Hydrodynamic Injection as a Technique for Systemic Nucleic Acid Delivery to Hepatocytes

Hydrodynamic tail vein injection is a unique physical method for delivering nucleic acids (DNA or RNA) to the liver. Unlike lipid nanoparticles or viral vectors that rely on cellular uptake mechanisms, hydrodynamic injection uses a rapid, high-volume infusion of solution to achieve gene transfer. This technique, often simply called hydrodynamic injection (HDI), can result in transfection of 5–40% of hepatocytes in a mouse liver with a single DNA injection, making it a powerful research tool for liver gene therapy modeling. Here, we discuss the principles of hydrodynamic injection, its ability to attain systemic hepatocyte delivery, and its applications in gene function studies and disease models. We also cover the practical considerations and limitations, especially regarding its scalability beyond small animals.

Scientific Context

Hydrodynamic injection was first reported in the late 1990s as a method to overcome the poor gene transfer of naked DNA. It involves injecting a large volume of plasmid DNA solution (typically 8–10% of body weight) into the bloodstream within a very short time (5–7 seconds in mice, via the tail vein). This causes a transient high pressure in the vena cava and hepatic veins, effectively “forcing” DNA across the fenestrated endothelium of the liver into hepatocytes. The liver’s sinusoids, being leaky and receiving most of the cardiac output, bear the brunt of this pressure surge. As a result, pores open or membranes stretch such that DNA can directly enter hepatocytes.

Mechanistically, HDI creates a hydrostatic pressure that drives fluid into the liver parenchyma. The hepatocytes, which normally are tightly packed with endothelium, experience pressure-mediated permeabilization. Studies have shown that within seconds of injection, plasmids appear inside hepatocyte nuclei of mice, with expression detectable as early as an hour after injection. Notably, gene delivery via HDI is highly efficient – for example, peak reporter expression can reach >500 µg/ml of a secreted protein in serum, far exceeding levels from conventional nonviral methods. One reference noted that single hydrodynamic injection in mice achieved 500–1000 µg/ml of protein in blood, which is orders of magnitude above typical naked DNA injection results.

HDI primarily targets the liver; roughly 90% of gene expression is in liver, with much lower levels in other organs. This is because the liver is highly perfused and susceptible to the pressure, whereas other organs either have tighter capillaries or receive less of the injected volume initially. Indeed, experiments have found only minimal gene expression in spleen, lung, kidney, heart, etc., after tail vein HDI – the liver is the main site of plasmid uptake. This liver selectivity is a big advantage for modeling liver diseases. Importantly, gene expression after HDI is typically transient (lasting days to weeks) unless some form of genome integration or non-dividing state is involved. Plasmid remains episomal and is diluted or silenced over time (often about 2–4 weeks in mice, though expression up to months has been observed with certain promoters.

Experimental Approaches

Optimizing hydrodynamic injection entails controlling volume, speed, and DNA dose. In mice, a common protocol is injecting ~1.6–2 mL (for a 20 g mouse) in 5–7 seconds via the lateral tail vein. This is often achieved with a syringe and a steady hand, or automated injectors for consistency. The solution can be just saline with naked plasmid DNA (no carrier needed). Achieving the right intravascular pressure is crucial: too slow an injection and the fluid will redistribute into circulation without permeabilizing hepatocytes; too fast or too large volume can cause cardiac overload or rupture tissue (in extreme cases). For mice, the ~8–10% body weight rule has been established empirically as safe yet effective.

Researchers have used HDI to deliver plasmids encoding reporters (like luciferase, GFP) to evaluate the fraction of transfected cells and expression levels. By sacrificing animals at intervals, they’ve shown gene expression peaking around 8–24 hours post-injection and gradually declining as the plasmid is diluted or silenced. Tissue analysis (e.g., X-gal staining for β-galactosidase plasmids) reveals a widespread distribution of transgene-positive hepatocytes throughout the liver lobules, often with a gradient (cells near central veins sometimes transfect better due to vascular pressure distribution).

