Familial orthostatic tachycardia due to norepinephrine transporter deficiency

Dysautonomia following Lyme disease: a key component of post-treatment Lyme disease syndrome?

Dysautonomia, or dysfunction of the autonomic nervous system (ANS), may occur following an infectious insult and can result in a variety of debilitating, widespread, and often poorly recognized symptoms. Dysautonomia is now widely accepted as a complication of COVID-19 and is an important component of Post-Acute Sequelae of COVID-19 (PASC or long COVID). PASC shares many overlapping clinical features with other infection-associated chronic illnesses including Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) and Post-Treatment Lyme Disease Syndrome (PTLDS), suggesting that they may share common underlying mechanisms including autonomic dysfunction. Despite the recognition of this complication of Lyme disease in the care of patients with PTLD, there has been a scarcity of research in this field and dysautonomia has not yet been established as a complication of Lyme disease in the medical literature. In this review, we discuss the evidence implicating Borrelia burgdorferi as a cause of dysautonomia and the related symptoms, propose potential pathogenic mechanisms given our knowledge of Lyme disease and mechanisms of PASC and ME/CFS, and discuss the diagnostic evaluation and treatments of dysautonomia. We also outline gaps in the literature and priorities for future research.

Biochemical Assessment of Pheochromocytoma and Paraganglioma

Pheochromocytoma and paraganglioma (PPGL) require prompt consideration and efficient diagnosis and treatment to minimize associated morbidity and mortality. Once considered, appropriate biochemical testing is key to diagnosis. Advances in understanding catecholamine metabolism have clarified why measurements of the O-methylated catecholamine metabolites rather than the catecholamines themselves are important for effective diagnosis. These metabolites, normetanephrine and metanephrine, produced respectively from norepinephrine and epinephrine, can be measured in plasma or urine, with choice according to available methods or presentation of patients. For patients with signs and symptoms of catecholamine excess, either test will invariably establish the diagnosis, whereas the plasma test provides higher sensitivity than urinary metanephrines for patients screened due to an incidentaloma or genetic predisposition, particularly for small tumors or in patients with an asymptomatic presentation. Additional measurements of plasma methoxytyramine can be important for some tumors, such as paragangliomas, and for surveillance of patients at risk of metastatic disease. Avoidance of false-positive test results is best achieved by plasma measurements with appropriate reference intervals and preanalytical precautions, including sampling blood in the fully supine position. Follow-up of positive results, including optimization of preanalytics for repeat tests or whether to proceed directly to anatomic imaging or confirmatory clonidine tests, depends on the test results, which can also suggest likely size, adrenal vs extra-adrenal location, underlying biology, or even metastatic involvement of a suspected tumor. Modern biochemical testing now makes diagnosis of PPGL relatively simple. Integration of artificial intelligence into the process should make it possible to fine-tune these advances.

Norepinephrine transporter defects lead to sympathetic hyperactivity in Familial Dysautonomia models

Familial dysautonomia (FD), a rare neurodevelopmental and neurodegenerative disorder affects the sympathetic and sensory nervous system. Although almost all patients harbor a mutation in ELP1, it remains unresolved exactly how function of sympathetic neurons (symNs) is affected; knowledge critical for understanding debilitating disease hallmarks, including cardiovascular instability or dysautonomic crises, that result from dysregulated sympathetic activity. Here, we employ the human pluripotent stem cell (hPSC) system to understand symN disease mechanisms and test candidate drugs. FD symNs are intrinsically hyperactive in vitro, in cardiomyocyte co-cultures, and in animal models. We report reduced norepinephrine transporter expression, decreased intracellular norepinephrine (NE), decreased NE re-uptake, and excessive extracellular NE in FD symNs. SymN hyperactivity is not a direct ELP1 mutation result, but may connect to NET via RAB proteins. We found that candidate drugs lowered hyperactivity independent of ELP1 modulation. Our findings may have implications for other symN disorders and may allow future drug testing and discovery.

The Relationship Between Hypermobile Ehlers-Danlos Syndrome (hEDS), Postural Orthostatic Tachycardia Syndrome (POTS), and Mast Cell Activation Syndrome (MCAS)

In recent years, an association between hypermobile Ehlers-Danlos syndrome (hEDS), mast cell activation syndrome (MCAS), and postural orthostatic tachycardia syndrome (POTS) has garnered attention and patients are increasingly presenting with this triad. However, a real relationship between these entities is unclear due to a lack of scientific validity. We conducted an extensive review of the literature using two different search strategies. A narrower strategy included 88 searches of various combinations of terms for each of the three conditions, yielding 19 unique papers. A broader search included 136 searches of various combinations of terms but included all forms of EDS and yielded 40 unique papers. Of these, only four and nine papers from the narrower and broader search strategies were original research articles. None of these papers resulted from a combination of the search terms for the three conditions. All three clinical entities are controversial in either existence or pathogenesis. MCAS is a poorly defined clinical entity, and many studies do not adhere to the proposed criteria when establishing the diagnosis. Patients previously diagnosed with EDS hypermobility type may not meet the new, stricter criteria for hEDS but may for a less severe hypermobility spectrum disorder (HSD). The pathophysiology of POTS is still unclear. An evidence-based, common pathophysiologic mechanism between any of the two, much less all three conditions, has yet to be described. Our review of the literature shows that current evidence is lacking on the existence of MCAS or hEDS as separate or significant clinical entities. Studies proposing a relationship between the three clinical entities are either biased or based on outdated criteria. The reason behind the purported association of these entities stems from an overlapping pool of vague, subjective symptoms, which is inadequate evidence to conclude that any such relationship exists.

