Protein Oxidation Rates Research Articles

Resting Energy Expenditure and Substrate Metabolism in Chinese Patients with Acute or Chronic Hepatitis B or Liver Cirrhosis

Patients with liver disease usually have an imbalanced nutrient and energy metabolism that leads to malnutrition and seriously affects their prognosis. Therefore, it is of great clinical interest to understand the resting energy expenditure (REE) and oxidation rates of glucose, fat, and protein in these patients. A total of 315 patients with liver diseases caused by hepatitis B virus were categorized into three groups: 20 acute hepatitis patients, 142 chronic hepatitis patients and 153 liver cirrhosis patients. The REE and the oxidation rates of glucose, fat and protein were assessed by indirect heat measurement. Energy intake data were also collected which were compared with the REE results. The REE per kg (REE/kg) were 27.34 ± 5.46 kJ/kg, 21.67 ± 5.01 kJ/kg and 19.07 ± 4.45 kJ/kg in acute, chronic hepatitis and liver cirrhosis patients (p=0.000), respectively. Respiratory quotient (RQ) tended to be lower in patients with chronic hepatitis and liver cirrhosis than that in acute hepatitis patients (p=0.023). Energy, protein and carbohydrate intakes were lower in liver cirrhosis patients. These data demonstrated that Chinese patients with chronic hepatitis B and liver cirrhosis had lower energy expenditure and abnormal substrate metabolism. Patients with chronic hepatitis and cirrhosis had a higher protein oxidation rate and a lower carbohydrate oxidation rate compared with acute hepatitis patients.

Effect of dietary macronutrient composition under moderate hypocaloric intake on maternal adaptation during lactation

Background: No evidence-based recommendations exist concerning what dietary macronutrient composition optimizes weight loss during lactation while maintaining milk production.Objectives: The study was designed to test the following hypotheses: compared with a reduced-calorie, high-carbohydrate (H-CHO) diet, an isonitrogenous, isocaloric high-fat (H-F) diet will decrease milk production and carbohydrate oxidation, increase gluconeogenesis and hexoneogenesis, and not affect energy balance.Design: Seven healthy lactating mothers and their infants were studied on 2 occasions in random order for 8 d separated by 1–2 wk. On one occasion, the subjects received the H-F (30% of energy as carbohydrate and 55% as fat) diet and on the other occasion received the H-CHO (60% of energy as carbohydrate and 25% as fat) diet. Milk production, infant intakes, and substrate and hormone concentrations were measured. Glucose rates of appearance, production, gluconeogenesis, glycogenolysis, and hexoneogenesis were measured by using stable-isotope gas chromatography–mass spectrometric techniques, and energy expenditure and substrate oxidation were measured by using indirect calorimetry.Results: Milk volume, lactose, and protein concentrations were unaffected. Milk fat, energy, and infant intakes were higher (P < 0.05) during the H-F diet. Neither gluconeogenesis nor hexoneogenesis was different. During the H-F diet, energy expenditure and fat and protein oxidation rates were higher (P < 0.05), and the daily energy balance deficit was greater (P < 0.01).Conclusions: Milk fat, energy output, and energy expenditure were higher during the H-F diet, which resulted in a greater negative energy balance. The lactating mothers adapted to a low carbohydrate intake by decreasing carbohydrate oxidation. Additional studies are warranted to determine whether a hypocaloric H-F diet might promote weight loss to a greater extent than the H-CHO diet while maintaining milk production.

