Attenuation of tumor necrosis factor-induced endothelial cell cytotoxicity and neutrophil chemiluminescence

Immune Evasion of Mycoplasma bovis

Mycoplasma bovis (M. bovis) causes various chronic inflammatory diseases, including mastitis and bronchopneumonia, in dairy and feed cattle. It has been found to suppress the host immune response during infection, leading to the development of chronic conditions. Both in vitro and in vivo studies have confirmed that M. bovis can induce proinflammatory cytokines and chemokines in the host. This consists of an inflammatory response in the host that causes pathological immune damage, which is essential for the pathogenic mechanism of M. bovis. Additionally, M. bovis can escape host immune system elimination and, thus, cause chronic infection. This is accomplished by preventing phagocytosis and inhibiting key responses, including the neutrophil respiratory burst and the development of nitric oxide (NO) and inducible nitric oxide synthase (iNOS) that lead to the creation of an extracellular bactericidal network, in addition to inhibiting monocyte and alveolar macrophage apoptosis and inducing monocytes to produce anti-inflammatory factors, thus inducing the apoptosis of peripheral blood mononuclear cells (PBMCs), inhibiting their proliferative response and resulting in their invasion. Together, these conditions lead to long-term M. bovis infection. In terms of the pathogenic mechanism, M. bovis may invade specific T-cell subsets and induce host generation of exhausted T-cells, which helps it to escape immune clearance. Moreover, the M. bovis antigen exhibits high-frequency variation in size and expression period, which allows it to avoid activation of the host humoral immune response. This review includes some recent advances in studying the immune response to M. bovis. These may help to further understand the host immune response against M. bovis and to develop potential therapeutic approaches to control M. bovis infection.

Effects of combined treatment of minocycline and methylprednisolone on the expression of tumor necrosis factor alpha and interleukine-6 in experimental spinal cord injury: a light and electron microscopic study

Spinal cord injury (SCI) is an important health problem, and there is no universal treatment protocol for it today. Following SCI pro-inflammatory mediators such as tumor necrosis factor- alpha (TNF-α) and interleukin-6 (IL-6) increase at the lesion site and play important roles in secondary tissue damage. Methylprednisolone (MP) is a glucocorticoid, and minocycline is a tetracycline-derived antibiotic both with neuroprotective effects on central nervous system trauma. However, there are limited studies on their effects on SCI. In this study, we aimed to evaluate effects of MP+minocycline combined treatment on cellular distribution and localization of TNF-α And IL-6 after SCI. Eighty Wistar rats were divided into three main groups as the intact control group, sham operation group, and experimental control group that received spinal cord compression injury. Following the injury, the experimental control group was subdivided into four groups as control, methylprednisolone treatment, minocycline treatment and, MP+minocycline combined treatment groups. Tissue samples were obtained from all groups at 24 hours and 72 hours after the injury. We found a significant decrease in TNF-α And IL-6 expressions in combined treatment group at 24 hours after injury. Also, there was a significant decrease in MDA and increase in SOD levels in this group. Furthermore, decreased lipid peroxidation and neuronal and glial cell death were also observed in combined treatment group. These results suggest that MP+minocycline combined treatment promotes functional recovery and, it should be considered as an effective treatment protocol following SCI.

Pentoxifylline and nephroprotection: effects on renal dysfunction and cardiovascular risks

Generalized data on nephroprotective efficacy of pentoxifylline in chronic kidney disease (CKD) are presented. The potential of this drug in treating people suffering from CKD and cardiovascular diseases (CVD) with a high risk of developing the terminal stage of renal dysfunction is considered. Antiproteinuric, antifibrotic and anti-inflammatory effects of pentoxifylline significantly reduce the risk of progression of CKD and joining of CVD in the future. Efficacy in preventing the onset of the uremic stage of CKD, safety andapplicability at all stages of renal dysfunction development make pentoxifylline a very appealing drug not only for nephrologists but also for physicians. Keywords: chronic kidney disease, progression, pentoxifylline, nephroprotection, cardiovascular diseases.

Neuroprotective effects of infliximab in experimental spinal cord injury

BACKGROUND

The aim of the study is to assess the effects of infliximab, a TNF-alpha receptor blocker, in a spinal cord clip compression injury model.

METHODS

Clip compression injury model was used for producing spinal cord injury on 32 adult, male Wistar rats (Gazi University Animal Research Laboratory, Ankara, Turkey). After exposing the vertebral column between T7 and T10, total laminectomy was performed with the assistance of a high-speed drill and a surgical microscope. The dura was left intact. Spinal cord injury was performed on all rats with application of a 70-g closing force aneurysm clip for 1 minute. The rats were randomly allocated into 4 groups. Control group received no further therapy, whereas the other 3 groups received methylprednisolone (30 mg/kg intraperitoneal), infliximab (5 mg/kg subcutaneous), and a mixture of these 2 agents. All rats were killed 72 hours later, and the level of lipid peroxides in traumatized spinal cord tissue were measured as thiobarbituric acid-reactive material and determined using the method of Mihara and Uchiyama (Determination of malonaldehyde precursor in tissue by thiobarbituric acid test. Anal Biochem 1978;86(1):271-8).

RESULTS

Treatment with infliximab and methylprednisolone decreased MDA levels in rats with spinal cord injury with a statistically significant difference. In addition, combined therapy achieved a more profound decrease in tissue MDA levels, which was also statistically significant.

CONCLUSIONS

Infliximab is found as effective as methylprednisolone on spinal cord clip compression injury. Moreover, the combination of these 2 agents demonstrated higher efficacy suggesting a synergistic effect between these 2 agents. However, further studies regarding functional and behavioral analyses as well as biochemical markers are required.

Granulocyte colony-stimulating factor (filgrastim) treatment primes for increased ex vivo inducible prostanoid release

We investigated whether anti-inflammatory effects of treatment with granulocyte colony-stimulating factor (G-CSF, filgrastim) are mediated via prostaglandin E(2) (PGE(2)) induction. In a double-blind crossover study, 10 healthy volunteers received 300 microg of filgrastim or saline 1 week apart. This was repeated after oral administration of 50 mg of flurbiprofen 1 h before injection. The increase in neutrophilic granulocytes initiated by G-CSF was augmented significantly by flurbiprofen. Lipopolysaccharide-induced PGE(2) and thromboxane (TxB(2)) release were increased 8 h after G-CSF treatment. This increase was abrogated by flurbiprofen. However, flurbiprofen did not affect G-CSF-mediated decrease in tumor necrosis factor-alpha or interferon-gamma release. Of the volunteers treated with G-CSF, eight reported side effects (headache and bone pain) against none in the saline group. When flurbiprofen was given before injection, one volunteer each reported side effects in the G-CSF and in the saline group. These data show that G-CSF primes for increased PGE(2) and TxB(2) release. Cyclooxygenase inhibition counteracts neither the hematopoietic nor the anti-inflammatory activity of G-CSF but reduces side effects.

Pentoxifyllin attenuates the systemic inflammatory response induced during isolated limb perfusion with recombinant human tumor necrosis factor-alpha and melphalan

BACKGROUND

Isolated limb perfusion (ILP) with recombinant human tumor necrosis factor-alpha (rhTNF-alpha) and melphalan harbors the risk of septic shock-like syndrome. Pentoxifyllin (PTX) produced a beneficial effect on cytokine response and survival in animal experiments of septic shock, and we were interested to explore its effect during TNF-ILP in humans.

METHODS

Eighteen consecutive patients underwent TNF-ILP and received PTX (30 mg/kg/day), whereas another 13 consecutive patients did not. PTX was given systemically after the limb extracorporeal circulation was started. Cardiac index, systemic vascular resistance (SVR), and pulmonary vascular resistance were recorded via a Swan-Ganz catheter. Blood levels of TNF-alpha, interleukin-6, procalcitonin, and lipopolysaccharide-binding protein were determined before, during, and after ILP.

