More than 20,000 patients have participated in clinical trials of more than 100 neuroprotective therapies, but no study has provided convincing evidence of benefit. Several improvements to the rigor of preclinical agent qualification have been identified to increase the likelihood of success in human clinical trials: stringent randomization and blinding techniques to mitigate observer bias; assessment in in time periods achievable in the clinical setting; testing in older animals with comorbidities; and robust and reproducible benefit magnitudes. Human clinical trials should start agents hyperacutely, in the first minutes and hours after onset, when treatment effect would be maximal; target enrolment of patients likely to have transient rather than permanent ischaemic exposure; and use factorial and platform trial designs that would permit efficient testing of combinations of agents able to block multiple ischaemic injury-mediating pathways concurrently, including both anti-necrotic and anti-apoptotic interventions. For agents that allow cells to endure ischaemic stress, human trial delivery approaches include: prehospital initiation; initiation immediately upon brain imaging in patients destined for endovascular intervention; and initiation at outside hospitals in patients undergoing transfer to a neurothrombectomy center. For agents that mitigate reperfusion injury, treatment start before or concurrent with reperfusion, including intra-arterial administration via catheter immediately after endovascular thrombectomy, should be pursued.
Normally, cerebral blood flow (CBF) is maintained by cerebral autoregulation at about 50 mL blood/100 g brain/min. In acute ischaemic stroke, a cerebral artery is occluded or there is a reduction in perfusion distal to a severe stenosis, resulting in focal brain ischaemia and infarction. As the regional CBF falls, the regional lack of oxygen and glucose results in a time- and flow-dependent cascade characterized by a fall in energy (adenosine triphosphate [ATP]) production. Neuronal function is affected in two stages. The first threshold is at a blood flow of about 20 mL blood/100 g brain/min, below which neuronal electrical function is compromised, generating clinical deficits, but cellular homeostasis is maintained and recovery remains possible. However, if blood flow falls below the second critical threshold of 10 mL blood/100 g brain/min, an ‘ischaemic cascade’ of injurious molecular events is triggered (Doyle et al., 2008; Sekerdag et al., 2018). Free radicals are generated. There is excessive release and impaired reuptake of excitatory amino acid (EAA) neurotransmitters such as glutamate, causing overstimulation of neuronal glutamate receptors (excitotoxicity), aerobic mitochondrial metabolism fails, inefficient anaerobic metabolism of glucose takes over, and harmful lactic acidosis evolves. Energy-dependent homoeostatic mechanisms of maintaining cellular ions fail, potassium leaks out of cells, and sodium, water, and calcium enter cells, leading to cytotoxic oedema and calcium-induced mitochondrial failure, respectively. If severe ischaemia (blood flow below 10 mL blood/100 g brain/min) is sustained, irreversible neuronal damage occurs and neuronal cell apoptosis and necrosis ensue.
Preclinical and neuroimaging studies indicate that the untreated penumbra deteriorates over time (Bardutzy et al., 2005; Heiss, 2011). This concept is supported by analyses of reperfusion therapies for acute cerebral ischaemia, which showed greater benefits of reperfusion by intravenous thrombolysis and by endovascular mechanical thrombectomy with earlier treatment (Emberson et al., 2014; Saver et al., 2016). Just how long ischaemic human brain may survive, and therefore the time window for therapeutic intervention, varies from individual to individual, reflecting degree of CBF compromise, robustness of collateral flow, differential tolerance of grey and white matter to ischaemia, and additional factors. Within the first 3–6 hours after ischaemia onset, nearly all patients still harbour salvageable tissue; from 6 to 24 hours and beyond, a steadily increasing proportion of patients have no remaining tissue at risk, having completed their strokes, but an important, slower progressing subset of patients still possess rescuable tissues.
Neuroprotective treatments are therapies that interrupt the cellular, biochemical, and metabolic processes that lead to brain injury during or after exposure to ischaemia and encompass a wide array of pharmacological and device interventions that block the molecular elaboration of cellular injury in brain tissues exposed to ischaemic stress (Ovbiagele et al., 2003). Neuroprotective treatments may have some mild potential benefits as standalone therapies in settings in which tissues are exposed to permanent ischaemia. However, the settings in which they are likely to exert their greatest benefit are those in which ischaemia will be transient, and neuroprotective interventions can enable ischaemic tissues to tolerate the ischaemic insult until the ischaemia is relieved. A major potential role of neuroprotective therapies is in spontaneous ischaemic stroke, where they can support the ischaemic penumbra until CBF is restored by intravenous thrombolysis and/or endovascular mechanical thrombectomy. They also could be helpful during surgical and endovascular procedures in which the brain is exposed to ischaemia for a delimited period of time.
