A Putative Tetrapeptide Antagonist Prevents β-Amyloid-Induced Long-Term Elevation of [Ca2+]iin Rat Astrocytes

Abstract

Comparative fluorimetric studies on the long-term (8-hour) action of β[1-42]amyloid and its shorter fragments β[1-40], β[25-35] and β[31-35] on the steady-state intracellular Ca2+concentration in primary cultures of rat astroglial cells using the Ca2+-sensitive fluorescent probe Fura-2 AM revealed higher 340/380 fluorescence excitation ratios in the treated cells as compared to the untreated controls. All the peptides were found to induce similar cellular effects, suggesting the [31-35] region as the putative active centre of the molecule. No significant alteration was detectable in Fura-2 fluorescence using the Ca2+-insensitive excitation wavelength of 367 nm, indicating that the observed changes reflect a real alteration in the Ca2+concentration of the cells. Moreover, no considerable difference was observed in the total protein content of treated and untreated cells. Co-treatment of the cells with Pr-Ile-Ile-Gly-Leu-NH2(Pr-IIGL) peptide, an analogue of the [31-34] region of β[1-42]-amyloid, was found to effectively antagonize the β[1-42]-amyloid-induced elevation of the fluorescence excitation ratio, leaving the 367-nm fluorescence unaffected. To the best of the authors’ knowledge, this is the first report on an analogue of β-amyloid peptide capable of blocking one of its physiological effects, thereby raising the possibility that this sequence could prove to be a lead compound for designing effective β-amyloid antagonists.