Protein Type, Protein Dose, and Age Modulate Dietary Protein Digestion and Phenylalanine Absorption Kinetics and Plasma Phenylalanine Availability in Humans.

BACKGROUND: Dietary protein ingestion stimulates muscle protein synthesis by providing amino acids to the muscle. The magnitude and duration of the postprandial increase in muscle protein synthesis rates are largely determined by dietary protein digestion and amino acid absorption kinetics. OBJECTIVE: We assessed the impact of protein type, protein dose, and age on dietary protein digestion and amino acid absorption kinetics in vivo in humans. METHODS: We included data from 18 randomized controlled trials with a total of 602 participants [age: 53 ± 23 y; BMI (kg/m2): 24.8 ± 3.3] who consumed various quantities of intrinsically l-[1-13C]-phenylalanine-labeled whey (n = 137), casein (n = 393), or milk (n = 72) protein and received intravenous infusions of l-[ring-2H5]-phenylalanine, which allowed us to assess protein digestion and phenylalanine absorption kinetics and the postprandial release of dietary protein-derived phenylalanine into the circulation. The effect of aging on these processes was assessed in a subset of 82 young (aged 22 ± 3 y) and 83 older (aged 71 ± 5 y) individuals. RESULTS: A total of 50% ± 14% of dietary protein-derived phenylalanine appeared in the circulation over a 5-h postprandial period. Casein ingestion resulted in a smaller (45% ± 11%), whey protein ingestion in an intermediate (57% ± 10%), and milk protein ingestion in a greater (65% ± 13%) fraction of dietary protein-derived phenylalanine appearing in the circulation (P < 0.001). The postprandial availability of dietary protein-derived phenylalanine in the circulation increased with the ingestion of greater protein doses (P < 0.05). Protein digestion and phenylalanine absorption kinetics were attenuated in older when compared with young individuals, with 45% ± 10% vs. 51% ± 14% of dietary protein-derived phenylalanine appearing in the circulation, respectively (P = 0.001). CONCLUSIONS: Protein type, protein dose, and age modulate dietary protein digestion and amino acid absorption kinetics and subsequent postprandial plasma amino acid availability in vivo in humans. These trials were registered at clinicaltrials.gov as NCT00557388, NCT00936039, NCT00991523, NCT01317511, NCT01473576, NCT01576848, NCT01578590, NCT01615276, NCT01680146, NCT01820975, NCT01986842, and NCT02596542, and at http://www.trialregister.nl as NTR3638, NTR3885, NTR4060, NTR4429, and NTR4492.

Acute dietary protein intake restriction is associated with changes in myostatin expression after a single bout of resistance exercise in healthy young men.

Skeletal muscle satellite cells (SCs) play an important role in the myogenic adaptive response to exercise. It remains to be established whether nutrition plays a role in SC activation in response to exercise. In the present study, we assessed whether dietary protein alters the SC response to a single bout of resistance exercise. Twenty healthy young (aged 21 ± 2 y) males were randomly assigned to consume a 4-d controlled diet that provided either 1.2 g protein ⋅ kg body weight(-1) ⋅ d(-1) [normal protein diet (NPD)] or 0.1 g protein ⋅ kg body weight(-1) ⋅ d(-1) [low protein diet (LPD)]. On the second day of the controlled diet, participants performed a single bout of resistance exercise. Muscle biopsies from the vastus lateralis were collected before and after 12, 24, 48, and 72 h of post-exercise recovery. SC content and activation status were determined using immunohistochemistry. Protein and mRNA expression were determined using Western blotting and reverse transcription polymerase chain reaction. The number of myostatin + SCs decreased significantly at 12, 24, and 48 h (range, -14 to -49%; P < 0.05) after exercise cessation, with no differences between groups. Although the number of myostatin + SCs returned to baseline in the type II fibers on the NPD after 72 h of recovery, the number remained low on the LPD. At the 48 and 72 h time points, myostatin protein expression was elevated (86 ± 26% and 88 ± 29%, respectively) on the NPD (P < 0.05), whereas it was reduced at 72 h (-36 ± 12% compared with baseline) in the LPD group (P < 0.05). This study demonstrates that dietary protein intake does not modulate the post-exercise increase in SC content but modifies myostatin expression in skeletal muscle tissue. This trial was registered at clinicaltrials.gov as NCT01220037.

Amino acid absorption and subsequent muscle protein accretion following graded intakes of whey protein in elderly men.

