Formulation and Characterization of Conjugate Vaccines to Reduce Opioid Use Disorders Suitable for Pharmaceutical Manufacturing and Clinical Evaluation

This study focused on formulating conjugate vaccines targeting oxycodone and heroin for technology transfer, good manufacturing practice (GMP), and clinical evaluation. Lead vaccines used the highly immunogenic carrier protein keyhole limpet hemocyanin (KLH), which poses formulation problems because of its size. To address this barrier to translation, an oxycodone-based hapten conjugated to GMP-grade subunit KLH (OXY-sKLH) and adsorbed on alum adjuvant was studied with regard to carbodiimide coupling reaction time, buffer composition, purification methods for conjugates, conjugate size, state of aggregation, and protein/alum ratio. Vaccine formulations were screened for post-immunization antibody levels and efficacy in reducing oxycodone distribution to the brain in rats. While larger conjugates were more immunogenic, their size prevented characterization of the haptenation ratio by standard analytical methods and sterilization by filtration. To address this issue, conjugation chemistry and vaccine formulation were optimized for maximal efficacy, and conjugate size was measured by dynamic light scattering prior to adsorption to alum. An analogous heroin vaccine (M-sKLH) was also optimized for conjugation chemistry, formulated in alum, and characterized for potency against heroin in rats. Finally, this study found that the efficacy of OXY-sKLH was preserved when co-administered with M-sKLH, supporting the proof of concept for a bivalent vaccine formulation targeting both heroin and oxycodone. This study suggests methods for addressing the unique formulation and characterization challenges posed by conjugating small molecules to sKLH while preserving vaccine efficacy.

Abuse liability assessment of an e-cigarette refill liquid using intracranial self-stimulation and self-administration models in rats

BACKGROUND

The popularity of electronic cigarettes (ECs) has increased dramatically despite their unknown health consequences. Because the abuse liability of ECs is one of the leading concerns of the Food and Drug Administration (FDA), models to assess it are urgently needed to inform FDA regulatory decisions regarding these products. The purpose of this study was to assess the relative abuse liability of an EC liquid compared to nicotine alone in rats. Because this EC liquid contains non-nicotine constituents that may enhance its abuse liability, we hypothesized that it would have greater abuse liability than nicotine alone.

METHODS

Nicotine alone and nicotine dose-equivalent concentrations of EC liquid were compared in terms of their acute effects on intracranial self-stimulation (ICSS) thresholds, acquisition of self-administration, reinforcing efficacy (i.e., elasticity of demand), blockade of these behavioral effects by mecamylamine, nicotine pharmacokinetics and nicotinic acetylcholine receptor binding and activation.

RESULTS

There were no significant differences between formulations on any measure, except that EC liquid produced less of an elevation in ICSS thresholds at high nicotine doses.

CONCLUSIONS

Collectively, these findings suggest that the relative abuse liability of this EC liquid is similar to that of nicotine alone in terms of its reinforcing and reinforcement-enhancing effects, but that it may have less aversive/anhedonic effects at high doses. The present methods may be useful for assessing the abuse liability of other ECs to inform potential FDA regulation of those products.

Bupropion and naltrexone for smoking cessation: A double-blind randomized placebo-controlled clinical trial

Combination of non-nicotine pharmacotherapies has been underexamined for cigarette smoking cessation. A randomized, double-blind, parallel-group double-dummy study evaluated two medications, bupropion (BUP) and naltrexone (NTX), in treatment-seeking cigarette smokers (N = 121) over a 7-week treatment intervention with 6-month follow-up. Smokers were randomized to either BUP (300 mg/day) + placebo (PBO) or BUP (300 mg/day) + NTX (50 mg/day). The primary outcome was biochemically verified (saliva cotinine, carbon monoxide) 7-day, point-prevalence abstinence. BUP + NTX was associated with significantly higher point-prevalence abstinence rates after 7-weeks of treatment (BUP + NTX, 54.1%; BUP + PBO, 33.3%), P = 0.0210, but not at 6-month follow-up (BUP + NTX, 27.9%; BUP + PBO, 15.0%), P = 0.09. Continuous abstinence rates did not differ, P = 0.0740 (BUP + NTX, 26.2%; BUP + PBO, 13.3%). Those receiving BUP + NTX reported reduced nicotine withdrawal, P = 0.0364. The BUP + NTX combination was associated with elevated rates of some side effects, but with no significant difference in retention between the groups.

Scientific overview: 2013 BBC plenary symposium on tobacco addiction

Nicotine dependence plays a critical role in addiction to tobacco products, and thus contributes to a variety of devastating tobacco-related diseases (SGR 2014). Annual costs associated with smoking in the US are estimated to be between $289 and $333 billion. Effective interventions for nicotine dependence, especially in smokers, are a critical barrier to the eradication of tobacco-related diseases. This overview highlights research presented at the Plenary Symposium of Behavior, Biology and Chemistry: Translational Research in Addiction Conference (BBC), hosted by the UT Health Science Center San Antonio, on March 9-10, 2013. The Plenary Symposium focused on tobacco addiction, and covered topics ranging from basic science to national policy. As in previous years, the meeting brought together globally-renowned scientists, graduate student recruits, and young scientists from underrepresented populations in Texas and other states with the goal of fostering interest in drug addiction research in young generations.

Selective effects of a morphine conjugate vaccine on heroin and metabolite distribution and heroin-induced behaviors in rats

Morphine conjugate vaccines have effectively reduced behavioral effects of heroin in rodents and primates. To better understand how these effects are mediated, heroin and metabolite distribution studies were performed in rats in the presence and absence of vaccination. In non-vaccinated rats 6-monoacetylmorphine (6-MAM) was the predominant opioid in plasma and brain as early as 1 minute after i.v. administration of heroin and for up to 14 minutes. Vaccination with morphine conjugated to keyhole limpet hemocyanin (M-KLH) elicited high titers and concentrations of antibodies with high affinity for heroin, 6-MAM, and morphine. Four minutes after heroin administration vaccinated rats showed substantial retention of all three opioids in plasma compared to controls and reduced 6-MAM and morphine, but not heroin, distribution to brain. Administration of 6-MAM rather than heroin in M-KLH vaccinated rats showed a similar drug distribution pattern. Vaccination reduced heroin-induced analgesia and blocked heroin-induced locomotor activity throughout 2 weeks of repeated testing. Higher serum opioid-specific antibody concentrations were associated with higher plasma opioid concentrations, lower brain 6-MAM and morphine concentrations, and lower heroin-induced locomotor activity. Serum antibody concentrations over 0.2 mg/ml were associated with substantial effects on these measures. These data support a critical role for 6-MAM in mediating the early effects of i.v. heroin and suggest that reducing 6-MAM concentration in brain is essential to the efficacy of morphine conjugate vaccines.

Co-administration of morphine and oxycodone vaccines reduces the distribution of 6-monoacetylmorphine and oxycodone to brain in rats

Opioid conjugate vaccines have shown promise in animal models as a potential treatment for opioid addiction. Individual vaccines are quite specific and each targets only a limited number of structurally similar opioids. Since opioid users can switch or transition between opioids, we studied a bivalent immunization strategy of combining 2 vaccines that could target several of the most commonly abused opioids; heroin, oxycodone and their active metabolites. Morphine (M) and oxycodone (OXY) haptens were conjugated to keyhole limpet hemocyanin (KLH) through tetraglycine (Gly)(4) linkers at the C6 position. Immunization of rats with M-KLH alone produced high titers of antibodies directed against heroin, 6-monoacetylmorphine (6-MAM) and morphine. Immunization with OXY-KLH produced high titers of antibodies against oxycodone and oxymorphone. Immunization with the bivalent vaccine produced consistently high antibody titers against both immunogens. Bivalent vaccine antibody titers against the individual immunogens were higher than with the monovalent vaccines alone owing, at least in part, to cross-reactivity of the antibodies. Administration of a single concurrent intravenous dose of 6-MAM and oxycodone to rats immunized with the bivalent vaccine increased 6-MAM, morphine and oxycodone retention in serum and reduced the distribution of 6-MAM and oxycodone to brain. Vaccine efficacy correlated with serum antibody titers for both monovalent vaccines, alone or in combination. Efficacy of the individual vaccines was not compromised by their combined use. Consistent with the enhanced titers in the bivalent group, a trend toward enhanced pharmacokinetic efficacy with the bivalent vaccine was observed. These data support the possibility of co-administering two or more opioid vaccines concurrently to target multiple abusable opioids without compromising the immunogenicity or efficacy of the individual components.

