Catharina Svanborg thought that she already knew how remarkable breast milk is. The immunologist had logged hundreds of lab hours documenting ways in which human milk helps babies fight infections. But when the
group decided to use cancerous lung cells to avoid the variability shown by normal cells in laboratory tests, Svanborg and her team at Lund University in Sweden were in for a surprise. They applied breast milk to the
cancerous lung cells, and all the cells died. Breast milk killed cancer cells.

"From that moment on, we've been working with it," Svanborg says.
Svanborg's serendipitous discovery of human milk's anticancer power is remarkable, but other researchers have also been finding that breast milk can both protect against and heal a remarkable variety of ailments. Perhaps these properties shouldn't be surprising: Of the thousands of substances that people eat, breast milk is the only one that evolved under natural pressure to keep people healthy.Research teams are now learning to exploit its tricks for purposes well beyond feeding babies. Components of breast milk are being developed as drugs that fight viruses and bacteria. A particular target is diarrhea, which kills about 2.2 million people every year, mostly children in developing countries. Other milk compounds may be added to food to
improve digestion. Some milk components might fight medic conditions ranging from arthritis to septic shock. Although some of these compounds are found in milk from other animals, others occur only in human milk, and the nonhuman versions are generally less potent in people. This presents challenge, since human-breast milk is not available for sale. So researchers are developing new sources for the compounds, including genetically modified bacteria, rice, goats, and cows.

The potential for therapies derived from milk is "enormous absolutely tremendous," says Marian Kruzel, an immunologist at the University of Texas Medical School in Houston

GOOD BUGS AND BAD BUGS The protective properties of mother's milk have long been apparent. Breast-fed babies, for instance, get diarrhea half as often as infants who are fed formula do. Decades ago, scientists began wondering how breast milk stops the pathogens that cause diarrhea In the 1950s, Lars Hanson, an immunologist at Goteborg Universily in Sweden, started to solve the puzzle. He found that mothers produce antibodies in their milk and that way pass on to their babies immunities that the women had acquired over their lifetimes.But the antibodies in breast milk didn't explain all the observations. For example, breast-fed babies have different bacteria in their guts than formula-fed babies do. The breast feeders harbor more of the beneficial, food-digesting bacteria, such as acidophilus and bifidus, as well as less of the coliform Escherichia coli and other germs that can make infants sick. When scientists started analyzing breast milk, they found that the third-largest constituent of breast milk, making up about l percent by volume, is a mixture of indigestible sugars known as oligosaccharides. Many of these sugars occur only in human milk,

Initially, the scientists thought that these were useless by-products of milk production. But why would mothers expend so much energy creating compounds that their babies can't use? In the past few years, scientists have solved this puzzle. David Newburg, of Massachusetts General Hospital in Charlestown and his colleagues genetically engineered mice to produce oligosaccharides in their milk. He then gave their pups campylobacter, a bacterium that causes diarrhea. The pups that drank oligosaccharides didn't get sick. Unlike the antibodies that mothers
pass along to their infants through breast milk, oligosaccharides can protect the
baby from pathogens to which the mother has never been exposed.For a pathogen to infect a person vie the digestive tract, it first has to latch on to the sugars that line the gut wall Oligosaccharides have binding sites that are identical to the ones on the gut-wall sugars, so the pathogens attach to the oligosaccharides instead of to the lining of the gut. Once bound to oligosaccharides, pathogens travel harmlessly through the intestinal tract.

Surprisingly, bacteria that aid digestion prosper in the presence of oligosaccharides. Bruce German, a nutritionist at the Univelsity of California, Davis, proposes that only the beneficial bacteria digest some of the oligosaccharides, thereby gaining an advantage over the harmful bacteria. This theory is controversial, however

German says that the beneficial microbes' advantage is a natural consequence of the coevolution of breast milk and gut bacteria. Oligosaccharides occur in thousands of slightly different forms, and the precise mix of types ofoliffosaccharides varies from woman to woman. Those who produced breast milk with oligosaccharides that only beneficial bacteria can eat must have had an evolutionary advantage.



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