The role of soluble proteins in generating aqueous outflow resistance in the bovine and human eye

Development and testing of a metabolic chamber for effluent collection during whole eye perfusions

Ocular hypertension is caused by dysregulated outflow resistance regulation by the conventional outflow (CO) pathway. The physiology of the CO pathway can be directly studied during ex vivo ocular perfusions. In addition to measuring outflow resistance generation by the CO tissues, perfusion media that is conditioned by CO pathway cells can be collected upon exiting the eye as effluent. Thus, contents of effluent include factors contributed by upstream cells that report on the (dys)functionality of the outflow tissues. Two methods have been used in the past to monitor effluent contents from perfused eyes, each with their limitations. To overcome these limitations, we designed and printed a metabolic chamber to accommodate eyes of different sizes during perfusions. To test this new chamber, human eyes were perfused for 4 h at constant flow rate of 2.5 μl/min, while pressure was continuously monitored and effluent was collected every hour. Facility was 0.28 ± 0.16 μl/min/mmHg for OD eyes and 0.33 ± 0.11 μl/min/mmHg for OS eyes (n = 3). Effluent samples were protein rich, with protein concentration ranging from 2700 to 10,000 μg/ml for all eyes and timepoints (N = 3). Effluent samples expressed proteins that were actively secreted by the TM and easily detectible including MYOC and MMP2. Taken together, our model provides a reliable method to collect effluent from ex vivo human eyes, while maintaining whole globe integrity.

Anterior chamber perfusion versus posterior chamber perfusion does not influence measurement of aqueous outflow facility in living mice by constant flow infusion

Mice are now routinely utilized in studies of aqueous humor outflow dynamics. In particular, conventional aqueous outflow facility (C) is routinely measured via perfusion of the aqueous chamber by a number of laboratories. However, in mouse eyes perfused ex-vivo, values for C are variable depending upon whether the perfusate is introduced into the posterior chamber (PC) versus the anterior chamber (AC). Perfusion via the AC leads to posterior bowing of the iris, and traction on the iris root/scleral spur, which may increase C. Perfusion via the PC does not yield this effect. But the equivalent situation in living mice has not been investigated. We sought to determine whether AC versus PC perfusion of the living mouse eye may lead to different values for C. All experiments were conducted in C57BL/6J mice (all ♀) between the ages of 20 and 30 weeks. Mice were divided into groups of 3-4 animals each. In all groups, both eyes were perfused. C was measured in groups 1 and 2 by constant flow infusion (from a 50 μL microsyringe) via needle placement in the AC, and in the PC, respectively. To investigate the effect of ciliary muscle (CM) tone on C, groups 3 and 4 were perfused live via the AC or PC with tropicamide (muscarinic receptor antagonist) added to the perfusate at a concentration of 100 μM. To investigate immediate effect of euthanasia, groups 5 and 6 were perfused 15-30 min after death via the AC or PC. To investigate the effect of CM tone on C immediately following euthanasia, groups 7 and 8 were perfused 15-30 min after death via the AC or PC with tropicamide added to the perfusate at a concentration of 100 μM. C in Groups 1 (AC perfusion) and 2 (PC perfusion) was computed to be 19.5 ± 0.8 versus 21.0 ± 2.1 nL/min/mmHg, respectively (mean ± SEM, p > 0.4, not significantly different). In live animals in which tropicamide was present in the perfusate, C in Group 3 (AC perfusion) was significantly greater than C in Group 4 (PC perfusion) (22.0 ± 4.0 versus 14.0 ± 2.0 nL/min/mmHg, respectively, p = 0.0021). In animals immediately following death, C in groups 5 (AC perfusion) and 6 (PC perfusion) was computed to be 21.2 ± 2.0 versus 22.8 ± 1.4 nL/min/mmHg, respectively (mean ± SEM, p = 0.1196, not significantly different). In dead animals in which tropicamide was present in the perfusate, C in group 7 (AC perfusion) was greater than C in group 8 (PC perfusion) (20.6 ± 1.4 versus 14.2 ± 2.6 nL/min/mmHg, respectively, p < 0.0001). C in eyes in situ in living mice or euthanized animals within 15-30 min post mortem is not significantly different when measured via AC perfusion or PC perfusion. In eyes of live or freshly euthanized mice, C is greater when measured via AC versus PC perfusion when tropicamide (a mydriatic and cycloplegic agent) is present in the perfusate.

