Dipeptidyl Peptidase-4 at the Interface Between Inflammation and Metabolism

Tannins-enriched fraction of TeMac™ protects against aluminum chloride induced Alzheimer's disease-like pathology by modulating aberrant insulin resistance and alleviating oxidative stress in diabetic rats

ETHNOPHARMACOLOGICAL RELEVANCE

Alzheimer's disease is the most common neurodegenerative disease with therapeutic limitations. Insulin resistance plays a role in the progression of Alzheimer's disease. Therapies that modulate insulin secretion and signaling, as well as oxidative stress in the brain are now being investigated for their potential role in the prevention of Alzheimer's disease (AD). Terminalia macroptera (Combretaceae) is a plant that different parts have been used traditionally for the treatment of metabolic and neurological conditions. Previous study has indicated that the crude extract exhibit anti-diabetic property. In addition, the plant is a rich source of tannins, phenolic acids, flavonoids, triterpenes. However, there is no study on its protective effect against biochemical alterations of AD in diabetic rats.

AIM OF THE STUDY

The present research study investigated the neuroprotective effects of TeMac™ on Alzheimer-like pathology induced by aluminum chloride (AlCl3) in diabetic rats.

METHODS

A phytochemical analysis of TeMac™ was carried out to quantify tannins. The potential effect of the tannins-enriched fraction (TEF) of TeMac™ to prevent the formation of senile plaques was conducted by its ability to inhibit the activities of β-secretase (EC 3.4.23.46), monoamine oxidase A (EC 1.4.3.4) and the fibrillation of Aβ. A diabetic model was induced from female Wistar rats by a single intraperitoneal injection of streptozotocin (STZ, 35 mg/kg BW). After that, the blood glucose level was measured to confirm the induction of diabetes. Three days after induction, animals received AlCl3 (75 mg/kg BW) alone (AD control) or concomitantly with 400 mg/kg BW of TEF of TeMac™ or 5 mg/kg BW Daonil by daily gavage for 42 days. At the end of the experiment, rats were sacrificed, blood and brains were collected. The levels of amyloid fibrils, glucose, albumin and the activities of DPP4, β-secretase and phosphatase, and markers of oxidative stress in the brain were assessed.

RESULTS

TEF of TeMac™ displays a potential ability to inhibit the activities of β-secretase, monoamine oxidase, and Aβ fibrillation. Treatment with TEF of TeMac™ significantly inhibited DPP4 and BACE1 activities and reduced brain glucose and amyloid fibril levels, and improved cerebral albumin levels and modulated oxidative stress markers.

CONCLUSION

Our findings indicate that TEF of TeMac™ prevents Alzheimer's-type pathology linked to insulin resistance in rats. TEF of TeMac™ may be a potential drug candidate for the treatment of diabetes-associated cognitive impairment.

DPP-4 inhibitors sitagliptin and PF-00734,200 mitigate dopaminergic neurodegeneration, neuroinflammation and behavioral impairment in the rat 6-OHDA model of Parkinson's disease

Epidemiological studies report an elevated risk of Parkinson's disease (PD) in patients with type 2 diabetes mellitus (T2DM) that is mitigated in those prescribed dipeptidyl peptidase 4 (DPP-4) inhibitors. With an objective to characterize clinically translatable doses of DPP-4 inhibitors (gliptins) in a well-characterized PD rodent model, sitagliptin, PF-00734,200 or vehicle were orally administered to rats initiated either 7-days before or 7-days after unilateral medial forebrain bundle 6-hydroxydopamine (6-OHDA) lesioning. Measures of dopaminergic cell viability, dopamine content, neuroinflammation and neurogenesis were evaluated thereafter in ipsi- and contralateral brain. Plasma and brain incretin and DPP-4 activity levels were quantified. Furthermore, brain incretin receptor levels were age-dependently evaluated in rodents, in 6-OHDA challenged animals and human subjects with/without PD. Cellular studies evaluated neurotrophic/neuroprotective actions of combined incretin administration. Pre-treatment with oral sitagliptin or PF-00734,200 reduced methamphetamine (meth)-induced rotation post-lesioning and dopaminergic degeneration in lesioned substantia nigra pars compacta (SNc) and striatum. Direct intracerebroventricular gliptin administration lacked neuroprotective actions, indicating that systemic incretin-mediated mechanisms underpin gliptin-induced favorable brain effects. Post-treatment with a threefold higher oral gliptin dose, likewise, mitigated meth-induced rotation, dopaminergic neurodegeneration and neuroinflammation, and augmented neurogenesis. These gliptin-induced actions associated with 70-80% plasma and 20-30% brain DPP-4 inhibition, and elevated plasma and brain incretin levels. Brain incretin receptor protein levels were age-dependently maintained in rodents, preserved in rats challenged with 6-OHDA, and in humans with PD. Combined GLP-1 and GIP receptor activation in neuronal cultures resulted in neurotrophic/neuroprotective actions superior to single agonists alone. In conclusion, these studies support further evaluation of the repurposing of clinically approved gliptins as a treatment strategy for PD.

Liraglutide, a glucagon-like peptide-1 receptor agonist, ameliorates inflammation and apoptosis via inhibition of receptor for advanced glycation end products signaling in AGEs induced chondrocytes

BACKGROUND

This study aimed to investigate functions of GLP-1R agonist by liraglutide (LIRA) and revealing the mechanism related to AGEs/RAGE in chondrocytes.

METHODS

To illustrate potential effect of GLP-1R agonist on AGEs induced chondrocytes, chondrocytes were administrated by AGEs with LIRA and GLP-1R inhibitor exendin. Inflammatory factors were assessed using ELISA. Real-time PCR was used to evaluate the catabolic activity MMPs and ADAMTS mRNA level, as well as anabolic activity (aggrecan and collagen II). RAGE expression was investigated by Western blotting. TUNEL, caspase3 activity and immunofluorescence were performed to test the apoptotic activity.

RESULTS

Our results showed that treatment with LIRA at > 100 nM attenuated the AGE-induced chondrocyte viability. Western bolt demonstrated that GLP-1R activation by LIRA treatment reduced RAGE protein expression compared with the AGEs groups. ELISA showed that LIRA hindered the AGEs-induced production of inflammatory cytokines (IL-6, IL-12 and TNF-α) in primary chondrocytes. AGEs induced catabolism levels (MMP-1, -3, -13 and ADAMTS-4, 5) are also attenuated by LIRA, causing the retention of more extracellular matrix (Aggrecan and Collagen II). TUNEL, caspase3 activity and immunofluorescence results indicated that LIRA inhibited the AGEs-induced production of inflammatory cytokines in primary chondrocytes and attenuated the caspase 3 level, leading to the reduced apoptotic activity. All the protective effects are reversed by exendin (GLP-1R blockers).

CONCLUSIONS

The present study demonstrates for the first time that LIRA, an agonist for GLP-1R which is commonly used in type 2 diabetes reverses AGEs induced chondrocyte inflammation and apoptosis through suppressing RAGE signaling, contributing to reduced catabolism and retention of more extracellular matrix. The above results indicate the possible effect of GLP-1R agonist on treating OA.

Fragment-based QSAR study to explore the structural requirements of DPP-4 inhibitors: a stepping stone towards better type 2 diabetes mellitus management

Dipeptidyl peptidase-4 (DPP-4) inhibitors belong to a prominent group of pharmaceutical agents that are used in the governance of type 2 diabetes mellitus (T2DM). They exert their antidiabetic effects by inhibiting the incretin hormones like glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide which, play a pivotal role in the regulation of blood glucose homoeostasis in our body. DPP-4 inhibitors have emerged as an important class of oral antidiabetic drugs for the treatment of T2DM. Surprisingly, only a few 2D-QSAR studies have been reported on DPP-4 inhibitors. Here, fragment-based QSAR (Laplacian-modified Bayesian modelling and Recursive partitioning (RP) approaches have been utilized on a dataset of 108 DPP-4 inhibitors to achieve a deeper understanding of the association among their molecular structures. The Bayesian analysis demonstrated satisfactory ROC values for the training as well as the test sets. Meanwhile, the RP analysis resulted in decision tree 3 with 2 leaves (Tree 3: 2 leaves). This present study is an effort to get an insight into the pivotal fragments modulating DPP-4 inhibition.

