Photodynamic therapy of arteries. A novel approach for treatment of experimental intimal hyperplasia

Photodynamic Therapy and Cardiovascular Diseases

Cardiovascular diseases are the third most common cause of death in the world. The most common are heart attacks and stroke. Cardiovascular diseases are a global problem monitored by many centers, including the World Health Organization (WHO). Atherosclerosis is one aspect that significantly influences the development and management of cardiovascular diseases. Photodynamic therapy (PDT) is one of the therapeutic methods used for various types of inflammatory, cancerous and non-cancer diseases. Currently, it is not practiced very often in the field of cardiology. It is most often practiced and tested experimentally under in vitro experimental conditions. In clinical practice, the use of PDT is still rare. The aim of this review was to characterize the effectiveness of PDT in the treatment of cardiovascular diseases. Additionally, the most frequently used photosensitizers in cardiology are summarized.

Photodynamic Therapy for Atherosclerosis

Atherosclerosis, which currently contributes to 31% of deaths globally, is of critical cardiovascular concern. Current diagnostic tools and biomarkers are limited, emphasizing the need for early detection. Lifestyle modifications and medications form the basis of treatment, and emerging therapies such as photodynamic therapy are being developed. Photodynamic therapy involves a photosensitizer selectively targeting components of atherosclerotic plaques. When activated by specific light wavelengths, it induces localized oxidative stress aiming to stabilize plaques and reduce inflammation. The key advantage lies in its selective targeting, sparing healthy tissues. While preclinical studies are encouraging, ongoing research and clinical trials are crucial for optimizing protocols and ensuring long-term safety and efficacy. The potential combination with other therapies makes photodynamic therapy a versatile and promising avenue for addressing atherosclerosis and associated cardiovascular disease. The investigations underscore the possibility of utilizing photodynamic therapy as a valuable treatment choice for atherosclerosis. As advancements in research continue, photodynamic therapy might become more seamlessly incorporated into clinical approaches for managing atherosclerosis, providing a blend of efficacy and limited invasiveness.

Photodynamic therapy for the treatment of atherosclerotic plaque: Lost in translation?

Acute coronary syndrome is a life-threatening condition of utmost clinical importance, which, despite recent progress in the field, is still associated with high morbidity and mortality. Acute coronary syndrome results from a rupture or erosion of vulnerable atherosclerotic plaque with secondary platelet activation and thrombus formation, which leads to partial or complete luminal obstruction of a coronary artery. During the last decade, scientific evidence demonstrated that when an acute coronary event occurs, several nonculprit plaques are in a "vulnerable" state. Among the promising approaches, several investigations provided evidence of photodynamic therapy (PDT)-induced stabilization and regression of atherosclerotic plaque. Significant development of PDT strategies improved its therapeutic outcome. This review addresses PDT's pertinence and major problems/challenges toward its translation to a clinical reality.

Evaluation of oxygen dependence on in vitro and in vivo cytotoxicity of photoimmunotherapy using IR-700-antibody conjugates

Photoimmunotherapy (PIT) using the near-infrared-absorbing photosensitizing phthalocyanine dye, IRDye 700DX (IR-700), conjugated with a tumor-targeting antibody such as panitumumab (Pan) has shown efficacy in in vitro studies and several preclinical models in mice with promise for clinical translation. PIT results in rapid necrotic cell death in vitro and tumor shrinkage in vivo. Photochemical studies with the Pan-IR-700 conjugate showed that this agent can support generation of singlet oxygen and also generate reactive oxygen species after exposure to near-infrared (NIR) light. Moreover, in vitro studies using A431 cells, singlet oxygen scavengers abrogated the efficacy of PIT with Pan-IR-700, while oxygen depletion to undetectable levels in the exposure chamber almost completely inhibited the cellular cytotoxicity of PIT. Survival of tumor bearing mice was prolonged in PIT-treated animals but mice whose tumors were made transiently hypoxic prior to PIT had no benefit from the treatment. The results from this study support a central role for molecular oxygen-derived species in cell death caused by PIT.

The changing face of vascular interventional radiology: the future role of pharmacotherapies and molecular imaging

Interventional radiology has had to evolve constantly because there is the ever-present competition and threat from other specialties within medicine, surgery, and research. The development of new technologies, techniques, and therapies is vital to broaden the horizon of interventional radiology and to ensure its continued success in the future. In part, this change will be due to improved chronic disease prevention altering what we treat and in whom. The most important of these strategies are the therapeutic use of statins, Beta-blockers, angiotensin-converting enzyme inhibitors, and substances that interfere with mast cell degeneration. Molecular imaging and therapeutic strategies will move away from conventional techniques and nano and microparticle molecular technology, tissue factor imaging, gene therapy, endothelial progenitor cells, and photodynamic therapy will become an important part of interventional radiology of the future. This review looks at these new and exciting technologies.

Physically facilitating drug-delivery systems

Facilitated/modulated drug-delivery systems have emerged as a possible solution for delivery of drugs of interest to pre-allocated sites at predetermined doses for predefined periods of time. Over the past decade, the use of different physical methods and mechanisms to mediate drug release and delivery has grown significantly. This emerging area of research has important implications for development of new therapeutic drugs for efficient treatments. This review aims to introduce and describe different modalities of physically facilitating drug-delivery systems that are currently in use for cancer and other diseases therapy. In particular, delivery methods based on ultrasound, electrical, magnetic and photo modulations are highlighted. Current uses and areas of improvement for these different physically facilitating drug-delivery systems are discussed. Furthermore, the main advantages and drawbacks of these technologies reviewed are compared. The review ends with a speculative viewpoint of how research is expected to evolve in the upcoming years.

