This blog post is part of a series celebrating the 100th anniversary of the discovery of insulin. You can check out previous blogs in this series, written by CIM Intern Eleanor Medley, here!
As an animal lover, I have found it both interesting and dismaying to learn about how many animals have been involved in the discovery and evolution of insulin. The ethics of animals in research can be debated at length; many animals are used in drug development as test subjects before clinical trials in humans. This post seeks to simply summarize the different ways animals have been involved in insulin research and manufacturing.
Dogs
Banting and Best’s primary experimental subjects for their early research that led to the discovery of insulin were dogs. Their general procedure consisted of surgically ligating the pancreatic ducts in dogs, then removing their pancreas some weeks later to isolate the extract. The extract would then be administered to a dog that was made diabetic by removal of its pancreas in hopes of improvement. [1]
At first, it was hard for the group to keep the dogs that they had operated on alive. Dr. Macleod, who oversaw the experiments in his lab, initially supplied a small allotment of 10 dogs.[2] By the end of the second week, 7 had already died. The team resorted to buying dogs on the streets of Toronto.[3] Banting commented, “dogs are very expensive and almost impossible sometimes to obtain.”[4]
In fact, it was desperation to keep one particular dog that Banting and Best had grown fond of alive that led to innovation in extract preparation.
Banting said “Necessity is the mother of invention…about the latter part of August we had a dog which we had become very much attached, because of its friendly habits and because of its obedience to orders and because of the love we had for the dog…he seemed so intelligent. He seemed to know the part he was playing in the experiments and what it was for”.[5] The scientists allowed this dog to run around the lab and simply called it when they needed a blood sample. The dog cooperated, and always demanded a piece of meat as a reward.[6]
After having its pancreas removed, the dog began to grow extremely weak, and Banting and Best were running out of available extract to treat it with. This led them to create the second version of their extract, which resulted in marked improvement in the dog. Banting recounted, “[the dog] was back in his former condition of the happy dog that was glad to see you, and was even able to jump out of his cage, two and a half feet to the ground, and ran around the floor wagging his tail”.[7]
Sadly, the dog ended up dying only 9 days later.[8]
Photograph of F.G. Banting and C.H. Best with a dog on the roof of the Medical Building. University of Toronto Libraries Thomas Fisher Rare Book Library, Insulin Collection, The Discovery and Early Development of Insulin, Best (Charles Herbert) Papers. Taken by Henry Mahon in August 1921. Dog 408.
Source: https://insulin.library.utoronto.ca/islandora/object/insulin%3AP10077
Cows
The next animal important in the discovery of insulin was cows. It was found that unborn animals have greater amounts of islets of Langerhans (tissue where insulin is produced in the pancreas) than adults, which led Banting and Best to obtain pancreatic extracts from fetal calves.[9] Depancreatized dogs responded well to this new kind of extract.
Then, the team tried a new technique using alcohol in the preparation of the fetal calf extract. They also tried the new method on a whole pancreas from an adult cow, and it worked! Once injected into a dog, the dog’s BG levels fell.[10] This was a major advancement, as beef pancreases could be easily acquired from the meatpacking industry. There was no longer a need to ligate the pancreatic ducts of dogs or use fetal calves.
Insulin continued to be sourced from beef (and pork) until biosynthetic human insulin hit the market in the 80s. Beef insulin is still available to Canadians through import from a manufacturer in the UK.[11]
Pigs
Large scale manufacturing of insulin was a challenge at first, so the University of Toronto accepted help from Eli Lilly and Co. in the U.S. who began to make preparations from pork pancreases.[12] Pork insulin is extremely similar to human insulin, differing at only one amino acid.[13]
Huge quantities of pig pancreases would be brought to Lilly’s headquarters in Indianapolis from surrounding pig farms by train. It took more than 2 tons of pig pancreata to produce only 8 ounces of purified insulin.[14] Lilly continued using pork pancreases to make insulin until the 1980s.[15]
Like beef insulin, pork insulin manufactured in the UK can still be purchased at Canadian pharmacies.[16]
Rabbits
In addition to dogs, the Toronto team of researchers also used rabbits in a lot of their early experimental work. After giving their insulin extracts to non-diabetic rabbits and observing a drop in BG, they figured insulin was fundamental to regulating BG levels in the body.[17]
Both the Toronto group and Eli Lilly used rabbits to determine the potency of their early insulin extracts. By observing how much insulin was needed to cause hypoglycemia in the rabbits, they could standardize potency. The original definition of a unit of insulin was (sadly) the amount of insulin that made a fasting rabbit go into convulsions.[18]
Fish
Insulin from certain kinds of fish is similar enough to human insulin to be effective.[19] In Japan after World War II, there was a shortage of mammalian materials to make insulin with, so insulin was sourced from bonito and tuna fish.[20]
Water Buffalo
Eva and Victor Saxl were a Jewish couple from Czechoslovakia living in Shanghai, China during World War II. Due to insulin shortages, they made their own insulin from water buffalo pancreases! (Read more about their story in another blog post, HERE). The couple also tested their extract on rabbits before administering it to people. [21]
Cone Snail
The award for the most interesting use of insulin in the animal kingdom goes to… the marine cone snail! These mollusks have insulin in their venom—they use it to stun their prey via hypoglycemia.[22]
The term “cone snail” includes a large group of over 500 different predatory snails. They can be found in warm tropical waters near reefs and they are extremely venomous—some are capable of killing a human in hours.[23] Cone snails can vary in size, but all have an armored spiral shell and a long appendage called a siphon to locate their prey. To hunt, cone snails fire a harpoon-like tooth with venom at their prey to immobilize it.
