Kallikrein-binding protein inhibits retinal neovascularization and decreases vascular leakage

Vascular Endothelial Growth Factor Receptor 1 Targeting Fusion Polypeptides with Stimuli-Responsiveness for Anti-angiogenesis

Genetically engineered fusion polypeptides have been investigated to introduce unique bio-functionality and improve some therapeutic activity for anti-angiogenesis. We report herein that stimuli-responsive, vascular endothelial growth factor receptor 1 (VEGFR1) targeting fusion polypeptides composed of a VEGFR1 (fms-like tyrosine kinase-1 (Flt1)) antagonist, an anti-Flt1 peptide, and a thermally responsive elastin-based polypeptide (EBP) were rationally designed at the genetic level, biosynthesized, and purified by inverse transition cycling to develop potential anti-angiogenic fusion polypeptides to treat neovascular diseases. A series of hydrophilic EBPs with different block lengths were fused with an anti-Flt1 peptide, forming anti-Flt1-EBPs, and the effect of EBP block length on their physicochemical properties was examined. While the anti-Flt1 peptide decreased phase-transition temperatures of anti-Flt1-EBPs, compared with EBP blocks, anti-Flt1-EBPs were soluble under physiological conditions. The anti-Flt1-EBPs dose dependently inhibited the binding of VEGFR1 against vascular endothelial growth factor (VEGF) as well as tube-like network formation of human umbilical vein endothelial cells under VEGF-triggered angiogenesis in vitro because of the specific binding between anti-Flt1-EBPs and VEGFR1. Furthermore, the anti-Flt1-EBPs suppressed laser-induced choroidal neovascularization in a wet age-related macular degeneration mouse model in vivo. Our results indicate that anti-Flt1-EBPs as VEGFR1-targeting fusion polypeptides have great potential for efficacious anti-angiogenesis to treat retinal-, corneal-, and choroidal neovascularization.

Kinins and Their Receptors as Potential Therapeutic Targets in Retinal Pathologies

The kallikrein-kinin system (KKS) contributes to retinal inflammation and neovascularization, notably in diabetic retinopathy (DR) and neovascular age-related macular degeneration (AMD). Bradykinin type 1 (B1R) and type 2 (B2R) receptors are G-protein-coupled receptors that sense and mediate the effects of kinins. While B2R is constitutively expressed and regulates a plethora of physiological processes, B1R is almost undetectable under physiological conditions and contributes to pathological inflammation. Several KKS components (kininogens, tissue and plasma kallikreins, and kinin receptors) are overexpressed in human and animal models of retinal diseases, and their inhibition, particularly B1R, reduces inflammation and pathological neovascularization. In this review, we provide an overview of the KKS with emphasis on kinin receptors in the healthy retina and their detrimental roles in DR and AMD. We highlight the crosstalk between the KKS and the renin–angiotensin system (RAS), which is known to be detrimental in ocular pathologies. Targeting the KKS, particularly the B1R, is a promising therapy in retinal diseases, and B1R may represent an effector of the detrimental effects of RAS (Ang II-AT1R).

Iripin-3, a New Salivary Protein Isolated From Ixodes ricinus Ticks, Displays Immunomodulatory and Anti-Hemostatic Properties In Vitro

Tick saliva is a rich source of pharmacologically and immunologically active molecules. These salivary components are indispensable for successful blood feeding on vertebrate hosts and are believed to facilitate the transmission of tick-borne pathogens. Here we present the functional and structural characterization of Iripin-3, a protein expressed in the salivary glands of the tick Ixodes ricinus, a European vector of tick-borne encephalitis and Lyme disease. Belonging to the serpin superfamily of protease inhibitors, Iripin-3 strongly inhibited the proteolytic activity of serine proteases kallikrein and matriptase. In an in vitro setup, Iripin-3 was capable of modulating the adaptive immune response as evidenced by reduced survival of mouse splenocytes, impaired proliferation of CD4+ T lymphocytes, suppression of the T helper type 1 immune response, and induction of regulatory T cell differentiation. Apart from altering acquired immunity, Iripin-3 also inhibited the extrinsic blood coagulation pathway and reduced the production of pro-inflammatory cytokine interleukin-6 by lipopolysaccharide-stimulated bone marrow-derived macrophages. In addition to its functional characterization, we present the crystal structure of cleaved Iripin-3 at 1.95 Å resolution. Iripin-3 proved to be a pluripotent salivary serpin with immunomodulatory and anti-hemostatic properties that could facilitate tick feeding via the suppression of host anti-tick defenses. Physiological relevance of Iripin-3 activities observed in vitro needs to be supported by appropriate in vivo experiments.

Sirt1: A Guardian of the Development of Diabetic Retinopathy

Diabetic retinopathy is a multifactorial disease, and the exact mechanism of its pathogenesis remains obscure. Sirtuin 1 (Sirt1), a multifunctional deacetylase, is implicated in the regulation of many cellular functions and in gene transcription, and retinal Sirt1 is inhibited in diabetes. Our aim was to determine the role of Sirt1 in the development of diabetic retinopathy and to elucidate the molecular mechanism of its downregulation. Using Sirt1-overexpressing mice that were diabetic for 8 months, structural, functional, and metabolic abnormalities were investigated in vascular and neuronal retina. The role of epigenetics in Sirt1 transcriptional suppression was investigated in retinal microvessels. Compared with diabetic wild-type mice, retinal vasculature from diabetic Sirt1 mice did not present any increase in the number of apoptotic cells or degenerative capillaries or decrease in vascular density. Diabetic Sirt1 mice were also protected from mitochondrial damage and had normal electroretinography responses and ganglion cell layer thickness. Diabetic wild-type mice had hypermethylated Sirt1 promoter DNA, which was alleviated in diabetic Sirt1 mice, suggesting a role for epigenetics in its transcriptional suppression. Thus strategies targeted to ameliorate Sirt1 inhibition have the potential to maintain retinal vascular and neuronal homeostasis, providing opportunities to retard the development of diabetic retinopathy in its early stages.

