Phthalocyanine mediated photodynamic thrombosis of experimental corneal neovascularization: effect of phthalocyanine dose and irradiation onset time on vascular occlusion rate

Photodynamic therapy monitoring with optical coherence angiography

Photodynamic therapy (PDT) is a promising modern approach for cancer therapy with low normal tissue toxicity. This study was focused on a vascular-targeting Chlorine E6 mediated PDT. A new angiographic imaging approach known as M-mode-like optical coherence angiography (MML-OCA) was able to sensitively detect PDT-induced microvascular alterations in the mouse ear tumour model CT26. Histological analysis showed that the main mechanisms of vascular PDT was thrombosis of blood vessels and hemorrhage, which agrees with angiographic imaging by MML-OCA. Relationship between MML-OCA-detected early microvascular damage post PDT (within 24 hours) and tumour regression/regrowth was confirmed by histology. The advantages of MML-OCA such as direct image acquisition, fast processing, robust and affordable system opto-electronics, and label-free high contrast 3D visualization of the microvasculature suggest attractive possibilities of this method in practical clinical monitoring of cancer therapies with microvascular involvement.

Contact transcleral ciliary body photodynamic therapy with verteporfin in pigmented rabbits: effect of repeated treatments

We studied the effect on the intraocular pressure (IOP) and the ciliary body (CB) morphology after four consecutive contact transcleral photodynamic treatments of the ciliary body (CB-PDT) with verteporfin in pigmented rabbits. Twenty-two pigmented rabbits underwent CB-PDT (study group), performed once (six rabbits) or repeated for up to four times (16 rabbits). Six additional rabbits received only laser treatment without photosensitizer administration (control group). CB-PDT was performed in one eye in rabbits of the study group, with the fellow eye serving as internal control. Verteporfin dosage was 1 mg kg(-1) as bolus injection and laser settings were 40 mW (600 microm core optical fiber) for 1.5 min per spot, for 10 spots. In repeated CB-PDT, treatments were performed in 4-day intervals. Daily IOP measurements were recorded. Histological studies were performed at selected time points. An IOP reduction, more sustained following repeated treatments, was detected in all treated eyes but not in fellow eyes or in the control group. On the average, the IOP was restored to pretreatment levels 4 days after the last treatment. No serious adverse events were observed and the CB architecture was intact at the end of the experiment. Repeated CB-PDT is safe and results in a short-term reduction of IOP. Induced CB alterations are reversible.

Contact transscleral ciliary body photodynamic therapy in pigmented rabbits using verteporfin and diode laser: evaluation of treatment parameters

PURPOSE

To evaluate the treatment parameters necessary for achieving ciliary body photodynamic damage, enough to significantly reduce IOP, using verteporfin and a diode laser.

DESIGN

Animal study.

METHODS

The right eye ciliary body of 30 pigmented rabbits was irradiated using verteporfin (Visudyne) and a diode laser. Photosensitizer dose ranged from 0.375 to 2 mg/kg. Three adjacent laser spots were applied 0.5 mm behind limbus at 12 o'clock position using a contact transscleral technique. The laser power was ranging from 10 to 70 mW and the duration of irradiation from 1 to 5 min per spot. The left eyes of the rabbits were used as controls. Animals were sacrificed 24 hours after the procedure and their eyes were evaluated by means of light and electron microscopy. A step-by-step approach was adopted with adjustment of experimental parameters according to histological findings. The end point was to identify the irradiation parameters necessary for induction of photodynamic damage while minimizing thermal damage. Subsequently, 10 more animals were used in order to verify the effectiveness of these irradiation parameters in reducing the intraocular pressure.

RESULTS

The therapy parameters that led to photodynamic effect avoiding thermal damage were laser power of 25 mW, irradiation time of 3 min per spot, and verteporfin dose of 1 mg/kg. Transscleral ciliary body irradiation using these parameters resulted in vascular thrombosis of ciliary vessels and in substantial edema, resulting in separation of the two ciliary epithelium layers. These parameters were applied to 4 rabbits, resulting in a mean IOP reduction of 1.8 mmHg +/- 1.2 that lasted for 4 days. An increase of the laser power to 35 mW tested in 6 additional animals, resulted in mean IOP reduction of 2.2 mmHg +/- 1.2, lasting 6 days; some minimal thermal damage was seen with the later settings.

