Theoretical and practical aspects relating to the photothermal therapy of tumors of the retina and choroid: A review.

Photothermal treatment of tumors of the retina and choroid such as retinoblastomas, malignant melanomas, benign tumors as well as of vascular malformations can be performed by using laser radiation. A number of basic physical laws have to be taken into account in this procedure. Of particular importance thereby are: Arrhenius' law to approximate the kinetics of protein denaturation and photocoagulation, furthermore the electromagnetic radiation field, the distribution of both radiant and thermal energy induced in tumors and vascular structures, the influence of the wavelength and laser pulse duration (exposure time), as well as of the optical properties of the tissue. Strict confinement of the extent of the photothermal damage is critical since such pathological entities are frequently located close to the macula or optic nerve head.The conditions for tumor destruction are best fulfilled when using radiation in the near-infrared range of the electromagnetic spectrum such as that emitted from the diode (810 nm) and the Nd: YAG (1064 nm) laser, because of the good optical penetration properties of these radiations in tissue. Short wavelength sources of radiation, such as the argon ion (488, 514 nm) or the freqeuency-doubled Nd: YAG (532 nm) laser are less well suited for the irradiation of large vascular structures due to their poor penetration depths. However, for vascular formations with a small thickness (1 mm or less), short wavelength sources appear to be the most appropriate choice. Optical coupling of radiant energy to the eye by means of indirect ophthalmoscopic systems or positive contact lenses is furthermore of importance. Strong positive lenses may lead to severe constrictions of the laser beam within the anterior segment, that leads to high irradiance increasing the probability for structures to be damaged; with negative contact lenses, such as the -64 D Goldmann type lens, this danger is largely absent.

Sterilization and protection of protein in combinations of Camellia sinensis green tea extract and gamma irradiation.

Sterilization of milk protein without heating is of great interest. Gamma irradiation is a very powerful method to decontaminated casein. Gamma-irradiation of proteins in aqueous media at doses higher than 5kGy is known to induce their aggregation (without oxygen) or degradation (in presence of oxygen). Camellia sinensis green tea extract addition before irradiation of caseins cow milk proteins was examined. It was found that the presence of C. sinensis green tea extract during irradiation in the presence of oxygen conditions prevented the protein aggregation even at doses higher than 10kGy, probably by scavenging oxygen radicals produced by irradiation. The protective role of C. sinensis green tea extract allowing the gamma-irradiation treatment of caseins cow milk proteins in solution, was asserted by sodium dodecyl-sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and by high performance liquid chromatography inverse phase (RP-HPLC). The total viable microorganisms content evaluated by Plate Count Agar (PCA) incubation for 12h at 37°C, showed that caseins protein preparations gamma-irradiated remained sterile at a dose 2kGy in absence of C. sinensis green tea extract and at a dose lower than 2kGy in the presence of C. sinensis green tea extract.

Laser-induced modification of the patellar ligament tissue: comparative study of structural and optical changes.

The effects of non-ablative infrared (IR) laser treatment of collagenous tissue have been commonly interpreted in terms of collagen denaturation spread over the laser-heated tissue area. In this work, the existing model is refined to account for the recently reported laser-treated tissue heterogeneity and complex collagen degradation pattern using comprehensive optical imaging and calorimetry toolkits. Patella ligament (PL) provided a simple model of type I collagen tissue containing its full structural content from triple-helix molecules to gross architecture. PL ex vivo was subjected to IR laser treatments (laser spot, 1.6 mm) of equal dose, where the tissue temperature reached the collagen denaturation temperature of 60 ± 2°C at the laser spot epicenterin the first regime, and was limited to 67 ± 2°C in the second regime. The collagen network was analyzed versus distance from the epicenter. Experimental characterization of the collagenous tissue at all structural levels included cross-polarization optical coherence tomography, nonlinear optical microscopy, light microscopy/histology, and differential scanning calorimetry. Regressive rearrangement of the PL collagen network was found to spread well outside the laser spot epicenter (>2 mm) and was accompanied by multilevel hierarchical reorganization of collagen. Four zones of distinct optical and morphological properties were identified, all elliptical in shape, and elongated in the direction perpendicular to the PL long axis. Although the collagen transformation into a random-coil molecular structure was occasionally observed, it was mechanical integrity of the supramolecular structures that was primarily compromised. We found that the structural rearrangement of the collagen network related primarily to the heat-induced thermo-mechanical effects rather than molecular unfolding. The current body of evidence supports the notion that the supramolecular collagen structure suffered degradation of various degrees, which gave rise to the observed zonal character of the laser-treated lesion.

In situ thermal denaturation of proteins in dunning AT-1 prostate cancer cells: implication for hyperthermic cell injury.

The in situ thermal protein denaturation and its correlation with direct hyperthermic cell injury in Dunning AT-1 prostate tumor cells were investigated in this study. The in situ thermal protein denaturation was studied using both Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The FTIR spectra at different temperatures show changes in protein secondary structure (from alpha helix to extended beta sheet) during in situ thermal protein denaturation within AT-1 cells. Calorimetric studies using DSC show that endothermic heat release is associated with the in situ thermal protein denaturation. Furthermore, both the secondary structure changes detected by FTIR and the calorimetric changes detected by DSC were quantified and the kinetics of the overall in situ thermal protein denaturation was derived under different heating conditions. The onset temperature where the overall in situ thermal protein denaturation is first detectable was found to be scanning rate dependent (approximately 41 degrees C at 2 degrees C min(-1) and approximately 44 degrees C at 5 degrees C min(-1)). The kinetics of the overall in situ thermal protein denaturation was derived from both DSC and FTIR measurements and was fit using kinetic and statistical models. The kinetic data determined by FTIR and DSC under the same heating conditions match well with each other. The activation energy of the overall in situ thermal protein denaturation is found to be strongly dependent on the temperature range considered (the activation energy ranges from approximately 110 kJ mol(-1) between 44 and 90 degrees C to approximately 750 kJ mol(-1) between 44 and 50 degrees C). However, its dependence on heating rate is negligible. Several denaturation peaks, including a dominant one between approximately 62 and 65 degrees C, are identifiable from both the DSC and the FTIR results. To investigate directly the relationship between thermally induced cell injury and the in situ thermal protein denaturation, both acute (propidium iodide dye exclusion, assessed 3-h postthermal treatment) and chronic (clonogenics, assessed 7-day postthermal treatment) cell injury were quantified using AT-1 cells prepared under the same conditions as for the DSC protein studies. Comparisons of the results from the cell injury studies and the DSC protein denaturation studies show that the overall in situ thermal protein denaturation correlates well with both the acute and the chronic cell injury, which suggests that overall in situ thermal protein denaturation is an important mechanism of direct hyperthermic cell injury in AT-1 cells at the macromolecular level.