Medical Biophysics

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Preclinical impact of high dose intermittent antiangiogenic tyrosine kinase inhibitor pazopanib in intrinsically resistant tumor models
(2018-11) Reguera-Nuñez, Elaine; Man, Shan; Xu, Ping; Kerbel, Robert S
Antiangiogenic tyrosine kinase inhibitors (TKIs) target vascular endothelial growth factor receptors and other receptor tyrosine kinases. As a result of toxicity, the clinical failures or the modest benefits associated with antiangiogenic TKI therapy may be related in some cases to suboptimal drug dosing and scheduling, thereby facilitating resistance. Most antiangiogenic TKIs, including pazopanib, are administered on a continuous daily basis. Here, instead, we evaluated the impact of increasing the dose and administering the drug intermittently. The rationale is that using such protocols, antitumor efficacy could be enhanced by direct tumor cell targeting effects in addition to inhibiting tumor angiogenesis. To test this, we employed two human tumor xenograft models, both of which manifest intrinsic resistance to pazopanib when it is administered continuously: the VHL-wildtype SN12-PM6-1 renal cell carcinoma (RCC) and the metastatic MDA-MB-231/LM2-4 variant breast cancer cell line, when treated as distant metastases. We evaluated four different doses and schedules of pazopanib in the context of primary tumors and advanced metastatic disease, in both models. The RCC model was not converted to drug sensitivity using the intermittent protocol. Using these protocols did not enhance the efficacy when treating primary LM2-4 tumors. However, one of the high-dose intermittent pazopanib protocols increased median survival when treating advanced metastatic disease. In conclusion, these results overall suggest that primary tumors showing sensitivity to continuous pazopanib treatment may predict response to this drug when given at high doses intermittently in the context of advanced metastatic disease, that are otherwise resistant to the conventional protocol.
Variable impact of three different antiangiogenic drugs alone or in combination with chemotherapy on multiple bone marrow-derived cell populations involved in angiogenesis and immunity
(Springer, 2019-11) Reguera-Nuñez, Elaine; Man, Shan; Xu, Ping; Hilberg, Frank; Kerbel, Robert S
In contrast to VEGF pathway-targeting antibodies, antiangiogenic tyrosine kinase inhibitors (TKIs) have failed to meet primary endpoints in almost all phase III clinical trials when combined with conventional chemotherapy. One exception is the combination of nintedanib and docetaxel as a second-line therapy for rapidly progressing advanced NSCLC. In addition to increased toxicity caused by this type of combination, thus necessitating drug dose reductions or treatment breaks, such phase III trial failures may also be related to the differential impact of host-mediated responses involving mobilization and tumor infiltration of bone marrow-derived cell populations (BMDCs), comprising both pro-angiogenic as well as immune effector cells. Herein, we evaluated two different antiangiogenic TKIs (sunitinib or nintedanib) and a VEGFR-2 antibody (DC101) either alone or combined with maximum tolerated dose paclitaxel for their differential impact on the BMDC host response, evaluating four different cell types. TKIs (in particular sunitinib) induced myelosuppression similar to paclitaxel, whereas DC101 had no such effect. Sunitinib also significantly decreased the number of tumor-infiltrating CD8 + T and B cells, MDSCs, and macrophages. In contrast, the effect of nintedanib on these BMDC populations was less marked, behaving closer to the VEGFR-2 antibody effects than sunitinib. The results raise the possibility that differences observed between antiangiogenic antibodies and TKIs in increasing chemotherapy efficacy could be related, at least in part, to differential effects on cells associated with local immunity within the tumor microenvironment.
Cognitive and behavioral risk factors for low quality of life in survivors of childhood acute lymphoblastic leukemia
(Nature Publishing Group, 2021-08) van der Plas, Ellen; Spencer Noakes, T Leigh; Butcher, Darci T; Weksberg, Rosanna; Galin-Corini, Laura; Wanstall, Elizabeth A; Te, Patrick; Hopf, Laura; Guger, Sharon; Hitzler, Johann; Schachar, Russell J; Ito, Shinya; Nieman, Brian J
With high survival rates for pediatric acute lymphoblastic leukemia (ALL), long-term quality of life is a prominent consideration in treatment. We concurrently evaluated cognition, behavior, and quality of life in child and adolescent ALL survivors and determined associations between them.
