ABSTRACT
The O-octanoylation of human ghrelin is a natural post-translational modification that enhances its binding to model membranes and could potentially play a central role in ghrelin biological activities. Here, we aimed to clarify the mechanisms that drive ghrelin to the membrane and hence to its receptor that mediates most of its endocrinological effects. As the acylation enhances ghrelin lipophilicity and that ghrelin contains many basic residues, we examined the electrostatic attraction and/or hydrophobic interactions with membranes. Using various liposomes and buffer conditions in binding, zeta potential and isothermal titration calorimetry studies, we found that whereas acylated and unacylated ghrelin were both electrostatically attracted towards the membrane, only acylated ghrelin penetrated into the headgroup and the lipid backbone regions of negatively charged membranes. The O-acylation induced a 120-fold increase in ghrelin local concentration in the membrane. However, acylated ghrelin did not deeply penetrate the membrane nor did it perturb its organisation. Conformational studies by circular dichroism and attenuated total reflection Fourier transformed infrared as well as in silico modelling revealed that both forms of ghrelin mainly adopted the same structure in aqueous, micellar and bilayer environments even though acylated ghrelin structure is slightly more α-helical in a lipid bilayer environment. Altogether our results suggest that membrane acts as a "catalyst" in acylated ghrelin binding to the ghrelin receptor and hence could explain why acylated and unacylated ghrelin are both full agonists of this receptor but in the nanomolar and micromolar range, respectively.
Subject(s)
Ghrelin/metabolism , Receptors, Ghrelin/metabolism , Acylation , Female , Ghrelin/chemistry , Humans , Hydrophobic and Hydrophilic Interactions , Male , Membrane Fluidity , Protein Conformation , Protein Transport , Receptors, Ghrelin/chemistry , Static ElectricityABSTRACT
An HPLC/UV method was first optimized for the separation and quantitation of human acylated and unacylated (or des-acyl) ghrelin from aqueous solutions. This method was validated by an original approach using accuracy profiles based on tolerance intervals for the total error measurement. The concentration range that achieved adequate accuracy extended from 1.85 to 59.30microM and 1.93 to 61.60microM for acylated and unacylated ghrelin, respectively. Then, optimal temperature, pH and buffer for sample storage were determined. Unacylated ghrelin was found to be stable in all conditions tested. At 37 degrees C acylated ghrelin was stable at pH 4 but unstable at pH 7.4, the main degradation product was unacylated ghrelin. Finally, this validated HPLC/UV method was used to evaluate the binding of acylated and unacylated ghrelin to liposomes.
Subject(s)
Chemistry, Pharmaceutical/standards , Ghrelin/analysis , Acylation , Chemistry, Pharmaceutical/methods , Chromatography, High Pressure Liquid/methods , Chromatography, High Pressure Liquid/standards , HumansABSTRACT
The development of DNA vaccines requires appropriate delivery technologies. Electrotransfer is one of the most efficient methods of non-viral gene transfer. In the present study, intradermal DNA electrotransfer was first optimised. Strong effects of the injection method and the dose of DNA on luciferase expression were demonstrated. Pre-treatments were evaluated to enhance DNA diffusion in the skin but neither hyaluronidase injection nor iontophoresis improved efficiency of intradermal DNA electrotransfer. Then, DNA immunisation with a weakly immunogenic model antigen, luciferase, was investigated. After intradermal injection of the plasmid encoding luciferase, electrotransfer (HV 700 V/cm 100 micros, LV 200 V/cm 400 ms) was required to induce immune response. The response was Th1-shifted compared to immunisation with the luciferase recombinant protein. Finally, DNA electrotransfer in the skin, the muscle or the ear pinna was compared. Muscle DNA electrotransfer resulted in the highest luciferase expression and the best IgG response. Nevertheless electrotransfer into the skin, the muscle and the ear pinna all resulted in IFN-gamma secretion by luciferase-stimulated splenocytes suggesting that an efficient Th1 response was induced in all case.
Subject(s)
Electroporation/methods , Skin/metabolism , Vaccines, DNA/administration & dosage , Animals , Cytomegalovirus/genetics , DNA/genetics , Female , Gene Expression , Genetic Vectors , Injections, Intradermal , Luciferases/genetics , Mice , Mice, Inbred BALB C , Plasmids/genetics , VaccinationABSTRACT
The application of short-duration high-voltage pulses to the skin has been shown to enhance transdermal drug delivery by several orders of magnitude and to transiently permeabilize cells in tissue. Both exponentially decaying (ED) pulses and square wave (SW) pulses have been applied. The latter have also been used for electrochemotherapy. To date, their effect on skin integrity has not been analyzed. The scope of this work was (i) to investigate the effect induced by SW pulses on the stratum corneum and the skin, (ii) to evaluate the safety issue associated with electroporation, (iii) to contribute to the understanding of drug transport. Biophysical techniques (transepidermal water loss, chromametry, impedance and laser Doppler velocimetry or imaging measurement) and histological methods were combined to provide a global picture of the effects. Ten SW pulses applied to the skin induced a mild impairment of the skin barrier function and a dramatic decrease in skin resistance. These changes were reversible. A transient decrease (<5 min) in blood flow was observed. Neither inflammation, nor necroses were observed. These studies confirm the tolerance of the skin to square wave pulses in vivo.
