Atherosclerosis: Getting to the root of the problem with a turbo gene

Interview with Prof Daniela Wenzel, Institute for Physiology at the University of Bonn

Many people suffer from atherosclerosis, especially in developed countries – and sometimes with deadly consequences. The buildup of fatty deposits inside the arterial blood vessels leads to strokes and heart attacks. Now, a new method is designed to get to the root of the problem, and with the help of nanoparticles inject new turbo replacement cells into the blood vessels which are intended to exert their curative effect and control blood pressure once they are at their target destination.


Photo: Daniela Wenzel

JProf. Daniela Wenzel; © Rolf Müller/Uni Bonn

In this interview with, assistant professor Daniela Wenzel explains how this gene replacement therapy works and how much more research is still needed before it can be used in human beings.

Prof. Wenzel, what are the risk factors for atherosclerosis and what role do endothelial cells play in this?

Daniela Wenzel: In the case of atherosclerosis, the endothelial function is impaired. Normally the thin layer of cells of the endothelium lines the interior surfaces of blood vessels and is also extremely important for the production of nitric oxide (NO). While NO is one of the major mediators of vascular relaxation and lowers blood pressure, NO also prevents thrombosis inside of blood vessels.
The result of endothelial dysfunction is reduced NO production. As the disease progresses, blood pressure elevates and deposits form on the endothelium that calcify and restrict the blood vessels which ultimately affects blood flow. Heart attacks and strokes can result if important organs are subsequently no longer sufficiently supplied with oxygen.

You have developed a method with which damaged endothelial cells can regenerate with "turbo replacement cells". How does this work?

Wenzel: Once blood vessel damage is diagnosed, the endothelium is typically irreparably impaired. The narrowings in blood vessels are mechanically expanded and permanently fixed with stents using currently available treatment methods. Another alternative is to surgically remove the deposits after the blood vessel has been surgically opened. However, both methods result in further damage of the endothelium which is not able to regenerate on its own. The basic concept of our project is to restore the original anatomy of the blood vessel. This is regenerative cell replacement therapy. This means new endothelial cells that exhibit good cell function are needed. This is why we wanted to combine cell replacement and gene therapy: initially endothelial cells were cultivated in a petri dish and their NO production increased using gene therapy with overexpression of endothelial cell NO synthase (eNOS). To accomplish this, lentiviruses were used as gene delivery systems since they are able to permanently deliver a gene into a cell. The endothelial cells that have been treated using gene therapy were subsequently used for cell replacement therapy.
Photo: Prof. Wenzel (left) and Dr. Sarah Rieck (right)

Wenzel (left) and Dr. Sarah Rieck examine how pathologically altered blood vessels regenerate by replacement cells. The picture shows a perfusion model, with which the researchers have repopulated the blood vessels of mice with endothelial cells; © Katharina Wislsperger/Ukom UKB

Magnetic nanoparticles are also used to treat damaged endothelial cells. What is their purpose?

Wenzel: The magnetic nanoparticles are needed for two things: first, to improve the gene transfer into the endothelial cells. Lentiviruses combined with magnetic nanoparticles form complexes that can very quickly and efficiently be exposed to the cells with the help of a magnet. Subsequently more cells are genetically modified in a shorter amount of time. After half an hour, the cells have absorbed the gene. The overall cell treatment process is thus significantly accelerated.

The second advantage of the nanoparticles results from their absorption into the cell. The nanoparticle-loaded cells can be controlled with external magnets after they have been injected into the blood vessel. By using a suitable magnetic field, they can be held at the vascular wall during blood flow. The magnetic design was specifically optimized for vessels by our cooperation partners at the Technical University of Munich to ensure an efficient radially symmetrical lining of the interior surface of the blood vessel.

How did the test series run so far?

Wenzel: We have conducted the first experiments in an ex vivo vessel perfusion model. To do this, we isolated the aorta from a mouse and removed the endothelium. After positioning the external magnet, the aorta was perfused multiple times with green fluorescent endothelial cells. The green fluorescence served to quickly identify the cells in the blood vessel. After the perfusion, green cells could actually be seen alongside the entire blood vessel. A cross section showed the radial symmetry of the deposit. Next we ventured into a live mouse and tested our magnet-based cell replacement strategy in a disease model where the endothelium of the carotid artery is being mechanically removed. The green endothelial cells were still at their point of destination in the carotid artery two days after the treatment. 
Photo: green fluorescent endothelial cells

The left image shows a blood vessel that has been repopulated with fluorescent cells (green). On the right a detail of a vascular wall marking eNOS protein in red; © Rieck/Vosen/Uni Bonn

Did the cells actually assume their function and produced NO?

Wenzel: We had already confirmed the functional capability of the treated endothelial cells in previous in vivo testing. The cells de facto produced more NO if they had been prepared with the complexes in the cell culture dish. We also measured the isometric force in the treated blood vessels both in our preliminary tests using a perfusion model and later using in vivo testing. That is to say, we have analyzed their force development during contraction. We were actually able to prove in these experiments that the treated blood vessels contracted less since they produce more NO.

When can we expect an application in humans?

Wenzel: To use this method in humans, an adjustment of the magnetic field is essential. Human blood vessels are considerably larger than those of mice and exhibit an increased blood flow. This is why experiments with large animals such as pigs should be conducted as an intermediate step to optimize the magnet arrangement. A first step toward using this method in humans would, therefore, be to promote the technological research pertaining to magnetic design and magnetic field strength. The preliminary tests have certainly already shown that the principle of magnet-based endothelial cell replacement can work.
Photo: Melanie Günther; Copyright: B. Frommann

© B. Frommann

The interview was conducted by Melanie Günther and translated by Elena O'Meara.