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

Cardiopulmonary Impact of Electronic Cigarettes and Vaping Products: A Scientific Statement From the American Heart Association

Vaping and electronic cigarette (e-cigarette) use have grown exponentially in the past decade, particularly among youth and young adults. Cigarette smoking is a risk factor for both cardiovascular and pulmonary disease. Because of their more limited ingredients and the absence of combustion, e-cigarettes and vaping products are often touted as safer alternative and potential tobacco-cessation products. The outbreak of e-cigarette or vaping product use-associated lung injury in the United States in 2019, which led to >2800 hospitalizations, highlighted the risks of e-cigarettes and vaping products. Currently, all e-cigarettes are regulated as tobacco products and thus do not undergo the premarket animal and human safety studies required of a drug product or medical device. Because youth prevalence of e-cigarette and vaping product use was as high as 27.5% in high school students in 2019 in the United States, it is critical to assess the short-term and long-term health effects of these products, as well as the development of interventional and public health efforts to reduce youth use. The objectives of this scientific statement are (1) to describe and discuss e-cigarettes and vaping products use patterns among youth and adults; (2) to identify harmful and potentially harmful constituents in vaping aerosols; (3) to critically assess the molecular, animal, and clinical evidence on the acute and chronic cardiovascular and pulmonary risks of e-cigarette and vaping products use; (4) to describe the current evidence of e-cigarettes and vaping products as potential tobacco-cessation products; and (5) to summarize current public health and regulatory efforts of e-cigarettes and vaping products. It is timely, therefore, to review the short-term and especially the long-term implications of e-cigarettes and vaping products on cardiopulmonary health. Early molecular and clinical evidence suggests various acute physiological effects from electronic nicotine delivery systems, particularly those containing nicotine. Additional clinical and animal-exposure model research is critically needed as the use of these products continues to grow.

Oral contraceptives and stroke: Foes or friends

Incidents of strokes are increased in young women relative to young men, suggesting that oral contraceptive (OC) use is one of the causes of stroke among young women. Long-term exposures to the varying combinations of estrogen and progestogen found in OCs affect blood clotting, lipid and lipoprotein metabolism, endothelial function, and de novo synthesis of neurosteroids, especially brain-derived 17β-estradiol. The latter is essential for neuroprotection, memory, sexual differentiation, synaptic transmission, and behavior. Deleterious effects of OCs may be exacerbated due to comorbidities like polycystic ovary syndrome, sickle cell anemia, COVID-19, exposures to endocrine disrupting chemicals, and conventional or electronic cigarette smoking. The goal of the current review is to revisit the available literature regarding the impact of OC use on stroke, to explain possible underlying mechanisms, and to identify gaps in our understanding to promote future research to reduce and cure stroke in OC users.

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 Marine-Derived Triterpenoid Frondoside A Inhibits Thrombus Formation

Background: The marine-derived triterpenoid frondoside A inhibits the phosphatidylinositol-3-kinase (PI3K) pathway in cancer cells. Because this pathway is also crucially involved in platelet activation, we studied the effect of frondoside A on thrombus formation. Methods: Frondoside A effects on platelet viability, surface adhesion molecule expression, and intracellular signaling were analyzed by flow cytometry and Western blot. The effect of frondoside A was analyzed by photochemically induced thrombus formation in the mouse dorsal skinfold chamber model and by tail vein bleeding. Results: Concentrations of up to 15 µM frondoside A did not affect the viability of platelets, but reduced their surface expression of P-selectin (CD62P) and the activation of glycoprotein (GP)IIb/IIIa after agonist stimulation. Additional mechanistic analyses revealed that this was mediated by downregulation of PI3K-dependent Akt and extracellular-stimuli-responsive kinase (ERK) phosphorylation. Frondoside A significantly prolonged the complete vessel occlusion time in the mouse dorsal skinfold chamber model of photochemically induced thrombus formation and also the tail vein bleeding time when compared to vehicle-treated controls. Conclusion: Our findings demonstrated that frondoside A inhibits agonist-induced CD62P expression and activation of GPIIb/IIIa. Moreover, frondoside A suppresses thrombus formation. Therefore, this marine-derived triterpenoid may serve as a lead compound for the development of novel antithrombotic drugs.

