Nicotine impairs endothelium-dependent dilatation in human veins in vivo

Acute infusion of nicotine impairs nNOS-dependent reactivity of cerebral arterioles via an increase in oxidative stress

Our goals were to determine whether acute exposure to nicotine alters neuronal nitric oxide synthase (nNOS)-dependent reactivity of cerebral arterioles and to identify a potential role for oxidative stress in nicotine-induced impairment in nNOS-dependent responses of cerebral arterioles. We measured in vivo diameter of cerebral arterioles to nNOS-dependent (N-methyl-d-aspartate and kainate) and -independent (nitroglycerin) agonists before and during acute treatment with nicotine. We found that nNOS-dependent, but not -independent, vasodilatation was impaired during treatment with nicotine. In addition, treatment of the cerebral microcirculation with tempol (1 h before infusion of nicotine) prevented nicotine-induced impairment in nNOS-dependent vasodilatation. Furthermore, the production of superoxide anion (lucigenin chemiluminescence) was increased in parietal cortex tissue of rats by treatment with nicotine, and this increase in superoxide anion production could be inhibited by tempol. Our findings suggest that acute exposure to nicotine impairs nNOS-dependent dilatation of cerebral arterioles by a mechanism that appears to be related to the formation of superoxide anion.

Cigarette smoking as a risk factor for atherosclerosis and renal disease: novel pathogenic insights

Cigarette smoking is the major cause of preventable morbidity and mortality in the United States. It is a major risk factor for atherosclerotic vascular disease and recently was identified as an important risk factor in the progression of chronic kidney disease. Several compounds in cigarette smoke, including nicotine and reactive aldehydes (eg, acrolein), have been implicated as mediators of endothelial dysfunction and atherosclerosis in smokers. In addition, studies have demonstrated that nicotine induces endothelial dysfunction in humans and accelerates atherosclerosis in animals. Large clinical trials have suggested that cigarette smoking is a risk factor for progression of chronic kidney disease in diabetics and nondiabetics, and in polycystic kidney disease, lupus nephritis, and IgA nephropathy. Recent studies suggest that nicotine has powerful mitogenic effects and induces extracellular matrix production in human mesangial cells via reactive oxygen species generation. These effects of nicotine may play a major role in the pathogenic mechanisms that mediate the deleterious effects of smoking in renal disease.

Nicotine-induced activation of AMP-activated protein kinase inhibits fatty acid synthase in 3T3L1 adipocytes: a role for oxidant stress

Recent studies suggest that the AMP-activated protein kinase (AMPK) acts as a major energy sensor and regulator in adipose tissues. The objective of this study was to investigate the role of AMPK in nicotine-induced lipogenesis and lipolysis in 3T3L1 adipocytes. Exposure of 3T3L1 adipocytes to smoking-related concentrations of nicotine increased lipolysis and inhibited fatty acid synthase (FAS) activity in a time- and dose-dependent manner. The effects of nicotine on FAS activity were accompanied by phosphorylation of both AMPK (Thr(172)) and acetyl-CoA carboxylase (ACC; Ser(79)). Nicotine-induced AMPK phosphorylation appeared to be mediated by reactive oxygen species based on the finding that nicotine significantly increased superoxide anions and 3-nitrotyrosine-positive proteins, exogenous peroxynitrite (ONOO(-)) mimicked the effects of nicotine on AMPK, and N-acetylcysteine (NAC) abolished nicotine-enhanced AMPK phosphorylation. Inhibition of AMPK using either pharmacologic (insulin, compound C) or genetic means (overexpression of dominant negative AMPK; AMPK-DN) abolished FAS inhibition induced by nicotine or ONOO(-). Conversely, activation of AMPK by pharmacologic (nicotine, ONOO(-), metformin, and AICAR) or genetic (overexpression of constitutively active AMPK) means inhibited FAS activity. Notably, AMPK activation increased threonine phosphorylation of FAS, and this effect was blocked by adenovirus encoding dominant negative AMPK. Finally, AMPK-dependent FAS phosphorylation was confirmed by (32)P incorporation into FAS in adipocytes. Taken together, our results strongly suggest that nicotine, via ONOO(-) activates AMPK, resulting in enhanced threonine phosphorylation and consequent inhibition of FAS.

Blood pressure circadian rhythm and endothelial function in heavy smokers: acute effects of transdermal nicotine

Nicotine replacement therapy appears to be safe when used by healthy patients to aid in smoking cessation; however, the immediate acute effects of nicotine replacement therapy on the circadian rhythm of blood pressure (BP) and endothelial function in heavy smokers are not well understood. Twenty-six heavy smokers were requested to stop smoking for 48 hours. BP and heart rate were recorded over 48 hours by ambulatory BP monitoring, with beat-to-beat changes being monitored for the first 10 hours by a noninvasive finger device. The reactivity of the brachial artery was evaluated using flow-mediated dilation immediately after smoking cessation, before the application of a 21-mg nicotine patch or placebo patch, and 24 hours after patch placement. Transdermal nicotine caused a mild but significant elevation in BP in the early morning in 21 of 26 volunteers. The decrease in nocturnal BP was attenuated in patients with the nicotine patch compared with the placebo patch; this was associated with impaired endothelium-dependent vasodilation.

