Neuron-specific deletion of VEGF or its receptor Flk-1 occludes the antidepressant-like effects of desipramine and fluoxetine in mice.

Vascular endothelial growth factor (VEGF) signaling is known to be involved in the antidepressant-like effects of conventional antidepressants, such as desipramine (DMI), a tricyclic antidepressant, and fluoxetine (FLX), a selective serotonin reuptake inhibitor; however, the precise role of neuronal VEGF signaling in mediating these effects remains unclear. Using mice with excitatory neuron-specific deletion of VEGF and its receptor, fetal liver kinase 1 (Flk-1) in the forebrain, we examined the effects of forebrain excitatory neuron-specific deletion of VEGF or Flk-1 on the antidepressant-like effects of repeated DMI and chronic FLX administration in the forced swim test (FST). Repeated intraperitoneal (i.p.) injections of DMI (10, 10, and 20 mg/kg at 24, 4, and 1 h before the FST, respectively) significantly decreased immobility in control mice; however, this effect was completely blocked in mice with neuron-specific VEGF or Flk-1 deletion. Although chronic treatment with FLX (18 mg/kg/day, i.p.) did not impact immobility in control mice 1 day after the 22nd injection, immobility was significantly reduced 1 day after the preswim and the 23rd FLX injection. However, in mice with neuron-specific Flk-1 deletion, chronic FLX treatment significantly increased immobility in the preswim and failed to produce antidepressant-like effects. Collectively, these findings indicate that neuronal VEGF-Flk-1 signaling contributes to the antidepressant-like actions of conventional antidepressants.

Desipramine induces eryptosis in human erythrocytes, an effect blunted by nitric oxide donor sodium nitroprusside and N-acetyl-L-cysteine but enhanced by Calcium depletion.

Background: Desipramine a representative of tricyclic antidepressants (TCAs) promotes recovery of depressed patients by inhibition of reuptake of neurotransmitters serotonin (SER) and norepinephrine (NE) in the presynaptic membrane by directly blocking their respective transporters SERT and NET.Aims: To study the effect of desipramine on programmed erythrocyte death (eryptosis) and explore the underlying mechanisms.Methods: Phosphatidylserine (PS) exposure on the cell surface as marker of cell death was estimated from annexin-V-binding, cell volume from forward scatter in flow cytometry. Hemolysis was determined photometrically, and intracellular glutathione [GSH]i from high performance liquid chromatography.Results: Desipramine dose-dependently significantly enhanced the percentage of annexin-V-binding cells and didn´t impact glutathione (GSH) synthesis. Desipramine-induced eryptosis was significantly reversed by pre-treatment of erythrocytes with either nitric oxide (NO) donor sodium nitroprusside (SNP) or N-acetyl-L-cysteine (NAC). The highest inhibitory effect was obtained by using both inhibitors together. Calcium (Ca2+) depletion aggravated desipramine-induced eryptosis. Changing the order of treatment, i.e. desipramine first followed by inhibitors, could not influence the inhibitory effect of SNP or NAC.Conclusion: Antidepressants-caused intoxication can be treated by SNP and NAC, respectively. B) Patients with chronic hypocalcemia should not be treated with tricyclic anti-depressants or their dose should be noticeably reduced.

Acid sphingomyelinase deactivation post-ischemia promotes brain angiogenesis and remodeling by small extracellular vesicles.