Although numerous neuroprotective agents have been found beneficial in various preclinical stroke models, successful translation to human stroke patients has been challenging. Over 100 neuroprotective interventions showing signals of effect in preclinical stroke models have been advanced to human clinical trial testing and none was found to be of definite proven benefit (O’Collins et al., 2006; Hong et al., 2011). Several deficiencies in preclinical study and clinical trial designs have been identified as likely contributing to this breakdown in translation (Ovbiagele et al., 2003; O’Collins et al., 2006; Fisher et al., 2009; Lapchak et al., 2013). Preclinical experimental studies have often failed to use robust randomization and blinding techniques to avert bias, started treatments much earlier than achievable in the human clinical setting, and tested agents in young, otherwise healthy rodents and other species rather than older animals with multiple comorbidities. Human clinical trials have often failed to start therapies in the very first minutes and hours after onset, when treatment effect would be maximal, and to confine enrolment to patients likely to have transient rather than permanent ischaemic exposure.
The promise of, and the need for, effective brain cytoprotection remains great, despite past disappointments in neuroprotective development programmes. Reperfusion therapies, which require brain imaging and transport to a treatment-capable centre prior to start, will always have their treatment benefit constrained by the brain injury that accumulates before they can be initiated. For example, in pivotal trials, endovascular mechanical thrombectomy tremendously improves patient outcomes compared with no endovascular intervention, and yet 73% of the patients treated with endovascular therapy still have disabled (modified Rankin Scale [mRS] 2–6) outcomes at 3 months. Neuroprotective agents, many of which are safe and potentially beneficial for haemorrhagic as well as ischaemic stroke, could be started much earlier than reperfusion therapies, in the ambulance or self-administered at home, preserving more brain in a salvageable state until reperfusion can be achieved, potentially substantially magnifying the benefit of CBF restoration. Given the robust signals of benefit of neuroprotection in preclinical focal ischaemic stroke models and the demonstrated benefit of neuroprotection with hypothermia in human global brain ischaemia, there is excellent reason to hope that improved preclinical and clinical study designs will yield clinically useful agents for human stroke.
Among the many classes and individual examples of neuroprotective agents that have been tested in ischaemic stroke, this chapter will review several of the most studied and most promising. A broad mechanistic classification of neuroprotective interventions, with listing of several individual agents, is shown in Table 12.1, and includes: (1) Metabolism Suppressors, (2) Promoters of Genetically Programmed Hypoxia/Injury Tolerance, (3) Free Radical Scavengers and Anti-Oxidants, (4) Promoters of Membrane Repair, (5) Modulators of Excitatory Amino Acids, (6) Modulators of Calcium Influx, (7) Sodium Channel Blockers, (8) Modulators of GABA Inhibition, (9) Nitric Oxide Donors, (10) Modulators of Carnitine + Mitochondrial Function, (11) Anti-Inflammatory, (12) Oxygen Delivery Enhancers, (13) Agents with Multiple Leading Mechanisms, and (14) Uncertain Mechanism.
|Promoters of Genetically Programmed Hypoxia/Injury Tolerance and Repair|
|Free Radical Scavengers and Antioxidants|
|Promoters of Membrane Repair||Citicoline*|
|Modulators of Excitatory Amino Acids|
|Modulators of Calcium Influx|
|Sodium Channel Blockers|
|Modulators of GABA Inhibition|
|Nitric Oxide Donors|
|Modulators of Carnitine + Mitochondrial Function|
|Oxygen Delivery Enhancers|
|Multiple Leading Mechanisms|
* Agents receiving focused analysis in this chapter, due to availability in practice, historical importance, and/or current promise.
NMDA: N-methyl-d-aspartate. AMPA: α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid. GABA: gamma-aminobutyric acid.
Hypothermia is a quintessentially pleiotropic neuroprotective intervention, concurrently inhibiting many of the molecular pathways that elaborate ischaemic injury to neural tissues (Kurisu and Yenari, 2018). Hypothermia decreases the cerebral metabolic rate and metabolic demand, reducing the mismatch between energy supply and energy demand. Hypothermia additionally reduces free radical production, excitotoxicity, apoptosis, and inflammation. Mild (35–36°C), moderate (32–34°C), and profound (<32°C) hypothermia all have protective effects in preclinical models of ischaemic stroke. Achieving profound hypothermia in human patients requires intubation and sedation, to prevent shivering and respiratory compromise. Moderate hypothermia, however, can be achieved in awake patients with concomitant medications to reduce shivering.
