Chiara Dalla Pellegrina

Effects of wheat germ agglutinin on human gastrointestinal epithelium: Insights from an experimental model of immune/epithelial cell interaction

Wheat germ agglutinin (WGA) is a plant protein that binds specifically to sugars expressed, among many others, by human gastrointestinal epithelial and immune cells. WGA is a toxic compound and an anti-nutritional factor, but recent works have shown that it may have potential as an anti-tumor drug and as a carrier for oral drugs. To quantitate the toxicity threshold for WGA on normal epithelial cells we previously investigated the effects of the lectin on differentiated Caco2 cells, and showed that in the micromolar range of concentrations WGA could alter the integrity of the epithelium layer and increase its permeability to both mannitol and dextran. WGA was shown to be uptaken by Caco2 cells and only approximately 0.1% molecules were observed to cross the epithelium layer by transcytosis. Here we show that at nanomolar concentrations WGA is unexpectedly bioactive on immune cells. The supernatants of WGA-stimulated peripheral blood mononuclear cells (PBMC) can alter the integrity of the epithelium layer when administered to the basolateral side of differentiated Caco2 cells and the effects can be partially inhibited by monoclonal antibodies against IL1, IL6 and IL8. At nanomolar concentrations WGA stimulates the synthesis of pro-inflammatory cytokines and thus the biological activity of WGA should be reconsidered by taking into account the effects of WGA on the immune system at the gastrointestinal interface. These results shed new light onto the molecular mechanisms underlying the onset of gastrointestinal disorders observed in vivo upon dietary intake of wheat-based foods.

Temperature-dependent decay of wheat germ agglutinin activity and its implications for food processing and analysis

Abstract A recently-described immunoenzymatic (ELISA) method for the quantitative determination of biologically-active wheat germ agglutinin (WGA) in unknown samples has been applied to measure the concentration of active WGA in raw and cooked wheat-derived foodstuffs. The method exploits the binding specificity of WGA to ovalbumin as a first step followed by identification of bound lectin with polyclonal antibodies. Purified WGA was used to obtain calibration curves. Detectable amounts of WGA were found in raw foodstuffs and wheat flours, whilst variable amounts of agglutinin were found in wholemeal pasta probably as a consequence of thermal inactivation during food processing. The thermal gradient gel electrophoresis (TGGE) technique was therefore applied to analyse the thermal stability of WGA. The biological activity of WGA decreased as a function of heating temperatures and time of exposure to thermal treatment in an S-shaped fashion with an inflection point around 65 °C. As a consequence, WGA might represent a biochemical “indicator” allowing one to determine the thermal treatment undergone by wheat-derived foods during processing.

Ab initio phenomenological simulation of the growth of large tumor cell populations

In a previous paper we have introduced a phenomenological model of cell metabolism and of the cell cycle to simulate the behavior of large tumor cell populations (Chignola and Milotti 2005 Phys. Biol. 2 8). Here we describe a refined and extended version of the model that includes some of the complex interactions between cells and their surrounding environment. The present version takes into consideration several additional energy-consuming biochemical pathways such as protein and DNA synthesis, the tuning of extracellular pH and of the cell membrane potential. The control of the cell cycle, which was previously modeled by means of ad hoc thresholds, has been directly addressed here by considering checkpoints from proteins that act as targets for phosphorylation on multiple sites. As simulated cells grow, they can now modify the chemical composition of the surrounding environment which in turn acts as a feedback mechanism to tune cell metabolism and hence cell proliferation: in this way we obtain growth curves that match quite well those observed in vitro with human leukemia cell lines. The model is strongly constrained and returns results that can be directly compared with actual experiments, because it uses parameter values in narrow ranges estimated from experimental data, and in perspective we hope to utilize it to develop in silico studies of the growth of very large tumor cell populations (10(6) cells or more) and to support experimental research. In particular, the program is used here to make predictions on the behavior of cells grown in a glucose-poor medium: these predictions are confirmed by experimental observation.

Egg-matrix for large-scale single-step affinity purification of plant lectins with different carbohydrate specificities.

Hen eggs represent an easily available and inexpensive source of glycoproteins expressing a variety of sugars. Egg glycoproteins might therefore be exploited to purify by affinity chromatography carbohydrate-binding proteins (lectins) with different specificities. A method to generate an affinity matrix from hen eggs is described. The matrix was assayed for its ability to purify in a single step biologically active phytohemagglutinin, wheat germ agglutinin, lentil lectin, and peanut agglutinin. Milligrams of purified lectins per gram of matrix was obtained, with the only exception of peanut agglutinin that was not efficiently retained into the affinity column. Hen egg chromatography is a relatively simple, fast, and reproducible method to purify high amount of plant lectins.

Thresholds, long delays and stability from generalized allosteric effect in protein networks

Post-transductional modifications tune the functions of proteins and regulate the collective dynamics of biochemical networks that determine how cells respond to environmental signals. For example, protein phosphorylation and nitrosylation are well known to play a pivotal role in the intracellular transduction of activation and death signals. A protein can have multiple sites where chemical groups can reversibly attach in processes such as phosphorylation or nitrosylation. A microscopic description of these processes must take into account the intrinsic probabilistic nature of the underlying reactions. We apply combinatorial considerations to standard enzyme kinetics and in this way we extend to the dynamic regime a simplified version of the traditional models on the allosteric regulation of protein functions. We link a generic modification chain to a downstream Michaelis–Menten enzymatic reaction and we demonstrate numerically that this accounts both for thresholds and long time delays in the conversion of the substrate by the enzyme. The proposed mechanism is stable and robust and the higher the number of modification sites, the greater the stability. We show that a high number of modification sites converts a fast reaction into a slow process, and the slowing down depends on the number of sites and may span many orders of magnitude; in this way multisite modification of proteins stands out as a general mechanism that allows the transfer of information from the very short time scales of enzyme reactions (milliseconds) to the long time scale of cell response (hours).