Testing the therapeutic potential of doxycycline in a Drosophila melanogaster model of Alzheimer disease.

Therapies for Alzheimer disease that reduce the production of pathogenic amyloid β (Aβ) peptides have been associated with a range of unwanted effects. For this reason, alternative strategies that promote the clearance of the peptide by preventing its aggregation and deposition in the brain have been favored. In this context we have studied doxycycline, a member of the tetracycline family of antibiotics that has shown neuroprotective effects in a number of models of neurodegenerative disease. We investigated the neuroprotective potential of doxycycline in a Drosophila model of Aβ toxicity and sought to correlate any effects with the aggregation state of the peptide. We found that administration of doxycycline to Aβ42-expressing flies did not improve their lifespan but was able to slow the progression of their locomotor deficits. We also measured the rough eye phenotype of transgenic flies expressing the E22G variant of Aβ42 and showed that doxycycline administration partially rescued the toxicity of Aβ in the developing eye. We correlated these in vivo effects with in vitro observations using transmission electron microscopy, dynamic light scattering, and thioflavin T binding. We found that doxycycline prevents Aβ fibrillization and favors the generation of smaller, non-amyloid structures that were non-toxic as determined by the lack of caspase 3 activation in a neuroblastoma cell line. Our confirmation that doxycycline can prevent amyloid β toxicity both in vitro and in vivo supports its therapeutic potential in AD.