Profound hypothermia is already routinely applied to counter the effects of cerebral hypoxia in neurosurgery and open-heart surgery. In cardiac arrest with global brain ischaemia, moderate (32–33°C) hypothermia improves outcome (Arrich et al., 2016). In acute stroke, a high body temperature has been associated with a worse prognosis (Marehbian and Greer, 2017) (see Chapter 5), but it is not known if lowering temperature improves prognosis. Some temperature-lowering agents, like non-steroidal anti-inflammatory drugs, have antiplatelet activity and could increase the risk of bleeding in acute ischaemic and haemorrhagic stroke. Other risks associated with induced hypothermia are mainly sepsis, pneumonia, and coagulopathy.
Hypothermia as a neuroprotective intervention for acute ischaemic stroke has largely been evaluated in small randomized trials designed to develop and validate technically effective regimens for rapid and sustained cooling to targeted temperature and control of shivering, using both surface cooling and indwelling vascular cooling devices. With more recent regimens, rapid attainment and tight maintenance of targeted moderate hypothermia in awake patients has been achieved, and absence of major adverse interaction with intravenous thrombolysis demonstrated. However, in these feasibility and regimen optimization studies, time from onset to enrolment and to time of first achievement of cerebral hypothermia has been prolonged. A meta-analysis of 6 randomized trials enrolling a total of 311 patients does not show a difference in the frequency of disability-free (mRS 0–1) outcome with hypothermia versus control, 25.9% versus 29.6%, risk ratio (RR) 0.88 (95% confidence interval [CI]: 0.64–1.47) (Figure 12.1) (Wan et al., 2014; Lyden et al., 2016).
Figure 12.1 Forest plot showing the effects of hypothermia vs control for acute ischaemic stroke on freedom from disability (mRS 0–1) at long-term follow-up.
Hypothermia has also been studied as an anti-oedema therapy for malignant middle cerebral artery infarction, as reviewed in Chapter 11.
Across the 6 randomized trials of hypothermia in human focal ischaemic stroke, mortality did not differ between treated and control groups. An increased risk of pneumonia was observed, 20.0% versus 7.6% (RR 2.65; 95% CI: 1.45–4.83). No differences were found for symptomatic intracerebral haemorrhage (SICH), fatal intracerebral haemorrhage (ICH), deep vein thrombosis (DVT), or atrial fibrillation.
Human clinical trials have refined device and shivering-control regimens to enable achievement of hypothermia efficiently in awake patients presenting with focal ischaemic stroke. However, there is no evidence from combined analysis of the small randomized controlled trials (RCTs) completed to date that hypothermia improves neurological outcomes in patients with acute ischaemic stroke. In addition, multiple studies have identified increased rates of pneumonia in the hypothermia group. With the advent of endovascular thrombectomy abrogating prolonged ischaemia in many large vessel occlusion patients, hypothermia as a prolonged neuroprotective intervention is no longer a needed therapy. However, hypothermia might play useful roles if it is: (1) initiated as soon as possible after onset, as bridging therapy in the prehospital setting; (2) given after successful reperfusion, to avert reperfusion injury (as in cardiac arrest and global brain ischaemia); or (3) delivered selectively to the cerebrum, via helmet, nasal, or other channels, enabling selective cerebral hypothermia with reduced systemic complications. Future trials evaluating these approaches are desirable.
In ischaemic conditioning, an organ is exposed to one or more brief, non-lethal cycles of ischaemia and reperfusion, activating endogenous cellular protective pathways rendering the target organ more tolerant of prolonged ischaemia. The intermittent ischaemia challenges can occur directly to the target organ; for example, transient ischaemic attacks may render the brain more resistant to subsequent infarction. But the intermittent ischaemia challenges may also be delivered to remote sites, typically simply by intermittent inflation of a blood pressure cuff placed on one or more limbs, with induction of humoral signals that activate hypoxia resistance pathways throughout the body, including the brain (Hess et al., 2015).
In various preclinical models, remote ischaemic conditioning has been found to reduce brain injury when applied before (pre-conditioning), during (per-conditioning), and soon after (post-conditioning) the cerebral ischaemic insult (Wang et al., 2015). Several molecular mechanisms appear to contribute to cerebral ischaemic conditioning, including: (1) increasing antioxidant production and increasing DNA repair capacity; (2) anti-excitotoxic effects by inhibiting glutamate and increasing gamma-aminobutyric acid (GABA) release; (3) anti-inflammatory effects by stimulating Toll-like receptors, which activate proinflammatory pathways; (4) prevention of mitochondrial-dependent cell death pathways; and (5) release of adenosine and activation of adenosine A1 receptors (Narayanan et al., 2013).
