Effect of dietary threonine on growth performance and muscle growth, protein synthesis and antioxidant-related signalling pathways of hybrid catfish Pelteobagrus vachelli♀ × Leiocassis longirostris♂

An insight into role of amino acids as antioxidants via NRF2 activation

Oxidative stress can affect the protein, lipids, and DNA of the cells and thus, play a crucial role in several pathophysiological conditions. It has already been established that oxidative stress has a close association with inflammation via nuclear factor erythroid 2-related factor 2 (NRF2) signaling pathway. Amino acids are notably the building block of proteins and constitute the major class of nitrogen-containing natural products of medicinal importance. They exhibit a broad spectrum of biological activities, including the ability to activate NRF2, a transcription factor that regulates endogenous antioxidant responses. Moreover, amino acids may act as synergistic antioxidants as part of our dietary supplementations. This has aroused research interest in the NRF2-inducing activity of amino acids. Interestingly, amino acids' activation of NRF2-Kelch-like ECH-associated protein 1 (KEAP1) signaling pathway exerts therapeutic effects in several diseases. Therefore, the present review will discuss the relationship between different amino acids and activation of NRF2-KEAP1 signaling pathway pinning their anti-inflammatory and antioxidant properties. We also discussed amino acids formulations and their applications as therapeutics. This will broaden the prospect of the therapeutic applications of amino acids in a myriad of inflammation and oxidative stress-related diseases. This will provide an insight for designing and developing new chemical entities as NRF2 activators.

Evaluation of Dietary Essential Amino Acid Supplementation on Growth, Digestive Capacity, Antioxidant, and Intestine Health of the Juvenile Redclaw Crayfish, Cherax quadricarinatus

The present study was an 8-week feeding trial investigating the effects of lysine and threonine supplementation in vegetable-based diets on growth, antioxidative capacity, and gut microbiota of juvenile redclaw crayfish, Cherax quadricarinatus (initial weight 11.52 ± 0.23 g). The lysine and threonine were supplemented to formulate five isonitrogenous (37%) and isolipidic (9%) diets containing 0% (control), 0.2% lysine (L0.2), 0.2% threonine (T0.2), 0.4% lysine (L0.4), and 0.4% threonine (T0.4), respectively. Compared to the control, weight gain rate (WGR) and specific growth rate (SGR) of C. quadricarinatus significantly increased with increasing dietary lysine and threonine supplementation from 0.2% to 0.4% (P < 0.05). Hepatopancreas trypsin activity significantly increased with increasing levels of lysine and threonine in diets (P < 0.05). However, the pepsin, lipase, and amylase activities were not affected by dietary levels of lysine and threonine (P > 0.05). Compared with the control, crayfish in T0.4 and L0.4 showed significantly higher glutathione peroxidase (GPx) activity (P < 0.05), lower alanine aminotransferase (ALT) activity, and lower malondialdehyde (MDA) content (P < 0.05). Supplementation with 0.4% lysine significantly changed the composition of the gut microbiota (P < 0.05), which showed a significantly increased relative abundance of Proteobacteria and decreased Firmicutes, Actinomycetes, and Pontomyces (P < 0.05). The PICRUSt analysis demonstrated that the abundance of the metabolism and cellular processes pathways in the L0.4 group were markedly decreased compared with the control (P < 0.05). Meanwhile, a tighter interaction of the microbiota community in crayfish was observed in the T0.4 experimental group. In conclusion, these results suggested that dietary supplementation with 0.4% threonine could significantly promote growth and improve microbial health in juvenile C. quadricarinatus.

Growth, survival, and myogenic gene expression in the post-larvae of Colossoma macropomum provisioned with Artemia nauplii

