Oleic acid as optimizer of the skin delivery of 5-aminolevulinic acid in photodynamic therapy

On the Possibility of Using 5-Aminolevulinic Acid in the Light-Induced Destruction of Microorganisms

Antimicrobial photodynamic inactivation (aPDI) is a method that specifically kills target cells by combining a photosensitizer and irradiation with light at the appropriate wavelength. The natural amino acid, 5-aminolevulinic acid (5-ALA), is the precursor of endogenous porphyrins in the heme biosynthesis pathway. This review summarizes the recent progress in understanding the biosynthetic pathways and regulatory mechanisms of 5-ALA synthesis in biological hosts. The effectiveness of 5-ALA-aPDI in destroying various groups of pathogens (viruses, fungi, yeasts, parasites) was presented, but greater attention was focused on the antibacterial activity of this technique. Finally, the clinical applications of 5-ALA in therapies using 5-ALA and visible light (treatment of ulcers and disinfection of dental canals) were described.

Fabrication and Characterization of Clozapine Nanoemulsion Sol-Gel for Intranasal Administration

Clozapine is the most effective antipsychotic for treatment-resistant schizophrenia. However, it causes many adverse drug reactions (ADRs), which lead to poor treatment outcomes. Nose-to-brain (N2B) drug delivery offers a promising approach to reduce peripheral ADRs by minimizing systemic drug exposure. The aim of the present study was to develop and characterize clozapine-loaded nanoemulsion sol-gel (CLZ-NESG) for intranasal administration using high energy sonication method. A range of oils, surfactants, and cosurfactants were screened with the highest clozapine solubility selected for the development of nanoemulsion. Pseudoternary phase diagrams were constructed using a low-energy (spontaneous) method to identify the microemulsion regions (i.e., where mixtures were transparent). The final formulation, CLZ-NESG (pH 5.5 ± 0.2), comprising 1% w/w clozapine, 1% w/w oleic acid, 10% w/w polysorbate 80/propylene glycol (3:1), and 20% w/w poloxamer 407 (P407) solution, had an average globule size of ≤30 nm with PDI 0.2 and zeta potential of -39.7 ± 1.5 mV. The in vitro cumulative drug release of clozapine from the nanoemulsion gel at 34 °C (temperature of nasal cavity) after 72 h was 38.9 ± 4.6% compared to 84.2 ± 3.9% with the control solution. The permeation study using sheep nasal mucosa as diffusion barriers confirmed a sustained release of clozapine with 56.2 ± 2.3% cumulative drug permeated after 8 h. Additionally, the histopathological examination found no severe nasal ciliotoxicity on the mucosal tissues. The thermodynamic stability studies showed that the gel strength and viscosity of CLZ-NESG decreased after temperature cycling but was still seen to be in "gel" form at nasal temperature. However, the accelerated storage stability study showed a decrease in drug concentration after 3 months, which can be expected at elevated stress conditions. The formulation developed in this study showed desirable physicochemical properties for intranasal administration, highlighting the potential value of a nanoemulsion gel for improving drug bioavailability of clozapine for N2B delivery.

Fabrication of Tizanidine Loaded Patches Using Flaxseed Oil and Coriander Oil as a Penetration Enhancer for Transdermal Delivery

Transdermal drug delivery is important to maintain plasma drug concentrations for therapeutic efficacy. The current study reports the design, formulation, and evaluation of tizanidine transdermal patches formulated using chitosan and thiolated chitosan, ethyl cellulose (EC), polyvinylpyrrolidone (PVP), and Eudragit RL100 in different ratios. The tizanidine patches were formulated using flaxseed oil and coriander oil in the concentrations of 1% v/w, 2% v/w, 3% v/w, 4% v/w, 5% v/w, and 10% v/w. The patches were subjected to characterization of physicochemical property (thickness, weight uniformity, drug content, efficiency, percentage moisture uptake/loss), in vitro drug release and drug permeation, skin irritation, in vivo application, pharmacokinetics analysis, and stability studies. The results indicate that the interaction of thiolated chitosan with the negative charges of the skin opens the tight junctions of the skin, whereas flaxseed and coriander oils change the conformational domain of the skin. The novelty of this study is in the use of flaxseed and coriander oils as skin permeation enhancers for the formulation of tizanidine transdermal patches. The formulations follow non-Fickian drug release kinetics. The FTZNE23, FTZNE36 and FTZNE54, with 5% v/w flaxseed oil loaded formulations, exhibited higher flux through rabbit skin compared with FTZNE30, FTZNE35, FTZNE42, and FTZNE47, formulations loaded with 10% v/w coriander oil. The study concludes that flaxseed oil is a better choice for formulating tizanidine patches, offering optimal plasma concentration and therapeutic efficacy, and recommends the use of flaxseed and coriander oil based patches as a novel transdermal delivery system for tizanidine and related classes of drugs.

