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Astronauts might one day grow and eat genetically modified plants to ward off disease associated with long spaceflights.

Researchers at the University of California, Davis College of Engineering have developed a transgenic, or genetically modified, lettuce producing a drug to protect against bone density loss in microgravity.

Our bones are constantly balanced between growth and resorption, allowing bones to respond to injury or changes in exercise. Spending time in microgravity disrupts this balance, tipping bones towards resorption, so astronauts lose bone mass. This can be treated with a drug called parathyroid hormone, or PTH, but it requires regular injections.

The transgenic lettuce expresses a fusion protein combining PTH with part of a human antibody protein. The fusion protein is designed to be stable in the bloodstream and to allow astronauts to potentially purify the drug from plant extracts, said Professor Somen Nandi at the UC Davis's Department of Chemical Engineering.

The team is evaluating the plants for how much of the drug they can produce, which leaves contain the most product and the best time to harvest the leaves.

Growing plants in space has multiple benefits, Nandi said. A mission to Mars might take several years to complete. Experience from the International Space Station shows that being able to grow some food in addition to pre-packaged meals is a big morale booster for astronauts, he said.

Long space flights also require supplies of medicines, such as PTH. But conventional medicines would expire on the way, so astronauts need ways to replenish supplies. By carrying medicines in the form of transgenic plant seeds, astronauts can both save weight and potentially have a new source of fresh drugs, Nandi said.

Ideally, the drug would be in an orally available form, so that astronauts could dose themselves with PTH by eating lettuce leaves. But if that turns out not to work, they should still be able to extract and purify the drug from the plants.

The findings were presented at the Spring meeting of the American Chemical Society in San Diego.