The epistatic interaction between the dopamine D3 receptor and dysbindin-1 modulates higher-order cognitive functions in mice and humans.

The dopamine D2 and D3 receptors are implicated in schizophrenia and its pharmacological treatments. These receptors undergo intracellular trafficking processes that are modulated by dysbindin-1 (Dys). Indeed, Dys variants alter cognitive responses to antipsychotic drugs through D2-mediated mechanisms. However, the mechanism by which Dys might selectively interfere with the D3 receptor subtype is unknown. Here, we revealed an interaction between functional genetic variants altering Dys and D3. Specifically, both in patients with schizophrenia and in genetically modified mice, concomitant reduction in D3 and Dys functionality was associated with improved executive and working memory abilities. This D3/Dys interaction produced a D2/D3 imbalance favoring increased D2 signaling in the prefrontal cortex (PFC) but not in the striatum. No epistatic effects on the clinical positive and negative syndrome scale (PANSS) scores were evident, while only marginal effects on sensorimotor gating, locomotor functions, and social behavior were observed in mice. This genetic interaction between D3 and Dys suggests the D2/D3 imbalance in the PFC as a target for patient stratification and procognitive treatments in schizophrenia.

Genetic blockade of the dopamine D3 receptor enhances hippocampal expression of PACAP and receptors and alters their cortical distribution.

Dopamine D3 receptors (D3Rs) are implicated in several aspects of cognition, but their role in aversive conditioning has only been marginally uncovered. Investigations have reported that blockade of D3Rs enhances the acquisition of fear memories, a phenomenon tightly linked to the neuropeptide pituitary adenylate cyclase-activating peptide (PACAP). However, the impact of D3R ablation on the PACAPergic system in regions critical for the formation of new memories remains unexplored. To address this issue, levels of PACAP and its receptors were compared in the hippocampus and cerebral cortex (CX) of mice devoid of functional D3Rs (D3R(-/-)) and wild-types (WTs) using a series of comparative immunohistochemical and biochemical analyses. Morphometric and stereological data revealed increased hippocampal area and volume in D3R(-/-) mice, and augmented neuronal density in CA1 and CA2/3 subfields. PACAP levels were increased in the hippocampus of D3R(-/-) mice. Expression of PACAP receptors was also heightened in mutant mice. In the CX, PACAP immunoreactivity (IR), was restricted to cortical layer V in WTs, but was distributed throughout layers IV-VI in D3R(-/-) mice, along with increased mRNAs, protein concentration and staining scores. Consistently, PAC1, VPAC1 and VPAC2 IRs were variably redistributed in CX, with a general upregulation in cortical layers II-IV in knockout animals. Our interpretation of these findings is that disturbed dopamine neurotransmission due to genetic D3R blockade may enhance the PACAP/PAC1-VPAC axis, a key endogenous system for the processing of fear memories. This could explain, at least in part, the facilitated acquisition and consolidation of aversive memories in D3R(-/-) mice.

Long-term efficacy of latanoprost in primary congenital glaucoma.

PURPOSE: To investigate the success (glaucoma control) of latanoprost therapy of primary congenital glaucoma (PCG) and factors affecting the long-term outcome. METHODS: Patients with PCG treated with latanoprost were re-examined. At study visit and from clinical charts, we evaluated: intraocular pressure, length of glaucoma control with latanoprost, need of further medication or glaucoma surgery, systemic and topical side effects. Multivariate analysis was used to test factors related to the final outcome of the treatment. RESULTS: Eighty-one eyes of 44 patients with PCG, and 42 eyes of 29 patients with previous glaucoma surgery, had received latanoprost therapy. In the first group, a success (glaucoma control by latanoprost therapy) was found in 24 eyes (29.6%), whereas 57 eyes (70.4%) had received surgery (45 eyes (55.6%) in the first year); among the eyes with previous surgery, a success was found in 12 eyes (28.6%), 13 eyes (31%) required an additional therapy, and 17 eyes (40.5%) had received further glaucoma surgery. No patient discontinued the treatment because of side effects. Factors related to the failure of the latanoprost treatment were: the high score of severity of glaucoma (P=0.014) and low age at PCG presentation (P=0.042). CONCLUSIONS: Long-term treatment with latanoprost is effective in about 30% of the eyes; factors related to failure were severe glaucomatous alterations, and young age at PCG presentation.

