A review on ethnobotany, phytochemistry, and pharmacology of Microdesmis keayana and Microdesmis puberula (Pandaceae)

Microdesmis keayana and Microdesmis puberula (Pandaceae) are two major plant species in the genus Microdesmis . They are dioecious shrubs, very similar in their morphology, botanical distribution, and medicinal uses, and native to most tropical and subtropical African regions. Traditionally, they are commonly used to treat erectile dysfunction, general body pain, snake bites, skin and intestinal infections, tumors, diarrhea, diabetes, obesity, headache, and migraine. This review is aimed to provide a compendium of ethnopharmacological and phytochemical information on the Microdesmis plants for future research and drug development initiatives. Relevant books and electronic databases were sourced during the literature review. Several phytochemical investigations resulted in the isolation and identification of about eight compounds from M. keayana and M. puberula , including four spermines and five spermidine alkaloids, and a quinoline, which were all isolated from the methanol and hydromethanolic root extracts of the two plants. In vivo and in vitro pharmacological studies of the plants showed aphrodisiac, antimalarial, antimicrobial, antioxidant, analgesic, antistress, and antisickling activities, which gave credence to their use in ethnomedicine. The plants can potentially be used for several disease conditions, including erectile dysfunction, malaria, infections, and pains, with a view to isolating bioactive lead compounds for drug development.


INTRODUCTION
Microdesmis keayana J.Leonard and Microdesmis puberula Hook.f.ex Planch.are two major species out of about 11 species found in the genus Microdesmis, Pandaceae (van Welzen, 2011).The plants are well spread in the tropical and subtropical African regions, including Ghana, Congo Republic, Ivory Coast, Nigeria, Sierra Leone (Royal Botanical Garden Kew, 2022), Burundi, Gabon, and Rwanda (Dounias, 2008).Both species are comparable in their morphology and medicinal uses, and in some regions, are confused as similar species (Alvarez Crus, 2008;Dounias, 2008).Besides their medicinal uses, the plants are important leafy vegetables with essential nutritional content eaten by some tribes as chew sticks by locals (Dounias, 2008) and browse plants for animals (Esonu et al., 2004;Okon et al., 2018;Umoh et al., 2004).
All parts of the studied species, including roots, leaves, stems, fruits, and whole plants, are used by locals for traditional medicinal purposes, including erectile dysfunction and infertility, malaria, skin and intestinal infections, pains, diabetes, diarrhea, and tumors.Their extensive ethnomedicinal utility could be due to their exceptional pharmacological activities, which include antimicrobial, antioxidant, antisickling, analgesic, aphrodisiac, antistress, analgesic, and antimalarial (Bouquet and Debray, 1974;Egunyomi et al., 2009, Okany et al., 2012;Roumy et al., 2008;Zamblé et al., 2006aZamblé et al., , 2006b)).Medicinal plants' recent global acceptance and popularity due to their safe, low cost, easy accessibility, and effectiveness (Ogunmefun, 2018;Sofowora et al., 2013) makes M. keayana and M. puberula potential source of bioactive compounds for drug discovery.Although some in vitro and in vivo pharmacological studies of the plants have been reported by several researchers, there is a need for more pharmacologic and clinical studies to prove its efficacy and safety, and support its use in traditional medicine.
Microdesmis keayana and M. puberula share several similarities ranging from their ethnobotanical description, distribution, uses, and phytochemical constituents (Dounias, 2008;Roumy et al., 2008).An ethnobotanical survey in Southwestern Nigeria carried out at the early stage of this research revealed that the local names, "Idi-apata" and "Aringo" in Yoruba, are used mutually for both species among many traditional medicine practitioners and botanists and, thus, informed the need to report both species in this review article.
The present review is aimed to offer a firsthand compilation and databank of ethnopharmacology, phytochemistry, and biological activities of the plants, creating quick access information for future research on the plants.

METHODOLOGY
Relevant literature in this review was accessed from several electronic bibliographic databases, which include PubMed, Medline, Google, Google Scholar, Research Gate, Royal Botanical Garden Kew, JSTOR, The Plant List, and Academia, using several search terms, such as Microdesmis, M. puberula, M. keayana, chemical constituents, and ethnopharmacology of Microdesmis species.The search terms yielded more than 100 publications accessible online.The scientific names of the plants were validated using Royal Botanical Garden Kew, JSTOR, and The Plant List online websites.

