Wednesday, December 06, 2006

Perfecting the Formula

Researchers have identified compounds in breast milk that might account for its oft-discussed ability to protect against certain diseases.

By Jennifer Chu

Researchers at UC Davis deconstructed complex sugars in human breast milk with this lab on a chip developed by Agilent Technologies. Credit: Agilent Technologies

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.