Comparative safety of tenecteplase vs alteplase for acute ischemic stroke.

INTRODUCTION: Tenecteplase has been compared to alteplase in acute stroke randomized trials, with similar outcomes and safety measures, but higher doses of tenecteplase have been associated with higher hemorrhage rates in some studies. Limited data are available on the safety of tenecteplase outside of clinical trials. METHODS: We examined the safety measures of intracranial hemorrhage, angioedema, and serious extracranial adverse events in a 21-hospital integrated healthcare system that switched from alteplase (0.9 mg/kg, maximum dose 90 mg) to tenecteplase (0.25 mg/kg, maximum dose 25 mg) for acute ischemic stroke. RESULTS: Among 3,689 subjects, no significant differences were seen between tenecteplase and alteplase in the rate of intracranial hemorrhage (ICH), parenchymal hemorrhage, or volume of parenchymal hemorrhage. Symptomatic hemorrhage (sICH) was not different between the two agents: sICH by NINDS criteria was 2.0 % for alteplase vs 2.3 % for tenecteplase (P = 0.57), and sICH by SITS criteria was 0.8 % vs 1.1 % (P = 0.39). Adjusted logistic regression models also showed no differences between tenecteplase and alteplase: the odds ratio for tenecteplase (vs alteplase) modeling sICH by NINDS criteria was 0.9 (95 % CI 0.33 - 2.46, P = 0.83) and the odds ratio for tenecteplase modeling sICH by SITS criteria was 1.12 (95 % CI 0.25 - 5.07, P = 0.89). Rates of angioedema and serious extracranial adverse events were low and did not differ between tenecteplase and alteplase. Elapsed door-to-needle times showed a small improvement after the switch to tenecteplase (51.8 % treated in under 30 min with tenecteplase vs 43.5 % with alteplase, P < 0.001). CONCLUSION: In use outside of clinical trials, complication rates are similar between tenecteplase and alteplase. In the context of a stroke telemedicine program, the rates of hemorrhage observed with either agent were lower than expected based on prior trials and registry data. The more easily prepared tenecteplase was associated with a lower door-to-needle time.

Bcl-2 family proteins participate in mitochondrial quality control by regulating Parkin/PINK1-dependent mitophagy.

Mitophagy facilitates the selective elimination of impaired or depolarized mitochondria through targeting the latter to autophagosomes. Parkin becomes localized to depolarized mitochondria in a PINK1-dependent manner and polyubiquitinates multiple mitochondrial outer membrane proteins. This permits ubiquitin-binding proteins (e.g., p62 and NBR1) to target impaired mitochondria to autophagosomes via Atg8/LC3II. Bcl-2 family proteins regulate mitochondrial outer membrane permeabilization during apoptosis and can also influence macroautophagy via interactions with Beclin-1. Here, we show that Parkin-dependent mitophagy is antagonized by prosurvival members of the Bcl-2 family (e.g., Bcl-xL and Mcl-1) in a Beclin-1-independent manner. Bcl-2 proteins suppressed mitophagy through inhibition of Parkin translocation to depolarized mitochondria. Consistent with this, Parkin translocation to mitochondria was enhanced by BH3-only proteins or a BH3-only mimetic. Taken together with their role as regulators of apoptosis-associated mitochondrial permeabilization, as well as mitochondrial fission/fusion dynamics, this suggests that Bcl-2 family proteins act as global regulators of mitochondrial homeostasis.

Fas/CD95-induced chemokines can serve as "find-me" signals for apoptotic cells.

Apoptosis is commonly thought to represent an immunologically silent or even anti-inflammatory mode of cell death, resulting in cell clearance in the absence of explicit activation of the immune system. However, here we show that Fas/CD95-induced apoptosis is associated with the production of an array of cytokines and chemokines, including IL-6, IL-8, CXCL1, MCP-1, and GMCSF. Fas-induced production of MCP-1 and IL-8 promoted chemotaxis of phagocytes toward apoptotic cells, suggesting that these factors serve as "find-me" signals in this context. We also show that RIPK1 and IAPs are required for optimal production of cytokines and chemokines in response to Fas receptor stimulation. Consequently, a synthetic IAP antagonist potently suppressed Fas-dependent expression of multiple proinflammatory mediators and inhibited Fas-induced chemotaxis. Thus, in addition to provoking apoptosis, Fas receptor stimulation can trigger the secretion of chemotactic factors and other immunologically active proteins that can influence immune responsiveness toward dying cells.

