J.L. van Delft

CO oxidation over promoted Pt catalysts

Abstract A study of CO oxidation by O2 over Pt catalysts, promoted by MnOx and CoOx, is described. The activities of Pt/SiO2, Pt/MnOx/SiO2 and Pt/CoOx/SiO2 are compared with commercial Pt/Al2O3, Pt/Rh/Al2O3 and Pt/CeOx/Al2O3 catalysts. Since these catalysts differ in dispersion and weight loading of platinum, the turnover frequencies are also compared. The following order in activity in CO oxidation after a reductive pretreatment is found: Pt/CoOx/SiO2 > Pt/MnOx/SiO2, Pt/CeOx/Al2O3 > Pt/Al2O3, Pt/Rh/Al2O3, Pt/SiO2. Over Pt/CoOx/SiO2 CO is already oxidised at room temperature. Possible models to account for the high activity of Pt/CoOx/SiO2 in the CO/O2 reaction are presented and discussed. Partially reduced metal oxides are necessary to increase the activity of the Pt/CoOx/SiO2, Pt/MnOx/SiO2 or Pt/CeOx/Al2O3 catalysts. It was shown that mild ageing treatments did not affect the activity of the Pt/CoOx/SiO2 catalyst in CO oxidation.

Topical application of 5-Fluorouracil in premalignant lesions of cornea, conjunctiva and eyelid

Local application of 5-Fluorouracil was practised on 5 patients. In 3 patients with multiple premalignant oculo-cutaneous lesions, two of whom had also premalignant epibulbar lesions, local 5% 5-Fu cream and/or 1% 5-Fu eyedrops were applied. In 2 other patients who had only premalignant lesions on the cornea and conjunctiva, 1% 5-Fu eyedrops were used only. In animal experiments 1% 5-Fu was not found to cause any damage to normal corneal and conjunctival epithelium. The frequency of the applications and the duration of the treatment were dependent on the location and extent of the lesions. Except for easily treatable lesions, caused by the separation of the tumour epithelium, no complications of local 5-Fu treatment were seen. The visual acuity improved in all 4 patients in whom the cornea was affected. In these premalignant conditions the diagnosis and assessment of the therapy were based on exfoliative cytology and biopsies.

Hematoporphyrin derivative photoradiation treatment of experimental malignant melanoma in the anterior chamber of the rabbit

The effects of Hematoporphyrin Derivative Photoradiation Therapy (HpD-PRT) on Greenes amelanotic melanoma implanted into the anterior chamber of rabbits have been examined by biomicroscopy, fluorescein angiography and histopathology. The tumors were irradiated 24 hours after injection of HpD when both the porphyrin concentration and the porphyrin ratio tumor/iris were highest. Blanching and shrinkage of tumors were the first signs of tumor destruction. Fluorescein angiography as soon as 20 minutes after irradiation found non-perfusion of blood vessels at the tumor surface. Histopathological observation of vessel wall destruction is in agreement with this finding. Subtotal tumor necrosis was demonstrated in 12 out of 13 experiments. Necrosis was complete in only one experiment. Clusters of viable tumor cells were found when shielded behind pigment, at the tumor periphery and around some blood vessels. Lens damage was observed after irradiation when the iris pigment epithelium was disorganized by the tumor. The iris contained high concentrations of porphyrin and PRT resulted in depigmentation, non-perfusion of the capillary bed, damage to larger iris vessels and finally atrophy. Light intensity measurements were performed in vivo during PRT. The average effective attenuation coefficient at 630 nm was 0.56 mm-1 at the beginning of irradiation and 0.87 nm-1 at the end. Results indicate that as a treatment HpD-PRT in itself might be insufficient but may prove to be an effective modality in combination with other tumor destructive therapies.

A comparison of the effects of non-steroidal compounds on the disruption of the blood-aquous barrier

The anti-inflammatory agents, diclofenac, flurbiprofen and indomethacin, were examined to determine their inhibitory effect on the breakdown of the blood-aqueous barrier in rabbit eyes, following paracentesis. In treated eyes, compared to the non-treated eyes, the increase in protein and fluorescein in the secondary aqueous was inhibited in a dose-dependent manner. Dose-response curves for the non-steroidal compounds were comparable and were in the range of 3×10−6–10−2 m . However, indomethacin did not completely inhibit the breakdown of the aqueous barrier. The observed effects were strongly dependent of the pH of the vehicle and partly correlated with lipid solubility of the agents.