Artemia nauplii are widely used as fish larvae feed due to its beneficial nutritional characteristics for larval development; however, efficient feeding strategies are needed to balance its high costs. Therefore, we evaluated the effects of different densities of Artemia nauplii (100, 250, 500, 750, and 1000 nauplii/post-larvae) on the growth, survival, water quality, and myogenic gene expression of tambaqui (Colossoma macropomum) post-larvae cultivated in a recirculating aquaculture system. After 2 weeks of trial, there was a significant decrease in dissolved oxygen concentration with the increase in nauplii density, but it did not interfere with larval performance and survival. In the first week, larvae fed with fewer than 500 nauplii/post-larvae presented slower growth, while in the second week, larvae fed with 1000 nauplii/post-larvae had the highest final weight and length. Regression analysis suggests that the optimum feeding density of Artemia nauplii during the first week is 411 nauplii/post-larvae, while for the second week, the growth increased proportionally to the feeding densities. The relative expression of the myod, myog, and mstn genes was higher in larvae fed with fewer than 500 nauplii/post-larvae. Although low-growing larvae showed increased expression of myod and myog genes, responsible for muscle hyperplasia and hypertrophy, respectively, mstn expression may have played a significant inhibitory role in larval development. Further research is needed to better determine the effects of the live food on the zootechnical performance and the expression of the myogenic genes in the initial phase of the life cycle of the tambaqui post-larvae.

Dietary threonine improves muscle nutritional value and muscle hardness associated with collagen synthesis in grass carp (Ctenopharyngodon idella)

To further explain the improvement effect of threonine (Thr) on the fillet quality of fish, a 9-week feeding experiment was conducted. After feeding graded levels of Thr (2.38, 5.38, 8.38, 11.38, 14.38 and 17.38 g/kg), the compositions of fillet hydrolyzed amino acid and fatty acid, and the muscle hardness associated with collagen biosynthesis were mainly analyzed in grass carp (Ctenopharyngodon idella). The results showed that Thr increased the pH value, changed the amino acids and fatty acid composition of fillets, especially essential amino acid (EAA), C22:6n3 (DHA) and C20:5n3 (EPA). Furthermore, this study revealed for the first time that the improvement of muscle hardness by Thr was associated with collagen biosynthesis, and the TGF-β1/Smads, LARP6a and Hsp47 regulate transcriptional processes, translation initiation and post-translational modifications in collagen biosynthesis, respectively. This study offered a basis for exploring the contribution of Thr in improving muscle quality in sub-adult grass carp.

Dietary Leucine Improves Fish Intestinal Barrier Function by Increasing Humoral Immunity, Antioxidant Capacity, and Tight Junction

This study attempted to evaluate the possible impact and mechanism of leucine (Leu) on fish intestinal barrier function. One hundred and five hybrid Pelteobagrus vachelli ♀ × Leiocassis longirostris ♂ catfish were fed with six diets in graded levels of Leu 10.0 (control group), 15.0, 20.0, 25.0, 30.0, 35.0, and 40.0 g/kg diet for 56 days. Results showed that the intestinal activities of LZM, ACP, and AKP and contents of C3, C4, and IgM had positive linear and/or quadratic responses to dietary Leu levels. The mRNA expressions of itnl1, itnl2, c-LZM, g-LZM, and β-defensin increased linearly and/or quadratically (p < 0.05). The ROS, PC, and MDA contents had a negative linear and/or quadratic response, but GSH content and ASA, AHR, T-SOD, and GR activities had positive quadratic responses to dietary Leu levels (p < 0.05). No significant differences on the CAT and GPX activities were detected among treatments (p > 0.05). Increasing dietary Leu level linearly and/or quadratically increased the mRNA expressions of CuZnSOD, CAT, and GPX1α. The GST mRNA expression decreased linearly while the GCLC and Nrf2 mRNA expressions were not significantly affected by different dietary Leu levels. The Nrf2 protein level quadratically increased, whereas the Keap1 mRNA expression and protein level decreased quadratically (p < 0.05). The translational levels of ZO-1 and occludin increased linearly. No significant differences were indicated in Claudin-2 mRNA expression and protein level. The transcriptional levels of Beclin1, ULK1b, ATG5, ATG7, ATG9a, ATG4b, LC3b, and P62 and translational levels of ULK1, LC3Ⅱ/Ⅰ, and P62 linearly and quadratically decreased. The Beclin1 protein level was quadratically decreased with increasing dietary Leu levels. These results suggested that dietary Leu could improve fish intestinal barrier function by increasing humoral immunity, antioxidative capacities, and tight junction protein levels.