Computational Screening for the Dipeptidyl Peptidase-IV Inhibitory Peptides from Putative Hemp Seed Hydrolyzed Peptidome as a Potential Antidiabetic Agent

Dipeptidyl peptidase-IV (DPPIV) inhibitory peptides are a class of antihyperglycemic drugs used in the treatment of type 2 diabetes mellitus, a metabolic disorder resulting from reduced levels of the incretin hormone GLP-1. Given that DPPIV degrades incretin, a key regulator of blood sugar levels, various antidiabetic medications that inhibit DPPIV, such as vildagliptin, sitagliptin, and linagliptin, are employed. However, the potential side effects of these drugs remain a matter of debate. Therefore, we aimed to investigate food-derived peptides from Cannabis sativa (hemp) seeds. Our developed bioinformatics pipeline was used to identify the putative hydrolyzed peptidome of three highly abundant proteins: albumin, edestin, and vicilin. These proteins were subjected to in silico digestion by different proteases (trypsin, chymotrypsin, and pepsin) and then screened for DPPIV inhibitory peptides using IDPPIV-SCM. To assess potential adverse effects, several prediction tools, namely, TOXINpred, AllerCatPro, and HemoPred, were employed to evaluate toxicity, allergenicity, and hemolytic effects, respectively. COPID was used to determine the amino acid composition. Molecular docking was performed using GalaxyPepDock and HPEPDOCK, 3D visualizations were conducted using the UCSF Chimera program, and MD simulations were carried out with AMBER20 MD software. Based on the predictive outcomes, FNVDTE from edestin and EAQPST from vicilin emerged as promising candidates for DPPIV inhibitors. We anticipate that our findings may pave the way for the development of alternative DPPIV inhibitors.

Hepatic transcriptome analyses of juvenile white bass (Morone chrysops) when fed diets where fish meal is partially or totally replaced by alternative protein sources

White bass (Morone chrysops) are a popular sportfish throughout the southern United States, and one parent of the commercially-successful hybrid striped bass (M. chrysops ♂ x M. saxatilis ♀). Currently, white bass are cultured using diets formulated for other carnivorous fish, such as largemouth bass (Micropterus salmoides) or hybrid striped bass and contain a significant percentage of marine fish meal. Since there are no studies regarding the utilization of alternative proteins in this species, we evaluated the global gene expression of white bass fed diets in which fish meal was partially or totally replaced by various combinations of soybean meal, poultry by-product meal, canola meal, soy protein concentrate, wheat gluten, or a commercial protein blend (Pro-Cision™). Six isonitrogenous (40% protein), isolipidic (11%), and isocaloric (17.1 kJ/g) diets were formulated to meet the known nutrient and energy requirements of largemouth bass and hybrid striped bass using nutrient availability data for most of the dietary ingredients. One of the test diets consisted exclusively of plant protein sources. Juvenile white bass (40.2 g initial weight) were stocked into a flow-through aquaculture system (three tanks/diet; 10 fish/tank) and fed the test diets twice daily to satiation for 60 days. RNA sequencing and bioinformatic analyses revealed significant differentially expressed genes between all test diets when compared to fish meal control. A total of 1,260 differentially expressed genes were identified, with major ontology relating to cell cycle and metabolic processes as well as immune gene functions. This data will be useful as a resource for future refinements to moronid diet formulation, as marine fish meal becomes limiting and plant ingredients are increasingly added as a reliable protein source.

The protective effects of alpha-pinene on high glucose-induced oxidative stress and inflammation in HepG2 cells

Objectives

Hyperglycemia, a prevalent metabolic condition observed in diabetes, leads to oxidative damage, inflammatory responses, and other consequences. Natural compounds alleviate the adverse impacts of diabetes. We aimed to explore the effects of alpha-pinene (AP) as a monoterpene on oxidative damage and inflammation caused by high glucose (HG) in the human hepatocellular liver carcinoma (HepG2) cell line.

Materials and Methods

The HepG2 cells were subjected to non or HG concentration (50 mM) and treated with or without AP (8, 16, and 32 μg/ml) for 48 hr. The effect of treatments on cellular viability, malondialdehyde (MDA), glutathione (GSH), and activity of anti-oxidant enzymes, including glutathione peroxidase (GPx), catalase (CAT), superoxide dismutase (SOD), was determined. The gene expression levels of nuclear factor-κβ (NF-κB), tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and dipeptidyl peptidase-4 (DPP-4) were estimated using quantitative real-time polymerase chain reaction (qRT-PCR).

Results

HG exposure significantly increased cell death, MDA formation, and depletion of GSH content and GPx, CAT, and SOD activity (P<0.05). We have also seen a significant induction in NF-κB, TNF-α, IL-6, and DPP-4 gene expression in hepatocytes under HG conditions (P<0.05). Interestingly, co-treatment with AP in a dose-dependent manner improved cell death and altered levels of MDA and GSH, and activity of GPx and CAT (P<0.05). AP could also modulate the gene expression of NF-κB and inflammatory biomarkers dose-dependently (P<0.05).

Conclusion

Our findings suggested the protective effect of AP on hepatocytes under HG conditions through attenuating oxidative stress markers and suppression of inflammatory pathways.

Immunomodulatory activity of dipeptidyl peptidase-4 inhibitors in immune-related diseases

Dipeptidyl peptidase-4 (DPP-4), also known as CD26, is a 110-kDa cell surface glycoprotein with enzymatic and signal transducing activity. DPP-4/CD26 is expressed by various cells, including CD4+ and CD8+ T cells, B cells, dendritic cells, macrophages, and NK cells. DPP-4 inhibitors (DPP-4i) were introduced to clinics in 2006 as new oral antihyperglycemic drugs approved for type 2 diabetes mellitus treatment. In addition to glucose-lowering effects, emerging data, from clinical studies and their animal models, suggest that DPP-4i could display anti-inflammatory and immunomodulatory effects as well, but the molecular and immunological mechanisms of these actions are insufficiently investigated. This review focuses on the modulatory activity of DPP-4i in the immune system and the possible application of DPP-4i in other immune-related diseases in patients with or without diabetes.

In vitro and in silico analysis proving DPP4 inhibition and diabetes-associated gene network modulation by a polyherbal formulation: Nisakathakadi Kashaya

Dipeptidyl-peptidase IV (DPP4) inhibitors are an important class of anti-diabetic drugs recognised for their systemic biological actions. Polyherbal preparations like Ayurveda formulations are considered to be ideal sources for discovering novel DPP4 inhibitors owing to their rich phytochemical composition. The current study reports the DPP4 inhibitory potential of a clinically established Ayurvedic anti-diabetic formulation Nisakathakadi Kashaya (NK) using in vitro assay and substantiates it by identifying potential bioactives responsible for DPP4 inhibition using computational biology tools. NK showed a dose-dependent DPP4 inhibition with an IC50 of 2.06 μg GAE/mL, and the molecular docking and simulation studies showed three compounds, namely Terchebin, Locaracemoside B and 1,2,4,6 Tetra o Galloyl Beta D Glucose having stable interactions with DPP4 similar to the standard drug Vildagliptin. Further, for the reason that polyherbal formulations exert a network pharmacology mode of action, in silico analysis was carried out to identify the other putative phytochemical-protein networks modulated by NK. The complex pharmacological network of the formulation was explored further using a subnetwork of diabetes proteins and their relationship with diabetes-associated comorbidities. A number of key targets like TNFα, TGFβ1, SOD1, SOD2, AKT1, DPP4 and GLP1R were identified in the protein-protein interaction network that is vital to diabetic progression and complications. A combination of in vitro and in silico methods allowed us to prove the DPP4 inhibition potential of NK as well as provided insights into the possible pharmacological networking through which NK potentially exerts its systemic effect in diabetes management.Communicated by Ramaswamy H. Sarma.

