Why have neuroprotectants failed?

Cell Therapy in Stroke-Cautious Steps Towards a Clinical Treatment

In the future, stroke patients may receive stem cell therapy as this has the potential to restore lost functions. However, the development of clinically deliverable therapy has been slower and more challenging than expected. Despite recommendations by STAIR and STEPS consortiums, there remain flaws in experimental studies such as lack of animals with comorbidities, inconsistent approaches to experimental design, and concurrent rehabilitation that might lead to a bias towards positive results. Clinical studies have typically been small, lacking control groups as well as often without clear biological hypotheses to guide patient selection. Furthermore, they have used a wide range of cell types, doses, and delivery methods, and outcome measures. Although some ongoing and recent trial programs offer hints that these obstacles are now being tackled, the Horizon2020 funded RESSTORE trial will be given as an example of inconsistent regulatory requirements and challenges in harmonized cell production, logistic, and clinical criteria in an international multicenter study. The PISCES trials highlight the complex issues around intracerebral cell transplantation. Therefore, a better understanding of translational challenges is expected to pave the way to more successful help for stroke patients.

Magnesium: potential roles in neurovascular disease

OBJECTIVE

Magnesium therapy has been studied extensively in pre-clinical and clinical trials in multiple organ systems. Cerebrovascular diseases may benefit from its neuroprotective properties. This review summarizes current studies of magnesium in a wide range of neurovascular diseases.

METHODS

We searched relevant terms in the National Library of Medicine PubMed database and selected research including basic science, translational reports, meta-analyses, and clinical studies.

RESULTS

Studies examining magnesium administration in ischemic stroke have failed to show any benefit in clinical outcome. Data on magnesium for intracerebral hemorrhage (ICH) are limited. Preliminary investigations in subarachnoid hemorrhage (SAH) were promising, but definitive studies did not reveal differences in clinical outcome between magnesium and placebo-treated groups. Studies examining magnesium administration in global ischemia following cardiac arrest suggest a trend toward improved clinical outcome. The strongest evidence for clinically relevant neuroprotection following magnesium administration derives from studies of pre-term infants and patients undergoing cardiac bypass and carotid endarterectomy procedures. Magnesium was found to have an excellent safety profile across all investigations.

CONCLUSION

Magnesium is easy to administer and possesses a favorable safety profile. Its utility as a neuroprotectant in cardiac surgery, carotid endarterectomy, and pre-term infant hypoxia remain promising. Value as a therapeutic agent in ischemic stroke, ICH, and SAH is unclear and appears to be limited by late administration. Ongoing clinical trials assessing magnesium administration in the first hours following symptom onset may help clarify the role of magnesium therapy in these disease processes.

Prospects for stem cell-derived therapy in stroke

The prospects for stem cell-derived therapy in stroke look promising, with a myriad of cell therapy products developed from brain, blood, bone marrow, and adipose tissue in early clinical development. Eight clinical trials have now reported final results, and several are currently registered recruiting patients or pending to start. Products passing the safety hurdle are recruiting patients for large efficacy studies. Besides identifying the most appropriate cell type, other issues to resolve include optimal timing for intervention, optimal delivery route, cell dose, patient selection, relevant clinical endpoints, and monitoring for effectiveness, to advance cell therapy through the hurdles of clinical research. In this chapter, we present the products and strategies used in the current cell therapy trials in ischemic stroke, provide an update on relevant preclinical research, and discuss the vital developments still needed to advance their clinical application as a future therapeutic option.

A randomized trial of brimonidine versus timolol in preserving visual function: results from the Low-Pressure Glaucoma Treatment Study

PURPOSE

To compare the alpha2-adrenergic agonist brimonidine tartrate 0.2% to the beta-adrenergic antagonist timolol maleate 0.5% in preserving visual function in low-pressure glaucoma.

DESIGN

Randomized, double-masked, multicenter clinical trial.

