Tobacco smoke: a critical etiological factor for vascular impairment at the blood-brain barrier

Personally Modifiable Risk Factors Associated with Pediatric Hearing Loss: A Systematic Review

BACKGROUND

Pediatric hearing loss is an increasingly recognized problem with significant implications. Increasing our quantitative understanding of potentially modifiable environmental risk factors for hearing loss may form the foundation for prevention and screening programs.

OBJECTIVE

To determine whether specific threshold exposure levels of personally modifiable risk factors for hearing loss have been defined, with the overarching goal of providing actionable guidance for the prevention of pediatric hearing loss.

DATA SOURCES

A systematic review was performed. Computerized searches of PubMed, EMBASE, and the Cochrane Library were completed and supplemented with manual searches.

REVIEW METHODS

Inclusion/exclusion criteria were designed to determine specific threshold values of personally modifiable risk factors on hearing loss in the pediatric population. Searches and data extraction were performed by independent reviewers.

RESULTS

There were 38 criterion-meeting studies, including a total of 50,651 subjects. Threshold noise exposures significantly associated with hearing loss in youth included: (1) more than 4 hours per week or more than 5 years of personal headphone usage, (2) more than 4 visits per month to a discotheque, and (3) working on a mechanized farm. Quantified tobacco levels of concern included any level of in utero smoke exposure as well as secondhand exposure sufficient to elevate serum cotinine.

CONCLUSIONS

Specific thresholds analyses are limited. Future studies would ideally focus on stratifying risk according to clearly defined levels of exposure, in order to provide actionable guidance for children and families.

Vorinostat positively regulates synaptic plasticity genes expression and spine density in HIV infected neurons: role of nicotine in progression of HIV-associated neurocognitive disorder

Background

HIV-associated neurocognitive disorder (HAND) is characterized by development of cognitive, behavioral and motor abnormalities, and occurs in approximately 50% of HIV infected individuals. In the United States, the prevalence of cigarette smoking ranges from 35-70% in HIV-infected individuals compared to 20% in general population. Cognitive impairment in heavy cigarette smokers has been well reported. However, the synergistic effects of nicotine and HIV infection and the underlying mechanisms in the development of HAND are unknown.

Results

In this study, we explored the role of nicotine in the progression of HAND using SK-N-MC, a neuronal cell line. SK-N-MC cells were infected with HIV-1 in the presence or absence of nicotine for 7 days. We observed significant increase in HIV infectivity in SK-N-MC treated with nicotine compared to untreated HIV-infected neuronal cells. HIV and nicotine synergize to significantly dysregulate the expression of synaptic plasticity genes and spine density; with a concomitant increase of HDAC2 levels in SK-N-MC cells. In addition, inhibition of HDAC2 up-regulation with the use of vorinostat resulted in HIV latency breakdown and recovery of synaptic plasticity genes expression and spine density in nicotine/HIV alone and in co-treated SK-N-MC cells. Furthermore, increased eIF2 alpha phosphorylation, which negatively regulates eukaryotic translational process, was observed in HIV alone and in co-treatment with nicotine compared to untreated control and nicotine alone treated SK-N-MC cells.

Conclusions

These results suggest that nicotine and HIV synergize to negatively regulate the synaptic plasticity gene expression and spine density and this may contribute to the increased risk of HAND in HIV infected smokers. Apart from disrupting latency, vorinostat may be a useful therapeutic to inhibit the negative regulatory effects on synaptic plasticity in HIV infected nicotine abusers.

Oxidative and pro-inflammatory impact of regular and denicotinized cigarettes on blood brain barrier endothelial cells: is smoking reduced or nicotine-free products really safe?

Background

Both active and passive tobacco smoke (TS) potentially impair the vascular endothelial function in a causative and dose-dependent manner, largely related to the content of reactive oxygen species (ROS), nicotine, and pro-inflammatory activity. Together these factors can compromise the restrictive properties of the blood–brain barrier (BBB) and trigger the pathogenesis/progression of several neurological disorders including silent cerebral infarction, stroke, multiple sclerosis and Alzheimer’s disease. Based on these premises, we analyzed and assessed the toxic impact of smoke extract from a range of tobacco products (with varying levels of nicotine) on brain microvascular endothelial cell line (hCMEC/D3), a well characterized human BBB model.

