Stem cell therapies and Alzheimer’s disease
of treatment is the potential for tumorigenicity, which is the uncontrollable division of stem cells. 48 Producing the many different types of neurons needed to replace the damaged or lost cells and at the right number is tricky. Secondly, the damage caused by AD affects many different neurons throughout the brain, making each individual case unique and can make it harder to treat each part of the brain in one patient. Putting new cells into a brain with AD will not fix the root of the problem. However, early screening and early diagnosis where there has not been widespread damage to the brain is crucial in implementing the stem cells as early as possible. Furthermore, treatments can still offer a great deal of help to the patients, as they can occur side by side with current treatments. Furthermore, the transplanting of stem cells raises certain issues. By taking these new neurons and inserting them into parts of the brain most badly affected by AD, it is not easy to integrate this into the brain circuitry. However, some studies suggest there are other benefits of stem cells other than that of the regeneration of neurons. Stem cells, when implanted in the brain have been shown to produce neurotrophic and neuroprotective factors. Several of the neurotrophic factors released by stem cells are decreased in the AD brain. A trophic factor is a molecule that supports the survival of cells. Neurotrophic factor therefore are proteins that regulate the proliferation, survival, migration, and differentiation of cells in the nervous system, and are essential weaponry against the effects of Alzheimer’s. Stem cells can also migrate beyond the transplantation site, to other areas of injury. 49 Hence, simply with this neurotrophic support stem cells can boost synaptic density by 67% in the hippocampus, as one study suggests. 50 In other trials, neuronal toxicity due to increased sensitivity to oxidative stress arose when new stem cells are put into the host brain. Oxidative stress is a state of physiological stress in the body that arises from exposure to high levels of reactive oxygen atoms (relative to the level of neutralising antioxidants (chemicals that stabilise the reactivity of these oxygen atoms). These reactive oxygen molecules can cause large chain reactions in the body because they react so easily with other molecules. Oxidative stress can lead to further damage of neurons, potentially exacerbating the damage already caused by AD in the brain. 51 Again, more research is needed to discover the potential of stem cells after transplantation, if they can integrate into the human brain, and if there are any benefits or risks to the patients that affect our judgement of the success of these treatments.
3.4: Judgement and comparison to current treatments
Although the volume of studies that has been undertaken is considerable, elements of the disease mechanism remain uncertain. Animal models have yet to fully recapitulate human AD. Thus it will take time for these treatments to come to clinical use. As the number of patients and types of neurological diseases being modelled increase, new patterns will emerge that could aid in developing earlier diagnostics tools and facilitate effective drug design. There has been significant success of studies displaying decreased cognitive decline in mice. At the University of Michigan, mice with transplanted NSCs were monitored and closely followed. The mice that had received the NSCs showed
48 Nguyen et al. 2019. 49 Alzheimer’s disease: how could stem cells help? n.d. 50 Jebelii 2017a: 148. 51 Dix 2018.
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