Transdermal Delivery of Cytochrome C—A 12.4 kDa Protein—Across Intact Skin by Constant–Current Iontophoresis

Efficient Assembly of Cytochrome-Based Protoporphyrin IX Composite and Its Characterization as a Photosensitizer

Apo-rC552 C14A/M69F, a heme-deficient mutant of cytochrome c552 from Thermus thermophilus HB8, forms a thermally stable composite with protoporphyrin IX (PPIX). However, the apoprotein yield was compromised because of contamination of the purified protein with the holo-protein bearing a covalently attached heme moiety, impeding efficient composite preparation and subsequent studies on the composite. A newly prepared rC552 mutant involving quadruple mutations, C11A, C14A, H15F, and M69F (rC552-qm), addressed this problem while preserving the inherent thermal stability of a thermophilic bacterial protein. The results obtained for the R125A mutant of rC552-qm corroborated the hypothesis that PPIX occupies the cavity of rC552-qm with an orientation similar to that of heme c in the wild-type protein. The PPIX composite with rC552-qm (PPIX@rC552-qm) exhibited superior singlet oxygen (1O2) production activity compared to the PPIX composite with human serum albumin (PPIX@HSA). Stern-Volmer quenching analysis suggested that the enhanced 1O2 production of PPIX@rC552-qm stems from the facilitated access of O2 to photoexcited PPIX within PPIX@rC552-qm relative to PPIX@HSA. Photoexcitation of PPIX@rC552-qm induced the self-oxidation of PPIX in an aqueous medium, yielding a composite containing a particular chlorin derivative (photo-PPIX) as the degradation intermediate. The photo-PPIX@rC552-qm composite was stable in the solution and showed 1O2 production activity upon exposure to red light because of the characteristic of an absorption band of the chlorin ring. This study proposes the rC552-qm mutant as a platform for readily creating a stable cytochrome-based photosensitizer responsive to visible and red light in combination with readily available PPIX.

Intracorneal iontophoretic delivery of triamcinolone acetonide prodrugs: Physicochemical parameters guiding electrotransport

Intracorneal delivery of ten amino acid (alanine, arginine, asparagine, glutamine, glycine, histidine, isoleucine, lysine, methionine and valine) ester prodrugs of triamcinolone acetonide (TA-AA) was investigated in vitro, using a corneal iontophoresis device (IONTOFOR-CXL; SOOFT Italia S.p.A.) approved for clinical use in the treatment of keratoconus. Short duration iontophoresis (1 mA for 5 min) was performed and intracorneal deposition of TA was quantified by HPLC-UV and UHPLC-MS/MS. The data evidenced the clear advantage of TA-AA prodrug iontophoresis compared to passive delivery and revealed unexpected and prodrug dependent deposition profiles. Despite their superior electrical mobility, intracorneal delivery of dications, TA-Arg and TA-Lys, did not outperform that of TA-Ala and TA-Gly. In silico investigations to relate the TA-AA prodrugs' physicochemical properties to their electrotransport confirmed that increased lipophilicity potential did not favour iontophoretic transport. For TA-Ala and TA-Gly, it was hypothesized that the greater charge distribution and decreased tendency to interact with the corneal tissue via electrostatic and H-bonds contributed to their successful iontophoretic delivery. Intracorneal biodistribution of TA confirmed that TA-Gly iontophoresis resulted in supratherapeutic concentrations in deep corneal stroma, exceeding TA IC50 by ∼ 104-fold. The results clearly demonstrated the successful combination of the clinically approved SOOFT iontophoretic device and the TA-AA prodrugs for targeted corneal iontophoretic delivery.

Effect of gelatin nanoparticles' size and charge on iontophoretic targeted deposition to the hair follicles

Hair follicles (HFs) represent a route of interest to drug delivery for treating several skin conditions. Iontophoresis, on the other hand, is a physical method to enhance drug permeation by applying a low electrical current to the formulation. HFs can be targeted following topical iontophoretic application, as they represent a pathway of lower electrical resistance, as well as a drug reservoir, in particular useful for nanoparticles (NPs), which can preferably accumulate in these structures. Combining both strategies may provide optimal results, but the literature still lacks evidence of the ideal NP characteristics for the iontophoretic drug delivery targeting the HFs. Here, we aimed to evaluate the effect of gelatin NPs' size and charge under iontophoresis application on NPs' deposition into the HFs. Four gelatin NP formulations were produced with varying gelatin concentrations and gelatin types (positively charged type A and negatively charged type B), with sizes ranging from 220 to 770 nm. A fluorescent dye, TRITC-dextran 150 kDa, was encapsulated for monitoring NPs deposition. Cutaneous penetration experiments were performed in vitro with and without iontophoresis for 6 h with pig ear skin. The deposition profile was assessed by confocal laser scanning microscopy. Photomicrographs showed a higher accumulation of the larger positively charged NPs (AL), reaching deeper portions of HFs, and showed iontophoresis further increased their deposition, resulting in the highest signal. In conclusion, these findings shed light on the applications of NPs and bring novel treatment opportunities for several diseases compromising the hair follicles.

