Gemigliptin, a dipeptidyl peptidase-4 inhibitor, inhibits retinal pericyte injury in db/db mice and retinal neovascularization in mice with ischemic retinopathy

Manifestation of Pathology in Animal Models of Diabetic Retinopathy Is Delayed from the Onset of Diabetes

Diabetic retinopathy (DR) is the most common complication that develops in patients with diabetes mellitus (DM) and is the leading cause of blindness worldwide. Fortunately, sight-threatening forms of DR develop only after several decades of DM. This well-documented resilience to DR suggests that the retina is capable of protecting itself from DM-related damage and also that accumulation of such damage occurs only after deterioration of this resilience. Despite the enormous translational significance of this phenomenon, very little is known regarding the nature of resilience to DR. Rodent models of DR have been used extensively to study the nature of the DM-induced damage, i.e., cardinal features of DR. Many of these same animal models can be used to investigate resilience because DR is delayed from the onset of DM by several weeks or months. The purpose of this review is to provide a comprehensive overview of the literature describing the use of rodent models of DR in type-1 and type-2 diabetic animals, which most clearly document the delay between the onset of DM and the appearance of DR. These readily available experimental settings can be used to advance our current understanding of resilience to DR and thereby identify biomarkers and targets for novel, prevention-based approaches to manage patients at risk for developing DR.

Pericyte Loss in Diseases

Pericytes are specialized cells located in close proximity to endothelial cells within the microvasculature. They play a crucial role in regulating blood flow, stabilizing vessel walls, and maintaining the integrity of the blood-brain barrier. The loss of pericytes has been associated with the development and progression of various diseases, such as diabetes, Alzheimer's disease, sepsis, stroke, and traumatic brain injury. This review examines the detection of pericyte loss in different diseases, explores the methods employed to assess pericyte coverage, and elucidates the potential mechanisms contributing to pericyte loss in these pathological conditions. Additionally, current therapeutic strategies targeting pericytes are discussed, along with potential future interventions aimed at preserving pericyte function and promoting disease mitigation.

Association Between DPP-4 Inhibitors and Events of Colorectal and Liver Cancers in Patients With Diabetes Receiving Second-Line Agents: A Nested Case-Control Study

Objective

Plasma dipeptidyl peptidase-4 (DPP4) levels were significantly lower in patients with colorectal and liver cancers, and animal studies also showed DPP4 inhibitors (DPP4is) have procarcinogenic effects in colorectal cancer. Until now, whether DPP4is therapy affects the progression of liver cancer and colorectal cancer in patients with T2DM has not been well investigated. We investigated the association between cumulative defined daily dose (cDDD) of DPP4is exposure and risks of liver and colorectal cancers in patients with type 2 diabetes.

Materials and Methods

We identified 268,520 patients with diabetes receiving DPP4is as second-line agents between March 1, 2009, and December 31, 2013, from Taiwan’s National Health Insurance Research Database, Taiwan Cancer Registry, and National Death Registry of Taiwan. The amount of DPP4is were divided into three groups (low, medium, and high) based on the interquartile range of the cDDD of the DPP4is.

Results

The data showed that the low cDDD of DPP-4is was associated with a reducing risk of colorectal cancer [adjusted odds ratio (OR), 0.49; 95% CI, 0.32–0.75; P=0.001]. However, the high cDDD of DPP-4is was associated with an increasing risk of colorectal cancer (adjusted OR, 1.86; 95% CI, 1.32–2.61; P<0.001). No association between DPP4is use and liver cancer risk was observed.

Conclusions

This nested case study revealed a J-shaped association between the cDDD of DPP-4is and colorectal cancer risk, but not liver cancer risk. Therefore, the effects of long-term DPP4is use on colorectal cancer risk warrant further study.

