The role of platelets in blood-aqueous barrier breakdown induced by anterior chamber paracentesis in the rabbit

Expression of alphasmooth muscle actin in lens epithelia from human donors and cataract patients

In order to re-evaluate functional implications of alphasmooth muscle actin (alphaSMA) expression in lens epithelial cells (LECs), we assessed its presence in donor lenses without visible opacities (DON), lenses with mature cataract (CAT), and cataractous lenses with posterior subcapsular opacities (PSO) or anterior subcapsular fibrosis (ASF). The levels of alphaSMA and transforming growth factor-beta2 (TGFbeta2) mRNAs were measured by classical and real-time PCR. Expression and structural organisation of alphaSMA protein and beta-catenin were monitored by Western blotting and confocal microscopy. All DON analysed contained measurable amounts of alphaSMA mRNA. In CAT without and with PSO, mRNA expression was increased and, again more than doubled in ASF. TGFbeta2 mRNA expression varied widely between the individual samples but was slightly increased in ASF. No correlation existed between alphaSMA or TGFbeta2 expression and the age of the donors in any of the lens categories. Confocal microscopy revealed that, in DON and CAT, alphaSMA was preferentially expressed in a simple granular pattern in single or small clusters of LECs within a normally shaped cobblestone epithelium. Locally, the granules were merged into short stretches at the cell margin. In CAT, a few abnormally shaped cells contained polygonal alphaSMA structures and short stress fibres. In CAT with PSO and ASF, polygons and stress fibre bundles predominated in spindle-shaped cells. Expression patterns of different complexity were often present in the same epithelium. Apical polygons and basal stress fibres were detected within the same cell and may reflect instability of the interface between epithelium and cortical fibres and changes in adhesion to the capsule, respectively. High levels of betacatenin mRNA and protein were present in all lens types. However, with increasing complexity of alphaSMA organisation, betacatenin staining disappeared from the cell margin and basal infoldings and was shifted towards the cytoplasm and nucleus. The presence of alphaSMA in DON, the absence of any correlation between mRNA level and age, and the modest increase in complexity of alphaSMA-containing structures in CAT argue against an inevitable link between alphaSMA expression and the development of age-related cataract. Low levels of alphaSMA expression may reflect repair of normal wear and tear. In pathologic situations such as PSO and ASF, persisting stimulation and additional incentives may induce increased alphaSMA expression and more elaborate patterning, eventually leading to completion of EMT.

Lack of correlation between intraocular inflammation and after-cataract formation in the rabbit eye

PURPOSE

To determine whether an increased or reduced inflammatory response following cataract surgery influences the development of after-cataract.

SETTING

Department of Preclinical Ophthalmology, Pharmacia, Uppsala, Sweden.

METHODS

Rabbits that had had cataract surgery were given endotoxin, ovalbumin, dexamethasone, or diclofenac. Aqueous humor, leukocytes, and prostaglandin E(2) (PGE(2)) were analyzed, and the wet weight of the after-cataract was determined.

RESULTS

The wet weight of the after-cataract was unaffected by endotoxin and 67% lower in the eyes treated with ovalbumin than in the control eyes on day 56. Aqueous humor concentrations of leukocytes and PGE(2) were 94% and 87% lower in the group treated with dexamethasone than in the control group on day 7, and the concentration of PGE(2) was 98% lower in the diclofenac group; however, the wet weight of the after-cataract was unaffected by both treatments.

CONCLUSION

This study suggests that an increased inflammatory response does not increase the development of after-cataract and a reduction in the inflammatory response does not reduce the development of after-cataract.

Microdialysis evaluation of the ocular pharmacokinetics of propranolol in the conscious rabbit

PURPOSE

This study was conducted to assess the effects of anesthesia and aqueous humor protein concentrations on ocular disposition of propranolol.

METHODS

Rabbits were anesthetized and a microdialysis probe was inserted into the anterior chamber of one eye; the contralateral eye served as a control. At timed intervals after probe placement, a 100-microl sample of aqueous humor was aspirated from each eye to determine protein concentration. In vitro protein binding parameters were used to simulate the impact of protein concentration on propranolol disposition. To assess the influence of anesthesia, probes were implanted in the anterior chamber of each eye. After >5-day stabilization, conscious and anesthetized rabbits (n = 3/group) received a 200-microg topical dose of [3H]DL-propranolol in each eye; propranolol was assayed in probe effluent.