Manganese import is a key element of the OxyR response to hydrogen peroxide in Escherichia coli

Very little manganese is imported into Escherichia coli under routine growth conditions: the import system is weakly expressed, the manganese content is low, and a manganese-dependent enzyme is not correctly metallated. Mutants that lack MntH, the importer, grow at wild-type rates, indicating that manganese plays no critical role. However, MntH supports the growth of iron-deficient cells, suggesting that manganese can substitute for iron in activating at least some metalloenzymes. MntH is also strongly induced when cells are stressed by hydrogen peroxide. This adaptation is essential, as E. coli cannot tolerate peroxide stress if mntH is deleted. Other workers have observed that manganese improves the ability of a variety of microbes to tolerate oxidative stress, and the prevailing hypothesis is that manganese does so by chemically scavenging hydrogen peroxide and/or superoxide. We found that manganese does not protect peroxide-stressed cells by scavenging peroxide. Instead, the beneficial effects of manganese correlate with its ability to metallate mononuclear enzymes. Because iron-loaded enzymes are vulnerable to the Fenton reaction, the substitution of manganese may prevent protein damage. Accordingly, during H2O2 stress, mutants that cannot import manganese and/or are unable to sequester iron suffer high rates of protein oxidation.

Protein coingestion stimulates muscle protein synthesis during resistance-type exercise

In contrast to the effect of nutritional intervention on postexercise muscle protein synthesis, little is known about the potential to modulate protein synthesis during exercise. This study investigates the effect of protein coingestion with carbohydrate on muscle protein synthesis during resistance-type exercise. Ten healthy males were studied in the evening after they consumed a standardized diet throughout the day. Subjects participated in two experiments in which they ingested either carbohydrate or carbohydrate with protein during a 2-h resistance exercise session. Subjects received a bolus of test drink before and every 15 min during exercise, providing 0.15 g x kg(-1) x h(-1) carbohydrate with (CHO + PRO) or without (CHO) 0.15 g x kg(-1) x h(-1) protein hydrolysate. Continuous intravenous infusions with l-[ring-(13)C(6)]phenylalanine and l-[ring-(2)H(2)]tyrosine were applied, and blood and muscle biopsies were collected to assess whole body and muscle protein synthesis rates during exercise. Protein coingestion lowered whole body protein breakdown rates by 8.4 +/- 3.6% (P = 0.066), compared with the ingestion of carbohydrate only, and augmented protein oxidation and synthesis rates by 77 +/- 17 and 33 +/- 3%, respectively (P < 0.01). As a consequence, whole body net protein balance was negative in CHO, whereas a positive net balance was achieved after the CHO + PRO treatment (-4.4 +/- 0.3 vs. 16.3 +/- 0.4 micromol phenylalanine x kg(-1) x h(-1), respectively; P < 0.01). In accordance, mixed muscle protein fractional synthetic rate was 49 +/- 22% higher after protein coingestion (0.088 +/- 0.012 and 0.060 +/- 0.004%/h in CHO + PRO vs. CHO treatment, respectively; P < 0.05). We conclude that, even in a fed state, protein coingestion stimulates whole body and muscle protein synthesis rates during resistance-type exercise.

Effect of dietary protein level on whole body protein turnover in the adult cat (Felis catus)

The domestic cat is an obligate carnivore and as such has a high protein requirement. However, little is known about how protein turnover is affected by dietary protein intake in the cat. In the current study, kinetics of [1‐13C]Leu metabolism were used to quantify rates of whole body protein synthesis, degradation, and oxidation in adult cats (n = 6) fed diets containing 15, 40, or 65% of the ME intake as CP. Cats were fed the test diets to maintain BW for a minimum of 3 wk before the day of [1‐13C]Leu infusion. They were fed hourly on day of infusion. Values for Leu flux, non‐oxidative Leu disposal (NOLD, an indication of protein synthesis), Leu rate of appearance into the plasma (Ra, an indication of protein degradation), and Leu oxidation on different diets were as follows:As indicated by rate of whole body Leu flux, cats fed a diet that supplied 65% of ME intake as CP had elevated rates of whole body protein turnover via chiefly increased rates of amino acid oxidation. This study showed that during a period of marginal protein intake, cats modulated protein turnover to conserve body protein. Research supported by the Massey University Research Fund.

