University of Nebraska–Lincoln scientists partnered with medical researchers from the National University of Singapore to develop a molecule that can inhibit an enzyme linked with the onset of stroke. The team found that its molecule, known as 6S, reduced the death of brain tissue by as much as 66% when administered to the cerebrum of a rat that had recently suffered a stroke.
It also appeared to reduce the inflammation that typically accompanies stroke, which the World Health Organization has estimated kills more than 6 million people annually.
“The fact that this inhibitor remained effective when given as post-stroke treatment … is encouraging, as this is the norm in the treatment of acute stroke,” the researchers reported in a study (“Zipped Synthesis” by Cross-Metathesis Provides a Cystathionine β-Synthase Inhibitor that Attenuates Cellular H2S Levels and Reduces Neuronal Infarction in a Rat Ischemic Stroke Model“) published in ACS Central Science.
The inhibitor works by binding to cystathionine ß-synthase, or CBS, an enzyme that normally helps regulate cellular function but can also trigger production of toxic levels of hydrogen sulfide in the brain. Although hydrogen sulfide is an important signaling molecule at normal concentrations, stroke patients exhibit elevated concentrations believed to initiate the brain damage they often suffer.
David Berkowitz, Ph.D., and his UNL colleagues modeled their inhibitor on a naturally occurring molecule produced by the CBS enzyme, tailoring the molecule's structure to improve its performance. By swapping out amines with hydrazines, the team ultimately increased the inhibitor's binding time from less than a second to hours.
“We wanted a compound that would bind well, specifically to this enzyme,” said Dr. Berkowitz, a Willa Cather Professor of chemistry. “But we also wanted one that could be synthesized easily. Those are two very different considerations.”
Dr. Berkowitz and his colleagues achieved the latter goal, in part, by plucking out the molecule's carbon–sulfur bond and replacing it with a double bond. Slicing that double bond gave the researchers two identical halves of the molecule. With the assistance of a Nobel Prize–winning technique called cross-metathesis, the team was then able to “synthesize two halves of the molecule for the price of one,” Dr. Berkowitz said.
To test the effectiveness of the 6S molecule in treating stroke, he and fellow UNL chemist Christopher McCune, Ph.D., reached out to Peter Wong, Ph.D., professor of pharmacology at the National University of Singapore.
“We started researching this and came upon Peter's work pretty quickly,” Dr. Berkowitz said. “We saw that he was one of the protagonists, one of the guys who is on the leading edge of understanding how (hydrogen sulfide) signaling works. Peter ended up latching onto the chemistry more than we did, and we ended up latching onto the biology.”
Because the 6S inhibitor has demonstrated its effects in cell cultures and the brain tissue of rats, Dr. Berkowitz cautioned that it represents just an initial step toward developing a stroke-treating drug for humans. However, he said the proof-of-principle experiments effectively illustrate the concept's promise.
Dr. Berkowitz also expressed optimism that the synthesis method detailed in the study could streamline the more general production of enzyme-targeting inhibitors.
“We started out with a very fundamental science perspective on understanding the chemistry of this whole class of vitamin B6–dependent enzymes,” he said. “We're in a good place now, because that science has allowed us to make these inhibitors and many others. We're now working on several enzymes that may represent important targets for translation of the basic inhibitor chemistry into truly therapeutic goals.”