Effect of charge and molecular weight on transdermal peptide delivery by iontophoresis

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.

Strategies for transportation of peptides across the skin for treatment of multiple diseases

An established view in genetic engineering dictates an increase in the discovery of therapeutic peptides to enable the treatment of multiple diseases. The use of hypodermic needle for delivery of proteins and peptides occurs due to the hydrophilic nature, sensitivity toward proteolytic enzymes and high molecular weight. The non-invasive nature of the transdermal delivery technique offers multiple advantages over the invasive route to release drugs directly into the systemic circulation to enhance bioavailability, better patient compliance, reduced toxicity and local irritability. The transdermal route seems highly desirable from the pharmaco-therapeutic and patient compliance point of view, however, the lipophilic barrier of skin restricts the application. The use of several techniques like electrical methods (iontophoresis, sonophoresis etc.), chemical penetration enhancers (e.g. protease inhibitors, penetration enhancers, etc.) and nanocarriers (dendrimers, lipid nanocapsules, etc.) are utilized to improve the passage of drug molecules across the biomembranes. Additionally, such clinical interventions facilitate the physicochemical characteristics of peptides, to enable effective preservation, conveyance and release of therapeutic agents. Moreover, strategies ensure the attainment of the intended targets and enhance treatment outcomes for multiple diseases. This review article focuses on the techniques of peptide transportation across the skin to advance the delivery approaches and therapeutic efficiency.

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

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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

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Enhanced topical paromomycin delivery for cutaneous leishmaniasis treatment: Passive and iontophoretic approaches

Conventional treatments for cutaneous leishmaniasis, a neglected vector-borne infectious disease, can frequently lead to serious adverse effects. Paromomycin (PAR), an aminoglycoside antibiotic, has been suggested for the topical treatment of disease-related lesions, but even when formulated in high drug-loading dosage forms, presents controversial efficacy. The presence of five ionizable amino groups hinder its passive cutaneous penetration but make PAR an excellent candidate for iontophoretic delivery. The objective of this study was to verify the feasibility of using iontophoresis for cutaneous PAR delivery and to propose a topical passive drug delivery system that could be applied between iontophoretic treatments. For this, in vitro iontophoretic experiments evaluated different application durations (10, 30, and 360 min), current densities (0.1, 0.25, and 0.5 mA/cm2), PAR concentrations (0.5 and 1.0 %), and skin models (intact and impaired porcine skin). In addition, 1 % PAR hydrogel had its penetration profile compared to 15 % PAR ointment in passive transport. Results showed iontophoresis could deliver suitable PAR amounts to dermal layers, even in short times and with impaired skin. Biodistribution assays showed both iontophoretic transport and the proposed hydrogel delivered higher PAR amounts to deeper skin layers than conventional ointment, even though applying 15 times less drug. To our knowledge, this is the first report of PAR drug delivery enhancement by iontophoresis. In summary, the association of iontophoresis with a topical application of PAR gel seems appropriate for improving cutaneous leishmaniasis treatment.

Peptide-containing nanoformulations: Skin barrier penetration and activity contribution

Transdermal drug delivery presents a less invasive pathway, circumventing the need to pass through the gastrointestinal tract and liver, thereby reducing drug breakdown, initial metabolism, and gastrointestinal discomfort. Nevertheless, the unique composition and dense structure of the stratum corneum present a significant barrier to transdermal delivery. This article presents an overview of the current developments in peptides and nanotechnology to address this challenge. Initially, we sum up peptide-containing nanoformulations for transdermal drug delivery, examining them through the lenses of both inorganic and organic materials. Particular emphasis is placed on the diverse roles that peptides play within these nanoformulations, including conferring functionality upon nanocarriers and enhancing the biological efficacy of drugs. Subsequently, we summarize innovative strategies for enhancing skin penetration, categorizing them into passive and active approaches. Lastly, we discuss the therapeutic potential of peptide-containing nanoformulations in addressing a range of diseases, drawing insights from the biological activities and functions of peptides. Furthermore, the challenges hindering clinical translation are also discussed, providing valuable insights for future advancements in transdermal drug delivery.

