Bio-prospecting endemic Mascarene Aloes for potential neuroprotectants

LC-MS Based Phytochemical Profiling towards the Identification of Antioxidant Markers in Some Endemic Aloe Species from Mascarene Islands

Aloe plant species have been used for centuries in traditional medicine and are reported to be an important source of natural products. However, despite the large number of species within the Aloe genus, only a few have been investigated chemotaxonomically. A Molecular Network approach was used to highlight the different chemical classes characterizing the leaves of five Aloe species: Aloe macra, Aloe vera, Aloe tormentorii, Aloe ferox, and Aloe purpurea. Aloe macra, A. tormentorii, and A. purpurea are endemic from the Mascarene Islands comprising Reunion, Mauritius, and Rodrigues. UHPLC-MS/MS analysis followed by a dereplication process allowed the characterization of 93 metabolites. The newly developed MolNotator algorithm was usedfor molecular networking and allowed a better exploration of the Aloe metabolome chemodiversity. The five species appeared rich in polyphenols (anthracene derivatives, flavonoids, phenolic acids). Therefore, the total phenolic content and antioxidant activity of the five species were evaluated, and a DPPH-On-Line-HPLC assay was used to determine the metabolites responsible for the radical scavenging activity. The use of computational tools allowed a better description of the comparative phytochemical profiling of five Aloe species, which showed differences in their metabolite composition, both qualitative and quantitative. Moreover, the molecular network approach combined with the On-Line-HPLC assay allowed the identification of 9 metabolites responsible for the antioxidant activity. Two of them, aloeresin A and coumaroylaloesin, could be the principal metabolites responsible for the activity. From 374 metabolites calculated by MolNator, 93 could be characterized. Therefore, the Aloe species can be a rich source of new chemical structures that need to be discovered.

Medicinal Mascarene Aloes: An audit of their phytotherapeutic potential

A phytochemical and biological investigation of the endemic Mascarene Aloes (Aloe spp.), including A. tormentorii (Marais) L.E.Newton & G.D.Rowley, A. purpurea Lam, A. macra Haw., A. lomatophylloides Balf.f and A. vera (synonym A. barbadensis Mill.), which are used in the traditional folk medicine of the Mascarene Islands, was initiated. Methanolic extracts of the Aloes under study were analysed using high resolution LC-UV-MS/MS and compounds belonging to the class of anthraquinones, anthrones, chromones and flavone C-glycosides were detected. The Mascarene Aloes could be distinguished from A. vera by the absence of 2″-O-feruloylaloesin and 7-O-methylaloeresin. GC-MS analysis of monosaccharides revealed the presence of arabinose, fucose, xylose, mannose and galactose in all the Mascarene Aloes and in A. vera. The crude extracts of all Aloes analysed displayed antimicrobial activity against Bacillus cereus, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. Only extracts of A. macra were active against P. aeruginosa and Klebsiella pneumoniae, while none of the Aloe extracts inhibited Propionibacterium acnes. A. macra displayed anti-tyrosinase activity, exhibiting 50% inhibition at 0.95mg/mL, and extracts of A. purpurea (Mauritius) and A. vera displayed activity in a wound healing-scratch assay. In vitro cytotoxicity screening of crude methanolic extracts of the Aloes, using the MTT (3-(4, 5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide) showed that only A. purpurea (Réunion) elicited a modest toxic effect against HL60 cells, with a percentage toxicity of 8.2% (A. purpurea-Réunion) and none of the Aloe extracts elicited a toxic effect against MRC 5 fibroblast cells at a concentration of 0.1mg/mL. Mascarene Aloe species possess noteworthy pharmacological attributes associated with their rich phytochemical profiles.