Two clinical trials have been completed evaluating remote ischaemic per-conditioning (RIPerC) as neuroprotection in the acute ischaemic stroke setting. In a single centre, open-label, blinded outcome observer, prehospital trial in Denmark, 443 patients were randomized and final outcome data were available in 224, with data missingness due to withdrawal of patients without final diagnosis of acute cerebral ischaemia and failure to initially obtain informed consent among patients in the control arm (Hougaard et al., 2014). The intervention arm received 4 inflations of a standard upper limb blood pressure cuff to 200, or 25 mm Hg above the patient’s systolic blood pressure, each lasting 5 minutes and separated by 5 minutes of cuff deflation. Among the 133 RIPerC and 91 control patients with final diagnoses of ischaemic stroke or transient ischaemic attack, mixed effects were observed, with a favourable trend in symptom-free outcome (mRS 0), 57% versus 47%, RR 1.21 (95% CI: 0.93–1.57); no difference in disability-free (mRS 0–1) outcome, 72% versus 73%, RR 0.96 (95% CI: 0.81–1.13); and an adverse effect for functional independence (mRS 0–2), 80% versus 88%, RR 0.89 (95% CI: 0.79–0.99).
In a smaller, single centre, sham-controlled, in-hospital trial in Great Britain, 26 patients with ischaemic stroke were randomized to 4 cycles of 5 minutes’ inflation in the nonparetic arm, 20 mm Hg above systolic blood pressure in the active group versus 30 mm Hg total in the sham group. The lead tolerability aim of the trial was met, with 12/13 active RIPerC arm patients tolerating and completing the intervention. No difference in disability levels at 3 months was noted, mean mRS for intervention versus control, 2.46 (±1.39) versus 2.69 (±1.79), p = 0.8 (England et al., 2017).
In the larger Danish trial, patients randomized to rPerC had a higher recall of pain (p = 0.006), but not of anxiety, sweating, palpitations, headaches, or nausea. There was no difference in mortality among the acute cerebral ischaemia patients, RIPerC versus control, 4% versus 1%, RR 3.42 (95% CI: 0.41–28.80).
Remote ischaemic per-conditioning has been shown to be feasible in patients with acute cerebral ischaemia, and without marked adverse effects. Whether further signals to activate hypoxia protection systems generated by remote induced ischaemia in the limbs usefully adds to the signals already being generated directly in the brain during an episode of prolonged cerebral ischaemia remains an open question. Larger trials are needed to definitively assess RIPerC for efficacy in patients experiencing acute cerebral ischaemia, as well as to explore remote ischaemic post-conditioning (RIPostC) to mitigate reperfusion injury and incomplete reperfusion among patients with successful thrombolytic or endovascular thrombectomy reperfusion.
Growth factors are proteins that regulate the differentiation, survival, and proliferation of neurones, glia, fibroblasts, endothelial cells, and other cell types. Basic fibroblast growth factor (bFGF) promotes neuronal sprouting and proliferation of capillaries and glia during stroke recovery, facilitating neural repair and functional recovery (Paciaroni and Bogousslavsky, 2011). In addition, in stroke models, bFGF initiates a signal transduction cascade, resulting in the expression of cytoprotective genes and their proteins, facilitating cell survival, and reducing infarct volume.
Trafermin, a recombinant native form of basic fibroblast growth factor, was studied in 3 double-blind trials in acute ischaemic stroke patients, including 1 dose-escalation trial and 2 pivotal trials. A phase 3 trial in patients within 6 hours of stroke onset in North America was halted after enrolment of 303 patients on advice of the Data and Safety Monitoring Board (DSMB), due to an increase in adverse neurological events and mortality with active agent. In contrast, a European–Australian phase 3 trial was stopped early for futility, rather than safety, after randomizing 286 patients within 6 hours of stroke onset to 5 or 10 mg of trafermin or placebo intravenously (IV) infused over 24 hours (Paciaroni and Bogousslavsky, 2011). The primary endpoint was favourable outcome at 90 days on a categorized combination of the Barthel and Rankin scales, and did not differ for the 5 mg of trafermin versus placebo (odds ratio [OR]: 1.2, 95% CI: 0.72–2.00, p = 0.48) or 10 mg of trafermin versus placebo (OR: 0.74, 95% CI: 0.44–1.22, p = 0.24). Mortality rates at 90 days were 17% in the 5 mg group, 24% in the 10 mg group, and 18% in the placebo group. Treatment with trafermin was associated with an increase in leucocytosis and a mean greater decrease in systolic blood pressure (BP) versus placebo of 11 mm Hg in the 5 mg group and 13 mm Hg in the 10 mg group. In a post hoc subgroup analysis, patients in the 5 mg group treated more than 5 hours after the onset of symptoms showed an apparent advantage over placebo (OR: 2.1, 95% CI: 1.00–4.41, p = 0.044; after age adjustment: OR: 1.9, 95% CI: 0.91–4.13, p = 0.08).
