Dietary glycine supplementation enhances the growth performance of hybrid striped bass (Morone saxatilis ♀× Morone chrysops ♂) fed soybean meal-based diets

Gut microbiota-bile acid crosstalk and metabolic fatty liver in spotted seabass (Lateolabrax maculatus): The role of a cholesterol, taurine and glycine supplement

The prevalent practice of substituting fishmeal with plant protein frequently leads to disturbances in bile acid metabolism, subsequently increasing the incidence of metabolic liver diseases. Bile acid nutrients such as cholesterol, taurine and glycine have been shown to enhance bile acid synthesis and confer beneficial effects on growth. Therefore, this study aimed to investigate the effects of cholesterol-taurine-glycine (Ch-Tau-Gly) supplement on bile acid metabolism and liver health in spotted seabass (Lateolabrax maculatus) fed a plant-based diet. Two isonitrogenous and isolipidic diets were formulated: (1) plant protein-based diet (PP); (2) PP supplemented 0.5% cholesterol, 0.5% taurine and 1.3% glycine (CTG). Each experimental diet was randomly fed to quadruplicate groups of 30 feed-trained spotted seabass in each tank. The results revealed that supplementing plant-based diet with Ch-Tau-Gly supplement led to an increase in carcass ratio (meat yield) in spotted seabass (P < 0.05), indirectly contributing positively to their growth. The dietary supplement effectively suppressed endogenous cholesterol synthesis in the liver, promoted the expression of bile acid synthesis enzyme synthesis, and simultaneously the expression of intestinal fxr and its downstream genes, including hnf4α and shp (P < 0.05). The reduction in Lactobacillus_salivarius and bile salt hydrolase (BSH) were observed in CTG group with concurrently increased conjugated chenodeoxycholic acid (CDCA) bile acids (P < 0.05), suggesting the enhancement of the hydrophilicity of the bile acid pool. In CTG group, fatty liver was alleviated with a corresponding increase in lipid metabolism, characterized by a downregulation of genes associated with lipogenesis and lipid droplet deposition, along with an upregulation of genes related to lipolysis. Our study underscored the ability of Ch-Tau-Gly supplement to influence the gut microbiota, leading to an increase in the levels of conjugated CDCA (P < 0.05) in the bile acid pool of spotted seabass. The interplay between the gut microbiota and bile acids might constitute a crucial pathway in the promotion of liver health. These findings offer a promising solution, suggesting that Ch-Tau-Gly supplement have the potential to promote the growth of aquatic species and livestock fed on plant-based diets while addressing issues related to metabolic fatty liver.

Dietary glycine supplementation enhances syntheses of creatine and glutathione by tissues of hybrid striped bass (Morone saxatilis ♀ × Morone chrysops ♂) fed soybean meal-based diets

BACKGROUND

We recently reported that supplementing glycine to soybean meal-based diets is necessary for the optimum growth of 5- to 40-g (Phase-I) and 110- to 240-g (Phase-II) hybrid striped bass (HSB), as well as their intestinal health. Although glycine serves as an essential substrate for syntheses of creatine and glutathione (GSH) in mammals (e.g., pigs), little is known about these metabolic pathways or their nutritional regulation in fish. This study tested the hypothesis that glycine supplementation enhances the activities of creatine- and GSH-forming enzymes as well as creatine and GSH availabilities in tissues of hybrid striped bass (HSB; Morone saxatilis♀ × Morone chrysops♂).

METHODS

Phase-I and Phase-II HSB were fed a soybean meal-based diet supplemented with 0%, 1%, or 2% glycine for 8 weeks. At the end of the 56-d feeding, tissues (liver, intestine, skeletal muscle, kidneys, and pancreas) were collected for biochemical analyses.

RESULTS

In contrast to terrestrial mammals and birds, creatine synthesis occurred primarily in skeletal muscle from all HSB. The liver was most active in GSH synthesis among the HSB tissues studied. In Phase-I HSB, supplementation with 1% or 2% glycine increased (P < 0.05) concentrations of intramuscular creatine (15%-19%) and hepatic GSH (8%-11%), while reducing (P < 0.05) hepatic GSH sulfide (GSSG)/GSH ratios by 14%-15%, compared with the 0-glycine group; there were no differences (P > 0.05) in these variables between the 1% and 2% glycine groups. In Phase-II HSB, supplementation with 1% and 2% glycine increased (P < 0.05) concentrations of creatine and GSH in the muscle (15%-27%) and liver (11%-20%) in a dose-dependent manner, with reduced ratios of hepatic GSSG/GSH in the 1% or 2% glycine group. In all HSB, supplementation with 1% and 2% glycine dose-dependently increased (P < 0.05) activities of intramuscular arginine:glycine amidinotransferase (22%-41%) and hepatic γ-glutamylcysteine synthetase (17%-37%), with elevated activities of intramuscular guanidinoacetate methyltransferase and hepatic GSH synthetase and GSH reductase in the 1% or 2% glycine group. Glycine supplementation also increased (P < 0.05) concentrations of creatine and activities of its synthetic enzymes in tail kidneys and pancreas, and concentrations of GSH and activities of its synthetic enzymes in the proximal intestine.

CONCLUSIONS

Skeletal muscle and liver are the major organs for creatine and GSH syntheses in HSB, respectively. Dietary glycine intake regulates creatine and GSH syntheses by both Phase-I and Phase-II HSB in a tissue-specific manner. Based on the metabolic data, glycine is a conditionally essential amino acid for the growing fish.