Postural tachycardia syndrome - Diagnosis, physiology, and prognosis

Postural tachycardia syndrome (POTS) is a heterogeneous clinical syndrome that has gained increasing interest over the past few decades due to its increasing prevalence and clinical impact on health-related quality of life. POTS is clinically characterized by sustained excessive tachycardia upon standing that occurs in the absence of significant orthostatic hypotension and other medical conditions and or medications, and with chronic symptoms of orthostatic intolerance. POTS represents one of the most common presentations of syncope and presyncope secondary to autonomic dysfunction in emergency rooms and in cardiology, neurology, and primary care clinics. The most sensitive method to detect POTS is a detailed medical history, physical examination with orthostatic vital signs or brief tilt table test, and a resting 12-lead electrocardiogram. Additional diagnostic testing may be warranted in selected patients based on clinical signs. While the precise etiology remains unknown, the orthostatic tachycardia in POTS is thought to reflect convergence of multiple pathophysiological processes, as a final common pathway. Based on this, POTS is often described as a clinical syndrome consisting of multiple heterogeneous disorders, with several underlying pathophysiological processes proposed in the literature including partial sympathetic neuropathy, hyperadrenergic state, hypovolemia, mast cell activation, deconditioning, and immune-mediated. These clinical features often overlap, however, making it difficult to categorize individual patients. Importantly, POTS is not associated with mortality, with many patients improving to some degree over time after diagnosis and proper treatment. This review will outline the current understanding of diagnosis, pathophysiology, and prognosis in POTS.

DNA methylation in the norepinephrine transporter gene promoter region is not associated with depression and hypertension

OBJECTIVE

This study aims to detect the role of DNA methylation in norepinephrine transporter (NET) gene promoter region on the association between depression and hypertension.

METHODS

A total of 162 subjects were categorized into four groups based on depression scores and blood pressure. DNA was extracted from peripheral white blood cells and methylation levels of nine CpG sites in NET gene promoter region were investigated by pyrosequencing.

RESULTS

For each CpG site and the average value of nine CpG sites, there were no significant differences in DNA methylation of the NET gene promoter between healthy controls and patients with depression or hypertension. And there were no significant differences among groups after adjusting for age and body mass index. However, DNA methylation levels of the CpG sites adjacent to transcription start site tended to be low. In addition, CpG1.2-CpG5.2 were highly correlated with CpG4 as the first principle component, while CpG2 and the part of CpG1 and 3 were the second principle components. The total participants were clustered into three subgroups by hierarchical cluster analysis of methylated levels.

CONCLUSION

Our study indicates that DNA methylation levels of nine CpG sites in NET gene promoter region are not associated with depression and hypertension.

Postural Tachycardia Syndrome: Diagnosis and Management in Adolescents and Young Adults

Postural tachycardia syndrome (POTS) represents a common form of orthostatic intolerance that disproportionately affects young women from puberty through adulthood. Patients with POTS have day-to-day orthostatic symptoms with the hallmark feature of an excessive, sustained, and symptomatic rise in heart rate during orthostatic testing. Although considerable overlap exists, three subtypes of POTS have been described: neuropathic, hyperadrenergic, and hypovolemic forms. The wide spectrum of symptoms and comorbidities can make treatment particularly challenging. Volume expansion with fluid and salt, exercise, and education constitute a reasonable initial therapy for most patients. Several medicines are also available to treat orthostatic intolerance and the associated comorbidities. Defining the POTS subtypes clinically in each patient may help to guide medicine choices. A multidisciplinary approach to overall management of the patient with POTS is advised. This review highlights several aspects of POTS with a specific focus on adolescent and young adult patients. [Pediatr Ann. 2017;46(4):e145-e154.].

Associations Between Neurotransmitter Genes and Fatigue and Energy Levels in Women After Breast Cancer Surgery

CONTEXT

Fatigue is a common problem in oncology patients. Less is known about decrements in energy levels and the mechanisms that underlie both fatigue and energy.

OBJECTIVES

In patients with breast cancer, variations in neurotransmitter genes between lower and higher fatigue latent classes and between the higher and lower energy latent classes were evaluated.

METHODS

Patients completed assessments before and monthly for six months after surgery. Growth mixture modeling was used to identify distinct latent classes for fatigue severity and energy levels. Thirty candidate genes involved in various aspects of neurotransmission were evaluated.

RESULTS

Eleven single-nucleotide polymorphisms or haplotypes (i.e., ADRB2 rs1042718, BDNF rs6265, COMT rs9332377, CYP3A4 rs4646437, GALR1 rs949060, GCH1 rs3783642, NOS1 rs9658498, NOS1 rs2293052, NPY1R Haplotype A04, SLC6A2 rs17841327, and 5HTTLPR + rs25531 in SLC6A4) were associated with latent class membership for fatigue. Seven single-nucleotide polymorphisms or haplotypes (i.e., NOS1 rs471871, SLC6A1 rs2675163, SLC6A1 Haplotype D01, SLC6A2 rs36027, SLC6A3 rs37022, SLC6A4 rs2020942, and TAC1 rs2072100) were associated with latent class membership for energy. Three of 13 genes (i.e., NOS1, SLC6A2, and SLC6A4) were associated with latent class membership for both fatigue and energy.

CONCLUSIONS

Molecular findings support the hypothesis that fatigue and energy are distinct, yet related symptoms. Results suggest that a large number of neurotransmitters play a role in the development and maintenance of fatigue and energy levels in breast cancer patients.

