Protective Effect Of Pentoxifylline Research Articles

EFFECT OF PENTOXIFYLLINE ON ISCHEMIC ACUTE RENAL FAILURE IN RABBITS

Previous studies have demonstrated that levels of tumor necrosis factor-α (TNF-α) or its mRNA expression are increased in acute renal failure of various types including ischemia/reperfusion injury. This study was undertaken to determine whether pentoxifylline (PTX), an inhibitor of TNF-α production, provides a protective effect against ischemic acute renal failure in rabbits. Renal ischemia was induced by clamping bilateral renal arteries for 60 min. Animals were pretreated with PTX (30 mg/kg, i.v.) 10 min before release of clamp. At 24 h of reperfusion of blood after ischemia, changes in renal function, renal blood flow, and the expression of TNF-α mRNA were evaluated. Ischemia/reperfusion caused a marked reduction in GFR, which was accompanied by an increase of serum creatinine levels. Such changes were significantly attenuated by PTX pretreatment. PTX ameliorated the impairment of renal tubular function, but it had no effect on the reduction of renal blood flow induced by ischemia/reperfusion. The protective effect of PTX on functional changes was supported by morphological studies. The impairment of glucose and phosphate reabsorption in postischemic kidneys was associated with a depression in the expression of Na+-glucose and Na+-Pi transporters. The expression of TNF-α mRNA was increased after reperfusion, which was inhibited by PTX pretreatment. The PTX pretreatment in vitro prevented the release of lactate dehydrogenase induced by an oxidant t-butylhydroperoxide in rabbit renal cortical slices, but it did not produce any effect on the oxidant-induced lipid peroxidation, suggesting that PTX protection is not resulted from its antioxidant action. These results suggest that PTX may exert a protective effect against ischemic acute renal failure by inhibiting the production of TNF-α in rabbits.

Pentoxifylline attenuates bacterial lipopolysaccharide-induced enhancement of allyl alcohol hepatotoxicity.

Small amounts of exogenous lipopolysaccharide (LPS) (10 ng/kg-100 microg/kg) enhance the hepatotoxicity of allyl alcohol in male Sprague-Dawley rats. This augmentation of allyl alcohol hepatotoxicity appears to be linked to Kupffer cell function, but the mechanism of Kupffer cell involvement is unknown. Since Kupffer cells produce tumor necrosis factor-alpha (TNF alpha) upon exposure to LPS, and this cytokine has been implicated in liver injury from large doses of LPS, we tested the hypothesis that TNF alpha contributes to LPS enhancement of allyl alcohol hepatotoxicity. Rats were treated with LPS (10-100 microg/kg iv) 2 h before allyl alcohol (30 mg/kg ip). Co-treatment with LPS and allyl alcohol caused liver injury as assessed by an increase in activity of alanine aminotransferase in plasma. Treatment with LPS caused an increase in plasma TNF alpha concentration, which was prevented by administration of either pentoxifylline (PTX) (100 mg/kg iv) or anti-TNF alpha serum (1 ml/rat iv) one h prior to LPS. Only PTX protected rats from LPS-induced enhancement of allyl alcohol hepatotoxicity; anti-TNF alpha serum had no effect. Exposure of cultured hepatocytes to LPS (1-10 microg/ml) or to TNF alpha (15-150 ng/ml) for 2 h did not increase the cytotoxicity of allyl alcohol (0.01-200 microM). These data suggest that neither LPS nor TNF alpha alone was sufficient to increase the sensitivity of isolated hepatocytes to allyl alcohol. Furthermore, hepatocytes isolated from rats treated 2 h earlier with LPS (i.e., hepatocytes which were exposed in vivo to TNF alpha and other inflammatory mediators) were no more sensitive to allyl alcohol-induced cytotoxicity than hepatocytes from naïve rats. These data suggest that circulating TNF alpha is not involved in the mechanism by which LPS enhances hepatotoxicity of allyl alcohol and that the protective effect of PTX may be due to another of its biological effects.

Pentoxifylline Prevents Upregulation of Monocyte Tissue Factor in Renal Transplant Recipients Undergoing Post-graft Complications

Pentoxifylline (PTX) has been demonstrated to improve graft survival in renal transplant recipients undergoing post graft complications. As activated monocytes are possible initiators of vascular damage through tissue factor (TF) expression, we evaluated the monocyte TF expression and endothelium activation markers in 140 consecutive patients receiving cadaveric kidney grafts, randomized in a double-blind study comparing PTX versus placebo. Monocyte TF expression and plasma von Willebrand factor, tissue plasminogen activator, thrombomodulin and tumor necrosis factor-alpha (TNF-alpha) levels were determined before transplantation and each month after. Additional samplings were realized in case of acute rejection. TF and TNF-alpha expression were significantly modified after graft. In patients with complications, PTX prevented the increase of TF expression at month one, and after rejection episodes. Endothelium activation markers were significantly modified after graft and in patients with complications but PTX had no significant effect on their plasma levels. These results suggest that the protective effect of PTX on graft survival could be related to the prevention of monocyte TF upregulation associated with complications.

