Biomedical subjects

N Michaud

Publications and source records attributed to N Michaud.

At least 19 recordsLinked to original sources

PubMed2001

Tattoo darkening and nonresponse after laser treatment: a possible role for titanium dioxide.

OBJECTIVE: To examine relationships between chemical composition, biopsy findings, and clinical outcome in laser-treated tattoos. DESIGN: Observational nonblinded retrospective study. SETTINGS: University-based dermatology clinic and private practice. PARTICIPANTS: Twenty patients who underwent biopsy of laser-treated tattoos. MAIN OUTCOME MEASURES: Biopsy specimens were analyzed after laser treatment, and the depths of changed particles were recorded. Ultrastructure of the changed particles was examined by electron microscopy. Presence of inorganic chemicals was determined by x-ray diffraction. Correlation between x-ray diffraction, microscopy, and clinical response was attempted. RESULTS: Of the 20 tattoos, 7 lightened, 9 failed to change, and 4 darkened after laser treatment. There was a significant association between presence of titanium dioxide and poor response to laser therapy. Microscopic studies showed variable changes in the ink particles, but there was a trend toward residual deep green pigment in the resistant tattoos. Also, round dark stippling was observed superficially in the darkened specimens. CONCLUSIONS: Titanium is overrepresented in tattoos that respond poorly to laser treatment. Further studies are necessary to show whether this metal is the primary cause of this poor response.

Coloring Agents↗

PubMed1999

Verteporfin photodynamic therapy retreatment of normal retina and choroid in the cynomolgus monkey.

OBJECTIVE: This study evaluated the effect of repeated photodynamic therapy (PDT) applications on normal primate retina and choroid using an intravenous infusion of liposomal benzoporphyrin derivative (verteporfin). DESIGN: This was an experimental study in a primate model. ANIMALS/CONTROLS: Six cynomolgus monkeys were used as experimental subjects and one monkey was used as a control subject. INTERVENTION: Three consecutive PDT treatments at 2-week intervals were applied over the center of the fovea or the optic nerve of each eye. Verteporfin was delivered by intravenous infusion at a dose of 6 mg/m2, 12 mg/m2, or 18 mg/m2. Laser irradiation was then applied using a diode laser (689 nm) with light doses and spot sizes kept constant. MAIN OUTCOME MEASURES: Findings were documented by fundus photography, fluorescein angiography, and light and electron microscopy. RESULTS: A cumulative dose response was seen angiographically and histologically with more severe damage to the retina and choroid noted at higher dye doses. Photodynamic therapy applied to the macula using the 6-mg/m2 verteporfin dose showed recovery of choriocapillaris, with mild retinal pigment epithelium and outer photoreceptor damage at 6 weeks. At this dose, the optic nerve showed few focal sites of axon atrophy and capillary loss. Treatments over the macula using the 12-mg/m2 and 18-mg/m2 doses led to chronic absence of choriocapillaris and photoreceptors at 6 weeks. One of two optic nerves became atrophic after PDT applications using dye doses of 12 mg/m2, and both optic nerves became atrophic in the 18-mg/m2 dye dose group. CONCLUSION: Limited damage to the retina, choroid, and optic nerve was present in primates treated with multiple PDT sessions using 6 mg/m2 verteporfin with light doses and the timing of irradiation kept constant. However, PDT using higher dye doses of 12 mg/m2 and 18 mg/m2 led to significant chronic damage to the normal retina, choroid, and optic nerve.

Animals↗

PubMed1999

Effects of photodynamic therapy using verteporfin on experimental choroidal neovascularization and normal retina and choroid up to 7 weeks after treatment.

