Albumin and fibrinogen syntheses increase while muscle protein synthesis decreases in head-injured patients

Albumin and fibrinogen kinetics in sepsis: a prospective observational study

Background

The measurement of circulating substrate concentrations does not provide information about substrate kinetics. It, therefore, remains unclear if a decrease in plasma concentration of albumin, as seen during critical illness, is a consequence of suppressed production in the liver or increased peripheral clearance. In this study, using stable isotope tracer infusions, we measured albumin and fibrinogen kinetics in septic patients and in a control group of non-septic subjects.

Methods

With the approval from the institutional Research Ethics Board and after obtaining written informed consent from patients or their substitute decision maker, mechanically ventilated patients with sepsis and patients scheduled for elective coronary artery bypass grafting were enrolled. Patients in the non-sepsis group were studied on the day before surgery. The stable isotope L-[ring-²H₅]phenylalanine was used to measure absolute synthesis rates (ASR) of albumin and fibrinogen. A priming dose of L-[ring-²H₅]phenylalanine (4 µmol/kg) was given followed by a six-hour infusion at a rate of 0.15 µmol/kg/min. At baseline and hourly thereafter, blood was drawn to measure isotope enrichments by gas chromatography/mass spectrometry. Very low density lipoprotein apolipoprotein-B 100 isotopic enrichment was used to represent the isotopic enrichment of the phenylalanine precursor pool from which the liver synthesizes proteins. Plasma albumin and fibrinogen concentrations were also measured.

Results

Mean plasma albumin in septic patients was decreased when compared to non-septic patients, while synthesis rates were comparable. Mean plasma fibrinogen and ASR in septic patients was increased when compared to non-septic patients. In non-septic patients, no statistically significant correlation between plasma albumin and ASR was observed but plasma fibrinogen significantly correlated with ASR. In septic patients, plasma albumin and fibrinogen significantly correlated with ASR.

Conclusions

While septic patients showed lower plasma albumin levels than non-septic patients, albumin synthesis was similar in the two groups suggesting that hypoalbuminemia during sepsis was not caused by suppressed hepatic production but a result of enhanced clearance from the circulation. Hyperfibrinogenemia in septic patients was a consequence of increased fibrinogen production.

Trial registration: ClinicalTrials.gov: NCT02865408 (registered on August 12, 2016) and ClinicalTrials.gov: NCT02549443 (registered on September 15, 2015).

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-021-03860-7.

Blood-Related Toxicity after Traumatic Brain Injury: Potential Targets for Neuroprotection

Emergency visits, hospitalizations, and deaths due to traumatic brain injury (TBI) have increased significantly over the past few decades. While the primary early brain trauma is highly deleterious to the brain, the secondary injury post-TBI is postulated to significantly impact mortality. The presence of blood, particularly hemoglobin, and its breakdown products and key binding proteins and receptors modulating their clearance may contribute significantly to toxicity. Heme, hemin, and iron, for example, cause membrane lipid peroxidation, generate reactive oxygen species, and sensitize cells to noxious stimuli resulting in edema, cell death, and increased morbidity and mortality. A wide range of other mechanisms such as the immune system play pivotal roles in mediating secondary injury. Effective scavenging of all of these pro-oxidant and pro-inflammatory metabolites as well as controlling maladaptive immune responses is essential for limiting toxicity and secondary injury. Hemoglobin metabolism is mediated by key molecules such as haptoglobin, heme oxygenase, hemopexin, and ferritin. Genetic variability and dysfunction affecting these pathways (e.g., haptoglobin and heme oxygenase expression) have been implicated in the difference in susceptibility of individual patients to toxicity and may be target pathways for potential therapeutic interventions in TBI. Ongoing collaborative efforts are required to decipher the complexities of blood-related toxicity in TBI with an overarching goal of providing effective treatment options to all patients with TBI.

In vivo hepatotoxicity of chemically modified nanocellulose in rats

Chemical modification of cellulose is currently attracting attention as researchers attempt to take advantage of the abundance of hydroxyl groups on its surface to introduce extra biological functionality. However, the possible deleterious effect of exposure to functionalized nanocellulose (CSN) remains a concern. Therefore, this study aims to explore the potential mechanisms of hepatotoxicity of CSN modified with oxalate ester (NCD) in rats. A 7-day repeated oral toxicity study of NCD at the doses of 50 and 100 mg kg−1body weight was conducted, and plasma and liver tissue samples were assayed using biochemical analysis, liver histopathology, and protein expression. NCD, at both doses, did not significantly ( p > 0.05) alter the relative weight of liver, alkaline phosphatase activity, and lipid peroxidation levels of the animals. However, NCD at the dose of 100 mg kg−1body weight significantly elevated aspartate aminotransferase, alanine aminotransferase, and myeloperoxidase activities. NCD also enhanced the immunohistochemical expression of inducible nitric oxide synthase and Bcl-2-associated X protein in the liver of rats. Histological observations revealed necrosis and severe cellular infiltration at the high-dose treatment. Our study provides an experimental basis for the safe application of NCDs.

