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

The Influence of Stroke Risk Factors and Comorbidities on Assessment of Stroke Therapies in Humans and Animals

The main driving force behind the assessment of novel pharmacological agents in animal models of stroke is to deliver new drugs to treat the human disease rather than to increase knowledge of stroke pathophysiology. There are numerous animal models of the ischaemic process and it appears that the same processes operate in humans. Yet, despite these similarities, the drugs that appear effective in animal models have not worked in clinical trials. To date, tissue plasminogen activator is the only drug that has been successfully used at the bedside in hyperacute stroke management. Several reasons have been put forth to explain this, but the failure to consider comorbidities and risk factors common in older people is an important one. In this article, we review the impact of the risk factors most studied in animal models of acute stroke and highlight the parallels with human stroke, and, where possible, their influence on evaluation of therapeutic strategies.

Transcriptional control of maladaptive and protective responses in alcoholics: a role of the NF-κB system

Alcohol dependence and associated cognitive impairment appear to result from maladaptive neuroplasticity in response to chronic alcohol consumption, neuroinflammation and neurodegeneration. The inherent stability of behavioral alterations associated with the addicted state suggests that transcriptional and epigenetic mechanisms are operative. NF-κB transcription factors are regulators of synaptic plasticity and inflammation, and responsive to a variety of stimuli including alcohol. These factors are abundant in the brain where they have diverse functions that depend on the composition of the NF-κB complex and cellular context. In neuron cell bodies, NF-κB is constitutively active, and involved in neuronal injury and neuroprotection. However, at the synapse, NF-κB is present in a latent form and upon activation is transported to the cell nucleus. In glia, NF-κB is inducible and regulates inflammatory processes that exacerbate alcohol-induced neurodegeneration. Animal studies demonstrate that acute alcohol exposure transiently activates NF-κB, which induces neuroinflammatory responses and neurodegeneration. Postmortem studies of brains of human alcoholics suggest that repeated cycles of alcohol consumption and withdrawal cause adaptive changes in the NF-κB system that may permit the system to better tolerate excessive stimulation. This type of tolerance, ensuring a low degree of responsiveness to applied stimuli, apparently differs from that in the immune system, and may represent a compensatory response that protects brain cells against alcohol neurotoxicity. This view is supported by findings showing preferential downregulation of pro-apoptotic gene expression in the affected brain areas in human alcoholics. Although further verification is needed, we speculate that NF-κB-driven neuroinflammation and disruption to neuroplasticity play a significant role in regulating alcohol dependence and cognitive impairment.

Neuroadaptations in human chronic alcoholics: dysregulation of the NF-kappaB system

Background

Alcohol dependence and associated cognitive impairments apparently result from neuroadaptations to chronic alcohol consumption involving changes in expression of multiple genes. Here we investigated whether transcription factors of Nuclear Factor-kappaB (NF-κB) family, controlling neuronal plasticity and neurodegeneration, are involved in these adaptations in human chronic alcoholics.

Methods and Findings

Analysis of DNA-binding of NF-κB (p65/p50 heterodimer) and the p50 homodimer as well as NF-κB proteins and mRNAs was performed in postmortem human brain samples from 15 chronic alcoholics and 15 control subjects. The prefrontal cortex involved in alcohol dependence and cognition was analyzed and the motor cortex was studied for comparison. The p50 homodimer was identified as dominant κB binding factor in analyzed tissues. NF-κB and p50 homodimer DNA-binding was downregulated, levels of p65 (RELA) mRNA were attenuated, and the stoichiometry of p65/p50 proteins and respective mRNAs was altered in the prefrontal cortex of alcoholics. Comparison of a number of p50 homodimer/NF-κB target DNA sites, κB elements in 479 genes, down- or upregulated in alcoholics demonstrated that genes with κB elements were generally upregulated in alcoholics. No significant differences between alcoholics and controls were observed in the motor cortex.

Conclusions

We suggest that cycles of alcohol intoxication/withdrawal, which may initially activate NF-κB, when repeated over years downregulate RELA expression and NF-κB and p50 homodimer DNA-binding. Downregulation of the dominant p50 homodimer, a potent inhibitor of gene transcription apparently resulted in derepression of κB regulated genes. Alterations in expression of p50 homodimer/NF-κB regulated genes may contribute to neuroplastic adaptation underlying alcoholism.

