Kigelia africana

Kigelia africana (Lam.) Benth. — The Sausage Tree

1. Identity, Botanical Classification, and Natural Source

Accepted scientific name: Kigelia africana (Lam.) Benth. The genus Kigelia consists of only one species, Kigelia africana, synonymous with Kigelia pinnata, which occurs throughout tropical Africa and is cultivated elsewhere in the tropics. Additional historical synonyms include Bignonia africana Lam., Tecoma africana (Lam.) G.Don, Crescentia pinnata Jacq., Kigelia abyssinica A.Rich., Kigelia aethiopica Decne., and Kigelia aethiopum (Fenzl) Dandy.

Family: Bignoniaceae. Kigelia is generally considered to be a highly variable monospecific genus of the family Bignoniaceae. The genus name Kigelia is based on an African name, while africana means "from Africa." The genus Kigelia has one species and occurs only in Africa.

Common names: English: sausage tree; Afrikaans: worsboom; Zulu: umVunguta, umFongothi; North Sotho: Modukguhlu; Venda: Muvevha. Among Kenyan ethnic groups, additional vernacular names include Muratina (Kikuyu and Meru), Muatini and Kiatine (Kamba), Hwasini and Mvongonia (Teita), Ol-Suguroi and Ol-Darpoi (Masai), Yago (Luo), and Morabe (Kakamega).

Botanical description: K. africana is a large tree, growing to 20 m in height, and widely used for the treatment of a wide range of diseases and conditions in addition to its use as an agroforestry plant. The rough, pinnate-compound, yellowish-green leaves grow to 8 inches long, each with 3–8 leaflets. The inflorescence is a pendant panicle (3–6 feet long) of wrinkled, bell-shaped, dark red flowers with 5 lobes each. Flowers have abundant nectar and a fetid aroma, opening at night and pollinated primarily by bats, as well as hawk moths and birds. The flowers are followed by woody, gray-brown fruits, up to 24 inches long and 4 inches in diameter, which look like very large sausages suspended vertically on long stems. Ripe and unripe fruits are poisonous, causing formation of blisters in the mouth and on the skin.

Geographic distribution: Kigelia africana, commonly called sausage tree, is native to riverbanks, floodplains, open woodlands, and savannas from sub-Saharan central Africa to South Africa. Its tropical African range extends from Eritrea and Chad south to northern South Africa, and west to Senegal and Namibia.

Plant parts used as sources of extract: All parts of the tree — fruit, bark (stem and root), leaves, seeds, wood, and roots — have been used in traditional medicine and subjected to scientific investigation. Whilst the fruits are most often cited in pharmacological studies, other plant parts are also used in herbal preparations.

Common forms and preparations: Historically, parts of the sausage tree have been used in a variety of applications, including herbal medicines for treating infections, wounds, and digestive/respiratory problems; treatment of ulcers, sores, and syphilis; and skin ointments from fruit extracts. In scientific research, extracts are produced using water, methanol, ethanol, ethyl acetate, chloroform, hexane, dichloromethane, and butanol as solvents, each yielding different phytochemical profiles. Commercially available products have been formulated from K. africana, though many have not been fully standardized.

2. Traditional and Historical Uses

Kigelia africana has been used in the management of human ailments since time immemorial. Ethnobotanists have documented the traditional uses of K. africana, which include treatment of skin disorders, cancer, and gynecological complaints, among others. The preparation and use of K. africana plant parts in traditional medicine differs across and within communities. Despite the differences in preparation and application, there is still a lot of overlap, with similar uses appearing in different regions or countries. Kigelia africana has interested many ethnobotanists and cultural anthropologists across the world who have intensively engaged in documenting its uses in several communities.

Ethnopharmacological studies have revealed the therapeutic relevance of various preparations from different K. africana parts to treat a wide range of skin complications, dysentery, constipation, wounds, ulcers, gonorrhoea, rheumatism, and abscesses.

