Reduced expression of the ferroptosis inhibitor glutathione peroxidase-4 in multiple sclerosis and experimental autoimmune encephalomyelitis

Glutathione peroxidase 4 (GPx4) is the only enzyme capable of reducing toxic lipid hydroperoxides in biological membranes to the corresponding alcohols using glutathione as the electron donor. GPx4 is the major inhibitor of ferroptosis, a non-apoptotic and iron-dependent programmed cell death pathway, which has been shown to occur in various neurological disorders with severe oxidative stress. In this study, we investigate whether GPx4 expression is altered in multiple sclerosis and its animal model experimental autoimmune encephalomyelitis (EAE). The results clearly show that mRNA expression for all three GPx4 isoforms (cytoplasmic, mitochondrial and nuclear) decline in multiple sclerosis gray matter and in the spinal cord of MOG_35-55 peptide-induced EAE. The amount of GPx4 protein is also reduced in EAE, albeit not in all cells. Neuronal GPx4 immunostaining, mostly cytoplasmic, is lower in EAE spinal cords than in control spinal cords, while oligodendrocyte GPx4 immunostaining, mainly nuclear, is unaltered. Neither control nor EAE astrocytes and microglia cells show GPx4 labeling. In addition to GPx4, two other negative modulators of ferroptosis (γ-glutamylcysteine ligase and cysteine/glutamate antiporter), which are critical to maintain physiological levels of glutathione, are diminished in EAE. The decrease in the ability to eliminate hydroperoxides was also evidenced by the accumulation of lipid peroxidation products and the reduction in the proportion of the docosahexaenoic acid in non-myelin lipids. These findings, along with presence of abnormal neuronal mitochondria morphology, which includes an irregular matrix, disrupted outer membrane and reduced/absent cristae, are consistent with the occurrence of ferroptotic damage in inflammatory demyelinating disorders.

Effects of methylprednisolone and 4-chloro-3-hydroxyanthranilic acid in experimental spinal cord injury in the guinea pig appear to be mediated by different and potentially complementary mechanisms

STUDY DESIGN

Blinded, placebo-controlled, parallel treatment group studies of the effects of methylprednisolone (MP) or 4-chloro-3-hydroxyanthranilate (4-Cl-3-HAA) on behavioral outcome and quinolinic acid tissue levels from experimental thoracic spinal cord injury in adult guinea pigs.

OBJECTIVES

To compare the effects of treatment with high-dose MP, a corticosteroid, and 4-Cl-3-HAA, a compound that inhibits synthesis of the neurotoxin quinolinic acid (QUIN) by activated macrophages. To explore the effect of different times of treatment using these two approaches to ameliorating secondary tissue damage.

SETTING

Laboratory animal studies at the University of North Carolina, Chapel Hill, NC, USA.

METHODS

Standardized spinal cord injuries were produced in anesthetized guinea pigs, using lateral compression of the spinal cord. Behavioral impairment and recovery were measured by placing and toe-spread responses (motor function), cutaneus trunci muscle reflex receptive field areas and somatosensory-evoked potentials (sensory function). Tissue quinolinic acid levels were measured by gas chromatograph/mass spectrometry.

RESULTS

The current experiments showed a reduction in delayed loss of motor and sensory function in the guinea pig with MP (150 mg kg(-1), intraperitoneally in split doses between 0.5 and 6 h), but no significant reduction in tissue QUIN. Improved sensory function was seen with a single dose of 60 mg kg(-1) MP intraperitoneally at 5 h after injury, but not at 10 h after injury. A single dose of 4-Cl-3-HAA at 5 h in the guinea pig did not produce the sensory and motor improvements seen in previous studies with 12 days of dosing, beginning at 5 h.

CONCLUSION

These studies, together with earlier findings, indicate that both drugs can attenuate secondary pathologic damage after SCI, but through separate mechanisms. These are most likely an acute reduction by MP of oxidative processes and reduction by 4-Cl-3-HAA of QUIN synthesis.

Methylprednisolone induces reversible clinical and pathological remission and loss of lymphocyte reactivity to myelin oligodendrocyte glycoprotein in experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is an animal model of human multiple sclerosis (MS). EAE, induced by immunisation with myelin-associated autoantigens, is characterised by an inflammatory infiltrate in the central nervous system (CNS) associated with axonal degeneration, demyelination and damage. We have recently shown in an experimental mouse model of autoimmune gastritis that methylprednisolone treatment induces a reversible remission of gastritis with regeneration of the gastric mucosa. Here, we examined the effect of oral methylprednisolone on the mouse EAE model of human MS induced by immunisation with myelin oligodendrocyte glycoprotein peptide (MOG(35-55)). We examined the clinical scores, CNS pathology and lymphocyte reactivity to MOG(35-55) following treatment and withdrawal of the steroid. Methylprednisolone remitted the clinical signs of EAE and the inflammatory infiltrate in the CNS, accompanied by loss of lymphocyte reactivity to MOG(35-55) peptide. Methylprednisolone withdrawal initiated relapse of the clinical features, a return of the CNS inflammatory infiltrate and lymphocyte reactivity to MOG(35-55) peptide. This is the first study to show that methylprednisolone induced a reversible remission in the clinical and pathological features of EAE in mice accompanied by loss of lymphocyte reactivity to the encephalitogen. This model will be useful for studies directed at a better understanding of mechanisms associated with steroid-induced disease remission, relapse and remyelination and also as an essential adjunct to an overall curative strategy.

