A TLR7/8 agonist increases efficacy of anti-fentanyl vaccines in rodent and porcine models

Opioid use disorders (OUD) and overdose are public health threats worldwide. Widespread access to highly potent illicit synthetic opioids such as fentanyl is driving the recent rise in fatal overdoses. Vaccines containing fentanyl-based haptens conjugated to immunogenic carrier proteins offer a long-lasting, safe, and cost-effective strategy to protect individuals from overdose upon accidental or deliberate exposure to fentanyl and its analogs. Prophylactic or therapeutic active immunization with an anti-fentanyl vaccine induces the production of fentanyl-specific antibodies that bind the drug in the blood and prevent its distribution to the brain, which reduces its reinforcing effects and attenuates respiratory depression and bradycardia. To increase the efficacy of a lead anti-fentanyl vaccine, this study tested whether the incorporation of synthetic toll-like receptor (TLR) 4 and TLR7/8 agonists as vaccine adjuvants would increase vaccine efficacy against fentanyl challenge, overdose, and self-administration in either rats or Hanford miniature pigs. Formulation of the vaccine with a nucleolipid TLR7/8 agonist enhanced its immunogenicity and efficacy in preventing fentanyl-induced respiratory depression, analgesia, bradycardia, and self-administration in either rats or mini-pigs. These studies support the use of TLR7/8 adjuvants in vaccine formulations to improve their clinical efficacy against OUD and potentially other substance use disorders (SUD).

Attenuating nicotine's effects with high affinity human anti-nicotine monoclonal antibodies

Use of nicotine-specific monoclonal antibodies (mAbs) to sequester and reduce nicotine distribution to brain has been proposed as a therapeutic approach to treat nicotine addiction (the basis of tobacco use disorder). A series of monoclonal antibodies with high affinity for nicotine (nic•mAbs) was isolated from B-cells of vaccinated smokers. Genes encoding 32 unique nicotine binding antibodies were cloned, and the mAbs expressed and tested by surface plasmon resonance to determine their affinity for S-(–)-nicotine. The highest affinity nic•mAbs had binding affinity constants (K_D) between 5 and 67 nM. The 4 highest affinity nic•mAbs were selected to undergo additional secondary screening for antigen-specificity, protein properties (including aggregation and stability), and functional in vivo studies to evaluate their capacity for reducing nicotine distribution to brain in rats. The 2 most potent nic•mAbs in single-dose nicotine pharmacokinetic experiments were further tested in a dose-response in vivo study. The most potent lead, ATI-1013, was selected as the lead candidate based on the results of these studies. Pretreatment with 40 and 80 mg/kg ATI-1013 reduced brain nicotine levels by 56 and 95%, respectively, in a repeated nicotine dosing experiment simulating very heavy smoking. Nicotine self-administration was also significantly reduced in rats treated with ATI-1013. A pilot rat 30-day repeat-dose toxicology study (4x200mg/kg ATI-1013) in the presence of nicotine indicated no drug-related safety concerns. These data provide evidence that ATI-1013 could be a potential therapy for the treatment of nicotine addiction.

The reinforcement threshold and elasticity of demand for nicotine in an adolescent rat model of depression

BACKGROUND

The Food and Drug Administration (FDA) is considering setting a nicotine standard for tobacco products to reduce their addictiveness. Such a standard should account for the apparent greater vulnerability to nicotine addiction in some subpopulations, such as adolescents with depression. The present study examined whether the reinforcement threshold and elasticity of demand (i.e., reinforcing efficacy) for nicotine in a genetic inbred rat model of depression (Flinders Sensitive Line [FSL]) differs from an outbred control strain.

METHODS

Acquisition of nicotine self-administration (NSA) across a wide range of nicotine doses was measured in both FSL and Sprague-Dawley (SD) control adolescent rats. At the highest dose, elasticity of demand was also measured. Nicotine pharmacokinetics was examined to determine whether it might modulate NSA, as it does smoking in humans.

RESULTS

FSL rats acquired self-administration quicker and showed more inelastic demand (greater reinforcing efficacy) than SDs at the highest unit dose. However, there was no strain difference in the reinforcement threshold of nicotine. FSL rats exhibited faster nicotine clearance, larger volume of distribution, and lower plasma and brain nicotine concentrations. However, these differences were not consistently related to strain differences in NSA measures.

CONCLUSION

These findings are consistent with studies showing greater dependence and reinforcing efficacy of cigarettes in smokers with depression and those with relatively fast nicotine metabolism. However, these findings also suggest that a nicotine standard to reduce initiation of tobacco use should be similarly effective in both the general adolescent population and those with depression.

Alum as an adjuvant for nanoparticle based vaccines: A case study with a hybrid nanoparticle-based nicotine vaccine

The treatment efficacy of a nicotine vaccine largely relies on its ability to induce high titers of nicotine-specific antibodies. Due to its strong immune-potentiating effects, aluminum salt (Alum) has been commonly used as an adjuvant in various nicotine vaccine formulations. In this study, we attempted to improve the immunological performance of a hybrid nanoparticle-based nicotine vaccine (NanoNicVac) by co-administering it with Alum. It was found that Alum severely restricted the release of NanoNicVac at the site of injection. Moreover, Alum damaged the hybrid structure of the vaccine. In the animal trial, mice immunized with NanoNicVac alone achieved an anti-nicotine IgG titer of 3.5 ± 0.2 × 10⁴ after three injections. Unexpectedly, Alum with quantities of 125, 250, 500, and 1000 μg did not enhance the immunogenicity of NanoNicVac. In addition, Alum did not improve the ability of the vaccine to reduce the entry of nicotine into the brain.

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.

A Fentanyl Vaccine Alters Fentanyl Distribution and Protects against Fentanyl-Induced Effects in Mice and Rats

Fentanyl is an extremely potent synthetic opioid that has been increasingly used to adulterate heroin, cocaine, and counterfeit prescription pills, leading to an increase in opioid-induced fatal overdoses in the United States, Canada, and Europe. A vaccine targeting fentanyl could offer protection against the toxic effects of fentanyl in both recreational drug users and others in professions at risk of accidental exposure. This study focuses on the development of a vaccine consisting of a fentanyl-based hapten (F) conjugated to keyhole limpet hemocyanin (KLH) carrier protein or to GMP-grade subunit KLH (sKLH). Immunization with F-KLH in mice and rats reduced fentanyl-induced hotplate antinociception, and in rats reduced fentanyl distribution to the brain compared with controls. F-KLH did not reduce the antinociceptive effects of equianalgesic doses of heroin or oxycodone in rats. To assess the vaccine effect on fentanyl toxicity, rats immunized with F-sKLH or unconjugated sKLH were exposed to increasing subcutaneous doses of fentanyl. Vaccination with F-sKLH shifted the dose-response curves to the right for both fentanyl-induced antinociception and respiratory depression. Naloxone reversed fentanyl effects in both groups, showing that its ability to reverse respiratory depression was preserved. These data demonstrate preclinical selectivity and efficacy of a fentanyl vaccine and suggest that vaccines may offer a therapeutic option in reducing fentanyl-induced side effects.

