Ethnobotanical Description and Biological Activities of Senna alata

Senna alata is a medicinal herb of Leguminosae family. It is distributed in the tropical and humid regions. The plant is traditionally used in the treatment of typhoid, diabetes, malaria, asthma, ringworms, tinea infections, scabies, blotch, herpes, and eczema. The review is aimed at unveiling the ethnobotanical description and pharmacological activities of S. alata. Different parts of the plant are reported in folk medicine as therapeutic substances for remediation of diverse diseases and infections. The extracts and isolated compounds displayed pronounced pharmacological activities. Display of antibacterial, antioxidant, antifungal, dermatophytic, anticancer, hepatoprotective, antilipogenic, anticonvulsant, antidiabetic, antihyperlipidemic, antimalarial, anthelmintic, and antiviral activities could be due to the array of secondary metabolites such as tannins, alkaloids, flavonoids, terpenes, anthraquinone, saponins, phenolics, cannabinoid alkaloids, 1,8-cineole, caryophyllene, limonene, α-selinene, β-caryophyllene, germacrene D, cinnamic acid, pyrazol-5-ol, methaqualone, isoquinoline, quinones, reducing sugars, steroids, and volatile oils present in different parts of the plant. The review divulges the ethnobotanical and pharmacological activities of the plant and also justifies the ethnomedical claims. The significant medicinal value of this plant necessitates a scientific adventure into the bioactive metabolites which constitute various extracts.


Introduction
e primary and safest therapeutic approach since prehistoric time is herbal medicine which has displayed significant role in primary health care development [1].
e World Health organization (WHO) appraised that 80% of inhabitants in developing countries basically rely on herbal medicines [2,3]. Recently, it was discovered that one-third of the commonly used drugs are obtained from natural sources.
is has led to the documentation of about 40,000-70,000 medicinal plant species with outstanding therapeutic potentials [4]. e scientific appraisal of the pharmacological activities of herbal plants revealed about 200,000 phytochemicals. ese compounds contribute to the apparent medicinal activities displayed by plants and invariably justify the involvement of natural products in the development of novel drugs [5]. Despite these achievements, the use of herbal drugs was not universally accepted in contemporary medicine due to lack of scientific evidence and proper documentation. However, the significance of herbs in pharmacology has necessitated the provision of scientific facts on bioactive compounds and pharmacological assays of plants [6,7].
Medicinal plants with immense biological applications have been viewed as the principal sources of therapeutic substances which could lead to novel therapeutic compounds. e search for these compounds from medicinal plants usually ends in the isolation of novel compounds and, eventually, drug developments [8]. Several medicinal plants with diverse interesting pharmacophore have been scientifically investigated, and one of these plants is Senna alata.
is review appraises the ethnobotanical and pharmacological activities of S. alata, thus justifying diverse traditional applications of the plant.

Review Methodology
Relevant documents were obtained from major scientific catalogues such as Pubmed, Google Scholar, EBSCO, Sci-Finder, Scopus, Medline, and Science Direct. Many publications sites were queried to procure information on ethnobotanical description and pharmacological activities of S. alata.

Ethnobotanical Description
3.1. Description and Classification. S. alata (L.) Roxb. is a flowering shrub of the Fabaceae family. It has the name "candle bush" owing to the framework of its inflorescences [34]. It is an annual and occasionally biannual herb, with an average height of 1 to 4 m, burgeoning in sunlit and humid zones. e leaves are oblong, with 5 to 14 leaflet sets, robust petioles (2 to 3 mm), caduceus bracts (2 × 3 by 1 × 2 cm), and dense flowers (20 × 50 by 3 × 4 cm). Zygomorphic flowers have bright yellow color with 7 stamens and a pubertal ovary. e fruit exists as a 10 to 16 × 1.5 cm tetragonal pod, thick, flattened wings, brown when ripe with many diamond-shaped brown seeds. It is propagated by seeds and dispersed to about 1,500 m above the sea level [35,36].

Geographical
Distribution. S. alata is widely distributed in Ghana, Brazil, Australia, Egypt, India, Somalia, Sri Lanka, and all over Africa [37]. It is an ornamental plant native to the Amazon Rainforest [38]. Like other Senna species, it is cultivated in humid and tropic regions of Africa, Asia, West Indices, Mexico, Australia, South America, the Caribbean Islands, Polynesia, Hawaii, Melanesia, and different parts of India [39]. In Philippines, ailand, and Indonesia, this shrub is widely dispersed and is cultivated for medicinal purposes [40].

