Layer Thickness of SPF 30 Sunscreen and Formation of Pre-vitamin D

BACKGROUND

Most studies have demonstrated that sunscreens with lower sun protection factor (SPF) do not prevent the production of vitamin D because much lower amount of sunscreen (SPF<30) is applied than recommended (2 mg/cm(2)) indicating that a significant amount of UV radiation can penetrate the skin. Since less sunscreen is applied, higher SPF sunscreens may be used to achieve the desired protection. However, there is little information regarding the application of high-SPF sunscreen and vitamin D formation. The aim of this study was to measure the influence of the amount of two SPF 30 sunscreens on pre-vitamin D formation in a cuvette with 7-dehydrocholesterol.

RESULTS

Sunscreen with physical (reflecting) or chemical (absorbing) UV filters exhibits different levels of protection in vitro even if the SPF is the same. The level of photoprotection is differentially reduced when less sunscreen than the recommended application thickness is applied.

CONCLUSION

The usual application of 0.8-1 mg/cm(2) is below the recommended value of 2 mg/cm(2), and pre-vitamin D may be formed when lower amounts of SPF ≤30 sunscreen are applied, showing that a significant amount of UV radiation may enter the skin.

Effect of vitamin D supplementation and ultraviolet B exposure on serum 25-hydroxyvitamin D concentrations in healthy volunteers: a randomized, crossover clinical trial

BACKGROUND

Solar ultraviolet (UV) radiation during the summer and vitamin D supplementation are two major sources of vitamin D for humans at northern latitudes. However, little is known about the relative efficiency of these two vitamin D sources.

OBJECTIVES

The main goal was to compare the efficiency of high-dose oral vitamin D3 supplementation (2000 IU per day for 30 days) with a simulated summer UV exposure [10 sunbed sessions to a total dose of 23·8 standard erythema doses (SED)] to improve vitamin D status.

METHODS

Healthy volunteers were randomized into two groups: group 1 received vitamin D supplementation followed by 10 whole-body sunbed exposures; group 2 started with 10 sunbed exposures followed by vitamin D supplementation.

RESULTS

The oral supplementation with vitamin D3 resulted in a mean (SEM) serum 25-hydroxyvitamin D [25(OH)D] increase of 25·3 (5·4) nmol L(-1) . A similar increase, 19·8 (5·4) nmol L(-1) , was observed after simulated summer UV exposure. At the end of the study, serum 25(OH)D concentrations were similar in both groups.

CONCLUSIONS

Twice-weekly whole-body sunbed exposure to a dose of 4·8 SED is equal to 2000 IU daily of oral vitamin D supplementation for 30 days and enough to achieve and maintain serum 25(OH)D concentrations > 75 nmol L(-1) in ~55% of cases. Based on our calculations, this dose corresponds to a cumulative weekly whole-body exposure of 3·4 SED (~ 40 min around midday during the summer at the latitude of Oslo).

Clearance mechanism of protoporphyrin IX from mouse skin after application of 5-aminolevulinic acid

BACKGROUND

5-Aminolevulinic acid (ALA) or its esters mediated photodynamic therapy (PDT) is the most widely practiced form of PDT in dermatology. One of its advantages is that undesirable photosensitization lasts only for 24-48 h. In order to optimize ALA-PDT it is necessary to understand the mechanisms of intracellular production and clearance of PpIX (efflux from cells into blood stream and/or its conversion into haem). The aim of this study is to investigate the factors controlling the clearance of intracellular PpIX from healthy skin of mice.

METHODS

PpIX was induced in mouse skin by topical or systemic application of ALA or by topical application of the iron chelator ethylenediaminetetraacetic acid (EDTA). Fluorescence spectroscopy was used to study PpIX kinetics in alive and dead skin.

RESULTS

Topical application of ALA or EDTA leads to porphyrin production in living skin, but not in excised skin. The clearance rates of PpIX from alive and dead skin were the same in the absence of an intracellular ALA pool. The clearance half-life of EDTA-induced PpIX was 4-7 times longer than that of PpIX after application of ALA.