Paradox of PEGylation in fabricating hybrid nanoparticle-based nicotine vaccines

Polyethylene glycol (PEG) has long been used in nanoparticle-based drug or vaccine delivery platforms. In this study, nano-nicotine vaccines (NanoNicVac) were PEGylated to different degrees to investigate the impact of PEG on the immunological efficacy of the vaccine. Hybrid nanoparticles with various degrees of PEGylation (2.5%-30%) were assembled. It was found that 30% PEGylation resulted in a hybrid nanoparticle of a compromised core-shell structure. A higher concentration of PEG also led to a slower cellular uptake of hybrid nanoparticles by dendritic cells. However, increasing the quantity of the PEG could effectively reduce nanoparticle aggregation during storage and improve the stability of the hybrid nanoparticles. Subsequently, nicotine vaccines were synthesized by conjugating nicotine haptens to the differently PEGylated hybrid nanoparticles. In both in vitro and in vivo studies, it was found that a nicotine vaccine with 20% PEGylation (NanoNicVac 20.0) was significantly more stable than the vaccines with lower PEGylation. In addition, NanoNicVac 20.0 induced a significantly higher anti-nicotine antibody titer of 3.7 ± 0.6 × 10⁴ in mice than the other NanoNicVacs with lower concentrations of PEG. In a subsequent pharmacokinetic study, the lowest brain nicotine concentration of 34 ± 11 ng/g was detected in mice that were immunized with NanoNicVac 20.0. In addition, no apparent adverse events were observed in mice immunized with NanoNicVac. In summary, 20% PEGylation confers NanoNicVac with desirable safety, the highest stability, and the best immunological efficacy in mice.

The nicotine-degrading enzyme NicA2 reduces nicotine levels in blood, nicotine distribution to brain, and nicotine discrimination and reinforcement in rats

BACKGROUND

The bacterial nicotine-degrading enzyme NicA2 isolated from P. putida was studied to assess its potential use in the treatment of tobacco dependence.

RESULTS

Rats were pretreated with varying i.v. doses of NicA2, followed by i.v. administration of nicotine at 0.03 mg/kg. NicA2 had a rapid onset of action reducing blood and brain nicotine concentrations in a dose-related manner, with a rapid onset of action. A 5 mg/kg NicA2 dose reduced the nicotine concentration in blood by > 90% at 1 min after the nicotine dose, compared to controls. Brain nicotine concentrations were reduced by 55% at 1 min and 92% at 5 min post nicotine dose. To evaluate enzyme effects at a nicotine dosing rate equivalent to heavy smoking, rats pretreated with NicA2 at 10 mg/kg were administered 5 doses of nicotine 0.03 mg/kg i.v. over 40 min. Nicotine levels in blood were below the assay detection limit 3 min after either the first or fifth nicotine dose, and nicotine levels in brain were reduced by 82 and 84%, respectively, compared to controls. A 20 mg/kg NicA2 dose attenuated nicotine discrimination and produced extinction of nicotine self-administration (NSA) in most rats, or a compensatory increase in other rats, when administered prior to each daily NSA session. In rats showing compensation, increasing the NicA2 dose to 70 mg/kg resulted in extinction of NSA. An enzyme construct with a longer duration of action, via fusion with an albumin-binding domain, similarly reduced NSA in a 23 h nicotine access model at a dose of 70 mg/kg.

CONCLUSIONS

These data extend knowledge of NicA2's effects on nicotine distribution to brain and its ability to attenuate addiction-relevant behaviors in rats and support its further investigation as a treatment for tobacco use disorder.

Opioid Dose- and Route-Dependent Efficacy of Oxycodone and Heroin Vaccines in Rats

Heroin and oxycodone abuse occurs over a wide range of drug doses and by various routes of administration characterized by differing rates of drug absorption. The current study addressed the efficacy of a heroin vaccine [morphine hapten conjugated to keyhole limpet hemocyanin (M-KLH)] or oxycodone vaccine [oxycodone hapten conjugated to keyhole limpet hemocyanin (OXY-KLH)] for reducing drug distribution to brain after intravenous heroin or oxycodone, or subcutaneous oxycodone. Rats immunized with M-KLH or keyhole limpet hemocyanin (KLH) control received an intravenous bolus dose of 0.26 or 2.6 mg/kg heroin. Vaccination with M-KLH increased retention of heroin and its active metabolites 6-acetylmorphine (6-AM) and morphine in plasma compared with KLH controls, and reduced total opioid (heroin + 6-AM + morphine) distribution to brain but only at the lower heroin dose. Immunization also protected against respiratory depression at the lower heroin dose. Rats immunized with OXY-KLH or KLH control received 0.22 or 2.2 mg/kg oxycodone intravenously, the molar equivalent of the heroin doses. Immunization with OXY-KLH significantly reduced oxycodone distribution to brain after either oxycodone dose, although the magnitude of effect of immunization at the higher oxycodone dose was small (12%). By contrast, vaccination with OXY-KLH was more effective when oxycodone was administered subcutaneously rather than intravenously, reducing oxycodone distribution to brain by 44% after an oxycodone dose of 2.3 mg/kg. Vaccination also reduced oxycodone-induced antinociception. These data suggest that the efficacy of OXY-KLH and M-KLH opioid vaccines is highly dependent upon opioid dose and route of administration.

Rational incorporation of molecular adjuvants into a hybrid nanoparticle-based nicotine vaccine for immunotherapy against nicotine addiction

Current clinically-tested nicotine vaccines have yet shown enhanced smoking cessation efficacy due to their low immunogenicity. Achieving a sufficiently high immunogenicity is a necessity for establishing a clinically-viable nicotine vaccine. This study aims to facilitate the immunogenicity of a hybrid nanoparticle-based nicotine vaccine by rationally incorporating toll-like receptor (TLR)-based adjuvants, including monophosphoryl lipid A (MPLA), Resiquimod (R848), CpG oligodeoxynucleotide 1826 (CpG ODN 1826), and their combinations. The nanoparticle-delivered model adjuvant was found to be taken up more efficiently by dendritic cells than the free counterpart. Nanovaccine particles were transported to endosomal compartments upon cellular internalization. The incorporation of single or dual TLR adjuvants not only considerably increased total anti-nicotine IgG titers but also significantly affected IgG subtype distribution in mice. Particularly, the nanovaccines carrying MPLA+R848 or MPLA+ODN 1826 generated a much higher anti-nicotine antibody titer than those carrying none or one adjuvant. Meanwhile, the anti-nicotine antibody elicited by the nanovaccine adjuvanted with MPLA+R848 had a significantly higher affinity than that elicited by the nanovaccine carrying MPLA+ODN 1826. Moreover, the incorporation of all the selected TLR adjuvants (except MPLA) reduced the brain nicotine levels in mice after nicotine challenge. Particularly, the nanovaccine with MPLA+R848 exhibited the best ability to reduce the level of nicotine entering the brain. Collectively, rational incorporation of TLR adjuvants could enhance the immunological efficacy of the hybrid nanoparticle-based nicotine vaccine, making it a promising next-generation immunotherapeutic candidate for treating nicotine addiction.

