Propentofylline and iloprost suppress the production of TNF-alpha by macrophages but fail to ameliorate experimental autoimmune encephalomyelitis in Lewis rats

Arachidonic acid-derived lipid mediators in multiple sclerosis pathogenesis: fueling or dampening disease progression?

BACKGROUND

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system (CNS), characterized by neuroinflammation, demyelination, and neurodegeneration. Considering the increasing prevalence among young adults worldwide and the disabling phenotype of the disease, a deeper understanding of the complexity of the disease pathogenesis is needed to ultimately improve diagnosis and personalize treatment opportunities. Recent findings suggest that bioactive lipid mediators (LM) derived from ω-3/-6 polyunsaturated fatty acids (PUFA), also termed eicosanoids, may contribute to MS pathogenesis. For example, disturbances in LM profiles and especially those derived from the ω-6 PUFA arachidonic acid (AA) have been reported in people with MS (PwMS), where they may contribute to the chronicity of neuroinflammatory processes. Moreover, we have previously shown that certain AA-derived LMs also associated with neurodegenerative processes in PwMS, suggesting that AA-derived LMs are involved in more pathological events than solely neuroinflammation. Yet, to date, a comprehensive overview of the contribution of these LMs to MS-associated pathological processes remains elusive.

MAIN BODY

This review summarizes and critically evaluates the current body of literature on the eicosanoid biosynthetic pathway and its contribution to key pathological hallmarks of MS during different disease stages. Various parts of the eicosanoid pathway are highlighted, namely, the prostanoid, leukotriene, and hydroxyeicosatetraenoic acids (HETEs) biochemical routes that include specific enzymes of the cyclooxygenases (COXs) and lipoxygenases (LOX) families. In addition, cellular sources of LMs and their potential target cells based on receptor expression profiles will be discussed in the context of MS. Finally, we propose novel therapeutic approaches based on eicosanoid pathway and/or receptor modulation to ultimately target chronic neuroinflammation, demyelination and neurodegeneration in MS.

SHORT CONCLUSION

The eicosanoid pathway is intrinsically linked to specific aspects of MS pathogenesis. Therefore, we propose that novel intervention strategies, with the aim of accurately modulating the eicosanoid pathway towards the biosynthesis of beneficial LMs, can potentially contribute to more patient- and MS subtype-specific treatment opportunities to combat MS.

Iloprost Attenuates Oxidative Stress-Dependent Activation of Collagen Synthesis Induced by Sera from Scleroderma Patients in Human Pulmonary Microvascular Endothelial Cells

Endothelial cell injury is an early event in systemic sclerosis (SSc) pathogenesis and several studies indicate oxidative stress as the trigger of SSc-associated vasculopathy. Here, we show that circulating factors present in sera of SSc patients increased reactive oxygen species (ROS) production and collagen synthesis in human pulmonary microvascular endothelial cells (HPMECs). In addition, the possibility that iloprost, a drug commonly used in SSc therapy, might modulate the above-mentioned biological phenomena has been also investigated. In this regard, as compared to sera of SSc patients, sera of iloprost-treated SSc patients failed to increased ROS levels and collagen synthesis in HPMEC, suggesting a potential antioxidant mechanism of this drug.

The Effects of PDE Inhibitors on Multiple Sclerosis: a Review of in vitro and in vivo Models

BACKGROUND

Multiple sclerosis (MS) is a chronic inflammatory and immune-mediated disease, whose current therapeutic means are mostly effective in the relapsing-remitting form of MS, where inflammation is still prominent, but fall short of preventing long term impairment. However, apart from inflammationmediated demyelination, autoimmune mechanisms play a major role in MS pathophysiology, constituting a promising pharmacological target. Phosphodiesterase (PDE) inhibitors have been approved for clinical use in psoriasis and have undergone trials suggesting their neuroprotective effects, rendering them eligible as an option for accessory MS therapy.

OBJECTIVE

In this review, we discuss the potential role of PDE inhibitors as a complementary MS therapy.

METHODS

We conducted a literature search through which we screened and comparatively assessed papers on the effects of PDE inhibitor use, both in vitro and in animal models of MS, taking into account a number of inclusion and exclusion criteria.

