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Stable isotopes trace organic compounds in vivo

Published: 07-03-2016, | Member: IsoLife

Many health claims rest on the effectiveness of carbohydrates, proteins and other organic compounds after they are ingested in the body. But their effectiveness can only be determined if these compounds are detected in humans or animals and their conversion is measured. And this is no easy task. One innovative means of tracing nutrients in the body is stable isotopes. The technology supplied by IsoLife, in Wageningen, offers a solution: organic compounds with an isotope ‘label’.

Modern science has made it possible to distinguish two molecules of the same protein by labeling one of them without changing its characteristic properties. The same technology can also be used to label and distinguish other organic compounds, such as sugars and fats.

The labels consist of isotopes: different forms of the same chemical element with varying masses. The most prevalent type of carbon, for instance, has an isotopic mass of 12, but carbon can also have a mass of 13 or 14, meaning its atoms are slightly heavier. The various carbon isotopes can be built into a molecule without affecting its structure, effectively creating a label that helps technicians to identify a particular molecule inside the body amongst others that strongly resemble it.

Mass spectrometry
Molecules containing different isotopes can be distinguished based on their mass through the use of mass spectrometry. Analyzed using this method, particular isotopes show a distinct set of peaks. This allows food researchers to trace where labeled compounds end up in the body and how they are converted. To this end, they take a sample of blood, feces or muscle and analyze it using mass spectrometry.

To trace plant-based compounds, plants are labeled with a carbon isotope. This is IsoLife’s specific expertise. IsoLife supplies plants and plant products whose carbon molecules consist of 97% heavier (Carbon-13 instead of Carbon-12) isotopes. “We have special facilities for growing plants whose leaves, stems, fruits and roots are all labeled with a Carbon-13 isotope,” says Ton Gorissen, one of IsoLife’s co-founders. Gorissen and Ries de Visser founded Isolife ten years ago. They produce stable-isotopes labeled plants and plant products for use in commercial and scientific R&D programs.

More accurate information
At Wageningen University’s Animal Nutrition department, Wilbert Pellikaan used isotopes to study the nutritional value of grass silage. His study, focusing on the digestive tract of dairy cows, compared the passage kinetics of C-13 labeled grass silage with that of externally marked grass silage. Usually, animal nutrition researchers use externally marked compounds. They might link a chromium molecule, for instance, to the organic compound they want to observe. Pellikaan’s study was meant to determine whether marking of compounds with a metal affects the outcome.

The labeled grass silage study was part of wider research into the digestion rate of various types of silage. Animal nutrition specialists want to know how long it takes cows to digest different types of silage as this will enable them to optimize its digestibility. Pellikaan explained how his comparison worked. “We timed the excretion of chromium-marked compounds with that of isotope-labeled grass silage in cow dung. As it turned out, the chromium-marked compound was excreted almost twice as quickly as the isotope-labeled silage.”

Based on these measurements, Wageningen University’s animal nutrition scientists concluded that using external markers distorted their findings because grass silage actually stays in the rumen longer than previously assumed. As Pellikaan explained, “That extended dwell time in the rumen influences the estimates of nutrient absorption from the grass silage. For purposes of comparing the nutritional value of various types of grass silage, C-13 labeled grass gives a more realistic idea of the digestive process than chromium-marked grass.”

Widely applicable
Carbon-13 labeled plant products have also produced good results in other nutritional research, both in humans and animals. There are several examples, Ries de Visser said. “RIKILT, Wageningen University’s main research lab, is developing a test method that uses isotopes to detect poisonous alkaloids in food products. And a Dutch plant breeding company has used the technology to study how much lutein from a particular vegetable is transported by the bloodstream to the eyes and what effect it has there. Also, researchers in London have shown how labeled dietary fiber is digested in the large intestine and how this enhances satiety in the brain. And currently, several isotope studies are being done into the anti-carcinogenic properties of plant fiber.”

Nutritional research with labeled plant compounds has several benefits, the IsoLife experts contended. Because nutrients can be traced more precisely in vivo and the variation in research results is smaller compared to results obtained using non-labeled compounds, clinical trials can be held with fewer subjects. This reduces costs. The increased significance of the results means that health claims can be better substantiated before submitting them to the European Food Safety Authority (EFSA) for approval.

High percentage
De Visser and Gorissen are witnessing a growing interest in labeled plant products in the food industry. Their company is an experienced grower of many different types of labeled plants, which it supplies to customers all over the world.

Gorissen stressed IsoLife’s versatility. “In principle, we can grow and label any type of higher plant. Not just oats, tomatoes and broccoli and so on, but we’ve even grown trees in our chambers. New species are generally not a problem. We supply whole plants, parts of plants, freeze-dried plant powders and purified compounds. Every type of molecule that is present in plants – DNA, RNA, protein, carbohydrates and secondary metabolites – is labeled. More than 97% of the carbon in the plants grown in our chambers has the heavier isotope. We’re the only company in the world that can do that.”