Table 1. Basic Profile of insulin lispro
|Description||Rapid-acting human insulin analog|
|Generic Name||insulin lispro|
|Combination Drug(s)||Humalog® Mix 25, Humalog® Mix 50|
|Other Synonyms||insulin lispro (genetical recombination), insulin lispro (rDNA origin), insulin lispro protamine, insulin lispro protamine recombinant, insulin lispro recombinant, insulin lispro human/rDNA, insulin lispro protamine/rDNA|
|Example PDB identifier||1lph|
|3D Structure of Lispro Bound to Target Protein (Insulin Receptor)||N/A|
|Figure 1a. Linear schematic showing amino acid sequence of insulin lispro. Amino acids in the A-chain are shown as blue spheres, while that of the B-chain are shown in green spheres. The engineered insulin has the amino acid residues at positions 28 and 29 in the B-chain switched and is shown in a yellow sphere. The disulfide bridges are shown as yellow lines.||Figure 1b: 3D structure of hexameric conformation of insulin detemir PDB ID 1lph. Click here to view this interactively.|
Insulin lispro is a soluble, rapid-acting human insulin analog that is used to lower postprandial blood glucose levels and is most effective when administered immediately before a meal. It has a rapid onset of action, and thus can exert its effects quicker than human insulin (Howey, D.C. et al, 1994). It was designed by an inversion of the prolyl, lysyl sequence at the end of the C-terminal of the B-chain (Figure 1a). Selected chemical and physical properties of insulin lispro are listed in Table 2.
Table 2. Chemical and Physical Properties (DrugBank, or *drugcentral.org)
|Predicted topological surface area (TPSA)||2299 Å2*|
Rationale for Rapid Action
In the pharmaceutical formulations, insulin lispro is a hexamer, stabilized by zinc and phenol-cresol. Once injected into the subcutaneous layer, m-cresol rapidly diffuses out, weakening dimer interactions in this insulin and leads to hexamer disassembly (Bakaysa et al., 1996) into monomers (Figure 2). Once the insulin monomers have formed they diffuse through the paracellular junctions (adherens junctions) of the local microvasculature in to the blood, where they are carried throughout the body to target tissues, principally muscle, liver, and adipose tissue. Monomers bind to insulin receptors on cells, which, in turn, promotes glucose uptake.
|Figure 2. Image depicting subcutaneous injection to diffusion of insulin lispro in blood capillaries. Insulin lispro monomers are shown as purple ovals, while the presence of zinc and phenol are represented by ovals colored yellow and green, respectively.|
Crystallographic studies have revealed that insulin lispro can exists as a T3Rf3 hexamer (Ciszak et al., 1995) (link to Layer 1), isomorphous with human insulin hexamer '4Zn insulin' (Bentley et al., 1976); however, solution studies would suggest that formulated insulin lispro exists in an R6 conformation (Bakaysa, et al 1996). Interactions stabilizing the various oligomeric assemblies of insulin lispro are discussed in the following paragraphs.
Insulin lispro hexamers, in the pharmaceutical formulation, are each stabilized by two zinc ions and three phenolic ligands (Figure 3).
|Figure 3: Insulin lispro hexamer (PDB ID 1lph, Ciszak et al., 1995), shown in ribbon representation. a. View looking down the Rf3 face of the hexamer; and b. View looking from the side so that the Rf3 face is on the top and the T3 face is down. The insulin A-chains are colored blue and B-chains are colored green. The zinc, chloride, waters, and phenolic ligands are colored using CPK colors, shown in ball and stick representations, and labeled. Circles with red dashed lines represent areas of the structure expanded in Figures 4a, 4b and 5.|
Both zinc ions are coordinated by three neighboring His residues at position 10 in the B-chain (also written as HisB10) sidechains. The Rf3 face of the hexamer has an overall convex shape, and there is less space around the zinc ion due to the presence of the longer N-terminal α-helices in the B-chain. The zinc ion, close to this face, is tetrahedrally coordinated by the HisB10 residues plus a chloride ion (Figure 4a). The T3 face of the hexamer has a more concave shape and is less crowded, so the zinc ion close to this face is octahedrally coordinated by the HisB10 residues and three waters (Figure 4b).
|Figure 4: Insulin lispro hexamer (PDB ID 1lph, Ciszak et al., 1995), in ribbon representation, showing a close-up of a. tetrahedral zinc binding by the Rf3 trimer; and b. octahedral zinc binding by the T3 trimer. Color coding as in Figure 3.|
The first two residues of insulin lispro’s B-chain (PheB1 and ValB2) are in Rf3 conformation are not part of the N-terminal helix. Crystal packing, seen in the PDB ID 1lph (Ciszak et al., 1995), suggests that these residues, positioned in the convex face of the hexamer, interact with the select hydrophobic residues in the concave T3 face of an adjacent hexamer, facilitating inter-hexamer interactions between the T and Rf trimers. These interactions may or may not be present and relevant in pharmaceutical formulations of insulin lispro.
