Insulin Aspart

Table 1. Basic Profile of insulin aspart

Description Rapid-acting human insulin analog
Target(s) Insulin receptor
Generic Name insulin aspart
Commercial Name Novolog®
Combination Drug(s) Ryzodeg® (insulin aspart + insulin degludec)
Other Synonyms insulin aspart, aspart insulin, B28-Aspart-Insulin, INA-X14, insulin aspart protamine recombinant, insulin aspart recombinant, insulin X14, insulin, Asp(B28)
IUPAC Name N/A
Example PDB identifier 4gbn
3D Structure of Aspart Bound to Target Protein (Insulin Receptor) N/A
Figure 1a. Linear schematic showing amino acid sequence of insulin aspart. Amino acids in the A-chain are shown as blue spheres, while that of the B-chain are shown in green spheres. The engineered mutation at position 28 in the B-chain B shown in a yellow sphere. The disulfide bridges are shown as yellow lines. Figure 1b. 3D structure of hexameric conformation of insulin aspart PDB ID 4gbn. Click here to view this interactively.

Drug Information

Insulin aspart is a soluble, rapid-acting human insulin analog, used to lower postprandial blood glucose levels and is effective when administered immediately before a meal. It was designed by engineering an aspartate at position 28 in the B-chain (also written as AspB28) replacing the native proline. This analog has a shorter duration of action than injected wild-type human insulin and can achieve higher maximum insulin concentrations in a shorter time (Setter et al., 2000). Selected chemical and physical properties of insulin aspart are listed in Table 2.

Table 2. Chemical and Physical Properties (DrugBank)

Chemical formula C256H381N65079S6
Molecular weight 5826 Da

Rationale for Rapid Action

In the pharmaceutical formulation, hexamers, dimers, and monomers of insulin aspart are in equilibrium (Palmieri et al., 2013). Introducing an aspartic acid at amino acid residue 28 in the B-chain changes the van der Waals interactions at the dimer interface and contributes to changes in the dissociation behavior of insulin aspart. The normal tendency to form hexamers is decreased after injection; instead, breakdown into active monomers is accelerated (Figure 2) (Setter et al., 2000). Once the insulin monomers have diffused out of the site of injection and into blood via paracellular junctions, they are carried throughout the body in blood plasma, to target tissues, principally kidney, muscle, liver, and adipose tissue. Monomers bind to the insulin receptors, which, in turn, promotes glucose uptake.

Figure 2. Image depicting subcutaneous injection to diffusion of insulin aspart in blood. Insulin aspart monomers are shown as purple ovals, while the presence of zinc and phenol are represented by ovals colored yellow and green, respectively.
Figure 2. Image depicting subcutaneous injection to diffusion of insulin aspart in blood. Insulin aspart monomers are shown as purple ovals, while the presence of zinc and phenol are represented by ovals colored yellow and green, respectively.

Critical Interactions

Crystallographic studies have revealed that insulin aspart can exist in a T3R3 conformation, made up of TR dimers (Palmieri et al, 2013). Interactions stabilizing the various oligomeric assemblies of insulin aspart are discussed in the following paragraphs.

Hexamers

Insulin aspart hexamers, in the pharmaceutical formulation, are stabilized by two zinc ions and several phenolic ligands, e.g., phenol and cresol as shown in Figure 3. In the formulation, insulin aspart is thought exist in an R6-state as opposed to the crystallographic T3R3 state.

Figure 3: Insulin aspart hexamer (PDB ID 4gbc, Palmeri et al., 2013), shown in ribbon representation. a. View looking down the R3 face of the hexamer; and b. View looking from the side so that the R3 face is up 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 5b.
Figure 3: Insulin aspart hexamer (PDB ID 4gbc, Palmeri et al., 2013), shown in ribbon representation. a. View looking down the R3 face of the hexamer; and b. View looking from the side so that the R3 face is up 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 5b.

Both zinc ions are coordinated three symmetry-related HisB10 sidechains in each trimer. In the R3 trimer, the zinc adopts a tetrahedral coordination state with the chloride ion occupying the 4th ligand position. In the T3 trimer, the zinc adopts an octahedral coordination chemistry composed of three HisB10 sidechains and three water molecules. On the R3 face of the hexamer, the zinc ion is less exposed due to the presence of the longer N-terminal α-helices in N-terminus of the B-chain (Figure 4a), while on the T3 face the neighborhood of zinc is more exposed (Figure 4b).

Figure 4: Insulin aspart hexamer (PDB ID 4gbc, Palmeri et al., 2013), in ribbon representation, showing a close-up of tetrahedral zinc binding by the a. R3 trimer; and b. T3 trimer. Color coding as in Figure 3.
Figure 4: Insulin aspart hexamer (PDB ID 4gbc, Palmeri et al., 2013), in ribbon representation, showing a close-up of tetrahedral zinc binding by the a. R3 trimer; and b. T3 trimer. Color coding as in Figure 3.

Additional interactions that stabilize the insulin aspart hexamer include, electrostatic interactions between adjacent AsnB3 residues at the R3 trimer end (Figure 5a) and phenolic ligands (cresol) at the interface of adjacent dimers. Residues lining the phenol-binding site are mostly hydrophobic in nature; however, the hydroxyl moiety is H-bonded to the A6 and A11 residues (Figure 5b). Following injection, the phenolic ligands diffuse from the hexamer, these interactions are lost.

