Antiamoebic activity of iridoids from Morinda morindoides leaves

An aqueous decotion (AD), an 80% methanolic extract (ME) from the leaves of Morinda morindoides (Rubiaceae) together with five iridoid lactones isolated from the ME extract were evaluated in vitro for their activity against Entamoeba histolytica [1] and their cytotoxicity [2]. AD and ME extracts exhibited a promising antiamoebic activity with IC₅₀ values of 3.1±1.7 and 1.7±0.6µg/ml, respectively. All tested iridoids displayed antiamoebic activity, the most active being epoxygaertneroside (IC₅₀ 1.7±0.4µg/ml) and methoxygaertneroside (IC₅₀: 2.3±0.7µg/ml) [3]. Gaertneroside, acetylgaertneroside and gaertneric acid also showed a good activity with IC₅₀ values of 4.3±1.8, 5.4±1.4 and 7.1±1.4µg/ml, respectively. Synergistic effects between the iridoids tested, or with other constituents, may explain the high activity of the extracts. All extracts and iridoids were devoid of any cytotoxic effect against MT-4 cells at the highest test concentration of 250µg/ml. These findings support at least in part the traditional use of Morinda morindoides leaves for the treatment of amoebiasis in traditional medicine in the Democratic Republic of Congo.

	R1	R2	R3	R4
1	CH3	OH	H	gluc.
2	CH3	OH	H	6-acetylgluc.
3	H	OH	H	gluc.
4	CH3	OH	OCH3	gluc.

	R1	R2	R3	R4
5	CH3	OH	H	gluc.

References:

1. Tona et al. (1998)J. Ethnopharmacol. 61: 57–65. 2. Pauwels et al. (1988)J. Virol. Methods 20: 309–321. 3. Cimanga et al. (2006) Planta Med. 72: 751–753.