Radiobiology 6 MCQ

Ionizing Radiation-Induced Metabolic Oxidative Stress and Prolonged Cell Injury

• Ionizing radiation absorption by cells directly disrupts atomic structures, triggering chemical and biological alterations.
• This damage can also occur indirectly through water radiolysis, generating reactive chemical species that harm nucleic acids, proteins, and lipids.
• Both direct and indirect radiation effects lead to biochemical and molecular signaling events, potentially repairing the damage or causing permanent physiological changes or cell death.
• Early biochemical modifications, occurring during or shortly after exposure are thought to primarily cause radiation damage.
• However, oxidative changes continue to develop for days or months following exposure.
• This is due to continuous generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS).
• RNS, derived from nitric oxide, is a family of antimicrobial molecules.
• Radiation-induced oxidative stress may spread from targeted cells to neighbouring (bystander) cells through intercellular communication.
• Nitric oxide (NO) is an intra- and extracellular messenger, mediating diverse signaling pathways in target cells and playing a role in neuronal signalling, immune response, inflammation, ion channels, phagocytosis, penile erection, and cardiovascular homeostasis.
• Cardiovascular system is affected by NO production, affecting cardiovascular tone, myocardial contractivity, cell proliferation, and inhibiting platelet activity.
• Cellular biochemical machinery responsible for free radical and reactive species production can remain disrupted for minutes, hours, days, and even years post-exposure.
• Reactive oxygen and nitrogen species were previously associated with oxidative damage and disease development.
• Recent evidence suggests their crucial role in intracellular signalling cascades.
• Deleterious effects arise from the formation of highly reactive secondary species (e.g., hydroxyl radical, peroxy nitrite), from the reaction of primary species (like superoxide radical, nitric oxide) and a transition metal.
• These secondary species damage a wide array of biomolecules.
• Primary reactive species (e.g., superoxide) are well-controlled by enzymes (like superoxide dismutase, catalase).
• Reversible reactions allow them to be essential components of intracellular signaling.

Outline of Ionizing Radiation Effects

• Introduction: Briefly discusses the effects of ionizing radiation on cells.
• Primary effects of ionizing radiation:
  • Water radiolysis and generation of reactive oxygen species (ROS).
  • Generation of reactive nitrogen species (RNS).
  • Ionizing radiation track structure and induced biological effects.
  • Endogenous and radiation-induced DNA alterations.
• Reactive oxygen species and cellular homeostasis: Explains the role of ROS in cellular processes.

Stages of Ionizing Radiation

• Physical Stage: Energy deposition from incident radiation generates secondary electrons.
• Physicochemical Stage: Radicals and molecules are distributed non-uniformly within a track structure. Secondary electrons lose energy, becoming trapped and hydrated. Trapped electrons are captured by surrounding water molecules forming solvated electrons.
• Non-homogeneous Chemistry Stage: Reactive chemical species diffuse and react with each other or their surroundings.
• Biological Stage: Cells respond to the damage and biological responses affecting long-term consequences occur.

Explore the effects of ionizing radiation on cellular structures and metabolism. This quiz delves into the mechanisms of direct and indirect damage, the role of reactive species, and the long-term consequences of oxidative stress. Understand how these processes affect biochemical and molecular signaling in cells.