The diarrhetic shellfish-poisoning toxin, okadaic acid, provokes gastropathy, dysbiosis and susceptibility to bacterial infection in a non-rodent bioassay, Galleria mellonella

Abstract

Diarrhetic shellfish-poisoning (DSP) toxins such as okadaic acid and dinophysistoxins harm the human gastrointestinal tract, and therefore, their levels are regulated to an upper limit of 160 μg per kg tissue to protect consumers. Rodents are used routinely for risk assessment and studies concerning mechanisms of toxicity, but there is a general move toward reducing and replacing vertebrates for these bioassays. We have adopted insect larvae of the wax moth Galleria mellonella as a surrogate toxicology model. We treated larvae with environmentally relevant doses of okadaic acid (80–400 μg/kg) via intrahaemocoelic injection or gavage to determine marine toxin-related health decline: (1) whether pre-exposure to a sub-lethal dose of toxin (80 μg/kg) enhances susceptibility to bacterial infection, or (2) alters tissue pathology and bacterial community (microbiome) composition of the midgut. A sub-lethal dose of okadaic acid (80 μg/kg) followed 24 h later by bacterial inoculation (2 × 105Escherichia coli) reduced larval survival levels to 47%, when compared to toxin (90%) or microbial challenge (73%) alone. Histological analysis of the midgut depicted varying levels of tissue disruption, including nuclear aberrations associated with cell death (karyorrhexis, pyknosis), loss of organ architecture, and gross epithelial displacement into the lumen. Moreover, okadaic acid presence in the midgut coincided with a shift in the resident bacterial population over time in that substantial reductions in diversity (Shannon) and richness (Chao-1) indices were observed at 240 μg toxin per kg. Okadaic acid-induced deterioration of the insect alimentary canal resembles those changes reported for rodent bioassays.

Immune-modulatory effects of low dose γ-radiation on wax moth (Galleria mellonella) larvae

“…Interestingly, at higher temperature (25 °C), there was a similar response with pupation as it was faster with larvae exposed to a higher dose of radiation and likely due to a response to environmental stressors as seen with silkworms exposed to non-ionising (ultraviolet) radiation (Nojima et al 2019). Incidentally, G. mellonella fed an altered diet also triggered early pupation (Emery et al 2021; reviewed by Zhang et al, 2019) and this was observed in other insects exposed to environmental stressors such as house fly (exposed to ozone; Levy et al, 1972) and butterfly species (exposed to haze smoke; Tan et al, 2018) – though those stressors have other significant impacts on the survivability and development of those insect models, including smaller pupae and emergent adults. Interestingly, it is the faecal load produced by G. mellonella exposed to ionising radiation that produced a significant effect.…”

“…This effect of environmental stress leading to increased faecal pellet production can also be observed in Mongolian gerbils (Barone et al, 1990; Okano et al, 2005). It will not be surprising if the nature of viable bacteria varies under ionising radiation as it is known that stress (be it psychological, physical and environmental) alters the gut microbiota (Karl et al, 2018; Emery et al, 2021). For example, ozone (O 3 ) and nitrogen dioxide (NO 2 ) as air pollutants alter the human gut microbiome (Fouladi et al, 2020).…”

“…Therefore, to understand the role chronic low-dose radiation exposure has on the immune system, we used insect larvae from the Greater wax moth, Galleria mellonella. Wax moth larvae are much larger than traditional insect models like Drosophilids, thereby making it easier to obtain large number of cells for downstream experiments, and no specialist equipment and training are needed (Coates et al, 2019;Emery et al, 2019Emery et al, , 2021. They are also ethically more acceptable than 3 vertebrate work therefore allowing larger experimental numbers to be utilised and thus improving statistical discrimination (Mather 2001;Mylonakis 2008;Lionakis 2011).…”

Current Trends and New Challenges in Marine Phycotoxins

“…This possible association agrees with the alterations in the pattern of expression of 10 genes related to carcinogenic processes in SH-SY5Y neuronal cells exposed to OA [ 182 ]. Poisoning with toxins from the OA group at sub-regulatory levels could have long-term adverse effects on the digestive tract in people, leading to an increased risk of bacteriosis, likely from an existing resident gut symbiont or pathobiont [ 199 , 200 ]. The disruption of epithelial integrity by OA may affect the colonic microbiota, which, in turn, leads to various diseases such as colorectal cancer [ 201 ].…”

Impaired Dopamine Release and Latent Learning in Alzheimer’s Disease Model Zebrafish

“…OKA is a polyether fatty acid extracted from marine sponges, and it has been widely used to study the propagation of neurotoxicity of different animal models. − OKA selectively inhibits protein phosphatases PP1 and PP2A. Inhibition of PP2A, in particular, combined with triggered activation of several major phosphorylating pathways, including MAPK and ERK, induce the hyperphosphorylation of the tau protein, thereby giving rise to the tau aggregates.…”