Efficacy, toxicity, and pharmacokinetics of pentoxifylline and its analogs in experimental Staphylococcus aureus infections

A Neonatal Murine Escherichia coli Sepsis Model Demonstrates That Adjunctive Pentoxifylline Enhances the Ratio of Anti- vs. Pro-inflammatory Cytokines in Blood and Organ Tissues

Introduction: Neonatal sepsis triggers an inflammatory response that contributes to mortality and multiple organ injury. Pentoxifylline (PTX), a phosphodiesterase inhibitor which suppresses pro-inflammatory cytokines, is a candidate adjunctive therapy for newborn sepsis. We hypothesized that administration of PTX in addition to antibiotics decreases live bacteria-induced pro-inflammatory and/or enhances anti-inflammatory cytokine production in septic neonatal mice without augmenting bacterial growth.

Methods: Newborn C57BL/6J mice (< 24 h old) were injected intravenously with 10⁵ colony forming units (CFUs)/g weight of a bioluminescent derivative of the encapsulated clinical isolate Escherichia coli O18:K1. Adequacy of intravenous injections was validated using in vivo bioluminescence imaging and Evans blue. Pups were treated with gentamicin (GENT), PTX, (GENT + PTX) or saline at 0, 1.5, or 4 h after sepsis initiation, and euthanized after an additional 4 h. CFUs and cytokines were measured from blood and homogenized organ tissues.

Results: GENT alone inhibited bacterial growth, IL-1β, and IL-6 production in blood and organs. Addition of PTX to GENT profoundly inhibited E. coli-induced TNF and enhanced IL-10 in blood of newborn mice at all timepoints, whereas it primarily upregulated IL-10 production in peripheral organs (lung, spleen, brain). PTX, whether alone or adjunctive to GENT, did not increase microbial colony counts in blood and organs.

Conclusion: Addition of PTX to antibiotics in murine neonatal E. coli sepsis promoted an anti-inflammatory milieu through inhibition of plasma TNF and enhancement of IL-10 production in plasma and organs without increasing bacterial growth, supporting its utility as a potential adjunctive agent for newborn sepsis.

Vancomycin Is Protective in a Neonatal Mouse Model of Staphylococcus epidermidis-Potentiated Hypoxic-Ischemic Brain Injury

Infection is correlated with increased risk of neurodevelopmental sequelae in preterm infants. In modeling neonatal brain injury, Toll-like receptor agonists have often been used to mimic infections and induce inflammation. Using the most common cause of bacteremia in preterm infants, Staphylococcus epidermidis, we present a more clinically relevant neonatal mouse model that addresses the combined effects of bacterial infection together with subsequent hypoxic-ischemic brain insult. Currently, there is no neuroprotective treatment for the preterm population. Hence, we tested the neuroprotective effects of vancomycin with and without adjunct therapy using the anti-inflammatory agent pentoxifylline. We characterized the effects of S. epidermidis infection on the inflammatory response in the periphery and the brain, as well as the physiological changes in the central nervous system that might affect neurodevelopmental outcomes. Intraperitoneal injection of postnatal day 4 mice with a live clinical isolate of S. epidermidis led to bacteremia and induction of proinflammatory cytokines in the blood, as well as transient elevations of neutrophil and monocyte chemotactic cytokines and caspase 3 activity in the brain. When hypoxia-ischemia was induced postinfection, more severe brain damage was observed in infected animals than in saline-injected controls. This infection-induced inflammation and potentiated brain injury was inoculum dose dependent and was alleviated by the antibiotic vancomycin. Pentoxifylline did not provide any additional neuroprotective effect. Thus, we show for the first time that live S. epidermidis potentiates hypoxic-ischemic preterm brain injury and that peripheral inhibition of inflammation with antibiotics, such as vancomycin, reduces the extent of brain injury.

Pentoxifylline Alone or in Combination with Gentamicin or Vancomycin Inhibits Live Microbe-Induced Proinflammatory Cytokine Production in Human Cord Blood and Cord Blood Monocytes In Vitro

