Syzygium Cordatum Hochst. ex Krauss: An Overview of Its Ethnobotany, Phytochemistry and Pharmacological Properties

Syzygium cordatum is a valuable medicinal plant in the materia medica of east and southern Africa. The aim of this study was to review the botany, medicinal uses, phytochemistry and ethnopharmacological properties of S. cordatum. Relevant literature search was carried out using internet sources such as ACS, Web of Science, Wiley, SpringerLink, Scopus, Mendeley, Google Scholar, Pubmed, SciFinder, BioMed Central, Science Direct and Elsevier. Other literature sources were conference papers, book chapters, books, theses and websites. The leaves, roots, bark and fruits of S. cordatum are used as ethnomedicines against 24 human diseases such as gastro-intestinal disorders, burns, sores, wounds, colds, cough, respiratory complaints, sexually transmitted infections (STIs), tuberculosis, fever and malaria. Several phytochemical compounds including alkaloids, anthocyanidin, essential oils, flavonoids, leucoanthocyanidin, phenols, phytosterols, saponins, simple sugars, terpenoids and triterpenoid have been identified from S. cordatum. Pharmacological evaluations revealed that S. cordatum is characterized by several biological activities including antibacterial, antifungal, antidiarrheal, anti-sexually transmitted infections, antidiabetic, anticholinesterase, anti-inflammatory, antileishmanial, antioxidant, antiplasmodial and anti-proteus. These pharmacological findings lend credence to the traditional ethnomedicinal uses and ethnopharmacological importance of S. cordatum. Future research on the species should identify the biological compounds, their mode of action and physiological pathways and clinical relevance.


Introduction
Syzygium cordatum Hochst. ex Krauss (family Myrtaceae) is a valuable herbal medicine in east and southern Africa and it is included in the monographic guide of the most valuable herbal medicines in South Africa [1]. In Uganda, a survey conducted by Katumba et al. [2] aimed at identifying medicinal plant species that are widely used and traded in the country identified S. cordatum as one of the priority species for domestication and on-farm planting to promote sustainable utilization of the species. In Swaziland, S. cordatum is regarded as a multipurpose plant species which is important for local livelihoods as herbal medicine, food source as its fruits are edible, source of fuel wood and charcoal, timber, building materials and fences, and for landscaping purposes as an ornamental plant [3]. Similarly, in South Africa, S. cordatum is used as an ornamental plant; it is an important source of strong and durable timber; the fruits are consumed by humans and animals; the fruits are made into potent alcoholic drink; the bark and leaves are consumed by livestock and game; and the bark and fruits are used for dyeing [4][5][6]. According to van Wyk [7], S. cordatum bark has commercial potential as remedy for respiratory ailments and stomach complaints. Research focusing on African medicinal and aromatic plants of commercial importance revealed that the bark of S. cordatum feature prominently in Zimbabwe, infections (STIs); tuberculosis (TB); fever; and malaria (Table 2) are the most commonly treated human diseases and ailments using concoctions prepared from S. cordatum. In traditional medicine, stem bark and root infusion of S. cordatum is used against diarrhea in Kenya, Zambia, Malawi, South Africa and Namibia [1,5,[15][16][17][18][19][20] (Table 1). Bark or leaf decoction of S. cordatum is used against dysentery in Malawi [15] and gastro-intestinal complications in Kenya [21]. In Swaziland, stem bark of S. cordatum is mixed with bark of Breonadia salicina (Vahl) Hepper & J.R.I. Wood and Ozoroa sphaerocarpa R. Fern. & A. Fern. as remedy for diarrhea [22]. Leaf and bark infusion of S. cordatum is taken orally for stomach ache in South Africa and Swaziland [1,5,7,23,24]. Bark infusion