Enhanced skin retention and permeation of a novel peptide via structural modification, chemical enhancement, and microneedles

Hyperpigmentation is a common skin condition with serious psychosocial consequences. Decapeptide-12, a novel peptide, has been found to be safer than hydroquinone in reducing melanin content, with efficacy up to more than 50% upon 16 weeks of twice-daily treatment. However, the peptide suffers from limited transcutaneous penetration due to its hydrophilicity and high molecular weight. Therefore, decapeptide-12 was modified by adding a palmitate chain in an attempt to overcome this limitation. Molecular docking results showed that the two peptides exhibited similar biological activity towards tyrosinase. We also tested the effect of chemical penetration enhancers and microneedles to deliver the two peptides into and through skin, using an in vitro human skin permeation method. It was shown that the palm-peptide achieved the best skin retention owing to the increased lipophilicity. In addition, skin permeation of the palm-peptides was enhanced by the chemical skin penetration enhancers, namely, oleic acid and menthol. Skin permeation of the native peptide was enhanced by the microneedle patch but not the chemical skin penetration enhancers. Cutaneous absorption of the palm-peptides was estimated to have achieved its therapeutic concentration within skin. The combinatory approach of using molecular modification, chemical penetration enhancement, and microneedle patch proves to be useful to enhanceskin permeation of the peptides.

Fabrication of Alginate-Based O/W Nanoemulsions for Transdermal Drug Delivery of Lidocaine: Influence of the Oil Phase and Surfactant

Transdermal drug delivery of lidocaine is a good choice for local anesthetic delivery. Microemulsions have shown great effectiveness for the transdermal transport of lidocaine. Oil-in-water nanoemulsions are particularly suitable for encapsulation of lipophilic molecules because of their ability to form stable and transparent delivery systems with good skin permeation. However, fabrication of nanoemulsions containing lidocaine to provide an extended local anesthetic effect is challenging. Hence, the aim of this study was to address this issue by employing alginate-based o/w nanocarriers using nanoemulsion template that is prepared by combined approaches of ultrasound and phase inversion temperature (PIT). In this study, the influence of system composition such as oil type, oil and surfactant concentration on the particle size, in vitro release and skin permeation of lidocaine nanoemulsions was investigated. Structural characterization of lidocaine nanoemulsions as a function of water dilution was done using DSC. Nanoemulsions with small droplet diameters (d < 150 nm) were obtained as demonstrated by dynamic light scattering (DLS) and cryo-TEM. These nanoemulsions were also able to release 90% of their content within 24-h through PDMS and pig skin and able to the drug release over a 48-h. This extended-release profile is highly favorable in transdermal drug delivery and shows the great potential of this nanoemulsion as delivery system.

Nanoemulsions with Chloroaluminium Phthalocyanine and Paromomycin for Combined Photodynamic and Antibiotic Therapy for Cutaneous Leishmaniasis

BACKGROUND

Photodynamic therapy (PDT) using chloroaluminium phthalocyanine (ClAlPc) and paromomycin sulfate (PM) can be effective against New World Leishmania species involved in cutaneous leishmaniasis (CL). The aim of this study is to assay the skin permeation and the antileishmanial effects of a nanoemulsion (NE) containing both ClAlPc and PM in experimental CL by Leishmania (Viannia) braziliensis.

MATERIAL AND METHODS

Cremophor ELP/castor oil-based NEs were prepared by a low-energy method and characterized for their physicochemical parameters. The NEs were used to deliver both ClAlPc and PM to leishmania cells. The in vitro toxicity of NEs were tested in vitro against L. (V.) braziliensis and THP-1 cells. The in vivo toxicity was assessed in non-infected BALB/c mice. Ex-vivo permeation and retention studies using healthy mice skin were also conducted. Finally, the in vivo activity of NE-PM+ClAlPc after PDT was tested in BALB/c mice infected with parasites.

RESULTS

NEs are colloidally stable with average droplet diameter of 30 nm, polydispersity index (PDI) below 0.2, and zeta potential near zero. Both promastigotes and intracellular amastigotes treated with NE-PM, NE-ClAlPc and NE-PM+ClAlPc were inhibited at >50%, >95%, >88%, respectively, after PDT with a phototoxic index (PI) >1.2. No skin ClAlPc permeation was observed. In contrast, PM skin permeation was 80-fold higher using PM-loaded NE formulation in comparison to aqueous PM solution. Topical treatment with NE formulations showed no signs of local toxicity or genotoxicity. In addition, concentrations of PM between 27.3 - 292.5 μM/25 mg of tissue were detected in different organs. In vivo, the NE-PM+ClAlPc treatment did not reduce skin lesions.

