http://www.nrc.nl/krant/artikel/print/1126504390855.html

(Translated from Dutch) 10 September 2005

Cultivated Meat

The Dutch cultivate minced meat in a petri dish

Marianne Heselmans

Vegetarian alternatives for meat will get competition from real artificial meat. The universities of Eindhoven, Utrecht and Amsterdam are working to cultivate muscles out of the stem cells of a pig.

SOON THERE COULD BE a meatmaker by the breadmaker. In the evening we throw some pig stem cells in the warm bioreactor and the following morning we get minced pork. During the night, we sleep soundly, not feeling guilty about stressed piglets and vast soy fields, as the stem cells transform into myoblasts, the myoblasts transform into small muscle fibers and the muscle fibers form tissue.

The idea is not so bizarre anymore, since the Senter/Novem Institute of the Department of Economic Affairs has allotted a two million euro subsidy for a project to cultivate pork meat out of stem cells. "Six years from now we might already have a product," says Dr. Henk Haagsman, Professor of Meat Sciences at the University of Utrecht. "No loin, yet, but indeed a kind of minced meat the catering industry can use in pizza's or sauces.''

Haagsman is the leading researcher on this meat cultivation project, which started in April. Five researchers have started at the Universities of Eindhoven, Utrecht and Amsterdam. Cell biologists at Utrecht are searching for suitable stem cells and methods to let them grow into as much muscle as possible. Microbiologists at Amsterdam design the environment for growth. And tissue engineers at Eindhoven design bioreactors in which small muscle tissue grows quickly. Sausage manufacturer Stegeman, as of now owned by the American Sara Lee company, has also joined. Aside from the Senter/Novem-subsidy, the participants together allot an additional 2.3 million euros to the project.

The Netherlands is the first country where manufacturing cultivated meat is being approached in a systematic way. The only patent in this field is owned by a Dutch citizen. Researcher and industrialist Willem van Eelen took a patent, together with Willem van Kooten and Dr. Wiete Westerhof, in 1999 on a method to produce meat in vitro. For the patent, on which Van Eelen worked for about 25 years, he engaged in primary research and he consulted experts. Van Eelen, now 82, is still actively involved in the project. He managed the subsidy request for Senter, and now also raises funds around the world. Yet the idea is much older.

In a 1932 essay, Winston Churchill, a journalist at that time, suggested that it would be more efficient to cultivate wings and breasts in vitro rather than growing an entire chicken. Churchill was probably inspired by Nobel Prize winner and surgeon, Alexis Carrel. In 1912, Carrel cut a piece of heart muscle from a chicken embryo and placed it in a bowl with nutrients. He continued to feed the little muscle well and, when he died 32 years later, the muscle was still growing. If you can keep a chicken muscle alive by feeding it in a bowl, why would one not be able to similarly grow pieces of chicken?

The first laboratory that tried to produce meat in vitro was SymbioticA, a laboratory of the University of Western Australia, where artists work together with tissue engineers. First they tried to produce some meat from the muscle stem cells of sheep. That didn’t work out so well. But later they indeed succeeded to grow muscle tissue from a frog. They presented the rather minuscule frog meat with a calvados sauce on a exhibition in Nantes, France.

At about the same time, tissue engineers at Touro College in New York grew muscle tissue from a goldfish, expanding it fourteen percent in a week. This research for NASA, published in 2002 in Acta Astronautica, was meant to develop a means of providing meat to astronauts. The Americans used serum from fetuses of calves as part of the growth medium. Making meat this way is expensive, however, so they also experimented with a liquid made of crushed maitake. Maitake is a nutritious mushroom, and in this medium, the goldfish tissue managed to survive, but did not grow as quickly.

"Very funny to read", comments meat scientist Haagsman about the experiments so far. "Certainly those things about these bio-artists. But it is not efficient. You throw some muscle tissue in a growth medium and you watch if the tissue will grow. You will always get little growth this way."

The Dutch are going to work on it thoroughly. They will investigate how one can get abundant amounts of muscle tissue in a controlled and cheap way. Such muscle tissue, they believe, cannot be built from an existing piece of muscle, but from well-characterized cells. The first step is to search for stem cells that produce the maximum number of daughter cells. This is necessary, because you need to have many cells in the bioreactor in order to get plenty of meat. Then one must be able to easily change these stem cells into muscle cells. Quite a lot is already known about "satellite cells," which can grow into new muscle. But the people from Utrecht are still looking for better muscle stem cells, called MDSC (muscle derived stem cells). These split longer and easily grow into muscle cells. They have been isolated from muscle tissue of humans, mice and rats, and should likewise be possible to isolate from piglets. And, says Haagsman, the predecessors of the satellite cells in the fetuses are also promising.

Utrecht wants to research the capacities of embryo stem cells out of which the muscle cells develop. Well-characterized stem cells have already been isolated from the embryos of humans, mice, and rhesus-monkeys, and the researchers now hope to have generated stem cells out of embryos of pigs within two years. They do this by letting artificially inseminated egg cells grow into a blasto-cyst. From that ball they pick the inner cells with a long needle. That is not that difficult. It is more difficult to keep the cells undifferentiated during the cultivation. This is now done by letting them grow on the embryo cell of mice, which excrete growth factors naturally. But this is cumbersome, so one has to search for other growth factors, so that these can be added to the growth medium.

