This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. A major goal in translating neuroprotective and neuroreparative strategies for MS from the bench to the bedside is to develop surrogate measures of myelin and axon integrity that can be used in phase II clinical trials to screen for preliminary efficacy. The utility of gadolinium-enhancing lesions as a surrogate marker of inflammation in phase II/III trials of immunomodulatory drugs is now well accepted. Nonetheless, even in the absence of apparent inflammation, clinical disability progresses. This is thought to occur as a result of axon degeneration mediated by numerous downstream factors. Radiological studies have demonstrated evidence of distant Wallerian degeneration and atrophy that ensue months to years after active inflammatory demyelination (230). The correlation between disability and conventional measures such as T1 volume (post-gadolinium), T2 volume, and atrophy or T1 black holes is only modest (correlation coefficients between 0.3 and 0.6 in a variety of studies), presumably because all of these measures lack specificity for permanent brain tissue pathology. Recent advances in magnetic resonance imaging (MRI) such as magnetization transfer imaging (MTI), proton magnetic resonance spectroscopy (1H-MRS), and diffusion tensor imaging (DTI) offer promise as more sensitive and specific measures of underlying structural pathology. There is a great need to develop and optimize these measures so as to be able to non-invasively quantify the extent of demyelination and axon degeneration in MS patients. We are focusing on developing DTI and MTI to allow quantitative measurement of pathology along white-matter tracts, which can then be used as outcome measures for clinical trials of potential neuroprotective and neuroreparative agents. DTI gives information on the directionality and integrity of white-matter tracts. MTI has been shown to be associated with both axon density and myelin integrity, and therefore may be relevant to tracking local and distant changes in axons that pass through areas of damaged myelin, as well as a measure of myelin repair. Fiber-tracking software allows the 3 dimensional reconstruction of specific pathways distal and proximal to a region of interest (ROI) or between two or more ROIs. In this way, multiple types of quantitative information can then be acquired both locally and at distant sites from an acute inflammatory lesion. Moreover, we can interrogate the reconstructed pathways to measure changes over time in an individual patient. Since all of the MR images are coregistered we can compare DTI and MTI tract specific information, which may improve our ability to discern different pathologies along the trajectories.
The aims of this project are based on the notions that: (1) there is significant axon damage both within and distant from the acute inflammatory demyelinating MS plaque; and (2) progressive changes in axon integrity occur in the chronically demyelinated setting and account for the disabling progressive stages of the disease. We hypothesize that: (1) fractional anisotropy (FA) predominantly reflects disruption of the integrity of axons whereas the magnetization transfer ratio (MTR) predominantly reflects changes in myelin integrity; and (2) the extent and duration of white-matter tract damage in MS patients, as measured by FA and MTR will have concurrent and predictive validity for functional impairment related to the involved pathways.
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