of S. cordatum is used against TB in South Africa and Zimbabwe [1,[25][26][27]. Bark and root infusion of S. cordatum is applied topically on wounds in Kenya and South Africa [23,28,29]. In South Africa, bark, fruits, leaves and roots are taken orally for wounds in the mouth and ulcers [30,31]. In South Africa, bark decoction of S. cordatum is applied topically on burns or sores as monotherapy or mixed with bark of Acacia burkei Benth., Ozoroa engleri R. Fern. & A. Fern., Sclerocarya birrea (A. Rich.) Hochst., Tabernaemontana elegans Stapf. and Lippia javanica (Burm. f.) Spreng. [32]. Bark infusion of S. cordatum is used against STIs as monotherapy, mixed with S. birrea or mixed with Aloe marlothii A. Berger, Hypoxis hemerocallidea Fisch., C.A. Mey & Avé-Lall, Senecio serratuloides DC. and S. birrea [33,34]. Bark decoction of S. cordatum is used as emetics in South Africa and Swaziland [1,5,[24][25][26]. In Tanzania and Uganda, the bark or leaf decoction of S. cordatum is applied topically for skin rash [29,35,36]. Bark and leaf decoction of S. cordatum is taken orally mixed with leaves of S. birrea as remedy for gonorrhea [37]. Bark and leaf decoction of S. cordatum is taken orally against colds in South Africa and Kenya [20,23]. In South Africa, bark, leaf or root infusion of S. cordatum is used against amenorrhea [23,28], chest complaints [25], colds [23], fever [23], headache [23] and respiratory ailments [1,7]. In Tanzania, bark or leaf decoction of S. cordatum is used against herpes simplex and zoster [35,36], while, in Tanzania and Zambia, bark or leaf decoction is used against malaria [38][39][40]. In Uganda, bark, leaf or root infusion of S. cordatum is used against anemia, hepatic jaundice [41] and dry cough [29].

Antibacterial Activity
Samie et al. [54] evaluated the antibacterial activities of methanol, acetone and hexane bark and leaf extracts of S. cordatum against Aeromonas hydrophila, Bacillus cereus, Bacillus pumilus, Bacillus subtilis, Enterobacter cloacae, Enterococcus fecalis, Escherichia coli, Klebsiella pneumoniae, Pantoea agglomerans, Proteus mirabilis, Pseudomonas aeruginosa, Salmonella enterica, Serratia marcescens, Shigella flexneri and Staphylococcus aureus using the disc diffusion and the microdilution methods with gentamicin as positive control. The extracts exhibited activities with zones of inhibition ranging from 8.0 mm to 22.0 mm which was comparable to zone of inhibition of 18-30 mm exhibited by gentamicin (30 µg), the control. The MIC values ranged from 0.2 mg/mL to > 12.0 mg/mL. Mathabe et al. [16] evaluated antibacterial activities of acetone, ethanol, methanol and aqueous extracts of S. cordatum against Escherichia coli, Salmonella typhyi, Shihella boydii, Shigella dysenterae, Shigella flexneri, Shigella sonnei, Staphylococcus aureus and Vibrio cholerae using agar-well diffusion and serial dilution assays with dimethyl sulfoxide (DMSO) as negative control, and nalidixic acid, erythromycin and cotrimoxazole as positive controls. The extracts showed activities with zone of inhibition ranging from 11.7 mm to 25.0 mm against all the tested pathogens. The minimum inhibition concentration (MIC) values against the pathogens ranged from 0.08 mg/mL to 0.31 mg/mL [16]. Pallant and Steenkamp [48] evaluated antibacterial activities of methanol and water bark extracts of S. cordatum against Haemophilis influenzae, Klebsiella pneumoniae, Mycobacterium smegmatis, Staphylococcus aureus and Streptococcus pneumoniae using the disc diffusion and broth microdilution assays with ampicillin as the positive control. The aqueous extract exhibited activities against Haemophilis influenzae and Staphylococcus aureus with zone of inhibition ranging from 21.2 ± 0.2 mm to 22.5 ± 0.9 mm which was comparable to the zone of inhibition of 21.2 ± 0.4 mm to 39.7 ± 0.2 mm exhibited by ampicillin (30 µg), the control. The MIC values of both extracts against Staphylococcus aureus was 0.5 mg/mL [48].