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.

Anti-inflammatory ethosomal nanoformulation in combination with iontophoresis in chronic wound healing: An ex vivo study

Prescription of anti-inflammatory drugs may be considered as a promising strategy in chronic wound healing where the inflammatory disturbance has delayed the healing process. It seems that hydrocortisone 17-butyrate (HB17) would be promising in the form of a nano-formulation to enhance drug delivery efficacy. In the present study, transdermal delivery of nano-HB17 in combination with iontophoresis was investigated ex vivo. Ethosomal-HB17 was synthesised using lecithin, ethanol and cholesterol with a different ratio by hot method. The negative ethosomal-HB17 particle size was around 244 ± 4.3 nm with high stability of up to 30 days. Additionally, evaluated entrapment efficiency of HB17 in ethosomes by high performance liquid chromatography was 40.6 ± 2.21%. Moreover, the permeation speed and amount of H17B in complete-thickness rat skin in the presence and absence of iontophoresis showed that the penetration of free H17B and ethosomal-H17B formulations were zero and 7.98 μg/cm² in 120 min, respectively. Whereas in the case of applying iontophoresis, permeation amount obtained was zero and 19.69 μg/cm² in 30 min in free H17B and ethosomal-H17B formulations, respectively. It has been concluded that transdermal delivery of ethosomal-H17B is an effective strategy to enhance drug delivery and it will be improved when it is combined with iontophoresis.

The Emerging Role of Topical Ocular Drugs to Target the Posterior Eye

The prevalence of chronic fundus diseases is increasing with the aging of the general population. The treatment of these intraocular diseases relies on invasive drug delivery because of the globular structure and multiple barriers of the eye. Frequent intraocular injections bring heavy burdens to the medical care system and patients. The use of topical drugs to treat retinal diseases has always been an attractive solution. The fast development of new materials and technologies brings the possibility to develop innovative topical formulations. This article reviews anatomical and physiological barriers of the eye which affect the bioavailability of topical drugs. In addition, we summarize innovative topical formulations which enhance the permeability of drugs through the ocular surface and/or extend the drug retention time in the eye. This article also reviews the differences of eyes between different laboratory animals to address the translational challenges of preclinical models. The fast development of in vitro eye models may provide more tools to increase the clinical translationality of topical formulations for intraocular diseases. Clinical successes of topical formulations rely on continuous and collaborative efforts between different disciplines.

Synthesis, characterization, and evaluation of novel cell-penetrating peptides based on TD-34

In this study, six N-1, N-2, or N-11 derivatives of TD-34 (a cationic cyclic cell-penetrating peptide [CPP], ACSSKKSKHCG) were designed and synthesized including both linear peptides and cyclic peptides, such as DL-1 (KWSSKKSKHCG), DLCC-1 (cyclopeptide, KWSSKKSKHCG), DL-2 (KWSSKKSKHCG-NH₂ ), DLCC-2 (cyclopeptide, KWSSKKSKHCG-NH₂ ), DL-3 (RWSSKKSKHCG), and DLCC-3 (cyclopeptide, RWSSKKSKHCG). The cyclic peptides were synthesized by disulfide bound linkages formed by N-2 and N-10 cysteine. In vitro penetration experiment was conducted to investigate the transdermal enhancement ability of these derivatives, using triptolide (TP) as model drug. The results display that at the presence of DLCC-2, the accumulative penetration amount of TP increased 1.71-fold (P < .05) within 12 hours, displaying better transdermal enhancing ability than TD-34. Meanwhile, DL-3 and DLCC-3 slightly decreased the transdermal delivery of TP, and the presence of DL-1 and DLCC-1 shows no obvious effect. In order to clarify the factors on the transdermal ability of peptides, the solubility of TP in phosphate buffer saline (PBS) at the presence of different peptides and the mechanism of transdermal delivery of CPPs was investigated. The result shows that most of these peptides have no significant effect on the solubility of TP except DLCC-3 (the solubility of TP slightly increased). And in order to investigate transdermal absorption route of DLCC-2, polyarginine linked to rhodamine b (Rh b) derivative is used. The result proved that the transdermal route of polyarginine is via hair follicle, which may change the transdermal route of its cargo molecule (TP). Our group previously proved that polyarginine and TD-34 have similar transdermal enhancing mechanism (changing the transdermal route of their cargo molecule); it is reasonably speculated that the transdermal route of DLCC-2 is the same as polyarginine and then changes the transdermal absorption route of TP. Furthermore, such results have laid a solid foundation for further investigation of CPPs and paved a way for both designing and synthesizing of new drug delivery system for therapy molecules.