Detection and photodynamic therapy of inflamed atherosclerotic plaques in the carotid artery of rabbits

Photodynamic therapy (PDT) has been applied in the treatment of artery restenosis following balloon injury. This study aimed to detect the accumulation of 5-aminolevulinic acid (ALA)-derived protoporphyrin IX (PpIX) in inflamed atherosclerotic plaque in rabbit model and evaluate the efficacy of PDT. The inflamed atherosclerotic plaque in the common carotid artery was produced by combination of balloon denudation injury and high cholesterol diet. After intravenous administration of ALA, the fluorescence of PpIX in plaque was detected. At the peak time, the correlation between the fluorescence intensity of PpIX and the macrophage infiltration extent in plaque was analyzed. Subsequently, PDT (635nm at 50J/cm(2)) on the atherosclerotic plaques (n=48) was performed and its effect was evaluated by histopathology and immunohistochemistry. The fluorescence intensity of PpIX in the plaque reached the peak 2h after injection and was 12 times stronger than that of adjacent normal vessel segment, and has a positive correlation with the macrophage content (r=0.794, P<0.001). Compared with the control group, the plaque area was reduced by 59% (P<0.001) at 4week after PDT, the plaque macrophage content decreased by 56% at 1week and 64% at 4week respectively, the smooth muscle cells (SMCs) was depleted by 24% at 1week (P<0.05) and collagen content increased by 44% at 4week (P<0.05). It should be pointed out that the SMC content increased by 18% after PDT at 4week compared with that at 1week (P<0.05). Our study demonstrated that the ALA-derived PpIX can be detected to reflect the macrophage content in the plaque. ALA mediated PDT could reduce macrophage content and inhibit plaque progression, indicating a promising approach to treat inflamed atherosclerotic plaques.

The Intra-Vascular Stent as a Site-Specific Local Drug Delivery System

The current review focuses on utilization of a tubular structure (coated or uncoated, balloon expandable or self expanding) known as a "stent" for localized intravascular drug delivery. Emphasis of the review is on technologies currently employed for immobilization and coating for drug onto the stent prior to its placement in various lumen of the body. A brief discussion on stent design, comparison of angioplasty and coronary stenting, and market status complements the review for researchers new to this area.

Long-term inhibition of intimal hyperplasia using vascular photodynamic therapy in balloon-injured carotid arteries

Flexible treatments for intimal hyperplasia after angioplasty are still needed. The aim of this study was to demonstrate the long-term effects of vascular photodynamic therapy with talaporfin sodium on intimal hyperplasia following interventional injury. Intimal hyperplasia was induced by balloon distension injury to the carotid artery in 31 rabbits. Talaporfin, 5.0 mg/kg, was delivered systemically immediately after balloon injury. The injury site was irradiated with a diode laser light of wavelength 664 nm using a fluence of 50 J/cm2 after 30 min. At day 3 and weeks 3, 6, 9, 15, and 25 after photodynamic therapy, the treated artery of each rabbit was excised and examined immunohistochemically. Thirty minutes after talaporfin administration, drug fluorescence was found only in the balloon-injured carotid artery wall. At 3 days, no smooth muscle cells were seen in the media of the photodynamic therapy-treated arterial segments. Intimal hyperplasia developed progressively in the balloon-injured and untreated segments; however, in the segments treated with photodynamic therapy, intimal hyperplasia was markedly suppressed until 25 weeks and the media was repopulated by smooth muscle cells without macrophages. Vascular photodynamic therapy with talaporfin may be used to inhibit restenosis after vascular intervention.

Inhibition of in-stent restenosis in rabbit iliac arteries with photodynamic therapy

OBJECTIVES

Photodynamic therapy (PDT, the combination of light with a photosensitising drug in the presence of oxygen) inhibits restenosis after angioplasty without stenting. This study assesses the potential of PDT for prevention of in-stent re-stenosis.

DESIGN AND METHODS

Normal rabbits were given the photosensitising agent 5-aminolaevulinic acid (ALA) 60 mg/kg, 3 h prior to endovascular illumination of the iliac artery (635 nm at 50 J/cm(2)) either immediately before or after deployment of an oversized (3 mm diameter) stent. PDT treated arteries were retrieved 3 or 28 days later and assessed for cell counts and vascular morphometry. Control arteries (stent but no PDT) were examined at 28 days.

RESULTS

There were no adverse events and all vessels were patent at the end of the study. At 3 days there was almost complete medial cell ablation when light was delivered before stent deployment (17+/-1 cells/hpf), with little effect when illumination followed stent deployment (184+/-17 cells/hpf, p<0.0001). Twenty-eight days after PDT, the neointimal areas were 1.41+/-0.52 mm(2) (stent with no PDT), 1.24+/-0.54 mm(2) (light after stent) and 0.60+/-0.21 mm(2) (light before stent) (p=0.004).

CONCLUSIONS

PDT before stent deployment caused almost complete medial cell ablation at 3 days with inhibition of in-stent restenosis at 28 days. PDT is worthy of further study as an adjuvant to percutaneous intervention in patients with vascular disease.

Technique d’imagerie par fluorescence : intérêt diagnostique et thérapeutique en gynécologie

Fluorescence techniques are presently used by several medical and surgical disciplines (dermatology, pneumology, urology, gastrointestinal surgery) for the diagnosis of pre-cancerous and cancerous lesions. The technique is based on the application of 5-aminolevulinic acid (5-ALA) which induces the production of an endogen photosensitizer: protoporphyrin IX (PpIX). Fluorescence detection of the infraclinical dysplasia lesion is based on the contrast between fluorescent pathological tissue and non-fluorescent healthy tissue. Moreover, there is a correlation between the degree of tissue dysplasia and fluorescence intensity. Fluorescence imaging could allow easier detection of infraclinical lesions enabling more well-targeted treatment. In gynecology, many experimental and clinical studies have been conducted on the detection and treatment of cervical dysplasia and the diagnosis and treatment of vaginal and vulvar diseases as well as the diagnosis of peritoneal micrometastasis from ovarian cancer, the diagnosis and treatment of endometrial alterations, and the treatment of locoregional recurrent skin breast cancer. The aim of this work is to present the fundamental principles of fluorescence imaging technical and to expose the diagnostic and therapeutic prospects in gynecology.

Free radical attenuation prevents thrombosis and enables photochemical inhibition of vein graft intimal hyperplasia

OBJECTIVE

Photodynamic therapy (PDT) inhibits post-interventional stenosis in balloon-injured arteries, but causes thrombosis when applied to vein grafts. This may result from added free radicals produced during the hypoxia-reperfusion injury of vein graft implantation. The purposes of this study were to determine whether a free radical scavenger could inhibit vein graft thrombosis, enabling PDT to inhibit intimal hyperplasia; and to investigate the role of neutrophils, also a source of radicals, in this setting.

METHODS

Jugular vein bypass grafts of the common carotid artery were performed in rats. PDT was administered in situ to the vein graft and artery in the presence or absence of deferoxamine (DFX), an OH- scavenger.

