Population Pharmacokinetic–Pharmacodynamic Modeling of Subcutaneous and Pulmonary Insulin in Rats

Hollow fiber-combined glucose-responsive gel technology as an in vivo electronics-free insulin delivery system

Accumulating evidence demonstrates that not only sustained elevation of blood glucose levels but also the glucose fluctuation represents key determinants for diabetic complications and mortality. Current closed-loop insulin therapy option is limited to the use of electronics-based systems, although it poses some technical issues with high cost. Here we demonstrate an electronics-free, synthetic boronate gel-based insulin-diffusion-control device technology that can cope with glucose fluctuations and potentially address the electronics-derived issues. The gel was combined with hemodialysis hollow fibers and scaled suitable for rats, serving as a subcutaneously implantable, insulin-diffusion-active site in a manner dependent on the subcutaneous glucose. Continuous glucose monitoring tests revealed that our device not only normalizes average glucose level of rats, but also markedly ameliorates the fluctuations over timescale of a day without inducing hypoglycemia. With inherent stability, diffusion-dependent scalability, and week-long & acute glucose-responsiveness, our technology may offer a low-cost alternative to current electronics-based approaches.

Here, the authors develop an in vivo insulin delivery system which consists of a glucose responsive gel combined with hemodialysis hollow fibers. This system is electronics-free, temperature independent, and can stably sustain acute glucose-responsiveness in rats.

Excipient-free pulmonary insulin dry powder: Pharmacokinetic and pharmacodynamics profiles in rats

A novel pure insulin spray-dried powder for DPI product (Ins_SD) was studied with respect to physico-chemical stability, in vitro respirability, bioavailability, activity and tolerability. Ins_SD powder exhibited a very high in vitro respirability, independently of the DPI product preparation (manual or semi-automatic). Physico-chemical characteristics of Ins_SD powder remained within the pharmacopoeia limits during 6 months of storage at room temperature. PK/PD profiles were measured in rats that received the pulmonary powders by intratracheal insufflation and compared with Afrezza inhalation insulin. Due to the low drug powder mass to deliver, both insulin powders were diluted with mannitol. Insulin from Ins_SD was promptly absorbed (t_max 15 min and C_maxx4.9 ± 1.5 mU/ml). Afrezza had a slower absorption (t_max 30 min and C_max of 1.8 ± 0.37 mU/ml). After glucose injection, Ins_SD determined a rapid reduction of glucose level, similar to Afrezza. As reference, insulin subcutaneous injection showed a long-lasting hypoglycemic effect due to the slow absorption that prolonged insulin plasma level. In summary, Ins_SD product is suitable for post-prandial glucose control, providing a convenient and compliant product, in particular in the event of using a disposable device. Albeit the product has to be stored in fridge, its stability at room temperature allows the diabetic individual to carry the daily dose in normal conditions.

A Bottom-Up Whole-Body Physiologically Based Pharmacokinetic Model to Mechanistically Predict Tissue Distribution and the Rate of Subcutaneous Absorption of Therapeutic Proteins

The ability to predict subcutaneous (SC) absorption rate and tissue distribution of therapeutic proteins (TPs) using a bottom-up approach is highly desirable early in the drug development process prior to clinical data being available. A whole-body physiologically based pharmacokinetic (PBPK) model, requiring only a few drug parameters, to predict plasma and interstitial fluid concentrations of TPs in humans after intravenous and subcutaneous dosing has been developed. Movement of TPs between vascular and interstitial spaces was described by considering both convection and diffusion processes using a 2-pore framework. The model was optimised using a variety of literature sources, such as tissue lymph/plasma concentration ratios in humans and animals, information on the percentage of dose absorbed following SC dosing via lymph in animals and data showing loss of radiolabelled IgG from the SC dosing site in humans. The resultant model was used to predict t_max and plasma concentration profiles for 12 TPs (molecular weight 8–150 kDa) following SC dosing. The predicted plasma concentration profiles were generally comparable to observed data. t_max was predicted within 3-fold of reported values, with one third of the predictions within 0.8–1.25-fold. There was no systematic bias in simulated C_max values, although a general trend for underprediction of t_max was observed. No clear trend between prediction accuracy of t_max and TP isoelectric point or molecular size was apparent. The mechanistic whole-body PBPK model described here can be applied to predict absorption rate of TPs into blood and movement into target tissues following SC dosing.

