Solid Phase Synthesis of an Analogue of Insulin, A0:R glargine, That Exhibits Decreased Mitogenic Activity

Numerous analogues of insulin have been prepared over the past three decades for use in diabetic therapy. However, only two long-acting insulins have been approved for clinical use. One is Levemir (Novo Nordisk) and the other is Lantus (Sanofi-Aventis). Glargine (commercial name: Lantus) is characterized by a substitution of Gly in place of Asn at the C terminus of the A-chain and addition of two Arg residues to the C terminus of the B-chain. Despite the clinical advantages of glargine, it is not without concern that its increased affinity for the IGF-1 receptor may correlate with increased mitogenic activity. Recently, a systematic study of modified analogues of glargine showed that placement of an extra Arg residue at the N terminus of the A-chain conferred improved insulin:IGF-1 receptor selectivity without significant loss of pharmacological profile. However, as it is difficult to prepare such an analogue in high yield by recombinant DNA methods, we undertook its chemical assembly by our refined solid phase synthesis method. We describe herein its chemical preparation and biological activity in both insulin receptor binding assays and DNA synthesis assays. The synthetic analogue, A0:R glargine, showed slightly reduced affinity for IR-B (twofold) compared to native insulin. In stimulating DNA synthesis, A0:R glargine was slightly less potent compared to insulin or glargine. This result ultimately confirms the previous report that A0:R glargine has a lower potency in mitogenic assays compared to glargine. This glargine analogue thus could be a potential lead compound for drug design and development for the treatment of diabetes.     

Cost-effectiveness of insulin analogues for diabetes mellitus

Background

Insulin analogues may be associated with fewer episodes of hypoglycemia than conventional insulins. However, they are costly alternatives. We compared the cost-effectiveness of insulin analogues and conventional insulins used to treat type 1 and type 2 diabetes mellitus in adults.

Methods

We conducted a cost-effectiveness evaluation of insulin analogues versus conventional insulins using the Center for Outcomes Research Diabetes Model. We compared rapid-acting analogues (insulin aspart and insulin lispro) with regular human insulin, and long-acting analogues (insulin glargine and insulin detemir) with neutral protamine Hagedorn insulin. We derived clinical information for the comparisons from meta-analyses of randomized controlled trials. We obtained cost and utility estimates from published sources. We performed sensitivity analyses to test the robustness of our results.

Results

For type 1 diabetes, insulin aspart was more effective and less costly than regular human insulin. Insulin lispro was associated with an incremental cost of Can$28 996 per quality-adjusted life-year. The incremental cost per quality-adjusted life-year was Can$87 932 for insulin glargine and Can$387 729 for insulin detemir, compared with neutral protamine Hagedorn insulin. For type 2 diabetes, insulin aspart was associated with an incremental cost of Can$22 488 per quality-adjusted life-year compared with regular human insulin. For insulin lispro, the incremental cost was Can$130 865. Compared with neutral protamine Hagedorn insulin, insulin detemir was less effective and more costly. Insulin glargine was associated with an incremental cost of Can$642 994 per quality-adjusted life-year. The model was sensitive to changes in the effect size of hemoglobin A_1c and to decrements applied to utility scores when fear of hypoglycemia was included as a factor.

Interpretation

The cost-effectiveness of insulin analogues depends on the type of insulin analogue and whether the patient receiving the treatment has type 1 or type 2 diabetes. With the exception of rapid-acting insulin analogues in type 1 diabetes, routine use of insulin analogues, especially long-acting analogues in type 2 diabetes, is unlikely to represent an efficient use of finite health care resources.Insulin agents available for the treatment of diabetes mellitus include conventional insulins and insulin analogues. Insulin analogues were developed to mimic more closely the separate bolus and basal components of insulin secretion.¹ Rapid-acting (bolus or mealtime) and long-acting (basal or background) analogue formulations are available. This new class of drugs has been promoted as providing more flexible treatment schedules and a reduced risk of hypoglycemia relative to conventional insulins.¹The cost of insulin analogues exceeds that of conventional insulins.^2,3 More than US$7.3 billion was spent globally on the purchase of insulin products in 2005 — an increase of 19% over the previous year.⁴ It has been suggested that the increased expenditure was due to both the increasing prevalence of diabetes and the increased use of insulin analogues.⁵We performed an analysis of the cost-effectiveness of insulin analogues compared with conventional insulins in the management of type 1 or type 2 diabetes in adults.     