Completed RCTs are modest in size but do not suggest a major neuroprotective effect of bFGF in the acute period of ischaemic stroke. Given its blood pressure lowering effects, which may reduce collateral flow in the acute setting, and its potential for enhancing neuroplasticity in the subacute period, additional studies of bFGF as a subacute neuroreparative agent may be worthwhile.
Free radical, reactive oxygen and nitrogen species are produced by cellular enzymes in settings of oxidative stress, including ischaemia, and damage cellular integrity. Enzymatic and non-enzymatic antioxidant molecules react in one-electron reactions with free radicals to avert oxidative damage (Davis and Pennypacker, 2017).
Uric acid is the end product of purine degradation in humans and the most abundant antioxidant in the human body, accounting for up to 60% of plasma antioxidative capacity. Exogenously administered uric acid reduces infarct volume in rodent models of focal cerebral ischaemia (Romanos et al., 2007). In a meta-analysis of 10 observational studies with a total of 8131 acute ischaemic stroke patients, high compared with low serum uric acid level was associated with reduced poor outcomes after acute ischaemic stroke (hazard ratio [HR] = 0.77, 95% CI: 0.68–0.88, p = 0.0001) (Wang et al., 2016).
Uric acid has been studied in one double-blind, placebo-controlled trial, with 421 ischaemic stroke patients treated with alteplase randomized to 1000 mg intravenous uric acid or placebo over 90 minutes (Chamorro et al., 2014). In the active treatment group, median time from onset to start of alteplase was 140 minutes and from onset to start of uric acid 175 minutes. For the primary 3-month outcome, freedom from disability (mRS 0–1) or continued functional independence if premorbid mRS was 2, a trend to benefit was noted: 39% versus 33%, adjusted RR 1.23 (95% CI: 0.96–1.56), p = 0.10). For the secondary endpoint of favourable shift toward reduced disability at 3 months (on a 6-level version of the mRS), a favourable trend was also noted, OR 1.40 (95% CI: 0.99–1.98), p = 0.06. The frequency of mortality, symptomatic ICH, and gouty arthritis was similar between the two treatment groups.
One moderate-sized randomized trial non-significantly suggests that uric acid may be beneficial as a neuroprotective agent in acute ischaemic stroke. Larger randomized trials are warranted to definitively evaluate the potential benefits of acute uric acid therapy.
Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) is a broad scavenger of free hydroxyl radicals and peroxynitrite radicals, with evidence in mechanistic studies of protecting neurones, glia, and vascular endothelial cells against oxidative stress.
Edaravone has been tested in at least 16 randomized trials for ischaemic stroke, including 10 trials with entire or reported subgroup enrolment within the early post-onset (<48 h) period, enrolling 983 patients (Yang et al., 2015). In these trials, daily edaravone dosage was 60 mg in all, and duration of treatment was median 14 (7–28) days. Adequate protection against bias was not clearly present in the trials, with allocation concealment not clearly described in all trials and double-blind conduct only clearly described in 1 of 10 trials. Among the 3 trials with disability outcome assessment, in 250 patients (127 edaravone, 123 control) edaravone was associated with increased functional independence at long-term follow-up, 79.5% versus 57.7%, RR 1.38 (95% CI: 1.16–1.64), p = 0.0003 (Figure 12.2). Among the 8 trials assessing neurological deficit at long-term follow-up on the 100-point European Stroke Scale, in 843 patients (421 edaravone, 422 control), edaravone was associated with reduced neurological deficit, mean difference 7.09 (95% CI: 5.12–9.05), p < 0.00001.
Figure 12.2 Forest plot showing the effects of edaravone vs control for acute ischaemic stroke on functional independence (mRS 0–2 or nearest equivalent) at long-term follow-up.
Adverse events were analysed across randomized trials for patients with both ischaemic and haemorrhagic stroke. The only signal of a potential adverse event was a trend toward increased mild renal impairment in 3.25% (11/338) versus 1.49% (5/335), RR 1.78 (95% CI: 0.74–4.29), p = 0.20.