Whey protein ingestion has been shown to effectively stimulate postprandial muscle protein accretion in older adults. However, the impact of the amount of whey protein ingested on protein digestion and absorption kinetics, whole body protein balance, and postprandial muscle protein accretion remains to be established. We aimed to fill this gap by including 33 healthy, older men (73 ± 2 yr) who were randomly assigned to ingest 10, 20, or 35 g of intrinsically l-[1-¹³C]phenylalanine-labeled whey protein (n = 11/treatment). Ingestion of labeled whey protein was combined with continuous intravenous l-[ring-²H5]phenylalanine and l-[ring-²H2]tyrosine infusion to assess the metabolic fate of whey protein-derived amino acids. Dietary protein digestion and absorption rapidly increased following ingestion of 10, 20, and 35 g whey protein, with the lowest and highest (peak) values observed following 10 and 35 g, respectively (P < 0.05). Whole body net protein balance was positive in all groups (19 ± 1, 37 ± 2, and 58 ± 2 µmol/kg), with the lowest and highest values observed following ingestion of 10 and 35 g, respectively (P < 0.05). Postprandial muscle protein accretion, assessed by l-[1-¹³C]phenylalanine incorporation in muscle protein, was higher following ingestion of 35 g when compared with 10 (P < 0.01) or 20 (P < 0.05) g. We conclude that ingestion of 35 g whey protein results in greater amino acid absorption and subsequent stimulation of de novo muscle protein synthesis compared with the ingestion of 10 or 20 g whey protein in healthy, older men.

Intragastric protein administration stimulates overnight muscle protein synthesis in elderly men.

The loss of skeletal muscle mass with aging has been attributed to an impaired muscle protein synthetic response to food intake. Therefore, nutritional strategies are targeted to modulate postprandial muscle protein accretion in the elderly. The purpose of this study was to assess the impact of protein administration during sleep on in vivo protein digestion and absorption kinetics and subsequent muscle protein synthesis rates in elderly men. Sixteen healthy elderly men were randomly assigned to an experiment during which they were administered a single bolus of intrinsically l-[1-(13)C]phenylalanine-labeled casein protein (PRO) or a placebo (PLA) during sleep. Continuous infusions with l-[ring-(2)H(5)]phenylalanine and l-[ring-(2)H(2)]tyrosine were applied to assess in vivo dietary protein digestion and absorption kinetics and subsequent muscle protein synthesis rates during sleep. We found that exogenous phenylalanine appearance rates increased following protein administration. The latter stimulated protein synthesis, resulting in a more positive overnight whole body protein balance (0.30 ± 0.1 vs. 11.8 ± 1.0 µmol phenylalanine·kg(-1)·h(-1) in PLA and PRO, respectively; P < 0.05). In agreement, overnight muscle protein fractional synthesis rates were much greater in the PRO experiment (0.045 ± 0.002 vs. 0.029 ± 0.002%/h, respectively; P < 0.05) and showed abundant incorporation of the amino acids ingested via the intrinsically labeled protein (0.058 ± 0.006%/h). This is the first study to show that dietary protein administration during sleep is followed by normal digestion and absorption kinetics, thereby stimulating overnight muscle protein synthesis. Dietary protein administration during sleep stimulates muscle protein synthesis and improves overnight whole body protein balance. These findings may provide a basis for novel interventional strategies to attenuate muscle mass loss.

The effects of imagery training on fast isometric knee extensor torque development.

We hypothesized that imagery training would improve the fast onset of neuromuscular activation and thereby fast knee extensor isometric torque development. Forty young healthy participants, not involved in strength training, were assigned to one of four groups: physical training, imagery training, placebo training or control. The three training groups had three 15 min sessions per week for 4 weeks, with a 90 ° knee angle but were tested also at 120 °. At 90 ° knee angle, maximal torque increased (-8%) similarly in all three training groups. The torque-time integral (contractile impulse) over the first 40 ms after torque onset (TTI40) increased (P < 0.05) after physical training (by -100%), but only at 90 °. This increase was significantly different from the delta values (change pre to post) in the control and placebo groups, whereas delta values in the imagery group were similar to those in the placebo group. The increases in TTI40 following physical training were related (r (2) = 0.81, P < 0.05) to significant increases of knee extensor rectified surface EMG at torque onset (EMG40). In conclusion, only physical training led to a knee angle specific increase of contractile impulse that was significantly different from placebo and controls and that was related to improved onset of neuromuscular activation.

Post-exercise protein synthesis rates are only marginally higher in type I compared with type II muscle fibres following resistance-type exercise.

