Kynurenic acid synthesis in bovine retinal slices--effect of glutamate agonists

The purpose of the present study was to investigate the effect of glutamate agonists upon kynurenic acid (KYNA) production in bovine retinal slices. Quantitative analysis of newly synthesized KYNA was carried out using an HPLC system and detected fluorimetrically. Glutamate at the concentration of 0.01, 0.1 and 1 mM reduced KYNA synthesis in the retinal slices to 70% (p < 0.05), 35% (p < 0.01) and 23% (p < 0.001), respectively. The concentration of glutamate reducing production of KYNA by 50% (IC(50)) was 0.035 mM (0.02-0.06). Aspartate at the concentration of 0.01, 0.1 and 1 mM lowered KYNA synthesis in the retinal slices to 80% (p < 0.01), 57% (p < 0.001) and 43% (p < 0.001), respectively. In contrast, kainic acid (up to 5 mM), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) (up to 1 mM) and 1-aminocyclopentane-trans-1,3-dicarboxylic acid (t-ACPD) (up to 3 mM) turned out to be ineffective in diminishing KYNA synthesis. These data demonstrate that glutamate, aspartate and N-methyl-D-aspartate (NMDA) inhibit KYNA synthesis in bovine retinal slices with different potency.

Presence of kynurenic acid and kynurenine aminotransferases in the inner retina

Kynurenine aminotransferases (KATs I and II) are pivotal to the synthesis of kynurenic acid (KYNA), the only known endogenous glutamate receptor antagonist and neuroprotectant. This study is the first to identify KYNA in the rat retina and to examine immunohistochemically the distribution of KAT isoforms. As determined by HPLC, KYNA concentration in the retina was 99.9 +/- 24.6 pmol/g wet wt. Immunohisto- chemical experiments showed that both KATs were present in the retina. KAT I was preferentially localised on Müller cell endfeet while KAT II was expressed in cells within the ganglion cell layer. In conclusion, KYNA is present and synthesised in the inner retina. This may suggest a modulatory role in glutamate-mediated retinal neurotransmission.

Evidence for intraocular synthesis of kynurenic acid, a putative endogenous neuroprotectant

Kynurenic acid (KYNA), an excitatory amino acid antagonist preferentially active at glycine binding site of the NMDA receptor, has been previously identified in the brain. This study was designed to examine its presence in the rabbit vitreous humor. Mean (+/- SD) level of KYNA in the vitreous was 22.3 +/- 3.9 pmol/ml as determined by HPLC. Intravitreal administration of 10 mmol aminooxyacetic acid (AOAA), a KYNA synthesis inhibitor, diminished its production by 9.6% after 2 h, 47.8% after 24 h and 21.5% after 48 h. It can be concluded that AOAA decreases the intravitreal concentration of KYNA, providing evidence of its intraocular origin.

[Evaluation and monitoring of selected inflammation patterns in uveitis using laser tyndallometry]

AIM

The purpose of the present study was to evaluate the degree of inflammation and to monitor the dynamics of the blood-aqueous barrier disruption in selected cases of uveitis using laser tyndalometry.

MATERIAL AND METHOD

Measurements with the use of laser tyndalometer (Kowa FM-500) were performed in 72 patients (90 eyes) with various types of uveitis. They were divided into four groups: anterior uveitis (28 eyes), intermediate uveitis (pars planitis) (28 eyes), posterior uveitis (26 eyes) and panuveitis (8 eyes). Aqueous flare values were expressed as photon counts per millisecond.

RESULTS

Tyndalometric mean values in control eyes were 4.8 +/- 1.0 ph/msec. Mean initial flare was pronounced in multifocal choroiditis and panuveitis--196.0 ph/msec, HLA-B27 positive acute anterior uveitis--145.4 ph/msec, and in acute herpes zoster anterior uveitis--52.4 ph/msec. It was mild to moderate in Fuchs uveitis syndrome--7.8 ph/msec, pars planitis--15.7 ph/msec, posterior uveitis in toxoplasmosis--6.8 ph/msec and toxocariasis--17.5 ph/msec. The potential of laser flare-meter for precise follow-up and adjustment of therapy was demonstrated in selected cases.