Prescreening of Nicotine Hapten Linkers in Vitro To Select Hapten-Conjugate Vaccine Candidates for Pharmacokinetic Evaluation in Vivo

Since the demonstration of nicotine vaccines as a possible therapeutic intervention for the effects of tobacco smoke, extensive effort has been made to enhance nicotine specific immunity. Linker modifications of nicotine haptens have been a focal point for improving the immunogenicity of nicotine, in which the evaluation of these modifications usually relies on in vivo animal models, such as mice, rats or nonhuman primates. Here, we present two in vitro screening strategies to estimate and predict the immunogenic potential of our newly designed nicotine haptens. One utilizes a competition enzyme-linked immunoabsorbent assay (ELISA) to profile the interactions of nicotine haptens or hapten-protein conjugates with nicotine specific antibodies, both polyclonal and monoclonal. Another relies on computational modeling of the interactions between haptens and amino acid residues near the conjugation site of the carrier protein to infer linker-carrier protein conjugation effect on antinicotine antibody response. Using these two in vitro methods, we ranked the haptens with different linkers for their potential as viable vaccine candidates. The ELISA-based hapten ranking was in an agreement with the results obtained by in vivo nicotine pharmacokinetic analysis. A correlation was found between the average binding affinity (IC50) of the haptens to an anti-Nic monoclonal antibody and the average brain nicotine concentration in the immunized mice. The computational modeling of hapten and carrier protein interactions helps exclude conjugates with strong linker-carrier conjugation effects and low in vivo efficacy. The simplicity of these in vitro screening strategies should facilitate the selection and development of more effective nicotine conjugate vaccines. In addition, these data highlight a previously under-appreciated contribution of linkers and hapten-protein conjugations to conjugate vaccine immunogenicity by virtue of their inclusion in the epitope that binds and activates B cells.

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.

Predictors of the nicotine reinforcement threshold, compensation, and elasticity of demand in a rodent model of nicotine reduction policy

BACKGROUND

The FDA is considering reducing the nicotine content in tobacco products as a population-based strategy to reduce tobacco addiction. Research is needed to determine the threshold level of nicotine needed to maintain smoking and the extent of compensatory smoking that could occur during nicotine reduction. Sources of variability in these measures across sub-populations also need to be identified so that policies can take into account the risks and benefits of nicotine reduction in vulnerable populations.

METHODS

The present study examined these issues in a rodent nicotine self-administration model of nicotine reduction policy to characterize individual differences in nicotine reinforcement thresholds, degree of compensation, and elasticity of demand during progressive reduction of the unit nicotine dose. The ability of individual differences in baseline nicotine intake and nicotine pharmacokinetics to predict responses to dose reduction was also examined.

RESULTS

Considerable variability in the reinforcement threshold, compensation, and elasticity of demand was evident. High baseline nicotine intake was not correlated with the reinforcement threshold, but predicted less compensation and less elastic demand. Higher nicotine clearance predicted low reinforcement thresholds, greater compensation, and less elastic demand. Less elastic demand also predicted lower reinforcement thresholds.

CONCLUSIONS

These findings suggest that baseline nicotine intake, nicotine clearance, and the essential value of nicotine (i.e. elasticity of demand) moderate the effects of progressive nicotine reduction in rats and warrant further study in humans. They also suggest that smokers with fast nicotine metabolism may be more vulnerable to the risks of nicotine reduction.

Pharmacokinetic correlates of the effects of a heroin vaccine on heroin self-administration in rats

The purpose of this study was to evaluate the effects of a morphine-conjugate vaccine (M-KLH) on the acquisition, maintenance, and reinstatement of heroin self-administration (HSA) in rats, and on heroin and metabolite distribution during heroin administration that approximated the self-administered dosing rate. Vaccination with M-KLH blocked heroin-primed reinstatement of heroin responding. Vaccination also decreased HSA at low heroin unit doses but produced a compensatory increase in heroin self-administration at high unit doses. Vaccination shifted the heroin dose-response curve to the right, indicating reduced heroin potency, and behavioral economic demand curve analysis further confirmed this effect. In a separate experiment heroin was administered at rates simulating heroin exposure during HSA. Heroin and its active metabolites, 6-acetylmorphine (6-AM) and morphine, were retained in plasma and metabolite concentrations were reduced in brain in vaccinated rats compared to controls. Reductions in 6-AM concentrations in brain after vaccination were consistent with the changes in HSA rates accompanying vaccination. These data provide evidence that 6-AM is the principal mediator of heroin reinforcement, and the principal target of the M-KLH vaccine, in this model. While heroin vaccines may have potential as therapies for heroin addiction, high antibody to drug ratios appear to be important for obtaining maximal efficacy.

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.

Portion size effects on weight gain in a free living setting

OBJECTIVE

Examine the effect of weekday exposure over 6 months to different lunch sizes on energy intake and body weight in a free-living sample of working adults.

METHODS

Adults (n = 233) were randomly assigned to one of three lunch size groups (400 kcal, 800 kcal, and 1,600 kcal) or to a no-free lunch control group for 6 months. Weight and energy intake were measured at baseline, and months 1, 3, and 6.

RESULTS

Lunch energy was significantly higher in the 800 and 1,600 kcal groups compared with the 400 kcal group (P < 0.0001). Total energy was significantly higher for the 1,600 kcal group compared with the 400 and 800 kcal groups (P = 0.02). Body weight change at 6 months did not significantly differ at the 5% level by experimental group (1,600 kcal group: +1.1 kg (SD = 0.44); 800 kcal group: -0.1 kg (SD = 0.42); 400 kcal group: -0.1 kg (SD = 0.43); control group: 1.1 (SD = 0.42); P = 0.07). Weight gain over time was significant in the 1,600 kcal box lunch group (P < 0.05).

CONCLUSIONS

Weekday exposure for 6 months to a 1,600 kcal lunch caused significant increases in total energy intake and weight gain.

