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Photodynamic therapy (PDT) utilizes the potential of photosensitizing substances to absorb light energy and produce reactive oxygen species. Tetra-cationic porphyrins, which have organic or coordination compounds attached to their periphery, are heterocyclic derivatives with well-described antimicrobial and antitumoral properties. This is due to their ability to produce reactive oxygen species and their photobiological properties in solution. Consequently, these molecules are promising candidates as new and more effective photosensitizers with biomedical, environmental, and other biomedical applications. Prior to human exposure, it is essential to establish the toxicological profile of these molecules using in vivo models. In this study, we used Caenorhabditis elegans, a small free-living nematode, as a model for assessing toxic effects and predicting toxicity in preclinical research. We evaluated the toxic effects of porphyrins (neutral and tetra-cationic) on nematodes under dark/light conditions. Our findings demonstrate that tetra-methylated porphyrins (3TMeP and 4TMeP) at a concentration of 3.3 µg/mL (1.36 and 0.93 µM) exhibit high toxicity (as evidenced by reduced survival, development, and locomotion) under dark conditions. Moreover, photoactivated tetra-methylated porphyrins induce higher ROS levels compared to neutral (3TPyP and 4TPyP), tetra-palladated (3PdTPyP and 4PdTPyP), and tetra-platinated (3PtTPyP and 4PtTPyP) porphyrins, which may be responsible for the observed toxic effects., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The action of irradiated cationic Fe(III)TMPyP and anionic Fe(III)TPPS4 forms of mesoporphyrins on mitochondrial functions was investigated using experimental conditions that caused minimal effects on mitochondria in the dark. Treatment of mitochondria with 1 microM Fe(III)TMPyP for 2 min decreased the respiratory control by 3% in the dark and 28% after irradiation. Fe(III)TPPS4 (1 microM) had no significant effect on respiratory control under any of the above conditions. Both porphyrins increased the mitochondrial production of reactive oxygen species in the presence of Ca2+; however, the effect of Fe(III)TMPyP was significantly stronger. In both cases, this overproduction was associated with membrane lipid peroxidation. It was also observed that the association constant of Fe(III)TMPyP with mitochondria was 11 times higher than that of Fe(III)TPPS4. In conclusion, the damage to isolated mitochondria induced by Fe(III)TMPyP under illumination was larger than by Fe(III)TPPS4, probably because its cationic charge favors association with the mitochondrial membrane. This is supported by the decrease in the association constant of Fe(III)TMPyP with mitochondria in higher salt medium.

Hematoporphyrin derivatives have been recommended for photodynamic therapy of malignant processes. We administered TPPS4, and Photosan 3 (PS 3) in chick embryo in ovo, with or without subsequent blue light (400-550 nm) irradiation. The aim was to analyze and compare the effects of both substances on organogenesis under different light conditions. The embryotoxic effect (embryonic death and malformations) was detected after a single intra-amniotic injection of 5 different doses (0.3 to 300 microg) of TPPS4 or PS 3 at embryonic day 3-5. The beginning of the embryotoxicity range (minimal embryotoxic dose) was determined in non-irradiated embryos to be between 0.3-3.0 microg PS 3 and 3.0-30.0 microg TPPS4. Malformations of surviving embryos were similar after both substances, represented by trunk hyperlordosis combined with incomplete closure of the ventral body wall and protrusion of viscera as consequences of amnion contraction, reduction limb deformities, eye malformations and cleft beak. Ten minutes light irradiation in ovo following two hours after intra-amniotic injection of TPPS4 or PS 3 increased by one order of magnitude their embryotoxic effects. Even dark-ineffective doses became highly embryotoxic. Contraction of the amniotic sac and extraembryonic vessels seemed to be a common mechanism of photosensitizer action.

Photodynamic therapy (PDT), a novel treatment for a variety of human malignancies, usually consists of visible light irradiation of lesions following the systemic administration of a photosensitizer. Induction of the endogenous photosensitizer protoporphyrin IX by the systemic or topical administration of delta-aminolevulinic acid (delta-ALA) is being investigated for use in PDT. We have determined that the incubation of two human and two rodent tumor cell lines in culture with delta-ALA over a 24 h period results in an increase in the accumulation of fluorescent porphyrins in all of these cell lines. However, the two human cell lines produce fluorescent porphyrin at different rates from those seen in the rodent cell lines. The uptake of 14C-delta-ALA was concentration dependent, similar for all the cell lines studied and rapidly reached an intra/extracellular equilibrium after delta-ALA was added to the culture medium. The increase in intracellular fluorescent porphyrin was dependent on the level of delta-ALA in the medium and the incubation time and was directly related to the phototoxicity observed upon exposure of cultured monolayers to light. The data demonstrate that equivalent levels of phototoxicity can be attained by exposing cells to 0.04 mM delta-ALA for 24 h or to 0.5 mM delta-ALA for 2 h. These findings may have implications for optimization of PDT treatment regimens that use delta-ALA.

Cationic porphyrins have been shown to photoinduce the direct inactivation of Gram-positive (G+) and Gram-negative (G-) bacteria, thereby differing from anionic or neutral porphyrins which can photosensitize the G- bacteria only after permeabilization of their outer membrane. The present data show that the differences between these positively and negatively charged porphyrins are not related by a difference in the intrinsic photosensitizing efficiency, as determined by the photo-oxidation of model substrates or the yield of 1O2 generation; moreover, there are only minor differences in the quantum yield of porphyrin photobleaching. Rather, it appears that the positive charge promotes an electrostatic binding of the porphyrin to the outer cell surface inducing an initial limited damage which favours the penetration of the photosensitizer. Actually, the overall photoprocess is inhibited by the preincorporation of the porphyrin into liposomes, while it is enhanced by using amphiphilic dicationic porphyrins which bind to endocellular sites in larger amounts and in a more stable form.

