Physiological increments in plasma insulin concentrations have selective and different effects on synthesis of hepatic proteins in normal humans

The anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans

The belief that the anabolic response to feeding during postexercise recovery is transient and has an upper limit and that excess amino acids are being oxidized lacks scientific proof. Using a comprehensive quadruple isotope tracer feeding-infusion approach, we show that the ingestion of 100 g protein results in a greater and more prolonged (>12 h) anabolic response when compared to the ingestion of 25 g protein. We demonstrate a dose-response increase in dietary-protein-derived plasma amino acid availability and subsequent incorporation into muscle protein. Ingestion of a large bolus of protein further increases whole-body protein net balance, mixed-muscle, myofibrillar, muscle connective, and plasma protein synthesis rates. Protein ingestion has a negligible impact on whole-body protein breakdown rates or amino acid oxidation rates. These findings demonstrate that the magnitude and duration of the anabolic response to protein ingestion is not restricted and has previously been underestimated in vivo in humans.

Hemorheological Parameters in Diabetic Patients: Role of Glucose Lowering Therapies

Diabetes mellitus influences several important hemorheological parameters including blood viscosity, erythrocyte aggregation and deformability. In the present study, 159 type-2 diabetic patients and 25 healthy controls were involved. Patient's age, body weight, body mass index (BMI), smoking habits, physical activity, history of cardiovascular diseases, current antidiabetic therapy and concomitant medication were recorded. Patients were grouped according to their antidiabetic treatment with insulin, or with one or more of the following antidiabetic drugs: metformin, sulfonylureas, acarbose, or no antidiabetic therapy. Hemorheological measurements (hematocrit, erythrocyte aggregation, plasma fibrinogen, whole blood and plasma viscosity), von Willebrand factor activity, and platelet aggregation measurements were performed. Platelet aggregation was investigated with the method of Born. Plasma viscosity and red blood cell aggregation were significatly higher in diabetes. No significant difference was found in hemorheological parameters between different antidiabetic regimens. Whole blood and plasma viscosity and red blood cell aggregation correlated with glucose levels but not with HbA1C levels. In conclusion, plasma and whole blood viscosity, as well as red blood cell aggregation appear to be associated with concurrent hyperglycemia, but not with the quality of glycemic control or the applied antidiabetic treatment. Platelet aggregation induced by ADP or epinephrine does not seem to be associated with diabetes even at subthreshold doses.

Fibrin(ogen) in human disease: both friend and foe

Fibrinogen is an abundant protein synthesized in the liver, present in human blood plasma at concentrations ranging from 1.5-4 g/L in healthy individuals with a normal half-life of 3-5 days. With fibrin, produced by thrombin-mediated cleavage, fibrinogen plays important roles in many physiological processes. Indeed, the formation of a stable blood clot, containing polymerized and cross-linked fibrin, is crucial to prevent blood loss and drive wound healing upon vascular injury. A balance between clotting, notably the conversion of fibrinogen to fibrin, and fibrinolysis, the proteolytic degradation of the fibrin mesh, is essential. Disruption of this equilibrium can cause disease in distinct manners. While some pathological conditions are the consequence of altered levels of fibrinogen, others are related to structural properties of the molecule. The source of fibrinogen expression and the localization of fibrin(ogen) protein also have clinical implications. Low levels of fibrinogen expression have been detected in extra-hepatic tissues, including carcinomas, potentially contributing to disease. Fibrin(ogen) deposits at aberrant sites including the central nervous system or kidney, can also be pathological. In this review, we discuss disorders in which fibrinogen and fibrin are implicated, highlighting mechanisms that may contribute to disease.

Increased serotransferrin and ceruloplasmin turnover in diet-controlled patients with type 2 diabetes

Type 2 diabetes mellitus (T2DM) is associated with oxidative stress and perturbed iron metabolism. Serotransferrin (Trf) and ceruloplasmin (Cp) are two key proteins involved in iron metabolism and anti-oxidant defense. Non-enzymatic glycation and oxidative modification of plasma proteins are known to occur under hyperglycemia and oxidative stress. In this study, shotgun proteomics and 2H2O-based metabolic labeling were used to characterize post-translational modifications and assess the kinetics of Trf and Cp in T2DM patients and matched controls in vivo. Six early lysine (Amadori) and one advanced arginine glycation were detected in Trf. No glycation, but five asparagine deamidations, were found in Cp. T2DM patients had increased fractional catabolic rates of both Trf and Cp that correlated with HbA1c (p < 0.05). The glycated Trf population was subject to an even faster degradation compared to the total Trf pool, suggesting that hyperglycemia contributed to an increased Trf degradation in T2DM patients. Enhanced production of Trf and Cp kept their levels stable. The changes in Trf and Cp turnover were associated with increased systemic oxidative stress without any alteration in iron status in T2DM. These findings can help better understand the potential role of altered Trf and Cp metabolism in the pathogenesis of T2DM and other diseases.

Nutritional regulation of the anabolic fate of amino acids within the liver in mammals: concepts arising from in vivo studies

At the crossroad between nutrient supply and requirements, the liver plays a central role in partitioning nitrogenous nutrients among tissues. The present review examines the utilisation of amino acids (AA) within the liver in various physiopathological states in mammals and how the fates of AA are regulated. AA uptake by the liver is generally driven by the net portal appearance of AA. This coordination is lost when demands by peripheral tissues is important (rapid growth or lactation), or when certain metabolic pathways within the liver become a priority (synthesis of acute-phase proteins). Data obtained in various species have shown that oxidation of AA and export protein synthesis usually responds to nutrient supply. Gluconeogenesis from AA is less dependent on hepatic delivery and the nature of nutrients supplied, and hormones like insulin are involved in the regulatory processes. Gluconeogenesis is regulated by nutritional factors very differently between mammals (glucose absorbed from the diet is important in single-stomached animals, while in carnivores, glucose from endogenous origin is key). The underlying mechanisms explaining how the liver adapts its AA utilisation to the body requirements are complex. The highly adaptable hepatic metabolism must be capable to deal with the various nutritional/physiological challenges that mammals have to face to maintain homeostasis. Whereas the liver responds generally to nutritional parameters in various physiological states occurring throughout life, other complex signalling pathways at systemic and tissue level (hormones, cytokines, nutrients, etc.) are involved additionally in specific physiological/nutritional states to prioritise certain metabolic pathways (pathological states or when nutritional requirements are uncovered).

Blood viscosity, lipid profile, and lipid peroxidation in type-1 diabetic patients with good and poor glycemic control

Background:

In diabetic patients, persistent hyperglycemia and poor glycemic control cause disturbances of lipid profiles, especially an increased production of oxygen free radicals. Lipid peroxidation has been considered to be a pathogenic factor of diabetic complications in Type-1 Diabetes mellitus.

Aims:

The aim of the present study was to investigate the effect of glycemic control on blood viscosity, lipid profile, and lipid peroxidation in Type-1 Diabetic subjects.

Materials and Methods:

The study included three groups; Group-I (age-matched healthy control subjects, n = 50), Group-II (Type-1 Diabetics with good glycemic control, n = 10), and Group-III (Type-1 Diabetics with poor glycemic control, n = 15). The Type 1 diabetic patients with duration of diabetes for more than 5 years were taken. Blood samples of all subjects were analyzed for all biochemical, hematological, and oxidative stress parameters.

Results:

The Erythrocyte malondialdehyde level was non-significantly changed (P = NS) in group–II patients but significantly increased (P < 0.001) in group-III patients, and no significant changes were found (P = NS) in Blood viscosity of both the groups (group-II and group-III), as compared to healthy control subjects (group-I).

Conclusions:

Our findings suggest that the monitoring of Oxidative stress and Blood Viscosity in poorly controlled Type-1 diabetic patients may be very useful marker of diabetic complications.

Albumin synthesis rates are not responsive to hyperglycemic hyperinsulinemia in postoperative patients

BACKGROUND

Insulin regulates albumin synthesis in vitro and in various experimental models. The current study was undertaken to determine the effects of a physiologic hyperinsulinemia on albumin synthesis in postoperative patients in whom plasma albumin concentrations are decreased.

METHODS

Studies were performed in postabsorptive patients after major abdominal operations. Mass spectrometry techniques were used to directly determine the incorporation rate of 1-[(13)C]-leucine into albumin. Consecutive blood samples were taken during a continuous isotope (D-Glc) infusion (0.16 µmol/kg/min). Isotopic enrichments were determined at baseline (period I) and after a 4-hour D-glucose (D-Glc) infusion at currently recommended rates (170 mg/kg/h, n = 10) or after infusion of saline (control group, n = 8) (period II).

RESULTS

After D-Glc infusion, plasma insulin concentrations increased significantly (period I, 6.6 ± 1.8 µU/mL; period II, 21.4 ± 2.1 µU/mL; P < .01). In contrast, plasma insulin concentration remained constant in control patients (period I, 3.8 ± 0.9 µU/mL(-1); period II, 5.9 ± 1.1 µU/mL; not significant vs period I, but P < .005 vs the corresponding value at the end of period II in the control group). Hyperinsulinemia was without effect on fractional albumin synthesis (period I, 12.8% ± 1.9%/d; period II, 11.9% ± 1.9%/d; not significant), and synthesis rates corresponded to those measured in controls (period I, 13.0% ± 1.2%/d; period II, 12.1% ± 0.1%/d; not significant vs period I and vs D-Glc infusion).

