Adamantanes for the treatment of neurodegenerative diseases in the presence of SARS-CoV-2.

Advent of the acute respiratory coronavirus SARS-CoV-2 has resulted in the search for novel antiviral agents and in the repurposing of existing agents with demonstrated efficacy against other known coronaviruses in the search for an agent with antiviral activity for use during the COVID-19 pandemic. Adamantanes including amantadine, rimantadine, and memantine have well-established benefit in the treatment of neurodegenerative diseases including Parkinson's disease (PD), Alzheimer's disease (AD) and fatigue related to Multiple sclerosis (MS) all of which are known comorbidities related to COVID-19 Moreover, results of basic pharmacological studies both in vitro and in vivo reveal that amantadine has the potential to inhibit SARS-CoV-2 via down-regulation of host-cell proteases resulting in impaired viral genome release into the host cell and via amantadine's property as an NMDA receptor antagonist resulting in the prevention of the acute lung injury and respiratory distress that is characteristic of COVID-19. Cases suggestive of COVID-19 prophylaxis have been reported in patients with PD or MS or severe cognitive impairment treated in all cases for several months with an adamantane [amantadine or memantine] who were subsequently infected with SARS-CoV-2 confirmed by RT-PCR, and, in all cases, no signs of infectious disease were encountered. Amantadine is effective for the treatment of fatigue in MS and for the neurological complications of Traumatic Brain Injury (TBI).

Potential for the Repurposing of Adamantane Antivirals for COVID-19.

Several adamantanes have established actions against coronaviruses. Amantadine, rimantadine, bananins and the structurally related memantine are effective against human respiratory coronavirus HCoV-OC43, bovine coronavirus and severe acute respiratory syndrome coronavirus 1 (SARS-CoV-1) and a spiroadamantane amine is effective against the coronavirus strain 229E. Molecular docking studies suggest that amantadine may block the viral E protein channel, leading to impaired viral propagation. Additionally, amantadine analogues may inhibit entry of the virus into the host cell by increasing the pH of the endosomes and thus inhibiting the action of host cell proteases such as Cathepsin L. High-throughput drug screen gene expression analysis identified compounds able to down-regulate Cathepsin L expression where the fifth most potent agent of 466 candidates was amantadine. Amantadine inhibits severe acute respiratory syndrome coronavirus 2 replication in vitro but does not inhibit the binding of the spike protein to ACE2. Adamantanes also may act against coronaviruses including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) via antagonism of glutamate (NMDA) and the α-7 subtype of the nicotinic acetylcholine receptor located on bronchial and alveolar epithelial cells. As an NMDA receptor antagonist, memantine has the potential to inhibit entry of SARS-CoV-2 into these cell populations. Amantadine and memantine are widely employed for the treatment of neurodegenerative diseases and a pathophysiologic link between the antiviral and anti-Parkinson actions of amantadine has been entertained. Case reports involving 23 patients with reverse transcription polymerase chain reaction-confirmed coronavirus disease 2019 (COVID-19) and a range of co-morbidities including type 2 diabetes mellitus, Parkinson's disease, multiple sclerosis and severe cognitive impairment reveal significant potential benefits of amantadine and memantine for the prevention and/or treatment of coronavirus disease 2019 and its neurological complications.

Ammonia Removal by Metabolic Scavengers for the Prevention and Treatment of Hepatic Encephalopathy in Cirrhosis.

