Evaluation of Prolonged Exposure to Varenicline in Adult Rats: Haematological, Biochemical and Anatomopathological Studies

Anti-smoking drugs cytisine and varenicline reduce cardiac reperfusion injury in rat model of myocardial ischemia

Evidence to date indicates that activation of nicotinic acetylcholine receptors (nAChRs) can reduce cardiac injury from ischemia and subsequent reperfusion. The use of nAChR agonists in various animal models leads to a reduction in reperfusion injury. Earlier this effect was shown for the agonists of α7 nAChR subtype. In this work, we demonstrated the expression of mRNA encoding α4, α6 and β2 nAChR subunits in the left ventricle of rat heart. In a rat model of myocardial ischemia, we studied the effect of α4β2 nAChR agonists cytisine and varenicline, medicines used for the treatment of nicotine addiction, and found them to significantly reduce myocardium ischemia-reperfusion injury, varenicline manifesting a higher protection. Dihydro-β-erythroidine, antagonist of α4β2 nAChR, as well as methyllycaconitine, antagonist of α7 and α6β2-containing nAChR, prevented protective effect of varenicline. This together with the presence of α4, α6 and β2 subunit mRNA in the left ventricule of rat heart raises the possibility that the varenicline effect is mediated by α4β2 as well as by α7 and/or α6β2-containing receptors. Our results point to a new way for the use of cytisine and varenicline as cardioprotective agents.

The effects of varenicline on lumbar spinal fusion in a rat model

BACKGROUND CONTEXT

Smoking is detrimental to obtaining a solid spinal fusion mass with previous studies demonstrating its association with pseudoarthrosis in patients undergoing spinal fusion. Varenicline is a pharmacologic adjunct used in smoking cessation which acts as a partial agonist of the same nicotinic receptors activated during tobacco use. However, no clinical or basic science studies to date have characterized if varenicline has negative effects on spinal fusion and bone healing by itself.

PURPOSE

Our study's aim was to elucidate whether varenicline affects the frequency or quality of posterolateral spinal fusion in a rodent model at an endpoint of 12 weeks.

STUDY DESIGN

Randomized control trial.

PATIENT SAMPLE

Fourteen male Lewis rats randomly separated into two experimental groups.

OUTCOME MEASURES

Manual palpation of fusion segment, radiography, μCT imaging, and four-point bend.

METHODS

Fourteen male Lewis rats were randomly separated into two experimental groups undergoing L4-L5 posterior spinal fusion procedure followed by daily subcutaneous injections of human dose varenicline or saline (control) for 12 weeks postsurgery. Spine samples were explanted, and fusion was determined via manual palpation of segments by two independent observers. High-resolution radiographs were obtained to evaluate bridging fusion mass. μCT imaging was performed to characterize fusion mass and consolidation. Lumbar spinal fusion units were tested in four-point bending to evaluate stiffness and peak load. Study funding sources include $5000 OREF Grant. There were no applicable financial relationships or conflicts of interest.

RESULTS

At 3 months postsurgery, 12 out of 14 rats demonstrated lumbar spine fusion (86% fused) with no difference in fusion frequency between the varenicline and control groups as detected by manual palpation. High-resolution radiography revealed six out of seven rats (86%) having complete fusion in both groups. μCT showed no significant difference in bone mineral density or bone fraction volume between groups in the region of interest. Biomechanical testing demonstrated no significant different in the average stiffness or peak loads at the fusion site of the varenicline and control groups.

CONCLUSION

Based on the results of our rat study, there is no indication that varenicline itself has a detrimental effect on the frequency and quality of spinal fusion.

Preclinical toxicological study of prolonged exposure to ketamine as an antidepressant

BACKGROUND

Depression is one of the most common mentally debilitating diseases in the world. Ketamine has been recently identified as a potential novel antidepressant. Further animal model evaluations of the use of ketamine as an antidepressant are necessary to determine safety parameters for clinical use. Therefore, the objective of this study was to perform toxicological tests of prolonged treatment using three different doses of ketamine in adult male rats.

METHODS

The animals were divided into four groups: three treated with 5, 10 or 20 mg/kg of ketamine and a control group treated with saline solution. Intraperitoneal route of treatment was administered daily for 3 weeks. Body weight, water and food intake were measured once a week, as well as evaluation of the functional observational battery, which includes methodic monitoring of motor activity, motor coordination, behavioral changes, and sensory/motor reflex responses. Upon completion of treatment period, all animals were euthanized by decapitation followed by immediate collection of samples, which included brain structures and blood for neurochemical, hematological and biochemical analyses.

RESULTS

Rats treated with the highest tested dosage (20 mg/kg) of ketamine had lower weight gain in the 1st and 2nd weeks of treatment and all experimental groups had measurable alterations in the serotoninergic system.

CONCLUSIONS

Our data indicate that the alterations observed are minor and due to a predicted mechanism of action, which implies that ketamine is a promising drug for repurposing as an antidepressant.

Prolonged exposure of rats to varenicline increases anxiety and alters serotonergic system, but has no effect on memory

Varenicline is a drug used for smoking addiction cessation treatment and acts as a partial agonist of nicotinic cholinergic receptors. Recent clinical trial data support use of varenicline for treatment of conditions/addictions that are not related to smoking cessation. Considering the importance of this issue and the need for new studies on its effects, especially on behavior, more studies using animal models are necessary. Thus, the aim of this study was to evaluate the effects of prolonged exposure to varenicline in anxiety-like behavior and memory, as well as in cerebral neurochemistry of rats. Male rats received three different doses of varenicline: 0.03 (therapeutic dose for humans), 0.1 and 0.3 mg/kg orally (gavage) for 30 days. Animal behavior was analyzed through open field, elevated plus maze, light/dark box, social interaction, Barnes maze and novel object recognition tests. Neurotransmitter levels and their metabolites in different brain structures (hippocampus, striatum and frontal cortex) were measured. Results showed that prolonged exposure of rats to varenicline: 1) did not interfere in motor activity, but caused an anxiogenic effect on elevated plus maze, light/dark box and social interaction testes; 2) did not alter memory; and 3) promoted alterations on serotoninergic system in the striatum and frontal cortex. In conclusion, compilation of the data indicates that prolonged exposure of rats to varenicline promoted anxiogenic effects and alteration in serotonergic system, which corroborated behavioral findings.