Serotonin stimulates DNA synthesis in fibroblasts acting through 5-HT1B receptors coupled to a Gi-protein

Environmental fluoxetine promotes skin cell proliferation and wound healing

This study investigates the effects of environmentally-relevant concentrations of fluoxetine (FLX, commercial name: Prozac) on wound healing. Pollution of water systems with pharmaceutical and personal care products, including antidepressants such as FLX and other selective serotonin reuptake inhibitors, is a growing environmental concern. Environmentally-relevant FLX concentrations are known to impact physiological functions and behaviour of aquatic animals, however, the effects of exposure on humans are currently unknown. Using a combination of human skin biopsies and a human keratinocyte cell line, we show that exposure to environmental FLX promotes wound closure. We show dose-dependent increases in wound closure with FLX concentrations from 125 ng/l. Using several -omics and pharmaceutical approaches, we demonstrate that the mechanisms underlying enhanced wound closure are increased cell proliferation and serotonin signalling. Transcriptomic analysis revealed 350 differentially expressed genes after exposure. Downregulated genes were enriched in pathways related to mitochondrial function and metabolism, while upregulated genes were associated with cell proliferation and tissue morphogenesis. Kinase profiling showed altered phosphorylation of kinases linked to the MAPK pathway. Consistent with this, phosphoproteomic analyses identified 235 differentially phosphorylated proteins after exposure, with enriched GO terms related to cell cycle, division, and protein biosynthesis. Treatment of skin biopsies and keratinocytes with ketanserin, a serotonin receptor antagonist, reversed the increase in wound closure observed upon exposure. These findings collectively show that exposure to environmental FLX promotes wound healing through modulating serotonin signalling, gene expression and protein phosphorylation, leading to enhanced cell proliferation. Our results justify a transition from the study of behavioural effects of environmental FLX in aquatic animals to the investigation of effects of exposure on wound healing in aquatic and terrestrial animals, including direct impacts on human health.

Carcinoid Heart Disease Management: A Multi-Disciplinary Collaboration

Carcinoid heart disease (CaHD) is an important complication among patients with metastatic neuroendocrine tumors and carcinoid syndrome (CS). CS patients (25%-65%) eventually develop CaHD; these patients face a significantly increased risk of morbidity and mortality. Guidance papers (eg, clinical practice guidelines, consensus guidelines, and expert statements) have been established by major organizations across the disciplines of cardiology and oncology; however, these recommendations are not routinely implemented. The aim of this article is to encourage the integration of current recommendations from national societies into clinical practice. Early screening upon recognition of CS and prior to the development of CaHD symptoms is paramount, as no existing therapies are approved to reverse the fibrotic damage to the heart once it occurs. Valvular replacement is the only definitive treatment for CaHD once it has developed. When patients are noted to have urinary 5-hydroxyindoleacetic acid (5-HIAA) levels ≥300 µmol/24 h and/or serum N-terminal pro B-type natriuretic peptide (NT-proBNP) levels >260 pg/mL, echocardiography is recommended. Systemic approaches to control tumor growth and hormonal secretion include somatostatin analogs (SSAs), followed by options including peptide receptor radiotherapy (PRRT), everolimus and liver embolization. Telotristat is the primary choice for control of diarrhea refractory to SSA. Diuretics are the mainstay of heart failure symptom management for patients who develop CaHD. Considerations for future research are discussed, including the ongoing TELEHEART (TELotristat Ethyl in a HEART biomarker study) trial involving telotristat and not yet activated CHARRT (Carcinoid Heart disease And peptide Receptor Radiotargetted Therapy) study involving PRRT with lutetium 177 (177Lu) dotatate.

Inhibition of serotonin biosynthesis in neuroendocrine neoplasm suppresses tumor growth in vivo

Small bowel neuroendocrine tumors (SBNETs) originate from enterochromaffin cells in the intestine which synthesize and secrete serotonin. SBNETs express high levels of tryptophan hydroxylase 1 (Tph1), a key enzyme in serotonin biosynthesis. Patients with high serotonin level may develop carcinoid syndrome, which can be treated with somatostatin analogues and the Tph1 inhibitor telotristat ethyl in severe cases. Although the active drug telotristat can efficiently reduce serotonin levels, its effect on tumor growth is unclear. This study determined the effect of serotonin inhibition on tumor cell growth in vitro and in vivo . The levels of Tph1 in various neuroendocrine neoplasms (NENs) were determined and the biological effects of Tph1 inhibition in vitro and in vivo using genetic and pharmacologic approaches was tested. Gene and protein expression analyses were performed on patient tumors and cancer cell lines. shRNAs targeting TPH1 were used to create stable knockdown in BON cells. Control and knockdown lines were assessed for their growth rates in vitro and in vivo , angiogenesis potential, serotonin levels, endothelial cell tube formation, tumor weight, and tumor vascularity. TPH1 is highly expressed in SBNETs and many cancer types. TPH1 knockdown cells and telotristat treated cells showed similar growth rates as control cells in vitro . However, TPH1 knockdown cells formed smaller tumors in vivo and tumors were less vascularized. Although Tph1 inhibition with telotristat showed no effect on tumor cell growth in vitro , Tph1 inhibition reduced tumor formation in vivo . Serotonin inhibition in combination with other therapies is a promising new avenue for targeting metabolic vulnerabilities in NENs.

First quantitative dosages: Strong correlations between non-5-HT2Rs serotonin receptors on normal human heart valves

Objectives

Although critical in animal and human development and pathology, a measurement of the quantitative expression of 5-HTR serotonin receptors on animal or human valvular tissues has never been performed.

Methods

Quantification of the most frequent 5-HTRs reported as being present in human peripheral tissue was performed using radiolabeled agonists/antagonists. A membrane protein extract from normal human valves (aortic/mitral/tricuspid and some pulmonary) and associated diseased left myocardium, all unusable in clinics, were obtained from the Homograft bank.

Results

We analyzed 5-HT1AR/5-HT1B/DR/5-HT2AR/5-HT2BR/5-HT 2CR/5-HT4R/5-HT7R from 28 hearts. We confirmed the presence of tissue and measured the quantitative content for respective proteins in femtomol/mg of protein extracts: for 5-HT2AR (35.9+/−0.7), 5-HT2BR (28.8+/−1.3) but also a newly observed and robust expression for 5-HT4R (38+/−4.2). We identified one, 5-HT1ARs (4.9+/−0.3), and the possible expression, but at a very low level, of previously reported 5-HT1B/DRs (1.3+/−0.5) as well as the new 5-HT7Rs (3.5+/0.1) and 5-HT2CRs (1.2+/−0.1). Interestingly, by using univariate analysis, we were able to observe many correlations between the different 5-HTR levels of expression especially between 5-HT1AR/5-HT1B/DR and also between 5-HT4R/5-HT7R, but none were observed between 5-HT2AR and 5-HT2BR. Using multivariate analyses for a specific 5-HTR level of expression, after adjustment for implantation sites and other 5-HTRs, we found that 5-HT1AR was correlated with 5-HT1B/DR;5-HT4R with 5-HT7R and 5-HT1AR;5-HT2BR with 5-HT2AR only. For 5-HT2C, no correlation was observed.

