Abstract
Polysaccharide containing extracts from immature fruits of okra (Abelmoschus esculentus) are known to exhibit antiadhesive effects against bacterial adhesion of Helicobacter pylori (H. pylori) to stomach tissue. The present study investigates structural and functional features of polymers responsible for this inhibition of bacterial attachment to host cells. Ammonium sulfate precipitation of an aqueous extract yielded two fractions at 60% and 90% saturation with significant antiadhesive effects against H. pylori, strain J99, (FE60% 68% ± 15%; FE90% 75% ± 11% inhibition rates) after preincubation of the bacteria at 1 mg/mL. Sequential extraction of okra fruits yielded hot buffer soluble solids (HBSS) with dose dependent antiadhesive effects against strain J99 and three clinical isolates. Preincubation of H. pylori with HBSS (1 mg/mL) led to reduced binding to 3ʹ-sialyl lactose, sialylated Lea and Lex. A reduction of bacterial binding to ligands complementary to BabA and SabA was observed when bacteria were pretreated with FE90%. Structural analysis of the antiadhesive polysaccharides (molecular weight, monomer composition, linkage analysis, stereochemistry, and acetylation) indicated the presence of acetylated rhamnogalacturonan-I polymers, decorated with short galactose side chains. Deacetylation of HBSS and FE90% resulted in loss of the antiadhesive activity, indicating esterification being a prerequisite for antiadhesive activity.
Highlights
The immature fruits of Abelmoschus esculentus (A. esculentus) (L.) Moench, Malvaceae, known as okra or lady’s finger, are widely used as a food vegetable in Asia, Africa, and South America
The antiadhesive effects of the crude extract are caused by an interaction with the bacteria, while pretreatment of human stomach tissue with the plant polysaccharides prior to the addition of H. pylori does not lead to reduced bacterial adhesion [1,2]
Due to the increasing interest in development of antiadhesive compounds against bacterial pathogens the above described experiments are to our knowledge the first study, which indicates that acetylated rhamnogalacturonans can influence bacterial adhesion
Summary
The immature fruits of Abelmoschus esculentus (A. esculentus) (L.) Moench, Malvaceae, known as okra or lady’s finger, are widely used as a food vegetable in Asia, Africa, and South America. Despite the fact that the aqueous extract inhibits the adhesive binding of the membrane proteins BabA, SabA and HpA to its specific ligands, it has been shown that radiolabeled ligands of this extract bind non- to membrane structures in the vicinity of the bacterial adhesins, but do not necessarily interact directly with BabA/SabA [2]. This lead to the conclusion that non-specific, charge-dependent interactions between high molecular compounds from Okra fruits and the H. pylori surface lead to strong antiadhesive effects under in vitro conditions. As shown by the following investigation, esterified pectin-like rhamnogalacturonan I polymers are responsible for the antiadhesive effects; interestingly, the antiadhesive activity was shown to be dependent on the esterification
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