The therapeutic window after spinal cord injury can accommodate T cell-based vaccination and methylprednisolone in rats

Immune system activity has traditionally been considered harmful for recovery after spinal cord injury (SCI). Recent evidence suggests, however, that immune activity--and specifically autoimmune activity--is evoked by the insult, is beneficial if properly regulated and is amenable to boosting. Thus, for example, vaccination with an altered peptide ligand derived from myelin basic protein reduces the progressive degeneration of neurons that escaped the initial insult, thereby promoting recovery after SCI. As the steroid drug methylprednisolone (MP) is currently the only treatment available for patients with SCI, our purpose in the present study was to examine the mutual compatibility of the two treatments within the post-traumatic therapeutic window. We show, using rats of two different strains, that if MP is injected concomitantly with the therapeutic vaccination, the beneficial effect of the vaccination is diminished. However, if MP is given immediately after the insult and the vaccination 48 h later, MP does not detract from the beneficial effect of the vaccination. These results demonstrate that the therapeutic window after SCI can accommodate immediate administration of MP plus a delayed therapeutic vaccination.

Correlation between MRI and clinico-pathological manifestations in Lewis rats protected from experimental allergic encephalomyelitis by acylated synthetic peptide of myelin basic protein

Experimental allergic encephalomyelitis (EAE) is an autoimmune disease of the central nervous system which constitutes an accepted animal model for multiple sclerosis (MS). The disease can take an acute or chronic form depending on the injection route, animal strain and nature of the disease-inducing antigen administered. The neuroinflammation associated with the acute form can be detected with T2-weighted, T1-weighted and diffusion MRI, and blood-brain barrier changes can be investigated with Gd-DTPA-enhanced T1-weighted imaging, similar to that of MS patients. A synthetic peptide of myelin basic protein (MBP) encephalitogenic for the Lewis rat (MBP 68-86) was acylated by the attachment of a palmitoyl residue (PAL68-86), and was shown to confer almost complete protection against EAE, when administered to rats before and after an encephalitogenic challenge. In this study, treatment of Lewis rats with PAL68-86 prevented the appearance of clinical signs (p < 0.0001) after challenge with the native peptide (p68-86) in complete Freund's adjuvant (CFA), and reduced considerably the MRI and histopathological signs of the disease (p < 0.0001). Measurement of the gadolinium leakage due to neuroinflammation revealed a significant decrease in permeability from 4.09 +/- 2.1 to 2.95 +/- 1.79% pixels > mean + 2 SD (p = 0.011). Therefore, quantitative MRI measurements correlate very well with the reduced cellular infiltration in the CNS and the absence of clinical signs in the EAE-protected animal.

Role of poly(ADP-ribose)synthetase in inflammation

Peroxynitrite and hydroxyl radicals are potent initiators of DNA single strand breakage, which is an obligatory stimulus for the activation of the nuclear enzyme poly(ADP-ribose)synthetase (PARS). Rapid activation of PARS depletes the intracellular concentration of its substrate, NAD+, slowing the rate of glycolysis, electron transport and ATP formation. This process can result in acute cell dysfunction and cell necrosis. Accordingly, inhibitors of PARS protect against cell death under these conditions. In addition to the direct cytotoxic pathway regulated by DNA injury and PARS activation, PARS also appears to modulate the course of inflammation by regulating the expression of a number of genes, including the gene for intercellular adhesion molecule 1, collagenase and the inducible nitric oxide synthase. The research into the role of PARS in inflammatory conditions is now supported by novel tools, such as novel, potent inhibitors of PARS, and genetically engineered animals lacking the gene for PARS. In vivo data demonstrate that inhibition of PARS protects against various forms of inflammation, including zymosan or endotoxin induced multiple organ failure, arthritis, allergic encephalomyelitis, and diabetic islet cell destruction. Pharmacological inhibition of PARS may be a promising novel approach for the experimental therapy of various forms of inflammation.

Lazaroids: Mechanisms of Action and Implications for Disorders of the CNS

Oxygen radical-induced lipid peroxidation to cerebrovascular or brain parenchymal cell membranes has been implicated as a pathophysiological mechanism in both acute and chronic neurodegenerative disorders, including brain and spinal cord trauma, ischemic and hemorrhagic stroke, Alzheimer's and Parkinson's diseases, and amyotrophic lateral sclerosis. As a result, pharmacological strategies have been aimed at antagonizing lipid peroxidative damage in a safe and effective manner. Perhaps the first successful antioxidant neuroprotective approach is high dose treatment with the glucocorticoid steroid methylprednisolone, which has been reported to be effective in improving neurological recovery after blunt spinal cord injury in animals and humans. After a determination that these effects were based upon inhibition of posttraumatic lipid peroxidative reactions rather than steroid receptor interactions, a new class of 21-aminosteroids (“lazaroids”) was discovered. The lazaroids are more effective inhibitors of lipid peroxidation and, at the same time, devoid of glucocorticoid side effect potential. One of them, tirilazad (U-74006F), was found protective in a variety of preclinical neuroprotection models and is currently the subject of Phase III clinical trials. Thus far, the compound has been demonstrated to significantly improve 3-month survival and neurological recovery after subarachnoid hemorrhage in humans. Although tirilazad does penetrate the injured CNS, much of its protective activity is mediated by an action on vascular endothelium. Recently, the 21-aminosteroids have been followed up with a newer series of non-steroidal compounds, the pyrrolopyrimidines, which possess even greater antioxidant efficacy and brain penetration that may be useful for the treatment of chronic neurodegenerative disorders.