Peter Kurtzhals

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

AbstractPurpose. 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.

Soluble, fatty acid acylated insulins bind to albumin and show protracted action in pigs.

SummaryWe have synthesized insulins acylated by fatty acids in the ε-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 (p<0.001), and with less inter-pig variation (p<0.001). 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 (p<0.04). 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 detemir: from concept to clinical experience.

Insulin detemir (Levemir®, Novo Nordisk) is a novel, biologically engineered analogue of human insulin that has been successfully developed for clinical use in diabetes as a basal insulin. Its unique mechanism of prolongation of action, achieved through acylation to give reversible albumin binding and additional self-association, goes some way to addressing one of the fundamental limitations of previously available, subcutaneously administered basal insulins, a high level of within-person variability in time–action profile from one injection to another. The pharmacological profile of insulin detemir, characterised in a series of studies, suggested it had the potential to offer efficacy and tolerability advantages in the clinical setting. Such advantages, in comparison to NPH (neutral protamine Hagedorn) insulin, have subsequently been illustrated in trials. Despite glucose control targets that are identical to comparators, insulin detemir achieved levels of glycaemic control that, overall, were at least as good as NPH insulin in the Phase III development programme, with lower variability being a consistent finding. This was associated with consistent risk reductions in nocturnal hypoglycaemic events, which are closely linked with the basal component of insulin therapy. Another consistent finding has been a significantly reduced propensity for weight gain. An all-analogue regimen combining insulin detemir with the rapid-acting insulin aspart illustrated the potential benefits achievable when insulins that are designed to achieve defined pharmacokinetic profiles are employed clinically; blood glucose control, including hypoglycaemia, was significantly superior to a human insulin-based mealtime plus basal regimen. Insulin detemir is, therefore, a valuable addition to the range of exogenous insulins, as it should enable treatment regimens to be constructed that offer good outcomes of efficacy and tolerability.

Insulin X10 revisited: a super-mitogenic insulin analogue

The molecular safety of insulin analogues has received a great deal of attention over the last year. In particular, attention has been directed to the mitogenic properties of insulin analogues as compared with human insulin. Understanding the mechanisms implicated in mediating mitogenic effects of insulin is therefore of particular interest. In this review we detail the story of the rapid-acting insulin analogue known as X10, which was the first insulin analogue in clinical development, but ended up being discontinued at an early clinical development stage following findings of mammary tumours in female Sprague–Dawley rats. The molecular characteristics of insulin X10, along with its interaction at both the IGF-1 receptor and the insulin receptor, have provided us with important insights into mechanisms implicated in metabolic and mitogenic signalling of insulin analogues.

Pharmacology of Insulin Detemir

Insulin detemir (Levemir [Novo Nordisk A/S, Bagsvaerd, Denmark]) is a soluble, long-acting basal insulin analog. It differs from human insulin in that the amino acid threonine in position B30 has been removed and a 14-carbon fatty acid (myristic acid) has been acylated to lysine at B29. This modification increases self-association and enables albumin binding of insulin detemir. In this manuscript, the unique molecular properties and the resulting pharmacodynamics of insulin detemir are reviewed. The protracted duration of action, smooth activity profile, and low intrapatient variability of insulin detemir are presented as properties that may potentially help patients maximize glycemic control and minimize the long-term complications of diabetes.

Insulin aspart: a novel rapid-acting human insulin analogue.

In order to improve therapy and increase the quality of life for diabetic patients, it has been of significant interest to develop rapid-acting insulin preparations that mimic the physiological meal-time profile of insulin more closely than soluble human insulin. Insulin aspart (B28Asp human insulin) is a novel rapid-acting insulin analogue that fulfils this criterion. The B28Asp modification weakens the self-association of the insulin molecule and provides a more rapid absorption from the sc. injection site. The preclinical evaluation in vitro and in vivo demonstrates that apart from the more rapid absorption, insulin aspart is equivalent to human insulin. Thus, insulin aspart is equivalent to human insulin on key in vitro parameters such as insulin receptor affinity, insulin receptor dissociation rate, insulin receptor tyrosine kinase activation, IGF-I receptor binding affinity, metabolic and mitogenic potency. In accordance with the equivalent in vitro profiles, the toxico-pharmacological properties of insulin aspart and human insulin are also identical. The available data for insulin aspart and other rapid-acting insulin analogues supports that in vitro assays are sensitive and valuable in the preclinical evaluation of insulin analogues. Clinical studies demonstrate that insulin aspart has a pharmacokinetic and pharmacodynamic profile superior to that of soluble human insulin. In Type 1 diabetic patients on a basal-bolus injection regimen, insulin aspart given immediately before the meals provides an improved postprandial glycaemic control and an improved long-term metabolic control, as compared to soluble human insulin given 30 min before the meals, without increasing the risk of hypoglycaemia. Taken together, the data support the hope that insulin aspart will allow the diabetic patient to combine a more flexible lifestyle with better glycaemic control, without any increased safety risk.

Action Profile of Cobalt(III)-Insulin: A Novel Principle of Protraction of Potential Use for Basal Insulin Delivery

The Co3+-insulin hexamer is an extraordinary stable insulin hexamer that has no affinity for the insulin receptor per se but is converted into active insulin in vivo. In the present study, we evaluated the action profile of Co3+-insulin after subcutaneous injection into nondiabetic pigs and showed that the Co3+-hexamer does not dissociate before absorption. After absorption, Co3+-insulin is accumulated in the bloodstream because the complex is distributed and eliminated more slowly than human insulin. The degree of protraction of Co3+-insulin is similar to that of NPH insulin when evaluated in an euglycemic glucose clamp. We suggest that the long plasma half-life and a gradual in vivo activation contribute to prolong the effect of Co3+-insulin. The Co3+-insulin hexamer provides a novel principle of protraction of potential use for basal insulin delivery to the diabetic patient.

Insulin aspart: promising early results borne out in clinical practice

The novel, rapid-acting insulin analogue insulin aspart® (IAsp; Novo Nordisk) has been shown in preclinical studies to be more rapidly absorbed than human insulin (HI) when administered subcutaneously. IAsp reaches higher peak serum concentrations in a shorter time than HI, whilst maintaining a similar receptor binding and safety profile. The physiological pharmacokinetic profile of IAsp compared to that of HI has been demonstrated in both adult and paediatric populations and was accompanied by small but statistically significant reductions in HbA1c, lower postprandial glucose excursions and a reduced risk of late postprandial and major nocturnal hypoglycaemia. Benefits may be maximised by dose optimisation, using bolus doses that result in effective postprandial glucose reduction, as well as higher and multiple basal insulin doses. The safety profile, including cardiovascular risk, is equivalent to HI.

Fatty acid acylated insulins display protracted action due to binding to serum albumin

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