Effect of cocaine metabolites on behavior: possible neuroendocrine mechanisms

Zwitterionic Polymer Coated and Aptamer Functionalized Flexible Micro-Electrode Arrays for In Vivo Cocaine Sensing and Electrophysiology

The number of people aged 12 years and older using illicit drugs reached 59.3 million in 2020, among which 5.2 million are cocaine users based on the national data. In order to fully understand cocaine addiction and develop effective therapies, a tool is needed to reliably measure real-time cocaine concentration and neural activity in different regions of the brain with high spatial and temporal resolution. Integrated biochemical sensing devices based upon flexible microelectrode arrays (MEA) have emerged as a powerful tool for such purposes; however, MEAs suffer from undesired biofouling and inflammatory reactions, while those with immobilized biologic sensing elements experience additional failures due to biomolecule degradation. Aptasensors are powerful tools for building highly selective sensors for analytes that have been difficult to detect. In this work, DNA aptamer-based electrochemical cocaine sensors were integrated on flexible MEAs and protected with an antifouling zwitterionic poly (sulfobetaine methacrylate) (PSB) coating, in order to prevent sensors from biofouling and degradation by the host tissue. In vitro experiments showed that without the PSB coating, both adsorption of plasma protein albumin and exposure to DNase-1 enzyme have detrimental effects on sensor performance, decreasing signal amplitude and the sensitivity of the sensors. Albumin adsorption caused a 44.4% sensitivity loss, and DNase-1 exposure for 24 hr resulted in a 57.2% sensitivity reduction. The PSB coating successfully protected sensors from albumin fouling and DNase-1 enzyme digestion. In vivo tests showed that the PSB coated MEA aptasensors can detect repeated cocaine infusions in the brain for 3 hrs after implantation without sensitivity degradation. Additionally, the same MEAs can record electrophysiological signals at different tissue depths simultaneously. This novel flexible MEA with integrated cocaine sensors can serve as a valuable tool for understanding the mechanisms of cocaine addiction, while the PSB coating technology can be generalized to improve all implantable devices suffering from biofouling and inflammatory host responses.

Effects of Cebranopadol on Cocaine-induced Hyperactivity and Cocaine Pharmacokinetics in Rats

Cebranopadol is known as a highly potent analgesic. Recent studies also demonstrated that administration of cebranopadol significantly decreased cocaine self-administration and significantly reduced cue-induced cocaine-seeking behaviors in rats. However, it was unclear whether these interesting behavioral observations are related to any potential effects of cebranopadol on cocaine pharmacokinetics or cocaine-induced hyperactivity. In principle, a promising therapeutic candidate for cocaine dependence treatment may alter the cocaine pharmacokinetics and/or attenuate cocaine-induced reward and hyperactivity and, thus, decrease cocaine self-administration and reduce cue-induced cocaine-seeking behaviors. In this study, we examined possible effects of cebranopadol on cocaine pharmacokinetics and cocaine-induced hyperactivity for the first time. According to our animal data in rats, cebranopadol did not significantly alter the pharmacokinetics of cocaine. According to our more extensive locomotor activity testing data, cebranopadol itself also dose-dependently induced hyperactivity in rats at doses higher than 50 µg/kg. Cebranopadol at a low dose of 25 µg/kg (p.o.) did not induce significant hyperactivity itself, but significantly potentiated cocaine-induced hyperactivity on Days 4 to 7 after the repeated daily dosing of the drug.

Effects of ecgonine methyl ester on cognition in scopolamine-impaired and aged rats

RATIONALE

Searches for antidotes to cocaine, and for cognition enhancers potentially applicable to Alzheimer's disease, have revealed a novel regulatory site on nicotinic acetylcholine receptors. In the presence of an agonist, inhibitors binding to this site changed the ion channel equilibrium from the open-channel form towards the closed form. Other, related, molecules could bind to the site without changing the equilibrium. These latter compounds were predicted to displace the inhibitors without affecting receptor function per se. These compounds alleviated the inhibition. One of them is ecgonine methyl ester (EME), which is generally described as inactive, but this work suggested a beneficial effect on cognition.

OBJECTIVE

This in vivo study tested for cognitive enhancement by EME in scopolamine-impaired, and aged, rats.