We examined the effect of an acute bout of resistance exercise on fractional muscle protein synthesis rates in human type I and type II muscle fibres. After a standardised breakfast (31 ± 1 kJ kg(-1) body weight, consisting of 52 Energy% (En%) carbohydrate, 34 En% protein and 14 En% fat), 9 untrained men completed a lower-limb resistance exercise bout (8 sets of 10 repetitions leg press and leg extension at 70% 1RM). A primed, continuous infusion of L: -[ring-(13)C(6)]phenylalanine was combined with muscle biopsies collected from both legs immediately after exercise and after 6 h of post-exercise recovery. Single muscle fibres were dissected from freeze-dried biopsies and stained for ATPase activity with pre-incubation at a pH of 4.3. Type I and II fibres were separated under a light microscope and analysed for protein-bound L: -[ring-(13)C(6)]phenylalanine labelling. Baseline (post-exercise) L: -[ring-(13)C(6)]phenylalanine muscle tissue labelling, expressed as (∂(13)C/(12)C), averaged -32.09 ± 0.28, -32.53 ± 0.10 and -32.02 ± 0.16 in the type I and II muscle fibres and mixed muscle, respectively (P = 0.14). During post-exercise recovery, muscle protein synthesis rates were marginally (8 ± 2%) higher in the type I than type II muscle fibres, at 0.100 ± 0.005 versus 0.094 ± 0.005%/h, respectively (P < 0.05), whereby rates of mixed muscle protein were 0.091 ± 0.005%/h. Muscle protein synthesis rates following resistance-type exercise are only marginally higher in type I compared with type II muscle fibres.

The Muscle Protein Synthetic Response to Whey Protein Ingestion Is Greater in Middle-Aged Women Compared With Men.

Rationale: Muscle mass maintenance is largely regulated by the postprandial rise in muscle protein synthesis rates. It remains unclear whether postprandial protein handling differs between women and men. Methods: Healthy men (43 ± 3 years; body mass index, 23.4 ± 0.4 kg/m2; n = 12) and women (46 ± 2 years; body mass index, 21.3 ± 0.5 kg/m2; n = 12) received primed continuous infusions of l-[ring-2H5]-phenylalanine and l-[ring-3,5-2H2]-tyrosine and ingested 25 g intrinsically l-[1-13C]-phenylalanine-labeled whey protein. Blood samples and muscle biopsies were collected to assess dietary protein digestion and amino acid absorption kinetics as well as basal and postprandial myofibrillar protein synthesis rates. Results: Plasma phenylalanine and leucine concentrations rapidly increased after protein ingestion (both P < 0.001), with no differences between middle-aged women and men (Time × Sex, P = 0.307 and 0.529, respectively). The fraction of dietary protein-derived phenylalanine that appeared in the circulation over the 5-hour postprandial period averaged 56 ± 1% and 53 ± 1% in women and men, respectively (P = 0.145). Myofibrillar protein synthesis rates increased (Time, P = 0.010) from 0.035 ± 0.004%/h and 0.030 ± 0.002%/h in the postabsorptive state (t test, P = 0.319) to 0.045 ± 0.002%/h and 0.034 ± 0.002%/h in the 5-hour postprandial phase in middle-aged women and men, respectively, with higher postprandial myofibrillar protein synthesis rates in women compared with men (t test, P = 0.005). Middle-aged women showed a greater increase in myofibrillar protein synthesis rates during the early (0 to 2 hours) postprandial period compared with men (Time × Sex, P = 0.001). Conclusions: There are no differences in postabsorptive myofibrillar protein synthesis rates between middle-aged women and men. The myofibrillar protein synthetic response to the ingestion of 25 g whey protein is greater in women than in men.

One Week of Hospitalization Following Elective Hip Surgery Induces Substantial Muscle Atrophy in Older Patients.

OBJECTIVES: Short successive periods of skeletal muscle disuse have been suggested to substantially contribute to the observed loss of skeletal muscle mass over the life span. Hospitalization of older individuals due to acute illness, injury, or major surgery generally results in a mean hospital stay of 5 to 7 days, during which the level of physical activity is strongly reduced. We hypothesized that hospitalization following elective total hip arthroplasty is accompanied by substantial leg muscle atrophy in older men and women. DESIGN AND PARTICIPANTS: Twenty-six older patients (75 ± 1 years) undergoing elective total hip arthroplasty participated in this observational study. MEASUREMENTS: On hospital admission and on the day of discharge, computed tomographic (CT) scans were performed to assess muscle cross-sectional area (CSA) of both legs. During surgery and on the day of hospital discharge, a skeletal muscle biopsy was taken from the m. vastus lateralis of the operated leg to assess muscle fiber type-specific CSA. RESULTS: An average of 5.6 ± 0.3 days of hospitalization resulted in a significant decline in quadriceps (-3.4% ± 1.0%) and thigh muscle CSA (-4.2% ± 1.1%) in the nonoperated leg (P < .05). Edema resulted in a 10.3% ± 1.7% increase in leg CSA in the operated leg (P < .05). At hospital admission, muscle fiber CSA was smaller in the type II vs type I fibers (3326 ± 253 µm2 vs 4075 ± 279 µm2, respectively; P < .05). During hospitalization, type I and II muscle fiber CSA tended to increase, likely due to edema in the operated leg (P = .10). CONCLUSIONS: Six days of hospitalization following elective total hip arthroplasty leads to substantial leg muscle atrophy in older patients. Effective intervention strategies are warranted to prevent the loss of muscle mass induced by short periods of muscle disuse during hospitalization.