PURPOSE: To study the long-term effects of photodynamic therapy (PDT), using liposomal benzoporphyrin derivative (BPD) or Verteporfin, on experimental choroidal neovascularization (CNV) and on normal retina and choroid (with no CNV) in the cynomolgus monkey eye. METHODS: Photodynamic therapy was performed in 8 cynomolgus monkey eyes with experimental CNV induced by laser injury. The effect of PDT on normal retina and choroid (with no CNV) was studied in 9 monkey eyes. Liposomal BPD was administered intravenously (0.375 mg/kg) either as a bolus, as a slow infusion over 32 minutes, or as a fast infusion over 10 minutes. Photodynamic therapy was performed using light at a wavelength of 689 or 692 nm, with an irradiance of 600 mW/cm2 and fluence of 150 J/cm2. Follow-up studies, including fundus photography and FA, were performed at 24 hours after PDT and then weekly. Indocyanine green and BPD angiography were performed in selected cases. Tissues were examined with light and electron microscopy at the end of follow-up. RESULTS: Twenty-three of the 32 areas of CNV treated with PDT showed absence of angiographic leakage at 24 hours. Twenty-eight areas of CNV were followed for 4 weeks; 22 of 28 showed absence of angiographic leakage at 2 weeks; and 20 of 28 at 4 weeks of follow-up. Forty spots on the normal retina and choroid were treated with PDT and were followed for 4 to 7 weeks. These spots showed pigment-laden cells in the outer retina, variably pigmented retinal pigment epithelium (RPE) in the treated area, intact neurosensory retina, and reperfusion of the choriocapillaris. CONCLUSIONS: Photodynamic therapy leads to absence of angiographic leakage for at least 4 weeks in experimental CNV in the monkey model. In the normal monkey eye the RPE and choriocapillaris show generalized recovery with preservation of the neurosensory retina 7 weeks after PDT.

Animals↗

PubMed1998

Comparison of responses of tattoos to picosecond and nanosecond Q-switched neodymium: YAG lasers.

OBJECTIVE: To test the hypothesis that picosecond laser pulses are more effective than nanosecond domain pulses in clearing of tattoos. DESIGN: Intratattoo comparison trial of 2 laser treatment modalities. SETTING: A large interdisciplinary biomedical laser laboratory on the campus of a tertiary medical center. PATIENTS: Consecutive patients with black tattoos were enrolled; all 16 patients completed the study. INTERVENTION: We treated designated parts of the same tattoo with 35-picosecond and 10-nanosecond pulses from 2 neodymium:YAG lasers. Patients received a total of 4 treatments at 4-week intervals. All laser pulse parameters were held constant except pulse duration. Radiation exposure was 0.65 J/cm2 at the skin surface. Biopsies were performed for routine microscopic and electron microscopic analysis at the initial treatment session and 4 weeks after the final treatment in 8 consenting patients. Also, ink samples were irradiated in vitro. MAIN OUTCOME MEASURES: In vivo, on the completion of treatment, a panel of dermatologists not associated with the study (and blinded to the treatment type) evaluated photographs to assess tattoo lightening. Formalin-fixed specimens were examined for qualitative epidermal and dermal changes as well as depth of pigment alteration. Electron micrographs were examined for particle electron density and size changes (in vivo and in vitro). The gross in vitro optical density changes were measured. RESULTS: In 12 of 16 tattoos, there was significant lightening in the picosecond-treated areas compared with those treated with nanosecond pulses. Mean depth of pigment alteration was greater for picosecond pulses, but the difference was not significant. In vivo biopsy specimens showed similar electron-lucent changes for both pulse durations. In vitro results were similar for both pulse durations, showing increases in particle sizes and decreased electron density as well as gross ink lightening. CONCLUSIONS: Picosecond pulses are more efficient than nanosecond pulses in clearing black tattoos. Black tattoos clear principally by laser-induced changes in the intrinsic optical properties of the ink.

Aluminum Silicates↗

PubMed1997

Photodynamic therapy and digital angiography of experimental iris neovascularization using liposomal benzoporphyrin derivative.

