Lung ischemia reperfusion injury: the therapeutic role of dipeptidyl peptidase 4 inhibition

Functional roles of CD26/DPP4 in lipopolysaccharide-induced lung injury

Acute respiratory distress syndrome (ARDS) is characterized by dysregulated inflammation and increased permeability of lung microvascular cells. CD26/dipeptidyl peptidase-4 (DPP4) is a type II membrane protein that is expressed in several cell types and mediates multiple pleiotropic effects. We previously reported that DPP4 inhibition by sitagliptin attenuates lipopolysaccharide (LPS)-induced lung injury in mice. The current study characterized the functional role of CD26/DPP4 expression in LPS-induced lung injury in mice, isolated alveolar macrophages, and cultured lung endothelial cells. In LPS-induced lung injury, inflammatory responses [bronchoalveolar lavage fluid (BALF) neutrophil numbers and several proinflammatory cytokine levels] were attenuated in Dpp4 knockout (Dpp4 KO) mice. However, multiple assays of alveolar capillary permeability were similar between the Dpp4 KO and wild-type mice. TNF-α and IL-6 production was suppressed in alveolar macrophages isolated from Dpp4 KO mice. In contrast, in cultured mouse lung microvascular endothelial cells (MLMVECs), reduction in CD26/DPP4 expression by siRNA resulted in greater ICAM-1 and IL-6 expression after LPS stimulation. Moreover, the LPS-induced vascular monolayer permeability in vitro was higher in MLMVECs treated with Dpp4 siRNA, suggesting that CD26/DPP4 plays a protective role in endothelial barrier function. In summary, this study demonstrated that genetic deficiency of Dpp4 attenuates inflammatory responses but not permeability in LPS-induced lung injury in mice, potentially through differential functional roles of CD26/DPP4 expression in resident cellular components of the lung. CD26/DPP4 may be a potential therapeutic target for ARDS and warrants further exploration to precisely identify the multiple functional effects of CD26/DPP4 in ARDS pathophysiology.NEW & NOTEWORTHY We aimed to clarify the functional roles of CD26/DPP4 in ARDS pathophysiology using Dpp4-deficient mice and siRNA reduction techniques in cultured lung cells. Our results suggest that CD26/DPP4 expression plays a proinflammatory role in alveolar macrophages while also playing a protective role in the endothelial barrier. Dpp4 genetic deficiency attenuates inflammatory responses but not permeability in LPS-induced lung injury in mice, potentially through differential roles of CD26/DPP4 expression in the resident cellular components of the lung.

Multilineage-Differentiating Stress-Enduring Cells (Muse Cells): An Easily Accessible, Pluripotent Stem Cell Niche with Unique and Powerful Properties for Multiple Regenerative Medicine Applications

Cell-based therapy in regenerative medicine is a powerful tool that can be used both to restore various cells lost in a wide range of human disorders and in renewal processes. Stem cells show promise for universal use in clinical medicine, potentially enabling the regeneration of numerous organs and tissues in the human body. This is possible due to their self-renewal, mature cell differentiation, and factors release. To date, pluripotent stem cells seem to be the most promising. Recently, a novel stem cell niche, called multilineage-differentiating stress-enduring (Muse) cells, is emerging. These cells are of particular interest because they are pluripotent and are found in adult human mesenchymal tissues. Thanks to this, they can produce cells representative of all three germ layers. Furthermore, they can be easily harvested from fat and isolated from the mesenchymal stem cells. This makes them very promising, allowing autologous treatments and avoiding the problems of rejection typical of transplants. Muse cells have recently been employed, with encouraging results, in numerous preclinical studies performed to test their efficacy in the treatment of various pathologies. This review aimed to (1) highlight the specific potential of Muse cells and provide a better understanding of this niche and (2) originate the first organized review of already tested applications of Muse cells in regenerative medicine. The obtained results could be useful to extend the possible therapeutic applications of disease healing.

A Single Center Observational Study of Spirometry Assessments in Children with Congenital Heart Disease after Surgery

Background: Children with congenital heart disease (CHD) have impaired pulmonary function both before and after surgery; therefore, pulmonary function assessments are important and should be performed both before and after open-heart surgery. This study aimed to compare pulmonary function between variant pediatric CHD types after open-heart surgery via spirometry. Methods: In this retrospective study, the data for forced vital capacity (FVC), forced expiratory volume in the first second (FEV1), and the ratio between FEV1 and FVC (FEV1/FVC) were collected from patients with CHD who underwent conventional spirometry between 2015 and 2017. Results: A total of 86 patients (55 males and 31 females, with a mean age of 13.24 ± 3.32 years) were enrolled in our study. The diagnosis of CHD included 27.9% with atrial septal defects, 19.8% with ventricular septal defects, 26.7% with tetralogy of Fallot, 7.0% with transposition of the great arteries, and 46.5% with other diagnoses. Abnormal lung function was identified by spirometry assessments after surgery. Spirometry was abnormal in 54.70% of patients: obstructive type in 29.06% of patients, restrictive type in 19.76% of patients, and mixed type in 5.81% of patients. More abnormal findings were found in patients who received the Fontan procedure (80.00% vs. 35.80%, p = 0.048). Conclusions: Developing novel therapies to optimize pulmonary function will be critical for improving clinical outcomes.

