Artificial β-cell: clinical experience toward an implantable closed-loop insulin delivery system

Automated insulin delivery systems: from early research to routine care of type 1 diabetes

Automated insulin delivery (AID) systems, so-called closed-loop systems or artificial pancreas, are based upon the concept of insulin supply driven by blood glucose levels and their variations according to body glucose needs, glucose intakes and insulin action. They include a continuous glucose monitoring device which provides a signal to a control algorithm tuning insulin delivery from an infusion pump. The control algorithm is the key of the system since it commands insulin administration in order to maintain blood glucose in a predefined target range and close to a near-normal glucose level. The last two decades have shown dramatic advances toward the use in free life of AID systems for routine care of type 1 diabetes through step-by-step demonstrations of feasibility, safety and efficacy in successive hospital, transitional and outpatient trials. Because of the constraints of pharmacokinetics and dynamics of subcutaneous insulin delivery, the currently available AID systems are all 'hybrid' or 'semi-automated' insulin delivery systems with a need of meal and exercise announcements in order to anticipate rapid glucose variations through pre-meal bolus or pre-exercise reduction of infusion rate. Nevertheless, these AID systems significantly improve time spent in a near-normal range with a reduction of the risk of hypoglycemia and the mental load of managing diabetes in everyday life, representing a milestone in insulin therapy. Expected progression toward fully automated, further miniaturized and integrated, possibly implantable on long-term and more physiological closed-loop systems paves the way for a functional cure of type 1 diabetes.

Investigation of the In Vitro Antioxidant Potential Of Polyphenolic-Rich Extract of Artocarpus heterophyllus Lam Stem Bark and Its Antidiabetic Activity In Streptozotocin-Induced Diabetic Rats

Artocarpus heterophyllus Lam (Moraceae) stem bark has been used locally in managing diabetes mellitus with sparse scientific information. This study investigates the in vitro antioxidant potential of polyphenolic-rich extract of A heterophyllus stem bark as well as its antidiabetic activity in streptozotocin-induced diabetic rats. Fifty male Wistar rats were used with the induction of diabetes by a single intraperitoneal injection of streptozotocin (45 mg/kg body weight) and were orally administered 400 mg/kg free and bound phenols of A heterophyllus stem bark. The animals were sacrificed on the 28th day of the experiment using the cervical dislocation method; antihyperglycemia and anti-inflammatory parameters were subsequently assessed. The polyphenolic extracts demonstrated antioxidant potentials (such as hydrogen peroxide and diphenyl-1-picrylhydrazyl), as well as strong inhibitory activity against amylase and glucosidase. There was a significant (P < .05) increase in glycogen, insulin concentration, pancreatic β-cell scores (HOMA-β), antioxidant enzymes and hexokinase activities, as well as glucose transporter concentration in diabetic animals administered the extracts and metformin. Also, a significant (P < .05) reduction in fasting blood glucose, lipid peroxidation, glucose-6-phosphatase, and all anti-inflammatory parameters were observed in diabetic rats administered the extracts and metformin. The extracts demonstrated antidiabetic potential, which may be useful in the management of diabetes mellitus

Realizing a Closed-Loop (Artificial Pancreas) System for the Treatment of Type 1 Diabetes

Recent, rapid changes in the treatment of type 1 diabetes have allowed for commercialization of an "artificial pancreas" that is better described as a closed-loop controller of insulin delivery. This review presents the current state of closed-loop control systems and expected future developments with a discussion of the human factor issues in allowing automation of glucose control. The goal of these systems is to minimize or prevent both short-term and long-term complications from diabetes and to decrease the daily burden of managing diabetes. The closed-loop systems are generally very effective and safe at night, have allowed for improved sleep, and have decreased the burden of diabetes management overnight. However, there are still significant barriers to achieving excellent daytime glucose control while simultaneously decreasing the burden of daytime diabetes management. These systems use a subcutaneous continuous glucose sensor, an algorithm that accounts for the current glucose and rate of change of the glucose, and the amount of insulin that has already been delivered to safely deliver insulin to control hyperglycemia, while minimizing the risk of hypoglycemia. The future challenge will be to allow for full closed-loop control with minimal burden on the patient during the day, alleviating meal announcements, carbohydrate counting, alerts, and maintenance. The human factors involved with interfacing with a closed-loop system and allowing the system to take control of diabetes management are significant. It is important to find a balance between enthusiasm and realistic expectations and experiences with the closed-loop system.

A New Animal Model of Insulin-Glucose Dynamics in the Intraperitoneal Space Enhances Closed-Loop Control Performance

Current artificial pancreas systems (AP) operate via subcutaneous (SC) glucose sensing and SC insulin delivery. Due to slow diffusion and transport dynamics across the interstitial space, even the most sophisticated control algorithms in on-body AP systems cannot react fast enough to maintain tight glycemic control under the effect of exogenous glucose disturbances caused by ingesting meals or performing physical activity. Recent efforts made towards the development of an implantable AP have explored the utility of insulin infusion in the intraperitoneal (IP) space: a region within the abdominal cavity where the insulin-glucose kinetics are observed to be much more rapid than the SC space. In this paper, a series of canine experiments are used to determine the dynamic association between IP insulin boluses and plasma glucose levels. Data from these experiments are employed to construct a new mathematical model and to formulate a closed-loop control strategy to be deployed on an implantable AP. The potential of the proposed controller is demonstrated via in-silico experiments on an FDA-accepted benchmark cohort: the proposed design significantly outperforms a previous controller designed using artificial data (time in clinically acceptable glucose range: 97.3±1.5% vs. 90.1±5.6%). Furthermore, the robustness of the proposed closed-loop system to delays and noise in the measurement signal (for example, when glucose is sensed subcutaneously) and deleterious glycemic changes (such as sudden glucose decline due to physical activity) is investigated. The proposed model based on experimental canine data leads to the generation of more effective control algorithms and is a promising step towards fully automated and implantable artificial pancreas systems.

