Kevin J. Tracey

Cytokine production in a model of wound healing: The appearance of MIP-1, MIP-2, cachectin/TNF and IL-I

Macrophages are essential for normal wound repair and many of their effects on healing wounds are likely to be mediated by the secretion of cytokines. This study examines the appearance of messenger RNA (mRNA) for cachectin/tumor necrosis factor (TNF), IL 1, and macrophage inflammatory proteins 1 and 2 (MIP-1 and MIP-2), as well as the mature peptides, in a model of wound healing using wound chambers. RNA for all four cytokines can be detected in wound inflammatory cells by polymerase chain reaction amplification throughout the first 7 days. Cachectin/TNF and IL 1 protein levels peaked on the first day after wound chamber implantation, and MIP-1 and MIP-2 were detected only on day 3. The data suggest that these cytokines participate in the early inflammatory response to wounding.

Tumor Necrosis Factor and Regulation of Metabolism in Infection: Role of Systemic versus Tissue Levels

Abstract Tumor necrosis factor (TNF), a pleiotropic cytokine, is produced by macrophages and other cells in a variety of infectious and noninfectious diseases. Ultimately, the net biological effects of TNF may be either beneficial or injurious to the host. For instance, during overwhelming bacterial infection, the acute overproduction of TNF causes septic shock syndrome characterized by hypotension, organ failure, and death. Antibodies against TNF prevent and reverse these sequelae in animal models of septic shock, and their use in humans is currently under investigation in clinical trials. In another instance, TNF has been implicated as an injurious mediator in the state of malnutrition that complicates the course of chronic infection and cancer. Termed cachexia, this chronic syndrome inevitably causes the afflicted host to succumb from weight loss, anorexia, and catabolism of protein and lipid. Experimental studies of animals exposed to TNF for protracted periods indicate that this cytokine is capable of causing cachexia, and the biochemical basis for these catabolic changes has been identified. More recent data indicate that the detrimental metabolic effects of TNF are not dependent upon its circulating levels in the bloodstream, but rather are dependent upon its actions locally in vital organs (e.g., brain). Thus, the metabolic basis for cachexia in infection may be largely dependent upon the amount of cytokine produced in metabolically important tissues. As a result, circulating TNF levels in cachectic patients may not accurately reflect the metabolic state of the host, and do not correlate to weight loss. These and other studies have advanced our understanding of the role of TNF in the host response to infection, and it is hoped that this will foster the development of new therapies based on inhibiting its injurious effects.

Cachectin: a pluripotent hormone released during the host response to invasion.

Publisher Summary The two monokines, interleukin 1 (IL-1) and cachectin (tumor necrosis factor, TNF) are structurally distinct proteins that do not bind to the same receptor; however, they share many biological properties. This chapter focuses on cachectin/TNF because it has several unique properties that implicate it as an endogenous mediator of the catabolic state and shock observed in infected animals. The determination of the amino acid sequence of mouse cachectin revealed a surprising finding. In addition, the mouse cachectin had similar biological activity in killing the tumor cell line L929. Subsequent cloning studies have confirmed the identity of these two proteins: mouse TNF and mouse cachectin are identical. Cachectin has many physical similarities to IL-1; in addition, both of them also prompt a number of biological responses in common. This overlap in activity has been of interest as many of the properties once believed to be the domain of IL-1 exclusively are, in fact, shared with cachectin. Presumably, similar overlaps occur with other monokines and lymphokines as well.

Influence of substrate background on peripheral tissue responses to growth hormone

To evaluate the effects of substrate and hormonal background on the peripheral response to methionyl human growth hormone (met-hGH), metabolic measurements were performed in 10 normal subjects before and at the end of a 6-hr infusion of met-hGH. Five subjects were studied in the postabsorptive state and five were studied on the 10th day of intravenous repletion. Measurements of hormonal levels, serum amino acid levels, and free fatty acid levels, as well as extremity amino acid and free fatty acid fluxes, were performed. Met-hGH in the postabsorptive setting had no effect on extremity amino acid flux but significantly increased extremity free fatty acid efflux. In contrast, met-hGH in the background of intravenous feeding produced a significant extremity uptake of total amino acids but had no effect on free fatty acid flux. These data suggest a relationship between the substrate background and the actions of met-hGH on both peripheral protein and lipid metabolism. Therefore, the adequacy and composition of the feeding regimen may be important when considering growth hormone as an adjunct to nutritional therapy.

Peripheral tissue metabolism in man with varied disease states and similar weight loss.

