Microscopic localisation of protoporphyrin IX in normal mouse skin after topical application of 5-aminolevulinic acid or methyl 5-aminolevulinate

Photodynamic therapy: An emerging therapeutic modality in dentistry

Photodynamic Therapy (PDT) is a rapidly evolving, non-invasive treatment modality with considerable promise in dental pharmacotherapeutics. This review article comprehensively examines PDT, beginning with its principles and then delving into its diverse applications in dentistry, including periodontal disease, endodontics, oral cancer, dental implants, and dental caries. Each area presents the latest research and discusses the potential benefits and challenges. The unique advantages of PDT are highlighted, such as selective targeting, broad-spectrum antimicrobial effect, lack of resistance development, and its synergistic effect with other treatments. However, challenges such as photosensitizer delivery, light penetration, oxygen availability, and the need to standardize protocols are also acknowledged. The review further explores future perspectives of PDT in dentistry, including advancements in photosensitizer design, overcoming hypoxic limitations, personalized protocols, integration with other therapies, and standardization and regulation. The potential of advanced technologies, such as nanotechnology and synthetic biology, to improve PDT outcomes is also discussed. The review concludes that while PDT has shown immense potential to revolutionize dental pharmacotherapeutics, further high-quality research is needed to translate this potential into everyday dental practice. The promising future of PDT in dentistry suggests a more effective and less invasive treatment option for a range of dental conditions.

Protoporphyrin IX-induced phototoxicity: Mechanisms and therapeutics

Protoporphyrin IX (PPIX) is an intermediate in the heme biosynthesis pathway. Abnormal accumulation of PPIX due to certain pathological conditions such as erythropoietic protoporphyria and X-linked protoporphyria causes painful phototoxic reactions of the skin, which can significantly impact daily life. Endothelial cells in the skin have been proposed as the primary target for PPIX-induced phototoxicity through light-triggered generation of reactive oxygen species. Current approaches for the management of PPIX-induced phototoxicity include opaque clothing, sunscreens, phototherapy, blood therapy, antioxidants, bone marrow transplantation, and drugs that increase skin pigmentation. In this review, we discuss the present understanding of PPIX-induced phototoxicity including PPIX production and disposition, conditions that lead to PPIX accumulation, symptoms and individual differences, mechanisms, and therapeutics.

Daylight-PDT: everything under the sun

5-Aminolevulinic acid-based photodynamic therapy (ALA-PDT) was first implemented over three decades ago and has since been mainly part of clinical practice for the management of pre-cancerous and cancerous skin lesions. Photodynamic therapy relies on the combination of a photosensitizer, light and oxygen to cause photo-oxidative damage of cellular components. 5-Aminolevulinic acid (ALA) is a natural precursor of the heme biosynthetic pathway, which when exogenously administered leads to the accumulation of the photoactivatable protoporphyrin IX. Although, effective and providing excellent cosmetic outcomes, its use has been restricted by the burning, stinging, and prickling sensation associated with treatment, as well as cutaneous adverse reactions that may be induced. Despite intense research in the realm of drug delivery, pain moderation, and light delivery, a novel protocol design using sunlight has led to some of the best results in terms of treatment response and patient satisfaction. Daylight PDT is the protocol of choice for the management of treatment of multiple or confluent actinic keratoses (AK) skin lesions. This review aims to revisit the photophysical, physicochemical and biological characteristics of ALA-PDT, and the underlying mechanisms resulting in daylight PDT efficiency and limitations.

Optimizing treatment of acne with photodynamic therapy (PDT) to achieve long-term remission and reduce side effects. A prospective randomized controlled trial

Photodynamic therapy with methyl aminolevulinate (MAL-PDT) is an effective treatment of acne vulgaris, but is associated with side effects. We performed a prospective randomized split-face study aimed at optimizing MAL-PDT treatment. Patients (n = 33) were randomized to two or four treatments of PDT with MAL on one cheek and placebo vehicle on the other cheek, 1-2 weeks apart. A 1.5-h pre-treatment with the MAL cream was followed by illumination with red light (20 J/cm²). Assessments were performed before treatment and 4, 10, and 20 weeks after the last treatment. In comparison to baseline, the number of inflammatory lesions at 20 weeks on cheeks treated with MAL-PDT showed a relative decrease of 74% in the group with two treatments and 85% in the group with four treatments. This new treatment regimen for both MAL-PDT and red-light-only PDT, with shortened pre-treatment and reduced light dose, could be an effective modality.

