Assessing the potential use of purified microbial sophorolipid subspecies in skincare formulations

Allergic reactions and skin irritation associated with the use of skincare products formulated with synthetically derived ingredients such as sodium lauryl ether sulphate (SLES) have encouraged the search for natural, biocompatible, and more sustainable alternatives. Microbial sophorolipids, a major class of glycolipid biosurfactants have been demonstrated in several in-vitro studies as less toxic surfactants with wound healing, skin moisturizing, and immunomodulatory effects. Most of these studies however used either the crude or poorly characterized mixtures 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 (acidic and lactonic SL) on spontaneously transformed human keratinocytes (HaCaT) in comparison with SLES as an attempt to investigate the potential use of microbial sophorolipids in skincare formulations to substitute synthetic surfactants. HPLC -MS/ESI was used to chemically characterize both acidic and lactonic SL followed by cell viability assays and morphological analyses using XTT and Live/Dead staining assays, respectively. Our acidic SL was 100% pure and the lactonic SL was 90% pure. Both Lactonic SL and SLES had significant inhibitory effects on HaCaT cell viability at concentrations above 60 μg mL-1 (p < 0.05) with 100 μg mL-1 treatment concentrations significantly affecting cell morphology and reducing cell population through necrotic cell death. Acidic SL however, at concentrations up to 500 μg mL-1 showed no significant inhibitory effects on either cell viability or morphology. These results suggest that both lactonic and acidic SL have different effects on human keratinocyte depending on their chemical structure. Furthermore, acidic SL have been demonstrated to be less toxic when compared to SLES, hence, a potential candidate to substitute for SLES in skincare formulations.