Tranilast attenuates connective tissue growth factor-induced extracellular matrix accumulation in renal cells

Unlocking the potential of tranilast: Targeting fibrotic signaling pathways for therapeutic benefit

Fibrosis is the excessive deposition of extracellular matrix in an organ or tissue that results from an impaired tissue repair in response to tissue injury or chronic inflammation. The progressive nature of fibrotic diseases and limited treatment options represent significant healthcare challenges. Despite the substantial progress in understanding the mechanisms of fibrosis, a gap persists translating this knowledge into effective therapeutics. Here, we discuss the critical mediators involved in fibrosis and the role of tranilast as a potential antifibrotic drug to treat fibrotic conditions. Tranilast, an antiallergy drug, is a derivative of tryptophan and has been studied for its role in various fibrotic diseases. These include scleroderma, keloid and hypertrophic scars, liver fibrosis, renal fibrosis, cardiac fibrosis, pulmonary fibrosis, and uterine fibroids. Tranilast exerts antifibrotic effects by suppressing fibrotic pathways, including TGF-β, and MPAK. Because it disrupts fibrotic pathways and has demonstrated beneficial effects against keloid and hypertrophic scars, tranilast could be used to treat other conditions characterized by fibrosis.

Suramin derivatives play an important role in blocking the interaction between FGF1 and FGFRD2 to inhibit cell proliferation

The inhibition of protein function by small compounds plays a critical role in controlling cell proliferation. We report on a new class of small molecule (NCTU-Alan-2026) inhibitors for cell proliferation. NCTU-Alan-2026 blocks the interaction between FGF1 and its receptor FGF1R2D2. Extensive NMR studies combined with fluorescence experiments provided the specific mechanism of how NCTU-Alan-2026 could inhibit cell proliferation. We describe an innovative therapeutic approach for anti-proliferation and demonstrate an example of inhibition of small molecules by blocking the protein-protein interaction. We found that the compound NCTU-Alan-2026 blocked the interaction between the two proteins FGF1 and FGF1R2D2 and inhibited cell proliferation. The toxicity of NCTU-Alan-2026 is lower than that of suramin. Thus, NCTU-Alan-2026 could be a better drug than suramin in the treatment of cancer.

Tranilast Inhibits Pulmonary Fibrosis by Suppressing TGFβ/SMAD2 Pathway

Purpose

Idiopathic pulmonary fibrosis (IPF) is characterized by the accumulation of extracellular matrix (ECM) protein in the lungs. Transforming growth factor (TGF) β-induced ECM protein synthesis contributes to the development of IPF. Tranilast, an anti-allergy drug, suppresses TGFβ expression and inhibits interstitial renal fibrosis in animal models. However, the beneficial effects of tranilast or its mechanism as a therapy for pulmonary fibrosis have not been clarified.

Methods

We investigated the in vitro effect of tranilast on ECM production and TGFβ/SMAD2 pathway in TGFβ2-stimulated A549 human alveolar epithelial cells, using quantitative polymerase chain reaction, Western blotting, and immunofluorescence. In vitro observations were validated in the lungs of a murine pulmonary fibrosis model, which we developed by intravenous injection of bleomycin.

Results

Treatment with tranilast suppressed the expression of ECM proteins, such as fibronectin and type IV collagen, and attenuated SMAD2 phosphorylation in TGFβ2-stimulated A549 cells. In addition, based on a wound healing assay in these cells, tranilast significantly inhibited cell motility, with foci formation that comprised of ECM proteins. Histological analyses revealed that the administration of tranilast significantly attenuated lung fibrosis in mice. Furthermore, tranilast treatment significantly reduced levels of TGFβ, collagen, fibronectin, and phosphorylated SMAD2 in pulmonary fibrotic tissues in mice.

Conclusion

These findings suggest that tranilast inhibits pulmonary fibrosis by suppressing TGFβ/SMAD2-mediated ECM protein production, presenting tranilast as a promising and novel anti-fibrotic agent for the treatment of IPF.

Development of Sustained-Release Ophthalmic Formulation Based on Tranilast Solid Nanoparticles

Eye drops containing Tranilast (TL), N-(3,4-dimethoxycinnamoyl) anthramilic acid, are used as an anti-allergic conjunctivitis drug in the ophthalmic field. Traditional eye drops are very patient compliant, although the bioavailability (BA) of most eye drops is low since eye drops cannot be instilled beyond the capacity of the conjunctival sac due to its limited volume. Thus, traditional eye drops have low BA and a short duration of the drug on the ocular surface, so solutions to these problems are highly anticipated. In this study, we designed a sustained-release drug-delivery system (DDS) for TL nanoparticles. TL nanoparticles were prepared by bead mill treatment, and the gel formulations containing TL nanoparticles (TL-NPs-Gel, particle size 50 nm–100 nm) were provided by carboxypolymethylene. The crystal structure of TL with and without bead mill treatment is the same, but the TL solubility in formulations containing nanoparticles was 5.3-fold higher compared with gel formulations containing TL microparticles (TL-MPs-Gel). The photo and thermal stabilities of TL-NPs-Gel are also higher than those of dissolved TL. Moreover, when TL-NPs-Gel is applied to the upper eyelid skin (outside), the TL is released as nanoparticles, and delivered to the lacrimal fluid through the meibomian glands. In addition, the TL release profile for TL-NPs-Gel was sustained over 180 min after the treatment. These findings can be used to develop a sustained-release DDS in the ophthalmic field.

A tranilast and BMP-2 based functional bilayer membrane is effective for the prevention of epidural fibrosis during spinal lamina reconstruction

Failed Back Surgery Syndrome (FBSS) is a common complication of lumbar surgery.