The mechanism of 5-aminolevulinic acid photodynamic therapy in promoting endoplasmic reticulum stress in the treatment of HR-HPV-infected HeLa cells

BACKGROUND

5-aminoketovaleric acid, as a precursor of the strong photosensitizer protoporphyrin IX (PpIX), mainly enters the mitochondria after entering the cell, and the formed PpIX is also mainly localized in the mitochondria. So at present the research on the mechanism of 5-aminoketovalerate photodynamic therapy (ALA-PDT) mainly focuses on its impact on mitochondria. There are few reports on whether ALA-PAT can affect the endoplasmic reticulum and trigger endoplasmic reticulum stress (ERS).

AIMS/OBJECTIVES

Here we investigated the effects of ALA-PDT on endoplasmic reticulum and its underlying mechanisms in high-risk human papillomavirus (HR-HPV) infection.

MATERIALS AND METHODS

The human cervical cancer cell line HeLa (containing whole genome of HR-HPV18) was treated with ALAPDT, and cell viability, ROS production, the level of Ca2+ in the cytoplasm and apoptosis were evaluated by CCK8, immunofluorescence and flow cytometry, respectively. The protein expression of the markers of ERS and autophagy and CamKKβ-AMPK pathway was examined by western blot.

RESULTS

The results showed that ALA-PDT inhibited cell viability of HeLa cells in vitro; ALA-PDT induced autophagy in HeLa cells ; ALA-PDT induced autophagy via the Ca2+-CamKKβ-AMPK pathway, which could be suppressed by the inhibition of ERS;ALA-PDT induced ERS-specific apoptosis via the activation of caspase 12.

CONCLUSIONS

Our study demonstrated that ALA-PDT could exert a killing effect by inducing HeLa cell apoptosis, including endoplasmic reticulum-specific apoptosis. Meanwhile, ERS via the Ca2+ -CamKKβ-AMPK pathway promoted the occurrence of autophagy in HeLa cells. Inhibition of autophagy could increase the apoptosis rate of HeLa cells after ALA-PDT, suggesting that autophagy may be one of the mechanisms of PDT resistance; The Ca2+-CamKKβ-AMPK pathway and autophagy may be targets to improve the killing effect of ALA-PDT in treating HR-HPV infection.

A Pilot Study on the Association of Mitochondrial Oxygen Metabolism and Gas Exchange During Cardiopulmonary Exercise Testing: Is There a Mitochondrial Threshold?

Background: Mitochondria are the key players in aerobic energy generation via oxidative phosphorylation. Consequently, mitochondrial function has implications on physical performance in health and disease ranging from high performance sports to critical illness. The protoporphyrin IX-triplet state lifetime technique (PpIX-TSLT) allows in vivo measurements of mitochondrial oxygen tension (mitoPO₂). Hitherto, few data exist on the relation of mitochondrial oxygen metabolism and ergospirometry-derived variables during physical performance. This study investigates the association of mitochondrial oxygen metabolism with gas exchange and blood gas analysis variables assessed during cardiopulmonary exercise testing (CPET) in aerobic and anaerobic metabolic phases. Methods: Seventeen volunteers underwent an exhaustive CPET (graded multistage protocol, 50 W/5 min increase), of which 14 were included in the analysis. At baseline and for every load level PpIX-TSLT-derived mitoPO₂ measurements were performed every 10 s with 1 intermediate dynamic measurement to obtain mitochondrial oxygen consumption and delivery (mito V . O₂, mito D . O₂). In addition, variables of gas exchange and capillary blood gas analyses were obtained to determine ventilatory and lactate thresholds (VT, LT). Metabolic phases were defined in relation to VT1 and VT2 (aerobic: <VT1, aerobic-anaerobic transition: ≥VT1 and <VT2 and anaerobic: ≥VT2). We used linear mixed models to compare variables of PpIX-TSLT between metabolic phases and to analyze their associations with variables of gas exchange and capillary blood gas analyses. Results: MitoPO₂ increased from the aerobic to the aerobic-anaerobic phase followed by a subsequent decline. A mitoPO₂ peak, termed mitochondrial threshold (MT), was observed in most subjects close to LT2. Mito D . O₂ increased during CPET, while no changes in mito V . O₂ were observed. MitoPO₂ was negatively associated with partial pressure of end-tidal oxygen and capillary partial pressure of oxygen and positively associated with partial pressure of end-tidal carbon dioxide and capillary partial pressure of carbon dioxide. Mito D . O₂ was associated with cardiovascular variables. We found no consistent association for mito V . O₂. Conclusion: Our results indicate an association between pulmonary respiration and cutaneous mitoPO₂ during physical exercise. The observed mitochondrial threshold, coinciding with the metabolic transition from an aerobic to an anaerobic state, might be of importance in critical care as well as in sports medicine.

