Survival from sepsis. The significance of altered protein metabolism regulated by proteolysis inducing factor, the circulating cleavage product of interleukin-1

Persistence of long COVID symptoms in COVID-19 survivors worldwide and its potential pathogenesis - A systematic review and meta-analysis

The study sought to determine the prevalence of persistent long COVID symptoms such as anxiety, depression, dizziness, chest pain, sleep difficulty, palpitations, weight loss, and hair loss among coronavirus disease 2019 (COVID-19) survivors worldwide and to discuss the potential pathogeneses. Potential studies were searched in three databases (PubMed, Scopus, and Web of Science) as of January 30, 2021. Data on study characteristics, patient characteristics during the follow-up, the number of patients with persistent long COVID symptoms and total COVID-19 survivors were collected according to PRISMA guidelines. To assess the quality of studies, the Newcastle-Ottawa scale was used. The estimated prevalence of each long COVID symptom and the association between COVID-19 severity and the occurrence of prolonged symptoms was assessed, if appropriate. The global prevalence of prolonged anxiety was 15.76% (95%CI: 6.36%, 25.15%). Chest pain persisted in 10.36% (239/3,224) of COVID-19 patients (95%CI: 4.92%, 15.80%). Prolonged depression was found in 24 of 548 COVID-19 survivors with an estimated prevalence of 4.32% (95%CI: 2.62%, 6.03%) and dizziness was presented in 4.83% (118/2,219, 95%CI: 1.50%, 8.16%) after recovery. Hair loss was complained by 527 of 2,251 recovered patients (cumulative prevalence of 24.76%, 95%CI: 19.60%, 29.91%), while weight loss was identified in 37 cases among 452 COVID-19 survivors (8.19%, 95%CI: 5.66%, 10.71%). Prolonged palpitation was experienced by 19.38% (211/1,926) survivors with 95%CI: 2.40%, 41.16%. Sleep difficulty was found in 541 of 2,622 COVID-19 survivors (17.87%, 95%CI: 7.55%, 28.20%). The association between COVID-19 severity and the occurrence of persistent long COVID symptoms was not analyzed due to the lack of data. In conclusion, persistent psychological symptoms are frequently reported among COVID-19 survivors. Follow-up studies with a longer duration and larger population are warranted to assess the extent of prolonged symptoms and the quality of life of COVID-19 survivors. Despite various potential pathogeneses that have been hypothesized, a definitive mechanism is yet to be addressed. PROSPERO registration: CRD42021247172.

Comprehensive metabolic amino acid flux analysis in critically ill patients

Amino acid (AA) metabolism is severely disturbed in critically ill ICU patients. To be able to make a more scientifically based decision on the type of protein or AA nutrition to deliver in ICU patients, comprehensive AA phenotyping with measurements of plasma concentrations and whole body production (WBP) is needed. Therefore, we studied ICU patients and matched control subjects using a novel pulse isotope method to obtain in-depth metabolic analysis. In 51 critically ill ICU patients (SOFA~6.6) and 49 healthy controls, we measured REE and body composition/phase-angle using BIA. In the postabsorptive state, we collected arterial (ized) blood for CRP and AA. Then, we administered an 8 mL solution containing 18 stable AA tracers as a pulse and calculated WBP. Enrichments: LC-MS/MS and statistics: t-test, ANCOVA. Compared to healthy, critically ill ICU patients had lower phase-angle (p < 0.00001), and higher CRP (p < 0.0001). Most AA concentrations were lower in ICU patients (p < 0.0001), except tau-methylhistidine and phenylalanine. WBP of most AA were significantly (p < 0.0001) higher with increases in glutamate (160%), glutamine (46%), and essential AA. Remarkably, net protein breakdown was lower. There were only weak relationships between AA concentrations and WBP. Critically ill ICU patients (SOFA 8-16) had lower values for phase angle (p = 0.0005) and small reductions of most plasma AA concentrations, but higher tau-methylhistidine (p = 0.0223) and hydroxyproline (p = 0.0028). Remarkably, the WBP of glutamate and glutamine were lower (p < 0.05), as was their clearance, but WBP of tau-methylhistidine (p = 0.0215) and hydroxyproline (p = 0.0028) were higher. Our study in critically ill ICU patients shows that comprehensive metabolic phenotyping was able to reveal severe disturbances in specific AA pathways, in a disease severity dependent way. This information may guide improving nutritional compositions to improve the health of the critically ill patient. CLINICAL TRIAL REGISTRY: Data are from the baseline measurements of study NCT02770092 (URL: https://clinicaltrials.gov/ct2/show/NCT02770092) and NCT03628365 (URL: https://clinicaltrials.gov/ct2/show/NCT03628365).

The anabolic role of the Warburg, Cori-cycle and Crabtree effects in health and disease

In evolution, genes survived that could code for metabolic pathways, promoting long term survival during famines or fasting when suffering from trauma, disease or during physiological growth. This requires utilization of substrates, already present in some form in the body. Carbohydrate stores are limited and to survive long, their utilization is restricted to survival pathways, by inhibiting glucose oxidation and glycogen synthesis. This leads to insulin resistance and spares muscle protein, because being the main supplier of carbon for new glucose production. In these survival pathways, part of the glucose is degraded in glycolysis in peripheral (muscle) tissues to pyruvate and lactate (Warburg effect), which are partly reutilized for glucose formation in liver and kidney, completing the Cori-cycle. Another part of the glucose taken up by muscle contributes, together with muscle derived amino acids, to the production of substrates consisting of a complete amino acid mix but extra non-essential amino acids like glutamine, alanine, glycine and proline. These support cell proliferation, matrix deposition and redox regulation in tissues, specifically active in host response and during growth. In these tissues, also glucose is taken up delivering glycolytic intermediates, that branch off and act as building blocks and produce reducing equivalents. Lactate is also produced and released in the circulation, adding to the lactate released by muscle in the Cori-cycle and completing secondary glucose cycles. Increased fluxes through these cycles lead to modest hyperglycemia and hyperlactatemia in states of healthy growth and disease and are often misinterpreted as induced by hypoxia.

Hypermetabolism and Nutritional Support in Sepsis

BACKGROUND

Surgical metabolism has been a founding field of investigation in surgery without which the boundaries of critical care, trauma, and surgical oncology could not have advanced. Traditionally, understanding the shifts in electrolytes, carbohydrates, fats, and amino acids that could explain the rapidly evolving proteolysis after catabolic stress and tumor growth has been a major focus of research that led to our current approach to maintaining homeostasis over the course of major surgical intervention and injury.

METHOD

Review of the English-language literature.