Comparison of Functional Free-Breathing Pulmonary 1H and Hyperpolarized 129Xe Magnetic Resonance Imaging in Pediatric Cystic Fibrosis
(Elsevier, 2020-06-10) Couch, Marcus J; Munidasa, Samal; Rayment, Jonathan H; Voskrebenzev, Andreas; Seethamraju, Ravi Teja; Vogel-Claussen, Jens; Ratjen, Felix; Santyr, Giles
Rationale and Objectives: Phase resolved functional lung (PREFUL) magnetic resonance imaging (MRI) is a free-breathing 1H-based technique that produces maps of fractional ventilation (FV). This study compared ventilation defect percent (VDP) calculated using PREFUL to hyperpolarized (HP) 129Xe MRI and pulmonary function tests in pediatric cystic fibrosis (CF). Materials and Methods: 27 pediatric participants were recruited (mean age 13.0 ± 2.7), including 6 with clinically stable CF, 11 CF patients undergoing a pulmonary exacerbation (PEx), and 10 healthy controls. Spirometry was performed to measure forced expiratory volume in 1 second (FEV1), along with nitrogen multiple breath washout to measure lung clearance index (LCI). VDP was calculated from single central coronal slice PREFUL FV maps and the corresponding HP 129Xe slice. Results: The stable CF group had a normal FEV1 (p = 0.41) and elevated LCI (p = 0.007). The CF PEx group had a decreased FEV1 (p < 0.0001) and elevated LCI (p < 0.0001). PREFUL and HP 129Xe VDP were significantly different between the CF PEx and healthy groups (p < 0.05). In the stable CF group, PREFUL and HP 129Xe VDP were not significantly different from the healthy group (p = 0.18 and 0.08, respectively). There was a correlation between PREFUL and HP 129Xe VDP (R2 = 0.31, p = 0.004), and both parameters were significantly correlated with FEV1 and LCI. Conclusion: PREFUL MRI is feasible in pediatric CF, distinguishes patients undergoing pulmonary exacerbations compared to healthy subjects, and correlates with HP 129Xe MRI as well as functional measures of disease severity. PREFUL MRI does not require breath-holds and is straight forward to implement on any MRI scanner.
Sensitive tumour detection and classification using plasma cell-free DNA methylomes
(Nature, 2018-11-14) Shen, Shu Yi; Singhania, Rajat; Fehringer, Gordon; Chakravarthy, Ankur; Roehrl, Michael H A; Chadwick, Dianne; Zuzarte, Philip C; Borgida, Ayelet; Wang, Ting Ting; Li, Tiantian; Kis, Olena; Zhao, Zhen; Spreafico, Anna; Medina, Tiago da Silva; Wang, Yadon; Roulois, David; Ettayebi, Ilias; Chen, Zhuo; Chow, Signy; Murphy, Tracy; Arruda, Andrea; O'Kane, Grainne M; Liu, Jessica; Mansour, Mark; McPherson, John D; O'Brien, Catherine; Leighl, Natasha; Bedard, Philippe L; Fleshner, Neil; Liu, Geoffrey; Minden, Mark D; Gallinger, Steven; Goldenberg, Anna; Pugh, Trevor J; Hoffman, Michael M; Bratman, Scott V; Hung, Rayjean J; De Carvalho, Daniel D
The use of liquid biopsies for cancer detection and management is rapidly gaining prominence1. Current methods for the detection of circulating tumour DNA involve sequencing somatic mutations using cell-free DNA, but the sensitivity of these methods may be low among patients with early-stage cancer given the limited number of recurrent mutations2-5. By contrast, large-scale epigenetic alterations-which are tissue- and cancer-type specific-are not similarly constrained6 and therefore potentially have greater ability to detect and classify cancers in patients with early-stage disease. Here we develop a sensitive, immunoprecipitation-based protocol to analyse the methylome of small quantities of circulating cell-free DNA, and demonstrate the ability to detect large-scale DNA methylation changes that are enriched for tumour-specific patterns. We also demonstrate robust performance in cancer detection and classification across an extensive collection of plasma samples from several tumour types. This work sets the stage to establish biomarkers for the minimally invasive detection, interception and classification of early-stage cancers based on plasma cell-free DNA methylation patterns.
