Reversible anti-settlement activity against Amphibalanus (=Balanus) amphitrite, Bugula neritina, and Hydroides elegans by a nontoxic pharmaceutical compound, mizolastine

Abstract

Mizolastine, an antihistamine pharmaceutical, was found to significantly inhibit larval settlement of the barnacle Amphibalanus (=Balanus) amphitrite, the bryozoan Bugula neritina, and the polychaete Hydroides elegans with EC₅₀ values of 4.2, 11.2, and 4.1 µg ml⁻¹, respectively. No toxicity against the larvae of these three species was observed at the concentration range tested during incubations with mizolastine. To determine whether the anti-settlement activity of mizolastine is reversible, recovery bioassays using these three species were conducted. More than 70% of the larvae that had been exposed for 4 h to mizolastine at concentrations four-fold greater than their respective EC₅₀ values completed normal metamorphosis. The results of the recovery bioassay provide evidence that the anti-settlement effect of mizolastine is reversible in addition to being nontoxic. The anti-settlement activities of several intermediates of the synthesis process of mizolastine were also examined. One of the intermediates, 2-chloro-1-(4-fluorobenzyl)-1H-benzo[d]imidazole, inhibited larval settlement and metamorphosis with low toxicity. These results may improve the understanding of the key functional group responsible for the anti-settlement activity of mizolastine.

Keywords:

• mizolastine
• larvae
• anti-settlement activity
• Amphibalanus (=Balanus) amphitrite
• Bugula neritina
• Hydroides elegans

Acknowledgments

This study was supported by a grant from the Chinese Ocean Mineral Resources Research and Development Association (COMAR06/07.SC02), and the CAS/SAFEA International Partnership Program for Creative Research Teams as well as a research fund from KAUST International Partnership Program (KAUST005-CML.07/08) to Qian P.-Y.