The PKCbeta/HuR/VEGF pathway in diabetic retinopathy.

We investigated whether the diabetes-related PKCbeta activation affects VEGF expression through the mRNA-stabilizing human embryonic lethal abnormal vision (ELAV) protein, HuR, in the retina of streptozotocin (STZ)-induced diabetic rats. Diabetes was induced in rats by STZ injection. Retinal tissues were processed to detect PKCbetaI, PKCbetaII, VEGF and HuR contents, as well as HuR phosphorylation. Immunoprecipitation coupled to RT-PCR was employed to evaluate HuR binding to VEGF mRNA in RiboNucleoProteic (RNP) complexes. Statistical analysis was performed by ANOVA followed by an appropriate post hoc comparison test. Following experimental diabetes PKCbetaI and PKCbetaII levels were increased compared to sham; there was also a PKC-mediated phosphorylation/activation of HuR. These effects were blunted by the in vivo co-administration of a selective PKCbeta inhibitor. A specific binding between the HuR protein and the VEGF mRNA was also detected. The PKCbeta/HuR activation was accompanied by enhanced VEGF protein expression that was, again, blunted by the PKCbeta inhibitor. These findings first demonstrate the activation, in the retina, of the PKCbeta/HuR/VEGF pathway following experimental diabetes and disclose a new potential pharmacological target to counteract pathologies implicating VEGF deregulation, such as diabetic retinopathy.

A water-soluble carbon monoxide-releasing molecule (CORM-3) lowers intraocular pressure in rabbits.

BACKGROUND: Carbon monoxide-releasing molecules (CORMs) are a novel group of substances that are capable of modulating physiological functions via the liberation of CO. AIMS: This study was undertaken to investigate the effects of CORM-3, a water-soluble CO-releasing agent, on two rabbit models of ocular hypertension. METHODS: Ocular hypertension was induced by injecting alpha-chymotrypsin in the rabbit eye. The dose-response effect of CORM-3 on IOP was assessed by topical administration of the drug (0.001, 0.01, 0.1 and 1%). Ocular hypertension was also obtained by weekly subconjunctival injection of betamethasone, and animals were treated topically with CORM-3. A group of animals in both models was treated with the inactive form of the drug (iCORM-3). RESULTS: CORM-3 induced a dose-dependent reduction in IOP in rabbits treated with alpha-chymotrypsin. A similar reduction in IOP was observed in rabbits with betamethasone-induced ocular hypertension treated with the drug. Treatment with the iCORM-3 had no effect on IOP in both models. CONCLUSIONS: Treatment with CORM-3 is associated with a reduction in IOP in two different rabbit models of ocular hypertension. These results support previous findings on the effect of haem oxygenase-derived CO on IOP and suggest a direct involvement of CO system in the regulation of ocular pressure probably through the modulation of aqueous humour dynamics.

Evaluation of cell tolerability of a series of lipoamino acids using biological membranes and a biomembrane model.

The interaction of a series of amphiphilic 2-alkyl aminoacids (lipoamino acids, LAAs) with different cell cultures and biomembrane models was investigated. LAAs can be useful promoieties to modify the physico-chemical properties of many drugs, and in particular their lipophilicity. Tests were performed in vitro on mammalian cells (murine astrocytes) and human red blood cells (haemolysis), and in vivo on rabbit eye as alternative models to assess the tolerability or the potential damaging effects of these compounds on different biological systems. The mode of interaction of LAAs with pure phospholipid multilamellar liposomes, taken as a biomembrane model, was also analysed by differential scanning calorimetry experiments. Different tolerability/toxicity patterns were obtained in the various models; in particular, the most lipophilic terms of the series, methyl 2-aminohexadecanoate (LAA16), displayed haemolytic activity and toxicity for mouse astrocyte cultures. A specific assay confirmed that LAA16 acted at level of cell membranes, while neither any damaging effects on nucleus or apoptotic induction were observed. The shorter-chain LAAs and the tetradecyl homologue (LAA14) showed the best compatibility with the various cell models.

Enhancement of availability of cloricromene at brain level by a lipophilic prodrug.