Edaravone shows potential promise as a neuroprotective agent for acute ischaemic stroke. However, encouraging efficacy and safety findings among completed trials must be interpreted cautiously, as risk of bias is formally present in all trials reported to date. In addition, the relatively late start and prolonged duration of administration of edaravone in completed trials suggests that completed trials have not closely explored acute neuroprotection for the presenting ischaemic stroke, but rather focused more upon prophylactic neuroprotection against recurrent ischaemic insults and neuroreparative effects. Further trials with rigorous double-blinding and hyperacute treatment start are merited.
Tirilazad mesylate is a lipid soluble synthetic, non-glucocorticoid, 21-aminosteroid (or lazaroid) that inhibits iron-dependent lipid peroxidation within membranes. However, in 6 randomized trials enrolling 1757 patients with acute ischaemic stroke, tirilazad was associated with increased odds of being dead or disabled at long-term follow-up on the expanded Barthel Index (OR 1.23, 95% CI: 1.01–1.51) and increased odds of infusion site phlebitis (OR 2.81, 95% CI: 2.14–3.69) (Bath et al., 2001). Accordingly, tirilazad has not entered clinical practice and is no longer under active development.
Disufenton sodium (NXY-059) is a free-radical trapping agent. Although a first phase 3 trial enrolling 1722 patients had positive results on the primary endpoint of degree of disability at 3 months post-stroke, a second phase 3 trial was non-confirmatory. Pooled, individual participant-level analysis of 5028 patients across both trials found no effect in shifting to a lower disability level, OR 1.02 (95% CI: 0.92–1.13), p = 0.68, and no difference in mortality, 16.6% versus 16.4% (Diener et al., 2008). Accordingly, disufenton sodium has not entered clinical practice and is no longer under active development.
Citicoline (or cytidine-5′-diphosphoholine, CDP-choline) is an intermediate metabolite in membrane phosphatide biosynthesis, normally present in all cells in the body. In preclinical models, exogenously administered citicoline promotes rapid repair of injured cell surface and mitochondrial membranes and maintenance of cell integrity and bioenergetic capacity, downregulates phospholipases to avert apoptotic and necrotic cell death, and reduces free fatty acid release and ensuing generation of injurious free radicals (Saver, 2008).
A meta-analysis identified 10 randomized trials of citicoline in ischaemic stroke, enrolling 4420 patients (Secades et al., 2016) The preponderance of trials enrolled patients within 24–48 hours of onset, with 2 trials enrolling 305 patients (7%) having longer enrolment windows of 7–14 days. Few patients in any trial were enrolled in the first few hours of onset; in the largest ICTUS trial, which had a 24-hour enrolment window, the median time from onset to enrolment was 6.7 hours (Dávalos et al., 2012). Across trials, study treatment was administered for up to 10 days to 6 weeks, and doses ranged from 500–2000 mg daily.
Across the 10 trials, treatment with citicoline was associated with an increased frequency of functional independence (mRS 0–2 or nearest equivalent) at long-term follow-up, 36.4% versus 31.6%, RR (random effect) 1.20 (95% CI: 1.05–1.55), p = 0.02 (Figure 12.3). However, substantial heterogeneity was noted, I2 = 68%, and funnel plot analysis showed some asymmetry suggesting potential publication bias with under-reporting of smaller, nonpositive or less positive trials. The largest and most recent trial, ICTUS, enrolled 2298 patients, accounting for 52% of all patients in the 10-trial meta-analysis, and had neutral results (Dávalos et al., 2012).
Figure 12.3 Forest plot showing the effects of citicoline vs control for acute ischaemic stroke for functional independence (mRS 0–2 or nearest equivalent) at long-term follow-up.
None of the trials reported any adverse events occurring more frequently in the citicoline than the control groups.
In the large ICTUS trial, enrolling 2298 patients, overall results were neutral on the primary endpoint of recovery at 90 days, measured by a global test combining three measures of success, mRS ≤ 1, National Institutes of Health Stroke Scale (NIHSS) ≤ 1, and Barthel Index ≥ 95, with OR 1.03 (95% CI: 0.86–1.25; p = 0.36). However, heterogeneity of effect was noted for 3 of the 5 prespecified subgroups, with signals of greater benefit and less harm among patients over versus under age 70, pinteraction = 0.001, patients with less initial deficit severity (NIHSS 8–14 vs 15–22 and 22–42), pinteraction = 0.02, and patients ineligible for IV tPA, pinteraction = 0.04. Nonetheless, none of the better performing subgroup categories showed nominally significant benefit: age above 70 (OR 1.17, 95% CI: 0.82–1.50); lesser presenting deficit, (NIHSS 8–14, OR 1.08, 95% CI: 0.86–1.35); and IV tissue plasminogen activator (tPA) ineligible (OR 1.11, 95% CI: 0.85–1.46).
