Neuropathy of Lead

1
Introduction A Lead-In Since antiquity,
mankind has used lead for both industrial and
commercial uses. The malleability and
preservative properties of lead have made it
ideal for pigments, glazes, piping, lubricants,
gasoline, and a plethora of other objects we see
and use everyday. Today, we are all exposed to
environmental lead but neuropathy remains
confined to workers in industry that use lead or
in which lead is a by-product (2). Lead
ions unique ionic radius and divalent charge
allows it to masquerade as calcium and trick the
human body into absorbing lead in calciums
place. However, leads extra electrons (in
relation to calcium) ultimately allow lead to
interrupt calcium-dependent processes and cause
various imbalances in the body. In the nervous
system, lead can indirectly disrupt hormonal
triggers in the brain, and lead can directly
interfere with calcium triggers in the nerves.
While a great amount of lead has been removed
from public use, we may still be exposed to
low-levels of lead from trace contaminants.
Although we may not overtly feel the effects
low-levels of lead have on our body, our
neurological systems can still be adversely
affected. Thus, we are required to ask, what
are the effects of lead on our nervous system and
what can we do about it?
References 1)   Subclinical
neurophysiological effects of lead A review on
peripheral, central, and autonomic nervous system
effects in lead workersAmerican Journal of
Industrial MedicineVolume 37, Issue 2,
Date February 2000, Pages 193-204Shunichi
Araki, Hajime Sato, Kazuhito Yokoyama, Katsuyuki
Murata 2)   Neuropathies associated with
excessive exposure to leadMuscle
NerveVolume 33, Issue 6, Date June 2006,
Pages 732-741Ruth M. Thomson, Gareth J.
Parry   3)   The Influence of Milk Intake on The
Lead Toxicity to The Sensory Nervous System in
Lead WorkersNeuroToxicology,  Volume 25, Issue
6, December 2004, Pages 941-949Hung-Yi Chuang,
Song-Yen Tsai, Kun-Yu Chao, Chen-Yu Lian,
Chun-Yuh Yang, Chi-Kung Ho, Trong-Neng Wu 4)  
How dangerous are low (not moderate or high)
doses of lead for children's intellectual
development?Archives of Clinical
Neuropsychology,  Volume 16, Issue 4, May 2001,
Pages 403-431Alan S. Kaufman   5)
Neuropsychological function in children with
blood lead levels lt10 µg/dL NeuroToxicology,
Volume 28, Issue 6, November 2007, Pages
1170-1177Pamela J. Surkan, Annie Zhang, Felicia
Trachtenberg, David B. Daniel, Sonja McKinlay,
David C. Bellinger 6) Effects of Lead Salts on
the Uptake, Release, and Binding of
-Aminobutyric Acid The Importance of Buffer
CompositionJournal of NeurochemistryVolume 52,
Issue 2, Date February 1989, Pages 433-440Colle
en A. Drew, Ian Spence, Graham A. R. Johnston 7)
Low Level Lead Exposure Decreases In Vivo Release
of Dopamine in the Rat Nucleus Accumbens A
Microdialysis StudyJournal of NeurochemistryVolu
me 65, Issue 4, Date October 1995,
Pages 1631-1635Subbarao V. Kala
Neuropathy of Lead
Toxicological Profile for Lead (1989)
Nerve picture - http//en.wikipedia.org/wiki/Image
Complete_neuron_cell_diagram_en.svg
Low-Lead Levels Exposure Detecting the
symptoms and signs from low-level lead exposure
can help us identify and treat lead-poisoned
individuals before they experience permanent
neurological damages. The following is a summary
of the data found in journal 1 regarding
discoveries in subclinical lead poisoning on
different aspects of the nervous system
Got Cure? The best way to prevent lead
neuropathy is to adhere to the regulatory
standards and to be vigilant in lead testing.