The pharmacokinetics of a lipophilic alkylamino acid (LAA) prodrug of cloricromene (AD6), name CLOR-C4, was studied in rat plasma and brain. In particular, we observed that the intraperitoneal administration of CLOR-C4 to rats was able to provide a slight but statistically significant higher concentration of the active drug metabolite (cloricromene acid) in the brain compared with the parent drug administered by the same way. The correlation between pharmacokinetic data and calculated partition (LogP) and brain distribution coefficients (LogBB) supported the hypothesis that the amphiphilic nature of the LAA promoiety could be responsible for a better penetration into the brain, more than the simple increase of lipophilicity gained with respect to the parent drug.

Enhancer effects on in vitro corneal permeation of timolol and acyclovir.

The aim of this study was to evaluate the ability of two non-toxic skin penetration enhancers, N-methylpyrrolidone (NMP) and a positively charged phospholipid mixture (PS), to increase in vitro corneal permeation of timolol maleate (TM) and acyclovir (AC) in comparison with two corneal absorption promoters, polyethylene glycol octadecyl ether (Brij 78) and sodium taurocholate (TA). In vitro experiments were performed on corneas from albino rabbits which were mounted in a perfusion apparatus. The concentrations of the enhancers being tested were: Brij 78 1%, PS 1%, TA 1%, NMP 5%, NMP 10%. The safety of the enhancers being tested was assessed in vitro by determining their effects on corneal hydration and in vivo by means of a modified Draize test. Calculating the amount of drug permeated at different time points (90 and 180 min) we observed that TA, PS and NMP 5% significantly increased the cumulative amount of AC permeated after 90 min but only PS was effective after 180 min. TA, Brij 78 and PS were able to increase significantly the amount of TM permeated after 90 min but after 180 min only Brij 78 retained its effect. TA, Brij 78 and NMP 10% significantly increased the percent hydration levels (% HL) compared to the control while PS and NMP 5% did not affect % HL. The results of in vivo ocular tolerability studies showed that the enhancers which caused an in vitro increase of % HL produced in vivo conjunctival and/or corneal damages. The results of this study suggest that PS could be regarded as a potential corneal enhancer to increase the intraocular bioavailability of AC and TM.

Ocular tolerability of Eudragit RS100 and RL100 nanosuspensions as carriers for ophthalmic controlled drug delivery.

Polymeric nanoparticle suspensions were prepared from inert polymer resins (Eudragit RS100, RS, and RL100, RL). When loaded with drugs, these resins have been recently proposed as delivery systems to prolong the release and improve ocular availability of the drug. To verify the absence of toxicity toward the ocular structures, blank RS and RL nanosuspensions were applied to rabbit eye and a modified Draize test was performed. Polymer nanoparticles appeared to be avoiding of any irritant effect on cornea, iris, and conjunctiva up to 24 h after application, thus appearing to be a suitable inert carrier for ophthalmic drug delivery.

Flurbiprofen-loaded acrylate polymer nanosuspensions for ophthalmic application.

Polymeric nanoparticle suspensions were prepared from Eudragit RS100R and RL100R polymer resins and loaded with flurbiprofen (FLU), with the aim at improving the availability of the drug at an intra-ocular level for the prevention of the myosis induced during extracapsular cataract surgery. Nanosuspensions were prepared by a quasi-emulsion solvent diffusion technique using different formulation parameters (drug-to-polymer ratio, initial polymer concentration, agitation speed, etc.). The resulting nanoparticles showed mean sizes around 100 nm and a fixed positive charge (zeta-potential around +40/+60 mV). Stability tests after mid-time storage (4 degrees C or room temperature) or freeze-drying were carried out to optimise a possible final pharmaceutical preparation. In vitro, dissolution tests showed a controlled release profile of FLU from the nanoparticles. In vivo anti-inflammatory efficacy was assessed in the rabbit eye after induction of an ocular trauma (paracentesis). FLU-loaded nanosuspensions did not show toxicity on ocular tissues. Moreover, an inhibition of the miotic response to the surgical trauma comparable to a control eye-drop formulation was obtained, even though an actual lower concentration of free drug in the conjunctival sac was achieved from the nanoparticle system. Drug levels in the aqueous humour were also higher after application of the nanosuspensions.

Biocompatibility and biodegradation of intravitreal hyaluronan implants in rabbits.

