Development and characterization of a vitreous mimicking material for radiation force imaging

In many medical ultrasound applications tissue-mimicking phantoms are of fundamental importance for the performance of controlled experiments. Traditionally, such phantoms have been constructed using gelatin and agar gels. Although the use of these materials has become standard, few alternative materials have not been fully explored. In this paper, we present a protocol developed in our laboratory that reliably produces very soft, acrylamide-based phantoms that can mimic both acoustical and mechanical characteristics of the vitreous body of the eye. Following the described protocol, a series of phantoms were constructed ranging in acrylamide concentration from 1.60% to 1.70%. Measurements across the series yielded attenuation coefficients of 0.067-0.140 dB/cm/MHz, depending on acrylamide concentration. Speed of sound ranged between 1499 and 1510 m/s, also depending on acrylamide concentration. Published values for the vitreous gel indicate an attenuation of 0.10 dB/cm/MHz and a speed of sound of 1510 m/s, making our phantoms an excellent analog of this tissue. One application of these acrylamide phantoms is to test the efficacy of the Kinetic Acoustic Vitreoretinal Examination (KAVE), a tool developed in our laboratory with the potential to aid in the diagnosis of vitreoretinal disorders. KAVE utilizes acoustic radiation force to generate small, localized displacements within the vitreous-mimicking gel. These localized displacements are quantified to yield maximum displacement, relative elasticity, and relative viscosity images. We present KAVE images of a set of four phantoms with different gel concentrations. Although B-mode and relative viscosity images exhibit no significant differences, maximum displacement, and relative elasticity images clearly differentiate gels of different concentrations. Maximum displacements ranged between 30 and 5 microns, depending on acrylamide concentration. The results presented in this paper show that soft gel phantoms can be produced in a range of elasticities not previously reported, and that these phantoms are useful for testing ultrasound instruments designed for evaluation of the vitreous gel. Furthermore, the use of acrylamide-based gels may also offer a valuable and attractive alternative for many other ultrasound applications.

Changes in gene expression of ARPE-19 cells in response to vitreous treatment

PURPOSES

The purpose of this study is to determine the changes in gene expression by a human retinal pigment epithelium (RPE) cell line (ARPE-19) in response to vitreous treatment, which induces RPE proliferation and phenotypic changes in vitro that mimic the repair response observed in vivo during proliferative vitreoretinopathy.

METHODS

ARPE-19 cells were grown for more than 4 weeks and their gene expression studied in: (1) subconfluent cultures treated with 50% human vitreous for 72 h; (2) subconfluent cultures without vitreous treatment, and (3) a confluent, nondividing monolayer. Total RNA was extracted from RPE cells and differential gene expression between each condition was determined using gene arrays (Clontech, Palo Alto, Calif., USA). Semiquantitative RT-PCR was used to confirm the upregulation of 4 genes related to vitreous treatment. In addition, the secretion of 1 of these upregulated gene products, monocyte chemotactic protein 1 (MCP-1), was confirmed by ELISA.

RESULTS

A greater than threefold increase in the expression of mRNA for cell cycle regulators, intracellular transducers, cell adhesion proteins, growth factors and chemokines was observed following vitreous treatment of the RPE cell line and a corresponding decrease in the expression of genes related to apoptosis. RT-PCR confirmed the increased gene expression of MCP-1, intercellular adhesion molecule-1, vascular cell adhesion protein 1 precursor and vascular endothelial growth factor in vitreous-treated cells. Immunoassays further showed an increased MCP-1 secretion by vitreous-treated RPE.

CONCLUSIONS

These findings suggest that in this in vitro vitreous treatment model, ARPE-19 cells participate in a mock repair response by upregulating genes encoding for proteins associated with inflammation and wound healing.

Effects of endothelin-1 on components of anterograde axonal transport in optic nerve

PURPOSE

Increased levels of endothelins (ETs) are associated with glaucoma and have been said to contribute to the development of glaucomatous optic neuropathy. In glaucoma, movement of selected components of anterograde axonal transport essential in ganglion cell survival is impaired-specifically, the transport of mitochondria. This study evaluates the effect(s) of a single administration of intravitreous ET-1 on anterograde axonal transport in the rat optic nerve.

METHODS

Proteins for anterograde axonal transport were pulse labeled by intravitreous injection of (35)S-methionine plus or minus ET-1 (2 nmol) in HEPES buffer (pH 7.4). At appropriate time intervals, optic nerves were dissected, sectioned while frozen, and homogenized in denaturing buffer, and transported protein was quantitated by liquid scintillation counting. Counts corrected for efficiency, quench, background, and decay were statistically evaluated (ANOVA, n = 7).