Dynamic coordination of macronutrient balance during infant growth: Insights from a mathematical model

We developed a mathematical model that quantitatively integrates longitudinal data on body composition changes and CO2 production rates from the doubly‐labeled water method to calculate both the energy intake requirements and, for the first time, the macronutrient oxidation rates during normal infant growth. The figure shows that the calculated net fat oxidation rate was initially less than 20 kcal/kg/day despite consuming more than 60 kcal/kg/day of dietary fat. Fat oxidation increased over the first several months but slowly decreased from 6 months onward, while carbohydrate and protein oxidation rates dropped immediately after birth before continuously increasing from 3 months onward. The calculated energy intake requirements were slightly lower than previous estimates and were robust to realistic variations in body weight, body composition, and diet composition, but depended sensitively on variations in CO2 production data. The model presents a dynamic picture of how macronutrient oxidation adapts in concert with changes of diet and energy expenditure to give rise to normal tissue deposition and growth.

Resting energy expenditure and glucose, protein and fat oxidation in severe chronic virus hepatitis B patients

To study and determine the resting energy expenditure (REE) and oxidation rates of glucose, fat and protein in severe chronic hepatitis B patients. A total of 100 patients with liver diseases were categorized into three groups: 16 in the acute hepatitis group, 56 in the severe chronic hepatitis group, and 28 in the cirrhosis group. The REE and the oxidation rates of glucose, fat and protein were assessed by indirect heat measurement using the CCM-D nutritive metabolic investigation system. The REE of the severe chronic hepatitis group (20.7 +/- 6.1 kcal/d per kg) was significantly lower than that of the acute hepatitis group (P = 0.014). The respiratory quotient (RQ) of the severe chronic hepatitis group (0.84 +/- 0.06) was significantly lower than that of the acute hepatitis and cirrhosis groups (P = 0.001). The glucose oxidation rate of the severe hepatitis group (39.2%) was significantly lower than that of the acute hepatitis group and the cirrhosis group (P < 0.05), while the fat oxidation rate (39.8%) in the severe hepatitis group was markedly higher than that of the other two groups (P < 0.05). With improvement of liver function, the glucose oxidation rate increased from 41.7% to 60.1%, while the fat oxidation rate decreased from 26.3% to 7.6%. The glucose oxidation rate is significantly decreased, and a high proportion of energy is provided by fat in severe chronic hepatitis. These results warrant a large clinical trail to assess the optimal nutritive support therapy for patients with severe liver disease.

Metabolic Effects of Oral Versus Transdermal Estrogen in Growth Hormone-Treated Girls with Turner Syndrome

Transdermal (TD) estrogen is often preferred over the oral route in postmenopausal and GH-deficient women taking estrogen, but this has not been studied in detail in girls. Our objective was to study the metabolic effects of oral vs. TD estrogen in GH-treated girls with Turner syndrome. Eleven girls with Turner syndrome, mean age 13.4 +/- 0.5 (se) yr, on GH for at least 6 months were recruited. Studies included [(13)C]leucine and d5-glycerol infusions, indirect calorimetry, dual-emission x-ray absorptiometry, and hormone and substrate measurements. They received, in random order, 17beta-estradiol orally (0.5, 1, and 2 mg for 2 wk each) and TD (0.025, 0.0375, and 0.05 mg for 2 wk each), and studies were repeated after each 6-wk course with 4 wk washout in between. Rates of whole-body protein turnover, oxidation and synthesis, lipolysis, lipid and carbohydrate oxidation, and resting energy expenditure were unaffected by either form of estrogen; nor were lipids, insulin, and fibrinogen concentrations affected. Plasma IGF-I concentrations did not change clinically significantly with either form of estrogen, despite higher estrogen concentrations after oral estrogen. Estradiol concentrations did not correlate with any variables measured. In GH-treated girls with Turner syndrome, neither oral nor TD estrogen adversely affected rates of protein turnover, lipolysis, and lipid oxidation rates or plasma lipids, fibrinogen, or fasting insulin concentrations. There was no clinically significant change in IGF-I concentrations after either form of estrogen. In aggregate, these data suggest that the route of delivery of estrogen does not adversely affect these metabolic effects of GH in young girls with Turner syndrome.

