PHOTODYNAMIC RELEASE OF PROTOPORPHYRIN FROM INTACT ERYTHROCYTES IN ERYTHROPOIETIC PROTOPORPHYRIA: THE EFFECT OF SMALL REPETITIVE LIGHT DOSES

Abstract— Erythrocytes from patients with erythropoietic protoporphyria contain large amounts of protoporphyrin bound to (hemo)globin. Irradiation of these cells causes a shift in fluorescence emission maximum and a decreased fluorescence intensity which is consistent with transfer of protoporphyrin from (hemo)globin to the cell membrane. When the erythrocytes were irradiated intermittently, nearly 70% of the protoporphyrin was released and the hemolysis was less than 3%. Giving the total light dose as a single pulse, resulted in 84% protoporphyrin release and 16% hemolysis.
In vivo the erythrocytes obtain small, repetitive light doses when circulating in the dermal capillaries. We suggest the possibility that in patients with erythropoietic protoporphyria these small light pulses could be sufficient to photodamage the binding place of protoporphyrin on (hemo)globin. In the dark, protoporphyrin can then move from (hemo)globin through the cell membrane and bind to albumin in the serum. Our findings indicate that if protoporphyrin is not present in the cell membrane during irradiation, no photohemolysis will occur. This may explain why patients with erythropoietic protoporphyria have no abnormal hemolysis. The effect of intermittent light pulses may also contribute to the understanding of the protoporphyrin release from erythrocytes in patients with erythropoietic protoporphyria.     

ERYTHROPOIETIC PROTOPORPHYRIA: PHOTODYNAMIC TRANSFER OF PROTOPORPHYRIN FROM INTACT ERYTHROCYTES TO OTHER CELLS

Erythrocytes in patients with erythropoietic protoporphyria (EPP) contain large amounts of protoporphyrin and are regarded as the main source of protoporphyrin in this disease. Cells in the skin of EPP patients accumulate protoporphyrin released from the erythrocytes and upon sun exposure endothelial cells are photodamaged. In the present study a light-induced transfer of protoporphyrin directly from EPP erythrocytes to cultured cells is demonstrated. Erythrocytes were layered upon cultured cells and irradiated. The nearness of erythrocyte and cultured cell membranes potentiated the transfer of protoporphyrin between these cells. This transfer was rapid and preceded the release of protoporphyrin to proteins in the medium. Further irradiation of the protoporphyrin-enriched cultured cells, after removal of the erythrocytes, caused severe photodamage to the cells and survival was dependent on both the amount of protoporphyrin transferred and on the light fluence. Clinical observations and the results of this study indicate that light energy may be involved in two steps in the pathophysiology of EPP: (A) light-induced release of protoporphyrin from erythrocytes to endothelial cells and (B) photodynamic damage to protoporphyrin-enriched endothelial cells.     

Dynamic masking of PIV images using the Radon transform in free surface flows

Particle image velocimetry (PIV) processing of free surface flow images often requires the use of digital masks to overcome the problems caused by the interface. In cases where a large number of particle images are collected it is essential that the time-varying boundary between the two phases can be tracked automatically to produce the binary masks. The Radon transform-based technique presented in this paper allows the automatic detection of the air–water interface in a stream of particle images acquired from a single camera. It is applied to time-resolved PIV measurements in the liquid phase of a stratified multiphase flow in a circular pipe. Accuracy estimations are provided using synthetic and real wave profiles. An extension to the more complex case of an overturning wave is also discussed.     

Local search for the surgery admission planning problem

We present a model for the surgery admission planning problem, and a meta-heuristic algorithm for solving it. The problem involves assigning operating rooms and dates to a set of elective surgeries, as well as scheduling the surgeries of each day and room. Simultaneously, a schedule is created for each surgeon to avoid double bookings. The presented algorithm uses simple Relocate and Two-Exchange neighbourhoods, governed by an iterated local search framework. The problem’s search space associated with these move operators is analysed for three typical fitness surfaces, representing different compromises between patient waiting time, surgeon overtime, and waiting time for children in the morning on the day of surgery. The analysis shows that for the same problem instances, the different objectives give fitness surfaces with quite different characteristics. We present computational results for a set of benchmarks that are based on the admission planning problem in a chosen Norwegian hospital.     

On parallel local search for permutations

We investigate some ways in which massively parallel computing devices can be exploited in local search algorithms. We show that the substantial speedups that can be gained from parallel neighbourhood evaluation enables an efficient best improvement local search, and that this in turn enables further speedups through selection and parallel application of a set of independent, improving moves. Our experiments demonstrate a total speedup of up to several hundred times compared to a classical, sequential best improvement search. We also demonstrate how an exchange of good partial solutions between the incumbent and best found solutions improves the efficiency of the Iterated Local Search algorithm.     