CONCLUSIONS

Skin temperature and intracellular iron availability strongly affect PpIX clearance, while ALA application mode (topical versus systemic) and skin viability (dead versus alive) have no influence on PpIX decay. These results demonstrate that the clearance kinetics of PpIX from skin are determined mostly by the conversion of PpIX into haem, while the cellular efflux of PpIX into blood plays a minor role.

Novel patch-based systems for the localised delivery of ALA-esters

In photodynamic therapy (PDT) a combination of visible light and a sensitising drug causes the destruction of selected cells. Aminolaevulinic acid (ALA) has been widely used in topical PDT for over 15 years. However, ALA does not possess favourable physicochemical properties for skin penetration. Consequently, the clearance rates for difficult to treat lesions, such as nodular basal cell carcinomas are relatively low. For the first time, equimolar concentrations of ALA, methyl-ALA (m-ALA) and hexyl-ALA (h-ALA) have been incorporated into a bioadhesive patch-based system. In vitro penetration studies into excised porcine skin revealed that ALA patches containing relatively high loadings (226.7 micromol cm(-2)) were associated with significantly greater tissue concentrations (70.7 micromol cm(-3)) than patches containing m-ALA (16.3 micromol cm(-3)) or h-ALA (17.4 micromol cm(-3)). ALA was also found to be the most efficient inducer of protoporphyrin (PpIX) fluorescence in mice, in vivo (maximum mean fluorescence: ALA=236.2 a.u., m-ALA=175.1 a.u., h-ALA=193.5 a.u.). However, when the lipophilic hexylester was formulated in a pressure sensitive adhesive (PSA) patch, significantly higher PpIX levels were achieved compared to all bioadhesive systems tested. Of major importance, PSA patches containing relatively low h-ALA loadings induced high PpIX levels, which were localised to the application area. This study has highlighted the importance of rational selection of both the active agent and the delivery system. Bioadhesive preparations containing ALA are ideal for delivery to moist environments; whereas h-ALA-loaded PSA systems may facilitate enhanced delivery to dry areas of skin. In addition, owing to the relatively low loadings of h-ALA required in PSA patches, the costs of clinical PDT may potentially be reduced.

5-Methyltetrahydrofolate can be photodegraded by endogenous photosensitizers

Folate deficiency is linked to serious birth defects, pregnancy complications, male infertility, cardiovascular diseases, and even the evolution of human skin color. Conflicting data exist on whether exposure to sun or artificial UV sources may deplete the levels of blood folate in humans. Blood contains several photosensitizers and proteins, as well as antioxidants, which when exposed to UV radiation and visible light may be involved in the degradation of folate. In this study the photodegradation of 5-methyltetrahydrofolate (5MTHF) in aqueous and deuterious solutions exposed to UVB, UVA, or visible light in the absence or presence of riboflavin, uroporphyrin, and conjugated bilirubin was investigated by absorption spectroscopy. 5MTHF is stable under exposure to visible light and UVA radiation, whereas it is slowly photooxidized under UVB exposure. However, it is rapidly oxidized by UVA or visible radiation in the presence of riboflavin or uroporphyrin, but not in the presence of conjugated bilirubin, which acts in a protective manner. Reactive oxygen species produced in type I and/or type II reactions were involved. This study suggests that 5MTHF in blood can be photodegraded in the presence of the flavins and porphyrins, but protected by bilirubins. This may have health and evolutionary implications.

Photodegradation of 5-methyltetrahydrofolate in the presence of Uroporphyrin

The main form of folate in human plasma is 5-methyltetrahydrofolate (5MTHF). The observation that folate in human serum is photosensitive supports the hypothesis that humans developed dark skin in high ultraviolet fluences areas in order to protect folate in the blood from UV radiation. However, folates alone are quite photostable. Therefore, in this study, we examined for the first time the photodegradation of 5MTHF in the presence of the endogenous photosensitizer uroporphyrin (Uro), which is sometimes present in low concentration in human serum, under UV and near-UV light exposure. We found strong indications that while 5MTHF alone is rather photostable, it is degraded quickly in the presence of Uro. Using deuterium oxide (D(2)O) as an enhancer of the lifetime of singlet oxygen and the singlet oxygen sensor green reagent (SOSG) as a scavenger of singlet oxygen, we have found that the photodegradation most likely proceeds via a type II photosensitization. Our results show that singlet oxygen is likely to be the main intermediate in the photodegradation of 5MTHF mediated by Uro. Our findings may be useful for further studies the evolution of human skin colours.

