Morinda citrifolia (Noni): A comprehensive review on its industrial uses, pharmacological activities, and clinical trials

3.1 Natural preservative

M. citrifolia is recognized as a novel food ingredient under the name of Noni fruit puree (Efsa, 2009), however, food industry is mainly interested in Tahitian M. citrifolia due to its leaf, fruit and root antioxidant properties which are similar to vitamin E, and they also contain butylated hydroxytoluene (a phenol derivative) which has a natural preservative activity (Zin et al., 2002), and was effective in blocking warmed-over flavor in formerly stewed beef pies, by reducing lipid oxidation, as well as enhancing color stability and the shelf life of the final aerobically wrapped pies (Nathan et al., 2012). Despite of the proven in vivo safety of Tahitian M. citrifolia as a food ingredient (West et al., 2011), yet, the unpleasant off-taste of its puree might restrict its use as a preservative (Nathan et al., 2012). Interestingly, the addition of maltodextrin to the M. citrifolia pulp powder (Fabra et al., 2011), as well as to the spray dried seedless M. citrifolia fruit powder, successfully eliminated M. citrifolia bad smell and unpleasant taste, and increased its resistance to humidity (Anwar and Arsyadi, 2007), yet no study has observed the effect of maltodextrin complexation with M. citrifolia on enhancing its preservative effects with less or no distasteful flavor and odor.

3.2 M. citrifolia juice

The M. citrifolia juice products are a corner stone within its industrial sector. Fresh Noni juice is obtained by compressing the fruits immediately after harvesting (Newton, 2002), whereas homemade juice is prepared by letting the fruits decompose naturally (Brown, 2012), and commercial juice is made by fruit fermentation (Nelson, 2006). The chemical composition of M. citrifolia juice depends majorly upon the method of juice extraction. The physiochemical screening of the fermented Indian M. citrifolia fruit showed that it contains anthraquinones, saponins, and scopoletin (Satwadhar et al., 2011), while the bioactive screening of the Thai M. citrifolia fermented fruit juice recorded a superior vitamins content (C, B1, B2, B3, B12) in comparison to the vitamin content of the American M. citrifolia fruit, it was also containing alkaloids, anthraquinones, antioxidants, essential oils, flavonoids, saponins, scopoletin and sugars, and these results were congruent to the content of the commercial Thai fruit juice content (Nandhasri et al., 2005). To overcome problems associated with transport and storage, M. citrifolia juice was concentrated (Valdés et al., 2009). However, its processing methods and storage conditions influence juice stability. For example, heat affects the organoleptic nature of the concentrated M. citrifolia juice (Valdés et al., 2009), while a fermentation process for 90 days caused about 90% reduction of its radical-scavenging activity (RSA), and a dryness at 50 °C reduced the RSA by 20%, as for freshly prepared M. citrifolia juice, the RSA is decreased by more than 90% if it is stored at 24 °C for 90 days, whereas the RSA of the juice or powder is reduced by 10–55% when stored for 90 days at −18 °C and 4 °C, respectively (Yang et al., 2007). M. citrifolia beverages taste was enhanced in an economic juice recipe which was prepared by mixing 10% of fermented juice extract of an Indian M. citrifolia ripe fruit with 14% total suspended solids (T.S.S.) and 2% ginger extract (Joshi et al., 2012). Only one published research has studied the stability of M. citrifolia final products where the concentrated Thai fruit juices and its dried powders showed stability for 451 days (Rawangban et al., 2011). This is indicating that stability factor should be considered more in future studies.

Many of M. citrifolia commercial juice parameters should be fixed including its concentrations variations, the prevalent bioactive component in the fermented products, pasteurization impact on these bioactive compounds, and the specification regarding the juice source for being fermented, and for how long, and pasteurized or unpasteurized (Brown, 2012).

