Genus Morinda: An insight to its ethnopharmacology, phytochemistry, pharmacology and Industrial Applications

5.1.1 Phytosterols and polyphenols

Plant sterols and polyphenolic compounds are two essential secondary metabolites found in medicinal plants (Fig 3). Some important phytosterols such as stigmasterol (112), β-sitosterol (113) and campesterol (114) were isolated from M. lucida leaf and stem bark respectively (Chithambo et al., 2017; Nweze, 2012). Also, pharmacologically active phytosterols such as daucosterol (115), scopoletin (116), 3β, 20(R) - butyl, 5-alkenylcholesterol (117), 3β,5-alkenyl-spirostol (118) have been isolated from the root of M. offinalis (Li et al., 2010a,b).

Few polyphenolic compounds have been isolated from the genus Morinda. Some of the isolated metabolites include epicatechin (119) and catechin hydrate (120). These compounds were isolated from the leaf of M. lucida (Okeniyi et al., 2015).

5.1.2 Terpenes, terpenoids and iridoids

Several terpenoids and terpenes such as monoterpenes, diterpenes, and triterpenes have been isolated from the different parts of the genus Morinda. Structural moieties of selected terpenes, iridoids and terpenoids are shown in Fig. 4. The pronounced antimalarial activity of this genus could be linked to this class of secondary metabolite. From literature, leaf is widely used in folkloric application compared to other parts such as bark, stem, leaves, fruit and root, this could be linked to the assorted terpenes reported in leaf (Bekono et al., 2020).

Iridoids are large group of phytochemicals with monoterpenoids-based structural moiety on a cyclopentan-[C]-pyran skeleton and display assorted health benefits. Eleven anti-inflammatory iridoids have been isolated from the aerial parts of M. officinalis How and characterized via spectroscopic techniques. The metabolites isolated were identified as officinaloside A-G (121–127), monotropein (128), asperulosidic acid (129), daphylloside (130), asperuloside (131) (Cai et al., 2021). Cytotoxic Iridoids isolated from the aerial parts of M. umbellata were identified as umbellatolides A (132) and B (133) via characterization by spectroscopic techniques (Ban et al., 2013).

A small number of monoterpenes, diterpenes and triterpenes have been isolated from the genus Morinda, however, despite the numbers, they exhibited exceptional biological potentials. A diterpene identified as phytol (134) and triterpenes identified as ursolic acid (135), cycloartenol (136) and oleanolic acid (137) were isolated from leaf and stem-bark of M. lucida respectively (Chithambo et al., 2017; Elufioye et al., 2015). A monoterpenoids of an iridoid ferulate, identified as Oruwacin (138) and a tetracyclic iridoids, molucidin (139) were isolated from the leaves of M. lucida (Suzuki et al., 2015; Adesogan, 1979). The volatile oils isolated from leaf and root of M. lucida were characterized as identified as cis-sabinene hydrate (140), cis-ρ-menth-2-en-1-ol (141), trans-ρ-menth-2-en-1-ol (142), borneol (143), neryl acetate (144), β-fenchyl alcohol (145) (Okoh et al., 2011; Owolabi et al., 2014).

Some of the monoterpenes which have been isolated from the genus Morinda include α-terpinene (145), β-bisabolene (146), α-thujene (147), camphene (148), 1,8-cineole (149), α-terpinyl acetate (150), sabinene (151), β-pinene (152), myrcene (153), α-phellandrene (154), α-3-carene (155), γ-terpinene (156), ρ-cymene (157), limonene (158), δ-terpineol (159), ρ-terpineol (160), nerol (161), linalool (162), terpinen-4-ol (163) and trans-sabinyl acetate (164) (Okoh et al., 2011; Owolabi et al., 2014). From essential oils isolated from leaf and root of M. lucida, about eight sesquiterpenes were isolated and characterized via spectroscopic s leaf and root oils respectively (Okoh et al., 2011; Owolabi et al., 2014).

5.1.3 Organic and fatty acids

Organic acids from plants are well documented for their antimicrobial, antitumor, antithrombotic as well as other applications (Chen, 2009). Few organic acids have been isolated from the genus Morinda (fig 5). Two organic acids identified as fumaric acid (165) and sucinnic acid (166) were isolated from the root of M. owerensis. These isolates displayed exceptional antidepressant activity (Cui and Yang, 1995; Zhang et al., 2010). In addition, two bioactive organic acids identified as 2-hydroxy-methyl benzoic acid (167) and 1,2-benzedicarboxylic acid (168) were isolated from the root oil (Okoh et al., 2011).