Immunocytochemical localization and immunochemical characterization of an insulin-related peptide in the pancreas of the urodele amphibian,Ambystoma mexicanum

Summary The pancreas of the axolotl, Ambystoma mexicanum, was investigated by immunocytochemical methods for the presence of immunoreactivity to a number of antisera raised against mammalian insulins. All anti-insulin antisera tested revealed substantial amounts of reaction products confined solely to the aldehyde-fuchsinophilic B cells of the endocrine pancreas. The reactive cell population was detected by use of one polyclonal antiserum against bovine insulin and eight different monoclonal antibodies against insulins from various mammalian species. Six of these antibody clones have known specificity to sub-regions of the insulin molecule. Additionally, fractions of an ethanol-HCl extract of pancreatic tissue from Ambystoma was studied in both conventional dot-blot tests by means of the same panel of antibodies and a two-site sandwich time-resolved immunofluorometric assay for human insulin involving two of the monoclonal antibodies. These experiments support the immunocytochemical observations by demonstrating the existence of an insulin-related peptide with a great deal of structural resemblance to mammalian insulins and displaying antigenic determinants in common at least with the amino acid residues A_8–10 and B_26–30. In conclusion, we interpret the findings as indicating that the immunocytochemically revealed tissue bound antigen in the Ambystoma pancreatic B-cells may be a peptide related to human insulin.Supported in part by SNF grant 11-5082 (G.N.H.). The authors are indebted to Dr. P. Rosenkilde for the gift of the Ambystoma material     

Effect of N-methylation of selected peptide bonds on the biological activity of insulin. [2-N-methylisoleucine-A]insulin and [3-N-methylvaline-A]insulin

Hydrogen bonding involving peptide bonds of the backbone of the insulin molecule may play an important role in insulin-receptor interaction. Our previous work suggested that the A2-A8 helical segment of the hormone molecule participates in this interaction. To investigate the possible involvement of peptide bonds of this segment in insulin-receptor interaction the [2-N-methylisoleucine-A]insulin and [3-N-methylvaline-A]insulin ([MeIle2-A]- and [MeVal3-A]insulins) were synthesized. The circular dichroic spectra of the analogues were obtained and their properties were examined in several biological assays. The circular dichroic spectra suggested that the analogues remained monomeric at concentrations at which insulin is predominantly dimeric, and that their A2-A8 helical segments are distorted. The in vitro biological activity and the receptor binding affinity of these analogues were compared with that of natural insulin. Both analogues are weak full agonists. [MeIle2-A]insulin displayed a potency of 5.4 +/- 0.3% in stimulating lipogenesis and 4.6 +/- 2.3% in receptor binding affinity in rat fat cells and rat liver plasma membranes respectively. [MeVal3-A]insulin displayed a potency of 2.1 +/- 0.2% in lipogenesis and 1.0 +/- 0.3% in receptor binding assays. In radioimmunoassays [MeIle2-A]- and [MeVal3-A]insulins exhibited potencies of 13% and 11% respectively relative to the natural hormone. The substantially decreased biological activity and receptor binding affinity of these analogues may be attributed partly to the change of conformation and partly to the loss of hydrogen bonding capacity of the A2-A8 segment brought about by N-methylation of the A1-A2 or A2-A3 peptide bonds.     

Interaction between the A2 and A19 amino acid residues is of critical importance for high biological activity in insulin: [19-leucine-A]insulin

The replacement of tyrosine at position A19 by leucine in the insulin molecule led to an analogue, [19-leucine-A]insulin [( Leu19-A]insulin), displaying insignificant receptor binding affinity and in vitro biological activity less than 0.1 and 0.05%, respectively, compared to the natural hormone. This analogue along with the previously reported [2-glycine-A]-, [2-alanine-A]-, and [2-norleucine-A]insulins is the least potent insulin analogue we have examined. Circular dichroic studies showed that all these analogues are monomeric at concentrations at which insulin is primarily dimeric. We conclude that an aromatic ring at position A19 and the presence of the side chain of isoleucine at position A2 are each of critical importance for high biological activity in insulin. It appears that the van der Waals interaction between the side chain of isoleucine A2 and tyrosine A19, present in crystalline insulin, is among the most important determinants for high biological activity in insulin.     

