Enzyme inhibition and antioxidant functionality of eleven Inula species based on chemical components and chemometric insights

The members of the genus Inula have been widely used in traditional medicinal. In the present study, 11 Inula species were investigated for their phytochemical composition, antioxidant and enzyme inhibitory effects. While quinic acid was the principal compound in I. anatolica, I. britannica, I. inuloides, I. oculus-christi, I. peacockiana, I. sechmenii, I. thapsoides and I. viscidula extracts (22.43–42.02 mg/g dry extract (DE)), I. aucheriana and I. discoidea extracts contained rutin as their most abundant compound (23.28 and 79.10 mg/g extract, respectively). Interestingly, all the Inula extracts were active inhibitors of the five key clinical enzymes (acetylcholinesterase (3.56–5.13 mg galantamine equivalent (GALAE)/g), butyrylcholinesterase (1.49–7.34 mg GALAE/g), tyrosinase (112.31–122.13 mg kojic acid equivalent (KAE)/g), α-glucosidase (0.77–2.08 mmol acarbose equivalent (ACAE)/g) and α-amylase (0.73–0.90 mmol ACAE/g)). Furthermore, the extracts were observed to exhibit substantial antioxidant capacity (1,1-diphenyl-2-picrylhydrazyl (DPPH): 58.99–188.22 mg trolox equivalent (TE)/g); 2,2-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) (ABTS): 90.51–220.97 mg TE/g; cupric reducing antioxidant capacity (CUPRAC): 169.88–460.53 mg TE/g; ferric reducing antioxidant power (FRAP): 81.57–237.99 mg TE/g; metal chelating activity: 8.31–25.39 mg ethylenediamine tetraacetate equivalent (EDTAE)/g; phosphomolybdenum: 1.55–2.49 mmol TE/g). In conclusion, the Inula species studied herein showed promising pharmacological potentials justified by the presence of a panoply of bioactive compounds.