Therapeutic Targets for Regulating Oxidative Damage Induced by Ischemia-Reperfusion Injury: A Study from a Pharmacological Perspective

Ischemia-reperfusion (I-R) injury is damage caused by restoring blood flow into ischemic tissues or organs. This complex and characteristic lesion accelerates cell death induced by signaling pathways such as apoptosis, necrosis, and even ferroptosis. In addition to the direct association between I-R and the release of reactive oxygen species and reactive nitrogen species, it is involved in developing mitochondrial oxidative damage. Thus, its mechanism plays a critical role via reactive species scavenging, calcium overload modulation, electron transport chain blocking, mitochondrial permeability transition pore activation, or noncoding RNA transcription. Other receptors and molecules reduce tissue and organ damage caused by this pathology and other related diseases. These molecular targets have been gradually discovered and have essential roles in I-R resolution. Therefore, the current study is aimed at highlighting the importance of these discoveries. In this review, we inquire about the oxidative damage receptors that are relevant to reducing the damage induced by oxidative stress associated with I-R. Several complications on surgical techniques and pathology interventions do not mitigate the damage caused by I-R. Nevertheless, these therapies developed using alternative targets could work as coadjuvants in tissue transplants or I-R-related pathologies

Lidocaine attenuates hypoxia/reoxygenation‑induced inflammation, apoptosis and ferroptosis in lung epithelial cells by regulating the p38 MAPK pathway

Lung ischemia-reperfusion (I/R) injury poses a serious threat to human health, worldwide. The current study aimed to determine the role of lidocaine in A549 cells, in addition to the involvement of the p38 MAPK pathway. Oxygen deprivation/reoxygenation-induced A549 cells were utilized to simulate I/R injury in vitro. Cell viability and apoptosis were detected using MTT and TUNEL assays, respectively. The levels of IL-6, IL-8, TNF-α, malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase, iron and reactive oxygen species (ROS) were measured using corresponding commercial kits. The corresponding protein expression levels were also measured using western blotting. Moreover, a monolayer cell paracellular permeability assay was performed to determine the permeability of A549 cells. The results demonstrated that, whilst lidocaine had no influence on untreated A549 cells, it significantly increased the viability of hypoxia/reoxygenation (H/R)-induced A549 cells. A549 cell apoptosis and the release of inflammatory cytokines in the H/R group were decreased after the addition of lidocaine. When compared with the H/R group, increased MDA level and decreased SOD level were observed in H/R-induced A549 cells following lidocaine treatment. In addition, the permeability of H/R-induced A549 cells was markedly decreased following lidocaine treatment. Compared with the H/R group, the expression levels of tight junction and ferroptosis-related proteins were significantly upregulated by lidocaine, whereas the expression of transferrin was downregulated. However, p79350, an agonist of p38, reversed the effects of lidocaine on H/R-induced A549 cells. In conclusion, lidocaine exerted a protective role in HR-induced lung epithelial cell injury, which may serve as a potential agent for the treatment of patients with lung I/R injury.

The Roles of Dipeptidyl Peptidase 4 (DPP4) and DPP4 Inhibitors in Different Lung Diseases: New Evidence

CD26/Dipeptidyl peptidase 4 (DPP4) is a type II transmembrane glycoprotein that is widely expressed in various organs and cells. It can also exist in body fluids in a soluble form. DPP4 participates in various physiological and pathological processes by regulating energy metabolism, inflammation, and immune function. DPP4 inhibitors have been approved by the Food and Drug Administration (FDA) for the treatment of type 2 diabetes mellitus. More evidence has shown the role of DPP4 in the pathogenesis of lung diseases, since it is highly expressed in the lung parenchyma and the surface of the epithelium, vascular endothelium, and fibroblasts of human bronchi. It is a potential biomarker and therapeutic target for various lung diseases. During the coronavirus disease-19 (COVID-19) global pandemic, DPP4 was found to be an important marker that may play a significant role in disease progression. Some clinical trials on DPP4 inhibitors in COVID-19 are ongoing. DPP4 also affects other infectious respiratory diseases such as Middle East respiratory syndrome and non-infectious lung diseases such as pulmonary fibrosis, lung cancer, chronic obstructive pulmonary disease (COPD), and asthma. This review aims to summarize the roles of DPP4 and its inhibitors in infectious lung diseases and non-infectious diseases to provide new insights for clinical physicians.

Functional Roles for CD26/DPP4 in Mediating Inflammatory Responses of Pulmonary Vascular Endothelial Cells

Excessive inflammation in the lung is a primary cause of acute respiratory distress syndrome (ARDS). CD26/dipeptidyl peptidase-4 (DPP4) is a transmembrane protein that is expressed in various cell types and exerts multiple pleiotropic effects. We recently reported that pharmacological CD26/DPP4 inhibition ameliorated lipopolysaccharide (LPS)-induced lung injury in mice and exerted anti-inflammatory effects on human lung microvascular endothelial cells (HLMVECs), in vitro. However, the mechanistic roles of CD26/DPP4 in lung injury and its effects on HLMVECs remain unclear. In this study, transcriptome analysis, followed by various confirmation experiments using siRNA in cultured HLMVECs, are performed to evaluate the role of CD26/DPP4 in response to the pro-inflammatory involved in inflammation, barrier function, and regenerative processes in HLMVECs after pro-inflammatory stimulation. These are all functions that are closely related to the pathophysiology and repair process of lung injury. Confirmatory experiments using flow cytometry; enzyme-linked immunosorbent assay; quantitative polymerase chain reaction; dextran permeability assay; WST-8 assay; wound healing assay; and tube formation assay, reveal that the reduction of CD26/DPP4 via siRNA is associated with altered parameters of inflammation, barrier function, and the regenerative processes in HLMVECs. Thus, CD26/DPP4 can play a pathological role in mediating injury in pulmonary endothelial cells. CD26/DPP4 inhibition can be a new therapeutic strategy for inflammatory lung diseases, involving pulmonary vascular damage.

