Enhanced transduction and improved photoreceptor survival of retinal degeneration by the combinatorial use of rAAV2 with a lower dose of adenovirus

Maintenance and gene electrotransfer efficiency of antibiotic resistance gene-free plasmids encoding mouse, canine and human interleukin-12 orthologues

Interleukin 12 (IL-12) is a cytokine used as a therapeutic molecule in cancer immunotherapy. Gene electrotransfer mediated delivery of IL-12 gene has reached clinical evaluation in the USA using a plasmid that in addition to IL-12 gene also carry an antibiotic resistance gene needed for its production in bacteria. In Europe however, European Medicines Agency recommends against the use of antibiotics during the production of clinical grade plasmids. We have prepared several antibiotic resistance gene-free plasmids using an antibiotic-free selection strategy called operator-repressor titration, including plasmids encoding mouse, canine and human IL-12 orthologues. The aim of this study was to evaluate the maintenance of these plasmids in bacterial culture and test their transfection efficiency using gene electrotransfer. Plasmid maintenance was evaluated by determining plasmid yields and topologies after subculturing transformed bacteria. Transfection efficiency was evaluated by determining the plasmid copy number, expression and cytotoxicity after gene electrotransfer to mouse, canine and human melanoma cells. The results demonstrated that our IL-12 plasmids without an antibiotic resistance gene are stably maintained in bacteria and provide sufficient IL-12 expression after in vitro gene electrotransfer; therefore, they have the potential to proceed to further in vivo evaluation studies.

A statistical framework for determination of minimal plasmid copy number required for transgene expression in mammalian cells

Plasmid DNA (pDNA) has been widely used for non-viral gene delivery. After pDNA molecules enter a mammalian cell, they may be trapped in subcellular structures or degraded by nucleases. Only a fraction of them can function as templates for transcription in the nucleus. Thus, an important question is, what is the minimal amount of pDNA molecules that need to be delivered into a cell for transgene expression? At present, it is technically a challenge to experimentally answer the question. To this end, we developed a statistical framework to establish the relationship between two experimentally quantifiable factors - average copy number of pDNA per cell among a group of cells after transfection and percent of the cells with transgene expression. The framework was applied to the analysis of electrotransfection under different experimental conditions in vitro. We experimentally varied the average copy number per cell and the electrotransfection efficiency through changes in extracellular pDNA dose, electric field strength, and pulse number. The experimental data could be explained or predicted quantitatively by the statistical framework. Based on the data and the framework, we could predict that the minimal number of pDNA molecules in the nucleus for transgene expression was on the order of 10. Although the prediction was dependent on the cell and experimental conditions used in the study, the framework may be generally applied to analysis of non-viral gene delivery.

Decreased d-Serine Levels Prevent Retinal Ganglion Cell Apoptosis in a Glaucomatous Animal Model

Purpose

The purpose of this study was to determine d-Serine and d-Serine synthetase serine racemase (SR) expression and whether decreased d-Serine expression has protective effects on retinal ganglion cells (RGCs) in a glaucomatous animal model.

Methods

The rat chronic intraocular hypertension (COH) model was generated as a glaucomatous animal model by cauterizing three episcleral veins. Quantitative analysis of RGC survival was determined by the counting of retrograde FluoroGold-labeled RGCs. The level of d-Serine in the retinas and aqueous humor was determined by Ultra High Performance Liquid Chromatography coupled to triple-quadrupole Mass Spectrometry (UHPLC-MS/MS). Retinal expression of serine racemase (SR) protein was determined by immunohistochemistry and Western blot analysis. The TUNEL assay was used to detect cell apoptosis.

Results

The content of d-Serine increased significantly in the glaucomatous retina of the COH model 2 weeks after surgery compared with the control retina. d-Serine synthetase SR expression in the right glaucomatous eye increased slightly after surgery compared with that in the left control eye and remained at this high level for 6 weeks after surgery. SR-positive cells were located mainly in the ganglion cell layer (GCL) of the retina. d-Amino acid oxidase (DAAO) treatment significantly increased RGC survival in the glaucomatous eyes, and the TUNEL assay was used to confirm that DAAO reduced the number of TUNEL-positive cells in glaucomatous eyes. However, excess d-Serine could not exacerbate RGC loss in the COH model.

Conclusions

Increased d-Serine and SR expressions in the retina of the COH model were detected. DAAO treatment significantly increased RGC survival in the glaucomatous eyes. These results suggest that decreased d-Serine expression has protective effects on RGCs.

