Pharmaceutical analysis of 5-aminolevulinic acid in solution and in tissues

Derivative Matrix-Isopotential Synchronous Spectrofluorimetry and Hantzsch Reaction: A Direct Route to Simultaneous Determination of Urinary δ-Aminolevulinic Acid and Porphobilinogen

Early and sensitive detection of δ-aminolevulinic acid (δ-ALA) and porphobilinogen (PBG) is the cornerstone of diagnosis and effective treatment for acute porphyria. However, at present, the quantifying strategies demand multiple solvent extraction steps or chromatographic approaches to separate δ-ALA and PBG prior to quantification. These methods are both time-consuming and laborious. Otherwise, in conventional spectrofluorimetry, the overlapping spectra of the two analytes cause false diagnosis. To overcome this challenge, we present a two-step approach based on derivative matrix-isopotential synchronous fluorescence spectrometry (DMISFS) and the Hantzsch reaction, realizing the simple and simultaneous detection of δ-ALA and PBG in urine samples. The first step is chemical derivatization of the analytes by Hantzsch reaction. The second step is the determination of the target analytes by combining MISFS and the first derivative technique. The proposed approach accomplishes following advantages: 1) The MISFS technique improves the spectral resolution and resolves severe spectral overlap of the analytes, alleviating tedious and complicated pre-separation processes; 2) First derivative technique removes the background interference of δ-ALA on PBG and vice versa, ensuring high sensitivity; 3) Both the analytes can be determined simultaneously via single scanning, enabling rapid detection. The obtained detection limits for δ-ALA and PBG were 0.04 μmol L−1 and 0.3 μmol L−1, respectively. Within-run precisions (intra and inter-day CVs) for both the analytes were <5%. Further, this study would serve to enhance the availability of early and reliable quantitative diagnosis for acute porphyria in both scientific and clinical laboratories.

A method for determining δ-aminolevulinic acid synthase activity in homogenized cells and tissues

OBJECTIVE

In mammalian cells the rate-limiting step in heme biosynthesis is the formation of δ-aminolevulinic acid (ALA). The reaction intermediates, porphyrins and iron and the final product, heme can be highly cytotoxic if allowed to accumulate. The importance of maintaining the levels of metabolic intermediates and heme within a narrow range is apparent based on the complex homeostatic system(s) that have developed. Ultimately, determining the enzymatic activity of ALA synthase (ALAS) present in the mitochondria is highly beneficial to confirm the effects of the transcriptional, translational and post-translational events. The aim of this study was to develop a highly sensitive assay for ALAS that could be used on whole tissue or cellular homogenates.

DESIGN AND METHODS

A systematic approach was used to optimize steps in formation of ALA by ALAS. Reducing the signal to noise ratio for the assay was achieved by derivatizing the ALA formed into a fluorescent product that could be efficiently separated by ultra performance liquid chromatography (UPLC) from other derivatized primary amines. The stability of ALAS activity in whole tissue homogenate and cellular homogenate was determined after extended storage at -80 °C.

CONCLUSIONS

A method for assaying ALAS has been developed that can be used with tissue homogenates or cellular lysates. There is no need to purify mitochondria and radiolabeled substrates are not needed for this assay. General laboratory reagents can be used to prepare the samples. Standard UPLC chromatography will resolve the derivatized ALA peak. Samples of tissue homogenate can be stored for approximately one year without significant loss of enzymatic activity.