RESULTS

PDT alone induced thrombosis in all untreated vein grafts. DFX administration or inhibition of neutrophil adhesion to the graft prevented PDT-induced vein graft thrombosis. Moreover, DFX given together with PDT significantly decreased vein graft intimal hyperplasia (0.010 mm2 +/- 0.005 mm2; P<.002) as compared with DFX alone (0.113 mm2 +/- 0.009 mm2) or untreated control animals (0.112 +/- 0.007 mm2).

CONCLUSIONS

OH- radicals and neutrophils both have key roles in PDT-induced vein graft thrombosis. By inhibiting free radical production or neutrophil adhesion to the graft, adequate PDT can be administered for successful inhibition of vein graft intimal hyperplasia.

Arterial wall strength after endovascular photodynamic therapy

BACKGROUND AND OBJECTIVES

Vascular photodynamic therapy (PDT) inhibits intimal hyperplasia (IH) induced by angioplasty in rat iliac arteries by eradicating the proliferating smooth muscle cells. This process may jeopardise the structure and strength of the arterial wall, reflected by a decreased bursting pressure.

STUDY DESIGN/MATERIALS AND METHODS

Thirty male Wistar rats of 250-300 g were subdivided into 3 groups (n = 10). In all groups, IH was induced by balloon injury (BI). One experimental group received PDT at 50 J/cm diffuser length, the other group at 100 J/cm diffuser length. The third group served as control group and received no PDT. In half of each group the bursting pressure was analyzed after 2 hours (n = 5), in the other half after 1 year.

RESULTS

Two hours after the procedure the bursting pressure was 3.37 +/- 0.58 (+/-SEM) bar in the BI + PDT 50 and 3.96 +/- 0.43 bar in the BI + PDT 100 group, compared to 2.20 +/- 0.27 bar in the BI group (P < 0.05). After 1 year these values were 3.18 +/- 0.87 bar in the BI + PDT 50 (P < 0.05) and 2.02 +/- 0.31 bar in the BI + PDT 100 group, compared to 2.10 +/- 0.30 bar in the BI group (NS). In the BI + PDT 100 group, 3 out of 5 rats appeared to have aneurysmal dilatation after 1 year.

CONCLUSIONS

Endovascular PDT increases the arterial wall strength as measured by the bursting pressure at short-term. After 1 year, wall strength is not diminished as measured by bursting pressure, but aneurysmal dilatation nevertheless developed with 100 J/cm. dl. This may limit the use of high energy PDT.

Aminolaevulinic acid-induced protoporphyrin IX pharmacokinetics in central and peripheral arteries of the rat

Photodynamic therapy (PDT) based on the photosensitive protoporphyrin IX (PpIX) may prevent restenosis after transluminal angioplasty. PpIX is synthesized in mitochondria, which differ in number and activity among various tissues. Therefore, we questioned whether the course of PpIX concentration after systemic aminolaevulinic acid (ALA) administration differed among various arteries. ALA was administered intravenously (200 mg/kg) to male Wistar rats (n = 21). At varying time intervals (0, 1, 2, 3, 6, 12 and 24 h) both central and peripheral arteries were isolated and homogenized, and the concentration of the various heme intermediates was determined by a fluorometric extraction method. The maximal PpIX concentration was more than two-fold higher in peripheral arteries (20.49 +/- 3.0 to 24.0 +/- 7.5 pmol/mg protein) than in central arteries (0-9.46 +/- 0.01 pmol/mg protein) (P < 0.004). However, the amount of citrate synthase, reflecting the mitochondrial mass, was lower (0.14-0.61 and 1.87-2.32 U/mg protein, respectively). Apparently, the level of PpIX cannot simply be explained by the mitochondrial content of the arteries. The time interval of maximal PpIX accumulation was similar in peripheral and central arteries (2 h and 27 min vs. 2 h and 8 min) (P = 0.13). Thus, if the efficacy of PDT in vivo is directly related to the tissue concentration of PpIX, more effect can be expected in peripheral arteries than in central arteries.

Photodynamic therapy for cancer

The therapeutic properties of light have been known for thousands of years, but it was only in the last century that photodynamic therapy (PDT) was developed. At present, PDT is being tested in the clinic for use in oncology--to treat cancers of the head and neck, brain, lung, pancreas, intraperitoneal cavity, breast, prostate and skin. How does PDT work, and how can it be used to treat cancer and other diseases?

New catheter-based technology for the treatment of restenosis

Catheter-based vascular interventions have been in development worldwide for several decades, leading to remarkable progress in device technology. Mechanical interventional devices, such as angioplasty balloons, atherectomy devices, and stents, were invented and have contributed greatly to the treatment of atherosclerotic vascular stenosis. However, mechanical approaches do not effectively prevent subsequent intimal growth. Recently, several biological approaches, including radiation therapy and drug-eluting stents, have shown striking inhibition of intimal growth. These significant results are likely to change the treatment strategy in the field of interventional cardiology. Furthermore, additional catheter-based technologies for vascular interventions are presently being evaluated. These latest technologies designed to prevent intimal proliferation include intravascular sonotherapy, cryotherapy, photoangioplasty, and soft X ray. To date, intravascular sonotherapy has proven its efficacy in animal studies and safety in human studies. Cryotherapy, the application of cold thermal energy during angioplasty, enhances the acute effects of conventional dilation while decreasing the likelihood of restenosis. Photoangioplasty has a unique property based on its selective mechanism of action to treat atheromatous plaque. Soft X ray systems provide convenient device handling and well-controlled radiation dose. Some of these technologies may play an important role in vascular interventions in the near future.

Endovascular photodynamic therapy with aminolaevulinic acid prevents balloon induced intimal hyperplasia and constrictive remodelling

BACKGROUND AND OBJECTIVE

intimal hyperplasia (IH) and constrictive remodelling are important causes of restenosis following endovascular interventions, such as percutaneous transluminal angioplasty. Photodynamic therapy (PDT) with 5-aminolaevulinic (ALA) may prevent restenosis by cellular depletion and the elimination of cholinergic innervation.

STUDY DESIGN/MATERIALS AND METHODS

rats (n=90) were subdivided into 4 main groups. In the experimental group (n=36: 3 replications x 4 doses x 3 examination time-points), ALA was administered (200mg/kg i.v.) 2-3h before balloon injury (BI) of the common iliac artery followed by endovascular illumination with 633nm at either 12.5, 25, 50 or 100J/cm diffuser length (dl BI+PDT group). As control groups served the BI+Light only (LO) group (n=36) that received no ALA, the BI only group (n=9) (BI), and a group (n=9) that received a Sham procedure (Sham group).