Coingestion of carbohydrate with protein does not further augment postexercise muscle protein synthesis

The present study was designed to assess the impact of coingestion of various amounts of carbohydrate combined with an ample amount of protein intake on postexercise muscle protein synthesis rates. Ten healthy, fit men (20 +/- 0.3 yr) were randomly assigned to three crossover experiments. After 60 min of resistance exercise, subjects consumed 0.3 g x kg(-1) x h(-1) protein hydrolysate with 0, 0.15, or 0.6 g x kg(-1) x h(-1) carbohydrate during a 6-h recovery period (PRO, PRO + LCHO, and PRO + HCHO, respectively). Primed, continuous infusions with L-[ring-(13)C(6)]phenylalanine, L-[ring-(2)H(2)]tyrosine, and [6,6-(2)H(2)]glucose were applied, and blood and muscle samples were collected to assess whole body protein turnover and glucose kinetics as well as protein fractional synthesis rate (FSR) in the vastus lateralis muscle over 6 h of postexercise recovery. Plasma insulin responses were significantly greater in PRO + HCHO compared with PRO + LCHO and PRO (18.4 +/- 2.9 vs. 3.7 +/- 0.5 and 1.5 +/- 0.2 U.6 h(-1) x l(-1), respectively, P < 0.001). Plasma glucose rate of appearance (R(a)) and disappearance (R(d)) increased over time in PRO + HCHO and PRO + LCHO, but not in PRO. Plasma glucose R(a) and R(d) were substantially greater in PRO + HCHO vs. both PRO and PRO + LCHO (P < 0.01). Whole body protein breakdown, synthesis, and oxidation rates, as well as whole body protein balance, did not differ between experiments. Mixed muscle protein FSR did not differ between treatments and averaged 0.10 +/- 0.01, 0.10 +/- 0.01, and 0.11 +/- 0.01%/h in the PRO, PRO + LCHO, and PRO + HCHO experiments, respectively. In conclusion, coingestion of carbohydrate during recovery does not further stimulate postexercise muscle protein synthesis when ample protein is ingested.

Co-ingestion Of Carbohydrate With Protein Does Not Stimulate Post-exercise Muscle Protein Synthesis Rates

Endurance athletes maximize post-exercise muscle glycogen synthesis by ingesting ample amounts of carbohydrate following exercise. In contrast, resistance athletes generally focus on protein intake during recovery to augment muscle protein anabolism. It has been suggested that both carbohydrate and protein should be ingested to maximize muscle protein synthesis rates. As many recreational athletes perform resistance type exercise for health and/or esthetic purposes, they generally prefer to restrict their caloric intake during recovery. Therefore, it is of importance to assess the need for co-ingestion of carbohydrate with protein on post-exercise muscle protein synthesis. PURPOSE: To determine the impact of the co-ingestion of different amounts of carbohydrate with protein on post-exercise muscle protein synthesis. METHODS: Ten healthy, untrained men were randomly assigned to 3 randomized cross-over trials. After 60 min of resistance exercise, subjects consumed 0.3 g·kg-1·h-1 protein hydrolysate with 0, 0.15 or 0.6 g·kg-1·h-1 carbohydrate during a 6 h recovery period (PRO, PRO+LCHO, and PRO+HCHO, respectively). Primed, continuous infusions of L-[ring-13C6]phenylalanine, L-[ring-2H2]tyrosine, and [6,6-2H2]glucose were applied, and blood and muscle samples were collected to assess whole-body protein turnover, glucose kinetics and fractional synthetic rate (FSR) in the vastus lateralis muscle over 6 h of recovery. RESULTS: Plasma insulin response was significantly higher in HCHO+PRO compared to LCHO+PRO and PRO (18.4±2.9 vs. 3.7±0.5 and 1.5±0.2 U·6h·L-1, respectively, P<0.001). Plasma glucose rate of appearance (Ra) and disappearance (Rd) increased over time in HCHO+PRO and LCHO+PRO but not in PRO. Plasma glucose Ra and Rd were substantially greater in HCHO+PRO vs. LCHO+PRO (P<0.01). Whole-body protein breakdown, synthesis and oxidation rates, as well as whole-body protein balance did not differ between trials. In accordance mixed muscle FSR did not differ between trials and averaged 0.114±0.010, 0.104±0.009% and 0.100±0.009%·h-1 in the HCHO+PRO, LCHO+PRO and PRO trial, respectively (NS). CONCLUSIONS: Co-ingestion of carbohydrate with an ample amount of protein hydrolysate (0.3 g·kg-1·h-1) does not further augment muscle protein synthesis rate during post-exercise recovery.