Results

Initial profiling of TS showed a significant release of reactive oxygen (ROS) and reactive nitrogen species (RNS) in full flavor, nicotine-free (NF, “reduced-exposure” brand) and ultralow nicotine products. This release correlated with increased oxidative cell damage. In parallel, membrane expression of endothelial tight junction proteins ZO-1 and occludin were significantly down-regulated suggesting the impairment of barrier function. Expression of VE-cadherin and claudin-5 were also increased by the ultralow or nicotine free tobacco smoke extract. TS extract from these cigarettes also induced an inflammatory response in BBB ECs as demonstrated by increased IL-6 and MMP-2 levels and up-regulation of vascular adhesion molecules, such as VCAM-1 and PECAM-1.

Conclusions

In summary, our results indicate that NF and ultralow nicotine cigarettes are potentially more harmful to the BBB endothelium than regular tobacco products. In addition, this study demonstrates that the TS-induced toxicity at BBB ECs is strongly correlated to the TAR and NO levels in the cigarettes rather than the nicotine content.

Neuropathology of cigarette smoking

It is well established that cigarette smoking is hazardous to health and is a risk factor for many chronic diseases. However, its impact on the brain, whether it be from prenatal exposure to maternal cigarette smoking, cerebrovascular disease, Alzheimer's disease (AD) or Parkinson's disease, is still not very clear. Neuroimaging and neuropathological investigations suggest that there are heterogeneous effects of cigarette smoking on the brain. On the one hand, it is quite clear that cigarette smoking causes damage to endothelial cells, resulting in increased risk of cerebrovascular disease. On the other hand, it seems to be associated with different Alzheimer's pathologies in post-mortem brains and experimental models, despite the fact that epidemiological studies clearly indicate a positive correlation between cigarette smoking and increased risk for AD. Interestingly, cigarette smoking appears to be associated with reduced Parkinson's pathology in post-mortem brains. However, although nicotine in cigarettes may have some neuroprotective actions, the effects of all the other toxic compounds in cigarettes cannot be ignored. It is, therefore, our aim to summarize what is known about the neuropathology of cigarette smoking and, in particular, its implications for neurodegenerative diseases.

Cigarette smoke and inflammation: role in cerebral aneurysm formation and rupture

Smoking is an established risk factor for subarachnoid hemorrhage yet the underlying mechanisms are largely unknown. Recent data has implicated a role of inflammation in the development of cerebral aneurysms. Inflammation accompanying cigarette smoke exposure may thus be a critical pathway underlying the development, progression, and rupture of cerebral aneurysms. Various constituents of the inflammatory response appear to be involved including adhesion molecules, cytokines, reactive oxygen species, leukocytes, matrix metalloproteinases, and vascular smooth muscle cells. Characterization of the molecular basis of the inflammatory response accompanying cigarette smoke exposure will provide a rational approach for future targeted therapy. In this paper, we review the current body of knowledge implicating cigarette smoke-induced inflammation in cerebral aneurysm formation/rupture and attempt to highlight important avenues for future investigation.

Nicotine enhances proliferation, migration, and radioresistance of human malignant glioma cells through EGFR activation

It has been suggested that continued tobacco use during radiation therapy contributes to maintenance of neoplastic growth despite treatment with radiation. Nicotine is a cigarette component that is an established risk factor for many diseases, neoplastic and otherwise. The hypothesis of this work is that nicotine promotes the proliferation, migration, and radioresistance of human malignant glioma cells. The effect of nicotine on cellular proliferation, migration, signaling, and radiation sensitivity were evaluated for malignant glioma U87 and GBM12 cells by use of the AlamarBlue, scratch healing, and clonogenic survival assays. Signal transduction was assessed by immunoblotting for activated EGFR, ERK, and AKT. At concentrations comparable with those found in chronic smokers, nicotine induced malignant glioma cell migration, growth, colony formation, and radioresistance. Nicotine increased phosphorylation of EGFR(tyr992), AKT(ser473), and ERK. These molecular effects were reduced by pharmacological inhibitors of EGFR, PI3K, and MEK. It was therefore concluded that nicotine stimulates the malignant behavior of glioma cells in vitro by activation of the EGFR and downstream AKT and ERK pathways.