To study the biocompatibility and the biodegradation rate in vivo of new intravitreal implants made with three different hyaluronic acid esters: Hyaff7, Hyaff11 and Hyaff11p75 (100% ethyl ester, 100 and 75% benzyl esters, respectively), the plugs were implanted through a sclerotomy at 3.5 mm from the limbus of rabbit eyes. In order to evaluate the in vivo biodegradation the shaft diameter of the plugs was measured by ultrasound biomicroscopy. Slit lamp microscopy, ophthalmoscopy and ERG were performed periodically. The effects of the implants on ocular tissues were also evaluated histologically. All the plugs showed a good biocompatibilitv. Plugs of both the total esters, Hyaff7 and Hyaff11, were found to undergo a slow dissolution process for 60 and 150 days, respectively. The partial benzyl ester, Hyaff11p75, was completely reabsorbed after 15 days. Analysis of variance showed a high correlation between biodegradation rate and the time of resorption (F = 90.5; p < 0.001). The biodegradation rate of each implant is related to the chemical structure of the three types of Hyaff (F = 4.51; p = 0.005). The present data suggest that intravitreal implants based on hyaluronic acid esters represent useful biocompatible and biodegradable devices for a potential drug delivery system in the treatment of posterior segment ocular diseases.

Ocular tolerability and in vivo bioavailability of poly(ethylene glycol) (PEG)-coated polyethyl-2-cyanoacrylate nanosphere-encapsulated acyclovir.

Acyclovir-loaded polyethyl-2-cyanoacrylate (PECA) nanospheres were prepared by an emulsion polymerization process in the micellar phase and characterized. The influence of the presence of nonionic surfactant as well as other substances [i.e., 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CyD) and poly(ethylene glycol) (PEG)], on formulation parameters and loading capacity was investigated. In particular, the presence of PEG resulted in an increase of mean size and size distribution. To obtain PEG-coated PECA nanospheres with a mean size of < 200 nm, Pluronic F68 at concentrations > 1.5% (w/v) should be used during preparation. The presence of PEG also resulted in a change in zeta potential, from -25.9 mV for uncoated nanospheres to -12.2 mV for PEG-coated PECA nanospheres. The presence of HP-beta-CyD elicited an increase of nanosphere size and size distribution, but zeta potential was not influenced. In vitro drug release from nanospheres was determined in both phosphate buffer (pH 7.4) and plasma. The presence of HP-beta-CyD and PEG did not influence the acyclovir release rate in plasma. In the case of release in phosphate buffer, PEG-coated nanospheres showed a slower release. Ocular tolerability of PEG-coated PECA nanospheres was evaluated by the in vivo Draize test. This colloidal carrier was well tolerated, eliciting no particular inflammation at the level of the various ocular structures. In vivo ocular bioavailability was evaluated by instilling 50 microL of the acyclovir-loaded nanospheres only once in the conjunctival sac of rabbit eyes. At various time intervals, aqueous humour acyclovir content was determined by high-performance liquid chromatography. Acyclovir-loaded PEG-coated PECA nanospheres were compared with an aqueous solution of the drug and a physical mixture of acyclovir nanospheres. The acyclovir-loaded PEG-coated PECA nanospheres showed a significant (p < 0.001) increase of drug levels (25-fold) in aqueous humor compared with the free drug or the physical mixture. This finding is probably due to an improved ocular mucoadhesion of PEG-coated PECA nanospheres.

Pharmacological profile of a new topical pilocarpine formulation.

A new formulation based on pilocarpine hyaluronate salt has been shown to improve the bioavailability of the drug and to extend the duration of activity. We evaluated the extent of intraocular pressure reduction, the duration of action and the kinetics of miotic response of this formulation in comparison with a commercial preparation with the same drug concentration. Ocular hypertension in the rabbit was induced by alpha-chymotrypsin or by water loading. The hypotensive effect of the new formulation treatment was significantly greater and longer than that observed in rabbit eyes treated with the commercial preparation both in the normotensive and in the hypertensive animals. Furthermore, we evaluated the miotic response in normotensive rabbits showing a greater miotic response and an extended duration when the eyes were treated with the new formulation. The pharmacological profile of the new formulation described in this study indicates an increase of efficacy and duration of action compared to the commercial preparation.

Characterization and in-vivo ocular absorption of liposome-encapsulated acyclovir.