Binge alcohol exposure in the second trimester attenuates fetal cerebral blood flow response to hypoxia

Alcohol is detrimental to the developing brain and remains the leading cause of mental retardation in developed countries. The mechanism of alcohol brain damage remains elusive. Studies of neurological problems in adults have focused on alcohol's cerebrovascular effects, because alcoholism is a major risk factor for stroke and cerebrovascular injuries. However, few studies have examined similar cerebrovascular effects of fetal alcohol exposure. We examined the effect of chronic binge alcohol exposure during the second trimester on fetal cerebrovascular and metabolic responses to hypoxia in near-term sheep and tested the hypothesis that fetal alcohol exposure would attenuate cerebrovascular dilation to hypoxia. Pregnant ewes were infused with alcohol (1.5 g/kg) or saline intravenously at 60–90 days of gestation (full term = 150 days). At 125 days of gestation, we measured fetal cerebral blood flow (CBF) and oxygen metabolism at baseline and during hypoxia. Maternal blood alcohol averaged 214 ± 5.9 mg/dl immediately after the 1.5-h infusion, with similar values throughout the month of infusion. Hypoxia resulted in a robust increase in CBF in saline-infused fetuses. However, the CBF response to hypoxia in fetuses chronically exposed to alcohol was significantly attenuated. Cerebral oxygen delivery decreased in both groups of fetuses during hypoxia but to a greater degree in the alcohol-exposed fetuses. Prenatal alcohol exposure during the second trimester attenuates cerebrovascular responses to hypoxia in the third trimester. Altered cerebrovascular reactivity might be one mechanism for alcohol-related brain damage and might set the stage for further brain injury if a hypoxic insult occurs.

The effects of chronic exposure to ethanol and cigarette smoke on the formation of peroxynitrite, level of nitric oxide, xanthine oxidase and myeloperoxidase activities in rat kidney

The aim of this study was to investigate the effects of chronic ethanol intake and cigarette smoke exposure on rat kidney. The animals were divided into four experimental groups: (1) the control group (C), (2) the ethanol group (E), (3) the cigarette smoke group (CS), and (4) the cigarette smoke plus ethanol group (CS+E). Rats in E, CS and CS+E groups were treated with ethanol and/or cigarette smoke for 6 months. The animals were killed and the kidneys were removed to determine the activity of xanthine oxidase (XO), myeloperoxidase (MPO) and the levels of nitric oxide (NO). Histopathological and immunohistochemical analysis were performed in kidney tissues. The activity of XO/g protein were 2.8 +/- 0.3, 5.2 +/- 0.3, 3.2 +/- 0.1, and 7.4 +/- 0.7 U for C, E, CS and CS+E groups, respectively. In groups E, and CS+E, the XO values were significantly higher than in group C (P < 0.05). The increase in XO activity of CS was not significantly different from group C (P > 0.05). There was a significant increase in XO activity of group CS+E as compared to CS and E groups (P < 0.05), and also a significant difference in XO activity between E and CS was observed (P < 0.05). The activity of MPO/g protein were 13.5 +/- 0.6, 16.2 +/- 1.1, 14.7 +/- 1.1, 23.8 +/- 0.9 U for C, E, CS, and CS+E groups, respectively. While MPO activity of kidneys from group CS+E were significantly higher as compared to C, CS, and E groups (P < 0.05), there was no significant difference among the groups of C, CS, E (P > 0.05). The levels of NO/g wet tissue were 347.7 +/- 8.5, 261.1 +/- 4.8, 329.8 +/- 5.6, and 254.2 +/- 3.8 nmol for C, E, CS, and CS+E groups, respectively. In groups of E and CS+E, the NO values were significantly lower than that of group C animals (P < 0.05). Although we detected lower NO levels in the E and CS+E groups than in CS group (P < 0.05), a significant difference in NO levels between CS+E and E groups was not observed. In the histopathological analysis of the kidney slices, severe degenerations in kidney tissues of group CS, E, CS+E were observed. Generally, the histological changes in kidney of CS+E and E groups were more severe than those observed in CS alone. While we observed a strong immunoreactivity for anti-nitrotyrosine antibody in kidneys of group CS+E, examination of sections from rat kidneys in group E revealed moderate staining. On the other hand, group CS had very little immunostaining. There was no immunostaining in group C. We concluded that chronic ethanol administration and cigarette smoke exposure may cause oxidative and nitrosative stress which lead to rat kidney damage.

