Human Insulin: Definition, Types and Examples

Human insulin is a laboratory-grown artificial insulin that resembles the natural insulin produced by the human body. It helps in moving the sugar out from the blood to other tissues of the body where it is utilised as a source of energy. This type of insulin controls the excess sugar produced by the liver. It was developed through the decades of the 1960s and 1970s and got legal approval for pharmaceutical use in 1982. Before its discovery, animal insulin extracted from the pancreas of cattle and pigs (porcine) was used.

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What is Human Insulin?

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Human insulin is one of the recent discoveries of biotechnology. Earlier, cattle and pig insulin were used to treat diabetes but due to some allergic reactions caused after its use, the first synthetic insulin was produced. If we compare insulin extracted from animals and human insulin, the human biosynthetic insulin has better imitation of natural human insulin and therefore reduces antibody formation in the human body.

• Experiments on safflower are going on to figure out a new style of producing insulin by introducing human insulin into the plant, called biopharming.
• Even though the structure of human insulin is similar to natural insulin, it does not work the same, once injected.
• It is because the injected insulin clumps together and hence its absorption in the body is delayed, making synchronization with the body difficult.
• The main reason human Insulin discovery was to make cheaper insulin for people allergic to animal proteins.

History of Human Insulin

In 1975, the first successful Human Insulin was synthesized by Dr. Teusche in Switzerland. Later in the year 1982, it was approved by the US Food and Drug Administration (FDA). In the 1990s, analogue insulin was developed. It is more advanced as it allows short-acting insulins to act rapidly and longer-acting ones to have a steady action.

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Production of Human Insulin

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Insulin has two short polypeptide chains, A and B that are linked together by disulfide bridges. In mammals, the insulin is synthesized as pro hormone, i.e., it needs to be processed before maturation.

• Before maturation, it also has a chain C, which helps in processing and then removes itself before maturation.
• The main challenge at first was to develop chains A and B imitating insulin produced by humans.
• After 1983, when it was developed, they introduced it to the E.coli to produce insulin chains.
• Thus, human insulin is produced through rDNA technology by introducing synthetic insulin into the plasmid of E.coli for further multiplication.
• The plasmid (bacterial DNA) is first removed from the E. coli, then supplemented with the human insulin quality into it.
• The plasmid is put back to the bacteria and then the recombinant bacteria is placed in a fermentation tank where the bacteria utilizes the gene to start delivering human insulin. 

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Types of Human Insulin

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Fast-acting, intermediate and long-acting insulin are the three main categories of human insulin.

Regular Human Insulin

Regular Human Insulin is also called short or fast-acting insulin which starts showing its effects in just 30 minutes after injecting into the blood stream. The peak action is shown between 2-3 hours.

• The greater the dose, the quicker the onset of action, but it shows slower its effect.
• The total duration is up to 10 hours. Example of fast acting insulin include Actrapid, and Humulin S.

Neutral Protamine Hagedorn

Neutral Protamine Hagedorn or NPH also called intermediate acting insulin is a suspension, and hence should be rolled repeatedly to ensure uniform cloudiness of the solution. The most common example of intermediate acting insulin are Insulatard, and Humulin.

• It takes at least 2-4 hours to start acting, usually shows peak between 4-10 hours and has duration of up to 18 hours.
• The smaller the dose, earlier it shows the peak effect, while increased doses may show prolonged effects.

Premixed Human Insulin

It is an advanced form that is a mix of both regular and NPH insulin, hence the name pre-mixed human insulin. It is available in several different ratios. Example of pre-mixed insulin are Humulin M5 which has 50% of both the insulins while Humulin M3 has 30% regular and 70% NPH.

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Advantages and Disadvantages of Human Insulin

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The following are the advantages and disadvantages of Human Insulin:

Advantages of Human Insulin

• It does not cause much degradation at the site of injection.
• They are more quickly absorbed. 
• It is much cheaper than animal insulin.
• It is a better alternative to animal protein, especially for people having an allergy to animal insulin.

Disadvantages of Human Insulin

• The disadvantage of having human insulin is that it may result in side effects such as tiredness, weight gain, swelling, etc.
• Another drawback is that it takes more time to be effective.

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Things to Remember

• Human insulin is genetically engineered insulin that functions as normal insulin.
• Humulin S and Actrapid are the two examples of regular human insulin.
• Over dose of human insulin can cause hypoglycemia.
• Wheezing, sweating, and muscle cramps are side effects of consuming these.
• The onset of NPH is 1-2 hours.

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