Thromboangiitis obliterans (Buerger's disease): searching for a therapeutic strategy

Treatment of thromboangiitis obliterans (Buerger's disease) includes both surgical and nonsurgical approaches, or a combination of both. A definite therapeutic approach has not yet been set. This article reviews the proposed therapeutic strategies and considers the advantages and disadvantages of each treatment. Cessation of smoking seems to be the only globally accepted therapeutic measure to prevent disease progression. A number of promising novel therapeutic strategies may prove useful for the treatment of this physically and socially mutilating disease.

Distinct effects of acute and chronic nicotine application on microvascular thrombus formation and endothelial function in male and female mice

BACKGROUND AND AIMS

Cigarette smoking is linked to thromboembolic events; however, a relationship between nicotine exposition and thrombosis has not been established. Thus, we intended to study the effect of acute and chronic nicotine application in an in vivo mouse model.

MATERIALS AND METHODS

In microvessels of the dorsal skin fold chamber, light-dye-induced thrombus formation was analyzed using intravital fluorescence microscopy. Male and female C57BL/6J mice received nicotine chronically via the drinking water (100 microg/ml) for 8 weeks. An additional series of experiments was performed with acute iv nicotine treatment (3 mg/kg body weight).

RESULTS

No significant differences in microvascular thrombus formation were detected after chronic nicotine application in male and female animals when compared with controls. Accordingly, flow cytometric analysis did not show significant effects on platelet activity. Chronic nicotine treatment resulted in a significantly reduced endothelial activation in male, but not in female mice. In contrast, acute iv application of nicotine revealed significantly shorter thrombosis times in arterioles of female mice and a significantly increased endothelial P-selectin expression in mice of both genders.

CONCLUSION

Chronic nicotine application does not promote microvascular thrombus formation in mice of either gender, whereas acute high-dose iv administration caused a significant increase of arteriolar thrombosis in female animals probably via a synergistic effect of increased endothelial P-selectin expression and female hormone levels. A gender-dependency of acute nicotine action can be presumed.

A Clinical Imperative: Assisting Patients Who Smoke to Reduce Their Risk of Cardiovascular Disease

The role of tobacco smoking as a cause of cardiovascular disease is now unequivocal and well-documented in literally hundreds of epidemiologic and biomedical studies over the past 50 years. Cessation of smoking, on the other hand, swiftly and profoundly reduces the risks of a cardiovascular event. Thus, smoking cessation should be seen as perhaps the most effective lifesaving intervention in the physician's armamentarium. Despite this widely available knowledge, and evidence that most smokers want to quit, relatively few physicians offer cessation support to their smoking patients, even those at high risk for a cardiovascular event. This article reviews the links between tobacco smoking and cardiovascular disease, argues for a greater role for physicians in assisting smokers to quit, and highlights the most effective interventions currently available.

Potentially reduced exposure cigarettes accelerate atherosclerosis: evidence for the role of nicotine

The tobacco industry markets potentially reduced exposure products (PREPs) as less harmful or addictive alternatives to conventional cigarettes. This study compared the effects of mainstream smoke from Quest, Eclipse, and 2R4F reference cigarettes on the development of atherosclerosis in apolipoprotein E-deficient (apoE -/-) mice. Mice were exposed to smoke from four cigarette types for 12 weeks beginning at age of 12 weeks, and in a separate study for 8 weeks, beginning at age of 8 weeks. In both studies, mice exposed to smoke from high-nicotine, high-tar Quest 1, and 2R4F cigarettes developed greater areas of lipid-rich aortic lesions than did non-smoking controls. Exposure to smoke from the lower-nicotine products, Eclipse, and Quest 3, was associated with smaller lesion areas, but animals exposed to smoke from all of the tested types of cigarette had larger lesions than did control animals not exposed to smoke. Urinary levels of isoprostane F2 alpha VI, increased proportionally to cigarette nicotine yield, whereas induction of pulmonary cytochrome P4501A1 was proportional to tar yield. Lesion area was associated with both nicotine and tar yields, although in multiple regression analysis only nicotine was a significant predictor of lesion area. Smoke exposure did not alter systolic blood pressure (SBP), heart rate (HR), blood cholesterol, or leukocyte count. Taken together, these observations suggest that smoking may accelerate atherosclerosis by increasing oxidative stress mediated at least in part via the actions of nicotine.