Non-Invasive Delivery of Negatively Charged Nanobodies by Anodal Iontophoresis: When Electroosmosis Dominates Electromigration

Iontophoresis enables the non-invasive transdermal delivery of moderately-sized proteins and the needle-free cutaneous delivery of antibodies. However, simple descriptors of protein characteristics cannot accurately predict the feasibility of iontophoretic transport. This study investigated the cathodal and anodal iontophoretic transport of the negatively charged M7D12H nanobody and a series of negatively charged variants with single amino acid substitutions. Surprisingly, M7D12H and its variants were only delivered transdermally by anodal iontophoresis. In contrast, transdermal permeation after cathodal iontophoresis and passive diffusion was Collapse

Key Words

• anti-EGFR 7D12 nanobody
• electroosmosis
• iontophoresis
• nanobodies
• protein expression and purification
• skin topical and transdermal delivery

Collapse

MESH Headings Collapse

Grants Collapse

Affiliation(s)

Phedra Firdaws Sahraoui School of Pharmaceutical Sciences, University of Geneva, CMU-1 Rue Michel Servet, 1211 Geneva, Switzerland; Institute of Pharmaceutical Sciences of Western Switzerland, University of Geneva, CMU-1 Rue Michel Servet, 1211 Geneva, Switzerland
Oscar Vadas Department of Microbiology and Molecular Medicine, Faculty of Medicine, University of Geneva, CMU-1 Rue Michel Servet, 1211 Geneva, Switzerland;
Yogeshvar N. Kalia School of Pharmaceutical Sciences, University of Geneva, CMU-1 Rue Michel Servet, 1211 Geneva, Switzerland; Institute of Pharmaceutical Sciences of Western Switzerland, University of Geneva, CMU-1 Rue Michel Servet, 1211 Geneva, Switzerland

Collapse

Collaborators Collapse

Iontophoresis for the cutaneous delivery of nanoentraped drugs

INTRODUCTION

The skin is an attractive route for drug delivery. However, the stratum corneum is a critical limiting barrier for drug permeation. Nanoentrapment is a way to enhance cutaneous drug delivery, by diverse mechanisms, with a notable trend of nanoparticles accumulating into the hair follicles when topically applied. Iontophoresis is yet another way of increasing drug transport by applying a mild electrical field that preferentially passes through the hair follicles, for being the pathway of lower resistance. So, iontophoresis application to nanocarriers could further increase actives accumulation into the hair follicles, impacting cutaneous drug delivery.

AREAS COVERED

In this review, the authors aimed to discuss the main factors impacting iontophoretic skin transport when combining nanocarriers with iontophoresis. We further provide an overview of the conditions in which this combination has been studied, the characteristics of nanosystems employed, and hypothesize why the association has succeeded or failed to enhance drug permeation.

EXPERT OPINION

Nanocarriers and iontophoresis association can be promising to enhance cutaneous drug delivery. For better results, the electroosmotic contribution to the iontophoretic transport, mainly of negatively charged nanocarriers, charge density, formulation pH, and skin models should be considered. Moreover, the transfollicular pathway should be considered, especially when designing the nanocarriers.

Iontophoresis application for drug delivery in high resistivity membranes: nails and teeth

Iontophoresis has been vastly explored to improve drug permeation, mainly for transdermal delivery. Despite the skin's electrical resistance and barrier properties, it has a relatively high aqueous content and is permeable to many drugs. In contrast, nails and teeth are accessible structures for target drug delivery but possess low water content compared to the skin and impose significant barriers to drug permeation. Common diseases of these sites, such as nail onychomycosis and endodontic microbial infections that reach inaccessible regions for mechanical removal, often depend on time-consuming and ineffective treatments relying on drug's passive permeation. Iontophoresis application in nail and teeth structures may be a safe and effective way to improve drug transport across the nail and drug distribution through dental structures, making treatments more effective and comfortable for patients. Here, we provide an overview of iontophoresis applications in these "hard tissues," considering specificities such as their high electrical resistivity. Iontophoresis presents a promising option to enhance drug permeation through the nail and dental tissues, and further developments in these areas could lead to widespread clinical use.

Non-Invasive Iontophoretic Delivery of Cytochrome c to the Posterior Segment and Determination of Its Ocular Biodistribution

The intact porcine eye globe model was used to demonstrate that transscleral iontophoresis could deliver a small protein, cytochrome c (Cyt c), to the posterior segment and to investigate post-iontophoretic biodistribution in the different ocular compartments. The effects of Cyt c concentration (1, 5, and 10 mg/mL), current density (3.5 and 5.5 mA/cm²), and duration of the current application (10 min and 1, 2, and 4 h) were evaluated. The data confirmed that transscleral iontophoresis enhanced the intraocular delivery of Cyt c under all conditions as compared to passive controls (same setup but without the current application). Increasing the Cyt c concentration resulted in a proportional enhancement in the Cyt c delivery. Increasing the current density from 3.5 to 5.5 mA/cm² increased iontophoretic delivery at a Cyt c concentration of 10 mg/mL but did not appear to do so at 5 mg/mL; this was attributed in part to the effect of melanin binding. Short duration iontophoresis (10 min, 3.5 mA/cm²) of a 10 mg/mL Cyt c solution created a depot in the sclera. When this was followed by a 4 h incubation period, post-iontophoretic Cyt c diffusion from the sclera resulted in a different biodistribution, and Cyt c could be quantified in the posterior segment.

