Yossi Gilgun-Sherki

Oxidative stress induced-neurodegenerative diseases : the need for antioxidants that penetrate the blood brain barrier

Oxidative stress (OS) has been implicated in the pathophysiology of many neurological, particularly neurodegenerative diseases. OS can cause cellular damage and subsequent cell death because the reactive oxygen species (ROS) oxidize vital cellular components such as lipids, proteins, and DNA. Moreover, the brain is exposed throughout life to excitatory amino acids (such as glutamate), whose metabolism produces ROS, thereby promoting excitotoxicity. Antioxidant defense mechanisms include removal of O(2), scavenging of reactive oxygen/nitrogen species or their precursors, inhibition of ROS formation, binding of metal ions needed for the catalysis of ROS generation and up-regulation of endogenous antioxidant defenses. However, since our endogenous antioxidant defenses are not always completely effective, and since exposure to damaging environmental factors is increasing, it seems reasonable to propose that exogenous antioxidants could be very effective in diminishing the cumulative effects of oxidative damage. Antioxidants of widely varying chemical structures have been investigated as potential therapeutic agents. However, the therapeutic use of most of these compounds is limited since they do not cross the blood brain barrier (BBB). Although a few of them have shown limited efficiency in animal models or in small clinical studies, none of the currently available antioxidants have proven efficacious in a large-scale controlled study. Therefore, any novel antioxidant molecules designed as potential neuroprotective treatment in acute or chronic neurological disorders should have the mandatory prerequisite that they can cross the BBB after systemic administration.

Antioxidant Therapy in Acute Central Nervous System Injury: Current State

Free radicals are highly reactive molecules generated predominantly during cellular respiration and normal metabolism. Imbalance between cellular production of free radicals and the ability of cells to defend against them is referred to as oxidative stress (OS). OS has been implicated as a potential contributor to the pathogenesis of acute central nervous system (CNS) injury. After brain injury by ischemic or hemorrhagic stroke or trauma, the production of reactive oxygen species (ROS) may increase, sometimes drastically, leading to tissue damage via several different cellular molecular pathways. Radicals can cause damage to cardinal cellular components such as lipids, proteins, and nucleic acids (e.g., DNA), leading to subsequent cell death by modes of necrosis or apoptosis. The damage can become more widespread due to weakened cellular antioxidant defense systems. Moreover, acute brain injury increases the levels of excitotoxic amino acids (such as glutamate), which also produce ROS, thereby promoting parenchymatous destruction. Therefore, treatment with antioxidants may theoretically act to prevent propagation of tissue damage and improve both the survival and neurological outcome. Several such agents of widely varying chemical structures have been investigated as therapeutic agents for acute CNS injury. Although a few of the antioxidants showed some efficacy in animal models or in small clinical studies, these findings have not been supported in comprehensive, controlled trials in patients. Reasons for these equivocal results may include, in part, inappropriate timing of administration or suboptimal drug levels at the target site in CNS. Better understanding of the pathological mechanisms of acute CNS injury would characterize the exact primary targets for drug intervention. Improved antioxidant design should take into consideration the relevant and specific harmful free radical, blood brain barrier (BBB) permeability, dose, and time administration. Novel combinations of drugs providing protection against various types injuries will probably exploit the potential synergistic effects of antioxidants in stroke.

The role of oxidative stress in the pathogenesis of multiple sclerosis: The need for effective antioxidant therapy

Abstract.Accumulating data indicate that oxidative stress (OS) plays a major role in the pathogenesis of multiple sclerosis (MS). Reactive oxygen species (ROS), leading to OS, generated in excess primarily by macrophages, have been implicated as mediators of demyelination and axonal damage in both MS and experimental autoimmune encephalomyelitis (EAE), its animal model. ROS cause damage to cardinal cellular components such as lipids, proteins and nucleic acids (e. g., RNA, DNA), resulting in cell death by necrosis or apoptosis. In addition, weakened cellular antioxidant defense systems in the central nervous system (CNS) in MS, and its vulnerability to ROS effects may increase damage. Thus, treatment with antioxidants might theoretically prevent propagation of tissue damage and improve both survival and neurological outcome. Indeed, several experimental studies have been performed to see whether dietary intake of several antioxidants prevents or reduces the progression of EAE. Although a few antioxidants showed some efficacy in these studies, little information is available on the effect of treatments with such compounds in patients with MS. Well-designed clinical studies using antioxidant intake, as well as investigations based on larger cohorts studied over a longer periods of time, are needed in order to assess whether antioxidant intake together with other conventional treatments, might be beneficial in treating MS.