Schizophrenia and the alpha7 nicotinic acetylcholine receptor

In addition to the devastating symptoms of psychosis, many people with schizophrenia also suffer from cognitive impairment. These cognitive symptoms lead to marked dysfunction and can impact employability, treatment adherence, and social skills. Deficits in P50 auditory gating are associated with attentional impairment and may contribute to cognitive symptoms and perceptual disturbances. This nicotinic cholinergic-mediated inhibitory process represents a potential new target for therapeutic intervention in schizophrenia. This chapter will review evidence implicating the nicotinic cholinergic, and specifically, the alpha7 nicotinic receptor system in the pathology of schizophrenia. Impaired auditory sensory gating has been linked to the alpha7 nicotinic receptor gene on the chromosome 15q14 locus. A majority of persons with schizophrenia are heavy smokers. Although nicotine can acutely reverse diminished auditory sensory gating in people with schizophrenia, this effect is lost on a chronic basis due to receptor desensitization. The alpha7 nicotinic agonist 3-(2,4 dimethoxy)benzylidene-anabaseine (DMXBA) can also enhance auditory sensory gating in animal models. DMXBA is well tolerated in humans and a new study in persons with schizophrenia has found that DMXBA enhances both P50 auditory gating and cognition. alpha7 Nicotinic acetylcholine receptor agonists appear to be viable candidates for the treatment of cognitive disturbances in schizophrenia.

Involvement of DDAH/ADMA/NOS pathway in nicotine-induced endothelial dysfunction

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase (NOS) inhibitor, is a key contributor for endothelial dysfunction. Decrease in activity of dimethylarginine dimethylaminohydrolase (DDAH), a major hydrolase of ADMA, causes accumulation of ADMA under cardiovascular abnormalities. The study was to determine whether nicotine-induced endothelial dysfunction is related to modulating DDAH/ADMA/NOS pathway. Four-week oral nicotine treatment (5 mg/kg/day) significantly increased the plasma level of ADMA and decreased aortic DDAH expression as well as impaired endothelial function in Sprague-Dawley rats. Similarly, the medium levels of both ADMA and lactate dehydrogenase were markedly elevated in umbilical vein endothelial cells (HUVECs) treated with nicotine (10 microM) for 48 h. Nicotine-induced endothelial damages were markedly attenuated by L-arginine or overexpression of DDAH-II. Nicotine greatly downregulated both mRNA and protein levels of DDAH-II, and decreased DDAH activity in HUVECs. HUVECs express alpha7 nicotinic acetylcholine receptor (alpha7 nAChR), whose antagonists could block these effects of nicotine mentioned above. Intracellular Ca2+ chelator did not affect nicotine-induced decrease in DDAH-II mRNA level. In conclusion, nicotine modulates DDAH/ADMA/NOS pathway of endothelial cell via activation of alpha7 nAChR, which may be involved in endothelial dysfunction associated to smoking.

The Protective Effect of Captopril on Nicotine-Induced Endothelial Dysfunction in Rat

This study was designed to examine the in vivo and in vitro effects of captopril, an angiotensin-converting enzyme inhibitor, on nicotine-induced endothelial dysfunction in rats. Endothelial dysfunction was induced by exposing isolated rat mesenteric arteries to nicotine (0.01, 0.1, or 1 mM) for 24 hr using an organ culture system, or by treating rats with nicotine (2 mg/kg/day, intraperitoneally) for 4 weeks. The protective effects of captopril were tested by exposing isolated mesenteric arteries to captopril (0.01, 0.03, or 0.1 mM) + nicotine (0.1 mM) for 24 hr, or by treating rats with captopril (3 mg/kg/day, intravenously) + nicotine (2 mg/kg/day, intraperitoneally) for 4 weeks. Exposure of the isolated mesenteric arteries to nicotine induced a significant concentration -dependent inhibition of endothelium-dependent relaxation. Co-culture of segments of mesenteric artery with captopril (0.03 or 0.1 mM) attenuated the nicotine-induced impairment of vasorelaxation in a dose-dependent manner. Administration of nicotine to rats for 4 weeks significantly impaired endothelium-dependent relaxation compared with control rats. This impairment was accompanied by a reduction in nitrite/nitrate, nitric oxide (NO) synthase (NOS), and superoxide dismutase (SOD) activities in the serum and aorta. Chronic captopril treatment not only improved the impairment of endothelium-dependent relaxation, but also prevented the reduction of nitrite/nitrate contents and of NOS and SOD activities in the serum and aorta. However, there were no significant differences in serum angiotensin-converting enzyme activity among the three groups. These results indicate that captopril can be used to attenuate nicotine-induced endothelial dysfunction, an effect that may be related not only to antioxidation, but also to enhancing NO production by preventing the decrease in NOS.

