Nanoparticles reboot blood flow in brain

A nanoparticle developed at Rice University and tested in collaboration with Baylor College of Medicine (BCM) may bring great benefits to the emergency treatment of brain-injury victims, even those with mild injuries.

Combined polyethylene glycol-hydrophilic carbon clusters (PEG-HCC), already being tested to enhance cancer treatment, are also adept antioxidants. In animal studies, injections of PEG-HCC during initial treatment after an injury helped restore balance to the brain's vascular system.

The results were reported this month in the American Chemical Society journal ACS Nano.

A PEG-HCC infusion that quickly stabilizes blood flow in the brain would be a significant advance for emergency care workers and battlefield medics, said Rice chemist and co-author James Tour.

"This might be a first line of defense against reactive oxygen species (ROS) that are always overstimulated during a medical trauma, whether that be to an accident victim or an injured soldier," said Tour, Rice's T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and materials science and of computer science. "They're certainly exacerbated when there's trauma with massive blood loss."

In a traumatic brain injury, cells release an excessive amount of an ROS known as superoxide (SO) into the blood. Superoxides are toxic free radicals, molecules with one unpaired electron, that the immune system normally uses to kill invading microorganisms. Healthy organisms balance SO with superoxide dismutase (SOD), an enzyme that neutralizes it. But even mild brain trauma can release superoxides at levels that overwhelm the brain's natural defenses.

"Superoxide is the most deleterious of the reactive oxygen species, as it's the progenitor of many of the others," Tour said. "If you don't deal with SO, it forms peroxynitrite and hydrogen peroxide. SO is the upstream precursor to many of the downstream problems."

SO affects the autoregulatory mechanism that manages the sensitive circulation system in the brain. Normally, vessels dilate when blood pressure is low and constrict when high to maintain an equilibrium, but a lack of regulation can lead to brain damage beyond what may have been caused by the initial trauma.

"There are many facets of brain injury that ultimately determine how much damage there will be," said Thomas Kent, the paper's co-author, a BCM professor of neurology and chief of neurology at the Michael E. DeBakey Veterans Affairs Medical Center in Houston. "One is the initial injury, and that's pretty much done in minutes. But a number of things that happen later often make things worse, and that's when we can intervene."

Kent cited as an example the second burst of free radicals that can occur after post-injury resuscitation. "That's what we can treat: the further injury that happens because of the necessity of restoring somebody's blood pressure, which provides oxygen that leads to more damaging free radicals."

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Nanoparticles reboot blood flow in brain