3.3 M. citrifolia probiotic juice

Seedless fermented M. citrifolia fruit juice from Taiwan showed potentials for the production of probiotic which was produced by reacting M. citrifolia juice (as a raw substrate) with lactic acid bacteria (Lactobacillus casei and Lactobacillus plantarum) or Bifido-bacteria (Bifidobacterium longum). After 48 h. of fermentation, all tested strains grew well on M. citrifolia juice and colony-forming reached nearly 10⁹ units/ml. Lactobacillus casei produced less lactic acid than Bifidobacterium longum, whereas Lactobacillus plantarum, Bifidobacterium longum and Lactobacillus plantarum survived under low-pH conditions in a cold storage at 4 °C for a period of 4 weeks. The results indicated that Bifidobacterium longum and Lactobacillus plantarum bacteria are selective for producing a probiotic M. citrifolia juice (Wang et al., 2009a).

3.4 Natural source of medicines

Scientists are looking at the M. citrifolia as a natural source for the medicinal production by using a bioreactor cultivation technology to produce specific medicinal compounds at a rate similar or superior to natural grown M. citrifolia. Data have shown that casual root cultures of M. citrifolia could be a useful way for the commercial production of biotechnology based chemicals such as rubiadin, flavonoids, phenolics and anthraquinones (Baque et al., 2012).

The aqueous root extract of Indian M. citrifolia was also used in nanobiotechnology field for the synthesis of ecological noble metal nanoparticles due to the presence of anthraquinones. Silver nanoparticles were prepared by the reduction of silver nitrate into silver ions upon adding M. citrifolia root aqueous extract and incubating for an overnight to yield particles between 30 and 55 nm with a cytotoxic activity against the HeLa cell lines (Suman et al., 2013). Gold nanoparticles were prepared by mixing M. citrifolia root aqueous extract with aqueous solution of chloroauric acid to produce gold nanoparticles. This preparation was predicted to have a higher anticancer activity due to its smaller size (12.17–38.26 nm) (Suman et al., 2014). However, before proceeding in this drug development program, a comprehensive phytochemical profiling of M. citrifolia, pharmaco-therapeutics, toxicity and clinical trials are needed (Singh, 2012).

3.5 Natural source of chemical reagents

Acetone extract of Thai M. citrifolia dried roots was reported as a source of natural reagents for the flow injection spectrophotometric technique in quantitative assays. Extract containing anthraquinones like alizarin was successfully detecting aluminum at a concentration range of 0.1–1.0 mg L⁻¹ in instant tea samples. Anthraquinone compounds were acting as a complexing agent by reacting with aluminum and forming a reddish complex which could be measured at 499.0 nm (Tontrong et al., 2012). The potentials of M. citrifolia in being a green chemical reagent opened a new era of research in the analytical and biochemical fields.

3.6 Green insecticidal

The mosquitocidal activity of Indian M. citrifolia was successfully proved at various concentrations range (100–500 ppm). The activities of hexane, chloroform, acetone, methanol, and water leaf extracts were sequentially observed on the developing phases of malarial vector, Anopheles stephensi, Dengue vector, Aedes aegypti and Filarial vector culex quinquefasciatus. The studies were conducted for 24 and 48 h. showing that methanol extract had the highest larval and pupal mortality rate (Kovendan et al., 2012). The Indian M. citrifolia leaf ethanol extract was also reported for its larvicidal and pupicidal activities against the malarial vector Anopheles stephensi either alone at a range of 18.30–97.78 mg/L, or as a combination of M. citrifolia at a concentration range of 16.73–138.10 mg/L with Metarhizium anisopliae (an entomopathogenic fungi) at a concentration range of 150.15–806.67 mg/mL. The combination therapy showed the highest larval and pupal mortality rate (Kovendana et al., 2014).

