Immune consequences of intraocular administration of modified adenoviral vectors

To investigate the immune consequences of intraocular administration of modified adenoviral vectors, C57BL/6 normal and retinal degeneration C57BL/6 (rd/rd) mice were immunized with subcutaneous, subretinal, vitreal, or anterior chamber injections of replication-deficient adenovirus (AdV) containing the Escherichia coli beta-galactosidase gene (AdV-LacZ). Fourteen days after the initial inoculation, the animals were immune challenged with an injection of AdV-LacZ in the right ear pinna. Antigen-induced delayed type hypersensitivity (DTH) was measured by determining relative ear swelling. Normal C57BL/6 mice immunized with subretinal, vitreal, or anterior chamber injections did not demonstrate a DTH response. The rd/rd C57BL/6 mice injected in the anterior chamber with the viral construct also did not respond with DTH in a manner similar to normal mice responding to intraocular injection and subsequent challenge. However, the rd/rd C57BL/6 mice immunized by the subretinal or vitreal route did respond to immune challenge with a DTH response. Histologic examination of the eyes showed a lack of infiltration by inflammatory cells. Although these results suggest that the potential for immune consequences is reduced when modified adenoviral vectors are used in the normal ocular environment, these vectors used in the vitreal cavity of rd/rd animals may induce a systemic response to the vectors.

Cataract development in gamma-glutamyl transpeptidase-deficient mice

The present study was undertaken to analyse the relationship of lens glutathione (GSH) and light to cataract development in mice deficient in gamma-glutamyl transpeptidase (GGT). These mice have reduced levels of cysteine and GSH in the eye and develop cataracts. GGT-deficient mice raised under normal vivarium conditions, showed no cataractous changes at birth, but by 1 week they had developed nuclear opacities. By 3 weeks more severe cataracts develop, and lens GSH levels are approximately 6-7% of wild type levels. By 6-11 weeks cataracts show nuclear and cortical involvement, liquefaction and calcification. Single cell DNA electrophoresis (comet assay) demonstrated mild DNA damage in the lens epithelium. GGT-deficient mice raised in the dark beginning the day after conception all developed cataracts, but these were less severe than those in GGT-deficient mice raised with normal vivarium lighting. Administration of N -acetyl cysteine (NAC) raises lens GSH and almost completely prevents cataract development. Our data indicate that cataract development in GGT-deficient mice is multifactorial and results from exogenous damage (exposure to light), reduced lens GSH levels, and nutritional effects secondary to low cysteine levels.

Metastatic and nonmetastatic models of retinoblastoma

To generate animal models of retinoblastoma that closely resemble metastatic and nonmetastatic human disease for the purposes of examining tumor biology and developing alternate treatments, human retinoblastoma cell lines were injected into the vitreal cavities of immunodeficient mice. Two reproducible animal models with contrasting biological behaviors analogous to human retinoblastoma have been developed. The Y79 retinoblastoma model demonstrated specific tumor evolution similar to that seen in human invasive and metastatic disease. Y79 retinoblastoma cells formed intraocular tumors that were initially confined to the vitreal cavity. Tumors progressively invaded the retina, subretinal space, choroid, optic nerve head, and anterior chamber of the eye. Tumors progressed into the subarachnoid space and focally invaded the brain. Metastases were detected in the contralateral optic nerve. Large tumors developed extraocular extensions. The histology of the tumors showed a poorly differentiated pattern with high mitotic rate, foci of necrosis, and calcification. The WERI-Rb model more closely resembled nonmetastatic human retinoblastoma. WERI- Rb tumors were localized in the eye with only anterior choroidal invasion at late stages. To examine potential biological differences in vitro, the retinoblastoma cell lines were cocultured with adherent choroid cells or adherent glioma cells which represent the targets of invasive retinoblastoma in vivo. Consistent with the in vivo observations, Y79 cells but not WERI-Rb cells adhere specifically to both the choroidal and the glioma cell lines.