CONCLUSIONS

A standard D-Glc infusion is insufficient to increase albumin synthesis in postoperative patients.

[Serum albumin and heart failure: recent advances on a new paradigm]

Hypoalbuminemia is a common condition in patients with heart failure and is mainly related to the malnutrition-inflammation complex syndrome. Other causal factors can be involved, which include hemodilution, liver dysfunction, increased transcapillary escape rate, renal and enteral loss. Evidence is growing that hypoalbuminemia independently predicts incident heart failure in patients with end-stage renal disease and elderly patients, as well as mortality in patients with heart failure regardless of left ventricular ejection fraction and clinical presentation. Hypoalbuminemia induces a low plasma oncotic pressure, which facilitates pulmonary edema in patients without critical increase in pulmonary capillary hydrostatic pressures. Hypoalbuminemia may also contribute to the progression of heart failure by favoring myocardial edema, volume overload, diuretic resistance and exacerbation of oxidative stress and inflammation. If relevant, removal of subclinical excess of fluid and renutrition may be indicated in patients with heart failure and hypoalbuminemia. Additional research is warranted to determine the specific role of serum albumin in the pathophysiologic process of heart failure and the potential benefits of targeted therapeutic interventions.

Albumin synthesis rates in post-surgical infants and septic adolescents; influence of amino acids, energy, and insulin

BACKGROUND & AIMS

To investigate the effects of glucose, parenteral amino acids, and intravenous insulin on albumin synthesis rates in critically ill children.

METHODS

Two studies were performed in 8 post-surgical infants (age 9.8 ± 1.9 months; weight 9.5 ± 1.1 kg) and 9 septic adolescents (age 15 ± 1 yr; BMI 23 ± 4 kg m(-2)), respectively. All received a primed, constant, tracer infusion with [1-(13)C]Leucine. The infants in study 1 were randomized to receive low (2.5 mg kg(-1) min(-1)) and standard (5.0 mg kg(-1) min(-1)) glucose intake in a cross-over setting of two periods of 4 h each. The adolescents in study 2 were randomized to receive total parenteral nutrition with standard (1.5 g kg(-1) day(-1)) and high (3.0 g kg(-1) day(-1)) amino acid intake in a two day cross-over setting. On both study days, during the last 3 h of the tracer study, they received insulin infused at 80 mU m(-2) min(-1).

RESULTS

The post-surgical infants and the septic adolescents were mildly hypoalbuminemic (∼2.5 g dL(-1)) with high synthesis rates, which were not affected by different intakes of glucose, amino acids, or insulin infusion.

CONCLUSIONS

Albumin synthesis rates in hypoalbuminemic critically ill children are high but were not upregulated through nutrient supply, and in septic adolescents are unaffected by insulin.

Enhanced albumin synthesis in severely burned adults

Albumin plays an important role in maintaining physiological homeostasis. Although decreased albumin concentration has been well described as an acute-phase response following injury, it is unclear whether the decrease is due to compromised synthesis of albumin, dilution, or imbalance between synthesis and breakdown rates, particularly after injury. We investigated changes in albumin synthesis in severely burned patients using stable isotope infusion techniques. Five patients (29 ± 3 years; 80 ± 7 kg) with burn of 48% ± 4% total body surface area (TBSA) were enrolled and studied in the ICU at the Burn Unit of the US Army Institute of Surgical Research. Five age- and sex-matched healthy volunteers (33 ± 5 years; 81 ± 6 kg) were included as controls. On the study day (13 ± 3 days after burn), a primed constant infusion (4 h) of stable isotope d5-phenlylalanine and d3-ketoisocaproic acid was given. Hourly arterial blood samples were drawn during the infusion to determine albumin synthesis rates, using gas chromatography-mass spectrometry analysis. Burned patients had higher heart and respiration rates. Plasma total protein in burn patients (4.5 ± 0.3 g · dL-1) was lower compared with controls (6.8 ± 0.2 g · dL-1). Plasma albumin concentration in burn patients (1.1 ± 0.1 g · dL-1) was also lower compared with controls (3.8 ± 0.1 g · dL-1; both P < 0.05). Albumin synthesis rate in burn patients (4.6 ± 0.2 mg · kg-1 · h-1) was enhanced compared with controls (2.2 ± 0.2 mg · kg-1 · h-1; P < 0.05). Despite the decrease in albumin concentration, albumin synthesis was enhanced in severely burned patients during the flow phase.

Intersection between metabolic dysfunction, high fat diet consumption, and brain aging

Deleterious neurochemical, structural, and behavioral alterations are a seemingly unavoidable aspect of brain aging. However, the basis for these alterations, as well as the basis for the tremendous variability in regards to the degree to which these aspects are altered in aging individuals, remains to be elucidated. An increasing number of individuals regularly consume a diet high in fat, with high-fat diet consumption known to be sufficient to promote metabolic dysfunction, although the links between high-fat diet consumption and aging are only now beginning to be elucidated. In this review we discuss the potential role for age-related metabolic disturbances serving as an important basis for deleterious perturbations in the aging brain. These data not only have important implications for understanding the basis of brain aging, but also may be important to the development of therapeutic interventions which promote successful brain aging.

High-sensitivity C-reactive protein predicts cardiovascular risk in diabetic and nondiabetic patients: effects of insulin-sensitizing treatment with pioglitazone

Systemic inflammatory activity has turned out to play a key pathogenic role in vascular atherosclerosis, insulin resistance, and type 2 diabetes mellitus. Inflammatory biomarkers may therefore be a valuable tool for risk evaluation. Among them, the best evidence to date supports the use of high-sensitivity C-reactive protein (hs-CRP) to monitor insulin resistance and cardiovascular risk in diabetic and nondiabetic individuals. Data suggest that hs-CRP may also participate directly in the process of atherogenesis. A growing number of clinical trials tested the hypothesis that antidiabetic drugs specifically targeting insulin resistance could benefit individuals by reducing inflammation, atherogenesis, and thus cardiovascular risk. One such class are the thiazolidinediones (pioglitazone and rosiglitazone). These agents act as selective ligands of the nuclear transcription factor peroxisome proliferator-activated receptor-gamma (PPARgamma). This article reviewed published data on hs-CRP changes with the thiazolidinedione agent pioglitazone. Here we found pronounced insulin-sensitizing and anti-inflammatory properties in different clinical settings, including diabetic and nondiabetic individuals. Coadministration of pioglitazone to antilipidemic statin therapy resulted in additional effects on low-grade inflammation, and hs-CRP reduction has been demonstrated to occur independently of glucose lowering. The anti-inflammatory effect appeared to be a rapid physiologic reaction on PPARgamma activation and could be observed within a short-term interval after starting pioglitazone therapy. In summary, clinical study results underline the benefit of an early insulin resistance treatment to oppose systemic vascular inflammation and cardiometabolic syndrome in patients with elevated levels of high-sensitivity C-reactive protein.

Fibrinogen kinetics and protein turnover in obese non-diabetic males: effects of insulin

BACKGROUND

Although hyperfibrinogenemia and insulin resistance are common in obesity and diabetes mellitus, the impact of obesity per se on fibrinogen turnover and the insulin effects on fibrinogen and protein kinetics is unknown.

METHODS

We measured fibrinogen and albumin fractional (FSR) and absolute (ASR) synthesis rates, as well as protein turnover, in non-diabetic, obese and in control male subjects both before and following an euglycemic, euaminoacidemic, hyperinsulinemic clamp, using L-[(2)H(3)]-Leucine isotope infusion.

RESULTS

In the obese, basal fibrinogen concentrations was approximately 25% greater (p < 0.035), and fibrinogen pool approximately 45% greater (p < 0.005), than in controls. Both FSR and ASR of fibrinogen were similar to control values. With hyperinsulinemia, although fibrinogen FSR and ASR were not significantly modified with respect to baseline in either group, fibrinogen ASR resulted to be approximately 50% greater in the obese than in controls (p < 0.015). Hyperinsulinemia equally stimulated albumin synthesis and suppressed leucine appearance from endogenous proteolysis in both groups. Amino acid clearance was also similar. In the obese, the insulin-mediated glucose disposal was approximately 50% lower (p < 0.03) than in controls, and it was inversely correlated with fibrinogen ASR during the clamp in both groups (r = - 0.58).

CONCLUSIONS

In obese, non-diabetic males, post absorptive fibrinogen production is normal. Whole-body amino acid disposal, basal and insulin-responsive protein degradation, and albumin synthesis are also normal. However, the greater fibrinogen ASR in the obese with hyperinsulinemia, and the inverse relationship between insulin sensitivity and clamp fibrinogen production, suggest a role for hyperinsulinemia and/or insulin resistance on fibrinogen production in obesity.

Fibrinogen kinetics and protein turnover in hypertension: Effects of insulin

BACKGROUND AND AIM

Hyperfibrinogenemia, a cardiovascular risk factor, is frequent in hypertension and largely unexplained. In this study, we measured fibrinogen production and whole-body protein turnover under both basal and hyperinsulinemic states, in hypertensive [H] and control [C] subjects, using a leucine stable isotope tracer and precursor-product relationships.