Kallistatin exerts anti-lymphangiogenic effects by inhibiting lymphatic endothelial cell proliferation, migration and tube formation

Kallistatin has been recognized as an endogenous angiogenic inhibitor. However, its effects on lymphatic endothelial cells and lymphangiogenesis remain poorly understood. Lymphangiogenesis is involved in tumor metastasis via the lymphatic vasculature in various types of tumors. The aim of this study was to investigate the effects of kallistatin on lymphangiogenesis and the mechanism of action involved. Treatment with kallistatin recombinant protein or overexpression of kallistatin inhibited the proliferation, migration and tube formation of human lymphatic endothelial cells (hLECs), and induced apoptosis of hLECs. Furthermore, our results showed that the lymphatic vessel density (LVD) was reduced in lung and stomach sections from kallistatin-overexpressing transgenic mice. Treatment with kallistatin recombinant protein decreased the LVD in the implanted gastric xenograft tumors of nude mice. To the best of our knowledge, the present study is the first to demonstrate that kallistatin possesses anti-lymphangiogenic activity in vitro and in vivo. Moreover, kallistatin inhibited proliferation and migration of hLECs by reducing the phosphorylation of ERK and Akt, respectively. These findings suggested that kallistatin may be a promising agent that could be used to suppress cancer metastasis by inhibiting both angiogenesis and lymphangiogenesis.

The Potential Role of Kallistatin in the Development of Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a vascular condition that causes permanent dilation of the abdominal aorta, which can lead to death due to aortic rupture. The only treatment for AAA is surgical repair, and there is no current drug treatment for AAA. Aortic inflammation, vascular smooth muscle cell apoptosis, angiogenesis, oxidative stress and vascular remodeling are implicated in AAA pathogenesis. Kallistatin is a serine proteinase inhibitor, which has been shown to have a variety of functions, potentially relevant in AAA pathogenesis. Kallistatin has been reported to have inhibitory effects on tumor necrosis factor alpha (TNF-α) signaling induced oxidative stress and apoptosis. Kallistatin also inhibits vascular endothelial growth factor (VEGF) and Wnt canonical signaling, which promote inflammation, angiogenesis, and vascular remodeling in various pre-clinical experimental models. This review explores the potential protective role of kallistatin in AAA pathogenesis.

Role of heparin and non heparin binding serpins in coagulation and angiogenesis: A complex interplay

Pro-coagulant, anti-coagulant and fibrinolytic pathways are responsible for maintaining hemostatic balance under physiological conditions. Any deviation from these pathways would result in hypercoagulability leading to life threatening diseases like myocardial infarction, stroke, portal vein thrombosis, deep vein thrombosis (DVT) and pulmonary embolism (PE). Angiogenesis is the process of sprouting of new blood vessels from pre-existing ones and plays a critical role in vascular repair, diabetic retinopathy, chronic inflammation and cancer progression. Serpins; a superfamily of protease inhibitors, play a key role in regulating both angiogenesis and coagulation. They are characterized by the presence of highly conserved secondary structure comprising of 3 β-sheets and 7-9 α-helices. Inhibitory role of serpins is modulated by binding to cofactors, specially heparin and heparan sulfate proteoglycans (HSPGs) present on cell surfaces and extracellular matrix. Heparin and HSPGs are the mainstay of anti-coagulant therapy and also have therapeutic potential as anti-angiogenic inhibitors. Many of the heparin binding serpins that regulate coagulation cascade are also potent inhibitors of angiogenesis. Understanding the molecular mechanism of the switch between their specific anti-coagulant and anti-angiogenic role during inflammation, stress and regular hemostasis is important. In this review, we have tried to integrate the role of different serpins, their interaction with cofactors and their interplay in regulating coagulation and angiogenesis.

The role of pharmacogenetics and advances in gene therapy in the treatment of diabetic retinopathy

Diabetic retinopathy (DR) and its complications such as diabetic macular edema continue to remain a major cause for legal blindness in the developed world. While the introduction of anti-tVEGF agents has significantly improved visual outcomes of patients with DR, unpredictable response, largely due to genetic polymorphisms, appears to be a challenge with this therapy. With advances in identification of various genetic biomarkers, novel therapeutic strategies consisting of gene transfer are being developed and tested for patients with DR. Application of pharmacogenetic principles appears to be a promising futuristic strategy to attenuate diabetes-mediated retinal vasculopathy. In this comprehensive review, data from recent studies in the field of pharmacogenomics for the treatment of DR have been provided.

Ras-related C3 botulinum toxin substrate 1 activation is involved in the pathogenesis of diabetic retinopathy