Adolescent fatigue, POTS, and recovery: a guide for clinicians

Many teenagers who struggle with chronic fatigue have symptoms suggestive of autonomic dysfunction that may include lightheadedness, headaches, palpitations, nausea, and abdominal pain. Inadequate sleep habits and psychological conditions can contribute to fatigue, as can concurrent medical conditions. One type of autonomic dysfunction, postural orthostatic tachycardia syndrome, is increasingly being identified in adolescents with its constellation of fatigue, orthostatic intolerance, and excessive postural tachycardia (more than 40 beats/min). A family-based approach to care with support from a multidisciplinary team can diagnose, treat, educate, and encourage patients. Full recovery is possible with multi-faceted treatment. The daily treatment plan should consist of increased fluid and salt intake, aerobic exercise, and regular sleep and meal schedules; some medications can be helpful. Psychological support is critical and often includes biobehavioral strategies and cognitive-behavioral therapy to help with symptom management. More intensive recovery plans can be implemented when necessary.

Favorable effects of carotid endarterectomy on baroreflex sensitivity and cardiovascular neural modulation: a 4-month follow-up

Carotid surgery variably modifies carotid afferent innervation, thus affecting arterial baroreceptor sensitivity. Low arterial baroreflex sensitivity is a well-known independent risk factor for cardiovascular diseases. The aim of this study was to assess the 4-mo effects of carotid endarterectomy (CEA) on arterial baroreceptor sensitivity and cardiovascular autonomic profile in patients with unilateral carotid stenosis. We enrolled 20 patients (72 ± 8 yr) with unilateral >70% carotid stenosis. ECG, beat-by-beat blood pressure, and respiration were continuously recorded before and 126 ± 9 days after CEA, at rest and during a 75° head-up tilt. Both pharmacological (modified Oxford technique, BRS) and spontaneous (index α, spectral analysis) arterial baroreflex sensitivity were assessed. Cardiovascular autonomic profile was evaluated by plasma catecholamines and spectral indexes of cardiac sympathovagal modulation [low-frequency R-R interval (LFRR), low frequency-to high frequency ratio (LF/HF), high-frequency R-R interval (HFRR)] and sympathetic vasomotor control [low-frequency systolic arterial pressure (LFSAP)] obtained from heart rate and SAP variability. After CEA, both the index α and BRS were higher (P < 0.02) at rest. SAP variance decreased both at rest and during tilt (P < 0.02). Before surgery, tilt did not modify the autonomic profile compared with baseline. After CEA, tilt increased LF/HF and LFSAP and reduced HFRR compared with rest (P < 0.02). Four months after CEA was performed, arterial baroreflex sensitivity was enhanced. Accordingly, the patients' autonomic profile had shifted toward reduced cardiac and vascular sympathetic activation and enhanced cardiac vagal activity. The capability to increase cardiovascular sympathetic activation in response to orthostasis was restored. Baroreceptor sensitivity improvement might play an additional role in the more favorable outcome observed in patients after carotid surgery.

Testing the autonomic nervous system

Autonomic testing is used to define the role of the autonomic nervous system in diverse clinical and research settings. Because most of the autonomic nervous system is inaccessible to direct physiological testing, in the clinical setting the most widely used techniques entail the assessment of an end-organ response to a physiological provocation. The noninvasive measures of cardiovascular parasympathetic function involve the assessment of heart rate variability while the measures of cardiovascular sympathetic function assess the blood pressure response to physiological stimuli. Tilt-table testing, with or without pharmacological provocation, has become an important tool in the assessment of a predisposition to neurally mediated (vasovagal) syncope, the postural tachycardia syndrome, and orthostatic hypotension. Distal, postganglionic, sympathetic cholinergic (sudomotor) function may be evaluated by provoking axon reflex mediated sweating, e.g., the quantitative sudomotor axon reflex (QSART) or the quantitative direct and indirect axon reflex (QDIRT). The thermoregulatory sweat test provides a nonlocalizing measure of global pre- and postganglionic sudomotor function. Frequency domain analyses of heart rate and blood pressure variability, microneurography, and baroreflex assessment are currently research tools but may find a place in the clinical assessment of autonomic function in the future.

Norepinephrine transporter function and human cardiovascular disease

Approximately 80-90% of the norepinephrine released in the brain or in peripheral tissues is taken up again through the neuronal norepinephrine transporter (NET). Pharmacological studies with NET inhibitors showed that NET has opposing effects on cardiovascular sympathetic regulation in the brain and in the periphery. Furthermore, NET is involved in the distribution of sympathetic activity between vasculature, heart, and kidney. Genetic NET dysfunction is a rare cause of the postural tachycardia syndrome. The condition is characterized by excessive adrenergic stimulation of the heart, particularly with standing. Conversely, NET inhibition may be beneficial in hypoadrenergic states, such as central autonomic failure or neurally mediated syncope, which results from acute sympathetic withdrawal. Biochemical studies suggested reduced NET function in some patients with essential hypertension. Furthermore, cardiac NET function appears to be reduced in common heart diseases, such as congestive heart failure, ischemic heart disease, and stress-induced cardiomyopathy. Whether NET dysfunction is a consequence or cause of progressive heart disease in human subjects requires further study. However, studies with the nonselective NET inhibitor sibutramine suggest that reduced NET function could have an adverse effect on the cardiovascular system. Given the widespread use of medications inhibiting NET, the issue deserves more attention.