Mulaudzi et al. [50] evaluated antibacterial activities of petroleum ether, dichloromethane, ethanol and water leaf extracts of S. cordatum against Bacillus subtilis, Escherichia coli, Klebsiella pneumoniae and Staphylococcus aureus using microdilution assay with neomycin as a positive control. The extracts exhibited activities with MIC values ranging from 0.01 µg/mL to 6.3 µg/mL [50]. Maliehe et al. [46] evaluated antibacterial activities of fruit and seed extracts of S. cordatum against bacteria causing gastro-intestinal tract infections which included Bacillus cereus, Enterococcus hirae, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella typhimurium, Staphylococcus aureus, Vibrio fluvialis and Vibrio vulnificus using agar dilution and serial microdilution methods with DMSO and ciprofloxacin as negative and positive controls, respectively. Pulp extract exhibited the lowest MIC values ranging from 3.1 mg/mL to 6.3 mg/mL and minimum bactericidal concentration (MBC) values of 3.1 mg/mL to 12.5 mg/mL against Bacillus cereus, Enterococcus hirae, Klebsiella pneumoniae, Pseudomonas aeruginosa and Staphylococcus aureus. The seed extract exhibited MIC values ranging from 3.1 mg/mL to 25.0 mg/mL and MBC values ranging from 12.5 mg/mL to 50.0 mg/mL against Bacillus cereus, Enterococcus hirae, Klebsiella pneumoniae, Pseudomonas aeruginosa and Staphylococcus aureus [46]. Maliehe et al. [47] evaluated antibacterial activities of S. cordatum pulp and seed extracts against Bacillus cereus, Enterococcus hirae, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Vibrio vulnificus using the microdillution method with DMSO and ciprofloxacin as negative and positive controls, respectively. Extracts exhibited activities with MIC and MBC values ranging from 3.1 mg/mL to 50.0 mg/mL which was comparable to MIC and MBC values of ciprofloxacin, the positive control ranging from 1.6 mg/mL to 12.5 mg/mL [47]. Maliehe et al. [52] evaluated antibacterial activities of methanol pulp extract of S. cordatum against Bacillus cereus, Enterococcus hirae, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella typhimurium, Staphylococcus aureus, Vibrio fluvialis and Vibrio vulnificus using serial microdilution method with DMSO and ciprofloxacin as negative and positive controls, respectively. The extract exhibited activities with MIC and MBC values ranging from 3.1 mg/mL to 6.3 mg/mL and 3.1 mg/mL to 12.5 mg/mL, respectively; and these values are comparable to MIC and MBC values of the control which ranged from 1.6 mg/mL to 3.1 mg/mL and 3.1 mg/mL to 12.5 mg/mL, respectively [52].
Nciki et al. [53] evaluated antibacterial activities of aqueous and dichloromethane:methanol (1:1) bark extracts of S. cordatum against Brevibacterium agri, Brevibacterium linens, Escherichia coli, Propionibacterium acnes, Pseudomonas aeruginosa, Staphylococcus aureus and Staphylococcus epidermidis using the micro-titer plate dilution assay with ciprofloxacin as a positive control. The antibacterial interaction of S. cordatum used in combination with S. birrea and also in combination with A. burkei, O. engleri, S. birrea, T. elegans and L. javanica was determined by calculating the sum of the fractional inhibitory concentrations (∑FIC) against Pseudomonas aeruginosa, Staphylococcus aureus and Staphylococcus epidermidis. The ∑FIC value was used to determine if the combined plants had synergistic effect (∑FIC ≤ 0.5), additive (∑FIC > 0.5−1.0), non-interactive (∑FIC > 1.0 ≤ 4.0) or antagonistic (∑FIC > 4.0) [53]. The extracts showed activities with MIC values ranging from 60.0 µg/mL to > 8000.0 µg/mL which was much higher than MIC values of 0.1 µg/mL to 1.25 µg/mL exhibited by ciprofloxacin, the control. The combination of S. cordatum with S. birrea resulted in ∑FIC values ranging from 0.1 to 1.5, indicating synergistic to non-interactive effect, and with A. burkei, O. engleri, S. birrea, T. elegans and L. javanica resulted in ∑FIC values ranging from of 0.57 to 2.45, indicating additive to non-interactive effects [53]. Antibacterial evaluations of S. cordatum combined with other species showed some evidence of synergistic and additive effects [53], thus supporting the traditional method of preparing these combined remedies for burns [32], diarrhea [22], gonorrhea [37], STIs [34] and sores [32].
