Inhibition by methylprednisolone acetate suggests an indirect mechanism for TGF-B induced angiogenesis

Mediators of neovascularization and the hypoxic cornea

The maintenance of corneal avascularity is essential to vision. The mechanisms by which the cornea becomes vascularized in response to inflammation or hypoxic stress are beginning to be elucidated. A detailed understanding of the molecular responses of the cornea to hypoxia is critical for prevention and development of novel treatments for neovascularization in a range of disease states. Here, we have examined the current literature on the major mediators of angiogenesis, which have previously been reported during hypoxia in the cornea in order to better understand the mechanisms by which corneal angiogenesis occurs in circumstances where the available oxygen is reduced. The normal cornea produces angiogenic factors that are regulated by the production of anti-angiogenic molecules. The various cell types of the cornea respond differentially to inflammatory and hypoxic stimuli. An understanding of the factors that may predispose patients to development of corneal blood vessels may provide an opportunity to develop novel prophylactic strategies. The difficulties with extrapolating data from other cell types and animal models to the cornea are also examined.

Spatial and Temporal Expression of Types I and II Receptors for Transforming Growth Factor beta in Normal Equine Skin and Dermal Wounds

OBJECTIVE

To describe immunolocalization of TGF-beta receptors (RI and RII) in normal equine skin and in thoracic or limb wounds, healing normally or with exuberant granulation tissue (EGT).

STUDY DESIGN

Group A: six wounds on one metacarpus and one midthoracic area. Group B: six wounds on both metacarpi, one of which was bandaged to stimulate EGT. Immunohistochemistry was used to detect RI and RII expression in wound margins.

ANIMALS

Eight horses, randomly assigned to one of two study groups.

METHODS

Neutralizing polyclonal anti-rabbit RI and RII antibodies were used to detect spatial expression of RI and RII in biopsies obtained before wounding, at 12 and 24 hours, and 5, 10 and 14 days after wounding.

RESULTS

RI and RII were co-localized in both unwounded and wounded skin. There were no differences in cell types staining positively between tissues obtained from the limb and the thorax, or from normally healing limb wounds and limb wounds with EGT, at any time. Because of increased cellularity within EGT, staining intensity of limb wounds with 'proud flesh' was greater than limb wounds healing normally, and thoracic wounds, during the proliferative phase of repair.

CONCLUSIONS

Strong expression of RI and RII, particularly in limb wounds with EGT, suggested that signalling for stimulation of matrix proteins is in place to contribute to scarring.

CLINICAL RELEVANCE

This information may help determine the appropriate time for using receptor antagonists to prevent scarring of limb wounds of horses.

Temporal localization of immunoreactive transforming growth factor beta1 in normal equine skin and in full-thickness dermal wounds

OBJECTIVE

To describe the localization of immunoreactive transforming growth factor (TGF)-beta1 in both normal skin and full-thickness dermal wounds of the limb and the thorax of the horse.

STUDY DESIGN

Six full-thickness excisional wounds were created on the lateral aspect of one metacarpal region and on the midthoracic area of each horse. Sequentially collected tissue specimens from wound margins were assessed for TGF-beta1 expression by immunohistochemistry.

ANIMALS

Four horses (2 to 4 years of age).

METHODS

A neutralizing monoclonal anti-human TGF-beta1 antibody was used to detect the spatial expression of TGF-beta1 protein by immunohistochemical localization in biopsies obtained before wounding and at 12 and 24 hours, and 5, 10, and 14 days.

RESULTS

No differences in localization of immunoreactive TGF-beta1 were detected between limb and thorax, for either intact skin or wounds. Unwounded epidermis stained moderately for TGF-beta1 protein throughout all layers, whereas the dermis was relatively devoid of immunoreactivity. During the acute stage of repair, migrating epithelium lost its stain, whereas cells of epidermal appendages remained strongly immunoreactive. The epithelium recovered its TGF-beta1 immunoreactivity during wound remodeling, although cells of the stratum corneum remained negative. Macrophages of the inflammatory exudate had positive cytoplasmic staining that diminished with time. Immunoreactivity of granulation tissue fibroblasts was evident early on and increased throughout the repair process.

