Noninvasive transdermal delivery of peptides and proteins

Enhancement of Wound Healing Efficacy by Increasing the Stability and Skin-Penetrating Property of bFGF Using 30Kc19α-Based Fusion Protein

The instability of recombinant basic fibroblast growth factor (bFGF) is a major disadvantage for its therapeutic use and means frequent applications to cells or tissues are required for sustained effects. Originating from silkworm hemolymph, 30Kc19α is a cell-penetrating protein that also has protein stabilization properties. Herein, it is investigated whether fusing 30Kc19α to bFGF can enhance the stability and skin penetration properties of bFGF, which may consequently increase its therapeutic efficacy. The fusion of 30Kc19α to bFGF protein increases protein stability, as confirmed by ELISA. 30Kc19α-bFGF also retains the biological activity of bFGF as it facilitates the migration and proliferation of fibroblasts and angiogenesis of endothelial cells. It is discovered that 30Kc19α can improve the transdermal delivery of a small molecular fluorophore through the skin of hairless mice. Importantly, it increases the accumulation of bFGF and further facilitates its translocation into the skin through follicular routes. Finally, when applied to a skin wound model in vivo, 30Kc19α-bFGF penetrates the dermis layer effectively, which promotes cell proliferation, tissue granulation, angiogenesis, and tissue remodeling. Consequently, the findings suggest that 30Kc19α improves the therapeutic functionalities of bFGF, and would be useful as a protein stabilizer and/or a delivery vehicle in therapeutic applications.

Hydration effects on skin microstructure as probed by high-resolution cryo-scanning electron microscopy and mechanistic implications to enhanced transcutaneous delivery of biomacromolecules

Although hydration is long known to improve the permeability of skin, penetration of macromolecules such as proteins is limited and the understanding of enhanced transport is based on empirical observations. This study uses high-resolution cryo-scanning electron microscopy to visualize microstructural changes in the stratum corneum (SC) and enable a mechanistic interpretation of biomacromolecule penetration through highly hydrated porcine skin. Swollen corneocytes, separation of lipid bilayers in the SC intercellular space to form cisternae, and networks of spherical particulates are observed in porcine skin tissue hydrated for a period of 4-10 h. This is explained through compaction of skin lipids when hydrated, a reversal in the conformational transition from unilamellar liposomes in lamellar granules to lamellae between keratinocytes when the SC skin barrier is initially established. Confocal microscopy studies show distinct enhancement in penetration of fluorescein isothiocyanate-bovine serum albumin (FITC-BSA) through skin hydrated for 4-10 h, and limited penetration of FITC-BSA once skin is restored to its natively hydrated structure when exposed to the environment for 2-3 h. These results demonstrate the effectiveness of a 4-10 h hydration period to enhance transcutaneous penetration of large biomacromolecules without permanently damaging the skin.

Transdermal iontophoresis of insulin. Part 1: A study on the issues associated with the use of platinum electrodes on rat skin

We have studied the issues associated with the use of platinum electrodes for transdermal iontophoretic delivery of peptides, using insulin as a model peptide. Insulin permeation was studied using full-thickness rat skin by varying the donor solution pH as a function of electrode polarity. The stability of insulin under the iontophoretic conditions was studied using TLC, SDS-polyacrylamide gel electrophoresis and HPLC. Large pH shifts were observed during anodal iontophoresis (AI), when the donor solution pH was above the isoelectric point of insulin and in cathodal iontophoresis (CI), when the donor solution pH was below the isoelectric point of insulin. The direction and magnitude of electroosmotic flow was influenced by pH of the donor solution and the electrode polarity. On the other hand, the buffer used to maintain the pH governed the contribution of electrorepulsion to the overall transport of insulin. Electrochemical degradation of insulin was significant during Al at pH 7.4. Among the pH investigated, Al of insulin at pH 3.6 and Cl at pH 8.35 were better, as the pH shift was relatively less and electrochemically more stable during iontophoresis as compared with other pH. In summary, the pH shift caused by platinum electrodes had a significant influence on the permeation and stability of insulin.

Enhancement of transdermal drug delivery via synergistic action of chemicals

Transdermal drug delivery is an attractive alternative to conventional techniques for administration of systemic therapeutics. One challenge in designing transdermal drug delivery systems is to overcome the natural transport barrier of the skin. Chemicals offer tremendous potential in overcoming the skin barrier to enhance transport of drug molecules. Individual chemicals are however limited in their efficacy in disrupting the skin barrier at low concentrations and usually cause skin irritation at high concentrations. Multicomponent mixtures of chemicals, however, have been shown to provide high skin permeabilization potency as compared to individual chemicals without necessarily causing irritation. Here we review systems employing synergistic mixtures of chemicals that offer superior skin permeation enhancement. These synergistic systems include solvent mixtures, microemulsions, eutectic mixtures, complex self-assembled vesicles and inclusion complexes. Methods for design and discovery of such synergistic systems are also discussed.

