The effects of the molecular weight of chitosan on the tissue inflammatory response.

The molecular weight of chitosan (CS) may affect its physical properties and its ability to induce an appropriate host response. The biocompatibilities of CS membranes of low (LMWCS) and high (HMWCS) molecular weight were investigated by inserting these materials into the subcutaneous tissue of rats for 1-28 days and evaluating leukocyte infiltration, granulation tissue, fibrosis, arginase-1 immunostaining, as well as nuclear factor-κB (NF-κΒ) and fibroblast growth factor (FGF)-2 expressions. Both CS membranes induced a peak of leukocyte infiltration on the first day of insertion and stimulated granulation and fibrous tissue generation when compared to control. LMWCS induced more collagen deposition a week earlier, when compared to the control and HMWCS membrane. The membranes also increased arginase-1 immunostaining, a M2 macrophage marker. M2 macrophage is recognized as anti-inflammatory and pro-regenerative. NF-κB is an essential biomarker of the inflammatory process and induces the expression of several pro-inflammatory cytokines. The LMWCS membrane reduced inflammation, as indicated by a reduced nucleus/cytoplasm NF-κB ratio in surrounding tissue from days 7 to 14 when compared to control. On the first day, the expression of FGF-2, a biomarker of inflammatory resolution, was increased in the tissue of the LWMCS group, when compared with HMWCS, which was consistent with the type I collagen deposition. Thus, LWMCS was associated with a prior reduction of the inflammatory response and improved wound healing.