Transgenic Vegetables - Transgenic Horticultural Crops: Challenges and Opportunities - page 44

t herapeutIc p roductS
A.range.of.other.therapeutic.agents.have.been.derived.from.transgenic.plants,.includ-
ing.potato,.rice,.wheat,.and.corn. 77 .Recently,.there.has.been.increasing.focus.on.the.
use.of.vegetable.crops.to.produce.these.therapeutic.products,.since.they.can.be.con-
sumed.raw.(Table.2.1)..The.biopharmaceuticals.produced.to.date.in.vegetables.include.
enzymes,.interleukins,.and.antimicrobial.peptides.for.humans.and.animals.as.well.as.
blood-clotting.peptides..These.therapeutic.products.were.previously.or.are.currently.
produced.in.animal,.yeast,.or.bacterial-cell.cultures..Plant-based.products.have.the.
potential.for.signiicantly.lower.costs.and.reduced.potential.for.contamination. 78 .Oral.
consumption.of.transgenic.tomato.fruit.containing.human.interleukin-12.resulted.in.
a.dramatic.reduction.in.the.symptoms.of.tuberculosis.in.mice. 79 .The.production.of.
transgenic.lettuce.expressing.chicken.interferon.has.indicated.the.possibility.of.using.
transgenic.forage.crops.for.avian.feed.and.potentially.for.other.livestock. 80
For.the.most.part,.the.amount.of.pharmaceutical.proteins.produced.in.the.trans-
genic.vegetables.would.be.quite.low.(less.than.1%.of.total.soluble.protein)..This.level.
of.expression.is.insuficient.for.compounds.that.are.not.highly.active,.such.as.blood.
coagulation.factors. 81 .These.proteins.would.either.need.to.be.extracted.and.further.
puriied,.or.an.alternative.expression.system.would.need.to.be.employed.
A. limitation. of. using. edible. biopharmaceuticals. is. the. low. absorption. of. the.
active.agent.through.the.mucosal.lining,.without.excessive.degradation..To.increase.
the. absorption,. the. use. of. nontoxic. bacterial. adjuvants. has. been. investigated. 82 .
Potentially,.very.promising.results.have.been.seen.in.lettuce.expressing.proinsulin.
fusion.protein.with.a.bacterial.adjuvant.in.the.chloroplast. 83 .The.fusion.allowed.for.
easier. uptake.of. the. insulin.and. alleviated. the. symptoms. of. pancreatic. insulitis. in.
mice,.a.condition.similar.to.type.I.diabetes.
NUTRITIONAL MODIFICATIONS
e nhanced n utrItIonal Q ualIty
Vegetable. crops. are. a. major. nutritional. source. of. many. essential. human. .nutrients,.
including.vitamins,.carotenoids,.and.lavonoids,.as.well.as.other.important..nutrients..
However,.not.all.vegetables.are.rich.in.all.these.essential.nutrients..Folate.or..vitamin B9.
is.an.essential.cofactor.for.the.synthesis.of.many.amino.acids.and.purines..Humans.
cannot.synthesize.folates.that.must.be.supplemented.through.the.diet,.which.is.mainly.
from.plant.sources..Leafy.greens.contain.high.natural.levels.of.folate;.however,.many.
of.the.worldwide.food.staples.(grains.and.tubers).contain.inadequate.levels.of.folate,.
which.can.lead.to.widespread.deiciencies. 84 .Folate.deiciency.can.lead.to.neural.tube.
defects. and. other. human. diseases. and. is. a. global. health. problem.. Because. plants.
are. major. folate.sources.for.humans,. there.is.always. scope. to. enhance.plant. folate.
levels.(biofortiication)..Plants.synthesize.folate.from.pteridine,. p -aminobenzoic.acid.
(PABA),.and.glutamate.moieties..A.synthetic.mammalian. GTP cyclohydrolase1 .was.
expressed.in.tomato.in.a.fruit-speciic.manner. 84 .As.a.result,.the.fruit.pteridine.and.
folate.increased.relative.to.controls. 84 .PABA.pools.were.depleted.in.engineered.fruit.
that.were.higher.in.folate,.and.supplying.such.fruit.with.PABA.further.increased.their.