A low molecular weight copper chelator crosses the blood-brain barrier and attenuates experimental autoimmune encephalomyelitis

Increasing evidence suggests that enhanced production of reactive oxygen species (ROS) activates the MAP kinases, c‐Jun N‐terminal protein kinase (JNK) and mitogen‐activated protein kinase MAPK (p38). These phosphorylated intermediates at the stress‐activated pathway induce expression of matrix metalloproteinases (MMPs), leading to inflammatory responses and pathological damages involved in the etiology of multiple sclerosis (MS). Here we report that N‐acetylcysteine amide (AD4) crosses the blood–brain barrier (BBB), chelates Cu2+, which catalyzes free radical formation, and prevents ROS‐induced activation of JNK, p38 and MMP‐9. In the myelin oligodendrocyte glycoprotein (MOG)‐induced experimental autoimmune encephalomyelitis (EAE), a mouse model of MS, oral administration of AD4 drastically reduced the clinical signs, inflammation, MMP‐9 activity, and protected axons from demylination damages. In agreement with the in vitro studies, we propose that ROS scavenging by AD4 in MOG‐treated animals prevented MMPs induction and subsequent damages through inhibition of MAPK pathway. The low toxicity of AD4 coupled with BBB penetration makes this compound an excellent potential candidate for the therapy of MS and other neurodegenerative disorders.

Riluzole suppresses experimental autoimmune encephalomyelitis: implications for the treatment of multiple sclerosis

Recent studies suggest that glutamate neurotoxicity is involved in the pathogenesis of multiple sclerosis (MS), and that treatment with glutamate receptor (AMPA/kainate) antagonists inhibits experimental autoimmune encephalomyelitis (EAE), the conventional model of MS. Therefore, we examined whether riluzole, an inhibitor of glutamate transmission, affects the pathogenesis and clinical features of MS-like disease in myelin oligodendrocyte glycoprotein (MOG)-induced EAE in mice. Here we report that riluzole (10 mg/kgx2/day, i.p.), administered before and even after the appearance of clinical symptoms, dramatically reduced the clinical severity of MOG-induced EAE, while all the MOG-immunized control mice developed significant clinical manifestations. Moreover, the riluzole-treated mice demonstrated only mild focal inflammation, and less demyelination, compared to MOG-treated mice, using histological methods. Furthermore, riluzole markedly reduced axonal disruption, as assessed by Bielshoweskys silver staining and by antibodies against non-phosphorylated neurofilaments (SMI-32). No difference was detected in the immune system potency, as T-cell proliferative responses to MOG were similar in both groups. In conclusion, our study demonstrates, for the first time, that riluzole can reduce inflammation, demyelination and axonal damage in the CNS and attenuate the clinical severity of MOG-induced EAE. These results suggest that riluzole, a drug used in amyotrophic lateral sclerosis (ALS), might be beneficial for the treatment of MS.

Antioxidant treatment in alzheimer’s disease

Accumulating data from experimental and human studies indicate that oxidative stress (OS) plays a major role in the pathogenesis of Alzheimer’s disease (AD). The production of reactive oxygen species (ROS), which leads to OS, can occur very early, even before the appearance of symptoms and molecular events (β-amyloid plaques and neurofibrillary tangles), leading to tissue damage via several different cellular molecular pathways. ROS can cause damage to cardinal cellular components such as lipids, proteins, and nucleic acids (e.g., RNA, DNA), causing cell death by modes of necrosis or apoptosis. The damage can become more widespread because of the weakened cellular antioxidant defense systems. Therefore, treatment with antioxidants might theoretically act to prevent propagation of tissue damage and improve both survival and neurological outcome. Indeed, several studies preformed to date examined whether dietary intake of several antioxidants, mainly vitamins, might prevent or reduce the progression of AD. Although a few of the antioxidants showed some efficacy in these trials, no answer is yet available as to whether antioxidants are truly protective against AD. Reasons for these results might include, in part, blood-brain barrier (BBB) permeability, inappropriate timing of administration, or suboptimal drug levels at the target site in the central nervous system. Thus, antioxidant cocktails or antioxidants combined with other drugs may have more successful synergistic effects. Further, well-designed intervention, as well as observational investigations based on large cohorts studied over a long period of time with several methods for assessing antioxidant exposure, including relation to BBB penetration, are needed to test this hypothesis.

Axonal damage is reduced following glatiramer acetate treatment in C57/bl mice with chronic-induced experimental autoimmune encephalomyelitis.

