Recent advances in magnetoliposome for heart drug delivery

Abstract

Magnetic nanoparticles (NPs) also have been subject of interest to the therapeutic and imaging field because of their unique magnetic properties. Magnetoliposomes (MLs) are made up of a combination of liposomes and magnetic NPs, and they have been proven to be a potential biomaterial to fields like magnetic-targeted drug delivery, MRI, etc. The efficiency of a drug delivery system to the heart determines the treatment strategy for most of the heart diseases. In this review article, we summarize the recent development and updates in the application of MLs as a drug delivery system for heart/cardiac diseases.

Keywords:

• Magnetoliposome
• liposome
• heart
• drug delivery
• cardiac

Introduction

Cardiovascular disease, specifically ischemic impairment, is one of the main causes of morbidity and mortality in the world. The heart is a pumping organ and an organ of interest at both molecular and pathological level [1]. Cardiac diseases in human involves anomaly in morphogenesis in the heart structure, functionality and repair of muscle and rhythmic contraction of cardiac muscles [2]. Cardiomyocytes are non-differentiating cells and as such, cannot proliferate, thereby resulting to the non-regenerative abilities of the cardiomyocytes which may lead to chronic cardiac dysfunction [3].

About 50% of patients suffering from MI die within 5 years [4]. The only potential cure for terminally ill cardiac patients is heart transplantation as such a potential cure to heart disease entails specific delivering of cardio-protective drugs into the infarcted myocardium region [5]. The urgency for new and potent cure has brought about development of specific drug delivery to the heart [6].

Previous researches have proposed the idea of specific targeted delivery magic bullet that cause apoptosis on affected cells but without incurring any damages to the normal and healthy tissues [7]. The effectiveness of targeted drug delivery depends on activeness of an agent and the delivery abilities of their carriers into the unhealthy tissue with reduced effects on neighbouring normal tissues after systemic administration [8].

Recent therapeutic strategies developed to prevent the occurrence of heart failure after myocardial infarction (MI) [9] relies mainly on the administration of pro-angiogenic agents and stem cell therapy [10]; however, some of these data show the lack of effectiveness of these active bio-molecules because of their short radioactive half-life and reduced stability [11]. Therefore, there is an urgent need to develop a more efficient heart-targeted nanoparticle (NP) drug delivery system.

Magnetic NP (MNP) synthesis and magnetoliposome (MP) formation

MNPs are commonly studied carriers that show a variety of characteristics [12]. They can be easily manipulated and worked on within a magnetic field, they are easily modified to act as potential particles for drug delivery strategies, and, are important part of magnetic resonance imaging (MRI) device. However, the applications of MNPs (Figure 1) are truncated by some limitations, such as inefficiency of the magnet systems. For this reason, it is necessary to put into consideration many important factors when designing a heart-targeted magnetic drug delivery system [13]. These factors include but not limited to the magnetic properties, size of the particles, the strength of the magnetic field, the drug loading capacity, the accessibility to the target tissue, and the rate of blood flow.

Figure 1. A diagram of magnet liposomes is shown.

Regardless of these limitations, there are still few applications of magnet-liposomes (Figure 2). Ferric oxide NPs (Fe₃O₄ and ɣ-Fe₂O₃) are the only type of MNPs approved by US Food and Drug Administration for clinical use and trial. Their favourable features that make them suitable for magnet nano particle include simple single-step synthesis, stability in physiological conditions, and flexibility of chemical modification [14]. The common encapsulating shell for MNPs is gold, polymer, silane, or dendrimer [15] (Figure 3). Their occurrence in the body shows that they are biocompatible and non-lethal at physiological concentrations [16]. It should be noted that delivery of drug-loaded MNPs to diseased cardiac tissues depends on the interaction between the ligands conjugated to the surface of MNPs and the surface of the infected cardiac tissue.

Figure 2. Schematic diagram of multi-functionalities of magnetioliposomes.

Figure 3. Different nanoparticle heart-targeted delivery systems including magnet lipid nanoparticle are shown.

A perfect nanoscale DDS allows for a control release of drug compound over a specified period of time. Amstad et al. [17] show that this can be attained by stealth liposomes encompassing self-assembled superparamagnetic iron oxide NPs (SPIONs) individually stabilized with palmityl-nitroDOPA encapsulated in lipid membrane. Alternating magnetic fields were employed in time controlling and dose, of continually released drug compound from such vesicles, by heating its membrane locally, and changing its porousness without a major environmental effect.

In a study by Zhang et al. [18], they developed a reliable magnetic NP-adenoviral vector multi-molecule for the treatment of severe MI by successfully delivering the therapeutics drug into the infarcted heart [19]. MNP with capsules has been suggested for many applications, including imaging and triggered drug delivery. A future exciting approach to disease therapy is the combination of SPIONs with liposome drug delivery technology; however, this needs a capable technique of fabrication and formulation compatible with pharmaceutical uses [20].