CONCLUSION

The Cremophor ELP/castor oil NE formulation increases the permeation of PM through the skin and can be used to co-deliver PM plus ClAlPc for combined PDT protocols. However, the lack of efficacy in the in vivo model evidences that the therapeutical scheme has to be improved.

Effect of nanoemulsion modification with chitosan and sodium alginate on the topical delivery and efficacy of the cytotoxic agent piplartine in 2D and 3D skin cancer models

Due to the limited options for topical management of skin cancer, this study aimed at developing and evaluating nanoemulsions (NE) for topical delivery of the cytotoxic agent piplartine (piperlongumine). NEs were modified with chitosan or sodium alginate, and the effects on the physicochemical properties, piplartine delivery and formulation efficacy were evaluated. The nanoemulsion droplets displayed similar size (96-112 nm), but opposite charge; the polysaccharides improved piplartine penetration into and across the skin (1.3-1.9-fold) in a similar manner, increasing the ratio "drug in the skin/receptor phase" by 1.4-1.5-fold compared to the plain NE and highlighting their relevance for cutaneous localization. Oleic acid addition to the chitosan-containing NE further increased drug penetration (~1.9-2.0-fold), as did increases in drug content from 0.5 to 1%. The cytotoxicity of piplartine was ~2.8-fold higher when the drug was incorporated in the chitosan-containing NE compared to its solution (IC50 = 14.6 μM) against melanoma cells. The effects of this nanocarrier on 3D melanoma tissues were concentration-related; at 1%, piplartine elicited marked epidermis destruction. These results support the potential applicability of the chitosan-modified nanoemulsion containing piplartine as a new strategy for local management of skin cancer.

In vitro Studies of Antitumor Effect, Toxicity/Cytotoxicity and Skin Permeation/Retention of a Green Fluorescence Pyrene-based Dye for PDT Application

Photosensitizers (PS) are compounds that can generate reactive oxygen species under irradiation of appropriate light and are widely used in photodynamic therapy (PDT). Currently, topical PDT is an effective treatment for several skin diseases, including bacterial infections, fungal mycoses and psoriasis. In addition, PDT is also used to treat nonmelanoma skin cancer and can be a potential tool for melanoma, associated with other treatments. In this work, we evaluated the antitumor photoactivity of a new pyrene-based PS (TPPy) by using the murine melanoma cell line (B16F10). The in vitro permeation/retention tests in porcine ear skin were also performed in order to evaluate the potential application of the PS for topical use in skin cancer. Moreover, to determine the toxicity in vivo, we used the Galleria mellonella as an alternative animal model of study. The results showed that TPPy is a promising PS for application in PDT, with potential antitumor photoactivity (IC₅₀ 6.5 μmol L^-1 ), absence of toxicity in the G. mellonella model at higher concentration (70.0 mmol L^-1 ) and the accumulation tendency in the epidermis plus dermis sites (165.20 ± 4.12 ng cm^-2 ).

A New Method for Percutaneous Drug Delivery by Thermo-Mechanical Fractional Injury

BACKGROUND AND OBJECTIVES

Percutaneous drug delivery (PDD) is a means of increasing the uptake of topically applied agents into the skin. Successful delivery of a photosensitizer into the skin is an important factor for effective photodynamic therapy. To evaluate the efficacy of pretreatment by thermomechanical fractional injury (TMFI) (Tixel®, Novoxel®, Israel) at low-energy settings in increasing the permeability of the skin to a known hydrophilic-photosensitizer medication, 5-amino-levulinic-acid hydrochloride (ALA) in compounded 20% ALA gel. To compare the effect of TMFI on ALA permeation into the skin in compounded gel to three commercial photosensitizing medications in different vehicles: ALA microemulsion gel, methyl-amino-levulinic-acid hydrochloride (MAL) cream, and ALA hydroalcoholic solution.

STUDY DESIGN/MATERIALS AND METHODS

Five healthy subjects were treated in two separate experiments and on a total of 136 test sites, with four topical photosensitizer preparations as follows: compounded 20% ALA gel prepared in a good manufacturing practice (GMP)-certified pharmacy (Super-Pharm Professional, Israel), 10% ALA microemulsion gel (Ameluz®, Biofrontera Bioscience GmbH, Leverkusen, Germany), 16.8% MAL cream (Metvix®, Galderma, Lausanne, Switzerland), and 20% ALA hydroalcoholic solution (Levulan Kerastick®, DUSA Pharmaceuticals, Inc., Wilmington, MA, USA). The dermal sites were pretreated by Tixel® (Novoxel® Ltd., Israel) prior to topical drug application. One site was untreated to serve as control. Protoporphyrin IX (PpIX) fluorescence intensity readouts were taken immediately and 1, 2, 3, 4, and 5 hours posttreatment.

