Pipecolate and Taurine are Rat Urinary Biomarkers for Lysine and Threonine Deficiencies

BACKGROUND

The consumption of poor-quality protein increases the risk of essential amino acid (EAA) deficiency, particularly for lysine and threonine. Thus, it is necessary to be able to detect easily EAA deficiency.

OBJECTIVES

The purpose of this study was to develop metabolomic approaches to identify specific biomarkers for an EAA deficiency, such as lysine and threonine.

METHODS

Three experiments were performed on growing rats. In experiment 1, rats were fed for 3 weeks with lysine (L30), or threonine (T53)-deficient gluten diets, or nondeficient gluten diet (LT100) in comparison with the control diet (milk protein, PLT). In experiments 2a and 2b, rats were fed at different concentrations of lysine (L) or threonine (T) deficiency: L/T15, L/T25, L/T40, L/T60, L/T75, P20, L/T100 and L/T170. Twenty-four-hour urine and blood samples from portal vein and vena cava were analyzed using LC-MS. Data from experiment 1 were analyzed by untargeted metabolomic and Independent Component - Discriminant Analysis (ICDA) and data from experiments 2a and 2b by targeted metabolomic and a quantitative Partial Least- Squares (PLS) regression model. Each metabolite identified as significant by PLS or ICDA was then tested by 1-way ANOVA to evaluate the diet effect. A two-phase linear regression analysis was used to determine lysine and threonine requirements.

RESULTS

ICDA and PLS found molecules that discriminated between the different diets. A common metabolite, the pipecolate, was identified in experiments 1 and 2a, confirming that it could be specific to lysine deficiency. Another metabolite, taurine, was found in experiments 1 and 2b, so probably specific to threonine deficiency. Pipecolate or taurine breakpoints obtained give a value closed to the values obtained by growth indicators.

CONCLUSIONS

Our results showed that the EAA deficiencies influenced the metabolome. Specific urinary biomarkers identified could be easily applied to detect EAA deficiency and to determine which AA is deficient.

Growth Retardation Induced by Protein and Indispensable Amino Acid Deficiencies Can Not Be Catch Up by a Supplementation in Growing Rats

Objectives

In developing countries, children are exposed to a risk of growth retardations due to their low protein (LP) intake or poor quality of protein sources with unbalanced indispensable amino acid (IAA) composition. However, the specificity of each IAA and the ability of children to catch-up their growth retardation remains unclear. The aim of this study was to assess the supplementation efficiency following a protein or IAA (lysine, threonine, and methionine) deficiencies in growing rats, and to identify the specific IAA deficiency effect.

Methods

Sixty growing rats were fed by a control (20% of proteins; P20), a LP (5% of proteins; LP) or IAA deficient (25% of the rat's requirement in lysine, threonine, or methionine; L25, T25 and M25) diets for 3w. Thereafter, all rats were supplemented by the control (P20) or a control-equivalent diet containing free AA. Body weight (BW) and food intake were daily recorded. Naso-anal length (NAL), bone mineral density (BMD) and body composition were measured at the end of each period.

Results

During the deficiency, IAA as LP diets reduced BW gain from day 2 for LP, L25 and M25 and from day 1 for T25. At the end of the deficiency, BW was reduced by 30% for L25 and M25, 50% for LP and 60% for T25. NAL was also reduced by 9, 18, 25% for L25/M25, LP and T25. At the end of the deficiency, all groups had less lean body mass (LBM), whereas only LP and T25 had a decreased BMD. Furthermore, the fat mass was only decreased for LP and T25 groups. During the supplementation, growth resumes and the weight's gap between each group was reduced, but remains after supplementation. The BW were reduced by 15, 25 and 35% for L25/M25, LP and T25, respectively. For NAL and LBM, the gap slightly reduced too, but the difference remains after the supplementation. Indeed, the NAL was reduced by 5% for L25 and M25, 8% for LP and 10% for T25. All groups had reduced kidney, muscle and carcass weight, and LP and T25 had a reduced liver weight and BMD. The T25 group was the most affected by the deficiency, even more than LP.

Conclusions

A single IAA deficiency as LP induced growth retardation, and the LBM is highly affected. A supplementation allows growth resume, but the growth retardation cannot be catch up. The stronger effect observed for threonine deficiency, could be due to a wrong estimation of threonine requirement.

Funding Sources

This work was supported by CEFIPRA and AlimH -INRAe.

