As the VLF and LF are mainly driven by sympathetic activity, RMSSD, NN9, pNN9, and HF are driven by the parasympathetic, SDNN reflects the overall HRV, these results suggested that all of these products decreased the overall HRV, especially the sympathetic modulations. To determine if different smoking/vaping products may induce cardiac fibrosis, heart sections were stained for interstitial fibrosis in red and cardiomyocytes in green. As shown in Fig. 6, interstitial fibrosis in LA, RA, and LV was significantly increased in all non-air groups relative to the Air group . There was no significant difference among non-air groups. Measurement of fibrotic biomarkers including galectin-3 , matrix metalloproteinase-9 , and its endogenous tissue inhibitor-1 showed only MMP-9 was reduced comparably in all non-air groups, identifying MMP-9 potentially as the main mediator. Transverse sections stained with GS-I were analyzed to assess changes in microvessels. As shown in Fig. 7, both density and area percentage of microvessels were significantly decreased in non-air groups, suggesting adverse effects on the microcirculation. This study shows that 8 weeks of daily exposure to smoke or aerosol from tobacco cigarettes, e-cigs, HTPs, or marijuana can cause comparable pathophysiological changes, consequently leading to hypertension, cardiac dysfunction, and arrhythmias. Cardiac electrical, structural, and neural remodeling are all involved in inducible atrial fibrillation and ventricular tachycardia caused by smoking or vaping. It is notable that these adverse effects resulted from a single smoking/vaping session per day, with each session reflecting a relatively modest exposure mimicking 10 “puffs” over 5 minutes; i.e.,grow table we did not use an extreme exposure model. We have used the same conditions to study acute effects of a single session of cigarette smoking, IQOS use, and multiple types of e-cigarette vaping sessions.
In the course of these studies, we have validated the relevance of our exposure conditions to human real-world use by using nose cone pulsatile exposure to enable immediate switching between brief pulses of undiluted smoke/aerosol and interim periods of clean air, showing that circulating plasma nicotine and cotinine levels after a single session of exposure to Marlboro Red cigarette smoke were comparable to circulating levels in humans after smoking one cigarette, and confirming an approximate dose response relationship between number of exposure cycles in one session and resulting plasma nicotine levels.Exposure to tobacco and marijuana products progressively increased pre-exposure SBP. Within each individual measurement day, tobacco products and cannabinoid-depleted marijuana acutely increased SBP. In contrast, regular marijuana acutely reduced SBP but not all the way to baseline day 0 values, indicating that cannabinoids have a blood pressure lowering effect that may be not sufficient to counteract the prohypertensive effect of marijuana smoke. The increased norepinephrine levels in all non-air groups, with no change in angiotensin levels, suggests that the sympathetic neural drive may be more important in smoking-caused hypertension, rather than the renin-angiotensin system. Thus, beta-blockers may be better than angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers in the treatment of smoking-related hypertension. Autonomic nerve function is an important determinant of arrhythmogenesis.It is intriguing that chronic exposure to e-cigs, HTPs, and marijuana all caused reduced overall HRV, of which both sympathetic and parasympathetic nerve function were down regulated as indicated by the results from the time domain method and change of LF band from frequency domain method.
