Pharmacokinetics of Fluoxetine in Elderly Men and Women

Exploring gender differences in pharmacokinetics of central nervous system related medicines based on a systematic review approach

Due to the inevitable differences in physiological and/or genetic factors between genders, the possibility that differences in pharmacokinetics between genders may occur when exposed to the same dose of the same drug is subject to reasonable inference and suspicion. Nevertheless, a significant number of medicines still rely on empirical usage and uniform clinical application without consideration of inter-individual diversity factors. In particular, in the pharmacokinetic diversity of medicines related to central nervous system (CNS) activity, consideration of gender factors and access to comparative analysis are very limited. The purpose of this study was to conduct an integrated analysis and review of differences in pharmacokinetics between genders that have not been specifically reported to date for medicines related to CNS effects, which are a group of drugs with relatively significant concerns about systemic side effects. This study was accessible through extensive data collection and analyzes using a web-based scientific literature search engine of pharmacokinetic results of CNS-related drugs performed on humans, taking gender into account. As a result, significant differences in pharmacokinetics between genders were identified for many drugs related to CNS. And most of the pharmacokinetic differences between genders suggested a higher in vivo exposure in females. This study suggests that consideration of gender factors cannot be ignored and will be an important point of interest in the precision medicine application of CNS-related medicines.

In silico analysis of the antidepressant fluoxetine and similar drugs as inhibitors of the human protein acid sphingomyelinase: a related SARS-CoV-2 inhibition pathway

Acid Sphingomyelinase (ASM) is a human phosphodiesterase that catalyzes the metabolism of sphingomyelin (SM) to ceramide and phosphocholine. ASM is involved in the plasma membrane cell repair and is associated with the lysosomal inner lipid membrane by nonbonding interactions. The disruption of those interaction would result in ASM release into the lysosomal lumen and consequent degradation of its structure. Furthermore, SARS-CoV-2 infection has been linked with ASM activation and with a ceramide domain formation in the outer leaflet of the plasma membrane that is thought to be crucial for the viral particles recognition by the host cells. In this study, we have explored in silico the behavior of fluoxetine and related drugs as potential inhibitors of ASM. Theoretically, these drugs would be able to overpass lysosomal membrane and reach the interactions that sustain ASM structure, breaking them and inhibiting the ASM. The analyses of docking data indicated that fluoxetine allocated mainly in the N-terminal saposin domain via nonbonding interactions, mostly of hydrophobic nature. Similar results were obtained for venlafaxine, citalopram, atomoxetine, nisoxetine and fluoxetine's main metabolite norfluoxetine. In conclusion, it was observed that the saposin allocation may be a good indicative of the drugs inhibition mechanism, once this domain is responsible for the binding of ASM to lysosomal membrane and some of those drugs have previously been reported to inhibit the phosphodiesterase by releasing its structure in the lysosomal lumen. Our MD data also provides some insight about natural ligand C18 sphingomyelin conformations on saposin.Communicated by Ramaswamy H. Sarma.

Intersection of Sex and Depression: Pathogenesis, Presentation, and Treatments

Major Depressive Disorder (MDD) is a highly prevalent, debilitating disorder. According to the World Health Organization, approximately 5% of adults suffer from depression worldwide and more women than men are affected. Yet, we have a very limited understanding of the pathogenesis of the disease, how sex and genetics influence the pathophenotype of MDD, and how they contribute to the responses to pharmacological treatment. This chapter addresses key theories about the etiology of depression, the variations in epidemiology and presentation, and the treatment options with respect to sex and gender. Additionally, we discuss the emerging wave of treatment modalities, diagnosis, and research focusing on MDD.

Psychotropic drug-induced hyponatremia: results from a drug surveillance program-an update

