Permeability of the blood-brain barrier to lead
Karl Loren's simple understanding of this scientific study:
Whether or not toxic metals, such as lead, can be moved across the "blood brain barrier" has been an important subject for study. Chelation therapy is well proven to remove lead from the body. However, the question that some have suggested is, as yet, unanswered, is whether during the chelation process, while admittedly some lead is removed from the body, is there a possibility that some other amount of the lead, because it is bound to and with EDTA or Cysteine, might be able to move across the blood-brain barrier, thus introducing the metal into the brain. A test which showed that the metals in the urine are increased doesn't necessarily mean that SOME amount of the metal might also get into the brain. In general any amount of these toxic metals that moves into the brain would be considered far more harmful to the body than any health benefit from that metal which is being removed through the urine.
This study speaks to this point.
Rats were used in this study.
The rats had "infusions" of lead into their bodies and some of this lead was marked with radioactive markers -- so that it was possible to test for where this lead went within the body. This infusion was done with the rats both WITH and WITHOUT certain well-known chelating substances in the blood stream.
Thus, when the lead was infused into the rat, and no chelating substance was present, there was a rapid increase of lead that went into the brain (thus suggesting that the so-called blood-brain barrier may not be much of a barrier). But, when that lead was infused into the rats WHILE the rats had the chelating substances in their blood, there was ZERO lead that moved into the brain.
This suggests that the chelating materials absorbed, or bound to, or chelated, the lead and that this new complex did NOT then move into the brain.
This would generally mean that it is safe to use Cysteine, EDTA or other chelating substances to remove metals without fear that the process would also allow some of the lead to pass through the blood-brain barrier and enter the brain.
| 1: Neurotoxicology 1993 Summer-Fall;14(2-3):131-6 |
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Permeability of the
blood-brain barrier to lead.
Bradbury MW, Deane R.
Division of Biomedical Sciences
(Physiology), King's College, London.
This review examines the kinetics and
possible mechanisms of lead transport into
brain across the microvessel endothelium (the
blood-brain barrier). Although severe lead
poisoning both in neonatal rats and in young
children may cause microvessel damage, there
is little evidence that there is either
damage or even disturbance of specific
transport mechanisms at blood leads < 80
micrograms/dl.
When 203Pb was continuously infused intravenously into adult rats, radiotracer uptake into different brain regions was linear with time up to 4 hours, reaching spaces in relation to plasma of 6.6 - 8.2 ml/100 g in cerebral tissues at one hour.
The concentration of free Pb+ in serum is of the order of 10(-12)M, the majority of lead being bound to protein and to sulfhydryl compounds, such as L-cysteine.
Transport into brain has been further studied during short vascular perfusion of one cerebral hemisphere of the rat with oxygenated and buffered physiological saline. This allows total control of the fluid perfusing the cerebral microvessels.
In the absence of organic ligands for lead, 203Pb entered brain very fast, with a space of 9.7 ml/100 g in frontal cortex at one min.
The presence of albumin, L-cysteine or EDTA abolished measurable uptake.
Experiments designed to reveal a role for the anion exchanger or calcium channels gave negative results. However, the effects of potassium depolarization and of varying pH indicated that the lead species passively entering the endothelium might be PbOH+.
Experiments with various metabolic inhibitors, including vanadate, suggested that Pb uptake in the endothelium is mitigated by active back transport of lead into blood by the Ca-ATPase pump.
(ABSTRACT
TRUNCATED AT 250 WORDS)
Publication Types:
-
Review
-
Review, Tutorial
PMID: 8247388 [PubMed - indexed for MEDLINE
Infusion
(in-FYOU-zhon)
The introduction of a fluid (other
than blood) into a vein. Also refers to an
extract made by steeping herbs in water.
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