Comparison of the uptake of 5-aminolevulinic acid and its methyl ester in keratinocytes and skin

Abstract

Photodynamic therapy is widely used in the treatment of superficial skin cancers. 5-Aminolevulinic acid (ALA) and its methylated form, methyl-ALA (MAL), are frequently used as precursors to photosensitizing substances. Nevertheless, the mechanism of the uptake of ALA and MAL in keratinocytes and of their skin penetration is still controversial. Since both compounds are not sufficiently lipophilic to penetrate through lipid membranes, they must employ specific uptake systems which may vary between different cell types. Here, we studied ALA and MAL uptake in keratinocyte cell lines originating from healthy cells (CCD 1106 KERTr cells) or keratinocyte tumors (A431 cells). ALA uptake resulted in faster protoporphyrin IX (PpIX) production than MAL uptake. A pharmacological characterization of the uptake systems revealed that PpIX formation was most efficiently reduced with GABA transporter (GAT) substrates. GABA, β-alanine, and (S)-SNAP-5114 reduced ALA uptake and, to a lesser extent, MAL uptake in the cell lines. The pharmacology of these compounds indicates that ALA and MAL are taken up by normal and pathological keratinocytes via GAT-3. Furthermore, the amino acids arginine, cysteine, and histidine also inhibited the uptake of ALA, and even more so MAL, suggestive of an additional involvement of amino acid transporters. To show that PpIX formation in vivo is restricted to the application site, which has been questioned for ALA in one other report, we applied clinically used ALA and MAL formulations to the skin of nude mice. Contrary to the results of these previous authors, the resulting PpIX fluorescence increased over time and was restricted to the application site for both preparations.

Doxycycline potentiates antitumor effect of 5-aminolevulinic acid-mediated photodynamic therapy in malignant peripheral nerve sheath tumor cells

“…This is similar to a prior report with keratinocytes [48]. In the present study, we found that doxycycline could potentiate this effect more prominently with ALA uptake, and to a lesser extent with me-ALA uptake.…”

A review of BF-200 ALA for the photodynamic treatment of mild-to-moderate actinic keratosis

“…The advantage of such a physical stabilization is that unmodified ALA is provided to the cells so uptake and metabolism can start immediately. This faster conversion of ALA into PpIX has been shown in neoplastic keratinocytes [58]. While in healthy keratinocyte cells low level conversion of ALA and MAL to PpIX has been observed, the treatment of neoplastic SCC cells with ALA revealed higher PpIX fluorescence after 2.5 and 4.5 h compared with MAL-treated sample.…”

“…The drawback of this approach lies in the biological need to have the ester cleaved by cellular enzymes before ALA can enter the heme biosynthetic pathway. Thus, some ALA esters, especially MAL, have been shown to induce less PpIX compared with ALA after the same incubation time [57][58][59]. Additionally, the concentration of short-chained ALA-esters (C1-C3), which is required to induce half-maximal PpIX accumulation, was clearly higher in several cell lines than the corresponding concentration of ALA [56].…”

Acumulación celular y el efecto de anti-Leishmania de protoporfirina IX exógena y endógena después del tratamiento fotodinámico

“…Cellular localization is an important issue, since it is related with the mechanism of cell death trigger. Photosensitizers localized within mitochondria are mostly associated with the apoptotic (some autophagic) death mechanism involved, i.e., caspase (or caspase-independent) activation and mitochondrial dysfunction (potential disruption of mitochondrial membrane and cytochrome C release) giving rise to morphological changes: bleeding, chromatin condensation and alteration of cell adhesion molecules (29)(30)(31)(32)(33)(34). Confocal images show overlapping of PpIX red fluorescence and MitoTracker Green fluorescence which strongly suggest PpIX mitochondrial localization in infected and non-infected THP-1 cells.…”