METHODS

Memory was the primary endpoint, but thigmotaxis became an important secondary endpoint in the light of observations made during the study. Impaired cognition was pharmacologically induced by scopolamine in young rats, and spontaneously present in aged rats. Learning ability before and after administration of EME was tested in Morris water maze protocols. Concentrations of EME in the brain and plasma were analyzed by gas chromatography-mass spectrometry.

RESULTS

A single dose of EME reversed scopolamine impairment, indicating involvement of acetylcholine receptors. Longer-term treatment improved cognition in aged rats, with enhanced rates of learning in the absence of an exogenous cognition-impairing compound. Impairment returned with a new challenge; the improvement could be re-established with continued dosing. EME also reversed thigmotaxis seen in aged rats; thigmotaxis is believed to indicate anxiety. The concentrations of EME in the brain proved adequate drug exposure.

CONCLUSIONS

Since other investigators have shown cognition impairment caused by cocaine in aged rats, this work shows that cocaine and EME have opposite effects in Morris water maze models. EME might induce cognitive enhancement and relief of anxiety in cocaine-impaired humans, and in other cognitive disorders.

LC/MS/MS evaluation of cocaine and its metabolites in different brain areas, peripheral organs and plasma in cocaine self-administering rats

BACKGROUND

We employed a cocaine intravenous self-administration model based on positive reinforcement of animals' instrumental reactions (i.e., lever pressing) rewarded by a dose of the drug. We also carried out simultaneous characterization of the pharmacokinetics of cocaine and its metabolites in rats during withdrawal; in this part of the experiments, we investigated the cocaine (2 mg/kg, iv)-induced changes in the distribution, rate constant, clearance and t₁/₂ of the parent drug and its metabolites in different structures of the brain and in peripheral tissues.

METHODS

By using liquid chromatography-tandem mass spectrometry (LC/MS/MS) we measured the levels of cocaine and its major metabolites.

RESULTS

Our results demonstrate differences in the levels of cocaine after cocaine self-administration in the rat, with the highest concentration seen in the striatum and the lowest in the cerebellum. Cocaine metabolites determined in the rat brain remained at very low levels (benzoylecgonine), irrespectively of the brain area, whereas the norcocaine concentration varied from 1.56 μg/g (the nucleus accumbens) to 2.73 μg/g (the striatum).

CONCLUSION

A tandem LC/MS/MS is a valid method for evaluation of brain and peripheral levels of cocaine and its metabolites. Our results demonstrate brain area-dependent differences in the levels of cocaine after its self-administration in the rat. There were also differences in pharmacokinetic parameters among the brain areas and peripheral tissues following a bolus iv injection of cocaine to rats withdrawn from cocaine; among brain structures the slowest metabolic rate was detected for the striatum.

Interception of cocaine by enzyme or antibody delivered with viral gene transfer: a novel strategy for preventing relapse in recovering drug users

Recent progress in enzyme engineering has led to versions of human butyrylcholinesterase (BChE) that hydrolyze cocaine efficiently in plasma, reduce concentrations reaching reward neurocircuity in the brain, and weaken behavioral responses to this drug. Along with enzyme advances, increasingly avid anti-cocaine antibodies and potent anti-cocaine vaccines have also been developed. Here we review these developments and consider the potential advantages along with the risks of delivering drug-intercepting proteins via gene transfer approaches to treat cocaine addiction.

Sex and dose-related differences in methylphenidate adolescent locomotor sensitization and effects on brain-derived neurotrophic factor

This study analyzed repeated methylphenidate (MPH) administration and its effects on brain-derived neurotrophic factor (BDNF) in the dorsal striatum and nucleus accumbens of male and female adolescent rats. In Experiment 1, rats were administered intraperitoneal (ip) saline, 1, 3, or 5 mg/kg dose of MPH every second day from postnatal day (P)33-P49. Locomotor activity was analyzed for 10 min after each administration. Results revealed that the 1 mg/kg dose of MPH produced locomotor suppression, however, the 5 mg/kg dose of MPH produced locomotor sensitization and robust behavioral activation in females as compared to males. In Experiment 2, animals were administered ip saline or the 5 mg/kg dose of MPH using an identical regimen but a 30 min behavioral test was employed. Dorsal striatum and nucleus accumbens tissue was assayed for BDNF at P50. Females demonstrated sensitization to MPH and increased locomotor activation compared to males. Interestingly, females given MPH demonstrated a significant 42% decrease of striatal BDNF whereas males administered MPH demonstrated a significant 50.4% increase of striatal BDNF compared to controls. There were no effects on accumbal BDNF. This report demonstrates robust sex differences in the behavioral response, but sex-dependent changes in striatal BDNF in response to MPH in adolescence.

