Cultured Meat

Abdus Anwar April 03, 2018
Cultured Meat
The science of cultured meat
Advances in tissue engineering have allowed us to make great strides forward in the
healthcare industry by allowing us to repair damaged muscle tissue via the use of stem
cells. Well it turns out that the very same technology is now being used to grow different
cuts of meat from individual stem cells rather than by growing an entire animal, only to eat
specific parts (1).
The advent of three technologies has allowed for the possibility of cultured meat: stem cell
isolation and identification, ex vivo/in vitro cell culture, and tissue engineering. The first step
requires choosing an initial type of cell from the desired animal. The most commonly used
cells are undifferentiated skeletal muscle cells known as myoblasts or satellite cells.
Myoblasts are adult stem cells which are responsible for regenerating human muscle tissue
after injury. Once they have been isolated and cell lines have been established for
renewability, they can be cultured in two phases: proliferation followed by differentiation.
Myoblasts are extremely easy to differentiate but difficult to proliferate without
differentiation. This is because self-renewal of stem cells requires very specific conditions
and factors in order to remain multipotent, or capable of self-renewal. During the
proliferation phase, the goal is to promote self-renewal of the myoblasts in order to establish
the largest number of cells possible, in order to achieve a high yield. With current
methodologies, the number of doublings in cell number is 20. One way to prolong the
undifferentiated state is to use a combination of mild enzymatic treatment and trituration
during harvesting and then growing the stem cells in an environment containing stem cell
maintenance factors. Once a critical mass of stem cells has been established, they can be
differentiated into skeletal muscle cells by using differentiation markers like MyoD,
myogenin and embryonic isoforms of muscle myosin heavy chain (2).
This is the process used by a Tennessee-based start-up company, that is paving the way
for cultured meat to become mainstream. A patent was filed by Memphis Meats in 2014 that
protects the method for producing cultured muscle tissue by: modifying a self-renewing cell
line of an animal species with a myogenic transcription factor to produce a myogenic-
transcription-factor-modified cell line, and inducing it using an inducible/repressible system
to maintain self-renewal or differentiate the cell line. This system is essentially an on-off
switch where the addition of doxycycline but the absence of 17B-Estradiol, will prolong the
self-renewal phase of the stem cells. Once the cells have reached a critical mass, they can
be transferred to a media that is absent of doxycycline and contains 17B-Estradiol, which
will cause their proliferation (Figure 1) (9).
Additionally, scaffolds and mechanical stimuli are very salient to triggering the proliferation
phase and causing the protein to organize into contractile units in a similar fashion to that of
muscle in a living organism. This type of environment is achieved by the use of a collagen-
like gel or a biodegradable scaffold on the surface of the dish. However, scaling this
process up will require the use of 3-D scaffolds that are able to provide nutrients and
oxygenate the tissue, as well as provide the necessary scaffold and mechanical stresses
necessary for proper and efficient growth of the cells. This is what allows the cells to carry
Abdus Anwar April 03, 2018
out their essential functions necessary for muscle growth such as deposition of collagen in a
tight fiber between the anchors in the scaffolds. Research is ongoing as to whether cyclic
mechanical stretching or electrical stimulation promote muscle growth in culture (4).
Oxygenation in physiological conditions is carried out by myoglobin, which is a heme-
carrying protein that is likely responsible for the taste of meat. This protein is central to the
production of skeletal muscle because it oxygenates the tissues and gives them their red
color. Oxygenation of the tissue culture environment to promote maximal myoglobin
function is one of the big challenges of the process, especially at larger scales. It requires
the use of three-dimensional scaffolds that provide the suitable mechanical stresses for
proliferation, as well as innervation of the tissue with an oxygen supply (2). In order to scale
up the process of culturing meat, bioreactors with large production capacities as well as
large surface areas for sufficient tissue oxygenation would be required. One creative
solution to problem of oxygenation is the use of oxygen carriers in suspension which are
advantageous because they can oxygenate tissues without the use of fixed structures (5).
Sustainability and health
Humans have been domesticating livestock for comestible purposes for thousands of years
and as the demand for meat rises due to population growth and increasing incomes, so too
will the need for more sustainable means of meat production. It is expected that the demand
for meat will double between 1999 and 2050. Currently, the environmental impact of
comestible livestock is staggering. Of the global contribution, it's use constitutes 30% of
land, 8% of freshwater, and 18% of greenhouse gas (GHG) emissions. The sources of the
greenhouse gasses are deforestation, ruminant fermentation, and manure management (1)
Researchers performed a life cycle assessment (LCA) to glean the environmental impact of
large-scale cultured meat production. The study concluded that to produce 1000 kg of
cultured meat, it requires 26-33 GJ energy, 367-521 m3 water, 190-230 m2 land, and emits
1900-2240 kg CO2-eq GHG emissions. When compared to conventional meat production,
this is 7-45% lower energy use, 78-96% lower GHG emissions, 99% lower land use, and 82
- 96% lower water use. Thus, cultured meat is more environmentally friendly in every
respect. It is also important to note that this process will almost certainly become more
efficient as advances are made in tissue culture technology, thus further reducing the
environmental impact; the same cannot be said about factory farming (1). In fact, it appears
that conventional meat production is close to its maximum capacity due to it's 2-dimentional
use of land. Thus, food prices will continue to increase as land runs out. With the current
bioconversion rate of pigs and cattle being 15%, there a wide margin for improvement (2).
