A temporary tattoo might someday help control a chronic disease, according to scientists at Baylor College of Medicine testing antioxidant nanoparticles created at Rice University.
A proof-of-principle study led by Baylor scientist Dr. Christine Beeton and published today by Nature's online, open-access journal Scientific Reports shows that nanoparticles modified with polyethylene glycol are preferentially taken up by cells in the immune system.
That could be a plus for patients with autoimmune diseases like multiple sclerosis, one focus of study at the Beeton lab. “Placed just under the skin, the carbon-based particles form a dark spot that fades over about one week as the particles are slowly released into the circulation,” Beeton said.
T and B lymphocytes and macrophages are key cellular components of the immune system. However, in many autoimmune diseases such as multiple sclerosis, T cells are the key players. One suspected cause is that the T cells lose their ability to distinguish between invaders and healthy tissue, attacking both. In tests at Baylor, T cells internalized the nanoparticles, which inhibited their function, but macrophages ignored the nanoparticles.
“The ability to selectively inhibit one type of cell over others in the same environment may help doctors gain more control over autoimmune diseases,” Beeton said.
“The majority of current treatments are general, broad-spectrum immunosuppressants," said first author Redwan Huq, a graduate student in the Beeton lab. "Because they are broad-spectrum, they are going to affect all of these immune cells. As a result, patients are exposed to side effects from infections to increased chances of developing cancer. So we get excited when we see something new that could potentially enable selectivity." Because the nanoparticles seem to only affect T cells and not macrophages and other splenic immune cells, most of the patients’ existing immune system remains intact.
The soluble nanoparticles were synthesized by the Rice lab of chemist Dr. James Tour and have shown no signs of acute toxicity in prior rodent studies. The scientists combine polyethylene glycol with hydrophilic carbon clusters, hence their name, PEG-HCCs. The nanoparticles are 35 nanometer long, 3 nanometer wide and one atom thick and have proven to be efficient scavengers of reactive oxygen species called superoxide molecules, which are expressed by cells the immune system uses to kill invading microorganisms.
T cells use superoxide in a signaling step to become activated. PEG-HCCs remove this superoxide from the T cells, preventing their activation without killing the cells.
Beeton became aware of PEG-HCCs during a presentation by former Baylor graduate student Taeko Inoue, a co-author of the new study.
“As she talked, I was thinking, ‘That has to work in models of multiple sclerosis,’” Beeton said. “I didn’t have a good scientific rationale, but I asked for a small sample of PEG-HCCs to see if they affected immune cells. We found the nanoparticles affected the T lymphocytes and not the other splenic immune cells, like the macrophages. It was completely unexpected.”
The Baylor lab's tests on animal models showed that small amounts of PEG-HCCs injected under the skin are slowly taken up by T lymphocytes, where they collect and inhibit the cell’s function. They also found the nanoparticles did not remain in T cells, dispersing within days after uptake by the cells.
“That’s an issue because you want a drug that’s in the system long enough to be effective, but not so long that, if you have a problem, you can't remove it,” Beeton said. “PEG-HCCs can be administered for slow release and don’t stay in the system for long. This gives us much better control over the circulating half-life.”
“The more we study the abilities of these nanoparticles, the more surprised we are at how useful they could be for medical applications,” Tour said. The Rice lab has published papers with collaborators at Baylor and elsewhere on using functionalized nanoparticles to deliver cancer drugs to tumors and to quench the overproduction of superoxides after traumatic brain injuries.
Beeton suggested delivering carbon nanoparticles just under the skin rather than into the bloodstream would keep them in the system longer, making them more available for uptake by T cells. And the one drawback – a temporary but visible spot on the skin – could actually be a perk to some.
“We saw the nanoparticles made a black mark when we injected them, and at first we thought that’s going to be a real problem if we ever take this new treatment into the clinic,” Beeton said. “But we can work around that. We can inject into an area that’s hidden, or use micropattern needles and shape the black mark.
“For some patients, for instance, a child who wants a tattoo and could never get her parents to go along, this could be a good way to convince them to get the nanoparticle treatment,” said Beeton.
Co-authors are Rice alumnus Errol Samuel and graduate students William Sikkema and Lizanne Nilewski; Baylor College of Medicine rotation student Thomas Lee, graduate students Mark Tanner, Rajeev Tajhya and alumni Fatima Khan and Rutvik Patel; and Paul Porter, an instructor in the Department of Medicine, Division of Immunology, Allergy and Rheumatology at Baylor; Robia Pautler, an associate professor in the Department of Molecular Physiology and Biophysics, and David Corry, a professor of medicine and chief of the Division of Immunology, Allergy and Rheumatology, all at Baylor.
This work was supported by the Baylor College of Medicine and the National Multiple Sclerosis Society award PP1715, the T32 awards HL007676, GM088129 and AI053831 and by F31 award AR069960 from the National Institutes of Health. The Baylor College of Medicine Cytometry and Cell Sorting and Pathology and Histology cores are supported in part by funding from the National Institutes of Health (RR024574, AI036211, and CA125123) and the Dan L. Duncan Cancer Center. The Integrated Microscopy Core at Baylor College of Medicine is supported in part by funding from the National Institutes of Health (HD007495, DK56338, and CA125123), the Dan L Duncan Comprehensive Cancer Center, and the John S. Dunn Gulf Coast Consortium for Chemical Genomics. The work at Rice University was supported by the Traumatic Brain Injury Consortium, funded by the US Army (W81XHW-08-2-0143), and the National Institutes of Health through Baylor College of Medicine (DK093802).