Effect of cigarette smoking on nitric oxide, structural, and mechanical properties of mouse arteries

Cigarette smoking (CS) is a major risk factor for vascular disease. The aim of this study was to quantitatively assess the influence of CS on mouse arteries. We studied the effect of short-term (6 wk) and long-term (16 wk) CS exposure on structural and mechanical properties of coronary arteries compared with that of control mice. We also examined the reversibility of the deleterious effects of CS on structural [e.g., wall thickness (WT)], mechanical (e.g., stiffness), and biochemical [e.g., nitric oxide (NO) by-products] properties with the cessation of CS. The left and right coronary arteries were cannulated in situ and mechanically distended. The stress, strain, elastic modulus, and WT of coronary arteries were determined. Western blot analysis was used to analyze endothelial NO synthase (eNOS) in the femoral and carotid arteries of the same mice, and NO by-products were determined by measuring the levels of nitrite. Our results show that the mean arterial pressure was increased by CS. Furthermore, CS significantly increased the elastic modulus, decreased stress and strain, and increased the WT and WT-to-radius ratio compared with those of control mice. The reduction of eNOS protein expression was found only after long-term CS exposure. Moreover, the NO metabolite was markedly decreased in CS mice after short- and long-term exposure of CS. These findings suggest that 16 wk of CS exposure can cause an irreversible deterioration of structural and elastic properties of mouse coronary arteries. The decrease in endothelium-derived NO in CS mice was seen to significantly correlate with the remodeling of arterial wall.

Inhibition of NADPH oxidase improves impaired reactivity of pial arterioles during chronic exposure to nicotine

Our goals were to determine whether chronic exposure to nicotine alters nitric oxide synthase (NOS)-dependent reactivity of cerebral (pial) arterioles and to identify a potential role for NADPH oxidase in impaired NOS-dependent responses during chronic exposure to nicotine. We measured in vivo diameter of pial arterioles to NOS-dependent (acetylcholine and ADP) and -independent (nitroglycerin) agonists in saline-treated rats and rats chronically treated with nicotine (2 mg.kg(-1).day(-1) for 2 wk via an osmotic minipump). We found that NOS-dependent, but not -independent, vasodilatation was impaired in nicotine-treated compared with saline-treated rats. In addition, the production of superoxide anion (lucigenin chemiluminescence) was increased in rats treated with nicotine compared with saline-treated rats. Furthermore, using Western blot analysis, we found that chronic exposure to nicotine increased p47phox protein in the parietal cortex. Finally, we found that apocynin (40 mg.kg(-1).day(-1)) in the drinking water to inhibit NADPH oxidase alleviated impaired NOS-dependent cerebral vasodilatation in nicotine treated rats but did not alter NOS-dependent responses in saline treated rats and did not alter NOS-independent reactivity in saline- or nicotine-treated rats. These findings suggest that chronic exposure to nicotine impairs NOS-dependent dilatation of pial arterioles by a mechanism that appears to be related to the formation of superoxide anion via activation of NADPH oxidase.

Angiotensin II type 1 (AT1)-receptor blocker prevents impairment of endothelium-dependent cerebral vasodilation by acute cigarette smoking in rats

Our aim was to test for smoking-induced endothelial dysfunction in rat cerebral vessels, then to evaluate the effect of valsartan [angiotensin II type I (AT1)-receptor blocker] on that impairment. In pentobarbital-anesthetized, mechanically ventilated Sprague-Dawley rats, we used a cranial window preparation to measure changes in pial vessel diameters following topical applications of acetylcholine (Ach) (before and after smoking or intravenous nicotine infusion; n = 6 in each group), and adenosine (n = 6 for before and after smoking). Then, after intravenous valsartan pretreatment we reexamined the pial vasodilator response to topical Ach (before and after cigarette smoking). Under control conditions, cerebral arterioles were dilated by 6.9 +/- 4.2% and 13.6 +/- 4.8% by topical Ach (10(-6) M and 10(-5) M, respectively) and by 6.4 +/- 2.5% and 12.2 +/- 3.1% by topical adenosine (10(-5) M and 10(-4) M, respectively). One hour after a 1-min inhalation of mainstream smoke (1-mg nicotine cigarette), 10(-5) M Ach constricted cerebral arterioles (-4.4 +/- 4.1%), while 10(-4) M adenosine dilated them by 13.4 +/- 3.4%. One hour after a 1-min nicotine infusion (0.05 mg), 10(-5) M Ach dilated cerebral arterioles by 9.9 +/- 2.4%. Thus, vasodilator response to topical Ach was impaired after smoking, whereas that to adenosine was unaffected. However, the vasodilator response to Ach was unaffected by intravenous nicotine. Valsartan prevented smoking from impairing Ach-induced vasodilation. In conclusion, acute single-cigarette smoking causes a dysfunction of endothelium-dependent, but not endothelium-independent, vasodilation of rat cerebral vessels in vivo, and the effect was not mimicked by intravenous nicotine. AT1-receptor blockade prevented the above smoking-induced impairment of endothelium-dependent vasodilation.

