Actin depolymerization and inhibition of capping induced by pentoxifylline in human lymphocytes and neutrophils

Preoperative oral pentoxifylline in case of coronary artery bypass grafting with left ventricular dysfunction (ejection fraction equal to/less than 30%)

OBJECTIVE

Most coronary artery bypass grafts are done by applying cardiopulmonary bypass, which usually induces unwanted inflammatory reactions and impairs the outcomes. In order to minimize the perilous response of cardiopulmonary bypass, pentoxifylline was getting used orally.

METHODS

In a prospective, placebo-controlled, randomized clinical trial, 178 coronary artery bypass graft candidates with ejection fraction lower/equal to 30%, divided into two equal groups (pentoxifylline and control), participated in the study. Pentoxifylline patients received 400 mg pentoxifylline 3 times a day for 3 days before operation. The outcomes were compared between groups using student's t-test, Mann-Whitney U-test, Pearson chi-square, or Fisher's exact test.

RESULTS

Pentoxifylline administration did not significantly affect troponin-T (p=0.68), but it reduced tumor necrosis factor-α (p=0.01) and interleukin-6 (p=0.01). It improved left ventricular ejection fraction significantly (p=0.01). White blood cell and platelet counts, hemoglobin, and hematocrit were not influenced by pentoxifylline. The drug did not affect blood urea nitrogen and creatinine, occurrence of renal failure, cerebrovascular accidents, and in-hospital mortality rate. The need for an intra-aortic balloon pump, cardiopulmonary bypass, and aortic cross-clamp times were not affected, either. Pentoxifylline decreased the intensive care unit stay (p<0.001), ventilation time, 10.4 hours in the pentoxifylline group against 14.7 hours in the control group (p=0.01), and the requirement of inotropic agents (p=0.02) and blood transfusion (p=0.01).

CONCLUSION

Pentoxifylline has more beneficial potencies in reducing adverse events after coronary artery bypass graft using cardiopulmonary bypass, than what are known.

Pentoxifylline impedes migration in B16F10 melanoma by modulating Rho GTPase activity and actin organisation

Cancer cell migration is a hallmark of metastatic cascade and compounds that can intervene in this process are clinically important. Pentoxifylline (PTX), a methyl xanthine derivative, inhibits B16F10 melanoma lung homing by inhibiting F10 invasion, MMP secretion and adhesion to matrix components. However, its effect on B16F10 migration remained unexamined, which we investigated in the present study. PTX significantly inhibits F10 migration in scratch wound assay. Elevation in cAMP levels inhibits F10 migration and PTX mediated inhibition of the process was found to be, in part, due to an increase in cellular cAMP levels. PTX induces Protein Kinase A (PKA) activity and PKA inhibitor partly reversed its effects on F10 motility. RhoA and Rac1 GTPases induce B16F10 motility and PTX was found to inhibit migration by affecting these molecules. Stress fibres and lamellipodial protrusions reduced significantly. This was accompanied with inhibition in RhoA and Rac1 membrane localisation. A stark inhibition in RhoA-GTP bound form was also observed. Taken together, the results indicate that PTX, through its phosphodiesterase action, inhibits RhoGTPases and associated actin organisation in B16F10 melanoma, thereby inhibiting cell motility.

Potentiation of antimetastatic activity of pentoxifylline in B16F10 and B16F1 melanoma cells through inhibition of glutathione content

PURPOSE

The aim of this work is to evaluate the antioxidative activity of antimetastatic agent pentoxifylline (PTX) in B16F10 and B16F1 melanoma cells.

MATERIALS AND METHODS

B16F10 and B16F1 cell lines were treated with PTX with different doses at different time intervals. Reduced glutathione, glutathione-S-transferase, and lipid peroxides were estimated to evaluate the action of PTX.

RESULTS

The activity of pentoxifylline treatment showed glutathione depletion, increased glutathione-S-transferase activity with upregulation of lipid peroxidation in B16F10 and B16F1 melanoma cells. However, the effect on GSH, GST, and LPOs was dependent on dose concentrations and time intervals.

CONCLUSIONS

Pentoxifylline, an effective membrane modifier, showed significant depletion in glutathione level in conjunction with increased lipid peroxidation. The results suggested an antimetastatic property by PTX at a nontoxic dose in B16F10 and B16F1 melanoma cells.