RESULTS

In vitro studies indicated that PDE inhibitors promote remyelination and axonal sustenance, while curbing inflammatory cell infiltration, hindering oligodendrocyte and neuronal loss and suppressing cytokine production. In vivo studies underlined that these agents alleviate symptoms and reduce disease scores in MS animal models.

CONCLUSION

PDE inhibitors proved to be effective in addressing various aspects of MS pathogenesis both in vitro and in vivo models. Given the latest clinical trials proving that the PDE4 inhibitor Ibudilast exerts neuroprotective effects in patients with progressive MS, research on this field should be intensified and selective PDE4 inhibitors with enhanced safety features should be seriously considered as prospective complementary MS therapy.

Effect of intraperitoneally administered propentofylline in a rat model of postoperative pain

Background

In this study, we sought to evaluate whether systemic propentofylline (PPF) has antiallodynic effects in a rat model of postoperative pain, and to assess the mechanism involved.

Methods

After plantar incision, rats were intraperitoneally injected with various doses of PPF to evaluate its antiallodynic effect. To investigate the involved mechanism, rats were intraperitoneally injected with yohimbine, dexmedetomidine, prazosin, naloxone, atropine or mecamylamine, following the incision of the rat hind paws, and then PPF was administered intraperitoneally. The mechanical withdrawal threshold (MWT) was evaluated using von Frey filaments at various time points and serum levels of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 were measured to determine the inflammatory response level.

Results

MWT was significantly increased after intraperitoneal injection of 30 mg/kg of PPF when compared with the control group. Injection of PPF and yohimbine, atropine or mecamylamine showed significant decreases in the MWT, while injection of PPF and dexmedetomidine showed a significant increase. Systemic administration of PPF inhibited the post-incisional increase in serum level of TNF-α and IL-1β.

Conclusions

Systemic administration of PPF following surgery presented antiallodynic effects in a rat model of postoperative pain. The antiallodynic effects against mechanical allodynia could be mediated by α-adrenergic and cholinergic receptors.

A Systematic Review on the Role of Arachidonic Acid Pathway in Multiple Sclerosis

BACKGROUND & OBJECTIVE

Multiple sclerosis (MS) is an inflammatory neurodegenerative disease characterized by destruction of oligodendrocytes, immune cell infiltration and demyelination. Inflammation plays a significant role in MS, and the inflammatory mediators such as eicosanoids, leukotrienes, superoxide radicals are involved in pro-inflammatory responses in MS. In this systematic review we tried to define and discuss all the findings of in vivo animal studies and human clinical trials on the potential association between arachidonic acid (AA) pathway and multiple sclerosis.

METHODS

A systematic literature search across Pubmed, Scopus, Embase and Cochrane database was conducted. This systematic review was performed according to PRISMA guidelines.

RESULTS

A total of 146 studies were included, of which 34 were conducted in animals, 58 in humans, and 60 studies reported the role of different compounds that target AA mediators or their corresponding enzymes/ receptors, and can have a therapeutic effect in MS. These results suggest that eicosanoids have significant roles in experimental autoimmune encephalomyelitis (EAE) and MS. The data from animal and human studies elucidated that PGI2, PGF2α, PGD2, isoprostanes, PGE2, PLA2, LTs are increased in MS. PLA2 inhibition modulates the progression of the disease. PGE1 analogues can be a useful option in the treatment of MS.

CONCLUSIONS

All studies reported the beneficial effects of COX and LOX inhibitors in MS. The hybrid compounds, such as COX-2 inhibitors/TP antagonists and 5-LOX inhibitors can be an innovative approach for multiple sclerosis treatment. Future work in MS should shed light in synthesizing new compounds targeting arachidonic acid pathway.