Accelerating cocaine metabolism as an approach to the treatment of cocaine abuse and toxicity

One pharmacokinetic approach to the treatment of cocaine abuse and toxicity involves the development of compounds that can be safely administered to humans and that accelerate the metabolism of cocaine to inactive components. Catalytic antibodies have been developed and shown to accelerate cocaine metabolism, but their catalytic efficiency for cocaine is relatively low. Mutations of human butyrylcholinesterase and a bacterial cocaine esterase found in the soil of coca plants have also been developed. These compounds accelerate cocaine metabolism and antagonize the behavioral and toxic effects of cocaine in animal models. Of these two approaches, the human butyrylcholinesterase mutants show the most immediate promise as they would not be expected to evoke an immune response in humans.

Protracted time-dependent increases in cocaine-seeking behavior during cocaine withdrawal in female relative to male rats

RATIONALE

Female rats display higher sensitivity to cocaine relative to males under a variety of conditions. Time-dependent increases in cocaine-seeking behavior (as measured by nonreinforced operant responses) during cocaine withdrawal have been reported in male, but not female, rats.

OBJECTIVES

The present study determines sex and estrous cycle influences on time-dependent changes in cocaine-seeking behavior.

MATERIALS AND METHODS

Male and female Sprague-Dawley rats were reinforced for "active lever" responses by a cocaine infusion (0.50 mg/kg/infusion, i.v., fixed ratio schedule of reinforcement, FR1) followed by a 20-s time-out when reinforcement was not delivered. Infusions were paired with a light + tone conditioned stimulus. Next, rats underwent cocaine withdrawal for 1, 14, 60, or 180 days before testing cocaine-seeking behavior. Each rat was tested for extinction of operant responding, conditioned-cued reinstatement, and cocaine-primed (10 mg/kg, i.p.) reinstatement.

RESULTS

Both males and females displayed a time-dependent increase in cocaine-seeking behavior (active lever presses) under extinction of operant responding and conditioned-cued reinstatement conditions after 60 days of cocaine withdrawal. Moreover, cocaine-seeking behavior during extinction of operant responding in females, but not males, remained elevated at 180 days of cocaine withdrawal. Furthermore, females tested during estrus exhibited higher cocaine-seeking behavior under both extinction of operant responding and cocaine-primed reinstatement conditions relative to other rats independent of the duration of cocaine withdrawal.

CONCLUSIONS

The effects of reproductive cycle and withdrawal duration on cocaine-seeking behavior are additive and time-dependent increases in cocaine-seeking behavior are more enduring in females than in male rats.

Positional linker effects in haptens for cocaine immunopharmacotherapy

Cocaine use remains a serious problem, despite intensive efforts to curb abuse. Given the lack of effective pharmacotherapeutics for the treatment of cocaine addiction, research groups have targeted immunopharmacotherapy in which the drug user's immune system is trained to recognize and remove cocaine prior to entry into the central nervous system. Antibody cocaine esterases and simple binders have been procured, however, rates and/or affinities still need improvement before clinical trials are warranted. Herein, we report the synthesis and testing of two new haptens for the procurement of cocaine binding antibodies and cocaine esterase catalytic antibodies. Central in the design of these haptens was the placement of the linker functionality distal from the anticipated cocaine epitopes in an attempt to bury the hapten deep within an antibody combining site to gain possible entropic and enthalpic advantages.

