Serotonin Receptors as a Potential Target in the Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia worldwide that has an increasing impact on aging societies. Besides its critical role in the control of various physiological functions and behavior, brain serotonin (5-HT) system is involved in the regulation of migration, proliferation, differentiation, maturation, and programmed death of neurons. At the same time, a growing body of evidence indicates the involvement of 5-HT neurotransmission in the formation of insoluble aggregates of β-amyloid and tau protein, the main histopathological signs of AD. The review describes the role of various 5-HT receptors and intracellular signaling cascades induced by them in the pathological processes leading to the development of AD, first of all, in protein aggregation. Changes in the functioning of certain types of 5-HT receptors or associated intracellular signaling mediators prevent accumulation of β-amyloid plaques and tau protein neurofibrillary tangles. Based on the experimental data, it can be suggested that the use of 5-HT receptors as new drug targets will not only improve cognitive performance in AD, but will be also important in treating the causes of AD-related dementia.

Atypical antipsychotic use and mortality risk in Parkinson disease

INTRODUCTION

Dopamine receptor blocking atypical antipsychotic (DRB-AAP) use has previously been associated with increased adverse effects and mortality risk among persons with Parkinson disease (PD). Pimavanserin, the only AAP indicated for PD psychosis in the U.S., is a serotonin receptor inverse agonist/antagonist with no known DRB activity. Early observational data have reported inconsistent findings regarding mortality risk associated with pimavanserin. The objective of this study was to estimate all-cause mortality risks of pimavanserin as compared to DRB-AAPs.

METHODS

We conducted a retrospective cohort study using a large U.S. commercial insurance database. Cox proportional hazards models were used to compare all-cause mortality risks between propensity score-matched groups of PD patients who were new users of pimavanserin or a DRB-AAP, further dividing DRB-AAPs into preferred (quetiapine, clozapine) and non-preferred (other remaining AAPs).

RESULTS

We identified 775, 4,563, and 1,297 individuals on pimavanserin, preferred, and non-preferred DRB-AAPs, respectively. There was no difference in mortality risk for pimavanserin vs. preferred DRB-AAPs [adjusted hazard ratio (aHR) 0.99, 95% CI: 0.81-1.20], or pimavanserin vs. non-preferred DRB-AAPs (aHR 0.98, 95% CI: 0.79-1.22) in intention-to-treat analyses.

CONCLUSION

Mortality risk among PD patients using AAPs did not differ by antipsychotic drug categorization based on mechanism of action. Research on the comparative efficacy and morbidity of AAPs, and the mortality associated with psychosis itself is needed to guide clinical decision-making in the PD population.

The influence of the 5‐HT3receptor antagonist tropisetron on pain in fibromyalgia: a functional magnetic resonance imaging pilot study

OBJECTIVE

Central pain processing is altered in patients with fibromyalgia syndrome (FMS). The serotonin metabolism, especially the 5-HT3 receptor, seems to play an important role.

METHODS

We investigated the effect of the local injection of the 5-HT3 receptor antagonist tropisetron on the perception and central processing of pain in FMS patients using painful mechanical stimulation and functional magnetic resonance imaging (fMRI) within the framework of a pre-/posttreatment double-blind design.

RESULTS

In the contralateral primary somatosensory cortex, contralateral posterior insula, and anterior cingulate cortex, we found that the activation was significantly reduced after treatment. On average, patients rated the stimulation-induced pain intensity as stronger in the session after treatment compared to before treatment, although the individual data revealed a heterogeneous pattern. All patients showed sensitisation during the painful stimulation, which was not influenced by the treatment.

CONCLUSIONS

Both the sensory-discriminative and motivational-affective components of pain as measured by fMRI were altered by tropisetron.