Ethnobotanical Uses.
In Ayurvedic, Sinhala, Chinese, and African traditional medicine, various parts of S. alata have shown diverse therapeutic activities in diseases control. In northern Nigeria, the stem, leaf, and root decoctions is used in treatment of wound, skin and respiratory tract infection, burns, diarrhoea, and constipation [41,42]. Also, in the south-western regions, leaf decoction serves as an antidote to body and abdominal pain, stress, and toothache [43]. It also cures dermal infections, convulsion, and as purgative [44,45]. In Egypt, the leaf decoction was observed to be used as a bowel stimulant to stimulate peristaltic shrinkages and decrease water absorption from the colon in attempt to prevent constipation [46]. In Cameroon, the stem, bark, and leaves were reported to be used as a remedy for gastroenteritis, hepatitis, ringworm, and dermal infections [47].
In India, Philippines, and China, S. alata's stem, bark, and leaf decoction were found to be effective in treating haemorrhoids, inguinal hernia, syphilis, intestinal parasitosis, and diabetes [48]. Currently, seeds and roots are used in regulating uterus disorder and worms [18,49]. e leaves and flowers are typically used as antifungal agents and laxatives [35]. In China, the seeds are used in treating asthma and to improve visibility [50]. In Guatemela, Brazil, and Guinea, the whole plant is currently used in the treatment of flu and malaria [36]. e flower and leaves decoction was observed to be used in treatment of ringworms, scabies, blotch, eczema, scabies, and tine infections [11,51]. e leaves are currently used in Sierra Leone to relieve abortion pain and facilitate baby delivery [51]. In west and east Africa, bark decoction is spread on cuts during tribal mark incision and tattoo making [52]. In China, India, Benin republic, Ghana, Nigeria, and Togo, the whole plant is used as a curative for Diabetes mellitus [34,53]. Fresh leaves of the plant are used in the treatment of skin rashes, mycosis, and dermatitis [54]. From the traditional uses, the frequent use of S. alata leaves is more than that of roots, flowers, roots, and stem-bark owing to more active metabolites reported in the leaves. Besides its pharmacological activities, it is processed into capsule, pellet, and tea in Nigeria for preventing diseases and maintaining sound health.

Pharmacological Activities.
Medicinal plants belonging to the Fabaceae family have extensively been investigated for their pharmacological activities. Plants synthesised array of secondary metabolites which contribute to its therapeutic activities ( Figure 1). erapeutic appraisal of S. alata authenticates the ethnobiological claims and establishes the pharmacological activities (Table 1). ere are many published articles connected to diverse therapeutic activities of S. alata which are mainly related to antibacterial, antidiabetic, antilipogenic, antifungal, antioxidant, dermatophytic, antihyperlipidemic, and anthelmintic activities among others. Few studies have also reported its antimalarial activities.

Antibacterial Activities.
e antibacterial potentials of medicinal herbs are appraised using zone of inhibition (ZOI) or minimum inhibitory concentration (MIC). e in vivo antibacterial potential of S. alata was assessed against methicillin-resistant S. aureus (MRSA), extended spectrum beta-lactamase, and carbapenemase-resistant. Enterobacteriaceae was isolated from infectious patients, via Mueller-Hinton broth via the microdilution technique. e extract showed significant activities at 512 mg/ ml due to the flavonoids, quinones, tannins, sterols, alkaloids, and saponins analysed [75]. S. alata leaves collected from an Indian aboriginal tribe, displayed significant ZOI of 21 to 27 mm against clinical isolates of multidrug-resistant (MDR) bacteria, obtained from infected patients, when subjected to ASTs via Kirbye Bauer's disc diffusion assay (KBDD) [58].

Evidence-Based Complementary and Alternative Medicine
Anthraquinone and flavonoid glycosides detected in S. alata extracts significantly inhibited the growth of E. coli and S. aureus with ZOI between 9.7 and 14.8 mm [22,23]. e crude extracts and isolates obtained from purified fractions of S. alata flower extract (anthraquinone glycosides, steroids, tannins, and volatile oils) were assessed on selected bacteria isolates. Strong inhibitory activities were displayed at MIC of 500 mg/ml against the clinical isolates of S. faecalis, B. subtilis, S. aureus, Pseudomonas putida, and M. Luteus. At 500 mg/ml, ZOI of 10 to 25 mm was observed, with close proximity to the inhibitory activities displayed by streptomycin, penicillin, and methicillin [41]. e synergic effect of Eugenia uniflora and S. alata leaves was examined on clinical isolates of B. subtilis and S. aureus. e dried leaves were processed into a local antiseptic herbal soap and the antibacterial potential was assessed via hole-in-plate agar diffusion assay. e herbal soap significantly inhibited the growth of the tested organisms [78].

