Ulam herbs : A review on the medicinal properties of Anacardium occidentale and Barringtonia racemosa

1 Faculty of Applied Sciences, UCSI University, 56000 Cheras, Kuala Lumpur, Malaysia. 2 Secretariat, International Society for Mangrove Ecosystems, c/o Faculty of Agriculture, University of the Ryukyus, Okinawa 903-0129, Japan. 3 Centre for Environmental Biology and Ecosystem Studies, National Institute for Environmental Studies, Onogawa, Tsukuba 305-0053, Japan. 4 School of Science, Monash University Sunway, Petaling Jaya 46150, Selangor, Malaysia.


INTRODUCTION
In Southeast Asian countries, particularly Malaysia, Thailand and Indonesia, some herbs are consumed raw as condiment (ulam), and they form an important component of the traditional diet.Dipped in hot and spicy sauce made from shrimp or fish paste, these herbs would whet the appetite during meals.These herbs are believed to have health-promoting properties, and their regular intake can assist in preventing degenerative diseases, delaying aging and improving overall health (Sulaiman et al., 2011;Reihani and Azhar, 2012).Young leaves of herbs commonly consumed as ulam include Anacardium occidentale (cashew), Barringtonia racemosa (common putat), Centella asiatica (pennywort), Cosmos caudatus (wild cosmos), Murraya koenigii (curry leaf), Oenanthe javanica (water dropwort), Persicaria hydropiper (water pepper) and Piper sarmentosum (wild pepper).Major chemical constituents reported in ulam herbs are flavonoids and phenolic acids.These compounds are known to possess various health benefits with a multitude of bioactivities including antioxidant, antimicrobial, anti-proliferative, antiallergic, anti-inflammatory, anti-hypertensive and vasodilating properties (Pietta et al., 2003;Yao et al., 2004).Herbs with multiple pharmacological functions mediated by complex interactions of phytochemicals are effective in treating multiple diseases and age-related disorders (Satoh, 2014).Their anti-aging effects and improvement of blood circulation have also been reported.Unlike Labiatae herbs which are widely used in western cuisines, herbs consumed as ulam in eastern cuisines are not well reviewed.This review updates the current knowledge on the phytochemistry and pharmacology of leaves of A. occidentale (cashew) and B. racemosa (putat) with some description of their botany and uses.
Currently, there is only one review on A. occidentale with focus on the nuts (Leite et al., 2016), and two reviews on all plant parts of B. racemosa (Kabir et al., 2013;Osman et al., 2015).However, this review is deemed relevant and appropriate as it is focused on the leaves of A. occidentale and B. racemosa.

Botany and uses
Anacardium occidentale L. (cashew) of the family Anacardiaceae is native to Brazil (Lim, 2012a).It is a small-sized tree with a dome-shaped crown.The bark is brown or grey, and smooth to rough with longitudinal fissures.Leaves are leathery and obovate with a rounded apex.Borne on terminal clusters, leaves are pliable, lustrous and reddish when young, and dark green when mature with prominent yellow veins.Occurring as terminal panicles, flowers are whitish turning pinkish-red.Fruits are a kidney-shaped nut attached to the distal end of an enlarged pear-shaped receptacle called the cashew apple.
The young and tender leaves of A. occidentale (Figure 1) are a popular herb consumed raw as ulam and sometimes blanched to reduce their stringent taste.In traditional medicine, leaves are used for treating dysentery, diarrhoea and piles, and an infusion of bark and leaves are applied to relief toothache and sore gums (Akinpelu, 2001).Other uses of leaves include remedy for rheumatism and hypertension (Andarwulan et al., 2012;Nugroho et al., 2013).

