Publicação
Benefits of a marine macroalgae enriched-diet on the biochemical status of the eyes and brain in fish exposed to formalin
| Resumo: | Many health benefits have been associated with bioactive compounds of marine macroalgae (MM), including protection against oxidative stress and synaptic loss that are hallmarks of human neurodegenerative disorders. While the benefits of macroalgae have been largely explored with a focus on human health associated with neurological status (among others), advantages to farmed fish health remain elusive. Based on similarities of neurological pathways between fish and mammals, as well as on identical structures of the brain and sensory organs, beneficial effects of MM-enriched feeds can be expected on fish. These benefits are probably more evident when fish are under exogenous challenging conditions to their neurological status, as can be the case of formalin exposure (a frequently used disinfectant in aquaculture), which has been associated with neurotoxic effects in mammals. The current dissertation was designed under this context, aiming to address, for the first time, the antioxidant and neurotransmission protection afforded by a MM-enriched diet to the eyes and brain of the gilthead seabream (Sparus aurata) under baseline conditions, as well as after formalin exposure. For this purpose, fish were fed for 2 months with a MM-enriched feed [total incorporation of 5%, with the species Fucus vesiculosus, Gracilaria gracilis and Ulva rigida in equal parts - algae supplementation fish group (A)], while non-supplemented fish were fed with a standard diet (S) (without MM). Then, both dietary background groups were subjected to a formalin (F) bath for 1 hour (fish groups AF and SF). Such formalin treatment was repeated 2 days later. Control groups, unexposed to formalin, were maintained along the experiment (A and S) that lasted 18 days after the first formalin exposure. During the whole experiment, fish were fed twice a day, while water quality was monitored daily. Fish of the different groups (A, S, AF, SF) were sacrificed 4 and 18 days after the formalin exposure, with the eyes and brain being collected for the determination of the following biochemical parameters: (i) enzymatic (catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione - s - transferase (GST), glutathione reductase (GR) and non-enzymatic antioxidants (total glutathione (GSHt)); (ii) damage indicators (lipid peroxidation – LPO; protein oxidation - PO); (iii) acetylcholinesterase (AChE) activity used in this research as a proxy of neurotransmission. Besides that, a gross assessment of fish condition was made. No significant changes were recorded on weight, total length and condition factor of the fish over the experimental time, regardless the treatment. This suggests that MM can be included in gilthead seabream diet without compromising growth rates, and therefore with no detrimental effect on fish production revenues. Differently, two months after macroalgae supplementation, there were a few significant alterations on the eyes and brain biochemical parameters, although difficult to be straightforward associated to the different dietary backgrounds afforded to S. aurata. Moreover, lipid peroxidation and protein oxidation in the eyes of fish supplemented with MM and non-exposed to formalin (control group - A) was recorded at day 4, fetching some doubts on the benefits of the macroalgae-enriched diet per se, i.e., in the absence of a pro-oxidant challenge. Four and 18 days after the formalin exposure, the antioxidants, lipid peroxidation and the AChE activity showed similar variations in the brain of the supplemented fish, represented by significant increases in A and AF conditions. This pattern similarity may indicate that MM dietary supplementation can be important to modulate the brain defence mechanisms in S. aurata. Yet, in the 18 days period it was reported a few exceptions. However, upon formalin exposure, the effects of MM supplementation on the pro-oxidant status and neurotransmission of those organs were remarkable. Four days after formalin exposure, fish fed with a macroalgae-supplemented diet (AF) displayed an improvement on the non-enzymatic antioxidant defense of the eyes against formalin, as depicted on the increase of total glutathione levels (GSHt). Accordingly, MM-enriched diet impaired the occurrence of protein oxidation and AChE enhancement promoted by formalin in the eyes of fish fed with a standard diet (SF). After 18 days, it was evident a persistence of the macroalgae protection in the eyes, as depicted on the capacity to avoid formalin-induced GSHt depletion, oxidative stress (as PO and LPO increases) and neurotoxicity (as AChE inhibition) observed in the eyes of non-supplemented fish (SF). A delayed impact of formalin was perceived in the brain in comparison to the eyes, since formalin effects were detected only 18 days after formalin exposure. By this time, lipid peroxidation was prevented in fish supplemented with macroalgae (AF), which cannot be dissociated from a notorious increase on GSHt content (that also occurred in fish fed with standard diet - SF). Formalin induced a late effect (day 18) on AChE as displayed by its activity increase, suggesting an imbalance on the cholinergic homeostasis, which was not prevented by the macroalgae enrichment. Results on AChE in the brain did not unveil the benefits of MM on neurotransmission. In conclusion, formalin presents a higher and earlier effect on S. aurata eyes when compared with the brain tissue, probably associated with its exposure route (water). The physiological alterations provoked by the formalin brought into light the shielding proprieties of MM supplementation in the fish neurosensory function. However, the MM beneficial proprieties deserve more research under the aquaculture context, specifically at the level of neuronal and sensory effects of formalin. |
|---|---|
| Autores principais: | Teixeira, Guilherme Marques |
