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STUDIO
DEL PROBLEMA ALZHEIMER
Ipotesi sulla
patogenesi della Malattia di Alzheimer
 Le cause che determinano
l'insorgenza della Malattia di Alzheimer non sono tuttora state chiarite. Non si
sa, infatti, quanto rilevante sia l'incidenza dei fattori genetici nel
determinare l'insorgenza di
AD, in particolare la forma sporadica (LOAD).
L'ipotesi genetica è attualmente quella
presa maggiormente in considerazione dai ricercatori, i quali
cercano di tracciare un profilo di suscettibilità genetica che possa predire in
anticipo se un dato individuo si ammalerà di Alzheimer, e possibilmente
di prevenirne l'insorgenza o ritardarla il più possibile. Tuttavia, insieme
all'ipotesi genetica ne esistono altre altrettanto interessanti e comunque
valide, che meritano certamente un'attenzione approfondita. In questo spazio
verranno elencate le ipotesi, i riferimenti e/o gli articoli originali che
descrivono la patogenesi della Malattia di Alzheimer. ::
Results from the Boyd Haley Laboratory relating to toxic effects of
mercury to excerabation of the medical condition classified as
Alzeimer's Disease:
Research regarding Alzheimer's disease (AD) in our
laboratory has been directed towards detecting aberrancy in the
nucleotide binding proteins of AD post-mortem brain versus age matched
control brain samples. Basic to all of our findings is the following
observation. Two very important brain nucleotide binding proteins,
tubulin and creatine kinase (CK), show greatly diminished nucleotide
binding ability and they are abnormally partitioned into the membrane
fraction of AD brain tissue (1,2). What tubulin and CK have in common
is that both have a very reactive sulfhydryl in their active sites
that, if modified, inhibits their biological activity (14, 15).
Mercury has a very high affinity for sulfhydryls and has been proven
to be a potent inhibitor of both of these proteins biological
activity.
After our laboratory demonstrated that tubulin had
diminished biological activity in AD brain, and only AD brain, we
searched for possible toxicants that might mimic this biological
problem. Our finding was simple and straight-forward. After testing
numerous heavy metals we observed that only mercury-II cation (Hg2+)
could mimic this effect in homogenates of normal brain at
concentrations that might be expected to be found under toxic
conditions (3,4). The observation was that Hg2+ at 1-5
micromolar levels could selectively and totally abolish the binding
activity of tubulin without any noticeable effect on other proteins.
This gave a nucleotide binding profile that was identical to that
observed in AD brain (4,5,6). Further, recent results in our
laboratory have shown that the addition of Hg2+ to control
brain homogenates not only caused the decrease in nucleotide
interaction but could also cause the abnormal partitioning of tubulin
into the particulate fraction as observed in AD brain (7). This was
especially effected in the presence of other metals (see below).
The next set of experiments was to determine if
mercury vapor, the form that escapes from dental amalgams, could mimic
the effect in rats exposed to such vapor for various periods of time
(5). Rats are different from humans in that their cells can synthesize
vitamin C whereas humans have to ingest vitamin C. Vitamin C is
thought to be somewhat protective against heavy metal toxicity and
other oxidative stresses. However, we observed that the tubulin in the
brains of rats exposed to mercury vapor lost between 41 and 75 percent
of the nucleotide binding capability demonstrating a Hg2+
induced similarity to the aberrancy observed in AD brain (5).
Consistent with this was a recent report by Dr. Michael Aschner of
Wake Forrest University at the 1998 Spring IAOMT meeting. He stated
that Western blot analysis of brains of rats exposed to mercury vapor
(as above) showed elevated levels of an enzyme called glutamine
synthetase (GS) when compared to non-treated controls. This is
consistent with a report published from our laboratory in 1992 where
we predicted that the elevation of GS in the cerebrospinal fluid of AD
patients had potential as a diagnostic marker for AD (12). This
potential value of GS as a diagnostic aid for AD was recently
confirmed by German scientists (16). We feel that, while mercury has
effects on tubulin, CK and GS and that these proteins are proven to be
aberrant in AD, this still does not conclusively prove that mercury
exposure causes AD. However, it definitely proves that chronic, daily
exposure to mercury would exacerbate the clinical conditions of
Alzheimer's disease by the ability of low doses of mercury to inhibit
enzymes known to be inhibited in AD brain.