Pharmacological properties of leaves Antioxidant
Among the leaves of 10 species of ulam herbs assessed for antioxidant properties, values of A. occidentale leaves were by far the highest (Chan et al., 2014).The total phenolic content (3890 mg GAE/100 g) and free radical scavenging ability (6620 mg AA/100 g) of A. occidentale leaves were 1.7 and 2.6 times those of Persicaria hydropiper, which ranked second, and 16 and 30 times those of Centella asiatica, which ranked last.Antioxidant properties of cashew leaves were significantly stronger than western culinary herbs such as rosemary, thyme and marjoram (Chan et al., 2012a(Chan et al., , 2012b)).Similarly, the total phenolic content and antioxidant activities of A. occidentale leaves were the strongest amongst herbs and vegetables studied (Sulaiman et al., 2011;Huda-Faujan et al., 2015).
The methanol leaf extract of A. occidentale yielded higher total phenolic content, free radical scavenging and ferric reducing properties than ethyl acetate and hexane extracts (Razali et al., 2008).Based on DPPH radical and NO scavenging activities, the ethanol leaf extract of A. occidentale possessed the strongest activities followed by aqueous and petroleum ether extracts (Jaiswal et al., 2010).In Thailand, the phenolic content and antioxidant activities of young leaves of cashew ranked second out of 13 indigenous vegetables screened by Kongkachuichai et al. (2015).The phenolic content of young cashew leaves was 10 times higher than that of fruits.

Antibacterial and antiviral
When tested against Gram-positive bacteria of Brevibacillus brevis, Micrococcus luteus and Staphylococcus cohnii, and Gram-negative bacteria of Escherichia coli, Pseudomonas aeruginosa and Salmonella enterica using the discdiffusion method, leaves of A. occidentale inhibited all bacterial species except S. enterica (Tan and Chan, 2014).Minimum inhibitory dose (MID) ranged from 0.13−0.50mg/disc.Against E. coli, P. aeruginosa, Bacillus cereus, Bacillus megaterium and Cryptococcus neoformans, cashew leaves inhibited all bacterial species except E. coli (Mackeen et al., 1997) 2015) also reported on the antibacterial properties of A. occidentale leaves.Inhibition of the leaf extract of A. occidentale was stronger than that of the bark extract (Manasa et al., 2013) while the flower extract displayed the strongest inhibition (da Silva et al., 2016).The essential oil extracted from leaf shoots of cashew also possessed antimicrobial activity (Nor Ayshah Alia et al., 2016).Among 12 medicinal plant species screened for simian (SA-11) and human (HCR3) rotavirus inhibition in Brazil, the aqueous leaf extract of A. occidentale inhibited the growth of SA-11 by 85% at non-cytotoxic concentration of 4.0 µg/ml (Gonçalves et al., 2005).Rotaviruses are known to be major agents of diarrhoea in infants and young children.

Anti-quorum sensing
Using the violacein inhibition assay with Chromobacterium violaceum as the test organism, Tan et al. (2015) reported that A. occidentale leaves exhibited strong antiquorum sensing (QS) activity.Diameters of inhibition zones (DIZ) of violacein production and of C. violaceum growth were 22 mm and 15 mm, respectively.Minimum inhibitory dose (MID) of violacein production and C. violaceum growth were 0.013 and 0.25 mg/disc.From the methanol leaf extract of cashew, methyl gallate (methyl ester of gallic acid) was isolated using column chromatography, and identified by NMR and MS analyses.Violacein production inhibition of methyl gallate at 0.05 mg/disc was 14.5 mm for DIZ, 0.006 mg/disc for MID and 0.10 mg/ml for minimum inhibition concentration (MIC).The closely-related gallic acid, however, did not display any anti-QS activity, suggesting that the methyl moiety in methyl gallate may be responsible for the QS inhibition.Using reversed-phase HPLC, the content of methyl gallate was quantified as 1.83 mg/g.Tan et al. (2015) was the first report on the systematic isolation and quantification of methyl gallate with potent QS inhibition from leaves of A. occidentale.

Antifungal
Cashew leaves have been shown to have antifungal activity based on an interesting study conducted on the microbiology of dentures of 50 elderly people from Mangalore in Karnataka, India (Shetty et al., 2014).Total Candida counts were conducted on swabs collected from their dentures before and after application of cleansing agents.Results showed that cashew leaves can be used as a natural cleansing agent although their antifungal activity was not as effective as denture cleansing tablets of triphala.

Tyrosinase inhibition
The anti-tyrosinase activity of A. occidentale leaves (40%) was comparable to that of Psidium guajava (41%) and Hibiscus tiliaceus (42%) used as positive controls (Tan and Chan, 2014).Compared to fresh cashew leaves, inhibition was not affected by blanching (44%) but was significantly enhanced by microwave treatment (49%).The leaf extract of A. occidentale inhibited tyrosinase and reduced melanin in human epidermal melanocytes for more than 24 h, suggesting their potential use as therapy for pigmentation problem (Gaffar et al., 2008).