Modulation of Prostanoids Profile and Counter-Regulation of SDF-1α/CXCR4 and VIP/VPAC2 Expression by Sitagliptin in Non-Diabetic Rat Model of Hepatic Ischemia-Reperfusion Injury

Molecular mechanisms underlying the beneficial effect of sitagliptin repurposed for hepatic ischemia-reperfusion injury (IRI) are poorly understood. We aimed to evaluate the impact of IRI and sitagliptin on the hepatic profile of eicosanoids (LC-MS/MS) and expression/concentration (RTqPCR/ELISA) of GLP-1/GLP-1R, SDF-1α/CXCR4 and VIP/VPAC1, VPAC2, and PAC1 in 36 rats. Animals were divided into four groups and subjected to ischemia (60 min) and reperfusion (24 h) with or without pretreatment with sitagliptin (5 mg/kg) (IR and SIR) or sham-operated with or without sitagliptin pretreatment (controls and sitagliptin). PGI₂, PGE₂, and 13,14-dihydro-PGE₁ were significantly upregulated in IR but not SIR, while sitagliptin upregulated PGD₂ and 15-deoxy-12,14-PGJ₂. IR and sitagliptin non-significantly upregulated GLP-1 while Glp1r expression was borderline detectable. VIP concentration and Vpac2 expression were downregulated in IR but not SIR, while Vpac1 was significantly downregulated solely in SIR. IRI upregulated both CXCR4 expression and concentration, and sitagliptin pretreatment abrogated receptor overexpression and downregulated Sdf1. In conclusion, hepatic IRI is accompanied by an elevation in proinflammatory prostanoids and overexpression of CXCR4, combined with downregulation of VIP/VPAC2. Beneficial effects of sitagliptin during hepatic IRI might be mediated by drug-induced normalization of proinflammatory prostanoids and upregulation of PGD₂ and by concomitant downregulation of SDF-1α/CXCR4 and reinstating VIP/VCAP2 signaling.

Differential urine proteome analysis of a ventilator-induced lung injury rat model by label-free quantitative and parallel reaction monitoring proteomics

Urine is a promising resource for biomarker research. Therefore, the purpose of this study was to investigate potential urinary biomarkers to monitor the disease activity of ventilator-induced lung injury (VILI). In the discovery phase, a label-free data-dependent acquisition (DDA) quantitative proteomics method was used to profile the urinary proteomes of VILI rats. For further validation, the differential proteins were verified by parallel reaction monitoring (PRM)-targeted quantitative proteomics. In total, 727 high-confidence proteins were identified with at least 1 unique peptide (FDR ≤ 1%). Compared to the control group, 110 proteins (65 upregulated, 45 downregulated) were significantly changed in the VILI group (1.5-fold change, P < 0.05). The canonical pathways and protein-protein interaction analyses revealed that the differentially expressed proteins were enriched in multiple functions, including oxidative stress and inflammatory responses. Finally, thirteen proteins were identified as candidate biomarkers for VILI by PRM validation. Among these PRM-validated proteins, AMPN, MEP1B, LYSC1, DPP4 and CYC were previously reported as lung-associated disease biomarkers. SLC31, MEP1A, S15A2, NHRF1, XPP2, GGT1, HEXA, and ATPB were newly discovered in this study. Our results suggest that the urinary proteome might reflect the pathophysiological changes associated with VILI. These differential proteins are potential urinary biomarkers for the activity of VILI.

SARS-CoV-2 and diabetes: A potential therapeutic effect of dipeptidyl peptidase 4 inhibitors in diabetic patients diagnosed with COVID-19

COVID-19 is caused by severe acute respiratory syndrome coronavirus 2 and has become an urgent economic and health challenge. Dipeptidyl peptidase 4 (DPP4), also mentioned as a cluster of differentiation 26 (CD26) is a serine exopeptidase found in two arrangements: a soluble form (sDPP-4) and a plasma membrane-bound form. Because other coronaviruses enter the cells by binding to DPP-4, it has been speculated that DPP-4 inhibitors may exert activity against COVID-19. Therefore, this review aimed to summarize the potential therapeutic effect of dipeptidyl peptidase 4 inhibitors in diabetic patients diagnosed with COVID-19. To include different studies, publications related to Dipeptidyl peptidase-4 inhibitor use and clinical outcomes from COVID-19 were searched from the databases such as Web of Science, PubMed, Medline, Elsevier, Google Scholar, and SCOPUS, via English key terms. A direct engrossment of DPP4 in COVID-19 needs to be elucidated, there is also evidence confirming that DPP4 inhibitors exert anti-fibrotic and modulate inflammation activity. Thus, the use of DPP-4 inhibitors could reduce mortality due to COVID-19 or improve the progression of COVID-19; this evidence may support the management of diabetic patients diagnosed with COVID-19; however more well-designed investigation is urgently required.

