung troubles, hemorrhages and asthma.83 It has also been used to bandage surface wounds, skin eruptions, and boils.84 The concoction of U. strigosa was taken orally for the treatment of headaches.58 Moreover, in Ireland U. subfloridana was used to treat sore eyes. In China, it was used to treat painful and reddened eyes, bleeding from external injuries, and swelling.76 The traditional Chinese herbal medicine, U. trichodeoides has been used to treat coughs, pulmonary tuberculosis, headaches, blurred vision, inflamed cornea, swellings, sores, and pus discharge, bleeding from external injuries, bloody feces, uterine bleeding, menstrual disorders, and vaginal discharge.
S. No. | Chemical constituent | Source | References |
---|---|---|---|
(A) Polysachharides | |||
1 | Lichenan | U. barbata, U. longissima, U. bayleyi | 86 |
2 | Isolichenin | U. fasciata | 87 |
(B) Fatty acids | |||
3 | 18R-Hydroxydihydroallopr-otolichensterinic acid | U. longissima | 175 |
4 | Murotic acid | U. longissima | 175 |
5 | Iso-muronic acid | U. longissima | 102 |
6 | Lichesterinic acid | U. longissima | 149 |
7 | Neuropogolic acid | U. longissima | 149 |
8 | Bourgeanic acid | U. esperatiana, U. florida | 4 and 89 |
9 | Caperatic acid | U. lapponica, U. angulata, U. nipparensis, U. orientalis, U. florida, U. sinensis | 89 |
10 | Methyl 3,4-dicarboxy-3-hydroxy-19-oxoeicosanoate | U. meridensis | 88 |
(C) Depsides | |||
11 | Aciculiferin A | U. aciculifera | 95 |
12 | Atranorin | U. aciculifera, U. articulate | 95 and 96 |
13 | Baeomycesic acid | U. pacificana | 20 |
14 | 4-O-Demethylbarbatic acid | U. longissima | 109 |
15 | Barbatic acid | U. diplotypes, U. fulvoreaquens, U. lapponica, U. pacificana, U. substerilis, U. wasmuthii, U. pangiana, U. dendritica, U. fragilis, U. norketti, U. nilgirica, U. certaina | 22 |
16 | Diffractaic acid | U. longissima, U. baileyi, U. aciculifera, U. certaina, U. fulvoreagens, U. diffracta | 22,97 and 109 |
17 | 3b-Hydroxy-glutin-5-ene | U. longissima | 104 |
18 | 7-Hydroxy-5-methoxy-6-methylphthalide | U. aciculifera | 95 |
19 | Alectorialic acid | U. dendritica, U. florida, U. subflorida | 22 |
20 | Methyl hematommate | U. aciculifera | 95 |
21 | Ethyl hematommate | U. longissima | 104 |
22 | Ethyl orsellinate | U. longissima | 104 |
23 | Evernic acid | U. madeirensis, U. longissima | 97 |
24 | Barbatinic acid | U. longissima, U. aciculifera | 95 and 104 |
25 | Barbatolic acid | U. barbata | 87 |
26 | Methyl orsellinate | U. longissima, U. undulate, U. aciculifera | 95 and 104 |
27 | Methyl β-orsellinate | U. aciculifera, U. undulate | 95 and 176 |
28 | Methyl-2,4-dihydroxy-3,6-dimethylbenzoate | U. longissima | 104 |
29 | Thamnolic acid | U. subfloridana, U. hirta, U. florida | 22 and 87 |
30 | Squamatic acid | U. pacificana, U. subfloridana, U. fragilescens, U. florida, U. longissima | 22 |
31 | 4-O-Demethylbarbatic | U. dendritica, U. longissima | 36 |
32 | Methyl β-orcinol carboxylate | U. articulate | 93 |
33 | Decarboxy stenosporic acid | U. diffracta | 15 |
(D) Depsidones | |||
34 | 2-O-Methylhypostictic acid | U. undulate | 97 and 98 |
35 | Menegazziaic acid | U. undulate, U. aciculifera | 97 |
36 | Norstictic acid | U. baileyi, U. hakonensis, U. undulata, U. cornuta, U. flammea, U. frgilescens, U. fulvoreagens, U. hirta, U. wirthi, U. aciculifera, U. angulate, U. vulneraria, U. subfloridana | 95 and 97 |
37 | Constictic acid | U. aciculifera | 36 |
38 | Protolichesterinic acid | U. albopunctata | 22 and 87 |
39 | Protocetraric acid | U. albopunctata, U. articulta, U. glabrata, U. madeirensis, U. firmula, U. dasaea, U. maculate, U. trichodeoides | 87 |
40 | Psoromic acid | U. complanata, U. bornmuelleri, U. dasaea, U. inermis, U. pseudosinensis, U. subfloridana | 22,87 and 177 |