PURPOSE: To study the efficacy of liposomal benzoporphyrin derivative (BPD) (Verteportin) for the angiographic visualization and photodynamic therapy (PDT) of experimental iris neovascularization. METHODS: Experimental iris neovascularization was induced in eight cynomolgus monkey eyes by occluding all the branch retinal veins with a dye-yellow (577-nm) laser. Iris angiography was done with sodium fluorescein, indocyanine green (ICG), and liposomal BPD to compare the visualization of normal and neovascular vessels by these three dyes. PDT was performed using an intravenous infusion of liposomal BPD (0.375-0.75 mg/kg), followed by irradiation with 689-nm light from a diode laser/slit-lamp delivery system using 600 mW/cm2 irradiance and 150 J/cm2 fluence. The effect of treatment was followed by iris photography and angiography, and the findings were confirmed by histopathology using light and electron microscopy. RESULTS: Iris fluorescein angiography (FA) showed superficial tortuous and leaky new vessels. Liposomal BPD and ICG angiography of the same eye demonstrated deeper dilated and tortuous iris vessels, with minimal dye leakage. PDT of the iris with irradiation, performed within 20 minutes of the start of dye infusion (0.75 mg/kg), resulted in angiographic and histologic occlusion of iris vessels examined at 24 hours. Three to nine days after PDT, histopathologic examination showed regression of the iris neovascular membrane, with some open vessels. CONCLUSIONS: Liposomal BPD and ICG provided angiographic visualization of deeper normal and neovascular iris vessels. PDT using liposomal BPD leads to effective early closure to experimental iris neovascularization.

Angiography, Digital Subtraction↗

PubMed1996

Intravenous infusion of liposomal benzoporphyrin derivative for photodynamic therapy of experimental choroidal neovascularization.

OBJECTIVE: To compare the effectiveness of photodynamic therapy to close experimental choroidal neovascularization using an intravenous infusion of liposomal benzoporphyrin derivative (verteporfin) with previous work using a rapid intravenous injection, before initiating clinical trials. METHODS: Choroidal neovascularization was induced in cynomolgus monkey eyes using argon laser. Liposomal benzoporphyrin derivative was delivered by an intravenous infusion pump for 10 or 32 minutes at a dose of 0.375 mg/kg. Irradiation was performed with 689- or 692-nm laser light (600-mW/cm2 irradiance and 150-J/cm2 fluence) in 7 normal eyes and 11 eyes with choroidal neovascularization between 30 and 105 minutes after the start of dye infusion. Findings were documented by fundus photography, fluorescein angiography, and light and electron microscopy. RESULTS: Irradiation within 32 to 50 minutes of the start of the fast (10 minutes) or slow (32 minutes) dye infusion resulted in closure of choroidal neovascularization. In normal eyes, this technique caused choriocapillaris closure and retinal pigment epithelium damage with minimal damage to surrounding tissues. CONCLUSION: Photodynamic therapy using intravenous infusion of liposomal benzoporphyrin derivative selectively closed experimental choroidal neovascularization. This may be a suitable modality for clinical use.

Animals↗

PubMed1996

Liposomal benzoporphyrin derivative verteporfin photodynamic therapy. Selective treatment of choroidal neovascularization in monkeys.

PURPOSE: The authors have previously shown that photodynamic therapy (PDT) using lipoprotein-delivered benzoporphyrin derivative mono-acid (BPD) effectively closed experimental choroidal neovascularization (CNV). In the current study, the authors used a clinical preparation, liposomal BPD verteporfin in the same model, with experiments designed to establish optimal dye and light doses, and the timing of laser light irradiation after dye injection, for effective and selective closure of CNV. METHODS: Experimental CNV was induced in the maculae of cynomolgus monkeys. Liposomal BPD verteporfin was injected intravenously at doses of 1.0, 0.5, 0.375, and 0.25 mg/kg. Laser light at 692 nm then was applied to CNV, with an irradiance of 600 mW/cm2 and fluence of 150 J/cm2, at various times after dye injection, ranging from 5 to 120 minutes. Treatment effect was assessed by fundus photography and fluorescein angiography and confirmed by light and electron microscopy. The PDT of experimental CNV was studied to assess efficacy; PDT performance on normal eyes was studied to investigate selectivity. RESULTS: The CNV closure was demonstrated by fluorescein angiography and histopathologic findings at all tested dye doses. A dye dose of 0.375 mg/kg, with laser light irradiation applied 20 to 50 minutes after dye injection, optimized CNV closure with minimal retinal and choroidal damage. No major local adverse effects were noted, and the drug was well tolerated systematically. CONCLUSIONS: Liposomal BPD verteporfin is a potent photosensitizer, and PDT using this dye is a potentially effective and selective treatment for CNV.

