Zur weiteren Kenntnis des Chlorophylls und des Hämins, XXX1)Photoprotoporphyrine und ihre Umwandlung in Spirographis- sowie Isospirographis-porphyrin2)

The effect of fluence rate and wavelength on the formation of protoporphyrin IX photoproducts

Photodynamic diagnosis and therapy (PDD and PDT) are emerging techniques for diagnosing and treating tumors and malignant diseases. Photoproducts of protoporphyrin IX (PpIX) used in PDD and PDT may be used in the diagnosis and treatment, making a detailed analysis of the photoproduct formation under various treatment and diagnosis conditions important.Spectroscopic and mass spectrometric analysis of photoproduct formation from PpIX dissolved in dimethyl sulfoxide were performed under commonly used irradiation conditions for PDD and PDT, i.e., wavelengths of 405 and 635 nm and fluence rates of 10 and 100 mW/cm2. Irradiation resulted in the formation of hydroxyaldehyde photoproduct (photoprotoporphyrin; Ppp) and formyl photoproduct (product II; Pp II) existing in different quantities with the irradiation wavelength and fluence rate. Ppp was dominant under 635 nm irradiation of PpIX, with a fluorescence peak at 673 nm and a protonated monoisotopic peak at m/z 595.3. PpIX irradiation with 405 nm yielded more Pp II, with a fluorescence peak at 654 nm. A higher photoproduct formation was observed at a low fluence rate for irradiation with 635 nm, while irradiation with 405 nm indicated a higher photoproduct formation at a higher fluence rate.The photoproduct formation with the irradiation conditions can be exploited for dosimetry estimation and may be used as an additional photosensitizer to improve the diagnostics and treatment efficacies of PDD and PDT. Differences in environmental conditions of the present study from that of a biological environment may result in a variation in the photoproduct formation rate and may limit their clinical utilization in PDD and PDT. Thus, further investigation of photoproduct formation rates in more complex biological environments, including in vivo, is necessary. However, the results obtained in this study will serve as a basis for understanding reaction processes in such biological environments.

Molecular Taphonomy of Heme: Chemical Degradation of Hemin under Presumed Fossilization Conditions

The metalloporphyrin heme acts as the oxygen-complexing prosthetic group of hemoglobin in blood. Heme has been noted to survive for many millions of years in fossils. Here, we investigate its stability and degradation under various conditions expected to occur during fossilization. Oxidative, reductive, aerobic, and anaerobic conditions were studied at neutral and alkaline pH values. Elevated temperatures were applied to accelerate degradation. High-performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) identified four main degradation products. The vinyl residues are oxidized to formyl and further to carboxylate groups. In the presence of air or H₂O₂, cleavage of the tetrapyrrole ring occurs, and hematinic acid is formed. The highest stability of heme was observed under anaerobic reductive conditions (half-life 9.5 days), while the lowest stability was found in the presence of H₂O₂ (half-life 1 min). We confirmed that the iron cation plays a crucial role in degradation, since protoporphyrin IX, lacking iron, remained significantly more stable. Under anaerobic, reductive conditions, the above-mentioned degradation products were not observed, suggesting a different degradation pathway. To our knowledge, this is the first molecular taphonomy study on heme, which will be useful for understanding its fate during fossilization.

Mass Spectrometric Analysis of the Photobleaching of Protoporphyrin IX Used in Photodynamic Diagnosis and Therapy of Cancer

Photobleaching and photoproduct formations are considered essential phenomena in improving the efficacy of photodynamic diagnosis and therapy (PDD and PDT). We investigated the photobleaching of protoporphyrin IX (PpIX) by measuring its concentration with mass spectrometry (MS). The reduction in the concentration of PpIX dissolved in dimethyl sulfoxide was measured during PDD and PDT conditions using lasers with wavelengths of 405 and 635 nm, respectively, at a power density of 10, 50 or 100 mW/cm² . The obtained results were compared with the results of conventional fluorescence spectroscopy and previously reported results. Our results demonstrate the variation in the MS-based photobleaching coefficient of PpIX with the power density, while the fluorescence-based photobleaching coefficient was independent of the power density. The results of MS also show faster photobleaching of PpIX in comparison with that obtained from fluorescence. The difference may be attributed to the change in the fluorescence quantum yield of PpIX with its concentration and the effect of fluorescence emission from the PpIX photoproducts. Thus, an MS-based investigation of the photobleaching poses to be a more stable investigation form. Our finding highlights the importance of recognizing the potential significance of these discoveries in the PDD and PDT dosimetry and efficacy.

