Advancing continuous subcutaneous insulin infusion in vivo: New insights into tissue challenges

The DERMIS Study: Methodologies, Results, and Implications for the Future

Ongoing innovation in diabetes technologies has led to the development of advanced tools such as automated insulin delivery (AID) systems that adjust insulin delivery in response to current and predicted glucose levels, residual insulin action, and other inputs (eg, meal and exercise announcements). However, infusion sets continue to be the "Achilles heel" of accurate and precise insulin delivery and continued device use. A recent study by Kalus et al (DERMIS Study) revealed higher vessel density and signals of inflammation by optical coherence tomography (OCT), in addition to increased inflammation, fat necrosis, fibrosis, and eosinophilic infiltration by histopathology. Although the study provided a comprehensive description of what was happening, the results raise important questions that require additional research. On February 29, 2024, the Leona M. and Harry B. Helmsley Charitable Trust sponsored a conference to begin addressing these issues. This article summarizes the DERMIS study findings and testing methodologies discussed at the conference and proposes the next steps for developing insulin infusion sets that reduce the variability in insulin delivery and extend wear.

Therapeutic Insulin Analogue Concentrations at Infusion Sites Enhanced the Pro-Inflammatory Response and Apoptosis in an In Vitro Macrophage-Material Interaction Model

Continuous subcutaneous insulin infusion for Type 1 diabetes relies upon insulin infusion sets (IIS) to reliably deliver insulin to a subcutaneous depot, where it is absorbed into systemic circulation. However, IIS are plagued by short wear times and high failure rates, due in part to inconsistent insulin absorption that can arise over time. While emerging evidence suggests that the local inflammatory response to the IIS cannula may impact both wear times and unreliable insulin adsorption, the mechanisms are poorly understood. Here, we investigated the effects of local infused insulin concentrations on the biomaterial host response to better understand the underlying factors that limit the IIS performance. We first modeled the insulin concentration for a constant basal infusion rate to select a relevant insulin concentration range of 0.1-10 U/mL within the infusion site. We then examined the influence of a commercial insulin analogue (Humulin-N) using an in vitro macrophage-material model, which uses adsorbed fibroblast lysate (containing damage-associated molecular patterns) to activate macrophages and recapitulates macrophage responses on implanted biomaterials. RAW-Blue macrophages cultured on lysate-adsorbed surfaces had increased nuclear factor-κB (NF-κB) and activating protein 1 (AP-1) activity and intracellular reactive oxygen species (ROS) accumulation compared to control surfaces. Humulin-N concentration (0.5-10 U/mL) enhanced the NF-κB/AP-1 activity and ROS accumulation in macrophages on lysate-adsorbed surfaces. However, Humulin-N had no effect on NF-κB/AP-1 or ROS in the absence of the inflammatory stimulus. Additionally, high insulin concentrations arising from therapeutic doses induced macrophage apoptosis with and without adsorbed lysate. This study contributes to emerging evidence that infused insulin affects the tissue response to IIS.

Comprehensive investigation of insulin-induced amyloidosis lesions in patients with diabetes at clinical and histological levels: A systematic review

INTRODUCTION

Insulin-derived amyloidosis (AIns), a skin complication in patients with diabetes, causes impaired insulin absorption. This systematic review aims to get a better understanding of this overlooked condition.

METHODS

Comprehensive literature searches were performed in Scopus, PubMed, EMBASE, and Web of Science databases until June 17, 2023. From 19,343 publications, duplicate and irrelevant records were eliminated by title, and the full texts of the remaining studies were examined for validity. Clinical, pathological, and therapeutic findings were extracted from 44 papers.

RESULTS

Forty-four articles were studied that covered 127 insulin-treated patients with diabetes. From the 62 patients with reported age and sex, males had a mean age of 58 years, and females 68.5 years. While AIns were twice as likely to develop in men (66.13 %) as in women (33.87 %), the administered insulin dose was significantly higher in males (p = 0.017). The most common insulin injection site was the abdominal wall (77.63 %). Histological findings showed the presence of amorphous material with the occasional presence of lymphocytes, plasma cells, macrophages, adipocytes, histocytes, and giant cells. The mean HbA1c level was 8.8 % and the need for receiving insulin was increased in AIns. Changing the site of insulin injections and/or surgically removing the nodules were the most common treatments to obtain better insulin uptake and controlled serum glucose levels.

CONCLUSION

This study highlights the importance of AIns, proper rotation of insulin injection site, and post-treatment patient follow-up to recognize and prevent the development of amyloid nodules.

