Effects of Dietary Levels of Glycine, Threonine and Protein on Threonine Efficiency and Threonine Dehydrogenase Activity in Hepatic Mitochondria of Chicks

Abstract

This study was carried out to evaluate the relationship between threonine (Thr) efficiency and Thr dehydrogenase (TDG) activity as an indicator of Thr oxidation on chicks fed with levels of diets (CP [17.5% and 21.5%] and Thr [3.8 and 4.7 g/100 g CP]; glycine [Gly][0.64% and 0.98%] and true digestible Thr [dThr] [0.45% and 0.60%]). Calculation of the Thr efficiency was based on N-balance data and an exponential N-utilization model, and TDG activity was determined as accumulation of aminoacetone and Gly during incubation of hepatic mitochondria. This study found that in the liver of chicks who received a diet containing up to 0.79% Thr (4.7 g Thr/100 g of CP) in the 17.5% CP diet, no significant (p>0.05) effect on TDG activity was observed. However, significantly (p = 0.014) increased TDG activity was observed with a diet containing 21.5% CP (4.7 g Thr/100 g of CP) and the efficiency of Thr utilization showed a significant (p = 0.001) decrease, indicating the end of the Thr limiting range. No significant (p>0.05) effect on the total TDG activity and accumulation of Gly was observed with addition of Gly to a diet containing 0.45% dThr. In addition, addition of Gly to a diet containing 0.60% dThr also did not result in a change in accumulation of Gly. Due to an increase in accumulation of aminoacetone, an elevated effect on total TDG activity was also observed. No significant (p>0.05) reduction in the efficiency of Thr utilization was observed after addition of Gly at the level of 0.45% dThr. However, significantly (p<0.001) reduced efficiency of Thr utilization was observed after addition of Gly at the level of 0.60% dThr. Collectively, we found that TDG was stimulated not only by addition of Thr and protein to the diet, but also by addition of Gly, and efficiency of Thr utilization was favorably affected by addition of Gly at the level near to the optimal Thr concentration. In addition, no metabolic requirement of Gly through the TDG pathway was observed with almost the same accumulation of Gly and a slight increase in TDG activity by addition of Gly. Thus, our findings suggest that determination of TDG activity and parameter of efficiency of Thr utilization may be useful for evaluation of dietary Thr level.

Effects of dietary threonine supplementation on productivity and expression of genes related to protein deposition and amino acid transportation in breeder hens of yellow-feathered chicken and their offspring

“…The TDH activity increases significantly under conditions with dietary Thr imbalance in chickens (Davis and Austic, 1997). Lee et al (2014) found that the TDH levels in chickens can be measured to evaluate the utilization of Thr. The present study is the first to investigate the effects of dietary Thr levels on the expression of the TDH gene in broiler breeders.…”

Increasing the availability of threonine, isoleucine, valine, and leucine relative to lysine while maintaining an ideal ratio of lysine:methionine alters mammary cellular metabolites, mammalian target of rapamycin signaling, and gene transcription

“…The fact that Thr uptake by mammary gland is in excess of its output in milk protein (Lapierre et al, 2012) indicates this AA is likely metabolized to other compounds. The enzyme threonine dehydrogenase metabolizes Thr to Gly, and its activity is positively correlated with Thr concentration (Floc'h et al, 1996;Davis and Austic, 1997;Lee et al, 2014). If metabolism of supplemental Thr enhanced Gly synthesis via threonine dehydrogenase, it could have had a positive effect on regulation of cellular proliferation and the synthesis of Ser as part of the one-carbon metabolism pathway (Han et al, 2013;Tang et al, 2014).…”

Implications of elevated threonine plasma concentrations in the development of reduced-crude protein diets for broiler chickens

“…This would be expected to elevate free threonine plasma concentrations, but a dietary CP of 320 g/kg is very much higher than standard. However, Lee et al (2014) found that TDH activity in chicks was stimulated by additional dietary threonine and protein and, presumably, lowering dietary concentrations of threonine and/ or protein would have the reverse effect. The mean analysed dietary threonine concentration was 8.16 g/kg and ranged from 7.4 to 9.1 g/kg in the five nominated experiments; therefore, there were no gross variations in dietary threonine concentrations in association with dietary CP reductions.…”

“…Thus, it is plausible that elevated free threonine plasma concentrations in broiler chickens are essentially generated by the downregulation of hepatic TDH activity. Several investigations into TDH activity in poultry have been completed (Davis and Austic 1997;Yuan et al 2000;Yuan and Austic 2001;Lee et al 2011Lee et al , 2014Lee et al , 2016 without reaching finite conclusions. The activity of TDH in hepatic mitochondria was specifically examined in Davis and Austic (1997) and it was suggested that hepatic TDH activity is influenced more so by concentrations of dietary protein or other amino acids than by threonine per se.…”