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Open Access Publications from the University of California

Scholarly Works (27 results)

  • Article
  • Peer Reviewed
UC Irvine Previously Published Works (2022)
Exposure to radiation during the treatment of CNS tumors leads to detrimental damage of the blood brain barrier (BBB) in normal tissue. Effects are characterized by leakage of the vasculature which exposes the brain to a host of neurotoxic agents potentially leading to white matter necrosis, parenchymal calcification, and an increased chance of stroke. Vasculature of the blood tumor barrier (BTB) is irregular leading to poorly perfused and hypoxic tissue throughout the tumor that becomes resistant to radiation. While current clinical applications of cranial radiotherapy use dose fractionation to reduce normal tissue damage, these treatments still cause significant alterations to the cells that make up the neurovascular unit of the BBB and BTB. Damage to the vasculature manifests as reduction in tight junction proteins, alterations to membrane transporters, impaired cell signaling, apoptosis, and cellular senescence. While radiotherapy treatments are detrimental to normal tissue, adapting combined strategies with radiation targeted to damage the BTB could aid in drug delivery. Understanding differences between the BBB and the BTB may provide valuable insight allowing clinicians to improve treatment outcomes. Leveraging this information should allow advances in the development of therapeutic modalities that will protect the normal tissue while simultaneously improving CNS tumor treatments.
    Cover page: Breaking barriers: Neurodegenerative repercussions of radiotherapy induced damage on the blood-brain and blood-tumor barrier
    • Thesis
    • Peer Reviewed
    UC Irvine Electronic Theses and Dissertations (2023)

    Radiotherapy has long been used to control tumor growth by causing ionization of cellular macromolecules including DNA, RNA, lipids and proteins, leading to lethal or sublethal damage to a cell. Typically, convention radiotherapy (CONV-RT) is delivered at a dose rate between 0.07–0.1 Gy⋅s−1 and fractionated over an extended treatment plan (1 -2 months), allowing healthy normal tissue to mend sublethal damage while repair-compromised tumor tissue accumulates damage. Previous studies have identified that fractions under 2 Gy are required to reduce long-term neurocognitive damage1. These normal tissue dose tolerances limit the therapeutic benefit of radiotherapy. A recent breakthrough in radiation delivery modalities have shown that using ultra-high dose rates (>100 Gy⋅s−1), or ‘FLASH’ irradiation, can reduce cognitive damage, spare normal tissue injury, and minimize harm to critical systems like the blood brain barrier (BBB), all while maintaining isoefficient tumor control2–4. This new radiation modality has the potential to greatly extend the therapeutic benefit of radiotherapy while limiting the unintended neurological sequelae that are frequently caused by treatment.

    At this point, our lab has produced substantial evidence that FLASH irradiation reduces damage done to the CNS normal tissue, protecting the homeostasis, and potentially reducing the onset and severity of late radiation-injury in brain tumor survivors subjected to cranial radiotherapy. Experiments performed by ourselves and collaborators have examined the FLASH effect using preclinical models of fish, rodents, cats, and mini-pigs2,5–8 and has successfully been used clinically in a single patient to treat multiresistant CD30+ T-cell cutaneous lymphoma4. While a plethora of data is available on the FLASH effect, the underlying mechanisms are still not fully understood. Our lab has shown that oxygenation levels of the tissue play a vital role in radiation induce tissue damage through mitigation of reactive oxygen species (ROS)2; however, there are likely other key mechanisms at play. The importance of tissue oxygenation and the role the BBB plays in maintaining CNS homeostasis are why we consider the vasculature to be a key element in deciphering the FLASH effect.