The KCa3.1 blocker TRAM34 reverses renal damage in a mouse model of established diabetic nephropathy

Despite optimal control of hyperglycaemia, hypertension, and dyslipidaemia, the number of patients with diabetic nephropathy (DN) continues to grow. Strategies to target various signaling pathways to prevent DN have been intensively investigated in animal models and many have been proved to be promising. However, targeting these pathways once kidney disease is established, remain unsatisfactory. The clinical scenario is that patients with diabetes mellitus often present with established kidney damage and need effective treatments to repair and reverse the kidney damage. In this studies, eNOS-/- mice were administered with streptozotocin to induce diabetes. At 24 weeks, at which time we have previously demonstrated albuminuria and pathological changes of diabetic nephropathy, mice were randomised to receive TRAM34 subcutaneously, a highly selective inhibitor of potassium channel KCa3.1 or DMSO (vehicle) for a further 14 weeks. Albuminuria was assessed, inflammatory markers (CD68, F4/80) and extracellular matrix deposition (type I collagen and fibronectin) in the kidneys were examined. The results clearly demonstrate that TRAM34 reduced albuminuria, decreased inflammatory markers and reversed extracellular matrix deposition in kidneys via inhibition of the TGF-β1 signaling pathway. These results indicate that KCa3.1 blockade effectively reverses established diabetic nephropathy in this rodent model and provides a basis for progressing to human studies.

Tranilast-induced stress alleviation in solid tumors improves the efficacy of chemo- and nanotherapeutics in a size-independent manner

Accumulation of mechanical stresses during cancer progression can induce blood and lymphatic vessel compression, creating hypo-perfusion, hypoxia and interstitial hypertension which decrease the efficacy of chemo- and nanotherapies. Stress alleviation treatment has been recently proposed to reduce mechanical stresses in order to decompress tumor vessels and improve perfusion and chemotherapy. However, it remains unclear if it improves the efficacy of nanomedicines, which present numerous advantages over traditional chemotherapeutic drugs. Furthermore, we need to identify safe and well-tolerated pharmaceutical agents that reduce stress levels and may be added to cancer patients' treatment regimen. Here, we show mathematically and with a series of in vivo experiments that stress alleviation improves the delivery of drugs in a size-independent manner. Importantly, we propose the repurposing of tranilast, a clinically approved anti-fibrotic drug as stress-alleviating agent. Using two orthotopic mammary tumor models, we demonstrate that tranilast reduces mechanical stresses, decreases interstitial fluid pressure (IFP), improves tumor perfusion and significantly enhances the efficacy of different-sized drugs, doxorubicin, Abraxane and Doxil, by suppressing TGFβ signaling and expression of extracellular matrix components. Our findings strongly suggest that repurposing tranilast could be directly used as a promising strategy to enhance, not only chemotherapy, but also the efficacy of cancer nanomedicine.

Effective treatment for prevention of post-operative adhesion after strabismus surgery in experimental rabbit model: 0.5 % tranilast ophthalmic solution

Background

Postoperative adhesion is one of the major complications of strabismus surgery and result in motility dysfunction that brings unpredictable surgical outcomes. However, there was no definitely accepted treatment method to prevent postoperative adhesion.

Methods

A prospective, randomized, controlled experimental animal study was performed. Both eyes of each of 14 New Zealand White rabbits underwent superior rectus muscle recession. After the surgical procedure, the subjects were divided randomly into two groups; 0.5 % tranilast ophthalmic solutions and fluoroquinolone antibiotic eye drops were administered to the group tranilast (N = 14), while the group control (N = 14) received fluoroquinolone eye drops only. Five weeks after surgery, we evaluated gross adhesions with a numeric score (0 to 4). In addition, histopathologic examination with hematoxylin & eosin staining, Masson’s-trichrome staining, and anti-transforming growth factor beta 1 (TGF-β1) immuno-histochemical staining were done.

Results

The group tranilast showed significantly less gross adhesion and inflammation than the group control (P = 0.01 and P < 0.001, respectively). Masson’s-trichrome staining revealed that post-operative collagen deposition was more prominent in the group control than the group tranilast (P < 0.001). Moreover, remarkable TGF-β1 expression was observed in areas with excessive collagen deposition.

Conclusions

Instillation of 0.5 % tranilast ophthalmic solution is a simple and effective method for preventing post-operative adhesion after strabismus surgery.

Precursor-Directed Combinatorial Biosynthesis of Cinnamoyl, Dihydrocinnamoyl, and Benzoyl Anthranilates in Saccharomyces cerevisiae

Biological synthesis of pharmaceuticals and biochemicals offers an environmentally friendly alternative to conventional chemical synthesis. These alternative methods require the design of metabolic pathways and the identification of enzymes exhibiting adequate activities. Cinnamoyl, dihydrocinnamoyl, and benzoyl anthranilates are natural metabolites which possess beneficial activities for human health, and the search is expanding for novel derivatives that might have enhanced biological activity. For example, biosynthesis in Dianthus caryophyllus is catalyzed by hydroxycinnamoyl/benzoyl-CoA:anthranilate N-hydroxycinnamoyl/ benzoyltransferase (HCBT), which couples hydroxycinnamoyl-CoAs and benzoyl-CoAs to anthranilate. We recently demonstrated the potential of using yeast (Saccharomyces cerevisiae) for the biological production of a few cinnamoyl anthranilates by heterologous co-expression of 4-coumaroyl:CoA ligase from Arabidopsis thaliana (4CL5) and HCBT. Here we report that, by exploiting the substrate flexibility of both 4CL5 and HCBT, we achieved rapid biosynthesis of more than 160 cinnamoyl, dihydrocinnamoyl, and benzoyl anthranilates in yeast upon feeding with both natural and non-natural cinnamates, dihydrocinnamates, benzoates, and anthranilates. Our results demonstrate the use of enzyme promiscuity in biological synthesis to achieve high chemical diversity within a defined class of molecules. This work also points to the potential for the combinatorial biosynthesis of diverse and valuable cinnamoylated, dihydrocinnamoylated, and benzoylated products by using the versatile biological enzyme 4CL5 along with characterized cinnamoyl-CoA- and benzoyl-CoA-utilizing transferases.

KCa3.1: a new player in progressive kidney disease

PURPOSE OF REVIEW

Hypertension and hyperglycaemia are major risk factors that result in chronic kidney disease (CKD). Achievement of blood pressure goals, optimal control of blood glucose levels and the use of agents to block the renin-angiotensin-aldosterone system slow the progression of CKD. However, not all patients are benefited by these interventions and novel strategies to arrest or reverse the pathological processes inherent in CKD are needed. The therapeutic potential of targeting KCa3.1 in CKD will be discussed in this review.