This study used a streptozotocin (STZ)-induced rat model of diabetes to investigate whether Ras-related C3 botulinum toxin substrate 1 (Rac1) was involved in the pathogenesis of diabetic retinopathy. The effects of Rac1 inhibition on vascular endothelial (VE)-cadherin and β-catenin expression in high glucose-induced rat retinal endothelial cells (RRECs) were additionally examined. Rac1 activation in the retinas from STZ-induced diabetic rats and in high glucose-induced RRECs was measured by reverse transcription-quantitative polymerase chain reaction analysis, immunohistochemistry and western blot analysis. The expression levels of VE-cadherin and β-catenin were also examined with or without Rac1 inhibition through small interfering (si)RNA transfection. STZ-induced diabetes was associated with an increase in the vascular permeability of the retina. Furthermore, Rac1 activation was increased in the retina of STZ-induced diabetic rats and in high glucose-induced RRECs compared with that in the controls. Immunohistochemistry showed that immunostaining of Rac1 was localized in the outer plexiform, inner nuclear, inner plexiform and ganglion cell layers and in the retinal microvasculature of rats. The expression of β-catenin was increased in the retinas of the diabetic rats at four, eight and 12 weeks after the induction of diabetes compared with that in the controls. Additionally, Rac1 activation was required for the high glucose-induced VE-cadherin expression decrease and for β-catenin expression in high glucose-induced RRECs. Rac1 inhibition by Rac1-siRNA transfection effectively prevented hyperpermeability, β-catenin expression and the VE-cadherin expression decrease in high glucose-induced RRECs. In conclusion, diabetes affects the expression of Rac1 in the retina. Rac1 may be involved in the diabetes-induced damage and/or alterations to the blood-retinal barrier through changes in VE-cadherin and β-catenin expression.

Integrin-linked kinase inhibition attenuates permeability of the streptozotocin-induced diabetic rat retina

Integrin-linked kinase (ILK), as a multi-functional regulator, has been associated with diabetic retinopathy (DR). In this study, we investigated whether inhibition of ILK could result in therapeutic effects. Diabetes mellitus's rats were induced by streptozotocin (STZ) injection. After 1 weeks induction, rats were injected intraperitoneally daily with ILK inhibitor, QLT0267, at 5 mg/kg. Then, the rats were examined by 4, 8, and 12 weeks after first STZ injection. We found that QLT0267 treatment could not only lower ILK level in retina at as early as 3 weeks after the onset of diabetes but also attenuate retina permeability, which was measured by Evan's blue. Maximum effect was found in 11 weeks treatment. Meanwhile, QLT0267 did not disturbed blood glucose concentration. Furthermore, QLT0267 inhibited Akt (Ser473) activation and reduced expression of HIF1α and VEGF which were evaluated by western blot, real time PCR, and immunohistochemistry. We conclude that ILK may be a new target for DR.

The kallikrein-kinin system in diabetic retinopathy

Diabetic retinopathy (DR) is a major microvascular complication associated with type 1 and type 2 diabetes mellitus, which can lead to visual impairment and blindness. Current treatment strategies for DR are mostly limited to laser therapies, steroids, and anti-VEGF agents, which are often associated with unwanted side effects leading to further complications. Recent evidence suggests that kinins play a primary role in the development of DR through enhanced vascular permeability, leukocytes infiltration, and other inflammatory mechanisms. These deleterious effects are mediated by kinin B1 and B2 receptors, which are expressed in diabetic human and rodent retina. Importantly, kinin B1 receptor is virtually absent in sane tissue, yet it is induced and upregulated in diabetic retina. These peptides belong to the kallikrein-kinin system (KKS), which contains two separate and independent pathways of regulated serine proteases, namely plasma kallikrein (PK) and tissue kallikrein (TK) that are involved in the biosynthesis of bradykinin (BK) and kallidin (Lys-BK), respectively. Hence, ocular inhibition of kallikreins or antagonism of kinin receptors offers new therapeutic avenues in the treatment and management of DR. Herein, we present an overview of the principal features and known inflammatory mechanisms associated with DR along with the current therapeutic approaches and put special emphasis on the KKS as a new and promising therapeutic target due to its link with key pathways directly associated with the development of DR.

Kallistatin modulates immune cells and confers anti-inflammatory response to protect mice from group A streptococcal infection

Group A streptococcus (GAS) infection may cause severe life-threatening diseases, including necrotizing fasciitis and streptococcal toxic shock syndrome. Despite the availability of effective antimicrobial agents, there has been a worldwide increase in the incidence of invasive GAS infection. Kallistatin (KS), originally found to be a tissue kallikrein-binding protein, has recently been shown to possess anti-inflammatory properties. However, its efficacy in microbial infection has not been explored. In this study, we transiently expressed the human KS gene by hydrodynamic injection and investigated its anti-inflammatory and protective effects in mice via air pouch inoculation of GAS. The results showed that KS significantly increased the survival rate of GAS-infected mice. KS treatment reduced local skin damage and bacterial counts compared with those in mice infected with GAS and treated with a control plasmid or saline. While there was a decrease in immune cell infiltration of the local infection site, cell viability and antimicrobial factors such as reactive oxygen species actually increased after KS treatment. The efficiency of intracellular bacterial killing in neutrophils was directly enhanced by KS administration. Several inflammatory cytokines, including tumor necrosis factor alpha, interleukin 1β, and interleukin 6, in local infection sites were reduced by KS. In addition, KS treatment reduced vessel leakage, bacteremia, and liver damage after local infection. Therefore, our study demonstrates that KS provides protection in GAS-infected mice by enhancing bacterial clearance, as well as reducing inflammatory responses and organ damage.

SERPINA3K induces apoptosis in human colorectal cancer cells via activating the Fas/FasL/caspase-8 signaling pathway

SERPINA3K, also known as kallikrein-binding protein (KBP), is a serine proteinase inhibitor with anti-inflammatory and anti-angiogenic activities. Our previous studies showed that SERPINA3K inhibited proliferation in a dose-dependent manner and induced apoptosis of endothelial cells but had no influence on SGC-7901 gastric carcinoma cells or HepG2 hepatocarcinoma cells. However, it is unknown whether SERPINA3K has a direct impact on other carcinoma cells and which mechanisms are involved. In this study, we report for the first time that SERPINA3K not only decreased cell viability but also induced apoptosis in the colorectal carcinoma cell lines SW480 and HT-29. SERPINA3K-induced apoptosis of SW480 and HT-29 was rescued by interference with Fas ligand (FasL) small hairpin RNA. Moreover, SERPINA3K increased the expression of FasL and activated caspase-8. Peroxisome proliferator-activated receptor γ (PPARγ), a transcription factor of FasL, was also upregulated by SERPINA3K in a dose-dependent manner. The upregulation effect of FasL induced by SERPINA3K was reversed after interference with PPARγ small interfering RNA. These results demonstrated that SERPINA3K-induced SW480 and HT-29 cell apoptosis was mediated by the PPARγ/Fas/FasL signaling pathway. Therefore, our study provides additional insight into the direct anti-tumor function by inducing tumor cell apoptosis of SERPINA3K in colorectal tumors.

