Robert Malcolm

The Role of Cystine-Glutamate Exchange in Nicotine Dependence in Rats and Humans

BACKGROUND The present study determined if, akin to cocaine, nicotine self-administration in rats induces adaptations in the expression of glutamate transporters and cystine-glutamate exchangers in brain nuclei implicated in reinforcement and if treating cigarette smokers with a drug that restores cystine-glutamate exchange affects the number of cigarettes smoked. METHODS Rats self-administered nicotine intravenously for 12 hours/day or received nicotine through osmotic minipumps for 21 days. Somatic signs of withdrawal were measured and immunoblotting was performed 12 hours after the last nicotine exposure to determine if the catalytic subunit of the cystine-glutamate exchanger, xCT, or the glial glutamate transporter, GLT-1, were altered in the ventral tegmental area (VTA), nucleus accumbens, prefrontal cortex, or amygdala. For the smoking reduction study in humans, nicotine-dependent smokers were treated for 4 weeks with N-acetylcysteine (2400 mg daily) to promote cystine-glutamate exchange or placebo. Participants provided weekly ratings of withdrawal symptoms, craving, and carbon monoxide (CO) measurements and logged daily cigarette and alcohol use. RESULTS Rats receiving nicotine via self-administration or minipumps displayed somatic signs of withdrawal, but only nicotine self-administering rats showed decreased xCT expression in the nucleus accumbens and VTA and decreased GLT-1 expression in the nucleus accumbens. Human smokers treated with N-acetylcysteine reported a reduction in cigarettes smoked, and there was no effect of N-acetylcysteine on estimates of CO levels, craving, or withdrawal. CONCLUSIONS These results indicate that the cystine-glutamate exchanger and the glial glutamate transporter are downregulated after nicotine self-administration, and augmenting exchanger activity with N-acetylcysteine reduced the number of cigarettes smoked in nicotine-dependent individuals.

Two CES1 Gene Mutations Lead to Dysfunctional Carboxylesterase 1 Activity in Man: Clinical Significance and Molecular Basis

The human carboxylesterase 1 (CES1) gene encodes for the enzyme carboxylesterase 1, a serine esterase governing both metabolic deactivation and activation of numerous therapeutic agents. During the course of a study of the pharmacokinetics of the methyl ester racemic psychostimulant methylphenidate, profoundly elevated methylphenidate plasma concentrations, unprecedented distortions in isomer disposition, and increases in hemodynamic measures were observed in a subject of European descent. These observations led to a focused study of the subjects CES1 gene. DNA sequencing detected two coding region single-nucleotide mutations located in exons 4 and 6. The mutation in exon 4 is located in codon 143 and leads to a nonconservative substitution, p.Gly143Glu. A deletion in exon 6 at codon 260 results in a frameshift mutation, p.Asp260fs, altering residues 260-299 before truncating at a premature stop codon. The minor allele frequency of p.Gly143Glu was determined to be 3.7%, 4.3%, 2.0%, and 0% in white, black, Hispanic, and Asian populations, respectively. Of 925 individual DNA samples examined, none carried the p.Asp260fs, indicating it is an extremely rare mutation. In vitro functional studies demonstrated the catalytic functions of both p.Gly143Glu and p.Asp260fs are substantially impaired, resulting in a complete loss of hydrolytic activity toward methylphenidate. When a more sensitive esterase substrate, p-nitrophenyl acetate was utilized, only 21.4% and 0.6% catalytic efficiency (V(max)/K(m)) were determined in p.Gly143Glu and p.Asp260fs, respectively, compared to the wild-type enzyme. These findings indicate that specific CES1 gene variants can lead to clinically significant alterations in pharmacokinetics and drug response of carboxylesterase 1 substrates.

Safety and Tolerability of N-Acetylcysteine in Cocaine-Dependent Individuals

A double-blind placebo-controlled crossover Phase I trial was conducted to assess the safety and tolerability of N-Acetylcysteine (NAC) in healthy, cocaine-dependent humans. Thirteen participants attended a three-day hospitalization in which they received placebo or NAC. Subjects were crossed over to receive the opposite medication condition during a second three-day hospitalization, which occurred the following week. Across placebo and NAC conditions, only mild side effects were noted, and the number of subjects reporting side effects did not differ. There were trends for a greater reduction in withdrawal symptoms and craving within the NAC condition. These preliminary results suggest that NAC is well tolerated in healthy, cocaine-dependent individuals and may reduce cocaine-related withdrawal symptoms and craving.