RESULTS

planimetric analysis showed IH of 0.28+/-0.12mm(2) (BI), 0.27+/-0.12mm(2) (BI+LO at 100J/cmdl) in contrast to 0.02+/-0.02mm(2) after BI+PDT at 100J/cmdl at 16 weeks (p<0.05). In the BI+PDT groups, a light-dose increase of a factor 2 led to an IH decrease of 17% (p<0.05). In the BI and BI+LO groups constrictive remodelling was found, in contrast to BI+PDT treated groups at 16 weeks. The staining of cholinergic innervation of the tunic media of the blood vessel wall in BI+PDT showed no damage at the highest fluence.

CONCLUSION

endovascular ALA-PDT prevents IH and constrictive remodelling after BI without damage of cholinergic innervation of the tunica media. The effective light fluence rate in the rat is 50-100J/cmdl.

Photochemotherapy of vascular cells with 8-methoxypsoralen and visible light: differential effects on endothelial and smooth muscle cells

BACKGROUND

The long-term efficacy of percutaneous transluminal coronary angioplasty is limited by the restenosis which occurs in approximately 40% of patients, usually within 6 months of the procedure.

PURPOSE

The present study was designed to evaluate the effects of 8-methoxypsoralen (8-MOP) activated with visible light on the properties of bovine aortic smooth muscle cells (SMC) and endothelial cells (EC) in vitro.

METHODS

Cells were seeded in polystyrene wells, allowed to attach over a 24-h period, incubated with 1, 20, or 50 microg/ml 8-MOP and then exposed to 12 J/cm2 visible light (447 nm). Cell counts were performed for up 14 days (n = 4-6 wells per time point), and each experiment was performed in triplicate. Cellular migration, morphology, and size were also analyzed.

RESULTS

The lowest 8-MOP dose (1 microg/ml) had no significant effect on SMC proliferation, while the highest dose (50 microg/ml) induced cytostasis. An intermediate dose of 8-MOP (20 microg/ml) produced a transient and reversible inhibition of proliferation. There was no significant effect on proliferation of EC at lowest dose of 8-MOP (1 microg/ml). However, in contrast to the SMC experiments, a transient and reversible inhibition of EC proliferation was seen at both 20 and 50 microg/ml 8-MOP.

CONCLUSIONS

These experiments demonstrate that while 8-MOP photoactivated with 447 nm visible light can reversibly inhibit the proliferation of both SMC and EC in a dose-dependent fashion, SMC are more sensitive to the treatment than EC.

Photodynamic therapy mediated induction of accelerated re-endothelialisation following injury to the arterial wall: implications for the prevention of postinterventional restenosis

OBJECTIVE

Accelerated re-endothelialisation may inhibit the development of restenosis. Basic Fibroblast Growth Factor (bFGF) plays a key role for early proliferative activity in the artery following injury. Therefore, this study was devised to examine the effect of photodynamic therapy (PDT) on post-injury re-endothelialisation in vivo, and bFGF-mRNA expression in endothelial cells (EC) in vitro.

MATERIALS AND METHODS

Rat carotid arteries were balloon-injured prior to PDT. Arteries were analysed after 1, 3, 5, 14 and 30 days. Morphometric measurements were undertaken following injection of 0.5% Evans Blue which stains non-endothelialised surfaces only. To identify EC, immunohistochemistry (CD-31) was performed. Proliferation was assessed by fluorescence cell counting. PCR quantification of bFGF-mRNA expression and proliferation were assessed in bovine aortic EC which were plated on isolated, PDT-treated EC-derived extracellular matrix at (12), 24, 48 (72 h).

RESULTS

Three days following PDT, arteries displayed significantly increased endothelial lining (p = 0.02), which was more pronounced at 5 (p = 0.03) and 14 days (p = 0.02). At 30 days no relevant differences between PDT and control were noted. EC proliferation on PDT-treated matrix was significantly increased at 24, 48, and 72 h (p = 0.0004), whereas bFGF-mRNA expression was significantly increased at 24 h only (p = 0.007).

CONCLUSION

Post-injury PDT appears to accelerate re-endothelialisation. Expression of bFGF-mRNA, however, although increased shortly after PDT, may not be responsible for a constant stimulation of EC proliferation.

Up-regulation of Hsp27 plays a role in the resistance of human colon carcinoma HT29 cells to photooxidative stress

The Photofrin-resistant cell line (HT29-P14) was used in the present study to investigate the mechanism(s) involved in Photofrin-mediated photodynamic therapy (PDT). We compared gene expression profiles between the resistant cell line and its parental cell line (HT29) using DNA microarray analysis. A significant up-regulation of small heat shock protein 27 (Hsp27) was found in HT29-P14 cells. The elevated Hsp27 level may play an important role in the resistance of HT29-P14 to Photofrin-PDT. To test this hypothesis, we stably transfected HT29 cells with human Hsp27 complementary DNA. The potential role of Hsp27 in the resistance to PDT was examined in Hsp27-overexpressing cells. Stable trasnfected cells (H13) showed an increased survival after Photofrin-PDT, suggesting that the up-regulation of Hsp27 is related to the induced resistance to Photofrin-PDT. Phosphorylation of Hsp27 has been suggested to play an important role in cytoprotection. We have examined the phosphorylation activity of Hsp27 among the parental and resistant cells, as well as the overexpression cells. An elevated level of Hsp27 resulted in an increased ability of phosphorylation in both resistant and overexpressing cells after PDT. The activation of the phosphorylation of Hsp27 induced by PDT was not mediated by the p38 mitogen-activated protein kinase. These data suggest that Hsp27 may play an important role in mediating the adaptive response to Photofrin-PDT-induced oxidative stress and that the pathways leading to Hsp27 phosphorylation may contribute to the resistance of the cells to photooxidative damage.