RESULTS

After reperfusion, systemic levels of TNF-alpha were significantly less increased in the PTX group (peak, 2.8 vs. 1.3 ng/mL; P <.05), as were interleukin-6 values (peak, 68 vs. 22 pg/mL; P <.02) and lipopolysaccharide-binding protein plasma levels (peak, 215 vs. 105 micro g/mL; P <.03). Differences in cardiac index, SVR, and mean arterial blood pressure were not significantly different. Norepinephrine or dobutamine to maintain SVR was less required in the PTX group.

CONCLUSIONS

PTX attenuates systemic cytokine production and influences components of the systemic inflammatory response after TNF-ILP. PTX may play a beneficial role in the management of septic shock-like syndrome, particularly in patients with leakage from the ILP circuit.

Determination of the eicosanoid response to inflammatory stimuli in whole blood and its pharmacological modulation ex vivo

Recognition of pathogens by immune cells initiates the release of numerous signaling molecules, including cytokines and eicosanoids. Here, we describe a simple procedure by which eicosanoids such as prostaglandin E(2) (PGE(2)), leukotriene B(4) (LTB(4)) and thromboxane B(2) (TxB(2)) can be measured using commercial enzyme immunoassays (EIAs) in the supernatant of whole blood stimulated with inflammatory stimuli. This is illustrated for numerous stimuli. The kinetics by which lipopolysaccharide (LPS) induces cyclooxygenase (COX)-2 expression in this setup were determined by quantitative reverse transcription polymerase chain reaction (RT-PCR). The eicosanoid response of the blood of 160 healthy volunteers to 1 microg/ml LPS was measured. To determine whether the action of a drug in vivo is represented ex vivo in the eicosanoid response of blood, one volunteer took a standard dose of a number of commercially available cyclooxygenase inhibitors on different days and the eicosanoid response of his blood to LPS was determined before ingestion as well as 2 and 6 h afterwards. The efficacy of the different pharmaceuticals on cyclooxygenase but not lipoxygenase products or cytokines could be monitored ex vivo. Similarly, ex vivo eicosanoid release was measured in blood from 10 volunteers who had taken 50 mg flurbiprofen. The method described extends approaches for studying whole blood cytokine release to the lipid mediators formed from arachidonic acid. These important signaling molecules represent targets for pharmacological intervention, which can now be monitored in vitro, as well as ex vivo employing the same model. Furthermore, the assay could be used to characterize the immune status of patient groups or to monitor the course of disease.

Perinatal immunomodulation

The fetus and the neonate are particularly vulnerable to injury caused directly by immunologic mechanisms or inflicted by infectious agents that take advantage of their relatively immature and inexperienced immune system. With increasing survival of high-risk neonates in the surfactant era, prevention/treatment of sepsis and chronic lung disease (CLD) has emerged as an area of priority in neonatal research. Considering the role of inflammatory mediators in the pathogenesis of sepsis and CLD, the clinical application of immunomodulator therapy to neonatology is perhaps more important at present than ever. Advances in molecular biology and immunology have led to development of newer immune modulator therapies that are directed towards specific cells or cytokines rather than resulting in a general suppression of the immune response. Failure of promising, newer immunomodulator therapies in sepsis trials in adults has, however, clearly documented the difficulties in diagnosing/correcting the imbalance between pro- and anti-inflammatory responses. As in the case of sepsis, development of a single magic bullet for prevention/management of a multi-factorial illness like CLD may be difficult, as prevention of prematurity - the single most important high-risk factor for CLD - is an unachievable goal at present. As new frontiers are being explored, older, well-established therapies like antenatal anti-D immunoglobulin prophylaxis continue to emphasize the tremendous potential of immunomodulator therapy in neonatology/perinatology. The current immunomodulators/immunotherapeutic agents with established/potential clinical applications in the perinatal period are reviewed.

Effects of pentoxifylline on the different steps during adhesion and transendothelial migration of flowing neutrophils

We used a flow system to observe the stepwise adhesion and migration of neutrophils on cultured human umbilical vein endothelial cells (HUVEC) stimulated with tumour necrosis factor-alpha (TNF) for 4 h, and to evaluate the effects of pentoxifylline (PTX) at each step. When HUVEC had been stimulated with 100 U ml(-1) TNF, treatment of neutrophils with PTX did not reduce the number captured from flow but did cause nearly all adherent cells ( > 90%) to roll, whereas most untreated cells became immobilized and approximately 30% transmigrated within minutes. On washout of the PTX, many rolling cells halted and started to migrate. Treatment of the HUVEC with PTX at the same time as 100 U ml(-1) TNF did not affect the number of neutrophils adhering, but there was a significant increase in the percentage of cells rolling even though PTX was no longer present. Thus PTX reduced presentation of activating agents by HUVEC, as well as inhibiting the response by neutrophils to surface-presented activating agent(s). If HUVEC were stimulated with 10 U ml(-1) TNF with PTX, the adhesion of flowing neutrophils was greatly inhibited compared to TNF alone. Surface ELISA indicated that PTX reduced TNF-induced upregulation of E-selectin. This reduction was only sufficient to reduce capture of neutrophils at the low dose of TNF. Thus, by using a flow-based model, we have been able to separate the effects of a multipotent agent such as pentoxifylline, which acts on leucocytes and endothelial cells, at each stage of migration.

Role of leukocytes in spinal cord injury in rats

Spinal cord injury (SCI) is a serious condition that produces life-long disabilities. Only limited therapeutic measures are currently available for its treatment. This review describes the role of leukocytes in pathologic mechanisms of trauma-induced SCI in rats, which contributes to new understanding of the pathologic process involved in SCI and could lead to the development of new therapeutic strategies by which leukocyte activation can be regulated. SCI induced by trauma is a consequence of an initial physical insult that is followed by a progressive injury process which involves various pathochemical events that lead to tissue destruction. Therapeutic intervention in SCI should therefore be directed at reducing or alleviating this secondary process. Although the mechanisms are not fully understood, progressive vascular events, especially activated neutrophil-induced endothelial cell damage, have been shown to be implicated. We have found that some therapeutic agents, which inhibit leukocyte activation directly or indirectly, alleviate the motor disturbances observed in a rat model of SCI. Methylprednisolone (MPS) and GM1 ganglioside, which are the only two pharmacological agents currently clinically available for treatment of acute SCI, do not inhibit neutrophil activation in this rat model. Taken together, these observations raise a possibility that pharmacological agents that inhibit leukocyte activation used in conjunction with MPS or GM1 may have a synergistic effect in the clinical treatment of traumatic SCI in humans.

Pentoxifylline attenuates hypoxic-ischemic brain injury in immature rats

Inflammatory mediators are implicated in the pathogenesis of ischemic injury in immature brain. The phosphodiesterase inhibitor pentoxifylline inhibits production of tumor necrosis factor-alpha and platelet-activating factor. We hypothesized that pentoxifylline treatment would attenuate hypoxic-ischemic brain injury in immature rats. Seven-day-old rats (n = 79) underwent right carotid ligation, followed by hypoxia (FiO2 = 0.08). Rats received pentoxifylline immediately before and again after hypoxia (two doses, 25-150 mg/kg/dose, n = 34), or vehicle (n = 27). In separate experiments, rats received pentoxifylline treatment (40 mg/kg/dose, n = 8), or vehicle (n = 10) immediately and again 3 h after hypoxia-ischemia. Severity of injury was assessed 5 d later by visual evaluation of ipsilateral hemisphere infarction and by measurement of bilateral hemispheric cross-sectional areas. Pentoxifylline pretreatment reduced the incidence of liquefactive cerebral infarction, from 75% in controls to 10% with pentoxifylline, 40 mg/kg/dose (p<0.001, chi2 trend test). Quantification of hemispheric areas confirmed these findings. In contrast, posthypoxic-ischemic treatment with pentoxifylline resulted in only a modest reduction in cortical damage, without an overall reduction in incidence of infarction. Phosphodiesterase inhibition may be an effective strategy to use to decrease the severity of neonatal hypoxic-ischemic brain injury. Pretreatment regimens could be clinically relevant in settings in which an increased risk of cerebral ischemia can be anticipated, such as in infants undergoing surgery to correct congenital heart disease.