Some of the isolated fatty constituents from stem and root of M. lucida include hexacosanoic acid (169), hexadecanoic acid (170), dodecanoic acid (171), tetradecanoic acid (172) and 9-octadecanoic acid (173) (Adesida and Adesogan, 1972; Okoh et al., 2011),

5.1.4 Polysaccharides, mono- and oligosaccharides

Another prominent group of constituents in M. lucida is saccharides (Fig. 6). A diversity of oligosaccharides have been isolated from Morinda such as bajijiasu (174), mannose (175), nystose (176), 1F-fructofuranosyl nystose (177), inulintype hexasaccharide (178), heptasaccharide (179), sucrose (180), inulin-type trisaecharide (181), inulotriose (182), inulotetraose (183) and inulopentaose (184) (Li et al., 2004; Chen, 2009).

6.1.1 Antimicrobial potentials

The antimicrobial potency is regarded as one of the most widely studied curative application of the genus Morinda. The activities reported in this section will be shown on the significance to human health via minimum inhibitory concentration (MIC) or minimum bactericidal concentration (MBC). The in vitro antifungal potency of hexane, ethyl acetate and methanol extracts of M. citrifolia were investigated in Aspergillus flavus, Aspergillus niger, Candida albicans, Fusarium species, Penicillium species, Rhizopus species and Trichophyton mentagrophytes. The percentage inhibitory of 62.06% and 79.30% were exhibited by ethyl acetate and methanol extract against T. mentagrophytes while activities of ≤ 50% was exhibited by methanolic extract against Fusarium. Penicillium and Rhizopus spp. C. albicans, A. niger and A. flavus were resistant to all solvent extracts tested (Jayaraman et al., 2008). Similarly, n-hexane, ethyl acetate and methanolic extracts of M. citrifolia were tested against Salmonella typhi, Klebsiella pneumonia, Shigella flexneri, Aeromonas hydrophila, Staphylococcus aureus, Enterococcus faecalis, Lactococcus lactis, Pseudomonas aeruginosa, Streptococcus thermophilus, Bacillus subtilis, Chromobacterium violaceum, Pseudomonas aeruginosa, Vibrio harveyi, Escherichia coli, Salmonella paratyphi, Klebsiella pneumonia and Vibrio cholera. Methanolic extract significantly developed resistance against all tested microbial isolates while hexane extracts displayed sparingly activities against some isolates (Jayaraman et al., 2008). The remediation potency of fruit juice obtained from M. citrifolia was tested against Enterococcus faecalis inoculated teeth cultured for 37 days in a CO₂ atmosphere (37 °C). The inhibitory activity (smear layer removed) demonstrated by the fruit juice is comparable to NaOCl (when in synergy with EDTA) when viewed under electron microscopy. Though, toxicological profile and biocompatibility via preclinical and clinical trials were not reported (Murray et al., 2008). The antibacterial activity of butanol extract of M. citrifolia fruit partitioned with methanol was assessed in vitro against C. albicans, S. aureus and E. coli. A significant activity was displayed against C. albicans while moderate activity was exhibited against S. aureus. The activity could be linked to asperulosidic acid and deacetylasperulosidic acid analyzed (West et al., 2012). The damnacanthal isolated from M. citrifolia fruit exhibited pronounced in vitro anti-viral activity against human immunodeficiency viruses type 1 (HIV-1) accessory proteins in a Hela cells via an unfamiliar mechanism. Further studies to elucidate the mechanism of M. citrifolia that could be resourceful in assessing the efficacy as antiviral agents is inevitable (Kamata et al., 2006).