Monoamine transporter structure, function, dynamics, and drug discovery: a computational perspective

With the breakthrough crystallization of the bacterial leucine transporter protein LeuT, the first available X-ray structure for the neurotransmitter/sodium symporter family, development of 3-D computational models is suddenly essential for structure-function studies on the plasmalemmal monoamine transporters (MATs). LeuT-based MAT models have been used to guide elucidation of substrate and inhibitor binding pockets, and molecular dynamics simulations using these models are providing insight into conformations involved in the substrate translocation cycle. With credible MAT models finally in hand, structure-based virtual screening for novel ligands is yielding lead compounds toward the development of new medications for psychostimulant dependence, attention deficit hyperactivity, depression, anxiety, schizophrenia, and other disorders associated with dopamine, norepinephrine, or serotonin dysregulation.

Discovery of novel selective serotonin reuptake inhibitors through development of a protein-based pharmacophore

The serotonin transporter (SERT), a member of the neurotransmitter sodium symporter (NSS) family, is responsible for the reuptake of serotonin from the synaptic cleft to maintain neurotransmitter homeostasis. SERT is established as an important target in the treatment of anxiety and depression. Because a high-resolution crystal structure is not available, a computational model of SERT was built based upon the X-ray coordinates of the leucine transporter LeuT, a bacterial NSS homologue. The model was used to develop the first SERT structure-based pharmacophore. Virtual screening (VS) of a small molecule structural library using the generated SERT computational model yielded candidate ligands of diverse scaffolds. Pharmacological analysis of the VS hits identified two SERT-selective compounds, potential lead compounds for further SERT-related medication development.

Unique pentafluorobenzylation and collision-induced dissociation for specific and accurate GC-MS/MS quantification of the catecholamine metabolite 3,4-dihydroxyphenylglycol (DHPG) in human urine

In the human body, the catecholamine norepinephrine is mainly metabolized to 3,4-dihydroxyphenylglycol (DHPG) which therefore serves as an important biomarker for norepinephrine's metabolism. Most data on DHPG concentrations in human plasma and urine has been generated by using HPLC-ECD or GC-MS technologies. Here, we describe a stable-isotope dilution GC-MS/MS method for the quantitative determination of DHPG in human urine using trideutero-DHPG (d(3)-DHPG) as internal standard and a two-step derivatization process with pentafluorobenzyl bromide (PFB-Br) and N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA). Two pentafluorobenzyl (PFB) trimethylsilyl (TMS) derivatives were obtained and identified, i.e., two isomeric DHPG-PFB-(TMS)(3) derivatives and the later eluting DHPG-tetrafluorobenzyl-(TMS)(2) derivative, i.e., DHPG-TFB-(TMS)(2). To our knowledge the DHPG-TFB-(TMS)(2) derivative and the underlying reaction have not been reported previously. In this reaction both vicinal aromatic hydroxyl groups of DHPG react with PFB-Br to form a heterocyclic seven-membered [1,4]dioxepin compound. The DHPG-TFB-(TMS)(2) derivative was used for quantitative GC-MS/MS analysis in the electron-capturing negative-ion chemical ionization mode by selected-reaction monitoring of m/z 351 from m/z 401 for DHPG and of m/z 352 from m/z 404 for d(3)-DHPG. Validation experiments on human urine samples spiked with DHPG in a narrow (0-33 nM) and a wide range (0-901 nM) revealed high recovery (86-104%) and low imprecision (RSD; 0.01-2.8%). LOD and relative LLOQ (rLLOQ) values of the method for DHPG were determined to be 76 amol and 9.4%, respectively. In urine of 28 patients suffering from chronic inflammatory rheumatic diseases, DHPG was measured at a mean concentration of 238 nM (38.3 μg/g creatinine). The DHPG concentration in the respective control group of 40 healthy subjects was measured to be 328 nM (39.2 μg/g creatinine). Given the unique derivatization reaction and collision-induced dissociation, and the straightforwardness the present method is highly specific, accurate, precise, and should be useful in clinical settings.

Norepinephrine transport-mediated gene expression in noradrenergic neurogenesis

Background

We have identified a differential gene expression profile in neural crest stem cells that is due to deletion of the norepinephrine transporter (NET) gene. NET is the target of psychotropic substances, such as tricyclic antidepressants and the drug of abuse, cocaine. NET mutations have been implicated in depression, anxiety, orthostatic intolerance and attention deficit hyperactivity disorder (ADHD). NET function in adult noradrenergic neurons of the peripheral and central nervous systems is to internalize norepinephrine from the synaptic cleft. By contrast, during embryogenesis norepinephrine (NE) transport promotes differentiation of neural crest stem cells and locus ceruleus progenitors into noradrenergic neurons, whereas NET inhibitors block noradrenergic differentiation. While the structure of NET und the regulation of NET function are well described, little is known about downstream target genes of norepinephrine (NE) transport.

Results

We have prepared gene expression profiles of in vitro differentiating wild type and norepinephrine transporter-deficient (NETKO) mouse neural crest cells using long serial analysis of gene expression (LongSAGE). Comparison analyses have identified a number of important differentially expressed genes, including genes relevant to neural crest formation, noradrenergic neuron differentiation and the phenotype of NETKO mice. Examples of differentially expressed genes that affect noradrenergic cell differentiation include genes in the bone morphogenetic protein (BMP) signaling pathway, the Phox2b binding partner Tlx2, the ubiquitin ligase Praja2, and the inhibitor of Notch signaling, Numbl. Differentially expressed genes that are likely to contribute to the NETKO phenotype include dopamine-β-hydroxylase (Dbh), tyrosine hydroxylase (Th), the peptide transmitter 'cocaine and amphetamine regulated transcript' (Cart), and the serotonin receptor subunit Htr3a. Real-time PCR confirmed differential expression of key genes not only in neural crest cells, but also in the adult superior cervical ganglion and locus ceruleus. In addition to known genes we have identified novel differentially expressed genes and thus provide a valuable database for future studies.

