Surgery for cardiovascular problems often requires the
implantation of vascular grafts and stents to prop open failing or narrowed blood vessels. However, while this solves the immediate
problem of restoring blood flow, it introduces the risk of blood clots.
This artist’s impression shows the coating on the inside of the improved vascular graft (in the magnified section).
Image credit: ITMO University/Yulia Chapurina
Now, in a new study published in the Journal of Medicinal Chemistry, chemists
from ITMO University in St. Petersburg, Russia, describe how they developed and tested a
new type of artificial blood vessel coating that resists blood clot formation.
The coating is a thin film of densely packed nanorods made of aluminum oxide blended
with a substance that activates a clot-busting enzyme – the substance is called
urokinase-type plasminogen activator.
When the team used this film to coat the inner surface of a vascular graft, it
generated a stable concentration of plasmin – an enzyme that dissolves blood
clots.
The unique properties of the film arise from its structure – a porous matrix that
holds the plasminogen activator. The matrix protects the plasminogen activator while at
the same time allowing it to react – through the system of pores – with plasminogen in
the blood.
When the plasminogen – a substance that occurs naturally in the blood – meets with the plasminogen activator inside
the matrix of pores, it produces the clot-dissolving enzyme plasmin.
‘Drug-entrapped’ vascular grafts dissolved blood clots in lab tests
The team ran several experiments to test the properties of the new film-coated
vascular grafts. For example, for one test they grew artificial clots made of blood
plasma mixed with thrombin and placed them inside the graft.
Lead author and lab researcher Yulia Chapurina, who set up the experiments, says:
“The results of the experiment amazed us. Very soon the clot started to
dissolve and leak through the graft. In reality, our coating would destroy clots at the
stage of formation, constantly ensuring an unobstructed blood flow in the
graft.”
The new film promises to be an improvement on the latest types of grafts and stents –
the so-called “drug-eluting” types. These are coated with drugs that are slowly released
into the blood, but their lifetime is limited by the amount of drug they store.
The team believes their system, because it is based on the entrapment of the drug
inside a porous protective shell, will last much longer, offering a practically
“unlimited” lifetime for the artificial blood vessels.
Senior author Vladimir Vinogradov, who heads the international lab the study team
works in, says their findings are not restricted to artificial blood vessels but to any
kind of implants. It all depends on the type of drug you use in the coating, as he
explains:
“For example, after the implantation of an artificial ureter, urease
crystals often start to grow inside and doctors do not know how to deal with this
problem. It is possible to apply a similar drug-containing coating that dissolves
urease.”
“The same approach may be used for kidney or liver surgery, but these are plans for
the future,” he concludes.
Meanwhile, another study that Medical News Today recently reported found
that the process of aging may protect blood vessels from
oxidative stress.
In The Journal of Physiology, researchers from University of Missouri School
of Medicine say their findings suggest healthy aging spurs a natural, adaptive response
that counteracts the effect of oxidative stress on blood vessels.
Written by Catharine Paddock PhD
Copyright: Medical News Today
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