Submitted: 04 June 2020 | Approved: 17 June 2020 | Published: 18 June 2020
How to cite this article: Arya V, Parmar RK. A Perspective on therapeutic potential of weeds. J Plant Sci Phytopathol. 2020; 4: 042-054.
DOI: 10.29328/journal.jpsp.1001050
ORCiD ID: orcid.org/0000-0002-6808-1754
Copyright License: © 2020 Arya V, et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Keywords: New Zealand; Phytoconstituents; Phytoremediation; Weeds
1Assistant Professor, Government College of Pharmacy, Rohru, Shimla, Himachal Pradesh, India 2Home Maker, Pranav Kuteer, Jayanti Vihar, Kangra, Himachal Pradesh, India
*Address for Correspondence: Vikrant Arya, Assistant Professor, Government College of Pharmacy, Rohru, Shimla, Himachal Pradesh-171207, India, Tel: 8628998699; Email: [email protected]
Nature gives us a diverse plethora of floral wealth. Weeds have been recognized as invasive plant by most of scholars in today’s world with extraordinary travel history. They are considered to be noxious for adjoining plant species and also as economic hazard. Weeds inhabited in almost entire biomes and have capability to survive in harsh conditions of environment thereby become source of inspiration for finding novel phytoconstituents. Weeds play a significant role in absorbing harmful micro pollutants that are affecting ecosystem adversely. There are so many examples like canna lily, bladder wort, coltsfoot, giant buttercup etc. playing crucial part in sustaining environment. Different isolation and characterization approaches like high pressure liquid chromatography, gas chromatography, ion exchange chromatography, nuclear magnetic resonance, mass spectroscopy etc. have also been fetched for obtaining novel constituents from weeds. The main aim of this review is to analyze the therapeutic potential of weeds established in New Zealand and effort to unfold the wide scope of its applications in biological sciences. Upon exploration of various authorized databases available it has been found that weeds not only are the reservoir of complex phytoconstituents exhibiting diverse array of pharmacological activities but also provide potential role in environment phytoremediation. Phytoconstituents reported in weeds have immense potential as a drug targets for different pathological conditions. This review focuses on the literature of therapeutic potential of weeds established in New Zealand and tried to unveil the hidden side of these unwanted plants called weeds.
‘Horse Hoeing Husbandry’ named famous writing by Jethro Tull (1731) mentioned first time the word ‘weed’ [1]. Weeds may be considered as plants whose abundance must be over or above a specific level can cause major environmental concern [2]. Aldrich and Kremer, 1997 defined weed as a part of dynamic ecosystem [3]. Plant originated in natural environment and, in response to imposed or natural environments, evolved, and continues to do so, as an interfering associate with crops and activities. Weeds may interfere with the utilization of land and water resources thereby adversely affect human welfare [4]. According to Ancient Indian Literature earth is blessed with diverse flora and every existing plant has their own importance. Some plants are considered unwanted but they may have beneficial properties. Scholars are trying hard to explore the hidden potential of such unwanted plants [5]. Weeds have interactions with other organisms and some of these interactions can have direct effects on the functioning of agro-ecosystem [6]. They serve as an indirect resource for predatory species [7] and it could alternative food sources for organisms that play prominent role in insect control [8]. Weeds have a unique travel history. Clinton L. Evans in his book ‘The war on weeds in the prairie west- An Environmental History’ mentioned about travelling of weeds in ships, railways, automobiles from one country to another as food contaminants, animal feed, farm implements etc. during trade [9]. Weeds are firmly distributed and established all over New Zealand. Authors Ian Popay, Paul Champion and Trevor James in their book ‘An Illustrated Guide to Common Weeds of New Zealand’ (edition 3rd) published by New Zealand Plant Protection Society in 2010 mentioned the detailed description of around 380 weed species established in New Zealand [10]. Different scientific databases/ information resources (governmental, private, universities, initiatives, organizations etc.) of New Zealand extensively explored over a year as mentioned in table 1 to obtain data pertaining to weeds prevalent within geographical boundaries of New Zealand. After obtaining desired data of different weeds, a literature search was performed using the keyword ‘‘Name of weed (e.g. Aristea ecklonii) Pharmacology’’, ‘‘New Zealand plants’’, ‘‘weed pharmacology’’, ‘‘therapeutic weed’’ individually or all together in different scientific databases of Scopus, Web of Science and Pubmed to obtain therapeutic potential of weeds. Celastrus orbiculatus (Climbing spindle berry) [59], Robinia pseudoacacia (False acacia) [63], Daphne laureola (Green daphne laurel) [66], Glaucium flavum (Horned poppy) [70], Senecio latifolius (Pink ragwort) [80], Solanum nigrum (Black night shade) [86] have potent anticancer activities. Aristea ecklonii (Aristea) [50], Alocasia brisbanensis (Elephant ear) [62], Lycopus europaeus (Gypsywort) [68] exhibited antimicrobial activities. Pseudosasa japonica (Arrow bamboo) [51], Sambucus nigra (Elder) [61], Equisetum arvense (Field horsetail) [65] showed antioxidant effect. Hedera helix (Ivy) [72], Persicaria hydropiper (Mexican water lily) [75], Persicaria hydropiper (Water pepper) [106] showed anti-inflammatory properties. Weeds like Zantedeschia aethiopica (Arum lily) [112], Utricularia gibba (Bladderwort) [113], Canna indica (Canna lilly) [114], Tussilago farfara (Coltsfoot) [115], Egeria densa (Eregia) [116], Ranunculus acris (Giant buttercup) [117], Cytisus scoparius (Broom) [118], Poa annua (Annual poa) have prominent role in biomonitoring of heavy metals in multiple environments [119].