    The Limoli lab has been publishing regularly on the benefits of FLASH irradiation in pre-clinical models for the last 4 years, highlighting the normal tissue sparing effects in the CNS. My work in particular has focused on the effect of both CONV and FLASH irradiation on the normal tissue and the BBB. I performed initial experiments utilizing FLASH and CONV radiation to determine effects on the BBB at early timepoints which led to a publication in Radiation Research9. Following this, I spent time exploring the literature behind CNS vasculature, radiotherapy, and new experimental therapeutic techniques which culminated into a published review in Free Radical Biology and Medicine10. I have used this rationale to examine the cognitive and vasculature effects of FLASH on juveniles11, a particularly radiation susceptible population. Results from the juvenile model have guided us to explore the neurological mechanistic basis of the effect we find in an adult model while simultaneously testing the threshold of dose tolerance. Further experiments on a similar cohort of adult animals to measure blood flow and tissue oxygenation levels using spatial frequency and domain imaging. Results from this publication are expected to be concluded soon. The objective of this dissertation is to, in part, determine if the normal tissue sparing effect of FLASH irradiation reduces radiation-induced pathology of the BBB, further explicate the neuro-mechanistic basis of cognitive protection and determine the effects on tumor vascularization. Results produced from this body of work will not only provide additional justification for clinical translation, but it may also help illuminate key mechanistic differences between cancer and normal tissue that may one day be used for therapeutic gain.

    My field of focus has been the effects of ultra-high dose rate FLASH radiotherapy in pre-clinical models. In particular, my work has focused on both clinical and FLASH dose rates and their effect on the normal tissue, cognition, neuroinflammation, and the BBB. My graduate work led to numerous publications and is challenging the fundamental principles used in the field to improve .

      Cover page: FLASH irradiation protects the central nervous system
      • Article
      • Peer Reviewed
      UC Irvine Previously Published Works (2015)
      Exposure to the space radiation environment poses risks for a range of deleterious health effects due to the unique types of radiation encountered. Galactic cosmic rays are comprised of a spectrum of highly energetic nuclei that deposit densely ionizing tracks of damage along the particle trajectory. These tracks are distinct from those generated by the more sparsely ionizing terrestrial radiations, and define the geometric distribution of the complex cellular damage that results when charged particles traverse the tissues of the body. The exquisite radiosensitivity of multipotent neural stem and progenitor cells found within the neurogenic regions of the brain predispose the central nervous system to elevated risks for radiation induced sequelae. Here we show that human neural stem cells (hNSC) exposed to different charged particles at space relevant fluences exhibit significant and persistent oxidative stress. Radiation induced oxidative stress was found to be most dependent on total dose rather than on the linear energy transfer of the incident particle. The use of redox sensitive fluorogenic dyes possessing relative specificity for hydroxyl radicals, peroxynitrite, nitric oxide (NO) and mitochondrial superoxide confirmed that most irradiation paradigms elevated reactive oxygen and nitrogen species (ROS and RNS, respectively) in hNSC over a 1 week interval following exposure. Nitric oxide synthase (NOS) was not the major source of elevated nitric oxides, as the use of NOS inhibitors had little effect on NO dependent fluorescence. Our data provide extensive evidence for the capability of low doses of charged particles to elicit marked changes in the metabolic profile of irradiated hNSC. Radiation induced changes in redox state may render the brain more susceptible to the development of neurocognitive deficits that could affect an astronaut's ability to perform complex tasks during extended missions in deep space.
