Strokes are a leading cause of death and disability worldwide, leaving a pressing need for effective neuroprotective drugs.
A team of researchers from the University of Copenhagen led by Prof Petrine Wellendorph have developed a promising drug candidate that may offer a chance for improving brain function and working memory among stroke patients.
Their work is funded by the Novo Nordisk foundation, and details can be seen on the Wellendorph Lab webpage here: https://drug.ku.dk/disciplines/molecular-and-cellular-pharmacology/wellendorph-lab/
Read their original article here: https://journals.sagepub.com/doi/10.1177/0271678X231167920
Image source: Adobe Image Stock / Freedomz
Hello and welcome to Research Pod! Thank you for listening and joining us today.
In this episode, we explore the research of Professor Petrine Wellendorph from the University of Copenhagen and her colleagues on the largely unmet clinical need for effective neuroprotective drugs for stroke patients. With the aim of preventing devastating long-term effects of stroke, the team used animal studies to demonstrate neuroprotective characteristics of a promising new drug. Importantly, the drug is specific for a protein complex that is dysregulated following stroke and therefore offers an attractive therapy that improves brain function and working memory.
As the third main cause of death and disability worldwide, six point five million people die each year from strokes and, of those that survive, more than fifty percent suffer permanent disability. There are two types of strokes, ischaemic and haemorrhagic – with the former being the most common. Ischaemic stroke is caused by a blocked blood vessel restricting blood flow to a part of the brain. Without this blood supply, brain cells die because the signals controlling their function become abnormal and there is a build-up of reactive oxygen species, and inflammation. Haemorrhagic stroke is different to ischaemic stroke and is caused by a ruptured blood vessel – resulting in bleeding in the brain. Both types of strokes have damaging and often long-lasting effects.
To understand what goes wrong during an ischaemic stroke, let’s start off with what is normally going right. Healthy cells require oxygen and glucose carried by the blood to function, and these make the molecules of chemical energy that fuel all the cells in your body – adenosine triphosphate, or ATP for short. When blood vessels rupture or get blocked by a blood clot, the absence of oxygenated blood has immediate impacts on cell health.
To explain further, the resultant lack of energy leads to build up of a neurotransmitter called glutamate. Neurotransmitters are important chemical messengers in the synapse or gaps between neurons – that either help transmit the signal or inhibit it. As the name implies, excitatory neurotransmitters excite or stimulate neurons to pass on signalling as opposed to inhibitory ones that downplay the signal.
Because glutamate is the chief excitatory neurotransmitter, it’s excess seen after ischemia causes many problems in cell signalling – resulting in ischaemic cell death. Death of cells and tissues affect brain function, in particular sensorimotor function and cognitive function depending on where the damage occurs in the brain. Sensorimotor function is when our brain is stimulated by senses like touch, sight, or sound and responds by moving. Cognitive function refers to our ability to memorise and think. Both are part of our everyday functioning.
For treatment of stroke patients, the clots blocking blood vessels can be either physically removed or broken-down using medication. This is known as recanalization therapy because the blood vessels or canals are reopened. But not all patients meet the criteria to undergo such therapy; and as the medication must be given very soon after the stroke, there is also a very short time to administer the treatment once symptoms begin. Even then, many patients still suffer permanent damage and new therapies that improve patient outcomes are therefore desperately needed.
So, what can be done to improve treatment options for stroke patients? One key avenue of therapeutic development is known as neuroprotection. Neuroprotection aims to protect the nervous system or in the case of ischaemic stroke, to preserve and save dying tissue. A review by other researchers in the field have called for exploration of such neuroprotective or cytoprotective drugs as an adjunctive therapy to existing recanalization therapies. The advent of advanced technologies gives scientists real hope that the development of such therapies is not only possible but could be key in improving patient outcomes.
Professor Wellendorph and her team have conducted research in animal models, demonstrating the neuroprotective effects of a molecule derived from a common inhibitory neurotransmitter. To know what this molecule is and how it works, first you need to understand its target.
The target is known as Calcium-calmodulin-dependent protein kinase two, or CaMKII. Calcium is an important signalling molecule throughout the body, and the signalling pathways in many types of cells depend on it to drive their intracellular processes. The CaMKII complex is a key mediator of such calcium dependent signalling pathways, especially the glutamate signalling needed for learning and memory. Although there are four variants of CaMKII present throughout the body, such as in heart and brain, the alpha and beta variants are particularly prominent in the brain. As such, these have been the focus of the researchers work investigating neuroprotective agents in stroke.