Neonatal sepsis and its accompanying inflammatory response contribute to substantial morbidity and mortality. Pentoxifylline (PTX), a phosphodiesterase inhibitor which suppresses transcription and production of proinflammatory cytokines, is a candidate adjunctive therapy for newborn sepsis. We hypothesized that PTX decreases live microbe-induced inflammatory cytokine production in newborn blood. Cord blood was stimulated with live microorganisms commonly encountered in newborn sepsis (Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis, or Candida albicans) and simultaneously treated with antimicrobial agents (gentamicin, vancomycin, or amphotericin B) and/or clinically relevant concentrations of PTX. Microbial colony counts were enumerated by plating, supernatant cytokines were measured by multiplex assay, intracellular cytokines and signaling molecules were measured by flow cytometry, and mRNA levels were measured by quantitative reverse transcription-PCR. PTX inhibited concentration-dependent E. coli-, S. aureus-, S. epidermidis-, and C. albicans-induced tumor necrosis factor (TNF) and E. coli-induced interleukin-1β (IL-1β) production in whole blood, with greater suppression of proinflammatory cytokines in combination with antimicrobial agents. Likewise, PTX suppressed E. coli-induced monocytic TNF and IL-1β, whereby combined PTX and gentamicin led to significantly greater reduction of TNF and IL-1β. The anti-inflammatory effect of PTX on microbe-induced proinflammatory cytokine production was accompanied by inhibition of TNF mRNA expression and was achieved without suppressing the production of the anti-inflammatory IL-10. Of note, microbial colony counts in newborn blood were not increased by PTX. Our findings demonstrated that PTX inhibited microbe-induced proinflammatory cytokine production, especially when combined with antimicrobial agents, without enhancing microbial proliferation in human cord blood in vitro, thus supporting its utility as candidate adjunctive agent for newborn sepsis.

A neonatal model of intravenous Staphylococcus epidermidis infection in mice <24 h old enables characterization of early innate immune responses

Staphylococcus epidermidis (SE) causes late onset sepsis and significant morbidity in catheterized preterm newborns. Animal models of SE infection are useful in characterizing disease mechanisms and are an important approach to developing improved diagnostics and therapeutics. Current murine models of neonatal bacterial infection employ intraperitoneal or subcutaneous routes at several days of age, and may, therefore, not accurately reflect distinct features of innate immune responses to bacteremia. In this study we developed, validated, and characterized a murine model of intravenous (IV) infection in neonatal mice <24 hours (h) old to describe the early innate immune response to SE. C57BL/6 mice <24 h old were injected IV with 10⁶, 10⁷, 10⁸ colony-forming units (CFU) of SE 1457, a clinical isolate from a central catheter infection. A prospective injection scoring system was developed and validated, with only high quality injections analyzed. Newborn mice were euthanized between 2 and 48 h post-injection and spleen, liver, and blood collected to assess bacterial viability, gene expression, and cytokine production. High quality IV injections demonstrated inoculum-dependent infection of spleen, liver and blood. Within 2 h of injection, SE induced selective transcription of TLR2 and MyD88 in the liver, and increased systemic production of plasma IL-6 and TNF-α. Despite clearance of bacteremia and solid organ infection within 48 h, inoculum-dependent impairment in weight gain was noted. We conclude that a model of IV SE infection in neonatal mice <24 h old is feasible, demonstrating inoculum-dependent infection of solid organs and a pattern of bacteremia, rapid and selective innate immune activation, and impairment of weight gain typical of infected human neonates. This novel model can now be used to characterize immune ontogeny, evaluate infection biomarkers, and assess preventative and therapeutic modalities.

Protective effect of pentoxifylline on growth plate in neonatal rats following long-term phototherapy

We demonstrated previously that receiving long-term phototherapy was associated with early impairment of growth plate structure in neonatal rats, and oxidative stress may be the main risk factor for growth plate injury. The purpose of this study was to examine the histomorphometric effects of pentoxifylline treatment on the growth plate. Sixty weanling Sprague-Dawley rats were randomly separated into three equal groups. Group A, the control group, did not receive phototherapy and pentoxifylline. Groups B and C were exposed to phototherapy for 7 d. In addition to phototherapy, group C was also given pentoxifylline during the study period. Compared with zonal lengths on d 7 after initiation of phototherapy, group B had significantly lower values than group A for all zonal lengths (p < 0.001). Zonal lengths of growth plate were increased significantly with pentoxifylline treatment in group C for 7 d compared with group B (p < 0.001). After phototherapy, group B had significantly higher values than groups A and C for plasma malondialdehyde levels (p < 0.001). The pentoxifylline was found here to have some potential to reduce the effects of phototherapy on growth plate in neonatal rats at a relatively low dose.