Electrooxidation of Phenol on Polyelectrolyte Modified Carbon Electrodes for Use in Insulin Pump Infusion Sets

BACKGROUND

Many type 1 diabetes patients using continuous subcutaneous insulin infusion (CSII) suffer from the phenomenon of unexplained hypoglycemia or "site loss." Site loss is hypothesized to be caused by toxic excipients, for example, phenolic compounds within insulin formulations that are used as preservatives and stabilizers. Here, we develop a bioinspired polyelectrolyte-modified carbon electrode for effective electrooxidative removal of phenol from insulin and eventual incorporations into an infusion set of a CSII device.

METHODS

We modified a carbon screen printed electrode (SPE) with poly-L-lysine (PLL) to avoid passivation due to polyphenol deposition while still removing phenolic compounds from insulin injections. We characterized these electrodes using scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) and compared their data with data from bare SPEs. Furthermore, we performed electrochemical measurements to determine the extent of passivation, and high-performance liquid chromatography (HPLC) measurements to confirm both the removal of phenol and the integrity of insulin after phenol removal.

RESULTS

Voltammetry measurements show that electrode passivation due to polyphenol deposition is reduced by a factor of 2X. HPLC measurements confirm a 10x greater removal of phenol by our modified electrodes relative to bare electrodes.

CONCLUSION

Using bioinspired polyelectrolytes to modify a carbon electrode surface aids in the electrooxidation of phenolic compounds from insulin and is a step toward integration within an infusion set for mitigating site loss.

Mast Cell Deficiency in Mice Attenuates Insulin Phenolic Preservative-Induced Inflammation

One major obstacle that limits the lifespan of insulin infusion pumps is surmounting the tissue site reaction at the device implantation site. All commercial insulin formulations contain insulin phenolic preservatives (IPPs) designed to ensure insulin protein stability and prolong shelf-life. However, our laboratory demonstrated that these preservatives are cytotoxic and induce inflammation. Mature mast cells (MCs) reside in cutaneous tissue and are one of the first responders to an epidermal breach. Upon activation, MCs release proinflammatory and immunomodulatory prepacked mediators that exacerbate these inflammatory reactions. Thus, we hypothesized that once the epidermis is breached, cutaneous MCs are triggered inciting the inflammatory response to IPP-induced inflammation. This hypothesis was pursued utilizing our modified in vivo mouse air pouch model, including a c-kit dependent (C57BL/6J-kitW-sh/W-sh) and a c-kit independent (Cpa3-Cre; Mcl-1fl/fl) MC-deficient mouse model. Leukocytes were quantified in the mouse air pouch lavage fluid following flow cytometry analysis for IPP infusion under three different states, insulin-containing phenolic preservatives (Humalog®), insulin preservatives alone, and normal saline as a control. The air pouch wall was assessed using histopathological evaluations. Flow cytometry analysis demonstrated a statistically significant difference in inflammatory cell recruitment for both MC-deficient mouse models when compared to the control strain including infused control saline. Significantly less inflammation was observed at the site of infusion for the MC-deficient strains compared to the control strain. Overall, concordant results were obtained in both mouse types, C57Bl6-kitW-sh/W-sh and Cpa3-Cre; Mcl-1fl/fl. These findings in multiple model systems support the conclusion that MCs have important or possible unique roles in IPP-induced inflammation.

The Strategies of Development of New Non-Toxic Inhibitors of Amyloid Formation

In recent years, due to the aging of the population and the development of diagnostic medicine, the number of identified diseases associated with the accumulation of amyloid proteins has increased. Some of these proteins are known to cause a number of degenerative diseases in humans, such as amyloid-beta (Aβ) in Alzheimer's disease (AD), α-synuclein in Parkinson's disease (PD), and insulin and its analogues in insulin-derived amyloidosis. In this regard, it is important to develop strategies for the search and development of effective inhibitors of amyloid formation. Many studies have been carried out aimed at elucidating the mechanisms of amyloid aggregation of proteins and peptides. This review focuses on three amyloidogenic peptides and proteins-Aβ, α-synuclein, and insulin-for which we will consider amyloid fibril formation mechanisms and analyze existing and prospective strategies for the development of effective and non-toxic inhibitors of amyloid formation. The development of non-toxic inhibitors of amyloid will allow them to be used more effectively for the treatment of diseases associated with amyloid.

Insulin Derived Fibrils Induce Cytotoxicity in vitro and Trigger Inflammation in Murine Models

BACKGROUND

Effective exogenous insulin delivery is the cornerstone of insulin dependent diabetes mellitus management. Recent literature indicates that commercial insulin-induced tissue reaction and cellular cytotoxicity may contribute to variability in blood glucose as well as permanent loss of injection or infusion site architecture and function. It is well accepted that insulin formulations are susceptible to mechanical and chemical stresses that lead to insulin fibril formation. This study aims to characterize in vitro and in vivo toxicity, as well as pro-inflammatory activity of insulin fibrils.

