This study investigated and compared vascular actions of leguminous lectins obtained from the Canavalia genus (Canavalia brasiliensis, Canavalia gladiata, and Canavalia maritima) in the rat models of paw edema and isolated aorta. Paw edema was induced by subcutaneous injection of lectins (0.01-1 mg/kg) in animals pre-treated or not with indomethacin or L-NAME. In isolated aorta, cumulative concentration curves of C. gladiata or C. brasiliensis (1-100 microg/ml) were performed at the contraction plateau induced by phenylephrine or at tissue basal tonus. The mechanism of the lectin relaxant action was investigated by previous addition of L-NAME, indomethacin, or tetraethylammonium. In both models, the lectin domain involvement was evaluated by incubation of lectins with their ligand and non-ligand sugars. The lectins induced paw edema paralleled by protein leakage. The edematogenic activity elicited by C. gladiata and C. brasiliensis involves prostaglandins and nitric oxide (NO), while that of C. maritima occurs without NO interference. C. gladiata and C. brasiliensis elicited aorta relaxation involving NO and prostacyclin, while that of C. gladiata included EDHF. All lectin effects were prevented by their binding sugars. The present study demonstrated important vasodilator effects of different degrees and mechanisms in vivo and in vitro of Canavalia lectins. In vivo, the edematogenic activity was paralleled by plasma exudation, and in vitro, aorta relaxation was strictly dependent on intact endothelium. All effects occurred via interaction with lectin domains and participation of NO and/or prostanoids.
Lectins from Diocleinae subtribe belong to the family of legume lectins and are characterized by high identity between their amino acids sequences. It has been shown that punctual differences in amino acid sequences, such as one single amino acid or an alternative conformation, represent changes in biological activities caused by these lectins. Therefore, a more detailed understanding of three-dimensional structures of these proteins is essential for accurate analyzing the relationship between structure and function. In this study lectins purified from the seeds of Dioclea violacea (DVL) and Dioclea rostrata (DRL) were compared with regard to crystal structure and vasorelaxant properties. Differences in structure of lectins were found to be reflected in differences in vasorelaxant effects based on their high specificity and selectivity for cell glycans. Binding activity was related to the position of specific residues in the carbohydrate recognition domain (CRD). DVL complexed structure was solved by X-ray crystallography and was compared to native DVL and DRL. Therefore, DVL was co-crystallized with X-Man, and a molecular modeling with X-Man complexed with DVL was done to compare the complexed and native forms adjusted fit. The relatively narrow and deep CRD in DVL promotes little interaction with carbohydrates; in contrast, the wider and shallower CRD in DRL favors interaction. This seems to explain differences in the level of relaxation induced by DVL (43%) and DRL (96%) in rat aortic rings.
The novel N-acetyl-D-glucosamine-binding lectin isolated from L. araripensis seeds presents anti-inflammatory effect involving the lectin domain and the inhibition of 5-HT, BK, PGE2, NO, TNF-α and leukocyte rolling and adhesion.
The objective of this study was to evaluate the antinociceptive effects of a lectin from Canavalia brasiliensis (ConBr) when administered orally to murine models of chemical and thermal nociception. ConBr up to 100 mg/kg produced significant and dose-dependent antinociceptive effects: 81% reduction in abdominal writhing induced by 0.6% acetic acid; 26 and 52% reduction in early- and late-stage paw licking, respectively, induced by 2.5% formalin; and 155% increase in reaction latency (heightened thermal pain threshold). In all models, the antinociceptive effect was reversed by the lectin-binding carbohydrate α-d-methyl-mannoside and by the nonselective opioid antagonist naloxone. The antinociceptive effect observed in the formalin test was inhibited by the δ-selective antagonist naltrindole and the κ-selective antagonist nor-binaltorphimine but not by the μ-selective antagonist cyprodime. In conclusion, when administered orally to Swiss mice, the ConBr lectin displayed antinociceptive activity, both peripheral and central, mediated by the opioid system and involving δ-and κ-receptors and the lectin domain.
Sulfated polysaccharides (SP) of brown algae (Phaeophyta) are composed mainly of α-L-fucose, being classified as fucans, with recognized role in inflammation but not in nociception, which was already described for SP obtained from red algae. Here the SP of the brown marine alga S. schroederi (named Ss-SP) was isolated and assayed for the antinociceptive effect. Ss-SP was isolated by DEAE-cellulose, analyzed by agarose gel electrophoresis and evaluated in nociception models (Formalin, Hot plate, Von Frey) using Swiss mice (20-25g). Anion exchange chromatography provided four major fractions being F1 (Ss-SP) that of highest metachromatic activity and sugar content. Ss-SP inhibited both phases of the formalin test. In the first phase the paw licking (55.2±8.07s) was reduced by 45% (30.5±6.51s) and 40% (32.85±8.66s) at 0.1 and 1 mg/kg, respectively. In the second phase, Ss-SP was also inhibitory about 39%, but only at 1 mg/kg (83.0±15.70s) compared to formalin (136.8±10.27s). This inhibitory effect suggests a mixed mechanism similar to morphine, which was not confirmed in the hot plate test, a model of pain associated with central neurotransmission. However, Ss-SP reduced the animal reaction in response to stimulation withVon Frey filament at the 2nd and 3rd h (20.8±6.86% versus carrageenan: 47.9±5.83%; 33.3±7.71% versus carrageenan: 62.5±9.83%). Accordingly, the paw edema induced by carrageenan (0.08±0.01g) was potently reduced in 45.35% by Ss-SP pre-treatment (0.02±0.003g), corroborating the anti-inflammatory activity demonstrated for brown seaweed polysaccharides. In conclusion our data revealed for the first time the antinociceptive effect of Ss-SP which could be used as a new source of analgesic substances.
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