Conclusion

5-HT2AR/5-HT2BR and 5-HT4R were all observed to have a high and equal level of expression on human valves, but that of 5-HT1AR was more limited. Since these non-5-HT2Rs are coupled with different G-proteins, with specific signaling, theoretically they may control the main 5-HT2R signaling (i.e., PLC/DAG-PKC-ERK/Ras/Src signaling) involved in valvular fibrosis and degeneration.

Molecular Cloning and Functional Characterization of Three 5-HT Receptor Genes (HTR1B, HTR1E, and HTR1F) in Chickens

The serotonin (5-hydroxytryptamine, 5-HT) signaling system is involved in a variety of physiological functions, including the control of cognition, reward, learning, memory, and vasoconstriction in vertebrates. Contrary to the extensive studies in the mammalian system, little is known about the molecular characteristics of the avian serotonin signaling network. In this study, we cloned and characterized the full-length cDNA of three serotonin receptor genes (HTR1B, HTR1E and HTR1F) in chicken pituitaries. Synteny analyses indicated that HTR1B, HTR1E and HTR1F were highly conserved across vertebrates. Cell-based luciferase reporter assays showed that the three chicken HTRs were functional, capable of binding their natural ligands (5-HT) or selective agonists (CP94253, BRL54443, and LY344864) and inhibiting intracellular cAMP production in a dose-dependent manner. Moreover, activation of these receptors could stimulate the MAPK/ERK signaling cascade. Quantitative real-time PCR analyses revealed that HTR1B, HTR1E and HTR1F were primarily expressed in various brain regions and the pituitary. In cultured chicken pituitary cells, we found that LY344864 could significantly inhibit the secretion of PRL stimulated by vasoactive intestinal peptide (VIP) or forskolin, revealing that HTR1F might be involved in the release of prolactin in chicken. Our findings provide insights into the molecular mechanism and facilitate a better understanding of the serotonergic modulation via HTR1B, HTR1E and HTR1F in avian species.

FAPI PET/CT: Will It End the Hegemony of 18F-FDG in Oncology?

For over 40 years, ¹⁸F-FDG has been the dominant PET tracer in neurology, cardiology, inflammatory diseases, and, most particularly, oncology. Combined with the ability to perform whole-body scanning, ¹⁸F-FDG has revolutionized the evaluation of cancer and has stifled the adoption of other tracers, except in situations where low avidity or high background activity limits diagnostic performance. The strength of ¹⁸F-FDG has generally been its ability to detect disease in the absence of structural abnormality, thereby enhancing diagnostic sensitivity, but its simultaneous weakness has been a lack of specificity due to diverse pathologies with enhanced glycolysis. Radiotracers that leverage other hallmarks of cancer or specific cell-surface targets are gradually finding a niche in the diagnostic armamentarium. However, none have had sufficient sensitivity to realistically compete with ¹⁸F-FDG for evaluation of the broad spectrum of malignancies. Perhaps, this situation is about to change with development of a class of tracers targeting fibroblast activation protein that have low uptake in almost all normal tissues but high uptake in most cancer types. In this review, the development and exciting preliminary clinical data relating to various fibroblast activation protein-specific small-molecule inhibitor tracers in oncology will be discussed along with potential nononcologic applications.

Multicenter phase 2 trial of nintedanib in advanced nonpancreatic neuroendocrine tumors

BACKGROUND

Antiangiogenic-targeting agents have low response rates in patients with nonpancreatic neuroendocrine tumors (NETs). Nintedanib is an oral antiangiogenic agent that has inhibitory effects on the fibroblast growth factor receptor, which is highly expressed in NETs. The authors hypothesized that nintedanib would be active in patients with nonpancreatic NETs.

METHODS

Patients with advanced, grade 1 or 2, nonpancreatic NETs who were receiving a stable dose of somatostatin analogue were enrolled. Nintedanib was administered at a dose of 200 mg twice daily in 28-day cycles. The primary endpoint was progression-free survival (PFS) at 16 weeks.

RESULTS

Thirty-two patients were enrolled, and 30 were evaluable for the primary outcome. Most had radiographic disease progression within 12 months before enrollment. The 16-week PFS rate was 83%, and the median PFS and overall survival were 11.0 months and 32.7 months, respectively. Nintedanib was well tolerated and delayed deterioration in quality of life. The baseline serotonin level had a strong, positive correlation with activated but exhausted T cells.

CONCLUSIONS

Nintedanib is active in nonpancreatic NETs. The immunosuppressive effect of serotonin should be targeted in future clinical trials.

Pathogenesis and Clinical Management of Mesenteric Fibrosis in Small Intestinal Neuroendocine Neoplasms: A Systematic Review

Mesenteric fibrosis (MF) constitutes an underrecognized sequela in patients with small intestinal neuroendocrine neoplasms (SI-NENs), often complicating the disease clinical course. The aim of the present systematic review, carried out by Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodology, is to provide an update in evolving aspects of MF pathogenesis and its clinical management in SI-NENs. Complex and dynamic interactions are present in the microenvironment of tumor deposits in the mesentery. Serotonin, as well as the signaling pathways of certain growth factors play a pivotal, yet not fully elucidated role in the pathogenesis of MF. Clinically, MF often results in significant morbidity by causing either acute complications, such as intestinal obstruction and/or acute ischemia or more chronic conditions involving abdominal pain, venous stasis, malabsorption and malnutrition. Surgical resection in patients with locoregional disease only or symptomatic distant stage disease, as well as palliative minimally invasive interventions in advanced inoperable cases seem clinically meaningful, whereas currently available systemic and/or targeted treatments do not unequivocally affect the development of MF in SI-NENs. Increased awareness and improved understanding of the molecular pathogenesis of MF in SI-NENs may provide better diagnostic and predictive tools for its timely recognition and intervention and also facilitates the development of agents targeting MF.

5-Hydroxytryptophan (5-HTP)-induced intracellular syndrome in mouse non-neural embryonic cells is associated with inhibited proliferation and cell death

Biogenic monoamines are involved in the regulation of various processes in both neural and non-neural cells during development. The present study aimed to identify the regulatory effects of serotonin (5-HT) and its precursors (l-tryptophan and 5-hydroxytryptophan, 5-HTP) on proliferation and cell death in mouse embryonic stem cells (ESCs) and embryonic fibroblasts (MEFs and 3T3 cells). The concentration-dependent cell growth and viability of the ESCs, MEFs and 3T3 cells were analyzed after treatment with l-tryptophan, 5-HTP and 5-HT in the concentration range 10^-6 - 10^-2 M. Treating the cells with 5-HTP, but not l-tryptophan and 5-HT, induced reversible toxic effects. 5-HTP treatment (10^-3 - 10^-2 M) significantly inhibited cell proliferation through blocking of the S-phase of the cell cycle and increasing apoptotic and necrotic cell death. Moreover, 5-HTP treatment stimulated a reorganization of the actin and tubulin networks and upregulated the gene expression of enzymes involved in 5-HT synthesis and metabolism: aromatic amino acid decarboxylase (Aadc/Ddc), monoamine oxidase A (Maoa), and transglutaminase 2 (Tgm2). HPLC analysis found no changes in the intracellular and extracellular levels of 5-HT after 5-HTP treatment, but a significant increase of intracellular 5-HTP levels. However, inhibition of AADC with NSD-1015 or transglutaminase with cystamine prevented 5-HTP-induced cell growth impairment and attenuated the toxic effects of 5-HTP treatment. Our results suggest that 5-HTP can induce toxic effects through cell cycle arrest and cell death in embryonic stem and somatic cells by enhancing the levels of 5-HT-mediated protein modifications. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Role of the tumor microenvironment in digestive neuroendocrine tumors