RESULTS

With the emerging field of inflammation and the discovery of cytokines and chemokines, surgical metabolism has taken a second seat in the surgical research arena. Yet central to all patient management after injury is an understanding of how catabolic stress erodes vital organ function and how current approaches can support metabolism through the most physiologically stressful perturbations known to man, for which there is no evolutionary precedent. Although it is well accepted that unabated proteolysis is not a sustainable physiologic state, in the era of modern medicine, precisely how to manipulate the body nutritionally to drive a recovery-directed immune response remains highly debated. This review incorporates multiple lines of inquiry in surgical metabolism, with a particular focus on sepsis.

CONCLUSION

The changing landscape of previous paradigms in the field is discussed. Finally, how next-generation technology might spark renewed interest in this field among surgical investigators is considered.

Nutrition in critical illness: a current conundrum

Critically ill people are unable to eat. What’s the best way to feed them? Nutrition authorities have long recommended providing generous amounts of protein and calories to critically ill patients, either intravenously or through feeding tubes, in order to counteract the catabolic state associated with this condition. In practice, however, patients in modern intensive care units are substantially underfed. Several large randomized clinical trials were recently carried out to determine the clinical implications of this situation. Contradicting decades of physiological, clinical, and observational data, the results of these trials have been claimed to justify the current practice of systematic underfeeding in the intensive care unit. This article explains and suggests how to resolve this conundrum.

Meta-analysis is not enough: The critical role of pathophysiology in determining optimal care in clinical nutrition

Evidence based medicine has preferably been based on prospective randomized controlled trials (PRCT's) and subsequent meta-analyses in many fields including nutrition and metabolism. These meta-analyses often yield convincing, contradictory or no proof of effectiveness. Consequently recommendations and guidelines of varying validity and quality have been published, often failing to convince the medical, insurance and government worlds to support nutritional care. Causes for lack of adequate proof of effectiveness are manifold. Many studies and meta-analyses lacked pathophysiological depth in design and interpretation. Study populations were not homogenous and endpoints not always clearly defined. Patients were included not at nutritional risk, unlikely to benefit from nutritional intervention. Others received nutrients in excess of requirements or tolerance due to organ failure. To include all available studies in a meta-analysis, study quality and homogeneity were only assessed on the basis of formal study design and outcome rather than on patient characteristics. Consequently, some studies showed benefit but included patients suffering harm, other studies were negative but contained patients that benefited. Recommendations did not always emphasize these shortcomings, confusing the medical and nutritional community and creating the impression that nutritional support is not beneficial. Strong reliance on meta-analyses and guidelines shifts the focus of education from studying clinical and nutritional physiology to memorizing guidelines. To prevent or improve malnutrition more physiological knowledge should be acquired to personalize nutritional practices and to more correctly value and evaluate the evidence. This also applies to the design and interpretation of PRCT's and meta-analyses.

Pathologic metabolism: an exploratory study of the plasma metabolome of critical injury

BACKGROUND

Severe trauma is associated with massive alterations in metabolism. Thus far, investigations have relied on traditional bioanalytic approaches including calorimetry or nuclear magnetic resonance. However, recent strides in mass spectrometry (MS)-based metabolomics present enhanced analytic opportunities to characterize a wide range of metabolites in the critical care setting.

METHODS

MS-based metabolomics analyses were performed on plasma samples from severely injured patients' trauma activation field blood and plasma samples obtained during emergency department thoracotomy. These were compared against the metabolic profiles of healthy controls.

RESULTS

Few significant alterations were observed between trauma activation field blood and emergency department thoracotomy patients. In contrast, we identified trauma-dependent metabolic signatures, which support a state of hypercatabolism, driven by sugar consumption, lipolysis and fatty acid use, accumulation of ketone bodies, proteolysis and nucleoside breakdown, which provides carbon and nitrogen sources to compensate for trauma-induced energy consumption and negative nitrogen balance. Unexpectedly, metabolites of bacterial origin (including tricarballylate and citramalate) were detected in plasma from trauma patients.

CONCLUSION

In the future, the correlation between metabolomics adaptation and recovery outcomes could be studied by MS-based approaches, and this work can provide a method for assessing the efficacy of alternative resuscitation strategies.

Have we enough glutamine and how does it work? A clinician's view

There is a gap between the scientific basis of the claim that in several disease states glutamine is lacking and the widespread belief that supplementation of glutamine to the nutritional regimen is beneficial in severely ill patients. Glutamine shortage exists when consuming tissues, playing a crucial role in the response to trauma and disease, receive insufficient amounts of glutamine. In these tissues (immune system, wound), glutamine is only partly oxidized but has more specific roles as nontoxic nitrogen carrier, precursor of several crucial metabolites required for cell proliferation and for maintenance of the redox potential, and as osmolyte. In inflammatory states, glutamine concentrations in plasma and tissues are decreased due to many disease-related factors, precluding its use as a reliable indicator of shortage. Isotope studies have yielded equivocal results, precluding their use as a reliable indicator of glutamine shortage or adequacy. The increase in the net release of glutamine from peripheral tissues to central tissues (immune system, liver, spleen, wound) in inflammatory states provides a better basis for the necessity to supplement the organism with extra glutamine in these conditions. Glutamine supplementation was beneficial in a few studies in burn or trauma patients. The clinical benefit of parenteral glutamine supplementation in patients with severe inflammation has been demonstrated more convincingly. The amounts of glutamine supplemented approximate the amounts released by peripheral tissues and utilized by central organs operative in host defense and are therefore in the physiological range.

Dangers, and benefits of the cytokine mediated response to injury and infection

The inflammatory response is essential for survival in an environment where continuous exposure to noxious events threaten the integrity of the organism. However, the beneficial effects of the response are influenced by factors, which disadvantage individuals within a population. These factors include malnutrition, infection, genotype, gender, pre-existing inflammation, and chronic intoxication. Although the inflammatory response is generally successful in dealing with noxious events, life-long exposure to these events takes its toll on the integrity of the body and becomes apparent as chronic disease, atherosclerosis, organ failure, and frailty. Progress in ameliorating the consequences of lifetime exposure to inflammatory events can only occur if a fuller understanding can be obtained of the factors, which influence the persistence and outcome of the inflammatory response at an individual level. A multitude of studies has shown that specific nutrients, diets, and dietary restriction are able to modulate the inflammatory response in the population as a whole. To advance in this area, precise knowledge is needed of how the disadvantageous factors, mentioned above, affect the individual's response to anti-inflammatory nutrients.

The effect of malnutrition on the metabolic response to surgery

The effect of previous malnutrition on the metabolic response to surgical hysterectomy was investigated in adult female rats. Malnutrition was achieved by feeding a 20 g protein/kg diet and restricting food intake to 50 % of normal. This dietary regimen was maintained for 3 weeks before surgery and for 4 d after surgery. Unoperated control rats were pair-fed with the hysterectomized rats after surgery. Energy balance was measured by the comparative carcass technique and, in a second experiment, urinary N excretion was measured. Surgery caused energy expenditure to increase by 37 % in ad libitum-fed rats but in malnourished rats it increased by only 22 %. Urinary N excretion rose immediately after surgery. In the ad libitum-fed rats it was on average 85 % greater in hysterectomized rats than controls for the first 3 d after surgery, whereas in the restricted rats it was 74 % greater on the first day and not significantly elevated thereafter. Thus, malnutrition attenuated the metabolic response to surgery but did not abolish it completely.