CONCLUSION

The combination of verteporfin and 690 nm diode laser is effective for the induction of ciliary body photodynamic damage, which results in significant but temporary IOP reduction, after transscleral PDT in pigmented rabbits. With appropriate parameter selection, intraocular pressure reduction can be achieved while thermal damage is kept to a minimum.

Application of femtosecond ultrashort pulse laser to photodynamic therapy mediated by indocyanine green

BACKGROUND/AIMS

To evaluate treatment with high peak power pulse energy by femtosecond ultrashort pulse laser (titanium sapphire laser) delivered at an 800 nm wavelength for corneal neovascularisation using photodynamic therapy (PDT) mediated by indocyanine green (ICG).

METHODS

Using a gelatin solid as an in vitro corneal model, the safety of laser power was studied to determine if it degenerated gelatin with or without ICG. The authors then induced corneal neovascularisation in rabbit eyes by an intracorneal suturing technique. Fluorescein angiography was used to evaluate occlusion before PDT and 0, 1, 3, and 10 days after PDT. The authors performed light microscopy with haematoxylin eosin staining and transmission electron microscopy to determine thrombosis formation in the neovascular regions.

RESULTS

The threshold of peak laser power density ranged from 39 to 53 W/cm(2). Laser irradiation was started 30 seconds after a 10 mg/kg ICG injection, and all irradiated segments were occluded at 0, 1, 3, and 10 days at 3.8 J/cm(2). Light and electron microscopy documented thrombosis formation in the neovascular region.

CONCLUSION

Femtosecond pulse laser enhanced by ICG can be used for PDT. Because of effective closure of corneal neovascularisation at a low energy level, the high peak power pulse energy of the femtosecond pulse laser might be more efficacious than continuous wave laser for use with PDT.

Treatment parameters for selective occlusion of experimental corneal neovascularization by photodynamic therapy using a water soluble photosensitizer, ATX-S10(Na)

Time dependent change of an accumulation of an amphiphilic photosensitizer, ATX-S10(Na) on rabbit corneal neovascularization (CoNV) was evaluated by angiography using ATX-S10(Na) as a fluorescent dye on three rabbits. The angiography showed that the dye accumulated on CoNV 3-5 hr after dye injection when the dye in the iris was minimum. The results suggested 3-5 hr after might be the optimal time to start photodynamic therapy (PDT) to occlude CoNV selectively without damage to the surrounding normal tissue such as the iris. Then the optimal treatment parameters in PDT using ATX-S10(Na) for selective occlusion of the CoNV were investigated on rabbit eyes. PDT was performed with two different time intervals between dye injection and laser irradiation of a diode laser (670 nm), different laser doses and three different dye doses on 21 animals. PDT performed immediately after dye injection selectively occluded CoNV with laser irradiations from 30.6 to 38.2 J cm(-2)and a 2 mg kg(-1)dose of ATX-S10(Na), as well as with 15.3 J cm(-2)and a 6 mg kg(-1)dose. PDT performed 4 hr after dye injection with 107.0-152.8 J cm(-2)and a 6 mg kg(-1)dose, as well as with 38.2-53.5 J cm(-2)and a 12 mg kg(-1)dose was also effective. Although PDT performed either immediately or 4 hr after ATX-S10(Na) injection selectively occluded CoNV, the width of the optimal range of radiant exposures seemed wider in PDT performed 4 hr after dye injection. It is supposed that this result is associated with the difference of dye accumulation between in CoNV and in normal tissue as shown by the present angiographical findings.