Physiological inhibitors of Wnt signaling

Wnt signaling is crucial for cell proliferation and differentiation. It represents a complex network with mechanisms of self-regulation through positive and negative feedback. Recent increasing interest in this signaling pathway has led to the discovery of many new proteins that down-regulate Wnt activity. Here, we provide a short description of the most important and best-studied inhibitors, group them according to the target molecule within the Wnt cascade, and discuss their clinical potential. Although most of the inhibitors discussed here may also interact with proteins from other signaling pathways, we focus only on their ability to modulate Wnt signaling.

Thyroid hormone and COUP-TF1 regulate kallikrein-binding protein (KBP) gene expression

Kallikrein-binding protein (KBP) is a component of the kallikrein-kinin system that mediates vasodilation and inhibits tumor growth by antagonizing vascular endothelial growth factor-mediated angiogenesis. We demonstrate that KBP gene expression is repressed by T(3) and modulated by the orphan nuclear receptor, chicken ovalbumin upstream promoter transcription factor 1 (COUP-TF1). In hypothyroid mice, KBP mRNA expression in the testis was increased 2.1-fold compared with euthyroid mice. We have identified two negative thyroid hormone response elements (nTREs) in the mouse KBP gene, nTRE1 located in the 5' flanking region (-53 to -29) and nTRE2, located in the first intron (104-132). We used functional assays, cofactor knockdown, and chromatin immunoprecipitation assays to characterize nTRE1 and nTRE2 in hepatic (HepG2) and testes (GC-1spg) cell lines. Reporter expression directed by both elements was enhanced with addition of thyroid hormone receptor and repressed with the addition of T(3). COUP-TF1 enhanced basal expression of both elements but blunted unliganded thyroid hormone receptor enhancement and T(3) repression of nTRE1 but not nTRE2. Both nTREs bound nuclear corepressor and binding increased in response to T(3). Nuclear corepressor knockdown resulted in loss of T(3) repression of both nTRE1 and nTRE2. COUP-TF1, which usually represses T(3) induction of positive thyroid hormone response elements, reverses T(3) repression mediated by nTRE1 in the mouse KBP gene. Endogenous KBP expression is repressed by T(3) and two functional nTREs, both of which are required, have been characterized in the KBP gene. COUP-TF1 may be an important factor to modulate expression of genes that are repressed by T(3).

Anti-angiogenic and anti-inflammatory effects of SERPINA3K on corneal injury

SERPINA3K is a member of the serine proteinase inhibitor (SERPIN) family. Here we evaluated the therapeutic effects of SERPINA3K on neovascularization and inflammation in a rat cornea alkali burn model that is commonly employed to study corneal wounding. Topical treatment of the injured rat cornea with SERPINA3K (20 µg/eye/day) for 7 days significantly decreased the neovascular area, compared with the groups treated with BSA or PBS. The SERPINA3K treatment also ameliorated the corneal inflammation as evaluated by the inflammatory index. Furthermore, SERPINA3K enhanced the recovery of corneal epithelium after the alkali injury. Toward the mechanism of action, SERPINA3K down-regulated the expression of the pro-angiogenic and pro-inflammatory factors, vascular endothelial growth factor and tumor necrosis factor-α and up-regulated the expression of the anti-angiogenic factor, pigment epithelium-derived factor. SERPINA3K specifically inhibited growth of vascular endothelial cells. Meanwhile, SERPINA3K significantly up-regulated the expression of EGFR in the corneal epithelium. These findings suggest that SERPINA3K has therapeutic potential for corneal inflammation and NV.

Wnt pathway antagonists and angiogenesis

Dysregulation of the Wnt pathway has been extensively studied in multiple diseases, including some angiogenic disorders. Wnt signaling activation is a major stimulator in pathological angiogenesis and thus, Wnt antagonists are believed to have therapeutic potential for neovascular disorders. Actually, some Wnt antagonists have been identified directly from the anti-angiogenic factor family. This review summarizes the recent progress toward understanding of the roles of Wnt pathway antagonists in angiogenic regulation and their mechanism of action, and exploring their therapeutic potential.

The potential of nanomedicine therapies to treat neovascular disease in the retina

Neovascular disease in the retina is the leading cause of blindness in all age groups. Thus, there is a great need to develop effective therapeutic agents to inhibit and prevent neovascularization in the retina. Over the past decade, anti-VEGF therapeutic agents have entered the clinic for the treatment of neovascular retinal disease, and these agents have been effective for slowing and preventing the progression of neovascularization. However, the therapeutic benefits of anti-VEGF therapy can be diminished by the need for prolonged treatment regimens of repeated intravitreal injections, which can lead to complications such as endophthalmitis, retinal tears, and retinal detachment. Recent advances in nanoparticle-based drug delivery systems offer the opportunity to improve bioactivity and prolong bioavailability of drugs in the retina to reduce the risks associated with treating neovascular disease. This article reviews recent advances in the development of nanoparticle-based drug delivery systems which could be utilized to improve the treatment of neovascular disease in the retina.