Effect of mRNA Delivery Modality and Formulation on Cutaneous mRNA Distribution and Downstream eGFP Expression

In vitro transcribed messenger ribonucleic acid (mRNA) constitutes an emerging therapeutic class with several clinical applications. This study presents a systematic comparison of different technologies—intradermal injection, microneedle injection, jet injection, and fractional laser ablation—for the topical cutaneous delivery of mRNA. Delivery of Cy5 labeled mRNA and non-labeled enhanced green fluorescent protein (eGFP) expressing mRNA was investigated in a viable ex vivo porcine skin model and monitored for 48 h. Forty 10 µm-thick horizontal sections were prepared from each skin sample and Cy5 labeled mRNA or eGFP expression visualized as a function of depth by confocal laser scanning microscopy and immunohistochemistry. A pixel-based method was used to create a semi-quantitative biodistribution profile. Different spatial distributions of Cy5 labeled mRNA and eGFP expression were observed, depending on the delivery modality; localization of eGFP expression pointed to the cells responsible. Delivery efficiencies and knowledge of delivery sites can facilitate development of efficient, targeted mRNA-based therapeutics.

The influence of skin barrier impairment on the iontophoretic transport of low and high molecular weight permeants

The effect of skin barrier impairment on the iontophoretic transport of low (acetaminophen (ACM), lidocaine (LD), ketorolac (KT)) and high molecular weight permeants, (cytochrome c (Cyt c) and ribonuclease T1 (RNase T1)), was evaluated using tape-stripping (TS) and fractional laser ablation for "large-scale" and "localized" barrier disruption. Interestingly, removal of the stratum corneum did not invariably lead to an increase in iontophoretic delivery of the permeants. Decrease of electroosmotic (EO) flow and facilitated transport of Cl^- ions in the cathode-to-anode direction, which reduced cation electromigration (EM), both impacted cation delivery by anodal iontophoresis but the effects were partly offset by enhanced passive diffusion. Decrease in EO increased cathodal iontophoresis of KT but not that of RNase T1. Permeability coefficients confirmed the superiority of EM over EO for small molecules, LD > KT > ACM. A combination of fractional laser ablation and iontophoresis was advantageous for both positively and negatively charged small molecules as passive penetration was significantly enhanced. In conclusion, results demonstrated that (i) skin ablation prior to anodal iontophoresis decreased EO and EM but could be advantageous for delivery if the ablative technique enhanced passive penetration thereby compensating reduction of electrotransport and (ii) reduced EO favored cathodal electrotransport.

Non-invasive transdermal delivery of chemotherapeutic molecules in vivo using superparamagnetic iron oxide nanoparticles

Background

The skin is both a target and a potential conduit for the delivery of drugs, but its cornified cell layer resists penetration by most molecules. This study investigated the potential of superparamagnetic iron oxide nanoparticles to facilitate the transdermal delivery of anticancer agents.

Results

Chemotherapeutic cancer drugs were applied with or without nanoparticles to the skin of hairless mice, and their ability to penetrate the skin was assessed using fluorescence microscopy and tumor growth. Nanoparticles enhanced the penetration of the skin by doxorubicin and 5-fluorouracil as determined by fluorescence microscopy and growth retardation of experimental melanoma in immunocompetent, syngeneic mice. This drug enhancement did not require conjugation or encapsulation of the drugs by the nanoparticles—simple co-administration sufficed. Nanoparticles applied topically to melanomas increased the cytotoxicity and immune cell infiltration induced by co-administered 5-fluorouracil, and also reduced vascularization of the tumors independently of 5-fluorouracil.

Conclusion

Correctly formulated superparamagnetic iron oxide nanoparticles can facilitate the chemotherapeutic effectiveness of cytotoxic drugs on skin tumors by both increasing their transdermal penetration and ameliorating host–tumor interactions. This enhancement of skin penetration occurs without the need for conjugation or encapsulation of the co-administered drugs, and so will likely be applicable to other drugs, also.

Non-invasive drug delivery technology: development and current status of transdermal drug delivery devices, techniques and biomedical applications

Pay-load deliveries across the skin barrier to the systemic circulation have been one of the most challenging delivery options. Necessitated requirements of the skin and facilitated skin layer cross-over delivery attempts have resulted in development of different non-invasive, non-oral methods, devices and systems which have been standardized, concurrently used and are in continuous upgrade and improvements. Iontophoresis, electroporation, sonophoresis, magnetophoresis, dermal patches, nanocarriers, needled and needle-less shots, and injectors are among some of the methods of transdermal delivery. The current review covers the current state of the art, merits and shortcomings of the systems, devices and transdermal delivery patches, including drugs' and other payloads' passage facilitation techniques, permeation and absorption feasibility studies, as well as physicochemical properties affecting the delivery through different transdermal modes along with examples of drugs, vaccines, genes and other payloads.

Non-invasive targeted iontophoretic delivery of cetuximab to skin

Background: Cetuximab (CTX) is a glycosylated anti-EGFR monoclonal antibody of great interest in the treatment of non-melanoma skin cancers. Its intravenous administration is associated with severe side effects. This is the first report on the noninvasive iontophoretic-targeted topical delivery of CTX to skin.Methods: Iontophoretic transport of CTX (0.5 mA/cm²) was studied as a function of formulation pH (4, 5.5 and 7) and duration of current application (2, 4 and 8 h). CTX cutaneous biodistribution was determined; electrotransport mechanisms and penetration pathways were investigated.Results: Electrophoretic mobility measurements of CTX isoforms and co-iontophoresis of acetaminophen at each pH demonstrated that CTX electrotransport was due to electroosmosis: despite an ~8-fold reduction in charge, CTX skin deposition was greater at pH 7 than pH 4 (8.974 ± 1.952 and 0.482 ± 0.165 μg/mm³) - consistent with the increased electroosmotic flow at pH 7. Iontophoresis of an Alex488-CTX conjugate showed that skin penetration occurred by the intercellular and follicular routes. Therapeutic concentrations of CTX in the viable epidermis, upper dermis and lower dermis were achieved following iontophoresis for 2, 4 and 8 h, respectively.Conclusion: The results demonstrate the topical delivery of a 152 kDa monoclonal antibody into skin in a targeted, controlled and entirely noninvasive manner.