Effective lowering of circulating ammonia is the mainstay strategy in the prevention and treatment of hepatic encephalopathy in cirrhosis and there is increasing interest in agents with the metabolic potential for the active removal of ammonia by the liver and skeletal muscle by agents including L-ornithine L-aspartate, branched-chain amino acids, as well as the re-purposing of benzoate and phenylacetate currently employed for the control of hyperammonaemia in congenital urea-cycle enzymopathies. Based upon results of multiple systematic reviews with meta-analyses, L-ornithine L-aspartate demonstrably lowers circulating ammonia in patients with cirrhosis with concomitantly improved mental status. Distinct mechanisms responsible include optimisation of hepatic metabolic pathways for ammonia removal as well as direct hepatoprotective effects involving the release of glutathione and of nitric oxide with beneficial effects on hepatic microcirculation. L-ornithine L-aspartate also prevents cirrhosis-related sarcopenia, leading to increased capacity for ammonia removal by skeletal muscle. Branched-chain amino acids continue to be prescribed as nutritional supplements with the potential to result in improvements in liver function. Sodium benzoate, glycerol phenylbutyrate and an analogous compound L-ornithine phenylacetate were also evaluated. Glycerol phenylbutyrate was the only agent with a beneficial effect on both hyperammonaemia and hepatic encephalopathy. None were superior to lactulose for the lowering of blood ammonia.

Region-selective permeability of the blood-brain barrier to α-aminoisobutyric acid during thiamine deficiency and following its reversal.

Thiamine deficiency (TD) results in focal lesions in several regions of the rat brain including the thalamus and inferior colliculus. Since alterations in blood-brain barrier (BBB) integrity may play a role in this damage, we have examined the influence of TD on the unidirectional blood-to-brain transfer constant (Ki) of the low molecular weight species α-aminoisobutyric acid (AIB) in vulnerable and non-vulnerable brain regions at different stages during progression of the disorder, and following its reversal with thiamine. Analysis of the regional distribution of Ki values showed early (day 10) increased transfer of [14C]-AIB across the BBB in the vulnerable medial thalamus as well as the non-vulnerable caudate and hippocampus. At the acute symptomatic stage (day 14), more widespread BBB permeability changes were detected in most areas including the lateral thalamus, inferior colliculus, and non-vulnerable cerebellum and pons. Twenty-four hours following thiamine replenishment, a heterogeneous pattern of increased BBB permeability was observed in which many structures maintained increased uptake of [14C]-AIB. No increase in the [3H]-dextran space, a marker of intravascular volume, was detected in brain regions during the progress of TD, suggesting that BBB permeability to this large tracer was unaffected. These results indicate that BBB opening i) occurs early during TD, ii) is not restricted to vulnerable areas of the brain, iii) is progressive, iv) persists for at least 24 h following treatment with thiamine, and v) is likely selective in nature, depending on the molecular species being transported.

Beneficial effects of L-ornithine L-aspartate for prevention of overt hepatic encephalopathy in patients with cirrhosis: a systematic review with meta-analysis.

The present systematic review with meta-analysis was undertaken to review the evidence base in support of a beneficial effect of L-ornithine L-aspartate (LOLA) for the prevention/prophylaxis of overt hepatic encephalopathy (OHE) in patients with cirrhosis. Using appropriate keywords and electronic and manual searches together with established inclusion/exclusion criteria, six randomized controlled trials (RCTs) for a total of 384 patients were identified five of which were of high quality and low risk of bias according to Jadad-Cochrane criteria. Treatment with LOLA resulted in significant reductions in the risk of progression to OHE in MHE patients (3 studies) with RR: 0.23 [95% CI: 0.07, 0.73], p < 0.01. LOLA was also effective for secondary OHE prophylaxis with RR: 0.389 [95% CI: 0.174-0.870] p < 0.002 as well as for primary prophylaxis for OHE following acute variceal bleeding [RR: 0.42 [95% CI: 0.16-0.98] p < 0.03 and for OHE prophylaxis post-TIPSS [RR: 0.30 [95% CI: 0.03-2.66] compared to placebo/no intervention in all cases. OHE prevention/prophylaxis was accompanied by significant reductions of blood ammonia. Both oral and intravenous formulations of LOLA appeared to be effective for the prevention of progression to OHE in patients with MHE. These findings provide the first direct evidence of potential benefit of LOLA for the prevention of OHE in cirrhosis across a range of clinical presentations.