Local photodynamic therapy with Zn(II)-phthalocyanine in an experimental model of intimal hyperplasia

Photodynamic therapy (PDT) appears to be a novel promising modality to prevent intimal hyperplasia (IH) and restenosis after angioplasty. Local PDT, that consists of local delivery of photosensitizing agents followed by intraluminal local irradiation, represents a recent advancement. This methodology requires optimization in order to achieve the best prompt outcome especially in terms of pharmacokinetics of the photosensitizing agent. We studied the pharmacokinetic properties by using the photosensitizing agent Zn(II)-phthalocyanine (ZnPc), locally released by a channeled balloon. The efficacy of local PDT in reducing IH was evaluated in an experimental rabbit model of arterial injury. The maximum accumulation of ZnPc was found at 30 min: the injured portion of the artery gave a ZnPc recovery of 1.18 micromol/mg, as compared with undetectable amounts of ZnPc in the non injured arteries; within 90 min after the local delivery, clearance of the agent was almost complete. Local PDT produced an effective reduction of IH in our vascular injury model: at 7, 14, 21 and 28 days IH and intima/media ratio (IMR) was significantly reduced as compared with balloon injured arteries. The local delivery of ZnPc showed favourable pharmacokinetic properties, that allow the performance of PDT immediately after the vascular injury. Local PDT performed in these conditions represents a promising approach to prevent IH after balloon injury. Further studies are needed to better clarify the biological response of the injured arterial wall to local PDT.

Selective occlusion of choroidal neovascularization by photodynamic therapy with a water-soluble photosensitizer, ATX-S10

BACKGROUND AND OBJECTIVE

To determine the optimal treatment parameters for selective occlusion of choroidal neovascularization (CNV) by photodynamic therapy (PDT) by using the photosensitizer ATX-S10 and a diode laser (wavelength = 670 nm).

MATERIALS AND METHODS

Experimental CNV was induced in rat fundi by argon laser photocoagulation. The distribution of ATX-S10 in the chorioretina was analyzed by fluorescence microscopy, and the optimal treatment parameters for selective occlusion of CNV were investigated by changing the dosage and timing of laser irradiation. CNV closure and resulting damage of the surrounding tissue were documented by fluorescein angiography and light and electron microscopies.

RESULTS

Fluorescence of ATX-S10 was observed to be localized in the vascular lumen of the retina and choroid within 5 min after dye injection and increased in intensity in CNV up to 2-6 h and decreased rapidly in normal tissue. Laser irradiation with radiant exposures of 7.4 J/cm2 applied immediately after dye injection or with 22.0 J/cm2 at 2-4 h later effectively occluded the induced CNV without causing significant damage to normal retinal capillaries and large choroidal vessels.

CONCLUSIONS

PDT using ATX-S10 can selectively occlude CNV. ATX-S10 is a potentially useful photosensitizer for the treatment of CNV.

Photodynamic effect of a new photosensitizer ATX-S10 on corneal neovascularization

In order to elucidate the mechanism by which a new photosensitizer ATX-S10 causes the photodynamic effect on neovasculature, we investigated the kinetics and localization of dye accumulation in the neovascular cornea of rats after systemic administration and the development of vascular injury induced by subsequent laser irradiation, compared to those in the normal iris. Under a fluorescence microscope, the neovascular cornea always exhibited more intense fluorescence than the iris between 0.5 and 4 hr after ATX-S10 administration, indicating the preferential deposit of dye in the former tissue. The fluorescence was found inside the vascular lumen at the earliest time period and thereafter in the vascular lining cells, interstitial tissue and infiltrating neutrophils until 6 hr. As observed using light and electron microscopy, laser irradiation performed 2.5 hr after ATX-S10 injection caused extensive vascular thrombosis with endothelial destruction, which persisted for at least 3 days. The proportion of thrombosed vessels at 6 hr after laser irradiation in the neovascular cornea (64+/-5%; n=3) was significantly (P<0.01) higher than that in the normal iris (44+/-8%; n=3). In the non-thrombosed vessels from heparinized rats, in which thrombosis-related ischemic effect was excluded, mitochondrial vacuolation was the pathologic change commonly seen in the endothelial cells, pericytes and neutrophils. Morphometric analysis revealed that the mitochondria of endothelial cells in the corneal new vessels were more severely injured than those in the iris vessels. The present results indicate that ATX-S10 is a potent photosensitizer which induces photodynamic occlusion particularly of new vessels probably due to the preferential biodistribution of dye in the neovascular tissue.

