NEONATAL SKIN--BARRIER FUNCTION AND DRUG DELIVERY

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The long-term objectives of our proposed research are: (1) to identify how the compromised barrier function of the premature neonate can be brought to full maturation as quickly as possible; and (2) to develop transdermal drug delivery systems for the treatment of withdrawal symptoms of infants born to drug-dependent mothers and of infants undergoing iatrogenic narcotic dependency. Transdermal delivery is an administrative strategy of clear advantage to this subject population, but the mechanisms and factors that affect transport through the skin of premature and full-term infants are not well understood. To attain our objectives requires a detailed understanding of the neonatal skin barrier and its development as a function of gestational and postnatal age. The specific aims of the project are: [1] To characterize, using infrared (IR) spectroscopy, differential scanning calorimetry (DSC), and small-angle X-ray diffraction (SAXD) on excised neonatal tissue, the biophysical changes in the stratum corneum (SC) lipids which accompany skin maturation. [2] To study, using transmission electron microscopy (TEM) and laser-scanning confocal microscopy (LSCM), the structural and ultrastructural characteristics of the SC. [3] To determine the skin lipid composition of neonatal SC. [4] To evaluate barrier function in vitro with LSCM and in vivo using measurements of transepidermal water loss (TEWL). [5] To correlate the in vivo data with the biophysical, biochemical, and morphological measurements, and to determine how the SC develops to control percutaneous transport. The principal experimental strategies involve: (a) the use of IR spectroscopy, DSC, and SAXD to probe the biophysical bases of SC barrier function; (b) the use of chromatographic methods to analyze the lipids of neonatal SC; (c) the visualization of the SC with TEM and LSCM to investigate the structural landmarks of neonatal skin. The research proposed is intended to answer the following questions: (1) What are the chemical and biophysical requirements of a functional barrier in the neonate? What changes in these constituents accompany barrier development? (2) How does the structure of the SC depend on gestational and postnatal age? What are the morphological differences between neonatal SC and adult SC? (3) Can measurements of permeability from TEWL and LSCM be correlated with biophysical and biochemical measurements of barrier function? (4) Ultimately, based on the insight we gain into the development of the neonatal skin barrier, can we accelerate premature neonatal skin development to full functionality and design transdermal formulations which deliver, safely and effectively, therapeutic doses of drugs to treat withdrawal symptoms in the neonate?