L-Ornithine L-Aspartate for the Treatment of Sarcopenia in Chronic Liver Disease: The Taming of a Vicious Cycle.

Sarcopenia is a common complication of cirrhosis with a negative impact on posttransplant outcome, health-related quality of life (HRQOL), and patient survival. Studies in experimental animals and in patients demonstrate that ammonia is directly implicated in the pathogenesis of sarcopenia in cirrhosis via mechanisms involving increased expression of myostatin and of autophagy markers such as LC3 lipidation and p62 leading to muscle dysmetabolism and sarcopenia. Paradoxically, skeletal muscle replaces liver as the primary ammonia-detoxifying site as a result of the modification of genes coding for key proteins implicated in ammonia-lowering pathways in cirrhosis. Thus, a vicious cycle occurs whereby hyperammonemia causes severe muscle damage and sarcopenia that, in turn, limits the capacity of muscle to remove excess blood-borne ammonia and the cycle continues. Randomized clinical trials and meta-analyses confirm that L-ornithine L-aspartate (LOLA) is an effective ammonia-lowering agent currently employed for the treatment of hepatic encephalopathy (HE) that stimulates both urea synthesis by residual hepatocytes and muscle glutamine synthesis together with putative hepatoprotective actions. Treatment of cirrhotic patients with LOLA limits ammonia-induced sarcopenia by improving muscle protein synthesis and function. It is conceivable that the antisarcopenic action of LOLA contributes to its efficacy for the treatment of HE in cirrhosis.

Hepatic Encephalopathy in Cirrhosis: Pathology and Pathophysiology.

Neuropathology of hepatic encephalopathy (HE) in cirrhosis is primarily astroglial in nature characterized by Alzheimer type 2 astrocytosis together with activation of microglia indicative of neuroinflammation. Focal loss of neurons may also occur in the basal ganglia, thalamus and cerebellum. Pathophysiology of HE in cirrhosis is multifactorial, involving brain accumulation of ammonia and manganese, systemic and central inflammation, nutritional/metabolic factors and activation of the GABAergic neurotransmitter system. Neuroimaging and spectroscopic techniques reveal early deactivation of the anterior cingulate cortex in parallel with neuropsychological impairment. T1-weighted MR signal hyperintensities in basal ganglia resulting from manganese lead to a novel entity, 'Parkinsonism in cirrhosis'. Elucidation of the pathophysiological mechanisms has resulted in novel therapeutic approaches to HE aimed at reduction of brain ammonia, reduction of systemic and central inflammation, and reduction of GABAergic tone via the discovery of antagonists of the neurosteroid-modulatory site on the GABA receptor complex.

L-Ornithine L-Aspartate (LOLA) for Hepatic Encephalopathy in Cirrhosis: Results of Randomized Controlled Trials and Meta-Analyses.

This manuscript represents an appraisal of the evidence in support of L-ornithine-L-aspartate (LOLA) for the management and treatment of hepatic encephalopathy (HE) in cirrhosis. Meta-analyses of randomized controlled trials (RCTs) conducted over the last two decades generally reveal evidence of benefit of LOLA in a range of clinical presentations. This included improvement of mental state grade in overt HE (OHE) assessed by West Haven criteria as well as in minimal HE (MHE) assessed by psychometric testing where the oral formulation of LOLA was determined to be particularly effective. However, concerns over study quality were noted in one meta-analysis. Nevertheless, the concomitant lowering of fasting blood ammonia was reported in all RCTs using this endpoint. Network meta-analyses showed that LOLA appears to be comparable (or superior) in efficacy to non-absorbable disaccharides or probiotics. Emerging evidence from single RCTs show efficacy of LOLA for the treatment of post-transjugular intrahepatic portosystemic shunt (TIPSS) HE as well as for secondary HE prophylaxis. These findings provide support for the use of LOLA in the treatment of HE and future trials should focus on the use of LOLA for prophylaxis.