RECENT FINDINGS

Blockade of KCa3.1 ameliorates activation of renal fibroblasts in diabetic mice by inhibiting the transforming growth factor-β1/small mothers against decapentaplegic pathway. A concomitant reduction in nuclear factor-κB activation in human proximal tubular cells under diabetic conditions has been observed. Advanced glycosylated endproducts induce both protein expression and current density of KCa3.1, which, in turn, mediates migration and proliferation of vascular smooth muscle cells via Ca²⁺-dependent signalling pathways.

SUMMARY

Studies have clearly demonstrated a causal role of chronic hyperglycaemia and hypertension in the development of CKD. However, a large proportion of patients develop end-stage kidney disease despite strict glycaemic control and the attainment of recommended blood pressure goals. Therefore, it is essential to identify and validate novel targets to reduce the development and progression of CKD. Recent findings demonstrate that genetic deletion or pharmacologic inhibition of KCa3.1 significantly reduces the development of diabetic nephropathy in animal models. However, the consequences of blockade of KCa3.1 in preventing and treating established diabetic nephropathy in humans warrants further study.

Thioredoxin-interacting protein: a potential therapeutic target for treatment of progressive fibrosis in diabetic nephropathy

Thioredoxin-interacting protein (TXNIP) is an endogenous inhibitor of the antioxidant thioredoxin, and a critical agent in the in vivo regulation of glucose. The well-described induction of TXNIP by high glucose may represent an important pathogenic trigger of complications arising in the diabetic environment, with sustained overexpression of TXNIP triggering the increased production of reactive oxygen species and collagen, both major contributors to the development of diabetic nephropathy (DN). To examine a possible therapeutic role for targeted TXNIP inhibition in DN, transgenic (mRen-2)27 rats were rendered diabetic with streptozotocin and then treated with 20 μM TXNIP deoxyribozyme (DNAzyme) delivered continuously over 12 weeks by an implanted osmotic mini-pump. Renal injury was measured using biochemical parameters of kidney function along with histological markers of damage. Catalytic activity of TXNIP DNAzyme was determined by TXNIP gene and peptide expression in the rat kidneys. TXNIP DNAzyme localization was demonstrated with a fluorescent-labelled TXNIP DNAzyme. A panel of markers was used to assess the extent of oxidative stress and renal fibrosis including superoxide level, nitrotyrosine staining, TGF-β1, NLRP3 and collagen IV expression. Fluorescent-labelled TXNIP DNAzyme was localized to tubulo-epithelial cells, but was not identified in glomeruli or endothelial cells. Elevated renal cortical TXNIP gene and protein expression seen in kidneys of DN animals were significantly attenuated by TXNIP DNAzyme (p < 0.05). Downstream markers of TXNIP activity, particularly oxidative stress, inflammasome signalling, tubulo-interstitial fibrosis and collagen deposition, were also attenuated in the tubulo-interstitium of DN rats treated with TXNIP DNAzyme. Consistent with the identified site of action of the DNAzyme, the effects of the TXNIP inhibition were limited to the tubulo-interstitial compartment. This study supports the role of TXNIP as an important mediator of progressive tubulo-interstitial fibrosis in DN, and also supports the notion of TXNIP inhibition as a potential new therapeutic target for DN.

Potential Renoprotective Agents through Inhibiting CTGF/CCN2 in Diabetic Nephropathy

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease (ESRD). The development and progression of DN might involve multiple factors. Connective tissue growth factor (CCN2, originally known as CTGF) is the one which plays a pivotal role. Therefore, increasing attention is being paid to CCN2 as a potential therapeutic target for DN. Up to date, there are also many drugs or agents which have been shown for their protective effects against DN via different mechanisms. In this review, we only focus on the potential renoprotective therapeutic agents which can specifically abolish CCN2 expression or nonspecifically inhibit CCN2 expression for retarding the development and progression of DN.

Acute suppression of TGF-ß with local, sustained release of tranilast against the formation of fibrous capsules around silicone implants

We propose the acute, local suppression of transforming growth factor beta (TGF-ß), a major profibrotic cytokine, to reduce fibrosis around silicone implants. To this end, we prepared silicone implants that were able to release tranilast, a TGF-ß inhibitor, in a sustained manner for 5 days or 15 days. We performed histologic and immunohistochemical analyses for 12 weeks after the implantation of the implants in living rats. The capsule thicknesses and collagen densities significantly decreased compared with those around the non-treated silicone implants. Notably, early suppression of TGF-ß affected the fibrogenesis that actually occurs at the late stage of wound healing. This change may be ascribed to the decrease in monocyte recruitment mediated by early TGF-ß during the acute inflammatory reaction. Thus, a significant decrease in differentiated macrophages was observed along with a decrease in the quantity of TGF-ß and fibroblasts during the subsequent inflammation stage; these changes led to a diminished fibrotic capsule formation.

Tranilast: a review of its therapeutic applications

Tranilast (N-[3',4'-dimethoxycinnamoyl]-anthranilic acid) is an analog of a tryptophan metabolite. Initially, tranilast was identified as an anti-allergic agent, and used in the treatment of inflammatory diseases, such as bronchial asthma, atypical dermatitis, allergic conjunctivitis, keloids and hypertrophic scars. Subsequently, the results showed that it could be also effective in the management of a wide range of conditions. The beneficial effects of tranilast have also been seen in a variety of disease states, such as fibrosis, proliferative disorders, cancer, cardiovascular problems, autoimmune disorders, ocular diseases, diabetes and renal diseases. Moreover, several trials have shown that it has very low adverse effects and it is generally well tolerated by patients. In this review, we have attempted to accurately summarize previously published studies relating to the use of tranilast for a range of disorders and discuss the drug's possible mode of action. The major mode of the drug's efficacy appears to be the suppression of the expression and/or action of the TGF-β pathway, but the drug affects other factors as well. The findings presented in this review demonstrate the potential of tranilast for the control of a vast array of pathological situations, furthermore, it is a prescribed drug without severe side effects.