Estrogen and progesterone affect cocaine pharmacokinetics in female rats

Several studies have reported sex differences in behavioral responses to cocaine whereby females display a greater degree of locomotor activity. Fluctuations in estrogen and progesterone during the estrous cycle have been postulated to underlie these behavioral differences. In this study, we tested the hypothesis that hormonal replacement (estrogen or progesterone) in ovariectomized rats affects cocaine pharmacokinetics. We found that estrogen replacement did not affect cocaine-induced locomotor activity, but progesterone attenuated locomotor counts in comparison with control groups receiving only sesame oil. Estrogen, however, decreased brain levels of cocaine and norcocaine 30 min after cocaine administration in comparison to the group-receiving vehicle at that time point. In addition, in progesterone-treated rats, levels of benzoylecgonine and ecgonine methylester were higher at 30 min post-administration than at 15 min. No changes were found in blood levels of the metabolites. These findings suggest that while progesterone has an impact on locomotor behavior, pharmacokinetic effects may have a limited role in mediating behavioral responses to cocaine.

Intravenous butyrylcholinesterase administration and plasma and brain levels of cocaine and metabolites in rats

Butyrylcholinesterase is a major cocaine-metabolizing enzyme in humans and other primates, catalyzing hydrolysis to ecgonine methylester. Increasing butyrylcholinesterase activity may be a treatment for cocaine addiction. We evaluated the effect of 30-min pretreatment with horse-derived butyrylcholinesterase (5-15,000 U i.v.) or with the selective butyrylcholinesterase inhibitor cymserine (10 mg/kg i.v.) on the metabolism of cocaine (17 mg/kg i.p.) in anesthetized rats. Venous blood samples were collected for two hours after cocaine administration and later assayed for cocaine and metabolites by gas chromatography/mass spectroscopy. Whole brains were collected after the last blood sample and similarly assayed. Butyrylcholinesterase significantly increased plasma and brain ecgonine methylester levels and decreased cocaine plasma half-life from 26.2 min (saline) to 16.4 min (15,000 U). Butyrylcholinesterase had no significant effect on plasma or brain cocaine or benzoylecgonine levels. Cymserine had no effect on any variable. These findings suggest that butyrylcholinesterase treatment may have benefits in enhancing cocaine metabolism and in increasing levels of ecgonine methylester, which may have a protective action against cocaine.

Plasma cocaine levels, metabolites, and locomotor activity after subcutaneous cocaine injection are stable across the postpartum period in rats

Plasma levels of cocaine (COC) and two of its principle metabolites, benzoylecgonine (BE) and ecgonine methyl ester (EME) were determined by liquid chromatography-tandem mass spectrometry (LC/MS/MS) in samples collected up to 3 h after a subcutaneous injection of cocaine (10 mg/kg) on six different days between days 4 and 24 postpartum, a period of dramatic change in the endocrine state of the female rat. Locomotor activity was measured in the same animals during this period using automated animal activity monitors. Additional measures in males provide a link to existing literature. We found that plasma levels of cocaine and its metabolites, as well as their respective time courses, are remarkably uniform across the postpartum period in female rats, as are the effects of cocaine on locomotor activity. Data from males show accord with prior published values. COC and BE, but not EME levels, were higher in males, and the time courses of COC and BE levels after injection varied somewhat between postpartum females and males; however, neither baseline nor cocaine-induced locomotor activity differed between postpartum females and males. We conclude that in the postpartum rat, there are no significant differences in the peripheral processing or general accessibility of cocaine to the brain to activate motor systems across the postpartum period. These data are critical to our understanding of differences in the reward salience of cocaine across the postpartum period and in other adult rat models [Mattson BJ, Williams S, Rosenblatt JS, Morrell JI. Comparison of two positive reinforcing stimuli: pups and cocaine throughout the postpartum period. Behav Neurosci 2001;115:683-94, Mattson BJ, Williams SE, Rosenblatt JS, Morrell JI. Preferences for cocaine- or pup-associated chambers differentiate otherwise behaviorally identical postpartum maternal rats. Psychopharmacology (Berl) 2003;167:1-8].

Ecgonine Methyl Ester Protects Against Cocaine Lethality in Mice

BACKGROUND

Plasma cholinesterase (PChE) metabolizes cocaine to ecgonine methyl ester (EME). Limited data demonstrate that EME is a mild vasodilator. Exogenous PChE protects against cocaine-induced seizures and lethality. It is unclear whether this protective effect results from enhanced degradation of cocaine, the loss of active metabolites (benzoylecgonine, norcocaine), or the production of a beneficial metabolite (EME). This study was designed to further investigate the pharmacologic effects of EME.

