Erythrocytes membrane fluidity changes induced by adenylyl cyclase cascade activation: study using fluorescence recovery after photobleaching.

In this study, fluorescence recovery after photobleaching (FRAP) experiments were performed on RBC labeled by lipophilic fluorescent dye CM-DiI to evaluate the role of adenylyl cyclase cascade activation in changes of lateral diffusion of erythrocytes membrane lipids. Stimulation of adrenergic receptors with epinephrine (adrenaline) or metaproterenol led to the significant acceleration of the FRAP recovery, thus indicating an elevated membrane fluidity. The effect of the stimulation of protein kinase A with membrane-permeable analog of cAMP followed the same trend but was less significant. The observed effects are assumed to be driven by increased mobility of phospholipids resulting from the weakened interaction between the intermembrane proteins and RBC cytoskeleton due to activation of adenylyl cyclase signaling cascade.

Influence of optical clearing agents on the scattering properties of human nail bed and blood microrheological properties: In vivo and in vitro study.

Optical clearing agents (OCAs) are substances that temporarily modify tissue's optical properties, enabling better imaging and light penetration. This study aimed to assess the impact of OCAs on the nail bed and blood using in vivo and in vitro optical methods. In the in vivo part, OCAs were applied to the nail bed, and optical coherence tomography and optical digital capillaroscopy were used to evaluate their effects on optical clearing and capillary blood flow, respectively. In the in vitro part, the collected blood samples were incubated with the OCA and blood aggregation properties were estimated using diffuse light scattering techniques. The results indicate that OCAs significantly influence the optical properties of the nail bed and blood microrheology. These findings suggest that OCAs hold promise for improving optical imaging and diagnostics, particularly for nail bed applications, and can modify blood microrheology.

Label-Free Multiphoton Microscopy: The Origin of Fluorophores and Capabilities for Analyzing Biochemical Processes.

Multiphoton microscopy (MPM) is a method of molecular imaging and specifically of intravital imaging that is characterized by high spatial resolution in combination with a greater depth of penetration into the tissue. MPM is a multimodal method based on detection of nonlinear optical signals - multiphoton fluorescence and optical harmonics - and also allows imaging with the use of the parameters of fluorescence decay kinetics. This review describes and discusses photophysical processes within major reporter molecules used in MPM with endogenous contrasts and summarizes several modern experiments that illustrate the capabilities of label-free MPM for molecular imaging of biochemical processes in connective tissue and cells.

Numerical Simulation of Light Propagation and Scattering in Turbid Biological Media.

This article considers the processes of light propagation and scattering in biological tissues. The results obtained made it possible to estimate basic signal parameters and their dependence on various optical parameters with respect to the laser Doppler flowmeter and laser Doppler microscope. We also developed a new method to determine the indicatrix asymmetry of single and multiple light scattering by a suspension of oriented spheroidal particles that simulated erythrocytes in a shear flow. It was found that the angular dependence of the asymmetry index provides information on the shape and orientation of particles. In addition, we obtained single scattering indicatrices, which may improve the accuracy of computer simulation of light scattering by blood.

Characterization at the individual cell level and in whole blood samples of shear stress preventing red blood cells aggregation.

The aggregation of red blood cells (RBC) is an intrinsic feature of blood that has a strong impact on its microcirculation. For a number of years it has been attracting a great attention in basic research and clinical studies. Here, we study a relationship between the RBC aggregation parameters measured at the individual cell level and in a whole blood sample. The home made optical tweezers were used to measure the aggregating and disaggregating forces for a pair of interacting RBCs, at the individual cell level, in order to evaluate the corresponding shear stresses. The RheoScan aggregometer was used for the measurements of critical shear stress (CSS) in whole blood samples. The correlation between CSS and the shear stress required to stop an RBC pair from aggregating was found. The shear stress required to disaggregate a pair of RBCs using the double channel optical tweezers appeared to be about 10 times higher than CSS. The correlation between shear stresses required to prevent RBCs from aggregation at the individual cell level and in whole blood samples was estimated and assessed quantitatively. The experimental approach developed has a high potential for advancing hemorheological studies.

[Reduction of erythrocyte deformability in Krushinskii-Molodkina rats in acute hemorrhagic cerebrovascular circulation disorders].