ACE2, ACE, DPPIV, PREP and CAT L enzymatic activities in COVID-19: imbalance of ACE2/ACE ratio and potential RAAS dysregulation in severe cases

OBJECTIVE AND DESIGN

Circulating enzymatic activity and RAAS regulation in severe cases of COVID-19 remains unclear, therefore we measured the serum activity of several proteases as potential targets to control the SARS-CoV-2 infection.

MATERIAL OR SUBJECTS

152 patients with COVID-19-like symptoms were grouped according to the severity of symptoms (COVID-19 negative, mild, moderate and severe).

METHODS

Serum samples of COVID-19 patients and controls were subjected to biochemical analysis and enzymatic assays of ACE2, ACE, DPPIV, PREP and CAT L. One-way ANOVA and multivariate logistic regression analysis were used. Statistical significance was accepted at p < 0.05.

RESULTS

We detected a positive correlation among comorbidities, higher C-reactive protein (CRP) and D-dimer levels with disease severity. Enzymatic assays revealed an increase in serum ACE2 and CAT L activities in severe COVID-19 patients, while ACE, DPPIV and PREP activities were significantly reduced. Notably, analysis of ACE2/ACE activity ratio suggests a possible imbalance of ANG II/ANG(1-7) ratio, in a positive association with the disease severity.

CONCLUSION

Our findings reveal a correlation between proteases activity and the severity of COVID-19. These enzymes together contribute to the activation of pro-inflammatory pathways, trigger a systemic activation of inflammatory mediators, leading to a RAAS dysregulation and generating a significant damage in several organs, contributing to poor outcomes of severe cases.

Milk protein digestion and the gut microbiome influence gastrointestinal discomfort after cow milk consumption in healthy subjects

Many healthy people suffer from milk-related gastrointestinal discomfort (GID) despite not being lactose intolerant; the mechanisms underpinning such condition are unknown. This study aimed to explore milk protein digestion and related physiological responses (primary outcome), gut microbiome and gut permeability in 19 lactose-tolerant healthy nonhabitual milk consumers [NHMCs] reporting GID after consuming cow milk compared to 20 habitual milk consumers [HMCs] without GID. NHMCs and HMCs participated in a milk-load (250 mL) test, underwent blood sample collection at 6 time points over 6 h after milk consumption and collected urine samples and GID self-reports over 24 h. We measured the concentrations of 31 milk-derived bioactive peptides (BAPs), 20 amino acids, 4 hormones, 5 endocannabinoid system mediators, glucose and the dipeptidyl peptidase-IV (DPPIV) activity in blood and indoxyl sulfate in urine samples. Subjects also participated in a gut permeability test and delivered feces sample for gut microbiome analysis. Results showed that, compared to HMCs, milk consumption in NHMCs, along with GID, elicited a slower and lower increase in circulating BAPs, lower responses of ghrelin, insulin, and anandamide, a higher glucose response and serum DPPIV activity. The gut permeability of the two groups was similar, while the habitual diet, which was lower in dairy products and higher in the dietary-fibre-to-protein ratio in NHMCs, possibly shaped the gut microbiome; NHMCs exhibited lower abundance of Bifidobacteria, higher abundance of Prevotella and lower abundance of protease-coding genes, which may have reduced protein digestion, as evidenced by lower urinary excretion of indoxyl sulfate. In conclusion, the findings showed that a less efficient digestion of milk proteins, supported by a lower proteolytic capability of the gut microbiome, may explain GID in healthy people after milk consumption.

COVID-19 therapeutics: Clinical application of repurposed drugs and futuristic strategies for target-based drug discovery

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) causes the complicated disease COVID-19. Clinicians are continuously facing huge problems in the treatment of patients, as COVID-19-specific drugs are not available, hence the principle of drug repurposing serves as a one-and-only hope. Globally, the repurposing of many drugs is underway; few of them are already approved by the regulatory bodies for their clinical use and most of them are in different phases of clinical trials. Here in this review, our main aim is to discuss in detail the up-to-date information on the target-based pharmacological classification of repurposed drugs, the potential mechanism of actions, and the current clinical trial status of various drugs which are under repurposing since early 2020. At last, we briefly proposed the probable pharmacological and therapeutic drug targets that may be preferred as a futuristic drug discovery approach in the development of effective medicines.

COVID-19 Outcomes and Diabetes Mellitus: A Comprehensive Multicenter Prospective Cohort Study

The link between type 2 diabetes (T2D) and the severe outcomes of COVID-19 has raised concerns about the optimal management of patients with T2D. This study aimed to investigate the clinical characteristics and outcomes of T2D patients hospitalized with COVID-19 and explore the potential associations between chronic T2D treatments and adverse outcomes. This was a multicenter prospective cohort study of T2D patients hospitalized with COVID-19 in Greece during the third wave of the pandemic (February-June 2021). Among the 354 T2D patients included in this study, 63 (18.6%) died during hospitalization, and 16.4% required ICU admission. The use of DPP4 inhibitors for the chronic management of T2D was associated with an increased risk of in-hospital death (adjusted odds ratio (adj. OR) 2.639, 95% confidence interval (CI) 1.148-6.068, p = 0.022), ICU admission (adj. OR = 2.524, 95% CI: 1.217-5.232, p = 0.013), and progression to ARDS (adj. OR = 2.507, 95% CI: 1.278-4.916, p = 0.007). Furthermore, the use of DPP4 inhibitors was significantly associated with an increased risk of thromboembolic events (adjusted OR of 2.249, 95% CI: 1.073-4.713, p = 0.032) during hospitalization. These findings highlight the importance of considering the potential impact of chronic T2D treatment regiments on COVID-19 and the need for further studies to elucidate the underlying mechanisms.

Overview of the cardio-metabolic impact of the COVID-19 pandemic

Evidence has shown that cardiometabolic disorders (CMDs) are amongst the top contributors to COVID-19 infection morbidity and mortality. The reciprocal impact of COVID-19 infection and the most common CMDs, the risk factors for poor composite outcome among patients with one or several underlying diseases, the effect of common medical management on CMDs and their safety in the context of acute COVID-19 infection are reviewed. Later on, the changes brought by the COVID-19 pandemic quarantine on the general population's lifestyle (diet, exercise patterns) and metabolic health, acute cardiac complications of different COVID-19 vaccines and the effect of CMDs on the vaccine efficacy are discussed. Our review identified that the incidence of COVID-19 infection is higher among patients with underlying CMDs such as hypertension, diabetes, obesity and cardiovascular disease. Also, CMDs increase the risk of COVID-19 infection progression to severe disease phenotypes (e.g. hospital and/or ICU admission, use of mechanical ventilation). Lifestyle modification during COVID-19 era had a great impact on inducing and worsening of CMDs. Finally, the lower efficacy of COVID-19 vaccines was found in patients with metabolic disease.

Role of antidiabetic agents in type 2 diabetes patients with chronic kidney disease

Insulin resistance is a condition in which the target tissues have a decreased response to insulin signaling, resulting in glucose uptake defect, and an increased blood sugar level. Pancreatic beta cells thus enhance insulin production to compensate. This situation may cause further beta cell dysfunction and failure, which can lead diabetes mellitus (DM). Insulin resistance is thus an important cause of the development of type 2 DM. Insulin resistance has also been found to have a strong relationship with cardiovascular disease and is common in chronic kidney disease (CKD) patients. The mechanisms of insulin resistance in CKD are complex and multifactorial. They include physical inactivity, inflammation and oxidative stress, metabolic acidosis, vitamin D deficiency, adipose tissue dysfunction, uremic toxins, and renin-angiotensin-aldosterone system activation. Currently, available anti-diabetic agents, such as biguanides, sulfonylureas, thiazolidinediones, alfa-glucosidase inhibitors, glucagon-like peptide-1-based agents, and sodium-glucose co-transporter-2 inhibitors, have different effects on insulin resistance. In this short review, we describe the potential mechanisms of insulin resistance in CKD patients. We also review the interaction of currently available anti-diabetic medications with insulin resistance.

