Anti-angiogenic effects of the DPP-4 inhibitor linagliptin via inhibition of VEGFR signalling in the mouse model of oxygen-induced retinopathy

Diabetes mellitus: Classification, mediators, and complications; A gate to identify potential targets for the development of new effective treatments

Nowadays, diabetes mellitus has emerged as a significant global public health concern with a remarkable increase in its prevalence. This review article focuses on the definition of diabetes mellitus and its classification into different types, including type 1 diabetes (idiopathic and fulminant), type 2 diabetes, gestational diabetes, hybrid forms, slowly evolving immune-mediated diabetes, ketosis-prone type 2 diabetes, and other special types. Diagnostic criteria for diabetes mellitus are also discussed. The role of inflammation in both type 1 and type 2 diabetes is explored, along with the mediators and potential anti-inflammatory treatments. Furthermore, the involvement of various organs in diabetes mellitus is highlighted, such as the role of adipose tissue and obesity, gut microbiota, and pancreatic β-cells. The manifestation of pancreatic Langerhans β-cell islet inflammation, oxidative stress, and impaired insulin production and secretion are addressed. Additionally, the impact of diabetes mellitus on liver cirrhosis, acute kidney injury, immune system complications, and other diabetic complications like retinopathy and neuropathy is examined. Therefore, further research is required to enhance diagnosis, prevent chronic complications, and identify potential therapeutic targets for the management of diabetes mellitus and its associated dysfunctions.

Secular trends in the prevalence, incidence, and progression of diabetic retinopathy: the Hisayama Study

PURPOSE

To examine the secular trends in the prevalence, incidence, and progression rates of diabetic retinopathy (DR) in a Japanese community.

METHODS

Community-dwelling Japanese residents aged ≥ 40 years with diabetes participated in comprehensive systemic and ophthalmological surveys, including an examination for DR, in 1998 (n = 220), 2007 (n = 511), 2012 (n = 515), and 2017 (n = 560). DR was assessed using colour fundus photographs after pupil dilation according to the modified Airlie House classification system. To compare the frequencies of newly developed or progressed DR between the studied decades, two eye cohorts were established (the 2000s cohort included 145 participants examined in 1998 and 2007; the 2010s cohort included 255 participants examined in 2007, 2012, and 2017). Trends in the prevalence, incidence, and progression rate of DR were tested by logistic regression analysis with a generalised estimating equation.

RESULTS

The age-adjusted prevalence of DR among individuals with diabetes decreased significantly with time from 1998 to 2017 (27.4% in 1998, 22.8% in 2007, 12.8% in 2012, and 6.4% in 2017; p for trend < 0.001). During this period, the prevalence of DR was decreasing in every haemoglobin A_1c category, but it remained constant in the high systolic blood pressure category. In addition, the rates of new-onset of DR were significantly lower in the 2010s compared to the 2000s (p < 0.001).

CONCLUSION

Our findings suggest that the prevalence and incidence of DR among diabetic people significantly decreased with time over the past two decades in a general Japanese population.

Mechanism of vascular endothelial cell-derived exosomes modified with vascular endothelial growth factor in steroid-induced femoral head necrosis

Steroid-induced avascular necrosis of the femoral head (SANFH) is an intractable orthopedic disease. This study investigated the regulatory effect and molecular mechanism of vascular endothelial cell (VEC)-derived exosomes (Exos) modified with vascular endothelial growth factor (VEGF) in osteogenic and adipogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) in SANFH. VECs were culturedin vitroand transfected with adenovirus Adv-VEGF plasmids. Exos were extracted and identified.In vitro/vivoSANFH models were established and treated with VEGF-modified VEC-Exos (VEGF-VEC-Exos). The internalization of Exos by BMSCs, proliferation and osteogenic and adipogenic differentiation of BMSCs were determined by the uptake test, cell counting kit-8 (CCK-8) assay, alizarin red staining, and oil red O staining. Meanwhile, the mRNA level of VEGF, the appearance of the femoral head, and histological analysis were assessed by reverse transcription quantitative polymerase chain reaction and hematoxylin-eosin staining. Moreover, the protein levels of VEGF, osteogenic markers, adipogenic markers, and mitogen-activated protein kinase (MAPK)/extracellular regulated protein kinases (ERK) pathway-related indicators were examined by Western blotting, along with evaluation of the VEGF levels in femur tissues by immunohistochemistry. Glucocorticoid (GC) induced adipogenic differentiation of BMSCs and inhibited osteogenic differentiation. VEGF-VEC-Exos accelerated the osteogenic differentiation of GC-induced BMSCs and inhibited adipogenic differentiation. VEGF-VEC-Exos activated the MAPK/ERK pathway in GC-induced BMSCs. VEGF-VEC-Exos promoted osteoblast differentiation and suppressed adipogenic differentiation of BMSCs by activating the MAPK/ERK pathway. VEGF-VEC-Exos accelerated bone formation and restrained adipogenesis in SANFH rats. VEGF-VEC-Exos carried VEGF into BMSCs and motivated the MAPK/ERK pathway, thereby promoting osteoblast differentiation of BMSCs in SANFH, inhibiting adipogenic differentiation, and alleviating SANFH.

