Antiviral Potential of Spiraea Extracts (Prepared by Repercolation) Against Influenza A (H1N1) Virus

An antiviral effect of extracts prepared from aerial parts of nine species and from leaves of two species of the genus <i>Spiraea</i> L. was investigated for potential antiviral activity toward influenza A (H1N1) virus. The toxicity of dry extracts was analyzed, and the most selective extract was identified in vitro. The study's material was collected in the Asian part of Russia. The plant extracts were prepared via three-stage countercurrent repercolation involving a complete cycle. All 40%-ethanolic extracts from <i>Spiraea</i> manifested antiviral activity against influenza A (H1N1) virus, with a selectivity index (SI) ranging from 1 to 10. IC₅₀ values indicated that the <i>S. salicifolia</i> L. S15 leaf extract (5.9 µg/mL) has the most pronounced antiviral effect and the lowest toxicity (CC₅₀ = 57.6 µg/mL) among the studied samples. The SI of this extract was 10, which exceeded that of the antiviral agent rimantadine (SI = 6). Biologically active compounds in the extract with the highest antiviral activity were identified using UV spectrometry and high-performance liquid chromatography. The <i>S. salicifolia</i> leaf extract was found to contain phenolic acids (chlorogenic, gentisic, caffeic, ferulic, and cinnamic acids), flavonols (quercetin, quercetin-3-glucuronoside, hyperoside, isoquercitrin, rutin, spiraeoside, avicularin, quercitrin, kaempferol, nicotiflorin, astragalin, and isorhamnetin-3-rutinoside), flavones (orientin, luteolin-7-glucoside, and vitexin), and coumarin. Predominant biologically active compounds in the <i>S. salicifolia</i> S15 leaf extract were such flavonols as rutin (19.3 mg/g), isoquercitrin (16.6 mg/g), isorhamnetin-3-rutinoside (10.6 mg/g), and astragalin (9.5 mg/g). Extraction of <i>S. salicifolia</i> leaves by repercolation is a more suitable method for extracting active ingredients with an antiviral effect.