Linagliptin Protects against Endotoxin-Induced Acute Kidney Injury in Rats by Decreasing Inflammatory Cytokines and Reactive Oxygen Species

Septic shock can increase pro-inflammatory cytokines, reactive oxygen species (ROS), and multiple organ dysfunction syndrome (MODs) and even lead to death. Dipeptidyl peptidase-4 (DPP-4) inhibitors have been proven to exert potential antioxidant and anti-inflammatory effects. We investigated the effects of linagliptin on endotoxic shock and acute kidney injury (AKI) in animal and cell models. In the cell model, linagliptin attenuated ROS by activating the AMP-activated protein kinase (AMPK) pathway, restoring nuclear-factor-erythroid-2-related factor (Nrf2) and heme oxygenase 1 (HO-1) protein, and decreasing pro-inflammatory cytokines (tumor necrosis factor alpha (TNF-α) and interleukin 1 beta (IL-1β)). In the animal model, 14-week-old conscious Wistar–Kyoto rats were randomly divided into three groups (n = 8 in each group). Endotoxin shock with MODs was induced by the intravenous injection of Klebsiella pneumoniae lipopolysaccharide (LPS, 20 mg/kg). Linagliptin improved animal survival without affecting hemodynamic profiles. In the histopathology and immunohistochemistry examinations of the rat kidneys, linagliptin (10 mg/kg) suppressed nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and inducible nitric oxide synthase (iNOS), decreased injury scores, and preserved E-cadherin expression from LPS damage. In conclusion, linagliptin ameliorated endotoxin-shock-induced AKI by reducing ROS via AMPK pathway activation and suppressing the release of TNF-α and IL-1β in conscious rats.

Sitagliptin activates the p62-Keap1-Nrf2 signalling pathway to alleviate oxidative stress and excessive autophagy in severe acute pancreatitis-related acute lung injury

Acute lung injury (ALI) is a complication of severe acute pancreatitis (SAP). Sitagliptin (SIT) is a DPP4 inhibitor that exerts anti-inflammatory and antioxidant effects; however, its mechanism of action in SAP-ALI remains unclear. In this study, we investigated the effects of SIT on SAP-ALI and the specific pathways involved in SAP-induced lung inflammation, including oxidative stress, autophagy, and p62-Kelch-like ECH-associated protein 1 (Keap1)-NF-E2-related factor 2 (Nrf2) signalling pathways. Nrf2 knockout (Nrf2-/-) and wild-type (WT) mice were pre-treated with SIT (100 mg/kg), followed by caerulein and lipopolysaccharide (LPS) administration to induce pancreatic and lung injury. BEAS-2B cells were transfected with siRNA-Nrf2 and treated with LPS, and the changes in inflammation, reactive oxygen species (ROS) levels, and autophagy were measured. SIT reduced histological damage, oedema, and myeloperoxidase activity in the lung, decreased the expression of pro-inflammatory cytokines, and inhibited excessive autophagy and ROS production via the activation of the p62-Keap1-Nrf2 signalling pathway and promotion of the nuclear translocation of Nrf2. In Nrf2-knockout mice, the anti-inflammatory effect of SIT was reduced, resulting in ROS accumulation and excessive autophagy. In BEAS-2B cells, LPS induced ROS production and activated autophagy, further enhanced by Nrf2 knockdown. This study demonstrates that SIT reduces SAP-ALI-associated oxidative stress and excessive autophagy through the p62-Keap1-Nrf2 signalling pathway and nuclear translocation of Nrf2, suggesting its therapeutic potential in SAP-ALI.

DPP4 gene silencing inhibits proliferation and epithelial-mesenchymal transition of papillary thyroid carcinoma cells through suppression of the MAPK pathway

PURPOSE

Papillary thyroid carcinoma (PTC) is characterized by epithelial malignancy and is the most prevalent thyroid neoplasm with the best overall prognosis. Notably, recently published studies have indicated remarkably high expression of dipeptidyl peptidase 4 (DPP4) in PTC. However, the underlying molecular mechanism and regulatory factors of PTC progression remain unknown. Therefore, the current study aimed to elucidate the effects of DPP4 gene silencing on PTC and further investigated whether the mechanism of PTC progression is related to the mitogen-activated protein kinase (MAPK) pathway.

METHODS

Herein, microarray-based gene expression profiling of PTC was conducted to identify the differentially expressed genes between tumor thyroid tissue and normal thyroid tissue as well as the underlying signaling pathway involved in PTC pathogenesis. Moreover, protein quantification was performed to assess the protein expression of DPP4 in PTC tissues collected from 65 patients. In addition, DPP4 was silenced in PTC cell lines (GLAG-66 and TPC-1) through siRNA-mediated DPP4 knockdown or sitagliptin (inhibitor of DPP4)-mediated inhibition to assess the effects of DPP4 on the MAPK pathway and cellular processes, including proliferation, apoptosis, and epithelial-to-mesenchymal transition (EMT).

RESULTS

Intriguingly, our data revealed markedly high expression of DPP4 in PTC tissues. However, in GLAG-66 and TPC-1 cells, the silencing of DPP4 resulted in significantly reduced expression of ERK1/2, JNK1, P38 MAPK, VEGF, FGFR-1, TGF-β1, Snail, HIF-1α, N-cadherin, and Bcl-2 along with reduced phosphorylation of ERK1/2, JNK1, and P38 MAPK, whereas the expression of E-cadherin and Bax was increased. Furthermore, DPP4 silencing was found to hinder cell proliferation and potentiate cell apoptosis.

CONCLUSION

Collectively, the present study demonstrated that DPP4 gene silencing inhibits PTC cell proliferation and EMT and promotes cell apoptosis via suppression of the MAPK pathway, thus highlighting a possible regulatory pathway in PTC progression.

Systematic Understanding of Pathophysiological Mechanisms of Oxidative Stress-Related Conditions-Diabetes Mellitus, Cardiovascular Diseases, and Ischemia-Reperfusion Injury

Reactive oxygen species (ROS) plays a role in intracellular signal transduction under physiological conditions while also playing an essential role in diseases such as hypertension, ischemic heart disease, and diabetes, as well as in the process of aging. The influence of ROS has some influence on the frequent occurrence of cardiovascular diseases (CVD) in diabetic patients. In this review, we considered the pathophysiological relationship between diabetes and CVD from the perspective of ROS. In addition, considering organ damage due to ROS elevation during ischemia-reperfusion, we discussed heart and lung injuries. Furthermore, we have focused on the transient receptor potential (TRP) channels and L-type calcium channels as molecular targets for ROS in ROS-induced tissue damages and have discussed about the pathophysiological mechanism of the injury.