In vitro and in vivo photosensitization by protoporphyrins possessing different lipophilicities and vertical localization in the membrane

Photodynamic therapy (PDT) is being evaluated in clinical trials for treatment of various oncologic and ophthalmic diseases. The main cause for cell inactivation and retardation of tumor growth after photoactivation of sensitizers is very short-lived singlet oxygen molecules that are produced and have limited diffusion distances. In this paper we show that the extent of biological damage can be modulated by using protoporphyrin, which was modified to increase its lipophilicity, and which also places the tetrapyrrole core deeper within the membrane by the carboxylate groups being anchored at the lipid:water interface. The uptake of the parent molecule (PPIX) and its diheptanoic acid analogue (PPIXC6) by WiDR and CT26 cells was investigated by fluorescence microscopy and by fluorescence intensity from the cells. The uptake of PPIXC6 increased almost linearly with incubation length for over 24 h, whereas for PPIX only 1 h was needed to reach maximal intracellular concentration. Fluorescence microscopy of both cell lines indicated that both drugs were distributed diffusely in the plasma membrane and cytoplasm, but remained outside the nucleus. The efficiency of in vitro inactivation of WiDr and CT26 cells increased with the length of the alkylcarboxylic chain. Tumors in mice that were treated with PPIX-PDT grew more slowly than control tumors. However, tumors that were given PPIXC6 followed by light exposure showed a significant delay in their growth.

Topical application of 5-aminolaevulinic acid, methyl 5-aminolaevulinate and hexyl 5-aminolaevulinate on normal human skin

BACKGROUND

5-Aminolaevulinic acid (ALA) and its ester derivatives are used in photodynamic therapy. Despite extensive investigations, the differences in biodistribution and pharmacokinetics of protoporphyrin IX (PpIX) induced by ALA and its derivatives are still not well understood, notably for humans.

OBJECTIVES

To study porphyrin accumulation after topical application of ALA and two of its ester derivatives in normal human skin.

METHODS

Creams containing 0.2%, 2% and 20% (w/w) of ALA, methyl 5-aminolaevulinate (MAL) and hexyl 5-aminolaevulinate (HAL) were applied on normal human skin of six volunteers. The amount and distribution of porphyrins formed in the skin was investigated noninvasively by means of fluorescence spectroscopy.

RESULTS

Fluorescence emission and excitation spectra exhibited similar spectral shapes for the all drugs, indicating that mainly PpIX was formed. Low concentrations (0.2% and 2%) of MAL induced considerably less PpIX in normal human skin than similar concentrations of ALA and HAL. A high concentration (20%) of ALA gave higher PpIX fluorescence in normal human skin than was found for MAL and HAL.

CONCLUSIONS

The concentrations inducing half of the maximal PpIX fluorescence are around 2% for ALA, 8% for MAL and 1% for HAL.

Topical bioadhesive patch systems enhance selectivity of protoporphyrin IX accumulation

In clinical 5-aminolevulinic acid (ALA)-based photodynamic therapy (PDT) of skin tumors it is desirable to develop vehicles that minimize the penetration of ALA through normal stratum corneum and maximize it through the compromised stratum corneum of the tumors to improve tumor selectivity. We have designed a bioadhesive patch, which may be able to achieve this aim. It induces levels of protoporphyrin IX (PpIX) in skin overlying tumors similar to those induced by the proprietary cream (Porphin) but at the same time induces less PpIX to form in normal skin and at distant sites. The mechanisms of action of the patch, as compared with that of the cream, were studied by means of Cuprophan barriers that mimic compromised tumor stratum corneum and in a mouse model with transplanted tumors.

