Chemical Constituents of Dioscorea collettii var. hyplauca

Antiparasitic Efficacy of Herbal Extracts and Active Compound Against Gyrodactylus kobayashii in Carassius auratus

Gyrodactylus spp. Nordmann, 1832 (Monogenea: Gyrodactylidae) are common ectoparasites of teleost fishes. Infection with these parasites can increase the mortality of fish and cause considerable economic losses in intensive aquaculture. To find an effective antiparasitic agent for the control of gyrodactylosis, antiparasitic efficacy of crude extracts of 36 herbal medicines was evaluated using a Carassius auratus (Cypriniformes, Cyprinidae)—Gyrodactylus kobayashii model. Among all tested medicines, methanol extract of Dioscorea collettii var. hypoglauca (Dioscoreales, Dioscoreaceae) was the most efficient, with an EC₅₀ value of 4.17 mg/L. This extract showed 100% antiparasitic efficacy against G. kobayashii at 10 mg/L and had a therapeutic index (TI, LC₅₀/EC₅₀) of 5.26, which is higher than that of formaldehyde (TI = 4.58), a widely used parasiticide in aquaculture. Subsequently, the potential mechanism of antiparasitic activity of dioscin, an active compound isolated from D. collettii var. hypoglauca was investigated and the histopathological alterations in goldfish after exposure to dioscin were also studied. The in vivo trial indicated dioscin showed significant antiparasitic activity with a 24 h-EC₅₀ value of 1.58 mg/L and it exhibited 100% antiparasitic efficacy at 0.6 mg/L. Also, G. kobayashii could be completely removed in vivo within 2 h at 0.6 mg/L dioscin. Whereas, mean survival time of this worm in vitro was 4.99 h, and some individuals even reached 12 h at the same concentration of dioscin. These results indicated that 0.6 mg/L of dioscin did not completely kill all worms within 2 h, but just temporarily remove the worms from goldfish. Scanning electron microscopy (SEM) analysis showed that most of the microvilli on the tegument surface of G. kobayashii dropped after exposure to dioscin. This might be one of the potential mechanisms of antiparasitic activity of dioscin against G. kobayashii. Furthermore, no severe histopathological alteration was observed after exposure to a high concentration of dioscin for a short time. Considering both effectiveness and safety, therapeutic baths with a high concentration of dioscin for a short time might be a more optimal choice for the treatment of gyrodactylosis in aquaculture.

Natural Phenyldihydroisocoumarins: Sources, Chemistry and Bioactivity

The present review gives an overview about naturally occurring phenyldihydroisocoumarins, their sources, and bioactivities. In total, 54 compounds are covered, including eight substances which are in fact alkaloids or protoalkaloids. These nitrogen containing compounds were exclusively found in the Papaveraceae family. The remaining 46 compounds have been reported from twelve different source families, ranging from mosses to angiosperms. Six of the nitrogen free compounds feature additional rings, while 40 are simple phenyldihydroisocoumarins with substituents in all possible positions, except 3, 2’, and 6’. Common substituents of these simple phenyldihydroisocoumarins are hydroxy groups, methoxy groups, and glucosyloxy groups; on the other hand, acuminosyloxy and rutinosyloxy groups have so far been found only in one and two naturally occurring phenyldihydroisocoumarins, respectively. Though a number of bioactivities have been proven for phenyldihydroisocoumarins, ranging from anticancer and antidiabetic to antimicrobial and anti-inflammatory activities, so far only one taxon, Hydrangea macrophylla var. thunbergii, is widely used. Moreover, the usage of this taxon is mainly due to the sweet taste properties of the contained phenyldihydroisocoumarin phyllodulcin and less based on the alleged health-promoting effects of its constituents.