Adjunctive Therapies for Sepsis and Septic Shock

The inflammatory cascade that ensues after an infectious insult is protean in its manifestations, resulting in mild self-limited illness in some patients, while progressing to fulminant sepsis and multisystem organ failure in others. Research into the pathophysiology of this cascade has been intense, but advances in the treatment of sepsis have been few and far between. Although mortality rates have been impacted slightly in patients with sepsis--with improved survival in certain patient subgroups--overall survival still reaches only 55% to 60%. In this paper we will review some of the most recent advances in the therapy of the sepsis syndrome, specifically the roles of cytokine modifiers, supranormal delivery of oxygen, granulocyte colony-stimulating factor administration in leukopenic patients, and parenteral nutrition. Hopefully, these modalities represent additional steps in the path towards a meaningful improvement in survival from this catastrophic condition.

Additive effect of tumor necrosis factor-alpha and endotoxin on bilirubin cytotoxicity

Clinical observations suggest that sepsis may enhance the risk of kernicterus. This study investigated the combined effects of bilirubin, endotoxin, and tumor necrosis factor-alpha (TNF-alpha), which simulate sepsis in a jaundiced mouse fibroblast cell line. The horseradish peroxidase oxidation method was applied for bilirubin-albumin titration studies to test the effect of endotoxin and TNF-alpha on bilirubin-albumin binding. A modified 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide method was used to study cytotoxicity. Bilirubin caused cytotoxicity in a dose-dependent manner in the cultured mouse fibroblasts. Such an effect was significantly amplified by TNF-alpha and endotoxin. TNF-alpha and endotoxin had no effect on the bilirubin-albumin titration curves. Our results have shown that TNF-alpha and endotoxin increase the cytotoxicity of bilirubin. These findings provide supportive evidence that sepsis would increase the risk of tissue damage by bilirubin.

Mediator-dependent effects of pentoxifylline on endothelium for transmigration of neutrophils

In the present study, we investigated the effects of the anti-inflammatory drug pentoxifylline (PTX) on activation of endothelial cells for enhanced adhesion and transmigration of neutrophils by lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF), interleukin-1 (IL-1) and granulocyte colony-stimulating factor (G-CSF). To evaluate the mechanism by which PTX exerts its effect, human umbilical vein endothelial cells (HUVEC) were pretreated with theophylline, 2'-O-dibutyryl-3', 5'-cyclic adenosine monophosphate (db cAMP), and 3-isobutyl-1-methylxanthine, respectively, prior to stimulation. Pretreatment of HUVEC with PTX significantly antagonized TNF-, IL-1-, and G-CSF-activated transmigration of neutrophils. Additive stimulatory effects of PTX were seen with LPS. With the exception of theophylline, all other test cAMP-raising agents stimulated transmigration in similar fashion to PTX. Upon stimulation with TNF or LPS, HUVEC produced IL-8 and PTX affected this process in opposing fashions, with inhibition of the effects of TNF and augmentation of those of LPS. These results demonstrate that PTX differentially affects mediator-induced activation of HUVEC. The present IL-8 dependent and cAMP-regulated augmentation of LPS-induced stimulation of transmigration is the first description of an additive effect of PTX with a pro-inflammatory agent.

Spinal cord injury in the rat

Only limited therapeutic measures are currently available for the treatment of spinal cord injury. This review describes the pathologic mechanisms of trauma-induced spinal cord injury in rats, which will contribute to new understanding of the pathologic process leading to spinal cord injury and to further development of new therapeutic strategies. Spinal cord injury induced by trauma is a consequence of an initial physical insult and a subsequent progressive injury process that involves various pathochemical events leading to tissue destruction; the latter process should therefore be a target of pharmacological treatment. Recently, activated neutrophils have been shown to be implicated in the latter process of the spinal cord injury in rats. Activated neutrophils damage the endothelial cells by releasing inflammatory mediators such as neutrophil elastase and oxygen free radicals. Adhesion of activated neutrophils to the endothelial cell could also play a role in endothelial cell injury. This endothelial cell injury could in turn induce microcirculatory disturbances leading to spinal cord ischemia. We have found that some therapeutic agents that inhibit neutrophil activation alleviate the motor disturbances observed in the rat model of spinal cord injury. Methylprednisolone (MPS) and GM1 ganglioside, which are the only two pharmacological agents currently clinically available for treatment of acute spinal cord injury, do not inhibit neutrophil activation in this rat model. Taken together, these observations raise a possibility that other pharmacological agents that inhibit neutrophil activation used in conjunction with MPS or GM1 ganglioside may have a synergistic effect in the treatment of traumatic spinal cord injury in humans.

Glutathione peroxidase mimics prevent TNFalpha- and neutrophil-induced endothelial alterations

Based on the assumption that glutathione peroxidase (GPx) activity might be limiting in preventing peroxide-induced impairment of endothelial regulatory functions, we studied the effect of a series of new selenium-containing GPx mimics on endothelial cells exposed to an inflammatory stress. The two compounds that have the highest GPx activity, BXT-51072 and BXT-51077, were shown to be the most efficient inhibitors of leukocyte recruitment by human umbilical vein endothelial cells (HUVEC), upon incubation with neutrophils (10-fold excess over HUVEC) and with 1 ng/ml TNF-alpha for 1 or 3.5 h. When HUVEC were pre- and cotreated with 10 microM of either compound, neutrophil adhesion and endothelial alteration were markedly inhibited, as assessed by immunoassays of myeloperoxidase and von Willebrand factor, respectively. These two GPx mimics were also found to be the most efficient inhibitors of the TNFalpha-induced endothelial expression of P- and E-selectin and of the TNFalpha- or interleukin1-induced endothelial release of interleukin-8. Our results demonstrate that GPx mimics such as BXT-51072 behave as potent antagonists of TNF-alpha and interleukin-1 through the downregulation of endothelial proinflammatory responses.

Differences in the anti-inflammatory effects of theophylline and pentoxifylline: important for the development of asthma therapy?

Antiasthma drugs are now being re-evaluated for their anti-inflammatory effects. Theophylline is an immunomodulator; however, weak effects and the narrow therapeutic window make it a controversial drug. We compared the immunomodulatory potencies of theophylline with those of the xanthines pentoxifylline (POF) and A802715. Using a whole-blood, cell-culture system, we studied the effects on the release of tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), and interleukin-6 (IL-6) in six healthy subjects, and, in granulocyte suspensions, the effects on the release of reactive oxygen species (ROS). We also studied the influence of a 14-day treatment with theophylline or POF on the release of the cytokines named above in 14 asthmatics. We found that equimolar concentrations of A802715 most effectively inhibit ROS generation, followed by POF; the effects of theophylline were weakest. A802715-inhibited release of TNF-alpha was four times as potent as that of theophylline, and POF two times as potent. Inhibition of IFN-gamma by A802715 was three times as potent, and by POF two times. Neither drug influenced IL-6 release. After a 14-day treatment of asthmatics, POF proved to inhibit TNF-alpha release more effectively (by 44.3%) than theophylline (7.5%). It is concluded that study of xanthine derivatives in asthmatics might help the development of asthma therapy. POF seems to be an especially promising candidate.

Pentoxifylline prevents concanavalin A-induced hepatitis by reducing tumor necrosis factor alpha levels and inhibiting adhesion of T lymphocytes to extracellular matrix

BACKGROUND/AIMS

Concanavalin A activates T lymphocytes and causes T cell-mediated hepatic injury in mice. Tumor necrosis factor alpha is a critical mediator in this experimental model. T-cell-mediated liver injury involves the migration of immune cells, notably CD4+ T lymphocytes, into liver tissue. Pentoxifylline is a strong suppressor of tumor necrosis factor alpha release and prevents leukocyte adherence to vascular endothelium and down-regulates the expression of intercellular adhesion molecule-1 in monocytes. In this study, we examined the efficacy of pentoxifylline as a potential therapeutic compound for the treatment of concanavalin A hepatitis.

