Stent implantation for mesenteric bypass graft stenosis

PURPOSE

To present a case of symptomatic mesenteric bypass graft stenosis treated with Palmaz stent implantation.

METHODS AND RESULTS

A 65-year-old man with a history of mesenteric ischemia and superior mesenteric artery (SMA) occlusion presented with recurrent symptoms 3 years after Dacron graft revision surgery for occlusion of a venous aorto-SMA bypass graft. Graft thrombectomy revealed a tortuous segment of narrowed graft proximally, and a Palmaz stent was deployed across the defect. Adequate flow was restored through the conduit, and the patient has remained asymptomatic for 2 years.

CONCLUSIONS

Mesenteric ischemia is a rare and potentially fatal condition requiring major vascular intervention. Revision surgery may be avoided by angioplasty and stent insertion across flow-limiting stenoses, even in prosthetic grafts.

Photodynamic treatment of neoplastic lesions of the gastrointestinal tract. Recent advances in techniques and results

Photodynamic therapy (PDT) is a form of cancer treatment based on the selective accumulation of a photosensitizer (by exogenous or endogenous means) in neoplastic tissue. Subsequent activation of the photosensitizer by a specific wavelength of light results in tumor cell death. Activation of a photosensitizer to the appropriate energy state results in the production of singlet oxygen, a powerful oxidizing agent. PDT can kill cells by three mechanisms: direct cell death by photooxidation, apoptosis, or as a consequence of vascular shutdown. The toxicity of PDT is site specific and dependent on the organ being irradiated and the selectivity of the photosensitizer for target tissue over normal tissue. However, there are also reactions related to the sensitizer per se that are independent of those related to the treatment site. Such reactions include cutaneous photosensitization, nausea, vomiting, hypotension, and altered liver 'function' tests. Excitation of photosensitizer by an incident photon produces reemission of a fluorescent photon, which can be used to detect a tumor that is not ordinarily evident. The major limiting factor in using PDT is the depth of tumor kill. The majority of clinical experience involving PDT of the gastrointestinal tract involves patients who are considered to be poor operative risks, and reported follow-ups after treatment are not only limited but also variable.

Cells in cryptophycin-induced cell-cycle arrest are susceptible to apoptosis

Exposure of murine leukemia L1210 cells to the antitumor antibiotic cryptophycin 52 (C52) led to cell-cycle arrest at the prometaphase/metaphase interface within 18 h, but apoptotic nuclei did not appear until 36 h later. To determine whether accumulation of cells in early metaphase might have delayed the apoptotic process, cells were treated with C52 for 18 h and a photodynamic process was used to initiate the release of mitochondrial cytochrome c. Apoptosis was observed within 60 min, indicating that the slow apoptotic response was not caused by an impaired ability of genomic DNA to undergo endonucleosomal cleavage during cell-cycle arrest induced by cryptophycin 52.

Lutetium texaphyrin (Lu-Tex): a potential new agent for ocular fundus angiography and photodynamic therapy

PURPOSE

To investigate the suitability of lutetium texaphyrin (lu-tex) as a fluorescence imaging agent in the delineation of retinal vascular and choroidal vascular diseases. The utilization of an efficient fluorescent molecule that is also a photosensitizer represents a unique opportunity to couple diagnosis and therapy.

METHODS

Fundus fluorescence angiography comparing lu-tex (motexafin lutetium, Optrin, Pharmacyclics Inc, Sunnyvale, California) with the conventional angiographic dyes, sodium fluorescein, and indocynanine green (ICG), was performed on the eyes of normal and laser-injured New Zealand white rabbits. Plasma pharmacokinetic data and plasma protein binding were assessed in addition to light microscopy of the retina in both imaged and laser-injured eyes.

RESULTS

Normal retinal and choroidal vasculature was well delineated by lu-tex angiography. Experimentally induced choroidal and retinal vascular lesions were enhanced by lu-tex and demonstrated different staining patterns than fluorescein or ICG, particularly at the margins of the lesions. Lu-tex cleared rapidly from the plasma, with 39.7% bound to the high-density lipoprotein (HDL) fraction while 15.8% was bound to the low-density lipoprotein (LDL) fraction. No evidence of retinal toxicity after dye administration was observed by either ophthalmoscopy and fundus photography or by light microscopy.