Hypoalbuminemia: Pathogenesis and Clinical Significance

Hypoalbuminemia is associated with inflammation. Despite being addressed repeatedly in the literature, there is still confusion regarding its pathogenesis and clinical significance. Inflammation increases capillary permeability and escape of serum albumin, leading to expansion of interstitial space and increasing the distribution volume of albumin. The half‐life of albumin has been shown to shorten, decreasing total albumin mass. These 2 factors lead to hypoalbuminemia despite increased fractional synthesis rates in plasma. Hypoalbuminemia, therefore, results from and reflects the inflammatory state, which interferes with adequate responses to events like surgery or chemotherapy, and is associated with poor quality of life and reduced longevity. Increasing or decreasing serum albumin levels are adequate indicators, respectively, of improvement or deterioration of the clinical state. In the interstitium, albumin acts as the main extracellular scavenger, antioxidative agent, and as supplier of amino acids for cell and matrix synthesis. Albumin infusion has not been shown to diminish fluid requirements, infection rates, and mortality in the intensive care unit, which may imply that there is no body deficit or that the quality of albumin “from the shelf” is unsuitable to play scavenging and antioxidative roles. Management of hypoalbuminaemia should be based on correcting the causes of ongoing inflammation rather than infusion of albumin. After the age of 30 years, muscle mass and function slowly decrease, but this loss is accelerated by comorbidity and associated with decreasing serum albumin levels. Nutrition support cannot fully prevent, but slows down, this chain of events, especially when combined with physical exercise.

Previous physical exercise alters the hepatic profile of oxidative-inflammatory status and limits the secondary brain damage induced by severe traumatic brain injury in rats

KEY POINTS

An early inflammatory response and oxidative stress are implicated in the signal transduction that alters both hepatic redox status and mitochondrial function after traumatic brain injury (TBI). Peripheral oxidative/inflammatory responses contribute to neuronal dysfunction after TBI Exercise training alters the profile of oxidative-inflammatory status in liver and protects against acute hyperglycaemia and a cerebral inflammatory response after TBI. Approaches such as exercise training, which attenuates neuronal damage after TBI, may have therapeutic potential through modulation of responses by metabolic organs. The vulnerability of the body to oxidative/inflammatory in TBI is significantly enhanced in sedentary compared to physically active counterparts.

ABSTRACT

Although systemic responses have been described after traumatic brain injury (TBI), little is known regarding potential interactions between brain and peripheral organs after neuronal injury. Accordingly, we aimed to investigate whether a peripheral oxidative/inflammatory response contributes to neuronal dysfunction after TBI, as well as the prophylactic role of exercise training. Animals were submitted to fluid percussion injury after 6 weeks of swimming training. Previous exercise training increased mRNA expression of X receptor alpha and ATP-binding cassette transporter, and decreased inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), tumor necrosis factor (TNF)-α and interleukin (IL)-6 expression per se in liver. Interestingly, exercise training protected against hepatic inflammation (COX-2, iNOS, TNF-α and IL-6), oxidative stress (decreases in non-protein sulfhydryl and glutathione, as well as increases in 2',7'-dichlorofluorescein diacetate oxidation and protein carbonyl), which altered hepatic redox status (increases in myeloperoxidase and superoxide dismutase activity, as well as inhibition of catalase activity) mitochondrial function (decreases in methyl-tetrazolium and Δψ, as well as inhibition of citrate synthase activity) and ion gradient homeostasis (inhibition of Na⁺ ,K⁺ -ATPase activity inhibition) when analysed 24 h after TBI. Previous exercise training also protected against dysglycaemia, impaired hepatic signalling (increase in phosphorylated c-Jun NH2-terminal kinase, phosphorylated decreases in insulin receptor substrate and phosphorylated AKT expression), high levels of circulating and neuronal cytokines, the opening of the blood-brain barrier, neutrophil infiltration and Na⁺ ,K⁺ -ATPase activity inhibition in the ipsilateral cortex after TBI. Moreover, the impairment of protein function, neurobehavioural (neuromotor dysfunction and spatial learning) disability and hippocampal cell damage in sedentary rats suggests that exercise training also modulates peripheral oxidative/inflammatory pathways in TBI, which corroborates the ever increasing evidence regarding health-related outcomes with respect to a physically active lifestyle.

Human serum albumin homeostasis: a new look at the roles of synthesis, catabolism, renal and gastrointestinal excretion, and the clinical value of serum albumin measurements

Serum albumin concentration (CP) is a remarkably strong prognostic indicator of morbidity and mortality in both sick and seemingly healthy subjects. Surprisingly, the specifics of the pathophysiology underlying the relationship between CP and ill-health are poorly understood. This review provides a summary that is not previously available in the literature, concerning how synthesis, catabolism, and renal and gastrointestinal clearance of albumin interact to bring about albumin homeostasis, with a focus on the clinical factors that influence this homeostasis. In normal humans, the albumin turnover time of about 25 days reflects a liver albumin synthesis rate of about 10.5 g/day balanced by renal (≈6%), gastrointestinal (≈10%), and catabolic (≈84%) clearances. The acute development of hypoalbuminemia with sepsis or trauma results from increased albumin capillary permeability leading to redistribution of albumin from the vascular to interstitial space. The best understood mechanism of chronic hypoalbuminemia is the decreased albumin synthesis observed in liver disease. Decreased albumin production also accounts for hypoalbuminemia observed with a low-protein and normal caloric diet. However, a calorie- and protein-deficient diet does not reduce albumin synthesis and is not associated with hypoalbuminemia, and CP is not a useful marker of malnutrition. In most disease states other than liver disease, albumin synthesis is normal or increased, and hypoalbuminemia reflects an enhanced rate of albumin turnover resulting either from an increased rate of catabolism (a poorly understood phenomenon) or enhanced loss of albumin into the urine (nephrosis) or intestine (protein-losing enteropathy). The latter may occur with subtle intestinal pathology and hence may be more prevalent than commonly appreciated. Clinically, reduced CP appears to be a result rather than a cause of ill-health, and therapy designed to increase CP has limited benefit. The ubiquitous occurrence of hypoalbuminemia in disease states limits the diagnostic utility of the CP measurement.

