337 Efficient RFI Bulls Presented Lower Fractional Synthesis Rates of Plasma Proteins When Fed Corn but Not Grass Based Diets

Protein turnover (PT), the continual synthesis and degradation of body proteins not leading to protein gain, is an essential high energy-demanding process. We assumed that PT might explain the between-animal variations of residual feed intake (RFI). The objective was to measure PT in extreme RFI cattle fed two contrasted diets (grass or corn-based). We conducted a RFI test for 84 days with 100 Charolais bulls and we selected the 32 most extreme (8 per diet and RFI group) for PT measurements using 1) the urinary 3-methyl-histidine to creatinine ratio, as a biomarker of the fractional protein degradation rate (FDR) of skeletal-muscle and 2) the isotopic N turnover rate measured in urine and plasma, as a proxy, respectively, of the whole-body FDR and the fractional protein synthesis rates (FSR) of plasma proteins. The 3-methyl-histidine and creatinine were determined from 10 d total urine collection. Isotopic N turnover in urine and plasma was evaluated by modelling the 15N depletion rate over 112 d following an isotopic N dietary change. Higher plasma FSR and higher skeletal-muscle and whole-body FDR were observed with corn-vs-grass diets (≥11%; P ≤ 0.03), in line with higher metabolizable protein and net energy intakes (≥10%, P = 0.001). Differences between extreme RFI animals were noted with the corn diets only, where efficient animals presented significant lower plasma FSR (-10%; P = 0.04) and numerically lower skeletal-muscle and whole-body FDR (-13% and - 8.9%; P > 0.16 respectively) than non-efficient. Non-significant differences were probably due to an insufficient size of our experimental setup. Plasma FSR is related to the PS of hepatic exportation, hence the lower plasma FSR observed in efficient RFI animals fed corn diets may reflect a lower organs to carcass ratio. Altogether results suggests that efficient RFI bulls fed corn diets had a lower hepatic PT with no-significant changes of whole-body and skeletal muscle PT.

Comparison of Arterial-Venous Balance and Tracer Incorporation Methods for Measuring Muscle Fractional Synthesis and Fractional Breakdown Rates

Loss of muscle mass in response to injury or immobilization impairs functional capacity and metabolic health, thus hindering rehabilitation. Stable isotope techniques are powerful in determining skeletal muscle protein fluxes. Traditional tracer incorporation methods to measure muscle protein synthesis and breakdown are cumbersome and invasive to perform in vulnerable populations such as children. To circumvent these issues, a two-bolus stable isotope amino acid method has been developed; although, measured rates of protein synthesis and breakdown have not been validated simultaneously against an accepted technique such as the arterial-venous balance method. The purpose of the current analysis was to provide preliminary data from the simultaneous determination of the arteriovenous balance and two-bolus tracer incorporation methods on muscle fractional synthesis and breakdown rates in children with burns. Five were administered a primed-constant infusion of L-[ 15N]Threonine for 180 minutes (Prime: 8 µmol/kg; constant: 0.1 µmol·kg -1·min -1). At 120 and 150 minutes, bolus injections of L-[ring- 13C6]Phenylalanine and L-[ 15N]Phenylalanine (50 µmol/kg each) were administered, respectively. Blood and muscle tissue samples were collected to assess mixed muscle protein synthesis and breakdown rates. The preliminary results from this study indicate there is no difference in either fractional synthesis rate (mean ± SD; arteriovenous balance: 0.19 ± 0.17 %/h; tracer incorporation: 0.14 ± 0.08 %/h; P = 0.42) or fractional breakdown rate (arteriovenous balance: 0.29 ± 0.22 %/h; tracer incorporation: 0.23 ± 0.14 %/h; P = 0.84) between methods. These data support the validity of both methods in quantifying muscle amino acid kinetics; however, the results are limited and adequately powered research is still required.