4.1 Antimicrobial and antiseptic activity

The anti-microbial activity of Tahitian M. citrifolia fruit in a methanol partitioned with n-butanol extract was assessed in an in vitro assay on Escherichia coli, Candida albicans and Staphylococcus aureus. Candida albican was the most sensitive to M. citrifolia antimicrobial activity, while Staphylococcus aureus sensitivity was the lowest. This activity was linked to the rich iridoid content of the fruit, particularly, deacetylasperulosidic acid and asperulosidic acid (West et al., 2012). Another anti-microbial in vitro assay was conducted on methanol, ethyl acetate and hexane Indian M. citrifolia fruit extracts against a wide range of organisms including the following: Bacillus subtilis, Staphylococcus aureus, Lactococcus lactis, Streptococcus thermophilus, Pseudomonas aeruginosa, Salmonella typhi, Escherichia coli, Vibrio harveyi, Klebsiella pneumonia, Shigella flexneri, Salmonella paratyphi A, Aeromonas hydrophila, Vibrio cholera, Chromobacterium violaceum, and Enterococcus faecalis. Among the three tested extracts, methanol extract was the most effective, ethyl acetate was effective against all the tested micro-organisms except for Pseudomonas aeruginosa and Klebsiella pneumonia, and hexane extract was ineffective against all tested microorganisms (Jayaraman et al., 2008). The antimicrobial activities of the Australian M. citrifolia leaf against Salmonella, Enterica serovar typhi (S76), Staphylococcus aureus (B313) and Myco. phlei CSL, were attributed to the presence of phenolic compounds such as acubin, l-asperuloside, alizarin and scopoletin (Atkinson, 1956). On the other hand, an in vitro study reported M. citrifolia as an oral antiseptic through teeth inoculation with Enterococcus faecalis at 37 °C in a CO₂ atmosphere for 30 days, and then treating them with Tahitian noni fruit juice (TNJ), NaOCl, chlorhexidine gluconate (CHX), and TNJ/CHX respectively, followed by a final flush with 17% ethylene diamine tetra acetic acid (EDTA). Upon scanning the teeth with electron microscopy, and examining the removed smear layer, TNJ efficacy found to be similar to NaOCl when it is used together with EDTA, authors recommended preclinical and clinical trials to evaluate TNJ biocompatibility and safety (Murray et al., 2008). The previous results were confirmed with another study which additionally revealed TNJ safety on the micro-hardness property of root canal dentin (Saghiri et al., 2013).

4.2 Antifungal activity

The antifungal properties of Indian M. citrifolia fruit extract in three different solvents, methanol, ethyl acetate and hexane were tested in an in vitro assay on different fungi including Candida albicans, Aspergillus niger, Trichophyton mentagrophytes, Penicillium species, Fusarium species, Aspergillus fumigates, Rhizopus species, Aspergillus flavus, and Mucor species. The maximum inhibition was in the methanol and ethyl acetate extract of 79.3% and 62.06%, respectively against Trichophyton mentagrophytes, while almost 50% inhibition was recorded in the methanol extract against Penicillium, Fusarium and Rhizopus species, and none of the extracts were active against either Candida albicans or Aspergillus species (Jayaraman et al., 2008).

Despite the fact that in vitro results for anti-bacterial and anti-fungal studies are promising yet further in vivo and clinical research are highly recommended using different routes of administrations.

4.3 Antioxidant activity

Australian M. citrifolia fruit juice showed an anti-oxidant activity 2.8 and 1.4 times higher than vitamin C and pycnogenol, respectively. This antioxidant activity was similar to grape seed powder at the daily dose recommended by U.S. RDAs and manufacturers (Atkinson, 1956). Neolignan and americanin A were the potent antioxidant constituent of the American M. citrifolia fruit (Su et al., 2005). The optimum magnitudes of radical scavenging activity (RSA), and total phenolic content of Malaysian seedless M. citrifolia fruit methanol extract were 55.60% and 43.18 mg GAE/10 g, respectively (Krishnaiah et al., 2015). In other study, M. citrifolia anti-oxidant activity was evaluated as a natural anti-pigmentation agent by observing the effect of 50% ethanol extracts of Tahitian M. citrifolia fruit flesh, leaves, and seeds, on the tyrosinase enzyme responsible for controlling the production of melanin. The in vitro test was carried out using tyrosinase inhibitory assay, showing that seed extract had stronger tyrosinase inhibitory (from 20 to 500 μg/ml) and antioxidant activity than the fruit (500 μg/ml), while leaf extract did not have any tyrosinase inhibitory activity at any concentration. The tyrosinase inhibitory activity was linked to the presence of lignans in M. citrifolia, particularly 3,3′-bisdemethylpinoresinol and americanin A (Masuda et al., 2009). The same seed extract was found to have anti-photoaging activity at concentrations ranging from 0.5 to 1.0 mg/ml (Matsuda et al., 2013), and also inhibited blood hemagglutination at concentrations ranging from 50 to 500 μg/ml (Matsuda et al., 2011); ursolic acid was the responsible chemical for the both activities.