METHODS

Balb/c mice were injected with 12 mg/kg concanavalin A with or without a single injection of pentoxifylline (5-300 mg/kg), 2 h prior to concanavalin A administration. Liver damage was evaluated by determining serum levels of liver enzymes and tumor necrosis factor alpha, and hepatic histopathology compared to mice treated with concanavalin A only. We also assessed the effects of pentoxifylline on the adhesive properties of T lymphocytes to fibronectin, as a paradigm for immune cell-extracellular matrix interactions required for migration. Pretreatment with pentoxifylline significantly reduced serum levels of liver enzymes (3800+/-650 vs 150+/-28 IU/l) and tumor necrosis factor alpha (710+/-105 vs 113+/-15 pg/ml) with no evidence of inflammation in histopathologic examination compared to control mice treated with concanavalin A. Pentoxifylline also inhibited the binding of murine T cells to fibronectin. All the effects of pentoxifylline were dose-dependent.

CONCLUSIONS

These results indicate that high doses of pentoxifylline can prevent concanavalin A hepatitis by suppression of tumor necrosis factor alpha release and inhibition of T cells adhesion to extracellular matrix.

Pentoxifylline treatment attenuates pulmonary vasomotor dysfunction in acute lung injury

Acute lung injury (ALI) is characterized by pulmonary hypertension. Although the pathophysiology of ALI is complex, cytokine production, especially tumor necrosis factor-alpha (TNF-alpha), is known to mediate histologic lung injury. Pentoxifylline (PTX) is known to inhibit the expression of many cytokines, including TNF-alpha. The purpose of this study was to determine the effect of PTX treatment on endotoxin-induced impairment of endothelium-dependent mechanisms of pulmonary vasorelaxation. Mechanisms of endothelium-dependent relaxation were studied with the muscarinic receptor agonist, acetylcholine (ACh), and the receptor-independent calcium ionophore, A23187. Endothelium-independent pulmonary vasorelaxation was examined by direct stimulation of smooth muscle guanylate cyclase with the nitric oxide donor, sodium nitroprusside (SNP). Five rats received PTX (50 mg/kg) and endotoxin (20 mg/kg), endotoxin alone, or saline ip. After 6 hr, dose-response curves to ACh, A23187, and SNP were determined in isolated pulmonary artery rings preconstricted with phenylephrine (PE). PTX attenuated but did not eliminate endotoxin-induced impairment of endothelium-dependent and -independent pulmonary vasorelaxation. These data suggest that PTX may offer a therapeutic modality for the treatment of pulmonary hypertension in ALI.

Reduction of spinal cord injury by administration of iloprost, a stable prostacyclin analog

To investigate whether iloprost, a stable analog of prostacyclin, is useful for the prevention of posttraumatic spinal cord injury, we examined its effects on compression trauma-induced spinal cord injury in rats. Spinal cord injury was induced by applying a 20-g weight for 20 minutes to the spinal cord at the level of T-12, resulting in motor disturbances in the hindlimbs. These motor disturbances, evaluated using Tarlov's index, were markedly attenuated in rats with nitrogen mustard-induced leukocytopenia. Administration of iloprost also attenuated the motor deficits. Histological examination revealed that intramedullary hemorrhages observed 24 hours after trauma were significantly attenuated in leukocytopenic animals and in animals that received iloprost. The accumulation of leukocytes at the site of trauma, evaluated by measuring tissue myeloperoxidase activity, significantly increased with time following the trauma, peaking at 3 hours postinjury. Spinal cord myeloperoxidase activity in sham-operated animals did not increase postoperatively. Leukocyte depletion and administration of iloprost reduced the accumulation of leukocytes in the damaged spinal cord segment 3 hours posttrauma. These findings indicate that iloprost attenuates motor disturbances induced by spinal cord trauma and that its therapeutic efficacy can be partly explained by its inhibition of leukocyte accumulation at the traumatized site.

Subthreshold hyperoxia potentiates TNF-alpha-induced ICAM-1 expression on cultured pulmonary microvascular endothelial cells

The effects of combined exposure to subthreshold hyperoxia and the inflammatory cytokine tumor necrosis factor alpha (TNF-alpha) on the expression of intercellular adhesion molecule-1 (ICAM-1) were examined in bovine lung microvascular endothelial cells (BLuEC). The expression of total ICAM-1 was not affected by 50% hyperoxia conditions alone, indicating that this level is subthreshold for BLuEC. In the presence of 5 ng/mL TNF-alpha, which has minimal influence on BLuEC alone, the amount of total ICAM-1 expression under 50% hyperoxia was higher than that in normoxic conditions (approximately 30%) throughout the culture period. The amount of soluble ICAM-1 that has been released into the culture medium increased after joint exposure to hyperoxia and TNF-alpha. These results suggest that exposure to subthreshold hyperoxia, which does not by itself cause damage to the endothelial cells or induce ICAM-1 expression, potentiates the effects of low-level TNF-alpha exposure.

Gabexate mesilate, a synthetic protease inhibitor, prevents compression-induced spinal cord injury by inhibiting activation of leukocytes in rats

OBJECTIVE

Gabexate mesilate is a synthetic protease inhibitor capable of inhibiting both coagulation and cytokine production by monocytes. To investigate whether gabexate mesilate is useful for the prevention of posttraumatic spinal cord injury, we examined its effect on compression trauma-induced spinal cord injury in rats.

DESIGN

Prospective, randomized, blinded, controlled study.

SETTING

Research laboratory at a university medical center.

SUBJECTS

Male Wistar rats weighing 300 to 350 g.

INTERVENTIONS

Spinal cord injury was induced by applying a 20-g weight extradurally to the spinal cord at the level of the 12th thoracic vertebra for 20 mins. Spinal cord injury was evaluated by assessing the motor function of the rats 24 hrs posttrauma. The accumulation of leukocytes and histologic changes in the injured spinal cord tissue also were examined. Rats received gabexate mesilate (10 or 20 mg/kg i.p.) 30 mins before or after the compressive trauma. The effects of heparin or an inactive derivative of activated factor X (a selective inhibitor of thrombin generation) on compressive trauma-induced spinal cord injury also were examined. Leukocytopenia was induced by the administration of nitrogen mustard.

MEASUREMENTS AND MAIN RESULTS

The motor disturbances observed following traumatic spinal cord compression, evaluated by Tarlov's score, and the accumulation of leukocytes in the injured tissue, evaluated by measuring tissue myeloperoxidase activity, were markedly reduced by leukocyte depletion induced by nitrogen mustard and by pre- or posttreatment of animals with gabexate mesilate. Neither heparin nor the inactive derivative of activated factor X prevented the motor disturbances and the accumulation of leukocytes. Histologic examination demonstrated that intramedullary hemorrhages observed 24 hrs after trauma at the 12th thoracic vertebra were significantly attenuated by nitrogen mustard-induced leukocytopenia and the administration of gabexate mesilate.

CONCLUSIONS

The compression trauma-induced spinal cord injury demonstrated by this model was mainly mediated by leukocytes. Gabexate mesilate prevented spinal cord injury not by inhibiting coagulation, but by inhibiting the activation of leukocytes.