Traditional uses reported across sub-Saharan Africa span an extraordinarily wide range of conditions:

• Skin disorders: Most traditional healers use the plant to treat a wide range of skin ailments, including fungal infection, boils, psoriasis, and eczema. Topical preparations from the fruit pulp were applied directly to affected areas.
• Digestive complaints: Roots, bark, leaves, and fruits were used to alleviate diarrhea, stomachaches, and to act as laxatives. The fruits, pickled in vinegar, are used as an appetizer, against constipation, and to remove kidney stones.
• Infections and sexually transmitted diseases: In African folk medicine, K. africana is used for the treatment of dysentery, venereal diseases, and as a topical application on wounds and abscesses. In the area around Nsukka, Nigeria, the bark is used for the treatment of venereal diseases.
• Internal parasites and infections: Internal applications include treatments for dysentery, ringworm, tapeworm, post-partum haemorrhage, malaria, diabetes, pneumonia, and toothache.
• Wounds and abscesses: In Africa, K. africana, Hypoxis hemerocallidea, and Senecio serratuloides leaves and roots decoction is used to treat sexually transmitted infections and sores. In Uganda, Spathodea campanulata bark mixed with K. africana fruits is used as a dressing for wounds and in the treatment of various skin diseases.
• Polyherbal combinations: K. africana is traditionally considered potent; some traditional medicine preparations involve using K. africana in combination with other medicinal plants or mollusks, like snails, or other foods.
• Food use: The leaves provide nutritional support, and seeds can be consumed during famines.
• Cultural and spiritual use: Kigelia africana holds significant cultural and spiritual importance for many African communities. The tree is held to be sacred, and the fruits are widely traded in local markets as talismans thought to bring good luck.

An ethnobotanical survey in Benin (West Africa) conducted across 26 municipalities with 1,210 participants documented local use patterns, finding that socio-cultural group, gender, level of education, and age group have a significant influence (p ≤ 0.05) on levels of knowledge and use of K. africana organs.

3. Phytochemistry: Key Constituents and Active Compounds

Phytochemical analysis of Kigelia africana subsp. africana has revealed the presence of approximately 145 compounds extracted from different parts of the plant. A complementary review in the Journal of Ethnopharmacology (2016) put this figure slightly higher: approximately 150 compounds have been characterized from different parts of the plant. Iridoids, naphthoquinones, flavonoids, terpenes, and phenylethanoglycosides are the major classes of compounds isolated.

Overall, more than 150 secondary metabolites — including naphthoquinones, iridoids, flavonoids, coumarins, terpenes, terpenoids, and steroids — have been reported in K. africana extracts. Iridoids were found to be the major chemical compounds in K. africana.

3.1 Iridoids

The major iridoids found in the root and stem bark have been identified as catalpol derivatives esterified with phenylpropanoic acid derivatives at C-6, and identified as specioside, verminoside, minecoside, and norviburtinal. These iridoid glycosides are considered particularly important for the plant's anti-inflammatory and antiparasitic activities. Chemical analysis of a polar extract of fruit from K. africana indicated the presence of verminoside, an iridoid, as a major constituent, and of a series of polyphenols such as verbascoside.

3.2 Naphthoquinones

Monoterpenoid naphthoquinones (pinnatal, isopinnatal, kigelinol, and isokigelinol) are unique to K. africana. Ethanolic extracts have been shown to contain the aromatic monoterpenes pinnatal, isopinnatal, kigelinol, and isokigelinol. Benzene root extracts have been shown to contain the steroids stigmasterol and β-sitosterol, the naphthoquinone lapachol, 6-methoxymellein, and kigelin. Wood benzene extracts have been isolated that contain naphthoquinones kigelinone, lignan kigeliol, lapachol, and dehydro-α-lapachone. From the root and its bark, the usual plant substances stigmasterol, β-sitosterol, ferulic acid, the naphthoquinones lapachol, 6-methoxymellein, and two new phenolic compounds have been isolated. Kigelin is the main component of the plant (mp 144°C, molecular formula C₁₂H₁₄). A minor component, 6-methoxymellein (mp 76–77°C, molecular formula C₁₁H₁₂O₄), has been elucidated.