CONCLUSIONS

TGF-beta1 is constitutively expressed in normal, unwounded equine epithelium. Its expression is upregulated within the skin on injury and is associated with the cells involved in wound repair.

CLINICAL RELEVANCE

A more precise understanding of the temporal and spatial expression of TGF-beta1 during wound repair in horses should provide the groundwork for possible future manipulations of both normal and aberrant tissue repair.

Mechanisms of normal and tumor-derived angiogenesis

Often those diseases most evasive to therapeutic intervention usurp the human body's own cellular machinery or deregulate normal physiological processes for propagation. Tumor-induced angiogenesis is a pathological condition that results from aberrant deployment of normal angiogenesis, an essential process in which the vascular tree is remodeled by the growth of new capillaries from preexisting vessels. Normal angiogenesis ensures that developing or healing tissues receive an adequate supply of nutrients. Within the confines of a tumor, the availability of nutrients is limited by competition among actively proliferating cells, and diffusion of metabolites is impeded by high interstitial pressure (Jain RK. Cancer Res 47: 3039-3051, 1987). As a result, tumor cells induce the formation of a new blood supply from the preexisting vasculature, and this affords tumor cells the ability to survive and propagate in a hostile environment. Because both normal and tumor-induced neovascularization fulfill the essential role of satisfying the metabolic demands of a tissue, the mechanisms by which cancer cells stimulate pathological neovascularization mimic those utilized by normal cells to foster physiological angiogenesis. This review investigates mechanisms of tumor-induced angiogenesis. The strategies used by cancer cells to develop their own blood supply are discussed in relation to those employed by normal cells during physiological angiogenesis. With an understanding of blood vessel growth in both normal and abnormal settings, we are better suited to design effective therapeutics for cancer.

Elevated TGFbeta signaling inhibits ocular vascular development

Alterations in the ocular vasculature are associated with retinal diseases such as retinopathy of prematurity and diabetic retinopathy. Vascular endothelial growth factor (VEGF) as a potent stimulator for normal and abnormal vascular growth has been extensively studied. However, little is known about secreted factors that negatively regulate vascular growth in ocular tissues. We now report that expression of a self-activating TGFbeta1 in the ocular lens of transgenic mice results in inhibition of retinal angiogenesis followed by retinal degeneration. Transgenic TGFbeta1 can rescue the hyperplasic hyaloid tissue and reverse the corneal deficiency in TGFbeta2-null embryos. These results demonstrate that TGFbeta signaling modulates development of ocular vasculature and cornea in a dosage-dependent manner and that TGFbeta1 can substitute for TGFbeta2 in ocular tissues.

Immunohistochemical localization of vascular endothelial growth factor, transforming growth factor alpha, and transforming growth factor beta1 in human corneas with neovascularization

PURPOSE

To analyze presence and distribution of vascular endothelial growth factor (VEGF), transforming growth factor (TGF)alpha, and TGFbeta1 in human corneas with neovascularization due to different corneal diseases.

METHODS

Indirect immunohistochemistry for VEGF, TGFalpha, and TGFbeta1, was performed on paraffin-embedded corneas obtained by keratoplasty. Corneas from each of the four main groups of histopathologic diagnoses associated with corneal neovascularization were analyzed (scarring after keratitis, graft rejection/insufficiency, acute necrotizing keratitis, scarring after mechanical/chemical injury). Subclassification of inflammatory infiltrates was done using immunohistochemistry for CD3 (T-lymphocytes) and CD68 (macrophages).

RESULTS

The analyzed angiogenic factors were detectable in corneas from all four histopathologic groups in a similar distribution; capillary endothelial cells, stromal and intravascular inflammatory cells (T-lymphocytes, macrophages), and basal corneal epithelial cells stained positive for the tested angiogenic factors.

