Promising anti-diabetic potential of Artemisia capillaris and its constituents

Abstract

Artemisia, a diverse genus of the family Asteraceae, has been used as anti-pyretic, anti-diabetic, anti-hypertensive, anti-hepatotoxic, anti-inflammatory, eczema, jaundice, and anti-hemorrhoid. Recently, Artemisia genus has emerged as a source of naturally occurring therapeutic agents for the treatment of diabetes and related complications due to the presence of wide varieties of bioactive substances including caffeoyl quinic acids, flavonoids, and coumarins. As a part of our ongoing search for anti-diabetic constituents from natural sources, we selected methanol (MeOH) extracts of 12 species of the genus Artemisia based on their frequent use in traditional medicines and investigated their anti-diabetic potential via α-glucosidase, protein tyrosine phosphatase 1B (PTP1B), and advanced glycation end products (AGE) formation inhibitory assays. The MeOH extracts of different species exhibited promising inhibitory activities ranging from 34.12 to 64.17% at a concentration of 250 μg/mL against α-glucosidase and 27.40 to 98.60% at a concentration of 10 μg/mL against PTP1B while their AGE formation inhibitory activities ranging from 21.40 to 87.47% at a concentration of 10 μg/mL. Since the MeOH extract of A. capillaris exhibited the highest α-glucosidase and AGE formation inhibitory activities together with significant PTP1B inhibitory activity, it was selected for detailed investigation. Repeated column chromatography of different fractions yielded 46 compounds including 13 coumarins (esculetin, esculin, scopolin, isoscopolin, scoparone, scopoletin, isoscopoletin, artemicapin A, fraxidin, 5,6,7-trimethoxy coumarin, 6-methoxy artemicapin C, tomerin, umbelliferone) and 19 flavonoids (cirsilineol, cirsimaritin, arcapillin, linarin, quercetin, hyperoside, isorhamnetin 3-O-robinobioside, quercetin 5-O-glucoside, quercetin 3-O-glucoside, quercetin 3-O-robinobioside, chrysoeriol-7-O-rutinoside, quercetin 7-O-galatopyranosyl 7-O-rhamnoside, isorhamnetin 3-O-galactoside, isorhamnetin 3-O-glucoside, acacetin-7-O-(6″-O-acetyl)-β-D-glucopyranosyl-(1→2)[α-L-rhamnopyranosyl]-(1→6)-β-D-glucopyranoside, acacetin-7-O-β-D-glucopyranosyl-(1→2)[α-L-rhamnopyranosyl]-(1→6)-β-D-glucopyranoside, isorhamnetin-3-O-arabinopyranoside, vicenin 2, apigenin), 6 caffeoylquinic acid derivatives (4,5 di-O-caffeoyl quinic acid, 3,5 di-O-caffeoyl quinic acid, 3,4 di-O-caffeoyl quinic acid, chlorogenic acid, cryptochlorogenic acid, neochlorogenic acid), 2 chromones (capillarisin and 7-methyl capillarisin), 2 essential oils (capillin and capllinol), and 4 phenolic compounds (paramethoxy phenyl glucoside, eugenol glucoside, koaburaside and 4-hydroxy-3-O-glucopyranosyl benzoic acid). Among them, acacetin-7-O-(6″-O-acetyl)-β-D-glucopyranosyl-(1→2)[α-L-rhamnopyranosyl]-(1→6)-β-D-glucopyranoside is a new acetylated flavonoid glycoside isolated for the first time. Among the isolated compounds esculetin, quercetin, scopoletin, isorhamnetin, vicenin 2, cirsilineol, 3,5-O-dicaffeoylquinic acid, 1,5-O-dicaffeoylquinic acid, 3,4-O-dicaffeoylquinic acid, 4,5-O-dicaffeoylquinic acid, exhibited potent inhibitory activities in α-glucosidase and PTP1B inhibitory assays with IC50 values of 82.92, 58.93, 159.16, 141.17, 270.53, 351.71, 217.40, 146.06, 128.07, and 229.94 μM, respectively, compared to the positive control acarbose wth IC50 value of 130.52 μM against α-glucosidase and 10.08, 20.35, 227.28, 43.88, 139.75, 206.78, 2.02, 16.05, 2.60, and 3.21 μM, respectively compared to the positive control ursolic acid with an IC50 value of 4.05 μM against PTP1B. Interestingly, 3-O-caffeoylquinic acid, 6-methoxy artemicapin C and capillarisin exhibited potent inhibitory activity against PTP1B while hyperoside exhibited potent inhibitory activity against α-glucosidase rather than PTP1B. In addition, two essential oils, capillin and capillinol were also found to be potent inhibitors of α-glucosidase, PTP1B and RLAR. Kinetic analysis revealed that capllin noncompetitively inhibited both α-glucosidase and RLAR, while it showed mixed type inhibition against PTP1B. On the other hand, capllinol showed mixed type inhibiton against both α-glucosidase and PTP1B. In case of AGE formation inhibitory assay, esculetin, scopoletin, isoscopoletin, isoscopolin, scopolin, quercetin, hyperoside, vicenin 2, 4,5 di-O-caffeoyl quinic acid, and chlorogenic acid showed remarkable inhibitory potential against AGE formation with IC50 values of 5.02, 3.90, 18.78, 41.04, 60.10, 24.35, 48.20, 54.43, 6.48 and 21.08 μM, respectively compared to the positive control aminoguanidine with IC50 an value of 932.66 μM. Vcenin 2 also strongly inhibited RLAR with an IC50 value of 7.85 μM compared to the positive control quercetin with an IC50 value of 11.64 μM. Further study with vicenin 2 revealed that it can inhibit the formation of fluorescent AGE and non-fluorescent AGE such as (Nε-(carboxymethyl) lysine (CML). Vicenin 2 also inhibited protein oxidation indicated by decreasing protein carbonyl formation and thiol modification in BSA-glucose-fructose system. Moreover, vicenin 2 also suppressed the formation of β-cross amyloid structures of BSA. Therefore, the results of the present study clearly demonstrate the promising α-glucosidase, PTP1B, and AGE formation inhibitory potential of A. capillaris as well as its isolated constituents, which could be further explored to develop therapeutic or preventive agents for the treatment of diabetes and related complications.