Seeding blood protein production

A staple food for half of the world’s population, rice has been the focus of many studies, primarily to increase yields. In early October, the United Nations’ Food and Agricultural Organization forecast that the total rice production worldwide for 2011 would exceed 480 million metric tons.

Chinese researchers have recently proposed to use rice for a different kind of harvest, using the plant to enable the large-scale production of an important protein in the human blood. While highlighting their technique, the report also took note of safety and environmental concerns to be addressed in order to achieve the stated goal.

Global demand

Human serum albumin makes up more than half of the protein found in blood plasma, the yellowish liquid component in blood. The HSA protein transports blood-clotting factors and is used in treatments for severe burns, shock and cirrhosis of the liver, among other conditions. In the report by Yang He from China’s Wuhan University and his colleagues, global demand for the HSA protein is about 500 tons annually. However, according to the World Health Organization, some 92 million blood donations are collected annually worldwide, which is not enough to meet the demand.

Previous studies have focused on developing non-animal-based, low-cost alternatives to producing the blood protein in large quantities. Researchers have developed production methods using bacteria, yeast and plants such as tobacco and potatoes, but the yields haven’t been high enough for large-scale tests.

In looking at rice for what they called “molecular farming” to produce important proteins for pharmaceutical applications, He and his colleagues point to the stability of cereal crop seeds and the seeds’ ability to store high levels of protein for long periods of time. Additionally, they said, rice has a fairly low risk of contaminating other plants outside of the laboratory and causing harm instead of the intended health benefits.

This is not the first time people have turned to nonhuman sources to produce needed compounds. For example, flu vaccines have been produced for decades in fertilized chicken eggs. Recent studies have shown the vaccine can be successfully produced in bacteria as well, which is good news for people with egg allergies who might otherwise risk harmful side effects from a flu shot.

For the study, He and his team genetically modified brown rice plants to produce the blood protein. Seeds from the viable transgenic plants were harvested and the protein was extracted and purified. Tests of the extracted protein on rats being treated for cirrhosis of the liver indicated that the rice-produced blood protein “was equivalent to the plasma-derived HSA.”

Researchers were able to produce 2.75 grams of the blood protein per kilogram of rice grown. They estimated that the world demand for the HSA protein annually is 500 tons, and a single metric ton is equivalent to a million grams. “Due to the high dosage of HSA in clinical applications,” they noted, “large-scale production of [rice-derived protein] requires field production of transgenic rice.”

Several challenges

This idea poses several challenges since it involves allocating rice fields for protein production while also ensuring that enough of the staple food crop is grown to meet global demand. Safety and environmental concerns will need to be addressed to realize this plan, the scientists acknowledged in their conclusion.

The study was published online the week of October 31 in the journal Proceedings of the National Academy of Sciences USA.

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