METHODS AND RESULTS

Since hypertension is often a feature of the "metabolic", insulin resistance syndrome, which in turn affects both fibrinogen kinetics and whole-body protein turnover, we selected hypertensive subjects without the metabolic syndrome. Following basal measurements, an euglycemic, approximately euaminoacidemic, hyperinsulinemic clamp was performed, with plasma insulin raised to 700-900 pmol/L. In H, rates of the fractional and absolute synthesis (FSR and ASR, respectively) of fibrinogen were 30%-40% greater (p<0.05 or less) than in C in both states, whereas leucine turnover was normal. Hyperinsulinemia did not modify fibrinogen synthesis in either group with respect to baseline, whereas it suppressed leucine appearance from endogenous proteolysis by approximately 40% to same extent in both groups. Amino acid clearance was similar in both the H and C subjects. In H, the insulin-mediated glucose disposal (M) was approximately 25% lower, (although insignificantly) than in controls, showing no overall insulin resistance. There was an inverse correlation between M and fibrinogen FSR during the clamp.

CONCLUSIONS

In essential hypertension fibrinogen production is increased, is not further stimulated by insulin, and is inversely related to insulin sensitivity at high-physiological insulin concentrations. Amino acid disposal and basal as well as insulin-responsive protein degradation rates are instead normal.

Feeding acutely stimulates fibrinogen synthesis in healthy young and elderly adults

Fibrinogen is a positive acute-phase protein and its hepatic synthesis is enhanced following inflammation and injury. However, it is not clear whether fibrinogen synthesis is also responsive to oral nutrients and whether the response to a meal may be affected by age. Our aim in this study was to investigate the acute effect of oral feeding on fibrinogen synthesis in both young and elderly men and women. Fibrinogen synthesis was determined in 3 separate occasions from the incorporation of l[(2)H(5)]phenylalanine (43 mg/kg body weight) in 8 young (21-35 y) and 8 elderly (>60 y) participants following the ingestion of water (control), a complete liquid meal (15% protein, 30% fat, and 55% carbohydrate), or only the protein component of the meal. The ingestion of the complete meal enhanced fibrinogen fractional synthesis rates (FSR) by 17 +/- 6% in the young and by 38 +/- 10% in the elderly participants compared with the water meal (P < 0.02). A comparable stimulation of FSR occurred with only the protein component of the meal in both young (29 +/- 7%) and elderly participants (41 +/- 9%) compared with the water meal (P < 0.005). Similar results were obtained when fibrinogen synthesis was expressed as absolute synthesis rates (i.e. mg.kg(-1).d(-1)). The results demonstrate that fibrinogen synthesis is acutely stimulated after ingestion of a meal and that this effect can be reproduced by the protein component of the meal alone, both in young and elderly adults.

Supraphysiological hyperinsulinaemia is necessary to stimulate skeletal muscle protein anabolism in older adults: evidence of a true age-related insulin resistance of muscle protein metabolism

AIMS/HYPOTHESIS

The physiological increase in muscle protein anabolism induced by insulin is blunted in healthy, glucose-tolerant older adults. We hypothesised that the age-related defect in muscle protein anabolism is a true insulin resistance state and can be overridden by supraphysiological hyperinsulinaemia.

METHODS

We used dye dilution, stable isotopic and immunoblotting techniques to measure leg blood flow, muscle protein synthesis, protein kinase B/mammalian target of rapamycin (Akt/mTOR) signalling, and amino acid kinetics in 14 healthy, glucose-tolerant older volunteers at baseline, and during an insulin infusion at postprandial (PD, 0.15 mU min(-1) 100 ml(-1)) or supraphysiologically high (HD, 0.30 mU min(-1) 100 ml(-1)) doses.

RESULTS

Leg blood flow, muscle protein synthesis, and Akt/mTOR signalling were not different at baseline. During hyperinsulinaemia, leg blood flow (p < 0.01) and muscle protein synthesis increased in the HD group only (PD [%/h]: from 0.063 +/- 0.006 to 0.060 +/- 0.005; HD [%/h]: from 0.061 +/- 0.007 to 0.098 +/- 0.007; p < 0.01). Muscle Akt phosphorylation increased in both groups, but the increase tended to be greater in the HD group (p = 0.07). The level of p70 ribosomal S6 kinase 1 (S6K1) phosphorylation increased in the HD group only (p < 0.05). Net amino acid balance across the leg improved in both groups, but a net anabolic effect was observed only in the HD group (p < 0.05).

CONCLUSIONS/INTERPRETATION

We conclude that supraphysiological hyperinsulinaemia is necessary to stimulate muscle protein synthesis and anabolic signalling in healthy older individuals, suggesting the existence of a true age-related insulin resistance of muscle protein metabolism.

Response of fractional synthesis rate (FSR) of fibrinogen, concentration of D-dimer and fibrinolytic balance to physical activity-based intervention in obese children

BACKGROUND

Physical activity-induced reduction in obesity-related hyperfibrinogenemia in children has been reported. The underlying mechanisms remain elusive. Further, the effect of such interventions on fibrinolysis in children is scarce.

OBJECTIVES

To investigate in obese children, before and after a physical activity-based intervention: (i) the mechanistic role of fractional synthesis rate (FSR) of fibrinogen in the reduction of hyperfibrinogenemia; and (ii) the changes in fibrinolytic factors.

METHODS

Subjects included 21 (age > 14 < 18 years; Tanner stage, IV-V) children (15 obese, BMI >95%tile for age and sex and six lean, BMI <85%tile). After baseline measurements of FSR of fibrinogen, and concentrations of fibrinogen, D-dimer, PAI-1 and t-PA in all children, studies were repeated after a 3-month randomized controlled physical activity-based lifestyle intervention in obese children only.

RESULTS

FSR of fibrinogen was higher (P = 0.002) in the obese (vs. lean) group, which was reduced (P = 0.001) after intervention. This almost completely accounted for the reduction in obesity-related hyperfibrinogenemia. High levels of D-dimer decreased (P = 0.001) after intervention, whereas fibrinolysis was not enhanced.

CONCLUSIONS

The direct reduction in the FSR of fibrinogen and the remarkable correlation between the magnitudes of reduction in fibrinogen FSR and concentration signify a mechanistic role for FSR in the regulation of physical activity-induced reversal of hyperfibrinogenemia in obese children. The congruent reductions in the FSR of fibrinogen and the concentrations of fibrinogen and D-dimer in response to intervention despite depressed fibrinolysis suggest an overall improvement in the hypercoagulable state in obese children with physical activity-based lifestyle intervention.

Effects of dietary protein restriction on albumin and fibrinogen synthesis in macroalbuminuric type 2 diabetic patients

AIMS/HYPOTHESIS

Diabetic nephropathy is associated with hypoalbuminaemia and hyperfibrinogenaemia. A low-protein diet has been recommended in patients with diabetic nephropathy, but its effects on albumin and fibrinogen synthesis are unknown.

METHODS

We compared the effects of a normal (NPD; 1.38 +/- 0.08 g kg(-1) day(-1)) or low (LPD; 0.81 +/- 0.04 g kg(-1) day(-1)) -protein diet on endogenous leucine flux (ELF), albumin and fibrinogen synthesis (L-[5,5,5,-2H3]leucine infusion), and markers of inflammation in nine type 2 diabetic patients with macroalbuminuria. Six healthy participants on NPD served as control participants.

RESULTS

In comparison with healthy participants, type 2 diabetic patients on an NPD had similar ELF, reduced serum albumin (38 +/- 1.1 vs 42 +/- 0.8 g/l; p < 0.05), similar fractional synthesis rates (FSR) and absolute synthesis rates (ASR) of albumin, and both increased plasma fibrinogen concentration [10.7 +/- 0.6 vs 7.2 +/- 0.5 micromol/l (3.64 +/- 0.22 vs 2.45 +/- 0.18 g/l); p < 0.05] and fibrinogen ASR [11.03 +/- 1.17 vs 6.0 +/- 1.8 micromol 1.73 m(-2) day(-1) (3.7 +/- 0.4 vs 1.9 +/- 0.3 g 1.73 m(-2) day(-1)); p < 0.01]. After LPD, type 2 diabetic patients had the following changes in comparison with NPD: reduced proteinuria (2.74 +/- 0.4 vs 4.51 +/- 0.8 g/day; p < 0.05), ELF (1.93 +/- 0.08 vs 2.11 +/- 0.08 micromol kg(-1) min(-1); p < 0.05) and total fibrinogen pool; increased serum albumin (42 +/- 1 vs 38 +/- 1 g/l; p < 0.01) and albumin ASR (14.1 +/- 1 vs 9.9 +/- 1 g 1.73 m(-2) day(-1); p < 0.05); and reduced plasma IL-6 levels, which were correlated with albumin ASR (r = -0.749; p < 0.05).

CONCLUSIONS/INTERPRETATION

LPD in type 2 diabetic patients with diabetic nephropathy reduces low-grade inflammatory state, proteinuria, albuminuria, whole-body proteolysis and ASR of fibrinogen, while increasing albumin FSR, ASR and serum concentration.

