Nicotine and estrogen synergistically exacerbate cerebral ischemic injury

Electronic Cigarette Vape Exposure Exacerbates Post-Ischemic Outcomes in Female but Not in Male Rats

BACKGROUND

Nicotine-containing electronic cigarette (EC) vaping has become popular worldwide, and our understanding of the effects of vaping on stroke outcomes is elusive. Using a rat model of transient middle cerebral artery occlusion, the current exploratory study aims to evaluate the sex-dependent effects of EC exposure on brain energy metabolism and stroke outcomes.

METHODS

Adult Sprague-Dawley rats of both sexes were randomly assigned to air/EC vapor (5% nicotine Juul pods) exposure for 16 nights, followed by randomization into 3 cohorts. The first cohort underwent exposure to air/EC preceding randomization to transient middle cerebral artery occlusion (90 minutes) or sham surgery, followed by survival for 21 days. During the survival period, rats underwent sensorimotor and Morris water maze testing. Subsequently, brains were collected for histopathology. A second cohort was exposed to air/EC after which brains were collected for unbiased metabolomics analysis. The third cohort of animals was exposed to air/EC and received transient middle cerebral artery occlusion/sham surgery, and brain tissue was collected 24 hours later for biochemical analysis.

RESULTS

In females, EC significantly increased (P<0.05) infarct volumes by 94% as compared with air-exposed rats, 165±50 mm3 in EC-exposed rats, and 85±29 mm3 in air-exposed rats, respectively, while in males such a difference was not apparent. Morris water maze data showed significant deficits in spatial learning and working memory in the EC sham or transient middle cerebral artery occlusion groups compared with the respective air groups in rats of both sexes (P<0.05). Thirty-two metabolites of carbohydrate, glycolysis, tricarboxylic acid cycle, and lipid metabolism were significantly altered (P≤0.05) due to EC, 23 of which were specific for females. Steady-state protein levels of hexokinase significantly decreased (P<0.05) in EC-exposed females; however, these changes were not seen in males.

CONCLUSIONS

Even brief EC exposure over 2 weeks impacts brain energy metabolism, exacerbates infarction, and worsens poststroke cognitive deficits in working memory more in female than male rats.

Bioinformatics Analysis of Hub Genes Involved in Smoke-Induced Hemifacial Microsomia Pathogenesis

OBJECTIVE

Tobacco smoke is a recognized teratogen, which increases the risk for hemifacial microsomia (HFM) of the fetus during maternal pregnancy. The present study aimed to explore potential mechanisms and verify hub genes of HFM associated with smoke and tobacco smoke pollution (TSP) via bioinformatics methods.

METHODS

Hemifacial microsomia and smoke and TSP pathogenic genes were obtained. A protein-protein interactional (PPI) network was constructed. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses and molecular complex detection were performed by Metascape. Finally, we used the cytoHubba plug-in to screen the hub genes.

RESULTS

A total of 43 HFM genes and 50 optimal smoke candidate genes were selected. Functional enrichment analysis largely focused on tissue morphogenesis and development. Two modules were identified from the PPI network, and 10 hub genes were screened out. The genes most relevant to smoke-induced HFM pathogenesis included TP53 , ESR1 , ESR2 , and HNRNPL.

CONCLUSIONS

This study identified some significant hub genes, pathways, and modules of HFM related to smoke by bioinformatics analyses. Our results suggest that the TP53 , ESR1 , ESR2 , and HNRNPL gene subfamilies may have played a major role in HFM induced by smoke and TSP.

The Impact of Nicotine along with Oral Contraceptive Exposure on Brain Fatty Acid Metabolism in Female Rats