Biological effects of nicotine exposure: A narrative review of the scientific literature

The emergence of new tobacco heating products and electronic nicotine delivery systems (ENDS) is changing the way humans are exposed to nicotine. The purpose of this narrative review is to provide a broad overview of published scientific literature with respect to the effects of nicotine on three key health-related areas: 1) cardiovascular risk, 2) carcinogenesis and 3) reproductive outcomes. These areas are known to be particularly vulnerable to the effects of cigarette smoke, and in addition, nicotine has been hypothesized to play a role in disease pathogenesis. Acute toxicity will also be discussed. The literature to February 2019 suggests that there is no increased cardiovascular risk of nicotine exposure in consumers who have no underlying cardiovascular pathology. There is scientific consensus that nicotine is not a direct or complete carcinogen, however, it remains to be established whether it plays some role in human cancer propagation and metastasis. These cancer progression pathways have been proposed in models in vitro and in transgenic rodent lines in vivo but have not been demonstrated in cases of human cancer. Further studies are needed to determine whether nicotine is linked to decreased fertility in humans. The results from animal studies indicate that nicotine has the potential to act across many mechanisms during fetal development. More studies are needed to address questions regarding nicotine exposure in humans, and this may lead to additional guidance concerning new ENDS entering the market.

Cardiovascular, carcinogenic and reproductive effects of nicotine exposure: A narrative review of the scientific literature

The emergence of new tobacco heating products and electronic nicotine delivery systems (ENDS) is changing the way humans are exposed to nicotine. The purpose of this narrative review is to provide a broad overview of published scientific literature with respect to the effects of nicotine on three key health-related areas: 1) cardiovascular risk, 2) carcinogenesis and 3) reproductive outcomes. These areas are known to be particularly vulnerable to the effects of cigarette smoke, and in addition, nicotine has been hypothesized to play a role in disease pathogenesis. Acute toxicity will also be discussed. The literature to February 2019 suggests that there is no increased cardiovascular risk of nicotine exposure in consumers who have no underlying cardiovascular pathology. There is scientific consensus that nicotine is not a direct or complete carcinogen, however, it remains to be established whether it plays some role in human cancer propagation and metastasis. These cancer progression pathways have been proposed in models in vitro and in transgenic rodent lines in vivo but have not been demonstrated in cases of human cancer. Further studies are needed to determine whether nicotine is linked to decreased fertility in humans. The results from animal studies indicate that nicotine has the potential to act across many mechanisms during fetal development. More studies are needed to address questions regarding nicotine exposure in humans, and this may lead to additional guidance concerning new ENDS entering the market.

The dorsal skinfold chamber: A valuable model for the in vivo evaluation of topical formulations

In this study, we introduce the mouse dorsal skinfold chamber model as a valuable approach for the in vivo evaluation of topical formulations. For this purpose, dorsal skinfold chambers were implanted into BALB/c mice. Tumor necrosis factor (TNF)-α was administered to the chamber tissue for the local induction of inflammation followed by the application of diclofenac-containing or diclofenac-free (control) gel onto the skin of the chamber backside. Intravital fluorescence microscopy was repetitively performed throughout an observation period of 24 hours to study macromolecular leakage, leucocyte-endothelial cell interactions and microhaemodynamic parameters. In addition, infiltration of the inflamed tissue with different immune cell subtypes was assessed by immunohistochemistry. In a second set of experiments, the effect of dermal application of a diclofenac-containing gel on photochemically induced thrombus formation was analysed. It was observed that macromolecular leakage, numbers of adherent leucocytes and tissue infiltrating myeloperoxidase (MPO)-positive neutrophilic granulocytes and CD68-positive macrophages were significantly reduced in dorsal skinfold chambers treated with diclofenac-containing gel when compared to controls. Moreover, the diclofenac-containing gel exerted an anti-thrombotic activity, as indicated by a significantly prolonged complete vessel occlusion time. These findings demonstrate that the mouse dorsal skinfold chamber represents a valid and versatile tool to evaluate the effects of topical formulations in vivo.

