Project Identifier: LLNL-94-103
Project Title:
Percutaneous Absorption of Radiolabeled Chemicals in Humans
Principle Investigator:
Dr. John S. Vogel
Project started in: 1994
Project Funding Information:
Project received funding in Fiscal Year 1995.
Project used human subjects in Fiscal Year 1995.
Funding Sources:
Total Funding: $2,000
Project does not involve use of multiple protocols/subprojects.
IRB Review:
Type of Review: Full Board
Most Recent Approval: March 22, 1995
IRB Approval Number: 94-103
Number of Human Subjects in the Last Reporting Period for this Project: 3
(Reporting periods vary.)
Type of Human Subjects Involvement:
Basic research. R.S. used as tracer.
Basic research. CS used as tracer.
Objectives: The ultimate objective of this research is to develop and experimentally validate algorithms which predict the absorbed dose following topical application or dermal exposure to chemical substances of therapeutic and toxicological interest. The initial objectives of the experiments are: (a) To measure, in vivo in man, the cutaneous uptake of a series of substituted phenols following exposure to the skin. (b) To quantify uptake by application of the chemical 'spiked' with a very small amount of 14C (~nCi) and assessing the mass entering the stratum corneum via repeated adhesive tape-stripping and analysis of the strips for 14C. (c) To alternatively quantify uptake by selecting phenol derivatives of unique infrared (IR) spectroscopic characteristics and using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) to again determine the quantity of chemical taken up into the stratum corneum (once more, using the adhesive tape-stripping routine). (d) To correlate the results from the two methods and to demonstrate that they may be used interchangeably. (e) To compare the experimentally determined levels of chemical within the stratum corneum at the end of the exposure period with those amounts predicted by dermal uptake models.
Methodology: Radiochemical Methodology: Aqueous solutions of the penetrants, 'spiked' with a very low level of 14C-radiolabel (~10 nCi) will be applied, under occlusion, to the ventral forearms of the human volunteers. Administration will involve saturation of a gauze pad (area = 20 cm2) with approximately 1 mL of solution. After application, the delivery system will be covered with an adhesive, occlusive dressing and left in place for a defined period of time, not to exceed 3 hours. At the end of the exposure time, the gauze is removed and the skin surface is carefully dried with cotton Q-tips. Delivery system and Q-tips will be reserved for analysis. After 10 minutes, sequential layers of stratum corneum at the application site will be removed using preweighed pieces of adhesive tape in the standard way. Up to a maximum of 20 tape-strips will be removed (this is sufficient to excise the entire stratum corneum in most individuals). The tape-strips will then be extracted in methanol and taken to the Center for Accelerator Mass Spectrometry (CAMS) for analysis of 14C. Background levels will be assessed from tape-strips removed from the contralateral, untreated forearm skin. In this way, the concentration profile of chemical across the stratum corneum, and the absolute amount taken up into the membrane during the exposure period will be evaluated.
ATR-FTIR Technique: ATR-FTIR is used to obtain spectral measurements of the phenols in the skin of the human volunteers. Prior to administration, a pretreatment spectrum of each subject's stratum corneum will be recorded with ATR-FTIR. After exposure, sequential tape-stripping and spectroscopy will be performed, thereby providing an alternative assay of the distribution of chemical as a function of depth into the stratum corneum (weight of the tape-strips again being used as a marker for position within the membrane). Therefore, the 14C and IR determinations will be performed at the same time; that is, the applied solution of chemical will be both "spiked" with radioactivity and with a spectroscopic marker. Assay of uptake by CAMS can be utilized, then, as a further calibration of the spectroscopic measurements.
Radioactive and Chemical Substances: The chemicals chosen for the study are a series of phenol derivatives, which are commercially available both 14C-radiolabelled and (separately) with significant deuteration [with the exception of cyanophenol, which possesses an inherently unique IR absorbance via the -C(N) functionality]. Chemical doses are from 10-50 mg/mL. Radioactive doses are 10 nCi/mL.
Involvement of Human Subjects: Human subjects have an occlusive patch (2 X 9 cm) moistened with a 1-ml chemical solution (10-50 mg/ml) applied to their forearm for periods up to 3 hours. The application site is then serially tape-stripped and analyzed for chemical penetration with ATR-FTIR. Approximately 10 mg of outer skin tissue is removed from each human subject. Little if no physical risk is posed to the human subject by this procedure. Dose estimates for the application site and whole body are 0.134 rad/cm2 and 0.0075 mr.