CONCLUSION

Lu-tex angiography is a potentially valuable method for retinal vascular and choroidal vascular evaluation, and it has advantages over fluorescein and ICG angiography. The same agent could conceivably be used for both the identification of abnormal vasculature and subsequent photodynamic treatment.

Determinants of the apoptotic response to lysosomal photodamage

Studies with mouse leukemia L1210 cells revealed that selective lysosomal photodamage caused by any of three photosensitizing agents was followed by a gradual loss of the mitochondrial membrane potential (delta psi m), release of cytochrome c into the cytosol, increased DEVDase activity (a measure of levels of caspase-3) and a limited apoptotic response. Similar effects were observed in the murine hepatoma 1c1c7 cell line. Immunofluorescence techniques employing 1c1c7 cells demonstrated the immediate release of the lysosomal enzyme cathepsin B following lysosomal photodamage. These studies suggest that the cytotoxic effects of lysosomal photodamage are initiated by released lysosomal proteases that either directly and/or indirectly activate caspases as a consequence of the induction of mitochondrial damage.

Sites of photodamage induced by photodynamic therapy with a chlorin e6 triacetoxymethyl ester (CAME)

The acetoxymethyl ester of chlorin e6 (CAME) was initially designed to be a hydrophobic photosensitizing agent that would be recognized by an endocytic pathway and initially accumulated in lysosomes. This was expected to lead to hydrolysis of the ester groups, followed by redistribution of the free chlorin to other subcellular sites. In this study, we examined the patterns of localization of CAME and of subsequent photodamage in murine leukemia L1210 cells. The drug was initially localized at intracellular sites, yielding a pattern similar to that obtained with a fluorescent probe for acidic intracellular vesicles and endosomes. A brief (30 min) incubation with 10 microM CAME followed by irradiation led to mitochondrial photodamage and apoptotic cell death. At a higher drug level, or with a longer incubation time, we observed additional photodamage to the plasma membrane and to lysosomes. The higher photodynamic therapy dose led to inhibition of apoptosis, with cell death likely occurring via a necrotic process. Distribution of CAME among the components of human plasma was to albumin > high-density lipoprotein > low-density lipoprotein. These results have implications concerning the likely mechanism of CAME accumulation and subcellular distribution.

Enhanced responsiveness to photodynamic therapy-induced apoptosis after mitochondrial DNA depletion

Several lines of evidence indicate that mitochondria are an especially sensitive target for photodamage. Reports of cross resistance between photodynamic therapy (PDT) and the drug cisplatin, along with evidence that depletion of mitochondrial DNA (mtDNA) sensitized cells to cisplatin suggested a study of the photodynamic responsiveness of murine leukemia control L1210 cells versus cells depleted of mtDNA. Loss of mtDNA led to an increased sensitivity to mitochondrial photodamage, while the cytotoxic effects of lysosomal photodamage were not affected. Cells depleted of mtDNA showed an enhanced apoptotic response to PDT involving a mitochondrial target, compared with control cells.

Protein-binding patterns of the antitumor antibiotic cryptophycin 52 as measured with a two-phase partitioning system

Exposure of murine leukemia L1210 cells to the antitumor antibiotic cryptophycin 52 (C52) resulted in a rapid and dose-dependent increase in cell-surface hydrophobicity, as measured with a two-phase partitioning system. This effect was not observed with inactive drug analogs that lacked an epoxy residue. While the C52 has distinctly hydrophobic properties, the drug does not uniformly bind to all proteins. Affinity for human high- and low-density lipoprotein and albumin was demonstrated, but the drug binds only to the albumin fraction of mouse plasma, in spite of the high HDL level in the latter species.