Utility of Photodynamic Therapy in Dentistry: Current Concepts

The significant growth in scientific and technological advancements within the field of dentistry has resulted in a wide range of novel treatment modalities for dentists to use. Photodynamic therapy (PDT) is an emerging, non-invasive treatment method, involving photosensitizers, light of a specific wavelength and the generation of singlet oxygen and reactive oxygen species (ROS) to eliminate unwanted eukaryotic cells (e.g., malignancies in the oral cavity) or pathogenic microorganisms. The aim of this review article is to summarize the history, general concepts, advantages and disadvantages of PDT and to provide examples for current indications of PDT in various subspecialties of dentistry (oral and maxillofacial surgery, oral medicine, endodontics, preventive dentistry, periodontology and implantology), in addition to presenting some images from our own experiences about the clinical success with PDT.

5-aminolaevulinic acid-based photodynamic therapy inhibits ultraviolet B-induced skin photodamage

To evaluate the photoprotective effect of 5-aminolaevulinic acid-based photodynamic therapy (ALA-PDT) on ultraviolet B (UVB)-induced skin photodamage. In vivo experiments, the dorsal skin of hairless mice were treated with ALA-PDT or saline-PDT, and then exposed to 180 mJ/m2 UVB. Results showed that the number of sunburn cells and apoptotic cells in the epidermis of ALA-PDT-treated groups at 24 h after UVB irradiation were significantly decreased compared with those in the UVB groups. And the removal rate of CPDs was obviously higher in ALA-PDT-treated groups. At 48 h, the number of Ki67 positive nuclei in ALA-PDT-UVB group was significantly fewer than that in UVB group. Further in vitro experiments, human keratinocyte cell line (HaCaT) cells of two groups (one treated with ALA-PDT, the other untreated), were exposed to 60 mJ/m2 UVB irradiation. We found 0.5 mmol/L of ALA and 3 J/cm2 of red light did not affect the vitality of cells, and could reduce UVB induced apoptosis, accelerate the clearance of CPDs, inhibit proliferation and activate p53. Thus, our data demonstrate that ALA-PDT pretreatment can induce a protective DNA damage response that protects skin cells from UVB-induced photodamages.

Development of triptolide-nanoemulsion gels for percutaneous administration: physicochemical, transport, pharmacokinetic and pharmacodynamic characteristics

Background

This work aimed to provide useful information on the use of nanoemulsions for the percutaneous administration of triptolide. Lipid nanosystems have great potential for transdermal drug delivery. Nanoemulsions and nanoemulsion gels were prepared to enhance percutaneous permeation. Microstructure and in vitro/in vivo percutaneous delivery characteristics of triptolide (TPL)-nanoemulsions and TPL-nanoemulsion gels were compared. The integrity of the nanoemulsions and nanoemulsion gels during transdermal delivery and its effects on the surface of skin were also investigated. The penetration mechanisms of nanoemulsions and nanoemulsion gels were investigated by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). The transport characteristics of fluorescence-labelled nanoemulsions were probed using laser scanning confocal microscopy. A chronic dermatitis/eczema model in mice ears and the pharmacodynamic of the TPL-nanoemulsion gels were also investigated.

Results

Compared to TPL gels, significantly greater cumulative amounts of TPL-nanoemulsion gels and TPL-nanoemulsions penetrated rat skin in vitro. The in vivo microdialysis showed the concentration–time curve AUC_0–t for TPL-NPs is bigger than the TPL-gels. At the same time, TPL-NPs had a larger effect on the surface of skin. By hydrating keratin and changing the structure of both the stratum corneum lipids and keratin, nanoemulsions and nanoemulsion gels influence skin to promote percutaneous drug penetration. Both hairfollicles and the stratum corneum are also important in this transdermal drug delivery system. Moderate and high dosages of the TPL-nanoemulsion gels can significantly improve the symptoms of dermatitis/eczema inflammation and edema erythematic in mice ears and can reduce the expression of IFN-γ and IL-4. Moreover, the TPL-nanoemulsion gels cause less gastrointestinal damage than that of the Tripterygium wilfordii oral tablet does.

Conclusions

Nanoemulsions could be suitable for transdermal stably releasing drugs and maintaining the effective drug concentration. The TPL-nanoemulsion gels provided higher percutaneous amounts than other carriers did. These findings suggest that nanoemulsion gels could be promising percutaneous carriers for TPL. The TPL-nanoemulsion gels have a significant treatment effect on dermatitis/eczema in the mice model and is expected to provide a new, low-toxicity and long-term preparation for the clinical treatment of dermatitis/eczema in transdermal drug delivery systems.

Electronic supplementary material

The online version of this article (10.1186/s12951-017-0323-0) contains supplementary material, which is available to authorized users.