Weeds established in New Zealand encompass wide array of therapeutic phytoconstituents. Weeds serve as biosynthetic factory for synthesis of phytochemicals. They are sources of rich medicinal wealth which includes primary metabolites (polysaccharides) and secondary metabolites (alkaloids, flavonoids, glycosides, tannins, volatile oils etc.). They are the potential sources of complex phytoconstituents. Selaginella kraussiana (African club moss) [11], Lonicera japonica (Japnese honeysuckle) [32], Eriobotrya japonica (Loquat) [35] and Anredera cordifolia (Mignonette vine) [38] contains polysaccharides. Alternanthera philoxeroides (Alligator weed) [13] and Rhamnus alaternus (Evergreen buckthorn) [26] contains anthraquinone glycosides. Lamium galeobdolon (Artillery plant) [14] and Heracleum mantegazzianum (Giant hogweed) [27] contains appreciable amount of volatile oil. Modern spectroscopic methods have been explored for structural elucidation of bioactive constituents present in weeds. LC-MS has been used for quantitative detection of xyloglucan oligosaccharide in Selaginella kraussiana [11], betulonic acid in Alnus glutinosa (Black alder) [12], jasmonic acid in Drosera capensis (Cape sundew) [20], flavonoids in Gunnera tinctoria (Chilean rhubarb) [24], pyrrolizidine alkaloid esters in Gymnocoronis spilanthoides (Senegal tea) [42]. NMR employed for characterization of compounds present in Fraxinus excelsior (Ash) [15], Berberis glaucocarpa (Barberry) [17], Ligustrum sinense (Chinese privet) [25], Rhamnus alaternus [26], Cestrum parqui (Green cestrum) [30], Ranunculus sardous (Hairy buttercup) [49]. Detailed summary of chemical compounds isolated from weeds established in New Zealand indicated in table 2.
Weeds have been explored for diverse pharmacological actions like anti cancer, anti microbial, anti-inflammatory, antioxidant, antiviral etc. as mentioned in table 3 and figure 1.
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Figure 1: Therapeutic potential of weeds.
Anticancer weeds: Some important cytotoxic weeds include Clematis flammula [58], Hakea sericea (Needlebush) [77], Robinia pseudoacacia (False acacia) [63], Daphne laureola [66]. Myricaria germanica (False tamarisk) [64], Senecio latifolius (Pink ragwort) [80]. Osmunda regalis (Royal fern) [82]. Parvifloron D isolated from Plectranthus ecklonii via flash dry column chromatography exhibited antiproliferative effects against pancreatic cancer when evaluated against HaCat, BxPC3, Caco-2, MCF-7, Ins1-E and PANC-1 cell lines [53]. Aqueous extract of weed Solanum nigrum at concentration of 10 g/l caused 43% cytotoxicity in MCF7 cell line by inhibiting migration, suppression of hexokinase and pyruvate kinase [86]. Triterpene (28-Hydroxy-3-oxoolean-12-en-29-oic acid) present in Celastrus orbiculatus showed inhibitory activity on SGC-7901 and BGC-823 cells lines [59]. Bocconoline alkaloid isolated from dried roots of Glaucium flavum (Horned poppy) exhibited cytotoxicity with IC50 value of 7.8µM [70].