Diabetic retinopathy: Involved cells, biomarkers, and treatments

Diabetic retinopathy (DR), a leading cause of vision loss and blindness worldwide, is caused by retinal neurovascular unit dysfunction, and its cellular pathology involves at least nine kinds of retinal cells, including photoreceptors, horizontal and bipolar cells, amacrine cells, retinal ganglion cells, glial cells (Müller cells, astrocytes, and microglia), endothelial cells, pericytes, and retinal pigment epithelial cells. Its mechanism is complicated and involves loss of cells, inflammatory factor production, neovascularization, and BRB impairment. However, the mechanism has not been completely elucidated. Drug treatment for DR has been gradually advancing recently. Research on potential drug targets relies upon clear information on pathogenesis and effective biomarkers. Therefore, we reviewed the recent literature on the cellular pathology and the diagnostic and prognostic biomarkers of DR in terms of blood, protein, and clinical and preclinical drug therapy (including synthesized molecules and natural molecules). This review may provide a theoretical basis for further DR research.

Emerging Targets in Type 2 Diabetes and Diabetic Complications

Type 2 diabetes is a metabolic, chronic disorder characterized by insulin resistance and elevated blood glucose levels. Although a large drug portfolio exists to keep the blood glucose levels under control, these medications are not without side effects. More importantly, once diagnosed diabetes is rarely reversible. Dysfunctions in the kidney, retina, cardiovascular system, neurons, and liver represent the common complications of diabetes, which again lack effective therapies that can reverse organ injury. Overall, the molecular mechanisms of how type 2 diabetes develops and leads to irreparable organ damage remain elusive. This review particularly focuses on novel targets that may play role in pathogenesis of type 2 diabetes. Further research on these targets may eventually pave the way to novel therapies for the treatment-or even the prevention-of type 2 diabetes along with its complications.

Association between Add-On Dipeptidyl Peptidase-4 Inhibitor Therapy and Diabetic Retinopathy Progression

This study aimed to investigate the association of add-on dipeptidyl peptidase-4 inhibitor (DPP4i) therapy and the progression of diabetic retinopathy (DR). In this retrospective population-based cohort study, we examined Taiwanese patients with type 2 diabetes, preexisting DR, and aged ≥40 years from 2009 to 2013. Prescription of DPP4i was defined as a medication possession ratio of ≥80% during the first 6 months. The outcomes included vitreous hemorrhage (VH), tractional retinal detachment, macular edema, and interventions including retinal laser therapy, intravitreal injection (IVI), and vitrectomy. Of 1,767,640 patients, 62,824 were eligible for analysis. After matching, the DPP4i and non-DPP4i groups each contained 20,444 patients. The risks of VH (p = 0.013) and macular edema (p = 0.035) were higher in the DPP4i group. The DPP4i group also had higher risks of receiving surgical interventions (retinal laser therapy (p < 0.001), IVI (p = 0.049), vitrectomy (p < 0.001), and any surgical intervention (p < 0.001)). More patients in the DPP4i group received retinal laser therapy (p < 0.001) and IVI (p = 0.001) than in the non-DPP4i group. No between-group differences in cardiovascular outcomes were noted. In the real-world database study, add-on DPP4i therapy may be associated with the progression of DR in patients with type 2 diabetes. No additional cardiovascular risks were found. The early progression of DR in rapid glycemic control was inconclusive in our study. The possible effect of add-on DPP4i therapy in the progression of DR in patients with type 2 diabetes requires further research.