RESULTS

The highest average PpIX fluorescence intensity measurements were obtained for the compounded 20% ALA gel following pre-treatment by TMFI at 6 milliseconds pulse duration. After 2 and 3 hours, TMFI-treated sites exhibited an increased hourly rate in readouts of FluoDerm units, which were 156-176% higher than the control rates (P ≤ 0.004). TMFI pre-treatment did not enhance the percutaneous permeation of either ALA or MAL following the microemulsion gel, hydroalcoholic solution, and cream applications.

CONCLUSIONS

Pretreatment with low-energy TMFI at a pulse duration of 6 milliseconds increased the percutaneous permeation of ALA linearly over the first 5 hours from application when the compounded 20% ALA gel was used. Formulation characteristics have substantial influence on the ability of TMFI pretreatment to significantly increase the percutaneous permeation of ALA and MAL. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

Pharmacotherapeutic approaches for transportation of anticancer agents via skin

Cancer is the largest family of diseases that involve abnormal uncontrolled cell growth which metastasizes to other parts of the body. The most common type of cancers includes lung, liver, colorectal, prostate, stomach, breast and cervical cancer with skin cancer excluding melanoma (contribute up to 40% of the cases). The conventional treatment approaches like surgery, chemotherapy, etc., have several side effects such as severe inflammation and pain. Hence, pharmacotherapeutic approaches of antineoplastic agents can be advantageous for treating various forms of cancer through the skin. Novel transdermal techniques and preparations have been emerged to overcome the limitations of skin and to penetrate inside the cancerous cells by transporting through the deeper tissues of the skin. The transdermal penetration of drugs using different formulations such as nanocarriers, physical penetration enhancement techniques, chemical penetration enhancers and newer technologies such as gels, dendrimers, needle-free injection jet etc., show improved patient compliance, abolition of scars and economic value. The topical delivery of antineoplastic agents is an attractive choice for increasing site-specific delivery, reducing side effects and improving therapeutic effects. The objective of this review is to present insights into pharmacotherapeutic techniques, which can be used for transdermal delivery of anticancer agents through skin due to its potential to create a new frontier in treatment of cancer.

Chemical approaches for the enhancement of 5-aminolevulinic acid-based photodynamic therapy and photodiagnosis

The development of photodynamic therapy and photodiagnosis with 5-aminolevulinic acid presents a number of challenges that can be addressed by applying chemical insight and a range of novel prodrug strategies.

Potential of Non-aqueous Microemulsions to Improve the Delivery of Lipophilic Drugs to the Skin

In this study, non-aqueous microemulsions were developed because of the challenges associated with finding pharmaceutically acceptable solvents for topical delivery of drugs sparingly soluble in water. The formulation irritation potential and ability to modulate the penetration of lipophilic compounds (progesterone, α-tocopherol, and lycopene) of interest for topical treatment/prevention of skin disorders were evaluated and compared to solutions and aqueous microemulsions of similar composition. The microemulsions (ME) were developed with BRIJ, vitamin E-TPGS, and ethanol as surfactant-co-surfactant blend and tributyrin, isopropyl myristate, and oleic acid as oil phase. As polar phase, propylene glycol (MEPG) or water (MEW) was used (26% w/w). The microemulsions were isotropic and based on viscosity and conductivity assessment, bicontinuous. Compared to drug solutions in lipophilic vehicles, MEPG improved drug delivery into viable skin layers by 2.5-38-fold; the magnitude of penetration enhancement mediated by MEPG into viable skin increased with drug lipophilicity, even though the absolute amount of drug delivered decreased. Delivery of progesterone and tocopherol, but not lycopene (the most lipophilic compound), increased up to 2.5-fold with MEW, and higher amounts of these two drugs were released from MEW (2-2.5-fold). Both microemulsions were considered safe for topical application, but MEPG-mediated decrease in the viability of reconstructed epidermis was more pronounced, suggesting its higher potential for irritation. We conclude that MEPG is a safe and suitable nanocarrier to deliver a variety of lipophilic drugs into viable skin layers, but the use of MEW might be more advantageous for drugs in the lower range of lipophilicity.

Nanostructured lipid carrier in photodynamic therapy for the treatment of basal-cell carcinoma

Topical photodynamic therapy (PDT) is a promising alternative for malignant skin diseases such as basal-cell carcinoma (BCC), due to its simplicity, enhanced patient compliance, and localization of the residual photosensitivity to the site of application. However, insufficient photosensitizer penetration into the skin is the major issue of concern with topical PDT. Therefore, the aim of the present study was to enable penetration of photosensitizer to the different strata of the skin using a lipid nanocarrier system. We have attempted to develop a nanostructured lipid carrier (NLC) for the topical delivery of second-generation photosensitizer, 5-amino levulinic acid (5-ALA), whose hydrophilicity and charge characteristic limit its percutaneous absorption. The microemulsion technique was used for preparing 5-ALA-loaded NLC. The mean particle size, polydispersity index, and entrapment efficiency of the optimized NLC of 5-ALA were found to be 185.2 ± 1.20, 0.156 ± 0.02, and 76.8 ± 2.58%, respectively. The results of in vitro release and in vitro skin permeation studies showed controlled drug release and enhanced penetration into the skin, respectively. Confocal laser scanning microscopy and cell line studies respectively demonstrated that encapsulation of 5-ALA in NLC enhanced its ability to reach deeper skin layers and consequently, increased cytotoxicity.