Conclusion

Loss of NET function during embryonic development in the mouse deregulates signaling pathways that are critically involved in neural crest formation and noradrenergic cell differentiation. The data further suggest deregulation of signaling pathways in the development and/or function of the NET-deficient peripheral, central and enteric nervous systems.

Psychiatric profile and attention deficits in postural tachycardia syndrome

OBJECTIVES

Patients with postural tachycardia syndrome (POTS) often appear anxious and report inattention. Patients with POTS were formally assessed for psychiatric disorders and inattention and compared with patients with attention deficit hyperactivity disorder (ADHD) and control subjects.

METHODS

Patients with POTS (n = 21), ADHD (n = 18) and normal control subjects (n = 20) were assessed for DSM-IV psychiatric disorders and completed a battery of questionnaires that assessed depression, anxiety and ADHD characteristics.

RESULTS

Patients with POTS did not have an increased prevalence of major depression or anxiety disorders, including panic disorder, compared with the general population. Patients with POTS had mild depression. They scored as moderately anxious on the Beck Anxiety Inventory but did not exhibit a high level of anxiety sensitivity. Patients with POTS scored significantly higher on inattention and ADHD subscales than control subjects. These symptoms were not present during childhood.

CONCLUSIONS

Patients with POTS do not have an increased lifetime prevalence of psychiatric disorders. Although they may seem anxious, they do not have excess cognitive anxiety. They do experience significant inattention which may be an important source of disability.

Genetic aspects of vasovagal syncope: a systematic review of current evidence

Knowledge on the aetiology of vasovagal syncope (VVS) is of great importance to optimize its diagnostic and therapeutic options. To unravel the largely unknown pathophysiology, studies on genetic aspects of VVS can be of use. This systematic review on all available literature aims to provide an overview of the current knowledge of VVS genetics. The MEDLINE and EMBASE database were systematically searched for all studies discussing genetic factors as a cause of VVS. Hereditary aspects of VVS were studied in 19 studies. Six studies determined a positive family history in, respectively, 19-90% of the VVS patients. These numbers, however, are not higher than the cumulative incidence of VVS in the general population (35-39%). Four studies examined potential genetic polymorphisms associated with VVS. Only a Gly389 allele was more frequently present in VVS patients with a positive HUT test, although the significance level was set much higher than usual in genetic studies, and this result has not been replicated so far. Knowledge on genetic aspects of VVS could be very useful in clinical practice and research, but the current evidence that it has a genetic basis is not very strong.

Three-dimensional quantitative structure-activity relationship (3D QSAR) and pharmacophore elucidation of tetrahydropyran derivatives as serotonin and norepinephrine transporter inhibitors

Three-dimensional quantitative structure-activity relationship (3D QSAR) using comparative molecular field analysis (CoMFA) was performed on a series of substituted tetrahydropyran (THP) derivatives possessing serotonin (SERT) and norepinephrine (NET) transporter inhibitory activities. The study aimed to rationalize the potency of these inhibitors for SERT and NET as well as the observed selectivity differences for NET over SERT. The dataset consisted of 29 molecules, of which 23 molecules were used as the training set for deriving CoMFA models for SERT and NET uptake inhibitory activities. Superimpositions were performed using atom-based fitting and 3-point pharmacophore-based alignment. Two charge calculation methods, Gasteiger-Hückel and semiempirical PM3, were tried. Both alignment methods were analyzed in terms of their predictive abilities and produced comparable results with high internal and external predictivities. The models obtained using the 3-point pharmacophore-based alignment outperformed the models with atom-based fitting in terms of relevant statistics and interpretability of the generated contour maps. Steric fields dominated electrostatic fields in terms of contribution. The selectivity analysis (NET over SERT), though yielded models with good internal predictivity, showed very poor external test set predictions. The analysis was repeated with 24 molecules after systematically excluding so-called outliers (5 out of 29) from the model derivation process. The resulting CoMFA model using the atom-based fitting exhibited good statistics and was able to explain most of the selectivity (NET over SERT)-discriminating factors. The presence of -OH substituent on the THP ring was found to be one of the most important factors governing the NET selectivity over SERT. Thus, a 4-point NET-selective pharmacophore, after introducing this newly found H-bond donor/acceptor feature in addition to the initial 3-point pharmacophore, was proposed.

Synthesis of enantiomerically pure milnacipran analogs and inhibition of dopamine, serotonin, and norepinephrine transporters

A series of Milnacipran analogs with variation in the aromatic moiety were prepared in high enantiomeric excess. Structure-activity relationships for two parallel enantiomeric series are described. The (-)-(1R,2S)-naphthyl analog (8h) showed the highest potency in the two series and is a triple reuptake inhibitor of the SERT, NET, and DAT.