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.

Glycated Hemoglobin (HbA1c): Clinical Applications of a Mathematical Concept

Background and purpose:

Glycated hemoglobin (HbA1c) reflects the cumulative glucose exposure of erythrocytes over a preceding time frame proportional to erythrocyte survival. HbA1c is thus an areal function of the glucose-time curve, an educationally useful concept to aid teaching and clinical judgment.

Methods:

An ordinary differential equation is formulated as a parsimonious model of HbA1c. The integrated form yields HbA1c as an area-under-the-curve (AUC) of a glucose-time profile. The rate constant of the HbA1c model is then derived using the validated regression equation in the ADAG study that links mean blood glucose and HbA1c with a very high degree of goodness-of-fit.

Results:

This model has didactic utility to enable patients, biomedical students and clinicians to appreciate how HbA1c may be conceptually inferred from discrete blood glucose values using continuous glucose monitoring system (CGMS) or self-monitored blood glucose (SMBG) glucometer readings as shown in the examples. It can be appreciated how hypoglycemia can occur with rapid HbA1c decline despite poor glycemic control.

Conclusions:

Being independent of laboratory assay pitfalls, computed ‘virtual’ HbA1c serves as an invaluable internal consistency cross-check against laboratory-measured HbA1c discordant with SMBG readings suggestive of inaccurate/fraudulent glucometer records or hematologic disorders including thalassemia and hemoglobinopathy. This model could be implemented within portable glucometers, CGMS devices and even smartphone apps for deriving tentative ‘virtual’ HbA1c from serial glucose readings as an adjunct to measured HbA1c. Such predicted ‘virtual’ HbA1c readily accessible via glucometers may serve as feedback to modify behavior and empower diabetic patients to achieve better glycemic control.

Vascular Glucose Sensor Symposium: Continuous Glucose Monitoring Systems (CGMS) for Hospitalized and Ambulatory Patients at Risk for Hyperglycemia, Hypoglycemia, and Glycemic Variability

Hyperglycemia, hypoglycemia, and glycemic variability have been associated with increased morbidity, mortality, length of stay, and cost in a variety of critical care and non-critical care patient populations in the hospital. The results from prospective randomized clinical trials designed to determine the risks and benefits of intensive insulin therapy and tight glycemic control have been confusing; and at times conflicting. The limitations of point-of-care blood glucose (BG) monitoring in the hospital highlight the great clinical need for an automated real-time continuous glucose monitoring system (CGMS) that can accurately measure the concentration of glucose every few minutes. Automation and standardization of the glucose measurement process have the potential to significantly improve BG control, clinical outcome, safety and cost.

Closed loop insulin delivery in diabetes

The primary goal of type 1 diabetes treatment is attaining near-normal glucose values. This currently remains out of reach for most people with type 1 diabetes despite intensified insulin treatment in the form of insulin analogues, educational interventions, continuous glucose monitoring, and sensor augmented insulin pump. The main remaining problem is risk of hypoglycaemia, which cannot be sufficiently reduced in all patient groups. Additionally, patients' burn-out often develops with years of tedious day-to-day diabetes management, rendering available diabetes-related technology less efficient. Over the past 40 years, several attempts have been made towards computer-programmed insulin delivery in the form of closed loop, with faster developments especially in the past decade. Automated insulin delivery has reduced human error in glycaemic control and considerably lessened the burden of routine self-management. In this chapter, data from randomized controlled trials with closed-loop insulin delivery that included type 1 diabetes population are summarized, and an evidence-based vision for possible routine utilization of closed loop is provided.

Modulation of antioxidant status in streptozotocin-induced diabetic male Wistar rats following intake of red palm oil and/or rooibos

OBJECTIVE

To investigate the role of red palm oil (RPO), rooibos tea extract (RTE) and their combined treatment (RPO + RTE) on antioxidant status in streptozotocin (STZ)-induced diabetic rats.

METHODS

Diabetes mellitus was induced by a single administration of streptozotocin (50 mg/kg) and the rats were treated for 7 weeks. Antioxidant enzymes [catalase (CAT), glutathione peroxidase (GPx), superoxide dismutase (SOD)], antioxidant capacity [trolox equivalence antioxidant capacity (TEAC), oxygen radical absorbance capacity (ORAC)] as well as total protein, albumin, globulin, total glutathione, conjugated diene and thiobarbituric acid reactive substances (TBARS) were investigated.

RESULTS

Treatment with RPO, RTE and RPO + RTE significantly (p>0.05) improved liver SOD and plasma ORAC in the diabetic rats. Similarly, diabetic rats treated with RTE and RPO + RTE enhanced liver GPx. A significant (P<0.05) increase in the plasma TBARS in the diabetic control group was observed when compared with the normal control group. Treatment of diabetic rats with RTE and RPO + RTE reduced plasma TBARS to a level not significantly different at P<0.05 from the normal control group.

CONCLUSIONS

The results revealed the anti-oxidative potentials of red palm oil, rooibos and their combination in diabetic conditions and hence, they could be useful in the management of diabetes and its complications.

