Chief EditorPradeep K. Sharma
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Application of Rhododendron for Human Welfare: A Review
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First Online 03-08-2021|
Phytochemical and nutriitional profile
Rhododendron contains Mn, Fe, Zn, Cu, Na, Cr, Co, Cd, Mo, Ni, Pb and arsenic that play a vital role to maintain some physicochemical processes that are very essential for life. Sodium (Na) is important to maintain the osmotic balance between cells and interstitial fluid (Soetan et al., 2010). Rhododendron contains good amount of secondary metabolites like tannins, steroids, alkaloids, flavonoids, saponins, glycosides and phlobatannins (Nisar et al., 2013). Various phtyochemicals have been recognised and isolated from the different parts of R. arboreum that have protective or disease preventive properties. They include - flavonoids, alkaloids, saponins, tannins, phytosterols, reducing sugars and phenolic compounds. Isolated flavonoids include Quercetin-3-O-galactoside and Quercetin from flower and leaves while sterols include beta-sistosterol from leaves. Flavonol glycoside rutin isolated from leaves and quercitrin from flower whereas triterpenoid 3-O-acetylbetulinic acid, betulin and lupeol generated from bark. Many phytochemicals from different parts have also been isolated from which are as under:
Petroleum ether extract of the bark contained a triterpenoid substances 3-0-acetylbetulinic acid (C32H50O4), beta -sitosterol-3-O-beta – D glucosidose (C32H50O4), 3-beta-acetoxyurs-11-en-13-beta,28-olide(C32H48O4);botulin (C30H50O2); lupeol (C30H50O); 3-O acetylursolic acid (C32H50O4); taraxerol(C30H50O);ursolic acid (C30H48O3);15-oxoursolic acid (C30H46O4). The ether extract of the bark following petroleum ether extract showed the identity of betulinic acid (C30H48O3) while acetone extract gave leuco-pelargonidin (C15H14O6) (Hariharan and Rangaswami, 1966).
Quercetin -3-O-glactoside (C21H20O12) is a flavonoid compound extracted from R.arboreum. Three active phenolic compounds i.e. quercetin (C15H10O7), rutin (C27H30O16) and coumaric acid (C9H8O3) have been reported in flowers of R. arboreum using high-performance thin-layer chromatography (HPTLC). There are many other compounds that isolated in methanolic flower extract (Swaroop, 2005).
The green leaves of the plant contain flavonoids Quercetin -3-O-glactoside (C21H20O12) and quercetin (C15H10O7). It contains sterol beta-sitosterol (C29H50O), a new triterpenoid named campanulin, quercetin and hyperoside (C21H20O12). Chemical analysis of arboreum indicated the presence of pentacyclictriterpenoid compounds which include alpha-amyrin, beta-amyrin, friedelin(C30H50O). Leaves are also reported to contain the flavone glycoside rutin (C27H30O16) and dimethyl ester of terephthalic acid (Painuli et al., 2015; Jegan and Selvaraj, 2016). Jegan and Selvaraj (2016) reported about 34 compounds out of it some are major compounds detected in Gas chromatography and mass spectrometry analysis of methanolic extract of leaves. Compounds detected were beta-amyrin, heptadecane, 22-stigmasten-3-one, tetradecane, methyl ester, linoleic, linoleyl alcohol, beta-citronellol, dodecane, L-ascorbic acid, 2, 6- dihexadecanoate, alpha-amyrin and dibutyl phthalate (Gautam et al., 2018). In ethanolic leaf extract, about 13 compounds were identified out of these five compounds which included geraniolformate, 1-hexadecene, 1, 2, 3, propanetriyl ester, 1-octadecanol and docosanoic acid. Gautam et al., (2018) reported 26, 24 and 17 compounds in chloroform, ethyl acetate and hexane fractions respectively. The phenolic compounds, quercitrin, syringic acid, epicatechin and quercetin-3-O-galactoside in the methanolic leaves were extracted by RP-HPTLC and gallic acid in the leaves, three triterpenoids (ursolic acid, β-sitosterol and lupeol) in the flowers and leaves confirmed by HPTLC (Shilajan and Swar, 2013).
Many wooden products like packsaddles, handles and gift-boxes are made from the wood of R. arboreum and wood is used as fuel (Chettri and Sharma, 2009; Rana et al., 2015). Paste of the bark is helpful to heal the cuts (Bhattacharyya, 2011). The beautiful flowers which attract everyone, is normally used in houses decorations. Due to its sweet-sour taste, flowers are eaten raw or made into chutneys or juice. Juice is used as a freshener and is beneficial to cure fever, diabetes, rheumatism, headache and stomachache while dried flower powder is used as a drug to cure the bloody dysentery (Semwal, 2010; Sharma and Samant, 2014; Krishna, 2014; Sharma, 2010; Shilajan and Swar, 2013). Fig 1 and Table 2 shows traditional use of different parts of R. arboreum.
Pharmacological and biological properties
Medicinal value of plants has assumed importance during past few decades with diverse group of secondary metabolites with antioxidant potential which serve as plant defence mechanism against predation by insects, herbivores and microorganisms. Som et al., (2019) reported that diterpenes, triterpenes, flavonoids, steroids, tannin, phenolics, saponin, glycosides, alkaloids, tannin, quercetin and gallic acid etc. isolated from Rhododendron sp. has potent anti-stress activity and strong anti-oxidant activity due to which it might be responsible for adaptogenic activity.
The ethyl acetate fraction of Rhododendron arboretum flowers showed potent antidiarrheal activity. The fraction significantly inhibited the number of diarrheal faeces in the castor oil induced diarrhoea (Verma et al., 2010).
