Perfecting the Formula
Researchers have identified compounds in breast milk that might account for its oft-discussed ability to protect against certain diseases.
When it comes to infant nutrition, there’s plenty of evidence to suggest that a mother’s milk is not just the best food: it’s also a baby’s best defense against bacteria and viruses. Yet the reasons haven’t been clear. Now, researchers at the University of California at Davis and at Agilent Technologies have identified a class of complex sugars in breast milk that may act as molecular protectors against gastrointestinal and other diseases.
Complex sugars called oligosaccharides are the third most common solid component of human breast milk, after lipids and proteins. But unlike lipids and proteins, oligosaccharides have no nutritional value, and babies can’t digest them. Instead, these molecules have been found to bind to bacteria in the gut, preventing agents like E. coli and Campylobacter jejuni from attaching to the intestinal wall and causing diseases such as diarrhea in infants.
To date, scientists have identified 200 different kinds of oligosaccharides in human breast milk–the most of any mammalian species. Carlito Lebrilla, professor of chemistry at UC Davis and lead author of a study published in the Journal of Agricultural and Food Chemistry, says that identifying the structural differences within these molecules would be a big step toward understanding their various mechanisms of defense. It could also be a first step toward incorporating oligosaccharides into artificial baby formula, which is traditionally made with cow’s milk and does not naturally contain these molecules.
“The people who formulated artificial milk sort of neglected [oligosaccharides],” says Lebrilla. “But new data is showing they’re extremely important.”
That’s thanks to new lab-on-a-chip technology developed by Kevin Killeen, project manager of microfluidic systems, and other researchers at Agilent. Killeen designed a chip specifically for analyzing molecules like oligosaccharides. The chip itself incorporates miniaturized versions of conventional technologies–most important, high-performance liquid chromatography (HPLC). Most scientists use traditional bench-top HPLC to separate out various components of a sample at the milligram level–an amount that has proved too large for the fine complexity of oligosaccharides. By using the credit-card-size chip, scientists like Lebrilla can study samples in finer detail, investigating compounds found only at levels of nano- and picograms.
“Scientists didn’t have the ability to chemically separate a broad class of oligosaccharides,” says Killeen. “They were looking at the trees, and we basically gave them the picture of the forest.”
Armed with this technology, Lebrilla’s team analyzed breast milk from five women, each in single runs. Researchers first concentrated the oligosaccharides, separating them out from the rest of the breast-milk samples. After diluting this mixture, they injected a picogram of each sample into the top of a tiny column in the chip. Depending on their composition, each molecule will, as Lebrilla puts it, “parade out at different times” from the bottom of the column. These molecules are then vaporized and transferred directly into a bench-top, high-accuracy mass spectrometer, which then determines the mass and composition of each individual oligosaccharide.
The researchers found large variations from woman to woman in both the number and type of oligosaccharides present. For instance, the total number varied for each individual from 33 to 124. Lebrilla suggests that this might be due to the different times during lactation at which each sample was taken, but that data was not gathered as a part of the study.
However, Lebrilla did find an intriguing consistency: regardless of the variation among the women, 60 percent of all oligosaccharides had a specific component, called fucose, that is known to bind to the cell walls of bacteria. It’s a finding that Lebrilla did not expect but which may help explain exactly how oligosaccharides might ward off diseases in infants.
“The goal here is to say, If milk is the perfect food, what about milk makes it perfect?” says Lebrilla. “So once we’ve figured out which components are important, I think you’ll start to see the synthesis of these things for human milk.”
Artificial-milk companies have been searching for the perfect baby formula for decades, adding vitamins and nutrients such as omega-3 and omega-6 to cow’s milk, as well as decreasing naturally present levels of sodium, which has been shown to increase the risk of dehydration and diarrhea. Even with increasing knowledge of the composition of human breast milk, researchers like Michael Kramer, professor of pediatrics at McGill University, say we’re not even close to replicating nature. Kramer is encouraged by Lebrilla’s results, however, and he sees applications for adults as well as for infants.
“This could lead to new discoveries about these pathogenic bacteria and viruses themselves, which could lead to the development of antivirals and new drugs,” he says. “It’s a ways off, but we could see this work in protecting infants that could also protect adults from the common cold.”
For now, Lebrilla’s lab is looking at a much wider sample of lactating women and analyzing the presence of oligosaccharides from specific lactation periods. In the future, he plans to study other factors, such as diet, race, and what makes human breast milk unique among all mammalian species. Down the line, he also hopes to use the chip to see which oligosaccharides interact with which bacteria–a line of research that may one day lead to not only improved baby formula, but also better nutrients for adults.
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