Tumor blood-flow changes following protoporphyrin IX-based photodynamic therapy in mice and humans

The effects of aminolevulinic acid (ALA)-based photodynamic therapy (PDT) on tumor blood flow are controversial. This study examines the effects of ALA and Photofrin-based PDT on blood flow of Colon-26 tumors implanted in mice as well as the effects of ALA-based PDT on blood flow of human colorectal carcinomas and a carcinoid tumor in situ. Tumors are implanted in both flanks of mice. One tumor of each animal serves as a control. Blood flow is measured using a laser Doppler method. Tumor blood flow in mice not receiving a photosensitizer but treated with three different light fluences (50, 100 and 150 J/cm2) does not differ significantly from blood flow in the untreated tumor in the opposite flank. PDT after ALA administration using the three different light fluences does not significantly affect blood flow. In contrast, PDT after Photofrin administration causes a significant decrease in tumor blood flow with each light fluence, but this change is not as dramatic as reported in other studies. In contrast to mice, six patients who receive ALA prior to surgery all show a decrease in blood flow (mean = 51.8%, p < 0.001) after PDT using 100 J/cm2. Comparison with other published results suggests that it is likely that flow measurement by the laser Doppler method underestimates the effects of PDT on tumor blood flow due to the depth of laser penetration. Nevertheless, the present observations on blood flow suggest that the effects of ALA-based PDT on adenocarcinomas of the colon and rectum as well as an intra-abdominal carcinoid tumor in humans are more pronounced than would be predicated by some animal studies.

Subclavian stents and stent-grafts: cause for concern?

PURPOSE

To report cases of stent and stent-graft fracture in the subclavian vessels.

METHODS AND RESULTS

Three patients with self-expanding stents of 3 different types in 1 subclavian artery and 2 subclavian veins presented with recurrent symptoms 6 months to 2 years after stenting. All devices showed signs of compression with stent fracture. The covered stent in the subclavian artery was excised. Of the 2 venous patients, 1 was treated with first rib resection and the other refused further treatment.

CONCLUSIONS

The subclavian vessels are prone to flexion during movement, and the vessels may be compressed by external structures, including the clavicle and first rib. Stents that have not been designed to withstand these forces may be damaged.

Enhanced apoptotic response to photodynamic therapy after bcl-2 transfection

Apoptosis is a cellular death process involving the sequential activation of a series of caspases, endonucleases, and other enzymes. The initiation of apoptosis can be inhibited by overexpression of bcl-2 and certain other members of a related family of proteins. We examined the effects of bcl-2 overexpression on the apoptotic response to photodynamic therapy (PDT), using aluminum phthalocyanine as the photosensitizing agent. In this study, we compared the immortalized human breast epithelial cell line MCF10A with a subline (MCF10A/bcl-2) transfected with the human bcl-2 gene. The latter was approximately 2-fold more sensitive to the phototoxic effects of PDT. At a 50 mJ/cm2 light dose, photodamage to MCF-10A/bcl-2 resulted in a greater loss of the mitochondrial membrane potential (delta(psi)m), enhanced release of mitochondrial cytochrome c, a more rapid and greater activation of caspase-3, and a greater apoptotic response. Western blot analysis revealed that the transfected cell line showed overexpression of both bcl-2 and bax, and that PDT caused selective destruction of bcl-2, leaving bax unaffected. The greater apoptotic response by the transfected line is, therefore, attributed to the higher bax:bcl-2 ratio after photodamage.

Current concepts in gastrointestinal photodynamic therapy

OBJECTIVE

To review current concepts of photodynamic therapy (PDT) applied to the treatment of tumors of the gastrointestinal tract.

SUMMARY BACKGROUND DATA

PDT initially involves the uptake or production of a photosensitive compound by tumor cells. Subsequent activation of the photoreactive compound by a specific wavelength of light results in cell death, either directly or as a result of vascular compromise and/or apoptosis.

METHODS

The authors selectively review current concepts relating to photosensitization, photoactivation, time of PDT application, tissue selectivity, sites of photodynamic action, PDT effects on normal tissue, limitations of PDT, toxicity of photosensitizers, application of principles of PDT to tumor detection, and current applications of PDT to tumors of the gastrointestinal tract.

RESULTS

PDT is clearly effective for small cancers, but it is not yet clear in which cases such treatment is more effective than other currently acceptable approaches. The major side effect of PDT is cutaneous photosensitization. The major limitation of PDT is depth of tumor kill. As data from current and future clinical trials become available, a clearer perspective of where PDT fits in the treatment of cancers will be gained. Many issues regarding pharmacokinetic data of photosensitizers, newer technology involved in light sources, optimal treatment regimens that take advantage of the pharmacophysiology of photoablation, and light dosimetry still require solution. One can foresee application of differing sensitizers and light sources depending on the specific clinical situation. As technologic advances occur, interstitial PDT may have significant application.