Controlled Iontophoretic Delivery in Vitro and in Vivo of ARN14140-A Multitarget Compound for Alzheimer's Disease

ARN14140 is a galantamine-memantine conjugate that acts upon both cholinergic and glutamatergic pathways for better management of Alzheimer's disease. Poor oral bioavailability and pharmacokinetics meant that earlier preclinical in vivo studies employed intracerebroventricular injection to administer ARN14140 directly to the brain. The aim of the present study was to evaluate the feasibility of using constant current transdermal iontophoresis for the noninvasive systemic delivery of ARN14140 and to quantify the amounts present in the blood and the brain. Preliminary experiments in vitro were performed using porcine skin and validated with human skin. Cumulative ARN14140 permeation across the skin increased linearly with current density and concentration. Delivery efficiency (i.e., fraction of the amount applied that is delivered) reached an exceptional 76.9%. Statistically equivalent delivery was observed after iontophoresis across human and porcine skin. In vivo studies in male Wistar rats showed that iontophoretic transport of ARN14140 could be controlled using the current density (426.7 ± 42 and 1118.3 ± 73 nmol/cm² at 0.15 and 0.5 mA/cm² for 6 h) and demonstrated that transdermal iontophoresis was able to deliver ARN14140 noninvasively to the brain. This is the first report quantifying drug levels in the blood and the brain following transdermal iontophoresis.

Potential of iontophoresis as a drug delivery method for midazolam in pediatrics

Drug delivery to the neonatal and premature pediatric populations is very challenging. This research assessed the potential of delivering midazolam by transdermal iontophoresis as an alternative strategy in pediatric therapy. In vitro experiments used intact and tape-stripped porcine skin as models for the skin barrier function of full-term and premature newborns, respectively. Midazolam transdermal transport was significantly enhanced by applying higher currents, increasing the formulation pH, and optimizing the drug's mole fraction in the vehicle. When the skin barrier was decreased to half of its baseline competence, the passive permeation of midazolam increased by approximately 60-fold; and complete stratum corneum removal led to an additional 20-fold enhancement in permeation. Iontophoresis retained control of the drug transport trough partially compromised skin. However, a very high passive contribution undermined the iontophoretic control when the barrier was fully compromised. Overall, midazolam delivery could be rate-controlled by iontophoresis in most circumstances, and therapeutically useful fluxes could be achieved.

Controlled non-invasive iontophoretic delivery of triamcinolone acetonide amino acid ester prodrugs into the posterior segment of the eye

This study investigated short duration transscleral iontophoretic delivery of four triamcinolone acetonide (TA) amino acid ester prodrugs (TA-AA) (alanine, Ala; arginine, Arg; isoleucine, Ile and lysine, Lys) using whole porcine eyes globes in vitro. Post-iontophoretic biodistribution of TA was quantified by UHPLC-MS/MS in the different ocular compartments (cornea, aqueous humor, sclera, ciliary body, choroid and retinal pigmented epithelium (RPE), neural retina and vitreous humor). Transscleral iontophoresis (3 mA/cm² for 10 min) increased total drug delivery of the TA-AA prodrugs by 14-30-fold as compared to passive diffusion. The TA-AA prodrugs had distinct biodistribution profiles - the penetration depth achieved was dependent on their physicochemical properties (e.g. lipophilicity for TA-Ile) and susceptibility to hydrolysis (e.g. TA-Arg). Intraocular drug distribution was also influenced by prodrug binding to melanin (TA-Lys). Interestingly, under conditions of equivalent charge (6 mA/cm² for 5 min vs. 1.5 mA/cm² for 20 min, i.e. 1.44 C respectively) the longer duration (20 min) at lower current density resulted in ∼6 times more TA delivery into the vitreous humor. Overall, the study provided further evidence of the potential of transscleral iontophoresis for the non-invasive treatment of posterior segment inflammatory diseases.

