Interleukin-6 infusion during human endotoxaemia inhibits in vitro release of the urokinase receptor from peripheral blood mononuclear cells

Leucocyte expression of the urokinase receptor [urokinase-type plasminogen activator receptor (uPAR)] is regulated by inflammatory mediators. This study investigated the in vivo effect of endotoxin, interleukin (IL)-6 and tumour necrosis factor (TNF)-alpha on uPAR-release in vivo and in vitro in humans. Healthy subjects received intravenous endotoxin injection [high-dose, 2 ng/kg (n=8) and low-dose, 0.06 ng/kg (n=7)], coadministration of 0.06 ng/kg endotoxin and 3 h recombinant human (rh)IL-6 infusion (n=7) or 3 h infusion of rhIL-6 (n=6), rhTNF-alpha (n=6) or NaCl (n=5). Soluble uPAR (suPAR) was measured by enzyme-linked immunosorbent assay in plasma and supernatants from unstimulated and phytohaemagglutinin and lipopolysaccharide-stimulated peripheral blood mononuclear cell (PBMC) cultures incubated for 24 h. The spontaneous and stimulated uPAR-release from PBMC cultures was enhanced 5 h after low-dose endotoxin (both P <0.05), but coadministration of rhIL-6 during low-dose endotoxaemia abolished this enhanced uPAR release. High-dose endotoxin increased plasma suPAR levels (P <0.001) whereas low-dose endotoxin, rhIL-6 or TNF-alpha did not influence uPAR release in vivo to such degree that a systemic effect on the plasma suPAR level was detectable. Even subclinical doses of endotoxin in vivo enhance the capacity of PBMC to release uPAR after incubation in vitro. The inhibitory effect of IL-6 on endotoxin-mediated uPAR-release in vitro suggests that IL-6 has anti-inflammatory effects on endotoxin-mediated inflammation.     

Common studied polymorphisms do not affect plasma cytokine levels upon endotoxin exposure in humans

The aim of this study was to investigate to what extent single nucleotide polymorphisms (SNPs) in promoter regions of genes of Toll-like receptor (TLR)-4, tumour necrosis factor (TNF)-alpha, interleukin (IL)-18, interferon (IFN)-gamma, IL-6 and IL-10 affect the cytokine response during a controlled low-grade inflammatory response in vivo. Two hundred healthy young male volunteers were genotyped, and cytokine levels were measured in response to a low-dose intravenous bolus of Escherichia coli endotoxin. No association was detected between SNPs (TLR-4299, TLR-4399, TNF-308, IL-18-137, IL-18-607, IFN-gamma+874, IL-6-174, IL-10-592 and IL-10-1082) and endotoxin-induced changes in plasma levels of TNF-alpha, IL-6 and IL-10. IL-18 levels were unaffected by endotoxin. In conclusion, the investigated SNPs did not affect endotoxin-induced low-grade cytokine production of TNF-alpha, IL-6, IL-18 or IL-10 in healthy young men. Previous reports of a major heritability factor in the inflammatory response may be due to other target genes or effects in older age groups or women.     

Short-term simvastatin treatment has no effect on plasma cytokine response in a human in vivo model of low-grade inflammation

Statins reduce plasma cholesterol, but clinical trials and in vitro studies indicate that they might also possess anti-inflammatory properties. The effect of simvastatin on circulating cytokines and leucocytes was evaluated in a human in vivo model of low-grade inflammation. Thirty young healthy male participants received an injection of the bacterial cell wall product endotoxin (0.06 ng/kg) to induce systemic inflammation. Participants were then randomized into a control and a simvastatin group. The simvastatin group received simvastatin 20 mg daily for 14 days. All participants returned after 14 days to receive a second endotoxin injection. Plasma concentrations of tumour necrosis factor (TNF)-alpha, interleukin (IL)-6 and IL-1 receptor antagonist were measured by enzyme-linked immunosorbent assay (ELISA) before and hourly for 6 hours after endotoxin administration. Plasma cytokines as well as total leucocyte counts increased in all participants upon endotoxin challenge but were not affected by simvastatin treatment. Tolerance to endotoxin was observed in both groups after 14 days. Short-term treatment with simvastatin (20 mg/day) did not influence circulating cytokine levels during endotoxaemia in this human in vivo study.     