Impact of Systemic Dipeptidyl Peptidase-4 Inhibitor Use in Diabetic Macular Edema

BACKGROUND AND OBJECTIVE

To evaluate impact of baseline systemic dipeptidyl peptidase-4 (DPP-4) inhibitor use in diabetic macular edema (DME).

PATIENTS AND METHODS

This was a post hoc exploratory analysis of previously completed randomized, controlled clinical trials (VISTA and VIVID) in patients with DME evaluating intravitreal aflibercept injection (IAI) every 4 weeks (2q4) or every 8 weeks (2q8) or macular laser photocoagulation.

RESULTS

Overall, a small number of patients (12.2% [n = 35], 9.7% [n = 28], and 15.4% [n = 44]) in the laser control, 2q4, and 2q8 groups reported baseline DPP-4 inhibitor use. There were no differences in changes from baseline in best-corrected visual acuity, central subfield thickness, or rates of 2-or-greater-step improvement in Diabetic Retinopathy Severity Scale score based on DPP-4 inhibitor use within each treatment group.

CONCLUSION

DPP-4 inhibitor use at baseline did not influence the magnitude of visual and anatomic benefit in patients with DME being treated with IAI or laser. [Ophthalmic Surg Lasers Imaging Retina. 2020;51:226-234.].

Evogliptin, a dipeptidyl peptidase-4 inhibitor, attenuates pathological retinal angiogenesis by suppressing vascular endothelial growth factor-induced Arf6 activation

Dipeptidyl peptidase-4 (DPP-4) inhibitors are used for the treatment of type 2 diabetes mellitus (DM). Recent studies have shown that beyond their effect in lowing glucose, DPP-4 inhibitors mitigate DM-related microvascular complications, such as diabetic retinopathy. However, the mechanism by which pathological retinal neovascularization, a major clinical manifestation of diabetic retinopathy, is inhibited is unclear. This study sought to examine the effects of evogliptin, a potent DPP-4 inhibitor, on pathological retinal neovascularization in mice and elucidate the mechanism by which evogliptin inhibits angiogenesis mediated by vascular endothelial growth factor (VEGF), a key factor in the vascular pathogenesis of proliferative diabetic retinopathy (PDR). In a murine model of PDR, an intravitreal injection of evogliptin significantly suppressed aberrant retinal neovascularization. In human endothelial cells, evogliptin reduced VEGF-induced angiogenesis. Western blot analysis showed that evogliptin inhibited the phosphorylation of signaling molecules associated with VEGF-induced cell adhesion and migration. Moreover, evogliptin substantially inhibited the VEGF-induced activation of adenosine 5′-diphosphate ribosylation factor 6 (Arf6), a small guanosine 5′-triphosphatase (GTPase) that regulates VEGF receptor 2 signal transduction. Direct activation of Arf6 using a chemical inhibitor of Arf-directed GTPase-activating protein completely abrogated the inhibitory effect of evogliptin on VEGF-induced activation of the angiogenic signaling pathway, which suggests that evogliptin suppresses VEGF-induced angiogenesis by blocking Arf6 activation. Our results provide insights into the molecular mechanism of the direct inhibitory effect of the DPP-4 inhibitor evogliptin on pathological retinal neovascularization. In addition to its glucose-lowering effect, the antiangiogenic effect of evogliptin could also render it beneficial for individuals with PDR.

Pathological retinal angiogenesis, the damaging formation of new blood vessels in the retina, which is associated with various diseases including diabetes, could be reduced using the anti-diabetic drug evogliptin to inhibit the effects of a vascular growth factor. Researchers in South Korea led by Wonhee Suh and Koung Li Kim at Chung-Ang University in Seoul investigated the molecular mechanism underlying evogliptin’s effects. In studies using mice and cultured human cells they found that evogliptin inhibited the activation of signaling molecules that mediate the effects of vascular endothelial growth factor. They also identified an enzyme in the signaling pathway that is directly inhibited by evogliptin. The results offer molecular level insights into the additional benefit gained from using evogliptin to treat diabetes, distinct from the drug’s established effects in lowering blood glucose.

