Selected essential oils inhibit key physiological enzymes and possess intracellular and extracellular antimelanogenic properties in vitro

Zaahira Aumeeruddy-Elalfi ^a, Namrita Lall ^b, Bianca Fibrich ^b, Analike Blom van Staden ^b, Muzzammil Hosenally ^c, Mohamad Fawzi Mahomoodally ^a,*

^a Department of Health Sciences, Faculty of Science, University of Mauritius, Reduit, Mauritius

^b Plant Sciences Complex, Medicinal Plant Science (Department of Plant and Soil Sciences), University of Pretoria, Pretoria, South Africa

^c Department of Economics and Statistics, Faculty of Social Studies & Humanities, University of Mauritius, Reduit, Mauritius

Essential oils (EOs) extracted from six medicinal herbs and food plants [Cinnamomum zeylanicum (CZ), Psiadia arguta (PA), Psiadia terebinthina (PT), Citrus grandis (CGp), Citrus hystrix (CH), and Citrus reticulata (CR)] were studied for any inhibitory potential against key physiological enzymes involved in diabetes (α-glucosidase), skin aging (collagenase and elastase), and neurodegenerative disorders (acetylcholinesterase). Kinetic studies of the active EOs on the aforementioned enzymes were determined using Lineweaver–Burk plots. The intracellular and extracellular antimelanogenic potential of the EOs were evaluated on B16F10 mouse melanocytes. CH and CR were found to significantly inhibit (2.476 ± 0.13 μg/mL and 3.636 ± 0.10 μg/mL, respectively) acetylcholinesterase, compared with galantamine (3.989 ± 0.16 μg/mL). CH inhibited collagenase (50% inhibitory concentration 28.71 ± 0.16 μg/mL) compared with the control (24.45 ± 0.19 μg/mL). The percentage inhibition in the elastase assay of CH was 63.21% compared to the positive control (75.09%). In addition, CH, CR, CGp, CZ, and PT were found to significantly inhibit α-glucosidase (276.70 ± 0.73 μg/mL, 169.90 ± 0.58 μg/mL, 240.60 ± 6.50 μg/mL, 64.52 ± 0.69 μg/mL, and 313.0 ± 5.0 μg/mL, respectively), compared to acarbose (448.80 ± 0.81 μg/mL). Active EOs showed both uncompetitive and competitive types of inhibition. The EOs also inhibited intracellular (50% inhibitory concentration 15.92 ± 1.06 μg/mL, 23.75 ± 4.47 μg/mL, and 28.99 ± 5.70 μg/mL for CH, CR, and CGp, respectively) and extracellular (< 15.625 μg/mL for CH, CR, CGp, and PT) melanin production when tested against B16F10 mouse melanocytes. Results from the present study tend to show that EOs extracted from these medicinal plants can inhibit key enzymes and may be potential candidates for cosmetic and pharmaceutical industries