Superficial hemangioma is better treated by topical 5-aminolevulinic followed by 595-nm pulsed dye laser therapy rather than 595-nm laser therapy alone

The aim of this study was to compare the efficacy and adverse effects of a 595-nm pulsed dye laser therapy alone (PDL alone) with a 5-aminolevulinic (5-ALA) local application followed by a 595-nm PDL (5-ALA PDL) in the treatment of superficial hemangioma (SH). A prospectively randomized study in 181 patients with SH was carried out over a period of 24 months. One hundred and ninety-three patients were seen. One hundred and eighty-one patients with SH were enrolled, of which 165 completed final follow-up. One hundred and nineteen patients received PDL alone and 46 received 5-ALA PDL. The patients were assessed clinically and the patient's parents were given a satisfaction questionnaire. Baseline patient data (gender, lesion size, lesion site, treatment times, cure rate, and adverse reactions) were recorded and the results of the treatment of the two groups were analyzed and compared. Complete clearing of the lesion (recovery grade 4) was achieved in 44/119 (37.0%) of the PDL alone group and 31/46 (67.4%) of the 5-ALA PDL group (X ² = 10.30, p < 0.001). Atrophic scars, hyper- and hypopigmentation occurred in both groups (X ² = 3.32, p = 0.564). The patients' parents' satisfaction was greater in the 5-ALA PDL group. The clinical outcome of 5-ALA PDL was superior to that of PDL alone in the treatment of SH and only minor adverse events occurred in each group.

Light Fractionation Significantly Increases the Efficacy of Photodynamic Therapy Using BF-200 ALA in Normal Mouse Skin

BACKGROUND

Light fractionation significantly increases the efficacy of 5-aminolevulinic acid (ALA) based photodynamic therapy (PDT) using the nano-emulsion based gel formulation BF-200. PDT using BF-200 ALA has recently been clinically approved and is under investigation in several phase III trials for the treatment of actinic keratosis. This study is the first to compare BF-200 ALA with ALA in preclinical models.

RESULTS

In hairless mouse skin there is no difference in the temporal and spatial distribution of protoporphyrin IX determined by superficial imaging and fluorescence microscopy in frozen sections. In the skin-fold chamber model, BF-200 ALA leads to more PpIX fluorescence at depth in the skin compared to ALA suggesting an enhanced penetration of BF-200 ALA. Light fractionated PDT after BF-200 ALA application results in significantly more visual skin damage following PDT compared to a single illumination. Both ALA formulations show the same visual skin damage, rate of photobleaching and change in vascular volume immediately after PDT. Fluorescence immunohistochemical imaging shows loss of VE-cadherin in the vasculature at day 1 post PDT which is greater after BF-200 ALA compared to ALA and more profound after light fractionation compared to a single illumination.

DISCUSSION

The present study illustrates the clinical potential of light fractionated PDT using BF-200 ALA for enhancing PDT efficacy in (pre-) malignant skin conditions such as basal cell carcinoma and vulval intraepithelial neoplasia and its application in other lesion such as cervical intraepithelial neoplasia and oral squamous cell carcinoma where current approaches have limited efficacy.

Using Imiquimod-Induced Psoriasis-Like Skin as a Model to Measure the Skin Penetration of Anti-Psoriatic Drugs

Objective

Psoriasis is a chronic inflammatory skin disease and topical therapy remains a key role for treatment. The aim of this study is to evaluate the influence of psoriasis-like lesions on the cutaneous permeation of anti-psoriatic drugs.

Methods

We first set up imiquimod-induced dermatitis in mice that closely resembles human psoriasis lesions. The development of the lesions is based on the IL-23/IL17A axis for phenotypical and histological characteristics. Four drugs, 5-aminolevulinic acid (ALA), tacrolimus, calcipotriol, and retinoic acid, were used to evaluate percutaneous absorption.

Results

The most hydrophilic molecule, ALA, revealed the greatest enhancement on skin absorption after imiquimod treatment. Imiquimod increased the skin deposition and flux of ALA by 5.6 to 14.4-fold, respectively, compared to normal skin. The follicular accumulation of ALA was also increased 3.8-fold. The extremely lipophilic drug retinoic acid showed a 1.7- and 3.8-fold increase in skin deposition and flux, respectively. Tacrolimus flux was enhanced from 2 to 21 μg/cm²/h by imiquimod intervention. However, imiquimod did not promote skin deposition of this macrolide. The lipophilicity, but not the molecular size, dominated drug permeation enhancement by psoriatic lesions. The in vivo percutaneous absorption of ALA and rhodamine B examined by confocal microscopy confirmed the deficient resistance of epidermal barrier for facilitating cutaneous delivery of drugs via psoriasis-like skin.

Conclusion

We established the topical delivery profiles of anti-psoriatic drugs via imiquimod-treated psoriasis-like skin.