Protein fractional synthesis rates within tissues of high- and low-active mice

With the rise in physical inactivity and its related diseases, it is necessary to understand the mechanisms involved in physical activity regulation. Biological factors regulating physical activity are studied to establish a possible target for improving the physical activity level. However, little is known about the role metabolism plays in physical activity regulation. Therefore, we studied protein fractional synthesis rate (FSR) of multiple organ tissues of 12-week-old male mice that were previously established as inherently low-active (n = 15, C3H/HeJ strain) and high-active (n = 15, C57L/J strain). Total body water of each mouse was enriched to 5% deuterium oxide (D2O) via intraperitoneal injection and maintained with D2O enriched drinking water for about 24 h. Blood samples from the jugular vein and tissues (kidney, heart, lung, muscle, fat, jejunum, ileum, liver, brain, skin, and bone) were collected for enrichment analysis of alanine by LC-MS/MS. Protein FSR was calculated as -ln(1-enrichment). Data are mean±SE as fraction/day (unpaired t-test). Kidney protein FSR in the low-active mice was 7.82% higher than in high-active mice (low-active: 0.1863±0.0018, high-active: 0.1754±0.0028, p = 0.0030). No differences were found in any of the other measured organ tissues. However, all tissues resulted in a generally higher protein FSR in the low-activity mice compared to the high-activity mice (e.g. lung LA: 0.0711±0.0015, HA: 0.0643±0.0020, heart LA: 0.0649± 0.0013 HA: 0.0712±0.0073). Our observations suggest that high-active mice in most organ tissues are no more inherently equipped for metabolic adaptation than low-active mice, but there may be a connection between protein metabolism of kidney tissue and physical activity level. In addition, low-active mice have higher organ-specific baseline protein FSR possibly contributing to the inability to achieve higher physical activity levels.

Comparable Organ Protein Fractional Synthesis Rate of High and Low-Active Mice

Objectives With the rise in physical inactivity and its related diseases, it is necessary to understand the mechanisms involved in physical activity regulation. Scientists have explored physical activity regulation by investigating various physiological mechanisms involving hormones, neurotransmitters, and genetics; however, little is known about the role of metabolism on physical activity level. We hypothesize that protein turnover in specific organs like the muscle is higher in mice previously exhibiting high physical activity levels, as a mechanism to adapt to the increased demand. Therefore, we studied protein fractional synthesis rate (FSR) in tissues of inherently high and low active mice. Methods In order to study protein FSR of various organs, we assessed 12-week-old male inherently low-active (LA) mice (n = 23, lean body mass: 21.0 ± 1.1 g, C3H/HeJ strain) and high active (HA) mice (n = 20, lean body mass: 22.5 ± 1.3, C57L/J strain). One day before tissue collection, a D2O bolus was administered via intraperitoneal injection, and mice were provided D2O enriched drinking water to enrich the total body water to about 5% D2O. Eleven tissues (kidney, heart, lung, muscle, fat, jejunum, ileum, liver, brain, skin, and bone) were collected and analyzed for enrichment of alanine in the intracellular and protein-bound pool (LC-MS/MS). FSR was calculated as -ln(1-enrichment) as fraction per day. Data are mean ± SE (unpaired t-test: GraphPad Prism 8.2). Results We did not find significant differences between protein FSR of HA and LA mice in any measured organ. Example: Protein FSR (fraction/day): muscle (LA: 0.0326±-0.0026, HA: 0.0331 ± 0.0018, P = 0.8673), liver (0.3568 ± 0.0219, 0.3499 ± 0.0217, P = 0.8263), brain (0.0981 ± 0.0056, 0.1041 ± 0.0063, P = 0.4758). Conclusions The observed lack of significant differences in high and low-active mice suggests that differences in specific organ tissue protein turnover may not be a mechanism regulating inherent physical activity level. Since protein turnover is representative of the ability to adapt through upregulation and downregulation of metabolic processes, these results show that high-active mice are inherently no more equipped for metabolic regulation than the low active mice. Funding Sources Sydney and J.L. Huffines Institute for Sports Medicine, Human Performance Student Research Grant and CTRAL Grant.

Fractional Synthesis Rates of Individual Proteins in Rat Soleus and Plantaris Muscles

Differences in the protein composition of fast- and slow-twitch muscle may be maintained by different rates of protein turnover. We investigated protein turnover rates in slow-twitch soleus and fast-twitch plantaris of male Wistar rats (body weight 412 ± 69 g). Animals were assigned to four groups (n = 3, in each), including a control group (0 d) and three groups that received deuterium oxide (D2O) for either 10 days, 20 days or 30 days. D2O administration was initiated by an intraperitoneal injection of 20 μL of 99% D2O-saline per g body weight, and maintained by provision of 4% (v/v) D2O in the drinking water available ad libitum. Soluble proteins from harvested muscles were analysed by liquid chromatography–tandem mass spectrometry and identified against the SwissProt database. The enrichment of D2O and rate constant (k) of protein synthesis was calculated from the abundance of peptide mass isotopomers. The fractional synthesis rate (FSR) of 44 proteins in soleus and 34 proteins in plantaris spanned from 0.58%/day (CO1A1: Collagen alpha-1 chain) to 5.40%/day NDRG2 (N-myc downstream-regulated gene 2 protein). Eight out of 18 proteins identified in both muscles had a different FSR in soleus than in plantaris (p < 0.05).

Effect of ursodeoxycholic acid on lipid metabolism: through the prism of evidence from 2019.