NEUTRALIZATION OF TUMOR NECROSIS FACTOR IN PRECLINICAL MODELS OF SEPSIS

Tumor necrosis factor (TNFalpha), a cardinal early mediator of the innate host inflammatory response, has been an attractive target for therapeutic intervention in human sepsis. However, pooled data from 12 completed randomized controlled trials show only a very modest impact on mortality in a highly heterogeneous population of patients. To gain insight into the preclinical in vivo biology of TNFalpha that might aid in better identifying appropriate patient populations for therapeutic intervention, we undertook a systematic review of published reports of preclinical studies assessing the consequences of neutralization of TNFalpha in models of acute infection or inflammation. We identified 143 reports incorporating 484 unique experimental comparisons in seven different animal species. The effects of neutralization of TNFalpha in these were quite variable. Neutralization of TNFalpha was beneficial in endotoxemia, or after systemic challenge with gram-negative organisms, Staphylococcus aureus, or Group B streptococci. On the other hand, neutralization was detrimental in infections caused by Streptococcus pneumoniae, Candida spp., or intracellular pathogens such as Listeria and Mycobacterium tuberculosis, and in models of pneumonia. Treatment was more efficacious when delivered before infectious challenge, and the therapeutic signal increased as the baseline mortality in the placebo group increased. Evidence of neutralization of TNFalpha bioactivity, and of attenuation of inflammation, was typically accompanied by evidence of impairment of antimicrobial defenses. Multiple specific and nonspecific therapeutic strategies were identified. We conclude that the beneficial effects of TNF in systemic inflammation occur at the cost of impaired antimicrobial defenses, and that a better understanding of the consequences of neutralization of TNFalpha in vivo could aid in better defining optimal patient populations for therapeutic intervention.

Pharmacokinetics of pentoxifylline in dogs after oral and intravenous administration

OBJECTIVE

To evaluate the pharmacokinetics of pentoxifylline (PTX) and its 5-hydroxyhexyl-metabolite, metabolite 1 (M1), in dogs after IV administration of a single dose and oral administration of multiple doses.

ANIMALS

7 sexually intact, female, mixed-breed dogs.

PROCEDURE

A crossover study design was used so that each of the dogs received all treatments in random order. A drug-free period of 5 days was allowed between treatments. Treatments included IV administration of a single dose of PTX (15 mg/kg of body weight), oral administration of PTX with food at a dosage of 15 mg/kg (q 8 h) for 5 days, and oral administration of PTX without food at a dosage of 15 mg/kg (q 8 h) for 5 days. Blood samples were taken at 0.25, 0.5, 1, 1.5, 2, 2.5, and 3 hours after the first and last dose of PTX was administered PO, and at 5, 10, 20, 40, 80, and 160 minutes after PTX was administered IV.

RESULTS

PTX was rapidly absorbed and eliminated after oral administration. Mean bioavailability after oral administration ranged from 15 to 32% among treatment groups and was not affected by the presence of food. Higher plasma PTX concentrations and apparent bioavailability were observed after oral administration of the first dose, compared with the last dose during the 5-day treatment regimens.

CONCLUSIONS AND CLINICAL RELEVANCE

In dogs, oral administration of 15 mg of PTX/kg results in plasma concentrations similar to those produced by therapeutic doses in humans, and a three-times-a-day dosing regimen is the most appropriate.

Role of tumor necrosis factor alpha, interleukin-1beta, and interleukin-6 in a mouse model of group B streptococcal arthritis

Intravenous inoculation of CD1 mice with 10(7) CFU of type IV group B Streptococcus (GBS IV) results in a high incidence of diffuse septic arthritis. In this study the roles of tumor necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta), and IL-6 in articular pathology were evaluated. Cytokine levels were quantified in the serum and joints by enzyme-linked immunosorbent assay in mice injected with GBS IV and tested or not tested with pentoxifylline (PTF), a methylxanthine that affects cytokine production. PTF was administered intraperitoneally at a dose of 1 mg/mouse (50 mg/kg of body weight) 1 h after GBS infection and then at 24-h intervals for 4 days. High levels of IL-1beta and IL-6, but not TNF-alpha, were detected in the joints of mice injected with GBS IV from 5 to 15 days after infection, when articular lesions were most frequent and severe. IL-1beta and IL-6 concentrations in the joints significantly (P < 0.001) exceeded those detected in the serum, confirming a strong local production. PTF treatment resulted in a strong reduction of cytokine production and in a marked decrease in both the incidence and severity of arthritis. Inoculation of exogenous murine recombinant IL-1beta or IL-6 in mice treated with GBS IV plus PTF resulted in an incidence and severity of articular lesions similar to those obtained with inoculation of GBS IV alone. No significant effect was obtained with TNF-alpha administration. These data show a strong involvement of IL-1beta and IL-6, but not TNF-alpha, in the pathogenesis of GBS arthritis.

Beneficial effects of pentoxifylline in neonatal rats infected with group B streptococci

Previous studies have indicated that tumor necrosis factor-alpha (TNF-alpha) may play a pathophysiologic role in experimental sepsis by group B streptococci (GBS). We tested the efficacy of some TNF-alpha and eicosanoid inhibitors in a neonatal rat model of GBS disease. The drugs tested included cloricromene, SKF86002, pentoxifylline, CGS8515, ibuprofen and LY203647. None of these compounds were protective against GBS infection, with the exception of pentoxifylline, that produced a moderate enhancement of survival time. Further studies are needed to ascertain if specific inhibitors of TNF-alpha, alone or in conjunction with antibiotics, may be effective as therapeutic agents in neonatal GBS sepsis.