Involvement of TLR4/type I IL-1 receptor signaling in the induction of inflammatory mediators and cell death induced by ethanol in cultured astrocytes

Activated astroglial cells are implicated in neuropathogenesis of many infectious and inflammatory diseases of the brain. A number of inflammatory mediators and cytokines have been proposed to play a key role in glial cell-related brain damage. Cytokine production seems to be initiated by signaling through TLR4/type I IL-1R (IL-1RI) in response to their ligands, LPS and IL-1beta, playing vital roles in innate host defense against infections, inflammation, injury, and stress. We have shown that glial cells are stimulated by ethanol, up-regulating cytokines and inflammatory mediators associated with TLR4 and IL-1RI signaling pathways in brain, suggesting that ethanol may contribute to brain damage via inflammation. We explore the possibility that ethanol, in the absence of LPS or IL-1beta, triggers signaling pathways and inflammatory mediators through TLR4 and/or IL-1RI activation in astrocytes. We show in this study that ethanol, at physiologically relevant concentrations, is capable of inducing rapid phosphorylation within 10 min of IL-1R-associated kinase, ERK1/2, stress-activated protein kinase/JNK, and p38 MAPK in astrocytes. Then an activation of NF-kappaB and AP-1 occurs after 30 min of ethanol treatment along with an up-regulation of inducible NO synthase and cyclooxygenase-2 expression. Finally, we note an increase in cell death after 3 h of treatment. Furthermore, by using either anti-TLR4- or anti-IL-1RI-neutralizing Abs, before and during ethanol treatment, we inhibit ethanol-induced signaling events, including NF-kappaB and AP-1 activation, inducible NO synthase, and cyclooxygenase-2 up-regulation and astrocyte death. In summary, these findings indicate that both TLR4 and IL-1RI activation occur upon ethanol treatment, and suggest that signaling through these receptors mediates ethanol-induced inflammatory events in astrocytes and brain.

Ethanol increases nuclear factor-kappa B activity in human astroglial cells

Alcohol abuse adversely affects essentially all the organs of the body, either directly or indirectly. Ethanol may contribute to brain damage via inflammation. Ethanol may also alter CNS immunocompetence and further the progression of certain CNS infections. Nuclear factor (NF)-kappa B helps regulate inflammatory gene expression in glia. It is possible that ethanol effects on CNS pathology are partly a consequence of ethanol modulation of NF-kappa B-associated pathways in glia. We have assessed the effects of 0.5-6 h ethanol exposure on cytokine (5 ng/ml interleukin-1 beta + 100 ng/ml interferon gamma + 30 ng/ml tumor necrosis factor-alpha)-induced NF-kappa B activation in human A172 astroglial cells. Immunoblot analysis indicated that NF-kappa B p65 nuclear translocation occurred within 0.5 h after cytokine stimulation. Stimulation in the presence of ethanol resulted in increased nuclear p65 levels at 3 h, with 200 mM causing a greater increase than 50 mM ethanol. Gel shift assay data suggested that cytokine-induced NF-kappa B binding activity was greatest in cells exposed to 50 mM ethanol, followed by 200 and 0 mM ethanol exposed cells, respectively. Thus, in cytokine-stimulated cells, 200 mM ethanol resulted in greater nuclear p65 levels, yet, 50 mM ethanol exposure resulted in more pronounced DNA binding by NF-kappa B. These findings demonstrate that acute ethanol enhances p65 activity in human astroglia and further support the hypothesis that ethanol-mediated brain pathology involves modulation of NF-kappa B pathways. A better understanding of the mechanistic events involved in ethanol-induced CNS pathology should provide for therapeutic strategies to combat detrimental effects of alcohol on the CNS.