Plasma kallikrein and diabetic macular edema

Recent proteomic studies have identified components of the kallikrein kinin system, including plasma kallikrein, factor XII, and kininogen, in vitreous obtained from individuals with advanced diabetic retinopathy. In rodent models, activation of plasma kallikrein in vitreous increases retinal vascular permeability; whereas inhibition of the kallikrein kinin system reduces retinal leakage induced by diabetes and hypertension. These findings suggest that intraocular activation of the plasma kallikrein pathway may contribute to excessive retinal vascular permeability that can lead to diabetic macular edema. The kallikrein kinin system contains two separate and independently regulated serine proteases that generate bradykinin peptides: plasma kallikrein and tissue kallikrein. Tissue kallikrein is expressed in the retina and ciliary body, where it has been implicated in exerting autocrine or paracrine effects via bradykinin receptors that are colocalized in these tissues. Emerging evidence suggests that plasma kallikrein inhibitors may provide a new therapeutic opportunity to reduce retinal vascular permeability.

Inhibition of connective tissue growth factor overexpression in diabetic retinopathy by SERPINA3K via blocking the WNT/beta-catenin pathway

OBJECTIVE

Connective tissue growth factor (CTGF) is a major fibrogenic factor. Increased retinal CTGF levels have been implicated to play a role in diabetic retinopathy. SERPINA3K is a serine proteinase inhibitor, and its levels were decreased in retinas with diabetic retinopathy. The purpose of this study was to investigate the role of SERPINA3K in the regulation of CTGF and fibrogenesis and its mechanism of action.

RESEARCH DESIGN AND METHODS

Adenovirus expressing SERPINA3K was injected intravitreally into streptozotocin-induced diabetic rats. CTGF expression was measured using Western blot analysis and real-time RT-PCR. Fibrosis was evaluated by quantifying retinal fibronectin using enzyme-linked immunosorbent assay. Wnt pathway activation was determined by phosphorylation of LDL receptor-related protein 6, a coreceptor of Wnt ligands, and stabilization of beta-catenin, an essential effector of the canonical Wnt pathway.

RESULTS

Ad-SERPINA3K attenuated the CTGF and fibronectin overexpression in retinas of diabetic rats. In cultured retinal cells, SERPINA3K blocked the overproduction of CTGF induced by high glucose. Dickkopf-1, a specific Wnt antagonist, also attenuated the high-glucose-induced CTGF overexpression, indicating a role of Wnt signaling in CTGF overexpression in diabetes. Similarly, increased SERPINA3K blocked Wnt pathway activation in diabetic retinas and in cells treated with high glucose. Further, SERPINA3K also attenuated the Wnt3a-induced activation of the canonical Wnt pathway and the overexpression of CTGF.

CONCLUSION

SERPINA3K is an antifibrogenic factor, and its antifibrogenic activity is through blocking the Wnt pathway. Decreased SERPINA3K levels may contribute to the fibrosis in diabetic retinopathy.

Blocking the Wnt pathway, a unifying mechanism for an angiogenic inhibitor in the serine proteinase inhibitor family

The Wnt pathway regulates multiple biological and pathological processes including angiogenesis and inflammation. Here we identified a unique inhibitor of the Wnt pathway, SERPINA3K, a serine proteinase inhibitor with anti-inflammatory and angiogenic activities. SERPINA3K blocked the Wnt pathway activation induced by a Wnt ligand and by diabetes. Coprecipitation and ligand binding assay showed that SERPINA3K binds to low-density lipoprotein receptor-like protein 6 (LRP6) with a K(d) of 10 nM, in the range of its physiological concentration in the retina. Under the same conditions, SERPINA3K did not bind to the frizzled (Fz) receptor or low-density lipoprotein receptor. Further, SERPINA3K bound to LRP6 at the extracellular domain and blocked its dimerization with the Fz receptor induced by a Wnt ligand. The antagonizing activity of SERPINA3K to LRP6 was further confirmed by Xenopus axis duplication assay. These results suggest that SERPINA3K is a high-affinity, endogenous antagonist of LRP6. The blockade of Wnt signaling may represent a unifying mechanism for the anti-inflammatory and anti-angiogenic effects of SERPINA3K.

Pigment epithelium-derived factor suppresses adipogenesis via inhibition of the MAPK/ERK pathway in 3T3-L1 preadipocytes

We previously reported that circulating levels of pigment epithelium-derived factor (PEDF), a newly identified adipokine, are increased in patients with type 2 diabetes, correlating with body mass index. However, the role of PEDF in adipogenesis remains elusive. In the present study, we have investigated the effects and mechanisms of PEDF on adipocyte differentiation in 3T3-L1 preadipocytes. Differentiation of 3T3-L1 preadipocytes was induced in the presence or absence of human recombinant PEDF protein. The effects of PEDF on adipogenic gene expression, mitotic clonal expansion (MCE), and MAPK activation were investigated. Physiological concentrations of human PEDF protein inhibited adipocyte differentiation, evidenced by decreased lipid accumulation, downregulation of adipocyte markers, and inhibition of master adipogenic transcription factors such as C/EBP-alpha and PPARgamma. The antiadipogenic effects of PEDF were observed only when PEDF was added to the cells on day 0, but not on day 3 during differentiation, suggesting that PEDF targets some early adipogenic events. Similarly, overexpression of PEDF by adenovirus attenuated adipocyte differentiation. Further studies revealed that PEDF, or U-0126, a specific MAPK/ERK inhibitor, sequentially inhibited the early activation of ERK and MCE. Moreover, PEDF attenuated expression and the phosphorylation of C/EBP-beta at Thr(188), an essential step for transcriptional activation of C/EBP-beta. In addition, PEDF expression was decreased significantly in the first 24 h during adipocyte differentiation, suggesting that downregulation of PEDF may be essential for the initiation of MCE and adipogenesis. We conclude that PEDF inhibits adipogenesis in 3T3-L1 preadipocytes partially because of inhibition of the MAPK/ERK signaling pathway and MCE.

