June 3-4 2008, Rome. BIOLOGICAL EFFECTS of RADIATION DURING STRATOSPHERIC FLIGHTS. Mariano Bizzarri Dept. of Experimental Medicine University La Sapienza - Roma. On 4 February 1902, Robert Falcon Scott became the first man to go up in a balloon over Antarctica.
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June 3-4 2008, Rome
BIOLOGICAL EFFECTS of RADIATION DURING STRATOSPHERIC FLIGHTS
Dept. of Experimental Medicine
University La Sapienza - Roma
On 4 February 1902, Robert Falcon Scott became the first man to go up in a balloon over Antarctica.
It was a modest balloon filled with 226 cubic metres of hydrogen. It rose 243 metres enough for Scott,
who was precariously perched in a basket below the balloon, to see over the edge of the Ross Ice Shelf,
the biggest ice shelf in the world.
In 1930 he built a balloon to study cosmic rays.
In 1932 he developed a new cabin design for balloons
and in the same year ascended by balloon in a
pressurised gondola to 16,916 mt
In the ManHigh II Program, experiments were
conducted to investigate the nearspace
environment and its effects on humans
in preparation for spaceflight.
The Strato-Lab Program was designed to conduct aeromedical research on flight crews, astrophysical investigations, and geophysical observations.
In addition, studies of air pollutants and spectrographic and photographic studies of
the Sun and Venus were conducted.
Major Simons piloted the second Manhigh flight on August 19 - 20, 1957.
He climbed 101,516 feet above the Earth using a 3-million cubic foot balloon.
Simons was the first person to see a sunset and a sunrise from the edge of space
Stratospheric balloon, program ODISSEA
Cosmicradiation and lymphocyte activation
Stratospheric balloon, program ODISSEA (balloon failure)
Cosmicradiation and lymphocyte activation
By 1970, there were over 500 yearly scientific highaltitude manned and unmanned balloon launches in the United States.
These flights were used to study aeronomy, solar physics, astronomy, magnetic fields, cosmic dust, biology, and other areas of scientific interest.
Are balloon-borne experiments
reliable for Microgravity and
g values are in fact only minimally reduced in stratospheric flights
A microgravity payload module (MIKROBA) released from a balloon at the
peack attitude was made operational in 1990 and can offer a microgravity
level of 10-3g (with a free fall duration of 55 sec.)
This kind of facility is far to reach the expected
times required by biological experiments
COMPOSITION of (primary) COSMIC RADIATION
The earth’s atmosphere is bombarded
by high-energy particles from our galaxy
(primary cosmic radiation). In the upper
atmospheric layers, these particles react
with air molecules. As a result of nuclear
reactions, a great number of secondary
particles (secondary cosmic radiation) is
formed. Some of these secondary particles
decay again, are absorbed in the atmosphere
or possibly penetrate into the earth. The
radiation fluence generated in this way
is subdivided into three main components:
electrons/photons, hadrons (nuclear components)
and myons (heavy electrons).
The figure shows that the relative dose
fraction at flight altitudes (10 Km) mainly
originates from neutrons (n) and electrons
and photons (e-) with a smaller proton
component (p), whereas myons (µ) and
a small fraction of neutrons mainly
contribute to the dose on the ground level.
The unit of dose is the gray (abbreviated Gy) which represents the absorbtion
of an average of one joule of energy per kilogram of mass in the target
material. This new unit has officially replaced the rad, an older unit (but still
seen a lot in the radiation literature). One gray equals 100 rads. Absorbed
dose was originally measured for x-rays and gamma radiation but has been
extended to describe protons and HZE particles. When used in predicting
biological damage, a further distinction must be made as to the "quality"
of the radiation, in order to evaluate the “biological impact”.
Although the Absorbed Dose of of some radiation may be measured, another
level of consideration must be made before the biological effects of this
radiation can be predicted.
The problem is that although two different types of heavy charged particle
may deposit the same average energy in a test sample, living cells and tissues
do not necessarily respond in the same way to these two radiations.