Current randomized trial evidence largely addresses relatively late start and prolonged continued administration of citicoline, and thus evaluates more for potential subacute neuroreparative than acute neuroprotective treatment effects. The trials have demonstrated agent safety but provide mixed indications of potential benefit. Evidence of potential publication bias and neutral results in the largest single trial indicate caution when interpreting the mild favourable effect seen in meta-analytic summary of all trials. Brief administration of citicoline during the first few hours after onset, until reperfusion is achieved, is a strategy not yet explored in human clinical trials of citicoline. The greater signal of potential benefit observed in the large ICTUS trial among patients with older age and moderately severe rather than extremely severe presenting deficits perhaps hints at beneficial neuroreparative effects among patients with less intrinsic neuroplasticity (older age) and more intact brain systems to recruit into recovery pathways (less severe deficits). However, further, larger trials in these patient groups are needed before firm conclusions can be reached regarding potential agent benefit.
Focal cerebral ischaemia causes excess release of EAA neurotransmitters, particularly glutamate, from pre-synaptic vesicles and prevents normal reuptake of glutamate, resulting in very high synaptic concentrations. Glutamate is toxic in neuronal cell culture and in vivo. It acts at post-synaptic receptors, notably the N-methyl-d-aspartate (NMDA) receptor complex (to promote entry of calcium and sodium into neurones) and the α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor (to promote principally sodium entry). Resultant cellular depolarization and calcium overload activate intracellular second messenger systems with consequent cell death.
In preclinical models of stroke, antagonists of glutamate release or of postsynaptic glutamate receptors substantially reduce the volume of histological neuronal infarction and improve functional recovery, even when administered up to several hours after the onset of ischaemia (Muir and Lees, 2003). Drugs that modulate EAA toxicity (EAA antagonists) encompass a diversity of pharmacological agents and a number of potential mechanisms of action, including principally inhibition of glutamate release, NMDA receptor antagonism, and AMPA receptor antagonism. The NMDA receptor itself has several modulatory sites that are amenable to pharmacological modification. However, despite multiple supportive studies in preclinical models and advance of many EAA antagonists into human clinical trials, no agent has yet been proven beneficial in acute ischaemic stroke. This section will briefly survey early studied molecular agents and then provide further details on agents of more recent interest.
A systematic review analysed RCTs of EAA antagonists and related agents in acute stroke completed by 2001 (Muir and Lees, 2003). Restricting consideration to agents that had EAA antagonism as their leading or co-leading mechanism, there were 33 completed RCTs evaluating 13 agents. Eight agents were 8 NMDA receptor antagonists, 2 AMPA receptor antagonists, 2 agents that were both sodium channel blockers (reducing glutamate release) and also active calcium channel or cyclic guanosine-3′,5′-monophosphate (cGMP) nitric oxide pathway inhibitors, and 1 agent that was both an NMDA receptor antagonist and a sodium channel inhibitor. Time to treatment averaged under 5 hours in many trials, although only a minority of patients were treated in 3 hours or less after stroke onset.
A total of 23 randomized trials testing 10 agents and enrolling 9762 patients provided data on death or dependency at long-term follow-up (Figure 12.4). Random allocation to an EAA antagonist was associated with no significant effect on death or dependency at final follow-up compared with control (53.1% vs 51.7%, OR 1.06; 95% CI: 0.98–1.15). There was moderate heterogeneity across agents, I2 = 44%.
Figure 12.4 Forest plot showing the effects of excitatory amino acid inhibitors vs control for acute ischaemic stroke on death or dependency at long-term follow-up in RCTs reported between 1984 and 2001 (primarily 1995–2001).
Random allocation to an EAA antagonist was associated with no significant effect on death at final follow-up compared with control (20.7% vs 19.6%, OR 1.02, 95% CI: 0.92–1.12) (Figure 12.5). There was only mild heterogeneity across study agents, I2 = 20%.
Figure 12.5 Forest plot showing the effects of excitatory amino acid inhibitors vs control for acute ischaemic stroke on death at long-term follow-up in RCTs reported between 1984 and 2001 (primarily1995–2001).