Hyponatremia (HN) is the most common electrolyte imbalance (defined as a serum sodium concentration Na(S) of  < 130 mmol/l) and often induced by drugs including psychotropic drugs. AMSP (Arzneimittelsicherheit in der Psychiatrie) is a multicenter drug surveillance program that assesses severe or unusual adverse drug reactions (ADRs) occurring during treatment with psychotropic drugs. This study presents data from 462,661 psychiatric inpatients treated in participating hospitals between 1993 and 2016 and serves as an update of a previous contribution by Letmaier et al. (JAMA 15(6):739–748, 2012). A total of 210 cases of HN were observed affecting 0.05% of patients. 57.1% of cases presented symptomatically; 19.0% presented with severe symptoms (e.g., seizures, vomiting). HN occurred after a median of 7 days following the first dose or dose increase. Incidence of HN was highest among the two antiepileptic drugs oxcarbazepine (1.661% of patients treated) and carbamazepine (0.169%), followed by selective serotonin-norepinephrine reuptake inhibitors (SSNRIs, 0.088%) and selective serotonin reuptake inhibitors (0.071%). Antipsychotic drugs, tricyclic antidepressants, and mirtazapine exhibited a significantly lower incidence of HN. The risk of HN was 16–42 times higher among patients concomitantly treated with other potentially HN-inducing drugs such as diuretic drugs, angiotensin-converting-enzyme inhibitors, angiotensin II receptor blockers, and proton pump inhibitors. Female SSNRI-users aged  ≥ 65 years concomitantly using other HN-inducing drugs were the population subgroup with the highest risk of developing HN. The identification of high-risk drug combinations and vulnerable patient subgroups represents a significant step in the improvement of drug safety and facilitates the implementation of precautionary measures.

Higher dose weekly fluoxetine in hemodialysis patients: A case series report

OBJECTIVE

The antidepressant medication fluoxetine at 90 mg dosed weekly is as effective and safe as standard formulation fluoxetine 20 mg dosed daily in patients with major depressive disorder. Weekly fluoxetine has not been well studied in hemodialysis patients, and doses beyond 90 mg/week have not been described in this population. This case series, derived from a larger study on depression in hemodialysis patients, describes the use of weekly fluoxetine at dosages beyond 90 mg/week.

METHOD

Hemodialysis patients with depressive symptom severity scored ≥10 on the 9-item Patient Health Questionnaire and major depressive disorder confirmed with Mini International Neuropsychiatric Interview were initially prescribed daily fluoxetine for two weeks and then transitioned to weekly fluoxetine. Dosage titration was made at the discretion of the prescribing clinician. Fluoxetine was continued for a total of 12 weeks.

RESULTS

Four women, aged 24 to 65 years, on hemodialysis for 1 to 18 years, were started on weekly fluoxetine that was increased over several weeks up to 180 mg. Side effects included restlessness, dry mouth, sedation, and lightheadedness. Two patients ultimately had their weekly fluoxetine decreased back to 90 mg. However, all four continued weekly fluoxetine as part of poststudy aftercare and no longer met diagnostic criteria for major depressive disorder, current episode.

CONCLUSIONS

Weekly fluoxetine at doses of 180 mg may be a reasonable treatment consideration for hemodialysis patients who have partial or insufficient antidepressant response. Side effects may limit tolerance of the 180 mg dose in some individuals. Future research should investigate longer term health outcomes of weekly fluoxetine in this population.

Post-traumatic stress disorder mistaken for behavioural and psychological symptoms of dementia: case series and recommendations of care

In late life, traumas may act cumulatively to exacerbate vulnerability to post-traumatic stress disorder (PTSD). PTSD is also a risk factor for cognitive decline. Major neurocognitive disorder (MND) can be associated with worsening of already controlled PTSD symptoms, late-life resurgence or de novo emergence. Misidentifying PTSD symptoms in MND can have negative consequences for the patient and families. We review the literature pertaining to PTSD and dementia and describe five cases referred for consultation in geriatric psychiatry initially for behavioural and psychological symptoms of dementia (BPSD), which were eventually diagnosed and treated as PTSD in MND subjects. We propose that certain PTSD symptoms in patients with MND are misinterpreted as BPSD and therefore, not properly addressed. For example, flashbacks could be interpreted as hallucinations, hypervigilance as paranoia, nightmares as sleep disturbances, and hyperreactivity as agitation/aggression. We suggest that better identification of PTSD symptoms in MND is needed. We propose specific recommendations for care, namely: clarifying diagnosis by distinguishing PTSD symptoms coexisting with different types of dementia from a specific dementia symptom (BPSD), gathering a detailed history of the trauma in order to personalise non-pharmacological interventions, adapting psychotherapeutic strategies to patients with dementia, using selective serotonin reuptake inhibitors as first-line treatment and avoiding antipsychotics and benzodiazepines. Proper identification of PTSD symptoms in patients with MND is essential and allows a more tailored and efficient treatment, with decrease in inappropriate use of physical and chemical restraints.