Skeletal muscle fiber characteristics in patients with chronic heart failure: impact of disease severity and relation with muscle oxygenation during exercise.

Skeletal muscle function in patients with heart failure and reduced ejection fraction (HFrEF) greatly determines exercise capacity. However, reports on skeletal muscle fiber dimensions, fiber capillarization, and their physiological importance are inconsistent. Twenty-five moderately impaired patients with HFrEF and 25 healthy control (HC) subjects underwent muscle biopsy sampling. Type I and type II muscle fiber characteristics were determined by immunohistochemistry. In patients with HFrEF, enzymatic oxidative capacity was assessed, and pulmonary oxygen uptake (V̇o2) and skeletal muscle oxygenation during maximal and moderate-intensity exercise were measured using near-infrared spectroscopy. While muscle fiber cross-sectional area (CSA) was not different between patients with HFrEF and HC, the percentage of type I fibers was higher in HC (46 ± 15 vs. 37 ± 12%, respectively, P = 0.041). Fiber type distribution and CSA were not different between patients in New York Heart Association (NYHA) class II and III. Type I muscle fiber capillarization was higher in HFrEF compared with HC[capillary-to-fiber perimeter exchange (CFPE) index: 5.70 ± 0.92 vs. 5.05 ± 0.82, respectively, P = 0.027]. Patients in NYHA class III had slower V̇o2 and muscle deoxygenation kinetics during onset of exercise and lower muscle oxidative capacity than those in class II (P < 0.05). Also, fiber capillarization was lower but not compared with HC. Higher CFPE index was related to faster deoxygenation (rspearman = -0.682, P = 0.001), however, not to muscle oxidative capacity (r = -0.282, P = 0.216). Type I muscle fiber capillarization is higher in HFrEF compared with HC but not in patients with greater exercise impairment. Greater capillarization may positively affect V̇o2 kinetics by enhancing muscle oxygen diffusion.NEW & NOTEWORTHY The skeletal myopathy of chronic heart failure (HF) includes a greater percentage of fatigable type II fibers and, for less impaired patients, greater skeletal muscle fiber capillarization. Near-infrared spectroscopy measurements of skeletal muscle oxygenation indicate that greater capillarization may compensate for reduced blood flow in mild HF by enhancing the diffusive capacity of skeletal muscle. This thereby augments and speeds oxygen extraction during contractions, which is translated into faster pulmonary oxygen uptake kinetics.

Neuromuscular electrical stimulation prior to presleep protein feeding stimulates the use of protein-derived amino acids for overnight muscle protein synthesis.

Short periods of muscle disuse result in substantial skeletal muscle atrophy. Recently, we showed that both neuromuscular electrical stimulation (NMES) as well as presleep dietary protein ingestion represent effective strategies to stimulate muscle protein synthesis rates. In this study, we test our hypothesis that NMES can augment the use of presleep protein-derived amino acids for overnight muscle protein synthesis in older men. Twenty healthy, older [69 ± 1 (SE) yr] men were subjected to 24 h of bed rest, starting at 8:00 AM. In the evening, volunteers were subjected to 70-min 1-legged NMES, while the other leg served as nonstimulated control (CON). Immediately following NMES, 40 g of intrinsically l-[1-13C]-phenylalanine labeled protein was ingested prior to sleep. Blood samples were taken throughout the night, and muscle biopsies were obtained from both legs in the evening and the following morning (8 h after protein ingestion) to assess dietary protein-derived l-[1-13C]-phenylalanine enrichments in myofibrillar protein. Plasma phenylalanine concentrations and plasma l-[1-13C]-phenylalanine enrichments increased significantly following protein ingestion and remained elevated for up to 6 h after protein ingestion (P < 0.05). During overnight sleep, myofibrillar protein-bound l-[1-13C]-phenylalanine enrichments (MPE) increased to a greater extent in the stimulated compared with the control leg (0.0344 ± 0.0019 vs. 0.0297 ± 0.0016 MPE, respectively; P < 0.01), representing 18 ± 6% greater incorporation of presleep protein-derived amino acids in the NMES compared with CON leg. In conclusion, application of NMES prior to presleep protein feeding stimulates the use of dietary protein-derived amino acids for overnight muscle protein synthesis in older men. NEW & NOTEWORTHY: Neuromuscular electrical stimulation (NMES) as well as presleep dietary protein ingestion represent effective strategies to stimulate muscle protein synthesis rates. Here we demonstrate that in older men after a day of bed rest, the application of NMES prior to presleep protein feeding stimulates the use of dietary protein-derived amino acids for overnight muscle protein synthesis by 18% compared with presleep protein feeding only.