Optimization of protoporphyrin IX skin delivery for topical photodynamic therapy: Nanodispersions of liquid-crystalline phase as nanocarriers

Nanodispersions of liquid-crystalline phases (NLPs) composed of monoolein and oleic acid were chosen as nanocarriers to improve the topical retention of the photosensitizer protoporphyrin IX (PpIX) and thereby optimize photodynamic therapy (PDT) using this photosensitizer. The nanodispersions were characterized by polarized light microscopy, small-angle X-ray diffraction and dynamic light scattering. The stability and encapsulation efficiency (EE%) of the nanodispersions were also evaluated. In vitro and in vivo skin penetration studies were performed to determine the potential of the nanodispersions for cutaneous application. In addition, skin penetration and skin irritancy (in an animal model) after in vivo application were visualized by fluorescence light microscopy. The nanodispersion obtained was characterized as a monodisperse system (~150.0 nm) of hexagonal liquid-crystalline phase, which provided a high encapsulation efficiency of PpIX (~88%) that remained stable over 90 days of investigation. Skin penetration studies demonstrated that the nanodispersion enhanced PpIX skin uptake 11.8- and 3.3-fold (in vitro) and 23.6- and 20.8-fold (in vivo) compared to the PpIX skin uptake of control formulations, respectively. In addition, the hexagonal phase nanodispersion did not cause skin irritation after application for two consecutive days. Overall, the results show that the nanocarrier developed is suitable for use in topical PDT with PpIX.

Chemical penetration enhancers

To achieve an efficient skin penetration of most compounds it is necessary to overcome the barrier function of the skin, provided mainly (but not only) by the stratum corneum. Among various strategies used or studied to date, chemical penetration enhancers are the most frequently employed with one of the longest histories of use. There is a multitude of agents described as penetration enhancers, and they present varying properties and structures. In this manuscript, we aim to provide a brief overview of traditional enhancers and some of their properties, focusing on the benefits of combination of chemical enhancers and on selected novel compounds that have shown promise to increase drug delivery into/across the skin.

Chitosan-based mucoadhesive films containing 5-aminolevulinic acid for buccal cancer's treatment

Photodynamic therapy (PDT) is a relatively new method to treat various kinds of tumors, including those of the oral cavity. The topical 5-ALA-PDT treatment for tumors of the oral mucosa is preferred, since when administered systemically, there is a general photosensitization drawback in the patient. However, 5-ALA is a hydrophilic molecule and its penetration and retention is limited by topical route, including oral mucosa. We propose a topical delivery system of chitosan-based mucoadhesive film, aiming to promote greater retention of 5-ALA in tissue. The chitosan (CHT) films (4% w/w) were prepared using the solvent evaporation/casting technique. They were tested without 5-ALA resulting in permeability to water vapor (W.V.P=2.15-8.54 g mm/(h cm(2)Pa) swelling ∼300.0% (±10.5) at 4 h or 24 h and in vitro residence time >24 h for all tests. CHT films containing 10.0% (w/w) 5-ALA have resulted in average weight of 0.22 g and thickness of 0.608 mm as suitable characteristics for oral application. In the presence of CHT films both in vitro permeation and retention of 5-ALA (1.0% or 10.0%) were increased. However, 10.0% 5-ALA presented highest values of permeation and retention (∼4 and 17 times respectively, compared to propylene glycol vehicle). On the other hand, in vitro mucoadhesion of CHT films was decreased (18.2-fold and 3.1-fold) by 5-ALA addition (1.0% or 10.0% respectively). However, CHT film containing 10.0% of 5-ALA can be a potential delivery system for topical use in the treatment of tumors of the oral cavity using PDT because it favored the retention of 5-ALA in this tissue and has shown convenient mucoadhesion.