The Marine-Derived Kinase Inhibitor Fascaplysin Exerts Anti-Thrombotic Activity

Background: The marine-derived kinase inhibitor fascaplysin down-regulates the PI3K pathway in cancer cells. Since this pathway also plays an essential role in platelet signaling, we herein investigated the effect of fascaplysin on thrombosis. Methods: Fascaplysin effects on platelet activation, platelet aggregation and platelet-leukocyte aggregates (PLA) formation were analyzed by flow cytometry. Mouse dorsal skinfold chambers were used to determine in vivo the effect of fascaplysin on photochemically induced thrombus formation and tail-vein bleeding time. Results: Pre-treatment of platelets with fascaplysin reduced the activation of glycoprotein (GP)IIb/IIIa after protease-activated receptor-1-activating peptide (PAR-1-AP), adenosine diphosphate (ADP) and phorbol-12-myristate-13-acetate (PMA) stimulation, but did not markedly affect the expression of P-selectin. This was associated with a decreased platelet aggregation. Fascaplysin also decreased PLA formation after PMA but not PAR-1-AP and ADP stimulation. This may be explained by an increased expression of CD11b on leukocytes in PAR-1-AP- and ADP-treated whole blood. In the dorsal skinfold chamber model of photochemically induced thrombus formation, fascaplysin-treated mice revealed a significantly extended complete vessel occlusion time when compared to controls. Furthermore, fascaplysin increased the tail-vein bleeding time. Conclusion: Fascaplysin exerts anti-thrombotic activity, which represents a novel mode of action in the pleiotropic activity spectrum of this compound.

Effect of agmatine on experimental vascular endothelial dysfunction

This study was designed to investigate the effect of agmatine sulfate (AG, CAS2482-00-0) in nicotine (NIC)-induced vascular endothelial dysfunction (VED) in rabbits. NIC was administered to produce VED in rabbits with or without AG for 6 weeks. Serum lipid profile, serum thiobarbituric acid reactive substances, reduced glutathione, superoxide dismutase generation, serum nitrite/nitrate, serum vascular cellular adhesion molecule-1 (VCAM-1), and aortic nuclear factor κB (NF-κB) levels were analyzed.Treatment with AG markedly improves lipid profile and prevented NIC-induced VED and oxidative stress. The mechanism of AG in improving NIC-induced VED may be due to the significant reduction in serum VCAM-1 levels and aortic NF-κB. Thus, it may be concluded that AG reduces the oxidative stress, nitric oxide production, VCAM-1 levels, and aortic NF-κB expression, thereby consequently improving the integrity of vascular endothelium.

Analysis of the influence of antithrombin on microvascular thrombosis: anti-inflammation is crucial for anticoagulation

Purpose

Microvascular thrombosis during septic conditions is of essential clinical relevance, but the pathomechanisms are not yet completely understood. The purpose of this study was to study the distinguished differentiation of the interactions of inflammation and coagulation using antithrombin (AT), a mediator of anticoagulation and anti-inflammation.

Methods

Using a thrombosis model in a cremaster muscle preparation of male C57Bl/6J mice (n = 83), we quantitatively assessed microvascular thrombus formation by using intravital fluorescence microscopy. Experimental groups consisted of animals treated with AT or with tryptophan⁴⁹-blocked AT (TrypAT), which exerts only anticoagulant but no anti-inflammatory effects. To further see whether endothelial glycosaminoglycan (GAG) binding with consecutive prostacyclin (PGI₂) release is mandatory for the anticoagulant process of AT, animals were administered heparin or indomethacin either alone or in combination with AT.

Results

The antithrombotic capacity of AT significantly differs in the experimental groups in which anti-inflammation was antagonized. This is given by the significantly prolonged occlusion times (p < 0.05) and higher patency rates in case of application of AT alone; while all other groups in which the anti-inflammatory action of AT was blocked by TrypAT, heparin or indomethacin revealed thrombus kinetics comparable to controls.

Conclusions

The anti-inflammatory influence of AT is essentially linked to its anticoagulant effect in the microvascular system. Those specifications of the active profile of AT characterize the intimate interactions of the anticoagulant and anti-inflammatory pathways. This might be of relevance for AT as a therapeutic agent in critically diseased patients and the clinical understanding of microvascular thrombosis.

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.

Risk of serious adverse cardiovascular events associated with varenicline: a systematic review and meta-analysis

BACKGROUND

There have been postmarketing reports of adverse cardiovascular events associated with the use of varenicline, a widely used smoking cessation drug. We conducted a systematic review and meta-analysis of randomized controlled trials to ascertain the serious adverse cardiovascular effects of varenicline compared with placebo among tobacco users.

METHODS

We searched MEDLINE, EMBASE, the Cochrane Database of Systematic Reviews, websites of regulatory authorities and registries of clinical trials, with no date or language restrictions, through September 2010 (updated March 2011) for published and unpublished studies. We selected double-blind randomized controlled trials of at least one week's duration involving smokers or people who used smokeless tobacco that reported on cardiovascular events (ischemia, arrhythmia, congestive heart failure, sudden death or cardiovascular-related death) as serious adverse events asociated with the use of varenicline.

