Quantitative bioluminescence imaging of transgene expression in vivo

Bioluminescent imaging (BLI) is a widely used in vivo method to determine the location and relative intensity of luciferase expression in mice. Luciferase expression is observed following an i.p. dose of d-luciferin, resulting in bioluminescence that is detected in anesthetized mice by a charge-coupled device camera. To establish whether BLI could be used as a quantitative measurement of non-viral-mediated luciferase expression, precise quantities of plasmid DNA encoding the luciferase gene were hydrodynamically dosed in mice. The results established a linear correlation between the DNA dose and the BLI response measured in liver which spanned five orders of magnitude. The level of luciferase expression was found to be a direct function of d-luciferin dose. The time course of luciferase expression and the influence of multidosing of substrate were measured by BLI. The recovery of luciferase from the liver of hydrodynamically dosed mice allowed calibration of the BLI measurements. The results establish BLI's limit-of-detection at 20 pg of luciferase per liver following a hydrodynamic dose of 100 pg of plasmid DNA. These results demonstrate that BLI is both sensitive and linear and should allow for the direct comparison of the efficiency of gene transfer vectors that target the liver.     

An efficient gene transfer method mediated by ultrasound and microbubbles into the kidney

BACKGROUND: Safety issues are of paramount importance in clinical human gene therapy. From this point of view, it would be better to develop a novel non-viral efficient gene transfer method. Recently, it was reported that ultrasound exposure could induce cell membrane permeabilization and enhance gene expression. METHODS: In this study, we examined the potential of ultrasound for gene transfer into the kidney. First, we transfected rat left kidney with luciferase plasmid mixed with microbubbles, Optison, to optimize the conditions (duration of ultrasound and concentration of Optison). Then, 4, 7, 14 and 21 days after gene transfer, luciferase activity was measured. Next, localization of gene expression was assessed by measuring luciferase activity and green fluorescent protein (GFP) expression. Expression of GFP plasmid was examined under a fluorescence microscope at 4 and 14 days after gene transfer. Finally, to examine the side effects of this gene transfer method, biochemical assays for aspartate aminotransferase (AST), alanine aminotransferase (ALT), blood urea nitrogen (BUN) and creatinine (Cre) were performed. RESULTS: Optison and/or ultrasound significantly enhanced the efficiency of gene transfer and expression in the kidney. Especially, 70-80% of total glomeruli could be transfected. Also, a significant dose-dependent effect of Optison was observed as assessed by luciferase assay (Optison 25%: 12.5 x 10(5) relative light units (RLU)/g tissue; 50%: 31.3 x 10(5) RLU/g tissue; 100%: 57.9 x 10(5) RLU/g tissue). GFP expression could be observed in glomeruli, tubules and interstitial area. Results of blood tests did not change significantly after gene transfer. CONCLUSIONS: Overall, an ultrasound-mediated gene transfer method with Optison enhanced the efficiency of gene transfer and expression in the rat kidney. This novel non-viral method may be useful for gene therapy for renal disease.     

Chitosan-DNA nanoparticles delivered by intrabiliary infusion enhance liver-targeted gene delivery

The goal of this study was to examine the efficacy of liver-targeted gene delivery by chitosan-DNA nanoparticles through retrograde intrabiliary infusion (RII). The transfection efficiency of chitosan-DNA nanoparticles, as compared with PEI-DNA nanoparticles or naked DNA, was evaluated in Wistar rats by infusion into the common bile duct, portal vein, or tail vein. Chitosan-DNA nanoparticles administrated through the portal vein or tail vein did not produce detectable luciferase expression. In contrast, rats that received chitosan-DNA nanoparticles showed more than 500 times higher luciferase expression in the liver 3 days after RII; and transgene expression levels decreased gradually over 14 days. Luciferase expression in the kidney, lung, spleen, and heart was negligible compared with that in the liver. RII of chitosan-DNA nanoparticles did not yield significant toxicity and damage to the liver and biliary tree as evidenced by liver function analysis and histopathological examination. Luciferase expression by RII of PEI-DNA nanoparticles was 17-fold lower than that of chitosan-DNA nanoparticles on day 3, but it increased slightly over time. These results suggest that RII is a promising routine to achieve liver-targeted gene delivery by non-viral nanoparticles; and both gene carrier characteristics and mode of administration significantly influence gene delivery efficiency.     