Suicide gene therapy for treatment of retinoblastoma in a murine model

Children presenting with large retinoblastomas are currently treated by enucleation. As most patients are young children, the long-term repercussions of such surgery are often devastating. Subsequent radiation or chemotherapy, although effective in managing residual tumor, greatly increase the probability of the development of second malignancies later in life. Smaller tumors can sometimes be managed with local cryo- or laser surgery, thus saving the eye. The hypothesis that gene therapy could be used to reduce the tumor size sufficiently to allow local control was tested using a murine model of retinoblastoma. Y79Rb human retinoblastoma cells can be killed in vitro when transduced with an adenoviral vector containing the herpes simplex thymidine kinase gene (AdV-TK) followed by treatment with the prodrug ganciclovir. Intravitreal injections of Y79Rb cells in immunodeficient mice produce an aggressive, metastatic murine model of retinoblastoma. When these murine retinoblastomas were transduced in vivo with AdV-TK and the animals treated with intraocular injections of ganciclovir, 70% showed a complete ablation of detectable tumor. Treated animals had a significant prolongation of progression-free survival as compared with untreated controls. Gene therapy effectively reduced the tumor burden in this murine model of retinoblastoma. Thus gene therapy, in conjunction with local surgical control, may provide an effective alternative to enucleation, systemic chemotherapy, or radiotherapy for treatment of large, nonmetastatic retinoblastomas in children.

Suramin inhibits wound healing following filtering procedures for glaucoma

BACKGROUND

Trabeculectomies are the most frequently performed procedures in surgically treating eyes with glaucoma. Failures are caused by fibrosis in the external ostium of the filtering procedure. In order to inhibit the fibrotic wound healing reaction, a new pharmacological approach using suramin, which inhibits a variety of important growth factors was used.

METHODS

Pigmented rabbits were used and filtering procedures performed. Suramin was applied with concentrations ranging from 10 mg/ml to 333 mg/ml once during surgery and four times following surgery. The success of the filtering procedure was assessed by intraocular pressure measurements. To evaluate possible intraocular toxic effects, treated eyes were histopathologically evaluated after 4 weeks, and the ciliary body adjacent to the site of application was examined using electron microscopy.

RESULTS

With concentrations of suramin of 200 mg/ml and 333 mg/ml, the trabeculectomies were patent longer than in the controls and in eyes operated with mitomycin C, which currently is the most frequently used antiproliferative drug to enhance the outcome of surgery in humans. No severe toxic effects to the ciliary epithelium were seen in suramin treated eyes.

CONCLUSIONS

This study demonstrates for the first time the efficiency of a substance that broadly inhibits the action of growth factors on target cells in the setting of ocular wound healing. In this in vivo model, suramin has been shown to be highly effective in preventing scarring and in having fewer toxic side effects than usually used antimetabolites. These results therefore may suggest a new approach to the surgical treatment of glaucoma.

A mouse model to study the wound healing response following filtration surgery

BACKGROUND

Failure of trabeculectomy is attributed to an exaggerated wound healing response at the episcleral level. We have developed a simple technique in mice that creates corneoscleral wounds and used it to study the role of growth factors in wound healing associated with loss of fistular patency. In addition, the effect of suramin on the wound healing response has been investigated.

MATERIALS AND METHODS

Using black C57B1/6 mice, we created a fistula from the subconjunctival space to the anterior chamber by external penetration with a 25-gauge needle through the bulbur conjunctiva. Eyes were examined by light microscopy at different times following surgery and evaluated for the presence of growth factors in the sclerosing wound by immunohistochemistry. In an additional group, suramin (1.0 mg/ml) was applied topically five times.