The scientific investigations of the genus Morinda could be traced to undocumented facts about its therapeutic potency in management of microbial infections. Several reports on the antimicrobial potency of leaves, bark and fruits of M. lucida have been documented, some of these are detailed below. The chloroform crude extract of M. lucida leaf was reported to exhibit pronounced bactericidal activity at 100 mg/mL and bacteriostatic activity at concentration of 12.5 to 100 mg/mL, authenticating the folkloric usage of this plant for the management of typhoid fever (Musa et al., 2014). Even at a low concentration of 10 mg/mL, leaf extract of Brimstone tree exhibited strong inhibitory activity against P. aeruginosa and S. aureus (Addy et al., 2013). Polar solvent extracts (methanolic and aqueous) of stems, roots and bark of M. lucida were active against bacteria isolates such as E. coli, S. paratyphi, S. typhi and S. typhorium with promising activity higher than ciprofloxacin and chloramphenicol (concentrations of 5, 10 and 20 mg/mL) (Fakoya et al., 2014). M. lucida root (erthanolic) extract exhibited strong inhibitory activities against gram positive bacteria isolates such as Micrococcus luteus and S. aureus (Chukwujekwu et al., 2005). Similarly, ethanolic and aqueous extracts of Brimstone tree (stem-bark) exhibited strong inhibitory activities against S. typhi, P. aeruginosa, Klebsiella pneuoniae, S. aureus, Flavobacterium sp. and Bacillus subtilis,(Adomi and Umukoro, 2010). Methanolic extract of M. lucida leaves also exhibit in vitro and in vivo antimicrobial potency against E. coli (Ogundare and Onifade, 2009). The antifungal activity of M. lucida leaves extract against isolates such as C. albicans is well documented (Anowi et al., 2013).

The antibacterial potency of fresh and fermented fruit juice of M. citrifolia was experimented in ten bacterial isolates using well diffusion method. The assay was carried out taking note of bactericidal concentration (MBC) and Minimum Inhibitory concentration (MIC). After incubation, MBC values ranges from 10 to 29 mg/mL while MIC from 2.5 to 5.0 mg/mL respectively. This indicate that fresh and fermented fruit juice exhibit bacteriostatic effects on bacteria strains. However, Fresh juice has a bacteriostatic effect on S. epidermidis and E. coli, while fermented juice induce bacteriostatic effect on S. epidermidis, Streptococcus oralis and Enterococcus faecalis. (Sina et al., 2021).

In spite of the plethora antimicrobial applications of this genus, there is scarcity of documented information on the antibacterial compounds isolated and the mechanisms of action of such metabolites.

6.1.2 Antiplasmodial/ antimalarial potentials

Malaria is a parasitic disease of global health concern especially in the tropical and subtropical regions. Over 228 million cases of malaria was reported in 2018, with 93% from Africa (Oladeji et al., 2020, 2021; WHO, 2015). This parasitic infection is caused by Plasmodium species transmitted by bite of female Anopheles mosquitoes (Oladeji et al., 2021; Oladeji and Oyebamiji, 2020; Saini et al., 2022). In view of this, several scientific investigations have explored and authenticate the therapeutic potency (antiplasmodial and antimalarial) of medicinal plants (Table 4).

The curative antiplasmodial potency of stem bark and leaf extracts of M. lucida was investigated in Plasmodium berghei NK65 infected Swiss Albino mice using curative assay. The solvent extracts significantly increase the packed cell volume and decrease in body weight of infected mice was observed after treatment. Chloroquine treated group exhibited 100% inhibition while the lowest inhibitory effect of 72.16% was observed in 200 mg/kg ethanolic bark extract treated group. The pronounced activity could be linked to high phenol, flavonoids and tannin contents in the extracts (Oladeji et al., 2021). Partially purified cysteine-stabilized peptide extract of M. lucida leaf was evaluated against P. berghei NK65 (in vivo) and P. falciparum W2 (in vitro). The purified extract exhibited no inhibitory activity against P. falciparum W2 (IC₅₀: >50 μg/mL, in vitro), on the other hand, it exhibited 75.8% parasitaemia reduction against P. berghei NK65 (in vivo) (Adebayo et al., 2017). The schizontocidal potency of leaf extract of M. lucida was assessed in P. berghei infected Swiss Albino mice and inhibitory effect against early and established infections were assessed using chloroquine as control. A single dose of the extract was administered on daily basis while combination of pyrimethamine with extract was evaluated. For early infection, leaf extract exhibited close inhibitory activity to that exhibited by chloroquine treated group, however, daily decrease was observed in chloroquine (5 mg/kg bw) treated and extract treated groups (administered intravenously) with a significant reduction in level of parasitaemia starting from day 2. Furthermore, a pronounced reduction of 70.0% and 80.5% chemosuppresssion of parasitaemia in infected mice of pyrimethamine (1.2 mg/kg bw) and 1/6 dilution of stock of extract were observed after treatment (Makinde and Obih, 1985).