Antidepressants have been reported to enhance stroke recovery independent of the presence of depressive symptoms. They have recently been proposed to exert their mood-stabilizing actions by inhibition of acid sphingomyelinase (ASM), which catalyzes the hydrolysis of sphingomyelin to ceramide. Their restorative action post-ischemia/reperfusion (I/R) still had to be defined. Mice subjected to middle cerebral artery occlusion or cerebral microvascular endothelial cells exposed to oxygen-glucose deprivation were treated with vehicle or with the chemically and pharmacologically distinct antidepressants amitriptyline, fluoxetine or desipramine. Brain ASM activity significantly increased post-I/R, in line with elevated ceramide levels in microvessels. ASM inhibition by amitriptyline reduced ceramide levels, and increased microvascular length and branching point density in wildtype, but not sphingomyelinase phosphodiesterase-1 ([Smpd1]-/-) (i.e., ASM-deficient) mice, as assessed by 3D light sheet microscopy. In cell culture, amitriptyline, fluoxetine, and desipramine increased endothelial tube formation, migration, VEGFR2 abundance and VEGF release. This effect was abolished by Smpd1 knockdown. Mechanistically, the promotion of angiogenesis by ASM inhibitors was mediated by small extracellular vesicles (sEVs) released from endothelial cells, which exhibited enhanced uptake in target cells. Proteomic analysis of sEVs revealed that ASM deactivation differentially regulated proteins implicated in protein export, focal adhesion, and extracellular matrix interaction. In vivo, the increased angiogenesis was accompanied by a profound brain remodeling response with increased blood-brain barrier integrity, reduced leukocyte infiltrates and increased neuronal survival. Antidepressive drugs potently boost angiogenesis in an ASM-dependent way. The release of sEVs by ASM inhibitors disclosed an elegant target, via which brain remodeling post-I/R can be amplified.

Combined intervention with N-acetylcysteine and desipramine alleviated silicosis development by regulating the Nrf2/HO-1 and ASMase/ceramide signaling pathways.

Silicosis is a systemic disease characterized by diffuse fibrosis of the lung tissue caused by long-term inhalation of large amounts of free silica (SiO2) dust. The pathogenesis of silicosis has not been fully elucidated, and there is a lack of effective treatment methods. N-acetylcysteine (NAC) can potentially treat pulmonary fibrosis by exerting antioxidant effects. Desipramine (DMI) can influence pulmonary fibrosis development by inhibiting acid sphingomyelinase (ASMase) activity and regulating ceramide concentrations. Both can interfere with pulmonary fibrosis through different mechanisms, but the intervention effects of NAC combined with DMI on silicosis fibrosis have not been reported. Therefore, this study established a rat silicosis model using a single tracheal drip of SiO2 dust suspension in Wistar rats to investigate the effect of NAC combined with DMI on SiO2 dust-induced silicosis and its related molecular mechanisms. The histopathological examination of the SiO2 dust-induced silicosis rats suggested that NAC and DMI alone or in combination could decrease the severity of pulmonary fibrosis in rats. The combined intervention had a better effect on reducing fibrosis than the individual interventions. NAC and DMI, alone or in combination, decreased the levels of markers related to pulmonary fibrosis in rats (smooth muscle α-actin (α-SMA), collagen (Col) I, Col III, hydroxyproline (HYP), inflammatory factors (transforming growth factor-ß1 (TGF-ß1) and tumor necrosis factor-α (TNF-α)), and lipid peroxidase malondialdehyde (MDA)). The nuclear factor-erythroid 2-related factor 2 (Nrf2)/heme-oxygenase-1 (HO-1) and ASMase/ceramide pathways were inhibited to some extent by increasing the superoxide dismutase (SOD) levels of antioxidant enzymes and 8-iso-prostaglandin F2α (8-iso-PGF2α) levels of lipid peroxides. The combined intervention and NAC alone inhibited the SiO2 dust-induced elevation of matrix metalloproteinase 1 (MMP-1) and tissue inhibitor matrix metalloproteinase 1 (TIMP-1), but the effect was not significant in the DMI-treated group. Combining DMI and NAC inhibited Col I deposition and reduced HO-1, TIMP-1, and ASMase levels in lung tissues compared to individual treatments. In summary, the SiO2 dust could induce oxidative stress and inflammation in rats, resulting in an imbalance in extracellular matrix (ECM) synthesis/catabolism and ASMase/ceramide signaling pathway activation, leading to silicosis development.The combined intervention of DMI and NAC may synergistically regulate the Nrf2/HO-1 pathway, maintain the anabolic balance of the ECM, inhibit ASMase/ceramide signaling pathway activation by suppressing the inflammatory response and effectively delay silicosis fibrosis progression.

