Current experience with 5-HT3 receptor antagonists in fibromyalgia

Involvement of peripheral mast cells in a fibromyalgia model in mice

Fibromyalgia is a painful disorder of unknown aetiology that presents activation and recruitment of innate immune cells, including mast cells. Efforts have been made to understand its pathogenesis to manage it better. Thus, we explored the involvement of peripheral mast cells in an experimental model of fibromyalgia induced by reserpine. Reserpine (1 mg/kg) was subcutaneously (s.c.) injected once daily in the back of male Swiss mice for three consecutive days. We analysed mechanical and cold allodynia, muscle fatigue and number of mast cell in plantar tissue. The fibromyalgia induction produced mast cell infiltration (i.e., mastocytosis) in the mice's plantar tissue. The depletion of mast cell mediators with the compound 48/80 (0.5-4 mg/kg, intraperitoneal (i.p.)) or the mast cell membrane stabilizer ketotifen fumarate (10 mg/kg, oral route (p.o.) widely (80-90 %) and extensively (from 1 up to 10 days) prevented reserpine-induced mechanical and cold allodynia and muscle fatigue. Compound 48/80 also prevented the reserpine-induced mastocytosis. Finally, we demonstrated that PAR-2, 5-HT2A, 5-HT3, H1, NK1 and MrgprB2 receptors, expressed in neuronal or mast cells, seem crucial to mediate fibromyalgia-related cardinal symptoms since antagonists or inhibitors of these receptors (gabexate (10 mg/kg, s.c.), ENMD-1068 (10 mg/kg, i.p.), ketanserin (1 mg/kg, i.p.), ondansetron (1 mg/kg, p.o.), promethazine (1 mg/kg, i.p.), and L733,060 (5 mg/kg, s.c.), respectively) transiently reversed the reserpine-induced allodynia and fatigue. The results indicate that mast cells mediate painful and fatigue behaviours in this fibromyalgia model, representing potential therapy targets to treat fibromyalgia syndrome.

Why use nutraceutical strategies for the Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a chronic functional bowel disorder, often stress-related, identified by many abdominal symptoms, the most important of which is the chronic visceral abdominal pain. Therefore, IBS commonly impairs the quality of life of patients, moreover it is frequently linked to depressive and anxiety symptoms. The treatment of IBS primarily focuses on symptoms relief. Unfortunately, up to now, no efficacious therapies have been found. Therefore, it would be important to develop new anti-IBS interventions. The aim of this brief review is to summarize the current evidence of nutraceutical supplementation in IBS treatment, with probiotics, prebiotics, synbiotics, butyrate, palmitoylethanolamide and colostrum. Since nutraceutics are over the counter products, the review has the purpose to better inform the medicinal chemist and the practitioner about the possible benefit mechanisms and the many advantages that these therapies offer. All of these compounds present multiple mechanisms of action, such as restoring the physiological microbiota, potentiating gastrointestinal barrier's function, immunomodulatory, anti-inflammatory and antinociceptive activities. From the literature data it results that these compounds are not only capable to improve IBS symptomatology, but mainly display an optimal safety and tolerability profile. Although extensive studies must be carried out to reinforce the evidences from the so far limited clinical trials, the supplementation with these compounds may be useful considering the warnings of prescription medicines for special populations of patients, such as elders, youngsters, or patients who need a combination therapy. Finally, the nutraceutical approach may improve adherence to treatment, given its better acceptance by the patients compared to pharmacological therapy.

Implications of palonosetron in elderly patients undergoing laparoscopic cholecystectomy with respect to its anti-shivering effect

BACKGROUND

The elderly are vulnerable to hypothermia and have a higher risk of cardiovascular events induced by marked increases in oxygen consumption due to shivering. Five-hydroxytryptamine-3 (5-HT3) receptor antagonists have been previously reported to reduce post-anesthesia shivering.

AIM

In the present study, the authors investigated the effects of palonosetron, a new-generation 5-HT3 antagonist, on core hypothermia and the incidence of shivering after laparoscopic cholecystectomy in elderly patients.

METHODS

Forty-eight patients (65-80 years) were randomly assigned to one of two groups and administered palonosetron 0.075 mg (palonosetron group, n = 24) or the same volume of normal saline (control group, n = 24) before anesthesia induction. Core body temperatures and hemodynamic variables were monitored during and after operation. Post-anesthetic shivering (PAS) and pain scores were obtained in a post-anesthetic care unit.

RESULTS

Intraoperative esophageal temperature changed significantly over time (P = 0.010), but significant intergroup difference in change was not observed (P = 0.706). Furthermore, shivering frequencies were similar in the two groups (P = 0.610). However, postoperative pain scores at 30 min after entering the post-anesthesia care unit were significantly lower in the palonosetron group (P = 0.002).

DISCUSSION

Regardless of the previously reported anti-shivering effect of 5-HT3 receptor antagonists, pre-operative palonosetron 0.075 mg did not influence perioperative hypothermia or PAS in this study. This discrepancy might be due to the dose responsiveness of palonosetron to PAS and relatively low incidence of PAS in the elderly.

CONCLUSIONS

Pre-operative administration of palonosetron 0.075 mg did not influence perioperative hypothermia or post-anesthesia shivering in elderly patients undergoing laparoscopic cholecystectomy. However, palonosetron might be beneficial for reducing early postoperative pain in elderly patients with opioid-based patient-controlled analgesia.