Previous studies have also suggested that chronic and acute tobacco smoking are associated with reduced overall HRV.A recent study suggested that exposure to vanillin-flavored e-cig aerosol for 10 weeks also influences autonomic nerve activity by increasing the predominance of sympathetic nerve function in mice.The reduced HRV is independently associated with the arrhythmogenesis of both AF and VT and is involved in the development of hypertension.Moreover, in the present study, we observed cardiac sympathetic hyperinnervation and parasympathetic withdrawal in rats exposed to tobacco and marijuana products. Cardiac neural remodeling plays an important role in arrhythmogenesis by inducing triggered activity and changing the automaticity of cardiomyocytes.The over-innervation of sympathetic nerves is associated with the arrhythmogenesis of both AF and VT.Both ECNS and ICNS are equally important in maintaining a normal cardiac physiology. Without ECNS control, pathological change of ICNS itself could be proarrhythmogenic.Our observed cardiac sympathetic hyperinnervation and parasympathetic withdrawal may be the cause of the subsequent cardiac electrical remodeling. Although we did not directly link the neural remodeling to electrical remodeling, previous studies have demonstrated that sympathetic hyperinnervation in the ICNS can promote Ca2+-initiated triggered activity.One reasonable explanation for the shortened APD80 and prolonged CaTD80 is that sympathetic nerves activate intracellular Ca2+ transients, while parasympathetic nerves activate IKAch, leading to triggered activity due to the late phase-3 early after depolarizations.The development of fibrosis and the decrease in capillary density in post-smoking/vaping hearts may be the consequence of the elevated SBP. In non-ischemic conditions, cardiac fibrosis leads to hypertension, cardiac hypertrophy, or heart failure with preserved ejection fraction, of which the latter is often accompanied by microvascular rarefaction.
This provides an important indication that smoking or vaping may cause multiple aspects of cardiovascular disease beyond arrhythmias, because the latter could be a symptom of other severe CVD; and the pathological findings including changes in fibrosis, microvessels, and nerves may cause more problems than we observed. Moreover, the increased ratio of TIMP1/MMP9 or the decreased MMP9 was known to accelerate fibrosis and microvessel remodeling. Accordingly, the increase of MMP9 may be able to inhibit fibrosis and restore vascular network.The present study therefore identified the important role of MMP9 in smoking-related cardiac fibrotic and microvessel remodeling. Smoking/vaping-related CVD affects countless people but is not named as a disease. Given the increasing use of marijuana and novel tobacco products including e-cigs and HTPs, and common perceptions that these products are relatively free of health risks, our results indicate that all of these products may still carry substantial risk of development of cardiac disease. Our findings may provide clues to treat smoking/vaping-related CVD by preventing hypertension, targeting HRV, intracellular calcium handling, and fibrosis. An improvement of calcium regulation may benefit heart function and reduce susceptibility to arrhythmia. In addition, since the neural remodeling of the heart, which here mainly refers to increased sympathetic innervation, is highly associated with CVD development, nerve ablation or stimulation may be a potential therapeutic measure applied to such pathophysiological changes. The improvement of HRV by multiple interventions may be accompanied by the improvements of sympatho-vagal rebalance and calcium handling. A limitation is that while most procedures underwent completely blinded analysis, only one investigator was able to access the lab during the COVID-19 shutdown and thus the exposures and the cardiac function and SBP data collection were performed by the same person. Those data were subsequently coded, randomized, and the investigator analyzed the data at least 2 weeks later,ebb flow table now blinded to the identity of each animal. Another limitation is that our study used entirely young, healthy rats; age or comorbidities presumably result in a more complex physiological effect. Whether smoking-related cardiac nerve activity correlates with frequency of arrhythmia episodes needs to be further investigated. This study was not designed to assess the effects of life-long product use, so we do not know whether the adverse effects that we observed were at their saturation point, or would have continued to worsen with continued chronic exposure. Together with nicotine, they represent a relevant health problem because of the clinical consequences of their abuse. Their psychotropic effects are well known and recent research has shown that there is a close link between cannabis and alcohol . The endogenous cannabinoid system [a functional set of lipid transmitters and receptors that is the target of both natural and synthetic cannabinoids ] has been shown to mediate some of the pharmacological and behavioral aspects of alcohol . Both cannabinoids and alcohol activate the same reward pathways and the cannabinoid CB1 receptor plays an important role in regulating the positive reinforcing effects of alcohol as well as alcohol relapse . Several studies have documented that endocannabinoid transmission becomes hyperactive in reward-related areas during chronic ethanol administration.