Substance Abuse in an Inpatient Psychiatric Sample

The relationship between psychoactive drug abuse and psychopathology is complex. There have been few systematic explorations of substance abuse in psychiatric populations since the recent epidemic of cocaine abuse. To update and further explore the relationship between psychiatric illness and substance abuse, 100 consecutively admitted patients to an inpatient psychiatry unit were administered a drug and alcohol use/abuse questionnaire. Sixty-four percent endorsed current or past problems with substance abuse and 29% met DSM-III-R criteria for substance abuse in the 30 days prior to admission. For the major diagnostic categories, there were no significant differences between groups in percentages of patients with substance abuse disorders. There was a trend (p less than or equal to .2) toward an increased number of lifetime psychiatric hospitalizations in the substance-abusing group. Alcohol was the most common drug of choice followed by stimulants, cannabis, and sedative hypnotics. Differences in drug choices between diagnostic categories are discussed. Forty-three percent of urine drug screens obtained were positive, and of those with positive urine drug screens, 42% denied drug use upon admission. Only 40% of patients with current or past substance abuse problems had received treatment for their chemical dependency. In our sample, while substance abuse was very prevalent, it was underreported and undertreated.

Modafinil: preclinical, clinical, and post-marketing surveillance--a review of abuse liability issues.

Modafinil is an agent that is frequently used in the treatment of narcolepsy. More recently it has been used in the treatment of a variety of psychiatric, neurological, and medical illnesses. Due to its ability to improve wakefulness, modafinil has been viewed as a stimulant. Based on the potential for modafinil to become widely used in a variety of syndromes and settings, evidence from preclinical in vitro and in vivo studies, human laboratory studies, and post-marketing experiences examining the potential abuse liability of modafinil were reviewed. Initial evidence suggests that modafinil has limited potential for large-scale abuse.

Glutamatergic medications for the treatment of drug and behavioral addictions.

Historically, most pharmacological approaches to the treatment of addictive disorders have utilized either substitution-based methods (i.e., nicotine replacement or opioid maintenance) or have targeted monoaminergic or endogenous opioidergic neurotransmitter systems. However, substantial evidence has accumulated indicating that ligands acting on glutamatergic transmission are also of potential utility in the treatment of drug addiction, as well as various behavioral addictions such as pathological gambling. The purpose of this review is to summarize the pharmacological mechanisms of action and general clinical efficacy of glutamatergic medications that are currently approved or are being investigated for approval for the treatment of addictive disorders. Medications with effects on glutamatergic transmission that will be discussed include acamprosate, N-acetylcysteine, d-cycloserine, gabapentin, lamotrigine, memantine, modafinil, and topiramate. We conclude that manipulation of glutamatergic neurotransmission is a relatively young but promising avenue for the development of improved therapeutic agents for the treatment of drug and behavioral addictions.

Consequences of Multiple Withdrawals From Alcohol

This article represents the proceedings of a symposium at the 2003 annual meeting of the Research Society on Alcoholism in Fort Lauderdale, FL, organized by Theodora Duka and chaired by Dai Stephens. The purpose of the symposium was to examine the effects of multiple experiences of withdrawal from alcohol in animals made dependent on alcohol and in humans who are alcohol dependent. Parallels were drawn to the effects of repeated short-lived high-content alcohol exposures in animals and in humans who are social drinkers but indulge in binge drinking. The presentations were (1) Multiple detoxifications and risk of relapse in abstinent alcoholics, by John Gentry and Robert Malcolm; (2) Emotional and cognitive impairments after long-term use of alcohol: relationship to multiple detoxifications and binge drinking, by Theodora Duka; (3) The effect of repeated withdrawal from ethanol on conditioning to appetitive stimuli, by Tamzin Ripley, Gilyanna Borlikova, and Dai Stephens; (4) Alcohol withdrawal kindling: electrographic measures in a murine model of behavioral seizure sensitization, by Lynn Veatch and Howard Becker; and (5) Binge drinking induced changes in CNS, by Fulton Crews.

