Original research articlePotent spermicidal effect of oleanolic acid 3-beta-d-glucuronide, an active principle isolated from the plant Sesbania sesban Merrill☆
Introduction
The explosive growth of the global population coupled with the relentless spread of sexually transmitted diseases (STDs), especially human immunodeficiency virus (HIV), has adversely affected the socioeconomic equilibrium. The predicament is more profound in the developing and underdeveloped nations wherein lack of education, consumer unwillingness and disparity in widespread dissemination of health services have prevented the embracement of safe contraceptive options [1], [2], [3], [4], [5], [6]. Therefore, our goal was to explore active spermicidal principle(s) that could be developed as potential safe vaginal contraceptive formulation(s).
Plants have served as natural sources of medicinal agents for thousands of years since the dawn of civilization. The medicinal plants, especially those used in traditional medicine, are presently being revisited as sources for novel bioactive agents. Quite a good number of plants are reported to possess spermicidal activity [7], [8]. The scientific quest for unique active component(s) from traditional medicine complements the success of modern medicine. The present compound oleanolic acid 3-beta-d-glucuronide (OAG) was isolated from Sesbania sesban Merrill, a shrub belonging to the Leguminosae family. It is a soft-wooded fast-growing plant cultivated throughout India up to an altitude of 1200 m [9] and can also be found in the wild. Different parts of the plant are used in various tribal medicines. Seeds are emmenagogue, stimulant, astringent and are used also for the treatment of diarrhea. The root is anti-helminthic and carminative. The Kandha tribe in the Kandhamal district of Orissa, India, uses the root extracts as contraceptive [10]. The seed and flower extracts have been reported to have potent antifertility activity in rodents [11]. Phytochemical examination revealed that different parts of the plant contain derivatives of oleanolic acid. Oleanolic acid was reported to inhibit sperm motility [12]. In seeds, oleanolic acid, stigmastane-5.24(28)-diene-3β-O-β-d-galactopyranoside and galactomannan are present [13], [14].
Flavonols and anthocyanidins were reported to have been derived from flowers [15], [16]. Gluconide derivatives of oleanolic acid, 3-O-[α-l-rhamnopyranosyl-(1,3)-β-d-glucuronopyranosyl]-oleanolic acid, extracted from leaves showed molluscidal activity [15], [16]. Lack of specific and detailed information pertaining to the fertility-regulating property and chemical constituents of the root extract formed the basic premise of the present study. Fractionation of the alcoholic part revealed two glycosides as stigmasterol 3-O-β-d-glucoside and OAG. OAG is a derivative of oleanolic acid. OAG is reported to have different biological activities including anti-neoplastic effect and spermicidal action [17], [18]. All of the above information instigated us to investigate the spermicidal activity of OAG. Moreover, determining the contraceptive efficacy of OAG, compatibility with vaginal flora, irritability index and probable mutagenic potential compounded further mechanistic details.
Section snippets
Plant material
The roots of S. sesban were collected from the Midnapore district of West Bengal and authenticated by Dr. Debjani Basu [Assistant Director, Botanical Survey of India, JC Bose (National) Botanical Garden, Howrah, West Bengal, India]. Roots were washed thoroughly, dried and then pulverized in an industrial blender.
Preparation of extracts
Two kilograms of the powdered roots was percolated with rectified spirit (90% ethanol). The extract was concentrated under reduced pressure to obtain 32 g of brown solid. The solid
Spermicidal activity
Fig. 2 depicts the effect of varying concentrations of OAG on sperm motility. There was a dose-dependent increase in sperm immobilization with an increase in concentration of OAG. The MEC that induced 100% immobilization of the sperm was 50 mcg/mL.
Sperm membrane integrity
More than 97% of the control sperm were HOS responsive, whereas OAG-treated sperm was non-HOS responsive as depicted via tail curling (Fig. 3A–C). Loss of HOS responsiveness indicated compromised sperm membrane integrity post OAG treatment,
Discussion
The present study focuses on the assessment of the root extract of S. sesban for its prospective sperm immobilizing or spermicidal activity. Activity-guided fractionation study led to identification of the compound OAG as an active principle. Sperm immobilization, contraceptive efficacy and other related parameters of OAG as spermicidal agent were verified in a series of in vitro and in vivo experiments. Results demonstrated that the compound exerted a dose-dependent sperm immobilizing
Acknowledgments
We thank Mr. S.N. Dey for his help in the electron microscopic studies. We are also grateful to the Council of Scientific and Industrial Research (CSIR) and the University Grants Commission, New Delhi, for providing fellowship to N. Das and P. Chandran (UGC/SRF), respectively.
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This research was financially supported by the CSIR, New Delhi, India.