Ageing is associated with a prolonged fever response in human endotoxemia

The purpose of this study was to investigate whether an age-associated impaired acute-phase response exists. Nine healthy elderly volunteers (median, 66 years; range, 61 to 69 years) and eight young controls (median, 24 years; range, 20 to 27 years) were given an intravenous bolus of endotoxin (2 ng/kg). The rectal temperature was monitored continuously, and blood samples for cytokine measurements were obtained before endotoxin administration as well as 0.5, 1, 1.5, 2, 3, 4, 8, 12, and 24 h after the injection. The elderly subjects showed a more prolonged fever response compared to the young controls. Levels of tumor necrosis factor alpha (TNF-alpha), soluble TNF receptors (sTNFR-I), interleukin-6 (IL-6), IL-8, IL-10, and IL-1 receptor antagonist (IL-1ra) in plasma increased markedly following endotoxin administration in both groups. The elderly group showed larger initial increases in TNF-alpha and sTNFR-I levels and prolonged increased levels of sTNFR-I. Monocyte concentrations decreased in both groups, with the elderly group showing a more rapid decrease and a slower subsequent increase than did the young group. Furthermore, the elderly group had a more rapid increase in C-reactive protein levels than did the young group. In conclusion, ageing is associated with an altered acute-phase response including initial hyperreactivity, prolonged inflammatory activity, and prolonged fever response.     

Cholecystokinin blockade alters the systemic immune response in rats with acute pancreatitis

Acute pancreatitis (AP) is characterized by initial pancreatic injury resulting from the activation of digestive enzymes and, later, widespread inflammation to distant organs. The aim of this study was to study whether the time-course of inflammatory events during AP induced by bile-pancreatic duct obstruction (BPDO) varies after lowering the acinar enzyme content by L364,718 (0.1 mg/kg/day) administration over 7 days before inducing AP. Flow cytometric immunophenotyping was used to analyse the following at different AP stages: distribution of major circulating leucocyte subsets, activation state of circulating neutrophils and monocytes as reflected by CD11b expression and tumour necrosis factor-alpha (TNF-alpha) production and the contribution of T-cell-derived pro-(TNF-alpha) and anti-(IL-10) inflammatory mediators. TNF-alpha plasma levels and neutrophil infiltration in pancreas and lung were also measured. At early BPDO times, L364,718 treatment partially inhibited leukocytosis and increase in peripheral blood neutrophils and monocytes as well as TNF-alpha expression by monocytes. However, from 6 h onwards after BPDO, L364,718 treatment was unable to prevent either pancreatic and lung neutrophil infiltration or the release of TNF-alpha from activated monocytes. By its action on circulating lymphocytes, L364,718 treatment enhanced the severity of the inflammatory response induced by BPDO. Peripheral blood lymphocytes were recruited from earlier BPDO times, and 12 h after BPDO, T cells displayed a significantly higher reserve of TNF-alpha able to be released under stimulation but lower functional reserve of interleukin-10 (IL-10) than observed in untreated rats. It is concluded that lowering the acinar enzyme content through L364,718 treatment prevents earlier systemic immune events in BPDO-induced AP. However, at the point of maximal injury, the inflammatory response became pronounced, largely due to the role played by activated T lymphocytes.     