Antioxidant Activities.
e antioxidant or scavenging activities is important in appraisal of therapeutic potential of medicinal herbs. Plants played significant role in protecting cell against oxidative stress caused by active free radicals [79]. e free radical scavenging potentials of plants are appraised by antibiotic sensitivity tests (ASTs); 2,2-diphenyl-1-picrylhydrazyl (DPPH); ferric-reducing antioxidant power (FRAP); 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS); hydroxyl radical scavenging activity (HRSA), and metal ion chelating activity (MICA). e methanolic and n-hexane leaves extracts of S. alata were explored for their scavenging effects via DPPH assay. e methanolic extract displayed pronounced scavenging activities when compared to n-hexane extract. e methanolic extract was fractionated, leading to isolation of three major bioactive compounds (kaempferol, butylated hydroxytoluene, and emodin). e kaempferol fraction displayed pronounced scavenging activity than the butylated hydroxytoluene and emodin fractions [80]. Several bioactive compounds such as ascorbic acid, flavonoids, tocopherol, anthraquinone, and carotene assessed contributed to scavenging activities displayed [77]. Evidence-Based Complementary and Alternative Medicine Different parts of S. alata, significantly inhibited the action of free radicals causing oxidative stress [82]. e in vitro DPPH assay of ethyl acetate-DCM, methanol-DCM, and oil fractions of S. alata leaves was assessed using L-ascorbic acid as control. e radical scavenging activities measured at 517 nm significantly inhibited the free radicals at 500 g/ml. e concentration at 50% inhibition (IC 50 ) of the fractions revealed activities of methanol-DCM (65.03%), ethyl acetate-DCM (62.33%), and oil fraction (64.10%). e strong scavenging activities could be due to polyphenol and flavonoid analysed [76].
Volatile oils extracted from S. alata flowers were assessed against standard strains and clinical isolates of Candida and Aspergillus species. e oils significantly inhibited the growth of the tested microbes [86]. e methanolic extract and purified n-hexane and ethanolic fractions of S. alata flower displayed strong inhibitory activities against A. Niger, C. utilis, G. candidum, A. brevipes, and Penicillium species with an MIC of 0.312 to 5 mg/ml. However, at different concentrations, the purified fractions exhibited prominent inhibitory activities than the methanolic extracts. Likewise, mycelia growth was significantly inhibited by the purified fractions, with a total suppression of sporulation for 96 h at 2 mg/ml, compared to less sporulation after 48 h for methanolic extracts [87]. e aqueous and ethanolic leaf and bark extracts of S. alata was assessed via disc diffusion assay against M. canis, C. albicans, and A. fumigatus. e bark extracts displayed prominent concentration-dependent susceptibility against C. albicans. On the contrary, the aqueous extract showed a strong ZOI of 12 and 16 mm, while ethanolic extracts exhibited 10 and 14 mm. However, tioconazole displayed strong inhibitory activities of 18 mm which are significantly higher than the extracts at equivalent concentration [64].
S. alata flowers and leaves collected from Ogbomoso, Southwest Nigeria, were examined in an attempt to justify the indigenous claims of its antifungal efficacy. In vitro antifungal activities of ethanolic and methanolic extracts were investigated using the disc diffusion approach. Ethanolic extracts showed pronounced inhibitory activities when compared to methanolic extracts. e IC 50 value of the ethanolic extract was two folds higher than the methanolic extracts against the fungi isolates. e inhibitory activities displayed could be due to methaqualone, cinnamic acid, isoquinoline, and toluidine detected [71].

Dermatophytic Activities.
Currently, the leaves, flowers, and bark of S. alata are used for treating various kinds of skin infections and diseases. In ailand, the plant was mentioned as one of the 54 medicinal plants used for treating scabies, shingles, urticarial, itching, pityriasis versicolor, and ringworm [88]. e dermatophytic activities displayed by S. alata are linked to the bioactive compounds such as anthranols, anthrones, flavonoids, phenols, tannins, and anthracene derivatives [89]. Leaves decoction displayed strong inhibitory activities against S. pyogenes, S. aureus, K. pneurnoniae, E. coli, S. rnarcescens, P. cepacia, and P. aeruginosa [90,91].