        Cover page: Persistent oxidative stress in human neural stem cells exposed to low fluences of charged particles
        • Article
        • Peer Reviewed
        UC Irvine Previously Published Works (2018)
        Clinical management of primary and secondary central nervous system (CNS) malignancies frequently includes radiotherapy to forestall tumor growth and recurrence after surgical resection. While cranial radiotherapy remains beneficial, adult and pediatric brain tumor survivors suffer from a wide range of debilitating and progressive cognitive deficits. Although this has been recognized as a significant problem for decades, there remains no clinical recourse for the unintended neurocognitive sequelae associated with these types of cancer treatments. In previous work, multiple mechanisms have been identified that contribute to radiation-induced cognitive dysfunction, including the inhibition of neurogenesis caused by the depletion of radiosensitive populations of stem and progenitor cells in the hippocampus. To explore the potential neuroprotective properties of a pro-neurogenic compound NSI-189, Long-Evans rats were subjected to a clinically relevant fractionated irradiation protocol followed by four weeks of NSI-189 administered daily by oral gavage. Animals were then subjected to five different behavioral tasks followed by an analysis of neurogenesis, hippocampal volume and neuroinflammation. Irradiated cohorts manifested significant behavioral decrements on all four spontaneous exploration tasks. Importantly, NSI-189 treatment resulted in significantly improved performance in four of these tasks: novel place recognition, novel object recognition, object in place and temporal order. In addition, there was a trend of improved performance in the contextual phase of the fear conditioning task. Importantly, enhanced cognition in the NSI-189-treated cohort was found to persist one month after the cessation of drug treatment. These neurocognitive benefits of NSI-189 coincided with a significant increase in neurogenesis and a significant decrease in the numbers of activated microglia compared to the irradiated cohort that was given vehicle alone. The foregoing changes were not accompanied by major changes in hippocampal volume. These data demonstrate that oral administration of a pro-neurogenic compound exhibiting anti-inflammatory indications could impart long-term neurocognitive benefits in the irradiated brain.
          Cover page: Remediation of Radiation-Induced Cognitive Dysfunction through Oral Administration of the Neuroprotective Compound NSI-189
          • Article
          • Peer Reviewed
          UC Irvine Previously Published Works (2017)
          [This corrects the article on p. 42 in vol. 9, PMID: 27375429.].
            Cover page: Corrigendum: Adenosine Kinase Inhibition Protects against Cranial Radiation-Induced Cognitive Dysfunction
            • Article
            • Peer Reviewed
            UC Irvine Previously Published Works (2019)
            Numerous clinical studies have established the debilitating neurocognitive side effects of chemotherapy in the treatment of breast cancer, often referred as chemobrain. We hypothesize that cognitive impairments are associated with elevated microglial inflammation in the brain. Thus, either elimination of microglia or restoration of microglial function could ameliorate cognitive dysfunction. Using a rodent model of chronic Adriamycin (ADR) treatment, a commonly used breast cancer chemotherapy, we evaluated two strategies to ameliorate chemobrain: 1) microglia depletion using the colony stimulating factor-1 receptor (CSF1R) inhibitor PLX5622 and 2) human induced pluripotent stem cell-derived microglia (iMG)-derived extracellular vesicle (EV) treatment. In strategy 1 mice received ADR once weekly for 4 weeks and were then administered CSF1R inhibitor (PLX5622) starting 72 h post-ADR treatment. ADR-treated animals given a normal diet exhibited significant behavioral deficits and increased microglial activation 4-6 weeks later. PLX5622-treated mice exhibited no ADR-related cognitive deficits and near complete depletion of IBA-1 and CD68+ microglia in the brain. Cytokine and RNA sequencing analysis for inflammation pathways validated these findings. In strategy 2, 1 week after the last ADR treatment, mice received retro-orbital vein injections of iMG-EV (once weekly for 4 weeks) and 1 week later, mice underwent behavior testing. ADR-treated mice receiving EV showed nearly complete restoration of cognitive function and significant reductions in microglial activation as compared to untreated ADR mice. Our data demonstrate that ADR treatment elevates CNS inflammation that is linked to cognitive dysfunction and that attenuation of neuroinflammation reverses the adverse neurocognitive effects of chemotherapy.
              Cover page: Attenuation of neuroinflammation reverses Adriamycin-induced cognitive impairments.