Protective effects of DPP-4 inhibitor on podocyte injury in glomerular diseases

BACKGROUND

Dipeptidyl peptidase-4 (DPP-4) is a serine protease that inhibits the degradation of glucagon-like peptide 1. DPP-4 inhibitors are used worldwide to treat type 2 diabetes mellitus and were recently shown to have pleiotropic effects such as anti-oxidant, anti-inflammatory, and anti-fibrotic actions. DPP-4 inhibitors improve albuminuria and renal injury including glomerular damage independent of its hypoglycemic effect. Although DPP-4 is mainly expressed in the kidney, the physiological function of DPP-4 remains unclear.

METHODS

The localization of renal DPP-4 activity was determined in human renal biopsy specimens with glycyl-1-prolyl-4-methoxy-2-naphthylamide and the effects of a DPP-4 inhibitor were examined in human cultured podocyte.

RESULTS

DPP-4 activity under normal conditions was observed in some Bowman's capsular epithelial cells and proximal tubules, but not in the glomerulus. DPP-4 activity was observed in crescent formation in anti-neutrophil myeloperoxidase cytoplasmic antigen antibody nephritis, nodular lesions in diabetic nephropathy, and some podocytes in focal segmental glomerulosclerosis. Notably, the DPP-4 inhibitor saxagliptin suppressed DPP-4 activity in podocytes and the proximal tubules. To assess the effect of DPP-4 inhibitor on podocytes, human cultured podocytes were injured by Adriamycin, which increased DPP-4 activity; this activity was dose-dependently suppressed by saxagliptin. Treatment with saxagliptin maintained the structure of synaptopodin and RhoA. Saxagliptin also improved the detachment of podocytes.

CONCLUSIONS

DPP-4 activity induces degradation of synaptopodin and reduction of RhoA, resulting in destruction of the podocyte cytoskeleton. Saxagliptin may have pleiotropic effects to prevent podocyte injury.

Glucagon-like Peptide 1 Receptor Agonists, Diabetic Retinopathy and Angiogenesis: The AngioSafe Type 2 Diabetes Study

AIMS

Recent trials provide conflicting results on the association between glucagon-like peptide 1 receptor agonists (GLP-1RA) and diabetic retinopathy (DR). The aim of the AngioSafe type 2 diabetes (T2D) study was to determine the role of GLP-1RA in angiogenesis using clinical and preclinical models.

METHODS

We performed two studies in humans. In study 1, we investigated the effect of GLP-1RA exposure from T2D diagnosis on the severity of DR, as diagnosed with retinal imaging (fundus photography). In study 2, a randomized 4-week trial, we assessed the effect of liraglutide on circulating hematopoietic progenitor cells (HPCs), and angio-miRNAs.We then studied the experimental effect of Exendin-4, on key steps of angiogenesis: in vitro on human endothelial cell proliferation, survival and three-dimensional vascular morphogenesis; and in vivo on ischemia-induced neovascularization of the retina in mice.

RESULTS

In the cohort of 3154 T2D patients, 10% displayed severe DR. In multivariate analysis, sex, disease duration, glycated hemoglobin (HbA1c), micro- and macroangiopathy, insulin therapy and hypertension remained strongly associated with severe DR, while no association was found with GLP-1RA exposure (o 1.139 [0.800-1.622], P = .47). We further showed no effect of liraglutide on HPCs, and angio-miRNAs. In vitro, we demonstrated that exendin-4 had no effect on proliferation and survival of human endothelial cells, no effect on total length and number of capillaries. Finally, in vivo, we showed that exendin-4 did not exert any negative effect on retinal neovascularization.

CONCLUSIONS

The AngioSafe T2D studies provide experimental and clinical data confirming no effect of GLP-1RA on angiogenesis and no association between GLP-1 exposure and severe DR.

The impact of sitagliptin on macrophage polarity and angiogenesis in the osteointegration of titanium implants in type 2 diabetes

BACKGROUND

Clinical evidence indicates that sitagliptin treatment improves bone quality in diabetic patients, but the mechanisms involved remain elusive. Here, we studied the role of angiogenesis with sitagliptin treatment in diabetes-induced poor osteointegration of titanium implants and the underlying mechanisms.

METHODS

In vitro, Human Umbilical Vein Endothelial Cells (HUVECs) incubated on titanium (Ti) surface were subjected to 1) normal milieu (NM); 2) diabetic milieu (DM); 3) DM + sitagliptin; 4) NM + macrophage; 5) DM + macrophage; or 6) DM + macrophage + sitagliptin. Microphage and HUVECs were cultured alone or co-cultured in a Transwell system. In vivo, DM was induced by high-fat diet and administration of streptozotocin (STZ) in rats. Titanium screws were implanted in the femurs of rats in three groups: Control, DM, Sitagliptin-treated DM.

