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Purpose To study the self-association states of insulin degludec and insulin aspart alone and combined in pharmaceutical formulation and under conditions simulating the subcutaneous depot. Methods Formulations were made of 0.6 mM degludec at 3 and 5 Zn/6 insulin monomers, and 0.6 mM aspart (2 Zn/6 insulin monomers). Self-association was assessed using size-exclusion chromatography (SEC) monitored by UV and orthogonal reverse-phase chromatography. Results Simulating pharmaceutical formulation, degludec eluted as dihexamers, whereas aspart eluted as hexamers and monomers. Combining degludec at low zinc with aspart increased dihexamer content, indicating hybrid hexamer formation. At high zinc concentration, however, there was no evidence of this. Simulating the subcutaneous depot by removing preservative, degludec eluted as multihexamers and aspart as monomers. Aspart was incorporated into the multihexamer structures when combined with degludec at low zinc, but there was no such interaction with high-zinc degludec. SEC using progressively diluted concentrations of phenol and m-cresol showed that dissociation of aspart into monomers occurs before the formation of degludec multihexamers. Conclusion Insulins degludec and aspart can be combined without forming hybrid hexamers, but this combinability is dependent on zinc and preservative concentration, and requires that degludec is fully dihexameric before addition of aspart.

This study was conducted to assess the suitability of insulin analogs acylated by various cholic acid derivatives for use as basal insulin, and to test the most promising of these, LysB29(N ɛ-lithocholyl-γ-Glu) des(B30) human insulin (NN344) in pigs. Circular dichroism spectroscopy and size-exclusion chromatography were used to explore the physicochemical properties of the analogs, and affinities for albumin and insulin receptors were determined. After subcutaneous injection in pigs, disappearance half-times were measured, and the plasma profile and glucose-lowering effect in a euglycemic clamp were assessed for NN344. NN344 showed glucose-lowering activity lasting more than 24 h. Glucose infusion rate was essentially constant from 5 to 19 h after injection. NN344 seemed to be a dodecamer in the presence of zinc ions and phenol. Without phenol, the apparent molecular mass was >5000 kDa. Formation of such a self-assembly at the site of s.c. injection and its subsequent slow decomposition might explain the long duration of action of NN344. A measurable affinity for albumin of the lithocholic acid ligand may also contribute to the prolonged action. NN344 is a candidate for a neutral soluble basal insulin that might offer people with diabetes a prolonged duration, smooth, and predictable basal insulin supplement.

Derivatization of insulin with phenylboronic acids is described, thereby equipping insulin with novel glucose sensing ability. It is furthermore demonstrated that such insulins are useful in glucose-responsive polymer-based release systems. The preferred phenylboronic acids are sulfonamide derivatives, which, contrary to naïve boronic acids, ensure glucose binding at physiological pH, and simultaneously operate as handles for insulin derivatization at LysB29. The glucose affinities of the novel insulins were evaluated by glucose titration in a competitive assay with alizarin. The affinities were in the range 15-31 mM (K(d)), which match physiological glucose fluctuations. The dose-responsive glucose-mediated release of the novel insulins was demonstrated using glucamine-derived polyethylene glycol polyacrylamide (PEGA) as a model, and it was shown that Zn(II) hexamer formulation of the boronated insulins resulted in steeper glucose sensitivity relative to monomeric insulin formulation. Notably, two of the boronated insulins displayed enhanced insulin receptor affinity relative to native insulin (113%-122%) which is unusual for insulin LysB29 derivatives.