The ability of erythrocytes to change their shapes in the shear flow under acute strokes of hemorrhagic type in rats of the Krushinsky-Molodkina line was studied. The rigidity of membranes and the internal viscosity of erythrocytes were investigated by the laser diffraction method. The method consists in obtaining diffraction images from a thin layer of a dilute suspension of erythrocytes moving in the shear flow and subsequent computer processing of these images. It was shown that strokes of hemorrhagical type in rats of the Krushinsky-Molodkina line cause a reduction in the ability of erythrocytes to change theirs shapes.

Self-localization of laser induced tumour coagulation limited by heat diffusion through active tissue.

We analyse necrosis growth due to thermal coagulation induced by laser light absorption and limited by heat diffusion into the surrounding live tissue. The tissue is assumed to contain a tumour in the undamaged tissue where the blood perfusion rate does not change during the action. By contrast, normal tissue responds strongly to an increase in the tissue temperature and the blood perfusion rate can grow by tenfold. We study in detail necrosis formation under conditions typical of a real course of thermal therapy treatment. The duration of the treatment is about 5 minutes when a necrosis domain of about 1 cm or above is formed. In particular, if the tumour size is sufficiently large, i.e. it exceeds 1 cm, and the tissue response is not too delayed, i.e. the delay time does not exceed 1 min, then there are conditions under which the relative volume of the damaged normal tissue is small in comparison with the tumour volume after the tumour is totally coagulated.

[A drop in "apparent" blood viscosity due to administration of high-molecular polymer capable of augmenting viscosity].

Influence of a high-molecular compound capable of augmenting viscosity, namely: polyethylene oxide Polyox WSR-301, on hemodynamic parameters in rat mesenteric microvessels was investigated. A substantial decrease in the arteriolar hemodynamic resistance caused by the polymer was revealed. Special research has shown that this reaction is not connected with a vasodilatation and, therefore, is caused by a reduction in the "apparent" viscosity of the blood, i.e., it is a consequence of changed properties of the blood flow.

Reduction of erythrocyte deformability in rats with cerebral ischemia.

Erythrocyte deformability was studied by laser interferometry in rats with cerebral ischemia. Ninety minutes after ligation of both common carotid arteries the erythrocyte deformability coefficient decreased by 11+/-2% in experimental group in comparison with the baseline level and by 12% in comparison with sham-operated animals and remained 16% decreased after 4 days.

[Study of kinetic parameters of singlet molecular oxygen in aqueous porphyrin solutions. Effect of detergents and the quencher sodium azide]. / Issledovanie kineticheskikh parametrov singletnogo molekuliarnogo kisloroda v vodnykh rastvorakh porfirinov. Vliianie detergentov i tushitelia--azida natriia.

The kinetic parameters of porphyrin-photosensitized formation and deactivation of singlet molecular oxygen (1O2) and their dependence on the concentration of the 1O2 quencher sodium azide were investigated in air-saturated water, ethanol, and aqueous micellar solutions of detergents using time-resolved measurements of oxygen phosphorescence under pulsed laser excitation. The lifetimes of 1O2 formation and deactivation and the rate constants of 1O2 quenching by sodium azide were determined. It was shown that, with no azide in the solutions, the rise in phosphorescence intensity after the laser flash corresponded to the kinetics of energy transfer from the porphyrin triplet molecules to oxygen, while the decay kinetics corresponded to the kinetics of 1O2 deactivation. In the presence of detergent, a considerable increase in the 1O2 lifetime was observed, which is likely due to the localization of 1O2 molecules mostly in lipophilic micelles and not in the water phase. If relatively high azide concentrations were used, the lifetime of the porphyrin triplet state did not change but the 1O2 lifetime decreased to values similar to those in living cells. In this case, the inversion of the phosphorescence kinetic phases was observed. The rise corresponded to 1O2 deactivation, and the decay, to the energy transfer from triplet porphyrin to oxygen. The data suggest that, in living cells, 1O2 molecules are also located mainly in lipophilic structures and the 1O2 lifetime determines the kinetics of the phosphorescence rise after the laser pulse.

Guest editorial: special section on optical diagnostics of biological fluids.

This Special Section Guest Editorial provides an overview of the topical area and an introduction to the articles featured in the special section.

Aggregation and disaggregation of erythrocytes in whole blood: study by backscattering technique.

