A rapid method for measuring drug enrichment in epidermis

Area of Science:

• Dermatology
• Pharmacokinetics
• Biophysical Chemistry

Background:

• Accurate measurement of small molecule enrichment in epidermal tissue is crucial for understanding drug delivery and efficacy.
• Existing methods for quantifying tissue-bound substances can be complex and time-consuming.

Purpose of the Study:

• To develop and validate a rapid, simple method for measuring small molecule enrichment in human epidermis.
• To quantify the enrichment of specific small molecules in epidermal tissue and elucidate the underlying mechanisms.

Main Methods:

• A small epidermal tissue sample (2-10 mg) was equilibrated with a buffered solution of a labeled substance (12-36 h).
• Tissue concentration was determined indirectly by measuring the decrease in solution radioactivity, and directly after NaOH digestion.
• Human epidermis specific density (1.20 g/cm³) was used to convert weight to volume for concentration calculations.

Main Results:

• The method accurately measured the enrichment of alpha-estradiol, thiopyronin, 8-methoxypsoralen (8-MOP), 5-methoxypsoralen (5-MOP), and theophylline in human epidermis.
• Four of the five substances showed significant epidermal enrichment (10-500 times higher than buffer concentration).
• Analysis suggested reversible binding for thiopyronin and 8-MOP, and partitioning for 5-MOP and alpha-estradiol.

Conclusions:

• The described method provides a rapid and simple approach for assessing small molecule enrichment in epidermal tissue.
• This technique can be utilized for screening drug candidates or quantitatively characterizing drug concentrations in the skin.
• Understanding enrichment mechanisms (binding vs. partitioning) is vital for optimizing topical drug delivery.