Bixner et al. [20] reported a facile method of producing a large, unilamellar, and homogeneously sized MLs with a high amount of monodisperse, hydrophobic SPIONs embedded in the membrane of the lipid through solvent inversion method. For a low lipid concentration, monodisperse and unilamellar vesicles were attained which became increasingly multilamellar with higher proportion of lipid. The fabrication of NP-loaded vesicles is demonstrated in different biologically essential media, yielding a formulation of ready-to-use ML.

In a study by Montis et al. [21], the fabrication and characterization of a drug delivery system (DDS) with hydrophobic Fe₃O₄ NPs embedded in the bilayer of bicontinuous cubic lipid NPs of glyceryl monooleate (GMO) was reported. The "magnetocubosomes" synthesized are investigated and characterized by their ability to incorporate and release both hydrophobic and hydrophilic drugs. Magnetocubosomes were reported for the first time as a novel multifunctional, biocompatible, and responsive DDS [21]. This novel hybrid composite can represent an extremely flexible and interesting device for the targeted delivery of diagnostic agents and multiple therapeutic.

Chen et al. [22] reported the fabrication, characterization, and release features of bilayer-decorated MLs (dMLs) prepared by encapsulating small hydrophobic SPIO NPs at different ratios of lipid molecule/NP within dipalmitoylphosphatidylcholine (DPPC) bilayers. The mechanism of release is associated with the combination of bilayer permeabilization and partial dML rupture.

Synthesis of MNPs

Bottom up and top down method are the two main methods used in the production of magnetic NPs, although, the bottom-up method is the most preferred, because of particle size limitations of top-down method [23]. The bottom-up method can be co-precipitation, thermal decomposition, reverse micelle, and hydrothermal [24].

Types of MLs

There are two basic types of MLs synthesized via the process of co-precipitation, these include liposomes entrapped in a magnet NP called aqueous MLs (AMLs), and MLs covered within a lipid bilayer called solid MLs (SMLs) [25]. The two types of MLs exhibit a size around 150 nm [26]. The final shape and size distribution, surface chemistry, and magnetic properties depend on the preparation method of the magnetic NPs [16].

Magneto-sensitive liposomes are fabricated from a process of encapsulation of MNPs into liposomes forming MLs, combining both the physical and magnetic properties of NPs and magnet, respectively (Figure 1). The most potential applications of MLs in therapy are magnetic drug delivery and hyperthermia. The spinel structure of MNPs of transition metal ferrites makes them a potential material for biomedical industry.

Formation of MLs

Various MLs preparation methods have been described to date [27–29]. The encapsulation of pharmaceutical agents and water soluble SPIONs into liposome lumen was first demonstrated by Amstad et al. [17], Sabaté et al. [30], and Bulte et al. [31]. Although there are some major limitations in this approach. First, unstabilized SPIONs react with the membrane of liposome causing a leakage, but, well-stabilized SPIONs take up large volume. Second, SPIONs heating to induce a thermal transition necessitates heating the entire environment [17]. However, hydrophobic SPIONs embedded in the bilayer of the lipid bilayer were shown to act on the capsule wall directly without the need to heat the surrounding for release [17,22]. The limitation is that the efficiency of encapsulation relies on the size of the particles [32,33].

A smaller SPIONs can be incorporated in the membrane, but SPIONs >5 nm may to lead to the formation of micelle. Small SPIONs are thought to react less with magnetic fields because of their weaker magnetic moment (∼d3). The density and stability of NPs hydrophobic surface also influences stability and membrane permeability of liposomes. Excess physisorbed ligands can result in the leakage of compounds encapsulated [17,22]. Optimal ML fabrication will thus gave a high loading capacity of monodisperse SPIONs, as large as it can fit in the membrane, to maximize its efficiency; this necessitates a stable and heavy hydrophobic coating.

Whereas the prospect of such MLs for release has been verified, to date, the control over high loading of monodisperse hydrophobic SPIONs in the liposomal membrane has not been realized. Previous techniques employed extrusion and rehydration to fabricate a unilamellar vesicle, incompatible with the present techniques for liposome drug formulation. Carrier liquids with lipids and expensive drugs are injected to ensure high encapsulation, a similar method for ML fabrication compatible with high efficiency of encapsulation in a large lumen is, therefore, preferred.

There are three different structures of MLs according to the location of MNPs. The most commonly used strategy is an MNP surrounded by lipid bilayers especially on the hydrophobic side and the process of thermal decomposition synthesizes them [34]. The method of binding MNPs on the surface of liposome has not been widely adopted. Most widely adopted method for MLs preparation is the thin film hydration method and it involves the dispersion of MNPs in aqueous medium followed by hydration and extrusion of the liposomes is done to reduce the its size [35].