The effect of total starvation and very low energy diet in lean men on kinetics of whole body protein and five hepatic secretory proteins

It is unclear whether the rate of weight loss, independent of magnitude, affects whole body protein metabolism and the synthesis and plasma concentrations of specific hepatic secretory proteins. We examined 1) whether lean men losing weight rapidly (starvation) show greater changes in whole body protein kinetics, synthesis, and circulating concentrations of selected hepatic secretory proteins than those losing the same amount of weight more slowly [very low energy diet (VLED)]; and 2) whether plasma concentrations and synthetic rates of these proteins are related. Whole body protein kinetics were measured using [1-(13)C]leucine in 11 lean men (6 starvation, 5 VLED). Fractional and absolute synthetic rates of HDL-apolipoprotein A1 (apoA1), retinol binding protein, transthyretin, alpha(1)-antitrypsin (alpha(1)-AT), and transferrin were measured using a prime-constant intravenous infusion of [(13)C(2)]glycine. Compared with VLED group, the starvation group showed greater increases (at a 5% weight loss) in whole body protein oxidation (P < 0.05); fractional synthetic rates of HDL-apoA1 (25.3 vs. -1.52%; P = 0.003) and retinol binding protein (30.6 vs. 7.1%; P = 0.007); absolute synthetic rates of HDL-apoA1 (7.1 vs. -3.8 mg.kg(-1).day(-1); P = 0.003) and alpha(1)-AT (17.8 vs. 3.6 mg.kg(-1).day(-1); P = 0.02); and plasma concentration of alpha(1)-AT (P = 0.025). Relationships between synthetic rates and plasma concentrations varied between the secreted proteins. It is concluded that synthetic rates of hepatic secreted proteins in lean men are more closely related to the rate than the magnitude of weight loss. Changes in concentration of these secreted proteins can occur independently of changes in synthetic rates, and vice versa.

Response of albumin synthesis to oral nutrients in young and elderly subjects

BACKGROUND

The synthesis of albumin after oral ingestion of nutrients provides a means of storing amino acids, which can be made available during periods of fasting.

OBJECTIVE

This study was undertaken to see whether the response of albumin synthesis to the oral intake of nutrients is compromised in elderly subjects.

DESIGN

Albumin synthesis was determined from the incorporation of 43 mg l-[(2)H(5)]phenylalanine/kg body wt. Eight elderly subjects (aged >60 y) and 8 young subjects (aged 21-35 y) were studied on 3 separate occasions: after the intake of water, a liquid meal (with 15% of energy from protein, 30% of energy from fat, and 55% of energy from carbohydrate), or an isonitrogenous but not isocaloric meal containing only protein.

RESULTS

Mean (+/-SEM) albumin synthesis, expressed as an absolute rate (ie, the amount of albumin synthesized per day), was significantly lower in elderly subjects (108 +/- 7 mg . kg body wt(-1) . d(-1)) than in young subjects (141 +/- 7 mg . kg body wt(-1) . d(-1)). In response to the complete meal, albumin synthesis was significantly increased in both the elderly (144 +/- 7 mgkg body wt(-1) . d(-1)) and the young (187 +/- 11 mg . kg body wt(-1) . d(-1)) subjects. The protein component of the meal was sufficient to stimulate albumin synthesis in both the elderly (147 +/- 14 mg . kg body wt(-1) . d(-1)) and the young (182 +/- 6 mg . kg body wt(-1) . d(-1)) subjects.

CONCLUSIONS

Elderly subjects have lower rates of albumin synthesis than do young subjects during fasting, but they stimulate albumin synthesis proportionately in response to the oral ingestion of protein. The intakes of additional fat and carbohydrate do not stimulate albumin synthesis further.

Effect of insulin on human skeletal muscle protein synthesis is modulated by insulin-induced changes in muscle blood flow and amino acid availability

Insulin promotes muscle anabolism, but it is still unclear whether it stimulates muscle protein synthesis in humans. We hypothesized that insulin can increase muscle protein synthesis only if it increases muscle amino acid availability. We measured muscle protein and amino acid metabolism using stable-isotope methodologies in 19 young healthy subjects at baseline and during insulin infusion in one leg at low (LD, 0.05), intermediate (ID, 0.15), or high (HD, 0.30 mUxmin(-1)x100 ml(-1)) doses. Insulin was infused locally to induce muscle hyperinsulinemia within the physiological range while minimizing the systemic effects. Protein and amino acid kinetics across the leg were assessed using stable isotopes and muscle biopsies. The LD did not affect phenylalanine delivery to the muscle (-9 +/- 18% change over baseline), muscle protein synthesis (16 +/- 26%), breakdown, or net balance. The ID increased (P < 0.05) phenylalanine delivery (+63 +/- 38%), muscle protein synthesis (+157 +/- 54%), and net protein balance, with no change in breakdown. The HD did not change phenylalanine delivery (+12 +/- 11%) or muscle protein synthesis (+9 +/- 19%), and reduced muscle protein breakdown (-17 +/- 15%), thus improving net muscle protein balance but to a lesser degree than the ID. Changes in muscle protein synthesis were strongly associated with changes in muscle blood flow and phenylalanine delivery and availability. In conclusion, physiological hyperinsulinemia promotes muscle protein synthesis as long as it concomitantly increases muscle blood flow, amino acid delivery and availability.

Gastrointestinal tract as a target organ for orally administered insulin

The intestine is not considered to be a classic target tissue for insulin. Recent in vitro and in vivo experiments suggest that intestinal as well as systemic effects are observed following oral administration of insulin. Local effects include enhancement of intestinal growth, cell maturation, enzyme expression, gut adaptation after intestinal resection and reduction of intestinal permeability. Systemic effects, at least in animal models, include favorable effects on blood glucose and lipid profile and on the prevention of autoimmunity and attenuating the atherosclerotic process.

Diabetic nephropathy is associated with increased albumin and fibrinogen production in patients with type 2 diabetes

AIMS/HYPOTHESIS

Hyperfibrinogenaemia and albuminuria are cardiovascular risk factors, often coexisting in diabetic and non-diabetic people. Albuminuria in turn is associated with a compensatory albumin overproduction in non-diabetic patients. It is not known whether the presence of albuminuria in patients with type 2 diabetes mellitus is associated with greater albumin and fibrinogen production rates than in normoalbuminuric patients. SUBJECTS, MATERIALS, AND METHODS: Using leucine isotope methods, we measured fractional and absolute synthesis rates (FSR, ASR) of albumin and fibrinogen in post-absorptive type 2 diabetic patients with either normal (n=11) or increased (n=10) urinary albumin excretion.

RESULTS

In albuminuric patients, albumin FSR (16.2+/-1.5%/day) and ASR (20.5+/-1.9 g/day) were greater (p<0.02 and p<0.05, respectively) than in normoalbuminuric patients (FSR=11.5+/-1.1%/day; ASR=15.7+/-1.2 g/day). Fibrinogen FSR was similar between patients with normal and increased albumin excretion, but concentration, the circulating pool and ASR of fibrinogen were 40 to 50% greater (p<0.035) in patients with albuminuria. Albuminuria was positively correlated with albumin ASR, with fibrinogen concentration, the fibrinogen pool and ASR, whereas albumin synthesis was inversely correlated with calculated oncotic pressure.

CONCLUSIONS/INTERPRETATION

Synthesis of albumin and fibrinogen is upregulated in type 2 diabetic patients with increased urinary albumin excretion. Albuminuria is associated with enhanced fibrinogen and albumin synthesis.

Contemporary issues in protein requirements and consumption for resistance trained athletes

In recent years an explosion of research papers concerning protein consumption has been published. The need to consolidate this information has become critical from both practical and future research standpoints. For this reason, the following paper presents an in depth analysis of contemporary issues in protein requirements and consumption for resistance trained athletes. Specifically, the paper covers: 1.) protein requirements for resistance trained athletes; 2.) the effect of the digestion rate of protein on muscular protein balance; 3.) the optimal timing of protein intake relative to exercise; 4.) the optimal pattern of protein ingestion, relative to how an individual should consume their protein throughout a 24 hour period, and what sources are utilized during this time frame; 5.) protein composition and its interaction with measures of protein balance and strength performance; 6.) the combination of protein and carbohydrates on plasma insulin levels and protein balance; 7.) the efficacy of protein supplements and whole food protein sources. Our goal is to provide the reader with practical information in optimizing protein intake as well as for provision of sound advice to their clients. Finally, special care was taken to provide future research implications.

Differences in protein and energy metabolism following portal versus systemic administration of insulin in diabetic dogs

AIMS/HYPOTHESIS

In non-diabetic people, insulin levels in the liver are two-fold higher than those in the systemic circulation. In contrast, patients with type 1 diabetes have similar hepatic and systemic insulin levels because insulin is administered peripherally. The aim of this study was to compare the effects of systemic (SI) and pre-portal (PI) insulin administration on energy, glucose and protein metabolism in chronic insulin-dependent ketosis-prone diabetic dogs.

MATERIALS AND METHODS

We applied glucose-controlled insulin infusion, indirect calorimetry and stable isotope and radioisotope techniques to measure energy, protein and glucose metabolism. We maintained near-normoglycaemia at identical levels under both study conditions for 20 h.