Glatiramer acetate (GA) is efficacious in reducing demyelinating-associated exacerbations in patients with relapsing-remitting multiple sclerosis (RRMS) and in several experimental autoimmune encephalomyelitis (EAE) models. Here we report that GA reduced the clinical and pathological signs of mice in chronic EAE induced by myelin oligodendrocyte glycoprotein (MOG). GA-treated mice demonstrated only mild focal inflammation, and less demyelination, compared with controls. Moreover, we also found minimal axonal disruption, as assessed by silver staining, antibodies against amyloid precursor protein (APP) and non-phosphorylated neurofilaments (SMI-32), in the GA-treated group. In conclusion, our study demonstrated for the first time that axonal damage is reduced following GA treatment in C57/bl mice with chronic MOG-induced EAE.

A novel thiol antioxidant that crosses the blood brain barrier protects dopaminergic neurons in experimental models of Parkinson's disease.

It is believed that oxidative stress (OS) plays an important role in the loss of dopaminergic nigrostriatal neurons in Parkinsons disease (PD) and that treatment with antioxidants might be neuroprotective. However, most currently available antioxidants cannot readily penetrate the blood brain barrier after systemic administration. We now report that AD4, the novel low molecular weight thiol antioxidant and the N‐acytel cysteine (NAC) related compound, is capable of penetrating the brain and protects neurons in general and especially dopaminergic cells against various OS‐generating neurotoxins in tissue cultures. Moreover, we found that treatment with AD4 markedly decreased the damage of dopaminergic neurons in three experimental models of PD. AD4 suppressed amphetamine‐induced rotational behaviour in rats with unilateral 6‐OHDA‐induced nigral lesion. It attenuated the reduction in striatal dopamine levels in mice treated with 1‐methyl‐4‐phenyl‐1,2,3,6,‐tetrahydropyridine (MPTP). It also reduced the dopaminergic neuronal loss following chronic intrajugular administration of rotenone in rats. Our findings suggest that AD4 is a novel potential new neuroprotective drug that might be effective at slowing down nigral neuronal degeneration and illness progression in patients with PD.

Anti-Inflammatory Drugs in the Treatment of Neurodegenerative Diseases: Current State

Increasing evidence indicates that inflammation is involved in the pathogenesis of many neurological, particularly neurodegenerative diseases. Even if inflammation is not a primary causative process, its presence may contribute to the continued loss of CNS neurons. Therefore, it seems reasonable to propose that use of anti-inflammatory drugs might diminish the cumulative effects of inflammation in the brain. Indeed, some epidemiological studies performed to date, especially in Alzheimers disease, suggests that sustained use of anti-inflammatory drugs (AIDs) may prevent or slow down the progression of neurodegenerative diseases. However, small number of clinical trials carried out so far using AIDs, were minimal and equivocal in their outcome. Potential reasons for these mixed results include timing of AIDs administration, nonselective inhibition of cyclooxygenase (COX), inappropriate use of particular anti-inflammatory drugs for a given disease or disease progression/ severity, sub-optimal dose in target site, or limited penetration to the brain through the blood-brain barrier (BBB). Therefore, design of AIDs for the treatment of neurodegenerative diseases based upon better BBB penetration, and with minimal adverse events, would be appropriate. In addition, relevant genetic differences among patients should be considered planning new AIDs, for improved efficacy. Furthermore, due to the possible co-involvement of oxidative stress and excitotoxicity in the pathogenesis of these diseases, combination therapy with antioxidants or glutamate antagonists or a multi-potent drug might be much more effective in successfully treating neurodegenerative diseases.

Safety, pharmacokinetics, and pharmacodynamics of TV‐1380, a novel mutated butyrylcholinesterase treatment for cocaine addiction, after single and multiple intramuscular injections in healthy subjects

Human plasma butyrylcholinesterase (BChE) contributes to cocaine metabolism and has been considered for use in treating cocaine addiction and cocaine overdose. TV‐1380 is a recombinant protein composed of the mature form of human serum albumin fused at its amino terminus to the carboxy‐terminus of a truncated and mutated BChE. In preclinical studies, TV‐1380 has been shown to rapidly eliminate cocaine in the plasma thus forestalling entry of cocaine into the brain and heart. Two randomized, blinded phase I studies were conducted to evaluate the safety, pharmacokinetics, and pharmacodynamics of TV‐1380, following single and multiple administration in healthy subjects. TV‐1380 was found to be safe and well tolerated with a long half‐life (43–77 hours) and showed a dose‐proportional increase in systemic exposure. Consistent with preclinical results, the ex vivo cocaine hydrolysis, TV‐1380 activity clearly increased upon treatment in a dose‐dependent manner. In addition, there was a direct relationship between ex vivo cocaine hydrolysis (kel) and TV‐1380 serum concentrations. There was no evidence that TV‐1380 affected heart rate, the uncorrected QT interval, or the heart‐rate‐corrected QTcF interval. TV‐1380, therefore, offers a safe once‐weekly therapy to increase cocaine hydrolysis.