Poly-L-lysine induces fibrosis on alginate microcapsules via the inductionof cytokines

Alginate-poly-L-lysine (PLL) microcapsules can be used for transplantation of insulin-producing cells for treatment of type I diabetes. In this work w e wanted to study the inflammatory reactions against implanted microcapsule s due to PLL. Vile have seen that by reducing the PLL layer, less overgrowt h of the capsule is obtained. By incubating different cell types with PLL a nd afterwards measuring cell viability with MTT, we found massive cell deat h at concentrations of PLL higher than 10 mug/ml. Staining with annexin V a nd propidium iodide showed that PLL induced necrosis but not apoptosis. The proinflammatory cytokine, tumor necrosis factor (TNF), was detected in sup ernatants from monocytes stimulated with PLL. The TNF response was partly i nhibited with antibodies against CD14, which is a well-known receptor for l ipopolysaccharide (LPS). Bactericidal permeability increasing protein (BPI) and a lipid A analogue (B-975), which both inhibit LPS, did not inhibit PL L from stimulating monocytes to TNF production. This indicates that PLL and LPS bind to different sites on monocytes, but because they both are inhibi ted by a p38 MAP kinase inhibitor, they seem to have a common element in th e signal transducing pathway. These results suggest that PLL may provoke in flammatory responses either directly or indirectly through its necrosis-ind ucing abilities. By combining soluble PLL and alginate both the toxic and T NF-inducing effects of PLL were reduced. The implications of these data are to use alginate microcapsules with low amounts of PLL for transplantation purposes.