Antiadhesive phthalides from Apium graveolens fruits against uropathogenic E. coli.

Fruits of Apium graveolens (celery) are used traditionally in Persian and European medicine for the treatment of uncomplicated urinary tract infections.The study aimed at identifying potential antiadhesive compounds from celery extracts to provide strategies for improved standardization of the herbal material.Decoction, hydroalcoholic and acetone extracts were prepared from celery fruits. Bioassay-guided fractionation was performed by Fast Centrifugal Partition Chromatography and preparative HPLC, followed by LC-MS and NMR investigations for structure elucidation. The antiadhesive activity of extracts, fractions and purified compounds was assessed by flow cytometry, evaluating the adhesion of fluorescent-labelled uropathogenic bacteria (UPEC NU14) to T24 bladder cells; mannose served as positive control. Influence of the extract on gene expression of selected adhesins and fitness genes was monitored by qPCR.

Concentration-dependent antiadhesive activity was found for the hydroalcoholic and even more for the acetone extract AE (IC₅₀ 85 μg/mL) from celery fruits. Bioassay-guided fractionation revealed the presence of the phthalides senkyunolide (1, inactive) and sedanenolide (2, IC₅₀ 790 μM). 2 is assessed as the main antiadhesive compound, which accounts for 4.0% in the water extract, for 18% in the hydroethanolic extract and for 71% in AE. Additionally a similar phthalide, Z-ligustilide (5), was shown to exert an IC₅₀ of 611 μM. Furthermore, AE caused a significant upregulation of fimH and sfaG in free floating, non-attached UPEC and significantly down-regulated these genes in adherent bacteria.

Phthalides were identified as the main active compounds in polar and semi-polar extracts, which exert strong antiadhesive activity against uropathogenic E. coli. The current findings support the traditional use in phytotherapy for urinary tract infections and provide a base for standardization of the herbal material.