2-Methoxyestradiol Protects Against Lung Ischemia/Reperfusion Injury by Upregulating Annexin A1 Protein Expression

Background: 2-Methoxyestradiol (2ME), a natural 17-β estradiol metabolite, is a potent anti-inflammatory agent, but its effect on ischemia/reperfusion (IR)-induced acute lung inflammation remains unknown. Annexin A1 (AnxA1), a glucocorticoid-regulated protein, is effective at inhibiting neutrophil transendothelial migration by binding the formyl peptide receptors (FPRs). We aimed to investigate whether 2ME upregulates the expression of AnxA1 and protects against IR-induced lung damage. Methods: IR-mediated acute lung inflammation was induced by ischemia for 40 min followed by reperfusion for 60 min in an isolated, perfused rat lung model. The rat lungs were randomly treated with vehicle or 2ME, and the functional relevance of AnxA1 was determined using an anti-AnxA1 antibody or BOC2 (a pan-receptor antagonist of the FPR). In vitro, human primary alveolar epithelial cells (HPAECs) and rat neutrophils were pretreated with 2ME and an AnxA1 siRNA or anti-AnxA1 antibody and subjected to hypoxia-reoxygenation (HR). Results: 2ME significantly decreased all lung edema parameters, neutrophil infiltration, oxidative stress, proinflammatory cytokine production, lung cell apoptosis, tight junction protein disruption, and lung tissue injury in the IR-induced acute lung inflammation model. 2ME also increased the expression of the AnxA1 mRNA and protein and suppressed the activation of nuclear factor-κB (NF-κB). In vitro, 2ME attenuated HR-triggered NF-κB activation and interleukin-8 production in HPAECs, decreased transendothelial migration, tumor necrosis factor-α production, and increased apoptosis in neutrophils exposed to HR. These protective effects of 2ME were significantly abrogated by BOC2, the anti-AnxA1 antibody, or AnxA1 siRNA. Conclusions: 2ME ameliorates IR-induced acute lung inflammation by increasing AnxA1 expression. Based on these results, 2ME may be a promising agent for attenuating IR-induced lung injury.

Linagliptin Regulates the Mitochondrial Respiratory Reserve to Alter Platelet Activation and Arterial Thrombosis

Background: The pharmacological inhibition of dipeptidyl peptidase-4 (DPP-4) potentiates incretin action, and DPP-4 is a drug target for type 2 diabetes and reducing cardiovascular risk. However, little is known about the non-enteroendocrine pathways by which DPP-4 might contribute to ischaemic cardiovascular events.

Methods: We tested the hypothesis that inhibition of DPP-4 can inhibit platelet activation and arterial thrombosis by preventing platelet mitochondrial dysfunction and release. The effects of pharmacological DPP-4 inhibition on carotid artery thrombosis, platelet aggregation, and platelet mitochondrial respiration signaling pathways were studied in mice.

Results: Platelet-dependent arterial thrombosis was significantly delayed in mice treated with high dose of linagliptin, a potent DPP-4 inhibitor, and fed normal chow diet compared to vehicle-treated mice. Thrombin induced DPP-4 expression and activity, and platelets pretreated with linagliptin exhibited reduced thrombin-induced aggregation. Linagliptin blocked phosphodiesterase activity and contrained cyclic AMP reduction when thrombin stimulates platelets. Linagliptin increases the inhibition of platelet aggregation by nitric oxide. The bioenergetics profile revealed that platelets pretreated with linagliptin exhibited decreased oxygen consumption rates in response to thrombin. In transmission electron microscopy, platelets pretreated with linagliptin showed markedly reversed morphological changes in thrombin-activated platelets, including the secretion of α-granules and fewer mitochondria.

Conclusion: Collectively, these findings identify distinct roles for DPP-4 in platelet function and arterial thrombosis.

Repurposing existing drugs for COVID-19: an endocrinology perspective

BACKGROUND

Coronavirus Disease 2019 (COVID-19) is a multi-systemic infection caused by the novel Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), that has become a pandemic. Although its prevailing symptoms include anosmia, ageusia, dry couch, fever, shortness of brief, arthralgia, myalgia, and fatigue, regional and methodological assessments vary, leading to heterogeneous clinical descriptions of COVID-19. Aging, uncontrolled diabetes, hypertension, obesity, and exposure to androgens have been correlated with worse prognosis in COVID-19. Abnormalities in the renin-angiotensin-aldosterone system (RAAS), angiotensin-converting enzyme-2 (ACE2) and the androgen-driven transmembrane serine protease 2 (TMPRSS2) have been elicited as key modulators of SARS-CoV-2.

MAIN TEXT

While safe and effective therapies for COVID-19 lack, the current moment of pandemic urges for therapeutic options. Existing drugs should be preferred over novel ones for clinical testing due to four inherent characteristics: 1. Well-established long-term safety profile, known risks and contraindications; 2. More accurate predictions of clinical effects; 3. Familiarity of clinical management; and 4. Affordable costs for public health systems. In the context of the key modulators of SARS-CoV-2 infectivity, endocrine targets have become central as candidates for COVID-19. The only endocrine or endocrine-related drug class with already existing emerging evidence for COVID-19 is the glucocorticoids, particularly for the use of dexamethasone for severely affected patients. Other drugs that are more likely to present clinical effects despite the lack of specific evidence for COVID-19 include anti-androgens (spironolactone, eplerenone, finasteride and dutasteride), statins, N-acetyl cysteine (NAC), ACE inhibitors (ACEi), angiotensin receptor blockers (ARB), and direct TMPRSS-2 inhibitors (nafamostat and camostat). Several other candidates show less consistent plausibility. In common, except for dexamethasone, all candidates have no evidence for COVID-19, and clinical trials are needed.