Update on topical photodynamic therapy for skin cancer

Topical photodynamic therapy has become an established therapy option for superficial non-melanoma skin cancers with a substantial evidence base. In this update the increased choice in photosensitizers and light sources are reviewed as well as novel protocols to move beyond lesional treatment and address field therapy. Daylight PDT is emerging as an alternative to conventional office/hospital-based PDT that offers the advantage of much reduced pain. Although most studies have assessed efficacy of PDT in immune-competent patients, there is accumulating evidence for topical PDT being considered an option to assist in reducing the skin cancer burden in organ transplant recipients. The fluorescence associated with photosensitizer application can help delineate lesions prior to full treatment illumination and offers a useful adjunct to treatment in patients where diagnostic uncertainty or poor lesion outline complicates clinical care. PDT may also offer significant benefit in delaying/preventing new cancer development and combined with its recognized photo-rejuvenating effects, is emerging as an effective therapy capable of clearing certain superficial skin cancers, potentially preventing new lesions as well as facilitating photo-rejuvenating effects in treated areas.

Topical photodynamic therapy using different porphyrin precursors leads to differences in vascular photosensitization and vascular damage in normal mouse skin

Different distributions of hexyl aminolevulinate (HAL), aminolevulinic acid (ALA) and methyl aminolevulinate (MAL) in the superficial vasculature are not well studied but they are hypothesized to play an important role in topical photodynamic therapy (PDT). The colocalization of fluorescent CD31 and protoporphyrin IX (PpIX) was calculated using confocal microscopy of mouse skin sections to investigate the vascular distribution after topical application. Vascular damage leads to disruption of the normal endothelial adherens junction complex, of which CD144 is an integral component. Therefore, normal CD31 combined with loss of normal fluorescent CD144 staining was visually scored to assess vascular damage. Both the vascular PpIX concentration and the vascular damage were highest for HAL, then ALA and then MAL. Vascular damage in MAL was not different from normal contralateral control skin. This pattern is consistent with literature data on vasoconstriction after PDT, and with the hypothesis that the vasculature plays a role in light fractionation that increases efficacy for HAL and ALA-PDT but not for MAL. These findings indicate that endothelial cells of superficial blood vessels synthesize biologically relevant PpIX concentrations, leading to vascular damage. Such vascular effects are expected to influence the oxygenation of tissue after PDT which can be important for treatment efficacy.

Photosensitizer fluorescence and singlet oxygen luminescence as dosimetric predictors of topical 5-aminolevulinic acid photodynamic therapy induced clinical erythema

The need for patient-specific photodynamic therapy (PDT) in dermatologic and oncologic applications has triggered several studies that explore the utility of surrogate parameters as predictive reporters of treatment outcome. Although photosensitizer (PS) fluorescence, a widely used parameter, can be viewed as emission from several fluorescent states of the PS (e.g., minimally aggregated and monomeric), we suggest that singlet oxygen luminescence (SOL) indicates only the active PS component responsible for the PDT. Here, the ability of discrete PS fluorescence-based metrics (absolute and percent PS photobleaching and PS re-accumulation post-PDT) to predict the clinical phototoxic response (erythema) resulting from 5-aminolevulinic acid PDT was compared with discrete SOL (DSOL)-based metrics (DSOL counts pre-PDT and change in DSOL counts pre/post-PDT) in healthy human skin. Receiver operating characteristic curve (ROC) analyses demonstrated that absolute fluorescence photobleaching metric (AFPM) exhibited the highest area under the curve (AUC) of all tested parameters, including DSOL based metrics. The combination of dose-metrics did not yield better AUC than AFPM alone. Although sophisticated real-time SOL measurements may improve the clinical utility of SOL-based dosimetry, discrete PS fluorescence-based metrics are easy to implement, and our results suggest that AFPM may sufficiently predict the PDT outcomes and identify treatment nonresponders with high specificity in clinical contexts.

The effect of light fractionation with a 2-h dark interval on the efficacy of topical hexyl-aminolevulinate photodynamic therapy in normal mouse skin

BACKGROUND

Light fractionation with a 2-h dark interval increases the efficacy of topical aminolevulinic acid (ALA) photodynamic therapy (PDT). Hexyl-aminolevulinate (HAL) is the hexyl ester of ALA. Both HAL and ALA lead to protoporphyrin IX (PpIX) accumulation in endothelial cells and to vascular effects, which are important for light fractionation. We investigated light fractionation for HAL-PDT in a mouse skin model and compared this with ALA.

METHODS

Three illumination schemes were studied: (a) 100 J cm(-2) in a single illumination; (b) 50+50 J cm(-2) in a twofold illumination; (c) a small first light fraction until 50% of PpIX was photobleached (ca. 3 J cm(-2)), followed by 97 J cm(-2) 2h later. PpIX fluorescence was measured continuously during illumination. Efficacy was evaluated by daily visual skin damage scoring up to 7 days after PDT.