Heart-targeted drug delivery systems

Reduced blood perfusion is one of the main causes of cardiovascular diseases. In the heart, development of new blood vessels around an ischemic region leads to increase in the level of oxygen and nutrients, thereby halting the process of apoptosis and scar formation [36].

Researchers have formulated several therapeutic strategies to protect the cardiac vasculature against any damages under any disease condition. In addition, previous studies have proven that the endothelium was a crucial target site for vascular therapy. The endothelium correlates with normal and pathological conditions like angiogenesis, myocardial infarction, cardiac ischemia, and atherosclerosis. Galagudza et al. [37] reported that targeted therapeutics agent to the region of myocardium infarcted led to great improvement during a clinical trial, however, outcome of some of these treatment option have been judged inefficient as they resulted in patients developing series of life-threatening side effects. Furthermore, it has been reported that heart-target NP vehicles are important and responsible for protecting therapeutics agents from degradation in the blood circulation (Table 1 and Figure 3).

Table 1. Some of nanoparticles which have been used for heart drug delivery.

Type	Studied by	Structure	Function in Heart
Dendrimers	Bella et al. [54]	Three-dimensional (3D)	Improved cardioprotective potency through theactivation of A3 adenosine receptor (A3AR) on the cardiac muscle cells surface
	Johnson et al. [55]
			Protect the affected cardiac tissue against oxidative stress
Liposomes	Kohane’s group [56]	Vesicular structures with a phospholipid bilayer	liposomal adenosine was able to improve thecardioprotective effects of adenosine againstischemia injury and decrease any its unfavourable systemic effects
Polymeric nanoparticles	Somasuntharam et al. [57]	The size of nanoparticles ranges between 10 and 100 nm	Acid-degradable polyketal particles efficientlydelivered Nox2-siRNA to the affected cardiac sites and improved the heart functions.
Microparticles	Hesford et al. [58].	Spherical structure containing a matrix	The polymeric microparticles loaded with anti-inflammatory drugs has proven to be efficient in the treatment of myocardial infarction and other heart, also to improve the half-life and stability of cardioprotective drugs, such as VEGF

Liposomes (Figure 3) are type of NPs that are mostly used for heart-targeted drug system [38]. Liposomes are responsible for encapsulating the NPs or drugs by protecting them against biomolecular adsorption. Therefore, NPs or drugs can be delivered through established liposome delivery methods. However, liposomal drug delivery strategies are impeded by the reticulo-endothelial system if administered by intravenous injection into the bloodstream [39]. The integration of polyethyleneglycol (PEG) and distearoylphosphatidyl ethanolamine (DSPE) with liposomes can decrease their recognition by the reticulo-endothelial system as reported by Chang et al. [40] that the use of NPs delivers growth factors to the heart by integrating electrostatically, insulin growth factor 1 with poly (lactic-co-glycolic acid) PLGA, while polyethylenimine (PEI) served as the NPs (74.4 ± 11.3 nm) that was injected into the affected region immediately following MI in mice [3,41]. NP delivery improved the circulation of insulin growth factor 1 up to 24 h post-injection, but no evidence of insulin growth factor 1 retention after 72 h. The PLGA–PEI complex formulation was more effective in decreasing the left ventricular diastolic/systolic dimension, thickening, and reducing infarct wall area when compared with un-encapsulated insulin growth factor 1. Recently, a study reported that anti-P-selectin-conjugated immuno-liposomes integrated with vascular endothelial growth factor could significantly increase vascularization and cardiac function based on the up-regulation of P-selection in the MI [42]. Kohane’s group integrated liposomes with a ligand complex targeted to angiotensin II type1 (AT1), their result showed that MNPs have the potency to deliver the drug to the affected cardiac tissue after systematic administration in vivo [43]. Stealth liposomes integrated with adenosine were prepared by hydration method; assessment was made after 30 min of ligation. Pharmacokinetic data confirmed that the liposomes were able increase the residence time of adenosine in the blood, results from the study proved that PEGylated liposomal adenosine was able to improve the cardioprotective effects of adenosine against ischemia injury and decrease any unfavorable systemic effects [44]. However, liposomes drug delivery works better with diffusion of its content through its disrupted bilayer with high permeability, which is in-turn increased by melting temperature across the membrane (T_m), as such the content of liposomes can only be released at a temperature higher than the membrane temperature (T_m). A temperature higher than T_m causes liposomes leakage during circulation, to circumvent this inefficiency in liposome release and low passive leakage, liposomes are recently been loaded and integrated with MNPs to initiate cargo release under the effect of a high-frequency alternating magnetic field (AMF). Torchilin et al. [45] produced a rabbit model of acute myocardial infarction and in-labelled it with a stealth liposome modified with antimyosin antibody. They observed and recorded an increase in the level of PEG-coated immunoliposomes in the infarcted rabbit model’s myocardium. The data further established that the amount level of PEG in the membrane of the immunoliposomes was an important factor. PEG improved the half time and targeting potency of carriers in the body.

