Absorption kinetics of insulin after subcutaneous administration

A local glucose-and oxygen concentration-based insulin secretion model for pancreatic islets

BACKGROUND

Because insulin is the main regulator of glucose homeostasis, quantitative models describing the dynamics of glucose-induced insulin secretion are of obvious interest. Here, a computational model is introduced that focuses not on organism-level concentrations, but on the quantitative modeling of local, cellular-level glucose-insulin dynamics by incorporating the detailed spatial distribution of the concentrations of interest within isolated avascular pancreatic islets.

METHODS

All nutrient consumption and hormone release rates were assumed to follow Hill-type sigmoid dependences on local concentrations. Insulin secretion rates depend on both the glucose concentration and its time-gradient, resulting in second-and first-phase responses, respectively. Since hypoxia may also be an important limiting factor in avascular islets, oxygen and cell viability considerations were also built in by incorporating and extending our previous islet cell oxygen consumption model. A finite element method (FEM) framework is used to combine reactive rates with mass transport by convection and diffusion as well as fluid-mechanics.

RESULTS

The model was calibrated using experimental results from dynamic glucose-stimulated insulin release (GSIR) perifusion studies with isolated islets. Further optimization is still needed, but calculated insulin responses to stepwise increments in the incoming glucose concentration are in good agreement with existing experimental insulin release data characterizing glucose and oxygen dependence. The model makes possible the detailed description of the intraislet spatial distributions of insulin, glucose, and oxygen levels. In agreement with recent observations, modeling also suggests that smaller islets perform better when transplanted and/or encapsulated.

CONCLUSIONS

An insulin secretion model was implemented by coupling local consumption and release rates to calculations of the spatial distributions of all species of interest. The resulting glucose-insulin control system fits in the general framework of a sigmoid proportional-integral-derivative controller, a generalized PID controller, more suitable for biological systems, which are always nonlinear due to the maximum response being limited. Because of the general framework of the implementation, simulations can be carried out for arbitrary geometries including cultured, perifused, transplanted, and encapsulated islets.

Bioavailability and variability of biphasic insulin mixtures

Absorption of subcutaneously administered insulin is associated with considerable variability. Some of this variability was quantitatively explained for both soluble insulin and insulin suspensions in a recent contribution to this journal (Søeborg et al., 2009). In the present article, the absorption kinetics for mixtures of insulins is described. This requires that the bioavailability of the different insulins is considered. A short review of insulin bioavailability and a description of the subcutaneous depot thus precede the presentation of possible mechanisms associated with subcutaneous insulin degradation. Soluble insulins are assumed to be degraded enzymatically in the subcutaneous tissue. Suspended insulin crystals form condensed heaps that are assumed to be degraded from their surface by invading macrophages. It is demonstrated how the shape of the heaps affects the absorption kinetics. Variations in heap formation thus explain some of the additional variability associated with suspended insulins (e.g. NPH insulins) compared to soluble insulins. The heap model also describes how increasing concentrations of suspended insulins lead to decreasing bioavailability and lower values of Cmax. Together, the findings constitute a comprehensive, quantitative description of insulin absorption after subcutaneous administration. The model considers different concentrations and doses of soluble insulin, including rapid acting insulin analogues, insulin suspensions and biphasic insulin mixtures. The results can be used in both the development of novel insulin products and in the planning of the treatment of insulin dependent diabetic patients.

Monosize microbeads for pseudo-affinity adsorption of human insulin

Affinity adsorption technique is increasingly used for protein purification, separation and other biochemical applications. Therapeutic molecules such as antibodies, cytokines, therapeutic DNA and plasma proteins must be purified before characterization and utilization. The aim of this study was to prepare micronsized spherical polymeric beads and to investigate the extent of their human insulin adsorption capability. Monosize poly(ethylene glycol dimethacrylate-N-methacryloyl-(L)-histidine) [poly(EDMA-MAH)] beads were prepared by modified suspension copolymerization. Functional monomer (MAH) was synthesized using methacryloyl chloride and L-histidine. The beads were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, swelling test and elemental analysis. MAH incorporation into monosize polymeric beads, having an average size around 2-3 μm, was estimated as 55.3 μmol MAH/g bead. Equilibrium swelling ratios of poly(EDMA-MAH) and poly(EDMA) beads were 65% and 55%, respectively. Adsorption experiments were performed under different conditions (i.e., pH, temperature, protein concentration and ionic strength). It was found that adsorption characteristics are strongly depend on these conditions. Maximum insulin adsorption capacity was achieved as 24.7 mg insulin/g poly(EDMA-MAH) beads. Results were well fitted to the Langmuir isotherm model. Compared with poly(EDMA-MAH), nonspecific insulin adsorption onto poly(EDMA) beads was very low (0.61 mg insulin/g bead) and can be negligible. It was observed that insulin could be repeatedly adsorbed and desorbed (at least 10 times) without significant loss in adsorption capacity.

Microneedle-based intradermal delivery enables rapid lymphatic uptake and distribution of protein drugs

PURPOSE

The purpose of this research was to examine the pharmacokinetics (PK) of drug uptake for microneedle-based intradermal (ID) delivery of several classes of protein drugs compared to standard subcutaneous (SC) administration.

