Radiation Exposure, Too many Questions
Recent events in Japan have caused the world to focus on unintended radiation exposure.
Exposure to radiation can be a cause for concern, especially if radiation levels reach or exceed 1 Gy. Radiation targets rapidly proliferating cells of the body. Cells of the hematopoietic system (bone marrow) and the gastrointestinal (GI) tract are 2 such cell types. Damage to these cells initiates programmed cell death (apoptosis).
First responders, healthcare professionals, and citizens lack sufficient medications to prevent cellular damage and death due to exposure to significant levels of whole-body irradiation. Agents that protect from radiation exposure are divided into 3 categories:
- Agents that must be administered before cellular exposure to ionizing radiation or “radio-protectants;”
- Agents that can be administered after exposure and which will forestall the cascade of events leading to radiation-induced damage or “radio-mitigants;” and
- Agents that can facilitate or promote endogenous recovery from radiation-induced damage or “regenerators.”
To date, the US FDA has approved a few radio-protectants.
- Prophylactic potassium iodide to protect the thyroid from exposure to excess I 132,
- Laxatives and chelating agents (i.e. diethylene triamine pentaacetic acid (“DTPA”), etc decrease exposure by binding and promoting urinary excretion,
- Absorbing agents such as Prussian Blue to limit GI absorption or high oral doses of calcium to compete with intestinal absorption of milk contaminated with strontium 90,
- There are a small handful of agents presently under development as radio-mitigants.
The Bottom Line: Japan is looking for answers; all part of the ripple effect and havoc from the nuclear power plant’s 6 reactors which led to the release of unknown quantities of radioactive vapors. Experts do know that direct radiation exposure (without a conduit like food or water) can be deadly. Radiation doses ingested through food is really very poorly understood. In the current crisis, the iodine-131 isotope is a by-product of nuclear reactors. Iodine-131 differs from regular iodine because it is radioactive. It collects in the human thyroid gland because the thyroid readily absorbs iodine and assumes the iodine-131 strain is like any other form. The thyroid produces some of the body’s most important hormones, which play a role in functions such as food metabolism and regulation of body temperature. To fight off iodine-131, doctors typically prescribe iodine pills that fill up the thyroid so there’s no more room and force the iodine -131 out of the body. There’s little evidence, too, that consuming radiation-contaminated food will cause genetic mutations that can be passed on to one’s offspring. Iodine’s 8 day half-life, the time it takes for a radioactive isotope to decay by half, means that in eight days, half of its radioactivity level will disappear. By contrast, cesium-137 has a half life of about 30 years, so it lingers for much longer. Stem cells therapies have yet to make it into mainstream civilian medicine, but that hasn’t stopped the US military betting on them to save its personnel if there’s a nuclear explosion or radiological attack. The DoD had funded biotech firms to develop a treatment for radiation sickness based on stem cells extracted from the bone marrow of healthy adult donors. Prochymal by Osiris (OSIR) MUST be fast-tracked by the FDA to provide for humanitarian purposes to alleviate high doses of radiation that “could” damage the DNA of fast-dividing cells in the gut and bone marrow of affected Japanese populace. Cellerant (a private company) is also developing a treatment (CLT-008) for chemotherapy induced neutropenia, protection following exposure to acute radiation (see 3/28/11 blog). In ARS applications, CLT-008 is intended to provide hematopoietic cellular support after exposure to ionizing radiation from a nuclear or radiological weapon, or from a nuclear accident. Cellerant has conducted various preclinical studies to indicate that a single administration of CLT-008 could provide effective treatment for ARS in an emergency situation, and could be administered up to 5 days post-exposure to radiation.