This distinction is made via the concept of Relative Biological Effectiveness
(RBE) which is a measure of how damaging a given type of particle is when
compared to an equivalent dose of x-rays.
Basically, the RBE is determined by comparing the damage of the radiation to
the cells/tissue of interest to that with an equal dose of gammas or x-rays.
For example, the RBE of alpha particles has been determined to be 20
(apparently not very dependent on the energy of these particles). This
means that 1 Gy of alphas is equivalent to 20 Gy of gammas/xrays.
Another way to say this is to use a new unit, the sievert (Sv) which measures
the Dose Equivalent (the old unit is the rem; 1 sievert = 100 rem).
Thus 1 Gy absorbed dose of alpha particles is 20 Sv dose equivalent.
The sievert is the unit used in NASA's radiation limits for humans in
Low Earth Orbit.
The measurement of the clonogenic survival is a first step, to
determinate the influence of a radiation on cells. Photon irradiation
leads in most cases to a shouldered dose-effect curve that can be
described by the linear-quadratic equation
The shoulder that is characterised be the ratio α/β is a measure for the
repair capacity of the cell.
Particle irradiation leads to a reduction in the shoulder with increasing
LET up to pure exponential curves. This is caused by the higher local
ionisation density in the ion track. The resulting higher efficiency of
the ions is described by the relation Dphoton/Dparticle leading to the same
biological effect and is called Relative Biological Effectiveness (RBE)
Although the potential hazards to living systems from the heavy nucleii component of galactic cosmic radiation was recognized, very little active
research was conducted until the crews of Apollo 11 and subsequent Apollo missions reported experiencing a visual light flash phenomenon
Exposure to HZE particles during a spaceflight mission offers several unique advantages, principally, exposure to the primary spectra modified only by the interactions in the relatively lightly shielded space vehicle.
It is a matter of debate ifballoon-borneexposures are limited to a spectrum
significantly modified by the shielding of the remaining atmosphere and by the geomagnetic field
The crew of a spacecraft is exposed to secondary cosmic radiation:
while the walls of a spacecraft stop most primary GCR particles,
some can penetrate the wall material.
The resulting interactions yeld secondary particles of the same
nature but weaker in energy, as well as neutrons and X-rays.
On the ground, while certain protons do reach the surface of Earth,
most of the GCR is stopped by the atmosphere: α particles and heavy
ions practically disappear at an altitude of 20,000 m, but HZE particles
can penetrate deeper.
All of these particles collide with the oxigen and nitrogen atoms of
the atmosphere. The resulting interactions give rise to electromagnetic
radiation (γ-rays, neutrons, mesons, electrons)
The high atomic number-high energy particle component (HZE particles) of galactic
cosmic radiation was discovered in 1948 and radiobiologists soon became concerned
as to the effect this new type of ionizing radiation might have upon living systems
exposed to it.
Soon after discovery of the HZE particles, Tobias in 1952 predicted that a visual light
flash sensation could be experienced by individuals exposed to these particles.
There followed direct experimental evidence of the character and effectiveness of HZE
Chase (1954) describes graying of hair in balloon-borne black mice.
Eugster (1955) demonstrated cellular death by single hits of heavy ions on Artemia Salina
eggs; and similar effects were reported by Brustad (1961) on maize embryos.
Brain injury studies were attempted by Yagoda and co-workers (1963) and by Haymaker
and co-workers (1970) in balloon-borne mice and monkeys, respectively.
G1 S G2 G1
Relative survivability of cells irradiated in different phases of the cell cycle. Synchronised cells in late G2 and in mitosis (M) showed greatest sensitivity to cell killing.
