Pathogenesis of acute stroke and the role of inflammasomes

Targeted delivery of extracellular matrix protected against neurologic defects after focal ischemia reperfusion in rats

Ischemic stroke is one of the leading causes of morbidity and mortality worldwide and characterized by defective angiogenesis. The functional sequences (RGDs, GRGDSPASSPISC) derived from fibronectin have been confirmed to augment angiogenesis in vivo and in vitro. However, delivery of peptides into the brain parenchyma has been hampered by the presence of the blood-brain barrier (BBB). We fused RGDs with penetratin (Antp) derived from Drosophila antennapedia homeodomain protein to improve the penetration of peptides through BBB into ischemic hemisphere. We found Antp-RGDs successfully not only penetrate the SH-SY5Y cells but also penetrated through BBB into ischemic hemisphere by intraperitoneal injection. In addition, application of Antp-RGDs to the focal cerebral ischemic reperfusion injury in rats resulted in the reduction of cerebral ischemic volume and the improvement of neurologic score according to the 21-point score. We further demonstrated that activation of phosphorylation-extracellular-signal related kinase 1/2 (p-ERK 1/2) and upregulation of gene VEGF resulted from post-treatment with Antp-RGDs 2 hours after reperfusion onset might at least partly contribute to the benefic changes after focal cerebral ischemic reperfusion injury in rats. Our data suggested that Antp-RGDs may serve as an attractive therapeutic intervention for treating ischemic stroke.

Early reperfusion injury is associated to MMP2 and IL-1β elevation in cortical neurons of rats subjected to middle cerebral artery occlusion

The pathophysiological processes implicated in ischemic brain damage are strongly affected by an inflammatory reaction characterized by activation of immune cells and release of soluble mediators, including cytokines and chemokines. The pro-inflammatory cytokine interleukin (IL)-1β has been implicated in ischemic brain injury, however, to date, the mechanisms involved in the maturation of this cytokine in the ischemic brain have not been completely elucidated. We have previously suggested that matrix metalloproteinases (MMPs) may be implicated in cytokine production under pathological conditions. Here, we demonstrate that significant elevation of IL-1β occurs in the cortex as early as 1h after the beginning of reperfusion in rats subjected to 2-h middle cerebral artery occlusion (MCAo). At this early stage, we observe increased expression of IL-1β in pericallosal astroglial cells and in cortical neurons and this latter signal colocalizes with elevated gelatinolytic activity. By gel zymography, we demonstrate that the increased gelatinolytic signal at 1-h reperfusion is mainly ascribed to MMP2. Thus, MMP2 seems to contribute to early brain elevation of IL-β after transient ischemia and this mechanism may promote damage since pharmacological inhibition of gelatinases by the selective MMP2/MMP9 inhibitor V provides neuroprotection in rats subjected to transient MCAo.

Intermittent fasting attenuates inflammasome activity in ischemic stroke

Recent findings have revealed a novel inflammatory mechanism that contributes to tissue injury in cerebral ischemia mediated by multi-protein complexes termed inflammasomes. Intermittent fasting (IF) can decrease the levels of pro-inflammatory cytokines in the periphery and brain. Here we investigated the impact of IF (16h of food deprivation daily) for 4months on NLRP1 and NLRP3 inflammasome activities following cerebral ischemia. Ischemic stroke was induced in C57BL/6J mice by middle cerebral artery occlusion, followed by reperfusion (I/R). IF decreased the activation of NF-κB and MAPK signaling pathways, the expression of NLRP1 and NLRP3 inflammasome proteins, and both IL-1β and IL-18 in the ischemic brain tissue. These findings demonstrate that IF can attenuate the inflammatory response and tissue damage following ischemic stroke by a mechanism involving suppression of NLRP1 and NLRP3 inflammasome activity.

Perinatal asphyxia: CNS development and deficits with delayed onset

Perinatal asphyxia constitutes a prototype of obstetric complications occurring when pulmonary oxygenation is delayed or interrupted. The primary insult relates to the duration of the period lacking oxygenation, leading to death if not re-established. Re-oxygenation leads to a secondary insult, related to a cascade of biochemical events required for restoring proper function. Perinatal asphyxia interferes with neonatal development, resulting in long-term deficits associated to mental and neurological diseases with delayed clinical onset, by mechanisms not yet clarified. In the experimental scenario, the effects observed long after perinatal asphyxia have been explained by overexpression of sentinel proteins, such as poly(ADP-ribose) polymerase-1 (PARP-1), competing for NAD⁺ during re-oxygenation, leading to the idea that sentinel protein inhibition constitutes a suitable therapeutic strategy. Asphyxia induces transcriptional activation of pro-inflammatory factors, in tandem with PARP-1 overactivation, and pharmacologically induced PARP-1 inhibition also down-regulates the expression of proinflammatory cytokines. Nicotinamide has been proposed as a suitable PARP-1 inhibitor. Its effect has been studied in an experimental model of global hypoxia in rats. In that model, the insult is induced by immersing rat fetus into a water bath for various periods of time. Following asphyxia, the pups are delivered, treated, and nursed by surrogate dams, pending further experiments. Nicotinamide rapidly distributes into the brain following systemic administration, reaching steady state concentrations sufficient to inhibit PARP-1 activity for several hours, preventing several of the long-term consequences of perinatal asphyxia, supporting the idea that nicotinamide constitutes a lead for exploring compounds with similar or better pharmacological profiles.