RESULTS

Light fractionation showed a trend towards increased efficacy for HAL-PDT. Both the initial PpIX synthesis and the PpIX resynthesis during the dark interval were higher for ALA, but these were not correlated with efficacy. Single HAL-PDT was more effective than single ALA-PDT. Photobleaching rates of HAL and ALA were similar indicating similar biodistributions at depth.

CONCLUSION

Our results provide evidence to support that light fractionation may be beneficial for HAL-PDT. We are cautious because we found only a non-significant increase in response. However, combining our results with literature data suggest that the illumination scheme may be further optimized for HAL-PDT to potentially enhance the effect of light fractionation.

Techniques for fluorescence detection of protoporphyrin IX in skin cancers associated with photodynamic therapy

Photodynamic therapy (PDT) is a treatment modality that uses a specific photosensitizing agent, molecular oxygen, and light of a particular wavelength to kill cells targeted by the therapy. Topically administered aminolevulinic acid (ALA) is widely used to effectively treat cancerous and precancerous skin lesions, resulting in targeted tissue damage and little to no scarring. The targeting aspect of the treatment arises from the fact that ALA is preferentially converted into protoporphyrin IX (PpIX) in neoplastic cells. To monitor the amount of PpIX in tissues, techniques have been developed to measure PpIX-specific fluorescence, which provides information useful for monitoring the abundance and location of the photosensitizer before and during the illumination phase of PDT. This review summarizes the current state of these fluorescence detection techniques. Non-invasive devices are available for point measurements, or for wide-field optical imaging, to enable monitoring of PpIX in superficial tissues. To gain access to information at greater tissue depths, multi-modal techniques are being developed which combine fluorescent measurements with ultrasound or optical coherence tomography, or with microscopic techniques such as confocal or multiphoton approaches. The tools available at present, and newer devices under development, offer the promise of better enabling clinicians to inform and guide PDT treatment planning, thereby optimizing therapeutic outcomes for patients.

Intracutaneous ALA photodynamic therapy: dose-dependent targeting of skin structures

BACKGROUND

Photodynamic therapy (PDT) using topical aminolevulinic acid (ALA) depends on local drug uptake, metabolism to porphyrins, and depth of light penetration using different wavelengths. Topical ALA-PDT has limited depth of drug penetration. We studied induced porphyrin distribution and PDT after intradermal ALA administration using different drug concentrations followed by high-fluence red light irradiation.

MATERIALS AND METHODS

Intradermal injections (∼2 mm deep) of ALA concentrations from 0.0005% to 1% were studied in swine to evaluated porphyrin fluorescence before PDT and clinical and histological damage 24 hours after PDT. Porphyrin accumulation was measured by fluorescence microscopy of frozen section. PDT was performed 3 hours after intradermal injections using a 635 nm LED array at a fluence of 200 J/cm2 . Skin responses to PDT were observed grossly and by histology (blind evaluation).

RESULTS

Intradermal ALA caused porphyrin accumulation in epidermis, hair follicles (HF), sebaceous glands (SG), sweat glands (eccrine glands, EG and apocrine glands, AG), and subcutaneous fat. Significant differences of fluorescence intensity were observed between different skin structures (P < 0.05), but there was no significant difference comparing HF to SG; epidermis with either HF or SG; and dermis with fat (P > 0.05). Intradermal ALA is potent. ALA concentrations ≥0.25% followed by red light exposures caused a very intense vascular PDT reaction. Moderate doses of injected ALA concentration (∼0.06%), selectively targeted EG. Low doses (≤0.016%) targeted fat; producing fat necrosis with minimal inflammation, manifested both clinically and histologically. In contrast to topical ALA-PDT, intradermal ALA-PDT can effectively photosensitize deep skin structures.

CONCLUSION

Potentially, intradermal ALA-PDT using various ALA concentrations may be useful for treating vascular lesions (malformations, hemangiomas, tumors), EG/AG disorders, fat or deep targets in skin.

Validation of the protoporphyrin IX-triplet state lifetime technique for mitochondrial oxygen measurements in the skin

Mitochondrial oxygen tension can be measured in vivo by means of oxygen-dependent quenching of delayed fluorescence of protoporphyrin IX (PpIX). Here we demonstrate that mitochondrial PO(2) (mitoPO(2)) can be measured in the skin of a rat after topical application of the PpIX precursor 5-aminolevulinic acid (ALA). Calibration of mitoPO(2) measurements was done by comparison with simultaneous measurements of the cutaneous microvascular PO(2) This was done under three different conditions: in normal skin tissue, in nonrespiration skin tissue due to the application of cyanide, and in anoxic skin tissue after the ventilation with 100% nitrogen. The results of this study show that it is feasible to measure the mitoPO(2) after the topical application of ALA cream by means of the PpIX-triplet state lifetime technique.