The aggregation phenomenon is of great importance for the evaluation of performance of the microcirculation system because of its influence on the blood viscosity at low shear stresses. Some important features and consequences of this phenomenon in vivo can be predicted in the in vitro experiments using optical methods. These methods are considered to be the most informative and applicable not only for the basic study of the aggregation phenomenon, but also for the diagnosis of a number of diseases and for the monitoring of therapeutic treatment in clinics. Results presented in this paper prove that the backscattering technique allows one to detect different changes of aggregational ability and deformability of erythrocytes and to get reliable and reproducible results distinguishing normal blood and blood with different pathologies. © 1999 Society of Photo-Optical Instrumentation Engineers.

Effect of blood vessel discreteness on necrosis formation during laser induced thermal coagulation limited by heat diffusion.

When heated, living tissue exhibits random nonuniformities in temperature that are due to the discreteness of vessel arrangement. Because of the strong temperature dependence of the thermal coagulation rate these nonuniformities should substantially affect the necrosis growth induced by local heating. In the present work we study the effect of vessel discreteness on the form of a necrosis domain when its growth is limited by heat diffusion into the surrounding tissue. Namely, we analyze the characteristics of the necrosis boundary that are due to vessel discreteness. In particular, we find the mean amplitude Î´Γ and the correlation length lΓ of the necrosis boundary perturbations depending on the main tissue parameters. In addition, it is shown that there are universal relations between the mean size ℜ of the necrosis domain and the characteristics δΓ,lΓ of the boundary perturbations, which are due to the fractal structure of the vascular network. © 1999 Society of Photo-Optical Instrumentation Engineers.

Clinical application of the measurement of spontaneous erythrocyte aggregation and disaggregation. A pilot study.

Aggregation and disaggregation kinetics of erythrocytes in samples of whole blood were studied using a backscattering nephelometry technique. Blood was drawn from normal subjects and from patients suffering from different diseases: chronic glomerulonephritis, systemic lupus erythematosus, hereditary hypercholesterolemia, pulmonary hypertension, intestinal tumors preoperatively (age > 60 years), psoriasis, psoriatic arthritis, ischemia and ischemia with diabetes. Blood samples of healthy donors were used as controls. The backscattering signal in the erythroaggregometer was processed according to algorithms yielding quantitative data on the full amplitude of aggregation, characteristic times of spontaneous aggregation, average hydrodynamic strength of all aggregates and, whenever possible, additionally, strength of the largest aggregates. The obtained results confirm that the complexity of erythrocyte aggregation kinetics requires multiparametric description which, when applied to clinical material, enables the differentiation of aggregation characteristics between diseases.

Effective interface dynamics of laser-induced heat diffusion-limited thermal coagulation.

The general problems of describing local thermal coagulation dynamics leading to the growth of necrosis that is limited by heat diffusion to surrounding live tissue is considered. It is demonstrated that in this case the typically used distributed model for thermal coagulation is based on a self-inconsistent approach, and a more rigorously justified free boundary model is derived. This free boundary model takes into account only the general properties of thermal coagulation and so provides a self-consistent description. It is shown that the two models, nevertheless, predict practically the same dynamics of necrosis growth because this growth is insensitive to the particular properties of heat transfer in the thin layer of partially damaged tissue. Necrosis growth is also simulated numerically under various physical conditions to verify the assumptions adopted. © 1998 Society of Photo-Optical Instrumentation Engineers.

Feasibility of picosecond laser-Doppler flowmetry provides basis for time-resolved Doppler tomography of biological tissues.

A detectable signal is obtained from a laser Doppler flowmeter operating in the heterodyne mode with nano- and pico-second pulse laser sources. The ultrashort pulse probing may be useful for depth-dependent time-resolved laser Doppler velocity measurements of blood perfusion in biological tissues. © 1998 Society of Photo-Optical Instrumentation Engineers.

On refraction in Monte-Carlo simulations of light transport through biological tissues.

To obtain reliable results from Monte-Carlo simulations of light scattering experiments, a statistically accurate procedure for positioning the photons after refraction between two different scattering media is necessary. Two statistically equivalent algorithms for calculating the position of the photons immediately after crossing an interface are described and justified.

Probabilistic model of multiple light scattering based on rigorous computation of the first and the second moments of photon coordinates.

We consider a concise method based on recurrent relations that permit rigorous computing of the first and the second moments of the components of the vector locating a randomly walking photon in an infinite homogeneous light-scattering medium. On assumption that the components obey a three-dimensional Gaussian distribution a probability density for the photon locations at the Nth scattering event can readily be written down and the light-intensity distribution in the medium may be calculated. The results from theoretical analyses are compared with the solution of a light-diffusion equation and with results of Monte Carlo simulations and show a better fit with simulated data than the diffusion approximation.