Bioassay-Guided Isolation of Anthelmintic Components from Semen pharbitidis, and the Mechanism of Action of Pharbitin

by Selleckchem | Oct 07 2023

Parasitic helminths continue to pose problems in human and veterinary medicine, as well as in agriculture. Semen pharbitidis, the seeds of Pharbitis nil (Linn.) Choisy (Convolvulaceae), is a well-known traditional Chinese medicinal botanical preparation widely used for treating intestinal parasites in China owing to its desirable efficacy. However, the anthelmintic compounds in Semen pharbitidis and their mechanism of action have not been investigated yet. This study aimed to identify the compounds active against helminths from Semen pharbitidis, and to establish the mechanism of action of these active compounds. Bioassay-guided fractionation was used to identify the anthelmintic compounds from Semen pharbitidis. The anthelmintic assay was performed by monitoring Caenorhabditis elegans (C. elegans) motility with a WMicrotracker instrument. Active compounds were identified by high-resolution mass spectrometry. Several (analogues of) fragments of the anthelmintic compounds were purchased and tested to explore the structure-activity relationship, and to find more potent compounds. A panel of C. elegans mutant strains resistant to major currently used anthelmintic drugs was used to explore the mechanism of action of the active compounds. The bioassay-guided isolation from an ethanol extract of Semen pharbitidis led to a group of glycosides, namely pharbitin (IC50: 41.0 ± 9.4 μg/mL). Hit expansion for pharbitin fragments yielded two potent analogues: 2-bromohexadecanoic acid (IC50: 1.6 ± 0.7 μM) and myristoleic acid (IC50: 35.2 ± 7.6 μM). One drug-resistant mutant ZZ37 unc-63 (x37) demonstrated a ~17-fold increased resistance to pharbitin compared with wild-type worms. Collectively, we provide further experimental scientific evidence to support the traditional use of Semen pharbitidis for the treatment of intestinal parasites. The anthelmintic activity of Semen pharbitidis is due to pharbitin, whose target could be UNC-63 in C. elegans.

Comments:

The study you mentioned investigated the anthelmintic (anti-parasitic) properties of Semen pharbitidis, a traditional Chinese medicinal preparation derived from the seeds of Pharbitis nil (Linn.) Choisy. Semen pharbitidis has been traditionally used in China for treating intestinal parasites. However, the specific compounds responsible for its anthelmintic activity and the mechanism of action of these compounds were unknown prior to this study.

The researchers employed a bioassay-guided fractionation approach to isolate the active compounds from Semen pharbitidis. They conducted anthelmintic assays using Caenorhabditis elegans (C. elegans) as a model organism and monitored their motility with a WMicrotracker instrument. Active compounds were identified using high-resolution mass spectrometry. To gain insights into the structure-activity relationship and discover more potent compounds, the researchers purchased and tested analogues and fragments of the anthelmintic compounds. Additionally, they used a panel of C. elegans mutant strains that were resistant to commonly used anthelmintic drugs to explore the mechanism of action of the active compounds.

Through this bioassay-guided isolation, the researchers identified a group of glycosides called pharbitin as the active compounds in Semen pharbitidis. Pharbitin exhibited anthelmintic activity, with an IC50 value (the concentration required for 50% inhibition) of 41.0 ± 9.4 μg/mL. Further exploration of pharbitin fragments led to the discovery of two potent analogues: 2-bromohexadecanoic acid (IC50: 1.6 ± 0.7 μM) and myristoleic acid (IC50: 35.2 ± 7.6 μM).

To investigate the mechanism of action of the active compounds, the researchers used a C. elegans mutant strain called ZZ37 unc-63 (x37), which exhibited approximately 17-fold increased resistance to pharbitin compared to wild-type worms. This suggests that the target of pharbitin in C. elegans could be UNC-63.

Overall, this study provides experimental evidence supporting the traditional use of Semen pharbitidis for treating intestinal parasites. The anthelmintic activity of Semen pharbitidis is attributed to pharbitin, and the target of pharbitin in C. elegans is potentially UNC-63.