Photodynamic therapy (PDT) and fluorescence diagnosis (FD) are being developed for a number of cl... more Photodynamic therapy (PDT) and fluorescence diagnosis (FD) are being developed for a number of clinical applications. Since fluorophores and photosensitising drugs are usually given systemically their effect on blood elements are of significant importance. Photodynamic effects on erythrocytes occur naturally in patients with erythropoietic protoporphyria (EPP). Exposure to small fluences, as obtained by the erythrocytes when they pass capillaries in the skin, leads to transfer of the photosensitiser protoporphyrin IX (PP IX), from EPP erythrocytes to endothelial cells. Thus, the erythrocytes are partly protected while the endothelial cells suffer photodamage. During photodynamic therapy in vivo erythrocytes are regularly photosensitised. This side effect is partly intended but mostly unwanted, and a summary of this topic is given. Furthermore, the effect of UV-A on erythrocytes that is accompanied with the formation of bilirubin is reviewed. Erythrocytes serve as convenient model cells for experimental research. Such use of erythrocytes to screen new photosensitisers may be of limited value. A combination of photohaemolysis and haemoglobin oxygenation may become the basis for an assay for in vitro phototoxicity. Erythrocytes from birds are good model cells for exploration of physiological and molecular mechanisms involved in PDT. A potential mechanism of PDT induced behaviour resembling apoptosis in erythrocytes is provided.PDT for sterilisation of erythrocyte concentrates has a potential for medical use. Photodynamic effects on the erythrocytes themselves should be avoided. This is realised by choosing a virus-selective photosensitiser, low fluences and treatment of the concentrates with agents like dipyridamole and antioxidants. Future aspects of applications of photosensitisation of red blood cells are discussed.
Many reviews on PDT have been published. This field is now so large, and embraces so many sub-spe... more Many reviews on PDT have been published. This field is now so large, and embraces so many sub-specialties, from laser technology and optical penetration through diffusing media to a number of medical fields including dermatology, gastroenterology, ophthalmology, blood sterilization and treatment of microbial-viral diseases, that it is impossible to cover all aspects in a single review. Here, we will concentrate on a few basic aspects, all important for the route of development leading PDT to its present state: early work on hematoporphyrin and hematoporphyrin derivative, second and third generation photosensitizers, 5-aminolevulinic acid and its derivatives, oxygen and singlet oxygen, PDT effects on cell organelles, mutagenic potential, the basis for tumour selectivity, cell cooperativity, photochemical internalization, light penetration into tissue and the significance of oxygen depletion, photobleaching of photosensitizers, optimal light sources, effects on the immune system, and, finally, future trends.
Many medical applications, including photodynamic therapy for cancer (PDT), involve the use of la... more Many medical applications, including photodynamic therapy for cancer (PDT), involve the use of lasers. However, the coherence of laser light is not necessary for PDT, and attempts have been made to construct non-coherent light sources for PDT, which are relatively inexpensive, stable and easy to operate, require simple maintenance but differ fundamentally from the lasers in their output characteristics. In the present work we compared two clinically used lamps, CureLight1, which is a broadband source (560–740 nm) based on a filtered halogen lamp, and CureLight2, which is a narrowband source based on light-emitting diodes (LEDs), with respect to several parameters of crucial significance for PDT efficiency in vivo: (a) depth of action in tissues, (b) heating effects, (c) pain generation, (d) photodegradation of PpIX in solution, in cells and in mouse skin and (e) photo-inactivation of cells in vitro. We conclude that CureLight2 (LED), relative to CureLight1 (halogen) has deeper PDT action in tissue, similar efficiency for bleaching PpIX in mouse skin, better efficiency for bleaching PpIX in cells and solutions and good efficiency for inactivating cells in vitro. CureLight2 gives less heating of the tissue and less pain in unsensitised human skin. All these differences are related to difference in the spectra of the lamps. Thus, PDT light sources with emissions that are visually similar have significantly different photobiological properties.