Risk of Distal Embolization From tPA (Tissue-Type Plasminogen Activator) Administration Prior to Endovascular Stroke Treatment.

BACKGROUND AND PURPOSE: In large artery occlusion stroke, both intravenous (IV) tPA (tissue-type plasminogen activator) and endovascular stroke treatment (EST) are standard-of-care. It is unknown how often tPA causes distal embolization, in which a procedurally accessible large artery occlusion is converted to a more distal and potentially inaccessible occlusion. METHODS: We analyzed data from a decentralized stroke telemedicine program in an integrated healthcare delivery system covering 21 hospitals, with 2 high-volume EST centers. We captured all cases sent for EST and examined the relationship between IV tPA administration and the rate of distal embolization, the rate of target recanalization (modified Treatment in Cerebral Infarction scale 2b/3), clinical improvement before EST, and short-term and long-term clinical outcomes. RESULTS: Distal embolization before EST was quite common (63/314 [20.1%]) and occurred more often after IV tPA before EST (57/229 [24.9%]) than among those not receiving IV tPA (6/85 [7.1%]; P<0.001). Distal embolization was associated with an inability to attempt EST: after distal embolization, 26/63 (41.3%) could not have attempted EST because of the new clot location, while in cases without distal embolization, only 8/249 (3.2%) were unable to have attempted EST (P<0.001). Among patients who received IV tPA, 13/242 (5.4%) had sufficient symptom improvement that a catheter angiogram was not performed; 6/342 (2.5%) had improvement to within 2 points of their baseline NIHSS. At catheter angiogram, 2/229 (0.9%) of patients who had received tPA had complete recanalization without distal embolization. Both IV tPA and EST recanalization were associated with improved long-term outcome. CONCLUSIONS: IV tPA administration before EST for large artery occlusion is associated with distal embolization, which in turn may reduce the chance that EST can be attempted and recanalization achieved. At the same time, some IV tPA-treated patients show symptomatic improvement and complete recanalization. Because IV tPA is associated with both distal embolization and improved long-term clinical outcome, there is a need for prospective clinical trials testing the net benefit or harm of IV tPA before EST.

Apoptosis: controlled demolition at the cellular level.

Apoptosis is characterized by a series of dramatic perturbations to the cellular architecture that contribute not only to cell death, but also prepare cells for removal by phagocytes and prevent unwanted immune responses. Much of what happens during the demolition phase of apoptosis is orchestrated by members of the caspase family of cysteine proteases. These proteases target several hundred proteins for restricted proteolysis in a controlled manner that minimizes damage and disruption to neighbouring cells and avoids the release of immunostimulatory molecules.

A perspective on mammalian caspases as positive and negative regulators of inflammation.

Members of the caspase family of cysteine proteases coordinate the morphological and biochemical events that typify apoptosis. However, neutralization of caspase activity in mammals fails to block death in response to most proapoptotic stimuli. This is because many cell death triggers provoke mitochondrial dysfunction upstream of caspase activation as a consequence of BAX/BAK channel opening. Although genetic or pharmacological inactivation of caspases fails to block cell death in most instances, it does convert the phenotype from apoptosis to necrosis. This has important implications for how the immune system responds to such cells, as necrotic cells provoke inflammation whereas apoptotic cells typically do not. Here, we propose an alternative perspective on apoptosis-associated caspase function by suggesting that these proteases are activated, not to kill, but to extinguish the proinflammatory properties of dying cells. This perspective unifies the mammalian caspase family as either positive or negative regulators of inflammation.

Staying alive: defensive strategies in the BCL-2 family playbook.

Much debate surrounds how prosurvival members of the BCL-2 family repress opening of the BAX/BAK channel to block apoptosis; in this issue Llambi et al. (2011) identify two modes of apoptosis inhibition that exhibit surprisingly different behavior upon repeat proapoptotic challenges by BH3-only proteins.

Granzyme B-dependent proteolysis acts as a switch to enhance the proinflammatory activity of IL-1α.