RESULTS

Effects of treatment with intravitreous ET-1 on anterograde axonal transport were significant, biphasic, and prolonged (4 hours to 21 days). The initial phase was a significant enhancement of transport at times normally associated with small, fast-moving tubulovesicles (4 and 24 hours), followed by significant impairments at times normally associated with transport of mitochondria (28-36 hours), cytoplasmic matrix (4 days), and cytoskeletal proteins (21 days). The most pronounced effect of ET-1 was decreased axonal transport at times associated with normal anterograde transport of mitochondrial proteins (28, 32, and 36 hours, P = < 0.001, P < 0.015, and P < 0.001, respectively). This was mimicked by ET-3 at 28 hours.

CONCLUSIONS

Effects of intravitreous ET-1 are consistent with a receptor-mediated role for elevated ETs in pathologic misregulation(s) of anterograde axonal transport.

Magnetic resonance imaging studies of the volume of the rabbit eye with intravenous mannitol

PURPOSE

Changes in the volume of rabbit eyes after intravenous mannitol injection were studied non-invasively using 3D-magnetic resonance imaging (MRI).

METHODS

Images of eight rabbit eyes were obtained using a 3D-gradient echo technique before and at 30, 60 and 90 minutes after mannitol injection at 4 g/kg. To evaluate the volume, the cross-sectional area of the eye in the central 5 slices was traced and totaled. The intraocular pressure (IOP) of five rabbits was measured before and after administration.

RESULTS

The total area of the eyeball decreased significantly at 60 minutes. The total area of the anterior chamber, iris plus ciliary body decreased rapidly and then recovered. The decrease in the vitreous and the IOP was consistently significant during the 90-minute observation period.

CONCLUSIONS

Consecutive MRIs enabled us to measure the changes in eye volume of the same rabbit before and after mannitol injection in a non-invasive manner.

Vitreous treatment of cultured human RPE cells results in differential expression of 10 new genes

PURPOSE

To analyze the differential gene expression in cultured human retinal pigment epithelial (RPE) cells after treatment with vitreous.

METHODS

Cultured human RPE cells were incubated for 48 hours with 25% human vitreous from donor eyes. Total RNA from treated and untreated cells was extracted. The gene expression was analyzed by differential expression analysis (DEmRNA-PCR). The differentially expressed genes were identified by gene bank searches. Differential expression was verified by a quantitative real-time RT-PCR fluorescent nucleic acid staining system. The in vivo mRNA expression of these genes in RPE cells was shown by gene-specific RT-PCR.

RESULTS

Vitreous treatment of human RPE cells resulted in the reduced expression of NFIB2, KE03 (NY-REN-25ag), PIG-B, DKFZp564BC462, LKHA, G3BP, PAM, UEV-1, and MAP1B calibrated to the expression of GAPDH when compared with their expression in untreated cells. The reduced expression after vitreous treatment was quantified by gene-specific quantitative real-time RT-PCR and varied from 0.69 to 0.17 compared with untreated cells. The mRNA expression of UDP-GalNac mRNA remained constant. The mRNA expression of eight of these genes was demonstrated in this study for the first time in human RPE cells.

CONCLUSIONS

Vitreous treatment of cultured RPE cells induces the differential expression of a variety of genes with functions in transcription, mediation of signal transduction and inflammation, glycosylation, ubiquitination and protein-protein interaction. Further examination of these genes may locate additional targets for treatment of diseases caused by contact of RPE cells with vitreous, typical in proliferative vitreoretinopathy.

The role of the vitreous in retinal detachment surgery with external buckling

PURPOSE

To prove the role of the vitreous in retinal detachment surgery with scleral buckling procedures, we retrospectively investigated the charts of patients who were operated on for retinal detachment by scleral buckling between January 1995 and June 1997.

METHODS

Out of a total of 718 cases, 41 retinal detachments occurred in previously vitrectomized eyes. The buckling procedure consisted of silicone sponge explants in 513 cases (254 radial, 259 circumferential) and of encircling elements in 202 cases. Three eyes received a temporary balloon. The minimal follow-up was 3 months.

RESULTS

After primary surgery in the 677 nonvitrectomized eyes, the retina was attached in 482 eyes (71.2%), after reoperation in 627 eyes (92.6%). With up to 3 reoperations (including vitrectomy with gas or silicone oil tamponade in 79 eyes), the final success rate was 98.7%. The corresponding reattachment rates in the 41 vitrectomized eyes were 82.9% after primary surgery and 97.6% after reoperation. Repeated surgery in 6 eyes consisted of successful internal tamponade by silicone oil. The reattachment rates after primary buckle procedure are of most interest to the role of the vitreous: the highest success rate (82.9%) was achieved in the vitrectomized eyes versus 71.2% in the nonvitrectomized eyes. The difference is statistically not significant.

