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obfuscation from Glamorgan



Following Stanley Ewan's comments on the safety of CaMV promoter a number of plant genetic engineering "authorities" have rebutted Ewan's comments by a bizarre comments to the effect that the CaMV promoter in the CaM virus is a safe and probably nutritious food because virus infected cauliflower are a popular food in UK and cabbage, cauliflower and broccoli are believed to be anti-cancer foods. Such comments seem to be crude efforts at obfuscation. The CaM virus never integrated into the DNA of the chromosome and it is circular. The virus replicates from RNA copies in the cytoplasm to make protein bound virus particles in the plant cell cytoplasm. In contrast the CaMV promoter used in most genetic constructions is integrated into the chromosome from a bacterial plasmid and its neighboring genes are most frequently synthetic transgenes along with the bacterial sequences.The CaMV promoter in the chromosome is a hot spot for genetic recombination ( presumably a consequence of transcription related recombination and mutation). It is not reasonable and certainly not good science to claim the eating CaM virus is equivalent to eating the viral promoter inserted into the plant chromosome . What should have been done , prior to the extensive release of GM crops with CaMV promoter, was to study ingestion of the CaMV promoter DNA in the configuration with which it is used in GM crops. Finally, Denise Murphy seems to have put together a story on the nice features of cabbage, broccoli and cauliflower that is totally unrelated to the real issues of CaMV promoter use in GM crops. Of course the whole story may be a dry satire, like a Monty Python sketch?

CaMV DNA is not a novel cancer risk

Dr Stanley Ewen recently warned of cancer risk from GM crops in a
statement delivered to the Health and Community Care Committee of the
Scottish Parliament. In particular, he was concerned that a cauliflower
virus used in some GM foods (actually, only the viral gene promoter is
present) could increase the risk of stomach and colon cancers. The story
was reported in a prominent Scottish newspaper (Sunday Herald) and has
doubtless further alarmed an already fearful public about the risks of GM
foods (http://www.sundayherald.com/29821).

However, there is nothing new about this story and Dr Ewan’s claims can
readily be laid to rest. The virus in question is the cauliflower mosaic
virus (CaMV) and, as almost any vegetable gardener will tell you, it is
one of the most common diseases of all our brassica crops. These crops
include such important staples as cabbage, Brussels sprouts, cauliflower,
broccoli, turnip and Swede, as well as major seed crops like mustard and
oilseed rape.

CaMV is a virus that occurs worldwide, principally infects brassicas and
other members of the Cruciferae, but otherwise has a restricted host
range. In the UK, for example, CaMV incidence in oilseed rape varies from
year to year. In 1991 and 1993, between 14% and 25% of plants sampled from
test fields were infected with CaMV (1). Also, 60% of naturally occurring
wild cabbage plants (B. oleracea) in Dorset (UK), were found to be
infected with CaMV (2). In short, CaMV has a variable but significant
incidence in many locations over a wide geographical region.

Dr Ewan characterises CaMV as a potential “growth factor in the stomach or
colon, encouraging the growth of polyps”. But the relatively frequent
incidence of CaMV in so many staple food crops means that humans must have
been inadvertently ingesting the virus for many millennia. Given this long
history of exposure to such an apparently worrisome virus, it is curious
that there have as yet been no reports on the adverse effects of brassica
vegetables on the human gut (or anywhere else for that matter).

Quite to the contrary in fact, as has been shown in the evidence linking
brassica isothiocyanates with anti-cancer activity, both in cultured human
cells and in animal model systems (3). Researchers at the Harvard School
of Public Health recently confirmed the added cancer protection that
Brassica vegetables provide. They followed over 47,000 men in the Health
Professionals Follow-up Study and complied food intake data over the
course of eight years. They found that eating Brassica vegetables was
linked to a 51% reduction in the risk of bladder cancer. In contrast, no
association was found with eating other vegetables or fruits (4).

Furthermore, Dr Richard Mithen and co-workers, have developed new
varieties of vegetables, such as broccoli, that are particularly enriched
in these cancer-protecting compounds (5,6).  Several companies have
licensed the use of such brassica vegetables for marketing as “healthy
eating” options in supermarkets. Interestingly, these modern scientific
studies merely confirm centuries-old folk traditions about the efficacy of
brassica vegetables in protecting people against the risk of cancer
(http://www.hort.purdue.edu/newcrop/duke_energy/Brassica_napus.html).

