Antihyperglycaemic and Anti-oxidant Activities of Eugenia uniflora Leaf: Evaluation of Ethnomedical Claims IV

Eugenia uniflora leaf is used ethnomedically in some tropical countries, including Nigeria, in the management of diabetes. Its extrapancreatic anti-diabetic and -oxidant activities have been reported while its insulin stimulation is unknown. In vivo anti-hyperglycaemic activities of its methanolic extract (A) and partition fractions and their in vitro insulin releasing abilities, using glucose loaded rats and INS-1 cells, respectively were investigated. Their anti-oxidant properties as well as in vivo insulin stimulatory effects of n-butanol (B ₄) and aqueous (B ₅) fractions were also studied. The VLC subfractions of most active n-hexane (B ₁) were similarly tested for anti-hyperglycaemic and -oxidant activities. Extract (200 and 400 mg/kg) gave significant (p < 0.05) time and dose dependent activities in glucose loaded rats, which were higher than that of glibenclamide (GLIB, 5 mg/kg). B ₁ was the most active and its lowered activity compared to A, suggested synergism in the actions of the constituents. The > 150% insulin releases elicited by B₁ and ethylacetate (B ₃) fractions from INS-1 cells agreed with their anti-hyperglycaemic and -oxidant effects and suggested a role of antioxidant in the former activity. The plasma insulinotropic activities of B ₄ and B ₅ confirmed their in vitro abilities and established insulin stimulation as an additional mechanism of action. Anti-hyperglycaemic and -oxidant activities of VLC fractions C ₆ and C ₇ were similar (p > 0.05) and higher than those of B ₁ and GLIB. Subfraction E ₃ was the highest for these two activities, and would contain the main insulinotropic constituents. Also, constituents of E ₂, E ₆ and E ₇ should contribute to these activities. Thefore, contribution of the antioxidant activity of the plant to its antihyperglycaemic property was established, insulin release was established as another mechanism of action of the plant while its ethnomedical usage was justified.

Tab. 1: The antihyperglycaemic Eugenia uniflora leaf methanolic extract and its successive chromatographic fractions with high anti-hyperglycaemic activities.

TEST Agent	IC50 (mg/ml)
	DPPH	ABTS	FRAP	TAC
A	0.0860 ± 0.004	0.4616 ± 0.002	0.5941 ± 0.098	0.3837 ± 0.014
B1	0.707 ± 0.088	3.922 ± 0.021	0.320 ± 0.030	1.103 ± 0.069
C6	1.4436 ± 0.178a,b	2.6740 ± 0.464a,b	2.0987 ± 0.279	0.4174 ± 0.003
C7	1.6587 ± 0.016a,b	3.8963 ± 0.175a,b	3.4409 ± 0.348	0.1752 ± 0.011
E2	0.5223 ± 0.018a,b	1.7239 ± 0.054	2.3119 ± 0.117	1.1784 ± 0.022
E3	0.6044 ± 0.047a,b	1.8507 ± 0.715	1.0269 ± 0.015	1.0315 ± 0.007
E6	0.9887 ± 0.004a,b	0.4402 ± 0.029	3.4403 ± 0.174	0.6689 ± 0.008
E7	1.2184 ± 0.072a,b	3.5776 ± 0.462a,b	4.9450 ± 0.975	0.4949 ± 0.003
Vit. C	0.0083 ± 0.000a,b		0.6596 ± 0.100	0.5613 ± 0.023
Trolox		0.1438 ± 0.020
A: methanolic extract of Eugenia uniflora leaf. B 1: n-hexane partition fraction of A; C 6 and C 7 most active VLC fractions of B 1; E 2, E 3, E 5 and E 7; most active CC sub-fractions of the combined C 6 and C 7; Vit. C: vitamin C (ascorbic acid, positive control). Trolox: Trolox (positive control). a: p < 0.05 vs. MeOH; b: p < 0.05 vs. respective positive control.

Fig. 1: The antihyperglycaemic Eugenia uniflora leaf methanolic extract and its successive highly active chromatographic fractions (200 mg/kg) using glucose loaded rats. Values are given as mean = SEM. N = 5.