Effect of apoE/ATP-containing liposomes on hepatic energy state

Enhanced cell survival of pH-sensitive bioenergetic nucleotide nanoparticles in energy/oxygen-depleted cells and their intranasal delivery for reduced brain infarction

Nucleotides (NTs) (e.g., adenosine triphosphate) are very important molecules in the body. They generate bioenergy through phosphate group release, are involved in various biological processes, and are used to treat various diseases that involve energy depletion. However, their highly anionic characteristics might limit delivery of exogenous NTs into the cell, which is required to realize their functions as bioenergy sources. In this study, ionic complexation between Ca(2+) and NT phosphates was used to form Ca(2+)/NT nanocomplexes (NCs), and branched polyethyleneimine (bPEI1.8kDa) was coated on the surface of Ca(2+)/NT NCs via a simple electrostatic coating. The resultant Ca(2+)/NT/bPEI1.8kDa NCs were approximately 10-25nm in size and had positive zeta-potentials, and their NT loading efficiency and content were approximately 60-75% and 10-20 wt%, respectively. Faster NT release from Ca(2+)/NT/bPEI1.8kDa NCs was induced by lower pH and by NTs with fewer phosphates. Reductions in cell viability in response to low temperature, serum deprivation, or hypoxia were recovered by NT delivery in Ca(2+)/NT/bPEI1.8kDa NCs. In a middle cerebral artery occlusion (MCAO)-induced post-ischemic rat model, the BBB (blood brain barrier)-detoured intranasal administration of Ca(2+)/ATP/bPEI1.8kDa NCs induced a better reduction in infarct volume and neurological deficits than did free ATP. In conclusion, intracellular NT delivery using Ca(2+)/NT/bPEI1.8kDa NCs might potentially enhance cell survival and reduce infarction in energy-/oxygen-depleted environments.

STATEMENT OF SIGNIFICANCE

This study describes bioenergetic nucleotide delivery systems and their preparation, physicochemical characterization, and biological characterization both in vitro and in vivo. Nucleotides, such as adenosine triphosphate (ATP) and guanosine triphosphate (GTP), are very important signaling and energy molecules in the body. However, research on these nucleotides using nanosized carriers has been very limited. Liposomal ATP delivery has been reported in heart and renal ischemia studies. Notably, although this delivery system has potential in energy-depleted environments (e.g., low temperature, serum deprivation, and hypoxia) and in brain ischemia, studies are lacking regarding these systems. Thus, we designed polycation-shielded Ca(2+)/nucleotide nanocomplexes using simple mixing, which produced 10- to 25-nm-sized particles. The nanocomplexes released nucleotides in response to acidic pH, and they enhanced cell survival rates under conditions of low temperature, serum deprivation, or hypoxia. Importantly, the nanocomplexes reduced cerebral infarct volumes in a post-ischemic rat model. Thus, our study demonstrates that a novel nucleotide nanocomplex could have potential for preventing or treating diseases that involve energy depletion, such as cardiac, cerebral, and retinal ischemia, and liver failure.

Synthetic polynucleotides as endosomolytic agents and bioenergy sources

Nucleotides (NTs), such as adenosine triphosphate (ATP) and guanosine triphosphate (GTP), are signaling and bioenergy molecules to mediate a range of cellular pathways. We recently reported their significant endosomolytic activity. To evaluate whether polymeric NTs keep endosomolytic and bioenergetic functions of NTs in drug delivery and cell survival, NTs were polymerized by a coupling reaction to form polynucleotides (pNTs: pATP and pGTP) with their molecular weights around 500kDa. The cellular toxicity, indicated by IC50, of pNT was as low as that of corresponding monomeric NT. pNTs were degraded by an intracellular enzyme, alkaline phosphatase. Introduction of pNTs in a polycation-gene complex (polyplex) enhanced the extent of gene expression in cancerous, non-cancerous, and stem cells, up to 1500-fold higher than that of pNT-free polyplex. In addition, cells stored in a pATP solution resulted in a significantly higher survival rate (e.g., up to 20% increase) when exposed to low temperatures than pATP-free solution. The presence of pNT in polyplexes prevented the reduction of transfection efficiency induced by a low temperature. The findings in this study suggest that endosomolytic and bioenergetic pNTs serve as a non-toxic gene carrier component and protect cells from a cold shock or energy depletion.

Nucleotides as nontoxic endogenous endosomolytic agents in drug delivery

Nontoxic endogenous nucleotides such as adenosine triphosphate and guanosine triphosphate have secondary phosphate groups, causing proton-buffering capacity and/or hemolytic activity in endolysosomal pH ranges. Nucleotides co-delivered in single polymeric pDNA nanocarrier induce highly enhanced transfection efficiency with negligible cytotoxicity due to their endosomolytic functions.

