Anti-inflammatory activity of verbascoside- and isoverbascoside-rich Lamiales medicinal plants

Abstract

Verbascoside and isoverbascoside are two active phenylethanoid glycosides mainly found in plants of the order Lamiales. This study analyzes the verbascoside and isoverbascoside levels and the total phenolic contents in the water and ethanolic extracts of 20 medicinal plants of the order Lamiales commonly used in Thailand. The related bioactivities, including the antioxidant activity via the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reduction activity potential assays and anti-tyrosinase and -inflammatory activities via the cyclooxygenase and nitric oxide assays are also investigated. The extracts of several plant species, including Barleria prionitis, B. lupulina, Rhinacanthus nasutus, Orthosiphon aristatus, and Nicoteba betonica, exhibit high verbascoside and isoverbascoside content levels. The correlation analysis between the bioactive activities and the active compounds demonstrates a significant association between the verbascoside level in the water extracts and both the DPPH antioxidant activity and the nitric oxide level in the anti-inflammatory assays. This study provides the first report on the verbascoside and isoverbascoside quantification of several plant samples. The findings provide valuable insights for future research on lesser-studied plants possessing high verbascoside and isoverbascoside levels, which exhibit promising anti-inflammatory activities.

Keywords: Acteoside; Isoverbascoside; Lamiales; Medicinal plants; Phenylethanoid glycoside; Verbascoside; anti-inflammatory.

Fig. 1

Plant samples used in this study. a) Ocimum africanum Lour., b) Clinacanthus nutans (Burm.f.) Lindau, c) Mentha × villosa Huds., d) Mentha pulegium L., e) Mentha canadensis L., f) Andrographis paniculata (Burm.f.) Nees, g) Ocimum tenuiflorum L., h) Ocimum basilicum L., i) Clerodendrum indicum Kuntze, j) Orthosiphon aristatus (Blume) Miq., k) Nicoteba betonica Lindau, l) Barleria prionitis L., m) Clinacanthus siamensis Bremek., n) Acanthus ebracteatus Vahl, o) Thunbergia laurifolia Lindl., p) Justicia valida Ridl., q) Barleria lupulina Lindl., r) Rhinacanthus nasutus (L.) Kurz, s) Barleria strigosa Willd, and t) Leonotis nepetifolia (L.) R.Br.

Fig. 2

HPLC chromatograms of standard compound (upper) and B. prionitis water extract (lower). (a) verbascoside and (b) isoverbascoside.

Fig. 3

Total phenolic content form ethanol and water extracts of 20 plant samples. The letters indicate a significant difference between plants within the same solvent group at p < 0.01.

Fig. 4

Antioxidant capacity of 10 μg/mL verbascoside, 10 μg/mL isoverbascoside, and 20 plant samples, extracted with ethanol (a) and water (b), by DPPH assays. The letters indicate a significant difference between plants within the same solvent group at p < 0.01.

Fig. 5

Antioxidant capacity of 10 μg/mL verbascoside, 10 μg/mL isoverbascoside, and 20 plant samples, extracted with ethanol (a) and water (b) by FRAP assay. The letters indicate a significant difference between plants within the same solvent group at p < 0.01.

Fig. 6

Mushroom tyrosinase inhibition percentage of 10 μg/mL verbascoside, 10 μg/mL isoverbascoside, and 20 plant samples, extracted with ethanol and water. Kojic acid at 12.5 and 25.0 μg/mL were positive control.

Fig. 7

In vitro inhibitory percentage of COX-1 (a) and COX-2 (b) by 10 μg/mL verbascoside, 10 μg/mL isoverbascoside, and 20 plant samples, extracted with ethanol and water. Indomethacin at 10.0 mM was positive control.

Fig. 8

Nitric oxide level and viability of LPS-induced RAW 264.7 cells after treated with 10 μg/mL verbascoside, 10 μg/mL isoverbascoside, and 20 plant samples, extracted with ethanol (a) and water (b). Indomethacin 0.3 mM was positive control. *Significant difference compared with the untreated group (DMSO) at p < 0.01.