**3. Tobacco smoke**

#### **3.1 Exacerbation of viral myocarditis by tobacco smoke as a cause of heart failure**

In this study (Bae et al. 2010), we determined whether exposure to tobacco smoke will exacerbate the severity of viral myocarditis in mice. Viral myocarditis was generated n 4 week old male BALB/c mice by ί.ρ. injection of encephalomyocarditis virus (EMCV). Mice were exposed to cigarette smoke for 90 minutes/day 5x/week. Four groups were studied: 1) Control (C, no smoke and no virus), 2) Smoke (S) only, and 3) Virus only (V), and 4) Preexposure to smoke for l week prior to virus injection (S+V). We observed an over 2-fold

Exacerbation of Viral Myocarditis by

minimizing exposure to this agent in our environment.

exposure: the catecholamine hypothesis.

Abelmann, W.H. Myocarditis. *N Engl J Med,* (1966), 275:944-945.

**5. Acknowledgement** 

**6. References** 

35:458-63.

Tobacco Smoke: The Catecholamine Hypothesis 177

Additional animal and human studies will be necessary to further elucidate the several factors that may be involved. However, taken together, the available data indicate that tobacco smoke can exacerbate myocarditis which in turn may result in irreversible cardiac dysfunction and failure. Even in the absence of additional data, these results provide another example of the adverse effects of tobacco smoke and strengthen the argument for

Fig. 2. Proposed primary mechanism for exacerbation of viral myocarditis by tobacco smoke

This manuscript is dedicated to the memory of Dr. Walter H. Abelmann (1921-2011) who made many contributions to our understanding of myocarditis in the laboratory and clinic. We acknowledge the generous support provided by the Flight Attendant Medical Research Institute (FAMRI) for tobacco smoke related studies in our laboratory. We also express our appreciation to Ms. Patricia Crilley for her expert assistance in manuscript preparation.

Adamopoulos, D., van de Borne, P. & Argacha, J.F. New insights into the sympathetic,

endothelial, and coronary effects of nicotine. *Clin Exp Pharmacol Physiol*, (2008),

increase in mortality among mice that were pre-exposed to smoke compared to the virus alone. Tobacco smoke alone did not affect mortality. There was a significant increase in virus load among hearts from mice exposed to S+V compared to V alone.

In this study, we also investigated the rate of apoptosis 5 days after ί.ρ. injection of virus. Viral exposure alone significantly increased the number of apoptotic cells. The number of apoptotic cells was increased further by smoke exposure prior to viral injection. Viral injection increased the translocation of apoptosis-inducing factor from mitochondria, a hallmark of caspace-independent apoptosis activation. Exposure to tobacco smoke exacerbated these effects without changing the total expression of apoptosis-inducing factor suggesting activation of caspace-independent apoptotic pathways as well.

Apoptosis has been shown to play an important role in human and animal heart failure (Kang et al., 2000; Kang & Izumo, 2003). Other investigators have demonstrated EMCVinduced apoptosis in the hearts of mice and pigs (for example, see Mizutani et al., 1996 and Brewer et al., 2001). Activation of caspaces may be a critical facilitator of viral infection in cardiomyocytes (DeBiasi et al., 2004, Kyoto et al., 2004). In fact, DeBiasi et al., have shown that inhibition of caspaces effectively blocks virus-induced apoptosis in vitro, although caspace-independent factors also appeared to be involved. Apoptosis-inducing factor release from mitochondria is one important caspace-independent factor, and appears to play an important role in EMCV-infection related apoptosis, as shown in our study. These data were later to show that viral infection induced a significant increase in apoptosis, through caspace-independent apoptosis, and that preexposure to tobacco smoke exacerbated this effect.

Several studies have shown a relationship between myocyte apoptosis and increased sympathetic activity in patients with underlying heart disease, most commonly heart failure (Singh et al., 2001). Communal et al., 1998 showed that over-stimulation by norepinephrine produced apoptosis in ventricular myocytes of adult rats and blocking the beta-receptor decreased apoptosis. These data are consistent with our hypotheses that catecholamines are a major factor inducing inflammation and cell death in tobacco smoke exposed animals.