Antimetastatic efficacy of niosomal pentoxifylline and its combination with activated macrophages in murine B16F10 melanoma model

The aims of the present study were a) to enhance the effectiveness of antimetastatic agent, Pentoxifylline (PTX) by encapsulation in niosomes and b) to investigate the anticancer activity by combination therapy involving activated macrophages and PTX solution/PTX niosomes. Niosomes were prepared by lipid film hydration method. Particle size distribution revealed bimodal distribution with median vesicle size of 462 nm. The entrapment efficacy of PTX niosomes was found to be 9.64%. A cumulative release of 82.43% from niosomal suspension was observed at the end of 21 hours. Intravenous administration of niosomal PTX (6 mg/kg and 10 mg/kg) resulted in significant reduction in lung nodules in an experimental metastatic B16F10 model suggesting accumulation of PTX in a distant target organ-lung. Light microscopic observations of histologic sections showed a decrease in number of tumor islands in the lung. Macrophages activated by intraperitoneal injection of Iscove's Modified Dulbecco's Medium (IMDM) containing 20% fetal calf serum (FCS) followed by in vitro incubation with muramyl dipeptide (MDP) were more effective in controlling tumor spread than those activated by FCS alone. Combination therapy of activated macrophages and PTX solution/niosomal PTX showed no additive or synergistic effect in controlling tumor spread. Carbon clearance studies revealed that PTX inhibits the phagocytic ability of activated macrophages, thereby resulting in the failure of combination therapy.

Studies on the mechanisms responsible for inhibition of experimental metastasis of B16-F10 murine melanoma by pentoxifylline

Pentoxifylline (PTX), a methylxanthine derivative widely used as a hemorheological agent in the treatment of peripheral vascular disease, was studied to unveil the mechanisms responsible for its inhibitory action on B16-F10 experimental metastasis. In vitro pretreatment of B16-F10 cells with noncytotoxic concentrations of PTX significantly inhibited their adhesion to reconstituted basement membrane Matrigel(R) and type IV collagen as well as the relative activity of secreted 92 kD metalloproteinase. However, PTX pretreatment of B16-F10 cells did not affect their in vitro invasiveness. Heterotypic organ adhesion assays carried out with B16-F10 cells and suspended organ tissues demonstrated that pretreatment with noncytotoxic concentrations of PTX of both, tumor cells or lung tissue, brought about a dose-dependent inhibition of melanoma cell adhesion to lung. Immunohistochemical studies using antibodies against CD31 adhesion molecule (PECAM-1) revealed that B16-F10 cells adhere to lung endothelial cells. Our results suggest that PTX may exert its inhibitory effect on tumor lodgment, and as a consequence of that on experimental metastases, through an inhibitory action on cell adhesion molecules.

Pentoxifylline inhibits tumor necrosis factor-alpha (TNF alpha)-induced T-lymphoma cell adhesion to endothelioma cells

Pentoxifylline, a methylxanthine derivative, has been shown to inhibit T-cell-mediated cutaneous immune response by yet ill-understood mechanisms. Because cell adhesion to endothelial cells is a critical step in the initiation of such immune responses, we analyzed whether pentoxifylline would affect this process. To address this issue, adhesion of mouse T-lymphoma cells (TK-1) to mouse endothelioma cells (eEnd.2), either untreated or stimulated with tumor necrosis factor-alpha (TNF alpha), was studied. Pentoxifylline reduced the ability of endothelioma cells stimulated with different concentrations of TNF alpha, but not of untreated endothelioma cells, to bind T-lymphoma cells in dose-dependent (10(-5)-10(-3) M) fashion. Selective incubation of either endothelioma cells or T-lymphoma cells revealed that pentoxifylline acted exclusively on the endothelioma cells, even when added after TNF alpha stimulation. We questioned whether pentoxifylline suppressed T-lymphoma cell/endothelioma cell interactions by interfering with adhesion molecules expressed by either cell. However, as determined by flow cytometry, pentoxifylline did not alter TNF alpha-induced upregulation of intercellular adhesion molecule-1 or vascular cellular adhesion molecule-1 on endothelioma cells nor did it affect constitutive CD11a, CD18, or alpha 4-integrin expression on T-lymphoma cells, suggesting that rather than affecting quantitative expression of these adhesion molecules, pentoxifylline might modulate their avidity. We conclude that pentoxifylline in therapeutically achievable concentrations is a potent inhibitor of TNF alpha-induced T-lymphoma cell adhesion to endothelioma cells. This finding may account, at least in part, for the recently discovered anti-inflammatory action of pentoxifylline.