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) represent a group of heterogeneous tumors whose incidence increased over the past few years. Around half of patients already present with metastatic disease at the initial diagnosis. Despite extensive efforts, cytotoxic and targeted therapies have provided only limited efficacy for patients with metastatic GEP-NETs, mainly due to the development of a certain state of resistance. One factor contributing to both the failure of systemic therapies and the emergence of an aggressive tumor phenotype may be the tumor microenvironment (TME), comprising dynamic and adaptative assortment of extracellular matrix components and non-neoplastic cells, which surround the tumor niche. Accumulating evidence shows that the TME can simultaneously support both tumor growth and metastasis and contribute to a certain state of resistance to treatment. In this review, we summarize the current knowledge of the TME of GEP-NETs and discuss the current therapeutic agents that target GEP-NETs and those that could be of interest in the (near) future.

Serotonin enhances megakaryopoiesis and proplatelet formation via p-Erk1/2 and F-actin reorganization

Our previous studies have shown that serotonin (5-hydroxytryptamine; 5-HT) is a growth factor for hematopoietic stem/progenitor cells. In this study, we proposed a possible mechanism: 5-HT may enhance megakaryopoiesis and proplatelet formation via Erk1/2 pathway and cytoskeleton reorganization. Here, 5-HT(2B)R was first identified in megakaryocytic cells. 5-HT also promoted the megakaryocytes (MKs) proliferation and reduced the cell apoptosis via the activation of 5-HT(2B)R and Akt pathway. The effects were reduced by the 5-HT2B R inhibitor ketanserin. The effect of 5-HT on proplatelet formation in bone marrow MKs were further confirmed: the 5-HT treated group had more proplatelet bearing MKs compared with the control group. To determine whether 5-HT has effects on cytoskeleton reorganization of MKs, and whether these effects could be reduced by ketanserin or Erk1/2 inhibitor PD98059, MKs were stained with the F-actin specific binder rhodamine-phalloidin. The polymerized actin level was lower in the control group than the 5-HT group and was distributed throughout the cytoplasm with occasional aggregations. Our data demonstrated that Erk1/2 was activated in MKs treated with 5-HT. This study suggests that 5-HT has a potent effect on platelet formation and this effect is likely mediated via 5HT(2B)R with subsequent activation of p-Erk1/2 and consequent F-actin reorganization and proplatelet formation. We also demonstrated that melatonin, the metabolite of 5-HT, exerts a protective effect on MK and platelet recovery in the irradiated mouse model. This study suggested that 5-HT plays an important role in platelet formation via 5HT(2B)R, p-Erk1/2, and F-actin reorganization.

Development of inhibitors of heterotrimeric Gαi subunits

Heterotrimeric G-proteins are the immediate downstream effectors of G-protein coupled receptors (GPCRs). Endogenous protein guanine nucleotide dissociation inhibitors (GDIs) like AGS3/4 and RGS12/14 function through GPR/Goloco GDI domains. Extensive characterization of GPR domain peptides indicate they function as selective GDIs for Gαi by competing for the GPCR and Gβγ and preventing GDP release. We modified a GPR consensus peptide by testing FGF and TAT leader sequences to make the peptide cell permeable. FGF modification inhibited GDI activity while TAT preserved GDI activity. TAT-GPR suppresses G-protein coupling to the receptor and completely blocked α2-adrenoceptor (α2AR) mediated decreases in cAMP in HEK293 cells at 100nM. We then sought to discover selective small molecule inhibitors for Gαi. Molecular docking was used to identify potential molecules that bind to and stabilize the Gαi-GDP complex by directly interacting with both Gαi and GDP. Gαi-GTP and Gαq-GDP were used as a computational counter screen and Gαq-GDP was used as a biological counter screen. Thirty-seven molecules were tested using nucleotide exchange. STD NMR assays with compound 0990, a quinazoline derivative, showed direct interaction with Gαi. Several compounds showed Gαi specific inhibition and were able to block α2AR mediated regulation of cAMP. In addition to being a pharmacologic tool, GDI inhibition of Gα subunits has the advantage of circumventing the upstream component of GPCR-related signaling in cases of overstimulation by agonists, mutations, polymorphisms, and expression-related defects often seen in disease.

Serotonin and the 5-HT7 receptor: the link between hepatocytes, IGF-1 and small intestinal neuroendocrine tumors

Platelet-derived serotonin (5-HT) is involved in liver regeneration. The liver is also the metastatic site for malignant enterochromaffin (EC) cell "carcinoid" (neuroendocrine) neoplasms, the principal cellular source of 5-HT. We hypothesized that 5-HT produced by metastatic EC cells played a role in the hepatic tumor-microenvironment principally via 5-HT₇ receptor-mediated activation of hepatocyte IGF-1 synthesis and secretion. Using isolated rat hepatocytes, we evaluated 5-HT₇ receptor expression (using PCR, sequencing and western blot). ELISA, cell transfection and western blots delineated 5-HT-mediated signaling pathways (pCREB, AKT and ERK). IGF-1 synthesis/secretion was evaluated using QPCR and ELISA. IGF-1 was tested on small intestinal neuroendocrine neoplasm proliferation, while IGF-1 production and 5-HT₇ expression were examined in an in vivo SCID metastasis model. Our results demonstrated evidence for a functional 5-HT₇ receptor. 5-HT activated cAMP/PKA activity, pCREB (130-205%, P < 0.05) and pERK/pAKT (1.2-1.75, P < 0.05). Signaling was reversed by the 5-HT₇ receptor antagonist SB269970. IGF-1 significantly stimulated proliferation of two small intestinal neuroendocrine neoplasm cell lines (EC₅₀: 7-70 pg/mL) and could be reversed by the small molecule inhibitor BMS-754807. IGF-1 and 5-HT were elevated (40-300×) in peri-tumoral hepatic tissue in nude mice, while 5-HT₇ was increased fourfold compared to sham-operated animals. We conclude that hepatocytes express a cAMP-coupled 5-HT₇ receptor, which, at elevated 5-HT concentrations that occur in liver metastases, signals via CREB/AKT and is linked to IGF-1 synthesis and secretion. Because IGF-1 regulates NEN proliferation, identification of a role for 5-HT₇ in the hepatic metastatic tumor microenvironment suggests the potential for novel therapeutic strategies for amine-producing mid-gut tumors.

