Adenovirus-mediated expression of ciliary neurotrophic factor (CNTF) rescues axotomized rat retinal ganglion cells but does not support axonal regeneration in vivo

Rat optic nerve (ON) transection leads to mainly apoptotic cell death of about 85% of the retinal ganglion cell (RGC) population within 14 days after lesion. In the present study, we tested the effect of adenovirally delivered CNTF (Ad-CNTF) on survival and regeneration of axotomized adult RGCs in vivo. Single intravitreal Ad-CNTF injection led to stable CNTF mRNA and protein expression for at least 18 days and significantly enhanced RGC survival by 155% when compared to control animals 14 days after ON transection. ON stump application of Ad-CNTF also resulted in an increased number of surviving RGCs. Ad-CNTF injection led to better preservation of intraretinal RGC axons but did not support regeneration of axotomized RGCs into a peripheral nerve graft. Thus, adenovirus-mediated neurotrophic factor supply is a suitable approach for reducing axotomy-induced RGC death in vivo and may constitute a relevant strategy for clinical treatment of traumatic brain injury.

Visual pigments, oil droplets, ocular media and cone photoreceptor distribution in two species of passerine bird: the blue tit (Parus caeruleus L.) and the blackbird (Turdus merula L.)

The spectral absorption characteristics of the retinal photoreceptors of the blue tit (Parus caeruleus) and blackbird (Turdus merula) were investigated using microspectrophotometry. The retinae of both species contained rods, double cones and four spectrally distinct types of single cone. Whilst the visual pigments and cone oil droplets in the other receptor types are very similar in both species, the wavelength of maximum sensitivity (lambda(max)) of long-wavelength-sensitive single and double cone visual pigment occurs at a shorter wavelength (557 nm) in the blackbird than in the blue tit (563 nm). Oil droplets located in the long-wavelength-sensitive-single cones of both species cut off wavelengths below 570-573 nm, theoretically shifting cone peak spectral sensitivity some 40 nm towards the long-wavelength end of the spectrum. This raises the possibility that the precise lambda(max) of the long-wavelength-sensitive visual pigment is optimised for the visual function of the double cones. The distribution of cone photoreceptors across the retina, determined using conventional light and fluorescence microscopy, also varies between the two species and may reflect differences in their visual ecology.

Thrombospondin-1, a natural inhibitor of angiogenesis, is present in vitreous and aqueous humor and is modulated by hyperglycemia

Negative regulators of angiogenesis play a major role in maintaining vascular homeostasis. Thrombospondin-1 (TSP1) is a natural inhibitor of angiogenesis. This report examines the presence of TSP1 in ocular samples and determines whether its production is altered in diabetes. Western blot analysis detected a 140 kDa antiangiogenic fragment of TSP1(gp140) in vitreous samples prepared from normal human and rat eyes. Intact TSP1 was detected in aqueous humor samples prepared from normal rat and bovine eyes. In contrast, TSP1 was virtually absent in vitreous and aqueous humor samples prepared from diabetic rat eyes. Furthermore, production of TSP1 by microvascular endothelial cells in culture was sensitive to high concentrations of glucose. Retinal blood vessels appeared nonuniform and dilated in diabetic animals when compared to control animals. These results demonstrate that TSP1 and its antiangiogenic fragment are present in aqueous humor and vitreous of normal rat eyes and are dramatically reduced in diabetes. Thus, TSP1 may play a role in ocular vascular homeostasis and its absence may contribute to vascular dysfunctions associated with diabetes.

Interfaces

There are important similarities in molecular composition and structural organization of the interface between the vitreous and retina and that between the retina and retinal pigment epithelium. It is striking that the two most common causes of severe vision loss in the western world involve neovascularization at these interfaces; i.e., proliferative diabetic vitreo-retinopathy at the vitreo-retinal interface and exudative age-related macular degeneration at the retina-retinal pigment epithelium interface. Improved knowledge of the physiology of these interfaces will lead to a better understanding of the effects of aging and diseases, especially those that involve neovascularization. Such advances will no doubt result in new treatment strategies offering more effective therapy, and, even more importantly, perhaps providing prevention from these devastating causes of blindness.