After the discovery of the method of ursodeoxycholic acid’s (UDCA) synthesis and the publication of evidence confirming its ability to reduce the lithogenic properties of bile, active clinical use of UDCA began in the world. This drug, which has pleiotropic effect (choleretic, cytoprotective, immunomodulatory, antiapoptic, litholytic, hypocholesterolemic), has proven its effectiveness in the treatment various diseases: primary biliary cholangitis, intrahepatic cholestasis of pregnancy, gallstone disease. Being a tertiary bile acid, UDCA stimulates bile acid synthesis by reducing the circulating fibroblast growth factor 19 and inhibiting the activation of the farnesoid X-receptor (FXR), which leads to the induction of cholesterol-7α-hydroxylase, a key enzyme in the synthesis of bile acid de novo, mediating the conversion of cholesterol into bile acids. Changes in the formation of bile acids and cholesterol while taking UDCA intake is accompanied by activation of the main enzyme of cholesterol synthesis - 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR). Under the influence of UDCA the activity of stearoyl-Coa desaturase (SCD) in visceral white adipose tissue increases. According to studies conducted in 2019, UDCA improves lipid metabolism by regulating the activity of the ACT/mTOR signaling pathway, reduces the synthesis of cholesterol, decreases the fractional synthesis rate of cholesterol and the fractional synthesis rate of triglycerides. It has been proved that UDCA is accompanied by a decrease in the level of total cholesterol and low density lipoprotein cholesterol.

The isotopic nitrogen turnover rate as a proxy to evaluate in the long-term the protein turnover in growing ruminants

Protein turnover is an energy-consuming process that is essential for ensuring the maintenance of living organisms. Gold standard methods for whole-body protein turnover (WBPT) measurement have inherent drawbacks precluding their generalization for large farm animals and use during long periods. Here, we proposed a non-invasive proxy for the WBPT over a long period of time and in a large number of beef cattle. The proxy is based on the rate at which urine-N and plasma proteins are progressively depleted in terms of 15N after a slight decrease in the isotopic N composition of the diet (i.e. diet switch). We aimed to test the ability of this proxy to adequately discriminate the WBPT of 36 growing-fattening young bulls assigned to different dietary treatments known to impact the WBPT rate, with different protein contents (normal v. high) and amino acid profiles (balanced v. unbalanced in methionine). The 15N depletion rate found in plasma proteins represented their fractional synthesis rate, whereas the slow depletion rate found in urine was interpreted as a proxy of the WBPT. The proxy tested in urine suggested different WBPT values between the normal- and high-protein diets but not between the balanced and unbalanced methionine diets. In contrast, the proxy tested in plasma indicated that both dietary conditions affected the fractional synthesis rate of plasma proteins. We considered that the rate at which urine is progressively 15N-depleted following an isotopic diet switch could be proposed as a non-invasive proxy of the WBPT rate in large farm animals.

The isotopic N turnover rate as a proxy to evaluate in the long-term the protein turnover in growing ruminants

ABSTRACTProtein turnover is an energy-consuming process essential for ensuring the maintenance of living organisms. Gold standard methods for protein turnover measurement are based on intravenous infusions of stable isotopes. Although accurate they have inherent drawbacks precluding their generalization for large farm animals and during long time periods. We proposed here a non-invasive proxy of the whole-body fractional protein degradation (WBFPDR; protein turnover for a growing animal) in the long term and in a large number of beef cattle. The proxy is based on the rate at which urine-N and plasma proteins are progressively depleted in 15N after a slight decrease in the isotopic N composition of diet (i.e. diet-switch). We aimed to test the ability of this proxy to adequately discriminate the WBFPDR of 36 growing-fattening young bulls assigned to different dietary treatments known to impact the protein turnover rate: the protein content and amino acid profile. To achieve this objective, the experimental diets were enriched with 15N labeled-urea during 35 days while the animals were adapted to diets. After stopping the 15N labeled-urea administration the animals were thereafter sampled for spot urines (n = 13) and blood (n = 10) over 5 months and analyzed for their 15N enrichments in total N and plasma proteins, respectively. Adequately fitting the 15N kinetics in plasma proteins and urines required mono- and bi-exponential models, respectively, and the model parameters were compared across dietary conditions using a non-linear mixed effect model. The single 15N depletion rate found in plasma proteins represented their fractional synthesis rate, whereas the slowest depletion rate found in urines was interpreted as a proxy of the WBFPDR. The proxy here tested in urines suggested different WBFPDR values between Normal vs High protein diets but not between balanced vs unbalanced methionine diets. In contrast, the proxy tested in plasma indicated that both dietary conditions affected the fractional synthesis rate of plasma proteins. We consider that the rate at which urines are progressively 15N-depleted following an isotopic diet-switch could be proposed as a non-invasive proxy of the long-term whole-body fractional protein degradation rate for large farm animals.