Targeting the serotonin pathway for the treatment of pulmonary arterial hypertension

As we uncover the complex pathophysiology underlying idiopathic and familial pulmonary arterial hypertension, multiple disease associated pathways, cell types and processes reveal links to elements of the serotonin system. Beyond the original 'serotonin hypothesis' observed with anorexigens, and the latterly demonstrated association with vascular tone and pulmonary artery smooth muscle cell proliferation, recent studies suggest links to BMPR2, PDGF and RhoK pathways, as well as an impact upon more complex lesion formation and pathologic bone marrow progenitor mobilization. Clinical experience with antagonists targeting the various elements of the serotonin pathway has been unsatisfactory, yet perhaps this is less than surprising given our expanding knowledge around serotonin production and signaling biology, which indicate opportunities for novel therapeutic options.

Role of 5-hydroxytryptamine 1B (5-HT1B) receptors in the regulation of ethanol intake in rodents

Evidence indicates that the serotonergic system is important in mediating dependence on and craving for alcohol. Among serotonin receptors, 5-hydroxytryptamine 1B (5-HT1B) receptors have been associated with drug abuse including alcohol. In this review, the neurocircuitry involving 5-HT1B receptors in central reward brain regions related to alcohol intake are discussed in detail. Emphasis has been placed on the pharmacological manipulations of 5-HT1B receptor-mediated alcohol intake. Furthermore, 5-HT1B auto- and hetero-receptors regulate alcohol intake through the regulatory mechanism involving release of 5-HT, gamma-aminobutyric acid (GABA), dopamine, and glutamate is evaluated. Thus, interactions between 5-HT1B receptors and these neurotransmitter systems are suggested to modulate alcohol-drinking behavior. This review on the role of 5-HT1B receptors in neurotransmitter release and consequent alcohol intake provides important information about the potential therapeutic role of 5-HT1B receptors for the treatment of alcohol dependence.

Serotonin: good or bad for bone

Besides its action as a neurotransmitter, serotonin has multiple physiological functions in several peripheral organs. Recently, Yadav et al. suggested that peripheral serotonin produced in the gut was a major negative regulator of osteoblast proliferation. These data were challenged by Cui et al. that showed no change in bone density in mature mice with a global invalidation of tryptophan hydroxylase 1, the enzyme responsible of serotonin synthesis in the periphery. In this context, we showed that osteoclasts are able to synthetize serotonin that acts locally to induce osteoclast precursors differentiation. Our data and previous results from others suggest that rather than acting as a hormone, serotonin produced in the bone could act locally on osteoclast and osteoblast realizing in the bone a complete micro-serotoninergic system.

Echocardiographic evidence for valvular toxicity of benfluorex: a double-blind randomised trial in patients with type 2 diabetes mellitus

Objectives

REGULATE trial was designed to compare the efficacy and safety of benfluorex versus pioglitazone in type 2 diabetes mellitus (DM) patients.

Methods

Double-blind, parallel-group, international, randomised, non-inferiority trial. More than half of the 196 participating centres were primary care centres. Patients eligible had type 2 DM uncontrolled on sulfonylurea. 846 were randomised. They received study treatment for 1 year. 423 patients were allocated to benfluorex (150 to 450 mg/day) and 423 were allocated to pioglitazone (30 to 45 mg/day). Primary efficacy criterion was HbA_1c. Safety assessment included blinded echocardiographic evaluation of cardiac and valvular status.

Results

At baseline, patients were 59.1±10.5 years old with HbA1c 8.3±0.8%, and DM duration 7.1±6.0 years. During the study, mean HbA1c significantly decreased in both groups (benfluorex: from 8.30±0.80 to 7.77±1.31 versus pioglitazone: from 8.30±0.80 to 7.45±1.30%). The last HbA1c value was significantly lower with pioglitazone than with benfluorex (p<0.001) and non-inferiority of benfluorex was not confirmed (p = 0.19). Among the 615 patients with assessable paired echocardiography (310 benfluorex, 305 pioglitazone), 314 (51%) had at least one morphological valvular abnormality and 515 (84%) at least one functional valvular abnormality at baseline. Emergent morphological abnormalities occurred in 8 patients with benfluorex versus 4 with pioglitazone (OR 1.99), 95% CI (0.59 to 6.69). Emergent regurgitation (new or increased by one grade or more) occurred more frequently with benfluorex (82 patients, 27%) than with pioglitazone (33 patients, 11%) (OR 2.97), 95% CI (1.91 to 4.63) and were mainly rated grade 1; grade 2 (mild) was detected in 2 patients with benfluorex and 3 with pioglitazone. There was no moderate or severe regurgitation.

Conclusion

After 1 year of exposure, our results show a 2.97 fold increase in the incidence of valvular regurgitation with benfluorex and provide evidence for the valvular toxicity of this drug.

Trial registration

www.controlled-trials.com ISRCTN 27354239. isrctn27354239

Serotonin expression in pancreatic neuroendocrine tumors correlates with a trabecular histologic pattern and large duct involvement

Pancreatic neuroendocrine tumors with prominent stromal fibrosis are often clinically, radiographically, and grossly indistinguishable from ductal adenocarcinoma. We recently described a small series of fibrotic pancreatic neuroendocrine tumors that express serotonin. To understand better the relationship between histopathologic patterns and serotonin expression, we reviewed 361 pancreatic neuroendocrine tumors to identify those with prominent stromal fibrosis exceeding 30% of total tumor area. We identified 52 cases and immunolabeled these neoplasms with antibodies to serotonin and Ki-67. Two predominant histologic subtypes were identified: 14 (26.9%) of 52 had a trabecular or trabecular-glandular cellular pattern with interspersed fibrosis, whereas 38 (73.1%) of 52 had solid architecture. Of the 52, 14 (26.9%) pancreatic neuroendocrine tumors showed at least focal serotonin immunoreactivity. Tumors with predominantly trabecular architecture were significantly more likely to express serotonin than those with solid architecture (P < .01). Only 2 of 34 pancreatic neuroendocrine tumors with fibrosis less than 30% of total tumor area expressed serotonin. The 14 serotonin-expressing tumors were less likely to have lymph node metastases (P = .016) and more likely to involve large pancreatic ducts (P < .01) than were the 38 serotonin-negative tumors. The serotonin-expressing tumors were also found in a younger patient population (P < .01). There was no significant association of serotonin immunoreactivity with Ki-67 proliferation index, tumor size, or distant metastases. Our data demonstrate a strong correlation between trabecular architecture and serotonin immunoreactivity in pancreatic neuroendocrine tumors with stromal fibrosis. Serotonin-expressing tumors are also less likely to have lymph node metastases and more likely to involve large pancreatic ducts.

Dopamine receptors and Parkinson's disease

Parkinson's disease (PD) is a progressive extrapyramidal motor disorder. Pathologically, this disease is characterized by the selective dopaminergic (DAergic) neuronal degeneration in the substantia nigra. Correcting the DA deficiency in PD with levodopa (L-dopa) significantly attenuates the motor symptoms; however, its effectiveness often declines, and L-dopa-related adverse effects emerge after long-term treatment. Nowadays, DA receptor agonists are useful medication even regarded as first choice to delay the starting of L-dopa therapy. In advanced stage of PD, they are also used as adjunct therapy together with L-dopa. DA receptor agonists act by stimulation of presynaptic and postsynaptic DA receptors. Despite the usefulness, they could be causative drugs for valvulopathy and nonmotor complication such as DA dysregulation syndrome (DDS). In this paper, physiological characteristics of DA receptor familyare discussed. We also discuss the validity, benefits, and specific adverse effects of pharmaceutical DA receptor agonist.