Regulation of angiotensin-converting enzyme production by nicotine in human endothelial cells

Nicotine, a component of cigarette smoke, has been implicated in the pathogenesis of cardiovascular disease. We examined whether nicotine regulates angiotensin-converting enzyme (ACE), an enzyme that plays an important role in the pathophysiology of atherosclerosis and hypertension. Human umbilical cord vein endothelial cells were treated with nicotine (0.1-1 microM) alone or in combination with vascular endothelial growth factor (VEGF; 0.5 nM) or GF-109203X (GFX; 2.5 microM). The amount of ACE in intact endothelial cells was measured by an inhibitor-binding assay method, and ACE mRNA levels were quantified using LightCycler technology. Phosphorylated PKC levels were measured by Western immunoblotting. Nicotine did not modulate basal ACE production but significantly potentiated VEGF-induced ACE upregulation. Treatment of endothelial cells with the PKC inhibitor GFX totally blocked VEGF- and nicotine-induced ACE upregulation. VEGF induced PKC phosphorylation, which was potentiated by cotreatment with nicotine. We conclude that nicotine significantly potentiated VEGF-induced ACE upregulation. This effect was probably mediated by PKC phosphorylation. The interaction of nicotine with VEGF in ACE induction may contribute to the pathogenesis of smoking-related cardiovascular disease.

Reduced endothelial nitric oxide synthase activity and concentration in fetal umbilical veins from maternal cigarette smokers

OBJECTIVE

This study aimed to investigate the effect of maternal cigarette smoking on endothelial nitric oxide synthase (eNOS) activity and concentration in the fetal umbilical vein, and subsequently, to relate the findings to the size of the newborn.

STUDY DESIGN

Forty-four nonsmoking and 30 smoking women were included in the study. Umbilical vein endothelial cells were isolated immediately after delivery. The eNOS activity was determined in the samples by the conversion of (14)C-L-arginine to (14)C-L-citrulline, and the eNOS concentration was determined by a human eNOS immunoassay.

RESULTS

Newborns of smokers had a lower weight (P=.014) and a smaller head circumference (P=.002) than those newborns of nonsmokers. The eNOS activity in fetal umbilical veins exposed to maternal smoking was 40% lower (P=.006), and the eNOS concentration 32% lower (P=.053) in newborns of smokers than in nonsmokers.

CONCLUSION

The findings suggest that maternal smoking reduces nitric oxide production in the fetal circulation. This may contribute to retarded fetal growth caused by the subsequent endothelial dysfunction with reduction of dilatory capacity of the vessels.

Alpha-7 nicotinic receptor agonists: potential new candidates for the treatment of schizophrenia

RATIONALE AND OBJECTIVE

Auditory sensory gating, a biological measurement of the ability to suppress the evoked response to the second of two auditory stimuli, is diminished in people with schizophrenia. Deficits in sensory gating are associated with attentional impairment, and may contribute to cognitive symptoms and perceptual disturbances. This inhibitory process, which involves the alpha(7) nicotinic receptor mediated release of gamma-aminobutyric acid (GABA) by hippocampal interneurons, represents a potential new target for therapeutic intervention in schizophrenia.

METHOD

This paper will review several lines of evidence implicating the nicotinic-cholinergic, and specifically, the alpha(7) nicotinic receptor system in the pathology of schizophrenia and the evidence that alpha(7) nicotinic receptor agonists may ameliorate some of these deficits.

RESULTS

Impaired auditory sensory gating has been linked to the alpha(7) nicotinic receptor gene on the chromosome 15q14 locus. Single nucleotide polymorphisms of the promoter region of this gene are more frequent in people with schizophrenia. Although nicotine can acutely reverse diminished auditory sensory gating in people with schizophrenia, this effect is lost on a chronic basis due to receptor desensitization. Clozapine is able to reverse auditory sensory gating impairment, probably through an alpha(7) nicotinic receptor mechanism, in both humans and animal models with repeated dosing. The alpha(7) nicotinic agonist 3-2,4 dimethoxybenzylidene anabaseine (DMXBA) can also enhance auditory sensory gating in animal models. DMXBA is well tolerated in humans and improves several cognitive measures.

CONCLUSION

Alpha-7 nicotinic receptor agonists appear to be reasonable candidates for the treatment of cognitive and perceptual disturbances in schizophrenia.