CONCLUSION

The angiogenic factors VEGF, TGFalpha, and TGFbeta1 are detectable in human corneas with neovascularization. Their distribution is quite uniform in different corneal diseases, resulting in corneal angiogenesis. An antiangiogenic therapy inhibiting corneal neovascularization by antagonizing angiogenic factors would have to counteract several angiogenic factors.

Corneal haze among blue eyes and brown eyes after photorefractive keratectomy

BACKGROUND

To compare the incidence and severity of corneal haze after photorefractive keratectomy (PRK) among white patients with blue eyes and Saudi patients with brown eyes.

DESIGN

Retrospective, nonrandomized, comparative trial.

PARTICIPANTS

A total of 150 patients (71 females and 79 males) were included in this study. Two hundred sixty-six eyes of 150 patients were subjected to PRK. One hundred blue eyes of 50 white patients and 166 brown eyes of 100 Saudi patients were included in this study.

METHODS

Two hundred sixty-six eyes of 150 patients were subjected to PRK with the Chiron Technolas Keracor 117C for the correction of myopia and astigmatism.

MAIN OUTCOME MEASURES

All patients had complete ophthalmologic examinations, visual acuity testing, intraocular pressure, pachymetry, corneal haze assessment (0-4+), and computerized corneal topography.

RESULTS

There were 266 eyes of 150 patients with 100 blue irides and 166 brown irides. The spherical equivalent was -0.50 diopter (D) to -8.75 D. The mean postoperative spherical equivalent at 6 months was -0.063 D (standard deviation [SD], +/-0.595) in blue eyes compared to -0.28 D (SD, +/-0.683) in brown eyes (P = 0.006). Ninety-five (95%) of 100 of the blue eyes achieved +/- 1 D of attempted correction compared to 148 (89.2%) of the 166 brown eyes. All patients with blue eyes had a visual acuity of 20/30 or better compared to 153 (92.2%) of the 166 brown eyes (P = 0.009). Forty-eight (18.04%) eyes had minimal to mild haze, 3 (1.12%) eyes had moderate haze, and 2 (0.75%) eyes had severe haze. The incidence of corneal haze among brown eyes was 48 (28.9%) of 166 eyes compared to 5 (5%) of 100 in blue eyes (P < 0.001). The difference remained significant after adjustment for age and gender with a P value of 0.0283. The relative risk for developing haze in brown eyes was found to be 7.72.

CONCLUSION

The incidence of corneal haze after PRK was significantly higher among Saudi patients with brown irides than among white patients with blue irides. This suggests that racial factors may play a role in the development of corneal haze.

Mast cells and their mediators in cutaneous wound healing--active participants or innocent bystanders?

Mast cells are traditionally viewed as effector cells of immediate type hypersensitivity reactions. There is, however, a growing body of evidence that the cells might play an important role in the maintenance of tissue homeostasis and repair. We here present our own data and those from the literature elucidating the possible role of mast cells during wound healing. Studies on the fate of mast cells in scars of varying ages suggest that these cells degranulate during wounding, with a marked decrease of chymase-positive cells, although the total number of cells does not decrease, based on SCF-receptor staining. Mast cells contain a plethora of preformed mediators like heparin, histamine, tryptase, chymase, VEGF and TNF-alpha which, on release during the initial stages of wound healing, affect bleeding and subsequent coagulation and acute inflammation. Various additional vasoactive and chemotactic, rapidly generated mediators (C3a, C5a, LTB4, LTC4, PAF) will contribute to these processes, whereas mast cell-derived proinflammatory and growth promoting peptide mediators (VEGF, FGF-2, PDGF, TGF-beta, NGF, IL-4, IL-8) contribute to neoangiogenesis, fibrinogenesis or re-epithelization during the repair process. The increasing number of tryptase-positive mast cells in older scars suggest that these cells continue to be exposed to specific chemotactic, growth- and differentiation-promoting factors throughout the process of tissue remodelling. All these data indicate that mast cells contribute in a major way to wound healing. their role as potential initiators of or as contributors to this process, compared to other cell types, will however have to be further elucidated.