Lost in translation: taking neuroprotection from animal models to clinical trials

Caffeinol has been proposed as a neuroprotectant for human trials. This review covers a variety of animal models used and various attempts to take animal protocols to human trials. The accompanying paper discusses the rabbit model that was used to identify the efficacy of tissue plasminogen activator (tPA) treatment. To date, this is the only model that was able to achieve laboratory to clinical translational success. Use of caffeinol as a cytoprotective agent in rat models yielded exciting results, which led to clinical trials. However, caffeinol given with tPA in rabbits leads to increased hemorrhage. Caffeinol alone does not prove to be neuroprotective, as vasodilation by itself is not efficacious. However, vasodilation combined with thrombolysis (caffeinol with tPA) poses an increased risk of hemorrhage. For a more translational approach to study neuroprotection and neuroprotective agents in human trials, it is necessary to demonstrate the efficacy of the procedure and purported agents in several animal models.

Pharmacology of caffeinol in embolized rabbits: clinical rating scores and intracerebral hemorrhage incidence

Caffeinol is currently being tested in acute ischemic stroke patients. However, little is known about the pharmacology or safety of caffeinol in preclinical embolic stroke models. We determined the pharmacological effects of caffeinol administration on clinical rating scores in rabbits following small clot embolic strokes (RSCEM). Male New Zealand white rabbits were embolized by injecting blood clots into the cerebral circulation via a carotid catheter. Behavioral analysis was conducted 24 h following embolization, allowing for the determination of the effective stroke dose (P50) or clot amount (mg) that produces neurological deficits in 50% of the rabbits. In the current study, the P50 values for the control groups were 1.32 +/- 0.23 and 1.66 +/- 0.29 mg for the bolus-injected and infused groups, respectively. Rabbits treated with caffeinol (bolus) starting 15 min following embolization had a P50 value of 1.70 +/- 1.18 mg. Caffeinol-infused rabbits had a P50 value of 2.05 +/- 0.47 and 1.67 +/- 0.48 mg for low- and high-dose ethanol, respectively. In tPA-treated rabbits (0.9 mg/kg), the group P50 was 1.58 +/- 0.43 mg. In caffeinol (bolus) and tPA-treated rabbits, we measured a decrease in the P50 value to 0.70 +/- 0.30 mg and an increase in the rate of intracerebral hemorrhage compared to control. This primary finding of this study indicates that neither bolus-injected nor infused caffeinol affects behavioral deficits following embolic strokes in rabbits. Moreover, the combination of caffeinol plus low-dose tPA does not improve behavioral deficits. However, our study suggests that there is the potential for exacerbation of stroke-induced behavioral deficits following caffeinol administration in combination with a thrombolytic that may be related to increased intracerebral hemorrhage.

Hippocampal and striated skeletal muscle changes in fatty acid composition induced by ethanol in alcohol-preferring rats

Chronic ethanol intake affects various organ systems of the body. The present study evaluated modifications of fatty acid concentrations both in brain and striated skeletal muscles of rats genetically selected for voluntary high ethanol intake. Three groups of rats were tracked for 10 weeks of access to ethanol only as fluid (group 1) to free choice of ethanol and water (group 2) or to water only (group 3). At the end of the period, the animals were sacrificed and their brain hippocampus and striated skeletal muscles were removed and fatty acid content of these tissues was determined. Long-chain fatty acid content increased in the hippocampus while it decreased in the striated skeletal muscles. Short chain fatty acid content decreased in the hippocampus while short chain fatty acid content increased in the striated skeletal muscles. The data show that brain and striated skeletal muscles differently modulate fatty acid content perhaps because these areas utilize different cell membrane functionality regulation systems.