None of the surge of EAA agents that entered human clinical trial testing in the period from 1993–2003 was found beneficial. In hindsight, in addition to the several weaknesses in preclinical and clinical study designs recognized at the time (Ovbiagele et al., 2003; O’Collins et al., 2006; Lapchak et al., 2013), another likely major factor was the absence at that time of highly effective reperfusion therapy with which the agents might be combined. EAA antagonists, and most other neuroprotective agents, have mechanisms of action that slow the pace of ischaemic injury, but that do not reduce its final extent if the ischaemic stress is not eventually relieved. Accordingly, chances of success are likely limited when EAAs are tested as standalone or post-reperfusion treatment therapies, rather than as early bridging therapies followed by reperfusion interventions.
NA-1 is a cell-permeant eicosapeptide that perturbs the protein–protein interactions of PSD-95, a postsynaptic scaffolding protein that links NMDA glutamate receptors to neurotoxic signalling pathways, including neuronal nitric oxide synthase, a free radical generator. NA-1 reduced infarct size in rodent and primate ischaemic stroke models.
In a phase 2, proof-of-concept trial undertaken to determine whether NA-1 could reduce MRI biomarker evidence of ischaemic injury in humans, 185 patients undergoing non-urgent endovascular repair of unruptured or ruptured aneurysms were randomized to an intravenous bolus of NA-1 or placebo started immediately after completion of the endovascular treatment (Hill et al., 2012). Delaying agent start modelled the post-onset rather than pre-onset initiation of therapy that would be achievable in spontaneous ischaemic stroke patients. None of the primary endpoints reached statistical significance after adjustment for multiplicity, but favourable trends were noted. The number of new diffusion magnetic resonance imaging (MRI) ischaemic lesions after the endovascular procedure was numerically lower in NA-1 versus placebo patients, mean 4.1 versus 7.3, nominal adjusted RR 0.53 (95% CI: 0.38–0.74), and the total volume of new diffusion MRI ischaemic lesions was numerically smaller, median 0.06 versus 0.12 mL, nominal adjusted p = 0.12. No difference was noted in the frequency of excellent neurological outcome (NIHSS 0–1) at 30 days, occurring in 89–94% of patients in both treatment groups, with, after adjustment for prognostic features, RR 1.0 (95% CI: 0.9–1.1). No adverse events occurred more frequently in the NA-1 compared with the placebo group.
Based on the signals of potential efficacy in reducing endovascular procedure-related, subclinical ischaemic brain injury in a phase 2, proof-of-concept trial, and the absence of evidence of any major safety concerns, NA-1 warrants testing in pivotal ischaemic stroke trials. Two trials are under way: the FRONTIER trial (NCT02315443), testing prehospital administration in a broad group of hyperacute suspected stroke patients, and the ESCAPE NA-1 trial (NCT02930018), testing administration in the Emergency Department among patients with acute ischaemic stroke due to large vessel occlusions bound for endovascular mechanical thrombectomy.
Massive calcium influx into ischaemic brain cells is a final common pathway leading to cell death, and agents that reduce calcium overload lower infarct volumes in preclinical stroke models (Doyle et al., 2008; Sekerdag et al., 2018). Furthermore, the calcium channel agent nimodipine was shown to be effective in decreasing the occurrence of death and disability after aneurysmal and traumatic subarachnoid haemorrhage (SAH) in humans, likely at least in part by conferring neuronal protection against ischaemic injury arising from delayed cerebral vasospasm (see Chapter 14). Nimodipine and other calcium antagonists can act as neuroprotective drugs by diminishing the influx of calcium ions through the voltage-sensitive calcium channels.
A systematic review identified 34 RCTs evaluating 6 calcium antagonist agents in 7731 patients predominantly with ischaemic stroke (but some with haemorrhagic stroke and some with no imaging to confirm stroke subtype), with nimodipine being the most predominantly studied agent (Zhang et al., 2012). The trials more closely evaluated calcium channel antagonism in the subacute rather than acute period. Entry windows were typically up to 24–72 hours post-onset; onset time in some trials may have been the time symptoms were first observed rather than time last known well; the study agent typically was continued for 3–21 days; and the first dose was often given orally, resulting in delayed peak serum levels.
Data regarding death or dependency at the end of follow-up were available from 22 RCTs evaluating 3 calcium antagonist agents in 6684 patients. The most common agent studied was nimodipine, evaluated in 19 of the trials and 91% (6093/6684) of the patients. Overall, a possible small detrimental effect of calcium antagonists was noted, 46.6% versus 41.5% (RR 1.05; 95% CI: 0.98–1.13; p = 0.16) (Figure 12.6). There was no evidence of heterogeneity by agent (I2 = 0%) but mild heterogeneity by individual trial was noted (I2 = 29%).