Aminolevulinic acid-photodynamic therapy combined with topically applied vascular disrupting agent vadimezan leads to enhanced antitumor responses

The tumor vascular-disrupting agent (VDA) vadimezan (5,6-dimethylxanthenone-4-acetic acid, DMXAA) has been shown to potentiate the antitumor activity of photodynamic therapy (PDT) using systemically administered photosensitizers. Here, we characterized the response of subcutaneous syngeneic Colon26 murine colon adenocarcinoma tumors to PDT using the locally applied photosensitizer precursor aminolevulinic acid (ALA) in combination with a topical formulation of vadimezan. Diffuse correlation spectroscopy (DCS), a noninvasive method for monitoring blood flow, was utilized to determine tumor vascular response to treatment. In addition, correlative CD31-immunohistochemistry to visualize endothelial damage, ELISA to measure induction of tumor necrosis factor-alpha (TNF-α) and tumor weight measurements were also examined in separate animals. In our previous work, DCS revealed a selective decrease in tumor blood flow over time following topical vadimezan. ALA-PDT treatment also induced a decrease in tumor blood flow. The onset of blood flow reduction was rapid in tumors treated with both ALA-PDT and vadimezan. CD31-immunostaining of tumor sections confirmed vascular damage following topical application of vadimezan. Tumor weight measurements revealed enhanced tumor growth inhibition with combination treatment compared with ALA-PDT or vadimezan treatment alone. In conclusion, vadimezan as a topical agent enhances treatment efficacy when combined with ALA-PDT. This combination could be useful in clinical applications.

Oil components modulate the skin delivery of 5-aminolevulinic acid and its ester prodrug from oil-in-water and water-in-oil nanoemulsions

The study evaluated the potential of nanoemulsions for the topical delivery of 5-aminolevulinic acid (ALA) and methyl ALA (mALA). The drugs were incorporated in oil-in-water (O/W) and water-in-oil (W/O) formulations obtained by using soybean oil or squalene as the oil phase. The droplet size, zeta potential, and environmental polarity of the nanocarriers were assessed as physicochemical properties. The O/W and W/O emulsions showed diameters of 216-256 and 18-125 nm, which, respectively, were within the range of submicron- and nano-sized dispersions. In vitro diffusion experiments using Franz-type cells and porcine skin were performed. Nude mice were used, and skin fluorescence derived from protoporphyrin IX was documented by confocal laser scanning microscopy (CLSM). The loading of ALA or mALA into the emulsions resulted in slower release across cellulose membranes. The release rate and skin flux of topical drug application were adjusted by changing the type of nanocarrier, the soybean oil O/W systems showing the highest skin permeation. This formulation increased ALA flux via porcine skin to 180 nmol/cm(2)/h, which was 2.6-fold that of the aqueous control. The CLSM results showed that soybean oil systems promoted mALA permeation to deeper layers of the skin from ∼100 μm to ∼140 μm, which would be beneficial for treating subepidermal and subcutaneous lesions. Drug permeation from W/O systems did not surpass that from the aqueous solution. An in vivo dermal irritation test indicated that the emulsions were safe for topical administration of ALA and mALA.

Fluorescence diagnosis in actinic keratosis and squamous cell carcinoma

BACKGROUND

As different tissue types have distinct capabilities to accumulate protoporphyrin IX, fluorescence diagnosis with aminolevulinic acid-induced porphyrins (FDAP) could be used to discriminate between different types of tissue. Previous results demonstrated higher fluorescence ratios in squamous cell carcinoma (SCC) compared with actinic keratoses (AKs).

OBJECTIVES

The lesional : non-lesional fluorescence ratio of AKs was compared with the ratio of SCC. Other factors influencing macroscopic fluorescence were also assessed, including stratum corneum thickness, which has been demonstrated to account for heterogeneous fluorescence in psoriasis and in AKs.

METHODS

After 1 week of keratolytic pretreatment, FDAP was performed in 13 patients with 36 lesions suspected for AK or SCC. Biopsies were taken for histopathological diagnosis and measurement of stratum corneum thickness.

RESULTS

No significant differences were found in the fluorescence ratio (lesional : non-lesional skin) between AKs and SCCs, although macroscopic fluorescence was significantly higher in Bowen's disease and micro-invasive SCCs.

CONCLUSIONS

There could be a potential applicability of FDAP to differentiate premalignant lesions with a tendency to progress into SCC and squamous cutaneous lesions already progressing into early invasive cancer from other squamous cutaneous (pre)malignancies. The amount of hyperkeratosis, invasiveness and degree of differentiation seem to be responsible for variations in fluorescence intensity.