CONCLUSIONS

We therefore conclude that the absence of the vitreous has no adverse effect on the results of buckling procedures for retinal detachment. The choice of the surgical technique in treating retinal detachments in vitrectomized eyes should only determined by retinal findings such as the number and extent of breaks or the presence and stage of proliferative vitreoretinopathy.

[A pilot study of bone marrow stromal cells intraocular transplantation in the S334 transgenic rats and Sprague-Dawley rats]

PURPOSE

To investigate the survival and differentiation of human bone marrow stromal cells (BMSC) intraocular transplantation in newborn S334 retinal degeneration transgenic rats and (Sprague-Dawley)SD rats.

METHODS

Human bone marrow stromal cells line was grown on the adhesive substrate in the condition media including a-Modified Eagle medium (a-MEM)/10% fetal bovine serum. The experiments were divided into four groups: Group 1: BMSC + (Retinoid Acid) RA transplanted in S334 transgenic rats (n = 5); Group 2: BMSC transplanted in S334 transgenic rats (n = 5); Group 3: BMSC + RA transplanted in SD rats (n = 5); Group 4: BMSC transplanted in SD rats (n = 5). 2 microl cell suspension (about 4 x 10(4) cells) was injected into the vitreous space in the transgenic rats and normal SD rats at Postnatal 1 (P1) respectively. The right eyes were treated eyes and the left eyes were used as control. At P14 and P23, the rats were killed and enucleated for histological assays using plastic section.

RESULTS

In Group 1, the transplanted cells were well survived. They could continue to differentiate and participate in late-stage retinal development. The number of inner nuclear layer increased. Moreover, the host retina increased their thickness, but photoreceptor cells were not rescued from transplant. In Group 2, at P14, the BMSC continue to differentiate toward their linage cell fate and formed into hemorrhage island structures with few neurons if RA was not applied. Group 3, BMSC could survive, migrate. The number of inner nuclear layer increased also. In Group 4, it revealed that host retina structures were disorganized and transplant cells formed atypical proliferating mass.

CONCLUSIONS

This pilot experiment indicated that bone marrow stromal cells could survival, differentiate and participate in the retinal development after transplanted into vitreous space in the new born transgenic rats and SD rats. Histological assays showed that transplanted cells integrated with inner nuclear layer of host retina. Thus, bone marrow stromal cells may be a useful vehicle for auto- transplantation for the therapy of variety of retinal degenerative disorders.

Age-related changes in vitreous mobility as measured by video B scan ultrasound

Many vitreoretinal disorders increase in incidence with age. The vitreous is known to liquefy and separate from the retina in aging patients. Liquefaction and partial vitreous separation alter the biomechanics of the vitreous and change the tractional forces exerted by the vitreous on the retina. These forces may play a role in the development of a variety of vitreoretinal pathologies including retinal tears, cystoid macular edema, and macular holes. The purpose of this study is to test the hypothesis that the biomechanical properties of the vitreous change with aging and can be quantified by analysis of kinetic B scan ultrasound recordings. Kinetic B scan ultrasound recordings were made of the vitreous gel of 38 subjects from ages 18 to 91 during standard eye motions. The recordings were graded for speckle density (hyperreflective areas on ultrasound) and were examined for the presence or absence of posterior vitreous detachment. Tracking of the speckles on a polar grid allowed for the calculation of the angle travelled by the speckle relative to the angle travelled by the eye. The recordings were also analysed for "overshoot time", or the amount of time that the speckles continued to travel after the cessation of eye movement. The vitreous of subjects of age less than 46 years demonstrated significantly less speckle density (P < 0.001), less overshoot time (P < 0.001), and less angle travelled by the speckle relative to the angle travelled by the eye when compared to older subjects (P = 0.006). The presence or absence of PVD as diagnosed by kinetic ultrasound was not a significant predictor for speckle density, overshoot time, or ratio of angular motions. The results indicate that aging affects the biomechanics of the vitreous in ways which can be quantified with kinetic ultrasound analysis using the grading system described above.

Angiotensin converting enzyme inhibiting therapy is associated with lower vitreous vascular endothelial growth factor concentrations in patients with proliferative diabetic retinopathy

AIMS/HYPOTHESIS

Vascular endothelial growth factor (VEGF) is thought to be instrumental in the progression of diabetic retinopathy. Indications exist that the renin-angiotensin system is involved in VEGF overexpression. We assessed the vitreous VEGF concentrations in patients and related them to anti-hypertensive treatment, with special interest in the use of ACE-inhibitors.