In situ and in vivo efficacy of peroral absorption enhancers in rats and correlation to in vitro mechanistic studies

The present investigation attempts to increase intestinal permeability and hence absorption of biopharmaceutic classification system (BCS) Class III (cefotaxime sodium (CX)) and Class IV (cyclosporin A (CSA)) drugs by employing certain absorption enhancers. Drugs were co-perfused with sodium caprate (SC, 0.25% w/v), piperine (P, 0.004% w/v) and sodium deoxycholate (SD, 1.0% w/v) separately in rat in situ single pass intestinal perfusion model. These additives increased intestinal permeability (P(app)) and absorption rate constant (K(a)) up to two and fourfold, respectively. SC exhibited substantial absorption enhancement of both CX and CSA, while SD and P enhanced absorption of CX and CSA, respectively. Co-administration of SC significantly enhanced peroral bioavailability of CX (from 29.4 +/- 1.7 to 69.6 +/- 3.2) and CSA (from 18.4 +/- 15.6 to 49.6 +/- 25.1) in rats, while P increased bioavailability of CSA (from 18.4 +/- 15.6 to 33.1 +/- 17.7). Transmission electron microscopy of intestinal mucosa revealed that SC and SD act on lipid and protein domains of absorptive membrane. P showed no effect on intestinal P(app) and oral bioavailability of CX but has a profound effect on CSA, a known P-glycoprotein (P-gp) substrate. These results indicated that P enhances intestinal absorption of CSA by modulating P-gp mediated efflux transport. Release of lactate dehydrogenase in situ from intestinal mucosa in the presence of absorption enhancer was taken as index of its local toxicity. All the absorption enhancers showed significantly less release of LDH compared to positive control, sodium dodecyl sulfate (60% w/v). Overall, the data indicate that the features of these commonly used food ingredients or endogenous bile salts can effectively improve bioavailability of various BCS Class III and Class IV drugs.

Transdermal Iontophoresis of Insulin

The delivery of large peptides through the skin poses a significant challenge, and various strategies are under active investigation for enhancing the transdermal permeation. For large peptides, it is difficult to achieve significant permeation using iontophoresis alone. Hence a combination of fatty acids with iontophoresis was hypothesized to result in higher enhancement than achieved with either of them alone. Saturated fatty acids and cis unsaturated fatty acids were studied in combination with iontophoresis using excised rat skin. The skin was pretreated for 2 h with an ethanolic (EtOH) solution of 5% w/v or v/v fatty acids, namely lauric acid (LA), oleic acid (OA), linoleic acid (LOA) and linolenic acid (LLA), followed by either passive or iontophoretic permeation (0.5 mA/cm2 for 6 h). Fourier transform infrared spectroscopy (FT-IR) was used to investigate the biophysical changes on treatment with fatty acid/EtOH or neat fatty acid, mainly focusing on the infrared region at 2,920, 1,710 and 1,720 cm(-1). Unsaturated fatty acids showed higher enhancement than LA, and the enhancement increased with the number of double bonds. On the other hand, in the presence of iontophoresis, LA/EtOH showed the highest enhancement. Neat LOA did not show any significant difference (p > 0.05) compared to the LOA/EtOH combination. FT-IR studies revealed that fatty acids act by interacting with the skin lipids. All the fatty acids showed synergistic enhancement when combined with iontophoresis. The flux enhancement was highest with LA, which in the presence of iontophoresis showed 20 times enhancement of insulin flux in comparison to passive flux and 9 times enhancement as compared to iontophoresis alone. Flux enhancement of unsaturated fatty acids was in the following decreasing order LOA > OA > LLA.

The effect of pretreatment with terpenes on transdermal iontophoretic delivery of arginine vasopressin

This study investigates the effects of terpenes and iontophoresis on the in vitro permeation of arginine vasopressin (AVP) through rat skin and the biophysical changes induced by the chemical enhancers in the stratum corneum (SC) lipids by FT-IR spectroscopy. Pretreatment with terpenes (e.g. 5% w/v, carvone, pulegone, cineole and menthol in EtOH:W (2:1) system) increased (P < 0.05) the flux of AVP in comparison to control (not pretreated with enhancer) but was not significantly different (P > 0.05) in comparison to iontophoresis. Amongst different terpenes studied maximum enhancement ratio was observed with cineole. In combination, iontophoresis did not further increase (P > 0.05) the permeation of AVP through the enhancer pretreated epidermis in comparison to pretreatment with enhancer or iontophoresis alone. Hence it was concluded that although the combination was effective in flux enhancement compared to control, there was no synergism in action between terpenes and iontophoresis. FT-IR spectroscopic studies revealed that EtOH:W (2:1) system is not effective in lipid extraction. The area under the symmetric and asymmetric stretching peaks at 2850 and 2920 cm(-1) revealed that at the concentration used terpenes did not extract any lipids from the epidermis. The mode of action of terpenes is attributed to the breaking of hydrogen bonds between the ceramide head groups of lipids in the SC leading to greater fluidization of the SC lipids.

