Colostrinin (CLN), a mixture of
proline-rich
polypeptides, has shown a stabilizing effect on cognitive function in Alzheimer's patients measured by the
Alzheimer's disease Assessment Scale-cognitive (ADAS-cog) and in Instrumental
Activities of Daily Living (ILDL) in recently conducted clinical trials. The aim of this study was to elucidate a possible mode of action of CLN in the treatment of
Alzheimer's disease. Here, we report that CLN prevents the aggregation of
beta-amyloid peptide Abeta (1-40) in vitro. The impact of CLN on the fibril formation was monitored by optical and electron microscopy. The electron micrographs illustrate that, at 25 microM, Abeta (1-40)
peptides formed fibrils after 24-48 h of incubation. The presence of 0.25 microM CLN completely abolished the fibril formation. Abeta (1-40)
peptides grow into dense fibers when examined at the 20th day. In the presence of CLN, however, the fibrils are much shorter and less dense. Addition of CLN as late as the 17th day can still dissolves the preformed fibrils. These observations were compared to the effect of CLN on the neurotoxic activity of
beta-amyloid peptides in the cell culture model (SHSY-5Y). The
beta-amyloid peptides were pre-incubated with CLN at various times and used to treat SHSY-5Y
neuroblastoma cells for up to 4 days. The cytotoxic effect was monitored by
trypan blue exclusion. We demonstrated that 24-48 h treatment was the onset of toxicity of 10-50 microM of
beta-amyloid peptides. Pre-incubation of 0.0025-0.25muM of CLN with 25 microM of
beta-amyloid peptides leads to near-complete abolition of cytotoxicity. Low doses of CLN (2.5 nM) can attain cytotoxic protection levels similar to those of highest doses (0.25 microM). Thus, the time course for the appearance of
beta-amyloid fibrils coincides with that for cytotoxicity, and that the reduction of fibrils of
beta-amyloid peptides by CLN is concomitant with the reduction of the cytotoxic effects of
beta-amyloid on SHSY-5Y
neuroblastoma cells. Our studies suggest that the
neuroprotective effects exerted by CLN are related to the reduction of
beta-amyloid fibrils.