The artificial pancreas: current status and future prospects in the management of diabetes

Recent advances in insulins, insulin pumps, continuous glucose-monitoring systems, and control algorithms have resulted in an acceleration of progress in the development of artificial pancreas devices. This review discusses progress in the development of external systems that are based on subcutaneous drug delivery and subcutaneous continuous glucose monitoring. There are two major system-level approaches to achieving closed-loop control of blood glucose in diabetic individuals. The unihormonal approach uses insulin to reduce blood glucose and relies on complex safety mitigation algorithms to reduce the risk of hypoglycemia. The bihormonal approach uses both insulin to lower blood glucose and glucagon to raise blood glucose, and also relies on complex algorithms to provide for safety of the user. There are several major strategies for the design of control algorithms and supervision control for application to the artificial pancreas: proportional-integral-derivative, model predictive control, fuzzy logic, and safety supervision designs. Advances in artificial pancreas research in the first decade of this century were based on the ongoing computer revolution and miniaturization of electronic technology. The advent of modern smartphones has created the ability to utilize smartphone technology as the engineering centerpiece of an artificial pancreas. With these advances, an artificial or bionic pancreas is within reach.

A model of glucose-insulin-pramlintide pharmacokinetics and pharmacodynamics in type I diabetes

Type 1 diabetes mellitus (T1DM) complications are significantly reduced when normoglycemic levels are maintained via intensive therapy. The artificial pancreas is designed for intensive glycemic control; however, large postprandial excursions after a meal result in poor glucose regulation. Pramlintide, a synthetic analog of the hormone amylin, reduces the severity of postprandial excursions by reducing appetite, suppressing glucagon release, and slowing the rate of gastric emptying. The goal of this study is to create a glucose-insulin-pramlintide physiological model that can be employed into a controller to improve current control approaches used in the artificial pancreas. A model of subcutaneous (SC) pramlintide pharmacokinetics (PK) was developed by revising an intravenous (IV) pramlintide PK model and adapting SC insulin PK from a glucose-insulin model. Gray-box modeling and least squares optimization were used to obtain parameter estimates. Pharmacodynamics (PD) were obtained by choosing parameters most applicable to pramlintide mechanisms and then testing using a proportional PD effect using least squares optimization. The model was fit and validated using 27 data sets, which included placebo, PK, and PD data. SC pramlintide PK root mean square error values range from 1.98 to 10.66 pmol/L. Pramlintide PD RMSE values range from 10.48 to 42.76 mg/dL. A new in silico model of the glucose-insulin-pramlintide regulatory system is presented. This model can be used as a platform to optimize dosing of both pramlintide and insulin as a combined therapy for glycemic regulation, and in the development of an artificial pancreas as the kernel for a model-based controller.

Insulin pump therapy in youth with type 1 diabetes: toward closed-loop systems

INTRODUCTION

Insulin pump technology has advanced considerably over the past three decades, leading to more favorable metabolic control and less hypoglycemic events when compared with multiple daily injection therapy. The use of insulin pumps is increasing, particularly in children and adolescents with type 1 diabetes.

AREAS COVERED

This review outlines recent developments in insulin pump therapy from a pediatric perspective. 'Smart' pumps, sensor-augmented pump therapy and threshold-suspend feature of insulin pumps are reviewed in terms of efficacy, safety and psychosocial impact. The current status of closed-loop systems focusing on clinical outcomes is highlighted.

EXPERT OPINION

Closed-loop insulin delivery is gradually progressing from bench to the clinical practice. Longer and larger studies in home settings are needed to expand on short- to medium-term outpatient evaluations. Predictive low glucose management and overnight closed-loop delivery may be the next applications to be implemented in daily routine. Further challenges include improvements of control algorithms, sensor accuracy, duration of insulin action, integration and size of devices and connectivity and usability. Gradual improvements and increasing sophistication of closed-loop components lie on the path toward unsupervised hands-off fully closed-loop system.

Closed-loop artificial pancreas systems: engineering the algorithms

In this two-part Bench to Clinic narrative, recent advances in both the preclinical and clinical aspects of artificial pancreas (AP) development are described. In the preceding Bench narrative, Kudva and colleagues provide an in-depth understanding of the modified glucoregulatory physiology of type 1 diabetes that will help refine future AP algorithms. In the Clinic narrative presented here, we compare and evaluate AP technology to gain further momentum toward outpatient trials and eventual approval for widespread use. We enumerate the design objectives, variables, and challenges involved in AP development, concluding with a discussion of recent clinical advancements. Thanks to the effective integration of engineering and medicine, the dream of automated glucose regulation is nearing reality. Consistent and methodical presentation of results will accelerate this success, allowing head-to-head comparisons that will facilitate adoption of the AP as a standard therapy for type 1 diabetes.

Wearable and implantable pancreas substitutes

A lifelong-implanted and completely automated artificial or bioartificial pancreas (BAP) is the holy grail for type 1 diabetes treatment, and could be a definitive solution even for other severe pathologies, such as pancreatitis and pancreas cancer. Technology has made several important steps forward in the last years, providing new hope for the realization of such devices, whose feasibility is strictly connected to advances in glucose sensor technology, subcutaneous and intraperitoneal insulin pump development, the design of closed-loop control algorithms for mechatronic pancreases, as well as cell and tissue engineering and cell encapsulation for biohybrid pancreases. Furthermore, smart integration of the mentioned components and biocompatibility issues must be addressed, bearing in mind that, for mechatronic pancreases, it is most important to consider how to recharge implanted batteries and refill implanted insulin reservoirs without requiring periodic surgical interventions. This review describes recent advancements in technologies and concepts related to artificial and bioartificial pancreases, and assesses how far we are from a lifelong-implanted and self-working pancreas substitute that can fully restore the quality of life of a diabetic (or other type of) patient.

