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Bryan Haycock's
Research Update column recently described a gene therapy experiment
in which an adenovirus was reprogrammed to carry genes for IGF-1 and
myosin light chain mRNA. When mice were
transfected with the engineered virus, young mice gained new muscle,
and more significantly, old mice regained muscle lost in the aging
process.
Remarkable as this experiment is, it is by no means unique. Gene therapy
is showing potential in fighting cancer, renewing damaged hearts,
overcoming muscular dystrophy, and in a myriad of other fields. For
those of us interested in the scientific aspects of bodybuilding there
are new applications showing up on almost a monthly basis that could
revolutionize the sport if applied properly. Nor are these techniques
always so high-tech and expensive that they are beyond the means of
athletes.
HGF Gene Transfer
Apart from its near-miraculous effects healing liver and
ulcers and raising the level of HDL ("good cholesterol") [Ueki1999,
Tahara1999,
Takahashi1996], Hepatocyte Growth Factor (HGF) is the first
of the growth factors to activate satellite cells after injury
(including traumatic exercise). [Gal-Levi1998,
Tatsumi1998]. Under the influence of HGF, satellite cells
proliferate, differentiate, and form new muscle. One of the ways in
which prostaglandins build muscle is by inducing secretion of HGF.
In addition to its
mitogenic effect, HGF has a potent
chemotactic and
chemokinetic effect on satellite cells. Muscle regeneration is not
solely dependent on satellite cells in the vicinity of the affected
muscle. When muscle is crushed for example, it releases HGF, which acts
as a chemical distress signal to summon muscle precursors from other
locations.
Scientists at Osaka University in Japan have used the Hemaglutinating
Virus of Japan (HVJ, also known as the "Sendai" virus) as a
vector to
transduce HGF into the muscles and liver of rats. HVJ has a big
advantage over replication-defective adenovirus (RDAd), which has been
favored by Americans. RDAd presents
antigens, leading to attack by cells of the immune system [Hirano1998].
This results in loss of persistence of the effect desired. HVJ on the
other hand can be repeatedly injected with only the most minor immune
system response [Kafri1998].
In the experiment, rats were injected with a poison called
dimethylnitrosamine (DMN) for three days each week. DMN selectively
damages the liver, causing cell destruction and fibrous scarring similar
to liver cirrhosis in humans. The illness was progressive, causing death
of all rats by the seventh week, unless they received the
HVJ virus with its recombinant human HGF payload.
Beginning after the fourth weekly administration of DMN, at a time when
damage to the livers was already widespread, rats were injected once
weekly with either 20 mg. of a HVJ-liposome
mix, 40 mg. of HVJ-liposome, or a placebo. Analyses showed the serum
level of human HGF rose quickly, remained at the higher level for a
week, and rose to an even higher level after a second injection. As
well, the rats' own endogenous HGF rose after the injections, and
remained elevated (see figures).
HGF gene therapy (from Ueki et al., 1999)
Physiologically, treatment with HVJ-HGF reduced fibrosis
by 70% and prevented
apoptosis caused by DMN. Rats given the smaller dose of HVJ-HGF
survived 26% longer, and those given the higher dose were completely
cured. All were free of cirrhosis 50 days after the beginning of the
experiment.
So this therapy cures cirrhosis, a disease that kills tens of thousands
of people each year. More relevantly for bodybuilders, it
provides a safe and reliable method for increasing HGF levels in
muscles. Although very high levels of HGF can result in tumor formation
[Takayama1997],
experiments at the U.S. National Cancer Institute show that in
transgenic mice with HGF levels 200-300% over normal, tumors were
suppressed. The transfection experiment we've described here also
produced increased HGF at this lower level. Hence treatment by
transfection is likely to be safe.
If this treatment for cirrhosis becomes widespread, it is just a matter
of time before it is used by bodybuilders to produce new gains in muscle
-- not just hypertrophy, but actual increases in the number of muscle
fibers due to activation and proliferation of satellite cells and other
muscle precursors by Hepatocyte Growth Factor.
Leptin Gene Transfer
It's not enough for a bodybuilder to have massive muscles, there also
must be a bare mimimum of fat for the seperation of the muscles to be
evident. What better way to remove fat than to increase leptin, the main
substance controlling body composition?
Scientists at Merk Laboratories in Pennsylvania have used a
second-generation helper-dependent adenovirus (HDAd) to deliver
leptin genes to both normal and genetically obese mice [Morsy1998].
Whereas first-generation adenovirus vectors produced immune reactions
and liver toxicity, the HDAd delivery system had significantly improved
safety and produced a prolonged increase in serum leptin levels,
resulting in weight loss. Actually the real problem with this system is
that it accepts such a large genetic payload (37
kilobases) that it is tempting to insert a few more genes just for
good measure...
Erythropoietin Gene Transfer
What will the Tour de France be like when the muscles of
bicycle racers can be transduced with erythropoietin (EPO), the doping
substance that gives them greater endurance by creating more blood
cells? That day may not be far off, judging from recent reports.
Credible EPO gene therapy experiments have been reported since 1994 [Tripathy1994,
Kessler1996]. Recently, a team from Chiron Corporation showed that a
single injection of an adeno- associated virus (AAV) encoded with the
EPO gene produced sustained high circulating EPO levels in monkeys. By
week #10 after the injection, the monkey's
hematocrit had doubled.
However, having a hematocrit that is too high can be as dangerous as
anemia. Therefore new experiments reported in the last two years have
sought to transfer the EPO gene in a way that production of EPO can be
fine-tuned. This is accomplished by adding a transcription factor that
can be regulated by dosing with a harmless drug like tetracycline [Ye1999,
Bohl1998,
Rendahl1998].
The Future
Gene therapy is attracting some of the best minds in
science, and the potential rewards in fighting disease are almost beyond
imagining. On the way to the lofty goals of suppressing cancer,
rebuilding damaged hearts and so on, there will be opportunities for
those of us who simply want to get stronger and look better. Imagine a
clinic in Brazil that you visit once a year to get your HGF and leptin
genes reset. Imagine a scientist at the Pasteur Institute with a
lucrative but secret practice catering to bicyclists. These technologies
exist today. They just require a modest laboratory capable of sustaining
a viral culture. It won't be long.
References
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Control of erythropoietin delivery by doxycycline in mice after
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Mar 12.
Hepatocyte growth factor plays a dual role in regulating skeletal
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Full text]
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