Effects of DL-methionine and a methionine hydroxy analogue (MHA-Ca) on growth, amino acid profiles and the expression of genes related to taurine and protein synthesis in common carp (Cyprinus carpio)

Abstract

In this trial, nine diets were formulated to investigate the effects of DL-methionine (DL-Met) and a methionine hydroxy analogue (MHA-Ca) on growth, amino acid profiles and the expression of genes related to taurine and protein synthesis in common carp. The basal diet was prepared without methionine supplementation and the other diets were formulated with 0.1%, 0.2%, 0.3% and 0.4% of DL-Met or MHA-Ca, respectively. After the eight-week feeding trial, fish fed with DL-Met or MHA-Ca supplemented diets had higher growth performance and feed utilization when compared with basal diet and two-way ANOVA showed the growth performance and feed utilization were significantly increased in fish fed DL-Met supplemented diets (P < 0.05). The concentrations of free amino acids in serum (Met, Leu, His, Lys, Val, Arg, Ile, Phe and Tau) and muscle (Tau) significantly increased as dietary DL-Met and MHA-Ca increased. Moreover, two-way ANOVA showed that taurine was higher in common carp fed with DL-Met diets compared with MHA-Ca diets. To find out how DL-Met and MHA-Ca affect taurine synthesis, genes involved in methionine degradation and taurine synthesis were further investigated. DL-Met or MHA-Ca supplementation decreased the expression of methionine adenosyltransferase II, alpha (MAT2A) and methionine synthase (MS) and increased the expression of the cysteine dioxygenase (CDO). Moreover, DL-Met supplementation significantly increased the expression of CDO and cysteine sulfinate acid decarboxylase (CSD) when compared with MHA-Ca supplementation. As for protein synthesis, the mRNA expression of mechanistic target of rapamycin (mTOR) in liver was not significantly different among all diet groups. But the expression of eukaryotic translation initiation factor 4E-Binding protein 1 (4EBP1), general control nonderepressible2 (GCN2) and asparagine synthetase (ASNS) in liver were significantly down-regulated as dietary DL-Met or MHA-Ca increased. Compared with MHA-Ca diets, the expression of S6 (ribosomal protein s6) and eIF4E (eukaryotic translation initiation factor 4E binding protein 2) were markedly elevated in DL-Met groups by the analysis of two-way ANOVA. This study indicated that dietary DL-Met or MHA-Ca supplement could increase free essential amino acids in serum, as well as improve taurine synthesis and protein synthesis in common carp. Multi-exponential regression analysis showed that MHA-Ca was less utilized by common carp than DL-Met with bioavailability values of 41% to 50% on weight-for-weight basis.