Visual pigments, cone oil droplets, ocular media and predicted spectral sensitivity in the domestic turkey (Meleagris gallopavo)

A microspectrophotometric survey conducted on the retinal photoreceptors of the domestic turkey (Meleagris gallopavo) revealed the presence of five different types of vitamin A1-based visual pigment (rhodopsin) in seven different types of photoreceptor. A single class of rod contained a medium wavelength-sensitive visual pigment (wavelength of maximum absorbance, lambda max, 504 nm). Four different types of single cone contained visual pigment maximally sensitive to wavelengths in either the long (LWS, lambda max 564 nm), medium (MWS, lambda max 505 nm), short (SWS, lambda max 460 nm) or violet (VS, lambda max 420 nm) spectral ranges. The LWS, MWS and SWS single cones contained pigmented oil droplets with cut-off wavelengths (lambda cut) at 514, 490 and 437 nm, respectively. The VS single cone contained a transparent oil droplet which displayed no significant absorbance above 330 nm. A single class of double cone was also identified, both the principal and accessory members of which contained the LWS cone visual pigment. The principal member contained an oil droplet with a lambda cut at 436 nm. No oil droplet was observed in the accessory member. The use of a glycerol-based cell mountant, which reduced wavelength dependent measurement artefacts in the microspectrophotometric measurements, is described. Predictions of cone effective spectral sensitivity, incorporating measurements of the spectral transmission of the ocular media, suggest that turkeys have considerable sensitivity to wavelengths in the ultraviolet-A (UV-A, 315-400 nm) spectral range. This has implications for both the visual ecology of wild birds and the welfare of intensively farmed individuals.

Intravitreally injected platelet activating factor induces retinitis in experimental animals

PURPOSE

Platelet activating factor is a lipid which has been strongly implicated in anterior uveitis. In order to investigate further the role of platelet activating factor in intraocular inflammation, we have characterized the histological changes associated with the intravitreal injection of platelet activating factor, PAF analogs, or lyso-PAF in laboratory rabbits and rats.

METHODS

Initial studies utilized a PAF analog (rac 1-0-octadecyl 2-0-ethyl glycero phosphoryl choline or ethoxy PAF), because this compound is relatively resistant to degradation by hydrolase, the major degradative enzyme for PAF. Doses ranging from 1 ug to 5 mg and time points from 6 hours to 7 days after injection were studied.

RESULTS

In either rats or rabbits, 100 ug of ethoxy PAF consistently induced a marked uveitis with the predominance of inflammation focused in the retina and choroid. Retinitis was also induced in rabbits by either 1 mg PAF injected intravitreally or a similar dose of the PAF precursor/metabolite, lyso PAF. Retinal inflammation was not induced by an inactive lipid, 1,1-0,0-dihexadecyl-rac-glycero-3-phosphocholine, although this compound resulted in mild vitreous inflammation. The histological changes induced by PAF could be readily distinguished from the predominantly anterior inflammation induced by intravitreal injections of substances such an interleukin-1 or endotoxin.

CONCLUSIONS

Recent studies indicating that PAF antagonists inhibit a variety of retinal toxicities and our own observations suggest that PAF could be a major mediator of retinal inflammation.

Contribution of rod, on-bipolar, and horizontal cell light responses to the ERG of dogfish retina

