Evaluation of reconstituted high-density lipoprotein (rHDL) as a drug delivery platform – a detailed survey of rHDL particles ranging from biophysical properties to clinical implications

High-Density Lipoprotein Subclasses and Their Role in the Prevention and Treatment of Cardiovascular Disease: A Narrative Review

The association between high-density lipoprotein cholesterol (HDL-C) and cardiovascular disease (CVD) is controversial. HDL-C is one content type of high-density lipoprotein (HDL). HDL consists of diverse proteins and lipids and can be classified into different subclasses based on size, shape, charge, and density, and can change dynamically in disease states. Therefore, HDL-C levels alone cannot represent HDLs' cardioprotective role. In this review, we summarized the methods for separating HDL subclasses, the studies on the association between HDL subclasses and cardiovascular risk (CVR), and the impact of lipid-modifying medications and nonpharmacological approaches (exercise training, dietary omega fatty acids, and low-density lipoprotein apheresis) on HDL subclasses. As HDL is a natural nanoplatform, recombinant HDLs (rHDLs) have been used as a delivery system in vivo by loading small interfering RNA, drugs, contrast agents, etc. Therefore, we further reviewed the HDL subclasses used in rHDLs and their advantages and disadvantages. This review would provide recommendations and guidance for future studies on HDL subclasses' cardioprotective roles.

Recent progress in biomimetic nanomedicines based on versatile targeting strategy for atherosclerosis therapy

Atherosclerosis (AS) is considered to be one of the major causes of cardiovascular disease. Its pathological microenvironment is characterised by increased production of reactive oxygen species, lipid oxides, and excessive inflammatory factors, which accumulate at the monolayer endothelial cells in the vascular wall to form AS plaques. Therefore, intervention in the pathological microenvironment would be beneficial in delaying AS. Researchers have designed biomimetic nanomedicines with excellent biocompatibility and the ability to avoid being cleared by the immune system through different therapeutic strategies to achieve better therapeutic effects for the characteristics of AS. Biomimetic nanomedicines can further enhance delivery efficiency and improve treatment efficacy due to their good biocompatibility and ability to evade clearance by the immune system. Biomimetic nanomedicines based on therapeutic strategies such as neutralising inflammatory factors, ROS scavengers, lipid clearance and integration of diagnosis and treatment are versatile approaches for effective treatment of AS. The review firstly summarises the targeting therapeutic strategy of biomimetic nanomedicine for AS in recent 5 years. Biomimetic nanomedicines using cell membranes, proteins, and extracellular vesicles as carriers have been developed for AS.

The effect of lipid composition on the thermal stability of nanodiscs

Discoidal lipid nanoparticles (LNPs) called Nanodiscs (NDs) are derived from human high-density lipoprotein (HDL). Such biomimetics are ideally suited for the stabilization and delivery of pharmaceuticals, including chemicals, bio-active proteins and vaccines. The stability and circulation lifetimes of reconstituted HDL nanoparticles, including NDs, are variable. Lipids found in thermophilic archaea and bacteria are prime candidates for the stabilization of LNPs. We report the thermal stability of NDs prepared with lipids that differ in saturation, have either ether- or ester linkages between the fatty acid and glycerol backbone or contain isoprenoid fatty acid tails (phytanyl lipids). NDs with two saturated fatty acids show a much greater long-term thermostability than NDs with an unsaturated fatty acid. Ether fatty acid linkages, commonly found in thermophiles, did not improve stability of NDs compared to ester fatty acid linkages when using saturated lipids. NDs containing phytanyl and saturated alkyl fatty acids show similar stability at 37 °C. NDs assembled with phytanyl lipids contain three copies of the membrane scaffolding protein as opposed to the canonical dimer found in conventional NDs. The findings present a strong basis for the production of thermostable NDs through the selection of appropriate lipids and are likely broadly applicable to LNP development.

Lipid nanoparticles for targeted delivery of anticancer therapeutics: Recent advances in development of siRNA and lipoprotein-mimicking nanocarriers

The limitations inherent in conventional cancer treatment methods have stimulated recent efforts towards the design of safe nanomedicines with high efficacy for combating cancer through various promising approaches. A plethora of nanoparticles has been introduced in the development of cancer nanomedicines. Among them, different lipid nanoparticles are attractive for use due to numerous advantages and unique opportunities, including biocompatibility and targeted drug delivery. However, a comprehensive understanding of nano-bio interactions is imperative to facilitate the translation of recent advancements in the development of cancer nanomedicines into clinical practice. In this contribution, we focus on lipoprotein-mimicking nanoparticles, which possess unique features and compositions facilitating drug transport through receptor binding mechanisms. Additionally, we describe potential applications of siRNA lipid nanoparticles in the future design of anticancer nanomedicines. Thus, this review highlights recent progress, challenges, and opportunities of lipid-based lipoprotein-mimicking nanoparticles and siRNA nanocarriers designed for the targeted delivery of anticancer therapeutic agents.

Advances in drug delivery to atherosclerosis: Investigating the efficiency of different nanomaterials employed for different type of drugs

Atherosclerosis is the build-up of fatty deposits in the arteries, which is the main underlying cause of cardiovascular diseases and the leading cause of global morbidity and mortality. Current pharmaceutical treatment options are unable to effectively treat the plaque in the later stages of the disease. Instead, they are aimed at resolving the risk factors. Nanomaterials and nanoparticle-mediated therapies have become increasingly popular for the treatment of atherosclerosis due to their targeted and controlled release of therapeutics. In this review, we discuss different types of therapeutics used to treat this disease and focus on the different nanomaterial strategies employed for the delivery of these drugs, enabling the effective and efficient resolution of the atherosclerotic plaque. The ideal nanomaterial strategy for each drug type (e.g. statins, nucleic acids, small molecule drugs, peptides) will be comprehensively discussed.

Biokinetics, radiopharmacokinetics and estimation of the absorbed dose in healthy organs due to Technetium-99m transported in the core and on the surface of reconstituted high-density lipoprotein nanoparticles

The development of rHDL-radionuclide theragnostic systems requires evaluation of the absorbed doses that would be produced in healthy tissues and organs at risk. Technetium-99m is the most widely used radionuclide for diagnostic imaging, therefore, the design of theragnostic reconstituted high density-lipoprotein (rHDL) nanosystems labeled with Technetium-99m offers multiple possibilities.