Sex differences in the pharmacology of itch therapies-a narrative review

BACKGROUND

Chronic itch is the most common skin-related condition, associated with a high psychosocial and economic burden. In recent years, increasing evidence of sex differences in the perception, clinical presentation and treatment requirements of itch points towards potential benefits when using sex-adapted therapies. It is well-known that body composition, absorption, metabolism, elimination and adverse drug reactions (ADRs) differ between sexes, but only little is known about the impact of sex in the pharmacology of itch treatments, which could help to rationalise sex-adapted treatment strategies.

AIM

To evaluate and review sex effects in the pharmacokinetics and /-dynamics of drugs used to treat itch.

METHODS

In this narrative review we performed a PubMed and MEDLINE (Ovid) search using the terms (itch OR pruritus) AND (gender OR sex) AND (drug OR medication OR pharmacokinetics OR pharmacodynamics). Additional searches were performed for the topical and systemic drugs recommended by the European Guideline on Chronic Pruritus.

RESULTS

We found numerous reports with variable levels of evidence of sex effects with respect to the pharmacokinetics and/or pharmacodynamics of 14 drug classes used for the treatment of itch, including a total of 19 systemic and 3 topical drugs. Women seem to present higher plasma levels of several drugs used in itch treatment, including tri- and tetracyclic antidepressants (e.g. doxepin, amitriptyline, mirtazapine), serotonin reuptake inhibitors (e.g. paroxetine, sertraline, fluoxetine), immunosuppressive drugs (e.g. cyclosporine, mycophenolate mofetil), serotonin receptor antagonists (e.g. ondansetron) and betablockers (e.g. propranolol). Adverse drug reactions (ADRs) were generally more common in women. Being female was reported to be an independent risk factor for QTc-prolongation associated with antihistamines and tetracyclic antidepressants. Additionally, women seem to be more prone to sedative effects of antihistamines, and to suffer from a higher frequency as well as severity of side effects with systemic calcineurin inhibitors, opioid agonists, and opioid antagonists. Women were also sensitised more often to topically applied drugs. Of note, apart from only one experimental study with capsaicin, none of these reports were designed specifically to assess the effect of sex (and gender) in the treatment of itch.

DISCUSSION/CONCLUSION

Our review supports previous reports that sex is of importance in the pharmacokinetics and /-dynamics of several drugs used to treat itch although those drugs were mostly evaluated for non-itch indications. However, the results are limited by methodological limitations evident in most studies such as underrepresentation of women in clinical trials. This emphasises the need to study the impact of sex (and gender) in future itch trials to yield better outcomes and prevent ADRs in both sexes.

Potential Adverse Cardiovascular Effects of Treatment With Fluoxetine and Other Selective Serotonin Reuptake Inhibitors (SSRIs) in Patients With Geriatric Depression: Implications for Atherogenesis and Cerebromicrovascular Dysregulation

Late life depression is an important public health problem, which associates with increased risk of morbidity and mortality. Selective serotonin reuptake inhibitors (SSRIs), including fluoxetine, are often prescribed to treat geriatric depression. There is increasing evidence that fluoxetine and other SSRIs exert a wide range of cardiovascular side effects. Furthermore, there is evidence that aging may increase plasma level of SSRIs. In this overview, the potential role of side effects of treatment with fluoxetine and other SSRIs in the pathogenesis of age-related cardiovascular diseases, including atherogenesis, cardiac pathologies, and cerebromicrovascular impairment, is discussed.

Sex Differences in Reported Adverse Drug Reactions of Selective Serotonin Reuptake Inhibitors

INTRODUCTION

Several studies have investigated sex as a risk factor for the occurrence of adverse drug reactions (ADRs) and found that women are more likely to experience ADRs than men.

OBJECTIVE

The aim of this explorative study was to investigate whether differences exist in reported ADRs of selective serotonin reuptake inhibitors (SSRIs) for men and women in the database of the Netherlands Pharmacovigilance Centre Lareb.

METHODS

A ratio of reports concerning women and men, corrected for the number of users, was calculated for all the ADRs reported on SSRIs.

RESULTS

We found that 16 ADRs were statistically significantly more reported in women than men, and four ADRS were reported more in men than women.