Histological Evaluation of Phthalocyanine Mediated Photodynamic Occlusion of Corneal Neovascularization Enhanced by Hyperbaric Oxygenation

PURPOSE

We evaluated the effective irradiation parameters for photodynamic thrombosis of experimental corneal neovascularization enhanced by simultaneous hyperbaric oxygenation.

METHODS

Neovascularization was provoked in both eyes of each of 35 albino rabbit corneas using the intracorneal suture technique. The lasered animals were divided in 3 groups. Group 1 (10 rabbits) was treated under hyperbaric conditions (28 atm for 25 min.); group 2 (5 rabbits) was treated breathing pure oxygen delivered by a face mask; group 3 (10 rabbits) was treated breathing room air. The fourth group (10 rabbits) was used for control. Animals were anaesthetized, and irradiation of new corneal vessels was carried out 30 minutes after the injection of 5 mg/kg chloroaluminum sulfonated phthalocyanine. A 670 nm diode laser with a power 4 mW and a spot diameter 350 mm was used. Exposure times necessary for vascular occlusion were registered. Histological examination was carried out at the end of the follow-up time.

RESULTS

Exposure times were significantly lower in groups 1 and 2 as compared to group 3 (1.75 +/- 0.15 min., 3.1 +/- 0.4 min., and 4.75 +/- 0.15 min. respectively). Total light dose averaged 490 J/cm,2 870 J/cm,2 and 1330 J/cm,2 respectively. Histological examination revealed thrombus formation in the targeted vessels of all three investigated groups.

CONCLUSION

Combination of PDT with hyperbaric oxygenation results in an acceleration of the photodynamic process and provides for a possibility of significant reduction of photodynamic dose.

Photothrombosis of retinal and choroidal vessels in rabbit eyes using chloroaluminum sulfonated phthalocyanine and a diode laser

BACKGROUND AND OBJECTIVES

Photothrombosis is a relatively new photodynamic application leading to vascular occlusion. In the current work the effectiveness of phthalocyanine and a diode laser in photothrombosis of normal retinal and choroidal vessels was evaluated.

STUDY DESIGN, MATERIALS AND METHODS

Big retinal vessels of temporal myelin wing were irradiated using a 670 nm diode laser (2 mW, 0.5 mm2) after the injection of chloroaluminum sulfonated phthalocyanine (5 mg/kg) in twenty albino rabbits. Animals were followed up to a maximum of 7 months using fundus photography, fluoroangiography, and histology.

RESULTS

Photothrombosis of the irradiated retinal vessels and of underlying choroidal vessels resulted in all treated eyes after 13 to 17.5 min of irradiation. The retinal vessels were patent again by the 7th day after the procedure. Choroidal vessels remained closed during the whole follow-up period. Light and electron microscopy demonstrated occupation of irradiated choroidal and retinal vessels by platelet thrombi. Damage of endothelial cell structure of these vessels could be seen. Outer retinal and RPE damage localized at irradiation area was observed.

CONCLUSION

The combination of phthalocyanine with a low power diode laser is a simple and effective way for the induction of photodynamic thrombosis in fundus vessels.

Lasers in ophthalmology

This article reviews the principle uses of ophthalmic lasers, providing historical background with an emphasis on new applications and areas of investigation. Ophthalmic photocoagulation was the first medical laser application and has restored or maintained vision in millions of people. More recently, photodisruption and, increasingly, ablation have gained prominence for treating a wide range of ocular pathology. The unique properties of lasers have also been harnessed for diagnostic purposes, with optical coherence tomography representing a significant improvement over existing imaging methods. Many ophthalmic applications of lasers have been developed, but the field is a dynamic one which continues to evolve along with laser technology itself.