Anti-inflammatory and anti-nociceptive activity
The ethyl extract fraction of flower showed significant ant-inflammatory and anti-nociceptive effects. Gautam et al., (2018) found that ethyl acetate extract of bark of the tree showed anti-inflammatory activity against rat paw oedema. The anti-inflammatory or nociceptive effect of the extract may be due to the presence of flavonoids, tannins, saponins and other phytochemicals present either as single or in combination. The significant level of anti-inflammatory activity of the ethyl acetate extract could be attributed to high amounts of flavonoids present in the extract.
Anti-oxidant and anti-mutagenic activity
In this era of urbanization and environmental pollution, antioxidants and anti-mutagens derived from plants are the best safeguards for health of humans. Hexane, chloroform and ethyl acetate fractions of R. arboreum leaf extract, decreased the production of nitric oxide radicals and inhibited the lipid peroxidation. These activities might be due to the synergistic effect of phytochemicals reported in the GC-MS profiling and the presence of phytochemicals while vitamin E might be responsible for the antioxidant activity (Prakash et al., 2007).
Acharya et al., (2011) found that the methanolic leaf extract was moderate in antioxidant effect as compared to standard quercetin, while another study revealed that the ethanolic flower extract was high in antioxidant effect and nitric oxide synthase activation (Bhandari and Rajbhandari, 2014). Sonar et al., (2012) isolated quercetin from flower petals and estimated total flavonoid phenolic and antioxidant activity of various parts of Rhododendron arboretum.
Ethanolic leaf extract exhibited dose-dependent, significant activity against Agrobacterium tumefaciens induced tumour in potato disc. Isolated compound rutin and quercetin may be responsible for antitumor activity (Bhandary and Kuwabata, 2008).
Anti-diabetic activity was examined in Rhododendron arboreum flower and active compounds isolated from it. According to Parcha et al., (2017), ethyl acetate soluble part was more effective in a-glucosidase inhibitory activity than the water-soluble part.
Distinctive secondary metabolites of R. arboreum showed the potential to defuse hazardous and harmful molecules. Ethanolic extract of R. arboreum whole plant, significantly decreased the activity of alanine transaminase (ALT), aspartate transaminase (AST), lactate dehydrogenase (LDH) enzymes and decreased the levels of Mass drug administration (MDA) in serum, heart tissue and increased the activity of Superoxide dismutases (SOD), catalase, glutathione peroxidase (GPx) and glutathione (GSH) in isoproterenol-treated rats. Murty et al., (2010) showed ethanolic flower extract was more effective than aqueous extract, which significantly decreased the release of lactate dehydrogenase and creatine kinase in albino rats, while the n-butanol fraction of ethanolic extract showed maximum cardio protective activity among all the extracts.
Oral administration of Hyppophae ramnoides fruit juice + Rhododendron arboreum flower juice in 1:4 significantly reduced total cholesterol, triglycerides, low-density lipoprotein and antherogenic index (Verma et al., 2011).
Hepatoprotective and Immuno-modulatory activity
Ethyl acetate fraction of flower extract exhibited hepatoprotective potential against carbon tetrachloride (CCl4) induced liver damage in preventive and curative models. In addition, ethyl acetate fraction also significantly prevented the elevation of hepatic malondialdehyde formation and depletion of reduced glutathione content in the liver of CCl4 intoxicated rats in a dose dependent manner (Painuli et al., 2015). In another study, the ethanolic leaf extract significantly reduced the serum enzyme Alkaline phosphatase (ALP), serum glutamic oxaloacetic transaminase (SGOT), serum glutamic pyruvic transaminase (SGPT), triglyceride, total bilirubin, cholesterol and excretion of ascorbic acid in urine to the normal level in carbon tetrachloride treated rats (Acharya et al., 2011). Alcoholic extract of the leaves of R. arboreum was an effective and safe immunosuppressive agent (Bhandary and Kuwabata, 2008).
Toxicity and anti-microbial activity
The leaves exhibited significant cytotoxicity, while stem, roots had moderate effect with bark showing least significance. The presence of glycosides, alkaloids and flavonoids in the extract might be responsible for activity (Ali et al., 2008). The methanolic crude extracts of flower, leaf, stem and roots of R. arboreum possessed significant potency against B. subtilus, Salmonella typhi and S. aureus (Ali et al., 2008; Prakash et al., 2008). Prakash et al., (2008) stated that the leaf extract was fairly effective, than flower extract. The zone of inhibition of methanol and aqueous leaves extracts for S. aureus, Klebsiella pneumoniae, Streptococcus pyogene and E. coli. (Chauhan et al., 2016). Sharma et al., (2013) reported that ethanolic flower extract was very effective against B. subtilis, S. aureus, Salmonella typhi and Escherichia coli. Ethanol, methanol extract and isolated quercetin showed lowest effective concentration against E. coli and S. Aureus (Bhandary and Kuwabata, 2008). In another study, the ethanolic flower extract showed significant role against E. coli, S. epidermidis and S. aureus respectively and also showed antifungal activity against Aspergillus flavus, Candida albicans and Aspergillus parasiticus while the water extract, showed significant result against Candida albicans, Aspergillus parasiticus and for Aspergillus flavus (Saranya and Ravi 2016). Methanol and the ethyl acetate extract showed effective antifungal activity against Fusarium solani, Aspergillus niger, Microsporum canis, Cantharellus flavus, Candida albacan and Candida glaberata. The high activity of betulin and 3β-acetoxyurs-11, 12- epoxy-13β might be due to its hydrophilic nature (Ali et al., 2008). Chauhan et al., (2016) reported that methanol and aqueous leaf extract wereeffective against the fungus Trichoderma viride and Candida.
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