Simultaneous extracellular ERG and intracellular recordings from horizontal and ON-bipolar cells were obtained from the dark-adapted retina of the dogfish. The light intensity-peak response relation (IR) and time course of on-bipolar cell responses closely resembled that of the ERG b-wave, but only at low light intensities [<10 rhodopsin molecules bleached per rod (Rh*)]. Block of on-bipolar cell responses with 50 microM 2-amino-4-phosphonobutyrate (APB) abolished the b-wave and unmasked a vitreal-negative wave. Subtraction from the control ERG resulted in the isolation of a vitreal-positive ERG with an IR which matched that of on-bipolar cells over the full range of light intensities. The D.C. component of the ERG arises as a result of sustained depolarization of on-bipolar cells in response to long (>0.5 s) dim light stimuli, or following bright light flashes. The IR of horizontal cells and the vitreal-negative wave unmasked by APB could be matched by scaling at low light intensities (<5 Rh*). However, horizontal cell responses saturated at about 30 Rh*, while the vitreal-negative wave continued to increase in amplitude. The time course of horizontal cell membrane current with dim flashes could be matched to the rising phase of the vitreal-negative wave, assuming that the delay in generating the voltage response in horizontal cells is due to their long (100 ms) membrane time constant. Blocking post-photoreceptor activity resulted in a much smaller vitreal-negative wave than that unmasked by APB alone. We conclude that the b-wave arises from on-bipolar cell depolarization, while the leading edge of the a-wave is a composite of the change in extracellular voltage drop across the rod layer and a component (proximal PIII) reflecting a decrease in extracellular K+ as horizontal cell synaptic channels close with light.

[Expression of brain-derived neurotrophic factor gene in retina following vitreous tap]

PURPOSE

Mechanical injuries to the retina following vitreous tap are reported to protect photoreceptor cells in a rat model of the retinal degeneration and enhance the survival rate of retinal ganglion cells in the optic nerve transection. Neurotrophic factors are presumably involved in the protective mechanisms. In order to see whether neurotrophic factors are synthesized in the retina, we studied the expression of neurotrophic factors in the retina following vitreous tap in rats.

MATERIALS AND METHODS

One eye each of 20 mature rats received transscleral vitreous taps at three points of entry and retinal injury. The retinas were removed and examined at day 0 to 14 of treatment.

RESULTS

Following injury, the retina showed increased expression of glial fibrillary acidic protein (GFAP) mRNA and brain-derived neurotrophic factor (BDNF) mRNA. There was no enhancement of neurotrophin-3 (NT-3) mRNA when examined by reverse transcription-polymerase chain reaction (RT-PCR).

CONCLUSIONS

Activated retinal glial cells may produce BDNF which prevents retinal neuronal cell damage following injury.

Regenerative sprouting of retinal ganglion cells of adult hamsters induced by the epineurium of a peripheral nerve

Although it is known that transplantation of a peripheral nerve (PN) to the damaged central nervous system (CNS) promotes axonal regeneration, the interactions of cellular components of the PN with CNS neurons are still not well defined. Schwann cells in the PN are thought to be the major element involved in supporting CNS regeneration, but very little information exists with regard to whether other PN components also play an active role. Using our previously established model of transplanting a PN segment into the vitreous to stimulate regenerative sprouting of retinal ganglion cells (RGCs), we found that the epineurium isolated from a PN which had been pre-injured by transection was able to induce RGC sprouting when implanted intravitreally. Since the epineurium is composed mainly of connective tissue components and is devoid of Schwann cells, our results suggest that other cellular elements of the PN besides Schwann cells may have the potential to support CNS regeneration.

Immunogold evidence suggests that coupling of K+ siphoning and water transport in rat retinal Müller cells is mediated by a coenrichment of Kir4.1 and AQP4 in specific membrane domains

Postembedding immunogold labeling was used to examine the subcellular distribution of the inwardly rectifying K+ channel Kir4.1 in rat retinal Müller cells and to compare this with the distribution of the water channel aquaporin-4 (AQP4). The quantitative analysis suggested that both molecules are enriched in those plasma membrane domains that face the vitreous body and blood vessels. In addition, Kir4. 1, but not AQP4, was concentrated in the basal approximately 300-400 nm of the Müller cell microvilli. These data indicate that AQP4 may mediate the water flux known to be associated with K+ siphoning in the retina. By its highly differentiated distribution of AQP4, the Müller cell may be able to direct the water flux to select extracellular compartments while protecting others (the subretinal space) from inappropriate volume changes. The identification of specialized membrane domains with high Kir4.1 expression provides a morphological correlate for the heterogeneous K+ conductance along the Müller cell surface.

