Cyclophosphamide causes activation of protein kinase A (PKA) in the brainstem of vomiting least shrews (Cryptotis parva)

A Comparative Study of the Antiemetic Effects of α2-Adrenergic Receptor Agonists Clonidine and Dexmedetomidine against Diverse Emetogens in the Least Shrew (Cryptotis parva) Model of Emesis

In contrast to cats and dogs, here we report that the α2-adrenergic receptor antagonist yohimbine is emetic and corresponding agonists clonidine and dexmedetomidine behave as antiemetics in the least shrew model of vomiting. Yohimbine (0, 0.5, 0.75, 1, 1.5, 2, and 3 mg/kg, i.p.) caused vomiting in shrews in a bell-shaped and dose-dependent manner, with a maximum frequency (0.85 ± 0.22) at 1 mg/kg, which was accompanied by a key central contribution as indicated by increased expression of c-fos, serotonin and substance P release in the shrew brainstem emetic nuclei. Our comparative study in shrews demonstrates that clonidine (0, 0.1, 1, 5, and 10 mg/kg, i.p.) and dexmedetomidine (0, 0.01, 0.05, and 0.1 mg/kg, i.p.) not only suppress yohimbine (1 mg/kg, i.p.)-evoked vomiting in a dose-dependent manner, but also display broad-spectrum antiemetic effects against diverse well-known emetogens, including 2-Methyl-5-HT, GR73632, McN-A-343, quinpirole, FPL64176, SR141716A, thapsigargin, rolipram, and ZD7288. The antiemetic inhibitory ID50 values of dexmedetomidine against the evoked emetogens are much lower than those of clonidine. At its antiemetic doses, clonidine decreased shrews' locomotor activity parameters (distance moved and rearing), whereas dexmedetomidine did not do so. The results suggest that dexmedetomidine represents a better candidate for antiemetic potential with advantages over clonidine.

RNA sequencing least shrew (Cryptotis parva) brainstem and gut transcripts following administration of a selective substance P neurokinin NK1 receptor agonist and antagonist expands genomics resources for emesis research

The least shrew is among the subset of animals that are capable of vomiting and therefore serves as a valuable research model for investigating the biochemistry, molecular biology, pharmacology, and genomics of emesis. Both nausea and vomiting are associated with a variety of illnesses (bacterial/viral infections, bulimia, exposure to toxins, gall bladder disease), conditions (pregnancy, motion sickness, emotional stress, overeating) and reactions to drugs (chemotherapeutics, opiates). The severe discomfort and intense fear associated with the stressful symptoms of nausea and emesis are the major reason for patient non-compliance when being treated with cancer chemotherapeutics. Increased understanding of the physiology, pharmacology and pathophysiology underlying vomiting and nausea can accelerate progress for developing new antiemetics. As a major animal model for emesis, expanding genomic knowledge associated with emesis in the least shrew will further enhance the laboratory utility of this model. A key question is which genes mediate emesis, and are they expressed in response to emetics/antiemetics. To elucidate the mediators of emesis, in particular emetic receptors, their downstream signaling pathways, as well as the shared emetic signals, we carried out an RNA sequencing study focused on the central and peripheral emetic loci, the brainstem and gut. Thus, we sequenced RNA extracted from brainstem and gut tissues from different groups of least shrews treated with either a neurokinin NK1 receptor selective emetic agonist, GR73632 (5 mg/kg, i.p.), its corresponding selective antagonist netupitant (5 mg/kg, i.p.), a combination of these two agents, versus their corresponding vehicle-pretreated controls and drug naïve animals. The resulting sequences were processed using a de novo transcriptome assembly and used it to identify orthologs within human, dog, mouse, and ferret gene sets. We compared the least shrew to human and a veterinary species (dog) that may be treated with vomit-inducing chemotherapeutics, and the ferret, another well-established model organism for emesis research. The mouse was included because it does not vomit. In total, we identified a final set of 16,720 least shrew orthologs. We employed comparative genomics analyses as well as gene ontology enrichment, KEGG pathway enrichment and phenotype enrichment to better understand the molecular biology of genes implicated in vomiting.

