Effects of biodegradable polylactic acid fibers and dexamethasone on classically and alternatively activated macrophages

M Hämäläinen1, EL Paukkeri1, A Pekurinen1, R Nieminen1, M Kellomäki2, M Talja3, E Moilanen1. 1The Immunopharmacology Research Group, University of Tampere School of Medicine and Tampere University Hospital, Tampere, Finland, 2Department of Biomedical Engineering, Tampere University of Technology, Tampere, Finland, 3Department of Surgery, Päijät-Häme Central Hospital, Finland

Fully biodegradable medical devices are under development for various applications including vascular and urinary track stents. Addition of drug-eluting properties to biodegradable devises extends their usefulness e.g. in conditions complicated with inflammatory and fibrotic reactions. On the other hand, the biodegradable material itself may trigger inflammatory responses. In the present study we investigated the effects of pure and drug-eluting biodegradable fiber on macrophage activation.

Human and mouse macrophages were cultured in the absence or presence of pure or dexamethasone-eluting PLA 96/4 (polylactide consisting of 96% L-lactide and 4% D-lactide) fiber, and dexamethasone (1 µM), bacterial lipopolysaccharide (LPS, 10 ng/ml) or IL-4 (10 ng/ml) and IL-13 (10 ng/ml) were added after 72h incubation. After an additional 24h incubation culture media were collected for protein antibody array and ELISA measurements, and cells lysed for RNA extraction. Results are expressed as mean±SEM, n=4.

PLA 96/4 was found to induce a low-level inflammatory reaction in macrophages which was attenuated by dexamethasone as detected by an antibody array measuring 79 cytokines and other inflammatory factors. Also, dexamethasone and dexamethasone-releasing PLA 96/4 fiber were found to inhibit the production of IL-8 (inhibition by 77.7±4.9% and 89.5±4.2%, respectively), TNFα (98.3±6.1 and 99.2±3.0%), VEGF (66.7±2.2 and 66.7±3.3) and MCP-1 (82.2±5.6 and 89.6±8.3%) in cultured human macrophages activated through TLR4 pathway by exposing the cells to LPS.

To further study the effect of PLA96/4 fiber on macrophages, markers typical for “classical” (M1) and “alternative” (M2) macrophage activation were investigated. Murine J774 macrophages were cultured on PLA96/4 fibers and exposed to LPS or a combination of IL-4 and IL-13 to induce classical (M1) or alternative (M2) activation, respectively. The PLA fiber had a minor inhibitory effect on the LPS-induced production of the classical inflammatory mediators IL-12 (inhibited by 36.6±6.9%) and nitric oxide (24.9±7.2%), and no effect on IL-6. On the other hand, the PLA fiber clearly attenuated IL-4 and IL-13 induced expression of alternative activation markers arginase-1 (inhibition by 71.8±3.7%), Fizz1 (95.2±1.9%), Ym-1 (79.8±4.9%) and IL-10 (85.8±8.1%).

In the present study, we investigated the effect of polylactic acid (96% L-lactide/4% D-lactide), a fully biodegradable material used in experimental medical devices such as vascular and urinary track stents, on macrophage responses. PLA96/4 was found to suppress alternative (M2) type activation while only minor effects were found on classical (M1) type activation. The results are implicated in the biocompatibility of biodegradable medical devices and can be utilized in the development of improved drug-eluting materials and devises.