Background Photodynamic therapy (PDT) is based on the combination of an exogenously administered... more Background Photodynamic therapy (PDT) is based on the combination of an exogenously administered precursor of photosensitizer [protoporphyrin IX (PpIX)] synthesis and exposure to light. Choosing the optimal wavelength is important. Red light penetrates deeper into tissue, while violet light is more efficient in activating PpIX but does not penetrate so deeply.Objectives We studied PpIX formation and the PDT effect after application to human skin of creams containing aminolaevulinic acid (ALA) and aminolaevulinic acid methyl ester (MAL). The aim of the study was to investigate whether the wavelength of the light used has an influence on pain sensations during topical PDT with the different prodrugs.Methods ALA cream (10%) and MAL cream (10%) were topically applied on the skin of 10 healthy volunteers. After 24 h the application site was exposed to 8 mW cm−2 violet laser or to 100 mW cm−2 red laser light. The erythema index was monitored up to 24 h after light exposure. For the first time the pain during topical ALA- and MAL-PDT was assessed by measuring the time taken for pain to occur. Also, for the first time, the intensities of the light sources were calibrated so as to have the same relative quantum efficiency.Results The pain sensation during ALA-PDT with red light came 22 s sooner than during ALA-PDT with violet light, which is statistically significant (P < 0·05). Moreover, ALA-PDT with red light gave stronger and more persistent erythema than ALA-PDT with violet light. ALA induced about three times more PpIX than MAL. No statistically significant differences were found for erythema, or for the time for pain to occur, in the case of MAL-PDT with red vs. violet light.Conclusions Topical ALA-PDT with violet light allows longer exposure times before pain is induced and gives less erythema as compared with topical ALA-PDT with red light.
The fluorescence of PpIX induced by topical application of 5-aminolevulinic acid (ALA) in normal ... more The fluorescence of PpIX induced by topical application of 5-aminolevulinic acid (ALA) in normal mouse skin was studied noninvasively by means of a fibre optic probe. The fluorescence excitation spectrum of PpIX exhibits five distinct peaks at around 408. 510, 543, 583 and 633 nm under fluorescence monitoring at the second emission peak of PpIX (705 nm). The transmission of the excitation light is wavelength dependent: the long wavelength light (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;600 nm) penetrates deeper into the tissues by a factor of 6 compared with the short wavelength light (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;590 nm). Thus, the fluorescence excitation spectrum of PpIX measured on the surface of the skin can be used to estimate the depth of the penetration of topically applied ALA. The fluorescence excitation spectra calculated for the depth 1.1 mm obtained the best fit with the experimentally measured spectra after topical application of ALA.
5-Methyltetrahydrofolate (5MTHF) is the main form of folate in human plasma, and an important vit... more 5-Methyltetrahydrofolate (5MTHF) is the main form of folate in human plasma, and an important vitamin for human health. Photodegradation of folates may have played a role in the development of different human skin colours. 5MTHF can be degraded directly by exposure to ultraviolet radiation or by exposure to visible light in the presence of endogenous sensitizers like riboflavin (RF). These photochemical reactions were studied by absorption spectroscopy. While 5MTHF is stable under UV and visible light exposure in pure aqueous media, it is quickly degraded in the presence of RF during UVA and blue light exposure. The degradation of 5MTHF is dependent on the concentration of RF, but not on the concentration of 5MTHF itself. UVA and blue light gave similar reactions. Further investigations are necessary to evaluate the consequences of large light exposures in vivo in humans. Our findings should be taken into the ongoing discussion about the development of human skin colours. Due to the presence of RF in human blood, folate can be significantly degraded during prolonged or intense blue light exposure. Thus, a dark skin colour may be favourable for prevention of folate degradation under high solar fluence rates, such as in equatorial areas.
Background Sunscreens are being widely used to reduce exposure to harmful ultraviolet (UV) radiat... more Background Sunscreens are being widely used to reduce exposure to harmful ultraviolet (UV) radiation. The fact that some sunscreens are photounstable has been known for many years. Since the UV-absorbing ingredients of sunscreens may be photounstable, especially in the long wavelength region, it is of great interest to determine their degradation during exposure to UV radiation. Our aim was to investigate the photostability of seven commercial sunscreen products after natural UV exposure (UVnat) and artificial UV exposure (UVart). Methods Seven commercial sunscreens were studied with absorption spectroscopy. Sunscreen product, 0.5 mg/cm2, was placed between plates of silica. The area under the curve (AUC) in the spectrum was calculated for UVA (320–400 nm), UVA1 (340–400 nm), UVA2 (320–340 nm) and UVB (290–320 nm) before (AUCbefore) and after (AUCafter) UVart (980 kJ/m2 UVA and 12 kJ/m2 of UVB) and before and after UVnat. If theAUC Index (AUCI), defined as AUCI = AUCafter/AUCbefore, was > 0.80, the sunscreen was considered photostable. Results Three sunscreens were unstable after 90 min of UVnat; in the UVA range the AUCI was between 0.41 and 0.76. In the UVB range one of these sunscreens was unstable with an AUCI of 0.75 after 90 min. Three sunscreens were photostable after 120 min of UVnat; in the UVA range the AUCI was between 0.85 and 0.99 and in the UVB range between 0.92 and 1.0. One sunscreen showed in the UVA range an AUCI of 0.87 after UVnat but an AUCI of 0.72 after UVart. Five of the sunscreens were stable in the UVB region. Conclusion The present study shows that several sunscreens are photounstable in the UVA range after UVnat and UVart. There is a need for a standardized method to measure photostability, and the photostability should be marked on the sunscreen product.