We were interested in the genetic research
regarding AD and followed this work to see if it correlated to our
results. That is, does susceptibility to heavy metal toxicity have any
relationship to AD? When we read the correlation of APO-E4 to age of
onset of AD we were intrigued enough to look at the primary structure
of this protein and its alleles, APO-E2 and APO-E3. In general, the
story is this. Individual with APO-E2 or combinations of APO-E2 and E3
are much less likely to get AD than are individuals who have inherited
APO-E4 genes. Also, APO-E2 appears to be more protective than APO-E3
against AD. What is the basic structural difference between these
three alleles? Simply, the protective APO-E2 has two sulfhydryls
(cysteines) which can bind mercury or other heavy metals that APO-E4
lacks. For example, in APO-E3, one of these cysteines is replaced by
an arginine and in APO-E4, both of the cysteines are replaced by
arginine. Therefore, lack of protection against AD follows loss of
sulfhydryls from APO-E proteins (6). What does APO-E protein do. It is
involved in cholesterol transport and all three forms work reasonably
well at this. However, APO-E is classified as a "housekeeping
protein". That is, in contrast to tubulin and CK which are meant to
stay inside of cells where they are synthesized, APO-E is meant to
leave the cell carrying out unwanted material for the body to dispose
of. In the brain, APO-E protein leaves brain cells and goes into the
cerebrospinal fluid (CSF) and then crosses the blood brain barrier
into the blood plasma. It is cleared from the blood by processes that
dispose of the unwanted material that it is carrying. It is our
hypothesis that while APO-E2 or E3 are leaving the brain cells and
traversing the CSF they likely bind any heavy metal or other
sulfhydryl reactive toxin that may have made it into the central
nervous system (6). APO-E4 could not do this and therefore loses the
protective parameters that APO-E2 and E3 have. It is interesting to
note that the second highest level of APO-E protein is in the CSF that
bathes and protects the brain cells.
There was considerable debate concerning whether or
not mercury reaches levels in the brain that could be considered
toxic. The determination of the levels of mercury toxicity that could
cause neurological disease has been done using animals, such as rats,
under tightly controlled laboratory conditions where the diet is
carefully monitored to exclude other toxicants. However, humans do not
live under such restricted conditions and heavy metal imbalances in AD
brains have been reported numerous times. For example, lead (Pb)
toxicity is not that uncommon in the inter-city environment or for
those exposed to leaded gasoline fumes for many years. The latest
research in our laboratory has shown that one can add various metals
to human brain homogenates to levels that do not affect nucleotide
binding to tubulin yet the very presence of these metal potentiate the
toxicity of mercury. That is, the presence of Zn2+ and
Cd2+, at non-toxic levels, decrease the amount of Hg2+
required for 50% inhibition of tubulin or creatine kinase viability.
When we compare the toxicity of Hg2+ in brain homogenates
as described above (refs. 3 & 4) the addition of 0, 10 and 20
micromolar Zn2+ increases the inhibition of GTP binding to
tubulin from 4% to 50% and 76%, respectively (7,13). In other words,
mercury is much more toxic in the presence of other metals that
compete with mercury for the binding sites on protective biomolecules
(e.g., APO-E2 & E3, glutathione, metallo-thionine, ect.). This
observation probably explains some observations on the toxicity of
solutions in which dental amalgams have been soaked. The most recent
publication in this area seems to put an end to the argument as to
whether or not mercury from dental amalgams pose a threat to the
exacerbation of AD. Olivieri et al. demonstrated that exposure of
neuroblastoma cells to 36 X 10-9 molar Hg2+
caused an increased secretion of ß-amyloid protein 4 to 6 hours later
and increased phosphorylation of the microtubulin protein Tau (17).