Population pharmacodynamic modeling of exenatide after 2-week treatment in STZ/NA diabetic rats

The purpose of this study is to investigate the effect of exenatide on glycemic control following two administration routes in a streptozotocin/nicotinamide (STZ/NA)-induced diabetic rat model, and to develop a pharmacodynamic model to better understand the disease progression and the action of exenatide in this experimental system. Two groups of STZ/NA-induced diabetic rats were treated for 2 weeks with 20 (μg/kg/day) of exenatide, either by continuous subcutaneous (SC) infusion or two SC injections daily. Disease progression was associated with slower glucose utilization. Fasting blood glucose was significantly reduced by 30 mg/dL in both treatment groups at the end of 2 weeks. A subsequent intravenous glucose tolerance test (IVGTT) confirmed an improved glucose tolerance in both treatment groups; however, overall glycemic control was similar between groups, likely due to the relatively low and short-term drug exposure. A population indirect response model was successfully developed to simultaneously describe the STZ/NA-induced disease progression, responses to an IVGTT, and exenatide effects on these systemic challenges. The unified model includes a single set of parameters, and the cumulative area under the drug-receptor concentration curve was used as a unique driving force to account for systemic effects long after drug elimination.

Pharmacokinetic/pharmacodynamic studies on exenatide in diabetic rats

AIM

To quantitatively evaluate the blood glucose-lowering effect of exenatide in diabetic rats.

METHODS

Male Harlan-Sprague-Dawley rats were treated with high-fat diet/streptozotocin to induce type 2 diabetes. After subcutaneous administration of a single dose of exenatide (4.2, 42, or 210 μg/kg), serum exenatide, insulin concentration and blood glucose were measured. The pharmacokinetics of exenatide was characterized by a two-compartment model with first-order absorption. Insulin turnover was characterized by an effect compartment and indirect response combined model. Glucose turnover was described using an indirect response model with insulin (in effect compartment) stimulating glucose disposition and insulin (in insulin compartment) inhibiting glucose production simultaneously. The model parameters were estimated using nonlinear mixed-effects model program. Visual predictive check and model evaluation were used to make assessments.

RESULTS

Exenatide exhibited rapid absorption with k(a)=4.45 h(-1), and the two-compartment model well described its pharmacokinetic profile. For the pharmacodynamic model, exenatide increased insulin release with the estimated S(m1) of 0.822 and SC(50) of 4.02 μg/L. It was demonstrated that insulin stimulated glucose dissipation (S(m2)=0.0513) and inhibited the production of glucose (I(m)=0.0381). Visual predictive check and model evaluation study indicated that a credible model was developed.

CONCLUSION

The glucose-lowering effect of exenatide in diabetic rats is reliably described and predicted by the combined effect compartment/indirect response model.

Pharmacokinetic/pharmacodynamic modeling of GLP-1 in healthy rats

PURPOSE

To provide a mechanism-based model to quantitatively describe GLP-1 pharmacokinetics (PK) and pharmacodynamics (PD) in rats.

METHODS

Intravenous (IV), infusion (IF), subcutaneous (SC), and intraperitoneal (IP) doses of GLP-1 were administered after glucose challenge in healthy Sprague-Dawley rats. Blood was analyzed for GLP-1, glucose, and insulin. The PK-PD modeling was performed with ADAPT 5. The concentration-response curve was generated and analyzed in comparison with other incretin-related therapeutics.

RESULTS

The PK of GLP-1 was described using a two-compartment model with a zero-order input accounting for endogenous GLP-1 synthesis. For SC and IP dosing, sequential zero-order and first-order absorption models reasonably described the rapid absorption process and flip-flop kinetics. In dynamics, GLP-1 showed insulinotropic effects (3-fold increase) after IV glucose challenge in a dose-dependent manner. The concentration-response curve was bell-shaped, which was captured using a biphasic two-binding site Adair model. Receptor binding of GLP-1 exhibited high capacity and low affinity kinetics for both binding sites (K(D) = 9.94 × 10(3) pM, K(2) = 1.56 × 10(-4) pM(-1)).