Propentofylline Prevents Sickness Behavior and Depressive-Like Behavior Induced by Lipopolysaccharide in Rats via Neuroinflammatory Pathway

Recent studies have demonstrated the intimate relationship between depression and immune disturbances. Aware of the efficacy limits of existing antidepressant drugs and the potential anti-inflammatory properties of propentofylline, we sought to evaluate the use of propentofylline as a depression treatment. We used a rat model of depression induced by repetitive lipopolysaccharide (LPS) administrations. We have studied sickness behavior, by assessing daily body weight, open field behavior, and TNF-α plasmatic levels. Anxiety-like behavior (light-dark test), depressive-like behavior (forced swim test), plasmatic levels of the brain-derived neurotrophic factor (BDNF, depression biomarker), and central glial fibrillary acidic protein (GFAP) expression (an astrocyte biomarker) were also evaluated. LPS induced body weight loss, open field behavior impairments (decreased locomotion and rearing, and increased immobility), and increased TNF-α levels in rats, compared with control group. Thus, LPS induced sickness behavior. LPS also increased the immobility and reduced climbing in the forced swim test, when compared with the control group, i.e., LPS induced depressive-like behavior in rats. Propentofylline prevented sickness behavior after four days of consecutive treatment, as well as prevented the depressive-like behavior after five days of consecutive treatments. Propentofylline also prevented the increase in GFAP expression induced by LPS. Neither LPS nor propentofylline has influenced the anxiety and BDNF levels of rats. In conclusion, repetitive LPS administrations induced sickness behavior and depressive-like behavior in rats. Propentofylline prevented both sickness behavior and depressive-like behavior via neuroinflammatory pathway. The present findings may contribute to a better understanding and treatment of depression and associated diseases.

Modulation of spinal glial reactivity by intrathecal PPF is not sufficient to inhibit mechanical allodynia induced by nerve crush

Spinal glial reactivity has been strongly implicated in pain that follows peripheral nerve injury. Among the many therapeutic agents that have been tested for anti-allodynia through immune modulation is the atypical methylxanthine propentofylline. While propentofylline shows a potent anti-allodynia effect after nerve transection injury, we here demonstrate that, when propentofylline is used intrathecally at the effective immune-modulatory dose, allodynia after rat nerve crush injury is completely preserved. Microglial/macrophage Iba-1 and astrocytic GFAP expression, increased in the dorsal horn of nerve crushed animals, was, however, effectively attenuated by propentofylline. Effective modulation of spinal glial reactivity is, thus, no assurance for anti-allodynia.

Systemic administration of propentofylline, ibudilast, and (+)-naltrexone each reverses mechanical allodynia in a novel rat model of central neuropathic pain

Central neuropathic pain (CNP) is a debilitating consequence of central nervous system damage for which current treatments are ineffective. To explore mechanisms underlying CNP, we developed a rat model involving T13/L1 dorsal root avulsion. The resultant dorsal horn damage creates bilateral below-level (L4-L6) mechanical allodynia. This allodynia, termed spinal neuropathic avulsion pain, occurs in the absence of confounding paralysis. To characterize this model, we undertook a series of studies aimed at defining whether spinal neuropathic avulsion pain could be reversed by any of 3 putative glial activation inhibitors, each with distinct mechanisms of action. Indeed, the phosphodiesterase inhibitor propentofylline, the macrophage migration inhibitory factor inhibitor ibudilast, and the toll-like receptor 4 antagonist (+)-naltrexone each reversed below-level allodynia bilaterally. Strikingly, none of these impacted spinal neuropathic avulsion pain upon first administration but required 1 to 2 weeks of daily administration before pain reversal was obtained. Given reversal of CNP by each of these glial modulatory agents, these results suggest that glia contribute to the maintenance of such pain and enduring release of macrophage migration inhibitory factor and endogenous agonists of toll-like receptor 4 is important for sustaining CNP. The markedly delayed efficacy of all 3 glial modulatory drugs may prove instructive for interpretation of apparent drug failures after shorter dosing regimens.

PERSPECTIVE

CNP that develops after trauma is often described by patients as severe and intolerable. Unfortunately, current treatments are not effective. This work suggests that using pharmacologic treatments that target glial cells could be an effective clinical treatment for CNP.