Modulation of Electroosmotic Flow through Skin: Effect of Poly(Amidoamine) Dendrimers

The objective of this work is to evaluate the effect of polyamidoamine (PAMAM) dendrimers on electroosmotic flow (EOF) through skin. The effect of size and concentration of dendrimer was studied, using generation 1, 4 and 7 dendrimer (G1, G4 and G7, respectively). As a marker molecule for the direction and magnitude of EOF, a neutral molecule, acetoaminophen (AAP) was used. The visualization of dendrimer permeation into the current conducting pore (CCP) of skin was made using G4-fluorescein isothiocyanate (FITC) conjugate and confocal microscopy. Without dendrimer, anodal flux of AAP was much higher than cathodal or passive flux. When G1 dendrimer was added, anodal flux decreased, presumably due to the decrease in EOF by the association of G1 dendrimer with net negative charge in CCP. As the generation increased, larger decrease in anodal flux was observed, and the direction of EOF was reversed. Small amount of methanol used for the preparation of dendrimer solution also contributed to the decrease in anodal flux of AAP. Cross-sectional view perpendicular to the skin surface by confocal laser scanning microscope (CLSM) study showed that G4 dendrimer-FITC conjugate (G4-FITC) can penetrate into the viable epidermis and dermis under anodal current. The permeation route seemed to be localized on hair follicle region. These results suggest that PAMAM dendrimers can permeate into CCP and change the magnitude and direction of EOF. Overall, we obtained a better understanding on the mechanistic insights into the electroosmosis phenomena and its role on flux during iontophoresis.

NO Exchange for a Water Molecule Favorably Changes Iontophoretic Release of Ruthenium Complexes to the Skin

Ruthenium (Ru) complexes have been studied as promising anticancer agents. Ru nitrosyl complex (Ru-NO) is one which acts as a pro-drug for the release of nitric oxide (NO). The Ru-aqueous complex formed by the exchange of NO for a water molecule after NO release could also possess therapeutic effects. This study evaluates the influence of iontophoresis on enhancing the skin penetration of Ru-NO and Ru-aqueous and assesses its applicability as a tool in treating diverse skin diseases. Passive and iontophoretic (0.5 mA·cm⁻²) skin permeation of the complexes were performed for 4 h. The amount of Ru and NO in the stratum corneum (SC), viable epidermis (VE), and receptor solution was quantified while the influence of iontophoresis and irradiation on NO release from Ru-NO complex was also evaluated. Iontophoresis increased the amount of Ru-NO and Ru-aqueous recovered from the receptor solution by 15 and 400 times, respectively, as compared to passive permeation. Iontophoresis produced a higher accumulation of Ru-aqueous in the skin layers as compared to Ru-NO. At least 50% of Ru-NO penetrated the SC was stable after 4 h. The presence of Ru-NO in this skin layer suggests that further controlled release of NO can be achieved by photo-stimulation after iontophoresis.

Epirubicin-loaded superparamagnetic iron-oxide nanoparticles for transdermal delivery: cancer therapy by circumventing the skin barrier

The transdermal administration of chemotherapeutic agents is a persistent challenge for tumor treatments. A model anticancer agent, epirubicin (EPI), is attached to functionalized superparamagnetic iron-oxide nanoparticles (SPION). The covalent modification of the SPION results in EPI-SPION, a potential drug delivery vector that uses magnetism for the targeted transdermal chemotherapy of skin tumors. The spherical EPI-SPION composite exhibits excellent magnetic responsiveness with a saturation magnetization intensity of 77.8 emu g(-1) . They feature specific pH-sensitive drug release, targeting the acidic microenvironment typical in common tumor tissues or endosomes/lysosomes. Cellular uptake studies using human keratinocyte HaCaT cells and melanoma WM266 cells demonstrate that SPION have good biocompatibility. After conjugation with EPI, the nanoparticles can inhibit WM266 cell proliferation; its inhibitory effect on tumor proliferation is determined to be dose-dependent. In vitro transdermal studies demonstrate that the EPI-SPION composites can penetrate deep inside the skin driven by an external magnetic field. The magnetic-field-assisted SPION transdermal vector can circumvent the stratum corneum via follicular pathways. The study indicates the potential of a SPION-based vector for feasible transdermal therapy of skin cancer.