CONCLUSION

While dexamethasone may reduce mortality in severely ill patients with COVID-19, in the absence of evidence of any specific drug for mild-to-moderate COVID-19, researchers should consider testing existing drugs due to their favorable safety, familiarity, and cost profile. However, except for dexamethasone in severe COVID-19, drug treatments for COVID-19 patients must be restricted to clinical research studies until efficacy has been extensively proven, with favorable outcomes in terms of reduction in hospitalization, mechanical ventilation, and death.

Tetrahydropalmatine protects against acute lung injury induced by limb ischemia/reperfusion through restoring PI3K/AKT/mTOR-mediated autophagy in rats

BACKGROUND

Limb ischemia/reperfusion (I/R) is a common clinical process that frequently induces acute lung injury (ALI). Tetrahydropalmatine (THP) is a major bioactive constituent of various traditional Chinese medicine with protective effects on inflammation and oxidation. In this study, we aimed to investigate the possible protective effect of THP on ALI induced by limb I/R.

METHODS

Rats were used to establish ALI through limb I/R. After administration of three doses of THP, the lung injury was evaluated by hematoxylin-eosin staining, tissue wet/dry weight ratio and ELISA examination of myeloperoxidase (MPO), malondialdehyde (MDA) and Super Oxide Dismutase (SOD). Additionally, PI3K/AKT/mTOR pathway and autophagy markers were determined by Western blot. To confirm the role of autophagy in the effect of THP on ALI, 3-methyladenine (3-MA), THP or THP + rapamycin (RAPA) was given to the model rats, and then evaluated the parameters above mentioned.

RESULTS

The pulmonary histological lesions and wet/dry were significantly induced after limb I/R. Concurrently, I/R significantly increased MPO and MDA, and decreased SOD in lung tissues. These changes were reversed after THP treatment. Additionally, THP exerted inhibitory effect on the I/R-induced decrease of phosphorylation of PI3K/AKT/mTOR and increase of autophagy activity. The effects by THP on lung injury, PI3K/AKT/mTOR signaling and autophagy were also observed after treatment with 3-MA, an autophagy inhibitor, whereas were blocked by combinational treatment with RAPA, an autophagy inducer.

CONCLUSION

Our data suggested that THP had significant protection against ALI and this might be achieved by autophagy inhibition through rescuing PI3K/AKT/mTOR activity.

DPP4 and ACE2 in Diabetes and COVID-19: Therapeutic Targets for Cardiovascular Complications?

COVID-19 outbreak, caused by severe acute respiratory syndrome (SARS)-CoV-2 coronavirus has become an urgent health and economic challenge. Diabetes is a risk factor for severity and mortality of COVID-19. Recent studies support that COVID-19 has effects beyond the respiratory tract, with vascular complications arising as relevant factors worsening its prognosis, then making patients with previous vascular disease more prone to severity or fatal outcome. Angiotensin-II converting enzime-2 (ACE2) has been proposed as preferred receptor for SARS-CoV-2 host infection, yet specific proteins participating in the virus entry are not fully known. SARS-CoV-2 might use other co-receptor or auxiliary proteins allowing virus infection. In silico experiments proposed that SARS-CoV-2 might bind dipeptidyl peptidase 4 (DPP4/CD26), which was established previously as receptor for MERS-CoV. The renin-angiotensin-aldosterone system (RAAS) component ACE2 and DPP4 are proteins dysregulated in diabetes. Imbalance of the RAAS and direct effect of soluble DPP4 exert deleterious vascular effects. We hypothesize that diabetic patients might be more affected by COVID-19 due to increased presence ACE2 and DPP4 mediating infection and contributing to a compromised vasculature. Here, we discuss the role of ACE2 and DPP4 as relevant factors linking the risk of SARS-CoV-2 infection and severity of COVID-19 in diabetic patients and present an outlook on therapeutic potential of current drugs targeted against RAAS and DPP4 to treat or prevent COVID-19-derived vascular complications. Diabetes affects more than 400 million people worldwide, thus better understanding of how they are affected by COVID-19 holds an important benefit to fight against this disease with pandemic proportions.

Neuroprotective effect of alogliptin on oxaliplatin-induced peripheral neuropathy in vivo and in vitro

Oxaliplatin is a platinum-based antineoplastic drug commonly used for treating colorectal, gastric, and pancreatic cancer. However, it frequently causes peripheral neuropathy as dose-limiting toxicity and is lacking a strategy for prevention. Alogliptin, a dipeptidyl peptidase 4 (DPP-4) inhibitor, is an oral antidiabetic drug. Previous studies have shown that DPP-4 inhibitors have pleiotropic effects, including neuroprotection. In this study, we investigated the effects of alogliptin on oxaliplatin-induced peripheral neuropathy using in vitro and in vivo models. In PC12 cells, alogliptin attenuated neurite disorders induced by oxaliplatin and cisplatin. The repeated injection of oxaliplatin caused mechanical allodynia and axonal degeneration of the sciatic nerve in rats. These neuropathies were ameliorated by co-administration of alogliptin. Moreover, alogliptin did not attenuate tumor cytotoxicity of oxaliplatin in the cultured colon, gastric, or pancreatic cancer cell lines and tumor-bearing mice. These findings suggest that alogliptin may be beneficial for preventing oxaliplatin-induced peripheral neuropathy.

