Medical Hypotheses 82 (2014) 700–702

Contents lists available at ScienceDirect

Medical Hypotheses

journal homepage: www.elsevier .com/locate /mehy

Next target of tranilast: Inhibition of corneal neovascularization

http://dx.doi.org/10.1016/j.mehy.2014.03.0070306-9877/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author at: Medical Biology Research Center, P.O. Box 1568,Sorkheh Ligeh, Kermanshah, Iran. Tel.: +98 9188564304; fax: +98 831 4276471.

E-mail addresses: Norooznezhad@student.tums.ac.ir, Norooznezhad@gmail.com(A.H. Norooznezhad).

Amir Hossein Norooznezhad a,b,⇑, Fatemeh Norooznezhad a, Kimia Ahmadi b

a Medical Biology Research Center, Kermanshah University of Medical Sciences, Kermanshah, Iranb College of Medicine, Tehran University of Medical Sciences, Tehran, Iran

a r t i c l e i n f o a b s t r a c t

Article history:Received 5 November 2013Accepted 5 March 2014

Corneal neovascularization (CN) which is associated with angiogenesis and inflammation is seen in dif-ferent pathological conditions. Among all these situations inflammation and angiogenesis factors such asvascular endothelial growth factor (VEGF), matrix metalo proteinases (MMPs), tumor necrosis factor-a(TNF-a) and other related factors are involved in CN regardless of the etiology. Thus inhibition of theseagents that lead to suppression of angiogenesis and inflammation is one the most important strategiesto treat CN. Tranilast (TR) is an anti-allergic medicine which has been used in Japan and South Koreain clinic. TR is able to inhibit VEGF, MMP-2 and MMP-9, TNF-a and some other angiogenic and inflamma-tory factors. According to the anti-angiogenic and anti-inflammatory activity of TR, we hypothesize onthe probable efficacy of TR in treating CN. Also topical application of TR in human eye is reported tobe safe, so it would be easier to have additional research on therapeutic potential of TR in clinic.

� 2014 Elsevier Ltd. All rights reserved.

Introduction

Corneal neovascularization (NV) can be detected in variouspathological situations such as infection, corneal transplantationand different immunological diseases [1]. Corneal NV is a resultof an imbalance between angiogenic and anti-angiogenic factorsand modulators which leads to the induction of NV [2]. Accordingto the data, 1.4 billion people in United States (4% of its popula-tion) suffering from corneal NV each year. This pathological con-dition may lead to corneal ulcer, edema and inflammation whichin turn results in the loss of eye vision [3]. Angiogenesis, forma-tion of new blood vessels, is a complex morphogenetic processwhich was first suggested by Dr. Judah Folkman as a step ofgrowth in solid tumors [4]. This mechanism plays a critical rolein physiological conditions such as wound healing, female repro-ductive cycle and embryonic growth. In pathological conditions,angiogenesis has been proved to be of great importance. It takespart in progressive mechanisms of corneal neovascularization,psoriasis, diabetic retinopathy, tumor growth and metastasis [5].Formation of new blood vessels happens with different stepsincluding: basement membrane hydrolysis and digestion, prolif-eration, migration and tube formation of endothelial cells (ECs).There are several angiogenic and pro-angiogenic factors involved

