Hematoporphyrin derivative uptake by atheroma in atherosclerotic rabbits: the spectra of fluorescence from hematoporphyrin derivative demonstrated by an excimer dye laser

Photodynamic therapy in a cell culture model of human intimal hyperplasia

OBJECTIVE

To investigate the effectiveness of photodynamic therapy (PDT) in eliminating proliferating vascular smooth muscle cells (VSMCs). This may have a potential role in reducing restenosis rates clinically.

MATERIALS AND METHODS

Human VSMCs were successfully cultured from 15 long saphenous veins (SV) and seven restenotic lesions (RL) removed during revision coronary and peripheral vein graft surgery. Cultured VSMCs were incubated with photofrin at doses of 0-5 micrograms/ml for 48 h, and then exposed to 4 J/cm2 of polychromatic light. Cell destruction was quantified by a colorimetric assay using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide.

RESULTS

Results are expressed as a mean percentage survival +/- standard error. Cells were minimally affected by either photofrin alone (SV: 95.5% +/- 5.3; RL: 119.8 +/- 4.8) or light alone (SV: 75.38% +/- 3.99; RL: 100.1 +/- 11.0). The combination of 2 micrograms/ml of photofrin and 4 J/cm2 of polychromatic light energy, i.e. PDT, was severely toxic to cells derived from saphenous veins (5.52% +/- 0.85) as well as cells derived from restenotic lesions (9.6 +/- 2.3). These doses are comparable to doses that can be achieved in vivo.

CONCLUSION

PDT in the appropriate drug and light doses can eliminate human VSMCs, including those responsible for vascular restenosis.

Determining the optimal dose of Photofrin in miniswine atherosclerotic plaque

The purpose of this study was to determine the lowest dose of Photofrin (P) that would produce a 3:1 or greater ratio between atherosclerotic (AS) and control arterial walls. Aortoiliac AS was created in 24 Yucatan miniswine by a combination of balloon endothelial injury and 2% cholesterol and 15% lard diet for 7 weeks. Arteriography was then performed to demonstrate AS lesions. Following this, swine were given intravenously P in one of the following single dosages: 2.5, 1.0 or 0.5 mg/kg. Twenty-four hours later, swine were sacrificed and aortoiliac and control carotid artery segments removed and photographed with ultraviolet light to differentiate fluorescent from nonfluorescent areas. Arterial specimens were submitted for histologic analysis and chemical extraction for determination of fluorescence using a spectrofluorometer. Tissue concentration (ng/g tissue) of P from AS vessels were: Group I, 130.4 +/- 82.7; Group II, 10.0 +/- 1.2; and Group III, 9.1 +/- 0.6, respectively (P < 0.05). Ratios of P concentration in AS: control vessels were: Group I, 8.1 +/- 13.7; Group II, 1.1 +/- 0.2; and Group III, 0.9 +/- 0.1, respectively (P < 0.05). These results demonstrated that a P dose of 2.5 mg/kg provided at least a 3:1 ratio between AS: control artery wall.

Assessing Photofrin uptake in atherosclerosis with a fluorescent probe: comparison with photography and tissue measurements

The purpose of this study was to assess Photofrin porfimer sodium (P*) concentration in atherosclerotic plaque (ASP) using a fluorescence detector (Fluoroprobe) compared with fluorescent photography and chemical extraction of P*. ASP was created in the aortoiliac segments of Yucatan miniswine by a combination of balloon endothelial injury and 2% cholesterol and 15% lard diet for 7 weeks. At that time, swine were given P* I.V. in one of the following single dosages: Group I, 2.5; Group II, 1.0; or Group III, 0.5 mg/kg. Swine were sacrificed 24 hours later and aortoiliac and control carotid artery segments removed. Fluorescence was determined from these segments using photographic techniques, the Fluoroprobe, and a spectrofluorometer after chemical extraction. ASP were identified in all swine using photography and the Fluoroprobe. The intensity of fluorescence measured with the Fluoroprobe for Groups I to III was 1,098 +/- 524, 471 +/- 337, and 295 +/- 173 units, respectively (P < 0.01). The tissue concentration of P* in ASP from each group was 130.4 +/- 82.7, 10.0 +/- 1.2, and 9.1 +/- 0.6 ng/g, respectively (P < 0.01). There was a linear correlation between the fluorescence intensity measured with the Fluoroprobe and the extracted tissue concentration (r = 0.88, P < 0.0001). This study showed that a fluorescent detector such as the Fluoroprobe accurately detects the uptake of P* into atherosclerotic plaque.

In vitro uptake of dicarboxylic porphyrins by human atheroma. Kinetic and analytical studies

Human atheromatous aorta segments as well as presumably disease-free control aorta were obtained at autopsy. They were incubated with solutions of various purified dicarboxylic porphyrins including hematoporphyrin (HP) and hydroxyethylvinyldeuteroporphyrin (HVD), and with solutions of Photofrin. Selective labelling of the atheroma was shown by macroscopic and microscopic observations of the characteristic porphyrin fluorescence associated with the atheromatous plaques. The time dependence of the uptake, monitored by absorption spectrophotometry or by high performance liquid chromatography, was inferred from the disappearance of the porphyrins in the incubation medium. Significant binding was observed in the absence of albumin or serum proteins. The uptake of HP was less than that of the more hydrophobic compounds HVD or Photofrin when these porphyrins were used alone. The presence of albumin or serum drastically reduces atheroma labelling. Some competition between HP and HVD for binding sites is also seen. The present results do indicate that hydrophobic porphyrins have an intrinsic affinity for atheroma and that they can be taken up through passive processes. Taking into account previous data on animal models (Photochem. Photobiol. (1989), 731-737), it appears however that, in vivo, interactions with proteins and pharmacokinetics will primarily determine plaque labelling.