FFA-Fetuin-A regulates DPP-IV expression in pancreatic beta cells through TLR4-NFkB pathway

Dipeptidyl peptidase 4 (DPP-IV) is a ubiquitous proteolytic enzyme that cleaves incretin hormones, such as glucagon-like peptide 1 (GLP1) and gastric inhibitory protein (GIP), leading to reduced glucose stimulated insulin secretion from the pancreatic beta cells. The functionally active enzyme is present in a membrane bound form in several cell types as well as in a soluble form in the circulation. The present report deals with DPP-IV expression and its regulation in the pancreatic beta cells in presence of free fatty acids (FFAs) and Fetuin-A, a circulatory glycoprotein associated with insulin resistance in humans and animals. FFA and Fetuin-A individually or in combination trigger DPP-IV expression in MIN6 cells. Islets isolated from high fat diet fed (HFD) mice (16 weeks) showed higher levels of DPP-IV expression than standard diet (SD) fed mice. Fetuin-A increased DPP-IV expression in HFD mice (4 weeks). Inhibition of TLR4 or NFkB prevented palmitate-Fetuin-A mediated DPP-IV expression in MIN6. It has been seen that Fetuin-A alone also could trigger DPP-IV expression in MIN6 cells via NFkB. Additionally, palmitate treatment exhibited reduced level of soluble DPP-IV in the media of MIN6 culture, which corroborated with the expression pattern of its protease, KLK5 that cleaves and releases the membrane bound DPP-IV into the secretion. Our results demonstrate that FFA-Fetuin-A upregulates DPP-IV expression in the pancreatic beta cells through the TLR4-NFkB pathway.

COVID-19: Diabetes Perspective-Pathophysiology and Management

Recent evidence relating to the impact of COVID-19 on people with diabetes is limited but continues to emerge. COVID-19 pneumonia is a newly identified illness spreading rapidly throughout the world and causes many disabilities and fatal deaths. Over the ensuing 2 years, the indirect effects of the pandemic on healthcare delivery have become prominent, along with the lingering effects of the virus on those directly infected. Diabetes is a commonly identified risk factor that contributes not only to the severity and mortality of COVID-19 patients, but also to the associated complications, including acute respiratory distress syndrome (ARDS) and multi-organ failure. Diabetic patients are highly affected due to increased viral entry into the cells and decreased immunity. Several hypotheses to explain the increased incidence and severity of COVID-19 infection in people with diabetes have been proposed and explained in detail recently. On the other hand, 20-50% of COVID-19 patients reported new-onset hyperglycemia without diabetes and new-onset diabetes, suggesting the two-way interactions between COVID-19 and diabetes. A systematic review is required to confirm diabetes as a complication in those patients diagnosed with COVID-19. Diabetes and diabetes-related complications in COVID-19 patients are primarily due to the acute illness caused during the SARS-CoV-2 infection followed by the release of glucocorticoids, catecholamines, and pro-inflammatory cytokines, which have been shown to drive hyperglycemia positively. This review provides brief insights into the potential mechanisms linking COVID-19 and diabetes, and presents clinical management recommendations for better handling of the disease.

Hepatocyte-derived DPP4 regulates portal GLP-1 bioactivity, modulates glucose production, and when absent influences NAFLD progression

Elevated circulating dipeptidyl peptidase-4 (DPP4) is a biomarker for liver disease, but its involvement in gluconeogenesis and metabolic associated fatty liver disease progression remains unclear. Here, we identified that DPP4 in hepatocytes but not TEK receptor tyrosine kinase-positive endothelial cells regulates the local bioactivity of incretin hormones and gluconeogenesis. However, the complete absence of DPP4 (Dpp4-/-) in aged mice with metabolic syndrome accelerates liver fibrosis without altering dyslipidemia and steatosis. Analysis of transcripts from the livers of Dpp4-/- mice displayed enrichment for inflammasome, p53, and senescence programs compared with littermate controls. High-fat, high-cholesterol feeding decreased Dpp4 expression in F4/80+ cells, with only minor changes in immune signaling. Moreover, in a lean mouse model of severe nonalcoholic fatty liver disease, phosphatidylethanolamine N-methyltransferase mice, we observed a 4-fold increase in circulating DPP4, in contrast with previous findings connecting DPP4 release and obesity. Last, we evaluated DPP4 levels in patients with hepatitis C infection with dysglycemia (Homeostatic Model Assessment of Insulin Resistance > 2) who underwent direct antiviral treatment (with/without ribavirin). DPP4 protein levels decreased with viral clearance; DPP4 activity levels were reduced at long-term follow-up in ribavirin-treated patients; but metabolic factors did not improve. These data suggest elevations in DPP4 during hepatitis C infection are not primarily regulated by metabolic disturbances.

Dipeptidyl peptidase 4(DPP4) inhibitors stride up the management of Parkinson's disease

Parkinson's disease (PD) is the 2^nd most common age-related hypokinetic disorder, characterized by dopaminergic degeneration and movement abnormalities. Dopaminergic degeneration in the basal ganglia is primarily seen in PD patients. The therapeutic strategies currently under investigation are to rescue dopaminergic degeneration and promote neuronal regeneration, which could halt disease progression. On the other hand, the therapeutic efficacy of existing drugs used in other disorders has been repurposed in neurodegenerative pathologies. DPP4 inhibitors widely used in treating diabetes have been considered viable target sites and are being tested for efficacy in neurodegenerative pathologies. DPP4 inhibitors have been reported to rescue neuronal degeneration and improve motor functions in various preclinical and clinical PD studies. The current review is focused on the neuroprotective potential, molecular mechanisms and therapeutic potential of DPP4 inhibitors in PD pathology.

DPP4 Inhibitors: Could they be One of the Solutions for COVID-19 Patients with Prediabetes?

Recent reports suggest that prediabetes is a risk factor for developing severe COVID-19 complications through underlying mechanisms involving undiagnosed sub-clinical inflammation. However, we remain without a clinical approach for managing COVID-19 in prediabetic cases. The subclinical inflammation in prediabetes is associated with elevated DPP4 levels and activity. DPP4 has pleiotropic actions, including glycaemia regulation and immuno-modulation. Recently, DPP4 has been recognised as a co-receptor for COVID-19 for entering host cells. In addition to improving glycaemia, DPP4 inhibition is associated with reduced inflammation. In this submission, we explore the potential use of DPP4 inhibitors as therapeutic agents for prediabetic patients in managing the deleterious effects of COVID-19. DPP4 inhibitors (gliptins), such as linagliptin and sitagliptin, have therapeutic effects, which have been shown to extend beyond glycaemic control with no risk of hypoglycaemia. By the nature of their mechanism of action, gliptins are not associated with hypoglycaemia, unlike their anti-glycaemic counterparts, as they mainly target postprandial glycaemia. Moreover, DPP4 inhibitors may represent a safer option for prediabetic individuals in managing prediabetes either as a prophylactic or curative treatment for COVID-19. We envisage that beyond improved glycaemic control, the use of DPP4 inhibitors would also alleviate the cytokine storm, resulting in a reduction in the severity of COVID-19 symptoms and consequently reducing the morbidity and mortality in prediabetic COVID- 19 patients.

Expression Profile of Sphingosine Kinase 1 Isoforms in Human Cancer Tissues and Cells: Importance and Clinical Relevance of the Neglected 1b-Isoform

Background

Overexpression of sphingosine kinase 1 (SphK1) is casually associated with many types of cancer, and inhibitors of SphK1 sensitize tumors to chemotherapy. SphK1 is expressed as two major isoforms, SphK1a and SphK1b. To date, no information has been reported on the SphK1 isoform expression profile and its clinical relevance.

Objective

The objective is to examine the expression profile of the SphK1a and SPhK1b isoforms in human cancer and noncancer tissues and cell lines and explore their clinical relevance.

Methods

We used PCR to qualitatively examine the expression profile of these two isoforms in breast, liver, and prostate cancer tissues plus paired adjacent tissues and in 11 cancer and normal cell lines (breast, cervical, bone, prostate, colon, brain, mesothelioma tumor and benign, and human kidney cells).

Results

We found that SphK1a was ubiquitously expressed in all cancer cells and tissues tested; in contrast, SphK1b was only expressed in selective cell types in breast, prostate, and lung cancer.