METHODS

Systemic absorption kinetics of various proteins were analyzed following microneedle-based ID delivery and standard injection methods in the swine model. Comparative PK data were determined using standard non-compartmental techniques based on blood serum levels.

RESULTS

Delivery of proteins using microneedles resulted in faster systemic availability, measured via t(max,) and increased maximal drug concentration, C(max,) over SC delivery for all proteins tested. Some agents also exhibited increased bioavailability for the ID route. Imaging studies using reporter dyes showed rapid lymphatic-mediated uptake.

CONCLUSIONS

Microneedle delivery is applicable to a wide variety of protein drugs and is capable of effective parenteral administration of therapeutic drug dosages. This delivery route alters absorption kinetics via targeting a tissue bed better perfused with lymphatic and blood vessels than the SC space. Microneedle delivery may afford various advantages, including a robust method to increase the absorption rate and bioavailability of proteins that have been challenging to deliver at therapeutic levels or with physiologically relevant profiles.

Review of the mechanism of action and clinical efficacy of recombinant human hyaluronidase coadministration with current prandial insulin formulations

For patients with type 1 or type 2 diabetes, achieving good glycemic control is critical for successful treatment outcomes. As many patients remain unable to reach glycemic goals with currently available rapid-acting analog insulins, ultrafast insulin products are being developed that provide an even faster pharmacokinetic profile compared with current rapid prandial insulin products. The overall strategy of these ultrafast insulin products is to better mimic the normal physiologic response to insulin that occurs in healthy individuals to further improve glycemic control. Recombinant human hyaluronidase (rHuPH20) is a genetically engineered soluble hyaluronidase approved by the U.S. Food and Drug Administration as an adjuvant to increase the absorption and dispersion of other injected drugs; mammalian hyaluronidases as a class have over 6 decades of clinical use supporting the safety and/or efficacy of hyaluronidase coadministration. Clinical findings have demonstrated that coadministration of rHuPH20 with insulin or an insulin analog achieved faster systemic absorption, reduced inter- and intrapatient variability of insulin absorption, and achieved faster metabolic effects compared with injection of either insulin formulation alone. The magnitude of this acceleration is similar to the incrementally faster absorption of prandial insulin analogs as compared with regular insulin. In addition, coadministration of rHuPH20 with regular insulin or insulin analog also improved the achievement of prandial glycemic targets. Thus, rHuPH20 coadministration shows promise as a method of establishing a more rapid insulin profile to prandial insulin in patients with diabetes and has the potential to yield substantial improvements in postprandial glycemic excursion.

Differential effects of insulin detemir and neutral protamine Hagedorn (NPH) insulin on hepatic glucose production and peripheral glucose uptake during hypoglycaemia in type 1 diabetes

AIMS/HYPOTHESIS

We compared the symptoms of hypoglycaemia induced by insulin detemir (NN304) (B29Lys(epsilon-tetradecanoyl),desB30 human insulin) and equally effective doses of neutral protamine Hagedorn (NPH) insulin in relation to possible differential effects on hepatic glucose production and peripheral glucose uptake.

METHODS

After overnight intravenous infusion of soluble human insulin 18 participants with type 1 diabetes received subcutaneous injections of NPH insulin or insulin detemir (0.5 U/kg body weight) on separate occasions in random order. During the ensuing gradual development of hypoglycaemia cognitive function and levels of counter-regulatory hormones were measured and rates of endogenous glucose production and peripheral glucose uptake continuously evaluated using a primed constant infusion of [6,6-(2)H(2)]glucose. The study was terminated when plasma glucose concentration had fallen to 2.4 mmol/l or had reached a minimum at a higher concentration.

RESULTS

During the development of hypoglycaemia no difference between the two insulin preparations was observed in symptoms or hormonal responses. Significant differences were seen in rates of glucose flux. At and below plasma glucose concentrations of 3.5 mmol/l suppression of endogenous glucose production was greater with insulin detemir than with NPH insulin, whereas stimulation of peripheral glucose uptake was greater with NPH insulin than with insulin detemir.

CONCLUSIONS/INTERPRETATION

In participants with type 1 diabetes subcutaneously injected insulin detemir exhibits relative hepatoselectivity compared with NPH insulin, but symptoms of hypoglycaemia and hormonal counter-regulation are similar.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00760448.

Numerical analysis of a comprehensive in silico subcutaneous insulin absorption compartmental model

Development of safe and effective glucose management algorithms for remediation of inpatient hyperglycemia reduces nursing workload and improves patient outcomes by providing decision support at the bedside. Computer simulation of drug pharmacokinetics and pharmacodynamics enables evaluation and testing of glycemic control algorithms prior to in vivo investigations without risk to patients. For subcutaneous insulin dosing, in silico testing requires an accurate model of diffusion and availability of insulin from the time of injection. Wong et al. [1, 2] have recently proposed a comprehensive compartmental model of pharmacokinetics for six types of insulin to serve as the basis for available brands. The compartmental model is efficient for processing a large number of virtual patients. Herein we analyze numerical integration properties for the Wong et al. model, as a guide for achieving peak efficiency of simulations.