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A longitudinal neuroimaging study of the effects of early versus late anti-inflammatory treatment in the TgF344-AD rat model of Alzheimer’s disease1Biological and Biomedical Engineering, McGill University, Douglas Mental Health University Institute, Montreal, QC, Canada, 2Douglas Mental Health University Institute, Montréal, QC, Canada, 3Psychiatry, McGill University, Douglas Mental Health University Institute, Montréal, QC, Canada
Synopsis
Alzheimer’s disease (AD) is a progressive neurodegenerative disorder with no effective treatments or known biomarkers for definitive diagnosis, substantiating the need for early detection and intervention. This project employs Magnetic Resonance Spectroscopy to measure neurochemical changes in the TgF344-AD rat model of AD in response to treatment with a common non-steroidal anti-inflammatory drug. Progression of neurochemical changes over time and in response to treatment are compared to behavioural measures of cognition and histopathology. Preliminary results suggest neurochemical changes are present before onset of cognitive impairment, and treatment response depends on whether treatment is administered early or late into disease progression.
Introduction
- Alzheimer’s disease (AD) is a progressive neurodegenerative disorder with no effective treatments or known biomarkers for definitive diagnosis, substantiating the need for early detection and intervention. Pre-clinical development of biomarkers and testing of treatment options in animal models of AD represents an important step towards clinical trials. As such, the general aim of this study is to assess longitudinal changes in neurochemistry and cognition related to AD pathology in the TgF344-AD rat model of AD under treatment conditions. This project employs Magnetic Resonance Spectroscopy (MRS) to monitor changes in hippocampal neurochemical levels. Previous proton MRS (1H MRS) studies in rodent models of AD have identified reduced levels of N-acetylaspartate and glutamate (indicative of neuronal loss), increased levels of myo-inositol and glutamine (indicating gliosis) and increased taurine (an osmoregulatory agent).1–5 Importantly, neurochemical changes in AD animal models are consistent with those observed in MRS studies of AD in humans, and the in vivo MRS methods used for studying animal models are fully translatable to human AD subjects.1,6 In this study, progression of imaging biomarkers is compared to changes in cognition tested using the Barnes Maze spatial learning and memory task, and AD pathology is assessed via immunohistochemistry (data not shown). Treatment consists of either early or late intervention with Naproxen, a common non-steroidal anti-inflammatory drug (NSAID), which has been shown to have beneficial effects on disease progression, but only when administered during pre-symptomatic stages of the disease.7–10 Preliminary results suggest changes in metabolite levels exist before onset of significant cognitive impairment, and treatment response depends on whether treatment is administered early or late into disease progression.
Methods
Proton MRS acquisition and analyses: All 1H MRS data were acquired on a 7 Tesla Bruker Biospec 70/30 scanner. A high-resolution anatomical image was used to guide placement of a region of interest for localized MRS in the dorsal hippocampus. Automated localized shimming was performed using the FASTMAP method (water linewidth 10.8 +/- 1.2 Hz)11 prior to PRESS MRS acquisition (TR/TE = 3000/11ms). The FID-A toolkit was used to perform pre-processing and to generate a basis set for LCModel12 analysis of the MRS data. Metabolite concentrations are reported as a ratio to total creatine.13 Barnes Maze: A five-trial training protocol with a one-session probe test was used to assess cognitive function. Primary latency, path length, and number of errors were recorded during training trials. Time spent and holes searched per quadrant were recorded during the probe trial.14 Drug Treatment: Naproxen (Millipore Sigma, 615 ppm) was formulated into animal chow (Envigo) and groups received either normal chow or Naproxen chow ad libitum. Naproxen chow was administered either from one week post weaning until 10-months of age (early treatment), or from 10-months until 16-months (late treatment) (Figure 1).Results and Discussion
Proton MRS enables quantitative measurement of the concentrations of up to 20 different metabolites in the brain, many of which are established biomarkers of known pathological traits. MRS measurements in 4, 10, and 16-month-old wildtype no treatment, transgenic no treatment, transgenic early treatment, and transgenic late treatment rats show changes in myo-inositol, taurine, and glutamine levels as a function of disease state and/or treatment condition (Figure 2). Similarly, cognitive function assessed by the Barnes Maze task differs between groups (Figure 3). At 16-months of age, NAA is stable across groups, suggesting neuronal loss has not yet occurred in this AD model. Unexpectedly, glutamate is trending towards increases in untreated Tg and treated Tg rats relative to WT controls, though this may be explained by glutamate excitotoxicity known to occur during AD. Across the three timepoints, myo-Inositol, taurine, and glutamine display differences between genotypes and with treatment. Interestingly, the inflammatory marker, myo-Inositol, initially decreases with treatment but is increased in treated animals by 16-months, with late treatment exacerbating this increase. As such, it appears that treatment effects differ depending on the stage of disease progression during which they are administered, as shown in other pre-clinical NSAID studies;8–10 additional animals and analysis of the final time point at 20-months will enable more complete interpretation of these preliminary results. Wildtype treatment groups are also incorporated into this study but for simplicity, these data are not shownConclusion
These preliminary results confirm the value of MRS measurements as a tool for monitoring disease progression and treatment response in an AD rodent model. Together, the neuroimaging paradigm and anti-inflammatory therapeutic intervention represent a promising step towards a better understanding of disease progression, as well as the development of new prevention and treatment strategies.Acknowledgements
This research is funded by CIHR and FRQS awarded to Dr. Jamie Near, as well as a fellowship from the Healthy Brains for Healthy Lives Graduate Student Competition awarded to Caitlin Fowler.References
1. Marjańska M, Curran GL, Wengenack TM, et al. Monitoring disease progression in transgenic mouse models of Alzheimer’s disease with proton magnetic resonance spectroscopy. Proc Natl Acad Sci. 2005;102(33):11906-11910. doi:10.1073/pnas.0505513102.