Differential effects of prophylactic,concurrent and therapeutic lactoferrin treatment on LPS-induced inflammatory responses in mice

Mice injected with endotoxin develop endotoxaemia and endotoxin-induced death, accompanied by the oxidative burst and overproduction of inflammatory mediators. Lactoferrin, an iron binding protein, provides a natural feedback mechanism to control the development of such metabolic imbalance and protects against deleterious effects of endotoxin. We investigated the effects of intraperitoneal administration of human lactoferrin on lipopolysaccharide (LPS)-induced release of tumour necrosis factor alpha (TNF-alpha), interleukin 6 (IL-6), interleukin 10 (IL-10) and nitric oxide (NO) in vivo. Lactoferrin was administered as a prophylactic, concurrent or therapeutic event relative to endotoxic shock by intravenous injection of LPS. Inflammatory mediators were measured in serum at 2, 6 and 18 h post-shock induction. Administration of lactoferrin 1 h before LPS resulted in a rather uniform inhibition of all mediators; TNF by 82%, IL-6 by 43%, IL-10 by 47% at 2 h following LPS injection,and reduction in NO (80%) at 6 h post-shock. Prophylactic administration of lactoferrin at 18 h prior to LPS injection resulted in similar decreases in TNF-alpha (95%) and in NO (62%), but no statistical reduction in IL-6 or IL-10. Similarly, when lactoferrin was administered as a therapeutic post-induction of endotoxic shock, significant reductions were apparent in TNF-alpha and NO in serum, but no significant effect was seen on IL-6 and IL-10. These results suggest that the mechanism of action for lactoferrin contains a component for differential regulation of cellular immune responses during in vivo models of sepsis.     

Intratracheal injection of endotoxin and cytokines. II. Interleukin-6 and transforming growth factor beta inhibit acute inflammation.

The nature of the endogenous mediators that down-regulate and curtail the exodus of neutrophils into local acute inflammatory sites is unknown. In the present report, interleukin-6 (IL-6) and transforming growth factor beta (TGF beta), members of a family of macrophage-derived proteins known as cytokines, are shown to inhibit significantly the acute neutrophilic exodus caused by an intratracheal injection of endotoxin (LPS), a proinflammatory component of the cell walls of gram-negative bacteria. Transforming growth factor beta (10 micrograms) and IL-6 (10 micrograms) coinjected intratracheally with LPS (10 micrograms) each inhibited the number of neutrophils in 6-hour bronchoalveolar lavage (BAL) specimens by approximately 50%. The intratracheal coinjection of IL-6, TGF beta, and LPS inhibited the LPS-induced neutrophilic inflammatory exodus by nearly 75%. Interleukin-6 also is shown to be endogenously upregulated within the lung after intratracheal challenge with endotoxin, providing evidence that IL-6 may represent an endogenous negative feedback mechanism to inhibit endotoxin-initiated cytokine-mediated acute inflammation. Interleukin-6 and TGF beta both strongly inhibited the quantity of TNF-alpha recovered in the BAL fluid of LPS-challenged rats, suggesting that downregulation of LPS-induced TNF-alpha production within the lung represents one mechanism whereby IL-6 and TGF beta exert an antiinflammatory action. Interleukin-6 and TGF beta represent novel pharmacologic and, probably, endogenous inhibitors of acute inflammation.     

Endotoxin administration to humans primes alveolar macrophages for increased production of inflammatory mediators

To elucidate potential mechanisms of the acute lung injury associated with endotoxemia, we evaluated the effect of intravenously administered endotoxin on the ability of alveolar macrophages isolated by bronchoalveolar lavage from normal subjects to produce inflammatory mediators. Within 1 hr of endotoxin (4 ng/kg body weight) administration, all 12 study subjects developed constitutional symptoms and leukopenia, and within 3 hr, lowgrade fever. Resolution of symptoms and fever by 6 hr was accompanied by systemic granulocytosis. Although intravenously administered endotoxin appeared to activate a subset of circulating monocytes, it did not alter the bronchoalveolar lavage cell number, phenotype (95% macrophages), or constitutively expressed high levels of surface HLA-DR and O ₂ ^– . In contrast, intravenous endotoxin primed the alveolar macrophages for enhanced lipopolysaccharide-induced secretion of interleukin-1 (11.8 to 25.8 U/ml;P=0.04), tumor necrosis factor- (titer, 6.8 to 13.6;P=0.20), and prostaglandin E₂ (38.4 to 116.3 ng/ml;P=0.035). These results demonstrate that low-dose intravenous endotoxin primes human alveolar macrophages, which are already differentiatedin situ, for enhanced secretion of inflammatory mediators. Such mediators may contribute to the pulmonary changes associated with endotoxemia and acute lung injury.     

