Placental extracts have been reported to have anti-oxidative and 
anti-inflammatory activities. Because there is increasing evidence that ionizing 
radiation induces the release of reactive oxygen species (ROS) and inflammatory 
cytokines, we examined the protective effects of a placental extract against 
radiation injury. C57BL/6 mice were exposed to 1 Gy of γ-ray radiation every day 
for 5 days, and placental extract (1 mg/day) was administrated orally soon after 
each exposure. At 2 days after the last irradiation, mice were euthanized to 
examine the numbers, colony-forming capacity, and DNA damage of stem/progenitor 
cells in the peripheral blood and bone marrow. To understand the related 
mechanisms, we also measured the levels of intracellular and mitochondrial ROS, 
and 8-OHdG in the plasma and urine, and IL-6 and TNF-α in the plasma. Compared 
with the placebo treatment, oral administration of placental extract 
significantly increased the number and colony-forming capacity, but decreased 
the DNA damage of bone marrow stem/progenitor cells. However, neither the levels 
of intracellular and mitochondrial ROS in bone marrow cells, nor the levels of 
8-OHdG in the urine and plasma significantly differed between groups. 
Interestingly, in comparison with the placebo treatment, placental extract 
significantly decreased the levels of the inflammatory cytokines IL-6 and TNF-α 
in the plasma. Placental extract significantly attenuated the acute radiation 
injury to bone marrow-derived stem/progenitor cells, and this protection is 
likely to be related to the anti-inflammatory activity of the placental extract.