The effect of folic acid on porphyrin synthesis in tumors and normal skin of mice treated with 5-aminolevulinic acid or methyl 5-aminolevulinate

5-Aminolevulinic acid (ALA) or its derivative methyl 5-aminolevulinate (MAL) combined with folic acid was applied in nude mice bearing human colon adenocarcinoma. The aim of the study is to see whether folic acid may increase biosynthesis of porphyrins in tumor tissue after systemic or topical administration of ALA or MAL. The production of porphyrins was determined by spectrofluorometric measurements with an optical fibre probe. It was found that the porphyrin production after i.p injection of 200 mg kg(-1) ALA or MAL was significantly increased by i.p injection of 100 mg kg(-1) folic acid. However, in the case of topically applied 20% ALA, folic acid had no effect. In the case of topically applied 20% MAL, folic acid (i.p or topically applied) reduced the porphyrin synthesis. This might be used for the protection of normal skin against photosensitization. The effects of folic acid were similar in tumors and normal skin. Two mechanisms may explain the results: enhancement of the efficiency of the rate-limiting enzyme porphobilinogen deaminase by folic acid or interference of folic acid with the transport of ALA and MAL to and into the cells synthesizing porphyrins in the tissues. The present data seem to favour the latter mechanism. Folic acid may have a role as an adjuvant in photodynamic therapy with systemically administered ALA and its derivatives.

The effect of skin permeation enhancers on the formation of porphyrins in mouse skin during topical application of the methyl ester of 5-aminolevulinic acid

The influence of skin permeation enhancers, such as dimethyl sulphoxide (DMSO) and 1-[2-(decylthio)ethyl]azacyclopentan-2-one (HPE-101), Labrafac CC, Labrafil, Labrasol and Transcutol in a concentration of 10% (wt./wt.) on the formation of porphyrins in normal mouse skin from topical application of creams with methyl 5-aminolevulinate (MAL) was studied. The concentration of porphyrins in the mouse skin was determined by direct fluorescence measurements. The results show that studied permeation enhancers increase the formation of porphyrins, and therefore also the skin penetration 2% MAL whereas for 10% and 20% (wt./wt.) MAL concentrations only DMSO, HPE-101 and Labrafac CC increased the porphyrin formation. At all studied MAL concentrations DMSO gave the largest enhancing effect, similarly to that of HPE-101. This suggests that in 2-20% MAL creams HPE-101 may be substituted by Labrafac CC to reduce skin irritation induced by HPE-101 without impairing the porphyrin formation.

Influence of light exposure on the kinetics of protoporphyrin IX formation in normal skin of hairless mice after application of 5-aminolevulinic acid methyl ester

The rates of protoporphyrin IX (PpIX) photodegradation and reappearance after light exposure at 420 and 632 nm were measured in mouse skin at different times after 1 h topical application of 5-aminolevulinic acid methyl ester (ALA-Me). After ALA-Me application (1 h) and removal, the fluorescence of PpIX increased for about 1 h, and then reached a maximum and started to decrease. Reappearance of PpIX fluorescence after exposures (degrading 60%-80% of the PpIX) was faster for exposures 0.5 h after ALA-Me application than for exposures 3 h. The bleaching rate was largest in the former case. This indicates that PpIX is located deeper in the skin after 3 h than after 0.5 h, whereas the pool of ALA-Me in the skin is largest at 0.5 h. In all cases, the reappearance was faster at a skin temperature of 35 degrees C than at 23 degrees C. Reappearance of PpIX fluorescence was faster after exposure to light at 420 nm than at 632 nm. The rate of elimination of PpIX from the volume of detection was faster after 420 nm light irradiation than that after 632 nm. These findings are discussed in view of penetration depths of light and ALA-Me, and diffusion of PpIX.

The influence of light and darkness on cutaneous fluorescence in mice

The present work was carried out to investigate the role of light and darkness on the endogenous biosynthesis of porphyrins in mammalian skin (hairless BALB/c mouse) in vivo. In the skin of mice that were constantly kept in darkness (DD), increased endogenous porphyrin fluorescence was observed, which mainly originated from protoporphyrin IX (PpIX). No significant increase in the porphyrin levels was observed in mice that were kept under a normal day-night cycle (LD 12:12 h). The presence of cutaneous PpIX together with ambient light may comprise a photosensitizing mechanism by which PpIX may be a photomessenger between ambient light and internal rhythms.