New insights into the effect of mutations on affibody-Fc interaction,a molecular dynamics simulation approach

Staphylococcal protein A (SpA) domain B (the basis of affibody) has been widely used in affinity chromatography and found therapeutic applications against inflammatory diseases through targeting the Fc part of immunoglobulin G (IgG). We have performed extensive molecular dynamics simulation of 41 SpA mutants and compared their dynamics and conformations to wild type. The simulations revealed the molecular details of structural and dynamics changes that occurred due to introducing point mutations and helped to explain the SPR results. It was observed in some variants a point mutation caused extensive structural changes far from the mutation site, while an effect of some other mutations was limited to the site of the mutated residue. Also, the pattern of hydrogen bond networks and hydrophobic core arrangements were investigated. We figured out mutations that occurred at positions 128, 136, 150 and 153, affected two hydrophobic cores at the interface as well as mutations introduced at positions 129 and 154 interrupted two hydrogen bond networks of the interface, SPR data showed all of these mutations reduced binding affinity significantly. Overall, by scanning the SpA-Fc interface through the large numbers of introduced mutations, the new insights have been gained which would help to design high- affinity ligands of IgG.     

Possible involvement of the A20-A21 peptide bond in the expression of the biological activity of insulin. 3. [21-Desasparagine,20-cysteine ethylamide-A]insulin and [21-desasparagine,20-cysteine 2,2,2-trifluoroethylamide-A]insulin

We have synthesized [21-desasparagine,20-cysteine ethylamide-A]insulin and [21-desasparagine,20-cysteine 2,2,2-trifluoroethylamide-A]insulin, which differ from natural insulin in that the C-terminal amino residue of the A chain, asparagine, has been removed and the resulting free carboxyl group of the A20 cysteine residue has been converted to an ethylamide and a trifluoroethylamide group, respectively. [21-Desasparagine,20-cysteine ethylamide-A]insulin displayed equivalent potency in receptor binding and biological activity, ca. 12% and ca. 14%, respectively, relative to bovine insulin. In contrast, [21-desasparagine,20-cysteine 2,2,2-trifluoroethylamide-A]insulin displayed a divergence in these properties, ca. 13% in receptor binding and ca. 6% in biological activity. This disparity is ascribed to a difference in the electronic state of the A20-A21 amide bond in these two analogues. A model is proposed to account for the observation of divergence between receptor binding and biological activity in a number of synthetic insulin analogues and naturally occurring insulins. In this model, changes in the electronic state and/or the orientation of the A20-A21 amide bond can modulate biological activity independently of receptor binding affinity. The A20-A21 amide bond is thus considered as an important element in the "message region" of insulin.     

Insulin analogues with modifications at position B26. Divergence of binding affinity and biological activity

In this study, we prepared several shortened and full-length insulin analogues with substitutions at position B26. We compared the binding affinities of the analogues for rat adipose membranes with their ability to lower the plasma glucose level in nondiabetic Wistar rats in vivo after subcutaneous administration, and also with their ability to stimulate lipogenesis in vitro. We found that [NMeHisB26]-DTI-NH 2 and [NMeAlaB26]-DTI-NH 2 were very potent insulin analogues with respect to their binding affinities (214 and 465%, respectively, compared to that of human insulin), but they were significantly less potent than human insulin in vivo. Their full-length counterparts, [NMeHisB26]-insulin and [NMeAlaB26]-insulin, were less effective than human insulin with respect to binding affinity (10 and 21%, respectively) and in vivo activity, while [HisB26]-insulin exhibited properties similar to those of human insulin in all of the tests we carried out. The ability of selected analogues to stimulate lipogenesis in adipocytes was correlated with their biological potency in vivo. Taken together, our data suggest that the B26 residue and residues B26-B30 have ambiguous roles in binding affinity and in vivo activity. We hypothesize that our shortened analogues, [NMeHisB26]-DTI-NH 2 and [NMeAlaB26]-DTI-NH 2, have different modes of interaction with the insulin receptor compared with natural insulin and that these different modes of interaction result in a less effective metabolic response of the insulin receptor, despite the high binding potency of these analogues.     