Thermodynamic properties and phase transtions in the H2O/CO2/CH4 system

The availability of free energy densities as functions of temperature, pressure and the composition of all components is required for the development of a three-component phase field theory for hydrate phase transitions. We have broadened the extended adsorption theory due to Kvamme and Tanaka (J. Phys. Chem., 1995, 99, 7114) through derivation of the free energy density surface in case of CO(2) and CH(4) hydrates. A combined free energy surface for the liquid phases has been obtained from a SRK equation of state and solubility measurements outside hydrate stability. The full thermodynamic model is shown to predict water-hydrate equilibrium properties in agreement with experiments. Molecular dynamics simulations of hydrates in contact with water at 200 bar and various temperatures allowed us to estimate hard-to-establish properties needed as input parameters for the practical applications of proposed theories. The 5-95 confidence interval for the interface thickness for the methane hydrate/liquid water is estimated to 8.54 A. With the additional information on the interface free energy, the phase field theory will contain no adjustable parameters. We provide a demonstration of how this theory can be applied to model the kinetics of hydrate phase transitions. The growth of hydrate from aqueous solution was found to be rate limited by mass transport, with the concentration of solute close to the hydrate approaching the value characterizing the equilibrium between the hydrate and the aqueous solution. The depth of the interface was estimated by means of the phase field analysis; its value is close to the interface thickness yielded by molecular simulations. The variation range of the concentration field was estimated to approximately 1/3 of the range of the phase field.     

Two approaches for modelling hydrate growth

We consider two different approaches to model growth of CO₂ hydrate, phase field theory and a model based on cellular automata. The two approaches are applied to simulations of hydrate growth from supersaturated aqueous solution of CO₂. The thermodynamic models for the solution properties are derived from experimental solubility data while the hydrate thermodynamics is based on adsorption theory with reference properties derived from molecular simulations. We show that the cellular automata approach has the benefit of being much more computationally efficient, and are still giving results which are consistent with results from the phase field theory.     

Toward real-time particle tracking using an event-based dynamic vision sensor

Optically based measurements in high Reynolds number fluid flows often require high-speed imaging techniques. These cameras typically record data internally and thus are limited by the amount of onboard memory available. A novel camera technology for use in particle tracking velocimetry is presented in this paper. This technology consists of a dynamic vision sensor in which pixels operate in parallel, transmitting asynchronous events only when relative changes in intensity of approximately 10% are encountered with a temporal resolution of 1 μs. This results in a recording system whose data storage and bandwidth requirements are about 100 times smaller than a typical high-speed image sensor. Post-processing times of data collected from this sensor also increase to about 10 times faster than real time. We present a proof-of-concept study comparing this novel sensor with a high-speed CMOS camera capable of recording up to 2,000 fps at 1,024 × 1,024 pixels. Comparisons are made in the ability of each system to track dense (ρ >1 g/cm³) particles in a solid–liquid two-phase pipe flow. Reynolds numbers based on the bulk velocity and pipe diameter up to 100,000 are investigated.     

Mechanisms of photosensitivity in porphyric patients with special emphasis on erythropoietic protoporphyria

In erythropoietic protoporphyria, protoporphyrin overproduction occurs mainly in erythroid tissue. Protoporphyrin can be released from erythrocytes in the dark, but the release is greatly increased if the erythrocytes are exposed to small amounts of light. Protoporphyrin can be bound in plasma either to albumin or to low density or high density lipoprotein. The cutaneous symptoms in erythropoietic protoporphyria are primarily elicited by protoporphyrin-sensitized photodamage of endothelial cells due to the presence of protoporphyrin in lipid structures. Which structures are damaged first in endothelial cells is unknown. Endothelial cells probably accumulate protoporphyrin from albumin or lipoproteins present in the plasma. A direct transfer from the erythrocyte membrane to the endothelial cell membrane can also occur. The transfer processes are probably facilitated by light exposure.

Degranulation of mast cells, invasion of neutrophus into interstitial tissue and complement activation seem to be of less importance than endothelial cell injury in the pathogenesis of erythropoietic protoporphyria. These processes may, however, participate in the final expression of the cutaneous symptoms.

Uroporphyrin and coproporphyrin are hydrophilic and are probably unbound in plasma, although weak binding to plasma proteins cannot be excluded. In the hepatic porphyrias and in erythropoietic porphyria, the clinical symptoms are probably evoked by uroporphyrin and coproporphyrin present in the interstitial tissue. Very little is known about the primary targets of uroporphyrin and coproporphyrin photodamage in these disorders, but photodamage to intercellular structures probably represents the initial event. Activation of complement may contribute to the final expression of the cutaneous symptoms.     

The effect of gradient sampling schemes on diffusion metrics derived from probabilistic analysis and tract-based spatial statistics

Purpose

The purpose was to systematically evaluate the effect of diffusion gradient encoding scheme on estimated fractional anisotropy (FA), mean diffusivity (MD) and the voxel-wise probability of identifying crossing fibers in the brain.

Materials and Methods

Eight healthy volunteers (mean age 26.5±1.3 years, 5 males, 3 females) were imaged using a Spin-Echo Echo-Planar-Imaging sequence acquired with two signal averages [number of signals averaged (NSA)], 127 diffusion directions, and b-values of 750 s/mm² and 1500 s/mm². The number of diffusion gradient directions (N_d) was reduced from the original value whilst maintaining a homogeneous gradient distribution enabling direct comparison of subsampled data sets with N_d=15, 28, 43, 84, 112 and 127. FA and MD maps were generated and analyzed using tract-based spatial statistics. Effect of N_d on estimated FA and MD was tested with voxel-wise statistics in 13 regions of interest. The number of voxels supporting two fiber populations (NV²) at different N_d values was estimated using Bayesian estimation of diffusion parameters.

Results

Low FA values decreased significantly with increasing N_d and with increasing NSA. MD was only marginally sensitive to N_d and NSA. NV₂ increased significantly with N_d but not with NSA. Thus, we conclude that accurate estimation of standard diffusion metrics FA and MD is mainly dependent on the signal-to-noise ratio (SNR), whereas the ability to differentiate multiple fiber populations requires a high diffusion sampling density.