An In Vitro Perfusion System to Enhance Outflow Studies in Mouse Eyes

PURPOSE

The molecular mechanisms controlling aqueous humor (AQH) outflow and IOP need much further definition. The mouse is a powerful system for characterizing the mechanistic basis of AQH outflow. To enhance outflow studies in mice, we developed a perfusion system that is based on human anterior chamber perfusion culture systems. Our mouse system permits previously impractical experiments.

METHODS

We engineered a computer-controlled, pump-based perfusion system with a platform for mounting whole dissected mouse eyes (minus lens and iris, ∼45% of drainage tissue is perfused). We tested the system's ability to monitor outflow and tested the effects of the outflow-elevating drug, Y27632, a rho-associated protein kinase (ROCK) inhibitor. Finally, we tested the system's ability to detect genetically determined decreases in outflow by determining if deficiency of the candidate genes Nos3 and Cav1 alter outflow.

RESULTS

Using our system, the outflow facility (C) of C57BL/6J mouse eyes was found to range between 7.7 and 10.4 nl/minutes/mm Hg (corrected for whole eye). Our system readily detected a 74.4% Y27632-induced increase in C. The NOS3 inhibitor L-NG-nitroarginine methyl ester (L-NAME) and a Nos3 null mutation reduced C by 28.3% and 35.8%, respectively. Similarly, in Cav1 null eyes C was reduced by 47.8%.

CONCLUSIONS

We engineered a unique perfusion system that can accurately measure changes in C. We then used the system to show that NOS3 and CAV1 are key components of mechanism(s) controlling outflow.

Focus on molecular events in the anterior chamber leading to glaucoma

Primary open-angle glaucoma is a multifactorial disease that affects the retinal ganglion cells, but currently its therapy is to lower the eye pressure. This indicates a definite involvement of the trabecular meshwork, key region in the pathogenesis of glaucoma. This is the first target of glaucoma, and its functional complexity is a real challenge to search. Its functions are those to allow the outflow of aqueous humor and not the reflux. This article describes the morphological and functional changes that happen in anterior chamber. The "primus movens" is oxidative stress that affects trabecular meshwork, particularly its endothelial cells. In these develops a real mitochondriopaty. This leads to functional impotence, the trabecular meshwork altering both motility and cytoarchitecture. Its cells die by apoptosis, losing barrier functions and altering the aqueous humor outflow. All the morphological alterations occur that can be observed under a microscope. Intraocular pressure rises and the malfunctioning trabecular meshwork endotelial cells express proteins that completely alter the aqueous humor. This is a liquid whose functional proteomics complies with the conditions of the trabecular meshwork. Indeed, in glaucoma, it is possible detect the presence of proteins which testify to what occurs in the anterior chamber. There are six classes of proteins which confirm the vascular endothelium nature of the anterior chamber and are the result of the morphofunctional trabecular meshwork decay. It is possible that, all or in part, these proteins can be used as a signal to the posterior pole.