The purpose of this study was to identify the effects of tumor burden and benign inflammatory disease on peripheral tissue metabolism independent of antecedent weight loss. This was accomplished by comparing forearm substrate flux profiles in cachectic cancer and benign disease patients to those of normal subjects before and after 10 days of total protein calorie depletion. Tumor-bearing patients (CA), benign disease patients (BD), and starved (ST) normal volunteers had similar weight loss. Resting energy expenditure was not significantly different between the study populations. Efflux of total amino acids (TAA [nmole/100 ml tissue-min]) decreased significantly (P less than 0.05) in the normals after 10 days of starvation (-886 +/- 185 postabsorptive (PA) vs -278 +/- 60 (ST]. CA patients had TAA efflux of -428 +/- 52 which was significantly (P less than 0.05) less than PA normals. In contrast, BD patients had a significantly (P less than 0.05) elevated TAA efflux of -895 +/- 165 compared to ST normals. CA patients had a significantly (P less than 0.05) elevated glucose uptake and lactate efflux compared to ST normals (glucose: +1.12 +/- 0.21 (CA) vs +0.11 +/- 0.09 (ST), lactate: -0.84 +/- 0.13 (CA) vs -0.38 +/- 0.13 (ST) [mumole/100 ml tissue-min]). The data suggest that tumor-bearing patients are able to maintain their peripheral tissue protein sparing adaptation to nutritional depletion in the presence of accelerated glucose utilization. However, clinically stable patients with benign disease do not demonstrate this adaptation and may be at greater risk for lean tissue dissolution than previously appreciated.

The influence of substrate background on the acute metabolic response to epinephrine and cortisol.

The acute metabolic effects of epinephrine and cortisol, as well as the influence of substrate background on the effects of these two hormones were investigated in normal subjects. While receiving a hypocaloric dextrose feeding (50 ng/kg/h) (DEX), the subjects received a 6-hour continuous intravenous infusion of epinephrine (30 ng/kg-min) (EPI), followed by a 6-hour infusion of a combination of epinephrine (30 mg/kg-min) and cortisol (3.0 microgram/kg-min) (EC). The hormone infusion was repeated 1 week after a continuous intravenous feeding regimen (TPN) was begun with a caloric content of 1.5 times the measured metabolic rate. Under both DEX and TPN, EPI produced increased energy expenditure, hyperglycemia, hyperlactic acidemia, and hypoaminoacidemia. Except for a further increase in circulating glucose levels during the DEX condition, these variables were not altered by the addition of cortisol. Epinephrine under both feeding conditions increased lactate efflux from the extremity without changes in peripheral oxygen or glucose uptake. The hypoaminoacidemic response to EPI in the DEX condition was associated with a decrease in extremity efflux of amino acids (-654 +/- 89 nmol/min/100 cm3 tissue at baseline vs -330 +/- 86 nmol/min/100 cm3 for EPI, p less than 0.05). No change in extremity amino acid flux was noted in response to EPI during total parenteral nutrition. Even with addition of cortisol no significant efflux of amino acids above baseline levels was noted in either feeding condition. We therefore conclude that (1) total parenteral nutrition cannot abolish the hypermetabolic or hyperglycemic response to epinephrine and cortisol; (2) increased extremity lactate efflux and lactic acidosis can occur in response to epinephrine without evidence of diminished oxygen delivery to the extremity; and (3) these two hormones are not primary mediators of acute extremity nitrogen loss.

Studies of Cachexia in Parasitic Infection

Chronic illness caused by infection with parasites, viruses, or bacteria is frequently associated with a potentially fatal syndrome termed “cachexia.” The stricken host dies from progressive weight loss, anemia, immune suppression, and terminal organ injury, even when the invasive burden may be relatively small. Until recently the biochemical basis of these harmful effects of infection‐associated cachexia was not understood. They are now known to be mediated primarily by endogenous factors released in response to invasive infection. The search for these mediators led to the identification, isolation, and cloning of the cytokine known as cachectin/TNF (tumor necrosis factor).

The Biochemical Basis of Cachexia of Infection

It is the same with phthisis ( tuberculosis ): in the beginning it seems scarcely a slight indisposition; in its last stages it strikes down the strongest man, it devours, consumes and reduces to a skeleton those whose plumpness, freshness and health appear inalterable.

Cachectin/TNF: A Mediator of Lethal Endotoxemia

Invasive infections and bacteremia frequently precipitate the syndrome of sepsis which is a serious complication of an increasing number of medical treatments and surgical procedures. The incidence of sepsis is difficult to quantify, but this syndrome is estimated to cause 20,000 – 60,000 deaths per year in the United States (1). Advances in medical technology for the treatment of critically ill patients with sepsis have led to the use of antibiotics for the eradication of the infectious focus and additional modes of long-term support for end organ failure. However, the mortality of sepsis has remained high (30–50%). Current investigations are extending our understanding of the mechanisms involved during sepsis and may lead to the development of new therapeutic modalities.

T Cell Subpopulations Following Thermal Injury Effect of the Acute Stress Response

In his now famous treatise of 1897, “Adaptation in Pathological Processes,” Doctor William Welch discussed the dynamic physiologic and evolutionary mechanisms at work in an organism’s adaptive response to various 1ife-threatening pathologic processes. In his paper, Doctor Welch aptly suggested: that the adaptability of this mechanism to bring about useful adjustments has been in large part determined by the factors of organic evolution, but that in only relatively few cases can we suppose these evolutionary factors to have intervened on behalf of morbid states. For the most part, the agencies employed are such as exist primarily for physiologic uses, and while these may be all that are required to secure a good pathologic adjustment, often they have no special “fitness for this purpose”