Impact of low and high doses of ionizing radiation on the hematopoietic system: molecular mechanisms of cellular response and clinical manifestations

Bulgarian Medical Journal, 2025, 19(2), 16-22.

G. Racheva

Research Laboratory of Radiation Protection and Radiobiology, Military Medical Academy ‒ Sofia

Abstract. The hematopoietic system is among the most radiosensitive systems in the human organism. Cellular responses to ionizing radiation, regardless of dose magnitude, share common regulatory mechanisms, particularly in the control of oxidative stress. Oxidative stress plays a critical role in cellular senescence and in the dysregulation of stem cell proliferative capacity. Exposure to high doses of ionizing radiation (≥ 1 Gy) leads to significant physiological consequences, with severity increasing proportionally with dose. Acute hematopoietic syndrome, a subsyndrome of acute radiation syndrome, typically manifests following exposure to doses between 2 and 6 Gy. Clinical symptoms emerge within hours postexposure, progressively exacerbating due to severe impairment of hematopoietic organs, vasculature, and bone marrow. Prompt diagnosis and therapeutic intervention are essential for mitigating disease progression and facilitating recovery. Conversely, prolonged exposure to low doses of ionizing radiation is associated with delayed stochastic effects, often manifesting long after initial exposure. Although these effects do not exhibit a direct dose-response relationship, the risk of long-term hematopoietic dysfunction increases with cumulative radiation dose. In all cases, ionizing radiation exposure necessitates comprehensive biodosimetric assessment, precise dose estimation, early diagnosis, and the implementation of effective therapeutic strategies. This review aims to examine systematically the comparative effects of highand low-dose ionizing radiation on the hematopoietic system, with a particular emphasis on the molecular mechanisms influencing stem cell function and the potential clinical pathologies that may arise.

Key words: hematopoietic system, ionizing radiation, hematopoietic syndrome, stochastic effects, leukemia

Address for correspondence: Galina Petrova Racheva, PhD, Research Laboratory of Radiation Protection And Radiobiology, Military Medical Academy, Bg – 1606 Sofia, 3 ”Georgi Sofiyski” st., e-mail: , ORCID ID: 0009- 0006-3269-0992.