In terms of health, current meat production processes are highly susceptible to
contamination which is very conducive to the spread of animal-borne illnesses (1). This is
due to the meat's prolonged and frequent exposure to the external environment where it
can easily become contaminated by harmful pathogens such as avian and swine flu (2).
One study found that 120g of meat/day or 30g of processed meat/day would significantly
raise the relative risk of colorectal cancers. Growing meat in aseptic environments has the
potential to reduce these health risks by preventing contaminants that can infiltrate tissue
during the life of the animal and by contamination from fecal matter or blood components
Abdus Anwar April 03, 2018
from within the animal, at the time of slaughter. The other method of preventing food-borne
illnesses is by carefully selecting an initial batch of stem cells that are free of potential
cancer cells, which are normally present in conventional meat. This allows for the
customization of not only the percent protein in the meat but also the minimization of the
possibility that there may be cancer cells present in the meat (7).
Challenges and prospects
Apart from the scientific and technological barriers addressed earlier, there is a concern that
there will be resistance to the adoption of cultured meat as an alternative to traditional meat
(6). The reasons are often quite irrational such as the idea being creepy, unnatural, or
unsafe. The first thing to note is that there is nothing natural about factory farming where the
animals are pumped full of antibiotics and growth hormones and are living in such disease-
ridden conditions. And regarding the point about safety, the ability to control exactly what
cells your meat is made of and under what conditions its grown, among other things, makes
it a much safer option.
Current meat production also has large implications for animal welfare. The conditions in
factory farms are what many would call, without ambiguity, highly unethical, yet we continue
to participate in it for a lack of alternatives apart from going cold turkey. Studies have shown
that public debate on animal welfare has increased steadily and the consumption of meat by
non-vegetarians has decreased proportionally. Additionally, meat substitutes based on Soy,
milk and wheat proteins have also been increasing. In 2010, frozen meat substitute sales
reached 267 million USD. Thus, this may indicate that non-animal-based meat alternatives
may be a viable alternative (2).
The advantages of cultured meat are not limited to environmental and health benefits but
also nutritional, taste, and textural aspects. Culturing meat in this way allows for precise
control of the entire process, from selection of the types of cells to the components of the
growth media, which allows for endless customization of the final product in terms of
protein/fat content as well as pure muscle cells without contamination from cancer cells (1).
If cultured meat is to replace factory farming as the norm, it should ideally mimic meat in all
of its physical sensations, such as appearance, smell, texture, and taste. This will no doubt
require careful selection of skeletal muscle cells and optimization of growth media
conditions (2). Memphis Meats has already managed to grow hamburgers and, recently, a
crispy chicken sandwich, both of which have passed the taste test. The price of these meat
alternatives has also been dropping exponentially since their introduction in 2013. The cost
of a synthetic hamburger has dropped 3000-fold from $325,000 in 2013 to $11.36 in 2017
(8).
In conclusion, cultured meat has proven itself to be superior to factory farming in almost
every respect: sustainability, environmentally friendliness, and even health. However, there
are some challenges that are to be overcome before it can be universally adopted. These
are scaling up, overcoming public perception, and decreasing the cost. Nevertheless, the
technology is progressing at a very fast pace and is getting closer to market every day.
Abdus Anwar April 03, 2018
Appendix
Figure 1. Inducible promotor systems for the controlled self-renewal and
differentiation of stem cells.
Abdus Anwar April 03, 2018
References
1. https://pubs.acs.org/doi/abs/10.1021/es200130u
2. https://www.sciencedirect.com/science/article/abs/pii/S0309174012001210
3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3551074/
4. https://www.ncbi.nlm.nih.gov/pubmed/15998207
5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4648904/
6. https://www.emeraldinsight.com/doi/abs/10.1108/BFJ-11-2012-0288
7. https://www.ncbi.nlm.nih.gov/pubmed/24214798
8. https://www.sciencealert.com/lab-grown-burger-patty-cost-drops-from-325-000-to-12
9. https://patents.google.com/patent/WO2015066377A1/en

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