Plumbagin ameliorates diabetic nephropathy via interruption of pathways that include NOX4 signalling

NADPH oxidase 4 (Nox4) is reported to be the major source of reactive oxygen species (ROS) in the kidneys during the early stages of diabetic nephropathy. It has been shown to mediate TGFβ1-induced differentiation of cardiac fibroblasts into myofibroblasts. Despite TGFβ1 being recognised as a mediator of renal fibrosis and functional decline role in diabetic nephropathy, the renal interaction between Nox 4 and TGFβ1 is not well characterised. The aim of this study was to investigate the role of Nox4 inhibition on TGFβ1-induced fibrotic responses in proximal tubular cells and in a mouse model of diabetic nephropathy. Immortalised human proximal tubular cells (HK2) were incubated with TGFβ1 ± plumbagin (an inhibitor of Nox4) or specific Nox4 siRNA. Collagen IV and fibronectin mRNA and protein expression were measured. Streptozotocin (STZ) induced diabetic C57BL/6J mice were administered plumbagin (2 mg/kg/day) or vehicle (DMSO; 50 µl/mouse) for 24 weeks. Metabolic, physiological and histological markers of nephropathy were determined. TGFβ1 increased Nox4 mRNA expression and plumbagin and Nox4 siRNA significantly inhibited TGF-β1 induced fibronectin and collagen IV expression in human HK2 cells. STZ-induced diabetic C57BL/6J mice developed physiological features of diabetic nephropathy at 24 weeks, which were reversed with concomitant plumbagin treatment. Histologically, plumbagin ameliorated diabetes induced upregulation of extracellular matrix protein expression compared to control. This study demonstrates that plumbagin ameliorates the development of diabetic nephropathy through pathways that include Nox4 signalling.

Tranilast inhibits the cell growth of normal human keratinocytes in vitro

Tranilast is used clinically as a drug for hypertrophic scars or keloids. Recently, the roles of keratinocytes in the pathogenesis of those conditions have been noted. Therefore, we first examined the effect of tranilast on the cell growth of normal human keratinocytes. A cell growth assay demonstrated that the cell number significantly decreased during 48 h cultures with the addition of tranilast (5-400 μM) compared with a control (tranilast 0) in a dose-dependent manner. Morphologically, cell spreading was decreased and the cell body was elongated with higher concentrations (200-400 μM) of tranilast, and the cell area decreased significantly. The effect was not due to cytotoxicity. The inhibition of cell growth and the changes in cell morphology by the treatment of 100 μM tranilast reversed after the removal of the tranilast. Immunohistochemical staining revealed that F-actin and vinculin expression with tranilast-treated keratinocytes decreased significantly in a dose-dependent manner (100-400 μM). In addition, cell cycle examination showed that 400 μM of tranilast caused G0/G1 arrest with the keratinocytes. From these data we concluded that tranilast inhibited the growth of normal human keratinocytes, and one of its mechanisms may involve decreasing cell spreading by inhibition of F-actin fiber and focal contact formation with the cells.

Tranilast ameliorates impaired hepatic functions in Schistosoma mansoni-infected mice

The ability of tranilast, a mast cell stabilizer and anti-transforming growth factor(β) (TGF(β)) to improve impaired hepatic functions in Schistosoma mansoni (S. mansoni)-infected mice, was investigated, providing the first evidence on the ability of tranilast to improve hepatic impairment due to schistosomal infection. Tranilast had significant beneficial effects against progression of hepatic fibrosis in S. mansoni-infected mice treated with praziquantel and those untreated. Different aspects of drug activity were investigated. Its effect on serum liver functions was evaluated by estimating: alanine aminotransferase, aspartate aminotransferase, total bilirubin, alkaline phosphatase and albumin. Its effect on the extent of liver fibrosis, through estimation of hepatic hydroxyproline and hepatic collagen content in liver hydrolysates, was also evaluated. Also, the expression of profibrogenic mediators, such as serum TGF(β1), was estimated. Finally, the effect on S. mansoni infection itself was studied, via histopathological examination of liver specimens stained with both hematoxylin-eosin and Masson's trichome stains. Tranilast ameliorated the harmful effects of S. mansoni infection on the liver. Such action was manifested in its significant ability to improve impaired hepatic functions, reduce histopathological changes, lower hepatic collagen content and finally reduce serum TGF(β1) levels. The beneficial effect of tranilast may be in part due to its ability to reduce the production of profibrogenic mediators in the infected animals by improving the host immune response or by interfering with critical steps in the fibrogenic cascade.

The role of EMT in renal fibrosis

It is clear that the well-described phenomenon of epithelial-mesenchymal transition (EMT) plays a pivotal role in embryonic development, wound healing, tissue regeneration, organ fibrosis and cancer progression. EMTs have been classified into three subtypes based on the functional consequences and biomarker context in which they are encountered. This review will highlight findings on type II EMT as a direct contributor to the kidney myofibroblast population in the development of renal fibrosis, specifically in diabetic nephropathy, the signalling molecules and the pathways involved in type II EMT and changes in the expression of specific miRNA with the EMT process. These findings have provided new insights into the activation and development of EMT during disease processes and may lead to possible therapeutic interventions to suppress EMTs and potentially reverse organ fibrosis.