M. citrifolia anti-oxidant property was also linked to other health enhancements activities. In an in vitro evaluation of methanol, chloroform, ethanol, butanol and aqueous extract of Indonesian M. citrifolia fruit, all extracts were able to inhibit Low-density lipoprotein (LDL) oxidation due to M. citrifolia lignans, such as americanol A, americanin A, americanoic acid A, morindolin, and isoprincepin (Kamiya et al., 2004). Other in vitro study suggested Malaysian M. citrifolia leaf ethanol extract was a highly effective natural anti-obesity supplement than its fruit. Leaf and fruit methanol extracts inhibited the lipoprotein lipase activity 66% ± 2.1 and 54.5% ± 2.5%, respectively. Both extracts contain high levels of phenolic constituents including catechin, epicatechin and rutin which acted synergistically to demonstrate this activity (Pak-Dek et al., 2008). Furthermore, Tahitian M. citrifolia juice was able to reduce obesity related to insulin resistance in an in vitro mouse muscle cells C2C12 culture, by inhibiting the reactive oxygen species and mitochondrial damage (Nerurkar and Eck, 2008).

A clinical study was carried out on twenty-two participants (16 women and 6 men), aged between 18 and 65 years old for 12 weeks trial of a weight-loss program with a fixed study factors including Tahitian M. citrifolia -based dietary supplements (US brand), daily calorie reduction, and exercise. All participants experienced weight loss with significant decrease in fat mass without side effects. However, the researchers suggested that further clinical studies should be carried out to include more male participants, and ethnic diversity (Palu et al., 2011). Antidyslipidemia activity was related to M. citrifolia antioxidant property in the aqueous-ethanol extracts of its Indian fruits, leaves, and roots in Sprague–Dawley rats and mice of either sex, all these different parts extracts caused significant reduction in total cholesterol, triglyceride (TC), low density lipoprotein-cholesterol, atherogenic index and TC/HDL ratio. There were no behavioral changes, toxicity or mortality occurred up to 10 g/kg of M. citrifolia intake, as compared to control group (Mandukhail et al., 2010). Hepato-protective effects M. citrifolia was also affined to anti-oxidant effects in its Taiwanese fermented fruit juice at a dose range of 3–9 mL NJ/kg BW on hamsters fed with a high-fat diet (Lin et al., 2013).

4.4 Anti-inflammatory activity

In an in vitro study, the anti-inflammatory activity was detected in the Costa Rican M. citrifolia fruit juice by measuring its direct inhibitory activities on cyclooxygenase (COX)-1 and -2 (Dussossoy et al., 2011). The in vivo study on Tahitian M. citrifolia fruit juice showed a reduction in the induced carrageenan paw edema in rats, revealing a strong anti-inflammatory effect comparable to that of non-steroidal inflammatory drugs, such as acetylsalicylic acid, indomethacin and celecoxib, without side effects (Su et al., 2001). Tahitian M. citrifolia seeds oil showed topical anti-inflammatory activity by inhibiting both COX-2 and 5-LOX enzymes in an in vitro assay at concentrations of 0.5 and 1 mg/ml (Palu et al., 2012). The topical safety of the M. citrifolia seed oil was evaluated on 49 adult volunteers using the patch test whereas topical comedogenic effect of the seed oil was studied on 23 Caucasian adolescent volunteers. Both studies were conducted for four weeks, and results indicated that the topical M. citrifolia seed oil was safe and non-comedogenic, in addition to showing a very little risk of causing allergic dermatitis which could be due to seed high fatty acids content, mainly linoleic acid (Palu et al., 2012).

A randomized double-blind placebo-controlled trial using a M. citrifolia dietary supplement (U.S brand) was first performed on 100 women above 18 years old, however, only 80 women completed the study. The aim of the study was to find out the potential natural anti-inflammatory efficacy of M. citrifolia. This study included some variables such as age, parity, body mass index, pain, menstrual blood loss, hemoglobin, packed cell volume and erythrocyte sedimentation rate before and after treatment. Patients were observed for three menstrual cycles after being exposed to 400 mg of M. citrifolia capsules or placebo (38 in the placebo group and 42 in the M. citrifolia group) and there were no significant differences in any of the variables studied between treated and placebo group, further studies using higher doses of M. citrifolia with a larger sample size were recommended (Fletcher et al., 2013).