Ablation of matrix metalloproteinase-9 gene decreases cerebrovascular permeability and fibrinogen deposition post traumatic brain injury in mice

Traumatic brain injury (TBI) is accompanied with enhanced matrix metalloproteinase-9 (MMP-9) activity and elevated levels of plasma fibrinogen (Fg), which is a known inflammatory agent. Activation of MMP-9 and increase in blood content of Fg (i.e. hyperfibrinogenemia, HFg) both contribute to cerebrovascular disorders leading to blood brain barrier disruption. It is well-known that activation of MMP-9 contributes to vascular permeability. It has been shown that at an elevated level (i.e. HFg) Fg disrupts blood brain barrier. However, mechanisms of their actions during TBI are not known. Mild TBI was induced in wild type (WT, C57BL/6 J) and MMP-9 gene knockout (Mmp9(-/-)) homozygous, mice. Pial venular permeability to fluorescein isothiocyanate-conjugated bovine serum albumin in pericontusional area was observed 14 days after injury. Mice memory was tested with a novel object recognition test. Increased expression of Fg endothelial receptor intercellular adhesion protein-1 and formation of caveolae were associated with enhanced activity of MMP-9 causing an increase in pial venular permeability. As a result, an enhanced deposition of Fg and cellular prion protein (PrP(C)) were found in pericontusional area. These changes were attenuated in Mmp9(-/-) mice and were associated with lesser loss of short-term memory in these mice than in WT mice. Our data suggest that mild TBI-induced increased cerebrovascular permeability enhances deposition of Fg-PrP(C) and loss of memory, which is ameliorated in the absence of MMP-9 activity. Thus, targeting MMP-9 activity and blood level of Fg can be a possible therapeutic remedy to diminish vasculo-neuronal damage after TBI.

Albumin and fibrinogen levels' relation with orthopedics traumatic patients' outcome after massive transfusion

Background:

Severe bleeding is common during limb trauma. It can lead to hemorrhagic shock required to massive blood transfusion. Coagulopathy is the major complication of massive transfusion-induced increased mortality rate. Aim of this study was evaluation of fibrinogen and albumin levels association with orthopedics traumatic patients’ outcome who received massive transfusion.

Methods:

In a cross sectional study, 23 patients with severe limb injury admitted to orthopedic emergency department were studied. All the patients received massive transfusion, that is, >10 unit blood. Albumin and fibrinogen levels are measured at admission and 24 h later, and compared according to final outcome.

Results:

Twenty-three traumatic patients with severe limb injuries were studied, out of which ten (43.2%) died and 13 (56.8%) were alive. There was significant difference between patients outcome in fibrinogen level after 24 h, but no difference was observed in albumin levels. Based on regression model, fibrinogen after 24 h had a significant role in determining the final outcome in traumatic patients who received massive transfusion (odds ratio 0.48, 95% confidence interval 0.15–0.92, P = 0.02).

Conclusions:

According to our results, fibrinogen level is the most important factor in determination of orthopedics traumatic patients when received massive transfusion. However, serum albumin does not play any role in patients’ outcome.

Dynamics of albumin synthetic response to intra-abdominal abscess in patients with gastrointestinal fistula

BACKGROUND

Low serum albumin concentration is a predictor of failure of source control for intra-abdominal infection. However, data on dynamics of albumin synthesis in these patients and to what extent these changes contribute to hypoalbuminemia are relatively scarce. We investigated in a group of patients with gastrointestinal fistula the dynamic response of liver albumin synthesis to intra-abdominal abscess and how these related to hypoalbuminemia and circulating endocrine hormone profiles.

METHODS

Eight gastrointestinal fistula patients scheduled to undergo percutaneous abscess sump drainage were enrolled prospectively to measure albumin synthesis rates at different stages of the inflammatory response (immediately after diagnosis and 7 d following sump drainage when clinical signs of intra-abdominal sepsis had been eradicated). Eight age-, sex-, and body mass index-matched intestinal fistula patients were studied as control patients. Consecutive arterial blood samples were drawn during a primed-constant infusion (priming dose: 4 micromol·kg(-1), infusion rate: 6 micromol·kg(-1)·min(-1)) to determine the incorporation rate of L-[ring-(2)H5]-phenylalanine directly into plasma albumin using gas chromatography/mass spectrometry analysis.

RESULTS

Patients suffering from intra-abdominal infection had reduced plasma albumin and total plasma protein concentrations, compared with control patients. Albumin fractional synthesis rates in patients with intra-abdominal abscess were decreased, compared with those in the control group. When the source of infection was removed, albumin synthesis rates returned to control values, whereas albumin concentrations did not differ significantly from the corresponding concentrations in control subjects and patients with intra-abdominal abscess.

CONCLUSION

Despite nutritional intervention, albumin synthesis rate is decreased in intestinal fistula patients with intra-abdominal abscess; albumin synthesis returns to control values during convalescence.