Gene therapy for ocular diseases meditated by ultrasound and microbubbles (Review)

The eye is an ideal target organ for gene therapy as it is easily accessible and immune‑privileged. With the increasing insight into the underlying molecular mechanisms of ocular diseases, gene therapy has been proposed as an effective approach. Successful gene therapy depends on efficient gene transfer to targeted cells to prove stable and prolonged gene expression with minimal toxicity. At present, the main hindrance regarding the clinical application of gene therapy is not the lack of an ideal gene, but rather the lack of a safe and efficient method to selectively deliver genes to target cells and tissues. Ultrasound‑targeted microbubble destruction (UTMD), with the advantages of high safety, repetitive applicability and tissue targeting, has become a potential strategy for gene‑ and drug delivery. When gene‑loaded microbubbles are injected, UTMD is able to enhance the transport of the gene to the targeted cells. High‑amplitude oscillations of microbubbles act as cavitation nuclei which can effectively focus ultrasound energy, produce oscillations and disruptions that increase the permeability of the cell membrane and create transient pores in the cell membrane. Thereby, the efficiency of gene therapy can be significantly improved. The UTMD‑mediated gene delivery system has been widely used in pre‑clinical studies to enhance gene expression in a site‑specific manner in a variety of organs. With reasonable application, the effects of sonoporation can be spatially and temporally controlled to improve localized tissue deposition of gene complexes for ocular gene therapy applications. In addition, appropriately powered, focused ultrasound combined with microbubbles can induce a reversible disruption of the blood‑retinal barrier with no significant side effects. The present review discusses the current status of gene therapy of ocular diseases as well as studies on gene therapy of ocular diseases meditated by UTMD.

Enhanced downregulation of transforming growth factor‑β2 in rat retinal pigment epithelium cells by adeno‑associated virus‑mediated ribonucleic acid interference combined with ultrasound or microbubbles

The present study was designed to determine the efficiency and safety of ultrasound (US) and/or US contrast agent microbubbles (MBs) in the delivery of type 2 recombinant adeno-associated virus‑delivered transforming growth factor‑β2 short hairpin ribonucleic acid encoding the enhanced green fluorescent protein gene (rAAV2‑TGFβ2 shRNA‑EGFP) and the downregulation of TGFβ2 in rat retinal pigment epithelium (RPE‑J) cells. The effects of US and/or MBs on the delivery of rAAV2‑EGFP and rAAV2‑TGFβ2 shRNA‑EGFP were evaluated by fluorescence microscopy and flow cytometry. The potential toxicity of cell viability under various US or MB conditions was assessed by CellTiter 96® AQueous One solution cell proliferation assay. The level of TGFβ2 mRNA in RPE‑J cells under various conditions was estimated by reverse transcription‑quantitative polymerase chain reaction analysis. The results obtained demonstrated that low-intensity US (0.5 W/cm2 and 30 sec) or SonoVue (MB:cell ratio, 40:1) increased the delivery efficiency of rAAV2‑EGFP and rAAV2‑TGFβ2 shRNA‑EGFP to RPE‑J cells, whereas the combination of US with MBs did not further increase but instead decreased rAAV transfection. Under the optimal conditions of rAAV delivery, enhanced TGFβ2 gene silencing with a combination of US or SonoVue with rAAV2‑TGFβ2 shRNA resulted in a significant decrease in mRNA levels compared with rAAV2‑TGFβ2 shRNA alone. US or SonoVue was used safely to enhance the delivery of rAAV2‑TGFβ2 shRNA to RPE‑J cells. A combination of the biological (rAAV2‑TGFβ2 shRNA) and physical (US or SonoVue) approaches downregulated the mRNA level of TGFβ2 more effectively.

Immunology of AAV-Mediated Gene Transfer in the Eye

The eye has been at the forefront of translational gene therapy largely owing to suitable disease targets, anatomic accessibility, and well-studied immunologic privilege. These advantages have fostered research culminating in several clinical trials and adeno-associated virus (AAV) has emerged as the vector of choice for many ocular therapies. Pre-clinical and clinical investigations have assessed the humoral and cellular immune responses to a variety of naturally occurring and engineered AAV serotypes as well as their delivered transgenes and these data have been correlated to potential clinical sequelae. Encouragingly, AAV appears safe and effective with clinical follow-up surpassing 5 years in some studies. As disease targets continue to expand for AAV in the eye, thorough and deliberate assessment of immunologic safety is critical. With careful study, the development of these technologies should concurrently inform the biology of the ocular immune response.

Gene therapy for cardiovascular disease mediated by ultrasound and microbubbles

Gene therapy provides an efficient approach for treatment of cardiovascular disease. To realize the therapeutic effect, both efficient delivery to the target cells and sustained expression of transgenes are required. Ultrasound targeted microbubble destruction (UTMD) technique has become a potential strategy for target-specific gene and drug delivery. When gene-loaded microbubble is injected, the ultrasound-mediated microbubble destruction may spew the transported gene to the targeted cells or organ. Meanwhile, high amplitude oscillations of microbubbles increase the permeability of capillary and cell membrane, facilitating uptake of the released gene into tissue and cell. Therefore, efficiency of gene therapy can be significantly improved. To date, UTMD has been successfully investigated in many diseases, and it has achieved outstanding progress in the last two decades. Herein, we discuss the current status of gene therapy of cardiovascular diseases, and reviewed the progress of the delivery of genes to cardiovascular system by UTMD.