An oxycodone conjugate vaccine elicits drug-specific antibodies that reduce oxycodone distribution to brain and hot-plate analgesia

Opioid conjugate vaccines have shown promise in attenuating the behavioral effects of heroin or morphine in animals. The goal of this study was to extend this approach to oxycodone (OXY), a commonly abused prescription opioid. Haptens were generated by adding tetraglycine (Gly)(4) or hemisuccinate (HS) linkers at the 6-position of OXY. Immunization of rats with OXY(Gly)(4) conjugated to the carrier proteins bovine serum albumin (BSA) or keyhole limpet hemocyanin (KLH) produced high-titer antibodies to OXY and its metabolite oxymorphone with substantially lower affinities for other structurally related opioid agonists and antagonists. There was no measurable binding of antibody by the (Gly)(4) linker alone or off-target opioids methadone and buprenorphine. OXY(HS) conjugates were less immunogenic despite achieving protein haptenation ratios comparable to OXY(Gly)(4)-BSA. In rats given a single intravenous dose of OXY, immunization with OXY(Gly)(4)-KLH increased OXY protein binding and retention in serum while decreasing its unbound (free) concentration in plasma and distribution to brain. Vaccine efficacy correlated with serum antibody titers, and it was greatest in rats given the lowest OXY dose (0.05 mg/kg) but was significant even after a larger OXY dose (0.5 mg/kg), equivalent to the high end of the therapeutic range in humans. These effects of OXY(Gly)(4)-KLH on drug disposition were comparable to those of nicotine or cocaine vaccines that are in clinical trials as addiction treatments. Immunization with OXY(Gly)(4)-KLH also reduced OXY analgesia in a thermal nociception test. These data support further study of vaccination with the OXY(Gly)(4)-KLH immunogen as a potential treatment option for OXY abuse or addiction.

Vaccination against nicotine alters the distribution of nicotine delivered via cigarette smoke inhalation to rats

Preclinical models of nicotine vaccine pharmacology have relied on i.v. or s.c. administration of nicotine. Models using cigarette smoke inhalation might more accurately simulate nicotine exposure in smokers. Nicotine vaccine effects were examined in rats using two cigarette smoke exposure models: a 10 min nose-only exposure (NSE) producing serum nicotine levels equivalent to the nicotine boost from 1 cigarette in a smoker, and a 2h whole-body exposure (WBE) producing serum nicotine levels similar to those associated with regular mid-day smoking. Vaccination prior to 10min smoke NSE reduced nicotine distribution to brain by 90%, comparable to its effect on nicotine administered i.v. Vaccination prior to 2 h smoke WBE reduced nicotine distribution to brain by 35%. The nicotine concentration in broncheoalveolar lavage (BAL) fluid obtained after 2 h WBE was increased by 230% in vaccinated rats but was also increased in rats passively immunized with a nicotine-specific monoclonal antibody, and so was likely due to transfer of antibody from serum rather than local production at the pulmonary mucosa. Nicotine-specific IgA was not detectable in BAL fluid, but titers in serum were appreciable at 21-25% of the IgG titer and could contribute to vaccine efficacy. Both vaccination and passive immunization are effective in reducing nicotine distribution to brain in rats when nicotine is delivered via inhaled cigarette smoke. These data validate results previously obtained in rodents for nicotine vaccines using i.v. or s.c. nicotine dosing and provide a quantitative method for studying aspects of nicotine exposure which are unique to cigarette smoke inhalation.

Enhanced immunogenicity of a bivalent nicotine vaccine

The efficacy of nicotine vaccines for smoking cessation is dependent upon their ability to elicit sufficiently high serum antibody concentrations. This study compared two nicotine immunogens representing different hapten presentations, 3'-aminomethyl nicotine conjugated to recombinant Pseudomonas exoprotein A (3'-AmNic-rEPA) and 6-carboxymethlureido nicotine conjugated to keyhole limpet hemocyanin (6-CMUNic-KLH), and assessed whether their concurrent administration would produce additive serum antibody concentrations in rats. Effects of vaccination on nicotine pharmacokinetics were also studied. Vaccination of rats with these immunogens produced non cross-reacting nicotine-specific antibodies (NicAb). Serum NicAb concentrations elicited by each individual immunogen were not affected by whether the immunogens were administered alone as monovalent vaccines or together as a bivalent vaccine. The total NicAb concentration in the bivalent vaccine group was additive compared to that of the monovalent vaccines alone. Higher serum NicAb concentrations, irrespective of which immunogen elicited the antibodies, were associated with greater binding of nicotine in serum, a lower unbound nicotine concentration in serum, and lower brain nicotine concentration. These results demonstrate that it is possible to design immunogens which provide distinct nicotine epitopes for immune presentation, and which produce additive serum antibody levels. The concurrent administration of these immunogens as a bivalent vaccine may provide a general strategy for enhancing the antibody response to small molecules such as nicotine.

Vaccination against nicotine does not prevent nicotine-induced changes in fetal nicotinic receptor binding and c-fos mRNA expression in rats

Gestational exposure of rats to nicotine produces long-lasting alterations in brain development. Vaccination of adult female rats against nicotine reduces the distribution of maternally administered nicotine to fetal brain, suggesting that vaccination might protect against these effects. In the current study, the effects of vaccination on nicotine-induced changes in fetal (3)H-epibatidine binding and c-fos mRNA expression were evaluated using tissue from a previous pharmacokinetic study of vaccination. An intermittent nicotine dosing regimen designed to resemble nicotine intake in a smoker was administered from GD1-20. Peak nicotine levels in fetal brain were reduced by vaccination, whereas the chronic accumulation of nicotine in fetal brain was not. Gestational nicotine exposure produced significant increases in (125)I-epibatidine binding to brain and spinal cord on GD20, and decreased c-fos mRNA expression in fetal striatum, adrenal and lung. Vaccination did not significantly alter these effects. These data suggest that nicotine dosing, using a clinically relevant intermittent bolus dose regimen, produces substantial changes in fetal nicotinic receptor and c-fos mRNA expression. The decrease in c-fos mRNA expression contrasts with previously reported increases, and suggests that the nicotine dosing regimen used may influence its effects. The lack of effect of vaccination suggests that the cumulative exposure of fetal tissues to nicotine may influence the measured parameters to a greater extent than peak exposure levels.

Changes in maternal and fetal nicotine distribution after maternal administration of monoclonal nicotine-specific antibody to rats

Vaccination against nicotine to elicit the production of nicotine-specific antibodies is a potential treatment for tobacco addiction which reduces nicotine distribution from serum to brain. Vaccination of pregnant rats also reduces the distribution of maternally-administered nicotine to the fetal brain. Whether this is due to maternal antibody reducing the transfer of nicotine from mother to fetus, or to fetal antibody altering the distribution of nicotine within the fetus, is not clear. In the current study, passive immunization of rats with the murine monoclonal nicotine-specific antibody Nic311 was used as a surrogate for vaccination because antibody transfer to the fetus was anticipated to be lower than with vaccination. Pregnant rats received nicotine from gestational day (GD) 18-20 as frequent i.v. boluses to simulate nicotine exposure from smoking. Nic311 was administered at doses of 30, 80 or 240 mg/kg on GD 19. Fetal serum Nic311 levels on GD 20 were <3% of concurrent maternal levels, but concentrations of up to 20 ug/ml in fetal serum were obtained owing to the very high levels in maternal serum. Accumulation of the chronically administered nicotine, measured on GD 20, was not changed by Nic311 treatment in either maternal or fetal brain. The early distribution of nicotine to maternal brain, measured 5 min after a dose, was markedly reduced by Nic311, while the early distribution of nicotine to whole fetus and fetal brain was not substantially altered. These data suggest that the limited transfer of Nic311 to the fetus in turn limits the ability of Nic311 to reduce nicotine distribution to the fetal brain.