Animals↗

PubMed1995

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

OBJECTIVE: To investigate photodynamic therapy of experimental choroidal neovascularization using benzoporphyrin derivative monoacid (Verteporfin). METHODS: Photodynamic therapy using benzoporphyrin derivative monoacid was investigated in cynomolgus monkeys. Following intravenous injection of benzoporphyrin derivative monoacid (1 to 2 mg/kg) complexed with low-density lipoprotein, the eyes were irradiated with 692-nm light at a fluence of 50 to 150 J/cm2 and irradiance of 150 to 600 mW/cm2. Choroidal neovascularization was documented before photodynamic therapy and closure was demonstrated by fundus photography, fluorescein angiography, and light and electron microscopic examination. RESULTS: Following photodynamic therapy, vessels within choroidal neovascularization were occluded, and there was damage to the choroidal neovascularization endothelium and the subjacent choriocapillaris. Damage to the retinal pigment epithelium and photoreceptors was also observed. CONCLUSION: Photodynamic therapy with lipoprotein-delivered benzoporphyrin derivative monoacid was effective in this animal model of choroidal neovascularization and may be a promising, potentially selective, therapy for choroidal neovascularization.

Animals↗

PubMed1994

Vascular targeting in photodynamic occlusion of subretinal vessels.

PURPOSE: To evaluate the potential of photodynamic therapy (PDT) using benzoporphyrin derivative (BPD) for occlusion of subretinal neovascular membranes, the authors studied efficiency and collateral damage of PDT-induced photothrombosis in the rabbit choriocapillary layer. METHOD: Benzoporphyrin derivative, a new photosensitizer, currently in clinical trials for tumor therapy, was used. Low-density lipoprotein served as a carrier to enhance selective targeting of vascular endothelial cells. RESULTS: Complete choriocapillary occlusion was achieved at a BPD dose of 2 mg/kg and a radiant exposure as low as 10 J/cm2. When PDT was performed 3 hours after BPD application, damage to the neural retina was minimal. Only inner photoreceptor segments showed mitochondrial swelling probably secondary to choroidal ischemia. Bruch's membrane remained intact. Retinal pigment epithelium was invariably damaged as seen with other photosensitizers. CONCLUSION: Compared with photocoagulation BPD-PDT allows endothelial-bound intraluminal photothrombosis, sparing important structures such as neural retina and Bruch's membrane. It may thus provide a more selective treatment of juxtafoveal and subfoveal neovascular membranes.

Animals↗

PubMed1994

Photodynamic therapy inhibition of experimental intimal hyperplasia: acute and chronic effects.

PURPOSE: Intimal hyperplasia (IH) is a focal arterial problem that still eludes successful therapy. We have previously demonstrated the feasibility of use of photodynamic therapy (PDT) for the acute treatment of experimental IH with light to activate an otherwise biologically inert photosensitizer. The purpose of this study was to determine the acute and long-term effects of PDT inhibition of IH on the artery wall. METHODS: Segmental IH was induced by balloon injury localized to the cervical common carotid artery of 33 rats. The photosensitizer chloroaluminum sulfonated phthalocyanine (5 mg/kg) for the experimental group or saline solution for the control group was administered intravenously. Twenty-four hours later, all instrumented portions of arteries were irradiated at 675 nm to induce cytotoxic injury in the PDT-treated arteries as compared with laser only-treated arteries for controls. Animals were killed at 1, 2, 4, and 16 weeks. RESULTS: There were no untoward side effects in either group. All PDT-treated arteries were devoid of smooth muscle or inflammatory cells in the treated media. There was no evidence of arterial degeneration of PDT-treated arteries. Only three arteries in the PDT group developed IH, whereas it was universal in all controls. In control arteries, immunocytochemistry with bromodeoxyuridine revealed maximal intimal and medial cell proliferation at 1 week, and morphometric analysis demonstrated a maximal IH at 2 weeks. Immunocytochemistry staining for smooth muscle cell actin was positive for the IH in control and when present in PDT-treated arteries, whereas the adventitia of PDT-treated arteries were positive after 2 weeks. Electron microscopy demonstrated early myofibroblast migration to the adventitia, and at 16 weeks occasional myofibroblasts were noted in the media of PDT-treated arteries. There was complete reendothelial cell covering of the intima by 4 weeks. CONCLUSIONS: These in vivo data demonstrate that PDT is an effective local method for the treatment of experimental IH. There is no evidence of significant recurrence of IH or arterial degeneration. Further studies with PDT may provide novel approaches to the understanding and treatment of arterial IH.