CONCLUSION

ADRs more reported in women than men when using SSRIs were usually dose-related ADRs or commonly occurring ADRs. Differences in the pharmacokinetics of SSRIs between men and women may explain why these reports of dose-related ADRs when using SSRIs concern women more than men.

Fluoxetine administration during adolescence attenuates cognitive and synaptic deficits in adult 3×TgAD mice

Fluoxetine (FLX) has broad neurobiological functions and neuroprotective effects; however, the preventive effects of FLX on cognitive impairments in Alzheimer's disease (AD) have not been reported. Here, we studied whether adolescent administration of fluoxetine can prevent memory deficits in AD transgenic mice that harbour PS1_m146v, APP_swe and TauP_301L mutations (3 × TgAD). FLX was applied through peritoneal injection to the mice at postnatal day 35 (p35) for 15 consecutive days, and the effects of FLX were observed at 6-month. We found that adolescent administration of FLX improved learning and memory abilities in 6-month-old 3 × TgAD mice. FLX exposure also increased the sizes of the hippocampal CA1, dentate gyrus (DG) and extensive cortex regions, with increased numbers of neurons and higher dendritic spine density. Meanwhile, the synaptic plasticity of neurons in the hippocampus was remodelled, and the expression levels of synaptic-related proteins were increased along with activation of the cyclic AMP response element-binding (CREB) protein/brain-derived neurotrophic factor (BDNF) signalling pathway. Finally, we found that FLX effectively prevented the increase of beta-amyloid (Aβ) levels. These data suggest that adolescent administration of the antidepressant drug FLX can efficiently preserve cognitive functions and improve pathologies in 3×Tg AD mice.

Pharmacokinetics and pharmacodynamics of psychotropic drugs: effect of sex

Data on the specific effects of sex on pharmacokinetics, as well as tolerability, safety, and efficacy of psychotropic medications are still meager, mainly because only recently sex-related issues have attracted a certain degree of interest within the pharmacological domain. Therefore, with the present study, we aimed to provide a comprehensive review of the literature on this topic, through careful MEDLINE and PubMed searches of the years 1990-2012. Generally, data on pharmacokinetics are more consistent and numerous than those on pharmacodynamics. Sex-related differences have been reported for several parameters that influence pharmacokinetics, such as gastric acidity, intestinal motility, body weight and composition, blood volume, liver enzymes (mainly the cytochrome P450), or renal excretion, which may alter plasma drug levels. Sex-related peculiarities may also account for a different sensitivity of men and women to side effects and toxicity of psychotropic drugs. Further, some differences in drug response, mainly to antipsychotics and antidepressants, have been described. Further studies are, however, necessary to explore more thoroughly the impact of sex on the pharmacokinetics and pharmacodynamics of psychotropic drugs, in order to reach the most appropriate and tailored prescription for each patient.

Beers-Fick criteria and drugs available through the Farmácia Dose Certa program

CONTEXT AND OBJECTIVE

Farmácia Dose Certa is a program available in the State of São Paulo that is a national reference for providing drugs free of charge to the population. Elderly people receiving care deserve special attention regarding drugs that are appropriate for their age group. The objective was to assess the drugs in the program considered to be inappropriate for the elderly.

DESIGN AND SETTING

Descriptive study evaluating free drug distribution in the State of São Paulo, Brazil.

METHODS

Following the criteria proposed by Beers and Fick (drugs or drug classes that should be avoided among elderly people, independent of the diagnosis or clinical condition, because of the high risk of side effects and because other, safer drugs are available), the drugs in the Farmácia Dose Certa program that might be inappropriate for elderly people and the levels of evidence for each drug included were assessed.

RESULTS

Among the available drugs, 10 (25.6%) were included within the Beers-Fick criteria. The drugs selected were: amitriptyline, cimetidine, diazepam, digoxin, fluoxetine, methyldopa, nifedipine, promethazine, thioridazine and ferrous sulfate.

CONCLUSION

The list of drugs available within the Farmácia Dose Certa program may be considered appropriate for the general population, but not completely for the elderly population. Adjusting this list to the pharmacological aspects of aging will reduce the risks of drug interactions, falls, mental confusion and excessive sedation that result from drugs that are considered inappropriate for consumption by elderly people.