Transdermal iontophoresis of insulin: IV. Influence of chemical enhancers

Transdermal iontophoresis per se may not be able to achieve significant permeation of large peptides like insulin, thereby necessitating the use of combination strategies involving chemical enhancers and iontophoresis. The study investigated effect of pre-treatment with commonly used vehicles such as ethanol (EtOH), propylene glycol (PG), water and their binary combinations, dimethyl acetamide (DMA), 10% dimethyl acetamide in water, ethyl acetate (EtAc) and isopropyl myristate (IPM) on insulin iontophoresis. Solvents, which acted on the lipid bilayer, were able to produce a synergistic enhancement with iontophoresis. The binary solvent systems produced either additive or no effect, when combined with iontophoresis. FT-IR studies showed that EtOH, DMA, EtAc caused lipid extraction and the former two also caused changes in skin proteins, whereas IPM caused increase in lipid fluidity. TGA studies showed that EtOH and PG caused dehydration of skin. Skin barrier property was severely compromised with DMA, followed by EtOH and EtAc, while IPM and PG had relatively minimum skin barrier altering potential. Thus, this study demonstrates the possibility of achieving higher permeation of large peptides like insulin by combining iontophoresis with chemical enhancers that act on the intercellular lipids.

Physicochemical considerations in the iontophoretic delivery of a small peptide: in vitro studies using arginine vasopressin as a model peptide

Transdermal iontophoresis (TI) is a physical enhancement technique to facilitate the delivery of primarily charged molecules across the skin. TI of peptides is influenced by a complex interplay of several factors and one of the main issues in optimizing iontophoretic delivery of peptides is to improve the transport efficiency. From this perspective, this study investigates the effect of the physicochemical parameters on the TI of a peptide arginine vasopressin (AVP). The permeation of AVP showed a linear dependence on the concentration of drug in the donor medium. The iontophoretic flux of AVP was strongly influenced by the pH of the donor solution. Increasing the pH from 5.16 to 7.4 resulted in a decrease in the enhancement ratio by 4.5 times. When the ionic strength was increased by varying the amount of NaCl from 0.05 to 0.25 M the flux was found to decrease by 3.2 times. Replacing normal saline in the receptor compartment by HEPES buffer showed a resultant four times increase in drug permeation. The physiochemical parameters of the donor medium play a significant role in the efficiency of drug delivery by iontophoresis for a small peptide like AVP. Though electrorepulsion would be expected to be the main mechanism involved in the movement of charged molecules across the skin by iontophoresis, for peptides in the molecular weight range of AVP, other associated secondary effects like osmosis, electroosmosis and counter ion flow may also play a significant role in transport across the skin.

Transdermal iontophoresis of insulin. V. Effect of terpenes

To increase the skin permeation of large peptides like insulin, it is necessary to utilize a combination of enhancement strategies. In this regard, this study investigated the effect of terpenes/EtOH combination in comparison to EtOH and neat terpene on transdermal iontophoretic permeation of insulin. Ex-vivo experiments were conducted using full thickness rat skin after pre-treatment for 2 h with 5% of menthol, menthone, cineole and pulegone in EtOH; EtOH alone; neat menthone with and without iontophoresis (0.5 mA/cm(2); 6 h). FT-IR studies were carried out using rat epidermal sheets after pre-treatment with enhancer solution for 2 h and tritiated water permeation studies was used to investigate the alteration in skin barrier property after enhancer or current treatment. The lag time was significantly reduced (P<0.05) with terpene/EtOH pre-treatment in comparison to passive control and EtOH pre-treatment, although there was no significant difference (P>0.05) among the terpenes. Synergistic enhancement in flux was observed with terpene/EtOH, and menthone/EtOH showed highest enhancement among the terpene/EtOH combinations. On the other hand, enhancement with neat menthone was higher than with menthone/EtOH. FT-IR studies showed that terpene/EtOH, EtOH and neat terpene act at the intercellular lipids. The skin barrier property was significantly (P<0.05) compromised with neat menthone treatment. Iontophoresis had a lesser effect on skin barrier property compared to chemical enhancer pre-treatment. Terpene/EtOH caused synergistic enhancement of insulin permeation when combined with iontophoresis and was influenced by the type and concentration of terpene.

Drug delivery: an odyssey of 100 years

Drug delivery has metamorphosed from the concept of a pill to molecular medicine in the past 100 years. Better appreciation and integration of pharmacokinetic and pharmacodynamic principles in design of drug delivery systems has led to improved therapeutic efficacy. A greater understanding of the molecular transport in relation to physico-chemical properties has led to the evolution of a biopharmaceutics classification system, which should be a future road map, governing drug design, development and delivery. While drugs belonging to class I and II will be delivered by established platform technologies, novel delivery strategies will evolve and mature to realize the potential of 'new generation' biotech and non biotech drugs belonging to class III and IV, respectively.