Stem cell therapies and Alzheimer’s disease
neurotransmitters), neurons the same as those in the Central Nervous System are made. 45 These are ready for transplantation.
These therapies have never been tested in a human brain before. Most stem cells studies have used rats and mice, since these models are convenient to use. If preliminary studies with rodent stem cells are successful, scientists will attempt to transplant human stem cells into rodents. Studies may then be carried out in primates, and only when these results have shown promising results will human treatments be considered.
3.3: Challenges of potential stem cell therapies
Arguably, as regenerative medicine is a relatively new field, scientists need to be very cautious when undergoing research with other animals and translating this to humans. Most research is being undertaken in mice models, and this does not fully replicate the disease pathology, or the microenvironment of a human brain. A mouse has a brain that is not exactly like humans. In mice models, no significant neuron loss or cognitive dysfunction occurs before high beta amyloid levels are detected in the brain. Thus, more testing is required in humans or closely related species to find if there are any side effects of treatments, and if they are successful. Furthermore, iPS treatments are early in the trialling process, and are inefficient in terms of rapid production. Early treatments involving iPS cells found issues with reprogramming cells. The cells often developed unpredictable characteristics as some retained a memory of their adult origins. These were also therapeutically impractical because it takes 5 months to regenerate them, creating the additional drawback of being very costly. 46 More trials are needed for these to be more efficiently produced, as a large-scale treatment would require iPS being formed quickly. There is also an issue of the availability of NSCs. NSCs are found in neurons in the body. Every day, neurogenesis occurs in our bodies, whereby neurons, and hence NSCs are made. More recent studies have found that neurogenesis occurs in only a few places in a few regions of the brain. These regions contain neural stem cells. Neurogenesis decreases as one grows older, meaning that the source of neural stem cells declines with age. Promoting the self-renewal rate of the stem cells themselves and maintaining the supply in a patient for a longer time is a key issue here. Furthermore, our knowledge of NSCs is very basic. There are many fundamental issues that need to be resolved before clinical utility occurs. For example, the markers that give NSCs homogeneity (homogeneity is the quality that the cells are the same) is still unknown. It is also tricky identifying a NSC within the body, as there are type of undifferentiated cells (not stem cells) that possess different characteristics and fates. For example, neural progenitor cells do have the capacity to proliferate into more than one cell type, but they have limited proliferative ability and do not exhibit self-renewal. 47
Even if the stem cells were readily available and could be transplanted safely, there are more problems to overcome before any benefits can be seen. One of the greatest risks with using stem cells for any type
45 Jebelli 2017a: 144. 46 Jebelli 2017a: 141. 47 Ahmed 2008.
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