Inflammatory markers in blood and exhaled air after short-term exposure to cooking fumes

Objectives:

Cooking fumes contain aldehydes, alkanoic acids, polycyclic aromatic hydrocarbons, and heterocyclic compounds. The inhalation of cooking fumes entails a risk of deleterious health effects. The aim of this study was to see if the inhalation of cooking fumes alters the expression of inflammatory reactions in the bronchial mucosa and its subsequent systemic inflammatory response in blood biomarkers.

Methods:

Twenty-four healthy volunteers stayed in a model kitchen on two different occasions for 2 or 4h. On the first occasion, there was only exposure to normal air, and on the second, there was exposure to controlled levels of cooking fumes. On each occasion, samples of blood, exhaled air, and exhaled breath condensate (EBC) were taken three times in 24h and inflammatory markers were measured from all samples.

Results:

There was an increase in the concentration of the d-dimer in blood from 0.27 to 0.28mg ml^–1 on the morning after exposure to cooking fumes compared with the levels the morning before (P-value = 0.004). There was also a trend of an increase in interleukin (IL)-6 in blood, ethane in exhaled air, and IL-1β in EBC after exposure to cooking fumes. In a sub-analysis of 12 subjects, there was also an increase in the levels of ethane—from 2.83 parts per billion (ppb) on the morning before exposure to cooking fumes to 3.53 ppb on the morning after exposure (P = 0.013)—and IL-1β—from 1.04 on the morning before exposure to cooking fumes to 1.39 pg ml^–1 immediately after (P = 0.024).

Conclusion:

In our experimental setting, we were able to unveil only small changes in the levels of inflammatory markers in exhaled air and in blood after short-term exposure to moderate concentrations of cooking fumes.

Portal glucose delivery stimulates muscle but not liver protein metabolism

Portal vein glucose delivery (the portal glucose signal) stimulates glucose uptake and glycogen storage by the liver, whereas portal amino acid (AA) delivery (the portal AA signal) induces an increase in protein synthesis by the liver. During a meal, both signals coexist and may interact. In this study, we compared the protein synthesis rates in the liver and muscle in response to portal or peripheral glucose infusion during intraportal infusion of a complete AA mixture. Dogs were surgically prepared with hepatic sampling catheters and flow probes. After a 42-h fast, they underwent a 3-h hyperinsulinemic (4× basal) hyperglucagonemic (3× basal) hyperglycemic (≈160 mg/dl) hyperaminoacidemic (hepatic load 1.5× basal; delivered intraportally) clamp (postprandial conditions). Glucose was infused either via a peripheral (PeG; n = 7) or the portal vein (PoG; n = 8). Protein synthesis was assessed with a primed, continuous [(14)C]leucine infusion. Net hepatic glucose uptake was stimulated by portal glucose infusion (+1 mg·kg(-1)·min(-1), P < 0.05) as expected, but hepatic fractional AA extraction and hepatic protein synthesis did not differ between groups. There was a lower arterial AA concentration in the PoG group (-19%, P < 0.05) and a significant stimulation (+30%) of muscle protein synthesis associated with increased expression of LAT1 and ASCT2 AA transporters and p70S6 phosphorylation. Concomitant portal glucose and AA delivery enhances skeletal muscle protein synthesis compared with peripheral glucose and portal AA delivery. These data suggest that enteral nutrition support may have an advantage over parenteral nutrition in stimulating muscle protein synthesis.

Skeletal muscle is anabolically unresponsive to an amino acid infusion in pediatric burn patients 6 months postinjury

OBJECTIVE

To evaluate leg muscle, whole-body muscle, and whole-body nonmuscle protein response to anabolic signaling of amino acids in pediatric burn patients at 6 months after injury.

BACKGROUND

Burn injury is associated with a catabolic state persisting years after the injury. The tissue response to nutritional signaling (eg, amino acids) plays a critical role in tissue protein net balance via coordination of protein synthesis and breakdown mechanisms.

METHODS

A total of 10 patients (7.4 ± 3.8 years; 27.4 ± 14.7 kg) and 5 healthy young males (22 ± 3 years; 76 ± 15 kg) underwent an 8-hour stable isotope infusion study. During the last 3 hours, an amino acid solution (10% Travasol, Clintec Nutrition, Deerfield, IL) was infused. Femoral arterial and venous blood samples and muscle biopsy samples were collected throughout the study. A P value of less than 0.05 was considered statistically different.

RESULTS

During amino acid infusion, leg muscle protein synthesis rate significantly increased (P < 0.05) in both groups, however, in the burn group, protein breakdown also increased, although nonsignificantly. As a result, protein net balance remained negative. In the control group, breakdown nonsignificantly decreased resulting in a significant increase (P < 0.05) in muscle protein net balance. Whole-body protein breakdown was significantly higher in the burn patients.

CONCLUSION

In pediatric burn patients at 6 months postinjury, leg muscle protein net deposition is unresponsive to amino acid infusion; and whole-body protein breakdown is significantly higher than in the control group.