UVB-activated psoralen reduces luminal narrowing after balloon dilation because of inhibition of constrictive remodeling

In this study we have explored the potential of PUVB (8-MOP + UVB) therapy for the reduction of luminal narrowing after arterial injury. In 15 rabbits, balloon dilation of iliac arteries was performed. In 20 arteries, dilation was combined with the delivery of pulsed ultraviolet light B (UVB) irradiation with 10 arteries being previously subjected to sensitizer infusion. Changes in vessel diameter, proliferation and extracellular matrix protein content at 6 weeks were evaluated by means of angiography and histomorphometry-immunohistochemistry. We found that PUVB, applied at the time of dilation, induced reduction in late loss (LL) at 6 weeks (percutaneous transluminal angioplasty vs UVB vs PUVB: 0.64 +/- 0.15 mm vs 0.61 +/- 0.05 mm vs 0.29 +/- 0.05 mm; p = 0.018). The same holds true for constrictive remodeling (0.53 +/- 0.15 mm vs 0.45 +/- 0.06 mm vs 0.15 +/- 0.05 mm; p = 0.016). In the irradiation groups, LL was independent of acute gain (AG), as opposed to the control. Collagen content increased significantly after PUVB in media and adventitia, without increased cellular proliferation in all vessel layers. Thus, PUVB at the time of dilation reduced luminal narrowing at follow-up without effecting proliferation. This effect was independent of AG and was associated with increased collagen content in media and adventitia.

Endovascular photodynamic therapy using mono-L-aspartyl-chlorin e6 to inhibit Intimal hyperplasia in balloon-injured rabbit arteries

BACKGROUND AND OBJECTIVE

Intimal hyperplasia (IH) leading to restenosis is a major complication of arterial revascularization. The purpose of this study was to investigate the effect of photodynamic therapy (PDT) using mono-L-aspartyl chlorin e6 (NPe6) as a photosensitizer and intraluminal radial irradiation for inhibition of IH experimentally.

STUDY DESIGN/MATERIALS AND METHODS

Study of laser transmission through the blood indicated that exclusion of blood is a prerequisite for intraluminal PDT. For homogeneous radial laser irradiation to the vessel wall, we used a newly developed cylindrical diffusing balloon laser fiber. Injuries were induced by pulling a balloon catheter through the right iliac artery of rabbits. One and 6 hours after the NPe6 injection (5mg/kg i.v.), drug distribution was examined by fluorescence microscopy. Nineteen rabbits received NPe6 at the time of injuries and PDT was performed with 664-nm laser at 30 and 10 J/cm(2) (20, 30, 40 mW/cm(2)) 1 hour after the injuries. The arteries were harvested at 2 days. In a second group of rabbits, PDT was given at 30 mW/cm(2) (30 J/cm(2)). Two weeks after treatment, the arteries were removed and examined histologically.

RESULTS

NPe6 was found to be distributed selectively in the injured media. Endovascular NPe6-PDT showed complete depletion of smooth muscle cells even with 10 J/cm(2) at 2 days. IH was significantly inhibited at 14 days after PDT.

CONCLUSIONS

Endovascular PDT of injured artery using NPe6 can prevent IH in this model of arterial wall injury and may become clinically useful for the prophylaxis of IH.

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.

Photodynamic therapy induces apoptosis in intimal hyperplastic arteries

Photodynamic therapy (PDT) generates free radicals through the absorption of light by photosensitizers. PDT shows promise in the treatment of intimal hyperplasia, which contributes to restenosis, by completely eradicating cells in the vessel wall. This study investigates the mechanisms of PDT-induced cell death. PDT, using the photosensitizer chloroaluminum-sulfonated phthalocyanine (1 mg/kg) and laser light (lambda = 675 nm) 100 J/cm(2) was administered to rat carotid arteries after balloon injury-induced intimal hyperplasia. Apoptosis was determined by cell morphology with light microscopy and transmission electron microscopy, DNA cleavage by terminal dUTP nick-end labeling staining, and nucleosomal fragmentation (ladder pattern) by DNA agarose gel electrophoresis. Four hours after PDT, apoptosis was observed in vascular cells, as evidenced by terminal dUTP nick-end labeling staining and transmission electron microscopy. Within 24 hours no cells were present in the neointima and media. Immunofluorescence using an alpha-smooth muscle cell actin antibody confirmed the disappearance of all neointimal and medial cells within 24 hours. No inflammatory cell infiltrate was observed during this time frame. Apoptosis was sharply confined to the PDT treatment field. These data demonstrate that vascular PDT induces apoptosis as a mechanism of rapid, complete, and precise cell eradication in the artery wall. These findings and the lack of inflammatory reaction provide the basis for understanding and developing PDT for a successful clinical application in the treatment of hyperplastic conditions such as restenosis.

Kinetics of release of heparin from alginate hydrogel

PURPOSE

Injected sodium alginate may be a useful perivascular drug delivery vehicle. This study was performed to determine the release rates of heparin from sodium alginate hydrogels cross-linked with varying amounts of calcium gluconate.

MATERIALS AND METHODS

Six hydrogels, composed of 0.16 mEq sodium alginate and 4,000 units unfractionated heparin, were cross-linked with calcium gluconate to yield ion equivalence (IE) ratios (calcium:alginate) of 0.2, 0.4, 0.58, 0.8, 1.0, or 1.2. Two milliliters of normal saline was placed on top of each gel and allowed to remain in contact for up to 10 days. At set time intervals, the amount of heparin in the eluent was determined with use of high-performance liquid chromatography.

RESULTS

Gels with 0.2 and 0.4 IE were partially liquid at 24 hours; the other gels solidified within 10 minutes. The 0.58 IE gel was slowest to solidify but immobilized the most heparin and released heparin slowest over 10 days. At 10 days, between 5.5% and 9.8% of the heparin immobilized was retained in the gel.

CONCLUSION

This hydrogel shows promise as a vehicle for in vivo perivascular heparin delivery. The 0.58:1 IE ratio hydrogel has slowest release rate and the greatest immobilization despite its longer cross-linking time.

Signaling pathways in cell death and survival after photodynamic therapy

Photodynamic therapy (PDT) is a cytotoxic treatment, which can induce cells to initiate a rescue response, or to undergo cell death, either apoptosis or necrosis. The many signaling pathways involved in these processes are the topic of this review. The subcellular localization of the photosensitizer has been shown to be a key factor in the outcome of PDT. Mitochondrial localized photosensitizers are able to induce apoptosis very rapidly. Lysosomal localized photosensitizers can elicit either a necrotic or an apoptotic response. In the plasma membrane, a target for various photosensitizers, rescue responses, apoptosis and necrosis is initiated. Several protein phosphorylation cascades are involved in the regulation of the response to PDT. Finally, a number of stress-induced proteins play a role in the rescue response after PDT. Notably, the induction of apoptosis by PDT might not be crucial for an optimal outcome. Recent studies indicate that abrogation of the apoptotic pathway does alter the clonogenic survival of the cells after PDT. Further studies, both in vitro and especially in vivo could lead to more efficient combination therapies in which signaling pathways, involved in cell death or rescue, are either up- or downregulated before PDT.