4.5 Anti-arthritic activity

An Indian brand of M. citrifolia fruit juice was orally administered to arthritic rats at doses 1.8 ml/kg and 3.6 ml/kg, and showed a dose dependent significant reduction in paw thickness, arthritic index, secondary lesions, mononuclear infiltration and pannus formation. Similar changes were also recorded by the administration of indomethacin except for the reduction of secondary lesions. The anti-arthritic activity could be due to the presence of flavonoids and phenols (Saraswathi et al., 2012). Precise investigations can add a therapeutical value by specifying the chemicals owning such activities and their effective and safe doses.

4.6 Anti-cancer activity

M. citrifolia natural components are mostly reported as a natural anticancer cure where sulphated polysaccharide stops metastasis by destabilizing the interaction between glycosaminoglycan and certain proteins (Liu et al., 2000) while damnacanthal inhibits the formation of tumors either by interfering with the growth of ras gene activation (Hiramatsu et al., 1993), or by increasing apoptosis in human colorectal cancer cell lines (Nualsanit et al., 2012). Alizarin has an antiangiogenic effect through blocking blood circulation to malignant tumors. Limonene prevents mammary, liver, and lung cancers by stimulating thymus gland to secrete more T cells which destroys the carcinoma cells. Last but not the least, ursolic acid inhibits the growth of cancerous cells and induces apoptosis by modulating the body immune process (Lv et al., 2011).

4.7 Antidiabetic activity

Indian M. citrifolia commercial fruit juice was administered orally to induced steroid diabetic (diabetes type 2) female Wistar rats, at a dose of 1.8 and 3.6 ml/kg for 10 days. The blood glucose level was significantly decreased compared to control induced diabetic rats by dexamethasone. At higher oral dose (3.6 ml/kg, twice a day) M. citrifolia fruit juice had better results than rosiglitazone, but caused liver damage in rats (Puranik et al., 2013). On the other hand, fermented juice of South American M. citrifolia also controlled blood sugar induced diabetic rats by streptozotocin. Diabetic standard animals, treated with hypoglycemic drug, glibenclamide, while diabetic experimental animals treated with 2 ml/kg M. citrifolia twice a day for 20 days exhibited a significant reduction in blood glucose level of 125 mg/dl and 150 mg/dl, respectively, as compared to untreated diabetic rats with fasting blood sugar of 360.0 mg/dl (Shivananda Nayak et al., 2011). Hypoglycemic activity of Tahitian M. citrifolia fruit Juice was investigated by administering the juice to male Sprague–Dawley rats at a dose of 1 ml/150 g body weight, twice daily for 4 weeks prior to diabetic induction using alloxan. After induction, a rise in blood glucose levels occurred but followed by a steady decline due to M. citrifolia juice prophylaxis against the diabetogenic agent, alloxan (Horsfal et al., 2008).

Based on a microarray analysis data, hypoglycemic properties of Hawaiian fermented M. citrifolia fruit juice were associated with the ability to modulate transcription factors (FoxO1) in order to regulate the gluconeogenesis process. Fermented M. citrifolia juice supplement at a dose of 1.5 μl/g body weights, twice a day for 12 weeks improved glucose and insulin tolerance as well as fasting blood glucose level in male mice. Gluconeogenic genes which are regulated by insulin including phosphoenolpyruvate C kinase and glucose-6-phosphatase were also inhibited by more than 80% (Nerurkar et al., 2012). It was suggested that M. citrifolia antidiabetic effect might be due to the stimulatory effect on the remnant ß-cells to secrete more insulin (Mustaffa et al., 2011). Saponins as well as flavonoids in M. citrifolia fruit such as rutin may also act as a secretagogue by enhancing insulin secretion (Shivananda Nayak et al., 2011). M. citrifolia is showing promising in vivo results as a natural antidiabetic agent; however scientist should pay a great concern on its safety particularly liver. If the doses are adjusted within a safe range and a proven efficacy, preclinical studies will be recommended.