OBJECTIVE

To determine the biokinetics, radiopharmacokinetics and estimate the absorbed doses induced in healthy organs by Technetium-99m transported in the core and on the surface of rHDL.

METHODS

Biokinetic and radiopharmacokinetic models of rHDL/[99mTc]Tc-HYNIC-DA (Technetium-99m in the core) and [99mTc]Tc-HYNIC-rHDL (Technetium-99m on the surface) were calculated from their ex vivo biodistribution in healthy mice. Absorbed doses were estimated by the MIRD formalism using OLINDA/EXM and LMFIT softwares.

RESULTS

rHDL/[99mTc]Tc-HYNIC-DA and [99mTc]Tc-HYNIC-rHDL show instantaneous absorption in kidney, lung, heart and pancreas, with slower absorption in spleen. rHDL/[99mTc]Tc-HYNIC-DA is absorbed more slowly in the intestine, while [99mTc]Tc-HYNIC-rHDL is absorbed more slowly in the liver. The main target organ for rHDL/[99mTc]Tc-HYNIC-DA, which is hydrophobic in nature, is the liver, whereas the kidney is for the more hydrophilic [99mTc]Tc-HYNIC-rHDL. Assuming that 925 MBq (25 mCi) of Technetium-99m, carried in the core or on the surface of rHDL, are administered, the maximum tolerated doses for the organs of greatest accumulation are not exceeded.

CONCLUSION

Theragnostic systems based on 99mTc-labeled rHDL are safe from the dosimetric point of view. The dose estimates obtained can be used to adjust the 99mTc-activity to be administered in future clinical trials.

Engineered rHDL Nanoparticles as a Suitable Platform for Theranostic Applications

Reconstituted high-density lipoproteins (rHDLs) can transport and specifically release drugs and imaging agents, mediated by the Scavenger Receptor Type B1 (SR-B1) present in a wide variety of tumor cells, providing convenient platforms for developing theranostic systems. Usually, phospholipids or Apo-A1 lipoproteins on the particle surfaces are the motifs used to conjugate molecules for the multifunctional purposes of the rHDL nanoparticles. Cholesterol has been less addressed as a region to bind molecules or functional groups to the rHDL surface. To maximize the efficacy and improve the radiolabeling of rHDL theranostic systems, we synthesized compounds with bifunctional agents covalently linked to cholesterol. This strategy means that the radionuclide was bound to the surface, while the therapeutic agent was encapsulated in the lipophilic core. In this research, HYNIC-S-(CH2)3-S-Cholesterol and DOTA-benzene-p-SC-NH-(CH2)2-NH-Cholesterol derivatives were synthesized to prepare nanoparticles (NPs) of HYNIC-rHDL and DOTA-rHDL, which can subsequently be linked to radionuclides for SPECT/PET imaging or targeted radiotherapy. HYNIC is used to complexing 99mTc and DOTA for labeling molecules with 111, 113mIn, 67, 68Ga, 177Lu, 161Tb, 225Ac, and 64Cu, among others. In vitro studies showed that the NPs of HYNIC-rHDL and DOTA-rHDL maintain specific recognition by SR-B1 and the ability to internalize and release, in the cytosol of cancer cells, the molecules carried in their core. The biodistribution in mice showed a similar behavior between rHDL (without surface modification) and HYNIC-rHDL, while DOTA-rHDL exhibited a different biodistribution pattern due to the significant reduction in the lipophilicity of the modified cholesterol molecule. Both systems demonstrated characteristics for the development of suitable theranostic platforms for personalized cancer treatment.

225Ac-rHDL Nanoparticles: A Potential Agent for Targeted Alpha-Particle Therapy of Tumors Overexpressing SR-BI Proteins

Actinium-225 and other alpha-particle-emitting radionuclides have shown high potential for cancer treatment. Reconstituted high-density lipoproteins (rHDL) specifically recognize the scavenger receptor B type I (SR-BI) overexpressed in several types of cancer cells. Furthermore, after rHDL-SR-BI recognition, the rHDL content is injected into the cell cytoplasm. This research aimed to prepare a targeted ²²⁵Ac-delivering nanosystem by encapsulating the radionuclide into rHDL nanoparticles. The synthesis of rHDL was performed in two steps using the microfluidic synthesis method for the subsequent encapsulation of ²²⁵Ac, previously complexed to a lipophilic molecule (²²⁵Ac-DOTA-benzene-p-SCN, CLog P = 3.42). The nanosystem (13 nm particle size) showed a radiochemical purity higher than 99% and stability in human serum. In vitro studies in HEP-G2 and PC-3 cancer cells (SR-BI positive) demonstrated that ²²⁵Ac was successfully internalized into the cytoplasm of cells, delivering high radiation doses to cell nuclei (107 Gy to PC-3 and 161 Gy to HEP-G2 nuclei at 24 h), resulting in a significant decrease in cell viability down to 3.22 ± 0.72% for the PC-3 and to 1.79 ± 0.23% for HEP-G2 at 192 h after ²²⁵Ac-rHDL treatment. After intratumoral ²²⁵Ac-rHDL administration in mice bearing HEP-G2 tumors, the biokinetic profile showed significant retention of radioactivity in the tumor masses (90.16 ± 2.52% of the injected activity), which generated ablative radiation doses (649 Gy/MBq). The results demonstrated adequate properties of rHDL as a stable carrier for selective deposition of ²²⁵Ac within cancer cells overexpressing SR-BI. The results obtained in this research justify further preclinical studies, designed to evaluate the therapeutic efficacy of the ²²⁵Ac-rHDL system for targeted alpha-particle therapy of tumors that overexpress the SR-BI receptor.

