Light and electron microscopic analysis of tattoos treated by Q-switched ruby laser.

Short-pulse laser exposures can be used to alter pigmented structures in tissue by selective photothermolysis. Potential mechanisms of human tattoo pigment lightening with Q-switched ruby laser were explored by light and electron microscopy. Significant variation existed between and within tattoos. Electron microscopy of untreated tattoos revealed membrane-bound pigment granules, predominantly within fibroblasts and macrophages, and occasionally in mast cells. These granules contained pigment particles ranging from 2-in diameter. Immediately after exposure, dose-related injury was observed in cells containing pigment. Some pigment particles were smaller and lamellated. At fluences greater than or equal to 3 J/cm2, dermal vacuoles and homogenization of collagen bundles immediately adjacent to extracellular pigment were occasionally observed. A brisk neutrophilic infiltrate was apparent by 24 h. Eleven days later, the pigment was again intracellular. Half of the biopsies at 150 d revealed a mild persistent lymphocytic infiltrate. There was no fibrosis except for one case of clinical scarring. These findings confirm that short-pulse radiation can be used to selectively disrupt cells containing tattoo pigments. The physial alteration of pigment granules, redistribution, and elimination appear to account for clinical lightening of the tattoos.

Response of the retinal pigment epithelium to selective photocoagulation.

Multiple short argon laser pulses can coagulate the retinal pigment epithelium selectively, while sparing the adjacent neural retina and choroid; in contrast, continuous-wave laser irradiation typically damages the neural retina and choroid. The healing response to selective photocoagulation of the retinal pigment epithelium was studied in rabbits during a period of 4 weeks. The lesions were never visible ophthalmoscopically. During the healing period, the epithelium was reformed by a single sheet of hypertrophic retinal pigment epithelial cells. In contrast to continuous-wave photocoagulation, only minimal inflammatory response was found. Retinal pigment epithelial cells showed clear signs of viability, eg, phagocytized outer segments. The local edema in the photoreceptor layer and subretinal space found in the early stage disappeared when the blood-retinal barrier was reestablished. The choriocapillaris remained unaffected. No subsequent damage to the photoreceptors was found. This type of photocoagulation may be useful for retinal pigment epithelium-related diseases, eg, diffuse diabetic macular edema.

Disruption of insect photoreceptor membrane by divalent ions: dissimilar sensitivity of light- and dark-adapted mosquito rhabdomeres.

The conditions that lead to the formation of myelin figures in rhabdomere microvilli were studied in the larval ocelli of the mosquito Aedes aegypti. These artifacts can result from the addition of divalent ions, such as Ca2+, to primary-aldehyde fixatives, but they form subsequently during postfixation with OsO4. In light-adapted ocelli, myelin figures are concentrated at the proximal ends of the microvilli along the cytoplasmic margin of the rhabdomere. The severity of the artifact is proportional to the ion concentration: scattered myelin whorls are induced by Ca2+ concentrations as low as 5 mM; they become abundant at 15 mM to 25 mM, and displace much of the rhabdomere margin at 50 mM. In contrast, even at high concentrations of Ca2+ few membrane whorls form in dark-adapted rhabdomeres, and these are mostly located at the distal ends of the microvilli. The differential response of the rhabdomere microvilli in light and darkness does not result from a direct action of light during fixation; it reflects an underlying difference between light- and dark-adapted photoreceptor membranes. We suggest that this differential sensitivity to divalent ions is associated with the shedding of membranes from the rhabdomere, a process that is enhanced by light and reduced in darkness.

An electron microscopic study on the process of acid demineralization of cortical bone.

Demineralization has been shown to foster osteoinductive properties of cortical bone grafts, yet little is known about the process of demineralization and how to control it. The purpose of this study was to investigate the process of cortical bone demineralization by using scanning electron microscopy to evaluate how hydrochloric acid demineralizes cortical bone. Results showed that in the demineralization of diaphyseal cortical bone specimens using hydrochloric acid, a uniformly thick circumferential band of demineralized bone matrix surrounds an inner undecalcified bone core as the process of demineralization occurs. The interface between the demineralized and mineralized section of the bone specimens was extremely sharp. This interface between demineralized and undemineralized bone was noted to advance as a reaction front with increasing demineralization which resulted in continuous shrinkage of the inner cortical bone core. This study suggests that cortical bone demineralization can be best described using an advancing reaction front theory, and this explanation can be used for implementation of the concept of controlled demineralization.

Photodynamic therapy inhibits experimental allograft rejection. A novel approach for the development of vascular bioprostheses.

BACKGROUND: Biological vascular allografts have proved unsatisfactory because of thrombosis, occlusion, and aneurysmal degeneration during chronic rejection. Photodynamic therapy (PDT), a technique that leads to the production of cytotoxic free radicals, was investigated as a novel method to prepare arterial allografts. METHODS AND RESULTS: Shortly after impregnation with the photosensitizer drug chloroaluminum sulfonated phthalocyanine, infrarenal aortas of ACI rats were PDT-treated and orthotopically grafted in Lewis rats (PDT). The transplanted grafts were sequentially analyzed at 2, 4, and 8 weeks by morphometry, immunohistochemistry, and scanning electron microscopy. Of 25 untreated allografts, 4 (16%) developed aneurysms compared with 0 of 33 in PDT or untreated isografts (ISO, P < .001). PDT treatment of allografts significantly inhibited intimal hyperplasia (P < .001) and resulted in intimal areas comparable to those in ISO. However, medial thickness in both control allografts and PDT grafts was markedly decreased compared with ISO. External graft diameters of control allografts at 8 weeks were significantly enlarged (P < .02) compared with PDT or ISO. At all time points, T lymphocytes were found in a substantially larger number in untreated control grafts than in PDT or ISO. Scanning electron microscopy at 4 weeks confirmed complete repopulation with endothelial cells in PDT, which was not seen in the control allografts. CONCLUSIONS: Our findings suggest that local PDT treatment of arterial allografts inhibits inflammatory infiltration, aneurysmal dilatation, and development of intimal hyperplasia and may be used to develop vascular bioprostheses for use in humans.

Photodynamic therapy of experimental choroidal melanoma using lipoprotein-delivered benzoporphyrin.

BACKGROUND: Benzoporphyrin derivative monoacid (BPD) is a new photosensitizer currently undergoing clinical trial for cutaneous malignancies. Compared with the clinically most frequently used sensitizer, Photofrin, BPD may offer higher tumor phototoxicity, better tissue penetration, and absence of significant skin sensitization. Low-density lipoprotein (LDL) carriers heighten efficiency and selectivity of BPD because neovascular and tumor cells express an increased number of LDL receptors. Hence, in addition to the vaso-occlusive effects similar to most other photosensitizers, LDL-BPD also has been shown to cause direct tumor cell damage. METHODS: Benzoporphyrin derivative monoacid was complexed with human LDL and used in photodynamic treatment of choroidal melanomas experimentally induced in eight albino rabbits. Five rabbits served as controls. Three hours after intravenous injection of 2 mg/kg body weight of LDL-BPD, eight tumors were irradiated at 692 nm and 100 J/cm2 via an argon-pumped dye laser coupled into a slit lamp. RESULTS: Angiography and histologic findings showed immediate photothrombosis after disintegration of endothelial membranes. After complete necrosis of tumor cells within 24 hours, a small fibrotic scar slowly developed. No tumor regrowth was noted up to 6 weeks when animals were killed. CONCLUSION: These data suggest that photodynamic treatment with LDL-BPD may be a promising modality for multiple clinical applications, including tumors and neovascularizations II.