Transforming growth factor-beta1 fails to stimulate wound healing and impairs its signal transduction in an aged ischemic ulcer model: importance of oxygen and age

Clinical trials of exogenous growth factors in treating chronic wounds have been less successful than expected. One possible explanation is that most studies used animal models of acute wounds in young animals, whereas most chronic wounds occur in elderly patients with tissue ischemia. We described an animal model of age- and ischemia-impaired wound healing and analyzed the wound-healing response as well as the transforming growth factor (TGF)-beta1 effect in this model. Rabbits of increasing ages were made ischemic in the ear where dermal ulcers were created. Histological analysis showed that epithelium ingrowth and granulation tissue deposition were significantly impaired with increased age under ischemia. TGF-beta1 stimulated wound repair under both ischemic and non-ischemic conditions in young animals, although it showed no statistical difference in aged animals. Procollagen mRNA expression decreased under ischemic conditions and with aging. Neither TGF-beta1 nor procollagen alpha1(I) mRNA expression increased in response to TGF-beta1 treatment under ischemia in aged animals. Therefore, the wound-healing process is impaired additively by aging and ischemia. The lack of a wound-healing response to TGF-beta1 in aged ischemic wounds may play a role in the chronic wounds.

Effect of Transforming Growth Factor β1 on Stromal Haze following Excimer Laser Photorefractive Keratectomy in Rabbits

BACKGROUND

Transforming growth factor beta (TGF-beta) has been shown to affect wound repair. Anti-transforming growth factor beta 1 antibodies have been shown to neutralize its activity.

METHODS

Seventeen New Zealand White rabbits underwent unilateral photorefractive keratectomy followed by corneal staining with dichlorotriazinyl fluorescein. Three groups received topical transforming growth factor beta 1: 1 microgram/ml, 10 micrograms/ml, and 100 micrograms/ml; one group topical anti-transforming growth factor beta antibody (200 micrograms/ml); and a control group vehicle only. Corneal haze was graded from 0 to 4, weekly. Rabbits were sacrificed at 5 weeks and histopathological analysis and fluorescence microscopy performed.

RESULTS

All treated eyes developed haze and had epithelial erosions. No statistically significant differences in haze score were seen among individual treatment groups (Kruskal Wallis p > 0.05). The anti-transforming growth factor beta antibody group had less haze than all other groups at every week after the first. Comparing all transforming growth factor beta 1 treated eyes as one group to the antibody group, significantly less haze was seen at weeks 3 and 4 in the antibody treated group (p = 0.028 and 0.013, respectively). This study is limited by small group size and further studies are needed to confirm these results.

CONCLUSION

TGF-beta may be involved in stromal haze formation, and topical anti-TGF-beta 1 antibody may help reduce the development of stromal haze.

Transforming growth factor-beta: vasculogenesis, angiogenesis, and vessel wall integrity

Genetic studies have recently revealed a role for transforming growth factor-beta-1 (TGF-beta 1) and its receptors (TGF-beta Rs I and II as well as endoglin) in embryonic vascular assembly and in the establishment and maintenance of vessel wall integrity. The purpose of this review is threefold: first, to reassess previous studies on TGF-beta and endothelium in the light of these recent findings; second, to describe some of the well-established as well as controversial issues concerning TGF-beta and its regulatory role in angiogenesis; and third, to explore the notion of "context' with respect to TGF-beta and endothelial cell function. Although the focus of this review will be on the endothelium, other vascular wall cells are also likely to be important in the pathogenesis of the vascular lesions revealed by genetic studies.