A contemporary concept of the blood-aqueous barrier

This review traces the evolution of the concept of the blood-aqueous barrier (BAB) during the past 20 years. The Classical model simply stipulated that the tight junctions of the iris vasculature and ciliary epithelium excluded plasma proteins from the aqueous humor (AH). It failed to reconcile the presence of AH protein levels equal to 1% of that found in plasma. Moreover, models of barrier kinetics assumed that the processes of AH secretion and plasma protein entry were directly linked. Thus, elevations of AH protein levels could only be explained by a pathological breakdown of the BAB. Over the last 20 years it has been shown that the plasma proteins in normal AH by-pass the posterior chamber entirely. Instead, these proteins diffuse from the capillaries of ciliary body stroma, into the iris stroma and then into the anterior chamber. This creates a reservoir of plasma-proteins in the iris stroma that is not derived from the iris vessels. This reservoir is prevented from diffusing posteriorly by tight junctions in the posterior iris epithelium. The one-way valve created by the pupil resting on the anterior lens capsule, combined with the continuous, forward flow of AH through the pupil, prevents protein reflux into the posterior chamber. Importantly, in the new paradigm, secretion of AH and the entry of plasma proteins into AH, are semi-independent events. This opens the possibility that AH protein levels could increase in the absence of breakdown of the BAB. Clinical consequences of this new paradigm of the BAB are discussed.

Relationship of aqueous outflow resistance to age and total volume perfused in rhesus and cynomolgus monkeys

PURPOSE

The effect of total volume perfused on outflow resistance (the reciprocal of outflow facility) and the effect of age on the rate of change in resistance as a function of total volume were determined in rhesus and cynomolgus monkeys.

METHODS

Outflow facility was measured under general anesthesia by two-level constant pressure perfusion in one eye of 22 rhesus and 17 cynomolgus monkeys (ranging in age, respectively, from 4 to 25 and from 3 to 12 years). Total volume perfused was calculated from data obtained during the perfusion.

RESULTS

Resistance decreased in both cynomolgus and rhesus monkeys as total volume perfused increased (-0.085 ± 0.021 and -0.022 ± 0.011 mm Hg/μL/min/μL(tot); P = 0.001 and P = 0.047, respectively). Rate of change in resistance significantly increased in cynomolgus monkeys as total volume perfused increased (0.0018 ± 0.0.0007 mm Hg/μL/min/μL(tot), P = 0.033); however, this was not the case in rhesus monkeys. After accounting for total volume perfused, the rate of change in resistance significantly decreased with increasing age in rhesus monkeys (-0.0068 ± 0.0026 [mm Hg/μL/min]/μL(tot)/y, P = 0.017). There was no significant difference in rate of change in resistance with age, after accounting for total volume, in the cynomolgus monkeys.

CONCLUSIONS

The present study supports previous findings indicating that total washout is largely dependent on perfusion volume. However, in populations with old/elderly animals, such as our rhesus group, we found that age does play a significant role in rate of change in resistance, and may be an even more important factor to consider in the rate of resistance change than volume perfused in aged animals.

Similar hydrodynamic and morphological changes in the aqueous humor outflow pathway after washout and Y27632 treatment in monkey eyes

