A stroke happens when there is a loss of blood flow to part of the brain, which can cause permanent brain damage, long-term disability, or even death.
Stroke is one of major public health threats around the globe. In 2002, WHO estimated that there were 15.3 million strokes worldwide, about 5.5 million of which resulted in death, accounting for nearly 10% of all deaths worldwide. Many factors can raise the risk of a stroke, some of which are not modifiable such as age, ethnicity, gender and familial history while the others can be modified to lower the risk of a stroke such as high blood pressure, diabetes, substance abuse, obesity and life style choices. The prevalence of risk factors for stroke vary among regions, ethnic groups or socioeconomic status. Stroke incidence and mortality are greater in the developing world.
Stroke is generally classified into two main categories: ischemic stroke, which is caused by a blockage of a blood vessel in the brain, and hemorrhagic stroke, which is caused by a blood vessel rupture and consequently bleeding into the brain. Hemorrhagic stroke consists of two subtypes: intracerebral and subarachnoid hemorrhage. A large-scale study in China (2013) has shown that out of 48,068 stroke cases, ischemic strokes account for 77.8%, hemorrhagic stroke for 15.8% and subarachnoid hemorrhage accounts for 4.4% of all patients. The symptoms of strokes often happen quickly and include sudden numbness or weakness in a part of the body, sudden headache, sudden trouble seeing, confusion, sudden difficulty in walking, etc.
Treatments for stroke include medicines, surgery, and rehabilitation. The therapeutic strategy for each patient varies depending on the type of stroke and the stage of pathology. Treatments for ischemic strokes tends to focus on restoring an adequate blood flow to the brain and preventing neuronal damage. Specifically, medicines like tissue plasminogen activator (tPA) and blood thinner (e.g. aspirin) that clear the clots and surgical procedures that mechanically correct a clotted or narrowed artery, are commonly used. It is estimated that the morbidity/mortality rate among hospitalized ischemic stroke patients is 34.5-37.1% at three months, and 33.4-33.8% at one year post-stroke.
Treatments for hemorrhage strokes focus on stropping the bleeding and reducing the pressure on the brain. Causes of the bleeding include high blood pressure, aneurysm, and arteriovenous malformation (AVM). A combination of drugs that reduce pressure in the brain, control the blood pressure, counteract effects of the blood thinners if required, and prevent seizures is commonly used. For patients with ruptured blood vessels due to aneurysm and AVM, a surgical procedure is required to stop the bleeding. Hemorrhage strokes have a high fatality rate, reaching 35-52% at one month post stroke.
A high percentage of stroke survivors contend with severe long-term disabilities. Function recovery therapies and rehabilitation are commonly used for patients to regain quality of life.
The Latest Research Progress of Stem Cell Therapy for Stroke
Mesenchymal stem cells (MSCs) are multipotent cells with self-renewing, differentiation capacity and immunomodulatory properties. Those attractive features have made them a promising cell therapy treating stroke patients. More than 50 clinical trials testing stem cells on stroke patients are registered with FDA currently. Preclinical studies with animal models and clinical trials in stroke patients have achieved limited favorable results. The potential mechanisms of stem cell therapy can be summarized below:
1) Stem cells can be differentiated into neuronal or vascular cells, replacing damaged cells, and compensating for lost functions;
2) Stem cells secret various trophic factors such as cytokines, chemokines, and growth factors, which reduce inflammation-induced damage and promote regeneration of neuronal circuits.
ImStem has conducted preclinical studies investigating T-MSC cell infusion in ischemic stroke rat models. We found that T-MSC cells could facilitate neuronal replacement, reduce the size of the infarction area and restore neurological functions in stroke rats. Further studies will be performed to explore the safety and efficacy of T-MSCs in treating stroke patients.