Hepatoprotection by L-Ornithine L-Aspartate in Non-Alcoholic Fatty Liver Disease.

BACKGROUND: Non-alcoholic fatty liver disease (NAFLD) is the leading chronic hepatic condition worldwide and new approaches to management and treatment are limited. SUMMARY: L-ornithine L-aspartate (LOLA) has hepatoprotective properties in patients with fatty liver of diverse etiology and results of a multicenter randomized clinical trial reveal that 12 weeks treatment with oral LOLA (6-9 g/d) results in a dose-related reduction in activities of liver enzymes and triglycerides together with significant improvements of liver/spleen CT ratios. A preliminary report described improvements of hepatic microcirculation in patients with non-alcoholic steatohepatitis (NASH) following treatment with LOLA. Mechanisms responsible for the beneficial effects of LOLA in NAFLD/NASH involve, in addition to its established ammonia-lowering effect, metabolic transformations of the LOLA-constituent amino acids L-ornithine and L-aspartate into L-glutamine, L-arginine, and glutathione. These metabolites have well-established actions implicated in the prevention of lipid peroxidation, improvement of hepatic microcirculation in addition to anti-inflammatory, and anti-oxidant properties. Key Messages: (1) LOLA is effective for the treatment of key indices in NAFLD/NASH. (2) Mechanisms other than LOLA's ammonia-lowering action have been postulated. (3) Further assessments in the clinical setting are now required.

Efficacy of l-Ornithine l-Aspartate for the Treatment of Hepatic Encephalopathy and Hyperammonemia in Cirrhosis: Systematic Review and Meta-Analysis of Randomized Controlled Trials.

BACKGROUND/OBJECTIVES: l-Ornithine l-Aspartate (LOLA) is a mixture of two endogenous amino acids with the capacity to fix ammonia in the form of urea and/or glutamine. Its' efficacy for the treatment of Hepatic Encephalopathy (HE), a known hyperammonemic disorder, remains the subject of debate. This study quantitatively analyzed the efficacy of LOLA in patients with cirrhosis and HE. METHODS: Efficacy was defined as the extent of lowering of blood ammonia and improvement of mental state assessed in clinically overt HE (OHE) by Westhaven criteria or psychometric testing for assessment of Minimal HE (MHE). Appropriate keywords were used for electronic and/or manual searches of databases to identify RCTs for inclusion. Study quality and risk of bias were assessed using the Jadad Composite Scale together with The Cochrane Scoring Tool. Random Effects Models were used to express pooled Risk Ratio (RR) or Mean Difference (MD) with associated 95% Confidence Intervals (CI). RESULTS: 10 RCTs (884 patients) were included. Regression analysis showed no evidence of publication bias or other small study effects. Eight RCTs had low risk of bias by Jadad/Cochrane criteria. Comparison with placebo/no intervention controls revealed that LOLA was significantly more effective for improvement of mental state in all types of HE (RR 1.36 (95% CI 1.10-1.69), p = 0.005), OHE (RR: 1.19, 95% CI of 1.01-1.39, test for overall effect: Z = 2.14, p = 0.03), MHE (RR: 2.15 (1.48-3.14), p < 0.0001) and for lowering of blood ammonia (MD: -17.50 µmol/l (-27.73 to (-7.26)), p = 0.0008). Improvement of mental state was greater in trials with low risk of bias. Heterogeneity was reduced in trials from Europe or with >100 participants. Oral LOLA appeared particularly effective for the treatment of MHE. CONCLUSION: LOLA appears to improve mental state and lower ammonia in patients with HE or MHE. Further studies are required in some subgroups of HE and in the era of HE reclassification.

Pathogenesis of hepatic encephalopathy in cirrhosis: the concept of synergism revisited.

