The principle of hydrodynamic delivery was initially used to develop a method for the delivery of plasmids into mouse hepatocytes through tail vein injection and has been expanded for use in the delivery of various biologically active materials to cells in various organs in a variety of animal species through systemic or local injection, resulting in significant advances in new applications and technological development. The development of regional hydrodynamic delivery directly supports successful gene delivery in large animals, including humans. This review summarizes the fundamentals of hydrodynamic delivery and the progress that has been made in its application. Recent progress in this field offers tantalizing prospects for the development of a new generation of technologies for broader application of hydrodynamic delivery.

An intra-abdominal abscess can sometimes become serious and difficult to treat. The current standard treatment strategy for intra-abdominal abscess is percutaneous imaging-guided drainage. However, in cases of subphrenic abscess, it is important to avoid passing the drainage route through the thoracic cavity, as this can lead to respiratory complications. The spread of intervention techniques involving endoscopic ultrasonography (EUS) has made it possible to perform drainage via the transmural route. We describe two cases of subphrenic abscess that occurred after intra-abdominal surgery. Both were treated successfully by EUS-guided transmural drainage (EUS-TD) without severe complications. Our experience of these cases and a review of the literature suggest that the drainage catheters should be placed both internally and externally together into the abscess cavity. In previous cases there were no adverse events except for one case of mediastinitis and pneumothorax resulting from transesophageal drainage. Therefore, we consider that the transesophageal route should be avoided if possible. Although further studies are necessary, our present two cases and a literature review suggest that EUS-TD is feasible and effective for subphrenic abscess, and not inferior to other treatments. We anticipate that this report will be of help to physicians when considering the drainage procedure for this condition. As there have been no comparative studies to date, a prospective study involving a large number of patients will be necessary to determine the therapeutic options for such cases.

Exosomes, the smallest extracellular vesicles, have gained significant attention as key mediators in intercellular communication, influencing both physiological and pathological processes, particularly in cancer progression. A recent review article by Wang et al was published in a timely manner to stimulate future research and facilitate practical developments for targeted treatment of hepatocellular carcinoma using exosomes, with a focus on the origin from which exosomes derive. If information about the mechanisms for delivering exosomes to specific cells is incorporated, the concept of targeted therapy for hepatocellular carcinoma using exosomes could be more comprehensively understood.

A hemodynamic study of hydrodynamic gene delivery (HGD) from the tail vein in rodents has inspired a mechanism and an approach to further improve the efficacy of this procedure. However, there is no report on the hemodynamics of a regional HGD, which is an inevitable approach in large animals. Here, we report the hemodynamics of a regional hydrodynamic injection in detail based on 3D volume data and the dynamism of tissue intensity over time by using computed tomography (CT) both during and after a regional hydrodynamic injection that targeted the liver of a pig weighing 15.6 kg. Contrast medium (CM) was injected at a steady speed of 20 mL/s for 7.5 s under the temporal balloon occlusion of the hepatic vein (HV). A retrograde flow formed a wedge-shaped strong enhancement area downstream of the corresponding HV within 2.5 s, which was followed by drainage into another HV beginning from the target area and the portal vein (PV) toward a non-target area of the liver. After the injection, the CM was readily eliminated from the PV outside the target area. These data suggest that an interventional radiology approach is effective in limiting the hydrodynamic impacts in large animals at a target area and that the burden overflowing into the PV is limited. A further investigation that simultaneously evaluates gene delivery efficiency and hemodynamics using CT is needed to establish feasible parameters for a regional HGD in large animals.