41 | Hypocon stictic acid | U. undulate | 97 |
42 | Lobaric acid | U. florida, U. barbata | 51 |
43 | Salazinic acid | U. rubrotincta, U. baileyi, U. trichodeoides, U. pangiana, U. longissima, U. complanata, U. compressa, U. corallina, U. dendritica, U. dasaea, U. himalayana, U. luridorufa, U. norketti, U. orientalis, U. pangiana, U. perplexans, U. picta, U. rigidula, U. robusta, U. sordida, U. rubicunda, U. splendens, U. subfloridana, U. trichodeoides, U. undulate | 87 and 97 |
44 | Galbinic acid | U. undulate | 97 |
45 | Static acid | U. aciculifera, U. cornuta, U. flammea,U. frgilescens, U. fulvoreagens, U. bismolliuscula, U. complanata, U. dasaea, U. eumitrioides, U. fischeri, U. himalayana, U. himantodes, U. indica, U. lucea, U. luridorufa, U. picta, U. pectinata, U. nipparensis, U. pseudojaponica, U. rigidula, U. rubicunda, U. spinosula, U. stigmatoides, U. stigmata | 22,87 and 176 |
46 | Fumarprotocetraric acid | U. articulate, U. glabrata | 22 |
(E) Terpenoids and triterpenes | |||
47 | β-Amyrin | U. longissima | 104 |
48 | Zeorin | U. longissima | 104 |
49 | Oleanolic acid | U. longissima | 104 |
50 | Friedelin | U. longissima | 104 |
51 | Glutinol | U. longissima | 99 |
(F) Benzofurans | |||
52 | Ethyl 2-(3,3-bis(7-acetyl-4,6-dihydroxy-3,5-dimethylbenzofuran-2-yl)acryloyl) | U. longissima | 102 |
53 | 7-Acetyl-C((7-acetyl-2,3-dihydro-4,6-dihydro-3,5-dimethyl-2-oxo)-3-benzofuranyl)-4,6-dihydroxy-3,5-dimethyl-B-oxo-, ethyl ester | U. longissima | 175 |
54 | Ethyl 4-(7-acetyl-4,6-dihydroxy-3,5-dimethyl-2-oxo-2,3-dihydrobenzofuran-3-yl)-4-(7-acetyl-4,6-dihydroxy-3,5-dimethylbenzofuran-2-yl)-3-oxobutanoate | U. longissima | 175 |
55 | (4aR,9bS)-2,6-Diactyl-3,4a,7,9-tetrahydroxy-8,9b-dimethyl-1-oxo-1,4,4a,9b-tetrahydrodibenzo[b,d] furan diethanone | U. longissima | 175 |
56 | (Z)-2-Acetyl-5,5-bis(7-acetyl-4,6-dihydroxy-3,5-dimeth-ylbenzofuran-2-yl)-4-hydroxypenta-2,4-dienal | U. longissima | 175 |
57 | 3,6-Diacetyl-2,7,9-trihydroxy-8,9b-dimethyl-1[9bH]-dibenzofuranone (longiusnine) | U. longissima | 102 and 104 |
58 | Usnic acid | U. florida, U. barbata, U. longissima, U. rigida, U. hirta, U. subflorida, U. undulate | 97 and 109 |
59 | 2-Benzofuranbutanoic acid | U. longissima | 7 |
(G) Sterols | |||
60 | β-Sitosterol | U. longissima | 104 |
61 | Ergosterol | U. longissima | 175 |
62 | 5,8-Epidioxy-5alpha,8alpha-ergosta-6,22E-dien-3beta-ol | U. longissima | 175 |
(H) Others | |||
63 | Longissiminone A & B | U. longissima | 99 |
64 | Atranol | U. aciculifera | 178 |
65 | Quercetin | U. longissima | 28 |
66 | Longissimausnone | U. longissima | 104 |
67 | Hirtusneanoside | U. hirta | 103 |
68 | Orcinol | U. longissima | 175 |
69 | Apigenin 7-O′-D-glucuronide | U. longissima | 175 |
70 | Eumitrin B, eumitrin A2, eumitrin A1 | U. baileyi | 36 |
71 | Arabitol | U. longissima | 175 |
Fig. 8 Secondary metabolites of Usnea spp. synthesized by acetyl-polymalonate pathway, shikimic acid pathway and mevalonic acid pathway. |
S. No. | Extract/compound | Source | Bioactivity | Target/system | Mode of action | Dose | References |
---|---|---|---|---|---|---|---|
(a) In vitro studies | |||||||
1 | Methanol extract | U. filipendula | Anti-population | Human lung cancer (A549, PC3), liver cancer (Hep3B) and rat glioma (C6) cells | Induces apoptosis like cell death | 1.56–100 μg mL−1 | 129 |
2 | Methanol, acetone extracts | U. artarctica, U. auranticoatra | Antioxidant | In vitro system | Scavenges free radicals | IC50: 1 mg mL−1 | 179 |
3 | Acetone extract | U. barbata | Anti-cancer, anti-oxidant | FemX (human melanoma) and LS174 (human colon carcinoma) | Reduces cell viability | IC50: 102.65 and 130.73 μg mL−1 | 18 |