Conclusions

Our data suggest that SphK1a is important for generic SphK1/S1P functions, and SphK1b mediates specialized and/or unique pathways in a specific type of tissue and could be a biomarker for cancer. This discovery is important for future SphK1-related cancer research and may have clinical implications in drug development associated with SphK1-directed cancer treatment.

Critical Review for the Production of Antidiabetic Peptides by a Bibliometric Approach

The current bibliometric review evaluated recent papers that researched dietary protein sources to generate antidiabetic bioactive peptides/hydrolysates for the management of diabetes. Scopus and PubMed databases were searched to extract bibliometric data and, after a systematic four-step process was performed to select the articles, 75 papers were included in this review. The countries of origin of the authors who published the most were China (67%); Ireland (59%); and Spain (37%). The journals that published most articles on the subject were Food Chemistry (n = 12); Food & Function (n = 8); and Food Research International (n = 6). The most used keywords were ‘bioactive peptides’ (occurrence 28) and ‘antidiabetic’ (occurrence 10). The most used enzymes were Alcalase^® (17%), Trypsin (17%), Pepsin, and Flavourzyme^® (15% each). It was found that different sources of protein have been used to generate dipeptidyl peptidase IV (DPP-IV), α-amylase, and α-glucosidase inhibitory peptides. In addition to antidiabetic properties, some articles (n = 30) carried out studies on multifunctional bioactive peptides, and the most cited were reported to have antioxidant and antihypertensive activities (n = 19 and 17, respectively). The present review intended to offer bibliometric data on the most recent research on the production of antidiabetic peptides from dietary proteins to those interested in their obtention to act as hypoglycemic functional ingredients. The studies available in this period, compiled, are not yet enough to point out the best strategies for the production of antidiabetic peptides from food proteins and a more systematic effort in this direction is necessary to allow a future scale-up for the production of these possible functional ingredients.

DPP4 as a Potential Candidate in Cardiovascular Disease

The rising prevalence of cardiovascular disease has become a global health concern. The occurrence of cardiovascular disease is the result of long-term interaction of many risk factors, one of which is diabetes. As a novel anti-diabetic drug, DPP4 inhibitor has been proven to be cardiovascular safe in five recently completed cardiovascular outcome trials. Accumulating studies suggest that DPP4 inhibitor has potential benefits in a variety of cardiovascular diseases, including hypertension, calcified aortic valve disease, coronary atherosclerosis, and heart failure. On the one hand, in addition to improving blood glucose control, DPP4 inhibitor is involved in controlling cardiovascular risk factors. On the other hand, DPP4 inhibitor directly regulates the occurrence and progression of cardiovascular diseases through a variety of mechanisms. In this review, we summarize the recent advances of DPP4 in cardiovascular disease, aiming to discuss DPP4 inhibitor as a potential option for cardiovascular therapy.

Role of Dipeptidyl Peptidase-4 (DPP4) on COVID-19 Physiopathology

DPP4/CD26 is a single-pass transmembrane protein with multiple functions on glycemic control, cell migration and proliferation, and the immune system, among others. It has recently acquired an especial relevance due to the possibility to act as a receptor or co-receptor for SARS-CoV-2, as it has been already demonstrated for other coronaviruses. In this review, we analyze the evidence for the role of DPP4 on COVID-19 risk and clinical outcome, and its contribution to COVID-19 physiopathology. Due to the pathogenetic links between COVID-19 and diabetes mellitus and the hyperinflammatory response, with the hallmark cytokine storm developed very often during the disease, we dive deep into the functions of DPP4 on carbohydrate metabolism and immune system regulation. We show that the broad spectrum of functions regulated by DPP4 is performed both as a protease enzyme, as well as an interacting partner of other molecules on the cell surface. In addition, we provide an update of the DPP4 inhibitors approved by the EMA and/or the FDA, together with the newfangled approval of generic drugs (in 2021 and 2022). This review will also cover the effects of DPP4 inhibitors (i.e., gliptins) on the progression of SARS-CoV-2 infection, showing the role of DPP4 in this disturbing disease.

Distal mutation V486M disrupts the catalytic activity of DPP4 by affecting the flap of the propeller domain

Dipeptidyl peptidase-4 (DPP4) plays a crucial role in regulating the bioactivity of glucagon-like peptide-1 (GLP-1) that enhances insulin secretion and pancreatic β-cell proliferation, making it a therapeutic target for type 2 diabetes. Although the crystal structure of DPP4 has been determined, its structure-function mechanism is largely unknown. Here, we examined the biochemical properties of sporadic human DPP4 mutations distal from its catalytic site, among which V486M ablates DPP4 dimerization and causes loss of enzymatic activity. Unbiased molecular dynamics simulations revealed that the distal V486M mutation induces a local conformational collapse in a β-propeller loop (residues 234-260, defined as the flap) and disrupts the dimerization of DPP4. The "open/closed" conformational transitions of the flap whereby capping the active site, are involved in the enzymatic activity of DPP4. Further site-directed mutagenesis guided by theoretical predictions verified the importance of the conformational dynamics of the flap for the enzymatic activity of DPP4. Therefore, the current studies that combined theoretical modeling and experimental identification, provide important insights into the biological function of DPP4 and allow for the evaluation of directed DPP4 genetic mutations before initiating clinical applications and drug development.

Trends in insulin resistance: insights into mechanisms and therapeutic strategy

The centenary of insulin discovery represents an important opportunity to transform diabetes from a fatal diagnosis into a medically manageable chronic condition. Insulin is a key peptide hormone and mediates the systemic glucose metabolism in different tissues. Insulin resistance (IR) is a disordered biological response for insulin stimulation through the disruption of different molecular pathways in target tissues. Acquired conditions and genetic factors have been implicated in IR. Recent genetic and biochemical studies suggest that the dysregulated metabolic mediators released by adipose tissue including adipokines, cytokines, chemokines, excess lipids and toxic lipid metabolites promote IR in other tissues. IR is associated with several groups of abnormal syndromes that include obesity, diabetes, metabolic dysfunction-associated fatty liver disease (MAFLD), cardiovascular disease, polycystic ovary syndrome (PCOS), and other abnormalities. Although no medication is specifically approved to treat IR, we summarized the lifestyle changes and pharmacological medications that have been used as efficient intervention to improve insulin sensitivity. Ultimately, the systematic discussion of complex mechanism will help to identify potential new targets and treat the closely associated metabolic syndrome of IR.

TNF-α/IFN-γ synergy amplifies senescence-associated inflammation and SARS-CoV-2 receptor expression via hyper-activated JAK/STAT1

Older age and underlying conditions such as diabetes/obesity or immunosuppression are leading host risk factors for developing severe complications from COVID-19 infection. The pathogenesis of COVID-19-related cytokine storm, tissue damage, and fibrosis may be interconnected with fundamental aging processes, including dysregulated immune responses and cellular senescence. Here, we examined effects of key cytokines linked to cellular senescence on expression of SARS-CoV-2 viral entry receptors. We found exposure of human umbilical vein endothelial cells (HUVECs) to the inflammatory cytokines, TNF-α + IFN-γ or a cocktail of TNF-α + IFN-γ + IL-6, increased expression of ACE2/DPP4, accentuated the pro-inflammatory senescence-associated secretory phenotype (SASP), and decreased cellular proliferative capacity, consistent with progression towards a cellular senescence-like state. IL-6 by itself failed to induce substantial effects on viral entry receptors or SASP-related genes, while synergy between TNF-α and IFN-γ initiated a positive feedback loop via hyper-activation of the JAK/STAT1 pathway, causing SASP amplification. Breaking the interactive loop between senescence and cytokine secretion with JAK inhibitor ruxolitinib or antiviral drug remdesivir prevented hyper-inflammation, normalized SARS-CoV-2 entry receptor expression, and restored HUVECs proliferative capacity. This loop appears to underlie cytokine-mediated viral entry receptor activation and links with senescence and hyper-inflammation.