3.3 Flavonoids, Phenolic Acids, and Polyphenols

Analyses of K. africana fruit extracts (ethanol, hexane, ethylacetate, butanol, and aqueous) have been shown to contain flavonoids, alkaloids, carbohydrates, tannins, glycosides, phenols, sterols, and saponins. Root, wood, and leaf extracts contain kigelinone, vernolic acid, kigelin, luteolin, 6-hydroxyluteolin, and various iridoid derivatives. Verbascoside, a phenylpropanoid glycoside (phenylethanoglycoside), is found alongside verminoside in polar fruit extracts and has demonstrated antioxidant and antimicrobial properties. Novel compounds with potent antioxidant, antimicrobial, and anticancer effect such as verbascoside, verminoside, and pinnatal, among others, have been identified.

3.4 Steroids, Terpenes, and Other Constituents

The leaf and stem bark of K. africana were reported to contain tannins in varying amounts, steroids, saponins, glycosides, and carbohydrates. The major constituents of leaf and flower oils are non-terpenes hexadecanoic acid, ethyl limonene, and the monoterpene α-pinene. A rapid evaporative ionization mass spectrometry (REIMS) characterization of the fruit identified 78 biomolecules, including phenols, fatty acids, and phospholipids. The methanolic leaf and fruit extract (KAE) was found to contain molecules including cholesterol sulfate, lignoceric acid, embelin, isostearic acid, linoleic acid, and 9-octadecenamide (oleamide), among others.

3.5 Distribution of Phytochemicals Across Plant Parts

Iridoids and quinones have been identified in all plant parts. The stem bark has a higher diversity of phytochemicals compared to other plant parts. Alkanes are common in the leaves. Not much has been done to identify phytochemicals in Kigelia flowers, which relates to their relatively low degree of usage in traditional medicine preparations.

4. Mechanisms of Action

4.1 Anti-inflammatory Mechanisms

In vitro assays showed that verminoside had significant anti-inflammatory effects, inhibiting both iNOS expression and NO release in the LPS-induced J774.A1 macrophage cell line. The anti-inflammatory effects of Kigelia africana are attributed to its active compounds, such as verminoside, which inhibit inflammatory mediators like iNOS and NO. The ethanolic extract has shown significant analgesic and anti-inflammatory properties in studies. At a broader level, the anti-inflammatory activity of K. africana has been proposed to act by suppressing inflammatory mediators. Research has ascertained this activity through inhibition of ROS (antioxidant activity), 15-LOX, NO, COX-2, proinflammatory cytokines, and anti-inflammatory cytokines to enhance understanding of the possible mechanisms of activity against inflammation.

4.2 Anticancer / Cytotoxic Mechanisms

Some studies have identified unique compounds such as 2-(1-hydroxyethyl)-naphtho[2,3-b]furan-4,9-dione, lapachol, kigelin, demethylkigelin, and ferulic acid as potent cytotoxins within K. africana extracts, suggesting possible mechanisms involving DNA damage, mitochondrial disruption, and reactive oxygen species (ROS) generation. These phytoconstituents, particularly naphthoquinones and iridoids, likely underpin many of the observed antiproliferative effects. In a study of breast cancer cell lines, BCL-2, EGFR, HER-2, and TP53 proteins/receptors were targeted.

4.3 Antimicrobial Mechanisms

The iridoids and naphthoquinones have been shown to display antibacterial activity and the ability to inhibit the growth of yeasts. The mechanisms underlying these effects likely involve disruption of bacterial cell membranes and interference with cell-wall biosynthesis, consistent with the general action of naphthoquinones, though precise mechanistic studies specific to K. africana constituents remain limited.