An approach to evaluate metabolite-related phototoxicity with combined use of photochemical properties and skin deposition.

Some chemicals have been reported to cause metabolite-related phototoxicity, and this study aimed to verify the applicability of photosafety assessment based on photochemical and pharmacokinetic properties to evaluate the metabolite-related phototoxicity risk. The phototoxic risk of imipramine (IMI) and its metabolite, desipramine (DMI), was evaluated by photochemical and pharmacokinetic analyses. IMI and DMI were found to have similar photoreactivities based on the generation of reactive oxygen species. The skin concentrations of IMI and DMI reached maximal levels at approximately 1 and 4 h, respectively, after oral administration of IMI (10 mg/kg), and DMI showed high skin deposition compared with IMI. According to the results, DMI was identified as a contributor to phototoxicity induced by orally-taken IMI. In in vivo phototoxicity testing, ultraviolet A irradiation from 3 to 6 h after oral administration of IMI (100 mg/kg) caused more potent phototoxic reactions compared with that from 0 to 3 h, and DMI yielded by metabolism of IMI would be associated with phototoxic reactions caused by orally-administered IMI. In addition to the data on IMI, a parent chemical, photochemical and pharmacokinetic profiling of its metabolite, DMI, led to reliable phototoxicity prediction of orally-administered IMI. Thus, characterization of the photosafety of metabolites would generate reliable information on the phototoxicity risk of parent chemicals, and the proposed strategy may facilitate comprehensive photosafety assessment of drug candidates in pharmaceutical development.

Effects of the antidepressants desipramine and fluvoxamine on latency to immobility and duration of immobility in the forced swim test in adult male C57BL/6J mice.

The forced swim test in rodents allows rapid detection of substances with antidepressant-like activity, evidenced as a decreased duration of immobility that is produced by the majority of clinically used antidepressants. Antidepressants also increase the latency to immobility, and this additional measure reportedly can increase the sensitivity of the forced swim test in mice. Extending these findings, the present study examined the effects of desipramine and fluvoxamine in a forced swim test in C57BL/6J mice, a strain commonly used as background for genetic modifications, analyzing results with a method (i.e. survival analysis) that can model the skewed distribution of latencies and that can deal with censored data (i.e. when immobility does not occur during the test), in comparison with the more traditional Student's t-test. Desipramine increased the latency to immobility at 32 mg/kg, but not at lower doses. Fluvoxamine also did not affect latency at lower doses, but in contrast to desipramine, fluvoxamine decreased the latency to immobility at the highest dose (i.e. 32 mg/kg). At doses affecting latency to immobility, neither desipramine nor fluvoxamine significantly affected duration of immobility. Together, these results are generally consistent with the suggestion that inclusion of the latency measure can increase the sensitivity of the forced swim test to detect antidepressant-like effects in mice.

Desipramine rescues emotional memory deficit induced by low doses of reserpine.

Emotional memory deficit is a well-known complication in early Parkinson's disease. However, its molecular mechanism is still not well known. To address this issue, we examined the cue-related fear-conditioning task and long-term potentiation (LTP) of the thalamus to the lateral amygdala in rats treated with low doses of reserpine (Res). We found that low-dose Res treatment impaired emotional memory and LTP. We also found that exogenous upregulation of norepinephrine (NE) ameliorated the impairment of LTP by facilitating ß-adrenergic receptors. Finally, acute treatment with NE or desipramine rescued the impaired emotional memory induced by a low-dose of Res. These results imply a pivotal role for NE in synaptic plasticity and associative fear memory in rats treated with low doses of Res and suggest that desipramine is a potential candidate for treating Parkinson's disease-related emotional memory deficit.