Activation of the Wnt pathway plays a pathogenic role in diabetic retinopathy in humans and animal models

Although Wnt signaling is known to mediate multiple biological and pathological processes, its association with diabetic retinopathy (DR) has not been established. Here we show that retinal levels and nuclear translocation of beta-catenin, a key effector in the canonical Wnt pathway, were increased in humans with DR and in three DR models. Retinal levels of low-density lipoprotein receptor-related proteins 5 and 6, coreceptors of Wnts, were also elevated in the DR models. The high glucose-induced activation of beta-catenin was attenuated by aminoguanidine, suggesting that oxidative stress is a direct cause for the Wnt pathway activation in diabetes. Indeed, Dickkopf homolog 1, a specific inhibitor of the Wnt pathway, ameliorated retinal inflammation, vascular leakage, and retinal neovascularization in the DR models. Dickkopf homolog 1 also blocked the generation of reactive oxygen species induced by high glucose, suggesting that Wnt signaling contributes to the oxidative stress in diabetes. These observations indicate that the Wnt pathway plays a pathogenic role in DR and represents a novel therapeutic target.

Omic analyses unravels global molecular changes in the brain and liver of a rat model for chronic Sake (Japanese alcoholic beverage) intake

The effects of chronic administration of Sake (Japanese alcoholic beverage, Nihonshu) on brain and liver of female F334 (Fisher) rats were surveyed via global omic analyses using DNA microarray, 2-DE, and proton nuclear magnetic resonance. Rats weaned at 4 wk of age were given free access to Sake (15% alcohol), instead of water. At 13 months of age, and 24 h after withdrawal of Sake supply, rats were sacrificed, and the whole brain and liver tissues dissected for analyses. In general, molecular changes in brain were found to be less than those in liver. Transcriptomics data revealed 36 and 9, and 80 and 62 up- and down-regulated genes, in the brain and liver, respectively, with binding and catalytic activity gene categories the most prominently changed. Results suggested Sake-induced fragility of brain and liver toxicity/damage, though no significant abnormalities in growth were seen. At protein level, a striking decrease was found in the expression of NADH dehydrogenase (ubiquinone) Fe-S protein 1 in brain, suggesting attenuation of mitochondrial metabolism. In liver, results again suggested an attenuation of mitochondrial function and, in addition, glycoproteins with unknown function were induced at protein and gene levels, suggesting possible changes in glycoprotein binding in that organ. Metabolomic analysis of brain revealed significant increases in valine, arginine/ornithine, alanine, glutamine, and choline with decreases in isoleucine, N-acetyl aspartate, taurine, glutamate, and gamma aminobutyric acid. Our results provide a detailed inventory of molecular components of both brain and liver after Sake intake, and may help to better understand effects of chronic Sake drinking.

SERPINA3K prevents oxidative stress induced necrotic cell death by inhibiting calcium overload

Background

SERPINA3K, an extracellular serine proteinase inhibitor (serpin), has been shown to have decreased levels in the retinas of diabetic rats, which may contribute to diabetic retinopathy. The function of SERPINA3K in the retina has not been investigated.

Methodology/Principal Findings

The present study identified a novel function of SERPINA3K, i.e. it protects retinal cells against oxidative stress-induced cell death including retinal neuronal cells and Müller cells. Flow-cytometry showed that the protective effect of SERPINA3K on Müller cells is via reducing oxidation-induced necrosis. Measurements of intracellular calcium concentration showed that SERPINA3K prevented the intracellular calcium overload induced by H₂O₂. A similar protective effect was observed using a calcium chelator (BAPTA/AM). Further, SERPINA3K inhibited the phosphorylation of phospholipase C (PLC)-gamma1 induced by H₂O₂. Likewise, a specific PLC inhibitor showed similar protective effects on Müller cells exposed to H₂O₂. Furthermore, the protective effect of SERPINA3K was attenuated by a specific PLC activator (m-3M3FBS). Finally, in a binding assay, SERPINA3K displayed saturable and specific binding on Müller cells.

Conclusion/Significance

These results for the first time demonstrate that SERPINA3K is an endogenous serpin which protects cells from oxidative stress-induced cells death, and its protective effect is via blocking the calcium overload through the PLC pathway. The decreased retinal levels of SERPINA3K may represent a new pathogenic mechanism for the retinal Müller cell dysfunction and neuron loss in diabetes.

Kallikrein-binding protein inhibits growth of gastric carcinoma by reducing vascular endothelial growth factor production and angiogenesis

Kallikrein-binding protein (KBP) has been identified as an endogenous angiogenic inhibitor. We previously showed that KBP inhibited rat retinal neovascularization by down-regulation of vascular endothelial growth factor (VEGF) in endothelial cells. However, its antiangiogenic potential for inhibition of gastric carcinoma and the effect on VEGF in tumor cells have not been elucidated. The present study was designed to investigate the effect of KBP on growth of gastric carcinoma and the possible molecular mechanism. Recombinant KBP dose dependently inhibited proliferation and induced apoptosis of endothelial cells, but no effect on proliferation and apoptosis of SGC-7,901 gastric carcinoma cells. I.p. injection of KBP resulted in growth inhibition of both heterotopic and orthotopic gastric carcinoma xenografts at 61.4% and 52.3%, respectively. Microvessel density in tumor tissues treated with KBP was significantly decreased, suggesting that KBP suppressed tumor growth by antiangiogenesis. The expression and release of VEGF, a major angiogenic stimulator, were down-regulated by KBP in SGC-7,901 cells and gastric carcinoma xenografts. RNA levels of VEGF in SGC-7,901 cells were also decreased by KBP, thus suggesting the regulation at the transcriptional level. Therefore, hypoxia-inducible factor 1alpha (HIF-1alpha), a crucial transcriptional factor for VEGF expression, was examined in SGC-7,901 cells treated by KBP. KBP reduced HIF-1alpha protein level and nuclear translocation, which may be responsible for the down-regulation of VEGF transcription. Down-regulation of VEGF expression and release in tumor cells through inhibiting HIF-1alpha, thus attenuating the paracrine effect of VEGF on endothelial cell proliferation and vascular permeability in tumor tissues, may represent a novel mechanism for the antiangiogenic and antitumor activity of KBP.