Photodynamic therapy (PDT) and fluorescence diagnosis (FD) are being developed for a number of cl... more Photodynamic therapy (PDT) and fluorescence diagnosis (FD) are being developed for a number of clinical applications. Since fluorophores and photosensitising drugs are usually given systemically their effect on blood elements are of significant importance. Photodynamic effects on erythrocytes occur naturally in patients with erythropoietic protoporphyria (EPP). Exposure to small fluences, as obtained by the erythrocytes when they pass capillaries in the skin, leads to transfer of the photosensitiser protoporphyrin IX (PP IX), from EPP erythrocytes to endothelial cells. Thus, the erythrocytes are partly protected while the endothelial cells suffer photodamage. During photodynamic therapy in vivo erythrocytes are regularly photosensitised. This side effect is partly intended but mostly unwanted, and a summary of this topic is given. Furthermore, the effect of UV-A on erythrocytes that is accompanied with the formation of bilirubin is reviewed. Erythrocytes serve as convenient model cells for experimental research. Such use of erythrocytes to screen new photosensitisers may be of limited value. A combination of photohaemolysis and haemoglobin oxygenation may become the basis for an assay for in vitro phototoxicity. Erythrocytes from birds are good model cells for exploration of physiological and molecular mechanisms involved in PDT. A potential mechanism of PDT induced behaviour resembling apoptosis in erythrocytes is provided.PDT for sterilisation of erythrocyte concentrates has a potential for medical use. Photodynamic effects on the erythrocytes themselves should be avoided. This is realised by choosing a virus-selective photosensitiser, low fluences and treatment of the concentrates with agents like dipyridamole and antioxidants. Future aspects of applications of photosensitisation of red blood cells are discussed.
Many reviews on PDT have been published. This field is now so large, and embraces so many sub-spe... more Many reviews on PDT have been published. This field is now so large, and embraces so many sub-specialties, from laser technology and optical penetration through diffusing media to a number of medical fields including dermatology, gastroenterology, ophthalmology, blood sterilization and treatment of microbial-viral diseases, that it is impossible to cover all aspects in a single review. Here, we will concentrate on a few basic aspects, all important for the route of development leading PDT to its present state: early work on hematoporphyrin and hematoporphyrin derivative, second and third generation photosensitizers, 5-aminolevulinic acid and its derivatives, oxygen and singlet oxygen, PDT effects on cell organelles, mutagenic potential, the basis for tumour selectivity, cell cooperativity, photochemical internalization, light penetration into tissue and the significance of oxygen depletion, photobleaching of photosensitizers, optimal light sources, effects on the immune system, and, finally, future trends.
Many medical applications, including photodynamic therapy for cancer (PDT), involve the use of la... more Many medical applications, including photodynamic therapy for cancer (PDT), involve the use of lasers. However, the coherence of laser light is not necessary for PDT, and attempts have been made to construct non-coherent light sources for PDT, which are relatively inexpensive, stable and easy to operate, require simple maintenance but differ fundamentally from the lasers in their output characteristics. In the present work we compared two clinically used lamps, CureLight1, which is a broadband source (560–740 nm) based on a filtered halogen lamp, and CureLight2, which is a narrowband source based on light-emitting diodes (LEDs), with respect to several parameters of crucial significance for PDT efficiency in vivo: (a) depth of action in tissues, (b) heating effects, (c) pain generation, (d) photodegradation of PpIX in solution, in cells and in mouse skin and (e) photo-inactivation of cells in vitro. We conclude that CureLight2 (LED), relative to CureLight1 (halogen) has deeper PDT action in tissue, similar efficiency for bleaching PpIX in mouse skin, better efficiency for bleaching PpIX in cells and solutions and good efficiency for inactivating cells in vitro. CureLight2 gives less heating of the tissue and less pain in unsensitised human skin. All these differences are related to difference in the spectra of the lamps. Thus, PDT light sources with emissions that are visually similar have significantly different photobiological properties.