β-Formyl- and β-Vinylporphyrins: Magic Building Blocks for Novel Porphyrin Derivatives

Porphyrins bearing formyl or vinyl groups have been explored as starting materials to prepare new compounds with adequate features for different applications. In this review it is discussed mainly synthetic strategies based on the reaction of meso-tetraarylporphyrins bearing those groups at β-pyrrolic positions. The use of some of the obtained porphyrin derivatives for further transformations, namely via pericyclic reactions, is also highlighted.

Porphyrins and other pyrrolic macrocycles in cycloaddition reactions

Porphyrins and other pyrrolic macrocycles can participate in a range of pericyclic reactions. This review deals mainly with their use in Diels-Alder reactions (as dienes and dienophiles) and in 1,3-dipolar cycloadditions (as 1,3-dipoles and dipolarophiles)

Assessment of the quality attributes of cod caviar paste by means of front-face fluorescence spectroscopy

This paper describes the fluorescent behavior of cod caviar paste, stored under different conditions, in terms of light exposure and concentration of oxygen in the headspace. Multivariate curve resolution was employed to decompose the overall fluorescence spectra into pure fluorescent components and calculate the relative concentrations of these components in the different samples. Profiles corresponding to protoporphyrin IX, photoprotoporphyrin, and fluorescent oxidation products were identified. Sensory evaluation, TBARS, and analysis of volatiles are typical methods employed in the routine analysis and quality control of such food. Successful calibration models were established between fluorescence and those routine methods. Correlation coefficients higher than 0.80 were found for 79% and higher than 0.90 for 50% of the assessed odors and flavors. For instance, R values of 0.94, and 0.96 were obtained for fresh and rancid flavors respectively, and 0.89 for TBARS. On the basis of these data, it can be argued that front-face fluorescence spectroscopy can substitute all of these expensive and tedious methodologies.

Photodynamic therapy of actinic keratosis at varying fluence rates: assessment of photobleaching, pain and primary clinical outcome

BACKGROUND

Although photodynamic therapy (PDT) is becoming an important treatment method for skin lesions such as actinic keratosis (AK) and superficial basal cell carcinoma, there are still discussions about which fluence rate and light dose are preferable. Recent studies in rodents have shown that a low fluence rate is preferable due to depletion of oxygen at high fluence rates. However, these results have not yet been verified in humans.

OBJECTIVES

The objective was to investigate the impact of fluence rate and spectral range on primary treatment outcome and bleaching rate in AK using aminolaevulinic acid PDT. In addition, the pain experienced by the patients has been monitored during treatment.

PATIENTS/METHODS

Thirty-seven patients (mean age 71 years) with AK located on the head, neck and upper chest were treated with PDT, randomly allocated to four groups: two groups with narrow filter (580-650 nm) and fluence rates of 30 or 45 mW cm(-2), and two groups with broad filter (580-690 nm) and fluence rates of 50 or 75 mW cm(-2). The total cumulative light dose was 100 J cm(-2) in all treatments. Photobleaching was monitored by fluorescence imaging, and pain experienced by the patients was registered by using a visual analogue scale graded from 0 (no pain) to 10 (unbearable pain). The primary treatment outcome was evaluated at a follow-up visit after 7 weeks.

RESULTS

Our data showed a significant correlation between fluence rate and initial treatment outcome, where lower fluence rate resulted in favourable treatment response. Moreover, the photobleaching dose (1/e) was found to be related to fluence rate, ranging from 4.5 +/- 1.0 J cm(-2) at 30 mW cm(-2), to 7.3 +/- 0.7 J cm(-2) at 75 mW cm(-2), indicating higher oxygen levels in tissue at lower fluence rates. After a cumulative light dose of 40 J cm(-2) no further photobleaching took place, implying that higher doses are excessive. No significant difference in pain experienced by the patients during PDT was observed in varying the fluence rate from 30 to 75 mW cm(-2). However, the pain was found to be most intense up to a cumulative light dose of 20 J cm(-2).

CONCLUSIONS

Our results imply that the photobleaching rate and primary treatment outcome are dependent on fluence rate, and that a low fluence rate (30 mW cm(-2)) seems preferable when performing PDT of AK using noncoherent light sources.