CONCLUSIONS

Laser tyndalometry has been proved to be a useful tool for the objective and quantitative evaluation of anterior chamber flare in uveitis and for monitoring the effectiveness of the treatment, thus improving therapeutic efficacy of uveitis.

[Clinical evaluation of isopropyl unoprostone (Rescula), in the adjunctive treatment of primary open angle glaucoma]

AIM

To investigate the clinical characteristics of docosanoid derivative, isopropyl unoprostone in the treatment of primary open angle glaucoma (POAG).

MATERIAL AND METHODS

In 17 patients (22 eyes) with POAG we analysed prospectively the effect of Rescula upon intraocular pressure, aqueous flare, pupil size, ocular signs and symptoms. Patients were followed up every 2 weeks for at least 8 weeks with complete ocular examination. Concomitant topical therapeutics were used in the study: 0.5% Timolol--group I (16 eyes), and 0.5% Timolol + 2% Dorzolamide--group II (6 eyes).

RESULTS

Mean (+/- SD) pretreatment pressure was 24.7 +/- 4.3 mm Hg in group I and it was reduced by 3.7 mm Hg (13.5%) (p < 0.05) at the end of the follow up. In group I Rescula was very effective (delta T% > 25%) in 6/16 eyes (37.5%) and it was ineffective (delta T% < 10%) in the same number of eyes. In group II pretreatment pressure was 24.8 +/- 2.6 mm Hg and it was reduced by 2.6 mm Hg (10.6%) (p = 0.1). Rescula induced no elevation of the aqueous flare during the treatment. No effect on pupil size was observed, either. Eye stinging/conjunctival hyperaemia was noted in 2/17 patients and punctate epitheliopathy in 1 patient (5.9%) that caused discontinuation of drops.

CONCLUSIONS

Unoprostone produced significant additive effect to Timolol. Thus, it may be a valuable option for adjunctive therapy. However, interindividual differences need to be considered, as in some patients the response was insignificant.

[Capsule contraction syndrome]

AIM

To analyse the occurrence of the anterior capsule contraction following cataract surgery. Capsule contraction syndrome (CCS) is defined as an extreme reduction in diameter of anterior capsulectomy, capsular bag diameter and, occasionally, displacement of the IOL after extracapsular cataract extraction. It is relatively frequent in pseudoexfoliation, advanced age, in association with uveitis, pars planitis and myotonic muscular dystrophy.

MATERIALS AND METHODS

5965 eyes of patients were operated on cataract between 1.01.1994 and 31.12.1997 in Tadeusz Krwawicz Chair of Ophthalmology and 1st Eye Hospital, Medical School in Lublin. Two types of surgical procedures were performed: "divide and conquer" phacoemulsification with 4.5-8 mm continuous curvilinear capsulorhexis (3385 eyes) and extracapsular cataract extraction with "can opener" capsulotomy (2580 eyes).

RESULTS

20 cases of clinically apparent CCS were referred to the Department: in the course of intensive postoperative inflammation--5, in patients over 80--4, in pseudoexfoliation syndrome--2, myotonic dystrophy--1, ectopia lentis--2, other causes--6. In order to improve visual acuity in 4 cases surgical removal of the distorted and opaque anterior capsule was performed, in 3 cases relaxing radial tears were done, in 3 cases secondary anterior capsulotomy was performed using Q-switched Nd:YAG laser.

CONCLUSIONS

In cases where the occurrence of CCS is especially high large diameter capsulorhexis should be performed and IOL designed to provide maximal peripheral capsular bag expansion should be implanted.

[Corneal astigmatism after trabeculectomy]

PURPOSE

The aim of the present study was to investigate the effect of conventional and mitomycin trabeculectomy on the corneal astigmatism.

SUBJECT AND METHODS

Measurements with the use of computer-assisted videokeratography (Eye-Sys) were performed in 34 glaucoma patients who underwent trabeculectomy. Color-coded topography maps were analyzed to obtain astigmatic data.