Overcoming the challenges in administering biopharmaceuticals: formulation and delivery strategies

The formulation and delivery of biopharmaceutical drugs, such as monoclonal antibodies and recombinant proteins, poses substantial challenges owing to their large size and susceptibility to degradation. In this Review we highlight recent advances in formulation and delivery strategies--such as the use of microsphere-based controlled-release technologies, protein modification methods that make use of polyethylene glycol and other polymers, and genetic manipulation of biopharmaceutical drugs--and discuss their advantages and limitations. We also highlight current and emerging delivery routes that provide an alternative to injection, including transdermal, oral and pulmonary delivery routes. In addition, the potential of targeted and intracellular protein delivery is discussed.

Controlled iontophoretic delivery of pramipexole: electrotransport kinetics in vitro and in vivo

The objective of the study was to investigate the anodal iontophoretic delivery of pramipexole (PRAM), a dopamine agonist used for the treatment of Parkinson's disease, in order to determine whether therapeutic amounts of the drug could be delivered across the skin. Preliminary iontophoretic experiments were performed in vitro using porcine ear and human abdominal skin. These were followed by a pharmacokinetic study in male Wistar rats to determine the drug input rate in vivo. Stability studies revealed that after current application (0.5 mA/cm(2) for 6h), the solution concentration of PRAM was only 60.2 ± 5.3% of its initial value. However, inclusion of sodium metabisulfite (0.5%), an antioxidant, increased this to 97.2 ± 3.1%. Iontophoretic transport of PRAM across porcine skin in vitro was studied as a function of current density (0.15, 0.3, 0.5 mA/cm(2)) and concentration (10, 20, 40 mM). Increasing the current density from 0.15 to 0.3 and 0.5 mA/cm(2), resulted in 2.5- and 4-fold increases in cumulative permeation, from 309.5 ± 80.2 to 748.8 ± 148.1 and 1229.1 ± 138.6 μg/cm(2), respectively. Increasing the PRAM concentration in solution from 10 to 20 and 40 mM resulted in a 2-fold increase in cumulative permeation (816.4 ± 123.3, 1229.1 ± 138.6 and 1643.6 ± 201.3 μg/cm(2), respectively). Good linearity was observed between PRAM flux and both the applied current density (r(2)=0.98) and drug concentration in the formulation (r(2)=0.99). Co-iontophoresis of acetaminophen showed that electromigration was the dominant electrotransport mechanism (accounting for >80% of delivery) and that there was no inhibition of electroosmotic flow at any current density. Cumulative iontophoretic permeation across human and porcine skin (after 6h at 0.5 mA/cm(2)) was also shown to be statistically equivalent (1229.1 ± 138.6 and 1184.8 ± 236.4 μg/cm(2), respectively). High transport and delivery efficiencies were achieved for PRAM (up to 7% and 58%, respectively). The plasma concentration profiles obtained in the iontophoretic studies in vivo (20 mM PRAM; 0.5 mA/cm(2) for 5h) were modelled using constant and time-variant input models; the latter gave a superior quality fit. The drug input rate in vivo suggested that PRAM electrotransport rates would be sufficient for therapeutic delivery and the management of Parkinsonism.