4.4 Antidiabetic Mechanisms

Both the aqueous extract and ethyl acetate fraction of the aqueous extract exhibited dose-dependent inhibition of alpha-amylase activity. At a concentration of 500 μg/mL, the aqueous extract caused an alpha-glucosidase inhibition of 64.10 ± 2.7%, with an estimated IC50 of 193.7 μg/mL, while the ethyl acetate fraction had an inhibition of 89.82 ± 0.8% and an estimated IC50 of 10.41 μg/mL. The K. africana fruit fraction demonstrated significant alpha-glucosidase inhibitory activity, while its alpha-amylase inhibitory activity was limited. This study suggests a potential natural alpha-glucosidase inhibitor and phytocompounds that could serve as leads for developing antidiabetic agents.

4.5 Antiparasitic Mechanisms

The antitrypanosome activity of the stem bark and root bark extracts is attributed to 2-(1-hydroxyethyl)-naphtho-[2,3-b]-furan-4,9-quinone and three naphthoquinoids: isopinnatal, kigelinol, and isokigelinol. Lapachol in the methanol extract of the root and a quinone obtained from the wood showed antimalarial activity.

5. Scientific Evidence by Area of Use

5.1 Anti-inflammatory and Analgesic Activity

Evidence strength: Moderate in vitro; limited in vivo (animal); no human/clinical trials.

Pharmacological investigations confirm the anti-inflammatory, analgesic, antioxidant, and anticancer activity of extracts from different parts of the plant. A published study in the Journal of Natural Products (Picerno et al., 2005) evaluated verminoside from a polar fruit extract: in vitro assays showed that verminoside had significant anti-inflammatory effects, inhibiting both iNOS expression and NO release in the LPS-induced J774.A1 macrophage cell line. Cytotoxicity and cutaneous irritation of the extract and of verminoside and verbascoside were investigated. The crude extract and verminoside did not affect cell viability in vitro either in cells grown in monolayers or in the reconstituted human epidermis (RHE, 3D) model; neither caused release of pro-inflammatory mediators or histomorphological modification of the RHE.

A subsequent PMC-indexed study assessed anti-inflammatory activity by testing methanolic and aqueous fruit extracts: the methanolic extract of K. africana fruits combined with Spathodea campanulata leaves (SPK04), the K. africana aqueous fruit extract (KFM02), and the K. africana acetone fruit extract (KFM05) were subjected to antioxidant and anti-inflammatory assays. Antioxidant activity was evaluated using the ABTS radical scavenging assay, and the MTT cell viability assay was used for cytotoxicity. The extracts were assayed for 15-LOX and COX-2 enzyme activity using an ELISA method. Nitric oxide (NO) inhibitory effect of the extracts was evaluated and measurement of proinflammatory cytokines (IL-1β, TNF-α, and IL-6) and the anti-inflammatory cytokine IL-10 was done using ELISA kits. The authors recommended further research to isolate, identify, and characterize the bioactive compounds responsible for the activities. Taken together, anti-inflammatory evidence is compelling at the cellular level but no controlled human clinical trials have been conducted.

5.2 Anticancer / Cytotoxic Activity

Evidence strength: Preliminary; exclusively in vitro (cell line) and limited animal studies; no human clinical trials.

Higgins and colleagues investigated the cytotoxic activity of K. africana fruit extracts against melanoma and two breast cancer cell lines. They used a bioactivity-driven separation approach to identify demethylkigelin, kigelin, ferulic acid, and 2-(1-hydroxyethyl)-naphtho[2,3-b]furan-4,9-dione as the compounds thought to be responsible for the cytotoxicity. Of these, 2-(1-hydroxyethyl)-naphtho[2,3-b]furan-4,9-dione was a particularly potent cytotoxic agent. Potent antiproliferative activity against the Caco-2 and HeLa carcinoma cell lines was noted for K. africana methanolic fruit extracts.