CONCLUSIONS

PDT has a potentially important role either as a primary or adjuvant mode of treatment of tumors of the gastrointestinal tract.

Photoproduct formation from a zinc benzochlorin iminium salt detected by fluorescence microscopy

When examined by fluorescence microscopy, tumor cells loaded with a zinc benzochlorin iminium salt showed a very faint deep-red fluorescence that was rapidly transformed to a substantially brighter red-orange fluorescence. Fourier transfer spectroscopy analysis with a red-sensitive detection system revealed that an initial fluorescence at 770 nm was gradually converted to 640 nm fluorescence during excitation. Image analysis showed that photoproduct formation was accompanied by a change in the site of drug localization from the cytoplasm to the nucleus. These studies illustrate the power of interferometry for the characterization of photoproducts and changes in sensitizer localization during photoproduct formation.

Transport and localisation of m-THPC in vitro

The hydrophobic photosensitising agent meta-tetrahydroxyphenylchlorin (m-THPC) must be formulated with an appropriate vehicle before administration. Studies were carried out with murine leukaemia cells in vitro to assess the role of formulation in drug pharmacokinetics. The rate-limiting step in m-THPC accumulation was the slow conversion of drug aggregates to monomers upon dilution into growth media. Only non-viable cells with damaged membranes showed a rapid drug uptake, otherwise m-THPC accumulation was a slow process. It was found that m-THPC was localised mainly at mitochondrial loci. Subsequent irradiation resulted in the release of cytochrome c into the cytosol, triggering a rapid activation of caspase-3, which led to an apoptotic response. Plasma distribution of m-THPC involved binding to lipoprotein species, with only a slight appearance of the drug in the albumin fraction.

Stepping-table gadolinium-enhanced digital subtraction MR angiography of the aorta and lower extremity arteries: preliminary experience

PURPOSE

To compare stepping-table digital subtraction gadolinium-enhanced magnetic resonance (MR) angiography of the distal aorta and lower extremity arteries with conventional catheter digital subtraction x-ray angiography in patients with arterio-occlusive disease.

MATERIALS AND METHODS

Twenty patients underwent both conventional catheter angiography and fast three-dimensional gadolinium-enhanced MR angiography of the aorta and outflow vessels at 1.5 T; the images were acquired in three consecutive imaging locations during a single infusion of a gadolinium chelate.

RESULTS

Compared with catheter angiography, according to the findings of two blinded independent reviewers, MR angiography had sensitivities of 81% and 89% and specificities of 91% and 95%, respectively, for demonstration of insignificant (< or = 50%) stenosis versus significant (51%-100%) stenosis. For demonstration of occlusion, the sensitivity and specificity were 94% and 97%, respectively, by consensus. There was good interobserver correlation between the two readers overall (kappa = 0.65 for reporting the degree of narrowing in all lesions; 0.86, for reporting of insignificant versus significant stenoses; and 0.928, for reporting of occluded versus patient segments).

CONCLUSION

Stepping-table digital subtraction contrast material-enhanced MR angiography has high accuracy compared with catheter angiography in patients with arterio-occlusive disease of the aorta and outflow vessels. These preliminary study results suggest that this technique may ultimately provide a safe, noninvasive, and cost-effective alternative to catheter angiography.

The endovascular management of blue finger syndrome

OBJECTIVES

To review our experience of the endovascular management of upper limb embolisation secondary to an ipsilateral proximal arterial lesion.

DESIGN

A retrospective study.

MATERIALS AND METHODS

Over 3 years, 17 patients presented with blue fingers secondary to an ipsilateral proximal vascular lesion. These have been managed using transluminal angioplasty (14) and arterial stenting (five), combined with embolectomy (two) and anticoagulation (three)/anti-platelet therapy (14).

RESULTS

All the patients were treated successfully. There have been no further symptomatic embolic episodes originating from any of the treated lesions, and no surgical amputations. Complications were associated with the use of brachial arteriotomy for vascular access.