Smoking-derived nicotine (N) and oral contraceptive (OC) synergistically exacerbate ischemic brain damage in females, and the underlying mechanisms remain elusive. In a previous study, we showed that N + OC exposure altered brain glucose metabolism in females. Since lipid metabolism complements glycolysis, the current study aims to examine the metabolic fingerprint of fatty acids in the brain of female rats exposed to N+/-OC. Adolescent and adult Sprague-Dawley female rats were randomly (n = 8 per group) exposed to either saline or N (4.5 mg/kg) +/-OC (combined OC or placebo delivered via oral gavage) for 16-21 days. Following exposure, brain tissue was harvested for unbiased metabolomic analysis (performed by Metabolon Inc., Morrisville, NC, USA) and the metabolomic profile changes were complemented with Western blot analysis of key enzymes in the lipid pathway. Metabolomic data showed significant accumulation of fatty acids and phosphatidylcholine (PC) metabolites in the brain. Adolescent, more so than adult females, exposed to N + OC showed significant increases in carnitine-conjugated fatty acid metabolites compared to saline control animals. These changes in fatty acyl carnitines were accompanied by an increase in a subset of free fatty acids, suggesting elevated fatty acid β-oxidation in the mitochondria to meet energy demand. In support, β-hydroxybutyrate was significantly lower in N + OC exposure groups in adolescent animals, implying a complete shunting of acetyl CoA for energy production via the TCA cycle. The reported changes in fatty acids and PC metabolism due to N + OC could inhibit post-translational palmitoylation of membrane proteins and synaptic vesicle formation, respectively, thus exacerbating ischemic brain damage in female rats.

Red Cell Microparticles Suppress Hematoma Growth Following Intracerebral Hemorrhage in Chronic Nicotine-Exposed Rats

Spontaneous intracerebral hemorrhage (sICH) is a disabling stroke sub-type, and tobacco use is a prominent risk factor for sICH. We showed that chronic nicotine exposure enhances bleeding post-sICH. Reduction of hematoma growth is a promising effective therapy for sICH in smoking subjects. Red-blood-cell-derived microparticles (RMPs) are hemostatic agents that limit hematoma expansion following sICH in naïve rats. Considering the importance of testing the efficacy of experimental drugs in animal models with a risk factor for a disease, we tested RMP efficacy and the therapeutic time window in limiting hematoma growth post-sICH in rats exposed to nicotine. Young rats were chronically treated with nicotine using osmotic pumps. sICH was induced in rats using an injection of collagenase in the right striatum. Vehicle/RMPs were administered intravenously. Hematoma volume and neurological impairment were quantified ≈24 h after sICH. Hematoma volumes in male and female nicotine-exposed rats that were treated with RMPs at 2 h post-sICH were significantly lower by 26 and 31% when compared to their respective control groups. RMP therapy was able to limit hematoma volume when administered up to 4.5 h post-sICH in animals of both sexes. Therefore, RMPs may limit hematoma growth in sICH patients exposed to tobacco use.

Potential Disruption of Systemic Hormone Transport by Tobacco Alkaloids Using Computational Approaches

Tobacco/nicotine is one of the most toxic and addictive substances and continues to pose a significant threat to global public health. The harmful effects of smoking/nicotine affect every system in the human body. Nicotine has been associated with effects on endocrine homeostasis in humans such as the imbalance of gonadal steroid hormones, adrenal corticosteroid hormones, and thyroid hormones. The present study was conducted to characterize the structural binding interactions of nicotine and its three important metabolites, cotinine, trans-3'-hydroxycotinine, and 5'-hydroxycotinine, against circulatory hormone carrier proteins, i.e., sex-hormone-binding globulin (SHBG), corticosteroid-binding globulin (CBG), and thyroxine-binding globulin (TBG). Nicotine and its metabolites formed nonbonded contacts and/or hydrogen bonds with amino acid residues of the carrier proteins. For SHBG, Phe-67 and Met-139 were the most important amino acid residues for nicotine ligand binding showing the maximum number of interactions and maximum loss in ASA. For CBG, Trp-371 and Asn-264 were the most important amino acid residues, and for TBG, Ser-23, Leu-269, Lys-270, Asn-273, and Arg-381 were the most important amino acid residues. Most of the amino acid residues of carrier proteins interacting with nicotine ligands showed a commonality with the interacting residues for the native ligands of the proteins. Taken together, the results suggested that nicotine and its three metabolites competed with native ligands for binding to their carrier proteins. Thus, nicotine and its three metabolites may potentially interfere with the binding of testosterone, estradiol, cortisol, progesterone, thyroxine, and triiodothyronine to their carrier proteins and result in the disbalance of their transport and homeostasis in the blood circulation.