One study systematically evaluated K. africana fruit extract (KAE) in an in vitro model of HT-29 colorectal carcinoma cells, focusing on its cytotoxic effects, mechanistic impact on protein expression, and synergy with cisplatin chemotherapy. Across 42 oncology-related proteins covering cell survival, apoptosis, adhesion, invasion, and signaling, KAE demonstrated extensive but typically moderate modulation, while cisplatin produced more pronounced responses in most markers. Protein changes linked to metastasis, therapy resistance, and survival were broadly suppressed. Notably, co-treatment with KAE and cisplatin in HT-29 cells resulted in marked synergistic cytotoxicity, permitting lower cisplatin doses while maintaining efficacy.

Various solvent fractions (methanol, dichloromethane, ethyl acetate) from both fruit and stem bark have shown marked inhibition of cell growth in models ranging from breast (MDA-MB-231), melanoma, to primary hepatocellular carcinoma (HepG2) and choriocarcinoma. A 2024 PLOS ONE study characterizing the gene expression and anticancer evaluation using MDA-MB-231 and MCF-7 breast cancer cell lines found that the extract modulated key targets including BCL-2, EGFR, HER-2, and TP53 proteins/receptors via a long-timescale docking procedure.

Despite this body of cell-line data, the current state of evidence has significant limitations. There are few reports regarding the IC50 of K. africana on normal cells, leaving open the question of whether the species is selectively toxic to cancer cells when taken as a remedy. There is a need to do more in vivo studies regarding the biological activity of K. africana, as this would provide a clearer picture of pharmacokinetics and pharmacodynamics. Several researchers have concluded that if a plant has a cytotoxic effect it has anticancer properties, which may not be correct. It is only after positive clinical trials for cancer treatment that any substance or compound can be confirmed anticancer.

5.3 Antimicrobial and Antifungal Activity

Evidence strength: Moderate in vitro; no human clinical trials.

The iridoids and naphthoquinones have been shown to display antibacterial activity and the ability to inhibit the growth of yeasts. Considerable in vitro cytotoxicity has been demonstrated by extracts of the fruits and barks. In studies of antifungal activity, the methanol, water, and ethyl acetate extracts showed broad growth inhibitory activity against 75% of the fungi tested. Only P. chrysogenum was resistant to all the extracts. Fruit extracts have also been reported to inhibit the opportunistic yeast Cryptococcus neoformans, and the chloroform extract exhibited substantial antileishmanial activity against Leishmania donovani.

5.4 Antiparasitic Activity (Malaria, Trypanosomiasis, Amoebiasis)

Evidence strength: Preliminary in vitro; limited in vivo animal data; no human clinical trials.

Three iridoids — specioside, verminoside, and minecoside — isolated from the butanol extract of the stem bark possess antiamoebic activity. It was found that verminoside has two-fold antiamoebic activity compared to the standard drug metronidazole, while specioside showed comparable activity with metronidazole.

Akeng'a Ayuko et al. investigated the antiplasmodial activity of K. africana chloroform, methanol, and ethyl acetate extracts against two P. falciparum strains — chloroquine-sensitive P. falciparum from Sierra Leone (D-6) and chloroquine-resistant P. falciparum from Vietnam (W-2) — using chloroquine as a positive control and an in vitro semiautomated microdilution assay technique. A study also explored the interaction between Kigelia africana compounds and antimalarial drugs like artemether and quinine, revealing potential synergistic effects against multidrug-resistant Plasmodium falciparum strains.

The hexanes and the chloroform extracts of K. africana exhibited inhibitory activity against the pathogenic parasite Trypanosoma brucei; the ethyl acetate extract showed the same activity. No in-human studies exist for antiparasitic applications.

5.5 Antidiabetic Activity

Evidence strength: Preliminary; predominantly animal and in vitro data; no human clinical trials.

