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Left: Mean values of plasma lorazepam concentration versus pharmacodynamic EEG effect at corresponding times generic diltiazem 180 mg, with arrows indicating the direction of increasing time diltiazem 60mg with visa. The data points (closed triangles) are the hypothetical effect site concentrations and pharmacodynamic effect values at corresponding times discount diltiazem 60mg amex. The solid line is the link model function determined by nonlinear regression,yielding the indicated valuesof EmaxandEC50. For the CYP isoforms nous dosage, for example, maximum effects may be delayed most relevant to human drug metabolism, each has its own for an average of 30 minutes after dosage. Experimental distinct pattern of relative abundance, anatomic location, studies of the time-course of whole-brain concentrations mechanism of regulation, substrate specificity, and suscepti- of lorazepam, or of the degree of benzodiazepine receptor bility to inhibition and induction by other drugs or foreign occupancy, indicate that the delay is attributable to the slow chemicals (Table 38. The expression and in vivo function physical entry of lorazepam into brain tissue, probably be- of at least two CYP isoforms (CYP2D6 and CYP2C19) cause of the relatively low lipid solubility of lorazepam (34, are regulated by a genetic polymorphism, such that some 38,39). The delay was mathematically consistent with a ki- members of a population fail to express 'normal' levels netic-dynamic model incorporating a hypothetical 'effect of enzyme or expresses poorly functional protein (56–62). The half-life Individuals identified as 'CYP2D6 poor metabolizers,' as for equilibration between plasma and the effect compart- an example, have very low clearance of drugs that are major ment was approximately 9 minutes. This matches clinical substrates for biotransformation by CYP2D6 (such as desi- experience indicating that intravenous lorazepam cannot pramine, nortriptyline, venlafaxine, tramadol, and dextro- easily be used in situations requiring minute-to-minute ti- methorphan). Such individuals are at risk for developing tration of sedative or amnestic effects (40). Nonetheless, high and potentially toxic plasma concentrations of these intravenous lorazepam can be used for the treatment of sta- tus epilepticus, although its onset of action may be some- what slower than that of intravenous diazepam (46,47). CYTOCHROMES P-450 IN PSYCHOPHARMACOLOGY: THE IMPORTANCE OF P-450-3A ISOFORMS FIGURE 38. Nomenclature system for the cytochrome P-450 (CYP)superfamily ofenzymes. Following theCYP designation,the The cytochrome P-450 (CYP) superfamily of drug metabo- number-letter-number sequence indicates the family, subfamily, lizing enzymes is now established as being of primary impor- and specific isoform. OVERVIEW OF HUMAN CYTOCHROMES P-450 Relative Hepatic Genetic CYP Isoform Abundance Polymorphism Representative Substrates 1A2 13%? Caffeine, theophylline, tacrine 2B6 <1% − Bupropion, propofol 2C9 15% + S-warfarin, phenytoin, tolbutamide, NSAIDs 2C19 4% + S-mephenytoin, omeprazole (partial contributor to many others) 2D6 2% + Some psychotropic and cardiac drugs 2E1 7% − Chlorzoxazone, some inhaled anesthetics 3A4/5 29%a − Many (see also Table 38. It is not established to what extent hepatic CYP3A5 is of clinical significance for drug-metabolizing The CYP3A Isoforms activity. The location and sequence of the genetic element responsible The overall importance of the CYP3A subfamily of drug- metabolizing enzymes, particularly in the field of psycho- for CYP3A4 expression have been identified, as well as a pharmacology, has become increasingly evident over the last regulatory segment located on the 5′ flanking region corre- decade (6–9,63–69) (Table 38. Its high substrate capacity is a consequence of liver (70) (Table 38. Within the CYP3A subfamily, both the relatively high value of maximum reaction velocity CYP3A4 is the most important in the adult human, in terms (Vmax, expressed in nanomoles of product produced per unit of drug-metabolizing activity as well as quantitative domi- time per milligram of protein) in a Michaelis-Menten rela- nance. CYP3A5, another CYP3A isoform, is also detected tionship, as well as the high quantitative abundance of the protein in hepatic tissue. The low-affinity characteristic is reflected in the high Km value (substrate concentration cor- responding to 50% of Vmax) in a Michaelis-Menten relation- TABLE 38. One consequence is that CYP3A-mediated metabo- FOR HUMAN CYP3A lism usually is not 'saturable' at substrate concentrations within the therapeutic range, because this range is likely to Contribution of CYP3A to Net Clearance be far below the reaction Km. Furthermore, in