(WHS-L2.04) PROPHYLACTIC, ONE TIME DOSE OF RAC INHIBITOR MITIGATES FOREIGN BODY RESPONSE THROUGH IMMUNOMODULATION AT BOTH EARLY AND LATE TIME POINTS
Thursday, May 16, 2024
10:30 AM – 11:30 AM East Coast USA Time
Purpose: Our study explores how a single prophylactic dose of Rac inhibitor can significantly diminish the foreign body response around biomedical implants, potentially improving the efficacy and durability of such devices in patient care.
Methods: We used our previously published mechanically stimulated implants (MSIs) (Padmanabhan et al, 2023, Nat Biomed Eng) to create severe, pathological human FBR in mice. These MSIs were made of polydimethylsiloxane (PDMS) and encapsulated coin motors connected to external 3V batteries to initiate mechanical stimulation through vibration to create significant FBR fibrosis. Mice either received saline only (vehicle) or a prophylactic 5mg/kg NSC Rac inhibitor dose. After 7 days of vibration (POD 11), samples from 5 no vibration (NV), 5 MSI with saline (MSI+S) and 5 MSI with Rac Inhibitor (MSI+RI) were collected. After a month (POD30), 5 NV, 10 MSI+S, and 10 MSI+RI samples were collected. For this explanted tissue, FBR tissue was analyzed using staining including picrosirius red, hematoxylin and eosin, trichrome, and immunohistochemistry (IHC) for aSMA, F4/80, and DAPI.
Results: At POD 7, MSI+S significantly increased FBR compared to NV (p= 0.0465), and MSI with Rac Inhibitor treatment significantly reduced FBR by 47% from 284.8 to 133.8 µm compared to MSI+S (p=0. 0331) to be close to NV levels. Similarly, at POD30, MSI+S significantly increased FBR compared to NV (p=0.005), and MSI with Rac Inhibitor treatment significantly reduced FBR by 51% from 370.2 to 183.2 µm compared to MSI+S (p=0. 0.008), and not significantly different than NV levels. At early time points, MSI+S significantly reduced the length (p=0.037) while increasing alignment (p=0.001) and density (p=0.004) compared to NV. MSI+RI restored these collagen metrics (p=0.016, p=0.104, p=0.001) back to NV levels. At late time points, these effects were blunted. Using trichrome imaging, distinct architecture layers were evident in the MSI+S capsule, with a unique inner layer that had less wide, dense, and aligned collagen fibers (p=0.0020, p=0.0078, p=0.0051, respectively) compared to mechanically inhibited FBR which possessed no layering. Finally, we observed that Rac inhibition significantly reduced the number of macrophages (F4/80, p=0.02) and myofibroblasts (ASMA, p=0.03) compared to MSI+S.
Conclusions: Our study demonstrates that disrupting mechanical signaling with a one time prophylactic dose of Rac inhibitor notably reduces FBR capsule size and fibrotic ECM architecture. We observed a previously unreported layering in severe, pathological FBR, which seemed to linked with distinct layers of macrophages and fibroblasts within the capsule. Disrupting mechanical signaling with a one time, prophylactic therapeutic could have clinically meaningful effects for patients, and future biomedical implants could even be coated in a one time dose of this drug.