Palmitoylation regulates norepinephrine transporter trafficking and expression and is potentially involved in the pathogenesis of postural orthostatic tachycardia syndrome

Postural orthostatic tachycardia syndrome (POTS) is an adrenergic signaling disorder characterized by excessive plasma norepinephrine, postural tachycardia, and syncope. The norepinephrine transporter (NET) modulates adrenergic homeostasis via reuptake of extracellular catecholamines and is implicated in the pathogenesis of adrenergic and neurological disorders. Previous research has outlined that NET activity and trafficking is modulated via reversible post-translational modifications like phosphorylation and ubiquitylation. S-palmitoylation, or the addition of a 16-carbon saturated fatty acid, is another post-translational modification responsible for numerous biological mechanisms. In this study, we reveal that NET is dynamically palmitoylated and inhibition of this modification with the palmitoyl acyltransferase (DHHC) inhibitor, 2-bromopalmitate (2BP), results in decreased NET palmitoylation within 90 min of treatment. This result was followed closely with a reduction in transport capacity, cell surface, and total cellular NET expression after 120 min of treatment. Increasing 2BP concentrations and treatment time revealed a nearly complete loss of total NET protein. Co-expression with individual DHHCs revealed a single DHHC enzyme, DHHC1, promoted WT hNET palmitoylation and elevated NET protein levels. The POTS associated NET mutant, A457P, exhibits dramatically decreased transport capacity and cell surface levels which we have confirmed in the current study. In an attempt to recover A457P NET expression we co-expressed the A457P variant with DHHC1 to drive expression as seen with the WT protein but instead saw an increase in NET N-terminal immuno-detectable fragments. Further investigation of A457P NET palmitoylation and surface expression is necessary, but our preliminary novel findings reveal palmitoylation as a mechanism of NET regulation and suggest that dysregulation of this process may contribute to the pathogenesis of POTS.

Post-translational mechanisms in psychostimulant-induced neurotransmitter efflux

The availability of monoamine neurotransmitters in the brain is under the control of dopamine, norepinephrine, and serotonin transporters expressed on the plasma membrane of monoaminergic neurons. By regulating transmitter levels these proteins mediate crucial functions including cognition, attention, and reward, and dysregulation of their activity is linked to mood and psychiatric disorders of these systems. Amphetamine-based transporter substrates stimulate non-exocytotic transmitter efflux that induces psychomotor stimulation, addiction, altered mood, hallucinations, and psychosis, thus constituting a major component of drug neurochemical and behavioral outcomes. Efflux is under the control of transporter post-translational modifications that synergize with other regulatory events, and this review will summarize our knowledge of these processes and their role in drug mechanisms.

Dopamine transporter membrane mobility is bidirectionally regulated by phosphorylation and palmitoylation

The primary regulator of dopamine availability in the brain is the dopamine transporter (DAT), a plasma membrane protein that drives reuptake of released dopamine from the extracellular space into the presynaptic neuron. DAT activity is regulated by post-translational modifications that establish clearance capacity through impacts on transport kinetics, and dysregulation of these events may underlie dopaminergic imbalances in mood and psychiatric disorders. Here, using fluorescence recovery after photobleaching, we show that phosphorylation and palmitoylation induce opposing effects on DAT lateral membrane mobility, which may influence functional outcomes by regulating subcellular localization and binding partner interactions. Membrane mobility was also impacted by amphetamine and in polymorphic variant A559V in directions consistent with enhanced phosphorylation. These findings grow the list of DAT properties controlled by these post-translational modifications and highlight their role in establishment of dopaminergic tone in physiological and pathophysiological states.

Palmitoylation Regulates Human Serotonin Transporter Activity, Trafficking, and Expression and Is Modulated by Escitalopram

In the central nervous system, serotonergic signaling modulates sleep, mood, and cognitive control. During serotonergic transmission, the synaptic concentration of serotonin is tightly controlled in a spatial and temporal manner by the serotonin transporter (SERT). Dysregulation of this process is implicated in the pathogenesis of major-depressive, obsessive-compulsive, and autism-spectrum disorders, which makes SERT a primary target for prescription therapeutics, most notably selective serotonin reuptake inhibitors (SSRIs). S-Palmitoylation, the reversible addition of a 16-carbon fatty acid to proteins, is an increasingly recognized dynamic post-translational modification responsible for modulating protein kinetics, trafficking, and localization patterns in response to physiologic/cellular stimuli. In this study, we reveal that human SERTs are a target for palmitoylation, and using the irreversible palmitoyl acyltransferase inhibitor 2-bromopalmitate (2BP), we have identified several associated functions. Using a lower dose of 2BP in shorter time frames, inhibition of palmitoylation was associated with reductions in SERT Vmax, without changes in Km or surface expression. With higher doses of 2BP for longer time intervals, inhibition of palmitoylation was consistent with the loss of cell surface and total SERT protein, suggesting palmitoylation is an important mechanism in regulating SERT trafficking and maintenance of SERT protein through biogenic or anti-degradative processes. Additionally, we have identified that treatment with the SSRI escitalopram decreases SERT palmitoylation analogous to 2BP, reducing SERT surface expression and transport capacity. Ultimately, these results reveal that palmitoylation is a major regulatory mechanism for SERT kinetics and trafficking and may be the mechanism responsible for escitalopram-induced internalization and ultimately decreased cellular SERT protein levels.

Palmitoylation regulates human serotonin transporter activity, trafficking, and expression and is modulated by escitalopram

In the central nervous system, serotonergic signaling modulates sleep, mood, and cognitive control. During neuronal transmission, the synaptic concentration of serotonin is tightly controlled in a spatial and temporal manner by the serotonin transporter (SERT). Dysregulation of serotonergic signaling is implicated in the pathogenesis of major-depressive, obsessive-compulsive, and autism-spectrum disorders, which makes SERT a primary target for prescription therapeutics, most notably selective-serotonin reuptake inhibitors (SSRIs). S-palmitoylation is an increasingly recognized dynamic post-translational modification, regulating protein kinetics, trafficking, and localization patterns upon physiologic/cellular stimuli. In this study, we reveal that human SERTs are a target for palmitoylation, and using the irreversible palmitoyl acyl-transferase inhibitor, 2-bromopalmitate (2BP) we have identified several associated functions. Using a lower dose of 2BP in shorter time frames, inhibition of palmitoylation was associated with reductions in SERT V max , without changes in K m or surface expression. With higher doses of 2BP for longer time intervals, inhibition of palmitoylation was consistent with the loss of cell surface and total SERT protein, suggesting palmitoylation is an important mechanism in regulating SERT trafficking and maintenance of SERT protein through biogenic or anti-degradative processes. Additionally, we have identified that treatment with the SSRI escitalopram decreases SERT palmitoylation analogous to 2BP, reducing SERT surface expression and transport capacity. Ultimately, these results reveal palmitoylation is a major regulatory mechanism for SERT kinetics and trafficking and may be the mechanism responsible for escitalopram-induced internalization and loss of total SERT protein.