The kinetics of photoinduced damage sensitized by chlorine e6 and its derivatives was studied in Escherichia coli and Bacillus subtilis. The effectiveness of E. coli photoinactivation in the presence of chlorines was 100-200 times lower as compared with that of B. subtilis. The structural organisation of bacterial cell walls apparently played an essential role in the penetration of tetrapyrrole pigments into the cell and in their binding.

Study Objective: In situ production of reactive oxygen intermediates (singlet oxygen and superoxide) during the photoactivation of rose bengal can induce arrhythmias in the aerobically perfused rat heart. The present study was undertaken (1) to assess whether these effects occur with other photosensitizers; (2) to identify the injurious intermediates; (3) to probe the site of action of these phenomena. DESIGN - The study involved the use of meso-tetra-(4-sulphonatophenyl)-porphine (TPPS), a porphyrin which, in contrast to rose bengal, promotes the production of singlet oxygen alone when illuminated. After 10 min of TPPS free perfusion, rat hearts (n = 6 per group) were perfused aerobically with TPPS (1, 5, 10 or 50 mumol.litre-1) for 25 min; during the last 20 min, the hearts were illuminated (3600 lux). In additional studies, TPPS (50 mumol.litre-1) was washed out before illumination., Experimental Material: Hearts from 30 male Wistar rats, weighing 220-280 g, were excised and perfused retrogradely., Measurements and Main Results: Cardiac function was unaffected with TPPS alone. Upon illumination, electrocardiographic changes (increase in QT interval and/or T wave changes) and arrhythmias developed in a dose dependent manner. At the highest dose, electrocardiographic changes occurred within 7.0(SEM 0.4) s; all hearts exhibited ventricular premature beats and complete atrioventricular block; 67% developed ventricular tachycardia and 17% ventricular fibrillation. During illumination, hearts also exhibited a dose and time dependent decrease in coronary flow. In additional studies, despite the absence of TPPS in the perfusate, all hearts exhibited complete atrioventricular block, 67% developed ventricular premature beats and 33% ventricular tachycardia; none exhibited ventricular fibrillation., Conclusions: The results suggest that singlet oxygen, as opposed to superoxide, is responsible for the injury which occurs at tissue surfaces to which photosensitizer is bound.

The strongly light-absorbing metalloporphyrin tin(IV)-protoporphyrin IX (SnPP) is currently being considered as a chemotherapeutic agent for preventing severe hyperbilirubinemia in newborns, a condition usually treated by phototherapy with visible light. To assess the potential phototoxicity of SnPP we studied the photophysics of the drug in aqueous and nonaqueous solutions using laser flash photolysis and pulse radiolysis. Quantum yields for formation of triplet-state excited SnPP were measured, along with triplet lifetimes and extinction coefficients. In addition, we measured quantum yields for the SnPP-photosensitized formation of singlet oxygen in MeO2H and 2H2O containing cetyltrimethylammonium bromide, using a time-resolved luminescence technique. Quantum yields for formation of triplet SnPP from monomeric ground-state SnPP are high (approximately equal to 0.6-0.8), and triplet lifetimes are long (approximately equal to 0.1-0.2 ms). Efficient quenching of triplet SnPP by molecular oxygen was seen with rate constants greater than 10(9) M-1.s-1. SnPP-photosensitized formation of singlet oxygen in aqueous and nonaqueous solvents was confirmed by the detection of the characteristic luminescence at 1270 nm (phi delta = 0.58 in MeO2H). The photophysical parameters and singlet oxygen-sensitizing efficiency of SnPP are similar to those reported for hematoporphyrin and other metal-free porphyrins known to be phototoxic to humans. These observations suggest that cutaneous photosensitivity arising from singlet-oxygen damage is likely to be an undesirable side-effect of SnPP therapy.

Photoradiation with photosensitizing porphyrins offers a potentially useful approach to the diagnosis and treatment of certain human cancers. The mechanism of porphyrin photosensitivity as studied in cultured cells or in the skin has been studied thoroughly. Possible targets that have been identified include membranous cellular organelles, DNA, and the plasma membrane. Mediators of the reaction include reactive oxygen species, particularly singlet oxygen, that may elicit lipid peroxidation and the activation of complement. Further research is needed to identify photosensitizers with greater selectivity for malignant cells and to develop even better sources of radiant energy.

In recent years porphyrins and related materials have been tested as antitumor agents. A technique was devised to obtain dose-response curves for the sensitizer fraction that resists one day of elution by tissue culture medium--the retained fraction. We found a steep "threshold" dose response relationship that helps to explain tumor destruction without damage to normal tissues. The family of dose-response curves produced by a wide range of light exposures suggests that chlorins and porphyrins do not act by identical mechanisms. Moreover, they suggest that chlorins will prove superior in practical use.

The in vivo uptake of two cationic porphyrins: mesotetra (4-N-methylpyridyl) porphine (T4MPyP) and its zinc complex (ZnT4MPyP) was determined in Allium cepa meristematic cells. Both photosensitizers (10(-7) M for 4 h) penetrated into the nucleus producing a red fluorescence of chromatin under blue-violet (436 nm) exciting light. The ability of T4MPyP and ZnT4MPyP to induce DNA photodamage was measured by the sister chromatid exchange (SCE) test. 5-Bromo-2'-deoxyuridine-substituted chromosomes treated with both the porphyrins (10(-8)M for 4 h) showed increased frequencies of SCE when they were postirradiated with 436 nm light. A higher genotoxic effect was observed for ZnT4MPyP than the other compound.