Chronic Nicotine Exposure Increases Hematoma Expansion Following Collagenase-Induced Intracerebral Hemorrhage in Rats

Spontaneous intracerebral hemorrhage (sICH) is a deadly stroke subtype, and tobacco use increases sICH risk. However epidemiological studies show that, there are no confirmatory studies showing the effect of tobacco use on sICH outcome. Therefore, we evaluated the effect of chronic nicotine exposure (as a surrogate for tobacco use) on outcomes following sICH. Young male and female rats were randomly assigned to either nicotine (4.5 mg/kg b.w. per day) or vehicle (saline) treatment (2–3 weeks) groups. sICH was induced by injecting collagenase into the right striatum. Neurological score and hematoma volume were determined 24 h post-sICH. The hematoma volumes in nicotine-treated male and female rats were significantly higher by 42% and 48% when compared to vehicle-treated male and female rats, respectively. Neurological deficits measured in terms of neurological score for the nicotine-treated male and female groups were significantly higher when compared to the respective vehicle-treated male and female groups. Our results show that chronic nicotine exposure increases hematoma volume post-sICH in rats of both sexes. Identifying the mechanism of nicotine-dependent increase in hematoma growth post-sICH will be crucial to understanding the detrimental effect of tobacco use on the severity of bleeding following intracerebral hemorrhage.

Sex Differences in the Nicotinic Acetylcholine Receptor System of Rodents: Impacts on Nicotine and Alcohol Reward Behaviors

Alcohol and nicotine are the two most widely used and misused drugs around the world, and co-consumption of both substances is highly prevalent. Multiple lines of evidence show a profound effect of sex in many aspects of alcohol and nicotine reward, with women having more difficulty quitting smoking and showing a faster progression toward developing alcohol use disorder compared with men. Both alcohol and nicotine require neuronal nicotinic acetylcholine receptors (nAChRs) to elicit rewarding effects within the mesolimbic system, representing a shared molecular pathway that likely contributes to the frequent comorbidity of alcohol and nicotine dependence. However, the majority of preclinical studies on the mechanisms of alcohol and nicotine reward behaviors utilize only male rodents, and thus our understanding of alcohol and nicotine neuropharmacology relies heavily on male data. As preclinical research informs the development and refinement of therapies to help patients reduce drug consumption, it is critical to understand the way biological sex and sex hormones influence the rewarding properties of alcohol and nicotine. In this review, we summarize what is known about sex differences in rodent models of alcohol and nicotine reward behaviors with a focus on neuronal nAChRs, highlighting exciting areas for future research. Additionally, we discuss the way circulating sex hormones may interact with neuronal nAChRs to influence reward-related behavior.

Simultaneous nicotine and oral contraceptive exposure alters brain energy metabolism and exacerbates ischemic stroke injury in female rats

Smoking-derived nicotine (N) and oral contraceptives (OC) synergistically exacerbate ischemic brain damage in the females and underlying mechanisms remain elusive. Our published study showed that N toxicity is exacerbated by OC via altered mitochondrial function owing to a defect in the activity of cytochrome c oxidase. Here, we investigated the global metabolomic profile of brains of adolescent female Sprague-Dawley rats exposed to N ± OC. Rats were randomly exposed to saline or N + /-OC for 16-21 days followed by random allocation into two cohorts. One cohort underwent transient middle cerebral artery occlusion and histopathology was performed 30 days later. From the second cohort, cortical tissues were collected for an unbiased global metabolomic profile. Pathway enrichment analysis showed significant decrease in glucose, glucose 6-phosphate and fructose-6-phosphate, along with a significant increase in pyruvate in the N + /-OC exposed groups when compared to saline (p < 0.05), suggesting alterations in the glycolytic pathway which were confirmed by Western blot analyses of glycolytic enzymes. Infarct volume quantification showed a significant increase following N alone or N + OC as compared to saline control. Because glucose metabolism is critical for brain physiology, altered glycolysis deteriorates neural function, thus exacerbating ischemic brain damage.