The key role of CaMKII alpha is in synaptic plasticity where synapses can strengthen or weaken signal transmission depending on increased or decreased activity. Like how exercising a muscle strengthens it while inactivity weakens it, persistent activity strengthens the signals between neurons and is termed long-term potentiation, or LTP. Conversely, a lack of activity weakens signals between neurons and is termed long-term depression or LTD. Interestingly, CaMKII alpha can induce both long-term potentiation and long-term depression. It is widely thought that synaptic plasticity is needed for the brain to create memories from experiences. In fact, researchers believe understanding mechanisms of synaptic plasticity could explain brain function during both normal and pathological conditions.
So what exactly happens to CaMKII alpha during ischemic conditions? We know that such conditions promote a dysregulation of internal phosphorylation of Threonine 286 within CaMKII alpha, a modification of CaMKII alpha which is otherwise essential for CaMKII to carry out its various functions related to synaptic plasticity. This dysregulation of CaMKII alpha causes activation of cell-death mechanisms and changes in long-term potentiation in neurons. This ultimately alters brain function and memory. More research is needed to understand the underlying mechanisms and open avenues for therapeutic development.
Professor Wellendorph and colleagues reviewed this protein complex as a possible target for neuroprotection in ischemic stroke. The previous studies showing CaMKII inhibition can reduce cell death are encouraging, but the researchers say that any potential therapeutics inhibiting CaMKII carry the potential disadvantage of inhibiting synaptic memory, and thus risk to not only affect pathological processes but also the protein’s normal physiological functioning.
Therapeutic inhibitors must be specific for their target meaning they must recognise and bind only to their intended target and not others at the dose used. If they are not specific enough, the inhibitor causes unwanted effects known as off-target effects. As such, commonly used CaMKII inhibitors have the limitation that they do not discriminate between CaMKII variants found throughout the body, which could lead for example to unwanted cardiac side effects.
Gamma aminobutyric acid or GABA is an abundant inhibitory neurotransmitter in the central nervous system. Its metabolite, gamma hydroxybutyrate or GHB occurs naturally in the brain and studies in rats and mice demonstrate its neuroprotection. Furthermore, GHB has a strong affinity for CaMKII alpha in particular meaning it could specifically target this variant that is so important in stroke but also has other targets in the brain. To move this forward, scientists have developed analogues of GHB that specifically target CaMKII alpha.
Structurally, the CaMKII alpha is a complex made up of a central hub domain that is surrounded by and connects the protein subunits. In their 2021 paper, the researchers revealed for the first time, detailed information about the specific binding site within this central hub domain. A GHB analogue called 3-hydroxycyclopent-1-enecarboxylic acid from now on, known as HOCPCA is a perfect match for the complex showing excellent selectivity for CaMKII alpha and binds stronger than GHB. They discovered, the binding site of these GHB analogues could be “moulded” to fit the cavity in the hub domain of CaMKII alpha making it specific for this alpha variant therefore reducing unwanted off target effects. Furthermore, it is brain permeable and also specific for the pathological state meaning it doesn’t interfere with normal physiological functioning.
In their recent innovative study, the team wanted to find out if HOCPCA is neuroprotective in stroke. They did this by inducing two types or models of stoke in distinct groups of mice. One model represented permanent blockage of the middle cerebral artery, a key artery supplying blood to the brain which is often affected by stroke in humans. From now on this is known as the occlusion model. The other model is known as the thromboembolic stroke model where the blockage was not permanent and blood flow was restored. The researchers explain that this model more closely resembles what happens in humans because the blood flow returns slowly. Their study is the first to examine CaMKII alpha abnormality in this model.
Their findings clearly show HOCPCA can reduce CaMKII alpha dysregulation after a stroke, improving sensorimotor function and cognitive function in mice. The team also suggest that phopsphorylation of threonine 286 needed for CaMKII alpha activation may have different effects on cell signalling depending on where CaMKII alpha is located that is in the cytosol or in the membrane.
The researchers found HOCPCA can reverse the known reduction in phosphorylation of threonine 286 of cytosolic CaMKII alpha that ischaemia induces thereby offering neuroprotection. However, we still do not know exactly how it does this. Neither do we know how HOCPCA reduces inflammation, and more research is needed to understand how this is achieved. Interestingly, HOCPCA was less effective in thromboembolic stroke than in the occlusion model, and the researchers think this could be because the blood supply that returns in thromboembolic stroke could further stimulate CaMKII alpha dysregulation.
The revelation of such a specific drug that addresses the CaMKII alpha dysregulation in stroke pathology offers renewed hope that this could one day be an effective treatment for patients. However, further research is now needed to establish if these results could be translated from animals to humans.
That’s all for this episode – thanks for listening. Links to Professor Wellendorph and her team’s original research will be linked in the show notes below and, as always, stay subscribed to Research Pod for more of the latest science.
See you again soon.