Comparison of the photodynamic effect of exogenous photoprotoporphyrin and protoporphyrin IX on PAM 212 murine keratinocytes

A comparative study of the cellular photosensitizing properties of protoporphyrin IX (PpIX) and photoprotoporphyrin (Ppp) was carried out in the transformed murine keratinocyte cell line, PAM 212. Time-course fluorescence studies were performed to determine the rate of uptake by cells together with fluorescence microscopy. The sensitized cells were laser irradiated with a range of light doses at 635 or 670 nm to determine the phototoxicity of the two compounds and to investigate their relative fluorescence photobleaching properties. Ppp showed enhanced phototoxicity at both its optimal activation wavelength of 670 nm (eight times more phototoxic than PpIX activated at its optimal wavelength of 635 nm for the same fluence) and at 635 nm (three times more phototoxic than PpIX at the same wavelength), using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. The photobleaching rate of Ppp in cells was found to be higher using 670 nm irradiation compared with that of PpIX at 635 nm irradiation. At 635 nm, however, the photobleaching rate of Ppp was comparable to that of PpIX. The photobleaching quantum yields of the two compounds in cells were found to be similar at approximately 5 x 10(-4), with the same value confirmed at both 670 and 635 nm irradiation for Ppp. The fluorescence lifetime of Ppp in cells was measured as 5.4 ns using time-correlated single photon counting.

Protoporphyrin IX fluorescence kinetics in UV-induced tumours and normal skin of hairless mice after topical application of 5-aminolevulinic acid methyl ester

Accumulation of protoporphyrin IX (PpIX) was investigated in normal skin and UV-induced tumours in hairless mice after topical application of a cream containing 2, 8 or 16% of 5-aminolevulinic acid methyl ester (ALA-Me). Higher levels of PpIX were measured in tumours compared to normal skin. The maximal amount of PpIX was reached at 1.5, 3 and 4 h after 2, 8 and 16% ALA-Me application, respectively. Higher tumour to normal skin PpIX fluorescence ratios were measured after application of 8 and 16% ALA-Me than after application of 2%. After irradiation with a broad spectrum of visible light from a slide projector, more than 90% of PpIX was bleached by fluences of 36 and 48 J/cm2, at fluence rates of 10 and 40 mW/cm2 respectively. At these fluences, the PpIX photobleaching rate was significantly higher (P<0.05) in normal mouse skin than in tumours. In addition, for a given fluence, more PpIX was photobleached at the lower fluence rate (10 mW/cm2) than at the higher fluence rate (40 mW/cm2) in normal skin (P<0.001) as well as in tumours (P<0.05) after exposure to 24 J/cm2 of light. In conclusion, the highest tumour to normal skin PpIX ratio was observed 3 h after application of 8% ALA-Me, suggesting that light exposure should be performed at this time in order to achieve an optimal PDT effect in this tumour model.

The use of 5-aminolaevulinic acid as a photosensitiser in photodynamic therapy and photodiagnosis

Photodynamic therapy (PDT) is a treatment for cancer and pre-malignant conditions, which involves the administration of a photosensitising agent followed by exposure of the tissue to light. 5-Aminolaevulinic acid (ALA) is a naturally occurring compound in the haem biosynthetic pathway, which is metabolised to a photosensitive product, protoporphyrin IX (PpIX). The major advantage of ALA when compared to synthetic photosensitisers is the rapid metabolism, which significantly reduces the period of cutaneous photosensitivity. This review focuses on the development of ALA as a photosensitiser in photodynamic therapy and photodiagnosis, and the wide range of clinical applications in which ALA is now being used as a therapeutic modality.

Fluorescence spectroscopy of normal mouse skin exposed to 5-aminolaevulinic acid and red light

Photobleaching and phototransformation of protoporphyrin IX (PpIX) was investigated in normal mouse skin. The PpIX was induced by topical application of 5-aminolaevulinic acid (ALA). Exposure to laser light (635 nm) caused photobleaching of PpIX fluorescence and formation of fluorescent products. Analysis of the fluorescence spectra revealed appearance of new fluorescent photoproducts during light exposure. The main photoproduct, supposedly chlorin-type photoprotoporphyrin (PPp), exhibited fluorescence with an emission maximum at 675 nm. The other products exhibited main fluorescence peaks at around 588 and 623 nm that can presumably be attributed to an endogenous metallo-porphyrin and water-soluble porphyrin(s), respectively. Our results indicate that light exposure causes alterations in the enzymatic pathway of PpIX synthesis from ALA and leads to accumulation of intermediate water-soluble porphyrins. ALA-induced porphyrins are transported away from the treated area and partly deposited in remote skin sites.