RESULTS

Changes in aqueous humor protein concentrations were observed following probe insertion. Simulations demonstrated that the unbound propranolol AUC (approximately 2.4-fold) in aqueous humor should be reduced due to protein influx. Intraocular propranolol exposure in anesthetized rabbits was approximately 8-fold higher than in conscious rabbits, and approximately 1.9-fold higher than in rabbits without a post-surgical recovery period.

CONCLUSIONS

Anesthesia and time-dependent aqueous humor protein concentrations may alter ocular pharmacokinetics, and must be taken into account in the design of microdialysis experiments.

Effect of sodium naproxen on inflammatory response induced by anterior chamber paracentesis in the rabbit

This study evaluated the effect of sodium naproxen (a reversible competitive inhibitor of cyclo-oxygenase) and phenylephrine (a mydriatic alpha-adrenergic agent) eye drops in maintaining atropine mydriasis in the rabbit after paracentesis. Moreover, to assess the influence of these treatments on vascular and cellular inflammatory responses in the rabbit eye, several biochemical parameters were considered. Anterior chamber paracentesis significantly reduced atropine-induced mydriasis and a parallel elevation of proteins, polymorphonuclear leucocytes (PMNs), prostaglandin E2 (PGE2) and leukotriene B4 (LTB4) levels in the secondary aqueous humour (obtained 120 min later) was observed. A significant increase in PMNs in the aqueous humour and a parallel increase in myeloperoxidase activity, a measure of PMN infiltration, in the iris-ciliary body were detected. Atropine-induced mydriasis was maintained in rabbits treated with either sodium naproxen or phenylephrine eye drops. However, only in the former group were the inflammatory parameters significantly reduced, with the exception of aqueous LTB4 levels. The inhibition of the protein influx in the aqueous humour and of the miosis produced by sodium naproxen can be related to the high drug levels in the aqueous humour that were effective in inhibiting the cyclo-oxygenase pathway of arachidonic acid metabolism, whereas the effects on PMN infiltration appear to be independent of significant release of the potent chemotactic agent LTB4, synthesized via the 5-lipoxygenase pathway.

Intracamerally injected platelet activating factor (PAF) induces marked intraocular inflammatory reactions

An inflammatory response was elicited in the rabbit eye by intracameral injection of platelet activating factor (PAF). PAF induced severe aqueous flare, corneal edema, pupillary constriction and marked biphasic changes in intraocular pressure (IOP) in a dose-dependent manner. All of the responses to PAF were inhibited by the PAF receptor antagonist, BN 52021 (20 mg/kg, i.p.). The cyclooxygenase inhibitor, indomethacin (30 mg/kg, i.p.) caused significant inhibition of the early phase PAF-induced aqueous flare, pupillary constriction and intraocular hypertension, but did not effect PAF-induced corneal edema or intraocular hypotension. NDGA (10 mg/kg, i.p.), a lipoxygenase inhibitor, did not inhibit the inflammatory effects of PAF. PAF-induced chemotactic response was evaluated by tissue chemiluminescence. Intracamerally injected PAF did not significantly increase chemiluminescence in cornea or iris-ciliary body, but intracorneal injection of PAF did cause a chemotactic response in both the conjunctiva and cornea. These data suggest that PAF may be an important mediator of intraocular inflammation and that some PAF-induced effects are prostaglandin dependent, while others may be independent of eicosanoid synthesis and release.

d-Ibuprofen in ocular inflammation induced by paracentesis of the rabbit eye

The anti-inflammatory compound d-ibuprofen has been investigated for anti-inflammatory and cyclooxygenase inhibitory activity in ocular inflammation induced by paracentesis of eyes of living rabbits. d-Ibuprofen is the dextro-rotary isomer of ibuprofen, a potent non-steroidal anti-inflammatory agent. Eyes pretreated topically with d-ibuprofen 0.8% showed a significant inhibition of aqueous protein (73.0%) and prostaglandin E2 (96.4%) increase after paracentesis as compared to paracentesized untreated fellow eyes and control eyes. In aqueous humor no significant correlation between the increase in prostaglandin E2 and protein could be established after paracentesis. These results indicate that d-ibuprofen could be a useful ocular anti-inflammatory agent as cyclooxygenase inhibitor.