Extension of in vivo nucleic acid transfection techniques and increased information about those transfection properties and side effects are urgently needed to advance biological research and drug therapy. Tissue pressure-mediated transfection, involving lightly pressing the target tissue after intravenous injection of plasmid DNA or small-interfering RNA (siRNA), is a promising approach because of its high transfection efficiency and resulting low tissue damage. In this study, the gene expression/silencing properties and proinflammatory cytokine production associated with tissue pressure-mediated transfection were evaluated to extend its application. We have found that tissue pressure-mediated transfection can be applied to plasmid DNA and siRNA transfection to the spleen and siRNA transfection to the liver. In addition, we have demonstrated that these methods induce little production of proinflammatory cytokines, including tumor necrosis factor-alpha, interleukin (IL)-6, IL-12, and interferon-gamma. Moreover, we succeeded in controlling and quantifying the degree of pressure on the spleen and kidney and found that 0.59 N/cm(2) is sufficient for efficient and highly reproducible plasmid DNA transfection to the spleen and kidney in mice. Tissue pressure-mediated transfection of the kidney, liver, and spleen exhibits well-balanced characteristics including (1) simple and convenient manipulation, (2) tissue-specific, effective broad transfection properties, and (3) a low inflammatory response. Therefore, this information could be useful for a molecular-level mechanism analysis of diseases at an individual level in mammals, exploration of therapeutic target molecules and evaluation of gene therapy and nucleic acid-based therapy approaches, as well as potential clinical applications.

It is generally recognized that in vivo gene transfection is one of the most important techniques used in the post-genome era. Above all, naked plasmid DNA transfection has attracted much attention because of its advantages including convenience of preparation and handling and lack of toxicity associated with the transfection agents. We have investigated tissue pressure-mediated transfection performed by light and controlled pressure of the target tissue after normal intravenous injection of plasmid DNA. So far, we have demonstrated that plasmid DNA and small-interfering RNA (siRNA) are very efficiently transfected into murine kidney, liver and spleen without causing marked tissue damage. In this study, in order to understand the key physiological phenomena affecting transgene expression, we performed a set of experiments involving tissue pressure-mediated transfection, including the biodistribution and cellular transport of plasmid DNA and activation of transcriptional factors and obtained the following results: i) plasmid DNA transfer to the target tissue and its cells increased although the transferred fraction was small compared to the total administered plasmid DNA, ii) a transient increase in cellular translocation of plasmid DNA was induced, and iii) transcriptional factors were activated. Taking all these results into consideration, it would appear that tissue pressure-mediated transfection enhances plasmid DNA transfer to the target tissue and its cells and also activation of the transcriptional process. This information will allow a better understanding of in vivo transgene expression based on naked plasmid DNA transfection involving tissue pressure-mediated transfection.

We previously developed a renal pressure-mediated transfection method (renal pressure method) as a kidney-specific in vivo gene delivery system. However, additional information on selecting other injection routes and applicable animals remains unclear. In this study, we selected renal arterial and ureteral injections as local administration routes and evaluated the characteristics of gene delivery such as efficacy, safety, and distribution in pressured kidney of rat. Immediately after the naked pDNA injection, via renal artery or ureter, the left kidney of the rat was pressured using a pressure controlling device. Transfection efficiency of the pressured kidney was about 100-fold higher than that of the injection only group in both administration routes. The optimal pressure intensity in the rat kidney was 1.2 N/cm2 for renal arterial injection and 0.9 N/cm2 for ureteral injection. We found that transgene expression site differs according to administration route: cortical fibroblasts and renal tubule in renal arterial injection and cortical and medullary tubule and medullary collecting duct in ureteral injection. This is the first report to demonstrate that the renal pressure method can also be effective, after renal arterial and ureteral injections, in rat kidney.