Advances in pump technology: insulin patch pumps, combined pumps and glucose sensors, and implanted pumps

This review discusses the most recent developments in insulin pump technology. The benefits of the insulin pump to patients with type 1 diabetes are recognized both for its metabolic effectiveness and its positive effects on quality of life. The current pumps are reliable, small and light, and are becoming more and more sophisticated. Nevertheless, there remain practical and psychological constraints for the patient. However, recent patch-pump advances should simplify the technical aspects of pump treatment and enhance patient comfort. Another advance combines the insulin pump with a glucose sensor. Such a combination is logical for optimizing pump use and, to that end, developing an automated or 'closed-loop'system that permits the delivery of subcutaneous insulin adjusted according to measured levels of subcutaneous glucose. Finally, implanted insulin pumps have proven their worth not only because of their simple use, but also for their contribution in the artificial pancreas project. Indeed, the prompt response with intraperitoneal administration of insulin makes it of interest for use in a closed-loop system.

Materials for diabetes therapeutics

This review is focused on the materials and methods used to fabricate closed-loop systems for type 1 diabetes therapy. Herein, we give a brief overview of current methods used for patient care and discuss two types of possible treatments and the materials used for these therapies-(i) artificial pancreases, comprised of insulin producing cells embedded in a polymeric biomaterial, and (ii) totally synthetic pancreases formulated by integrating continuous glucose monitors with controlled insulin release through degradable polymers and glucose-responsive polymer systems. Both the artificial and the completely synthetic pancreas have two major design requirements: the device must be both biocompatible and be permeable to small molecules and proteins, such as insulin. Several polymers and fabrication methods of artificial pancreases are discussed: microencapsulation, conformal coatings, and planar sheets. We also review the two components of a completely synthetic pancreas. Several types of glucose sensing systems (including materials used for electrochemical, optical, and chemical sensing platforms) are discussed, in addition to various polymer-based release systems (including ethylene-vinyl acetate, polyanhydrides, and phenylboronic acid containing hydrogels).

Closed-loop insulin delivery in type 1 diabetes

Advances in diabetes technology have led to significant improvements in the quality of life and care received by individuals with diabetes. Despite this, achieving tight glycemic control through intensive insulin therapy and modern insulin regimens is challenging because of the barrier of hypoglycemia, the most feared complication of insulin therapy as reported by patients, caregivers, and physicians. This article outlines the individual components of the closed-loop system together with the existing clinical evidence. The artificial pancreas prototypes currently used in clinical studies are reviewed as well as obstacles and limitations facing the technology.

Closed-loop insulin delivery for treatment of type 1 diabetes

Type 1 diabetes is one of the most common endocrine problems in childhood and adolescence, and remains a serious chronic disorder with increased morbidity and mortality, and reduced quality of life. Technological innovations positively affect the management of type 1 diabetes. Closed-loop insulin delivery (artificial pancreas) is a recent medical innovation, aiming to reduce the risk of hypoglycemia while achieving tight control of glucose. Characterized by real-time glucose-responsive insulin administration, closed-loop systems combine glucose-sensing and insulin-delivery components. In the most viable and researched configuration, a disposable sensor measures interstitial glucose levels, which are fed into a control algorithm controlling delivery of a rapid-acting insulin analog into the subcutaneous tissue by an insulin pump. Research progress builds on an increasing use of insulin pumps and availability of glucose monitors. We review the current status of insulin delivery, focusing on clinical evaluations of closed-loop systems. Future goals are outlined, and benefits and limitations of closed-loop therapy contrasted. The clinical utility of these systems is constrained by inaccuracies in glucose sensing, inter- and intra-patient variability, and delays due to absorption of insulin from the subcutaneous tissue, all of which are being gradually addressed.

Antihypertriglyceridemia and anti-inflammatory activities of monascus-fermented dioscorea in streptozotocin-induced diabetic rats

The rice fermented by Monascus, called red mold rice (RMR), and has a long tradition in East Asia as a dietary staple. Monascus-fermented dioscorea called red mold dioscorea (RMD) contains various metabolites to perform the ability of reducing oxidative stress and anti-inflammatory response. We used Wistar rats and induced diabetes by injecting streptozotocin (STZ, 65 mg/kg i.p.). RMD was administered daily starting six weeks after disease onset. Throughout the experimental period, significantly (P < .05) lowered plasma glucose, triglyceride, cholesterol, free fatty acid and low density lipoprotein levels were observed in the RMD-treated groups. The RMD-treated diabetic rats showed higher activities of glutathione disulfide reductase, glutathione reductase, catalase and superoxide dismutase (P < .05) in the pancreas compared with the diabetic control rats. RMD also inhibited diabetes-induced elevation in the levels of interleukin (IL)-1β, IL-6, interferon-γ and tumor necrosis factor-α. Pancreatic β-cells damaged by STZ in the RMD supplemented groups were ameliorated. The results of this study clearly demonstrated that RMD possesses several treatment-oriented properties, including the control of hyperglycemia, antioxidant effects, pancreatic β-cell protection and anti-inflammatory effects. Considering these observations, it appears that RMD may be a useful supplement to delay the development of diabetes and its complications.

