Nick D. Tsihlis

Cardiovascular disease is associated with significant morbidity and mortality worldwide. Current medical and surgical interventions have limitations related to side-effects and long-term efficacy. Hence, there is a need for novel therapeutics tailored specifically for cardiovascular disease. Peptide amphiphile nanofibers are well-suited for this role. Here we discuss the molecular architecture and self-assembly process of peptide amphiphile nanofibers that make them ideal drug delivery vehicles, their adaptability and durability in physiologic conditions, and many successes in the field in developing targeted nanotherapeutics for drug delivery in the cardiovascular realm. The literature search was performed via PubMed using pertinent keywords with no restriction for dates of publication. When relevant publications were identified, these papers were used to find additional references. Despite their complexity, peptide amphiphile nanofibers offer a promising platform through which to deliver nanotherapeutics to treat cardiovascular disease. The future involves further development and evaluation of this technology in large animal models to strengthen translational data, discovery of additional physiologic targets, large scale standardized production, and incorporation of novel therapeutics. Importantly, we look forward to incorporating antioxidants into our existing PA nanofiber delivery vehicles to hopefully produce a synergistic effect of our targeted therapeutics.

Severe peripheral arterial disease (PAD) is often treated with surgical bypass grafting using autologous vein. When veins are unavailable, small-diameter expanded polytetrafluoroethylene (ePTFE) grafts are used but are associated with long-term poor performance. To address this, we developed poly(1,8-octanediol-co-citrate-co-ascorbate) (POCA) elastomer coatings for small-diameter ePTFE grafts that indirectly release nitric oxide via decomposition of circulating S-nitrosothiols (RSNO). Graft in vivo efficacy was assessed using a guinea pig aortic interposition model to evaluate neointimal formation. After 4 weeks, POCA-Grafts demonstrated significantly less occlusion compared to uncoated ePTFE grafts (16.8 % versus 29.7 %, p < 0.0005) and POC (poly(1,8-octanediol-co-citrate))-Grafts without ascorbate (16.8 % versus 19.9 %, p < 0.005). POCA-Grafts showed a 1.6-fold increase in endothelial cell coverage and significantly reduced leukocyte and macrophage infiltration compared to uncoated ePTFE grafts, particularly in female animals. These results suggest that the POCA coating enhances graft biocompatibility by promoting endothelialization and reducing inflammation, thereby inhibiting neointimal hyperplasia and improving graft patency. Overall, these results highlight the therapeutic potential of an ascorbate-functionalized poly(diol-co-citrate) elastomer for vascular applications and support future evaluation in large animal models.

The relationship between nanoparticle size, charge, shape, and in vivo biodistribution is of great importance for the rational design and selection of intravenously administered nanoparticles. A resource that aids in the selection and design of nanomaterials for this purpose would be a valuable tool. Previous literature reviews have examined narrow categories of nanomaterials or have not statistically analyzed a broad range of nanomaterial literature. Here, data regarding the biodistribution of intravenously administered synthetic and organic nanomaterials in animal models from literature available in PubMed is collected. This work outlines the effect of nanoparticle size, charge, shape, animal sex, and animal disease status on biodistribution of intravenously administered nanomaterials. Particle size and charge are found to significantly and independently influence biodistribution to several organs. Finally, animal sex and disease state are observed to function as effect modifiers for biodistribution.

An abdominal aortic aneurysm (AAA) is a localized dilation of the aorta located in the abdomen that poses a severe risk of death when ruptured. The cause of AAA is not fully understood, but degradation of medial elastin due to elastolytic matrix metalloproteinases is a key step leading to aortic dilation. Current therapeutic interventions are limited to surgical repair to prevent catastrophic rupture. Here we report the development of injectable supramolecular nanofibers using peptide amphiphile molecules designed to localize to AAA by targeting fragmented elastin, matrix metalloproteinase 2 (MMP-2), and membrane type 1 matrix metalloproteinase. We designed four targeting peptide sequences from X-ray crystallographic data and incorporated them into PA molecules via solid phase peptide synthesis. After co-assembling targeted and diluent PAs at different molar ratios, we assessed their ability to form nanofibers using transmission electron microscopy and to localize to AAA in male and female Sprague Dawley rats using light sheet fluorescence microscopy. We found that three formulations of the PA nanofibers were able to localize to AAA tissue, but the MMP-2 targeting PA substantially outperformed the other nanofibers. Additionally, we demonstrated that the MMP-2 targeting PA nanofibers had an optimal dose of 5 mg (~12 mg/kg). Our results show that there was not a significant difference in targeting between male and female Sprague Dawley rats. Given the ability of the MMP-2 targeting PA nanofiber to localize to AAA tissue, future studies will investigate potential diagnostic and targeted drug delivery applications for AAA.