4.8 Wound healing activity

Fresh Tahitian M. citrifolia leaf juice (1 mg/ml), its leaf ethanol extract (10–200 μg/ml), and its methanol and hexane fractions (10–200 μg/ml), were investigated for their topical wound healing properties. Receptors involved in wound healing such as platelet-derived growth factor (PDGF) and adenosine A2A receptor were studied on male mice. All M. citrifolia extracts showed a wound healing activity at a concentration dependent manner; however, leaf methanol extract significantly increased wound closure and reduced the half closure time in treated mice compared to the control, suggesting that the probable mechanism underlying this effect was the ligand binding to PDGF/A2A receptor which promoted wound closure (Palu et al., 2010). The promising results in this study should be confirmed through further in vivo studies on various models to draw a sharp conclusion about the healing mechanism.

4.9 Memory enhancing activity

Observations in a scopolamine induced memory impairment mice model suggested that Indian M. citrifolia dry fruit may be useful in enhancing memory at concentration range of 5–400 μg/ml. The fruit ethanol extract and its ethyl acetate fraction were containing rutin, scopoletin and quercetin, while the chloroform fraction was containing rutin and scopoletin, have showed positive effects. However, butanol fraction containing rutin alone had no effect. The mechanism of action was thought to be by inhibiting acetylcholinesterase activity, and the enhancement of the cerebral circulation (Pachauri et al., 2012). Results should be confirmed by further research to justify M. citrifolia effects on different in vivo models with precise illustration of chemicals responsible of such activity and the precise mechanism of memory enhancement.

4.10 Anxiolytic and sedative activity

A preliminary in vitro study revealed that Tahitian M. citrifolia freeze dried fruit methanol extract had anxiolytic and sedative effects by showing an affinity to the gamma-aminobutyric acid A (GABAa) inhibitory neurotransmitter receptors at a concentration of 100 μg/ml. The action could be due to the presence of competitive ligand(s) bind to the GABAa receptor as an agonist that induced anxiolytic and sedative effects. However, in vivo studies and clinical trials were recommended by the authors to confirm the newly reported activity (Deng et al., 2007a). Furthermore, a US brand of Tahitian M. citrifolia fruit juice at 10 ml/kg/day showed to have an in vivo brain protection from the stress-induced impairment of cognitive function on male ICR mice. This beneficial effect may be partly mediated by the improvement in angiogenesis induced by M. citrifolia (Muto et al., 2010). In an in vivo study on the Swiss albino mice, Malaysian M. citrifolia unripe dried fruit methanol extract was also reported for its anti-dopaminergic effects at 1, 3, 5, 10 g/kg oral doses. The suggested mechanism of action was due to the possible inhibition of the Methamphetamine-induced stereotypy behavior in a dose dependent manner. Further studies to isolate and characterize the responsible compounds for anti-psychiatric disorders were recommended (Pandy et al., 2012).

4.11 Analgesic activity

Tahitian M. citrifolia fruit juice was reported for its analgesic effect in rats by using the hotplate assay. The rats tolerated more pain after feeding with 10% or 20% M. citrifolia juice (Wang et al., 2002). In another study, the lyophilized aqueous African M. citrifolia dry root extract had also demonstrated analgesic properties at dose of 800 mg/kg given intraperitoneal injections. The analgesic activity was observed using three methods, the antagonistic action of naloxone, the writhing test, and the hotplate assay (Younos et al., 1990).

4.12 Gastric ulcer healing activity

Thai dried mature unripe M. citrifolia fruit aqueous extract was reported for its in vivo gastro-esophageal anti-inflammatory effects in rats at a range of 0.63–2.50 g/kg, with possible mechanisms of reducing the formation of acute gastric lesions, blocking the esophagus reflux and acting as an antisecretory agent similar to ranitidine and lansoprazole (Mahattanadul et al., 2011). In an open-label, two-period crossover study, 20 healthy volunteers from 18 to 45 years old were given a single-dose of Thai M. citrifolia fruit aqueous extract containing 25.15 ± 0.11 μg/ml scopoletin. After 30 min the volunteer were given 1 tablet of ranitidine (300 mg) and blood samples were collected for 12 h. The results showed that M. citrifolia acted as a ranitidine absorbance inducer due to the presence of scopoletin which stimulated the 5-HT4 receptor. Further clinical trial using more patients having specific gastric motility defect or symptoms was recommended to provide stronger evidence (Nima et al., 2012).