RESULTS

We analyzed data from 14 double-blind randomized controlled trials involving 8216 participants. The trials ranged in duration from 7 to 52 weeks. Varenicline was associated with a significantly increased risk of serious adverse cardiovascular events compared with placebo (1.06% [52/4908] in varenicline group v. 0.82% [27/3308] in placebo group; Peto odds ratio [OR] 1.72, 95% confidence interval [CI] 1.09-2.71; I(2) = 0%). The results of various sensitivity analyses were consistent with those of the main analysis, and a funnel plot showed no publication bias. There were too few deaths to allow meaningful comparisons of mortality.

INTERPRETATION

Our meta-analysis raises safety concerns about the potential for an increased risk of serious adverse cardiovascular events associated with the use of varenicline among tobacco users.

Antioxidants alleviate nicotine-induced platelet aggregation in cerebral arterioles of mice in vivo

Experimental data on the effect of nicotine on cerebral microvessel thrombosis is lacking. Therefore, this study was carried out to elucidate the effects of nicotine on platelet aggregation in cerebral (pial) microcirculation of the mouse, and the possible protective effect of vitamins C and E. Male TO mice were divided into six groups, and injected i.p. with saline as a control, nicotine (1 mg/kg), vitamin C alone (100 mg/kg), vitamin E alone (100 mg/kg), nicotine plus vitamin C or nicotine plus vitamin E, all for one week before the experiment. After one week, platelet aggregation in cerebral microvessels of these groups of mice were studied in vivo. The appearance of the first platelet aggregation and total blood flow stop in arterioles and venules were timed in seconds. In the animals treated with nicotine, venules did not show any alteration in the platelet aggregation time in comparison to the control animals. However, in arterioles platelet aggregation time was significantly accelerated (p<0.001) in nicotine-treated animals as compared to controls. Both vitamins C and E prevented the shortening of arteriolar platelet aggregation time significantly (p<0.001) when applied with nicotine but not alone. It can be concluded that nicotine enhances the susceptibility to thrombosis in the cerebral arterioles in vivo and that vitamins C and E have alleviating effect on nicotine-induced thrombotic events in mice pial microvessels.

Nicotine-induced morphological changes in rat aorta: the protective role of melatonin

We analyzed the morphological changes in rat aortas during nicotine administration in order to investigate the involvement of vascular smooth muscle cells (VSMCs) in the regulation of vascular wall homeostasis. We also considered the possibility of restoring VSMC changes using melatonin as an antioxidant. We studied 4 groups of animals over 56 days. Three groups of rats were used as controls (the first without treatment, the second with melatonin alone and the third with nicotine alone). The last group of rats was orally treated with nicotine for the first 28 days and with melatonin for the last 28 days. Morphological changes in vessels were evaluated by histological procedures and immunohistochemical analysis using thrombospondin-1 (TSP-1), transforming growth factor-β1 (TGF-β1), plasminogen activator inhibitor-1 (PAI-1) and CD31 antibodies. We demonstrated that TSP-1, TGF-β1 and PAI-1 increased after nicotine administration. We believe that TSP-1 is responsible for neointima formation and that it is able to influence TGF-β1 and PAI-1 expression. Histological and immunohistochemical analysis by CD31 antibody showed that only a few endothelial cells were present in the aorta after nicotine administration compared to controls and rats treated with melatonin after nicotine administration. Moreover, histological analysis showed that neointima formation was present after nicotine treatment. Furthermore, melatonin inhibited neointima formation increasing TSP-1 expression. The ability of melatonin to inhibit neointima formation suggests that it could be a useful treatment for homeostasis of vascular walls.