Nicotine Exposure Along with Oral Contraceptive Treatment in Female Rats Exacerbates Post-cerebral Ischemic Hypoperfusion Potentially via Altered Histamine Metabolism

Smoking-derived nicotine (N) and oral contraceptives (OCs) synergistically exacerbate ischemic brain damage in the female, and the underlying mechanisms remain elusive. Our published study showed that N toxicity is exacerbated by OC via altered mitochondrial electron transport chain function. Because mitochondria play an important role in cellular metabolism, we investigated the global metabolomic profile of brains of adolescent and adult female Sprague-Dawley rats exposed to N with or without OC (N+/-OC). Rats were randomly exposed to saline or N+/-OC for 16-21 days followed by random allocation into two cohorts. The first cohort was used to characterize the cortical metabolome. Pathway enrichment analysis showed a significant increase in several histamine metabolites including 1-methylhistamine, 1-methyl-4-imidazoleacetate, and 1-ribosyl-imidazleacetate, along with carnosine and homocarnosine in adolescent and adult animals treated with N and N+OC in relation to respective saline controls, which may be reflective of altered histamine metabolism with nicotine treatment. We also observed reduced levels of the neurotransmitters N-acetyl-aspartyl-glutamate (NAAG), gamma-aminobutyrate (GABA), and N-methyl-GABA in N+OC treatment in adolescent animals. The second cohort underwent bilateral carotid artery occlusion and hypotension followed by cerebral blood flow (CBF) assessment a day later. Autoradiographic images of the brain 24 h after ischemic episodes showed severe reduction in cortical and hippocampal local CBF in N+/-OC-exposed rats compared with saline treated. Because GABA and histamine are critical for CBF maintenance, altered metabolism of these neurotransmitters may be responsible for observed severe post-ischemic hypoperfusion, which in turn exacerbates ischemic brain damage.

The peri-menopause in a woman's life: a systemic inflammatory phase that enables later neurodegenerative disease

The peri-menopause or menopausal transition—the time period that surrounds the final years of a woman’s reproductive life—is associated with profound reproductive and hormonal changes in a woman’s body and exponentially increases a woman’s risk of cerebral ischemia and Alzheimer’s disease. Although our understanding of the exact timeline or definition of peri-menopause is limited, it is clear that there are two stages to the peri-menopause. These are the early menopausal transition, where menstrual cycles are mostly regular, with relatively few interruptions, and the late transition, where amenorrhea becomes more prolonged and lasts for at least 60 days, up to the final menstrual period. Emerging evidence is showing that peri-menopause is pro-inflammatory and disrupts estrogen-regulated neurological systems. Estrogen is a master regulator that functions through a network of estrogen receptors subtypes alpha (ER-α) and beta (ER-β). Estrogen receptor-beta has been shown to regulate a key component of the innate immune response known as the inflammasome, and it also is involved in regulation of neuronal mitochondrial function. This review will present an overview of the menopausal transition as an inflammatory event, with associated systemic and central nervous system inflammation, plus regulation of the innate immune response by ER-β-mediated mechanisms.

Structural binding perspectives of a major tobacco alkaloid, nicotine, and its metabolite cotinine with sex-steroid nuclear receptors

Globally, more than a billion people smoke tobacco making it one of the biggest public health problems and a leading risk factor for global deaths. Nicotine, the main alkaloid in tobacco, has been shown to be associated with fertility problems in men and women. The adverse effects of tobacco/nicotine on reproduction have been attributed to deleterious effects on gametes, steroidogenic imbalance, and competitive inhibition of steroid receptors. The present study reports the sex-steroid receptor disrupting potential of nicotine and its major metabolite cotinine against the estrogen receptor-α (ERα), ERβ, androgen receptor (AR), and progesterone receptor (PR). Both ligands bound in the ligand-binding pockets of ERα, ERβ, AR and PR and formed important hydrophobic interactions with different amino-acid residues of receptors. Most of the residues of ERα, ERβ, AR and PR interacting with nicotine and cotinine were common with those of native/bound ligands of the receptors. Interacting amino acids most important for binding of nicotine and cotinine with each receptor were identified by loss in accessible surface area. Amino acids Leucine-346, Leucine-384 and Phenylalanine-404 for ERα; Methionine-336, Phenylalanine-356 and Leucine-298 for ERβ; and Leucine-704 and Leucine-718, respectively for AR and PR, were the most important residues for binding with nicotine and cotinine. Among the four receptors, based on the number of interactions, nicotine and cotinine had greater potential to interfere in the signaling of ERβ. In conclusion, the results suggested that nicotine and cotinine bind and interact with sex-steroid nuclear receptors and have potential to interfere in the steroid hormone signaling resulting in reproductive dysfunction.