Long-term immunotherapeutic intervention with pentoxifylline in a mouse model of thermal injury and infection

Major thermal or traumatic injury often results in abnormalities of immune function, and these abnormalities contribute to the increased susceptibility to infection observed in these patients. Abnormalities of T-cell function, including decreased proliferation and secretion of cytokines are observed following major injury and, conversely, there is markedly increased monokine production. Thus, therapy of this syndrome might logically be aimed at modulating the immune system to upregulate T-cell function and downregulate monocyte hyperactivation. Pentoxifylline (PTX), a methylxanthine derivative, has been shown to be therapeutically effective in several animal models. The purpose of this study was to evaluate PTX and its effect on cytokine production in a mouse model of thermal injury and to study its effect on survival after septic challenge. The results show that PTX therapy after injury can restore T-cell production of IL-2 and downregulate the hyperactive macrophage secretion of proinflammatory cytokines. However, improvement in survival resulting from this therapy following thermal injury and septic challenge depends on timing of dosage.

Swinholide A is a microfilament disrupting marine toxin that stabilizes actin dimers and severs actin filaments

Swinholide A, isolated from the marien sponge Theonella swinhoei, is a 44-carbon ring dimeric dilactone macrolide with a 2-fold axis of symmetry. Recent studies have elucidated its unusual structure and shown that it has potent cytotoxic activity. We now report that swinholide A disrupts the actin cytoskeleton of cells grown in culture, sequesters actin dimers in vitro in both polymerizing and non-polymerizing buffers with a binding stoichiometry of one swinholide A molecule per actin dimer, and rapidly severs F-actin in vitro with high cooperativity. These unique properties are sufficient to explain the cytotoxicity of swinholide A. They also suggest that swinholide A might be a model for studies of the mechanism of action of F-actin severing proteins and be therapeutically useful in conditions where filamentous actin contributes to pathologically high viscosities.

Pentoxifylline prevents a decrease in arterial oxygen tension in oleic acid-induced lung injury

OBJECTIVES

a) To determine whether pentoxifylline has a preventive effect on the decrease in PaO2 that is caused by oleic acid, and whether pentoxifylline facilitates normalization of PaO2 from the decreased state. b) To examine whether pentoxifylline can attenuate an increase in pulmonary vascular permeability that is induced by oleic acid.

DESIGN

Prospective trial.

SETTING

University laboratory.

SUBJECTS

a) A total of 48 guinea pigs (700 to 1100 g) for blood gas analysis. b) A total of 28 guinea pigs (390 to 670 g) for measurement of pulmonary vascular permeability.

INTERVENTIONS

a) For blood gas analysis, the guinea pigs were mechanically ventilated. Oleic acid (15 microL/kg) was injected into the guinea pigs to decrease PaO2. Pentoxifylline (5 or 20 mg/kg) was administered 40 or 3 mins before oleic acid injection or 13 mins after oleic acid injection. b) For measurement of pulmonary vascular permeability, the guinea pigs were anesthetized with pentobarbital and catheterized via the external jugular vein for drug administration. Pentoxifylline (20 mg/kg) plus Evans blue (30 mg/kg) or theophylline (20 mg/kg) plus Evans blue (30 mg/kg) were administered at 40- and 1-min intervals before oleic acid (15 microL/kg) injection, respectively. Perfusion with saline was performed through the aorta 90 mins after the oleic acid injection. The airways were removed and separated into the trachea, the main bronchus, the proximal bronchus, and the distal bronchus. Evans blue was extracted from the airways with formamide for 18 hrs and measured.

MEASUREMENTS AND MAIN RESULTS

a) We measured PaO2, PaCO2, and pH, and recorded airway pressure and systemic blood pressure at 15, 10, and 5 mins before oleic acid injection and at 6, 10, 15, 35, 55, and 75 mins after oleic acid injection. Compared with the control groups, a decrease in PaO2 by oleic acid was significantly prevented when pentoxifylline (5 or 20 mg/kg) was administered 40 mins before oleic acid injection. However, a decrease in PaO2 by oleic acid was not significantly reduced when pentoxifylline was administered 3 mins before oleic acid injection. Pentoxifylline administered 13 mins after oleic acid injection did not affect the recovering course of PaO2 significantly. b) An increase in pulmonary vascular permeability by oleic acid was significantly attenuated by both pentoxifylline and theophylline. The effect of theophylline was significantly stronger than the effect of pentoxifylline in the main bronchi. The effect of theophylline was not significantly different from the effect of pentoxifylline in other areas.