Tofacitinib Ameliorates Retinal Vascular Leakage in a Murine Model of Diabetic Retinopathy with Type 2 Diabetes

We have previously reported that inhibition of the Janus kinase 1 (JAK1) signaling ameliorates IL-17A-mediated blood-retinal barrier (BRB) dysfunction. Higher levels of IL-17A have been observed in the blood and intraocular fluids in patients with diabetic retinopathy (DR), in particular those with diabetic macular oedema. This study aimed to understand whether JAK1 inhibition could prevent BRB dysfunction in db/db mice, a model of type 2 diabetes (T2D). An in vitro study showed that high glucose treatment disrupted the junctional distribution of claudin-5 in bEnd3 cells and ZO-1 in ARPE19 cells and that tofacitinib citrate treatment prevented high glucose-mediated tight junction disruption. Albumin leakage, accompanied by increased levels of the phosphorylated form of JAK1 (pJAK1), was observed in three-month-old db/db mice. Treatment of two-and-a-half-month-old db/db mice with tofacitinib citrate for two weeks significantly reduced retinal albumin leakage and reduced pJAK1 expression. pJAK1 expression was also detected in human DR retina. Our results suggest that JAK1 inhibition can ameliorate BRB dysfunction in T2D, and JAK1 inhibitors such as tofacitinib citrate may be re-purposed for the management of diabetic macular oedema.

Gemigliptin suppresses salivary dysfunction in streptozotocin-induced diabetic rats

Patients with diabetes commonly experience hyposalivation, which induces discomfort in eating, swallowing, dryness, smell, and speaking, as well as increases the incidence of periodontal disease. Dipeptidyl peptidase-4 (DPP4) inhibitors are frequently used as antidiabetic drugs that lower glucose levels by utilizing similar mechanisms; however, additional protective functions of each gliptin have been discovered. In this study, the protective roles of gemigliptin, a DPP4 inhibitor, against salivary dysfunction under diabetic conditions were investigated. Streptozotocin-induced diabetic rats received gemigliptin 10 mg/kg or 100 mg/kg via oral gavage for 3 weeks. The weights of salivary gland tissues, saliva secretion, and antioxidant capacity in salivary glands were reduced after diabetes induction, but were significantly preserved following gemigliptin treatment. In salivary gland analysis, expression of apoptotic proteins, as well as amylase and aquaporin-5 (AQP5) protein expression, were increased following gemigliptin treatment. Furthermore, the number of TUNEL-positive cells decreased after gemigliptin treatment. Therefore, gemigliptin has protective roles against salivary dysfunction observed in diabetes, mediated via antioxidant, anti-apoptotic, and salivary secretion mechanisms. These results may help in selecting a suitable drug for patients with diabetes experiencing salivary dysfunction.

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.

Aucuba japonica extract inhibits retinal neovascularization in a mouse model of oxygen-induced retinopathy, with its bioactive components preventing VEGF-induced retinal vascular hyperpermeability

Neovascularization in the retina is common pathophysiology of diabetic retinal microvasculopathy and exudative macular degeneration. Our study assessed the inhibitory activity of an ethanol-based extract of Aucuba japonica (AJE) on abnormal angiogenesis in the retina with a hyperoxia-induced neovascular retinopathy model. The inhibitory effects of aucubin, quercetin, and kaempferol, bioactive compounds, from A. japonica, on retinal vascular hyperpermeability were also examined. On the 7th postnatal day (P7), the C57BL/6 pups were exposed to a hyperoxic environment with 75% oxygen to develop the experimental angiogenesis in retinas. On the 12th postnatal day (P12), the pups were then returned to the normal atmospheric pressure of oxygen. From P12 to P16, the administration was intraperitoneal. The dose per day was 250 mg per kg weight. Retinal neovascularization was measured with retinal flat mounts prepared on P17. We also measured the vascular leakage mediated by the vascular endothelial growth factor (VEGF) in retinas. Mice treated with AJE had markedly smaller neovascular lesions, in comparison with vehicle-administered mice. AJE downregulated the expression of both VEGF protein and mRNA. In addition, aucubin, quercetin, and kaempferol ameliorated VEGF-induced retinal vascular leakage. The results of our study suggest that AJE is a potent antiangiogenic substance. AJE could also serve as a therapeutic agent for abnormal growth of vessels in the retina in patients with ischemic retinopathy. The bioactive compounds of AJE may be responsible for its antiangiogenic abilities.