The antiplasmodial activities of solvent fractions of Brimstone tree have been reported. The fractions obtained from petroleum ether extract (leaves) was appraised in vivo against P. berghei berghei. The fractions exhibited significant schizontocidal activity against early and established infections, however, it showed no repository effect (Awe and Makinde, 1998). The curative potency of methanolic root extract and synergic effect of root and leaf extracts of M. lucida were assessed in plasmodium infected mice. The combined extracts produced higher parasitaemia inhibitory activity compared to activity exhibited by single extract (root extract) (Umar et al., 2013). Dichloromethane and ethanolic extracts of M. lucida leaves exhibited about 60.0% inhibitory activity against P. falciparum (in vitro) at a concentration of 6 μg/mL. Aqueous extract of M. lucida leaf was investigated against early, established and residual parasitaemia infections in P. berghei NK65–infected mice. The leaf extracts all exhibited strong inhibitory activity against the infected mice (dose-dependent). The inhibitory activity of 50.2% was observed in 200 mg/kg b.w treated group after four-day inoculation .

6.2.1 Purgative/anti-diarrhoeal activity

Purgatives or laxatives are chemical substances or drugs which aid bowel movement, treat constipation and loosen stools. The folkloric usage of genus Morinda as purgative is well known, however, few scientific validation have been reported. The oral administration of methanolic extract of Brimstone tree leaves significantly induced purging in experimental mice. In a similar study, oral administration of 12.5 to 100 mg/kg body weight of M. lucida methanolic leaf extract induced purging of wet feaces in Swiss albino rats (Olajide et al., 1999). The aqueous fruit and leaf extract of Brimstone tree lessen castor oil-induced diarrhea in rat model (Adejo et al., 2015). These differences in the activities and possible toxicity of administered extracts need more clarification.

6.3.1 Cognition enhancement

Cognitive disorders (CDs), also known as neurocognitive disorders, are a broad category of mental health illnesses that affect problem-solving, perception, memory, and learning abilities.

Plants have been used in folkloric medicine in several parts of Africa and Asia to treat memory loss, improve memory, and cure any neurological illnesses associated with aging or other interesting factors. The ethyl acetate fractions collected from the leaf of M. lucida was assessed for its butyrylcholinesterase and acetylcholinesterase activities. The fractions significantly increase the function of cholinergic neuron and potency in repairing cholinergic memory impairment. The activity exhibited was linked to the presence of phytol which act as major inhibitor to cholinergic impairment (Elufioye et al., 2013). In scopolamine-induced amnesic mice, the leaf extract (M. lucida) has been shown to improve cognitive function (Elufioye and Hameed, 2017). Administration of aqueous extract of M. owariensis (11.25 to 45 g/kg) significantly enhance the memory and learning impairment caused or induced by D-galactose in experimental mice. The dose concentrations administered for 28 days significantly reduced serum glycosylated hemoglobin, aldose reductase and the damage to brain cells however, glycosylation end products was increased (Ye et al., 2015).

The call for memory enhancers and boosters derived from natural or synthetic sources is growing on a daily basis as a result of environmental and societal influences on the human brain and emotions. The memory enhancement potency of dried fruits of M. citrifolia was assessed in scopolamine induced memory impairment in mice with concentrations ranging from 5 to 400 µg/mL. Ethanolic extract and ethyl acetate fraction successfully enhance the memory of experimental mice while butanol fraction had no effects on impaired experimental mice. The activity reported followed the pathway reported by Pachuari et al., that is, acetylcholinesterase inhibitory and cerebral circulation augmentation. Secondary metabolites such as scopoletin, rutin, quercetin analyzed could be responsible for this activity (​Pachauri et al., 2012). Also, administrations of various dosage of aqueous extracts of M. owariensis significantly enhanced memory capacity of rats induced by natrium nitrosum and D-galactose after 30 days. The extract decreased malonaldehyde, mRNA expression and activity of monoamine oxidase-B, however, SOD activity was increased under step-down test (Wang et al., 2013). According to the reports of Chen et al., oligosaccharides of M. owariensis lessen memory or learning impairments or dysfunction caused by β-amyloid in experimental mice. This compound improve oxidation resistance, monoamine neurotransmitter, brain energy metabolism and also, reduce brain neuron apoptosis and injury to the cholinergic system. In a similar study, a dimeric fructose isolated from M. owariensis identified as Bajijiasu lessen Aβ-induced memory or learning impairments, boost energy metabolism, anti-oxidation and attenuated cholinergic system damage in neurotoxicity rats caused by injection of Aβ25–35 into the bilateral CA1 region of the experimental rat. The compound also increase potentiation but also, reduce time lapse of the frequency of population spike in the anoxic condition and enhance the resurgence after re-oxygenation. These features indicate the potency of Bajijiasu in enhancing and protecting memory and neurons against anoxic injury.

