Photosensitization Reaction-Induced Acute Electrophysiological Cell Response of Rat Myocardial Cells in Short Loading Periods of Talaporfin Sodium or Porfimer Sodium

A Three-Compartment Pharmacokinetic Model to Predict the Interstitial Concentration of Talaporfin Sodium in the Myocardium for Photodynamic Therapy: A Method Combining Measured Fluorescence and Analysis of the Compartmental Origin of the Fluorescence

To evaluate the effectiveness of photodynamic therapy occurring in the interstitial space of the myocardium, we estimated the interstitial concentration of talaporfin sodium in the canine myocardium by constructing a three-compartment pharmacokinetic model based on measured changes in talaporfin sodium plasma concentration and myocardial fluorescence. Differential rate equations of talaporfin sodium concentration in the plasma, interstitial space, and cell compartment were developed with individual compartment volume, concentration, and rate constants. Using measured volume ratios based on histological examinations, we defined that the myocardial fluorescence consisted of the linear addition of fluorescence generated from these three compartments. The rate constants were obtained by fitting to minimize the sum of the squared errors between the measured talaporfin sodium concentrations and the calculated concentrations divided by the number of data points using the conjugate gradient method in MATLAB. We confirmed that this fitting operation may be appropriate, because a coefficient of determination between the measured talaporfin sodium changes and the calculated concentrations using our equations was 0.99. Consequently, to estimate the interstitial concentration in the canine myocardium, we propose a three-compartment pharmacokinetic model construction methodology using measured changes in talaporfin sodium plasma concentration and changes in myocardial fluorescence.

Development of a practical animal model of photodynamic therapy using a high concentration of extracellular talaporfin sodium in interstitial fluid: influence of albumin animal species on myocardial cell photocytotoxicity in vitro

Photodynamic reaction-induced photocytotoxicity using talaporfin sodium is inhibited by serum proteins binding to talaporfin sodium. The serum albumin binding site for talaporfin sodium differs among animal species. To identify a practical animal therapeutic model, we studied the ability of human, canine, bovine, and porcine albumin to influence talaporfin sodium-induced photocytotoxicity in rat myocardial cells in vitro. Human, canine, bovine, and porcine serum albumins were used. The ratio of talaporfin sodium binding, which is strongly associated with photocytotoxicity, was measured by ultrafiltration with an albumin concentration of 0.5-20 mg/ml and 20 μg/ml talaporfin sodium to mimic interstitial fluid. Rat myocardial cell lethality was measured by the WST assay 2 h after samples were exposed to a radiant exposure of 20 J/cm² by a red diode laser (Optical Fuel™, Sony, Tokyo, Japan) with a wavelength of 663 nm. The binding ratio dependence on albumin concentration differed among the animal species. Bovine albumin exhibited the largest difference from human albumin, with a maximum difference of 31% at 2 mg/ml albumin. The cell lethality characteristic was similar between human and canine albumin. The cell lethality dependence on albumin was not in the same order as the binding ratio. Cell lethality was lowest for human albumin with higher albumin concentrations between 5 and 20 mg/ml. There were no significant differences in cell lethality between bovine and porcine albumin and between human and canine albumin. We suggest that the canine model may be a useful animal therapeutic model for evaluating photodynamic therapy using a high concentration of the photosensitizer in the extracellular space.

Effect of a photosensitization reaction performed during the first 3 min after exposure of rat myocardial cells to talaporfin sodium in vitro

To better understand the mechanism of photodynamic cardiac ablation, we studied the effects of a photosensitization reaction (PR) performed during the first 3 min after rat myocardial cells were exposed to talaporfin sodium. A 3-mm-square microelectrode array with 64 electrodes was used to continuously measure the action potentials of the myocardial cells. A 30 μg/mL talaporfin sodium solution, a chlorine photosensitizer, was used, along with a 663-nm red diode laser (86 mW/cm² for up to 600 s). The first trough of the measured action potential waveform corresponding to Na⁺ dynamics decreased exponentially with increasing PR duration. The average decay time of the exponential function from PR onset was 20.1 s. Marked morphological changes in the myocardial cells was observed after the PR. These results indicated that the behavior of the action potential waveform measured by the microelectrode array might be used as a less invasive method to evaluate the electrophysiological effects of a PR on myocardial cells.