| Assunto: | Macroalgae Functional foods Fish farming Formalin Neurosensory structures Sparus aurata |
| Ano: | 2018 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Aveiro |
| Idioma: | inglês |
| Origem: | RIA - Repositório Institucional da Universidade de Aveiro |
| Resumo: | Many health benefits have been associated with bioactive compounds of marine macroalgae (MM), including protection against oxidative stress and synaptic loss that are hallmarks of human neurodegenerative disorders. While the benefits of macroalgae have been largely explored with a focus on human health associated with neurological status (among others), advantages to farmed fish health remain elusive. Based on similarities of neurological pathways between fish and mammals, as well as on identical structures of the brain and sensory organs, beneficial effects of MM-enriched feeds can be expected on fish. These benefits are probably more evident when fish are under exogenous challenging conditions to their neurological status, as can be the case of formalin exposure (a frequently used disinfectant in aquaculture), which has been associated with neurotoxic effects in mammals. The current dissertation was designed under this context, aiming to address, for the first time, the antioxidant and neurotransmission protection afforded by a MM-enriched diet to the eyes and brain of the gilthead seabream (Sparus aurata) under baseline conditions, as well as after formalin exposure. For this purpose, fish were fed for 2 months with a MM-enriched feed [total incorporation of 5%, with the species Fucus vesiculosus, Gracilaria gracilis and Ulva rigida in equal parts - algae supplementation fish group (A)], while non-supplemented fish were fed with a standard diet (S) (without MM). Then, both dietary background groups were subjected to a formalin (F) bath for 1 hour (fish groups AF and SF). Such formalin treatment was repeated 2 days later. Control groups, unexposed to formalin, were maintained along the experiment (A and S) that lasted 18 days after the first formalin exposure. During the whole experiment, fish were fed twice a day, while water quality was monitored daily. Fish of the different groups (A, S, AF, SF) were sacrificed 4 and 18 days after the formalin exposure, with the eyes and brain being collected for the determination of the following biochemical parameters: (i) enzymatic (catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione - s - transferase (GST), glutathione reductase (GR) and non-enzymatic antioxidants (total glutathione (GSHt)); (ii) damage indicators (lipid peroxidation – LPO; protein oxidation - PO); (iii) acetylcholinesterase (AChE) activity used in this research as a proxy of neurotransmission. Besides that, a gross assessment of fish condition was made. No significant changes were recorded on weight, total length and condition factor of the fish over the experimental time, regardless the treatment. This suggests that MM can be included in gilthead seabream diet without compromising growth rates, and therefore with no detrimental effect on fish production revenues. Differently, two months after macroalgae supplementation, there were a few significant alterations on the eyes and brain biochemical parameters, although difficult to be straightforward associated to the different dietary backgrounds afforded to S. aurata. Moreover, lipid peroxidation and protein oxidation in the eyes of fish supplemented with MM and non-exposed to formalin (control group - A) was recorded at day 4, fetching some doubts on the benefits of the macroalgae-enriched diet per se, i.e., in the absence of a pro-oxidant challenge. Four and 18 days after the formalin exposure, the antioxidants, lipid peroxidation and the AChE activity showed similar variations in the brain of the supplemented fish, represented by significant increases in A and AF conditions. This pattern similarity may indicate that MM dietary supplementation can be important to modulate the brain defence mechanisms in S. aurata. Yet, in the 18 days period it was reported a few exceptions. However, upon formalin exposure, the effects of MM supplementation on the pro-oxidant status and neurotransmission of those organs were remarkable. Four days after formalin exposure, fish fed with a macroalgae-supplemented diet (AF) displayed an improvement on the non-enzymatic antioxidant defense of the eyes against formalin, as depicted on the increase of total glutathione levels (GSHt). Accordingly, MM-enriched diet impaired the occurrence of protein oxidation and AChE enhancement promoted by formalin in the eyes of fish fed with a standard diet (SF). After 18 days, it was evident a persistence of the macroalgae protection in the eyes, as depicted on the capacity to avoid formalin-induced GSHt depletion, oxidative stress (as PO and LPO increases) and neurotoxicity (as AChE inhibition) observed in the eyes of non-supplemented fish (SF). A delayed impact of formalin was perceived in the brain in comparison to the eyes, since formalin effects were detected only 18 days after formalin exposure. By this time, lipid peroxidation was prevented in fish supplemented with macroalgae (AF), which cannot be dissociated from a notorious increase on GSHt content (that also occurred in fish fed with standard diet - SF). Formalin induced a late effect (day 18) on AChE as displayed by its activity increase, suggesting an imbalance on the cholinergic homeostasis, which was not prevented by the macroalgae enrichment. Results on AChE in the brain did not unveil the benefits of MM on neurotransmission. In conclusion, formalin presents a higher and earlier effect on S. aurata eyes when compared with the brain tissue, probably associated with its exposure route (water). The physiological alterations provoked by the formalin brought into light the shielding proprieties of MM supplementation in the fish neurosensory function. However, the MM beneficial proprieties deserve more research under the aquaculture context, specifically at the level of neuronal and sensory effects of formalin. |
|---|