4.13 Antiemetic activity

To study the antiemetic activity of M. citrifolia, a preliminary randomized double blinded, placebo-controlled clinical trial was done on 100 patients with a high risk of postoperative nausea and vomiting (PONV), their ages were 18–65 years old. In one group Thai M. citrifolia fruit was given 1 h. before the surgery at a dose of 600 mg, beside that the patients were also received the standard general anesthesia as well as the post-operative analgesia. The results revealed that patients who received M. citrifolia experienced significantly less nausea during the first 6 h compared to the placebo group (Prapaitrakool and Itharat, 2010), to understand this activity further in vitro, in vivo and clinical trials should be conducted to specify by which mechanism(s) M. citrifolia is acting as an antiemetic, and what if it could be used in reducing emetic symptoms caused by different cases rather than PONV.

4.14 Gout and hyperuricemia healing activity

The in vitro bioassay of xanthine oxidase (XO) inhibiting effects revealed that the Tahitian noni juice (TNJ) is having a dose dependent natural anti-gout and anti-hyperuricemic effects. The half maximal inhibitory concentration (IC50) of M. citrifolia was 3.8 mg whereas IC50 of allopurinol was 2.4 μm. The concentrated methanol extract of this fruit juice at concentration of 0.1 mg/ml exhibited higher XO enzyme inhibition rate (64%) compared to XO enzyme inhibition rate of TNJ itself (11%) at concentration of 1 mg/ml. However, the authors recommended further studies to isolate the active compounds, and to conduct clinical trials in an aim of supporting this hypothesis (Palu et al., 2009).

4.15 Anti-psoriasis healing activity

M. citrifolia was reported to act as an anti-psoriasis healing factor in a 31-year old man who received treatment of M. citrifolia fruit powder (4 g/day) and a weekly methotrexate. After one month treatment, his psoriatic skin lesions significantly improved. This could be due to the immune-modulation effect of both M. citrifolia and methotrexate on skin lesion (Okamoto, 2012). So far, this is the only case report about that activity, thus, such cases should be deeply investigated on in vitro, in vivo and clinical scales.

4.16 Immunity enhancing activity

The immunity enhancement activity of both Tahitian and commercial M. citrifolia fruit juices was reported in an in vivo study on mice, suggesting that M. citrifolia is modulating the immune system by activating the CB2 receptors, and suppressing the interleukin-4, as well as increasing the production of interferon gamma cytokines. However, authors recommended further in vivo and clinical research to illustrate the dosage and actual mode of action of M. citrifolia on the immune system (Palu et al., 2008).

4.17 Anti-viral activity

M. citrifolia fruit component damnacanthal showed to have an in vitro anti-viral activity via inhibiting one of the human immunodeficiency viruses type 1 (HIV-1) accessory proteins in a Hela cells through an unknown mechanism. Authors suggested further studies to elucidate the anti-viral mechanism of M. citrifolia that could be useful in assessing the treatment of HIV-1 and other viral diseases (Kamata et al., 2006).

4.18 Anti-parasitic activity

Brazilian M. citrifolia fruit aqueous extract at 50.1 mg/mL and ethanolic extract at 24.6 mg/mL were given for three days to chickens naturally infected by Ascardiagalli. The aqueous extract showed lower parasite mortality rate (27.08%) than ethanol extract (66.67%), and the authors recommended repeating the in vivo experiment using higher concentrations (Brito et al., 2009).

4.19 Anti-tuberculosis activity

The Filipino M. citrifolia leaves ethanol extract and hexane fractions at 100 μg/ml reported to have an anti-tubercular activity in Mycobacterium tuberculosis cultures, with inhibition rates of 89% and 95% respectively. It is suggested that the activity may come from E-Phytol compounds, which is a mixture of ketosteroids, and epidioxysterol (Saludes Jonel et al., 2002). Future studies should select a proper positive control to assess this activity.