CONCLUSIONS

The PK of GLP-1 was linear and bi-exponential and its PD showed glucose-dependent insulinotropic effects. All profiles were captured by the present mechanistic model and the dynamic analysis yields several implications for incretin-related therapies.

Pharmacodynamics of cibenzoline-induced hypoglycemia in rats

Hypoglycemia is one of the serious adverse effects induced by cibenzoline (CBZ), an antiarrhythmic agent. In order to clarify the pharmacodynamics of CBZ-induced hypoglycemia, CBZ was administered intravenously to conscious rats at a dose of 5, 10 or 20 mg/kg and serum samples were collected periodically to determine the concentrations of CBZ, insulin and glucose. The pharmacokinetics of CBZ showed nonlinear characteristics and could be described by a two-compartment model with Michaelis-Menten elimination kinetics. CBZ induced a rapid increase in the serum concentration of insulin. As the CBZ dose was increased, a greater hypoglycemic effect occurred. The indirect response model was applied to account for the CBZ-induced increase in insulin secretion and the subsequent decrease in serum glucose. A linear relationship was assumed between the serum concentration of CBZ and its stimulating effect on insulin secretion. A nonlinear relationship was assumed between the serum concentration of insulin and its stimulating effect on the elimination of serum glucose. The time courses of serum concentrations of CBZ, insulin and glucose after intravenous injection of CBZ could be described by the pharmacokinetic and pharmacodynamic model developed. This approach will be useful for the identification of variable factors related to CBZ-induced hypoglycemia.

Pharmacokinetic/pharmacodynamic modeling of glucose clamp effects of inhaled and subcutaneous insulin in healthy volunteers and diabetic patients

The pharmacokinetics and pharmacodynamics (PK/PD) of inhaled insulin in humans have not been modeled previously. We rationalized a model for the effects of inhaled insulin on glucose infusion rate during a euglycemic clamp study based on the mechanism of insulin action and compared parameter estimates between subcutaneous and inhaled insulin in healthy and diabetic subjects. Published data from two studies in 11 healthy volunteers and 18 type 1 diabetes patients were digitized. The subjects received four different doses of inhaled insulin and one or three different doses subcutaneously at the start of a 10 h glucose clamp. All data were modeled simultaneously using NONMEM VI. Insulin pharmacokinetics were described by a one-compartment model with one (inhaled) or two (subcutaneous insulin) first-order absorption processes and first-order elimination. Insulin effects on glucose were described by an indirect response model. A biophase direct effect equation for the glucose infusion rate was implemented. Pharmacodynamic parameter estimates were 15.1 mg/min/kg for maximal glucose infusion rate (GIR(max)) and 88.0 mIU/L for SC(50) for diabetic patients and 62.9 mIU/L for healthy subjects. A PK/PD model based on fundamental principles of insulin action and glucose turnover suggests comparable potencies of inhaled and subcutaneous insulin.

Pharmacokinetics and pharmacodynamics of controlled release insulin loaded PLGA microcapsules using dry powder inhaler in diabetic rats

The pulmonary route is an alternative route of administration for the systemic delivery of peptide and proteins with short-half lives. A long-acting formulation of insulin was prepared by encapsulation of protein into respirable, biodegradable microcapsules prepared by an oil in oil emulsification/solvent evaporation method. Insulin-loaded PLGA microcapsules prepared as a dry powder inhaler formulation were administered via the pulmonary route to diabetic rats and serum insulin and glucose concentrations were monitored. Control treatments consisted of respirable spray-dried insulin (RSDI) powder administered by intratracheal insufflation, insulin-loaded PLGA microcapsules and NPH (long-acting) insulin administered by subcutaneous (SC) administration. Pharmacokinetic analysis demonstrated that insulin administered in PLGA microcapsules illustrated a sustained release profile which resulted in a longer mean residence time, 4 and 5 fold longer than those after pulmonary administration of RSDI and SC injection of NPH insulin, respectively. Accordingly, the hypoglycemic profile followed a stable and sustained pattern which remained constant between 10 and 48 h. Results of the in vitro experiments were in good agreement with those of in vivo studies. Bronchoalveolar lavage fluid analysis indicated that microcapsules administration did not increase the activities of lactate dehydrogenase and total protein. However, histological examination of the lung tissue indicated a minor but detectable effect on the normal physiology of the rat lung. These findings suggest that the encapsulation of peptides and proteins into PLGA microcapsules technique could be a promising controlled delivery system for pulmonary administration.