6.3.2 Anti-rheumatoid arthritis activity

Morinda plants are well documented in traditional Chinese medicine as antidote to rheumatism. Ethanolic extracts of M. oweriensis reduced paw swelling, serum levels of IL-6, interleukin-lβ (IL-lβ) and TNF-α in adjuvant arthritis rats (Shi et al., 2015). It also decrease prostaglandin E2 caused by Freund's complete adjuvant, and the writhing occurrence of mice caused by glacial acetic acid (Chen et al., 2011). In some part of China, combination of two or more medicinal plants, that is, Morinda species and other plants have significantly reduce rheumatism in man. This synergy was assessed in the combination of M. oweriensis and Achyranthes bidentata (ethanolic root) at dosage of 75, 150 and 300 µg/ml. The synergy increased the mRNA, proliferation, cyclin D1 of chondrocytes and protein expressions of cyclin-dependent kinase 4 (Wu et al., 2017). Similarly, synergic reactions between the roots of M. owariensis and Achyranthes bidentata significantly enhanced the proliferation of chondrocytes however, based on synergic effects, the rations was not optimized. According to spectroscopic data, ethanolic extract of M. owariensis exceptionally reduced the effects of glucose and lipid metabolism in rats with carrageenan-induced acute inflammation. The polysaccharides isolated from M. owariensis and Eucommia ulmoides at dosage concentrations of 800, 400, 200, 100 and 50 µg/mL significantly enhanced the rat chondrocytes (in vitro) (Fu et al., 2014).

6.3.3 Anti-fatigue and anti-aging activity

Fatigue is an overall feeling of tiredness which could be linked to lifestyle, mental or physical health conditions. The genus Morinda is well authenticated in folkloric medicine as energy booster or anti-fatigue therapeutic substances. Polysaccharides of M. owariensis extended swimming time of experimental mice and hepatic glycogen, and subsequently reduced blood lactic acid and serum urea nitrogen at dosage of 50, 100 and 200 mg/kg. The polysaccharides MP-1, MP-2 and MP-3 were analyzed to be 27.32%, 7.85% and 20.57%, respectively (Zhang et al., 2009). The anti-aging effects of genus Morinda is known to proceed via antiapopotic or anti-oxidative mechanism. Ethanolic leaf extract of M. owariensis significantly decreased the content of MDA, increased apoptotic index of purkinje fibers, expression of Bax protein in the cerebellum and SOD, the expression of B cell leukemia-2 gene product (Bcl-2) protein at 700 mg/kg and 2100 mg/kg body weight in aged rats. The extract also induce the immune system via spleen and thymus gland, B lymphocyte stimulation index, level of IL-2 and the number of positive CD28 + cells in D-galactose damaged rats (Wang et al., 2013). Similarly, M. owariensis leaf extracts (1 g/ml) enhanced cell vitality, mRNA expression of myosin heavy chain-α and reduced the activity of β-galactosidase and mRNA expression of myosin heavy chain-β in cardiomyocytes damaged by D-galactose (Zhang et al., 2011).

6.3.4 Effect on muscle contractility

Muscle contractility is a major concern in Africa caused by shortened muscle cells under stress or pressure. To the best of our knowledge, there has been no documented report on the use of genus Morinda as muscle relaxants in African folkloric medicine despite been listed among genus with cardio-active potencies. In spite of this, Ettarh and Emeka, reported that aqueous extract obtained from Brimstone tree leaf exhibited a significant vasorelaxant effect by endothelium-dependent and endothelium-independent mechanisms on vascular muscle (smooth) of rat aorta (Ettarh and Emeka, 2004). Similarly, aqueous extract of M. lucida exhibited pronounced relaxant effect on both pregnant and non-pregnant mice (uterine smooth muscle). The extract repressed the frequency of contractile responses and inhibited responses of contractile to acetylcholine and oxytocin in the muscle (Elias et al., 2007).

6.3.5 Anti-inflammatory activity

The human body is designed in a way that self-defense or healing could be accomplished by activating certain some body cells or tissues. Generally, certain drugs or chemicals have potency in reactivation or restoration of weaken cells. One of the common natural substance is the genus Morinda. This genus is widely used in folk medicine in lessen pain and treat inflammation either acute or chronic (Choi et al., 2005; Palu et al., 2012). The methanolic extract of M. owariensis significantly inhibited cyclooxygenase (COX-2), iNOS and TNF-α expression through down-regulation of the NF-κB binding activity (Kim et al., 2005). The activity was enhanced by pretreatment with either 20 mg/kg or 30 mg/kg monotropein. This lessen stretching episodes and extended activity in experimental mice (hot plate), also, increase antinociceptive properties and reduced acute paw edema caused by carrageenan in test organisms. These activities could be linked to monotropein administered (Choi et al., 2005). This compound could also inhibit mRNA expression of IL-1β, COX-2, iNOS and TNF-α, lessen the DNA binding activity, degradation of IκB-α and lessen phosphorylation in LPS induced RAW 264.7 macrophages (Shin et al., 2013; Zhang et al., 2016).