Adjustment of Dysregulated Ceramide Metabolism in a Murine Model of Sepsis-Induced Cardiac Dysfunction.

Cardiac dysfunction, in particular of the left ventricle, is a common and early event in sepsis, and is strongly associated with an increase in patients' mortality. Acid sphingomyelinase (SMPD1)-the principal regulator for rapid and transient generation of the lipid mediator ceramide-is involved in both the regulation of host response in sepsis as well as in the pathogenesis of chronic heart failure. This study determined the degree and the potential role to which SMPD1 and its modulation affect sepsis-induced cardiomyopathy using both genetically deficient and pharmacologically-treated animals in a polymicrobial sepsis model. As surrogate parameters of sepsis-induced cardiomyopathy, cardiac function, markers of oxidative stress as well as troponin I levels were found to be improved in desipramine-treated animals, desipramine being an inhibitor of ceramide formation. Additionally, ceramide formation in cardiac tissue was dysregulated in SMPD1+/+ as well as SMPD1-/- animals, whereas desipramine pretreatment resulted in stable, but increased ceramide content during host response. This was a result of elevated de novo synthesis. Strikingly, desipramine treatment led to significantly improved levels of surrogate markers. Furthermore, similar results in desipramine-pretreated SMPD1-/- littermates suggest an SMPD1-independent pathway. Finally, a pattern of differentially expressed transcripts important for regulation of apoptosis as well as antioxidative and cytokine response supports the concept that desipramine modulates ceramide formation, resulting in beneficial myocardial effects. We describe a novel, protective role of desipramine during sepsis-induced cardiac dysfunction that controls ceramide content. In addition, it may be possible to modulate cardiac function during host response by pre-conditioning with the Food and Drug Administration (FDA)-approved drug desipramine.

Variability in metabolism of imipramine and desipramine using urinary excretion data.

Variability in imipramine and desipramine metabolism was evaluated using urinary excretion data from patients with pain. Liquid chromatography-tandem mass spectrometry was used to quantitate concentrations in urine specimens. Interpatient population contained 600 unique imipramine specimens, whereas intrapatient population had 137 patients with two or more specimens. Normal concentration ranges of imipramine, desipramine and the desipramine/imipramine metabolic ratio (MR) were established, and various factors were tested for MR impact. Geometric mean of imipramine urine concentration was 0.46 mg/g of creatinine, and desipramine was 0.67 mg/g of creatinine. Gender, concomitant known CYP2C19 inhibitor use and urine pH did not affect MR. However, proton-pump inhibitor (PPI) users had a significantly lower mean MR than those without a listed PPI. Early age group (18-36 years) had a significantly higher mean MR than middle (37-66 years) and late (67-90 years) age groups. Approximately one-third were positive for one or more of hydrocodone, oxycodone, hydromorphone or oxymorphone. Patients with no opioids reported in the medication list had a significantly lower geometric mean MR than those with prescribed opioids (1.03 vs. 1.54, P = 0.004). Patients with only one prescribed opioid had a lower MR than those with two or more prescribed opioids. Patients with younger age, prescribed opioids and no listed PPI were more likely to have a higher geometric mean urinary desipramine/imipramine MR.

Inhibition of P-glycoprotein enhances transport of imipramine across the blood-brain barrier: microdialysis studies in conscious freely moving rats.