situations in Complete or which CYP3A is one of several cytochromes contributing Nearly Complete Partial Small to metabolism [e. However, this is not in- Bromazepam Clonazepam variably true. Nefazodone is a CYP3A substrate, but Km Nefazodone Zolpidem values for production of the various metabolites are rela- Trazodone Citalopram Reboxetine Haloperidol tively low (74), and kinetics are nonlinear (75). Midazolam Buspirone Clozapine has a low Km for the principal pathway (76,77), and there Gepirone Olanzapine is evidence of nonlinear kinetics at higher concentrations Adinazolam Mirtazapine in humans (78). Quetiapine Amitriptyline Significant quantities of CYP3A exist in gastrointestinal Sildenafil Imipramine (GI) tract mucosa (65,69,79). The quantitative expression/ 38: Pharmacokinetics, Pharmacodynamics, and Drug Disposition 515 TABLE 38. REPRESENTATIVE DRUGS HAVING CLINICALLY IMPORTANT EFFECTS ON THE HUMAN CYP ENZYMES Drug Inhibition of: Induction of: Azole antifungals Ketoconazole CYP3A Itraconazole CYP3A Fluconazole CYP3A, 2C9 Terbinafine CYP2D6 Antidepressants Fluoxetine CYP2D6 Paroxetine CYP2D6 Fluvoxamine CYP1A2, 2C19, 3A Nefazodone CYP3A St. Relativecontributions of CYP3Aenzymes present Antipsychotics in gastrointestinal (GI) tract mucosa, and in the liver, to net bio- Perphenazine CYP2D6 availability (F) of orally administered midazolam and triazolam. Anticonvulsants Both of these compounds have net F values of less than 50% (29% Carbamazepine CYP3A for midazolam, 44% for triazolam). Both compounds undergo Antithrombotics approximately 50% extraction during passage through the G. However midazolam undergoes another 38% ex- traction across the liver, compared to only 12% for triazolam. Antiinfectives Erythromycin CYP3A Clarithromycin CYP3A Ciprofloxacin CYP1A2 Rifampin CYP3A activity of GI tract CYP3A is not correlated with its expres- Viral protease inhibitors sion/activity in liver, even though the expressed protein is Ritonavir CYP3A CYP3A identical at the two sites. For a number of moderate or high- Nonnucleoside reverse transcriptase inhibitors Delavirdine CYP3A clearance CYP3A substrates (e.
Phosphorylation of mammalian proteins in relative size and charge purchase 180mg diltiazem otc. Proteins resolved by gel electrophoresis can be transferred Serine/threonine phosphorylation is widely recognized to to a membrane composed of nitrocellulose or polyvinyl di- regulate GPCRs trusted 60mg diltiazem. Tyrosine phosphorylation order diltiazem 60 mg without prescription, a more recently fluoride (PVDF). This allows many manipulations to be discovered modification that is well established to mediate performed, such as detection of a specific protein from a signaling via non-GPCR growth factor receptors (39), may complex mixture by the ability of the protein to be bound also play a role in regulating certain GPCRs (40). Other kinases, such as the GPCRs resolved by gel electrophoresis can also be ana- 3′,5′-cyclic adenosine monophosphate (cAMP)-dependent lyzed by chemical sequencing, typically by a process called protein kinase (PKA) and protein kinase C can also regulate Edman degradation, which sequentially cleaves residues GPCRs by phosphorylating distinct cytoplasmic serine/ from the amino-terminal end of the protein. A very powerful method for phorylated by other kinases, such as GRKs, are more diffi- determining amino acid sequence and detecting posttransla- cult to predict because they do not conform to a rigidly tional modifications of proteins is via mass spectrometric defined consensus sequence. For example, with tandem mass spectrometry it is enzymes with relatively well-understood substrate specificity possible to measure the mass of specific protein fragments in vitro, there are major limitations to the use of sequence with an accuracy of one part in 10,000 up to 12,000 daltons analysis for predicting phosphorylation sites in vivo. The impressive dues conforming to a specific consensus sequence are not accuracy of this method makes it possible to detect phos- always phosphorylated under physiologic conditions, and, phorylation as well as many other posttranslational modifi- conversely, in some cases residues that do not conform to cations, even those that cause subtle changes in the protein a well-defined consensus sequence can be phosphorylated size or charge. Thus it is important to determine the Chromatography, which refers to any separation based phosphorylation of GPCRs when expressed in the appropri- on differential behavior of a molecule between a stationary ate mammalian cells. High-performance liquid chroma- tography (HPLC) using reverse-phase (e. By compar- There are many ways of detecting phosphorylated proteins. Subsequently, these fragments can be isolated and