Ultrasonically and Iontophoretically Enhanced Drug-Delivery System Based on Dissolving Microneedle Patches

A multifunctional system comprised of hyaluronic acid microneedles was developed as an effective transdermal delivery platform for rapid local delivery. The microneedles can regulate the filling amount on the tip, by controlling the concentration of hyaluronic acid solution. Ultrasonication induces dissolution of the HA microneedles via vibration of acoustic pressure, and AC iontophoresis improves the electrostatic force-driven diffusion of HA ions and rhodamine B. The effect of ultrasound on rhodamine release was analyzed in vitro using a gelatin hydrogel. The frequency and voltage dependence of the AC on the ion induction transfer was also evaluated experimentally. The results showed that the permeability of the material acts as a key material property. The delivery system based on ultrasonication and iontophoresis in microneedles increases permeation, thus resulting in shorter initial delivery time than that required by delivery systems based on passive or ultrasonication alone. This study highlights the significance of the combination between ultrasonic waves and iontophoresis for improving the efficiency of the microneedles, by shortening the reaction duration. We anticipate that this system can be extended to macromolecular and dependence delivery, based on drug response time.

Drug Transport across Porcine Intestine Using an Ussing Chamber System: Regional Differences and the Effect of P-Glycoprotein and CYP3A4 Activity on Drug Absorption

Drug absorption across viable porcine intestines was investigated using an Ussing chamber system. The apparent permeability coefficients, P_app,pig, were compared to the permeability coefficients determined in humans in vivo, P_eff,human. Eleven drugs from the different Biopharmaceutical Classification System (BCS) categories absorbed by passive diffusion with published P_eff,human values were used to test the system. The initial experiments measured P_app,pig for each drug after application in a Krebs–Bicarbonate Ringer (KBR) buffer and in biorelevant media FaSSIF V2 and FeSSIF V2, mimicking fasted and fed states. Strong sigmoidal correlations were observed between P_eff,human and P_app,pig. Differences in the segmental P_app,pig of antipyrine, cimetidine and metoprolol confirmed the discrimination between drug uptake in the duodenum, jejunum and ileum (and colon); the results were in good agreement with human data in vivo. The presence of the P-gp inhibitor verapamil significantly increased P_app,pig across the ileum of the P-gp substrates cimetidine and ranitidine (p < 0.05). Clotrimazole, a potent CYP3A4 inhibitor, significantly increased P_app,pig of the CYP3A4 substrates midazolam, verapamil and tamoxifen and significantly decreased the formation of their main metabolites. In conclusion, the results showed that this is a robust technique to predict passive drug permeability under fasted and fed states, to identify regional differences in drug permeability and to demonstrate the activity of P-gp and CYP3A4.

Current Advancements in Transdermal Biosensing and Targeted Drug Delivery

In this manuscript, recent advancements in the area of minimally-invasive transdermal biosensing and drug delivery are reviewed. The administration of therapeutic entities through the skin is complicated by the stratum corneum layer, which serves as a barrier to entry and retards bioavailability. A variety of strategies have been adopted for the enhancement of transdermal permeation for drug delivery and biosensing of various substances. Physical techniques such as iontophoresis, reverse iontophoresis, electroporation, and microneedles offer (a) electrical amplification for transdermal sensing of biomolecules and (b) transport of amphiphilic drug molecules to the targeted site in a minimally invasive manner. Iontophoretic delivery involves the application of low currents to the skin as well as the migration of polarized and neutral molecules across it. Transdermal biosensing via microneedles has emerged as a novel approach to replace hypodermic needles. In addition, microneedles have facilitated minimally invasive detection of analytes in body fluids. This review considers recent innovations in the structure and performance of transdermal systems.

Skin Delivery of Hydrophilic Biomacromolecules Using Marine Sponge Spicules

We report the development of sponge Haliclona sp. spicules, referred to as SHS, and its topical application in skin delivery of hydrophilic biomacromolecules, a series of fluorescein isothiocyanate-dextrans (FDs). SHS are silicious oxeas which are sharp-edged and rod-shaped (∼120 μm in length and ∼7 μm in diameter). SHS can physically disrupt skin in a dose-dependent manner and retain within the skin over at least 72 h, which allows sustained skin penetration of hydrophilic biomacromolecules. The magnitude of enhancement of FD delivery into skin induced by SHS treatment was dependent on its molecular weight. Specifically, SHS topical application enhanced FD-10 (MW: 10 kDa) penetration into porcine skin in vitro by 33.09 ± 7.16-fold compared to control group (p < 0.01). SHS dramatically increased the accumulation of FD-10 into and across the dermis by 62.32 ± 13.48-fold compared to the control group (p < 0.01). In vivo experiments performed using BALB/c mice also confirmed the effectiveness of SHS topical application; the skin absorption of FD-10 with SHS topical application was 72.14 ± 48.75-fold (p < 0.05) and 15.39 ± 9.91-fold (p < 0.05) higher than those from the PBS and Dermaroller microneedling, respectively. Further, skin irritation study and transepidermal water loss (TEWL) measurement using guinea pig skin in vivo indicated that skin disruption induced by SHS treatment is self-limited and can be recovered with time and efficiently. SHS can offer a safe, effective, and sustained skin delivery of hydrophilic biomacromolecules and presents a promising platform technology for a wide range of cosmetic and medical applications.