Analysis of factors influencing nitrogen balance during acute starvation in obese subject with and without type 2 diabetes

Patients with type 2 diabetes (T2DM) tend to loose more lean body mass during both long-term weight reduction and short-term very-low-calorie diet. We ask what factors influence protein loss during acute starvation in T2DM. In a prospective in-hospital observational study, we compared 10 subjects with T2DM and 10 age-weight-sex matched obese controls (OB) during 60 h of fasting and used frequent blood sampling and indirect calorimetry to describe metabolic and endocrine response. We analyzed factors influencing nitrogen balance using stepwise multiple regressions. Despite comparable pattern of plasma insulin, free fatty acid, 3-hydroxybutyrate and almost identical behavior of growth hormone axis, our T2DM subjects remained hyperglycaemic and in contrast to OB subjects they failed to reduce the rate of protein oxidation, even though muscle protein breakdown rate declined similarly in both groups. Regression analysis revealed that protein oxidation rate in T2DM group was enhanced by hyperglycemia and sympathetic activity and suppressed by circulating insulin and 3-hydroxybutyrate. Liver insulin resistance increases peripheral insulin concentrations and enhances the conversion of non-esterified fatty acids (NEFA) to ketones and thus it might be a protein-saving factor. Relative deficiency of circulating insulin and hyperglycemia play a pivotal role in the impairment of protein sparing in T2DM during a short-term fasting.

A low-calorie diet improves the rate of nutrient oxidation, lowers body fat, and maintains lean mass in morbidly obese Brazilian women

To assess the effect of a low calorie diet on the resting metabolic rate (RMR), substrate oxidation, body composition, and to compare measured and calculated RMR of obese Brazilian women, we selected 19 patients aged 31 ± 9 years, with a body mass index of 51 ± 8 kg/m 2, for admission to the Metabolic Unit of the University Hospital for 8 weeks, who were then submitted to a 3.3 to 4.2 MJ/d (800-1000 kcal/d) diet. Weight, height, and circumferences were measured on the first and last days of the study. Body composition was assessed by bioelectrical impedance, and RMR and substrate oxidation rate by indirect calorimetry. A decrease in body weight (134 ± 23 kg vs 121 ± 21 kg, P < .05), waist (136 ± 17 cm vs 123 ± 17 cm, P < .05), and hip circumference (149 ± 14 cm vs 137 ± 16 cm, P < .05) occurred during the study. Mean RMR measured by indirect calorimetry (10.6 ± 1.7 MJ/d; 2540 ± 420 kcal/d) was 16% higher ( P < .05) than that calculated by Harris-Benedict and World Health Organization equations (8.7 ± 0.9 MJ/d; 2070 ± 210 kcal/d and 9.0 ± 1.4 MJ/d; 2161 ± 344 kcal/d, respectively) at the beginning, but not at the end of the study. Lipid oxidation rate was 45% of RMR at the beginning of the study, reaching 59% at the end ( P > .05). Present data suggest that equations to estimate RMR of obese females are reliable after a low-calorie diet and weight loss. Resting metabolic rate was correlated with fat-free mass and body fat. A low-calorie diet with balanced macronutrients is effective for weight loss, leading to a maintenance of lipid oxidation rate and to a reduction of carbohydrate and protein oxidation rates. The low-calorie diet reduced body fat and maintained lean mass.