METHODS

All experiments used female ICR Swiss albino mice weighing 20-30 grams. Mice were acclimated to 12 h alternating light-dark cycles and given food and water ad libitum. Using a randomized, blinded protocol, 80 mice were then pretreated with either IP EME (50 mg/kg) in a 0.9% sodium chloride solution or an equal volume of 0.9% sodium chloride solution as control. Five minutes later, all animals received 126 mg/kg of cocaine IP and were observed for seizures and death. Fatality was compared using a Fisher's exact test, and the time to seizures and death were compared using a Mann-Whitney U statistic.

RESULTS

Pretreatment with EME increased survival following cocaine (9/40 vs. 2/40, for EME vs. control, respectively, p<0.05). The median times to seizure and death for both groups were 2.0 vs. 1.5 min (p>0.05), and 4.5 vs. 4.6 min (p>0.05) (EME vs. control for seizures and death, respectively).

CONCLUSION

In this animal model, EME is protective against cocaine lethality. This effect is consistent with the previously described vasodilatory effects of EME. Further studies are indicated to determine whether the increase in EME produced by exogenous PChE administration contributes to the benefits that occur when PChE is given to cocaine-poisoned animals.

Sex differences in cocaine-induced behavioral responses, pharmacokinetics, and monoamine levels

Female rats display a more robust behavioral response to acute cocaine administration than do male rats. However, a clear understanding of the biological mechanisms underlying these differences remains elusive. The present study investigated whether sexual dimorphisms in cocaine-induced motor behavior might be based on monoaminergic levels and/or cocaine pharmacokinetics. An acute injection of cocaine (5, 15, 20 or 30 mg/kg) or saline was administered to male and female rats, and behavioral activity was monitored for 3 h. Following acute cocaine or saline administration motor behavior varied according to dose and sex; overall, female rats displayed greater rearing counts and stereotypic scores, greater total locomotor counts at 15, 20, and 30 mg/kg of cocaine, and greater ambulatory counts at 20 and 30 mg/kg of cocaine than did male rats. Neurochemical determinations in post-mortem tissue showed that both male and female rats had increases in total dopamine (DA) in the caudate putamen (CPu) 15 min following cocaine administration. Additionally, male rats had a decrease in dihydroxyphenylacetic acid (DOPAC)/DA turnover. Female rats showed significant reductions in total levels of DA, DOPAC, HVA, serotonin (5-HT), 5-hydroxyindole acetic acid (5-HIAA), and DOPAC/DA turnover in the nucleus accumbens (NAc). Male rats displayed a reduction only in DOPAC/DA turnover and increases in 5-HT in the NAc following cocaine administration. Furthermore, sex differences in cocaine metabolism were observed where females had greater brain/blood levels of norcocaine and ecgonine methyl ester while male rats had higher blood levels of benzoylecgonine. These results suggest that sex differences in the behavioral responses to cocaine administration could be explained in part by intrinsic differences in both monoaminergic levels and metabolic processes.

The role of ketamine on plasma cocaine pharmacokinetics in rat

Ketamine has gained attention recently because of re-emergence of its abuse especially in combination with cocaine. When more than one drug is present simultaneously, the potential for drug--drug interaction exists, which can be pharmacokinetic, pharmacodynamic or both in nature. The objective of this study was to investigate the effect of ketamine on plasma cocaine pharmacokinetics to assess the role that the kinetic component may play in the interaction of these agents. Moreover, the effect of repetitive administration of ketamine pretreatment on the pharmacokinetics of cocaine was addressed. Male Sprague-Dawley rats were treated with cocaine alone (5 mg/kg i.v.), ketamine alone (100 mg/kg by gavage), or ketamine followed by cocaine (the same routes and doses). Blood samples were withdrawn at different time points post-injection and analyzed for determination of cocaine, its metabolites (benzoylecgonine and norcocaine) and ketamine. The results demonstrated that ketamine caused a significant decrease in cocaine's area under the curve (AUC) and elimination half-life while its total clearance was increased. The AUC of benzoylecgonine was increased by 1.5-fold after the combination compared with cocaine alone. However, cocaine did not affect ketamine's pharmacokinetic parameters. In the pretreatment study, ketamine was given orally for 3 days, followed 18 h later by a single i.v. of cocaine. Further enhancement of cocaine metabolism occurred with the appearance of norcocaine. This investigation revealed that ketamine enhances cocaine metabolism and may affect its toxicological profile.