Chlorin-type photosensitizers photochemically derived from vinyl porphyrins

The reaction of singlet oxygen with four vinyl-substituted dicarboxylic porphyrins, vinyldeuteroporphyrin (VD), ethylvinyldeuteroporphyrin (EVD), hydroxyethylvinyldeuteroporphyrin (HVD) and protoporphyrin (PP) in organic solutions is investigated. The main products, the "hydroxyaldehyde" chlorin-type derivatives, are formed with a concentration-dependent photochemical quantum yield that reaches a maximum of 7.4 +/- 1.6 x 10(-3). However, owing to the high turnover of singlet-oxygen production, these chlorin-type compounds are easily prepared photochemically with a chemical yield of 70% and little side product formation. In chemical ionization mass spectrometry, these compounds display an unusual fragmentation with a loss of 16 mass units. This is attributed to the loss of the oxygen bound to the saturated carbon of the modified pyrrole unit. All these compounds sensitize the formation of singlet oxygen with a yield around 0.8. They interact with singlet oxygen with rate constants of 5 x 10(6)-9 x 10(6) M-1 s-1, lower than those measured for vinyl porphyrins. These data are likely to help in the characterization of photoproducts of vinyl porphyrins relevant to photodynamic therapy (PP, HVD). As exemplified with VD and EVD, they also point out the reaction of singlet oxygen as an efficient route to chlorin-type photosensitizers.

Phototransformations of 5-aminolevulinic acid-induced protoporphyrin IX in vitro: a spectroscopic study

Human adenocarcinoma cells of the line WiDr were incubated with 5-aminolevulinic acid to induce protoporphyrin IX (PpIX) and then exposed to laser light of wavelength 635 nm. The PpIX fluorescence decreased with increasing exposure. The decay rate was slightly dependent on the initial PpIX concentration. The PpIX fluorescence was halved by a fluence of about 40 J/cm2. Several fluorescing photoproducts were formed. The main one, supposedly the chlorine-type photoprotoporphyrin (Ppp), had a fluorescence excitation spectrum stretching out to about 680 nm with a maximum at around 668 nm. The formation kinetics of this product was dependent on the initial PpIX concentration. Moreover, it was selectively bleached by exposure to light at 670 nm. A photoproduct with an emission maximum at 652 nm, different from Ppp, remained after this exposure. Traces of a photoproduct(s) with fluorescence emission slightly blue-shifted compared with that of PpIX, supposedly water-soluble porphyrins, were also detected after light exposure.

Wittig reactions on photoprotoporphyrin IX: new synthetic models for the special pair of the photosynthetic reaction center

A first example of spirochlorin-chlorin dimer with fixed distances and orientations as potential model for the "special pair" of the photosynthetic reaction center is discussed. For the preparation of such a novel structure, the Wittig reagent of the desired "spacer" 5 was reacted with photoprotoporphyrin IX dimethyl ester 3 to produce the intermediate dimer 6, which on intramolecular [4 + 2] Diels-Alder cycloaddition gave an unexpected spirochlorin-chlorin dimer 9. Dehydration of dimer 6 under acid-catalyzed conditions generated the corresponding spirochlorin-porphyrin dimer 16 in quantitative yield. The asymmetry in dimer 6 caused by the biphenyl-type anisotropic effect was confirmed by NMR and model studies. The formation of dihydrobenzoporphyrin 14 by reacting chlorin 3 with the phosphonium salt of p-methylbenzylbromide 10 and isolation of 8-phenanthrenevinylporphyrin 19 from chlorin 7 further confirmed our proposed mechanism for the formation of a spirochlorin-chlorin dimer 9. Following a similar approach, chlorin 3 on reacting with bis-phosphonium salt of 4, 4'-bischloromethylbiphenyl produced conjugated chlorin dimer 25. The spectroscopic data obtained from these dimers suggest that, in these compounds, the individual chromophores are not behaving as an individual molecule, but as a single macrocycle. To examine whether the pi-pi interaction exhibited by dimer 9 resembles the structural arrangement of bacteriochlorophylls in reaction center (RC), we investigated the geometrical parameters used to characterize the pi-pi interactions in tetrapyrrolic macrocycles. Starting from the crystallographic coordinates of 9, the molecular mechanics energy minimization was performed to obtain the model dimer structure. The geometrical parameters that measure the single pyrrole ring overlap were used to compare the model structure with the crystallographic coordinates of the special pair in photosynthetic reaction center. The results indicated that the ring A of spirochlorin and the ring C of chlorin in our model dimer 9 mimic the ring A-ring A interaction found in the crystallographic special pairs, which are strategically placed by the surrounding photosynthetic reaction center protein matrix.