In recent years, analogs of human insulin have been engineered with the aim of improving therapy for people with diabetes. To ensure that the safety profile of the human hormone is not compromised by the molecular modifications, the toxico-pharmacological properties of insulin analogs should be carefully monitored. In this study, we compared the insulin and IGF-I receptor binding properties and metabolic and mitogenic potencies of insulin aspart (B28Asp human insulin), insulin lispro (B28Lys,B29Pro human insulin), insulin glargine (A21Gly,B31Arg,B32Arg human insulin), insulin detemir (NN304) [B29Lys(epsilon-tetradecanoyl), desB30 human insulin], and reference insulin analogs. Receptor affinities were measured using purified human receptors, insulin receptor dissociation rates were determined using Chinese hamster ovary cells overexpressing the human insulin receptor, metabolic potencies were evaluated using primary mouse adipocytes, and mitogenic potencies were determined in human osteosarcoma cells. Metabolic potencies correlated well with insulin receptor affinities. Mitogenic potencies in general correlated better with IGF-I receptor affinities than with insulin receptor off-rates. The 2 rapid-acting insulin analogs aspart and lispro resembled human insulin on all parameters, except for a slightly elevated IGF-I receptor affinity of lispro. In contrast, the 2 long-acting insulin analogs, glargine and detemir, differed significantly from human insulin. The combination of the B31B32diArg and A21Gly substitutions provided insulin glargine with a 6- to 8-fold increased IGF-I receptor affinity and mitogenic potency compared with human insulin. The attachment of a fatty acid chain to LysB29 provided insulin detemir with reduced receptor affinities and metabolic and mitogenic potencies but did not change the balance between mitogenic and metabolic potencies. The safety implications of the increased growth-stimulating potential of insulin glargine are unclear. The reduced in vitro potency of insulin detemir might explain why this analog is not as effective on a molar basis as human insulin in humans.

The fatty acid acylated insulin, Lys(B29)-tetradecanoyl, des-(B30) human insulin, has been crystallized and the structure determined by X-ray crystallography. The fatty acid substituent on residue B29 Lys binds reversibly to circulating albumin protein in vivo, and by this mechanism the hormone's action is prolonged. Crystals of the fatty acid insulin grow in space group R3, with two dimers in the asymmetric unit, and diffract to 1.8 A spacing. The structure has been solved by molecular replacement and refined using a maximum likelihood method. The crystal structure consists of R6 zinc insulin hexamers which contain phenol. The fatty acids can be seen bound between the hexamers, making specific interactions with the side chains of residue B1 Phe; however, the lysine side chains to which the fatty acids are covalently attached are mostly disordered. The mode of binding of the fatty acids appears to be determined by crystal packing, and whether or not they interact with the protein in this way in solution remains uncertain.

We have synthesized insulins acylated by fatty acids in the epsilon-amino group of LysB29. Soluble preparations can be made in the usual concentration of 600 nmol/ml (100 IU/ml) at neutral pH. The time for 50% disappearance after subcutaneous injection of the corresponding TyrA14(125I)-labelled insulins in pigs correlated with the affinity for binding to albumin (r = 0.97), suggesting that the mechanism of prolonged disappearance is binding to albumin in subcutis. Most protracted was LysB29-tetradecanoyl des-(B30) insulin. The time for 50% disappearance was 14.3 +/- 2.2 h, significantly longer than that of Neutral Protamine Hagedorn (NPH) insulin, 10.5 +/- 4.3 h (p0.001), and with less inter-pig variation (p0.001). Intravenous bolus injections of LysB29-tetradecanoyl des-(B30) human insulin showed a protracted blood glucose lowering effect compared to that of human insulin. The relative affinity of LysB29-tetradecanoyl des-(B30) insulin to the insulin receptor is 46%. In a 24-h glucose clamp study in pigs the total glucose consumptions for LysB29-tetradecanoyl des-(B30) insulin and NPH were not significantly different (p = 0.88), whereas the times when 50% of the total glucose had been infused were significantly different, 7.9 +/- 1.0 h and 6.2 +/- 1.3 h, respectively (p0.04). The glucose disposal curve caused by LysB29-tetradecanoyl des-(B30) insulin was more steady than that caused by NPH, without the pronounced peak at 3 h. Unlike the crystalline insulins, the soluble LysB29-tetradecanoyl des-(B30) insulin does not elicit invasion of macrophages at the site of injection. Thus, LysB29-tetradecanoyl des-(B30) insulin might be suitable for providing basal insulin in the treatment of diabetes mellitus.