This hypothesis is based on two findings. First, the increase in the levels of both anandamide and 2-arachidonylglicerol, the two main endocannabinoids, observed in animals chronically exposed to ethanol. Second, the down-regulation of CB1 receptors induced by endocannabinoid-mediated over-stimulation . Following this rationale, cannabinoid CB1 receptor knockout mice show reduced alcohol preference and selfadministration . However, the role of cannabinoids in alcohol- and drug-induced reward modulation demands further research because of the few studies addressing the actions of cannabinoid CB1 receptors on self administration paradigms, with respect to the more extensive research performed in alcohol consumption tests. Cannabinoid CB1 receptor agonists increase ethanol consumption in normal and alcohol-preferring ⁄ alcohol-avoiding rodent strains . The involvement of cannabinoid CB1 receptors is further supported by the effects of the cannabinoid receptor antagonist SR141716A, which reduces ethanol intake and preference . This modulatory action of cannabinoid CB1 receptors in the reinforcing ⁄ rewarding effects of ethanol is further indicated by the reduction of ethanol rewarding properties in cannabinoid CB1 receptor knockout mice . Although the activation of cannabinoid CB1 receptor increases ethanol consumption, there are no clear indications that it may result in enhanced ethanol self-administration or relapse . Moreover, studies suggest that activation of CB1 receptor reduces operant responding for drugs and food in a variety of paradigms . As an example, cannabinoid CB1 receptor agonists decrease both cocaine intravenous self-administration in rats and the reinforcing actions of cocaine ; another study by Braida & Sala confirmed that the combination of the cannabinoid CB1 receptor agonist CP55 940 with methylene dioxy methylamphetamine reduced the number of drug-associated lever pressings. However, the cannabinoid CB1 receptor antagonist SR141716A has been shown to block the rewarding properties of both food and most drugs of abuse. The treatment with SR141716A reduced both the self-administration and the subjective effects of tetrahydrocannabinol in rats, monkeys and humans . It also decreased heroin self-administration as well as morphine-induced conditioned place preference , nicotine self-administration and nicotine-induced conditioned place preference . In at least one study, cannabinoid receptor antagonism produces a biphasic effect, with a transient increase in heroin self-administration followed by a profound inhibition of operant responding for the opiate . The different effects of cannabinoid receptor agonists on alcohol consumption vs. alcohol self-administration have been interpreted as being due to differences in apparatus, experimental design and subjects used. To date, although there is a consensus in the literature with regard to the ability of cannabinoids to increase ethanol consumption, we need to clarify the role of cannabinoid receptors in operant responding for ethanol. This is important in order to establish the contribution of the endogenous cannabinoid system in alcoholism and may help to design new endocannabinoid-based therapies for this common addiction. The wide distribution of cannabinoid receptors and their role as a modulator of synaptic transmission make difficult the interpretation of these actions of direct cannabinoid receptor agonists⁄ antagonists on alcoholism. They also limit the utility of direct cannabinoid CB1 receptor ligands for the treatment of drug abuse. A pharmacological alternative that might reduce these problems may be offered by anandamide reuptake inhibitors. These drugs have been used in vivo in an effort to demonstrate their ability to inhibit cellular accumulation of anandamide and thereby stimulate cannabimimetic signaling. The anandamide reuptake inhibitor N- arachidonoyl-ethanolamide produces physiological effects similar to anandamide in vivo and potentiates the receptor-mediated effects of exogenously administered anandamide . Although numerous studies have examined and compared the pharmacology of cannabinoid agonists and antagonists in reinforcing effects of ethanol, there are no studies addressing the effects of the anandamide transport blocker AM404 on alcohol-seeking behaviors . Considering the importance of the endocannabinoid system in ethanol intake and reward, as well as the dynamic changes in anandamide production during acute and chronic ethanol exposure , we decided to study both the effects of the administration of the anandamide reuptake blocker AM404 in rats trained to self-administer ethanol and its actions in rats exposed to relapse induced by contextual stimuli previously associated with ethanol.Training and testing were conducted in standard operant chambers located in sound-attenuating, ventilated environmental cubicles. Each chamber was equipped with a drinking reservoir , positioned 4 cm above the grid floor in the center of the front panel of the chamber, and a retractable lever, located 3 cm to the right of the drinking receptacle. Auditory and visual stimuli were presented via a speaker and a light located on the front panel.