Shortened insulin analogues: marked changes in biological activity resulting from replacement of TyrB26 and N-methylation of peptide bonds in the C-terminus of the B-chain

The role of three highly conserved insulin residues PheB24, PheB25, and TyrB26 was studied to better understand the subtleties of the structure-function relationship between insulin and its receptor. Ten shortened insulin analogues with modifications in the beta-strand of the B-chain were synthesized by trypsin-catalyzed coupling of des-octapeptide (B23-B30)-insulin with synthetic peptides. Insulin analogues with a single amino acid substitution in the position B26 and/or single N-methylation of the peptide bond at various positions were all shortened in the C-terminus of the B-chain by four amino acids. The effect of modifications was followed by two types of in vitro assays, i.e., by the binding to the receptor of rat adipose plasma membranes and by the stimulation of the glucose transport into the isolated rat adipocytes. From our results, we can deduce several conclusions: (i) the replacement of tyrosine in the position B26 by phenylalanine has no significant effect on the binding affinity and the stimulation of the glucose transport of shortened analogues, whereas the replacement of TyrB26 by histidine affects the potency highly positively; [HisB26]-des-tetrapeptide (B27-B30)-insulin-B26-amide and [NMeHisB26]-des-tetrapeptide (B27-B30)-insulin-B26-amide show binding affinity 529 and 5250%, respectively, of that of human insulin; (ii) N-methylation of the B24-B25 peptide bond exhibits a disruptive effect on the potency of analogues in both in vitro studies regardless the presence of amino acid in the position B26; (iii) N-methylation of the B23-B24 peptide bond markedly reduces the binding affinity and the glucose transport of respective analogue [NMePheB24]-des-tetrapeptide (B27-B30)-insulin-B26-amide.     

Analogues et dosages d’insuline : le cas général et le cas particulier de la glargine

Since 1996, genetic engineering has allowed modifications of insulin yielding to multiple modified insulins with different pharmacokinetic and/or pharmacodynamic properties. Molecules with maintained pharmacodynamic and modified pharmacokinetic profiles have been selected. Currently available rapid-acting analogues (lispro, aspart and glulisine) achieve plasma peak concentrations about twice as high and within approximately half the time compared with regular human insulin thus closely mimicking the physiological insulin response to a meal. Long-acting analogues (glargine and detemir) ensure the steady supplement of basal insulin plasma levels, with a plateau type of profile. Main analytical pitfalls of commercially human insulin immunoassays include crossreactivity with analogues and their metabolites. These crossreactivities are of great concern for interpreting insulin levels in patients treated with analogues. The development of more specific analytical methods to quantify separately the concentrations of endogenous insulin, rapid-acting and long-acting analogues and metabolites would be of utmost importance: (1) to further understand long-acting analogue variability in terms of efficiency; (2) to perform analogue kinetic studies; (3) to measure analogues in routine toxicology (forensic medicine) and (4) to assess intact glargine or glargine metabolite in vivo toxicity: recent debates about glargine safety have highlighted the lack of data about metabolite status (proportion of metabolized glargine and bioactivity of its metabolite). This goal could be achieved by specific immunoassay development or/and mass spectrometry analysis.     

Preliminary Structure–Function Relationship Studies on Insulin-Like Peptide 5 (INSL5)

Insulin-like peptide 5 (INSL5) is a two-chain, three-disulfide bonded member of insulin/relaxin superfamily of peptides that includes insulin, insulin-like growth factor I and II (IGFI and IGFII), insulin-like peptide 3, 4, 5 and 6 (INSL3, 4, 5 and 6), relaxin-1 (H1 relaxin), -2 (H2 relaxin) and -3 (H3 relaxin). Although it is expressed in relatively high levels in the gut, its biological function remains unclear. However, recent reports suggest a significant orexigenic action and a role in the regulation of insulin secretion and β-cell homeostasis, which implies that both agonists and antagonists of the peptide may have significant therapeutic applications. Modern solid phase synthesis techniques together with regioselective disulfide bond formation were employed for a preliminary structure–function relationship study of mouse INSL5. Two point mutated analogues, mouse INSL5 A-B(R24A, W25A) and mouse INSL5 A-B(K6A, R14A, Y18A) were chemically prepared, where the residues in the B-chain that may be involved in receptor activation and affinity binding, were respectively mutated. Synthetic mouse INSL5 A-B(R24A, W25A) analogue was inactive on RXFP4, the native receptor for INSL5, suggesting Arg^B24 and Trp^B25 are probably directly involved in INSL5 receptor activation. Mouse INSL5 A-B(K6A, R14A, Y18A) analogue had both decreased affinity and potency on RXFP4 (pIC₅₀ 7.7 ± 0.2, pEC₅₀ 7.87 ± 0.18) which indicated that one or more of these residues are critical for the binding to the receptor.     

