Potential beneficial effects of purified glycolipid biosurfactant congeners on the human skin and skin bacteria in-vitro

Abstract

Glycolipid biosurfactants such as sophorolipids and rhamnolipids offer a potential alternative to sodium lauryl ether sulphate (SLES) for skincare applications. However, most studies on the bioactivities of these glycolipids were performed using mixed or impure congeners, resulting insignificant interstudy variations. This project, therefore, assessed the effects of purified and chemically characterised sophorolipid and rhamnolipid congeners on the normal human skin and skin bacteria in-vitro in comparison with SLES. The glycolipid congeners were purified using solid and liquid phase extraction methods and characterised via HPLC-MS/ ESI analysis. Preparations of non-acetylated acidic sophorolipids (Acidic SL) were 100% pure, di-acetylated lactonic sophorolipids (Lactonic SL) were 90% pure, mono-rhamnolipids (Mono-RL) were 96%pure, and di-rhamnolipids (Di-RL) were 97% pure. Bioactivities of the purified glycolipid congeners were assessed in-vitro on selected skin bacteria, skin cells, and 3D in-vitro skin model. Broth dilution and Live/Dead BacLight staining assays revealed that except for Lactonic SL, all glycolipids utilised in this research had non-inhibitory effects on skin bacteria comparable to SLES. Lactonic SL reduced bacterial viability only at concentrations exceeding 60 μgmL-1. XTT cell viability assays showed that compared with SLES, Acidic SL and Mono-RL had negligible cytotoxic effects on healthy human keratinocytes. On added functionalities, Mono-RL and Di-RL modulated cytokine production in lipopolysaccharide-treated human keratinocytes, Acidic SL and Lactonic SL improved in-vitro wound healing, Lactonic SL selectively inhibited malignant human melanocytes whereas all glycolipids demonstrated anti-metastatic effects at low concentrations. Also, Acidic SL had non-deleterious effects on morphology, filaggrin expression, and pro-inflammatory cytokine stimulation in 3D in-vitro skin model comparable to SLES. Taken together, this thesis demonstrates that purified glycolipid congeners have differential effects on skin bacteria, skin cells, and 3D in-vitro skin models dependent on molecular structure and that these glycolipids could provide sustainable and skin compatible alternative to SLES with added functionalities such as wound healing, immunomodulation, and anticancer effects.

Date of Award	May 2023
Original language	English
Sponsors	Northern Ireland Centre for Food and Health (NICHE)
Supervisor	Ibrahim Banat (Supervisor), Patrick Naughton (Supervisor), Roger Marchant (Supervisor), Patrick Naughton (Supervisor), Ibrahim Banat (Supervisor) & Roger Marchant (Supervisor)