The concept of synergistic mechanisms as the pathophysiologic basis of hepatic encephalopathy started with the pioneering work of Les Zieve in Minneapolis some 60 years ago where synergistic actions of the liver-derived toxins ammonia, methanethiol, and octanoic acid were described. More recently, synergistic actions of ammonia and manganese, a toxic metal that is normally eliminated via the hepatobiliary route and shown to accumulate in brain in liver failure, on the glutamatergic neurotransmitter system were described. The current upsurge of interest in brain inflammation (neuroinflammation) in relation to the CNS complications of liver failure has added a third dimension to the synergy debate. The combined actions of ammonia, manganese and pro-inflammatory cytokines in brain in liver failure result in oxidative/nitrosative stress resulting from activation of glutamate (NMDA) receptors and consequent nitration of key brain proteins. One such protein, glutamine synthetase, the sole enzyme responsible for brain ammonia removal is nitrated and inactivated in brain in liver failure. Consequently, brain ammonia levels increase disproportionately resulting in alterations of brain excitability, impaired brain energy metabolism, encephalopathy and brain swelling. Experimental therapeutic approaches for which proof-of-principle has been established include the NMDA receptor antagonist memantine, N-acetyl cysteine (recently shown to have antioxidant properties at both hepatic and cerebral levels) and probiotics.

The concept of "the inflamed brain" in acute liver failure: mechanisms and new therapeutic opportunities.

The presence and severity of a systemic inflammatory response is a major predictor of brain edema and encephalopathy in acute liver failure (ALF) and polymorphisms of the gene coding for the proinflammatory cytokine TNF-alpha are known to influence the clinical outcome in ALF. Recent reports provide robust evidence for a role of neuroinflammation(inflammation of the brain per se) in ALF with the cardinal features of neuroinflammation including activation of microglial cells and increased production in situ of pro-inflammatory cytokines such as TNF-alpha and interleukins IL-1beta and IL-6. Multiple liver-brain signalling pathways have been proposed to explain the phenomenon of neuroinflammation in liver failure and these include direct effects of systemically-derived cytokines, recruitment of monocytes relating to microglial activation as well as effects of liver failure-derived toxins and altered permeability of the blood-brain barrier. Synergistic mechanisms involving ammonia and cytokines have been proposed. Currently-available strategies aimed at lowering of blood ammonia such as lactulose, probiotics and rifaximin have the potential to dampen systemic inflammation as does the anti-oxidant N-acetyl cysteine, mild hypothermia and albumin dialysis. Experimental studies demonstrate that deletion of genes coding for TNF-alpha or IL-1 leads to attenuation of the CNS consequences of ALF and administration of the TNF-alpha receptor antagonist etanercept has comparable beneficial effects in experimental ALF. Together, these findings confirm a major role for central neuroinflammatory mechanisms in general and mechanisms involving TNF-alpha in particular in the pathogenesis of the cerebral consequences of ALF and open the door to novel therapeutic interventions in this often fatal disorder.

Neurosteroids in hepatic encephalopathy: Novel insights and new therapeutic opportunities.

Hepatic encephalopathy (HE) is a serious neuropsychiatric disorder resulting from liver failure. Symptoms of HE include mild cognitive impairment, stupor and coma. Morphological changes to neuroglia (both astrocytes and microglia) occur in HE consisting of cytotoxic brain edema (astrocyte swelling) in acute liver failure and Alzheimer type-2 astrocytosis in cirrhosis. Visual-evoked responses in animals with liver failure and HE manifest striking similarities to those in animals treated with agonists of the GABA-A receptor complex. Neurosteroids are synthesized in brain following activation of translocator protein (TSPO), a mitochondrial neuroglial cholesterol-transporter protein. TSPO sites are activated in both animal models of HE as well as in autopsied brain tissue from HE patients. Activation of TSPO sites results in increased cholesterol transport into the mitochondrion followed by stimulation of a metabolic pathway culminating in the synthesis of allopregnanolone (ALLO) and tetrahydrodeoxycorticosterone (THDOC), neurosteroids with potent positive allosteric modulatory action on the GABA-A receptor complex. Concentrations of ALLO and THDOC in brain tissue from mice with HE resulting from toxic liver injury are sufficient to induce sedation in animals of the same species and significant increases in concentrations of ALLO have been reported in autopsied brain tissue from cirrhotic patients with HE leading to the proposal that "increased GABAergic tone" in HE results from that increased brain concentrations of this neurosteroid. Agents with the potential to decrease neurosteroid synthesis and/or prevent their modulatory actions on the GABA-A receptor complex may provide novel approaches to the management and treatment of HE. Such agents include indomethacin, benzodiazepine receptor inverse agonists and a novel series of compounds known as GABA-A receptor-modulating steroid antagonists (GAMSA).

