Carcinogenicity of aromatic compounds

Bill Melchior, NCTR/FDA wmelchior at NTDOC.NCTNET.GOV
Fri Apr 17 16:06:04 EST 1992

> 	I've received a few letters and have seen a brief discussion
> 	without any sort of resolution on the rumour I posted sbout
> 	DMAE, it's solvent and cancer.  A reader contacted twinlabs
> 	(tm) and stated the nervous operator shakily confirmed that
> 	the only solvent that they used with their DMAE was water.
> 	I recently found a DMAE bottle in a healthfood store and
> 	found the DMAE in TWinlabs to be in  a PABA (para-amino ben-
> 	zoic acid) base.  The solvent is indeed water.
> 	So I checked out the biomed libraries' reports on PABA.  I
> 	found a few reports of similar substances being
> 	carcinogenic.  I'm an amateur and I don't have these
> 	articles handy, but I believe these were pyrridines.  I
> 	found Peter Alex the med student on the shuttle today and
> 	he suggested the benzoic acid was the problem.  He
> 	said that it is hypothesized that benzene itself is the
> 	culprit in causing cancer.  We talked a little about the
> 	chemical structure and the floating electrons of the
> 	benzene ring and the efficacy of this structure in fucking
> 	with DNA replication.  Benzene is the same thing responsible
> 	for the potent carcinogenic activities of burnt barbeque
> 	meterial which is basically just a clump of benzene riings.
> 	The journals were mostly unreadable to this novice but
> 	by the availability of benzocaine, sunscreens containing
> 	benzene-type chemicals (which react with UV light to create
> 	free raqdicals) that this issue is either unresolved or
> 	not yet critical (as the journals seemed to suggest- in-
> 	conclusive.)  PATMS (peter alex the med student) believed
> 	the necessity of these products in medical practices
>         currently outweighs their dangers.  This didn't make sense
> 	to me, aS the use in suncreen is to PREVENT cancer while
> 	he claimed these same substances CAUSED cancer.
> 	Maybe this shouldn't be taken all that seriously.  But
> 	I'm sure a few others as well as myself would appreciate
> 	it if a more biochemically-minded reader could make sense
> 	of this and give a few words to the newsgroups.

Although the carcinogenicity of aromatic hydrocarbons is not my field, 
perhaps I can shed some light on this problem.

First, there is a big difference between benzene, C6H6, and the much
larger "polycyclic aromatic hydrocarbons" ("PAH"s), which have multiple
rings joined together along their edges.  The mechanisms by which PAHs
damage DNA have been extensively studied.  Such damage depends on
metabolism of the compounds to oxidized species which can react with
groups on the DNA.  The degree of metabolism, first, and the amount and
type of damage to DNA, second, depend on several details of the
structure of the molecule, such as the geometric layout of the rings
and the presence of other side chains attached to the rings.  The DNA
damage, with resulting mutations and tumor formation, are well characterized.

Benzene, on the other hand, has been associated with leukemia, but
experimental studies are mostly lacking.  This means that the interaction
with DNA is not well characterized, either as to the nature of the
reacting compound or the type of the resulting damage.  Oxidation has been
proposed as playing a role here, also, but benzene is much less reactive
than PAHs, so experiments are less informative.

A couple of points should be kept in mind.  1)  The majority of chemicals that
react with DNA do so after being metabolized -- changed into more reactive
compounds -- by enzymes in the body.  2)  Caution is needed in proposing
that a chemical may cause cancer merely because an apparently similar one
does; simply moving methyl group from one place to another on a molecule
may change its carcinogenecity by orders of magnitude.  (Remember that common
salt, NaCl, is made up of sodium and chlorine atoms.  Both sodium and chlorine
are dangerous in their elemental state, but NaCl is not only harmless in
reasonable amounts, but absolutely vital to life.)  Thus it is totally
wrong to say something like
>       Benzene is the same thing responsible
> 	for the potent carcinogenic activities of burnt barbeque
> 	meterial which is basically just a clump of benzene rings.

The opinions stated are mine, not those of NCTR or its sponsoring organizations.

Bill Melchior                                ||   Evolution, as described in
National Center for Toxicological Research   ||   J. A. Paulos' _Innumeracy_:
Jefferson, AR  72079                         ||
(501) 543-7206                               ||  "Eventually, primitive life
                                             ||   develops, and then shopping
wmelchior at                   ||   malls."

More information about the Bioforum mailing list