Elderly and drugs: risks and necessity of rational use

In recent decades, the world has undergone a demographic transformation with a rapid growth of the elderly population, resulting in an increased demand for funds to maintain their health and drug consumption. Pharmacokinetic and pharmacodynamic changes occurring in the elderly can interfere directly in the adverse effects of drugs and increase the risk of intoxication. In addition, there are external factors interfering with the pharmacotherapy of the elderly, such as inappropriate use and the lack of access to information. Many therapeutic classes of drugs should be used with caution or avoided in the elderly population, such as anti-inflammatory and some anti-hypertensive drugs, diuretics and digitalis. If not managed carefully, these medicines can affect the safety and quality of life in the elderly. Thus, the aim of this review was to identify drugs that should be used with caution in elderly patients in order to avoid intoxication and/or adverse drug events.

Using explicit criteria to evaluate the quality of prescribing in elderly Italian outpatients: a cohort study

BACKGROUND AND OBJECTIVE

Inappropriate prescribing in the elderly population is a well-recognized problem in public health. The Beers criteria have been widely used to evaluate the quality of prescribing for the elderly. However, because the Beers criteria were developed in the United States, they are not fully applicable in Italy. The purpose of this study was to establish explicit criteria for potentially inappropriate medication prescribing (PIP) for the elderly and assess the prevalence of and factors associated with PIP among elderly residents in the Local Health Unit of Parma, Italy according to the developed criteria.

METHODS

A nine-member expert panel was convened to identify a list of inappropriate medications reflecting the Italian prescribing habits. The panel decided to refine and update the 2002 Beers criteria. Consensus through a Nominal Group Technique was reached to classify the identified 23 inappropriate medications into three categories: 17 medications to be always avoided, three medications rarely appropriate, and three medications with some indications but often misused. A retrospective cohort study using the 2006 Parma Local Health Unit automated outpatient prescriptions database was conducted. The cohort comprised 91 741 elderly individuals >or=65 years with at least one prescription medication. PIP was defined as having a prescription claim for at least one inappropriate medication.

RESULTS AND DISCUSSION

A total of 23 662 elderly in the cohort (25.8%) had at least one PIP. Of these, 14.1% received prescriptions for two medications of concern, and 2.0% for three or more. Using the expert panel's categories, 59.2% of the elderly receiving PIP had prescriptions for drugs that should always be avoided, 33.9% for rarely appropriate drugs, and 19.1% for drugs that have some indications but are often misused. Non-steroidal anti-inflammatory drugs (35.7% of subjects) were the most frequently occurring PIP, followed by ticlopidine (17.6%), doxazosin (15.5%), and amiodarone (13.6%). Female, older age, overall number of drugs prescribed, greater number of chronic conditions were factors associated with greater odds of receiving PIP.

CONCLUSION

Via the developed criteria, the study corroborates that PIP among elderly outpatients is a substantial issue in Parma Local Health Unit, Italy. Knowledge of the prevalence of PIP and associated factors should gear efforts to develop strategies to reduce PIP in outpatient settings in Italy.

Sex differences in the pharmacokinetics and pharmacodynamics of antidepressants: an updated review

BACKGROUND

An increasing number of studies have reported differences in the pharmacokinetics and/or pharmacodynamics of antidepressants between women and men.

OBJECTIVES

This article updates previously published literature describing sex differences in the pharmacokinetics and pharmacodynamics of antidepressants, and examines specific issues that face women with psychiatric illness.

METHODS

An English-language literature search was performed with the PubMed database (March 2003-December 2008) using combinations of the search terms sex, gender, and antidepressants. In addition, each antidepressant was identified in the 63rd edition of the Physicians' Desk Reference.

RESULTS

The current data suggest that the pharmacokinetics of antidepressants can be substantially different between women and men. Likewise, the response to antidepressants can be quite variable, including sex differences in adverse effects and time to response.

CONCLUSIONS

Despite the many sex differences reported, there is still little published work systematically evaluating potential sex differences in antidepressant pharmacokinetics and pharmacodynamics. More research is needed to guide the treatment of depression and other mental illnesses.

