Catheter survival during long-term insulin therapy with an implanted programmable pump. The Implantable Insulin Pump Trial Study Group

The evolution of insulin therapy

Evolution in medicine is generally driven by clinical need, hand in hand with opportunities generated by novel chemical and mechanical engineering technologies. Since 1921 that has been a continuing paradigm for insulin therapy, some advances being a continual process, and others arising from external scientific or engineering developments. Purification of insulin preparations was an early issue, resolved in the 1970s, then challenged by the switch to manufacture in microorganisms. The nature of insulin was established serially, in 1928 as a polypeptide, in 1955 by amino acid sequence, and later by 3-dimensional structure (1969), laying foundations for understandings on routes of administration, and later the engineering of novel insulins. Insulin was the first, and remains the predominant, pharmaceutical therapy to benefit from scientific advances underlying the genetic code, and thus recombinant DNA technology. Advances in mechanical and chemical engineering have contributed to important changes in insulin delivery devices. Biological science, including both cellular mechanisms and whole organism physiology, has led to considerable understandings of clinical defects in insulin action, but currently has been disappointing in its applicability to the insulins available for clinical practice, something perhaps now changing. The pathways of these changes are reviewed here.

A Novel Catheter System for Totally Implantable Intravenous Drug Therapy: Assessment of Catheter Function and Patency with Trepostinil Therapy

Background

Catheter failure, either due to dislodgment, occlusion or infection is the leading complication of chronic intravenous drug therapy. Better drug delivery techniques are required to advance life saving therapies that require this delivery method. This study evaluated the chronic performance of a fully implantable drug delivery system that incorporates a novel intravenous catheter. The system was designed to reduce complications associated with intravascular drug delivery including catheter occlusion, breakage, migration, and infection.

Methods

Twelve canines were implanted with a novel central venous catheter (Model 10642; Medtronic, Minneapolis, MN) connected to a totally implanted programmable drug pump (Model 8637 SynchroMed II®, Medtronic). The drug delivery systems infused saline (n=6) or treprostinil (n=6) (Remodulin®; United Therapeutics, Research Triangle Park, NC) for either 12 or 26 weeks at a continuous flow rate of 540 μL/day. Catheter performance was assessed at 0 (implant), 2, 4, 8, 12, 16, 20, and 24 weeks by quantifying delivery pressure, delivery volume and steady state Treprostinil concentrations.

Results

All catheters remained patent and free of complications for the duration of the study. Analysis of pressure waveforms during bolus delivery showed low and unchanged catheter resistance throughout the study. Measurement of pump delivery volume accuracy showed that the delivered volume was statistically similar to the calculated delivery (product of flow rate and elapsed time). Measurement of plasma treprostinil levels showed stable concentrations over the study period. There were no catheter dislodgments or breakage. Pathology showed all catheters free from fibrosis and thrombus and minimal changes to the vascular endothelium.

Conclusions

The Model 10642 vascular catheter along with the SynchroMed II implantable drug delivery system showed promising performance in a chronic animal model.

Finding the right route for insulin delivery - an overview of implantable pump therapy

INTRODUCTION

Implantable pump therapy adopting the intraperitoneal route of insulin delivery has been available for the past three decades. The key rationale for implantable pump therapy is the restoration of the portal-peripheral insulin gradient of the normal physiology. Uptake in clinical practice is limited to specialized centers and selected patient populations. Areas covered: Implantable pump therapy is discussed, including technical aspects, rationale for its use, and glycemic and non-glycemic effects. Target populations, summaries of clinical studies and issues related to implantable pump therapy are highlighted. Limitations of implantable pump therapy and its future outlook in clinical practice are presented. Expert opinion: Although intraperitoneal insulin delivery appears closer to the normal physiology, technical, pharmacological, and costs barriers prevent a wider adoption. Evidence from clinical studies remains scarce and inconclusive. As a consequence, the use of implantable pump therapy will be confined to a small population unless considerable technological progress is made and well-conducted studies can demonstrate glycemic and/or non-glycemic benefits justifying wider application.