Assessing the feasibility of hyperpolarized 129 Xe multiple-breath washout MRI in pediatric cystic fibrosis
(Wiley, 2019-11-25) Couch, Marcus J; Morgado, Felipe; Kanhere, Nikhil; Kowalik, Krzysztof; Rayment, Jonathan H; Ratjen, Felix; Santyr, Giles
Purpose: To assess the feasibility of hyperpolarized 129Xe multiple‐breath washout MRI in pediatric cystic fibrosis (CF) participants with preserved lung function. Fractional ventilation (r), defined as the fractional gas replacement per breath, was mapped using 2 signal models: (1) constant T1 and (2) variable T1 as a function of the hyperpolarized gas washout. Methods: A total of 17 pediatric participants were recruited (mean age 11.7 ± 2.8 years), including 7 children with clinically stable CF and 10 aged‐matched healthy controls. Pulmonary function tests were performed, including spirometry, to measure the forced expiratory volume in 1 second and nitrogen multiple‐breath washout to measure the lung clearance index. Hyperpolarized 129Xe MRI was performed during consecutive breaths of air following a single 129Xe inhalation, and fractional ventilation maps were calculated. Results: The forced expiratory volume in 1 second was similar in both groups (P = .32), but there was a statistically significant difference in lung clearance index between healthy and CF participants (P = .001). With variable T1 modeling, CF participants had a mean r of 0.44 ± 0.08 and healthy participants had a mean r of 0.37 ± 0.12 (P = .20). With constant T1 modeling, CF participants had a mean r′ of 0.48 ± 0.08, and healthy participants had a mean r′ of 0.43 ± 0.12 (P = .32). Therefore, assuming a constant T1 leads to a relative bias in r of 15.1% ± 6.4% and 20.8% ± 7.4% for CF and healthy participants, respectively (P = .12). Conclusion: This study demonstrates that hyperpolarized 129Xe multiple‐breath washout imaging is feasible in pediatric participants with CF, and inclusion of variable T1 modeling reduces bias in the fractional ventilation measurements.
Ultrasound Detection of Abnormal Cerebrovascular Morphology in a Mouse Model of Sickle Cell Disease Based on Wave Reflection
(Elsevier, 2019-12) Cahill, Lindsay S; Pilmeyer, Jesper; Yu, Lisa X; Steinman, Joe; Hare, Gregory M T; Kassner, Andrea; Macgowan, Christopher K; Sled, John G
Sickle cell disease (SCD) is associated with a high risk of stroke, and affected individuals often have focal brain lesions termed silent cerebral infarcts. The mechanisms leading to these types of injuries are at present poorly understood. Our group has recently demonstrated a non-invasive measurement of cerebrovascular impedance and wave reflection in mice using high-frequency ultrasound in the common carotid artery. To better understand the pathophysiology in SCD, we used this approach in combination with micro-computed tomography to investigate changes in cerebrovascular morphology in the Townes mouse model of SCD. Relative to controls, the SCD mice demonstrated the following: (i) increased carotid artery diameter, blood flow and vessel wall thickness; (ii) elevated pulse wave velocity; (iii) increased reflection coefficient; and (iv) an increase in the total number of vessel segments in the brain. This study highlights the potential for wave reflection to aid the non-invasive clinical assessment of vascular pathology in SCD.
Accelerated interleaved spiral-IDEAL imaging of hyperpolarized 129 Xe for parametric gas exchange mapping in humans
(Wiley, 2019-04-16) Zanette, Brandon; Santyr, Giles
Purpose: To demonstrate the feasibility of mapping gas exchange with single breath-hold hyperpolarized (HP) 129Xe in humans, acquiring parametric maps of lung physiology. The potential benefit of acceleration using parallel imaging for this application is also explored. Methods: Six healthy volunteers were scanned with a modified spiral-IDEAL sequence to acquire gas exchange-weighted images using a single dose of 129Xe. These images were fit with the model of xenon exchange (MOXE) on a voxel-wise basis calculating parametric maps of lung physiology, specifically: air-capillary barrier thickness (δ), alveolar septal thickness (d), capillary transit time (tx), pulmonary hematocrit (HCT), and alveolar surface area-to-volume ratio (SVR). An accelerated version of the sequence was also tested in subset of four volunteers and compared to the fully-sampled (FS) results. Results: Mean image-wide values calculated from MOXE parametric maps derived from FS dissolved 129Xe spiral-IDEAL images were: δ=0.89±0.17μm, d=7.5±0.5μm, tx=1.1±0.2s, HCT=28.8±2.3%, and SVR=140±16cm-1, in good agreement with previously published values based on whole-lung spectroscopy of healthy human subjects. Parallel imaging sufficiently reduces artifacting in accelerated images, but increases disagreement with MOXE parameters derived from FS data with mean voxel-wise relative differences of: δ=39±9%, d=22±3%, tx=117±43%, HCT=11±2%, and SVR=31±12%. Conclusion: Dissolved HP 129Xe spiral-IDEAL imaging for gas exchange mapping is feasible in humans using a single breath-hold. Accelerated gas exchange mapping is also shown to be feasible, but requires further improvements to increase quantitative accuracy.