BACKGROUND AND PURPOSE: Recent studies indicate that efflux of antidepressants by the multidrug resistance transporter P-glycoprotein (P-gp) at the blood-brain barrier (BBB) may contribute to treatment-resistant depression (TRD) by limiting intracerebral antidepressant concentrations. In addition, clinical experience shows that adjunctive treatment with the P-gp inhibitor verapamil may improve the clinical outcome in TRD. Therefore, the present study aimed to investigate the effect of P-gp inhibition on the transport of the tricyclic antidepressant imipramine and its active metabolite desipramine across the BBB. EXPERIMENTAL APPROACH: Intracerebral microdialysis in rats was used to monitor brain levels of imipramine and desipramine following i.v. imipramine administration, with or without pretreatment with one of the P-gp inhibitors verapamil or cyclosporin A (CsA). Plasma drug levels were also determined at regular intervals. KEY RESULTS: Pretreatment with either verapamil or CsA resulted in significant increases in imipramine concentrations in the microdialysis samples, without altering imipramine plasma pharmacokinetics. Furthermore, pretreatment with verapamil, but not CsA, led to a significant elevation in plasma and brain levels of desipramine. CONCLUSIONS AND IMPLICATIONS: The present study demonstrated that P-gp inhibition enhanced the intracerebral concentration of imipramine , thus supporting the hypothesis that P-gp activity restricts brain levels of certain antidepressants, including imipramine. These findings may help to explain reports of a beneficial response to adjunctive therapy with verapamil in TRD.

Reactive metabolites of desipramine and clomipramine: The kinetics of formation and reactivity with DNA.

Tricyclic antidepressants (TCAs), along with phenothyazines and some industrial chemicals, are shown to react with enzymes that exhibit peroxidase activity. These reactions result in the formation of reactive intermediates having unpaired electrons. The peroxidase oxidation and reactivity of two TCAs, desipramine and clomipramine, were investigated. As a model of peroxidase, horseradish peroxidase (HRP) was employed. The products of the peroxidase catalyzed oxidation of desipramine and clomipramine were identified as N-dealkylated compounds iminodibenzyl and 3-chloroiminodibenzyl using the GC/MS technique. Both drugs formed broad UV/vis absorption spectra in the presence of HRP and H(2)O(2), indicating the formation of a radical cations-reactive intermediate of the oxidation reaction. The dynamics of the formation of the desipramine intermediate was studied using UV/vis spectroscopy. The extinction coefficient was measured for the reactive intermediate, 7.80×10(3)M(-1)cm(-1), as well as the apparent Michaelis-Menten and catalytic constants, 4.4mM and 2.3s(-1), respectively. Both desipramine and clomipramine degraded DNA in the presence of HRP/H(2)O(2), as was revealed by agarose gel electrophoresis and PCI extraction. Manipulating the kinetic parameters of drug's radical formation and determining the extent of degradation to biomolecules could be potentially used for designing effective agents exhibiting specific reactivity.

Difficulties in dopamine transporter radioligand PET analysis: the example of LBT-999 using [18F] and [11C] labelling Part I: PET studies.

BACKGROUND: LBT-999 (E)-N-(4-fluorobut-2-enyl)-2ß-carbomethoxy-3ß-(4'-tolyl)nortropane is a dopamine transporter (DAT) ligand. [(18)F]LBT-999 was first labelled with carbon-11; we will now describe its in vivo behaviour in comparison to that of [(11)C]LBT-999. METHODS/RESULTS: Positron emission tomography (PET) experiments (baboons) confirmed the high affinity/specificity of [(18)F]LBT-999 for DAT. The brain regional distribution was in accordance with that of DAT. Pre-treatment with LBT-999 (1 mg/kg iv), but not with desipramine, a norepinephrine (NET) antagonist, reduced the striatum-to-cerebellum ratio by 96%, confirming the specificity for DAT vs. NET. The parent compound decreased rapidly and represented 24.3 ± 5.0% of plasma radioactivity at 30 min pi. Whole-body scans showed an important bone uptake of free fluorine following metabolism of [(18)F]LBT-999. In the cerebellum and striatum, distribution volumes increased by 30-40% between 80 and 230 min, suggesting the polluting role of a radiometabolite(s). [(11)C]LBT-999 exhibited a 40% higher standardized uptake value in the striata. This difference is likely due to N-dealkylation followed by [(18)F]fluoride release. 2ß-Carbomethoxy-3ß-(4'-tolyl) nortropane is then formed, while [(11)C]2ß-carbomethoxy-3ß-(4'-tolyl) nortropane is formed following injection of [(11)C]LBT-999. This metabolite has high affinity for the DAT. In one specific PET experiment, intravenous injection of this metabolite induced a strong displacement of [(18)F]LBT-999 in the striata, confirming that this metabolite readily crosses the blood-brain barrier (BBB) and binds to DAT. CONCLUSIONS: [(18)F]LBT-999 is N-dealkylated in vivo to yield (1) a nonradioactive metabolite that crosses the BBB and has a high affinity for the DAT and (2) a [(18)F]fluoro-alkyl chain which is further defluorinated. The temporal changes in distribution volumes are consistent with the accumulation of a radiometabolite(s) in the brain. Therefore, the quantification of DAT density with [(18)F]LBT-999 is rather difficult.