METHODS

Samples of vitreous fluid (10-80 microl) were obtained from 39 patients both with Type I (insulin-dependent) and Type II (non-insulin-dependent) diabetes mellitus and 11 non-diabetic patients undergoing intra-ocular surgery. The VEGF-A concentrations were assessed by immunoassay.

RESULTS

Control patients and patients without proliferative diabetic retinopathy ( n = 8) had low and comparable VEGF concentrations (medians < 50 pg/ml). In contrast, patients with proliferative diabetic retinopathy ( n = 31) had high vitreous VEGF concentrations (median 1134 pg/ml), which showed a negative correlation with the use of ACE inhibiting medication (Spearman rank-R = - 0.54; p = 0.002, n = 13). Diastolic and systolic blood pressure did not differ significantly between the two subgroups with proliferative diabetic retinopathy, i. e. those patients receiving ACE-inhibition (medians 88/160 mm Hg, respectively) and the others (90/160). For the mostly used ACE-inhibitor in the proliferative diabetic retinopathy group, i. e. enalapril ( n = 8), a linear dose-effect relation was observed (-20 +/- 4 pg x ml(-1) x mg(-1) x day(-1); p = 0.024; coefficient +/- SEM).

CONCLUSION/INTERPRETATION

Treatment with ACE-inhibitors attenuates retinal overexpression of VEGF-A in patients with proliferative diabetic retinopathy, probably by interference with a local effect of angiotensin II.

TGFbeta1-dependent contraction of fibroblasts is mediated by the PDGFalpha receptor

PURPOSE

Contraction of fibroblasts and the resultant tractional force is a contributing factor to fibrotic diseases of the eye, such as proliferative vitreoretinopathy (PVR). Transforming growth factor (TGF)-beta is abundant in the eye, and is one of the growth factors thought to contribute to the development of PVR. A second is platelet-derived growth factor (PDGF). In the current study, the relationship between TGFbeta1 and PDGF was investigated at the level of cellular contraction.

METHODS

To study cellular contraction, an in vitro type I collagen gel contraction assay was used with a panel of fibroblast lines that expressed the PDGFalpha receptor (alphaPDGFR) or PDGFbeta receptor (betaPDGFR) or no PDGFRs. The agents tested included rabbit vitreous, TGFbeta1, and PDGF.

RESULTS

Vitreous promoted cellular contraction, and approximately 60% of this activity was eliminated by preincubation of the vitreous with neutralizing TGFbeta antibodies. The alphaPDGFR-expressing cells responded better than cells expressing the betaPDGFR or no PDGFRs. Both of the PDGFR-expressing cell lines contracted in response to PDGF, whereas the best response to TGFbeta1 was observed with cells expressing the alphaPDGFR. Finally, TGFbeta1 promoted the tyrosine phosphorylation of both of the PDGFRs, and the alphaPDGFR was more strongly phosphorylated than the betaPDGFR.

CONCLUSIONS

The results show that the vitreous promotes cellular contraction, that TGFbeta is the major factor responsible, and that at least a portion of the TGFbeta-dependent contraction proceeds through the alphaPDGFR-that is, indirectly. Therefore, the alphaPDGFR is responsible for mediating cellular contraction of multiple growth factors: TGFbeta and members of the PDGF family.

Differential effects of intravitreal optic nerve and sciatic nerve grafts on the survival of retinal ganglion cells and the regeneration of their axons

We have investigated the effects of intravitreal sciatic nerve (SN) and/or optic nerve (ON) grafts on the survival and the axonal regeneration of retinal ganglion cells (RGCs). Following transection of the ON, approximately 40% RGCs survived at 7 days post-axotomy (dpa). Results showed that the intravitreal ON graft significantly promoted the survival of RGCs at 7 dpa (39,063 vs 28,246). Intravitreal SN graft, however, did not rescue axotomized RGCs at 5, 7 or 14 dpa. Axotomized RGCs could be induced to regenerate axons along a segment of SN graft attached to the proximal stump of ON. On average, 608 axotomized RGCs were induced to regenerate axons along the attached SN graft. The presence of intravitreal SN graft promoted about 100% increase in the number of regenerating RGCs (1,227) relative to the control groups. The intravitreal ON graft, surprisingly, also induced about 100% more regenerating RGCs (1220) than in the control group. When SN and ON grafts were co-transplanted into the vitreous, about 200% more regenerating RGCs (1916) were observed than in the control group. These findings illustrated that the intravitreal ON graft rescued axotomized RGCs and enhanced the regeneration of retinal axons. This is the first report to show that ON promotes RGC axonal regeneration. The intravitreal SN graft did not rescue RGCs but promoted axonal regeneration. The differential effects of intravitreal ON and SN grafts on the survival and the RGC regeneration suggest that these might be two independently operating events.