Kappa Opioid Receptor Antagonism Rescues Genetic Perturbation of Dopamine Homeostasis: Molecular, Physiological and Behavioral Consequences

Aberrant dopamine (DA) signaling is implicated in schizophrenia, bipolar disorder (BPD), autism spectrum disorder (ASD), substance use disorder, and attention-deficit/hyperactivity disorder (ADHD). Treatment of these disorders remains inadequate. We established that the human DA transporter (DAT) coding variant (DAT Val559), identified in individuals with ADHD, ASD, or BPD, exhibits anomalous DA efflux (ADE) that is blocked by therapeutic amphetamines and methylphenidate. As the latter agents have high abuse liability, we exploited DAT Val559 knock-in mice to identify non-addictive agents that can normalize DAT Val559 functional and behavioral effects ex vivo and in vivo. Kappa opioid receptors (KORs) are expressed by DA neurons and modulate DA release and clearance, suggesting that targeting KORs might offset the effects of DAT Val559. We establish that enhanced DAT Thr53 phosphorylation and increased DAT surface trafficking associated with DAT Val559 expression are mimicked by KOR agonism of wildtype preparations and rescued by KOR antagonism of DAT Val559 ex vivo preparations. Importantly, KOR antagonism also corrected in vivo DA release and sex-dependent behavioral abnormalities. Given their low abuse liability, our studies with a construct valid model of human DA associated disorders reinforce considerations of KOR antagonism as a pharmacological strategy to treat DA associated brain disorders.

The Effect of Short-Term Exposure to Cadmium on the Expression of Vascular Endothelial Barrier Antigen in the Developing Rat Forebrain and Cerebellum: A Computerized Quantitative Immunofluorescent Study

Clinical and laboratory studies have shown that environmental exposure to cadmium produces damage to several organs, including bones, lungs, and kidneys. The involvement of cadmium in central nervous system (CNS) disorders has also been widely reported, but the precise pathophysiological mechanism is not yet fully understood. Children who were exposed to cadmium during pregnancy are known to suffer from developmental delays, learning difficulties, attention deficit hyperactivity disorder (ADHD), and other cognitive and neurobehavioral deficits. Results from numerous studies suggest that dysfunction of the blood-brain barrier (BBB) structures is an important step in the neurotoxicity of cadmium. A rat-specific BBB marker protein, the endothelial barrier antigen (EBA), has been previously isolated and classified by Sternberger and others. The mouse IgG1 clone, anti-endothelial barrier antigen (anti-EBA), detects a protein triplet (23.5kDa, 25 kDa, and 30kDa) localized to the luminal surface of central and peripheral nervous system (CNS and PNS) vascular endothelial cells with selective permeability barrier functions. This marker has been widely used for characterizing BBB alterations under demyelinating, inflammatory, and other CNS pathologies. Many studies have been published using the rat model system for studying the neurotoxic effect of acute and chronic exposure to cadmium.

We applied the indirect immunofluorescent techniques using the anti-EBA antibody in conjunction with the Olympus cellSens computerized image analysis to detect and quantify the surface areas of BBB-competent microvessel profiles in paraformaldehyde-fixed, paraffin-embedded brains of term-delivered young rats after intraperitoneal injection of a single dose of cadmium chloride. We detected a statistically significant reduction in EBA-positive microvessel surface areas in the forebrain (t = 5.86, df = 1789, p-value < 0.001) and cerebellum (t=73.40, df=1337, p < 0.001) of cadmium-treated rats compared to the normal controls. Thus, this study supports the hypothesis that the EBA is a sensitive and measurable indicator for quantitative assessment of the impact of cadmium exposure in the developing rat brain.

Sodium hydrogen exchanger (NHE1) palmitoylation and potential functional regulation

AIMS

Determine the effect of palmitoylation on the sodium hydrogen exchanger isoform 1 (NHE1), a member of the SLC9 family.

MAIN METHODS

NHE1 expressed in native rat tissues or in heterologous cells was assessed for palmitoylation by acyl-biotinyl exchange (ABE) and metabolic labeling with [3H]palmitate. Cellular palmitoylation was inhibited using 2-bromopalmitate (2BP) followed by determination of NHE1 palmitoylation status, intracellular pH, stress fiber formation, and cell migration. In addition, NHE1 was activated with LPA treatment followed by determination of NHE1 palmitoylation status and LPA-induced change in intracellular pH was determined in the presence and absence of preincubation with 2BP.

KEY FINDINGS

In this study we demonstrate for the first time that NHE1 is palmitoylated in both cells and rat tissue, and that processes controlled by NHE1 including intracellular pH (pHi), stress fiber formation, and cell migration, are regulated in concert with NHE1 palmitoylation status. Importantly, LPA stimulates NHE1 palmitoylation, and 2BP pretreatment dampens LPA-induced increased pHi which is dependent on the presence of NHE1.

SIGNIFICANCE

Palmitoylation is a reversible lipid modification that regulates an array of critical protein functions including activity, trafficking, membrane microlocalization and protein-protein interactions. Our results suggest that palmitoylation of NHE1 and other control/signaling proteins play a major role in NHE1 regulation that could significantly impact multiple critical cellular functions.

Effect of urine-specific gravity on performance of bacteriuria in predicting urine culture results

OBJECTIVE

To determine the effect of urine-specific gravity (USG) on using microscopic evaluation of bacteriuria to predict urine culture results in dogs and cats.

MATERIALS AND METHODS

We performed a retrospective medical record review of canine and feline patients that had a urinalysis and urine culture performed simultaneously. The sensitivity, specificity, positive predictive value and negative predictive value of microscopic bacteriuria for predicting urine culture results were calculated, stratified by USG. Multivariable regression was performed to test the effect of USG, pyuria, haematuria and species on the agreement between microscopic bacteriuria and culture results.

RESULTS

A total of 481 dogs and 291 cats with paired urinalysis and urine culture results were included in the study. Microscopic bacteriuria had moderate sensitivity (76% in dogs, 64% in cats) and high specificity (97% in dogs, 96% in cats) for predicting urine culture bacterial growth. Samples with rod bacteria were more likely to have bacterial growth than those with cocci (OR=Infinity, 95% CI 4.8 - Infinity). As compared to isosthenuric+hyposthenuric samples (USG ≤1.012), agreement was lower in moderately concentrated (OR=0.44, 95% CI 0.19 to 0.91) samples. Absence of bacteriuria, pyuria and haematuria had a high negative predictive value for no bacterial growth (96%).

CLINICAL SIGNIFICANCE

Microscopic bacteriuria has a high specificity in predicting urine culture results, regardless of USG. The finding that microscopic bacteriuria has better agreement with urine culture results in isosthenuric+hyposthenuric urine argues against reflex culture in these samples, especially if pyuria and haematuria are also absent. Urine microscopy can aid clinicians in determining the likelihood of urine culture growth.