fur- PAGE, proteins dissolved in SDS are loaded onto one end ther analyzed by methods such as Edman degradation or of a porous gel and exposed to an electric field, which causes mass spectrometry. By using Methods to Examine Regulation of appropriate radiolabeled compounds (such as inorganic Receptors byLocalization and Trafficking phosphate added to the culture medium), it is possible to apply the technique of autoradiography to specifically detect It has been appreciated for many years that a critical parame- radioactive, phosphorylated proteins resolved by SDS- ter that can regulate the strength of functional signal trans- PAGE. It is also possible to use gel electrophoresis to sepa- duction via GPCRs is the actual number of receptors present rate proteins according to relative charge, a property that in target tissues and, in particular, the number of receptors is modified predictably by certain modifications such as present in the plasma membrane of individual cells. These types of separation can be com- disturbances in the regulation of receptor number and/or bined in the use of two-dimensional gel electrophoresis, distribution may be of primary importance in the patho- 22: G-Protein–Coupled Receptors 283 physiology of certain neuropsychiatric disorders. For exam- which antibodies recognizing the native receptor are not ple, long-term administration of dopamine receptor antago- available. In either case the general scheme is as follows: nists can induce upregulation of specific receptors, which Cells or tissues expressing the receptor of interest are fixed may contribute to the apparent supersensitivity of dopamine using standard histologic methods. The fixed cells or tissue receptors associated with tardive dyskinesia (46). This phenomenon is termed bodies recognizing the receptor of interest. Studies using ra- tive epitopes in the specimen (typically several hours), the dioligand binding and subcellular fractionation techniques specimens are washed extensively to remove nonspecifically provided early evidence that multiple mechanisms are capa- associated antibodies. The directly visualizing the subcellular localization of GPCRs secondary antibody is typically coupled to a fluorochrome and for performing biochemical studies of specific receptor (such as fluorescein), a recognizable particle (such as colloi- trafficking mechanisms. GPCRs can be detected in situ in cell or tissue preparations using immunochemical techniques and receptor-specific an- Biochemical Methods to AssaySpecific tibodies. Antibodies that recognize the native receptor pro- Receptor Trafficking Processes tein can be used to examine the localization of endogenously expressed receptors, whereas epitope-tagging methods (see Whereas microscopic imaging can readily provide a great above) can be used to detect mutated versions of the receptor deal of qualitative information about GPCR localization protein or as a means to detect recombinant receptors for and trafficking, it can be quite challenging to quantitiate A B FIGURE 22. Visualization of HA epitope-tagged dopamine D1 receptors in transfected cells, using a fluorochrome-labeled secondary antibody and fluorescence microscopy. The ability of this receptortoundergoregulatedinternalizationis indicatedbythedopamine-inducedredistribution of immunoreactive receptors from the plasma membrane (visualized as linear staining at the cell periphery) to endocytic vesicles (visualized as punctate structures located throughout the cytoplasm). In addition to being extremely a specific subcellular localization or to measure accurately useful for examining posttranslational modifications of the rate or extent of specific trafficking processes. The im- GPCRs, in some cases it is possible to use these techniques portance of these processes has motivated the development to isolate receptor-containing complexes that presumably of biochemical methods for examining GPCR trafficking. The In addition to their utility for receptor localization, antibod- basic idea is to immunopurify a specific GPCR from cell ies specifically recognizing GPCRs facilitate biochemical or tissue extracts (or from a partially purified subcellular studies of GPCR trafficking using techniques adapted from fraction prepared from a cell or tissue lysate) using an anti- other areas of cell and molecular biology. For example, one body recognizing the native receptor or an engineered epi- method that has been extremely useful for quantitative stud- tope tag, and then to analyze proteins specifically associated ies of GPCR endocytosis is cell-surface biotinylation cou- with this complex using a different antibody. In general, pled with immunoprecipitation of receptors. Proteins pres- this is accomplished by immunoprecipitation