Safety assessments indicate that HDI, while acute, causes only transient liver damage. Liver enzymes (ALT/AST) spike briefly but normalize within hours. Histology shows minor centrilobular hepatocyte ballooning or some apoptotic cells early on, but the liver regenerates quickly. In rodents, this procedure is well-tolerated; however, in larger animals like dogs or pigs, it requires more finesse (e.g., catheterization of the hepatic vein or portal vein to localize the high pressure to the liver, because a tail vein injection of equivalent volume might not be feasible or safe).

One variant is liver-isolated HDI (via portal vein or hepatic vein catheter in larger animals or in localized lobes), which has been tested in dogs and baboons with some success. Though not as straightforward as in mice, there have been reports of significant gene expression in pig liver via hydrodynamic injection using balloon catheters to restrict fluid to the liver circulation.

Application to Research and Therapeutics

Hydrodynamic injection has become a staple in preclinical gene therapy research for liver. It offers an inexpensive, virus-free way to introduce genes or gene-silencing constructs in vivo. Scientists have used it to:

• Express therapeutic proteins for disease models: e.g., delivering Factor VIII or IX plasmids in hemophilia mouse models to evaluate bleeding correction, or insulin gene plasmids to diabetic mice. One notable study achieved remission of diabetes in mice by HDI of an insulin-expressing plasmid.
• Perform gene knockdown via shRNA/siRNA plasmids: hydrodynamic injection of siRNA-expressing plasmids can phenocopy knockout models temporarily. For instance, knocking down an oncogene in a liver cancer model to observe tumor response.
• Test genome editing tools: With CRISPR-Cas9 systems, HDI can be used to deliver Cas9 and sgRNA plasmids to edit liver genes (in mice). Indeed, proof-of-concept has been shown for in vivo CRISPR-mediated gene knockout in hepatocytes via HDI of CRISPR plasmids or ribonucleoproteins, leading to desired phenotypic changes.
• Model Wilson’s disease or other metabolic conditions by introducing mutant genes or by delivering toxic gene products to the liver.

A major use is in HCC research: hydrodynamic injection can co-deliver an oncogene and a CRISPR to knock out tumor suppressor in hepatocytes, inducing liver tumors that closely mimic human HCC with defined mutations. This so-called hydrodynamic tail vein tumor model has become a powerful tool – for example, injecting a plasmid for activated β-catenin and another for a Cre recombinase to delete p53 in floxed mice generates HCC nodules in situ. Researchers then use these models to study cancer progression or test therapies.

Clinically, HDI itself is not directly practical due to the large volume required. However, the concepts derived from HDI inform device-based gene delivery. There have been attempts at isolated liver perfusion or hydrodynamic injection confined to a specific organ via balloon catheters – for instance, targeting a segment of the liver in a patient and injecting a high-pressure burst of fluid. Some trials for gene therapy in localized liver cancer have attempted infusing gene vectors under pressure into the hepatic artery after occluding outflow. These are complex and not routine, but they echo the HDI principle.

HDI has also been used in large animal research to some degree: e.g., in a dog model of hemophilia, a hydrodynamic infusion via the portal vein of a Factor IX plasmid led to therapeutic levels of FIX protein for several weeks. While not yet in human use, these studies show that with the right approach, hydrodynamic gene delivery can be scaled at least partially.

Relevance of Altogen Products and Services

Altogen Biosystems primarily provides chemical transfection reagents, but the spirit of hydrodynamic delivery – achieving high-efficiency transfection of liver cells – is shared by some of their offerings. For example, their in vivo transfection kits (like the liver-targeted nanoparticle kits) aim to replicate the robust gene expression seen with HDI but in a more controlled manner. However, for researchers specifically wanting to perform hydrodynamic injections, Altogen’s role could be in supplying quality plasmid preparations and support reagents. They offer plasmid DNA preparation services and might provide consultation on plasmid design for strong expression in liver (e.g., using promoters that remain active after HDI, such as the CMV or sleeping beauty transposon systems to extend expression.