Lipid cubic phases for improved topical drug delivery in photodynamic therapy

We have evaluated the efficacy of lipid cubic phases, highly ordered self-assembly systems on the nanometer level, as drug delivery vehicles for in vivo topical administration of delta-aminolevulinic acid (ALA) and its methyl ester (m-ALA) on nude mice skin. ALA, a precursor of heme, induces the production of the photosensitizer protoporphyrin IX (PpIX) in living tissue. Measuring the PpIX fluorescence at the skin surface, after topical administration, makes indirect quantification of the penetration of ALA into the tissue possible. Cubic phases were formed of lipid (monoolein or phytantriol), water and drug. In some cases, propylene glycol was included in the cubic phase as well. The drug concentration was 3% (w/w, based on the total sample weight) in all investigated vehicles. When the formulations were applied for 1 h, the monoolein cubic systems and the three-component phytantriol sample showed higher fluorescence compared to the standard ointment during the 10 h of measurement. Both ALA and m-ALA yielded similar results, although the differences between the investigated vehicles were more pronounced when using m-ALA. For the 24-h applications, the monoolein cubic systems with m-ALA showed faster PpIX formation than the standard ointment, implying higher PpIX levels at short application times (less than 4 h). The systemic PpIX fluorescence of ALA was elevated by using the lipid cubic formulations. Notably, a small systemic effect was also observed for the monoolein cubic sample with m-ALA. These results imply improved PpIX formation when using the lipid cubic systems, most probably due to enhanced drug penetration.

Effectiveness of different light sources for 5-aminolevulinic acid photodynamic therapy

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.

Kinetics of protoporphyrin IX formation in rat oral mucosa and skin after application of 5-aminolevulinic acid and its methylester

The kinetics of accumulation of protoporphyrin IX (PpIX) after topical application of 5-aminolevulinic acid (ALA) and its methylester (5-aminolevulinic acid methylester [ALA-Me]) was studied on rat oral mucosa. The accumulation of PpIX in mucosa and skin after intravenous injection of ALA and ALA-Me was also studied. The elimination rate of PpIX was dependent on drug and dose as well as on administration route. Application of ALA on rat oral mucosa and skin caused a systemic effect with PpIX building up in remote skin sites not exposed to the drugs. No such systemic effect was seen after application of ALA-Me either in mucosa or on skin. Intravenous injection of the drugs (0.2 g/kg) leads to more fluorescence in the skin than topical application of the drug (20%). For mucosa, the opposite is true. Maximal PpIX fluorescence appeared later after application of high concentrations of the drugs (around 8 h for 5% and 20% wt/wt) than after application of low concentrations (around 3-5 h for 1% and 2% wt/wt).

Photodegradation and phototransformation of 5,10,15,20-tetrakis(m-hydroxyphenyl)bacteriochlorin (m-THPBC) in solution

The kinetics of photobleaching and formation of photoproducts upon irradiation (735 nm) of 5,10,15,20-tetrakis(m-hydroxyphenyl)bacteriochlorin (m-THPBC) in phosphate buffer saline (PBS) supplemented with human serum albumin (HSA) were studied by means of absorption and steady-state fluorescence spectroscopy. Measurements were performed either immediately after the dye was dissolved in the HSA solution (0 h) or after six hours incubation in the HSA solution (6 h). Spectroscopic studies indicated that the dye was mainly present as aggregates in freshly prepared solutions, whereas incubation favored monomerisation. Irrespective to incubation time, the rates of photobleaching obtained by fluorescence measurements were higher than those obtained from absorbance measurements. Photobleaching of freshly prepared m-THPBC can be described by a single exponential decay, while the absorbance and fluorescence decays of the incubated dye solutions better fit a bi-exponential decay. Two photobleaching rates probably reflect differences in the photosensitivity of monomer (bound to proteins) and aggregated (non-bound) forms. Irradiation of the freshly prepared m-THPBC solution led to phototransformation of 50% of the bleached m-THPBC into 5,10,15,20-tetrakis(m-hydroxyphenyl)chlorin (m-THPC), a clinically used second generation photosensitizer. For irradiation 6 h after dissolving m-THPBC, different kinetics of m-THPC formation were found. A rapid decrease in concentration of m-THPBC was accompanied by a slow formation of m-THPC. The quantum yield of this process was small since only 5% of m-THPBC was transformed to m-THPC. The kinetics characteristics of m-THPBC photobleaching reported in the present study, together with the different kinetics of photoproduct formation during m-THPBC photobleaching, may provide important indications in the m-THPBC-based PDT dosimetry.

