Cationic lipids employed for antisense oligodeoxynucleotide transport may inhibit vascular cell adhesion molecule-1 expression in human endothelial cells: a word of caution

Modulating endothelial adhesion and migration impacts stem cell therapies efficacy

BACKGROUND

Limited knowledge of stem cell therapies` mechanisms of action hampers their sustainable implementation into the clinic. Specifically, the interactions of transplanted stem cells with the host vasculature and its implications for their therapeutic efficacy are not elucidated. We tested whether adhesion receptors and chemokine receptors on stem cells can be functionally modulated, and consequently if such modulation may substantially affect therapeutically relevant stem cell interactions with the host endothelium.

METHODS

We investigated the effects of cationic molecule polyethylenimine (PEI) treatment with or without nanoparticles on the functions of adhesion receptors and chemokine receptors of human bone marrow-derived Mesenchymal Stem Cells (MSC). Analyses included MSC functions in vitro, as well as homing and therapeutic efficacy in rodent models of central nervous system´s pathologies in vivo.

FINDINGS

PEI treatment did not affect viability, immunomodulation or differentiation potential of MSC, but increased the CCR4 expression and functionally blocked their adhesion receptors, thus decreasing their adhesion capacity in vitro. Intravenously applied in a rat model of brain injury, the homing rate of PEI-MSC in the brain was highly increased with decreased numbers of adherent PEI-MSC in the lung vasculature. Moreover, in comparison to untreated MSC, PEI-MSC featured increased tumour directed migration in a mouse glioblastoma model, and superior therapeutic efficacy in a murine model of stroke.

INTERPRETATION

Balanced stem cell adhesion and migration in different parts of the vasculature and tissues together with the local microenvironment impacts their therapeutic efficacy.

FUNDING

Robert Bosch Stiftung, IZEPHA grant, EU grant 7 FP Health.

Stabilizing endothelium of donor hearts with fusogenic liposomes reduces myocardial injury and dysfunction

BACKGROUND

Myocardial injury after heart transplantation is a consequence of pathophysiologic events initiated by local ischemia/reperfusion injury that is further aggravated by the inflammatory response due to blood exposure to the pump's artificial surfaces during cardiopulmonary bypass. The purpose of the present study was to determine the effectiveness of fusogenic lipid vesicles (FLVs) in enhancing the cardioprotective effect of St. Thomas organ preservation solution (ST). We hypothesized that donor hearts preserved with ST+FLVs will stabilize the endothelium during reperfusion, which, in turn, will reduce both endothelial barrier dysfunction and myocardial damage.

METHODS

To examine the effect of ST+FLVs therapy in vitro, C3b deposition and adhesion molecule expression studies were performed on human umbilical vein endothelial cells challenged with plastic contact-activated plasma. To assess the therapy in vivo, a cervical heterotopic working heart transplantation model in rats was used. Donor hearts were preserved for 1 h at 27°C (15 min) and 4°C (45 min) and, after transplantation, were followed up for 2 h. Left ventricular function and the blood cardiac troponin I levels were quantified.

RESULTS

Human umbilical vein endothelial cells treated with ST+FLVs had reduced C3b deposition and expression of adhesion molecules compared with ST alone (P < 0.05). Donor hearts receiving ST+FLVs therapy had reduced left ventricular dysfunction and cardiac troponin I compared with ST alone.

CONCLUSIONS

We concluded that FLVs enhanced the cardioprotective effect of ST and reduced postischemic left ventricular dysfunction and myocardial damage. The mechanism of protection appears to be associated with the stabilization of endothelial cell membranes owing to incorporation of FLV-derived lipids.

Radiolabeled oligonucleotides for antisense imaging

Oligonucleotides radiolabeled with isotopes emitting γ-rays (for SPECT imaging) or positrons (for PET imaging) can be useful for targeting messenger RNA (mRNA) thereby serving as non-invasive imaging tools for detection of gene expression in vivo (antisense imaging). Radiolabeled oligonucleotides may also be used for monitoring their in vivo fate, thereby helping us better understand the barriers to its delivery for antisense targeting. These developments have led to a new area of molecular imaging and targeting, utilizing radiolabeled antisense oligonucleotides. However, the success of antisense imaging relies heavily on overcoming the barriers for its targeted delivery in vivo. Furthermore, the low ability of the radiolabeled antisense oligonucleotide to subsequently internalize into the cell and hybridize with its target mRNA poses additional challenges in realizing its potentials. This review covers the advances in the antisense imaging probe development for PET and SPECT, with an emphasis on radiolabeling strategies, stability, delivery and in vivo targeting.

