Τόμος 7 (1989) – Τεύχος 3 – Άρθρο 2 – Επιθεώρηση Κλινικής Φαρμακολογίας και Φαρμακοκινητικής-Ελληνική Έκδοση – Volume 7 (1989) – Issue 3 – Article 2 – Epitheorese Klinikes Farmakologias και Farmakokinetikes-Greek Edition

7: 156-168 (1989)

PHARMAKON-Press: Epitheorese Klin. Farmakol. Farmakokinet.

7: 156-168 (1989)

Human insulin, a hormone secreted by the beta cells of the islets of Langerhans of the pancreas, is a polypeptide (MW 5734) consisting of two chains of amino acids, A and B, linked by disulfide bridges (fig. 1). Insulin is synthesised (fig. 2) as prepro­insulin (M.W. —11,500) carrying a hydrophobic 23-amino-acid pre-sequence that directs the molecule into the cisternae of the endoplasmatic reticulum and then it is removed, leaving the 9000-MW proinsulin molecule. The latter undergoes a series of peptide cleavages by the trypsin like and carboxypeptidase B-like. pro-teases (fig. 3). Since the first production of insulin for human use in 1922, the general principles of the process have remained rela­tively unchanged and the conventional com­mercial insulin preparations available up to 1972 are obtained by extraction of beef or pig pancreases and purified by recrystallisation. Human insulin, identical in chemical structure to pancreatic insulin in man, is at  present  being prepared in 4 ways: by extraction from pancreases of human cadavers; by full chemi­cal synthesis; by enzymatic conversion of porcine insulin (semi synthetic “human” in­sulin, or insulin emp); and by use of recombi­nant DNA technology (biosynthetic “human” insulin). The basic principles of recombinant DNA technology for “human” insulin produ­ction include (a) the insertion of an insulin gene (foreign DNA string from Ε. co1i) into a cloning vector (plasmid), i.e. an extrachromo­somal autonomously replicating DNA molecule (fig. 4), by the use of restriction endonucleases; then the resulting recombinant plasmid is introduced into a new host (microbe or yeast) (fig. 5); (b) the gene expression-protein synthe­sis, i.e. the transcription of DNA to messenger RNA (mRNA), mediated by the RNA polymerise (the enzyme at first is binded to recognition sites of the DNA-promoters- and then travels along the DNA molecule until a termination signal is encountered) (fig. 6), the translation of the mRNA into a polypeptide sequence, a complex process involving the mRNA and ribosomes interaction (after binding the ribo­some moves along the mRNA and initiates protein synthesis) (fig. 7 and 8), the post-translational conversion of the protein (pro-insulin or insulin precursor with modified C-peptide) to insulin (fig. 9). The large scale production of biosynthetic “protein” insulin is made mainly by two methods, the Novo’s method (cloning host: Saccharomyces cerevi­sial, insulin precursor with modified C-peptide) (fig. 10) and Lilly’s method (cloning host: Ε. coli, proinsulin). Independently of the manu­facturing method, “insulin is insulin is insulin”.

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