Cytotoxic
Screening of 42 families of edible plants from Malaysia for Epstein-Barr virus (EBV) activation in Raji cells showed that the methanol leaf extract of A. occidentale (8 μg/ml) was strongly active (Murakami et al., 2000).The ethanol leaf extract of cashew was reported to be cytotoxic to Jurkat cells by inducing apoptosis (Konan et al., 2012).Agathisflavone, a biflavonoid isolated, displayed high anti-proliferative effect on Jurkat cells with IC 50 value of 2.4 μg/ml.When tested against human gingival fibroblast and Chinese hamster lung fibroblast (V79) cell lines, the ethanol leaf extract of A. occidentale resulted in 26% and 22% mortality, respectively (Anand et al., 2015).These values were significantly weaker than the commercial mouth rinse of rexidin (41% and 49%) and betadine (46% and 50%) indicating that the extract was much less toxic.

Hypoglycaemic
Leaves of A. occidentale were found to have hypoglycaemic properties.The blood glucose level of rats administered with the aqueous leaf extract of cashew increased by 48% compared with 208% increase in streptozotocin (STZ)induced diabetic rats (Kamtchouing et al., 1998).Results indicated that cashew leaves have a protective effect against STZ-induced diabetes in rats.A related study reported that oral administration of the methanol leaf extract of A. occidentale at doses of 35, 175 and 250 mg/kg significantly reduced blood glucose levels in diabetic rats after 3 h (Sokeng et al., 2007).Maximum reduction of 37% and 35% in blood glucose levels was observed with doses of 175 and 250 mg/kg, respectively.When administered repeatedly with 175 mg/kg of extract, the decline in blood glucose (48%) was more pronounced.The hexane leaf extract of cashew (300 mg/kg) had no nephrotoxic effect in normal rats, and effectively reduced diabetes-induced functional and histological alterations in the kidney (Tedong et al., 2006).The leaf extract of A. occidentale has been reported to significantly lower blood glucose levels in normoglycaemic and hyperglycaemic rabbits (Esimone et al., 2001), in normoglycaemic rats (Saidu et al., 2012), and in alloxaninduced diabetic rats (Fagbohun and Odufuwa, 2010).The lowering of blood glucose levels is accompanied by hypoglycaemic and hypolipidemic effects in alloxan-induced diabetic rats (Elekofehinti et al., 2016).Another related study showed that the cashew leaf extract ameliorated the level of thiobarbituric acid reactive substances, and improved the activities of glucose-6-phosphate dehydrogenase, superoxide dismutase and glutathione peroxidase in the testicular homogenate of STZinduced diabetic rats (Ukwenya et al., 2013).

Anti-cholesterolemic
The anti-cholesterolemic activity of the aqueous leaf extract of A. occidentale has been reported in male rabbits supplemented with a high cholesterol diet (Fazil et al., 2011).In vitro toxicity screening of the extract demonstrated very low LC 50 values and no IC 50 value was detected.In cholesterolemic rabbits, the extract was able to inhibit the increment of liver enzymes.

Anti-ulcerogenic
The aqueous ethanol leaf extract of A. occidentale exhibited anti-ulcerogenic effect in rats (Konan and Bacchi, 2007).The extract inhibited gastric lesions induced by HCl/ethanol in female rats, with an ED 50 value of 150 mg/kg.Extract doses higher than 100 mg/kg were more effective than 30 mg/kg of lansoprazol in preventing gastric lesions.No signs of acute toxicity were observed when the rats were treated with extract doses up to 2000 mg/kg.

Anti-hypertensive
A purified A. occidentale leaf extract has shown to have in vitro anti-hypertensive effects using the isolated organ technique (Nugroho et al., 2013).At 0.5 and 1.0 mg/ml, the extract reduced the contraction of isolated rat aorta induced by phenylephrine by 26% and 40%, respectively.This finding was complemented by reports that the aglycones and glycosides of quercetin (major constituents of cashew leaves) have the ability to reduce hypertension (Duarte et al., 2001), to stimulate vasorelaxation of aortic vessels (Khoo et al., 2010), and to lower blood pressure (Edwards et al., 2007;Larson et al., 2012) in animal models and human subjects.