The future of antisense oligonucleotides in the treatment of respiratory diseases

Antisense oligonucleotides (ASO) are short synthetic DNA molecules designed to inhibit translation of a targeted gene to protein via interaction with messenger RNA. More recently, small interfering (si)RNA have been developed as potent tools to specifically inhibit gene expression. ASO directed against signaling molecules, cytokine receptors, and transcription factors involved in allergic immune and inflammatory responses, have been applied in experimental models of asthma and demonstrate potential as therapeutics. Several ASO-based drugs directed against oncogenes have been developed for therapy of lung cancer, and some have recently reached clinical trials. ASO and siRNA to respiratory syncytial virus infection have demonstrated good potential to treat this condition, particularly in combination with an antiviral drug. Although ASO-based therapeutics are promising for lung diseases, issues of specificity, identification of correct molecular targets, delivery and carrier systems, as well as potential adverse effects must be carefully evaluated before clinical application.

Antisense-mediated knockdown of iNOS expression in the presence of cytokines

The impact of nitric oxide (NO) synthesized after activation by proinflammatory cytokines and/or bacterial products by an inducible NO synthase (iNOS) is still contradictory. Various methods to inhibit iNOS expression or activity have been established. A relatively new approach to inhibit iNOS-derived NO production is the antisense (AS) technique, which theoretically provides a specific and efficient method for inhibiting gene expression and function. This chapter focuses on the application of iNOS-specific AS-oligodeoxynucleotide (ODN) and highlights some of the pitfalls that must be considered to use this technique effectively.

What sense lies in antisense inhibition of inducible nitric oxide synthase expression?

The impact of nitric oxide (NO) synthesized after activation by proinflammatory cytokines and/or bacterial products by an inducible NO synthase (iNOS) is still contradictory. Expression of iNOS in inflammatory reactions is often found predominantly in cells of epithelial origin, and in these cases NO may serve as a protective agent limiting pathogen spreading, downregulating local inflammatory reactions by inducing production of Th2-like responses in a classical feedback circle, or limiting tissue damage during stress conditions. However, an abundant amount of data on chronic human disorders with predominant proinflammatory Th1-like reactions points to a destructive role of iNOS activity calling for a specific inhibition. Various methods to inhibit iNOS have been established to elucidate a protective versus a destructive role of NO during various stresses. In this review, we focus on antisense (AS)-mediated gene knock-down as a relatively new method to inhibit NO production and summarize the techniques applied and their successes. At least in theory, it provides a specific, rapid, and potentially high-throughput method for inhibiting gene expression and function. We here discuss the opportunities of iNOS-directed AS-ODN, and extensively deal with limitations and experimental problems.

On the biological activity of anti-ICAM-1 oligonucleotides complexed to non-viral carriers

An important challenge in antisense technology remains the adequate delivery of the oligonucleotides (ON) to individual cells. Understanding the subcellular distribution of ONs and their carrier is essential to explain the (lack of) biological activity. The ability of several cationic carriers to efficiently deliver anti-ICAM-1 oligonucleotides to their site of action was studied using a cell-based assay. In this assay we evaluated the ability of the ONs to downregulate the expression of the ICAM-1-protein in A549 cells. To understand why some carrier/ONs combinations showed biological activity while others failed, flow cytometry and confocal laser scanning microscopy (CLSM) measurements were used to study cellular uptake and intracellular distribution of the (fluorescently labeled) ONs. We showed that free ONs (both PS-ONs and PO-ONs) and ONs complexed to pEGpEI failed to decrease the ICAM-1 protein level. This was due to the inability of the (free or complexed) ONs to enter the cell, as shown by flow cytometry and CLSM. Flow cytometry and CLSM showed cellular uptake when PO-ONs and PS-ONs were complexed to graft-pDMAEMA and Lipofectin. However, while the uptake and intracellular localization seemed similar for ONs complexed to, respectively, graft-pDMAEMA and Lipofectin, the biological activity of the ONs was clearly dependent on their carrier: both PO-ONs and PS-ONs complexed to graft-pDMAEMA reduced the ICAM-1 expression; however, when complexed to Lipofectin only PS-ONs showed biological activity. Also, PS-ONs complexed to graft-pDMAEMA were more active than PO-ONs complexed to graft-pDMAEMA which could not be explained by the results from CLSM and flow cytometry. While the ICAM-1 assay proves whether a certain pharmaceutical carrier successfully delivers ONs or not, it does not answer the important question why one carrier is successful while another one fails. Also, our study shows that flow cytometry and CLSM, although useful techniques, failed to clearly explain the difference in transfection behavior between graft-pDMAEMA and Lipofectin. As ONs become susceptible to degradation by cytosolic DNase as soon as they are released from their carrier, one could argue that a better understanding of the time and (intracellular) place at which the dissociation of the complexes occurs could be crucial to fully explain our observations.