CONCLUSION

Pentoxifylline is a noteworthy drug that could be a candidate as a therapy to help prevent hypoxemia in lung injuries that share a common mechanism with oleic acid-induced lung injury.

Effects of xanthine derivatives on phosphatidylcholine secretion in primary culture of rat type II pneumocytes

Xanthine derivatives, pentoxifylline, aminophylline, theophylline and chinoin-170, increased phosphatidylcholine secretion in a primary culture of rat type II pneumocytes. However, these xanthines alone had no effect on intracellular cAMP levels in type II pneumocytes. In contrast, terbutaline-induced secretion of phosphatidylcholine was augmented by these xanthines, and the augmentation depended on the increase of cAMP levels. These results suggest that the xanthines induce phosphatidylcholine secretion possibly through cAMP-dependent and cAMP-independent pathways in the primary culture of rat type II pneumocytes.

Improved tumour oxygenation and radiosensitization by combination with nicotinamide and pentoxifylline

We hypothesized that the combination of pentoxifylline (PTX) and nicotinamide (NA) can reduce the radioresistance of FSaII murine fibrosarcoma by improving oxygenation of the hypoxic tumour cells. The purpose of this study was to test the hypothesis; first, tumour blood flow after treatment with NA, PTX, and the combination (PTX+NA) was measured using laser Doppler flowmetry. Second, intratumour pO2 after various treatments was measured polarographically using O2 microelectrodes. Third, the radiation response was also measured, i.e. after an exposure to 20 Gy, the time required to reach a four-fold increase in initial tumour volume was 18 days in the saline-treated control group, 21 days in the NA-treated group, 26 days in the PTX-treated group, but was 36 days in PTX+NA treated group. Interestingly, tumour blood flow significantly increased at 10 min after injection of PTX+NA. The mean pO2 in untreated control tumours was 7.5 mmHg, increasing to 13.1 mmHg after 500 mg/kg of NA alone. Repeated injections of PTX with 100 mg/kg/day for 3 days significantly increased intratumour pO2 to 17.2 mmHg. Compared with PTX alone, PTX+NA slightly increased intratumour pO2 from 17.2 to 18.5 mmHg. However, the percentage of regions having values < 2.5 mmHg significantly decreased from 5% with PTX alone to 1% with PTX+NA. In conclusion, single or multiple injections of PTX may increase available O2 in the tumour and thus ameliorate hypoxia in tumour microregions. As previously reported, the subsequent injection of NA may efficiently oxygenate acutely hypoxic cells. Consequently, PTX+NA may increase the radioresponse of tumours by oxygenating chronic as well as acutely hypoxic cells. PTX alone or in combination with NA is potentially useful to radiosensitize tumours.

Pentoxifylline inhibits the expression of tissue factor mRNA in endotoxin-activated human monocytes

Tissue factor (TF) is a transmembrane glycoprotein which, in association with factor VII(a), is the main activator of coagulation. In illnesses such as Gram-negative endotoxemia, circulating monocytes synthesize and express substantial TF activity, resulting in extensive disseminated intravascular coagulation. We investigated the way in which TF is suppressed by pentoxifylline (PTX), and found that PTX down-regulates immunologic TF expression and specific mRNA production in response to LPS. Since TF mRNA stability is not altered, this effect appears to take place at the transcriptional level.

The effect of endotoxin and tumour necrosis factor on erythrocyte and leucocyte deformability in vitro

