Knowing about insulinPancreas is an organ lying horizontally in the abdomen behind the stomach between liver and spleen. Insulin is a hormone produced by the beta cells in the islets of pancreas.Deficiency of insulin (in Type 1 Diabetes) or decreased responsiveness of insulin (in Type 2 Diabetes) causes high blood sugar levels in the blood.In 1921, Sir Fredrick Grant Banting and Charles Herbert Best conducted a series of experiments to understand the role of the pancreas and to identify the secret hormone secreting from the organ that controls blood sugar levels. Banting was of the opinion that the secretion is being hampered by the pancreatic juices and if he could shut the pancreas and keep the islets open, he could trace the secret substance. After consistent trials, they succeeded in extracting the hormones secreting from the islets and termed it as insulin.Insulin is a polypeptide hormone consisting of A and B chains of amino acids (protein).Chain A contains 21 amino acids and chain B contains 30 amino acids. The amino acid sequence is unique to each species. For example, the difference in the amino acid sequence of human, porcine (pork from pig) and bovine (beef from cow) insulin is:.Porcine insulin differs from human insulin only by one amino acid as opposed to bovine insulin which differs by three amino acids.The human insulin is produced by a recombinant DNA technology (the process by which desirable fragments of DNA from two different species are inserted into a host, where it is replicated) using yeast or E. coli bacteria. Insulin analogues are created by altering the amino acid sequences using genetic engineering techniques.Functioning of insulinImagine the cells as lock and insulin as key for the glucose to enter in to the cells. When food is consumed, the glucose released from it reaches the blood. The beta cells in the pancreas are signalled to release insulin (the key) for the cells (the lock) to take in the glucose. Insulin helps to push the glucose from the blood into the cells so it could be used for energy.Characteristics of insulinInsulin cannot be taken as a pill, as it is a protein and will be digested by the stomach enzymes. It is administered as a subcutaneous injection (in the fat below the skin). Insulin is characterised by the time it takes to reach the blood from the injected site (onset of action), peak action at which maximum effect of insulin is produced (peak), followed by the time it continues to lower the sugar levels (duration of action). Based on these three characteristics, insulin is divided into three types - short, intermediate and long-acting insulin.In humans, insulin is produced continuously even when the food is not eaten to maintain the blood sugar levels produced by liver and other organs (background insulin). When the food is consumed, sugar spikes produced from the breaking down of food particles also cause spurts of insulin (meal time insulin). To mimic this physiological pattern, long-acting or intermediate acting insulin is given that acts as a background or basal insulin and short or rapid-acting insulin is given with meals that acts as mealtime or prandial insulin.Pre-mixed insulinDifferent combinations (30 or 50) of short-acting or rapid-acting insulin with intermediate acting insulin are given twice a day to mimic body's insulin production. (Example: Mixtard 30/70 contains 30 per cent of regular or short-acting insulin and 70 per cent of intermediate acting insulin. Similarly, Humalog mix 50 contains 50 per cent of lispro or rapid-acting insulin and 50 per cent of intermediate acting protamine lispro insulin).Even though they are relatively economical, they are not as effective as four times of insulin injection therapy involving one long acting insulin therapy at bed time, followed by three meal times (prandial) insulin therapy.Newer insulinInsulin degludec, one of the newer insulin analogues and whose effect lasts up to 42 hours, seems to cause less hypoglycaemia. Also a premixed combination of 30 per cent aspart or rapid-acting insulin with 70 per cent of degludec is available as ryzodeg (30/70).Insulin inhaler is available in the United States. It is taken as pre-meal or prandial insulin. Even though it may have the disadvantage of taking large doses to achieve the right insulin concentration in the blood, it has the advantage of inhalation instead of injection. (This can be an enticing option for people with needle apprehension.) Currently weekly once insulin injection is undergoing trials.Mode of administrationAll types of insulin are generally administered subcutaneously (in the fat under the skin). During hospitalisation, regular or rapid-acting insulin is administered intravenously depending on the clinical situation of the person.Administration techniqueGenerally abdomen, upper and outer part of the thighs and backside of the upper arms are the sites where insulin is administered. However, abdomen is the preferred site as it helps in uniform and fast insulin absorption..Any scarred tissue, muscle and other such areas should be avoided. Insulin can be given through syringes or through pens with insulin cartridges. After withdrawing theright dose of insulin in units, the needle of the loaded syringe is inserted perpendicular to the skin surface and the plunger is pushed gently. The syringe is held in place until a count of 10 to make sure that the required amount has been delivered. The syringe is then withdrawn along with the needle. The injected site should not be rubbed. In case of insulin pen loaded with insulin cartridge, the knob of the pen should be dialed to the right dose before the needle attached to the pen is inserted. The plunger has to be pushed and after counting to 10 while holding the plunger down, it should be made sure that the measured dose has been delivered.It is recommended to change the needle after a maximum of three to four uses .Insulin injection site should also be changed after each administration to avoid lumps and bumps.StorageInsulin can be stored at a room temperature for about a month. It should not be placed under direct sunlight (like on window sills) or in the glove compartment of the car. Insulin pens can also be carried in purse.If the insulin is stored in the fridge, after withdrawing insulin in the syringe, it should be rolled in between both hands few times before administration to avoid the pain from injecting cold insulin.While travelling, cooling packs for insulin storage are also available.Adverse reactionsWith the advent of purified human insulin, chances of adverse effects are very rare.Giving insulin in scar tissue or not rotating so injection site will not only result in lumps and bumps (lipodystrophy i.e. thickening or thinning of fatty layer) but also cause pain while injection and poor absorption.CautionWhile taking insulin, food should be taken as per instructions, especially with prandial insulin. If the person takes prandial insulin and does not take food at the right time or skips the meal, he or she may have low sugar levels (blood sugar levels below 70 or hypoglycaemia).Advantages of insulin•\tBetter and faster sugar control.•\tInsulin almost always works in all kinds of Diabetes.•\tInsulin injection therapy is usually designed to mimic body's insulin production.Disadvantages of insulin•\tExpensive•\tChance of weight gainCandidates for insulin administration•\tPeople with Diabetes.•\tPeople with Diabetes and who had oral anti-diabetic medication failure.•\tPregnant women with Diabetes.•\tPeople with Diabetes hospitalised for surgery or for serious infection.•\tPeople with Diabetes and with renal failure.•\tPeople with pancreatic damage related Diabetes (example, chronic pancreatic damage because of alcoholism).Insulin pumpsInsulin pump is a good option, especially for people with Type 1Diabetes, as it eliminatesfive times per day of insulin injection pricks. It is a pager-like device that injects insulin 24 hours a day. A small motor pushes the piston which delivers insulin through a tube to an area under the skin.This tube has to be changed every three days.Advanced models also have the facility of wireless connection with glucose monitoring device, which predicts the hypoglycaemia trends in people.The future of insulin therapyThe ultimate goal is to eliminate the need of injecting insulin from outside and restoring the ability of pancreas to secrete insulin.Closed loop insulin delivery system, also known as artificial pancreas, is being explored currently and hopefully soon will become the future of insulin therapy. Dr Suganthi Kumaran is a consultantDi.abetologist.