Analgesic and anti-inflammatory
The analgesic and anti-inflammatory effects of cashew leaf extracts have also been reported.Leaves successively extracted with petroleum ether, chloroform and methanol were screened for analgesic and anti-inflammatory activity using the carrageenan-induced rat paw oedema assay by Pawar et al. (2000).Results showed that the petroleum ether and chloroform leaf extracts, and the acetone soluble fraction of the methanol extract exhibited 57%, 48% and 62% inhibition of paw oedema, respectively.The aqueous, hexane, dichloromethane and methanol leaf extracts of A. occidentale investigated for analgesic effects on acetic acid-induced pain in mice showed that the extracts significantly reduced the number of writhing and the highest analgesic effect was seen in the dichloromethane extract (Onasanwo et al., 2012).A recent study on the anti-inflammatory properties of cashew leaves reported stronger activity in the ethanol extract than the aqueous extract (Thomas et al., 2015).

Toxicity studies of leaves
Studies on the toxicity of cashew leaves have been conducted by Tedong et al. (2007).In the acute toxicity study, oral administration of a single dose of hexane leaf extract of A. occidentale in mice showed no toxic symptoms at 6 g/kg and no mortality up to 14 g/kg after a week.At doses higher than 6 g/kg, signs of toxicity included asthenia, anorexia, diarrhoea and syncope.The LD 50 of the extract was found to be 16 g/kg.In the sub-chronic study, oral administration to mice at doses of 6, 10 and 14 g/kg for eight weeks resulted in reduction in food intake and weight gain.Histopathological examinations revealed evidence of microscopic lesions in the liver or kidney caused by changes in biochemical parameters of blood samples.

Botany and uses
Barringtonia racemosa (L.) Spreng (putat) of the family Lecythidaceae is a small tree with greyish-brown bark (Giesen et al., 2007;Yaplito, 2001).Leaves, clustered at the end of branches, are oblong-obovate and have serrated margins.Inflorescences are long and pendulous, bearing many fragrant pink flowers with conspicuous stamens (Figure 2).Fruits are oblong or pear-shaped and bear single seeds.Occurring in association with mangrove and other coastal forests, the natural distribution of B. racemosa stretches from East and South Africa eastwards though South, Southeast and East Asia to Polynesia (Giesen et al., 2007).
In Southeast Asia, leaf shoots and young leaves of B. racemosa are consumed raw as ulam or cooked as vegetables (Yaplito, 2001;Lim, 2012b).As ethnomedicine, leaves have been used to treat high blood pressure, itchiness and chicken pox (Kabir et al., 2013;Osman et al., 2015).Known to be rich in saponins, the bark and fruits of B. racemosa are used by coastal communities as fish poison (Giesen et al., 2007).

Phytochemistry of leaves
Using HPLC analysis, phenolic compounds of gallic acid, protocatechuic acid, ellagic acid, quercetin and kaempferol have been identified in sequential leaf extracts of B. racemosa (Kong et al., 2012).In a follow-up study, the contents were of the order: gallic acid > ellagic acid > quercetin > protocatechuic acid > rutin > kaempferol (Kong et al., 2014).The contents of gallic acid and ellagic acid were 2200 and 1450 μg/g in freeze-dried leaves, and 2270 and 1140 μg/g in air-dried leaves, respectively.Earlier, gallic acid, ferulic acid, naringin, rutin, luteolin and kaempferol have been reported in the methanol leaf extract of B. racemosa (Hussin et al., 2009).

Antioxidant
Antioxidant activities of leaf extracts of B. racemosa, measured using the ferric thiocyanate, thiobarbituric acid and 1,1diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging assays, showed strongest activities in the chloroform extract followed by extracts of hexane and ethanol (Behbahani et al., 2007).The phenolic contents and antioxidant activities of different plant parts of B. racemosa were studied by Mariam et al. (2008).Results showed that the methanol extracts of twigs and barks yielded higher total phenolic and flavonoid contents, respectively.A study on the total phenolic content and antioxidant properties of different stages of young leaves of B. racemosa showed variable results depending on the solvent used for extraction and the type of assays employed (Dalilah et al., 2015).
The antioxidant properties of water, ethanol, ethyl acetate and hexane extracts of leaf shoots of B. racemosa were assessed by Kong et al. (2012).The water extract had the highest polyphenol and ascorbic acid contents while the contents of flavonoids and carotenoids were highest in the leaf ethyl acetate extract.The water extract had the highest ferric reducing activities and scavenging activities against DPPH, ABTS and superoxide anion radicals.
The protective effects of leaves of B. racemosa against low-density lipid (LDL), serum and haemoglobin oxidation have been reported by Kong et al. (2014).In all three oxidation assays, the leaf extract was stronger than the stem extract.