Methane attenuates lung ischemia-reperfusion injury via regulating PI3K-AKT-NFκB signaling pathway

Objective: This study aims to investigate the protective effects and possible mechanism of methane-rich saline (MS) on lung ischemia-reperfusion injury (LIRI) in rats.Methods: MS (2 ml/kg and 20 ml/kg) was injected intraperitoneally in rats after LIRI. Lung injury was assayed by Hematoxylin-eosin (HE) staining and wet-to-dry weight (W/D). The cells in the bronchoalveolar lavage fluid (BALF) and blood were counted. Oxidative stress was examined by the level of malondialdehyde (MDA) and superoxide dismutase (SOD). Inflammatory factors including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-10 (IL-10) were determined by ELISA. Lung tissue apoptosis was detected by TUNEL staining and western blotting of Bcl-2, Bax, and caspase-3. The expressions of IкBα, p38, PI3K, AKT, and NF-κB were analyzed with Western blotting.Results: MS effectively decreased the lung W/D ratio as well as the lung pathological damage and reduced the localized infiltration of inflammatory cells. Methane suppressed the expression of the PI3K-AKT-NFκB signaling pathway during the lung IR injury, which inhibited the activation of NF-kB and decreased the level of inflammatory cytokines, such as TNF-α, IL-1β, and IL-10. Moreover, we found that MS treatment relieved reactive oxygen species (ROS) damage by downregulating MDA and upregulating SOD. MS treatment also regulated apoptosis-related proteins, such as Bcl-2, Bax, and caspase-3.Conclusions: MS could repair LIRI and reduce the release of oxidative stress, inflammatory cytokines, and cell apoptosis via the PI3K-AKT-NFκB signaling pathway, which may provide a novel and promising strategy for the treatment of LIRI.

DPP-4 inhibition: А novel therapeutic approach to the treatment of pulmonary hypertension?

Pulmonary hypertension (PH) is a progressive disorder characterized by alterations of the vascular structure and function in the lungs. Despite the success in its stabilisation by targeting pulmonary vascular tone and endothelial dysfunction, the prognosis remains poor and new therapeutic approaches via neglected macromolecular targets are needed. In the pathophysiology of PH the early stages of vascular remodelling are considered to be reversible, while endothelial to mesenchymal transition and proliferation/migration of fibroblasts play a critical role in staging the irreversible phase. Dipeptidyl peptidase-4 (DPP-4)/CD26 is present and active in the lungs and is expressed constitutively on lung fibroblasts, on which it exerts proliferative effects. Further, it is a marker of migrating fibroblasts and of their functional activation, including collagen synthesis and inflammatory cytokine secretion. Inhibiting DPP-4 improves the reversible phases of vascular dysfunction in PH, but is also highly likely to attenuate endothelial to mesenchymal transition and decrease the proliferation and migration of fibroblasts, preventing fibrosis and, consequently, should prolong or even inhibit entrance to the potentially irreversible phase of PH. Proposed mechanisms that support the multifaceted aspects of DPP-4 inhibition in terms of improving PH, involve pathways and mediators in pulmonary vascular and connective tissue remodelling. The latter are affected by the inhibition of this protease resulting in the synergistic beneficial antioxidative, anti-inflammatory and antifibrotic effects. We offer here an evidence-supported hypothesis that DPP-4 inhibitors are likely to be effective in the irreversible phase of remodelling in PH. Accordingly, we propose PH as a possible novel therapeutic indication for existing and new DPP-4 inhibitors.

Carnosol suppresses interleukin-6 production in mouse lungs injured by ischemia–reperfusion operation and in RAW264.7 macrophages treated with lipopolysaccharide

Carnosol is a naturally occurring herbal compound, known for its antioxidative properties. We previously found that carnosol protected mouse lungs from ischemia–reperfusion injury in ex vivo cultures. To elucidate the molecular mechanisms underpinning carnosol-mediated lung protection, we analyzed modes of interleukin-6 (IL-6) gene expression, which is associated with lung ischemia–reperfusion injury. Microarray analysis of mouse lungs suggested that IL-6 mRNA levels were elevated in the mouse lungs subjected to clamp-reperfusion, which was associated with elevated levels of other inflammatory modulators, such as activating transcription factor 3 (ATF3). Carnosol pretreatment lowered the IL-6 protein levels in mouse lung homogenates prepared after the clamp-reperfusion. On the other hand, the ATF3 gene expression was negatively correlated with that of IL-6 in RAW264.7 cells. IL-6 mRNA levels and gene promoter activities were suppressed by carnosol in RAW264.7 cells, but rescued by ATF3 knockdown. When RAW264.7 cells were subjected to hypoxia–reoxygenation, carnosol treatment lowered oxygen consumption after reoxygenation, which was coupled with a correlation with a transient production of mitochondrial reactive oxygen species and following ATF3 gene expression. These results suggest that carnosol treatment could be a new strategy for protecting lungs from ischemia–reperfusion injury by modulating the ATF3–IL-6 axis.