in each step [6–7]. Vascular endothelial growth factor (VEGF)seems to be the most important pro-angiogenic factor responsiblefor ECs growth, survival, permeability, migration and vesselremodeling. This factor is expressed under hypoxia situation intissues and attaches to its receptor on the ECs surface to inducejust mentioned activities [8–9]. VEGF could be secreted by ECs,macrophages, T cells and astrocytes [10–11]. So far, severalstudies have shown that corneal NV could be both inhibitedand treated by targeting VEGF using different agents such asmonoclonal anti-bodies, VEGF trap, siRNA and tyrosine kinaseinhibitors [12]. Matrix metalloproteinases (MMPs) are a groupof zinc dependent proteases and can directly effect on ECs migra-tion due to their proteolytic activity on basement membrane andextracellular matrix [13]. So far, expression of two major types ofMMPs is confirmed in the eye and especially in cornea; MMP-2[14] and MMP-9 [15]. Two different studies on MMP-2 deficientmice showed a delay in corneal NV and inflammation in compres-sion to normal controls [16–17]. It is also shown in mouse modelsthat MMP-2 has an undeniable role in choroidal neovasculariza-tion [18]. Basic fibroblast growth factor (bFGF) is a substantialmember of angiogenesis molecular system that is approved tobe playing a role in corneal NV as well [19]. Moreover, integrinsav and b3 are verified to have an effect on ECs proliferation,migration and survival in order to advance angiogenesis process[20]. Other study on intra cellular adhesion molecule-1(ICAM-1) deficient mouse showed a lower level of corneal NVand neutrophils count in cornea in compression to control group.Also this type of deficiency directly resulted in reducing VEGF

A.H. Norooznezhad et al. / Medical Hypotheses 82 (2014) 700–702 701

mRNA levels [21]. The role of vascular cell adhesion molecule-1(VCAM-1) in angiogenesis is also being recognized as well asother factors [22].

The balance between angiogenic and anti-angiogenic factors isseen in an intact cornea and is one of the necessities of normal vi-sion. Some pathological conditions such as inflammation can man-age to affect this balanced system and drag it into angiogenesisinduced situation [23]. One of the important and well knowninflammatory cytokines involved in corneal inflammation (CI) isIL-1 which is expressed by corneal epithelial cells, infiltrated mac-rophages and monocytes [24]. According to the data, binding ofIL-1 to its receptor on the surface of corneal fibroblasts inducesexpression of some other proinflammatory chemokines [25]. An-other inflammatory cytokine, secreted TNF-a, is responsible forexpression of some angiogenic cytokines such as VEGF, bFGF andIL-8 [26]. Through the inflammation pathway, cyclooxygenase-2(COX-2), except for playing its role in converting arachidonic acidto prostaglandins, affects different angiogenic steps such as prolif-eration and migration of ECs [3]. Suppression of COX-2, using aselective inhibitor which showed to yield satisfactory result intreatment of corneal NV, supports that the COX-2 has got a majorrole in inflammation and corneal NV [27]. All the mentioned andother factors and stimulators which together take part in patholog-ical corneal NV could be considered as targets in treatment ofcorneal NV.

Hypothesis

Tranilast therapy could be reasonably effective in order to treator decrease the damage range in corneal NV. This hypothesis isbased on both anti-angiogenic and anti-inflammatory activity oftranilast.

Evaluation of hypothesis

According to the data inhibition of angiogenesis and inflam-mation is the most important strategy in treatment of cornealneovascularization. Thus inhibition of corneal NV using a safeand strong anti-angiogenic and anti-inflammatory agent stronglyinfluences the treatment process [3]. In both in vitro and in vivomodels, tranilast (TR) was significantly potent in angiogenesisinhibition. To go into detail, it suppressed angiogenesis by inhibi-tion of human microvascular endothelial cells proliferation, che-motaxis and tube formation [28]. Another study revealed thatTR was also able to inhibit VEGF induced proliferation, migrationand tube formation of bovine retinal endothelial cells (BRETs) andbFGF induced proliferation as well [29]. Inhibitory effect of TR onboth of TGF-b isoforms expression has been reported in injuredarteries of rats. Likewise, it was able to inhibit TGF-b inducedexpression of integrins av and b3 mRNA. All these actions weredue to influence of TR on TGF-b receptor mRNA levels [30]. More-over, in the corneal fibroblast cells, TR could suppress TNF-a andIL-4 induced VCAM-1 expression [31]. Inhibition of TNF-a in-duced expression of ICAM-1, VCAM-1 and E-selectin in humanumbilical endothelial cells, was recognized to be under the effectof TR working on nuclear factor-jB (NF-jB) [32]. Furthermore TRhas been used in order to suppress MMP-2 and MMP-9 in fibro-blasts in response to TNF-a and MMP-9 in neutrophils as well[33–34]. Other than all these anti-angiogenic activity of TR, ithas been proved to suppress laser induced chroidal neovascular-ization in vivo [35]. TR showed its anti-inflammatory activityvia down-regulation of COX-2 and up-regulation of heme oxygen-ase-1 expression as an anti-inflammatory agent [36]. Besides theinflammatory inhibition pathway TR is assumed to be running, it