Physiologic insulin delivery with insulin feedback: a control systems perspective

Individuals with type 1 diabetes mellitus must effectively manage glycemia to avoid acute and chronic complications related to aberrations of glucose levels. Because optimal diabetes management can be difficult to achieve and burdensome, research into a closed-loop insulin delivery system has been of interest for several decades. This paper provides an overview, from a control systems perspective, of the research and development effort of a particular algorithm--the external physiologic insulin delivery system. In particular the introduction of insulin feedback, based on β-cell physiology, is covered in detail. A summary of human clinical trials is provided in the context of the evolution of this algorithm, and this paper outlines some of the research avenues that show particular promise.

Overnight closed loop insulin delivery (artificial pancreas) in adults with type 1 diabetes: crossover randomised controlled studies

OBJECTIVE

To compare the safety and efficacy of overnight closed loop delivery of insulin (artificial pancreas) with conventional insulin pump therapy in adults with type 1 diabetes.

DESIGN

Two sequential, open label, randomised controlled crossover, single centre studies.

SETTING

Clinical research facility.

PARTICIPANTS

24 adults (10 men, 14 women) with type 1 diabetes, aged 18-65, who had used insulin pump therapy for at least three months: 12 were tested after consuming a medium sized meal and the other 12 after consuming a larger meal accompanied by alcohol.

INTERVENTION

During overnight closed loop delivery, sensor measurements of glucose were fed into a computer algorithm, which advised on insulin pump infusion rates at 15 minute intervals. During control nights, conventional insulin pump settings were applied. One study compared closed loop delivery of insulin with conventional pump therapy after a medium sized evening meal (60 g of carbohydrates) at 1900, depicting the scenario of "eating in." The other study was carried out after a later large evening meal (100 g of carbohydrates) at 2030, accompanied by white wine (0.75 g/kg ethanol) and depicted the scenario of "eating out."

MAIN OUTCOME MEASURES

The primary outcome was the time plasma glucose levels were in target (3.91-8.0 mmol/L) during closed loop delivery and a comparable control period. Secondary outcomes included pooled data analysis and time plasma glucose levels were below target (≤ 3.9 mmol/L).

RESULTS

For the eating in scenario, overnight closed loop delivery of insulin increased the time plasma glucose levels were in target by a median 15% (interquartile range 3-35%), P = 0.002. For the eating out scenario, closed loop delivery increased the time plasma glucose levels were in target by a median 28% (2-39%), P = 0.01. Analysis of pooled data showed that the overall time plasma glucose was in target increased by a median 22% (3-37%) with closed loop delivery (P < 0.001). Closed loop delivery reduced overnight time spent hypoglycaemic (plasma glucose ≤ 3.9 mmol/L) by a median 3% (0-20%), P=0.04, and eliminated plasma glucose concentrations below 3.0 mmol/L after midnight.

CONCLUSION

These two small crossover trials suggest that closed loop delivery of insulin may improve overnight control of glucose levels and reduce the risk of nocturnal hypoglycaemia in adults with type 1 diabetes. Trial registration ClinicalTrials.gov NCT00910767 and NCT00944619.

Closed-loop insulin delivery: from bench to clinical practice

Automated closed-loop insulin delivery, also referred to as the 'artificial pancreas', has been an important but elusive goal of diabetes treatment for many decades. Research milestones include the conception of continuous glucose monitoring in the early 1960s, followed by the production of the first commercial hospital-based artificial pancreas in the late 1970s that combined intravenous glucose sensing and insulin delivery. In the past 10 years, research into the artificial pancreas has gained substantial momentum and focused on the subcutaneous route for glucose measurement and insulin delivery, which reflects technological advances in interstitial glucose monitoring and the increasing use of the continuous subcutaneous insulin infusion. This Review discusses the design of an artificial pancreas, its components and clinical results, as well as the advantages and disadvantages of different types of automated closed-loop systems and potential future advances. The introduction of the artificial pancreas into clinical practice will probably occur gradually, starting with simpler approaches, such as overnight control of blood glucose concentration and temporary pump shut-off, that are adapted to more complex situations, such as glycemic control during meals and exercise.

Can technological solutions for diabetes replace islet cell function?

The central objective of diabetes research and management is to restore the deficient secretion of insulin, thereby restoring a state of euglycemia and minimizing short- and long-term risks associated with poor glucose control. The development of the artificial pancreas seeks to imitate the action of the pancreatic beta cell by employing closed-loop control to respond to glycemic excursions by appropriately infusing appropriate amounts of insulin. This article examines progress towards implementing an artificial pancreas in the context of the pancreatic islet as the ideal model for controlling blood glucose. Physiologic insulin secretion will form our foundation for considering the technical design elements relevant to electromechanically imitating the beta cell. The most recent clinical trials using closed-loop control are reviewed and this modality is compared to other curative approaches including islet cell transplantation and preservation. Finally, the potential of the artificial pancreas as a method to adequately reestablish euglycemia is considered.

Use of a continuous glucose sensor in an extracorporeal life support circuit

BACKGROUND

Standard care for infants on extracorporeal life support (ECLS) relies on intermittent measurement of blood glucose (BG); however, this can lead to significant changes in BG that go unrecognized for several hours. The present study was designed to assess performance and clinical applicability of a subcutaneous glucose sensor technology modified for use as a blood-contacting sensor within the ECLS circuit.

METHODS

Twelve children, aged 3 years or less, requiring ECLS support were studied. Three continuous glucose sensors (Medtronic MiniMed) were inserted into hubs placed in line with the ECLS circuit. Blood glucose was assessed with a laboratory analyzer (BG(LAB); Bayer Rapidlab 860) approximately every 5 h (mean 4.9 ± 3.3 h) with more frequent samples obtained with a bedside monitor (HemoCue) as needed. Sensor current (I(SIG)) was transmitted to a laptop computer and retrospectively calibrated using BGLAB. Sensor performance was assessed by mean absolute relative difference (MARD), linear regression slope and intercept, and correlation, all with BGLAB as reference.