Insulin degludec, an engineered acylated insulin, was recently reported to form a soluble depot after subcutaneous injection with a subsequent slow release of insulin and an ultralong glucose-lowering effect in excess of 40 h in humans. We describe the structure, ligand binding properties, and self-assemblies of insulin degludec using orthogonal structural methods. The protein fold adopted by insulin degludec is very similar to that of human insulin. Hexamers in the R(6) state similar to those of human insulin are observed for insulin degludec in the presence of zinc and resorcinol. However, under conditions comparable to the pharmaceutical formulation comprising zinc and phenol, insulin degludec forms finite dihexamers that are composed of hexamers in the T(3)R(3) state that interact to form an R(3)T(3)-T(3)R(3) structure. When the phenolic ligand is depleted and the solvent condition thereby mimics that of the injection site, the quaternary structure changes from dihexamers to a supramolecular structure composed of linear arrays of hundreds of hexamers in the T(6) state and an average molar mass, M(0), of 59.7 × 10(3) kg/mol. This novel concept of self-assemblies of insulin controlled by zinc and phenol provides the basis for the slow action profile of insulin degludec. To the best of our knowledge, this report for the first time describes a tight linkage between quaternary insulin structures of hexamers, dihexamers, and multihexamers and their allosteric state and its origin in the inherent propensity of the insulin hexamer for allosteric half-site reactivity.

Purpose Basal insulins with improved kinetic properties can potentially be produced using acylation by fatty acids that enable soluble, high-molecular weight complexes to form post-injection. A series of insulins, acylated at B29 with fatty acids via glutamic acid spacers, were examined to deduce the structural requirements. Methods Self-association, molecular masses and hexameric conformations of the insulins were studied using size exclusion chromatography monitored by UV or multi-angle light scattering and dynamic light scattering, and circular dichroism spectroscopy (CDS) in environments (changing phenol and zinc concentration) simulating a pharmaceutical formulation and changes following subcutaneous injection. Results With depletion of phenol, insulin degludec and another fatty diacid–insulin analogue formed high molecular mass filament-like complexes, which disintegrated with depletion of zinc. CDS showed these analogues adopting stable T3R3 conformation in presence of phenol and zinc, changing to T6 with depletion of phenol. These findings suggest insulin degludec is dihexameric in pharmaceutical formulation becoming multihexameric after injection. The analogues showed weak dimeric association, indicating rapid release of monomers following hexamer disassembly. Conclusions Insulins can be engineered that remain soluble but become highly self-associated after injection, slowly releasing monomers; this is critically dependent on the acylation moiety. One such analogue, insulin degludec, has therapeutic potential.

Aim: To compare the properties of insulin detemir with human insulin or insulin aspart in various in vitro and in vivo experiments, thereby highlighting the importance of performing dose–response studies when investigating insulin analogues, in this study specifically insulin detemir. Methods: Displacement of membrane-associated insulin receptors from human and rat hepatocytes, and from Chinese Hamster Ovary cells over-expressing human insulin receptor (CHO-hIR) at varying albumin concentrations is measured. Lipogenesis in primary rat adipocytes over time and the effects in the simultaneous presence of insulin detemir and human insulin or insulin aspart are assessed. The hyperinsulinaemic euglycaemic clamp technique in rats is used to establish dose–response curves for multiple metabolic endpoints and to investigate the effects of the simultaneous presence of insulin detemir and human insulin. Results: Both in vitro and in vivo, insulin detemir shows full efficacy and right-shifted parallel dose–response curves compared with human insulin. The potency estimates are different between the in vivo and in vitro conditions and among different in vitro conditions, that is the potency decreases in vitro with increasing albumin concentration. The effects of insulin detemir and human insulin are additive both in vitro and in vivo. Conclusions: Insulin detemir is fully efficacious compared with human insulin on all metabolic endpoints measured in vitro and in vivo. The fact that the potency estimates are method-dependent emphasizes the importance of establishing full dose–response relationships when characterizing insulin detemir.