Exogenous asymmetric dimethylarginine (ADMA) in pathogenesis of ischemia-reperfusion-induced gastric lesions: interaction with protective nitric oxide (NO) and calcitonin gene-related peptide (CGRP)

Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide (NO) synthesis inhibitor and pro-inflammatory factor. We investigated the role of ADMA in rat gastric mucosa compromised through 30 min of gastric ischemia (I) and 3 h of reperfusion (R). These I/R animals were pretreated with ADMA with or without the combination of l-arginine, calcitonin gene-related peptide (CGRP) or a small dose of capsaicin, all of which are known to afford protection against gastric lesions, or with a farnesoid X receptor (FXR) agonist, GW 4064, to increase the metabolism of ADMA. In the second series, ADMA was administered to capsaicin-denervated rats. The area of gastric damage was measured with planimetry, gastric blood flow (GBF) was determined by H₂-gas clearance, and plasma ADMA and CGRP levels were determined using ELISA and RIA. ADMA significantly increased I/R-induced gastric injury while significantly decreasing GBF, the luminal NO content, and the plasma level of CGRP. This effect of ADMA was significantly attenuated by pretreatment with CGRP, l-arginine, capsaicin, or a PGE₂ analogue. In GW4064 pretreated animals, the I/R injury was significantly reduced and this effect was abolished by co-treatment with ADMA. I/R damage potentiated by ADMA was exacerbated in capsaicin-denervated animals with a further reduction of CGRP. Plasma levels of IL-10 were significantly decreased while malonylodialdehyde (MDA) and plasma TNF-α contents were significantly increased by ADMA. In conclusion, ADMA aggravates I/R-induced gastric lesions due to a decrease of GBF, which is mediated by a fall in NO and CGRP release, and the enhancement of lipid peroxidation and its pro-inflammatory properties.

The role of the inflammasome in cardiovascular diseases

Inflammasome is a very important signaling platform sensing a variety of triggers of the innate immune system. Inflammasome promotes the production of important pro-inflammatory cytokines such as IL-1β and IL-18. Tight control of inflammasome activity is, therefore, essential and occurs at multiple levels. The activation of inflammasome pathways is linked to the pathogenesis of various prevalent disorders including cardiovascular disease such as atherosclerosis, ischemic injury, cardiomyopathy, and Kawasaki disease. The study of the inflammasome in the cardiovascular system has led to the identification of important triggers and endogenous modulators, and to the exploration of new treatment strategies based on the inhibition of inflammasome activation or its end products, i.e., IL-1β and IL-18. In summary, the discovery of the inflammasome has greatly advanced our understanding of how the innate immune system interferes with cardiovascular disease development and progression, and targeting inflammasome provides new avenues for the treatment and management of cardiovascular diseases.

Carotid surgery affects plasma kynurenic acid concentration: a pilot study

BACKGROUND

An increase in plasma kynurenic acid (KYNA) concentration has been observed following surgery, inflammation, and cerebral pathologies. The aim of the present study was to analyze the changes in plasma KYNA concentration in patients undergoing carotid surgery (CS).

MATERIAL AND METHODS

Adult patients undergoing elective carotid endarterectomy (CEA) or carotid angioplasty with stent placement (CAS) were studied. Plasma KYNA concentrations were analyzed before surgery and at 4 time points after CS. The amount of inflammation was measured as neutrophil-lymphocyte ratio (NLR).

RESULTS

Forty patients (10 female and 30 male) aged 55-86 years of age were evaluated in this study. In patients with unstable carotid plaque, the plasma KYNA concentration was higher than in patients with stable carotid plaque. Moreover, the NLR was significantly higher in patients with unstable carotid plaque undergoing CEA than in patients undergoing CAS. Plasma KYNA concentration increased after surgery in patients undergoing CEA and CAS. There was a strong correlation between plasma KYNA concentration and NLR in patients with postoperative neurological disorders.

CONCLUSIONS

CS increases plasma KYNA concentration, and changes in plasma KYNA concentration can indicate neurologic outcomes in patients undergoing CS.