Pork insulin

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Insulin Preparations. Since diabetes mellitus is a defect of one or more of insulin production, secretion, or action, the administration of insulin replacement as a treatment for diabetes in the 1920s was a landmark discovery. Historically, most commercial insulin came from either bovine or porcine sources. Beef insulin differs from human insulin by three amino acid substitutions pork insulin differs by only one residue. For many years, standard insulin preparations were 70% beef and 30% porcine. However, the biosynthesis of human insulin has now displaced the animal insulins, especially bovine insulin which was more antigenic. Mass production of human insulin by recombinant DNA methods is achieved by inserting the human proinsulin gene into either E. coli or yeast and treating the resulting proinsulin to yield the human insulin molecule. Insulin preparations may be divided into four major types ... 

Insulin is composed of 51 amino acids arranged in two polypeptide chains, designated A and B, which are linked together by two di- sulfide bridges (Figure 23.3A). The insulin molecule also contains an j intramolecular disulfide bridge between amino acid residues of the A chain. Beef insulin differs from human insulin at three amino add positions, whereas pork insulin varies at only one position. 

Human forms are derived from recombinant or biosynthetic human insulin. Animal sources are derived from purified pork insulin. 

The radioimmunoassay of insulin permits detection of insulin in picomolar quantities. The assay is based on antibodies developed in guinea pigs against bovine or pork insulin. Because of the similarities between these two insulins and human insulin, the assay successfully measures the human hormone as well. 

Historically, commercial insulin in the USA contained beef or pork insulin. Beef insulin differs by three amino acids from human insulin, whereas only a single amino acid distinguishes pork and human insulins (Figure 41-1). The beef hormone is slightly more antigenic than pork insulin in humans. Of the insulins manufactured from animal sources, only purified pork insulin is still available and it requires special ordering. 

Human insulin, which is now less expensive than monospecies pork insulin and is also less immunogenic, has supplanted purified pork insulins. 

Human insulins appear to be as effective as—and considerably less immunogenic in diabetic patients than—beef-pork insulin mixtures and slightly less immunogenic than pork insulin. 

Insulin is isolated from beef and pork pancreas. However, human insulin is replacing the animal hormone for therapy. Human insulin is produced by a special strain of Escherichia coli that has been genetically altered to contain the gene for human insulin. Pork insulin is closest in structure to human insulin, differing by only one amino acid. 

Berson SA, Yalow RS (1959) Species-specificity of human antibeef, pork insulin serum. J Clin Invest 38 2017-2025 Chard T (ed) (1990) An Introduction to Radioimmunoassay and Related Techniques. Elsevier Amsterdam... 

Both pork and human insulin are definitively less immunogenic than beef insulin, producing fewer circulating insulin antibodies, but several studies have indicated no detectable change in antibody concentrations on switching from pork to human insulin or vice versa. Antibodies cause lipoatrophy and are responsible for the substantial insulin resistance seen in some patients, but both events are rare now that purified pork insulin is in common use. Interest has recently been revived in the possible contribution of antibodies in modifying metabolic control. In the short term and under hospital conditions, they are known to prolong the intravenous half-life of injected insulin and to delay the appearance in the circulation of a subcutaneously administered bolus dose. 

The dose of pork insulin for patients with insulin resistance caused by antibodies to beef insulin may be only a fraction of that of beef insulin. Insulin resistance is frequently self-limited after several weeks or months of high dosage, responsiveness may be regained and dosage can be reduced. Insulin resistance is a common feature of insulinoma and can be shown even... 

Figure 5. Insulin-related bioactivity of the extract of Tetra-hymena pyriformis. Key , pork insulin standard A, Tetra-hymena extract , Tetrahymena with anti-insulin antibody added. Reproduced from RefT 4. )...

Beef regular Iletin 11 Pork regular Iletin 11 Regular purified pork insulin Human (purified)... 

