Leucine Supplementation in a Chronically Protein-Restricted Diet Enhances Muscle Weight and Postprandial Protein Synthesis of Skeletal Muscle by Promoting the mTOR Pathway in Adult Rats

Low protein intake causes a decrease in protein deposition in most animal tissues. The purpose of this study was to investigate whether leucine supplementation would increase the synthesis rate of protein and muscle weight in adult rats, which chronically consume only 58.8% of their protein requirements. Thirty-six male Sprague-Dawley rats were assigned to one of three dietary treatments including a 20% casein diet （CON）, a 10% casein ＋ 0.44% alanine diet （R）, and a 10% casein ＋ 0.87% leucine diet （RL）. After a 10 d dietary treatment, plasma amino acid levels were measured after feeding, the gastrocnemius muscles and soleus muscles were harvested and weighed, and the fractional synthesis rate （FSR） and mammalian target of rapamycin （mTOR） signaling proteins in skeletal muscle were measured. Regarding the plasma amino acid level, the RL group had the highest concentration of leucine （P 〈 0.05） and the lowest concentration of isoleucine （P 〈 0.05） among the three groups, and the CON group had a lower concentration of valine （P 〈 0.05） than the R and RL groups. Compared with the R and RE groups, the CON group diet significantly increased （P 〈 0.05） feed intake, protein synthesis rate, and the phosphorylation of eukaryutic initiation factor 4E binding protein 1 （4E-BP1）, and decreased the weight of abdominal adipose. Compared with the R group, the RL group significantly increased in gastrocnemius muscle weight, protein synthesis rate, and phosphorylation of both ribosomal protein $6 kinase 1 （56K1） and 4E-BP1. In conclusion, when protein is chronically restricted in adult rat diets, leucine supplementation moderately improves body weight gain and increases muscle protein synthesis through mTOR activation,

Association of ratios of visceral fat area/subcutaneous fat area and muscle area/standard body weight at T12 CT level with the prognosis of acute respiratory distress syndrome

Background:It is well-known that body composition metrics can influence the prognosis of various diseases.This study investigated how body composition metrics predict acute respiratory distress syndrome(ARDS)prognosis,focusing on the ratio of visceral fat area(VFA)to subcutaneous fat area(SFA),SFA to standard body weight(SBW),VFA to SBW,and muscle area(MA)to SBW.These metrics were assessed at the level of the twelfth thoracic vertebra(T12 computed tomography[CT]level)to determine their correlation with the outcomes of ARDS.The goal was to utilize these findings to refine and personalize treatment strategies for ARDS.Methods:Patients with ARDS admitted to the intensive care units(ICUs)of three hospitals from January 2016 to July 2023 were enrolled in this study.Within 24 hours of ARDS onset,we obtained chest CT scans to mea-sure subcutaneous fat,visceral fat,and muscle area at the T12 level.We then compared these ratios between survivors and non-survivors.Logistic regression was employed to identify prognostic risk factors.Receiver oper-ating characteristic(ROC)curve analysis was utilized to determine the optimal cutofffor predictors of in-hospital mortality.Based on this cutoff,patients with ARDS were stratified.To reduce confounding factors,1:1 propensity score matching(PSM)was applied.We conducted analyses of clinical feature and prognostic differences pre-and post-PSM between the stratified groups.Additionally,Kaplan-Meier survival curves were generated to compare the survival outcomes of these groups.Results:Of 258 patients with ARDS,150 survived and 108 did not.Non-survivors had a higher VFA/SFA ra-tio(P<0.001)and lower SFA/SBW and MA/SBW ratios(both P<0.001).Key risk factors were high VFA/SFA ratio(OR=2.081;P=0.008),age,acute physiology and chronic health evaluation(APACHE)II score,and lac-tate levels,while MA/SBW and albumin were protective.Patients with a VFA/SFA ratio≥0.73 were associated with increased mortality,while those with an MA/SBW ratio>1.55 cm^(2)/kg had lower mortality,both pre-and post-PSM(P=0.001 and P<0.001,respectively).Among 170 patients with pulmonary-origin ARDS,87 survived and 83 did not.The non-survivor group showed a higher VFA/SFA ratio(P<0.001)and lower SFA/SBW and MA/SBW(P=0.003,P<0.001,respectively).Similar risk and protective factors were observed in this cohort.For VFA/SFA,a value above the cutoffof 1.01 predicted higher mortality,while an MA/SBW value below the cutoffof 1.48 cm2/kg was associated with increased mortality(both P<0.001 pre-/post-PSM).Conclusions:Among all patients with ARDS,the VFA to SFA ratio,MA to SBW ratio at the T12 level,age,APACHE II score,and lactate levels emerged as independent risk factors for mortality.