Effect of currently approved carriers and adjuvants on the pre-clinical efficacy of a conjugate vaccine against oxycodone in mice and rats

Vaccination against the highly abused prescription opioid oxycodone has shown pre-clinical efficacy for blocking oxycodone effects. The current study further evaluated a candidate vaccine composed of oxycodone derivatized at the C6 position (6OXY) conjugated to the native keyhole limpet hemocyanin (nKLH) carrier protein. To provide an oxycodone vaccine formulation suitable for human studies, we studied the effect of alternative carriers and adjuvants on the generation of oxycodone-specific serum antibody and B cell responses, and the effect of immunization on oxycodone distribution and oxycodone-induced antinociception in mice and rats. 6OXY conjugated to tetanus toxoid (TT) or a GMP grade KLH dimer (dKLH) was as effective as 6OXY conjugated to the nKLH decamer in mice and rats, while the 6OXY hapten conjugated to a TT-derived peptide was not effective in preventing oxycodone-induced antinociception in mice. Immunization with 6OXY-TT s.c. absorbed on alum adjuvant provided similar protection to 6OXY-TT administered i.p. with Freund's adjuvant in rats. The toll-like receptor 4 (TLR4) agonist monophosphoryl lipid A (MPLA) adjuvant, alone or in combination with alum, offered no advantage over alum alone for generating oxycodone-specific serum antibodies or 6OXY-specific antibody secreting B cells in mice vaccinated with 6OXY-nKLH or 6OXY-TT. The immunogenicity of oxycodone vaccines may be modulated by TLR4 signaling since responses to 6OXY-nKLH in alum were decreased in TLR4-deficient mice. These data suggest that TT, nKLH and dKLH carriers provide consistent 6OXY conjugate vaccine immunogenicity across species, strains and via different routes of administration, while adjuvant formulations may need to be tailored to individual immunogens or patient populations.

New directions in nicotine vaccine design and use

Clinical trials of nicotine vaccines suggest that they can enhance smoking cessation rates but do not reliably produce the consistently high serum antibody concentrations required. A wide array of next-generation strategies are being evaluated to enhance vaccine efficacy or provide antibody through other mechanisms. Protein conjugate vaccines may be improved by modifications of hapten or linker design or by optimizing hapten density. Conjugating hapten to viruslike particles or disrupted virus may allow exploitation of naturally occurring viral features associated with high immunogenicity. Conjugates that utilize different linker positions on nicotine can function as independent immunogens, so that using them in combination generates higher antibody concentrations than can be produced by a single immunogen. Nanoparticle vaccines, consisting of hapten, T cell help peptides, and adjuvants attached to a liposome or synthetic scaffold, are in the early stages of development. Nanoparticle vaccines offer the possibility of obtaining precise and consistent control of vaccine component stoichiometry and spacing and immunogen size and shape. Passive transfer of nicotine-specific monoclonal antibodies offers a greater control of antibody dose, the ability to give very high doses, and an immediate onset of action but is expensive and has a shorter duration of action than vaccines. Viral vector-mediated transfer of genes for antibody production can elicit high levels of antibody expression in animals and may present an alternative to vaccination or passive immunization if the long-term safety of this approach is confirmed. Next-generation immunotherapies are likely to be substantially more effective than first-generation vaccines.

Immunogenicity of individual vaccine components in a bivalent nicotine vaccine differ according to vaccine formulation and administration conditions

Structurally distinct nicotine immunogens can elicit independent antibody responses against nicotine when administered concurrently. Co-administering different nicotine immunogens together as a multivalent vaccine could be a useful way to generate higher antibody levels than with monovalent vaccines alone. The immunogenicity and additivity of monovalent and bivalent nicotine vaccines was studied across a range of immunogen doses, adjuvants, and routes to assess the generality of this approach. Rats were vaccinated with total immunogen doses of 12.5 - 100 μg of 3′-aminomethyl nicotine conjugated to recombinant Pseudomonas exoprotein A (3′-AmNic-rEPA), 6-carboxymethylureido nicotine conjugated to keyhole limpet hemocyanin (6-CMUNic-KLH), or both. Vaccines were administered s.c. in alum or i.p. in Freund’s adjuvant at matched total immunogen doses. When administered s.c. in alum, the contributions of the individual immunogens to total nicotine-specific antibody (NicAb) titers and concentrations were preserved across a range of doses. Antibody affinity for nicotine varied greatly among individuals but was similar for monovalent and bivalent vaccines. However when administered i.p. in Freund’s adjuvant the contributions of the individual immunogens to total NicAb titers and concentrations were compromised at some doses. These results support the possibility of co-administering structurally distinct nicotine immunogens to achieve a more robust immune response than can be obtained with monovalent immunogens alone. Choice of adjuvant was important for the preservation of immunogen component activity.

Increased efficacy of a trivalent nicotine vaccine compared to a dose-matched monovalent vaccine when formulated with alum

Vaccination against nicotine is a potential treatment for tobacco smoking. Clinical trials show effect only in high antibody responders; therefore it is necessary to increase the effectiveness of nicotine vaccines. The use of a multivalent vaccine that activates several B cell populations is a possible approach to increase antibody response. The aim of this study was to investigate whether three different nicotine immunogens could be mixed to generate independent responses resulting in additive antibody titers, and whether this would alter nicotine distribution to a greater extent than antibodies generated by a monovalent vaccine. When immunogens were administered s.c. with alum adjuvant, the trivalent vaccine generated significantly higher titers and prevented the distribution of an i.v. nicotine dose to brain to a greater extent than an equivalent dose of a monovalent vaccine. The number of rats with antibody titers >1:10,000 was significantly increased in the trivalent group compared to the monovalent group. There were no correlations between the titers generated by the different nicotine immunogens in the trivalent vaccine, supporting the hypothesis that the immunogens generated independent responses from distinct populations of B cells. In contrast, when administered i.p. in Freund's adjuvant, the trivalent nicotine vaccine was not more immunogenic than its component monovalent vaccine. Vaccine immunogenicity was suppressed if unconjugated protein was added to the monovalent vaccine formulated in Freund's adjuvant, compared to monovalent vaccine alone. These data suggest a protein-protein interaction that affects titers negatively and is apparent when the vaccines are formulated with Freund's adjuvant. In summary, a trivalent nicotine vaccine formulated with alum showed significantly higher efficacy than a dose-matched monovalent vaccine and may offer a strategy for increasing nicotine vaccine immunogenicity. This approach may be generalizable to other nicotine immunogens or vaccines for other addictive drugs.

Reduced antinociception of opioids in rats and mice by vaccination with immunogens containing oxycodone and hydrocodone haptens

Prescription opioids abuse and associated deaths are an emerging concern in the USA. Vaccination against prescription opioids may provide an alternative to pharmacotherapy. An oxycodone hapten containing a tetraglycine linker at the C6 position (6OXY(Gly)(4)OH) conjugated to keyhole limpet hemocyanin (KLH) has shown early proof-of-efficacy in rodents as a candidate immunogen (6OXY(Gly)(4)-KLH) for the treatment of oxycodone abuse. In this study, oxycodone-based and hydrocodone-based haptens were conjugated to KLH to generate immunogens that would recognize both oxycodone and hydrocodone. Vaccination with 6OXY(Gly)(4)-KLH increased drug binding in serum, reduced drug distribution to brain, and blunted analgesia for both oxycodone and hydrocodone. An analogous C6-linked hydrocodone vaccine blocked hydrocodone effects but less so than 6OXY(Gly)(4)-KLH. C8-Linked hydrocodone immunogens had only limited efficacy. Amide conjugation showed higher haptenation ratios and greater efficacy than thioether conjugation to maleimide activated KLH (mKLH). The 6OXY(Gly)(4)-KLH vaccine may be used for treatment of prescription opioid abuse.