Animals↗

PubMed1994

[Selective vascular occlusion by repetitive short laser pulse].

The occlusion of arterioles and venules (30 microns in diameter) by means of repeated dye laser pulses (577 nm, 160 microseconds, 0.5 Hz) was studied in the hamster cheek pouch model. Microscopically visible changes during and after irradiation were recorded and monitored by a video system. The energy necessary per pulse for vessel occlusion with a single pulse (arterioles 5 J/cm2, venules 3.5 J/cm2) can be lowered more than 50% with 100 pulses (1.8 J/cm2, 1.2 J/cm2). Rupture of vessels, which regularly occurs with a single pulse, can be totally avoided with 100 repetitive laser pulses. Investigations of the temperature dependence of the occlusion rate of arterioles showed different interaction mechanisms with one pulse and 100 pulses (mechanical and thermal respectively). Light and electron microscopic investigations supported this concept of selective occlusion using repeated short laser pulses. Possible clinical applications are portwine stains of the eyelid, neovascularisation on the cornea and subretinal neovascularisation.

Animals↗

PubMed1993

An NAD derivative produced during transfer RNA splicing: ADP-ribose 1"-2" cyclic phosphate.

Transfer RNA (tRNA) splicing is essential in Saccharomyces cerevisiae as well as in humans, and many of its features are the same in both. In yeast, the final step of this process is removal of the 2' phosphate generated at the splice junction during ligation. A nicotinamide adenine dinucleotide (NAD)-dependent phosphotransferase catalyzes removal of the 2' phosphate and produces a small molecule. It is shown here that this small molecule is an NAD derivative: adenosine diphosphate (ADP)-ribose 1"-2" cyclic phosphate. Evidence is also presented that this molecule is produced in Xenopus laevis oocytes as a result of dephosphorylation of ligated tRNA.

Adenosine Diphosphate Ribose↗

PubMed1993

Most nuclear proteins are imported by a single pathway.

Using kinetic competition analysis, we show that the import of most Xenopus oocyte nuclear proteins is directed by a single family of nuclear localization signals (NLS). The transport of microinjected [35S]methionine-labeled nuclear proteins into oocyte nuclei was challenged with saturating concentrations of SV40 large T-antigen NLS peptide-BSA (P(Lys)-BSA) and was assessed by SDS-acrylamide gel electrophoresis and fluorography. P(Lys)-BSA was effective at competing the import of virtually all larger polypeptides but had a less marked effect on the mediated import of many smaller polypeptides. Wheat germ agglutinin, an inhibitor of nuclear pore complex function, enhanced the competitive effects of P(Lys)-BSA on the import of both large and small polypeptides. These data indicate that most 35S-labeled Xenopus oocyte nuclear proteins, including nucleoplasmin, contain NLSs that are functionally related to the T-antigen NLS and probably employ the same cytosolic NLS receptor(s).

Amino Acid Sequence↗

PubMed1993

[Histology of retinal lesions after continuous irradiation and selective micro-coagulation of the retinal pigment epithelium].