Drug-induced nanocarrier assembly as a strategy for the cellular delivery of nucleotides and nucleotide analogues

The natural nucleotide adenosine triphosphate (ATP) and nucleotide analogues such as azidothymidine triphosphate (AZT-TP) display important pharmacological activities for the treatment of ischemia and HIV infections, respectively. Their clinical use is, however, limited mostly due to their hydrophilicity, which highly restricts their diffusion into the target cells. Few nanocarriers have been proposed to address the challenge of ATP/AZT-TP cellular delivery, but the loading efficiency, preparation complexity, and efficient cellular delivery remain important barriers to their development. In this study, we propose an original, straightforward and versatile design of nucleotide and nucleotide analogue nanocarriers based on the natural polysaccharide chitosan (CS). We show that the drugs ATP and AZT-TP can induce ionotropic gelation of CS, leading to CS/ATP and CS/AZT-TP nanoparticles with high drug entrapment efficiency and loading rate-up to 44%. Such nanocarriers release ATP and AZT-TP in physiological media and allow an efficient in vitro cellular delivery of these molecules down to the cell cytoplasm.

Cationic phospholiposomes: efficient delivery vehicles of anticancer derivatives of ATP to multiple myeloma cells

Analogs of adenosine triphosphate (ATP) with substitutions at the 8-position have been shown to be cytotoxic to multiple myeloma, one of the most prevalent and serious blood cancers. However, these drugs do not readily cross biological membranes and are very sensitive to phosphatases present in body fluids. To circumvent these disadvantages, 8-substituted ATPs were encapsulated into cationic phospholiposomes generated from cationic phosphatidylcholines (EDOPC; 1,2-dioleoyl-sn-glycero-3-ethylphosphocholine, and EDPPC, the corresponding dipalmitoyl homolog), compounds with low toxicity that readily form liposomes. Vortexing was an efficient encapsulation procedure, more so than freeze-thawing. At the lipid:drug ratio of 5:1 (mol/mol), 20% of 8-Br-ATP was encapsulated within EDOPC liposomes. Efficient encapsulation and retention of 8-NH₂-ATP required the inclusion of cholesterol. Liposomes of EDOPC:cholesterol (55:45 mole/mole), at a lipid:drug mole ratio of 10:1, captured ~40% of the drug presented. Cytotoxicity assays of this formulation on multiple myeloma cells in culture showed encapsulated drug to be up to 10-fold more effective than free drug, depending upon dose. Intracellular distribution studies (based on fluorescent derivatives of lipids and of ATP) revealed that both liposomes and drug were taken up by multiple myeloma cells, and that uptake of a fluorescent ATP derivative was significantly greater when encapsulated than when free. Liposomes prepared from EDPPC, having a higher phase-transition temperature than EDOPC, captured 8-NH₂-ATP satisfactorily and released it more slowly than the unsaturated formulations, but were also less cytotoxic. The superior encapsulation efficiencies of the positively charged liposomes can be understood in terms of the electrostatic double layer due to a very high positive charge density on their inner surface. Electrostatic augmentation of encapsulation for small vesicles can be dramatic, easily exceeding an order of magnitude.

Formulation and evaluation of ATP-containing liposomes including lactosylated ASGPr ligand

An original ligand (Lac-10-Chol) designed to interact with asialoglycoprotein receptors to potentially target hepatocyte was synthesised by grafting a lactose head to a cholesteryl structure, which was then included in liposomes. Preliminary formulation tests led to the selection of conventional formulations based on soybean phosphatidylcholine/cholesterol/DOTAP (+/- DOPE) (+/- Lac-10-Chol) that present reproducible absolute entrapment value (1.45 +/- 0.10%), with a size of 109 +/- 7 nm and a slight positive charge (3.77 +/- 1.59 mV). Cell viability (via the MTT test), expressed as the percentage of nontreated cells in HepG2 cells, was very close to the control. Internalization tests evidenced an intracellular penetration of fluorescent liposomes, but no specific ligand effect was demonstrated (P > 0.05). Nevertheless, regarding the adenosine triphosphate (ATP) assay, a slight increase was obtained with liposome loaded with ATP incorporating Lac-10-chol after 24 hours (P < 0.05).

[Solutions for organ preservation and other cardioplegic liquid formulations. Role of the hospital pharmacist]

Solid organ transplantation is an increasing need and a well-established activity which requires maintaining the quality of the transplant from procurement through the entire, storage, transport and graft procedure. Solutions for organ preservation play a key role in this procedure, by minimizing the deleterious effects of both ischemia and reperfusion. As such, their qualitative and quantitative compositions have to be optimized and validated. The development strategy and formulations proposed for these solutions are analyzed in this review as well as the results of the clinical studies which have set up the relevant pharmacological and physicochemical criteria. The French regulatory status of these products is also discussed. A clear distinction has to be made between solutions for organ preservation which are classified as produits thérapeutiques annexes (therapeutic ancillary products) and cardioplegic liquid formulations which are considered as medicinal products and are subject to marketing approval. Finally, the roles of the hospital pharmacist in the evaluation, selection, purchase and proper use of these products are described.