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The human body, like that of other mammals, has certain structures
which are particularly susceptible to wear or damage by
environmental conditions or a certain number of harmful physical
or chemical agents, especially in the presence of synergism which
enhances the harmful effects.
The nervous system is the system which is at the top of this
hierarchical scale both for its vital importance and its
susceptibility to harmful agents. Alongside this we find two
particularly important sense organs, the eye and the inner ear,
which allow us to communicate with the outside world. All the
individual components of both these structures are indispensable
and highly susceptible to lesions caused by environmental disease.
In
the eye, apart from retina lesions described as complications of
diabetic hyperglycemia, the crystalline lens is particularly prone
to environmentally-induced damage. The lens is located behind the
diaphragm formed by the iris and the anterior chamber of the eye
which contains aqueous humour, and in front of the posterior
chamber containing vitreous humour. This wonderful structure
performs a function which can be compared with that of a camera
lens, allowing us to focus images, by making the lens more or less
flat using the ciliary muscles. As in all good lenses, when we
start out in life, the lens is completely transparent. This
fundamental principle depends on the reduced state of the SH
functional groups found in the protein molecules that make up the
crystalline lens. The chemical and physical properties of the lens
proteins allow us to see and focus on the retina images of
observed objects, then these are transmitted to the brain by the
optical nerve. When all this functions correctly, at the beginning
of our lifespan, and throughout our younger days, these functions
are perfectly satisfactory. However, with ageing, as we approach
old age or senility, as a result of a long sequence of oxidative
or peroxidative phenomena, the transparent proteins of the
crystalline lens lose their chemical and physical properties, for
the transformation of the reduced SH groups into oxidised
disulfide bridges. This somewhat arid biochemical term explains
the phenomenon which is the cause of the increasing opaqueness of
the crystalline lens that leads to a cataract and which can be
compared to what happens to the albumen of a egg when it is
cooked. As always occurs in the development of many forms of
environmental disease, it is rare that only one harmful agent acts
at a time. In effect the harmful agents attack as a team with a
perverse cocktail-like synergism, which worsens and/or anticipates
considerably the natural evolution of the cataract. In the
scientific literature we find that the development of cataracts
has been attributed to ultraviolet radiation, ionising radiation,
oxidative stress, diabetic hyperglycemia and monosodium glutamate
which is used as a taste enhancer.
Among the agents which cause cataracts, one stands out for the
direct harm it causes and for the specificity of its
disease-causing mechanisms and this is naphthalene, a molecule
used in mothballs. The risk of exposure to the vapours of this
poison not only involves the working environment, during
production, packing or storage or use, but in everyday life in
that a person who puts on a woollen garment that has been
protected with mothballs can inhale varying quantities of the
harmful compound. The naphthalene vapours enter the body though
the respiratory system and then are taken up in the bloodstream
which conveys them to the liver. Here the moth poison is
transformed by the microsomal enzymatic system into di-hydrodiol
naphthalene .
This first metabolite leaves the liver and is transported by the
bloodstream, past the pulmonary vasculature to the eye. Here it
undergoes the crucial metabolic transformation becoming
naphthalene epoxide, the real molecular poison for the natural
proteins of the crystalline lens. The lens loses its transparency
irremediably as a result of these molecular alterations.
This particular manifestation of environmental disease, the
cataract, appears in many individuals generally in late old age
when it is due to so-called natural causes. Another evolution –
and one that occurs much more quickly – is the one which depends
on a synergism between various cataract-causing agents, having a
cocktail effect.
If
we wish to really prevent cataracts then we must avoid or at least
limit as much as possible 1) exposure to UVA radiation ionising
radiation (X-rays) 2) the choice of dishes in Chinese restaurants
which are particularly rich in monosodium glutamate, as well as
soup cubes which are based on it – there are alternative non
monosodium glutamate cubes available, 3) the consumption of food
with a high sugar content to spare the pancreas from overwork. |
