The relationship between parameters of serotonin metabolism and emetogenic potential of platinum-based chemotherapy regimens

5-Hydroxyindoleacetic acid and substance P profiles in patients receiving emetogenic chemotherapy

Background. Even though direct cause and effect has not been proved, clinical evidence suggests serotonin and substance P (SP) are involved in the emetic response following chemotherapy. Because of several parallels, we hypothesized that SP release, like serotonin, may be propagated by chemotherapy and both substances can be measured in biological fluids, and correlated with a particular phase of emesis.

Methods. Urinary 5-hydroxyindoleacetic acid (5-HIAA) was assessed by HPLC; serum and urine SP were measured by immunoassay. In addition to construction of neurotransmitter profiles, all SP data were grouped according to cisplatin dosages, = or>75 mg/m 2 versus <75 mg/m2, and phase of emesis, acute versus delayed. Analyses of these data were performed by repeated measures analysis of variance.

Results. Samples were collected over a 72-hour period from 26 adult patients who received cisplatin-( n=13) or non-cisplatin-containing ( n=13) chemotherapy. Mean baseline 5-HIAA: creatinine ratios were 5.23 and 5.16 in females and males, respectively; mean baseline SP levels were 392 and 181 pg/mL in females and males, respectively. Comparisons between SP data stratified by cisplatin dosage and emetic phase were significantly different, P <0.0001.

Conclusions. Laboratory studies provide additional evidence that serotonin and SP are involved primarily, though not exclusively, in acute and delayed vomiting, respectively.

Receptor-selective agonists induce emesis and Fos expression in the brain and enteric nervous system of the least shrew (Cryptotis parva)

Research on the mechanisms of emesis has implicated multiple neurotransmitters via both central (dorsal vagal complex) and peripheral (enteric neurons and enterochromaffin cells) anatomical substrates. Taking advantage of advances in receptor-specific agonists, and utilizing Fos expression as a functional activity marker, this study demonstrates a strong, but incomplete, overlap in anatomical substrates for a variety of emetogens. We used cisplatin and specific agonists to 5-HT(3) serotonergic, D(2)/D(3) dopaminergic, and NK(1) tachykininergic receptors to induce vomiting in the least shrew (Cryptotis parva), and quantified the resulting Fos expression. The least shrew is a small mammal whose responses to emetic challenges are very similar to its human counterparts. In all cases, the enteric nervous system, nucleus of the solitary tract, and dorsal motor nucleus of the vagus demonstrated significantly increased Fos immunoreactivity (Fos-IR). However, Fos-IR induction was notably absent from the area postrema following the dopaminergic and NK(1) receptor-specific agents. Two brain nuclei not usually discussed regarding emesis, the dorsal raphe nucleus and paraventricular thalamic nucleus, also demonstrated increased emesis-related Fos-IR. Taken together, these data suggest the dorsal vagal complex is part of a common pathway for a variety of distinct emetogens, but there are central emetic substrates, both medullary and diencephalic, that can be accessed without directly stimulating the area postrema.

Serotonin and GI clinical disorders

Serotonin is widely distributed throughout the gut within both the enteric nerves and enterochromaffin (EC) cells. EC cells are located in the gut mucosa with maximal numbers in the duodenum and rectum where they act as signal transducers, responding to pressure and luminal substances both bacterial and dietary. Activation leads to serotonin release which acts on a range of receptors on mucosal afferent and myenteric interneurones to initiate secretomotor reflexes. These cause nausea and vomiting as well as intestinal secretion, propulsion and if pronounced, diarrhoea. Inflammation in animal models acts via T lymphocytes to increase EC cell numbers and mucosal serotonin (5-HT) content while inflammatory cytokines decrease serotonin transporter (SERT) function. Inflammation due to coeliac disease and following gastrointestinal infection increases mucosal 5-HT availability by a combination of increased EC cells and depressed SERT. Irritable bowel syndrome (IBS) developing after gastrointestinal infection and IBS with diarrhoea is associated with excess 5-HT. The associated diarrhoeal symptoms respond well to 5-HT(3) receptor antagonists. These drugs also inhibit the nausea and vomiting occurring in patients undergoing chemotherapy which cause a marked increase in release of 5-HT as well as other mediators. Other conditions including IBS-C and constipation may have inadequate 5-HT release and benefit from both 5-HT(3) and 5-HT(4) receptor agonists.

5-HT(3)-receptor antagonists in the management of nausea and vomiting in cancer and cancer treatment

The 5-HT(3)-receptor antagonists, considered as 'gold standard' therapy for cancer patients, are generally perceived to have similar efficacy and safety profiles, andmost antiemetic guidelines do not distinguish between agents. However, important pharmacological differences exist between agents, which may translate into potential benefits for some patients. In particular, 5-HT(3)-receptor antagonists vary in the nature of their receptor antagonism and plasma half-lives, possibly leading to differences in duration of action. Agents with a longer duration of action provide antiemetic protection throughout the acute emetic period (24 h) with a single daily dose, whereas shorter-acting agents, e.g. ondansetron, may require multiple dosing for full efficacy. Differences also exist between agents in their hepatic metabolism and cardiovascular safety, which may present particular problems for elderly patients who often receive additional medications for comorbid conditions, increasing the risk of drug-drug interaction. Recent antiemetic guidelines from the National Comprehensive Cancer Network recommend preferential use of palonosetron for moderately emetogenic chemotherapy; however, this agent is newly approved and key clinical questions remain unanswered by clinical trial data. Selection of an appropriate 5-HT(3)-receptor antagonist should be based on proven efficacy and safety, as well as on the individual characteristics of the patient.