Zinc/insulin complex

The release rate and therefore the duration of action of injectable insulin, in the form of insulin zinc, is controlled by its crystallinity coupled with its particle size. The crystallinity and particle size of insulin zinc, which is precipitated as an insoluble complex when insulin is reacted with zinc chloride, is controlled by the pH. The amorphous complex of small particle size, Prompt Insulin Zinc Suspension USP, is rapidly absorbed and has a relatively short duration of action. In contrast, the crystalline complex of large particle size, Extended Insulin Zinc Suspension USP, is slowly absorbed and has a relatively long duration of action. The intermediate form, Insulin Zinc Suspension USP, consists of seven parts of the crystalline form to three parts of the amorphous form and has an intermediate rate of absorption and duration of action. 

Theory Insulin zinc suspension is nothing but a neutral suspension of insulin in the form of water insoluble complex with ZnCl2. Determination of both total zinc and zinc in solution is performed on a sample of the supernatant liquid obtained by centrifuging the suspension. The percentage of total zinc and of zinc in solution varies according to the strength of the preparation viz., 40, 80 or 100 units ml-1. 

A number of zinc compounds and complexes have been developed for therapeutic purposes. Several zinc complexes of cyclam-based ligands have proved potent inhibitors of HIV, while hydroxypyridinone complexes are being assessed as insulin mimics for the treatment of diabetes. There is some evidence that the administration of certain zinc chelates may help to ward off strokes, while a suberoylanihde hydroxamate complex has been in clinical trials as an anticancer agent since 2000. 

Zinc complexes with hydroxypyranones, for example, maltol or kojic acid, have been known for many years. These, and analogous complexes with hydroxypyridinones, have been assessed as zinc supplements in cases of severe zinc deficiency, and more recently as potential insulin mimics. 

Intermediate-acting insulins are either the neutral protamine Hagedorn insulin (NPH isophane insulin suspension) or the Lente insulin (insulin zinc suspension) the former is a suspension of the insulin-protamine-zinc complex in a phosphate buffer and the latter is a mixture of crystallized and amorphous insulin in acetate buffer. These preparations have an onset of action within about 2h, peak activity after about 4-12 h, and a duration of up to 24 h (Table 4). Commercially available mixtures of soluble insulins and isophane insulins have activities that would normally place them within the intermediate-acting category. Mixed insulin-zinc suspensions are sometimes classified as either intermediate- or long-acting as the duration of action may be up to 30 h. 

These interactions are always unwanted. A good example is the inappropriate mixing of insulins. Slower release insulins are complexed with protamine zinc in excess, while the conjugation of insulin with such adjuvant takes place slowly, especially in the relatively low temperature of a refrigerator. Drawing up the lente insulin first, and then sticking the needle into the soluble insulin,... 

Insulin and two fractions Insulin, zinc-free Insulin, zinc compound 3-I.actoglobulin, dodecylsulfate complex Lj sozyme... 

Chemistry and biochemistry of insulin-mimetic vanadium and zinc complexes. Trial for treatment of diabetes mellitus (2006), ] focusing on the current state of insulin-mimetic metal ions (VO + and Zn +), including speciation and mechanistic aspects. 

Perhaps the most well-known example of a parenteral suspension formulation is insulin. Many insulin formulations also take advantage of the different physical forms which can be produced when insulin is complexed with zinc. Suspensions of the amorphous form of insulin zinc have a faster onset of action and shorter duration of action compared to those of the crystalline form. In order to provide both a rapid onset and a long duration of action, many formulations are composed of a mixture of amorphous and crystalline zinc insulin. 

The insulin complex must first be degraded, because free insulin is the active form. Thus, the protein-protein interactions and also the zinc complexes must be disrupted. Because these interactions take time to disrupt, there is a lag time before the free insulin is released, resulting in slower onset. Because the complexed form allows more insulin to be administered per dose, the duration is long, because free insulin is released constantly upon disruption of the protein/zinc interactions. 

Chemistry and biochemistry of insulin-mimetic vanadium and zinc complexes (including pyridine, pyrimidine, thiazole, and porphyrin derivatives) 06BCJ1645. 

The importance of coordination in the biochemistry of essential metallic elements may be illustrated by numerous examples of metal complexes of which the following are representative the iron complex hemoglobin and numerous enzymes containing the heme and related structures such as catalases, peroxidases and cytochromes and the iron-containing proteins ferritin, transferrin, and hemosiderin the zinc complexes zinc-insulin, carbonic anhydrase and the carboxypeptidases the cobalt complex vitamin B12 the copper complex, ceruloplasmin the molybdenum-containing enzymes, xanthine oxidase, and nitrate reductase DNA-metal ion complexes. 

