Effects of a panel of dietary lectins on cholecystokinin release in rats

Differential Apoptotic and Mitogenic Effects of Lectins in Zebrafish

Plant lectins represent a major group of anti-nutritional factors that can be toxic to human and animals. However, the mechanisms by which lectins regulate cell fates are not well-understood. In the present study, the cellular and molecular impacts of three common lectins, agglutinins from wheat germ [wheat germ agglutinin (WGA)], soybean [soybean agglutinin (SBA)], and peanut [peanut agglutinin (PNA)] were examined in zebrafish embryo and liver cells. WGA and SBA were found to induce cell apoptosis both in vitro and in vivo, while PNA stimulated cell proliferation. WGA and SBA reduced levels of B cell lymphoma-2 (Bcl-2), phosphorylation of Bcl-2-associated death promoter (Bad), cyclin-dependent kinase 4 (Cdk4), and phosphorylation of the retinoblastoma (Rb). WGA and SBA also inhibited the activities of cell survival pathways including protein kinase B (Akt), extracellular signal-regulated protein kinases 1 and 2 (Erk1/2), and target of rapamycin (Tor). Furthermore, WGA and SBA shifted the cellular metabolism characterized by reduced expression of glucose-6-phosphate dehydrogenase (g6pd) and increased expression of glutamine synthetase (glul) and glutamate dehydrogenase (glud). However, PNA showed the opposite effects toward these molecular markers compared to those of WGA and SBA. Therefore, our results revealed some plant lectins (WGA and SBA) were toxic while the other (PNA) was mitogenic. Further characterization of the distinct functions of individual lectins should be valuable for both nutrition and other potential applications.

Origin and mediation of secretion induced by oral phytohaemagglutinin (PHA) in rats

After oral administration several gut-binding lectins induce accumulation of liquor and amylase in the proximal small intestine. Orally administered Phaseolus vulgaris phytohaemagglutinin (PHA) was used to study the mediation of these effects in rats. The regulation of amylase secretion clearly differed from that of the liquor. The amylase activity was of pancreatic origin, in agreement with the known cholecystokinin-releasing effect of PHA. It appears that CCK exerts its effect both directly and by facilitating neural stimulatory pathways. Intestinal secretion was identified as the source of the liquor, without a contribution by other secretions. It was mediated by a local cholinergic reflex with the involvement of both muscarinic and nicotinic acetylcholine receptors. It is speculated that the observed enteric reflex may enable the gut to transport secreted antibacterial peptides or secretory antibodies from the crypts to adherent bacteria on adjacent villi.