Fibrin as a delivery vehicle for active macrophage activator lipoprotein-2 peptide: in vitro studies

Fibrin sealants have been used in hemostasis and tissue sealing for over 25 years and recent studies have shown them to be an ideal delivery vehicle for cells and bioactive substances. We examined the use of fibrin as a delivery vehicle for the macrophage activator lipoprotein peptide (MALP)-2. MALP-2, secreted by mycoplasma, plays an important role in an early influx of leukocytes and infiltration by monocytes and their subsequent activation into macrophages as detected by their secretion of cytokines and chemoattractants. We first showed that MALP-2 activated several monocytic cell lines by increasing the expression of cytokines and chemoattractants in these cells. Furthermore, using a reverse transcription-polymerase chain reaction approach, we found that MALP-2 affected the gene expression of its own receptors: TLR2 and TLR4 in various cell types including fibroblasts, keratinocytes, and endothelial cells. Furthermore, the conditioned medium, containing secreted cytokines and chemoattractants, collected from monocytes treated with MALP-2 enhanced fibroblast migration using a standard wound culture assay. Next, we examined MALP-2's effect on the human monocyte cell line when it is mixed with fibrin. Monocytes seeded on three-dimensional fibrin containing MALP-2 secreted more cytokines such as interleukin-6, tumor necrosis factor-alpha, and chemoattractants such as macrophage inflammatory protein 1 alpha and monocyte chemoattractant protein 1 when compared with monocytes seeded on three-dimensional fibrin in the absence of MALP-2. This study supports the use of fibrin to deliver MALP-2, and possibly other peptides, in an active form that might enhance wound healing.