Excessive energy intake does not modify fed-state tissue protein synthesis rates in adult rats

Plant Protein Can Be as Efficient as Milk Protein to Maintain Fat Free Mass in Old Rats, Even When Fat and Sugar Intakes Are High

BACKGROUND

Alternative, sustainable, and adequate sources of protein must be found to meet global demand.

OBJECTIVES

Our aim was to assess the effect of a plant protein blend with a good balance of indispensable amino acids and high contents of leucine, arginine, and cysteine on the maintenance of muscle protein mass and function during aging in comparison to milk proteins and to determine if this effect varied according to the quality of the background diet.

METHODS

Old male Wistar rats (n = 96, 18 mo old) were randomly allocated for 4 mo to 1 of 4 diets, differing according to protein source (milk or plant protein blend) and energy content (standard, 3.6 kcal/g, with starch, or high, 4.9 kcal/g, with saturated fat and sucrose). We measured: every 2 mo, body composition and plasma biochemistry; before and after 4 mo, muscle functionality; after 4 mo, in vivo muscle protein synthesis (flooding dose of L-[1-13C]-valine) and muscle, liver, and heart weights. Two-factor ANOVA and repeated measures 2-factor ANOVA were conducted.

RESULTS

There was no difference between protein type on the maintenance during aging of lean body mass, muscle mass, and muscle functionality. The high-energy diet significantly increased body fat (+47%) and heart weight (+8%) compared to the standard energy diet but had no effect on fasting plasma glucose and insulin. Muscle protein synthesis was significantly stimulated by feeding to the same extent in all groups (+13%).

CONCLUSIONS

Since high-energy diets had little impact on insulin sensitivity and related metabolism, we could not test the hypothesis that in situations of higher insulin resistance, our plant protein blend may be better than milk protein. However, this rat study offers significant proof of concept from the nutritional standpoint that appropriately blended plant proteins can have high nutritional value even in demanding situations such as aging protein metabolism.

Differential changes to splanchnic and peripheral protein metabolism during the diet-induced development of metabolic syndrome in rats

Little is known about the effects of the development of metabolic syndrome (MS) on protein and amino acid (AA) metabolism. During this study, we took advantage of the variability in interindividual susceptibility to high fat diet-induced MS to study the relationships between MS, protein synthesis, and AA catabolism in multiple tissues in rats. After 4 mo of high-fat feeding, an MS score (Z_MS) was calculated as the average of the z-scores for individual MS components [weight, adiposities, homeostasis model for the assessment of insulin resistance (HOMA-IR), and triglycerides]. In the small intestine, liver, plasma, kidneys, heart, and muscles, tissue protein synthesis was measured by ²H₂O labeling, and we evaluated the proportion of tissue AA catabolism (relative to protein synthesis) and nutrient routing to nonindispensable AAs in tissue proteins using natural nitrogen and carbon isotopic distances between tissue proteins and nutrients (Δ¹⁵N and Δ¹³C), respectively. In the liver, protein mass and synthesis increased, whereas the proportion of AA catabolism decreased with Z_MS. By contrast, in muscles, we found no association between Z_MS and protein mass, protein synthesis (except for a weak positive association in the gastrocnemius muscle only), and proportion of AA catabolism. The development of MS was also associated with altered metabolic flexibility and fatty acid oxidation, as shown by less routing of dietary lipids to nonindispensable AA synthesis in liver and muscle. In conclusion, MS development is associated with a greater gain of both fat and protein masses, with higher protein anabolism that mainly occurs in the liver, whereas muscles probably develop anabolic resistance due to insulin resistance.

Effects of chronic high-fat feeding on skeletal muscle mass and function in middle-aged mice

BACKGROUND AND AIMS

Increased adipose tissue may promote catabolic events in skeletal muscle. The aim of this study was to test whether high-fat diet (HFD)-induced obesity would accelerate the onset of muscle wasting in middle-aged mice.

METHODS

Muscle was collected from C57BL/6 mice at 9 months of age (baseline) and 14 months of age after consuming a control (C) or HFD. Mice in C and HFD were also subjected to evaluations of body composition and function before and after their respective diets.

RESULTS

HFD demonstrated significant (p < 0.05) losses of grip strength (-15 %) and sensorimotor coordination (-11 %), whereas C did not. Lean mass decreased to a greater degree in HFD although not significantly (C: -20.69 ± 7.94 vs. HFD: -31.14 ± 5.49 %, p > 0.05). Gastrocnemius, quadriceps, and hamstrings mass in C and HFD were significantly reduced from baseline (-27 to 43 and -39 to 47 %, respectively, p < 0.05) with no differences between the two; however, soleus mass was lower only in HFD (-24 %, p = 0.03). Myofiber area, satellite cells, and myonuclei of the gastrocnemius were lower only in HFD (-23, -19, and -16 %, respectively, p < 0.05) compared to baseline.