Microcirculatory disorders are a common finding in sepsis. We have analysed the influence of two factors released in sepsis, endotoxin and tumour necrosis factor (TNF), on rheological properties of blood cells. The deformability of mixed cell suspensions, isolated erythrocytes, mononuclear cells, or polymorphonuclear leucocytes exposed to endotoxin and TNF in vitro was assessed by filtration through pores of different sizes. Mixed blood cell suspensions showed an increase in cell rigidity when incubated with 100 ng/ml endotoxin. The filtration resistance of isolated erythrocytes, mononuclear or polymorphonuclear leucocytes was not affected by endotoxin. Incubation with TNF in physiological concentrations increased the rigidity of mixed blood cells and of isolated polymorphonuclear leucocytes in a dose- and time-dependent manner, while erythrocytes and mononuclear leucocytes remained unaffected. Polymorphonuclear cells showed decreased deformability associated with shape changes (polarized and non-polar cells with surface protrusions and a shift of F-actin into protrusions). The decrease in deformability was reversed by cytochalasin B or xanthin derivatives such as pentoxifylline. We conclude that TNF decreases the passive deformability of polymorphonuclear leucocytes, which may affect the microcirculation in sepsis. The reversibility with xanthin derivatives may represent a new therapeutic approach for the high morbidity and mortality in sepsis.

Pentoxifylline modulates deformability, F-actin content, and superoxide anion production of polymorphonuclear leukocytes from diabetic cats

Capillary occlusion is an early event in the development of diabetic retinopathy, and white blood cells have recently been shown to be involved. We have shown previously that pentoxifylline improves deformability and decreases F-actin content of unstimulated polymorphonuclear leukocytes from normal human subjects. The purpose of this study was to determine if pentoxifylline would improve three properties of unstimulated polymorphonuclear leukocytes from diabetic cats. The measured parameters were mechanical (whole cell deformability), structural (F-actin content) and biochemical (rate of superoxide anion production). Chronic hyperglycemia was induced in three cats by partial pancreatectomy, and they were kept in poor glycemic control for at least 6 months prior to the study. Polymorphonuclear leukocytes were isolated and the entry time of individual passive cells was measured during aspiration into a 4-micron micropipette under constant suction pressure (-15 cmH2O). Deformability was defined as the inverse of the entry time. F-actin content of passive cells was measured by NBD-phallacidin labeling followed by flow cytometry. The rate of superoxide anion production was measured spectrophotometrically by superoxide dismutase-inhibitable cytochrome c reduction. Following incubation for 15 min with 0.1, 1.0 and 10.0 mM pentoxifylline, the average entry time of passive polymorphonuclear leukocytes was reduced from control by 11 +/- 5% (P = 0.045), 17 +/- 6% (P = 0.007), and 36 +/- 5% (P < 0.001), respectively. The F-actin content decreased by 0%, 4 +/- 0.6% (P < 0.001), and 10 +/- 3% (P < 0.001), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Lack of effect of pentoxifylline on red blood cell deformability

The proposed mechanism of action for pentoxifylline's beneficial effect in peripheral vascular disease is an improvement in red blood cell deformability. Likewise, single doses of pentoxifylline in healthy volunteers have been shown to improve whole blood filterability, which was suggested to occur as a result of augmented red blood cell deformability. To further assess this, the authors studied the effects of short-term pentoxifylline administration (400 mg three times daily for 7 days) on red blood cell deformability in ten healthy, methylxanthine-free, nonsmoking volunteers. Blood samples were obtained at baseline and after 1 week of therapy (steady-state). Samples were analyzed for red blood cell deformability by ektacytometry, which showed no significant change in deformability in any subject. Despite the improvement in whole blood filterability associated with both single-dose and short-term administration of pentoxifylline, the current study demonstrates no effect on red blood cell deformability after short-term administration in healthy volunteers.

Vasodilator action of pentoxifylline on microcirculation of rat cremaster muscle

Pentoxifylline improves microvascular blood flow in conditions of vascular insufficiency. The clinical benefits of pentoxifylline have been attributed to its effects on the cellular elements of whole blood, although a few studies suggest it may also be a vasodilator. The purpose of this study was to determine whether pentoxifylline has a vasodilator effect on the luminal diameter of small arteries preconstricted with norepinephrine and on resting small arteries in the rat cremaster muscle. Intravital videomicroscopy was used in order to observe directly the vasodilator capacity of topically applied pentoxifylline. The results reveal that pentoxifylline (100 microM and more) can significantly dilate small arteries preconstricted with norepinephrine. Pentoxifylline had no effect on the diameter of resting small arteries. These results suggest that vasodilation may play a role in the ability of pentoxifylline to improve arterial blood flow.