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.

High immunogenicity of nicotine vaccines obtained by intradermal delivery with safe adjuvants

Immunotherapy for tobacco addiction may offer a safe, alternative treatment if the immunogenicity of the current nicotine vaccines can be improved. We show here that intradermal (ID) immunization induces the production of antibody directed against nicotine (NicAb) at a much higher level than conventional intramuscular (IM) immunization. The magnitude and duration of NicAb production was further increased robustly by non-inflammatory laser vaccine adjuvant (LVA), slightly inflammatory monophosphoryl lipid A (MPL) or a combination of MPL and CpG adjuvants. Consequently, significantly fewer vaccination doses were required to attain a high level of NicAb production for an extended period of time and reduce nicotine entry into the brain in the presence of LVA, MPL or MPL/CpG adjuvant, respectively. Yet, the potency of these adjuvants to augment ID nicotine vaccine immunogenicity came at the expense of local skin reactogenicity, with LVA causing little skin reaction and MPL/CpG stimulating overt skin irritation. These observations underscore a necessity of a balance between optimal adjuvant potency and undesired local reactogenicity. In summary, our study presents a novel approach to significantly improve nicotine vaccine immunogenicity by a combination of safe cutaneous vaccine adjuvants with ID immunization.

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.

Enhanced attenuation of nicotine discrimination in rats by combining nicotine-specific antibodies with a nicotinic receptor antagonist

Tobacco addiction requires activation by nicotine of a variety of central nicotinic acetylcholine receptors (nAChRs). In animals, both nAChR antagonists and immunization against nicotine can reduce nAChR activation by nicotine and block a variety of addiction-relevant behaviors. However, clinical use of nAChR antagonists for smoking cessation is limited by dose-related side effects, and immunization does not reliably produce sufficient antibody levels in smokers to enhance smoking cessation rates. Combining these approaches may be one way of addressing the limitations of each while enhancing overall efficacy. This study examined the individual and combined effects of passive immunization with the monoclonal nicotine-specific antibody Nic311 and the nicotinic receptor antagonist mecamylamine (MEC) on nicotine's discriminative stimulus effects. Rats were trained to discriminate 0.4 mg/kg of nicotine from saline using a two-lever operant discrimination procedure. Antagonism of nicotine discrimination by Nic311 (160 mg/kg i.v.) and ascending doses of MEC (0.03, 0.1, 0.3, and 1.0 mg/kg s.c.) was assessed across four consecutive daily 2-min extinction test sessions using a 2×2 design. Nic311 alone produced a 24-48% reduction in % nicotine-lever responding (%NLR) across all four test sessions. MEC produced a dose-dependent decrease in %NLR, with no effect at the two lowest doses and 80-93% attenuation at the two highest doses. Nic311 combined with MEC significantly suppressed %NLR at every MEC dose (85-92% reduction across all four test sessions). Very low doses of MEC that were ineffective alone completely blocked nicotine discrimination when combined with Nic311. These data demonstrate that nicotine-specific antibodies and MEC can work synergistically to suppress the subjective effects of nicotine and suggest that low doses of MEC may significantly enhance the efficacy of immunotherapy.

Delivery of nicotine in an extract of a smokeless tobacco product reduces its reinforcement-attenuating and discriminative stimulus effects in rats

RATIONALE

Animal models of tobacco addiction rely on administration of nicotine alone or nicotine combined with isolated constituents. Models using tobacco extracts derived from tobacco products and containing a range of tobacco constituents might more accurately simulate tobacco exposure in humans.

OBJECTIVE

To compare the effects of nicotine alone and an aqueous smokeless tobacco extract in several addiction-related animal behavioral models.

METHODS

Nicotine alone and nicotine dose-equivalent concentrations of extract were compared in terms of their acute effects on intracranial self-stimulation (ICSS) thresholds, discriminative stimulus effects, and effects on locomotor activity.

RESULTS

Similar levels of nicotine and minor alkaloids were achieved using either artificial saliva or saline for extraction, supporting the clinical relevance of the saline extracts used in these studies. Extract produced reinforcement-enhancing (ICSS threshold-decreasing) effects similar to those of nicotine alone at low to moderate nicotine doses, but reduced reinforcement-attenuating (ICSS threshold-increasing) effects at a high nicotine dose. In rats trained to discriminate nicotine alone from saline, intermediate extract doses did not substitute for the training dose as well as nicotine alone. Locomotor stimulant effects and nicotine distribution to brain were similar following administration of extract or nicotine alone.

CONCLUSIONS

The reinforcement-attenuating and discriminative stimulus effects of nicotine delivered in an extract of a commercial smokeless tobacco product differed from those of nicotine alone. Extracts of tobacco products may be useful for evaluating the abuse liability of those products and understanding the role of non-nicotine constituents in tobacco addiction.

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.

Combined active and passive immunization against nicotine: minimizing monoclonal antibody requirements using a target antibody concentration strategy

Nicotine vaccines have shown preliminary evidence of efficacy for enhancing smoking cessation rates, but the serum nicotine-specific antibody (NicAb) concentrations produced are highly variable and many subjects do not develop effective levels. As an alternative to vaccination, passive immunization with nicotine-specific monoclonal antibodies could produce more uniform serum NicAb concentrations, but its use is limited by their high cost and shorter elimination half-life. This study investigated supplementing vaccination with monoclonal antibodies in a targeted fashion to increase vaccine efficacy while minimizing the required monoclonal antibody dose. Rats were vaccinated and then given individualized supplemental doses of the nicotine-specific monoclonal antibody Nic311 to achieve a target total serum NicAb concentration known to be effective for blocking locomotor sensitization (LMS) to nicotine. Rats received vaccine, Nic311, both, or neither, followed by 0.3 mg/kg nicotine s.c. for 10 days to produce LMS. Combination immunotherapy completely blocked the development of LMS, while monotherapy with vaccine or Nic311 alone was only minimally effective. Lower brain nicotine levels were associated with reduced locomotor activity averaged over days 7-10. Despite its greater efficacy, combination immunotherapy did not reduce the variability in the resulting total serum NicAb concentrations. Variability in total serum NicAb concentrations was contributed to by both vaccine-generated antibody and by Nic311. These data show that combination immunotherapy, using a Nic311 dose that is by itself only minimally effective, can substantially enhance nicotine vaccine efficacy. However, variability in serum NicAb levels with combination immunotherapy may make translation of this approach challenging.

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.