A Spine-Specific Phased Array for Transvertebral Ultrasound Therapy: Design and Simulation
(IEEE, 2019-04-18) Xu, Rui; O'Reilly, Meaghan A
Objective: To design and simulate the performance of two spine-specific phased arrays in sonicating targets spanning the thoracic spine, with the objective of efficiently producing controlled foci in the spinal canal. Methods: Two arrays (256 elements each, 500 kHz) were designed using multi-layered ray acoustics simulation: a four-component array with dedicated components for sonicating via the paravertebral and transvertebral paths, and a two-component array with spine-specific adaptive focusing. Mean array efficiency (canal focus pressure/water focus pressure) was evaluated using forward simulation in neutral and flexed spines to investigate methods that reduce spine-induced insertion loss. Target-specific four-component array reconfiguration and lower frequency sonication (250 kHz) were tested to determine their effects on array efficiency and focal dimensions. Results: When neutral, two- and four-component efficiencies were 32 ± 11% and 29 ± 13%, respectively, spine flexion significantly increased four-component efficiency (36 ± 18%), but not two-component efficiency (33 ± 15%). Target-specific four-component re-configuration significantly improved efficiency (36 ± 8%). Both arrays produced controlled foci centered within the canal with similar 50% pressure contour dimensions: 10.8-11.9 mm (axial), 4.2-5.6 mm (lateral), and 5.9-6.2 mm (vertical). Simulation at 250 kHz also improved two- and four-component efficiency (43 ± 17% and 36 ± 13%, respectively), but doubled the lateral focal dimensions. Conclusion: Simulation shows that the spine-specific arrays are capable of producing controlled foci in the thoracic spinal canal. Significance: The complex geometry of the human spine presents geometrical and acoustical challenges for transspine ultrasound focusing, and the design of these spine-specific ultrasound arrays is crucial to the clinical translation of focused ultrasound for the treatment of spinal cord disease.
Simulating transvertebral ultrasound propagation with a multi-layered ray acoustics model
(IOPScience, 2018-07-17) Xu, Rui; O'Reilly, Meaghan A
The simulation accuracy of transvertebral ultrasound propagation using a multi-layered ray acoustics model based on CT-derived vertebral geometry was investigated through comparison with experimental measurements of pressure fields in ex vivo human vertebral foramen. A spherically focused transducer (5 cm diameter, f-number 1.2, 514 kHz) was geometrically focused to the centre of individual thoracic vertebral foramen, through the posterior bony elements. Transducer propagation paths through the laminae and the spinous processes were tested. Simulation transducer-vertebra configurations were registered to experiment transducer-vertebra configurations, and simulation accuracy of the simulation model was evaluated for predicting maximum transmitted pressure to the canal, voxel pressure in the canal, and focal distortion. Accuracy in predicting maximum transmitted pressure was calculated by vertebra, and it is shown that simulation predicts maximum pressure with a greater degree of accuracy than a vertebra-specific insertion loss. Simulation error in voxel pressure was evaluated using root-mean-square error and cross-correlation, and found to be similar to the water-only case. Simulation accuracy in predicting focal distortion was evaluated by comparing experiment and simulation maximum pressure location and weighted >50% focal volume location. Average simulation error across all measurements and simulations in maximum pressure location and weighted >50% focal volume location were 2.3 mm and 1.5 mm, respectively. These errors are small relative to the dimensions of the transducer focus (4.9 mm full width half maximum), the spinal cord (10 mm diameter), and vertebral canal diameter (15-20 mm diameter). These results suggest that ray acoustics can be applied to simulating transvertebral ultrasound propagation.
