Fatty acid oxygenase activity of human hair roots

The extent to which fatty acid oxygenases are activated in the normal epidermis is not known. Characterization of the regio- and stereospecificity of the monohydroxylated derivatives of arachidonic and linoleic acid produced by human hair roots is needed to define the enzymatic origin of these compounds and to define a possible role for fatty acid oxygenases in growth, differentiation, and pathology of human hair. Hair roots epilated from normal human volunteers were incubated with radiolabeled arachidonic acid or linoleic acid and the monohydroxylated derivatives produced in vitro were characterized. Incubation of hair roots with [¹⁴C]arachidonic acid resulted in the production of 15(S)-[¹⁴C]hydroxyeicosatetraenoic acid and 12(S,R)- [¹⁴C]hydroxyeicosatetraenoic acid (mean S/R ratio, 2.5). 13(S)- [¹⁴C]hydroxyoctadecadienoic acid was the principal product of incubations with [¹⁴C]linoleic acid. No radiolabeled products were derived from incubations with heat-denatured hair roots. The fatty acid oxygenase activity of anagen hair roots was inhibited by nordihydroguaiaretic acid and was greatest in the hair root bulb. The strict S-stereospecificity and the regiospecificity of the n-6 oxygenase are strong evidence for the presence of a 15-lipoxygenase in human hair roots, similar to that identified in cultured human keratinocytes. The stereospecificity of the 12-HETE produced by human hair roots is not compatible with the sole action of 12-lipoxygenase.