Temperature Influence on Myocardial Cell Cytotoxicity of the Extracellular Photosensitization Reaction with Talaporfin Sodium and Serum Proteins at 17°-37°C

BACKGROUND

We investigated the binding of talaporfin sodium with albumin and its photocytotoxicity during temperature changes by measuring absorbance spectra. The targeted tissue temperature differs according to the procedure. The photocytotoxicity efficiency should be investigated quantitatively because efficiency changes arising from temperature changes are expected.

MATERIALS AND METHODS

The temperature dependence of talaporfin sodium binding with human serum albumin (0-20 mg/mL), high-density lipoprotein (0-0.04 mg/mL), and low-density lipoprotein (0-0.14 mg/mL) was investigated at 17°C, 27°C, and 37°C by measurement of absorbance spectra. Cell lethality was measured using a water-soluble tetrazolium-8 assay at 2 h after the photosensitization reaction at 17°C and 37°C.

RESULTS

The binding ratios of talaporfin sodium with high-density lipoprotein decreased by 6.3% and those with low-density lipoprotein decreased by 12.8% when the temperature increased from 17°C to 37°C. Cell lethality increased significantly with a temperature rise from 17°C to 37°C at irradiation exposure of 20 and 40 J/cm² and talaporfin sodium concentration of 20 μg/mL.

CONCLUSIONS

From our in vitro data, we can predict that the change in photocytotoxicity efficiency would be negligible with a temperature decrease of <5°C from the body temperature in the case of photodynamic ablation with a short drug-light interval.

Irradiance dependence of the conduction block of an in vitro cardiomyocyte wire

BACKGROUND

To obtain therapeutic condition precisely by in vitro experiment, we studied the irradiance dependence of the electrical conduction blockage caused by a photodynamic reaction using a high extracellular concentration of talaporfin sodium on a novel in vitro cardiomyocyte electrical conduction wire.

METHODS

The cardiomyocyte wires were constructed on patterned cultivation cover glass, which had cultivation areas 60μm in width, and a maximum length of 10mm. The talaporfin sodium concentration was set to 20μg/mL. The photodynamic reaction with a high extracellular photosensitizer concentration was performed with a short time interval (approximately 15min) between photosensitizer exposure and irradiation. A 663-nm laser was applied to the cardiomyocyte wire, and the irradiance was varied between 3 and 120mW/cm². The cardiomyocyte electrical conduction was evaluated using the cross-correlation function of intracellular Ca²⁺ probe fluorescence brightness from an upper and lower section outside the laser irradiation area of a wire every 10s, which lasted up to 600s.

RESULTS

The onset of electrical conduction blockage was defined by an 85% decrease in the cross-correlation function, compared with its initial value. The time for the electrical conduction blockage decreased from 600 to 300s as the irradiance was increased. Also, the probability of electrical conduction blockage was found to increase with increasing irradiance.

CONCLUSIONS

We found a strong dependence on the irradiance for the time and probability of electrical conduction blockage.

Phototoxicity of Vascular Endothelial Cells Caused by Contact with Talaporfin Sodium for 15-120 Min: In Vitro and In Vivo Studies

OBJECTIVE

To reveal the mechanism of vascular patency in the myocardium after photosensitization immediately after talaporfin sodium (TS) injection in a canine model, we investigated acute injury to vascular endothelial cells (VECs) in vitro and in vivo.

BACKGROUND DATA

There are many reports of vascular shutdown within the target region in photodynamic therapy with TS. Vascular patency within healthy canine myocardium in which a photosensitization reaction starts immediately after injection of TS has been reported.

MATERIALS AND METHODS

TS fluorescence in human umbilical vein endothelial cells and cell lethality were measured with drug contact time (DCT) up to 120 min at 20 μg/mL. Dependence of radiant exposure on cell lethality with 60 min DCT was investigated using two albumin concentrations that corresponded to those in plasma and interstices. Irradiation (21 mW/cm) outside the adventitia of canine cervical veins for 167 or 667 sec was emitted through a diffuser probe 30 min after intravenous injection of TS (2.5 mg/kg). Veins were extracted ∼30 min after the reaction and stained with von Willebrand factor.