Altered brain morphology after focal radiation reveals impact of off-target effects: implications for white matter development and neurogenesis
(Oxford Academic, 2018-06) Beera, Kiran G; Li, Yu-Qing; Dazai, Jun; Stewart, James; Egan, Shannon; Ahmed, Mashal; Wong, C Shun; Jaffray, David A; Nieman, Brian J
Background: Children with brain tumors treated with cranial radiation therapy (RT) often exhibit cognitive late effects, commonly associated with reduced white matter (WM) volume and decreased neurogenesis. The impact of radiation damage in particular regions or tissues on brain development as a whole has not been elucidated. Methods: We delivered whole-brain or focal radiation (8 Gy single dose) to infant mice. Focal treatments targeted white matter (anterior commissure), neuronal (olfactory bulbs), or neurogenic (subventricular zone) regions. High-resolution ex vivo MRI was used to assess radiation-induced volume differences. Immunohistochemistry for myelin basic protein and doublecortin was performed to assess associated cellular changes within white matter and related to neurogenesis, respectively. Results: Both whole-brain and focal RT in infancy resulted in volume deficits in young adulthood, with whole-brain RT resulting in the largest deficits. RT of the anterior commissure, surprisingly, showed no impact on its volume or on brain development as a whole. In contrast, RT of the olfactory bulbs resulted in off-target volume reduction in the anterior commissure and decreased subventricular zone neurogenesis. RT of the subventricular zone likewise produced volume deficits in both the olfactory bulbs and the anterior commissure. Similar off-target effects were found in the corpus callosum and parietal cortex. Conclusions: Our results demonstrate that radiation damage locally can have important off-target consequences for brain development. These data suggest that WM may be less radiosensitive than volume change alone would indicate and have implications for region-sparing radiation treatments aimed at reducing cognitive late effects.
p53 Loss Mitigates Early Volume Deficits in the Brains of Irradiated Young Mice
(Elsevier, 2019-02) de Guzman, A Elizabeth; Ahmed, Mashal; Li, Yu-Qing; Wong, C Shun; Nieman, Brian J
Purpose: Pediatric cranial radiation therapy results in lasting changes in brain structure. Though different facets of radiation response have been characterized, the relative contributions of each to altered development is unclear. We sought to determine the role of radiation-induced programmed cell death, as mediated by the Trp53 (p53) gene, on neuroanatomic development. Methods and Materials: Mice having a conditional knockout of p53 (p53KO) or wildtype p53 (WT) were irradiated with a whole-brain dose of 7 Gy (IR; n = 30) or 0 Gy (sham; n = 28) at 16 days of age. In vivo magnetic resonance imaging was performed before irradiation and at 4 time points after irradiation, until 3 months posttreatment, followed by ex vivo magnetic resonance imaging and immunohistochemistry. The role of p53 in development was assessed at 6 weeks of age in another group of untreated mice (n = 37). Results: Neuroanatomic development in p53KO mice was normal. After cranial irradiation, alterations in neuroanatomy were detectable in WT mice and emerged through 2 stages: an early volume loss within 1 week and decreased growth through development. In many structures, the early volume loss was partially mitigated by p53KO. However, p53KO had a neutral or negative impact on growth; thus, p53KO did not widely improve volume at endpoint. Partial volume recovery was observed in the dentate gyrus and olfactory bulbs of p53KO-IR mice, with corresponding increases in neurogenesis compared with WT-IR mice. Conclusions: Although p53 is known to play an important role in mediating radiation-induced apoptosis, this is the first study to look at the cumulative effect of p53KO through development after cranial irradiation across the entire brain. It is clear that apoptosis plays an important role in volume loss early after radiation therapy. This early preservation alone was insufficient to normalize brain development on the whole, but regions reliant on neurogenesis exhibited a significant benefit.
