John Tulip

Scanning electron microscopic analysis of canal wall dentin following neodymium-yttrium-aluminum-garnet laser irradiation

Five maxillary canines were split labiolingually and the canal concavities were debrided. At a series of evenly spaced locations along the canal wall, the concavity was flattened by an inverted cone bur to form small circular areas to be utilized as target locations. The specimens were stored in a thymolwater solution and subsequently rinsed in a 5.25% NaOCl solution for 1 min before lasing. The specimens were dried and lased from 10 to 90 W and 0.1 to 0.9 with a neodymium-yttrium-aluminum-garnet laser. Scanning electron microscopic analysis showed the effects of lasing to vary from no effects to disruption of the smeared layer to actual melting and recrystallization of the dentin, depending on such factors as power level, duration of exposure, and color of the dentin. The recrystallized canal wall dentin appeared to be nonporous and continuous in nature and could conceivably demonstrate reduced permeability to fluids.

Preclinical assessment of hypocrellin B and hypocrellin B derivatives as sensitizers for photodynamic therapy of cancer: progress update.

Abstract— Hypocrellins are perylenequinone pigments with substantial absorption in the red spectral region and high singlet oxygen yield. They are available in pure monomelic form and may be derivatized to optimize properties of red light absorption, tissue biodistribution and toxicity. In vitro screening of synthetic derivatives of the naturally occurring compound, hypocrellin B (HB), for optimal properties of cyto‐(dark) toxicity and phototoxicity resulted in selection of three compounds for preclinical evaluation: HBEA‐R1 (ethanolaminated HB), HBBA‐R2 (butylaminated HB) and HBDP‐R1 [2‐(N,N‐dimethylami‐no)‐propylamine‐HB]. Extinction coefficients at 630 nm (φ630) are 6230, 6190 and 4800, respectively; and 1O2 quantum yields, φ, 0.60, 0.32 and 0.42. Intracellular uptake is essentially complete within 2 h (HBEA‐R1, HBBA‐R2) and 20 h (HBDP‐R1). Greatest uptake is associated with lysosomes and Golgi. The HBEA‐R1 and HBBA‐R2 elicit phototoxicity in vitro primarily via the type II mechanism, with some type I activity under stringently hypoxic conditions. Transcutaneous phototherapy with HBEA‐R1 permanently ablates EMToVEd tumors growing in the flanks of Balb/c mice, with minimal cutaneous effects. The HBBA‐R2 does not elicit mutagenic activity in strains TA98 and TA100 of Salmonella typhi‐murium. Further development of selected hypocrellin derivatives as photosensitizers for photodynamic therapy is warranted.

Pulsed quantum cascade laser-based cavity ring-down spectroscopy for ammonia detection in breath

Breath analysis can be a valuable, noninvasive tool for the clinical diagnosis of a number of pathological conditions. The detection of ammonia in exhaled breath is of particular interest for it has been linked to kidney malfunction and peptic ulcers. Pulsed cavity ringdown spectroscopy in the mid-IR region has developed into a sensitive analytical technique for trace gas analysis. A gas analyzer based on a pulsed mid-IR quantum cascade laser operating near 970 cm(-1) has been developed for the detection of ammonia levels in breath. We report a sensitivity of approximately 50 parts per billion with a 20 s time resolution for ammonia detection in breath with this system. The challenges and possible solutions for the quantification of ammonia in human breath by the described technique are discussed.

Laser Doppler imaging of burn scars: a comparison of wavelength and scanning methods

UNLABELLED Laser Doppler perfusion imaging (LDI) is a useful tool for the early clinical assessment of burn depth and prognostic evaluation of injuries that may require skin grafting. We have evaluated two commercially available laser Doppler imagers for the perfusion measurement of normal and burn scar tissue. METHODS A single wavelength (635 nm), step-wise scanning LDI and a dual wavelength (633 and 780 nm), continuous scanning LDI were used. Twenty patients with hypertrophic burn scars (time since injury: 1 month-8 years) were recruited and the color and elevation of the scar was clinically assessed using a modified Vancouver Burn Scar Scale. Perfusion of each scar region was measured using both imagers. A symmetric contralateral region of unburned skin was also imaged to record baseline perfusion. RESULTS Comparisons of wavelength and scanning technique were made using perfusion values obtained from 22 burn scars. Highly significant positive correlation was observed in all comparisons. In addition, output from both instruments was strongly and significantly correlated with the clinical grading of the scar. SIGNIFICANCE Both LDI scanners perform similar perfusion measurements. The results also indicate that red and near-infrared (NIR) wavelength photons provide similar blood flow information. The faster, continuous scanning method provides a clinical advantage without a significant loss of blood flow information. However, a critical evaluation of both instruments suggests that caution must be exercised when using these optical diagnostic techniques and that some knowledge of light-tissue interaction is required for the proper analysis and interpretation of clinical data.

Ultraviolet photoionization in TEA lasers

Measurements of UV photoionization parameters for TEA CO 2 gas lasers are presented. Electron density and ionization decay times are given as a function of pressure for several gases and gas mixtures. Penetration depth of ionizing radiation in the gases is determined. The effect of selected additives on photoionization is demonstrated. The results show that a significant enhancement in electron density can be achieved. The X -band microwave interferometer data provide additional insight into the mechanisms involved and further substantiate the effectiveness of the technique in high-powered CO 2 laser design.

