|Dr Be'eri Niego (right) with honours|
student Mr Felix Lee in
Prof Rob Medcalf's lab.
Around the world, the race is on to find new ways to treat ischaemic (blood clot-derived) stroke. Some of these efforts are aimed at increasing the safety of the main treatment currently in use, the clot-busting enzyme tissue-type Plasminogen Activator (t-PA). t-PA is effective in improving recovery if administered quickly – within 4.5 hours of a stroke. But as it dissolves the clots that cause stroke, t-PA also weakens the blood vessels in the brain that form what’s called the blood-brain barrier (BBB), increasing the risk of bleeding in the brain, potentially lethally, which limits the therapy’s use.
Just-published research by Monash University researchers has pointed to a potential new way to protect the blood-brain barrier from t-PA-induced damage. Moreover, clinically-approved drugs exist that may be suitable to do this.
Whilst the study used cell culture based models, the research may ultimately contribute to helping stroke patients, said co-lead author, Australian Centre for Blood Diseases (ACBD) and National Heart Foundation Research Fellow Dr Be’eri Niego.
More than 50,000 strokes occur in Australia each year, making stroke one of the country’s biggest killers and a leading cause of disability.
The researchers investigated two variants of an enzyme associated with thrombolysis (clot dissolving therapy) and BBB breakdown that are both activated by t-PA – Rho-kinase (ROCK) 1 and 2. They found that selectively inhibiting ROCK-2 with the molecule KD025 provided better protection of an in vitro blood-brain barrier from t-PA than a non-selective inhibition strategy.
The study built on previous PhD research by Dr Niego published in 2012. However, that research didn’t distinguish between the two types of ROCK; former Monash (now La Trobe) scientist Dr Michael De Silva recommended testing the enzymes separately.
The recent research indeed suggests that the isoforms have opposing roles.
“We found it was beneficial to block ROCK-2, which has a detrimental role, and keep ROCK-1 alive as it might actually play a beneficial role. If you blocked both, you get less effective consequences,” Dr Niego said.
“Selective ROCK-2 inhibition seems an ideal way to cut off interactions of t-PA with layers of blood vessels in the brain and to ensure that t-PA does only what it’s supposed to do, which is to dissolve blood clots,” he said. “This was a nice closure of the original story.”
Dr Niego said he and co-lead author Professor Robert Medcalf are now conducting preclinical trials and are also working with clinicians to generate funds to take the work to clinical trial.
“Ahead of us are pretty significant confirmatory experiments on mouse models but the potential is there. Because the ROCK inhibitors fasudil and KD025 are already in clinical use, it could be quite feasible to translate this research into clinical trials if we see some positive results in preclinical models,” he said.
Research assistant Ms Natasha Lee was a co-first author on the study and Dr Pia Larsson from the University of Gothenburg, Sweden, provided technical expertise together with Dr Amanda E-Ling Au (Walter and Eliza Hall Institute) and Ms Fiona McCutcheon (ACBD).
The research has been generously supported by the National Heart Foundation as well as the NHMRC, Dr Niego said.
Be’eri Niego, Natasha Lee, Pia Larsson, T. Michael De Silva, Amanda E-Ling Au, Fiona McCutcheon, Robert L. Medcalf Selective inhibition of brain endothelial Rho-kinase-2 provides optimal protection of an in vitro blood-brain barrier from tissue-type plasminogen activator and plasmin.16 May 2017 PLOS ONE https://doi.org/10.1371/journal.pone.0177332
Niego B, Freeman R, Puschmann TB, Turnley AM, Medcalf RL. t-PA-specific modulation of a human blood-brain barrier model involves plasmin-mediated activation of the Rho kinase pathway in astrocytes. Blood. 2012 May 17;119(20):4752-61. doi: 10.1182/blood-2011-07-369512. Epub 2012 Jan 19.