Sibandze et al. [22] [34]. These results corroborate the potential of S. cordatum in the treatment and management of STIs and, therefore, support its traditional uses against this disease in South Africa [33,34]. Anti-sexually transmitted infections interaction evaluations of S. cordatum combined with other species showed some evidence of synergy [34], thus supporting the traditional method of preparing these combined remedies for STIs in South Africa [34].

Antifungal Activity
Steenkamp et al. [55] evaluated antifungal activities of methanol and water bark extracts of S. cordatum against Candida albicans using plate-hole diffusion assay with amphotericin B as the positive control. The extract exhibited activity with MIC values ranging from 0.8 mg/mL to 3.8 mg/mL. Pallant and Steenkamp [48] evaluated antifungal activities of methanol and water bark extracts of S. cordatum against Candida albicans using the disc diffusion and broth microdilution assays with amphotericin B as the positive control. Both methanol and water extracts exhibited activities with zone of inhibition ranging from 21.7 ± 0.7 mm to 24.3 ± 0.2 mm which was comparable to zone of inhibition of 33.5 ± 3.2 mm exhibited by amphotericin B (20 µg), the control. The MIC values of both extracts were > 1 mg/mL [48]. Mangoyi and Mukanganyama [56] evaluated the antifungal activities of bark and leaf extracts of S. cordatum against Candida albicans and Candida krusei using the agar disc diffusion and broth dilution methods with miconazole as the positive control. The extracts exhibited activities with zone of inhibition ranging from 12.0 ± 0.1 mm to 15.0 ± 0.1 mm, and MIC and minimum fungicidal concentration (MFC) values ranging from 0.6 mg/mL to 2.5 mg/mL against both species. The zone of inhibition exhibited by miconazole, the control, was 20.0 ± 0.8 mm to 22.6 ± 0.7 mm, and the MIC and MFC values ranged from 0.3 mg/mL to 0.6 mg/mL [56].
Mulaudzi et al. [50] evaluated antifungal activities of petroleum ether, dichloromethane, ethanol and water leaf extracts of S. cordatum against Candida albicans using microdilution assay with amphotericin B as the control. The extracts exhibited activities with MIC and MFC values ranging from 0.2 µg/mL to 6.3 µg/mL and 0.4 µg/mL to 12.5 µg/mL, respectively [50]. Masangwa et al. [57] evaluated antifungal activities of acetone, ethyl acetate and water leaf extracts of S. cordatum against Colletotrichum lindemuthianum and Colletotrichum dematium using the agar disc infusion and micro-titer double-dilution techniques with DMSO and the fungicide fludioxonil + mefenoxam (as commercial product Celest ® XL) as negative and positive controls, respectively. The same extracts were then tested for antifungal activity in vivo as seed treatments against anthracnose disease. All extracts showed activities against the tested fungi with MIC values ranging from 0.8 mg/mL to 6.3 mg/mL and the MIC value of the positive control, Celest ® XL was 0.1 mg/mL. The extracts reduced anthracnose disease of bean and cowpea and therefore, are potential seed treatments in anthracnose disease control [57]. Nciki et al. [53] evaluated antifungal activities of aqueous and dichloromethane and methanol (1:1) bark extracts of S. cordatum against Candida albicans, Microsporum canis and Trichophyton mentagrophytes using the micro-titer plate dilution assay with amphotericin B as a positive control. The extracts showed weak activities with MIC values ranging from 380.0 µg/mL to > 8000.0 µg/mL which was much higher than MIC values of 0.01 µg/mL to 0.1 µg/mL exhibited by amphotericin B (100 µg/mL), the control [53]. Njoki et al. [58] evaluated antifungal activities of aqueous bark extract of S. cordatum against Aspergillus flavus using disc diffusion and broth dilution methods. The extract exhibited activities with the zone of inhibition ranging from 9.5 ± 0.7 mm to 17.0 ± 1.3 mm which was comparable to the zone of inhibition ranging from 17.2 ± 0.4 mm to 22.0 ± 0.6 mm exhibited by the positive control at 250 mg/mL [58].