Blood lead level testing should be done quarterly
in industries where lead exposure is not
avoidable. This test gives relevant information
to lead exposure for the previous 3-5 weeks and
those with lead levels above 60 ug/dl should be
retested in 2 weeks to determine if additional
medical attention is needed (2). Trials done
by H.Y. Chuang has shown that the intake of milk
has a protective effect in individuals who are
exposed to lead. Chuang investigated the sensory
nervous function of Taiwanese lead industry
workers with a current perception threshold (CPT)
test. The study showed that those who drank
around 700g of calcium (two bottles a day) had
mild protection in nerves in the hand but not in
the feet. This was probably because the longer
nerve fibers, weaker blood barrier, made them
more susceptible to toxins (3). Chelation
therapy along with termination of exposure is
recommend for treating elevated blood lead
levels. Urination-inducing drugs like EDTA and
DMSA reduce the bodily burden of lead during the
chelation therapy. It should be noted that
chelation treatments can dangerously mobilize
un-reactive lead stored in bones. (2)
The Bigger Brain Lead is highly toxic to
the human body, but it is difficult to find
isolated cases of lead neuropathy. In children,
however, encephalopathy is an early and common
symptom of lead poisoning. Conversely, in
adults, encephalopathy is not usually present
except in special cases of massive exposure. In
adults, we usually see neuropathy after bone
marrow suppression anemia and leukopenia,
gastrointestinal tract effects (GI hemorrhage,
diarrhea), renal effects (proteinuria, renal
failure), hypertension and gout (2). This
difference of neuropathy susceptibility is
usually explained for two reasons. The first
reason is that calcium (and lead) is actively
used and transported more by growing children
than adults. This gets the lead to the brain
faster and ultimately causes edema (4). The
other reason is that child lead poisoning usually
results from ingesting a large amount of lead.
These large blood-lead levels increase the
permeability of the blood-brain barrier, which
ultimately causes edema. On the other hand,
adults usually experience chronic exposure to
small amounts of lead which cause neuropathy
(2). Lead neuropathy is ultimately dependent
on the rate and amount of exposure. Studies have
shown that short-term exposure (a few years) of
high levels of lead causes more motor
naturopathic problems, while long-term exposure
(gt10 years) causes sensory, motor, and autonomic
neuropathy (2). This length-dependent neuropathy
usually starts as distal weakness but it can
occur in proximal areas.
Peripheral To detect leads influence on the
peripheral nervous system, a nerve conduction
voltage (NCV) was measured in volunteers with
around 60 ug/Pb per dL blood. In 1976, Araki
and Honma proved that low-levels of lead
exposure can slow the peripheral nerve conduction
velocities (NCV) and that there were discoveries
linking blood lead levels and poor NCV (1).
In 1992, Yokoyama and Araki further suggested the
reduced NCV were from lead damaged axons which
thus gave poor reflex and causes wrists drops.
Central In 1979, Fox and Sillman indicated
that lead selectively affects the rods to
decrease night vision but not the cones. In
1993, Otto and Fox showed that blood lead levels
between 40 and 50 ug/dL inteferes with the
auditory pathway from the acoustic nerve to the
brainstem.
Autonomic In 1991, two independent Japanese
groups reported leads adverse effects on cardiac
autonomic functions in workers with a mean blood
lead level of 36 um/dL.
GABA Gama-aminobutyric acid (GABA) is the chief
inhibitory neurotransmitter in the central
nervous system. Its job is to secrete growth
hormones and control skeletal muscles by
inhibiting ALA-dehydrase (ALAD). However, when
lead is in the system, lead competes with calcium
at the presynaptic terminals and inhibits the
evoked transmitter release (6). Lead also causes
the overproduction of ALA which blocks GABA and
can cause seizures, stress, and anxiety.
Acetylcholine Acetylcholine is a neurotransmitter
responsible for contractions that act as
neuromodulator between the peripheral nervous
system (PNS) and the central nervous system
(CNS). Lead can act as a calcium trigger and
cause mussel fatigue, shaking, dangling, and
other periphery problems. This usually only
happens in adults with 80-100 ug/dL..
Protein Kinase C Protein kinase C regulates
long-term memory storage and helps regulate
membrane channels (Ch 8, Fitch). Lead can affect
protein kinase to increase permeability of the
blood brain barrier and cause cerebral edema or
seizures. This is very common in children and
lead can further cause learning deficiencies if
lead binds with protein kinase C.
Dopamine Dopamine controls movement and emotional
responses. Leads presence in the body can
produce dopaminergic mechanism changes to disrupt
behavior parameters and provoke learning deficits
and impaired cognitive functions. (7)




Krishna Bharani Science and Society 12/11/08
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