Composition and Molluscicidal Activity of the Essential Oil from the Stem Bark of Ocotea bracteosa (Meisn.) Mez

Abstract

The volatile oil of Ocotea bracteosa (Meisn.) Mez. stem bark was analyzed by GC and GC/MS and tested for molluscicidal activity on Biomphalaria glabrata. Twenty compounds were identified corresponding to about 70% of the oil. The major constituents were δ-cadinene (12.4%), ledene (11.1%), and globulol (10.1%). The oil showed significant molluscicidal activity against Biomphalaria glabrata, with an LC^sub 90^ value of 8.3 µg/mL, which falls below the threshold of 100 µg/mL, set for potential molluscicidal activity by the World Health Organization.

Key Word Index

Ocotea bracteosa, Lauraceae, essential oil composition, δ-cadinene, ledene, globulol, molluscicidal activity.

Introduction

Among human parasitic diseases, schistosomiasis (also called bilharzia) remains one of the most prevalent parasitic infections and has significant economic and public health consequences (1). The disease is endemic in 74 developing countries and 600 million people are exposed to the risk of infection, while 200 million individuals are currently infected. It is also estimated that 120 mdlion individuals are symptomatic, whde 20 mdlion suffer severe consequences of this disease (2). The aquatic mollusk Biomphalaria glabrata is the main intermediate host of schistosomiasis in South America. People acquire the parasite when they make contact with water containing infected snads.

Snad control strategies are considered a priority in the reduction of such transmission (3). The use of molluscicides, from plant extracts (4) or synthesis (5,6), can fonn a useful part of an integrated strategy for schistosomiasis control. In the search for plants with molluscicidal activity, several extracts (7), including essential od (8-10) have been found to be toxic to the snads diat carry schistosomes. Because of its wealth in biodiversity, Brazilian audiorities have stimulated and focused research into new naturally derived drugs and this interest has extended to focus the field of vector control.

Lauraceae Juss is a predominant tropical famdy of trees and shrubs with ca. 55 genera and 3,000 species (11), that are used in food, perfumery, cosmetics, the pharmaceutical industry, and folk medicine (12). The genus Ocotea Aublet is one of the largest genera of this famdy and comprises ca. 350 species, with distribution in the neotropical areas. In Brazd, the genus is wed represented, having about 150 species (13). Chemical stuthes carried out widi spices of diis genus, have often shown the presence of alkaloids ( 14-16), lignans ( 17-20) and essential ods (21-26).

The aim of the present study was to explore the molluscicidal activities of the essential od from Ocotea bracteosa using Biomphalaria glabrata as the target snad. This species grows abundandy in state of Paraiba and Pernambuco, northeastern Brazil, and the occurrences of bioactive compounds in the oil of other Ocotea spp encourage us to perform the present study.

Experimental

Plant material: The stem bark of Ocotea bracteosa was collected near the town of Santa Rita, State of Paraiba, Brazd, on May 2004. Voucher specimens (Agra & Coutinho 6481) were deposited at the Herbarium Lauro Pires Xavier (JPB), Universidade Federal da Paraíba.

Oil isolation: The fresh stem bark of O. bracteosa (2.4 g) were subjected to water distillation using a Clevenger-type apparatus for 8 h yielding 2.4 mL of the od, as described in the literature (24).

Identification of components: GC analysis was performed in a Hewlett Packard HP 5890, using the foUowing conditions: column: SP 2100 dimediylpolysdoxone DB-5 fused sdica capdlary column 30 m x 0.25 mm (0.1 pm film thickness). The conditions of the experiment were: carrier gas: He, (1 mL/min.); programmed column temperature 35°-180°C at 4°C/min. then 180°-280°C at 20°C/min. GC/MS analysis was carried out on the same column and conditions used as above, using a GC-coupIed to a HP 5971A mass selective detector operating at 70 eV. An aliquot (1 µL) of the oil was analyzed. The concentration of the components was calculated by using the individual peak areas for each substance. Each substance was identified by spectrometric analysis using the Wdey database, retention times and retention indices (28). Visual analysis of the other mass spectra and comparison widi literature data were used for confirmation of the results.

Molluscicidal assay of the oil: The bioassay was carried out as described by Sdva et al. (4,6) by dissolving the sample first in dimethyl sulfoxide (DMSO) and then adding dechlorinated water to give a solution 0. 1% in DMSO. Ten adult snads (9-16 mm in diameter) were placed in a beaker, containing 250 mL of the oil solution at four appropriate concentrations. Each test concentration was set in duplicate. Snads were exposed to the potential molluscicide for 24 h at room temperature and were kept under normal diurnal lighting. After 24 h, the suspension was decanted; the snads were washed with water and offered lettuce leaves as food. The tested snails were then left in water for another 24 h and at the end of diis period were examined to assess mortality. Snails were considered dead if tìiey eitiier remained motion less or did not respond to the presence of food or if the shell looked discolored. In order to verify the snad susceptibdity, two control sets were used: one widi cupric carbonate at 50 ppm and the other containing 0.1% DMSO dechlorinated water. The concentrations tíiat kdl 90% (LC90), 50% (LC^sub 50^) and l0% (LC^sub 10^) of the exposed snads (that would have survived in the negative-control cultures) was estimated by probit analysis, using the Origin 6.0 software package (Microcal Software, Northampton, MA).