Increasing Insulin Availability Does Not Augment Postprandial Muscle Protein Synthesis Rates in Healthy Young and Older Men.

CONTEXT: Skeletal muscle protein synthesis is highly responsive to food intake. It has been suggested that the postprandial increase in circulating insulin modulates the muscle protein synthetic response to feeding. OBJECTIVE: The objective of the study was to investigate whether a greater postprandial rise in circulating insulin level increases amino acid uptake in muscle and augments postprandial muscle protein synthesis rates. PARTICIPANTS AND DESIGN: Forty-eight healthy young (age 22 ± 1 y; body mass index 22.0 ± 0.3 kg/m2) and older males (age 68 ± 1 y; body mass index 26.3 ± 0.4 kg/m2) ingested 20 g intrinsically L-[1-13C]-leucine- and L-[1-13C]-phenylalanine-labeled casein protein with or without local insulin infusion. Primed continuous infusions of L-[1-13C]-leucine and L-[ring-2H5]-phenylalanine were applied, with arterial and venous blood samples and muscle biopsies being collected during a 5-hour postprandial period. RESULTS: Insulin administration did not increase overall leg blood flow (P = .509) but increased amino acid uptake over the leg in both young and older subjects (P = .003). The greater amino acid uptake over the leg did not further increase postprandial muscle protein synthesis rates (0.050% ± 0.006% and 0.037% ± 0.004% per hour vs 0.044% ± 0.004% and 0.037% ± 0.002% per hour in the insulin-stimulated vs control condition in the young and older groups, respectively; P = .804) and did not affect postprandial deposition of dietary protein-derived amino acids in de novo muscle protein (P = .872). CONCLUSION: Greater postprandial plasma insulin availability stimulates amino acid uptake over the leg but does not further augment postprandial muscle protein synthesis rates or stimulate the postprandial deposition of protein derived amino acids into de novo muscle protein in healthy young and older men.

Aging Is Accompanied by a Blunted Muscle Protein Synthetic Response to Protein Ingestion.

PURPOSE: Progressive loss of skeletal muscle mass with aging (sarcopenia) forms a global health concern. It has been suggested that an impaired capacity to increase muscle protein synthesis rates in response to protein intake is a key contributor to sarcopenia. We assessed whether differences in post-absorptive and/or post-prandial muscle protein synthesis rates exist between large cohorts of healthy young and older men. PROCEDURES: We performed a cross-sectional, retrospective study comparing in vivo post-absorptive muscle protein synthesis rates determined with stable isotope methodologies between 34 healthy young (22±1 y) and 72 older (75±1 y) men, and post-prandial muscle protein synthesis rates between 35 healthy young (22±1 y) and 40 older (74±1 y) men. FINDINGS: Post-absorptive muscle protein synthesis rates did not differ significantly between the young and older group. Post-prandial muscle protein synthesis rates were 16% lower in the older subjects when compared with the young. Muscle protein synthesis rates were >3 fold more responsive to dietary protein ingestion in the young. Irrespective of age, there was a strong negative correlation between post-absorptive muscle protein synthesis rates and the increase in muscle protein synthesis rate following protein ingestion. CONCLUSIONS: Aging is associated with the development of muscle anabolic inflexibility which represents a key physiological mechanism underpinning sarcopenia.

MECHANISMS IN ENDOCRINOLOGY: Exogenous insulin does not increase muscle protein synthesis rate when administered systemically: a systematic review.