IL-8 as a circulating cytokine: induction by recombinant tumour necrosis factor-alpha.

Tumour necrosis factor-alpha (TNF-alpha) is a pivotal cytokine at the centre of a cascade of cytokines and inflammatory mediators which modulate the host response to infection and trauma, and in particular the metabolic changes resulting in shock and subsequent multi-organ failure. The cytokine IL-8--predominantly an activator and chemotactic factor for circulating polymorphonuclear neutrophil leucocytes--is produced in response to TNF-alpha in vitro, and high circulating levels of IL-8 are found in septic primates. We have studied the release of IL-8 into the circulation of subjects with chronic hepatitis B undergoing a 10 week pilot trial of recombinant TNF-alpha (rTNF-alpha) therapy in doses of 15-100 micrograms/m2. A marked dose-dependent increase in plasma IL-8 levels was seen commencing at 30-60 min after the start of rTNF-alpha infusion and peaking between 2 and 3 h (mean peak level 4300 ng/l). The temporal pattern of IL-8 production exactly echoed that of IL-6, another component of the cytokine cascade, but peak plasma levels of IL-8 were up to 17 times higher than those of IL-6. This study confirms in vitro data suggesting that IL-8 is a component of the acute circulating cytokine cascade with a potential role in the modulation of the acute immune and metabolic response to infection and trauma.     

Induction of experimental endocarditis by continuous low-grade bacteremia mimicking spontaneous bacteremia in humans

Transient high-grade bacteremia following invasive procedures carries a risk of infective endocarditis (IE). This is supported by experimental endocarditis. On the other hand, case-control studies showed that IE could be caused by cumulative exposure to low-grade bacteremia occurring during daily activities. However, no experimental demonstration of this latter possibility exists. This study investigated the infectivity in animals of continuous low-grade bacteremia compared to that of brief high-grade bacteremia. Rats with aortic vegetations were inoculated with Streptococcus intermedius, Streptococcus gordonii or Staphylococcus aureus (strains Newman and P8). Animals were challenged with 10(3) to 10(6) CFU. Identical bacterial numbers were given by bolus (1 ml in 1 min) or continuous infusion (0.0017 ml/min over 10 h). Bacteremia was 50 to 1,000 times greater after bolus than during continuous inoculation. Streptococcal bolus inoculation of 10(5) CFU infected 63 to 100% vegetations compared to 30 to 71% infection after continuous infusion (P > 0.05). When increasing the inoculum to 10(6) CFU, bolus inoculation infected 100% vegetations and continuous infusion 70 to 100% (P > 0.05). S. aureus bolus injection of 10(3) CFU infected 46 to 57% valves. This was similar to the 53 to 57% infection rates produced by continuous infusion (P > 0.05). Inoculation of 10(4) CFU of S. aureus infected 80 to 100% vegetations after bolus and 60 to 75% after continuous infusion (P > 0.05). These results show that high-level bacteremia is not required to induce experimental endocarditis and support the hypothesis that cumulative exposure to low-grade bacteremia represents a genuine risk of IE in humans.     