Co-culture of primary rat hepatocytes with rat liver epithelial cells enhances interleukin-6-induced acute-phase protein response

Three different primary rat hepatocyte culture methods were compared for their ability to allow the secretion of fibrinogen and albumin under basal and IL-6-stimulated conditions. These culture methods comprised the co-culture of hepatocytes with rat liver epithelial cells (CC-RLEC), a collagen type I sandwich culture (SW) and a conventional primary hepatocyte monolayer culture (ML). Basal albumin secretion was most stable over time in SW. Fibrinogen secretion was induced by IL-6 in all cell culture models. Compared with ML, CC-RLEC showed an almost three-fold higher fibrinogen secretion under both control and IL-6-stimulated conditions. Induction of fibrinogen release by IL-6 was lowest in SW. Albumin secretion was decreased after IL-6 stimulation in both ML and CC-RLEC. Thus, cells growing under the various primary hepatocyte cell culture techniques react differently to IL-6 stimulation with regard to acute-phase protein secretion. CC-RLEC is the preferred method for studying cytokine-mediated induction of acute-phase proteins, because of the pronounced stimulation of fibrinogen secretion upon IL-6 exposure under these conditions.

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.

Effect of an enteral diet supplemented with a specific blend of amino acid on plasma and muscle protein synthesis in ICU patients

BACKGROUND & AIM

Polytrauma patients are characterized by a negative nitrogen balance and muscle wasting. Standard nutrition is relatively inefficient to improve muscle protein turnover. The aim of this study was to investigate the effect of enteral nutrition (EN) supplemented with specific amino acids on protein metabolism in polytrauma patients.

METHODS

In a double blind study, 12 polytrauma patients were randomized to receive EN supplemented with either a mixture of cysteine, threonine, serine and aspartate (AA patients) or alanine at isonitrogenous levels (Ala patients). An intravenous infusion of l-[1-(13)C]-leucine was performed in the fed state between day 9 and 12 post-injury (Df) in patients and in a group of healthy volunteers (n=8) (EN+Ala) to measure whole body leucine kinetics, plasma and muscle protein synthesis rates. Nitrogen balance, 3-methyl histidine excretion were measured from day 3 to Df.

RESULTS

The contribution of total plasma proteins to whole body protein synthesis was greatly increased, from 11% in healthy volunteers to about 25% in polytrauma patients. AA supplementation had no effect on nitrogen balance, leucine kinetics or plasma protein synthesis in patients. In contrast, the urinary excretion of 3-methyl histidine tended to decrease along the study in the AA supplemented group compared to an increase in the Ala group. Muscle protein synthesis tended to be higher in the AA group than in the Ala group (46%, P=0.065).

CONCLUSION

During injury, an increased supply of cysteine, threonine, serine and aspartate could be able to better cover the specific amino requirements, thus resulting in improved muscle protein synthesis without impairment of acute phase protein synthesis.

Acute changes in fibrinogen metabolism and coagulation after hemorrhage in pigs

Hemorrhagic coagulopathy is involved in the morbidity and mortality of trauma patients. Nonetheless, many aspects of the mechanisms underlying this disorder are poorly understood. We have therefore investigated changes in fibrinogen metabolism and coagulation function after a moderate hemorrhagic shock, using a new stable isotope approach. Twelve pigs were randomly divided into the control (C) and hemorrhage (H) groups. Hemorrhage was induced by bleeding 35% total blood volume over a 30-min period. A primed constant infusion of [1-(13)C]phenylalanine (Phe), d5-phenylalanine, and alpha-[1-(13)C]-ketoisocaproate (KIC) was given to quantify fibrinogen synthesis and breakdown, together with measurements of circulating liver enzyme activities and coagulation function. Mean arterial pressure was decreased by hemorrhage from 89 +/- 4 mmHg in C to 47 +/- 4 mmHg in H (P < 0.05), followed by a rebound to 68 +/- 5 mmHg afterward. Fibrinogen fractional synthesis rate increased from 2.7 +/- 0.2%/h in C to 4.2 +/- 0.4%/h in H by Phe (P < 0.05) and from 3.1 +/- 0.4%/h in C to 4.4 +/- 0.5%/h in H by KIC (P < 0.05). Fibrinogen fractional breakdown rate increased from 3.6 +/- 1.0%/h in C to 12.9 +/- 1.8%/h in H (P < 0.05). The absolute breakdown rate accelerated from 3.0 +/- 0.4 mg x kg(-1) x h(-1) in C to 5.4 +/- 0.6 mg x kg(-1) x h(-1) in H (P < 0.05), but the absolute synthesis rate remained unchanged. These metabolic changes were accompanied by a reduction in blood clotting time to 92.7 +/- 1.6% of the baseline value by hemorrhage (P < 0.05). No changes were found in liver enzyme activities. We conclude that the observed changes in coagulation after hemorrhagic shock are mechanistically related to the acute acceleration of fibrinogen degradation.

Does Hemodialysis Increase Protein Breakdown? Dissociation between Whole-Body Amino Acid Turnover and Regional Muscle Kinetics

Hemodialysis (HD) is a protein catabolic procedure. Whole-body amino acid turnover studies identify dialysate amino acid loss and reduced protein synthesis as the catabolic events; proteolysis is not increased. Regional amino acid kinetics, however, document enhanced muscle protein breakdown as the cause of the catabolism; muscle protein synthesis also increased but to a lesser magnitude than the increment in protein breakdown. This discordance between whole-body and regional kinetics is best explained by the contrasting physiology between the muscle and the liver. During HD, muscle releases amino acids, which then are taken up by the liver for de novo protein synthesis. There seems to be a somatic to visceral recycling of amino acids. Evidence supporting this concept includes the increased fractional synthesis of albumin and fibrinogen during HD. It should be emphasized that region- or organ-specific kinetics vary, and whole-body turnover is a composite of all of the visceral and somatic compartments taken together. Reduced whole-body protein synthesis may be a compensatory adaptation to dialysate amino acid loss with a consequent reduction in plasma amino acid concentration. Notwithstanding the protein catabolic nature of HD, evidence is accumulating that intradialytic nutritional supplementation may blunt its catabolic effect.

