Structural surface changes and inflammatory responses against alginate‐based microcapsules after exposure to human peritoneal fluid

Abstract

Microencapsulation of cells is a promising approach to prevent rejection in the absence of immunosuppression. Clinical application, however, is hampered by insufficient insight in factors influencing biocompatibility of the capsules in humans. In the present study we exposed alginate-based capsules prepared of different types of alginate to human peritoneal fluid. Subsequently we studied the physicochemical changes of the capsule's surface by applying micro-Fourier Transform Infrared Spectroscopy. We did test alginate-beads and alginate-poly-L-lysine capsules prepared of different types of alginate. In all tested capsule formulations we found adsorption of components from human peritoneal fluid and clear physicochemical changes of the surface. These changes were alginate-dependent. The adsorption had no significant effects on the permselective properties of the capsule but we found a strong increase of TNFα production by human peripheral blood mononuclear cells when exposed to alginate-beads treated with human peritoneal fluid. This elevated responsiveness was not observed with alginate-PLL capsules. The results show that alginate-based capsule surfaces always undergo physicochemical changes of the surface when exposed to human peritoneal fluid. This adsorption may lead to enhancement of the inflammatory responses against the microcapsules. Our result implicate that biocompatibility measurements should not only been done with freshly prepared capsules but also with capsules that have been exposed to fluid from the implantation site in order to predict the in vivo responses.

The association between in vivo physicochemical changes and inflammatory responses against alginate based microcapsules

“…As we implanted capsules with identical physico-chemical and mechanical properties we questioned whether the capsules might undergo changes in vivo that might be hold responsible for the differences in responses. As we found in a recent in vitro study [46] that the properties of the capsules surface may change after exposure to human peritoneal fluid we questioned whether there might be a difference in properties of the intermediate and high G capsules after implantation. To this end we implanted in a separate series of experiments capsules in the peritoneal cavity of rats which were retrieved by peritoneal lavage at 1, 3, and 7 days after implantation.…”

“…Upon exposure to body fluids microcapsules will adsorb bioactive components which will change the properties of the capsule surface and the responses against the capsules Table 3 Elemental surface composition of alginate-PLL capsules (n ¼ 4). [16,46]. In recent in vitro studies we showed that fluctuations in pH in body fluids changes the properties and charge density of capsules making capsules more susceptible for adsorption of body proteins and inflammatory responses [36].…”

“…After implantation, a non-specific immune response is activated with influx of cells and pH changes in the implantation site as a consequence [38,48e54]. This together with adsorption of proteins from the peritoneal fluid [46] may result in structural surface changes. Alginate-PLL capsules prepared of intermediate-G alginate seem to be resistant to the changing microenvironment in the implantation site.…”

“…Our data suggest that for predicting biocompatibility of alginate-based capsules we should not only focus on the properties of the freshly prepared capsules but also on the properties of the capsule surface after exposure to body fluids. Our recently published system in which capsules are first incubated to peritoneal fluid and subsequently exposed to human peripheral blood mononuclear cells to quantify inflammatory responses may serve as a fast in vitro assay to predict proinflammatory structural surface changes on alginate-based capsules after exposure to body fluids [46]. Our study was not only performed to identify the cause for the difference in responses against capsules prepared of different types of alginate but also to gain more insight in the composition of the inflammatory responses against alginate-based microcapsules.…”

Biocompatibility and Biotolerability Assessment of Microspheres Using a Whole Blood Model

“…Complement and coagulation proteins are present at other sites than in blood, such as in the peritoneal fluid 107,108 .…”