Granzyme B is a cytotoxic lymphocyte-derived protease that plays a central role in promoting apoptosis of virus-infected target cells, through direct proteolysis and activation of constituents of the cell death machinery. However, previous studies have also implicated granzymes A and B in the production of proinflammatory cytokines, via a mechanism that remains undefined. Here we show that IL-1α is a substrate for granzyme B and that proteolysis potently enhanced the biological activity of this cytokine in vitro as well as in vivo. Consistent with this, compared with full-length IL-1α, granzyme B-processed IL-1α exhibited more potent activity as an immunoadjuvant in vivo. Furthermore, proteolysis of IL-1α within the same region, by proteases such as calpain and elastase, was also found to enhance its biological potency. Thus, IL-1α processing by multiple immune-related proteases, including granzyme B, acts as a switch to enhance the proinflammatory properties of this cytokine.

Detection of Anterior Circulation Large Artery Occlusion in Ischemic Stroke Using Noninvasive Cerebral Oximetry.

BACKGROUND AND PURPOSE: Large artery occlusion (LAO) in ischemic stroke requires recognition and triage to an endovascular stroke treatment center. Noninvasive LAO detection is needed to improve triage. METHODS: Prospective study to test whether noninvasive cerebral oximetry can detect anterior circulation LAO in acute stroke. Interhemispheric ΔBrSO2 in LAO was compared with controls. RESULTS: In LAO stroke, mean interhemispheric ΔBrSO2 was -8.3±5.8% (n=19), compared with 0.4±5.8% in small artery stroke (n=17), 0.4±6.0% in hemorrhagic stroke (n=14), and 0.2±7.5% in subjects without stroke (n=19) (P<0.001). Endovascular stroke treatment reduced the ΔBrSO2 in most LAO subjects (16/19). Discrimination of LAO at a -3% ΔBrSO2 cut had 84% sensitivity and 70% specificity. Addition of the G-FAST clinical score (gaze-face-arm-speech- time) to the BrSO2 measure had 84% sensitivity and 90% specificity. CONCLUSIONS: Noninvasive cerebral oximetry may help detect LAO in ischemic stroke, particularly when combined with a simple clinical scoring system.

Suppression of interleukin-33 bioactivity through proteolysis by apoptotic caspases.

Interleukin-33 (IL-33) is a member of the IL-1 family and is involved in polarization of T cells toward a T helper 2 (Th2) cell phenotype. IL-33 is thought to be activated via caspase-1-dependent proteolysis, similar to the proinflammatory cytokines IL-1 beta and IL-18, but this remains unproven. Here we showed that IL-33 was processed by caspases activated during apoptosis (caspase-3 and -7) but was not a physiological substrate for caspases associated with inflammation (caspase-1, -4, and -5). Furthermore, caspase-dependent processing of IL-33 was not required for ST2 receptor binding or ST2-dependent activation of the NF-kappaB transcription factor. Indeed, caspase-dependent proteolysis of IL-33 dramatically attenuated IL-33 bioactivity in vitro and in vivo. These data suggest that IL-33 does not require proteolysis for activation, but rather, that IL-33 bioactivity is diminished through caspase-dependent proteolysis within apoptotic cells. Thus, caspase-mediated proteolysis acts as a switch to dampen the proinflammatory properties of IL-33.

Fas and TRAIL 'death receptors' as initiators of inflammation: Implications for cancer.

Fas (CD95/APO-1) and TRAIL (CD253, TNFSF10, APO2) are members of a subset of the TNF receptor superfamily known as 'death receptors'. To date, the overwhelming majority of studies on Fas and TRAIL (TNF-related apoptosis-inducing ligand) have explored the role of these receptors as initiators of apoptosis. However, sporadic reports also suggest that engagement of the Fas and TRAIL receptors can lead to other outcomes such as cytokine and chemokine production, cell proliferation, cell migration and differentiation. Indeed, although transformed cells frequently express Fas and TRAIL, most do not undergo apoptosis upon engagement of these receptors and significant effort has been devoted toward exploring how to sensitize such cells to the pro-apoptotic effects of 'death receptor' stimulation. Moreover, the expression of Fas and TRAIL receptors is greatly elevated in many cancer types such as hepatocellular carcinoma, renal carcinoma and ovarian cancer, suggesting that such tumors benefit from the expression of these receptors. Furthermore, several studies have shown that tumor proliferation, progression and invasion can be impaired through blocking or downregulation of Fas expression, but the mechanistic basis for these effects is largely unknown. Thus, the characterization of Fas and TRAIL as 'death receptors' is a gross oversimplification, especially in the context of cancer. It is becoming increasingly clear that 'death receptor' engagement can lead to outcomes, other than apoptosis, that become subverted by certain tumors to their benefit. Here we will discuss death-independent outcomes of Fas and TRAIL signaling and their implications for cancer.

