Combined intervention strategies as novel therapeutics for stroke
Stroke is a leading cause of death and the leading cause of disability in the UK. There is only one treatment for stroke which <5% of sufferers receive highlighting a pressing and urgent need to identify new interventions. A complex array of mechanisms are involved in stroke-induced brain damage including uncontrolled release of substances due to a lack of oxygen and glucose causing the brain cells to die. Destructive free radicals are generated which increase the levels of oxidative stress leading to further death due to an active death pathway called apoptosis. microRNAs are small molecules which reduce expression of genes. Uniquely, by altering expression of one microRNA effects on many pathways involved in stroke can be achieved. Rational polytherapy inhibiting multiple pathways may prove as useful for stroke intervention as it has in treating disorders such as high blood pressure. Using an animal model which reflects many of the risk factors seen in stroke sufferers (high blood pressure, altered metabolic handling) we aim to reduce damage and improve long-term outcome after experimental stroke by preventing both free radical generation and apoptosis by combining drugs and gene therapy approaches. Furthermore, using a novel gene delivery system shown to efficiently target the brain we will alter the expression of one or more microRNA(s) to elicit a polytherapy style outcome through a monotherapy approach.
Appointed on the BBSRC Integrative Mammalian Biology (IMB) initiative the central theme of my research is to allow the translation of knowledge gained from cell culture studies back to the whole organism, including in vivo studies. To date, my research has focused on therapeutic intervention for cardiovascular disease using both pharmacological agents and gene delivery protocols. My research group use combined drug and gene therapy interventions to reduce damage and improve long-term outcome after experimental stroke in hypertensive rats. In addition, we are interested in modulating microRNA (miRNA) expression following stroke as a means of achieving a polytherapy outcome but through a single administration of gene delivery vector.
Stroke accounts for ~53,000 deaths every year (www.heartstats.org) and is the major cause of long-term disability. Associated health and social care costs of stroke amounted to over £2.5 billion in 2006/7 with substantially higher total economic costs. The cornerstone of treatment for acute ischaemic stroke, reperfusion therapy with recombinant tissue plasminogen activator, is delivered to a fraction of patients (2-5%) due to a narrow time window (<4.5hrs) for delivery and associated risk of intracerebral haemorrhage. Furthermore, successful vessel recanalisation is only achieved in <50% of treated patients. Novel treatments for ischaemic stroke are sorely needed.
Transient or permanent interruption of cerebral blood flow by occlusion of a cerebral artery gives rise to an ischaemic stroke leading to irreversible damage or dysfunction to the cells within the affected tissue along with permanent or reversible neurological deficit. Extensive research has identified excitotoxicity, oxidative stress, inflammation and cell death as key contributory pathways underlying lesion progression. These diverse injury mechanisms may explain why pharmacotherapy clinical trials geared to manipulate single pathways have failed. A polytherapy that inhibits multiple pathways may be more effective and there is precedent for such approaches in other disorders such as hypertension. Increasingly, pre-clinical studies are looking to delay treatment >12hrs to days after stroke to improve subsequent translation.
For translational relevance we use spontaneously hypertensive stroke prone rats (SHRSP) as our animal model as the SHRSP have many existing stroke associated co-morbidities including hypertension, insulin resistance and inflammation. As in humans, blood pressure in the SHRSP increases with age with the reference Wistar Kyoto (WKY) strain remaining normotensive. Following middle cerebral artery occlusion (MCAO), SHRSPs display impaired functional recovery vs WKY, even with equivalent infarct size and distribution. MRI revealed a smaller volume of penumbra and more ischaemic damage in SHRSP vs WKY following permanent MCAO. Therefore, the SHRSP provides a good translational model given the close similarity to clinical stroke presentation, with self-reported history of hypertension being the strongest stroke risk factor clinically.
Through their ability to alter expression of multiple genes which may be implicated in stroke pathophysiology, microRNAs (miRNAs) offer a novel means of achieving a polytherapy style outcome through a monotherapy approach, both in the acute phase following stroke and beyond for more chronic rehabilitative style therapy. My research group aim to modulate miRNA as a means of targeting many contributory pathways underlying lesion progression and functional outcome, influencing all cells of the neurovascular unit within the affected area. Additionally, we are studying novel combinations of agents, using gene and drug-based approaches, in an attempt to identify novel therapeutic interventions for this debilitating disease.
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