Delayed type III hypersensitivity reaction with acute kidney injury in two dogs following administration of concentrated human albumin during treatment for hypoalbuminemia secondary to septic peritonitis

OBJECTIVE

To describe 2 dogs with acute kidney injury secondary to type III hypersensitivity reaction to 25% human serum albumin (HSA).

CASE SERIES SUMMARY

Two dogs were presented with evidence of septic peritonitis. The dogs were hospitalized following definitive surgical correction of a jejunal laceration following routine ovariohysterectomy, and removal of a jejunal foreign body. In the postoperative period, both dogs developed hypoalbuminemia and received 25% HSA. At the time of initial discharge, both dogs were doing well clinically and had normal renal parameters. Eleven and 18 days after HSA infusion, respectively, both dogs were re-presented with clinical signs of inappetence, vomiting, and lameness that progressed to urticaria, peripheral and angioedema, and petechiae, consistent with a delayed type III hypersensitivity reaction. Treatment for the type III hypersensitivity reaction to HSA included administration of diphenhydramine and glucocorticoids. Despite partial resolution of edema and joint swelling, both dogs developed progressive azotemia together with hypoalbuminemia and proteinuria. One dog developed an anuric acute kidney injury (AKI). Both dogs were humanely euthanized. Histopathology of the kidneys of both dogs was consistent with immune complex deposition and vasculitis.

NEW OR UNIQUE INFORMATION

Severe type III hypersensitivity reactions have been documented in healthy dogs and clinical patients following the administration of HSA. This report describes the first documented delayed type III hypersensitivity reaction in 2 dogs with septic peritonitis that resulted in AKI, glomerulonephritis, and oligo- to anuria in clinical patients following administration of 25% HSA.

Measurements of echocardiographic indices and biomarkers of kidney injury in dogs with chronic kidney disease

Pathophysiological cardiac and renal interactions are termed cardiovascular-renal disorder (CvRD). Cardiovascular disease/dysfunction secondary to kidney disease (CvRD_K), is a leading cause of death in human chronic kidney disease (CKD) patients. The presence and clinical impact of CvRD_K in dogs with CKD is unknown. We hypothesized that echocardiographic measurements, and cardiac and renal biomarkers, will be altered in dogs with CKD and associated with survival. Eleven dogs with CKD (n = 6 IRIS stage 2, n = 5 IRIS stage 3) and without primary cardiac disease, plus 12 healthy age-matched control dogs, were recruited to this prospective observational study. Dogs underwent standard echocardiography, glomerular filtration rate (GFR) estimation by iohexol clearance, and measurement of plasma cardiac troponin I and N-terminal pro-B-type natriuretic peptide (NT-proBNP), plasma and urinary cystatin B, and urinary clusterin and neutrophil gelatinase-associated lipocalin (NGAL). Values were compared between groups, and their association with all-cause mortality explored. Dogs with CKD had significantly lower GFR and higher NT-proBNP, urinary cystatin B, clusterin, and NGAL, compared to controls (P < 0.05). Echocardiographic measurements were similar between dogs with CKD and controls. Median follow-up time was 666 days, during which six dogs with CKD died. Risk of death was associated with increasing age, serum total protein, and normalized left ventricular posterior wall thickness (LVPWDN) and decreasing bodyweight and packed cell volume. Although baseline differences in echocardiographic measurements were not evident between dogs with moderate CKD and controls, the presence of CvRD_K was suggested by the association between LVPWDN and survival.

Palmitoylation by Multiple DHHC Enzymes Enhances Dopamine Transporter Function and Stability

The dopamine transporter (DAT) is a plasma membrane protein that mediates the reuptake of extracellular dopamine (DA) and controls the spatiotemporal dynamics of dopaminergic neurotransmission. The transporter is subject to fine control that tailors clearance of transmitter to physiological demands, and dysregulation of reuptake induced by psychostimulant drugs, transporter polymorphisms, and signaling defects may impact transmitter tone in disease states. We previously demonstrated that DAT undergoes complex regulation by palmitoylation, with acute inhibition of the modification leading to rapid reduction of transport activity and sustained inhibition of the modification leading to transporter degradation and reduced expression. Here, to examine mechanisms and outcomes related to increased modification, we coexpressed DAT with palmitoyl acyltransferases (PATs), also known as DHHC enzymes, which catalyze palmitate addition to proteins. Of 12 PATs tested, DAT palmitoylation was stimulated by DHHC2, DHHC3, DHHC8, DHHC15, and DHHC17, with others having no effect. Increased modification was localized to previously identified palmitoylation site Cys580 and resulted in upregulation of transport kinetics and elevated transporter expression mediated by reduced degradation. These findings confirm palmitoylation as a regulator of multiple DAT properties crucial for appropriate DA homeostasis and identify several potential PAT pathways linked to these effects. Defects in palmitoylation processes thus represent possible mechanisms of transport imbalances in DA disorders.

Dephosphorylation of human dopamine transporter at threonine 48 by protein phosphatase PP1/2A up-regulates transport velocity

Several protein kinases, including protein kinase C, Ca²⁺/calmodulin-dependent protein kinase II, and extracellular signal-regulated kinase, play key roles in the regulation of dopamine transporter (DAT) functions. These functions include surface expression, internalization, and forward and reverse transport, with phosphorylation sites for these kinases being linked to distinct regions of the DAT N terminus. Protein phosphatases (PPs) also regulate DAT activity, but the specific residues associated with their activities have not yet been elucidated. In this study, using co-immunoprecipitation followed by MS and immunoblotting analyses, we demonstrate the association of DAT with PP1 and PP2A in the mouse brain and heterologous cell systems. By applying MS in conjunction with a metabolic labeling method, we defined a PP1/2A-sensitive phosphorylation site at Thr-48 in human DAT, a residue that has not been previously reported to be involved in DAT phosphorylation. Site-directed mutagenesis of Thr-48 to Ala (T48A) to prevent phosphorylation enhanced dopamine transport kinetics, supporting a role for this residue in regulating DAT activity. Moreover, T48A-DAT displayed increased palmitoylation, suggesting that phosphorylation/dephosphorylation at this site has an additional regulatory role and reinforcing a previously reported reciprocal relationship between C-terminal palmitoylation and N-terminal phosphorylation.

Closure of the perineal defect after abdominoperineal excision for rectal adenocarcinoma - ACPGBI Position Statement

BACKGROUND

Perineal wound morbidity is common following abdominoperineal excision of the rectum (APE). There is no consensus on the optimum perineal reconstruction method after APE, and in particular 'extra-levator APE' (ELAPE).

METHODS

A systematic review of the PubMed, Embase and Cochrane databases was performed. This position statement formulated clinical questions and graded the evidence to make recommendations.