BACKGROUND: Though it is well appreciated that insulin plays an important role in the regulation of muscle protein metabolism, there is much discrepancy in the literature on the capacity of exogenous insulin administration to increase muscle protein synthesis rates in vivo in humans. OBJECTIVE: To assess whether exogenous insulin administration increases muscle protein synthesis rates in young and older adults. DESIGN: A systematic review of clinical trials was performed and the presence or absence of an increase in muscle protein synthesis rate was reported for each individual study arm. In a stepwise manner, multiple models were constructed that excluded study arms based on the following conditions: model 1, concurrent hyperaminoacidemia; model 2, insulin-induced hypoaminoacidemia; model 3, supraphysiological insulin concentrations; and model 4, older, more insulin resistant, subjects. CONCLUSIONS: From the presented data in the current systematic review, we conclude that: i) exogenous insulin and amino acid administration effectively increase muscle protein synthesis, but this effect is attributed to the hyperaminoacidemia; ii) exogenous insulin administered systemically induces hypoaminoacidemia which obviates any insulin-stimulatory effect on muscle protein synthesis; iii) exogenous insulin resulting in supraphysiological insulin levels exceeding 50, 000  pmol/l may effectively augment muscle protein synthesis; iv) exogenous insulin may have a diminished effect on muscle protein synthesis in older adults due to age-related anabolic resistance; and v) exogenous insulin administered systemically does not increase muscle protein synthesis in healthy, young adults.

Post-Prandial Protein Handling: You Are What You Just Ate.

BACKGROUND: Protein turnover in skeletal muscle tissue is highly responsive to nutrient intake in healthy adults. OBJECTIVE: To provide a comprehensive overview of post-prandial protein handling, ranging from dietary protein digestion and amino acid absorption, the uptake of dietary protein derived amino acids over the leg, the post-prandial stimulation of muscle protein synthesis rates, to the incorporation of dietary protein derived amino acids in de novo muscle protein. DESIGN: 12 healthy young males ingested 20 g intrinsically [1-13C]-phenylalanine labeled protein. In addition, primed continuous L-[ring-2H5]-phenylalanine, L-[ring-2H2]-tyrosine, and L-[1-13C]-leucine infusions were applied, with frequent collection of arterial and venous blood samples, and muscle biopsies throughout a 5 h post-prandial period. Dietary protein digestion, amino acid absorption, splanchnic amino acid extraction, amino acid uptake over the leg, and subsequent muscle protein synthesis were measured within a single in vivo human experiment. RESULTS: 55.3±2.7% of the protein-derived phenylalanine was released in the circulation during the 5 h post-prandial period. The post-prandial rise in plasma essential amino acid availability improved leg muscle protein balance (from -291±72 to 103±66 µM·min-1·100 mL leg volume-1; P<0.001). Muscle protein synthesis rates increased significantly following protein ingestion (0.029±0.002 vs 0.044±0.004%·h-1 based upon the muscle protein bound L-[ring-2H5]-phenylalanine enrichments (P<0.01)), with substantial incorporation of dietary protein derived L-[1-13C]-phenylalanine into de novo muscle protein (from 0 to 0.0201±0.0025 MPE). CONCLUSION: Ingestion of a single meal-like amount of protein allows ~55% of the protein derived amino acids to become available in the circulation, thereby improving whole-body and leg protein balance. About 20% of the dietary protein derived amino acids released in the circulation are taken up in skeletal muscle tissue following protein ingestion, thereby stimulating muscle protein synthesis rates and providing precursors for de novo muscle protein synthesis. TRIAL REGISTRATION: trialregister.nl 3638.

Immunological Adaptations to Pregnancy in Women with Type 1 Diabetes.

Despite adequate glycemic control, pregnancy outcome of women with type 1 diabetes (T1D) is still unfavorable as compared to healthy women. In a rat-model of T1D under normoglycemic conditions, adverse pregnancy outcome was also observed, which was associated with aberrant immunological adaptations to pregnancy. Because similar processes may occur in women with T1D we studied the systemic immune response in non-pregnant and pregnant women with and without T1D. The systemic immune response was assessed by using flow cytometry to evaluate the number and activational status of subpopulations of lymphocytes, Natural Killer cells and monocytes in peripheral blood of non-pregnant and pregnant women with and without T1D. An increased white blood cell count, an increased Th1/Th2 ratio, increased Natural Killer cell expression of CD335 and enhanced activation of intermediate and non-classical monocytes was observed in pregnant women with T1D vs. healthy pregnant women. Also, the pregnancy outcome (i.e. incidence of preterm delivery and macrosomia) of women with T1D was unfavorable as compared to healthy women. This study showed that in T1D, the immunological adaptations to pregnancy are disturbed. In addition to hyperglycemia, these different immunological adaptations may be responsible for the greater frequency of complications in pregnant women with T1D.

Increased Risk of Atrial Fibrillation After Treatment for Differentiated Thyroid Carcinoma.