The postural tachycardia syndrome

Postural tachycardia syndrome (POTS) is a disorder of unknown etiology, and patients with this condition exhibit orthostatic intolerance (OI) and excessive tachycardia. Excessive tachycardia with POTS has been defined as a rapid (within 10 minutes) increase in heart rate by more than 30 beats per minute or a heart rate that exceeds 120 beats per minute. Patients with POTS can experience difficulty with daily routines such as housework, shopping, eating, and attending work or school. The possibility exists that all forms of OI, including POTS, result from central hypovolemia even without tachycardia. The clinical findings of POTS are observed in an increasing number of patients who are usually female and aged 15 to 50 years. Adults with POTS do not have hypotension, whereas children may exhibit hypotension. Many patients with POTS are intolerant of exercise. "Idiopathic" POTS must be distinguished from other conditions that can reduce venous return to the heart and produce similar signs and symptoms such as dehydration, anemia, or hyperthyroidism. Therapies for POTS are directed at relieving the central hypovolemia or at compensating for the circulatory dysfunctions that may cause this disorder. Treatments have resulted in varying degrees of success and are often used in combination with each other.

Hipertensión arterial episódica asociada al síndrome de taquicardia postural ortostática

We report the case of a 17-year-old woman who presented to the emergency department on several occasions due to palpitations, tachycardia, syncope, short spells of dizziness and light-headedness with complete spontaneous recovery, and hypertension. The patient had been evaluated by several specialists, and multiple complementary examinations had revealed no abnormalities that could explain the symptoms. Due to suspicion of orthostatic intolerance or postural orthostatic tachycardia syndrome with hypertension, the patient underwent a 60-degree tilt table test, which confirmed the diagnosis. The patient was successfully treated with bisoprolol. The physiopathological mechanisms, diagnosis, and treatment of this syndrome are reviewed.

Phosphorylation of the Norepinephrine Transporter at Threonine 258 and Serine 259 Is Linked to Protein Kinase C-mediated Transporter Internalization

Recently, we have demonstrated the phosphorylation- and lipid raft-mediated internalization of the native norepinephrine transporter (NET) following protein kinase C (PKC) activation (Jayanthi, L. D., Samuvel, D. J., and Ramamoorthy, S. (2004) J. Biol. Chem. 279, 19315-19326). Here we tested an hypothesis that PKC-mediated phosphorylation of NET is required for transporter internalization. Phosphoamino acid analysis of 32P-labeled native NETs from rat placental trophoblasts and heterologously expressed wild type human NET (WT-hNET) from human placental trophoblast cells revealed that the phorbol ester (beta-PMA)-induced phosphorylation of NET occurs on serine and threonine residues. Beta-PMA treatment inhibited NE transport, reduced plasma membrane hNET levels, and stimulated hNET phosphorylation in human placental trophoblast cells expressing the WT-hNET. Substance P-mediated activation of the G alpha(q)-coupled human neurokinin 1 (hNK-1) receptor coexpressed with the WT-hNET produced effects similar to beta-PMA via PKC stimulation. In striking contrast, an hNET double mutant harboring T258A and S259A failed to show NE uptake inhibition and plasma membrane redistribution by beta-PMA or SP. Most interestingly, the plasma membrane insertion of the WT-hNET and hNET double mutant were not affected by beta-PMA. Although the WT-hNET showed increased endocytosis and redistribution from caveolin-rich plasma membrane domains following beta-PMA treatment, the hNET double mutant was completely resistant to these PKC-mediated effects. In addition, the PKC-induced phosphorylation of hNET double mutant was significantly reduced. In the absence of T258A and S259A mutations, alanine substitution of all other potential phosphosites within the hNET did not block PKC-induced phosphorylation and down-regulation. These results suggest that Thr-258 and Ser-259 serve as a PKC-specific phospho-acceptor site and that phosphorylation of this motif is linked to PKC-induced NET internalization.

An Overview of Pheochromocytoma: History, Current Concepts, Vagaries, and Diagnostic Challenges

Tragically as many as 50% of pheochromocytomas are discovered at autopsy, mainly because the diagnosis of this neuroendocrine tumor was not considered. Missing the diagnosis almost invariably results in devastating cardiovascular complications or death. Clinicians must always think of pheochromocytoma whenever evaluating a patient with sustained or paroxysmal hypertension or any manifestations suggesting hypercatecholaminemia. Very rarely, familial pheochromocytomas may cause no hypertension, symptoms, or signs. But biochemical testing can always establish the presence or absence of a pheochromocytoma, and localization with magnetic resonance imaging, computed tomography, or 131I or 123I-MIBG is almost always possible.

Postural orthostatic tachycardia syndrome: Dental treatment considerations

BACKGROUND

Postural orthostatic tachycardia syndrome (POTS) is a chronic, relatively common autonomic disorder typically affecting younger females. It is distinguished by a dramatic increase in heart rate on the assumption of an upright posture from the supine position.

METHODS

The authors provide an overview of the demographics, clinical assessment, diagnostic features, differential diagnoses, pathogeneses and medical treatment of patients with POTS, with an emphasis on the clinical treatment of the dental patient affected by the syndrome.

CONCLUSION

Patients frequently exhibit symptoms of lightheadedness, fatigue, palpitations and syncope. Patients with POTS may have Ehlers-Danlos syndrome, mitral valve prolapse, chronic fatigue syndrome or, rarely, the Brugada syndrome. Despite widespread dissemination of information regarding POTS in the medical literature, scant information on it has appeared in dental publications.

PRACTICE IMPLICATIONS

Dentists need to be familiar with the clinical features of POTS and be prepared to treat patients at risk of developing syncope.