Cation-independent mannose 6-phosphate receptor inhibitor (PXS25) inhibits fibrosis in human proximal tubular cells by inhibiting conversion of latent to active TGF-beta1

Hyperglycemia and hypoxia have independent and convergent roles in the development of renal disease. Transforming growth factor-β(1) (TGF-β(1)) is a key cytokine promoting the production of extracellular matrix proteins. The cationic-independent mannose 6-phosphate receptor (CI-M6PR) is a membrane protein that binds M6P-containing proteins. A key role is to activate latent TGF-β(1). PXS25, a novel CI-MPR inhibitor, has antifibrotic properties in skin fibroblasts, but its role in renal fibrosis is unclear. The aim was to study the role of PXS25 in matrix protein production under high glucose ± hypoxic conditions in human proximal tubule (HK-2) cells. HK-2 cells were exposed to high glucose (30 mM) ± 100 μM PXS25 in both normoxic (20% O(2)) and hypoxic (1% O(2)) conditions for 72 h. Cellular fibronectin, collagen IV, and matrix metalloproteinase-2 (MMP-2) and MMP-9 were assessed. Total and active TGF-β(1) were measured by ELISA. High glucose and hypoxia independently induced TGF-β(1) production. Active TGF-β(1), but not total TGF-β(1) was reduced with concurrent PXS25 in the presence of high glucose, but not in hyperglycemia+hypoxia conditions. Hyperglycemia induced fibronectin and collagen IV production (P < 0.05), as did hypoxia, but only hyperglycemia-induced increases in matrix proteins were suppressed by concurrent PXS25 exposure. High glucose induced MMP-2 and -9 in normoxic and hypoxic conditions, which was not modified in the presence of PXS25. High glucose and hypoxia can independently induce endogenous active TGF-β(1) production in human proximal tubular cells. PXS25 inhibits conversion of high glucose-induced release of active TGF-β(1), only in the absence of hypoxia.

Ramipril retards development of aortic valve stenosis in a rabbit model: mechanistic considerations

BACKGROUND AND PURPOSE

Aortic valve stenosis (AVS) is associated with significant cardiovascular morbidity and mortality. To date, no therapeutic modality has been shown to be effective in retarding AVS progression. We evaluated the effect of angiotensin-converting enzyme inhibition with ramipril on disease progression in a recently developed rabbit model of AVS.

EXPERIMENTAL APPROACH

The effects of 8 weeks of treatment with either vitamin D₂ at 25,000 IU for 4 days a week alone or in combination with ramipril (0.5 mg·kg⁻¹) on aortic valve structure and function were examined in New Zealand white rabbits. Echocardiographic aortic valve backscatter (AV(BS)) and aortic valve:outflow tract flow velocity ratio were utilized to quantify changes in valve structure and function.

KEY RESULTS

Treatment with ramipril significantly reduced AV(BS) and improved aortic valve :outflow tract flow velocity ratio. The intravalvular content of the pro-oxidant thioredoxin-interacting protein was decreased significantly with ramipril treatment. Endothelial function, as measured by asymmetric dimethylarginine concentrations and vascular responses to ACh, was improved significantly with ramipril treatment.

CONCLUSIONS AND IMPLICATIONS

Ramipril retards the development of AVS, reduces valvular thioredoxin-interacting protein accumulation and limits endothelial dysfunction in this animal model. These findings provide important insights into the mechanisms of AVS development and an impetus for future human studies of AVS retardation using an angiotensin-converting enzyme inhibitor.

Tranilast modulates fibrosis, epithelial-mesenchymal transition and peritubular capillary injury in unilateral ureteral obstruction rats

AIM

Tranilast is an anti-allergic compound suppressing transforming growth factor-beta 1 (TGF-β1) induced fibrosis. This study evaluated the efficacy of tranilast to attenuate renal fibrosis induced by unilateral ureteral obstruction (UUO) in rats in relation to epithelial-mesenchymal transition (EMT) and peritubular capillary injury.

METHODS

Rats were divided into four groups: UUO with vehicle or tranilast and sham operation with vehicle or tranilast. Tranilast (400 mg/kg/day) was administrated to rats for 7 and 14 days after UUO.

RESULTS

Fibrosis and tubular injuries were attenuated in UUO kidneys with tranilast (Tr-UUO kidneys) compared with UUO kidneys with vehicle (V-UUO kidneys). Decreased E-cadherin and increased vimentin expression in the tubular epithelium and Snail expression in V-UUO kidneys were also attenuated in Tr-UUO kidneys in which heparan sulfate proteoglycan in the tubular basement membrane was preserved and matrix metalloproteinase-2 expression was attenuated. Increased TGF-β1 and phospho-Smad2 expression and increased numbers of myofibroblasts and macrophages in V-UUO kidneys were attenuated by tranilast. Decreased VE-cadherin expression and cytoplasmic swelling of the endothelium of peritubular capillaries that occurred in V-UUO kidneys was prevented by tranilast.

CONCLUSIONS

Tranilast modulates fibrogenesis by reducing EMT, preventing disintegration of the tubular basement membrane, and reducing peritubular capillary injury in UUO kidneys.

Vascular basement membrane thickening in diabetic retinopathy

Vascular basement membrane (BM) thickening is a fundamental structural alteration of small blood vessels in diabetes. Over two decades of research has established hyperglycemia as the primary causal factor mediating this alteration. Various high glucose-induced mechanisms have been investigated and excess synthesis of BM components has been identified as a major contributing factor to BM thickening. Although BM thickening has been long hailed as the histological hallmark of diabetic microangiopathy, the consequences of BM thickening on the functionality of target organs of diabetes remain elusive even today. This review presents an overview of our current understanding of the BM structure and function, and focuses on how capillary BM thickening develops, its effect on retinal vascular function, and potential strategies for preventing the development of BM thickening in diabetic retinopathy.

Targeting fibrosis for the treatment of heart failure: a role for transforming growth factor-β

Chronic heart failure (CHF) is a growing health problem in developed nations. The pathological accumulation of extracellular matrix is a key contributor to CHF in both diabetic and nondiabetic states, resulting in progressive stiffening of the ventricular walls and loss of contractility. Proinflammatory disease processes, including inflammatory cytokine activation, contribute to accumulation of extracellular matrix in the heart. Transforming growth factor-β is a key profibrotic cytokine mediating fibrosis. Current therapeutic strategies do not directly target the profibrotic inflammatory processes occurring in the heart and hence there is a clear unmet clinical need to develop new therapeutic agents targeting fibrosis. Accordingly, strategies that inhibit proinflammatory cytokine activation and pathological accumulation of extracellular matrix (ECM) provide a potential therapeutic target for prevention of heart failure. This review focuses on the therapeutic targeting of TGF-β in the prevention of pathological fibrosis in the heart.

