Influence of low-energy diets on whole-body protein turnover in obese subjects

Comparison of the precursor, amino acid oxidation, and end-product methods for the evaluation of protein turnover in senior dogs

Stable isotope methods have been used to study protein metabolism in humans; however, there application in dogs has not been frequently explored. The present study compared the methods of precursor (13C-Leucine), end-products (15N-Glycine), and amino acid oxidation (13C-Phenylalanine) to determine the whole-body protein turnover rate in senior dogs. Six dogs (12.7 ± 2.6 years age, 13.6 ± 0.6 kg bodyweight) received a dry food diet for maintenance and were subjected to all the above-mentioned methods in succession. To establish 13C and 15N kinetics, according to different methodologies blood plasma, urine, and expired air were collected using a specifically designed mask. The volume of CO2 was determined using respirometry. The study included four methods viz. 13C-Leucine, 13C-Phenylalanine evaluated with expired air, 13C-Phenylalanine evaluated with urine, and 15N-Glycine, with six dogs (repetitions) per method. Data was subjected to variance analysis and means were compared using the Tukey test (P<0.05). In addition, the agreement between the methods was evaluated using Pearson correlation and Bland-Altman statistics. Protein synthesis (3.39 ± 0.33 g.kg-0,75. d-1), breakdown (3.26 ± 0.18 g.kg-0.75.d-1), and flux estimations were similar among the four methods of study (P>0.05). However, only 13C-Leucine and 13C-Phenylalanine (expired air) presented an elevated Pearson correlation and concordance. This suggested that caution should be applied while comparing the results with the other methodologies.

Ruminant metabolic systems biology: reconstruction and integration of transcriptome dynamics underlying functional responses of tissues to nutrition and physiological state

High-throughput ‘omics’ data analysis via bioinformatics is one key component of the systems biology approach. The systems approach is particularly well-suited for the study of the interactions between nutrition and physiological state with tissue metabolism and functions during key life stages of organisms such as the transition from pregnancy to lactation in mammals, ie, the peripartal period. In modern dairy cows with an unprecedented genetic potential for milk synthesis, the nature of the physiologic and metabolic adaptations during the peripartal period is multifaceted and involves key tissues such as liver, adipose, and mammary. In order to understand such adaptation, we have reviewed several works performed in our and other labs. In addition, we have used a novel bioinformatics approach, Dynamic Impact Approach (DIA), in combination with partly previously published data to help interpret longitudinal biological adaptations of bovine liver, adipose, and mammary tissue to lactation using transcriptomics datasets. Use of DIA with transcriptomic data from those tissues during normal physiological adaptations and in animals fed different levels of energy prepartum allowed visualization and integration of most-impacted metabolic pathways around the time of parturition. The DIA is a suitable tool for applying the integrative systems biology approach. The ultimate goal is to visualize the complexity of the systems at study and uncover key molecular players involved in the tissue’s adaptations to physiological state or nutrition.

Body composition and energy metabolism following Roux-en-Y gastric bypass surgery

Roux-en-Y gastric bypass (RYGB) surgery has become an accepted treatment for excessive obesity. We conducted a longitudinal study to assess regional body composition, muscle proteolysis, and energy expenditure before RYGB, and 6 and 12 months after RYGB. Whole-body and regional fat mass (FM) and lean mass (LM) were assessed via dual energy X-ray absorptiometry (DXA), and myofibrillar protein degradation was estimated by urinary 3-methylhistidine (3-MeH) in 29 subjects. Energy expenditure and substrate oxidation were also determined using a whole-room, indirect calorimeter in 12 of these subjects. LM loss constituted 27.8 +/- 10.2% of total weight loss achieved 12 months postoperatively, with the majority of LM loss (18 +/- 6% of initial LM) occurring in the first 6 months following RYGB. During this period, the trunk region contributed 66% of whole-body LM loss. LM loss occurred in the first 6 months after RYGB despite decreased muscle protein breakdown, as indicated by a decrease in 3-MeH concentrations and muscle fractional breakdown rates. Sleep energy expenditure (SEE) decreased from 2,092 +/- 342 kcal/d at baseline to 1,495 +/- 190 kcal/day at 6 months after RYGB (P < 0.0001). Changes in both LM and FM had an effect on the reduction in SEE (P < 0.001 and P = 0.005, respectively). These studies suggest that loss of LM after RYGB is significant and strategies to maintain LM after surgery should be explored.