The potential of liposomes as an in-vivo ophthalmic drug delivery system for acyclovir was investigated. The drug-membrane interaction was evaluated by means of differential scanning calorimetry analysis. These experiments showed that acyclovir is able to interact with both positively and negatively charged membranes via electrostatic or hydrogen bonds. No interaction was observed with neutral membranes made up of dipalmitoylphosphatidylcholine. Different liposome preparation procedures were carried out to encapsulate acyclovir. The drug encapsulation mainly depends on the amount of water which the liposome system is able to entrap. In the case of multilamellar vesicles, charged systems showed the highest encapsulation efficiency. No particular difference in the encapsulation efficiency was observed for oligolamellar vesicles prepared with the reverse-phase evaporation technique. Oligolamellar liposomes showed the highest acyclovir encapsulation parameters and had release profiles similar to those of multilamellar liposomes. In-vivo experiments using male New Zealand albino rabbits were carried out to evaluate the aqueous humour concentration of acyclovir bioavailability. The most suitable ophthalmic drug delivery system was oligolamellar systems made up of dipalmitoylphosphatidylcholine-cholesterol-dimethyldioctadecyl glycerole bromide (7:4:1 molar ratio), which presented the highest encapsulation capacity and were able to deliver greater amounts of the drug into the aqueous humour than a saline acyclovir solution or a physical liposome/drug blend.

Sigma1 recognition sites in rabbit iris-ciliary body: topical sigma1-site agonists lower intraocular pressure.

In this study, we examined the presence of sigma1 and sigma2 sites in the rabbit iris-ciliary body by receptor binding and investigated their effects on intraocular pressure (IOP) in albino rabbits. The iris-ciliary body has binding sites for the sigma1-site agonist [3H](+)-pentazocine (Kd = 4.6 nM; Bmax = 212 fmol/mg protein) and sigma2 sites labeled with [3H]1,3-di-o-tolylguanidine (DTG) (Kd = 8. 2 nM; Bmax = 1120 fmol/mg protein). In competition binding studies, (+)-pentazocine and the sigma antagonist NE-100 displayed high affinity for sigma1 sites (Ki = 2.1 and 2.4 nM, respectively), whereas (+)-N-allylnormetazocine (NANM) was less potent (Ki = 178 nM). Unilateral topical (+)-pentazocine (0.01-0.1%) caused a significant dose-related reduction of IOP in ocular normotensive rabbits and in the alpha-chymotrypsin model of ocular hypertension. (+)-NANM was less potent than (+)-pentazocine. Neither compound altered the IOP of the contralateral eye, and their hypotensive activity was blocked by NE-100 that, by itself, had no effect on IOP. (-)-Pentazocine, (-)-NANM, and DTG had no effect on IOP. DTG prevented the hypotensive effect of (+)-pentazocine, suggesting that it acts as a sigma1-site antagonist. sigma-Site ligands did not affect pupil diameter or cause ocular inflammation. Topical [3H](+)-pentazocine reaches the intraocular tissues within 30 min, and its uptake in the iris-ciliary body and retina was significantly reduced by topical pretreatment with NE-100, as expected for a receptor-specific agent. Reverse-phase HPLC confirmed the presence of intact (+)-pentazocine in iris-ciliary body homogenates. sigma1-Site agonists may offer a novel class of agents potentially effective in the control of ocular hypertension.

Pharmacological evaluation of a new timolol/pilocarpine formulation.

A new formulation (HYA) based on timolol hyaluronate and pilocarpine hyaluronate salts has been shown to improve the bioavailability of the drugs and to extend the duration of their action. Extent of the intraocular pressure lowering effect, duration of action and aqueous bioavailability of timolol and pilocarpine of HYA were compared with a commercial preparation. Ocular hypertension in the rabbit was induced by alpha-chymotrypsin or by water loading. The hypotensive effect of HYA treatment was significantly greater and longer than that observed in rabbit eyes treated with the commercial preparation both in the normotensive and in the hypertensive animals. Furthermore, we evaluated the miotic response; due to pilocarpine, normotensive rabbits showed a greater miotic response and an extended duration when the eyes were treated with HYA. The new formulation increased the aqueous availability of timolol and pilocarpine compared to the commercial preparation as determined by HPLC. The pharmacodynamic and pharmacokinetic profiles of HYA indicate an increase in efficacy and duration of action along with an increase in bioavailability of timolol and pilocarpine in comparison with the commercial preparation.

