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Milk in rice could curdle

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Biotech human breast milk growing but not bottled.

Genetically modified (GM) rice carrying a protein from human breast milk could be used to enhance infant formula, researchers hope. But at present, the protein would not gain approval for use in the United States.

Nutritionists agree that breast milk is best for a baby; infant formula is not as nourishing as the real thing. So for mothers unable to breast-feed, the biotech industry is engineering crops or animals to make human breast milk proteins to ’humanize’ formula.

Yuriko Adkins of the University of California, Davis and her colleagues, have modified rice plants to carry a human gene for a milk enzyme called lactoferrin. Babies need this to use iron efficiently and fight infection.

Rats fed the rice-raised ’recombinant’ enzyme together with a second enzyme, lysozyme, were better able to kill gastrointestinal bacteria, she told the Experimental Biology 2002 meeting this week in New Orleans. Sterilization inactivates the lactoferrin in current cow-based infant formula; the GM form is stable.

But the US Food and Drug Administration (FDA) will not approve the recombinant protein, warned Steve Taylor of the University of Nebraska, who has been involved in worldwide GM food committees. "I’m about to throw a bit of cold water on this debate," he said.

To test if GM products could cause an allergic reaction, the FDA compares a GM protein with known human allergens - including lactoferrin from cows.

The FDA’s regulations are designed to cover biotech plants that carry drugs or pesticides. They will have to be rethought before rice-grown lactoferrin, and other human proteins made by genetically modified organisms, can be approved for production, says Taylor.

Researchers may be able to bypass the regulatory process if they can prove that the recombinant protein acts identically in the gut to the human one. The two might then be treated as the same, hopes Todd Stoltz of Ventria Bioscience, the company planning commercial production of the human proteins in rice.

Murky milk

In future, recombinant proteins might be used to customize milk formulas, for example to enhance premature babies’ nutrient absorption or to help newborns fight HIV. HIV-positive mothers are advised against breast-feeding by the World Health Organization.

Human breast-milk proteins are already experimentally produced in organisms ranging from fungi to cows. "These proteins are out there by the tonne," says Bo Lonnerdal, who studies them at the University of California, Davis. Yet it is unclear exactly what some of them do in the body, or what tests must be done to demonstrate that they are safe and effective.

For example, there are no animal models that adequately mimic human allergy. And it is unclear whether an animal’s response to a human protein is comparable to that of a person.

Babies fed breast milk develop fewer infections than those on formula and have different gut bacteria. But there’s no guarantee that consumers will accept humanized biotech milk; they may be particularly concerned about feeding GM food to their baby. "It’s a very emotive issue," says Lonnerdal.

HELEN PEARSON | Quelle: © Nature News Service

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