Abstract Body (Do not enter title and authors here): Introduction
Myocardial infarction (MI) causes adverse remodeling, leading to heart failure. To reverse this damage, we applied and evaluated two anti-inflammatory therapies on neovascularization (NV) and fibrosis in in vivo mouse cardiac tissue using a custom-built optoacoustic tomography, verified with histological analysis by clinical pathologist. This study established a quantitative platform for assessing cardiac regeneration by modulating post-MI inflammation, supporting emerging antifibrotic therapies.

Methods
Eighteen-week-old cGAS-null mice (n = 12; 4/group; 5 female, 7 male) were randomized into 3 groups: (a) control (saline), (b) Lp-X nanoparticles, and (c) free drug (rapamycin, an anti-inflammatory). MI was induced by ligating the left anterior descending (LAD) coronary artery through the 3^rd and 4^th intercostal space. Weekly tail vein injections (100 μL, 1 mg/mL or saline) began immediately post-surgery for five weeks. At week 2, DiR-labeled Lp-X particles were used for tracking the uptake via IVIS SpectrumCT. Optoacoustic imaging monitored deoxygenated hemoglobin (Hb), oxygenated hemoglobin (HbO₂), and assess NV at 785 nm over five weeks. At week 5, hearts were excised and stained with H&E, Pentachrome, and Elastic Van Gieson for histological analysis. Fibrosis was quantified by collagen volume fraction (CVF = collagen area/total tissue area ×100%). All procedures followed UTSW protocol 2023-103473.

Results
After five weeks of treatment, Lp-X and rapamycin both reduced NV but had opposite effects on fibrosis (Fig.1a, 3). Lp-X reduced fibrosis (36.13%±27.15%) and NV (41.03%±34.32%), while rapamycin increased fibrosis (19.46%±17.32%) and decreased NV (9.34%±47.04%) compared to control (Fig.1d). CT-fluorescence imaging verified targeted drug delivery (Fig.2). Longitudinal quantification of Hb, HbO₂, and 785 nm signal intensity is shown with mean ± std (A.U., Fig.1b). A strong positive correlation was observed between HbO₂ levels and NV across all groups (Fig.1c), indicating that improved local oxygenation is closely associated with angiogenesis (R = 0.90 control, 0.71 Lp-X, 0.75 rapamycin).

Conclusions
Using noninvasive optoacoustic imaging, we quantified the effect of Lp-X nanoparticles and rapamycin on post-MI NV and fibrosis. Both inhibited NV but had opposite effects on fibrosis. This platform offers a robust method to assess cardiac repair and support precision medicine.