Transdermal therapeutic systems for memantine delivery. Comparison of passive and iontophoretic transport

Memantine is a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist used in the treatment of moderate to severe dementia including the symptoms of Alzheimer's disease (AD). It is administered orally but compliance, swallowing problems and the routine use of multiple medications in elderly AD patients means that an alternative route of administration would be of interest. The aim of the present study was to develop memantine hydrochloride occlusive transdermal therapeutic systems (TTS) for passive and iontophoretic delivery across the skin. Polyvinyl pyrrolidone (PVP) and a mixture with polyvinyl alcohol (PVA) were employed as polymeric matrices. The study involved the TTS characterization in addition to quantification of the memantine transport across porcine skin in vitro. The evaluation of the TTS physical properties suggested that systems were made more mechanically resistant by including PVA (6%) or high concentrations of PVP (24%). Moreover, a linear correlation was observed between the concentration of PVP and the bioadhesion of the systems. Drug delivery experiments showed that the highest transdermal flux provided by a passive TTS (PVP 24% w/w limonene) was 8.89±0.81μgcm^-2h^-1 whereas the highest iontophoretic transport was 46.4±3.6μgcm^-2h^-1. These innovative TTS would enable two dosage regimens that could lead to therapeutic plasma concentrations.

Controlled transdermal iontophoresis for poly-pharmacotherapy: Simultaneous delivery of granisetron, metoclopramide and dexamethasone sodium phosphate in vitro and in vivo

Iontophoresis has been used to deliver small molecules, peptides and proteins into and across the skin. In principle, it provides a controlled, non-invasive method for poly-pharmacotherapy since it is possible to formulate and to deliver multiple therapeutic agents simultaneously from the anodal and cathodal compartments. The objective of this proof-of-principle study was to investigate the simultaneous anodal iontophoretic delivery of granisetron (GST) and metoclopramide (MCL) and cathodal iontophoresis of dexamethasone sodium phosphate (DEX-P). In addition to validating the hypothesis, these are medications that are routinely used in combination to treat chemotherapy-induced emesis. Two preliminary in vitro studies using porcine skin were performed: Study 1 - effect of formulation composition on anodal co-iontophoresis of GST and MCL and Study 2 - combined anodal iontophoresis of GST (10mM) and MCL (110 mM) and cathodal iontophoresis of DEX-P (40 mM). The results from Study 1 demonstrated the dependence of GST/MCL transport on the respective drug concentrations when co-iontophoresed at 0.3 mA·cm(-2). Although they possess similar physicochemical properties, MCL seemed to be a more efficient charge carrier (JMCL=0.0591∗CMCLvs JGST=0.0414∗CGST). In Study 2, MCL permeation was markedly superior to that of GST (2324.83 ± 307.85 and 209.83 ± 24.84 μg·cm(-2), respectively); this was consistent with the difference in their relative concentrations; DEX-P permeation was 336.94 ± 71.91 μg·cm(-2). The in vivo studies in Wistar rats (10mM GST, 110 mM MCL and 40 mM DEX-P (0.5 mA·cm(-2) for 5h with Ag/AgCl electrodes and salt bridges) demonstrated that significant drug levels were achieved rapidly for each drug. This was most noticeable for dexamethasone (DEX) where relatively constant plasma levels were obtained from the 1 to 5h time-points; DEX-P was not detected in the plasma since it was completely hydrolyzed to the active metabolite. The calculated input rates in vivo (k01) for GST, MCL and DEX were 0.45 ± 0.05, 3.29 ± 0.48 and 1.97 ± 0.38 μg·cm(-2) · min(-1), respectively. The study confirmed that iontophoresis provided a controlled method for the simultaneous administration of multiple therapeutic agents and that it could be of use for poly-pharmacotherapy in general and more specifically that it was able to deliver different drugs used in the treatment of chemotherapy-induced emesis.

Transdermal Drug Delivery: Innovative Pharmaceutical Developments Based on Disruption of the Barrier Properties of the stratum corneum

The skin offers an accessible and convenient site for the administration of medications. To this end, the field of transdermal drug delivery, aimed at developing safe and efficacious means of delivering medications across the skin, has in the past and continues to garner much time and investment with the continuous advancement of new and innovative approaches. This review details the progress and current status of the transdermal drug delivery field and describes numerous pharmaceutical developments which have been employed to overcome limitations associated with skin delivery systems. Advantages and disadvantages of the various approaches are detailed, commercially marketed products are highlighted and particular attention is paid to the emerging field of microneedle technologies.

Transdermal iontophoretic drug delivery: advances and challenges

The stratum corneum continues to pose considerable impediment to transdermal drug delivery. One of the effective ways of circumventing this challenge is through the use of iontophoresis. Iontophoresis uses low-level current to drive charged compounds across the skin. This review discusses progress made in the field of iontophoretic transport of small and large molecules. The major obstacles are also touched upon and advances made in the last few decades described. A number of iontophoretic systems approved for clinical use by regulatory authorities is also discussed.