Differential effects of passive immunization with nicotine-specific antibodies on the acute and chronic distribution of nicotine to brain in rats

Vaccination against nicotine blocks or attenuates nicotine-related behaviors relevant to addiction in rats. Passive immunization with nicotine-specific antibodies is an alternative to vaccination with the potential advantages of allowing control of antibody dose and affinity. In the current study, the effects of two antibodies on the distribution of nicotine to brain were evaluated during chronic nicotine administration in rats; the monoclonal antibody Nic311 (K(d) = 60 nM) and nicotine-specific antiserum (K(d) = 1.6 nM). Nicotine was administered via repeated i.v. bolus doses over 2 days and antibody was administered during the first day. Neither antibody appreciably reduced the chronic accumulation of nicotine in brain, despite high protein binding of nicotine in serum (98.9%) and a 73% reduction in the unbound serum nicotine concentration with the highest Nic311 dose. However, both antibodies substantially reduced the early distribution of nicotine to brain 5 min after a dose. The higher affinity antibody was no more effective than Nic311. The highest Nic311 dose produced serum antibody levels 10 times higher than those reported with vaccination. The efficacy of Nic311 was dose-related, with the highest dose producing a 76% decrease in the early distribution of nicotine to brain. These findings, along with previous data, suggest that the primary effect of passive immunization is to slow, rather than prevent, the distribution of nicotine to brain. In the setting of chronic nicotine dosing, antibodies with a moderate affinity for nicotine produced substantial effects on the early distribution of nicotine to brain and were as effective as higher affinity antibodies.

Monoclonal nicotine-specific antibodies reduce nicotine distribution to brain in rats: dose- and affinity-response relationships

Vaccination against nicotine is being studied as a potential treatment for nicotine dependence. Some of the limitations of vaccination, such as variability in antibody titer and affinity, might be overcome by instead using passive immunization with nicotine-specific monoclonal antibodies. The effects of antibodies on nicotine distribution to brain were studied using nicotine-specific monoclonal antibodies (NICmAbs) with K(d) values ranging from 60 to 250 nM and a high-affinity polyclonal rabbit antiserum (K(d) = 1.6 nM). Pretreatment with NICmAbs substantially increased the binding of nicotine in serum after a single nicotine dose, reduced the unbound nicotine concentration in serum, and reduced the distribution of nicotine to brain. Efficacy was directly related to antibody affinity for nicotine. Efficacy of the highest affinity NICmAb, NICmAb311, was dose-related, with the highest dose reducing nicotine distribution to brain by 78%. NICmAb311 decreased nicotine clearance by 90% and prolonged the terminal half-life of nicotine by 120%. At equivalent doses, NICmAb311 was less effective than the higher affinity rabbit antiserum but comparable efficacy could be achieved by increasing the NICmAb311 dose. These data suggest that passive immunization with nicotine-specific monoclonal antibodies substantially alters nicotine pharmacokinetics in a manner similar to that previously reported for vaccination against nicotine. Antibody efficacy is a function of both dose and affinity for nicotine.

Tissue-dependent effects of immunization with a nicotine conjugate vaccine on the distribution of nicotine in rats

Vaccination of rats against nicotine reduces nicotine distribution to brain even at nicotine doses greatly exceeding the estimated binding capacity of the available antibody. This observation suggests a differential effect by which vaccination reduces nicotine distribution to brain to a greater extent than to other tissues. To test this hypothesis, vaccinated rats received a single intravenous nicotine dose equal to twice the estimated binding capacity of nicotine-specific antibody in vaccinated rats. The total and bound serum nicotine concentrations were higher in the vaccinated rats compared to controls, while the unbound serum nicotine concentration was lower. Distribution of nicotine to brain was reduced in vaccinated rats in a time-dependent manner, with a greater reduction at 1 min (64%) than at 25 min (45%). Vaccination reduced nicotine distribution to muscle, testis, spleen, liver, heart, and kidney, but to a lesser extent than to brain, while nicotine distribution to fat was increased. Chronically infused nicotine showed a similarly altered pattern of tissue distribution in vaccinated rats, but differences were in general smaller than after a single nicotine dose; brain nicotine concentration was 24% lower in vaccinated rats, while lung nicotine concentration was higher. The presence of nicotine-specific antibody in tissues may have contributed to the increased nicotine concentrations in fat and lung. These data suggest that vaccination reduces nicotine distribution to brain not only by sequestering nicotine in serum but also by redirecting tissue distribution disproportionately away from brain, such that nicotine concentrations are reduced to a greater extent in brain than in other tissues.

Biomarkers of tobacco exposure or harm: application to clinical and epidemiological studies. 25-26 October 2001, Minneapolis, Minnesota

Adverse outcomes from tobacco use may take decades to develop. Biomarkers are measures that can be used in the early stages of tobacco use to assess exposure to tobacco toxins or to predict adverse health outcomes with which they are associated. Examples of biomarkers include specific chemical components of tobacco or their metabolites; early biochemical, histological, or physiological effects; and early health effects. Mechanistically relevant and quantitatively valid biomarkers are essential for assessing the ultimate impact of new products, treatments, preventive measures, and public health policies on tobacco-related disease. The tobacco industry's recent introduction of a variety of new tobacco products or devices with implied claims of reduced health risks highlights the need to develop methods for assessing their potential for benefit or harm. A wide variety of biomarkers for tobacco exposure or harm has been studied. Although many questions about their use remain unanswered, substantial data exist regarding their validity and utility. This conference reviewed both the general issues surrounding biomarker use and the current state of knowledge regarding the most widely studied and promising biomarkers.

Preferences and practices among renters regarding smoking restrictions in apartment buildings

OBJECTIVE

This study assessed renters' preferences for official smoking policies in their buildings and their practices concerning restricting tobacco smoking in their apartments.

DESIGN

Renters (n = 301) living in large apartment complexes in a suburb of Minneapolis, Minnesota, completed a mail survey.

MAIN OUTCOME MEASURES

The survey asked about the official smoking policies in place in their apartment buildings, their preferences for policies, whether they had smelled tobacco smoke coming into their apartments from without, and, if so, what they had done about it.

RESULTS

The majority of non-smokers (79%) preferred that their building be smoke-free. When asked to identify the current smoking policy in their buildings, residents disagreed substantially. Most renters (60%) reported smoke-free policies in their own apartments and another significant proportion (23%) restricted smoking to certain areas or occasions or persons. 75% thought that enforcing a smoke-free policy for guests would not be difficult. 53% of those in non-smoking households had smelled tobacco smoke in their apartments; most of these reported being bothered by it. However, very few complained to the building owner or manager (15.5%) or to the smoker (6.9%).

CONCLUSIONS

The majority of non-smokers preferred that their buildings be smoke-free. A failure to report problems to apartment managers might be an impediment to instituting smoke-free policies in apartment buildings. The considerable disagreement among residents within apartment complexes about the current official smoking policy in their buildings suggests that policies are lacking or are not well communicated.

Maternal vaccination against nicotine reduces nicotine distribution to fetal brain in rats

Cigarette smoking during pregnancy is associated with a variety of adverse fetal outcomes. Nicotine is a likely contributor to these adverse effects, with fetal brain as one target organ. Vaccination of adult male rats against nicotine has been shown to reduce nicotine distribution to the brain. The current study examined whether vaccination of female rats before pregnancy would reduce the distribution to fetal brain of a single nicotine dose administered during gestation. Female rats immunized with a nicotine conjugate vaccine received a single dose of nicotine 0.03 mg/kg i.v. on gestational day 16 to 22. Five minutes later, vaccinated rats had substantially higher bound and lower unbound serum nicotine concentration and lower brain nicotine concentration than controls. Fetal brain nicotine concentration was reduced by 43% in vaccinated rats, comparable to the reduction in the maternal brain nicotine concentration. The whole-fetus nicotine concentration was not altered by vaccination. A similar experiment was performed in which pregnant rats were passively immunized with rabbit nicotine-specific IgG 7 or 21 mg/kg just before nicotine dosing. The effects of passive immunization on nicotine distribution in the mother were IgG dose-related and the higher dose reduced nicotine distribution to fetal brain by 60%. These data suggest that vaccine effects on nicotine distribution to serum and brain are similar in pregnant female rats to those previously reported in adult males. Vaccination of female rats before pregnancy, or passive immunization during pregnancy, can reduce the exposure of fetal brain to a single dose of maternally administered nicotine.

Inhibition of nicotine-induced seizures in rats by combining vaccination against nicotine with chronic nicotine infusion

The ability of a nicotine vaccine to protect against nicotine-induced seizures was studied in rats. Groups of 10 rats were vaccinated with 3 doses of either a nicotine conjugate vaccine over 6 weeks to elicit high titers of nicotine-specific antibodies or with a control vaccine. Rats were then pretreated with a 1-week subcutaneous infusion of either nicotine 1 mg/kg/day or saline and then received a single 2 mg/kg ip dose of nicotine to provoke seizures. Vaccination reduced the incidence of seizures. The combination of vaccination and pretreatment with nicotine infusion was more effective than either treatment alone. These data suggest that vaccination is protective against this toxic effect of nicotine and that combining vaccination and chronic nicotine administration may provide a novel strategy for blocking some effects of nicotine.

