ADAMTS13 gene deletion enhances plasma high-mobility group box1 elevation and neuroinflammation in brain ischemia-reperfusion injury

Highly adhesive glycoprotein von Willebrand factor (VWF) multimer induces platelet aggregation and leukocyte tethering or extravasation on the injured vascular wall, contributing to microvascular plugging and inflammation in brain ischemia-reperfusion. A disintegrin and metalloproteinase with thrombospondin type-1 motifs 13 (ADAMTS13) cleaves the VWF multimer strand and reduces its prothrombotic and proinflammatory functions. Although ADAMTS13 deficiency is known to amplify post-ischemic cerebral hypoperfusion, there is no report available on the effect of ADAMTS13 on inflammation after brain ischemia. We investigated if ADAMTS13 deficiency intensifies the increase of extracellular HMGB1, a hallmark of post-stroke inflammation, and exacerbates brain injury after ischemia-reperfusion. ADAMTS13 gene knockout (KO) and wild-type (WT) mice were subjected to 30-min middle cerebral artery occlusion (MCAO) and 23.5-h reperfusion under continuous monitoring of regional cerebral blood flow (rCBF). The infarct volume, plasma high-mobility group box1 (HMGB1) level, and immunoreactivity of the ischemic cerebral cortical tissue (double immunofluorescent labeling) against HMGB1/NeuN (neuron-specific nuclear protein) or HMGB1/MPO (myeloperoxidase) were estimated 24h after MCAO. ADAMTS13KO mice had larger brain infarcts compared with WT 24h after MCAO (p<0.05). The rCBF during reperfusion decreased more in ADAMTS13KO mice. The plasma HMGB1 increased more in ADAMTS13KO mice than in WT after ischemia-reperfusion (p<0.05). Brain ischemia induced more prominent activation of inflammatory cells co-expressing HMGB1 and MPO and more marked neuronal death in the cortical ischemic penumbra of ADAMTS13KO mice. ADAMTS13 deficiency may enhance systemic and brain inflammation associated with HMGB1 neurotoxicity, and aggravate brain damage in mice after brief focal ischemia. We hypothesize that ADAMTS13 protects brain from ischemia-reperfusion injury by regulating VWF-dependent inflammation as well as microvascular pluggin

Pathophysiology and treatment of focal cerebral ischemia. Part I: Pathophysiology.

This article examines the pathophysiology of lesions caused by focal cerebral ischemia. Ischemia due to middle cerebral artery occlusion encompasses a densely ischemic focus and a less densely ischemic penumbral zone. Cells in the focus are usually doomed unless reperfusion is quickly instituted. In contrast, although the penumbra contains cells "at risk," these may remain viable for at least 4 to 8 hours. Cells in the penumbra may be salvaged by reperfusion or by drugs that prevent an extension of the infarction into the penumbral zone. Factors responsible for such an extension probably include acidosis, edema, K+/Ca++ transients, and inhibition of protein synthesis. Central to any discussion of the pathophysiology of ischemic lesions is energy depletion. This is because failure to maintain cellular adenosine triphosphate (ATP) levels leads to degradation of macromolecules of key importance to membrane and cytoskeletal integrity, to loss of ion homeostasis, involving cellular accumulation of Ca++, Na+, and Cl-, with osmotically obligated water, and to production of metabolic acids with a resulting decrease in intra- and extracellular pH. In all probability, loss of cellular calcium homeostasis plays an important role in the pathogenesis of ischemic cell damage. The resulting rise in the free cytosolic intracellular calcium concentration (Ca++) depends on both the loss of calcium pump function (due to ATP depletion), and the rise in membrane permeability to calcium. In ischemia, calcium influx occurs via multiple pathways. Some of the most important routes depend on activation of receptors by glutamate and associated excitatory amino acids released from depolarized presynaptic endings. However, ischemia also interfers with the intracellular sequestration and binding of calcium, thereby contributing to the rise in intracellular Ca++. A second key event in the ischemic tissue is activation of anaerobic glucolysis. The main reason for this activation is inhibition of mitochondrial metabolism by lack of oxygen; however, other factors probably contribute. For example, there is a complex interplay between loss of cellular calcium homeostasis and acidosis. On the one hand, a rise in intracellular Ca++ is apt to cause mitochondrial accumulation of calcium. This must interfere with ATP production and enhance anaerobic glucolysis. On the other hand, acidosis must interfere with calcium binding, thereby contributing to the rise in intracellular Ca++

Cerebral metabolic changes in profound, insulin-induced hypoglycemia, and in the recovery period following glucose administration

Severe hypoglycemia was induced by insulin in lightly anaesthetized (70°o N2O) and artificially ventilated rats. Brain tissue was frozen in situ after spontaneous EEG potentials had disappeared for 5. 10. 15 or 30 min and cerebral cortex concentrations of labile organic phosphates, glycolytic metabolites, ammonia and amino acids were determined. In other experiments, recovery was induced by glucose injection at the end of the period of EEG silence. All animals with an isoelectric EEG showed extensive deterioration of the cerebral energy state. and gross perturbation of amino acid concentrations. The latter included a 4-fold rise in aspartate concentration and reductions in glutamate and glutamine concentrations to 20 and 5oo of control levels respectively. There was an associated rise in ammonia concentration to about 3μmol-g-1. Administration of glucose brought about extensive recovery of cerebral energy metabolism. For example, after an isoelectric period of 30 min tissue concentrations of phosphocreatine returned to or above normal, the accumulation of ADP and AMP was reversed, there was extensive resynthesis of glycogen and glutamine and full normalisation of tissue concentrations of pyruvate. α-ketoglutarate. GABA and ammonia. However, even after 3 h of recovery there was a reduction in the ATP concentration and thereby in adenine nucleotide pool, moderate elevations of lactate content and the lactate pyruvate ratio, and less than complete restoration of the amino acid pool. It is concluded that some cells may have been irreversibly damaged by the hypoglycemia

Free radicals and brain damage

Although free radicals have been suggested to contribute to ischemic brain damage for more than 10 years, it is not until quite recently that convincing evidence has been presented for their involvement in both sustained and transient ischemia. The hypothesis is examined against current knowledge of free radical chemistry, as it applies to biological systems, and of cellular iron metabolism. It is emphasized that those advents have changed our outlook on free radical-induced tissue damage. First, it has been realized that damage to DNA and proteins may be an earlier event than lipid peroxidation, perhaps also a more important one. Second, evidence now exists that the triggering event in free radical-induced damage is a disturbance of cellular iron metabolism, notably delocalization of protein-bound iron, and its chelation by compounds that trigger site-specific free radical damage. Third, methods have been developed that allow the demonstration of partially induced oxygen species in tissues, and scavengers have become available that can curb free radical reactions. As a result of these events, it has been possible to demonstrate formation of free radicals in oxygen toxicity, trauma, and ischemia, and their participation in the cell damage that is incurred in these conditions, particularly in causing vascular pathology and edema. It is suggested that in ischemia, free radical damage becomes pathogenetically important when the ischemia is of long duration, when conditions favor continued delivery of some oxygen to the ischemic tissue, and particularly when such partially oxygen-deprived tissue is reoxygenated