Effects of dietary threonine on growth and immune response of oriental river prawn (Macrobrachium nipponense)

A 70-day feeding trial was conducted to ascertain the effects of threonine on immune response of juvenile oriental river prawn (Macrobrachium nipponense). Six isonitrogen and isolipidic feeds were formulated according to levels of dietary threonine (0.35%, 0.79%, 1.18%, 1.67%, 2.08% and 2.48% respectively). The juvenile prawns were divided into six groups with four replicates, and stocked into 24 tanks with 50 prawns per tank (initial weight 0.20 ± 0.02 g). The results showed a significant increasing trend of final body weight, specific growth rate, protein efficiency ratio, and weight gain rate when threonine levels increased to 1.67% (P < 0.05). However, feed intake, feed conversion ratio, and whole-body lipid composition significantly decreased as threonine levels in the feed increased up to 1.67% (P < 0.05). Moreover, haemolymph N-urea content was significantly lowest at 1.67% threonine level (P < 0.05), whereas glucose was highest at 0.79% followed by 1.67% of threonine levels in the feeds. Aspartate aminotransferase (AST) enzyme activities were significantly decreased by an imbalance (except 1.67%) of threonine in the feed (P < 0.05). Activities of Alanine aminotransferase (ALT) and albumen (ALB) were not significantly affected by threonine in the feed (P > 0.05). Excessive dietary threonine level (2.48%) significantly activated haemolymph catalase (CAT) activity (P < 0.05), whereas malondialdehyde (MDA) content was significantly affected by deficient (0.35% and 0.79%) dietary threonine levels (P < 0.05). Inducible nitric oxide synthase (iNOS) activity and haemolymph complement component 4 (C4) content were significantly decreased by deficient levels of threonine in the feed (P < 0.05). Excess threonine concentration significantly down-regulated Toll, Dorsal, Relish, and heat shock protein 60 (Hsp60) gene expressions in the hepatopancreas of M. nipponense (P < 0.05), while all genes were significantly up-regulated by the optimal (1.67%) threonine level (P < 0.05). The threonine level at which maximum specific growth rate of M. nipponense occurred was estimated by second degree polynomial regression analysis as 1.65% of threonine level, equivalent to 4.44% dry weight bases of protein in the feed.

Dietary protein levels changed the hardness of muscle by acting on muscle fiber growth and the metabolism of collagen in sub-adult grass carp (Ctenopharyngodon idella)

Background

Nutrient regulation has been proven to be an effective way to improve the flesh quality in fish. As a necessary nutrient for fish growth, protein accounts for the highest proportion in the fish diet and is expensive. Although our team found that the effect of protein on the muscle hardness of grass carp was probably related to an increased collagen content, the mechanism for this effect has not been deeply explored. Moreover, few studies have explored the protein requirements of sub-adult grass crap (Ctenopharyngodon idella). Therefore, the effects of different dietary protein levels on the growth performance, nutritional value, muscle hardness, muscle fiber growth, collagen metabolism and related molecule expression in grass carp were investigated.

Methods

A total of 450 healthy grass carp (721.16 ± 1.98 g) were selected and assigned randomly to six experimental groups with three replicates each (n = 25/replicate), and were fed six diets with 15.91%, 19.39%, 22.10%, 25.59%, 28.53% and 31.42% protein for 60 d.

Results

Appropriate levels of dietary protein increased the feed intake, percentage weight gain, specific growth rate, body composition, unsaturated fatty acid content in muscle, partial free amino acid content in muscle, and muscle hardness of grass carp. These protein levels also increased the muscle fiber density, the frequency of new muscle fibers, the contents of collagen and IGF-1, and the enzyme activities of prolyl 4-hydroxylases and lysyloxidase, and decreased the activity of matrix metalloproteinase-2. At the molecular level, the optimal dietary protein increased collagen type I α1 (Colα1), Colα2, PI3K, Akt, S6K1, La ribonucleoprotein domain family member 6a (LARP6a), TGF-β1, Smad2, Smad4, Smad3, tissue inhibitor of metalloproteinase-2, MyoD, Myf5, MyoG and MyHC relative mRNA levels. The levels of the myostatin-1 and myostatin-2 genes were downregulated, and the protein expression levels of p-Smad2, Smad2, Smad4, p-Akt, Akt, LARP6 and Smad3 were increased.

Conclusions

The appropriate levels of dietary protein promoted the growth of sub-adult grass carp and improved muscle hardness by promoting the growth of muscle fibers, improving collagen synthesis and depressing collagen degradation. In addition, the dietary protein requirements of sub-adult grass carp were 26.21% and 24.85% according to the quadratic regression analysis of growth performance (SGR) and the muscle hardness (collagen content), respectively.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-022-00747-7.