Lower Synthesis and Higher Catabolism of Liver and Muscle Protein Compensate for Amino Acid Deficiency in Severely Protein-Restricted Growing Rat

Objectives

Severely low-protein (LP) diets induce a decrease in body weight and an increase in relative food including intake (FI) in rat. In the liver, changes in anabolic and catabolic protein pathways could transitorily participate to compensate for amino acid (AA) deficiency. The present study investigated these liver and muscle protein metabolic pathways on LP diet fed growing rats.

Methods

Growing rats were fed for three weeks different diets containing 3–5–8–12–15 or 20% energy from milk protein. Body weight and FI were measured daily. At the end of the experiment, rats were injected with 13C valine and tissues and biological fluids were collected for gene expression measurement, blood AA UPLC analysis and protein

synthesis rate determination in liver and muscle. Statistical analysis was done by 1- or 2-factor ANOVA, when data were repeated.

Results

P3, P5 and P8% diets resulted in significant growth retardation and significant decrease in lean mass. Severe protein deficiency induced a decrease in the rate of protein synthesis in the liver and muscle. In addition, the results showed activation of the GCN2 pathway, via ATF4-CHOP-TRB3 both in the liver and in the muscle, which suggests the inhibition of the initiation of translation at the level of the binding of the RNAt-Met. Liver proteolytic pathways were up-regulated including the ubiquitin-proteasome, the caspase system and the autophagy. In muscle, both the ubiquitin-proteasome pathway, and autophagy were increased as well as the calpain system. The GCN2 pathway, via ATF4-CHOP-TRB3 was activated in both liver and muscle, confirming the activation of protein degradation by the ubiquitin-proteasome pathways, and autophagy. In portal vein, indispensable AA were lower in severe protein deficient diet whereas in vena cava no difference was observed.

Conclusions

Severe protein restriction lowered protein synthesis and activated protein catabolism in both liver and muscle whereas no effect was observed for moderate protein restriction. These results confirm that the liver and muscle play a major role in supplying the body with indispensable AA in response to severe protein restriction.

Funding Sources

This study was funded by the doctoral school ABIES and AlimH-INRAE department.

Lysine and Threonine Restriction Reproduced the Lower Synthesis but Not the Higher Catabolism of Liver and Muscle Protein of Severely Protein Restricted Growing Rats

Objectives

The availability of indispensable amino acids (IAA) modulates protein turnover. More particularly AAI deficiency reduces protein synthesis while the consequence on proteolysis remains unclear. The present study aims to evaluate the specific response of both protein synthesis and proteolysis to a diet restricted on one strictly indispensable IAA, either lysine or threonine

Methods

Sixty-four growing rats were divided into 8 groups (n = 8/group). They were fed for 3 weeks isocaloric diets composed with different levels of lysine or threonine (L or T), 15, 25, 40, 60, 75, 100 or 170% of the theoretical lysine/threonine requirements. At the end of the experiment, rats were injected with valine13C and tissues and biological fluids were collected for gene expression measurement

and blood amino acids (AA). Protein synthesis rate (Fractional and Absolute rate synthesis, ie FSR, ASR) were determined in liver and muscle. Statistical analysis was done by 1- or 2-factor ANOVA, when data were repeated.

Results

Severe (L/T15, L/T25) and moderate (T40) lysine or threonine deficiency resulted in a decrease in body weight gain due to a decrease in lean body mass. Severe restriction (L15, T15, T25) decreased the muscle FSR whereas no effect was observed in the liver. When the rate of protein synthesis was expressed per tissue, the ASR was decreased by severe restriction of lysine and threonine in liver and muscle and by moderate threonine deficiency (T40, T60, T75) in muscle. In liver, no effect of lysine and threonine on proteolysis was observed. In muscle, only severe lysine (L15) deficiency increased proteolysis. Dietary lysine deficiency induced a decrease in lysine concentration in the portal vein and in the vena cava whereas for threonine deficiency, all AAIs except threonine were decreased in the portal vein and vena cava.

Conclusions

These results indicate that the decreased protein synthesis is the primary mechanism involved in decreased lean body mass in response to the severe deficiency in a single AAI. Deficiency of a single AAI reproduce the effect of the low protein diet on protein synthesis. Lysine and threonine deficiency differently affect for a part protein turnover probably in relation with the tissue where they are metabolized.

Funding Sources

This study was funded by the doctoral school ABIES and AlimH-INRAE department.