The claims by traditional herbal medicine practitioners that Kigelia africana has bioactivity against diabetes mellitus were investigated in one study, in which Type I diabetes was induced in mice by intraperitoneal administration of alloxan monohydrate, followed by treatment with aqueous and ethyl acetate leaf extracts of K. africana. The data appear to support the hypoglycemic effects of K. africana, validating its folkloric usage.

A separately published study (Kumar et al.) tested the methanolic flower extract in streptozotocin (STZ)-induced diabetic Wistar rats: the flower extract and glibenclamide were administered orally at doses of 250 and 500 mg/kg body weight for 21 days. Daily oral treatment with the extract and standard drug for 21 days significantly reduced blood glucose, serum cholesterol, and triglyceride levels. High-density lipoprotein-cholesterol level was found to be improved (P < 0.01) compared to the diabetic control group. The authors concluded that K. pinnata flowers extract has significant antidiabetic and hypolipidemic effect.

At the mechanistic level, an in vitro enzyme inhibition study found that at a concentration of 500 μg/mL, the aqueous extract caused an alpha-glucosidase inhibition of 64.10 ± 2.7% with an estimated IC50 of 193.7 μg/mL, while the ethyl acetate fraction had inhibition of 89.82 ± 0.8% and an estimated IC50 of 10.41 μg/mL. All antidiabetic data remain pre-clinical.

5.6 Wound Healing Activity

Evidence strength: Preliminary; in vitro cell-line data; one notable 2023 study using human cell lines; no controlled human clinical trials.

A 2023 study published in the Journal of Wound Care investigated whether a methanolic extract prepared from Kigelia africana (KAE) could promote wound healing in treated human normal epidermal keratinocyte (HaCaT) cells and human normal foreskin fibroblast cell line (BJ) cells compared with untreated cells. Experimental steps included the methanolic extraction of the leaf and fruit of the plant, preparation of HaCaT and BJ cell lines, cell culture with a stable tetrazolium salt-based proliferation assay, and evaluation of the wound healing effect of KAE at 2 μg/mL.

KAE effected faster wound healing in treated cells compared with untreated cells for both cell lines. HaCaT cells that had been mechanically injured and treated with KAE healed completely in 48 hours compared with 72 hours for untreated HaCaT cells. Treated BJ cells healed completely in 72 hours compared with 96 hours for untreated BJ cells. Concentrations of KAE up to 300 μg/mL had a very low cytotoxic effect on treated BJ and HaCaT cells. The experimental data in this study support the potential of KAE-based wound healing treatment to accelerate wound healing. This study used in vitro human cell lines, not human subjects; clinical confirmation is absent.

An in vivo wound contraction model also showed that extracts of K. africana (7.5% w/w) showed significant wound contraction (P < 0.05) on day 7 with a wound closure of 72%.

5.7 Antioxidant Activity

Evidence strength: Moderate in vitro; no human clinical data.

Phytochemical analyses indicated the presence of bioactive constituents, including flavonoids and phenolic acids, suggesting that the extracts of K. africana can interfere with reactive oxygen species-induced oxidative stress, inflammation, and microbial growth. Kigelia africana is a West African medicinal plant traditionally used to treat or alleviate various medical conditions such as skin ailments, respiratory disorders, and digestive problems. Radical scavenging assays (ABTS and related methods) have consistently demonstrated antioxidant activity across fruit, leaf, and bark extracts, but no human trial data are available.

5.8 Antiurolithic Activity

Evidence strength: Preliminary; pre-clinical only.

Bioactive extracts of the plant possess anti-inflammatory, antioxidant, antimicrobial, antidiabetic, antineoplastic, and anti-urolithic activities. The anti-urolithic (kidney stone-inhibiting) activity has been documented in pre-clinical models, consistent with traditional use of pickled fruits against kidney stones, but no clinical evidence has been generated.