Effects of treatment with pentoxifylline on the cardiovascular manifestations of group B streptococcal sepsis in the piglet

Pentoxifylline (PTXF) is a methylxanthine derivative which modifies leukocyte function and inhibits tumor necrosis factor (TNF)-alpha release. As TNF-alpha is considered a proximal mediator in the cascade leading to septic shock, we evaluated the ability of PTXF to attenuate the cardiovascular manifestations of sepsis secondary to an infusion of group B beta-hemolytic streptococci (GBS). Fifteen anesthetized, mechanically ventilated piglets (weight, 2815 +/- 552 g) were randomly assigned to a treatment group which received a continuous infusion of PTXF (5 mg/kg/h) beginning 30 min after GBS (7.5 x 10(8) colony-forming units/kg/min) administration was started or to a control group which received GBS plus saline as placebo. Comparison of the hemodynamic measurements and arterial blood gases over the first 120 min of bacterial infusion for treatment and control groups revealed the following statistically significant differences (120-min values presented): cardiac output was significantly higher in the PTXF group (0.159 +/- 0.035 versus 0.09 +/- 0.026 L/kg/min; p < 0.05) as was stroke volume (0.54 +/- 0.11 versus 0.27 +/- 0.126 mL/kg/beat; p < 0.01). Pulmonary and systemic vascular resistances remained lower in the PTXF-treated animals (167 +/- 45 versus 233 +/- 69 mm Hg/L/kg/min; p < 0.03) and (427 +/- 162 versus 828 +/- 426 mm Hg/L/kg/min; p < 0.03, respectively). Median survival time was significantly longer in the PTXF group (180 versus 120 min; p < 0.05). In an additional group of animals, PTXF administration before GBS infusion revealed no attenuation in the rise of TNF-alpha, accompanying sepsis. These data demonstrate that treatment with PTXF may ameliorate some of the deleterious hemodynamic manifestations of GBS sepsis and result in improved survival in a young animal model without significantly modifying plasma TNF-alpha levels.

Experimental brain injury induces differential expression of tumor necrosis factor-alpha mRNA in the CNS

In the present study, we examined the expression of tumor necrosis factor-alpha (TNF-alpha) mRNA i specific brain regions following experimental lateral fluid percussion traumatic brain injury (TBI) in rats. Adult Sprague-Dawley rats (n = 42) were anesthetized with sodium pentobarbital (60 mg/kg, i.p.) and subjected to lateral fluid percussion brain injury of moderate severity (2.4 atm.) centered over the left temporoparietal cortex, or 'sham' treatment (anesthesia and surgery without injury). Animals were killed by decapitation at 1, 6 or 24 h post injury, brains removed, and tissue samples of left (injured) parietal cortex (LC), right parietal cortex (RC), left adjacent cortex (LA), right adjacent cortex (RA), left hippocampus (LH) and right hippocampus (RH) were prepared. Total RNA was isolated and Northern blot hybridization was performed. TNF-alpha mRNA is expressed as the percent relative radioactivity of macrophage (positive control) RNA. In sham or naive animals, no consistent changes in expression of TNF-alpha mRNA were observed in any of the six brain areas at any times (less than 5%). A marked increase of TNF-alpha mRNA expression was observed in LH (104 +/- 17, P < 0.05 compared with sham), LC (105 +/- 21, P < 0.05) and LA (69 +/- 8, P < 0.01) in the traumatized hemisphere 1 h following injury. An increased TNF-alpha mRNA expression was also observed in LH (46 +/- 8, P < 0.05), LC(30 +/- 3, P < 0.01) and LA(32 +/- 3, P < 0.01) at 6 h which resolved by 24 h following injury. In the contralateral hemisphere, expression of TNF-alpha mRNA was increased in RH (46 +/- 2, P < 0.01) at 1 h and in RA (26 +/- 6%, P < 0.05) at 6 h. These results indicate that following parasagittal fluid percussion brain injury, the temporal expression of TNF-alpha mRNA is altered in specific brain regions, including those of the non-traumatized hemisphere. Post-traumatic alteration in gene expression of TNF-alpha might play an important role in both the acute and regenerative response to CNS trauma.

Effects of pentoxifylline on circulating cytokine concentrations and hemodynamics in patients with septic shock: results from a double-blind, randomized, placebo-controlled study

OBJECTIVE

To determine whether a continuous intravenous infusion of pentoxifylline, a methylxanthine derivative, alters the serum cytokine concentrations and/or hemodynamic measurements in patients with septic shock.

DESIGN

A prospective, randomized, double-blind, placebo-controlled study.

SETTING

Medical intensive care unit in a university hospital.

PATIENTS

Sixteen patients with septic shock.

INTERVENTIONS

Patients were randomly assigned to receive either pentoxifylline (1 mg/kg) followed by an infusion of 1.5 mg/kg/hr for 24 hrs (n = 8), or placebo (n = 8).

MEASUREMENTS AND MAIN RESULTS

Tumor necrosis factor (TNF) and interleukin (IL)-6 concentrations were measured by radioimmunoassays; IL-8 concentrations by an enzyme-linked immunosorbent assay (ELISA) and pentoxifylline concentrations by high-performance liquid chromatography at 0, 3, 6, 12, 18, 24 and 48 hrs after study entry. Pulmonary artery catheter-derived hemodynamics were measured at 0, 0.75, 3, 6, 12, 18, and 24 hrs. In pentoxifylline-treated patients, at 24 hrs, serum concentrations of TNF were significantly lower compared with controls (12 +/- 2 vs. 42 +/- 12 pg/mL, respectively, p = .04). Serum concentrations of IL-6 and IL-8 did not differ between the two treatment groups. There were also no significant differences in any hemodynamic and oxygenation measurements comparing the two treatment groups. Pentoxifylline concentrations were 1,544 +/- 241 ng/mL after the initial dose, and 5,776 +/- 1,781 ng/mL at the end of the 24-hr infusion. Five patients in the pentoxifylline group and four patients in the placebo group died.

CONCLUSIONS

Pentoxifylline is able to decrease serum TNF but not IL-6 or IL-8 serum concentrations during septic shock. Pentoxifylline was well tolerated by all eight patients with no adverse effect. Further studies are needed to determine if pentoxifylline's ability to lower circulating TNF concentration without altering hemodynamics will improve outcome in septic shock.

Effect of high-dose pentoxifylline on acute radiation-induced lung toxicity in a rat lung perfusion model

PURPOSE

The purpose of this study was to study the effect of high-dose oral pentoxifylline on radiation-induced acute lung injury as assessed with a rat lung perfusion model.

METHODS AND MATERIALS

Adult male Sprague-Dawley rats were used throughout this study. A preliminary experiment determined that treatment with 2 g/liter pentoxifylline in drinking water resulted in an average consumption of 1.38 g/m2/day, which is comparable to the maximum tolerated dosage in humans. Seventy-two rats were irradiated to the left hemithorax with single fraction doses ranging from 10 through 18 Gy. Half were treated with 2 g/liter pentoxifylline in drinking water from 1 week before radiation through 8 weeks after radiation. Lung vascular perfusion scanning was performed at 3, 4, 5, 6, and 8 weeks after radiation using 99mTc-macroaggregated albumin. The lung perfusion ratio was defined as the number of counts due to radioactivity within the irradiated left lung region of interest divided by the number of counts within the region of the nonirradiated right lung. This lung perfusion ratio has been shown to decrease with radiation-induced lung injury.

RESULTS

Although radiation led to a decreased lung perfusion ratio in all groups, those receiving pentoxifylline maintained higher ratios than irradiated controls from 3-5 weeks, especially for those receiving 15 or 18 Gy. However, from 6 through 8 weeks the irradiated controls exhibited partial recovery of lung perfusion ratio, whereas the pentoxifylline groups did not. By 8 weeks after 15 and 18 Gy, lung perfusion ratios were significantly higher for the irradiated controls than for pentoxifylline-treated rats-a reversal of the pattern observed at 3-5 weeks.

CONCLUSIONS

The protection by pentoxifylline against radiation-induced acute lung injury was transient and limited to the first 5 weeks after radiation. Subsequent recovery from lung injury was inhibited by this drug at later times within the acute phase.