Controlled iontophoretic transport of huperzine A across skin in vitro and in vivo: effect of delivery conditions and comparison of pharmacokinetic models

The aim of this study was to investigate constant current anodal iontophoresis of Huperzine A (HupA) in vitro and in vivo and hence to evaluate the feasibility of using electrically assisted delivery to administer therapeutic amounts of the drug across the skin for the treatment of Alzheimer's disease. Preliminary experiments were performed using porcine and human skin in vitro. Stability studies demonstrated that HupA was not degraded upon exposure to epidermis or dermis for 12 h and that it was also stable in the presence of an electric current (0.5 mA · cm(-2)). Passive permeation of HupA (2 mM) was minimal (1.1 ± 0.1 μg · cm(-2)); iontophoresis at 0.15, 0.3, and 0.5 mA · cm(-2) produced 106-, 134-, and 184-fold increases in its transport across the skin. Surprisingly, despite the use of a salt bridge to isolate the formulation compartment from the anodal chamber, which contained 133 mM NaCl, iontophoresis of HupA was shown to increase linearly with its concentration (1, 2, and 4 mM in 25 mM MES, pH 5.0) (r(2) = 0.99). This was attributed to the low ratio of drug to Cl¯ (in the skin and in the receiver compartment) which competed strongly to carry current, its depletion, and to possible competition from the zwitterionic MES. Co-iontophoresis of acetaminophen confirmed that electromigration was the dominant electrotransport mechanism. Total delivery across human and porcine skin was found to be statistically equivalent (243.2 ± 33.1 and 235.6 ± 13.7 μg · cm(-2), respectively). Although the transport efficiency was ∼ 1%, the iontophoretic delivery efficiency (i.e., the fraction of the drug load delivered) was extremely high, in the range of 46-81% depending on the current density. Cumulative permeation of HupA from a Carbopol gel formulation after iontophoresis for 6 h at 0.5 mA · cm(-2) was less than that from solution (135.3 ± 25.2 and 202.9 ± 5.2 μg · cm(-2), respectively) but sufficient for therapeutic delivery. Pharmacokinetic parameters were determined in male Wistar rats in vivo (4 mM HupA; 0.5 mA · cm(-2) for 5 h with Ag/AgCl electrodes) using two-compartment models with either constant or time-variant input rates. A superior fit was obtained using the time-variant model, and the input rate in vivo was significantly greater than that in vitro. Based on these results and the known pharmacokinetics, it was estimated that therapeutic amounts of HupA could be delivered for the treatment of Alzheimer's disease using a reasonably sized patch.

Laser-assisted topical drug delivery by using a low-fluence fractional laser: imiquimod and macromolecules

The aim of this study was to evaluate the ability of a low-fluence fractional erbium:yttrim-aluminum-garnet (Er:YAG) laser, with a wavelength of 2940 nm, for enhancing and controlling the skin permeation of imiquimod and macromolecules such as polypeptides and fluorescein isothiocyanate (FITC)-labeled dextran (FD). The in vitro permeation has been determined using a Franz diffusion cell, with porcine skin and nude mouse skin as the barriers. Hyperproliferative and ultraviolet (UV)-irradiated skins were also used as barrier models to mimic the clinical therapeutic conditions. Confocal laser scanning microscopy (CLSM) was used to examine the in vivo nude mouse skin uptake of peptide, FITC, and FD. Both in vitro and in vivo results indicated an improvement in permeant skin delivery by the laser. The laser fluence and number of passes were found to play important roles in controlling drug transport. Increases of 46- and 127-fold in imiquimod flux were detected using the respective fluences of 2 and 3 J/cm(2) with 4 pulses. An imiquimod concentration of 0.4% from aqueous vehicle with laser treatment was sufficient to approximate the flux from the commercial cream with an imiquimod dose of 5% without laser treatment, indicating a reduction of the drug dose by 125-fold. The enhancement of peptide permeation was size and sequence dependent, with the smaller molecular weight (MW) and more-hydrophilic entities showing greater enhancing effect. Skin permeation of FD with an MW of at least 150 kDa could be achieved with fractional laser irradiation. CLSM images revealed intense green fluorescence from the permeants after exposure of the skin to the laser. The follicular pathway was significant in laser-assisted permeation.