Thromboangiitis Obliterans (Buerger Disease) in a Female Mild Smoker Treated with Spinal Cord Stimulation

The authors report the case of a 42-year-old female mild smoker admitted to the Hospital of Ferrara for the onset of asymptomatic necrotic ulcerations localized to the second, third, and fourth toes of left foot. Physical examination showed asphygmia of inferior limb distal peripheral pulses, with localized extremity marbleized and cyanotic skin at the level of the left foot, where necrotic ulcers were present at the second, third, and fourth toes. Doppler ultrasonography and angiography revealed a severe obliterating arteriopathy of bilateral distal arterial circulation. Both blood chemistry panel (including autoimmune and hypercoagulable profile) and diagnostic examination findings were normal. Thus, the patient met several criteria to be diagnosed with Buerger disease. After an attempt at medical therapy with the intravenous administration of the prostaglandin-analogue iloprost, given the young age and the lack of viable distal target vessels for bypass grafting, a spinal cord stimulator was implanted. More than 2 years later, the patient has a normal life.

Risk factors for central serous chorioretinopathy: a case-control study

PURPOSE

To identify systemic factors associated with the development of central serous chorioretinopathy (CSCR).

DESIGN

Retrospective, case-control study.

PARTICIPANTS AND CONTROLS

312 cases and 312 controls.

RESULTS

By use of a multivariate analysis, the previously described risk factors, systemic steroid use (odds ratio [OR], 37.1; 95% confidence interval [CI], 6.2-221.8), and pregnancy (OR, 7.1; 95% CI, 1.0-50.7), were strongly associated with CSCR. Additional risk factors identified by this study include antibiotic use (OR, 6.2; 95% CI, 1.0-37.9), alcohol use (OR, 4.9; 95% CI, 1.5-16.3), untreated hypertension (OR, 3.3; 95% CI, 1.3-8.5), and allergic respiratory disease (OR, 2.5; 95% CI, 1.2-5.1).

CONCLUSIONS

A wide variety of systemic factors are associated with CSCR. Prospective studies are warranted to evaluate the nature and significance of these associations further.

Smoking and endothelial function

The arterial endothelium is a vital homeostatic cell layer responsible for a variety of functions such as thromboresistance, control of vessel tone, and vessel growth. Recent evidence has indicated that both active and passive cigarette smoking are associated with dysfunction of normal endothelial physiology, in a dose dependent and potentially reversible way. Endothelial abnormalities may predispose to the atherogenic and thrombotic problems associated with cigarette smoking.

Genetic influence on cigarette-induced cardiovascular disease

Cigarette smoking as an addictive habit has accompanied human beings for more than 4 centuries. It is also one of the most potent and prevalent environmental health risks human beings are exposed to, and it is responsible for more than 1000 deaths each day in the United States. With recent research progress, it becomes clear that cigarette smoking can cause almost all major diseases prevalent today, such as cancer or heart disease. These detrimental effects are not only present in active smokers who choose the risk, but also to innocent bystanders, as passive smokers, who are exposed to cigarettes not-by-choice. While the cigarette-induced harm to human health is indiscriminate and severe, the degree of damage also varies from individual to individual. This intersubject variability in cigarette-induced pathologies is partly mediated by genetic variants of genes that may participate in detoxification process, eg, cytochrome P450 (CYP), cellular susceptibility to toxins, such as p53, or disease development. Through population studies, we have learned that certain CYP1A1 variants, such as Mspl polymorphism, may render the carriers more susceptible to cigarette-induced lung cancer or severe coronary atherosclerosis. The endothelial nitric oxide synthase intron 4 rare allele homozygotes are more likely to have myocardial infarction if they also smoke. In vitro experimental approach has further demonstrated that cigarettes may specifically regulate these genes in genotype-dependent fashion. While we still know little about genetic basis and molecular pathways for cigarette-induced pathological changes, understanding these mechanisms will be of great value in designing strategies to further reduce smoking in targeted populations, and to implement more effective measures in prevention and treatment of cigarette-induced diseases.

Impairment of nitric oxide synthase-dependent dilatation of cerebral arterioles during infusion of nicotine

The effects of nicotine on nitric oxide synthase (NOS)-dependent reactivity of cerebral arterioles remain uncertain. Our first goal was to examine whether infusion of nicotine alters NOS-dependent reactivity of cerebral arterioles. Our second goal was to examine the mechanisms that may account for the effects of nicotine on cerebral arterioles. We measured the diameter of pial arterioles to NOS-dependent (ADP and acetylcholine) and NOS-independent (nitroglycerin) agonists before and after the infusion of nicotine (2 microg x kg(-1) x min(-1) iv for 30 min, followed by a maintenance dose of 0.35 microg x kg(-1) x min(-1)). ADP- and acetylcholine-induced vasodilatation was impaired after the infusion of nicotine. In contrast, nicotine did not alter vasodilatation to nitroglycerin. Next, we examined whether the impaired responses of pial arterioles during infusion of nicotine may be related to oxygen radicals. We found that application of superoxide dismutase or tetrahydrobiopterin during infusion of nicotine could prevent impaired NOS-dependent vasodilatation. Thus acute exposure of cerebral vessels to nicotine specifically impairs NOS-dependent dilatation via the production of oxygen radicals possibly related to an alteration in the utilization of tetrahydrobiopterin.