Molecular microfluorometry: converting arbitrary fluorescence units into absolute molecular concentrations to study binding kinetics and stoichiometry in transporters

Cotransporters use energy stored in Na+ or H+ gradients to transport neurotransmitters or other substrates against their own gradient. Cotransport is rapid and efficient, and at synapses it helps terminate signaling. Cotransport in norepinephrine (NET), epinephrine (EpiT), dopamine (DAT), and serotonin (SERT) transporters couples downhill Na+ flux to uphill transmitter flux. NETs, for example, attenuate signaling at adrenergic synapses by efficiently clearing NE from the synaptic cleft, thus preparing the synapse for the next signal. Transport inhibition with tricyclic antidepressants prolongs neurotransmitter presence in the synaptic cleft, potentially alleviating symptoms of depression. Transport inhibition with cocaine or amphetamine, which respectively block or replace normal transport, may result in hyperactivity. Little is known about the kinetic interactions of substrates or drugs with transporters, largely because the techniques that have been successful in discovering trans- porter agonists and antagonists do not yield detailed kinetic information. Mechanistic data are for the most part restricted to global parameters, such as Km and Vmax, measured from large populations of transporter molecules averaged over thousands of cells. Three relatively new techniques used in transporter research are electrophysiology, amperometry, and microfluorometry. This review focuses on fluorescence-based methodologies, which--unlike any other technique-permit the simultaneous measurement of binding and transport. Microfluorometry provides unique insights into binding kinetics and transport mechanisms from a quantitative analysis of fluorescence data. Here we demonstrate how to quantify the number of bound substrate molecules, the number of transported substrate molecules, and the kinetics of substrate binding to individual transporters. Although we describe experiments on a specific neurotransmitter transporter, these methods are applicable to other membrane proteins.

Regulation of monoamine transporters: influence of psychostimulants and therapeutic antidepressants

Synaptic neurotransmission in the central nervous system (CNS) requires the precise control of the duration and the magnitude of neurotransmitter action at specific molecular targets. At the molecular level, neurotransmitter signaling is dynamically regulated by a diverse set of macromolecules including biosynthetic enzymes, secretory proteins, ion channels, pre- and postsynaptic receptors and transporters. Monoamines, 5-hydroxytryptamine or serotonin (5-HT), norepinephrine (NE), and dopamine (DA) play an important modulatory role in the CNS and are involved in numerous physiological functions and pathological conditions. Presynaptic plasma membrane transporters for 5-HT (SERT), NE (NET), and DA (DAT), respectively, control synaptic actions of these monoamines by rapidly clearing the released amine. Monoamine transporters are the sites of action for widely used antidepressants and are high affinity molecular targets for drugs of abuse including cocaine, amphetamine, and 3,4-methylenedioxymetamphetamine (MDMA) "Ecstasy." Monoamine transporters also serve as molecular gateways for neurotoxins. Emerging evidence indicates that regulation of transporter function and surface expression can be rapidly modulated by "intrinsic" transporter activity itself, and antidepressant and psychostimulant drugs that block monoamine transport have a profound effect on transporter regulation. Therefore, disregulations in the functioning of monoamine transporters may underlie many disorders of transmitter imbalance such as depression, attention deficit hyperactivity disorder, and schizophrenia. This review integrates recent progress in understanding the molecular mechanisms of monoamine transporter regulation, in particular, posttranscriptional regulation by phosphorylation and trafficking linked to cellular protein kinases, protein phosphatases, and transporter interacting proteins. The review also discusses the possible role of psychostimulants and antidepressants in influencing monoamine transport regulation.

BIOMARKERS IN PSYCHOTROPIC DRUG DEVELOPMENT: Integration of Data across Multiple Domains

This review focuses on the current status of biomarkers and/or approaches critical to assessing novel neuroscience targets with an emphasis on new paradigms and challenges in this field of research. The importance of biomarker data integration for psychotropic drug development is illustrated with examples for clinically used medications and investigational drugs. The question remains how to verify access to the brain. Early imaging studies including micro-PET can help to overcome this. However, in case of delayed tracer development or because of no feasible application of brain imaging effects of the molecule, using CSF as a matrix could fill this gap. Proteomic research using CSF will hopefully have a major impact on the development of treatments for psychiatric disorders.

Substrate binding stoichiometry and kinetics of the norepinephrine transporter

The human norepinephrine (NE) transporter (hNET) attenuates neuronal signaling by rapid NE clearance from the synaptic cleft, and NET is a target for cocaine and amphetamines as well as therapeutics for depression, obsessive-compulsive disorder, and post-traumatic stress disorder. In spite of its central importance in the nervous system, little is known about how NET substrates, such as NE, 1-methyl-4-tetrahydropyridinium (MPP+), or amphetamine, interact with NET at the molecular level. Nor do we understand the mechanisms behind the transport rate. Previously we introduced a fluorescent substrate similar to MPP+, which allowed separate and simultaneous binding and transport measurement (Schwartz, J. W., Blakely, R. D., and DeFelice, L. J. (2003) J. Biol. Chem. 278, 9768-9777). Here we use this substrate, 4-(4-(dimethylamino)styrl)-N-methyl-pyridinium (ASP+), in combination with green fluorescent protein-tagged hNETs to measure substrate-transporter stoichiometry and substrate binding kinetics. Calibrated confocal microscopy and fluorescence correlation spectroscopy reveal that hNETs, which are homomultimers, bind one substrate molecule per transporter subunit. Substrate residence at the transporter, obtained from rapid on-off kinetics revealed in fluorescence correlation spectroscopy, is 526 micros. Substrate residence obtained by infinite dilution is 1000 times slower. This novel examination of substrate-transporter kinetics indicates that a single ASP+ molecule binds and unbinds thousands of times before being transported or ultimately dissociated from hNET. Calibrated fluorescent images combined with mass spectroscopy give a transport rate of 0.06 ASP+/hNET-protein/s, thus 36,000 on-off binding events (and 36 actual departures) occur for one transport event. Therefore binding has a low probability of resulting in transport. We interpret these data to mean that inefficient binding could contribute to slow transport rates.

