Structural Changes of Amyloid Beta in Hippocampus of Rats Exposed to Ozone: A Raman Spectroscopy Study

Selva Rivas-Arancibia, Erika Rodríguez-Martínez, Isidro Badillo-Ramírez, Ulises López-González, José M. Saniger

The aim of this work was to study the effect of oxidative stress on the structural changes of the secondary peptide structure of amyloid beta 1-42 (Aβ 1-42), in the dentate gyrus of hippocampus of rats exposed to low doses of ozone. The animals were exposed to ozone-free air (control group) and 0.25 ppm ozone during 7, 15, 30, 60, and 90 days, respectively. The samples were studied by: (1) Raman spectroscopy to detect the global conformational changes in peptides with α-helix and β-sheet secondary structure, following the deconvolution profile of the amide I band; and (2) immunohistochemistry against Aβ 1-42. The results of the deconvolutions of the amide I band indicate that, ozone exposure causes a progressively decrease in the abundance percentage of α-helix secondary structure. Furthermore, the β-sheet secondary structure increases its abundance percentage. After 60 days of ozone exposure, the β-sheet band is identified in a similar wavenumber of the Aβ 1-42 peptide standard. Immunohistochemistry assays show an increase of Aβ 1-42 immunoreactivity, coinciding with the conformational changes observed in the Raman spectroscopy of Aβ 1-42 at 60 and 90 days. In conclusion, oxidative stress produces changes in the folding process of amyloid beta peptide structure in the dentate gyrus, leading to its conformational change in a final β-sheet structure. This is associated to an increase in Aβ 1-42 expression, similar to the one that happens in the brain of Alzheimer's Disease (AD) patients.