Pentoxifylline and other methyl xanthines inhibit interleukin-2 receptor expression in human lymphocytes

Addition of pentoxifylline to lymphocytes caused a dose-dependent decrease in PHA-induced interleukin-2 receptor (IL-2R) expression. Expression of IL-2R protein and mRNA were inhibited by 60% at a concentration of 1 mM. Pentoxifylline also inhibited release of IL-2R into the medium by 85%. Treatment with recombinant IL-2 (50 U/ml) did not abrogate the effect of pentoxifylline. In addition to inhibition of IL-2R expression, pentoxifylline also decreased the expression of transferrin receptors and class I MHC antigens. Pentoxifylline also inhibited cell proliferation. However, aphidicolin, an inhibitor of DNA polymerase alpha inhibited cell proliferation to the same extent as pentoxifylline, but had no effect on IL-2R expression, indicating that inhibition of cell proliferation does not necessarily lead to inhibition of IL-2R expression. The inhibitory effect on IL-2R expression was also noted with other methylxanthines, theophylline and isobutylmethylxanthine, and with dbcAMP and forskolin. The inhibitory activity of pentoxifylline was prevented by W-13, a calmodulin antagonist, but not by HA-1004, a cyclic AMP-dependent protein kinase inhibitor. This suggests that pentoxifylline might act in part through a Ca2+/calmodulin-dependent mechanism. Pentoxifylline and other methylxanthines may prove useful in delineating the biochemical pathways involved in induction and expression of cell surface receptors.

Effect of pentoxifylline on decreased in vitro mononuclear leucocyte chemotaxis in vascular and polysystemic autoimmune diseases

Impaired mononuclear leucocyte (MNL) motility can be found both in vascular and autoimmune diseases. Pentoxifylline (PTX) has a well-known therapeutic effect in vascular diseases, which is based on the rearrangement of blood cell cytoskeleton and thus increased microcirculatory flow. Most data on PTX concern red blood cells and granulocytes so now the effect of PTX on previously decreased MNL migration and chemotaxis was investigated in vitro. The results of MNL chemotaxis studies described here suggest that this drug enhances impaired MNL motility in obliterative atherosclerosis and systemic lupus erythematosus and thus may also be introduced in the treatment of certain polysystemic autoimmune diseases with decreased in vitro MNL chemotaxis.

Attenuation of spontaneous pseudopod formation in human neutrophils by pentoxifylline

The effects of pentoxifylline (PTX) on spontaneous pseudopod formation in neutrophils in response to the tripeptide formyl-Met-Leu-Phe (fMLP), endotoxin, human complement C5a, and leukotriene B4 (LTB4) were examined in autologous plasma. Unseparated supernatant leukocyte suspensions from fresh heparinized venous human blood were incubated with PTX (0-5 mM) for 25 min and then stimulated for 5-25 min within a range of concentrations of fMLP, endotoxin, complement C5a, and LTB4. The cell suspensions were fixed with glutaraldehyde and stained with crystal violet in acetic acid; the percentage of neutrophils with pseudopods was determined under high-resolution light microscope. The results show that PTX significantly decreases formation of pseudopods in the presence of all four stimulators. The mechanism of pseudopod suppression appears to be independent of the adenosine receptor. PTX and its analogues, HWA 138 and HWA 448, decreased pseudopod formation by similar amounts when stimulated with 10(-8)M fMLP. These results suggest that PTX may improve microvascular perfusion and attenuate neutrophil-mediated injury by reducing the degree of neutrophil pseudopod formation in free suspension and microvascular entrapment.

Autographa californica M nuclear polyhedrosis virus and cytochalasin D: antagonists in the regulation of protein synthesis

During infection by the baculovirus Autographa californica multiple nuclear polyhedrosis virus (AcMNPV), synthesis of host proteins in IPLB-Sf-21 cells is inhibited. We report here that cytochalasin D (CD), a drug that specifically interacts with actin, behaved as an antagonist in the virus-mediated shutdown of host proteins actin and tubulin. In uninfected cells, CD caused an increase in actin synthesis but had no apparent effect on tubulin synthesis. In infected cells, CD similarly enhanced actin synthesis early in infection and delayed the virus shutoff of actin synthesis by 14 hr. The shutoff of tubulin synthesis was delayed by 8 hr. Addition of CD to infected cells after host protein synthesis ceased resulted in an induction of actin synthesis reversing viral inhibitory effects. Similarly, the removal of CD resulted in virus-induced inhibition of actin synthesis. Treatment of infected cells with CD caused a delay in the onset and/or shutoff of at least five viral proteins and inhibited the amplification of polyhedrin synthesis by at least 8 hr.