RESULTS

Perineal wound complications may be higher following ELAPE compared to 'conventional APE (cAPE)' however there is insufficient evidence to recommend cAPE over ELAPE with regards to the impact upon perineal wound healing. The majority of cAPE studies have used primary closure with varying complication rates reported. Where concerns regarding perineal wound healing exist, myocutaneous flap closure may be considered as an alternative method. There is minimal available evidence on perineal mesh reconstruction following cAPE. Primary closure, mesh use and myocutaneous flap reconstruction following ELAPE has been reported although variations in definitions and low-quality of available evidence limit comparison. There is insufficient evidence to recommend one particular method of perineal closure after ELAPE. Primary perineal closure is likely to have a higher risk of perineal herniation. Myocutaneous flaps and biological mesh have been effectively used in ELAPE closure. There is insufficient evidence to support one particular type of flap or mesh. Perineal wound complication rates are significantly increased when neo-adjuvant radiotherapy is delivered, regardless of surgical technique. There is no evidence that laparoscopy reduces APE perineal wound complications.

CONCLUSION

This position statement updates clinicians on current evidence around perineal closure after APE surgery.

Model systems for analysis of dopamine transporter function and regulation

The dopamine transporter (DAT) plays a critical role in dopamine (DA) homeostasis by clearing transmitter from the extraneuronal space after vesicular release. DAT serves as a site of action for a variety of addictive and therapeutic reuptake inhibitors, and transport dysfunction is associated with transmitter imbalances in disorders such as schizophrenia, attention deficit hyperactive disorder, bipolar disorder, and Parkinson disease. In this review, we describe some of the model systems that have been used for in vitro analyses of DAT structure, function and regulation, and discuss a potential relationship between transporter kinetic values and membrane cholesterol.

MPP+ decreases store-operated calcium entry and TRPC1 expression in Mesenchymal Stem Cell derived dopaminergic neurons

Parkinson's disease is a neurodegenerative disorder involving the progressive loss of dopaminergic neurons (DNs), with currently available therapeutics, such as L-Dopa, only able to relieve some symptoms. Stem cell replacement is an attractive therapeutic option for PD patients, and DNs derived by differentiating patient specific stem cells under defined in-vitro conditions may present a viable opportunity to replace dying neurons. We adopted a previously published approach to differentiate Mesenchymal Stem Cells (MSCs) into DN using a 12-day protocol involving FGF-2, bFGF, SHH ligand and BDNF. While MSC-derived DNs have been characterized for neuronal markers and electrophysiological properties, we investigated store-operated calcium entry (SOCE) mechanisms of these DNs under normal conditions, and upon exposure to environmental neurotoxin, 1-methyl, 4-phenyl pyridinium ion (MPP+). Overall, we show that MSC-derived DNs are functional with regard to SOCE mechanisms, and MPP+ exposure dysregulates calcium signaling, making them vulnerable to neurodegeneration. Since in-vitro differentiation of MSCs into DNs is an important vehicle for PD disease modeling and regenerative medicine, the results of this study may help with understanding of the pathological mechanisms underlying PD.

Inhibitor mechanisms in the S1 binding site of the dopamine transporter defined by multi-site molecular tethering of photoactive cocaine analogs

Dopamine transporter (DAT) blockers like cocaine and many other abused and therapeutic drugs bind and stabilize an inactive form of the transporter inhibiting reuptake of extracellular dopamine (DA). The resulting increases in DA lead to the ability of these drugs to induce psychomotor alterations and addiction, but paradoxical findings in animal models indicate that not all DAT antagonists induce cocaine-like behavioral outcomes. How this occurs is not known, but one possibility is that uptake inhibitors may bind at multiple locations or in different poses to stabilize distinct conformational transporter states associated with differential neurochemical endpoints. Understanding the molecular mechanisms governing the pharmacological inhibition of DAT is therefore key for understanding the requisite interactions for behavioral modulation and addiction. Previously, we leveraged complementary computational docking, mutagenesis, peptide mapping, and substituted cysteine accessibility strategies to identify the specific adduction site and binding pose for the crosslinkable, photoactive cocaine analog, RTI 82, which contains a photoactive azide attached at the 2β position of the tropane pharmacophore. Here, we utilize similar methodology with a different cocaine analog N-[4-(4-azido-3-I-iodophenyl)-butyl]-2-carbomethoxy-3-(4-chlorophenyl)tropane, MFZ 2-24, where the photoactive azide is attached to the tropane nitrogen. In contrast to RTI 82, which crosslinked into residue Phe319 of transmembrane domain (TM) 6, our findings show that MFZ 2-24 adducts to Leu80 in TM1 with modeling and biochemical data indicating that MFZ 2-24, like RTI 82, occupies the central S1 binding pocket with the (+)-charged tropane ring nitrogen coordinating with the (-)-charged carboxyl side chain of Asp79. The superimposition of the tropane ring in the three-dimensional binding poses of these two distinct ligands provides strong experimental evidence for cocaine binding to DAT in the S1 site and the importance of the tropane moiety in competitive mechanisms of DA uptake inhibition. These findings set a structure-function baseline for comparison of typical and atypical DAT inhibitors and how their interactions with DAT could lead to the loss of cocaine-like behaviors.

Phosphorylation mechanisms in dopamine transporter regulation

The dopamine transporter (DAT) is a plasma membrane phosphoprotein that actively translocates extracellular dopamine (DA) into presynaptic neurons. The transporter is the primary mechanism for control of DA levels and subsequent neurotransmission, and is the target for abused and therapeutic drugs that exert their effects by suppressing reuptake. The transport capacity of DAT is acutely regulated by signaling systems and drug exposure, providing neurons the ability to fine-tune DA clearance in response to specific conditions. Kinase pathways play major roles in these mechanisms, and this review summarizes the current status of DAT phosphorylation characteristics and the evidence linking transporter phosphorylation to control of reuptake and other functions. Greater understanding of these processes may aid in elucidation of their possible contributions to DA disease states and suggest specific phosphorylation sites as targets for therapeutic manipulation of reuptake.

Dopamine transporter phosphorylation site threonine 53 is stimulated by amphetamines and regulates dopamine transport, efflux, and cocaine analog binding

The dopamine transporter (DAT) controls the spatial and temporal dynamics of dopamine neurotransmission through reuptake of extracellular transmitter and is a target for addictive compounds such as cocaine, amphetamine (AMPH), and methamphetamine (METH). Reuptake is regulated by kinase pathways and drug exposure, allowing for fine-tuning of clearance in response to specific conditions, and here we examine the impact of transporter ligands on DAT residue Thr-53, a proline-directed phosphorylation site previously implicated in AMPH-stimulated efflux mechanisms. Our findings show that Thr-53 phosphorylation is stimulated in a transporter-dependent manner by AMPH and METH in model cells and rat striatal synaptosomes, and in striatum of rats given subcutaneous injection of METH. Rotating disc electrode voltammetry revealed that initial rates of uptake and AMPH-induced efflux were elevated in phosphorylation-null T53A DAT relative to WT and charge-substituted T53D DATs, consistent with functions related to charge or polarity. These effects occurred without alterations of surface transporter levels, and mutants also showed reduced cocaine analog binding affinity that was not rescued by Zn²⁺ Together these findings support a role for Thr-53 phosphorylation in regulation of transporter kinetic properties that could impact DAT responses to amphetamines and cocaine.

