BIOLOGICAL EFFECTS of RADIATION DURING STRATOSPHERIC FLIGHTS

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BIOLOGICAL EFFECTS of RADIATION DURING
STRATOSPHERIC FLIGHTS
June 3-4 2008, Rome

• Mariano Bizzarri
• Dept. of Experimental Medicine
• University La Sapienza - Roma

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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.
Auguste Piccard
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
3
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.
4
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
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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.
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Are balloon-borne experiments reliable for
Microgravity and Radiation studies?
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g values are in fact only minimally reduced in
stratospheric flights
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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 10-3 g (with a free fall duration of
55 sec.)
This kind of facility is far to reach the
expected times required by biological
experiments
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RADIATION EXPOSITION in the ATMOSPHERE
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COMPOSITION of (primary) COSMIC RADIATION

• SOLAR WIND
• visible light
• ultraviolet and infrared radiation
• X-rays and ?-rays (photons)
• Electrons and protons (H nuclei) with few keV

• SOLAR FLARES
• sudden short-liven light phenomena
• associated with large emissions of charged
  particles (protons) solar protonic
• events (SPE)
• while SPE pose no threat to human beings on the
  ground on in low-orbit
• missions, SPEs constitute a serious risk for
  planetary missions

• GALACTIC COSMIC RAYS (GCR)
• protons (87)
• a particles (helium nuclei, 12)
• heavy ions (1) with Zgt2 (C, Fe) HZE particles

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The earths 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).
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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.
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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.
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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. 
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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.
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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 a/ß 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)
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RBE of different radiations
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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 if balloon-borne exposures
are limited to a spectrum significantly modified
by the shielding of the remaining atmosphere and
by the geomagnetic field
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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 a
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 (?-rays, neutrons,
mesons, electrons)
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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 particles. 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.
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BIOLOGICAL MECHANISMSof INTERACTION
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INFLUENCING FACTORS of RADIATION INJURY

• Dose rate and fractionation
• LET
• Radiation quality (RBE)
• Temperature
• Chemical modification
• Oxygen
• Radiosensitizing agents
• Radioprotective agents

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Radiation quality
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Survival curve for mammalian cells exposed to
high- (A) and low-LET (B) radiation
n
Dq
1-1/e
1-1/e
,037
D0
D0
B
A
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Radiosensitivity of cell in cell cycle
Relative Survivability
G1 S G2
G1
M
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.
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Mechanisms of damage at molecular level
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Relation between LET and action type

• 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

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Biochemical reactions with ionizing radiation

• DNA is primary target for cell damage from
  ionizing radiation

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Types of radiation induced lesions in DNA
Base damage
Single-strand breaks
Double strand breaks
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Direct action
Ionizing radiation RH R- H
?
?
Bond breaks
OH I R C NH imidol (enol)
O II R C NH2 amide (ketol)
Tautomeric Shifts
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Indirect action
OH-
H
O
H
e-
X ray ? ray
H
Ho
P
OHo
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Lifetimes of free radicals
RO2o
HO2o
Ho
OHo
3nm
OHo
Ho
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
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Effects of oxygen on free radical formation

• Oxygen can modify the reaction by enabling
  creation of other free radical species with
  greater stability and longer lifetimes
• H0O2 ? HO20 (hydroperoxy free radical)
• R0O2 ?RO20 (organic peroxy free radical)

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OTHER EFFECTS
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Effect of radiation on cell Cell kinetics
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RADIATION-INDUCED DAMAGE in CELL
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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
possible.  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.
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First reports on harmful effects of radiation

• First radiation-induced skin cancer reported
• in 1902
• First radiation-induced leukemia described
• in 1911

• 1920s bone cancer among radium dial painters
• 1930s liver cancer and leukemia due to
  Throtrast administration
• 1940s excess leukemia among first radiologists

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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
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• HIGHER PRIORITY
• assessing the carcinogenic risk
• effects on central nervous system (CNS) of
  exposure to GCR
• how to extrapolate experimental data from
  rodents to humans

• LOW-PRIORITY RECOMMENDATIONS
• estimate the effects of chronic exposure to GCR
  on fertility and cataract
• formation
• to determine whether drugs could be used to
  protect against the effects
• of exposure to GCR
• to assess whether biological response to GCR
  depend only on the Linear
• Energy Transfer (LET) or on the values of the
  atomic number and energy
• separately

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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 IMPOSSIBLE
TECHNOLOGICALLY
H. PLANEL, 2004
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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 Stategy Report
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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
GCR
stratosphere
heavy ions
biological layer
emulsion
BIOSTACK
STRATOSPHERIC BALLOONS
GENETIC and METABOLOMIC ANALYSIS
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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.
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HOW TO STUDYGENETIC and METABOLICALTERATIONS
in RADIATIOPN-EXPOSED BIOLOGICAL SAMPLES?HOW
TO COPE WITH COMPLEXITY ?
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BIOLOGICAL PROCESSES
NETWORK
genes
proteins
metabolites
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PROTEOMICS
CELL CULTURE
GENOMICS
CELL CYCLE APOPTOSIS DIFFERENTIATION STRUCTURE
METABOLOMICS
MATHEMATICAL NON-LINEAR MODELLING of the
BIOLOGICAL NETWORK
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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 monitored and
can give important information about the
consequences of the genetic modification on the
cell.
NMR- based METABONOMICS is the technique used to
characterize the changes in the metabolome of the
cell.
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.thanks