Rapid-Acting Insulin Analogues in Basal-Bolus Regimens in Type 1 Diabetes Mellitus

ObjectiveTo compare rapid-acting insulin analogues with regular human insulin in terms of hemoglobin A_1c, hypoglycemia, and insulin dose when used in a basal-bolus regimen in patients with type 1 diabetes mellitus.MethodsMEDLINE and congress proceedings were searched for randomized controlled trials comparing pran- dial insulins in a basal-bolus regimen in adults or children/ adolescents with type 1 diabetes. Studies in pregnancy, ob- servational studies, studies that compared premixed insulin or continuous subcutaneous insulin infusion/insulin pumps, and studies where the basal insulin was also changed were excluded. Only studies reporting baseline-endpoint change in insulin dose, or baseline and/or endpoint values, were included.ResultsTwenty-eight studies were identified (insulin glulisine, 4; insulin aspart, 7; insulin lispro, 17). Twenty- five studies compared a rapid-acting insulin analogue with regular human insulin, and 3 trials compared 2 rapid-acting insulin analogues. Overall, rapid-acting insulin analogues in a basal-bolus regimen provided similar or greater im- provements in glycemic control than regular human insulin at similar insulin doses, as well as a lower incidence of hypoglycemia.ConclusionsResults of the studies identified in this literature review indicate that a basal-bolus regimen with prandial rapid-acting insulin analogue provides advan- tages over basal-bolus regimens using prandial regular hu- man insulin, providing improvements in glycemic control comparable to those obtained with regular human insulin, as well as a lower incidence of hypoglycemia. (Endocr Pract. 2010;16:486-505)     

Structural basis for the lower affinity of the insulin-like growth factors for the insulin receptor

Insulin and the insulin-like growth factors (IGFs) bind with high affinity to their cognate receptor and with lower affinity to the noncognate receptor. The major structural difference between insulin and the IGFs is that the IGFs are single chain polypeptides containing A-, B-, C-, and D-domains, whereas the insulin molecule contains separate A- and B-chains. The C-domain of IGF-I is critical for high affinity binding to the insulin-like growth factor I receptor, and lack of a C-domain largely explains the low affinity of insulin for the insulin-like growth factor I receptor. It is less clear why the IGFs have lower affinity for the insulin receptor. In this study, 24 insulin analogues and four IGF analogues were expressed and analyzed to explore the role of amino acid differences in the A- and B-domains between insulin and the IGFs in binding affinity for the insulin receptor. Using the information obtained from single substituted analogues, four multiple substituted analogues were produced. A "quadruple insulin" analogue ([Phe(A8), Ser(A10), Thr(B5), Gln(B16)]Ins) showed affinity as IGF-I for the insulin receptor, and a "sextuple insulin" analogue ([Phe(A8), Ser(A10), Thr(A18), Thr(B5), Thr(B14), Gln(B16)]Ins) showed an affinity close to that of IGF-II for the insulin receptor, whereas a "quadruple IGF-I" analogue ([His(4), Tyr(15), Thr(49), Ile(51)]IGF-I) and a "sextuple IGF-II" analogue ([His(7), Ala(16), Tyr(18), Thr(48), Ile(50), Asn(58)]IGF-II) showed affinities similar to that of insulin for the insulin receptor. The mitogenic potency of these analogues correlated well with the binding properties. Thus, a small number of A- and B-domain substitutions that map to the IGF surface equivalent to the classical binding surface of insulin weaken two hotspots that bind to the insulin receptor site 1.     

Engineering of insulin receptor isoform-selective insulin analogues

Background

The insulin receptor (IR) exists in two isoforms, A and B, and the isoform expression pattern is tissue-specific. The C-terminus of the insulin B chain is important for receptor binding and has been shown to contact the IR just adjacent to the region where the A and B isoforms differ. The aim of this study was to investigate the importance of the C-terminus of the B chain in IR isoform binding in order to explore the possibility of engineering tissue-specific/liver-specific insulin analogues.

