Dietary Methionine Improves the European Seabass (Dicentrarchus labrax) Immune Status, Inflammatory Response, and Disease Resistance

Abstract

Methionine presents a pivotal role in the regulation of many cellular events with crucial impact on the immune system, such as in processes involved in the control of inflammation and polyamines synthesis. Accordingly, the present study aimed to assess the modulatory effects of dietary methionine on the European seabass (Dicentrarchus labrax) immune status, inflammatory response and disease resistance to Photobacterium damselae subsp. piscicida (Phdp). For this purpose, fish were randomly distributed in three independent groups (three replicates per group) and each was fed the corresponding diet: a control diet (CTRL) formulated to meet the established amino acid requirements for the species; a diet supplemented with methionine at 0.5% of feed weight relative to the CTRL diet (8.2% of methionine concentration above CTRL); and one supplemented with methionine at 1% of feed weight to the CTRL diet (11.8% of methionine concentration above CTRL). To evaluate the immune status of fish fed with each of the diets before being submitted to bacterial infection fish were sampled from each group at 2 and 4 weeks after the beginning of feeding. Non-sampled fish were injected intraperitoneally with Phdp (5 × 103 cfu/fish) at 4 weeks after initiation of feeding and the inflammatory response (at 4, 24, and 48 h post-infection) and survival (lasting 21 days post-infection) evaluated. Fish hematological profile, peripheral cell dynamics, plasma humoral immune parameters, leucocyte migration to the inflammatory focus and head-kidney gene expression were evaluated. Results show that methionine dietary supplementation improves seabass cellular immune status without evidence of activation of pro-inflammatory mechanisms. Additionally, the observed enhanced immune status provided by methionine supplementation translated into an improved immune response to infection, as higher cellular differentiation/proliferation and recruitment to the inflammatory focus, improved plasma humoral immune parameters and modulation of key immune-related genes was observed. Lastly, after a bacterial challenge, higher survival was observed in fish fed supplemented diets, ultimately corroborating the positive effect of methionine administration for 4 weeks in the cellular immune status.

Dietary methionine supplementation improves the European seabass (Dicentrarchus labrax) immune status following long-term feeding on fishmeal-free diets

“…To the best of our knowledge, this is the first study to explore the role of dietary methionine levels in the context of a FM-free diet for the European seabass. Previous studies reported a clear modulatory effect of dietary methionine supplementation in FM-based diets in the European seabass immune status after only 2 or 4 weeks of feeding (20,21) . The latter study showed that methionine can enhance the peripheral cellular immune status without triggering pro-inflammatory humoral indicators as well as down-regulate pro-inflammatory genes.…”

“…After total AA analysis in feed (Table 2), methionine content in MET0•65 was 20 % below CTRL, while methionine supplementation led to 39 and 70 % increase above CTRL (MET1•25 and MET1•5, respectively). Methionine supplementation levels were chosen according to previous works (18,20,21) and with the aim to assess the effects of methionine deficiency and its graded supplementation levels in an alternative feed formulation (i.e. 0 % FM) context.…”

“…The immune system is in fact highly dependent on AA availability since their metabolism is found altered in stress and inflammatory situations (11,(13)(14)(15)(16)(17) . A growing interest on the role of several AA in the immune functions of fish, as in higher vertebrates, has shown that specific AA can specially modulate the innate immune responses (18)(19)(20)(21)(22) . Additionally, the AA requirement levels often established by optimal growth overlook the metabolic needs associated with immune responses, health, reproduction and cell signalling (11) .…”

“…As a precursor of S-adenosylmethionine, a universal methyl donor group, methionine participates in the regulation of many cellular events involved in polyamine synthesis, formation of signalling molecules essential for cellular function, hormones, bioactive amines, enzymes, neurotransmitters, nitric oxide, DNA methylation and the control of inflammation (25)(26)(27)(28) . In fact, increased levels of dietary methionine, above the required optimal growth, led to an improved immune response in poultry (29,30) , while in fish, recent results show that methionine dietary supplementation improved seabass cellular immune status without evidences of activation of proinflammatory mechanisms (20,21) . Moreover, increased methionine level improved disease resistance against Photobacterium damselae subsp.…”

“…Moreover, increased methionine level improved disease resistance against Photobacterium damselae subsp. piscicida in European seabass (21) . On the other hand, Wu et al (29) discussed that also methionine dietary deficiency could impair cellular immune function in broilers.…”