INGAP-Peptide Variants as a Novel Therapy for Type 1 Diabetes: Effect on Human Islet Insulin Secretion and Gene Expression

Abstract

Islet transplantation offers a long-term cure for Type 1 Diabetes (T1D), freeing patients from daily insulin injections. Therapeutic peptides have shown potential to increase the insulin output of pancreatic islets, maximizing the impact of grafted cells. The islet neogenesis-associated protein (INGAP), and its bioactive core (INGAP-P), stimulate beta-cell function and viability, offering the possibility for islet treatment prior to implant. However, dosing efficacy is limited by low circulation time and enzyme degradation. This proof-of-concept study presents the investigation of novel molecular variants of INGAP-P to find a more bioactive form. Custom-designed peptide variants of INGAP-P were synthesized and tested for their effect on the insulin secretion and gene expression of live human islets. We exposed the live islets of five donors to varying glucose concentrations with INGAP-P variants in solution. We identified four peptide variants (I9, I15Tyr, I19 and I15Cys) which displayed statistically significant enhancements over negative controls (representing a 1.6–2.8-fold increase in stimulation index). This is the first study that has assessed these INGAP-P variants in human islets. It highlights the potential for customized peptides for type 1 diabetes therapy and provides a foundation for future peptide-screening experiments.

Renewable Human Cell Model for Type 1 Diabetes Research: EndoC-βH5/HUVEC Coculture Spheroids

“…Figure 3(b) shows the response of 100% EndoC-βH5 spheroids to 0 mM and 20 mM glucose containing 1 μg/mL INGAP-P modified with cysteine (I15Cys) or glycine (I15Gly) residues, with inset showing the corresponding stimulation indices. Details of synthetic INGAP-P peptide screening are covered in our previous work [15]. Peptides were custom synthesized as analogues of the 15 amino acid sequence, INGAP-P, to find stable conformations with increased stimulatory effect.…”

“…Maximizing the insulin production and survival of implanted cells are critical to islet graft efficacy and longevity. Our previous work highlighted the variability in drug screening studies on human islets due to individual differences between donors [15]. Age, BMI, comorbidities, and drug history all act to confound the accuracy of studies with limited donor access.…”

“…Our previous work has shown the potential of INGAP-P-based peptides to improve insulin secretion and expression of certain beta-cell gene mRNAs but dealt with high variability among human donors [15]. Here, we selected I15Cys and I15Gly for their potential to improve insulin secretion, possibly in conjunction with upregulation of PDX1 expression.…”

“…Endothelial cells regulate immune mediators, acting to protect the glucose sensing mechanism and control permeability on the outer boundaries of islets [14]. Factors such as INGAP-P, exendin-4, or IBMX promote insulin secretion, maximizing the effect of smaller beta-cell populations [15][16][17]. Identifying therapeutic compounds relies on stimulating human islets, posing challenges due to their short in vitro lifetimes, lack of proliferation, and significant donor-to-donor variation [18].…”

A Concerted Vision to Advance the Knowledge of Diabetes Mellitus Related to Immune Checkpoint Inhibitors

“…As regards the treatment of irDM, a major challenge is the lack of antihyperglycemic treatments for irDM other than the known antidiabetic medications. In-depth understanding of the pathophysiology of irDM may yield future therapeutic perspectives, namely: (i) the empowerment of a so-called shut-off strategy to inhibit key inflammatory processes with limited immunosuppressive impact on the response of tumor to ICPi [149,150] through innovative immunosuppressive agents, such as vedolizumab (anti-integrin α4β7), infliximab (a chimeric monoclonal anti-tumor necrosis factor (TNF) alpha (TNF-α) antibody), tocilizumab (anti-interleukin (IL)-6 (IL-6) receptor antibody), mycophenolate mofetil, cyclophosphamide, and intravenous immunoglobulins [10]; (ii) the use of breakthrough modalities of regenerative medicine, such as the pancreatic islet neogenesis-associated protein (INGAP), which induces the neogenesis of the native endocrine pancreas [151,152]; (iii) the modulation of the gut microbiome through diet, probiotics, prebiotics, synbiotics, postbiotics, and fecal microbiota transplantation (FMT) to create a composition capable of protecting the host against irDM [70,106].…”