Antimicrobial weeds: Invasive weed Aristea ecklonii containing Plumbagin exhibited antimicrobial activity with minimum inhibitory concentration between 2 μg/ml and 16 μg/ml [50]. Antimicrobial peptides isolated from arum lily (Zantedeschia aethiopica) exhibited potent antimicrobial activity [67]. Euroabienol (abietane-type diterpenoid) isolated from fruits of Lycopus europaeus exhibited broad spectrum antimicrobial activity [68]. Compounds 3-[3-(3-pyridinyl)-1,2,4-oxadiazol-5-yl] benzonitrile and [3,5-Bis (1,1-dimethylethyl)-4-hydroxyphenyl] isolated from weed Tropaeolum tuberosum when tested against Candida tropicalis exhibited antifungal activities with MICs of 100 μM and 50 μM [76]. Extracts obtained from leaves of weed Abutilon theophrasti elicit antimicrobial potential against Staphylococcus aureus, Salmonella, Streptococcus and E. coli species [85]. Essential oils isolated from weeds Conium maculatum, Leptospermum scoparium showed antimicrobial activity against several strains of Pseudomonas aeruginosa [96,97]. Ethanolic extracts of woolly mullein reported positive against gram positive bacteria (Bacillus cereus) [108]. Phenolic compounds from Dipsacus fullonum exerted inhibitory effects on Staphylococcus aureus DSM 799 and E. coli ATCC 10536 strains [109].
Antioxidant weeds: Strong antioxidant activity was reported by ferulic acid derived from leaves of weed Pseudosasa japonica when evaluated using DPPH (54 %) and ABTS (65 %) [51]. Antioxidant potential of Taraxacum officinale was determined using in vitro methods (DPPH, ABTS, FRAP). The ABTS method reveled that antioxidant activity was 156±5.28 µg/ml [92]. Other potential antioxidant weed includes Acanthus mollis [52], Sambucus nigra [61], Equisetum arvense [65].
Anti-inflammatory weeds: A study by Akhtar, et al. 2019 investigated the anti-inflammatory properties of Hedera helix and its major compounds on Staphylococcus aureus induced inflammation in mice. Hederacoside-C isolated from weed exerted profound anti-inflammatory effects [72]. Mexican water lily (Nymphaea mexicana) was found to be potent COX-2 inhibitor [75]. Active compounds isolated from aerial parts of weed Clematis vitalba when evaluated in vivo against carrageenan, serotonin, PGE-2 induced hind paw edema showed antinociceptive and antipyretic effects [78]. Methanolic extract of leaves of Tecomaria capensis significantly prevented increase in volume of paw edema [55]. Extract of Persicaria hydropiper exerted marked anti-inflammatory effects [106]. Aqueous extract alongwith compounds (calceorioside B, homoplantaginin, plantamajoside) isolated from the aerial parts of Plantago major showed inhibition against hyaluronidase enzyme [89].
Antiviral weeds: Methanolic extract of scrambling speedwell weed (Veronica persica) reported potent activity against herpes simplex viruses and synergistic activity in combination with acyclovir anti-HSV therapy [103]. Ursolic acid isolated form weed Prunella vulgaris inhibited IHNV infection in aquaculture with an inhibitory concentration of 99.3 % at 100 mg/l [104].
Weeds acting on CNS: Methanolic extract of stem bark of darwin’s barberry (Berberis darwinii) inhibited acetylcholinestrase in vitro with IC50 value of 1.23 ± 0.05 microg/mL thereby provide relief in alzheimer’s disease [60]. Alkaloid solanocapsine isolated from weed Solanum pseudocapsicum reported to inhibit activity of enzyme acetylcholinestrase [73]. Nettle (Urtica urens) exhibited anxiolytic activity in mice when evaluated using hole board test, light-dark box test and rota rod test. Extract showed increased head-dip duration and head-dip counts in hole board test [98]. Aqueous (50-400 mg/kg i.p.) and methanolic extracts (100-400 mg/kg i.p.) of Pig’s ear (Cotyledon orbiculata) exhibited anticonvulsant activity which predominantly delayed onset of seizures induced by N-methyl-dl-aspartic, bicuculline, picrotoxin in mice models [79].
Other pharmacological activities of weeds: Aqueous extract of Akebia quinata showed positive effect against fatigue in mice exposed to chronic restraint stress when evaluated using forced swimming behavioral test, sucrose preference and open field tests [57]. n-butanol fraction of weed Equisetum hyemale exerted antiprotozoal effects against Trypanosoma evansi trypomastigotes after nine hours exposure [81]. Chen, et al. 2019 reported osteogenic activities of Humulus lupulus in MC3T3-E1 cell lines [69]. Ethanolic extract of weed Galium aparine stimulated the transformational activity of immunocompetent blood cells in vitro [91]. Aqueous extract of aerial parts of Mentha pulegium (20 mg/kg) showed antihyperglycemic effect by marked improvement in oral glucose tolerance test in streptozotocin induced diabetic rats [99]. Butanolic extracts of aerial parts of Lamium album and Lamium pupureum showed haemostatic activity in wistar rats when evaluated by tail bleeding time determination and acenocoumarol carrageenan test compared to vitamin K [100]. Anagallis arvensis (Scarlet pimpernel) leaf extract showed molluscicidal activity against Biomphalaria alexandrina at LC50 37.9 mg/l and LC90 48.3 mg/l [101]. Hexane extract rich in lupeol acetate of weed scotch thistle (Cirsium vulgare) prevented carbon tetrachloride induced liver damage in rats by diminishing lipid peroxidation and nitric oxide levels [102]. Extracts of Sonchus oleraceus (Sow thistle) were reported to be nephroprotective against kidney ischemia reperfusion injury in wistar rats [105]. Water extract, ethanol extract, hexane/acetone extract obtained from Achillea millefolium (Yarrow) were effective against Babesia canis parasite at 2 mg/ml concentration [107].