Role of 5-HT3 Receptors in the Antidepressant Response

Serotonin (5-HT)₃ receptors are the only ligand-gated ion channel of the 5-HT receptors family. They are present both in the peripheral and central nervous system and are localized in several areas involved in mood regulation (e.g., hippocampus or prefrontal cortex). Moreover, they are involved in regulation of neurotransmitter systems implicated in the pathophysiology of major depression (e.g., dopamine or GABA). Clinical and preclinical studies have suggested that 5-HT₃ receptors may be a relevant target in the treatment of affective disorders. 5-HT₃ receptor agonists seem to counteract the effects of antidepressants in non-clinical models, whereas 5-HT₃ receptor antagonists, such as ondansetron, present antidepressant-like activities. In addition, several antidepressants, such as mirtazapine, also target 5-HT₃ receptors. In this review, we will report major advances in the research of 5-HT₃ receptor's roles in neuropsychiatric disorders, with special emphasis on mood and anxiety disorders.

Efficacy and tolerability of intravenous tropisetron in the treatment of fibromyalgia

OBJECTIVE

To determine the efficacy of a serotonin receptor (5-HT(3)) antagonist in the treatment of fibromyalgia (FM) in a prospective, randomized, double-blind, placebo-controlled, multicentre trial.

METHODS

Twenty-one female patients (age 21-63 years) with FM according to the American College of Rheumatology classification criteria for FM were assigned randomly to either a placebo group or to receive a daily intravenous bolus injection of 5 mg tropisetron for 5 days.

RESULTS

In patients receiving tropisetron, the visual analogue scale (VAS) score for pain decreased by 28.9 compared with a decrease of 6.8 in the placebo group [probability (p)=0.063; effect size: 0.794]. Similar results were obtained using a body diagram pain score as a secondary efficacy parameter: mean pain reduction was 27.2 in the tropisetron group, versus 2.8 in the placebo group (p=0.038; effect size: 0.902).

CONCLUSION

5-HT(3) receptor antagonists provide significant pain relief for a group of FM patients.

Pharmacological and electrophysiological properties of the naturally occurring Pro391Arg variant of the human 5-HT3A receptor

The 5-HT3A receptor, a ligand-gated ion channel, is involved in pain pathways, nausea and emesis, and irritable bowel syndrome, and may play a role in the pathogenesis of psychiatric diseases such as schizophrenia and depression. Recently, a naturally occurring variation (ProArg) in the second intracellular loop of the human (h) 5-HT3A receptor was identified in a schizophrenic patient. Because the substitution of proline, an alpha-imino acid, by arginine may affect the conformation of the whole receptor, the aim of the present study was to determine the pharmacological and functional properties of this variant compared to the wild-type receptor in stably transfected HEK293 cells. Studies of binding of [H]GR65630, a 5-HT3 receptor antagonist, to membranes (saturation and competition experiments with 5-HT3 receptor ligands) and patch-clamp studies of agonist-induced currents in outside-out patches were carried out. In comparison to the wild-type, the variant receptor exhibited no changes in the receptor density and the affinities for nine representative ligands (five agonists and four antagonists). The potencies and efficacies of three 5-HT3 receptor agonists in inducing currents through the ion channel and the potencies of two 5-HT3 receptor antagonists in blocking 5-HT-evoked currents did not differ between wild-type and variant receptors. In addition, there were no differences in the desensitization kinetics of both receptor isoforms. In conclusion, the ArgPro variation of the h5-HT3A receptor does not change ligand binding to the h5-HT3A receptor, nor does it modify current through the receptor channel.

Multifocal electroretinography evaluation for early detection of retinal dysfunction in patients taking hydroxychloroquine

PURPOSE

To evaluate macular function using multifocal electroretinography (mfERG) in a cohort of asymptomatic patients taking hydroxychloroquine and a patient with maculopathy secondary to hydroxychloroquine treatment.

METHODS

mfERG recordings were obtained for both eyes of 11 patients taking hydroxychloroquine without clinical signs of toxicity and 1 patient with toxic maculopathy. Initially, the classic m-sequence paradigm for the first-order kernel (103 hexagons; 2.7 candela x seconds/m2 peak luminance) was recorded. After that, another special stimulation mode was applied, which emphasized second-order adaptational effects (modulated multifocal flashes with interleaved global flashes, MF0F0 paradigm).

RESULTS

The patient with toxic maculopathy and one patient without toxicity had multiple areas of decreased retinal responses bilaterally (classic m-sequence). The patient with toxicity and another three patients without toxicity presented with multiple areas of decreased retinal function in both eyes with the second-order component of the MF0F0 paradigm. Repeated recordings of 1 patient 8 months after the initial recording demonstrated evidence for reproducibility of the second-order adaptive effects.

CONCLUSION

Clinically asymptomatic patients receiving hydroxychloroquine treatment can have substantial local decreases in their retinal function, as reflected by the changes in mfERG recordings, possibly indicating a preclinical stage of drug-related toxicity.

Management of fibromyalgia

Fibromyalgia is characterized by widespread pain, persistent fatigue, nonrestorative sleep, and generalized morning stiffness. The diagnosis is based on patients' reports of pain and fatigue, clinical findings of multiple tender points, and exclusion of a range of connective tissue and other medical disorders. Treatment of fibromyalgia is multidisciplinary with an emphasis on active patient participation, medications, cognitive behavioral therapy, and physical modalities. No single medication has been found to effectively control all the symptoms, and a rational combination of different medications is often necessary. Currently available medication classes include the selective serotonin uptake inhibitors, the serotonin and norepinephrine reuptake inhibitors, tricyclic antidepressants, analgesics, hypnotic agents, and anticonvulsants. Treatment modalities should be individualized for patients based on target symptoms and impairment in functioning. As is the case with several chronic disorders, the treatment is often prolonged and improvement may occur slowly. Patience and positive attitude on part of the physician and active involvement of patients and their families in treatment are likely to enhance improvement.