Adipocytes express a functional system for serotonin synthesis, reuptake and receptor activation

AIMS

Serotonergic pathways in the central nervous system (CNS) are activated in the regulation of food intake and body weight. We hypothesized that adipocytes, like other cells of mesenchymal origin, possess serotonin receptors and thus could be regulated by peripherally circulating serotonin.

METHODS

In vivo studies: four Sprague-Dawley rats were given daily serotonin (5HT) injections subcutaneously (s.c., 25 mg/kg) for 5 days; four controls received saline. In a long-term study, 12 rats were given serotonin s.c. for 4 months, 10 controls received saline. Body weight was registered throughout the studies, and visceral adipose tissue and plasma were collected and analysed. Adipocytes were isolated from normal rat visceral abdominal adipose tissue and analysed for the expression of serotonin receptors, the serotonin transporter (5HTT/SERT), activation of serotonin synthesis (tryptophan hydroxylase 1, Tph1) and secretion and serotonin-induced leptin regulation by RT-PCR and protein analyses.

RESULTS

Hyperserotoninergic rats had significantly lower body weight (-7.4 and -6.8%) and plasma leptin levels (-44 and -38%) than controls, after both short- and long-term serotonin treatment, respectively, whereas plasma ghrelin levels were unaffected. Compared to controls, serotonin induced a 40-fold upregulation of 5HTT mRNA in visceral adipose tissue after 5 days of treatment. In vitro experiments showed that adipocytes express serotonin receptors, Tph1 and 5HTT, synthesize and secrete serotonin and that serotonin regulates leptin in mature adipocytes.

CONCLUSIONS

These findings show that serotonin may regulate adipocyte function in a direct manner via the blood circulation and/or paracrine and autocrine mechanisms, and not only indirectly via the CNS as previously assumed.

Small intestinal neuroendocrine cell pathobiology: 'carcinoid' tumors

PURPOSE OF REVIEW

Neuroendocrine tumors, particularly small intestinal tumors, also grouped as 'carcinoids', are defined by an increasing incidence and prevalence, a poor response to current therapies, and confusion regarding appropriate models for drug development. Despite these issues, approximately 350 studies were published in the last year.

RECENT FINDINGS

Two sources of confusion are clearly apparent. First, pharmacotherapeutic studies using pancreatic tumor cell lines as models for small intestinal or 'carcinoid' tumor biology are considered appropriate. Second, there is continued inclusion and analysis of pancreatic endocrine tumors with small intestinal neuroendocrine tumors in clinical studies. One highlight of this year is additional data confirming the significant differences between pancreatic tumor cell lines and small intestinal cell lines, the different gene expressions, for example, PAX8, between these two tumor types, and the observations that these two tumors respond differently in clinical trials, for example, to mammalian target of rapamycin (mTOR) inhibitors. Other highlights include delineating the role of the tumor microenvironment in the development of fibrosis and developing a minimum pathology dataset and a prognostic nomogram that may have utility in stratifying patients for clinical studies.

SUMMARY

A number of interesting studies have been published during 2009-2010, but critical areas remain that require resolution. Current data, for the most part, reflect amplification of previously held concepts with modest advances in novel information.

Role of the serotonergic system in alcohol dependence: from animal models to clinics

Alcohol dependence remains among the most common substance abuse problems worldwide, and compulsive alcohol consumption is a significant public health concern. Alcohol is an addictive drug that alters brain function through interactions with multiple neurotransmitter systems. These neurotransmitter systems mediate the reinforcing effects of alcohol. Specifically, the serotonergic system is important in mediating alcohol reward, preference, dependence, and craving. In this review chapter, we first discuss the serotonin system as it relates to alcoholism, and then outline interactions between this system and other neurotransmitter systems. We emphasize the serotonin transporter and its possible role in alcoholism, then present several serotonergic receptors and discuss their contribution to alcoholism, and finally assess the serotonin system as a target for pharmacotherapy, with an emphasis on current and potential treatments.

Serotonergic drugs and valvular heart disease

BACKGROUND

The serotonin (5-HT) releasers (+/-)-fenfluramine and (+)-fenfluramine were withdrawn from clinical use owing to increased risk of valvular heart disease. One prevailing hypothesis (i.e., the '5-HT hypothesis') suggests that fenfluramine-induced increases in plasma 5-HT underlie the disease.

OBJECTIVE

Here, we critically evaluate the possible mechanisms responsible for fenfluramine-associated valve disease.

METHODS

Findings from in vitro and in vivo experiments performed in our laboratory are reviewed. The data are integrated with existing literature to address the validity of the 5-HT hypothesis and suggest alternative explanations.

CONCLUSIONS

The overwhelming majority of evidence refutes the 5-HT hypothesis. A more likely cause of fenfluramine-induced valvulopathy is activation of 5-HT(2B) receptors on heart valves by the metabolite norfenfluramine. Future serotonergic medications should be designed to lack 5-HT(2B) agonist activity.

Autoregulatory effects of serotonin on proliferation and signaling pathways in lung and small intestine neuroendocrine tumor cell lines

BACKGROUND

: Survival rates for gastrointestinal (GI) and bronchopulmonary (BP) neuroendocrine tumors (NETs) have not altered significantly (5-year survival rate: GI NETs, 64.1%; BP NETs, 87%-89%) in 30 years (from 1973 to 2004). No effective or specific antineoplastic agents are available to date, although somatostatin analogs inhibit NET 5-hydroxytryptophan (5-HT) secretion. Given the expression of 5-HT receptors on NETs, the authors hypothesized that 5-HT autoregulated NET proliferation.

METHODS

: Proliferation was evaluated in 3 NET cell lines using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide uptake; in addition, real-time polymerase chain reaction analyses and enzyme-linked immunosorbent assay studies were performed to delineate 5-HT-mediated signaling pathways. To determine the receptor and role of endogenous 5-HT production, the effects of ketanserin (5-HT receptor subtypes 2A and 2C [5-HT(2A/2C)]); ondansetron (5-HT(3)); and the suicide inhibitor of the rate-limiting enzyme for 5-HT synthesis, tryptophan hydroxylase (7-HTP) were investigated.