Direct action is predominant with high LET radiation, e.g. alpha particles and neutrons
Indirect action is predominant with low LET radiation,e.g. X and gamma rays
DNA is primary target for cell damage from ionizing radiation
Double strand breaks
Ionizing radiation + RH R- + H+
R – C = NH
R – C = NH2
Because short life of simple free radicals (10-10sec), only those formed in water column of 2-3 nm around DNA are able to participate in indirect effect
Oxygencan modify the reaction by enabling creation of other free radical species with greater stability and longer lifetimes
H0+O2 HO20 (hydroperoxy free radical)
R0+O2 RO20 (organic peroxy free radical)
DAMAGE in CELL
ACUTE EFFECTS The acute, or more immediately-seen effects of radiation can affect the
performance astronauts. These effects include skin-reddening,
vomiting/nausea and dehydration. Other tissue and organ effects are
LONG TERM EFFECTS
Given that only moderate doses of radiation are encountered (and thus acute
effects are not seen) the long-term effects of radiation become the most
important to consider. The passage of an energetic charged particle through
a cell produces a region of dense ionization along its track. The ionization of
water and other cell components can damage DNA molecules near the particle
path but a "direct" effect is breaks in DNA strands. Single strand breaks
(SSB) are quite common and Double Strand Breaks (DSB) are less common
but both can be repaired by built-in cell mechanisms.
"Clustered" DNA damage, areas where both SSB and DSB occur can lead to cell
death. DSB due to ionizing radiation (especially the high LET radiation found
in space) is an important component of long-term risk .
A more dangerous event may be the non-lethal change of DNA molecules which
may lead to cell proliferation and eventually to malignancy.
Spatial Agency Reports“gives estimates of the uncertainty in the health
(carcinogenic, mutagenic) risks from HZE particles.
The reason is that there is only ground-based carcinogenesis experiment on
cancer induction in animals.”
Furthermore “quantitative designs of appropriate countermeasures, such as
shielding, and biological or biochemical schemes to reduce the damage from
HZE particles are very rudimentary”.
The NASA Strategy Report“recommended a comprehensive research
program to determine the risks from different types and energies of HZE
particles and from high-energy protons for a number of biological end points”
“DUE TO ITS EXTENSIVE ENERGY SPECTRUM AND
HETEROGENEOUS COMPOSITION, COSMIC RADIATION IS
DIFFICULT TO REPRODUCE ON THE GROUND.
ACCELERATORS CAN ONLY GENERATE RADIATION OF A
FIXED NATURE AND ENERGY.
THIS DIFFICULTY IS ENHANCED AS COSMIC RADIATION AND
WEIGHTLESSNESS MAY HAVE COMBINED EFFECTS.
SIMULATION OF THESE TWO FACTORS IS CURRENTLY
H. PLANEL, 2004
The major facility for these experiments is the Alternating Gradient
Synchroton (AGS) at Brookhaven National Laboratory but it is available
for only two to four weeks per year.
At the present rate of progress it would take 20 or more years to
complete the high-priority experiments recommended in the
HENCE, NEW FACILITIES and NEWER METHODOLOGICAL
APPROACHES ARE NEEDED I N ORDER TO ENSURE A
RELIABLE UNDERSTANDING of THE BIOLOGICAL EFFECTS
RELATED to HZE PARTICLES and GCR
GENETIC and METABOLOMIC ANALYSIS
The new 120-metre-diameter ballloons will make possible long
duration experiments in biological fields, enabling studies and
performances until now never reached.
This balloon should fly for about 100 days (with relative costs)
at an altitude of 40/50.000 m.
Unlike the conventional balloons, the new balloons are sealed to
keep the helium at high pressure and their volume constant.
MATHEMATICAL NON-LINEAR MODELLING
of the BIOLOGICAL NETWORK
Determination of the biological system metabolites defines its metabolome, in other words its metabolic fingerprint, which allows us to identify and to dynamically follow its growth and/or its responses to environmental conditions.
The changes in metabolite levels due to altered gene expression can be monitoredand can give important information about the consequences of the genetic modification on the cell.
NMR- basedMETABONOMICS is the technique used to characterize the changes in the metabolome of the cell.