Evaluation of ethnomedical claims: Antiplasmodial and anti-hyperglycaemic activities of Gongronema latifolium root and stem

The combined root and stem of Gongronema latifolium Benth & Hook (Asclepiadaceae) is used in Africa for malaria and diabetes and its leaves as spice. Activity-directed fractionation to identify the active constituent(s) and justify these ethnomedicinal uses in Nigeria was done. Combined root and stem methanolic extract (GL), its vacuum liquid (VLC) and column chromatographic (CC) fractions were evaluated for anti-plasmodial activities using clinical isolates of Plasmodium falciparum- and P. yoelii nigeriensis-infected mice, and chloroquine-sensitive (D6) and chloroquine-resistant (W2) P. falciparum clones. Their blood glucose reducing and insulinotropic potentials were determined using glucose loaded rats and INS- 1 cells, respectively. Vacuum liquid chromatography of GL gave A ₁ as the most active VLC fraction while repeated CC of A ₁ gave C ₁ as the most active CC fraction. Repeated thin layer chromatography of C ₁ yielded a 1:1 mixture of α-amyrin and β-amyrin cinnamates (1a/1b), lupenyl cinnamate (2), lupenyl acetate (3) that were characterised using various spectroscopic experiments of IR, NMR and MS. The isolates were also tested against D6 and W2 clones and their in vitro insulinotropic abilities were similarly assessed, compared to chloroquine, artemisinin and glibenclamide (positive controls). Lupenyl acetate with IC₅₀ 0.033, 0.041 nmol/l against the D6 and W2 clones, respectively was the most active antiplasmodial constituent while 1:1 mixture of 1a/1b, with comparable high insulin release values as E ₁ and glibenclamide, was the most active antidiabetic constituent. These synergistically acting compounds justified the ethnomedical uses of G. latifolium.

Tab. 1: Effects of extract, fractions and isolates of Gongronema latifolium stem and root

Extract Traction Isolates Compounds	Insulin release (% of glucose effect at 5.6 mM)
	10 µg/ml	100 µg/ml
Glucose (3.0 mM. sub-stimulatory concentration)	62.8 ± 5.9*	62.8 ± 5.9*
Glucose (5.6 mM. negative control)	100.0	100.0
+ MeOH extract (GL)	117.6 ± 6.9	150.7 ± 9.5*
+ Fraction A1	119.9 ± 9.0	113.7 ± 12.6
+ Fraction A2	114.4 ± 6.5	133.7 ± 5.4*
+ Fraction A3	120.5 ± 5.4*	175.9 ± 6.8*
+ Fraction A4	84.82 ± 7.6	106.9 ± 6.4
+ Fraction A5	112.0 ± 11.3	127.1 ± 4.6*
+ Fraction A6	130.2 ± 3.6*	173.8 ± 7.4*
+ C1	134.6 ± 9.0	176.7 ± 7.5*
+ Y	120.5 ± 6.9	123.0 ± 8.3
+ 1a/1b	110.0 ± 7.0	178.5 ± 8.5*
+ 2	133.2 ± 5.3*	148.6 ± 6.3*
+ Z	122.9 ± 2.1*	152.5 ± 3.2*
+ 3	103.1 ± 5.0	152.8 ± 7.3*
+ Glibenclamide (positive control)	1.0	173.2 ± 6.5*
on glucose-mediated insulin release from INS-1 cells. GL: Methanolic extract of Gongronema latifolium stem and root: A1, A2, A3, A4, A 5 and A 6: VLC fractions of GL: C 1: CC subtraction of A 1: Y and Z unidentified isolated titerpenoids; 1a/1b: 1:1 mixture of α-(1a) and β-amyrin (1b) cinnamates; 2: lupenyl cinnamate; 3: lupenyl acetate. N ± 6 – 8. *: p < 0.5 vs. 5.6 mM of glucose.

Fig. 1: IC₅₀ and IC₉₀ of Gongronema latifolium stem and root methanolic extract and its fractions against Plasmodium falciparum clinical isolates.GL: methanolic extract; A₁, A₂, A₃, A₄, A₅, A₆: VLC fractions;. CQ: chloroquine; ART: artesunate; C₁: CC fraction. †: p < 0.05 comparison against GL; *: p < 0.05 comparison against CQ or ART, using one way analysis of variance followed by Bonferroni post-hoc test N = 6 – 8.