Ultrasound and transdermal drug delivery

Current challenges in non-invasive insulin delivery systems: a comparative review

The quest to eliminate the needle from insulin delivery and to replace it with non- or less-invasive alternative routes has driven rigorous pharmaceutical research to replace the injectable forms of insulin. Recently, various approaches have been studied involving many strategies using various technologies that have shown success in delivering insulin, which are designed to overcome the inherent barriers for insulin uptake across the gastrointestinal tract, mucosal membranes and skin. This review examines some of the many attempts made to develop alternative, more convenient routes for insulin delivery to avoid existing long-term dependence on multiple subcutaneous injections and to improve the pharmacodynamic properties of insulin. In addition, this article concentrates on the successes in this new millennium in developing potential non-invasive technologies and devices, and on major new milestones in modern insulin delivery for the effective treatment of diabetes.

Potential application of Metolose in a thermoresponsive transdermal therapeutic system

The purpose of the present study was to formulate a novel thermoresponsive membrane controlled therapeutic system from Metolose for possible transdermal application. Metolose gel shows thermal gelation property, which can be characterized by two (T(1), T(2)) temperatures. A sharp decrease of viscosity can be measured at T(1), but gelation can be observed at T(2). Different types of Metolose polymers were compared considering their thermoresponsive behaviour. Only thermal gelation was observed in the case of Metolose SM, while Metolose SH showed a sudden decrease of viscosity at T(1). Since this temperature is above the body temperature, so it should be shifted to the skin temperature in case of possible transdermal application. Modulation of thermoresponsibility was followed by rheological method, and the thermoresponsive drug release from Metolose gel was studied by static liberation test. Our results demonstrated that the effect of different salts (NaCl, NaHCO(3), KCl) of various concentrations in Metolose SH gel reduced T(1) to the skin temperature, which enabled enhanced drug release.

Investigation into the potential of low-frequency ultrasound facilitated topical delivery of Cyclosporin A

The potential for low-frequency ultrasound facilitated topical transport of Cyclosporin A was investigated using rat skin. Studies of intensity and exposure time acting on the deposition of Cyclosporin A into deeper skin of in vitro sonophoresis were performed. Low-frequency ultrasound increased the amount of Cyclosporin A retained in the skin only seven times than the passive diffusion. Furthermore, we also tested the synergistic effect of ultrasound and other approaches such as chemical enhancers and electroporation on topical drug delivery of Cyclosporin A. We found that the efficacy of low-frequency ultrasound in enhancing topical delivery could be further increased by pretreatment of skin with chemical enhancers, such as laurocapram (Azone) and sodium lauryl sulfate (SLS). Meanwhile only a small amount was seen to across the full skin into the receiver compartment. Trimodality treatment comprising of pretreatment with Azone+ultrasound in combination followed by electroporation was not effective in enhancing the topical delivery of Cyclosporin A. However, this combination strategy increased the penetration of Cyclosporin A through rat skin by order of 15. The histopathological findings revealed that there was almost no change observed in the structure of skin after ultrasound or combination with ultrasound and enhancers as compared with the control group. In general, the enhanced skin accumulation of Cyclosporin A by the combination of low-frequency ultrasound and chemical enhancers could help significantly to optimize the targeting of the drug without of a concomitant increase of the systemic side effects.

Transdermal delivery system of triamcinolone acetonide from a gel using phonophoresis

Triamcinolone acetonide (TA) is a corticosteroid that is used in the systemic and topical treatment of many inflammatory diseases. In this study, a phonophoretic drug delivery system was designed to enhance the TA permeability and the influence of ultrasound was examined. In order to establish the transdermal delivery system for TA, a hydrophilic carbopol gel containing TA was prepared after adopting phonophoresis. A permeation study through mouse skin was performed at 37 degrees C using a Franz diffusion cell, and the ultrasound treatment was carried out for 10 h. The level of TA permeation through the skin was evaluated under various ultrasound conditions including the frequency (1.0, 3.0 MHz), intensity (1.0, 2.5 W/cm2), and duty cycle (continuous, pulse mode) using a 0.5% TA gel. The highest permeation was observed under the ultrasound treatment conditions of low frequency, high intensity, and in continuous mode.

Cutaneous gene expression of plasmid DNA in excised human skin following delivery via microchannels created by radio frequency ablation

The skin is a valuable organ for the development and exploitation of gene medicines. Delivering genes to skin is restricted however by the physico-chemical properties of DNA and the stratum corneum (SC) barrier. In this study, we demonstrate the utility of an innovative technology that creates transient microconduits in human skin, allowing DNA delivery and resultant gene expression within the epidermis and dermis layers. The radio frequency (RF)-generated microchannels were of sufficient morphology and depth to permit the epidermal delivery of 100 nm diameter nanoparticles. Model fluorescent nanoparticles were used to confirm the capacity of the channels for augmenting diffusion of macromolecules through the SC. An ex vivo human organ culture model was used to establish the gene expression efficiency of a beta-galactosidase reporter plasmid DNA applied to ViaDerm treated skin. Skin treated with ViaDerm using 50 microm electrode arrays promoted intense levels of gene expression in the viable epidermis. The intensity and extent of gene expression was superior when ViaDerm was used following a prior surface application of the DNA formulation. In conclusion, the RF-microchannel generator (ViaDerm) creates microchannels amenable for delivery of nanoparticles and gene therapy vectors to the viable region of skin.

Transdermal protein delivery by a coadministered peptide identified via phage display

Efficient transdermal drug delivery of large hydrophilic drugs is challenging. Here we report that the short synthetic peptide, ACSSSPSKHCG, identified by in vivo phage display, facilitated efficient transdermal protein drug delivery through intact skin. Coadministration of the peptide and insulin to the abdominal skin of diabetic rats resulted in elevated systemic levels of insulin and suppressed serum glucose levels for at least 11 h. Significant systemic bioavailability of human growth hormone was also achieved when topically coadministered with the peptide. The transdermal-enhancing activity of the peptide was sequence specific and dose dependent, did not involve direct interaction with insulin and enabled penetration of insulin into hair follicles beyond a depth of 600 microm. Time-lapse studies suggested that the peptide creates a transient opening in the skin barrier to enable macromolecular drugs to reach systemic circulation.

Ultrasound guided site specific gene delivery system using adenoviral vectors and commercial ultrasound contrast agents

We have evaluated if ultrasound imaging (US) and various commercially available contrast microbubbles can serve as a non-invasive systemically administered delivery vehicle for site-specific adenoviral-mediated gene transfer in vitro and in vivo. The contrast agents were tested for their ability to enclose and to protect an adenoviral vector carrying the GFP marker gene (Ad-GFP) into the microbubbles. We have also evaluated the ability of the innate immune system to inactivate free adenoviruses as well as unenclosed viruses adsorbed on the surface of the contrast agents and in turn the ability of the microbubbles to enclose and to protect the viral vectors from such agents. In vitro as well as in vivo, innate components of the immune system were able to serve as inactivating agents to clear free viral particles and unenclosed adenoviruses adsorbed on the microbubbles' surface. Systemic delivery of Ad-GFP enclosed into microbubbles in the tail vein of nude mice resulted in specific targeting of the GFP transgene. Both fluorescence microscopy and GFP immunohistochemistry demonstrated US guided specific transduction in the targeted cells only, with no uptake in either heart, lungs or liver using complement-pretreated Ad-GFP microbubbles. This approach enhances target specificity of US microbubble destruction as a delivery vehicle for viral-mediated gene transfer.