Animal models for Alzheimer’s disease
The ethics of scientific research force animal testing to be kept to a minimum. However, animal models remain essential in order for us to understand the mechanisms of many human diseases and test therapeutic strategies. Traditionally, for practical reasons, the most commonly used animals for these purposes were rats and mice, but Alzheimer research faces the problem that these rodents do not naturally suffer from a process similar to Alzheimer’s disease. Therefore, in order to use them in this field it is necessary to artificially modify them by incorporating specific mutated human genes related to Alzheimer’s disease into their genotype.
Using this strategy, a variety of strains of transgenic mice have been produced. Studies performed with these transgenic mice have made an important contribution to our knowledge today about this disease. Nevertheless, the model is far from perfect and has several disadvantages, which lead to serious doubts when signs of the disease in people are to be interpreted in light of observations from these animals. The same uncertainty is also inevitable when predicting the possible efficacy of a new therapy for Alzheimer patients based on results obtained from transgenic mice.
This situation has led us to explore the possibility of using chicken embryos and dogs as two animal models for the study of Alzheimer’s disease.
The human beta-amyloid protein, the main cause of the disease in people, is identical to that of chickens. Moreover, chicken embryos show, from very early stages in their development, an enzymatic machinery for processing beta-amyloid which is virtually identical to that of humans. For these reasons and given the cheap price along with the fact it is simple to handle, we believe that the chicken embryo is a very useful model for testing new drugs aimed at reducing beta-amyloid in people’s brains by means of its action upon the enzymes involved in the synthesis and degradation of the beta-amyloid protein.
The dog is one of the few animals which may naturally suffer a cognitive deterioration related to age which has been reported as the canine equivalent to Alzheimer’s disease. This disease in dogs reproduces some of the essential traces of Alzheimer’s disease in a natural way including beta-amyloid deposits in the cerebral cortex, the degeneration of certain neuron populations and the deterioration of learning ability and memory. Furthermore, as in chickens but unlike the case of rodents, the beta amyloid protein in dogs is identical to that of humans.
Because of this similarity and together with the fact it is a natural model in which there is no interference between the animal’s own genes and those artificially implanted, it is considered that studies in dogs will be of major predictive value in understanding aspects of the disease in people.