Enhanced Anti-Atherosclerotic Efficacy of pH-Responsively Releasable Ganglioside GM3 Delivered by Reconstituted High-Density Lipoprotein

Recently, the atheroprotective role of endogenous GM3 and an atherogenesis-inhibiting effect of exogenous GM3 suggested a possibility of exogenous GM3 being recruited as an anti-atherosclerotic drug. This study seeks to endow exogenous GM3 with atherosclerotic targetability via reconstituted high-density lipoprotein (rHDL), an atherosclerotic targeting drug nanocarrier. Unloaded rHDL, rHDL loaded with exogenous GM3 at a low concentration (GM3_L-rHDL), and rHDL carrying GM3 at a relatively high concentration (GM3_H-rHDL) were prepared and characterized. The inhibitory effect of GM3-rHDL on lipid deposition in macrophages was confirmed, and GM3-rHDL did not affect the survival of red blood cells. In vivo experiments using ApoE^-/- mice fed a high fat diet further confirmed the anti-atherosclerotic efficacy of exogenous GM3 and demonstrated that GM3 packed in HDL nanoparticles (GM3-rHDL) has an enhanced anti-atherosclerotic efficacy and a reduced effective dose of GM3. Then, the macrophage- and atherosclerotic plaque-targeting abilities of GM3-rHD, most likely via the interaction of ApoA-I on GM3-rHDL with its receptors (e.g., SR-B1) on cells, were certified via a microsphere-based method and an aortic fragment-based method, respectively. Moreover, we found that solution acidification enhanced GM3 release from GM3-rHDL nanoparticles, implying the pH-responsive GM3 release when GM3-rHDL enters the acidic atherosclerotic plaques from the neutral blood. The rHDL-mediated atherosclerotic targetability and pH-responsive GM3 release of GM3-rHDL enhanced the anti-atherosclerotic efficacy of exogenous GM3. The development of the GM3-rHDL nanoparticle may help with the application of exogenous GM3 as a clinical drug. Moreover, the data imply that the GM3-rHDL nanoparticle has the potential of being recruited as a drug nanocarrier with atherosclerotic targetability and enhanced anti-atherosclerotic efficacy.

Targeted photodynamic therapy using reconstituted high-density lipoproteins as rhodamine transporters

Reconstituted high-density lipoprotein (rHDL) nanoparticles are excellent transporters of molecules and very useful for targeted therapy as they specifically recognize the scavenger receptor, class B1 (SR-B1) that is present on the surface of a wide range of tumor cells. However, they have rarely been employed to transport photosensitizers (PS) for photodynamic therapy (PDT). Rhodamine (R) compounds have been dismissed as useful PSs for PDT due to their low ¹O₂ production, excitation wavelengths with little tissue penetration, and poor selectivity for tumor cells. It was recently demonstrated that when irradiating at 532 nm or with Cerenkov radiation (CR) from a β-emitting radionuclide, R123, R6G, and RB undergo electron transfer reactions (type I reaction) with folic acid. R6G also produces type I reactions with O₂. In this work, the photodynamic effects of the rHDL-R system were evaluated in vitro. rHDL nanoparticles loaded with R123, R6G, and RB were synthesized, and the PS was internalized into T47D tumor cells. When cells were irradiated with a 532-nm laser in the presence of an rHDL-R systems, a cytotoxic photodynamic effect was obtained in the order R6G > R123 > RB. In the presence of CR from a ¹⁷⁷Lu source, cytotoxicity showed the order R6G > RB > R123. The higher cytotoxicity induced by R6G in both cases corresponds to higher cellular internalization and larger production of type I and II reactions. Thus, in this work, it is proposed that rHDL-R/¹⁷⁷Lu system can be applied in theragnostics as a multimodal radiotherapy-PDT-imaging system (imaging by SPECT or Cerenkov) and in hypoxic solid tumors in which external radiation is not effective and ¹⁷⁷Lu-CR acts as light source.

Reconstituted HDL as a therapeutic delivery device

Studies of "pre β" high density lipoprotein (HDL) and reconstituted HDL (rHDL) have contributed to our understanding of the Reverse Cholesterol Transport pathway. The relative ease with which discoidal rHDL can be generated in vitro has led to novel applications including a) infusion of rHDL into patients to promote regression of atherosclerosis; b) use of rHDL as a miniature membrane for integration of transmembrane proteins in a native-like conformation and c) incorporation of hydrophobic bioactive molecules into rHDL, creating a delivery device. The present review is focused on bioactive agent containing rHDL. The broad array of hydrophobic bioactive molecules successfully incorporated into these particles is discussed, as well as the use of natural lipids and synthetic lipid analogs to confer distinctive binding activity. This technology remains in its infancy with the full potential of these simple, yet elegant, nanoparticles still to be discovered.

Pitfalls and opportunities in quantitative fluorescence-based nanomedicine studies - A commentary

Fluorescence-based techniques are prevalent in studies of nanomedicine-targeting to cells and tissues. However, fluorescence-based studies are rarely quantitative, thus prohibiting direct comparisons of nanomedicine-performance across studies. With this Commentary, we aim to provoke critical thinking about experimental design by treating some often-overlooked pitfalls in 'quantitative' fluorescence-based experimentation. Focusing on fluorescence-labeled nanoparticles, we cover mechanisms like solvent-interactions and fluorophore-dissociation, which disqualify the assumption that 'a higher fluorescence readout' translates directly to 'a better targeting efficacy'. With departure in recent literature, we propose guidelines for circumventing these pitfalls in studies of tissue-accumulation and cell-uptake, thus covering fluorescence-based techniques like bulk solution fluorescence measurements, fluorescence microscopy, flow cytometry, and infrared fluorescence imaging. With this, we hope to lay a foundation for more 'quantitative thinking' during experimental design, enabling (for example) the estimation and reporting of actual numbers of fluorescent nanoparticles accumulated in cells and organs.

Reconstituted high density lipoprotein (rHDL), a versatile drug delivery nanoplatform for tumor targeted therapy

rHDL is a synthesized drug delivery nanoplatform exhibiting excellent biocompatibility, which possesses most of the advantages of HDL. rHDL shows almost no toxicity and can be degraded to non-toxic substances in vivo. The severe limitation of the application of various antitumor agents is mainly due to their low bioavailability, high toxicity, poor stability, etc. Favorably, antitumor drug-loaded rHDL nanoparticles (NPs), which are known as an important drug delivery system (DDS), help to change the situation a lot. This DDS shows an outstanding active-targeting ability towards tumor cells and improves the therapeutic effect during antitumor treatment while overcoming the shortcomings mentioned above. In the following text, we will mainly focus on the various applications of rHDL in tumor targeted therapy by describing the properties, preparation, receptor active-targeting ability and antitumor effects of antineoplastic drug-loaded rHDL NPs.