Nicotine and estrogen synergistically exacerbate cerebral ischemic injury

The greater incidence of myocardial infarction, cardiac arrest, and ischemic stroke among women who smoke and use oral contraception (OC) compared to women who do not smoke and who do or do not use OC may be due in part to how nicotine influences endocrine function in women. For example, we recently demonstrated that chronic exposure to nicotine, the addictive agent in tobacco smoke responsible for the elevated risk of cardiac arrest, abolishes the endogenous or exogenous 17β-estradiol-conferred protection of the hippocampus against global cerebral ischemia (a potential outcome of cardiac arrest) in naive or ovariectomized female rats. In the current study we examined the hypotheses that (1) a synergistic deleterious effect of nicotine plus oral contraceptives exacerbates post-ischemic hippocampal damage in female rats, and (2) nicotine directly inhibits estrogen-mediated intracellular signaling in the hippocampus. To test first hypothesis and to simulate smoking behavior-induced nicotine levels in the human body, we implanted osmotic pumps containing nicotine in the female rats for 16 days. Furthermore, we mimicked the use of oral contraceptives in females by administering oral contraceptives orally to the rat. Rats exposed to either nicotine alone or in combination with oral contraceptives were subjected to an episode of cerebral ischemia and the resultant brain damage was quantified. These results showed for the first time that nicotine with oral contraceptives did indeed exacerbate post-ischemic CA1 damage as compared to nicotine alone in naive female rats. In ex vivo hippocampal slice cultures, we found that nicotine alone or with 17β-estradiol directly hinders estrogen receptors-mediated phosphorylation of cyclic-AMP element binding protein, a process required for neuronal survival and also exacerbates ischemic damage. Thus, nicotine can affect the outcome of cerebral ischemia by influencing brain endocrine function directly rather than through indirect systemic effects.

Endothelin-1 as a potential marker of melatonin's therapeutic effects in smoking-induced vasculopathy

AIMS

Smoking is a significant independent risk factor for cardiovascular disease. Among the chemicals present in the cigarette smoke, nicotine is responsible for much of the damage; it induces marked vessel morphological dysfunction and vasoconstriction. Unfortunately, pharmacological or behavioural treatment is not useful against cigarette smoking. The purpose of this study is to test, in experimental conditions, the therapeutic ability of exogenous melatonin administered after smoking-induced vasculopathy and to evaluate the targets of its effects.

MAIN METHODS

Nicotine was orally administered for 28 days. Thereafter, the rats were orally treated with melatonin for another 28 days. Vessel damage, an important vasoconstrictor peptide (endothelin-1) and the oxidative stress markers were analysed.

KEY FINDINGS

Nicotine treatment induced marked endothelial damage and an obvious vasoconstriction in the aorta as evaluated by an increased endothelin-1 (ET-1) expression. These alterations were correlated with a reduction of endothelial nitric oxide synthase (eNOS) and superoxide dismutase (SOD) and with increases of heat shock protein (Hsp70) and inducible nitric oxide synthase (iNOS) activities. Melatonin not only improved the impairment of endothelial-dependent relaxation, but also induced the increase of eNOS and SOD and the reduction of iNOS and Hsp70.

SIGNIFICANCE

The findings indicate that nicotine is associated with an elevated synthesis of the vasoconstrictor peptide (ET-1); it also induces a reduction of nitric oxide-mediated vasodilatation (eNOS) and promotes oxidative stress in the vessel wall. We propose that melatonin should be considered as a therapeutic intervention for smokers since it reduces vasoconstriction and oxidative stress and improves endothelial physiology.

Beneficial effects of melatonin on nicotine-induced vasculopathy

Tobacco smoking is responsible for death of many people each year and increases the risk of developing numerous disorders, particularly cardiovascular disease and cancer. Among the components of cigarette smoke, nicotine is known to excert proatherosclerotic, prothrombotic and proangiogenic effects on vascular endothelial cells. The current study was designed to investigate the mechanisms by which nicotine induces endothelial dysfunction and further to examine whether melatonin protects against nicotine-induced vasculopathy. Four groups of male rats (controls, melatonin-treated, nicotine treated [100 microg/mL in drinking water], and nicotine plus melatonin [5 mg/kg/day] treated) were used in this study. After 28 days all the animals were killed by decapitation and the aorta was removed. We evaluated the hydroxyproline content, and the different expression of proteins involved in several types of stress (ERK1/2), in fibrosis (TGF-beta1, NF-kappaB) and in recruitment of circulating leukocytes onto the vessel wall, including intercellular adhesion molecule-1 (ICAM-1) and vascular cellular adhesion molecule-1 (VCAM-1). These metabolic pathways are important in the development of nicotine-induced atherosclerosis and hypertension. Our results show that nicotine induces marked structural and functional alterations in the aorta. Nicotine receptor binding results in activation and phosphorylation of ERK 1/2. This enzyme, in turn, activates both TGF-beta1 and NF-kappaB; they stimulate respectively the synthesis of type I collagen, responsible of fibrosis, and moreover ICAM-1, VCAM-1 and reactive oxygen species. Based on these findings, melatonin is able to minimize the negative effects of nicotine by blocking the activation of ERK and the other signalling pathways in which this enzyme is involved.