Prevention and reversal by cocaine esterase of cocaine-induced cardiovascular effects in rats

Abstract

The present study is the first to utilize bacterial cocaine esterase (CocE) to increase elimination of a lethal dose of cocaine and evaluate its cardioprotective effects. Rats received one of 5 treatments: CocE 1 min after saline; CocE 1 min after a lethal i.p. dose of cocaine; saline 1 min after a lethal i.p. dose of cocaine; CocE immediately after observing a cocaine-induced convulsion; and CocE 1 min after observing a cocaine-induced convulsion. Measures were taken of ECG, blood pressure, and cardiac troponin I (cTnI). The specificity of CocE against cocaine was determined by evaluating its actions against the cocaine analogue, WIN-35,065-2, which lacks an ester attack point for CocE. In addition, CocE's effects were compared with those of midazolam, a benzodiazepine often used to manage cocaine overdose. Whereas CocE alone had negligible cardiovascular effects, it blocked or reversed cocaine-induced QRS complex widening, increased QTc interval, ST elevation, bradycardia, and hypertension. When administered 1 min after cocaine, CocE inhibited myocardial damage; however, administered 1 min after a cocaine-induced convulsion (approximately 40 s before cocaine-induced death), CocE did not block cTnI release, but did restore cardiac function. Midazolam blocked convulsions, but exhibited inadequate protection against cocaine-induced cardiotoxicity. The majority of rats given cocaine plus midazolam died. CocE did not prevent the lethal cardiovascular effects of WIN-35,065-2. In all likelihood, CocE rapidly and specifically reduced the body burden of cocaine and inhibited or reversed the cardiovascular consequences of high-dose cocaine. These results support CocE as a potential therapeutic avenue in cocaine overdose.

Introduction

Over the past three decades, cocaine abuse has reached epidemic proportions in areas of the world. For example, increased cocaine use in the United States has resulted in a 47% increase in cocaine-related emergency room visits between 1999 and 2002 (SAMHSA, 2003). Among the numerous consequences of cocaine use, cardiovascular and cerebrovascular complications appear most life-threatening (Afonso et al., 2007, Kramer et al., 1990, Tseng et al., 1992). However, despite the fact that cocaine has been abused for more than 100 years, surprisingly little progress has been made in novel treatments of acute cocaine overdose (e.g., McCord et al., 2008).

Cocaine is a monoamine reuptake inhibitor acting at dopamine, norepinephrine, and serotonin transporters. It is absorbed quickly through mucous membranes and readily crosses the blood brain barrier, thereby rapidly increasing postsynaptic neurotransmitter levels via these different transporters. In addition, cocaine serves as a Na⁺ channel blocker, reducing electrical conduction in myocardial cells (Crumb and Clarkson, 1990). Current cocaine overdose treatments focus on managing the various symptoms of cocaine toxicity (McCord et al., 2008, Zimmerman, 2003). However, the pathogenesis of cocaine-mediated ischemia can be a result of increased oxygen demand, vasoconstriction, and/or enhanced platelet aggregation, making symptom-based treatment problematic. In addition to treating the cardiovascular response to cocaine overdose, seizures, metabolic acidosis, and respiratory alkalosis must also be controlled, further complicating the treatment strategy of a cocaine overdose patient.

An alternative strategy of controlling cocaine toxicity is to increase the rate of cocaine elimination. Over the past 30 years, human plasma butyrylcholinestrase (BChE) has been recognized for its ability to hydrolyze cocaine to non-toxic products (Inaba et al., 1978, Stewart et al., 1977). The most efficient mutations of BChE reverse the hemodynamic response to a non-lethal dose of cocaine (Gao and Brimijoin, 2004), and BChE has shown some promise in decreasing cocaine lethality in rats and mice (Hoffman et al., 1996). Recently, a bacterial cocaine esterase (CocE) found living in the soil surrounding the coca plant has been shown to hydrolyze cocaine with a catalytic efficiency that is nearly three orders of magnitude greater than that of endogenous esterases (Larsen et al., 2002, Turner et al., 2002). This action is highly specific: CocE does not metabolize WIN-35,065-2, a cocaine derivative that lacks cocaine's benzoyl ester bond (Cooper et al., 2006).

Given CocE's robust cocaine-hydrolyzing effect, it has some potential as a lead toward an antidote against cocaine-induced toxicity. Although our lab has shown that CocE protects against general cocaine toxicity and lethality in rats and mice as well as inhibiting cocaine-induced epileptogenic activity in rats (Cooper et al., 2006, Jutkiewicz et al., 2009, Ko et al., 2007), its specific ability to prevent the deleterious cardiovascular effects of cocaine toxicity has yet to be reported. The following studies utilized ECG and blood pressure telemetry in freely moving rats to determine CocE's ability to prevent or reverse the cardiac and hemodynamic alterations induced by cocaine overdose. Furthermore, the extent to which cocaine esterase prevented myocardial injury in the presence of a lethal dose of cocaine was assessed using a biomarker of cardiac injury, cardiac troponin I (cTnI). The selectivity of CocE for cocaine was explored by evaluating its effects on cardiotoxicity produced by WIN-35,065-2. In addition, because benzodiazepine treatment has been effective clinically to reduce cocaine-induced seizures (Spivey and Euerle, 1990) and cardiotoxicity (Baumann et al., 2000), we compared the effects of midazolam pretreatment with those of CocE.