Complications of continuous intraperitoneal insulin infusion with an implantable pump

AIM: To monitor the course of continuous intraperitoneal insulin infusion (CIPII) and to gain more insight into possible complications.

METHODS: A retrospective, longitudinal observational cohort study in patients with type 1 diabetes mellitus (T1DM) was performed. Only patients with “brittle” T1DM who started CIPII between January 1, 2000 and June 1, 2011, and were treated in the only centre in The Netherlands providing CIPII treatment (Isala clinics, Zwolle) were eligible for inclusion. Outcomes were defined as operation-free period (OFP), rate and type of complications. Subanalyses were made between patients starting CIPII from 2000 to 2007 and from 2007 onwards in order to study possible changes over time in complications and/or OFP. The OFP was calculated as the time from initial implantation to the date of first documented re-operation. If patients had not experienced an operation, their data were recorded at the date of last follow up or death. Kaplan-Meier curves were constructed to visualize the OFP. A (two-sided) P value of less than 0.05 was considered statistically significant.

RESULTS: Fifty-seven patients were treated with CIPII, although one patient was excluded from analyses because of self-induced complications. In the remaining 56 patients, 70 complications occurred during 283 patient years. Catheter occlusion (32.9%), pump dysfunction (17.1%), pain at the pump site (15.7%) and infections (10.0%) were the most frequent complications. This resulted in a median OFP of 4.5 years (95% confidence interval 4.1-4.8 years) without any difference between the time periods. Fifty re-operations were performed because of complications, one per 5.6 patient years, with a decrease in pump dysfunction (P = 0.04) and pump explantations (P = 0.02) after 2007. In total, 9 episodes of ketoacidosis occurred during follow up and there were 69 hospital re-admissions, with a median duration of 6 d. CIPII was ceased in five patients due to recurrent infections (n = 2), pain (n = 1), inadequate glycaemic control (n = 1) or by own choice (n = 1). No CIPII related mortality was reported.

CONCLUSION: The OFP has been stable over the last decade. No CIPII related mortality was reported. A significant decrease in pump dysfunction and explantation was seen after 2007 compared to the period 2000-2007. CIPII remains a safe treatment modality for specific patient groups.

Implantable insulin delivery pumps

Implantable insulin delivery pumps are a response to the search for an insulin therapy that would be more physiological, more comfortable and, finally, better adapted to instantaneous insulin needs by their connection to a long term glucose sensor. The last decade has been devoted to their technical finalization and to the acquisition of the clinical knowledge on how to use them, so that these devices can be safe and reliable. The forthcoming availability on the market of the specific insulin formulation they require and the present development of glucose sensors are two favourable conditions for the diffusion of this technology aiming at an improved diabetes treatment. This review summarizes the rationale for the choice of intraperitoneal insulin route, the key-steps in assessing their feasibility and effectiveness in blood glucose control of diabetic patients, and the present development of this technique toward an implantable artificial beta-cell.

Dosage Form Development, in Vitro Release Kinetics, and in Vitro–in Vivo Correlation for Leuprolide Released from an Implantable Multi-reservoir Array

PURPOSE

Implanted multi-reservoir arrays improve dosing control relative to osmotic pumps or polymer depots. The limited reservoir volume requires concentrated formulations. This report describes the development of a stable solid phase formulation of leuprolide acetate for chronic in vivo delivery from a multi-reservoir microchip and examines the correlation between in vitro release kinetics and serum pharmacokinetics.

MATERIALS AND METHODS

Concentrated formulations (>10% w/v) were prepared using small volume processing methods. Drug yield, release kinetics, and formulation stability were evaluated in vitro by HPLC. The correlation between in vitro and in vivo kinetic data was determined for a solid formulation by direct comparison of data sets and using absorption kinetics calculated from the Wagner-Nelson equation.

RESULTS

High yield and the control of release kinetics by altering peptide formulation or reservoir geometry were demonstrated. Lyophilized leuprolide in a soluble solid matrix exhibited reproducible release kinetics and was stable (>95% leuprolide monomer) after 6 months at 37 degrees C. A strong correlation was found between in vitro release kinetics and in vivo absorption by direct comparison of data sets and using the Wagner-Nelson absorption (slopes of 1.01 and 0.91; R(2) 0.99).