Tranilast attenuates the up-regulation of thioredoxin-interacting protein and oxidative stress in an experimental model of diabetic nephropathy

BACKGROUND

Diabetic nephropathy is the leading cause of kidney failure in the developed world. Tranilast has been reported to not only act as an anti-inflammatory and anti-fibrotic compound, but it also exerts anti-oxidative stress effects in diabetic nephropathy. Thioredoxin-interacting protein (Txnip) is the endogenous inhibitor of the anti-oxidant thioredoxin and is highly up-regulated in diabetic nephropathy, leading to oxidative stress and fibrosis. In this study, we aimed to investigate whether tranilast exerts its anti-oxidant properties through the inhibition of Txnip.

METHODS

Heterozygous Ren-2 rats were rendered diabetic with streptozotocin. Another group of rats were injected with citrate buffer alone and treated as non-diabetic controls. After 6 weeks of diabetes, diabetic rats were divided into two groups: one group gavaged with tranilast at 200 mg/kg/day and another group with vehicle.

RESULTS

Diabetic rats had a significant increase in albuminuria, tubulointerstitial fibrosis, peritubular collagen IV accumulation, reactive oxygen species (ROS) and macrophage infiltration (all P < 0.05). These changes were associated with an increase in Txnip mRNA and protein expression in the tubules and glomeruli of diabetic kidney. Treatment with tranilast for 4 weeks significantly attenuated Txnip up-regulation in diabetic rats and this was associated with a reduction in ROS, fibrosis and macrophage infiltration (all P < 0.05).

CONCLUSIONS

This is the first study to demonstrate that tranilast not only has anti-inflammatory and anti-fibrotic effects as previously reported but also attenuates the up-regulation of Txnip and oxidative stress in diabetic nephropathy.

Effects of tranilast and pentoxifylline in a mouse model of chronic asthma using house dust mite antigen

Tranilast has been used in allergic diseases because of its inhibitory effect on mast cells; it also has an anti-fibrotic effect in several diseases. Pentoxifylline (PTX), a methylxanthine derivative, is a potent anti-inflammatory drug that is known to manifest its effect through the inhibition of Th1 cytokine, but with an uncertain effect on Th2 cytokine. Seven-week-old female BALB/c mice were studied as a chronic asthma model. The mice were challenged with house dust mite (HDM) antigen for 7 weeks. Each group of mice was given an intraperitoneal injection of tranilast, PTX, or tranilast plus PTX before antigen administration. In this mouse model of chronic asthma, tranilast, and PTX each had an inhibitory effect on airway remodeling as well as on airway hyperresponsiveness (AHR) and airway inflammation. The improved events of these drugs were related with the inhibition of the Th2 cytokine IL-13 and TGF-beta 1. Immunohistochemical analysis showed that decreases in the peribronchial trichrome stained area in each treatment group were associated with improvements in the peribronchial smooth muscle hyperplasia, collagen type I, and collagen type III deposition. These drugs could have potential beneficial effects on chronic asthma, especially with respect to airway remodeling.

Evaluation and optimization of antifibrotic activity of cinnamoyl anthranilates

Tranilast is an anti-inflammatory drug in use for asthma and atopic dermatitis. In studies over the last decade it has been revealed that tranilast can reduce fibrosis occurring in the kidney during diabetes, thereby delaying and/or preventing kidney dysfunction. We report a structure-activity study aimed at optimizing the antifibrotic activity of tranilast. A series of cinnamoyl anthranilates were prepared and assessed for their ability to prevent TGF-beta-stimulated production of collagen in cultured renal mesangial cells. We reveal derivatives with improved potency and reduced cellular toxicity relative to tranilast. 3-Methoxy-4-propargyloxycinnamoyl anthranilate reduces albuminuria in a rat model of progressive diabetes, and thus has potential as an innovative treatment for diabetic nephropathy.

Transcription factors Krüppel-like factor 6 and peroxisome proliferator-activated receptor-{gamma} mediate high glucose-induced thioredoxin-interacting protein

We demonstrated recently that thioredoxin-interacting protein (Txnip) and the transcription factor Krüppel-like factor 6 (KLF6) were up-regulated in both in vivo and in vitro models of diabetic nephropathy, thus promoting renal injury. Conversely, peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists have been shown to be renoprotective. Hence, this study was undertaken to determine whether Txnip expression is regulated by the transcription factors KLF6 and PPAR-gamma. By using siRNAs and overexpressing constructs, the role of KLF6 and PPAR-gamma in Txnip transcriptional regulation was determined in human kidney proximal tubule cells and in streptozocin-induced diabetes mellitus in Sprague-Dawley rats, in vitro and in vivo models of diabetic nephropathy, respectively. KLF6 overexpression increased Txnip expression and promoter activity, which was inhibited by concurrent exposure to PPAR-gamma agonists. In contrast, reduced expression of KLF6 by siRNA or exposure to PPAR-gamma agonists attenuated high glucose-induced Txnip expression and promoter activity. KLF6-Txnip promoter binding was decreased in KLF6-silenced cells, whereas PPAR-gamma agonists increased PPAR-gamma-Txnip promoter binding. Indeed, silencing of KLF6 increased PPAR-gamma expression, suggesting endogenous regulation of PPAR-gamma expression by KLF6. Moreover, renal KLF6 and Txnip expression increased in rats with diabetes mellitus and was inhibited by PPAR-gamma agonist treatment; however, KLF6 expression did not change in HK-2 cells exposed to PPAR-gamma agonists. Hence, Txnip expression and promoter activity are mediated via divergent effects of KLF6 and PPAR-gamma transcriptional regulation.