Characterization of the PC4 binding domain and its interactions with HNF4alpha

In the presence of oxidative stress, the hepatocellular inflammatory-redox (IR) state upregulates inducible nitric oxide synthase (iNOS) expression as an anti-oxidant function. In IL-1beta and peroxide treated hepatocytes, we have identified hepatocyte nuclear factor-4alpha (HNF4) and the transcriptional co-activator, PC4, to be essential for upregulation of iNOS transcription in this setting. The co-activator, PC4, facilitates activator-dependent transcription via interactions with basal transcriptional machinery that are independent of PC4-DNA binding. The interaction between HNF4 and PC4 has not been previously characterized. In this study utilizing human HepG2 cells, we demonstrate the critical role for p38 MAP kinase mediated HNF4 Ser158 phosphorylation (P-HNF4-S158), binding of PC4 to P-HNF4-S158 and characterize the functional domain of PC4 required for P-HNF4-S158 binding. Our results indicate that the presence of the IR state enhances PC4-HNF4 binding to upregulate transcription of target hepatocyte genes, such as iNOS.

Post colon surgery complications: imaging findings

Several standardized types of colonic resections are available in the clinical practice. All of them may produce early and late complications. Diagnostic imaging plays a pivotal role in the recognition of post-operative colorectal complications and provides fundamental information for therapeutic planning. In this paper we review the imaging findings of early and late post-operative complications of colorectal surgery.

Redox-mediated upregulation of hepatocyte iNOS transcription requires coactivator PC4

BACKGROUND

Redox-mediated upregulation of transcription of hepatocyte inducible nitric oxide synthase (iNOS) requires hepatocyte nuclear factor IV-alpha (HNF-4alpha). In this setting, PC4 is often isolated with HNF-4alpha in DNA-protein pull-down studies. Transcriptional coactivator PC4 facilitates activator-dependent transcription via interactions with basal transcriptional machinery that are independent of PC4-DNA binding. We hypothesized that PC4 is a necessary component of HNF-4alpha-regulated redox-sensitive hepatocyte iNOS transcription.

METHODS

Murine CCL9.1 hepatocytes were stimulated with interleukin-1beta (IL-1beta; 1000 U/mL) in the presence and absence of peroxide (H(2)O(2); 50 nmol/L). Antisense and sense oligonucleotides to HNF-4alpha and PC4 were added selectively. Coimmunoprecipitation (Co-IP) studies determined the association between HNF-4alpha and PC4. Transient transfection was performed with the use of a luciferase reporter construct containing the murine iNOS promoter (1.8 kb). Chromatin immunoprecipitation assays determined in vivo binding of PC4 and HNF-4alpha to the iNOS promoter region.

RESULTS

Ablation of either HNF-4alpha or PC4 blunted the peroxide-mediated increase in the activation of the iNOS promoter. In IL-1beta+H(2)O(2) only, co-IP studies demonstrated the presence of an HNF-4alpha-PC4 protein complex, and chromatin immunoprecipitation assays demonstrated that this complex binds to the genomic iNOS promoter.

CONCLUSIONS

Redox-mediated upregulation of hepatocyte iNOS transcription requires an HNF-4alpha-PC4 transcriptional complex.

Amino Acid Adequacy in Pathophysiological States

Amino acid utilization and, therefore, demand differ between the healthy state and various disease states. In the healthy state most circulating amino acids are derived from dietary proteins that are stored and broken down in the gut and released gradually into the portal circulation, and from continuous turnover of body protein. In disease states, the amino acid composition of amino acids derived from periferal protein breakdown and released in the circulation, is different, for example because a substantial part of the branched-chain amino acids is broken down to yield glutamine and alanine, which are released in the circulation. It appears to be advantageous to mimic this continuous autoinfusion in patients, dependent of parenteral of enteral tube feeding. In disease, different endpoints should be used to assess the adequacy of the administered amino acid mix. Maintenance of a positive nitrogen balance and growth is less important than support of wound healing and immune function. Several amino acids such as glutamine, cysteine, and taurine are shown or suggested to be conditionally essential in disease, and to form substrate in the stressed patient for anabolic processes in liver, immune system, and injured sites. Amino acid toxicity is rare, and protein restriction for patients with renal or liver failure is obsolete because this only aggravated malnutrition. A true example of protein toxicity consists of gastrointestinal hemorrhage that precipitates hepatic encephalopathy in liver insufficiency, most likely because hemoglobin is an unbalanced protein because it lacks the essential amino acid isoleucine.

Serine/threonine phosphorylation regulates HNF-4alpha-dependent redox-mediated iNOS expression in hepatocytes

Nitric oxide (NO), endogenously synthesized by inducible NO synthase (iNOS), serves antioxidant and antiapoptotic functions in settings characterized by oxidative stress and proinflammatory cytokines such as sepsis and shock. However, the redox-sensitive mechanisms regulating hepatocyte expression of iNOS are largely unknown. In interleukin-1beta (IL-1beta)-stimulated hepatocytes exposed to superoxide, we demonstrate that hepatocyte nuclear factor-4alpha (HNF-4alpha) acts as an activator of redox-associated hepatocyte iNOS expression at the level of protein, mRNA, and promoter activation. In the absence of HNF-4alpha, this redox-mediated enhancement is ablated. HNF-4alpha functional activity is associated with a unique serine/threonine kinase-mediated phosphorylation pattern. This suggests that a redox-sensitive kinase pathway targets HNF-4alpha to augment hepatocyte iNOS expression. Previous studies have not addressed a redox-dependent kinase signaling pathway that targets HNF-4alpha and enhances hepatocyte iNOS gene transcription. A unique pattern of phosphorylation determines HNF-4alpha activity as a trans-activator of IL-1beta-mediated hepatocyte iNOS expression in the presence of oxidative stress.

Effects of tumor necrosis factor-binding protein on hepatic protein synthesis during chronic sepsis

BACKGROUND

Cytokines are thought to play a role in the stimulation of protein synthesis in liver during inflammation and sepsis. We previously showed that administration of tumor necrosis factor-binding protein (TNFbp) prevents the sepsis-induced inhibition of protein synthesis in skeletal muscle. The purpose of the present set of experiments was to investigate the effect of TNFbp on hepatic protein synthesis and its ability to modulate the mechanisms responsible for increased hepatic protein synthesis during chronic (5-day) intraabdominal sepsis.