Secondhand smoke and sensorineural hearing loss in adolescents

OBJECTIVE

To investigate the hypothesis that second-hand smoke (SHS) exposure is associated with sensorineural hearing loss (SNHL) in adolescents.

DESIGN

A complex, multistage, stratified geographic area design for collecting representative data from the noninstitutionalized US population.

PARTICIPANTS

Cross-sectional data from National Health and Nutrition Examination Survey (2005-2006) were available for 1533 participants 12 to 19 years of age who underwent audiometric testing, had serum cotinine levels available, and were not actively smoking.

MAIN OUTCOME MEASURES

SNHL was defined as an average pure-tone level greater than 15 dB for 0.5, 1, and 2 kHz (low frequency) and 3, 4, 6, and 8 kHz (high frequency).

RESULTS

Secondhand smoke exposure, as assessed by serum cotinine levels, was associated with elevated pure-tone hearing thresholds at 2, 3, and 4 kHz, a higher rate of unilateral low-frequency SNHL (11.8% vs 7.5%; P < .04), and a 1.83-fold increased risk of unilateral low-frequency SNHL in multivariate analyses (95% confidence interval, 1.08-3.41). The prevalence of SNHL was directly related to level of SHS exposure as reflected by serum cotinine levels. In addition, nearly 82% of adolescents with SNHL did not recognize hearing difficulties.

CONCLUSIONS

Secondhand smoke is associated with elevated pure-tone thresholds and an increased prevalence of low-frequency SNHL that is directly related to level of exposure, and most affected individuals are unaware of the hearing loss. Thus, adolescents exposed to SHS may need to be closely monitored for early hearing loss with periodic audiologic testing.

In vitro assessment of tobacco smoke toxicity at the BBB: do antioxidant supplements have a protective role?

BACKGROUND

Tobacco smoke (TS) contains highly reactive oxygen species (such as hydrogen peroxide, peroxynitrite, etc), which cause oxidative damage in vascular tissue and may exacerbate inflammatory events leading to the blood-brain barrier damage (BBBD) which accompanies the development of a variety of neurological disorders. Smokers often have elevated leukocyte counts (primarily neutrophils and monocytes), and significant decreases in plasma alpha-tocopherol (vitamin E) and ascorbic acid (vitamin C) levels due to increased anti-oxidative mobilization in response to oxidative stress evoked by TS. For this purpose, using static culture systems and a well-established dynamic in vitro BBB model (DIV-BBB) we tested the hypothesis that antioxidant vitamin supplementation (E and/or C) can protect the BBB during exposure to whole soluble TS.

RESULTS

TS exacerbates inflammatory events and leads to endothelial overexpression of vascular adhesion molecules (VCAM-1, P-selectin and E-selectin), release of pro-inflammatory cytokines (TNF-α and IL-6) and nitric oxide (NO), release and activation of matrix metalloproteinases (MMP-2 and MMP-9), monocytic maturation into macrophages, and adhesion to the vascular endothelium. Furthermore, TS altered the normal glucose metabolic behaviour of in vitro BBB capillaries and caused a period of transient anaerobic respiration to meet the cellular bioenergetic demand. Pre-treatment with antioxidant vitamins (C and/or E) effectively reduced the pro-inflammatory activity associated with TS, protecting the viability and functions of the BBB.

CONCLUSION

Our results have shown that loss of endothelial viability as well as BBB function and integrity caused by TS exposure can be prevented or at least reduced by normal physiologic concentrations of antioxidant vitamins in vitro.