A novel transfection method for eukaryotic cells using polyethylenimine coated albumin microbubbles

Albumin microbubbles have been intensively studied for their application in gene delivery. However, with negative surface potential, albumin microbubbles hardly bind plasmid DNA, which might contribute to their low transgene efficiency. In this study, we developed polyethylenimine (PEI) coated albumin microbubbles (PAMB) which were prepared by sonicating the mixture of human albumin, PEI, polyethylene glycol and glucose. CHO cells, COS cells and 293T cells were transfected with PEI, PEI + albumin, PAMB and Lipofectamine 2000, respectively. Our results showed that the surface potential was elevated and PAMB could bind plasmid DNA. The transgene efficiency of PAMB was higher than PEI and PEI + albumin (P < 0.05), and PAMB performed the same transgene effect as Lipofectamine 2000 did but with lower cytotoxicity than Lipofectamine 2000. Albumin microbubbles modified by PEI has high transgene efficiency and low cytotoxicity even without ultrasound medication, making it a useful non-virus gene delivery method in vitro.     

Activation of transgene expression in skeletal muscle by focused ultrasound

To correlate thermal dose from focused ultrasound (FUS) with gene expression and tissue injury, a temperature plateau strategy was employed. Plasmids encoding luciferase gene under the control of hsp70B promoter were transfected into the right gastrocnemius muscle in a rat via electroporation. One day after transfection, hind limbs were treated with 3.3-MHz focused ultrasound, using one of four different temperature plateaus with spatial-peak time-average focal temperatures (T_SPTA) of 46 °C, 48 °C, 51 °C and 62 °C. The treatment duration at the plateau temperature was varied from 0 to 30 s. Gene expression was analyzed in vivo one day following FUS treatment, and H&E staining was employed to assess tissue injury. Gene activation and tissue damage correlated closely with thermal dose. The highest level of gene activation was induced by FUS at T_SPTA = 51 °C for 20 s, which was found to be statistically equivalent to that produced by water-bath hyperthermia.     

Gene electro-transfer of an improved erythropoietin plasmid in mice and non-human primates

BACKGROUND: Anemia due to impaired erythropoietin (EPO) production is associated with kidney failure. Recombinant proteins are commonly administered to alleviate the symptoms of this dysfunction, whereas gene therapy approaches envisaging the delivery of EPO genes have been tried in animal models in order to achieve stable and long-lasting EPO protein production. Naked DNA intramuscular injection is a safe approach for gene delivery; however, transduction levels show high inter-individual variability in rodents and very poor efficiency in non-human primates. Transduction can be improved in several animal models by application of electric pulses after DNA injection. METHODS: We have designed a modified EPO gene version by changing the EPO leader sequence and optimizing the gene codon usage. This modified gene was electro-injected into mice, rabbits and cynomolgus monkeys to test for protein production and biological effect. CONCLUSIONS: The modified EPO gene yields higher levels of circulating transgene product and a more significant biological effect than the wild-type gene in all the species tested, thus showing great potential in clinically developable gene therapy approaches for EPO delivery.     

Regional hydrodynamic gene delivery to the rat liver with physiological volumes of DNA solution

BACKGROUND: The major barrier to the clinical application of hydrodynamic gene delivery to the liver is the large volume of fluid required using standard protocols. Regional hydrodynamic gene delivery via branches of the portal vein has not previously been reported, and we have evaluated this approach in a rat model. METHODS: The pGL3 plasmid with the luciferase reporter gene was used at 50 micro g/ml in isotonic solutions, and was administered with a syringe pump for precise control of the hydrodynamic conditions evaluated. Gene expression was individually measured in six anatomically distinct liver lobes. The effect of systemic chloroquine to promote endocytic escape and a (Lys)(16)-containing peptide to condense the DNA into approximately 100-nm nanoparticles was also evaluated. RESULTS: Hydrodynamic conditions for excellent gene delivery were obtained by using 3-ml volumes ( approximately 12 ml/kg) of isotonic DNA solution delivered at 24 ml/min to the right lateral lobe ( approximately 20% of the liver mass). Under these conditions, >95% of gene delivery usually occurred in the targeted right lateral lobe. Outflow obstruction was essential for gene delivery, both at optimal and at very low levels of hydrodynamic gene delivery. The use of systemic chloroquine to promote endocytic escape did not augment hydrodynamic gene delivery, while condensation of DNA in non-ionic isotonic solutions (5% dextrose) to nanoparticles of approximately 100 nm completely abolished gene delivery. CONCLUSIONS: Regional hydrodynamic gene delivery via a branch of the portal vein offers a physiological model of liver gene therapy, for experimental and clinical application.     