Psychotropic drugs have contrasting skeletal effects that are independent of their effects on physical activity levels

Popular psychotropic drugs, like the antidepressant selective serotonin reuptake inhibitors (SSRIs) and tricyclic antidepressants (TCAs), and the mood stabilizer lithium, may have skeletal effects. In particular, preclinical observations suggest a direct negative effect of SSRIs on the skeleton. A potential caveat in studies of the skeletal effects of psychotropic drugs is the hypoactive (skeletal unloading) phenotype they induce. The aim of this study was to investigate the contribution of physical inactivity to the skeletal effects of psychotropic drugs by studying bone changes in cage control and tail suspended mice treated with either vehicle, SSRI, TCA or lithium. Tail suspension was used to control for drug differences on physical activity levels by normalizing skeletal loading between groups. The psychotropic drugs were found to have contrasting skeletal effects which were independent of drug effects on animal physical activity levels. The latter was evident by an absence of statistical interactions between the activity and drug groups. Pharmacological inhibition of the 5-hydroxytryptamine (5-HT) transporter (5-HTT) using a SSRI reduced in vivo gains in lower extremity BMD, and negatively altered ex vivo measures of femoral and spinal bone density, architecture and mechanical properties. These effects were mediated by a decrease in bone formation without a change in bone resorption suggesting that the SSRI had anti-anabolic skeletal effects. In contrast, glycogen synthase kinase-3[beta] (GSK-3[beta]) inhibition using lithium had anabolic effects improving in vivo gains in BMD via an increase in bone formation, while TCA-mediated inhibition of the norepinephrine transporter had minimal skeletal effect. The observed negative skeletal effect of 5-HTT inhibition, combined with recent findings of direct and indirect effects of 5-HT on bone formation, are of interest given the frequent prescription of SSRIs for the treatment of depression and other affective disorders. Likewise, the anabolic effect of GSK-3[beta] inhibition using lithium reconfirms the importance of Wnt/beta-catenin signaling in the skeleton and it's targeting by recent drug discovery efforts. In conclusion, the current study demonstrates that different psychotropic drugs with differing underlying mechanisms of action have contrasting skeletal effects and that these effects do not result indirectly via the generation of animal physical inactivity.

Chronic treatment of astrocytes with therapeutically relevant fluoxetine concentrations enhances cPLA2 expression secondary to 5-HT2B-induced, transactivation-mediated ERK1/2 phosphorylation

INTRODUCTION

We have recently shown that fluoxetine, a serotonin-specific reuptake inhibitor (SSRI), has low micromolar affinity for the 5-HT(2C) receptor (but not for 5-HT(2A) and 5-HT(2B) receptors) in primary cultures of mouse astrocytes. This was determined as phosphorylation (stimulation) of extracellular-regulated kinase 1 and 2 (ERK(1/2)) by transactivation-mediated phosphorylation of the epidermal growth factor (EGF) receptor, followed by conventional EGF receptor signaling (Li et al., Psychopharmacology 194:333-334, 2007). Paroxetine has an identical effect. The present study shows that chronic fluoxetine treatment with even higher affinity (EC(50) = 0.5-2.0 microM) upregulates Ca(2+)-dependent phospholipase A(2) (cPLA(2)), which releases arachidonic acid from the sn-2 position of membrane-bound phospholipid, without effect on secretory PLA(2) (sPLA(2)) and intracellular PLA(2) (iPLA(2)).

DISCUSSION

This demonstration replicates the fluoxetine-induced cPLA(2) upregulation in rat brain shown by Rao et al. (Pharmacogenomics J 6:413-420, 2006) and provides the new information that upregulation (1) occurs in astrocytes, (2) is evoked by stimulation of 5-HT(2B) receptor, and (3) requires transactivation-mediated ERK(1/2) phosphorylation. Similar upregulation of cPLA(2) in intact brain in response to 5-HT(2)-mediated signaling by elevated serotonin levels and/or an SSRI during antidepressant treatment may explain the repeatedly reported ability of SSRIs to normalize regional decreases which occur in brain metabolism during major depression, since (1) arachidonic acid strongly stimulates glucose metabolism in cultured astrocytes (Yu et al., J Neurosci Res 64:295-303, 1993) and (2) plasma concentrations of arachidonic acid in depressed patients are linearly correlated with regional brain glucose metabolism (Elizabeth Sublette et al., Prostaglandins Leukot Essent Fatty Acids 80:57-64, 2009).

