Evaluation of six plant species used traditionally in the treatment and control of diabetes mellitus in South Africa using in vitro methods

Figures & data

Table 1. Plant species used to treat diabetes mellitus in the Newcastle region (Kwa-Zulu Natal).

Family	Scientific name	Local name	Parts used and mode of preparation
Caesalpiniaceae	Senna alexandrina Mill. (Cassia angustifolia Vahl.)	Senna leaves	Leaves are boiled in water and taken orally
Poaceae/Gramineae	Cymbopogon citratus Stapf.	Isiqunga (lemon grass)	An infusion of the whole plant in water
Curcuribitaceae	Cucurbita pepo L.	Intshunga (pumpkin leaves)	Infusion of the upper parts (leaves and stem) in water taken orally
Loganiaceae	Nuxia floribunda Benth.	Umlulama (forest elder)	Infusion of bark and roots in water taken orally
Hypoxidaceae	Hypoxis hemerocallidea Fisch. & Mey.	Inongwe (African potato)	Infusion of the corms boiled in water and taken orally
Lauraceae	Cinnamomum cassia Blume	Cinnamon	Infusion of the bark in water taken orally

Table 2. Published information on the six identified plants.

Plant	Description	Ethnomedical use	Use in diabetes	Describe mechanism
S. alexandrina	Shrub, about 1 m, has yellow flowers and papery pods containing six to eight seeds (Watt & Breyer-Brandwijk, 1962). Indigenous to hot barren regions and cultivated commercially in the Middle East	The plant is used medicinally in Mozambique as a purgative (Watt & Breyer-Brandwijk, 1962)	Although the plant is believed to have anti-diabetic activity, no specific activity has been quantified (Watt & Breyer-Brandwijk, 1962)	Non applicable
Cymbopogon  citratus	An aromatic tropical grass with clumped, bulbous stems that gives origin to the leaf blades. This plant is native to Asia (Sri Lanka, Indochina, etc.) (Watt & Breyer-Brandwijk, 1962)	Used to treat athlete’s foot, and is helpful in treating coughs, cuts, asthma, bladder disorders and headaches (Watt & Breyer-Brandwijk, 1962). Extract also have the ability to reduce serum cholesterol levels in vivo (Agbafor & Akubugwo, 2007)	Aqueous leaf extracts in animal models had the ability to lower fasting plasma glucose levels dose-dependently (Adeneye & Agbaje, 2007). The most significant hypoglycemic effect is seen at the oral dose of 500 mg/kg/ per day of the extract (Adeneye & Agbaje, 2007)	The fresh leaf aqueous extract is able to lower fasting plasma glucose dose-dependently (Adeneye & Agbaje, 2007; Leite et al., 1986)
Cucurbita pepo	Has a long prickly stem bears large downy leaves and deep yellow colored funnel-shaped flowers and it bears orange fruit containing numerous flat white seeds (Watt & Breyer-Brandwijk, 1962). This plant is endemic to Americas (Mexico) (Smith, 1997)	The seeds are used to treat the prostate gland and the oil from the seeds is used in the treatment of urinary ailments (Watt & Breyer-Brandwijk, 1962)	Pumpkin seed and fruit reduce blood glucose levels in type II diabetic patients at 30 g of pumpkin powder/person (Caili & Quanhong, 2006; Quanhong et al., 2005). The fruit and seeds of pumpkin have hypoglycemic activity in normal and alloxan-induced rats and rabbits (Peng, 2002; Zhang, 2001). The activity of pumpkin leaves is yet to be investigated	The protein bound polysaccharide isolated from pumpkin increases levels of serum insulin, reduces glucose levels and improve glucose tolerance in vivo albeit at very high dose (Quanhong et al., 2005).
N. floribunda	A small to medium sized tree 3–10 m tall and has sweetly scented cream-white flowers small in size, around 3 mm long-cymose panicles. This plant is endemic to southern and central tropical Africa (Von Breitenbach, 1965).	The forest elder has a number of uses as traditional Zulu medicine. Several parts of the plant are used to an array of ailments from coughs to colds and influenza (Hutchings et al., 1996)	No literature	Not applicable
H. hemerocallidea	This plant is a tuberous perennial plant with strap-like leaves and bright yellow star-shaped flowers. The leaves are up to 400 mm long. The lower surface of leaves is densely hairy. It is endemic to southern Africa (Eastern cape, Free state, KwaZulu-natal, Mpumalanga, Gauteng, and Limpopo) and occurs in open grassland and woodlands (Watt & Breyer-Brandwijk, 1962).	It is used by the Botswana people as a charm against thunder and storms (Watt & Breyer-Brandwijk, 1962). Traditional western ailments treated include urinary infections, hypertension, testicular tumors, and HIV/AIDS	In vivo rodent studies showed the aqueous plant extract to possess anti-diabetic agent (Drewes et al., 1984; Mahomed & Ojewole, 2003; Ojewole, 2002, 2006)	This plant’s aqueous extract causes a significant reduction in blood glucose levels through the stimulation of insulin which enhances the cellular uptake and utilization of glucose (Drewes et al., 1984; Mahomed & Ojewole, 2003; Ojewola, 2002 2006)
Cinnamomum cassia	A slender evergreen tree that grows up to 20 m high. Young branches are smooth and brown. It has small white flowers and green fleshly fruits with one seed and turns dark purple or black when mature. This plant is endemic to China (Barceloux, 2009)	Used as an astringent, germicide, chronic bronchitis and many other ailments (Barceloux, 2009, Table 1)	The efficacy of Cinnamomum cassia has been proven in several clinical trails suggesting its effectiveness in lowering plasma glucose levels in patients (Dugoua et al., 2007; Khan et al., 2003; Mang et al., 2006; Pham et al., 2007)	It has been reported that bark extracts of Cinnamomum cassia contains an insulin-like peptide, cinnanaldehyde known to inhibit aldose reductase and is more active than other derivatives of the compound (Lees, 2002)