Effects of propentofylline on CNS remyelination in the rat brainstem

Propentofylline (PPF) is a xanthine derivative with pharmacological effects distinct from those of the classical methylxanthines. It depresses activation of microglial cells and astrocytes which is associated with neuronal damage during neural inflammation and hypoxia. The aim of this study was to evaluate whether PPF had the capacity of affecting glial cells behavior during the process of demyelination and remyelination following ethidium bromide (EB) gliotoxic injury. EB injection into the CNS is commonly used as an experimental demyelinating model inducing local oligodendroglial and astrocytic death, which results in primary demyelination, blood-brain barrier and glia limitans disruption and Schwann cells invasion. Sixty Wistar rats were divided into four different groups receiving 10 microlitres of 0.1% EB or 0.9% saline solution into the cisterna pontis and treated or not with the xanthine. PPF treatment was done using 12.5 mg/kg/day by the intraperitonial route for 31 days of the experimental period. The rats were euthanized from 7 to 31 days after EB injection and brainstem sections were collected and processed for light and transmission electron microscopy studies. Results from both groups were compared by using a semi-quantitative method developed for documenting in semithin sections the extent and nature of remyelination of demyelinating lesions. Results showed that PPF administration after EB injection significantly increased both oligodendroglial and Schwann cell remyelination at 31 days (mean remyelination scores of 3.67 ± 0.5 for oligodendrocytes and 1.27 ± 0.49 for Schwann cells) compared to untreated animals (scores of 3.19 ± 0.57 and 0.90 ± 0.33, respectively).

Prostacyclin promotes oligodendrocyte precursor recruitment and remyelination after spinal cord demyelination

Adult oligodendrocyte precursor cells (OPCs) are located adjacent to demyelinated lesion and contribute to myelin repair. The crucial step in remyelination is the migration of OPCs to the demyelinated area; however, the mechanism of OPC migration remains to be fully elucidated. Here we show that prostacyclin (prostaglandin I2, PGI2) promotes OPC migration, thereby promoting remyelination and functional recovery in mice after demyelination induced by injecting lysophosphatidylcholine (LPC) into the spinal cord. Prostacyclin analogs enhanced OPC migration via a protein kinase A (PKA)-dependent mechanism, and prostacyclin synthase expression was increased in the spinal cord after LPC injection. Notably, pharmacological inhibition of prostacyclin receptor (IP receptor) impaired remyelination and motor recovery, whereas the administration of a prostacyclin analog promoted remyelination and motor recovery after LPC injection. Our results suggest that prostacyclin could be a key molecule for facilitating the migration of OPCs that are essential for repairing demyelinated areas, and it may be useful in treating disorders characterized by demyelination.

Angiogenesis induced by CNS inflammation promotes neuronal remodeling through vessel-derived prostacyclin

Angiogenesis is a prominent feature of central nervous system (CNS) disease and has roles in both the continued promotion of inflammation and the subsequent repair processes. Here we report that prostacyclin (or prostaglandin I(2) (PGI(2))) derived from new vessels promotes axonal remodeling of injured neuronal networks after CNS inflammation. In a localized model of experimental autoimmune encephalomyelitis (EAE), new vessels formed around the inflammatory lesion, followed by sprouting of adjacent corticospinal tract (CST) fibers. These sprouting fibers formed a compensatory motor circuit, leading to recovery of motor function. Capillary endothelial cell-derived prostacyclin bound to its receptor, the type I prostaglandin receptor (IP receptor), on CST neurons, promoting sprouting of CST fibers and contributing to the repair process. Inhibition of prostacyclin receptor signaling impaired motor recovery, whereas the IP receptor agonist iloprost promoted axonal remodeling and motor recovery after the induction of EAE. These findings reveal an important function of angiogenesis in neuronal rewiring and suggest that prostacyclin is a promising molecule for enhancing functional recovery from CNS disease.

Iloprost reduces colonic injury in ischemic colitis in rats

PURPOSE

Evaluate the effects of iloprost administration in the early period of ischemic colitis and the mechanism that how these effects develop.

METHODS

Thirty two Wistar albino female rats with an average weight of 220g were divided into four groups of eight rats. In group 1 the rats were given iloprost and sacrificed after 24 hours and in group 2 they were sacrificed after 24 hours without any iloprost. The rats in group 3 were administrated iloprost and sacrificed after 72 hours and in group 4 they were sacrificed at 72th hour without iloprost. The differences between the groups as tissue damage, vascularization or apoptosis were assessed statistically.

RESULTS

Oxidative damage and apoptosis were less pronounced and vascularization was better developed in rats that were given iloprost and sacrificed at 24th hour later in contrast to the rats that were not treated with iloprost. But there was no statistical difference among the groups at 72th hour.

CONCLUSION

Iloprost inhibited leucocyte infiltration, decreased proinflammatory cytokines and enhanced angiogenesis so that the oxidative stress and inflammatory response decreased resulting in lesser tissue damage.

