Leukocyte Endogenous Mediator Research Articles

Protein malnutrition and leukocyte endogenous mediator.

Journal Article Protein Malnutrition and Leukocyte Endogenous Mediator Get access Nutrition Reviews, Volume 41, Issue 8, August 1983, Pages 242–244, https://doi.org/10.1111/j.1753-4887.1983.tb07187.x Published: 01 August 1983

The Systemic Inflammatory Response to Cardiopulmonary Bypass

The Systemic Inflammatory Response to Cardiopulmonary Bypass

Cytokines, muscle proteolysis, and the catabolic response to infection and inflammation.

Apart from fever, the most striking characteristic of infection to the layman and the professional alike are the development of anorexia and associated weight loss. Although the unintentional weight loss is composed of both fat and lean tissue, it is the loss of the lean tissue representing protein (nitrogen) that has the greatest clinical impact. The relationship among inflammation and infection, protein metabolism, and endogenous mediators has been both a general research interest for others and a personal one of this laboratory for some time.Early studies demonstrated a catabolic nitrogen response to fever and infection (1, 2). Still other investigators reported that factors derived from white blood cells, which were at that time collectively termed leukocyte endogenous mediator (LEM), could be identified and postulated their role in these responses (3, 4). LEM was considered to be a group of low molecular weight, heat-labile proteins that were synthesized and released by circulating and fixed monocyte...

Leukocyte endogenous mediator fails to alter protein dynamics in a model of liver dysfunction.

This study examines the effect of a purified leukocyte-derived endogenous mediator (LEM) on protein metabolism during liver dysfunction and after sham surgery and the role of a nonsteroidal, antiinflammatory drug (indomethacin sodium trihydrate) in modifying this response. Febrile response, protein kinetics, urinary end products of protein metabolism, and plasma acute phase protein levels were studied in rats given a pyrogenic dose of LEM or saline solution, and these same indicators were studied after the administration of the same dose of LEM plus 2 mg/kg indomethacin 3 weeks after a portacaval shunt (PCS) or sham operation. In both surgical groups given LEM, a maximum of 1.1 degrees C fever was observed. LEM increased protein turnover and urinary excretion of nitrogen and urea in sham-operated rats but not in the PCS animals. Administration of indomethacin decreased the plasma oxidation of L[1-14C]leucine and prevented the increased excretion of total nitrogen and urea in sham-operated animals treated with LEM. PCS animals showed a constant excretion of nitrogen and urea independent of treatment. alpha 1-Acid glycoprotein levels increased significantly in sham-operated animals treated with LEM but not in the PCS group until indomethacin was added. The coadministration of LEM and indomethacin in shams also enhanced the levels of alpha 2-macroglobulin and alpha 1-acid glycoprotein over values found with LEM alone. These findings confirm the catabolic effect of LEM in normal animals and identify the essential role of the liver in the acute phase response. The data also suggest that indomethacin may modify the acute phase response by reducing plasma amino acid oxidation as well as enhancing the levels of some specific acute phase proteins.

Induction of metallothionein synthesis in human peripheral blood leukocytes

Metallothionein (MT), a low molecular weight, metal-binding protein, has recently been shown to protect murine mononuclear phagocytic cells from the cytotoxic effects of bacterial lipopolysaccharides (LPS), the endotoxic component of Enterobacteriaceae. MT appears to function intracellularly as an antioxidant since autolysis results from lipid peroxidation initiated by free radicals of O2. Since this activity is distinct from MT's capacity to specifically sequestrate heavy metals, we examined whether MT synthesis can be induced by direct membrane activation or through interaction with soluble leukocyte mediators. Normal human monocytes, polymorphonuclear neutrophils (PMN), and lymphocytes, isolated from heparinized whole blood, were incubated with and without LPS from Escherichia coli and Salmonella typhosa. MT in cell lysates was quantitated using a 203Hg-binding assay employing Sephadex G-10 "minicolumns." When incubated with monocytes, PMN, or lymphocytes, neither preparation of LPS (10-100 micrograms/ml) was capable of enhancing 203Hg-binding activity after 24 or 72 hr incubation. CdCl2 (2 micrograms/ml), however, increased binding activity in monocyte and lymphocyte cultures 4- and 15-fold, respectively. When monocytes and lymphocytes were cocultured with LPS, 203Hg-binding activity was not enhanced. Addition of human interleukin 1 (endogenous pyrogen) to these cultures had no significant effect. Leukocyte endogenous mediator (LEM), a product of LPS-activated PMN that possesses hypozincemic activity in vivo, did not induce MT synthesis. Collectively, these results demonstrate that leukocyte MT does not arise from direct LPS activation or from interaction with products secreted by LPS-activated cells. De novo synthesis of MT observed during endotoxemia and gram negative sepsis appears, therefore, to be induced by endogenously released corticosteroids.

