Purification and identification of high molecular weight products formed during storage of neutral formulation of human insulin.

PURPOSE: To identify High Molecular Weight Products (HMWP) formed in human insulin formulation during storage. METHODS: Commercial formulation of human insulin was stored at 37°C for 1 year and HMWP was isolated using preparative size exclusion chromatography (SEC) and reverse phase (RP) chromatography. The primary structure of the isolated species was analysed using liquid chromatography mass spectrometry (LC-MS) and tandem mass spectrometry (MS/MS). To test the hypothesis that amino groups of insulin are involved in HMWP formation, the HMWP content of various formulations spiked with amine compounds or formulations of insulin with modified amino groups was measured. RESULTS: More than 20 species of HMWP were observed and 16 species were identified using LC-MS. All identified species were covalent dimers of human insulin linked via A21Asn and B29Lys, formed via the formation of an anhydride intermediate at A21Asn. Two types of HMWP were identified, with the covalent link in the open or closed (succinimidyl) form. Some species also contained single deamidation at B3 or the desPhe(B1)-N-oxalyl-Val(B2) modification. Reduced rate of HMWP formation was observed after addition of L-lysine, L-arginine or piperazine or when insulin analogues with methylated N-terminals and side chain amines and A21Gly mutation were used. Formulations of human insulin without zinc and m-cresol were found to contain a different pool of HMWP. CONCLUSIONS: HMWP formed in formulation of human insulin at pH 7.4 with zinc and m-cresol consists primarily of covalent dimers linked via A21Asn and B29Lys. Insulin formulation properties determine the amount and identity of formed HMWP.

Traveling-wave ion mobility mass spectrometry of protein complexes: accurate calibrated collision cross-sections of human insulin oligomers.

RATIONALE: The collision cross-section (Ω) of a protein or protein complex ion can be measured using traveling-wave (T-wave) ion mobility (IM) mass spectrometry (MS) via calibration with compounds of known Ω. The T-wave Ω-values depend strongly on instrument parameters and calibrant selection. Optimization of instrument parameters and calibration standards are crucial for obtaining accurate T-wave Ω-values. METHODS: Human insulin and the fast-acting insulin aspart under native-like conditions (ammonium acetate, physiological pH) were analyzed on Waters SYNAPT G1 and G2 HDMS instruments. The calibrated T-wave Ω-values of insulin monomer, dimer, and hexamer ions were measured using many different combinations of denatured and native-like calibrants (masses between 2.85 and 256 kDa) and T-wave conditions. Drift-tube Ω-values were obtained on a modified SYNAPT G1. RESULTS: Insulin T-wave Ω-values were measured at 26 combinations of T-wave velocity and amplitude. Optimal sets of calibrants were identified that yield Ω-values with minimal dependence on T-wave conditions and calibration plots with high R(2)-values. The T-wave Ω-values determined under conditions satisfying these criteria had absolute errors <2%. Structural differences between human insulin and fast-acting insulin aspart were probed with IM-MS. Insulin aspart monomers have increased flexibility, while hexamers are more compact than human insulin. CONCLUSIONS: Accurate T-wave Ω-values that are indistinguishable from drift-tube values are obtained when using (1) native-like calibrants with masses that closely bracket that of the analyte, (2) T-wave velocities that maximize the R(2) of the calibration plot for those calibrants, and (3) at least three replicates at T-wave velocities that yield calibration plots with high R(2).

Molecular Engineering of Efficacious Mono-Valent Ultra-Long Acting Two-Chain Insulin-Fc Conjugates.

Here, we describe molecular engineering of monovalent ultra-long acting two-chain insulin-Fc conjugates. Insulin-Fc conjugates were synthesized using trifunctional linkers with one amino reactive group for reaction with a lysine residue of insulin and two thiol reactive groups used for re-bridging of a disulfide bond within the Fc molecule. The ultra-long pharmacokinetic profile of the insulin-Fc conjugates was the result of concertedly slowing insulin receptor-mediated clearance by (1) introduction of amino acid substitutions that lowered the insulin receptor affinity and (2) conjugating insulin to the Fc element. Fc conjugation leads to recycling by the neonatal Fc receptor and increase in the molecular size, both contributing to the ultra-long pharmacokinetic and pharmacodynamic profiles.

Molecular Engineering of Insulin Icodec, the First Acylated Insulin Analog for Once-Weekly Administration in Humans.

Here, we describe the molecular engineering of insulin icodec to achieve a plasma half-life of 196 h in humans, suitable for once-weekly subcutaneously administration. Insulin icodec is based on re-engineering of the ultra-long oral basal insulin OI338 with a plasma half-life of 70 h in humans. This systematic re-engineering was accomplished by (1) further increasing the albumin binding by changing the fatty diacid from a 1,18-octadecanedioic acid (C18) to a 1,20-icosanedioic acid (C20) and (2) further reducing the insulin receptor affinity by the B16Tyr → His substitution. Insulin icodec was selected by screening for long intravenous plasma half-life in dogs while ensuring glucose-lowering potency following subcutaneous administration in rats. The ensuing structure-activity relationship resulted in insulin icodec. In phase-2 clinical trial, once-weekly insulin icodec provided safe and efficacious glycemic control comparable to once-daily insulin glargine in type 2 diabetes patients. The structure-activity relationship study leading to insulin icodec is presented here.

Kinetic evidence for the sequential association of insulin binding sites 1 and 2 to the insulin receptor and the influence of receptor isoform.