Physico-chemical and physiological determinants of lipo-nanoparticle stability

Liposome-based nanoparticles (NPs) comprised mostly of phospholipids (PLs) have been developed to deliver diagnostic and therapeutic agents. Whereas reassembled plasma lipoproteins have been tested as NP carriers of hydrophobic molecules, they are unstable because the components can spontaneously transfer to other PL surfaces-cell membranes and lipoproteins-and can be degraded by plasma lipases. Here we review two strategies for NP stabilization. One is to use PLs that contain long acyl-chains: according to a quantitative thermodynamic model and in vivo tests, increasing the chain length of a PL reduces the spontaneous transfer rate and increases plasma lifetime. A second strategy is to substitute ether for ester bonds which makes the PLs lipase resistant. We conclude with recommendations of simple ex vivo and in vitro tests of NP stability that should be conducted before in vivo tests are begun.

Effect of apoA-I PEGylation on the Biological Fate of Biomimetic High-Density Lipoproteins

Biomimetic high-density lipoproteins (b-HDL) have in the past two decades been applied for various drug delivery applications. As b-HDL inherently have relatively long circulation half-life and high tumor accumulation, this has inspired researchers to use b-HDL to selectively deliver drugs to tumors. PEGylation of the b-HDL has been pursued to increase the circulation half-life and therapeutic efficacy even further. The b-HDL consist of lipids stabilized by a protein/peptide scaffold, and while PEGylation of the scaffold has been shown to greatly increase the circulation half-life of the scaffold, the effect of PEGylation of the lipids is much less significant. Still, it remains to be evaluated how the biological fate, including cellular uptake, biodistribution, and circulation half-life, of the b-HDL lipids is affected by PEGylation of the b-HDL scaffold. We studied this with apolipoprotein A-I (apoA-I)-based b-HDL and mono-PEGylated b-HDL (PEG b-HDL) both in vitro and in vivo. We found that PEGylation of the b-HDL scaffold only seemed to have minimal effect on the biological fate of the lipids. Both b-HDL and PEG b-HDL overall shared similar biological fates, which includes cellular uptake through the scavenger receptor class B type 1 (SR-BI) and relatively high tumor accumulation. This highlights that b-HDL are dynamic particles, and the biological fates of the b-HDL components (lipids and scaffold) can differ. A phenomenon that may also apply for other multicomponent nanoparticles.

A systematic review of the biodistribution of biomimetic high-density lipoproteins in mice

For the past two decades, biomimetic high-density lipoproteins (b-HDL) have been used for various drug delivery applications. The b-HDL mimic the endogenous HDL, and therefore possess many attractive features for drug delivery, including high biocompatibility, biodegradability, and ability to transport and deliver their cargo (e.g. drugs and/or imaging agents) to specific cells and tissues that are recognized by HDL. The b-HDL designs reported in the literature often differ in size, shape, composition, and type of incorporated cargo. However, there exists only limited insight into how the b-HDL design dictates their biodistribution. To fill this gap, we conducted a comprehensive systematic literature search of biodistribution studies using various designs of apolipoprotein A-I (apoA-I)-based b-HDL (i.e. b-HDL with apoA-I, apoA-I mutants, or apoA-I mimicking peptides). We carefully screened 679 papers (search hits) for b-HDL biodistribution studies in mice, and ended up with 24 relevant biodistribution profiles that we compared according to b-HDL design. We show similarities between b-HDL biodistribution studies irrespectively of the b-HDL design, whereas the biodistribution of the b-HDL components (lipids and scaffold) differ significantly. The b-HDL lipids primarily accumulate in liver, while the b-HDL scaffold primarily accumulates in the kidney. Furthermore, both b-HDL lipids and scaffold accumulate well in the tumor tissue in tumor-bearing mice. Finally, we present essential considerations and strategies for b-HDL labeling, and discuss how the b-HDL biodistribution can be tuned through particle design and administration route. Our meta-analysis and discussions provide a detailed overview of the fate of b-HDL in mice that is highly relevant when applying b-HDL for drug delivery or in vivo imaging applications.

Mechanistic Understanding From Molecular Dynamics Simulation in Pharmaceutical Research 1: Drug Delivery

In this review, we outline the growing role that molecular dynamics simulation is able to play as a design tool in drug delivery. We cover both the pharmaceutical and computational backgrounds, in a pedagogical fashion, as this review is designed to be equally accessible to pharmaceutical researchers interested in what this new computational tool is capable of and experts in molecular modeling who wish to pursue pharmaceutical applications as a context for their research. The field has become too broad for us to concisely describe all work that has been carried out; many comprehensive reviews on subtopics of this area are cited. We discuss the insight molecular dynamics modeling has provided in dissolution and solubility, however, the majority of the discussion is focused on nanomedicine: the development of nanoscale drug delivery vehicles. Here we focus on three areas where molecular dynamics modeling has had a particularly strong impact: (1) behavior in the bloodstream and protective polymer corona, (2) Drug loading and controlled release, and (3) Nanoparticle interaction with both model and biological membranes. We conclude with some thoughts on the role that molecular dynamics simulation can grow to play in the development of new drug delivery systems.

Endocytic recycling as cellular trafficking fate of simvastatin-loaded discoidal reconstituted high-density lipoprotein to coordinate cholesterol efflux and drug influx

Reconstituted high-density lipoproteins (rHDLs) hold promise as nanocarriers for atherosclerosis-targeted delivery, with biofunctions typified by mediating cholesterol efflux. The paradox is how rHDL offloads the delivered drugs into atherosclerotic foam cells, while simultaneously transferring cholesterol out of cells. Herein, simvastatin-loaded discoidal rHDL (ST-d-rHDL), constructed based on established paradigms, was employed to investigate its basic trafficking mechanism in foam cells. As proved, ST-d-rHDL was resecreted via lysosomal and Golgi apparatus-recycling endosome-mediated pathways following clathrin-mediated endocytosis. And the resecretion ratio reached 60% within 6-h chase with excessive ST-d-rHDLs. During the rHDL resecretion, 39% of cellular cholesterol efflux was detected, accompanied by 85% of the encapsulated cargo released intracellularly. Furthermore, the recycling rate was demonstrated to be promoted by smaller rHDL size and higher cellular lipid contents. Collectively, endocytic recycling confers the synergism in ST-d-rHDL to coordinate cholesterol efflux and intracellular drug release, providing new insights into design of biofunctional rHDL.