The fruit juice extracted from M. citrifolia obtained from Costa Rica inhibited the activity of cyclooxygenase (COX)-1 and -2 (in vitro) (Dussoss et al., 2011). In another study, M. citrifolia fruit juice from Tahiti reduced carrageenan paw edema in experimental rats, with anti-inflammatory effects similar to celecoxib, indomethacin, and acetylsalicylic acid (Su et al., 2001). Seed oils extracted from M. citrifolia inhibited both 5-LOX and COX-2 enzymes at concentrations of 0.5 and 1 mg/mL. The seed oil was reported to exhibit no side or toxic effects on test rats after examining for 28 days via patch test. The extracted seed oil demonstrated low risk of non-comedogenic or allergic dermatitis triggered by excessive fatty acid contents or linoleic acids in the seed (Palu et al., 2012). The anti-inflammatory potency of dietary supplements of M. citrifolia (400 mg, 38 in placebo group while 42 were treated with M. citrifolia) was assessed in women (100) using double-blind placebo-controlled approach by evaluating parameters such as menstrual blood loss, age, erythrocyte sedimentation rate, body size, packed cell volume, red blood cells and pain. There was no significant difference between the two groups after treatment period. To enhance its potency further study should involve the use of high dosage with a larger test population.

Several solvent extracts of genus Morinda have exhibited strong anti-inflammatory potentials (in vivo or in vitro). Methanolic and aqueous extracts of M. lucida leaf significantly inhibited acute inflammation and antipyretic activity in rabbit and experimental rat (Akah and Nwambie, 1994), and also, showed strong immunorestorative (in vivo) and immunostimulatory activities (in vitro). The dichloromethane extract of M. lucida leaf shown strong anti-inflammatory activity by inhibiting COX-2 activity while petroleum ether extract demonstrated strong inhibitory activity against COX-1 and COX-2 (Chukwujekwu et al., 2005). Similarly, aqueous extract of Brimstone tree doubled total IgG, IgG1, and IgG2a responses to ovalbumin when compared to control groups (Nworu et al., 2012). Ethanolic extract of M. lucida leaf improve immune system of Balb/c mice induced with rhabdomyosarcoma cells (Ala et al., 2017). Damnacanthal isolated from stem, bark and roots of M. lucida significantly suppressed and regulate lipopolysaccharide-induced nuclear factor-κB of paw and ear ede0ma in rats and mice (Koumaglo et al., 1992a,b; Nualsanit et al., 2011). These findings authenticate the folkloric uses of genus Morinda for the treatment of anti-inflammatory, immuno-inflammatory, immunostimulatory and infections.

6.3.6 Antiosteoporotic activity

Osteoporosis is a prevalent health disease marked by low bone mass and structural degradation of the bone, which increases the risk of fractures. The genus Morinda is widely used to treat bone atrophy in Traditional Chinese medicine (TCM). A clinical investigation including 50 patients found that the aqueous extract of M. owaiensis root is effective in the treatment of postmenopausal osteoporosis (Long et al., 2013). The administration of an aqueous extract of M. owaiensis root (50, 100, and 200 mg/kg) to sciatic neurectomized mice 3 days after neurectomy for 6 weeks for a prevention study, or 2 weeks after neurectomy for 12 weeks for a therapeutic study. These significantly and dose dependently suppressed the decrease in hind limb thickness, tibia failure load, and bone mineral density (BMD) with an increase in serum osteoclacin levels, as well as reversed (Seo et al., 2005). The administration of MO ethanol extracts to ovariectomized rats increased total BMD and trabecular BMD of the tibia, improved the levels of phosphorus, calcium, and osteoprotegerin (OPG), decreased the levels of deoxypyridinoline/Cr (DPD/Cr), tartrate resistant acid phosphates (TRAP), adrenocorticotropic hormone (ACTH), and corticosterone (CORT) in (Li et al., 2009). Antiosteoporotic activity was confirmed in eight anthraquinone compounds, particularly for suppressing osteoclastic bone resorption (Wu et al., 2009a,b). Moreover, osteoclasts synthesized from rat bone marrow cells were used to investigate the mechanism of these anthraquinones' inhibitory effect on bone resorption. In an osteoblast-osteoclast coculture system, serum from rats given MO aqueous extracts suppressed mRNA expression of carbonic anhydrase II (CA II) and nuclear factor of activated T cells (NFAT), as well as osteoclast differentiation and bone resorption activity. The current study, on the other hand, did not describe the chemical contents transported from M. owaiensis to rat serum, nor did it specify the active principles for reducing bone resorption (Zheng et al., 2013). Antiosteoporotic properties of MO polysaccharides have also been discovered. Oral administration of MO polysaccharides (100 or 300 mg/kg) to ovariectomized rats for 30 days enhanced BMD and bone mineral content while lowering cytokine levels in the blood, findings indicate that MO polysaccharides may prevent avert bone loss caused by ovariectomy (Zhu et al., 2008). However, there was no positive control in this trial, and serum biochemical indicators of bone metabolism, such as ALP and osteocalcin, as well as TRAP and cathepsin K activity, were not measured.