              • Article
              • Peer Reviewed
              UC Irvine Previously Published Works (2016)
              Cranial irradiation used to control CNS malignancies can also disrupt the vasculature and impair neurotransmission and cognition. Here we describe two distinct methodologies for quantifying early and late radiation injury in CNS microvasculature. Intravascular fluorescently labeled lectin was used to visualize microvessels in the brain of the irradiated mouse 2 days post exposure and RECA-1 immunostaining was similarly used to visualize microvessels in the brain of the irradiated rat 1-month post exposure. Confocal microscopy, image deconvolution and 3-dimensional rendering methods were used to define vascular structure in a ∼4 × 10(7) μm(3) defined region of the brain. Quantitative analysis of these 3D images revealed that irradiation caused significant short- and long-term reductions in capillary density, diameter and volume. In mice, irradiation reduced mean vessel volume from 2,250 to 1,470 μm(3) and mean vessel diameter from 5.0 to 4.5 μm, resulting in significant reductions of 34% and 10%, in the hippocampus respectively. The number of vessel branch points and area was also found to also drop significantly in mice 2 days after irradiation. For rats, immunostaining revealed a significant, three-fold drop in capillary density 1 month after exposure compared to controls. Such radiation-induced disruption of the CNS microvasculature may be contributory if not causal to any number of neurocognitive side effects that manifest in cancer patients following cranial radiotherapy. This study demonstrates the utility of two distinct methodologies for quantifying these important adverse effects of radiotherapy. Environ. Mol. Mutagen. 57:341-349, 2016. © 2016 Wiley Periodicals, Inc.
                Cover page: 3D surface analysis of hippocampal microvasculature in the irradiated brain.
                • Article
                • Peer Reviewed
                UC Irvine Previously Published Works (2020)
                Persistent vasculature abnormalities contribute to an altered CNS microenvironment that further compromises the integrity of the blood-brain barrier and exposes the brain to a host of neurotoxic conditions. Standard radiation therapy at conventional (CONV) dose rate elicits short-term damage to the blood-brain barrier by disrupting supportive cells, vasculature volume and tight junction proteins. While current clinical applications of cranial radiotherapy use dose fractionation to reduce normal tissue damage, these treatments still cause significant complications. While dose escalation enhances treatment of radiation-resistant tumors, methods to subvert normal tissue damage are clearly needed. In this regard, we have recently developed a new modality of irradiation based on the use of ultra-high-dose-rate FLASH that does not induce the classical pathogenic patterns caused by CONV irradiation. In previous work, we optimized the physical parameters required to minimize normal brain toxicity (i.e., FLASH, instantaneous intra-pulse dose rate, 6.9 · 106 Gy/s, at a mean dose rate of 2,500 Gy/s), which we then used in the current study to determine the effect of FLASH on the integrity of the vasculature and the blood-brain barrier. Both early (24 h, one week) and late (one month) timepoints postirradiation were investigated using C57Bl/6J female mice exposed to whole-brain irradiation delivered in single doses of 25 Gy and 10 Gy, respectively, using CONV (0.09 Gy/s) or FLASH (>106 Gy/s). While the majority of changes found one day postirradiation were minimal, FLASH was found to reduce levels of apoptosis in the neurogenic regions of the brain at this time. At one week and one month postirradiation, CONV was found to induce vascular dilation, a well described sign of vascular alteration, while FLASH minimized these effects. These results were positively correlated with and temporally coincident to changes in the immunostaining of the vasodilator eNOS colocalized to the vasculature, suggestive of possible dysregulation in blood flow at these latter times. Overall expression of the tight junction proteins, occludin and claudin-5, which was significantly reduced after CONV irradiation, remained unchanged in the FLASH-irradiated brains at one and four weeks postirradiation. Our data further confirm that, compared to isodoses of CONV irradiation known to elicit detrimental effects, FLASH does not damage the normal vasculature. These data now provide the first evidence that FLASH preserves microvasculature integrity in the brain, which may prove beneficial to cognition while allowing for better tumor control in the clinic.