RESULTS

The mean surgically-induced astigmatism in conventional trabeculectomy group was 2.2 D and in the mitomycin group 4.0 D, 1 day post-op, 1.3 D and 3.0 D after 10 days and 0.4 D and 1.1 D after 3 months, respectively.

CONCLUSION

There was an apparent correlation between the amount of induced astigmatism and the use of mitomycin. This may be related to the impaired healing process of trabeculectomy wound and lower intraocular pressure in the mitomycin group.

[Changes of some physicochemical parameters of gas exchange in aqueous humor of rabbits during treatment of experimental uveitis]

PURPOSE

To evaluate the usefulness of some parameters of the aqueous humor: pH, pO2 (oxygen pressure), pCO2 (carbon dioxide pressure) and HCO3- concentration in the diagnosis of uveitis. Changes of these parameters following conventional treatment and cryotherapy have also been investigated.

MATERIAL AND METHOD

We used 40 grey rabbits (weighing 2.5-3.0 kg). Uveitis was evoked by intravitreal injection of 5 mg of animal albumin. Cryotherapy was performed by transconjunctival, quintuple cryoapplication (30 s) over ciliary body. Samples of aqueous humor were collected 6, 12, 24 and 48 hours after albumin injection. pH, pO2, pCO2 values and HCO3- concentration were determined using Astrup microanalyser.

RESULTS

Parameters of aqueous humor, especially pH, pCO2 and HCO3- turned out to be fairly sensitive indicators reflecting the natural history of experimental uveitis. Cryotherapy characteristically modulates the pH, pCO2 and HCO3- values in the anterior chamber.

CONCLUSIONS

We came to the conclusion that monitoring of these parameters may give some important information about the intensity of the course of uveitis and the influence of the treatment. Normalisation of the values usually parallels clinical improvement.

[Evaluation of astigmatism and blood-aqueous barrier breakdown following procedures in the anterior eye segment]

PURPOSE

The aim of this study was to evaluate the disruption of the blood-aqueous barrier (BAB) and the induced astigmatism following phacoemulsification, trabeculectomy and phacotrabeculectomy.

MATERIAL AND METHODS

141 eyes of patients who underwent different surgical procedures of the anterior segment were examined with the use of computer-assisted videokeratography. All maps were recorded preoperatively, and one and five days after surgery. We also applied a laser flare-meter in 41 eyes in order to quantify aqueous flare following these procedures.

RESULTS

The mean surgically-induced astigmatism following conventional trabeculectomy was 2.1 D and 1.4 D one and five days postoperatively, phacoemulsification with sutures 2.7 D and 1.9 D and phacotrabeculectomy 3.0 D and 2.4 D, respectively. Lower values of astigmatism obtained after sutureless phacoemulsification were 0.6 D and 0.3 D one and five days postoperatively, respectively (p < 0.05 vs Phaco+IOL+Trab. group, p < 0.01 vs other groups). It was found that aqueous flare values following phacotrabeculectomy were 58.0 photon counts/milisec.--one day, 39.3--3 days, 24.4--7 days, 20.4--10 days postoperatively. Significantly reduced values were observed after phacoemulsification--27.6 one day after surgery and 17.6--3 days later (p < 0.01 vs Phaco+IOL+Trab.group).

CONCLUSIONS

It could be concluded that induced astigmatism and the amount of inflammation were the highest after triple procedure and the lowest after phacoemulsification.

[Corneal topography of keratoconus]

PURPOSE

The present study was designed to evaluate the topography of a series of keratoconus patients.

SUBJECTS AND METHODS

Using a computer-assisted videokeratography (Eye Sys) we determined the topographic findings of 85 eyes of 46 consecutive patients with keratoconus. We analysed some quantitative topographic parameters like: power at the apex, central corneal power, the amount of irregular astigmatism, distance between the apex and the visual axis, difference in central corneal power between the two eyes of the same individual and steepening of the inferior cornea compared with the superior cornea.