Vitreous-induced modulation of integrins in retinal pigment epithelial cells: effects of fibroblast growth factor-2

Growth in the presence of vitreous results in transformation of human RPE cells from an epithelioid to a fibroblast-like appearance and leads to an elevation of the expression of alpha(5) and alpha(2) integrins, while the level of alpha(3) integrin is reduced. These changes are inhibited by the presence of FGF-2. Vitreous treatment increases mobility, as does antibody neutralization of FGF-2 or antibody blockade of FGF receptors. The vitreous-induced rise in mobility depends on an increase in alpha(5) integrin expression since it is inhibited by anti-alpha(5) integrin antibodies. Expression of alpha(5) integrin as a result of infection of RPE cells with an alpha(5) integrin-encoding adenovirus induced morphological transformation and an increase in mobility similar to that seen with vitreous. It is concluded that a decrease in FGF-2 plays an important role in vitreous-induced alterations of RPE cell morphology, integrin expression and mobility. High FGF-2 levels prevent at least some of the increased mobility of RPE cells induced by vitreous. This is mediated via extracellular FGF-2 binding to FGF receptor(s) since antibodies to FGF-2 or to its receptor(s) mimic the effects of vitreous. Changes in mobility and morphology involve altered alpha(5) integrin expression since mobility is blocked by antibodies against these proteins while elevated alpha(5) integrin expression increases mobility and leads to morphological changes.

Increased expression and activation of poly(ADP-ribose) polymerase (PARP) contribute to retinal ganglion cell death following rat optic nerve transection

Excessive activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP) by free-radical damaged DNA mediates necrotic cell death in injury models of cerebral ischemia-reperfusion and excitotoxicity. We recently reported that secondary retinal ganglion cell (RGC) death following rat optic nerve (ON) transection is mainly apoptotic and can significantly but not entirely be blocked by caspase inhibition. In the present study, we demonstrate transient, RGC-specific PARP activation and increased retinal PARP expression early after ON axotomy. In addition, intravitreal injections of 3-aminobenzamide blocked PARP activation in RGCs and resulted in an increased number of surviving RGCs when compared to control animals 14 days after ON transection. These data indicate that secondary degeneration of a subset of axotomized RGCs results from a necrotic-type cell death mediated by PARP activation and increased PARP expression. Furthermore, PARP inhibition may constitute a relevant strategy for clinical treatment of traumatic brain injury.

Syneretic response to pressure in bovine and rhesus monkey vitreous

Excised bovine and rhesus monkey vitreous samples were subjected to different hydrostatic pressures (0.03, 1 and 2 atm) for 12 hr. At the end of the experiment the samples were frozen in a -70 degrees C dry ice-acetone bath and thereafter maintained in frozen conditions. Differential scanning calorimetry (DSC) was used to obtain freezable water (FW) content. The total water content of the samples was obtained by thermogravimetric (TGA) techniques. The non-freezable water (NFW) content was obtained as a difference between total and freezable water contents. The total water content did not show a trend in pressure dependence, neither in bovine nor in rhesus monkey vitreous samples. However, the free water/bound water ratio, i.e. FW/NFW, increased with increasing pressure in vitreous samples of both species. The trend of the average FW/NFW values as a function of hydrostatic pressure implies a simple syneretic response, i.e. the conversion of bound (non-freezable) water to free water as pressure was increased.

N-methyl-D-aspartate-induced excitotoxicity in adult rat retina is antagonized by single systemic injection of MK-801

Intravitreal injection of N-methyl-D-aspartate (NMDA) produced a substantial damage to the adult rat retina that was largely restricted to inner retinal layers, including the ganglion cell layer (GCL), inner nuclear layer (INL), inner, and outer plexiform layers. This retinal damage was significantly reduced by a systemic injection of a low dose of MK-801 (0.5 mg/kg), a potent NMDA-receptor antagonist. This neuroprotection was dose dependent and was most effective when the antagonist was given 1 h before NMDA insult. An intraperitoneal injection of 0.5 mg/kg MK-801 provided a virtually complete protection to the retina to the NMDA-induced toxicity, as indicated quantitatively by the number of DiI-filled retinal ganglion cells, the number of cells in the GCL and INL that undergo DNA fragmentation, and the edematous changes in retinal thickness. A post-lesion administration of MK-801 was still able to provide an effective neuroprotective effect to the retina, but this protection was lost when MK-801 was given 4 h after NMDA exposure. The current results indicate a therapeutic potential of systemic application of MK-801 in protecting the adult rat retina from neurologic disorders related to excessive activation of NMDA receptors.