Dietary isoleucine affects muscle fatty acid and amino acid profiles through regulating lipid metabolism and autophagy in hybrid catfish Pelteobagrus vachelli ♀ × Leiocassis longirostris ♂

The present study explored the impacts of Ile on muscle fatty acid and amino acid profiles, lipid metabolism, and autophagy in hybrid catfish. Seven isonitrogenous (387.8 g/kg protein) semi-purified diets were formulated to contain 5.0 (control), 7.5, 10.0, 12.5, 15.0, 17.5, and 20.0 g Ile/kg diet respectively. The fish (initial weight of 33.11 ± 0.09 g) were randomly assigned to 7 groups for a 56-day trial. Each group has 3 replicates with 30 fish per replicate, fed at 08:00 and 18:00 each day. Results showed that muscle protein and lipid, C14:0, C18:0, C22:0, C14:1, C18:1n-9, polyunsaturated fatty acid (PUFA), Arg, Ile, Ala, Cys, Gly, Tyr, essential amino acid (EAA), and total amino acid (TAA) contents and flavor amino acid (FAA)/TAA in muscle had positive linear and/or quadratic responses to dietary Ile levels (P < 0.05). Fatty acid synthase (FAS), stearoyl-CoA desaturase (SCD), acetyl-CoA carboxylase (ACC), and lipoprotein lipase (LPL) activities had positive linear and/or quadratic responses, but carnitine palmitoyl transferase 1 (CPT1) activity had a negative response with increasing dietary Ile levels (P < 0.05). The mRNA expressions of FAS, SCD, ACC, LPL, fatty acid binding protein 4 (FABP4), FATP1, sterol response element-binding protein 1c (SREBP-1c), sequestosome 1 (SQSTM1), and adenosine 5′-monophosphate-activated protein kinase (AMPK) had positive linear and/or quadratic responses to dietary Ile levels (P < 0.05). The mRNA expressions of hormone-sensitive lipase (HSL), CPT1, peroxisome proliferator-activated receptor α (PPARα), PPARγ, uncoordinated 51-like kinase 1 (ULK1), beclin1 (Becn1), autophagy-related protein 9α (Atg9α), Atg4b, Atg7, autophagy marker light chain 3 B (LC3B), and SQSTM1 in muscle had negative linear and/or quadratic responses to dietary Ile levels (P < 0.05). The p-AMPK and ULK1 protein levels, and p-AMPK/AMPK were decreased by 12.5 g Ile/kg in the diet (P < 0.05). Finally, SQSTM1 protein level had the opposite effect (P < 0.05). The above results indicate that dietary Ile improves fish muscle fatty acid and amino acid profiles potentially via respectively regulating lipid metabolism and autophagy. The Ile requirement of hybrid catfish (33 to 72 g) were estimated to be 12.63, 13.77, 13.75, 11.45, 10.50, 12.53 and 12.21 g/kg diet based on the regression analysis of protein, lipid, SFA, PUFA, FAA, EAA, and TAA muscle contents, respectively.

Effects of dietary tryptophan on muscle growth, protein synthesis and antioxidant capacity in hybrid catfish Pelteobagrus vachelli♀ × Leiocassis longirostris♂

The present study evaluated effects of dietary supplementation with tryptophan (Trp) on muscle growth, protein synthesis and antioxidant capacity in hybrid catfish Pelteobagrus vachelli♀ × Leiocassis longirostris♂. Fish were fed six different diets containing 2·6 (control), 3·1, 3·7, 4·2, 4·7 and 5·6 g Trp/kg diet for 56 d, respectively. Results showed that dietary Trp significantly (1) improved muscle protein content, fibre density and frequency of fibre diameter; (2) up-regulated the mRNA levels of PCNA, myf5, MyoD1, MyoG, MRF4, IGF-I, IGF-II, IGF-IR, PIK3Ca, TOR, 4EBP1 and S6K1; (3) increased phosphorylation levels of AKT, TOR and S6K1; (4) decreased contents of MDA and PC, and increased activities of CAT, GST, GR, ASA and AHR; (5) up-regulated mRNA levels of CuZnSOD, CAT, GST, GPx, GCLC and Nrf2, and decreased Keap1 mRNA level; (6) increased nuclear Nrf2 protein level and the intranuclear antioxidant response element-binding ability, and reduced Keap1 protein level. These results indicated that dietary Trp improved muscle growth, protein synthesis as well as antioxidant capacity, which might be partly related to myogenic regulatory factors, IGF/PIK3Ca/AKT/TOR and Keap1/Nrf2 signalling pathways. Finally, based on the quadratic regression analysis of muscle protein and MDA contents, the optimal Trp requirements of hybrid catfish (21·82-39·64 g) were estimated to be 3·94 and 3·93 g Trp/kg diet (9·57 and 9·54 g/kg of dietary protein), respectively.