Variations in post-perfusion immersion fixation and storage alter MRI measurements of mouse brain morphometry
(Elsevier, 2016-11-15) de Guzman, A Elizabeth; Wong, Michael D; Gleave, Jacqueline A; Nieman, Brian J
Ex vivo magnetic resonance imaging (MRI) requires chemical fixation to preserve tissue during storage or extended imaging sessions. Although it is commonly understood that fixation may alter tissue volume and shape, the potential confounding effects of fixation and storage on morphometric analyses have not been well characterized. With increasing use of ex vivo MRI for mouse brain phenotying and opportunities for inter-study comparisons, we sought to characterize how changes in fixation and/or storage times affected tissue volume, and how this might impact phenotyping results. Mouse brain samples that had been perfusion fixed, within the skull as per our standard protocol, were immersed in formaldehyde-based fixative for 1 to 5days before being stored in saline or water. Throughout fixation and storage, samples were repeatedly scanned using magnetic resonance imaging, and analyzed for volume expansion or shrinkage. We found that most of the brain continued to shrink post fixation, with the rate of shrinkage dependent on the solution in which the samples were submerged. Maximum changes in volume of 3.5% per day and 3% per month were detected during fixation and storage (in PBS), respectively. Most notably, changes were non-uniform, with some structures shrinking slower, or even expanding, when compared to other structures in the brain. Our results highlight that caution is necessary when interpreting results from experiments with inconsistent fixation and storage protocols, so as not to mistake these changes for phenotypic differences.
Radiation-induced alterations in mouse brain development characterized by magnetic resonance imaging
(Elsevier, 2012-12-01) Gazdzinski, Lisa M; Cormier, Kyle; Lu, Fred G; Lerch, Jason P; Wong, C Shun; Nieman, Brian J
Purpose: The purpose of this study was to identify regions of altered development in the mouse brain after cranial irradiation using longitudinal MRI. Methods and Materials: Female C57Bl/6 mice received a whole-brain radiation dose of 7Gy at an infant-equivalent age of 2.5 weeks. MRI was performed before irradiation, and at three time points following irradiation. Deformation-based morphometry was used to quantify volume and growth rate changes following irradiation. Results: Widespread developmental deficits were observed in both white and gray matter regions following irradiation. Most of the affected brain regions suffered an initial volume deficit followed by growth at a normal rate, remaining smaller in irradiated brains compared to controls at all time points examined. The one exception was the olfactory bulb, which in addition to an early volume deficit, grew at a slower rate thereafter, resulting in a progressive volume deficit relative to controls. Immunohistochemical assessment revealed demyelination in white matter and loss of neural progenitor cells in the subgranular zone of the dentate gyrus and subventricular zone. Conclusions: MRI can detect regional differences in neuroanatomy and brain growth after whole-brain irradiation in the developing mouse. Developmental deficits in neuroanatomy persist, or even progress, and may serve as useful markers of late effects in mouse models. The high-throughput evaluation of brain development enabled by these methods may allow testing of strategies to mitigate late effects after paediatric cranial irradiation.
White and Gray Matter Abnormalities After Cranial Radiation in Children and Mice
(Elsevier, 2015-11-15) Nieman, Brian J; de Guzman, A Elizabeth; Gazdzinski, Lisa M; Lerch, Jason P; Chakravarty, M Mallar; Pipitone, Jon; Strother, Douglas; Fryer, Chris; Bouffet, Eric; Laughlin, Suzanne; Laperriere, Normand; Riggs, Lily; Skocic, Jovanka; Mabbott, Donald J
Purpose: Pediatric patients treated with cranial radiation are at high risk of developing lasting cognitive impairments. We sought to identify anatomical changes in both gray matter (GM) and white matter (WM) in radiation-treated patients and in mice, in which the effect of radiation can be isolated from other factors, the time course of anatomical change can be established, and the effect of treatment age can be more fully characterized. Anatomical results were compared between species. Methods and Materials: Patients were imaged with T1-weighted magnetic resonance imaging (MRI) after radiation treatment. Nineteen radiation-treated patients were divided into groups of 7 years of age and younger (7−) and 8 years and older (8+) and were compared to 41 controls. C57BL6 mice were treated with radiation (n=52) or sham treated (n=52) between postnatal days 16 and 36 and then assessed with in vivo and/or ex vivo MRI. In both cases, measurements of WM and GM volume, cortical thickness, area and volume, and hippocampal volume were compared between groups. Results: WM volume was significantly decreased following treatment in 7− and 8+ treatment groups. GM volume was unchanged overall, but cortical thickness was slightly increased in the 7− group. Results in mice mostly mirrored these changes and provided a time course of change, showing early volume loss and normal growth. Hippocampal volume showed a decreasing trend with age in patients, an effect not observed in the mouse hippocampus but present in the olfactory bulb. Conclusions: Changes in mice treated with cranial radiation are similar to those in humans, including significant WM and GM alterations. Because mice did not receive any other treatment, the similarity across species supports the expectation that radiation is causative and suggests mice provide a representative model for studying impaired brain development after cranial radiation and testing novel treatments.
