The present invention concerns the use of peptidyl-prolyl isomerase cyclophilin 40 (CyP40) for reduction of neurotoxic fibrils and treatment and prevention of neurodegenerative diseases associated with amyloid fibril aggregation. Aspects of the invention include compositions, methods, dosage forms, and kits for treating or preventing a neurodegenerative disease or condition associated with amyloid fibril aggregation in a human or animal subject, and for disaggregating neurofibrillary aggregates in vitro or in vivo, using CyP40, or a biologically active fragment thereof.