Antilipogenic, Antidiabetic, and Antihyperlipidemic
Activities. In Africa and Asia, S. alata leaves and flowers are currently used to regulate lipid absorption, obesity, and fat levels in blood serum. Aqueous leaf extract considerably reduced blood glucose levels, serum cholesterol, triglyceride, hepatic triglyceride, serum leptin, and insulin levels in Wistar mice [57].
Diabetes is a threat to man leading to stern socio-economic and high rate of mortality [95]. Herbal decoction of S. alata is commonly used in Caribbean [96], Africa [34], and India [97] for the treatment of diabetes. e marked α-glucosidase inhibitory effect and antidiabetic activities displayed by S. alata are linked to bioactive compounds such as astragalin and kaempferol-3-O-gentiobioside [31,98]. Traditionally, the leaves decoction is used in regulation of sugar level in serum [99] and enhances the defence of hepato and renal organs to oxidative stress [56]. It also reduces fasting blood glucose and improves metabolic state via activation of PKB/Akt which helps regulate glucose uptake in the liver and muscles [100]. e antidiabetic potency of acarbose, n-butanol, and ethyl acetate fractions of methanolic S. alata leaf extract was assessed via inhibitory carbohydrate digestion mechanism. e antidiabetic drug (acarbose) significantly inhibits α-glucosidase with inhibitory concentration (IC 50 , 107.31 ± 12.31 µg/ml). n-Butanol and ethyl acetate fractions displayed inhibitory activities of IC 50 , 25.80 ± 2.01 µg/ml and IC 50 , 2.95 ± 0.47 µg/ml, respectively, due to kaempferol 3-O-gentiobioside analysed by HPLC and Combiflash chromatography [31,83]. α-Amylase and α-glucosidase inhibitory potential of acetone, hexane, and ethyl acetate leaf extracts of S. alata was assessed via Lineweaver-Burk plot. Acetone extract significantly inhibited α-amylase (IC 50 � 6.41 mg/mL), while hexane displayed strong inhibition against α-glucosidase (IC 50 � 0.85 mg/mL). n-Hexane substantially reduces (p < 0.05) postprandial blood glucose in sucrose-induced rats after 2 h of treatment [101]. e reduction in the oxidative stress in the aorta and heart of streptozotoc, hyperglycemic rats was investigated by DPPH free radical scavenging and antioxidant catalase assays.
e aqueous leaf extract significantly reduced lipid peroxidation (MDA levels), blood glucose; however, it increases in the antioxidant catalase and DPPH free radical scavenging activity was observed. e reversal of oxidative stress induced by cardiac dysfunction in hyperglycemic condition justified the ethnobiological claim of the plant [102]. In a similar study, the S. alata leaf extract significantly reduces oxidative stress causing diabetes in treated mice. Prominent activities were observed in the kidney and liver. e activity resulted in critical changes in the urea, protein, creatinine, and uric acid level in the blood serum [56].

Antimalarial Activities.
Malaria is a global threat contributing to serious sociocultural and health issues in humid and tropical regions [103,104]. Chemotherapy reported the antimalarial activities of S. alata could be linked to quinones, alkaloids, and terpenes [105,106]. Quinones isolated from S. alata significantly displayed in vitro antiplasmodial activity, against Plasmodium falciparum via the microdilution test of Desjardin [107]. Terpenes isolated from S. alata leaves displayed pronounce in vitro antiplasmodial assays against P. falciparum in ethylene glycol-water fractions. Significant activity was observed at concentration below 1 µg/ml [108]. e appraisal of aqueous leaf extract justifies the ethnomedical applications of S. alata as remedy for malaria and fever. e leaf extract considerably inhibited 3D7 strain of the P. falciparum parasite in Wistar mice [109].
3.4.7. Anthelmintic Activity. Traditionally, S. alata leaf and flower decoctions are used in treatment of intestinal worm infestation and stomach disorder. e anthelmintic potency of alcoholic leaves extract of S. alata and T. angustifolia at 10 to 100 mg/ml were assessed in clinical isolates of Ascardia galli and Pheretima posthuma by observing time of paralysis and point of death of the worms. e leaves extract significantly inhibit the worms (test organisms) more than piperazine citrate (standard anthelmintic drug) [110].