Anti-inflammatory effects of pentoxifylline in claudication

We measured neutrophil elastase/alpha 1 proteinase inhibitor complex (E/alpha) levels by ELISA in plasma samples drawn from 19 patients with claudication, before and at 1 and 2 months after initiation of pentoxifylline (PTF), 400 mg. p.o. tid. Plasma E/alpha levels declined in all eight patients whose initial values were more than 300 ng elastase per ml. Whole blood viscosity (wbv) was reduced by two months' treatment in 12 of 14 patients tested. The relative change in wbv was significantly related to the relative change in E/alpha (R2 = 0.8), for patients with elevated initial E/alpha levels, suggesting a common or related mechanism for the two effects. Plasma crosslinked fibrin D-dimer fragments (XDP) measured by ELISA as indicators of coagulation activity were lower compared to pretreatment levels in 9 of 10 samples drawn when symptoms were improved on PTF, whereas they were increased in 6 of 9 samples drawn when symptoms were worse or unchanged. Plasma viscosity, C-reactive protein and alpha 1-acid-glycoprotein did not change significantly with PTF treatment. Together these findings are consistent with the possibility that reduced microvascular neutrophil activation and coagulation play a role in the clinical efficacy of PTF in intermittent claudication.

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.

Amelioration of doxorubicin resistance by pentoxifylline in human chronic myeloid leukemia cells in vitro

Doxorubicin (DOX) is a potent anticancer agent, the use of which is limited by its cumulative dose-dependent cardiotoxicity. Pentoxifylline (PTX) is a non-toxic methylxanthine used clinically for the treatment of intermittent claudication. It is an active haemorheological agent, used for the treatment of defective microcirculation. In the present study, we employed PTX as a drug response modulator in combination with DOX to achieve increased cytotoxicity in human chronic myeloid leukemia (CML) cells. Inhibition of 3H-TdR incorporation was used as a measure of cytotoxicity. PTX at 100 microM concentration significantly (P less than 0.001) potentiated DOX-mediated DNA biosynthesis inhibition in CML cells in vitro. Significant synergistic inhibition was seen in 13 out of 22 CML samples. Decreased DOX accumulation is a characteristic feature of DOX resistant tumor cell lines. Drug accumulation studies demonstrated that PTX significantly (P less than 0.02) increased the intracellular accumulation of DOX in the CML cells. The enhanced DOX accumulation can be a mechanism of increased cytotoxicity by DOX-PTX combination.

Alteration of the functional effects of granulocyte-macrophage colony-stimulating factor on polymorphonuclear leukocytes by membrane-fluidizing agents

Locomotion and oxidative metabolism of polymorphonuclear leukocytes from 15 patients receiving recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF) were examined in vitro. At the end of each GM-CSF treatment course, polymorphonuclear leukocyte (PMN) chemotactic responses were suppressed and no enhancement of formyl-peptide-stimulated superoxide production was observed. The priming of PMN superoxide production normally seen after in vitro GM-CSF exposure was also blunted in these cells. By using control donor PMN, two membrane-fluidizing agents, pentoxifylline and butanol, were shown to normalize suppressed PMN chemotaxis caused by in vitro GM-CSF (1 nM) exposure. Pentoxifylline, but not butanol, also reversed the effects of in vitro GM-CSF on PMN superoxide production. When PMN obtained from six patients at the end of GM-CSF therapy were exposed to pentoxifylline in vitro, the chemotactic suppression typically observed was significantly improved. The data suggest that GM-CSF may affect PMN function via mechanisms involving membrane fluidity or cell deformability or both.

Pentoxifylline inhibits actin polymerization in human neutrophils after stimulation by chemoattractant factor

Pentoxifylline (PTX) has been recently reported to stimulate PMN chemotaxis under dense agarose. The present study was designed to characterize the effect of PTX on actin polymerization before and after stimulation by the chemotactic factor f-MLP- We used two different methods to determine the proportion of actin in the filamentous form: SDS-polyacrylamide gel electrophoresis to study the Triton X-100 insoluble cytoskeleton, and flow cytometry using fluorescent Rhodamine-Phalloidin to study actin conformation. PTX (10(-3) M) did not affect the amount of F-actin (polymerized G-actin) incorporated into the cytoskeleton, but reduced total F-actin in a dose-dependent manner, at all concentrations of f-MLP used. Moreover, this inhibitory effect appeared more clearly in PMN with the higher activation ratios. Thus F-actin is only partially incorporated into the cytoskeleton, and PTX-induced reduction of non-incorporated actin may reduce the stiffness of activated PMN. This could explain the increased chemotaxis of PMN across the small holes of dense agarose.