Flt3-L gene therapy enhances immunocytokine-mediated antitumor effects and induces long-term memory

Therapeutic treatment with hu14.18-IL-2 immunocytokine (IC) or Flt3-L (FL) protein is initially effective at resolving established intradermal NXS2 neuroblastoma tumors in mice. However, many treated animals develop recurrent disease. We previously found that tumors recurring following natural killer (NK) mediated IC treatment show augmented MHC class I expression, while the tumors that recurred following T cell dependent Flt3-L treatment exhibited decreased MHC class I expression. We hypothesized that this divergent MHC modulation on recurrent tumors was due to therapy-specific immunoediting. We further postulated that combining IC and Flt3-L treatments might decrease the likelihood of recurrent disease by preventing MHC modulation as a mechanism for immune escape. We now report that combinatorial treatment of FL plus hu14.18-IL-2 IC provides greater antitumor benefit than treatment with either alone, suppressing development of recurrent disease. We administered FL by gene therapy using a clinically relevant approach: hydrodynamic limb vein (HLV) delivery of DNA for transgene expression by myofibers. Delivery of FL DNA by HLV injection in mice resulted in systemic expression of >10 ng/ml of FL in blood at day 3, and promoted up to a fourfold and tenfold increase in splenic NK and dendritic cells (DCs), respectively. Furthermore, the combination of FL gene therapy plus suboptimal IC treatment induced a greater expansion in the absolute number of splenic NK and DCs than achieved by individual component treatments. Mice that received combined FL gene therapy plus IC exhibited complete and durable resolution of established NXS2 tumors, and demonstrated protection from subsequent rechallenge with NXS2 tumor.     

Targeted retroviral gene delivery using ultrasound

BACKGROUND: Achieving specificity of delivery represents a major problem limiting the clinical application of retroviral vectors for gene therapy, whilst lack of efficiency and longevity of gene expression limit non-viral techniques. Ultrasound and microbubble contrast agents can be used to effect plasmid DNA delivery. We therefore sought to evaluate the potential for ultrasound/microbubble-mediated retroviral gene delivery. METHODS: An envelope-deficient retroviral vector, inherently incapable of target cell entry, was combined with cationic microbubbles and added to target cells. The cells were exposed to pulsed 1 MHz ultrasound for 5 s and subsequently analysed for marker gene expression. The acoustic pressure profile of the ultrasound field, to which transduction efficiency was related, was determined using a needle hydrophone. RESULTS: Ultrasound-targeted gene delivery to a restricted area of cells was achieved using virus-loaded microbubbles. Gene delivery efficiency was up to 2% near the beam focus. Significant transduction was restricted to areas exposed to > or = 0.4 MPa peak-negative acoustic pressure, despite uniform application of the vector. An acoustic pressure-dependence was demonstrated that can be exploited for targeted retroviral transduction. The mechanism of entry likely involves membrane perturbation in the vicinity of oscillating microbubbles, facilitating fusion of the viral and cell membranes. CONCLUSIONS: We have established the basis of a novel retroviral vector technology incorporating favourable aspects of existing viral and non-viral gene delivery vectors. In particular, transduction can be controlled by means of ultrasound exposure. The technology is ideally suited to targeted delivery following systemic vector administration.     

Application of low intensity ultrasound to enhance the activity of anammox microbial consortium for nitrogen removal

In this study, effect of low intensity ultrasound on the activity of anammox microbial consortium for nitrogen removal was investigated through batch experiments at the same irradiation frequency of 25 kHz. Total nitrogen removal rate increased by about 25.5% when ultrasound intensity of 0.3 w cm⁻² was applied at an optimal irradiation time of 4 min, and further experiments demonstrated that this effect could last for about 6 days. Analysis of extracellular polymeric substances indicated that the maximum increase of carbohydrate, protein and total extracellular substances was obtained on the first day after ultrasound, which was 28.8%, 30.5% and 29.7%, respectively. As the time prolonged, the production rate of extracellular carbohydrate, protein decreased gradually. Transmission electron microscopy observation demonstrated that ultrasounded cell wall of anammox microbial consortium became thinner resulting in increased release of extracellular substances. The results suggested that application of low intensity ultrasound may enhance the activity of anammox microbial consortium and ultimately the potential for nitrogen removal.     