Changes in protein synthesis due to an inflammatory challenge.

Rates of protein synthesis in various chick tissues were examined 16 hr after an inflammatory challenge. Protein synthetic rates were calculated from the rate at which [14C]leucine was incorporated into protein and the specific activity of [14C]leucine in the precursor pool. An injection of either Escherichia coli or sheep red blood cells (SRBC) decreased the rate of protein synthesis in the gastrocnemius muscle, and increased the rate in liver, bursa, spleen, and thymus. E. coli, but not SRBC, decreased protein synthesis in the pectoralis muscle. E. coli significantly decreased the aggregation of pectoralis muscle polysomes and increased the aggregation of polysomes in the thymus, bursa, and spleen. E. coli increased the aggregation of free, but not bound, polysomes in liver, suggesting an increase in synthesis of export proteins. SRBC significantly increased polysomal aggregation in bursa and spleen only. A crude preparation of leukocyte endogenous mediator, isolated from peritoneal macrophages, decreased muscle-polysomal aggregation. These studies indicate that tissue-specific changes in protein synthesis occur after a noninfectious inflammatory challenge. These changes may be part of a homeostatic mechanism which supports the immune response.

In vitro leukocyte endogenous mediator production is not impaired following surgical stress in moderately malnourished patients.

Leukocyte endogenous mediator (LEM), a protein produced by phagocytizing cells, plays a critical role in the metabolic response to injury and infection. There is an important interaction between protein-calorie malnutrition and the capacity of cells to produce LEM, since severely malnourished or severely stressed individuals, have a reduced capacity to produce LEM. The leukocytes of 10 mildly to moderately malnourished patients undergoing elective major surgery, a moderate stress, had an intact ability to produce LEM on preoperative assessment. This ability was not affected by a 5-day postoperative period of hypocaloric nutrient intake despite a significant loss of body protein in one-half of the patients and a significant fall in serum protein concentrations. These results suggest a high biologic priority for LEM production during the metabolic response to injury and for infection.

A rationale for administering leukocyte endogenous mediator to protein malnourished, hospitalized patients

Leukocyte endogenous mediator is a low molecular-weight protein synthesized by circulating monocytes and fixed macrophages of the reticuloendothelial system. Exogenous administration of leukocyte endogenous mediator to a well-nourished animal stimulates both specific and nonspecific immune function and replicates the protein metabolic response to infection, characterized by fever and increased amino acid oxidation, skeletal protein degradation and synthesis of “acute-phase” proteins. Leukocyte endogenous mediator administration also affords protection against semilethal doses of bacteremia in the well-nourished animal. In the protein-depleted host, synthesis or release of leukocyte endogenous mediator in response to infection appears to be reduced and the attenuated metabolic response may be attributed, in part, to a deficit in its production. However, nutritional repletion of the malnourished patient results in restoration of the capacity to produce leukocyte endogenous mediator usually within three to seven days, if adequate dietary protein is provided. Since protein malnutrition is associated with increased incidence and severity of bacterial infections, we postulate that the reduced synthesis and/or release of leukocyte endogenous mediator in protein malnutrition is detrimental. In those critically-ill, malnourished patients who cannot endogenously synthesize leukocyte endogenous mediator, and for clinical reasons cannot be repleted rapidly or are already infected and/or undergoing operative stress, exogenous administration of leukocyte endogenous mediator should be considered along with nutritional support. Administration of this protein to a seriously-ill malnourished individual should produce a metabolic profile of fever, increased urinary nitrogen excretion and falls in serum albumin concentrations that are generally considered pathologic. However, administration of leukocyte endogenous mediator over short periods of time should also provide the anabolic impetus for the augmented synthesis of proteins beneficial to recovery. In most cases, these countervailing forces of anabolism and catabolism should be of benefit to the host if the response to infection and injury is viewed as a physiologic redistribution of endogenous nutrients to meet the more critical and immediate needs of the stressed patient.