The insulin example demonstrates that it is possible to alter pharmacokinetics and dynamics. By careful choice of ligand and site of substitution it is possible to provide the molecule with the desired characteristics without loosing potency. In this example the following characteristic of insulin has been obtained: 1. A prolonged acting insulin analogue which can be formulated as a neutral soluble preparation 2. Insulin has been provided with albumin binding properties 3. Improved duration of action compared to NPH insulin 4. Improved dynamic profile without sharp peeks of activity, i.e. smoother action

Purpose. Insulin detemir has been found in clinical trials to be absorbed with very low variability. A series of experiments were performed to elucidate the underlying mechanisms. Methods. The disappearance from an injected subcutaneous depot and elimination studies in plasma were carried out in pigs. Size-exclusion chromatography was used to assess the self-association and albumin binding states of insulin detemir and analogs. Results. Disappearance T50% from the injection depot was 10.2 ± 1.2 h for insulin detemir and 2.0 ± 0.1 h for a monomeric acylated insulin analog. Self-association of acylated insulin analogs with same albumin affinity in saline correlated with disappearance rate and addition of albumin to saline showed a combination of insulin detemir self association and albumin binding. Intravenous kinetic studies showed that the clearance and volume of distribution decreased with increasing albumin binding affinity of different acylated insulin analogs. Conclusions. The protracted action of detemir is primarily achieved through slow absorption into blood. Dihexamerization and albumin binding of hexameric and dimeric detemir prolongs residence time at the injection depot. Some further retention of detemir occurs in the circulation where albumin binding causes buffering of insulin concentration. Insulin detemir provides a novel principle of protraction, enabling increased predictability of basal insulin.

The addition of specific bulky hydrophobic groups to the insulin molecule provides it with affinity for circulating serum albumin and enables it to form soluble macromolecular complexes at the site of subcutaneous injection, thereby securing slow absorption of the insulin analogue into the blood stream and prolonging its half-life once there. N-Lithocholic acid acylated insulin [Lys(B29)-lithocholyl des-(B30) human insulin] has been crystallized and the structure determined by X-ray crystallography at 1.6 A resolution to explore the molecular basis of its assembly. The unit cell in the crystal consists of an insulin hexamer containing two zinc ions, with two m-cresol molecules bound at each dimer-dimer interface stabilizing an R(6) conformation. Six covalently bound lithocholyl groups are arranged symmetrically around the outside of the hexamer. These form specific van der Waals and hydrogen-bonding interactions at the interfaces between neighboring hexamers, possibly representing the kinds of interactions which occur in the soluble aggregates at the site of injection. Comparison with an equivalent nonderivatized native insulin hexamer shows that the addition of the lithocholyl group disrupts neither the important conformational features of the insulin molecule nor its hexamer-forming ability. Indeed, binding studies show that the affinity of N-lithocholyl insulin for the human insulin receptor is not significantly diminished.

Albumin is organized in three homologous domains formed by double loops stabilized by disulfide bonds. Utilizing a secretory expression system based on a synthetic secretory prepro-leader, the three human serum albumin domains were expressed in the yeastSaccharomyces cerevisiae.Human serum albumin domains I and III were efficiently expressed and secreted, indicating that these domains can form independent structural units capable of folding into stable tertiary structures. In contrast, albumin domain II was not secreted and disappeared early in the secretory pathway. Human serum albumin has the ability to bind a large number of small molecule ligands, including fatty acids, presumably due to its structure and structural flexibility. Purified albumin domain III bound myristic acid, whereas purified albumin domain I did not bind myristic acid. A new soluble long-acting insulin an alogue acylated with myristic acid (Markussen J.,et al., Diabetologia39, 281–288, 1996) bound to domain III and bound markedly more weakly to domain I.

NN304 (LysB29-tetradecanoyl, des(B30)-insulin) is a new soluble, long-acting insulin analogue that is tightly bound to human serum albumin differentiating it from human insulin. In the present study, we investigate the effect of fatty acids and selected drugs on the binding of NN304 to human serum albumin in vitro. Binding of the first fatty acid equivalent to albumin does not affect the binding of NN304. None of the tested drugs compete with the binding of NN304 at drug-to-albumin concentration ratios of < 1. The binding of NN304 is shown to be independent of binding of drugs in the two major binding pockets that are located in domains IIA and IIIA of the albumin molecule. Tolbutamide and glibenclamide do not compete with NN304 for binding to albumin at therapeutic drug-to-albumin concentration ratios. High concentrations of acetylsalicylic acid and ibuprofen decrease the affinity of NN304 for albumin, but these interactions occur at drug-to-albumin concentration ratios that are higher than clinically relevant. In conclusion, NN304 is unlikely to be involved in clinically significant drug interactions at the albumin binding level. The unique ligand binding properties of serum albumin and its abundance in the extracellular fluids makes fatty acid acylation and albumin binding an attractive protraction principle for insulin and potentially also for other peptide drugs.