RESULTS

The BGLAB averaged 107.6 ± 36.4 mg/dl (mean ± standard deviation) ranging from 58 to 366 mg/dl. The MARD was 11.4%, with linear regression slope (0.86 ± 0.030) and intercept (9.0 ± 3.2 mg/dl) different from 1 and 0, respectively (p < .05), and correlation (r² = 0.76; p < .001). The system was not associated with any adverse events, and placement and removal into the hubs was easily accomplished. Instances in which more frequent BG values were obtained using a bedside HemoCue (BGHEMO) monitor showed the sensor to respond rapidly to changes.

CONCLUSIONS

We conclude that continuous sensors can be adapted for use in an ECLS circuit with accuracy similar to or better than that achieved with the subcutaneous site. Continuous glucose monitoring in this population can rapidly detect changes in BG that would not otherwise be observed. Further studies will be needed to assess the benefit of continuous glucose monitoring in this population.

Feedforward-feedback multiple predictive controllers for glucose regulation in type 1 diabetes

Type 1 diabetic patients depend on insulin therapy to maintain blood glucose levels within safe range. The idea behind the "Artificial Pancreas" is to mimic, as close as possible, the functions of the natural pancreas in glucose sensing and insulin delivery, by using closed-loop control techniques. This work presents a model-based predictive control strategy for blood glucose regulation in diabetic patients. The controller is provided with a feedforward loop to improve meal compensation, a gain scheduling scheme to improve the controller performance in controlling the nonlinear glucose-insulin system, and an asymmetric cost function to reduce the hypoglycemic risk. Simulation scenarios with virtual patients are used to test the designed controller. The obtained results show a good controller performance in fasting conditions and meal disturbance rejection, and robustness against measurements errors, meal estimation errors, and changes in insulin sensitivity.

Therapeutics of diabetes mellitus: focus on insulin analogues and insulin pumps

Aim. Inadequately controlled diabetes accounts for chronic complications and increases mortality. Its therapeutic management aims in normal HbA1C, prandial and postprandial glucose levels. This review discusses diabetes management focusing on the latest insulin analogues, alternative insulin delivery systems and the artificial pancreas. Results. Intensive insulin therapy with multiple daily injections (MDI) allows better imitation of the physiological rhythm of insulin secretion. Longer-acting, basal insulin analogues provide concomitant improvements in safety, efficacy and variability of glycaemic control, followed by low risks of hypoglycaemia. Continuous subcutaneous insulin infusion (CSII) provides long-term glycaemic control especially in type 1 diabetic patients, while reducing hypoglycaemic episodes and glycaemic variability. Continuous subcutaneous glucose monitoring (CGM) systems provide information on postprandial glucose excursions and nocturnal hypo- and/or hyperglycemias. This information enhances treatment options, provides a useful tool for self-monitoring and allows safer achievement of treatment targets. In the absence of a cure-like pancreas or islets transplants, artificial “closed-loop” systems mimicking the pancreatic activity have been also developed. Conclusions. Individualized treatment plans for insulin initiation and administration mode are critical in achieving target glycaemic levels. Progress in these fields is expected to facilitate and improve the quality of life of diabetic patients.

Manual closed-loop insulin delivery in children and adolescents with type 1 diabetes: a phase 2 randomised crossover trial

BACKGROUND

Closed-loop systems link continuous glucose measurements to insulin delivery. We aimed to establish whether closed-loop insulin delivery could control overnight blood glucose in young people.

METHODS

We undertook three randomised crossover studies in 19 patients aged 5-18 years with type 1 diabetes of duration 6.4 years (SD 4.0). We compared standard continuous subcutaneous insulin infusion and closed-loop delivery (n=13; APCam01); closed-loop delivery after rapidly and slowly absorbed meals (n=7; APCam02); and closed-loop delivery and standard treatment after exercise (n=10; APCam03). Allocation was by computer-generated random code. Participants were masked to plasma and sensor glucose. In APCam01, investigators were masked to plasma glucose. During closed-loop nights, glucose measurements were fed every 15 min into a control algorithm calculating rate of insulin infusion, and a nurse adjusted the insulin pump. During control nights, patients' standard pump settings were applied. Primary outcomes were time for which plasma glucose concentration was 3.91-8.00 mmol/L or 3.90 mmol/L or lower. Analysis was per protocol. This trial is registered, number ISRCTN18155883.

FINDINGS

17 patients were studied for 33 closed-loop and 21 continuous infusion nights. Primary outcomes did not differ significantly between treatment groups in APCam01 (12 analysed; target range, median 52% [IQR 43-83] closed loop vs 39% [15-51] standard treatment, p=0.06;

INTERPRETATION

Closed-loop systems could reduce risk of nocturnal hypoglycaemia in children and adolescents with type 1 diabetes.

FUNDING

Juvenile Diabetes Research Foundation; European Foundation for Study of Diabetes; Medical Research Council Centre for Obesity and Related Metabolic Diseases; National Institute for Health Research Cambridge Biomedical Research Centre.