Update on Anticonvulsants for the Treatment of Alcohol Withdrawal

Some anticonvulsants have been shown to be as effective as some benzodiazepines for the treatment of alcohol withdrawal. Anticonvulsants may offer advantages over benzodiazepines in the outpatient treatment of alcohol withdrawal: they lack abuse potential, have minimal interactions with alcohol, and may be more effective in ameliorating psychiatric symptoms of alcohol withdrawal. Carbamazepine appears to be as effective as lorazepam and oxazepam in ameliorating the symptoms of alcohol withdrawal. In addition, a recent study indicates that carbamazepine may suppress post-withdrawal alcohol use. Divalproex may also reduce symptoms of alcohol withdrawal, based on several open-label studies. However, both carbamazepine and divalproex have limited usefulness in alcoholics with severe hepatic or hematologic complications. Newer anticonvulsants, such as gabapentin and vigabatrin, also appear to reduce alcohol withdrawal symptoms in preclinical and open-label clinical trials while lacking the toxicities of carbamazepine and divalproex. Controlled trials are underway exploring the efficacy and safety of newer anticonvulsants for the treatment of alcohol withdrawal.

A double-blind trial of gabapentin versus lorazepam in the treatment of alcohol withdrawal.

INTRODUCTION Some anticonvulsants ameliorate signs and symptoms of alcohol withdrawal, but have an unacceptable side effect burden. Among the advantages of using anticonvulsant agents in this capacity is their purported lack of interaction with alcohol that could increase psychomotor deficits, increase cognitive impairment, or increase intoxication. The aim of this study was to evaluate alcohol use and symptom reduction of gabapentin when compared with lorazepam in the treatment of alcohol withdrawal in a double-blinded randomized clinical trial. METHODS One hundred individuals seeking outpatient treatment of alcohol withdrawal with Clinical Institute Withdrawal Assessment for Alcohol-Revised (CIWA-Ar) ratings > or =10 were randomized to double-blind treatment with 2 doses of gabapentin (900 mg tapering to 600 mg or 1200 tapering to 800 mg) or lorazepam (6 mg tapering to 4 mg) for 4 days. Severity of alcohol withdrawal was measured by the CIWA-Ar on days 1 to 4 of treatment and on days 5, 7, and 12 post-treatment and alcohol use monitored by verbal report and breath alcohol levels. RESULTS CIWA-Ar scores decreased over time in all groups; high-dose gabapentin was statistically superior but clinically similar to lorazepam (p = 0.009). During treatment, lorazepam-treated participants had higher probabilities of drinking on the first day of dose decrease (day 2) and the second day off medication (day 6) compared to gabapentin-treated participants (p = 0.0002). Post-treatment, gabapentin-treated participants had less probability of drinking during the follow-up post-treatment period (p = 0.2 for 900 mg and p = 0.3 for 1200 mg) compared to the lorazepam-treated participants (p = 0.55). The gabapentin groups also had less craving, anxiety, and sedation compared to lorazepam. CONCLUSIONS Gabapentin was well tolerated and effectively diminished the symptoms of alcohol withdrawal in our population especially at the higher target dose (1200 mg) used in this study. Gabapentin reduced the probability of drinking during alcohol withdrawal and in the immediate postwithdrawal week compared to lorazepam.

Treatment of Insomnia in Cancer Patients Using Muscle Relaxation Training

Mean sleep onset latency was reduced from 124 to 29 min in 15 patients suffering from insomnia secondary to cancer; 15 subjects receiving routine care had means of 116 and 104 min in comparison. Muscle relaxation training was administered in individual sessions on three consecutive days. With 26 subjects available for follow-up 3 months later, the mean differences in sleep latency continued. The relatively greater success in this study than previously reported for a behavioral treatment of insomnia is discussed in light of possible differences between primary insomniacs and those subjects with insomnia secondary to a medical disease.