Fat Metabolism in Injury and Stress

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.

Nutrition and Nutritional Support in Critically Ill Patients

The use of intravenous nutritional support has increased dramatically in the last 20 years. Although it is not without controversy, administration of nutritional support is common practice in hospitalized patients including critically ill patients. Malnutrition continues to be reported in a significant number of hospitalized patients. The incidence of malnutrition in critically ill patients may be even higher than that reported in hospitalized patients overall. The consequences of malnutrition in a critically ill patient may be severe. Nutritional assessment and nutritional support can present special challenges to the intensivist. Techniques of nutritional assessment in critically ill patients are evaluated. Guidelines for the determination of the nutritional needs of these patients are outlined. Methods of delivery of nutritional support in critically ill patients are reviewed. Complications of nutritional support are discussed.

Metabolic modulators following trauma sepsis: Sex hormones

BACKGROUND

The development of metabolic perturbations following severe trauma/sepsis leading to decreased energy production, hyperglycemia, and lipolysis is often rapid. Gender is increasingly recognized as a major factor in the outcome of patients suffering from trauma/sepsis. Moreover, sex hormones influence energy, glucose, and lipid metabolism. Metabolic modulators, such as peroxisome proliferator-activated receptor-gamma coactivator-1 and peroxisome proliferator-activated receptor-alpha, which are required for mitochondrial energy production and fatty acid oxidation, are regulated by the estrogen receptor-beta and consequently contribute to cardioprotection following trauma hemorrhage. Additionally, sex steroids regulate inflammatory cytokines that cause hypermetabolism/catabolism via acute phase response, leading to increased morbidity and mortality.

MEASUREMENTS

This article examines the following: (1) the evidence for gender differences; (2) energy, glucose, and lipid metabolism and the acute phase protein response; (3) the mechanisms by which gender/sex hormones affect the metabolic modulators; and (4) the tissue-specific effect of sex hormone receptors and the effect of genomic and nongenomic pathways of sex hormones following trauma.

RESULTS AND CONCLUSIONS

The available information indicates that sex steroids not only modulate the immune/cardiovascular responses but also influence various metabolic processes following trauma. Thus, alteration or modulation of the prevailing hormone milieu at the time of injury appears to be a novel therapeutic adjunct for improving outcome after injury.

Nutritional support of the critically ill child

The pediatric metabolic response to injury and operation is proportional to the degree of stress and causes an increase in the turnover of proteins, fats, and carbohydrates. Thereby, substrates are made readily available for the immune response and wound healing. Because this process requires energy, the resting energy expenditure of ill patients increases. Whole-body protein degradation rates are elevated out of proportion to synthetic rates, and negative protein balance also ensues. Neonates and children are particularly susceptible to the loss of lean body mass and its attendant increased morbidity and mortality caused by an intrinsic lack of endogenous stores and greater baseline requirements. An appropriately designed mixed fuel system of nutritional support replete in protein does not quell this metabolic response but can result in anabolism and continued growth in ill children. In addition, the use of adequate analgesia and anesthesia is a readily available and proven means of reducing the magnitude of the catabolism associated with operation and injury. Finally, as hormonal- and cytokine-mediated metabolic alterations are better understood, therapeutic interventions may become available to directly modulate the metabolic response to illness, thus potentially further improving clinical outcome in pediatric surgical patients.

Effective and efficient nutritional support for the injured child

This article discusses the critical points in nutritional support of the injured child. Each applies currently understood basic science information to practical bedside care.