Evaluation of the potential of surface enhancement Raman spectroscopy for detection of tricyclic psychotropic drugs. Case studies on imipramine and its metabolite.

The potential use of surface Raman enhanced spectroscopy (SERS) for confirmatory identification and the semi-quantitative analysis of selected tricyclic antidepressants (TCAs) is examined utilizing a conventional silver colloid. Raman and SERS spectra of aqueous solutions of imipramine (Imi) and its metabolite, desipramine (Des), were recorded as the function of concentration using NIR excitation. A good linear correlation is observed for the dependence of the SERS signal at 684 cm(-1) (R(2) = 0.9997) on Imi concentration over the range of 0.75-7.5 µM. The limit of detection of imipramine in the silver colloidal solution is 0.98 µM. SERS spectra of Imi and Des were also recorded for blood plasma samples without prior purification as well as after the use of standard solid phase extraction. All spectra show the characteristic spectral profile of the molecules and moreover, stronger signal enhancement is observed for Imi in the "raw" samples as opposed to Imi extracted from a biological matrix.

Exocytosis of acid sphingomyelinase by wounded cells promotes endocytosis and plasma membrane repair.

Rapid plasma membrane resealing is essential for cellular survival. Earlier studies showed that plasma membrane repair requires Ca(2+)-dependent exocytosis of lysosomes and a rapid form of endocytosis that removes membrane lesions. However, the functional relationship between lysosomal exocytosis and the rapid endocytosis that follows membrane injury is unknown. In this study, we show that the lysosomal enzyme acid sphingomyelinase (ASM) is released extracellularly when cells are wounded in the presence of Ca(2+). ASM-deficient cells, including human cells from Niemann-Pick type A (NPA) patients, undergo lysosomal exocytosis after wounding but are defective in injury-dependent endocytosis and plasma membrane repair. Exogenously added recombinant human ASM restores endocytosis and resealing in ASM-depleted cells, suggesting that conversion of plasma membrane sphingomyelin to ceramide by this lysosomal enzyme promotes lesion internalization. These findings reveal a molecular mechanism for restoration of plasma membrane integrity through exocytosis of lysosomes and identify defective plasma membrane repair as a possible component of the severe pathology observed in NPA patients.

Sequential metabolism of secondary alkyl amines to metabolic-intermediate complexes: opposing roles for the secondary hydroxylamine and primary amine metabolites of desipramine, (s)-fluoxetine, and N-desmethyldiltiazem.