RESULTS

Intracellular fluorescence increased, but not cell lethality, with increasing DCT. Cell lethality increased gradually and reached 100% over 20 J/cm² in the albumin concentration in the interstices. Normal VECs were found at the acute phase over 20 J/cm² with a TS concentration in plasma of ∼14 μg/mL in vivo.

CONCLUSIONS

VEC injury after a photosensitization reaction to healthy tissue shortly after TS injection might be low enough for the blood vessels to be patent.

Dependence of damage within 10min to myocardial cells by a photodynamic reaction with a high concentration of talaporfin sodium outside cells in vitro on parameters of laser irradiation

BACKGROUND

To investigate the immediate occurrence of irreparable severe damage to myocardial cells up to 10min after a photodynamic reaction with a high concentration of photosensitizer outside cells, we measured the damage response time and the parameters that govern the response time via rat myocardial Ca(2+) concentration. In our proposed method for catheter ablation of tachyarrhythmia by photodynamic reaction, there are two components to the electrical conduction block: an immediate electrical conduction block of several tens of seconds to several minutes, and a permanent electrical conduction block.

METHODS

Rat myocardial intracellular Ca(2+) concentration changes before, during and after the photodynamic reaction with a high concentration of photosensitizer outside myocardial cells were continuously observed using a Fluo-4 AM Ca(2+) probe. Talaporfin sodium with 663-nm excitation was used to induce the photodynamic reaction. Talaporfin concentration was 10-30μg/ml, radiant exposure was 10-40J/cm(2), and irradiance was 30-290mW/cm(2). We evaluated the response time of irreparable severe damage to myocardial cells, according to Ca(2+) concentration.

RESULTS

The response time of the defined severe damage occurrence to myocardial cells ranged from 200 to 500s. The response time decreased with increasing irradiance and photosensitizer concentration, but exhibited no significant change with total radiant exposure.

CONCLUSIONS

We found that severe myocardial cell damage caused by a photodynamic reaction with a high concentration of photosensitizer outside cells occurred within a few minutes, which might be useful for catheter ablation for tachyarrhythmia that needs immediate response during the ablation procedure.

Talaporfin sodium binding and photocytotoxicity of photosensitization reaction on myocardial cell under various albumin concentrations and temperature

To understand the efficiency change of the extracellular photosensitization reaction by the external factor in myocardium interstitial space, we studied the efficiency change of the extracellular photosensitization reaction caused by talaporfin sodium binding with serum proteins under various serum proteins concentrations and temperature conditions. Talaporfin sodium Q band absorbance was measured with various albumin concentrations and the cell survival rate was measured by WST assay in the same conditions. The talaporfin sodium binding ratio with albumin, high-density lipoprotein, and low-density lipoprotein were measured by talaporfin sodium absorbance measurement after the ultrafiltration. The albumin concentration affects the photocytotoxicity strongly when the albumin concentration was over 2.1 mg/ml in the case of the extracellular photosensitization reaction. It would be useful to measure the peak wavelength in Q band absorbance was suggested to know the albumin concentration and the photocytotoxicity efficiency to realize the safety treatment. The binding ratios with high-density lipoprotein and low-density lipoprotein were decreased with the solution temperature rise from 17°C to 37 °C and the photocytotoxicity was increased with temperature rise from 17°C to 37°C involving this binding ratio change. It would be important to maintain the target organ temperature during the photosensitization reaction to keep the photosensitization reaction efficiency.

Comparison of myocardial cell survival 2 h and 24 h after extracellular talaporfin sodium-induced photodynamic reaction

BACKGROUND

We have proposed an application of photodynamic reaction for less-heated myocardial ablation which employs talaporfin sodium. Intracellular photodynamic reactions with ongoing uptake have the ability to induce apoptosis over time, raising the possibility of extending the lesion depth. The objective of this study was to understand how, in myocardial cells, the late cell survival levels change by incubation time with talaporfin sodium, and what dependence talaporfin sodium uptake has on the duration of incubation with talaporfin sodium in vitro.