Objective assessment of minimally invasive total mesorectal excision performance: a systematic review

INTRODUCTION

Laparoscopy is widely used in colorectal practice, but recent trial results have questioned its use in rectal cancer resections. Patient outcomes are directly linked to the quality of total mesorectal excision (TME) specimen. Objective assessment of intraoperative performance could help ensure competence and delivery of optimal outcomes. Objective tools may also contribute to TME intervention trials, but their nature, structure and utilisation is unknown.

AIM

To systemically review the available literature to report on the available tools for the objective assessment of minimally invasive TME operative performance and their use within multicentre laparoscopic TME randomised controlled trials.

METHODS

A systematic search of the PubMed and Cochrane databases was performed to identify tools used in the objective intraoperative assessment of minimally invasive TME performance in accordance with the PRISMA guidelines, independently by two authors. The identified tools were then evaluated within reported TME RCTs.

RESULTS

A total of 8642 abstracts were screened of which 12 papers met the inclusion criteria; ten prospective observational studies, one randomised trial and one educational consensus. Eight assessment methods were described, which include formative and summative tools. The tools were mostly adaptations of colonic surgery tools based on either operative video review or post-operative trainer rating. All studies reported objective assessment of intraoperative performance was feasible, but only 126 (7%) of the 1762 included laparoscopic cases were TME. No multicentre laparoscopic TME trial reported using any objective surgical performance assessment tool.

CONCLUSION

Objective intraoperative laparoscopic TME performance assessment is feasible, but most of the current tools are adaptation of colonic surgery. There is a need to develop dedicated assessment tools for minimal access rectal surgery. No multicentre minimally invasive TME RCT reported using any objective assessment tool.

Palmitoylation mechanisms in dopamine transporter regulation

The neurotransmitter dopamine (DA) plays a key role in several biological processes including reward, mood, motor activity and attention. Synaptic DA homeostasis is controlled by the dopamine transporter (DAT) which transports extracellular DA into the presynaptic neuron after release and regulates its availability to receptors. Many neurological disorders such as schizophrenia, bipolar disorder, Parkinson disease and attention-deficit hyperactivity disorder are associated with imbalances in DA homeostasis that may be related to DAT dysfunction. DAT is also a target of psychostimulant and therapeutic drugs that inhibit DA reuptake and lead to elevated dopaminergic neurotransmission. We have recently demonstrated the acute and chronic modulation of DA reuptake activity and DAT stability through S-palmitoylation, the linkage of a 16-carbon palmitate group to cysteine via a thioester bond. This review summarizes the properties and regulation of DAT palmitoylation and describes how it serves to affect various transporter functions. Better understanding of the role of palmitoylation in regulation of DAT function may lead to identification of therapeutic targets for modulation of DA homeostasis in the treatment of dopaminergic disorders.

Surgical timing after chemoradiotherapy for rectal cancer, analysis of technique (STARRCAT): results of a feasibility multi-centre randomized controlled trial

BACKGROUND

The optimal time of rectal resection after long-course chemoradiotherapy (CRT) remains unclear. A feasibility study was undertaken for a multi-centre randomized controlled trial evaluating the impact of the interval after chemoradiotherapy on the technical complexity of surgery.

METHODS

Patients with rectal cancer were randomized to either a 6- or 12-week interval between CRT and surgery between June 2012 and May 2014 (ISRCTN registration number: 88843062). For blinded technical complexity assessment, the Observational Clinical Human Reliability Analysis technique was used to quantify technical errors enacted within video recordings of operations. Other measured outcomes included resection completeness, specimen quality, radiological down-staging, tumour cell density down-staging and surgeon-reported technical complexity.

RESULTS

Thirty-one patients were enrolled: 15 were randomized to 6 and 16-12 weeks across 7 centres. Fewer eligible patients were identified than had been predicted. Of 23 patients who underwent resection, mean 12.3 errors were observed per case at 6 weeks vs. 10.7 at 12 weeks (p = 0.401). Other measured outcomes were similar between groups.

CONCLUSIONS

The feasibility of measurement of operative performance of rectal cancer surgery as an endpoint was confirmed in this exploratory study. Recruitment of sufficient numbers of patients represented a challenge, and a proportion of patients did not proceed to resection surgery. These results suggest that interval after CRT may not substantially impact upon surgical technical performance.

Effect of Fenoldopam Continuous Infusion on Glomerular Filtration Rate and Fractional Excretion of Sodium in Healthy Dogs

BACKGROUND

Acute kidney injury (AKI) is a common problem in small-animal patients and carries a guarded prognosis with substantial morbidity and mortality, particularly in oligoanuric dogs. Fenoldopam, a selective dopamine agonist, has been shown to increase urine output in healthy dogs and cats; however, the mechanism of action is unknown.

HYPOTHESIS/OBJECTIVES

To evaluate the effect of fenoldopam infusion on glomerular filtration rate (GFR) and fractional excretion of sodium (FeNa) in healthy dogs.

ANIMALS

Ten healthy, privately owned dogs.

METHODS

Randomized, crossover design with negative control. Ten healthy dogs were given fenoldopam diluted in 5% dextrose (D5W) as a continuous IV infusion of 0.8 μg/kg/min for 5 hours and a control infusion of D5W alone, 7 days apart. Glomerular filtration rate was measured by exogenous iohexol clearance, beginning 1 hour after the start of the fenoldopam infusion. Fractional excretion of sodium (FeNa) was measured before and after the infusion. Glomerular filtration rate and change in FeNa were compared between treatment days.

RESULTS

Fenoldopam infusion resulted in a significantly increased (P = .0166) GFR (median GFR, 3.33 mL/min/kg) in healthy dogs compared with D5W infusion (median GFR, 2.71 mL/kg/min). Fenoldopam also resulted in a significantly increased (P = .0148) FeNa (mean change, 0.106), whereas infusion of D5W alone did not (mean change, 0.016).

CONCLUSIONS AND CLINICAL IMPORTANCE

In healthy dogs, fenoldopam significantly increased GFR and FeNa compared with infusion of D5W alone. No adverse effects were seen.

Application of objective clinical human reliability analysis (OCHRA) in assessment of technical performance in laparoscopic rectal cancer surgery

BACKGROUND

Laparoscopic rectal resection is technically challenging, with outcomes dependent upon technical performance. No robust objective assessment tool exists for laparoscopic rectal resection surgery. This study aimed to investigate the application of the objective clinical human reliability analysis (OCHRA) technique for assessing technical performance of laparoscopic rectal surgery and explore the validity and reliability of this technique.