Experimental allergic encephalomyelitis is exacerbated in mice deficient for 12/15-lipoxygenase or 5-lipoxygenase

12/15-Lipoxygenase (12/15-LO) produces 15-hydroxyeicosatetraenoic acid (15-HETE) and 13-hydroxyoctadecadienoic acid (13-HODE) which are agonists for peroxisome proliferator-activated receptor-gamma (PPARgamma). PPARgamma agonists reduce clinical severity of experimental allergic encephalomyelitis (EAE), an animal model of multiple sclerosis. In contrast, 5-lipoxygenase (5-LO) produces the generally proinflammatory leukotrienes (LTs) which would be expected to worsen EAE. We tested the hypotheses that EAE severity would be exacerbated in 12/15-LO-deficient mice and attenuated in 5-LO-deficient mice. 12/15-LO deficiency conferred a significantly worse disease course, and surprisingly, 5-LO deficiency also caused significantly more severe EAE compared to control mice. These data suggest that PPARgamma-regulated gene expression and that 5-LO production of certain LTs have the ability to diminish EAE. Continued analysis will provide insight into the endogenous LO-generated effectors that assist in tempering EAE.

Prostaglandin E(2) and 6-keto-prostaglandin F(1alpha) production is elevated following traumatic injury to sciatic nerve

Sciatic nerve explants cultured either alone or in the presence of peritoneal macrophages were used to study prostaglandin E(2) (PGE(2)) and 6-keto-PGF(1alpha) production following traumatic peripheral nerve injury. Although barely detectable at early time points (1-3 h in vitro), the production of PGE(2) and 6-keto-PGF(1alpha) by sciatic nerve explants increased significantly after 18 h and remained elevated for up to 96 h. The cyclooxygenase-2 (COX-2) selective inhibitor, NS-398, inhibited PGE(2) and 6-keto-PGF(1alpha) production by injured sciatic nerve in a dose-dependent manner. Consistent with the observed effect of NS-398, peripheral nerve explants, as well as Schwann cells and perineural fibroblasts cultured from neonatal sciatic nerve, each contained COX-2 immunoreactivity after 24 h in vitro. Both Schwann cells and perineural fibroblasts produced significant amounts of PGE(2) and 6-keto-PGF(1alpha); but only in the presence of arachidonic acid. As observed for injured sciatic nerve, the production of PGE(2) and 6-keto-PGF(1alpha) by primary Schwann cells and perineural fibroblasts was completely inhibited by NS-398. Compared to macrophages cultured alone, macrophages cultured in the presence of sciatic nerve explants produced large amounts of PGE(2), whereas the level of 6-keto-PGF(1alpha) was unchanged. In contrast, macrophages treated with adult sciatic nerve homogenate did not produce significant amounts of either PGE(2) or 6-keto-PGF(1alpha) during the entire course of treatment. We conclude that injured sciatic nerves produce PGE(2) and 6-keto-PGF(1alpha) by a mechanism involving COX-2 activity and that macrophages produce large amounts of PGE(2) in response to soluble factors produced by injured nerve but not during the phagocytosis of peripheral nerve debris.

Tissue inflammatory response in subacute sclerosing panencephalitis (SSPE)

The pattern of inflammatory infiltration was studied in the frontal brain biopsies of 28 cases with subacute sclerosing panencephalitis (SSPE) by immunohistochemistry. Lymphocytic infiltration and gliosis were common pathologic findings. CD4+ T lymphocytes were often observed in perivascular areas and CD8+ lymphocytes in the parenchyma. B lymphocytes were located in large perivascular cuffs associated with longer and slower disease. Major histocompatibility complex antigens, interferon-gamma, and tumor necrosis factor-alpha (TNF-alpha) were expressed in endothelial and glial cells. The inflammatory lesions in subacute sclerosing panencephalitis consist of various cell subtypes and cytokines localized in particular areas of the brain tissue and show certain associations with clinical course.