Effects of bFGF and TGFbeta on the expression of amyloid precursor and B-cell lymphoma protooncogene proteins in the rat retina

The pattern of immunoreactivity for amyloid precursor (APP) and B-cell lymphoma protooncogene (Bcl-2) proteins in the rat retina was studied after intravitreal injection of basic fibroblast growth factor (bFGF) or transforming growth factor-beta (TGFbeta). In normal control retinas, intense immunostaining of APP and Bcl-2 was observed primarily in the endfeet and proximal part of radial processes of Müller glial cells. A dose-dependent reduction in immunostaining of APP and Bcl-2 in Müller cells was observed after injection of bFGF and TGFbeta. These results provide the first evidence that APP and Bcl-2 can be down-regulated by cytokines in vivo.

Glial cell line-derived neurotrophic factor (GDNF) promotes the survival of axotomized retinal ganglion cells in adult rats: comparison to and combination with brain-derived neurotrophic factor (BDNF)

Adult rat retinal ganglion cells (RGC) undergo degeneration after optic nerve transection. Studies have shown that exogenously applied neurotrophic factors such as brain-derived neurotrophic factor (BDNF) can attenuate axotomy-induced as well as developmental RGC death. Here, we examined whether glial cell line-derived neurotrophic factor (GDNF), a known neurotrophic factor for dopaminergic neurons and motor neurons, could provide neurotrophic support to RGC in adult rats. We determined whether RGC could retrogradely transport GDNF from their target tissue. After injection into the superior colliculus of adult rats, 125I-GDNF was retrogradely transported to contralateral eyes but not to ipsilateral eyes. The transport of 125I-GDNF could be blocked by coinjection of excess unlabeled GDNF, indicating that it was receptor mediated. We tested whether intravitreally applied GDNF could prevent axotomy-induced RGC degeneration. The RGC were prelabeled with Fluorogold (FG) and axotomized by intraorbital optic nerve transection. GDNF, BDNF (positive control), cytochrome c (negative control), or a GDNF/BDNF combination was injected intravitreally on days 0 and 7. On day 14, FG-labeled RGC were counted from whole-mount retinas. We found that, similar to BDNF, GDNF could significantly attenuate the degeneration of RGC in a dose-dependent fashion. Furthermore, the combination treatment of GDNF and BDNF showed better protection than either factor used individually. Our data indicate that GDNF is a neurotrophic factor for the adult rat RGC. GDNF, like BDNF, may be useful for the treatment of human RGC degenerative diseases.

The relationship between ocular melatonin and dopamine rhythms in the pigeon: effects of melatonin inhibition on dopamine release

Our previous study has shown that the phases of circadian rhythms of ocular melatonin and dopamine are always opposite and intraocular melatonin injection suppresses dopamine release. Therefore, it is possible that dopamine rhythms result from inhibitory action of melatonin. We have examined this possibility in the following experiments. In the first experiment effects of continuous light on melatonin and dopamine release were examined. The data indicated that continuous light exposure resulted in loss of circadian rhythmicity of melatonin and dopamine by suppressing melatonin and enhancing dopamine levels throughout the day. To further examine the effects of light in the second experiment, 2 h light pulse was applied during the night, then temporal changes of melatonin and dopamine release were studied. The light pulse rapidly suppressed melatonin release, whereas it rapidly increased dopamine release. These changes occurred within 30 min in both melatonin and dopamine. However, the recovery after the cessation of the light stimulus was slower in melatonin than dopamine. In the third experiment it was tested if dopamine release was increased by lowering melatonin release with an intraocular injection of the D2 agonist, quinpirol. Although quinpirol strongly inhibited melatonin release independently of the time of injection, dopamine did not always increase by the inhibition of melatonin. These results indicate that ocular dopamine rhythms are not simply produced by melatonin inhibitory action.

Vitreous treatment of retinal pigment epithelial cells results in decreased expression of FGF-2

PURPOSE

Changes in gene expression were investigated after treatment of cultured human retinal pigment epithelial (RPE) cells with vitreous. This may have implications for proliferative diseases such as proliferative vitreoretinopathy.