Pharmacological evaluation of anti-inflammatory pyrrole-acetic acid derivative eye drops.

The effects of mucoadhesive eye drops containing a pyrrole-acetic acid derivative (tolmetin) at 0.5% concentration on ocular inflammation produced by sodium arachidonate in the rabbit's eye were evaluated. Furthermore, the bioavailability of the mucoadhesive formulation in the aqueous humor against an aqueous-based solution was compared. Tolmetin eye drops significantly reduced the signs of ocular inflammation elicited by sodium arachidonate on conjunctiva and iris. Tolmetin treatment significantly reduced the levels of prostaglandin E2, polymorphonuclear leukocytes and protein concentration in aqueous samples obtained from the eyes treated with arachidonate. The de novo production of prostaglandin E2 by corneas obtained from rabbits sacrificed 2 hours after arachidonate instillation were significantly higher in samples taken from controls than in corneas obtained from the eyes treated with tolmetin eye drops. Furthermore, the drug treatment significantly reduced the rise in intraocular pressure arachidonate-induced. The mucoadhesive formulation showed a higher bioavailability in aqueous humor compared to the aqueous-based solution both in the uninflamed and in the inflamed rabbit eyes.

Methylprednisolone delivery by Hyalobend corneal shields and its effects on rabbit ocular inflammation.

Release of methylprednisolone from hyaluronic acid derivative corneal shields (Hyalobend), in vitro and in vivo, was evaluated as well as ocular anti-inflammatory activity in the rabbit eye. The release of methylprednisolone from Hyalobend corneal shields in vitro followed zero-order kinetics. After placing Hyalobend corneal shields in rabbit eye, aqueous and tear fluid methylprednisolone levels were detected up to 48 hours and compared with the levels obtained with methylprednisolone suspension. Hyalobend corneal shields maintained almost constant methylprednisolone levels in the rabbit tear fluid. On the contrary, the suspension gave very high tear values of steroid concentrations in the first 30 minutes but undetectable in less than 200 minutes. Hyalobend corneal shields ensured effective levels of methylprednisolone into the rabbit aqueous for up to 48 hours. Aqueous levels of drug, in the group treated with the suspension, decreased progressively and after 480 minutes were undetectable. Hyalobend corneal shields significantly reduced the conjunctival inflammation elicited by sodium arachidonate compared with control. Furthermore, Hyalobend corneal shields treatment significantly reduced the levels of PGE2 in the tear fluid. Hyalobend corneal shields increase the residence time of methylprednisolone in rabbit tear fluid and enhance the penetration into the aqueous humor as well as reduced the primary signs of ocular inflammation.

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.

The effect of ganglioside on oxidation-induced permeability changes in lens and in epithelial cells of lens and retina.

Several recent reports have indicated that ganglioside treatment both in vivo and in vitro has a protective effect on the loss of membrane permeability resulting from inhibition of transport enzyme(s) in different experimental models. In this study we have investigated the effect of monosialoganglioside on oxidation-induced changes in organ-cultured rabbit lenses and in cultured dog lens epithelium and human retinal pigment epithelial cells. Exposure of organ-cultured lenses to 0.5 mM hydrogen peroxide for 1 hr increased the efflux of 86Rb from intact lenses and loss of myoinositol from the capsule epithelium. Pretreatment of the lenses with monosialoganglioside significantly reduced the efflux rate of 86Rb and loss of myoinositol. Monosialoganglioside also prevented morphological changes induced by 0.1 mM hydrogen peroxide in dog lens epithelium and loss of cell viability caused by docosahexaenoic acid in dog lens epithelium and in human retinal pigment epithelial cells. In contrast to the protective effect of monosialoganglioside on permeability and morphological changes in cultured cells, it had no effect against single-strand breaks of DNA in dog lens epithelium resulting from exposure to hydrogen peroxide, X-ray and UV-B radiation. Although the molecular mechanisms by which monosialoganglioside prevents permeability and morphological changes induced by hydrogen peroxide and docosahexaenoic acid are not known, it appears that this ganglioside serves as a membrane stabilizer rather than as a free-radical scavenger.