Phospholipid vesicles as carriers in aquaculture: preparation and stability study of thiamine hydrochloride-loaded liposomes.

The aim of this work is to study liposomes as carriers of nutrients and therapeutic agents in aquaculture with Venerupis decussatus and Venerupis pullastra larvae. Multilamellar (MLVs) and large unilamellar (LUVs) vesicles were prepared from a commercial mixture of soy phosphatidylcholine, rich in unsaturated and polyunsaturated fatty acids, cholesterol, and hydrated with a solution of vitamin B1 both in distilled and sea water. Carboxyfluorescein-loaded liposomes were also prepared in order to test the uptake of vesicles by larvae. The stability of formulations was checked by monitoring the size of vesicles and their drug leakage. In order to limit the vitamin loss, liposome freeze-drying was studied. Dried formulations were also prepared by using different amounts of trehalose as cryoprotectant. We found that freeze-dried vesicles, rehydrated after two weeks, had a vitamin retention (R%) equal to 95%, while their diameter significantly increased. By contrast, liposomes freeze-dried in the presence of trehalose displayed a lower R%, but higher bilayer stability. Finally, when CF-loaded vesicles were added to Venerupis decussatus and Venerupis pullastra larvae incubated in filtered sea water, a bright and diffused fluorescence was present in most of the larvae, a fact which can be regarded as evidence of liposome uptake by Venerupis larvae.