Emerging therapeutic targets in focal stroke and brain trauma: cytokines and the brain inflammatory response to injury

Caspase inhibitors as neuroprotective agents

Apoptotic neuronal cell death has been demonstrated to occur in the central nervous system (CNS), following both acute injury and during chronic neurodegenerative conditions. Currently, the majority of experimental evidence for a role of caspases in CNS damage has been established following acute neuronal insults, including ischaemic stroke, traumatic brain injury and spinal cord injury. In vitro and in vivo models have been used to demonstrate caspase activation, and treatment with available caspase inhibitors can provide significant protection. Overall, acute neuronal injury represents a major unmet medical need and caspase inhibitors may be an attractive approach to preserve neuronal function by extending the therapeutic window and providing long-term neuroprotection. Currently, several inhibitors are in preclinical drug development and this review summarises recent advances in the development of novel caspase inhibitors for the treatment of acute neuronal injury.

Role of leukocytes in ethanol-induced microvascular injury in the rat brain in situ: potential role in alcohol brain pathology and stroke

Effects of acute and chronic alcohol ethanol administration on in vivo microvascular-leukocyte dynamics was studied in brains of naive and leukocyte-depleted rats by direct, quantitative intravital high-resolution TV microscopy, fluorescence microscopy and myeloperoxidase staining. Administration of alcohol produced dose-dependent venular vasospasm, and rolling and adherence of leukocytes to venular walls; leukocyte velocity concomitantly decreased. Intermediate to high doses of ethanol resulted in infiltration of leukocytes and macrophages across venular walls, and concentration-dependent increases in myeloperoxidase staining in parenchyma, and rupture of postcapillary venules with focal hemorrhages. Use of phosphorus 31-nuclear magnetic resonance spectroscopy on intact animals revealed that the latter were associated with whole brain losses in intracellular levels of ATP and phosphocreatine with concomitant rises in intracellular inorganic phosphate and hydrogen ion concentration. Vinblastine-depletion of circulating leukocytes prevented or ameliorated greatly the alcohol-induced microvascular damage and proinflammatory-like reactions. These new results, when viewed in light of other recent findings, suggest that alcohol-induced cerebral vascular and brain damage is dependent, to a large extent, on recruitment of leukocytes.

Pharmacological interventions for stroke: failures and future

Given the few options currently available for patients following ischaemic stroke, the recent disappointing failures of several large-scale Phase III clinical trials has made the search for novel therapeutic approaches even more critical. Experimental evidence has suggested that the majority of stroke patients have a slow evolution of brain injury which can occur over several hours. Progressive microcirculatory failure following the initial onset of ischaemia may contribute to the expansion of brain injury. Included among the pathophysiological changes that are speculated to occur as a secondary response to the initial ischaemia are free radical production, excitotoxicity (for example, glutamate) disruption of ionic homeostasis (for example, sodium and calcium influx), enzymatic changes, stimulation of the inflammatory process, endothelin release, activation of platelets and leukocytes, delayed coagulation and endothelial dysfunction. All of these pathophysiological reactions could contribute to an increase in local vascular resistance and therefore cause progressive hypoperfusion of the brain following the onset of stroke. The scope of this review will focus on recent clinical failures in addition to agents currently in clinical development, comparing vascular targets to the common neuroprotective strategies.

Inflammatory mediators and stroke: new opportunities for novel therapeutics

Contrary to previous dogmas, it is now well established that brain cells can produce cytokines and chemokines, and can express adhesion molecules that enable an in situ inflammatory reaction. The accumulation of neutrophils early after brain injury is believed to contribute to the degree of brain tissue loss. Support for this hypothesis has been drawn from many studies where neutrophil-depletion blockade of endothelial-leukocyte interactions has been achieved by various techniques. The inflammation reaction is an attractive pharmacologic opportunity, considering its rapid initiation and progression over many hours after stroke and its contribution to evolution of tissue injury. While the expression of inflammatory cytokines that may contribute to ischemic injury has been repeatedly demonstrated, cytokines may also provide "neuroprotection" in certain conditions by promoting growth, repair, and ultimately, enhanced functional recovery. Significant additional basic work is required to understand the dynamic, complex, and time-dependent destructive and protective processes associated with inflammation mediators produced after brain injury. The realization that brain ischemia and trauma elicit robust inflammation in the brain provides fertile ground for discovery of novel therapeutic agents for stroke and neurotrauma. Inhibition of the mitogen-activated protein kinase (MAPK) cascade via cytokine suppressive anti-inflammatory drugs, which block p38 MAPK and hence the production of interleukin-1 and tumor necrosis factor-alpha, are most promising new opportunities. However, spatial and temporal considerations need to be exercised to elucidate the best opportunities for selective inhibitors for specific inflammatory mediators.