Drug delivery nanoparticles in skin cancers

Nanotechnology involves the engineering of functional systems at nanoscale, thus being attractive for disciplines ranging from materials science to biomedicine. One of the most active research areas of the nanotechnology is nanomedicine, which applies nanotechnology to highly specific medical interventions for prevention, diagnosis, and treatment of diseases, including cancer disease. Over the past two decades, the rapid developments in nanotechnology have allowed the incorporation of multiple therapeutic, sensing, and targeting agents into nanoparticles, for detection, prevention, and treatment of cancer diseases. Nanoparticles offer many advantages as drug carrier systems since they can improve the solubility of poorly water-soluble drugs, modify pharmacokinetics, increase drug half-life by reducing immunogenicity, improve bioavailability, and diminish drug metabolism. They can also enable a tunable release of therapeutic compounds and the simultaneous delivery of two or more drugs for combination therapy. In this review, we discuss the recent advances in the use of different types of nanoparticles for systemic and topical drug delivery in the treatment of skin cancer. In particular, the progress in the treatment with nanocarriers of basal cell carcinoma, squamous cell carcinoma, and melanoma has been reported.

Current evidence and applications of photodynamic therapy in dermatology

In photodynamic therapy (PDT) a photosensitizer – a molecule that is activated by light – is administered and exposed to a light source. This leads both to destruction of cells targeted by the particular type of photosensitizer, and immunomodulation. Given the ease with which photosensitizers and light can be delivered to the skin, it should come as no surprise that PDT is an increasingly utilized therapeutic in dermatology. PDT is used commonly to treat precancerous cells, sun-damaged skin, and acne. It has reportedly also been used to treat other conditions including inflammatory disorders and cutaneous infections. This review discusses the principles behind how PDT is used in dermatology, as well as evidence for current applications of PDT.

Retained topical delivery of 5-aminolevulinic acid using cationic ultradeformable liposomes for photodynamic therapy

5-Aminolevulinic acid (5-ALA), inducing photodynamic protoporphyrin (PpIX), is a hydrophilic molecule, resulting in leashing the capacity to cross tissue barriers like stratum corneum (SC) of skin. Here, we aimed to develop 5-ALA loaded ultradeformable liposomes (UDL) with different surface charges, and to investigate their physicochemical characteristics and capability for the skin penetration and retention of 5-ALA for topical photodynamic therapy (PDT). The effects of surface charges of UDL on in vitro permeation of 5-ALA and in vivo accumulation of 5-ALA-induced PpIX in viable skin were determined and then compared with conventional neutral liposomes (nLiposome). All UDL showed smaller particle size and better deformability than nLiposome. However, entrapment efficiency of 5-ALA was similar to each vesicle. Among vesicles, the cationic UDL (cUDL) demonstrated higher stability and permeability, and could deliver 5-ALA into deep skin tissue by topical application. Moreover, the 5-ALA loaded in cUDL was long retained, and induced more amount of PpIX in viable skin than those in other UDL and nLiposome. Considering that the conversion of 5-ALA into PpIX occurs preferentially in epidermis, these results suggested that topical delivery of 5-ALA loaded in cUDL could be an interesting proposal to optimize PDT related to 5-ALA.

Celecoxib determination in different layers of skin by a newly developed and validated HPLC-UV method

A simple, rapid and sensitive analytical procedure for the measurement of celecoxib (CXB) levels in skin samples after in vitro penetration studies was developed and validated. In vitro permeability studies in porcine skin were performed for quantification of CXB at different layers of skin, the stratum corneum (SC) and epidermis plus dermis (EP + D) as well as in the acceptor solution (AS) to assess CXB permeation through skin. CXB was quantified by HPLC using a C18 column and UV detection at 251 nm. The mobile phase was methanol-water 72:28 (v/v) and the flow-rate was 0.8 mL/min. The CXB retention time was 5 min. The assay was linear for CBX in the concentration range of 0.1-3.0 μg/mL in the AS (drug permeated through skin) and 5.0-50.0 μg/mL for drug retained in SC and [EP + D] in vitro. The linear correlation coefficients for the different calibration curves were equal or greater than 0.99. Intra- and inter-assay variabilities were below 8.0%. Extraction of CXB from skin samples showed recoveries higher than 95.0% after 15 min of ultrasonic sound and centrifugation at 2500 rpm for 3 min. The method was considered appropriate for the assay of CXB in skin samples, after in vitro cutaneous penetration studies.

Fluorometric quantification of protoporphyrin IX in biological skin samples from in vitro penetration/permeation studies

A fluorometric analytical method was developed for quantification of protoporphyrin IX (PpIX) in skin samples and receptor phase solution after in vitro cutaneous penetration/permeation studies. Analytical conditions used were: excitation and emission wavelengths: 400 nm and 632 nm; bandwidth: 0.5 nm; excitation and emission slits: 10/10. PpIX was recovered from two different layers of skin, the stratum corneum (SC) and the epidermis plus dermis ([E+D]), by vortex homogenization, probe and bath sonication, using DMSO as an extraction solvent. The detection and quantification limits were 0.002 and 0.005 μg/mL, respectively. The assay was linear from 0.005 - 0.5 μg/mL. The within-day and between-day assay precision and accuracy in DMSO and receptor phase solution were each studied at the two concentration levels 0.04 and 0.2 μg/mL, and 0.01 and 0.08 μg/mL, respectively. The coefficients of variation and deviation from the theoretical values were lower than 5%. The skin recovery of PpIX from SC and [E+D] layers using two different concentrations (0.5 and 1.0 μg/mL) were all above 90.0%. The method described has potential application to in vitro penetration/permeation studies of PpIX using porcine skin as a biological membrane model.