RESULTS

: Exogenously added 5-HT stimulated proliferation in atypical BP NET NCI-H720 cells (+50%; half-maximal stimulatory concentration [EC(50)] = 10 nM), in typical BP NET NCI-H727 cells (+40%; EC(50) = 0.01 nM), and in GI NET KRJ-I cells (+60%; EC(50) = 25 nM). In NCI-H720 cells, proliferation was inhibited by ketanserin (half-maximal inhibitory concentration [IC(50)] = 0.06 nM) and ondansetron (IC(50) = 0.4 nM) and also was inhibited by 7-HTP (IC(50) = 0.3 nM). In NCI-H727 cells, ketanserin and 7-HTP inhibited proliferation (IC(50) = 0.3 nM and IC(50) = 2.3 nM, respectively), whereas ondansetron had no effect. In KRJ-I cells, ketanserin (IC(50) = 0.1 nM) and 7-HTP (IC(50) = 0.6 nM), but not ondansetron, inhibited proliferation. In all cell lines, 5-HT activated proliferation through extracellular signal-regulated kinase 1 (ERK1) and ERK2 phosphorylation and c-Jun N-terminal kinase (JNK)-mediated pathways (c-JUN and Ki-67 transcription). An autoregulatory effect was indicated by the 7-HTP-mediated inhibition of extracellular 5-HT and downstream effects on NET proliferation.

CONCLUSIONS

: Lung and GI NET proliferation was autoregulated by 5-HT through alterations in ERK and JNK signaling. Targeting NET cells with 5-HT(2) receptor antagonists and 7-HTP reversed proliferation. The current results indicated that 5-HT(2) receptor subtype-specific antagonists may represent a viable antiproliferative therapeutic strategy. Cancer 2009. (c) 2009 American Cancer Society.

Appetite suppressants, cardiac valve disease and combination pharmacotherapy

The prevalence of obesity in the United States is a major health problem associated with significant morbidity, mortality, and economic burden. Although obesity and drug addiction are typically considered distinct clinical entities, both diseases involve dysregulation of biogenic amine neuron systems in the brain. Thus, research efforts to develop medications for treating drug addiction can contribute insights into the pharmacotherapy for obesity. Here, we review the neurochemical mechanisms of selected stimulant medications used in the treatment of obesity and issues related to fenfluramine-associated cardiac valvulopathy. In particular, we discuss the evidence that cardiac valve disease involves activation of mitogenic serotonin 2B (5-HT2B) receptors by norfenfluramine, the major metabolite of fenfluramine. Advances in medication discovery suggest that novel molecular entities that target 2 different neurochemical mechanisms, that is, "combination pharmacotherapy," will yield efficacious antiobesity medications with reduced adverse side effects.

Drug-induced fibrotic valvular heart disease

The initial association between the development of valvular heart disease and drugs stems from observations made during the use of methysergide and ergotamine for migraine prophylaxis in the 1960s. Since then, the appetite suppressants fenfluramine and dexfenfluramine, the dopamine agonists pergolide and cabergoline, and more recently, the recreational drug ecstasy (3,4 methylenedioxymethamphetamine; MDMA) have been implicated. Results from clinical trials show that drug dose and treatment duration affect both the risk of developing the disease and its severity. The natural history of the disease remains unclear, although regression of valvular lesions after the end of treatment has been reported. Interference with serotonin metabolism and its associated receptors and transporter gene seems a likely mechanism for development of the drug-induced valvular heart disease. Physicians need to balance the benefits of continued therapy with these drugs against possible risks. Further investigation is needed to assist with treatment decisions. Continued vigilance is necessary because several commonly prescribed treatments interact with serotonergic pathways.

Serotonin and fluoxetine modulate bone cell function in vitro

Recent studies have proposed a role for serotonin and its transporter in regulation of bone cell function. In the present study, we examined the in vitro effects of serotonin and the serotonin transporter inhibitor fluoxetine "Prozac" on osteoblasts and osteoclasts. Human mononuclear cells were differentiated into osteoclasts in the presence of serotonin or fluoxetine. Both compounds affected the total number of differentiated osteoclasts as well as bone resorption in a bell-shaped manner. RT-PCR on the human osteoclasts demonstrated several serotonin receptors, the serotonin transporter, and the rate-limiting enzyme in serotonin synthesis, tryptophan hydroxylase 1 (Tph1). Tph1 expression was also found in murine osteoblasts and osteoclasts, indicating an ability to produce serotonin. In murine pre-osteoclasts (RAW264.7), serotonin as well as fluoxetine affected proliferation and NFkappaB activity in a biphasic manner. Proliferation of human mesenchymal stem cells (MSC) and primary osteoblasts (NHO), and 5-HT2A receptor expression was enhanced by serotonin. Fluoxetine stimulated proliferation of MSC and murine preosteoblasts (MC3T3-E1) in nM concentrations, microM concentrations were inhibitory. The effect of fluoxetine seemed direct, probably through 5-HT2 receptors. Serotonin-induced proliferation of MC3T3-E1 cells was inhibited by the PKC inhibitor (GF109203) and was also markedly reduced when antagonists of the serotonin receptors 5-HT2B/C or 5-HT2A/C were added. Serotonin increased osteoprotegerin (OPG) and decreased receptor activator of NF-kappaB ligand (RANKL) secretion from osteoblasts, suggesting a role in osteoblast-induced inhibition of osteoclast differentiation, whereas fluoxetine had the opposite effect. This study further describes possible mechanisms by which serotonin and the serotonin transporter can affect bone cell function.

Neural and cardiac toxicities associated with 3,4-methylenedioxymethamphetamine (MDMA)

(+/-)-3,4-Methylenedioxymethamphetamine (MDMA) is a commonly abused illicit drug which affects multiple organ systems. In animals, high-dose administration of MDMA produces deficits in serotonin (5-HT) neurons (e.g., depletion of forebrain 5-HT) that have been viewed as neurotoxicity. Recent data implicate MDMA in the development of valvular heart disease (VHD). The present paper reviews several issues related to MDMA-associated neural and cardiac toxicities. The hypothesis of MDMA neurotoxicity in rats is evaluated in terms of the effects of MDMA on monoamine neurons, the use of scaling methods to extrapolate MDMA doses across species, and functional consequences of MDMA exposure. A potential treatment regimen (l-5-hydroxytryptophan plus carbidopa) for MDMA-associated neural deficits is discussed. The pathogenesis of MDMA-associated VHD is reviewed with specific reference to the role of valvular 5-HT(2B) receptors. We conclude that pharmacological effects of MDMA occur at the same doses in rats and humans. High doses of MDMA that produce 5-HT depletions in rats are associated with tolerance and impaired 5-HT release. Doses of MDMA that fail to deplete 5-HT in rats can cause persistent behavioral dysfunction, suggesting even moderate doses may pose risks. Finally, the MDMA metabolite, 3,4-methylenedioxyamphetamine (MDA), is a potent 5-HT(2B) agonist which could contribute to the increased risk of VHD observed in heavy MDMA users.