METHODS

Laparoscopic rectal cancer resection operations were described in the format of a hierarchical task analysis. Potential technical errors were defined. The OCHRA technique was used to identify technical errors enacted in videos of twenty consecutive laparoscopic rectal cancer resection operations from a single site. The procedural task, spatial location, and circumstances of all identified errors were logged. Clinical validity was assessed through correlation with clinical outcomes; reliability was assessed by test-retest.

RESULTS

A total of 335 execution errors identified, with a median 15 per operation. More errors were observed during pelvic tasks compared with abdominal tasks (p < 0.001). Within the pelvis, more errors were observed during dissection on the right side than the left (p = 0.03). Test-retest confirmed reliability (r = 0.97, p < 0.001). A significant correlation was observed between error frequency and mesorectal specimen quality (r s = 0.52, p = 0.02) and with blood loss (r s = 0.609, p = 0.004).

CONCLUSIONS

OCHRA offers a valid and reliable method for evaluating technical performance of laparoscopic rectal surgery.

Reciprocal Phosphorylation and Palmitoylation Control Dopamine Transporter Kinetics

The dopamine transporter is a neuronal protein that drives the presynaptic reuptake of dopamine (DA) and is the major determinant of transmitter availability in the brain. Dopamine transporter function is regulated by protein kinase C (PKC) and other signaling pathways through mechanisms that are complex and poorly understood. Here we investigate the role of Ser-7 phosphorylation and Cys-580 palmitoylation in mediating steady-state transport kinetics and PKC-stimulated transport down-regulation. Using both mutational and pharmacological approaches, we demonstrate that these post-translational modifications are reciprocally regulated, leading to transporter populations that display high phosphorylation-low palmitoylation or low phosphorylation-high palmitoylation. The balance between the modifications dictates transport capacity, as conditions that promote high phosphorylation or low palmitoylation reduce transport Vmax and enhance PKC-stimulated down-regulation, whereas conditions that promote low phosphorylation or high palmitoylation increase transport Vmax and suppress PKC-stimulated down-regulation. Transitions between these functional states occur when endocytosis is blocked or undetectable, indicating that the modifications kinetically regulate the velocity of surface transporters. These findings reveal a novel mechanism for control of DA reuptake that may represent a point of dysregulation in DA imbalance disorders.

Opportunistic fungal infections in dogs treated with ciclosporin and glucocorticoids: eight cases

Glucocorticoids are the standard of care for the treatment of immune-mediated disorders, and ciclosporin is increasingly being used off-label as an adjunct immunosuppressive drug in dogs. However, opportunistic infections can develop during combination immunosuppressive regimens. This case series describes atypical fungal infections in eight dogs treated with immunosuppressive dosages of glucocorticoids and ciclosporin. The median duration of combined treatment prior to the identification of fungal infection was 31 (range, 13 to 201) days, although two dogs received glucocorticoids for prolonged periods prior to the addition of ciclosporin. The estimated prevalence of serious fungal infections with this drug combination appears to be low (approximately 1 · 67%), but these infections led directly or indirectly to death or euthanasia in five of eight (63%) dogs. These cases highlight the need for frequent clinical monitoring of dogs receiving immunosuppressive dosages of glucocorticoids and ciclosporin.

Impact of analgesic modality on stress response following laparoscopic colorectal surgery: a post-hoc analysis of a randomised controlled trial

BACKGROUND

Epidural analgesia is perceived to modulate the stress response after open surgery. This study aimed to explore the feasibility and impact of measuring the stress response attenuation by post-operative analgesic modalities following laparoscopic colorectal surgery within an enhanced recovery after surgery (ERAS) protocol.

METHODS

Data were collected as part of a double-blinded randomised controlled pilot trial at two UK sites. Patients undergoing elective laparoscopic colorectal resection were randomised to receive either thoracic epidural analgesia (TEA) or continuous local anaesthetic infusion to the extraction site via wound infusion catheter (WIC) post-operatively. The aim of this study was to measure the stress response to the analgesic modality by measuring peripheral venous blood samples analysed for serum concentrations of insulin, cortisol, epinephrine and interleukin-6 at induction of anaesthesia, at 3, 6, 12 and 24 h after the start of operation. Secondary endpoints included mean pain score in the first 48 h, length of hospital stay, post-operative complications and 30-day re-admission rates.

RESULTS

There was a difference between the TEA and WIC groups that varies across time. In the TEA group, there was significant but transient reduced level of serum epinephrine and a higher level of insulin at 3 and 6 h. In the WIC, there was a significant reduction of interleukin-6 values, especially at 12 h. There was no significant difference observed in the other endpoints.

CONCLUSIONS

There is a significant transient attenuating effect of TEA on stress response following laparoscopic colorectal surgery and within ERAS as expressed by serum epinephrine and insulin levels. Continuous wound infusion with local anaesthetic, however, attenuates cytokine response as expressed by interleukin-6.

Objective assessment of technique in laparoscopic colorectal surgery: what are the existing tools?

Assessment can improve the effectiveness of surgical training and enable valid judgments of competence. Laparoscopic colon resection surgery is now taught within surgical residency programs, and assessment tools are increasingly used to stimulate formative feedback and enhance learning. Formal assessment of technical performance in laparoscopic colon resection has been successfully applied at the specialist level in the English "LAPCO" National Training Program. Objective assessment tools need to be developed for training and assessment in laparoscopic rectal cancer resection surgery. Simulation may have a future role in assessment and accreditation in laparoscopic colorectal surgery; however, existing virtual reality models are not ready to be used for assessment of this advanced surgery.

Computational and biochemical docking of the irreversible cocaine analog RTI 82 directly demonstrates ligand positioning in the dopamine transporter central substrate-binding site

The dopamine transporter (DAT) functions as a key regulator of dopaminergic neurotransmission via re-uptake of synaptic dopamine (DA). Cocaine binding to DAT blocks this activity and elevates extracellular DA, leading to psychomotor stimulation and addiction, but the mechanisms by which cocaine interacts with DAT and inhibits transport remain incompletely understood. Here, we addressed these questions using computational and biochemical methodologies to localize the binding and adduction sites of the photoactivatable irreversible cocaine analog 3β-(p-chlorophenyl)tropane-2β-carboxylic acid, 4'-azido-3'-iodophenylethyl ester ([(125)I]RTI 82). Comparative modeling and small molecule docking indicated that the tropane pharmacophore of RTI 82 was positioned in the central DA active site with an orientation that juxtaposed the aryliodoazide group for cross-linking to rat DAT Phe-319. This prediction was verified by focused methionine substitution of residues flanking this site followed by cyanogen bromide mapping of the [(125)I]RTI 82-labeled mutants and by the substituted cysteine accessibility method protection analyses. These findings provide positive functional evidence linking tropane pharmacophore interaction with the core substrate-binding site and support a competitive mechanism for transport inhibition. This synergistic application of computational and biochemical methodologies overcomes many uncertainties inherent in other approaches and furnishes a schematic framework for elucidating the ligand-protein interactions of other classes of DA transport inhibitors.