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MESH Headings

• Adolescent
• Algorithms
• Biosensing Techniques
• Blood Glucose/metabolism
• Child
• Child, Preschool
• Cross-Over Studies
• Diabetes Mellitus, Type 1/blood
• Diabetes Mellitus, Type 1/drug therapy
• Female
• Humans
• Hypoglycemic Agents/administration & dosage
• Infusions, Subcutaneous
• Insulin/administration & dosage
• Insulin/blood
• Insulin Infusion Systems
• Male
• Treatment Outcome

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Grants

• G0600717 Medical Research Council

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Affiliation(s)

Roman Hovorka Department of Paediatrics, University of Cambridge, Cambridge, UK.
Janet M Allen
Daniela Elleri
Ludovic J Chassin
Julie Harris
Dongyuan Xing
Craig Kollman
Tomas Hovorka
Anne Mette F Larsen
Marianna Nodale
Alessandra De Palma
Malgorzata E Wilinska
Carlo L Acerini
David B Dunger

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Closed-loop insulin delivery using a subcutaneous glucose sensor and intraperitoneal insulin delivery: feasibility study testing a new model for the artificial pancreas

OBJECTIVE

Attempts to build an artificial pancreas by using subcutaneous insulin delivery from a portable pump guided by an subcutaneous glucose sensor have encountered delays and variability of insulin absorption. We tested closed-loop intraperitoneal insulin infusion from an implanted pump driven by an subcutaneous glucose sensor via a proportional-integral-derivative (PID) algorithm.

RESEARCH DESIGN AND METHODS

Two-day closed-loop therapy (except for a 15-min pre-meal manual bolus) was compared with a 1-day control phase with intraperitoneal open-loop insulin delivery, according to randomized order, in a hospital setting in eight type 1 diabetic patients treated by implanted pumps. The percentage of time spent with blood glucose in the 4.4-6.6 mmol/l range was the primary end point. RESULTS During the closed-loop phases, the mean +/- SEM percentage of time spent with blood glucose in the 4.4-6.6 mmol/l range was significantly higher (39.1 +/- 4.5 vs. 27.7 +/- 6.2%, P = 0.05), and overall dispersion of blood glucose values was reduced among patients. Better closed-loop glucose control came from the time periods excluding the two early postprandial hours with a higher percentage of time in the 4.4-6.6 mmol/l range (46.3 +/- 5.3 vs. 28.6 +/- 7.4, P = 0.025) and lower mean blood glucose levels (6.9 +/- 0.3 vs. 7.9 +/- 0.6 mmol/l, P = 0.036). Time spent with blood glucose <3.3 mmol/l was low and similar for both investigational phases.

CONCLUSIONS

Our results demonstrate the feasibility of intraperitoneal insulin delivery for an artificial beta-cell and support the need for further study. Moreover, according to a semiautomated mode, the features of the pre-meal bolus in terms of timing and amount warrant further research.

Overnight closed-loop insulin delivery with model predictive control: assessment of hypoglycemia and hyperglycemia risk using simulation studies

BACKGROUND

Hypoglycemia and hyperglycemia during closed-loop insulin delivery based on subcutaneous (SC) glucose sensing may arise due to (1) overdosing and underdosing of insulin by control algorithm and (2) difference between plasma glucose (PG) and sensor glucose, which may be transient (kinetics origin and sensor artifacts) or persistent (calibration error [CE]). Using in silico testing, we assessed hypoglycemia and hyperglycemia incidence during over-night closed loop. Additionally, a comparison was made against incidence observed experimentally during open-loop single-night in-clinic studies in young people with type 1 diabetes mellitus (T1DM) treated by continuous SC insulin infusion.

METHODS

Simulation environment comprising 18 virtual subjects with T1DM was used to simulate overnight closed-loop study with a model predictive control (MPC) algorithm. A 15 h experiment started at 17:00 and ended at 08:00 the next day. Closed loop commenced at 21:00 and continued for 11 h. At 18:00, protocol included meal (50 g carbohydrates) accompanied by prandial insulin. The MPC algorithm advised on insulin infusion every 15 min. Sensor glucose was obtained by combining model-calculated noise-free interstitial glucose with experimentally derived transient and persistent sensor artifacts associated with FreeStyle Navigator (FSN). Transient artifacts were obtained from FSN sensor pairs worn by 58 subjects with T1DM over 194 nighttime periods. Persistent difference due to FSN CE was quantified from 585 FSN sensor insertions, yielding 1421 calibration sessions from 248 subjects with diabetes.

RESULTS

Episodes of severe (PG < or = 36 mg/dl) and significant (PG < or = 45 mg/dl) hypoglycemia and significant hyperglycemia (PG > or = 300 mg/dl) were extracted from 18,000 simulated closed-loop nights. Severe hypoglycemia was not observed when FSN CE was less than 45%. Hypoglycemia and hyperglycemia incidence during open loop was assessed from 21 overnight studies in 17 young subjects with T1DM (8 males; 13.5 +/- 3.6 years of age; body mass index 21.0 +/- 4.0 kg/m2; duration diabetes 6.4 +/- 4.1 years; hemoglobin A1c 8.5% +/- 1.8%; mean +/- standard deviation) participating in the Artificial Pancreas Project at Cambridge. Severe and significant hypoglycemia during simulated closed loop occurred 0.75 and 17.11 times per 100 person years compared to 1739 and 3479 times per 100 person years during experimental open loop, respectively. Significant hyperglycemia during closed loop and open loop occurred 75 and 15,654 times per 100 person years, respectively.

