Lavender (Lavandula angustifolia) Essential Oil Nanoemulgel for Skin Ageing: Formulation, Physicochemical Characterization, and Preliminary Multi-Enzyme Inhibition Screening.

Background: The up-regulation of matrix metalloproteinase-9 (MMP-9), a zinc-dependent endopeptidase involved in the breakdown of type IV collagen at the junction between the dermis and epidermis is among the factors responsible for the premature aging of the skin. Methods: Essential oil characterization was performed using GC-MS. Oil-in-water nanoemulsions were prepared using high-shear mixing and probe ultrasonication techniques. Then essential oil-containing nanoemulsions were incorporated into carbopol hydrogel. Nanoemulsion droplet size, spreadability, pH, viscosity, zeta potential, Polydispersity Index, thermodynamic stability was examined. The optimized nanoemulsion and lavender oil were evaluated for their inhibitory activities against MMP-9, tyrosinase, xanthine oxidase, hyaluronidase and collagenase at one concentration (n=3) in comparison with the established reference inhibitor. One way ANOVA analysis was performed (p<0.05). Results: GC-MS analysis revealed the presence of 35 constituents, among which linalool (30.75%) and linalyl acetate (26.90%) were the main ones. The optimized formulation gave a nanoemulsion with mean hydrodynamic diameter 177.2 ± 1.95 nm, Polydispersity Index 24.0 ± 10.6% and zeta potential of −17.1 ± 0.09 mV; the resulting nanoemulgel showed no phase separation after centrifugation and freeze–thaw cycling with viscosity 8300 ± 124 mPa·s, pH 5.7 ± 0.08 and spreadability 26 ± 1.2 g·cm/s. The optimised nanoemulsion showed reduced but measurable activity: MMP-9 76.43 ± 3.8%, tyrosinase 44.0 ± 3.8%, xanthine oxidase 68.0 ± 4.0%, hyaluronidase 65.0 ± 3.9%, and collagenase 58.0 ± 3.6%. Conclusion: An optimized stable lavender oil nanoemulgel has been developed and at a single screening concentration, both the parent essential oil and the optimized nanoemulsion exhibited detectable enzyme inhibitory activity on a number of enzymes responsible for breaking down the ECM. As the experiments were conducted using a single non-biological concentration in one experiment, these results are presented merely as preliminary results and should not be used to make assumptions on potency, selectivity or topicality.