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[SANET-MG] crop testing
New Scientist, issue 2530
Letter to the Editor, 17 December 2005
Bill Freese, Washington DC, US
When expressed in transgenic peas, an innocuous bean protein elicits
immune reactions in mice, reviving concerns about the allergenic
potential of genetically modified foods (26 November, p 3 and p 5).
These "surprising results" from researchers in Australia raise several
Should regulators require the use of animal models? Allergenicity
assessments of transgenic proteins in GM crops are usually limited to in
vitro tests of digestive stability, database searches for sequence
similarities to known allergens, and in some cases a heat stability
test. While certainly cheap and convenient for GM crop developers, such
tests provide no direct immunological information and cannot rule out
allergenic proteins. Both the BALB/c mouse strain used in the Australian
pea study and the brown Norway rat have shown promise as predictors of
human allergic response.
Also, at present, all testing is performed on a bacterial surrogate of
the protein, rather than that produced by the plant. GM crop developers
complain that it is too inconvenient to extract sufficient quantities of
transgenic protein from their plant. But if peas and beans - both
legumes - can generate immunologically distinct proteins from the same
gene, surely the same is true of bacterium and plant. Thus, results of
testing on bacterial surrogates may not reflect the toxic or allergenic
profile of the in planta protein people are exposed to.
Other factors also argue against use of bacterial surrogates. For
example, allergenic proteins are often glycosylated, and plant
glycosylation patterns have been implicated in allergenicity. Bacteria,
in contrast, seldom glycosylate proteins.
Finally, perhaps regulators should demand full sequencing of the
transgenic proteins in plants. At present, the standard practice is to
sequence just 5 to 25 amino acids at the N-terminal as a demonstration
of "identity", even if the putative protein is 600-plus residues long.
Since the transformation process - the insertion of foreign DNA to a
cell - can be sloppy and even point mutations can transform an innocuous
protein into an immunogenic/aggregating one, it is unclear why this
basic information is not required.
The editor writes:
These are excellent suggestions, and perhaps such a test regime should
also be applied to new conventionally bred varieties. These can
sometimes generate unexpected allergens or toxins too. For example, a
potato variety called Lenape was withdrawn from the US market in the
1960s when it was found to contain dangerously high levels of potato
toxins called solanidine glycosides. And in the mid-1980s, American
growers abandoned a variety of celery because it contained high levels
of psoralens - chemicals which become irritants when activated by
sunlight. Workers picking the celery developed skin rashes. Psoralens
also occur in parsnips, and have been known to cause rashes through skin
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