The kallikrein-kinin system in diabetic retinopathy: lessons for the kidney

Diabetic retinopathy and diabetic nephropathy are common microvascular complications of diabetes. The kallikrein-kinin system (KKS) has been implicated in the development of both conditions, and, in particular, bradykinin and its receptors have been shown to exert angiogenic and proinflammatory actions. Several of the key processes that underlie the development of diabetic retinopathy, such as increased vascular permeability, edema, neovascularization, and inflammatory changes, have been associated with the KKS, and recent work has shown that components of the KKS, including plasma kallikrein, factor XIIa, and high-molecular-weight kininogen, are present in the vitreous of people with diabetic retinopathy. The role of the KKS in the development of diabetic nephropathy is controversial, with both adverse and protective effects of bradykinin and its receptors reported. The review examines the role of the KKS in pathways central to the development of diabetic retinopathy and compares this with reported actions of this system in diabetic nephropathy. The possibility of therapeutic intervention targeting bradykinin and its receptors as treatment for diabetic microvascular conditions is considered.

Kallikrein-kinin activation by altered vitreous pH: New perspectives for treatment and pathogenesis of diabetic macular edema?

Recently, Gao et al. published an experimental study based on the pathophysiology of diabetic macular edema in Nature Medicine (Nat Med. 2007 Feb;13(2):181-8). They found an increased amount of carbonic anhydrase in the vitreous, which causes a pH shift. This activates the kallikrein-kinin system and leads to increased retinal vascular permeability. In this comment the clinical implications of this article are discussed.

Kallikrein-binding protein suppresses growth of hepatocellular carcinoma by anti-angiogenic activity

Effect of kallikrein-binding protein (KBP), an endogenous angiogenic inhibitor, on the growth of hepatocellular carcinoma and the possible mechanism were investigated. KBP inhibited proliferation and induced apoptosis of endothelial cells, but had no effect on the proliferation and apoptosis of hepatocarcinoma cell line HepG2. Intraperitoneal injection of KBP significantly suppressed the tumor growth and inhibited intratumoral neovascularization both in grafted hepatocarcinoma mice and xenografted hepatocarcinoma athymic mice. Moreover, KBP reduced expression of VEGF and HIF-1alpha nuclear translocation in HepG2 cells and xenografts. Down-regulation of VEGF in tumor cells through inhibiting HIF-1alpha may represent a novel mechanism for the anti-angiogenic and anti-tumor activity of KBP.

Up-regulation of integrin-linked kinase in the streptozotocin-induced diabetic rat retina

OBJECTIVES

This study investigated whether integrin-linked kinase (ILK) is involved in the pathogenesis of diabetic retinopathy, by analyzing the expression and activity of ILK in the retina from a streptozotocin (STZ)-induced rat model of diabetes.

METHODS

ILK expression in the retina from both control and STZ-induced diabetic rats was measured by reverse transcription polymerase chain reaction, immunohistochemistry and Western blot analysis. The expressions of Akt and FOXO1A, the downstream molecules of ILK, were also examined.

RESULTS

The present study showed that the STZ-induced diabetes was associated with the increase in the vascular permeability in the retina. This elevated vascular permeability increased with the progression of diabetic retinopathy. Meanwhile, the results also showed that the expression of ILK increased in protein and mRNA levels in the retina of STZ-induced diabetic rats. Immunohistochemistry showed that immunostaining of ILK was localized in the outer plexiform layer (OPL), the inner nuclear layer (INL), the inner plexiform layer (IPL), the ganglion cell layer (GCL) and the retinal microvasculature of rats. However, the expression of Akt was reduced in the retinas at 8 and 12 weeks and increased in the retinas at 4 weeks after induction of diabetes. Meanwhile, the expression of the FOXO1A protein increased in the retinas at 8 and 12 weeks and decreased in the retinas at 4 weeks after induction of diabetes. The FOXO1A immunostaining was also observed in the retinal microvasculature and in the OPL, INL, IPL and GCL of rat retinas.

CONCLUSION

These results indicate that diabetes affects the expression of ILK in the retina. ILK may be involved in the diabetes-induced damage and/or alterations of neural and microvascular structures.

Inflammation in dry age-related macular degeneration

PURPOSE

To summarize the current information regarding the role of immune and inflammatory response in the pathogenesis of dry age-related macular degeneration (ARMD).

METHODS

A Pubmed search was conducted of the period January 1999 to 2005. Relevant information in the literature on the role of inflammation in early dry ARMD was reviewed.

RESULTS

Some important evidence for inflammation in early ARMD consists in the isolation of immunoglobulins, complement proteins, cytokines and activated microglia, in retinal pigment epithelium (RPE) cells and drusen. Pivotal mechanisms in early ARMD include the accumulation of debris and proteins along the RPE surface, followed by immune-complex deposition and complement activation. In contrast, the role of other plasma enzymes such as kallikrein-kinin-bradykinin, the Hageman factor, peptides and coagulation proteins in drusen formation and ARMD has yet to be determined.

CONCLUSION

A clear role for inflammatory mediators and cells has been established in recent years. Future studies should elucidate further mechanisms in ARMD development.