Both of these biochemical changes are uniquely observed in AD brain
tissues and ß-amyloid protein makes up the 'amyloid plaques' that are
the hallmark diagnostic marker for AD on brain pathology. A very
strong component of AD researchers believe that amyloid protein is the
cause of AD. Therefore, mercury exposure at nanomolar levels causes
neuroblastoma cells to produce a protein that is believed to be
involved directly in AD. However, this data supports the initial
contention from the Haley laboratory that mercury first inhibits
enzymes like tubulin, creatine kinase and glutamine synthetase and
dramatically affects metabolism. After these inhibitions occur the
cell responds to the cytotoxicity by producing and secreting amyloid
protein which forms the amyloid plaques observed on brain pathology
and used to substantiate the AD diagnosis. To the point, amyloid
plaques are the result of AD, not the cause. The cause is exposure to
environmental toxicants like mercury.
Wataha et al. (8) reported that extracts of the
amalgam material (trade name, Dispersalloy) "was severely cytotoxic
when Zn release was greatest, but less toxic between 48 and 72 hours
as Zn release decreased". Zn is an essential metal needed for health
and many times recommended by physicians to be taken in supplemental
form. It is my opinion that the increased toxicity was not caused by
direct Zn toxic effects. Rather, enhanced toxicity was due to the Zn
potentiated toxicity of mercury caused by Zn2+ occupying
biomolecule chelation sites resulting in a higher concentration of
free Hg2+ capable of inhibiting the activity of critical
nucleotide binding proteins such as tubulin and CK. This raises the
question if mercury is released from amalgams under similar
conditions. Chew et al. (9) tested the "long term dissolution of
mercury from a non-mercury-releasing amlagam (trade name Composil)".
Their results demonstrated "that the overall mean release of mercury
was 43.5 +/-3.2 micrograms/cm2/24hr, and the amount of
mercury released remained fairly constant during the duration of the
experiment (2 years)". In my opinion, this is not an insignificant
amount of mercury exposure if one considers the number of years a 70
year old individual living today may have been exposed. In the Haley
laboratory we soaked amalgam fillings in distilled water and then
tested the resulting solution for toxicity. The results were obvious,
the water was now extremely toxic and when added to brain homogenates
dramatically inhibited the viability of tubulin and creatine kinase,
exactly as observed when we added mercury cation. The bottom line is
that mercury toxicity is enhanced by the presence of other heavy
metals and both are released from dental amalgams. Additionally, when
one considers the toxicity of a certain body level of mercury it is
somewhat meaningless unless the body level of other heavy metals is
also considered.
Many recent literature and popular press reports
state that the presence of periodontal disease raises the risk factor
or exacerbates the condition of several other seemingly unrelated
diseases such as stroke, low birth weight babies, cardiovascular
disease (See October 1996 issue of Periodontology). The anerobic
bacteria of periodontal disease produce hydrogen sulfide (H2S)
and methyl thiol (CH3SH) from cysteine and methionine,
respectively. This accounts for the "bad breath" many individuals
have. However, in a mouth that produces H2S, CH3SH
(from periodontal disease) and Hgo (from amalgam fillings)
the very likely production of their reaction products, HgS (mercury
sulfide), CH3S-Hg-Cl (methyl thiol mercury chloride) and CH3S-Hg-S-CH3
(Dimethylthiol mercury) has to occur. This is simple, un-refutable
chemistry whose presence is supported by easily observable amalgam
tattoos. These tattoos are purple gum tissue surrounding certain teeth
where the gum and tooth meet and caused by HgS as determined by
mercury analysis of such tissue. HgS is one of the most stable forms
of mercury compounds and is the mineral form of mercury, called
cinnabar, from which mercury is mined from the earth). All of these
compounds are classified as extremely toxic and the latter compound,
dimethylthiol mercury is very hydrophobic and it solubility similar to
dimethyl mercury. Dimethyl mercury was the compound that was recently
in the press where only a small amount spilled on the latex gloves of
a Dartmouth University professor caused severe medical problems and
finally death. Logic implys that anyone with periodonatal disease,
anaerobic bacterial infected teeth and mercury containing fillings
would be exposed daily to these very toxic compounds. In the Haley
laboratory we synthesized the two methylthiol-mercury compounds and
tested them. They are extremely cytotoxic at 1 micromolar or less
levels and are potent, irreversible inhibitors of a number of
important mammalian enzymes, including tubulin and CK.