Intraretinal analysis of the a-wave of the electroretinogram (ERG) in dark-adapted intact cat retina

It has often been assumed that the recovery of the a-wave from its trough is caused by the intrusion of the b-wave. This study examined the recovery following the a-wave trough using intraretinal recordings in dark-adapted intact cat retina. Adult cats were anesthetized and paralyzed. The vitreal ERG was recorded between the vitreous humor and a reference electrode near the eye. Intraretinal recordings were made by referencing a microelectrode to the vitreal electrode. Bright flashes of diffuse white light were used to elicit a- and b-waves. Intravitreal injections of 2-amino-4-phosphonobutyrate (APB), cis 2,3-piperidine dicarboxylic acid (PDA), and kynurenic acid (KYN) were used to block the responses of bipolar and horizontal cells. Intravitreal injections of UL-FS 49 or DK-AH 269 were used to block Ih, a hyperpolarization-activated potassium current. Since the microelectrode was referenced to the vitreal electrode, recordings from the inner retina showed only the oscillatory potentials and b-waves. In the inner retina, the potential was flat until the b-wave became measurable, approximately 17 ms from the onset of the flash. The a-wave started to appear as the microelectrode reached the photoreceptors and its amplitude increased with depth until the microelectrode reached the choroid. The a-wave peaked at approximately 8 ms in response to flashes that saturated its amplitude and then began to recover well before any inner retinal responses were apparent. After injections of APB, PDA, and KYN, vitreal and intraretinal recordings showed only the a-wave, which consisted of an increase to peak at approximately 10 ms followed by a recovery to a plateau which was reached at approximately 25 ms. Blockers of Ih reduced the recovery, but did not eliminate it. The a-wave peaks and partially recovers before the b-wave intrudes. Both phases survive blockers of second-order neurons which implies that the photoreceptors generate both the rising and recovery phase of the a-wave. The recovery phase may be due to a current generated by the inner segment of photoreceptors.

Transcriptional up-regulation of the protooncogenes c-fos and c-jun following vitreous removal and short-term in vitro culture of bovine lenses

Chemical (mainly oxidative) and mechanical (anterior capsule injury) stresses have been reported to up-regulate the expression of the protooncogenes c-fos and c-jun in the lens. Another potentially stressful, yet largely unexplored condition, inherent to all experiments requiring the in vitro culturing of isolated lenses, is vitreous removal. Based on the results of an extensive RNA gel blot analysis conducted on epithelial/capsule preparations isolated from calf lenses dissected and cultured under different conditions, we show, here, that lens isolation and short-term culture (1-2.5 hr, without any significant GSH depletion) result in a strong and time-dependent up-regulation of the c-jun and c-fos mRNAs. This response, which relies on transcriptional protooncogene activation and is more intense for c-fos than for c-jun, is in part prevented by the preservation of the lens-vitreous contact, but not by the culture of vitreous-stripped lenses on a vitreous bed. Supplementation of the culture medium with the antioxidant N -acetyl-cysteine slightly reduced the c-jun, but not the c-fos response. Protooncogene up-regulation thus appears to be mainly determined by the disruption of critical lens-vitreous interactions. Since this response takes place in the epithelial cells, these data also point to the existence of a communication mechanism whereby a posteriorly applied mechanical stress is transmitted to, and perceived by, the anterior lens surface.

Fibronectin in the vitreous body--distribution and possible functional role

The presence of fibronectin in the bovine vitreous was demonstrated by immunohistochemical procedures which showed a uniform coating of the vitreous collagen network. A fractional extraction of bovine vitreous was carried out in order to determine the distribution of fibronectin and glycosaminoglycans as related to collagen fibers. About half of total fibronectin could be extracted with aqueous buffers with increasing concentrations of KCl, part of fibronectin remained however strongly associated with the insoluble collagen network even after a final extraction with 4 M urea and 0.05 M DTT. Total extractable fibronectin was of the order of 76 micrograms per vitreous, corresponding to approximately 0.17 nM fibronectin. Total quantity of GAG-s determined as uronic acid were of the order of 2200 micrograms/vitreous corresponding approximately to 4400 micrograms disaccharide units that is to about 11 nM disaccharide units of GAG per vitreous. The persistence of fibronectin, strongly associated with the collagen fibers even after repeated KCl and urea-DTT extractions was confirmed using immuno-gold labelling of vitreous collagen fibers. Gold particle density on the collagen fibers increased with the molarity of KCl used for the extractions. These findings suggest that KCl mainly removed fiber associated components probably GAG-s, which hindered the immune recognition of fiber-bound fibronectin. The strong association of fibronectin with vitreous collagen suggested a modified model for vitreous structure taking in account the binding of fibronectin both by collagen and GAG-s.