Development and evaluation of a cadaveric training curriculum for low rectal cancer surgery in the English LOREC National Development Programme

AIM

The National Development Programme for Low Rectal Cancer in England (LOREC) was commissioned in response to wide variation in the outcome of patients with low rectal cancer. One of the aims of LOREC was to enhance surgical techniques in managing low rectal cancer. This study reports on the development and evaluation of a novel national technical skills cadaveric training curriculum in extralevator abdominoperineal excision.

METHOD

Three sites were commissioned for the cadaveric workshops, each delivering the same training curriculum. Training was undertaken in pairs using a fresh-frozen cadaveric model under the supervision of expert mentors. Global assessment score (GAS) forms were developed to promote reflective learning. Feedback on the impact of the workshop was obtained from a sample of delegates at the end of the course, and also after 3-23 months via an online questionnaire.

RESULTS

Overall 112 consultant colorectal surgeons attended one of 15 cadaveric technical skills training workshops. Seventy-six per cent of delegates reported easy identification of anatomy in the cadaveric model; 67% found tissue planes easy to interpret. Ninety-six per cent of delegates felt the workshop would influence their future practice; 96% reported increased awareness of important anatomy. Only 2% of delegates wished to pursue supplementary formal training from LOREC.

CONCLUSION

Fresh-frozen cadavers could provide an effective training model for low rectal surgery. A structured 1-day cadaveric workshop has facilitated the dissemination of technical skills for management of low rectal cancer. Attending the cadaveric workshop enhanced delegates' confidence in performing this procedure.

Serum biomarkers of clinical and cytologic response in dogs with idiopathic immune-mediated polyarthropathy

Background

Immune‐mediated polyarthopathy (IMPA) is common in dogs, and is monitored by serial arthrocenteses.

Hypothesis/Objectives

Plasma C‐reactive protein (CRP), interleukin‐6 (IL‐6), and CXCL8 (interleukin‐8) would serve as noninvasive markers of joint inflammation in IMPA.

Animals

Nine client‐owned dogs with idiopathic IMPA; 6 healthy controls.

Methods

Prospective study. Plasma CRP, IL‐6, and CXCL8 were measured by ELISA at baseline, 2, and 4 weeks during treatment with prednisone at 50 mg/m²/day. Arthrocenteses, the canine brief pain inventory (CBPI), and accelerometry collars were used to assess joint inflammation, lameness, and mobility at all 3 time points.

Results

C‐reactive protein concentrations were higher in IMPA dogs (median 91.1 μg/mL, range 76.7–195.0) compared with controls (median <6.3 μg/mL, <6.3–13.7; P = .0035), and were significantly lower at week 2 (10.6 μg/mL, <6.3–48.8) and week 4 (<6.3 μg/mL, <6.3–24.4; P < .001).

C‐reactive protein was correlated with median CBPI scores (r = 0.68; P = .0004), joint cellularity (r = 0.49, P = .011), and mobility by accelerometry (r = −0.42, P = .048). Plasma IL‐6 concentrations were also higher in IMPA dogs (median 45.9 pg/mL), compared with controls (median <15.7 pg/mL; P = .0008). IL‐6 was lower in IMPA dogs by week 4 (<15.7 pg/mL; P = .0099), and was modestly correlated with CBPI scores (r = 0.47, P = .023). CXCL8 did not differ significantly between IMPA and healthy dogs.

Conclusions

Plasma CRP and IL‐6 might be useful surrogate markers of synovial inflammation and disease activity in dogs with IMPA.

A systematic review of patient reported outcomes and patient experience in enhanced recovery after orthopaedic surgery

INTRODUCTION

Orthopaedic enhanced recovery after surgery (ERAS) providers are encouraged to estimate the actual benefit of ERAS according to the patient's opinion by using patient generated data alongside traditional measures such as length of stay. The aim of this paper was to systemically review the literature on the use of patient generated information in orthopaedic ERAS across the whole perioperative pathway.

METHODS

Publications were identified using Embase(™), MEDLINE(®), AMED, CINAHL(®) (Cumulative Index to Nursing and Allied Health Literature), the Cochrane Library and the British Nursing Index. Search terms related to experiences, acceptance, satisfaction or perception of ERAS and quality of life (QoL).

FINDINGS

Of the 596 abstracts found, 8 papers were identified that met the inclusion criteria. A total of 2,208 patients undergoing elective hip and knee arthroplasty were included. Patient satisfaction was reported in 6 papers. Scores were high in all patients and not adversely affected by length of stay. QoL was reported in 2 papers and showed that QoL scores continued to increase up to 12 months following ERAS. Qualitative methods were used in one study, which highlighted problems with support following discharge. There is a paucity of data reporting on patient experience in orthopaedic ERAS. However, ERAS does not compromise patient satisfaction or QoL after elective hip or knee surgery. The measurement of patient experience should be standardised with further research.

Antagonist-induced conformational changes in dopamine transporter extracellular loop two involve residues in a potential salt bridge

Ligand-induced changes in the conformation of extracellular loop (EL) 2 in the rat (r) dopamine transporter (DAT) were examined using limited proteolysis with endoproteinase Asp-N and detection of cleavage products by epitope-specific immunoblotting. The principle N-terminal fragment produced by Asp-N was a 19kDa peptide likely derived by proteolysis of EL2 residue D174, which is present just past the extracellular end of TM3. Production of this fragment was significantly decreased by binding of cocaine and other uptake blockers, but was not affected by substrates or Zn(2+), indicating the presence of a conformational change at D174 that may be related to the mechanism of transport inhibition. DA transport activity and cocaine analog binding were decreased by Asp-N treatment, suggesting a requirement for EL2 integrity in these DAT functions. In a previous study we demonstrated that ligand-induced protease resistance also occurred at R218 on the C-terminal side of rDAT EL2. Here using substituted cysteine accessibility analysis of human (h) DAT we confirm cocaine-induced alterations in reactivity of the homologous R219 and identify conformational sensitivity of V221. Focused molecular modeling of D174 and R218 based on currently available Aquifex aeolicus leucine transporter crystal structures places these residues within 2.9Å of one another, suggesting their proximity as a structural basis for their similar conformational sensitivities and indicating their potential to form a salt bridge. These findings extend our understanding of DAT EL2 and its role in transport and binding functions.