Comparison of the behavioral effects of cigarette smoke and pure nicotine in rats

Animal models of tobacco dependence typically rely on parenteral administration of pure nicotine. Models using cigarette smoke inhalation might more accurately simulate nicotine exposure in smokers. The primary goal of this study was to validate methods for administering cigarette smoke to rats using exposure conditions that were clinically relevant and also produced brain nicotine levels similar to those produced by behaviorally active doses of pure nicotine. A secondary goal was to begin examining the behavioral effects of smoke. Nose-only exposure (NOE) to smoke for 10-45min or whole-body exposure (WBE) to smoke for 1-4h produced serum nicotine concentrations similar to those in smokers (14-55ng/ml), without excessive carbon monoxide exposure. Daily nicotine (0.1mg/kg, s.c.) induced locomotor sensitization whereas 45-min NOE producing brain nicotine levels within the same range did not. Nicotine 0.125mg/kg s.c. reversed withdrawal from a chronic nicotine infusion as measured by elevations in intracranial self-stimulation thresholds whereas 4-h WBE producing similar brain nicotine levels did not. These data demonstrate the feasibility of delivering cigarette smoke to rats at clinically relevant doses, and provide preliminary evidence that the behavioral effects of nicotine delivered in smoke may differ from those of pure nicotine.

Correlates of individual differences in compensatory nicotine self-administration in rats following a decrease in nicotine unit dose

RATIONALE

The ability of tobacco harm reduction strategies to produce significant reductions in toxin exposure is limited by compensatory increases in smoking behavior. Characterizing factors contributing to the marked individual variability in compensation may be useful for understanding this phenomenon and assessing the feasibility of harm reduction interventions.

OBJECTIVE

The objective of the study was to use an animal model of human compensatory smoking that involves a decrease in unit dose supporting nicotine self-administration (NSA) to examine potential contributors to individual differences in compensation.

METHODS

Rats were trained for NSA during daily 23-h sessions at a unit dose of 0.06 mg/kg/inf until responding was stable. The unit dose was then reduced to 0.03 mg/kg/inf for at least 10 sessions. Following reacquisition of NSA at the training dose and extinction, single-dose nicotine pharmacokinetic parameters were determined.

RESULTS

Decreases in nicotine intake following dose reduction were proportionally less than the decrease in unit dose, indicating partial compensation. Compensatory increases in infusion rates were observed across the course of the 23-h sessions. The magnitude of compensation differed considerably between rats. Rats exhibiting the highest baseline infusion rates exhibited the lowest levels of compensation. Nicotine pharmacokinetic parameters were not significantly correlated with compensation. Infusion rates immediately returned to pre-reduction levels when baseline conditions were restored.

CONCLUSIONS

These findings provide initial insights into correlates of individual differences in compensation following a reduction in nicotine unit dose. The present assay may be useful for characterizing mechanisms and potential consequences of the marked individual differences in compensatory smoking observed in humans.

Stability of the nicotine metabolite ratio in ad libitum and reducing smokers

BACKGROUND

The ratio of two nicotine metabolites, cotinine and trans-3'-hydroxycotinine (3-HC), has been validated as a method of phenotyping the activity of the liver enzyme cytochrome P450 (CYP) 2A6 and, thus, the rate of nicotine metabolism. Our objective was to evaluate the correlates and stability of the 3-HC to cotinine ratio in ad libitum and reducing smokers, using nicotine replacement therapy (NRT), over a period of months.

METHODS

Smokers (n = 123, 94% Caucasian) participated in a smoking reduction study, where one-third of the sample smoked ad libitum for 8 weeks (Waitlist phase), before joining the rest of the participants for 12 weeks of cigarette reduction (Reduction phase) using NRT. Urinary nicotine, cotinine, and 3-HC were measured at each visit.

RESULTS

The baseline 3-HC to cotinine ratio was significantly but weakly correlated with cigarettes per day (r = 0.19), BMI (r = -0.27), and waking at night to smoke (r = 0.23). As assessed by repeated measure ANOVA, the 3-HC to cotinine ratio was stable in the Waitlist phase [coefficient of variation for 3 to 4 measurements, 38% (range, 5-110%)], whereas minor variation was noted in the Reduction phase [coefficient of variation for 3-5 measurements, 35% (range, 10-107%)].

CONCLUSIONS

In nonreducing ad libitum smokers, the 3-HC to cotinine ratio was generally stable, whereas during smoking reduction using NRT, some small variation was detected. Although the current findings are suggestive of the stability of the 3-HC to cotinine ratio in a predominantly Caucasian sample smoking freely or reducing smoking with NRT, additional research is needed in more diverse populations.

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.

Combined active and passive immunization enhances the efficacy of immunotherapy against nicotine in rats

Vaccination against nicotine reduces the behavioral effects of nicotine in rats, and it is under clinical evaluation as a treatment for tobacco addiction. Efficacy is limited by the need for high serum nicotine-specific antibody (NicAb) levels, and currently available nicotine vaccines do not uniformly generate the required NicAb levels. Passive immunization with a nicotine-specific monoclonal antibody (Nic311) has also shown efficacy in rats. The principal aim of this study was to determine whether the combined use of vaccination and passive immunization would produce greater effects than vaccination alone on nicotine pharmacokinetics and locomotor sensitization (LMS) to nicotine. Rats were treated with vaccination alone, Nic311 alone, both, or neither, and then they were administered 10 daily injections of 0.3 mg/kg nicotine s.c. Treatment with Nic311 or vaccination alone increased the binding of nicotine in serum, reduced the unbound serum nicotine concentration and nicotine distribution to brain, and attenuated the development of LMS. Combined use of vaccination and passive immunization produced higher total serum NicAb levels, greater changes in nicotine pharmacokinetics, and a greater attenuation of LMS than either treatment alone. The total serum NicAb concentration was significantly correlated with brain nicotine levels and locomotor activity. These data indicate that providing higher serum NicAb concentrations improves the efficacy of immunotherapy against nicotine and that supplementing vaccination with passive immunization is a potential strategy to accomplish this.

Compensatory nicotine self-administration in rats during reduced access to nicotine: an animal model of smoking reduction

The ability of smoking reduction (e.g., decreasing cigarettes per day) to produce significant reductions in toxin exposure is limited by compensatory increases in smoking behavior. Characterizing factors contributing to the marked individual variability in compensation may be useful for understanding this phenomenon. The goal of the current study was to develop an animal model of smoking reduction and to begin to examine potential behavioral and pharmacokinetic contributors to compensation. Rats trained for nicotine self-administration (NSA) in unlimited access sessions were exposed to a progressive decrease in duration of access to nicotine from 23-hr/day to 10-, 6-, and 2-hr/day. Following a return to 23 hr/day access and extinction, single-dose nicotine pharmacokinetic parameters were determined. Rats exhibited a reduction in total daily nicotine intake during reduced access to NSA, but decreases in nicotine intake were not proportional to decreases in access duration. Compensatory increases in hourly infusion rate were also observed when access was decreased. The magnitude of compensation differed considerably among animals. Early session infusion rate during baseline was significantly correlated, while nicotine clearance was moderately correlated, with 1 measure of compensation. Infusion rates were transiently increased compared to prereduction levels when unlimited access was restored, and this effect was greatest in animals that had exhibited the greatest levels of compensation. These findings indicate that rats exhibit compensatory increases in NSA during reduced access to nicotine, with substantial individual variability. This model may be useful for characterizing underlying factors and potential consequences of compensatory smoking.