Pharmacokinetics and safety of an anti-vascular endothelial growth factor aptamer (NX1838) following injection into the vitreous humor of rhesus monkeys

PURPOSE

The objective of this study was to determine the pharmacokinetics and safety for NX1838 following injection into the vitreous humor of rhesus monkeys.

METHODS

Plasma and vitreous humor pharmacokinetics were determined following a single bilateral 0.25, 0.50, 1.0, 1.5, or 2.0 mg/eye dose. In addition, the pharmacokinetics and toxicological properties of NX1838 were determined following six biweekly bilateral injections of 0.25 or 0.50 mg/eye or following four biweekly bilateral injections of 0.10 mg per eye followed by two biweekly bilateral injections of 1.0 mg per eye.

RESULTS

Plasma and vitreous humor NX1838 concentrations were linearly related to the dose administered. NX1838 was cleared intact from the vitreous humor into the plasma with a half-life of approximately 94 h, which was in agreement with the plasma terminal half-life. Vascular endothelial growth factor (VEGF)-binding assays demonstrated that the NX1838 remaining in the vitreous humor after 28 days was fully active. No toxicological effects or antibody responses were evident.

CONCLUSIONS

The no observable effect level was greater than six biweekly bilateral 0.50 mg/eye doses or two biweekly bilateral 1.0 mg/eye doses. These pharmacokinetic and safety data support monthly 1 or 2 mg/eye dose regimens in human clinical trials.

Complement regulatory activity of normal human intraocular fluid is mediated by MCP, DAF, and CD59

PURPOSE

To identify the molecules in normal human intraocular fluid (aqueous humor and vitreous) that inhibit the functional activity of the complement system.

METHODS

Aqueous humor and vitreous were obtained from patients with noninflammatory ocular disease at the time of surgery. Samples were incubated with normal human serum (NHS), and the mixture assayed for inhibition of the classical and alternative complement pathways using standard CH(50) and AH(50) hemolytic assays, respectively. Both aqueous humor and vitreous were fractionated by microconcentrators and size exclusion column chromatography. The inhibitory molecules were identified by immunoblotting as well as by studying the effect of depletion of membrane cofactor protein (MCP), decay-accelerating factor (DAF), and CD59 on inhibitory activity.

RESULTS

Both aqueous humor and vitreous inhibited the activity of the classical pathway (CH(50)). Microcentrifugation revealed the major inhibitory activity resided in the fraction with an M(r) >/= 3 kDa. Chromatography on an S-100-HR column demonstrated that the most potent inhibition was associated with the high-molecular-weight fractions (>/=19.5 kDa). In contrast to unfractionated aqueous and vitreous, fractions with an M(r) >/= 3 kDa also had an inhibitory effect on the alternative pathway activity (AH(50)). The complement regulatory activity in normal human intraocular fluid was partially blocked by monoclonal antibodies against MCP, DAF, and CD59. Immunoblot analysis confirmed the presence of these three molecules in normal intraocular fluid.

CONCLUSIONS

Our results demonstrate that normal human intraocular fluid (aqueous humor and vitreous) contains complement inhibitory factors. Furthermore, the high-molecular-weight factors appear to be the soluble forms of MCP, DAF, and CD59.