Differential effects of transforming growth factor-beta 1 on interleukin-1-induced cellular inflammation and vascular permeability in the rabbit retina

Intra-vitreal injection of 300 U of interleukin (IL)-1 beta into the rabbit eye induces an inflammation of the retina characterized by hemorrhage, monocyte and neutrophil infiltration, and an increase in vascular permeability that peaks 24 h post-injection. Since the epiretinal vessels involved in this inflammation form part of the blood-retina barrier, we used this model to investigate the effects of the immunosuppressive cytokine TGF beta 1 on inflammation within the context of the central nervous system. We found that intra-vitreal injection of 1 microgram rh TGF beta administered concomitantly with rh IL-1 beta significantly reduced IL-1 beta-induced hemorrhage by 78%, and monocyte and neutrophil infiltration by 53% and 62%, respectively. In contrast, TGF beta did not reduce the IL-1 beta-induced increase in vascular permeability. However, TGF beta by itself caused a statistically significant increase in serum proteins in perfused tissues of the eye, to give a 3.1 +/- 0.4 fold increase in protein content over control values. No cellular inflammation accompanied this alteration in vascular permeability. These data indicate that whereas the local administration of TGF beta may be an effective inhibitor of cellular inflammation in the CNS, the effects on alterations in vascular permeability and accumulation of serum proteins may be more complex.

Tumor necrosis factor alpha (rhTNF) fails to stimulate angiogenesis in the rabbit cornea

BACKGROUND

The objective of this study was to thoroughly examine the in vivo angiogenesis activity of human recombinant tumor necrosis factor alpha (rhTNF).

METHODS

rhTNF (0.5 ng to 1.0 microgram) was incorporated into the slow release polymers Hydron or HYPAN and implanted into the rabbit cornea. Release of biologically active rhTNF from the polymers was determined with the L929 cytotoxicity assay.

RESULTS

All concentrations tested failed to elicit capillary formation beyond that observed for controls. Less than 2% of the rhTNF was released from the Hydron over 7 days. HYPAN released five times the amount of rhTNF in vitro, but even at doses of 500 ng (104.3 ng suggested release) no angiogenesis was stimulated.

CONCLUSIONS

Under the circumstances tested, rhTNF is not angiogenic in vivo.

Enhancement of neovascularization in regenerating skeletal muscle by the sustained release of erucamide from a polymer matrix

The angiogenic agent erucamide (cis-13-docosenamide), incorporated into a polymeric biomaterial (Elvax 40P, a copolymer of ethylene and vinyl acetate), was used to determine whether angiogenesis can be increased in the regenerating skeletal muscle, and whether the enhanced revascularization improves the new muscle formation. The angiogenic nature of this lipid was confirmed in a rat cornea-micropocket assay, prior to insertion of small strips of the polymer containing either 3 micrograms, 300 micrograms erucamide or only polymer as a control into the mid-region of crush-injured tibialis anterior (TA) muscles of forty-five adult male BALB/c mice. All TA muscles were sampled ten days after injury and analyzed morphometrically. Statistical analyses of the mean blood vessel area density in lesions from twelve perfused TA muscles (three from each of the erucamide-treated or control group), revealed a dose-dependent angiogenic effect of erucamide: a dosage of 3 micrograms increased mean blood vessel area density to 5.1% compared to 2.0% in controls, due to numerous large caliber, thin-walled vessels, whereas the mean vessel area density in both the 30-micrograms (3.5%) and 300-micrograms (1.5%) doses were similar to controls. However, at all three doses tested, erucamide did not significantly alter the degree of new muscle formation, connective tissue deposition, or removal of necrotic debris.

Age-related alterations in the morphology of femoral artery vasa vasorum in the rat

The objective of this study was to explore any age-related morphological changes in the vasa vasorum of the rat femoral artery. Vascular corrosion casts were prepared from 2, 12 and 24-month-old rats. Examination of the casts with the scanning electron microscope revealed dramatic differences in the appearance of the vessels of young and aged rats. The vasa vasorum of 2-month-old rats consisted of a dense network of capillaries. These vessels were dramatically reduced in number by 12 months, and even fewer capillaries were present at 24 months. This reduction in capillary density is consistent with the observed age-related decreases in oxygen tension and may explain why the aged are more prone to atherosclerosis.