To determine if toxic teeth could have an effect on
the enzymes/proteins of human brain we have done the following study.
Several very toxic teeth were incubated for 1 hour in distilled water.
Aliquots of these solutions were then added to control human brain
homogenates and the resulting samples tested for enzyme viability. The
result showed that several of the solutions, but not all, in which
toxic teeth had been incubated inhibited the viability of the same
enzymes that are found to be inhibited in AD brain. Therefore,
depending on the type of anerobic bacterial infection in avital teeth
it is possible to have a toxicant production that would exacerbate the
condition classified as AD.
In summary, the data on the effects of mercury on
the nucleotide binding properties and the abnormal partitioning of two
very important brain nucleotide binding proteins first suggested that
mercury must be considered as a contributor to the condition
classified as AD. This is strongly supported by the recent finds that
nanomolar levels of mercury causes neuroblastoma cells to secrete
ß-amyloid protein and increase phosphorylation of the microtubulin
associated protein Tau, both major biochemical observations related to
AD. Consideration of mercury as an exacerbating factor is especially
relevant when mercury is present in combination with other heavy
metals such as zinc (Zn) cadium (Cd) and lead (Pb). Bluntly, the
determination of safe body levels of mercury by using animal data
where the animals have not been exposed to other heavy metals is no
longer justifiable. Mercury is much more toxic to individuals with
other heavy metal exposures. As I have been sent numerous lab reports
on levels of elements in the hair and other tissues of suspected
mercury toxic patients I have noticed that many have exceedingly high
Pb, Cd, Cu, Zn, etc. levels. It is my opinion that one of the major
questions left to be answered concerning the toxic effects of mercury
is "does the combination of mercury with different heavy metals lead
to different clinical observations of toxicity?" There can be little
doubt that the elevated levels of other heavy metals increases the
toxicity of mercury. Further, the reaction of oral mercury from
amalgams and the reaction of this mercury with toxic thiols produced
by periodontal disease bacteria very likely enhances the toxicity of
the mercury being released. This makes any claim regarding the
determination of safe levels of mercury as obtained under controlled
conditions (e.g. in a system where other heavy metals are excluded)
very suspect when discussing toxic mercury effects in the uncontrolled
environment that humans are exposed to.
Bibliography
- Khatoon, S., Campbell, S.R., Haley, B.E. and Slevin, J.T.
Aberrant GTP ß-Tubulin Interaction in Alzheimer's Disease. Annals of
Neurology 26, 210-215 (1989).
- David, S., Shoemaker, M., and Haley, B. Abnormal Properties of
Creatine kinase in Alzheimer's Disease Brain: Correlation of Reduced
Enzyme Activity and Active Site Photolabeling with Aberrant
Cytosol-Membrane Partitioning. Molecular Brain Research accepted
(1997).
- Duhr, E.F., Pendergrass, J. C., Slevin, J.T., and Haley, B.
HgEDTA Complex Inhibits GTP Interactions With The E-Site of Brain
ß-Tubulin Toxicology and Applied Pharmacology 122, 273-288 (1993).
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to Tubulin in Rat Brain: Similarity to a Molecular Lesion in
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::
Come il mercurio causa la degenerazione dei
neuroni:
L'università di Calgary ha realizzato un video che descrive nel
dettaglio come il mercurio provochi la degenerazione dei neuroni
cerebrali.
Per scaricare il VIDEO
clicca
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