Using Pulsed-Field Gradient Spin-Echo NMR to Determine Permeation Mechanisms in Human Stratum Corneum

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).0854343BungeThe goal of this research is to study how lipophilic chemicals penetrate through the outermost layer of human skin, which is called the stratum corneum. The stratum corneum is a thin (20 to 40 um thick), composite membrane containing layers of flattened, dead skin cells called corneocytes surrounded by lipid (oily) molecules that are also organized into layers. The stratum corneum controls the rate at which many chemicals enter the body through the skin. Chemicals can penetrate the stratum corneum by two different paths: (1) through only the lipid layers, or (2) through the corneocytes and lipid layers in series. The prevailing opinion in the skin literature is that chemical penetration is restricted to the lipid layers alone, although no direct proof for this presently exists. Moreover, most arguments offered to support the claim that transport is through the lipid layers exclusively are equally applicable to the case of permeable corneocytes. The results of this research will provide direct evidence to answer the question: Can chemicals penetrate the stratum corneum through the corneocytes? The model chemical chosen for study, 2-(trifluoromethyl) benzonitrile, was selected to simulate chemicals that can penetrate the skin to produce either therapeutic or toxic effects in humans. The diffusion of this molecule in the stratum corneum will be studied using a method called pulsed-field gradient spin-echo nuclear magnetic resonance (NMR). This method measures translational molecular motion (i.e., diffusion) over short periods of time (i.e., millisecond to seconds). It also provides information about restrictive boundaries over short distances (i.e., 0.1-100 um), which will be used to distinguish diffusion through corneocytes and the lipid layers. Although this method has been used widely to study colloids and solid-state engineered materials, its use in the study of biological membranes has been limited. The new data generated in this project will improve our understanding of chemical permeation mechanisms in the stratum corneum, including how it changes with variations in water content. If diffusion within the corneocytes is shown to be a significant route for the absorption of lipophilic chemicals in human skin, the paradigm of skin science will shift, which will change existing strategies for transdermal drug delivery, treatment of skin diseases, and methods for predicting absorption of toxic chemicals through skin. The scientific challenges of using pulsed-field gradient spin-echo nuclear magnetic resonance to study diffusion in a composite medium like the stratum corneum arise in many other materials, both biological and non-biological, and the techniques used here will be applicable to these systems as well. The proposed studies of diffusion in the stratum corneum will be used to train graduate and undergraduate student researchers in the fundamentals of chemical transport in heterogeneous membranes and in applications of the pulsed-field gradient spin-echo nuclear magnetic resonance technique to materials from either biological or engineered systems that contain multiple phases. Women and other underrepresented minorities will be actively recruited into the project, which is designed to develop strong communication and organizational/management skills through experiences that are uniquely available in a research environment. In collaboration with an existing and successful outreach program at the Colorado School of Mines, the research team will develop educational modules on the topic of barrier membranes for elementary, middle and high school students and teachers.