New approach to gene correction for iron storage disease

Hereditary primary hemochromatosis is caused by a single faulty building block in a gene. This leads to iron overload, which can have serious consequences for organs and joints. In preclinical studies, researchers have already successfully treated this genetic defect using a targeted correction technique known as base editing. They have now further refined their method in the laboratory.

Instead of viral vectors, they are now using lipid nanoparticles as a delivery system, which are safer, more efficient and cheaper. If the treatment also works in humans, a single injection could protect against the consequences of the disease in the future. The work is published in the Journal of Hepatology.

Hereditary primary hemochromatosis is one of the most common congenital metabolic disorders in Europe. In this disorder, also known as iron storage disease, excessive amounts of iron accumulate in various organs. This can lead to severe symptoms such as joint pain and diabetes, as well as serious complications such as liver cancer.

The cause is a genetic defect that disrupts the regulation of iron absorption via the small intestine mucosa. A research team led by Prof. Dr. Michael Ott and Dr. Dr. Simon Krooss from the Department of Gastroenterology, Hepatology, Infectious Diseases and Endocrinology at Hannover Medical School (MHH) discovered an approach in 2022 to treat this hereditary disorder using targeted gene correction. The researchers have now further refined this method using cells from patients and in a mouse model.

Instead of delivering the molecular biology tools into the cells using a viral vector—also known as a “gene taxi”—they have now used so-called lipid nanoparticles (LNPs) to transport the therapeutic RNA into the liver. These offer decisive advantages over viral vectors, as they are safer, easier to produce and allow the gene-correction tools to remain in the body for a limited period of a few hours to days.

Impaired regulation of iron absorption

“In most cases, hemochromatosis is caused by a defect in the HFE gene, which is located on chromosome 6,” says Ott. It occurs only in people who have inherited this defect from both parents, meaning they do not have a “healthy” gene to counteract it. In more than 80% of those affected, a specific change—known as the C282Y mutation—is found in both copies of the HFE gene.

This leads to the replacement of an amino acid—that is, a building block of protein—in the HFE protein. As a result, the HFE protein loses its ability to regulate iron absorption. To deplete their iron stores and normalize iron levels in the body, patients must undergo bloodletting for the rest of their lives. This is a burden and, moreover, does not work for everyone affected. Medicines that bind to and thus neutralize iron directly in the body are also not ideal because of severe side effects.

Cell completes gene repair on its own

The MHH researchers, on the other hand, are tackling the problem at its root. They are using the body’s own repair mechanisms to repair the defective HFE gene. Using CRISPR/Cas technology—known as “genetic scissors”—and an enzyme linked to it, they specifically modify a tiny faulty building block in the mutated HFE gene. In technical terms, this procedure is known as base editing.

What makes this gene repair special is that the gene scissors are used in such a way that they do not simply cut the double-stranded DNA completely at the desired location, as in the conventional application. “A double-strand break always carries a certain risk of unwanted mutations,” explains Krooss.

In base editing, by contrast, the two single strands are separated from one another and only one of them is modified. As a result, the cell automatically initiates its natural repair program and incorporates the correct counterpart into the second strand as well, so that the C282Y mutation disappears from the entire double strand.

LNPs efficiently transport mRNA to the liver

The research team sends only the blueprint for the base-editing system in the form of so-called messenger RNA (mRNA), which is broken down in the body and disappears after 48 hours. This method is also used in mRNA vaccines, such as those against the SARS-CoV-2 coronavirus. Until now, the team had used viral vectors as delivery vehicles.

Now, the blueprint is packaged into lipid nanoparticles together with a “navigation aid” that guides the gene scissors precisely to the correct location on the DNA. These nanoparticles have a structure similar to the cell membranes in our bodies. Upon contact with the cell, they fuse with its outer membrane and release their contents. “LNPs consist of a combination of synthetic fats and are considered safe in terms of potential immune reactions,” says Ott. Furthermore, compared with viruses, they can be produced very quickly and cost-effectively in large quantities.

Iron overload is significantly reduced

“Firstly, we tested the system in a mouse model with iron overload,” says Krooss. “We also investigated it in cell cultures derived from mouse liver cells, as well as in cell cultures derived from human liver cells, which we obtained from blood cells of hemochromatosis patients that had been reprogrammed from induced pluripotent stem cells.”

The result: In the mouse model, the base-editing system successfully corrected up to 67% of the faulty bases, and iron overload in the liver was significantly reduced. In the mouse liver cells, the success rate was around 70%, while in cell cultures with human liver cells it was around 65%. With a correction rate of 50%, the body can access sufficient functional HFE proteins to regulate iron uptake adequately. For this reason, people with only one affected gene copy—heterozygous carriers—are not at risk.

“It is particularly noteworthy that the high efficiency of the gene correction was accompanied by a high degree of precision,” Krooss explains. “We were unable to detect any significant undesirable off-target effects. The gene scissors therefore acted specifically at the intended site in the genome without causing unwanted changes in other regions of the genome.”

Potential applications for other conditions

“These results provide evidence that gene correction is both safe and effective, that it effectively reduces iron accumulation in the liver and thus prevents harmful pathological processes in the liver,” emphasizes Ott. The aim now is to investigate the method in clinical trials at the MHH as soon as possible.

If the treatment proves effective in humans, a single injection could in the future protect carriers of the mutation from severe disease progression, liver cancer or even the need for an organ transplant. “An injection instead of a transplant” is how liver researcher Ott sums up this vision. In addition, the two researchers are working on applying base editing as a definitive treatment for many other congenital conditions.

Who’s behind this story?

Lisa Lock

BA art history, MA material culture. Former museum editor, paramedic, and transplant coordinator. Editing for Science X since 2021.

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Andrew Zinin

Master’s in physics with research experience. Long-time science news enthusiast. Plays key role in Science X’s editorial success.

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