Ameliorative effect of nicotine exposure on insulin resistance is accompanied by decreased cardiac glycogen synthase kinase-3 and plasminogen activator inhibitor-1 during oral oestrogen-progestin therapy

CONTEXT

Cigarette smoking is considered to be a major risk factor for the development of diabetes and cardiovascular disease. Oestrogen-progestin combined oral contraceptive (COC) use has been associated with adverse cardiometabolic events.

OBJECTIVE

We hypothesized that nicotine would ameliorate insulin resistance (IR) that is accompanied by decreased cardiac glycogen synthase kinase-3 (GSK-3) and plasminogen activator inhibitor-1 (PAI-1).

METHODS

Female Wistar rats received (po) low-(0.1 mg/kg) or high-nicotine (1.0 mg/kg) with or without COC containing 5.0 µg levonorgestrel plus 1.0 µg ethinylestradiol daily for 8 weeks.

RESULTS

Data showed that COC treatment or nicotine exposure led to IR, glucose deregulation, atherogenic dyslipidemia, increased corticosterone, aldosterone, cardiac and circulating GSK-3 values and PAI-1. However, these effects with the exception of corticosterone and aldosterone were ameliorated in COC + nicotine-exposed rats.

CONCLUSION

Amelioration of IR induced by COC treatment is accompanied by decreased circulating PAI-1, cardiac PAI-1 and GSK-3 instead of circulating aldosterone and corticosterone.

Nicotine Alters Estrogen Receptor-Beta-Regulated Inflammasome Activity and Exacerbates Ischemic Brain Damage in Female Rats

Smoking is a preventable risk factor for stroke and smoking-derived nicotine exacerbates post-ischemic damage via inhibition of estrogen receptor beta (ER-β) signaling in the brain of female rats. ER-β regulates inflammasome activation in the brain. Therefore, we hypothesized that chronic nicotine exposure activates the inflammasome in the brain, thus exacerbating ischemic brain damage in female rats. To test this hypothesis, adult female Sprague-Dawley rats (6–7 months old) were exposed to nicotine (4.5 mg/kg/day) or saline for 16 days. Subsequently, brain tissue was collected for immunoblot analysis. In addition, another set of rats underwent transient middle cerebral artery occlusion (tMCAO; 90 min) with or without nicotine exposure. One month after tMCAO, histopathological analysis revealed a significant increase in infarct volume in the nicotine-treated group (64.24 ± 7.3 mm³; mean ± SEM; n = 6) compared to the saline-treated group (37.12 ± 7.37 mm³; n = 7, p < 0.05). Immunoblot analysis indicated that nicotine increased cortical protein levels of caspase-1, apoptosis-associated speck-like protein containing a CARD (ASC) and pro-inflammatory cytokines interleukin (IL)-1β by 88% (p < 0.05), 48% (p < 0.05) and 149% (p < 0.05), respectively, when compared to the saline-treated group. Next, using an in vitro model of ischemia in organotypic slice cultures, we tested the hypothesis that inhibition of nicotine-induced inflammasome activation improves post-ischemic neuronal survival. Accordingly, slices were exposed to nicotine (100 ng/mL; 14–16 days) or saline, followed by treatment with the inflammasome inhibitor isoliquiritigenin (ILG; 24 h) prior to oxygen-glucose deprivation (OGD; 45 min). Quantification of neuronal death demonstrated that inflammasome inhibition significantly decreased nicotine-induced ischemic neuronal death. Overall, this study shows that chronic nicotine exposure exacerbates ischemic brain damage via activation of the inflammasome in the brain of female rats.

Inhibition of miRNA-210 reverses nicotine-induced brain hypoxic-ischemic injury in neonatal rats