Head-to-Head Comparison of the Penetration Efficiency of Lipid-Based Nanoparticles into Tumor Spheroids

Most tumor-targeted drug delivery systems must overcome a large variety of physiological barriers before reaching the tumor site and diffuse through the tight network of tumor cells. Many studies focus on optimizing the first part, the accumulation of drug carriers at the tumor site, ignoring the penetration efficiency, i.e., a measure of the ability of a drug delivery system to overcome tumor surface adherence and uptake. We used three-dimensional (3D) tumor spheroids in combination with light-sheet fluorescence microscopy in a head-to-head comparison of a variety of commonly used lipid-based nanoparticles, including liposomes, PEGylated liposomes, lipoplexes, and reconstituted high-density lipoproteins (rHDL). Whilst PEGylation of liposomes only had minor effects on the penetration efficiency, we show that lipoplexes are mainly associated with the periphery of tumor spheroids, possibly due to their positive surface charge, leading to fusion with the cells at the spheroid surface or aggregation. Surprisingly, the rHDL showed significantly higher penetration efficiency and high accumulation inside the spheroid. While these findings indeed could be relevant when designing novel drug delivery systems based on lipid-based nanoparticles, we stress that the used platform and the detailed image analysis are a versatile tool for in vitro studies of the penetration efficiency of nanoparticles in tumors.

Preparation and characterization of lipid emulsions containing styrene maleic acid copolymer for the development of pH-responsive drug carriers

Lipid emulsions are potential carriers for poorly water-soluble drugs. Previously, we revealed that lipid nanoparticles complexed with styrene maleic acid copolymer (SMA) disintegrate under acidic pH. In the present study, SMA-containing lipid emulsions (SMA emulsions) were prepared and their physicochemical and biological properties were examined to test whether SMA emulsions could be used as a trigger to facilitate drug release in response to pH reduction. By sonicating lipid and SMA mixtures, homogeneously sized SMA emulsion particles were prepared as verified via dynamic light scattering and transmission electron microscopy. Upon the reduction of solution pH, disintegration of SMA emulsions was observed, which may be utilized for drug release at mildly acidic pH. In addition, the sensitivity to pH changes could be controlled by altering the lipid composition. Serum proteins bound to SMA emulsions were analyzed to predict the metabolic fate upon intravenous injection. Predictably, apolipoproteins were abundantly bound, suggesting that SMA emulsions should avoid being recognized as foreign substances. Furthermore, subcellular distribution studies using a human breast cancer cell line (MDA-MB-231) demonstrated that SMA emulsions localize to lysosomes, which have a lower pH. These results suggest that SMA emulsions could be promising pH-responsive drug carriers.

Reconfiguring Nature's Cholesterol Accepting Lipoproteins as Nanoparticle Platforms for Transport and Delivery of Therapeutic and Imaging Agents

Apolipoproteins are critical structural and functional components of lipoproteins, which are large supramolecular assemblies composed predominantly of lipids and proteins, and other biomolecules such as nucleic acids. A signature feature of apolipoproteins is the preponderance of amphipathic α-helical motifs that dictate their ability to make extensive non-covalent inter- or intra-molecular helix-helix interactions in lipid-free states or helix-lipid interactions with hydrophobic biomolecules in lipid-associated states. This review focuses on the latter ability of apolipoproteins, which has been capitalized on to reconstitute synthetic nanoscale binary/ternary lipoprotein complexes composed of apolipoproteins/peptides and lipids that mimic native high-density lipoproteins (HDLs) with the goal to transport drugs. It traces the historical development of our understanding of these nanostructures and how the cholesterol accepting property of HDL has been reconfigured to develop them as drug-loading platforms. The review provides the structural perspective of these platforms with different types of apolipoproteins and an overview of their synthesis. It also examines the cargo that have been loaded into the core for therapeutic and imaging purposes. Finally, it lays out the merits and challenges associated with apolipoprotein-based nanostructures with a future perspective calling for a need to develop "zip-code"-based delivery for therapeutic and diagnostic applications.

Assembly and Characterization of Biocompatible Coenzyme Q10 -Enriched Lipid Nanoparticles

Coenzyme Q₁₀ (CoQ₁₀ ) is a strongly hydrophobic lipid that functions in the electron transport chain and as an antioxidant. CoQ₁₀ was conferred with aqueous solubility by incorporation into nanoparticles containing phosphatidylcholine (PtdCho) and apolipoprotein (apo) A-I. These particles, termed CoQ₁₀ nanodisks (ND), contain 1.0 mg CoQ₁₀ /5 mg PtdCho/2 mg apoA-I (97% CoQ₁₀ solubilization efficiency). UV/Vis absorbance spectroscopy of CoQ₁₀ ND revealed a characteristic absorbance peak centered at 275 nm. Incorporation of CoQ₁₀ into ND resulted in quenching of apoA-I tryptophan fluorescence emission. Gel filtration chromatography of CoQ₁₀ ND gave rise to a single major absorbance peak and HPLC of material extracted from this peak confirmed the presence of CoQ₁₀ . Incubation of cultured cells with CoQ₁₀ ND, but not empty ND, resulted in a significant increase in the CoQ₁₀ content of mitochondria as well as enhanced oxidative phosphorylation, as observed by a ~24% increase in maximal oxygen consumption rate. Collectively, a facile method to solubilize significant quantities of CoQ₁₀ in lipid nanoparticles has been developed. The availability of CoQ₁₀ ND provides a novel means to investigate biochemical aspects of CoQ₁₀ uptake by cells and/or administer it to subjects deficient in this key lipid as a result of inborn errors of metabolism, statin therapy, or otherwise.