Our previous studies in bovine eyes demonstrated that the structural correlate to the increase in outflow facility after either Rho-kinase inhibitor Y-27632 (Y27) treatment or washout appeared to be separation between the juxtacanalicular tissue (JCT) and inner wall (IW) of the aqueous plexus, the bovine equivalent of Schlemm's canal (SC). While these findings suggest that Y27 and washout may increase outflow facility through a similar mechanism, the anatomy of bovine outflow pathway differs considerably from both the human and monkey outflow pathway; however, only the human eye does not exhibit washout. In light of this, we compared the effects of Y27 and washout on outflow facility, hydrodynamic patterns of outflow, and the morphology of the IW and JCT in monkey eyes, given that their anatomy is closer to human eyes. Twelve freshly enucleated monkey eyes were used in this study. Eyes were perfused with Dulbecco's PBS containing 5.5 mM glucose (GPBS) to establish a baseline facility at 15 mmHg. Four eyes were perfused for a short-duration (30 min) as a control, 4 eyes for a long-duration (180 min) to induce washout, and 4 eyes with GPBS+50 μM Y27 for 30 min. All eyes were then perfused with fluorescent microspheres (0.5 μm; 0.002%) to label the hydrodynamic patterns of outflow and then perfusion-fixed. Confocal images of frontal sections were taken along the IW of SC. The total length (TL) and the tracer-decorated length (FL) of the IW were measured to calculate the average percent effective filtration length (PEFL = FL/TL). Sections with SC were examined by light and electron microscopy. The TL of the IW and the length exhibiting separation (SL) in the JCT were measured to calculate the average percent separation length (PSL = SL/TL). Outflow facility increased 149.2% (p < 0.01) from baseline after washout during long-duration perfusion, and 114.9% (p = 0.004) after Y27 treatment, but did not change significantly after short-duration perfusion in control eyes (p = 0.46). Distribution of the tracer labeling appeared punctate along the IW of control eyes, while a more uniform pattern was observed after washout and Y27 treatment. PEFL in washout (83.4 ± 2.1%) and Y27 treated eyes (82.5 ± 1.6%) was 3.4-fold larger compared to controls (24.2 ± 4.2%, P < 0.001). The JCT appeared distended with loss of connections between JCT cells and between JCT cells and their extracelluar matrix in eyes with washout or after Y-27 treatment. PSL in the JCT was 2.3-fold larger in washout eyes (77.4 ± 3.3%) and 2.2-fold larger in Y27 treated eyes (75.2 ± 5.3%) versus controls (33.5 ± 5.3%, p = 0.001). Significant positive correlations were found between outflow facility and PEFL, facility and PSL and between PEFL and PSL. Our data demonstrated that similar hydrodynamic and morphological changes occurred in the aqueous humor outflow pathway of monkey eyes after induction of washout and Y27 treatment. Both Y27 and washout increase outflow facility by redistributing aqueous outflow through a larger area in the JCT. These hydrodynamic changes are likely driven by morphologic changes associated with a decrease in cell-cell and cell-matrix connections in the JCT.

Outflow physiology of the mouse eye: pressure dependence and washout

PURPOSE

Mice are commonly used in glaucoma research, but relatively little is known about aqueous outflow dynamics in the species. To facilitate future use of the mouse as a model of aqueous humor outflow, several fundamental physiological parameters were measured in the mouse eye.

METHODS

Eyes from adult mice of either sex (C57BL/6 background) were enucleated, cannulated with a 33-gauge needle, and perfused at constant pressure while inflow was continuously measured.

RESULTS

At 8 mm Hg, total outflow facility (C(total)) was 0.022 ± 0.005 μL/min/mm Hg (all values mean ± SD; n = 21). The flow-pressure relationship was linear up to 35 mm Hg. The conventional outflow facility (C(conv)) was 0.0066 ± 0.0009 μL/min/mm Hg, and the unconventional outflow (F(u)) was 0.114 ± 0.019 μL/min, both measured at room temperature. At 8 mm Hg, 66% of the outflow was via the unconventional pathway. In a more than 2-hour-long perfusion at 8 mm Hg, the rate of facility change was 2.4% ± 5.4% (n = 11) of starting facility per hour. The ocular compliance (0.086 ± 0.017 μL/mm Hg; n = 5) was comparable to the compliance of the perfusion system (0.100 ± 0.004 μL/mm Hg).

CONCLUSIONS

Mouse eyes are similar to human eyes, in that they have no detectable washout rate and a linear pressure-flow relationship over a broad range of intraocular pressures. Because of the absence of washout and the apparent presence of a true Schlemm's canal, the mouse is a useful model for studying the physiology of the inner wall of Schlemm's canal and the conventional outflow tissues.