POOR NUTRITIONAL STATUS AND INFLAMMATION: Serum Albumin: Relationship to Inflammation and Nutrition

Hypoalbuminemia is the result of the combined effects of inflammation and inadequate protein and caloric intake in patients with chronic disease such as chronic renal failure. Inflammation and malnutrition both reduce albumin concentration by decreasing its rate of synthesis, while inflammation alone is associated with a greater fractional catabolic rate (FCR) and, when extreme, increased transfer of albumin out of the vascular compartment. A vicious cascade of events ensues in which inflammation induces anorexia and reduces the effective use of dietary protein and energy intake and augments catabolism of the key somatic protein, albumin. Hypoalbuminemia is a powerful predictor of mortality in patients with chronic renal failure, and the major cause of death in this population is due to cardiovascular events. Inflammation is associated with vascular disease and likely causes injury to the vascular endothelium, and hypoalbuminemia as two separate expressions of the inflammatory process. Albumin has a myriad of important physiologic effects that are essential for normal health. However, simply administering albumin to critically ill patients with hypoalbuminemia has not been shown to improve survival or reduce morbidity. Thus the inference from these clinical studies suggests that the cause of hypoalbuminemia, rather than low albumin levels specifically, is responsible for morbidity and mortality.

Protein synthesis rates of human PBMC and PMN can be determined simultaneously in vivo by using small blood samples

Immune cell functions can be evaluated in vivo by measuring their specific protein fractional synthesis rates (FSR). Using stable isotope dilution techniques, we describe a new method allowing simultaneous in vivo assessment of FSR in two leukocyte populations in healthy human subjects, using small blood samples. Peripheral blood mononuclear cell (PBMC) and polymorphonuclear neutrophil (PMN) FSR were measured during primed continuous intravenous infusion of l-[1-13C]leucine. Immune cells from 6 ml of whole blood were isolated by density gradient centrifugation. In a first study, we calculated the FSR using plasma [13C]leucine or α-[13C]ketoisocaproate (KIC) enrichments as precursor pools. In a second study, we compared protein FSR in leukocytes, using enrichments of either intracellular or plasma free [13C]leucine as immediate precursor pools. The present approach showed a steady-state enrichment of plasma and circulating immune cell free [13C]leucine precursor pools. The linearity of labeled amino acid incorporation rate within mixed PBMC and PMN proteins also was verified. Postabsorptive protein FSR was 4.09 ± 0.39%/day in PBMC and 1.44 ± 0.08%/day in PMN when plasma [13C]KIC was the precursor pool. The difference between PBMC and PMN FSR was statistically significant, whatever the precursor pool used, suggesting large differences in their synthetic activities and functions. Use of the plasma [13C]KIC pool led to an underestimation of leukocyte FSR compared with the intracellular pool (PBMC: 6.04 ± 0.94%/day; PMN: 2.98 ± 0.30%/day). Hence, the intracellular free amino acid pool must be used as precursor to obtain reliable results. In conclusion, it is possible to assess immune cell metabolism in vivo in humans by using small blood samples to directly indicate their metabolic activity in various clinical situations and in response to regulating factors.

Coordinated increase in albumin, fibrinogen, and muscle protein synthesis during hemodialysis: role of cytokines

Serum albumin, fibrinogen levels, and lean body mass are important predictors of outcome in end-stage renal disease (ESRD). We estimated the fractional synthesis rates of albumin (FSR-A), fibrinogen (FSR-F), and muscle protein (FSR-M) in nine ESRD patients and eight controls, using primed constant infusion of l-[ring-(13)C(6)]phenylalanine. Cytokine profile and arteriovenous balance of amino acids were also measured. ESRD patients were studied before (Pre-HD) and during hemodialysis (HD). Plasma IL-6, IL-10, and C-reactive protein increased significantly during HD. Despite a decrease in the delivery of amino acids to the leg, the outflow of the amino acids increased during HD. The net balance of amino acids became more negative during HD, indicating release from the muscle. HD increased leg muscle protein synthesis (45%) and catabolism (108%) but decreased whole body proteolysis (15%). FSR-A during HD (9.7 +/- 0.9%/day) was higher than pre-HD (6.5 +/- 0.9%/day) and controls (5.8 +/- 0.5%/day, P < 0.01). FSR-F increased during HD (19.7 +/- 2.6%/day vs. 11.8 +/- 0.6%/day, P < 0.01), but it was not significantly different from that of controls (14.4 +/- 1.4%/day). FSR-M intradialysis (1.77 +/- 0.19%/day) was higher than pre-HD (1.21 +/- 0.25%/day) and controls (1.30 +/- 0.32%/day, P < 0.001). Pre-HD FSR-A, FSR-F, and FSR-M values were comparable to those of controls. There was a significant and positive correlation between plasma IL-6 and the FSRs. Thus, in ESRD patients without metabolic acidosis, the fractional synthesis rates of albumin, fibrinogen, and muscle protein are not decreased pre-HD. However, HD increases the synthesis of albumin, fibrinogen, and muscle protein. The coordinated increase in the FSRs is facilitated by constant delivery of amino acids derived from the muscle catabolism and intradialytic increase in IL-6.