CONCLUSIONS

Reproducible releases of a stable solid leuprolide formulation from a multi-reservoir microchip were achieved in vitro. Chronic pulsatile release was subsequently performed in vivo. Comparison of in vitro and in vivo data reveals that pharmacokinetics were controlled by the rate of release from the device.

Implantable insulin pump therapy: an unusual presentation of a catheter-related complication

We report the case of a 63-year-old man who has a 19-year history of involvement in the implantable insulin pump program at Johns Hopkins University. After his most recent pump implantation in February 2004, his 24-h insulin requirement gradually increased from a baseline of 75 units to a peak of almost 500 units in June 2005. Surprisingly, insulin delivery from the pump and glycemic control remained satisfactory despite the dramatic change in insulin requirement. Laparotomy revealed a fibrous mass in the peritoneal cavity, with the track of the catheter extending into the mass. Insulin requirement declined post-resection of the mass and relocation of the catheter tip.

Chronic, programmed polypeptide delivery from an implanted, multireservoir microchip device

Implanted drug delivery systems are being increasingly used to realize the therapeutic potential of peptides and proteins. Here we describe the controlled pulsatile release of the polypeptide leuprolide from microchip implants over 6 months in dogs. Each microchip contains an array of discrete reservoirs from which dose delivery can be controlled by telemetry.

Vascularization of PEG-grafted macroporous hydrogel sponges: a three-dimensional in vitro angiogenesis model using human microvascular endothelial cells

Vascular tissue can penetrate implants that have an interconnected porous structure. The extent of vascularization is heavily dependent on a number of factors, including the nature of the material as well as the size and porosity of the implant's pore morphology. Currently, it is still not clear what mechanisms are controlling this response. In this work, in vitro human microvascular endothelial cell (HMVEC) experiments employed in angiogenesis research have been adapted as a screening technique for biomaterial vascularization. Hydrogels composed of poly(2-hydroxy ethyl methacrylate) (PHEMA) containing poly(ethylene glycol) (PEG) grafts were capable of supporting in vitro tubule formation. The sizes and lengths of tubules were dependent upon the porosity of the polymer network and pore sizes. When compared to the pure PHEMA sponges, PEG-grafted networks possessed a more lattice-type structure, with greater pore interconnection. As a result, these polymers were better suited to supporting tubule formation.

Human insulin production and amelioration of diabetes in mice by electrotransfer-enhanced plasmid DNA gene transfer to the skeletal muscle

A first-line gene therapy for type 1 diabetes should be based on a safe procedure to engineer an accessible tissue for insulin release. We evaluated the ability of the skeletal muscle to release human insulin after electrotransfer (ET)-enhanced plasmid DNA injection in mice. A furin-cleavable proinsulin cDNA under the CMV or the MFG promoter was electrotransferred to immune-incompetent mice with STZ-induced severe diabetes. At 1 week, mature human insulin was detected in the serum of 17/20 mice. After an initial peak of 68.5 +/- 34.9 microU/ml, insulin was consistently detected at significant levels up to 6 weeks after gene transfer. Importantly, untreated diabetic animals died within 3 weeks after STZ, whereas treated mice survived up to 10 weeks. Fed blood glucose (BG) was reduced in correspondence with the insulin peak. Fasting BG was near-normalized when insulin levels were 12.9 +/- 5.3 (CMV group, 2 weeks) and 7.7 +/- 2.6 microU/ml (MFG group, 4 weeks), without frank hypoglycemia. These data indicate that ET-enhanced DNA injection in muscle leads to the release of biologically active insulin, with restoration of basal insulin levels, and lowering of fasting BG with increased survival in severe diabetes. Therefore the skeletal muscle can be considered as a platform for basal insulin secretion.