UPTAKE KINETICS AND INTRACELLULAR LOCALIZATION OF HYPOCRELLIN PHOTOSENSITIZERS FOR PHOTODYNAMIC THERAPY: A CONFOCAL MICROSCOPY STUDY

Hypocrellins are naturally occurring compounds with photosensitizing properties in biological systems. We have prepared synthetic derivatives of hypocrellin B, which have promise as photosensitizers in the clinical application of photodynamic therapy. The intracellular localization and uptake kinetics of hypocrellin B and several selected hypocrellin congeners were determined semiquantitatively by fluorescence confocal microscopy in monolayer cultures of EMT6/Ed murine tumor cells. Each compound had unique uptake kinetics. Although no compound tested to date has demonstrated nuclear labeling, most could be detected in lysosomes, Golgi, endoplasmic reticulum and, to a minor extent, in cellular membranes. No two compounds gave identical labeling distributions. The differences are assumed to originate in physicochemical properties characteristic of each compound, which may ultimately impact upon the primary modality of phototoxicity.

Effects of Photoradiation Therapy on Normal Rat Brian

Laser photoradiation of the brain via an optical fiber positioned 5 mm above a burr hole was performed after the injection of hematoporphyrin derivative (HpD) in 33 normal rats and 6 rats with an intracerebral glioma. Normal rats received HpD, 5 or 10 mg/kg of body weight, followed by laser exposure at various doses or were exposed to a fixed laser dose after the administration of HpD, 2.5 to 20 mg/kg. One control group received neither HpD nor laser energy, and another was exposed to laser energy only. The 6 rats bearing an intracranial 9L glioma were treated with HpD, 5 mg/kg, followed by laser exposure at various high doses. The temperature in the cortex or tumor was measured with a probe during laser exposure. The rats were killed 72 hours after photoradiation, and the extent of necrosis of cerebral tissue was measured microscopically. In the normal rats, the extent of brain damage correlated with increases in the dose of both the laser and the HpD. In all 6 glioma-bearing rats, the high laser doses produced some focal necrosis in the tumors but also damaged adjacent normal brain tissue. We conclude that damage to normal brain tissue may be a significant complication of high dose photoradiation therapy for intracranial tumors.

Hypocrellins as photosensitizers for photodynamic therapy : a screening evaluation and pharmacokinetic study

Abstract Hypocrellin compounds were selected as potential photosensitizers for photodynamic therapy (PDT) owing to their high quantum yields of singlet oxygen (1O2), and facility for site-directed chemical modification to enhance phototoxicity, pharmacokinetics, solubility, and light absorption in the red spectral region, among other properties. Parent hypocrellins A and B share an absorption peak at 658 nm. These molecules may therefore be considered useful progenitors of derivatives which absorb more strongly in the red, considering that the ideal sensitizer should absorb in the 650–800 nm range, beyond the absorption range of hemoglobin and melanin, and where light penetration in tissues is maximized through reduced scattering. A series of pure, monomeric hypocrellin derivatives was tested for properties of dark cytotoxicity and photosensitizing potential by clonogenic assay in monolayer cultures of EMT6/Ed murine tumor cells. Their respective toxicities are reported on a molar basis. The in vitro screening assay has, to date, resulted in the selection of four hypocrellin derivatives for further development as photosensitizers for PDT. Cellular uptake for photosensitizing doses of selected compounds was determined by fluorimetry. Dose escalation studies in rodents indicate that potentially photosensitizing doses promote no demonstrable systemic toxicity.

Photoradiation therapy: Current status and applications in the treatment of brain tumors

Photoradiation therapy is achieved when a photosensitizing drug is activated by light to form products that are lethal to tumor cells. The most commonly used drug is hematoporphyrin derivative, which is preferentially taken up and retained by malignant tissue. Photoactivation is usually produced by using a dye laser tuned at 630 nm (red light). The primary mechanism of neoplastic cell damage in photoradiation therapy involves the production of free radicals formed during illumination of hematoporphyrin derivative by light of this wavelength. The treatment would seem to damage first the tumor cell membrane, then the cytoplasmic inclusions, and finally the nucleus. Photoradiation therapy has been quite effective in the treatment of superficial malignancies, especially in skin, breast, eye, bladder, bronchus, and stomach. Experience with brain tumors is still limited. Important unresolved problems in the application of photoradiation therapy to gliomas include relative uptake of hematoporphyrin derivative into the tumor, limited light penetration of the tissue, local heating, and damage induced in normal brain by photoradiation therapy.

OPTICAL PROPERTIES OF EXPERIMENTAL PROSTATE TUMORS in vivo

The optical properties of tumor tissue provide important information for optimizing treatment plans in photodynamic therapy, especially when intertitial application by multiple fibers is planned. Near infrared light, required to activate novel photosensitizers, should facilitate improved light penetrance of tumor tissue compared with 630 nm light used for activating Photofrin II. We have measured light energy fluence rates for 630 and 789 nm light along radial tracks from a single laterally diffusing optical fiber centrally implanted into Dunning R3327‐AT and R3327‐H rat tracks from a single laterally diffusing optical fiber centrally implanted into Dunning R3327‐AT and R3327‐H rat prostate tumors in anesthetized rats. A total of 20 R3327‐AT and 10 R3327‐H tumors were used in this study with volumes from 2.6 to 13.3 cm3. Light track data were analyzed by an empirical model that described light attenuation. At 630 nm, light attenuation coefficients (LAC) were T1.9 × higher than those at 789 nm for both tumors with the well‐differentiated, well‐perfused tumor (R3327‐H) attenuating to a greater extent than did the rapidly growing anaplastic tumor (R3327‐AT). The intertumor variation of LAC was greater than the spatial variations observed within individual tumors. LAC were a function of tumor volume for only 630 nm light in the R3327‐AT tumors.