Microbial sophorolipids: Natural surfactants for topical chemotherapy and cosmetic applications

Aim:
To assess the effects of purified sophorolipid subspecies on the viability of spontaneously transformed human keratinocytes (HaCaT) and melanoma cells (SK-MEL-28)

Methods and results:
Non-acetylated Acidic sophorolipids (ASL) and di-acetylated Lactonic sophorolipids (LSL) used in this study were chemically characterized using LC-MS/ESI. The results showed the relative abundance of congeners corresponding to ASL was 100% and for LSL, 90%.

HaCaT and SK-MEL-28 cells were cultured in high glucose DMEM and RPMI medium 1640 respectively for 24 hrs, serum-starved, and treated with varying concentrations of ASL, LSL, and sodium lauryl ether sulphate (SLES). XTT assay was used to assess cell viability and data was analysed using GraphPad Prism (v 5.0).

Cell viability assay on HaCaT cells showed that ASL were comparatively less toxic than SLES. Also, LSL exhibited significant lower IC₅₀ on SK-MEL-28 than on HaCaT cells (53.8 ± 1.6 vs 62.6 ± 1.3: p < 0.05).

Conclusions:
Purified sophorolipid subspecies have been demonstrated to have differential effects on HaCaT and SK-MEL-28 cells.

ASL have been shown to be less toxic to human keratinocytes than SLES, hence a potential candidate to substitute for SLES in skincare formulations. Moreover, the significantly lower IC₅₀ of LSL on SK-MEL-28 than on HaCaT cells is an indication that upon proper optimization, low concentrations of LSL could be used in topical chemotherapy without affecting healthy skin cells.

Significance of study:
Microbial sophorolipids (SLs) are a type of glycolipid biosurfactants mainly produced by Starmerella bombicola and exist as a crude mixture of lactonic and acidic forms. The potential advantages of SLs such as compatibility with the human skin, less toxicity, anticancer, and immunomodulatory effects have made them attractive for use in cosmetic and personal care formulations. However, most in-vivo and in-vitro studies on these properties are determined using the crude mixture of sophorolipids, resulting in significant inter-study variations, which are difficult to interpret. We therefore investigated the effects of highly purified and properly characterized sophorolipid subspecies on skin cells for use in topical chemotherapy and cosmetic applications