Background Photodynamic therapy (PDT) is based on the combination of an exogenously administered... more Background Photodynamic therapy (PDT) is based on the combination of an exogenously administered precursor of photosensitizer [protoporphyrin IX (PpIX)] synthesis and exposure to light. Choosing the optimal wavelength is important. Red light penetrates deeper into tissue, while violet light is more efficient in activating PpIX but does not penetrate so deeply.Objectives We studied PpIX formation and the PDT effect after application to human skin of creams containing aminolaevulinic acid (ALA) and aminolaevulinic acid methyl ester (MAL). The aim of the study was to investigate whether the wavelength of the light used has an influence on pain sensations during topical PDT with the different prodrugs.Methods ALA cream (10%) and MAL cream (10%) were topically applied on the skin of 10 healthy volunteers. After 24 h the application site was exposed to 8 mW cm−2 violet laser or to 100 mW cm−2 red laser light. The erythema index was monitored up to 24 h after light exposure. For the first time the pain during topical ALA- and MAL-PDT was assessed by measuring the time taken for pain to occur. Also, for the first time, the intensities of the light sources were calibrated so as to have the same relative quantum efficiency.Results The pain sensation during ALA-PDT with red light came 22 s sooner than during ALA-PDT with violet light, which is statistically significant (P < 0·05). Moreover, ALA-PDT with red light gave stronger and more persistent erythema than ALA-PDT with violet light. ALA induced about three times more PpIX than MAL. No statistically significant differences were found for erythema, or for the time for pain to occur, in the case of MAL-PDT with red vs. violet light.Conclusions Topical ALA-PDT with violet light allows longer exposure times before pain is induced and gives less erythema as compared with topical ALA-PDT with red light.
The fluorescence of PpIX induced by topical application of 5-aminolevulinic acid (ALA) in normal ... more The fluorescence of PpIX induced by topical application of 5-aminolevulinic acid (ALA) in normal mouse skin was studied noninvasively by means of a fibre optic probe. The fluorescence excitation spectrum of PpIX exhibits five distinct peaks at around 408. 510, 543, 583 and 633 nm under fluorescence monitoring at the second emission peak of PpIX (705 nm). The transmission of the excitation light is wavelength dependent: the long wavelength light (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;600 nm) penetrates deeper into the tissues by a factor of 6 compared with the short wavelength light (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;590 nm). Thus, the fluorescence excitation spectrum of PpIX measured on the surface of the skin can be used to estimate the depth of the penetration of topically applied ALA. The fluorescence excitation spectra calculated for the depth 1.1 mm obtained the best fit with the experimentally measured spectra after topical application of ALA.
5-Methyltetrahydrofolate (5MTHF) is the main form of folate in human plasma, and an important vit... more 5-Methyltetrahydrofolate (5MTHF) is the main form of folate in human plasma, and an important vitamin for human health. Photodegradation of folates may have played a role in the development of different human skin colours. 5MTHF can be degraded directly by exposure to ultraviolet radiation or by exposure to visible light in the presence of endogenous sensitizers like riboflavin (RF). These photochemical reactions were studied by absorption spectroscopy. While 5MTHF is stable under UV and visible light exposure in pure aqueous media, it is quickly degraded in the presence of RF during UVA and blue light exposure. The degradation of 5MTHF is dependent on the concentration of RF, but not on the concentration of 5MTHF itself. UVA and blue light gave similar reactions. Further investigations are necessary to evaluate the consequences of large light exposures in vivo in humans. Our findings should be taken into the ongoing discussion about the development of human skin colours. Due to the presence of RF in human blood, folate can be significantly degraded during prolonged or intense blue light exposure. Thus, a dark skin colour may be favourable for prevention of folate degradation under high solar fluence rates, such as in equatorial areas.
Background Sunscreens are being widely used to reduce exposure to harmful ultraviolet (UV) radiat... more Background Sunscreens are being widely used to reduce exposure to harmful ultraviolet (UV) radiation. The fact that some sunscreens are photounstable has been known for many years. Since the UV-absorbing ingredients of sunscreens may be photounstable, especially in the long wavelength region, it is of great interest to determine their degradation during exposure to UV radiation. Our aim was to investigate the photostability of seven commercial sunscreen products after natural UV exposure (UVnat) and artificial UV exposure (UVart). Methods Seven commercial sunscreens were studied with absorption spectroscopy. Sunscreen product, 0.5 mg/cm2, was placed between plates of silica. The area under the curve (AUC) in the spectrum was calculated for UVA (320–400 nm), UVA1 (340–400 nm), UVA2 (320–340 nm) and UVB (290–320 nm) before (AUCbefore) and after (AUCafter) UVart (980 kJ/m2 UVA and 12 kJ/m2 of UVB) and before and after UVnat. If theAUC Index (AUCI), defined as AUCI = AUCafter/AUCbefore, was > 0.80, the sunscreen was considered photostable. Results Three sunscreens were unstable after 90 min of UVnat; in the UVA range the AUCI was between 0.41 and 0.76. In the UVB range one of these sunscreens was unstable with an AUCI of 0.75 after 90 min. Three sunscreens were photostable after 120 min of UVnat; in the UVA range the AUCI was between 0.85 and 0.99 and in the UVB range between 0.92 and 1.0. One sunscreen showed in the UVA range an AUCI of 0.87 after UVnat but an AUCI of 0.72 after UVart. Five of the sunscreens were stable in the UVB region. Conclusion The present study shows that several sunscreens are photounstable in the UVA range after UVnat and UVart. There is a need for a standardized method to measure photostability, and the photostability should be marked on the sunscreen product.
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