Medium-chain fatty acid esters-Optimising their efficacy as anti-Malassezia agents

For fatty acid esters of monohydric alcohols, cleavage by exo-enzymes of Malassezia (M.) spp. and release of fatty acids with antimicrobial activity have been shown recently. On skin surface, this selective activation of antimicrobial activity might result in a 'self-kill' targeted locally at the site with the highest M. density.

As for the disadvantage of strong odour, use of these esters for topical therapy is limited to low concentrations. Therefore, cleavage was also tested for monoesters of octanoic and undec-10-enoic acid with the bihydric alcohol propane-1,3-diol or the trihydric glycerol.

In an agar dilution test, the minimal inhibitory concentrations of these compounds were determined for M. furfur, M. globosa, M. sympodialis and M. restricta, respectively. GC analysis of parent compounds and liberated fatty acids was used to reveal ester cleavage.

Ester cleavage started immediately. MICs for the test compounds ranged between ~1000-8000 ppm after 14 days of incubation. 1,3-propanediol esters, especially 3-hydroxypropyl octanoate and 3-hydroxypropyl undecylenate were most effective, binary combinations exerted synergistic effects.

The new substances are advantageous in terms of odour and substantivity and have also beneficial skin caring properties if not hydrolysed by M. spp. As a different panel of hydrolases of each single M. species is responsible for variation in efficacy among the test substances, tailored products to treat preferentially single species or blends with a broader effectivity can be designed. In vivo verification will be the next step for the successful development of this new therapeutical concept for M.-associated diseases.