Photodynamic therapy-induced immunosuppression in humans is prevented by reducing the rate of light delivery

Photodynamic therapy (PDT) of non-melanoma skin cancers currently carries failure rates of 10-40%. The optimal irradiation protocol is as yet unclear. Previous studies showed profound immunosuppression after PDT, which may compromise immune-mediated clearance of these antigenic tumors. Slower irradiation prevents immunosuppression in mice, and may be at least as effective as high-fluence-rate PDT in preliminary clinical trials. The photosensitizers 5-aminolaevulinic acid and/or methyl aminolaevulinate were applied to discrete areas on the backs of healthy Mantoux-positive volunteers, followed by narrowband red light irradiation (632 nm) at varied doses and fluence rates. Delayed type hypersensitivity (Mantoux) reactions were elicited at test sites and control sites to determine immunosuppression. Human ex vivo skin received low- and high-fluence-rate PDT and was stained for oxidative DNA photolesions. PDT caused significant, dose-responsive immunosuppression at high (75 mW cm(-2)) but not low (15 or 45 mW cm(-2)) fluence rates. DNA photolesions, which may be a trigger for immunosuppression, were observed after high-fluence-rate PDT but not when light was delivered more slowly. This study demonstrates that the current clinical PDT protocol (75 mW cm(-2)) is highly immunosuppressive. Simply reducing the rate of irradiation, while maintaining the same light dose, prevented immunosuppression and genetic damage and may have the potential to improve skin cancer outcomes.

Comparison of ALA- and ALA hexyl-ester-induced PpIX depth distribution in human skin carcinoma

Photodynamic therapy (PDT) based on the use of photoactivable porphyrins, such as protoporphyrin IX (PpIX), induced by the topical application of amino-levulinic acid (ALA) or its derivatives, ALA methyl-ester (m-ALA), is a treatment for superficial basal cell carcinoma (BCC), with complete response rates of over 80%. However, in the case of deep, nodular-ulcerative lesions, the complete response rates are lower, possibly related to a lower bioavailability of PpIX. Previous in vitro skin permeation studies demonstrated an increased penetration of amino-levulinic acid hexyl-ester (h-ALA) over ALA. In this study, we tested the validity of this approach in vivo on human BCCs. An emulsion containing 20% ALA (w/w) and preparations of h-ALA at different concentrations were applied topically to the normal skin of Caucasian volunteers to compare the PpIX fluorescence intensities with an optical fiber-based spectrofluorometer. In addition, the PpIX depth distribution and fluorescence intensity in 26 BCCs were investigated by fluorescence microscopy following topical application of 20% ALA and 1% h-ALA. We found that, for application times up to 24h, h-ALA is identical to ALA as a PpIX precursor with respect to PpIX fluorescence intensity, depth of penetration, and distribution in basal cell carcinoma, but has the added advantage that much smaller h-ALA concentrations can be used (up to a factor 13). We observed a non-homogenous distribution in BCCs with both precursors, independent of the histological type and depth of invasion in the dermis.

Monitoring ALA-induced PpIX photodynamic therapy in the rat esophagus using fluorescence and reflectance spectroscopy

The presence of phased protoporphyrin IX (PpIX) bleach kinetics has been shown to correlate with esophageal response to 5-aminolevulinic acid-based photodynamic therapy (ALA-PDT) in animal models. Here we confirm the existence of phased PpIX photobleaching by increasing the temporal resolution of the fluorescence measurements using the therapeutic illumination and long wavelength fluorescence detection. Furthermore fluorescence differential pathlength spectroscopy (FDPS) was incorporated to provide information on the effects of PpIX and tissue oxygenation distribution on the PpIX bleach kinetics during illumination. ALA at a dose of 200 mg kg(-1) was orally administered to 15 rats, five rats served as control animals. PDT was performed at an in situ measured fluence rate of 75 mW cm(-2) using a total fluence of 54 J cm(-2). Forty-eight hours after PDT the esophagus was excised and histologically examined for PDT-induced damage. Fluence rate and PpIX photobleaching at 705 nm were monitored during therapeutic illumination with the same isotropic probe. A new method, FDPS, was used for superficial measurement on saturation, blood volume, scattering characteristics and PpIX fluorescence. Results showed two-phased PpIX photobleaching that was not related to a (systematic) change in esophageal oxygenation but was associated with an increase in average blood volume. PpIX fluorescence photobleaching measured using FDPS, in which fluorescence signals are only acquired from the superficial layers of the esophagus, showed lower rates of photobleaching and no distinct phases. No clear correlation between two-phased photobleaching and histologic tissue response was found. This study demonstrates the feasibility of measuring fluence rate, PpIX fluorescence and FDPS during PDT in the esophagus. We conclude that the spatial distribution of PpIX significantly influences the kinetics of photobleaching and that there is a complex interrelationship between the distribution of PpIX and the supply of oxygen to the illuminated tissue volume.