Botanical description and distribution of M. keayana and M. puberula
Both Microdesmis species are nearly similar in morphology, making their identification difficult (Fig. 1).(Dounias, 2008).The two species are either short trees or shrubs that are dioecious, growing up to 6 m in height, with stems measuring up to about 8 cm in diameter.Their leaves are alternate and simple with about 4 mm long stipules.The petioles are generally 4-12 mm long with elliptical-oblong or ovate blades and asymmetrical bases looking cuneate to round with an acute and somewhat acuminate apex and finely toothed margin that is almost entire.Flowers are unisexual with green, short-hairy calyx, petals that are pink-orange, nearly circular to ovate-oblong, and short-hairy in the upper half; female flowers have superior ovaries.Fruits of both species are ovoid drupe-shaped, measuring 10-12 × 9-11 mm.They are usually smooth when fresh but appear wrinkled when hard and appear shiny and red (one to two seeded).Seeds are primarily ovate, compacted, and rounded seedlings with epigeal growth (Alvarez Crus, 2008;Baker, 1913;Burkill, 1997;Schmeizer and Gurib-Fakim, 2008;van Welzen, 2011) (Fig. 1).
Microdesmis keayana and M. puberula are small woody trees found in temperate regions of Africa (Fig. 2).They are the most widely distributed among the nine species in the genus Microdesmis found in Africa (Royal Botanical Garden Kew, 2022;van Welzen, 2011) (Fig. 2).

ETHNOMEDICINAL USES
Generally, almost all parts of M. keayana and M. puberula, such as fruits, leaves, leaf twigs, stem bark, root, and whole plants, are used for ethnomedicinal purposes.The plants have a vast range of traditional medicinal applications that include preparations, such as decoctions and paste for treating erectile dysfunction, pains, wound healing, and infections, respectively.Microdesmis puberula is used as a browse plant for cattle and goats (Esonu et al., 2004;Okon et al., 2017).The traditional use of the plants, their local names, and methods of preparation are shown summarized in Table 1.

CHEMICAL CONSTITUENTS
Previous investigations on Microdesmis species revealed the presence of polyamine alkaloids, such as spermine and spermidine derivatives as well as quinolones in M. keayana and M. puberula (Roumy et al., 2008;Zamblé et al., 2006aZamblé et al., , 2006b)).The leaves and roots were reported to possess important phytochemicals, such as alkaloids, flavonoids, saponins, steroids, tannins, and terpenoids (Akpanyung et al., 2013;Gbadamosi and Oloyede, 2014;Odesanmi et al., 2012;Okon et al., 2017).Coumarins and anthraquinones were found to be present in the roots and leaves of M. keayana by Acheampong et al. (2018), while Akpanyung et al. (2013) found reducing sugars in the roots of the plant.Studies to evaluate the nutritional and quantitative phytochemical properties of M. puberula revealed that the leaf contained alkaloids, saponins, cardiac glycosides, terpenes, and nutrients like carbohydrates, crude proteins, minerals, e.g., zinc, iron, calcium, potassium, magnesium, and phosphate alongside with other vitamins (A, B1, B2, and C) (Esonu et al., 2004;Okon et al., 2018;Umoh et al., 2004;Uwemedimo et al., 2018).Studies Abakedi and Sunday (2021) revealed that M. puberula leaf and root extracts inhibited the corrosion of aluminum in an acidic medium, which was predicted to be due to the presence of heteroatoms like nitrogen, oxygen, and sulfur in alkaloids, terpenes, and anthraquinones.