Leukocyte endogenous mediator alters protein dynamics in rats

Leukocyte endogenous mediator (LEM), a low-molecular-weight peptide synthesized by monocytic cells during phagocytosis, has been implicated as the host's initiator of the protein metabolic response to infection and inflammation. To determine whether administration of LEM would alter protein kinetics, appearance and oxidation of plasma tyrosine as well as the rates of protein synthesis in liver and skeletal muscle were determined in fasted rats that received a 30-hour continuous infusion of either physiologic saline, LEM, or heat-inactivated LEM. The LEM was obtained from rabbit peritoneal exudate and the treatment solutions supplied 2.8 × 10 8, cell equivalents 100 g of body weight (BW) per day. Endogenous tyrosine oxidation increased from 4.0 ± 0.4 μ mol 100 g , BW/h to 5.4 ± 0.7 μ mol 100 g , BW/h in animals infused with heat-inactivated LEM and to 7.5 ± 1.5 μ mol 100 g , BW/h in rats receiving LEM ( P < 0.01). Nonsecretory protein synthesis in the liver was greatest in rats administered LEM (2239 ± 325 mg/d) when compared with control groups receiving physiologic saline (1122 ± 195 mg/d) or heat-inactivated LEM (1374 ± 62 mg/d; P < 0.01), whereas skeletal protein synthetic rates were unchanged. Rates of muscle and collagen protein breakdown were estimated from the urinary excretion rate of N t-methylhistidine and hydroxyproline, respectively, and their excretion rose by 30% ( P < 0.05) and 42% ( P < 0.05) with LEM administration. These results suggest that administration of LEM stimulates a mobilization of amino acids from peripheral tissues to support increased visceral protein anabolism while whole body amino acid oxidation is also enhanced. Since similar effects follow fever and infection, these results suggest that LEM may play an underlying role in the protein metabolic response to infection and inflammation.

Effect of leukocyte endogenous mediator(s) on insulin and substrate profiles in the fasted rat

There has been increasing evidence that a group of mediators derived from phagocytes are involved in many aspects of the metabolic response to various illnesses and infections. The purpose of this study was to investigate the ability of leukocyte endogenous mediator(s) (LEM(s)) to alter energy metabolism as reflected by changes in serum insulin, whole blood glucose, β-hydroxybutyrate, and serum free fatty acid levels. Administration of rabbit LEM intravenously to the fasted rat produced hyperthermia and leukocytosis. During the subsequent 6 hr there was a 60% reduction in serum free fatty acids from 1.77 ± 0.25 μeq/ml ( P < 0.05) and a progressive decline in whole blood β-hydroxybutyrate levels ( P < 0.05 at 6 hr). At the same time both whole blood glucose and serum insulin concentrations were significantly increased (blood glucose from 4.27 ± 0.58 to 5.93 ± 0.09 m M at 3 hr and serum insulin from 21 ± 2 to 36 ± 5 mU at 6 hr). Since similar changes occur following most acute bacterial infections, it is postulated that LEM may also initiate the insulin and energy substrate responses to infection.