Oxidative stress during stressful heat exposure and recovery in the North Sea eelpoutZoarces viviparusL.

The interplay between antioxidants, heat shock proteins and hypoxic signaling is supposed to be important for passive survival of critical temperature stress, e.g. during unfavorable conditions in hot summers. We investigated the effect of mild (18 degrees C), critical (22 degrees C) and severe (26 degrees C) experimental heat stress, assumed to induce different degrees of functional hypoxia, as well as the effect of recovery following heat stress on these parameters in liver samples of the common eelpout Zoarces viviparus. Upon heat exposure to critical and higher temperatures we found an increase in oxidative damage markers such as TBARS (thiobarbituric reactive substances) and a more oxidized cellular redox potential, combined with reduced activities of the antioxidant enzyme superoxide dismutase at 26 degrees C. Together, these point to higher oxidative stress levels during hyperthermia. In a recovery-time series, heat-induced hypoxia and subsequent reoxygenation upon return of the fishes to 12 degrees C led to increased protein oxidation and chemiluminescence rates within the first 12 h of recovery, therein resembling ischemia/reperfusion injury in mammals. HSP70 levels were found to be only slightly elevated after recovery from sub-lethal heat stress, indicating minor importance of the heat shock response in this species. The DNA binding activity of the hypoxia-inducible transcription factor (HIF-1) was elevated only during mild heat exposure (18 degrees C), but appeared impaired at more severe heat stress. We suppose that the more oxidized redox state during extreme heat may interfere with the hypoxic signaling response.

Cigarette Smoke Extract Inhibits Expression of Peroxiredoxin V and Increases Airway Epithelial Permeability

Inhaled cigarette smoke induces oxidative stress in the epithelium of airways. Peroxiredoxin V (PRXV) is a potent antioxidant protein, highly expressed in cells of the airway epithelium. The goal of our study was to determine whether cigarette smoke extract (CSE) influenced expression of this protein in airway epithelia in vivo and in vitro. In Sprague-Dawley rats, we determined effects of CSE on airway epithelial permeability, mRNA levels and expression of PRXV protein. Exposure of isolated tracheal segment in vitro to 20% CSE for 4 h resulted in development of increased permeability to albumin, significantly reduced mRNA levels for PRXV, and reduced amounts of PRXV protein in the epithelium. In cultures of the airway epithelial cell lines (Calu-3, JME), primary airway cell culture (cow), and alveolar epithelial cells A549, CSE also significantly decreased transepithelial electrical resistance and expression of PRXV protein, and induced glutathione and protein oxidation. To demonstrate functional importance of PRXV, we exposed clones of HeLa cells with siRNA-downregulated PRXV to hydrogen peroxide, which resulted in increased rate of cell death and protein oxidation. CSE directly downregulates expression of functionally important antioxidant enzyme PRXV in the epithelial cells of airways, which represents one pathophysiological mechanism of cigarette smoke toxicity.

Energetics of a long-distance migrant shorebird (Philomachus pugnax) during cold exposure and running

The metabolic consequences of cold exposure and exercise are not well characterized in birds. Ruff sandpipers Philomachus pugnax are migrant shorebirds traveling between Africa and Siberia for up to 30,000 km annually. Our goal was to quantify the fuel selection pattern of these remarkable athletes during shivering and terrestrial locomotion. We used indirect calorimetry and nitrogen excretion analysis to measure their rates of lipid, carbohydrate and protein oxidation at different temperatures (22, 15, 10 or 5 degrees C) and different treadmill speeds (15, 20, 25, 30, 35 or 40 m min(-1)). Results show that lipid oxidation supplies nearly all the energy necessary to support shivering and running, and that the pattern of oxidative fuel selection is independent of shivering or running intensity. During shivering, total ATP production is unequally shared between lipids (82%), carbohydrates (12%) and proteins (6%). During running, lipids remain the dominant substrate (66%), with carbohydrates (29%) and proteins (5%) playing more minor roles. The prevailing use of lipids during intense shivering and high-speed running is not consistent with the fuel selection pattern observed in exercising and cold-exposed mammals. The exact mechanisms allowing birds to use lipids at extremely high rates are still largely unexplored, and quantifying the relative importance of different fuels during long-distance flight remains a major challenge for future research.