Physiological Functions of Threonine in Animals: Beyond Nutrition Metabolism

Threonine (Thr), an essential amino acid for animals and the limiting amino acid in swine and poultry diets, which plays a vital role in the modulation of nutritional metabolism, macromolecular biosynthesis, and gut homeostasis. Current evidence supports that the supplementation of Thr leads to benefits in terms of energy metabolism. Threonine is not only an important component of gastrointestinal mucin, but also acts as a nutritional modulator that influences the intestinal immune system via complex signaling networks, particularly mitogen-activated protein kinase (MAPK) and the target of the rapamycin (TOR) signal pathway. Threonine is also recognized as an indispensable nutrient for cell growth and proliferation. Hence, optimization of Thr requirement may exert a favorable impact on the factors linked to health and diseases in animals. This review focuses on the latest reports of Thr in metabolic pathways and nutritional regulation, as well as the relationship between Thr and relevant physiological functions.

Dietary isoleucine improved flesh quality, muscle antioxidant capacity, and muscle growth associated with AKT/TOR/S6K1 and AKT/FOXO3a signaling in hybrid bagrid catfish (Pelteobagrus vachelli♀ × Leiocassis longirostris♂)

Background

Muscle is the complex and heterogeneous tissue, which comprises the primary edible part of the trunk of fish and mammals. Previous studies have shown that dietary isoleucine (Ile) exerts beneficial effects on growth in aquatic animals. However, there were limited studies regarding the benefits of Ile on fish muscle and their effects on flesh quality and muscle growth. Thus, this study was conducted to explore whether dietary Ile had affected flesh quality and muscle growth in hybrid bagrid catfish (Pelteobagrus vachelli♀ × Leiocassis longirostris♂).

Methods

A total of 630 hybrid fish, with an initial average body weight of 33.11 ± 0.09 g, were randomly allotted into seven experimental groups with three replicates each, and respectively fed seven diets with 5.0, 7.5, 10.0, 12.5, 15.0, 17.5, and 20.0 g Ile/kg diets for 8 weeks.

Results

In the present study, we demonstrated that Ile significantly: (1) increased muscle protein and lipid contents and the frequency distribution of myofibers with ≤ 20 μm and ≥ 50 μm of diameter; (2) improved pH value, shear force, cathepsin B and L activities, hydroxyproline content, resilience, cohesiveness, and decreased cooking loss, lactate content, hardness, springiness, gumminess, and chewiness; (3) decreased reactive oxygen species (ROS), malondialdehyde (MDA), and protein carbonyl (PC) contents, GCLC and Keap1 mRNA levels, and up-regulated CuZnSOD, CAT, GPX1a, GST, and Nrf2 mRNA levels; (4) up-regulated the insulin-like growth factor 1, 2 (IGF-1, IGF-2), insulin-like growth factor 1 receptor (IGF-1R), proliferating cell nuclear antigen (PCNA), Myf5, Myod, Myog, Mrf4, and MyHC mRNA levels, and decreased MSTN mRNA level; (5) increased muscle protein deposition by activating AKT-TOR-S6K1 and AKT-FOXO3a signaling pathways.

Conclusion

These results revealed that dietary Ile improved flesh quality, which might be due to increasing nutritional content, physicochemical, texture parameters, and antioxidant ability; promoting muscle growth by affecting myocytes hyperplasia and hypertrophy, and muscle protein deposition associated with protein synthesis and degradation signaling pathways. Finally, the quadratic regression analysis of chewiness, ROS, and protein contents against dietary Ile levels suggested that the optimal dietary Ile levels for hybrid bagrid catfish was estimated to be 14.19, 12.36, and 12.78 g/kg diet, corresponding to 36.59, 31.87, and 32.96 g/kg dietary protein, respectively.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-021-00572-4.