siRNA-mediated silencing of PAI-1 gene acts as a promoter over the recanalization of endothelial progenitor cells in rats with venous thrombosis

With the changing lifestyle, venous thrombosis (VT) is becoming increasingly prevalent and poses a burden on the health economy. Endothelial progenitor cells (EPCs) are recruited into resolving VT. We aimed to investigate the effect of plasminogen activator inhibitor 1 (PAI-1) silencing on the recanalization of VT in rat EPCs. EPCs and VT rat models were cultured and treated with negative control-siRNA vector and PAI-1-siRNA vector, respectively. 4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, wound-healing test, and Matrigel-induced tubular experiment were performed to detect the ability of cell proliferation, migration, and EPCs lumen formation. Immunohistochemistry was used to observe the recanalization of thrombus. The messenger RNA (mRNA) and protein expression of PAI-1 and vascular endothelial growth factor (VEGF) were determined by reverse transcription quantitative polymerase chain reaction and Western blot analysis. PAI-1-siRNA enhances the luminal formation ability of EPCs and significantly promotes EPCs homing. In response to PAI-1 gene silencing, tissues from inferior vena cava displayed reduced mRNA and protein expression of PAI-1, increased VEGF expression as well as promoted lumen-like structures. PAI-1 gene silencing can promote the recanalization of VT by enhancement of the luminal formation ability of rats' EPCs.

Ginseng Extract Modified by Pectin Lyase Inhibits Retinal Vascular Injury and Blood-Retinal Barrier Breakage in a Rat Model of Diabetes

GS-E3D is an enzymatically modified ginseng extract by pectin lyase. In this study, we evaluated the preventive effects of GS-E3D on blood-retinal barrier (BRB) leakage in a rat model of diabetes. To produce diabetes, rats were injected with streptozotocin. GS-E3D was orally gavaged at 25, 50, and 100 mg/kg body weight for 6 weeks. We then compared the effect of GS-E3D with that of an unmodified ginseng extract (UGE) on retinal vascular leakage. The administration of GS-E3D significantly blocked diabetes-induced BRB breakdown. Immunofluorescence staining showed that GS-E3D reduced the loss of occludin in diabetic rats. In TUNEL staining, the number of apoptotic retinal microvascular cells was dose dependently decreased by GS-E3D treatment. GS-E3D decreased the accumulations of advanced glycation end products in the retinal vessels. In addition, the inhibition potential of GS-E3D on BRB breakage was stronger compared with UGE. These results indicate that GS-E3D could be a beneficial treatment option for preventing diabetes-induced retinal vascular injury.

Protective effects of gemigliptin against type II collagen degradation in human chondrocytes

Degradation of components of the extracellular matrix such as type II collagen in articular cartilage induced by matrix metalloproteinases (MMPs) has been considered as a major pathological characteristic of osteoarthritis (OA). Gemigliptin is a potent and a highly selective dipeptidyl peptidase-IV (DPP-IV) inhibitor, which has been clinically used as an oral agent for the treatment of type 2 diabetes. However, the effects of gemigliptin on articular cartilage destruction and the pathogenesis of OA remain unknown. In the current study, we addressed for the first time the inhibitory property of gemigliptin against interleukin-1β (IL-1β)-induced degradation of type II collagen in human chondrocytes. Our results demonstrate that gemigliptin treatment inhibited the expression of matrix metalloproteinase 1 (MMP-1), matrix metalloproteinase 3 (MMP-3), and matrix metalloproteinase 13 (MMP-13) at both the gene and protein levels. Mechanistically, our results indicate that gemigliptin inhibited activation of the nuclear factor-κB (NF-κB) signaling pathway by suppressing phosphorylation of IκB kinase (IKK)/nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor α (IκBα) and p38. Our results implicate that gemigliptin treatment might be a potential therapeutic strategy for chondroprotective therapy.