CONCLUSIONS

HFD-induced obesity adversely affected function in middle-aged mice. Atrophy of the soleus in HFD but not C suggests sensitivity of oxidative muscle to HFD-dependent catabolism more so than aging. In the muscles containing fast/mixed fibers, aging effects may have concealed the catabolic nature of HFD; however, morphological changes in the gastrocnemius including decreased fiber area, satellite cells, and myonuclei are consistent with an atrophic phenotype related to HFD.

Chronic Intake of Sucrose Accelerates Sarcopenia in Older Male Rats through Alterations in Insulin Sensitivity and Muscle Protein Synthesis

BACKGROUND

Today, high chronic intake of added sugars is frequent, which leads to inflammation, oxidative stress, and insulin resistance. These 3 factors could reduce meal-induced stimulation of muscle protein synthesis and thus aggravate the age-related loss of muscle mass (sarcopenia).

OBJECTIVES

Our aims were to determine if added sugars could accelerate sarcopenia and to assess the capacity of antioxidants and anti-inflammatory agents to prevent this.

METHODS

For 5 mo, 16-mo-old male rats were starch fed (13% sucrose and 49% wheat starch diet) or sucrose fed (62% sucrose and 0% wheat starch diet) with or without rutin (5 g/kg diet), vitamin E (4 times), vitamin A (2 times), vitamin D (5 times), selenium (10 times), and zinc (+44%) (R) supplementation. We measured the evolution of body composition and inflammation, plasma insulin-like growth factor 1 (IGF-I) concentration and total antioxidant status, insulin sensitivity (oral-glucose-tolerance test), muscle weight, superoxide dismutase activity, glutathione concentration, and in vivo protein synthesis rates.

RESULTS

Sucrose-fed rats lost significantly more lean body mass (-8.1% vs. -5.4%, respectively) and retained more fat mass (+0.2% vs. -33%, respectively) than starch-fed rats. Final muscle mass was 11% higher in starch-fed rats than in sucrose-fed rats. Sucrose had little effect on inflammation, oxidative stress, and plasma IGF-I concentration but reduced the insulin sensitivity index (divided by 2). Meal-induced stimulation of muscle protein synthesis was significantly lower in sucrose-fed rats (+7.3%) than in starch-fed rats (+22%). R supplementation slightly but significantly reduced oxidative stress and increased muscle protein concentration (+4%) but did not restore postprandial stimulation of muscle protein synthesis.

CONCLUSIONS

High chronic sucrose intake accelerates sarcopenia in older male rats through an alteration of postprandial stimulation of muscle protein synthesis. This effect could be explained by a decrease of insulin sensitivity rather than by changes in plasma IGF-I, inflammation, and/or oxidative stress.

Growing healthy muscles to optimise metabolic health into adult life

The importance of skeletal muscle for metabolic health and obesity prevention is gradually gaining recognition. As a result, interventions are being developed to increase or maintain muscle mass and metabolic function in adult and elderly populations. These interventions include exercise, hormonal and nutritional therapies. Nonetheless, growing evidence suggests that maternal malnutrition and obesity during pregnancy and lactation impede skeletal muscle development and growth in the offspring, with long-term functional consequences lasting into adult life. Here we review the role of skeletal muscle in health and obesity, providing an insight into how this tissue develops and discuss evidence that maternal obesity affects its development, growth and function into adult life. Such evidence warrants the need to develop early life interventions to optimise skeletal muscle development and growth in the offspring and thereby maximise metabolic health into adult life.

Impaired protein metabolism: interlinks between obesity, insulin resistance and inflammation

Metabolic and structural changes in skeletal muscle that accompany obesity are often associated with the development of insulin resistance. The first events in the pathogenesis of this disorder are considered as an accumulation of lipids within skeletal muscle due to blunted muscle capacity to oxidize fatty acids. Fat infiltration is also associated with muscle fibre typology modification, decrease in muscle mass and impairments in muscle strength. Thus, as a result of obesity, mobility and quality of life are affected, and this is in part due to quantitative and qualitative impairments in skeletal muscle. In addition, the insulin resistance related to obesity results not only in defective insulin-stimulated glucose disposal but has also detrimental consequences on protein metabolism at the skeletal muscle level and whole-body level. This review highlights the involvement of fat accumulation and insulin resistance in metabolic disorders occurring in skeletal muscle during the development of obesity, and the impairments in the regulation of protein metabolism and protein turnover in the links between obesity, metabolic inflammation and insulin resistance.

