Effect of poly‐L‐lysine coating on macrophage activation by alginate‐based microcapsules: Assessment using a new in vitro method

Abstract

The characteristics of the microcapsule surface, which interacts directly with the host macrophages, may have a role in the biocompatibility of alginate-poly-L-lysine (PLL)-alginate (APA) microcapsule. The objectives of the study were: 1) to develop and validate a simple, rapid, and sensitive in vitro method for assessing microcapsule biocompatibility, based on microcapsule coincubation with macrophages and measurement, by reverse transcriptase-polymerase chain reaction, of cytokine mRNA expression, and 2) to evaluate the effect of alginate purification and PLL coating on macrophage activation. The mRNA expression of tumor necrosis factor-alpha and interleukin-1beta was significantly higher when macrophages were coincubated with beads made with nonpurified compared with purified alginate (p<0.01, p<0.05, respectively) and negative control (p<0.001) or with APA microcapsules compared with non-PLL-coated alginate beads and negative control (p<0.001). The mRNA expression of interleukin-6 differed significantly only when APA microcapsules were compared with a negative control (p<0.05). These results confirm that alginate purification improves microcapsule biocompatibility, and suggest that PLL is not completely covered and/or neutralized by the second alginate incubation and thus has a role in the host macrophage activation. The assay is sensitive to both alginate contaminants and microcapsule surface characteristics and may be a useful tool for the development of biocompatible microcapsules.

Natural polymers for the microencapsulation of cells

“…Poly-L-lysine does not bind tightly to alginates with a high content of G blocks because, in contrast to M blocks, they do not allow complete interaction with the polycation. When these capsules are implanted or incubated they induce a stronger response than capsules without poly-L-lysine [93,94]. Alginates can also be combined with other biopolymers to improve the biological response of the host.…”

Emerging technologies in the delivery of erythropoietin for therapeutics

“…209,210 Previous analyses carried out by our research group evidenced that a careful selection of purified alginates, selection of cell lines with adequate features, and the development of small and uniform microcapsules are key requirements to ensure an optimal biocompatibility and long-term functionality of the therapeutic molecules. 205,[211][212][213] However, little research has involved the study of parameters such as the implantation site of the encapsulated cells, the feasibility of using the same approach for syngeneic or allogeneic transplantation, or the application of a well vascularized immobilization device to permit close contact between the encapsulated cells and the bloodstream and thus improve the long-term efficacy of the graft.…”

“…Factors limiting the long-term efficacy of microencapsulated cells have been extensively studied. 210,214 In an effort to evaluate the importance of the biocompatibility of the biomaterials employed, a next step toward the optimization of our Epo-secreting C 2 C 12 microencapsulation methodology was taken and the long-term functionality of genetically modified cells immobilized in microcapsules elaborated with alginates of different properties (purification degree, composition, and viscosity) was studied. 215 The aim of the work was to determine whether the main variables demonstrated to be key factors for the in vitro biocompatibility of alginates and alginate microcapsules were also responsible for the in vivo long-term functionality of these cell constructs.…”

Encapsulation technologies in beta cell replacement therapies for Type 1 diabetes

“…Over the last two decades, studies conducted using extravascular isletcontaining tubular devices and sealed hollow fiber devices [41][42][43][44][45][46] have demonstrated poorer outcomes compared to similar devices transplanted intravascularly. These results were presumed to be a result of inadequate oxygen and nutrient diffusion within tubular devices transplanted at extravascular sites.…”