A quantitativeex vivostudy of the interactions between reconstituted high-density lipoproteins and human leukocytes

Knowledge of the interactions between nanoparticles and immune cells is required for optimal design of nanoparticle-based drug delivery systems, either when aiming to avoid phagocytic clearance of the nanoparticles or promote an immune response by delivering therapeutic agents to specific immune cells. Several studies have suggested that reconstituted high-density lipoproteins (rHDL) are attractive drug delivery vehicles. However, detailed studies of rHDL interactions with circulating leukocytes are limited. Here, we evaluated the association of discoidal rHDL with leukocytes in human whole blood (HWB) using quantitative approaches. We found that while the rHDL of various lipid compositions associated preferentially with monocytes, the degree of association depended on the lipid composition. However, consistent with the long circulation half-life of rHDL, we show that only a minor fraction of the rHDL associated with the leukocytes. Furthermore, we used three-dimensional fluorescence microscopy and imaging flow cytometry to evaluate the possible internalization of rHDL cargo into the cells, and we show increased internalization of rHDL cargo in monocytes relative to granulocytes. The preferential rHDL association with monocytes and the internalization of rHDL cargo could possibly be mediated by the scavenger receptor class B type 1 (SR-BI), which we show is expressed to a higher extent on monocytes than on the other major leukocyte populations. Our work implies that drug-loaded rHDL can deliver its cargo to monocytes in circulation, which could lead to some off-target effects when using rHDL for systemic drug delivery, or it could pave the way for novel immunotherapeutic treatments aiming to target the monocytes.

We used novel quantitative methods to study the interactions between reconstituted high-density lipoproteins (rHDL) and human leukocytes – showing that rHDL cargo are preferentially taken up by monocytes.

The Composition of Reconstituted High-Density Lipoproteins (rHDL) Dictates the Degree of rHDL Cargo- and Size-Remodeling via Direct Interactions with Endogenous Lipoproteins

The application of reconstituted high-density lipoproteins (rHDL) as a drug-carrier has during the past decade been established as a promising approach for effective receptor-mediated drug delivery, and its ability to target tumors has recently been confirmed in a clinical trial. The rHDL mimics the endogenous HDL, which is known to be highly dynamic and undergo extensive enzyme-mediated remodulations. Hence, to reveal the physiological rHDL stability, a thorough characterization of the dynamics of rHDL in biologically relevant environments is needed. We employ a size-exclusion chromatography (SEC) method to evaluate the dynamics of discoidal rHDL in fetal bovine serum (FBS), where we track both the rHDL lipids (by the fluorescence from lipid-conjugated fluorophores) and apoA-I (by human apoA-I ELISA). We show by using lipoprotein depleted FBS and isolated lipoproteins that rHDL lipids can be transferred to endogenous lipoproteins via direct interactions in a nonenzymatic process, resulting in rHDL compositional- and size-remodeling. This type of dynamics could lead to misinterpretations of fluorescence-based rHDL uptake studies due to desorption of labile lipophilic fluorophores or off-target side effects due to desorption of incorporated drugs. Importantly, we show how the degree of rHDL remodeling can be controlled by the compositional design of the rHDL. Understanding the correlation between the molecular properties of the rHDL constituents and their collective dynamics is essential for improving the rHDL-based drug delivery platform. Taken together, our work highlights the need to carefully consider the compositional design of rHDL and test its stability in a biological relevant environment, when developing rHDL for drug delivery purposes.

Artificial High Density Lipoprotein Nanoparticles in Cardiovascular Research

Lipoproteins are endogenous nanoparticles which are the major transporter of fats and cholesterol in the human body. They play a key role in the regulatory mechanisms of cardiovascular events. Lipoproteins can be modified and manipulated to act as drug delivery systems or nanocarriers for contrast agents. In particular, high density lipoproteins (HDL), which are the smallest class of lipoproteins, can be synthetically engineered either as nascent HDL nanodiscs or spherical HDL nanoparticles. Reconstituted HDL (rHDL) particles are formed by self-assembly of various lipids and apolipoprotein AI (apo-AI). A variety of substances including drugs, nucleic acids, signal emitting molecules, or dyes can be loaded, making them efficient nanocarriers for therapeutic applications or medical diagnostics. This review provides an overview about synthesis techniques, physicochemical properties of rHDL nanoparticles, and structural determinants for rHDL function. We discuss recent developments utilizing either apo-AI or apo-AI mimetic peptides for the design of pharmaceutical rHDL formulations. Advantages, limitations, challenges, and prospects for clinical translation are evaluated with a special focus on promising strategies for the treatment and diagnosis of atherosclerosis and cardiovascular diseases.

Identifying and targeting angiogenesis-related microRNAs in ovarian cancer

Current anti-angiogenic therapy for cancer is based mainly on inhibition of the vascular endothelial growth factor pathway. However, due to the transient and only modest benefit from such therapy, additional approaches are needed. Deregulation of microRNAs (miRNAs) has been demonstrated to be involved in tumor angiogenesis and offers opportunities for a new therapeutic approach. However, effective miRNA-delivery systems are needed for such approaches to be successful. In this study, miRNA profiling of patient data sets, along with in vitro and in vivo experiments, revealed that miR-204-5p could promote angiogenesis in ovarian tumors through THBS1. By binding with scavenger receptor class B type 1 (SCARB1), reconstituted high-density lipoprotein-nanoparticles (rHDL-NPs) were effective in delivering miR-204-5p inhibitor (miR-204-5p-inh) to tumor sites to suppress tumor growth. These results offer a new understanding of miR-204-5p in regulating tumor angiogenesis.

Supramolecular Assembly of High-Density Lipoprotein Mimetic Nanoparticles Using Lipid-Conjugated Core Scaffolds

Synthetic high-density lipoprotein (HDL) mimics have emerged as promising therapeutic agents. However, approaches to date have been unable to reproduce key features of spherical HDLs, which are the most abundant human HDL species. Here, we report the synthesis and characterization of spherical HDL mimics using lipid-conjugated organic core scaffolds. The core design motif constrains and orients phospholipid geometry to facilitate the assembly of soft-core nanoparticles that are approximately 10 nm in diameter and resemble human HDLs in their size, shape, surface chemistry, composition, and protein secondary structure. These particles execute salient HDL functions, including efflux of cholesterol from macrophages, cholesterol delivery to hepatocytes, support lecithin:cholesterol acyltransferase activity, and suppress inflammation. These results represent a significant step toward a genuine functional mimic of human HDLs.