Optical genome mapping identifies rare structural variations as predisposition factors associated with severe COVID-19

Impressive global efforts have identified both rare and common gene variants associated with severe COVID-19 using sequencing technologies. However, these studies lack the sensitivity to accurately detect several classes of variants, especially large structural variants (SVs), which account for a substantial proportion of genetic diversity including clinically relevant variation. We performed optical genome mapping on 52 severely ill COVID-19 patients to identify rare/unique SVs as decisive predisposition factors associated with COVID-19. We identified 7 SVs involving genes implicated in two key host-viral interaction pathways: innate immunity and inflammatory response, and viral replication and spread in nine patients, of which SVs in STK26 and DPP4 genes are the most intriguing candidates. This study is the first to systematically assess the potential role of SVs in the pathogenesis of COVID-19 severity and highlights the need to evaluate SVs along with sequencing variants to comprehensively associate genomic information with interindividual variability in COVID-19 phenotypes.

Discovery of tight-binding competitive inhibitors of dipeptidyl peptidase IV

Dipeptidyl peptidase IV (DPP-IV, EC 3.4.14.5) is an abundant serine aminopeptidase that preferentially cleaves N-terminal Xaa-Pro or Xaa-Ala dipeptides from oligopeptides. Inhibitors of DPP-IV activity are used for treating type 2 diabetes mellitus and other diseases. DPP-IV is also involved in tumor progression. We identified four new non-peptide tight-binding competitive inhibitors of porcine DPP-IV by virtual screening and enzymatic assays. Molecular docking simulations supported the competitive behavior, and the selectivity of one of the compounds in the DPP-IV family. Since three of these inhibitors are also aminopeptidase N (APN) inhibitors, we tested their impact on APN+/DPP-IV+ and DPP-IV+ human tumor cells' viability. Using kinetic assays, we determined that HL-60 tumor cells express both APN and DPP-IV activities and that MDA-MB-231 tumor cells express DPP-IV activity. The inhibitors had a slight inhibitory effect on human HEK-293 cell viability but reduced the viability of APN+/DPP-IV+ and DPP-IV+ human tumor cells more potently. Remarkably, the intraperitoneal injection of these compounds inhibited DPP-IV activity in rat brain, liver, and pancreas. In silico studies suggested inhibitors binding to serum albumin contribute to blood-brain barrier crossing. The spectrum of action of some of these compounds may be useful for niche applications.

Potential Effect of DPP-4 Inhibitors Towards Hepatic Diseases and Associated Glucose Intolerance

Dipeptidyl-peptidase-4 (DPP-4) is an enzyme having various properties and physiological roles in lipid accumulation, resistance to anticancer agents, and immune stimulation. DPP-4 includes membrane-bound peptidases and is a kind of enzyme that cleaves alanine or proline-containing peptides such as incretins, chemokines, and appetite-suppressing hormones (neuropeptide) at their N-terminal dipeptides. DPP-4 plays a role in the final breakdown of peptides produced by other endo and exo-peptidases from nutritious proteins and their absorption in these tissues. DPP-4 enzyme activity has different modes of action on glucose metabolism, hunger regulation, gastrointestinal motility, immune system function, inflammation, and pain regulation. According to the literature survey, as DPP-4 levels increase in individuals with liver conditions, up-regulation of hepatic DPP-4 expression is likely to be the cause of glucose intolerance or insulin resistance. This review majorly focuses on the cleavage of alanine or proline-containing peptides such as incretins by the DPP-4 and its resulting conditions like glucose intolerance and cause of DPP-4 level elevation due to some liver conditions. Thus, we have discussed the various effects of DPP-4 on the liver diseases like hepatitis C, non-alcoholic fatty liver, hepatic regeneration and stem cell, hepatocellular carcinoma, and the impact of elevated DPP-4 levels in association with liver diseases as a cause of glucose intolerance and their treatment drug of choices. In addition, the effect of DPP-4 inhibitors on obesity and their negative aspects are also discussed in brief.

Systemic DPP4/CD26 is associated with natural HIV-1 control: Implications for COVID-19 susceptibility

The current intersection of the COVID-19 and HIV-1 pandemics, has raised concerns about the risk for poor COVID-19 outcomes particularly in regions like sub-Saharan Africa, disproportionally affected by HIV. DPP4/CD26 has been suggested to be a potential therapeutic target and a biomarker for risk in COVID-19 patients with high risk co-morbidities. We therefore evaluated soluble DPP4 (sDPP4) levels and activity in plasma of 131 HIV-infected and 20 HIV-uninfected South African individuals. Flow cytometry was performed to compare cell surface expression of DPP4/CD26 and activation markers on peripheral blood mononuclear cells of extreme clinical phenotypes. Progressors had lower specific DPP4 activity and lower frequency of CD3+ T-cells expressing CD26 than HIV-1 controllers, but more activated CD3+CD26+ T-cells. The frequency of CD26-expressing T-cells negatively correlated with HLA-DR+ and CD38+ T-cells. Divergent DPP4/CD26 expression between HIV-1 controllers and progressors may have implications for risk and treatment of COVID-19 in people living with HIV.

Anti-fibrotic activity of sitagliptin against concanavalin A-induced hepatic fibrosis. Role of Nrf2 activation/NF-κB inhibition

Sitagliptin is known for its anti-diabetic activity though it has other pleiotropic pharmacological actions. Its effect against concanavalin A (Con A)-induced hepatic fibrosis has not been investigated yet. Our target was to test whether sitagliptin can suppress the development of Con A-induced hepatic fibrosis and if so, what are the mechanisms involved? Con A (6 mg/kg) was injected once weekly to male Swiss albino mice for four weeks. Sitagliptin was daily administered concurrently with Con A. Results have shown the potent hepatoprotective activity of sitagliptin against Con A-induced hepatitis and fibrosis. That was evident through the amelioration of hepatotoxicity serum parameters (ALT, AST, ALP, and LDH) and the increase in the level of serum albumin in sitagliptin treated mice. Simultaneously, there was amendment of the Con A-induced hepatic lesions and repression of fibrosis in sitagliptin-treated animals. Hydroxyproline, collagen content and the immuno-expression of the fibrotic markers, TGF-β and α-SMA were depressed upon sitagliptin treatment. Sitagliptin suppressed Con A-induced oxidative stress and increased antioxidants. RT-PCR analysis showed enhancement of mRNA expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and its target genes (GCLc, GCLm, NQO-1, HO-1) by sitagliptin. Furthermore, sitagliptin ameliorated the level and immuno-expression of nuclear factor kappa-B (NF-κB) alongside the immuno-expression of the inflammatory cytokine, TNF-α. Taken together, this study demonstrates the hepatoprotective activity of sitagliptin which may be in part related to enhancement of Nrf2 signaling pathway and inhibition of NF-κB which interact inflammatory response in liver. Sitagliptin might be a new candidate to suppress hepatitis-associated fibrosis.

Using Dictyostelium to Develop Therapeutics for Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) involves damage to lungs causing an influx of neutrophils from the blood into the lung airspaces, and the neutrophils causing further damage, which attracts more neutrophils in a vicious cycle. There are ∼190,000 cases of ARDS per year in the US, and because of the lack of therapeutics, the mortality rate is ∼40%. Repelling neutrophils out of the lung airspaces, or simply preventing neutrophil entry, is a potential therapeutic. In this minireview, we discuss how our lab noticed that a protein called AprA secreted by growing Dictyostelium cells functions as a repellent for Dictyostelium cells, causing cells to move away from a source of AprA. We then found that AprA has structural similarity to a human secreted protein called dipeptidyl peptidase IV (DPPIV), and that DPPIV is a repellent for human neutrophils. In animal models of ARDS, inhalation of DPPIV or DPPIV mimetics blocks neutrophil influx into the lungs. To move DPPIV or DPPIV mimetics into the clinic, we need to know how this repulsion works to understand possible drug interactions and side effects. Combining biochemistry and genetics in Dictyostelium to elucidate the AprA signal transduction pathway, followed by drug studies in human neutrophils to determine similarities and differences between neutrophil and Dictyostelium chemorepulsion, will hopefully lead to the safe use of DPPIV or DPPIV mimetics in the clinic.

