Time of Administration of Acute or Chronic Doses of Imipramine Affects its Antidepressant Action in Rats

Circadian biology to advance therapeutics for mood disorders

Mood disorders account for a significant global disease burden, and pharmacological innovation is needed as existing medications are suboptimal. A wide range of evidence implicates circadian and sleep dysfunction in the pathogenesis of mood disorders, and there is growing interest in these chronobiological pathways as a focus for treatment innovation. We review contemporary evidence in three promising areas in circadian-clock-based therapeutics in mood disorders: targeting the circadian system informed by mechanistic molecular advances; time-tailoring of medications; and personalizing treatment using circadian parameters. We also consider the limitations and challenges in accelerating the development of new circadian-informed pharmacotherapies for mood disorders.

Decreased sensitivity to antidepressant drugs in Wistar Hannover rats submitted to two animal models of depression

The Wistar Hannover rat (WHR) is a strain commonly used for toxicity studies but rarely used in studies investigating depression neurobiology. In this study, we aimed to characterise the behavioural responses of WHR to acute and repeated antidepressant treatments upon exposure to the forced swim test (FST) or learned helplessness (LH) test. WHR were subjected to forced swimming pre-test and test with antidepressant administration (imipramine, fluoxetine, or escitalopram) at 0, 5 h and 23 h after pre-test. WHR displayed high immobility in the test compared to unstressed controls (no pre-swim) and failed to respond to the antidepressants tested. The effect of acute and repeated treatment (imipramine, fluoxetine, escitalopram or s-ketamine) was then tested in animals not previously exposed to pre-test. Only imipramine (20 mg/kg, 7 days) and s-ketamine (acute) reduced the immobility time in the test. To further investigate the possibility that the WHR were less responsive to selective serotonin reuptake inhibitors, the effect of repeated treatment with fluoxetine (20 mg/kg, 7 days) was investigated in the LH model. The results demonstrated that fluoxetine failed to reduce the number of escape failures in two different protocols. These data suggest that the WHR do not respond to the conventional antidepressant treatment in the FST or the LH. Only s-ketamine and repeated imipramine were effective in WHR in a modified FST protocol. Altogether, these results indicate that WHR may be an interesting tool to investigate the mechanisms associated with the resistance to antidepressant drugs and identify more effective treatments.

Pinus halepensis Essential Oil Ameliorates Aβ1-42-Induced Brain Injury by Diminishing Anxiety, Oxidative Stress, and Neuroinflammation in Rats

The Pinus L. genus comprises around 250 species, being popular worldwide for their medicinal and aromatic properties. The present study aimed to evaluate the P. halepensis Mill. essential oil (PNO) in an Alzheimer’s disease (AD) environment as an anxiolytic and antidepressant agent. The AD-like symptoms were induced in Wistar male rats by intracerebroventricular administration of amyloid beta1-42 (Aβ1-42), and PNO (1% and 3%) was delivered to Aβ1-42 pre-treated rats via inhalation route for 21 consecutive days, 30 min before behavioral assessments. The obtained results indicate PNO’s potential to relieve anxious–depressive features and to restore redox imbalance in the rats exhibiting AD-like neuropsychiatric impairments. Moreover, PNO presented beneficial effects against neuroinflammation and neuroapoptosis in the Aβ1-42 rat AD model.

Neuropsychopharmacological profiling of scoparone in mice

Scoparone (6,7-dimethoxycoumarin) is a simple coumarin from botanical drugs of Artemisia species used in Traditional Chinese Medicine and Génépi liquor. However, its bioavailability to the brain and potential central effects remain unexplored. We profiled the neuropharmacological effects of scoparone upon acute and subchronic intraperitoneal administration (2.5-25 mg/kg) in Swiss mice and determined its brain concentrations and its effects on the endocannabinoid system (ECS) and related lipids using LC-ESI-MS/MS. Scoparone showed no effect in the forced swimming test (FST) but, administered acutely, led to a bell-shaped anxiogenic-like behavior in the elevated plus-maze test and bell-shaped procognitive effects in the passive avoidance test when given subchronically and acutely. Scoparone rapidly but moderately accumulated in the brain (Cmax < 15 min) with an apparent first-order elimination (95% eliminated at 1 h). Acute scoparone administration (5 mg/kg) significantly increased brain arachidonic acid, prostaglandins, and N-acylethanolamines (NAEs) in the FST. Conversely, subchronic scoparone treatment (2.5 mg/kg) decreased NAEs and increased 2-arachidonoylglycerol. Scoparone differentially impacted ECS lipid remodeling in the brain independent of serine hydrolase modulation. Overall, the unexpectedly potent central effects of scoparone observed in mice could have toxicopharmacological implications for humans.