Passive immunization against nicotine prevents nicotine alleviation of nicotine abstinence syndrome

Passive immunization against nicotine interferes with its locomotor and pressor effects. The current study determined whether immunization could prevent another nicotine action: the reversal of nicotine abstinence syndrome. IgG containing 4.4-5.6% nicotine-specific antibody was isolated from rabbits immunized with 3'-amino-methyl-nicotine conjugated to a carrier protein. Twenty rats were rendered dependent by 7 days of subcutaneous infusion of 3.15 mg/kg/day nicotine (expressed as the base). Upon termination of nicotine infusion, each rat was injected intraperitoneally with 150 mg of IgG from normal serum (n=13) or from nicotine antiserum (n=7). Twenty-two and one-half hours later, all rats were observed over 15 min for baseline nicotine abstinence signs. Two and one-half hours after baseline observations, seven of the 13 rats pretreated with control IgG and all seven rats pretreated with nicotine-specific IgG were then challenged by 0.12 mg/kg (sc) nicotine. The remaining six rats pretreated with control IgG were challenged with saline alone. All rats were then observed again for abstinence signs. Nicotine injection caused significantly less reduction of abstinence signs in the immunized rats. The nicotine effect in immunized rats was comparable to the saline effect in nonimmunized rats. Immunization also significantly reduced free serum nicotine concentration and nicotine distribution to the brain. These results raise the possibility that immunization might prevent nicotine consumption from relieving the discomforts of smoking cessation.

Vaccination against nicotine during continued nicotine administration in rats: immunogenicity of the vaccine and effects on nicotine distribution to brain

Vaccination against nicotine has been proposed as a potential treatment for nicotine dependence. Because vaccination may take months to elicit satisfactory antibody levels, the clinical usefulness of this approach will be enhanced if vaccination can be accomplished during continued nicotine intake (e.g., before a smoker quits). The current study examined the immunogenicity of a nicotine conjugate vaccine during continued nicotine dosing in rats, and its effects on nicotine distribution to brain. In the first experiment, nicotine was administered over 11 weeks as 20 intra venous (i.v.) bolus injections per day during the rat's active cycle to simulate the usual pattern of nicotine intake from cigarette smoking. In the second experiment, rats received a continuous s.c. infusion of nicotine by osmotic pump for 11 weeks to provide serum nicotine concentrations equivalent to those of a heavy smoker and 24 h/day nicotine exposure. Nicotine-specific antibody titers after the third booster dose were not compromised by either regimen of concurrent nicotine administration compared to those of rats receiving saline. A single additional i.v. nicotine dose was administered at the end of each experiment. The distribution of this single nicotine dose to brain was reduced by 40-60% in vaccinated rats compared to controls. Vaccine efficacy in reducing nicotine distribution to brain was not compromised by concurrent nicotine administration. These data suggest that vaccination during concurrent nicotine administration is feasible, and that the ability of vaccination to reduce nicotine distribution to brain is preserved even after months of nicotine dosing at rates approximating cigarette smoking.

Carvedilol affects the physiological and behavioral response to smoked cocaine in humans

The noradrenergic system is implicated in mediating some of the physiological effects of cocaine. The purpose of this study was to investigate whether treatment with an adrenergic blocker, carvedilol, which would be expected to attenuate the physiological effects of cocaine, would also attenuate the subjective and behavioral response to cocaine in humans. Twelve crack cocaine users participated in this double-blind, placebo-controlled outpatient study. Acute treatment with 50 mg of oral carvedilol attenuated the smoked cocaine-induced increases in heart rate, systolic and diastolic blood pressure. The number of cocaine self-administrations was lower under 25 mg carvedilol treatment condition compared with 50 mg carvedilol or placebo treatment conditions. The subjective responses to smoked cocaine deliveries were not affected by carvedilol treatment. These results suggest that acute treatment with carvedilol attenuates the physiological effects of smoked cocaine. The effects of carvedilol on cocaine self-administration need to be studied further.

Effects of labetalol treatment on the physiological and subjective response to smoked cocaine

Adrenergic receptors mediate some of the physiological and possibly behavioral effects of cocaine. The purpose of this study was to investigate the effect of treatment with a peripherally acting adrenergic blocking drug labetalol on the cardiovascular and subjective response to repeated deliveries of smoked cocaine. In this double-blind, placebo-controlled, crossover study, 12 cocaine users were treated with a single 100 or 200 mg dose of labetalol, or placebo in each of three experimental sessions. Starting 2 h after the medication treatment, subjects received three doses of 0.4 mg/kg smoked cocaine, 30 min apart. Labetalol treatment significantly attenuated the cocaine-induced increases in heart rate and systolic blood pressure. This effect of labetalol on the cardiovascular response did not decrease with repeated cocaine deliveries. The subjective response to smoked cocaine deliveries was not affected by labetalol treatment. These results suggest that labetalol effectively attenuates the systolic blood pressure and heart rate increases induced by repeated doses of smoked cocaine, but does not alter subjective effects.

A nicotine conjugate vaccine reduces nicotine distribution to brain and attenuates its behavioral and cardiovascular effects in rats

Vaccination of animals to elicit drug-specific antibodies, or the passive transfer of such antibodies from other animals, can reduce the behavioral effects of drugs such as cocaine and heroin. To study the potential application of this approach to treating nicotine dependence, IgG was isolated from rabbits immunized with a nicotine-protein conjugate vaccine. Anesthetized rats received immune IgG containing nicotine-specific antibodies (Nic-IgG) or control-IgG i.v.. Thirty minutes later, rats received nicotine at 0.03 mg/kg i.v., equivalent on an mg/kg basis to the nicotine intake from two cigarettes by a smoker. Compared to control-IgG, Nic-IgG reduced the brain nicotine concentration in a dose-related manner (65% reduction at the highest IgG dose). Pretreatment with Nic-IgG also reduced the distribution to brain of five repeated doses of nicotine (equivalent to the nicotine intake from 10 cigarettes) administered over 80 min. To study blood pressure effects, rats received control-IgG or Nic-IgG 1 day prior to administering nicotine. Nicotine-induced systolic blood pressure increases were attenuated by Nic-IgG in a dose-related manner, and were almost completely blocked by the highest Nic-IgG dose. Pretreatment with Nic-IgG also completely prevented the nicotine-induced stimulation of locomotor activity observed in rats receiving control-IgG. Nic-IgG did not prevent locomotor activation from cocaine, demonstrating its specificity for nicotine. These data demonstrate that the administration of nicotine-specific antibodies can reduce or prevent some of the pharmacokinetic, cardiovascular, and behavioral consequences of nicotine in rats. Effects were observed at nicotine doses and nicotine serum concentrations equal to or exceeding those typically associated with nicotine exposure in cigarette smokers. A potential role for immunization in the treatment of nicotine dependence is suggested.

Predictors of cardiovascular response to smoked cocaine in humans

The purpose of this study was to examine the predictors of heart rate and blood pressure changes following cocaine administration. Sixty-two smoked cocaine users received a single 0.4 mg/kg dose of smoked cocaine. Male sex, African American race, higher body weight and current marijuana use predicted a greater cardiovascular response to cocaine. In contrast, higher baseline blood pressure, heart rate, amount and frequency of current cocaine use and presence of current cocaine snorting predicted a diminished cardiovascular response to cocaine. Whether these predictors of the cardiovascular response to smoked cocaine in the laboratory also predict cardiovascular complications from long-term cocaine use needs to be studied further.

Sex and menstrual cycle differences in the subjective effects from smoked cocaine in humans

To investigate sex and menstrual cycle effects in response to cocaine administration, data from existing studies were analyzed. First, responses to a single delivery of 0.4 mg/kg smoked cocaine were investigated. Women reported lower ratings for measures of paranoid/suspicious and heart racing/pounding than did men. In addition, women in the luteal phase reported diminished ratings for a measure of feel high than did both women in the follicular phase of the menstrual cycle and men. Second, responses to up to 6 deliveries of 0.4 mg/kg smoked cocaine were investigated. Women, compared with men, had lower ratings on feel high, heart racing/pounding, and feel stimulated. Results suggest that there are significant sex and menstrual phase differences in the subjective effects of cocaine.