Table 3. The inhibition of α-amylase activity (%) and EC₅₀ (mg/ml) for each of the solvents used in this study at the minimum and maximum doses.

Solvents	Acetone		Methanol		Ethyl acetate		Hexane
concentrations (mg/ml)	Emax	EC50 (mg/ml)	Emax	EC50 (mg/ml)	Emax	EC50 (mg/ml)	Emax	EC50 (mg/ml)
Acarbose in water	84.06	0.56	84.06	0.56	84.06	0.56	84.06	0.50
H. hemerocallidea	59.62	0.92	52.33	1.32	87.82	0.29	54.00	0.960
Cymbopogon citratus	88.21	0.65	88.07	0.31	44.81	1.2	34.99	1.30
Cinnamomum cassia	0	>1	100.88	0.12	0	>1	99.93	0.72
Cucurbita pepo	35.10	1.82	0	>1	0	>1	72.29	0.70
N. floribunda	0	>1	0	>1	37.91	1.6	55.11	0.88
S. alexandrina	0	>1	0	>1	0	>1	97.10	0.083

EC₅₀, concentration that produces 50% of the maximum response. E_max, maximum inhibitory activity (100% is maximum inhibition).

Table 4. The glucose quantity (mg) present after treatment of intestinal rat acetone powder and the α-glucosidase inhibitory activity (%) of different extracts of six plants used to treat and manage diabetes.

Plant species	Glucose quantity (%)^a				Inhibition (%)^b
	Ethyl acetate	Hexane	Methanol	Acetone	Ethyl acetate	Hexane	Methanol	Acetone
Acarbose	<0.0001	<0.0001	<0.0001	<0.0001	100	100	100	100
Cucurbita pepo	0.004	0.018	0.297	0.654	99.56	98.24	70.30	34.58
Cinnamomum cassia	0.004	0.126	1.066	0.624	99.64	87.38	NA^c	61.27
S. alexandrina	0.009	0.021	0.387	0.350	99.09	97.93	61.27	65.04
N. floribunda	0.005	<0.00001	0.871	0.659	99.53	100	12.85	34.11
H. hemerocallidea	0.052	0.010	0.414	0.156	94.83	99.01	58.61	84.35
Cymbopogon citratus	0.050	<0.0001	0.546	0.294	95.02	100	45.42	70.55

NA, no activity.

^aAmount of glucose produced was calculated as: glucose (mg): y = (17.75x + 0.0162) × 10 (y = OD; x = concentration (mg); 10 = dilution factor made in sample preparation). Values are means of n = 3.

^bPercentage inhibition was calculated as follows: inhibitory activity (%) = (100 − G_a), G_a is the percentage amount of glucose that was left over after the reaction was stopped.

^cNA, not detectable (active).

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