A new method to estimate the relative bioavailability of individual amino acids in fish larvae using 13C-NMR spectroscopy

Metabolic Fate Is Defined by Amino Acid Nature in Gilthead Seabream Fed Different Diet Formulations

Simple Summary

The maximisation of fish growth depends on amino acids’ availability in tissues at an optimum ratio since imbalances may lead to their utilisation for energy rather than growth. Amino acids may be catabolised in multiple pathways and be classified according to their metabolic fate: ketogenic and glucogenic. Ketogenic amino acids (e.g., lysine) are precursors of ketone bodies or long chain fatty acids and can be used in lipogenesis. Glucogenic amino acids (e.g., methionine) can be converted into glucose through gluconeogenesis. Some amino acids, such as tryptophan, can be ketogenic and glucogenic. This study aimed to evaluate how fish discriminate among different amino acids when they are fed different diets to attain the best utilisation of the feed. This trial was carried out in gilthead seabream juveniles fed experimental diets containing different levels of protein and/or distinct lipid levels. The metabolic fate and bioavailability of the indispensable amino acids lysine, methionine, and tryptophan were defined by their ketogenic and/or glucogenic nature rather than diet formulations. The optimisation of diets that consider the amino acids’ bioavailability will maximise protein retention in fish and is a viable solution to develop cost-effective fish diets.

Abstract

The sustainability of the Aquaculture industry relies on optimising diets to promote nitrogen retention and maximise fish growth. The aim of this study was to assess how different dietary formulations influence the bioavailability and metabolic fate of distinct amino acids in gilthead seabream juveniles. Amino acids (lysine, tryptophan, and methionine) were selected based on their ketogenic and/or glucogenic nature. Seabream were fed practical diets with different protein (44 and 40%) and lipid contents (21 and 18%): 44P21L, 44P18L, 40P21L, and 40P18L. After three weeks of feeding, the fish were tube-fed the correspondent diet labelled with ¹⁴C-lysine, ¹⁴C-tryptophan, or ¹⁴C-methionine. The amino acid utilisation was determined based on the evacuation, retention in gut, liver, and muscle, and the catabolism of the tracer. The metabolic fate of amino acids was mainly determined by their nature. Tryptophan was significantly more evacuated than lysine or methionine, indicating a lower availability for metabolic purposes. Methionine was more retained in muscle, indicating its higher availability. Lysine was mainly catabolised, suggesting that catabolism is preferentially ketogenic, even when this amino acid is deficient in diets. This study underpins the importance of optimising diets considering the amino acids’ bioavailability and metabolic fate to maximise protein retention in fish.

Integrated analysis of proteomics-delineated and metabolomics-delineated hepatic metabolic responses to (-)-hydroxycitric acid in chick embryos

(-)-Hydroxycitric acid [(-)-HCA] is widely used as a nutritional supplement to control body weight and fat accumulation in animals and humans, whereas the underlying biochemical mechanism is unclear. Broiler chicken was used as a model for studies of obesity due to its natural hyperglycemia and being insulin resistant. The current study aimed to obtain a systematic view of serum metabolites and hepatic proteins and well understand the mechanism of hepatic metabolic response to (-)-HCA treatment in chick embryos. The results showed that 22, 90, and 82 of differentially expressed proteins were identified at E14d, E19d, and H1d in chick embryos treated with (-)-HCA, respectively. Meanwhile, 5, 83, and 88 of serum metabolites significantly changed at E14d, E19d, and H1d in chick embryos after (-)-HCA treatment. Bioinformatics analysis showed that the key proteins and metabolites, which were significantly altered in chick embryos treated with (-)-HCA, were mainly involved in the citrate cycle, glycolysis/gluconeogenesis, fatty acid metabolism, and pyruvate metabolism. Our data indicated that (-)-HCA treatment might promote fat metabolism via regulating the key protein expression levels and metabolite contents in the citrate cycle, glycolysis/gluconeogenesis, and oxidative phosphorylation during chicken embryonic development. These results will deepen our understanding of the mechanism of fat reduction by (-)-HCA and provide substantial information for (-)-HCA as a nutritional supplement to control body weight gain and curb obesity-related diseases.

(-)-Hydroxycitric Acid Nourishes Protein Synthesis via Altering Metabolic Directions of Amino Acids in Male Rats

(-)-Hydroxycitric acid (HCA), a major active ingredient of Garcinia Cambogia extracts, had shown to suppress body weight gain and fat accumulation in animals and humans. While, the underlying mechanism of (-)-HCA has not fully understood. Thus, this study was aimed to investigate the effects of long-term supplement with (-)-HCA on body weight gain and variances of amino acid content in rats. Results showed that (-)-HCA treatment reduced body weight gain and increased feed conversion ratio in rats. The content of hepatic glycogen, muscle glycogen, and serum T4 , T3 , insulin, and Leptin were increased in (-)-HCA treatment groups. Protein content in liver and muscle were significantly increased in (-)-HCA treatment groups. Amino acid profile analysis indicated that most of amino acid contents in serum and liver, especially aromatic amino acid and branched amino acid, were higher in (-)-HCA treatment groups. However, most of the amino acid contents in muscle, especially aromatic amino acid and branched amino acid, were reduced in (-)-HCA treatment groups. These results indicated that (-)-HCA treatment could reduce body weight gain through promoting energy expenditure via regulation of thyroid hormone levels. In addition, (-)-HCA treatment could promote protein synthesis by altering the metabolic directions of amino acids. Copyright © 2016 John Wiley & Sons, Ltd.

Novel methodologies in marine fish larval nutrition

Major gaps in knowledge on fish larval nutritional requirements still remain. Small larval size, and difficulties in acceptance of inert microdiets, makes progress slow and cumbersome. This lack of knowledge in fish larval nutritional requirements is one of the causes of high mortalities and quality problems commonly observed in marine larviculture. In recent years, several novel methodologies have contributed to significant progress in fish larval nutrition. Others are emerging and are likely to bring further insight into larval nutritional physiology and requirements. This paper reviews a range of new tools and some examples of their present use, as well as potential future applications in the study of fish larvae nutrition. Tube-feeding and incorporation into Artemia of (14)C-amino acids and lipids allowed studying Artemia intake, digestion and absorption and utilisation of these nutrients. Diet selection by fish larvae has been studied with diets containing different natural stable isotope signatures or diets where different rare metal oxides were added. Mechanistic modelling has been used as a tool to integrate existing knowledge and reveal gaps, and also to better understand results obtained in tracer studies. Population genomics may assist in assessing genotype effects on nutritional requirements, by using progeny testing in fish reared in the same tanks, and also in identifying QTLs for larval stages. Functional genomics and proteomics enable the study of gene and protein expression under various dietary conditions, and thereby identify the metabolic pathways which are affected by a given nutrient. Promising results were obtained using the metabolic programming concept in early life to facilitate utilisation of certain nutrients at later stages. All together, these methodologies have made decisive contributions, and are expected to do even more in the near future, to build a knowledge basis for development of optimised diets and feeding regimes for different species of larval fish.