METHODS

Exclusion criteria included untreated intraocular pressure (IOP) >21 mm Hg, visual field mean deviation worse than -16 decibels, or contraindications to study medications. Both eyes received twice-daily monotherapy randomized in blocks of 7 (4 brimonidine to 3 timolol). Standard automated perimetry and tonometry were performed at 4-month intervals. Main outcome measure was field progression in either eye, defined as the same 3 or more points with a negative slope ≥-1 dB/year at P<5%, on 3 consecutive tests, assessed by pointwise linear regression. Secondary outcome measures were progression based on glaucoma change probability maps (GCPM) of pattern deviation and the 3-omitting method for pointwise linear regression.

RESULTS

Ninety-nine patients were randomized to brimonidine and 79 to timolol. Mean (± SE) months of follow-up for all patients was 30.0 ± 2. Statistically fewer brimonidine-treated patients (9, 9.1%) had visual field progression by pointwise linear regression than timolol-treated patients (31, 39.2%, log-rank 12.4, P=.001). Mean treated IOP was similar for brimonidine- and timolol-treated patients at all time points. More brimonidine-treated (28, 28.3%) than timolol-treated (9, 11.4%) patients discontinued study participation because of drug-related adverse events (P=.008). Similar differences in progression were observed when analyzed by GCPM and the 3-omitting method.

CONCLUSION

Low-pressure glaucoma patients treated with brimonidine 0.2% who do not develop ocular allergy are less likely to have field progression than patients treated with timolol 0.5%.

Tamoxifen mediated estrogen receptor activation protects against early impairment of hippocampal neuron excitability in an oxygen/glucose deprivation brain slice ischemia model

Pretreatment of ovarectomized rats with estrogen shows long-term protection via activation of the estrogen receptor (ER). However, it remains unknown whether activation of the ER can provide protection against early neuronal damage when given acutely. We simulated ischemic conditions by applying oxygen and glucose deprived (OGD) solution to acute male rat hippocampal slices and examined the neuronal electrophysiological changes. Pyramidal neurons and interneurons showed a time-dependent membrane potential depolarization and reduction in evoked action potential frequency and amplitude over a 10 to 15 min OGD exposure. These changes were largely suppressed by 10 microM TAM. The TAM effect was neuron-specific as the OGD-induced astrocytic membrane potential depolarization was not altered. The TAM effect was mediated through ER activation because it could be simulated by 17beta-estradiol and was completely inhibited by the ER inhibitor ICI 182, 780, and is therefore an example of TAM's selective estrogen receptor modulator (SERM) action. We further show that TAM's effects on OGD-induced impairment of neuronal excitability was largely due to activation of neuroprotective BK channels, as the TAM effect was markedly attenuated by the BK channel inhibitor paxilline at 10 microM. TAM also significantly reduced the frequency and amplitude of AMPA receptor mediated spontaneous excitatory postsynaptic currents (sEPSCs) in pyramidal neurons which is an early consequence of OGD. Altogether, this study demonstrates that both 17beta-estradiol and TAM attenuate neuronal excitability impairment early on in a simulated ischemia model via ER activation mediated potentiation of BK K(+) channels and reduction in enhanced neuronal AMPA/NMDA receptor-mediated excitotoxicity.

No neuroprotective effect of erythropoietin under clinical treatment conditions in a rabbit model of Escherichia coli meningitis