Haagsman thinks that they will succeed. Some proteins have already been found which keep cells undifferentiated, and with these it has recently been possible to proliferate human stem cells without mice cells. The professor thinks they will also succeed in discovering the most important growth factors which make an embryo cell grow into a muscle cell. Recent research has detailed conditions under which human stem cells can develop into muscle cells. (PLOS Medicine, June 2005). "The developments are so fast."' Haagsman expects that only a handful growth factors are needed for each step.

For texture and protein the muscle cells have to develop into fibers, very long cells which produce plenty of myosin and actine protein. The little fibers make the muscles. "We can already make small muscles with a length of two centimeters," says dr. Carlijn Bouten, tissue engineer of the technical university Eindhoven (TU/e). "And if we stimulate them with electricity they can also contract like a real muscle."' The small muscles of the TU/e, made to do research on how mechanical load damages muscles, are coming from muscle cells of mice grown in collagen gel.

Collagen is naturally found in the connective tissue within muscle and, therefore, within meat. The trick is to let the collagen gel shrink a little in one direction, so that the muscle cells are ordered one behind the other. One must also starve the cells a little, which causes them to develop into little fibers. The little fibers grow into bigger ones if, for example, you exercise them by submitting them to mechanical strain. With contractions, growth hormones may not be needed.

It took the researchers at Eindhoven four years to develop methods of making long small mice muscles. Bouten does not expect it will take longer to make small pig muscles. And then one in fact already has minced meat. But a loin will take longer. The problem with making loin is that inner cells need nutrition. Theoretically one could let tiny veins grow within. Researchers of the MIT were already successful in causing veins to grow in artificial human muscle tissue (Nature Biotechnology, July 2005). But for meat this technique would be too cumbersome.

An alternative solution, says Bouten, is to let a thin muscle sheet grow on a membrane which one then curls up into thicker meat, a kind of rolled ham or shoulder. Her group has already made some of these half centimeter thick tissue sheets, one of them in the shape of the logo of the TU Eindhoven. Bouten: "One can also simulate the blood flow by putting thin tubes in the tissue. Or you can pump the nutrients under pressure into the tissue."'

Short, thin fibers render meat tender; long fibers feel like wires. Tissue engineers could make varieties with that. But for a solid bite a loin must also contain connective tissue cells, which produce the elastin and collagen of the protein chains. And they need fat cells for the taste. Bouten would already add the connective tissue cells at the start of the cultivation, because these make collagen. She would add the fat cells later. "But I find it more important to design bioreactors wherein muscle fibers can be made quickly and economically, rather than making a loin'', says Bouten.

In short it seems technically possible indeed to cultivate meat, particularly minced meat. The technique will, however, only further develop if a sufficient number of parties see a market for it. A big advantage of cultivated meat over the meat industry is of course that it is animal friendly: only the stem cells come from an animal. In the growth medium the researchers don’t want any animal products, precisely because of the animal friendly image cultivated meat must maintain.

But will it be too expensive? Haagsman thinks that cultivated meat will be able to compete with pork and existing meat substitutes in terms of costs. The growth medium will predominantly consist of water and glucose. The growth factors can come a cheap source, such as modified fungi, a topic microbiologist Dr. Klaas Hellingwerf of the UvA presently focuses on.

Amino acids may be the most expensive ingredient. "Based on the present prices of amino acids, we have computed that one kilogram of cultivated meat will be as expensive as one kilogram of beef."' The energy for the bioreactors can come from the sun, and the consumption of water and the space needed will be significantly less than those of the meat industry. Whether it will also be less than with meat substitutes using vegetable proteins has yet to be determined.

Haagsman thinks the taste of cultivated meat will be very close to that of real meat. Taste is predominantly determined by the protein in the muscle tissue, and this same protein is in the cultivated meat. There is no blood in it, but there is hardly any blood in the meat of chicken. There is iron in it, however, because the muscle protein myosin contains iron.

One can also let vegetables and other vegetarian protein products resemble meat by adding artificial flavors, as is done at present. The pieces of Quorn (using fungus protein), and also those from the new meat substitute Valess (milk protein), already taste much like pork meat. Yes, Haagsman says: "But with that you certainly fool the consumer." And he admits, the taste of cultivated meat probably never will become as good as real meat. But given environmental pressures, real meat will become scarcer in the future, and may only be consumed on special occasions (as is the custom already in many cultures).

Cultivated meat could have the additional advantage of allowing one to control the fat content or improve the ratio of good fats to bad fats. And the danger for infection is lower, because the bioreactors can be kept sterile, unlike animal farms and slaughterhouses.

In the meantime the non-profit organization New Harvest has been created in the United States, with three Dutch people on the Board of Directors, working to bring cultivated meat closer to reality.