4 | Acetone extract | U. complanta | Anti-viral | Herpes simplex viruses (HSV) | Exhibits cytopathic effect | IC50: 100 μg mL−1 | 120 |
5 | Methanol extract | U. longissima | Melanogenesis inhibition | Human melanoma cells | Inhibits tyrosinase glycosylation | 0.1% | 147 |
6 | Acetone, methanol extracts | U. lapponica | Anti-bacterial | S. aureus, E. coli, P. aureginosa and Methicillin resistant S. aureus | Kills bacteria | MIC: 15.6 μg mL−1 | 116 |
7 | Acetone extract | U. barbata | Anti-mycobacterial | Mycobacterium tuberculosis, M. kansasii and M. avium | Inhibits growth of pathogenic bacteria and fungi | MIC: 32 μg mL−1 and 62 μg mL−1 | 18 |
8 | Polysaccharide | U. longissima | Anti-lipid peroxidation | In vitro system | Scavenges free oxygen radicals and hydroxyl radical oxygen and reduces DNA damage | 0.45–1.57 mg mL−1 | 121 |
9 | Methanol extract | U. artarctica | Anti-oxidant, anti-genotoxic | Human lymphocytes | Inhibits lipid peroxidation and enhances antioxidant enzyme activities | 5–20 μg mL−1 | 34 |
10 | Supercritical CO2-extract | U. barbata | Anti-inflammatory | HaCaT keratinocytes | Inhibits prostaglandin E2 synthesis and cyclooxygenase-2 (COX-2) expression | 60 μg mL−1 | 139 |
11 | Acetone extract | Antioxidant | In vitro system | Scavenges free radicals | 0.0008 to 0.5 mg mL−1 | 18 | |
12 | Acetone, methanol, aqueous extracts | Antimicrobial | In vitro system | Inhibits the growth of bacteria and fungi | IC50: 0.1 mg mL−1 | 60 | |
13 | Supercritical CO2-extract | Antimicrobial | Malassezia furfur, S. aureus | Inhibits the growth of bacteria and yeasts with dermatological relevance | — | 180 | |
14 | Ethanol, methanol | U. ghattensis | Antioxidant | In vitro system | Inhibits lipid peroxidation | 20 μg mL−1 | 123 |
15 | Diethyl ether, acetone, methanol, aqueous extract | U. fasciata | Cytotoxic | Sarcoma 180 and Ehrlich tumor cells | Decreases cell viability | — | 87 |
16 | Methanol extract | U. filipendula | Anti-oxidant, anti-genotoxic | Human lymphocytes | Inhibits lipid peroxidation and enhances antioxidant enzyme activities | 5–20 μg mL−1 | 34 |
17 | Methanol, aqueous extracts | U. longissima | Antioxidant | In vitro system | Scavenges free radicals | — | 124 |
18 | Acetone, methanol, ethanol extracts | U. ghattensis | Antibacterial | Human pathogenic bacteria | Inhibits the growth of bacteria | MIC: 3–200 μg mL−1 | 113 |
19 | Acetone, dimethyl sulphoxide, methanol, light petroleum extracts | Antibacterial | Human pathogenic bacteria | Inhibits the growth of bacteria | MIC: 5–10 μg mL−1 | 181 | |
20 | Different extracts of cultured mycobiont | Antioxidant | In vitro system | Inhibits lipid peroxidation and scavenges free radicals | 0.2 mg mL−1 | 123 | |
21 | Methanol extract | Antioxidant | In vitro system | Scavenges superoxide radicals | 2–20 μg mL−1 | 182 | |
22 | Methanol extract | Antioxidant | In vitro system | Quenches different types of free radicals | 20 μg mL−1 | 183 | |
23 | Methanol extract | U. longissima | Antigenotoxic, antioxidant | Human blood cells | Inhibits lipid peroxidation and induces antioxidant enzyme levels | — | 125 |
24 | Acetone extract | U. rubicunda | Antitumor | In vitro system | Inhibits tumor promoter-induced Epstein–Barr virus activation | — | 131 |
25 | n-Hexane, diethyl ether, methanol extracts | Cytotoxic | Cancer cell lines | Reduces cell viability | IC50: 20 μg mL−1 | 184 | |
26 | Methanol extract | U. siamensis | Antifungal | C. albicans | Inhibits the growth of fungus | — | 185 |
(b) In vivo studies | |||||||
1 | Aqueous extract | U. longissima | Anti-ulcer | Rats | — | 100 mg kg−1 | 52 |
2 | Methanol extract | U. longissima | Anti-platelet, anti-thrombotic | Mice | Anti-platelet activity | 100–200 mg kg−1 | 143 |