Plasma catecholamines in Buerger's disease: effects of cigarette smoking and surgical sympathectomy

OBJECTIVES

to study the influence of tobacco exposure and sympathectomy on basal sympathoadrenal function of patients with Buerger's disease.

DESIGN

plasma catecholamines were measured before and after smoking, in patients with Buerger's disease (n=13), in patients with Buerger's disease submitted to surgical bilateral lumbar sympathectomy (n=13), and in healthy volunteers (n=16).

MATERIALS AND METHODS

venous blood samples were collected before and 2h after smoking one cigarette (0.9mg nicotine). Plasma concentrations (pg/ml) of dihydroxiphenylalanine (pL-DOPA), noradrenalin (pNA), adrenalin (pAD) and 3,4-dihydroxiphenylacetic acid (pDOPAC) were determined.

RESULTS

Buerger's patients have low basal plasma catecholamines compared to volunteers: pNA (501 (196-927) vs 1858 (968-3663)) and pAD (71 (31-109) vs 193 (116-334)). Sympathectomy increased pL-DOPA, pAD and pDOPAC, but not pNA. After smoking, pNA only decreased in volunteers (1858 (968-3663) vs 1064 (535-2393)). In Buerger+sympathectomy group, smoking lowered pAD (700 (58-3379) vs 278 (54-429)).

CONCLUSIONS

in Buerger's disease there is an impairment of sympathoadrenal function with an altered peripheral adrenergic response to cigarette smoking. Patients submitted to sympathectomy have high pAD, but this benefit is reversed after smoking. This might be clinically relevant given the association between cigarette smoking and the manifestations of Buerger's disease and the controversy on the effectiveness of sympathectomy in the management of the disease.

Acute and chronic treatment with nicotine impairs reactivity of arterioles in response to activation of potassium channels

Although acute and chronic treatment with nicotine impairs nitric oxide synthase-dependent responses of large and small blood vessels, the effect of nicotine on other vasodilator pathways remains uncertain. The goal of the current study was to determine effects of nicotine on dilatation of arterioles to activation of ATP-sensitive potassium channels. Reactivity of cheek pouch arterioles ( approximately 50 microm) was measured during acute (1-2 h) and chronic (2-to 3-week) exposure to nicotine in response to aprikalim, cromakalim, and nitroglycerin. Acute treatment with nicotine impaired dilatation of arterioles in response to aprikalim and cromakalim but not nitroglycerin. Aprikalim and cromakalim (1.0 microM) dilated arterioles by 37 +/- 5% and 30 +/- 3%, respectively, before, but by only 21 +/- 4% and 16 +/- 3%, respectively, after infusion of nicotine (p < 0.05). Chronic exposure to nicotine did not alter vasodilatation to nitroglycerin but impaired vasodilatation to aprikalim and cromakalim. In vehicle-treated hamsters, aprikalim and cromakalim (1.0 microM) dilated arterioles by 28 +/- 1% and 32 +/- 3%, respectively. However, in nicotine-treated hamsters aprikalim and cromakalim (1.0 microM) dilated arterioles by only 3 +/- 1% and 13 +/- 1%, respectively. Next, the role of superoxide anion in impaired responses of arterioles to aprikalim and cromakalim during acute infusion of nicotine was examined. Treatment with superoxide dismutase attenuated the effects of nicotine on aprikalim and cromakalim. Thus, acute and chronic exposure to nicotine has profound affects on vasodilatation to activation of ATP-sensitive potassium channels, which may be mediated by superoxide anion.

Contribution of nicotine to acute endothelial dysfunction in long-term smokers

OBJECTIVES

The aim of this study was to determine whether nicotine, a constituent of cigarette smoke, contributes to acute endothelial dysfunction after smoking one cigarette.

BACKGROUND

Animal studies suggest that nicotine might cause an impairment of endothelium-dependent vasodilation via an increase in oxidative stress.

METHODS

Sixteen healthy smokers were entered into a randomized, observer-blinded crossover study comparing the effects of nicotine nasal spray (1-mg nicotine) and cigarette smoke (1-mg nicotine, 12 mg tar) on vascular reactivity in the brachial artery. Using high-resolution ultrasound, flow-mediated dilation (FMD) and endothelium-independent, nitroglycerin-induced dilation were assessed at baseline and 20 min after the administration of nicotine (spray or cigarette).