Antidiarrheal Activity
Deliwe and Amabeoku [51] evaluated antidiarrheal activities of leaf aqueous extract of S. cordatum in male albino mice using castor oil-induced diarrheal test. The extract significantly reduced the number of diarrheal episodes, decreased the stool mass and delayed the onset of castor oil-induced diarrhea in mice [51]. Maliehe et al. [47] evaluated antidiarrheal activities of S. cordatum pulp and seed extracts using the castor oil-induced rat model. The S. cordatum fruit-pulp and seed extracts both reduced the number of wet stools, total stools and onset time generally in comparison to the negative control (distilled water). The S. cordatum fruit-pulp and seed extracts, in a dose-related manner (400 mg/kg of rat), exerted the antidiarrheal properties by reducing intestinal motility [47]. Maliehe et al. [52] evaluated the antidiarrheal and antimotility activities of methanolic pulp extracts of S. cordatum using castor oil-induced diarrhea model in rats. The fruit pulp extract reduced the number of wet stools, total number of stools and onset time generally in comparison to the negative control (distilled water). Fruit pulp extract, in a dose-related manner (400 mg/kg of rat), exerted the antidiarrheal property by reducing intestinal motility as well [52]. These findings lend credence to the traditional uses of S. cordatum as remedy for diarrhea [1,5,[15][16][17][18][19][20]22], dysentery [15] and gastro-intestinal complications [21].

Antidiabetic Activity
Musabayane et al. [59] evaluated the hypoglycaemic effect of S. cordatum leaf extract in non-diabetic and streptozotocin-induced diabetic rats. Oral glucose tolerance tests were conducted in non-diabetic and streptozotocin-diabetic rats using orally administered glucose at 1.4 g/100 g body weight followed by either the leaf extract at 6 mg/100 g body weight or subcutaneous injection of metformin at 50 mg/100 g. Weekly plasma glucose and terminal hepatic glycogen concentrations were recorded in control streptozotocin-diabetic rats and diabetic rats orally treated with the leaf extract once every third day for four weeks. Administration of the leaf extract decreased plasma glucose from 7.7 ± 0.9 mmol/L to 3.7 ± 0.6 mmol/L and 21.1 ± 2.2 mmol/L to 12.5 ± 1.8 mmol/L in 2.5 h in non-diabetic and streptozotocin-diabetic rats, respectively [59]. Deliwe and Amabeoku [51] evaluated antidiabetic activities of leaf aqueous extract of S. cordatum using streptozotoxin-induced diabetes in Wistar rats. Both the extract at 12.5 mg/kg to 50.0 mg/kg and chlorpropamide at 250.0 mg/kg significantly lowered the blood glucose levels in both normal and streptozotoxin-induced diabetic rats. Since chlorpropamide is used to treat diabetes by stimulating insulin secretion from pancreatic beta cells and promoting peripheral glucose uptake and utilization, it is probable that S. cordatum acts in a similar manner [51]. Therefore, S. cordatum leaf extracts could be effective in mild diabetes mellitus or in cases of glucose tolerance impairment but might be less effective in severe hyperglycaemia.

Anti-Inflammatory Activity
Mulaudzi et al. [50] evaluated anti-inflammatory activities of petroleum ether, dichloromethane, ethanol and water extracts of S. cordatum by evaluating their ability to inhibit cyclooxygenase-1 and 2 (COX-1 and COX-2) enzymes. Petroleum ether and dichloromethane extracts exhibited high inhibition activity towards both COX-1 and COX-2 exceeding 75% [50]. Mzindle [60] evaluated anti-inflammatory activities of methanol and water extracts of S. cordatum using the lipoxygenase inhibitor screening assay with nordihydroguaiaretic acid as a positive control. The methanol and water extracts inhibited lipoxygenase enzyme by 78.6 ± 3.6% and 40.5 ± 6.7%, respectively, which was lower than 122% and 129% inhibition demonstrated by nordihydroguaiaretic acid, the control [60]. Mzindle [60] also evaluated the wound healing activities of ethanol and water extracts of S. cordatum using the scratch wound assay. The migration rate of the extracts ranged from 23.3 ± 18.1% to 60.2 ± 0.0% when compared to the untreated cells with a percentage migration rate of 24%. These findings support the traditional use of S. cordatum in managing inflammatory ailments and diseases such as burns, sores, ulcers and wounds [1,23,[28][29][30][31] and other problems that result in cell injury and death.