Restoration of Haemoglobin Level Using Hydrodynamic Gene Therapy with Erythropoietin Does Not Alleviate the Disease Progression in an Anaemic Mouse Model for TGFβ1-Induced Chronic Kidney Disease

Erythropoietin, Epo, is a 30.4 kDa glycoprotein hormone produced primarily by the fetal liver and the adult kidney. Epo exerts its haematopoietic effects by stimulating the proliferation and differentiation of erythrocytes with subsequent improved tissue oxygenation. Epo receptors are furthermore expressed in non-haematopoietic tissue and today, Epo is recognised as a cytokine with many pleiotropic effects. We hypothesize that hydrodynamic gene therapy with Epo can restore haemoglobin levels in anaemic transgenic mice and that this will attenuate the extracellular matrix accumulation in the kidneys. The experiment is conducted by hydrodynamic gene transfer of a plasmid encoding murine Epo in a transgenic mouse model that overexpresses TGF-β1 locally in the kidneys. This model develops anaemia due to chronic kidney disease characterised by thickening of the glomerular basement membrane, deposition of mesangial matrix and mild interstitial fibrosis. A group of age matched wildtype littermates are treated accordingly. After a single hydrodynamic administration of plasmid DNA containing murine EPO gene, sustained high haemoglobin levels are observed in both transgenic and wildtype mice from 7.5 ± 0.6 mmol/L to 9.4 ± 1.2 mmol/L and 10.7 ± 0.3 mmol/L to 15.5 ± 0.5 mmol/L, respectively. We did not observe any effects in the thickness of glomerular or tubular basement membrane, on the expression of different collagen types in the kidneys or in kidney function after prolonged treatment with Epo. Thus, Epo treatment in this model of chronic kidney disease normalises haemoglobin levels but has no effect on kidney fibrosis or function.     

Schistosoma mansoni U6 gene promoter-driven short hairpin RNA induces RNA interference in human fibrosarcoma cells and schistosomules

RNA interference (RNAi) mediated by short hairpin-RNA (shRNA) expressing plasmids can induce specific and long-term knockdown of specific mRNAs in eukaryotic cells. To develop a vector-based RNAi model for Schistosoma mansoni, the schistosome U6 gene promoter was employed to drive expression of shRNA targeting reporter firefly luciferase. An upstream region of a U6 gene predicted to contain the promoter was amplified from genomic DNA of S. mansoni. A shRNA construct driven by the predicted U6 promoter targeting luciferase was assembled and cloned into plasmid pXL-Bac II, the construct termed pXL-BacII_SmU6-shLuc. Luciferase expression in transgenic fibrosarcoma HT-1080 cells was significantly reduced 96 h following transduction with plasmid pXL-BacII_SmU6-shLuc, which encodes luciferase mRNA-specific shRNA. In a similar fashion, schistosomules of S. mansoni were transformed with the SmU6-shLuc or control constructs. Firefly luciferase mRNA was introduced into transformed schistosomules after which luciferase activity was analyzed. Significantly less activity was present in schistosomules transfected with pXL-BacII_SmU6-shLuc compared with controls. The findings revealed that the putative S. mansoni U6 gene promoter of 270 bp in length was active in human cells and schistosomes. Given that the U6 gene promoter drove expression of shRNA from an episome, the findings also indicate the potential of this putative RNA polymerase III dependent promoter as a component regulatory element in vector-based RNAi for functional genomics of schistosomes.     

17Beta-estradiol decreases hypoxic induction of erythropoietin gene expression

Exposure to chronic hypoxia induces erythropoietin (EPO) production to facilitate oxygen delivery to hypoxic tissues. Previous studies from our laboratory found that ovariectomy (OVX) exacerbates the polycythemic response to hypoxia and treatment with 17beta-estradiol (E2-beta) inhibits this effect. We hypothesized that E2-beta decreases EPO gene expression during hypoxia. Because E2-beta can induce nitric oxide (NO) production and NO can attenuate EPO synthesis, we further hypothesized that E2-beta inhibition of EPO gene expression is mediated by NO. These hypotheses were tested in OVX catheterized rats treated with E2-beta (20 microg/day) or vehicle for 14 days and exposed to 8 or 12 h of hypoxia (12% O(2)) or normoxia. We found that E2-beta treatment significantly decreased EPO synthesis and gene expression during hypoxia. E2-beta treatment did not induce endothelial NO synthase (eNOS) expression in the kidney but potentiated hypoxia-induced increases in plasma nitrates. We conclude that E2-beta decreases hypoxic induction of EPO. However, this effect does not appear to be related to changes in renal eNOS expression.     

