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**79**

**Chapter 5**

**Abstract**

**1. Introduction**

the solar system.

Space Radiation-Induced

*Huihong Zeng, Mengzhen Yue and Lijian Shao*

Hematopoietic Stem Cell Injury

Space radiation is an unavoidable health risk during space activities.

**Keywords:** space irradiation, proton irradiation, oxygen irradiation, apoptosis,

Human spaceflight and exploration began in the 1960s. Manned spaceflight activities have continually expanded in frequency and scope since that time, and plans are now forming for long-duration flights to deep-space destinations. However, numerous risk factors have potential to negatively affect the astronauts' health during deep-space missions, especially microgravity and space radiation. Exposure of astronauts to space radiation is relatively unpredictable yet inevitable. Space radiation comes from two major sources: solar particle events (SPE) emanating from the sun and galactic cosmic rays (GCR) originating from sources outside

SPE mainly includes protons and can lead to moderate- to high-dose rate exposures to ionizing radiation during long-term space mission [1, 2]. Astronauts may receive cumulative doses from 1 to 3 gray (Gy) during an SPE [3, 4]. Especially,

GCR contains high atomic number and energy (HZE) particles, such as 56Fe, 28Si, 16O, 12C, and so forth. HZE particles are characterized by dense tracks of ionization, a property quantified as high-linear energy transfer (LET). The properties of HZE particles are consistent with their stronger toxicities and higher energy to normal tissues than photon and proton radiation [6, 7]. Previous studies have documented that the value of RBE in relation to γ-ray radiation was 1.25 for 56Fe, 1.4 for 28Si, and 0.99 for 12C using a mouse model [6, 8]. Among HZE particles, 56Fe has

reactive oxygen species, hematopoietic stem cells, bone marrow

proton radiation contributes to more than 80% of SPE [1, 2, 5].

Hematopoietic cells are sensitive to radiation including proton and oxygen radiation and so on. Understanding the mechanisms responsible for detrimental effects of space radiation is important to achieve countermeasures protecting hematopoietic stem cells (HSCs), which generates different hematopoietic populations. However, the biological effects of various sources of space radiation on HSCs are not understood well. Induction of cellular apoptosis, reactive oxygen species (ROS), and DNA damage upon space radiation is believed to be critical mediators for HSC damage. In this chapter, we will mainly discuss the biological effectiveness of proton and oxygen radiation on the numbers and function of HSCs. Space radiation-induced apoptosis, ROS, and DNA damage were examined as well, which will provide foundation to develop novel strategies protecting HSCs from space radiation.