Characteristics of Nutrition and Metabolism in Dogs and Cats

Domestic dogs and cats have evolved differentially in some aspects of nutrition, metabolism, chemical sensing, and feeding behavior. The dogs have adapted to omnivorous diets containing taurine-abundant meat and starch-rich plant ingredients. By contrast, domestic cats must consume animal-sourced foods for survival, growth, and development. Both dogs and cats synthesize vitamin C and many amino acids (AAs, such as alanine, asparagine, aspartate, glutamate, glutamine, glycine, proline, and serine), but have a limited ability to form de novo arginine and vitamin D3. Compared with dogs, cats have greater endogenous nitrogen losses and higher dietary requirements for AAs (particularly arginine, taurine, and tyrosine), B-complex vitamins (niacin, thiamin, folate, and biotin), and choline; exhibit greater rates of gluconeogenesis; are less sensitive to AA imbalances and antagonism; are more capable of concentrating urine through renal reabsorption of water; and cannot tolerate high levels of dietary starch due to limited pancreatic α-amylase activity. In addition, dogs can form sufficient taurine from cysteine (for most breeds); arachidonic acid from linoleic acid; eicosapentaenoic acid and docosahexaenoic acid from α-linolenic acid; all-trans-retinol from β-carotene; and niacin from tryptophan. These synthetic pathways, however, are either absent or limited in all cats due to (a) no or low activities of key enzymes (including pyrroline-5-carboxylate synthase, cysteine dioxygenase, ∆6-desaturase, β-carotene dioxygenase, and quinolinate phosphoribosyltransferase) and (b) diversion of intermediates to other metabolic pathways. Dogs can thrive on one large meal daily, select high-fat over low-fat diets, and consume sweet substances. By contrast, cats eat more frequently during light and dark periods, select high-protein over low-protein diets, refuse dry food, enjoy a consistent diet, and cannot taste sweetness. This knowledge guides the feeding and care of dogs and cats, as well as the manufacturing of their foods. As abundant sources of essential nutrients, animal-derived foodstuffs play important roles in optimizing the growth, development, and health of the companion animals.

Analysis of Gizzerosine in Foodstuffs by HPLC Involving Pre-column Derivatization with o-Phthaldialdehyde

Gizzerosine [2-amino-9-(4-imidazolyl)-7-azanonanoic acid] is a toxic amino acid formed from histamine and lysine at high temperatures, and may be present in foodstuffs (e.g., fishmeal and meat-bone meal) for animals including cats and dogs. Here we developed a simple, rapid, sensitive, specific, and automated method for the analysis of gizzerosine in foodstuffs by high-performance liquid chromatography (HPLC) involving pre-column derivatization with o-phthaldialdehyde (OPA) in the presence of N-acetylcysteine (instead of the usual 2-mercaptoethanol or ethanethiol reagent). OPA reacted immediately (within 1 min) with gizzerosine in an autosampler at room temperatures (e.g., 20-25 °C), and their derivative was directly injected into the HPLC column. The highly fluorescent gizzerosine-OPA derivative was well separated from the OPA derivatives of all natural amino acids known to be present in physiological fluids (e.g., plasma), proteins and foodstuffs, and was detected at an excitation wavelength of 340 nm and an emission wavelength of 450 nm. The total time for chromatographic separation (including column regeneration) was 20 min per sample rather than 40 min and longer in previous HPLC methods. The detection limit for gizzerosine was at least 6 pmol/ml in an assay solution (HPLC vial) or at least 0.09 pmol per injection into the HPLC column. The analysis of gizzerosine was linear between 1 and 100 pmol per injection. When gizzerosine was extracted from foodstuffs, its detection limit was at least 875 pmol/g foodstuff or at least 0.21 mg/kg foodstuff. Our routine HPLC technique does not require any cleanup of samples or the OPA derivatization products (including the OPA-gizzerosine adduct), and is applicable for the analysis of gizzerosine in both foodstuffs and animal tissues.

Dietary glycine supplementation improves the growth performance of 110- to 240-g (phase II) hybrid striped bass (Morone saxatilis ♀× Morone chrysops ♂) fed soybean meal-based diets

We recently reported that supplementing glycine to soybean meal (SBM)-based diets is necessary for optimum growth of 5- to 40-g (phase I) hybrid striped bass (HSB). The present study tested the hypothesis that supplementing glycine to SBM-based diets may enhance the growth of 110- to 240-g (phase II) HSB. HSB (the initial body weight of approximately 110 g) were fed an SBM (58%)-based diet supplemented with 0%, 1%, or 2% of glycine, with l-alanine serving as the isonitrogenous control. There were four tanks per dietary group, with four fish per tank. The fish were fed their respective diets to apparent satiation twice daily. The feed intake and body weight of fish were recorded daily and every 2 wk, respectively. At the end of the 56-d feeding trial, plasma and tissue samples were collected to determine amino acid concentrations and histological alterations, and tissues were used to measure the oxidation of l-glutamate, l-glutamine, l-aspartate, and glycine. Results showed that dietary supplementation with 1% and 2% glycine dose-dependently increased (P < 0.05) the concentration of glycine in the plasma of HSB by 48% and 99%, respectively. Compared with the 0%-glycine group, dietary supplementation with 1% glycine did not affect (P > 0.05) the feed intake of HSB but increased (P < 0.05) their final body weight, weight gain, and gain:feed ratio during the whole period by 13%, 29%, and 21%, respectively. Compared with the 1% glycine group, dietary supplementation with 2% glycine increased (P < 0.05) the feed intake, final body weight, and weight gain of HSB by 13%, 7%, and 14%, respectively. Compared with the 0%-glycine group, fish fed with the 1%-glycine and 2%-glycine diets had a greater (P < 0.05) villus height in the proximal intestine, when compared with the 0%-glycine group. Collectively, these results indicated that SBM-based diets did not provide sufficient glycine for phase II HSB (110 to 240 g) and that dietary glycine supplementation is essential for their optimum growth and intestinal structure.