Species variations in primary stmctnre are also important in medicine, as illustrated by the comparison of human, beef, and pork insulin. Insulin is one of the hormones that are highly conserved between species, with very few amino acid substitutions and none in the regions that affect activity. Insulin is a polypeptide hormone of 51 amino acids that is composed of two polypeptide chains (Fig. 6.13). It is synthesized as a single polypeptide chain, but is cleaved in three places before secretion to form the C peptide and the active insulin molecule containing the A and B chains. The folding of the A and B chains into the correct three-dimensional structure is promoted by the presence of one intrachain and two interchain disulfide bonds formed by cysteine residues. The invariant residues consist of the cysteine residues engaged in disulfide bonds and the residues that form the surface of the insulin molecule that binds to the insulin receptor. The amino acid substitutions in bovine and porcine insulin (shown in blue in Fig. 6.13.) are not in amino acids that affect its activity. Consequently, bovine and pork insulin were used for many years for the treatment of diabetes mellitus. However, even with only a few different amino acids, some patients developed an immune response to these insulins. 

Fig. 6.13. The primary structure of human insuhn. The substituted amino acids in bovine (beef) and porcine (pork) insulin are shown in blue. Threonine 30 at the carboxy terminal of the B chain is replaced by alanine in both beef and pork insulin. In beef insulin, threonine 8 on the A chain is also replaced with alanine, and isoleucine 10 with vahne. The cysteine residues, which form the disulfide bonds holding the chains together, are invariant. In the bioengineered insulin Humalog (hspro insulin), the position of proline at B28 and lysine at B29 is switched. Insulin is synthesized as a longer precursor molecule, proinsulin, which is one polpeptide chain. Proinsulin is converted to insulin by proteolytic cleavage of certain peptide bonds (squiggly lines in the figure). The cleavage removes a few amino acids and the 31-amino acid C-peptide that connects the A and B chains. The active insulin molecule, thus, has two nonidentical chains.

Di Abietes. Di Abietes treatment was first changed to daily injections j of Humulin instead of beef insulin. Humulin is now mass-produced by recombinant DNA techniques that insert the human DNA sequences for the insulin A and B chains into the Escherichia coli or yeast genome (see Chapter 17). The insulin chains that are produced are then extracted from the media and treated to form the appropriate disulfide bonds between the chains. As costs have fallen for production of the synthetic human insulins, they have replaced pork insulin and the highly antigenic beef insulin. 

Isophane Insulin Suspension 1-2 24-28 NPH Insulin, NPH lletin 1 and II, NPH (Purified Pork) Insulin, Humulin hP, Insulatard NPH, Insulatard NPH Human. 

No adverse interaction normaiiy occurs between antidiabetics and benzodiazepines, but an isoiated case of hyperglycaemia has been seen in an insuiin-treated patient with type 2 diabetes associated with the use of chiordiazepoxide. The effects of lorazepam were found to be increased in patients given beef/pork insulin rather than human insuiin. Piogiitazone caused a minor decrease in the AUC of midazoiam, which is probabiy not clinically relevant. 

Transpeptidation reactions with proteolytic enzymes have been frequently observed, too the first example of Fraenkel-Conrat mentioned at the beginning of this section belongs to this type of reactions. A remarkable instance for a transpeptidation reaction is the transformation of pork insulin into human insulin by carboxypeptidase A [35]. This enzyme splits a carboxyl-terminal amino acid from the end of a polypeptide chain and also catalyzes the transpeptidation at the same linkage. Thus, in the B-chain of porcine insulin the terminal alanin is exchanged by threonine on incubation with the enzyme and a large excess of this amino acid. 

A more general use of proteolytic enzymes in peptide synthesis became feasible with the discovery (Sealock and Laskowsky 1969) of the effect of water miscible organic solvents on the equilibrium in enzyme catalyzed peptide bond hydrolysis and synthesis. In the presence of isopropanol (or dimethylfor-mamide, etc.) the dissociation of the carboxyl group is suppressed and, at least in a selected pH region, the equilibrium is shifted toward synthesis. A notable case is the conversion of porcine insulin to human insulin. Enzymatic cleavage of the C-terminal residue of the B-chain (alanine) with carboxypeptidase yields desalanino pork insulin. This cleavage is followed by the incorporation of... 

Insulins of human beings, bovine, and sheep show the following differences in the primary structure if compared with pork insulin... 

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