No abstract

Space radiation presents a substantial threat to travel beyond Earth. Relatively low doses of high-energy particle radiation cause physiological and behavioral impairments in rodents and may pose risks to human spaceflight. There is evidence that 56Fe irradiation, a significant component of space radiation, may be more harmful to males than to females and worsen Alzheimer’s disease pathology in genetically vulnerable models. Yet, research on the long-term, sex- and genotype-specific effects of 56Fe irradiation is lacking. Here, we irradiated 4-month-old male and female, wild-type and Alzheimer’s-like APP/PS1 mice with 0, 0.10, or 0.50 Gy of 56Fe ions (1GeV/u). Mice underwent microPET scans before and 7.5 months after irradiation, a battery of behavioral tests at 11 months of age and were sacrificed for pathological and biochemical analyses at 12 months of age. 56Fe irradiation worsened amyloid-beta (Aβ) pathology, gliosis, neuroinflammation and spatial memory, but improved motor coordination, in male transgenic mice and worsened fear memory in wild-type males. Although sham-irradiated female APP/PS1 mice had more cerebral Aβ and gliosis than sham-irradiated male transgenics, female mice of both genotypes were relatively spared from radiation effects 8 months later. These results provide evidence for sex-specific, long-term CNS effects of space radiation.

Whole-body exposure to high-energy particle radiation remains an unmitigated hazard to human health in space. Ongoing experiments at the NASA Space Radiation Laboratory and elsewhere repeatedly show persistent changes in brain function long after exposure to simulations of this unique radiation environment, although, as is also the case with proton radiotherapy sequelae, how this occurs and especially how it interacts with common comorbidities is not well-understood. Here, we report modest differential changes in behavior and brain pathology between male and female Alzheimer’s-like and wildtype littermate mice 7–8 months after exposure to 0, 0.5, or 2 Gy of 1 GeV proton radiation. The mice were examined with a battery of behavior tests and assayed for amyloid beta pathology, synaptic markers, microbleeds, microglial reactivity, and plasma cytokines. In general, the Alzheimer’s model mice were more prone than their wildtype littermates to radiation-induced behavior changes, and hippocampal staining for amyloid beta pathology and microglial activation in these mice revealed a dose-dependent reduction in males but not in females. In summary, radiation-induced, long-term changes in behavior and pathology, although modest, appear specific to both sex and the underlying disease state.

BackgroundPyroglutamate‐3Aβ (pGlu3Aβ) is a toxic N‐terminally truncated and modified form of Aβ that leads to faster aggregation and seeding of plaques, making it an important target in Alzheimer’s disease. Anti‐amyloid antibodies, e.g., bapineuzumab, are associated with Amyloid‐Related Imaging Abnormalities (ARIA) involving vasogenic edema and microhemorrhages in AD patients, especially in ApoE4 carriers. Previously, we demonstrated reductions in plaques and cognitive deficits using an anti‐pGlu3Ab mAb, 07/2a. Here, we tested a novel CDC‐mutant version (07/2a‐k, murine precursor to PBD‐C06) to avoid C1q activation to reduce vascular‐related inflammation associated with anti‐amyloid antibodies.MethodTo estimate an effective therapeutic dose, 12 mo‐old APP/PS1dE9 mice were treated weekly (i.p.) for 5 weeks with 150, 300 or 600 µg 07/2a‐k or IgG2a (n=10‐12/group). General Ab and pGlu3Aβ levels were quantified by ELISA and immunohistochemistry. Next, 16 mo‐old APP/PS1dE9; hApoE4 mice were treated weekly (i.p.) for 15 weeks with 350 µg of 07/2a‐k, 3D6‐L (a murine analog of bapineuzumab), or IgG2a, while hApoE4 mice were treated with PBS (n=10‐13 mice/group). Subsequently, cognitive testing was performed over 3 weeks using the Spatial Novelty Y Maze (SNYM), Novel Object Recognition (NOR), and the Barnes Maze followed by euthanasia.ResultFive weekly treatments with 07/2a‐k in the dosing study did not alter general and pGlu3 Aβ biochemical levels; however, hippocampal pGlu3Aβ plaques were significantly reduced (300 µg, p<0.0005; 600 µg, p<0.005). In the therapeutic study, 3D6‐L reduced Aβx‐42 levels (p<0.009) by ELISA but not Abx‐40 levels. 07/2a‐k did not significantly alter Aβx‐42 or Abx‐40 levels. Both antibodies improved performance in the NOR test (07/2a‐k, p<0.05; 3D6‐L, p=0.05) and showed a non‐significant trend for improvement in the SNYM and Barnes maze compared to IgG2a controls. Macro‐hemorrhages were visible in 33% of 3D6‐L treated mice but not in 07/2a‐k treated mice.ConclusionTreatment with the 3D6‐L mAb, a murine analog of bapineuzumab, lowered cerebral Aβ levels and improved cognition but induced macro‐hemorrhages in aged APP/PS1dE9;hApoE4 mice, while treatment with 07/2a‐k, the precursor to PBD‐C06, did not alter general Ab levels but improved cognition in the absence of macro‐hemorrhages. Further analyses are underway to quantify cerebral pGlu3Ab levels, plaques, CAA, microhemorrhages and gliosis. (NIH 1RF1AG058657‐CAL)

BackgroundThe development of immunotherapies against Aβ is burdened by clinical adverse events (AEs) observed as amyloid‐related imaging abnormalities (ARIA) on magnetic resonance imaging scans. The vascular inflammatory AEs have been reported in AD clinical trials administrating certain anti‐Aβ plaque‐binding antibodies and are thought to represent cerebral microhemorrhages and vasogenic edema. ARIA incidence appears apolipoprotein (APOE) genotype‐dependent, wherein APOE E4 allele carriers are at higher risk when compared to non‐carriers. With hopes to robustly model patients most at risk for the vascular complications of anti‐Aβ immunotherapy, we selected a relatively new transgenic mouse model bearing the human APOE E4 gene. The model has not yet been extensively characterized at multiple age points. To assess the face validity of the mouse model, we are conducting a battery of histological and biochemical tests.MethodsTo evaluate age‐ and sex‐related pathological changes, we collected brain and blood plasma from euthanized male and female APP/PS1dE9;hAPOE4 (APP/E4) mice across 3 ages: 8‐, 12‐ and 16‐months. General‐ and pGlu3‐Aβ levels were quantified using enzyme‐linked immunoassays (ELISA). Prussian Blue hemosiderin staining was used to examine microhemorrhages.ResultsImmunoassays of brain homogenates exhibited significantly higher insoluble Aβx‐40, Aβx‐42 and pGlu3Aβ levels in 16‐month‐old mice compared to 8‐ and 12‐month‐old mice. Moreover, the 16‐month‐old females demonstrated significantly higher levels of Aβx‐40 and pGlu3Aβ than age‐matched males. Hemosiderin staining was observed in all 12‐ and 16‐month mice, however no significant differences in abundance was found between the 2 age points. Immunostainings for plaque deposition of various Aβ species, vascular amyloid, dystrophic neurites and gliosis are ongoing.ConclusionsAge‐ and sex‐dependent increases in Aβ deposition were revealed in the APP/E4 mouse model. Preliminary evidence for microhemorrhage was observed. Subsequent analyses will better characterize the translational credibility of APP/E4 as a model for future nonclinical immunotherapies targeting Aβ. (1RF1AG058657‐CAL)