Protein turnover and amino acid transport kinetics in end-stage renal disease

Protein and amino acid metabolism is abnormal in end-stage renal disease (ESRD). Protein turnover is influenced by transmembrane amino acid transport. The effect of ESRD and hemodialysis (HD) on intracellular amino acid transport kinetics is unknown. We studied intracellular amino acid transport kinetics and protein turnover by use of stable isotopes of phenylalanine, leucine, lysine, alanine, and glutamine before and during HD in six ESRD patients. Data obtained from amino acid concentrations and enrichment in the artery, vein, and muscle compartments were used to calculate intracellular amino acid transport and muscle protein synthesis and catabolism. Fractional muscle protein synthesis (FSR) was estimated by the precursor product approach. Despite a significant decrease in the plasma concentrations of amino acids in the artery and vein during HD, the intracellular concentrations remained stable. Outward transport of the amino acids was significantly higher than the inward transport during HD. FSR increased during HD (0.0521 +/- 0.0043 vs. 0.0772 +/- 0.0055%/h, P < 0.01). Results derived from compartmental modeling indicated that both protein synthesis (118.3 +/- 20.6 vs. 146.5 +/- 20.6 nmol.min-1.100 ml leg-1, P < 0.01) and catabolism (119.8 +/- 18.0 vs. 174.0 +/- 14.2 nmol.min-1.100 ml leg-1, P < 0.01) increased during HD. However, the intradialytic increase in catabolism exceeded that of synthesis (57.8 +/- 13.8 vs. 28.0 +/- 8.5%, P < 0.05). Thus HD alters amino acid transport kinetics and increases protein turnover, with net increase in protein catabolism.

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.

The effects of the formula of amino acids enriched BCAA on nutritional support in traumatic patients

AIM: To investigate the formula of amino acid enriched BCAA on nutritional support in traumatic patients after operation.

METHODS: 40 adult patients after moderate or large abdominal operations were enrolled in a prospective, randomly and single-blind-controlled study, and received total parenteral nutrition (TPN) with either formula of amino acid (AA group, 20 cases) or formula of amino acid enriched BCAA (BCAA group, 20 cases). From the second day after operation, total parenteral nutrition was infused to the patients in both groups with equal calorie and equal nitrogen by central or peripheral vein during more than 12 hours per day for 6 days. Meanwhile, nitrogen balance was assayed by collecting 24 hours urine for 6 days. The markers of protein metabolism were investigated such as amino acid patterns, levels of total protein, albumin, prealbumin, transferrin and fibronectin in serum.

RESULTS: The positive nitrogen balance in BCAA group occurred two days earlier than that in AA group. The serum levels of total protein and albumin in BCAA group were increased more obviously than that in AA group. The concentration of valine was notably increased and the concentration of arginine was markedly decreased in BCAA group after the formula of amino acids enriched BCAA transfusion.

CONCLUSION: The formula of amino acid enriched BCAA may normalize the levels of serum amino acids, reduce the proteolysis, increase the synthesis of protein, improve the nutritional status of traumatic patients after operation.

Increased albumin plasma efflux contributes to hypoalbuminemia only during early phase of sepsis in rats

The mechanisms leading to hypoalbuminemia in sepsis were explored by measuring plasma volume, albumin distribution, plasma albumin transcapillary escape rate (TER), and efflux (TER x albumin intravascular pool). These parameters were quantified in infected rats, injected intravenously with live Escherichia coli, and pair-fed and well-fed rats using an injection of (35)S-albumin and measuring plasma and whole body albumin concentrations. Animals were studied on days 1, 6, and 10 after infection. In pair-fed rats, neither albumin distribution nor exchange rate between the intra- and extravascular compartments was modified. The increase of plasma volume after infection partly explained hypoalbuminemia. Infection resulted in a reduction of the total albumin pool of the body all along the experimental period, indicating a net loss of the protein. Albumin TER (%/day) was significantly increased 1 and 6 days after infection, but the absolute efflux was increased only on day 1. Normal values were observed on day 10. Therefore, an accelerated plasma efflux contributes to hypoalbuminemia only during the early period of sepsis. During this phase, the protein was retained in the extravascular space where it was probably catabolized. Later on, other factors are probably involved.

Effect of elective abdominal surgery on human colon protein synthesis in situ

OBJECTIVE

To determine the effect of elective abdominal surgery on the rate of human colon fractional protein synthesis in situ.

SUMMARY BACKGROUND DATA

Efficient intestinal protein synthesis plays an important role in the physiology and pathophysiology of the intestinal tract, allowing preservation of gut integrity and thereby preventing bacterial or endotoxin translocation. Because of species differences, animal studies have only limited applicability to human intestinal protein metabolism, and because of methodologic restrictions, no studies on colon protein synthesis in situ are available in humans.

METHODS

The authors used advanced mass spectrometry techniques (capillary gas chromatography and combustion isotope ratio mass spectrometry) to determine directly the incorporation rate of 1-[13C]-leucine into colon mucosal protein in control subjects and nonseptic postoperative patients. All subjects had a colostomy, which allowed easy access to the colon mucosa, and consecutive sampling from the same tissue was performed during continuous isotope infusion (0.16 micromol/kg per minute).