A novel transdermal delivery system for the anti-inflammatory lumiracoxib: influence of oleic acid on in vitro percutaneous absorption and in vivo potential cutaneous irritation

Transdermal delivery of non-steroidal anti-inflammatory drugs may be an interesting strategy for delivering these drugs to the diseased site, but it would be ineffective due to low skin permeability. We investigated whether oleic acid (OA), a lipid penetration enhancer in poloxamer gels named poloxamer-based delivery systems (PBDS), can improve lumiracoxib (LM) delivery to/through the skin. The LM partition coefficient (K) studies were carried out in order to evaluate the drug lipophilicity grade (K(octanol/buffer)), showing values >1 which demonstrated its high lipophilicity. Both in vitro percutaneous absorption and skin retention studies of LM were measured in the presence or absence of OA (in different concentrations) in PBDS using porcine ear skin. The flux of in vitro percutaneous absorption and in vitro retention of LM in viable epidermis increased in the presence of 10.0% (w/w) OA in 25.0% (w/w) poloxamer gel. In vivo cutaneous irritation potential was carried out in rabbits showing that this formulation did not provide primary or cumulative cutaneous irritability in animal model. The results showed that 25.0% poloxamer gel containing 10.0% OA is potential transdermal delivery system for LM.

Development of microemulsions to topically deliver 5-aminolevulinic acid in photodynamic therapy

The aim of this study was to obtain and to characterize microemulsions containing 5-aminolevulinic acid (5-ALA) and to investigate the influence of these systems in drug skin permeation for further topical photodynamic therapy (PDT). 5-ALA was incorporated in water-in-oil (W/O), bicontinuous (Bc), and oil-in-water (O/W) microemulsions obtained by the titration of ethyl oleate and PEG-8 caprylic/capric glycerides:polyglyceryl-6 dioleate (3:1) mixtures with water. Selected systems were characterized by conductivity, viscosity, size of the droplets, and drug release. The stability of the drug in the microemulsions was also assessed. Moreover, the in vitro and in vivo skin permeation of 5-ALA was investigated using diffusion cells and confocal scanning laser microscopy (CSLM), respectively. Despite the fact that the O/W microemulsion decreased the 5-ALA diffusion coefficient and retarded the drug release, it also significantly increased the in vitro drug skin permeation when compared to other 5-ALA carriers. It was observed by CSLM that the red fluorescence of the skin increased homogeneously in the deeper skin layers when the 5-ALA microemulsion was applied in vivo, probably due to the formation of the photoactive protoporphyrin IX. The microemulsion developed carried 5-ALA to the deeper skin layers, increasing the red fluorescence of the skin and indicating the potentiality of the system for topical 5-ALA-PDT.

Influence of ceramide 2 on in vitro skin permeation and retention of 5-ALA and its ester derivatives, for Photodynamic Therapy

Photodynamic therapy (PDT) based on topical 5-aminolevulinic acid (5-ALA), an endogenous precursor of protoporphyrin, is an interesting approach for the treatment of skin cancer. However, 5-ALA is a hydrophilic molecule and such a characteristic limits its appropriate cutaneous penetration and retention. In this way, more lipophilic molecules, such as esterified 5-ALA derivatives, have been under investigation in order to improve the skin penetration of this molecule. Drug formulation can also alter 5-ALA skin penetration. Therefore, the aim of this work was to study the influence of ceramide 2 - the main lipid of the SC- on the cutaneous delivery of 5-ALA and its ester derivatives in vitro, using Franz diffusion cell. The skin permeation of all studied drugs was decreased in the presence of ceramide, representing a desirable characteristic in order to avoid the risk of systemic side effects. Nevertheless, the SC and [epidermis + dermis] retention after 16 h has also been decreased in the presence of ceramide, as compared to control. In conclusion, ceramide was not a good adjuvant, meaning that research of other vehicles could be useful to improve cutaneous delivery of 5-ALA.