Developing the science base for reducing tobacco harm

The University of Minnesota Transdisciplinary Tobacco Use Research Center has been examining the multiple dimensions and the scientific evidence required to determine the feasibility of tobacco harm reduction as a means to reduce tobacco-related mortality and morbidity. Because of the complexity associated with exploring this area, an interdisciplinary approach is necessary. The research components that have been of particular focus at our center include (a) developing and validating biomarkers of tobacco-related exposure and toxicity, (b) developing animal models and designing studies with humans to assess a variety of smoking reduction approaches and potential reduced exposure products, and (c) determining individual differences in response to these interventions and products. A description of the ongoing activities and challenges in these areas is provided, along with projected directions for the future.

Effects of pregnancy on nicotine self-administration and nicotine pharmacokinetics in rats

RATIONALE

Because of the adverse effects of smoking during pregnancy, understanding the factors that influence maternal smoking may help in developing better treatments to help women quit smoking during pregnancy. Animal models could be useful for this purpose.

OBJECTIVE

The purpose of the present study was to begin the development of an animal model of smoking during pregnancy by initially characterizing nicotine self-administration (NSA) in pregnant rats. Another purpose was to begin to explore the effects of pregnancy on nicotine pharmacokinetics in rats.

MATERIALS AND METHODS

In experiment 1, female rats self-administering nicotine during 23-h sessions were examined throughout gestation and lactation. In experiment 2, locomotor activity was measured during pregnancy to assess further potential motor effects of pregnancy. Experiments 3 and 4 compared the single-dose pharmacokinetics of nicotine in male, nonpregnant female, and pregnant females in the first and third trimester of pregnancy and the first week of lactation.

RESULTS

NSA decreased over the course of pregnancy with NSA significantly lower in the third trimester compared to nonpregnant controls. NSA remained suppressed for up to 10 days into lactation. Locomotor behavior was also significantly suppressed during the second and third trimesters and throughout lactation. Nicotine elimination was slower in pregnant females compared to nonpregnant females only in the third trimester.

CONCLUSIONS

NSA, locomotor behavior, and nicotine elimination in rats are decreased during late pregnancy. The present study is the first to characterize NSA during pregnancy in animals, providing a potential model of maternal smoking in humans.

Prevalence, magnitude, and correlates of an extinction burst in drug-seeking behavior in rats trained to self-administer nicotine during unlimited access (23 h/day) sessions

RATIONALE

Animals trained to self-administer a variety of addictive drugs exhibit a temporary increase in response rate when saline is substituted for the drug (i.e., an "extinction burst"). However, the presence of an extinction burst in animal models of nicotine self-administration (NSA) has not been studied extensively.

OBJECTIVE

The objective of the study was to examine the prevalence, magnitude, and correlates of an extinction burst in nicotine-seeking behavior using data from a previously published study and recently trained animals.

MATERIALS AND METHODS

Rats were trained to self-administer nicotine (0.03 mg/kg per infusion) during daily 23-h sessions. Saline extinction was subsequently arranged, followed by reacquisition of NSA for some animals.

RESULTS

There was no increase in the daily infusion rate on the first day of extinction. However, a significant increase (35%) in mean peak 2-h infusion rates was observed within the first extinction session, indicative of an extinction burst. Greater extinction burst magnitude was correlated with higher infusion rates during the first 2 h of baseline sessions and smaller decreases in infusion rate at the end of extinction. In addition, animals with the slowest initial rates of extinction exhibited the fastest rates of reacquisition when unlimited access to nicotine was restored.

CONCLUSIONS

A modest increase in drug-seeking behavior occurred early within the first extinction session in rats trained to self-administer nicotine in unlimited access sessions. The presence of an extinction burst in nicotine-seeking behavior suggests similar mechanisms underlying extinction of NSA and self-administration of other drugs of abuse in animals and also parallels a similar phenomenon sometimes observed in smokers.

Acetaldehyde, a major constituent of tobacco smoke, enhances behavioral, endocrine, and neuronal responses to nicotine in adolescent and adult rats

We have previously shown that acetaldehyde, a constituent of tobacco smoke, increases nicotine self-administration in adolescent, but not adult, rats. The aim of this study was to determine whether acetaldehyde influences other behavioral, endocrine, or neuronal responses to nicotine at either age. Juvenile (postnatal day (P) 27) and adult (P90) male Sprague-Dawley rats were treated with saline, acetaldehyde (16 microg/kg/injection x 2, i.v.), nicotine (30 microg/kg/injection x 2, i.v.) or a combination of acetaldehyde and nicotine. Locomotion and center time were evaluated for 30 min in a novel open field, before measurement of plasma corticosterone levels and brain c-fos mRNA. Nicotine increased locomotor activity in juveniles but decreased it in adults; in contrast, center time was increased at both ages. Acetaldehyde potentiated nicotine's locomotor effects, but not center time. Nicotine induced c-fos expression in the bed nucleus of the stria terminalis, the central nucleus of the amygdala (CeA), nucleus accumbens, and the superior colliculus (SC) at both ages, whereas it activated the hypothalamic paraventricular nucleus (PVN) and consequent corticosterone secretion only in adults. Acetaldehyde potentiated nicotine-induced c-fos in CeA and SC, and activation of PVN c-fos expression/plasma corticosterone release; however, this drug interaction was only observed in behaviorally tested animals, not those that were minimally stressed. Thus, acetaldehyde may modulate the interaction of nicotine and stress. Although pharmacokinetic studies showed that acetaldehyde did not change nicotine levels in either brain or serum, nicotine penetration into the brain was slower in juveniles as compared to adults.

Effects of portion size on chronic energy intake

Background

This study experimentally examined the effects of repeated exposure to different meal portion sizes on energy intake.

Methods

Nineteen employees of a county medical center were given free box lunches for two months, one month each of 1528 and 767 average kcal. Foods were identical in the two conditions, but differed in portion size. Meals averaged 44% calories from fat. Participants self-reported how much of each lunch was eaten. Unannounced 24-hour dietary recalls were also conducted by phone twice per week during each exposure period.

Results

Mean energy intake at the lunch meal was 332 kcal/day higher in large lunch than in small lunch periods (p < .001). Mean 24-hour energy intake was 278 kcal/day higher in large versus small lunch periods (p < .001). There was no evidence of compensation over time. Average weight change over the month of large and small lunches was 0.64 ± 1.16 kg and 0.06 ± 1.03 kg, respectively, about what would be expected with the observed differences in energy intake.

Conclusion

This study suggests that chronic exposure to large portion size meals can result in sustained increases in energy intake and may contribute to body weight increases over time.