Epithelial organization of the mammalian lens

To understand the structural organization responsible for lens function, we have studied the three-dimensional arrangement of cells in the lens, and the location and molecular composition of specialized junctions controlling the paracellular and transcellular pathways. The lens is formed by a single layer of polarized cells that elongate along their apical-basal axis from the anterior to the posterior pole to form the cortex, and fold inward at the posterior pole to form the nucleus. The basal surfaces of all cells of the cortex (approximately two thirds of all lens cells) are bathed by the aqueous and vitreous humors. Therefore, their metabolism is not limited by diffusion of nutrients into the avascular lens. The apical surfaces of all cortical fibers are directed toward the interior of the lens, where they form two distinct structures here referred to as the 'apical interface' and the 'modiolus'. The apical interface is located at a point close to the anterior pole, and is formed by the association of the apical surface of anterior cortical cells and the apical surface of cortical fibers extending from the posterior pole. The modiolus is located close to the equator at the lateral edge of the apical interface, and is formed by the tapered apical ends of equatorial cortical fibers. The plasma membrane of cortical cells at the anterior pole are connected through 'leaky' tight junctions and small gap junctions. Extensive gap junction plaques composed of connexin43 connect equatorial fibers at the modiolus and posterior cortical fibers at the apical interface. Single cell-to-cell channels composed of connexin46 and connexin50 connect the lateral surfaces of equatorial and posterior cortical fibers. The lateral surfaces of these fibers also contain extensive junctions composed of aquaporin-0. The nucleus is connected to the humors through the paracellular pathway represented by the anterior (apical) and posterior (basal) suture lines. Therefore, the metabolic needs of nuclear fibers cannot be fulfilled by simple diffusion and requires the cell-to-cell pathway formed by specialized junctions. The lateral surfaces of nuclear fibers contain extensive wavy junctions composed of aquaporin-0, probably for the control of the permeability of the paracellular pathway. We propose a simple epithelium model for the lens in which nutrients move into the nucleus through the paracellular pathway represented principally by the suture lines, and the transcellular pathway represented by an extensive network of gap junction plaques composed of connexin43 at the apical surface, and single or small plaques of cell-to-cell channels composed of connexin46 and connexin50 in the lateral surfaces.

[Motion artifacts in the vitreous body during vitrectomy]

BACKGROUND

Movements and vibrations of intraocular structures can be observed during vitrectomy with mechanical cutting systems. We experimentally compared these intraocular motion artifacts between mechanical and erbium:YAG laser vitrectomy.

MATERIAL AND METHODS

The intraocular structures were reliably simulated by a 0.9-mm-wide foil (thickness 10 microns) in a water-filled cuvette. The movements caused by commercial mechanical cutter systems were compared with vibration induced by means of laser surgery probes (laser pulse energy 20 mJ). Laser triangulation was used to measure the movement amplitudes at various cutting rates of 2, 5, and 10 Hz and a constant suction force of 50 mmHg.

RESULTS

At all cutting rates the amplitude with the laser was less than that with the mechanical system. The ratio of the maximal amplitude between laser surgery probes (AL) and mechanical cutter system (AM) was AL/AM = 0.29 at 10 Hz, AL/AM = 0.33 at 5 Hz, and AL/AM = 0.45 at 2 Hz.

CONCLUSION

The reduced intraocular movements with erbium:YAG laser vitrectomy constitutes a potential advantage for the nonpulsatile vitrectomy.

Axonal regeneration of retinal ganglion cells: effect of trophic factors

A variety of neurotrophic factors can influence the cell functions of the developing, mature and injured retinal ganglion cells. The discovery that retinal ganglion cell loss can be alleviated by neurotrophic factors has generated a great deal of interest in the therapeutic potential of these molecules. Recently, evidence has provided valuable information on the receptors that mediate these events and the intracellular signaling cascades after the binding of these ligands. Signaling by neurotrophic factors does not seem to restrict to retrograde messenger from the target but also includes local interactions with neighbouring cells along the axonal pathways, anterograde signaling from the afferents and autocrine signaling. More insight into the mechanisms of action of neurotrophic factors and the signal transduction pathway leading to the protection and regeneration of retinal ganglion cells may allow the design of new therapeutic strategies.

[Refraction and anterior chamber depth change after vitrectomy for pseudophakia]

PURPOSE

To evaluate the association between the vitreous and the refractive error in pseudophakia.

METHODS

Vitrectomy was performed in 67 eyes of 61 patients who underwent cataract surgery. Vitrectomy was needed for epiretinal membrane in 30 eyes, macular edema in 22 eyes, macular hole in 3 eyes, lamelar macular hole in 2 eyes, vitreous opacity in 6 eyes, and vitreous hemorrhage in 4 eyes. Refraction was measured before the operation, and 1 month, 3 months, 6 months, and 12 months after operation. Anterior chamber depth was measured in 10 eyes before the operation, and 1 month, 3 months, and 6 months after operation. We evaluated the refractive error after vitrectomy in 49 eyes that had predicted refraction.

RESULTS

The mean value of refractive change was -0.3 D 1 month postoperatively, and then gradually became positive. The variation of refraction (6-month postoperative refraction minus preoperative refraction) was negatively correlated with preoperative refraction (p = 0.0052, R2 = 0.146). If preoperative refraction was more myopic than -1.5 D, then refraction became positive. If preoperative refraction was not more myopic than -1.5 D, then refraction became negative.

CONCLUSION

About 15% of postoperative refractive error may be associated with the vitreous, but further investigation is required.