Through binding to and signaling via the insulin receptor (IR), insulin is involved in multiple effects on growth and metabolism. The current model for the insulin-IR binding process is one of a biphasic reaction. It is thought that the insulin peptide possesses two binding interfaces (sites 1 and 2), which allow it to bridge the two alpha-subunits of the insulin receptor during the biphasic binding reaction. The sequential order of the binding events involving sites 1 and 2, as well as the molecular interactions corresponding to the fast and slow binding events, is still unknown. In this study we examined the series of events that occur during the binding process with the help of three insulin analogues: insulin, an analogue mutated in site 2 (B17A insulin), and an analogue in which part of site 1 was deleted (Des A1-4 insulin), both with and without a fluorescent probe attached. The binding properties of these analogues were tested using two soluble Midi IR constructs representing the two naturally occurring isoforms of the IR, Midi IR-A and Midi IR-B. Our results showed that in the initial events leading to Midi IR-insulin complex formation, insulin site 2 binds to the IR in a very fast binding event. Subsequent to this initial fast phase, a slower rate-limiting phase occurs, consistent with a conformational change in the insulin-IR complex, which forms the final high-affinity complex. The terminal residues A1-A4 of the insulin A-chain are shown to be important for the slow binding phase, as insulin lacking these amino acids is unable to induce a conformational change of IR and has a severely impaired binding affinity. Moreover, differences in the second phase of the binding process involving insulin site 1 between the IR-A and IR-B isoforms suggest that the additional amino acids encoded by exon 11 in the IR-B isoform influence the binding process.

Structure, Aggregation, and Activity of a Covalent Insulin Dimer Formed During Storage of Neutral Formulation of Human Insulin.

A specific covalently linked dimeric species of insulin high molecular weight products (HMWPs), formed during prolonged incubation of a neutral pharmaceutical formulation of human insulin, were characterized in terms of tertiary structure, self-association, biological activity, and fibrillation properties. The dimer was formed by a covalent link between A21Asn and B29Lys. It was analyzed using static and dynamic light scattering and small-angle X-ray scattering to evaluate its self-association behavior. The tertiary structure was obtained using nuclear magnetic resonance and X-ray crystallography. The biological activity of HMWP was determined using 2 in vitro assays, and its influence on fibrillation was investigated using Thioflavin T assays. The dimer's tertiary structure was nearly identical to that of the noncovalent insulin dimer, and it was able to form hexamers in the presence of zinc. The dimer exhibited reduced propensity for self-association in the absence of zinc but significantly postponed the onset of fibrillation in insulin formulations. Consistent with its dimeric state, the tested species of HMWP showed little to no biological activity in the used assays. This study is the first detailed characterization of a specific type of human insulin HMWP formed during storage of a marketed pharmaceutical formulation. These results indicate that this specific type of HMWP is unlikely to antagonize the physical stability of the formulation, as HMWP retained a tertiary structure similar to the noncovalent dimer and participated in hexamer assembly in the presence of zinc. In addition, increasing amounts of HMWP reduce the rate of insulin fibrillation.

Changes in glucose and fat metabolism in response to the administration of a hepato-preferential insulin analog.

Endogenous insulin secretion exposes the liver to three times higher insulin concentrations than the rest of the body. Because subcutaneous insulin delivery eliminates this gradient and is associated with metabolic abnormalities, functionally restoring the physiologic gradient may provide therapeutic benefits. The effects of recombinant human insulin (HI) delivered intraportally or peripherally were compared with an acylated insulin model compound (insulin-327) in dogs. During somatostatin and basal portal vein glucagon infusion, insulin was infused portally (PoHI; 1.8 pmol/kg/min; n = 7) or peripherally (PeHI; 1.8 pmol/kg/min; n = 8) and insulin-327 (Pe327; 7.2 pmol/kg/min; n = 5) was infused peripherally. Euglycemia was maintained by glucose infusion. While the effects on liver glucose metabolism were greatest in the PoHI and Pe327 groups, nonhepatic glucose uptake increased most in the PeHI group. Suppression of lipolysis was greater during PeHI than PoHI and was delayed in Pe327 infusion. Thus small increments in portal vein insulin have major consequences on the liver, with little effect on nonhepatic glucose metabolism, whereas insulin delivered peripherally cannot act on the liver without also affecting nonhepatic tissues. Pe327 functionally restored the physiologic portal-arterial gradient and thereby produced hepato-preferential effects.

Loss of Albino3 leads to the specific depletion of the light-harvesting system.

The chloroplast Albino3 (Alb3) protein is a chloroplast homolog of the mitochondrial Oxa1p and YidC proteins of Escherichia coli, which are essential components for integrating membrane proteins. In vitro studies in vascular plants have revealed that Alb3 is required for the integration of the light-harvesting complex protein into the thylakoid membrane. Here, we show that the gene affected in the ac29 mutant of Chlamydomonas reinhardtii is Alb3.1. The availability of the ac29 mutant has allowed us to examine the function of Alb3.1 in vivo. The loss of Alb3.1 has two major effects. First, the amount of light-harvesting complex from photosystem II (LHCII) and photosystem I (LHCI) is reduced >10-fold, and total chlorophyll represents only 30% of wild-type levels. Second, the amount of photosystem II is diminished 2-fold in light-grown cells and nearly 10-fold in dark-grown cells. The accumulation of photosystem I, the cytochrome b(6)f complex, and ATP synthase is not affected in the ac29 mutant. Mild solubilization of thylakoid membranes reveals that Alb3 forms two distinct complexes, a lower molecular mass complex of a size similar to LHC and a high molecular mass complex. A homolog of Alb3.1, Alb3.2, is present in Chlamydomonas, with 37% sequence identity and 57% sequence similarity. Based on the phenotype of ac29, these two genes appear to have mostly nonredundant functions.