A mouse model of antepartum stillbirth
(Elsevier, 2017-10) Rahman, Anum; Cahill, Lindsay S; Zhou, Yu-Qing; Hoggarth, Johnathan; Rennie, Monique Y; Seed, Mike; Macgowan, Christopher K; Kingdom, John C; Adamson, S Lee; Sled, John G
Background: Many stillbirths of normally formed fetuses in the third trimester could be prevented via delivery if reliable means to anticipate this outcome existed. However, because the etiology of these stillbirths is often unexplained and although the underlying mechanism is presumed to be hypoxia from placental insufficiency, the placentas often appear normal on histopathological examination. Gestational age is a risk factor for antepartum stillbirth, with a rapid rise in stillbirth rates after 40 weeks’ gestation. We speculate that a common mechanism may explain antepartum stillbirth in both the late-term and postterm periods. Mice also show increasing rates of stillbirth when pregnancy is artificially prolonged. The model therefore affords an opportunity to characterize events that precede stillbirth. Objective: The objective of the study was to prolong gestation in mice and monitor fetal and placental growth and cardiovascular changes. Study Design: From embryonic day 15.5 to embryonic day 18.5, pregnant CD-1 mice received daily progesterone injections to prolong pregnancy by an additional 24 hour period (to embryonic day 19.5). To characterize fetal and placental development, experimental assays were performed throughout late gestation (embryonic day 15.5 to embryonic day 19.5), including postnatal day 1 pups as controls. In addition to collecting fetal and placental weights, we monitored fetal blood flow using Doppler ultrasound and examined the fetoplacental arterial vascular geometry using microcomputed tomography. Evidence of hypoxic organ injury in the fetus was assessed using magnetic resonance imaging and pimonidazole immunohistochemistry. Results: At embryonic day 19.5, mean fetal weights were reduced by 14% compared with control postnatal day 1 pups. Ultrasound biomicroscopy showed that fetal heart rate and umbilical artery flow continued to increase at embryonic day 19.5. Despite this, the embryonic day 19.5 fetuses had significant pimonidazole staining in both brain and liver tissue, indicating fetal hypoxia. Placental weights at embryonic day 19.5 were 21% lower than at term (embryonic day 18.5). Microcomputed tomography showed no change in quantitative morphology of the fetoplacental arterial vasculature between embryonic day 18.5 and embryonic day 19.5. Conclusion: Prolongation of pregnancy renders the murine fetus vulnerable to significant growth restriction and hypoxia because of differential loss of placental mass rather than any compromise in fetoplacental blood flow. Our data are consistent with a hypoxic mechanism of antepartum fetal death in human term and postterm pregnancy and validates the inability of umbilical artery Doppler to safely monitor such fetuses. New tests of placental function are needed to identify the late-term fetus at risk of hypoxia to intervene by delivery to avoid antepartum stillbirth.
Human umbilical cord blood relaxation times and susceptibility at 3 T
(Wiley, 2018-06) Portnoy, Sharon; Milligan, Natasha; Seed, Mike; Sled, John G; Macgowan, Christopher K
Purpose To characterize the magnetic susceptibility and relaxation times (T1 and T2) of fetal blood at 3 T as a function of the hematocrit (Hct) and oxygen saturation (sO2). Methods Susceptibility and relaxometry measurements were performed on cord blood specimens (N = 90, derived from six caesarean deliveries) with a range of hematocrits and oxygen saturations (0.09 < Hct < 0.82, 7 < sO2 < 100%). To obtain simple, analytic relationships between MRI properties and blood properties, data were fit to established two‐compartment (plasma and erythrocytes) models. Results Two‐compartment models effectively described the cord blood data. The root‐mean‐squared deviation between the model and the data was 6.3, 10.3, and 1.3% for fits to T1, T2, and susceptibility measurements. Relaxometry data and estimated T1 and T2 model parameters were generally consistent with those reported in cord blood at 1.5 T and comparable to published values for adult blood. Notably, the measured value of Δχdeo, the susceptibility difference between fully oxygenated (sO2 = 100%) and deoxygenated (sO2 = 0) cord blood was approximately 20% lower than the established adult blood value (Δχdeo,cord = 2.64 ppm, Δχdeo,adult = 3.4 ppm). Conclusions The described models and associated parameter values can be used to inform acquisition parameters, and interpret fetal/neonatal blood susceptibility measurements and relaxometry data acquired at 3 T with respect to hematocrit and sO2. Magn Reson Med 79:3194–3206, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
