Cytotoxic and Hemolytic Activities of Extracts of the Fish Parasite Dinoflagellate Amyloodinium ocellatum

Abstract

The dinoflagellate Amyloodinium ocellatum is the etiological agent of a parasitic disease named amyloodiniosis. Mortalities of diseased fish are usually attributed to anoxia, osmoregulatory impairment, or opportunistic bacterial infections. Nevertheless, the phylogenetic proximity of A. ocellatum to a group of toxin-producing dinoflagellates from Pfiesteria, Parvodinium and Paulsenella genera suggests that it may produce toxin-like compounds, adding a new dimension to the possible cause of mortalities in A. ocellatum outbreaks. To address this question, extracts prepared from different life stages of the parasite were tested in vitro for cytotoxic effects using two cell lines derived from branchial arches (ABSa15) and the caudal fin (CFSa1) of the gilthead seabream (Sparus aurata), and for hemolytic effects using erythrocytes purified from the blood of gilthead seabream juveniles. Cytotoxicity and a strong hemolytic effect, similar to those observed for Karlodinium toxins, were observed for the less polar extracts of the parasitic stage (trophont). A similar trend was observed for the less polar extracts of the infective stage (dinospores), although cell viability was only affected in the ABSa15 line. These results suggest that A. ocellatum produces tissue-specific toxic compounds that may have a role in the attachment of the dinospores’ and trophonts’ feeding process.

Establishment of a gill cell line from yellowfin seabream (Acanthopagrus latus) for studying Amyloodinium ocellatum infection of fish

“…A. ocellatum is phylogenetically closely related to the toxin‐producing dinoflagellates of the genera Parvodinium , Pfiesteria and Paulsenella (Fensome et al., 1999; Litaker et al., 1999; Moreira et al., 2022). Extracts from A. ocellatum trophonts show cytotoxicity and a strong haemolytic effect in vitro, suggesting that A. ocellatum potentially release toxins during the feeding process.…”

Harmful Algae Impacting Aquatic Organisms: Recent Field and Laboratory Observations

“…Branchial arch (ABSa15) and caudal fin (CFSa1) cells as well as gilthead seabream erythrocytes were challenged against extracts from A. ocellatum , observing strong adverse effects from low-polar extracts obtained from parasitic (trophont) and infective (dinospores) life stages of the dinoflagellate. The ABSa15 cell line and fish erythrocytes were the most sensitive to these extracts (up to 74.5% loss of viability and 100% haemolysis, respectively), confirming the haemolytic and cytotoxic effects of this dinoflagellate [ 19 ].…”

Amyloodiniosis in aquaculture: A review

“…175 This could be due to the difficulty in the isolation and production of the three life stages of A. ocellatum (tomont-resting phase, dinospore-free-living phase, trophont-parasitic phase) and the fact that the more available form of the parasite, the tomont, is very difficult to work with due to the cyst form, and is also the less interesting for several research lines because it does not interact directly with the host. 165 T A B L E 2 Compilations of the gill lesions observed in histopathological analysis in different fish species (I-inflammation, LH-lamellar epithelium hyperplasia, LF-secondary lamellae fusion, McP-mucous cells proliferation, LIR-lymphocytic inflammatory reaction, ED-epithelial detachment, VsD-venous sinus dilatation, An-aneurysm, H-haemorrhage, V-vacuolization, Nec-necrosis) caused by Amyloodinium ocellatum. There is some work already available on the laboratory production of the three phases of A. ocellatum.…”

“…When looking at the host-parasite interaction, there is a clear lack of knowledge about the mechanisms of interaction of A. ocellatum dinospores and trophonts with the infested tissues (oropharyngeal cavity, gill, and skin). This gap has started to be addressed by Moreira et al 165 and Byadgi et al, 210 but further studies are needed to better understand these interaction mechanisms. Genomics, transcriptomics, and proteomic analysis of the different life stages of A. ocellatum can help to achieve this goal, enabling the F I G U R E 6 Existing degree of knowledge in different areas of research in the dinoflagellate parasite Amyloodinium ocellatum.…”

“…The feeding stage (trophont) of A. ocellatum , commonly attached to skin, fins, eyes, and gills, can interfere with gas exchange, osmoregulation, and tissue integrity thus resulting in spasmodic gasping, uncoordinated movements, and extensive mortalities of fish 44 . Most recently, Moreira et al 165 described that A. ocellatum dinospores and trophonts produce tissue‐specific toxic compounds that may have a role in the attachment and feeding process of this parasite, opening an entirely new area on the parasite–host interaction.…”