Graz conference report (fwd)

[Jan Hollan <jhollan@amper....muni.cz>]

sorry for fwding the excellent report by Thomas so late...

reminding that our posters are at http://amper.ped.muni.cz/noc/english

jenik

---------- Forwarded message ----------
Date: Fri, 19 Nov 2004 23:52:02 +0100
From: Thomas Posch <posch@astro....ac.at>

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William Hrushesky, in his talk on the influence of biological rhythms on
cancer, pointed out that normal skin cells are not subject to mitosis
during nighttime; neither are cancer cells. But during daytime, cancer
cells grow 2-3 times faster than normal cells. This indicates that
biological rhythms are essential for cancer development. In
chemotherapy, it has turned out that the time of the day when it is
applied is very decisive for the success of the treatment.
Solar radiation turned out to have a strong influence on the cancer
formation and growth rate, not only for skin cancer, but in general.
Many kinds of cancer have there maximum formation rate in August
(northern hemisphere).

Elizabeth Filipski also talked on circadian disorder and cancer growth.
She presented results of experiments with "jet-lagged mice", i.e. mice
that have been exposed to irregular rhythms of light and darkness
(instead of regular light-darkness rhythms). While mice without this
artificially introduced circadian disorder show very regular curves of
the blood temperature as function of the daytime, mice with circadian
disorder - the so-called "jet-lagged mice" - have very irregular curves
of the blood temperature as a function of time. Accordingly, the tumor
growth rate in the jet-lagged mice is significantly larger than in
normal mice. The conclusion is that chronic jet lag alters circadian
physiology and molecular clock expression, but also accelerates tumor
growth. (Note that chronic jet lag is just one particular form of
circadian disorder.)

George C. Brainard held a very interesting talk on "Photoreception for
human melatonin regulation. Relevance of light intensity and spectrum".
He pointed out that already in 1987, the "light/melatonin/cancer
hypothesis" has been presented. However, in the 1980s, illuminance
levels of about 2500 lux (!) have been considered as necessary in order
to suppress nocturnal plasma melatonin production. By contrast, recent
experiments showed that illuminance levels of about 1.3 lux (!!) are
sufficient to suppress melatonin production, if the light source has a
spectrum with a large output in the 446...472nm range, where the
receptors regulating melatonin production are most sensitive. This is
clearly a very important argument against bright (esp. "white / bluish")
artificial light at night! 5 lux emitted at 460nm are affecting the
melatonin production stronglier than 68 lux at 555nm, according to G.C.
Brainard. This is true not only for humans, but also for many animal
species.

Richard Stephens talked about "Light in the Built Environment: Circadian
Disruption in Endocrine Disruption". He made a very positive mention of
IDA in his talk. In the introduction, he pointed out that even the
"Nature" magazine had published an article entitled "Biologists demand:
turn down lights". Subsequently, he focussed on the mechanism
responsible for the regulation of the circadian rhythm. How does the
pineal gland "see" light? Interestingly, the visual photoreceptors are
not required for that, but only the retina. Berson et al., in 2002,
discovered intrinsically photosensitive retinal ganglion cells (ipRGCs)
responsible for the regulation of the circadian rhythm (via melanopsin,
not via rhodopsin). Stephens, too, pointed out that the action spectrum
of the ipRGCS peaks in the blue, implying that quite low light levels
suffice for melatonin suppression if the light source emits a
significant fraction of its radiation in the lambda<500nm range.

Christian Bartsch went one step further and examined the question
whether melatonin can be used as a drug to stop the growth of already
formed tumors. Experiments with animals seem to indicate that this is
indeed the case. However, the time of melatonin treatment is very
decisive. In the morning, for example, melatonin should not be used as a
drug, since the body's own melatonin production is then likely to get
out of phase. Again, the circadian rhythmicity of melatonin production
is the key. Christian Bartsch is co-author of a textbook entitled "The
Pineal Gland and Cancer".


-------------------------------
Dr. Thomas Posch
Lektor an der Universität Wien
Institut für Astronomie
Türkenschanzstraße 17
A-1180 Wien
Tel. +43 1 4277 518 83
Fax  +43 1 4277 9518
email: posch@astro....ac.at
-------------------------------