also inhibited releasing of IL-1b from both macrophages andmonocytes [37].

Discussion and conclusion

As mentioned in introduction, corneal NV is in need of bothangiogenesis and inflammation processes which are characterizedby different molecular agents that may have an overlap or synergiceffect on each other. Beside its anti-allergic activity, TR is con-firmed to have an acceptable view of its anti-angiogenic andanti-inflammatory potential. This pharmacologic substance re-strains angiogenesis in similar tissues to cornea in both in vitroand in vivo models; laser induced choroid neovascularization andVEGF induced ECs migration, proliferation and tube formation inBRETs. Ability of TR in inhibition of both angiogenesis and inflam-mation, considering the overlap of these mechanisms, could sug-gest a synergic anti-corneal NV effect. If TR ability in inhibitionof corneal NV is considered to be approved, the next challengewould be evaluating the susceptibility issues of using it in treat-ment. One of the most important factors for a pharmaceuticalproduct is for it to be safe, as less toxic as it can be and have theleast side effects possible. TR is already approved in Japan andSouth Korea as an anti-allergy drug in order to treat bronchial asth-ma [38]. In rabbit model of posterior capsule opacification (PCO),intracapsular TR microsphere is verified as one safe profitableagent in PCO [39] treatment. Moreover, in a pilot study on 52 pa-tients, using 0.5% TR eye drop to investigate on intraocular pres-sure and bleb formation after glaucoma filtering surgery, therewere satisfactory results and no side effect of TR on eye vision[40]. In addition TR has been used as an ophthalmic solution in or-der to prevention of conjunctival symblepharon and recurrence ofpterygium successfully [41]. In conclusion, considering theseexperimental and clinical data, using TR as a topical treatmentfor corneal NV seems to be safe, but more investigation is neces-sary for sure.

Conflict of interest statement

None.

Acknowledgements

Authors of this study are grateful for kindly views of ProfessorReza Dana (Harvard Medical School), Dr. Sahar Goodarzi and Dr.Hamid Reza Seddigh (Tehran University of Medical Sciences).

References

[1] Epstein RJ, Stulting RD, Hendricks RL, Harris DM. Corneal neovascularization.Pathogenesis and inhibition. Cornea 1987;6:250–7.

[2] Zhang SX, Ma JX. Ocular neovascularization: implication of endogenousangiogenic inhibitors and potential therapy. Prog Retin Eye Res 2007;26:1–37.

[3] Shakiba Y, Mansouri K, Arshadi D, Rezaei N. Corneal neovascularization:molecular events and therapeutic options. Recent Pat Inflammation AllergyDrug Discovery 2009;3:221–31.

[4] Ribatti D. Judah Folkman, a pioneer in the study of angiogenesis. Angiogenesis2008;11:3–10.

[5] Pandya NM, Dhalla NS, Santani DD. Angiogenesis, a new target for futuretherapy. Vascul Pharmacol 2006;44:265–74.

