The influence of UV exposure on 5-aminolevulinic acid-induced protoporphyrin IX production in skin

Protoporphyrin IX formation after topical application of methyl aminolaevulinate and BF-200 aminolaevulinic acid declines with age

BACKGROUND

Topical photodynamic therapy (PDT) is a popular treatment modality in dermatology. The effect of PDT in epidermal cells depends on formation of protoporphyrin IX (PpIX) from 5-aminolevulinic acid (ALA). A variety of physiological changes in epidermal function occur with increasing age, but no studies have investigated whether PpIX formation is age-related.

OBJECTIVES

To investigate a possible relationship between age and PpIX formation.

METHODS

Methyl aminolaevulinate cream (MAL) and 5-ALA gel (BF-200 ALA) were applied to two identical fields on the forearm of 30 healthy volunteers for 24 h. The volunteers were divided into two age groups: a young group under 55 years (range 18-54) and an older group over 55 years (range 65-85). PpIX formation was measured noninvasively every hour from 1-5 h, and after 18, 21 and 24 h. Skin phototype, stratum corneum hydration and ultraviolet (UV) damage were also assessed. Treatment efficacy in relation to age was evaluated in 100 basal cell carcinomas (BCCs) treated with MAL-PDT.

RESULTS

Both photosensitizers induced significantly more PpIX formation in the younger group. Linear regression revealed a significant age-related decline in PpIX formation after the standard application time of 3 h (P < 0.001 for both treatments). Skin phototype, stratum corneum hydration and UV damage were not associated with PpIX formation. The treatment efficacy of BCCs 3 months after MAL-PDT was higher in young patients (P =  0.012).

CONCLUSIONS

PpIX formation in human skin declines with age. No explanation could be attributed to skin phototype, stratum corneum hydration or UV damage. The consequence might be reduced efficacy of PDT in the elderly.

Photodynamic therapy in dermatology: Dundee clinical and research experience

Topical photodynamic therapy (PDT) is increasingly accepted and used as a highly effective treatment for superficial non-melanoma skin cancer and dysplasia. We describe the developments in topical PDT for the treatment of skin diseases in our own PDT Centre in Dundee, both clinically and from a research base. Improvements in PDT could be achieved by optimisation of photosensitiser and light delivery, and these goals underpin the aims of our centre. We hope to facilitate the dissemination of use of PDT in dermatology throughout Scotland and outline some of the progress in these areas.

An in vitro comparison of the effects of the iron-chelating agents, CP94 and dexrazoxane, on protoporphyrin IX accumulation for photodynamic therapy and/or fluorescence guided resection

Photodynamic therapy (PDT) utilizes the combined interaction of a photosensitizer, light and molecular oxygen to ablate tumor tissue. Maximizing the accumulation of the photosensitizer protoporphyrin IX (PpIX) within different cell types would be clinically useful. Dermatological PpIX-induced PDT regimes produce good clinical outcomes but this currently only applies when the lesion remains superficial. Also, as an adjuvant therapy for the treatment of primary brain tumors, fluorescence guided resection (FGR) and PDT can be used to highlight and destroy tumor cells unreachable by surgical resection. By employing iron chelators PpIX accumulation can be enhanced. Two iron-chelating agents, 1,2-diethyl-3-hydroxypyridin-4-one hydrochloride (CP94) and dexrazoxane, were individually combined with the porphyrin precursors aminolevulinic acid (ALA), methyl aminolevulinate (MAL) and hexyl aminolevulinate (HAL). Efficacies of the iron-chelating agents were compared by recording the PpIX fluorescence in human squamous epithelial carcinoma cells (A431) and human glioma cells (U-87 MG) every hour for up to 6 h. Coincubation of ALA/MAL/HAL with CP94 resulted in a greater accumulation of PpIX compared to that produced by coincubation of these congeners with dexrazoxane. Therefore the clinical employment of iron chelation, particularly with CP94 could potentially increase and/or accelerate the accumulation of ALA/MAL/HAL-induced PpIX for PDT or FGR.

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.

Characteristics of 5-aminolaevulinic acid-induced protoporphyrin IX fluorescence in human skin in vivo

BACKGROUND/PURPOSE

Topical photodynamic therapy (PDT) is increasingly being used to treat skin cancers. Knowledge of the detailed characteristics of 5-aminolaevulinic acid (ALA)-induced protoporphyrin IX (PpIX) fluorescence in diseased and normal skin is incomplete. Understanding the characteristics of PpIX fluorescence in normal skin may facilitate optimization of PDT regimes while minimizing side effects in the surrounding normal skin. We investigated the characteristics of ALA-induced PpIX fluorescence in normal skin.

METHODS

ALA was applied to the arm, back and leg skin of 21 healthy volunteers for 1-6 h, and PpIX fluorescence was measured for up to 24 h after ALA application using a fluorescent spectrometer. The effect of tape stripping on fluorescence was also examined.

RESULTS

Considerable inter-subject variation was observed in the time to reach peak PpIX fluorescence. Intra-subject variation in the time to peak fluorescence was dependent on ALA application time. Six hours after ALA application, no significant difference was observed in the degree of fluorescence achieved irrespective of ALA application times ranging between 1 and 6 h. PpIX fluorescence was reduced on the leg and increased by tape stripping.

CONCLUSIONS

Marked inter- and intra-subject variation in ALA-induced PpIX fluorescence occurs in normal human skin. ALA application time, body site and the state of the stratum corneum are all determinants of PpIX fluorescence within subjects and these factors need to be taken into account in optimization of PDT regimes.