Tender points as predictors of distress and the pharmacologic management of fibromyalgia syndrome

The object of this study was to determine the association between tender point pain ratings, tender point counts and distress in people with fibromyalgia and to review the pharmacotherapy of fibromyalgia. Demographic, psychosocial, and health status information was collected from 316 health maintenance organization members with fibromyalgia. A manual tender point exam was conducted. Tender point counts predicted 3.0%, and tender point severity ratings predicted 8.3%, of the variance in distress. Little difference was found between the variance predicted for physical versus psychologic distress. A principal components analysis of all measures produced four distinct factors: global-physical functioning, tender points, psychologic, and physical. Tender point pain ratings and counts predicted a small but significant amount of variance in distress. In addition, FMS involves at least four rather distinct factors, one of which is related to tender points. Pharmacotherapeutic management is provided on a patient-specific basis including pharmacokinetics, pharmacodynamic, pathophysiologic, and psychosocial needs designed and modulated for each individual patient.

[Prevention of side reactions--present status and problems--special references]

The toxicity of chemotherapy affects adversely the QOL of patients and limits the dose of chemotherapy that can be administered. In the last decade, several agents have been developed that offer possible reduction from the toxicity of a range of anticancer agents. Clinical trials to evaluate these agents are intrinsically more difficult to perform. Standardized assessment and management of chemotherapy-induced toxicities have been required to control these adverse events. Recently, practice guidelines are systematically developed statements to assist the practitioner and patients decision about appropriate management for specific clinical circumstances. Guidelines may be useful in producing better care and decreasing cost. Further clinical research is warranted to address significant questions about the most effective way to assess and treat these adverse events. However, it is important to realize that guidelines cannot always account for individual variation among patients. They are not intended to supplant physician judgment with respect to particular patients or special clinical situations. Dr. Rothenberg stated in his recent special article titled "Mortality associated with irinotecan plus bolus fluorouracil/leucovorin: summary findings of an independent panel" (J Clin Oncol 19: 3801-3807, 2001) that "Close clinical monitoring, early recognition of toxicities and toxicity syndromes, aggressive therapeutic interventions, and with holding therapy in the presence of unsolved drug-related toxicities is recommended for patients receiving intensive chemotherapy regimens".

Management of irritable bowel syndrome: novel approaches to the pharmacology of gut motility

Although it is unclear to what extent irritable bowel syndrome (IBS) symptoms represent a normal perception of abnormal function or an abnormal perception of normal function, many believe that IBS constitutes the clinical expression of an underlying motility disorder, affecting primarily the mid- and lower gut. Indeed, transit and contractile abnormalities have been demonstrated with sophisticated techniques in a subset of patients with IBS. As a consequence, drugs affecting gastrointestinal (GI) motility have been widely employed with the aim of correcting the major IBS manifestations, ie, pain and altered bowel function. Unfortunately, no single drug has proven to be effective in treating IBS symptom complex. In addition, the use of some medications has often been associated with unpleasant side effects. Therefore, the search for a truly effective and safe drug to control motility disturbances in IBS continues. Several classes of drugs look promising and are under evaluation. Among the motor-inhibiting drugs, gut selective muscarinic antagonists (such as zamifenacin and darifenacin), neurokinin2 antagonists (such as MEN-10627 and MEN-11420), beta3-adrenoreceptor agonists (eg, SR-58611A) and GI-selective calcium channel blockers (eg, pinaverium bromide and octylonium) are able to decrease painful contractile activity in the gut (antispasmodic effect), without significantly affecting other body functions. Novel mechanisms to stimulate GI motility and transit include blockade of cholecystokinin (CCK)A receptors and stimulation of motilin receptors. Loxiglumide (and its dextroisomer, dexloxiglumide) is the only CCKA receptor antagonist that is being evaluated clinically. This drug accelerates gastric emptying and colonic transit, thereby increasing the number of bowel movements in patients with chronic constipation. It is also able to reduce visceral perception. Erythromycin and related 14-member macrolide compounds inhibit the binding of motilin to its receptors on GI smooth muscle and, therefore, act as motilin agonists. This antibiotic accelerates gastric emptying and shortens orocecal transit time. In the large bowel a significant decrease in transit is observed only in the right colon, which suggests a shift in fecal distribution. Several 'motilinomimetics' have been synthesized. Their development depends on the lack of antimicrobial activity and the absence of fading of the prokinetic effect during prolonged administration. 5-hydroxytryptamine (5-HT)4 agonists with significant pharmacological effects on the mid- and distal gut (such as prucalopride and tegaserod) are available for human use. These 'enterokinetic' compounds are useful for treating constipation-predominant IBS patients. 5-HT3 receptor antagonists also possess a number of interesting pharmacological properties that may make them suitable for treatment of IBS. Besides decreasing colonic sensitivity to distension, these drugs prolong intestinal transit and may be particularly useful in diarrhea-predominant IBS. Finally, when administered in small pulsed doses, octreotide, besides reducing the perception of rectal distension, accelerates intestinal transit, although other evidence disputes such an effect.