Glutathione-dependent oxidative modification of protoporphyrin and other dicarboxylic porphyrins by mammalian and plant peroxidases

Protoporphyrin, an intermediate in heme and chlorophyll biosynthesis, can accumulate in human and plant tissues under certain pathological conditions and is a photosensitizer used in cancer phototherapy. We previously showed that protoporphyrin and the related non-natural dicarboxylic porphyrin deuteroporphyrin are rapidly oxidized by horseradish peroxidase in the presence of some thiols, especially glutathione. This study reports that bovine lactoperoxidase, but not leucocyte myeloperoxidase, can also catalyze this reaction and that Tween and ascorbic acid are inhibitors. Exogenous hydrogen peroxide is not required and cannot replace glutathione. Deuteroporphyrin was oxidized to a unique green chlorin product with two oxygen functions added directly to the characteristic reduced pyrrole ring of the chlorin. Spectroscopic and chromatographic results suggest that protoporphyrin was oxidized not to a green chlorin, but to a much more polar red porphyrin modified by oxidative addition to the two vinyl side chains. Two related nonnatural dicarboxylic porphyrins, with ethyl or hydroxyethyl instead of vinyl side chains, are not substrates or products for this enzymatic conversion.

5-aminolaevulinic-acid-induced formation of different porphyrins and their photomodifications

The relative amounts of 5-aminolaevulinic acid (ALA)-induced hydrophobic and hydrophilic porphyrins produced in normal mouse tissue and solid Ehrlich ascites carcinoma in mice were investigated as a function of added glucose, light irradiation and restricted blood flow to the tumour. Protoporphyrin IX (PpIX) is the predominant porphyrin produced from exogenous ALA in tissues that have viable mitochondria. However, under special conditions which seem to be connected with a reduced viability of the mitochondria, the formation of water-soluble porphyrins can be observed in vivo. Fluorescence maxima of the water-soluble porphyrins are located in the region between 615 and 625 nm. Irradiation can further lead to the formation of PpIX photoproduct(s), showing a fluorescence emission band at 676 nm. The photobleaching of PpIX in normal tissue and tumour tissue is different under restricted blood flow. ALA-induced PpIX can be observed in the normal blood stream, and can be linked to a slower photobleaching than in tissue with restricted blood flow.

5-Aminolevulinic acid-based photodynamic therapy. Clinical research and future challenges

BACKGROUND

Photodynamic therapy (PDT) for cancer patients has developed into an important new clinical treatment modality in the past 25-years. PDT involves administration of a tumor-localizing photosensitizer or photosensitizer prodrug (5-aminolevulinic acid [ALA], a precursor in the heme biosynthetic pathway) and the subsequent activation of the photosensitizer by light. Although several photosensitizers other than ALA-derived protoprophyrin IX (PpIX) have been used in clinical PDT, ALA-based PDT has been the most active area of clinical PDT research during the past 5 years. Studies have shown that a higher accumulation of ALA-derived PpIX in rapidly proliferating cells may provide a biologic rationale for clinical use of ALA-based PDT and diagnosis. However, no review updating the clinical data has appeared so far.

METHODS

A review of recently published data on clinical ALA-based PDT and diagnosis was conducted.

RESULTS

Several individual studies in which patients with primary nonmelanoma cutaneous tumors received topical ALA-based PDT have reported promising results, including outstanding cosmetic results. However, the modality with present protocols does not in general, appear to be superior to conventional therapies with respect to initial complete response rates and long term recurrence rates, particularly in the treatment of nodular skin tumors. Topical ALA-PDT does have the following advantages over conventional treatments: it is noninvasive; it produces excellent cosmetic results; it is well tolerated by patients; it can be used to treat multiple superficial lesions in short treatment sessions; it can be applied to patients who refuse surgery or have pacemakers and bleeding tendency; it can be used to treat lesions in specific locations, such as the oral mucosa or the genital area; it can be used as a palliative treatment; and it can be applied repeatedly without cumulative toxicity. Topical ALA-PDT also has potential as a treatment for nonneoplastic skin diseases. Systemic administration of ALA does not seem to be severely toxic, but the advantage of using this approach for PDT of superficial lesions of internal hollow organs is still uncertain. The ALA-derived porphyrin fluorescence technique would be useful in the diagnosis of superficial lesions of internal hollow organs.

CONCLUSIONS

Promising results of ALA-based clinical PDT and diagnosis have been obtained. The modality has advantages over conventional treatments. However, some improvements need to be made, such as optimization of parameters of ALA-based PDT and diagnosis; increased tumor selectivity of ALA-derived PpIX; better understanding of light distribution in tissue: improvement of light dosimetry procedure; and development of simpler, cheaper, and more efficient light delivery systems.