Zinc cross-links proteins in a manner similar to S-S bridges. For example, insulin may be formulated as its zinc complex in order to produce a slow-release form of the dmg. In the body, this cross-linking results in the formation of zinc fingers in receptor proteins which are important binding sites for hormones such as corticosteroids. 

Zinc is important biologically there are many zinc-protein complexes, and the human body contains about 2 g. In the human pancreas, zinc ions appear to play an essential part in the storage of insulin. 

Concerning drug delivery, electrically erodible polymer gels for controlled release of drugs have been prepared, and a measured release rate of insulin has been observed under electrical stimulus [69]. A suspension of zinc insulin in a mixed solution of poly(ethyloxazoline) and PMAA was formed into a gel by decreasing the pH of the suspension. The obtained complex gel with 0.5 wt% of insulin was attached to a woven platinum wire cathode which was 1 cm away from the anode and immersed in 0.9% saline solution. When a stepped function of electrical current of 5 mA was applied to the insulin-loaded gel matrix, insulin was released in a stepwise manner up to a release of 70%. The insulin rate measured was 0.10 mg/h. 

The concentration of insulin present in soluble insulin preparations (i.e. fast-acting insulins), is much higher (approximately 1 x KT2 3 mol I ). At this concentration, the soluble insulin exists as a mixture of monomer, dimer, tetramer and zinc-insulin hexamer. These insulin complexes have to dissociate in order to be absorbed from the injection site into the blood, which slows down the onset of hormone action. 

Trace metals Zinc Red meats, shellfish, wholegrain cereals Involved in many metabolic reactions stabilisation of structure RNA, DNA and ribosomes Binding of some transcription factors to DNA Stabilisation of insulin complex in storage granules... 

Insulin suspensions. When the hormone is injected as a suspension of insulin-containing particles, its dissolution and release in subcutaneous tissue are retarded (rapid, intermediate, and slow insulins). Suitable particles can be obtained by precipitation of apolar, poorly water-soluble complexes consisting of anionic insulin and cationic partners, e.g the polycationic protein protamine or the compound aminoqui-nuride (Surfen). In the presence of zinc and acetate ions, insulin crystallizes crystal size determines the rate of dissolution. Intermediate insulin preparations (NPH or isophane, lente or zinc insulin) act for 18 to 26 h, slow preparations (protamine zinc insulin, ultralente or extended zinc insulin) for up to 36 h. 

Another zinc-utilizing enzyme is carbonate/dehydratase C (Kannan et al., 1972). Here, the zinc is firmly bound by three histidyl side chains and a water molecule or a hydroxyl ion (Fig. 27). The coordination is that of a distorted tetrahedron. Metals such as Cu(II), Co(Il), and Mn(ll) bind at the same site as zinc. Hg(II) also binds near, but not precisely at, this site (Kannan et al., 1972). Horse liver alcohol dehydrogenase (Schneider et al., 1983) contains two zinc sites, one catalytic and one noncatalytic. X-Ray studies showed that the catalytic Zn(II), bound tetrahedrally to two cysteines, one histidine, and water (or hydroxyl), can be replaced by Co(II) and that the tetrahedral geometry is maintained. This is also true with Ni(Il). Insulin also binds zinc (Adams etai, 1969 Bordas etal., 1983) and forms rhombohedral 2Zn insulin crystals. The coordination of the zinc consists of three symmetry-related histidines (from BIO) and three symmetry-related water molecules. These give an octahedral complex... 

Protamine zinc insulin insulin complexed to excess protamine in order to prolong its duration of action... 

In general, transition metal ions are undesired in protein formulations because they can catalyze physical and chemical degradation reactions in proteins. However, specific metal ions are included in formulations when they are cofactors to proteins and in suspension formulations of proteins where they form coordination complexes (e.g., zinc suspension of insulin). Recently, the use of magnesium ions (10-120 mM) has been proposed to inhibit the isomerization of aspartic acid to isoaspartic acid (63). 

Figure 7-18 Stereoscopic MolScript ribbon drawings of the B chains (A chains omitted) of (A) hexameric 2-zinc pig insulin. (B) A phenol complex of the same protein. Within each dimer the B chains are shaded differently. The Zn2+ ions are represented by white spheres and the coordinating histidine side chains are shown. Six noncovalently bound phenol molecules can be seen, as can several conformational differences. From Whittingham et al.B7 Courtesy of Peter C. E. Moody.

In addition to its function in catalysis, zinc often plays an important structural role, e.g., in the zinc finger transcriptional regulators (Fig. 5-38).k Zinc ions bind to insulin and stabilize its hexameric structure (Fig. 7-18)/ Six Zn2+ ions are present in the hexagonal tail plate of the T-even bacteriophage (Box 7-C) and appear to be essential for invasion of bacteria.131 In carnivores, the tapetum, the reflecting layer behind the retina of the eye of many animals, contains crystals of the Zn2+-cysteine complex. 

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