A novel approach to attenuate proliferative vitreoretinopathy using ultrasound-targeted microbubble destruction and recombinant adeno-associated virus-mediated RNA interference targeting transforming growth factor-β2 and platelet-derived growth factor-B

BACKGROUND

To date, with the exception of surgery, there are no satisfactory treatments available for proliferative vitreoretinopathy (PVR). Ultrasound-targeted microbubble destruction (UTMD) represents a new approach for the gene therapy of eye diseases. The present study aimed to investigate the feasibility of the attenuation of PVR by a combinatorial use of UTMD and recombinant adeno-associated virus (rAAV)-mediated RNA interference (RNAi) targeting transforming growth factor (TGF)-β2 and platelet-derived growth factor (PDGF)-B.

METHODS

One hundred and eighty rats of the PVR model were averagely divided into six groups (G). The left eyes, respectively, received an intravitreal injection as follows: normal saline (G1), rAAV2-control small interfering RNA (siRNA) (G2), rAAV2-TGF-β2-siRNA (G3), rAAV2-PDGF-B-siRNA (G4), rAAV2-TGF-β2-siRNA and rAAV2-PDGF-B-siRNA (G5, G6) on day 3 after PVR induction. In G6, a condition of UTMD was used additionally. On days 14 and 28, pathological changes of eye fundus were assessed by ophthalmoscopic and histopathologic examination, and the protein and mRNA levels of TGF-β2 and PDGF-B expression were tested using enzyme-linked immunosorbent assay and a reverse transcriptase-polymerase chain reaction, respectively.

RESULTS

The average grade scales of proliferation and the protein and mRNA expression levels of TGF-β2 and PDGF-B in G6 were all lower than that in G5 on day 28 (p<0.05, unpaired t-test). They were all lower in G5 and G6 than in G1, G2, G3 and G4 on day 28 (p<0.05, one-way analysis of variance), although the protein and mRNA expression levels of PDGF-B in G6 did not differ from that in G1, G2, G3, G4 and G5 on day 14.

CONCLUSIONS

The combinatorial use of UTMD and rAAV2-mediated RNAi targeting TGF-β2 and PDGF-B can serve as a novel approach to attenuate PVR.

An immunohistochemical analysis of a rat model of proliferative vitreoretinopathy and a comparison of the expression of TGF-β and PDGF among the induction methods

Proliferative vitreoretinopathy (PVR) is a serious complication of retinal detachment surgery or ocular trauma. Our previous study indicated that intravitreal co-injection of retinal pigmented epithelial (RPE)-J cells and platelet-rich plasma (PRP) (not RPE-J cells or PRP alone) in Wistar rat eyes can successfully induce a model of PVR. But which cells are involved in this process and why different induction methods, intravitreal injection of RPE-J cells or/and PRP, induced a different situation remain to be unknown. In this study, immunohistochemistry was performed to identify the main cell types involved in this process. The expression levels of transforming growth factor (TGF)-β2, platelet-derived growth factor (PDGF)-AA and PDGF-BB were tested using enzyme-linked immunosorbent assay (ELISA). The results showed that RPE cells, glial cells, fibroblasts and macrophages took part in the pathogenesis of this model. The expression levels and durations of TGF-β2 and PDGF-BB partially explained the different results induced by the different induction methods. This provides an experimental proof for attenuation of the experimental PVR by targeting at a specific cells or growth factor.

Ultrasound-targeted microbubble destruction enhances AAV-mediated gene transfection in human RPE cells in vitro and rat retina in vivo

This study was conducted to investigate the efficacy and safety of ultrasound (US)-targeted microbubble (MB) destruction (UTMD)-mediated rAAV2-CMV-EGFP transfection to cultured human retinal pigment epithelium (RPE) cells in vitro and to the rat retina in vivo. In the in vitro study, cultured human RPE cells were exposed to US under different conditions with or without MBs. Furthermore, the effect of UTMD on rAAV2-CMV-EGFP itself and on cells was evaluated. In the in vivo study, gene transfer was examined by injecting rAAV2-CMV-EGFP into the subretinal space of rats with or without MBs and then exposed to US. We investigated enhanced green fluorescent protein (EGFP) expression in vivo by stereomicroscopy and performed quantitative analysis using Axiovision 3.1 software. Hematoxylin and eosin staining and frozen sections were used to observe tissue damage and location of the EGFP gene expression. In the in vitro study, the transfection efficiency of rAAV2-CMV-EGFP under optimal UTMD was significantly higher than that of the control group (P=0.000). Furthermore, there was almost no cytotoxicity to the cells and to rAAV2-CMV-EGFP itself. In the in vivo study, UTMD could be used safely to enhance and accelerate the transgene expression of the retina. Fluorescence expression was mainly located in the retinal layer. UTMD is a promising method for gene delivery to the retina.