RESULTS

Keratoconic topographic alterations were classified into two groups. Fifty seven of the cones (71%) could be described as peripheral with steepening of the cornea extending to the limbus. The remaining twenty three eyes (29%) had steepening confined to the central cornea. In many instances corneal topography was characterized by a high degree of nonsuperimposable mirror image symmetry (enantiomorphism) in the location of the topographic alterations between the two eyes of an individual patient. In all patients, irrespective of the topographic pattern, the inferior midperipheral cornea was steeper than superior cornea as quantified by an l-S value.

CONCLUSION

Study of the topography in keratoconus using this technique may prove useful for documenting the pattern of involvement of the anterior corneal surface and providing insight into the pathogenesis of this condition.

[Use of the laser-flare meter for early diagnosis of corneal graft rejection and for monitoring therapy]

AIM

The purpose of this study was to noninvasively quantify, with the use of a laser-flare meter, the alterations of the blood-aqueous barrier following penetrating keratoplasty. This could objectively indicate the disruption of this barrier in eyes with early allograft rejection, possibly even before the manifestation of the clinical signs, and would help to monitor the efficacy of the treatment.

MATERIAL AND METHODS

We used the laser flare-meter (Kowa FM-500) to investigate alterations of the blood-aqueous barrier following uncomplicated penetrating keratoplasty (PK) and in corneal allograft rejection. Examination was performed in 53 eyes of 50 patients after uncomplicated PK (7 days to 12 months after PK), in 20 normal control eyes and in 8 patients with acute allograft rejection before and during the treatment. The treatment consisted of systemic and topical administration of steroids and in some cases additionally topical immunosuppressants.

RESULTS

Mean flare values in the control eyes were 3.9 +/- 1.0 photon counts/ms. During the first two weeks after uncomplicated keratoplasty they were significantly increased (18.2 +/- 5.8) but were postoperatively slowly decreasing in time, nearly reaching the control values within 6-12 months. They were considerably higher in eyes with acute allograft rejection (34.0 +/- 13.1), but gradually diminished to 8.1 +/- 1.2 after successful treatment.

CONCLUSIONS

The application of laser flaremetry is useful in the follow-up of patients after perforating keratoplasty, especially after high risk grafts. The method helps to detect quantitatively early allograft rejection and is beneficial in monitoring the effectiveness of the treatment.

Influence of combined treatment with NMDA and non-NMDA receptor antagonists on electroconvulsions in mice

alpha-Amino-3-hydroxy-5-methyl-isoxazole-4-propionate/kainate (AMPA/kainate) receptor antagonists (at subthreshold doses against electroconvulsions), 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine (GYKI 52466 at maximally 5 mg/kg) and 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(F)quinoxaline (NBQX at maximally 20 mg/kg) enhanced the protective effects of NMDA receptor antagonists, MK-801 (dizocilpine) or 2-(2-carboxypiperazine-4-yl)-1-propenyl-1-phosphonic acid (D-CPP-ene), against electroconvulsions. Similarly, MK-801 or D-CPP-ene reduced the ED50 values of both NBQX and GYKI 52466 against maximal electroshock. The adverse effects of D-CPP-ene, evaluated in the chimney and rotorod tests, were potentiated by both GYKI 52466 (2.5 mg/kg) and NBQX (10 mg/kg). Also, D-CPP-ene (0.1 mg/kg) worsened the motor performance of mice pretreated with GYKI 52466 in the rotorod test. Neither MK-801 (0.025 mg/kg) nor D-CPP-ene (0.1 mg/kg) affected the NBQX-induced impairment of motor coordination. Similarly, GYKI 52466 (2.5 mg/kg) or NBQX (10 mg/kg) did not influence the performance of mice treated with MK-801 (0.2 mg/kg). It may be concluded that the blockade of more than one subtype of glutamate receptors leads to a more pronounced anticonvulsive effect when compared with the effect of blockade of an individual receptor subtype. In some cases more efficient seizure protection was not associated with increased adverse effects.