A large number of weed communities has been reported to clean environment through phytoremediation process and act as bioindicators (Figure 2). Phytoremediation is described as a process of eradicating toxic contaminants from soil, water and air. This process involves phytoextraction (harvesting of biomass), phytostabilization (contaminants stabilized into less toxic compounds), phytotransformation (chemical modification of contaminants), phytostimulation (rhizosphere degradation), phytovolatilization (conversion of toxic compounds into volatile form) and rhizofiltration (filtration through roots) [111]. Arum lily (Zantedeschia aethiopica) acts as micropollutant removal by removing accumulation of copper, zinc, carbamazepine and linear alkylbenxene sulphonates [112]. Bladderwort (Utricularia gibba) [113], canna lilly (Canna indica) [114], coltsfoot (Tussilago farfara) [115], egeria (Egeria densa) [116], giant buttercup (Ranunculus acris) [117], broom (Cytisus scoparius) [118], annual poa (Poa annua) have been involved in removing toxic metals (chromium, cadmium, zinc, lead) from the environment [119]. Parrot feather (Myriophyllum aquaticum) aids in removing antibiotic (tetracycline) from water [120]. Oxeye daisy (Leucanthemum vulgare) potentiated crude oil phytoremediation and used in eliminating pollution from environment [121]. Apart from these properties weeds have also been found to be employed in other industries e.g. buffalo grass weed (Stenotaphrum secundatum) used in turf grass industry [122]. Mucoadhesive properties of water soluble gum obtained from Hakea gibbosa added in sustained release dosage forms [123]. Silver nanoparticles having average particle size 20 nm synthesized from Cestrum nocturnum showed more antioxidant potential as compared to vitamin C alongwith strong antibacterial activity against Vibrio cholerae with MIC of 16 µg/ml [124]. Organic fertilizer manufactured via aquatic weed Salvinia molesta when evaluated using FT-IR, plant bioassay test for determination of its fertilizer value and chemical composition showed promising results as vermicompost [125]. Eragrostis species (E. capensis, E. curvula) and grass Stenotaphrum secundatum exhibited drought resistant ability [126,127].
Figure 2: An overview of Phytoremediation process.
Besides the therapeutic potential exhibited by weeds, toxicity profile should be taken into consideration while exploring them. Equisetum arvense (Field horsetail) exerted hepatotoxicity in rats [128], weeds like Zantedeschia aethiopica (Arum lily), Conium maculatum (Hemlock), Solanum nigrum (Black night shade) are considered poisonous in New Zealand [129]. Hedera helix (Ivy) caused contact dermatitis [130], Lantana camara exerted in vivo cell toxicity [131], Xanthium strumarium (Cocklebur) responsible for causing poisoning in cattle [132].
Humans define weeds as per their appropriateness and understanding of the plant. A plant investigated as weed in some region may be a plant of medicinal importance for another region. The usefulness of weeds has been ignored by humans for long time because of their invasive growth, competitors of genuine crop and no economic value. This human behaviour might be developed over time due to lack of proper knowledge of phytochemical screening as well as therapeutic potential of weeds. Weeds are the sources of human food, fodder in agriculture, shelter for some animals, helpful against soil erosion, indicators of soil nutrients, as well as sources of commercially important essential oils. In this era weeds have been extensively explored for their immense phytopharmacological prospects. It is evidenced that weeds have been sources of potential targets for different pathological conditions. However there is need of more scientific and clinical investigations required in assessment of toxicity profile to get the maximum potential of weeds. Weeds have protective role in environment as a component of phytoremediation and for sustainable ecosystem. Because of immense therapeutic potential implicit by weeds a new chain of thoughts emerge in our mind to consider the value of these important plants so called ‘weeds’. Are they need to be redefined or we need to rethink the concept of weeds? It is clear from the studies documented in this review that the approach of whether a plant is wanted or not should depends on its pharmacological potential and role in ecosystem other than merely the competitive effect of plant with the particular crop. Further advancements are required in order to spin the concept of weeds into therapeutic weeds.