3 | Methanol extract | U. articulate, U. filipendula | Anti-oxidative, anti-genotoxic | Rats | Increases the activities of superoxide dismutase, glutathione and glutathione peroxidase and decreases malondialdehyde formation | 5–20 μg mL−1 | 33 |
4 | Methanol extract | U. ghattensis | Hepato-protective | Rats | Inhibits lipid peroxidation and induces antioxidant enzymes | 20 μg mL−1 | 122 |
S. No. | Extract/compound | Source | Bioactivity | Target/system | Mode of action | Dose | References |
---|---|---|---|---|---|---|---|
(a) In vitro studies | |||||||
1 | Quercetin | U. longissima | Anti-fungal | Candida albicans | Suppressor of biofilm formation and hyphal formation | 0.2–1.0 mg mL−1 | 28 |
2 | Isodivaricatic acid | U. florida | Anti-fungal | Microsporum gypseum, Trichophyton mentagrophytes and T. rubrum, C. albicans, C. tropicalis, Saccharomyces cerevisiae, Aspergillus niger, A. flavus and A. fumigates | Inhibits growth of human pathogenic fungal pathogens | 50–100 μg mL−1 | 111 |
3 | Usnic acid | U. longissima | Anti-bacterial | E. aerogenes, B. brevis, M. luteus, E. coli, B. megaterium, P. aeruginosa, E. cloacae, S. aureus, C. albicans and S. cerevisiae | Increases the synthesis of some novel multifunctional hydroxyphenylimino ligands (L1, L2 and L3) | 0.25–2 mg mL−1 | 112 |
4 | Usnic and diffractaic acids | U. subcavata | Anti-proliferative | UACC-62 and B16-F10 melanoma cells | Increases genetic damage in the cell lines | IC50: 24.7–36.6 μg mL−1 (UACC-62) and 25.4 μg mL−1 (B16-F10) | 130 |
5 | Usnic, psoromic acids | U. complanata | Anti-oxidant | In vitro system | Scavenges free radicals | IC50: 22.86 to 25.0 μg mL−1 | 19 |
6 | Heptaketides, corynesporol, 1-hydroxydehydroherbarin | U. cavernosa | Anti-cancer | Human metastatic breast and prostate cancer cell lines including MDA-MB-231 and PC-3M MDA-MB-231 and PC-3M | Inhibits the migration of cancer cells | 5.0 μM | 132 |
7 | Heptaketides, corynesporol, 1-hydroxydehydroherbarin | U. cavernosa | Anti-cancer | Human metastatic breast and prostate cancer cell lines including MDA-MB-231 and PC-3M MDA-MB-231 and PC-3M | Inhibits the migration of cancer cells | 5.0 μM | 132 |
8 | L-Usnic, D-usnic acids | U. barbata | Anti-proliferative | Leukemic cells (K-562) and endometrial carcinoma cells (HEC-50) | Reduces cell viability | 50 μg mL−1 | 135,136 |
9 | Usnic acid | U. dasypoga | Anti-helicobacter pylori | Helicobacter pylori | MIC: 0.128–2 μg mL−1 | 118 | |
10 | Usnic acid | U. longissima | Anti-mutagenic | S. typhimurium TA1535, TA1537 and E. coli WP2uvrA | Prevents mutation | 20–100 μg per plate | 112 |
11 | Eumitrin A1 | U. blepharea | Cytotoxic | P388 cells | Inhibits cell viability | 4.5 μg mL−1 | 138 |
12 | Ambewelamide A, B | Usnea sp. | Cytotoxic | Cancer cell lines | Reduces cell viability | — | 106 |
13 | Barbatic acid, 4-O-demethylbarbatic acid, diffractaic acid | U. longissima | Antitumor | Tissue culture | Inhibits tumor promoter-induced Epstein–Barr virus activation | >1 μM | 131 |
14 | Diffractaic, usnic, norstictic, psoromic acids | U. subcavata | Cytotoxic | UACC-62 and B16-F10 melanoma cells and 3T3 normal cells | Decreases cell viability | 24.7 to 36.6 μg mL−1 | 130 |
15 | Diffractaic, norstictic, usnic, hypostictic, protocetraric acids | U. subcavata | Antimycobacterial | Mycobacterium tuberculosis | Inhibits the growth of bacterium | 15.5–125 μg mL−1 | 186 |
16 | Diffractaic, norstictic, usnic, hypostictic, protocetraric acids | U. longissima | Antioxidant, antimicrobial | DPPH radical system Gram-positive and Gram-negative bacteria and fungi | Scavenges free radicals and inhibits the growth of pathogenic microbes | — | 187 |
17 | Usnic acid | U. ghattensis | Antibacterial pro-apoptotic | Bacillus licheniformis | Inhibits the growth of bacteria | 0.005–0.01% | 187 |