Amelioration of ischemia-reperfusion injury in rat intestine by pentoxifylline-mediated inhibition of xanthine oxidase.

Intestinal ischemia-reperfusion (IR) injury results in cell destruction, which may be mediated by the generation of reactive oxygen species, potentially toxic metabolites of xanthine oxidase. Pentoxifylline (PTX) possesses a variety of biochemical and antioxidant properties that can improve capillary flow and tissue oxygenation. Because of these combined effects, it has been hypothesized that pentoxifylline would protect against intestinal IR. Young adult rats were randomly assigned to one of four experimental groups: IR/Placebo (n = 12) in which superior and inferior mesenteric arteries were clamped for 45 minutes and then reopened; IR/PTX (n = 11) in which IR was induced as in the Placebo group, but with 25 mg/kg PTX at 0, 30, and 60 minutes; No IR/Placebo (n = 12); and No IR/PTX (n = 6) in which placebo and PTX were applied with no IR. Blood and intestinal samples were taken for serial thiobarbituric acid-reducing substances (TBARS; index of lipid peroxidation), for xanthine oxidase-xanthine dehydrogenase ratios, glutathione, myeloperoxidase, and histopathology. Animals in the IR/PTX group had lower TBARS and the least severe histopathologic injury. Xanthine oxidasexanthine dehydrogenase ratios were elevated only in IR/ Placebo (0.67+/-0.22 vs. 0.45+/-0.14 in IR/PTX; 0.42+/-0.22 in No IR/Placebo; and 0.40+/-0.11 in No IR/PTX; p = 0.0009). Reduced glutathione was diminished in IR/PTX animals (38.9 +/-1.35 vs. 46.1+/-7.0 in IR/Placebo; 41.1+/-2.5 in No IR/ Placebo; 43.6+/-1.0 in No IR/PTX; p = 0.048). No differences were recorded in myeloperoxidase levels among groups. Pentoxifylline ameliorates histopathologic signs of injury and decreases lipid peroxidation (TBARS). Normal xanthine oxidase-xanthine dehydrogenase ratios in the treated compared with IR-only animals imply that the protective effect of PTX is at least partially mediated through inhibition of xanthine oxidase.

Oxidative modification of high-density lipoprotein 3 induced by human polymorphonuclear neutrophils. Protective effect of pentoxifylline.

The function of high-density lipoproteins (HDLs) in reverse cholesterol transport is impaired if HDLs are subjected to oxidative stress. Polymorphonuclear neutrophils (PMNs), which have been detected in the earliest stages of atherosclerotic lesions, are one of the most likely sources of the reactive oxygen species that cause such stress. In this study, we investigated the effect of a PMN oxidative burst on HDL3. We also studied the impact on these events of pentoxifylline, a drug that regulates granulocyte function. HDL3 (370 nmol.mL-1 cholesterol-HDL) was incubated with PMNs (2 x 106. mL-1) in NaCl/Pi in the presence or absence of an iron chelate complex (10 microm Fe-nitrilotriacetic acid) at 37 degreesC for 60 min or 24 h. Phorbol myristate acetate (PMA) or formyl-methionylleucyphenylalanine (fMetLeuPhe) was used to stimulate PMNs. In iron-free NaCl/Pi medium, PMA-stimulated PMNs had a 40% lower HDL3 alpha-tocopherol content, whatever the incubation time. In NaCl/Pi medium containing iron, there was 80% less HDL3 alpha-tocopherol at 60 min, and HDL3 alpha-tocopherol had almost disappeared after 24 h. In this latter condition, the amount of thiobarbituric acid-reactive substances was significantly higher than the respective control HDL3 (P < 0.05) and oxidation of HDL3 by PMA-stimulated PMNs was associated with cross-linking of apoprotein AI, which was detected by SDS/PAGE. Similar results were obtained with fMetLeuPhe-stimulated PMN except that HDL3 alpha-tocopherol was consumed much more slowly during the first 60 min. Pretreatment of PMNs with various concentrations of pentoxifylline (0.001-20 mm) led to the concentration-dependent inhibition of oxidative modification of HDL3 induced by stimulated PMNs. The addition of 20 mm pentoxifylline in the most extreme oxidative stress conditions resulted in 70% of HDL3 alpha-tocopherol being maintained, with no formation of thiobarbituric acid-reactive substances and a lower level of apoprotein AI cross-linking. Thus HDL3 is susceptible to oxidative modifications induced by stimulated PMNs, in the presence of an exogenous source of iron. Pentoxifylline inhibited the oxidative modification of HDL3 by PMNs.