Magnetic resonance imaging evidence of "silent" cerebrovascular toxicity in cocaine dependence

BACKGROUND

Cocaine and its metabolites can produce vasospasm. Cocaine-dependent (CD) patients are at increased risk for stroke, and a high frequency of brain perfusion defects has been observed in clinically asymptomatic CD subjects. This is the first controlled magnetic resonance imaging (MRI) study of clinically asymptomatic CD subjects.

METHODS

Two age-matched groups of male subjects (61 CD and 57 control) participated in the study. Subjects with a history of neurologic symptoms or major medical or neurologic illness, such as hypertension, diabetes, or significant head trauma, were excluded. The severity of hyperintense lesions observed on T2-weighted MRI images were rated on a 0-3-point scale by an experienced radiologist who was blind to all clinical data. Ratings of 3 were felt to be significant indicators of a possible disease process and were used in the data analysis. Three regions were separately rated: the cerebral white matter, subinsular white matter, and subcortical gray matter (basal ganglia and thalamus region).

RESULTS

Despite the exclusion criteria minimizing risk factors for cerebrovascular events, 17 of the 61 (27.9%) CD subjects and 4 of 57 (7%) of the control subjects had severe hyperintense lesions suggestive of subclinical or "silent" anoxic vascular events. Significant group differences were observed in the two white matter regions but not in the subcortical gray matter region. The risk of severe white matter lesions in the CD group increased with age, reaching 50% in the oldest age quartile (46-58 years), and this increase was not related to the number of years cocaine was used.

CONCLUSIONS

The data suggest that asymptomatic CD patients are a heterogeneous population with a significantly increased age-related risk of white matter neurovascular toxicity. Premature neurovascular damage may impact treatment outcomes and, as the CD population ages, may manifest as an increased incidence of cognitive deficits.

Cocaine and alcohol interactions in the rat: contribution of cocaine metabolites to the pharmacological effects

The pharmacokinetics and pharmacodynamics of cocaine and its three metabolites, benzoylecgonine, norcocaine, and cocaethylene, were investigated in awake, freely moving rats. This work was performed to examine the effect of alcohol coadministration on the metabolic profile of cocaine and to determine the contribution of cocaine metabolites to the pharmacological responses observed after cocaine administration. The plasma and brain extracellular fluid concentration-time profiles were characterized after intravenous (iv) administration of cocaine and the three metabolites in a crossover experimental design. The neurochemical response, measured as the change in dopamine concentration in the nucleus accumbens, and the cardiovascular responses, measured as the change in the mean arterial blood pressure, heart rate, and QRS interval, were monitored simultaneously. Cocaethylene had the highest brain-to-plasma distribution ratio, followed by cocaine, norcocaine, and benzoylecgonine. The estimated total body clearances for cocaine, benzoylecgonine, norcocaine, and cocaethylene were 140 +/- 19, 14.7 +/- 1.2, 130 +/- 19, and 111 +/- 16 mL/min/kg, respectively. Alcohol coadministration increased the formation of norcocaine, decreased the formation of benzoylecgonine, and resulted in the formation of the pharmacologically active metabolite cocaethylene. When cocaine was administered with alcohol, 12.9 +/- 3.1% to 15.3 +/- 2.9% of the cocaine dose was converted to cocaethylene. Benzoylecgonine did not have any central nervous system or cardiovascular activities after iv administration. Compared with cocaine, norcocaine and cocaethylene had more potent and prolonged effects on the neurochemical, heart rate, and QRS interval responses, and were equipotent in increasing the mean arterial blood pressure. These results indicate that changes in the cocaine metabolic profile and the formation of the pharmacologically active metabolite cocaethylene are, at least partially, responsible for the more intense and longer lasting effects reported after using this drug in combination with alcohol.