Methodology/Principal Findings

Insulin analogue libraries were constructed by total amino acid scanning mutagenesis. The relative binding affinities for the A and B isoform of the IR were determined by competition assays using scintillation proximity assay technology. Structural information was obtained by X-ray crystallography. Introduction of B25A or B25N mutations resulted in analogues with a 2-fold preference for the B compared to the A isoform, whereas the opposite was observed with a B25Y substitution. An acidic amino acid residue at position B27 caused an additional 2-fold selective increase in affinity for the receptor B isoform for analogues bearing a B25N mutation. Furthermore, the combination of B25H with either B27D or B27E also resulted in B isoform-preferential analogues (2-fold preference) even though the corresponding single mutation analogues displayed no differences in relative isoform binding affinity.

Conclusions/Significance

We have discovered a new class of IR isoform-selective insulin analogues with 2–4-fold differences in relative binding affinities for either the A or the B isoform of the IR compared to human insulin. Our results demonstrate that a mutation at position B25 alone or in combination with a mutation at position B27 in the insulin molecule confers IR isoform selectivity. Isoform-preferential analogues may provide new opportunities for developing insulin analogues with improved clinical benefits.     

Efficacy and safety of insulin analogues for the management of diabetes mellitus: a meta-analysis

Background

Although insulin analogues are commonly prescribed for the management of diabetes mellitus, there is uncertainty regarding their optimal use. We conducted meta-analyses to compare the outcomes of insulin analogues with conventional insulins in the treatment of type 1, type 2 and gestational diabetes.

Methods

We updated 2 earlier systematic reviews of the efficacy and safety of rapid-and long-acting insulin analogues. We searched electronic databases, conference proceedings and “grey literature” up to April 2007 to identify randomized controlled trials that compared insulin analogues with conventional insulins. Study populations of interest were people with type 1 and type 2 diabetes (adult and pediatric) and women with gestational diabetes.

Results

We included 68 randomized controlled trials in the analysis of rapid-acting insulin analogues and 49 in the analysis of long-acting insulin analogues. Most of the studies were of short to medium duration and of low quality. In terms of hemoglobin A_1c, we found minimal differences between rapid-acting insulin analogues and regular human insulin in adults with type 1 diabetes (weighted mean difference for insulin lispro: –0.09%, 95% confidence interval [CI] –0.16% to –0.02%; for insulin aspart: –0.13%, 95% CI –0.20% to –0.07%). We observed similar outcomes among patients with type 2 diabetes (weighted mean difference for insulin lispro: –0.03%, 95% CI –0.12% to –0.06%; for insulin aspart: –0.09%, 95% CI –0.21% to 0.04%). Differences between long-acting insulin analogues and neutral protamine Hagedorn insulin in terms of hemoglobin A_1c were marginal among adults with type 1 diabetes (weighted mean difference for insulin glargine: –0.11%, 95% CI –0.21% to –0.02%; for insulin detemir: –0.06%, 95% CI –0.13% to 0.02%) and among adults with type 2 diabetes (weighted mean difference for insulin glargine: –0.05%, 95% CI –0.13% to 0.04%; for insulin detemir: 0.13%, 95% CI 0.03% to 0.22%). Benefits in terms of reduced hypoglycemia were inconsistent. There were insufficient data to determine whether insulin analogues are better than conventional insulins in reducing long-term diabetes-related complications or death.