Altered disposition of repeated nicotine doses in rats immunized against nicotine

Active immunization of rats against nicotine reduces the distribution of a single intravenous dose of nicotine to brain. The current study examined the effects of immunization on the distribution of repeated doses of nicotine, and on estimates of nicotine pharmacokinetic parameters. Groups of rats received five repeated doses of nicotine over 80 min (total dose equivalent to the nicotine intake from one, three or 10 cigarettes in a human). The serum nicotine concentration in immunized rats was 160-430% higher than controls after the fifth dose, demonstrating binding of nicotine to antibody. Brain nicotine concentration in immunized rats was reduced by 30-46%. The reduction in distribution of nicotine to brain correlated with the serum hapten-specific antibody concentration, the percentage of nicotine bound in serum, and with the unbound nicotine concentration in serum. In immunized rats, nicotine had a smaller steady state volume of distribution, lower systemic clearance, and longer terminal half-life than in controls. These data demonstrate that immunization against nicotine reduces nicotine distribution to brain, even after multiple nicotine doses at rates approximating heavy cigarette smoking. Whether this reduction in nicotine distribution is large enough to alter nicotine's physiological or behavioral effects remains to be studied.

Sex and menstrual cycle differences in the subjective effects from smoked cocaine in humans

To investigate sex and menstrual cycle effects in response to cocaine administration, data from existing studies were analyzed. First, responses to a single delivery of 0.4 mg/kg smoked cocaine were investigated. Women reported lower ratings for measures of paranoid/suspicious and heart racing/pounding than did men. In addition, women in the luteal phase reported diminished ratings for a measure of feel high than did both women in the follicular phase of the menstrual cycle and men. Second, responses to up to 6 deliveries of 0.4 mg/kg smoked cocaine were investigated. Women, compared with men, had lower ratings on feel high, heart racing/pounding, and feel stimulated. Results suggest that there are significant sex and menstrual phase differences in the subjective effects of cocaine.

Immunization of rats reduces nicotine distribution to brain

The effect of active immunization against nicotine on the initial distribution of nicotine to brain was studied in anesthetized rats. Animals received nicotine 0.03 mg/kg nicotine (equivalent to the nicotine dose absorbed by a human smoking two cigarettes) as a rapid injection in the jugular vein. In control animals, the arterial serum nicotine concentration initially exceeded the venous concentration 4.6-fold, similar to the initial arteriovenous difference produced by cigarette smoking in humans. Animals immunized with the nicotine analog CMUNic maintained this arteriovenous gradient, but with both arterial and venous nicotine concentrations several times higher than in controls. The arterial nicotine concentration was higher in immunized animals even at the first (7.5 s) sampling time. The brain nicotine concentration at 3 min was 36% lower in the immunized animals. The time course of nicotine distribution to brain was studied in a second group of animals. Brain nicotine concentration was reduced in rats immunized with CMUNic over the entire 6-min sampling period immediately following nicotine dosing (mean reduction 38%). A reduction was found at the earliest sampling time (30 s) and was maximal at 1 min (48%). Nicotine protein binding in serum was markedly increased in animals immunized with CMUNic compared to controls (91.2 versus 10.9%), and the unbound nicotine concentration in serum was lower (10.0 versus 13.4 ng/ml). The reduction in brain nicotine concentration correlated with antibody affinity for nicotine, and the percentage of nicotine bound in serum. These data demonstrate that nicotine-specific antibodies produced by active immunization rapidly bind nicotine in arterial blood, reduce the unbound nicotine concentration, and reduce the early distribution of nicotine to brain. Effects were observed using a clinically relevant nicotine dose and route of administration. These data suggest that the use of immunization to modify the behavioral effects of nicotine may be possible.

Effects of phenytoin on cocaine self-administration in humans

The goal of this pilot study was to determine the effects of phenytoin on cocaine self-administration in a human laboratory model. Subjects were randomized to either phenytoin (n = 6) or placebo (n = 7). Those assigned to phenytoin treatment received a single oral loading dose of 20 mg/kg. The phenytoin and placebo treatment groups did not differ in the number of tokens valued at $5, exchanged for cocaine. Similarly, the cardiovascular and subjective response to cocaine administration did not show a statistically significant treatment effect. In this laboratory model, phenytoin did not alter either the self-administration or effects of cocaine.

Effects of cotinine on cigarette self-administration

Previous studies have shown that cotinine, a metabolite of nicotine, antagonizes some of the effects of nicotine. One study showed that cotinine eliminates the beneficial effects of the nicotine patch in reducing cigarette withdrawal symptoms. The purpose of this study was to examine the effects of various doses of cotinine on cigarette self-administration. Subjects were randomly assigned to one of three doses of cotinine fumarate (40, 80 and 160 mg) and placebo, each for a period of 10 days, in a randomized order. Outcome variables included measures of nicotine intake and subjective responses to smoked cigarettes. Results showed no differences in the number of cigarettes smoked, carbon monoxide levels, and weights of cigarette butts across the various doses of cotinine and placebo. However, higher nicotine serum levels were observed in the 160 mg cotinine fumarate condition compared to placebo and to 40 mg cotinine fumarate. No systematic effects of cotinine on subjective responses to cigarettes were observed. Cotinine appears potentially to have a selective modulatory effect on nicotine withdrawal symptoms but not on cigarette smoking.

Effects of dynorphin A(1-13) on opiate withdrawal in humans

The objectives of the current study were to determine 1) the effects of various doses of dynorphin A (1-13) on opiate withdrawal in humans and 2) the safety of dynorphin at these doses. Opiate dependent subjects who had been stabilized on morphine received a single IV dose of placebo, 150, 500 or 1000 microg/kg dynorphin after exhibiting spontaneous withdrawal using a randomized, double-blinded, between-subjects study design. Observer Withdrawal Scores were lower in the 150 and 1000 microg/kg groups as compared to placebo (P < 0.05) but no significant differences were observed on the observer-rated Wang or Sickness Scales. Significant decreases were also found for self-reported symptoms of nervousness, runny nose, sneezing, and painful joints in the 500 microg/kg group. Significant increases in serum prolactin levels were seen after all dynorphin doses; however, these were not dose-related. Dynorphin A (1-13) was well tolerated and safe, with no changes in physiologic parameters. We conclude that dynorphin A (1-13) has a modest effect in reducing mild opiate withdrawal in humans and is well tolerated at doses up to 1000 microg/kg.

Variation in human plasma cholinesterase activity during low-dose cocaine administration

BACKGROUND

Cocaine is metabolized by a number of enzymes, the activity of one of which, plasma cholinesterase has been associated with dinical manifestations of toxicity. Patients with life-threatening complications of cocaine intoxication have lower plasma cholinesterase activity than less toxic controls. In addition, relatively healthy cocaine users have lower plasma cholinesterase activity than noncocaine using controls. Thus, low plasma cholinesterase activity could be a contributing factor to cocaine toxicity, a consequence of cocaine use, or a confounding variable. The following study was designed to further assess the relationship between cocaine use and plasma cholinesterase activity.

METHODS

We studied fluctuations in plasma cholinesterase activity in nine subjects enrolled in an inpatient study of the behavioral pharmacology of smoked cocaine. Subjects used at least 2 g of cocaine weekly for at least 1 year prior to enrollment. The subjects were admitted to the research unit where they remained drug-free for 2 days. They then received smoked cocaine for 4 days (up to 405 mg over 5 hours daily) and were then drug-free again for 2 days. Plasma cholinesterase activity was measured at 9 AM and 4 PM each day.

RESULTS

Baseline plasma cholinesterase ranged from 265 to 930 U/L (normal > 450 U/L). The mean plasma cholinesterase increased 112+/-100 U/L from day 1 to day 8 (p = 0.025). There was no daily change in plasma cholinesterase levels from 9 AM to 4 PM (15+/-165 U/L, p > 0.6), and there was no difference in the daily change between high- and low-dose cocaine days (-3+/-137 U/L vs 28+/-165 U/L, p = 0.52).

CONCLUSION

These preliminary data suggest that plasma cholinesterase levels do not change over a 7-hour period as a result of cocaine administration, but may increase during a period of inpatient study. Such an increase could potentially influence the pharmacokinetics or effects of cocaine studied in an inpatient setting and may give insight into the etiology of the observed low-plasma cholinesterase activity in cocaine users.

