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Introduction
Citrullus colocynthis belongs to the cucurbitaceae family and is a well-recognized plant in traditional medicine. The plant has been previously utilized in rural areas as a purgative, antidiabetic, insecticide and antitumoral agent (1). In a previous study, the beneficial long-term effects of Citrullus colocynthis seed extracts on glucose homeostasis and body weight maintenance were documented in streptozotocin-induced diabetic rats (1).
The aim of the present study was to explore the direct in vitro effects of several distinct Citrullus colocynthis seed extracts on glucose-stimulated insulin release from rat isolated pancreatic islets.
Materials and methods
Citrullus colocynthis extracts
Six extracts from Citrullus colocynthis seeds were tested; a crude aqueous, defatted aqueous, ethyl acetate, H2O-methanol and n-butanol extract and an extract containing the major component of the ethyl acetate, n-butanol and H2O-methanol extracts, named fraction A.
Extract preparation
The preparation of the crude aqueous and defatted extracts was reported in a previous study (1). For the hydromethanolic extract, 50 g of seeds was ground and degreased in hexane. This material was heated and stirred 3 times for 3 h in a H2O-methanol mixture (30/70). Following filtration and centrifugation, the recovered solution was divided into 2 volumes; one was solidified to form a hygroscopic red-orange residue (H2O-methanol extract; 4.5% dry matter). The second volume underwent liquid-liquid extraction 3 times with ethyl acetate and n-butanol, for the preparation of the ethyl acetate (orange powder; 1.1% dry matter) and n-butanol (brown powder; 1.2% dry matter) extracts, respectively.
Thin layer chromatography
Following separation by thin layer chromatography, ethyl acetate, n-butanol and H2O-methanol extracts revealed the presence of a major single spot. Fractionation of these extracts on a column silica gel, using the elution system methanol/water (80/20), enabled material collection from these fractions (observed under UV light at 254 and 336 nm), which, following solidification, was referred to as fraction A (217 mg).
Analysis of insulin release
For measurement of insulin release, groups of 8 islets prepared by the collagenase method (2) were incubated for 90 min at 37°C in 1.0 ml salt-balanced medium (3) containing 2.5 mg/ml bovine serum albumin and equilibrated against a mixture of O2-CO2 (95-5, v-v). The insulin content of the incubation media was...