Fertility and aphrodisiac properties
Plant products that have antioxidant and sexually potentiating properties can be used as treatment choices for infertility in males (Muanya and Odukoya, 2008;Zamblé et al., 2009).The effect of M. keayana aqueous root extract on vasorelaxant and hypotensive activity in normotensive rabbits and guinea pig aorta strips using the organ bath was investigated by Zamblé et al. (2006aZamblé et al. ( , 2006b)).It was revealed that M. keayana root increased endothelial nitric oxide synthetase 3 (eNos) messenger ribonucleic acid (mRNA) (an important enzyme that synthesizes nitric oxide (NO), an essential mediator of erectile function) levels and NO production and also reversed oxidative stress due to its antioxidant properties.The result showed a positive correlation in its sexual behavioral functions, which supports the use of M. keayana use in ethnomedicine for the management of erection problems.Several studies have shown the expression and increased activity of eNOS during erection, which results in increased NO production (Li et al., 2019;Wen et al., 2011).Zamblé et al. (2008) further studied the sexual behavioral actions of aqueous root extract and two compounds keayanidine B and keayanine isolated from M. keayana, on male albino rats.The aqueous extract and pure isolated alkaloids were administered orally at doses of 150 and 3 mg/kg, respectively, to male albino rats.Microdesmis keayana root extract significantly increased mounting frequency, decreased mount latency, and increased intromission and ejaculatory frequencies after 1 hour 15 minutes and 3 hour 15 minutes.Zamblé et al. (2009) in a study to explore the pharmacologic basis surrounding the ethnomedicinal use of M. keayana for treating erection dysfunction, evaluated two compounds keayanidine B and keayanine (from M. keayana root extract) for their potential to induce vasodilation in isolated aortic rings of rats.Keayanidine B and keayanine, administered in ranging concentrations of 1.10 −9 -3.10 −4 M, were found to cause a relaxed contraction induced by phenylephrine with IC 50 of 23.3 ± 1.3 μM/l for keayanidine B and 27.5 ± 2.4 μM/l for keayanine in a dose-dependent fashion.The results showed that the vasodilating properties of the two isolated alkaloids were caused by their ability to increase eNos mRNA and NO levels.
Muanya and Odukoya ( 2008) investigated the fertility effect of M. keayana ethanol root extract and other plant root extracts commonly used in South West Nigeria for treating erectile dysfunction and boosting sperm count and libido in  males.Lipid peroxidation was used as an index to evaluate the aphrodisiac properties of these plants.The lipid peroxidation activity of the plants was assayed by measuring malondialdehyde levels in the homogenate of raw and cooked fish.The findings indicated that M. keayana root extract significantly decreased lipid peroxidation due to its antioxidant properties (Muanya and Odukoya, 2008).The aphrodisiac potential of the two Microdesmis species needs more exploration as some commercial herbal products in the market have M. keayana as one of the ingredients (Barlowesherbalelixirs, 2020).The evidence above supports the use of M. keayana as an aphrodisiac in folklore.However, no scientific discoveries existed to support the traditional use of M. puberula as an aphrodisiac or fertility enhancer.This scientific gap indicates the need for more pharmacological research on both plants, especially on fractions and isolated compounds.

Antimalarial activities
Malaria is an endemic disease that affects more than 3.5 billion people worldwide, with higher mortality rates in Africa (Snow and Omumbo, et al., 2006).It is transmitted by Plasmodium sp.majorly Plasmodium falciparum (Bawo et al., 2020;WHO, 2022).Microdesmis keayana is used traditionally for treating malaria.This ethnomedicinal claim was confirmed when the antiplasmodial and cytotoxic activity of M. keayana methylene chloride leaves extract was evaluated alongside three Ivorian plants (Vonthron-Sénécheau et al., 2003).Four of the extracts were tested on K1 chloroquine-resistant P. falciparum strain by in vitro microculture radioisotope technique, which uses the uptake of [ 3 H]hypoxanthine by parasites as an indicator of viability.The results showed that M. keayana methylene chloride and methanol leaf extract were able to inhibit P. falciparum growth by inhibiting the uptake of [ 3 H]hypoxanthine with IC 50 values of 12.2 µg/ml and >20 µg/ml for methylene chloride and methanol extracts, respectively (Vonthron-Sénécheau et al., 2003).Zirihi et al. (2005) studied the antiplasmodial and cytotoxicity of M. keayana ethanol root extract and 32 other West African plants against the chloroquine-resistant FcB1/Colombia strain of P. falciparum by in vitro models.The finding showed M. keayana extract was inactive against P. falciparum with IC 50 values >50 g/ml.The larvicidal activity of M. puberula hexane leaf extracts, along with two other plants, was evaluated using biolarvicidal bioassay protocols, and Dipex pesticide (1 ppm) was used as a positive control (Bawo et al., 2020).The result showed a significant increase in the mortality rate of mosquito larvae, with the highest and lowest mortality rate at 70 and 10 ppm, respectively.Similarly, the hexane leaf extracts also had a biolarvicidal effect at an LC 50 value of 32.83 ppm.
The report above shows some disparity in the in vitro antiplasmodial results of M. keayana.This necessitates the need for more scientific investigation on other solvent fractions and pharmacological screening techniques to validate the traditional usage of plants in curing malaria.Also, further research is encouraged on the isolation of bioactive compounds with antiplasmodial activity as a scaffold for new drug development for malaria treatment and to better understand the mechanism of action.