Maternal tobacco use in pregnancy increases the risk of neurodevelopmental disorders and neurobehavioral deficits in postnatal life. The present study tested the hypothesis that perinatal nicotine exposure exacerbated brain vulnerability to hypoxic-ischemic (HI) injury in neonatal rats through up-regulation of miR-210 expression in the developing brain. Nicotine was administered to pregnant rats via subcutaneous osmotic minipumps. Experiments of HI brain injury were performed in 10-day-old pups. Perinatal nicotine treatment significantly decreased neonatal body and brain weights, but increased the brain to body weight ratio. Perinatal nicotine exposure caused a significant increase in HI brain infarct size in the neonates. In addition, nicotine enhanced miR-210 expression and significantly attenuated brain-derived neurotrophic factor (BDNF) and tropomyosin-related kinase isoform B (TrkB) protein abundance in the brain. Of importance, intracerebroventricular administration of a miR-210 inhibitor (miR-210-LNA) significantly decreased HI-induced brain infarct size and reversed the nicotine-increased vulnerability to brain HI injury in the neonate. Furthermore, miR-210-LNA treatment also reversed nicotine-mediated down-regulation of BDNF and TrkB protein expression in the neonatal brains. These findings provide novel evidence that the increased miR-210 plays a causal role in perinatal nicotine-induced developmental programming of ischemic sensitive phenotype in the brain. It represents a potential novel therapeutic approach for treatment of brain hypoxic-ischemic encephalopathy in the neonate-induced by fetal stress.

Periodic Estrogen Receptor-Beta Activation: A Novel Approach to Prevent Ischemic Brain Damage

In women, the risk for cerebral ischemia climbs rapidly after menopause. At menopause, production of ovarian hormones; i.e., progesterone and estrogen, slowly diminishes. Estrogen has been suggested to confer natural protection to premenopausal women from ischemic stroke and some of its debilitating consequences. This notion is also strongly supported by laboratory studies showing that a continuous chronic 17β-estradiol (E2; a potent estrogen) regimen protects brain from ischemic injury. However, concerns regarding the safety of the continuous intake of E2 were raised by the failed translation to the clinic. Recent studies demonstrated that repetitive periodic E2 pretreatments, in contrast to continuous E2 treatment, provided neuroprotection against cerebral ischemia in ovariectomized rats. Periodic E2 pretreatment protects hippocampal neurons through activation of estrogen receptor subtype beta (ER-β). Apart from neuroprotection, periodic activation of ER-β in ovariectomized rats significantly improves hippocampus-dependent learning and memory. Difficulties in learning and memory loss are the major consequence of ischemic brain damage. Periodic ER-β agonist pretreatment may provide pharmacological access to a protective state against ischemic stroke and its debilitating consequences. The use of ER-β-selective agonists constitutes a safer target for future research than ER-α agonist or E2, inasmuch as it lacks the ability to stimulate the proliferation of breast or endometrial tissue. In this review, we highlight ER-β signaling as a guide for future translational research to reduce cognitive decline and cerebral ischemia incidents/impact in post-menopausal women, while avoiding the side effects produced by chronic E2 treatment.

Preconditioning provides neuroprotection in models of CNS disease: paradigms and clinical significance

Preconditioning is a phenomenon in which brief episodes of a sublethal insult induce robust protection against subsequent lethal injuries. Preconditioning has been observed in multiple organisms and can occur in the brain as well as other tissues. Extensive animal studies suggest that the brain can be preconditioned to resist acute injuries, such as ischemic stroke, neonatal hypoxia/ischemia, surgical brain injury, trauma, and agents that are used in models of neurodegenerative diseases, such as Parkinson's disease and Alzheimer's disease. Effective preconditioning stimuli are numerous and diverse, ranging from transient ischemia, hypoxia, hyperbaric oxygen, hypothermia and hyperthermia, to exposure to neurotoxins and pharmacological agents. The phenomenon of "cross-tolerance," in which a sublethal stress protects against a different type of injury, suggests that different preconditioning stimuli may confer protection against a wide range of injuries. Research conducted over the past few decades indicates that brain preconditioning is complex, involving multiple effectors such as metabolic inhibition, activation of extra- and intracellular defense mechanisms, a shift in the neuronal excitatory/inhibitory balance, and reduction in inflammatory sequelae. An improved understanding of brain preconditioning should help us identify innovative therapeutic strategies that prevent or at least reduce neuronal damage in susceptible patients. In this review, we focus on the experimental evidence of preconditioning in the brain and systematically survey the models used to develop paradigms for neuroprotection, and then discuss the clinical potential of brain preconditioning.