CONCLUSIONS

The incidence of severe and significant hypoglycemia reduced 2300- and 200-fold, respectively, during stimulated overnight closed loop with MPC compared to that observed during open-loop overnight clinical studies in young subjects with T1DM. Hyperglycemia was 200 times less likely. Overnight closed loop with the FSN and the MPC algorithm is expected to reduce substantially the risk of hypoglycemia and hyperglycemia.

Treatment of diabetes mellitus using an external insulin pump: the state of the art

The aim of diabetes treatment is to achieve tight glucose control to avoid the development of chronic diabetic complications while reducing the frequency of hypoglycaemic episodes. Continuous subcutaneous insulin infusion (CSII) using an external pump is an intensive diabetes therapy recognized to improve metabolic control and glycaemic instability, and to reduce the frequency of severe hypoglycaemia. For years, the theoretical advantages of the insulin pump (constancy of basal delivery, adjustable basal rates, and low insulin depots allowing the reduction of glycaemic variability) have contributed to its reported superiority compared with multiple daily injections (MDI). However, insulin pump therapy is now challenged by new MDI regimens based on long-acting insulin analogues that could replace the use of CSII. As a consequence, health professionals now have to determine which patients are likely to benefit the most from CSII. Recently, several studies reported that children and adolescents, and patients whose blood glucose imbalance was initially the most pronounced with basal-bolus regimens, would particularly benefit from CSII. Other indications were also proposed in marginal clinical situations with highly selected patients in whom a significant improvement of blood glucose was demonstrated. Finally, the use of CSII in type 2 diabetic patients now appears to be a good alternative to the ineffective MDI regimens observed in some of these patients. However, past experience with CSII indicates that candidates for insulin pump therapy must be carefully selected and strongly motivated to improve their glucose control. Use of CSII also requires strict medical supervision by physicians and a regular programme of patient education by paramedical teams, to ensure optimal responsible use of this technique by healthcare professionals.

Continuous glucose monitoring: a review of biochemical perspectives and clinical use in type 1 diabetes

Self-monitoring of blood glucose is a fundamental part of diabetes management. It is mandatory for tight glucose control. For the past 30 years, intermittent measurement of capillary blood glucose has been the method of choice for self-monitoring. The main disadvantage of such measurements is that they provide isolated glucose values which do not reflect variations occurring throughout the day and night. Hence systems monitoring blood glucose concentrations on a "continuous basis" have been developed. In clinical studies, different devices were shown to provide useful information on glycemic excursions in people with diabetes with sufficient accuracy. Thus, in clinical practice, this approach has also been shown to help in the medical management leading to a reduction in glycated hemoglobin and glycemic variability. However, because of lack of experience, this technology has yet to replace standard capillary blood glucose monitoring. In this paper, we review the biochemical perspectives of continuous glucose monitoring and its clinical use in type 1 diabetes.

Insulin delivery route for the artificial pancreas: subcutaneous, intraperitoneal, or intravenous? Pros and cons

Insulin delivery is a crucial component of a closed-loop system aiming at the development of an artificial pancreas. The intravenous route, which has been used in the bedside artificial pancreas model for 30 years, has clear advantages in terms of pharmacokinetics and pharmacodynamics, but cannot be used in any ambulatory system so far. Subcutaneous (SC) insulin infusion benefits from the broad expansion of insulin pump therapy that promoted the availability of constantly improving technology and fast-acting insulin analog use. However, persistent delays of insulin absorption and action, variability and shortterm stability of insulin infusion from SC-inserted catheters generate effectiveness and safety issues in view of an ambulatory, automated, glucose-controlled, artificial beta cell. Intraperitoneal insulin delivery, although still marginally used in diabetes care, may offer an interesting alternative because of its more-physiological plasma insulin profiles and sustained stability and reliability of insulin delivery.

Clinical experience with an implanted closed-loop insulin delivery system

AIM: To report the first clinical experience with a prototype of implanted artificial beta-cell. METHODS: The Long-Term Sensor System® project assessed the feasibility of glucose control by the combined implantation of a pump for peritoneal insulin delivery and a central intravenous glucose sensor, connected physically by a subcutaneous lead and functionally by PID algorithms. It was performed in 10 type 1 diabetic patients from 2000 to 2007. RESULTS: No harmful complication related to implants occurred. Insulin delivery was affected by iterative but reversible pump slowdowns due to insulin precipitation. Glucose measurement by the intravenous sensors correlated well with meter values (r = 0.83-0.93, with a mean absolute deviation of 16.5%) for an average duration of 9 months. Uploading of pump electronics by PID algorithms designed for closed-loop insulin delivery allowed in-patient 48 hourtrials. CONCLUSION: Although the concept of a fully implantable artificial beta-cell has been shown as feasible, improvements in the sensor structure to increase its longevity and decrease sensor delay that affected closed-loop control at meal-times are expected.

Continuous glucose monitoring and external insulin pump: towards a subcutaneous closed loop

The development of an artificial pancreas for the treatment of type 1 diabetes is a highly desired endeavour for type 1 diabetic patients, physicians, scientists and engineers. The development of the first miniaturized external pumps in the 70s and the pharmacokinetic properties of short acting insulin analogues, closer to physiology, have raised hopes for the elaboration of such a device. Recent technological progress in the development of continuous glucose sensors, have improved the reliability and accuracy of these devices. This has led to the development of prototypes of closed-loop system based on the combination of a continuous monitor, a control algorithm, and an insulin pump. This review focuses on the SC-SC approach, employing subcutaneous glucose monitoring and subcutaneous insulin delivery. The feasibility of this solution has been proven at a small scale, but remains to be confirmed in the home setting. Intermediate solutions, such as semi-automatic systems, might be immediately valuable.