Photobleaching of protoporphyrin IX in cells incubated with 5-aminolevulinic acid

Protoporphyrin IX (Pp IX) is the main photosensitizer in photochemotherapy with 5-aminolevulinic acid (ALA). Pp IX is photolabile and the present work shows that 70-95% of Pp IX in cells is degraded by clinically relevant light exposures (40-200 J cm(-2) at 630 nm). During light exposure a small yield of photoprotoporphyrin, which is also photolabile, is formed. A substantial fraction of Pp IX in cells incubated with ALA is bound to proteins. During light exposure these binding sites are destroyed, those close to tryptophan residues being the most sensitive. The rate of photodegradation of Pp IX in the cells is dependent on the initial concentration of Pp IX. The degradation mechanisms are therefore not only first order processes. Different degradation rates appear to be related to different types of binding sites. During light exposure, Pp IX molecules appear to move to different binding sites, evidently sites that are more vital for cell survival. Thus, the yield of photoinactivation of the cells, as measured per emitted photon of Pp IX fluorescence, increased during light exposure.

Photodynamic therapy (PDT) and photodiagnosis (PD) using endogenous photosensitization induced by 5-aminolevulinic acid (ALA): mechanisms and clinical results

5-Aminolevulinic acid (ALA), when added to many tissues, results in the accumulation of sufficient quantities of the endogenous photosensitizer protoporphyrin IX (PpIX) via the heme biosynthetic pathway, to produce a photodynamic effect when exposed to activating light. Therefore, ALA is the only photodynamic therapy (PDT) agent in current clinical development that is a biochemical precursor of a photosensitizer. Topical ALA application, followed by exposure to activating light (ALA PDT), has been reported effective for the treatment of a variety of dermatologic diseases including cutaneous superficial and nodular basal cell carcinoma, Bowen's disease, and actinic (solar) keratoses. Local internal application of ALA has also been used for selective endometrial ablation in animal model systems and in human clinical studies has shown selective formation of PpIX within the endometrium. PpIX induced by ALA application has also been used as a fluorescence detection marker for photodiagnosis (PD) of cancer and dysplastic conditions of the urinary bladder and other organs. Systemic, oral administration of ALA has been used for ALA PDT of superficial head and neck cancer, various gastrointestinal cancers, and the condition known as Barrett's esophagus. The current state of knowledge of the mechanisms of endogenous topical and systemic photosensitization using ALA, the results of published clinical trials, and possible methods of increasing the efficacy of endogenous photosensitization for ALA PDT are reviewed in this paper.

Formation of water-soluble porphyrins and protoporphyrin IX in 5-aminolevulinic-acid-incubated carcinoma cells

The bioconversion of 5-aminolevulinic acid (ALA) into hydrophobic protoporphyrin IX and other water-soluble porphyrins was investigated in Ehrlich ascite carcinoma (EAC) cells and in a myeloma cell line. The effects of irradiation (514 nm), temperature, incubation time and added glucose on the relative porphyrin concentrations (protoporphyrin vs. water-soluble porphyrins) were examined. Variations in these parameters induced a change in the amount of water-soluble porphyrins relative to protoporphyrin IX. The main component of the hydrophilic porphyrins was found to be uroporphyrin (Up), with minor components of coproporphyrin (Cp) and other carboxyporphyrins. The enhanced production of water-soluble porphyrins appears to be associated with alterations in the activities of the various enzymes in the heme biosynthetic pathway, resulting, for example, in the reduction in the activity of mitochondrial enzymes.

Oxygen binding properties of Eudistylia vancouverii chlorocruorin and its dodecamer subunit

The oxygen equilibrium curves of the extracellular chlorocruorin of the polychaete Eudistylia vancouverii and its dodecamer subunit were determined over the pH range from 7.1 to 8.1 and in the presence and absence of 100 mM Mg2+. Although the chlorocruorin has a very low oxygen affinity, high cooperativity and a moderate alkaline Bohr effect (P50 = 145 mmHg, nmax = 6.9, phi = -0.44 at pH 7.1 and 25 degrees C), the dodecamer subunit has higher affinity and lower cooperativity and Bohr coefficient (P50 = 58 mmHg, nmax = 1.7, phi = -0.22). The presence of 100 mM Mg2+ increased the oxygen affinity and cooperativity of the chlorocruorin but had no significant effect on the dodecamer subunit. The oxygen binding properties of the chlorocruorin reassociated subsequent to complete dissociation in 4 M urea at neutral pH were similar to the properties of the dodecamer and not to those of the native chlorocruorin. Fitting to the Monod-Wyman-Changeux allosteric model gave KT of 0.0013 mmHg-1, Kr of 0.22 mmHg-1 and L(o) of 2.5 x 10(13) together with a size of the allosteric unit, N = 9.