[Palliative therapy in cancer. 5. Side effects by anticancer drugs and their treatments]

Many chemotherapeutic agents have been evaluated during the last 40 years and some have now an established place in the management of malignant disease. However these agents have a level of toxicity well above any other group of drugs. Chemotherapeutic agents do not discriminate between normal and neoplastic tissue. Chemotherapeutic regimens that are toxic to rapidly dividing malignant cells, are liable to be particularly harmful to lymphoid tissues, bone marrow and the epithelium of the gastrointestinal tract. The side effects due to chemotherapy are classified as immediate, early, delayed and late. Immediate side effects are those that may occur within the first 24 hours of treatment. The most common immediate side effect is nausea and vomiting, due to direct central effect on the vomiting center of the brain. Cisplatin and nitrogen mustard are particularly prone to this complication. The antiemetics usually used are metoclopramide, domperidone and steroid. The efficacies of these drugs are not so good for nausea and vomiting due to cisplatin administration, however several blockades against serotonin M-receptor recently developed are quite effective to nausea and vomiting of chemotherapeutic regimens including cisplatin. Early side effects commence within about one month of therapy. The most common is bone marrow toxicity and can occur after therapy with the vast majority of anticancer drugs. The relative importance of leukopenia and thrombocytopenia vary between the drugs and their route of administration. Recently, hematopoietic cytokines, such as granulocyte-colony stimulating factor (G-CSF) and granulocyte-macrophage-colony stimulating factor (GM-CSP) have been introduced to granulocytopenia developed by cancer chemotherapy. In the phase II study of G-CSF, a rapid recovery of granulocytes after chemotherapy and marked efficacy on infection in granulocytopenic patients were observed. In addition to this, autologous bone marrow transplantation after chemotherapy has been described in patients with solid tumors.

Dose ranging phase I study of the serotonin antagonist GR38032F for prevention of cisplatin-induced nausea and vomiting

GR38032F is a specific 5-HT3 (serotonin) receptor antagonist with antiemetic activity in animal and early human studies. We performed a dose-ranging phase I study of GR38032F in 43 evaluable patients receiving cisplatin 60 120 mg/m2 for the first time (38 of these patients were chemotherapy-naive). Intravenous GR38032F was administered over a dose range from 0.01 to 0.48 mg/kg given three times at four-hour intervals beginning one half hour before cisplatin, and patients were observed for 24 hours. An additional five patients were treated with 0.18 mg/kg given three times at six-hour intervals. Excellent antiemetic efficacy was noted, with 44% of patients experiencing no vomiting and 26% no nausea. Major protection from vomiting (less than or equal to 2 episodes) and from nausea (less than or equal to 2 hours) was experienced by 81% and 44%, respectively. Mild to moderate headache (40%), lightheadedness (21%), and elevated transaminase (19%) were the most common adverse events reported. One patient experienced an apparent hypersensitivity reaction that responded to conventional medications. No extrapyramidal reactions or akathisia were seen. GR38032F was effective through most of the dose range. However, efficacy decreased at the 0.01 mg/kg level and number and intensity of adverse events increased at the 0.48 mg/kg level. Analysis of those patients receiving high-dose cisplatin (100 to 120 mg/m2) revealed a positive association of GR38032F dose and antiemetic activity (Fisher's exact test, two-sided; P less than .05). The 5-HT3 receptor antagonists may provide antiemetic efficacy similar to high-dose metoclopramide without antidopaminergic toxicity. The maximum recommended dose on this schedule of GR38032F is 0.36 mg/kg.