Non-invasive evaluation of blood oxygen saturation and hematocrit from T1 and T2 relaxation times: In-vitro validation in fetal blood
(Wiley, 2017-12) Portnoy, Sharon; Seed, Mike; Sled, John G; Macgowan, Christopher K
Purpose We propose an analytical method for calculating blood hematocrit (Hct) and oxygen saturation (sO2) from measurements of its T1 and T2 relaxation times. Theory Through algebraic substitution, established two‐compartment relationships describing urn:x-wiley:07403194:media:mrm26599:mrm26599-math-0001 and urn:x-wiley:07403194:media:mrm26599:mrm26599-math-0002 as a function of hematocrit and oxygen saturation were rearranged to solve for Hct and sO2 in terms of R1 and R2. Resulting solutions for Hct and sO2 are the roots of cubic polynomials. Methods Feasibility of the method was established by comparison of Hct and sO2 estimates obtained from relaxometry measurements (at 1.5 Tesla) in cord blood specimens to ground‐truth values obtained by blood gas analysis. Monte Carlo simulations were also conducted to assess the effect of T1, T2 measurement uncertainty on precision of Hct and sO2 estimates. Results Good agreement was observed between estimated and ground‐truth blood properties (bias = 0.01; 95% limits of agreement = ±0.13 for Hct and sO2). Considering the combined effects of biological variability and random measurement noise, we estimate a typical uncertainty of ±0.1 for Hct, sO2 estimates. Conclusion Results demonstrate accurate quantification of Hct and sO2 from T1 and T2. This method is applicable to noninvasive fetal vessel oximetry—an application where existing oximetry devices are unusable or require risky blood‐sampling procedures. Magn Reson Med 78:2352–2359, 2017. © 2017 International Society for Magnetic Resonance in Medicine.
Fetal brain sparing in a mouse model of chronic maternal hypoxia
(SAGE Journals, 2019-06-01) Cahill, Lindsay S; Hoggarth, Johnathan; Lerch, Jason P; Seed, Mike; Macgowan, Christopher K; Sled, John G
Hypoxic stress is a common occurrence during human pregnancy, yet little is known about its effects on the fetal brain. This study examined the fetal hemodynamic responses to chronic hypoxia in an experimental mouse model of chronic maternal hypoxia (11% O2 from E14.5 to E17.5). Using high-frequency Doppler ultrasound, we found fetal cerebral and ductus venosus blood flow were both elevated by 69% and pulmonary blood flow was decreased by 62% in the fetuses exposed to chronic hypoxia compared to controls. This demonstrates that brain sparing persists during chronic fetal hypoxia and is mediated by "streaming," where highly oxygenated blood preferentially flows through the ductus venosus towards the cerebral circulation, bypassing the liver and the lungs. Consistent with these changes in blood flow, the fetal brain volume measured by MRI is preserved, while the liver and lung volumes decreased compared to controls. However, hypoxia exposed fetuses were rendered vulnerable to an acute hypoxic challenge (8% O2 for 3 min), demonstrating global blood flow decreases consistent with imminent fetal demise rather than elevated cerebral blood flow. Despite this vulnerability, there were no differences in adult brain morphology in the mice exposed to chronic maternal hypoxia compared to controls.
Cryo-EM of ATP synthases
(Elsevier, 2018-09-18) Guo, Hui; Rubinstein, John L
ATP synthases are rotary enzymes found in bacteria, chloroplasts, and mitochondria. These complexes produce the majority of cellular ATP in aerobic cells using energy from the transmembrane proton motive force established by the electron transport chain. In mitochondria, dimeric ATP synthase is essential for formation of the inner membrane cristae. While rotary catalysis in the soluble F1 region has been studied extensively by X-ray crystallography, the structure of the membrane embedded FO region remained elusive until recently. In the past few years, electron cryomicroscopy structures of mitochondrial, chloroplast, and bacterial ATP synthases have revealed the architecture of the FO region, helping to explain the mechanisms of proton translocation, dimerization of the enzyme in mitochondria, and cristae formation. These structures also show that ATP synthases exist in different conformational states, illustrating the flexibility and dynamics of the complex.

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