1999 Volume 22 Issue 4 Pages 407-411
Enhancement of skin distribution of propylene glycol (PG) in the skin by high purity cis-unsaturated fatty acids with different alkyl chain lengths was studied in the rat using Fourier transform/attenuated total rellection (FT-IR/ATR) analysis. Two fatty acids with the double bond at the Δ9 position, palmitoleic acid (ω7, Δ9) and oleic acid (ω9, Δ9), enhanced PG flux into the dermis and increased the dermal steady state level of PG. In contrast, myristoleic acid (ω5, Δ9) was extremely weak in its action. A positional effect of the ω chain was observed. The rate of skin structural alteration increased in proportion to ω chain length. The application of three fatty acids with the double bond at the ω9 position, oleic acid (ω9, Δ9), gondoic acid (ω9, Δ11), erucic acid (ω9, Δ13) enhanced PG distribution in the skin. While, nervonic acid (ω9, Δ15) did not increase PG distribution in the skin. The relationship of the Δ/ω ratio to parameters characterizing the action of enhancers (PGpeak area max, Tmax alteration, and the slope) sugest that skin distribution increases as the position of the double bond is shifted toward the hydrophilic end. It is therefore likely that the ratio of the Δ/ω chain length of the cis-unsaturated fatty acid determines the efficacy of these compounds as skin penetration enhancers. An adequate molecular volume may be required for cis-unsaturated fatty acids to act as enhancers.