RESULTS

Control subjects demonstrated a colon protein fractional synthetic rate of 0.74 +/- 0.09% per hour. In postsurgical patients, colon protein synthesis was significantly higher and the tissue free leucine enrichment was significantly lower, compatible with an increased colon proteolytic rate.

CONCLUSIONS

Elective abdominal surgery followed by an uncomplicated postoperative course is associated with a stimulation of colon protein synthesis and possibly also of protein degradation. The postoperative rate of colon protein synthesis is, compared with other tissues, among the highest measured thus far in humans.

Methionine transsulfuration is increased during sepsis in rats

Methionine transsulfuration in plasma and liver, and plasma methionine and cysteine kinetics were investigated in vivo during the acute phase of sepsis in rats. Rats were infected with an intravenous injection of live Escherichia coli, and control pair-fed rats were injected with saline. Two days after injection, the rats were infused for 6 h with [(35)S]methionine and [(15)N]cysteine. Transsulfuration was measured from the transfer rate of (35)S from methionine to cysteine. Liver cystathionase activity was also measured. Infection significantly increased (P < 0.05) the contribution of transsulfuration to cysteine flux in both plasma and liver (by 80%) and the contribution of transsulfuration to plasma methionine flux (by 133%). Transsulfuration measured in plasma was significantly (P < 0.05) higher in infected rats than in pair-fed rats (0.68 and 0.25 micromol. h(-1). 100 g(-1), respectively). However, liver cystathionase specific activity was decreased by 17% by infection (P < 0.05). Infection increased methionine flux (16%, P < 0.05) less than cysteine flux (38%, P < 0.05). Therefore, the plasma cysteine flux was higher than that predicted from estimates of protein turnover based on methionine data, probably because of enhanced glutathione turnover. Taken together, these results suggest an increased cysteine requirement in infection.

Liver export protein synthetic rates are increased by oral meal feeding in weight-losing cancer patients

We have demonstrated previously that, in the fasting state, whereas albumin synthesis is similar in cachectic cancer patients compared with controls, fibrinogen synthesis is increased. Whether synthesis of these proteins is altered after an oral meal was examined in eight weight-losing pancreatic cancer patients and six healthy controls by use of an intravenous flooding dose of [(2)H(5)]- or [(2)H(8)]phenylalanine. Cancer patients had a median weight loss of 19%, a significantly lower serum albumin concentration, and a significantly higher plasma fibrinogen concentration than controls (P < 0.005). Fasting albumin synthesis rates were similar between cancer patients and controls (median total synthesis rate 11.3 vs. 13.9 g/day, respectively) and rose on feeding by a similar degree (median 29 and 24%). The fasting fibrinogen total synthetic rate was significantly higher in cancer patients than in controls (median 3.3 vs. 1.0 g/day, P = 0.0019). In cancer patients in the fed state, fibrinogen synthetic rate rose by a median of 38% (P = 0.012), whereas in controls there was no significant change. These findings demonstrate significant upregulation by feeding of acute-phase protein synthesis in cachectic cancer patients.

Synthesis rate of plasma albumin is a good indicator of liver albumin synthesis in sepsis

Plasma albumin is well known to decrease in response to inflammation. The rate of albumin synthesis from both liver and plasma was measured in vivo by use of a large dose of L-[(2)H(3)-(14)C]valine in rats injected intravenously with live Escherichia coli and in pair-fed control rats during the acute-phase period (2 days postinfection). The plasma albumin concentration was reduced by 50% in infected rats compared with pair-fed animals. Infection induced a fall in both liver albumin mRNA levels and albumin synthesis relative to total liver protein synthesis. However, absolute liver albumin synthesis rate (ASR) was not affected by infection. In plasma, albumin fractional synthesis rate was increased by 50% in infected animals compared with pair-fed animals. The albumin ASR estimated in the plasma was similar in the two groups. These results suggest that hypoalbuminemia is not due to reduced albumin synthesis during sepsis. Moreover, liver and plasma albumin ASR were similar. Therefore, albumin synthesis measured in the plasma is a good indicator of liver albumin synthesis.

Protein-sparing effect in skeletal muscle of growth hormone treatment in critically ill patients

OBJECTIVE

To investigate the effect of growth hormone (GH) treatment on skeletal muscle protein catabolism in patients with multiple organ failure in the intensive care unit (ICU).

SUMMARY BACKGROUND DATA

Skeletal muscle depletion affects the incidence of complications and the length of hospital stay. A protein-sparing effect of GH treatment in skeletal muscle of long-term ICU patients was hypothesized.

METHODS

Twenty critically ill ICU patients were randomized to treatment with GH (0.3 U/kg/day) or as controls. Percutaneous muscle biopsy samples were taken before and after a 5-day treatment period starting on day 3 to 42 of the patient's ICU stay. Protein content, protein synthesis, water, nucleic acids, and free amino acids in muscle were analyzed.

RESULTS

The protein content decreased by 8% +/- 11% in the control patients, with no significant change in the GH group. The fractional synthesis rate of muscle proteins increased in the GH group by 33% +/- 48%, and muscle free glutamine increased by 207% +/- 327% in the GH group. Total intramuscular water increased by 12% +/- 14% in the control group as a result of an increase in extracellular water of 67% +/- 86%; these increases were not seen in the GH group. In contrast, the intracellular water increased by 6% +/- 8% in the GH group.

CONCLUSION

Treatment with GH for 5 days in patients with multiple organ failure stimulated muscle protein synthesis, increased muscle free glutamine, and increased intracellular muscle water.