Age-related inflammatory cytokines and disease

Aging is associated with chronic low-grade increases in circulating levels of inflammatory markers. A wide range of environmental factors, including smoking, infections, and obesity, genetic factors, and the declining function of sex hormones may contribute to systemic low-grade inflammatory activity in older individuals. Age-associated disease may exacerbate this phenomenon. The multifunctional cytokines TNF-alpha and IL-6 have been associated with morbidity and mortality in the elderly. Evidence supports the direct role of TNF-alpha in the pathogeneses of atherosclerosis, type 2 DM, and AD in older individuals. Age-related increases in systemic levels of TNF-alpha could provide a unifying basis for these disorders. Furthermore, TNF-alpha induces a catabolic state that causes frailty. Circulating levels of IL-6 seem to be a strong risk factor for frailty in the elderly, which could reflect its association with increased production of TNF-alpha. IL-6 also may be a risk factor for thromboembolic complications. In healthy, elderly populations, high circulating levels of TNF-alpha and IL-6 predict mortality, independent of comorbidity, indicating that TNF-alpha and IL-6 cause morbidity and mortality. In cohorts of frail, older individuals, TNF-alpha and IL-6 also act as disease markers. Circulating levels of TNF-alpha seem to be the best predictor of mortality in frail, elderly populations with a high mortality rate, whereas IL-6 seems to be the strongest risk marker in healthy, elderly populations. This finding could reflect that in relatively healthy old populations the increase in circulating levels of IL-6 represent a systemic response to local proinflammatory activities; however, when age-related inflammatory diseases progress, levels of TNF-alpha increase in the circulation and become gradually a stronger risk marker than IL-6. In conclusion low-grade elevations in levels of circulating cytokines are strong independent risk factors of morbidity and mortality in the elderly, and lifestyle factors and comorbidities may modulate these levels. Exercise and dietary interventions may be possible strategies to decrease inflammatory activity and improve the health status of the elderly.     

Attenuation of Hyperoxia-induced Lung Injury in Rats by Adrenomedullin

Oxidative stress and inflammation are involved in the pathogenesis of acute lung injury (ALI). Adrenomedullin (AM) is an endogenous peptide with anti-inflammatory and antioxidant properties. This study investigated that whether AM treatment may ameliorate hyperoxia-induced ALI in rats via inhibition of oxidative stress and inflammation. Rats were randomized to receive continuous intravenous infusion of AM or saline through a microosmotic pump, and then ALI was induced by exposing the animals in sealed cages >95% oxygen for 72 h. Exposure to hyperoxia caused lung injury as increased infiltration of inflammatory cells and disruption of lung architecture. AM administration markedly improved these changes. Additionally, AM administration significantly increased glutathione peroxidase and superoxide dismutase activities. Meanwhile, hyperoxia-induced increase of lipid hydroperoxide level was markedly reduced by AM treatment. Moreover, nuclear factor-kappa B-DNA-binding activity, and production of the inflammatory mediators interleukin-6, keratinocyte-derived chemokine, and matrix metalloproteinase 9, were significantly inhibited by AM treatment. AM ameliorates hyperoxia-induced ALI in rats by suppression of oxidative stress and inflammation.     

A human model of inflammatory cardio-metabolic dysfunction; a double blind placebo-controlled crossover trial

ABSTRACT: BACKGROUND: Chronic inflammation may contribute to insulin resistance (IR), metabolic syndrome and atherosclerosis although evidence of causality is lacking in humans. We hypothesized that very low-dose experimental endotoxemia would induce adipose tissue inflammation and systemic IR during a low-grade but asymptomatic inflammatory response and thus provide an experimental model for future tests of pharmacologic and genomic modulation of cardio-metabolic traits in humans. METHODS: Ten healthy, human volunteers (50% male, 90% Caucasian, mean age 22.7 +/- 3.8) were randomized in a double-masked, placebo-controlled, crossover study to separate 36-hour inpatient visits (placebo versus intravenous-LPS 0.6ng/kg). We measured clinical symptoms via the McGill pain questionnaire and serial vital signs. Plasma and serum were collected for measurement of cytokines, C-reactive protein, insulin and glucose, serial whole blood & subcutaneous adipose tissue mRNA expression were measured by real-time PCR. HOMA-IR, a well-validated measure of IR was calculated to estimate insulin resistance, and frequently sampled intravenous glucose tolerance testing (FSIGTT) was performed to confirm an insulin resistant state. We performed ANOVA and within subject ANOVA to understand the differences in cytokines, adipose tissue inflammation and IR before and after LPS or placebo. RESULTS: There was no significant difference between placebo and LPS in clinical responses of symptom scores, body temperature or heart rate. However, low-dose endotoxemia induced a rapid and transient 25-fold induction of plasma TNF-alpha and 100-fold increase in plasma IL-6 (Figure 1b) (p<0.001 for both) both peaking at two hours, followed by modest inflammation in adipose tissue with increases in mRNA levels of several inflammatory genes known to modulate adipose and systemic insulin resistance. Adipose tissue mRNA levels of IL-6 (peak 6-fold, ANOVA F=27.5, p<0.001) and TNF-alpha (peak 1.8-fold, F=2.9, p=0.01) increased with MCP-1 (peak 10-fold, F=5.6, p<0.01) and fractalkine (CX3CL1) (peak 15-fold, F=13.3, p<0.001). Finally, HOMA-IR was 32% higher following LPS compared to placebo (p<0.01) and insulin sensitivity declined by 21% following LPS compared to placebo (p<0.05). CONCLUSIONS: We present a low dose human endotoxemia model of inflammation which induces adipose tissue inflammation and systemic insulin resistance in the absence of overt clinical response. Such a model has the potential for broad and safe application in the study of novel therapeutics and genomic influences in cardio-metabolic disease. KEYWORDS: inflammation, obesity, atherosclerosis, insulin resistance.     