Atherosclerotic plaque remains the leading contributor to cardiovascular disease and requires invasive surgical procedures for its removal. Nanomedicine offers a minimally invasive approach to alleviate plaque burden by targeted therapeutic delivery. However, nanocarriers are limited without the ability to sense and respond to the diseased microenvironment. In this study, targeted self‐assembled peptide amphiphile (PA) nanofibers are developed that cleave in response to biochemical cues expressed in atherosclerotic lesions—reactive oxygen species (ROS) and intracellular glutathione—to deliver a liver X receptor agonist (LXR) to enhance macrophage cholesterol efflux. The PAs release LXR in response to physiological levels of ROS and reducing agents and can be co‐assembled with plaque‐targeting PAs to form nanofibers. The resulting LXR PA nanofibers promoted cholesterol efflux from macrophages in vitro as well as LXR alone and with lower cytotoxicity. Further, the ApoA1‐LXR PA nanofibers target plaque within an atherosclerotic mouse model in vivo and activate ATP‐binding cassette A1 (ABCA1) expression as well as LXR alone with reduced liver toxicity. Taken together, these results demonstrate the potential of self‐assembled PA nanofibers for controlled therapeutic delivery to the atherosclerotic niche.

Pulmonary hypertension is a highly morbid disease with no cure. Available treatments are limited by systemic adverse effects due to non‐specific biodistribution. Self‐assembled peptide amphiphile (PA) nanofibers are biocompatible nanomaterials that can be modified to recognize specific biological markers to provide targeted drug delivery and reduce off‐target toxicity. Here, PA nanofibers that target the angiotensin I‐converting enzyme and the receptor for advanced glycation end‐products (RAGE) are developed, as both proteins are overexpressed in the lung with pulmonary hypertension. It is demonstrated that intravenous delivery of RAGE‐targeted nanofibers containing the targeting epitope LVFFAED (LVFF) significantly accumulated within the lung in a chronic hypoxia‐induced pulmonary hypertension mouse model. Using 3D light sheet fluorescence microscopy, it is shown that LVFF nanofiber localization is specific to the diseased pulmonary tissue with immunofluorescence analysis demonstrating colocalization of the targeted nanofiber to RAGE in the hypoxic lung. Furthermore, biodistribution studies show that significantly more LVFF nanofibers localized to the lung compared to major off‐target organs. Targeted nanofibers are retained within the pulmonary tissue for 24 h after injection. Collectively, these data demonstrate the potential of a RAGE‐targeted nanomaterial as a drug delivery platform to treat pulmonary hypertension.

Lack of long-term patency has hindered the clinical use of small-diameter prosthetic vascular grafts with the majority of these failures due to the development of neointimal hyperplasia. Previous studies by our laboratory revealed that small-diameter expanded polytetrafluoroethylene (ePTFE) grafts coated with antioxidant elastomers are a promising localized therapy to inhibit neointimal hyperplasia. This work is focused on the development of poly(diol-co-citrate-co-ascorbate) (POCA) elastomers with tunable properties for coating ePTFE vascular grafts. A bioactive POCA elastomer (@20 : 20 : 8, [citrate] : [diol] : [ascorbate]) coating was applied on a 1.5 mm diameter ePTFE vascular graft as the most promising therapeutic candidate for reducing neointimal hyperplasia. Surface ascorbate density on the POCA elastomer was increased to 67.5 ± 7.3 ng mg⁻¹ cm⁻². The mechanical, antioxidant, biodegradable, and biocompatible properties of POCA demonstrated desirable performance for in vivo use, inhibiting human aortic smooth muscle cell proliferation, while supporting human aortic endothelial cells. POCA elastomer coating number was adjusted by a modified spin-coating method to prepare small-diameter ePTFE vascular grafts similar to natural vessels. A significant reduction in neointimal hyperplasia was observed after implanting POCA-coated ePTFE vascular grafts in a guinea pig aortic interposition bypass graft model. POCA elastomer thus offers a new avenue that shows promise for use in vascular engineering to improve long-term patency rates by coating small-diameter ePTFE vascular grafts.