RESULTS

SI was associated with lower oxygen consumption (130+/-13 vs 161+/-8 ml/min), CO(2) production (99+/-10 vs 130+/-8 ml/min), respiratory quotient (0.76+/-0.02 vs 0.81+/-0.01) and energy expenditure (870+/-90 vs 1089+/-60 kcal/24 h) (p<0.05 for all differences). PI increased the respiratory quotient from the insulin-deprived state, whereas SI did not. Glucose kinetics were similar for SI and PI, whereas leucine oxidation (36+/-4 vs 54+/-5 micromol kg(-1) min(-1)) and the fractional synthesis rates of liver tissue protein (0.68+/-0.6 vs 0.83+/-0.07%/h), albumin (0.55+/-0.06 vs 0.68+/-0.4%/h), and fibrinogen (1.73+/-0.23 vs 2.59+/-0.25%/h) were all lower during SI than PI (p<0.05).

CONCLUSIONS/INTERPRETATION

The route of insulin administration did not alter glucose metabolism but did affect protein synthesis in the liver. The potential impact of this altered liver protein metabolism on chronic complications needs careful evaluation. A similar decrease in energy expenditure resulting from systemic insulin administration during tight glycaemic control is a potential cause of weight gain.

Insulin resistance of muscle protein metabolism in aging

A reduced response of older skeletal muscle to anabolic stimuli may contribute to the development of sarcopenia. We hypothesized that muscle proteins are resistant to the anabolic action of insulin in the elderly. We examined the effects of hyperinsulinemia on muscle protein metabolism in young (25+/-2 year) and older (68+/-1 year) healthy subjects using stable isotope tracer techniques. Leg blood flow was higher in the young at baseline and increased during hyperinsulinemia, whereas it did not change in the elderly. Glucose concentrations and muscle uptake were not different between groups at baseline and during hyperinsulinemia. Leg phenylalanine net balance was not different at baseline and significantly increased in both groups with hyperinsulinemia (P<0.05) but to a greater extent in the young (P<0.05). Muscle protein synthesis increased only in the young during hyperinsulinemia. Muscle protein breakdown did not significantly change in either group, although it tended to decrease in the elderly. Changes in muscle protein synthesis were correlated with changes in leg amino acid delivery (R=0.89; P=0.0001) and blood flow (R=0.90; P<0.0001). In conclusion, skeletal muscle protein synthesis is resistant to the anabolic action of insulin in older subjects, which may be an important contributor to the development of sarcopenia.

Short-term insulin and nutritional energy provision do not stimulate muscle protein synthesis if blood amino acid availability decreases

Muscle protein synthesis requires energy and amino acids to proceed and can be stimulated by insulin under certain circumstances. We hypothesized that short-term provision of insulin and nutritional energy would stimulate muscle protein synthesis in healthy subjects only if amino acid availability did not decrease. Using stable isotope techniques, we compared the effects on muscle phenylalanine kinetics across the leg of an amino acid-lowering, high-energy (HE, n = 6, 162 +/- 20 kcal/h) hyperglycemic hyperlipidemic hyperinsulinemic clamp with systemic insulin infusion to a low-energy (LE, n = 6, 35 +/- 3 kcal/h, P < 0.05 vs. HE) euglycemic hyperinsulinemic clamp with local insulin infusion in the femoral artery. Basal blood phenylalanine concentrations and phenylalanine net balance, muscle protein breakdown, and synthesis (nmol.min(-1).100 g leg muscle(-1)) were not different between groups. During insulin infusion, femoral insulinemia increased to a similar extent between groups and blood phenylalanine concentration decreased 27 +/- 3% in the HE group but only 9 +/- 2% in the LE group (P < 0.01 HE vs. LE). Phenylalanine net balance increased in both groups, but the change was greater (P < 0.05) in the LE group. Muscle protein breakdown decreased in the HE group (58 +/- 12 to 35 +/- 7 nmol.min(-1).100 g leg muscle(-1)) and did not change in the LE group. Muscle protein synthesis was unchanged in the HE group (39 +/- 6 to 30 +/- 7 nmol.min(-1).100 g leg muscle(-1)) and increased (P < 0.05) in the LE group (41 +/- 9 to 114 +/- 26 nmol.min(-1).100 g leg muscle(-1)). We conclude that amino acid availability is an important factor in the regulation of muscle protein synthesis in response to insulin, as decreased blood amino acid concentrations override the positive effect of insulin on muscle protein synthesis even if excess energy is provided.

Intestinal and systemic effects of oral insulin supplementation in rats after weaning

Oral insulin has intestinal trophic effects in suckling animals. In mice, lower glucose and lipid levels may be seen when oral insulin is given after the weaning period. The purpose of the present study is to examine local and systemic effects of oral insulin supplementation in rats in the postweaning period. Immediately after weaning, Sprague-Dawley rats received either drinking water (controls) or oral insulin in their drinking water (1 U/ml) for either 1 week or 6 weeks. Intestinal mucosal parameters (bowel and mucosal weight, mucosal DNA and protein) and histological changes were examined in all study groups. Glucose levels were monitored weekly, and at the end of the study, blood levels of glucose, lipids, and insulin were measured in the fasting state. After 1 week of insulin supplementation, mucosal weight in duodenum and jejunum as well as jejunal DNA content were significantly higher in insulin-supplemented rats compared to controls. Duodenal circumference and villus height in jejunum were significantly higher in insulin-supplemented rats compared to controls on both day 7 and day 42. Total cholesterol levels were significantly lower in the study group compared with the controls. We conclude that oral insulin supplementation exerts intestinal trophic effects, as well as systemic effects in the postweaning period in rats.

Mixed muscle and hepatic derived plasma protein metabolism is differentially regulated in older and younger men following resistance exercise

We sought to determine whether exercise-induced muscle protein turnover alters the subsequent production of hepatically derived acute-phase plasma proteins, and whether age affects how these proteins are regulated. We measured arteriovenous (a-v) balance and the synthesis of mixed muscle protein, albumin (A) and fibrinogen (F) before exercise (REST) and from the beginning of exercise to 10, 60, and 180 min following a single bout of moderate-intensity leg extension exercise (POST-EX) in postabsorptive untrained older (n = 6) and younger (n = 6) men using L-[ring-2H5]phenylalanine (Phe). Subjects performed 6 sets of 8 repetitions of leg extension at 80% of their 1-RM (one-repetition maximum). All data are presented as the difference from REST (Delta from REST at 10, 60, and 180 min POST-EX). Mixed muscle fractional synthesis rate (FSR-M) increased significantly from the beginning of exercise until 10 min POST-EX in the older men (DeltaFSR-M: 0.044%/h), whereas FSR-M in the younger men was not elevated until 180 min POST-EX (DeltaFSR-M: 0.030%/h). FSR-A and FSR-F increased at all POST-EX periods in the older men (DeltaFSR-A = 10 min: 1.90%/day; 60 min: 2.72%/day; 180 min: 2.78%/day; DeltaFSR-F = 10 min: 1.00%/day; 60 min: 3.01%/day; 180 min: 3.73%/day). No change occurred in FSR-A in the younger men, but FSR-F was elevated from the beginning of exercise until 10 and 180 min POST-EX (10 min: 3.07%/day and 180 min: 3.96%/day). Net balance of Phe was positive in the older men in the immediate POST-EX period. Our data indicate that mixed muscle and hepatic derived protein synthesis is differentially regulated in younger and older men in response to a single bout of moderate-intensity leg extension exercise. Moreover, our data suggest that with age may come a greater need to salvage or make available amino acids from exercise-induced muscle protein breakdown to mount an acute-phase response.

Postexercise protein metabolism in older and younger men following moderate-intensity aerobic exercise

Regular aerobic exercise strongly influences muscle metabolism in elderly and young; however, the acute effects of aerobic exercise on protein metabolism are not fully understood. We investigated the effect of a single bout of moderate walking (45 min at approximately 40% of peak O2 consumption) on postexercise (POST-EX) muscle metabolism and synthesis of plasma proteins [albumin (ALB) and fibrinogen (FIB)] in untrained older (n = 6) and younger (n = 6) men. We measured muscle phenylalanine (Phe) kinetics before (REST) and POST-EX (10, 60, and 180 min) using l-[ring-2H5]phenylalanine infusion, femoral arteriovenous blood samples, and muscle biopsies. All data are presented as the difference from REST (at 10, 60, and 180 min POST-EX). Mixed muscle fractional synthesis rate (FSR) increased significantly at 10 min POST-EX in both the younger (0.0363%/h) and older men (0.0830%/h), with the younger men staying elevated through 60 min POST-EX (0.0253%/h). ALB FSR increased at 10 min POST-EX in the younger men only (2.30%/day), whereas FIB FSR was elevated in both groups through 180 min POST-EX (younger men = 4.149, older men = 4.107%/day). Muscle protein turnover was also increased, with increases in synthesis and breakdown in younger and older men. Phe rate of disappearance (synthesis) was increased in both groups at 10 min POST-EX and remained elevated through 60 min POST-EX in the older men. A bout of moderate-intensity aerobic exercise induces short-term increases in muscle and plasma protein synthesis in both younger and older men. Aging per se does not diminish the protein metabolic capacity of the elderly to respond to acute aerobic exercise.