METHOD

In vitro cell culture evaluated cytotoxicity and fibril uptake by macrophages and our modified murine air-pouch model quantified inflammatory activity. The latter employed FLOW cytometry and histopathology to characterize fibril-induced inflammation in vivo, which included fibril uptake by inflammatory phagocytes.

RESULTS

These studies demonstrated that insulin derived fibrils are cytotoxic to cells in vitro. Furthermore, inflammation is induced in the murine air-pouch model in vivo and in response, macrophages uptake fibrils both in vitro and in vivo.

CONCLUSIONS

Administration of insulin fibrils can lead to cytotoxicity in macrophages. In vivo data demonstrate insulin fibrils to be pro-inflammatory which over time can lead to cumulative cell/tissue toxicity, inflammation, and destructive wound healing. Long term, these tissue reactions could contribute to loss of insulin injection site architecture and function.

A pharmacological approach assessing the role of mast cells in insulin infusion site inflammation

Background Extending the lifespan of subcutaneous insulin administration sets and infusion pumps requires overcoming unreliable insulin delivery induced by dermal reactions. All commercially available insulin formulations contain insulin phenolic preservatives (IPP), which stabilize the insulin molecule but result in unwanted cell and tissue toxicity. Mast cells, which are the first line of defense once the epithelium is breached, are particularly abundant beneath the skin surface. Thus, we hypothesize a sequence of events initiated by device insertion that activates skin mast cells (MC) that subsequently trigger neutrophil and monocyte/macrophage recruitment. The ensuing inflammatory response compromises effective insulin infusion therapy. Methods We employed a non-genetic, pharmacological approach to MC membrane stabilization using Cromolyn sodium (CS), which inhibits MC degranulation. These studies were conducted in our modified air pouch mouse model using non-diabetic and streptozotocin induced diabetic mice. We evaluated the impact of systemic CS through intraperitoneal injections, as well as the impact of local CS through co-infusion, on infusion catheter insertion and IPP-induced inflammation. Results CS at a concentration of 50 mg/kg minimized inflammation triggered in response to insulin phenolic preservatives present in standard insulin formulations. The resultant degree of tissue inflammation was comparable to that observed with saline injections. Conclusion Targeting MC has the potential to extend the longevity of insulin infusion sets by mitigating the inflammatory response. Future studies should be directed at employing other MC models, such as newer Cre/loxP mouse strains, to confirm the sentinel role of MC in insulin infusion therapy.

Feasibility study of a prototype extended-wear insulin infusion set in adults with type 1 diabetes

AIM

To assess the feasibility of a prototype insulin infusion set (IIS) for extended wear in adults with type 1 diabetes.

MATERIALS AND METHODS

The prototype Capillary Biomedical investigational extended-wear IIS (CBX IIS) incorporates a soft, flexible, reinforced kink-resistant angled nylon-derivative cannula with one distal and three proximal ports to optimize insulin delivery. Twenty adult participants with type 1 diabetes established on insulin pump therapy used the CBX IIS for two 7-day test periods while wearing a Dexcom G5 continuous glucose monitor.

RESULTS

Participants were able to wear the CBX IIS for an average of 6.6 ± 1.4 days. Eighty-eight percent (36 of 41) of sets were worn for 7 days. No serious adverse events were reported. Five infusion sets failed prematurely because of: unresolvable hyperglycaemia (three); hyperglycaemia with elevated ketones (one); or infection (one). Median time in range (3.9-10.0 mmol/L) was 62% (54-76). Average glucose levels per day of infusion set wear showed a statistically significant increase over time (p < .001).

CONCLUSIONS

Our preliminary observations confirm the tolerability of the prototype CBX IIS for extended wear, albeit with a deterioration in glucose control after the third day.

Electrical signals regulate the release of insulin from electrodeposited chitosan composite hydrogel: An in vitro and in vivo study

Electrical signal controlled drug release from polymeric drug delivery system provides an efficient way for accurate and demandable drug release. In this work, insulin was loaded on inorganic nanoplates (layered double hydroxides, LDHs) and coated on a copper wire by co-electrodeposition with chitosan. The formed structure in chitosan composite hydrogel entrapped insulin efficiently, which were proved by various techniques. In addition, the drug loaded chitosan composite hydrogel demonstrated good biocompatibility as suggested by cell attachment. In vitro drug release experiment showed fast responsive pulsed release of insulin by biasing electrical signals. The in vivo experiment in diabetic rats revealed controllable insulin release in plasma and stable decrease of blood glucose can be achieved by using appropriate electrical signal. In addition, HE staining suggested negligible effect to the tissue by electrical signals. This work suggests that the electrical signal controlled insulin release from chitosan composited hydrogel may be a promising administration route for insulin.