Effect of pentoxifylline on the flow of polymorphonuclear leukocytes through a model capillary

Pentoxifylline is a methylxanthine derivative used to increase blood flow in peripheral atherosclerosis. Pentoxifylline is known to increase whole blood filtration rate, and recent evidence suggests that pentoxifylline increases the filtration rate of polymorphonuclear leukocytes (PMNs). The purpose of this study was to directly observe and quantitate the effect of pentoxifylline on the flow of individual PMNs into a model capillary. Short-term incubation of human PMNs with 10 mM pentoxifylline inhibited cell activation, as judged by a significant reduction in the number of neutrophils forming pseudopods. Furthermore, incubation of PMNs from 6 healthy men with 0.1, 1.0 and 10 mM pentoxifylline significantly decreased the time required for individual cells to be aspirated into a 4 microns pipet under constant pressure by 16 +/- 5%, 21 +/- 7%, and 41 +/- 8%, respectively (mean +/- SEM, p less than or equal to 0.05), compared with control. These experiments are the first direct demonstration of increased deformability in neutrophils treated with pentoxifylline. The results are consistent with the hypothesis that the beneficial effect of pentoxifylline on microvascular perfusion is partly due to an inhibition of PMN stiffness and activation.

Rapid deformation of "passive" polymorphonuclear leukocytes: the effects of pentoxifylline

Entry times for spherical (no pseudopods) polymorphonuclear leukocytes (PMNs) into a 4 microns micropipet have been measured as a function of pipet suction pressure (2,500-20,000 dyn/cm2) and concentration of the drug pentoxifylline (PTX, 0.1-10.0 mM). For control cells (0 mM PTX), entry rates (reciprocal entry times) increased almost linearly with increasing suction pressure, indicating a Newtonian-like behavior. With incubation in PTX solutions, entry rate vs. suction pressure became increasingly non-linear, suggesting a shear-thinning effect for the dissipative structure. At a given suction pressure the rate of entry showed a dose-dependent increase with increasing PTX concentration, the effect being most pronounced at high suction pressures (20,000 dyn/cm2). Also, with increasing PTX concentration two other effects were observed: i) there was a decreased incidence of cells that displayed pseudopodia, and ii) there was an increased incidence of cells forming hernias and an increased streaming of cell cytoplasm during aspiration. The first observation points to a down-regulation of the cell's functional ability to "activate" in response to surface/chemical stimuli, and the second indicates that both the cortical and cytoskeletal networks are weakened either by disruption and/or reduction in density of the protein polymers. These observations are in line with other recently published experiments which suggest that the rheological effects of pentoxifylline on PMNs may be associated with the state of actin.

Effect of pentoxifylline on developmental changes in neutrophil cell surface mobility and membrane fluidity

Polymorphonuclear leukocytes (PMNs) from human neonates respond less efficiently to chemotactic factor stimulation than do PMNs from adults. The biologic mechanisms underlying this developmental process are poorly understood. In previous studies, we have found that pentoxifylline, an agent report to enhance membrane deformability, increased the chemotactic response of neonatal PMNs. In the present studies, we have examined the effect of pentoxifylline on cell surface mobility and membrane fluidity by assessing fluorescent concanavalin A (Con A) capping and fluorescent polarization (FP). Baseline Con A capping was lower in the PMNs of neonates when compared to PMNs from adult controls. Colchicine, which increases capping by disrupting microtubules, exaggerated the differences between the adult and neonatal PMNs. Following exposure of neonatal PMNs to pentoxifylline, colchicine enhanced Con A capping to levels equivalent to those of colchicine-treated PMNs from adults. Employing a fluorescence polarization (FP) assay, we found the fluid state of the membrane of PMNs from neonates was significantly less than that of adult controls. Pentoxifylline alone significantly increased the fluidity of the cell membranes of neonatal PMNs while decreasing elevated basal levels of F-actin in the cell. These data suggest an intrinsic cytoskeletal difference in the PMNs of neonates that may be responsive to pharmacologic manipulation.