MATERIALS AND METHODS

We examined the effects of TNFbp on hepatic protein synthesis during sepsis in four groups of rats: control, control + TNFbp, septic, and septic + TNFbp. Saline (1.0 ml) or TNFbp (1 mg/kg, 1.0 ml) was injected daily starting 4 h prior to the induction of sepsis. The effect of sepsis and TNFbp administration on hepatic protein synthesis in vivo was examined 5 days later.

RESULTS

Sepsis increased the rate of protein synthesis by 35% relative to controls. Accelerated rates of protein synthesis were accompanied by increased total RNA content, eukaryotic initiation factor (eIF) 2alpha content, and phosphorylation of p70S6 kinase. Injection of TNFbp into septic rats for 5 days did not diminish the sepsis-induced stimulation of hepatic protein synthesis. Compared with controls, septic rats treated with TNFbp also showed elevated total RNA content, elF2alpha content, and phosphorylation of p70S6 kinase. No significant differences in any of the parameters measured were observed between untreated and TNFbp-treated septic rats. Treatment of control animals with TNFbp for 5 days was without effect on any of the parameters examined.

CONCLUSIONS

TNFbp did not prevent the sepsis-induced stimulation of hepatic protein metabolism or modulate the septic-induced changes in factors regulating protein synthesis. Global rates of protein synthesis in livers from septic rats are accelerated by increases in the abundance or activity of components of translational apparatus.

The effect of burn subeschar tissue fluid on skeletal muscle and hepatic amino acid uptake in an experimental system in vitro

Burn injury is associated with major metabolic disturbances. Many factors or mediators are responsible for post-burn metabolic changes. The present study was designed to test the role of interstitial edema fluid from burn eschar in regulating amino acid transport into hepatic and muscle tissue. Subeschar tissue fluid (SEF) was collected from just under the full thickness burn area. Amino acid transport, determined as the uptake of [3H]-alpha-aminoisobutyric acid by incubated soleus muscles or liver slices in vitro, was reduced after the addition of subeschar tissue fluid. The suppression was more marked with fluids taken from patients with a large burn area. Significant findings were noted when the total surface burn area was more than 70%. There were significant differences in the SEF suppression effect between survivors and non-survivors, but not between inhalation and non-inhalation victims. The results suggest the presence of one or more factors in subeschar tissue fluid that inhibit both muscle and liver amino acid transport. The data also suggest that the inhibitory factors are most likely produced by the burned tissue. This suppression effect may be beneficial to burn victims in maintaining near-normal vascular osmolarity by way of an increased plasma amino acid level.

Effects of endotoxin challenge on hepatic amino acid transport during cancer

BACKGROUND

The hepatic uptake of amino acids is increased in both sepsis and cancer, and this response appears to be both global and essential in the catabolic host. Because immunocompromised cancer patients are susceptible to episodes of gram-negative sepsis, we examined the capacity of hepatocytes from normal and tumor-influenced livers to respond to the additional challenge of endotoxemia via increases in the Na+-dependent uptake of glutamine and zwitterionic amino acids by System N and System A, respectively.

MATERIALS AND METHODS

Fischer 344 rats were implanted with methylcholanthrene-induced fibrosarcomas. Control rats were sham-operated and pair-fed. Animal pairs (tumor burden = 8-32% carcass weight) were injected intraperitoneally with either Escherichia coli endotoxin (10 mg/kg) or PBS, and after 4 h, hepatocytes were isolated from the livers of the animals via collagenase perfusion and placed in primary culture. Three hours later, amino acid transport rates were measured using radiolabeled glutamine for System N and alpha-methylaminoisobutyric acid (MeAIB), a nonmetabolizable substrate specific for System A.

RESULTS

Cancer-independent of tumor size-and endotoxin each elicited similar 1.5- to 2-fold inductions of System N activity. When combined, their effects were additive rather than synergistic. In contrast, endotoxin induced an insignificant increase in System A activity, whereas cancer stimulated this carrier 2-fold in either the absence or the presence of endotoxin.

CONCLUSIONS

The primary glutamine and alanine carriers in hepatocytes are differentially influenced during catabolic states, and the tumor-influenced liver is competent to further increase glutamine uptake in response to additional catabolic insults.

The 1996 Nestlé International Clinical Nutrition Award for Enteral Nutrition. "Enteral versus parenteral nutrition: effects on gastrointestinal function and metabolism": background

Nutrition therapy for the critically ill patient is today an integral part of the treatment concept in intensive care medicine. Parenteral and enteral artificial nutrition are expensive, cost-intensive treatment procedures that are certainly not risk-free. For both ethical and economic reasons, the indications and principles of artificial nutrition must always be adapted to the latest knowledge.

Parenteral administration of different amounts of branch-chain amino acids in septic patients: clinical and metabolic aspects

OBJECTIVE

To study the effects of a total parenteral nutrition solution changing branch-chain amino acid concentrations and/or nitrogen supply on protein metabolism, length of stay, and mortality rate; and to evaluate the unique metabolic status of sepsis that leads to a search for specific total parenteral nutrition formulas.

DESIGN

Prospective, randomized, and multicenter study.

SETTING

Intensive care units (ICUs) in seven university hospitals.

PATIENTS

Sixty-nine septic patients.

MEASUREMENTS AND MAIN RESULTS

The patients were randomized into three groups according to the total parenteral nutrition administered. Group A (n = 22) and B (n = 25) patients received 1.5 g of amino acids/kg/day with a nonprotein ratio of 100:1 calories/g of nitrogen, and a varying branch-chain amino acids percentage (group A [23%); group B [45%]). Group C patients were treated with 1.1 g/kg/day of amino acids with a nonprotein ratio of 140:1 calories/g of nitrogen and 45% branch-chain amino acids. All diets were isocaloric. Prealbumin, retinol-binding protein, nitrogen balance, and plasma amino acid profiles (24 amino acids) were determined at baseline and after 3, 7, and 11 days of total parenteral nutrition. The length of stay and the mortality rate in the ICU were recorded. At baseline (preparenteral nutrition), no differences in age, gender, severity of the condition, or clinical chemistry were found between the groups. Prealbumin and retinol-binding protein increased in groups B (p < .004, p < .002, respectively) and C (p < .001, p < .002, respectively). Plasma arginine increased significantly in group C (p < .05), and plasma valine (p < .0001, p < .04, respectively), leucine (p < .005, p < .03, respectively), and isoleucine (p < .001, p < .0001, respectively) increased significantly in groups B and C. The length of stay in the ICU did not change between the groups. The mortality rate in groups B and C was less than in group A (p < .03).

CONCLUSIONS

Our results suggest that the branch-chain amino acids-rich formulas (45%) show a beneficial effect in septic patients.