Dual dopamine/serotonin releasers: potential treatment agents for stimulant addiction

"Agonist therapy" for cocaine and methamphetamine addiction involves administration of stimulant-like medications (e.g., monoamine releasers) to reduce withdrawal symptoms and prevent relapse. A significant problem with this strategy is that many candidate medications possess abuse liability because of activation of mesolimbic dopamine (DA) neurons in the brain. One way to reduce DA-mediated abuse liability of candidate drugs is to add in serotonin (5-HT) releasing properties, since substantial evidence shows that 5-HT neurons provide an inhibitory influence over mesolimbic DA neurons. This article addresses several key issues related to the development of dual DA/5-HT releasers for the treatment of substance use disorders. First, the authors briefly summarize the evidence supporting a dual deficit in DA and 5-HT function during withdrawal from chronic cocaine or alcohol abuse. Second, the authors discuss data demonstrating that 5HT release can dampen DA-mediated stimulant effects, and the "antistimulant" role of 5-HT-sub(2C) receptors is considered. Next, the mechanisms underlying potential adverse effects of 5-HT releasers are described. Finally, the authors discuss recently published data with PAL-287, a novel nonamphetamine DA/5-HT releasing agent that suppresses cocaine self-administration but lacks positive reinforcing properties. It is concluded that DA/5-HT releasers could be useful therapeutic adjuncts for the treatment of cocaine and alcohol addictions, as well as for obesity, attention-deficit disorder, and depression.

Long-term serotonin effects in the rat are prevented by terguride

Long-term hyperserotoninemia induces heart valve disease in rats, and cases of cardiac valvulopathies have been reported in patients using ergolines, possibly through activation of the 5-hydroxytryptamine(2B) (5HT(2B)) receptor. The ergoline terguride (transdihydrolisuride) is a 5HT(2B/2C) receptor antagonist. Using a rat model, we have investigated whether terguride could prevent serotonin-induced changes in general and heart disease specifically. During 4 months, twelve Sprague-Dawley rats were given daily subcutaneous serotonin injections; twelve rats received a combination of serotonin injections and terguride by gavage, whereas ten rats were untreated controls. Using echocardiography, rats with aortic insufficiency were found in all 3 groups, while pulmonary insufficiency was only found in two rats injected with serotonin alone. Animals given serotonin alone had significantly higher heart weights compared to the controls (p=0.029) and rats given terguride (p=0.034). Rats injected with serotonin alone developed macroscopic skin changes at the injection sites, histologically identified as orthokeratosis and acanthosis. Terguride completely prevented these changes (p=0.0001, p=0.0003). Liver weights were higher in the animals given serotonin alone compared to controls (p=0.014) and terguride treated animals (p=0.009). Stomach weights were higher in animals given serotonin alone compared to rats given terguride (p=0.012). In the mesenchymal cell-line MC3T3-E1, terguride almost completely inhibited serotonin-induced proliferation (p<0.01). Serotonin increases heart, liver and stomach weights, possibly through enhanced proliferation. Terguride inhibits these effects. We propose that terguride may have beneficial effects in the treatment of diseases such as carcinoid syndrome, where serotonin plays an important pathogenic role.

The mas oncogene as a neural peptide receptor: expression, regulation and mechanism of action

The human mas oncogene, which renders transfected NIH/3T3 cells tumorigenic, was identified as a subtype of angiotensin receptor by transient expression in Xenopus oocytes and stable expression in the mammalian neuronal cell line, NG115-401L. The mas receptor preferentially recognizes angiotensin III, and is expressed at high levels in brain. The mas/angiotensin receptor functions through the breakdown of inositol lipids and can drive DNA synthesis, unlike another inositol-linked peptide receptor, that for bradykinin. Comparative analysis of several early biochemical events elicited by either angiotensin or bradykinin stimulation of mas-transfected cells has not indicated a specific difference correlated with mitogenic activity. In particular, the inositol lipid kinase, phosphatidylinositol-3-kinase, thought to be involved in the mitogenic mechanism of platelet-derived growth factor receptors, is unaffected by activation of mas. These results have shown that a proto-oncogene encodes a neural peptide receptor, indicating that peptide receptors may be involved in differentiation and proliferation processes, as are other identified proto-oncogenes.

Growth factor-like action of lysophosphatidic acid: mitogenic signalling mediated by G proteins

Several classes of growth factors can be distinguished that act through different signal transduction pathways. One class is constituted by the peptide growth factors that bind to receptors with ligand-dependent protein tyrosine kinase activity. Another class of mitogens activates a phosphoinositide-specific phospholipase C via a receptor-linked G protein. An intriguing member of this class is lysophosphatidic acid (LPA). LPA mitogenicity is not dependent on other mitogens and is blocked by pertussis toxin. LPA evokes at least three separate signalling cascades: (i) activation of a pertussis toxin-insensitive G protein mediating phosphoinositide hydrolysis; (ii) release of arachidonic acid in a GTP-dependent manner, but independent of prior phosphoinositide hydrolysis; and (iii) activation of a pertussis toxin-sensitive Gi protein mediating inhibition of adenylate cyclase. The peptide bradykinin mimics LPA in inducing responses (i) and (ii), but fails to activate Gi and to stimulate DNA synthesis. Our results suggest that the mitogenic action of LPA occurs through Gi or a related pertussis toxin substrate and that, unexpectedly, the phosphoinositide hydrolysis pathway is neither required nor sufficient, by itself, for mitogenesis.

Decreased Hepatic 5-HT1A Receptors During Liver Regeneration and Neoplasia in Rats

In the present study we investigated the role of 5-hydroxytryptamine (5-HT) and 5-HT1A receptor during liver regeneration after partial hepatectomy (PH) and N-nitrosodiethylamine (NDEA) induced hepatocellular carcinoma in male Wistar rats. 5-HT content was significantly increased during liver regeneration after PH and NDEA induced hepatocellular carcinoma. Scatchard analysis using 8-OH-DPAT, a 5-HT1A specific agonist showed a decreased receptor during liver regeneration after PH and NDEA induced hepatocellular carcinoma. 5-HT when added alone to primary hepatocyte culture did not increase DNA synthesis but was able to increase the EGF mediated DNA synthesis and inhibit the TGF beta 1 mediated DNA synthesis suppression in vitro. This confirmed the co-mitogenic activity of 5-HT. 8-OH-DPAT at a concentration of 10(-4) M inhibited the basal and EGF-mediated DNA synthesis in primary hepatocyte cultures. It also suppressed the TGF beta 1-mediated DNA synthesis suppression. This clearly showed that activated 5-HT1A receptor inhibited hepatocyte DNA synthesis. Our results suggest that decreased hepatic 5-HT1A receptor function during hepatocyte regeneration and neoplasia has clinical significance in the control of cell proliferation.

Promoting effects of serotonin on hematopoiesis: ex vivo expansion of cord blood CD34+ stem/progenitor cells, proliferation of bone marrow stromal cells, and antiapoptosis

Serotonin is a monoamine neurotransmitter that has multiple extraneuronal functions. We previously reported that serotonin exerted mitogenic stimulation on megakaryocytopoiesis mediated by 5-hydroxytryptamine (5-HT)2 receptors. In this study, we investigated effects of serotonin on ex vivo expansion of human cord blood CD34+ cells, bone marrow (BM) stromal cell colony-forming unit-fibroblast (CFU-F) formation, and antiapoptosis of megakaryoblastic M-07e cells. Our results showed that serotonin at 200 nM significantly enhanced the expansion of CD34+ cells to early stem/progenitors (CD34+ cells, colony-forming unit-mixed [CFU-GEMM]) and multilineage committed progenitors (burst-forming unit/colony-forming unit-erythroid [BFU/CFU-E], colony-forming unit-granulocyte macrophage, colony-forming unit-megakaryocyte, CD61+ CD41+ cells). Serotonin also increased nonobese diabetic/severe combined immunodeficient repopulating cells in the expansion culture in terms of human CD45+, CD33+, CD14+ cells, BFU/CFU-E, and CFU-GEMM engraftment in BM of animals 6 weeks post-transplantation. Serotonin alone or in addition to fibroblast growth factor, platelet-derived growth factor, or vascular endothelial growth factor stimulated BM CFU-F formation. In M-07e cells, serotonin exerted antiapoptotic effects (annexin V, caspase-3, and propidium iodide staining) and reduced mitochondria membrane potential damage. The addition of ketanserin, a competitive antagonist of 5-HT2 receptor, nullified the antiapoptotic effects of serotonin. Our data suggest the involvement of serotonin in promoting hematopoietic stem cells and the BM microenvironment. Serotonin could be developed for clinical ex vivo expansion of hematopoietic stem cells for transplantation. Disclosure of potential conflicts of interest is found at the end of this article.