Relationships between increased aqueous outflow facility during washout with the changes in hydrodynamic pattern and morphology in bovine aqueous outflow pathways

Previous studies suggest that the structural correlate for the increased outflow facility (C) during washout in the bovine eye is separation between the inner wall (IW) and underlying juxtacanalicular connective tissue (JCT). However, how these structural changes affect hydrodynamic patterns of outflow during washout has not been studied. We hypothesize that an increase in the outflow facility during washout is associated with an increase in the effective filtration area (EFA) of aqueous outflow, which is regulated by a loss of the connectivity between the IW and JCT. To test this hypothesis, the relationship between C and the hydrodynamic patterns of outflow as well as the morphological changes in JCT and IW during the washout were investigated. Ten bovine eyes were perfused at 15 mmHg with Dulbecco's PBS + 5.5 mM glucose (DPBS) for 30 min to establish stable baseline C. After measuring baseline C, five eyes (short-duration group) were perfused with 0.5 mL DPBS containing 0.002% microspheres (0.5 microm) to trace the hydrodynamic pattern of outflow. Five other eyes (long-duration group) were perfused for 3 h to elicit a significant washout effect followed by subsequent perfusion of the same volume (0.5 mL) of microspheres to map out the outflow pattern after washout. All eyes were then perfusion-fixed. Anterior segments were sectioned and prepared for confocal and light microscopy. Total length (TL) and filtration length (FL) of the IW were measured in > or =15 images/eye to calculate percent effective filtration length (PEFL = FL/TL) while TL and length exhibiting JCT/IW separation (SL) were measured in > or =13 images/eye to calculate percent separation length (PSL = SL/TL). In long-duration eyes, C increased 170.5 +/- 21.3% (mean +/- SEM, 1.55 +/- 0.24 vs 4.13 +/- 0.55 microl/min/mmHg, p = 0.001) above baseline. Pre-fixation C (4.13 +/- 0.55 microl/min/mmHg) in long-duration was 1.6-fold greater than that (2.14 +/- 0.61 microl/min/mmHg; p = 0.042) in short-duration. A more uniform tracer labeling was observed in the JCT/IW of long-duration eyes compared to short-duration. PEFL was 2.3-fold larger (52.82 +/- 6.06 vs. 22.2 +/- 6.0%; p = 0.007) and PSL was 2.6-fold larger (54.2 +/- 6.0 vs. 20.5 +/- 1.3%; p = 0.004) in long-duration eyes compared to short-duration. Data from all eyes revealed a positive correlation between PEFL and PSL (p = 0.02). Both PEFL and PSL demonstrated significant positive correlations with the relative increase in C due to washout (p < or = 0.05). An additional experiment was performed in which unequal volumes of tracer (0.5 and 1.0 mL) were perfused in paired eyes for both short- and long-duration (N = 2 for each condition) to examine the affect on PEFL. No significant change in PEFL was found in eyes perfused with 0.5 and 1.0 mL within the same group. These data support our hypothesis that separations between the IW and JCT result in an increase in the EFA that then influences C. Altogether, these data suggest that outflow hydrodynamics and the tissue structure work together to regulate outflow resistance.

Direct effect of light on 24-h variation of aqueous humor protein concentration in Sprague-Dawley rats

Sprague-Dawley rats 10-12 weeks of age were entrained to a standard light-dark cycle with lights turned on at 6 am and off at 6 pm. Variations of 24-h aqueous humor protein concentration were determined. Samples were taken every 4h (N=10-14) under the standard light-dark condition at 8 pm, midnight, 4 am, 8 am, noon, and 4 pm. Under an acute constant dark condition, when lights were not turned on at 6 am, samples were collected at 8 am, noon, 4 pm, and 8 pm. Aqueous humor protein concentrations under the standard light-dark condition were found in the range of 0.305+/-0.115 mg/ml (mean+/-SD, N=10) at midnight to 1.505+/-0.342 mg/ml (N=14) at noon. The 3 light-phase protein concentrations were each higher than the 3 dark-phase concentrations. Aqueous humor protein concentrations at 8 am, noon, and 4 pm under the acute constant dark condition were each higher than the concentrations at 8 pm (after both 2h and 26 h in the dark), midnight, and 4 am, demonstrating an endogenously driven 24-h pattern. At 8 am, noon, and 4 pm, protein concentrations were 56-147% higher when exposed to light. Intraocular pressure (IOP) was monitored using telemetry in separate groups of light-dark entrained rats under the standard light-dark condition and the acute constant dark condition. The 24-h IOP pattern was inverse to the 24-h pattern of aqueous humor protein concentration under the standard light-dark condition, and this IOP pattern was not altered by the acute constant dark condition. In conclusion, an endogenously driven 24-h variation of aqueous humor protein concentration occurred in Sprague-Dawley rats with higher concentrations during the light-phase than the dark-phase. This endogenous pattern of protein concentration was accentuated by a direct effect of light, which was unrelated to the 24-h pattern of IOP.

