Potential role of incretins in diabetes and COVID-19 infection: a hypothesis worth exploring.

Patients with diabetes mellitus have been reported to be at a high risk of complications from SARS-CoV2 virus infection (COVID-19). In type 2 diabetes, there is a change in immune system cells, which shift from an anti-inflammatory to a predominantly pro-inflammatory pattern. This altered immune profile may induce important clinical consequences, including increased susceptibility to lung infections; and enhanced local inflammatory response. Furthermore, dipeptidyl peptidase 4 (DPP4) enzyme is highly expressed in the lung, and that it may have additional actions besides its effects on glucose metabolism, which might exert profound pro-inflammatory effects. We briefly review the impact on the inflammatory system of DPP4 for its possible detrimental effect on COVID-19 syndrome, and of DPP4 inhibitors (gliptins), currently used as glucose lowering agents, which may have the potential to exert positive pleiotropic effect on inflammatory diseases, in addition to their effects on glucose metabolism. Thanks to these ancillary effects, gliptins could potentially be "repurposed" as salutary drugs against COVID-19 syndrome, even in non-diabetic subjects. Clinical studies should be designed to investigate this possibility.

Therapeutic Effects of Endogenous Incretin Hormones and Exogenous Incretin-Based Medications in Sepsis.

BACKGROUND: Sepsis, a complex disorder characterized by a dysregulated immune response to an inciting infection, affects over one million Americans annually. Dysglycemia during sepsis hospitalization confers increased risk of organ dysfunction and death, and novel targets for the treatment of sepsis and maintenance of glucose homeostasis are needed. Incretin hormones are secreted by enteroendocrine cells in response to enteral nutrients and potentiate insulin release from pancreatic ß cells in a glucose-dependent manner, thereby reducing the risk of insulin-induced hypoglycemia. Incretin hormones also reduce systemic inflammation in preclinical studies, but studies of incretins in the setting of sepsis are limited. METHODS: In this bench-to-bedside mini-review, we detail the evidence to support incretin hormones as a therapeutic target in patients with sepsis. We performed a PubMed search using the medical subject headings "incretins," "glucagon-like peptide-1," "gastric inhibitory peptide," "inflammation," and "sepsis." RESULTS: Incretin-based therapies decrease immune cell activation, inhibit proinflammatory cytokine release, and reduce organ dysfunction and mortality in preclinical models of sepsis. Several small clinical trials in critically ill patients have suggested potential benefit in glycemic control using exogenous incretin infusions, but these studies had limited power and were performed in mixed populations. Further clinical studies examining incretins specifically in septic populations are needed. CONCLUSIONS: Targeting the incretin hormone axis in sepsis may provide a means of not only promoting euglycemia in sepsis but also attenuating the proinflammatory response and improving clinical outcomes.

GI inflammation Increases Sodium-Glucose Cotransporter Sglt1.

A correlation between gastrointestinal (GI) inflammation and gut hormones has reported that inflammatory stimuli including bacterial endotoxins, lipopolysaccharides (LPS), TNFα, IL-1ß, and IL-6 induces high levels of incretin hormone leading to glucose dysregulation. Although incretin hormones are immediately secreted in response to environmental stimuli, such as nutrients, cytokines, and LPS, but studies of glucose-induced incretin secretion in an inflamed state are limited. We hypothesized that GI inflammatory conditions induce over-stimulated incretin secretion via an increase of glucose-sensing receptors. To confirm our hypothesis, we observed the alteration of glucose-induced incretin secretion and glucose-sensing receptors in a GI inflammatory mouse model, and we treated a conditioned media (Mϕ 30%) containing inflammatory cytokines in intestinal epithelium cells and enteroendocrine L-like NCI-H716 cells. In GI-inflamed mice, we observed that over-stimulated incretin secretion and insulin release in response to glucose and sodium glucose cotransporter (Sglt1) was increased. Incubation with Mϕ 30% increases Sglt1 and induces glucose-induced GLP-1 secretion with increasing intracellular calcium influx. Phloridzin, an sglt1 inhibitor, inhibits glucose-induced GLP-1 secretion, ERK activation, and calcium influx. These findings suggest that the abnormalities of incretin secretion leading to metabolic disturbances in GI inflammatory disease by an increase of Sglt1.

Is there a role for the incretin system in blood pressure regulation?

Incretin-based therapies are now well established for diabetes management and are among the frontline agents for control of hyperglycemia. In addition to their antihyperglycemic effects, evidence is emerging on the role of these agents on blood pressure regulation, cardioprotective and renoprotective properties. Because of the pleiotropic nature of these affects, these agents could offer significant benefits with regards to the cardiorenal metabolic complications that are part of the diabetes and obesity epidemic in the United States and worldwide. We review the various known mechanisms or pathways by which incretin based therapy exerts its regulation of blood pressure with emphasis on novel mechanisms such as inflammation/immunomodulation and oxidative stress.

Dual-monoclonal, sandwich immunoassay specific for glucose-dependent insulinotropic peptide1-42, the active form of the incretin hormone.

BACKGROUND: Glucose-dependent insulinotropic peptide (GIP) is an incretin peptide secreted by intestinal K cells that stimulates insulin secretion in a glucose-dependent manner. It is secreted as an active, intact 42-amino acid peptide GIP(1-42), which is rapidly degraded by dipeptidyl peptidase 4 to GIP(3-42), which is inactive. There is currently no described monoclonal antibody-based sandwich immunoassay to quantify concentrations of GIP(1-42), the active form of the peptide. METHODS: To create a sandwich ELISA for GIP(1-42), we generated a monoclonal antibody specific for the intact N-terminus of the peptide, which was further optimized to increase its affinity. We used this antibody as a conjugate antibody in a sandwich ELISA and paired it with an anti-total GIP capture monoclonal antibody to create a dual monoclonal sandwich ELISA for GIP(1-42). RESULTS: The sandwich ELISA was highly specific for GIP(1-42) and did not recognize GIP(3-42). The ELISA demonstrated a broad dynamic range and a lower limit of quantification of 5 ng/L. Using the ELISA, we were able to show that GIP(1-42) concentrations in healthy volunteers increased dramatically in the postprandial state compared to the fasting state. GIP(1-42) values were correlated with total GIP values overall; however, there was substantial interindividual variation. CONCLUSIONS: The use of an N-terminal-specific monoclonal antibody in a sandwich ELISA format provides a robust and convenient method for measuring concentrations of GIP(1-42), the active form of the incretin hormone. This ELISA should help to improve our understanding of the role of GIP(1-42) in regulating glucose-dependent insulin secretion.