Iontophoretic skin permeation of peptides: an investigation into the influence of molecular properties, iontophoretic conditions and formulation parameters

The transdermal route offers advantages for delivery of peptides and proteins. However, these polar and large molecules do not permeate the skin barrier well. Various enhancement methods have been employed to address this problem. Iontophoresis is one of the methods that shows promise but its application to peptide delivery has yet to be fully explored. This study investigates the effects of different molecular properties and iontophoretic conditions on the skin permeation of peptides. In this study, the permeation of alanine-tryptophan dipeptide (MW 276 Da), alanine-alanine-proline-valine tetrapeptide (MW 355 Da), Argireline® (Acetyl hexapeptide-3, MW 889 Da) and Triptorelin acetate (decapeptide, MW 1311 Da) through excised human skin under passive or iontophoretic current of 0.4 mA was investigated. The effects of pH change (3.0-7.4, to provide different net negative, neutral, and positive charges) to the peptide, donor concentration (1-10 mg/ml), background electrolyte (34-137 mM NaCl and/or 5-20 mM HEPES) and current direction (anodal vs cathodal) were also studied. Peptides were analysed by high-performance liquid chromatography or liquid scintillation counting. Iontophoresis led up to a 30 times increase in peptide permeation relative to passive permeation for the peptides. Electroosmosis was an important determinant of the total flux for the high molecular weight charged peptides. Electrorepulsion was found to be considerable for low molecular weight charged moieties. Permeation was decreased at lower pH, possibly due to decreased electroosmosis. Results also showed that 10 times increase in donor peptide concentration increases permeation of peptides by about 2-4 times and decreases iontophoretic permeability coefficients by about 2.5-5 times. The addition of extra background electrolyte decreased the iontophoretic permeation coefficient of peptides by 2-60 times. This study shows that iontophoretic permeation of peptides is affected by a number of parameters that can be optimized for effective transdermal peptide delivery.

Transdermal delivery of proteins using a combination of iontophoresis and microporation

Aim: This study aimed to investigate transdermal delivery of proteins using combination of microporation and iontophoresis (ITP). Materials & methods & results: Delivery of model protein, Alexa Fluor 555 bovine serum albumin conjugate (AF-BSA) using ITP alone, microneedle (MN) alone, and ITP plus MN combination was assessed using confocal microscopy. Compared to MN alone, combination of MN plus ITP significantly increased skin's penetration depth of AF-BSA (300 vs 110 μm) and achieved lateral distribution of the model protein. Average fluorescence intensity quantified around each microchannel was 23.7-fold (8.2-fold, in vivo) higher for combination treatment compared with MN alone, in vitro. After 1 h in vitro permeation study, the unlabeled BSA amount delivered across skin was found to be 0, 1.4, 0.63 and 14 μg by passive, MN alone, ITP alone and ITP plus MN combination delivery, respectively.

Targeted local simultaneous iontophoresis of chemotherapeutics for topical therapy of head and neck cancers

The objective was to investigate the feasibility of using buccal iontophoresis for the simultaneous delivery of chemotherapeutic agents with a view to developing a new approach to treat head and neck cancers. Short duration cathodal iontophoresis of 5-fluorouracil (5-FU; 20mM) and leucovorin (LV; 10 mM) at 1 mA/cm(2) for 10 or 20 min from aqueous solution and a 2% hydroxyethyl cellulose gel at pH 7.6 was evaluated using bovine mucosa in vitro. Iontophoresis resulted in a statistically significant increase in the mucosal deposition of both drugs as compared to passive diffusion (Student's t-test, α=0.05); in each case, drug delivery was selective for deposition with no permeation being observed. After 20 min of iontophoresis, there was an ~ 8-fold enhancement for 5-FU (1.46 ± 0.86 and 11.93 ± 3.81 μg/cm(2), respectively) and a 3-fold increase for LV (8.31 ± 2.44 and 25.08 ± 6.89 μg/cm(2), respectively) when using aqueous solutions. The same trend was observed when the gel was applied for 10 min; passive delivery of 5-FU from the gel resulted in non-detectable levels in the mucosa, while 4.62 ± 1.76 μg/cm(2) were deposited in the mucosa following iontophoresis. Similarly, iontophoretic delivery of LV from the gel resulted in ~ 3-fold higher deposition as compared to passive diffusion (6.71 ± 1.36 and 21.12 ± 9.94 μg/cm(2), respectively). No drug permeation was observed in either case. In conclusion, iontophoresis can be used for targeted topical delivery of chemotherapeutics to the buccal mucosa and may enable less invasive local therapy of head and neck cancers.

Needle free parenteral drug delivery: leveraging active transdermal technologies for pediatric use

Administration of medications via the parenteral route directly to the systemic circulation is an effective way of overcoming the first pass effect, obtaining quicker onset of action, and achieving higher bioavailability. However, needle phobia and the pain perceived during the injection process often make this a less preferred route than oral in terms of patient acceptance and compliance, particularly for pediatrics. Needleless injection technologies that deliver medications via the transdermal interface have been an active area of pharmaceutical research for many years. This review summarizes the various emerging technologies in the area of active transdermal delivery that can be potentially extended to pediatric applications.

Turning theory into practice: the development of modern transdermal drug delivery systems and future trends

Despite its remarkable barrier function, the skin remains an attractive site for systemic drug delivery given its easy accessibility, large surface area and the possibility to bypass the gastrointestinal tract and the liver and so modify drug absorption kinetics. The pioneering work of Scheuplein, Higuchi and others in the 1960s helped to explain the processes involved in passive percutaneous absorption and led to the development of mathematical models to describe transdermal drug delivery. The intervening years have seen these theories turned to practice and a significant number of transdermal systems are now available including some that employ active drug delivery. This review briefly discusses the evolution of transdermal therapeutic systems over the years and the potential of newer transdermal technologies to deliver hydrophilic drugs and macromolecules through the skin.

