Paroxetine transporters

Antidepressants are used in the treatment of neuropathic pain and headache. They include the classic tricyclic compounds and are divided into nonselective nor-adrenaline/5-HT reuptake inhibitors (e.g., amitriptyline, imipramine, clomipramine, venlafaxine), preferential noradrenaline reuptake inhibitors (e.g., desipramine, nortriptyline) and selective 5-HT reuptake inhibitors (e.g., citalopram, paroxetine, fluoxetine). The reuptake block leads to a stimulation of endogenous monoaminer-gic pain inhibition in the spinal cord and brain. In addition, tricyclics have NMDA receptor antagonist, endogenous opioid enhancing, Na+ channel blocking, and K+ channel opening effects which can suppress peripheral and central sensitization. Block of cardiac ion channels by tricyclics can lead to life-threatening arrhythmias. The selective 5-HT transporter inhibitors have a different side effect profile and are safer in cases of overdose [3]. 

Selective serotonine reuptake inhibitor (SSRI) is an abbreviation for the class of antidepressants known as the Selective Serotonin Reuptake Inhibitors. Examples of SSRIs include fluoxetine, paroxetine, citalopram, and sertraline. These drugs selectively inhibit the serotonin transporter thus prolonging the synaptic lifespan of the neurotransmitter serotonin. 

Indeed, 5-HT is also a substrate for the 5-HT transporter, itself an important player in the treatment of depression, and more recently for the whole range of anxiety disorders spectrum (GAD, OCD, social and other phobias, panic and post-traumatic stress disorders). It is the target for SSRIs (selective serotonin reuptake inhibitors) such as fluoxetine, paroxetine, fluvoxamine, and citalopram or the more recent dual reuptake inhibitors (for 5-HT and noradrenaline, also known as SNRIs) such as venlafaxine. Currently, there are efforts to develop triple uptake inhibitors (5-HT, NE, and DA). Further combinations are possible, e.g. SB-649915, a combined 5-HTia, 5-HT1b, 5-HT1d inhibitor/selective serotonin reuptake inhibitor (SSRI), is investigated for the treatment of major depressive disorder. 

Pollock, B. G., Ferrell, R. E. et al. (2000). Allelic variation in the serotonin transporter promoter affects onset of paroxetine treatment response in late-life depression. Neuropsychopharmacology, 23(5), 587-90. 

Zanardi, R. et al. (2000). Efficacy of paroxetine in depression is influenced by a functional polymorphism within the promoter of the serotonin transporter gene. /. Clin. Psychopharmacol., 20(1), 105-7. 

These drugs increase synaptic serotonin by selectively blocking the serotonin reuptake transporter. In preclinical and human studies acute doses tend to be anxiogenic (Bell and Nutt 1998) but chronic administration has anxiolytic effects, possibly due to downregulation of presynaptic autoreceptors (Blier et al. 1990). There are five SSRIs widely available citalopram, fluoxetine, fluvoxam-ine, paroxetine and sertraline. Escitalopram, the S-enantiomer of citalopram. 

Yu YW, Tsai SJ, Chen TJ, Lin CH, Hong CJ (2002) Association study of the serotonin transporter promoter polymorphism and symptomatology and antidepressant response in major depressive disorders. Mol Psychiatry 7 1115-1119 Zanardi R, Benedetti F, Di Bella D, Catalano M, Smeraldi E (2000) Efficacy of paroxetine in depression is influenced by a functional polymorphism within the promoter of the serotonin transporter gene. J Clin Psychopharmacol 20 105-107 Zanardi R, Serretti A, Rossini D, et al (2001) Factors affecting fluvoxamine antidepressant activity influence of pindolol and 5-HTTLPR in delusional and nondelusional depression. Biol Psychiatry 50 323-330... 

In a 4-month open-label study of 15 adults with severe and profound mental retardation (seven with PDD), paroxetine at doses of 20 to 50 mg daily was significantly effective for symptoms of aggression at 1-month, but not at 4-month follow-up (Davanzo et al., 1998). The investigators hypothesized that adaptive changes may have occurred in 5-HT receptor density, availability of 5-HT, or in 5-HT transporter sensitivity. 

The selective serotonin reuptake inhibitors (SSRIs) represent a chemically diverse class of agents that have as their primary action the inhibition of the serotonin transporter (SERT) (Figure 30-3). Fluoxetine was introduced in the United States in 1988 and quickly became one of the most commonly prescribed medications in medical practice. The development of fluoxetine emerged out of the search for chemicals that had high affinity for monoamine receptors but lacked the affinity for histamine, acetylcholine, and adrenoceptors that is seen with the tricyclic antidepressants (TCAs). There are currently six available SSRIs, and they are the most common antidepressants in clinical use. In addition to their use in major depression, SSRIs have indications in GAD, PTSD, OCD, panic disorder, PMDD, and bulimia. Fluoxetine, sertraline, and citalopram exist as isomers and are formulated in the racemic forms, whereas paroxetine and fluvoxamine are not optically active. Escitalopram is the S enantiomer of citalopram. As with all antidepressants,... 

Fluoxetine Highly selective blockade of serotonin transporter (SERT) little effect on norepinephrine transporter (NET) Acute increase of serotonergic synaptic activity slower changes in several signaling pathways and neurotrophic activity Major depression, anxiety disorders panic disorder obsessive-compulsive disorder post-traumatic stress disorder perimenopausal vasomotor symptoms eating disorder (bulimia) Half-lives from 15-75 h oral activity Toxicity Well tolerated but cause sexual dysfunction Interactions Some CYP inhibition (fluoxetine 2D6, 3A4 fluvoxamine 1A2 paroxetine 2D6)... 

The majority of the alkaloids that had affinity to the serotonin transporter (SERT) were crinine-type alkaloids. However, cherylline 4, tazettine 8 and 1-0-acetyllycorine 53 are the only alkaloids that showed affinity to SERT among the cheiylline-, tazettine- and lycorine-type alkaloids, respectively (80). The activity of the crinine-type alkaloids was attributed to the presence of a 1,3-dioxole moiety in common with the chnically used SSRI paroxetin (79). 

Kato M, Ikenaga Y, Wakeno M, et al. Controlled clinical comparison of paroxetine and fluvoxamine considering the serotonin transporter promoter polymorphism. Int Clin Psychopharmacol 2005 20(3) 151—6. 

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