Manufacture
Insulin glargine is made by recombinant DNA technology with Escherichia coli.[1] Insulin glargine was originally created by Aventis Pharmaceuticals and was accepted for use in 2000 in the USA and the EU.[2] Insulin glargine is created through the manipulation of amino acids.[2] A glycine is added to the C-terminal A-chain asparagine and two arginines are added to the C-terminal B-chain threonine.[2] The final drug product forms at a pH of 4 through the expression of E. coli and the generation of the precursor proinsulin.[3]
Structure
Insulin glargine is a hormone protein consisting of 52 amino acids in an asymmetric unit. It has two unique chains, chain A and B. The structure was determined by X-ray diffraction and was measured at a resolution of 1.66 Angstroms. Chain A is 21 amino acids long and consists of two alpha helices and one beta sheet. It is modified from normal insulin by the substitution of asparagine for glycine at the twenty first amino acid of the chain. It also has an L-cystine protein modification at amino acids C6 and C11 of the chain.[4] This modification consists of a disulfide bond formed between the side chains of two cysteine residues within the amino acid chain; this occurs via an oxidation reaction.[5]
Chain B is 31 amino acids long and consists of two alpha helices and one beta sheet.[4][6] It is modified from normal insulin by the addition of two arginine residues to the C-terminus of the chain.[6] These modifications raise the isoelectric point (pI) from 5.4 to 6.7, improving solubility under mildly acidic conditions.[7]
These two chains are held together by formed between cysteine side chains on opposing chains. One disulfide bond is formed between the cysteine residues at amino acid seven of chain A and amino acid seven of chain B. Another disulfide bond is formed between the cysteine residues at amino acid 21 of chain A and amino acid 19 of chain B.[6]
These disulfide linkages, general structure of insulin glargine, and its sequence differences with normal human insulin are shown by a figure presented by Agin et. al.[6]
Mechanism
The affinity of insulin glargine for the receptor insulin is very similar to the affinity of human insulin for insulin, and has been documented by multiple reports.[8] Insulin glargine’s mechanism is akin to human insulin’s mechanism.[1] It has been shown that after subcutaneous injection of glargine, it becomes metabolized into M1 (A21-Gly-insulin) and M2 (A21-Gly-des-30B-Thr-insulin); M1 has been found to be the pharmacologically active metabolite of glargine.[9][10]
Medical Use
Insulin glargine functions as an insulin analogue, providing basal control of glycaemia for patients with Type 1 and Type 2 diabetes.[1] The pH 4 glargine solution is subcutaneously injected to form a microprecipitate in physiological pH. The effectiveness of glargine is dampened when mixed with more neutral insulins due to resulting disruption of precipitate formation.[11] Insulin glargine’s stability allows the formed microprecipitate to be slowly administered simulating non-diabetic basal insulin secretion.[7] This enables insulin glargine to be an extended release insulin treatment administered once per day.