Drug delivery using MLs

MLs were the first efficient hybrid liposome/NP produced and assembly for drug delivery, and several researchers have demonstrated the application of MLs in drug delivery. The magnetic properties of MLs make them a potent multifunctional drug delivery carrier with the ability for magnetic targeting. Several experimental strategies have been developed to treat infarcted heart, and it involves delivery of growth factors, cytokines, and biomolecules to the degenerating cardiac cells [46].

The delivery of these drugs can be through direct injection, injecting biomolecule-loaded micro-particles, or gels to the left ventricle [47], and in vivo and in vitro (Figure 4).

Figure 4. Clinical application of magnet liposome in both in vitro and in vivo assays is shown.

However, the potency of these strategies may be interfered by lack of retention ability of the micro-particles in the affected area, as such, there is a need for an alternative potent approach (use of biomaterials), with the ability to successfully deliver biomolecules to the affected site. Targeted MNPs can be administered intravenously to circulate via the blood throughout the body, and only delivers at the affected region or organ [48] (Figure 5). In addition, MNPs have been used successfully to target macrophages and blood vessels in an infarcted heart. Previous research has shown that after MI, the left ventricular blood vessels become permeable and leaky, and this may result to the penetration of nano-sized magnet particles similar to the process involved in enhanced permeation and retention (EPR) [49].

Figure 5. Liposome and magnet nanoparticle as a drug delivery system vehicle to the heart are shown.

In addition, Molavi et al. [50] reported that angiotensin receptor 1 is been overexpressed in the infarcted heart and as such can act as a target for MLs. A recent research reported that MNPs targets only the injured cardiac tissue thereby suggesting that it is a potential drug delivery system for post MI treatment. This is similar to the way and manner in which NPs are used to specifically target cancerous tumours. Angiotensin receptor 1 targeting has been reported to further improve delivery to the injured myocardium region. These two reports are potential way to decrease toxicity and increase systemic local therapeutic effect of the delivered drugs. In addition, reducing the size of the MNP and increasing the density of the loaded drug can increase the efficiency of the delivered drug. These systems are efficient in the constant release of bioactive molecules specifically to the infarcted heart and increase regeneration of cardiac tissue [51].

Recently, biocompatible SPIONs are regarded as one of the most efficient MNPs because they are easily synthesized and surface functionalized. They possess efficient magnetic properties as such SPIONs can be used for magnetic specific delivery of drugs which works by delivering magnetic NPs to the desired specific target area, via the principle of a magnetic field gradient. After positive delivery of the incorporated NP, SPIONs are finally released and discarded. Based on this strategy, Kumar et al. [52] demonstrated that magnetic NPs, when injected in the tail of mice, were able to be successfully directed and delivered to the myocardial infarcted heart via an external magnetic field.

Several research studies have reported various kinds of biomolecules as having therapeutic effect on a myocardia infarcted heart such as encapsulation of microparticles with a p38 inhibitor injected directly to the affected heart was potent enough to minimize the fibrotic region. In addition, the delivery of several growth factors such as insulin-like growth factor, hepatocyte growth factor platelet-derived growth factor closer to the cardiac infarcted region, was able to mitigate the rate of deterioration of the left ventricle [53].

Conclusion

Various MLs have been developed and investigated for drug delivery such as PEGylation of MLs, which increases their circulation in the blood, and conjugation of the MLs with antibody which increases the rate of active target to affected sites. However, successful heart-targeted MLs drug delivery systems are based on researchers understanding the fundamentals of various heart diseases, the activeness of the targeting properties and stability of the carriers, and the appropriate targeting ligands of the carrier, ensuring interaction between the carrier and the surface molecules of the targeted cells.

The application of MLs-based technologies to diagnose and treat cardiac-vascular disease has not been widely investigated as compared with its applications in oncology; however, MLs heart-targeted delivery system is a promising drug delivery system to unhealthy cardiac tissue like MI. Drug delivery using MLs has some limitations, such as toxicity, immunogenicity, and unwanted pharmacokinetic behaviour, which can be accomplish through extensive and in-depth research work.

Acknowledgements

The authors thank the Department of Medical Biotechnology, School of Advanced Technologies in Medicine, Tehran University of Medical Sciences, and the Department of Cardiology, Lorestan University of Medical Sciences, Khoramabad, Iran.

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.