[6] Folkman J. Angiogenesis. Annu Rev Med 2006;57:1–18.[7] Plank MJ, Sleeman BD. Tumor-induced angiogenesis. J Theor Med 2004;5:

137–53.[8] Holmes DI, Zachary I. The vascular endothelial growth factor (VEGF) family:

angiogenic factors in health and disease. Genome Biol 2005;6:209.[9] Li X, Eriksson U. Novel VEGF family members: VEGF-B, VEGF-C and VEGF-D. Int

J Biochem Cell Biol 2001;33:421–6.[10] Robinson CJ, Stringer SE. The splice variants of vascular endothelial growth

factor (VEGF) and their receptors. J Cell Sci 2001;114:853–65.[11] Holmes DI, Zachary I. The vascular endothelial growth factor (VEGF) family:

angiogenic factors in health and disease. Genome Biol 2005;6:209.

702 A.H. Norooznezhad et al. / Medical Hypotheses 82 (2014) 700–702

[12] Chang JH, Garg NK, Lunde E, Ha KY, Jain S, Azar DT. Corneal neovascularization:an anti-VEGF therapy review. Surv Ophthalmol 2012;57:415–29.

[13] Visse R, Nagase H. Matrix metalloproteinases and tissue inhibitors ofmetalloproteinases: structure, function, and biochemistry. Circ Res 2003;92:827–39.

[14] Zhang H, Li C, Baciu PC. Expression of integrins and MMPs during alkaline-burn-induced corneal angiogenesis. Invest Ophthalmol Vis Sci 2002;43:955–62.

[15] Ye HQ, Azar DT. Expression of gelatinases A and B, and TIMPs 1 and 2 duringcorneal wound healing. Invest Ophthalmol Vis Sci 1998;39:913–21.

[16] Samolov B, Steen B, Seregard S, van der Ploeg I, Montan P, Kvanta A. Delayedinflammation-associated corneal neovascularization in MMP-2-deficient mice.Exp Eye Res 2005;802:159–66.

[17] Ohno-Matsui K, Uetama T, Yoshida T, Hayano M, Itoh T, Morita I, et al. Reducedretinal angiogenesis in MMP-2 – deficient mice. Invest Ophthalmol Vis Sci2003;44:5370–5.

[18] Berglin L, Sarman S, van der Ploeg I, Steen B, Ming Y, Itohara S, et al. Reducedchoroidal neovascular membrane formation in matrix metalloproteinase-2-deficient mice. Invest Ophthalmol Vis Sci 2003;441:403–8.

[19] Chang JH, Gabison EE, Kato T, Azar DT. Corneal neovascularization. Curr OpinOphthalmol 2001;12:242–9.

[20] Eliceiri BP, Cheresh DA. The role of alphav integrins during angiogenesis:insights into potential mechanisms of action and clinical development. J ClinInvest 1999;103(9):1227–30.

[21] Moromizato Y, Stechschulte S, Miyamoto K, Murata T, Tsujikawa A, TsujikawaAM, et al. CD 18 and ICAM-1 dependent corneal neovascularization andinflammation after limbal injury. Am J Pathol 2000;157:1277–81.

[22] Zhu SN, Dana MR. Expression of cell adhesion molecules on limbal andneovascular endothelium in corneal inflammatory neovascularization. InvestOphthalmol Vis Sci 1999;40:1427–34.

[23] Clements JL, Dana R. Inflammatory corneal neovascularization:etiopathogenesis. Semin Ophthalmol 2011;26:235–45.

[24] Dana R. Comparison of topical interleukin-1 vs. tumor necrosis factor alphablockade with corticosteroid therapy on murine corneal inflammation,neovascularization and transplant survival (an American OphthalmologicalSociety thesis). Trans Am Ophthalmol Soc 2007;105:330–43.

[25] Hong JW, Liu JJ, Lee JS, Mohan RR, Mohan RR, Woods DJ, et al. Proinflammatorychemokine induction in keratocytes and inflammatory cell infiltration into thecornea. Invest Ophthalmol Vis Sci 2001;42:2795–803.

[26] Henricson BE, Benjamin WR, Vogel SN. Differential cytokine induction bydoses of lipopolysaccharide and monophosphoryl lipid A that result inequivalent early endotoxin tolerance. Infect Immun 1990;58:2429–37.