Noninvasive and efficient transdermal delivery of CpG-oligodeoxynucleotide for cancer immunotherapy

Oligodeoxynucleotides containing unmethylated cytosine-phosphate-guanosine motifs (CpG-ODN) possess immunostimulatory effects and potential antitumor activity. Since the skin is an easily available site of administration of CpG-ODN due to its accessibility and the presence of abundant antigen presenting cells, it is expected that the application of CpG-ODN to the skin would induce systemic immune response and antitumor activity. However, it is difficult to deliver hydrophilic macromolecules including CpG-ODN through the skin. We have previously demonstrated that small interfering RNA (siRNA) was efficiently delivered into rat epidermis by iontophoresis. In this report, we investigate the effect of transdermal iontophoretic delivery of CpG-ODN on the induction of immune responses and antitumor activity against B16F1 melanoma in mice. Iontophoresis promoted CpG-ODN delivery into the epidermis and dermis. Furthermore, iontophoretic delivery of CpG-ODN to the skin induced the expression of proinflammatory and Th1-type cytokines in the skin and draining lymph node. Finally, transdermal iontophoretic delivery of CpG-ODN led to antitumor activity against B16F1 melanoma. Interestingly, the CpG-ODN administration site is not restricted to the tumor area. In conclusion, CpG-ODN delivered transdermally induced potent antitumor activity, and our system is expected to serve as a simple and noninvasive approach for cancer immunotherapy.

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.

A fast screening strategy for characterizing peptide delivery by transdermal iontophoresis

Capillary zone electrophoresis (CZE) is a convenient experimental tool for mimicking the low-throughput in vitro skin model used to optimize the delivery of peptides by transdermal iontophoresis. This paper is devoted to the extraction of pertinent molecular parameters from CZE experiments at different pH values, the optimization of CZE experimental conditions, and the development of an in silico filter useful for drug design and development. The effective mobility (mu(eff)) of ten model dipeptides was measured by CZE at different pH values, enabling to determine their pK(a) values, charge and mu(eff) at any pH. The best linear correlation between the electromigration contribution to transdermal iontophoretic flux (J(EM)) measured across porcine skin with donor and acceptor compartments at pH 7.4 and charge/MW ratio was obtained at pH 6.5, which seems to be the most suitable pH to mimic the in vitro skin model. Therefore, the experimental strategy can be considerably shortened by using a single mu(eff) measurement at pH 6.5 as a predictor of J(EM). Additionally, pK(a) prediction software packages offer a fast access to charge/MW ratio using consensual molecular charges at pH 6.5, which suggests that this simple in silico filter can be used as a preliminary estimation of J(EM).

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

PURPOSE

To demonstrate the transdermal iontophoretic delivery of a small (12.4 kDa) protein across intact skin.

MATERIALS AND METHODS

The iontophoretic transport of Cytochrome c (Cyt c) across porcine ear skin in vitro was investigated and quantified by HPLC. The effect of protein concentration (0.35 and 0.7 mM), current density (0.15, 0.3 or 0.5 mA.cm(-2) applied for 8 h) and competing ions was evaluated. Co-iontophoresis of acetaminophen was employed to quantify the respective contributions of electromigration (EM) and electroosmosis (EO).

RESULTS

The data confirmed the transdermal iontophoretic delivery of intact Cyt c. Electromigration was the principal transport mechanism, accounting for approximately 90% of delivery; correlation between EM flux and electrophoretic mobility was consistent with earlier results using small molecules. Modest EO inhibition was observed at 0.5 mA.cm(-2). Cumulative permeation at 0.3 and 0.5 mA.cm(-2) was significantly greater than that at 0.15 mA.cm(-2); fluxes using 0.35 and 0.7 mM Cyt c in the absence of competing ions (J ( tot ) = 182.8 +/- 56.8 and 265.2 +/- 149.1 microg.cm(-2).h(-1), respectively) were statistically equivalent. Formulation in PBS (pH 8.2) confirmed the impact of competing charge carriers; inclusion of approximately 170 mM Na(+) resulted in a 3.9-fold decrease in total flux.

CONCLUSIONS

Significant amounts ( approximately 0.9 mg.cm(-2) over 8 h) of Cyt c were delivered non-invasively across intact skin by transdermal electrotransport.