METHODS

Cells were cultured in the presence or absence of human vitreous, and gene expression was examined using the differential display polymerase chain reaction technique. Differentially expressed RNAs were cloned, screened for differential expression, and sequenced. The expression of one of these RNAs (that for fibroblast growth factor [FGF]-2/basic FGF) was examined by in situ hybridization and ribonuclease protection assays. The level of FGF-2 protein was examined by immunoblot analysis. The effects of adding FGF-2 to cells cultured in the presence of vitreous were examined.

RESULTS

Treatment of low passage human RPE cells with 25% vitreous resulted in the epithelial-to-fibroblast-like morphologic changes reported by others and in the decreased expression of FGF-2 mRNA and FGF-2 protein. Addition of FGF-2 to cultures at the same time as addition of vitreous prevented some of the effects of vitreous on these cells.

CONCLUSIONS

Vitreous treatment of RPE cells in culture results in decreased expression of FGF-2 mRNA and protein. Because supplementation of FGF-2 prevents some of the vitreous-mediated effects, this may indicate that modulation of FGF-2 levels by the vitreous may play an important role in the phenotypic changes seen in RPE cells exposed to vitreous.

Involvement of calcium in retinal pigment epithelial cell proliferation and pigmentation

PURPOSE

The aim of this study is to explore the role of intracellular calcium in the mechanism of co-regulation of retinal pigment epithelial cells (RPE) by vitreous fluid and platelet mitogens, in order to evaluate the use of calcium modulating drugs in preventing RPE cell proliferation and contraction of fibrocellular membranes.

METHODS

Monolayers of human RPE cells were loaded with Fura-2-AM and examined in a fluorimeter for changes in intracellular free calcium in response to platelet mitogens (PDGFAB or TGFbeta1) and vitreous fluid (containing vitreous substrate proteins), both alone or in combination. The effect of the calcium antagonists TMB8 and verapamil and the calmodulin antagonists J8 and tamoxifen were then examined on RPE cell proliferation and pigmentation, both in the presence and absence of vitreous substrate and platelet mitogens.

RESULTS

We report that co-exposure of RPE cells to platelet mitogens and vitreous fluid produces an increase in intracellular free calcium of greater duration than that with either PDG-FAB, TGFbeta1 or vitreous fluid alone. Calcium and calmodulin antagonists significantly reduce RPE cell proliferation in both the presence and absence of vitreous substrate and platelet mitogens. Calcium antagonists also stimulate the accumulation of autofluorescent granules within RPE cells.

CONCLUSIONS

Calcium signalling plays a role in the co-regulation of RPE cells by vitreous substrate and platelet mitogens. Drugs that lower intracellular calcium or inhibit calmodulin may offer an additional approach to preventing the hyperproliferation of RPE cells in PVR.

A model for the fluid motion of vitreous humour of the human eye during saccadic movement

During saccadic motion the eyewall moves in a manner similar to a sinusoid or at least can be represented by a sine Fourier series. Motion of the vitreous is induced by the saccade and the vitreo-retinal interface is subjected to a time-dependent shear. This force may be a significant factor for retinal tearing in the neighbourhood of small retinal holes or tears. An analytical viscoelastic model and a numerical, Newtonian model of the motion of the vitreous are presented and compared. Under sinusoidal boundary motion the analytical model shows that a viscous wave propagates inward toward the axis of rotation and the characteristic length of this wave is a function of the Womersley number. The numerical solution indicates that the vitreous moves similarly to the analytical result with small secondary motion; however, this motion allows complete recirculation of the vitreous over large timescales. Excellent agreement is found between the analytical and numerical models. The time-dependent fluid shear is evaluated and from the analytical solution the maximum value of this is found to be proportional to R0 square root of v(omega)3, where R0 is the eye radius, v the modified complex viscosity and omega the sinusoidal frequency. This indicates that myopes have a larger shear force exerted on them by virtue of the larger eye size. Further work is directed toward a model which links the stress found in the sclera to that exerted on the vitreo-retinal interface by the vitreous fluid motion.