[27] Yamada M, Kawai M, Kawai Y, Mashima Y. The effect of selectivecyclooxygenase-2 inhibitor on corneal angiogenesis in the rat. Curr Eye Res1999;19:300–4.

[28] Isaji M, Miyata H, Ajisawa Y, Takehana Y, Yoshimura N. Tranilast inhibits theproliferation, chemotaxis and tube formation of human microvascularendothelial cells in vitro and angiogenesis in vivo. Br J Pharmacol1997;122:1061–6.

[29] Koyama S, Takagi H, Otani A, Suzuma K, Nishimura K, Honda Y. Tranilastinhibits protein kinase C-dependent signaling pathway linked to angiogenicactivities and gene expression of retinal microcapillary endothelial cells. Br JPharmacol 1999;127:537–45.

[30] Ward MR, Sasahara T, Agrotis A, Dilley RJ, Jennings GL, Bobik A. Inhibitoryeffects of tranilast on expression of transforming growth factor-b isoforms andreceptors in injured arteries. Atherosclerosis 1998;137:267–75.

[31] Adachi T, Fukuda K, Kondo Y, Nishida T. Inhibition by tranilast of the cytokine-induced expression of chemokines and the adhesion molecule VCAM-1 inhuman corneal fibroblasts. Invest Ophthalmol Vis Sci 2010;51:3954–60.

[32] Spiecker M, Lorenz I, Marx N, Darius H. Tranilast inhibits cytokine-inducednuclear factor kb activation in vascular endothelial cells. Mol Pharmacol2002;62:856–63.

[33] Shimizu T, Kanai K, Asano K, Hisamitsu T, Suzaki H. Suppression of matrixmetalloproteinase production in nasal fibroblasts by tranilast, an antiallergicagent, in vitro. Mediators Inflamm 2005;2005:150–9.

[34] Shimizu T, Kanai K, Kyo Y, Asano K, Hisamitsu T, Suzaki H. Effect of tranilast onmatrix metalloproteinase production from neutrophils in vitro. J PharmPharmacol 2006;58:91–9.

[35] Takehana Y, Kurokawa T, Kitamura T, Tsukahara Y, Akahane S, Kitazawa M,et al. Suppression of laser-induced choroidal neovascularization by oraltranilast in the rat. Invest Ophthalmol Vis Sci 1999;40:459–66.

[36] Pae HO, Jeong SO, Koo BS, Ha HY, Lee KM, Chung HT. Tranilast, an orally activeanti-allergic drug, up-regulates the anti-inflammatory heme oxygenase-1expression but down-regulates the pro-inflammatory cyclooxygenase-2 andinducible nitric oxide synthase expression in RAW264.7 macrophages.Biochem Biophys Res Commun 2008;371:361–5.

[37] Suzawa H, Kikuchi S, Ichikawa K, Koda A. Inhibitory action of tranilast, an anti-allergic drug, on the release of cytokines and PGE2 from human monocytes-macrophages. Jpn J Pharmacol 1992;60:85–90.

[38] Rogosnitzky M, Danks R, Kardash R. Therapeutic potential of tranilast, an anti-allergy drug, in proliferative disorders. Anticancer Res 2012;32:2471–8.

[39] Wang M, Zhang J, Jackson T, Sun X, Wu W, Marshall J. Safety and efficacy ofintracapsular tranilast microspheres in experimental posterior capsuleopacification. J Cataract Refract Surg 2007;33:2122–8.

[40] Etsuo C, Jin D, Haruyuki O, Sachiko H. Effects of tranilast on filtering blebs: apilot study. J Glaucoma 2002;11:127–33.

[41] Tsuji A, Kawai K, Fan H, Nakagawa Y, Suzuki T. A case in which tranilast ophthalmicsolution was thought to be effective for the prevention of symblepharon andrecurrence after pterygium surgery. Tokai J Exp Clin Med 2011;36:120–3.