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Special lettuce could protect astronauts from bone loss

NASA is preparing to send humans to Mars sometime in the next decade. However, a three-year long mission will expose space travelers to a long period of microgravity, which will cause them to lose bone mass. A new study presented at the meeting of the American Chemical Society (ACS) argues that a special, transgenic type of lettuce could be grown by astronauts embarked in long space trips, and may help them guard against bone loss through a bone-stimulated hormone that it contains.

Previous studies of astronauts on long space missions have shown that they lose an average of one percent of bone mass during each month spent in space – a condition called osteopenia. While at the moment, astronauts on the International Space Station perform certain physical exercises to maintain bone mass during their six-month long stays, a three-year long mission to Mars would leave astronauts vulnerable to osteopenia, and later, osteoporosis.

A medication containing a peptide fragment of human parathyroid hormone (PTH) stimulates bone formation and could guard astronauts against osteopenia, but it requires daily injections. According to scientists from the University of California, Davis, an easier and more practical way is to use plants such as lettuce to synthesize pharmaceuticals like PTH. 

In order to increase PTH’s stability and bioavailability in the body, the researchers attached a piece of another protein – the fragment crystallizable (Fc) domain of a human antibody – to PTH’s sequence. Fc increases the time that the attached peptide circulates in the blood, making it more effective. To introduce a gene encoding PTH-Fc to lettuce, the scientists infected plant cells with Agrobacterium tumefaciens, a species of bacteria used in the laboratory to transfer genes to plants. The resulting plants express about 10 to 12 milligrams of the modified peptide hormone per kilogram of fresh lettuce.

“One thing we’re doing now is screening all of these transgenic lettuce lines to find the one with the highest PTH-Fc expression,” said study co-author Karen McDonald, a chemical engineer at UC Davis. “We’ve just looked at a few of them so far, and we observed that the average was 10-12 mg/kg, but we think we might be able to increase that further. The higher we can boost the expression, the smaller the amount of lettuce that needs to be consumed.”

Before this lettuce can reach astronauts’ plates though, the scientists must optimize the PTH-Fc expression levels, and then test the lettuce for its ability to safely prevent bone loss in animal models and human clinical trials.  

By Andrei Ionescu, Staff Writer

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