Tachykinins as enhancers of prostaglandin E2-induced intraocular inflammation

The effects of tachykinins on prostaglandin E2 (PGE2)-induced intraocular inflammation were investigated. PGE2 (0.01% or 0.1%) instillation induced iridal hyperemia and protein leakage into the aqueous humor in rabbits, but caused minimal miosis. Intravitreally injected substance P (SP) or neurokinin A (NKA), on the other hand, did not induce protein leakage into the aqueous humor in normal rabbits, but they (SP 10 micrograms/eye or NKA 50 micrograms/eye) did induce long-lasting miosis. The miotic activity of SP was about fivefold stronger than that of NKA. Intravitreally injected SP (10 micrograms/eye) but not NKA (50 micrograms/eye) increased PGE2 concentration in the aqueous humor in normal rabbits. In addition, SP (10 micrograms/eye) or NKA (50 micrograms/eye) markedly enhanced protein leakage into the aqueous humor induced by PGE2 instillation. Pretreatment with indomethacin partially blocked the enhancing effect of SP on protein leakage, while it did not block that of NKA. These results suggest that SP or NKA may enhance intraocular inflammation in vivo. However, the mechanisms of these effects of SP and NKA may be different. The enhancing effect of SP in eye inflammation may be partially due to an increased turnover of arachidonic acid into PGE2 caused by activation of the enzyme cyclooxygenase.

Free radical depolymerization of hyaluronan by Maillard reaction products: role in liquefaction of aging vitreous

The degradation of hyaluronan was followed by viscosimetry and by HPLC in order to study the possible role of Maillard products (lysine-glucose) on the alteration of the vitreous gel in aging and diabetes. Lysine-glucose generated Maillard products produced a decrease of viscosity and of the number average molecular weight (Mn) of hyaluronan during a 1 h incubation at 37 degrees C. This effect was comparable to that produced by 1 U/ml of testicular hyaluronidase but was weaker than the effect of a Fenton-type reagent (Udenfriend's reagent). The polydispersity of hyaluronan incubated with Maillard products appeared higher than with hyaluronidase suggesting a more random reaction. Antioxydant enzymes (SOD, catalase), the iron chelators (desferrioxamine, transferrin) and the free radical scavengers (uric acid, carnosine) inhibited the degradation by Maillard products confirming its free radical nature and the intervention of trace metals. Maillard products have been detected in diabetic vitreous and may play a role in its accelerated modifications (liquefaction) in diabetes as compared to normal aging.

Vitreous-stabilizing, single-piece, mini-loop, plate-haptic silicone intraocular lens

PURPOSE

To evaluate the clinical and visual results of the Medevec VS5 intraocular lens (IOL) with mini-loops, determine the incision size required for its implantation and its usable optical zone size, and compare the sizes with those of other foldable lenses.

SETTING

Ophthalmology Department, St. Johannes Hospitals, Dortmund, Germany.

METHODS

The VS5 lens was folded with a forceps and implanted into an intact bag in 27 patients; incision size was measured. Postoperatively, centration was recorded after dilation and the lens periphery observed to ascertain whether the loops were fixed in the capsular bag. Postoperative A-scans were done in 22 eyes, and the preoperative and postoperative vitreous cavity lengths were compared. The size of the optical zone was compared with that of other foldable lenses.

RESULTS

Forceps implantation of the VS5 lens required a 2.7 to 3.0 mm incision; all lenses were fixated in the bag. A-scans in 22 eyes showed that the vitreous cavity was shortened by an average of 0.51 mm. Uncorrected visual acuity was 20/40 or better in 96% of eyes. One week postoperatively, the IOLs remained centered and there was no flare or cells. The usable optical zone was larger than that of the staked long-loop lenses.

CONCLUSION

The Medevec VS5 fixated in the bag, consistently locating in the posterior bag space and stabilizing the vitreous. It had a full 5.0 mm optical zone and could be implanted through an incision smaller that that required by other foldable IOLs.