New insight into the importance of formulation variables on parenteral growth hormone preparations: potential effect on the injection-site pain

Reducing injection-site pain (ISP) in patients with chronic conditions such as growth hormone deficiency is a valuable strategy to improve patient compliance and therapeutic efficiency. Thus understanding different aspects of pain induction following subcutaneous injection of biotherapeutics and identifying the responsible factors are vital. Here we have discussed the effects of formulation's viscosity, concentration, osmolality, buffering agents, pH, and temperature as well as injection volume, dosing frequency, and different excipients on ISP following subcutaneous injection of commercially available recombinant human growth hormone products. Our literature review found limited available data on the effects of different components of parenteral rhGH products on ISP. This may be due to high cost associated with conducting various clinical trials to assess each excipient in the formulation or to determine the complex interactions of different components and its impact on ISP. Recently, conducting molecular dynamics simulation studies before formulation design has been recommended as an alternative and less-expensive approach. On the other hand, the observed inconsistencies in the available data is mainly due to different pain measurement approaches used in each study. Moreover, it is difficult to translate data obtained from animal studies to human subjects. Despite all these limitations, our investigation showed that components of parenteral rhGH products can significantly contribute to ISP. We suggest further investigation is required for development of long acting, buffer-free, preservative-free formulations. Besides, various excipients are currently being investigated for reducing ISP which can be used as alternatives for common buffers, surfactants or preservatives in designing future rhGH formulations.

Characteristics and morphology of lipohypertrophic lesions in adults with type 1 diabetes with ultrasound screening: an exploratory observational study

INTRODUCTION

Lipohypertrophy is a common complication of exposure to insulin therapy. Despite the prevalence of lipohypertrophy and its potentially hazardous effects on glucose regulation, it remains a relatively understudied problem in diabetes. The objective of this study was to characterize lipohypertrophic tissue using ultrasound in adults with type 1 diabetes.

RESEARCH DESIGN AND METHODS

An observational study of 74 people with type 1 diabetes from a diabetes center in South East London. Participants' insulin exposed areas were scanned with ultrasound, with a high-frequency linear probe (6-13 MHz). The observed tissue changes were described, measured and graded according to nodule size and thickness of the dermal layer.

RESULTS

Participants mean age and diabetes duration were 40.6 (±14.2) and 18.3 (±10.9) years, respectively, and 60% (n=44) were male. A total of 740 lipohypertrophic nodules were observed, ranging from 1.8 mm to 40 mm in width. The mean (SD/range) number of nodules per participants was 10.4 (±6.2/1-29). Delineation between the dermal layers was disrupted in all current injection sites. In 52 participants (70%), there was a 30% increase in dermal thickness compared with local none injected tissue, and in 36 participants (48%) the increase was 50%. The level of thickness was >3 mm in the abdominal areas of 22 (40%) of these participants and in thighs of eight participants (17.8%). Hypoechogenic areas suggestive of necrotic tissue were observed within the lipohypertrophic nodules of 22 (30%) participants. Needle length and nodule depth were correlated (r=0.69, p<0.001). A conceptual model of the insulin exposed tissue changes observed was constructed.

CONCLUSIONS

The study confirms that insulin-exposed tissue changes are heterogenous and has provided conceptual and grading frameworks for classifying these changes. Further studies are required to establish the clinical implications of these classifications, in relation to glucose regulation and other clinical parameters.

Phenolic Preservative Removal from Commercial Insulin Formulations Reduces Tissue Inflammation while Maintaining Euglycemia

Background: Exogenous insulin therapy requires stabilization of the insulin molecule, which is achieved through the use of excipients (e.g., phenolic preservatives (PP)) that provide protein stability, sterility and prolong insulin shelf life. However, our laboratory recently reported that PP, (e.g., m-creosol and phenol) are also cytotoxic, inducing inflammation and fibrosis. Optimizing PP levels through filtration would balance the need for insulin preservation with PP-induced inflammation. Method: Zeolite Y (Z-Y), a size-exclusion-based resin, was employed to remove PP from commercial insulin formulations (Humalog) before infusion. Results: PP removal significantly decreased cell toxicity in vitro and inflammation in vivo. Infusion site histological analysis after a 3 day study demonstrated that leukocyte accumulation increased with nonfiltered preparations but decreased after filtration. Additional studies demonstrated that a Z-Y fabricated filter effectively removed excess PP such that the filtered insulin solution achieved equivalent glycemic control in diabetic mice when compared to nonfiltered insulin. Conclusion: This approach represents the proof of concept that using Z-Y for in-line PP removal assists in lowering inflammation at the site of insulin infusion and thus could lead to extending the functional lifespan of insulin infusion sets in vivo.