Nicotine pharmacokinetics and subjective effects of three potential reduced exposure products, moist snuff and nicotine lozenge

OBJECTIVE

To compare nicotine pharmacokinetics and subjective effects of three new smokeless tobacco potential reduced exposure products (PREPs; Ariva, Revel and Stonewall) with moist snuff (Copenhagen) and medicinal nicotine (Commit lozenge).

METHODS

10 subjects completed a randomised, within-subject, crossover study. Subjects used one product for 30 min at each of the five laboratory sessions. Maximal nicotine concentration (Cmax) was determined and area under the concentration time curve (AUC) was calculated for a 90-min period (during use and 60 min after use). Nicotine craving, withdrawal symptoms and ratings of product effects and liking were measured during product use.

RESULTS

Nicotine AUC and Cmax were higher for Copenhagen than for any other product (p<0.002) and higher for Commit than for either Ariva or Revel (p<0.001). Cmax for Commit was also higher than for Stonewall (p = 0.03). Craving was lowest during use of Copenhagen (p<0.03). Craving during use of Stonewall, Ariva and Commit was lower than during use of Revel (p<0.05). Withdrawal symptom score during use of Copenhagen was lower than during use of Revel (p = 0.009). Copenhagen scores were higher (p<0.005) than all other products in several measures of drug effects and liking (feel good effects, satisfaction, liking and desire for product, and strength of product).

CONCLUSION

The new smokeless tobacco PREPs result in lower nicotine concentrations and equivalent or lower reductions in subjective measures compared with medicinal nicotine. Since health effects of PREPs are largely unknown, medicinal nicotine should be preferentially encouraged for smokers or smokeless tobacco users wishing to switch to lower-risk products.

Effects of maternal intravenous nicotine administration on locomotor behavior in pre-weanling rats

Maternal tobacco use is associated with adverse developmental outcomes in offspring, including hyperactivity. Animal studies attempting to model this phenomenon have primarily used continuous s.c. nicotine infusion as the method of nicotine administration, which does not model the intermittent bolus delivery of nicotine associated with smoking in humans. The purpose of the present experiment was to examine the locomotor activity of pre-weanling offspring of pregnant rats exposed to an i.v. nicotine dosing protocol that approximates the pattern of nicotine exposure in moderate to heavy smokers. Pregnant rats were administered an i.v. bolus of 0.03 mg/kg nicotine (N=13) or saline (N=10) every 14 min for 16 h/day, resulting in a total daily dose of 2 mg/kg (base), from gestational day 4 to delivery. Pups from each litter were tested for spontaneous locomotor activity on postnatal days (PND) 19-21 and nicotine-induced locomotor activity on PND 22. Mean birth weight was significantly lower in nicotine-exposed pups compared to controls, but body weights were equivalent between groups by the time of behavioral testing. Mean total distance traveled, vertical counts, and stereotypy counts were lower on PND 19 in nicotine-exposed pups compared to controls, but only the difference in mean stereotypy counts was statistically significant. Within-session analysis revealed that both distance traveled and stereotypy were significantly decreased in nicotine-exposed pups in the first 5 min of the session on PND 19. Total time spent in the center of the field was also lower in nicotine-exposed pups. Nicotine-induced increases in activity on PND 22 did not differ according to gestational exposure. These findings demonstrate that prenatal nicotine exposure in a model that mimics the pattern of nicotine exposure from cigarette smoking in humans results in offspring that exhibit low birth weight and hypoactivity in a novel environment.

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.

Tobacco extract but not nicotine impairs the mechanical strength of fracture healing in rats

The influence of nicotine and tobacco extract (without nicotine) alone and in combination on and mechanical strength of closed femoral fractures in rats was investigated. One hundred four male Sprague-Dawley rats were divided into four groups receiving: nicotine, tobacco extract, tobacco extract plus nicotine, and saline. One week prior to fracture, osmotic pumps were implanted subcutaneously in all animals to administer nicotine equivalent to the serum level of nicotine observed in a smoker consuming one to two packs of cigarettes daily. An equivalent volume of saline was administered to the control animals. Tobacco extract was administered orally. A closed transverse femoral diaphysial fracture was performed, and stabilized with an intramedullary pin. The fractures were mechanically tested after 21 days of healing. Tobacco extract alone decreased the mechanical strength. Ultimate torque and torque at yield point of the tobacco extract group were decreased by 21% (p=0.010) and 23% (p=0.056), respectively, compared with the vehicle (saline) group, and by 20% (p=0.023) and 26% (p=0.004), respectively, compared with the nicotine group. No difference was found between the tobacco extract and tobacco extract plus nicotine groups. An 18% (p=0.013) reduction in torque at yield point was observed in the tobacco extract plus nicotine group compared with the nicotine group. No differences in ultimate stiffness, energy absorption, and callus bone mineral content at the fracture line were found between any of the groups. Serum levels of nicotine were between 40-50 ng/mL in the group given nicotine alone and the group given tobacco extract plus nicotine (equivalent to serum levels observed in persons smoking one to two packs of cigarettes per day).

Effects of nicotine withdrawal on performance under a progressive-ratio schedule of sucrose pellet delivery in rats

Although numerous studies have examined the motivational effects of nicotine withdrawal using intracranial self-stimulation (ICSS) threshold assays, relatively few have employed other methods for assessing motivation that use naturally reinforcing stimuli (e.g., food). The objective of the present study was to determine the effects of nicotine withdrawal on motivation using a progressive-ratio (PR) schedule of sucrose pellet delivery. Rats were trained to respond for sucrose pellets under a PR schedule. When stable breaking points and response rates were achieved, PR sessions were suspended and rats were exposed to a continuous infusion of saline or nicotine (3.2 or 8.0 mg/kg/day of the base) via subcutaneous osmotic minipump for nine days. On day nine, pumps were removed. PR sessions resumed 22 h later and continued daily for five consecutive days. Only rats exposed to 8.0 mg/kg/day nicotine exhibited a significant decrease in breaking point and overall response rate compared to saline-exposed rats on day one of nicotine withdrawal. These rats also showed an increasing trend in breaking point and overall response rate over the course of withdrawal, such that these measures were significantly increased on day five of withdrawal compared to baseline. Response rates under each ratio in the PR progression in rats exposed to 8.0 mg/kg/day did not differ from baseline or from those in saline-treated rats, suggesting suppression of breaking points and overall response rates were not attributable to nonspecific motor impairment. In addition, changes in performance throughout the protocol were not associated with changes in body weight. Consistent with findings from ICSS studies, the present study demonstrates that nicotine withdrawal can produce a motivational deficit as indexed under a PR schedule. However, in contrast to ICSS, PR performance appears to be sensitive to increases in motivation late in the withdrawal period. Therefore, PR schedules of natural reinforcement may provide information on the motivational effects of nicotine withdrawal complimentary to that obtained from ICSS threshold studies.