Abstract 16861: Liposomal Prednisolone Aggravates Atherosclerosis by Promoting Lipotoxicity in Macrophages

Abstract

Background: Whereas liposomal nanoparticles loaded with prednisolone phosphate (LN-PLP) reduced arterial wall inflammation in an atherosclerotic rabbit model, an unanticipated increase in arterial wall inflammation was observed in patients with atherosclerosis following LN-PLP infusions, despite proof of local accumulation in plaque macrophages. We hypothesized that this apparent discrepancy relates to the lipid-rich environment, and aimed to unravel the effect of LN-PLP upon local accumulation in lipid-laden macrophages. Methods & Results: LN-PLP administration for two weeks (10mg/kg biweekly) in LDLR-/- mice on a high fat diet (n=15/group) resulted in increased influx of CD11b+ monocytes (11±6%) in the plaque, compared to empty LN and PBS (<6%, p<0.01), assessed with flow cytometry. Monocyte staining (ER-MP58) was also increased in the plaque (24±11%) after LN-PLP, whereas monocyte number in plasma decreased. After six weeks of LN-PLP administration, plaque stages progressed more rapidly (40% of plaques in stage V) in LDLR-/- mice (n=15/group) compared to free PLP, empty LN and PBS (for all <10% of plaques in stage V). Immunohistochemical staining showed an increased macrophage content after LN-PLP (25±13% positivity for MAC3) compared to free PLP, empty LN or PBS (14%, p<0.01). Necrotic core area was also higher after LN-PLP (68±4%) compared to free PLP, empty LN and PBS (<50±3%, p2.00%, p<0.01), (ii) increased expression of ER stress (e.g. PERK 2.5±0.2 after LN-PLP versus <0.7±0.01 after empty LN or control, p<0.05), and (iii) 23% of macrophages underwent apoptosis compared to <3% of the macrophages in control conditions. Conclusion: Prednisolone, delivered locally in lipid-rich plaque macrophages, elicits a pro-atherogenic, lipotoxic effect, leading to more unstable plaques with larger necrotic core area and augmented macrophage apoptosis. These data bear direct consequences for future drug candidates aiming to target plaque macrophages; these require multifaceted screening taking the lipid-rich atherosclerotic milieu into account.