Pharmacological studies
Fertility and aphrodisiac activities

Antimalarial activity
Antimicrobial activity

Antioxidant activity
Antisickling activity

Toxicity studies
Antimalarial activity

Antimicrobial activity
Antioxidant activity
The use of M. keayana and M. puberula in treating infections and skin diseases in ethnomedicine is yet to be extensively proven scientifically.The above report shows they are active against designated microorganisms.Possible isolation of bioactive lead compounds with antibacterial and antifungal activities is vital and encouraged.

Antioxidant activity
Antioxidants are important defense mechanisms of the body against the deleterious effect of free radicals, such as reactive oxygen species, involved in the development of several disease conditions (Agarwal and Prabakaran, 2005).Previous studies have shown that M. keayana and M. puberula are natural antioxidant reservoirs (Acheampong et al., 2018, Zamblé et al., 2006a, 2006b).Acheampong et al. (2018) investigated the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging properties and total antioxidant capacity of M. puberula methanol and petroleum ether stem bark extracts.The results showed both extracts possess DPPH radical scavenging activity with IC 50 values of 1.1 and 1.2 µg/ml, respectively.The methanol extract proved more potent than the petroleum ether extract with a total antioxidant capacity of 21.75 mg ascorbic acid equivalent/gram of dry extract and 96.11 mg ascorbic acid equivalent/gram of dry extract for petroleum ether at the lowest extract concentration of 1.56 µg/ml.Studies by Zamblé et al. (2006aZamblé et al. ( , 2006b) ) on the antioxidant activity of M. keayana aqueous root extract on superoxide anion, hydrogen peroxide (H 2 O 2 ), hypochlorous acid (HOCl), and hydroxyl radical (HO•) revealed that the extract had a very significant dosedependent radical scavenging activities in two systems (cellular and noncellular) against superoxide radical-anion with IC 50 of 34.29 ± 2.384 and 19.46 ± 1.90 g/ml for noncellular and cellular systems, respectively.It also showed substantial scavenging activities against H 2 O 2 , HO•, and HOCl with IC 50 of 49.75 ± 0.25, 57.8 ± 0.75, and 63.5 ± 0.5 g/ml, respectively (Zamblé et al., 2006a(Zamblé et al., , 2006b)).In another study, Zamblé et al. (2009) investigated DPPH radical scavenging, O 2 •-, and H 2 O 2 antioxidant activity of keayanidine B and keayanine isolated from the root of M. keayana.Keayanidine B and keayanine showed strong antioxidant effects against DPPH with IC 50 values of 33.0 ± 0.7 and 30.2 ± 0.9 μM/l, respectively, and against superoxide anion and H 2 O 2 with IC 50 varying from 16.2 ± 0.4 to 20.2 ± 0.7 μM/l in the cell-free system and from 13.2 ± 0.7 to 16.3 ± 0.8 μM/l in the cellular system (Zamblé et al., 2009).The antioxidant activities of the root and stem bark extracts of M. keayana and M. puberula could be responsible for the pharmacological activity of the plants, which further gives credence to their use in folklore as fertility enhancers, aphrodisiacs and in the treatment of other disease conditions triggered by reactive oxygen species (Zamblé et al., 2006a(Zamblé et al., , 2006b(Zamblé et al., and 2009)).Further research is crucial to isolate antioxidant phytochemicals from the various parts of the plants.

Analgesic and antistress properties
Microdesmis keayana and M. puberula are used in ethnomedicine as pain relievers (Alvarez Crus, 2008;Ayensu, 1978;Betti, 2004;Muanya, 2018;Schmeizer and Gurib-Fakim, 2008).The analgesic property of M. puberula methanol stem wood extract was investigated by Okany et al. (2012) using standard analgesic models like the acetic acid writhing and the hot plate analgesic tests.It was revealed that the extract significantly ameliorated both neurogenic and inflammatory pain dosedependently at 600-2,400 mg/kg.Okany et al. (2012) employed the forced swimming test and immobilization stress-induced ulcer protocol to evaluate the antistress properties of M. puberula methanol stem wood extract.The results showed that the duration of immobility was significantly decreased by the extract at the dose of 600 mg/kg and also a reduced ulcer index in the stressed rats' group treated with the extract.