Insulins acylated with fatty acids at the epsilon-amino group of LysB29 constitute a new class of insulin analogs, which are prolonged-acting due to albumin binding. In the present study it is shown that the affinity of fatty acid acylated insulins for albumin varies considerably (> 50-fold) among species. The relative affinities of acylated insulin for albumin in human, pig, and rabbit serum are about 1:1:5:35. The several fold higher binding affinity in rabbit serum than in pig serum is reflected in a relatively more protracted effect after sc injection in rabbits than in pigs. Due to the similar binding affinities in pig serum and human serum, the pig model should provide a useful estimate of the degree of protraction of acylated insulin in humans. The results emphasize that species differences in ligand binding can be of major importance in the preclinical evaluation of highly albumin bound drugs.

Albumin is a multifunctional transport protein that binds a wide variety of endogenous substances and drugs. Insulins with affinity for albumin were engineered by acylation of the epsilon-amino group of LysB29 with saturated fatty acids containing 10-16 carbon atoms. The association constants for binding of the fatty acid acylated insulins to human albumin are in the order of 10(4)-10(5) M-1. The binding apparently involves both non-polar and ionic interactions with the protein. The acylated insulins bind at the long-chain fatty acid binding sites, but the binding affinity is lower than that of the free fatty acids and depends to a relatively small degree on the number of carbon atoms in the fatty acid chain. Differences in affinity of the acylated insulins for albumin are reflected in the relative timing of the blood-glucose-lowering effect after subcutaneous injection into rabbits. The acylated insulins provide a breakthrough in the search for soluble, prolonged-action insulin preparations for basal delivery of the hormone to the diabetic patient. We conclude that the biochemical concept of albumin binding can be applied to protract the effect of insulin, and suggest that derivatization with albumin-binding ligands could be generally applicable to prolong the action profile of peptide drugs.

The water-soluble albumin of the high-lysine barley called Hiproly was fractionated by means of ion exchange chromatography and gel filtration. Three high-lysine fractions were isolated, and from the chromatographic profiles it was deduced that two of these contribute prominently to the overall high lysine content of Hiproly albumin. The two polypeptides were purified, and antisera raised against them. Immunological cross reaction was observed suggesting that the smaller polypeptide with a molecular weight of 8,100 dalton is a fragment of the larger one with a molecular weight of 9,100 dalton. The fragment contains 6 and the larger polypeptide 8 lysine residues. Both proteins lacked cysteine, but were rich in valine, glutamine/glutamic acid and asparagine/aspartic acid.

Chymotrypsin inhibitors CI-1 and CI-2 from barley were subjected to limited hydrolysis by subtilisin Carlsberg, subtilisin Novo and chymotrypsin. Analysis of CI-2 derived peptides by amino acid sequencing identified peptide bond, Met59-Glu60, as the reactive site towards these three proteinases. In contrast, inhibitor CI-1 showed a single reactive site (Leu59-Asp60) towards chymotrypsin and two reactive sites (Met30-Ser31 and Leu59-Asp60) towards either of the subtilisins.

A basic protein was isolated from aqueous extracts of barley seeds. It contains 91 amino acid residues including 8 half-cystines, but no phenylalanine or tryptophan; the calculated molecular weight is 9.694. Amino acid composition and N-terminal sequence show that the protein corresponds to the probable amylase/protease inhibitor (PAPI) encoded by a formerly described cDNA. The protein is 50% homologous with an α-amylase inhibitor I-2 from seeds of Indian finger millet and it shows a distant homology with two Bowman Birk type protease inhibitors. However, the barley protein does not inhibit any of the enzymes tested. They include α-amylases, a β-amylase, β-glucanases, serine proteases, a sulfhydryl protease, aspartate proteases, and serine carboxypeptidases. Nevertheless, difference UV-spectroscopy indicated that the protein interacts with porcine pancreatic α-amylase. NMR-spectroscopy revealed that it possesses tertiary structure.