Cone snail venom is a complex mixture, or a cocktail if you will, of various compounds that cause paralysis.[24] One of the components is insulin which acts to induce hypoglycemic shock in the prey. For a long time, scientists wondered how the insulin in cone snail venom worked so quickly.[25]
In 2016, it was found that the cone snail insulin molecule doesn’t contain an extra region that makes human insulin molecules cluster together. Despite this, cone snail insulin can still bind to the human insulin receptor. Therefore, the cone snail may contain clues to making more rapid-acting insulin for people to use.[27] Who knew a killer cone snail could harbor helpful secrets to efficient insulin?
We have come a long way in insulin production and nowadays animals are not used nearly as much. In the 1980s, a method for making biosynthetic human insulin using bacteria was developed. Since then, animal-sourced insulin has become less common. As you can see, though, animals were critical to the development of insulin and continue to influence research. Thank you to all the animals that made life for people with diabetes better!
References
[1] Louis Rosenfeld, Insulin: Discovery and Controversy, >Clinical Chemistry, Volume 48, Issue 12, 1 December 2002, Pages 2270–2288, https://doi.org/10.1093/clinchem/48.12.2270
[2] Rosenfeld, “Insulin: Discovery and Controversy”
[3] Rosenfeld, “Insulin: Discovery and Controversy”
[4] University of Toronto Thomas Fisher Rare Book Library, Insulin Collections The Discovery and Early Development of Insulin, F.G. Banting Papers. “Fondness of Mongrel helped to find insulin” published in Toronto Daily Star January 30, 1923. insulin:C10041. https://insulin.library.utoronto.ca/islandora/object/insulin%3AC10041
[5] University of Toronto Thomas Fisher Rare Book Library, Toronto Daily Star, “Fondness of Mongrel helped to find insulin”
[6] University of Toronto Thomas Fisher Rare Book Library, Toronto Daily Star, “Fondness of Mongrel helped to find insulin”
[7] University of Toronto Thomas Fisher Rare Book Library, Toronto Daily Star, “Fondness of Mongrel helped to find insulin”
[8] University of Toronto Thomas Fisher Rare Book Library, Toronto Daily Star, “Fondness of Mongrel helped to find insulin”
[9] Rosenfeld, “Insulin: Discovery and Controversy”
[10] Rosenfeld, “Insulin: Discovery and Controversy”
[11] Health Canada, “Frequently Asked Questions: Animal Sourced Insulin.” Canada.ca, 15 Oct. 2010, www.canada.ca/en/health-canada/services/drugs-health-products/biologics-radiopharmaceuticals-genetic-therapies/activities/fact-sheets/questions-answers-animal-sourced-insulin.html.
[12] Rosenfeld, “Insulin: Discovery and Controversy”
[13] Gebel, Erika. “Making Insulin.” Diabetes Forecast, www.diabetesforecast.org/2013/jul/making-insulin.html.
[14] Gebel, “Making Insulin.”
[15] Gebel, “Making Insulin.”
[16] Health Canada, “Frequently Asked Questions: Animal Sourced Insulin.”
[17] University of Toronto Thomas Fisher Rare Book Library, Insulin Collection, F.G. Banting Papers. “The effects of pancreatic extract (insulin) on normal rabbits” published in the American Journal of Physiology September 22. insulin:T10038 https://insulin.library.utoronto.ca/islandora/object/insulin%3AT10038#page/1/mode/1up/search/rabbits
[18] Sahyun, Melville, and N. R. Blatherwick. “The Rabbit Method Of Standardizing Insulin.” American Journal of Physiology-Legacy Content, vol. 76, no. 3, 1926, pp. 677–684.,doi:10.1152/ajplegacy.1926.76.3.677.
[19] “Insulin.” Insulin – New World Encyclopedia, www.newworldencyclopedia.org/entry/Insulin.
[20] Ozawa H, Murai Y, Ozawa T. Yakushigaku Zasshi. 2003;38(1):11-27.
[21] Brown, Greg. “WWII Hero Saves T1D Lives with Home-Brew Insulin.” Beyond Type 1, 11 Oct. 2018, beyondtype1.org/wwii-hero-saves-t1d-lives-with-home-brew-insulin/.
[22] Cone snail venom reveals insulin insights. (2016, October 18). Retrieved September 07, 2020, from https://www.nih.gov/news-events/nih-research-matters/cone-snail-venom-reveals-insulin-insights
[23] Kapil S, Hendriksen S, Cooper JS. Cone Snail Toxicity. [Updated 2020 May 7]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470586/
[24] Kapil et al., “Cone Snail Toxicity”
[25] NIH, “Cone snail venom reveals insulin insights”
[26] NIH, “Cone snail venom reveals insulin insights”
[27] NIH, “Cone snail venom reveals insulin insights”