An integrative approach to in-vivo protein synthesis measurement: from whole tissue to specific proteins

PURPOSE OF REVIEW

In-vivo estimation of protein turnover by stable isotopes in animals and humans has provided much relevant information on metabolic regulation and alterations for decades. While it was first appreciated at the whole body level in the 1970s and 1980s, new approaches have allowed inter-organ or tissue protein turnover rates to be measured, notably the incorporation rate of a labelled amino acid in muscle. These technical improvements have recently been completed by new isolation methods for the study of protein synthesis rates in various muscle and hepatic protein fractions in different blood cells or tissues such as bone and skin.

RECENT FINDINGS

This new insight into tissue protein synthesis opens the door for exploration of single proteins, which may be fully achievable in the near future through the combination of proteomics analysis and technical progress in mass spectrometry. This is, therefore, a new area in which not only quantitative but also qualitative changes in specific proteins will be considered for a fully integrative approach to assessing protein metabolism in physiology and disease.

SUMMARY

To understand the mechanisms by which protein metabolism is altered during physiopathological situations, it is of importance to measure the effect on specific proteins rather than on the body as a whole. Procedures are currently under development with the aim of isolating individuals proteins and to measure their synthesis rates by isotopic methods. Such technical progress is needed to gain a better understanding of the regulation of protein metabolism in situations in which loss of body protein mass occurs.

C-reactive protein, its role in inflammation, Type 2 diabetes and cardiovascular disease, and the effects of insulin-sensitizing treatment with thiazolidinediones

Increased concentrations of the marker of inflammation, C-reactive protein (CRP), are associated with insulin resistance, Type 2 diabetes and the development of cardiovascular disease. In particular, inflammation is closely associated with endothelial dysfunction and is recognized as one of the cardiovascular risk factors clustering in the Insulin Resistance Syndrome or Metabolic Syndrome. The exact mechanisms linking insulin resistance and inflammation remain unclear. However, the close association between insulin resistance and inflammation in atherogenesis suggests that therapies that address both parameters may have benefits in reducing diabetes-related macrovascular complications. The thiazolidinedione class of oral anti-diabetic agents are powerful insulin sensitizers that also have anti-inflammatory properties. Treatment with these agents has a range of anti-atherogenic effects, including reduced levels of CRP, plasminogen activator inhibitor-1 (PAI-1), TNF-alpha and reactive oxygen species. Additionally, the insulin-sensitizing effect of thiazolidinediones improves other factors of the Insulin Resistance Syndrome, including dyslipidaemia and hypertension. Outcome studies are underway to determine if the effects of improving insulin sensitivity and reducing inflammation will translate into clinical benefits and reduce the cardiovascular morbidity and mortality associated with insulin resistance and Type 2 diabetes.

Insulin resistance, inflammation, and the prediabetic state

Type 2 diabetes is associated with a marked increase in the incidence of coronary artery disease (CAD); however, the correlation between glycemia and CAD in patients with type 2 diabetes is only modestly positive. This relatively weak association between glycemia and CAD in subjects with diabetes may be caused by the existence of an atherogenic prediabetic state. In the San Antonio Heart Study, subjects who start with normal glucose tolerance and later develop type 2 diabetes have increased triglyceride levels, increased systolic blood pressure, and decreased levels of high-density lipoprotein cholesterol before the onset of type 2 diabetes. The basis for these atherogenic prediabetic changes may be related to insulin resistance rather than reduced insulin secretion. Recently, interest has focused on a possible role of fibrinolysis and increased subclinical inflammation, as determined by high-sensitivity C-reactive protein (CRP) levels. The Insulin Resistance Atherosclerosis Study found that insulin resistance, as determined by a frequently sampled glucose tolerance test, is significantly related to higher CRP levels, higher fibrinogen, and higher plasminogen activator inhibitor-1 (PAI-1) levels. The investigators also have shown that high PAI-1 and CRP levels are predictors of the development of type 2 diabetes. In addition, the Women's Health Study has shown that high CRP levels predict type 2 diabetes. Insulin-sensitizing interventions have been demonstrated to reduce these nontraditional risk factors. Rosiglitazone, an agent with insulin-sensitizing properties, decreases PAI-1 and CRP levels. Some of the adverse cardiovascular effects seen in patients with type 2 diabetes may be reversed by insulin-sensitizing agents.

Dietary carbohydrate deprivation increases 24-hour nitrogen excretion without affecting postabsorptive hepatic or whole body protein metabolism in healthy men

Because insulin is an important regulator of protein metabolism, we hypothesized that physiological modulation of insulin secretion, by means of extreme variations in dietary carbohydrate content, affects postabsorptive protein metabolism. Therefore, we studied the effects of three isocaloric diets with identical protein content and low-carbohydrate/high-fat (2% and 83% of total energy, respectively), intermediate-carbohydrate/intermediate-fat (44% and 41% of total energy, respectively), and high-carbohydrate/low-fat (85% and 0% of total energy, respectively) content in six healthy men. Whole body protein metabolism was assessed by 24-h urinary nitrogen excretion, postabsorptive leucine kinetics, and fibrinogen and albumin synthesis by infusion of [1-(13)C]leucine and [1-(13)C]valine. The low-carbohydrate/high-fat diet resulted in lower absorptive and postabsorptive plasma insulin concentrations, and higher rates of nitrogen excretion compared with the other two diets: 15.3 +/- 0.9 vs. 12.1 +/- 1.1 (P = 0.03) and 10.8 +/- 0.5 g/24 h (P = 0.005), respectively. Postabsorptive rates of appearance of leucine and of leucine oxidation were not different among the three diets. In addition, dietary carbohydrate content did not affect the synthesis rates of fibrinogen and albumin. In conclusion, eucaloric carbohydrate deprivation increases 24-h nitrogen loss but does not affect postabsorptive protein metabolism at the hepatic and whole body level. By deduction, dietary carbohydrate is required for an optimal regulation of absorptive, rather than postabsorptive, protein metabolism.

Contribution of plasma proteins to splanchnic and total anabolic utilization of dietary nitrogen in humans

Splanchnic tissues are largely involved in the postprandial utilization of dietary amino acids, but little is yet known, particularly in humans, about the relative contributions of different splanchnic protein pools to splanchnic and total postprandial anabolism. Our aim was to develop a compartmental model that could distinguish dietary nitrogen (N) incorporation among splanchnic constitutive, plasma (splanchnic exported), and peripheral proteins after a mixed-protein meal in humans. Eight healthy subjects were fed a single mixed meal containing 15N-labeled soy protein, and dietary N postprandial kinetics were measured in plasma free amino acids, proteins, and urea and urinary urea and ammonia. These experimental data and others previously obtained for dietary N kinetics in ileal effluents under similar experimental conditions were used to develop the compartmental model. Six hours after the mixed-meal ingestion, 31.5, 7.5, and 21% of ingested N were predicted to be incorporated into splanchnic constitutive, splanchnic exported, and peripheral proteins, respectively. The contribution of splanchnic exported proteins to total splanchnic anabolism from dietary N was predicted to be approximately 19% and to remain steady throughout the simulation period. Model behavior and its predictions were strongly in line with current knowledge of the system and the scarce, specific data available in the literature. This model provides the first data concerning the anabolism of splanchnic constitutive proteins in the nonsteady postprandial state in humans. By use of only slightly invasive techniques, this model could help to assess how the splanchnic anabolism is modulated under different nutritional or pathophysiological conditions in humans.

Effects of fatty acids on hepatic amino acid catabolism and fibrinogen synthesis in young healthy volunteers

Increased synthesis rate of fibrinogen, an independent risk factor for cardiovascular disease, was recently reported in obese insulin-resistant female adolescents with chronic elevated nonesterified fatty acids (NEFA). It is unknown whether a short-term change of NEFA concentrations controls hepatic fibrinogen synthesis. Therefore, 10 healthy male volunteers (24.5 +/- 3.3 yr, body mass index 23.5 +/- 2.9 kg/m2) were investigated in random order under basal and elevated NEFA for 8 h. Leucine metabolism, the fractional synthesis rates (FSR) of plasma fibrinogen, and endogenous urea production rates were measured during primed, continuous infusion of [1-13C]leucine and [15N2]urea, respectively. Plasma alpha-[13C]ketoisocaproic acid and [15N2]urea enrichment values were measured with GC-MS. Plasma fibrinogen was isolated with the beta-alanine method, and fibrinogen-related [13C]leucine enrichment was analyzed by GC-CIRMS. Lipofundin infusion and subcutaneous heparin tripled NEFA and triglycerides in the tests. Plasma glucose, circulating insulin, human C-peptide, and plasma glucagon were not changed by the study procedure. Fibrinogen FSR were significantly lower in tests with NEFA elevation (18.44 +/- 4.67%) than in control tests (21.48 +/- 4.32%; P < 0.05). Plasma fibrinogen concentrations measured were not significantly different (NEFA test subjects: 1.85 +/- 0.33, controls: 1.97 +/- 0.54 g/l). Parameters of leucine metabolism, such as leucine rate of appearance, leucine oxidation, and nonoxidative leucine disposal, were not influenced by NEFA elevation, and endogenous urea production remained unchanged. NEFA contributes to short-term regulation of fibrinogen FSR in healthy volunteers under unchanged hormonal status, leucine metabolism, and overall amino acid catabolism. Its contribution might be of relevance at least after fat-rich meals, counteracting by reduction of FSR the blood viscosity increase implied by hyperlipidemia.

