Direct effects of wheat germ agglutinin on inositol phosphate formation and cytosolic-free calcium level in intestine 407 cells

The Plant Lectin Wheat Germ Agglutinin Inhibits the Binding of Pemphigus Foliaceus Autoantibodies to Desmoglein 1 in a Majority of Patients and Prevents Pathomechanisms of Pemphigus Foliaceus In Vitro and In Vivo

Pemphigus foliaceus (PF) is a life-threatening autoimmune blistering skin disease caused by pathogenic IgG autoantibodies against desmoglein 1 (dg1), a desmosomal cadherin-type adhesion glycoprotein. Using lectins and glycosidases, we have shown that dg1 displays an N-glycosylation pattern of the complex triantennary type. We have found that lectins and glycosidases interfere with N-bound sugar residues on the amino-terminal ectodomain of dg1 and completely abolish, in vitro, the antigenicity of dg1 in most of the patients' sera. Moreover, in an ex vivo model using punch biopsies from normal human skin, we demonstrate that preincubation of the epidermis in wheat germ agglutinin (WGA) prevents PF autoantibody binding, acantholysis, and subcorneal blistering. In addition, we show that topical treatment with WGA inhibits PF autoantibody binding to keratinocytes in both newborn BALB/c mice and in organotypic human epidermis grafted onto the back of SCID mice. The epidermis of these pretreated animals displays a regular morphology, whereas control animals develop the immunopathologic phenotype of PF. These findings suggest that WGA may interfere with autoantibody binding to dg1, preventing experimental PF without affecting the adhesive function of dg1. Our observations may provide a new approach to the therapy of PF.

Soybean agglutinin stimulated cholecystokinin release from cultured rabbit jejunal cells requires calcium influx via L-type calcium channels

We have studied the mechanism of soybean agglutinin (SBA) mediated cholecystokinin (CCK) release in enriched cultured cholecystokinin-secreting cells. 12-O-Tetradecanoylphorbol-13-acetate 1 mM significantly stimulated release of CCK-like-immunoreactivity (CCK-LI) by 55%+/-17% (p < 0.05), which was blocked by the protein kinase C inhibitor staurosporine 100 nM. Forskolin 10 mM stimulated CCK-LI by 82%+/-12% (p < 0.05) and this was inhibited by somatostatin 1 nM. 1-Phenylalanine 20 mM and Bay K 8644 1 mM stimulated CCK-LI by 69%+/-22% and 60%+/-19% respectively (p < 0.05), these responses were completely abolished by the L-type calcium channel antagonist verapamil 10 mM. SBA 10 and 100 microg/ml stimulated CCK-LI by 65%+/-22% and 74%+/-24% respectively (p < 0.05). The effect of SBA was inhibited by verapamil and N-acetylgalactosamine. We conclude that SBA stimulates CCK-LI through calcium flux via L-type calcium channels.

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

We previously showed that soybean lectin (SBL) releases cholecystokinin (CCK) and have now asked whether other dietary lectins have this effect and if extracellular calcium is involved. Lectins and vehicle were first infused into the duodenum of anesthetized rats. The CCK response to vehicle was 3.1 +/- 0.6 pmol/l (P < 0.05 vs. basal). SBL and peanut lectin (PNL) (84 microg/ml) significantly increased plasma CCK concentrations from 2.0 +/- 0.4 pmol/l to a maximum of 8.4 +/- 0.5 pmol/l (P < 0.01 vs. vehicle, mean +/- SE) and from 1.9 +/- 0.5 to 7.0 +/- 0.6 pmol/l (P < 0.05 vs. vehicle, mean +/- SE), respectively. Wheat germ lectin (WGL) (840 microg) also increased plasma CCK levels from 1.5 +/- 0.3 pmol/l to a maximum of 9.7 +/- 1.3 pmol/l (P < 0.05 vs. vehicle, mean +/- SE). Corresponding increases in pancreatic protein output occurred. Broad bean lectin (BBL) had no effect on either parameter. Dose-dependent responses were seen with SBL, PNL, and WGL (1, 10, and 100 microg/ml) in perifused rat intestinal cells. These responses were abolished in calcium-free medium and in the presence of the competing sugars of the lectins. Therefore, SBL, PNL, and WGL, which bind to motifs including N-acetyl-D-galactosamine, galactose, and N-acetylglucosamine, respectively, released CCK, but BBL, which binds to mannose and glucose, did not. Ingestion of lectins may have major CCK-mediated effects on gastrointestinal function and growth.