Pharmacology of protoporphyrin IX in nude mice after application of ALA and ALA esters

Aminolevulinic acid (ALA), ALA methylester (ALA-Me) and ALA hexylester (ALA-Hex) were topically applied for 5 and 20 hr, respectively, on normal skin of mice. The distribution of protoporphyrin IX (PpIX) induced in 7 different tissues by these drugs was determined either by spectrofluorometric measurements with an optical fibre probe or by chemical extraction of PpIX from the tissues. The results from these 2 types of measurements were compared. Both methods showed that ALA and the esters induced similar amounts of PpIX at the skin spot where they were applied and that the esters produced much less PpIX at remote skin spots (i.e., spots outside the location where the drugs were applied) than ALA did, notably after 20 hr application. After 20 hr of drug application ALA produced much more PpIX in liver, intestine and lungs than the esters did. In contrast with the direct fluorescence measurements, the extraction method showed detectable amounts of PpIX in liver, intestine and lung after application of the esters, notably of ALA-Me. The discrepancy is probably related to the fact that the pigmented tissues absorb light and, therefore, the direct fluorescence readings are misleading. Notably in the liver, which contains high concentration of light-absorbing pigments, very weak direct fluorescence was seen. In no case there was any accumulation of PpIX in muscle tissue nor in brain. The esters seem to penetrate less into the circulation than ALA, and PpIX formed by them in the skin is faster cleared than PpIX formed from ALA. This is also true after oral and i.p. administration of the drugs.

Production of protoporphyrin IX from 5-aminolevulinic acid and two of its esters in cells in vitro and tissues in vivo

5-Aminolevulinic acid (ALA) and two of its esters were studied in cells in vitro and in vivo on skin of healthy hairless mice. In vitro, both esters, which are more lipophilic than ALA, induced higher PpIX fluorescence at lower concentrations compared with ALA. In vivo, ALA induced PpIX fluorescence more efficiently than the esters. The difference between ALA and the esters may be related to structures in the stratum corneum or to rate of penetration through this skin layer. The stratum corneum may bind the esters temporarily, and slow down their penetration into the living cells where PpIX is formed.

Noninvasive fluorescence excitation spectroscopy during application of 5-aminolevulinic acid in vivo

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 (>600 nm) penetrates deeper into the tissues by a factor of 6 compared with the short wavelength light (<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.

Temperature effect on accumulation of protoporphyrin IX after topical application of 5-aminolevulinic acid and its methylester and hexylester derivatives in normal mouse skin

Significant amounts of protoporphyrin IX (PpIX) are formed after 6 min of topical application of 5-aminolevulinic acid (ALA) and its hexylester derivative, whereas PpIX is formed after 10 min of topical application of ALA-methylester derivative in normal mouse skin at 37 degrees C. Lowering the skin temperature to 28-32 degrees C by the administration of the anesthetic Hypnorm-Dormicum reduces the PpIX fluorescence by a factor of 2-3. Practically no PpIX was formed as long as the skin temperature was kept at 12-18 degrees C. At around 30 degrees C PpIX fluorescence appears later after application of ALA-ester derivatives (14-20 min) than after application of ALA (8 min), indicating differences in their bioavailability (delayed penetration through the stratum corneum, cellular uptake, conversion to ALA, PpIX production) in mouse skin in vivo. The difference in lag time in the PpIX formation after application of ALA and ALA-esters may be partly related to deesterification of the ALA-ester molecules. The temperature dependence of PpIX production may be used for improvement of photodynamic therapy with ALA and ALA-ester derivatives, where accumulation of PpIX can be selectively enhanced by increasing the temperature of the target tissue.