Antiviral
Activities. S. alata is an indispensable bactericidal and fungicidal natural therapy. However, the justification of antiviral activities is not properly documented. e antiviral efficacy of n-hexane, ethyl acetate, butanol, and aqueous leaf extracts was assessed on dengue virus (DENV) obtained from an infected pregnant woman in Indonesia via focus assay. e extracts significantly inhibited DENV-2 with IC 50 (<10 μg/ml), CC 50 (645.8 μg/ml) and SI (64.5 μg/ ml) [111].

Toxicological Studies of S. alata
Lately, medicinal plants and herbal products have come under spotlight owing to health hazards connected to indiscriminate handling of herbs and herbal products. Several reports were published relating to the use of herbal drugs. Despite the risks ascribed to most medicinal and herbal products, the number of herbal users still increases. is initiates the appraisal of herbs in an attempt to establish their safety [116]. e S. alata leaf extract was appraised by oral administration of Wistar rats (10 g/kg weight). e acute and subacute effects were assessed in every 24 h for 14 days at different dosages (250, 500, and 1000 mg/kg). After 24 h, no significant variation was observed in the liver, urea, bicarbonate, creatinine, and kidney of the tested organisms and control [117]. Aqueous flower extract at doses of 100, 400, and 800 mg/kg was orally administered to ten Wistar rats for 28 days. No significant difference on histological sections of the lung, liver, kidney, heart, and kidney was observed during the postmortem analysis of the mice [118].
Different doses (1,000, 2,000, and 3,000 mg/kg body weight) of ethanolic leaf extract do not display any behavioural, biochemical, haematological, and histopathological variations in the tested Swiss albino mice and control after 15 days of oral administration [119]. Hydroethanolic leaf extract increased the body weight, blood level, liver homogenates, and serum index after proper monitoring of the administered rats every 48 h for 26 days. Haematological parameters assessed displayed dose-dependent response, however, no significant variation was observed in liver histopathology [120]. Alkaloids isolated from aqueous S. alata leaf extract significantly reduces alkaline phosphate, uric acid, globulin, liver and kidney body weight ratio, urea, phosphate ions, bilirubin, potassium ions, serum concentrations of albumin, creatinine, gamma glutamyl transferase, alanine transaminases, and aspartate in the liver and kidney of pregnant rats after periodic observation for 18 days. is led to variation in serum enzymes, excretory, and secretory functions of liver and kidney of the test organisms [61].
Documented toxicological appraisals of S. alata present positive information regarding its safety; however, there is need to authenticate these reports through in vitro and in vivo assessments on clinical isolate. Fresh and dried plant Evidence-Based Complementary and Alternative Medicine parts, low-dosage concentrations, test organisms of different age groups and effect on other vital organs such as brain, intestine, and bladder should be considered during toxicological appraisals of medicinal plant or products. Ethnobiological appraisals described that ulcer patients, pregnant women, and children under the age of two should avoid S. alata decoction. Also, studies should be focused on appraisals of recommended dosage, safest mode of administration, and reaction mechanisms of the metabolites in living organisms.

Limitation, Conclusion, and Future Prospects
Based on this review, further studies on S. alata have become evident. Most studies focused on lipid-soluble and volatile components; however, appraisals on metabolites prepared in hydrophilic medium are deficient. Most phytochemical studies of S. alata focused on leaves, stems, and flowers, though study on seeds and roots are lacking. Many therapeutic appraisals have been investigated in cell and animal experiments; still, there remain important tasks. ese include secondary metabolites dictating the pharmacological activities are not well stated; relatively, few studies analytically appraised the mechanisms of action of secondary metabolites; systemic toxicological studies remain ambiguous. e phytochemical appraisals revealed there is a variation in some metabolites investigated due to geographical and climatic factors. is gives room for qualitative approach to authenticate the metabolites in this plant. e plant secondary metabolites contributed to the pronounced wound healing and antibacterial and antifungal activities [92,121]. Industrially, the plant is a key ingredient in detergents (foaming and surface active agents), molluscicides and pesticides. Summarily, comprehensive ethnobiological and pharmacological activities of S. alata, limitations, and future prospects were explored which could present novel research directions.

Conflicts of Interest
e authors declare that they have no conflicts of interest.