is sufficient for neuroprotection, it is not necessary for HDAC inhibitor neuroprotection, because these agents can completely protect neurons cultured from p21 waf1/cip1 -null mice. Together these findings demonstrate (1) that pulse inhibition of HDACs in cortical neurons can induce neuroprotection without apparent toxicity; (2) that p21 waf1/cip1 is sufficient but not necessary to mimic the protective effects of HDAC inhibition; and (3) that oxidative stress in this model induces neuronal cell death via cell cycle-independent pathways that can be inhibited by a cytosolic, noncanonical action of p21 waf1/cip1 .

Oxidative stress is implicated in the pathogenesis of ischemia/ reperfusion injury. Recently, we demonstrated that activation of CD36, a class B scavenger receptor, mediates free radical production and tissue injury in cerebral ischemia (1). Oxidized low density lipoproteins (oxLDL) are among the ligands that bind to CD36 and are elevated in acute cerebral infarction. SS31 is a cell-permeable antioxidant peptide that reduces intracellular free radicals and inhibits LDL oxidation/lipid peroxidation (2). The current study was designed to investigate whether treatment with SS31 normalizes ischemia-induced redox changes and attenuates CD36-mediated tissue injury. C57BL/6 mice were subjected to transient middle cerebral artery occlusion (MCAO). Redox status and infarct volume were measured in animals treated with either saline or SS31. Oxidative stress induced by ischemia/reperfusion profoundly depleted glutathione (GSH) concentrations in the ipsilateral cortex and striatum. Treating mice with SS31 immediately after reperfusion significantly attenuated ischemia-induced GSH depletion in the cortex and reduced infarct size. By contrast, the protective effect of SS31 was absent in CD36 knock-out mice, indicating that SS31 is acting through inhibition of CD36. Treating C57BL/6 mice with SS31 reduced CD36 expression in postischemic brain and mouse peritoneal macrophages (MPM). Further in vitro studies revealed that SS31 attenuated oxLDL-induced CD36 expression and foam cell formation in MPM. These in vivo and in vitro studies indicate that the down-regulation of CD36 by novel class antioxidant peptides may be a useful strategy to treat ischemic stroke victims. Generation of reactive oxygen species (ROS)2 and depletion of intracellular antioxidants following cerebral ischemia/reperfusion are hallmarks of oxidative stress and lead to tissue injury. Glutathione and ascorbate are major endogenous cerebral antioxidants that serve as biochemical markers of intracellular redox status (3). It is generally accepted that these antioxidants are important for protection of brain during post-ischemic oxidative stress, although dynamic interactions among antioxidants in vivo are not entirely clear. Depletion of intracellular antioxidants has been associated with stroke pathology and repletion of antioxidant status has reduced neuronal damage but has produced inconsistent improvement in stroke outcome (4 -8). Ischemic injury also causes a local inflammatory reaction by activated microglia and infiltrated inflammatory cells that further release pro-inflammatory cytokines and ROS within the injured site.CD36, a glycosylated surface receptor, belongs to a class B scavenger receptor and is localized in lipid rafts of plasma membrane and in mitochondria (9 -11). It is expressed on microglia, macrophages, microvascular endothelium, cardiac and skeletal muscle, adipocytes, and platelets and recognizes a variety of ligands including oxidized low density lipoproteins (oxLDL), advanced glycation end products, long chain fatty acids, fibrillar ␤-a...

Hyperlipidemia with accompanying increase in peripheral inflammation is a risk factor for stroke. The effect of excess lipids on strokeinduced injury and the mechanism by which lipid-mediated inflammatory responses contribute to stroke are not known. We investigated these uncertainties by subjecting normal and hyperlipidemic mice to transient middle cerebral artery occlusion, followed by measurement of stroke severity and inflammatory response. Infarct size, swelling, and lipid contents were significantly increased in the high-fat fed ApoE knock-out mice, as was the expression of the inflammatory mediators CD36 and monocyte chemoattractant protein 1 (MCP-1) in the brain and periphery. Furthermore, the hyperlipidemic mice exhibited numerous foam cells, a probable cause of increased swelling and postischemic inflammation, in the peri-infarct area. Genetic deletion of cd36 in the hyperlipidemic condition reduced proinflammatory chemokine/receptor and cytokines (MCP-1, CC chemokine receptor 2, and interleukins 1␤ and 6), in the brain 6 h after ischemia. The reduced proinflammatory response also resulted in smaller ischemic injury, less swelling, and fewer foam cells at 3 d after ischemia. The results show that hyperlipidemia-induced inflammation is a negative factor for stroke outcomes and indicate that downregulating CD36 may be an effective therapeutic strategy for reducing the impact of stroke in hyperlipidemic subjects.

BackgroundAlthough elicited inflammation contributes to tissue injury, a certain level of inflammation is necessary for subsequent tissue repair/remodeling. Diabetes, a chronic low-grade inflammatory state, is a predisposing risk factor for stroke. The condition is associated with delayed wound healing, presumably due to disrupted inflammatory responses. With inclusion of the diabetic condition in an experimental animal model of stroke, this study investigates whether the condition alters inflammatory response and influences stroke-induced brain injury.MethodsC57BL/6 mice were fed a diabetic diet (DD) for 8 weeks to induce an experimental diabetic condition or a normal diet (ND) for the same duration. Gene expression of inflammatory factors including monocyte chemoattractant protein-1 (MCP-1), interleukin-6 (IL-6), CCR2, and CD36 was assessed in the peripheral immune cells and brains of normal and diabetic mice before and after focal cerebral ischemia. The expression of these factors was also determined in lipopolysaccharide (LPS)-treated cultured normal and diabetic macrophages. Ischemic outcome was assessed in these mice at 3 days post-ischemia.ResultsDD intervention in mice resulted in obesity and elevated insulin and glucose level in the blood. The peritoneal immune cells from the diabetic mice showed higher MCP-1 mRNA levels before and after stroke. Compared to normal mice, diabetic mice showed reduced MCP-1, IL-6, and CCR2 gene expression in the brain at 6 h post-ischemia. LPS-stimulated inflammatory responses were also reduced in the diabetic macrophages. The diabetic mice showed larger infarct size and percent swelling.ConclusionsThese results showed that diabetic conditions deregulate acute inflammatory response and that the condition is associated with increased stroke-induced injury. The study suggests that interventions aimed at restoring appropriate inflammatory response in peripheral immune cells/macrophages may be beneficial in reducing stroke-induced brain injury in subjects with chronic inflammatory conditions.