Inflammation: the link between insulin resistance, obesity and diabetes

Recent data have revealed that the plasma concentration of inflammatory mediators, such as tumour necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6), is increased in the insulin resistant states of obesity and type 2 diabetes, raising questions about the mechanisms underlying inflammation in these two conditions. It is also intriguing that an increase in inflammatory mediators or indices predicts the future development of obesity and diabetes. Two mechanisms might be involved in the pathogenesis of inflammation. Firstly, glucose and macronutrient intake causes oxidative stress and inflammatory changes. Chronic overnutrition (obesity) might thus be a proinflammatory state with oxidative stress. Secondly, the increased concentrations of TNF-alpha and IL-6, associated with obesity and type 2 diabetes, might interfere with insulin action by suppressing insulin signal transduction. This might interfere with the anti-inflammatory effect of insulin, which in turn might promote inflammation.     

Tumor necrosis factor and interleukin-1 activities in free lung cells after single and repeated inhalation of bacterial endotoxin.

Bacterial endotoxins (lipopolysaccharides), important components of many organic dusts, are known to induce macrophages to produce the inflammatory mediators interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF-alpha). To investigate the role of these mediators in the early inflammatory responses in the lung, guinea pigs were exposed to an aerosol of bacterial endotoxin. A bronchoalveolar lavage (BAL) was then performed, and TNF-alpha and IL-1 in lysed BAL cells and in the supernatants from BAL cell cultures were studied. The effect of single and repeated LPS inhalation exposures on the activities of TNF and IL-1 was studied, as was the effect of LPS added to the cell culture medium. A single inhalation exposure to LPS caused an increase in the TNF-alpha and IL-1 activities in cell lysate and in the cell culture supernatant. After a second inhalation exposure, cell-associated and extracellular TNF-alpha activity could not be detected, whereas IL-1 activity was markedly enhanced. IL-1 activity was increased when LPS was added to the cell culture medium with or without a prior inhalation exposure. In contrast, TNF-alpha activity was not affected after a second exposure.     

ROS-deficient monocytes have aberrant gene expression that correlates with inflammatory disorders of chronic granulomatous disease

Chronic granulomatous disease is an immunodeficiency caused by an inability to produce reactive oxygen species. While the mechanism of hyper-sensitivity to infection is well understood in CGD, the basis for debilitating inflammatory disorders that arise in the absence of evident infection has not been fully explained. Herein it is demonstrated that resting and TLR-activated monocytes from individuals with CGD expressed significantly higher levels of inflammatory mediators than control cells; the expression in CGD cells resembled normal cells stimulated with lipopolysaccharide. The lack of acute illness, infection or circulating endotoxin in the blood of the CGD patients at the time of sampling was consistent with infection-free inflammation. The enhanced expression of inflammatory mediators correlated with elevated expression of NF-kappaB and was dependent on ERK1/2 signalling. The results are consistent with the hypothesis that ROS are anti-inflammatory mediators that control gene expression and potentially limit the development of sterile inflammatory disorders.     

