Assay-guided affinity fractionation and reverse phase high pressure liquid chromatography (HPLC) methodology to isolate, test and characterize the most active water-soluble ingredients within Cat's Claw, or Uncaria tomentos. These components appear to account for the majority of the amyloid or A.beta. fibrillogenesis inhibitory activity. Individual fractions and/or compounds as isolated by HPLC are tested in relevant in vitro and/or animal models, and found to consistently demonstrate inhibition of amyloid or A.beta. fibrillogenesis. Related extraction methods are disclosed.