Chemical enhancer induced changes in the mechanisms of transdermal delivery of zinc oxide nanoparticles

The overlapping wavelength of photoluminescence (PL) of zinc oxide nanoparticles (ZnO NPs) and autofluorescence (AF) from the stratum corneum (SC) has for a long time held back researchers from investigating the chemically enhanced penetration pathways of ZnO NPs into the SC lipids. However, the non-linear polarization effect of second harmonic generation (SHG) may be used for ZnO NPs to be distinguished from the AF of the SC. This study combined the SHG of ZnO NPs and the AF of the SC to image the transdermal delivery of ZnO NPs under the chemical enhancer conditions of oleic acid (OA), ethanol (EtOH) and oleic acid-ethanol (OA-EtOH). In addition to qualitative imaging, the microtransport properties of ZnO NPs were quantified to give the enhancements of the vehicle-to-skin partition coefficient (K), the SHG intensity gradient (G) and the effective diffusion path length (L). The results showed that OA, EtOH and OA-EtOH were all capable of enhancing the transdermal delivery of ZnO NPs by increasing the intercellular lipid fluidity or extracting lipids from the SC.

Photosensitiser delivery for photodynamic therapy. Part 1: Topical carrier platforms

BACKGROUND

Photodynamic therapy (PDT) is a medical treatment in which a combination of a photosensitising drug and visible light causes destruction of selected cells. Due to the lack of true selectivity of preformed photosensitisers for neoplastic tissue and their high molecular weights, PDT of superficial skin lesions has traditionally been mediated by topical application of the porphyrin precursor 5-aminolevulinic acid (ALA).

OBJECTIVE

This article aims to review the traditional formulation-based approaches taken to topical delivery of ALA and discusses the more innovative strategies investigated for enhancement of PDT mediated by topical application of ALA and preformed photosensitisers.

METHODS

All of the available published print and online literature in this area was reviewed. As drug delivery of agents used in PDT is still something of an emerging field, it was not necessary to go beyond literature from the last 30 years.

RESULTS/CONCLUSION

PDT of neoplastic skin lesions is currently based almost exclusively on topical application of simple semisolid dosage forms containing ALA or its methyl ester. Until expiry of patents on the current market-leading products, there is unlikely to be a great incentive to engage in design and evaluation of innovative formulations for topical PDT, especially those containing the more difficult-to-deliver preformed photosensitisers.

Photodynamic therapy of superficial nasal planum squamous cell carcinomas in cats: 55 cases

BACKGROUND

Squamous cell carcinomas (SCCs) are common skin tumors in cats. We investigated photodynamic therapy (PDT) using the photosensitizing agent 5-aminolaevulinic acid (5-ALA) topically and a high-intensity red light source.

HYPOTHESIS

PDT is a safe and effective treatment for feline SCCs.

ANIMALS

Fifty-five client-owned cats with superficial nasal planum SCCs.

METHODS

Prospective, uncontrolled clinical trial. PDT was performed using topical 5-ALA and light of peak wavelength 635 nm. Adverse effects, response, and tumor control were evaluated.

RESULTS

53/55 (96%) cats responded to therapy, and there was a complete response in 47/55 (85%). Six cats (11%) had a partial response. Of the 47 cats with complete response to a single treatment, 24 recurred (51%), with a median time to recurrence of 157 days (95% confidence interval, 109-205 days). Repeat PDT was performed in 22 cats, and at a median follow-up of 1,146 days, 23 (45%) cats were alive and disease free, 17 (33%) had to be euthanized due to tumor recurrence, and 11 (22%) were euthanized for other reasons. Only transient mild local adverse effects were observed after treatment.

CONCLUSIONS AND CLINICAL IMPORTANCE

PDT using 5-ALA and a red light source was safe, well tolerated, and effective in the treatment of superficial nasal planum SCCs of cats and offers an alternative to conventional therapy. Although initial response rates were high, this treatment did not lead to a durable remission or cure in all cases.

New method for delivering a hydrophobic drug for photodynamic therapy using pure nanocrystal form of the drug

A carrier-free method for delivery of a hydrophobic drug in its pure form, using nanocrystals (nanosized crystals), is proposed. To demonstrate this technique, nanocrystals of a hydrophobic photosensitizing anticancer drug, 2-devinyl-2-(1-hexyloxyethyl)pyropheophorbide (HPPH), have been synthesized using the reprecipitation method. The resulting drug nanocrystals were monodispersed and stable in aqueous dispersion, without the necessity of an additional stabilizer (surfactant). As shown by confocal microscopy, these pure drug nanocrystals were taken up by the cancer cells with high avidity. Though the fluorescence and photodynamic activity of the drug were substantially quenched in the form of nanocrystals in aqueous suspension, both these characteristics were recovered under in vitro and in vivo conditions. This recovery of drug activity and fluorescence is possibly due to the interaction of nanocrystals with serum albumin, resulting in conversion of the drug nanocrystals into the molecular form. This was confirmed by demonstrating similar recovery in presence of fetal bovine serum (FBS) or bovine serum albumin (BSA). Under similar treatment conditions, the HPPH in nanocrystal form or in 1% Tween-80/water formulation showed comparable in vitro and in vivo efficacy.