At the insulin lispro dimer interface, close to the tetrahedral zinc, there is a hydrophobic pocket where phenolic ligand can bind. Residues lining the phenolic binding site are shown in Figure 5. The hydroxyl group in the phenolic ligand also forms H-bonds with the backbone atoms of amino acids CysA6 and CysA11. Following injection, when the phenolic ligand diffuses out, these interactions are lost.
|Figure 5: Insulin lispro (PDB ID 1lph, Ciszak et al., 1995) in ribbon representation. showing a. Hydrophobic surface of the phenol binding site with a bound phenol. Adjacent dimer boundaries marked by a dashed line. b. Amino acid residues lining the phenol binding site, marked with their one letter code and position on the chain. H-bonds between phenolic ligand and CysA6 and CysA11 are not marked for clarity. Color coding as in Figure 3.|
Insulin dimers are stabilized by hydrogen bonds, formed between the B-chain β-strands of adjacent monomers. In wild-type human insulin, four hydrogen bonds, each ~2.9Å, stabilize the T:Rf dimers (Ciszak and Smith, 1994). In addition, van der Waals interactions between the Pro28/Lys29 of one monomer and the GlyB20-GlyB23 loop of the adjacent monomer also contribute to dimer formation (Figure 6a). Inversion of the prolyl and lysyl residues near the B-chain C-terminus changes path of the protein backbone and eliminates some van der Waals interactions between insulin monomers at the dimer interface (Figure 6b, Ciszak et al., 1995). Although the insulin lispro dimer forms the same number of hydrogen bonds between adjacent β-strands, the two that are closer to the engineered sequence change, are longer (~3.2 Å) than those seen in the wild-type human insulin. This weakened dimer interaction explains ready dissociation and rapid action of insulin lispro.
|Figure 6: Interactions stabilizing dimer formation of insulin: a. wild-type human insulin (PDB ID 1trz, Ciszak and Smith, 1994); and b. insulin lispro (PDB ID 1lph, Ciszak et al., 1995). The protein structures are shown in ribbon representation, while the interacting surfaces of the Gly20-Gly23 loop is also shown. Hydrogen bonds between the insulin monomer β-strands are shown as thin lines – (black lines ~2.9 Å and red lines ~3.2 Å.)|
Monomers of insulin lispro bind to insulin receptors on target cells in the same manner as normal insulin. Learn more about insulin receptors here.
Learn more about insulin: insulin receptor complexes here.
Pharmacologic Properties and Safety
Table 3. Pharmacokinetics: ADMET of insulin lispro.
|Tmax (hrs)||1 hour||DrugBank|
|Duration of Action||4-5 hours||DrugBank|
|Metabolism||Predominantly cleared by metabolic degradation via a receptor-mediated process||DrugBank|
|Excretion||Dose dependent; 21.0 mL/min/kg and 9.6 mL/min/kg (for 0.1 unit/kg and 0.2 unit/kg)||DrugBank|
|Adverse events||Signs of hypoglycemia, hyperkalemia; lipoatrophy and lipohypertrophy (rare)||DrugBank|
Drug Interactions and Side Effects
Table 4. Drug Interactions of Side Effects of insulin lispro
|Total Number of Drug Interactions||843 drugs||Drugs.com|
|Major Drug Interactions||gatifloxacin, tequin (gatifloxacin), tequin teqpaq (gatifloxacin)||Drugs.com|
|Alcohol/Food Interaction(s)||moderate interaction with alcohol (ethanol)||Drugs.com|
|Major Side Effects||anxiety, fever/chills, headache, irritability, blurred vision, lower back/side pain, confusion, cold sweats, confusion, depression, slurred speech, restless sleep, fast heartbeat, excessive hunger, drowsiness||Drugs.com|
|Minor Side Effects||body aches, runny nose, sneezing, sore throat, voice changes, congestion, swollen glands in neck||Drugs.com|
Humalog® (insulin lispro) was developed by Eli Lilly and Company and approved by the US FDA in 1996. It is prescribed as a fast-acting (meal time) insulin analog that is subcutaneously injected. It is available as pre-filled disposable injection pens or vials in 100 units/mL (U-100) and 200 units/mL (U-200) and is administered either 15 minutes before or after a meal.
Table 5. Links to Relevant Resources
|Food and Drugs Administration||https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c8ecbd7a-0e22-4fc7-a503-faa58c1b6f3f&audience=consumer|
|Liver Tox: National Institutes of Health (NIH)||https://www.ncbi.nlm.nih.gov/books/NBK548016/|
Bakaysa, D., Radziuk, J., Havel, H., Brader, M., Li, S., Dodd, S., Beals, J., Pekar, A., and Brems, D. (1996) Physicochemical basis for the rapid time-action of LysB28ProB29-insulin: Dissociation of a protein-ligand complex. Protein Science 5, 2521-2531. https://doi.org/10.1002/pro.5560051215
Bentley, G., Dodson, E., Dodson, G., Hodgkin, D., and Mericola, D. (1976) Structure of insulin in 4-zinc insulin. Nature 261, 166-168. https://doi.org/10.1038/261166a0
Ciszak, E., and Smith, G. (1994) Crystallographic Evidence for Dual Coordination Around Zinc in the T3R3 Human Insulin Hexamer. Biochemistry 33, 1512-1517. https://doi.org/10.1021/bi00172a030
Ciszak, E., Beals, J., Frank, B., Baker, J., Carter, N., and Smith, G. (1995) Role of C-terminal B-chain residues in insulin assembly: the structure of hexameric LysB28ProB29-human insulin. Structure 3, 615-622. https://doi.org/10.1016/S0969-2126(01)00195-2
Howey, D., Bowsher, R., Brunelle, R., and Woodworth, J. (1994) [Lys(B28), Pro(B29)]-Human Insulin: A Rapidly Absorbed Analogue of Human Insulin. Diabetes 43, 396-402. https://doi.org/10.2337/diab.43.3.396
August 2018, Shriya Patel, Dr. Shuchismita Dutta; Reviewed by Drs. Stephen K. Burley and John M. Beals