                  Cover page: Maintenance of Tight Junction Integrity in the Absence of Vascular Dilation in the Brain of Mice Exposed to Ultra-High-Dose-Rate FLASH Irradiation
                  • Article
                  • Peer Reviewed
                  UC Irvine Previously Published Works (2016)
                  Clinical radiation therapy for the treatment of CNS cancers leads to unintended and debilitating impairments in cognition. Radiation-induced cognitive dysfunction is long lasting; however, the underlying molecular and cellular mechanisms are still not well established. Since ionizing radiation causes microglial and astroglial activation, we hypothesized that maladaptive changes in astrocyte function might be implicated in radiation-induced cognitive dysfunction. Among other gliotransmitters, astrocytes control the availability of adenosine, an endogenous neuroprotectant and modulator of cognition, via metabolic clearance through adenosine kinase (ADK). Adult rats exposed to cranial irradiation (10 Gy) showed significant declines in performance of hippocampal-dependent cognitive function tasks [novel place recognition, novel object recognition (NOR), and contextual fear conditioning (FC)] 1 month after exposure to ionizing radiation using a clinically relevant regimen. Irradiated rats spent less time exploring a novel place or object. Cranial irradiation also led to reduction in freezing behavior compared to controls in the FC task. Importantly, immunohistochemical analyses of irradiated brains showed significant elevation of ADK immunoreactivity in the hippocampus that was related to astrogliosis and increased expression of glial fibrillary acidic protein (GFAP). Conversely, rats treated with the ADK inhibitor 5-iodotubercidin (5-ITU, 3.1 mg/kg, i.p., for 6 days) prior to cranial irradiation showed significantly improved behavioral performance in all cognitive tasks 1 month post exposure. Treatment with 5-ITU attenuated radiation-induced astrogliosis and elevated ADK immunoreactivity in the hippocampus. These results confirm an astrocyte-mediated mechanism where preservation of extracellular adenosine can exert neuroprotection against radiation-induced pathology. These innovative findings link radiation-induced changes in cognition and CNS functionality to altered purine metabolism and astrogliosis, thereby linking the importance of adenosine homeostasis in the brain to radiation injury.
                    Cover page: Adenosine Kinase Inhibition Protects against Cranial Radiation-Induced Cognitive Dysfunction
                    • Article
                    • Peer Reviewed
                    UC Irvine Previously Published Works (2021)
                    Despite advancements in the radiotherapeutic management of brain malignancies, resultant sequelae include persistent cognitive dysfunction in the majority of survivors. Defining the precise causes of normal tissue toxicity has proven challenging, but the use of preclinical rodent models has suggested that reductions in neurogenesis and microvascular integrity, impaired synaptic plasticity, increased inflammation, and alterations in neuronal structure are contributory if not causal. As such, strategies to reverse these persistent radiotherapy-induced neurological disorders represent an unmet medical need. AM251, a cannabinoid receptor 1 reverse agonist known to facilitate adult neurogenesis and synaptic plasticity, may help to ameliorate radiation-induced CNS impairments. To test this hypothesis, three treatment paradigms were used to evaluate the efficacy of AM251 to ameliorate radiation-induced learning and memory deficits along with disruptions in mood at 4 and 12 weeks postirradiation. Results demonstrated that acute (four weekly injections) and chronic (16 weekly injections) AM251 treatments (1 mg/kg) effectively alleviated cognitive and mood dysfunction in cranially irradiated mice. The beneficial effects of AM251 were exemplified by improved hippocampal- and cortical-dependent memory function on the novel object recognition and object in place tasks, while similar benefits on mood were shown by reductions in depressive- and anxiety-like behaviors on the forced swim test and elevated plus maze. The foregoing neurocognitive benefits were associated with significant increases in newly born (doublecortin+) neurons (1.7-fold), hippocampal neurogenesis (BrdU+/NeuN+mature neurons, 2.5-fold), and reduced expression of the inflammatory mediator HMGB (1.2-fold) in the hippocampus of irradiated mice. Collectively, these findings indicate that AM251 ameliorates the effects of clinically relevant cranial irradiation where overall neurological benefits in memory and mood coincided with increased hippocampal cell proliferation, neurogenesis, and reduced expression of proinflammatory markers.
                      Cover page: The Cannabinoid Receptor 1 Reverse Agonist AM251 Ameliorates Radiation-Induced Cognitive Decrements
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