Protective effect of pentoxifylline plus thalidomide against septic shock in mice.

Mortality caused by septic shock in experimental animals is reduced by thalidomide, an inhibitor of tumour necrosis factor alpha. Another drug that could act on the pathophysiological mechanisms of septic shock is pentoxifylline, an inhibitor of platelet aggregation that increases the flexibility of the erythrocyte membrane and has fibrinolytic activity. We studied the effect of pentoxifylline alone and combined with thalidomide in septic shock; 97 NIH mice were injected with lipopolysaccharides of Salmonella abortus equi and D galactosamine. Animals were separated in 4 groups; group A (n = 20) was used as control, group B (n = 15) received thalidomide 50 mg/kg, group C (n = 20) received pentoxifylline 40 mg/kg, and group D (n = 15) received thalidomide plus pentoxifylline. Mortality was recorded every hour. Additionally, 5 animals from each group were sacrificed 8 h after the induction of septic shock for histological analysis of heart, lung, brain, kidney, small intestine, adrenal glands and liver. Microscopic findings were rated as absent, mild, moderate and severe damage. In control animals histological analysis showed intense haemorrhage and necrosis in all organs studied. When compared with controls, treatment with pentoxifylline plus thalidomide reduced mortality (P < 0.03). The tissue damage was less severe in animals from the groups that received pentoxifylline or pentoxifylline plus thalidomide (P < 0.05). Pentoxifylline seems to potentiate the beneficial effects of thalidomide, reducing mortality and attenuating the pathological changes produced by septic shock.

Pentoxifylline prevention of altered hepatocyte calcium regulation during hemorrhagic shock/resuscitation.

To evaluate the effect of pentoxifylline on altered hepatocyte calcium regulation and hepatocyte oxidant injury after hemorrhagic shock. Prospective, randomized, controlled study. University research laboratory. Anesthetized, male Sprague-Dawley rats, weighing 220 to 300 g. Hemorrhagic shock was induced by bleeding rats to a mean arterial blood pressure of 40 mm Hg for 60 min. Rats were then resuscitated with 60% of shed blood and three-fold the bleed out volume of lactated Ringer's solution without and with pentoxifylline (50 mg/kg body weight). After hepatocyte isolation by portal collagenase perfusion, the rate of hepatocyte calcium influx (Ca2+in) in the absence and presence of epinephrine (100 nM), both cellular Ca2+ uptake (Ca2+up) and membrane Ca2+ flux (Ca2+flux) were determined, using 45Ca2+ incubation techniques. Hepatocyte lipid peroxidation was fluorometrically determined by thiobarbituric acid-reactive substances. Pentoxifylline inhibited the significant increase of hepatocyte Ca2+in, Ca2+up, and Ca2+flux observed in untreated rats subjected to hemorrhage/resuscitation. In shocked rats, pentoxifylline restored the impaired epinephrine-induced Ca2+ influx response and prevented increased hepatocyte lipid peroxidation. The protective effects of pentoxifylline could be attributed to its known anti-inflammatory properties reducing excessive in vivo stimulation of hepatocytes by Ca2+ agonistic mediators and attenuating oxygen radical-related disturbances of transmembrane Ca2+ transport mechanisms. Since altered cellular Ca2+ regulation is a key event of cellular dysfunction, resuscitation with pentoxifylline after hemorrhagic shock/resuscitation may provide an adjuvant therapeutic tool to prevent postischemic hepatic failure.