RESULTS

The limbal/scleral wounds closed rapidly. Granulation tissue consisting mostly of fibroblasts developed within the first 2 days, and the collagen component increased over time. By 4 weeks, the wound was completely healed. We found that within 1 day after surgery GF beta 2 reached high intensity. TGF beta 1 and PDGF A reached maximal intensity by day 2 and remained elevated for about a week, PDGF B was present at moderate intensity even before surgery. Myofibroblastic differentiation was observed from days 2 to 7. Suramin-treated wounds showed a decrease of cells and delay in fibroblast maturation. TGF beta 1 and TGF beta 2 levels persisted longer than in the controls, while PDGF A and PDGF B levels were lower than in the controls at all time points.

CONCLUSIONS

The mouse corneoscleral wound model that we have developed mimics the process of wound healing and fistulizing surgery that takes place in other animal models and in human eyes in which the outcome of the surgery is poor. Our analysis of the appearance of growth factors associated with wound healing demonstrates that PDGF A as well as TGF beta 1 and TGF beta 2 appear early in the process at high levels and are potential targets for interventive strategies to ensure channel patency. Suramin has a distinct effect on the wound healing process and expression of growth factors and may be a promising substance for clinical use.

Decorin and suramin inhibit ocular fibroblast collagen production

BACKGROUND

The process of ocular wound healing with respect to glaucomatous filtering procedures is of current interest. Delaying this response in patients could possibly lead to more favorable surgical results. So far, only highly toxic antimetabolites have come into frequent clinical use. The possible efficacy of other groups of substances such as growth factor inhibitors has not yet been examined in vitro.

METHODS

We exposed Tenon's capsule fibroblasts in tissue culture to various concentrations of decorin and suramin. The dose responses of type I and type III collagen to these inhibitors were measured using an ELISA-type dot blot assay. Total cellular protein production was assayed by measuring the incorporation of tritiated leucine.

RESULTS

At a concentration of 10 micrograms/ml, suramin reduced the collagen production by more than 80%. Decorin, at a concentration of 100 micrograms/ml, reduced type I collagen production by about 50% while type III collagen was reduced by 80%. At these concentrations, the total cellular protein production was not inhibited.

CONCLUSIONS

Both suramin and decorin, which specifically inhibit the action of growth factors on target cells, reduce the production of collagen synthesis by Tenon's capsule fibroblasts. This is a specific effect, because total protein production is not influenced. This sets these substances apart from antimetabolites. Decorin and suramin may have clinical relevance in that they appear to interfere with ocular wound healing more specifically than the substances so far frequently used.

Growth retardation and cysteine deficiency in gamma-glutamyl transpeptidase-deficient mice

gamma-Glutamyl transpeptidase (GGT) is an ectoenzyme that catalyzes the first step in the cleavage of glutathione (GSH) and plays an essential role in the metabolism of GSH and GSH conjugates of carcinogens, toxins, and eicosanoids. To learn more about the role of GGT in metabolism in vivo, we used embryonic stem cell technology to generate GGT-deficient (GGTm1/GGTm1) mice. GGT-deficient mice appear normal at birth but grow slowly and by 6 weeks are about half the weight of wild-type mice. They are sexually immature, develop cataracts, and have coats with a gray cast. Most die between 10 and 18 weeks. Plasma and urine GSH levels in the GGTm1/GGTm1 mice are elevated 6-fold and 2500-fold, respectively, compared with wild-type mice. Tissue GSH levels are markedly reduced in eye, liver, and pancreas. Plasma cyst(e)ine levels in GGTm1/GGTm1 mice are reduced to approximately 20% of wild-type mice. Oral administration of N-acetylcysteine to GGTm1/GGTm1 mice results in normal growth rates and partially restores the normal agouti coat color. These findings demonstrate the importance of GGT and the gamma-glutamyl cycle in cysteine and GSH homeostasis.