Interpretation

Rapid-and long-acting insulin analogues offer little benefit relative to conventional insulins in terms of glycemic control or reduced hypoglycemia. Long-term, high-quality studies are needed to determine whether insulin analogues reduce the risk of long-term complications of diabetes.Diabetes mellitus is associated with serious long-term complications and premature death.¹ Data from the Health Canada National Diabetes Surveillance System indicate that, in 2004/05, diabetes was diagnosed in about 5.5% (1.8 million) of Canadians aged 20 years and older.² Because the disease goes undetected in many cases, the true prevalence may approach 1.9 million.³Tight glycemic control, to maintain a hemoglobin A_1c concentration of 7.0% or less, is recommended for all patients with diabetes to reduce the risk of long-term complications such as cardiovascular-related death, retinopathy and nephropathy.⁴ Insulin is indicated for all patients with type 1 diabetes and for patients with type 2 diabetes if adequate glycemic control cannot be achieved through exercise, diet or oral antidiabetic therapy.⁴Conventional insulins include regular human insulin and intermediate-acting neutral protamine Hagedorn insulin. However, these agents do not replicate the pattern of basal and postprandial endogenous secretion of insulin. Insulin analogues are modified human insulins developed to address this limitation.⁵ The rapid-acting insulin analogues insulin lispro, insulin aspart and insulin glulisine are marketed in Canada as bolus insulins; the long-acting agents insulin glargine and insulin detemir are marketed as basal insulins.⁶Systematic reviews of the insulin analogues have been published previously.^7–10 However, through our comprehensive search of the literature, we did not identify any reviews of long-acting insulin analogues in the management of type 1 diabetes or gestational diabetes. In this article, we provide an up-to-date, comprehensive systematic review and meta-analysis of outcomes associated with the use of rapid-and long-acting insulin analogues in type 1 and type 2 diabetes (adult and pediatric patients) and gestational diabetes. Detailed methods and complete results are reported elsewhere.^11,12     

Mutations at the dimer, hexamer, and receptor-binding surfaces of insulin independently affect insulin-insulin and insulin-receptor interactions.

Mutagenesis of the dimer- and hexamer-forming surfaces of insulin yields analogues with reduced tendencies to aggregate and dramatically altered pharmacokinetic properties. We recently showed that one such analogue, HisB10----Asp, ProB28----Lys, LysB29----Pro human insulin (DKP-insulin), has enhanced affinity for the insulin receptor and is useful for studying the structure of the insulin monomer under physiologic solvent conditions [Weiss, M. A., Hua, Q. X., Lynch, C. S., Frank, B. H., & Shoelson, S. E. (1991) Biochemistry 30, 7373-7389]. DKP-insulin retains native secondary and tertiary structure in solution and may therefore provide an appropriate baseline for further studies of related analogues containing additional substitutions within the receptor-binding surface of insulin. To test this, we prepared a family of DKP analogues having potency-altering substitutions at the B24 and B25 positions using a streamlined approach to enzymatic semisynthesis which negates the need for amino-group protection. For comparison, similar analogues of native human insulin were prepared by standard semisynthetic methods. The DKP analogues show a reduced tendency to self-associate, as indicated by 1H-NMR resonance line widths. In addition, CD spectra indicate that (with one exception) the native insulin fold is retained in each analogue; the exception, PheB24----Gly, induces similar perturbations in both native insulin and DKP-insulin backgrounds. Notably, analogous substitutions exhibit parallel trends in receptor-binding potency over a wide range of affinities: D-PheB24 greater than unsubstituted greater than GlyB24 greater than SerB24 greater than AlaB25 greater than LeuB25 greater than SerB25, whether the substitution was in a native human or DKP-insulin background. Such "template independence" reflects an absence of functional interactions between the B24 and B25 sites and additional substitutions in DKP-insulin and demonstrates that mutations in discrete surfaces of insulin have independent effects on protein structure and function. In particular, the respective receptor-recognition (PheB24, PheB25), hexamer-forming (HisB10), and dimer-forming (ProB28, LysB29) surfaces of insulin may be regarded as independent targets for protein design. DKP-insulin provides an appropriate biophysical model for defining structure-function relationships in a monomeric template.     

The A14 position of insulin tolerates considerable structural alterations with modest effects on the biological behavior of the hormone