Reprint of: Nutrition in the Management of Cirrhosis and its Neurological Complications.

Malnutrition is a common feature of chronic liver diseases that is often associated with a poor prognosis including worsening of clinical outcome, neuropsychiatric complications as well as outcome following liver transplantation. Nutritional assessment in patients with cirrhosis is challenging owing to confounding factors related to liver failure. The objectives of nutritional intervention in cirrhotic patients are the support of liver regeneration, the prevention or correction of specific nutritional deficiencies and the prevention and/or treatment of the complications of liver disease per se and of liver transplantation. Nutritional recommendations target the optimal supply of adequate substrates related to requirements linked to energy, protein, carbohydrates, lipids, vitamins and minerals. Some issues relating to malnutrition in chronic liver disease remain to be addressed including the development of an appropriate well-validated nutritional assessment tool, the identification of mechanistic targets or therapy for sarcopenia, the development of nutritional recommendations for obese cirrhotic patients and liver-transplant recipients and the elucidation of the roles of vitamin A hepatotoxicity, as well as the impact of deficiencies in riboflavin and zinc on clinical outcomes. Early identification and treatment of malnutrition in chronic liver disease has the potential to lead to better disease outcome as well as prevention of the complications of chronic liver disease and improved transplant outcomes.

Pathogenesis of hepatic encephalopathy and brain edema in acute liver failure.

Neuropathologic investigations in acute liver failure (ALF) reveal significant alterations to neuroglia consisting of swelling of astrocytes leading to cytotoxic brain edema and intracranial hypertension as well as activation of microglia indicative of a central neuroinflammatory response. Increased arterial ammonia concentrations in patients with ALF are predictors of patients at risk for the development of brain herniation. Molecular and spectroscopic techniques in ALF reveal alterations in expression of an array of genes coding for neuroglial proteins involved in cell volume regulation and mitochondrial function as well as in the transport of neurotransmitter amino acids and in the synthesis of pro-inflammatory cytokines. Liver-brain pro-inflammatory signaling mechanisms involving transduction of systemically-derived cytokines, ammonia neurotoxicity and exposure to increased brain lactate have been proposed. Mild hypothermia and N-Acetyl cysteine have both hepato-protective and neuro-protective properties in ALF. Potentially effective anti-inflammatory agents aimed at control of encephalopathy and brain edema in ALF include etanercept and the antibiotic minocycline, a potent inhibitor of microglial activation. Translation of these potentially-interesting findings to the clinic is anxiously awaited.

Hepatic encephalopathy in alcoholic cirrhosis.