Three secondary amines desipramine (DES), (S)-fluoxetine [(S)-FLX], and N-desmethyldiltiazem (MA) undergo N-hydroxylation to the corresponding secondary hydroxylamines [N-hydroxydesipramine, (S)-N-hydroxyfluoxetine, and N-hydroxy-N-desmethyldiltiazem] by cytochromes P450 2C11, 2C19, and 3A4, respectively. The expected primary amine products, N-desmethyldesipramine, (S)-norfluoxetine, and N,N-didesmethyldiltiazem, are also observed. The formation of metabolic-intermediate (MI) complexes from these substrates and metabolites was examined. In each example, the initial rates of MI complex accumulation followed the order secondary hydroxylamine > secondary amine >> primary amine, suggesting that the primary amine metabolites do not contribute to formation of MI complexes from these secondary amines. Furthermore, the primary amine metabolites, which accumulate in incubations of the secondary amines, inhibit MI complex formation. Mass balance studies provided estimates of the product ratios of N-dealkylation to N-hydroxylation. The ratios were 2.9 (DES-CYP2C11), 3.6 [(S)-FLX-CYP2C19], and 0.8 (MA-CYP3A4), indicating that secondary hydroxylamines are significant metabolites of the P450-mediated metabolism of secondary alkyl amines. Parallel studies with N-methyl-d(3)-desipramine and CYP2C11 demonstrated significant isotopically sensitive switching from N-demethylation to N-hydroxylation. These findings demonstrate that the major pathway to MI complex formation from these secondary amines arises from N-hydroxylation rather than N-dealkylation and that the primary amines are significant competitive inhibitors of MI complex formation.

Efficacy of imipramine in psychotic versus nonpsychotic depression.

The purpose of the present study is to compare the efficacy of imipramine in the treatment of psychotic versus nonpsychotic depression. Previous studies report varying results of monotherapy with antidepressants in psychotic depression. Because psychotic depression is seriously underinvestigated, performing a post hoc analysis of randomized clinical trials consisting of both psychotic and nonpsychotic depressed patients may contribute to the discussion on the optimal treatment of depressed patients with mood-congruent psychotic features. A total of 112 patients diagnosed with major depression (Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition) (40 with psychotic depression and 82 without psychotic features) received treatment with imipramine for 6 weeks after a washout period of 7 days. Imipramine doses were adjusted to attain a predefined fixed plasma level. Treatment response was assessed with the Hamilton Rating Scale for Depression (HAM-D). A logistic regression analysis showed a significantly larger reduction in HAM-D score in the sample with psychotic features compared with the nonpsychotic sample (regression coefficient, -3.47; SE, 1.7; P = 0.04). According to the primary outcome criterion, that is, the change in HAM-D score, imipramine was significantly more effective in the sample with psychotic depression compared with the nonpsychotic depressed patients. The contradiction between our results and those of several previous studies may be due to the fixed plasma level dosing of imipramine refraining from concurrent psychotropic medication or limiting our patient sample to patients with mood-congruent psychotic features.

Enhanced norepinephrine output during long-term desipramine treatment: a possible role for the extraneuronal monoamine transporter (SLC22A3).

To study the delay (2-6 weeks) between initial administration of norepinephrine reuptake inhibitor antidepressants and onset of clinical antidepressant action, we examined the effects of desipramine treatment on urinary and plasma catecholamines and their metabolites during the initial 6 weeks of treatment in depressed patients. Catecholamines and metabolites in 24-h urine collections and 8:00 a.m. plasma samples were measured at baseline and after 1, 4, and 6 weeks of desipramine treatment. Desipramine treatment produced significant increases in urinary norepinephrine (NE) and normetanephrine (NMN) and plasma NE at Weeks 4 and 6, but not at Week 1. The ratio of urinary NE/NMN was increased at Weeks 4 and 6, suggesting a reduction in the metabolism of NE to NMN at extraneuronal sites by Weeks 4 and 6. The increases in urinary NE and NMN and plasma NE at Weeks 4 and 6 of desipramine treatment were associated with a reduction in the conversion of NE to NMN. This would be compatible with a blockade of the extraneuronal monoamine transporter (organic cation transporter 3; SLC22A3) by NMN. Inhibition of the extraneuronal monoamine transporter may be an important component in the clinical pharmacology of the norepinephrine reuptake inhibitor antidepressant drugs, such as desipramine.