Very short term dehydroepiandrosterone treatment in female adrenal failure: impact on carbohydrate, lipid and protein metabolism

In female adrenal insufficiency, dehydroepiandrosterone (DHEA) secretion is impaired and circulating androgen levels are severely reduced. We wanted to analyse the acute effects of physiological DHEA substitution on substrate metabolism. We studied nine females with adrenal insufficiency after 9 days of oral DHEA replacement (50 mg/day) in a double-blind, placebo-controlled crossover study. Whole body and regional substrate metabolism was assayed in the basal state and during a euglycemic hyperinsulinemic glucose clamp by means of isotope dilution techniques (glucose, phenylalanine, tyrosine), indirect calorimetry and in situ lipolysis (microdialysis technique). DHEA treatment normalized the levels of all androgens. Basal and insulin-stimulated total energy expenditure and rates of protein, lipid and glucose oxidation were unaffected by DHEA. Whole body turnover of glucose and protein were also unaffected by DHEA. Forearm breakdown of protein was reduced by insulin to the same extent after placebo and DHEA. Insulin sensitivity as expressed by the glucose infusion rate during the euglycemic clamp was similar after placebo and DHEA. Finally, the interstitial release of glycerol in adipose tissue was not significantly influenced by DHEA. Short-term oral DHEA replacement in women with adrenal insufficiency was not associated with measurable changes in total or regional substrate metabolism.

Flavonoid‐membrane Interactions: A Protective Role of Flavonoids at the Membrane Surface?

Flavonoids can exert beneficial health effects through multiple mechanisms. In this paper, we address the important, although not fully understood, capacity of flavonoids to interact with cell membranes. The interactions of polyphenols with bilayers include: (a) the partition of the more non-polar compounds in the hydrophobic interior of the membrane, and (b) the formation of hydrogen bonds between the polar head groups of lipids and the more hydrophilic flavonoids at the membrane interface. The consequences of these interactions are discussed. The induction of changes in membrane physical properties can affect the rates of membrane lipid and protein oxidation. The partition of certain flavonoids in the hydrophobic core can result in a chain breaking antioxidant activity. We suggest that interactions of polyphenols at the surface of bilayers through hydrogen bonding, can act to reduce the access of deleterious molecules (i.e. oxidants), thus protecting the structure and function of membranes.

Influence of plasma total antioxidant ability on lipid and protein oxidation products in plasma and erythrocyte ghost obtained from developing and adult rats pretreated with two vitamin K formulations

Ferric reducing ability of plasma (FRAP), as an index of total antioxidant capacity of plasma was found to be enhanced significantly (p < 0.05) in suckling rats pretreated either with vitamin K1 (28, 56 or 84 mg/kg/3 days) or menadione (vitamin K3) at a dose of 15 mg/kg b.w./3 days. The effect of vitamin K1 on FRAP was dose-dependent and it was inversely related to the formation of lipid peroxidation products in plasma as judged by thiobarbituric acid reacting substances (TBARS). Lack of influence of the drugs on FRAP in adults was corroborated with elevation in the levels of plasma TBARS. Possible role of FRAP on the rate of lipid peroxidation and protein oxidation (protein carbonyls) on erythrocyte membrane was also investigated following isolation of erythrocyte ghost from control and treated rats. Vitamin K1 as well as menadione failed to change the levels of protein carbonyls in erythrocyte ghost obtained from both the age groups. Analysis of major erythrocyte membrane proteins, using SDS-polyacrylamide gel electrophoresis (SDS-PAGE) substantiated these results. In spite of higher antioxidant capacity of plasma and erythrocytes obtained from young rats, the rate of lipid peroxidation in erythrocyte ghost preparation was also high in this age group (p < 0.05). These results suggest that the drug-related induction in FRAP occurs only in immature animals as a part of protective mechanism against lipid peroxidation products generated in plasma.