Comparative studies between species that do and do not exhibit the washout effect

Ocular perfusion studies from all non-human species performed to date consistently demonstrate a perfusion-volume-dependent increase in aqueous outflow facility known as the "washout" effect. However, this "washout" effect does not occur in human eyes. We have recently documented that, in bovine eyes, the washout associated increase in facility correlates with the extent of physical separation between the juxtacanalicular connective tissue (JCT) and the inner wall endothelium lining the aqueous plexus (the bovine equivalent of Schlemm's canal). We hypothesize that if washout truly correlates with inner wall/JCT separation then this separation should not occur in human eyes that do not exhibit the washout effect, even after prolonged perfusion. Eight enucleated human and eight bovine eyes were used in this study. Aqueous humor outflow facility was measured at 15 mmHg for long-duration (3 h) or short-duration (30 min to 1 h) perfusion (n=4 for each group). All eyes were perfusion-fixed at 15 mmHg, and examined morphologically with both light and electron microscopy. In bovine eyes, outflow facility increased 81% (p=0.049) from 1.06 +/- 0.06 microl/min per mmHg (mean+/-SEM) at baseline to 1.92 +/- 0.30 microl/min per mmHg after 3 h due to washout. The pre-fixation outflow facility in long-duration eyes (1.92 +/- 0.30 microl/min per mmHg) was 2-fold greater than pre-fixation facility in short-duration eyes (0.92 +/- 0.11 microl/min per mmHg; p=0.0387). In human eyes, washout was not observed; baseline outflow facility was similar between both groups (0.18 +/- 0.02 vs. 0.25 +/- 0.08 microl/min per mmHg; p=0.518); however, pre-fixation outflow facility in long-duration eyes showed a 40% decrease compared to baseline outflow facility in those same eyes (p=0.017, paired Student's t-test). In bovine eyes, significant expansion and rarefaction of the JCT and inner wall/JCT separation was much more prevalent in long-duration eyes, and data from all bovine eyes revealed a correlation between the extent of inner wall/JCT separation and the absolute value of outflow facility measured immediately prior to fixation (p=0.0024) as well as the washout-induced increase in outflow facility (p=0.0006). In human eyes, no significant morphologic differences were observed between long- and short-duration perfusion, with no observed change in inner wall/JCT separation or expansion between the two groups. Morphologic analysis revealed that the previously described "cribriform plexus" of elastic-like fibers was far more extensive in the JCT of human eyes, appearing to form numerous connections to the inner wall endothelium. The cribriform plexus appears to function as a mechanical tether that maintains inner wall/JCT connectivity in human eyes by opposing hydrodynamic forces generated during perfusion, potentially explaining the lack of washout in humans.