Chronic ethanol inhibits CXC chemokine ligand 10 production in human A172 astroglia and astroglial-mediated leukocyte chemotaxis

Astroglia are the most prevalent cell type in the human central nervous system (CNS) and perform important roles in normal tissue homeostasis, during pathological events and following trauma. Astroglial-derived chemokines have important neurotrophic effects and are important to CNS immunocompetence and response to injury, in part, due to their direct role in leukocyte and microglial cell recruitment. However, while ethanol is known to induce CNS pathologies and to be peripherally immunosuppressive, ethanol effects on chemokine expression in human astroglia are essentially unknown. We have demonstrated that chemotaxis of human U937 leukocytic cells, across a 0.5 microm pore polycarbonate transmembrane insert, is induced in response to culture media collected from 10 microg/ml lipopolysaccharide (LPS) + 10 ng/ml interleukin (IL)-1beta-stimulated A172 human astroglia cells. The involvement of the chemokine CXCL10 (also known as interferon-gamma inducible protein or IP-10) in astroglial-induced chemotaxis of U937 cells has been indicated, as chemotaxis can be reduced by an anti-CXCL10 neutralizing antibody. Interestingly, chemotaxis of U937 cells, in response to astroglial-exposed media, is reduced when astroglia are chronically (9 days) exposed to 50 mM ethanol before stimulation with LPS + IL-1beta. Furthermore, we observed that LPS + IL-1beta-stimulated CXCL10 production is inhibited in human A172 astroglia exposed to chronic 50 mM ethanol. Thus, alterations in astroglial CXCL10 expression may disrupt CNS immunocompetence and play an important role in ethanol-induced CNS pathologies.

Acute ethanol exposure modulates expression of inducible nitric-oxide synthase in human astroglia: evidence for a transcriptional mechanism

Astroglia are important in immunocompetence and response to injury within the CNS. Activated astroglia respond, in part, by expressing inducible nitric-oxide synthase (iNOS) and subsequent catalytic production of nitric oxide. Results from a previous study in our laboratory, in the human A172 astroglial cell line, revealed that induction of iNOS activity by tumor necrosis factor-alpha + interferon-gamma + interleukin-1 beta was inhibited by 24-h exposure to a high ethanol concentration (200 mM), but enhanced by 50 mM ethanol. In the work reported in this article, we tested the working hypothesis that ethanol acts transcriptionally to modulate cytokine-induced expression of the iNOS gene, NOS2A, in human astroglia. Ethanol, 50 or 200 mM, did not directly alter in vitro catalytic activity of the iNOS enzyme, indicating that ethanol does not affect the enzyme directly. Likewise, ethanol exposure after a 12-h cytokine-stimulation period had no effect on in vivo iNOS activity. However, when cells were simultaneously exposed to ethanol and cytokines for 12 h, in vivo iNOS activity was altered. That ethanol must be present during cytokine stimulation to influence iNOS activity is consistent with a transcriptional mechanism of action. In addition, steady-state expression of iNOS protein and NOS2A mRNA levels were modulated in a biphasic manner by ethanol similar to that noted previously for iNOS activity. These findings strongly support the suggestion that ethanol modulates cytokine-induced iNOS expression in A172 cells at a pretranslational site. These findings should be instrumental in the identification of the critical ethanol-sensitive elements involved in the regulation of NOS2A in human astroglia.

Effects of alcohol infusion on smoking-induced cerebrovascular changes in rat in vivo

The combined effects of alcohol and cigarette smoking on the cerebral circulation are unknown. The current study was designed (1) to compare the acute effects on cerebral vessels of cigarette smoking alone with those of alcohol plus cigarette smoking and (2) to clarify the mechanism or mechanisms underlying the cerebrovascular responses. In pentobarbital-anesthetized, mechanically ventilated Sprague-Dawley rats, we measured pial vessel diameters with the use of a cranial window preparation. Rats, pretreated with alcohol (n = 6; 1 g/kg/h, i.v.; 1-h infusion from t = -60 min to t = 0) or with saline (n = 6), were exposed to 60 puffs per minute of mainstream smoke from a 1 mg-nicotine cigarette. Inhalation of smoke caused pial arterioles to constrict at t = 30 s (8.4%) and, subsequently, to dilate (peak at t = 5-10 min; 18.7%). Pretreatment with alcohol caused pial vasodilation (14.0%), and, after inhalation of cigarette smoke, the pial vasodilation occurred earlier (peak at t = 1-5 min; 30.2%) and was larger, without an initial vasoconstriction. The plasma concentration of thromboxane (TX) B2 (a stable metabolite of TXA2) increased after this smoking, and alcohol pretreatment attenuated this increase (protocol as above). Cigarette smoking had a significant biphasic effect on cerebral arteriolar tone. However, alcohol suppressed the initial vasoconstriction, probably, at least in part, by attenuating the smoking-induced TXA2 production.

