Radiation dosing: During deep space missions, astronauts will be exposed to a protracted mix of high-linear energy transfer (LET) (densely ionizing) and low-LET (sparsely-ionizing) radiations. While the low-LET radiations dominate by dose, it is anticipated that the high-LET radiations will dominate most radiation risks. This work therefore focuses on high-LET radiation exposures, with low-LET photon exposures as a reference radiation. The mission-relevant high-LET radiations are a mix of galactic cosmic rays (GCR) heavy ions as well as a significant component of fast neutrons, and our studies will use acute and fractionated fast neutrons generated at the Columbia University Radiological Research Accelerator Facility (RARAF) as a convenient surrogate for the overall high-LET component of shielded GCR. The rationale for using fast neutrons in this context is that the neutron energy distribution and high-LET distributions from the high-LET GCR component in a spacecraft in deep space are similar to those produced by the neutron facilities at our Columbia RARAF accelerator facility. In Year 3, as we will conduct multiple campaigns at Brookhaven National Labs, and continue to assess our “comparison” doses at Columbia RARAF and to use our photon exposures at Columbia’s Radiological Research Center.

Drug delivery and development: CS-PEI(PBA)-based nanocarriers is that they will provide a versatile platform for oral delivery of biologics with excellent efficiency, reduced toxicity, and prolonged protection of cells and tissues from irradiation, as compared to the commonly used polyethyleneimine and chitosan-based nanocarriers. The CS-PEI(PBA) polymer was shown to be tunable by modulating the grafting ratio of PEI and PBA group to achieve optimal efficacy and minimized cytotoxicity. Another impact of the tailored CS-PEI(PBA) nanocarriers is their potential for scavenging radiation-generated DAMPs. Radiation stress may induce DNA damage response and DNA repair, apoptosis, or immune responses. Thus, the incorporation of PBA and PEI moieties in the drug carrier design presents an intriguing strategy for controlling drug release in response to specific amounts of reactive oxygen species (ROS) and scavenging the DAMPs to suppress the cytokine storms. By virtue of its large size, pegfilgrastim exhibits size-based limitations in the penetration of biological barriers. The CS-PEI(PBA) polymer may actively improve the transcellular absorption of the pegfilgrastim. Further, this system may utilize oral delivery of PF for patient compliance and convenience.

“Astronaut-on-a-chip”: As we are conducting studies on assessing the effects of radiation on engineered tissues and establishing the full astronaut-on-a-chip system, we are showing the immense promise of in vitro human models for answering difficult questions in space health and biology. Although our models can only recapitulate certain aspects of radiation biology, we are hoping our efforts identify novel biomarkers and targets for the development of new therapeutics to protect astronauts in a potential Mars mission. In our described studies, we are targeting organ functions in those most sensitive to radiation damage (bone marrow), those with anticipated chronic changes (heart muscle), those that are a site for metabolism (liver), and those that may recapitulate continuous remodeling and tissue development (vasculature). Further, our platform and techniques are uniquely suited to answer new questions that arise in future space travel work, and are already overlapping with questions that have risen in related fields, such as cancer. We hope to continue to improve our organ-on-a-chip systems to better recapitulate biology, as well as better recapitulate the patient-specific nature of human health research.

AIM 1: ESTABLISH A HUMAN TISSUE MODEL TO STUDY MISSION-RELEVANT SPACE RADIATION.

Our human tissue platform consists of bone marrow, heart muscle, and liver that are connected by vascular perfusion containing circulating immune cells. All tissues will be derived from the same iPS cells for individualized approaches to study the effects of space radiation and innovative countermeasures during long-term flights (e.g. Mars mission). Platform integration is enabled by the establishment of the optimal environment for each tissue, and separation of the tissue and vascular compartments by a selectively permeable endothelium, as in the body. Cell damage in each tissue, including the hematopoietic system, was evaluated over a period of 14 days, both for the individual tissues and for the integrated platform. In Aim 1, investigated the effects of low-LET photon radiation (acute exposure) and high-LET fast neutrons (acute and protracted exposure), both with a two-week follow-up. Our goal was to define mission-relevant dose and fractionation protocols for the month-long ground studies predictive of whole-body responses.

AIM 2: TEST ADVANCED COUNTERMEASURES AGAINST ACUTE AND PROTRACTED HIGH-LET RADIATION.

Protective countermeasures were based on pegylated granulocyte stimulating factor (pegfilgrastim, PF), an FDA-approved modulator of hematopoiesis. PF was tested in isolation, and in the platform’s vascular flow in a naked form (to establish the dose and pharmacokinetics required for effective protection) and via controlled release nanoparticles (to achieve similar protection via oral delivery). The nanoparticles was designed to provide sustained release of PF in systemic circulation, with bone marrow and liver as target tissues. Both approaches are motivated by the need for oral (i.e. not weekly injected) countermeasure delivery.

AIM 3: VALIDATE ADVANCED COUNTERMEASURES BY TESTING WITH SIMULATED GALACTIC COSMIC RAYS (GCRsim).

Studies in Aim 1 and Aim 2, done in parallel, resulted in the detailed assessment of the effects of radiation on highly susceptible human tissues, and the effectiveness of the proposed radiation protection measures. In Aim 3, we demonstrated feasibility of conducting these studies in an individualized manner by pursuing the “astronaut on a chip” approach enabled through stem cell and tissue engineering technologies. Our goal here was to measure radiation damage under simulated galactic space radiation (acute and protracted) at the NASA Space Radiation Laboratory (NSRL). We demonstrated the utility of engineered human tissue models for studying the effects of high energy radiation, designed to mimic those seen in long-range space travel to Mars. We believe that our study is the first to use engineered human tissue models in a multi-OoC context for studying simulated galactic cosmic and neutron radiation exposures, and to establish a proof-of-concept platform and framework for using engineered human tissue models for mitigating other NASA “Red Risks” on Earth. Personalizing these model systems would allow for unprecedented understanding of how an astronaut’s individual organ health may be impacted by space travel. It is critical, however, to compare data obtained in humanized radiation studies on Earth with those of past accidental nuclear exposures and animal studies. Human data have emerged from short-term studies of human cells in LEO experiments on the ISS, as well as data collected from astronauts after returning to Earth.