Macrophage Responses to Environmental Stimuli During Homeostasis and Disease

Work over the last 40 years has described macrophages as a heterogeneous population that serve as the frontline surveyors of tissue immunity. As a class, macrophages are found in almost every tissue in the body and as distinct populations within discrete microenvironments in any given tissue. During homeostasis, macrophages protect these tissues by clearing invading foreign bodies and/or mounting immune responses. In addition to varying identities regulated by transcriptional programs shaped by their respective environments, macrophage metabolism serves as an additional regulator to temper responses to extracellular stimuli. The area of research known as "immunometabolism" has been established within the last decade, owing to an increase in studies focusing on the crosstalk between altered metabolism and the regulation of cellular immune processes. From this research, macrophages have emerged as a prime focus of immunometabolic studies, although macrophage metabolism and their immune responses have been studied for centuries. During disease, the metabolic profile of the tissue and/or systemic regulators, such as endocrine factors, become increasingly dysregulated. Owing to these changes, macrophage responses can become skewed to promote further pathophysiologic changes. For instance, during diabetes, obesity, and atherosclerosis, macrophages favor a proinflammatory phenotype; whereas in the tumor microenvironment, macrophages elicit an anti-inflammatory response to enhance tumor growth. Herein we have described how macrophages respond to extracellular cues including inflammatory stimuli, nutrient availability, and endocrine factors that occur during and further promote disease progression.

Therapy of Type 2 Diabetes in Patients with SARS-CoV-2 Infection

COVID-19 infection poses an important clinical therapeutic problem, especially in patients with coexistent diseases such as type 2 diabetes. Potential pathogenetic links between COVID-19 and diabetes include inflammation, effects on glucose homeostasis, haemoglobin deoxygenation, altered immune status and activation of the renin-angiotensin-aldosterone system (RAAS). Moreover, drugs often used in the clinical care of diabetes (dipeptidyl peptidase 4 inhibitors, glucagon-like peptide 1 receptor agonists, sodium-glucose cotransporter 2 inhibitors, metformin and insulin) may influence the course of SARS-CoV-2 infection, so it is very important to verify their effectiveness and safety. This review summarises the new advances in diabetes therapy and COVID-19 and provides clinical recommendations that are essential for medical doctors and for patients suffering from type 2 diabetes.

Anti-inflammatory Effects of Empagliflozin and Gemigliptin on LPS-Stimulated Macrophage via the IKK/NF-κB, MKK7/JNK, and JAK2/STAT1 Signalling Pathways

Background

Sodium-glucose cotransporter 2 (SGLT2) and dipeptidyl peptidase-4 (DPP-4) inhibitors are glucose-lowering drugs whose anti-inflammatory properties have recently become useful in tackling metabolic syndromes in chronic inflammatory diseases, including diabetes and obesity. We investigated whether empagliflozin (SGLT2 inhibitor) and gemigliptin (DPP-4 inhibitor) improve inflammatory responses in macrophages, identified signalling pathways responsible for these effects, and studied whether the effects can be augmented with dual empagliflozin and gemigliptin therapy.

Methods

RAW 264.7 macrophages were first stimulated with lipopolysaccharide (LPS), then cotreated with empagliflozin, gemigliptin, or empagliflozin plus gemigliptin. We conducted quantitative RT-PCR (qRT-PCR) to determine the most effective anti-inflammatory doses without cytotoxicity. We performed ELISA and qRT-PCR for inflammatory cytokines and chemokines and flow cytometry for CD80, the M1 macrophage surface marker, to evaluate the anti-inflammatory effects of empagliflozin and gemigliptin. NF-κB, MAPK, and JAK2/STAT signalling pathways were examined via Western blotting to elucidate the molecular mechanisms of anti-inflammation.

Results

LPS-stimulated CD80⁺ M1 macrophages were suppressed by coincubation with empagliflozin, gemigliptin, and empagliflozin plus gemigliptin, respectively. Empagliflozin and gemigliptin (individually and combined) inhibited prostaglandin E₂ (PGE₂) release and COX-2, iNOS gene expression in LPS-stimulated RAW 264.7 macrophages. These three treatments also attenuated the secretion and mRNA expression of proinflammatory cytokines, such as TNF-α, IL-1β, IL-6, and IFN-γ, and proinflammatory chemokines, such as CCL3, CCL4, CCL5, and CXCL10. All of them blocked NF-κB, JNK, and STAT1/3 phosphorylation through IKKα/β, MKK4/7, and JAK2 signalling.

Conclusions

Our study demonstrated the anti-inflammatory effects of empagliflozin and gemigliptin via IKK/NF-κB, MKK7/JNK, and JAK2/STAT1 pathway downregulation in macrophages. In all cases, combined empagliflozin and gemigliptin treatment showed greater anti-inflammatory properties.

DPP-4 inhibitors may improve the mortality of coronavirus disease 2019: A meta-analysis

Aims

DPP-4 inhibitors are predicted to exert a protective effect on the progression of coronavirus disease 2019 (COVID-19). We conducted this meta-analysis to investigate this hypothesis.

Methods

Four databases, namely, PubMed, Web of Science, EMBASE and the Cochrane Library, were used to identify studies on DPP-4 and COVID-19. The outcome indicators were the mortality of COVID-19. Funnel plots, Begg’s tests and Egger’s tests were used to assess publication bias.

Results

Four articles were included with a total of 1933 patients with COVID-19 and type 2 diabetes. The use of DPP-4 inhibitors was negatively associated with the risk of mortality (odds ratio (OR) = 0.58 95% confidence interval (CI), 0.34–0.99).

Conclusions

DPP-4 inhibitors may improve the mortality of patients with COVID-19 and type 2 diabetes. As few relevant studies are available, more large-scale studies need to be performed.

A Non-Perturbative Molecular Grafting Strategy for Stable and Potent Therapeutic Peptide Ligands

The gut-derived incretin hormone, glucagon-like peptide-1 (GLP1), plays an important physiological role in attenuating post-prandial blood glucose excursions in part by amplifying pancreatic insulin secretion. Native GLP1 is rapidly degraded by the serine protease, dipeptidyl peptidase-4 (DPP4); however, enzyme-resistant analogues of this 30-amino-acid peptide provide an effective therapy for type 2 diabetes (T2D) and can curb obesity via complementary functions in the brain. In addition to its medical relevance, the incretin system provides a fertile arena for exploring how to better separate agonist function at cognate receptors versus susceptibility of peptides to DPP4-induced degradation. We have discovered that novel chemical decorations can make GLP1 and its analogues completely DPP4 resistant while fully preserving GLP1 receptor activity. This strategy is also applicable to other therapeutic ligands, namely, glucose-dependent insulinotropic polypeptide (GIP), glucagon, and glucagon-like peptide-2 (GLP2), targeting the secretin family of receptors. The versatility of the approach offers hundreds of active compounds based on any template that target these receptors. These observations should allow for rapid optimization of pharmacological properties and because the appendages are in a position crucial to receptor stimulation, they proffer the possibility of conferring "biased" signaling and in turn minimizing side effects.

Evidence for the existence and potential roles of intra-islet glucagon-like peptide-1

Glucagon-Like Peptide-1 (GLP-1) is an important peptide hormone secreted by L-cells in the gastrointestinal tract in response to nutrients. It is produced by the differential cleavage of the proglucagon peptide. GLP-1 elicits a wide variety of physiological responses in many tissues that contribute to metabolic homeostasis. For these reasons, therapies designed to either increase endogenous GLP-1 levels or introduce exogenous peptide mimetics are now widely used in the management of diabetes. In addition to GLP-1 production from L-cells, recent reports suggest that pancreatic islet alpha cells may also synthesize and secrete GLP-1. Intra-islet GLP-1 may therefore play an unappreciated role in islet health and glucose regulation, suggesting a potential functional paracrine role for islet-derived GLP-1. In this review, we assess the current literature from an islet-centric point-of-view to better understand the production, degradation, and actions of GLP-1 within the endocrine pancreas in rodents and humans. The relevance of intra-islet GLP-1 in human physiology is discussed regarding the potential role of intra-islet GLP-1 in islet health and dysfunction.