Assembled microneedle arrays enhance the transport of compounds varying over a large range of molecular weight across human dermatomed skin

In this study, we demonstrate the feasibility to use microneedle arrays manufactured from commercially available 30G hypodermal needles to enhance the transport of compounds up to a molecular weight of 72 kDa. Piercing of human dermatomed skin with microneedle arrays was studied by Trypan Blue staining on the SC side of the skin and transepidermal water loss measurements (TEWL). Passive transport studies were conducted with Cascade Blue (CB, Mw 538), Dextran-Cascade Blue (DCB, Mw 10 kDa), and FITC coupled Dextran (FITC-Dex, Mw 72 kDa). Microneedle arrays with needle lengths of 900, 700 and 550 micro m are able to pierce dermatomed human skin as evident from (a) the appearance of blue spots on the dermal side of the skin after Trypan Blue treatment and (b) elevated TEWL levels after piercing compared to non-treated human dermatomed skin. Microneedles with a length of 300 micro m did not pierce human skin in vitro. Transport studies performed with model compounds ranging from 538 Da to 72 kDa revealed that pretreatment with microneedle arrays enhanced the transport across dermatomed human skin. However, some degradation was also observed for FITC-Dex and DCB. We conclude that assembled microneedle arrays can be used to deliver compounds through the skin up to a molecular weight of at least 72 kDa.

Topical Iontophoresis of Valaciclovir Hydrochloride Improves Cutaneous Aciclovir Delivery

PURPOSE

To investigate the topical iontophoresis of valaciclovir (VCV) as a means to improve cutaneous aciclovir (ACV) delivery.

METHODS

ACV and VCV electrotransport experiments were conducted using excised porcine skin in vitro.

RESULTS

While the charged nature of the prodrug, VCV, enabled it to be more efficiently iontophoresed into the skin than the parent molecule, ACV, only the latter was detectable in the receptor chamber, suggesting that VCV was enzymatically cleaved into the active metabolite during skin transit. Iontophoresis of VCV was significantly more efficient than that of ACV; the cumulative permeation of ACV after 1, 2 and 3 h of VCV iontophoresis at 0.5 mA cm(-2) and using an aqueous 2 mM (approximately 0.06%) formulation was 20+/-10, 104+/-47 and 194+/- 82 microg cm( -2), respectively (cf. non-quantifiable levels, 0.1 and 1.0+/-0.7 microg cm(-2) after ACV iontophoresis).

CONCLUSIONS

These delivery rates provide ample room to reduce either current density or the duration of current application. Preliminary in vitro data serve to emphasize the potential of VCV iontophoresis to improve the topical therapy of cutaneous herpes simplex infections and merit further investigation to demonstrate clinical efficacy.

Capillary zone electrophoresis for the estimation of transdermal iontophoretic mobility

The objective of the study was to investigate the relationship between transdermal iontophoretic flux--specifically, the electromigratory component--and electrophoretic mobility as determined by capillary zone electrophoresis (CZE). First, the steady-state iontophoretic transport rates of a series of dipeptides across porcine skin were determined in vitro. Co-iontophoresis of acetaminophen was used to quantify the respective contributions of electroosmosis (EO) and electromigration (EM). Second, the electrophoretic mobilities of the dipeptides and three other cationic drugs (lidocaine, propranolol, and quinine) were determined, under equivalent experimental conditions, using CZE. Analysis of the transport data using the results of the CZE experiments revealed a linear dependence (r2 > 0.9) between EM flux and electrophoretic mobility. The CZE measurements also provided insight into the charge state of "zwitterionic" dipeptides, H-Glu-epsilon-Lys-OH and H-Tyr-Gln-OH, revealing that these molecules had partial net negative charges under the formulation conditions, accounting for the absence of anodal iontophoretic delivery. The results suggest that CZE might (i) enable identification of ionization states of complex molecules, (ii) serve as a preliminary screen to identify electrically mobile compounds suitable for iontophoretic delivery, and (iii) prove useful for predicting the EM contribution to transdermal iontophoretic flux.