Antileishmanial Activity
Bapela et al. [61] evaluated antileishmanial activities of dichloromethane and methanol leaf extracts of S. cordatum against Leishmania donovani. The dichloromethane extracts displayed high inhibitory effects on the growth of amastigote forms of Leishmania donovani with IC 50 values of 5.0 µg/mL. Bapela et al. [66] demonstrated that most of the non-polar extracts of medicinal plants used in the treatment of malaria also possess significant antiplasmodial activities, and, therefore, likely have antileishmanial properties as both malaria and leishmaniasis are protozoal infections sharing several unique metabolic pathways. Therefore, findings of this research imply that S. cordatum extracts may have potential as antileishmanial agents.

Anti-Proteus Activity
Cock and van Vuuren [65] evaluated the activities of methanol and water bark and leaf extracts of S. cordatum against Proteus mirabilis and Proteus vulgaris using modified disc diffusion method with ampicillin and chloramphenicol as positive controls and distilled water and methanol as negative controls. The extracts exhibited activities against tested pathogens with zone of inhibition ranging from 10.0 ± 1.0 mm to 13.7 ± 0.6 mm and the MIC value ranged from 49.0 µg/mL to 1325.0 µg/mL [65].

Cytotoxicity Activity
Verschaeve et al. [66] evaluated mutagenic and antimutagenic activities of dichloromethane extracts of leaf extracts of S. cordatum in Salmonella/microsome and micronucleus tests. None of the extracts tested in the Ames test were found to induce mutations or to modify the effect of the mutagen 4-nitroquinoline-oxide (4NQO). In the micronucleus test, the extracts significantly lowered the effect of the mutagen mitomycin C (MMC) [66]. Sibandze et al. [22] evaluated the cytotoxicity of combined effect of bark extracts of S. cordatum, B. salicina and O. sphaerocarpa against human kidney epithelial cells, using the MTT (3-[4,5-dimethylthiazol-2yl]-2,5diphenyltetrazolium bromide) cellular viability assay. The triple combination had a favorable cytotoxicity profile with an IC 50 value of 155.8 ± 11.9 µg/mL [22]. Mulaudzi et al. [50] evaluated the cytotoxicity activities of petroleum ether, dichloromethane, ethanol and water extracts of S. cordatum by evaluating the mutagenicity using the Salmonella/microsome assay using the plate-incorporation procedure with Salmonella typhimurium tester strains TA98, TA100 and TA102 with and without enzyme (S9) bioactivation. None of the extracts showed mutagenic effects [50]. Cordier et al. [45] evaluated the cytotoxicity activities of aqueous and methanolic bark extracts of S. cordatum in C2C12 myoblasts, 3T3-L1 pre-adipocytes, normal human dermal fibroblasts and U937 macrophage-like cells using the neutral red uptake assay. The extracts were most toxic to the 3T3-L1 with IC 50 values ranging from 25.0 ± 1.0 µg/mL to 74.6 ± 1.0 µg/mL and C2C12 with IC 50 values ranging from 20.5 ± 1.1 µg/mL to 95.6 ± 1.1 µg/mL and but not cytotoxic in the U937 and normal human dermal fibroblasts cultures with IC 50 values > 100 µg/mL [45]. Naidoo et al. [34] evaluated cytotoxicity of the dichloromethane and methanol (1:1) and aqueous leaf extracts of S. cordatum using the MTT cellular viability assay. The aqueous and organic extracts were non-toxic, they exhibited cellular viability at 104.0 ± 0.8 µg/mL and 102.0 ± 0.8 µg/mL, respectively against the human kidney epithelial cell line [34]. Bapela et al. [64] evaluated cytotoxicity activities of leaf extracts of S. cordatum against mammalian L-6 rat skeletal myoblast cells with podophyllotoxin as a control. The extract demonstrated IC 50 value of 65.7 µg/mL and selectivity index value of 10.7 which was considered to be toxic to rat skeletal myoblast L6 cells [64].