METHODS

Rat myocardial cells were incubated with talaporfin sodium for 5-360 min and intracellular concentrations measured using a fluorescence micro-plate reader after wash. Cell survival was measured using a water-soluble tetrazolium assay at 2 and 24 h after a photodynamic reaction using a red diode laser of 660 nm, following 15-180 min of incubation with talaporfin sodium. Cells were stained with Hoechst 33342 to observe nuclear changes.

RESULTS

Intracellular talaporfin sodium concentration increased with incubation time, with a marked increase between 0 and 60 min. Cell survival at 24 h decreased by 20% when the duration of incubation with talaporfin sodium was extended from 15 to 30 min. Following incubation time of 30-180 min with talaporfin sodium, cell survival was decreased by approximately 30% between measurements at 2 and 24 h. The intracellular talaporfin sodium concentration that induced higher levels of late cell death with cell nuclei fragmentation in these cells was approximately 0.2 μg/mL.

CONCLUSION

We obtained the characteristics of late cell death occurrence and talaporfin sodium uptake to myocardial cell with various incubation times with talaporfin sodium.

Effects of albumin binding on photocytotoxicity of extracellular photosensitization reaction using talaporfin sodium to rat myocardial cells

BACKGROUND

We previously proposed a new treatment for tachyarrhythmia using an extracellular photosensitization reaction occurring in the interstitial space of myocardia shortly after the injection of talaporfin sodium. Using myocardial cells, we studied the photocytotoxicity of this extracellular photosensitization reaction between talaporfin sodium and albumin.

METHODS

The albumin concentrations tested spanned the physiological range found in the interstitial space (0-15 mg/ml) while the talaporfin sodium concentration were varied from 0 to 40 μg/ml. The reactions were conducted in 96-well plates. To obtain the binding ratio and the amount of energy deposited into the photosensitizer, we measured the change in the absorbance spectra of talaporfin sodium solutions containing different concentrations of albumin.

RESULTS

Photocytotoxicity to myocardial cell due to the reaction decreased when physiological concentrations of albumin were added to the reaction mix, and decreased sharply when the molar concentration ratio of albumin to talaporfin sodium was between 0.3 and 1.2. A monotonic binding ratio was obtained, ranging from 10 to 80%, at albumin concentrations of 0.1-1.0 mg/ml. We found that the lethality of the extracellular photosensitization reaction towards myocardial cells had a threshold albumin concentration, even though the energy deposited into the talaporfin sodium solution was calculated to be almost constant (4.23 ± 0.19 J/well) in the presence of 0-15 mg/ml albumin.

CONCLUSIONS

Based on the likely concentration of albumin in the interstitial space, we conclude that the photodynamic efficacy of talaporfin, under conditions used here, will markedly decrease if the albumin level exceeds 0.65 mg/ml.

Immediate response and cytotoxicity effect on myocardial cells by extracellular photosensitization reaction varying irradiance

We investigated the extracellular photosensitization effect on myocardial cells using talaporfin sodium at various irradiance measuring cell lethality dependence on talaporfin sodium concentration and immediate response of intracellular Ca(2+) as a fundamental study of the application for tachyarrhythmia treatment. The myocardial cell lethality was measured 2 h after the photosensitization reaction by WST assay varying the irradiance from 0.12 to 0.66 W/cm(2). The intracellular Ca(2+) of myocardial cell was observed during and until 10 min after the extracellular photosensitization reaction using fluo-4 AM and a confocal microscope varying the irradiance. The linear increasing behavior of the myocardial cell lethality with talaporfin sodium concentration was similarly obtained in the case of 0.12 and 0.29 W/cm(2) in irradiance. The photocytotoxicity was not obtained in the case of 0.46 and 0.66 W/cm(2) in irradiance. The time response of necrosis occurrence after the beginning of the extracellular photosensitization reaction was decreased with the irradiance increasing. We prospect that it may be caused by oxygen depletion in our in vitro system using 96 well plate since the irradiance and talaporfin sodium concentration were higher comparing the in vitro conditions of the general PDT for cancer.