Time-course changes of muscle protein synthesis associated with obesity-induced lipotoxicity

The object of the study was to investigate the sequential changes of protein synthesis in skeletal muscle during establishment of obesity, considering muscle typology. Adult Wistar rats were fed a standard diet for 16 weeks (C; n = 14), or a high-fat, high-sucrose diet for 16 (HF16; n = 14) or 24 weeks (HF24; n = 15). Body composition was measured using a dual-energy X-ray absorptiometry scanner. The fractional synthesis rates (FSRs) of muscle protein fractions were calculated in tibialis anterior (TA) and soleus muscles by incorporation of l-13C-valine in muscle protein. Muscle lipid and mitochondria contents were determined using histochemical analysis. Obesity occurred in an initial phase, from 1 to 16 weeks, with an increase in weight (P < 0.05), fat mass (P < 0.001), muscle mass (P < 0.001) and FSR in TA (actin: 5.3 ± 0.2 vs. 8.8 ± 0.5% day−1, C vs. HF16, P < 0.001) compared with standard diet. The second phase, from 16 to 24 weeks, was associated with a weight stabilization, a decrease in muscle mass (P < 0.05) and a decrease in FSR in TA (mitochondrial: 5.6 ± 0.2 vs. 4.2 ± 0.4% day−1, HF16 vs. HF24, P < 0.01) compared with HF16 group. Muscle lipid content was increased in TA in the second phase of obesity development (P < 0.001). Muscle mass, lipid infiltration and muscle protein synthesis were differently affected, depending on the stage of obesity development and muscle typology. Chronic lipid infiltration in glycolytic muscle is concomitant with a reduction of muscle protein synthesis, suggesting that muscle lipid infiltration in response to a high-fat diet is deleterious for the incorporation of amino acid in skeletal muscle proteins.

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.

The nature of the ingested protein has no effect on lean body mass during energy restriction in overweight rats

Severe energy restriction in obesity not only leads to fat mass loss but also to lean mass loss. The aim of this study was to compare the capacity of casein, a slowly digested protein, and milk soluble proteins (MSP; rapidly digested) to limit the loss of lean mass induced by energy restriction. Obesity was first induced in male Wistar rats by a 5-week feeding with a high-fat high-sucrose diet. The impact of energy restriction was then studied with high-protein (32%) diets containing either casein, MSP, or a 50/50 mixture of both proteins for 3 weeks (n = 10 per group). Food intake, body weight, nitrogen balance, creatinine, and 3-methyl-histidine excretion were measured during energy restriction. Then, tissue weights, plasma metabolic parameters (amino acids, glucose, insulin, cholesterol, triglycerides), and in vivo liver and extensor digitorum longus (EDL) muscle protein synthesis rates were measured in postabsorptive state at the end of the experimental period. Although significant differences relevant to protein metabolism were observed between groups (protein intake, plasma amino acid concentrations, fecal nitrogen excretion, muscle protein synthesis rates), week per week, there were no significant differences in nitrogen balance whatever the protein used. In conclusion, our results show that in young overweight energy restricted rats, using a high-protein diet, the nature of protein intake has no influence on body protein retention.

Is protein metabolism changed with obesity?

PURPOSE OF REVIEW

Although it is well established that obesity is accompanied by various degrees of metabolic impairments especially in the regulation of carbohydrate and lipid metabolism, the influence of obesity on protein metabolism is not clearly understood. The purpose of this review is to present data describing the modification in protein metabolism that have been reported in the clinical setting of obesity.

RECENT FINDINGS

Recent findings suggest that protein metabolism at the whole-body level is less sensitive to insulin action. Impairments in skeletal muscle protein synthesis rates in the postabsorptive state and in response to anabolic factors are reported in obese human. Finally, chronic excessive energy intake and increased adiposity in rats, without the appearance of other metabolic disturbances, do not induce any changes in tissue protein synthesis rates.

SUMMARY

Body composition in obesity is characterized by elevated fat mass but also lean body mass which is considered either increased or decreased (in the case of sarcopenic obesity). Thus protein metabolism as reflected by changes in protein synthesis and breakdown might be modified in obese individuals but it is still largely debated. Only a few studies have investigated muscle protein kinetics during obesity and do not lead to the same conclusions prolonging the controversies. Indeed, obesity is associated with many metabolic disturbances which might constitute confounding factors differently affecting muscle protein metabolism.