A TRAIL-Delivered Lipoprotein-Bioinspired Nanovector Engineering Stem Cell-Based Platform for Inhibition of Lung Metastasis of Melanoma

Genetically engineered mesenchymal stem cells (MSCs), as non-viral gene delivery platforms, are rapidly evolving in tumor therapy due to their low immunogenicity and natural tumor-homing capacity. Methods: In this paper, we selected reconstituted high-density lipoprotein (rHDL), a lipoprotein-bioinspired nanovector with specific binding ability to scavenger receptor B type I (SR-BI) expressed on MSCs, as a transfection agent to genetically modify MSCs. pDNA encoding tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) was used as a functional gene to be transfected into the nucleus of MSCs for TRAIL expression. Lauric acid-coupled polyethyleneimine (PEI-LA) as an amphiphilic cationic polymer was synthesized to electrostatically bind to pDNA, and then incorporated into rHDL to form rHDL/PEI-LA/pDNA nanoparticles. Results: The nanoparticles exhibited homogenous particle size and excellent serum stability in vitro. Meanwhile, this SR-BI-targeted rHDL performed efficient intracellular gene delivery, specific lysosome-independent mechanism of cellular uptake and high transfection of pDNA towards MSCs. Moreover, high TRAIL expression in MSCs was detected after rHDL-mediated transfection. In vitro and in vivo results indicated that genetically engineered MSCs could accurately target to B16F10 cells, thereby producing significant apoptosis-inducing effect on aggressive melanoma. Conclusion: TRAIL-expressing MSCs engineered by rHDL nanovector was an efficient and hypotoxic method for stem cells-based pulmonary melanoma metastasis-targeting therapy.

[99mTc-HYNIC-N-dodecylamide]: a new hydrophobic tracer for labelling reconstituted high-density lipoproteins (rHDL) for radioimaging

Despite the widespread use of nanotechnology in radio-imaging applications, lipoprotein based delivery systems have received only limited attention so far. These studies involve the synthesis of a novel hydrophobic radio-imaging tracer consisting of a hydrazinonicotinic acid (HYNIC)-N-dodecylamide and 99mTc conjugate that can be encapsulated into rHDL nanoparticles (NPs). These rHDL NPs can selectively target the Scavenger Receptor type B1 (SR-B1) that is overexpressed on most cancer cells due to excess demand for cholesterol for membrane biogenesis and thus can target tumors in vivo. We provide details of the tracer synthesis, characterization of the rHDL/tracer complex, in vitro uptake, stability studies and in vivo application of this new radio-imaging approach.

Endocytosis of lipoproteins

During their metabolism, all lipoproteins undergo endocytosis, either to be degraded intracellularly, for example in hepatocytes or macrophages, or to be re-secreted, for example in the course of transcytosis by endothelial cells. Moreover, there are several examples of internalized lipoproteins sequestered intracellularly, possibly to exert intracellular functions, for example the cytolysis of trypanosoma. Endocytosis and the subsequent intracellular itinerary of lipoproteins hence are key areas for understanding the regulation of plasma lipid levels as well as the biological functions of lipoproteins. Indeed, the identification of the low-density lipoprotein (LDL)-receptor and the unraveling of its transcriptional regulation led to the elucidation of familial hypercholesterolemia as well as to the development of statins, the most successful therapeutics for lowering of cholesterol levels and risk of atherosclerotic cardiovascular diseases. Novel limiting factors of intracellular trafficking of LDL and the LDL receptor continue to be discovered and to provide drug targets such as PCSK9. Surprisingly, the receptors mediating endocytosis of high-density lipoproteins or lipoprotein(a) are still a matter of controversy or even new discovery. Finally, the receptors and mechanisms, which mediate the uptake of lipoproteins into non-degrading intracellular itineraries for re-secretion (transcytosis, retroendocytosis), storage, or execution of intracellular functions, are largely unknown.

Lipid composition dictates serum stability of reconstituted high-density lipoproteins: implications for in vivo applications

Nanolipoprotein particles (NLPs) are reconstituted high-density lipoproteins, consisting of a phospholipid bilayer stabilized by an apolipoprotein scaffold protein. This class of nanoparticle has been a vital tool in the study of membrane proteins, and in recent years has been increasingly used for in vivo applications. Previous work demonstrated that the composition of the lipid bilayer component affects the stability of these particles in serum solutions. In the current study, NLPs assembled with phosphatidylcholine lipids featuring different acyl chain structures were systematically tested to understand the effect that lipid composition has on NLP stability in both neat serum and cell culture media supplemented with 10% serum by volume. The time at which 50% of the particles dissociate, as well as the fraction of the initial population that remains resistant to dissociation, were correlated to key parameters obtained from all-atom simulations of the corresponding lipid bilayers. A significant correlation was observed between the compressibility modulus of the lipid bilayer and particle stability in these complex biological milieu. These results can be used as a reference to tune the stability of these versatile biological nanoparticles for in vitro and in vivo applications.

Reconstituted high-density lipoproteins: novel biomimetic nanocarriers for drug delivery

High-density lipoproteins (HDL) are naturally-occurring nanoparticles that are biocompatible, non-immunogenic and completely biodegradable. These endogenous particles can circulate for an extended period of time and transport lipids, proteins and microRNA from donor cells to recipient cells. Based on their intrinsic targeting properties, HDL are regarded as promising drug delivery systems. In order to produce on a large scale and to avoid blood borne pollution, reconstituted high-density lipoproteins (rHDL) possessing the biological properties of HDL have been developed. This review summarizes the biological properties and biomedical applications of rHDL as drug delivery platforms. It focuses on the emerging approaches that have been developed for the generation of biomimetic nanoparticles rHDL to overcome the biological barriers to drug delivery, aiming to provide an alternative, promising avenue for efficient targeting transport of nanomedicine.