Evaluation of collagen gel and hyaluronic acid as vitreous substitutes

We evaluated alkaline-solubilized collagen, hyaluronic acid (HA), and a substance formed from mixing both materials as vitreous substitutes in the rabbit. Fluorescein isothiocyanate (FITC)-labeled collagen (2%), fluorescein-labeled HA (FLHA, 1%), or the mixture was injected into the rabbit vitreous after vitrectomy. After 3 months, histologic study revealed that the substitutes caused no adverse effects on the ocular tissue. Kinetic studies showed that the half-lives of FITC-collagen, FL-HA, and the mixed substance were 5.70, 2.09, and 8.41 days, respectively. The results indicated that HA enhances the collagen half-life. The concomitant of collagen and HA is safe and effective for 3 months in rabbit's eye as a vitreous substitute, and the mixture is capable of tamponade.

Mechanisms of acute intraocular pressure increases after phacoemulsification lens extraction in dogs

OBJECTIVE

To investigate the mechanisms by which intraocular pressure (IOP) increases acutely after phacoemulsification (PE) lens extraction in clinically normal dogs.

ANIMALS

24 young adult dogs.

PROCEDURE

Intraocular pressure was monitored for up to 24 hours after unilateral intercapsular PE in 17 clinically normal, adult dogs. In 8 of these dogs, use of 2% hydroxypropyl methylcellulose (HPMC) aided capsulorhexis. Mean volume of irrigation, PE time, and power were constant between groups. After surgery, dogs were randomized then euthanatized, and eyes were examined grossly and histologically at 0 (n = 4), 3 (n = 7), and 24 hours (n = 6) after PE. Seven additional dogs underwent anterior chamber decompression alone (n = 4) or served as morphologic controls (n = 3).

RESULTS

Intraocular pressure peaked by postoperative hour 3 at 49.9 +/- 5.0 mm of Hg and normalized by 24 hours. Use of HPMC did not affect the peak or duration of IOP increase. Blood refluxed into the collecting channels and corneoscleral trabecular meshwork in operated eyes. Computer-aided morphologic analysis indicated significant (P < 0.001) reduction in ciliary cleft cross-sectional surface area and width immediately after PE, but not after anterior chamber decompression alone. Cleft collapse was significantly (P < 0.02) greater at 24 than at 3 hours, despite return of IOP to control values by 24 hours. Plasmoid aqueous also was found in the meshwork.

CONCLUSIONS AND CLINICAL RELEVANCE

Sudden, large increases in IOP with few overt clinical signs may occur immediately after lens extraction in dogs. Such increases risk compromising the corneal incision and may damage the optic nerve, thereby complicating lens extraction. Structural alterations in the trabecular meshwork persist after IOP has normalized in 24 hours and may contribute to genesis of glaucoma in the late postoperative period.

Tractional force generation by porcine Müller cells: stimulation by growth factors in human vitreous

PURPOSE

To examine the levels of Müller cell contraction-stimulating activity in human vitreous, correlate these levels with clinical presentation, and identify, the causative growth factors.

METHODS

Human vitreous was collected from patients undergoing pars plana vitrectomy (n = 84). Müller cells were isolated from porcine retina and maintained in tissue culture. Tractional forces generated by cells incubated on three-dimensional collagen gels were measured as changes in gel thickness. Contraction-stimulating activity in vitreous (VA) was calculated from the close-response profiles of gel contraction to vitreous protein. The contributions of individual growth factors to vitreous activity (n = 10) were assessed by inhibition with specific neutralizing antibodies.

RESULTS

The mean VA of patients with retinal detachment (3.65) and proliferative vitreoretinopathy stages A, B, and C (2.06) were elevated above that of patients without retinal pathology (vitreous activity = 0.23) or retinal defects alone (0.57). Mean activities in patients with epimacular proliferation (1.22) and vitreous hemorrhage (1.40) were also significantly elevated. The percentage of this activity attributable to insulin-like growth factor 1 (IGF-1) varied from 9.2% to 84.5% with a mean of 61.3%. Similarly, the percent contribution of platelet-derived growth factor (PDGF) ranged from 6.8% to 49.0% with a mean of 26.5%.

