25.7 : Insulin: Biosynthesis, Chemistry, and Preparation

The endoplasmic reticulum (ER) of pancreatic β-cells synthesizes preproinsulin, which consists of a signal peptide, A and B chains, and a C-peptide. Preproinsulin is then cleaved and folded into proinsulin, which translocates to the Golgi apparatus for sorting and packaging into secretory granules. In these granules, enzymatic clipping generates insulin and C-peptide.

Damage or functional impairment of β-cells inhibits insulin production, leading to diabetes. Diabetes treatment primarily uses recombinant human insulin in regular or neutral protamine hagedorn (NPH) formulations. Both rapid-acting and long-acting analogs of insulin, created by modifying the amino acid sequences or insulin structure, are available.

For instance, insulin lispro, created by reversing the 28th and 29th amino acids in the B chain, promotes rapid absorption by forming monomers. Insulin glargine, on the other hand, replaces asparagine at the 21st position with glycine and extends the B chain by adding two arginine. It precipitates at pH 7.4 upon injection, resulting in slower absorption and extended action. These modifications enhance diabetes management by tailoring insulin action to patient needs.