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Infants to benefit from golden eggs.

In a deep freeze at the Children's Nutrition Research Center in Houston, Texas, lie the remains of the hen that laid "golden" eggs. Her 23 eggs - also in the deep freeze - cost $1,300 each to produce. This is no fairy tale; it's real science. And the findings from this small study will be priceless to future research everywhere.

Nearly 99 percent of the carbon on Earth has an atomic weight of 12 - except in this hen and her eggs. They have about 65 percent of the heavier nonradioactive isotope - 13C. That's because his hen's diet was a lot more than chicken feed. It contained $30,000 worth of an alga in which virtually all the carbon was 13C.

Researchers in the Center's Stable Isotope Laboratory are testing the feasibility of using the alga, Spirulina, to determine which amino acids are essential for infants - those that need to be gotten from the diet because the body doesn't make them - and under what conditions a nonessential amino acid may need to be in the diet.

If you think science already knows this, consider the findings with this hen. During her last 4 weeks, she got regular feed plus the 13C-labeled alga, which contains all the amino acids. Chicken experts have long believed that the amino acid proline is nonessential - that it can be made by chicks. But most of the proline in the hen's tissues contained all 13C atoms. The same was true for the proline she put in the egg whites.

That meant the proline had come straight from the feed rather than undergoing breakdown and reassembly in the hen's liver, says Heiner K. Berthold, a visiting scientist supported by the German Research Society.

"This strongly implies that proline is an essential amino acid for the hen - at least under our experimental conditions." Berthold spent the last 2 years in Houston studying the priceless chicken and her eggs. [His findings were published last September in the Proceedings of the National Academy of Science.]

Not only is this method much more sensitive than standard methods for determining the essentiality of amino acids, he says, "you can measure all 18 amino acids in one study." So far, Berthold and colleagues have developed the analyses for measuring at least 14 of them.

The classic method of determining essentiality is to leave a single amino acid out of the diet, he says. "You may trigger effects not directly related to that nutrient, or you may not see effects for weeks."

Obviously, such a study is not appropriate on infants, and there's still some debate as to whether infants can make enough of their own proline, arginine, and glycine when these amino acids aren't supplied in their diet.

"We know certain amino acids are essential. And there's a group that is conditionally essential: they are not made under certain circumstances. But we don't know the circumstances exactly," explains Berthold, a physician and clinical pharmacologist. "This method could be used to determine exactly which amino acids need to be supplied by the diet during periods of development and growth or in relation to the infant's calorie intake." Infant formula makers could then fine-tune their products to the precise needs of infants during the first few months of life.

Before they attempted to use the method on infants, Berthold and colleagues tested it on adults. Four women took a dose of the uniformly labeled alga, then ate regular foods throughout the day to simulate normal eating. In a second experiment, they fasted for 36 hours while consuming the alga to see if their livers had kicked in to produce the amino acids they didn't get from foods. Sure enough, they synthesized a larger proportion of several amino acids during fasting than they did during a day of normal eating.

The researchers focused on a protein found in very-low-density lipoprotein (VLDL) - the tiny globule that carries the bulk of fat circulating in the blood. Since this protein B-100, has a short half-life - only a couple of hours - researchers can watch it come and go in under 8 hours.

Such a study can do far more than prove whether or not an infant can make an amino acid. It can show the degree and rate of absorption of amino acids as well as their metabolism.

For instance, after one subject consumed the dose of labeled alga, the 13C-labeled amino acids started appearing in blood plasma within a few minutes, peaking 1 hour later. And they begun to be incorporated in the B-100 protein within 40 minutes, peaking in 3 hours, says Berthold.

Using a uniformly labeled food source is like attaching a microscopic video camera to each amino acid and following its travels through the body. What's more, since all compounds in the alga are built on a backbone of 13C, researchers can study the fate of fatty acids, sugars, nucleic acids that make up DNA, and any other carbon-containing compounds.

A meal of Spirulina may not be considered haute cuisine, but it's a major source of protein is some parts of the world, says Berthold. Farmers in Africa and Mexico grow the alga in ponds, then dry out the ponds to harvest it. "It has an amino acid profile very similar to egg white," he notes.

The labeled Spirulina, however, was grown in a closed system by Martek a company in Columbia, Maryland, specializing in algal products for research applications. All the carbon dioxide piped into the system contains the heavier 13C, says Peter Klein, who initiated the research with Spirulina and heads the Stable Isotope Laboratory. As a result, the proteins, fats, carbohydrates, and other organic compounds are uniformly labeled with 13C, Well...almost uniformly. About 3 percent of the carbon is the ubiquitous 12C, which slipped into the system unnoticed.

As for the hen and her 23 golden eggs, they won't go to waste. They can be used just like the alga in future studies. But for now, they've proved that a uniformly labeled food source can be a powerful scientific tool.

Heiner K. Berthold and Peter D. Klein are at the USDA-ARS Children's Nutrition Research Center, 1100 Bates Street, Houston, TX 77030. Phone (713) 798-7000.
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Title Annotation:amino acid research involving chickens fed carbon isotope 13C
Author:McBride, Judy
Publication:Agricultural Research
Date:Dec 1, 1991
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