Perspectives of Antidiabetic Drugs in Diabetes With Coronavirus Infections

Diabetes mellitus (DM) increases the risk of viral infections especially during the period of poor glycemic controls. Emerging evidence has reported that DM is one of the most common comorbidities in the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) infection, also referred to as COVID-19. Moreover, the management and therapy are complex for individuals with diabetes who are acutely unwell with suspected or confirmed COVID-19. Here, we review the role of antidiabetic agents, mainly including insulin, metformin, pioglitazone, dipeptidyl peptidase-4 (DPP4) inhibitors, sodium-glucose cotransporter 2 (SGLT2) inhibitors, and glucagon-like peptide 1 (GLP-1) receptor agonists in DM patients with coronavirus infection, addressing the clinical therapeutic choices for these subjects.

Circadian Rhythm in Adipose Tissue: Novel Antioxidant Target for Metabolic and Cardiovascular Diseases

Obesity is a major risk factor for most metabolic and cardiovascular disorders. Adipose tissue is an important endocrine organ that modulates metabolic and cardiovascular health by secreting signaling molecules. Oxidative stress is a common mechanism associated with metabolic and cardiovascular complications including obesity, type 2 diabetes, and hypertension. Oxidative stress can cause adipose tissue dysfunction. Accumulating data from both humans and experimental animal models suggest that adipose tissue function and oxidative stress have an innate connection with the intrinsic biological clock. Circadian clock orchestrates biological processes in adjusting to daily environmental changes according to internal or external cues. Recent studies have identified the genes and molecular pathways exhibiting circadian expression patterns in adipose tissue. Disruption of the circadian rhythmicity has been suggested to augment oxidative stress and aberrate adipose tissue function and metabolism. Therefore, circadian machinery in the adipose tissue may be a novel therapeutic target for the prevention and treatment of metabolic and cardiovascular diseases. In this review, we summarize recent findings on circadian rhythm and oxidative stress in adipose tissue, dissect the key components that play a role in regulating the clock rhythm, oxidative stress and adipose tissue function, and discuss the potential use of antioxidant treatment on metabolic and cardiovascular diseases by targeting the adipose clock.

Neuropeptide Y Is an Immunomodulatory Factor: Direct and Indirect

Neuropeptide Y (NPY), which is widely distributed in the nervous system, is involved in regulating a variety of biological processes, including food intake, energy metabolism, and emotional expression. However, emerging evidence points to NPY also as a critical transmitter between the nervous system and immune system, as well as a mediator produced and released by immune cells. In vivo and in vitro studies based on gene-editing techniques and specific NPY receptor agonists and antagonists have demonstrated that NPY is responsible for multifarious direct modulations on immune cells by acting on NPY receptors. Moreover, via the central or peripheral nervous system, NPY is closely connected to body temperature regulation, obesity development, glucose metabolism, and emotional expression, which are all immunomodulatory factors for the immune system. In this review, we focus on the direct role of NPY in immune cells and particularly discuss its indirect impact on the immune response.

Soluble Dipeptidyl Peptidase-4 Induces Fibroblast Activation Through Proteinase-Activated Receptor-2

Fibroblasts are the chief secretory cells of the extracellular matrix (ECM) responsible for basal deposition and degradation of the ECM under normal conditions. During stress, fibroblasts undergo continuous activation, which is defined as the differentiation of fibroblasts into myofibroblasts, a cell type with an elevated capacity for secreting ECM proteins. Dipeptidyl peptidase-4 (DPP4) is a ubiquitously expressed transmembrane glycoprotein and exerts effects that are both dependent and independent of its enzymatic activity. DPP4 has been demonstrated to define fibroblast populations in human skin biopsies of systemic sclerosis. Shedding of DPP4 from different tissues into the circulation appears to be involved in the pathogenesis of the diseases. The mechanism underlying soluble DPP4–induced dermal fibrosis has not been clearly determined. The effects of DPP4 on murine 3T3 fibroblasts and human dermal fibroblasts were evaluated by measuring the expression of fibrotic proteins, such as α-SMA and collagen. Soluble DPP4 stimulated the activation of fibroblasts in a dose-dependent manner by activating nuclear factor-kappa B (NF-κB) and suppressor of mothers against decapentaplegic (SMAD) signaling. Blocking proteinase-activated receptor-2 (PAR2) abrogated the DPP4-induced activation of NF-κB and SMAD and expression of fibrosis-associated proteins in fibroblasts. Linagliptin, a clinically available DPP4 inhibitor, was observed to abrogate the soluble DPP4–induced expression of fibrotic proteins. This study demonstrated the mechanism underlying soluble DPP4, which activated NF-κB and SMAD signaling through PAR2, leading to fibroblast activation. Our data extend the current view of soluble DPP4. Elevated levels of circulating soluble DPP4 may contribute to one of the mediators that induce dermal fibrosis in patients.

Circulating levels of soluble Dipeptidylpeptidase-4 are reduced in human subjects hospitalized for severe COVID-19 infections

Dipeptidylpeptidase (DPP)-4 is a key regulator of the incretin system. For several years DPP-4 inhibitors in addition to GLP-1 analogues are of major importance in the clinical management of obesity and type 2 diabetes. DPP-4 is also known as CD26 and represents a membrane bound protease on the surface of several eukaryotic cell types. Of interest, DPP-4, like ACE2, has been shown to serve as a binding partner for corona-like viruses to enter host immune cells. Since metabolic diseases are major risk factors for the present COVID-19 pandemic, we examined circulating soluble DPP-4 serum concentrations in patients suffering from severe COVID-19 infection and in healthy human subjects in a case control design. In this analysis sDPP-4 levels were significantly lower in COVID-19 patients compared to controls (242.70 ± 202.12 ng/mL versus 497.70 ± 188.13 ng/mL, p = 0.02). We also examined sDPP-4 serum concentrations in patients suffering from sepsis not due to corona-like viruses. In these subjects, sDPP-4 levels were not different compared to healthy case controls (p = 0.14), which might suggest the decrease of sDPP-4 to be specific for corona-like virus infections. Currently, most data point towards membrane bound ACE2 in contrast to DPP-4 as the major binding partner for COVID-19 internalization into host immune cells. However, the finding that the circulating soluble form of DPP-4 is reduced in hospitalized patients might suggest a regulatory role for both, ACE and DPP-4, in COVID-19 infections, especially since obesity and type 2 diabetes are major risk factor for a severe course of the disease

COVID-19: is there a link between the course of infection and pharmacological agents in diabetes?

BACKGROUND

The Coronavirus disease 2019 (COVID-19) and type 2 diabetes (T2D) are two pandemics that share the dramatic impact on global mortality and economic resources. COVID-19 largely exhibits mild to moderate clinical manifestations. However, severe pneumonia with high fatality rate may occur, especially in the elderly and in patients with underlying conditions, such as diabetes and cardiovascular disease. SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) binds to the angiotensin-converting enzyme 2 (ACE2), a ubiquitous trans-membrane carboxypeptidase, to enter the cells.

AIMS

This short review discusses some open questions about the link between COVID-19 and diabetes, principally focusing on the possible effects of commonly used drugs in patients with diabetes.

RESULTS

Preclinical studies have reported that angiotensin receptor blockers (ARBs) and ACE inhibitors might increase ACE2 expression in several cell types. Hence, it has been speculated that the treatment with these agents might influence the course of the infection, and both harmful and beneficial effects have been supposed. Other pharmacological agents are thought to increase ACE2 expression, including statins and proliferator-activated receptor gamma (PPAR-γ) agonists. All these drug classes are broadly adopted in T2D. Besides ACE2, other unknown co-factors might be involved in cell infection. It has been recently observed that dipeptidyl peptidase-4 (DPP4), the receptor for MERS-CoV (Middle East respiratory syndrome-related coronavirus) and ACE2 have similar expression profiles in the lung. DPP4 has important metabolic and immune functions and is a target for commonly used therapies in T2D.

CONCLUSIONS

Although clinical data supporting an influence of all these drugs on the course of the disease are limited, this is an interesting background for further research that might help unravel the complex mechanisms underlying the link between COVID-19 and diabetes.