Differential effect of pentoxifylline on lipopolysaccharide-induced downregulation of cytochrome p450

It is now established that inflammatory stimuli such as lipopolysaccharides (LPS) and polyinosinic acid:polycytidylic (polyIC) suppress hepatic expression of cytochrome P450 (P450) genes in rat liver. Previous studies have suggested that LPS- or polyIC-induced downregulation of P450 was due to endogenously released inflammatory cytokines such as tumor necrosis factor-a (TNF-α), interleukin-1, interleukin-6, and interferons (IFNs). To improve our understanding of the role of inflammatory cytokines in mediating P450 depression, we investigated the possibility of preventing P450 downregulation with pentoxifylline. Pentoxifylline has been shown to inhibit LPS-induced TNF-a production by suppression of TNF-a gene expression. The present study shows that in uninduced male rats pentoxifylline selectively prevents the downregulation of microsomal P4501A2 and P4502B caused by LPS. No protective effect of pentoxifylline on the downregulation of P4502E1 and P4503A1/2 was observed. PolylC-induced downregulation of P4501A2, P4502B, P4502E1, and P4503A1/2 was not affected by pentoxifylline. These results suggest that the LPS-induced downregulation of P4501A2 and P4502B is mediated to a large extent by TNF-α. Other cytokines might be involved in the suppression of P4502E1 and P4503A1/2. The fact that polylC-induced downregulation is not protected by pentoxifylline is further evidence that this agent acts via a selective induction of IFNs.

EVIDENCE THAT PENTOXIFYLLINE REDUCES ANTI-CD3 MONOCLONAL ANTIBODY-INDUCED CYTOKINE RELEASE SYNDROME

Pretreatment with pentoxifylline (PTX), a methylxanthine known for its beneficial effects on tissue lesions induced by the injection of endotoxin or recombinant cytokines, was shown to decrease the systemic release of tumor necrosis factor and interleukin 2 occurring after the administration of the anti-CD3 monoclonal antibody 145-2C11 in mice. In parallel, PTX attenuated the hypothermia and the rise in blood urea nitrogen observed in this model. The protective effect of PTX on the toxicity of 145-2C11 was confirmed by the reduction of the mortality among D-galactosamine-sensitized animals. The mitigation by PTX of the release of cytokines did not affect the immunosuppression entailed by 145-2C11 as assessed by the unmodified cytotoxic T lymphocytes (CTL) unresponsiveness against alloantigens measured 48 hr after the injection of the mAb. In vitro experiments on human peripheral blood leukocytes indicated that PTX alone or in synergy with methylprednisolone (m-PDS) also inhibited the release of TNF and IL-2 induced by OKT3. Finally, in a preliminary pilot trial conducted in kidney transplant recipients, we observed that pretreatment with PTX (20 mg/kg i.v.) in addition to m-PDS (2 g i.v.) reduced by half the amount of TNF released in the blood stream after the first injection of OKT3, while no further reduction of the low levels of IL-2 was found.

PENTOXIFYLLINE IN THE ISOLATED PERFUSED RAT KIDNEY

The effects of pentoxifylline, a new methylxanthine with marked hemorrheologic properties, were studied following brief renal artery occlusion in the isolated rat kidney model perfused with cell-free Krebs-Henseleit buffer. Anuria was observed in 3 of 6 control kidneys within 5 min after reperfusion; urine flow was maintained in all rat kidneys perfused with pentoxifylline (2500 ng/ml). Glomerular filtration rate was significantly greater in kidneys administered pentoxifylline compared with controls following 40 min of postocclusion reperfusion (460 +/- 100 vs. 100 +/- 110 microliters/min/gKW; P less than 0.01). Pretreatment of kidneys with indomethacin, a nonspecific cyclooxygenase inhibitor, blocked the protective effects of pentoxifylline in this setting. These data suggest that the addition of pentoxifylline may prevent hypoxia-related changes in renal function of transplanted kidneys. Stimulation of renal prostaglandin synthesis, as well as an interaction at the level of the adenosine receptors, were most likely responsible for the observed beneficial effects of pentoxifylline.

Protective effect of pentoxifylline on gastric mucosa

Pentoxifylline (PF) has been shown to increase tissue oxygen tension. This study was performed to determine if PF has a protective effect on the gastric mucosa against alcohol (EtOH)-induced injury. Fasted Sprague-Dawley rats were pretreated with randomized test solution (control, normal saline, or PF, 75 mg/kg) intraperitoneally (ip). At 30 min, 100% EtOH (pH 8.5) was given intragastric. At 90 min, laparotomy was performed and gastric serosal stomach surface oxygen tensions ( pO 2) were measured. Stomachs were excised and opened and pH was measured. Photographs were taken and sections were obtained for histologic analysis to determine mucosal injury. The PF-pretreated rats had significantly higher serosal pO 2 and significantly lower intragastric pH than control animals. There was significantly less gross and histologic mucosal injury in PF-treated animals. We conclude that PF is protective against EtOH gastric mucosal injury. This effect correlates with increased gastric serosal pO 2 and is likely due to improved microcirculatory blood flow following PF administration.