Transforming growth factor-beta and angiotensin in fibrosis and burn injuries

This review considers the roles of transforming growth factor-beta (TGF-beta), the signaling Smad proteins, and angiotensin II (AT II) in conditions leading to human fibrosis. The goal is to update the burn practitioner and researcher about this important pathway and to introduce AT II as a possible synergistic signal to TGF-beta in burn scarring. Literature searches of the MEDLINE database were performed for English manuscripts combinations of TGF-beta, Smad, angiotensin, fibrosis, burn, and scar. AT II and TGF-beta both activate the Smad protein system, which leads to the expression of genes related to fibrosis. In fibrotic conditions, such as tubulointerstitial nephritis, systemic sclerosis, and myocardial infarctions, AT II acts both independently and synergistically with TGF-beta. Both AT II and TGF-beta act through a messenger system, the Smad proteins that lead to excessive extracellular matrix formation. Treatment and research implications are reviewed. The interaction between AT II and TGF-beta leading to fibrosis is well described in some human diseases. This pathway may be of importance in human burn scarring as well.

Tranilast inhibits the growth and metastasis of mammary carcinoma

Tranilast (N-[3,4-dimethoxycinnamonyl]-anthranilic acid) is a drug of low toxicity that is orally administered, and has been used clinically in Japan as an antiallergic and antifibrotic agent. Its antifibrotic effect is thought to depend on the inhibition of transforming growth factor-beta (TGF-beta). It has also been shown to exert antitumor effects, but its mode of action is unclear. Here, we explored the antitumor effects of tranilast in vitro and in vivo. Tranilast inhibited the proliferation of several tumor cell lines including mouse mammary carcinoma (4T1), rat mammary carcinoma stem cell (LA7), and human breast carcinoma (MDA-MB-231 and MCF-7). Tranilast blocked cell-cycle progression in vitro. In the highly metastatic 4T1 cell line, tranilast inhibited phospho-Smad2 generation, consistent with a blockade of TGF-beta signaling. It also inhibited the activation of MAP kinases (extracellularly regulated kinase 1 and 2 and JNK), which have been linked to TGF-beta-dependent epithelial-to-mesenchymal transition and, indeed, it blocked epithelial-to-mesenchymal transition. Although tranilast only partially inhibited TGF-beta production by 4T1 tumor cells, it potently inhibited the production of TGF-beta, interferon-gamma, IL-6, IL-10, and IL-17 by lymphoid cells, suggesting a general anti-inflammatory activity. In vivo, female BALB/c mice were inoculated with syngeneic 4T1 cells in mammary fat pads and treated with tranilast by gavage. Tranilast reduced (>50%) the growth of the primary tumor. However, its effects on metastasis were more striking, with more than 90% reduction of metastases in the lungs and no metastasis in the liver. Thus, tranilast has potential activity as an antimetastatic agent in breast cancer.

Antitransforming growth factor-beta therapy in fibrosis: recent progress and implications for systemic sclerosis

PURPOSE OF REVIEW

Transforming growth factor-beta (TGF-beta) is required for tissue homeostasis but is also implicated in disease processes including fibrosis, and thus represents a molecular target for therapy.

RECENT FINDINGS

Multiple strategies for inhibiting excessive TGF-beta function exist. The three principal platforms are RNA-based technologies, monoclonal antibodies and small molecules. Monoclonal antibodies targeting TGF-beta have been used in a small clinical trial, with disappointing results to date. Antibodies to the alphavbeta6 integrin prevent local activation of latent TGF-beta and show promise in preclinical studies. Over a dozen small molecules inhibit the kinase activity of TGF-beta receptors. Several commonly used drugs appear to have unanticipated anti-TGF-beta activity and may therefore have a role in antifibrotic therapy. Because TGF-beta has important physiological functions, inhibiting its activity might potentially lead to aberrant immune activation, epithelial hyperplasia and impaired wound healing; spontaneous autoimmunity in particular is a concern in an autoimmune disease such as systemic sclerosis. Novel insights from DNA microarray analysis and genetic polymorphisms in TGF-beta signaling will aid in defining patient populations most likely to respond to anti-TGF-beta treatment.

SUMMARY

Anti-TGF-beta therapies promise to have a major impact in systemic sclerosis. Significant concerns regarding efficacy and safety need to be addresed. The identification of optimal candidates for therapy, and of biomarkers of safety and efficacy, are critical challenges ahead.

Connective tissue growth factor stimulates renal cortical myofibroblast-like cell proliferation and matrix protein production

Myofibroblasts primarily contribute to the pathogenesis of renal interstitial fibrosis by unregulated cell proliferation and synthesis of excessive amounts of extracellular matrix (ECM) proteins. We used cultured myofibroblast-like cells obtained by outgrowth from explants of rat kidney cortex to study the effects and relevant signaling pathway of connective tissue growth factor (CTGF) on cell proliferation and ECM production. Exogenous CTGF stimulated proliferation of myofibroblast-like cells in a dose- and time-dependent manner. CTGF also increased the secretion of fibronectin and collagen I protein in the supernatant medium. Nevertheless, CTGF did not affect matrix-degrading metalloproteinases-2 and -9 activities in supernatant medium measured by gelatin zymography. CTGF induced activation of extracellular signal-regulated protein kinase (ERK)1/2 mitogen-activated protein kinase pathway as early as 5 minutes. Inhibition of ERK1/2 activation with PD98059 completely blocked CTGF-induced cell proliferation as well as secretion of fibronectin and collagen I protein. The above results indicate that CTGF triggers cell proliferation and production of ECM proteins in cultured myofibroblast-like cells through the ERK1/2 mitogen-activated protein kinase pathway.

Pathobiology of transforming growth factor beta in cancer, fibrosis and immunologic disease, and therapeutic considerations

Transforming growth factor beta (TGF-beta) is a highly pleiotropic cytokine that plays an important role in wound healing, angiogenesis, immunoregulation and cancer. The cells of the immune system produce the TGF-beta1 isoform, which exerts powerful anti-inflammatory functions, and is a master regulator of the immune response. However, this is context dependent, because TGF-beta can contribute to the differentiation of both regulatory (suppressive) T cells (Tr cells) and inflammatory Th17 cells. While TGF-beta might be underproduced in some autoimmune diseases, it is overproduced in many pathological conditions. This includes pulmonary fibrosis, glomerulosclerosis, renal interstitial fibrosis, cirrhosis, Crohn's disease, cardiomyopathy, scleroderma and chronic graft-vs-host disease. In neoplastic disease, TGF-beta suppresses the progression of early lesions, but later this effect is lost and cancer cells produce TGF-beta, which then promotes metastasis. This cytokine also contributes to the formation of the tumor stroma, angiogenesis and immunosuppression. In view of this, several approaches are being studied to inhibit TGF-beta activity, including neutralizing antibodies, soluble receptors, receptor kinase antagonist drugs, antisense reagents and a number of less specific drugs such as angiotensin II antagonists and tranilast. It might be assumed that TGF-beta blockade would result in severe inflammatory disease, but this has not been the case, presumably because the neutralization is only partial. In contrast, the systemic administration of TGF-beta for therapeutic purposes is limited by toxicity and safety concerns, but local administration appears feasible, especially to promote wound healing. Immunotherapy or vaccination stimulating TGF-beta production and/or Tr differentiation might be applied to the treatment of autoimmune diseases. The benefits of new therapies targeting TGF-beta are under intense investigation.