Efficacy of tumor necrosis factor alpha and eicosanoid inhibitors in experimental models of neonatal sepsis

The potential role of tumor necrosis factor alpha (TNF alpha) and eicosanoids in the pathogenesis of experimental neonatal sepsis models was investigated. Lethality was induced in neonatal rats by administration of heat killed group B streptococci (GBS, 7 mg kg-1 intracardially) or Salmonella enteritidis endotoxin (0.35 mg kg-1 intracardially). The relative efficacy of six compounds with putative TNF alpha and eicosanoid inhibitory actions were tested. These were: ibuprofen (3 and 20 mg kg-1), a cyclo-oxygenase inhibitor; CGS85515 (30 mg kg-1), a lipoxygenase inhibitor; LY203647 (30 mg kg-1), a leukotriene D4 receptor antagonist; pentoxifylline (10, 50 and 100 mg kg-1), a TNF inhibitor; cloricromene (2 and 10 mg kg-1), a thromboxane A2 synthetase inhibitor with TNF alpha inhibitory actions; and SKF86002 (2.5, 5, 10 and 20 mg kg-1), a dual cyclo-oxygenase/lipoxygenase inhibitor with TNF alpha inhibitory activity. Pentoxifylline, cloricromene and SKF86002, when given intraperitoneally 2 h before challenge, produced 45, 52 and 61% reductions, respectively, in plasma levels of TNF alpha at 2.5 h post-injection with killed GBS (P < 0.05). On the contrary, pretreatment with ibuprofen, CGS85515 or LY203647 did not significantly affect TNF alpha levels. All compounds significantly attenuated the lethality by killed GBS and S. enteritidis endotoxin. These data suggest that TNF alpha and eicosanoids contribute to the pathogenesis of shock induced by killed GBS and endotoxemia.

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.

Pentoxifylline and CD14 antibody additively inhibit priming of polymorphonuclear leukocytes for enhanced release of superoxide by lipopolysaccharide: possible mechanism of these actions

Lipopolysaccharide (LPS) primes human polymorphonuclear leukocytes (PMN) for enhanced O2- production in response to stimulation by N-formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe). Serum factor is essential for priming at lower concentrations of LPS. Complexes of LPS and LPS-binding protein are recognized by CD14 on PMN. We investigated the effects of a monoclonal antibody against CD14 (MY4) and of pentoxifylline (POF), a membrane fluidizer, alone and in combination, on LPS-LPS-binding protein activation of phospholipase D evidenced by increased phosphatidic acid formation. Phosphatidic acid formation and O2- production were inhibited by MY4 and POF. Our results suggest that the actions of these agents occur at an early step in the excitation-response sequence. In the absence of a second stimulus, LPS plus serum caused an increase in the amount of Gi alpha 2 associated with the membrane via CD14. POF, however, had no effect on Gi alpha 2 in the membrane. POF alone significantly changed the affinity (KD) of the fMet-Leu-Phe receptor of PMN (from 25.2 +/- 4.5 nM to 15.2 +/- 2.4 nM [P < 0.01; n = 4]) at 37 degrees C. The differences between the sites of action of MY4 and POF may lead to cooperation by these agents for inhibition of priming by LPS plus serum for enhanced O2- production. Clinical use of the antibody and POF may diminish tissue damage caused by PMN in clinical endotoxic shock.

Effect of dexamethasone or HWA-138 in combination with antibiotics in experimental Haemophilus influenzae type b infection

Modulation of the host's inflammatory response in bacterial meningitis may be beneficial. In this study, the effects of dexamethasone and HWA-138, an analog of pentoxifylline, on CSF cultures and cochlear inflammation in an infant rat model of Haemophilus influenzae type b were studied. Five-day-old infant rats were inoculated once intraperitoneally with 1 x 10(4) to 10 x 10(4) CFU of H. influenzae type b (strain 1406). Twenty-four hours later, infant rats were treated intraperitoneally with one dose of ampicillin (0.1 mg/g of body weight), cefotaxime (0.05 mg/g), or cefuroxime (0.05 mg/g) alone or in combination with one dose of dexamethasone (0.00015 mg/g) or HWA-138 (0.005 mg/g). Twenty-four hours after treatment with cefuroxime plus dexamethasone, animals had a significantly (P less than or equal to 0.04) greater incidence of bacteremia and meningitis (eight of nine animals) than that in animals of the other treatment groups. Overall, dexamethasone was associated with less inflammation (P less than 0.04) of the cochlear nerve compared with that from antibiotic treatment alone. In this model, when suboptimal antimicrobial therapy is administered, anti-inflammatory agents may be beneficial with respect to reducing cochlear inflammation. However, dexamethasone and cefuroxime lead to a higher rate of positive blood and cerebral spinal fluid cultures than cefuroxime alone.