Role of endothelial MCP-1 in monocyte adhesion to inflamed human endothelium under physiological flow

Monocyte chemoattractant protein-1 (MCP-1) is an essential chemokine involved in monocyte traffic across endo- and epithelial barriers both in vitro and in vivo. However, the contribution of endothelial MCP-1 signaling via its CCR2 receptor in monocyte adhesion to inflamed endothelium under flow is incompletely understood. A sensitive flow chamber assay was used to assess monocyte adhesion to TNF-alpha-activated primary human pulmonary artery endothelial cells (HPAEC) during physiological shear stress. Monocyte adhesion was markedly reduced ( approximately 45%) when HPAEC-derived MCP-1 was either neutralized with anti-MCP-1 mAb or inhibited by translational arrest of MCP-1 mRNA transcripts with MCP-1 antisense oligomers. Corresponding efficacy was observed for blockade of monocyte CCR2 receptor function by anti-CCR2 mAb or MCP-1 antagonists (9-76 analog). The impact of endothelial MCP-1 on monocyte-HPAEC adhesion occurred via beta(2)-integrin but not via beta(1)-integrin adhesion pathways. In this line, pretreatment of monocytes with MCP-1 but not RANTES provoked a rapid and transient neoepitope 24 expression on beta(2)-integrin alpha-chains, as analyzed by increased reporter mAb24 binding. Collectively, our data show an important cross talk of endothelial MCP-1 with monocyte CCR2 effecting monocyte firm adhesion to inflamed HPAEC under physiological flow conditions.

Impact of a phosphorothioate oligodeoxynucleotide MCP-1 on NF-kappaB, AP-1, SP1 and NF-kappaB, and AP-1 subunit composition in human pulmonary endothelial cells

Phosphorothioate oligodeoxynucleotides (PS-ODN) are widely used prototypic antisense oligomers for sequence-specific suppression of normal and diseased gene expression. As polyanionic molecules, however, PS-ODN may also evoke nonsequence-specific side effects. The objective of the present study was to evaluate the impact of PS-ODN treatment of human pulmonary artery endothelial cells (HPAEC) and microvascular endothelial cells of the lung (HMVEC-L) on the cellular pool of the transcription factors nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1) as well as Sp1, using gel shift assays. In addition, by performing supershift assays, we investigated whether antisense treatment of endothelial cells affected the subunit composition of NF-kappaB and AP-1. Our data show that pretreatment of HPAEC and HMVEC-L with PS-ODN doses ranging from 50 to 5000 nM did not affect the total NF-kappaB, AP-1, or Sp1 pool in tumor necrosis factor-alpha (TNF-alpha)-activated endothelial cells (EC) or the subunit composition of the transcription factors NF-kappaB and AP-1. These findings suggest that putative nonsequence-specific effects of PS-ODN are not due to interactions of these oligomers with the transcription factors NF-kappaB, AP-1, or Sp1, at least in the EC type, a common target in transfection studies.

The spherulites(TM): a promising carrier for oligonucleotide delivery

Concentric multilamellar microvesicles, named spherulites(TM), were evaluated as an oligonucleotide carrier. Up to 80% oligonucleotide was encapsulated in these vesicles. The study was carried out on two different spherulite(TM) formulations. The spherulite(TM) size and stability characteristics are presented. Delivery of encapsulated oligonucleotide was performed on a rat hepatocarcinoma and on a lymphoblastoid T cell line, both expressing the luciferase gene. We showed that spherulites(TM) were able to transfect both adherent and suspension cell lines and deliver the oligonucleotide to the nucleus. Moreover, 48-62% luciferase inhibition was obtained in the rat hepatocarcinoma cell line when the antisense oligonucleotide targeted to the luciferase coding region was encapsulated at 500 nM concentration in spherulites(TM) of different compositions.

Antisense oligomers for selective suppression of MCP-1 synthesis in human pulmonary endothelial cells

Endothelial synthesis of the C-C chemokine monocyte chemotactic protein-1 (MCP-1) has been implicated in the regulation of monocyte recruitment for extravascular pools under both physiologic and inflammatory conditions. We designed and characterized five antisense phosphorothioate oligodeoxynucleotides (PS-ODN) targeting MCP-1 secretion by human pulmonary artery endothelial cells (HPAEC) and pulmonary microvascular endothelial cells (HMVEC-L). The most effective PS-ODN (MCP-1 AS 2) dose-dependently suppressed the secretion of MCP-1 but not the secretion of the C-X-C chemokine interleukin-8 (IL-8) in both HPAEC and HMVEC-L in the nanomolar concentration range. Mismatch controls bearing 2 or 4 bp substitutions showed markedly reduced inhibitory capacity. MCP-1 mRNA levels were not affected even at the highest PS-ODN doses employed (ribonuclease protection assay), suggesting a translational arrest of MCP-1 production. Accordingly, PS-ODN exhibited no nonspecific side effects on immediate-early gene regulation of the transcription factor nuclear factor-kappaB (NF-kappaB), as analyzed by gel shift assays. Antisense pretreatment of HPAEC reduced the monocyte chemotactic bioactivity liberated from tumor necrosis factor-alpha (TNF-alpha)-activated endothelial cells (EC) and reduced the TNF-alpha-induced transendothelial monocyte migration. We conclude that nanomolar concentrations of specific antisense oligodeoxynucleotides effectively inhibit human endothelial MCP-1 synthesis and may thus provide a rational approach to modulate monocyte recruitment under inflammatory conditions.