Urine-Based Peptidomic Biomarkers Of Alzheimer's Disease

Alzheimer's disease(AD), which can be defined as a degenerative dementia and characterized by two types of lesion: senile plaques and neurofibrillary tangles,is a complex disease not yet fully understood. While many hypotheses have been provided as to the cause of AD, such as the amyloid cascade hypothesis, the aggregation of hyperphosphorylated tau, the neuroinflammation hypothesis and the oxidative stress hypothesis, the exact mechanisms remain elusive and difficult to verify. Most clinical trials of potential therapeutic disease-modifying agents have involved individuals with clinically manifest dementia and have been relatively unsuccessful to date. Earlier stages of the disease are now being targeted, posing a challenge as it is difficult to detect individuals at this stage of AD; brain pathology is developing silently and cognitive symptoms if detectable are subtle. It is, therefore, important to develop biomarkers from body fluids, in particular, in the preclinical or early phases that reflect the pathological characteristics of the disease and, moreover, could be of utility in triaging subjects for preventative therapeutic clinical trials. As biological fluid that is non-invasively and easily harvested, urine is important resource of biomarker of disease. Furthermore, urine generally reflect plasma situation,even the body. Peptides play a central role in many physiological processes and can reflect the unusual protein metabolism in vivo. Peptidomics is an emerging field banching from proteomincs that targets endogenous peptides of a whole organism or a subsystem, functions of it and change rules. To find a group of biomarkers for AD diagnosing, we separated and enriched peptides in urine of AD patients and healthy elders, then did peptidomic analysis. At first we established a new method of peptidomic analyzing by nano liquid chromatography-high resolution tandem mass spectrometry, which could identify not only the peptide sequences and the proteins that peptides were belong to, but also the posttranslational modifications of peptides. Then we did research on urine peptidome of healthy peoples to explore the compositional features and individual differences, illustrated the nonuniformity of urine peptidome's distribution, identified the normal proteins that urine peptides were belong to and proved different results of urine peptidome and proteome. Finally, we compared the each peptidome of mixture urines of 15 AD patients and 15 healthy elders and found that the total peptides, modificated peptides and total intensity were significantly increasing in urine of AD patiens. Furthermore, the combination of four groups of peptides were proposed as the candicate biomarker of AD. The detected peptides arised from those proteins that are related to epigenetic regulation and component of amyloid plaques, like Histone H2 B, Histone H2 A, Histone H3.2; the proteins take part in inflammation, such as the protein S100-A8, protein S100-A12, Osteopontin and so on; e proteins play important role in energy metabolism, including Transketolase, Pyruvate kinase PKM, GAPDH, Phosphoglycerate kinase1; the proteins are related with nervous system development, for instance, Cathepsin G, Haptoglobin, Apolipoprotein A-I et al; they participate in various ways in the process of AD. The verification of these candidates was did in individual urine of other 15 AD patients and 15 healthy elders. Finally, the qualitative peptidome technique was used to analyze the urine peptidome of AD group and control group, and we try to explain these differences from the point of protein and protein-protein interaction. Taken together, these results demonstrate urine peptidome may provide new noninvasive strategies for the detection of AD.