Mechanisms of Nausea and Vomiting: Current Knowledge and Recent Advances in Intracellular Emetic Signaling Systems

Nausea and vomiting are common gastrointestinal complaints that can be triggered by diverse emetic stimuli through central and/or peripheral nervous systems. Both nausea and vomiting are considered as defense mechanisms when threatening toxins/drugs/bacteria/viruses/fungi enter the body either via the enteral (e.g., the gastrointestinal tract) or parenteral routes, including the blood, skin, and respiratory systems. While vomiting is the act of forceful removal of gastrointestinal contents, nausea is believed to be a subjective sensation that is more difficult to study in nonhuman species. In this review, the authors discuss the anatomical structures, neurotransmitters/mediators, and corresponding receptors, as well as intracellular emetic signaling pathways involved in the processes of nausea and vomiting in diverse animal models as well as humans. While blockade of emetic receptors in the prevention of vomiting is fairly well understood, the potential of new classes of antiemetics altering postreceptor signal transduction mechanisms is currently evolving, which is also reviewed. Finally, future directions within the field will be discussed in terms of important questions that remain to be resolved and advances in technology that may help provide potential answers.

Dopamine receptors in emesis: Molecular mechanisms and potential therapeutic function

Dopamine is a member of the catecholamine family and is associated with multiple physiological functions. Together with its five receptor subtypes, dopamine is closely linked to neurological disorders such as schizophrenia, Parkinson's disease, depression, attention deficit-hyperactivity, and restless leg syndrome. Unfortunately, several dopamine receptor-based agonists used to treat some of these diseases cause nausea and vomiting as impending side-effects. The high degree of cross interactions of dopamine receptor ligands with many other targets including G-protein coupled receptors, transporters, enzymes, and ion-channels, add to the complexity of discovering new targets for the treatment of nausea and vomiting. Using activation status of signaling cascades as mechanism-based biomarkers to foresee drug sensitivity combined with the development of dopamine receptor-based biased agonists may hold great promise and seems as the next step in drug development for the treatment of such multifactorial diseases. In this review, we update the present knowledge on dopamine and dopamine receptors and their potential roles in nausea and vomiting. The pre- and clinical evidence provided in this review supports the implication of both dopamine and dopamine receptor agonists in the incidence of emesis. Besides the conventional dopaminergic antiemetic drugs, potential novel antiemetic targeting emetic protein signaling cascades may offer superior selectivity profile and potency.

Protective action of N-acetylcysteine on sperm quality in cyclophosphamide-induced testicular toxicity in male Wistar rats

Background:

Reductions in sperm quality due to free radical formation during cancer chemotherapy are well documented, hence the need for an adjunct antioxidant treatment during chemotherapy. This study was designed to investigate the effects of N-acetylcysteine on sperm quality following cyclophosphamide exposure in male Wistar rats.

Methods:

Twenty male Wistar rats weighing 150-170g were randomly assigned into 4 groups of five rats each, and were orally administered distilled water (Control), Cyclophosphamide (6mg/kg), N-acetylcysteine (100mg/kg) or Cyclophosphamide + N-acetylcysteine for 21 days. Sperm count, histone-protamine replacement, chromatin integrity, testicular histomorphometry and BAX Protein expression were assessed using standard procedures. The data was presented as mean ± SEM and analyzed using students' t- test. A p<0.05 was considered significant.

Results:

Sperm counts were significantly reduced (p<0.05) among the cyclophosphamide (69.95±7.78 x10⁶/ml) and cyclophosphamide + N-acetylcysteine (64.78±3.52 x10⁶/ml) treated rats, while it increased significantly (p<0.05) in the N-acetylcysteine (132.20±28.71 x10⁶/ml) treated rats compared to the control animals (115.30±8.70x10⁶/ml). Increased interstitial space distance, degenerated Leydig cells and impaired histone-protamine replacement observed among the cyclophosphamide-treated rats were ameliorated in the cyclophosphamide + N-acetylcysteine-treated rats. Sperm chromatin integrity, which was poor in the cyclophosphamide-treated rats, was considerably improved when compared with the Control and the N-acetylcysteine-treated rats. Bax protein expression was reduced in the cyclophosphamide (20%) and cyclophosphamide+N-acetylcysteine (20%) groups when compared with the Control (50%) and N-acetylcysteine (50%) groups.

