Biochemical and physiological properties of a novel series of long-acting insulin analogs obtained by acylation with cholic acid derivatives.

PURPOSE: 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(Nepsilon-lithocholyl-gamma-Glu) des(B30) human insulin (NN344) in pigs. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Reversible insulin self-assembly under carbohydrate control.

Insulin with built-in pairs of boronates and polyols can produce soluble high molecular weight self-assemblies under control by carbohydrates. The illustrated principle has potential utility for general protein and peptide protraction and controlled drug release.

Insulins with built-in glucose sensors for glucose responsive insulin release.

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.

The mechanism of protraction of insulin detemir, a long-acting, acylated analog of human insulin.

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.

Mechanism of action in dogs of slow-acting insulin analog O346.

We compared metabolic effects as well as plasma and interstitial fluid kinetics of fatty acid-acylated insulin, Lys(B29)(N(epsilon)-omega-carboxynonadecanoyl)-des(B30) human insulin (O346), with previously determined kinetics of native insulin and insulin detemir. Euglycemic clamps with iv injection of O346 (90 pmol/kg) or saline control were performed in 10 male mongrel dogs under inhalant anesthesia. The t(1/2) for the clearance of O346 from plasma was 375.7 +/- 26.7 min; the t(1/2) for the appearance of O346 in interstitial fluid was 137 +/- 20 min (mean +/- SEM). Glucose disposal with O346 injection was increased 4-fold (t = 480 min, 8.3 +/- 1.42 mg/min/kg) compared with preinjection (t = 0 min, 2.1 +/- 0.13 mg/min/kg; P < 0.05) or saline control (t = 480 min, 2.09 +/- 0.22 mg/min/kg; P < 0.05). O346 plasma elimination and transendothelial transport were 0.3% and 3.5% of regular insulin and 3% and 50% of insulin detemir, respectively. Combination of in vivo results and compartmental modeling suggests that the duration of action of O346 after iv injection is about 25-fold and 10-fold longer compared with regular human insulin and insulin detemir, respectively. This study demonstrates that O346 stimulates glucose disposal very slowly, but when injected iv, its effect may be maintained for as long as 48 h as estimated from simulation analysis. The data suggest that O346 bound to albumin in plasma acts as a storage compartment for O346 from which the analog is slowly released to insulin-sensitive tissues. Reduced liver clearance of O346 is suggested to be the major mechanism for the protracted action.

Assembly of high-affinity insulin receptor agonists and antagonists from peptide building blocks.

Insulin is thought to elicit its effects by crosslinking the two extracellular alpha-subunits of its receptor, thereby inducing a conformational change in the receptor, which activates the intracellular tyrosine kinase signaling cascade. Previously we identified a series of peptides binding to two discrete hotspots on the insulin receptor. Here we show that covalent linkage of such peptides into homodimers or heterodimers results in insulin agonists or antagonists, depending on how the peptides are linked. An optimized agonist has been shown, both in vitro and in vivo, to have a potency close to that of insulin itself. The ability to construct such peptide derivatives may offer a path for developing agonists or antagonists for treatment of a wide variety of diseases.

Mode of transcapillary transport of insulin and insulin analog NN304 in dog hindlimb: evidence for passive diffusion.

A defect in transcapillary transport of insulin in skeletal muscle and adipose tissue has been proposed to play a role in the insulin resistance that leads to type 2 diabetes, yet the mechanism of insulin transfer across the capillary endothelium from plasma to interstitium continues to be debated. This study examined in vivo the interstitial appearance of insulin in hindlimb using the fatty acid acylated insulin analog Lys(B29)-tetradecanoyl des-(B30) human insulin, or NN304, as a marker for insulin transport. If the insulin transport were a saturable process, then "swamping" the capillary endothelial insulin receptors with native insulin would suppress the subsequent appearance in interstitial fluid of the insulin analog NN304. This analog binds to insulin receptors with an affinity of about 50% of native insulin. Experimental conditions established a physiologic NN304 dose in the absence or presence of pharmacologic and saturating concentrations of regular human insulin. Euglycemic clamps were performed in dogs under inhalant anesthesia with deep hindlimb lymphatic sampling, representative of skeletal muscle interstitial fluid (ISF). In group 1 (n = 8), NN304 alone was infused (3.6 pmol center dot min(-1) center dot kg(-1)) from 60 to 360 min. In group 2 (n = 6), starting at time 0, human insulin was infused at a pharmacologic dose (60 pmol center dot min(-1) center dot kg(-1)) with the addition of NN304 infusion (3.6 pmol center dot min(-1) center dot kg(-1)) from 60 to 360 min. In group 3 (n = 4), the human insulin infusion was increased to a saturating dose (120 pmol center dot min(-1) center dot kg(-1)). Pharmacologic insulin infusion (group 2) established steady-state human insulin concentrations of 6,300 plus minus 510 pmol/l in plasma and 5,300 plus minus 540 pmol/l in ISF. Saturating insulin infusion (group 3) achieved steady-state human insulin concentrations of 22,000 plus minus 1,800 pmol/l in plasma and 19,000 plus minus 1,500 pmol/l in ISF. Total (bound and unbound) NN304 plasma concentrations rose from a steady state of 1,900 plus minus 110 (group 1) to 2,400 plus minus 200 pmol/l (group 2) and 3,100 plus minus 580 pmol/l (group 3), consistent with a competition-driven decline in NN304 clearance from plasma as the human insulin level increased (P < 0.05 by ANOVA). Steady-state interstitial NN304 concentrations also rose with increasing human insulin levels but did not achieve significance in comparison with analog alone (162 plus minus 15 vs. 196 plus minus 22 and 241 plus minus 53 pmol/l for group 1 versus groups 2 and 3, respectively; P = 0.20), yet the steady-state plasma:ISF ratio for NN304 remained essentially unchanged in the absence and presence of elevated human insulin levels (12.6 plus minus 1.2 vs. 12.4 plus minus 0.5 and 13.1 plus minus 1.5 for group 1 versus groups 2 and 3, respectively; P = 0.93). Last, NN304 rate of appearance in interstitial fluid (i.e., half-time to steady state) was similar between groups; mean half-time of 92 plus minus 4 min (NS between groups). In conclusion, appearance of the insulin analog NN304 in skeletal muscle interstitial fluid was constant whether in the absence or presence of human insulin concentrations sufficient to saturate the endothelial insulin receptors. These findings support the hypothesis, provided that the mechanism of insulin and NN304 transcapillary transport is similar, that transcapillary transport of insulin in skeletal muscle occurs primarily via a nonsaturable process such as passive diffusion via a paracellular or transcellular route.