19 | Evernic acid | U. longissima | Antitumor | Tissue culture | Inhibits tumor promoter-induced Epstein–Barr virus activation | >1 μM | 131 |
20 | Galbinic acid | U. undulata | Antimicrobial | B. cereus, B. subtilis, S. epidermidis | Shows inhibitory effect | 31–62.5 μg mL−1 | 176 |
21 | Gautinol | U. longissima | Anti-inflammatory, cytotoxic | Spectroscopic model system | Reduces cell viability | 200 μg mL−1 | 99 |
22 | Hirtusneanoside | U. hirta | Antibacterial | Gram-positive bacteriaS | Shows growth inhibitory activity | — | 103 |
23 | 2′-O-Methyl hypostictic acid | U. undulata | Antimicrobial | B. cereus, B. subtilis, S. epidermidis | Shows inhibitory effect | 31–62.5 μg mL−1 | 176 |
24 | Psoromic acid | U. camplanata | Antioxidant, cardiovascular protective | In vitro system | Scavenges free radicals and inhibits lipid peroxidation | 0.174–0.271 mg mL−1 | 20 |
25 | Norstictic acid | U. undulata | Antimicrobial | B. cereus, B. subtilis, S. epidermidis | Shows inhibitory effect | 31–62.5 μg mL−1 | 97 |
26 | Usnic acid | U. longissima | Anti-inflammatory | LPS-stimulated RAW264.7 macrophages | Decreases the TNF-alpha level | IC50: 12.8 μM | 140 |
27 | Methyl β-orsellinate | U. undulata | Antibacterial | B. cereus, B. subtilis, S. epidermidis | Shows inhibitory effect | 31–62.5 μg mL−1 | 97 |
(b) In vivo studies | |||||||
1 | Diffractaic acid | U. longissima | Pro-apoptotic | Rabbits | Activates the expressions of initiator caspases (Cas-2, -8 and -9) and executioner caspase (Cas-3) | 30 mg kg−1 | 133 |
2 | Usnic acid | Usnea species | Anti-genotoxicity | Mice | Modulation of enzyme activity (ALT and AST) | 60–120 μg mL−1 | 142 |
3 | Ambewelamide A | Usnea species | Cytotoxicity | Swiss mice and V79 cells | Reduces cell growth | 8.6 ng mL−1 | 106 |
4 | Diffractaic acid | U. longissima | Hepatoprotective | Mice | Induces levels of antioxidant enzymes | 50 mg kg−1 | 148 |
5 | Diffractaic, usnic acids | U. diffracta | Analgesic, anti-pyretic | Mice | — | 500–1 g kg−1 | 109 |
Two new metabolites, depside and isodivaricatic acid and three known metabolites, 5-propylresorcinol, divaricatinic acid and usnic acid were isolated from U. florida. These metabolites displayed antimicrobial activity against human pathogenic fungi Microsporum gypseum, Trichophyton mentagrophytes, and T. rubrum. Among them, isodivaricatic and divaricatinic acids exhibited antifungal effect towards M. gypseum, T. mentagrophytes, and T. rubrum with minimum inhibitory concentration (MIC) values of 50, 50, and 100 μg mL−1, respectively. However, isodivaricatic acid was found to be effective against Leishmania amazonensis, L. brasiliensis, and L. infantumpromastigotes by inducing 100% lysis at 100 μg mL−1.111
Extracts of U. ghattensis were prepared using different organic solvents and their antibacterial activity was determined using a disc diffusion assay. The ethanolic extract was most effective against B. cereus, P. aeruginosa, S. aureus, and Streptococcus faecalis with MIC values of 3.125, 200, 6.25, and 25 μg mL−1, respectively. Acetone and methanolic extracts presented almost similar effect against S. aureus.113 L-(−)-Usnic acid was isolated from U. subfloridana and showed promising antibacterial against methicillin-resistant S. aureus (MRSA). The MIC of L-(−)-usnic acid against MRSA was recorded by 50 μg mL−1. Similarly, a combined effect of L-(−)-usnic acid and 7.5% sodium chloride resulted in a reduced number of viable cells within 24 h compared to the control.114 Furthermore, an in vivo study showed that L-(−)-usnic acid significantly (p < 0.001) reduced the microbial load of rat spleen in a dose-dependent manner (1 to 5 mg kg−1).