As part of our aim to investigate the contribution of the tyrosine residue found in the 14 position of the A-chain to the biological activity of insulin, we have synthesized six insulin analogues in which the A14 Tyr has been substituted by a variety of amino acid residues. We have selected three hydrophilic and charged residues—glutamic acid, histidine, and lysine—as well as three hydrophobic residues—cycloleucine, cyclohexylalanine, and naphthyl-(1)-alanine—to replace the A14 Tyr. All six analogues exhibit full agonist activity, reaching the same maximum stimulation of lipogenesis as is achieved with procine insulin. The potency for five of the six analogues, [A14 Glu]-, [A14 His]-, [A14 Lys]-, [A14 cycloleucine]-, and [A14 naphthyl-(1)-alanine]-insulins in receptor binding assays ranges from 40–71% and in stimulation of lipogenesis ranges from 35-120% relative to porcine insulin. In contrast, the potency of the sixth analogue, [A14 cyclohexylalanine]insulin, in both types of assays is less than 1% of the natural hormone. The retention time on reversed-phase high-performance liquid chromatography for the first five analogues is similar to that of bovine insulin, whereas for the sixth analogue, [A14 cyclohexylalanine]insulin, it is approximately 11 min longer than that of the natural hormone. This suggests a profound change in conformation of the latter analogue. Apparently, the A14 position of insulin can tolerate a wide latitude of structural alterations without substantial decrease in potency. This suggests that the A14 position does not participate directly in insulin receptor interaction. Only when a substitution which has the potential to disrupt the conformation of the molecule is made at this position, is the affinity for the receptor, and hence the biological potency, greatly reduced.     

Parsing the effects of binding,signaling, and trafficking on the mitogenic potencies of granulocyte colony-stimulating factor analogues

The pharmacodynamic potency of a therapeutic cytokine interacting with a cell-surface receptor can be attributed primarily to three central properties: [1] cytokine/receptor binding affinity, [2] cytokine/receptor endocytic trafficking dynamics, and [3] cytokine/receptor signaling. Thus, engineering novel or second-generation cytokines requires an understanding of the contribution of each of these to the overall cell response. We describe here an efficient method toward this goal in demonstrated application to the clinically important cytokine granulocyte colony-stimulating factor (GCSF) with a chemical analogue and a number of genetic mutants. Using a combination of simple receptor-binding and dose-response proliferation assays we construct an appropriately scaled plot of relative mitogenic potency versus ligand concentration normalized by binding affinity. Analysis of binding and proliferation data in this manner conveniently indicates which of the cytokine properties-binding, trafficking, and/or signaling-are contributing substantially to altered potency effects. For the GCSF analogues studied here, two point mutations as well as a poly(ethylene glycol) chemical conjugate were found to have increased potencies despite comparable or slightly lower affinities, and trafficking was predicted to be the responsible mechanism. A third point mutant exhibiting comparable binding affinity but reduced potency was predicted to have largely unchanged trafficking properties. Surprisingly, another mutant possessing an order-of-magnitude weaker binding affinity displayed enhanced potency, and increased ligand half-life was predicted to be responsible for this net beneficial effect. Each of these predictions was successfully demonstrated by subsequent measurements of depletion of these five analogues from cell culture medium. Thus, for the GCSF system we find that ligand trafficking dynamics can play a major role in regulating mitogenic potency. Our results demonstrate that cytokine analogues can exhibit pharmacodynamic behaviors across a diverse spectrum of "binding-potency space" and that our analysis through normalization can efficiently elucidate hypotheses for the underlying mechanisms for further dedicated testing. We have also extended the Black-Leff model of pharmacological agonism to include trafficking effects along with binding and signaling, and this model provides a framework for parsing the effects of these factors on pharmacodynamic potency.     

Superactive insulins

The substitution of aspartic acid for the naturally-occurring histidine residue in position B10 in human insulin results in an insulin analogue which displays an in vitro potency 4- to 5-fold greater than the parent compound. This substitution has been introduced into six insulin analogues which, before modification, display potencies ranging from less than 0.01-fold to 3-fold relative to natural insulin. In each case, the resulting aspartic acid-substituted analogue is substantially more potent than the parent compound. Thus, it is now possible to prepare "tailor-made" insulins with enhanced potency.     

Interactions between insulins and liver membrane receptors of guinea pig,calf and chicken. Exclusion of a species-specific insulin receptor

Insulin binding experiments were performed with liver plasma membranes from guinea pig, calf and chicken. Bound insulin was separated from free insulin by a simple and rapid centrifugation of membranes through a layer of silicon oil. ¹²⁵I-labeled beef insulin was displaced from receptor sites by unlabelled guinea pig, beef and chicken insulin. The receptors of animals with insulins of different biological activity show similar basic characteristics and affinities to the different insulin molecules and thus are not specialised for the interactions with the homologous insulin molecule. The binding capacity of the membranes for beef insulin seems to be inversely related to the affinity of the homologous insulin to the receptor, guinea pig membranes showing the highest and chicken membranes the lowest receptor concentration