Cuprizone and piperonyl butoxide, proposed inhibitors of T-cell function, attenuate experimental allergic encephalomyelitis in SJL mice

Multiple sclerosis (MS) and its animal model, experimental allergic encephalomyelitis (EAE), are autoimmune demyelinating diseases with autoreactive T-cells acting as important mediators of pathogenesis. Cuprizone, a copper chelator, and piperonyl butoxide (PBO), a pesticide synergist, are implicated to inhibit T-cell activation and function. The purpose of this study was to assess whether either of these agents would suppress PLP-peptide-induced EAE in the SJL mouse. Indeed, treatment with cuprizone beginning 1 week prior to disease induction, and PBO administration from days 1 to 9 of EAE, significantly attenuated EAE clinical severity. Furthermore, both agents decreased blood CD4+/CD8+ ratios, and reduced signs of chronic graft vs. host disease (GVHD) indicating attenuation of an immune T-cell response. These results suggest that cuprizone and PBO suppress EAE and use of these agents will provide insights into the mechanisms of T-cell mediated diseases.

Activation of the complement system as an indicator of pyrogenic reaction to lipopolysaccharide (LPS)

The generation of biologically active complement split products through the direct reaction of microorganisms with complement proteins is one of the earliest events of the defence reaction in humans. Complement activation develops within minutes, which highly corresponds with the onset of a febrile reaction after exposure to pyrogens. The possibility of the use of complement activation in human plasma as an indicator of pyrogen contamination has been tested. Additionally, the co-stimulatory effect of complement activation on tumor necrosis factor-alpha (TNF-alpha) production by blood-separated macrophages exposed to lipopolysaccharide (LPS) has been demonstrated. As an indicator of complement activation in test samples, the concentration of the iC3b fragment was measured by using an ELISA system based on neoantigen formation. The 3-h exposure time has been identified as optimal for the test. The variability between iC3b concentrations in untreated control samples obtained from seven unrelated healthy donors was less than 10%, while after activation by 100 ng/ml LPS, it increased to 13%. The lower detection limit has been identified as 10 pg/ml LPS. As the complement test is not affected by drug-cell interactions or cell viability, the test can be used in situations where tested formulations contain active substances, which interfere with a cell-based test. We conclude that a test based on the detection of complement activation in human plasma should be considered as a valuable element of an in vitro pyrogenicity testing battery along with a cell-based assay.

Effects of iloprost, a stable prostacyclin analog, on intestinal leukocyte adherence and microvascular blood flow in rat experimental endotoxemia

OBJECTIVE

To investigate the effects of iloprost, a stable prostacyclin analog, on leukocyte adherence in intestinal venules and intestinal microvascular blood flow in experimental endotoxemia.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

Experimental laboratory.

SUBJECTS

Twenty-one male Wistar rats weighing 190 +/- 40 g.

INTERVENTIONS

The rats were divided equally into three groups: the first was a control group; the second received endotoxin (20 mg/kg lipopolysaccharide from Escherichia coli O55:B5 intravenously); and the third received endotoxin and intravenous iloprost infusion (2 ng.kg-1.min-1).

MEASUREMENTS AND MAIN RESULTS

The distal small intestine of the animals was examined by using intravital fluorescence videomicroscopy 2 hrs after endotoxin challenge. Leukocytes were stained in vivo by means of rhodamine 6G. Intestinal microvascular blood flow was measured by laser Doppler flowmetry in the terminal ileum. Iloprost treatment significantly attenuated the count of adherent leukocytes in collecting venules (control, 61 +/- 10 n/mm2; lipopolysaccharide, 364 +/- 60 n/mm2; iloprost, 232 +/- 29 n/mm2; p <.05) and in postcapillary venules (control, 96 +/- 14 n/mm2; lipopolysaccharide, 470 +/- 21 n/mm2; iloprost 390 +/- 41 n/mm2; p <.05). Intestinal microvascular blood flow was decreased significantly in the lipopolysaccharide group (-49%), whereas iloprost-treated animals showed no significant difference compared with the control group.

CONCLUSIONS

The study demonstrated that administration of iloprost attenuated leukocyte adherence in postcapillary and collecting intestinal venules and improved intestinal microvascular blood flow. Thus, iloprost treatment may impact endotoxin-induced intestinal injury.