BACKGROUND: Patients with differentiated thyroid carcinoma (DTC) have a favorable prognosis after treatment with thyroidectomy, radioiodine, and TSH suppression. However, treatment is associated with long-term cardiovascular toxicity. The aim of this study was to evaluate whether there is an increased risk of atrial fibrillation (AF) in DTC patients and whether AF occurrence is related to DTC treatment. PATIENTS AND METHODS: Incident AF was compared between 518 DTC patients and 1563 matched controls. A cumulative incidence curve was plotted, and competing risk regression analyses with adjustment for all-cause mortality were performed. Within the DTC cohort, associations between time-varying DTC treatment variables and incident AF were analyzed. RESULTS: For both cohorts, the mean age was 48.6 years (75% of subjects were women). The AF incidence rate was 6.2/1000 person-years for DTC patients and 2.7/1000 person-years for controls. DTC patients had a 2.25-fold (95% confidence interval [CI], 1.40-3.63) and 2.47-fold (95% CI, 1.55-3.95) increased AF risk in crude and fully adjusted analyses, respectively. Within the DTC cohort, the TSH level (which was suppressed in 85.7% of patients) was not associated with AF, whereas a higher cumulative radioiodine dose slightly increased AF risk: subdistribution hazard ratio, 1.04 (95% CI, 1.01-1.08) per 50 mCi (1.85 GBq) increase, after adjustment. CONCLUSION: Patients with DTC have an increased AF risk, independent from established AF risk factors. We could not demonstrate a relation between TSH and AF, whereas a higher cumulative radioiodine dose was associated with a slightly increased AF risk. Electrocardiogram screening for AF may be warranted during follow-up of DTC patients to allow early diagnosis and treatment of AF and to prevent its complications.

Carbohydrate coingestion delays dietary protein digestion and absorption but does not modulate postprandial muscle protein accretion.

BACKGROUND: Dietary protein digestion and absorption is an important factor modulating muscle protein accretion. However, there are few data available on the effects of coingesting other macronutrients with protein on digestion and absorption kinetics and the subsequent muscle protein synthetic response. OBJECTIVE: The objective of the study was to determine the impact of carbohydrate coingestion with protein on dietary protein digestion and absorption and muscle protein accretion in healthy young and older men. DESIGN: Twenty-four healthy young (aged 21± 1 y, body mass index 21.8 ±0.5 kg/m(2)) and 25 older (aged 75 ± 1 y, body mass index 25.4 ± 0.6 kg/m(2)) men received a primed continuous L-[ring-(2)H5]-phenylalanine and L-[ring-3,5-(2)H2]-tyrosine infusion and ingested 20 g intrinsically L-[1-(13)C]-phenylalanine-labeled protein with (Pro+CHO) or without (Pro) 60 g carbohydrate. Plasma samples and muscle biopsies were collected in a postabsorptive and postprandial state. RESULTS: Carbohydrate coingestion delayed the appearance of exogenous phenylalanine in the circulation (P = .001). Dietary protein-derived phenylalanine availability over the 5-hour postprandial period was lower in the older (62 ± 2%) when compared with the young subjects (74 ± 2%; P = .007), with no differences between conditions (P = .20). Carbohydrate coingestion did not modulate postprandial muscle protein synthesis rates (0.035 ± 0.003 vs 0.043 ± 0.004 and 0.033 ± 0.002 vs 0.035 ± 0.003%/h after Pro vs Pro+CHO in the young and older group, respectively). In accordance, no differences in muscle protein-bound L-[1-(13)C]-phenylalanine enrichments were observed between conditions (0.020 ± 0.002 vs 0.020 ± 0.002 and 0.019 ± 0.003 vs 0.022 ± 0.004 mole percent excess after Pro vs Pro+CHO in the young and older subjects, respectively). CONCLUSION: Carbohydrate coingestion with protein delays dietary protein digestion and absorption but does not modulate postprandial muscle protein accretion in healthy young or older men.

Skeletal muscle capillary density and microvascular function are compromised with aging and type 2 diabetes.