Nondo et al. [67] evaluated the cytotoxic activities of ethanol stem bark extract of S. cordatum using MTT assay on LLC-MK2 monkey kidney epithelial cells. The extract was non-cytotoxic and exhibited 50% cytotoxic concentration (CC 50 ) values above 200 µg/mL [67]. Bapela et al. [61] evaluated cytotoxicity activities of dichloromethane and methanol leaf extracts of S. cordatum by assessing the inhibition of mammalian cell growth by cultivating rat skeletal myoblast L6 cells in the presence of different extracts covering a concentration range from 0.002 to 100.0 µg/mL in 96 well culture plates with podophyllotoxin as a positive control. The methanol and dichloromethane extracts exhibited IC 50 values of 53.8 µg/mL and 65.7 µg/mL, respectively, which were much higher than IC 50 value of 0.007 µg/mL exhibited by podophyllotoxin, the control [61]. Maliehe et al. [52] evaluated the cytotoxicity activities of methanolic pulp extracts of S. cordatum using the MTT assay and exhibited IC 50 value of 92.0 µg/mL. Mzindle [60] evaluated cytotoxicity of methanol and water leaf extracts of S. cordatum using MTT assay using 3T3 NIH fibroblast cells by treating them with various concentrations of the extracts. The extracts exhibited 100% to 120% viability, indicating that the extracts were not toxic to the cells [60].

Toxicity
Cock and van Vuuren [65] evaluated toxicity of methanol and water bark and leaf extracts of S. cordatum using a modified Artemia franciscana nauplii lethality assay with sea water as the negative control. The extracts are non-toxic as the LC 50 values were above that of the negative control. Deliwe and Amabeoku [51] evaluated acute toxicity of leaf aqueous extract of S. cordatum using male albino mice. The extract was administered orally to mice in graded doses of 200, 400, 800, 1200, 1600, 2000, 2400, 2800, 3200, 3600 and 4000 mg/kg. The control group received 0.3 mL physiological saline orally; both the test and control animals were allowed access to food and water; and the animals were observed for five days for any deaths or acute toxicity symptoms such as hypoactivity, piloerection and salivation. The median lethal dose (LD 50 ) value obtained for the extract was over 4000 mg/kg orally. The relatively high LD 50 value obtained for the extract shows that S. cordatum is non-toxic to mice [51]. Nondo et al. [67] evaluated the toxicity activities of ethanol stem bark extract of S. cordatum using the brine shrimp (Artemia salina L.) lethality assay. The brine shrimp lethality assay demonstrated LC 50 value of 99.9 µg/mL and, therefore, non-toxic [67]. Further toxicological evaluations of S. cordatum should be carried out as powdered bark of the species is sometimes used as a fish poison [12,25]. Bark extracts of S. cordatum poisons small fish and turns water blue for a week although the poison is not potent for more than three days [25]. Therefore, it is important to determine if any toxicological effects can occur from its chronic or subchronic usage given the widespread use of S. cordatum as herbal medicine.

Conclusions
Pharmacological studies of the various parts of S. cordatum have supported and justified the traditional uses and ethnopharmacological importance of the species. The antimicrobial, anti-inflammatory, antioxidant and antiplasmodial activities are consistent with the use of S. cordatum in the treatment of burns, chest complaints, colds, cough, fever, gastro-intestinal problems, herpes simplex or zoster, malaria, respiratory complaints, STIs, skin rash, sores, TB and wounds. The anthocyanidin, essential oils, flavonoids, leucoanthocyanidin, phenolics, phytosterols and triterpenoids appear to be the major plant derivatives and active ingredients in the bark, fruits, leaves and seed extracts of S. cordatum. There are few to no pharmacological evaluations done to date focusing on the biological effects of the phytochemical compounds isolated from S. cordatum. Therefore, future research should focus on pharmacokinetics and clinical research of S. cordatum products and compounds. This research should be complemented by experimental animal studies, randomized clinical trials and target-organ toxicity studies involving S. cordatum products, compounds and its derivatives. Therefore, future research should identify the bioactive components, details of their molecular modes or mechanisms of action, pharmacokinetics and physiological pathways for specific bioactive compounds and plant parts of S. cordatum.