Despite effective antibiotic treatment, neuronal injury is frequent among children and adults with bacterial meningitis resulting in a high rate of death and neurologic sequelae. The hematopoietic cytokine erythropoietin (EPO) provides neuroprotection in models of acute and chronic neurologic diseases. We studied whether recombinant EPO (rEPO) reduces neuronal damage in a rabbit model of Escherichia coli meningitis. Inflammation within the central nervous system (CNS) was monitored by measurement of bacterial load, pleocytosis, protein, and lactate in the cerebrospinal fluid (CSF). Neuronal damage was measured by quantification of the density of apoptotic neurons in the hippocampal dentate gyrus and the concentration of the global neuronal destruction marker neuron-specific enolase (NSE) in CSF. To increase clinical relevance, rEPO was applied as adjunctive therapy from the beginning of antibiotic therapy 12 h after infection. EPO treatment applied as an intravenous injection at a dose of 1000 IU/kg body weight resulted in plasma concentrations of 6993 +/- 1406 mIU/mL, CSF concentrations of 1291 +/- 568 mIU/mL, and a CSF-to-plasma ratio of 0.18 +/- 0.07 (mean +/- SD) 6 h after injection. Under these treatment conditions, no anti-inflammatory or neuroprotective effect of EPO was observed. "

Neurotrophic cross-talk between the nervous and immune systems: relevance for repair strategies in multiple sclerosis?

Autoreactive T and B cells are regular components of the healthy immune system. It has been proposed that some of these cells might have a protective function. Recent studies support this notion by demonstrating that a) myelin-autoreactive T cells show neuroprotective effects in vivo, and b) activated antigen-specific human T cells and other immune cells produce bioactive brain-derived neurotrophic factor (BDNF) and other neurotrophic factors in vitro. Furthermore, neurotrophic factors are expressed in different types of inflammatory cells in brain lesions of patients with acute disseminated leukoencephalopathy or multiple sclerosis. It seems plausible that the immune cell-mediated import of neurotrophic factors into the central nervous system has functional consequences, with obvious implications for the therapy of multiple sclerosis and other neuroimmunological diseases.

Albumin therapy in acute stroke patients

Preclinical studies have recently shown that albumin has neuroprotective effects for stroke in animal models. Thus, we sought to evaluate the effects of albumin therapy in patients with acute cerebral infarcts. We prospectively studied 49 patients with moderate-to-severe cerebral infarcts within the middle cerebral arterial territory into one of two groups: the control group (N = 18) received saline, whereas the albumin group (N = 31) received either 40 g or 80 g of albumin within 24 h from symptom onset. The modified National Institutes of Health Stroke Scale (mNIHSS) and diffusion-weighted imaging (DWI) were serially checked. There was no adverse effect related to albumin therapy. Although there was no significant difference in both baseline mNIHSS score and DWI lesion volume on admission, the mNIHSS scores at the 14(th) day after treatment and the increase in DWI lesion volume 72-96 h after treatment were significantly reduced in patients of the albumin group (p = 0.001 and 0.012, respectively); these effects were dose- and time- related. The outcome on the 90(th) day after stroke onset was more favorable in the albumin group than in the control group. Within the albumin group, patients who had patent or recanalized vessels showed more significant improvement than patient without recanalization (p = 0.046). Our results indicate that albumin therapy is a safe and effective modality in patients with acute cerebral infarction. This study also suggests that the effects of albumin therapy may vary depending on vessel status of the patient.

Antiinflammatory but no neuroprotective effects of melatonin under clinical treatment conditions in rabbit models of bacterial meningitis

Neuronal injury is frequent in bacterial meningitis, resulting in a high rate of death and neurological sequelae. In a search of potential neuroprotective strategies for treatment of bacterial meningitis, the antioxidant melatonin was neuroprotective in cell culture experiments and in a rabbit Streptococcus pneumoniae meningitis model, when treatment was started at the time of infection. In the present study, adjunctive melatonin treatment applied from the beginning of antibiotic therapy 12 hr after infection at a dose of 1.67 mg/kg/hr resulted in plasma concentrations of 451 +/- 198 ng/ml, cerebrospinal fluid (CSF) concentrations of 154 +/- 57 ng/ml and a CSF-to-plasma ratio of 0.38 +/- 0.19 (mean +/- SD). Melatonin therapy had antiinflammatory effects but did not reduce neuronal injury in either a rabbit model of gram-positive Streptococcus pneumoniae or gram-negative Escherichia coli meningitis.