Inhibition of tumor necrosis factor production and ICAM-1 expression by pentoxifylline: beneficial effects in sepsis syndrome

Tumor necrosis factor (TNF) has a pivotal role in the pathogenesis of sepsis and septic shock. Suppression of its biosynthesis might therefore be one of the strategies in the treatment of sepsis. When peripheral white blood cells were stimulated with either E. coli lipopolysaccharide (LPS) or Staphylococcus aureus, pentoxifiline (PTX) inhibited TNF production. In contrast, only a moderate inhibitory effect was observed on the induction of interleukin 6 (IL-6). PTX inhibited not only the TNF production of monocytes, but also the TNF secretion of both granulocytes and unseparated whole blood. The in vitro TNF and IL-6 producing capacities were higher in septic patients (n = 31) than in healthy blood donors (n = 15). Administration of PTX (400 mg/day) to 20 of the septic patients resulted in TNF production similar to that found in healthy controls. It also subsequently led to an improvement of the clinical status classified by the APACHE II score. The soluble intercellular adhesion molecule-1 (sICAM-1) level was significantly higher in the sera of septic patients before PTX treatment (800-1200 ng/ml) than in normal individuals (50-150 ng/ml), but it decreased following PTX therapy. Cytofluorometric analysis revealed that the expression of ICAM-1 on stimulated mononuclear cells was inhibited by PTX. It is presumed that the suppressive effect of pentoxifylline on TNF production may be of clinical importance, improving the therapeutic strategies in septic syndrome.

The specific type IV phosphodiesterase inhibitor rolipram combined with adenosine reduces tumor necrosis factor-alpha-primed neutrophil oxidative activity

Monocytes and macrophages produce tumor necrosis factor-alpha (TNF alpha) in response to microbial products including endotoxin. TNF alpha is a potent primer of neutrophil (PMN) oxidative activity. Certain xanthine phosphodiesterase (PDE) inhibitors such as pentoxifylline have been shown to inhibit stimulated oxidative activity in PMN. In the present study, the non-xanthine PDE type IV inhibitor rolipram (4-[3'-cyclopentyloxy-4'-methoxyphenyl]-2-pyrrolidone) alone and in combination with adenosine is examined as a potential modulator of TNF alpha-primed PMN oxidative activity. Attainable in vivo concentrations of rolipram and physiological concentrations of adenosine alone and together synergistically decreased rhTNF alpha-primed suspended PMN oxidative activity stimulated by the chemoattractant f-met-leu-phe. The rolipram effect was reversible by washing, and rolipram had a comparable effect if added before or after priming, indicating that its effect was on the primed response rather than on priming per se. In addition, rolipram especially when combined with adenosine, decreased rhTNF alpha-stimulated PMN adherence to a fibrinogen-coated surface, and the oxidative burst of rhTNF alpha-stimulated adherent PMN. The specific adenosine A2a receptor agonists CGS 21680 and WRC-0474 had comparable activity to adenosine in these experiments. Adenosine (or CGS 21680) combined with rolipram synergistically increased f-met-leu-phe-stimulated PMN cAMP content. The effects of both adenosine and rolipram with adenosine could be only partly counteracted by treatment of the PMN with the protein kinase A inhibitor KT 5720, indicating that protein phosphorylation is only partially involved. Rolipram activity was about 1000 x (by molar concentration) greater than pentoxifylline in comparable assays. Thus, rolipram, especially when combined with adenosine, has potent modulating effects on PMN activation and may be useful in decreasing inflammatory tissue damage in patients with sepsis.

Effect of pentoxifylline on radiation-induced lung and skin toxicity in rats

PURPOSE

There is currently substantial clinical interest in pentoxifylline as an inhibitor of radiation-related normal tissue injury. To further assess this drug's potential toxicity-sparing effects, pentoxifylline was studied in rats using a radiation-induced lung injury model.

METHODS AND MATERIALS

Adult male rats were exposed to either sham irradiation or a single fraction of 21 Gy delivered to the left hemithorax. Four study groups were defined: those that received neither radiation nor pentoxifylline, those that received pentoxifylline (500 mg/L in drinking water) but no irradiation, those that underwent irradiation without pentoxifylline, and those that received both pentoxifylline and radiation. Lung injury was measured by changes in relative left:right lung perfusion ratios derived from quantitative gamma camera imaging of 99mTechnetium-macroaggregated albumin uptake in the pulmonary circulation. Serial scans were done over a 40-week period following radiation. Skin toxicity was also assessed. After 40 weeks, the animals were killed, and lung tissue was assayed for angiotensin converting enzyme activity as a marker for endothelial cell damage.

RESULTS

Both groups of radiated (with or without pentoxifylline) rats showed equivalent acute sharp decreases in left:right lung perfusion ratios compared to the nonirradiated groups, reaching a mean nadir value of 0.29 at week 4. Irradiated lung perfusion in subsequent weeks in the radiation-only group showed minimal recovery, with a plateau mean ratio of 0.37 (0.36-0.39). However, there was apparent later recovery of lung perfusion in the radiation with pentoxifylline group from weeks 14 through 40, to a mean ratio of 0.47 (0.43-0.52) (p < 0.01 compared to the radiation-only group). Angiotensin converting enzyme activity correlated closely with lung perfusion data. No effect of pentoxifylline on acute or late skin toxicity was detected.

CONCLUSIONS

This study suggests that pentoxifylline does not have any measurable effect on acute lung injury following hemithoracic irradiation in rats, but does result in sparing of later lung toxicity.

Caffeine consumption is associated with decreased severe late toxicity after radiation to the pelvis

PURPOSE

Recent studies have suggested that pentoxifylline, a methylxanthine, can prevent or ameliorate late radiation injury in animals and humans. Caffeine is a commonly consumed methylxanthine that provides a model for evaluating the impact of this category of drugs on radiation injury. A retrospective study was undertaken to determine if there is an association between caffeine consumption and a lower incidence of late radiation toxicity.

METHODS AND MATERIALS

From 1984 through 1990, 82 patients with cervical cancer and 53 patients with endometrial cancer were treated with primary or adjuvant radiation therapy at the University of Washington. Patients were interviewed regarding ingestion of caffeine-containing beverages, and average daily caffeine consumption during the time of radiotherapy was estimated. The evaluable patients (42 cervical, 31 endometrial) were stratified by quantity of caffeine consumption for correlation with the incidence of radiation toxicity.

RESULTS

Acute radiation toxicity was not associated with caffeine consumption for cervical or endometrial cancer. There was a nonstatistically significant trend toward a decrease in overall late radiation toxicity with increased caffeine intake for cervical cancer patients. Subgroup analysis revealed this trend to be attributable to a decreased incidence of severe late radiation injury in cervical cancer patients who consumed higher levels of caffeine at the time of their radiotherapy (p = 0.02). This relationship was not observable for late toxicity in the endometrial cancer patients due to the low incidence of severe late injury following radiation for that disease.

CONCLUSIONS

This investigation is supportive of previous studies showing a radioprotective effect for pentoxifylline, and suggests that the mechanisms of radioprotection may be common to methylxanthines as a drug class.

Tumor necrosis factor-alpha-induced inhibition of phosphatidylcholine synthesis by human type II pneumocytes is partially mediated by prostaglandins

TNF alpha seems to play an important role in the pathogenesis of adult respiratory distress syndrome. We studied the effect of TNF alpha on phospholipid synthesis by isolated type II pneumocytes and attempted to characterize the role of arachidonate metabolites and the influence of pentoxifylline on such an effect. Lung tissue obtained from both multiple organ donors (n = 14) and lung cancer patients (n = 11) was used for cell isolation. Surfactant synthesis was measured by the incorporation of D-[U-14C]glucose into phosphatidylcholine (PC). The basal PC synthesis was higher in the donor group than in the malignant group (3.44 +/- 0.19 vs 2.15 +/- 0.15 pmol/microgram protein x 120 min, P < 0.01), and, in the presence of 100 ng/ml of TNF alpha, the incorporation of labeled glucose into PC was reduced significantly in both donor (1.13 +/- 0.11 vs 3.44 +/- 0.19 pmol/microgram protein x 120 min, P < 0.01) and cancer (0.99 +/- 0.11 vs 2.15 +/- 0.15 pmol/microgram protein x 120 min, P < 0.01) groups. Indomethacin was able to completely block the cytokine-induced decrease in PC synthesis by pneumocytes from the malignant group and to attenuate the inhibitory effect of TNF alpha in those from donors, nordihydroguaiaretic acid having a similar effect. The TNF alpha effect can be blocked by pentoxifylline (100 micrograms/ml), a substance which can even succeed in reverting the basal secretory inhibition of cancer patients' pneumocytes to levels similar to those of the donor group. TNF alpha may contribute to the pathophysiology of adult respiratory distress syndrome by inhibiting the synthesis of surfactant. TNF alpha might be produced in lung tumors, resulting in chronic paracrine or systemic exposure of pneumocytes to low concentrations of the cytokine. The TNF alpha effect was not prevented completely by the blockage of the arachidonic acid metabolism, hence other mediators should also be implicated.

