Alginate may accumulate in cystic fibrosis lung because the enzymatic and free radical capacities of phagocytic cells are inadequate for its degradation

We sought an explanation for the accumulation, and apparent poor degradation by alveolar phagocytes, of alginate in cystic fibrosis lung. A crude intracellular lyase preparation extracted from Klebsiella pneumoniae was able to degrade seaweed alginic acid as well as forms purified from Pseudomonas aeruginosa bacteria from Cystic Fibrosis (CF) patient lungs. This was by a β-eliminative mechanism, as detected by an increase in the 232nm absorbance and activity was enhanced by deacetylation of the Pseudomonas aeruginosa alginates. Conditioned media or cell lysates from unstimulated or triggered phagocytic cells (including resident mouse peritoneal macrophages and the human macrophage cell line U937) had no effect in the same system. Free radicals generated by chemical systems or by gamma irradiation of water degraded alginate. Depolymerisation by free radicals, as detected by viscosity determinations and polyacrylamide gel electrophoresis, generated a wide range of fragment sizes. In contrast, mouse peritoneal macrophages or human polymorphonuclear neutrophils stimulated to generate free radicals had no significant effect on alginate. Under the conditions of our experiments, phagocytic cells representative of the CF lung are not able to degrade Pseudomonas aeruginosa alginate. This may explain the gross accumulation of alginate in CF lung.