CD36 is a novel and potential anti-fibrogenic target in albumin-induced renal proximal tubule fibrosis

Albumin is not only a risk factor for diabetic nephropathy (DN), but also a therapeutic target. Hence, scientists have long sought ways to elucidate the interactions between albumin and diabetic renal tubule fibrosis. CD36, a surface receptor for thrombospondin-1, has been reported to interact with latent transforming growth factor-beta1 (TGF-beta1) and activate its fibrogenic bioactivity. This study elucidates the interactions between CD36 and renal tubule fibrosis. LLC-PK1 cells were applied to represent renal proximal tubule cells. The expression of CD36 was evaluated by flow cytometry. Fibronectin was assayed by Western blot and enzyme-linked immunosorbent assay (ELISA). Bioactive TGF-beta1 was assayed by ELISA. We demonstrated that albumin was shown significantly to inhibit cell growth without affecting hypertrophy status since protein content and cell size remained unaffected under albumin treatment. Moreover, albumin dose-dependently (0, 1, or 10 mg/ml) enhanced the secretion of bioactive TGF-beta1 and fibronectin with the upregulation of CD36. Intriguingly, CD36 siRNA, a potent silencer for CD36 effectively suppressed the albumin-induced increase in CD36, TGF-beta1, and even fibronectin level. Accordingly, albumin is a pro-fibrogenic factor for proximal tubule cells since albumin per se markedly upregulated the expression of TGF-beta1 and fibronectin. Most importantly, CD36 may mediate albumin-induced cellular fibrosis since CD36 siRNA appeared to have anti-fibrosis effects. This work suggests that CD36 is a novel and potential therapeutic target for diabetic renal tubule fibrosis.

Therapeutic potential of TGF-beta inhibition in chronic renal failure

Chronic kidney diseases are emerging as a worldwide public health problem. The progression of kidney diseases closely correlates with the accumulation of extracellular matrix leading to glomerulosclerosis and tubulointerstitial injury. Transforming growth factor (TGF)-beta has been identified as a key mediator of kidney matrix accumulation. Overexpression of TGF-beta isoforms and their receptors was observed in a variety of renal diseases in both animals and humans. Given its crucial role in fibrotic kidney disease, TGF-beta has been recently considered as a possible target in the management of chronic renal diseases. This review discusses the role of TGF-beta in renal fibrosis and provides an overview of the strategies that, when interfering with TGF-beta expression and signalling, could be employed as new renoprotective treatments.

The interdependence of EGF-R and SGK-1 in fibronectin expression in primary kidney cortical fibroblast cells

BACKGROUND

Epidermal growth factor (EGF) has been shown to play a role in the nephromegaly and enhanced sodium reabsorption observed in diabetic nephropathy. This is recognized to be dependent on activation of serine threonine glucocorticoid kinase-1 (SGK-1). However, the roles of EGF and SGK-1 in renal fibrogenesis observed under high glucose conditions have not been established.

METHODS

Primary cultures of human cortical fibroblasts (CFs) were used as the model in which to study the dependent and independent effects of high glucose, EGF and SGK-1 on the expression of the extracellular matrix protein (ECM) fibronectin. Wild type CFs expressing SGK-1, or cells in which SGK-1 was effectively silenced using siRNA methodology, were exposed to normal (5mM) or high (25mM) glucose, or EGF (10ng/ml) for 48hr and fibronectin assessed. The role of the EGF-receptor and its relationship to SGK-1 signaling was studied using concurrent treatment with PKI166, a specific inhibitor of EGF-receptor.

RESULTS

Exposure of CF to high glucose and EGF increased phosphorylated EGF-R, SGK-1, and fibronectin expression in wild-type cells. Inhibition of the EGF-R reduced SGK-1 and fibronectin expression in control, and following exposure to EGF and high glucose conditions. In cells in which SGK-1 was silenced, fibronectin was reduced and there was no significant increase in pEGF-R, suggesting that SGK-1 is downstream of the EGF-R and negatively inhibits EGF-R activation.

CONCLUSION

These results suggest that high glucose induced fibronectin expression is mediated through the EGF-R and downstream expression of SGK-1.

Mast cell, a promising therapeutic target in tubulointerstitial fibrosis

Tubulointerstitial fibrosis is a final common pathway to the eventual structural desolation of kidneys. However, the mechanism involved in this phenomenon is still poorly understood, and current therapies are ineffective or only marginally effective. Mast cell has a variety of physiological and pathological functions through the production of heparin, histamine, neutrophil chemoattractants, immunoregulatory cytokines, and mast cell-specific serine proteases tryptase and chymase. The survival and proliferation of mast cell are dependent upon stem cell factor. Presently, mast cells are known to participate in the pathogenesis of tubulointerstitial fibrosis in many kidney diseases. Several therapeutic approaches to inhibit mast cell activation have already demonstrated some clinical utility in tissue fibrosis or inflammatory diseases such as the use of mast cell stabilizers, inhibitors of tryptase or chymase, blockade of stem cell factor and anti-IgE therapy. We hypothesize that mast cell has a significant role in the progression of tubulointerstitial fibrosis, thus the treatment strategies based on mast cell appear to be promising in these conditions. Development of these novel therapeutic approaches will enable us to target any types of renal disease.