Cotinine: effects with and without nicotine

The purpose of this study was to examine the effects of the metabolite of nicotine, cotinine, in comparison to the effects of the nicotine patch, and a combination thereof during cigarette abstinence. More specifically, this study examined the effects of cotinine on physiological measures, subjective measures assessing craving, withdrawal symptoms and mood, and performance measures. A between-subject, 2 x 2 factorial design was used, with the daily administration of a 15-mg nicotine patch (Nicotrol) versus placebo patch as one factor and 80 mg of oral cotinine fumarate versus placebo drug as the other factor. Baseline measures were obtained while the subjects smoked cigarettes on an ad lib basis for 1 week. Subjects (n = 106) were then randomly assigned to one of four treatment conditions and for the next 14 days were required to be abstinent from cigarettes and take the study drugs. Cotinine administration, with or without nicotine patch, produced serum cotinine concentrations 3 4 times higher than during ad lib smoking. Results showed a reduction of self-reported tobacco withdrawal symptoms using the nicotine patch alone. Cotinine alone had no effect on withdrawal symptoms. However, when nicotine patch was combined with cotinine, the beneficial effect of the nicotine patch on withdrawal symptoms was absent. Therefore, cotinine appears to antagonize the effects of nicotine in the alleviation of withdrawal symptoms at concentrations higher than that attained from normal smoking. This effect does not appear to be mediated by changes in nicotine disposition.

Active immunization alters the plasma nicotine concentration in rats

The ability of active immunization to alter nicotine distribution was studied in rats. Animals were immunized with 6-(carboxymethylureido)-(+/-)-nicotine (CMUNic) linked to keyhole limpet hemocyanin (KLH). Antibody titers determined by ELISA, using CMUNic coupled to albumin as the coating antigen, were greater than 1:10,000. Antibody binding was inhibited by neither of the nicotine metabolites cotinine and nicotine-N-oxide but was inhibited to a greater extent by CMUNic than by nicotine; this suggests the presence of antibodies to the linker structure as well as antibodies to nicotine. Antibody affinity for nicotine measured by soluble radioimmunoassay was 2.4 +/- 1.6 x 10(7) M-1, and binding capacity was 1.3 +/- 0.7 x 10(-6) M, which corresponds to 0.1 +/- 0.05 mg/ml of nicotine-specific IgG per milliliter of serum. One week after their second boost, groups of eight anesthetized rats immunized with either CMUNic-KLH or KLH alone received nicotine 0.03 mg/kg (equivalent to two cigarettes in a human) via the jugular vein over 10 sec. This dosing regimen was shown to mimic the arterio-venous nicotine concentration gradient typical of nicotine delivered by cigarette smoking in humans. Plasma nicotine concentrations at 10 to 40 min were 4 to 6-fold higher in the CMUNic-KLH rats than in controls (P < .001). Nicotine binding in plasma determined by equilibrium dialysis was markedly increased in the CMUNic-KLH group (83.4 +/- 6.8% vs. 16.4 +/- 14.2%), but brain nicotine concentrations at 40 min did not differ (37.9 +/- 4.5 vs. 44.0 +/- 8. 4 ng/g, CMUNic-KLH vs. KLH, P = .1). The amount of nicotine bound to antibody in plasma, estimated from the in vivo data, was 9% of the administered dose. These data demonstrate that active immunization can bind a significant fraction of a clinically relevant nicotine dose in plasma. Observing this effect with antibodies of modest affinity and titer is encouraging, but better immunogens may be needed to alter nicotine distribution to brain and modify nicotine's behavioral effects.

Safety of cotinine in humans: physiologic, subjective, and cognitive effects

Preliminary data suggest that cotinine, the major metabolite of nicotine, may be behaviorally active. Studies involving the administration of cotinine at doses that produce high blood concentrations (in excess of those produced by cigarette smoking) may be of interest. This inpatient, 10-day human study examined the safety and the effects from several high doses of oral cotinine fumarate (40, 80, or 160 mg) or placebo in abstinent cigarette smokers. All subjects smoked cigarettes ad lib during the first 2 days of the study, then were required to be abstinent beginning on the third day. All subjects were given placebo on this day to wash out nicotine before the administration of cotinine. Subjects were subsequently randomly assigned in a double-blind manner to cotinine or placebo for the next 3 days to determine the safety profile of cotinine. All subjects were given placebo on the final 3 days to examine cotinine withdrawal symptoms. The results showed no significant physiologic, subjective, or performance effects across the various doses of cotinine and placebo. Furthermore, no cotinine withdrawal effects were observed. This study demonstrates that short-term administration of cotinine to humans at levels as high as 10 times that attained from cigarette smoking is safe with no observable acute or withdrawal effects from cotinine in this setting.

High-level secretion of two antibody single chain Fv fragments by Pichia pastoris

The diagnostic and therapeutic applications of antibody single-chain Fv (sFv) fragments often require large amounts of protein that can be problematic and expensive to obtain. Here we report the secretion of two sFv fragments by the yeast Pichia pastoris at levels up to 250 mg/l. Soluble sFv fragments were purified from culture supernatants in one step by affinity or metal-chelating chromatography, and were indistinguishable from their bacterially expressed counterparts in terms of affinity. Secretion of functional sFv fragments by Pichia pastoris provides a low cost, high yield alternative to current sFv expression systems.

Bacterial expression and characterization of an anti-desipramine single-chain antibody fragment

Tricyclic antidepressant toxicity is a leading cause of death from intentional drug overdose. Monoclonal antibody Fab' fragments specific for the tricyclic antidepressant, desipramine, reverse acute drug toxicity but may themselves have adverse effects at therapeutic doses. To evaluate the characteristics of smaller antibody fragments, we cloned, expressed and characterized a 26 kD single chain Fv fragment (G5-sFv). A DNA sequence encoding VH-linker-V1 was constructed from hybridoma mRNA encoding a high affinity monoclonal desipramine specific IgG1 and expressed in E. coli. G5-sFv was produced at high levels as insoluble inclusion bodies. Single chain Fv was solubilized, folded in a redox buffer and affinity purified on desipramine-Sepharose. The affinity of G5-sFv for desipramine was similar to that of the corresponding monoclonal Fab' as measured by surface plasmon resonance (Fab' 5.5 +/- 0.5 x 10(8) M-1, sFv 2.3 +/- 0.5 x 10(8) M-1). G5-sFv administered to rats after a tracer dose of 3H-desipramine produced rapid and marked redistribution of drug from tissues into serum. G5-sFv was stable at 4 C for greater than 6 months but lost activity at higher temperatures. We conclude that desipramine-specific-single chain Fv expressed in E. coli retains the affinity of the parent antibody for desipramine. The pharmacokinetic effect of G5-sFv on desipramine distribution suggests that it may be useful as an antidote for desipramine overdose.

Nitric oxide contributes to desipramine-induced hypotension in rats

1. Anesthetized rats received the TCA desipramine (DMI) 60 mg kg-1 i.p. Administration of the nitric oxide synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester-(L-NAME) 15 min after DMI reversed hypotension within 5 min (P < 0.05). In contrast to its beneficial effect on blood pressure, L-NAME worsened DMI-induced prolongation of the electrocardiographic QRS interval. Dexamethasone, an inhibitor of NOS induction, did not prevent DMI-induced hypotension. 2. To study the effect of L-NAME on survival, DMI was administered to anesthetized rats as a continuous i.v. infusion until death. Despite initially improving blood pressure, L-NAME decreased the mean survival time by 33% (P < 0.01) compared to control treatment. Administration of the nitric oxide (NO) donor nitroglycerine to rats during DMI infusion likewise decreased the mean survival time. 3. L-NAME partially reversed the hypotensive effect of nitroprusside in both anesthetized and awake rats. 4. These data suggest that NO production attributable to constitutive NOS (cNOS) activity aggravates the hypotension associated with DMI toxicity in the anesthetized rat, and contributes to the pathophysiology of this overdose. The shortened survival time produced by both increasing and decreasing NO production suggests that cNOS activity during DMI overdose is regulated and adaptive. Ongoing cNOS activity also contributed to nitroprusside-induced hypotension, and may represent a feature common to other drug-induced hypotensive states.

Effects of recombinant drug-specific single chain antibody Fv fragment on [3H]-desipramine distribution in rats

Tricyclic antidepressant overdose can be reversed in rats by drug-specific antibody Fab fragments, but the required Fab dose may itself by toxic. We studied the potential use of a smaller, recombinant desipramine (DMI)-specific single chain Fv fragment (B9-sFv) for this purpose. Anesthetized rats received a tracer (subtoxic) dose of [3H]-DMI followed in 15 min by B9-IgG, B9-Fab, B9-sFv (0.1 mumol of binding sites) or BSA. Each of the active treatments produced a rapid and substantial increase in the serum radiolabel concentration, whereas BSA did not (P < 0.001). The increase in serum radiolabel concentration 1 min after treatment was 13.3-fold with B9-IgG, 10.0-fold with B9-Fab and 7.3-fold with B9-sFv. Serum antibody concentrations were also highest after B9-IgG and lower with B9-Fab or B9-sFv. The 24-hr urinary excretion of radiolabel did not differ among groups, but was extensive even in the BSA group and probably represented the excretion of DMI metabolites. B9-sFv concentrations in urine or buffer at 37 degrees declined by >90% over 24 hr, but this fragment was much more stable in serum, retaining 70% of its activity after 96 hr. These data demonstrate that B9-sFv can alter markedly the distribution of [3H]-DMI in vivo. The rapidity of this effect, and its magnitude in comparison with Fab fragment or IgG, suggest that further study of B9-sFv as a treatment of DMI overdose is warranted.