Preferential uptake of a water-soluble phthalocyanine by atherosclerotic plaques in rabbits

This study is the first demonstration of preferential accumulation of a water soluble phthalocyanine dye in atheromatous plaques in the rabbit. Two groups of rabbits with diet-induced atheromatous plaques were killed 4 and 24 h following intravenous administration of copper phthalocyanine tetrasulfonate. Uptake of the dye by plaque-containing and normal appearing aortae was evaluated macroscopically and quantitatively by extraction of the dye from the tissues. The concentration of the dye in the atheromatous plaques was 2.6 and 1.7 times higher than in the normal vessel wall at 4 and 24 h, respectively. The concentration of the dye in normal appearing aortae in the 2 study groups was similar to that of aortae of control rabbits which were fed a normal diet and exposed to the dye for the same time periods. We conclude that copper phthalocyanine accumulates preferentially in atheromatous plaques in rabbits. These findings provide a basis for the utilization of phthalocyanines for plaque identification and for photodynamic therapy of atherosclerosis.

Differential effect of Photofrin II on growth of human smooth muscle cells from nonatherosclerotic arteries and atheromatous plaques in vitro

The effect of dihematoporphyrin-ester or -ether (DHE), a photosensitizing porphyrin with different amounts of aggregates, on the growth of cultured smooth muscle cells obtained from nonatherosclerotic arteries and from atheromatous plaques (primary stenosing and restenosing lesions) was examined without photoactivation of the drug. Clinically relevant DHE concentrations ranging from 0.1 to 25 micrograms/ml were used. In all proliferation studies with cells of second and third passage (approximately 10 cumulative population doublings in vitro), the growth rates decreased in a dose-dependent manner. Smooth muscle cells from atherosclerotic lesions were significantly more sensitive than smooth muscle cells from normal arteries. Cells derived from restenosing lesions retained their increased sensitivity even after eight passages in culture (approximately 20 cumulative population doublings). Cell size measurements showed that the decreased proliferative activity mainly occurred in smooth muscle cell subpopulations consisting of small cells. A cytotoxic effect of DHE was observed at concentrations above 5 micrograms/ml, causing cytoplasmic protrusions, vacuoles, and even complete cell lysis. At a DHE concentration of 5 micrograms/ml, the number of viable cells was 73% +/- 14% (means +/- SD) for smooth muscle cells from nonatherosclerotic arterial media and only 38% +/- 11% (means +/- SD) for smooth muscle cells from atherosclerotic plaques. In all experiments, no significant difference in response to DHE treatment was observed between cells from primary stenosing and restenosing lesions, suggesting a specific mechanism for plaque-derived cells causing an increased sensitivity in comparison to smooth muscle cells from nonatherosclerotic arteries. The pronounced sensitivity of plaque cells against DHE treatment suggests that this drug--even without photoactivation--is potentially valuable in vivo as a therapeutic approach to vascular stenoses.

Responses of cultured smooth muscle cells from human nonatherosclerotic arteries and primary stenosing lesions after photoradiation: implications for photodynamic therapy of vascular stenoses

Cultured smooth muscle cells from human nonatherosclerotic arteries and from primary stenosing lesions were labeled with dihematoporphyrinester and ether, a photosensitizing probe used mainly for the detection and photodynamic therapy of tumors. After labeling for 24 h, cells were irradiated with ultraviolet light (wavelength 365 nm, energy densities ranging from 30 to 1,200 mJ/cm2). Twenty-four hours after photoradiation, 80% of smooth muscle cells from nonatherosclerotic arteries and only 20% of smooth muscle cells from atherosclerotic plaques were viable and still adherent. Moreover, dynamic cell and cytoskeletal alterations in response to irradiation are described. The differential sensitivity of smooth muscle cells from nonatherosclerotic arteries and from atherosclerotic plaques provides evidence that a photodynamic treatment might be a valuable therapeutic approach to vascular stenosis.

Photofrin II uptake by atheroma in atherosclerotic rabbits. Fluorescence and high performance liquid chromatographic analysis on post-mortem aorta

Atherosclerotic lesions were induced in normal and Watanabe rabbits by atherogenic diet and stripping of aorta endothelium. The rabbits were injected with Photofrin II and sacrificed two days later. Atheromatous aorta as well as normal aorta from control animals were characterized by their fluorescence spectra using front face excitation. Characteristic emission peaks at 631 and 694 nm were displayed at atheromatous plaques. The excitation spectrum shows a strong band at 394 nm and weaker bands at 446, 504, 536 and 574 nm. Although no fluorescence of normal aorta can be seen by visual inspection, emission with a maximum at 626 nm was detected by spectrofluorimetry. Normal phase high performance liquid chromatography analysis of extracts from atheroma and control aorta were also carried out. The specific labelling of atheroma involves mainly protoporphyrin, hematoporphyrin and also minor components of Photofrin II which are accumulated. Some other components are accumulated but do not appear to be specifically retained by atheroma.