Mild continuous wave (CW) irradiation (100 ms, 20 mW, 514 nm) and irradiation with 100 repetitive 5 microseconds laser pulses (3 or 6 microJ, 514 nm) at a repetition rate of 500 Hz was performed to the regio macularis of chinchilla rabbits. The angiographically visible lesions were histologically followed up to 4 weeks. With both irradiation modalities the original retinal pigment epithelium (RPE) was replaced by a monolayer of new RPE cells. Only minimal immediate and no subsequent damage to the photoreceptors was found after selective RPE photocoagulation. Only minimal inflammatory response was found after selective RPE photocoagulation in contrast to CW photocoagulation where macrophages, RPE cells and lymphocytes regularly appear in the damaged photoreceptor layer.

Animals↗

PubMed1992

Microinjected U snRNAs are imported to oocyte nuclei via the nuclear pore complex by three distinguishable targeting pathways.

The inhibitory effects of wheat germ agglutinin and mAb 414 on the nuclear import of all types of U snRNAs indicate that they cross the nuclear envelope through the nuclear pore complex. However, the import of different U snRNAs occurs by kinetically distinct targeting pathways that can be distinguished from one another by the competitive effects of free trimethylguanosine cap dinucleotide (m3GpppG) and P(Lys)-BSA, an efficient synthetic karyophile based on the nuclear localization signal of SV40 large T antigen. The import of U snRNAs that contain 5' m3GpppN caps and are complexed by Sm proteins (U1, U2, U4, and U5) is competed by coinjection with free m3GpppG, indicating a shared transport factor, but not by P(Lys)-BSA. The import of U6 snRNA, which lacks a m3GpppN cap and is not complexed by the Sm proteins, is competed by P(Lys)-BSA but not by free m3GpppG. Thus, by the criterion of kinetic competition, U6 snRNA import is identical to that of the karyophilic proteins P(Lys)-BSA and nucleoplasmin. Uniquely, the import of U3 snRNA, which contains a m3GpppN cap but does not bind Sm proteins is not competed by either free m3GpppG or P(Lys)-BSA. Thus, U3 snRNA appears to be imported by a novel third kinetic pathway.

Amino Acid Sequence↗

PubMed1991

Pathways for the nuclear transport of proteins and RNAs.

The nuclear pore complex catalyses the import and export of both proteins and RNAs. The molecular mechanisms of RNA and protein translocation through the nuclear pore are likely to be similar; however, their signals and targeting apparatus may differ. Recent insights into RNA transport have come from studies of kinetic control mechanisms and the preconditions for translocation that include processing, RNP assembly, and a targeting function for 5' caps.

Journal Article↗

PubMed1991

Multiple pathways in nuclear transport: the import of U2 snRNP occurs by a novel kinetic pathway.

Protein import to the nucleus is a signal-mediated process that exhibits saturation kinetics. We investigated whether signal bearing proteins compete with U2 and U6 snRNPs during import. When injected into Xenopus oocytes, saturating concentrations of P(Lys)-BSA, a protein bearing multiple nuclear localization signals from SV40 large T-antigen, reduce the rate of [125I]P(Lys)-BSA and of [125I]nucleoplasmin import, consistent with their competing for and sharing the same limiting component of the import apparatus. In contrast, saturating concentrations of P(Lys)-BSA do not reduce the rate of HeLa [32P]U2 snRNP assembly or import. The import of U6 snRNP is also competed by P(Lys)-BSA. We conclude that U2 snRNP is imported into oocyte nuclei by a kinetic pathway that is distinct from the one followed by P(Lys)-BSA, nucleoplasmin, and U6 snRNP.

Animals↗

PubMed1991

[Microcoagulation of the fundus. Experimental results of repeated laser pulse exposure].

Angiographically visible lesions were produced in the fundus of rabbit eyes with repetitive 5 microseconds pulses and continuous wave exposures with 50-ms to 1-s pulse duration from an modified argon laser (514 nm). The ophthalmoscopic and the fluorescein angiographic findings showed less damage in the neural retina and the choroid after repetitively pulsed irradiation. Light microscopy and transmission electron microscopy showed that the neural retina and the choroid can mostly be spared by using repetitive 5 microseconds pulses, even though the damage to the retinal pigment epithelium is similar to the damage caused by continuous wave irradiation. Possible clinical applications, e.g. for macular edema and central serous retinopathy, are discussed.

Animals↗