Our cells communicate using a molecular postal system; the blood is the postal service and hormones are the letters. Insulin is one of the most important hormones, carrying messages that describe the amount of sugar that is available from moment to moment in the blood. Insulin, made in the pancreas and added to the bloodstream when sugar levels are high, spreads throughout the body and binds to insulin receptors on the surface of liver, muscle, and fat cells. Insulin tells these organs to take out sugar from the blood and store it in the form of fat or glycogen.
However, when insulin function is impaired either by damage to the pancreas or old age, glucose level in the blood rises dangerously, leading to diabetes mellitus, commonly referred to as diabetes. High glucose levels lead to dehydration, as the body attempts to flush out the excess sugar with urine. It also leads to life-threatening changes in the pH of the blood, because the body turns to other acidic molecules for delivery of energy.
This lack of insulin is solved by using pig insulin instead, which only differs from the human insulin by one amino acid. The cow insulin is also extremely similar. Because of their similarity to the human insulin, these forms of insulin are recognized by our own cells and may be used in therapy for diabetes. However, since using other animals’ insulin may cause problems with impurities, scientists have engineered bacteria to manufacture pure human insulin through recombinant DNA technology. Yet, its effects wear off quickly after use.
Scientists now have found a new and better solution: slow-acting insulin. Insulin is stored in the pancreas as a hexameric complex (polymer with six subunits), which then falls apart to form the active monomer when it is released into the blood. To make a slow-acting molecule, scientists needed to stabilize the insulin hexamer so that it breaks apart more slowly. At first, scientists successfully fused fish protein with insulin to create a complex that slowly dissolved in blood. They then tinkered with the addition and substitution of proteins to make the insulin stable enough but still able to dissolve. One way of delaying the protein’s destabilization is through adding long hydrocarbon chains. The final result was the slow-acting insulin, a very effective upgrade to insulin treatments.
Even so, the search for a better treatment does not end there. Researchers are now also looking for ways to design ultra-stable insulin molecules that have only a single chain, further simplifying the design.