|
June / July 2005
ENVIRONMENTAL TOXINS & NEUROLOGICAL DISEASE
by Christopher A. Shaw
VIBRANT AND HEALTHIER
by Dr. Halanna B.Matthew, PhD
BUYER BE WARY
by Linda Fleury
HOW TO CARB OR NOT TO CARB...the
glycemic index
by Charlotte Starbey
REMEMBER THE HIGHEST POWER
by Margaret I. Jang
WEBSITES REVIEW
by Gisela Filion
|
vibrant and healthier
vegetarians, vegans and rawfoodists
by Dr. Halanna B.Matthew, PhD
The factors that give rise to Alzheimer’s disease, Parkinson’s
disease and Lou Gehrig’s disease
(also termed ALS) are currently
unknown. Possible candidates
include genetic abnormalities
and environmental toxins, alone or in combination.
Genetic mutations account for only a small
fraction of each of these disorders, leading to a
growing suspicion that the majority of what are
termed — “sporadic” forms of neurological
disease arise from the damage caused by specific
“neurotoxins”. Various studies have identified a
variety of both naturally-occurring and synthetic
molecules that could be responsible. Included in
these are various pesticides, heavy metals and
other industrial pollutants. Other possible
neurotoxins may come from various food sources.
My laboratory has focused on a peculiar
neurological disease that was once epidemic on
Guam and surrounding islands. Termed ALS-
parkinsonism dementia complex (ALS-PDC), the
disease often combined the various symptoms of
Alzheimer’s, Parkinson’s and ALS in the same
individual. During the 1950s and ‘60s, ALS-PDC
incidence on Guam was upwards of 100 times
more prevalent than for neurological diseases in
North America and elsewhere and often affected
a younger population. Because of its unique
features, neurologists recognized ALS-PDC as a
potential “neurological Rosetta Stone” and hoped
that identifying its causal factors would lead to
clues about neurological diseases elsewhere.
Extensive studies of ALS-PDC ruled out a primary
genetic defect. Population studies of the habits of
Guamanians instead suggested that the disease
arose due to consumption of the seeds of a local
variety of a palm-like tree, the cycad. Cycad seed
flour had long been used by Guamanians as a
staple food source, especially during times of food
shortage. The period of greatest consumption of
cycad seed flour corresponded with the highest
incidence of ALS-PDC. Similarly, as cycad
consumption declined, the disease declined as
well.
|
We began a series of studies using mice to explore the possibility that
cycad seed flour could cause damage to the nervous system that resembled ALS-PDC.
We fed adult male mice a diet containing 25% cycad seed flour and monitored their motor
behaviors and learning ability over
an extended period. Those mice fed cycad seed
flour rapidly developed all of the basic features
of ALS-PDC, including ALS and Parkinson’s-like motor defects and Alzheimer’s-like memory
defects. The brains of these animals resembled
those of victims of the human diseases. We next
performed an analysis of the compounds contained
in cycad seed flour in order to identify potential
neurotoxins.
Our analysis concluded that the primary
neurotoxins were various plant sterols, similar to
cholesterol, to which single glucose molecules
were attached. The identified toxins are thus
termed sterol glucosides. We have identified the
key sterol glucosides in cycad seed flour as b-
sitosterol b-D-glucoside (BSSG), campesterol b-
D-glucoside and stigmasterol b-D-glucoside. Each
of these is highly neurotoxic in cell culture, rapidly killing neurons in a
manner that resembles some of the stages of human neurological disease.
The same sterol glucosides when given to mice as part
of their diet induced a clear loss of motor neurons
in the spinal cord. Preliminary studies conducted
by our laboratory in collaboration with researchers
at Harvard University show that ALS victims have a higher
than normal level of sterol glucosides in their blood.
We believe that we have deciphered part of the mystery of
ALS-PDC by the duplication of the disease in an animal model
and by identifying the likely causal toxins. Clearly, however,
people in North America don’t eat cycad seeds so can these
toxins arise from other food sources? The answer is that sterol
glucosides can be found in all plants to some degree, with the
amount varying by plant variety, part of the plant, maturity,
etc. Outside of cycads, one of the highest concentrations of
plant sterol glucosides is found in soy beans. Soy beans are
widely used in various forms and soy products are contained
in a variety of food items in North America and elsewhere.
Whether the various forms of soy sold commercially contain
potentially toxic sterol glucosides is currently unknown.
Similarly, we know little about individual responses to sterol
glucosides including transport into the blood and brain,
interactions with other toxins and the role of genetic
susceptibility factors. Determining the potential of these
molecules to contribute to human neurological disease
remains a challenge for the future.
|
|