DPP4 inhibition by sitagliptin attenuates LPS-induced lung injury in mice

Acute respiratory distress syndrome (ARDS) is a severe clinical condition marked by acute respiratory failure and dysregulated inflammation. Pulmonary vascular endothelial cells (PVECs) function as an important pro-inflammatory source in ARDS, suggesting that modulation of inflammatory events at the endothelial level may have a therapeutic benefit. Dipeptidyl peptidase-4 (DPP4) inhibitors, widely used for the treatment of diabetes mellitus, have been reported to have possible anti-inflammatory effects. However, the potential anti-inflammatory effects of DPP4 inhibition on PVEC function and ARDS pathophysiology are unknown. Therefore, we evaluated the effects of sitagliptin, a DPP4 inhibitor in wide clinical use, on LPS-induced lung injury in mice and in human lung ECs in vitro. In vivo, sitagliptin reduced serum DPP4 activity, bronchoalveolar lavage protein concentration, cell number, and proinflammatory cytokine levels after LPS and alleviated histological findings of lung injury. LPS decreased the expression levels of CD26/DPP4 on pulmonary epithelial cells and PVECs isolated from mouse lungs, and the effect was partially reversed by sitagliptin. In vitro, human lung microvascular ECs (HLMVECs) expressed higher levels of CD26/DPP4 than human pulmonary arterial ECs. LPS induced the release of TNFα, IL-6, and IL-8 by HLMVECs that were inhibited by sitagliptin. LPS promoted the proliferation of HLMVECs, and sitagliptin suppressed this response. However, sitagliptin failed to reverse LPS-induced permeability in cultured ECs or lung epithelial cells in vitro. In summary, sitagliptin attenuates LPS-induced lung injury in mice and exerts anti-inflammatory effects on HLMVECs. These novel observations indicate DPP4 inhibitors may have potential as therapeutic drugs for ARDS.

The effects of S-nitrosoglutathione on intestinal ischemia reperfusion injury and acute lung injury in rats: Roles of oxidative stress and NF-κB

BACKGROUND

Intestinal ischemia and reperfusion (I/R) induces oxidative stress, inflammatory response, and acute lung injury. S-nitrosoglutathione (GSNO), a nitric oxide donor, has been documented to have protective effects on experimental ischemia models.

AIM

The aim of this study was to examine the effect of GSNO on I/R-induced intestine and lung damage and detect the potential mechanisms emphasizing the protective role of GSNO.

METHODS

Intestinal I/R was induced by occluding the superior mesenteric artery for 30 min followed by reperfusion for 180 min. GSNO was administered intravenously before reperfusion period (0.25 mg/kg). The levels of lipid peroxidation, reduced glutathione, and myeloperoxidase (MPO), histopathological evaluation and immunohistochemical expressions of both nuclear factor KappaB (NF-κB) and inducible nitric oxide (iNOS) in intestine and lung tissues were assessed.

RESULTS

Histolopathologic evaluation demonstrated that intestinal I/R induced severe damages in the intestine and the lung tissues. Histopathological scores decreased with GSNO treatment. GSNO treatment reduced lipid peroxidation and MPO levels and inhibited expression of NF-κB and iNOS in the intestine.

CONCLUSION

Our results suggest that GSNO treatment may ameliorate the intestinal and lung injury in rats, at least in part, by inhibiting inflammatory response and oxidative stress.

Molecular Evidence of Adenosine Deaminase Linking Adenosine A2A Receptor and CD26 Proteins

Adenosine is an endogenous purine nucleoside that acts in all living systems as a homeostatic network regulator through many pathways, which are adenosine receptor (AR)-dependent and -independent. From a metabolic point of view, adenosine deaminase (ADA) is an essential protein in the regulation of the total intracellular and extracellular adenosine in a tissue. In addition to its cytosolic localization, ADA is also expressed as an ecto-enzyme on the surface of different cells. Dipeptidyl peptidase IV (CD26) and some ARs act as binding proteins for extracellular ADA in humans. Since CD26 and ARs interact with ADA at opposite sites, we have investigated if ADA can function as a cell-to-cell communication molecule by bridging the anchoring molecules CD26 and A2AR present on the surfaces of the interacting cells. By combining site-directed mutagenesis of ADA amino acids involved in binding to A2AR and a modification of the bioluminescence resonance energy transfer (BRET) technique that allows detection of interactions between two proteins expressed in different cell populations with low steric hindrance (NanoBRET), we show direct evidence of the specific formation of trimeric complexes CD26-ADA-A2AR involving two cells. By dynamic mass redistribution assays and ligand binding experiments, we also demonstrate that A2AR-NanoLuc fusion proteins are functional. The existence of this ternary complex is in good agreement with the hypothesis that ADA could bridge T-cells (expressing CD26) and dendritic cells (expressing A2AR). This is a new metabolic function for ecto-ADA that, being a single chain protein, it has been considered as an example of moonlighting protein, because it performs more than one functional role (as a catalyst, a costimulator, an allosteric modulator and a cell-to-cell connector) without partitioning these functions in different subunits.

The Emerging Role of GLP-1 Receptors in DNA Repair: Implications in Neurological Disorders

Glucagon-like peptide-1 (GLP-1) is originally found as a metabolic hormone (incretin) that is able to regulate blood-glucose levels via promoting synthesis and secretion of insulin. GLP-1 and many analogues are approved for treatment of type II diabetes. Accumulating results imply that GLP-1 performs multiple functions in various tissues and organs beyond regulation of blood-glucose. The neuroprotective function of GLP-1 has been extensively explored during the past two decades. Three of our previous studies have shown that apurinic/apyrimidinic endonuclease 1 (APE1) is the only protein of the base excision repair (BER) pathway able to be regulated by oxidative stress or exogenous stimulations in rat primary cortical neurons. In this article, we review the role of APE1 in neurodegenerative diseases and its relationship to neuroprotective mechanisms of the activated GLP-1 receptor (GLP-1R) in neurodegenerative disorders. The purpose of this article is to provide new insight, from the aspect of DNA damage and repair, for studying potential treatments in neurodegenerative diseases.