Nicotine aggravates the brain postischemic inflammatory response

A substantial body of evidence suggests that nicotine adversely affects cerebral blood flow and the blood-brain barrier and is a risk factor for stroke. The present study investigated the effect of nicotine on cerebrovascular endothelium under basal and ischemia/reperfusion injury under in vivo condition. Nicotine (2 mg/kg sc) was administered to mice over 14 days, which resulted in plasma nicotine levels of ∼100 ng/ml, reflecting plasma concentrations in average to heavy smokers. An analysis of the phenotype of isolated brain microvessels after nicotine exposure indicated higher expression of inflammatory mediators, cytokines (IL-1β, TNF-α, and IL-18), chemokines (CCL2 and CX(3)CL1), and adhesion molecules (ICAM-1, VCAM-1, and P-selectins), and this was accompanied by enhanced leukocyte infiltration into brain during ischemia/reperfusion (P < 0.01). Nicotine had a profound effect on ischemia/reperfusion injury; i.e., increased brain infarct size (P < 0.01), worse neurological deficits, and a higher mortality rate. These experiments illuminate, for the first time, how nicotine regulates brain endothelial cell phenotype and postischemic inflammatory response at the brain-vascular interface.

Pathophysiological impact of cigarette smoke exposure on the cerebrovascular system with a focus on the blood-brain barrier: expanding the awareness of smoking toxicity in an underappreciated area

Recent evidence has indicated that active and passive cigarette smoking are associated, in a dose-dependent manner, with dysfunction of normal endothelial physiology. Tobacco smoke (TS) may predispose individuals to atherogenic and thrombotic problems, significantly increasing the risk for ischemic manifestations such as acute coronary syndrome and stroke. Despite the strong evidence for an association between smoking and vascular impairment, the impact of TS exposure on the blood-brain barrier (BBB) has only been marginally addressed. This is a major problem given that the BBB is crucial in the maintenance of brain homeostasis. Recent data have also shown that chronic smokers have a higher incidence of small vessel ischemic disease (SVID), a pathological condition characterized by leaky brain microvessels and loss of BBB integrity. In the brain TS increases the risk of silent cerebral infarction (SCI) and stroke owing to the pro-coagulant and atherogenic effects of smoking. In this article we provide a detailed review and analysis of current knowledge of the pathophysiology of tobacco smoke toxicity at the cerebrovascular levels. We also discuss the potential toxicity of recently marketed “potential-reduced exposure products”.

Neutrophils block permeability increases induced by oxygen glucose deprivation in a culture model of the human blood-brain barrier

Experimentally, oxygen glucose deprivation (OGD) has been widely used to mimic the environmental conditions present during cerebral ischemia-reperfusion (IR) injury. OGD is known to increase permeability across cultured cerebral endothelial cells, which models the effect of IR on permeability across the blood-brain barrier (BBB); however, studies have yet to be performed in a human model. The effect of neutrophils on the increase in BBB permeability associated with IR injury has yet to be modeled in vitro. To address these questions, the human brain endothelial cell line hCMEC/D3 was exposed to OGD with reoxygenation, and permeability was measured for a range of OGD exposure times (1-24h). One hour of exposure to OGD induced a reversible increase in permeability, unassociated with cytotoxicity (assessed from lactate dehydrogenase release). However, 12-24h OGD exposures induced sustained increases in permeability associated with cytotoxicity. The 1h permeability increase was inhibited with the nitric oxide synthase inhibitors l-NAME (10(-)(7)mol/l) and 1400W (10(-)(7)mol/l). Neutrophils (5x10(6)/ml) blocked the permeability increase associated with 1h OGD, whether applied during or after OGD exposure. Permeability remained low if neutrophils were activated with leukotriene (Lt)B(4) (10(-)(7)mol/l) or exposed to a transendothelial gradient of LtB(4), while neutrophil activation with phorbyl myristate acetate (4x10(-)(8)mol/l) induced a small increase. Neutrophils had no effect on the permeability increase induced by 12h OGD exposure. This study finds that OGD induces reversible increases in permeability linked to nitric oxide synthesis in a human culture model of the BBB and shows that neutrophils mitigate permeability increases in this context.