CONCLUSIONS

The vitreous of patients with retinal detachment, proliferative retinal disease, and vitreous hemorrhage contain varying amounts of growth factors that stimulate tractional force generation by Müller cells. The majority of the activity can be attributed to IGF-1 and a smaller proportion to PDGF.

Blood-retinal barrier (BRB) breakdown in experimental autoimmune uveoretinitis: comparison with vascular endothelial growth factor, tumor necrosis factor alpha, and interleukin-1beta-mediated breakdown

Experimental autoimmune uveoretinitis (EAU) induced in Lewis rats by immunization with S-antigen is a model of human uveitis. By using immunocytochemical staining for albumin, relatively minor blood-retinal barrier (BRB) breakdown was initially shown in the peripheral retina 8 days after immunization and in the posterior retina by 10 days. Albumin extravasation appeared to occur by opening of the retinal vascular endothelial (RVE) and the retinal pigmented epithelial (RPE) tight junctions, by transendothelial vesicular transport, and by permeating damaged RVE cells. Each of three anti-inflammatory agents reduced or delayed autoimmune-mediated cell destruction but did not eliminate any particular route of extravasation. Vascular endothelial growth factor (VEGF), tumor necrosis factor alpha (TNF alpha), and interleukin-1beta (IL-1beta) are intimately associated with the development of EAU and are capable of causing BRB dysfunction. A high percentage of RVE tight junctions appeared open ultrastructurally after intravitreal injection of VEGF (26.7%), TNF alpha (35.6%), or IL-1beta (22.1%) compared with saline-injected control (11.4%) or normal, untreated rabbits (4.1%). Heat treatment abolished the effect of IL-1beta on the BRB but only partially reduced the effect of VEGF. By 24 hr after injection, the effect of TNF alpha had reversed, but that of IL-1beta had not; VEGF-mediated BRB dysfunction was partially reversible. In addition, albumin-filled vesicle-like structures were seen in the RVE cytoplasm following treatment with each mediator. This study shows that VEGF, TNF alpha, and IL-1beta each cause BRB breakdown by opening tight junctions between RVE cells and possibly by increasing transendothelial vesicular transport. Each of these agents may contribute to BRB breakdown in EAU and in patients with uveitis.

Effect of human vitreous and hyalocyte-derived factors on vascular endothelial cell growth

PURPOSE

In the present study we have examined the effects of human vitreous and hyalocyte-conditioned medium on human umbilical vein endothelial cells (HUVEC).

METHODS

Human umbilical vein endothelial cells were cultured and treated in quadruplicate with human vitreous and hyalocyte-conditioned medium at different concentrations. Cell numbers were counted on days 1, 3, 5 and 7. Morphological changes and the viability of cells after treatment were also monitored.

RESULTS

The results indicate that both human vitreous and hyalocyte-conditioned medium inhibit proliferation and reduce the viability of HUVEC in vitro. These inhibitory effects were dose- and time-dependent.

CONCLUSIONS

The observations suggest that human hyalocytes and vitreous contain anti-angiogenic factors that influence vascular endothelial cell-growth. These results, combined with those of previous studies, may yield important information about the functional role of vitreous and hyalocytes in intraocular vascular regression.

[Aging of the vitreous body. Role of glycation and free radicals]

The vitreous body plays an important role in the structure and in the function of the eye. Its bio-rheological properties contribute crucially to the mechanical resistance and optical transparency of ocular tissues. The composition and structure of the vitreous body change during aging and more rapidly in diabetes. These changes may have deleterious consequences such as functional disturbances and retinal detachment. The mechanical and optical properties of the vitreous are the result of its particular macromolecular architecture composed of a hyaluronan gel supported by a fine collagen meshwork, essentially of type II and IX. These are held together by proteoglycans and by fibronectin. All these macromolecules are susceptible to free radical damage produced by UV and visible light, by metabolic processes as well as the Maillard reaction. The mechanisms by which Maillard products and free radicals play a role in the physiological or accelerated aging of the vitreous are discussed in this review.