Characterization of ApoJ-reconstituted high-density lipoprotein (rHDL) nanodisc for the potential treatment of cerebral β-amyloidosis

Cerebral β-amyloidosis is a major feature of Alzheimer’s disease (AD), characterized by the accumulation of β-amyloid protein (Aβ) in the brain. Several studies have implicated lipid/lipoprotein metabolism in the regulation of β-amyloidosis. In this regard, HDL (High Density Lipoprotein)-based therapies could ameliorate pathological features associated with AD. As apolipoprotein J (ApoJ) is a natural chaperone that interacts with Aβ, avoiding its aggregation and toxicity, in this study we propose to prepare reconstituted rHDL-rApoJ nanoparticles by assembling phospholipids with recombinant human ApoJ (rApoJ). Hence, rHDL particles were prepared using the cholate dialysis method and characterized by N-PAGE, dynamic light scattering, circular dichroism and electron transmission microscopy. The preparation of rHDL particles showed two-sized populations with discoidal shape. Functionally, rHDL-rApoJ maintained the ability to prevent the Aβ fibrillization and mediated a higher cholesterol efflux from cultured macrophages. Fluorescently-labelled rHDL-rApoJ nanoparticles were intravenously administrated in mice and their distribution over time was determined using an IVIS Xenogen® imager. It was confirmed that rHDL-rApoJ accumulated in the cranial region, especially in old transgenic mice presenting a high cerebral Aβ load. In conclusion, we have standardized a reproducible protocol to produce rHDL-rApoJ nanoparticles, which may be potentially considered as a therapeutic option for β-amyloid-related pathologies.

Synthetic lipoprotein as nano-material vehicle in the targeted drug delivery

High-density lipoprotein (HDL) and low-density lipoprotein (LDL), as human endogenous lipoprotein particles, have low toxicity, high selectivity, and good safety. They can avoid the recognition and clearance of human reticuloendothelial system. These synthetic lipoproteins (sLPs) have been attracted extensive attention as the nanovectors for tumor-targeted drug and gene delivery. Herein, recent advances in the field of anticancer based on these two lipid proteins and recombinant lipoproteins (rLPs) as target delivery vectors were analyzed and discussed.

Nanodiscs in Membrane Biochemistry and Biophysics

Membrane proteins play a most important part in metabolism, signaling, cell motility, transport, development, and many other biochemical and biophysical processes which constitute fundamentals of life on the molecular level. Detailed understanding of these processes is necessary for the progress of life sciences and biomedical applications. Nanodiscs provide a new and powerful tool for a broad spectrum of biochemical and biophysical studies of membrane proteins and are commonly acknowledged as an optimal membrane mimetic system that provides control over size, composition, and specific functional modifications on the nanometer scale. In this review we attempted to combine a comprehensive list of various applications of nanodisc technology with systematic analysis of the most attractive features of this system and advantages provided by nanodiscs for structural and mechanistic studies of membrane proteins.

Simultaneous delivery of anti-miR21 with doxorubicin prodrug by mimetic lipoprotein nanoparticles for synergistic effect against drug resistance in cancer cells

The development of drug resistance in cancer cells is one of the major obstacles to achieving effective chemotherapy. We hypothesized that the combination of a doxorubicin (Dox) prodrug and microRNA (miR)21 inhibitor might show synergistic antitumor effects on drug-resistant breast cancer cells. In this study, we aimed to develop new high-density lipoprotein-mimicking nanoparticles (HMNs) for coencapsulation and codelivery of this potential combination. Dox was coupled with a nuclear localization signal (NLS) peptide to construct a prodrug (NLS-Dox), thereby electrostatically condensing miR21 inhibitor (anti-miR21) to form cationic complexes. The HMNs were formulated by shielding these complexes with anionic lipids and Apo AI proteins. We have characterized that the coloaded HMNs had uniformly dispersed distribution, favorable negatively charged surface, and high coencapsulation efficiency. The HMN formulation effectively codelivered NLS-Dox and anti-miR21 into Dox-resistant breast cancer MCF7/ADR cells and wild-type MCF7 cells via a high-density-lipoprotein receptor-mediated pathway, which facilitated the escape of Pgp drug efflux. The coloaded HMNs consisting of NLS-Dox/anti-miR21 demonstrated greater cytotoxicity with enhanced intracellular accumulation in resistant MCF7/ADR cells compared with free Dox solution. The reversal of drug resistance by coloaded HMNs might be attributed to the suppression of miR21 expression and the related antiapoptosis network. Furthermore, the codelivery of anti-miR21 and NLS-Dox by HMNs showed synergistic antiproliferative effects in MCF7/ADR-bearing nude mice, and was more effective in tumor inhibition than other drug formulations. These data suggested that codelivery of anti-miR21 and chemotherapeutic agents by HMNs might be a promising strategy for antitumor therapy, and could restore the drug sensitivity of cancer cells, alter intracellular drug distribution, and ultimately enhance chemotherapeutic effects.

HDL infusion for the management of atherosclerosis: current developments and new directions

PURPOSE OF REVIEW

Because human genetic studies and large clinical trials have demonstrated that HDL-cholesterol levels are not causally related to cardiovascular disease risk, attention has shifted toward the functional properties of HDL. Infusion of HDL mimetics containing apolipoprotein A-I remains a potential strategy to exploit the atheroprotective effects of HDL.

RECENT FINDINGS

Three HDL mimetic drugs are under development and currently being evaluated in clinical trials. Upon infusion, these drugs increase cholesterol efflux capacity. Although proof-of-concept studies are promising, large outcome studies are awaited. Alternatively, HDL particles may be used for targeted drug delivery in a nanomedicine approach. Finally, links between cholesterol efflux and myelopoeisis may prove to be a target for HDL infusion in the future.

SUMMARY

Clinical studies are currently ongoing to evaluate the potential of several HDL mimetic drugs. Novel nanomedicinal approaches and emerging pathophysiological insights may further expand the relevance of HDL infusion.

Targeting SR-BI for Cancer Diagnostics, Imaging and Therapy

Scavenger receptor class B type I (SR-BI) plays an important role in trafficking cholesteryl esters between the core of high density lipoprotein and the liver. Interestingly, this integral membrane protein receptor is also implicated in the metabolism of cholesterol by cancer cells, whereby overexpression of SR-BI has been observed in a number of tumors and cancer cell lines, including breast and prostate cancers. Consequently, SR-BI has recently gained attention as a cancer biomarker and exciting target for the direct cytosolic delivery of therapeutic agents. This brief review highlights these key developments in SR-BI-targeted cancer therapies and imaging probes. Special attention is given to the exploration of high density lipoprotein nanomimetic platforms that take advantage of upregulated SR-BI expression to facilitate targeted drug-delivery and cancer diagnostics, and promising future directions in the development of these agents.