RESULTS

In response to similar increases in nicotine serum levels, FMD values declined from 10.2 +/- 4.4% to 6.7 +/- 4.0% after the spray (mean difference: -3.6 +/- 2.0%, 95% confidence interval: -4.6; -2.5, p < 0.0001) and from 9.4 +/- 3.8% to 4.3 +/- 2.8% after the cigarette (-5.1 +/- 2.6%, -6.5; -3.7, p < 0.0001). Nitroglycerin-induced dilation remained similar within both periods. Performing a period effect analysis of variance, a significant influence on FMD was found for the mode of administration (p = 0.017) and the baseline value (p = 0.021). The effect on FMD was more pronounced after the cigarette than after the spray (estimated average effect difference: 1.9% FMD). Oxidation parameters did not increase significantly after nicotine spray or tobacco exposure.

CONCLUSIONS

These results demonstrate that nicotine alone causes acute endothelial dysfunction, although to a lesser extent than smoking a cigarette of the same nicotine yield. However, the precise mechanisms by which nicotine leads to this altered vascular reactivity remain unclear.

Effect of nicotine on vasoconstrictor and vasodilator responses in human skin vasculature

Our objective was to test the hypothesis that acute exposure of human skin vasculature to nicotine may have deleterious effects on endothelial function. Vasoconstriction and vasorelaxation in isolated perfused human skin flaps (approximately 8 x 18 cm) derived from dermolipectomy specimens were assessed by studying changes in skin perfusion pressure measured by a pressure transducer, and skin perfusion was assessed by a dermofluorometry technique (n = 4 or 5). It was observed that nicotine (10(-7) M) amplified (P < 0.05) the norepinephrine (NE)-induced concentration-dependent (10(-7)-10(-5) M) increase in skin vasoconstriction compared with the control. This amplification effect of nicotine in NE-induced skin vasoconstriction was not blocked by the nicotine-receptor antagonist hexamethonium (10(-6) M) or the cyclooxygenase inhibitor indomethacin (10(-5) M). It was also observed that ACh and nitroglycerin (NTG) elicited a concentration-dependent (10(-8)-10(-5) M) vasorelaxation in skin flaps preconstricted with 8 x 10(-7) M of NE. The vasorelaxation induced by ACh was attenuated (P < 0.05) in the presence of nicotine (10(-7) M) compared with the control. However, skin vasorelaxation induced by NTG was not affected by nicotine (10(-7) M). ACh and NTG are known to induce endothelium-dependent and -independent vasorelaxation, respectively. The present findings were interpreted to indicate that acute exposure of human skin vasculature to nicotine was associated with 1) amplification of NE-induced skin vasoconstriction and 2) impairment of endothelium-dependent skin vasorelaxation. Cyclooxygenase products and nicotine receptors blocked by hexamethonium were not involved in the amplification of NE-induced skin vasoconstriction by nicotine. These findings may provide further insight into the pathogenesis of skin vasospasm in skin flap surgery and skin ischemic disease associated with cigarette smoking or use of smokeless tobacco.

Acute administration of nicotine impairs the hypotensive responses to bradykinin in rats

Nicotine may contribute to smoking-induced endothelial dysfunction because of its ability to impair endothelium-dependent vasodilatation. We investigated whether the acute administration of nicotine changes the hypotensive responses to bradykinin in rats. The effects of pre-treatment with losartan or enalapril on the nicotine-induced changes in the responses to bradykinin were also evaluated. In study 1, anesthetized rats were cannulated via carotid artery for the measurement of mean arterial pressure. Dose-response curves to bradykinin (0.1, 0.4, 1.6, 6.4, 25 and 100 microg/kg) were generated before and 10 min after the injection of nicotine (200 microg/kg, i.v.) or saline. The individual dose-response curves were fitted to a four-parameter logistic equation using the ALLFIT program, which provided an estimate of the maximal response (E(max)) and of the dose of bradykinin producing the half-maximal response (ED(50)). In study 2, rats were pre-treated orally with losartan (10 mg/kg/day) or enalapril maleate (25 mg/kg/day) for 2 weeks. Control rats received tap water alone. After pre-treatment, the rats were anesthetized and used as described in study 1. Nicotine decreased the E(max) (from 73.0+/-7.5 to 65.7+/-3.3 mm Hg; P<0.05) but did not affect the ED(50). In study 2, losartan or enalapril did not affect nicotine-induced decrease in responses to bradykinin; E(max) decreased in both groups (from 68.7+/-6.3 to 62.8+/-4.2 mm Hg, and from 53.8+/-13.0 to 43.1+/-7.1 mm Hg, respectively; P<0.05) without significantly changing the ED(50). These results suggest that nicotine impairs the endothelium-dependent hypotensive responses to bradykinin. This effect is not influenced by inhibition of the angiotensin-converting enzyme or by blockade of the angiotensin AT(1) receptors.