Pharmacological properties of the active metabolites of the antidepressants desipramine and citalopram.

Although major metabolites of some antidepressant drugs are known to be active, their pharmacological effects are poorly characterized. Two of the most selective antidepressants, desipramine (selectively inhibits norepinephrine reuptake) and citalopram (selectively inhibits serotonin reuptake) are frequently used in animal studies of antidepressant action, as well as being useful therapeutically. The primary aim of this study was to determine the affinity of desmethyldesipramine, an active metabolite of desipramine, for the rat norepinephrine and serotonin transporters, as well as for the rat alpha(2)-adrenoceptor. The pharmacological characteristics of desmethyldesipramine and desmethylcitalopram, an active metabolite of citalopram, were also determined for various human transporters and neurotransmitter receptors. Competition binding studies using [(3)H]nisoxetine and [(3)H]citalopram showed desipramine to be 25 times more selective for the rat norepinephrine as compared to serotonin transporter (6.2 nM vs. 158 nM) whereas desmethyldesipramine is 12 times more selective for the serotonin over the norepinephrine transporter (12.8 nM vs. 153 nM). Interestingly, the affinity of desmethyldesipramine for the serotonin transporter is similar to the affinity of desipramine for the norepinephrine transporter. Desipramine and desmethyldesipramine were found to have a lower affinity for the rat alpha(2A(D))-adrenoceptor than the transporters, suggesting that this receptor is not a major site of action for either compound. Thus, the pharmacological effects of desipramine in rats may be attributed not only to the inhibition of the norepinephrine transporter by desipramine but also to the inhibition of serotonin transporter by the active metabolite desmethyldesipramine.

LeuT-desipramine structure reveals how antidepressants block neurotransmitter reuptake.

Tricyclic antidepressants exert their pharmacological effect-inhibiting the reuptake of serotonin, norepinephrine, and dopamine-by directly blocking neurotransmitter transporters (SERT, NET, and DAT, respectively) in the presynaptic membrane. The drug-binding site and the mechanism of this inhibition are poorly understood. We determined the crystal structure at 2.9 angstroms of the bacterial leucine transporter (LeuT), a homolog of SERT, NET, and DAT, in complex with leucine and the antidepressant desipramine. Desipramine binds at the inner end of the extracellular cavity of the transporter and is held in place by a hairpin loop and by a salt bridge. This binding site is separated from the leucine-binding site by the extracellular gate of the transporter. By directly locking the gate, desipramine prevents conformational changes and blocks substrate transport. Mutagenesis experiments on human SERT and DAT indicate that both the desipramine-binding site and its inhibition mechanism are probably conserved in the human neurotransmitter transporters.

Appropriate dosing regimens for treating juvenile rats with desipramine for neuropharmacological and behavioral studies.

The tricyclic antidepressants, including desipramine (DMI), are no better than placebo in treating childhood and adolescent depression, but are effective in adult depression. Animal studies comparing the effects of DMI in juveniles and adults are complicated by age-related variations in elimination rates. Thus, different dosing regiments are needed to achieve similar brain drug levels in juvenile and adult rats. We compared the half-life of DMI as well as the brain and serum concentrations of DMI and its active metabolite desmethyldesipramine in juvenile and adult rats after various drug administration paradigms. After acute i.p. administration DMI is eliminated from the brain more slowly in postnatal day (PND) 21 and 28 rats as compared to adults. After chronic i.p. administration (for 4-5 days between PND 9 and 28), lower doses of DMI are needed with juvenile rats to obtain the same brain DMI concentrations as adults. By contrast, 2 weeks of continuous drug delivery (minipump) to PND 21-35 and adult rats result in similar brain DMI concentrations. Thus, the pharmacokinetic properties of DMI varies with the age of the animal and dosing of DMI and needs to be carefully adjusted in order to have appropriate brain levels of the drug.