Circadian Rhythms, Disease and Chronotherapy

Circadian clocks are biological timing mechanisms that generate 24-h rhythms of physiology and behavior, exemplified by cycles of sleep/wake, hormone release, and metabolism. The adaptive value of clocks is evident when internal body clocks and daily environmental cycles are mismatched, such as in the case of shift work and jet lag or even mistimed eating, all of which are associated with physiological disruption and disease. Studies with animal and human models have also unraveled an important role of functional circadian clocks in modulating cellular and organismal responses to physiological cues (ex., food intake, exercise), pathological insults (e.g. virus and parasite infections), and medical interventions (e.g. medication). With growing knowledge of the molecular and cellular mechanisms underlying circadian physiology and pathophysiology, it is becoming possible to target circadian rhythms for disease prevention and treatment. In this review, we discuss recent advances in circadian research and the potential for therapeutic applications that take patient circadian rhythms into account in treating disease.

Antidepressants and Circadian Rhythm: Exploring Their Bidirectional Interaction for the Treatment of Depression

Scientific evidence that circadian rhythms affect pharmacokinetics and pharmacodynamics has highlighted the importance of drug dosing-time. Circadian oscillations alter drug absorption, distribution, metabolism, and excretion (ADME) as well as intracellular signaling systems, target molecules (e.g., receptors, transporters, and enzymes), and gene transcription. Although several antidepressant drugs are clinically available, less than 50% of depressed patients respond to first-line pharmacological treatments. Chronotherapeutic approaches to enhance the effectiveness of antidepressants are not completely known. Even so, experimental results found until this day suggest a positive influence of drug dosing-time on the efficacy of depression therapy. On the other hand, antidepressants have also demonstrated to modulate circadian rhythmicity and sleep-wake cycles. This review aims to evidence the potential of chronotherapy to improve the efficacy and/or safety of antidepressants. It includes pre-clinical and clinical studies that demonstrate the relevance of determining the most appropriate time of administration for antidepressant drugs. In parallel, their positive influence on the resynchronization of disrupted circadian rhythms is also herein discussed. It is expected that this review will promote the investigation of chronotherapy for the treatment of depression, contribute to a better understanding of the relationship between antidepressants and circadian rhythms, and consequently promote the development of new therapeutics.

Antidepressants with different mechanisms of action show different chronopharmacological profiles in the tail suspension test in mice

The circadian system regulates sleep/wake cycles, metabolism, mood, and other functions. It also influences medication efficacy. In this study, we studied the chronopharmacological profiles of antidepressants with various modes of action. We also investigated the effects of dosing time on the pharmacological activity of several antidepressants acting on serotonergic, noradrenergic, and/or dopaminergic neurons. C57BL/6 mice were intraperitoneally administered fluoxetine, imipramine, venlafaxine, or bupropion at 08:00 h (morning), 14:00 h (mid-day), 20:00 h (evening), or 02:00 h (mid-night). Antidepressant activity was evaluated by the tail suspension test. All antidepressants reduced immobility, and their activities varied according to the dosing time. Fluoxetine and imipramine induced relatively strong rhythms with high amplitudes. Their maximal effects were observed in the morning and evening, respectively. Venlafaxine and bupropion induced weak rhythms with maximal effects in the evening and dawn, respectively. These results suggest that the antidepressant activity is associated with circadian fluctuation, and antidepressants with different modes of action have different chronopharmacological profiles. They affect locomotor activity in animals placed in novel (unfamiliar) environments. Fluoxetine, imipramine, and venlafaxine reduced locomotor activity, whereas bupropion increased it. The effects on locomotor activity also vary with circadian rhythm, and the tested drugs showed a maximal effect during the light phase. The peak time was different from that in TST. Plasma and brain levels of all drugs were slightly higher in the morning than in the evening. The dosing time dependency of the antidepressant activity did not correlate with the sedative/stimulatory activity or tissue drug level. Therefore, these latter two factors may have only a small impact on circadian antidepressant activity fluctuations. The relative activity of the serotonergic, noradrenergic, and dopaminergic systems may determine the chronopharmacological profiles of each drug. These results suggest the possibility that drug therapy be optimized by considering the dosing time when the antidepressant activity is high and other pharmacological activities leading to adverse effects are low. Further studies using animal models of depression and in clinical settings are necessary to confirm the effects of dosing time on depressed subjects.