2. Von Kienlin M, Künnecke B, Metzger F, et al. Altered metabolic profile in the frontal cortex of PS2APP transgenic mice, monitored throughout their life span. Neurobiol Dis. 2005;18(1):32-39. doi:10.1016/j.nbd.2004.09.005.
3. Dedeoglu A, Choi JK, Cormier K, Kowall NW, Jenkins BG. Magnetic resonance spectroscopic analysis of Alzheimer’s disease mouse brain that express mutant human APP shows altered neurochemical profile. Brain Res. 2004;1012(1-2):60-65. doi:10.1016/j.brainres.2004.02.079.
4. Nilsen LH, Melø TM, Saether O, Witter MP, Sonnewald U. Altered neurochemical profile in the McGill-R-Thy1-APP rat model of Alzheimer’s disease: a longitudinal in vivo 1 H MRS study. J Neurochem. 2012;123(4):532-541. doi:10.1111/jnc.12003.
5. Wu JY, Prentice H. Role of taurine in the central nervous system. J Biomed Sci. 2010;17(SUPPL. 1):2-7. doi:10.1186/1423-0127-17-S1-S1.
6. Gao F, Barker PB. Various MRS application tools for Alzheimer disease and mild cognitive impairment. Am J Neuroradiol. 2014;35(6 SUPPL.). doi:10.3174/ajnr.A3944.
7. Jantzen PT, Connor KE, DiCarlo G, et al. Microglial activation and beta -amyloid deposit reduction caused by a nitric oxide-releasing nonsteroidal anti-inflammatory drug in amyloid precursor protein plus presenilin-1 transgenic mice. J Neurosci. 2002;22(6):2246-2254. doi:22/6/2246 [pii].
8. Marjańska M, Weigand SD, Preboske G, et al. Treatment effects in a transgenic mouse model of alzheimer’s disease: A magnetic resonance spectroscopy study after passive immunization. Neuroscience. 2014;259:94-100. doi:10.1016/j.neuroscience.2013.11.052.
9. Choi J-K, Carreras I, Aytan N, et al. The effects of aging, housing and ibuprofen treatment on brain neurochemistry in a triple transgene Alzheimer’s disease mouse model using magnetic resonance spectroscopy and imaging. Brain Res. 2014;1590:85-96. doi:10.1016/j.brainres.2014.09.067.
10. Carreras I, McKee AC, Choi J-K, et al. R-flurbiprofen improves tau, but not Aß pathology in a triple transgenic model of Alzheimer’s disease. Brain Res. 2013;1541:115-127. doi:10.1016/j.brainres.2013.10.025.
11. Gruetter R. Automatic, localized in Vivo adjustment of all first???and second???order shim coils. Magn Reson Med. 1993;29(6):804-811. doi:10.1002/mrm.1910290613.
12. Provencher SW. Automatic quantitation of localized in vivo1H spectra with LCModel. NMR Biomed. 2001;14(4):260-264. doi:10.1002/nbm.698.
13. Simpson R, Devenyi GA, Jezzard P, Hennessy TJ, Near J. Advanced processing and simulation of MRS data using the FID appliance (FID-A)-An open source, MATLAB-based toolkit. Magn Reson Med. 2017;77(1):23-33. doi:10.1002/mrm.26091.
14. Attar A, Liu T, Chan WTC, et al. A shortened barnes maze protocol reveals memory deficits at 4-months of age in the triple-transgenic mouse model of Alzheimer’s disease. PLoS One. 2013;8(11). doi:10.1371/journal.pone.0080355.
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