Pentoxifylline

Pentoxifylline (oxpentifylline) is a methylxanthine derivative with potent hemorrheologic properties. In the United States it is marketed for the treatment of intermittent claudication. Human and animal studies have shown that pentoxifylline therapy results in a variety of physiological changes at the cellular level, which may be important in treating a diverse group of human afflictions. Immune modulation includes increased leukocyte deformability and chemotaxis, decreased endothelial leukocyte adhesion, decreased neutrophil degranulation and release of superoxides, decreased production of monocyte-derived tumor necrosis factor, decreased leukocyte responsiveness to interleukin 1 and tumor necrosis factor, inhibition of T and B lymphocyte activation, and decreased natural killer cell activity. Hypercoagulable states improve through decreased platelet aggregation and adhesion, increased plasminogen activator, increased plasmin, increased antithrombin III, decreased fibrinogen, decreased alpha 2-antiplasmin, decreased alpha 1-antitrypsin, and decreased alpha 2-macroglobulin. Wound healing and connective tissue disorders may respond to an increase in fibroblast collagenases and decreased collagen, fibronectin, and glycosaminoglycan production. Fibroblast responsiveness to tumor necrosis factor is also diminished. Potential medical uses of pentoxifylline are reviewed.

In vitro immunomodulatory effects of pentoxifylline

Pentoxifylline (PTX), a methylxanthine derivative and phosphodiesterase inhibitor, is known to influence production and/or function of some cytokines. We examined the effect of PTX on the in vitro expression of cytokine genes using endotoxin- or phytohaemagglutinin (PHA)-stimulated human blood mononuclear cells. The expression of tumour necrosis factor (TNF)alpha, TNF beta interleukin (IL)-2 and interferon (IFN)gamma was inhibited by PTX in a dose-dependent manner, whereas expression of IL-1 alpha, IL-1 beta, and IL-6 was unaffected at concentrations up to 300 microM of PTX. The amount of TNF beta mRNA in PHA-stimulated blood mononuclear cells was reduced by PTX. Finally, PTX stimulated PHA-induced cell proliferation whereas antigen-induced cell proliferation was inhibited in the presence of PTX. The PTX analogues HWA-138 and A-802715 inhibited TNF alpha mRNA expression from endotoxin-stimulated mononuclear cells. These data suggest that PTX-analogues affect the in vitro immune response at different target points and that the response depends upon the respective triggering mechanism(s).

Enhancement of neutrophil-mediated injury to bovine pulmonary endothelial cells by Pasteurella haemolytica leukotoxin

In this study, we used an in vitro coculture system to determine which virulence factor from Pasteurella haemolytica A1 was responsible for augmenting bovine polymorphonuclear neutrophil (PMN)-mediated killing of bovine pulmonary artery endothelial cells (BPAEC). A 51Cr release cytotoxicity assay was used as a measure of BPAEC killing. The mechanisms associated with this BPAEC killing were also studied. Our results demonstrated that the leukotoxin and not the lipopolysaccharide from P. haemolytica was responsible for augmenting the PMN-mediated killing of BPAEC. Furthermore, this augmented killing was related to the stimulation of PMNs by the leukotoxin. Killing of BPAEC by leukotoxin-stimulated PMNs was diminished in the presence of the H2O2 inactivator, catalase. The membrane-permeant H2O2, hydroxyl radical (HO.) scavenger 1,3-dimethyl-2 thiourea, and the HO. scavenger dimethyl sulfoxide but not the myeloperoxidase inhibitor sodium azide attenuated this BPAEC killing. Pretreatment of BPAEC with a 21-aminosteroid (U74500A), a potent iron chelator-antioxidant, provided the most effective protection against BPAEC killing induced by leukotoxin-stimulated PMNs. These data were compatible with the concept that the H2O2 generated by leukotoxin-stimulated PMNs interacts with intracellular iron in the endothelial cell to form highly reactive HO.. We suggest that HO. may be a key factor in BPAEC killing. Furthermore, since the elastase-specific inhibitor N-methoxy-succinyl-Ala-Ala-Pro-Val-chloromethyl ketone (CMK) also attenuated BPAEC killing and both CMK and 1,3-dimethyl-2 thiourea functioned additively in protecting against BPAEC killing, we conclude that both HO. and elastase may jointly contribute to BPAEC killing induced by leukotoxin-stimulated PMNs. This study broadens our understanding of how leukotoxin-stimulated PMNs injure lung endothelial cells and provides new insight into the pathogenesis of bovine pneumonic pasteurellosis.

Caffeine potentiates the lethality of tumour necrosis factor in cancer cells

In this study we have investigated the interaction of caffeine, a prototypic methylxanthine, and TNF on the induction of cell death in mouse and human cell lines during progression from G1 to successive phases of the cell cycle. Exposure of cells to TNF (0.1-100 ng ml-1) as single agent for 48 h caused low or no lethality. The rates of cell death increased significantly when cells cultured with TNF for 24 h were exposed to caffeine (2.5-20 mM). The magnitude of the enhancement by caffeine was TNF and caffeine dose-dependent. The most effective response to this combination was observed in the mouse cell lines, WEHI and L929, followed by the human cell lines, HeLa, A375 and MCF-7, respectively. In L929 cells, TNF treatment did not inhibit DNA synthesis during the first S phase of the cell cycle (20-24 h), but it did block the progress toward a second S phase, indicating the cells were arrested at G2 phase or mitosis. Caffeine had great enhancer effect on L929 cells exposed to TNF for 24 h, but the effect was reduced in cells with either less than 24 h or greater than 28 h of exposure. L929 cells stimulated with TNF died via apoptosis, as judged by both morphological criteria and the occurrence of internucleosomal DNA cleavage. Exposure of TNF-treated cells to caffeine caused a greater increase in the proportion of apoptotic cells as well as the extent of internucleosomal DNA fragmentation.

Regulation of neutrophil interleukin 8 gene expression and protein secretion by LPS, TNF-alpha, and IL-1 beta

Neutrophils are possibly involved in the pathogenesis of various lung diseases through the release of numerous mediators. In the present study, we studied the regulation of IL-8 gene induction and protein secretion in human blood neutrophils. Northern blot analysis revealed that LPS increased IL-8 mRNA levels in neutrophils, with a maximal fivefold increase by 2 h. IL-8 mRNa levels returned to baseline values within 12 h. In contrast, LPS-stimulated monocytes demonstrated a sustained increase of IL-8 mRNA levels for more than 24 h. TNF-alpha, IL-1 beta, and phorbol myristate acetate also increased IL-8 mRNA levels in neutrophils. Immunohistochemical analysis confirmed that IL-8 was localized within stimulated neutrophils. IL-8 secretion by neutrophils and monocytes was quantified using a specific ELISA for IL-8. Resting neutrophils secreted minimal IL-8 activity. However when cells were stimulated with LPS, TNF-alpha, or IL-1B, neutrophils secreted IL-8. IL-8 secretion was most marked during the first 2 h after stimulation and decreased thereafter. In contrast, monocytes maintained a high rate of IL-8 secretion over 12 h. Although a single monocyte secreted 70-fold more IL-8 than did a single neutrophil after 4 h of incubation, the high abundance of neutrophils in peripheral blood made the neutrophil-secreted IL-8 more significant. During the first 2 h, neutrophils secreted approximately 40% of the IL-8 released by monocytes in the same volume of blood. This ratio decreased to 9% after 12 h. Neutrophil-secreted IL-8 may play an autocrine or paracrine role during the initial stage of inflammation.