Elevated levels of serum antibodies to the lectin wheat germ agglutinin in celiac children lend support to the gluten-lectin theory of celiac disease

Lectins recognize carbohydrate moities of glycoproteins and glycolipids, and can elicit several biological effects, including cell agglutination, cell activation and mitogenesis. According to the gluten-lectin theory, celiac lesions represent a response to a toxic lectin, putatively wheat germ agglutinin (WGA). In this study we compared the serum antibody levels IgA, IgG and IgM to WGA and to gliadin in children under investigation for celiac disease (CD), as compared to reference children. We found that the levels of IgA and IgG to WGA as well as gliadin were significantly higher in celiac children on a gluten-containing diet, compared to children on gluten-free diet and reference children. These findings lend support to the concept that WGA is a biologically significant component of gluten. Since WGA can mimic the effects of epidermal growth factor (EGF) at the cellular level, we hypothesize that the crypt hyperplasia seen in celiac children could be due to a mitogenic response induced by WGA.

Salmonella entry into mammalian cells: different yet converging signal transduction pathways?

Salmonella bacteria have evolved means to subvert host cell signal transduction pathways to induce their uptake. Recently, progress has been made towards defining those pathways. Although it is clear that Salmonella evoke different signalling pathways in different cell lines, it is possible that these responses may be triggered by a common mechanism and that the diverse pathways may converge downstream in common effector molecules.

A human epithelial cell line, intestine 407, can produce 5-hydroxyeicosatetraenoic acid and leukotriene B4

The present study was carried out to further characterize the role of non-inflammatory cells in the inflammatory process. More specifically, we have investigated whether human epithelial cells can generate inflammatory lipid mediators via activation of the 5-lipoxygenase pathway. The cells were stimulated with the calcium ionophore A23187 (5 microM) for different periods of time, after which the production of eicosanoids was determined by gradient reverse-phase high performance liquid chromatography (RP-HPLC) and rapid spectral detection, permitting continuous ultraviolet spectroscopy. In both non-prelabeled cells and cells prelabeled with [1-14C]arachidonic acid, cell stimulation for 30 min or more resulted in the production of two important 5-lipoxygenase products: 5-hydroxyeicosatetraenoic acid (5-HETE) and leukotriene B4 (LTB4). Stimulation for 15 min or less, however, led solely to the formation of 5-HETE. The identities of 5-HETE and LTB4 were confirmed by HPLC retention times and UV spectra, as well as by gas chromatography-mass spectrometry for 5-HETE and radioimmunoassay for LTB4. It can therefore be concluded that human epithelial cells in general can produce important inflammatory mediators, which suggests that epithelial cells may play a more active role in the inflammatory process than is normally assumed.

Intestinal secretagogues increase cytosolic free Ca2+ concentration and K+ conductance in a human intestinal epithelial cell line

A human intestinal epithelial cell line (Intestine 407) is known to retain receptors for intestinal secretagogues such as acetylcholine (ACh), histamine, serotonin (5-HT) and vasoactive intestinal peptide (VIP). The cells were also found to possess separate receptors for secretin and ATP, the stimulation of which elicited transient hyperpolarizations coupled to decreased membrane resistances. These responses were reversed in polarity at the K+ equilibrium potential. The hyperpolarizing responses to six agonists were reversibly inhibited by quinine or quinidine. By means of Ca2(+)-selective microelectrodes, increases in the cytosolic free Ca2+ concentration were observed in response to individual secretagogues. The time course of Ca2+ responses coincided with that of hyperpolarizing responses. The responses to ACh and 5-HT were abolished by a reduction in the extracellular Ca2+ concentration down to pCa 7 or by application of Co2+. Thus, in Intestine 407 cells, not only the intestinal secretagogues, which are believed to act via increased cytosolic Ca2+ (ACh, 5-HT and histamine), but also those which elevate cyclic AMP (VIP, secretin and ATP) induce increases in cytosolic Ca2+, thereby activating the K+ conductance. It is likely that the origin of increased cytosolic Ca2+ is mainly extracellular for ACh- and 5-HT-induced responses, whereas histamine, VIP, secretin and ATP mobilize Ca2+ from the internal compartment.

Epidermal growth factor activates calcium-permeable channels in A 431 cells

The patch clamp technique in a cell-attached configuration was used to search for calcium-permeable channels in human carcinoma A 431 cells. Unitary inward currents were recorded with 100 mM CaCl2 in a pipette, with the mean slope conductance of 2.8 pS and a reversal potential (obtained by extrapolation) of +25.5 mV. Application of epidermal growth factor (EGF) into the extracellular solution produced a transient increase in the probability of these channels being open. The effect develops with delay of about 20 s and lasts thereafter for 36 s (mean values). We propose that these channels mediate an EGF-induced increase in the concentration of cytosolic free calcium.