<< Back to Abstract Listing by Category Board Number: J-09 Title: Assessment of Dermal Absorption, Metabolism, and Irritation Potential of Arachidonic Acid & Glyceryl Arachidonate Using In Vitro Diffusion Cell Techniques A. R. Eppler 1 , M. E.K. Kraeling 1 , R. R. Wickett 2 , R. L. Bronaugh 1 , 1 Office of Cosmetics and Colors, US FDA, Laurel, MD , 2 College of Pharmacy, University of Cincinnati, Cincinnati, OH                     Arachidonic acid (AA), which is known to be metabolized to pro-inflammatory mediators, and its glycerin ester, glyceryl arachidonate (GA), have been used as ingredients in cosmetic products.  Therefore, in vitro diffusion cell studies were conducted to evaluate skin absorption and metabolism of AA & GA and skin irritation by AA.  To simulate normal consumer use conditions, [14C]AA and [3H]GA were topically applied in an oil in water emulsion (2mg/cm2).  AA penetration in viable rat skin was found to be 50.3% of the applied dose while penetration in viable human skin was found to be 18.4%.  GA penetration in viable human, human cadaver, and Epiderm cultured skin was found to be 21.4%, 14.8%, and 55.8% respectively.  Approximately 3% of the absorbed dose of GA in Epiderm was metabolized to AA, based on HPLC analysis.  Skin irritation by model compounds and AA was assessed on rat skin and Epiderm assembled in flow-through diffusion cells.  Irritation was determined after 24hr exposure by evaluating barrier integrity changes using TEWL measurements and skin cell viability changes using the MTT assay.  TEWL measurements taken immediately prior to the skin surface wash were inaccurate due to the occlusion of the emulsion vehicle, while measurements taken immediately following the wash were elevated due to evaporation of the wash and rinse solutions.  For the emulsion-vehicle treatments (Tween 80, sodium lauryl sulfate, and AA applied in an oil in water emulsion at 10 mg/cm2), TEWL measurements obtained 40-60 minutes after the wash had returned to baseline values taken prior to dosing.  Therefore, no significant irritation could be observed with TEWL analysis of these treatments.  However, aqueous 5% sodium lauryl sulfate (78 µl/cm2) on rat skin resulted in a significant increase in TEWL.  Irritation assessment with the MTT assay showed greater sensitivity when using Epiderm than when using rat skin.  In conclusion, AA and GA dermal penetration was measured and Epiderm was determined to be potentially useful in metabolism studies.  Additionally, irritation assessment in flow-through diffusion cells may be possible by means of the MTT and TEWL assays. Category: J. Biological Endpoints: Microbiology, Virology, Allergenicity, Biochemistry, Toxicology