Symphytum officinale L.: Liquid-liquid chromatography isolation of caffeic acid oligomers and evaluation of their influence on pro-inflammatory cytokine release in LPS-stimulated neutrophils

Ethnopharmacological relevance: Symphytum officinale L. (comfrey, Boraginaceae) has been traditionally used for millennia in joint distortions, myalgia, bone fractures and hematomas. However, key activity-determining constituents and molecular mechanisms underlying its use have not been completely elucidated.

Aim of the study: The objective of this study was to isolate and identify the major compounds from a hydroethanolic root extract of S. officinale and evaluate their antioxidant potential, alongside their effect on the cytokine production of ex vivo stimulated neutrophils, thus providing scientific support for the traditional use of comfrey root.

Material and methods: Four caffeic acid oligomers were isolated from comfrey roots by liquid-liquid chromatography, their structures being established by MS and NMR analyses. In vitro antioxidant evaluation was performed by DPPH and ABTS assays. The cytotoxicity of isolated compounds was established by flow cytometry. The effect on cytokine release, such as interleukin (IL)-1β, IL-8 and tumor necrosis factor alpha (TNF-α), in lipopolysaccharide (LPS)-stimulated neutrophils was determined by enzyme-linked immunosorbent assay (ELISA).

Results: The main constituents found in comfrey root were represented by four caffeic acid oligomers, namely globoidnan B (1), rabdosiin (2), rosmarinic acid (3) and globoidnan A (4). Rabdosiin, globoidnans A and B were isolated for the first time from S. officinale. In the in vitro antioxidant tests, compound 2 was the most active, with EC₅₀ values in DPPH and ABTS assays of 29.14 ± 0.43 and 11.13 ± 0.39, respectively. Neutrophils' viability over the tested concentration domain of 12.5-50 μM was not altered. At 50 μM, all compounds significantly inhibited IL-1β release, with compound 3 (45.60% release vs. LPS stimulated neutrophils) being the most active, followed by compounds 1 (53.85%), 2 (69.89%) and 4 (60.68%).

Conclusions: The four caffeic acid oligomers reported in S. officinale root may contribute to the overall anti-inflammatory activity for which comfrey preparations are used in traditional medicine.

Chemical compounds studied in this article: Globoidnan A (PubChem CID: 56841780). Globoidnan B (SpectraBase CID: 6x5Eig4VgdC). Rabdosiin (PubChem CID: 471121). Rosmarinic acid (PubChem CID: 5281792).

Keywords: Symphytum officinale; caffeic acid oligomers; countercurrent chromatography; cytokine release inhibitory activity; interleukin 1β; liquid-liquid chromatography; stimulated neutrophils.