Monkey organ-cultured anterior segments: technique and response to H-7

In the intact primate eye in vivo, it may be difficult to determine whether an outflow facility response is due to direct effects on the trabecular meshwork or indirectly via an effect on ciliary muscle tone unless complicated surgical ciliary muscle disinsertion or isotope accumulation procedures are used. We established a monkey anterior segment organ culture system modeled after the human anterior segment organ culture system and determined its characteristics and response to H-7, an agent shown to increase trabecular outflow in vivo and in other organ culture systems. Outflow facility studies conducted using the monkey organ-cultured anterior segment system showed that: baseline values were comparable to those measured in vivo; washout occurred with time; the two-level constant pressure perfusion technique gave results comparable to the constant rate technique; species differences were found comparing baseline outflow facility and intraocular pressure in rhesus and cynomolgus monkey organ-cultured anterior segments; there was no effect of age on outflow facility in either species by one-way ANOVA; anterior segment exchange perfusion increased outflow facility if measured within 1 hr of the exchange; the magnitude of the response to H-7 was comparable to those reported in vivo and in other in vitro systems. The onset of the response to H-7 was delayed in most cases (day after H-7 exchange), compared to in vivo monkey studies (onset 6-9 min) and in vitro human and porcine organ culture systems (within 1 hr). Also the duration of the response (2-3 days from the onset) was longer than that found for in vitro human studies (1 day). Thus, the monkey organ-cultured anterior segment system can be used to determine the effects of pharmacological and biological agents on trabecular outflow.

Distribution of thrombospondin-4 in the bovine eye

PURPOSE

The purpose of this study was to analyze the distribution of thrombospondin-4 (TSP-4) in the bovine eye.

METHODS

Anterior and posterior segments of the bovine eyes were sectioned and stained by the indirect immunofluorescence method with an anti-TSP-4 antibody. The tissues were analyzed by reverse-transcription-polymerase chain reaction (RT-PCR) to determine where the TSP-4 mRNA is produced.

RESULTS

Immunohistochemical staining for TSP-4 indicated the presence of TSP-4 in the cornea (epithelium, basement membrane, and keratocytes), conjunctiva (epithelium and stroma), aqueous ducts, sclera, iris (stroma), ciliary processes and muscle, trabecular meshwork, Bruch's membrane, retina, lamina cribrosa, and optic nerve, and in all blood vessel walls. TSP-4 mRNA was expressed by the cells in all structures.

CONCLUSIONS

TSP-4 is widely distributed in the bovine eye where it may play a role in the functions of basement membranes in various tissues. It is abundant in the trabecular and uveo-scleral pathways and may play a role in the regulation of aqueous outflow resistance.

Antithrombin III, a serpin family protease inhibitor, is a major heparin binding protein in porcine aqueous humor

Our hypothesis is that the proteins in aqueous humor may be involved in the regulation of outflow facility through the trabecular meshwork and uveoscleral meshwork. In this study, we analyzed the profile of heparin-binding proteins present in porcine aqueous humor to identify and characterize secretory proteins with a binding affinity for heparin. A single step involving heparin-sepharose affinity chromatography of porcine aqueous humor yielded a approximately 60 kDa protein as the major heparin-binding species. This protein was specifically eluted from the column by heparin. The N-terminal sequence and immunological cross reactivity of this protein confirmed its identity as antithrombin III. Aqueous humor from different species, as well as cells from human trabecular meshwork, Schlemm's canal, and lens epithelium, contained detectable amounts of antithrombin III. Based on its known anticoagulative function in endothelial cells and effects on the production of prostacyclin, it is reasonable to speculate that antithrombin III present in aqueous humor might influence the physiology of the trabecular and uveoscleral meshwork and thereby regulate intraocular pressure.

Micropurification of beta- and gamma-crystallins from rabbit aqueous humor

Soluble crystallins are normally present in the aqueous humor, originating from the lens, and their concentration may increase in certain conditions such as cataract, possibly contributing to aqueous outflow pathway obstruction, leading to glaucoma. Whether the stability and the tendency of aqueous crystallins to aggregate are different in patients with certain forms of open-angle glaucoma has not so far been established, mainly due to the lack of a suitable purification procedure from this fluid in which crystallins are present at very low concentration together with dozens of other proteins. About 4 microg each of beta- and gamma-crystallins were obtained from 20 ml of rabbit aqueous humor by C8 reversed-phase high-performance liquid chromatography (HPLC) and high-performance electrophoresis chromatography (HPEC). The identity of the proteins was confirmed by amino acid analysis following sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and electrophoretic blotting onto polyvinylidene fluoride membranes, with or without previous digestion with Staphylococcus aureus protease V8.