Insulin lispro binds to the insulin receptor (IR), a heterotetrameric protein consisting of two extracellular alpha units and two transmembrane beta units. The binding of insulin to the alpha subunit of IR stimulates the tyrosine kinase activity intrinsic to the beta subunit of the receptor. The bound receptor autophosphorylates and phosphorylates numerous intracellular substrates such as insulin receptor substrates (IRS) proteins, Cbl, APS, Shc and Gab 1. Activation of these proteins leads to the activation of downstream signaling molecules including PI3 kinase and Akt. Akt regulates the activity of glucose transporter 4 (GLUT4) and protein kinase C (PKC), both of which play critical roles in metabolism and catabolism. In humans, insulin is stored in the form of hexamers; however, only insulin monomers are able to interact with IR. Reversal of the proline and lysine residues at positions B28 and B29 of native insulin eliminates hydrophobic interactions and weakens some of the hydrogen bonds that contribute to the stability of the insulin dimers that comprise insulin hexamers. Hexamers of insulin lispro are produced in the presence of zinc and m-cresol. These weakly associated hexamers quickly dissociate upon subcutaneous injection and are absorbed as monomers through vascular endothelial cells. These properties give insulin lispro its fast-acting properties.
Insulin is a natural hormone produced by beta cells of the pancreas. In non-diabetic individuals, a basal level of insulin is supplemented with insulin spikes following meals. Increased insulin secretion following meals is responsible for the metabolic changes that occur as the body transitions from a postabsorptive to absorptive state. Insulin promotes cellular uptake of glucose, particularly in muscle and adipose tissues, promotes energy storage via glycogenesis, opposes catabolism of energy stores, increases DNA replication and protein synthesis by stimulating amino acid uptake by liver, muscle and adipose tissue, and modifies the activity of numerous enzymes involved in glycogen synthesis and glycolysis. Insulin also promotes growth and is required for the actions of growth hormone (e.g. protein synthesis, cell division, DNA synthesis). Insulin lispro is a rapid-acting insulin analogue used to mimic postprandial insulin spikes in diabetic individuals. The onset of action of insulin lispro is 10-15 minutes. Its activity peaks 60 minutes following subcutaneous injection and its duration of action is 4-5 hours. Compared to regular human insulin, insulin lispro has a more rapid onset of action and a shorter duration of action. Insulin lispro is also shown to be equipotent to human insulin on a molar basis.
Insulin is predominantly cleared by metabolic degradation via a receptor-mediated process.
Inappropriately high dosages relative to food intake and/or energy expenditure may result in severe and sometimes prolonged and life-threatening hypoglycemia. Neurogenic (autonomic) signs and symptoms of hypoglycemia include trembling, palpitations, sweating, anxiety, hunger, nausea and tingling. Neuroglycopenic signs and symptoms of hypoglycemia include difficulty concentrating, lethargy/weakness, confusion, drowsiness, vision changes, difficulty speaking, headache, and dizziness. Mild hypoglycemia is characterized by the presence of autonomic symptoms. Moderate hypoglycemia is characterized by the presence of autonomic and neuroglycopenic symptoms. Individuals may become unconscious in severe cases of hypoglycemia. Rare cases of lipoatrophy or lipohypertrophy reactions have been observed.