Next generation intra- and transdermal therapeutic systems: using non- and minimally-invasive technologies to increase drug delivery into and across the skin

The number of drug molecules approved by the regulatory authorities for transdermal administration is relatively modest - less than two dozen. Many other therapies might benefit from the advantages offered by the transdermal route. That they have not already done so is due to the exceptional efficacy of the stratum corneum as a diffusional barrier and its remarkable ability to restrict molecular transport. As a result only extremely potent therapeutics possessing the necessary physicochemical properties can be delivered by passive diffusion across intact skin at pharmacologically relevent rates. This has led to the development of several delivery technologies that might be used to expand the range of medicinal agents that can be administered transdermally with the requisite delivery kinetics. There are essentially two approaches: (i) provide an improved driving force to increase the rate of transport (i.e., act on the molecule) or (ii) modify the properties of the microenvironment through which diffusion must occur (i.e., act on the stratum corneum). The challenge for the latter approach is to compromise the barrier in a reversible and relatively painless manner that minimises irritation, is practical for chronic conditions and has minimal risk of infection. Here, we review some of the physical methods that have been used to either transiently perturb the skin barrier or to provide additional driving forces to facilitate molecular transport with a particular focus on technologies that have either led to marketed products or have at least reached the clinical development stage.

In vivo sustained dermal delivery and pharmacokinetics of interferon alpha in biphasic vesicles after topical application

Biphasic vesicles, a novel nanostructured lipid-based delivery system show potential for topical application of interferon alpha (IFN α) for the treatment of human papillomavirus (HPV) infections (anogenital warts). Dermal delivery of IFN α encapsulated in biphasic vesicles (BPV-IFN α), applied topically to the skin, was characterized in a guinea pig model. BPV-IFN α (1g, 2 MIU/g) was topically applied either as a single or multiple treatments on the skin of guinea pigs. As a comparison with currently used regimens, IFN α solution was administered intravenously or intradermally. Skin and serum samples were collected over 96 h, IFN α levels were determined by an antiviral assay, and half-life (t₁/₂) and elimination (k) rates were calculated. Topical BPV-IFN α treatment resulted in maximum skin levels (about 100,000 U/100 cm(2)) of IFN α within 6h and maintained for 72-96 h. Clearance from the skin after intradermal injections was initially fast (t₁/₂ 0.62 h, k 1.1179 h(-1)), followed by a slower steady decrease after 6h. After intravenous and intradermal administration, IFN α was rapidly cleared from the serum, t₁/₂ 0.75 h, k 0.9271 h(-1) and t₁/₂ 1.28 h, k 0.5421 h(-1), respectively, whereas after topical application, IFN α levels remained below 100 U/mL. Topical application of BPV- IFN α resulted in sustained delivery of biologically active IFN α locally into skin with minimal systemic exposure.

Mathematical models to describe iontophoretic transport in vitro and in vivo and the effect of current application on the skin barrier

The architecture and composition of the stratum corneum make it a particularly effective barrier against the topical and transdermal delivery of hydrophilic molecules and ions. As a result, different strategies have been explored in order to expand the range of therapeutic agents that can be administered by this route. Iontophoresis involves the application of a small electric potential to increase transport into and across the skin. Since current flow is preferentially via transport pathways with at least some aqueous character, it is ideal for hydrosoluble molecules containing ionisable groups. Hence, the physicochemical properties that limit partitioning and passive diffusion through the intercellular lipid matrix are beneficial for electrically-assisted delivery. The presence of fixed ionisable groups in the skin (pI 4-4.5) means that application of the electric field results in a convective solvent flow (i.e., electroosmosis) in the direction of ion motion so as to neutralise membrane charge. Hence, under physiological conditions, cation electrotransport is due to both electromigration and electroosmosis-their relative contribution depends on the formulation conditions and the physicochemical properties of the permeant. Different mathematical models have been developed to provide a theoretical framework in order to explain iontophoretic transport kinetics. They usually involve solutions of the Nernst-Planck equation - using either the constant field (Goldman) or electroneutrality (Nernst) approximations - with or without terms for the convective solvent flow component. Investigations have also attempted to elucidate the nature of ion transport pathways and to explain the effect of current application on the electrical properties of the skin-more specifically, the stratum corneum. These studies have led to the development of different equivalent circuit models. These range from simple parallel arrangements of a resistor and a capacitor to the inclusion of the more esoteric "constant phase element"; the latter provides a better mathematical description of the "non-ideal" behaviour of skin impedance. However, in addition to simply providing a "mathematical" fit of the observed data, it is essential to relate these circuit elements to biological structures present in the skin. More recently, attention has also turned to what happens when the permeant crosses the epidermis and reaches the systemic circulation and pharmacokinetic models have been proposed to interpret data from iontophoretic delivery studies in vivo. Here, we provide an overview of mathematical models that have been proposed to describe (i) the effect of current application on the skin and the implications for potential iontophoretic transport pathways, (ii) electrotransport kinetics and (iii) the fate of iontophoretically delivered drugs once they enter the systemic circulation.