Adequate muscle perfusion is required for the maintenance of skeletal muscle mass. Impairments in microvascular structure and/or function with aging and type 2 diabetes have been associated with the progressive loss of skeletal muscle mass. Our objective was to compare muscle fiber type specific capillary density and endothelial function between healthy young men, healthy older men, and age-matched type 2 diabetes patients. Fifteen healthy young men (24 ± 1 yr), 15 healthy older men (70 ± 2 yr), and 15 age-matched type 2 diabetes patients (70 ± 1 yr) were selected to participate in the present study. Whole body insulin sensitivity, muscle fiber type specific capillary density, sublingual microvascular density, and dimension of the erythrocyte-perfused boundary region were assessed to evaluate the impact of aging and/or type 2 diabetes on microvascular structure and function. Whole body insulin sensitivity was significantly lower at a more advanced age, with lowest values reported in the type 2 diabetic patients. In line, skeletal muscle capillary contacts were much lower in the older and older type 2 diabetic patients when compared with the young. Sidestream darkfield imaging showed a significantly greater thickness of the erythrocyte perfused boundary region in the type 2 diabetic patients compared with the young. Skeletal muscle capillary density is reduced with aging and type 2 diabetes and accompanied by impairments in endothelial glycocalyx function, which is indicative of compromised vascular function.

The decline in skeletal muscle mass with aging is mainly attributed to a reduction in type II muscle fiber size.

BACKGROUND: The loss of skeletal muscle mass with aging has been attributed to a decline in muscle fiber number and muscle fiber size. OBJECTIVE: To define to what extent differences in leg muscle cross-sectional area (CSA) between young and elderly men are attributed to differences in muscle fiber size. METHODS: Quadriceps muscle CSA and type I and type II muscle fiber size were measured in healthy young (n=25; 23 ± 1 y) and older (n=26; 71 ± 1 y) men. Subsequently, the older subjects performed 6 months of resistance type exercise training, after which measurements were repeated. Differences in quadriceps muscle CSA were compared with differences in type I and type II muscle fiber size. RESULTS: Quadriceps CSA was substantially smaller in older versus young men (68 ± 2 vs 80 ± 2 cm(2), respectively; P<0.001). Type II muscle fiber size was substantially smaller in the elderly vs the young (29%; P<0.001), with a tendency of smaller type I muscle fibers (P=0.052). Differences in type II muscle fiber size fully explained differences in quadriceps CSA between groups. Prolonged resistance type exercise training in the elderly increased type II muscle fiber size by 24 ± 8% (P<0.01), explaining 100 ± 3% of the increase in quadriceps muscle CSA (from 68 ± 2 to 74 ± 2 cm(2)). CONCLUSION: Reduced muscle mass with aging is mainly attributed to smaller type II muscle fiber size and, as such, is unlikely accompanied by substantial muscle fiber loss. In line, the increase in muscle mass following prolonged resistance type exercise training can be attributed entirely to specific type II muscle fiber hypertrophy.

Aberrant Pregnancy Adaptations in the Peripheral Immune Response in Type 1 Diabetes: A Rat Model.

INTRODUCTION: Despite tight glycemic control, pregnancy complication rate in type 1 diabetes patients is higher than in normal pregnancy. Other etiological factors may be responsible for the development of adverse pregnancy outcome. Acceptance of the semi-allogeneic fetus is accompanied by adaptations in the maternal immune-response. Maladaptations of the immune-response has been shown to contribute to pregnancy complications. We hypothesized that type 1 diabetes, as an autoimmune disease, may be associated with maladaptations of the immune-response to pregnancy, possibly resulting in pregnancy complications. METHODS: We studied pregnancy outcome and pregnancy-induced immunological adaptations in a normoglycemic rat-model of type 1 diabetes, i.e. biobreeding diabetes-prone rats (BBDP; 5 non-pregnant rats, 7 pregnant day 10 rats and 6 pregnant day 18 rats) , versus non-diabetic control rats (i.e. congenic non-diabetic biobreeding diabetes-resistant (BBDR; 6 non-pregnant rats, 6 pregnant day 10 rats and 6 pregnant day 18 rats) and Wistar-rats (6 non-pregnant, 6 pregnant day 10 rats and 5 pregnant day 18 rats)). RESULTS: We observed reduced litter size, lower fetal weight of viable fetuses and increased numbers of resorptions versus control rats. These complications are accompanied by various differences in the immune-response between BBDP and control rats in both pregnant and non-pregnant animals. The immune-response in non-pregnant BBDP-rats was characterized by decreased percentages of lymphocytes, increased percentages of effector T-cells, regulatory T-cells and natural killer cells, an increased Th1/Th2-ratio and activated monocytes versus Wistar and BBDR-rats. Furthermore, pregnancy-induced adaptations in BBDP-rats coincided with an increased Th1/Th2-ratio, a decreased mean fluorescence intensity CD161a/NKR-P1b ratio and no further activation of monocytes versus non-diabetic control rats. CONCLUSION: This study suggests that even in the face of strict normoglycemia, pregnancy complications still occur in type 1 diabetic pregnancies. This adverse pregnancy outcome may be related to the aberrant immunological adaptations to pregnancy in diabetic rats.