Hepatic encephalopathy (HE) is a serious neuropsychiatric complication of cirrhosis in alcoholic patients that is characterized clinically by personality changes, sleep abnormalities, and impaired motor coordination, as well as cognitive dysfunction progressing to stupor and coma. Procedures used for diagnosis and grading of HE include neurologic assessment, electroencephalography, psychometric testing, and use of the critical flicker frequency test. Neuropathologically, HE in cirrhosis is principally a disorder of neuroglia characterized by Alzheimer type II astrocytosis and activation of microglia. However, thalamic and cerebellar neuronal pathologies have been noted as well as lesions to globus pallidus and substantia nigra, leading to a condition known as "parkinsonism in cirrhosis." Multiple mechanisms have been proposed to account for the pathogenesis of HE in cirrhosis, including the neurotoxic actions of ammonia and manganese (normally removed via the hepatobiliary route), impaired brain energy metabolism, central proinflammatory mechanisms, and alterations of both excitatory and inhibitory neurotransmission. Treatment of HE in cirrhosis continues to rely on ammonia-lowering strategies such as lactulose, antibiotics, probiotics and l-ornithine l-aspartate with nutritional management consisting of adequate (but not excessive) dietary protein and vitamin B1 supplements. l-DOPA may improve parkinsonian symptoms. Liver transplantation leads to recovery of central nervous system function in the majority of cases.

Pathophysiology of brain dysfunction in hyperammonemic syndromes: The many faces of glutamine.

Ineffective hepatic clearance of excess ammonia in the form of urea, as occurs in urea cycle enzymopathies (UCDs) and in liver failure, leads to increases in circulating and tissue concentrations of glutamine and a positive correlation between brain glutamine and the severity of neurological symptoms. Studies using 1H/13C Nuclear Magnetic Resonance (NMR) spectroscopy reveal increased de novo synthesis of glutamine in the brain in acute liver failure (ALF) but increases of synthesis rates per se do not correlate with either the severity of encephalopathy or brain edema. Skeletal muscle becomes primarily responsible for removal of excess ammonia in liver failure and in UCDs, an adaptation that results from a post-translational induction of the glutamine synthetase (GS) gene. The importance of muscle in ammonia removal in hyperammonemia accounts for the resurgence of interest in maintaining adequate dietary protein and the use of agents aimed at the stimulation of muscle GS. Alternative or additional metabolic and regulatory pathways that impact on brain glutamine homeostasis in hyperammonemia include (i) glutamine deamination by the two isoforms of glutaminase, (ii) glutamine transamination leading to the production of the putative neurotoxin alpha-ketoglutaramate and (iii) alterations of high affinity astrocytic glutamine transporters (SNATs). Findings of reduced expression of the glutamine transporter SNAT-5 (responsible for glutamine clearance from the astrocyte) in ALF raise the possibility of "glutamine trapping" within these cells. Such a trapping mechanism could contribute to cytotoxic brain edema and to the imbalance between excitatory and inhibitory neurotransmission in this disorder.

Perispinal etanercept for post-stroke neurological and cognitive dysfunction: scientific rationale and current evidence.

There is increasing recognition of the involvement of the immune signaling molecule, tumor necrosis factor (TNF), in the pathophysiology of stroke and chronic brain dysfunction. TNF plays an important role both in modulating synaptic function and in the pathogenesis of neuropathic pain. Etanercept is a recombinant therapeutic that neutralizes pathologic levels of TNF. Brain imaging has demonstrated chronic intracerebral microglial activation and neuroinflammation following stroke and other forms of acute brain injury. Activated microglia release TNF, which mediates neurotoxicity in the stroke penumbra. Recent observational studies have reported rapid and sustained improvement in chronic post-stroke neurological and cognitive dysfunction following perispinal administration of etanercept. The biological plausibility of these results is supported by independent evidence demonstrating reduction in cognitive dysfunction, neuropathic pain, and microglial activation following the use of etanercept, as well as multiple studies reporting improvement in stroke outcome and cognitive impairment following therapeutic strategies designed to inhibit TNF. The causal association between etanercept treatment and reduction in post-stroke disability satisfy all of the Bradford Hill Criteria: strength of the association; consistency; specificity; temporality; biological gradient; biological plausibility; coherence; experimental evidence; and analogy. Recognition that chronic microglial activation and pathologic TNF concentration are targets that may be therapeutically addressed for years following stroke and other forms of acute brain injury provides an exciting new direction for research and treatment.