Controlled intra- and transdermal protein delivery using a minimally invasive Erbium:YAG fractional laser ablation technology

The aim of the study was (i) to investigate the feasibility of using fractional laser ablation to create micropore arrays in order to deliver proteins into and across the skin and (ii) to demonstrate how transport rates could be controlled by variation of poration and formulation conditions. Four proteins with very different structures and properties were investigated - equine heart cytochrome c (Cyt c; 12.4 kDa), recombinant human growth hormone expressed in Escherichia coli (hGH; 22 kDa), urinary follicle stimulating hormone (FSH; 30 kDa) and FITC-labelled bovine serum albumin (FITC-BSA; 70 kDa). The transport experiments were performed using a scanning Er:YAG diode pumped laser (P.L.E.A.S.E.®; Precise Laser Epidermal System). The distribution of FITC-BSA in the micropores following P.L.E.A.S.E.® poration was visualised by using confocal laser scanning microscopy (CLSM). Porcine skin was used for the device parameter and CLSM studies; its validity as a model was confirmed by subsequent comparison with transport of Cyt c and FITC-BSA across P.L.E.A.S.E.® porated human skin. No protein transport (deposition or permeation) was observed across intact skin; however, P.L.E.A.S.E.® poration enabled total delivery after 24h of 48.2±8.9, 8.1±4.2, 0.2±0.1 and 273.3±30.6 μg/cm(2) for Cyt c, hGH, FSH and FITC-BSA, respectively, using 900 pores/135.9 cm(2). Calculation of permeability coefficients showed that there was no linear dependence of transport on molecular weight ((1.6±0.3), (0.1±0.05), (0.08±0.03) and (0.9±0.1)×10(-3) cm/h, for Cyt c, hGH, FSH and FITC-BSA, respectively); indeed, a U-shaped curve was observed. This suggested that molecular weight was not a sufficiently sensitive descriptor and that transport was more likely to be determined by the surface properties of the respective proteins since these would govern interactions with the local microenvironment. Increasing pore density (i.e. the number of micropores per unit area) had a statistically significant effect on the cumulative permeation of both Cyt c (at 100, 150, 300 and 600 pores/cm(2), permeation was 11.2±2.4, 15.3±11.8, 33.8±10.5 and 51.2±15.8 4 μg/cm(2), respectively) and FITC-BSA (at 50, 100, 150 and 300 pores/cm(2), it was 58.5±15.3, 132.6±40.0, 192.7±24.4, 293.3±76.5 μg/cm(2), respectively). Linear relationships were established in both cases. However, only the delivery of FITC-BSA was improved upon increasing fluence (53.3±22.5, 293.3±76.5, 329.6±11.5 and 222.1±29.4 μg/cm(2) at 22.65, 45.3, 90.6 and 135.9 J/cm(2), respectively). The impact of fluence - and hence pore depth - on transport will depend on the relative diffusivities of the protein in the micropore and in the 'bulk' epidermis/dermis. Experiments with Cyt c and FSH confirmed that delivery was dependent upon concentration, and it was shown that therapeutic delivery of the latter was feasible. Cumulative permeation of Cyt c and FITC-BSA was also shown to be statistically equivalent across porcine and human skin. In conclusion, it was demonstrated that laser microporation enabled protein delivery into and across the skin and that this could be modulated via the poration parameters and was also dependent upon the concentration gradient in the pore. However, the role of protein physicochemical properties and their influence on transport rates remains to be elucidated and will be explored in future studies.

Development and validation of an analytical method for the quantification of cytochrome c in skin transport studies

A simple isocratic HPLC method for the quantification of Cytochrome c in skin permeation samples was developed and validated. The mobile phase comprised a 41 : 59 mixture of an organic phase A (0.1% trifluoroacetic acid in a 90 : 10 mixture of MeCN-H(2)O) and an aqueous phase B (0.1% trifluoroacetic acid in H(2)O). The Cytochrome c retention and run times were 2.62 and 8.0 min, respectively--much shorter than those for existing gradient methods. The response was accurate, precise and linear from 2.5 to 25 microg/mL. The mean recoveries for intra-day and inter-day analysis ranged from 88.5 to 103.8% and the RSD varied from 0.05 to 1.55%. The assay was used to quantify transport of Cytochrome c across intact and laser-microporated porcine skin in vitro. Cytochrome c permeation and the amount of protein retained within the membrane over 24 h were quantified as a function of the number of micropores. Although no Cytochrome c permeation was observed across intact skin, laser microporation enabled delivery of 22.9 +/- 3.3 and 56.0 +/- 15.9 microg/cm(2) of the protein across skin samples with 300 and 1800 micropores, respectively. In conclusion, the HPLC method provided a fast, efficient means to quantify Cytochrome c in samples from skin transport studies.

Molecular charge mediated transport of a 13 kD protein across microporated skin

Transport of proteins across the skin is highly limited owing to their hydrophilic nature and large molecular size. This study was conducted to assess the skin transport abilities of a model protein across hairless rat skin during iontophoresis alone and in combination with microneedles as a function of molecular charge. The effect of microneedle pretreatment on electroosmotic flow was also investigated. Skin permeation experiments were carried out in vitro using daniplestim (DP) (MW, 12.76 kD; isoelectric point, 6.2) as a model protein molecule. The effect of molecular charge on protein transport was evaluated by performing studies in two different buffers--TRIS (pH 7.5) and acetate (pH 4.0). Iontophoretic transport mechanisms of DP varied with respect to molecular charge on the protein. The combination approach (iontophoresis and microneedles) gave much higher flux values compared to iontophoresis alone at both pH 4.0 and pH 7.5, however, the delivery in this case was also found to be charge dependent. The findings of this study indicate that electroosmosis persisted upon microporation, thus retaining skin's permselective properties. This enables us to explore the combination of microneedles and iontophoresis as a potential approach for delivery of proteins.