Glucocorticoid-dependent induction of interleukin-6 receptor expression in human hepatocytes facilitates interleukin-6 stimulation of amino acid transport

OBJECTIVE

The authors studied the effects of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) on glutamine and alanine transport in isolated human hepatocytes. They also evaluated the role of dexamethasone in modulating this response and its effects on the expression of the plasma membrane high-affinity IL-6 receptor.

SUMMARY BACKGROUND DATA

Animal studies indicate that cytokines are important mediators of the increased hepatic amino acid uptake that occurs during cancer and sepsis, but studies in human tissues are lacking. The control of transport by cytokines and cytokine receptor expression in the liver may provide a mechanism by which hepatocytes can modulate amino acid availability during catabolic disease states.

METHODS

Human hepatocytes were isolated from wedge biopsy specimens and plated in 24-well trays. Interleukin-6 and TNF-alpha, in combination with the synthetic glucocorticoid dexamethasone, were added to hepatocytes in culture, and the transport of radiolabeled glutamine and alanine was measured. Fluorescent-activated cell sorter (FACS) analysis was used to study the effects of dexamethasone on IL-6 receptor number in the well-differentiated human hepatoma HepG2.

RESULTS

Both IL-6 and TNF-alpha exerted a small stimulatory effect on alanine and glutamine transport. Dexamethasone alone did not alter transport rates, but pretreatment of cells augmented the effects of both cytokines on carrier-mediated amino acid uptake. Dexamethasone pretreatment and a combination of IL-6 and TNF-alpha resulted in a greater than twofold increase in transport activity. Fluorescent-activated cell sorter analysis demonstrated that dexamethasone induced a threefold increase in the expression of high-affinity IL-6 receptors.

CONCLUSIONS

Interleukin-6 and TNF-alpha work coordinately with glucocorticoids to stimulate amino acid uptake in human hepatocytes. Dexamethasone exerts a permissive effect on cytokine-mediated increases in transport by increasing IL-6 receptor expression on the cell surface. It is likely that this upregulation of IL-6 receptors "primes" human liver cells for subsequent stimulation by cytokines. The resulting increase in hepatic amino acid transport provides the liver with substrate to support key metabolic pathways during catabolic states.

Starvation and endotoxin act independently and synergistically to coordinate hepatic glutamine transport

OBJECTIVE

Because hepatic glutamine transport is markedly enhanced during critical illness, we tested the hypothesis that nutrient starvation and endotoxemia act coordinately to augment transport activity.

DESIGN

Fed or starved (48 hours) rats received Escherichia coli endotoxin (LPS, 10 mg/kg of body weight, intraperitoneally) or saline before hepatocyte isolation for measurement of glutamine transport.

MATERIALS AND METHODS

Hepatocytes were isolated from fed or fasted rats 4 hours after LPS treatment. [3H]glutamine uptake was measured and normalized to cellular protein. Data (mean +/- standard deviation, three separate determinations) were analyzed by Student's t test and analysis of variance.

MAIN RESULTS

Starvation induced a 1.6-fold increase in glutamine transport, while LPS treatment of fed rats increased transport activity 2.6-fold. Treatment of fasted animals with LPS induced a sixfold increase in glutamine transport. Kinetically, this effect in endotoxemic starved rats was mediated by both an increase in System N Vmax and the induction of a high affinity System A amino acid carrier which transports glutamine.

CONCLUSIONS

Starvation and endotoxemia regulate hepatocyte glutamine transport independently and synergistically. This hepatic response provides glutamine and other amino acids to support key metabolic pathways in the liver during critical illness.

The concentrations of free amino acids in human liver tissue obtained during laparoscopic surgery

The concentrations of the free amino acids in individual tissues gives information concerning amino acid, energy and protein metabolism. In muscle and intestinal mucosa, different metabolic states are distinctly characterized by an altered free amino acid pattern. Furthermore, the patterns are quite different in individual tissues. So far, liver tissue has not been investigated systematically in this respect. The aims of this investigation were to establish a standardized sampling procedure for liver tissue during laparoscopic surgery and to characterize the free amino acid concentrations in human liver tissue. Aspartate was the most abundant amino acid in the liver, followed by taurine, glutamine, glutamate, glycine and alanine. These six, and most abundant, amino acids constitute 90% of the total hepatic amino acid concentration. In the future, liver tissue sampling during laparoscopic surgery may be used as a model for investigating the influence of nutrition and hormones on hepatic amino acid and protein metabolism in man.

Prevention of skeletal muscle catabolism in sepsis does not impair visceral protein metabolism

We investigated whether the preservation of gastrocnemius proteins by interleukin-1 receptor antagonist (IL-1ra) during sepsis altered protein metabolism in visceral tissues. Sepsis was induced by creation of an abdominal abscess followed by infusion of saline of IL-1ra. Five days later, the tissue protein content and rate of protein synthesis were measured. IL-1ra did not significantly alter hepatic protein metabolism in septic or control animals. In kidney, the protein content and rate of protein synthesis were both decreased by sepsis and significantly ameliorated by the infusion of IL-1ra. Sepsis decreased the rate of protein synthesis in the small intestine. IL-1ra increased intestinal protein synthesis in both control and septic animals; however, the effects were localized to the seromuscular layer. The preservation of muscle protein by IL-1ra in sepsis did not adversely affect protein synthesis in any of the visceral tissues examined. IL-1 appears to mediate the sepsis-induced changes in protein synthesis in kidney and small intestine but not in liver or spleen. Protein synthesis in each visceral organ responds differently to the septic insult and modulation of IL-1 bioactivity.

Early postoperative change of plasma levels of amino acids in neonates with perforative peritonitis and its prognostic significance

As a possible prognostic index, plasma levels of amino acids were serially measured for 1 week in 22 neonates with perforative peritonitis including gastric rupture and necrotizing enterocolitis and 28 neonatal surgical patients without infection as a control, who were subjected to total parenteral nutrition with hypertonic glucose and amino acids formulated for neonates. Plasma levels of branched chain amino acids significantly increased on the first day after operation in peritonitis group, whereas plasma levels of phenylalanine and histidine increased on the third postoperative day and tyrosine increased seventh postoperative day. In the peritonitis group, 5 neonates died within 2 weeks after operation (early death group) because of cardiopulmonary failure and 5 neonates died with hyperbilirubinemia from 1 month to 6 months after operation (late death group). The early death group showed increased levels of total amino acids compared with those in the late death group and survivors. The late death group also showed higher levels of total amino acids than survivors. Plasma levels of tyrosine increased in the early and late death groups compared with survivors. These results indicated that serial measurements of plasma amino acids early after operation showed the existence of liver dysfunction in addition to the derangement of amino acid metabolism in the liver and muscle caused by septic insult, which predicted the prognosis of perforative peritonitis in neonates.