It is true that the CaMV promoter used in transgenic plants is randomly
integrated into the plant genome whereas, in an intact virus, the CaMV DNA
is protected by a protein coat. This point has been used by Dr. Mae-wan Ho
to stress that there is “a great deal of difference between the CaMV eaten
in vegetables every day, and the promoter CaMV. Viruses, she said, are
protected in the environment by a protein coat that also confers species
specificity. The CaMV cannot enter mammalian cells because its protein
coat is specific to plant cells. But the CaMV promoter used in GMOs comes
in the form of naked viral DNA and naked DNA of any sort is highly
infectious” (http://www.twnside.org.sg/title/gmo-cn.htm).

But Dr Ho is not correct in assuming that all of the CaMV ingested in
brassica vegetables would be in the form of intact virus particles
shielded by a protein coat. Many of the viruses would have penetrated into
the nuclei of infected plant cells, where their DNA replicates as naked
plasmids. This replicating form of the virus would be present in many
brassica vegetables. The viral DNA would be unshielded by its protein coat
and presumably therefore theoretically available for recombination with
other DNA, whether from different viruses or from bacterial or human cells
in the gut – just like the recombinant CaMV that Dr Ho warns us about
above.

Does this make you think twice about eating uncooked brassicas (e.g.
watercress)? I certainly hope not, especially given the evidence that, in
addition to its well-known generalised anti-cancer role (5), the
consumption of just 170g (6oz) of watercress per day protected smokers
from the major lung carcinogen in tobacco smoke (7).

In conclusion, Dr Ewan’s assertions would appear to be based on
speculation that does not take into account the prevalence of viruses like
CaMV in our normal diet. Much of our food contains viral DNA, either
intact or fragmented, and the kinds of theoretical risks from GM food
containing the CaMV gene promoter would therefore apply to many
long-standing and efficacious dietary components.

References

1. Hardwick NV, Davies JML, and Wright DM. 1994. The incidence of three
virus diseases of winter oilseed rape in England and Wales in the 1991/92
and 1992/93 growing seasons. Plant Pathology 43:1045-1049.

2. Raybould AF, et al. 1999.The prevalence and spatial distribution of
viruses in natural populations of Brassica oleracea. New Phytology
141:265-275

3. Zhang Y, Talalay P, Cho CG, Posner, GH. 1992 A major inducer of
anticarcinogenic protective enzymes from broccoli: isolation and
elucidation of structure. Proceedings of the National Academy of Science
USA 89:2399-2408

4. Michaud DS, Spiegelman D, Linton SK, Rimm EB, Willett WC, Giovannucci
EL. Fruit and vegetable intake and incidence of bladder cancer in a male
prospective cohort. J Natl Cancer Ins. 1999;91:605-613

5. Rose P, Faulkner K, Williamson G and Mithen R (2000)
7-Methylsulphinylheptyl and 8-methylsulphinyloctyl isothiocyanates from
watercress are potent inducers of phase II enzymes Carcinogenesis 21:
1983-1988

6. Faulkner, K., Mithen, R. and Williamson, G. (1998) Selective increase
of the potential anticarcinogen 4-methylsuphinylbutyl glucosinolate in
broccoli. Carcinogenesis 19: 605-609

7. Hecht SS, Chung F-L, Richie JP Jr, et al. 1995 Effects of watercress
consumption on metabolism of tobacco-specific lung carcinogen in smokers.
Cancer Epidemiol Biomarkers Prev.;4:877-884

Denis Murphy was Head of the Brassica & Oilseed Research Department at the
John Innes Centre, Norwich, UK, from 1990-2000 and is currently Head of
the Biotechnology Unit at the University of Glamorgan, UK.
++++++++++++++++++++++++++++++++++++++++++++++++

A Collection of Open Letters to the Participants in the Phony War Over
Biotechnology

Mark Mansour's full article at:

http://www.agbioworld.org/biotech_info/articles/mansour.html

.