Combined ingestion of protein and free leucine with carbohydrate increases postexercise muscle protein synthesis in vivo in male subjects

The present study was designed to determine postexercise muscle protein synthesis and whole body protein balance following the combined ingestion of carbohydrate with or without protein and/or free leucine. Eight male subjects were randomly assigned to three trials in which they consumed drinks containing either carbohydrate (CHO), carbohydrate and protein (CHO+PRO), or carbohydrate, protein, and free leucine (CHO+PRO+Leu) following 45 min of resistance exercise. A primed, continuous infusion of L-[ring-13C6]phenylalanine was applied, with blood samples and muscle biopsies collected to assess fractional synthetic rate (FSR) in the vastus lateralis muscle as well as whole body protein turnover during 6 h of postexercise recovery. Plasma insulin response was higher in the CHO+PRO+Leu compared with the CHO and CHO+PRO trials (+240 +/- 19% and +77 +/- 11%, respectively, P < 0.05). Whole body protein breakdown rates were lower, and whole body protein synthesis rates were higher, in the CHO+PRO and CHO+PRO+Leu trials compared with the CHO trial (P < 0.05). Addition of leucine in the CHO+PRO+Leu trial resulted in a lower protein oxidation rate compared with the CHO+PRO trial. Protein balance was negative during recovery in the CHO trial but positive in the CHO+PRO and CHO+PRO+Leu trials. In the CHO+PRO+Leu trial, whole body net protein balance was significantly greater compared with values observed in the CHO+PRO and CHO trials (P < 0.05). Mixed muscle FSR, measured over a 6-h period of postexercise recovery, was significantly greater in the CHO+PRO+Leu trial compared with the CHO trial (0.095 +/- 0.006 vs. 0.061 +/- 0.008%/h, respectively, P < 0.05), with intermediate values observed in the CHO+PRO trial (0.0820 +/- 0.0104%/h). We conclude that coingestion of protein and leucine stimulates muscle protein synthesis and optimizes whole body protein balance compared with the intake of carbohydrate only.

Synergistic effects of testosterone and growth hormone on protein metabolism and body composition in prepubertal boys

During human puberty there is a substantial increase in growth hormone (GH) and sex steroidal hormone concentrations, as well as in GH production rates and insulin-like growth factor-I (IGF-I) These studies were designed to investigate some of the interactions of testosterone (T) and GH in the metabolic changes of puberty. Ten boys with severe GH deficiency (GHD) were studied (mean age, 12.5 ± 0.5 years) using stable isotope infusions, indirect calorimetry, and body composition analysis. After the baseline study, they received 2 doses of T enanthate (50 to 75 mg, intramuscular [IM]), and they were studied again 4 weeks later. The boys were then begun on daily subcutaneous (SC) GH (0.3 mg/kg/wk), while T therapy was continued for another 4 weeks and the studies repeated a third time. The treatment order was randomized. Protein oxidation rates decreased after T alone (−28%, P < .01), decreasing further after combined T/GH treatment (−36% v baseline, P < .01). The nonoxidative leucine disposal (NOLD), a measure of whole body protein synthesis, increased significantly after combined T/GH regardless of treatment order. The combination of T/GH also resulted in greater changes in body composition than T alone, with comparable decreases in %FM and corresponding increases in fat free mass (FFM). Measures of carbohydrate (CHO) metabolism, including glucose production and oxidation rates, were unaffected by either T or T/GH combination. Plasma IGF-I concentrations increased after T treatment and even more after T/GH combination, regardless of the treatment order. In conclusion GH and T are synergistic on whole body protein anabolism and body composition in males, even at a young age, but the positive effects of T on protein anabolism and body composition appear to need a basal amount of GH for those effects to be observed. GH and T both potentiate the development of the full body composition and metabolic changes of puberty.