Photodynamic therapy with local photosensitizer delivery inhibits experimental intimal hyperplasia

BACKGROUND

Photodynamic therapy (PDT), the light activation of photosensitizer dyes for the production of free radicals, effectively inhibits experimental intimal hyperplasia with systemic administration of the photosensitizer. The local application of the photosensitizer directly into a vascular lesion to avoid systemic side effects and tightly control dose administration has theoretical appeal. The aim of this study was to quantify serum and arterial tissue uptake after site-specific photosensitizer delivery and, following PDT, determine its effectiveness at inhibiting intimal hyperplasia.

STUDY DESIGN/MATERIALS AND METHODS

The rat common carotid artery was balloon-injured, pressurized at 400 mm Hg for 2 minutes with the photosensitizer dye benzoporphyrin-derivative (BPD), and irradiated with 690 nm laser light at a fluence of 100 J/cm2. Control animals were pressurized with saline only, or received no additional treatment than balloon-injury.

RESULTS

Pressurization with BPD resulted in complete penetration of the intima and media and was associated with relatively high tissue, but almost no detectable serum BPD concentrations. No skin photosensitization or other systemic side effects were observed with photosensitizer administration. After 9 days, PDT-treated arteries displayed a significantly lower number of smooth muscle cells in the arterial wall than balloon-injured (P < 0.001) or saline-pressurized arteries (P < 0.0002), and no intimal hyperplasia. At 21 days, IH after PDT was significantly reduced as compared with balloon-injured (P < 0.0004), or saline-pressurized arteries (P < 0.003) with no arterial dilatation.

CONCLUSIONS

Site-specific delivery of liposomal BPD followed by PDT represents a safe method to treat arteries, and may be effectively used in vivo to inhibit the development of intimal hyperplasia.

Psoralen and long wavelength ultraviolet radiation as an adjuvant therapy for prevention of intimal hyperplasia and constrictive remodeling after balloon dilation: a study in the rabbit iliac artery

BACKGROUND AND OBJECTIVE

Restenosis after balloon angioplasty is the summated effect of intimal hyperplasia and arterial shrinkage, both caused by hyperproliferation. In the present study, the potential of a photochemotherapeutic modality (Psoralen + UVA: PUVA) for the prevention of angioplasty induced proliferation was explored.

STUDY DESIGN/MATERIALS AND METHODS

In rabbit iliac arteries, balloon dilation followed by PUVA-therapy (H = 1 J/cm2) was performed (n = 15). Contralateral arteries served as control. After 2 and 28 days of survival, the contribution of intimal hyperplasia and remodeling to lumen loss was determined by means of angiography and histological analysis.

RESULTS

After 2 days, large parts of the media had become acellular, while proliferation was occurring predominantly in the adventitia in both groups. After 28 days, late loss, arterial shrinkage, but not intimal hyperplasia were larger in the PUVA group (P < 0.05).

CONCLUSION

PUVA-therapy did not prevent intimal hyperplasia following balloon dilation but enhanced luminal narrowing by augmented constrictive remodeling.

Photodynamic modulation of wound healing with BPD-MA and CASP

BACKGROUND AND OBJECTIVE

Wound healing is an intricate process requiring the orchestration of cells, growth factors, cytokines, and the extracellular matrix. Cytokines, specifically TGF-beta, are believed to be instrumental in sustaining the fibrotic process, which leads to scarring. Photodynamic therapy (PDT) uses potent photosensitizers, which induce a wide range of effects on cells and the extracellular matrix. The influences of PDT on wound healing are not well known.

STUDY DESIGN/MATERIALS AND METHODS

Seven full-thickness incisional wounds were placed on each of 24 hairless Sprague Dawly rats, three wounds on one flank serving as dark controls and four on the contralateral side treated with PDT. Wounds were created two days before, one hour before, or one hour after red light exposure with an argon ion pumped dye laser. Twelve rats were injected with 0.25 mg/kg or 0.5 mg/kg of the PDT drug, BPD-MA, and the other 12 with 5 mg/kg or 10 mg/kg of the PDT drug, CASP, 3 and 24 hours prior to irradiation of light, respectively. At low doses of both photosensitizers, animals were irradiated with 1, 5, 10, and 20 J/cm2. At higher doses of BPD-MA and CASP animals were treated with 10, 20, 50, and 100 J/cm2 of light. Wounds were examined each day for 14 days and noted for edema, erythema, inflammation, necrosis, and quality of scarring. Wounds were also photographed at day 0, 2, 5, 8, and 14 post-irradiation. All animals were sacrificed 14 days after irradiation and the wounds were evaluated by light microscopy.

RESULTS

Grossly, animals treated with 0.25 mg/kg BPD-MA showed no effect with PDT. Animals treated with 0.5 mg/kg BPD, and 5 and 10 mg/kg CASP showed responses that varied with both light and drug dose. Erythema, edema, inflammation, and necrosis attributed to PDT were all observed, but there was no apparent influence of PDT on either the rate or final appearance of wound healing. Histologically, there were no apparent differences between treated and untreated sites, regardless of the drug, dose of light, or time of irradiation.

CONCLUSION

A single PDT treatment given before or after skin wounds does not apparently alter wound healing even when PDT caused brisk inflammatory reactions. PDT may have effects that were not detected. We conclude that PDT does not greatly influence incisional skin wound healing in the rat model.

Local photodynamic action of methylene blue favorably modulates the postinterventional vascular wound healing response

PURPOSE

Photodynamic therapy (PDT), the light activation of photosensitizers to produce free radicals, is known to inhibit experimental intimal hyperplasia (IH). However, its clinical application has been limited by the lack of a suitable approach and a clinically appropriate photosensitizer. The aim of this study was to determine the effectiveness of a clinical approach for PDT, while testing its ability to favorably modulate the vascular wound healing response.

METHODS

Rat carotid arteries were balloon-injured (BI), and for PDT, the arteries were irradiated with thermoneutral laser light (lambda = 660 nm, 100 J/cm(2)) after the photosensitizer methylene blue (MB) was delivered locally. Control rats included BI alone and MB after BI alone. Arteries were analyzed after 2 weeks with morphometric evaluation (n = 6) and in situ hybridization for versican and procollagen type I gene expression (digitized image pixel analyses, n = 3).