Bax- or Bak-induced mitochondrial fission can be uncoupled from cytochrome C release.

Bax and Bak promote apoptosis by perturbing the permeability of the mitochondrial outer membrane and facilitating the release of cytochrome c by a mechanism that is still poorly defined. During apoptosis, Bax and Bak also promote fragmentation of the mitochondrial network, possibly by activating the mitochondrial fission machinery. It has been proposed that Bax/Bak-induced mitochondrial fission may be required for release of cytochrome c from the mitochondrial intermembrane space, although this has been a subject of debate. Here we show that Bcl-xL, as well as other members of the apoptosis-inhibitory subset of the Bcl-2 family, antagonized Bax and/or Bak-induced cytochrome c release but failed to block mitochondrial fragmentation associated with Bax/Bak activation. These data suggest that Bax/Bak-initiated remodeling of mitochondrial networks and cytochrome c release are separable events and that Bcl-2 family proteins can influence mitochondrial fission-fusion dynamics independent of apoptosis.

Inhibitor of apoptosis proteins (IAPs) and their antagonists regulate spontaneous and tumor necrosis factor (TNF)-induced proinflammatory cytokine and chemokine production.

Inhibitor of apoptosis proteins (IAPs) play a major role in determining whether cells undergo apoptosis in response to TNF as well as other stimuli. However, TNF is also highly proinflammatory through its ability to trigger the secretion of multiple inflammatory cytokines and chemokines, which is arguably the most important role of TNF in vivo. Indeed, deregulated production of TNF-induced cytokines is a major driver of inflammation in several autoimmune conditions such as rheumatoid arthritis. Here, we show that IAPs are required for the production of multiple TNF-induced proinflammatory mediators. Ablation or antagonism of IAPs potently suppressed TNF- or RIPK1-induced proinflammatory cytokine and chemokine production. Surprisingly, IAP antagonism also led to spontaneous production of chemokines, particularly RANTES, in vitro and in vivo. Thus, IAPs play a major role in influencing the production of multiple inflammatory mediators, arguing that these proteins are important regulators of inflammation in addition to apoptosis. Furthermore, small molecule IAP antagonists can modulate spontaneous as well as TNF-induced inflammatory responses, which may have implications for use of these agents in therapeutic settings.

Cytotoxic and non-cytotoxic roles of the CTL/NK protease granzyme B.

The caspase family of cysteine proteases becomes activated in response to diverse cellular insults and coordinates apoptosis through proteolysis of hundreds of cellular substrates. Cytotoxic lymphocytes are adept at promoting apoptosis of virally infected or transformed cells through delivery of cytotoxic enzymes, such as granzyme B, into target cells via the granule exocytosis pathway. Granzyme B promotes apoptosis of target cells through direct processing of certain caspases, which leads to their autoactivation. Granzyme B can also activate caspases indirectly through proteolysis of Bid, a protein that promotes mitochondrial permeabilization and consequent activation of the apoptosome pathway to caspase activation. Evidence also indicates that granzyme B may contribute to antiviral immunity by directly suppressing viral replication through direct proteolysis of viral proteins that are essential for pathogenicity. Recent reports also suggest that granzyme B may have additional non-cytotoxic roles under certain circumstances and may also function in the extracellular space. Here, we discuss the cytotoxic and putative non-cytotoxic functions of granzyme B within the immune system.

THRIVE score predicts ischemic stroke outcomes and thrombolytic hemorrhage risk in VISTA.