Oxygen modulates production of bFGF and TGF-beta by retinal cells in vitro

Vasoproliferative retinopathies result from retinal capillary non-perfusion and consequent inner retinal hypoxia. However, it is not known whether oxygen mediates vasoproliferation directly (at the nuclear level) or indirectly by regulating the production of growth factors. We have investigated the effect of oxygen on the production of basic fibroblast growth factor and transforming-growth-factor-beta by a variety of retinal cell types in culture. Confluent cultures were maintained for 48 hr under varying oxygen tensions ranging from 135 to 18 mmHg. A reduction in basic fibroblast growth factor levels was observed in the cell lysates and extracellular matrix from retinal microvascular endothelial cell, retinal microvascular pericyte and retinal pigment epithelial cell cultures when the oxygen tension of the medium was reduced from 135 to 18 mmHg. Levels of basic fibroblast growth factor in conditioned media from microvascular endothelial and retinal pigment epithelial cell cultures also decreased when the oxygen tension of the medium was reduced from 135 to 18 mmHg. Total transforming-growth-factor-beta (and specifically isoforms 1 and 2) in the conditioned media from all three cell types was similarly modulated by oxygen i.e. it decreased as the oxygen tension of the medium was reduced from 135 to 18 mmHg. In contrast, the steady state messenger RNA levels for both basic fibroblast growth factor and transforming-growth-factor-beta 1 genes in RPE cells increased significantly when the oxygen tension of the medium was reduced from 135 to 18 mmHg. These results support the putative role of oxygen in influencing the balance of growth factors during the development of preretinal new vessels.

Transforming growth factor-beta 1 stimulates macrophage urokinase expression and release of matrix-bound basic fibroblast growth factor

Macrophage expression of urokinase-type plasminogen activator (uPA) appears to play a role in their release of matrix-bound basic fibroblast growth factor (bFGF) and transforming growth factor-beta (TGF-beta). In experiments reported here, we have examined the potential regulatory effects of bFGF and TGF-beta 1 on macrophage uPA expression. TGF-beta 1 stimulated in a dose- and time-dependent manner the expression of secreted membrane and intracellular uPA activities by a macrophage cell line (RAW264.7). When examined at similar concentrations, bFGF had little effect, and interleukin-1 alpha, tumor necrosis factor-alpha, and monocyte colony stimulating factor had no effect on macrophage uPA expression. Exposure of macrophages to TGF-beta 1 led to a rapid and sustained increase in the steady-state levels of uPA mRNA that was independent of de novo protein synthesis and was completely inhibited by actinomycin D. However, the TGF-beta 1-induced increase in uPA mRNA was largely unaffected by subsequent incubation of cells with actinomycin D. The protein kinase C inhibitor H7 markedly reduced the ability of TGF-beta 1 to stimulate expression of uPA activity. Likewise, okadaic acid and microcystin, inhibitors of serine/threonine phosphatases, potentiated the ability of TGF-beta 1 to upregulate macrophage uPA expression. TGF-beta 1 primed cells converted nearly all added plasminogen to plasmin and expressed sixfold more membrane-bound plasmin than control cells. Preincubation of TGF-beta 1 with either serum or methylamine-modified alpha 2-macroglobulin did not affect its ability to induce macrophage uPA expression. When control and TGF-beta 1-primed macrophages were cultured on matrices containing bound 125I-bFGF, their release of 125I-bFGF was increased five and tenfold, respectively, in the presence of plasminogen. The ability of TGF-beta to induce macrophage uPA expression and the plasmin-dependent release of matrix-bound bFGF may provide an indirect mechanism by which TGF-beta stimulates angiogenesis.