The metabolic needs of critically ill children and neonates

The pediatric metabolic response to injury and operation is proportional to the degree of stress and causes an increase in the turnover of proteins, fats, and carbohydrates. Thereby, substrates are made readily available for the immune response and wound healing. Because this process requires energy, the resting energy expenditure of ill patients increases. Whole-body protein degradation rates are elevated out of proportion to synthetic rates, and negative protein balance also ensues. Neonates and children are particularly susceptible to the loss of lean body mass and its attendant increased morbidity and mortality caused by an intrinsic lack of endogenous stores and greater baseline requirements. An appropriately designed mixed fuel system of nutritional support replete in protein does not quell this metabolic response but can result in anabolism and continued growth in ill children. In addition, the use of adequate analgesia and anesthesia is a readily available and proven means of reducing the magnitude of the catabolism associated with operation and injury. Finally, as hormonal- and cytokine-mediated metabolic alterations are better understood, therapeutic interventions may become available to directly modulate the metabolic response to illness, thus potentially further improving clinical outcome in pediatric surgical patients.

Metabolic consequences of sepsis. Correlation with altered intracellular calcium homeostasis

The availability of adequate substrate for energy homeostasis is a minimal requirement for vital organ function that normally is provided through dietary intake. When dietary sources of nutrients are inadequate, the body relies on alternate sources of energy provided by gluconeogenesis, lipolysis, and ketogenesis. Sepsis is associated with disruption of virtually all these provisional sources of energy substrate (see Fig. 4). In addition, sepsis impairs the function of the glycolytic pathway, the integrity of which is necessary for glucose to be used effectively for energy production. These abnormalities, coupled with disruption of the intracellular energy-producing machinery (e.g., glycolytic and gluconeogenic enzymes, mitochondria) eventually lead to a reduction in intracellular ATP. Furthermore, a reduction in intracellular ATP can undermine virtually all the energy-consuming functions of the cell, including energy substrate formation (e.g., failed gluconeogenesis), antioxidant production, and calcium homeostasis. High levels of intracellular calcium, in turn, are known to activate many potentially destructive enzymatic pathways (e.g., proteases, phospholipases, endonucleases) that further diminish cell function and may result in cell death. In this context, iCa2+ accumulation may play an important role in the progression from early sepsis to MODS, the most common cause of mortality in the ICU.

Weanling and adult rats differ in fatty acid and carnitine metabolism during sepsis

Increased oxidation of fat is an important host response to sepsis, and carnitine is essential for long-chain fatty acid oxidation. Because neonates have low levels of carnitine, their ability to respond to a septic insult may be impaired. The purpose of this study was to compare fatty acid and carnitine metabolism in septic weanling (60 to 85 g) and septic adult (285 to 310 g) rats. Sepsis was induced in weanling and adult male Sprague-Dawley rats by cecal ligation and puncture (CLP). The rats were killed 16 hours after CLP or sham operation, and serum glucose, lactate, beta-hydroxybutyrate, fatty acid, carnitine, liver fatty acid, and tissue carnitine levels were measured. The data suggest that during sepsis weanling rats may be more dependent on fatty acid oxidation than adult rats are, as evidenced by their elevated serum fatty acid and acylcarnitine levels, and relative hypoglycemia and hyperketonemia. In addition, although total serum carnitine levels were increased in both adult and weanling septic rats, tissue carnitine levels of weanling rats became significantly depleted during sepsis, unlike in adult rats. This study supports further investigation regarding the role of exogenous carnitine in newborn sepsis.

Nutritional support in the critical care setting (Part 1)

Over the past two decades nutritional support has rapidly become an integral part of the medical care of critically ill patients. As scientific evidence accumulates supporting the important role of underlying nutritional status in determining the eventual outcome of many illnesses, aggressive nutritional intervention has become commonplace in our medical and surgical ICUs. However, nutritional support, particularly parenteral alimentation, is expensive and associated with important morbidity and even mortality. Furthermore, definite evidence of its clinical efficacy under certain specific conditions is often lacking and in need of properly done prospective studies. This review summarizes the basic principles of nutrition as applied to the critically ill patient in the clinical setting. Special emphasis is on practical considerations regarding cost, efficacy (or lack thereof), and potential advantages, disadvantages, and risk of complications of each proposed approach.