BACKGROUND AND PURPOSE: In previous studies, the Totaled Health Risks in Vascular Events (THRIVE) score has shown broad utility, allowing prediction of clinical outcome, death, and risk of hemorrhage after tissue-type plasminogen activator (tPA) treatment, irrespective of the type of acute stroke therapy applied to the patient. METHODS: We used data from the Virtual International Stroke Trials Archive to further validate the THRIVE score in a large cohort of patients receiving tPA or no acute treatment, to confirm the relationship between THRIVE and hemorrhage after tPA, and to compare the THRIVE score with several other available outcome prediction scores. RESULTS: The THRIVE score strongly predicts clinical outcome (odds ratio, 0.55 for good outcome [95% CI, 0.53-0.57]; P<0.001), mortality (odds ratio, 1.57 [95% confidence interval, 1.50-1.64]; P<0.001), and risk of intracerebral hemorrhage after tPA (odds ratio, 1.34 [95% confidence interval, 1.22-1.46]; P<0.001). The relationship between THRIVE score and outcome is not influenced by the independent relationship of tPA administration and outcome. In receiver operator characteristic curve analysis, the THRIVE score was superior to several other available outcome prediction scores in the prediction of clinical outcome and mortality. CONCLUSIONS: The THRIVE score is a simple-to-use tool to predict clinical outcome, mortality, and risk of hemorrhage after thrombolysis in patients with ischemic stroke. Despite its simplicity, the THRIVE score performs better than several other outcome prediction tools. A free Web calculator for the THRIVE score is available at http://www.thrivescore.org.

The totaled health risks in vascular events (THRIVE) score predicts ischemic stroke outcomes independent of thrombolytic therapy in the NINDS tPA trial.

BACKGROUND: To date, no ischemic stroke outcome prediction scores have been validated for use in the setting of both endovascular and non-endovascular stroke treatments. The Totaled Health Risks in Vascular Events (THRIVE) score has been previously validated in patients undergoing endovascular stroke treatment, and we hypothesized that it would perform similarly well in patients receiving intravenous tissue plasminogen activator (tPA) or no acute therapy. METHODS: We compared the performance of the THRIVE score between patients in the National Institutes of Neurological Disorders and Stroke (NINDS) tPA trial and patients in the Mechanical Embolus Removal in Cerebral Ischemia (MERCI) trials of endovascular stroke treatment. The predictive performance of the THRIVE score was compared using receiver operator characteristic (ROC) curve analysis. In the NINDS cohort, separate analyses were also performed for patients receiving tPA versus those receiving placebo. RESULTS: ROC curve analysis revealed a good prediction of outcomes across the range of THRIVE scores in both the NINDS and MERCI datasets. As we have previously found in the MERCI datasets, the THRIVE score, which encompasses the National Institutes of Health Stroke Scale (NIHSS) score, age, and chronic disease burden, was a better predictor of outcomes than NIHSS and age alone in the NINDS trial dataset. THRIVE score and tPA administration both strongly predicted outcome, but these effects were statistically independent. CONCLUSIONS: The THRIVE score provides accurate prediction of long-term neurologic outcomes in patients with acute ischemic stroke regardless of treatment modality. Both the THRIVE score and tPA administration predict outcome, but the THRIVE score does not influence the impact of tPA on outcome, and tPA administration does not influence the impact of THRIVE score on outcome.

Statin use during ischemic stroke hospitalization is strongly associated with improved poststroke survival.

BACKGROUND AND PURPOSE: Statins reduce infarct size in animal models of stroke and have been hypothesized to improve clinical outcomes after ischemic stroke. We examined the relationship between statin use before and during stroke hospitalization and poststroke survival. METHODS: We analyzed records from 12 689 patients admitted with ischemic stroke to any of 17 hospitals in a large integrated healthcare delivery system between January 2000 and December 2007. We used multivariable survival analysis and grouped-treatment analysis, an instrumental variable method that uses treatment differences between facilities to avoid individual patient-level confounding. RESULTS: Statin use before ischemic stroke hospitalization was associated with improved survival (hazard ratio, 0.85; 95% CI, 0.79-0.93; P<0.001), and use before and during hospitalization was associated with better rates of survival (hazard ratio, 0.59; 95% CI, 0.53-0.65; P<0.001). Patients taking a statin before their stroke who underwent statin withdrawal in the hospital had a substantially greater risk of death (hazard ratio, 2.5; 95% CI, 2.1-2.9; P<0.001). The benefit was greater for high-dose (>60 mg/day) statin use (hazard ratio, 0.43; 95% CI, 0.34-0.53; P<0.001) than for lower dose (<60 mg/day) statin use (hazard ratio, 0.60; 95% CI, 0.54-0.67; P<0.001; test for trend P<0.001), and earlier treatment in-hospital further improved survival. Grouped-treatment analysis showed that the association between statin use and survival cannot be explained by patient-level confounding. CONCLUSIONS: Statin use early in stroke hospitalization is strongly associated with improved poststroke survival, and statin withdrawal in the hospital, even for a brief period, is associated with worsened survival.