The antibacterial activity of U. steineri was evaluated against Mycobacterium tuberculosis, M. kansasii, and M. avium. The (+)-usnic acid rich acetone extract displayed promising MIC values of 32 μg mL−1 for M. tuberculosis and 62 μg mL−1 for both M. kansasii, and M. avium.21,115 Acetone and methanol extracts of U. lapponica were screened against four pathogenic bacteria, namely S. aureus, E. coli, P. aeruginosa, and MRSA. The extracts inhibited growth of all tested bacteria except E. coli. Usnic acid was identified as the major active antimicrobial compound in the extracts. The acetone extract was found to be particularly active against MRSA and P. aeruginosa with a MIC value of 15.6 μg mL−1.116 A new formulation of U. barbata extract was developed using alkyl polyglucoside surfactants as a vehicle to examine the antimicrobial potential for skin infections. This formulation has implausible potential against Gram positive bacteria.117
A study was performed to assess the in vitro effect of usnic acid isolated from U. dasypoga against clinical isolates and standard Helicobacter pylori strains. The dual susceptibility rate to usnic acid and clarithromycin was detected as very high (97.3%). Usnic acid had a strong and dose-dependent activity against H. pylori strains. The synergism between usnic acid and clarithromycin was also observed and it may be effective in the treatment of H. pylori infection.118 Ethanolic and methanolic extracts of Usnea species showed a zone of inhibition against some pathogenic bacterial strains, S. aureus, P. aeruginosa, Klebsiella pneumoniae, Salmonella typhiand, and E. coli.112,119
Usnic acid was isolated from the acetone extract of U. barbata and its in vitro antioxidant potential was examined. The IC50 values for the O2−˙ scavenging and reducing power were 102.65 and 130.73 μg mL−1, respectively.19 The methanol extract of U. ghattensis has shown good antioxidant potential by inhibiting lipid peroxidation and scavenging free radicals with pretty similar values to those of reference antioxidant compounds.123 Moreover, U. longissima methanol extract was found to increase the level of antioxidant enzymes and inhibit lipid peroxidation124,125 and its water extract was able to revert the effects of indomethacin in vivo through activation of SOD and GST activities and a decrease of CAT activity.53 A depside, diffractaic acid was characterized as a major metabolite of U. longissima and also showed in vivo antioxidant properties.126 Cakir and colleagues demonstrated that the methanol extracts of U. articulata and U. lipendula showed a protective role against AFB1 in human lymphocytes by enhancing SOD and GPx enzymatic activity and by decreasing lipid peroxidation.64 Polysaccharides of U. longissima (PUS) scavenge the superoxide anion free radical (O2−˙) and hydroxyl free radical (˙OH) with considerable IC50 values of 0.45 mg mL−1 and 1.57 mg mL−1, respectively.121 Authors concluded that PUS weakly inhibits the lipid peroxidation of the hepatocyte homogenate of mice. Various extracts of U. complanata showed DPPH free radical quenching properties (IC50: 22.86–25 mg mL−1), nitric oxide radical scavenging activity (72.52–149.1 mg mL−1) and lipid peroxidation inhibition (74.58–157.9 mg mL−1). Usnic and psoromic acids were identified as the active substances of the cultured symbiont. Usnic acid demonstrated better radical quenching potential while psoromic acid presented higher lipid peroxidation inhibition.20
Two new heptaketides, including corynesporol (1) and 1-hydroxydehydroherbarin (2) along with herbarin (3) were isolated from an endolichenic fungal strain, Corynespora species BA-10763, associated with U. cavernosa. Aerial oxidation of corynesporol (1) yielded herbarin (3). The structures of 1–3 were elucidated from their spectroscopic data. Acetylation of 1 produced the naphthalene derivative 4, whereas acetylation of 3 yielded the corresponding naphthoquinone 6 and dehydroherbarin (5). All compounds were evaluated for their cytotoxicity and observed inhibitory effect on the migration of human metastatic breast cancer MDA-MB-231 and prostate cancer PC-3 cell lines.132 Diffractaic acid, a novel proapoptotic agent extracted from U. longissima and determined its in vivo anticancer activity. The orally and locally administered diffractaic acid showed the induction of apoptosis in tissues of titanium-implanted rabbits by activating initiator caspases (Cas-2, -8 and -9) and executioner caspase (Cas-3). It also showed strong effect on myeloperoxidase and inducible nitric oxide synthase activities, providing an alleviating effect.133 The in vitro cytotoxicity assay of two new derivatives of phenylalanine diketopiperazine, ambewelamide A and B was examined against murine leukemia P388 cells. Only ambewelamde A exhibited significant cytotoxicity with IC50 value 8.6 ng mL−1.106