Heme oxygenase-1 and NADPH cytochrome P450 reductase expression in experimental allergic encephalomyelitis: an expanded view of the stress response

Oxidative stress is implicated in the pathogenesis of experimental allergic encephalomyelitis (EAE), a model for multiple sclerosis. Heme oxygenase-1 (HO-1) is a heat shock protein induced by oxidative stress. HO-1 metabolizes the pro-oxidant heme to the antioxidant biliverdin and CO. HO-1 requires electrons, donated by NADPH cytochrome P450 reductase (henceforth, reductase), for catalytic activity. EAE was induced with a peptide of proteolipid protein in SJL mice, and the expression of HO-1 and reductase in the hindbrain was analyzed. HO-1 protein levels were significantly increased in EAE animals compared with control mice. HO-1 expression was present in ameboid macrophages, reactive microglia, and astrocytes in white matter tracks. Bergmann glia and ameboid macrophages also were occasionally stained in the molecular layer of the cerebellum. Unlike HO-1, reductase protein levels decreased with disease severity. HO-1 and reductase were associated with each other in endoplasmic reticulum micelles, suggesting that the decrease in reductase does not interfere with its association with HO-1. In cells that express HO-1, the association of reductase with HO-1 should competitively inhibit the interaction of reductase with cytochrome P450 isozymes and thereby limit free radical production as the latter two enzymes act cooperatively to produce superoxide. The increase in HO-1 together with the decrease in reductase may be part of a common defense mechanism attempting to minimize tissue damage in several neurological conditions.

TNF-receptor 1 deficiency fails to alter the clinical and pathological course in mice with globoid cell leukodystrophy (twitcher mice) but affords protection following LPS challenge

Twitcher mice have an autosomal recessive mutation in the gene for the lysosomal enzyme galactosylceramidase, which is the same gene that is affected in human globoid cell leukodystrophy (Krabbe's disease). The failure to digest galactosylceramide and psychosine leads to initial pathological changes in oligodendrocytes. Secondary pathological changes that include infiltrating macrophages and other inflammatory responses have been postulated to promote the disease course. TNFalpha levels are elevated in twitcher mice compared to control animals, and studies on another demyelinating disease, experimental allergic encephalomyelitis, indicate that TNF promotes pathogenesis via TNF-receptor 1 (TNF-R1). In the present study, twitcher/TNF-R1 deficient mice were generated, and the clinical and pathological course was compared between these mice and regular twitcher mice. There was no statistical evidence for any differences between these two groups of mice for all clinical (life span, weight loss, onset day of twitching) and pathological (demyelination, astrocyte gliosis, macrophage infiltration) measures that were examined. If mice were administered an intraperitoneal injection of LPS, then twitcher/TNF-R1 deficient mice had a longer [corrected] life span and a decreased [corrected] disruption to the blood-brain barrier compared to regular twitcher mice. These results showed that TNF-R1 is not sufficiently activated to affect the pathological and/or clinical signs during the natural course of this disease. However, when there is a secondary insult, TNF-R1 activation does lead to a significant acceleration of the development of clinical and pathological signs.

Concentration-dependent effects of pentoxifylline on migration and myelin phagocytosis by macrophages

The effects of pentoxifylline (POX) on macrophage migration and myelin uptake were studied in an in vitro model of myelin phagocytosis. The POX is a phosphodiesterase inhibitor which inhibits TNF-alpha (tumor necrosis factor alpha) production and reduces ICAM-1 (intercellular adhesion molecule-1) expression by macrophages. Both of these molecules have earlier been shown to be involved in the process of myelin recognition and degradation. In the present series of experiments, cocultured peripheral nerves and macrophages were treated with different concentrations of POX. Untreated controls were massively invaded by macrophages which ingested the degenerating myelin sheaths. High concentrations of POX (100 microg ml(-1)) inhibited macrophage invasion of the nerves. Lower POX concentrations (50 microg ml(-1)), in contrast, lead to an increased myelin uptake by phagocytic cells without affecting macrophage migration. These data indicate that POX may regulate different effector functions of macrophages such as migration and myelin phagocytosis during Wallerian degeneration. This is important for inflammatory demyelinating conditions in the central or peripheral nervous system (PNS) in which macrophages are also important effector cells. Since POX is used as an immunomodulatory drug in demyelinating diseases, its effects on the described macrophage functions may be of high relevance. An increased myelin uptake during Wallerian degeneration may also support a more efficient axonal regeneration by removing axonal outgrowth inhibitors.