Periodic 17β-estradiol pretreatment protects rat brain from cerebral ischemic damage via estrogen receptor-β

Although chronic 17β-estradiol (E2) has been shown to be a cognition-preserving and neuroprotective agent in animal brain injury models, concern regarding its safety was raised by the failed translation of this phenomenon to the clinic. Previously, we demonstrated that a single bolus of E2 48 hr prior to ischemia protected the hippocampus from damage in ovariectomized rats via phosphorylation of cyclic-AMP response element binding protein, which requires activation of estrogen receptor subtype beta (ER-β). The current study tests the hypothesis that long-term periodic E2-treatment improves cognition and reduces post-ischemic hippocampal injury by means of ER-β activation. Ovariectomized rats were given ten injections of E2 at 48 hr intervals for 21 days. Hippocampal-dependent learning, memory and ischemic neuronal loss were monitored. Results demonstrated that periodic E2 treatments improved spatial learning, memory and ischemic neuronal survival in ovariectomized rats. Additionally, periodic ER-β agonist treatments every 48 hr improved post-ischemic cognition. Silencing of hippocampal ER-β attenuated E2-mediated ischemic protection suggesting that ER-β plays a key role in mediating the beneficial effects of periodic E2 treatments. This study emphasizes the need to investigate a periodic estrogen replacement regimen to reduce cognitive decline and cerebral ischemia incidents/impact in post-menopausal women.

Oral contraceptives and nicotine synergistically exacerbate cerebral ischemic injury in the female brain

Oral contraceptives (OC) and smoking-derived nicotine (N) are known to synergistically increase the risk and severity of cerebral ischemia in women. Although it has been known for some time that long-term use of OC and nicotine will have an increased risk of peripheral thrombus formation, little is known about how the combination of OC and nicotine increases severity of brain ischemia. Recent laboratory studies simulating the conditions of nicotine exposure produced by cigarette smoking and OC regimen of women in female rats confirms that the severity of ischemic hippocampal damage is far greater in female rats simultaneously exposed to OC than to nicotine alone. These studies also demonstrated that the concurrent exposure of OC and nicotine reduces endogenous 17β-estradiol levels and inhibits estrogen signaling in the brain of female rats. The endogenous 17β-estradiol plays a key role in cerebrovascular protection in women during their pre-menopausal life and loss of circulating estrogen at reproductive senescence increases both the incidence and severity of cerebrovascular diseases. Therefore, OC and nicotine induced severe post-ischemic damage might be a consequence of lack of estrogen signaling in the brain. In the present review we highlight possible mechanisms by which OC and nicotine inhibits estrogen signaling that could be responsible for severe ischemic damage in females.

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.

Chronic nicotine exposure inhibits estrogen-mediated synaptic functions in hippocampus of female rats

Nicotine, the addictive agent in cigarettes, reduces circulating estradiol-17β (E₂) and inhibits E₂-mediated intracellular signaling in hippocampus of female rats. In hippocampus, E₂-signaling regulates synaptic plasticity by phosphorylation of the N-methyl-D-aspartic acid receptor subunit NR2B and cyclic-AMP response element binding protein (pCREB). Therefore, we hypothesized that chronic nicotine exposure induces synaptic dysfunction in hippocampus of female rats. Female rats were exposed to nicotine or saline for 16 days followed by electrophysiological analysis of hippocampus. Briefly, population measurements of excitatory post-synaptic field potentials (fEPSPs) were recorded from stratum radiatum of the CA1 hippocampal slice subfield. A strict software-controlled protocol was used which recorded 30 min of baseline data (stimulation rate of 1/min), a paired-pulse stimulation sequence followed by tetanic stimulation, and 1h of post-tetanus recording. EPSP amplitude and the initial EPSP slope were measured off-line. We then investigated by Western blot analysis the effects of nicotine on hippocampal estrogen receptor-beta (ER-β), NR2B and pCREB. The results demonstrated significantly decreased post-tetanic potentiation and paired-pulse facilitation at the 40, and 80 ms interval in nicotine-exposed rats compared to the saline group. Western blot analysis revealed that nicotine decreased protein levels of ER-β, NR2B, and pCREB. We also confirmed the role of E₂ in regulating NR2B and pCREB phosphorylation by performing Western blots in hippocapmal tissue obtained from E₂-treated ovariectomized rats. In conclusion, chronic nicotine exposure attenuates short-term synaptic plasticity, and the observed synaptic defects might be a consequence of loss of estradiol-17β-signaling. However, determining the exact molecular mechanisms of chronic nicotine exposure on synaptic plasticity specific to the female brain require further investigation.