Usnic acid obtained from U. barbata was examined for its anti-proliferative activity. L-Usnic acid caused moderate inhibition of murine P388 leukemia cells and also exhibited cytotoxic potential against cultured mouse leukemia Ll210 cells. It was inferred that the p-tri-ketone moiety was essential for optimum activity.134 On the other hand, D-usnic acid (50 μg mL−1) was found to reduce the cell counts of leukemic K-562 cells and endometrial carcinoma HEC-50 cells.135,136 Different extracts of U. fasciata containing usnic acid and isolichenin showed moderate anti-cancer activity against sarcoma 180 and Ehrlich tumor cells. However, high anti-tumoral activity, near 90% inhibition, was observed with the fraction containing raffinose.87 Recently, Zuo and colleagues have elucidated the molecular mechanism through which usnic acid mediates anti-cancer activity. Usnic acid selectively killed the human breast cancer MCF-7 cells by inducing the generation of reactive oxygen species (ROS), which triggered the activation of c-Jun-N-terminal kinase (JNK), loss of mitochondrial membrane potential (MMP), release of cytochrome-c, and activation of the caspase-cascade.137 Eventually, usnic acid was found to inhibit tumor growth in MCF-7 tumor-bearing mice without inducing significant toxicity. The authors suggested that usnic acid stimulated apoptosis through an ROS-dependent mitochondrial pathway in MCF-7 cells. Eumitrin A1, isolated from U. blepharea was evaluated for its cytotoxic activity against Murine Leukemia P388 cells. According to the observed IC50 value (4.5 μg mL−1), it is reported as a very active toxic compound for cancer cell lines.138
The methanolic extract of U. longissima was also applied to determine in vitro melanogenesis inhibitory effects.147 The extract was found to reduce melanin formation in human melanoma cells in concentration-dependent manner. Inhibition of melanin content by 51.1% and 34.9% were recorded at 0.01% and 0.1% solutions of the extract, respectively. The obtained results were compared to ascorbic acid. It has also determined that the extract affected the activity of tyrosinase via inhibition of glycosylation process.147
Chemical constituents of Usnea species exhibit acute toxicity against larvae of the polyphagous insect herbivore Spodoptera littoralis revealed the LD50 at 8.6 μM for (−)-usnic acid, 90.8 μM for (+)-usnic acid and 111.0 μM for vulpinic acid.153 Pramyothin et al. demonstrates that usnic acid showed no serum transminase activity when inducing swell in liver mitochondria and endoplasmic reticulum at a dose level of 50 or 200 mg kg−1 intraperitoneally for 5 days. Meanwhile a dose level of 1 mM usnic acid in rat primary hepatocytes triggered the release of hepatic transaminases, decreased the content of reduced glutathione, and caused a loss of cell membrane integrity.154 It was observed that the administration of 5 μM usnic acid for 16 h in mouse primary hepatocytes exhibited 98% necrosis rather than apoptosis by generating oxidative stress and acting directly on the uncoupling of oxidative phosphorylation of the electron transport chain in mitochondria. Usnic acid administration in sheep triggered serum creatine kinase, aspartate aminotransferase, and lactate dehydrogenase activities. It was also estimated that 485 and 647 mg kg−1 d−1 median toxic doses (ED50) in domestic sheep.155 Sheu and colleagues studied allergic content dermatitis by applying lichen acid mixture and usnic acid to four patients and observed that all patients showed positive results for patch test.156