5.9 Skin Care and Cosmeceutical Applications

Evidence strength: Marketed commercially; in vitro safety data available; no controlled clinical efficacy trials identified in peer-reviewed literature.

The effect of K. africana in the maintenance of skin has been recognized, resulting in a handful of skin formulations on the market. Kigelia africana is a plant used in Africa for anti-inflammatory, anti-microbial, and anti-skin-aging effects. The dermal safety of verminoside-containing fruit extract was assessed in both monolayer and 3D reconstituted human epidermis models, and found to be without significant cytotoxicity or pro-inflammatory effects at tested concentrations, providing a regulatory-relevant safety rationale for topical application.

6. Body Systems Associated with Kigelia africana

• Integumentary (skin): Wound healing, dermatitis, boils, eczema, psoriasis, skin infections, anti-aging formulations.
• Immune and inflammatory: Suppression of iNOS, NO, COX-2, 15-LOX, IL-1β, TNF-α, IL-6.
• Oncological (in vitro): Cytotoxicity against melanoma, breast cancer, colorectal carcinoma, renal carcinoma, hepatocellular carcinoma, rhabdomyosarcoma, and HeLa cells.
• Gastrointestinal: Antidiarrheal, laxative, antiamoebic, and digestive applications.
• Metabolic / endocrine: Alpha-glucosidase inhibition, hypoglycemic effects in animal models, hypolipidemic effects.
• Antimicrobial / antiparasitic: Activity against bacteria, fungi (including yeasts), Plasmodium falciparum, Trypanosoma brucei, Leishmania donovani, and Entamoeba histolytica.
• Urinary tract: Anti-urolithic activity; traditional use for kidney stones.
• Reproductive and gynecological: Traditional use for gynecological complaints, venereal diseases, and post-partum haemorrhage.

7. Dosage Forms and Dosages Reported in Studies

No standardized therapeutic dose of K. africana for human use has been established by any regulatory authority. The following dosages are drawn exclusively from peer-reviewed pre-clinical studies and are reported as found in the cited literature; they do not constitute recommendations.

• Antidiabetic (in vivo, rodent): The flower extract and glibenclamide (positive control) were administered orally at doses of 250 and 500 mg/kg body weight for 21 days in streptozotocin-induced diabetic rats.
• Wound healing (in vitro, human cell lines): The wound healing effect of KAE was evaluated at 2 μg/mL in BJ and HaCaT cells. Concentrations of KAE up to 300 μg/mL had a very low cytotoxic effect on treated BJ and HaCaT cells.
• Alpha-glucosidase inhibition (in vitro): At a concentration of 500 μg/mL, the aqueous extract caused an alpha-glucosidase inhibition of 64.10 ± 2.7%.
• Wound contraction (in vivo, animal model): Extracts of K. africana at 7.5% w/w showed significant wound contraction on day 7 with a wound closure of 72%.
• Acute oral toxicity threshold (rat): The methanolic fruit extract was tolerated well in male Sprague-Dawley rats at doses up to 400 mg/kg, but higher doses (6,400 mg/kg) led to toxicity symptoms and 60% mortality, with an estimated LD50 of 3,981.07 mg/kg.
• Chronic toxicity (rat, fruit): To evaluate the acute and chronic toxicity of the aqueous extract of K. africana fruit in Wistar albino rats, the aqueous extract was administered orally to rats at doses of 50 and 500 mg/kg body weight for the test of chronic toxicity; a group received 2,000 mg/kg for the acute toxicity test.

8. Safety Considerations

8.1 Raw Fruit Toxicity

The fruit is poisonous for humans when raw, but is also made into an alcoholic drink by tribes in Kenya. Ripe and unripe fruits are poisonous, causing formation of blisters in the mouth and on the skin. This acute oral toxicity of the raw fruit is well-established and distinct from processed or standardized extracts.