RESULTS

No IH developed in PDT-treated arteries (0 +/- 0 mm(2); compared with BI, 0.192 +/- 0.006 mm(2); P <.0001). The diameters remained unchanged (PDT, 0.95 +/- 0.04 mm; BI, 0.94 +/- 0.05 mm; uninjured artery, 0.91 +/- 0.06 mm). Arterial injury resulted in an increase of versican and procollagen type I messenger RNA (mRNA) in the adventitia and neointima. In the repopulating cells of the adventitia after PDT, there was a significant decrease in versican mRNA (% of positive pixels per high-power field: PDT, 1.13% +/- 0.39%; BI, 2.93% +/- 0.61%; P <.02), but not in procollagen type I mRNA.

CONCLUSION

The decrease of versican mRNA expression of repopulating cells after PDT reflects favorable healing on a molecular level. Site-specific delivery of MB, a clinically appropriate photosensitizer, followed by PDT represents a suitable method to promote favorable healing after balloon intervention and further supports its role for inhibiting postinterventional restenosis.

Photodynamic therapy for the prevention of intimal hyperplasia in balloon-injured rabbit arteries

This study was performed to demonstrate accumulation of the photosensitizer hematoporphyrin derivative (HPD) in atherosclerosis and to determine whether intimal hyperplasia, the main cause of restenosis after angioplasty, can be inhibited by photodynamic therapy (PDT). Forty Japanese White rabbits were subjected to balloon endothelial injury in the common iliac artery. Five groups of rabbits, ie, immediately after, or 3, 7, 14 or 28 days after the balloon injury, were injected with HPD. These rabbits were sacrificed 24h after HPD administration, and HPD fluorescence was investigated in the injured arteries by fluorescence microscopy. Other groups of rabbits were injected with HPD 24h before PDT, and they were then subjected to intravascular Hg-Xe flash-lamp irradiation immediately after (0D-PDT), or 3 days (3D-PDT), 7 days (7D-PDT), or 14 days (14D-PDT) after the balloon injury. All rabbits were sacrificed 28 days after the balloon injury, and histological sections of PDT-treated arteries were examined by light microscopy. Slight, uniform HPD accumulation was observed in the injured media immediately after the balloon injury, and throughout the entire media and the neointima on day 7. On day 14, HPD accumulation had diminished in the media and increased in the intima, and on day 28 no HPD remained in the media. In the 0D- or 3D-PDT groups, no inhibition of intimal hyperplasia was observed. In contrast, there was significant inhibition of intimal hyperplasia in the 7D- and 14D-PDT groups, and the most effective inhibition was in the 7D-PDT group. This study demonstrated that PDT with HPD inhibits smooth muscle cell growth and decreases the intimal hyperplasia response in rabbits.

Photodynamic therapy of atherosclerosis using YAG-OPO laser and Porfimer sodium, and comparison with using argon-dye laser

We performed photodynamic therapy (PDT) using the Yttrium Aluminium Garnet-Optical Parametric Oscillated (YAG-OPO) laser in cases of atherosclerosis, and examined its efficacy in vivo. We also performed PDT using an Argon-dye (Ar-dye) laser with the same output, and compared the efficacies. Following balloon denudation injury of the thoracoabdominal aorta, rabbits were raised on a cholesterol diet for 16 weeks, producing atheroma in that region. At 24 h following the administration of Photofrin 5 mg/kg, PDT was performed, and animals were sacrificed at 1 day, 1 week, and 2 weeks following the procedure to examine its efficacy. This was compared with the efficacy of PDT using the Ar-dye laser. Following PDT using a YAG-OPO laser, an increase in the vessel lumen was seen due to reduction of the hypertrophic intima and media, without the appearance of inflammatory cells. This result was seen more strongly in PDT using the pulse wave YAG-OPO laser than with the continuous wave Ar-dye laser, affecting not just the intima but also the media. These data demonstrated that PDT can effectively regress atherosclerotic lesions.

Intra-arterial photodynamic therapy using 5-ALA in a swine model

OBJECTIVES

To test the hypothesis that intravascular light could be delivered via a balloon catheter for arterial photodynamic therapy (PDT).

DESIGN

Pig non-injury model.

MATERIALS

Clinical catheter equipment.

METHODS

Large White pigs (15-20 micrograms) were photosensitised with 5-aminolaevulinic acid (5-ALA) induced protoporphyrin IX (PpIX) at a concentration of 120 mg/kg. Arterial biopsies were taken at intervals between 30 mins and 24 h and frozen sections analysed using a CCD camera to give a temporal profile of fluorescence in each arterial layer. PDT was given to normal arterial segments via a 4 mm transparent PTA balloon inflated so as to occlude flow, but not distend the artery. Animals were culled at 3 and 14 days and the above segments harvested.

RESULTS

Fluorescence peaked in the adventitia, intima and medial layers at 1.5, 4 and 6 h respectively. PDT at all time points produced VSMC depletion compared with controls. The degree of depletion mirrored the fluorescence profile of PpIX.

CONCLUSIONS

PDT can be delivered via a standard PTA balloon with a transparent channel. This depletes the VSMC population within the arterial wall without complications. Intra-arterial PDT is therefore a potential therapy to reduce the incidence of restenosis post-angioplasty.

Mediators of restenosis

The multitude of actions and interacting components involved in inciting and sustaining myointimal hyperplasia and restenosis effectively precludes the use of a single type of intervention. No pharmacologic approach has been conclusively shown to prevent coronary restenosis after balloon angioplasty or graft restenosis after peripheral arterial bypass. Although no human studies have been performed to prevent restenosis with gene therapy, the animal data are compelling, and the local delivery of various inhibitory agents may represent a novel way of preventing restenosis in vascular beds subjected to endovascular or traditional open procedures. Until these modalities are proved effective, the treatment of vascular stenosis due to internal hyperplasia remains within the domain of the surgeon.

Endovascular catheter-delivered photodynamic therapy in an experimental response to injury model

BACKGROUND

The effectiveness of local endovascular photodynamic therapy (PDT) in preventing tissue hyperplasia was evaluated in a vascular injury model.