Molecular signaling involved in regulating feeding and other mitivated behaviors

The metabolic and nutritional status of an organism influences multiple behaviors in addition to food intake. When an organism is hungry, it employs behaviors that help it locate and ingest food while suppressing behaviors that are not associated with this goal. Alternatively, when an organism is satiated, food-seeking behaviors are repressed so that the animal can direct itself to other goal-oriented tasks such as reproductive behaviors. Studies in both vertebrate and invertebrate model systems have revealed that food-deprived and -satiated behaviors are differentially executed and integrated via common molecular signaling mechanisms. This article discusses cellular and molecular mechanisms for how insulin, neuropeptide Y (NPY), and serotonin utilize common signaling pathways to integrate feeding and metabolic state with other motivated behaviors. Insulin, NPY, and serotonin are three of the most well-studied molecules implicated in regulating such behaviors. Overall, insulin signaling allows an organism to coordinate proper behavioral output with changes in metabolism, NPY activates behaviors required for locating and ingesting food, and serotonin modulates behaviors performed when an organism is satiated. These three molecules work to ensure that the proper behaviors are executed in response to the feeding state of an organism.

Cutaneous manifestations of internal malignancy: diagnosis and management

An association between systemic malignancy and cutaneous manifestations has long been recognized. The cutaneous features that can occur are numerous and heterogeneous, and many different etiologic mechanisms are represented - from direct tumor invasion of skin or distant metastases to a wide variety of inflammatory dermatoses that may occur as paraneoplastic phenomena. In addition, there are a number of inherited syndromes that carry an increased risk of cutaneous as well as internal malignancies. While some of these inherited syndromes and paraneoplastic phenomena are exceedingly rare, all clinicians will be aware of the common cutaneous manifestations of advanced malignant disease such as generalized xerosis and pruritus. This review classifies these wide-ranging cutaneous manifestations of internal malignancy into five basic groups and provides practical advice regarding diagnosis and screening of patients who initially present with a cutaneous complaint. Also included is up-to-date information on two rapidly expanding and exciting areas of research that are likely to have far-reaching clinical implications: (i) clarification of underlying humoral mechanisms, for example, in the malignant carcinoid syndrome; and (ii) identification of an increasing number of specific genetic defects that confer a susceptibility to malignancy.Increased clinician awareness regarding the associations between these lesions and internal malignancy or inherited syndromes will facilitate screening and early diagnosis.

Long-term serotonin administration leads to higher bone mineral density, affects bone architecture, and leads to higher femoral bone stiffness in rats

New evidence suggests a control of bone mass by the central nervous system. We have previously shown that functional serotonin receptors are present in bone cells and that serotonin stimulates proliferation of osteoblast precursor cells in vitro. In the present study we investigated the effects of serotonin on bone tissue in vivo. Ten, 2-month-old female Sprague-Dawley rats were injected with serotonin subcutaneously (s.c.) (5 mg/kg) once daily for 3 months, controls received saline. Using microdialysis and HPLC, free circulating serotonin levels were measured. DXA scans were made after 3 months of serotonin administration. Bone architecture and mechanical properties were investigated by micro-computed tomography (microCT), histomorphometry, and mechanical testing. A long-lasting hyperserotoninemia with a >10-fold increase in serotonin appeared. Total body BMD was significantly higher (0.1976+/-0.0015 vs. 0.1913+/-0.0012 g/cm2) in rats receiving serotonin. Cortical thickness (Ct.Th) measured by microCT analysis was also higher, whereas trabecular bone volume (BV) was lower. Interestingly, the perimeter and cross-sectional moment of inertia (MOI), a proxy for geometrical bone strength, were the same in both groups. These data suggest that serotonin reduces resorption or/and increases apposition of endosteal bone. Mechanical testing showed that femoral stiffness was higher in serotonin-dosed animals. The energy absorption also seemed slightly, but not significantly higher. In conclusion, hyperserotoninemia led to a higher BMD, altered bone architecture and higher femural bone stiffness in growing rats, demonstrating that serotonin may have important effects on bone in vivo.

Therapeutic Potentials of Sarpogrelate in Cardiovascular Disease*

In view of the pivotal role of serotonin (5-HT) in a wide variety of cardiovascular disorders, extensive effort has been made to develop different types of 5-HT receptor antagonists for therapeutic use. On the basis of experimental studies, this article is focused on the potentials of sarpogrelate, a specific 5-HT2A receptor antagonist as an antiplatelet, antithrombotic, antiatherosclerotic and antianginal agent. The major effects of sarpogrelate are due to the inhibition of 5-HT-induced platelet aggregation and smooth muscle cell proliferation. This agent was found to attenuate the 5-HT-mediated increase in intracellular Ca2+ and ischemia-reperfusion injury in the heart. Sarpogrelate has been found to have beneficial effects in peripheral vascular disease, restenosis after coronary stenting, pulmonary hypertension, acute and chronic myocardial infarction.

The effect of 5-hydroxtryptamine on the regulation of megakaryocytopoiesis

5-Hydroxtryptamine (5-HT, serotonin) has been recognized not only as a neurotransmitter and vasoactive agent, but also as a growth factor. 5-HT mainly binds to 5-HT2 receptors or 5-HT1 receptors on cell surfaces to stimulate cell proliferation through Ras or MAPK (mitogen-activated protein kinase) pathways in many cell types. It has been reported that 5-HT stimulates megakaryocytopoiesis via 5-HT receptors (5-HTR). The possible mechanism by which 5-HT regulates the proliferation and differentiation of megakaryocytes (MK) is discussed in this review article. In early stages of megakaryocytopoiesis, 5-HT may bind to 5-HT2B receptors on MK to promote their proliferation and differentiation. In the late stages, 5-HT may be involved in platelet release by inducing nitric oxide (NO) synthesis via 5-HT2A receptors. 5-HT can also antagonize the apoptotic effect induced by thrombospondin-1 (TSP-1) which is a platelet alpha-granule protein and has synergic effects with platelet-derived growth factor (PDGF) to enhance MK proliferation. Therefore, 5-HT is likely to be an important substance in the feedback regulation of thrombopoiesis.