Circulating adiponectin levels during human endotoxaemia

Adiponectin, an adipocytokine secreted by fat tissue, may prevent development of diabetes type II, as high adiponectin levels are linked with insulin sensitivity. In contrast, tumour necrosis factor (TNF)-alpha, which is also produced by fat tissue, leads to insulin resistance and furthermore inhibits adiponectin mRNA production and secretion of the protein. However, adiponectin also negatively regulates TNF-alpha levels. Therefore, we set out to test whether an infusion of endotoxin would influence circulating adiponectin levels in healthy human subjects. Twenty-three healthy human subjects were injected with endotoxin (2 ng/kg body weight); eight of these subjects were also injected with saline and served as controls. Plasma levels of adiponectin, TNF-alpha and interleukin-6 were measured at 0, 1.5, 2, 4, 8 and 24 h. TNF-alpha and interleukin-6 levels peaked at 1.5 h and 2 h, respectively. Control subjects injected with saline showed a decrease in adiponectin plasma levels with time (P < 0.05) presumably owing to the effect of fasting or physical inactivity. However, there was no change in adiponectin plasma levels in endotoxin injected subjects, thus the effect of fasting was opposed. In conclusion, circulating adiponectin levels are reduced during a resting and fasting state, an effect reversed by endotoxin injection.     

Effect of hypertriglyceridemia on endotoxin responsiveness in humans.

Triglyceride-rich lipoproteins can inhibit endotoxin activity in vitro and in rodents. We sought to determine whether Intralipid, a triglyceride-rich fat emulsion which in contact with plasma functions similarly to endogenous lipoproteins, can alter the human response to endotoxin. Intralipid inhibited endotoxin-induced cytokine production in human whole blood in vitro in a dose-dependent manner, with maximal inhibition (up to 70%) being achieved at a concentration of 10 g/liter. In healthy men, a bolus intravenous injection of endotoxin (lot EC-5; 20 U/kg of body weight) was given midway through a 4-h infusion (125 ml/h) of either 5% glucose (n = 5) or 20% Intralipid (n = 5). The infusion of Intralipid led to an increase in triglyceride levels in serum from 95 +/- 16 to 818 +/- 135 mg/dl prior to endotoxin administration, i.e., levels that importantly reduced cytokine production in endotoxin-stimulated whole blood. However, in vivo hypertriglyceridemia did not influence inflammatory responses to endotoxin (fever, release of tumor necrosis factor and soluble tumor necrosis factor receptors, and leukocytosis) or even potentiated endotoxin responses (release of interleukins 6 and 8 and neutrophil degranulation). Hypertriglyceridemia does not inhibit the in vivo responses to endotoxin in humans.     

Muscle wasting and impaired muscle regeneration in a murine model of chronic pulmonary inflammation

Muscle wasting and increased circulating levels of inflammatory cytokines, including TNF-alpha, are common features of chronic obstructive pulmonary disease. To investigate whether inflammation of the lung is responsible for systemic inflammation and muscle wasting, we adopted a mouse model of pulmonary inflammation resulting from directed overexpression of a TNF-alpha transgene controlled by the surfactant protein C (SP-C) promoter. Compared with wild-type mice, SP-C/TNF-alpha mice exhibited increased levels of TNF-alpha in the circulation and increased endogenous TNF-alpha expression in skeletal muscle, potentially reflecting an amplificatory response to circulating TNF-alpha. Decreased muscle and body weights observed in SP-C/TNF-alpha mice were indicative of muscle wasting. Further evaluation of the SP-C/TNF-alpha mouse musculature revealed a decreased muscle regenerative capacity, shown by attenuated myoblast proliferation and differentiation in response to reloading of disuse-atrophied muscle, which may contribute to skeletal muscle wasting. Importantly, incubation of cultured myoblasts with TNF-alpha also resulted in elevated TNF-alpha mRNA levels and inhibition of myoblast differentiation. Collectively, our results demonstrate that chronic pulmonary inflammation results in muscle wasting and impaired muscle regeneration in SP-C/TNF-alpha mice, possibly as a consequence of an amplificatory TNF-alpha expression circuit extending from the lung to skeletal muscle.