Novel Role of Kallistatin in Protection Against Myocardial Ischemia–Reperfusion Injury by Preventing Apoptosis and Inflammation

Kallistatin is a serine proteinase inhibitor that has been shown to reduce joint swelling and to inhibit inflammation in a rat model of arthritis. In this study, we investigated the effect and mechanisms of kallistatin on cardiac function after myocardial ischemia-reperfusion (I/R) injury. The human kallistatin gene in an adenoviral vector was delivered locally into rat heart 4 days before 30-min ischemia followed by 24-hr reperfusion. Kallistatin gene transfer significantly reduced myocardial infarct size and left ventricle end-diastolic pressure and improved cardiac contractility. Kallistatin significantly reduced I/R-induced cardiomyocyte apoptosis as identified by TUNEL and Hoechst staining, DNA laddering, cell viability, and caspase-3 activity in ischemic myocardium and in primary cultured cardiomyocytes. Kallistatin also reduced intramyocardial monocyte/macrophage and neutrophil accumulation in conjunction with decreased expression of monocyte chemoattractant protein-1, tumor necrosis factor-alpha, and intercellular adhesion molecule-1. Kallistatin delivery promoted cardiac endothelial nitric oxide synthase activation and increased nitric oxide (NO) formation, but inhibited NADH oxidase activity, p22phox expression, and superoxide production. Moreover, kallistatin reduced the phosphorylation of apoptosis signal-regulating kinase-1 and mitogen-activated protein kinases (MAPKs), but increased Akt and glycogen synthase kinase-3beta phosphorylation. The effects of kallistatin on cardiac function, oxidative stress, and these signal transduction events were all blocked by Nomega-nitro-L-argi-nine methyl ester. These results indicate a novel role of kallistatin in cardiac protection after I/R injury through increased NO formation and Akt-glycogen synthase kinase-3beta signaling and suppression of oxidative stress and MAPK activation.

Pigment epithelium‐derived factor (PEDF) is an endogenous antiinflammatory factor

Pigment epithelium-derived factor (PEDF) is a potent angiogenic inhibitor. Reduced PEDF levels are associated with diabetic retinopathy. However, the mechanism for the protective effects of PEDF against diabetic retinopathy (DR) is presently unclear. As inflammation plays a role in DR, the present study determined the effect of PEDF on inflammation. Western blot analysis and ELISA demonstrated that retinal and plasma PEDF levels were drastically decreased in rats with endotoxin-induced uveitis (EIU), which suggests that PEDF is a negative acute-phase protein. Intravitreal injection of PEDF significantly reduced vascular hyper-permeability in rat models of diabetes and oxygen-induced retinopathy, correlating with the decreased levels of retinal inflammatory factors, including VEGF, VEGF receptor-2, MCP-1, TNF-alpha, and ICAM-1. In cultured retinal capillary endothelial cells, PEDF significantly decreased TNF-alpha and ICAM-1 expression under hypoxia. Moreover, down-regulation of PEDF expression by siRNA resulted in significantly increases of VEGF and TNF-alpha secretion in retinal Müller cells. These findings suggest that PEDF is a novel endogenous anti-inflammatory factor in the eye. The decrease of ocular PEDF levels may contribute to inflammation and vascular leakage in DR.

Enhanced anti-angiogenic effect of a deletion mutant of plasminogen kringle 5 on neovascularization

Kringle 5 (K5), a proteolytic fragment of plasminogen, has been proved to be an angiogenic inhibitor. Previously, we have evaluated the effect of K5 on the vascular leakage and neovascularization in a rat model of oxygen-induced retinopathy. In this study, we expressed K5 and a deletion mutant of K5 (K5 mutant) in a prokaryocyte expression system and purified them by affinity chromatography. K5 mutant was generated by deleting 11 amino acids from K5 while retaining the three disulfide bonds. The anti-angiogenic activity of intact K5 and K5 mutant were compared in endothelial cells and retinal neovascularization rat model. K5 mutant inhibited the proliferation of primary human retinal capillary endothelial cells (HRCEC) in a concentration-dependent manner, with an apparent EC50 of approximate 35 nmol/L, which is twofold more potent than intact K5. In the even higher concentration range, K5 mutant did not inhibit pericytes from the same origin of HRCEC, which suggested an endothelial cell-specific inhibition. K5 mutant had no effect on normal liver cells and Bel7402 hepatoma cells even at high concentration range either. Intravitreal injection of the K5 and mutant in the oxygen-induced retinopathy rat model both resulted in significantly fewer neovascular tufts and nonperfusion area than controls with PBS injection, as shown by fluorescein angiography. Furthermore, K5 mutant exhibited more strong inhibition effect on neovascularization than intact K5 by quantification of vascular cells. These results suggest that this K5 deletion mutant is a more potent angiogenic inhibitor than intact K5 and may have therapeutic potential in the treatment of those disorders with neovascularization, such as solid tumor, diabetic retinopathy, age-related macular degeneration, rheumatoid arthritis, and hyperplasia of prostate.

The effect of angiostatin on vascular leakage and VEGF expression in rat retina

Angiostatin is a potent angiogenic inhibitor. The present study identified a new activity of angiostatin: reducing vascular leakage, which is associated with diabetic macular edema, tumor growth and inflammation. An intravitreal injection of angiostatin significantly reduced retinal vascular permeability in rats with oxygen-induced retinopathy and in those with streptozotocin-induced diabetes, but not in normal rats. Consistent with its effect on permeability, angiostatin downregulated vascular endothelial growth factor (VEGF) expression in the retina in both the rat models but not in normal controls. These results suggest that the effect of angiostatin on vascular leakage is mediated, at least in part, through blockade of VEGF overexpression.