Sex-specific effects of chronic fluoxetine treatment on neuroplasticity and pharmacokinetics in mice

Neurogenesis is a mechanism through which antidepressants may produce therapeutic effects. There is a dearth of information regarding the effects of antidepressants on neurogenesis and neurotrophin mobilization in females. This study examined sex differences in the alteration of cell proliferation and survival in multiple regions of the brain. Additional experiments examined brain-derived neurotrophic factor (BDNF) levels and pharmacokinetics of fluoxetine to determine whether they mediate sex differences. MRL/MpJ mice were treated with fluoxetine (5 and 10 mg/kg b.i.d.) for 21 days and received injections of 5-bromo-2'-deoxyuridine (200 mg/kg) to measure DNA synthesis. In the hippocampus, fluoxetine increased cell proliferation at both doses; females treated with 10 mg/kg produced more new cells than males. Fluoxetine did not alter survival in males, but 10 mg/kg reduced survival in females. In the frontal cortex, fluoxetine increased cell proliferation and survival in males treated with 10 mg/kg. In the cerebellum and amygdala, 10 mg/kg fluoxetine increased cell proliferation in both sexes but did not alter the incorporation of the new cells. Fluoxetine increased BDNF levels in the hippocampus of both sexes. BDNF levels correlated with cell proliferation in males but not females. Brain and plasma levels indicated that females metabolized fluoxetine faster than males and produced more of the metabolite norfluoxetine. These data suggest that fluoxetine acts on multiple areas of the brain to increase cell proliferation, and the pattern of activation differs between males and females. Sex-specific effects of fluoxetine on neurotrophin mobilization and pharmacokinetics may contribute to these differences in neural plasticity.

Ageing abolishes the effects of fluoxetine on neurogenesis

Depression constitutes a widespread condition observed in elderly patients. Recently, it was found that several drugs employed in therapies against depression stimulate hippocampal neurogenesis in young rodents and nonhuman primates. As the rate of neurogenesis is dramatically reduced during ageing, we examined the influences of ageing on neurogenic actions of antidepressants. We tested the impact of fluoxetine, a broadly used antidepressant, on hippocampal neurogenesis in mice of three different age groups (100, 200 and over 400 days of age). Proliferation and survival rate of newly generated cells, as well as the percentage of cells that acquired a neuronal phenotype were analyzed in the hippocampus of mice that received fluoxetine daily in a chronic manner. Surprisingly, the action of fluoxetine on neurogenesis was decreasing as a function of age and was only significant in young animals. Hence, fluoxetine increased survival and the frequency of neuronal marker expression in newly generated cells of the hippocampus in the young adult group (that is 100 days of age) only. No significant effects on neurogenesis could be detected in fluoxetine-treated adult and elderly mice (200 and over 400 days of age). The data indicate that the action of fluoxetine on neurogenesis is highly dependent on the age of the treated individual. Although the function of neurogenesis in the clinical manifestation of depression is currently a matter of speculation, this study clearly shows that the therapeutic effects of antidepressants in elderly patients are not mediated by neurogenesis modulation.

Prozac during puberty: distinctive effects on neurogenesis as a function of age and sex

Neurogenesis is a possible substrate through which antidepressants alleviate symptoms of depression. In adult male rodents and primates, chronic treatment with fluoxetine increases neurogenesis in the hippocampal formation. Little is known about the effects of the antidepressant on neurogenesis during puberty or in female animals at any age. Therefore we examined the effects of chronic fluoxetine treatment on cell proliferation and survival in male and female rats during puberty and adulthood. Adult and peri-pubescent male and female rats were treated chronically with fluoxetine (Prozac, 5 mg/kg) or saline. Subsequently rats received a single injection of 5-bromo-2'-deoxyuridine (BrdU; 200 mg/kg) to label DNA synthesis. Rats were sacrificed 2 h, 24 h, or 28 days after BrdU injection to examine cell proliferation, survival and cell fate. Fluoxetine increased cell proliferation in adult male rats but not in peri-pubescent males or female rats of any age or stage of the estrous cycle. Treatment did not alter the number of surviving cells in the male hippocampus but decreased survival in the female hippocampus. Thus, fluoxetine has distinctive effects on neurogenesis as a function of age and sex. Circulating levels of the stress hormone corticosterone were also examined. Treatment of female rats with fluoxetine during puberty decreased circulating levels of corticosterone in adults, even in the absence of the drug suggesting disruption of maturation of the hypothalamic-pituitary-adrenal axis.