Human and murine granzyme B exhibit divergent substrate preferences.

The cytotoxic lymphocyte protease granzyme B (GzmB) can promote apoptosis through direct processing and activation of members of the caspase family. GzmB can also cleave the BH3-only protein, BID, to promote caspase-independent mitochondrial permeabilization. Although human and mouse forms of GzmB exhibit extensive homology, these proteases diverge at residues predicted to influence substrate binding. We show that human and mouse GzmB exhibit radical differences in their ability to cleave BID, as well as several other key substrates, such as ICAD and caspase-8. Moreover, pharmacological inhibition of caspases clonogenically rescued human and mouse target cells from apoptosis initiated by mouse GzmB, but failed to do so in response to human GzmB. These data demonstrate that human and murine GzmB are distinct enzymes with different substrate preferences. Our observations also illustrate how subtle differences in enzyme structure can radically affect substrate selection.

Cardiovascular predictors of long-term outcomes after non-traumatic subarachnoid hemorrhage.

BACKGROUND AND PURPOSE: Cardiac injury is common after subarachnoid hemorrhage (SAH) and is associated with adverse early outcomes, but long-term effects are unknown. The first aim of this study was to compare the long-term rates of death, stroke, and cardiac events in SAH survivors versus a matched population without SAH. The second aim was to quantify the effects of cardiac injury on the outcome rates. METHODS: This was a retrospective cohort study of patients with and without non-traumatic SAH. For aim #1, the predictor variable was SAH and the outcome variables were all-cause and cerebrovascular mortality, stroke, cardiac mortality, acute coronary syndrome (ACS), and heart failure (HF) admission. A multivariable Cox proportional hazards analysis was performed. For aim #2, the predictor variables were cardiac injury (elevated serum cardiac enzymes or a diagnosis code for ACS) and dysfunction (pulmonary edema on X-Ray or a diagnosis code for HF). RESULTS: Compared with 4,695 members without SAH, the 910 SAH patients had higher rates of all-cause mortality (hazard ratio [HR 2.6], 95% confidence intervals [CI] 2.0-3.4), cerebrovascular mortality (HR 30.6, CI 13.5-69.4), and stroke (HR 10.2, CI 7.5-13.8). Compared with the non-SAH group, the SAH patients with cardiac injury had increased rates of all-cause mortality (HR 5.3, CI 3.0-9.3), cardiac mortality (HR 7.3, CI 1.7-31.6), and heart failure (HR 4.3, CI 1.53-11.88). CONCLUSIONS: SAH survivors have increased long-term mortality and stroke rates compared with a matched non-SAH population. SAH-induced cardiac injury is associated with an increased risk of death and heart failure hospitalization.

Executioner caspase-3 and caspase-7 are functionally distinct proteases.

Members of the caspase family of cysteine proteases play central roles in coordinating the stereotypical events that occur during apoptosis. Because the major executioner caspases, caspase-3 and caspase-7, exhibit almost indistinguishable activity toward certain synthetic peptide substrates, this has led to the widespread view that these proteases occupy functionally redundant roles within the cell death machinery. However, the distinct phenotypes of mice deficient in either of these caspases, as well as mice deficient in both, is at odds with this view. These distinct phenotypes could be related to differences in the relative expression levels of caspase-3 and caspase-7 in vivo, or due to more fundamental differences between these proteases in terms of their ability to cleave natural substrates. Here we show that caspase-3 and caspase-7 exhibit differential activity toward multiple substrate proteins, including Bid, XIAP, gelsolin, caspase-6, and cochaperone p23. Caspase-3 was found to be generally more promiscuous than caspase-7 and appears to be the major executioner caspase during the demolition phase of apoptosis. Our observations provide a molecular basis for the different phenotypes seen in mice lacking either caspase and indicate that these proteases occupy nonredundant roles within the cell death machinery.