Smoked cocaine self-administration in females

Although approximately 32% of all smoked cocaine ("crack") users are women, most studies investigating cocaine use have recruited only male subjects. Therefore, this study examined the smoked cocaine self-administration patterns of female crack abusers. A work requirement, where up to five tokens were earned by subjects, was followed by the administration of a sample delivery of one of three dose sizes [5.0 mg (placebo), 0.2 mg/kg, 0.4 mg/kg] of cocaine. The three dose sizes of cocaine were administered in counterbalanced order across subjects, with each subject receiving one dose size within a session and all dose sizes across the three experimental sessions. A self-administration phase followed the sample delivery, during which a token could be exchanged every 30 min for monetary reimbursement or a delivery of cocaine in the same dose size as the sample delivery. The results show that females' patterns of behavioral and subjective responding to smoked cocaine exhibit clear dose-related effects, thus affirming this self-administration model as safe and appropriate for use with women.

Effect of calcium chloride and 4-aminopyridine therapy on desipramine toxicity in rats

BACKGROUND

Hypotension is a major contributor to mortality in tricyclic antidepressant overdose. Recent data suggest that tricyclic antidepressants inhibit calcium influx in some tissues. This study addressed the potential role of calcium channel blockade in tricyclic antidepressant-induced hypotension.

METHODS

Two interventions were studied that have been shown previously to improve blood pressure with calcium channel blocker overdose. CaCl2 and 4-aminopyridine. Anesthetized rats received the tricyclic antidepressant desipramine IP to produce hypotension, QRS prolongation, and bradycardia. Fifteen min later, animals received CaCl2, NaHCO3, or saline. In a second experiment, rats received tricyclic antidepressant desipramine IP followed in 15 min by 4-aminopyridine or saline.

RESULTS

NaHCO3 briefly (5 min) reversed hypotension and QRS prolongation. CaCl2 and 4-aminopyridine failed to improve blood pressure. The incidence of ventricular arrhythmias (p = 0.004) and seizures (p = 0.03) in the CaCl2 group was higher than the other groups.

CONCLUSION

The administration of CaCl2 or 4-aminopyridine did not reverse tricyclic antidepressant-induced hypotension in rats. CaCl2 therapy may possibly worsen both cardiovascular and central nervous system toxicity. These findings do not support a role for calcium channel inhibition in the pathogenesis of tricyclic antidepressant-induced hypotension.

Drug-specific antibodies as antidotes for tricyclic antidepressant overdose

Drug-specific antibodies have been used clinically to treat digoxin or colchicine overdose. The lethal dose of tricyclic antidepressants (TCAs) is 100 times higher, and will require higher doses of antibodies (up to several g/kg) to reverse toxicity. Preliminary studies suggest that this is feasible. High affinity TCA-specific monoclonal Fab' or polyclonal Fab fragments rapidly reverse the cardiovascular toxicity of the TCA desipramine (DMI) in rats, and prolong survival. TCA-specific Fab' or Fab is generally well tolerated in rats, but doses several times higher than anticipated for human use may have adverse effects. Combining Fab with standard therapies for TCA overdose, such as NaHCO3, can reduce the required Fab dose. As an alternative, a recombinant single chain Fv fragment (sFv), one half the size of Fab, has been cloned which retains a high affinity for DMI and is able to alter DMI distribution in vivo. Because sFv has a shorter elimination half-life and more extensive renal excretion than Fab, it may have therapeutic advantages.

Cloning, expression, and purification of an anti-desipramine single chain antibody in NS/O myeloma cells

Drug-specific monoclonal antibodies and their antigen-binding Fab fragments reverse acute desipramine toxicity in a rat experimental model by inducing a redistribution of drug from cardiac tissue into serum and extracellular fluid. In order to investigate the use of smaller recombinant antibody fragments such as single chain Fv (sFv) as an antidote, an efficient murine NS/O myeloma expression system was developed. The variable light (VL) and variable heavy (VH) domains of a murine anti-desipramine monoclonal antibody were cloned and sequenced. A 270 amino acid VH-(Gly4Ser)3-VL sFv was prepared by overlapping polymerase chain reaction (PCR) amplification of VH with heavy chain leader peptide, VL, and the linker. This construct was subcloned into a mammalian expression vector which utilizes the SR alpha promoter, a hybrid promoter consisting of the SV40 early promoter with portions of the human T-cell leukemia virus type I long terminal repeat and also containing the Escherichia cloi xanthine-guanine phosphoribosyltransferase gene for selection. NS/O myeloma cells were transfected by electroporation. Stable recombinant NS/O clones were screened for expression of sFv using reverse transcriptase-PCR to detect mRNA and an enzyme-linked immunosorbent assay (ELISA) to detect sFv. Secreted sFv from clones capable of growth to a cell density of 2-4 x 10(6) viable cells/mL was purified in a single step using a desipramine affinity column resulting in 12-39 mg/L of purified sFv. Affinity-purified sFv had comparable desipramine binding activity to Fab when evaluated by competitive ELISA.

Reduction of desipramine cardiotoxicity and prolongation of survival in rats with the use of polyclonal drug-specific antibody Fab fragments

STUDY OBJECTIVE

Tricyclic antidepressants (TCAs) are a leading cause of death from intentional drug overdose. Available therapies are often unsatisfactory. In this study we evaluated the use of a high-affinity drug-specific polyclonal Fab fragment (TFab) as an antidote to desipramine toxicity.

DESIGN

We gave anaesthetized rats under mechanical ventilation IV desipramine so that we might study the effect of TFab on survival or IP desipramine to facilitate study of the interaction of TFab and hypertonic sodium bicarbonate (NaHCO3), the standard clinical treatment for TCA overdose.

INTERVENTIONS

For the study of the effects of TFab and NaHCO3 on survival, each rat was given a constant IV infusion of desipramine until it died, together with TFab 2 g/kg, bovine serum albumin, or .9% NaCl starting 5 minutes after the desipramine infusion. In the study of the interaction of TFab and NaHCO3, each rat received 30 mg/kg IP desipramine followed by TFab (molar TFab:desipramine ratio, .11), NaHCO3, TFab+NaHCO3, or NaCl at the time of maximal toxicity (15 minutes).

RESULTS

In the survival protocol, QRS-interval duration, systolic blood pressure, and heart rate were significantly improved by TFab, and survival was prolonged by 58% compared with that in the albumin and NaCl groups (P < .001). The molar ratio of TFab to administered desipramine was .21. The unbound fraction of desipramine in serum at the time of death was reduced by TFab, but the unbound desipramine concentration was not, suggesting that TFab prolonged survival by delaying the increase in the unbound serum desipramine concentration. In the interaction protocol, neither TFab nor NaHCO3 was effective alone, but the combination significantly reduced QRS-interval prolongation (P = .001).

CONCLUSION

These data demonstrate the efficacy of TFab in reducing desipramine-induced cardiovascular toxicity and prolonging survival. The pharmacokinetic effects of TFab in rats with severe desipramine toxicity were similar to those observed in sublethal desipramine toxicity. Therapeutic benefit is enhanced by the concurrent use of NaHCO3 and may be achieved despite binding only a fraction of the desipramine dose.