Normalization of tumor-induced increases in hepatic amino acid transport after surgical resection

BACKGROUND

The liver of the host with cancer requires increased amounts of amino acids to support the synthesis of glucose and key defense proteins. To study the effect of the growing tumor on hepatic amino acid uptake, the authors measured hepatic transport activity in tumor-bearing rats and in rats at various times after tumor resection.

METHODS

Fischer-344 rats were implanted subcutaneously with methylcholanthrene-induced fibrosarcoma cells (MCA sarcoma). When the tumors reached 10% of body weight, hepatic amino acid transport activity was assayed or the animals underwent surgical removal of the tumor. In animals that underwent tumor excision, livers were removed at 1, 3, or 5 days post-resection, and hepatic plasma membrane vesicles (HPMVs) were prepared. Nontumor-bearing pair-fed rats undergoing sham implantation or sham resection served as controls. System N (glutamine), System A (MeAIB), and System y+ (arginine) transport activity were assayed, which allowed the authors to compare differences in tumor-induced rates of transport and the influence of resection on transport activity.

RESULTS

System A transport activity was unaltered by tumor growth. In contrast, the presence of the growing tumor increased arginine and glutamine uptake by the liver. Hepatic glutamine transport remained elevated for 5 days after tumor resection, although by postoperative day 5 there was a trend toward normalization. In contrast, arginine transport remained increased by twofold onpost-resection day 1 and had normalized by postoperative day 3. The enhanced arginine transport was a result of an increase in maximal transport velocity (Vmax) rather than a change in carrier affinity.

CONCLUSIONS

Increases in hepatic amino acid transport normalize within several days of tumor resection, indicating a key role for the tumor in the induction of this response. The observation that hepatic glutamine transport activity remains augmented after tumor resection longer than any other transporter studied suggests a key role for this amino acid in overall hepatic nitrogen metabolism and may partially explain the persistent glutamine depletion that is characteristic of the tumor-bearing host.

Enhanced amino acid uptake in both skeletal muscle and liver by burn plasma in rats

The study was designed to test amino acid uptake in skeletal muscle after burn injury (up to 72 h). Also examined were the effects of plasma from burned rats over varying periods postburn (1-72 h), when plasma was added in vitro to incubated muscles and liver slices. Major burn injury (40 per cent total body surface area (TBSA)) was produced in male Sprague-Dawley rats weighing 60-80 g. Both soleus muscles were dissected intact at 1, 3, 6, 12, 24, 48 and 72 h postburn. Amino acid transport was measured by determining intracellular uptake of [3H] alpha-aminoisobutyric acid (AIB) during a 2 h incubation. In the second series of experiments, whole plasma from burned rats was added in vitro to incubated muscles and liver slices from healthy animals, and amino acid uptake was determined. AIB uptake in burned rat muscle was reduced by 24 per cent by 24 h postburn and 16 per cent by 48 h postburn. There was an increased effect from burn plasma on normal incubated muscles and liver slices, 72 per cent on muscles and 30 per cent on livers. Present results suggest an intrinsic decrease in amino acid uptake by muscle from burned rats. A factor or factors existed in plasma which increased both muscle and liver amino acid uptake postburn.

Independent and combined actions of interleukin-1 beta, tumor necrosis factor alpha, and glucagon on amino acid metabolism in the isolated perfused rat liver

Conflicting reports concerning the hepatic effects of interleukin-1 beta (IL-1 beta) and tumor necrosis factor alpha (TNF alpha) in the metabolic response to injury led us to investigate the influence of physiological concentrations of these cytokines on amino acid metabolism in the isolated perfused rat liver. IL-1 beta was ineffective at a concentration of 1 ng/mL, whereas TNF alpha (0.7 ng/mL) reduced the uptake of some of the main gluconeogenic amino acids (alanine, -55.3 +/- 4.9 v -72.9 +/- 13.7 nmol.min-1.g-1 in controls, P < .05) without affecting urea synthesis. TNF alpha increased glucose uptake by 237% and inhibited that of free fatty acids (-1.6 +/- 1.4 v -9.9 +/- 6.7 nmol.min-1.g-1 in controls, P < .05). IL-1 beta and TNF alpha potentiated glucagon-induced total amino acid uptake by 56% and 87%, respectively. They also affected glucagon-activated gluconeogenesis, leading to an initial potentiation of glucose release. Thereafter, IL-1 beta inhibited glucagon action, leading to an hepatic uptake of glucose. These results indicate that (1) in the conditions of the study, IL-1 beta has no direct effect on hepatic amino acid exchanges and utilization; (2) TNF alpha which exerted an inhibitory effect on these parameters, could be involved in the reduced amino acid exchanges during the end stage of sepsis; (3) the TNF alpha-induced increase in glucose uptake could be related to an inhibition of gluconeogenesis and/or to the activation of glucose utilization by Kupffer cells; (4) IL-1 beta and TNF alpha both potentiate the action of glucagon on hepatic amino acid uptake and utilization; and (5) complex interactions between Kupffer cells and hepatocytes on the one hand and between cytokines and hormones on the other hand could account for the differences in hepatic metabolism according to the stage of the response to injury.

Metabolic changes associated with malnutrition in the patients with multiple organ failure

To clarify the metabolic changes associated with malnutrition in the patients with multiple organ failure (MOF), we measured energy expenditure, nitrogen excretion, nonprotein respiratory quotient (NPRQ), caloric intake, and cumulative caloric balance (CCB) in 20 MOF patients (12 survivors and 8 non-survivors). The non-survivors exhibited significantly greater cumulative caloric deficit than the survivors. Metabolic activity tended to decline to normal in the survivors as organ failures were overcome. In the non-survivors, on the contrary, regardless of large caloric deficit hypermetabolism persisted and characteristically followed by the sudden decrease in metabolic activity at the time immediately prior to death. Compared to the survivors, the non-survivors generally exhibited poorer response in metabolic activity and greater NPRQ change to the altered amount of caloric intake. It seemed that protein sparing effect by increased caloric intake was preserved in both the survivors and the non-survivors only with CCB above -5 times basal energy expenditure. These results suggest that persistent hypermetabolism and poor metabolic response to nutritional support are partly responsible for existing organ failures and poor outcome in MOF patients.

Intestinal amino acid absorption during sepsis

Sepsis has been shown to cause a decrease in mesenteric blood flow in association with ultrastructural changes in the small intestine and impaired immune, barrier, and metabolic functions of the gut. These impairments in the structure and function of the gastrointestinal tract may have a detrimental effect on the morbidity and mortality of sepsis. Two recent studies have shown that the ability of the small intestine to absorb amino acids is also impaired during sepsis, but the systemic and cellular mechanisms of this impairment are not known. Release of cytokines induced by systemic bacteria or endotoxin may lead to a reduction in the synthesis of transporter proteins by the enterocyte at a time when there is reduced availability of both luminal (because of anorexia) and circulating (because of reduced mesenteric blood flow) substrates. Future research needs to investigate the systemic and local mediation of the sepsis-induced reduction in intestinal amino acid absorption and the possibility of correcting the defect by the administration of enteral nutrients, hormones, or drugs.