Human phenotypes and animal knockout models of genetic autonomic disorders

Norepinephrine (NE) is a crucial neurotransmitter involved in autonomic regulation of blood pressure. Dopamine beta-hydroxylase (DBH), the norepinephrine transporter (NET), and the vesicular monoamine transporter subtype 2 catalyze intracellular NE biosynthesis, NE reuptake from the synapse, and vesicular transport, respectively. Genetic disorders in humans have been identified that render DBH, and the NET dysfunctional and result in cardiovascular and neurological abnormalities. Vesicular monoamine transporter subtype 2 (VMAT2) activity protects against neurotoxins, and reduced VMAT2 expression is implicated in drug addiction. Further investigation of the consequences of these genetic abnormalities has been achieved by the construction of mice strains deficient in the genes encoding DBH, NET, and VMAT2.

N-terminal phosphorylation of the dopamine transporter is required for amphetamine-induced efflux

Amphetamine (AMPH) elicits its behavioral effects by acting on the dopamine (DA) transporter (DAT) to induce DA efflux into the synaptic cleft. We previously demonstrated that a human DAT construct in which the first 22 amino acids were truncated was not phosphorylated by activation of protein kinase C, in contrast to wild-type (WT) DAT, which was phosphorylated. Nonetheless, in all functions tested to date, which include uptake, inhibitor binding, oligomerization, and redistribution away from the cell surface in response to protein kinase C activation, the truncated DAT was indistinguishable from the full-length WT DAT. Here, however, we show that in HEK-293 cells stably expressing an N-terminal-truncated DAT (del-22 DAT), AMPH-induced DA efflux is reduced by approximately 80%, whether measured by superfusion of a population of cells or by amperometry combined with the patch-clamp technique in the whole cell configuration. We further demonstrate in a full-length DAT construct that simultaneous mutation of the five N-terminal serine residues to alanine (S/A) produces the same phenotype as del-22-normal uptake but dramatically impaired efflux. In contrast, simultaneous mutation of these same five serines to aspartate (S/D) to simulate phosphorylation results in normal AMPH-induced DA efflux and uptake. In the S/A background, the single mutation to Asp of residue 7 or residue 12 restored a significant fraction of WT efflux, whereas mutation to Asp of residues 2, 4, or 13 was without significant effect on efflux. We propose that phosphorylation of one or more serines in the N-terminus of human DAT, most likely Ser7 or Ser12, is essential for AMPH-induced DAT-mediated DA efflux. Quite surprisingly, N-terminal phosphorylation shifts DAT from a "reluctant" state to a "willing" state for AMPH-induced DA efflux, without affecting inward transport. These data raise the therapeutic possibility of interfering selectively with AMPH-induced DA efflux without altering physiological DA uptake.

Orthostatic intolerance is not necessarily related to a specific mutation (Ala457Pro) in the human norepinephrine transporter gene

BACKGROUND

Orthostatic intolerance (OI) is a syndrome characterized by lightheadedness, palpitations, fatigue, blurred vision, dizziness, chest discomfort, cognitive impairment, and occasionally syncope. These symptoms usually occur after upright posture and are associated with tachycardia and high plasma concentrations of norepinephrine. It has been proposed that a mutation in exon 9 of the norepinephrine transporter gene (Ala457Pro), resulting in more than 98% loss of function compared with the wild type, might provide a pathogenetic mechanism to explain the clinical symptoms of patients with OI.

METHODS

We studied 46 young men from military service who had sought medical advice because of dizziness while standing. Every patient underwent a tilt-table test, with monitoring of blood pressure, heart rate, and plasma catecholamines in supine position and during 30 minutes of standing. Fourteen patients showing the full-blown OI syndrome (30 bpm increase in heart rate and 600 pg/mL plasma norepinephrine levels while standing) underwent direct DNA sequencing of exon 9 of the norepinephrine-transporter gene.

RESULTS AND CONCLUSIONS

The specific mutation (Ala457Pro) was not detected in any of the 14 OI patients. Based on these findings, we doubt that this specific genetic transport defect is a frequent cause of the impaired uptake of norepinephrine in OI patients. Its routine determination will therefore not be helpful to establish the clinical diagnosis of OI.

Autonomic control of blood pressure in mice: basic physiology and effects of genetic modification

Control of blood pressure and of blood flow is essential for maintenance of homeostasis. The hemodynamic state is adjusted by intrinsic, neural, and hormonal mechanisms to optimize adaptation to internal and environmental challenges. In the last decade, many studies showed that modification of the mouse genome may alter the capacity of cardiovascular control systems to respond to homeostatic challenges or even bring about a permanent pathophysiological state. This review discusses the progress that has been made in understanding of autonomic cardiovascular control mechanisms from studies in genetically modified mice. First, from a physiological perspective, we describe how basic hemodynamic function can be measured in conscious conditions in mice. Second, we focus on the integrative role of autonomic nerves in control of blood pressure in the mouse, and finally, we depict the opportunities and insights provided by genetic modification in this area.