Altogen Labs, with its CRO capabilities, could facilitate hydrodynamic injection studies for clients. They have experience with rodent models and could perform tail vein injections of client-provided plasmids to evaluate gene function or therapeutic efficacy in liver. For instance, if a client has a new therapeutic gene they want tested in vivo quickly, Altogen Labs could perform hydrodynamic injection in mice and measure expression and effect within days – a service far faster and simpler than packaging into a virus. Altogen’s familiarity with liver models (including xenografts, as evidenced by their 90+ xenograft offerings altogen.com) means they are equipped to handle the procedural and post-care aspects of HDI (monitoring animals for transient effects, etc.). They likely have the apparatus or at least the expertise for high-speed tail vein injections, which can be technically challenging for newcomers.

Moreover, Altogen’s Transfection Resource provides protocols and tips that might include hydrodynamic injection as a technique. Since HDI is a well-known method in the gene delivery field, Altogen’s educational materials or blog could cover it, ensuring scientists are aware of it as an option when viral vectors or liposomes are not suitable.

One area Altogen products intersect is the use of DNA-condensing agents to possibly improve HDI. While naked DNA works, some have tried adding polymers or minor formulation to protect DNA from nucleases until it enters cells. Altogen’s in vivo transfection reagent could theoretically be mixed with plasmid prior to HDI to see if it further boosts expression or lowers required DNA dose. Their polymeric reagents, optimized for minimal toxicity, might not interfere with the pressure-mediated uptake but could help DNA remain intact intracellularly longer.

In summary, hydrodynamic injection provides a high benchmark for liver transfection efficiency (often considered the gold standard in mice). While Altogen’s chemical reagents strive to approach that efficiency in a more convenient format, they also support the research community in using HDI itself for those applications where it shines. Through services, protocols, and possibly custom solutions (like high-quality plasmid prep and liver-specific expression cassettes), Altogen aids scientists leveraging hydrodynamic injection to advance liver-targeted gene research.

References:

1. Liu et al., Gene Therapy, 1999 – First demonstrated high-level gene expression in mouse liver via rapid high-volume tail vein injection, establishing the HDI technique.
2. Zhang et al., Human Gene Therapy, 1999 – Reported ~10% of hepatocytes transfected and ~300 µg/ml serum protein from a single HDI of plasmid, with expression lasting ~4 weeks.
3. Herweijer & Wolff, Gene Therapy, 2003 – Comprehensive review of hydrodynamic delivery; noted 90% of gene expression confined to liver and <5–10% in other organs.
4. Suda et al., Molecular Therapy, 2008 – Refined hydrodynamic injection for large animals using catheter intervention; achieved significant liver expression in pigs with isolated liver perfusion.
5. Zhang et al., Gene Therapy, 2004 – Used HDI to deliver plasmid encoding human α-1 antitrypsin in mice, attaining therapeutic protein levels and assessing immune tolerance.
6. Huang et al., Nature Biotechnology, 2001 – Showed successful delivery of an HBV genome by HDI, resulting in HBV replication in mice (a model for hepatitis B).
7. Hamar et al., Nucleic Acids Research, 2004 – Achieved siRNA-mediated gene knockdown in mouse liver via hydrodynamic injection of siRNA expression plasmids, demonstrating functional gene silencing.
8. Köster et al., Scientific Reports, 2015 – Induced HCC in mice by hydrodynamically co-injecting c-Met and β-catenin oncogene plasmids, illustrating HDI’s utility in cancer modeling.
9. Altogen Labs – Service portfolio indicates proficiency in in vivo studies, including gene delivery and expression analyses in liver (could support HDI experiments for clients) altogen.com.
10. Kishida et al., Diabetes, 2002 – Demonstrated hydrodynamic injection of an insulin gene plasmid reverses hyperglycemia in diabetic mice, showcasing a potential metabolic disease application.