METHODS

Standardized unidirectional arterial injury with a directional atherectomy catheter was performed in porcine arteries (n = 180). Animals (n = 72) were randomly allocated to unidirectional injury only (Group 1), injury followed by drug delivery of photosensitizer with a porous balloon (Group 2), or by local exposure to monochromatic light (Group 3). In Group 4, injury was followed by local drug delivery of photosensitizer and subsequent exposure to light (PDT). Up to 21 days after treatment, all experimental vessels were excised, fixed and processed for histology, immunohistochemistry and transmission electron microscopy.

RESULTS

After vascular injury an inflammatory and myoproliferative response was observed in Groups 1, 2 and 3 (mean tissue hyperplasia/media ratio 1.0 +/- 0.5 at 21 days; area tissue hyperplasia: 1.57 +/- 0.9 mm2). Proliferation in injured vascular segments (Group 1-3) reached a maximum at 7 days, with 6%. Only in Group 4, after injury followed by photodynamic therapy, was there no significant vascular response (mean tissue hyperplasia/media ratio 0.3 +/- 0.2: area tissue hyperplasia: 0.1 +/- 0.05 mm2 p < 0.001, proliferating cells 0.3%).

CONCLUSION

Vascular response after unidirectional injury was suppressed only by endovascular photodynamic therapy.

Photodynamic therapy inactivates extracellular matrix-basic fibroblast growth factor: insights to its effect on the vascular wall

PURPOSE

Photodynamic therapy (PDT), the light activation of photosensitizer dyes for the production of oxygen and other free radical moieties without the generation of heat, has been shown to inhibit the development of experimentally induced intimal hyperplasia. The host response to PDT, a form of vascular injury that results in complete vascular wall cell eradication, is devoid of inflammation and proliferation and promotes favorable vascular wall healing. These effects do not result in intimal hyperplasia and are suggestive of PDT-induced changes in the extracellular matrix (ECM). As a model to better understand the biologic consequences of PDT on the vascular wall matrix proteins, the effect of PDT was studied on the powerful matrix-resident mitogen basic fibroblast factor (bFGF) in vitro.

METHODS

PDT (5 to 200 J/cm2, 100 mW/cm2, 675 nm) was used with the photosensitizer chloroaluminum sulfonated phthalocyanine (5 micrograms/ml) to inactivate bFGF in vitro while 100 J/cm2 of irradiation was administered 24 hours after 5 mg/ml of the photosensitizer was used in vivo. PDT was used on bFGF in solution and on endothelial cell-derived ECM. Enzyme-linked immunosorbent assay was used to quantitate bFGF in solution after PDT treatment or after extraction from the ECM by collagenase and heparin. Functional activity of matrix-associated bFGF was assessed by smooth muscle cell mitogenesis by 3H-thymidine incorporation. To demonstrate the in vivo relevance of these observations, immunohistochemical analysis of PDT-treated rat carotid arteries was undertaken.

RESULTS

PDT eliminated detectable levels of bFGF in solution. PDT of ECM significantly reduced matrix-bound bFGF (1.0 +/- 0.6 vs 27.5 +/- 1.3 pg/ml; p < 0.0001). This reduction in bFGF after PDT of the ECM was associated with a decrease in vascular smooth muscle cell mitogenesis (52.4% +/- 4.6%; p < 0.0001) when plated on PDT-treated matrix compared with nontreated matrix. Quantitative replenishment of exogenous bFGF to PDT-treated matrix restored proliferation to baseline levels. PDT of rat carotid arteries demonstrated a loss of bFGF staining compared with control nontreated arteries.

CONCLUSIONS

PDT inactivation of matrix-resident bFGF and possibly other bioactive molecules can provide a mechanism by which PDT suppresses smooth muscle cell proliferation in the vessel wall. This free radical-mediated alteration of matrix may contribute to favorable vascular healing when PDT is used for the inhibition of injury-induced intimal hyperplasia.

Photodynamic therapy inhibits transforming growth factor beta activity associated with vascular smooth muscle cell injury

PURPOSE

The multifunctional cytokine, transforming growth factor beta 1 (TGF-beta), plays an important role in the development of injury-associated intimal hyperplasia (IH). Strategies to suppress local TGF-beta activity may have a clinical potential to prevent restenosis caused by IH. Photodynamic therapy (PDT) involves the local generation of cytotoxic free radicals by light activation of photosensitizer dyes and has been shown to inhibit experimental IH. This study investigated whether PDT-generated free radicals can affect TGF-beta activity in a biologic system using vascular smooth muscle cells (SMCs).

METHODS

The release and activation of TGF-beta by injured SMCs in culture was compared between mechanical injury and PDT. Mechanical injury was induced with a rubber policeman, and PDT was performed with the photosensitizer chloroaluminum sulfonated phthalocyanine (5 micrograms/ml) and 675 nm laser light at subtherapeutic 10 J/cm2 and the in vivo therapeutic dose of 100 J/cm2. Cell viability was assessed by the tetrazolium salt conversion assay, and active and total (active + latent) TGF-beta was determined by enzyme-linked immunosorbent assay in the conditioned media of SMCs 24 hours after treatment. Functional TGF-beta activity was assessed by inhibition of endothelial cell mitogenesis.

RESULTS

Both forms of injury severely reduced (p < 0.0005) SMC viability to less than 15%. In untreated SMC conditioned media, only 14.5% of the total TGF-beta was active (27.7 +/- 8.7 pg per 1 x 10(5) cells). However, after mechanical injury and PDT with 10 J/cm2, there was a significant increase (p < 0.02) in active TGF-beta (60.1 +/- 10.1 pg and 48.6 +/- 21.0 pg, respectively), despite a total reduction of approximately 50%. In contrast to this result, PDT with 100 J/cm2 did not result in increased levels of active TGF-beta (8.1 +/- 3.5 pg), despite having similar levels of total TGF-beta. Consequently, the conditioned media of SMCs that had 100 J/cm2 PDT did not inhibit endothelial cell mitogenesis as compared with the conditioned media of SMCs with mechanical injury and 10 J/cm2 PDT (p < 0.0002).

CONCLUSIONS

This report describes two novel findings: (1) injury to SMCs in vitro induces the conversion of biologically latent TGF-beta to active TGF-beta; and (2) the therapeutic PDT dose interferes with this injury activation process. This study substantiates the concept of local cytokine inhibition by PDT in a biologic system and provides new insights into the mechanisms of PDT-mediated inhibition of experimental IH.