6.3.7 Antidepressant-like activity

Depression is one of the most frequent and severe disorders in the world, with significant socio - economic consequences. Compounds such as polysaccharides and oligosaccharides isolated from M. owariensis have been shown to have antidepressant-like activity in animal and cell experiments as well as human clinical trials (Qiu et al., 2016).

Post-traumatic stress disorder (PTSD) is a serious psychiatric disorder linked to the production of allopregnanolone. At a dose of 25.0–50.0 mg/kg, MO inulin-type oligosaccharides reversed behavioral deficits in single prolonged stress-treated rats, reduced freezing time in the contextual fear paradigm, increased the time and entries in open arms in the elevated plus maze test without affecting locomotor activity in the open field test, and increased the levels of allopregnanolone in the prefrontal cortex, hippocampus, and amygdala, demonstrating that (Qiu et al., 2016). Polysaccharides and oligosaccharides abundant in MO root. In an experimental depression model of rats, administration of MO polysaccharides reduced the number of T-type labyrinth test errors and increased the number of neurons and level of superoxide dismutase (SOD) in the hippocampus, indicating that MO polysaccharides could mitigate oxidative stress reactions and improve cognitive behavior (Liu, 2011). Administration of MO oligosaccharides (50, 25 and 12.5 mg/kg/d) for 14 days significantly enhanced sucrose preference in stressed rats, decreased the immobility time, and increased the protein levels of brain-derived neurotrophic factor (BDNF), glycogen synthase kinase-3β (GSK-3β), glutamate receptor subunit-1(GluR1), postsynaptic density-95(PSD 95) and synapsin 1 in the hippocampus, indicating that MO oligosaccharides exerted a therapeutic effect in the rat model of chronic stress-induced depression by regulating the BDNF signaling pathway and enhancing synaptic plasticity (Xu et al., 2015). The minimum effective dose of MO extracts for mice was found to be 75 mg/kg in this study, with desipramine serving as a positive control. It does not, however, provide a comparison of differences between MO extracts and desipramine. Furthermore, following 15 days of treatment of MO aqueous extract, 17-month Kunming mice were subjected to an intensive swimming test. MO aqueous extracts increased the swimming duration of the loaded mice and the levels of norepinephrine, epinephrine, and dopamine in the brain tissue, while decreasing the amount of 5-HTP, suggesting that MO may have a favorable effect on the brain via modulating monoamine neurotransmitter levels (Zhang et al., 2014).

6.4.1 Wound healing activity

Few reports of the genus Morinda have been reported. Although, leaf juice (1 mjg/mL), ethanolic and methanolic extracts (10 – 200 mg/mL) and hexane fractions (10 – 200 mg/mL) of M. citrifolia demonstrated distinct wound healing potentials in mice models. Ethanolic and methanolic leaf extracts exhibited strong wound healing potency compared to activity shown by control. This activity could be linked to ligand binding to PDGF/A2A receptor which initiated wound closure (Palu et al., 2010). The results should be substantiated via further in vivo assays and mechanism of activity needs further clarification.