Investigations of the use of bioavailability data to adjust occupational exposure limits for active pharmaceutical ingredients

Occupational exposure limits (OELs) for active pharmaceutical ingredients have traditionally been established using no-observed-adverse-effect levels derived from clinical studies employing po and iv routes of administration and by applying default uncertainty factors or chemical-specific adjustment factors. However, exposure by the inhalation or dermal route is more relevant in terms of occupational safety. In this investigation, to explore new methods for route-to-route extrapolation, the bioavailability of MK-0679, a leukotriene D(4) receptor antagonist, was compared following iv, po, intranasal (in), or intratracheal (it) administration. The relative bioavailability of MK-0679 was iv congruent with it > po congruent with in. Bioavailability correction factors (BCFs) of 2.0 and 0.6 were derived from these data to adjust a hypothetical OEL of 0.1 mg/m(3) for MK-0679 with particle sizes of 10 and 50 mum, respectively. These BCFs were used to adjust the OEL established using po clinical data, to reflect the differences in bioavailability following deposition in different regions of the respiratory tract. To further investigate how bioavailability data could be used in setting OELs, a preliminary pharmacokinetic (PK) model was developed to describe the time course of plasma concentrations using the data from the route comparison study. An inhalation study was then performed to test the validity of using either empirical data or modeling approaches to derive BCFs when setting OELs. These investigations demonstrated how the use of route-specific PK data could reduce some of the uncertainties associated with route-to-route extrapolation and allow for improved precision and quantitative adjustments when establishing OELs. Further investigations are needed to better understand the factors responsible for differences in systemic uptake following deposition in different regions of the respiratory tract and how these can be generalized across different classes of soluble compounds.

Efficacy of pulmonary insulin delivery in diabetic rats: use of a model-based approach in the evaluation of insulin powder formulations

The potential of N-trimethyl chitosan (TMC) with two degrees of quaternization (DQ), TMC20 (DQ 20%, as a mucoadhesive) and TMC60 (DQ 60%, as a mucoadhesive and a permeation enhancer), and dextran (as a non-mucoadhesive and non-permeation enhancer) microparticles as carriers for pulmonary delivery of insulin was studied in diabetic rats. The impact of the powder formulation on insulin bioavailability and its pharmacological effect was evaluated using a population pharmacokinetic-pharmacodynamic (PKPD) model. Insulin-loaded microparticles were prepared by a supercritical fluid (SCF) drying technique. They had a median volume diameter and median volume aerodynamic diameter of about 6-10 microm and 4 microm, respectively. The PK of insulin in the diabetic rats was analyzed by a one-compartment disposition model and the PD was described by the minimal model of glucose disappearance. The bioavailability of the pulmonarily administered dextran-, TMC20- and TMC60-insulin microparticles relative to subcutaneously (SC) administered insulin, was 0.48, 0.59 and 0.95, respectively. Histological examinations of the rats' lungs did not show any local adverse reactions after single administration of insulin powders. The pharmacodynamic model could describe the insulin-glucose relationship and pharmacodynamic efficiency of insulin formulations, which was about 0.6(*)10(-5) ml/microU, irrespective of the formulations. The current findings suggest that TMC microparticles are a promising vehicle for pulmonary delivery of insulin.

The role of mechanism-based pharmacokinetic-pharmacodynamic (PK-PD) modelling in translational research of biologics

Lack of predictability of clinical efficacy and safety is an important problem facing pharmaceutical research today. Translational PK-PD has the ability to integrate data generated from diverse test platforms during discovery and development in a mechanistic framework. Therefore, successful implementation of translational PK-PD modelling and simulation early in the development cycle could have a substantial impact on overall efficiency and success of pharmaceutical research. Three case studies are presented, which outline successful implementation of the translational PK-PD methodology in the rational development of biotherapeutics across various stages of discovery and development. Emerging developments within the field are also discussed.