Effects of microwave-induced hyperthermia on the anterior segment of healthy rabbit eyes

Hyperthermia was induced in nine healthy rabbit eyes by means of a microwave 2450 MHz stripline applicator. The anterior segment of each eye was heated to a fixed temperature of between 42° C and 46° C for 30 min. The temperature distribution in the eye was calculated using a thermal model and the actual boundary temperatures and microwave intensity were measured. The effects of treatment were evaluated by daily macroscopic examination, fluorescein angiography and fluorophotometry, as well as by histology. Histological examination of changes induced by this hyperthermic delivery system revealed a sharp transition at 44°–45° C from no permanent damage to the anterior chamber at lower temperatures to serious damage such as local necrosis, pigment disruption and local cataract at high temperatures. A sharp transition in the same temperature range was observed in vivo in the fluorescein leakage of the iris vessels by comparative fluorescein angiography and by anterior segment fluorophotometry.

The effect of Indomethacin on the anterior segment of the eye after paracentesis

The prostaglandin-inhibiting effect of Indomethacin (IN) was studied in rabbits, using paracentesis as a stimulus and rise in aqueous protein and fluorescein concentration after intravenous fluorescein injection as parameters. In eyes pre-treated with IN eye-drops the rise in fluorescein and protein concentration in the secondary aqueous was less than in the control eyes; the rise in the control eyes was less than in the eyes of rabbits not treated with IN. There was a good correlation between the rise in protein and the rise in fluorescein concentration in the secondary aqueous.The four different 0.5% IN suspensions used showed different PG-inhibiting activity, attributed to the difference in physicochemical composition.

Characterization of specific binding sites for PAF in the iris and ciliary body of rabbit

The protective effect exerted by BN 52021 a specific PAF-receptor antagonist in experimentally induced ocular inflammatory disorders led us to investigate the possible presence of specific receptors for PAF in rabbit iris and ciliary body. Two classes of PAF binding sites were found in isolated iris and ciliary process of pigmented rabbit eyes: a high affinity site Kd1 congruent to 4.9 +/- 0.47 nM, Bmax1 congruent to 3.17 +/- 0.50 pmoles/mg protein, a low affinity sites Kd2 congruent to 11.6 +/- 0.33 nM, Bmax2 congruent to 12.46 +/- 2.3 pmoles/mg protein for iris. The specific binding was not affected by lyso-PAF the biologically inactive precursor and metabolite of PAF, up to 10(-6) M; inhibition by unlabelled PAF demonstrated a biphasic curve partially antagonized by BN 52021. The present results demonstrate the presence of specific binding sites for PAF in rabbit eyes which could mediate the action of this mediator in eye inflammatory processes and explain the protective effect observed with BN 52021.

Specific receptor sites for PAF in iris and ciliary body of the rabbit eye

The existence of specific binding sites by using tritiated 1-O-alkyl-2-O-acetyl-sn-glycero-3-phosphocholine (3H-PAF) was investigated on iris and ciliary body tissue of pigmented rabbit eyes. The binding was saturable, specific, time-dependent and reversible. Scatchards analysis indicated the presence of two types of binding sites with a Kd1 4.90 +/- 0.47 nM, a Kd2 11.60 +/- 0.33 nM, a Bmax1 3.17 +/- 0.50 pmol/mg protein and a Bmax2 12.45 +/- 2.30 pmol/mg protein for iris tissue, and a Kd1 5.71 +/- 0.09 nM, a K2d 24.40 +/- 0.91 nM, a Bmax1 3.41 +/- 1.00 pmol/mg protein and a Bmax2 16.60 +/- 0.51 pmol/mg protein for ciliary body. The binding was fully displaced by unlabelled PAF in both iris and ciliary body preparations, and partially inhibited by the PAF antagonist BN 52021 in iris tissue.

Comparison of the effects of corticosteroids and indomethacin on the response of the blood-aqueous barrier to injury

Aqueous protein content was estimated as a measure of the integrity of the blood-aqueous barrier after paracentesis or argon laser photo-coagulation of the iris in rabbits. Corticosteroid pretreatment topically or by subconjunctival or intramuscular injection exerted only a moderate inhibitory effect on the breakdown of the blood-aqueous barrier. Instillation of 0.1% indomethacin however, strongly inhibited the response in both models. The results are indicative of the potential usefulness of topical administration of prostaglandin synthetase inhibitors in the treatment of non-infectious inflammatory diseases.

The effect of therapeutic ultrasound on the average of multiple intraocular pressures throughout the day in therapy-resistant glaucoma

The effect of therapeutic ultrasound was evaluated in 17 patients with therapy-resistant glaucoma by comparing average intraocular pressure (IOP) curves measured before and 3–4 months after insonification. The insonification regimen was standardized; the medication was identical during both pressure curve measurements. The average IOP decrease was 44% ± 24 SD (range, 73% decrease to 6% increase). In 82% of the patients the IOP decrease was more than 34%. There was no correlation between the percentage of IOP decrease and the average IOP before insonification (correlation coefficient, 0.21;P = 0.41).