of the receptor ent in the plasma membrane of cells can be specifically followed by analysis of associated proteins in the complex labeled by incubating intact cells in the presence of biotin by immunoblotting with the appropriate additional anti- coupled to an activated ester, which is membrane-imper- body. In some cases, the protein complexes are sufficiently meant and therefore forms a covalent bond only with ex- stable that they remain associated through the initial immu- posed amine moieties present in plasma membrane proteins. In other cases this is not true, In general, biotinylation in this manner does not adversely and the complexes dissociate before the receptor can be affect GPCR function, allowing biotinylation to be used as purified from the extract. In this case, various chemical a chemical tag for surface receptors.
Tissue injury liberates cytokines (complex molecules: gamma-interferon cheap 60mg diltiazem free shipping, interleukin 1 order 180 mg diltiazem fast delivery, interleukin 6 180mg diltiazem mastercard, tumour necrosis factor), which are carried by the circulation and have an immediate effect on the hypothalamus (Sapolsky, 1992). In the acute situation, the endogenous opioids are released, presumably to reduce pain (perhaps they also have a role in modulating the release of cortisol; Chrousos, 1992). Evidence also suggests that “dysregulation of the HPA axis” (chronic high cortisol levels) can contribute to depression, anxiety, posttraumatic stress disorder and irritable bowel syndrome. HPA axis dysfunction appears to involve hyper-stimulation of the CRF-1 (type 1) receptor. CRF-1 receptors are located at multiple anatomical sites. An oral CRF-1 receptor antagonist (which has few side effects) appears to be an effective treatment of stress related disorders, although further studies are required (Kehne, 2007). Journal of Neurology, Neurosurgery and Psychiatry 1999; 67: 492-496. The pathophysiology of chorea/ballism and Parkinsonism. Parallel organization of functionally segregated circuits linking basal ganglia and cortex. Linking mind and brain in the study of mental illnesses: a project for a scientific psychopathology. Defining the phenotype of schizophrenia: cognitive dysmetria and its neural mechanisms. Hippocampus and amygdalar volumes in patients with somatization disorder. Progress in Neuropsychopharmacology Biological Psychiatry 2011; 35:1699-1703. Review of structural neuroimaging in patients with refractory obsessive- compulsive disorder. NMDA receptor blockade at rest triggers rapid behavioral antidepressant responses. A post-mortem assessment of mammillary body volume, neruronal number and densities, and fornix volume in subjects with mood disorders. European Archives of Psychiatry and Clinical Neuroscience 2012 Feb 17 [Epub ahead of print]. Glial cells as key players in schizophrenia pathology: recent insights and concepts of therapy. MRI-based measurement of hippocampal volume in patients with combat-related posttraumatic stress disorder. A cognitive neuroscience account of post-traumatic stress disorder and its treatment. Altered resting-state functional connectivity of basolateral and centromedial amygdala complexes in posttraumatic stress disorder. Neuroanatomical circuits modulating fear and anxiety behaviours. White matter abnormalities of fronto-striato-thalamic circuitry in obsessive-compulsive disorder. Chua S, Cheung C, Cheung V, Tsang J, Chen E, Wong J, Cheung J, Yip L, Suckling J, McAlonan G. Cerebral grey, white matter and csf in never-medicated, first episode- schizophrenia. Regulation and dysregulation of the hypothalamic-pituitary-adrenal axis. Endocrinology and Metabolism Clinics of North America 1992; 21:833-858. A randomized add-on trial of an N-methyl- D-aspartate antagonist in treatment-resistant bipolar depression. Rapid resolution of suicidal ideation after a single infusion of an N-methyl-D-aspartate antagonist in patients with treatment-resistant major depressive disorder. Journal of Clinical Psychiatyry 2010; 71:1605-16011. Glucose metabolism in the amygdala in depression: relationship to diagnostic subtype and plasma cortisol levels. Pharmacology, Biochemistry and Behaviour 2002; 71:431-447. Ettinger U, Picchioni M, Landau S, Matsumoto K, van Haren N, Marshall N, Hall M, Schulze K, Toulopoulou T, Davies N, Ribchester T, McGuire P, Murray R. Magnetic resonance imaging of the thalamus and adhesio interthalamica in twins with schizophrenia. Fusar-Poli P, Smieskova R, Serafini G, Politi P, Borgwardt S. Neuroanatomical markers of genetic liability to psychosis and first episode psychosis: a voxelwise meta-analytical comparison. World J Biol Psychiatry 2012, Jan 27 [Epub ahead of print] Gould E, McEwen B, Tanapat P, Galea L, Fuchs E.