CONCLUSIONS

Endovascular techniques are safe and effective in the management of upper limb embolic phenomena associated with an ipsilateral proximal focal vascular lesion.

Size and age-sex distribution of pediatric practice: a study from Pediatric Research in Office Settings

OBJECTIVES

To estimate (1) the average number of patients per practitioner in Pediatric Research in Office Settings, the national practice-based research network of the American Academy of Pediatrics; (2) the total number of active patients cared for in the network; and (3) the age-sex distribution of patients seen in pediatric practice.

SETTING

Eighty-nine practices in 31 states with 373 Pediatric Research in Office Settings practitioners (59% of Pediatric Research in Office Settings members).

METHODS

Practices were asked to enumerate the number of patients visiting the practice during the 2-year period from January 1, 1991, through December 31, 1992. Patients making multiple visits were counted only once, resulting in a patient count rather than a visit count. Age-sex registers were completed using computer billing records or medical record sampling.

RESULTS

Study participants cared for 529513 active patients (50.7% male). Each practitioner cared for an average of 1546 patients. The number of patients per practitioner was significantly higher in less-populated areas and in solo practices. Children aged 12 years and younger comprised 81% of the patients seen by Pediatric Research in Office Settings practitioners, and more than half of the children were aged 6 years or younger. Before age 5 years, boys accounted for a slightly, but significantly, higher number of patients, whereas after age 14 years, girls comprised a significantly larger proportion of patients.

CONCLUSIONS

The average number of 1546 patients per practitioner derived from these private practice data is in line with health maintenance organization-based estimates. Pediatric practitioners predominantly serve younger children. These data provide the only current national estimates of the size and age-sex distribution of independent pediatric practices, and can help pediatricians and health service researchers plan for the future provision of health care to children.

Photodynamic therapy: a mitochondrial inducer of apoptosis

Photodamage to the mitochondria of murine leukemia P388 cells resulted in immediate loss of the mitochondrial membrane potential together with the release of cytochrome c into the cytosol. This was followed by a rapid activation of caspase 3-like proteases, as indicated by a marked rise in DEVDase activity. There was no significant effect on WEHDase or VEIDase activities, suggesting that only the late-stage caspases had been effected. The apoptotic response to mitochondrial photodamage was abolished by the broad-spectrum caspase inhibitor zVAD-fmk, but this did not prevent loss of viability after mitochondrial photodamage. These studies indicate that the release of cytochrome c from photodamaged mitochondria is sufficient to directly initiate a caspase-dependent apoptotic response.

Tumor versus vascular photodamage in a rat tumor model

The [4-(5-nitro-2-furyl)-2-thiazoyl] formamide (FANFT)-induced urothelial tumor in the rat is found to express the mdr gene. The resulting multidrug resistance (MDR) phenotype results in the expression of an outward transport system that prevents cellular accumulation of certain weakly cationic agents. Among the latter is a photosensitizer with known efficacy for the FANFT tumor, the copper benzochlorin iminium salt. FANFT cells are protected from direct cell kill mediated by this drug, suggesting that the substantial delay in tumor regrowth from this tumor/sensitizer combination can be attributed to vascular effects.

Photodynamic therapy

Photodynamic therapy involves administration of a tumor-localizing photosensitizing agent, which may require metabolic synthesis (i.e., a prodrug), followed by activation of the agent by light of a specific wavelength. This therapy results in a sequence of photochemical and photobiologic processes that cause irreversible photodamage to tumor tissues. Results from preclinical and clinical studies conducted worldwide over a 25-year period have established photodynamic therapy as a useful treatment approach for some cancers. Since 1993, regulatory approval for photodynamic therapy involving use of a partially purified, commercially available hematoporphyrin derivative compound (Photofrin) in patients with early and advanced stage cancer of the lung, digestive tract, and genitourinary tract has been obtained in Canada, The Netherlands, France, Germany, Japan, and the United States. We have attempted to conduct and present a comprehensive review of this rapidly expanding field. Mechanisms of subcellular and tumor localization of photosensitizing agents, as well as of molecular, cellular, and tumor responses associated with photodynamic therapy, are discussed. Technical issues regarding light dosimetry are also considered.