Precipitation of free fatty acids generated by Malassezia - a possible explanation for the positive effects of lithium succinate in seborrhoeic dermatitis.

BACKGROUND

Lithium succinate and gluconate are effective alternative options licensed for the topical treatment of seborrhoeic dermatitis (SD).

OBJECTIVE

Their mode of action is not fully elucidated. Minimal inhibitory concentrations against Malassezia (M.) yeasts, which play an important role in SD, are very high.

METHODS

An assay based on the hydrolysis of ethyl octanoate enables us to test the hydrolytic activity of reference strains of the species M. globosa, M. sympodialis and M. furfur solely without interference by fungal growth as the free octanoic acid generated has antifungal activity.

RESULTS

In this assay the presence of alkali salts (lithium, sodium and potassium succinate resp.) in concentrations of 2%, 4% and 8% does not influence hydrolytic activity but the availability of the generated free fatty acid in a dose-dependent manner which was analysed by means of high-performance thin layer chromatography and densitometry. This was best effected with the lithium, followed by the sodium and only to a low degree by the potassium salt. As shown by attenuated total reflection Fourier transform infrared spectroscopy the free fatty acid reacted to the respective alkali soap and precipitate from solution. The alkali soaps could not be utilized by the M. spp. as shown in a modified Tween auxanogram and in lack of fungal growth by ethyl oleate in the presence of 8% lithium succinate.

CONCLUSION

The effect of lithium succinate on growth of M. yeasts and presumably in SD can be explained by a precipitation of free fatty acids as alkali soaps limiting their availability for the growth of these lipid-dependent yeasts.