Hydrogel-forming and dissolving microneedles for enhanced delivery of photosensitizers and precursors

We present "one-step application" dissolving and hydrogel-forming microneedle arrays (MN) for enhanced delivery of photosensitizers/precursors. MN (280 μm) prepared from 20% w/w poly(methylvinylether/maelic acid) and cross-linked with glycerol by esterification to form hydrogels upon skin insertion, or allowed to dissolve rapidly in skin, were combined with patches containing 19 mg cm(-2) of 5-aminolevulinic acid (ALA) or meso-tetra (N-methyl-4-pyridyl) porphine tetra tosylate (TMP) for drug delivery. Both MN types were mechanically robust, with compression forces of 20.0 N only causing height reductions of 14%. Application forces as low as 8.0 N per array allowed >95% of the MN in each array type to penetrate excised porcine skin, with the MN penetrating to approximately 220 μm. MN significantly enhanced transdermal delivery of ALA and TMP in vitro, with the hydrogel-forming system comparable with the dissolving system for ALA delivery (approximately 3000 nmol cm(-2) over 6 h), but superior for delivery of the much larger TMP molecule (approximately 14 nmol cm(-2) over 24 h, compared to 0.15 nmol cm(-2)). As this technology clearly has potential in enhanced photodynamic therapy of neoplastic skin lesions, we are currently planning animal studies, to be followed by preliminary human evaluations. GMP manufacturing scale-up is ongoing.

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.

Processing difficulties and instability of carbohydrate microneedle arrays

BACKGROUND

A number of reports have suggested that many of the problems currently associated with the use of microneedle (MN) arrays for transdermal drug delivery could be addressed by using drug-loaded MN arrays prepared by moulding hot melts of carbohydrate materials.

METHODS

In this study, we explored the processing, handling, and storage of MN arrays prepared from galactose with a view to clinical application.

RESULTS

Galactose required a high processing temperature (160 degrees C), and molten galactose was difficult to work with. Substantial losses of the model drugs 5-aminolevulinic acid (ALA) and bovine serum albumin were incurred during processing. While relatively small forces caused significant reductions in MN height when applied to an aluminium block, this was not observed during their relatively facile insertion into heat-stripped epidermis. Drug release experiments using ALA-loaded MN arrays revealed that less than 0.05% of the total drug loading was released across a model silicone membrane. Similarly, only low amounts of ALA (approximately 0.13%) and undetectable amounts of bovine serum albumin were delivered when galactose arrays were combined with aqueous vehicles. Microscopic inspection of the membrane following release studies revealed that no holes could be observed in the membrane, indicating that the partially dissolved galactose sealed the MN-induced holes, thus limiting drug delivery. Indeed, depth penetration studies into excised porcine skin revealed that there was no significant increase in ALA delivery using galactose MN arrays, compared to control (P value < 0.05). Galactose MNs were unstable at ambient relative humidities and became adhesive.

CONCLUSION

The processing difficulties and instability encountered in this study are likely to preclude successful clinical application of carbohydrate MNs. The findings of this study are of particular importance to those in the pharmaceutical industry involved in the design and formulation of transdermal drug delivery systems based on dissolving MN arrays. It is hoped that we have illustrated conclusively the difficulties inherent in the processing and storage of carbohydrate-based dissolving MNs and that those in the industry will now follow alternative approaches.

Liquid chromatography assay for 5-aminolevulinic acid: application to in vitro assessment of skin penetration via Dermaportation

The purpose of the present study was to develop a reverse-phase high performance liquid chromatographic (HPLC) assay for quantifying 5-aminolevulinic acid (ALA). The assay was applied to study the skin permeation of ALA and the influence of a novel skin penetration enhancement technology. Separation was achieved utilizing a Phenomenex Jupiter C(18) column following fluorescence derivatization with fluorescamine. The assay was linear (r(2)>0.99) with a minimum limit of quantitation of 400 ng/mL. The inter- and intraday variation was 1.6 and 0.9% at the lower end of the linear range and 1.5 and 1.9% at the upper end, respectively. The HPLC assay and fluorescence derivatization procedure is sensitive, simple, rapid, accurate and reproducible and offers advantages with regard to stability of ALA in comparison to other fluorescence derivatization methods. Results from the preliminary skin permeation study demonstrated substantial skin penetration of ALA only when applied with Dermaportation as a skin penetration enhancement device.

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.