8.2 Acute and Subacute Toxicity in Animal Studies

In vitro, Kigelia africana bark and fruit were able to protect red cell membranes against heat- and hypotonicity-induced lysis. Oral acute toxicity assays did not show any mortality at 5 g/kg of plant extracts. The results indicated that the methanolic extracts of different plant parts of K. africana had no adverse effect on hematology of rats at sub-acute dosing and are safe at those doses.

The bark of Kigelia africana has been assessed as safe because the LD50 of the products is above 5,000 mg/kg. Weekly use of bark extracts revealed hepato- and cardio-protective activities. A drop in the percentage of urea and creatinine in administered rats was observed, as well as a gain in the percentage of blood platelets in the treated rats. These results showed that bark extracts did not generate any damage during the study period at the different doses studied.

Conversely, a study of the aqueous fruit extract in rats at doses of 100, 200, and 400 mg/kg/day found that the fruits of the plant given to experimental rats at doses of 100, 200, and 400 mg/kg/day orally were toxic but not fatal; the toxicity was characterized by lower body weight gain and tissue alterations. There were alterations in liver and kidney. No significant lesions were observed in the heart or spleen of the test rats. At the highest doses tested, the highest dose of the aqueous extract of K. africana fruit may have some hepatorenal toxic effects.

8.3 Cytotoxicity Profile

There are few reports regarding the IC50 of K. africana on normal cells, which leaves open the question of whether this species is selectively toxic to cancer cells when taken as a remedy. Importantly, the crude extract and verminoside did not affect cell viability in vitro either in cells grown in monolayers or in the reconstituted human epidermis (RHE, 3D) model, and neither caused release of pro-inflammatory mediators or histomorphological modification of RHE, at least at the concentrations studied by Picerno et al. (2005). Higher-concentration or high-dose scenarios have not been systematically characterized in humans.

8.4 Absence of Clinical Pharmacovigilance Data

Although many in vitro efficacy studies of K. africana have been reported by several researchers, more work needs to be done to clinically prove K. africana's efficacy in vivo before clinical applications. Many of its traditional medicinal uses have not been investigated scientifically. Further probing of the existing research on its pharmacological activity is recommended with the end-goal of unravelling the pharmacodynamics, pharmacokinetics, clinical relevance, and possible toxicity and side effects of both the extract and the active ingredients isolated. No formal pharmacovigilance system for K. africana preparations exists, and no drug interaction studies in humans have been published.

8.5 Ecological Toxicity Note

A study in aquatic organisms found that the aqueous bark extract of K. africana caused significant behavioral changes in juvenile Nile tilapia (Oreochromis niloticus). Haematological indices of the fish were affected with increasing extract concentration. Histology of the liver and gills showed variations in distortions and damages to the tissues, with severity increasing with increasing extract concentrations. This raises environmental disposal concerns for processing facilities but is not directly relevant to human supplemental use.

9. Summary of Evidence Landscape

K. africana has a rich body of in vitro efficacy studies reported by several researchers, but more work needs to be done to clinically prove its efficacy in vivo before clinical applications can be made. Despite many efforts by researchers to scientifically validate traditional uses of K. africana, many remain merely claims, underscoring the need to conduct more research, scientifically validate other traditional uses, isolate new bioactive phytochemicals, and standardize K. africana products. Its antimicrobial, antidiabetic, and anticancer activities are supported by diverse secondary metabolites that warrant further investigation. Continued research is essential for establishing safe and effective applications of the plant in modern medicine, including clinical trials.

In summary, as of the available published literature, K. africana has a well-documented phytochemical profile and a growing body of in vitro and animal-model data supporting anti-inflammatory, antimicrobial, antidiabetic, cytotoxic, and wound-healing activity. However, controlled human clinical trials are entirely absent. All pharmacological conclusions regarding therapeutic efficacy in humans remain provisional, and the toxicological profile — particularly of raw fruit preparations — warrants appropriate caution.

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