Insulin resistance and chronic cardiovascular inflammatory syndrome

Insulin resistance is increasingly recognized as a chronic, low-level, inflammatory state. Hyperinsulinemia and insulin action were initially proposed as the common preceding factors of hypertension, low high-density lipoprotein cholesterol, hypertriglyceridemia, abdominal obesity, and altered glucose tolerance, linking all these abnormalities to the development of coronary heart disease. The similarities of insulin resistance with another inflammatory state, atherosclerosis, have been described only in the last few decades. Atherosclerosis and insulin resistance share similar pathophysiological mechanisms, mainly due to the actions of the two major proinflammatory cytokines, TNF-alpha and IL-6. Genetic predisposition to increased transcription rates of these cytokines is associated with metabolic derangement and simultaneously with coronary heart disease. Dysregulation of the inflammatory axis predicts the development of insulin resistance and type 2 diabetes mellitus. The knowledge of how interactions between metabolic and inflammatory pathways occur will be useful in future therapeutic strategies. The effective administration of antiinflammatory agents in the treatment of insulin resistance and atherosclerosis is only the beginning of a promising approach in the management of these syndromes.

Insulin action on protein metabolism in acromegalic patients

Insulin resistance in acromegaly causes glucose intolerance and diabetes, but it is unknown whether it involves protein metabolism, since both insulin and growth hormone promote protein accretion. The effects of acromegaly and of its surgical cure on the insulin sensitivity of glucose and amino acid/protein metabolism were evaluated by infusing [6,6-(2)H(2)]glucose, [1-(13)C]leucine, and [2-(15)N]glutamine during a euglycemic insulin (1 mU x kg(-1) x min(-1)) clamp in 12 acromegalic patients, six studied again 6 mo after successful adenomectomy, and eight healthy controls. Acromegalic patients, compared with postsurgical and control subjects, had higher postabsorptive glucose concentration (5.5 +/- 0.3 vs. 4.9 +/- 0.2 micromol/l, P < 0.05, and 5.1 +/- 0.1 micromol/l) and flux (2.7 +/- 0.1 vs. 2.0 +/- 0.2 micromol x kg(-1) x min(-1), P < 0.01, and 2.2 +/- 0.1 micromol x kg(-1) x min(-1), P < 0.05) and reduced insulin-stimulated glucose disposal (+15 +/- 9 vs. +151 +/- 18%, P < 0.01, and 219 +/- 58%, P < 0.001 from basal). Postabsorptive leucine metabolism was similar among groups. In acromegalic and postsurgical subjects, insulin suppressed less than in controls the endogenous leucine flux (-9 +/- 1 and -12 +/- 2 vs. -18 +/- 2%, P < 0.001 and P < 0.05), the nonoxidative leucine disposal (-4 +/- 3 and -1 +/- 3 vs. -18 +/- 2%, P < 0.01 and P < 0.05), respectively, indexes of proteolysis and protein synthesis, and leucine oxidation (-17 +/- 6% in postsurgical patients vs. -26 +/- 6% in controls, P < 0.05). Within 6 mo, surgery reverses insulin resistance for glucose but not for protein metabolism. After adenomectomy, more leucine is oxidized during hyperinsulinemia.

Dual role of insulin in transcriptional regulation of the acute phase reactant ceruloplasmin

Insulin is a potent negative regulator of the response of hepatic cells to pro-inflammatory cytokines, particularly, interleukin (IL)-6. The action of insulin is target-selective because it inhibits transcription of most but not all acute phase genes. We here show that ceruloplasmin (Cp), an acute phase reactant with important functions in iron homeostasis, is subject to a unique dual regulation by insulin. IL-6 increased Cp mRNA expression in HepG2 cells by approximately 5-fold. Simultaneous treatment with insulin reduced this stimulation by half. Surprisingly, insulin by itself caused a 2-4-fold induction in Cp mRNA expression. The mechanism of induction by insulin was studied by transfecting into HepG2 cells chimeric constructs of the Cp 5'-flanking region driving luciferase. The activity of a 4800-bp segment of the Cp 5'-flanking region was increased 3-fold by insulin. Deletion and mutation analyses showed the requirement for a single hypoxia-responsive element in a 96-bp segment approximately 3600 bp upstream of the initiation site. The domains required for the two activities of insulin were distinct: The distal, hypoxia-responsive element-containing site was sufficient for Cp transactivation by insulin; in contrast, an 848-bp region adjacent to the initiation site was sufficient for IL-6 transactivation of Cp and for the inhibitory activity of insulin. The role of hypoxia-inducible factor-1 in the induction of Cp by insulin was shown by electrophoretic mobility shift assays and by the absence of insulin-stimulated Cp promoter activation in mouse Hepa c4 cells deficient in hypoxia-inducible factor-1 activity. Taken together these results show that insulin functions as a bidirectional, condition-dependent regulator of hepatic cell Cp expression. The unique regulation of Cp may reflect its dual roles in inflammation and iron homeostasis.

Effects of feeding on albumin synthesis in hypoalbuminemic hemodialysis patients

BACKGROUND

Hypoalbuminemia is a powerful predictor of morbidity and mortality in hemodialysis (HD) patients and results from a reduction in albumin synthesis. It is not known if this is associated with any impairment of the normal response to feeding.

METHODS

Protein turnover and albumin synthesis were measured in the fasting and fed state using a primed constant infusion of L-[1-(13)C]leucine in seven hypoalbuminemic (albumin < or = 36 g/L) HD patients (HHD), seven normoalbuminemic (albumin > or = 40 g/L) HD patients (NHD) and nine age-matched normal controls.

RESULTS

The increase in albumin synthesis on feeding was impaired in HHD patients (fasting 15.0 +/- 1.5 vs. fed 17.7 +/- 2.9%, P = NS) compared to NHD (fasting 13.7 +/- 0.9 vs. fed 17.4 +/- 1.0%, P < 0.05) and controls (fasting 12.9 +/- 0.6 vs. fed 15.2 +/- 0.6%, P < 0.05). In addition, body mass index and percent body fat were significantly (P < 0.05) lower in HHD (20.8 +/- 1.3 kg/m2, 23.4 +/- 2.0%) than NHD (26.7 +/- 1.3 kg/m2, 33.1 +/- 3.2%) or controls (26.2 +/- 1.1 kg/m2, 32.6 +/- 1.8%). There was no difference in dietary protein or energy intake in the three groups.

CONCLUSIONS

There are differences of body composition and protein metabolism in HHD patients that may be related to an impaired metabolic response to feeding.

Effects of wine intake on postprandial plasma amino acid and protein kinetics in type 1 diabetes

BACKGROUND

Alcohol may impair protein turnover and insulin sensitivity in vivo.

OBJECTIVE

The acute effects of moderate wine intake on amino acid kinetics and on the fractional synthetic rate (FSR) of albumin and fibrinogen in patients with type 1 diabetes were studied.

DESIGN

Six patients with type 1 diabetes ingested an elementary mixed meal (46 kJ/kg) over 4 h, first without and 3 mo later with approximately 300 mL red wine. Postprandial glucose concentrations were maintained at <10 mmol/L.

RESULTS

Postprandially, the FSR of fibrinogen was approximately 30% greater (21.5 +/- 6.6% compared with 14.1 +/- 3.6% of pool/d; P < 0.01) and glucagon concentrations were approximately 40% greater (103 +/- 20 compared with 61 +/- 13 ng/L; P < 0.015) with wine than without wine. However, the FSR of albumin and the rates of appearance of total and endogenous phenylalanine and leucine were not significantly different between treatments. First-pass splanchnic uptake (in micromol*kg(-1)*min(-1)) of dietary phenylalanine (0.22 +/- 0.02 compared with 0.19 +/- 0.02) and leucine (0.25 +/- 0.04 compared with 0.14 +/- 0.02) were greater with wine (P < 0.05), whereas dietary phenylalanine oxidation was lower with wine, by approximately 25% (0.10 +/- 0.02 compared with 0.14 +/- 0.01 micromol.kg(-1).min(-1); P < 0.05). Selected amino acid concentrations were significantly lower but glutamate concentrations were significantly higher with wine.

CONCLUSIONS

In insulin-infused patients with type 1 diabetes, moderate wine intake with a meal resulted in 1) a higher fibrinogen FSR, glucagon concentration, and first-pass splanchnic uptake of leucine and phenylalanine; 2) lower dietary phenylalanine oxidation; 3) selective changes in plasma amino acid concentrations; 4) and no impairment in endogenous proteolysis and albumin synthesis.