Usnea is a lichen; a combination of an algae and a fungus growing together. Usnea species are endemic to many parts of Asia, Africa, Europe, and America and are widely used in traditional medicine for various applications. It is used to treat stomachache, bronchitis, sterility, pneumonia, pulmonary diseases, strep throat, colds, flues, urinary tract, kidney, and bladder infections. Usnea is also beneficial for women with yeast infections, trichonomosas, bacterial vaginosis, and chlamydia. It could be useful for people with chronic fatigue, HIV, herpes, and other chronic conditions related to depressed immune systems. The phytochemical results have indicated a significantly diversity of structural types of chemical constituents. Pharmacological studies indicated that Usnea lichens and their bioactive constituents possess various biological properties, especially in the areas of anti-microbial, anti-cancer, anti-proliferative, anti-oxidant, anti-inflammatory, anti-ulcer, hepatoprotective, and anti-genotoxicity etc. To a certain extent, pharmacological results have shown that (a) traditional uses for the treatment of flues, gastroenteritis and bacterial/fungal infections, and strep throat were related to antimicrobial activities; (b) use for wounds, ulcers, and fevers were associated with anti-inflammatory activity; (c) the anti-cancer activity was due to the regulation of molecular targets including caspases; (d) the anti-oxidant, anti-ulcer, and anti-genotoxic properties have been investigated by in vitro and in vivo experiments. Regarding the constituents contributing to therapeutic values, the findings indicated that depsides, depsidones, and benzofurans are key phytochemicals for the treatment of microbial infections, oxidative stress, cancer, ulcer, and inflammation. It is imperative to discuss the stereo-chemistry and structure–activity relationships of depsides, depsidones, and benzofurans for evaluating medicinal properties of Usnea species. However, relating mode of action with chemical structure is difficult since, up to date, the number of investigated chemical constituents for each of these substance classes and pharmacological activities is not very large and the techniques applied and parameters estimated are very variable. As an example, for assessing cytotoxic activity, most of the current research evaluated the capacity of crude extracts and active compounds to inhibit cancer cell proliferation, without focusing on the mechanism of action. For anti-microbial activity, some researchers have focused on Gram positive bacteria, others on Gram negative bacteria, on fungi, on mycobacteria and some other on mixture of them. For estimating antioxidant activity, some researchers have examined the capacity of certain active compounds to scavenge free radicals, others assess their anti-lipidperoxidative property and others determine the level of endogenous antioxidants including CAT, SOD, and GST. Moreover, existing information on the relationships between chemical structure and pharmacological mechanism of action is very limited within natural products, taking as an example the plant kingdom, which is much more known than fungus.
It is noteworthy that current studies on the chemical constituents and pharmacological mechanisms of Usnea species lack depth and more investigations on phytochemistry and the mechanisms of the main active ingredients in demonstrating certain biological activities should be encouraged to fully understand the compounds responsible for the pharmacological effects and the mechanisms of action. The great progress on the phytochemistry and pharmacology of the genus Usnea that has been made confirm its traditional uses. However, there is a pressing need to investigate more conclusive molecular and clinical studies on the safety, efficacy, and toxicity of extracts as well as pure phytochemicals to gain a better understanding of this genus. Furthermore, a significant proportion of the collected pharmacological research has been performed on lichen extracts with promising results, being of interest for the determination of active principles.
Several hurdles were initially faced in the in vitro culture of lichens in order to obtain substantial quantities of lichen substances for various applications. However, advanced techniques such as mycobionts under adjusted culture conditions and heterologous expression of polyketide synthase gene in filamentous fungi, yeasts, and bacteria have recently contributed to great progress in lichen research. These could contribute to future pharmaceutical applications of selected substances of Usnea species, obtained in suitable amounts.
Footnotes |
† These authors contributed equally. |
‡ Present address: TERI-Deakin Nano Biotechnology Centre, The Energy and Resources Institute (TERI), Darbari Seth Block, IHC complex, Lodhi Road, New Delhi – 110003, India. |
This journal is © The Royal Society of Chemistry 2016 |