Multifunctional biomimetic porphyrin-lipid nanoparticles – novel nanoscale theranostics for atherosclerotic cardiovascular disease

Background: High-density lipoprotein (HDL) nanoagents have unrealized potential for atherosclerosis theranostics. Porphyrin-lipid HDL mimetic nanoparticles (Por-HDL-NPs) incorporate porphyrin-lipid which permits near infrared fluorescence imaging and positron emission tomography (PET) through chelation of Copper-64 (64Cu). The outer shell contains apolipoprotein A-I mimetic peptide R4F that interacts with scavenger receptor SR-BI, enabling macrophage targeting and therapeutic effects. We leveraged the theranostic properties of Por-HDL-NPs for testing in atherosclerosis. Methods and Results: In vitro, Por-HDL-NPs were internalised by immortalised bone marrow-derived macrophages (iBMDMs), visualised via fluorescence microscopy and flow cytometry. Por-HDL-NPs increased cholesterol efflux from [3H]-cholesterol-loaded iBMDMs, (49%, P<0.05), compared to reconstituted HDL. Incubation of iBMDMs with Por-HDL-NPs reduced mRNA levels of inflammatory mediators Il-1β (88%), Il-18 (54%) and Ccl5 (75%), and protein secretion of IL-1β (69%) and CCL5 (82%), P<0.05. Por-HDL-NPs suppressed inflammasome components Nlrp3 (69%) and Asc (36%), P<0.05. Studies using siRNA deletion of SR-B1 and methyl-β-cyclodextrin, revealed the anti-inflammatory properties of Por-HDL-NPs were independent of SR-B1 and cholesterol efflux. However, Por-HDL-NPs suppressed activation of inflammatory transcription factor NF-κB (53%, P<0.05). In Apoe-/- mice, PET imaging showed 64Cu-Por-HDL-NPs localised in hearts and detected increases in plaque over time with high-cholesterol diet. Por-HDL-NP fluorescence was visualised in aortic sinus plaques, co-localised with CD68+ macrophages, and by fluorescence IVIS imaging in aortic arch plaque. Por-HDL-NP-treated mice had smaller early-stage (22%) and unstable plaques (52%) and fewer circulating monocytes (32%) than control PBS-treated mice, P<0.05 for all. Conclusions: Por-HDL-NPs have theranostic properties, exhibiting both multi-modal imaging capabilities for identifying plaque and athero-protective therapeutic effects. ### Competing Interest Statement The authors have declared no competing interest.