Resistance training preserves fat-free mass without impacting changes in protein metabolism after weight loss in older women

This study assessed the effects of resistance training (RT) on energy restriction-induced changes in body composition, protein metabolism, and the fractional synthesis rate of mixed muscle proteins (FSRm) in postmenopausal, overweight women. Sixteen women (age 68 +/- 1 years, BMI 29 +/- 1 kg/m(2), mean +/- s.e.m.) completed a 16-week controlled diet study. Each woman consumed 1.0 g protein/kg/day. At baseline (weeks B1-B3) and poststudy (weeks RT12-RT13), energy intake matched each subject's need and during weeks RT1-RT11 was hypoenergetic by 2,092 kJ/day (500 kcal/day). From weeks RT1 to RT13, eight women performed RT 3 day/week (RT group) and eight women remained sedentary (SED group). RT did not influence the energy restriction-induced decrease in body mass (SED -5.8 +/- 0.6 kg; RT -5.0 +/- 0.2 kg) and fat mass (SED -4.1 +/- 0.9 kg; RT -4.7 +/- 0.5 kg). Fat free mass (FFM) and total body water decreased in SED (-1.6 +/- 0.4 and -2.1 +/- 0.5 kg) and were unchanged in RT (-0.3 +/- 0.4 and -0.4 +/- 0.7 kg) (group-by-time, P < or = 0.05 and P = 0.07, respectively). Protein-mineral mass did not change in either group (SED 0.4 +/- 0.2 kg; RT 0.1 +/- 0.4 kg). Nitrogen balance, positive at baseline (2.2 +/- 0.3 g N/day), was unchanged poststudy. After body mass loss, postabsorptive (PA) and postprandial (PP) leucine turnover, synthesis, and breakdown decreased. Leucine oxidation and balance were not changed. PA and total (PA + PP) FSRm in the vastus lateralis were higher after weight loss. RT did not influence these protein metabolism responses. In summary, RT helps older women preserve FFM during body mass loss. The comparable whole-body nitrogen retentions, leucine kinetics, and FSRm between groups are consistent with the lack of differential protein-mineral mass change.

Three weeks of caloric restriction alters protein metabolism in normal-weight, young men

The effects of prolonged caloric restriction (CR) on protein kinetics in lean subjects has not been investigated previously. The purpose of this study was to test the hypotheses that 21 days of CR in lean subjects would 1) result in significant losses of lean mass despite a suppression in leucine turnover and oxidation and 2) negatively impact exercise performance. Nine young, normal-weight men [23 +/- 5 y, 78.6 +/- 5.7 kg, peak oxygen consumption (Vo2 peak) 45.2 +/- 7.3 ml.kg(-1).min(-1), mean +/- SD] were underfed by 40% of the calories required to maintain body weight for 21 days and lost 3.8 +/- 0.3 kg body wt and 2.0 +/- 0.4 kg lean mass. Protein intake was kept at 1.2 g.kg(-1).day(-1). Leucine kinetics were measured using alpha-ketoisocaproic acid reciprocal pool model in the postabsorptive state during rest and 50 min of exercise (EX) at 50% of Vo2 peak). Body composition, basal metabolic rate (BMR), and exercise performance were measured throughout the intervention. At rest, leucine flux (approximately 131 micromol.kg(-1).h(-1)) and oxidation (R(ox); approximately 19 micromol.kg(-1).h(-1)) did not differ pre- and post-CR. During EX, leucine flux (129 +/- 6 vs. 121 +/- 6) and R(ox) (54 +/- 6 vs. 46 +/- 8) were lower after CR than they were pre-CR. Nitrogen balance was negative throughout the intervention ( approximately 3.0 g N/day), and BMR declined from 1,898 +/- 262 to 1,670 +/- 203 kcal/day. Aerobic performance (Vo2 peak, endurance cycling) was not impacted by CR, but arm flexion endurance decreased by 20%. In conclusion, 3 wk of caloric restriction reduced leucine flux and R(ox) during exercise in normal-weight young men. However, despite negative nitrogen balance and loss of lean mass, whole body exercise performance was well maintained in response to CR.

Whole-body protein metabolism due to trauma in man as estimated by L-[15N]alanine

Changes in whole-body protein metabolism due to several skeletal trauma were estimated in five male volunteers and four male trauma patients using a single pulse of [15N]alanine and [13C]urea. The isotopic decay data were computer curve-fitted to obtain the best estimates for eight parameters of a four-pool model. The trauma patients excreted almost 5 times as much urinary nitrogen and utilized 33% more energy than did the volunteers on the same hypocaloric, protein-free diet. Trauma was found to expand the "active metabolic nitrogen" pool and the transfer rates of nitrogen into and out of a "slow turnover protein" pool. Whole-body protein synthesis increased 37% above normal and protein breakdown increased 79% above normal due to trauma. These values were in agreement with those determined at the same time using a [14C]leucine continuous infusion method. The data show that trauma accelerates the nitrogen flow and both protein synthesis and breakdown. This mechanism for negative nitrogen balance is consistent with that found for other severe stresses but is different from milder stresses.

Stimulation of protein synthesis and breakdown by vaccination

Six normal volunteers were vaccinated against typhoid-cholera. 15N-Glycine was injected the morning after vaccination. The injection was repeated three to six days and 10 days later. All subjects ate the same diet on each occasion. Excretion of 15N in urinary ammonia and total urinary excretion of nitrogen, ammonia, and creatinine were determined after each injection of isotope. Urinary excretion of 15N was used to calculate rates of whole-body protein turnover. Total urinary nitrogen and ammonia excretions showed no appreciable change on all three days. Creatinine excretion was significantly higher the day after vaccination than on the other two days (p < 0.05). Rates of protein turnover were also significantly higher on this day: a 37% increase in synthesis and 55% increase in degradation were noted. These results show that during the reaction to vaccination there was a stimulation of whole-body protein metabolism that is similar to that produced by sepsis.