Apolipoprotein synthesis in nonalcoholic steatohepatitis

The pathophysiology of hepatic steatosis, a prerequisite of nonalcoholic fatty liver disease, is poorly understood. Because very-low-density lipoprotein (VLDL) formation is the chief route of hepatic lipid export, we hypothesized that the synthesis of apoB-100, a rate-determining step in hepatic VLDL formation, may be altered in patients with nonalcoholic steatohepatitis (NASH). This study evaluated the relative synthesis rates of apolipoprotein B-100 (apoB-100) in patients with NASH and in lean and body mass index (BMI)-matched (obese) controls without NASH. A primed continuous infusion of L-[1-(13)C] leucine was used to measure the absolute synthesis rates (ASR) of apoB-100 and fibrinogen in 7 patients with NASH and compared them with 7 lean and 7 obese (BMI-matched) controls without NASH. The ASRs of fibrinogen and albumin also were measured. The mean ASR of apoB-100 in patients with NASH was lower (31.5 +/- 3.4 mg/kg/d) than that of obese (115.2 +/- 7.2 mg/kg/d, P <.001) and lean controls (82.4 +/- 4.1 mg/kg/d, P =.002). In contrast, the mean ASR of fibrinogen was greater in subjects with NASH than in both control groups. These data indicate that NASH is associated with markedly altered hepatic synthesis of apoB-100. The finding that albumin synthesis was not similarly decreased in patients with NASH shows that the attenuation of apoB-100 synthesis is not on the basis of globally impaired hepatic protein synthesis. In conclusion, because apoB-100 synthesis is a rate-determining step in hepatocyte lipid export, decreased synthesis of this protein may be an important factor in the development of hepatic steatosis, a prerequisite for NASH.

Increased synthesis rate of fibrinogen as a basis for its elevated plasma levels in obese female adolescents

Increased concentrations of plasma fibrinogen, an independent risk factor for cardiovascular disease (CVD), in obese children have been reported. The underlying mechanism for this, however, remains to be defined. In the current study, we measured the fractional synthesis rates (FSR) of plasma fibrinogen in six healthy postpubertal obese girls [body mass index (BMI) 36.6 +/- 1.8 kg/m(2); age 16.6 +/- 0.5 yr] and six age-matched lean normal control girls (BMI 20.8 +/- 0.7 kg/m(2); age 16.4 +/- 0.4 yr) during a primed, continuous infusion of L-[1-(13)C]leucine in the postabsorptive state. The method involved purification of plasma fibrinogen by use of immunoaffinity chromatography followed by measurement of [(13)C]leucine enrichment using gas chromatography-combustion-isotope ratio mass spectrometry. The FSR of fibrinogen in obese girls (35.06 +/- 2.61%/day) was almost double that in lean girls (17.02 +/- 1.43%/day), and this increase was associated with a relative increase in plasma concentration of fibrinogen as well as BMI in the subjects studied. Obese subjects had high fasting insulin levels (138 +/- 47 pmol/l) compared with lean subjects (54 +/- 11 pmol/l), whereas their glucose concentrations were similar (4.5 +/- 0.3 mmol/l in obese and 4.4 +/- 0.4 mmol/l in lean subjects), suggesting insulin resistance. The doubling of the FSR of fibrinogen provides novel insight into the mechanism of elevated levels of plasma fibrinogen and suggests a primary role for increased synthesis in producing the hyperfibrinogenemia associated with obesity. This finding may have important implications in the design of therapies for modulating plasma fibrinogen levels in obesity and/or CVD in childhood.

Impairment of albumin and whole body postprandial protein synthesis in compensated liver cirrhosis

To investigate the anabolic effects of feeding in cirrhosis, we measured albumin fractional synthesis rate (FSR) and whole body protein synthesis in six nondiabetic patients with stable liver cirrhosis (three in the Child-Pugh classification Class A, three in Class B) and in seven normal control subjects, before and after administration of a 4-h mixed meal. Leucine tracer precursor-product relationships and whole body kinetics were employed at steady state. Basal levels of postabsorptive albumin concentration and FSR, whole body leucine rate of appearance, oxidation, and nonoxidative leucine disposal (NOLD, approximately equal to protein synthesis) were similar in the two groups. However, after the meal, in the patients neither albumin FSR (from 8.5 +/- 1.5 to 8.8 +/- 1.8 %/day) nor NOLD (from 1.69 +/- 0.22 to 1.55 +/- 0.26 micromol x kg(-1) x min(-1)) changed (P = nonsignificant vs. basal), whereas they increased in control subjects (albumin FSR: from 10.9 +/- 1.5 to 15.9 +/- 1.9 %/day, P < 0.002; NOLD: from 1.80 +/- 0.14 to 2.10 +/- 0.19 micromol x kg(-1) x min(-1), P = 0.032). Thus mixed meal ingestion did not stimulate either albumin FSR or whole body protein synthesis in compensated liver cirrhosis. The mechanism(s) maintaining normoalbuminemia at this disease stage need to be further investigated.

Insulin infusion normalizes fasting and post-prandial albumin and fibrinogen synthesis in Type 1 diabetes mellitus

AIMS

The effect of metabolic control on hepatic synthesis of plasma proteins in Type 1 diabetes mellitus (T1DM), in the post-absorptive and post-prandial state, is not known.

METHODS

We measured fractional synthetic rates (FSR) of albumin and fibrinogen in six insulin-infused T1DM patients and in five to nine control subjects, before and for approx. 4 h after a mixed liquid meal. Phenylalanine tracer precursor/product relationships and steady-state conditions were used. In the post-absorptive state, patients were studied in near euglycaemic conditions after an overnight intravenous insulin infusion. During the meal (approx. 11 kcal/kg), the insulin infusion rate was increased to maintain plasma glucose concentrations below approx. 10 mmol/l.

RESULTS

Post-absorptive FSR of albumin (5.7 +/- 0.6%/day) and fibrinogen (11.3 +/- 0.6%/day) in T1DM were similar to control values (6.4 +/- 0.9 and 13.1 +/- 1.1, respectively). After the meal, albumin FSR increased (P = 0.0032 by anova) in both groups (T1DM, to 14.4 +/- 2.7%/day; controls, to 18.2 +/- 3.7%/day). Fibrinogen FSR also increased (P = 0.0048 by anova) in both the T1DM (to 18.2 +/- 2.6) and the control subjects (to 27.3 +/- 6.2). There was no difference between T1DM and control subjects in the post-prandial FSR of both proteins.

CONCLUSIONS

Albumin and fibrinogen FSR in T1DM can be maintained within near-normal ranges by insulin infusion under post-absorptive and post-prandial conditions.

Testosterone administration in severe burns ameliorates muscle catabolism

OBJECTIVE

To assess the effects of testosterone administration on muscle protein metabolism after severe burn injury. We hypothesized that restoration of blood testosterone concentrations would restore an important anabolic stimulus to skeletal muscle, and would further increase the anabolic response of muscle to amino acid supplementation.

DESIGN

Pre- and postintervention trial conducted between September 1997 and July 1999.

SETTING

Burn intensive care unit.

PATIENTS

Six severely burned male patients (>70% total body surface area).

INTERVENTION

Testosterone enanthate, 200 mg/wk (intramuscularly), for 2 wks.

MEASUREMENTS AND MAIN RESULTS

Muscle protein synthesis, breakdown, and amino acid kinetics were determined. After a basal period in each study, we subsequently investigated the response to acute amino acid supplementation during enteral feeding. Total testosterone increased significantly from baseline to the low normal range after 1 wk, and to upper normal range after two injections (p <.001). Protein synthesis was unchanged, however, protein synthetic efficiency increased 2-fold (p <.01). Protein breakdown decreased almost 2-fold after testosterone enanthate (p <.05), resulting in an improvement in net amino acid balance to a value that was approximately zero (p <.0001). Amino acid supplementation at either time point provided no additional effects.

CONCLUSIONS

Restoration of blood testosterone can ameliorate the muscle catabolism of severe burn injury with normal feedings.

C-reactive protein and coronary heart disease in western Turkey

C-reactive protein (CRP) has been recognized as a useful marker for coronary or cardiovascular risk in healthy subjects or patients with coronary heart disease (CHD) in industrialized societies. We assessed whether CRP could serve as a marker of prevalent CHD risk in a cross-sectional study of a population with low cholesterol levels (4.61 mmol/L in men and 4.82 mmol/L in women) but higher prevalence of other risk factors. In 1,046 participants of the Turkish Adult Risk Factor Survey in 2000, high-sensitivity CRP as well as other risk variables were evaluated, and CHD was diagnosed, based on clinical findings and Minnesota coding of electrocardiograms at rest. Almost an equal number of men and women > or = 30 years of age constituted the population sample of the western regions of Turkey. Geometric mean value of CRP was 1.9 mg/L (interquartile range 0.8 to 4.3), without revealing a significant difference in gender. CRP was correlated with many variables, notably those involving central obesity, fibrinogen, and apolipoprotein-B, but not with smoking status (regardless of age adjustment). In multiple regression models, blood fibrinogen, waist circumference, total cholesterol, and physical activity grade were independently associated with log CRP concentrations. Among many risk variables, CRP quartiles and systolic blood pressure were, besides age and gender, the only significant independent determinants of CHD. The age-adjusted odds ratio for CHD in the highest as opposed to the lowest quartile was 4.48 (p < 0.001). Even after adjustment for the 5 previously mentioned determinants of CRP, a 4.2-fold increased risk of CHD still persisted between the highest and lowest quartiles. Thus, the observed increased risk was not in large part due to the intermediary effects of fibrinogen, nor were some indicators of insulin resistance, but interaction appeared to be independent of these effects. Thus, CRP values serve as a marker of prevalent CHD risk in populations with low cholesterol levels. This association is independent of, or in addition to, the effects of conventional risk factors, suggesting that the contribution of chronic low-grade inflammation to the atherothrombotic process is present even in the setting of low cholesterol levels.