Figure 5: Insulin aspart (PDB ID 4gbc, Palmeri et al., 2013) in ribbon representation. a. electrostatic interactions between adjacent AsnB3 residues in the R3 trimer. b. Hydrophobic amino acid residues lining the phenolic ligand (cresol) binding site, marked with their one letter code and position on the chain. Color coding as in Figure 3.
Figure 5: Insulin aspart (PDB ID 4gbc, Palmeri et al., 2013) in ribbon representation. a. electrostatic interactions between adjacent AsnB3 residues in the R3 trimer. b. Hydrophobic amino acid residues lining the phenolic ligand (cresol) binding site, marked with their one letter code and position on the chain. Color coding as in Figure 3.
Dimers

Insulin dimers are stabilized by hydrogen bonds and van der Waals interactions, formed between the B-chain β-strands of dimerizing 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 Pro28 of one monomer and GlyB23 of the dimerizing monomer also contribute to dimer formation (Figure 6a). Substituting Asp at position 28 in the B-chain enhances flexibility of the C-terminus and eliminates van der Waals interactions without affecting the hexamerizing potential in the presence of zinc and phenolic ligands (Whittingham et al., 1998). The gap between AspB28 in one chain and GlyB23 in the adjacent chain is evident in both the R and T conformations. In the T-form, the AspB28 sidechain makes hydrogen bonds with other neighboring sidechains within the same monomer, further supporting the stability of the monomer. Although the insulin aspart dimer forms the same hydrogen bonds between adjacent β-strands, reduced van der Waals interactions in the dimer interface explain ready dissociation into monomers and rapid action of insulin aspart.

Figure 6. Interactions stabilizing dimer formation of insulin: a. wild-type human insulin (PDB ID 1trz, Ciszak and Smith, 1994); and b. insulin aspart (PDB ID 4gbc, Palmeri et al., 2013). The protein structures are shown in ribbon representation. Color coding as in Figure 3. Atoms of GlyB23, AspB28 and ProB28 residues in the B-chain are shown as spheres. Hydrogen bonds between the insulin monomer β-strands are shown as thin lines.
Figure 6. Interactions stabilizing dimer formation of insulin: a. wild-type human insulin (PDB ID 1trz, Ciszak and Smith, 1994); and b. insulin aspart (PDB ID 4gbc, Palmeri et al., 2013). The protein structures are shown in ribbon representation. Color coding as in Figure 3. Atoms of GlyB23, AspB28 and ProB28 residues in the B-chain are shown as spheres. Hydrogen bonds between the insulin monomer β-strands are shown as thin lines.

Drug Target

Monomers of insulin aspart bind to insulin receptors on target cells in the same manner as normal insulin. Learn more about insulin receptors here.

Drug-Target Complex

Learn more about insulin: insulin receptor complexes here.

Pharmacologic Properties and Safety

Table 3. Pharmacokinetics: ADMET of insulin aspart

Features Comment(s) Source
Tmax (hrs) 81 minutes DrugBank
Duration of Action 4-5 hours DrugBank
Excretion 1.2 L/hr/kg excreted in urine 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 Aspart

Features Comment(s) Source
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, headache, irritability, blurred vision, confusion, cold sweats, confusion, depression, slurred speech, restless sleep, fast heartbeat, excessive hunger, drowsiness Drugs.com
Minor/Rare Side Effects dryness of mouth, nausea, sweating, loss of appetite, trouble breathing, irregular heartbeat, fast or weak pulse, skin rash, unusual weakness Drugs.com

Regulatory Approvals/Commercial

Developed by Novo Nordisk and approved by the US FDA in 2000, Novolog® (insulin aspart) is prescribed as a fast-acting (meal time) insulin analog that is injected into the subcutaneous layer of the body. It is available as pre-filled disposable injection pens or vials in 100 units/mL (U-100) and is administered either 5-10 minutes before a meal. There are no generic versions of Novolog® on the market at present.

Links

Table 5. Links to Relevant Resources

DrugBank DBO1306
Drugs.com https://www.drugs.com/mtm/insulin-aspart.html
Food and Drugs Administration https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=3a1e73a2-3009-40d0-876c-b4cb2be56fc5&audience=consumer
Liver Tox: National Institutes of Health (NIH) https://www.ncbi.nlm.nih.gov/books/NBK548016/

References

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

Palmieri, L., Fávero-Retto, M., Lourenço, D., and Lima, L. (2013) A T3R3 hexamer of the human insulin variant B28Asp. Biophysical Chemistry 173-174, 1-7. https://doi.org/10.1016/j.bpc.2013.01.003

Setter, S., Corbett, C., Campbell, R., and White, J. (2000) Insulin Aspart: A New Rapid-Acting Insulin Analog. Annals of Pharmacotherapy 34, 1423-1431. https://doi.org/10.1345/aph.19414

Whittingham, J., Edwards, D., Antson, A., Clarkson, J., and Dodson, G. (1998) Interactions of Phenol and m-Cresol in the Insulin Hexamer, and Their Effect on the Association Properties of B28 Pro → Asp Insulin Analogues‡. Biochemistry 37, 11516-11523. http://pubs.acs.org/doi/abs/10.1021/bi980807s

August 2018, Shriya Patel, Dr. Shuchismita Dutta; Reviewed by Drs. Stephen K. Burley and John M. Beals
http://dx.doi.org/10.2210/rcsb_pdb/GH/DM/drugs/Insulin/Aspart

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