Large amounts of radionuclides were released in the environment after
the Chernobyl (1986) or Fukushima-Daichii (2011) nuclear accidents, and mostly
cesium 137. Populations living in contaminated territories are chronically
exposed to radionuclides by ingestion of contaminated food. There is a real
interrogation about the potential effects that could be induced following such
ionizing exposure on physiological functions in the long term.
Concerning the cardiovascular system, there is a correlation between the
irradiation dose and the appearance of cardiovascular diseases. However, when
we focused on post-accidental situations, with a low dose exposure, available
data are not all in accordance, due to multifactorial aspect of these
pathologies. Epidemiological results should be interpreted carefully.
Thus, the aim of my thesis is to complete epidemiological studies about
chronic internal γ low
dose exposure, using cesium 137, in an atheromatous context. Atherosclerosis
and its consequences are known to be the main cause of mortality/morbidity in
industrialized countries.
Predisposed animals (ApoE-/- mice) were exposed to 137Cs
through the drinking water. The concentration range was 4 to 100 kBq.L-1,
to surround concentration found in contaminated territories around Chernobyl.
Exposure times were 3, 6 or 9 months to follow atherosclerosis progression.
After 3 months exposure, for the early stages, mice exposed to the highest
dose presented an increase in some inflammatory cytokines, notably IFN-γ and VCAM-1, with an intimal-medial
thickness increased compared to non-exposed animals. Moreover, at this time
exposure, we noticed concomitant variation of genic expression of pro and
anti-oxydative enzymes (p47, p67, GPx). These effects are only transient and do
not perdure over the time. Indeed, after 6 and 9 months exposure, atheromatous
plaque observed in the aortic sinus, present more stability parameters than the
control group (collagen), with also a decrease in pro-inflammatory profile
cytokines expression (CRP, TNF-α, MCP-1 et IFN-γ),
and MMPs expression, and increase in GPx activity compared to the control
group.
All together, these results suggest that chronic internal exposure to
low dose ionizing radition with 137Cs do not potentiate
atherosclerosis progression. Such exposure induces an adaptive response along
the experimental process, with an amelioration of atheromatous plaque
phenotype, acting on the balance of pro/anti-inflammatory cytokines, pro/anti
oxydant system.