Tumor necrosis factor stimulates amino acid transport in plasma membrane vesicles from rat liver

Severe infection is characterized by a translocation of amino acids from the periphery to the liver, an event that is mediated in part by cytokines such as tumor necrosis factor-alpha (TNF). We investigated the activities of Na(+)-dependent transport systems A, ASC, and N in hepatic plasma membrane vesicles (HPMVs) prepared from rats treated with TNF in vivo. TNF did not alter sodium uptake but resulted in time- and dose-dependent fivefold and 50% maximal increases in system A and system N activity, respectively, in HPMVs secondary to an increase in the transport Vmax. Maximal increases in transport were observed 4 h after exposure to TNF and had returned to basal levels within 24 h. Similarly, system ASC activity was stimulated 80% in HPMVs from rats treated with TNF. Incubation of HPMVs from normal rats in vitro with TNF did not alter transport activity. Pretreatment of animals with the glucocorticoid receptor antagonist RU 38486 attenuated the TNF-induced enhancement in transport activity by 50%. The marked increase in Na(+)-dependent amino acid transport activity by TNF is mediated in part by the glucocorticoid hormones and represents an important mechanism underlying the accelerated hepatic amino acid uptake that occurs during critical illness.

Individual regulation of different hepatocellular functions during sepsis

The purpose of this study was to test the hypothesis that different hepatocellular functions are regulated individually during sepsis. This was done by simultaneously measuring bile production, release of liver transaminases, and synthesis of secreted proteins in perfused livers from control and septic rats. Sepsis was induced by cecal ligation and puncture (CLP); control rats were sham-operated. After 16 hours, livers were perfused in situ, and bile flow, synthesis rates of albumin and alpha 1-acid glycoprotein (a major acute-phase protein in rats), and release of glutamic-oxaloacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT) into perfusate were determined. Within the same livers, sepsis resulted in a 54% increase in the synthesis of alpha 1-acid glycoprotein and approximately 30% inhibition of albumin synthesis concomitant with 50% lower bile flow. The concentrations of GOT and GPT in the perfusate increased slightly during the experiments, both when control and septic livers were perfused. The maintained tissue levels of adenosine triphosphate (ATP) and the uptake of Evans blue dye by less than 1% of the hepatocytes, although a late test of viability, suggest that both control and septic livers remained viable during perfusion. The results are consistent with the concept that different hepatocellular functions are individually regulated during sepsis. Thus, impairment of certain hepatocellular functions does not necessarily imply generalized liver failure.

Surgical trauma, Candida infection, and serum proteolytic activity

Both surgical trauma and infection can disturb the proteinase to proteinase inhibitor balance in the circulation. We sought to assess the effect of Candida albicans infection (INFX) on postoperative mortality, to correlate mortality with total serum proteolytic activity (PA), and to assess the impact of exogenous proteinase inhibitors (PI) on this mortality. Mice underwent midline laparotomy (LAP) and immediate postoperative intravenous C. albicans infection. LAP + INFX shortened mean survival compared to INFX or LAP alone. Quantitative renal cultures confirmed that death in the LAP + INFX and INFX groups was due to Candida sepsis. PA was measured using an 125I-labeled protein assay, yielding micrograms of acid-soluble peptides/100 microliters of serum. In control, sham-operated, and LAP groups, PA averaged less than 9.0, and mortality was 0. In INFX and LAP + INFX groups, PA averaged greater than 14.5 and mortality was high. To determine if high PA was related to high mortality, LAP + INFX mice were treated immediately preoperatively with a single dose of PI (1 mg alpha 1-proteinase inhibitor, 1 mg antithrombin, and 1000 KIU aprotinin). Mean survival increased with PI treatment. In conclusion, the addition of Candida infection to surgical trauma hastened mean time to death. More rapid death correlated with elevated PA and may reflect systemic imbalance in the proteinase to proteinase inhibitor ratio in the circulation. PI improved survival, suggesting that proteinase inhibition may prove useful in the future in the treatment of fungal sepsis in surgical patients.

Enteral feeding in the critically injured patient

Metabolic support is an integral component in the care of the critically injured patient. When hypermetabolism occurs, there are increases in energy demands along with changes in substrate utilization. This article reviews the prospective randomized clinical trials that were undertaken at Denver General Hospital over the past decade that address both the timing of nutritional support and the route of administration in this critically injured population. Also discussed is a review of a meta-analysis that attests to the feasibility of early postoperative enteral feeding with the possibility of decreased septic morbidity in high-risk surgical patients. With the clinical knowledge gained from these trials, an algorithm for nutritional intervention was developed that represents our current standard of practice.

Immediate enteral nutrition following multisystem trauma: a decade perspective

Metabolic support is an integral component of surgical critical care. Although prompt restoration of oxygen availability is clearly essential, the timing, composition, and route of nutritional support may also be decisive factors. The ensuing discussion will focus on: (a) timing of substrate delivery and (b) route of administration based on our clinical investigation over the past decade. The acutely injured patient was selected as a model of ICU hypermetabolism because of relative homogeneity with respect to age, comorbid factors, and stress level. Our first study hypothesis was that early nutritional support would improve outcome in the severely injured, but previously well-nourished patient. During an 18-month period, all patients undergoing laparotomy with a abdominal trauma index (ATI) greater than 15 were randomized to a control or total enteral nutrition (TEN) group. The control patients were given total parenteral nutrition (TPN) after POD 5, whereas the TEN cohort had a needle catheter jejunostomy (NCJ) inserted at laparotomy and received an elemental diet within 12 hours. The control (n = 31) and TEN (n = 32) groups were otherwise comparable with respect to risk stratification. The TEN patients, of course, shared improved nitrogen balance (p less than 0.001), but also had significantly (p less than 0.025) less septic morbidity. Nine (29%) of the controls developed major infections, contrasted to three (9%) of the TEN patients. Acknowledging the benefit of early nutrition, the next issue we addressed was the optimal route of substrate delivery; i.e., TEN vs TPN. The hypothesis was that TEN, compared to TPN, would reduce the injury stress response as reflected by the prioritization of hepatic protein synthesis. TEN given via NCJ and a nutritionally matched TPN solution were administered during the same postoperative period. Indeed, the TEN patients (n = 23) had significantly (p less than 0.05) higher constitutive proteins and lower acute-phase proteins, whereas the TPN patients manifested the opposite protein profile as measured by crossed immunoelectrophoresis. In view of these findings, we continued the study to ascertain clinical impact. Ultimately, 75 patients were randomized, providing groups with equivalent risk factors. Eleven (37%) of the TPN patients developed septic complications compared to five (17%) of the TEN group, and the incidence of major infection was six (20%) following TPN vs one (3%) with TEN. Thus, immediate TEN provided an additional clinical benefit compared to early TPN in these high-risk surgical patients.