Hypothesis: leukocyte endogenous mediator/ endogenous pyrogen/lymphocyte-activating factor modulates the development of nonspecific and specific immunity and affects nutritional status

We postulate that leukocyte endogenous mediator/endogenous pyrogen/lymphocyte-activating factor (LEM/EP/LAF) integrates the host's nonspecific and specific immune responses to infection by virtue of the panoply of physiological and metabolic activities it is capable of eliciting. The alterations in systemic metabolism modulated by LEM/EP/LAF, although apparently of value to the host in the defense against infection and the repair of tissue damage, result in negative nutrient balances. Severe infections, alone or in conjunction with injury, may result in malnutrition unless the patient is adequately nourished. Preexisting nutritional deficits can compromise host resistance to infection, in part by preventing production of LEM/EP/LAF. Additional studies of the sequelae of LEM/EP/LAF action and effects of nutrition on host resistance to infection appear warranted.

Investigation of an inflammatory humoral factor as a stimulator of fibrinogen synthesis

A purported stimulatory effect on fibrinogen synthesis of pyrogenic crude leukocyte extract (CLE) is controversial. To clarify this issue, a study was made of possible inflammatory cellular or humoral factors as stimulators of fibrinogen synthesis. Relative fibrinogen synthesis ratios were calculated by comparing the rate of incorporation of radiolabeled lysine into fibrinogen with that of incorporation into albumin. Significant increases in the ratio over baseline values were observed in rabbits after i. v. administration of CLE derived from 0.99 – 3. 35×10 9 homologous leukocytes harvested from inflammed rabbit peritoneal cavities (0.146±0.038 control and 0.249±0.119 after CLE, p<0.01). Wash fluid which was used to collect the peritoneal leukocytes was also infused and found to increase ratios above baseline (0.118±0.052 control and 0.226±0.094 after inflammed peritoneal, wash fluid). This difference, however, was only borderline statistically significant (p = 0.05). In contrast, no significant increases above baseline were observed in the ratio following intravenous administration of 1) blood leukocyte derived CLE, 2) intact blood leukocytes, or 3) plasma, all harvested from turpentine or glycogen injected animals. These data suggest that at inflammatory sites, granulocytes produce a mediator(s) which increases fibrinogen synthesis during inflammation. It is well known that during many types of inflammation plasma fibrinogen concentration increases. However, little is known of the mechanisms which mediate increased fibrinogen synthesis during inflammation. Pyrogenic substances released from rabbit granulocytes have been reported to cause increases in serum acute phase proteins in recipient rats (1–3). These factors, variably called leukocyte endogenous mediator (LEM), leukocyte pyrogen (LP), or crude leukocyte extract (CLE), have also been reported by Bocci (4) to result in an increase in plasma fibrinogen concentration over controls when given in “significant” amounts to homologous recipient rabbits. On the other hand, Seligsohn (5), while using a similar homologous rabbit model, failed to demonstrate a significant increase in plasma fibrinogen concentration or synthesis following CLE administration. With this controversy in mind, we investigated the possible existence of a cellular or humoral stimulator of fibrinogen synthesis during inflammatory states in a homologous rabbit system. As potential sources of mediator, we sampled materials from a site of inflammation. These were crude leukocyte extract derived from leukocytes and wash fluid from the peritoneum after sterile peritonitis was induced in rabbits. In addition, we sampled materials distant from the site of inflammation. These were peripheral blood, buffy-coat leukocytes and plasma as well as crude leukocyte extract derived from buffy-coat leukocytes. The effect of the infusion of these homologous experimental materials on fibrinogen synthesis was measured by determining the relative fibrinogen synthesis rate as adapted from that described by Koj (6). With this technique, the amount of incorporation of radiolabeled lysine into fibrinogen is compared to that of its incorporation into albumin during the same measurement period. Albumin is used since it is a non-inflammatory protein (6). The relative synthesis rate of fibrinogen (fg) versus albumin (alb), or fg/alb ratio, approximates the ratio of the absolute synthesis rate of the two proteins. Unlike techniques following 15Se-methionine incorporation into fibrinogen (7), this method allows sequential use of 3H and 14C-lysine permitting both a baseline control and experimental study in the same animal. Increases above control of this ratio indicates an increase in synthesis rate of fibrinogen. This method also has advantages over measuring changes in fibrinogen concentration, because it is faster and more sensitive.