4.20 Osteoporotic and otoscopic enhancer

Langford et al. (2004) investigated the ability of M. citrifolia fruit juice to enhance osteoporotic conditions and otoscopic deficiencies by conducting a pilot health survey using SF-36 measurements. Eight participants consumed 2 oz of either a placebo or a M. citrifolia juice (US brand), along with calcium supplement, two times a day for 3 months. The results showed an increase in bone reconstruction which is probably due to a slight increase in the mean value of the osteoclastic activity specific marker, the deoxypyridinoline crosslinks. The otoscopic evaluation showed a limited impact on hearing, with a possible prophylactic effect at the 8000 Hz sensorineural domains; however authors recommended further studies with a larger sample size and over longer time periods (Langford et al., 2004).

Table 2 shows the kinds of investigations (in vivo, in vitro and clinical trials) conducted on leaf, fruit seed and root of M. citrifolia.

Table 2 The list of M. citrifolia pharmacological activities along with their in vitro, in vivo and clinical trials.

Plant part	Activity	In vitro	In vivo	Clinical trial	Reference
Fruit	Intracanal irrigant				Murray et al. (2008) and Saghiri et al. (2013)
Fruit	Anti-viral				Kamata et al. (2006)
Fruit, leaf	Anti-microbial				West et al. (2012), Jayaraman et al. (2008) and Atkinson (1956)
Fruit	Anti-fungal				Jayaraman et al. (2008)
Fruit, leaf, root	Anti-dyslipidemia				Mandukhail et al. (2010)
Fruit, leaf	Anti-oxidant				Su et al. (2005), Krishnaiah et al. (2015) and Nerurkar and Eck (2008)
Fruit	Memory dysfunction				Pachauri et al. (2012)
Fruit, root	Analgesic activity				Wang et al. (2002) and Younos et al. (1990)
Fruit, leaf, seed	Anti-inflammatory				Dussossoy et al. (2011), Su et al. (2001), Palu et al. (2012) and Fletcher et al. (2013)
Fruit	Anti-arthritic				Saraswathi et al. (2012)
Fruit, leaf, root	Anti-cancer				Chan-Blanco et al. (2006), Kamiya et al. (2010), Liu et al. (2001), Nualsanit et al. (2012), Lv et al. (2011), Li et al. (2008b), Hirazumi and Furusawa (1999), Arpornsuwan and Punjanon (2006), Wong (2004), Gupta et al. (2013), Masuda et al. (2012), Furusawa et al. (2003), Stoner et al. (2010), Li et al. (2008a), Taskin et al. (2009), Clafshenkel William et al. (2012), Wang et al. (2009b) and Issell et al. (2009)
Fruit, leaf	Anthelminthic activity				Brito et al. (2009)
Fruit	Source of trace elements				Rybak and Ruzik (2013)
Fruit	Stress reduction				Muto et al. (2010)
Fruit	Anxiolytic and Sedative				Deng et al. (2007a)
Fruit	Probiotic activity				Wang et al. (2009a)
Fruit, leaf	Anti-obesity				Pak-Dek et al. (2008) and Palu et al. (2011)
Fruit	Hepatoprotective agent				Lin et al. (2013)
Fruit	Immunological stimulator				Krishnaiah et al. (2012) and Palu et al. (2008)
Fruit	Antisecretory proton pump inhibitor				Mahattanadul et al. (2011) and Nima et al. (2012)
Seed	Antithrombotic effect				Masuda et al. (2009)
Seed	Anti photoaging agent				Masuda et al. (2009)
Seed	Anti-wrinkle formation				Masuda et al. (2009)
Seed, Fruit	Anti-pigmentation				Masuda et al. (2009)
Fruit	Anti-psoriasis				Okamoto (2012)
Fruit	Antidiabetic activity				Puranik et al. (2013), Shivananda Nayak et al. (2011), Horsfal et al. (2008) and Nerurkar et al. (2012)
Fruit	Antipsychotic activity				Pandy et al. (2012)
Fruit	Antiemetic activity				Prapaitrakool and Itharat (2010)
Fruit	Osteoporosis and hearing problems				Langford et al. (2004)
Leaf	Wound healing activity				Palu et al. (2010)
Fruit	Gout healing factor				Palu et al. (2009)
Leaf	Anti-tubercular activity				Saludes Jonel et al. (2002)