Protective Effects of Gemigliptin, a Dipeptidyl Peptidase-4 Inhibitor, against Cisplatin-Induced Nephrotoxicity in Mice

Dipeptidyl peptidase-4 (DPP-4) inhibitors are widely used antihyperglycemic agents for the treatment of type 2 diabetes mellitus. Recently, the pleiotropic actions of DPP-4 inhibitors have drawn much attention. In the present study, we aimed to examine whether gemigliptin, a recently developed DPP-4 inhibitor, could protect against cisplatin-induced nephrotoxicity. We showed that pretreatment with gemigliptin attenuated cisplatin-induced renal dysfunction, as shown by analysis of plasma creatinine levels and blood urea nitrogen and histological damage. Elevated plasma levels of active glucagon-like peptide-1 were observed in gemigliptin-pretreated mice after cisplatin treatment, compared to that in cisplatin alone-treated mice. Gemigliptin attenuated cisplatin-induced apoptotic cell death, as assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling and Western blot analysis in the kidneys. Gemigliptin also decreased the plasma levels of tumor necrosis factor-α and monocyte chemoattractant protein-1 and attenuated nuclear staining of nuclear factor kappa-B p65 in the kidneys. In addition, gemigliptin increased the protein expression of heme oxygenase-1 (HO-1) and NAD(P)H:quinone oxidoreductase 1 (NQO1) in the kidneys of cisplatin-treated mice. Taken together, these results suggest that pretreatment with gemigliptin protects against cisplatin-induced nephrotoxicity in mice, possibly via inhibition of apoptotic cell death and inflammatory responses through induction of HO-1 and NQO1 expression.

EGHB010, a Standardized Extract of Paeoniae Radix and Glycyrrhizae Radix, Inhibits VEGF-Induced Tube Formation In Vitro and Retinal Vascular Leakage and Choroidal Neovascularization In Vivo

EGHB010 is a hot water extract of the rhizome mixture of Paeonia lactiflora Pallas and Glycyrrhiza uralensis Fisch. Choroidal neovascularization (CNV) and vascular leakage are the common pathophysiologies of age-related macular degeneration. In this study, we aimed to evaluate the effect of EGHB010 on retinal vascular leakage and laser-induced CNV in a rat model. Vascular endothelial growth factor- (VEGF-) induced tube formation was assayed in human retinal microvascular endothelial cells. Intravitreal VEGF-induced blood-retinal barrier breakdown was assayed in Sprague-Dawley rats. Experimental CNV was induced by laser photocoagulation in Brown Norway rats. EGHB010 (50 and 100 mg/kg/day) was administered orally for 10 days after laser photocoagulation. Choroidal flat mounts were prepared to measure the lesion size of CNV. Incubation of retinal vascular endothelial cells with EGHB010 (12.5 and 25 μg/mL) resulted in the inhibition of VEGF-induced tube formation in a dose-dependent manner. VEGF-mediated retinal vascular leakage was blocked by the oral administration of EGHB010. The CNV area was significantly lower in EGHB010-treated rats than in vehicle-treated rats. These results suggest that EGHB010 is a potent antiangiogenic agent. Thus, the oral administration of EGHB010 may have a beneficial effect in the treatment of vascular leakage and CNV in patients with age-related macular degeneration.

Gemigliptin: An Update of Its Clinical Use in the Management of Type 2 Diabetes Mellitus

Dipeptidyl peptidase-4 (DPP-4) inhibitors are a new class of oral antidiabetic agent for the treatment of type 2 diabetes mellitus. They increase endogenous levels of incretin hormones, which stimulate glucose-dependent insulin secretion, decrease glucagon secretion, and contribute to reducing postprandial hyperglycemia. Although DPP-4 inhibitors have similar benefits, they can be differentiated in terms of their chemical structure, pharmacology, efficacy and safety profiles, and clinical considerations. Gemigliptin (brand name: Zemiglo), developed by LG Life Sciences, is a potent, selective, competitive, and long acting DPP-4 inhibitor. Various studies have shown that gemigliptin is an optimized DPP-4 inhibitor in terms of efficacy, safety, and patient compliance for treatment of type 2 diabetes mellitus. In this review, we summarize the characteristics of gemigliptin and discuss its potential benefits in clinical practice.