Photobleaching of hypericin bound to human serum albumin, cultured adenocarcinoma cells and nude mice skin

Hypericin is a promising photosensitizer for photodynamic therapy (PDT) characterized by a high yield of singlet oxygen. Photobleaching of hypericin has been studied by means of absorption and fluorescence spectroscopy in different biological systems: in human serum albumin solution, in cultured human adenocarcinoma WiDr cells and in the skin of nude mice. Prolonged exposure to light (up to 95 min, 100 mW/cm2) of wavelength around 596 nm induced fluence-dependent photobleaching of hypericin in all studied systems. The photobleaching was not oxygen dependent, and singlet oxygen probably played no significant role. Emission bands in the spectral regions 420-560 nm and above 600 nm characterize the photoproducts formed. An emission band at 615-635 nm was observed after irradiation of cells incubated with hypericin or of mouse skin in vivo but not in albumin solution. The excitation spectrum of these products resembled that of hypericin. Hypericin appears to be more photostable than most sensitizers used in PDT, including mTHPC and Photofrin.

Topical application of 5-aminolevulinic acid and its methylester, hexylester and octylester derivatives: considerations for dosimetry in mouse skin model

Ester derivatives of 5-aminolevulinic acid (ALA-esters) have been proposed as alternative drugs for ALA in photodynamic therapy. After topical application of creams containing ALA, ALA methylester (ALA-Me), ALA hexylester (ALA-Hex) and ALA octylester (ALA-Oct) on mouse skin, typical fluorescence excitation and emission spectra of protoporphyrin IX (PpIX) were recorded, exhibiting a similar spectral shape for all the drugs in the range of concentrations (0.5-20%) studied. The accumulation kinetics of PpIX followed nearly a similar profile for all the drug formulations. The fluorescence of PpIX peaked at around 6-12 h of continuous cream application. Nevertheless, some differences in pharmacokinetics were noticed. For ALA cream, the highest PpIX fluorescence was achieved using 20% of ALA in an ointment. Conversely, 10% of ALA-Me and ALA-Hex, but not of ALA-Oct, in the cream was more efficient (P < 0.05) than was 20%. The cream becomes rather fluid when 20% of any of these ALA-esters is used in ointment, whereas 10% and lower concentrations of ALA-esters do not significantly increase fluidity of the cream. The dependence of PpIX accumulation on the concentration of ALA and ALA-ester in the applied cream followed (P < 0.002) kinetics as described by a mathematical model based on the Michaelis-Menten equation for enzymatic processes. Under the present conditions, the PpIX amount in the skin increased by around 50% by the application of ALA-Me, ALA-Hex or ALA-Oct for 4-12 h as compared with ALA for the same period. Observations of the mice under exposure to blue light showed that after 8-24 h of continuous application of ALA, the whole mouse was fluorescent, whereas in the case of ALA-Me, ALA-Hex and ALA-Oct the fluorescence of PpIX was located only at the area of initial cream application. The amount of the active compound in the applied cream necessary to induce 90% of the maximal amount of PpIX was determined for normal mouse skin. Optimal PpIX fluorescence can be attained using around 5% ALA, 10% ALA-Me and 5% ALA-Hex creams during short application times (2-4 h). Topical application of ALA-Oct may not gain optimal PpIX accumulation for short applications (<5 h). For long application times (8-12 h), it seems that around 1% ALA, 4% ALA-Me, 6% ALA-Hex and 16% ALA-Oct can give optimal PpIX fluorescence. But for long application times and high concentrations, systemic effect of ALA applied topically on relatively large areas should be considered.

Photosensitizing effect of protoporphyrin IX in pigmented melanoma of mice

No fluorescence of protoporphyrin IX (PpIX) was measured using a fiber optic probe in pigmented B16F10 melanoma in mice after topical application of 5-aminolevulinic acid methylester (ALA-Me). However, chemical extraction of tissues excised from mice after intratumoral administration of ALA-Me or its parent compound ALA revealed that this tumor had the capability to produce PpIX. Small amounts of endogenous porphyrins, mainly PpIX, were found in the melanoma not treated with these drugs. Topical application of ALA-Me followed by exposure with laser light (633nm) delayed the growth of the tumors slightly. Light alone also had a significant effect on the tumor growth.