Enhanced Q-starch/miRNA complexes penetration efficiency to the skin using multiple ultrasound exposures

In recent years it has been proposed to treat skin diseases, such as psoriasis, where there is an over-expression of specific proteins related to the development of the disease with microRNAs, a small RNA sequence (miRNA) that can silence expression of a specific protein in the cell.

Although miRNA have the potential for treating skin diseases, there are three main barriers to its topical delivery through the skin:1. miRNA molecule is not a stable molecule and may undergo enzymatic degradation.2. The inherent barrier properties of the top layer of the skin. 3. miRNA is negatively charged, as the cell membrane, and there is an electrostatic rejection between them. To overcome these barriers, modified starch was used as a carrier for the miRNA molecule, and ultrasound as a means of increasing skin permeability. Previous results from our laboratory confirmed the ability of one ultrasound application to insert nano-complexes of Q-starch/miRNA into the skin layers, but many of the nano-complexes were accumulated in the upper layer of the skin. Based on these results, the hypothesis of the current research is that repeated ultrasound exposure will improve the ability to uniformly spread the nano-complexes in all skin layers (enhancing the convective transport and or temporary modification of the skin structure (permeability)) and thereby increase the healing potential of the disease.

For first step, modified potato starch (Q-starch) was synthesized and characterized by elementary analysis and FTIR. Nano-complexes at different Q-starch to miRNA molar ratios were evaluated for their surface charge and size using Zeta potential and Nano-sight respectively. The skin permeability experiments were carried out on pig`s skin in diffusion cells, using fluorescently labeled nano-complexes. The applications of ultrasound on the skin were performed before the nano-complexes were placed and another 3 hours after the first application. Following the transport experiment the skin was scanned using confocal microscope. It was found that additional application of ultrasound has succeeded in introducing more nano-complexes into the lower layers of the skin and to spread them in a more homogeneous manner, indicating on the potential of this protocol to improve the efficacy of the proposed treatment.