RESULTS

In vitro, when cells were incubated alone, DM caused M1 polarization of macrophage, evidenced by the increased iNOS and decreased CD206 expressions, and obvious dysfunctions of HUVECs. The DM-induced injury of endothelial cells were significantly worsened when the two cells were co-cultured. The addition of sitagliptin markedly reversed the changes of macrophage but not of HUVECs in DM when cells were cultured alone. When cells co-cultured, however, both the abnormal macrophage polarization and the endothelial impairment in DM was significantly alleviated by sitagliptin. In vivo, compared with normal animals, DM animals showed imbalanced M1/M2 polarization, angiogenesis inhibition and poor bone formation on the bone-implant interface (BII), which were significantly ameliorated by sitagliptin treatment.

CONCLUSION

Our results demonstrate macrophage polarization imbalance as a crucial mechanism underlying the impaired angiogenesis and bone healing in diabetes, and provide sitagliptin as a promising novel drug for biomaterial-engineering to improve the osteointegration of titanium implants in diabetic patients.

Vascular and Neuronal Protection in the Developing Retina: Potential Therapeutic Targets for Retinopathy of Prematurity

Retinopathy of prematurity (ROP) is a common retinal disease in preterm babies. To prolong the lives of preterm babies, high oxygen is provided to mimic the oxygen level in the intrauterine environment for postnatal organ development. However, hyperoxia-hypoxia induced pathological events occur when babies return to room air, leading to ROP with neuronal degeneration and vascular abnormality that affects retinal functions. With advances in neonatal intensive care, it is no longer uncommon for increased survival of very-low-birth-weight preterm infants, which, therefore, increased the incidence of ROP. ROP is now a major cause of preventable childhood blindness worldwide. Current proven treatment for ROP is limited to invasive retinal ablation, inherently destructive to the retina. The lack of pharmacological treatment for ROP creates a great need for effective and safe therapies in these developing infants. Therefore, it is essential to identify potential therapeutic agents that may have positive ROP outcomes, especially in preserving retinal functions. This review gives an overview of various agents in their efficacy in reducing retinal damages in cell culture tests, animal experiments and clinical studies. New perspectives along the neuroprotective pathways in the developing retina are also reviewed.

DPP-4 inhibition by linagliptin prevents cardiac dysfunction and inflammation by targeting the Nlrp3/ASC inflammasome

We compared the effects of linagliptin (Lina, a DPP4 inhibitor) and GLP-1 receptor activation by exenatide followed by exendin-4 in an infusion pump (EX) on infarct size (IS), post-infarction activation of the inflammasome and remodeling in wild-type (WT) and db/db diabetic mice. Mice underwent 30 min ischemia followed by 24 h reperfusion. IS was assessed by TTC. Additional mice underwent permanent coronary artery occlusion. Echocardiography was performed 2w after infarction. Activation of the inflammasome in the border zone of the infarction was assessed by rt-PCR and ELISA 2w after reperfusion. Further in vitro experiments were done using primary human cardiofibroblasts and cardiomyocytes exposed to simulated ischemia-reoxygenation. Lina and EX limited IS in both the WT and the db/db mice. Lina and EX equally improved ejection fraction in both the WT and the db/db mice. mRNA levels of ASC, NALP3, IL-1β, IL-6, Collagen-1, and Collagen-3 were higher in the db/db mice than in the WT mice. Infarction increased these levels in the WT and db/db mice. Lina more than EX attenuated the increase in ASC, NALP3, IL-1β, IL-6, Collagen-1 and Collagen-3, TNFα and IL-1β, and decreased apoptosis, especially in the db/db mice. In vitro experiments showed that Lina, but not EX, attenuated the increase in TLR4 expression, an effect that was dependent on p38 activation with downstream upregulation of Let-7i and miR-146b levels. Lina and EX had similar effects on IS and post-infarction function, but Lina attenuated the activation of the inflammasome and the upregulation of collagen-1 and collagen-3 more than direct GLP-1 receptor activation. This effect depends on p38 activation with downstream upregulation of miR-146b levels that suppresses TLR4 expression.