6.4.2 Gastric ulcer healing activity

The gastro-esophageal (in vivo) antiinflammatory effects of Thai dried mature M. citrifolia fruit (unripe) aqueous extract in rats were reported at 0.63–2.50 g/kg. The probable mechanisms of action was observed to contribute to the emergence of acute gastric lesions and also, blocking esophageal reflux. The antisecretory activity of the extract is similar to that exhibited by lanzoprazole and ranitidine (Mahattanadul et al., 2011). Twenty healthy volunteers aged 18 to 45 were given a single dose of Thai M. citrifolia fruit extract (aqueous) containing 25.15 ± 0.11 lg/ml scopoletin in an open-label, two-period crossover research. After 30 min, the volunteers were administered one 300 mg ranitidine tablet and blood samples were collected for 12 h at fixed intervals. The presence of scopoletin in M. citrifolia stimulated the 5-HT4 receptor. To substantiate the findings, comprehensive clinical assessments needs to be carried out with patients with suffering from stomach motility defects or symptoms.

6.4.3 Immunity enhancing activity

The investigation (in vivo) of immunity potency of M. citrifolia (Tahitian and commercial fruit juices) on mice was observed to significantly enhanced the immunity of tested organisms. This indicated that M. citrifolia restrains the immune system by activating CB2 receptors, inhibiting interleukin-4, and augmenting the production of interferon gamma cytokines. Further study should focus on comprehensive in vivo and clinical assays to investigate the dosage and mode of action of M. citrifolia on the immune system (Palu et al., 2008).

6.4.4 Anticancer activity

Cancer is a huge public health concern around the world (Siegel et al., 2014). It refers to a group of disorders in which aberrant cells develop and spread abnormally (ACS, 2015). In ethnobotanical surveys done among traditional medicinal practitioners in South West Nigeria, M. lucida was referenced in recipes for the management of cancers and cancer-related disorders (Sowemimo et al., 2007). Generally, infusions and decoctions of M. lucida leaf and stem bark have been reported to be used in the cancer therapy in South West Nigeria (Ashidi et al., 2010). Aqueous extract of M. lucida leaf displayed antiproliferative action (in vitro) by triggering apoptotic cell death in HL-60 cells (Appiah-opong et al., 2016). Moreover, molucidin isolated from M. lucida leaves has been reported to be cytotoxic, with an MLD50 for some cancer cell lines of less than 10 μM. LoVo (colon cancer cell line) and KATO III (stomach cancer cell line) have MLD50 values as low as 0.11 and 0.21 μM, respectively, with strong selectivity indices (SI) for several cancer cell lines (Suzuki et al., 2015). The most active components of the methanolic extract of M. lucida leaf were cytotoxic to monkey kidney epithelial cells (LLCMK2), with the Median lethal dose (MLD50) ranging from 15.625 g/mL to 31.25 g/mL. Sulphated polysaccharide inhibits metastasis by disrupting the interface between glycosaminoglycan and certain proteins, while damnacanthal impedes tumor formation either by restricting with the growth of ras gene activation (Hiramatsu et al., 1993) or by increasing apoptosis in human colorectal cancer cell lines.

6.4.5 Antidiabetic activity

The hypoglycemic effect of Tahitian M. citrifolia fruit juice was examined by administering it to male Sprague– Dawley rats each day at a dose of 1 ml/150 g body weight for 4 weeks before diabetic induction with alloxan (Horsfal et al., 2008). Blood glucose levels increased after induction, but then decreased significantly due to M. citrifolia juice prophylaxis against the diabetogenic drug alloxan (Horsfal et al., 2008). For 10 days, induced steroid diabetic (diabetes type 2) female Wistar rats were given 1.8 and 3.6 ml/kg of Indian M. citrifolia commercial fruit juice orally. Dexamethasone significantly reduced blood glucose levels in diabetic rats compared to control rats. M. citrifolia fruit juice provided greater benefits than rosiglitazone at a higher oral dose (3.6 ml/kg, twice a day), but caused liver damage in rats (Puranik et al., 2013). On the other hand, streptozotocin-induced diabetic rats were regulated by fermented juice of South American M. citrifolia. Diabetic standard animals given the hypoglycemic drug glibenclamide, as well as diabetic experimental animals given 2 ml/kg M. citrifolia twice a day for 20 days, had blood glucose levels of 125 mg/dl and 150 mg/dl, respectively, when compared with untreated diabetic rats with fasting blood sugar of 360.0 mg/dl. Nayak et al. (2011) found that saponins and flavonoids in M. citrifolia fruit, such as rutin, may act as secretagogues by increasing insulin production. M. citrifolia has shown promise in vivo findings as a natural antidiabetic drug, but scientists should be concerned about its toxicity, especially in the liver. Preclinical trials will be recommended if the doses are modified within a reasonable level with proven efficacy.