Short-Term Supplementation of Dietary Arginine and Citrulline Modulates Gilthead Seabream (Sparus aurata) Immune Status

Abstract

Several amino acids (AA) are known to regulate key metabolic pathways that are crucial for immune responses. In particular, arginine (ARG) appears to have important roles regarding immune modulation since it is required for macrophage responses and lymphocyte development. Moreover, citrulline (CIT) is a precursor of arginine, and it was reported as an alternative to ARG for improving macrophage function in mammals. The present study aimed to explore the effects of dietary ARG and CIT supplementation on the gilthead seabream (Sparus aurata) immune status. Triplicate groups of fish (23.1 ± 0.4 g) were either fed a control diet (CTRL) with a balanced AA profile, or the CTRL diet supplemented with graded levels of ARG or CIT (i.e., 0.5 and 1% of feed; ARG1, CIT1, ARG2, and CIT2, respectively). After 2 and 4 weeks of feeding, fish were euthanized and blood was collected for blood smears, plasma for humoral immune parameters and shotgun proteomics, and head-kidney tissue for the measurement of health-related transcripts. A total of 94 proteins were identified in the plasma of all treatments. Among them, components of the complement system, apolipoproteins, as well as some glycoproteins were found to be highly abundant. After performing a PLS of the expressed proteins, differences between the two sampling points were observed. In this regard, component 1 (61%) was correlated with the effect of sampling time, whereas component 2 (18%) seemed associated to individual variability within diet. Gilthead seabream fed ARG2 and CIT2 at 4 weeks were more distant than fish fed all dietary treatments at 2 weeks and fish fed the CTRL diet at 4 weeks. Therefore, data suggest that the modulatory effects of AA supplementation at the proteome level were more effective after 4 weeks of feeding and at the higher inclusion level (i.e., 1% of feed). The bactericidal activity increased in fish fed the highest supplementation level of both AAs after 4 weeks. Peripheral monocyte numbers correlated positively with nitric oxide, which showed an increasing trend in a dose-dependent manner. The colony-stimulating factor 1 receptor tended to be up-regulated at the final sampling point regardless of dietary treatments. Data from this study point to an immunostimulatory effect of dietary ARG or CIT supplementation after 4 weeks of feeding in the gilthead seabream, particularly when supplemented at a 1% inclusion level.

Dietary Histidine, Threonine, or Taurine Supplementation Affects Gilthead Seabream (Sparus aurata) Immune Status

“…In the present study, data from the analyzed responses of fish fed supplemented diets suggest that the effects of Thr, His, and Tau supplementation on fish immune system seem to be of an indirect nature, when compared with other EAAs previously studied such as tryptophan, methionine, or arginine [ 32 , 61 , 62 ], which present stronger and more direct effects. In a previous work where the effects of dietary tryptophan supplementation were also explored in gilthead seabream, only a transient immune enhancement was observed in fish fed an extreme formulation (no FM inclusion) over a short-term feeding period (two weeks), suggesting that these putative advantageous effects seem to disappear over a longer feeding period (13 weeks) [ 33 ].…”

“…Moreover, Ramos-Pinto, Azeredo, Silva, Conceição, Dias, Montero, Torrecillas, Silva and Costas [ 32 ] described that arginine and citrulline, particularly when supplemented at a 1% of feed inclusion level, induced a stimulation of the fish immune system after a short-term feeding period, verified mostly by a modulation of the gilthead seabream plasma proteome and health-biomarkers after four weeks of exposure. Hence, the fact that arginine concentration was higher in the CTRL diet compared to the others could have translated into an increased gilthead seabream immune status.…”

“…Among Sparidae, the gilthead seabream ( Sparus aurata , L.) is one of the main carnivorous farmed fish species in the Mediterranean region [ 31 ]. A sustainable and profitable aquaculture relies on the production of healthy fish, which requires balanced feeds manufactured with high-quality ingredients [ 32 , 33 ]. The main goal of this study was to evaluate the effects of His, Thr, and Tau on gilthead seabream ( Sparus aurata ) immune function when added as a supplement to a practical aquafeed formulation during a transient (two weeks) and short-term (four weeks) feeding period.…”

Novel Insight Into Nutritional Regulation in Enhancement of Immune Status and Mediation of Inflammation Dynamics Integrated Study In Vivo and In Vitro of Teleost Grass Carp (Ctenopharyngodon idella): Administration of Threonine

“…It was clearly shown that inflammation suppressed by the effects of tryptophan than methionine, with a notable downregulation in mmp9 and IL-1β of juvenile European seabass ( 25 ). Arginine was confirmed to have no remarkable alteration for the inflammatory process but in IL-10 and IL-34 regulation in the head kidney of juvenile gilthead seabream ( 26 ). Thus, different effects addressed on immunoregulation by amino acids might be diverse in fish.…”

Arginine metabolism and its functions in growth, nutrient utilization, and immunonutrition of fish

“…In fish, arginine may function in immune responses in multiple ways including producing NO and polyamines, directly modulating gene expression, and regulating nutrient availability of immune cells. A recent study also uses the shotgun proteomics technique to reveal the candidate serum proteins involved in fish immune responses after dietary arginine supplementation ( Ramos-Pinto et al., 2020 ). Both in vivo and in vitro experiments with channel catfish showed that arginine supplementation improved the abilities of macrophage killing and phagocytosis, increased the lysozyme activity and erythrocyte number, and enhanced the proliferation of native lymphocytes after mitogenic exposure ( Buentello et al., 2007 ; Pohlenz et al., 2012 ).…”