φC31 integrase and liver-specific regulatory elements confer high-level,long-term expression of firefly luciferase in mouse liver

To improve the efficiency of expression of reporter transgenes delivered by hydrodynamic injection, we generated expression cassettes carrying different liver-specific regulatory elements using the firefly luciferase gene as a reporter. From our studies the human alpha-antitrypsin promoter together with the apolipoprotein E/C-I and albumin enhancer was the combination of choice for prolonged transgene expression, but reporter gene expression in vivo lasted for no more than 7 weeks. Subsequently, phage φC31 integrase was introduced as a potential tool to improve further the efficiency of expression of the delivered transgene. Long-term transgene expression in vivo was achieved by specific integration of the target gene into mouse livers. This study demonstrates the use of a combination of phage φC31 integrase and liver-specific regulatory elements for generation of transgenic mice.     

The potential benefits of nicaraven to protect against radiation-induced injury in hematopoietic stem/progenitor cells with relative low dose exposures

Nicaraven, a hydroxyl radical-specific scavenger has been demonstrated to attenuate radiation injury in hematopoietic stem cells with 5 Gy γ-ray exposures. We explored the effect and related mechanisms of nicaraven for protecting radiation injury induced by sequential exposures to a relatively lower dose γ-ray. C57BL/6 mice were given nicaraven or placebo within 30 min before exposure to 50 mGy γ-ray daily for 30 days in sequences (cumulative dose of 1.5 Gy). Mice were victimized 24 h after the last radiation exposure, and the number, function and oxidative stress of hematopoietic stem cells were quantitatively estimated. We also compared the gene expression in these purified stem cells from mice received nicaraven and placebo treatment. Nicaraven increased the number of c-kit⁺ stem/progenitor cells in bone marrow and peripheral blood, with a recovery rate around 60–90% of age-matched non-irradiated healthy mice. The potency of colony forming from hematopoietic stem/progenitor cells as indicator of function was completely protected with nicaraven treatment. Furthermore, nicaraven treatment changed the expression of many genes associated to DNA repair, inflammatory response, and immunomodulation in c-kit⁺ stem/progenitor cells. Nicaraven effectively protected against damages of hematopoietic stem/progenitor cells induced by sequential exposures to a relatively low dose radiation, via complex mechanisms.     

Phage phiC31 integrase-mediated genomic integration and long-term gene expression in the lung after nonviral gene delivery

BACKGROUND: Phage phiC31 integrase has emerged as a potent tool for achieving long-term gene expression in different tissues. The present study investigated the activity of phiC31 integrase in murine lungs. METHODS: Transfections in murine alveolar epithelial (MLE12) cells were performed with Lipofectamine 2000. For in vivo gene delivery, DNA was complexed with polyethylenimine (PEI) and PEI-DNA complexes were injected intravenously into mice. Expression of luciferase in mice was monitored by in vivo bioluminsecence imaging. Genomic integration and integration into a previously described 'hotspot' were confirmed by polymerase chain reaction (PCR). RESULTS: phiC31 integrase mediated intramolecular recombination between wild-type attB and attP sites in MLE12 cells. Long-term gene expression could be observed in MLE12 cells in the presence of integrase without any selection pressure. Long-term expression of luciferase after intravenous injection of PEI-DNA complexes could be observed only in the lungs of mice which were co-injected with the integrase-encoding plasmid. Increased amounts of integrase plasmid and administration of a second dose had no effect on the level of luciferase expression achieved with a single dose, which was three orders of magnitude lower than the values observed on 'day 1' post application. Genomic integration of the transgene in the mouse lungs was confirmed by PCR. Seven out of the fifteen treated mice showed integration at the mpsL1 site, a previously described 'hot spot' from liver. CONCLUSIONS: These results provide evidence for the activity of phiC31 integrase in lungs but also emphasize the need for optimization of the system to maintain long-term gene expression at high levels.