Antimicrobial
Dried leaves of 15 medicinal plants in South Africa were sequentially extracted (hexane, dichloromethane, acetone and methanol) and tested for inhibitory activity against Mycobacterium smegmatis which causes tuberculosis (Mmushi et al., 2010).Results showed that the leaf extracts of B. racemosa were among the most effective with minimum inhibitory concentration (MIC) ranging from 0.84−0.11mg/ml.The antifungal activity of methanol, ethanol and hot water extracts of B. racemosa leaves, twigs and barks has been tested against seven fungal species ( Hussin et al., 2009).Results showed that the methanol extracts showed strongest inhibitory activity, particularly against Fusarium (53%), Ganoderma (35%) and Aspergillus (32%).

Cytotoxic
The ethanol leaf extract of B. racemosa displayed cytotoxic activity against HeLa human cervical carcinoma cells with a 50% cytotoxic dose of 10 μg/ml (Mackeen et al., 1997).However, in another study, the methanol leaf extract of B. racemosa was found to show weak anti-proliferative activity (IC 50 value of 3.5 mg/ml) against cancer cells tested (Emylia et al., 2008).

Cytoprotective
The aqueous extract of the leaf shoots of B. racemosa was found to protect HepG2 cells against oxidative damage (Kong et al., 2016).Results of the cell viability assay revealed that the extract was non-cytotoxic at concentration less than 250 mg/ml.The extract improved the cellular antioxidant status and protected HepG2 cells against H 2 O 2 -induced cytotoxicity, and also inhibited lipid peroxidation and the production of reactive oxygen species.

Anti-inflammatory
Leaves of B. racemosa, successively extracted with chloroform, hexane and ethanol, were tested for anti-inflammatory activity using the Griess assay based on the inhibition of nitric oxide (NO) in RAW 264.7 cells (Behbahani et al., 2007).At concentrations of 25, 50, 100 and 200 µg/ml, non-polar extracts of chloroform (23−74% inhibition) and hexane (26−61% inhibition) were found to be strong inhibitors of NO.Using the xanthine oxidase (XO) and albumin denaturation inhibition assays, the leaf extract of B. racemosa (1.0 mg/ml) yielded inhibition of 59% and 65%, respectively (Osman et al., 2016).The results indicated that the leaves of B. racemosa have anti-inflammatory activities that can be used in alleviating gouty arthritis and XO-related diseases.

CONCLUSION
Leaves of A. occidentale possess a wide array of pharmacological properties, which reflect their health benefits, and confer their traditional uses as food and medicine.They include antioxidant, antibacterial, antiviral, antifungal, anti-tyrosinase and anti-quorum sensing, cytotoxic, hypoglycaemic, hypolipidemic, hypocholesterolemic, anti-ulcerogenic, anti-hypertensive, analgesic and anti-inflammatory activities.On the contrary, only pharmacological properties of antioxidant, antimicrobial, cytotoxic, cytoprotective and anti-inflammatory activities have been reported in leaves of B. racemosa, unlike other plant parts which have many more bioactivities.The oral administration of high dosage of A. occidentale leaves has toxic effects on mice, and the bark and fruits of B. racemosa are used as fish poison.One would therefore assume that the excessive consumption of these two ulam herbs may be detrimental to the human health, contrary to the belief that the regular intake of ulam herbs has healthpromoting properties and can assist in preventing degenerative diseases, delaying aging and improving overall health.Further studies can be conducted on the pharmacological properties of these ulam herbs.
They include isolating and identifying novel bioactive compounds; assessing the properties and elucidating the mechanisms of action of the isolated compounds; analysing the effects of different processing methods on these herbs; evaluating their toxic effects; and exploring their potentials of developing herbal and pharmaceutical products.Notwithstanding, the prospects of studies on new pharmacological properties are equally promising.
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. Other studies by Anand et al. (2015) and Thomas et al. (