Macrophage activation in type 1 diabetic patients with catheter obstruction during peritoneal insulin delivery with an implantable pump

OBJECTIVE

The purpose of this study was to evaluate the activation of macrophages in type 1 diabetic patients during peritoneal insulin delivery with an implantable pump against two types of insulin: that which was collected from the pump reservoir and that which came straight fromn the bottle (i.e., vial insltlin). Macrophage activation was studied in patients with and without cathcter obstruction and compared with activation in healthy subjects.

RESEARCH DESIGN AND METHODS

Human insulin (21 PH, 400 U/ml; Hoescht) was collected from the pump reservoir (Minimed) of diabetic patients with (n = 3) or without (n = 7) catheter obstruction, as assessed by histological examination of the catheter tip. Monocytes were obtained from venous blood samples from both kinds of diabetic patients and from healthy subjects (n = 5) and were differentiated into monocyte-derived macrophages in culture. Their chemotaxis and tumor necrosis factor-alpha (TNF-alpha) release were studied with respect to both types of insulin, as previously stated. Formyl-methionyl-leucyl-phenylalanine (fMLP) and lipopolysaccharide (LPS) were used as controls.

RESULTS

Neither insulin recovered from the pump reservoir nor vial insulin proved chemotactic to macrophages from either healthy subjects or those diabetic patients with and without catheter obstruction. The migration toward fMLP of macrophages from patients presenting a catheter obstruction was significantly higher than that observed with macrophages from either diabetic patients without obstruction or healthy subjects, the chemotactic index (mean +/- SD) was 3.81 +/- 0.36 vs. 2.30 +/- 0.89 and 2.60 +/- 0.80, respectively (P < 0.05). LPS significantly stimulated the TNF-alpha secretion of macrophages from diabetic subjects with a catheter obstruction, whereas both native and reservoir-recovered insulin had no effect on this release (144.83 +/- 67.25 vs. 5.15 +/- 2.93 and 5.27 +/- 2.43 pg/ml, P < 0.001).

CONCLUSIONS

The human insulin used in implantable pumps, regardless of how long it had remained in the pump reservoir, did not induce macrophage activation in diabetic patients treated through intraperitoneal insulin delivery. In some of these diabetic patients, catheter obstruction could be explained by their high capacity of macrophage chemotaxis.

Chronic intraperitoneal insulin delivery, as compared with subcutaneous delivery, improves hepatic glucose metabolism in streptozotocin diabetic rats

We have previously shown that chronic insulin treatment by the intraperitoneal route normalizes the elevated glucose production (GP) in streptozotocin (STZ) diabetic rats, while insulin delivered by the subcutaneous route only partially normalizes GP. To investigate the biochemical mechanism of the effect of chronic insulin delivery by either route on hepatic glucose metabolism, we measured the hepatic activity of glucose 6-phosphatase (G6Pase) and glucokinase (GK). Four groups of rats were used: (1) nondiabetic rats (N, n = 7), (2) untreated STZ diabetic rats (D, n = 8), (3) diabetic rats treated intraperitoneally (IP, n = 6), or (4) subcutaneously (SC, n = 8) (both 3 U of insulin/d). Glucose levels, higher in D, were normalized by insulin treatment regardless of route. Peripheral insulin levels were lowest in D and highest in SC as expected (N, 162 +/- 18 pmol/L; D, 66 +/- 12; IP, 360 +/- 96; SC, 798 +/- 198). STZ diabetes resulted in a 10-fold decrease in GK (P < .001), and a 2-fold increase in G6Pase activity (P < .01). Both intraperitoneal and subcutaneous treatments normalized G6Pase activity. In contrast, with subcutaneous but not intraperitoneal treatment, GK activity was still 35% less than normal (SC v N, P < .05). Glucose 6-phosphate (G6P) levels did not differ among the groups. In summary: (1) the increase in GP in D reflected increased activity of G6Pase and reduced activity of GK, (2) the partial suppression of GP with subcutaneous insulin treatment reflected correction of increased G6Pase activity, but only partial correction of low GK activity, and (3) the normalization of GP with intraperitoneal insulin treatment reflected correction of both increased G6Pase activity and low GK activity. Our current studies indicate that chronic intraperitoneal insulin treatment is superior to subcutaneous treatment with regard to hepatic glucose metabolism.