A clue about ethidium toxicity

Undergrad via methods%40net.bio.net (by sylvain.bauer from laposte.net)
Mon Jun 18 12:54:39 EST 2007

I made an error in the precedent message, the proportion of homidium
appearing consequently of isometamidium is still unknow. "less than 1%"
(which seems to be 0.25%) correspond to the usual homidium contamination of
isometamidium stock solution.
However I found an other 
interesting data   where toxicologist tried to establish a general ADI for
unknow chemical. 
In that paper they establish 3 groups :
(1) compounds that are likely to be carcinogenic, 
(2) compounds that are likely to be potent or highly toxic
(3) compounds that are not likely to be potent, highly toxic or

Each group have an attribuated ADI: 
1 microgramme a day for the first group; 
10 microgramme a day for the second group
100 microgramme a day for the last one. 

They make a strong like between carcinogenic potential and genotoxicity: if
the product is a weak genotoxic it should also be a "weak" carcigenic. I
guess that we could put etbr somewhere between the two first group. 

But this scale does not seems so reasonable when we look at carcinogene like
aflatoxin B1.... If anybody have a clue about that...  

By the way tom, if your stock solution is 10mg/ml 1microliters is 10

Tom Anderson-6 wrote:
> On Sun, 17 Jun 2007, Undergrad wrote:
>> As you know ethidium (aka homidium) is also used as trypanocide in
>> cattle,
>> sheep, goat ect... No ADI (admitted daily intake) are available for
>> ethidium
>> however there is one for isometamidium which is a closely related to
>> homidium and also intercalate in DNA. Also it was found that
>> isometamidium
>> is transform in homidium in the body (less thant
>> 1%)(http://www.inchem.org/documents/jecfa/jecmono/v31je10.htm).
>> The ADI of isometamidium is 0-100 microgramme/kg
>> (
>> ionsourcejecfa_JECFAEVAL57.html+isometamidium+who+adi&hl=en&ct=clnk&cd=1&gl=uk).
>> So if isomethidium give rise to 0.1% of homidium, the proportionnal ADI
>> of homidium could be : 0.1 microgramme par kg so 6 microgramme for a 60
>> kg person.
>> In this study, it is shown that isometamidium have a strongest toxic
>> effect than homidium:
>> http://www.inchem.org/documents/jecfa/jecmono/v25je10.htm
> Excellent info. So, assuming that these numbers apply to people (not
> entirely unreasonable, if the vets think they apply to both rats and
> cows!), it would seem 6 ug/day (possibly more, given the
> EtBr/isometamidium data) would be a safe therapeutic dose for a
> normal-sized person; my EtBr stock is at 10 mg/ml, which means i could
> drink 6 ul a day and expect to have no ill effects. I imagine splashing it
> on the skin leads to far less efficient absorbtion (although possibly a
> more powerful local effect).
> tom
> -- 
> Tom Anderson, MRC Laboratory for Molecular Cell Biology, UCL, London WC1E
> 6BT
> (t) +44 (20) 76797264   (f) +44 (20) 76797805   (e)
> thomas.anderson from ucl.ac.uk
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