Down-regulation of tumor necrosis factor expression by pentoxifylline in cancer patients: a pilot study

The wasting syndrome (cachexia) characterized by anorexia, malaise, and weight loss is observed in many patients with cancer or chronic infection. The excessive levels of tumor necrosis factor-alpha (TNF)/cachectin reported in 50% of cancer patients exhibiting clinically active disease may therefore mediate, at least in part, the cachexia associated with malignancy. Pentoxifylline, a substituted methylxanthine approved for treatment of intermittent claudication, has been shown in preclinical studies to down-regulate TNF RNA expression as well as TNF activity. We report that pentoxifylline suppressed TNF RNA levels on all three occasions in patients with initially elevated levels of TNF RNA. Pentoxifylline did not suppress TNF RNA to subnormal levels in all five patients with initially normal TNF RNA levels. Four patients reported an increased sense of well-being, improved appetite and ability to perform the activities of daily living. Two of these five patients with normal TNF levels each had a weight gain of more than 5% after 3 weeks of pentoxifylline therapy suggesting that, although TNF may be important in the pathogenesis of cancer cachexia, other anorexia-producing cytokines that are potentially affected by pentoxifylline may also be involved. No severe adverse effects were observed. Taken together these findings suggest that pentoxifylline can down-regulate TNF expression and improve the sense of well-being in cancer patients. A larger study with a randomized, double-blind, placebo-controlled design and more sophisticated estimates of quality of life will be needed to confirm these observations.

Subpopulation of hyperresponsive polymorphonuclear neutrophils in patients with adult respiratory distress syndrome. Role of cytokine production

To gain further insight into the pathogenesis of the adult respiratory distress syndrome (ARDS), we studied possible relationships among the activation status of circulating polymorphonuclear neutrophils (PMN), cytokine levels, and the severity of lung injury in 31 patients: 15 with ARDS, nine with severe pneumonia uncomplicated by ARDS, and seven mechanically ventilated with neither ARDS nor pneumonia. Nine healthy subjects served as controls. Using flow cytometry, we identified a subpopulation of PMN with an increased capacity to generate hydrogen peroxide after stimulation ex vivo in all three patient groups; significantly higher values were found in those with ARDS. The PMN stimulation index, a reflection of the degree of hyperresponsiveness, correlated with elevated levels of tumor necrosis factor-alpha (TNF alpha) in plasma, and both spontaneous and lipopolysaccharide-induced TNF alpha production by cultured monocytes. These biologic expressions of PMN activation and cytokine generation both correlated with indices of the severity of lung injury, but not with the overall clinical severity. In contrast, IL-6 and IL-1 beta showed little or no relationship with either the degree of lung injury or PMN hyperresponsiveness. We conclude that TNF-alpha-primed PMN may play a major role in the pathogenesis of ARDS-associated lung injury.

Nitric oxide mediates tumor necrosis factor-alpha cytotoxicity in endothelial cells

Tumor necrosis factor alpha (TNF-alpha) exerts multiple actions on endothelial cells including among others the expression of pro-coagulant activity and adhesion molecules, and secretion of cytokines. We now show that TNF-alpha induces a time- and dose-dependent cytotoxic effect on cultured bovine aortic endothelial cells. This TNF-induced cytotoxicity, which is preceded by increased production of nitric oxide (NO), is significantly decreased by the NO synthase inhibitor N-iminoethyl-L-ornithine (L-NIO). Dexamethasone, which prevents the expression of cytokine-induced NO synthase in endothelial cells, also inhibits TNF-alpha-dependent cytotoxicity. The results indicate that NO is involved in the cytotoxic effect of TNF-alpha on endothelial cells.

Tumor necrosis factor-induced protein phosphorylation in human neutrophils

Protein phosphorylation is central to multiple regulatory processes in cells. Tumor necrosis factor (TNF), a cytokine synthesized by macrophages, effects polymorphonuclear leukocyte (neutrophil) chemotaxis, induces superoxide anion generation, and mediates neutrophil adhesion to endothelial cells. Although protein phosphorylation is almost certainly involved in many TNF-mediated neutrophil functions, little is known about TNF's impact on neutrophil protein phosphorylation. Therefore, we studied human recombinant TNF-alpha-induced protein phosphorylation in human neutrophils. Neutrophils were preincubated with 32PO(4)2- and treated with a variety of stimulatory agents. One- and two-dimensional polyacrylamide gel electrophoresis was used to analyze phosphorylated proteins. Phosphoaminoacids were identified by two-dimensional thin layer chromatography electrophoresis. The findings were as follows: (1) TNF induces the phosphorylation of two 16-kD proteins (pI = 5.9 and 6.1) by 5- to 6-fold, and a 57-kD protein (pI = 5.8) by 3- to 4-fold compared with untreated neutrophils; (2) these proteins are phosphorylated as early as 15 min after stimulation with TNF, and phosphorylation is induced by concentrations of TNF as low as 1 ng/ml (10 U/ml); (3) TNF induces the phosphorylation of proteins at either serine or threonine residues and not at tyrosine; (4) TNF-stimulated neutrophils show a unique pattern of protein phosphorylation when compared to neutrophils treated with formylmethionylleucylphenylalanine; (5) lipopolysaccharide does not induce protein phosphorylation in neutrophils; (6) a 16-kD protein is phosphorylated in response to TNF in neutrophils but not in mononuclear cells; and (7) protein kinase inhibitors appear to have no effect on TNF-induced protein phosphorylation. Thus, the mechanism of action of TNF on neutrophils may involve protein phosphorylation.

Attenuation of LPS-induced neutrophil thromboxane b2 release and chemiluminescence

Polymorphonuclear leukocytes (PMN) may play a key role in acute lung injury and ARDS. The mechanisms of PMN-mediated lung injury include the release of inflammatory mediators, such as oxygen free radicals which cause direct tissue injury, and arachidonic acid metabolites which cause pulmonary vasoconstriction and increased vascular permeability. The goals of this in vitro study were 1) to assess the effects of PMN-activating agents (lipopolysaccharide, LPS; phorbol myristate acetate, PMA; tumor necrosis factor, TNF) on PMN thromboxane B2 (TXB2) release and oxygen free radical production and 2) to determine the effects of agents purported to suppress PMN activity (pentoxifylline, PTX; adenosine; dibutyryl cyclic AMP, DBcAMP; and terbutaline, TBN) on activator-induced PMN TXB2 release and oxygen free radical production. PMN TXB2 release was determined by radioimmunoassay and oxygen free radical production was monitored by chemiluminescence. Our results show that 1) LPS and PMA significantly increase PMN TXB2 release, whereas tumor necrosis factor (TNF) has no effect; 2) LPS and PMA significantly increase PMN chemiluminescence; 3) DBcAMP and TBN significantly reduce LPS-induced PMN TXB2 release whereas PTX and adenosine do not; 4) TBN significantly reduces PMA-induced PMN TXB2 release whereas other agents do not; 5) All agents (PTX, adenosine, DBcAMP, and TBN) significantly reduce LPS-induced PMN chemiluminescence but none attenuate PMA-induced PMN chemiluminescence. We conclude that: LPS and PMA activate PMN manifested by TXB2 release and chemiluminescence. Additionally, all the PMN suppressing agents do attenuate some PMN functions. Of interest, PTX, adenosine, DBcAMP, and TBN have different effects depending upon functional assay and activating agent. It will be important to investigate the mechanisms by which PMN suppressing agents alter signal transduction resulting in differential effects on PMN function.