Antisickling activity
The antisickling activities of two herbal recipes were evaluated by Egunyomi et al. (2009).The first recipe consisted of M. keayana methanol root extract and 27 other plants, while the second recipe consisted of seven plant extracts without M. keayana, p-hydroxybenzoic acid, and normal saline were used as controls.The two herbal recipes demonstrated antisickling activity against sickled erythrocytes.The first ethnobotanical recipe containing M. keayana inhibited red blood cell (RBC) sickling with 63.4% inhibition, while the second herbal recipe had a percentage inhibition of 78.2% at 180 minutes incubation (Egunyomi et al., 2009).More scientific work is required to validate the antisickling property of the plant and the possible isolation of bioactive compounds as new agents against sickle cell disease.

Toxicity studies
Investigations of the acute toxicity profile of M. keayana and M. puberula were carried out in several toxicity studies to determine the safety of extracts of both plants.Okany et al. (2012) revealed that M. puberula has a safety profile of 15 g/kg when administered orally with an LD 50 of 1,412.5 mg/kg.An acute toxicity study of M. puberula by oral administration on albino rats for 14 days revealed that the plant has a wide safety margin with an LD 50 of more than 5,000 mg/kg (Akpanyung et al., 2013).Aspartate transaminase and alanine transferase levels of rats in the treatment groups were reduced when compared with the control group.No toxic effect on the liver and kidney was obtained, and hematological parameters like packed cell volume, hemoglobin, mean corpuscular volume, mean corpuscular hemoglobin concentration, and RBC were not significantly elevated.In contrast, the serum lipid profile of low-density lipoprotein and triglycerides were significantly elevated with reduced high-density lipoprotein levels.Uwemedimo et al. (2018) investigated the acute toxicity of the leaf extract of M. puberula using albino mice by intraperitoneal (i.p.) route using the method of Lorke.The mean lethal dose (LD 50 ) of the extract was estimated to be 2,872.28mg/kg, which proposes that ingestion as a leaf meal may not be detrimental to livestock and humans.Microdesmis keayana aqueous root extract following oral administration caused no death or toxicity at a dose of 2 g/kg body weight in albino rats (Zamblé et al., 2008).Acute and subacute toxicity studies on M. keayana and M. puberula have shown substantial safety and acceptability on all investigated parameters, supporting their widespread use in ethnomedicine.

CONCLUSION
This review, for the first time, has provided a compendium of information on the ethnopharmacological and phytochemical properties of M. keayana and M. puberula.The plants possess an untapped reservoir of phytochemicals as leads for drug discovery and development.There is a need for substantial studies for a proper understanding of the taxonomy and pharmacognostic similarities and differences of both species.The different plant parts, such as root, bark, and leaf, have close characteristics in terms of morphology, distribution, and overlapping medicinal uses.Some biological activities reported on M. keayana include antimicrobial, toxicity, antioxidant, antisickling, analgesic, aphrodisiac, and antimalarial, whereas in M. puberula, they comprise antibacterial, toxicity, antioxidant, antistress, analgesic, and antimalarial activities have been reported.Despite the pharmacological studies reported for both Microdesmis species, several ethnomedicinal claims need scientific data for validation and a better understanding of their mechanism of pharmacological actions, especially at the molecular level.Phytochemical investigations on the two plants have yielded about eight chemical compounds, the majority belonging to the groups of spermine and spermidine alkaloids.Most of the studies on M. keayana and M. puberula were on crude extracts, which has created a gap for further research, particularly on the fractions and the isolated compounds.Clinical studies on both species are encouraged to establish the dose, efficacy, and safety of human subjects in managing disease conditions, as challenges such as dose and dosage optimization have continuously posed major drawbacks in herbal medicine use.Acute and subacute toxicity reports on both species revealed that they are safe and nontoxic, as higher doses of the extracts elicited no adverse effects in experimental animals.

Figure 3 .
Figure 3.Chemical structures and names of compounds reported from M. keayana and M. puberula.

Table 3 .
Summary of the similarities and differences between M. keayana and M. puberula.