Leonardo F. Castagna

Chitosan-induced phospholipase A2 activation and arachidonic acid mobilization in P388D1 macrophages

We have found that chitosan, a polysaccharide present in fungal cell walls, is able to activate macrophages for enhanced mobilization of arachidonic acid in a dose‐ and time‐dependent manner. Studies aimed at identifying the intracellular effector(s) implicated in chitosan‐induced arachidonate release revealed the involvement of the cytosolic Group IV phospholipase A2 (PLA2), as judged by the inhibitory effect of methyl arachidonoyl fluorophosphonate but not of bromoenol lactone. Interestingly, priming of the macrophages with lipopolysaccharide renders the cells more sensitive to a subsequent stimulation with chitosan, and this enhancement is totally blocked by the secretory PLA2 inhibitor 3‐(3‐acetamide)‐1‐benzyl‐2‐ethylindolyl‐5‐oxy‐propanesulfonic acid (LY311727). Collectively, the results of this work establish chitosan as a novel macrophage‐activating factor that elicits AA mobilization in P388D1 macrophages by a mechanism involving the participation of two distinct phospholipases A2.

Growth of milk fermentative bacteria in the presence of chitosan for potential use in cheese making

The effects of different molecular weight chitosans alone and their complexes with casein on the growth of three representative milk fermentative bacteria (Lactobacillus delbrueckii ssp. bulgaricus, Streptococcus thermophilus and Propionibacterium freudenreichii) were compared. In nutrient broth, all chitosans showed a dose dependent inhibition of S. thermophilus and L. delbrueckii ssp. bulgaricus growth. Chitosan of high and low molecular weight, but not chitosan oligosaccharides, showed a dose dependent inhibition of P. freudenreichii that was dependent on the initial bacterial load. The inhibiting effects of chitosan were greatly reversed when the biopolymers were incubated with milk before interaction with bacteria. Under these conditions a cheese like product was made with high molecular weight chitosan as the coagulating agent. The product had lower firmness than the respective cheese control, probably because of a higher water retention. The effect of chitosan on milk fermentative processes appeared to be dependent not only on its molecular weight and concentration, but also on the presence of casein micelles or milk fat, that, acting in a competitive manner, could prevent the inhibitory activity of these biopolymers on bacterial growth.