Retention of p53val135 wild-type function in transgenic mice

We targeted a mutant p53 gene (val135), previously shown to cause tumors in transgenic mice, to the kidney and eye using a gamma-glutamyltranspeptidase promoter. Although transgene RNA was expressed in both tissues, and mutant protein could be detected at high levels in the kidney and was appropriately localized to the nuclei of proximal tubules, no gross or microscopic lesions developed, even when mice were held as long as 75 weeks. When these mice were crossed with transgenic mice carrying HrasT24 (containing a codon 12 mutation) driven by the same promoter, the p53val135 transgene partially suppressed the mutant ras phenotype (proximal tubular hyperplasia and adenomas and carcinomas of the ciliary body and retinal pigment epithelium). The kidneys of double transgenic mice younger than 25 weeks showed less tubular hyperplasia and cystic change than littermates carrying gamma-glutamyltranspeptidase(I)rasT24 alone. By 33 weeks, there was no difference in the severity of the kidney lesions. The eye lesions were less aggressive, and no malignant lesions were identified. Our findings are consistent with the work of others, indicating that p53val135 is not tumorigenic under all conditions; in fact, in some circumstances, it retains some of the suppressing activity of wild-type p53.

Immunohistochemical comparison of transscleral continuous wave 1064-Nd:YAG laser retinopexy and cryoretinopexy

BACKGROUND

Transcleral retinopexy may be applied with either a cryoprobe or the newer contact laser delivery systems. Tissue responses to these modalities are studied.

METHODS

Transcleral 1064-nm continuous wave neodymium-ytrium-aluminum garnet (CW Nd:YAG) laser retinopexy lesions were compared with retinopexy lesions produced by a cryoprobe in a pigmented rabbit model. Equatorial transcleral CW Nd:YAG laser retinopexy or cryoretinopexy was applied. Rabbits were killed 1 day, 3 days, 1 week, or 1 month after treatment. Hematoxylin and eosin stains and immunohistochemical studies were conducted to determine the level of retinal damage and glial reaction. Antibodies against Müller cells (vimentin and glial fibrillary acidic protein), astrocytes (glial fibrillary acidic protein and S-100 protein), retinal pigment epithelial (RPE) cells (cytokeratin 8, 18, and 19 [5D3]), and macrophages (HAM 56) were used.

RESULTS

Lesions produced by cryotherapy showed significant overlying retinal destruction with intravitreal RPE cell (5D3 positive) migration. Lesions produced by transcleral CW Nd:YAG laser showed reaction primarily at the level of choroidal melanocytes and RPE. Marked expression of both glial fibrillary acidic protein and vimentin epitopes with a normal expression of S-100 was seen in the chronic lesion made with cryotherapy and with less intensity in lesions made with CW Nd:YAG laser.

CONCLUSION

Although less inner retinal destruction and no intravitreal RPE migration was observed in lesions formed by transcleral CW Nd:YAG laser, similar deep retinal Müller cell reaction occurred in lesions formed by both cryotherapy and laser as demonstrated by immunohistochemical studies.

Expression of the rasT24 oncogene in the ciliary body pigment epithelium and retinal pigment epithelium results in hyperplasia, adenoma, and adenocarcinoma

We examined eye lesions in five lines of transgenic mice carrying the human rasT24 oncogene driven by the type I gamma glutamyl transferase (gamma GT) promoter. In three lines, hyperplasia developed as early as 11.5 days postconception in the outer neuroectodermal layer, which gives rise to ciliary body and retinal pigment epithelium. At birth, the eyes from many animals contained adenomas, and by day 27, mice developed invasive adenocarcinomas originating in the region of the ciliary body. Microphthalmia, cataracts, and chronic nongranulomatous inflammation involving the anterior and/or posterior segments of the eye were also found. gamma GT is detectable histochemically as early as 11.5 gestational days in the outer neuroectodermal layer and after birth is more abundant in the ciliary body than in the retinal pigment epithelium. Using a reverse transcriptase-polymerase chain reaction, we found that type I (but not types II or III) gamma GT RNA is made by the mouse eye; the gamma GT(I)rasT24 transgene transcription product was detected in the eyes of all five transgenic lines. The sequential progression of hyperplasia to invasive neoplasms in the ciliary body in response to gamma GT(I)rasT24 expression differs from the process in the kidney of these animals in which tubular hyperplasia and microadenomas with little evidence of progression are the major lesions.