A review of biomarkers of Alzheimer's disease in noninvasive samples.

The discovery of biomarkers that confer high confidence of presymptomatic Alzheimer's disease (AD) diagnosis would be a valuable tool to study the etiology of the disease, to find risk factors, to discover more treatments and medicines. The present work reviews the potential biomarkers of AD based on the concentration changes of small molecules and chemical elements in noninvasive samples (urine, saliva, hair and others). An updated table with 74 target compounds is produced and ranked. Until the present date, there are a few biomarkers, present in urine, with the most promising potential: isoprostane 8,12-iso-iPF2a-VI, total free amino acids, 8-hydroxy-2'-deoxyguanosine, glycine and enzymatic activity of NaCl-stimulated PON1. All show increased levels in AD carriers, with the exception of NaCl-stimulated PON1.