The competitive NMDA antagonist, D-CPP-ene, potentiates the anticonvulsant activity of conventional antiepileptics against maximal electroshock-induced seizures in mice

D-CPP-ene[3-(2-carboxy-piperazine-4-yl)-1-propenyl-1-phosphonic acid; a competitive antagonist of N-methyl-D-aspartic acid] in a dose of 2 mg/kg (i.p.) significantly increased the threshold for electroconvulsions. When given in a dose half that affecting the electroconvulsive threshold, D-CPP-ene potentiated the anticonvulsant activity of carbamazepine, diazepam, diphenylhydantoin, phenobarbital and valproate against maximal electroshock (50 mA)-induced seizures in mice. However, this NMDA antagonist did not influence the plasma levels of the antiepileptic drugs studied, so a pharmacokinetic interaction, in terms of total plasma levels at least, is not probable. The chimney test and retention test in mice revealed that the combined treatment of D-CPP-ene at 1.0 mg/kg (i.p.) with either diazepam, diphenylhydantoin, phenobarbital or valproate (providing a 50% protection against maximal electroshock convulsions) resulted in motor impairment and caused impairment of long-term memory. On the other hand, a combination of D-CPP-ene and carbamazepine was devoid of adverse effects. It can be concluded that the potential utility of D-CPP-ene in combination with conventional antiepileptic drugs does not seem promising, except for carbamazepine.

The NMDA antagonist procyclidine, but not ifenprodil, enhances the protective efficacy of common antiepileptics against maximal electroshock-induced seizures in mice

Procyclidine (up to 20 mg/kg i.p.) did not influence the electroconvulsive threshold per se, but when given in a dose of 10 mg/kg, it potentiated the protective activity of carbamazepine, diphenylhydantoin, phenobarbital and valproate, and in a dose of 20 mg/kg, that of diazepam against maximal electroshock-induced convulsions in mice. Ifenprodil increased the threshold for electroconvulsions when applied at 20 and 40 mg/kg (i.p.), but surprisingly, when combined with all antiepileptics tested, it did not influence their anticonvulsant actions. The chimney test in mice revealed, that application of procyclidine at 10 mg/kg together with phenobarbital and valproate, and procyclidine at 20 mg/kg with diazepam resulted in motor impairment. However, when procyclidine was applied at 10 mg/kg together with carbamazepine or diphenylhydantoin, no motor impairment was noted. The combined treatment of procyclidine (10 mg/kg) with carbamazepine, diphenylhydantoin, phenobarbital or valproate, as well as procyclidine (20 mg/kg) with diazepam caused significant worsening of long-term memory. Finally, procyclidine did not alter the total plasma levels of carbamazepine, diazepam, diphenylhydantoin, phenobarbital and valproate. It may be concluded that not all agents interfering with NMDA receptor complex-mediated events lead to the potentiation of the anticonvulsant activity of antiepileptic drugs.

2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(F)quinoxaline enhances the protective activity of common antiepileptic drugs against maximal electroshock-induced seizures in mice

NBQX (2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(F)quinoxaline), a novel and selective AMPA antagonist, was tested to evaluate its influence upon anticonvulsant activity of common antiepileptic drugs in mice. NBQX (10, 20, 40 mg/kg, i.p.) had no influence upon the threshold for electroconvulsions. NBQX (10 mg/kg) enhanced the activity of anticonvulsant drugs decreasing their ED50S against maximal electroshock from 321 to 190 mg/kg for valproate, from 19.5 to 14.5 mg/kg for carbamazepine, from 31.0 to 21.4 mg/kg for phenobarbital, from 17.8 to 9.5 mg/kg for diphenylhydantoin and from 19.5 to 10.5 mg/kg for diazepam. In addition, NBQX (10 mg/kg) failed to impair motor performance and long-term memory determined in the chimney test and passive avoidance task. The combinations of NBQX (10 mg/kg) and carbamazepine, diphenylhydantoin or phenobarbital resulted in no adverse effects. Diazepam (10.5 mg/kg) alone impaired the motor performance and long-term memory and so it did when combined with NBQX. Also retention of the passive avoidance task and motor performance were impaired by valproate alone or given together with NBQX. Finally, NBQX (10 mg/kg) did not affect the plasma level of any antiepileptic drug. It is concluded that non-NMDA glutamate receptor blockade results in the considerable enhancement of the efficacy of common antiepileptic drugs.