Effects of high intravenous doses of dynorphin A(1-13) on tail flick latency and central nervous system histology in rats

Dynorphin A(1-13) blocks opiate withdrawal in rats without producing dependence, and enhances analgesia in morphine-tolerant animals. Its potential use in humans is therefore of interest. Dynorphin A(1-13) has little toxicity when administered at modest doses IV but has been reported to cause hindlimb paralysis and necrosis of the spinal cord in rats, at the catheter tip, when administered intrathecally. To further evaluate its potential neurotoxicity, we administered dynorphin A(1-13) to rats at very high doses IV. Rats (n = 6-10 per group) received dynorphin A(1-13) as bolus IV doses of 5 mg/kg, or as continuous IV infusions of 40 mg/kg/day for 1 day, with saline controls. The appearance and behavior of all animals was normal. Tail flick latencies remained unchanged (p > 0.5). There were no histologic abnormalities of the spinal cord or brain when examined by light microscopy. Two additional groups received bolus injections of dynorphin A(1-13) 50 or 100 mg/kg IV. Animals receiving 50 mg/kg showed cutaneous flushing, labored respirations, and decreased spontaneous movement, which resolved within 10 min. Histology at 1 week was normal. All six animals receiving 100 mg/kg convulsed and died within minutes. Three animals that received dynorphin A(1-13) 40 mg/kg/day for 7 days had normal behavior and histology. We conclude that the previously observed neurotoxicity of intrathecally administered dynorphin A(1-13) is a local effect that does not occur when dynorphin A(1-13) is administered IV, even at very high doses.

Reversal of flecainide-induced ventricular arrhythmia by hypertonic sodium bicarbonate in dogs

Flecainide occasionally produces incessant ventricular tachycardia that is difficult to treat. Reports of uncontrolled clinical studies have suggested a therapeutic role for hypertonic sodium bicarbonate (NaHCO3). To test this observation, spontaneous and pacing-induced arrhythmia canine models were designed. In the spontaneous model, flecainide was infused at 0.5 mg/kg/min until ventricular tachycardia occurred spontaneously. In the pacing-induced model, flecainide was infused at 1.0 mg/kg/min load (0.5 mg/kg/min maintenance) stepwise until the QRS was widened 50%, 75%, and 100%, with programmed ventricular stimulation at each step until ventricular arrhythmia was induced. Dogs who developed spontaneous arrhythmia were treated blindly with three doses of either NaHCO3 (3 mEq/kg/dose, with 1 minute between doses) or normal saline. Dogs who were induced in the second model were treated with the same three doses, 10 minutes apart, with programmed stimulation between each dose. Before unblinding in both protocols, dogs were classified as "responders" or "nonresponders" to therapy. In the spontaneous model, of 14 dogs with spontaneous ventricular tachycardia, all 7 dogs treated with NaHCO3 showed response, compared with only 1 of 7 dogs treated with saline (P < .01). Ventricular QRS complexes/min were reduced by NaHCO3 in that protocol. In the induced arrhythmia protocol, of 14 dogs with inducible arrhythmia, 6 of 7 responded to NaHCO3, and 1 of 7 responded to placebo (P < .05). In both protocols, arterial pH and the serum sodium concentration were increased by NaHCO3 but not by normal saline control treatment. QRS interval duration was shortened by NaHCO3 therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of specific antibody Fab fragments on desipramine pharmacokinetics in the rat in vivo and in the isolated, perfused liver

Drug-specific antibody fragments, which can reverse tricyclic antidepressant toxicity in rats, represent a potential clinical treatment for tricyclic antidepressant overdose in humans. To delineate the pharmacokinetic mechanisms, we studied the effects of a high-affinity, drug-specific Fab fragment on desipramine (DMI) disposition in rats and on DMI kinetics in the isolated, perfused rat liver. These studies were performed at high DMI and Fab doses, with Fab administered at the time of peak DMI toxicity, to simulate the treatment of overdose. Rats received 20 mg/kg DMI intravenously over 30 min followed in 10 min by DMI-specific ovine polyclonal Fab (DMI-Fab) or nonspecific human Fab (control-Fab) (1.1 g/kg; molar Fab-to-DMI ratio, 0.34) intravenously over 20 min. The serum DMI concentration increased by 50-fold 5 min after DMI-Fab administration. The mean area under the serum concentration-time curve increased by more than 3-fold. The steady-state volume of distribution was decreased by 90% and total body clearance was decreased by 70% after DMI-Fab administration compared with control-Fab. Renal clearance increased by 72% after DMI-Fab and total renal excretion of DMI increased by 7-fold due to the much higher serum DMI concentration. Ninety-four percent of DMI-Fab excretion and 87% of DMI excretion occurred in the first 12 h. The percent of DMI bound in urine was markedly increased by DMI-Fab (87.1 vs. 19.1%), as was the molar ratio of DMI to DMI-Fab in urine (0.75 vs. 0.08). Isolated rat livers were perfused with DMI alone, DMI and DMI-Fab or DMI and control-Fab.(ABSTRACT TRUNCATED AT 250 WORDS)

Toxicity of high doses of polyclonal drug-specific antibody Fab fragments

Drug-specific antibody Fab fragments have been used as a treatment for acute drug overdose. For some drugs, the required Fab dose may be very high (up to several g/kg) and may have adverse effects of its own. The current study evaluated the potential toxicity of an affinity purified sheep polyclonal Fab (TFab) directed at the two antidepressants desipramine (DMI) and nortriptyline. TFab 4 g/kg was administered to anesthetized rats i.v. over 10, 25 or 60 min, with or without a toxic dose of DMI. This high dose of TFab, which is in excess of that needed to reduce DMI toxicity, was used in order to exaggerate any adverse effects. In the absence of DMI, TFab produced minimal changes in the electrocardiographic QRS duration, systolic blood pressure and heart rate compared with control animals and was well tolerated. In the presence of DMI, groups receiving TFab as a 10 or 25 min infusion showed a therapeutic effect (lessening of DMI toxicity) over the first 60 min compared with the control group, but one of six animals in each of the TFab groups died prior to the end of the 180 min experiment. No control animals died, but progressive QRS prolongation and decreasing blood pressure toward the end of the experiment suggested that DMI toxicity was increasing over time. These data suggest that, when administered alone, very high doses of rapidly infused TFab are well tolerated. When administered with DMI, TFab is effective in initially reducing DMI toxicity. However, this dose of TFab may later aggravate DMI toxicity and/or the effects of prolonged anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Glutaramyl-beta-alanyl spacer group for haptenic coupling to proteins. Preparation of immunogens for antibody production against polychlorinated biphenyls

By use of a glutaramyl-beta-alanyl spacer group, a hapten for the polychlorinated biphenyl, 2,2',4,4',5,5'-hexachlorobiphenyl (1), viz., 2-amino-2',4,4',5,5'-pentachlorobiphenyl (2), was successfully conjugated to carrier proteins to provide immunogens with high hapten/protein molar substitution ratios (MSR's). The procedure allows for the incorporation of beta-[3H]-alanine into the immunogen, thereby providing an accurate radiochemical method for the quantitative assessment of MSR. The use of the glutaramyl spacer group was prompted by the observation that the corresponding succinamyl group was subject to side reactions manifested by succinimide formation during the carboxyl activation step to an activated ester for subsequent coupling to proteins, thus severely compromising the coupling yields. The glutaramyl-beta-alanyl spacer group should be generally applicable for protein conjugation of any hapten with an amino functional group in the molecule.

Redistribution and enhanced urinary excretion of 2,2',4,4',5,5'-hexachlorobiphenyl (HCB) in rats using HCB-specific IgG and Fab fragments

Drug-specific antibody fragments can enhance the elimination of some drugs by redistributing drug from tissues into serum and allowing renal excretion of the drug-antibody complex. This approach could potentially be used to enhance the elimination of compounds such as polychlorinated biphenyls that have very long elimination half-lives. As a first step in testing this hypothesis, the effects of 2,2',4,4',5,5'-hexachlorobiphenyl (HCB)-specific antibodies and their corresponding Fab fragments on HCB disposition were studied in rats. Antibodies to HCB were produced in chickens, and the corresponding Fab fragments were produced by digestion with papain. To study antibody effects on HCB distribution, [14C]HCB (0.1 mg) was administered i.v. to rats. Two weeks later, after distribution to tissues was complete, anti-HCB IgG or control IgG was administered i.v. The serum radiolabel concentration 2 hr after IgG administration increased 185 +/- 64% in animals treated with specific antibody vs 51 +/- 19% in control animals (P < 0.001). The increase in serum radiolabel concentration was apparent within 30 min and maximal at 2 hr. To study effects on HCB excretion, anti-HCB or control Fab fragment was administered 2 weeks after [14C]HCB. Urinary HCB excretion over the next 24 hr, measured by gas chromatography, was 10-fold greater in the group treated with anti-HCB Fab (P < 0.01). These data demonstrate that anti-HCB IgG can redistribute HCB rapidly from tissues into serum and that anti-HCB Fab can enhance urinary HCB excretion. While the magnitude of these changes was small, the data suggest that increasing HCB excretion using drug-specific antibody fragments is feasible, and can serve as a model for enhancing the excretion of compounds that have very long elimination half-lives.