HepG2 human hepatocarcinoma cells: an experimental model for photosensitization by endogenous porphyrins

Endogenous protoporphyrin IX (PpIX) synthesis after delta-aminolaevulinic acid (ALA) administration occurs in cancer cells in vivo; PpIX, which has a short half-life, may thus constitute a good alternative to haematoporphyrin derivative (HPD) (or Photofrin). This study assesses the ability of the human hepatocarcinoma cell line HepG2 to synthesize PpIX in vitro from exogenous ALA, and compares ALA-induced toxicity and phototoxicity with the photodynamic therapy (PDT) effects of HPD on this cell line. ALA induced a dose-dependent dark toxicity, with 79% and 66% cell survival for 50 and 100 micrograms ml-1 ALA respectively after 3 h incubation; the same treatment, followed by laser irradiation (lambda = 632 nm, 25 J cm-2), induced a dose-dependent phototoxicity, with 54% and 19% cell survival 24 h after PDT. Whatever the incubation time with ALA, a 3 h delay before light exposure was found to be optimal to reach a maximum phototoxicity. HPD induced a slight dose-dependent toxicity in HepG2 cells and a dose- and time-dependent phototoxicity ten times greater than that of ALA-PpIX PDT. After 3 h incubation of 2.5 and 5 micrograms ml-1 HPD, followed by laser irradiation (lambda = 632 nm, 25 J cm-2), cell survival was 59% and 24% respectively at 24 h. Photoproducts induced by light irradiation of porphyrins absorb light in the red spectral region at longer wavelengths than the original porphyrins. The possible enhancement of PDT effects after HepG2 cell incubation with ALA or HPD was investigated by irradiating cells successively with red light (lambda = 632 nm) and light (lambda = 650 nm)(ABSTRACT TRUNCATED AT 250 WORDS)

Photodynamic therapy of experimental colonic tumours with 5-aminolevulinic-acid-induced endogenous porphyrins

5-Aminolevulinic acid (5-ALA) is a precursor in the biosynthesis of haem. External application of 5-ALA leads to the formation of protoporphyrin IX, the last intermediate product before haem, which is an effective sensitiser. The 5-ALA-induced endogenous photosensitisation of tumour cells has been exploited for photodynamic therapy (PDT). Experimental human G-3 colonic tumours were transplanted into nude mice, and ten mice were treated by PDT. Ten animals served as controls. We measured a fluorescence intensity of the tumour that was about eight times higher than in the surrounding tissue; a good correlation between the fluorescence intensity and the photodynamic effect was found. Tumour growth was inhibited significantly after PDT, two tumours being destroyed completely after the second PDT treatment. In addition, on-line fluorescence detection during PDT showed a change in the intensity and the fluorescence spectrum of protoporphyrin IX caused by photobleaching and the formation of photoproducts.

Photodegradation of protoporphyrin-dimethylester in solution and in organized environments

The degradation of sensitizers used in photodynamic therapy (PDT) involves photooxidation either by molecular oxygen or by oxygen intermediates which leads to hydroxyaldehyde and formyl products or to ring opening. Our investigations focused on the spectroscopic changes which protoporphyrin-dimethylester (PP) exhibits upon irradiation. As the microenvironment strongly influences the effects, we used an aprotic organic solvent, L-alpha-phosphatidylcholine dioleoyl (DOPC) liposomes and isogenic fibrosarcoma cells (SSKII) as carriers for PP. Hydroxyaldehyde product isomers develop a new absorption band centred around 670 nm and a new emission band at 676 nm. These characteristics can be used to discriminate them from formyl products and intact PP. In organic solvents, the formation of the hydroxyaldehyde products dominates. In DOPC liposomes and cells, the hydroxyaldehyde yield drops and photooxidation results in attack of the macrocycle. Time-resolved fluorescence spectroscopy of monomeric PP in an organic solvent gives a monoexponential decay time tau of 10.1 +/- 1.3 ns. Upon irradiation a second component with a decay time of 4.9 +/- 0.6 ns, resulting from the hydroxyaldehyde product, was detected. In liposomes and cells the monomeric decay time was significantly longer (15 ns) due to the altered microenvironment. Additionally, we observed in liposomes and in cells a small contribution of a short component (1 ns) which is attributed to an aggregated sensitizer species. In irradiated cells the aggregated fraction doubles, indicating a change in the microenvironment caused by the photodynamic action of the sensitizer.

In vivo photoproduct formation during PDT with ALA-induced endogenous porphyrins

The administration of 5-aminolevulinic acid (ALA) in tumor-bearing nude mice leads to the formation of the fluorescent, photounstable photosensitizer protoporphyrin IX in tumor tissue. On-line fluorescence spectroscopy during photodynamic therapy (PDT) shows the in vivo formation of chlorintype photoproducts of protoporphyrin. The fluorescence of protoporphyrin as well as its photoproducts is bleached completely at the end of the PDT (100 J cm-2, 630 nm). These findings were also verified using ultrashort laser pulses and time-correlated single-photon counting. A photinduced shortening of the decay times and decrease in the integral fluorescence intensity were measured in vivo due to the photodestruction of the endogenous photosensitizer protoporphyrin IX in the tumor.

