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Taking Cultured Meat to the Next Level

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With its origins in the late 1990’s, lab-grown or cultured meat, is produced by providing stem cells extracted from the muscle of an animal with a suitable growth medium and nutrients, enabling them to proliferate and then differentiate to form muscle tissue. Creating meat in this way could help to address some of the environmental and ethical issues associated with livestock farming, as well as offer health benefits to consumers.

Pairing cellular agriculture with genetic engineering could also enable the development of novel foods, with non-native features, that may be nutritionally enhanced. In a study recently published in Metabolic Engineering, researchers from Tufts University engineered bovine cells to endogenously produce phytoene, lycopene and β-carotene, and found a reduction in lipid oxidation levels when this cultured meat was cooked.  

Technology Networks had the pleasure of speaking to Andrew Stout, lead author of the study, to learn how these cells were created and explore the benefits of engineering in the abilities to produce additional nutrients. Andrew also discussed some of the challenges that are so far limiting the wider commercialization of cultured meat and how this may change in the future.

Anna MacDonald (AM): Can you give us an overview of the process by which the cow cells were engineered to produce the carotenoids?

Andrew Stout (AS):
To do this, we inserted three genes into the cells which encode enzymes that convert native compounds into carotenoids. Specifically, the first gene in this pathway (phytoene synthase) takes a native chemical and turns it into the carotenoid phytoene. The second gene (phytoene desaturase) turns some of that phytoene into a second carotenoid called lycopene. And the third gene (lycopene cyclase) turns some of that lycopene into a third carotenoid called beta-carotene. In that way, we're able to get cow cells to produce three different carotenoids that aren't naturally produced in bovine tissue. To engineer the cells, we used a system called the Sleeping beauty transposon system. This system is essentially a "cut and paste" tool which randomly cuts open the cells' genomes and inserts new DNA which we provide (in this case, the genes for carotenoid-producing enzymes).

AM: Why were beta-carotene, phytoene and lycopene chosen in particular? 

There were several reasons for this. The first and most important was their role as dietary antioxidants. A key mechanistic link between red meat consumption and colorectal cancer is through lipid oxidation. This oxidation leads to the production of free radicals that can interact with tissue in the colon, damage cellular DNA, and ultimately contribute to cancer formation. Antioxidants can act to "quench" those free radicals, thus potentially inhibiting their cancer-causing potential. As carotenoids are powerful antioxidants, they offer a promising target for improving the nutritional features of cell-cultured meat.

Other reasons include the importance of beta-carotene as a vitamin A precursor, previous demonstrations of phytoene synthase efficacy in mammalian cells, and also as a sort of homage to golden rice, the first major demonstration of using genetic engineering to nutritionally enhance a food product.

AM: Were there any side-effects as a result of the nutritional engineering?

There were a few. The most obvious was a reduction in growth rate in bovine satellite cells that were engineered with carotenoid-producing enzymes. This would have negative implications for production processes if it proves to be unavoidable. Interestingly, though, in immortalized mouse muscle cells, this reduction in growth rate wasn't seen. Instead, cells producing carotenoids actually grew faster than non-engineered cells. One explanation for this could be that immortalized cells are more "robust" and are more amenable to engineering than the primary (non-immortalized) cow muscle cells we used. It's possible that immortalized cow cells would show growth-effects more like those seen in the mouse cells, which would turn this production down-side into a production up-side. Another side effect we saw was a change in color of the cells -- they took on a reddish tinge with the production of the carotenoids. I don't think this is really a "positive" or "negative" effect, but it is pretty interesting. Other potential side-effects that would need to be looked into would be the effects of carotenoids on cell differentiation, on the prevalence of other nutrients (e.g., cholesterol, etc.), and on flavor, texture, aroma, etc.

Karen Steward (KS): Why do you think you saw lower levels of lipid oxidation when the cell cultured meat was cooked compared to conventional meat?

Since carotenoids are antioxidants, they act to quench oxidation in cells during storage, cooking, etc., so we would expect lower lipid oxidation if the cells are producing carotenoids and therefore increasing the total cellular level of antioxidants.

KS: What do you see are the benefits of engineering in the abilities to produce additional phytonutrients to beef cells, as opposed say to having a traditional steak with some vegetables? Is there a risk that in providing these nutrients through meat intake a diet would consequently lack fibre which could impact gut health?

This is a fun question! I think we're an extremely long way from actually being able to use this technology to replace vegetables on our plates (and anyways, what a culinarily boring world that would be!) I like to think of this technology not as a replacement of vegetables, but an enhancement of meat. For instance, not all vegetables are high in carotenoids, so if you can get those nutrients from another source in your meal, then your overall consumption of them can increase. Also, the roll of carotenoids in specifically inhibiting oxidation in meat can act to mitigate some of the negative health implications of meat consumption without aiming to reduce vegetable consumption. As a final note, I'd like to think of this work as really just the tip of the iceberg of what's possible. There are so many options for enhancing meat with this or similar technologies--enhanced flavor, therapeutic activity, enhanced smell, etc. I think there's a world of totally novel foods that are possible and that would expand our culinary palette, not reduce it.

KS: Is there any need to start with cow cells? Could you essentially start with any cell type or are there limitations?

No need at all! I think this would likely work for all mammalian cells, and there's a strong chance it would work for avian and fish cells as well. We wanted to work with bovine cells because beef is such a major contributor to meat-associated greenhouse gas production and is one of the main red meats consumed around the world. As such, I think it's a really important target for all cultured meat work, including nutritional engineering.

AM: What challenges are so far limiting the wider commercialization of cultured meat?

The key hurdles are cost and scale. The field needs to reduce the cost of growth media (likely by reducing the cost of growth factors, reducing cellular reliance on growth factors, finding growth-factor alternatives, or other creative solutions), and to increase the scalability of cell culture (increased growth rate, increased maximum cell density, etc.). There are certainly plenty of other challenges, such as regulatory and consumer reception, demonstration of nutritional and food-quality value, and demonstration of food-safety, but I think that right now cost and scale still reign supreme.

AM: Where do you see the future of cellular agriculture headed?

A good question! I'll answer for two slightly different technologies.

First, for cultured meat specifically:

I think in the near future, the field is heading towards a bit of a "realignment" or specification in terms of goals, expectations, hype, etc. I think that this can be seen in some of the ways that companies are starting to look at their products with a bit more nuance, such as looking at the possibility of hybrid cell-based/plant-based products, which could overcome some of the cost/scale barriers of a fully cell-cultured product. Beyond that, I like to think that there will be an expansion of creative solutions to problems, or creative new ways of thinking about cell cultured meat. This could come in the form of looking at agricultural waste products for cell culture components, exploring novel genetic strategies to improve growth / reduce cost, or looking into alternate culture strategies / bioreactors.

Then for cellular agriculture more generally:

I think cellular agriculture in general, while certainly offering its own challenges and hurdles, is a lot further along the developmental pathway than cultured meat. I'm thinking here of products that are already on the market and demonstrably feasible such as recombinant milk proteins (Perfect Day Foods), recombinant collagen proteins (Geltor, Inc.), or recombinant proteins to improve plant-based products (Impossible Foods). I think these technologies are going to continue coming out and coming down in cost, allowing a bunch of new awesome products to come out and accelerate the development of plant-based or fermentation-derived products.

Andrew Stout was speaking to Anna MacDonald and Dr Karen Steward, Science Writers for Technology Networks.