A lysine-rich serine protease inhibitor, isolated from barley (H. vulgare, var. Hiproly) which inhibits subtilisin strongly, chymotrypsin weaker, but not trypsin, is shown to be homologous with potato inhibitor I (Richardson andCossins, FEBS Lett. 52, 161 (1975)) (45% of the amino acids in identical positions). The barley inhibitor seems to be the first example described of a protease inhibitor from higher plants in which the structure and reactive site is not stabilized by disulfide bonds.

Two lysine-rich components isolated from «Hiproly» barley have been subjected to sequence determination. The complete sequence of the smallest component, designated SP II B, has been determined. This protein consists of 72 amino acid residues and has a molecular weight of 8.072. The largest component, designated SP II A, was blocked to N-terminal Edman degradation, but sequence analyses of cyanogen bromide- and tryptic fragments showed that it was identical to the smallest component, except for the eight to eleven residues of which SP II A is longer in the N-terminus. Of these residues seven have been sequenced, and the following total sequence is reported (Glx, Val, Ser, Ser)-Lys-Lys-Pro-Glu-Gly-Val-Asn-Thr-Gly-Ala-Gly-Asp-Arg-His-Asn-Leu-Lys-Thr-Glu-Trp-Pro-Glu-Leu-Val-Gly-Lys-Ser-Val-Glu-Glu-Ala-Lys-Lys-Val-Ile-Leu-Gln-Asp-Lys-Pro-Glu-Ala-Gln-Ile-Ile-Val-Leu-Pro-Val-Gly-Thr-Ile-Val-Thr-Met-Glu-Tyr-Arg-Ile-Asp-Arg-Val-Arg-Leu-Phe-Val-Asp-Lys-Leu-Asp-Asn-Ile-Ala-Gln-Val-Pro-Arg-Val-Gly.

Quantitative extraction of salt and water soluble proteins from Hiproly, CI 4362 and Bomi barley was performed and their content of the lysine rich SP II albumin determined by a single radial immunodiffusion assay. The elevated content of SP II albumin in Hiproly accounted for 37% of the difference in crude protein lysine between Hiproly and Bomi and for 19% between Hiproly and its low lysine sisterline CI 4362. Apart from the lysine rich SP II albumin, other proteins contribute to the high lysine content of Hiproly.

Free and initially membrane bound polysomes were isolated from 20 day old endosperms of Bomi and Hiproly barley and used as templates in an in vitro protein synthesizing system based on wheat germ extract. Three35S-labelled translation products were identified as SP II albumin, β-amylase and chymotrypsin inhibitor CI-1 among the polypeptides synthesized by the polysomes of the endoplasmic reticulum. Identification employed immunoaffinity isolation. Protein Z was not detectable among the in vitro translation products of either initially membrane bound or free endosperm polysomes. Compared to Bomi barley the Hiproly endosperm is enriched for translatable mRNA coding for SP II albumin, β-amylase and chymotrypsin inhibitor CI-1. In vitro and in vivo synthesized β-amylases have identical molecular weights. Only one form of SP II albumin is produced in vitro, confirming that the lower molecular weight SP II B albumin is a proteolytic cleavage product of the SP II A albumin.

Californium-252 plasma desorption mass spectrometry (PDMS) has been employed for the characterization of a series of human insulin derivatives in order to evaluate the performance of this technique as an analytical tool in protein engineering. Several of the characterized modifications result in a 1 a.m.u. mass change. The precision in mass determination obtainable by PDMS analysis is not sufficient for unambiguous verification of such modifications based on the molecular weight alone. It is, however, possible to carry out in situ enzymatic digestion of the sample. Subsequent PDMS analysis will in most cases reveal if the modification has been introduced as intended.