Evidence in sheep for pre-natal transmission of scrapie to lambs from infected mothers

Natural scrapie transmission from infected ewes to their lambs is thought to occur by the oral route around the time of birth. However the hypothesis that scrapie transmission can also occur before birth (in utero) is not currently favoured by most researchers. As scrapie is an opportunistic infection with multiple infection routes likely to be functional in sheep, definitive evidence for or against transmission from ewe to her developing fetus has been difficult to achieve. In addition the very early literature on maternal transmission of scrapie in sheep was compromised by lack of knowledge of the role of the PRNP (prion protein) gene in control of susceptibility to scrapie. In this study we experimentally infected pregnant ewes of known PRNP genotype with a distinctive scrapie strain (SSBP/1) and looked for evidence of transmission of SSBP/1 to the offspring. The sheep were from the NPU Cheviot flock, which has endemic natural scrapie from which SSBP/1 can be differentiated on the basis of histology, genetics of disease incidence and strain typing bioassay in mice. We used embryo transfer techniques to allow sheep fetuses of scrapie-susceptible PRNP genotypes to develop in a range of scrapie-resistant and susceptible recipient mothers and challenged the recipients with SSBP/1. Scrapie clinical disease, caused by both natural scrapie and SSBP/1, occurred in the progeny but evidence (including mouse strain typing) of SSBP/1 infection was found only in lambs born to fully susceptible recipient mothers. Progeny were not protected from transmission of natural scrapie or SSBP/1 by washing of embryos to International Embryo Transfer Society standards or by caesarean derivation and complete separation from their birth mothers. Our results strongly suggest that pre-natal (in utero) transmission of scrapie may have occurred in these sheep.

Laparoscopic extralevator abdominoperineal excision of the rectum: short-term outcomes of a prospective case series

BACKGROUND

Laparoscopic approaches for the resection of low rectal cancer and the extralevator technique for abdominoperineal excision are both becoming increasingly popular. There are little published data regarding the combined application of these techniques to the resection of low rectal tumours. The aim of this study was to assess the feasibility of such an approach and to appraise short-term outcomes in a consecutive series of patients undergoing laparoscopic extralevator abdominoperineal excision (ELAPE).

METHODS

Consecutive patients undergoing laparoscopic ELAPE at our institution between 2008 and 2011 were identified from a prospectively maintained database. The abdominal phase of the operation was performed laparoscopically, and following extralevator resection, the perineum was reconstructed using a biologic mesh. All patients were enrolled in an enhanced recovery programme.

RESULTS

Of 166 patients undergoing radical resection of rectal cancer at our institution between 2008 and 2011, 28 underwent laparoscopic ELAPE. Median age was 70 years, median body mass index was 27.5 kg/m(2), and 71% were male. The conversion rate to laparotomy was 18%. Three patients (10.8%) had circumferential resection margins <1 mm; no intraoperative tumour perforation occurred. The median length of stay was 7 days, with a 30-day readmission rate of 21% and no 30-day mortality. Post-operative perineal wound complications occurred in 25%. At median 38-month follow-up (range 23-66 months), overall survival was 75%, disease-free survival was 71%, and there were three local recurrences (11%).

CONCLUSIONS

Laparoscopic extralevator abdominoperineal excision can be safely performed without compromising short-term outcomes.

Mechanisms of dopamine transporter regulation in normal and disease states

The dopamine (DA) transporter (DAT) controls the spatial and temporal dynamics of DA neurotransmission by driving reuptake of extracellular transmitter into presynaptic neurons. Many diseases such as depression, bipolar disorder, Parkinson's disease (PD), and attention deficit hyperactivity disorder (ADHD) are associated with abnormal DA levels, implicating DAT as a factor in their etiology. Medications used to treat these disorders and many addictive drugs target DAT and enhance dopaminergic signaling by suppressing transmitter reuptake. We now understand that the transport and binding properties of DAT are regulated by complex and overlapping mechanisms that provide neurons with the ability to modulate DA clearance in response to physiological demands. These processes are controlled by endogenous signaling pathways and affected by exogenous transporter ligands, demonstrating their importance for normal neurotransmission, drug abuse, and disease treatments. Increasing evidence supports the disruption of these mechanisms in DA disorders, implicating dysregulation of transport in disease etiologies and suggesting these processes as potential points for therapeutic manipulation of DA availability.

Phosphorylation of dopamine transporter serine 7 modulates cocaine analog binding

As an approach to elucidating dopamine transporter (DAT) phosphorylation characteristics, we examined in vitro phosphorylation of a recombinant rat DAT N-terminal peptide (NDAT) using purified protein kinases. We found that NDAT becomes phosphorylated at single distinct sites by protein kinase A (Ser-7) and calcium-calmodulin-dependent protein kinase II (Ser-13) and at multiple sites (Ser-4, Ser-7, and Ser-13) by protein kinase C (PKC), implicating these residues as potential sites of DAT phosphorylation by these kinases. Mapping of rat striatal DAT phosphopeptides by two-dimensional thin layer chromatography revealed basal and PKC-stimulated phosphorylation of the same peptide fragments and comigration of PKC-stimulated phosphopeptide fragments with NDAT Ser-7 phosphopeptide markers. We further confirmed by site-directed mutagenesis and mass spectrometry that Ser-7 is a site for PKC-stimulated phosphorylation in heterologously expressed rat and human DATs. Mutation of Ser-7 and nearby residues strongly reduced the affinity of rat DAT for the cocaine analog (-)-2β-carbomethoxy-3β-(4-fluorophenyl) tropane (CFT), whereas in rat striatal tissue, conditions that promote DAT phosphorylation caused increased CFT affinity. Ser-7 mutation also affected zinc modulation of CFT binding, with Ala and Asp substitutions inducing opposing effects. These results identify Ser-7 as a major site for basal and PKC-stimulated phosphorylation of native and expressed DAT and suggest that Ser-7 phosphorylation modulates transporter conformational equilibria, shifting the transporter between high and low affinity cocaine binding states.

Reconstruction of the perineum following extralevator abdominoperineal excision for carcinoma of the lower rectum: a systematic review

AIM

An improvement in oncological outcome has been reported following an extralevator approach to abdominoperineal excision (ELAPE) for low rectal carcinoma. A larger perineal defect following ELAPE and the impact of neoadjuvant radiotherapy are sources of considerable morbidity for patients. We report an evidence-based systematic review of published data on the outcome of perineal reconstruction following ELAPE for low rectal carcinoma, comparing the use of tissue flap and biological mesh techniques.

METHOD

A literature search was performed of electronic databases including the Medline, Embase and Scopus databases (1995-2011). Studies describing outcomes relating to the perineum following ELAPE were included for review.

RESULTS

Eleven small cohort studies reported the outcome relating to the perineum following ELAPE. Pooled-analysis of 255 combined patients undergoing flap repair and 85 undergoing biological mesh repair showed no significant difference in the rates of perineal wound complications or perineal hernia formation.

CONCLUSION

There is little information on the optimal technique of perineal wound closure following ELAPE. With the limited data available, there was no significant difference in complication rates between biological mesh and flap repair. There is a need for high-quality prospective trials to compare methods of reconstruction to determine the long-term results, quality of life and function.