Inhibitor of nuclear factor-Kappa B activation attenuates venular constriction, leukocyte rolling-adhesion and microvessel rupture induced by ethanol in intact rat brain microcirculation: relation to ethanol-induced brain injury

The present study was designed to test the hypothesis that acute, local administration of a specific inhibitor of nuclear factor-Kappa B activation (which prevents rapid proteolysis of IKB-alpha) will attenuate cerebral (cortical) venular constrictions, leukocyte-endothelial wall interactions and postcapillary damage induced by medium to high concentrations of ethanol in the intact rat brain. Perivascular or i.p. administration of ethanol (100, 250 mg/dl) to the intact rat brain resulted in concentration-dependent venular vasospasm, rolling and adherence of leukocytes to venular walls and rupture of postcapillary venules with focal hemorrhages. Superfusion of the in-situ brain with N(alpha)-L-tosyl-L-phenylalanine chloromethyl ketone (TPCK), a specific inhibitor of IKB-alpha proteolysis, attenuated greatly the spasmogenic, leukocyte rolling-endothelial cell adhesion and postcapillary hemorrhages induced by ethanol. These new data suggest that inhibition of alcohol-inducible degradation of IKB-alpha by TPKC can prevent much of the adverse microvascular actions of ethanol in the intact rat brain. Moreover, these new in-situ results suggest that activation of nuclear factor-Kappa B seems to play a major modulatory role in the adverse cerebral vascular actions of concentrations of alcohol found in the blood of alcohol-intoxicated subjects and human stroke victims.

Sphingomyelinase and ceramide analogs induce vasoconstriction and leukocyte-endothelial interactions in cerebral venules in the intact rat brain: Insight into mechanisms and possible relation to brain injury and stroke

This study was designed to test the hypothesis that the sphingomyelin-ceramide signaling pathway may be important in proinflammatory-like responses in the intact brain. Effects of neutral sphingomyelinase (N-SMase), ceramide analogs, phosphorylcholine and ceramide metabolites were studied on rat brain cerebral (cortical) venule lumen sizes, leukocyte rolling, velocity and endothelial cell wall adhesion, microvessel permeability, microvessel rupture and focal hemorrhages using in vivo high resolution TV microscopy. Perivascular and close intra-arterial administration of N-SMase, C(2)-, C(8)-, and C(16)-ceramide, but not either phosphorylcholine, C(6)-ceramide, nervonic (C(24):1) ceramide, lignoceric (C(24):0) ceramide, C(8)-ceramide-1-phosphate, glucosylceramide or 1-0-acylceramide, resulted in potent, concentration-dependent constriction (and spasm) of cortical venules, followed by increased leukocyte rolling, decreased leukocyte velocities, increased leukocyte-endothelial wall adhesion, increased venular wall permeability, postcapillary venule rupture and, often, micro-hemorrhaging at high concentrations; angiotensin II, serotonin and PGF(2alpha) didn't demonstrate these characteristics. Pretreatment with either one of three different antioxidants, including inhibitors of NF-kappaB activation, or two different Ca(2+) channel blockers either prevented or attenuated the adverse venular effects of N-SMase and the ceramides. Likewise, pretreatment with either a PKCalpha-beta antagonist or a MAP kinase antagonist also attenuated the adverse venular effects. These results suggest that N-SMase and several ceramides can result in potent venular cerebrovasospasm, leukocyte-endothelial chemoattraction, and microvessel wall permeability changes in the intact rat brain. These proinflammatory-like actions suggest that N-SMase and ceramides could produce brain-vascular damage by reperfusion injury triggering lipid peroxidation, release of reactive oxygen species and activation of diverse signaling pathways: PKCalpha-beta isozymes, MAP kinase and NF-kappaB.