11078-21-0 br Other PTMs in blood and CSF As
Other PTMs in blood and CSF As AD is a neurodegenerative disease, 11078-21-0 samples yield the most information regarding the mechanisms of the disease state. However, often time, brain samples are unavailable, particularly in the case of individuals with PCAD or individuals who have not begun showing symptoms. Therefore, another aspect of AD research that is currently lacking, is the development of methods for analyzing CSF, blood, and other peripheral fluids for potential biomarkers. A blood-based biomarker panel for the identification of PCAD would be invaluable and investigating varying levels of different blood proteins in different stages of AD by mass spectrometry is the first step to accomplishing this . In their review article, Blanco et al. discuss the increased levels of oxidized proteins in MCI fluids (blood, plasma, CSF etc.) but comment on the low statistical significance of much of the data on the subject . The authors document the various studies which have been completed with peripheral fluids from patients (PCAD, MCI, and advanced AD). Most studies have utilized blood and plasma and although most data have been shown to be not statistically relevant, there has been consistency in increased levels of oxidized proteins within the fluids with disease progression and lipid peroxidation has also been shown to increase with severity, suggesting that this may be an early AD biomarker. More advanced, and selective analytical techniques, such as mass spectrometry, should therefore be utilized to shed more light on the subject. Transthyretin (TTR), an important transport protein for thyroxine and retinol, is a primary protein that has been investigated as a biomarker for AD within CSF and blood [118,119]. Biroccio et al. described the ability of TTR to bind to amyloid-beta and to have certain neuroprotective properties . PTMs associated with the protein were investigated by nano-LC MS/MS and MALDI-TOF MS and it was found that oxidized forms of TTR were actually less abundant in CSF from AD patients as opposed to from healthy patients. Popov et al. described PTMs of transthyretin in blood by bottom-up and top-down proteomics . 11 different modifications of the protein were identified. Several of these modifications, such as glycosylation, are mutations of genes which are thought to lead to various diseases and affect aggregation and neurotoxicity of amyloid-beta in AD . Mass spectrometry surveys such as this are imperative in the better understanding of the changes that occur in CSF and blood proteins with disease progression.
Future directions While great progress has been made in understanding the roles of PTMs in Alzheimer's disease, particularly with the application of mass spectrometry as a go-to analytical technique, much is still unknown about the relationship between the structure and function of the modifications. The next step in determining the function of the modifications is to be able to determine their localization, and variation between tissue types (healthy and diseased). Preliminary work involving synthetic peptides and animal models are crucial for a basic understanding of disease etiology and determination of research focus, however, the development of techniques to easily analyze human tissue is imperative for clinical applications. Imaging mass spectrometry (IMS), mentioned briefly earlier, is a prime example of where mass spectrometry can take PTM research. There are few reports on the application of this technique to the analysis of PTMs [120,121]. A way in which we have been utilizing MALDI IMS involves the comparison of control and diseased (or damaged) serial tissue sections to investigate the identity of molecular targets specific to the damage type in an attempt to make better sense of the biological mechanisms occurring and potential means of therapy or recovery [, , ]. Hundreds of molecules from a single tissue section can be simultaneously analyzed for their molecular and spatial information [, , , ]. The primary advantages of MALDI imaging stem from the combination of pathological and histological approaches of tissue analysis and mass spectrometric approaches of complex biological systems analysis [124,125]. MALDI imaging is a label-free approach that does not rely on antibodies for species confirmation . Often times, antibodies are not selective for only one analyte in a complex mixture or antibodies do not exist for an analyte of interest, making some antibody-based confirmation experiments difficult . Additionally, if the complex sample involves unknown components, site-specific histology yields little information about the identities. The ability to resolve molecular localization without the need for labels makes MALDI IMS superior to common histological approaches. New molecular-based approaches of sample analysis are imperative to PTM and AD research in general if therapies are on the horizon.