Multiple Organ Failure Syndrome—Part I: Epidemiology, Prognosis, and Pathophysiology

The multiple organ failure syndrome (MOFS) is the leading cause of death in intensive care units. Although sepsis is an important cause of MOFS, it is clear that MOFS can occur in the absence of infection. The pathophysiology of MOFS is complex and multifactorial and includes derangements in oxygen delivery and consumption, the release of inflammatory and vasoactive mediators capable of inflicting tissue damage, and alterations in the barrier function of the intestinal mucosa. Although advances have been made in our understanding of MOFS, treatment remains nonspecific and largely supportive. Early and aggressive restoration of tissue perfusion, adequate treatment of infection, timely nutritional support, and support of individual failed organs remain the mainstay of therapy. Therapeutic agents directed against the various mediators associated with the pathophysiology of MOFS may prove useful in the future.

Nutrition and metabolism in sepsis and multisystem organ failure

Sepsis and organ failure produce profound metabolic changes that contribute to hepatic and musculoskeletal failure. When multiple organ failure develops, the mortality rate is high, and therapy is unlikely to be effective unless the causative process (e.g., infection, low cardiac output) can be eliminated. Thus, the prevention of multiple organ failure and the prevention or early treatment of infection are paramount. Organ and nutritional support to prevent complications is necessary. The gastrointestinal tract should be used for nutrition whenever possible with a blenderized regular diet with fiber, glutamine, and short-chain fatty acids to protect and preserve the gut. If parenteral nutrition is necessary, special solutions may be necessary for the liver, kidneys, or lungs. If not, protein with 45% branched-chain amino acid, medium- and short-chain triglycerides, glutamine supplementation, and carbohydrates seem best. Other substances are being evaluated that may be helpful in nutrition and organ support, including arginine, xylitol, growth hormone, and anabolic steroids. Multiple organ failure should be prevented, if at all possible, by stopping or controlling the injury, removing as much necrotic tissue as possible, improving blood flow and oxygen consumption, supporting metabolism, and preventing infection or treating it early and adequately. Nutritional support plays a key role in preventing metabolic failure.

Tumour necrosis factor increases hepatic cell mass

The effect of tumour necrosis factor (TNF) on hepatic cellularity was investigated in male Wistar rats maintained on total parenteral nutrition. Twenty-eight rats were infused with TNF (2 x 10(5) units TNF-alpha kg-1 24 h-1) or saline (controls) for 6 days. Wet and dry liver weights and nitrogen content were significantly increased by TNF (P less than 0.001), indicating an increase in liver mass. A further 81 rats were infused with TNF (2 or 4 x 10(5) units kg-1 24 h-1) or saline over 1, 3 and 6 days. Total liver DNA and protein content and counts of hepatocyte mitosis were determined. Liver DNA and protein increased with dose of TNF and time (P less than 0.001), suggesting that TNF increased hepatic cellularity. Histological examination demonstrated no significant inflammatory infiltrate to account for the increased cell mass. However, the number of hepatocyte mitoses increased with dose of TNF and time (P less than 0.05), indicating that the increase in liver cellularity was due to increased hepatocyte cell number. TNF-induced hepatic hyperplasia appears to be an additional feature of the integrated host response to injury and infection.

Cytokines and glucocorticoids in the regulation of the "hepato-skeletal muscle axis" in sepsis

Sepsis results in muscle catabolism and peripheral release of amino acids with a concomitant uptake of amino acids in liver and acute-phase protein synthesis. In addition, there appears to be a cytokine-induced process that blocks muscle amino acid uptake in sepsis, further diverting amino acids from the periphery to the liver. In this article, evidence that cytokines and glucocorticoids play an important role in the regulation of hepatic and muscle protein metabolism during sepsis is presented.

Hepatic protein synthesis in a modified septic rat model

The aim of this study was to develop a reproducible and sustained sepsis model in rats, lasting 3-4 days and characterized by appropriate metabolic changes, including increased hepatic protein synthesis, consistent with an acute-phase response. The rat cecal ligation and puncture (CLP) model was modified by decreasing the size and number of cecal punctures and increasing fluid resuscitation, which resulted in a 60% survival rate at 96 hr compared to 20% for standard CLP. Cultures of blood and peritoneal fluid 96 hr following induction of sepsis were positive in all septic animals with a mixed aerobic and anaerobic flora but with predominant growth of Escherichia coli. Septic rats demonstrated increased serum lactate levels and leukocytosis, while serum glucose and resting energy expenditure were not different from controls. Hepatic protein synthesis, measured in vivo by flooding dose technique, was increased by 74% in septic animals. Synthesis of the acute-phase proteins alpha 1-acid glycoprotein, complement component C3, and transferrin, measured by incorporation of [14C]leucine into proteins during a 120-min isolated liver perfusion, was increased twofold in septic animals. The present modified CLP model in rats may be useful in studies on the regulation of acute-phase protein synthesis during prolonged sepsis and in experiments aimed at modulating the septic response in liver by different treatments.

Effect of sepsis on amino acid transport system A and its response to insulin in incubated rat skeletal muscle

The effect of sepsis on neutral amino acid transport systems A, ASC, and L, was studied in incubated rat soleus (SOL) muscles. We also examined the effects of plasma from septic rats and of varying concentrations of insulin (10 to 10(5) microU/mL), added in vitro to incubated muscles, on system A amino acid transport. Sepsis was induced by cecal ligation and puncture (CLP) in rats weighing 40 to 60 g. Control rats were sham-operated. System A activity was assessed by determining uptake of 2-(methylamino)isobutyrate (MeAIB) 16 hours after CLP or sham-operation. System ASC was studied by measuring uptake of alpha-aminoisobutyric acid (AIB) in the presence of 25 mmol/L MeAIB and 25 mmol/L 2-amino-2-norbornane carboxylic acid (BCH) to inhibit uptake by systems A and L. System L activity was defined as sodium-independent uptake of cycloleucine. MeAIB uptake was reduced by 28% in muscles of septic rats, while amino acid transport by systems ASC and L was almost identical in muscles from control and septic rats. Addition of plasma from septic rats to incubated normal SOL muscles inhibited MeAIB uptake by 31%. Addition of insulin to the incubation medium resulted in increased uptake of MeAIB, both in nonseptic and septic muscle. The lowest hormone concentration tested that significantly enhanced MeAIB uptake in nonseptic muscle was 10(2) microU/mL and in septic muscle 10 microU/mL. The results suggest that sepsis in rats specifically inhibits amino acid transport system A and that reduced muscle amino acid uptake may be caused by a circulating factor in sepsis.(ABSTRACT TRUNCATED AT 250 WORDS)