Hierarchy of globin complexes. The quaternary structure of the extracellular chlorocruorin of Eudistylia vancouverii

The molecular dimensions of the extracellular, hexagonal bilayer chlorocruorin of the polychaete Eudistylia vancouverii, determined by scanning transmission electron microscopy (STEM) of negatively stained specimens, were diameter of 27.5 nm and height of 18.5 nm. STEM mass measurements of unstained, freeze-dried specimens provided a molecular mass (Mm) of 3480 +/- 225 kDa. The chlorocruorin had no carbohydrate and its iron content was 0.251 +/- 0.021 wt%, corresponding to a minimum Mm of 22.4 kDa. Mass spectra and nuclear magnetic resonance spectra of the prosthetic group confirmed it to be protoheme IX with a formyl group at position 3. SDS/polyacrylamide gel electrophoresis, reversed-phase chromatography and N-terminal sequencing suggested that the chlorocruorin consists of at least three chains of approximately 30 kDa and five chains of approximately 16 kDa; the two types of subunits occur in the ratio 0.26:0.74(+/- 0.08). Complete dissociation of the chlorocruorin at neutral pH in the presence of urea or guanidine hydrochloride, followed by gel filtration, produced elution profiles consisting of three peaks, B, C and D. Fractions B and C consisted of the approximately 16 kDa chains and fraction D consisted of the approximately 30 kDa subunits. Mass measurements of particles in STEM images of unstained, freeze-dried fractions B and C provided Mm of 208 +/- 23 kDa and 65 +/- 12 kDa, respectively, in agreement with 191 +/- 13 kDa and 67 +/- 5 kDa obtained by gel filtration. Particles with Mm = 221 +/- 21 kDa were also observed in STEM images of unstained, freeze-dried chlorocruorin. These results imply that the chlorocruorin structure, in addition to the approximately 30 kDa linker subunits that have 0.26 to 0.47 heme groups/chain, comprises approximately 65 kDa tetramers and approximately 200 kDa dodecamers (trimers of tetramers) of globin chains. The stoichiometry of the tetramer and linker subunits calculated from molar amino acid compositions was 34 +/- 4 and 43 +/- 9. The complete dissociation of the chlorocruorin was accompanied by a 50 to 75% loss of the 55 +/- 14 Ca2+/mol protein, and was decreased to approximately 35% by the presence of 10 to 25 mM-Ca2+. Reassociation of dissociated chlorocruorin was maximal in the presence of 2.5 to 5 mM-Ca2+. The dodecamer and/or tetramer subunits in the absence or presence of Ca2+ exhibited very limited (less than 10%) reassociation into hexagonal bilayer structures, only in the presence of the linker subunit.(ABSTRACT TRUNCATED AT 400 WORDS)

Regioselective photoreduction of zinc(II) porphyrins to give chlorins

The ascorbic acid/organic base photoreduction of zinc(II) porphyrins was investigated. It was established that certain substituents can direct the photoreduction to the site of the macrocycle to which they are attached. For example, zinc(II) vinylporphyrins (8, 12, 16, 20) are photoreduced with cis stereochemistry on the ring bearing the vinyl group to give the corresponding chlorins. Zinc(II) acetylporphyrins (22, 24) were likewise reduced to chlorins such that cis-hydrogenation took place on the ring bearing the acetyl group. Zinc(II) formylporphyrins 33 also appear to reduce at the ring bearing the formyl group. When the zinc(II) acrylic porphyrin 28 was photoreduced, reduction did take place at the ring bearing the acrylic side chain, but migration of the acrylate double bond was very rapid, and the product isolated was the corresponding porphyrin propionate 30. Reduction of a zinc(II) porphyrin 35 bearing both a vinyl group and a nuclear carboxylic ester took place at the ring bearing the carboxylic ester. The reaction provides a general method for regioselective synthesis of chlorins from zinc(II) porphyrins without any evidence of formation of over-reduction products characteristic of many other procedures for formation of chlorins from porphyrin precursors.

An internal standard for porphyrin analysis

The routine clinical analysis of the porphyrin precursors of heme requires an internal standard to determine the efficiency of the analytical procedure used. 2-Vinyl-4-hydroxymethyldeuteroporphyrin IX has been prepared as an internal standard. Its application to porphyrin analysis has been demonstrated using high-performance liquid chromatographic resolution of the uro- to protoporphyrins in normal and porphyric urine.