Conclusion:

We concluded that N-acetylcysteine might improve sperm histone protamine replacement, which is one of the stage-specific effect of cyclophosphamide toxicity.

Comparison between Antiemetic Effects of Palonosetron and Granisetron on Chemotherapy-Induced Nausea and Vomiting in Japanese Patients Treated with R-CHOP

In the present study, the antiemetic effect of palonosetron, not combined with dexamethasone and aprepitant, on chemotherapy-induced nausea and vomiting was evaluated in patients with malignant lymphoma receiving first-line rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) therapy, and was compared to that of granisetron. A total of 74 patients with non-Hodgkin lymphoma were included in this study (April 2007 to December 2015). Palonosetron (0.75 mg) or granisetron (3 mg) was intravenously administered before R-CHOP therapy. The proportions of patients with complete response (CR) during the overall (0-120 h after the start of R-CHOP therapy), acute (0-24 h) and delayed (24-120 h) phases were evaluated. CR was defined as no vomiting and no use of antiemetic rescue medication. A total of 32 and 42 patients were treated with palonosetron and granisetron, respectively. The CR rate in the palonosetron group was significantly higher than that in the granisetron group during the delayed phase (90.6 and 61.9%, respectively; p=0.007). Logistic regression analysis showed that use of palonosetron improved the CR rate during the delayed phase, compared to use of granisetron. Female sex, age less than 60 years, no habitual alcohol intake, and Eastern Cooperative Oncology Group performance status (ECOG-PS) score of 1 were significant risk factors associated with non-CR. The findings of this study suggested the superiority of palonosetron to granisetron, without accompanying dexamethasone and aprepitant, for chemotherapy-induced nausea and vomiting in patients with malignant lymphoma.

Differential and additive suppressive effects of 5-HT3 (palonosetron)- and NK1 (netupitant)-receptor antagonists on cisplatin-induced vomiting and ERK1/2, PKA and PKC activation

To better understand the anti-emetic profile of the 5-HT3 (palonosetron)- and the tachykinin NK1 (netupitant) -receptor antagonists, either alone or in combination, we evaluated the effects of palonosetron and/or netupitant pretreatment on cisplatin-evoked vomiting and changes in the phosphorylation of brainstem kinases such as the extracellular signal-regulated protein kinases 1 and 2 (ERK1/2), protein kinase C alpha/beta (PKCα/β), and protein kinase A (PKA) in the least shrew. Our results demonstrate that cisplatin (10mg/kg, i.p.) causes emesis in the least shrew over 40h with respective peak early- and delayed-phases occurring at 1 - 2 and 32 - 34h post-injection. During the early phase (0 - 16h post cisplatin), palonosetron (0.1mg/kg, s.c.) significantly protected shrews from vomiting with a near complete suppression of vomit frequency. Palonosetron also significantly protected shrews from vomiting during the delayed phase (27 - 40h post cisplatin), but the reduction in mean vomit frequency failed to achieve significance. On the other hand, netupitant (5mg/kg, i.p.) totally abolished vomiting during the delayed phase, and tended to suppress the mean vomit frequency during the acute phase. The combined treatment protected shrews almost completely from vomiting during both phases. Brainstem pERK1/2 levels were significantly elevated at all time-points except at 40h post-cisplatin administration. PKA phosphorylation tended to be elevated throughout the delayed phase, but a significant increase only occurred at 33h. Brainstem pPKCα/β levels were enhanced during acute-phase with a significant elevation at 2h. Palonosetron, netupitant or their combination had no effect on elevated pERK1/2 levels during acute phase, but the combination reversed ERK1/2 phosphorylation at 33h post-cisplatin treatment. In addition, only the combined regimen prevented the cisplatin-induced PKCα/β phosphorylation observed at the acute phase. On the other hand, palonosetron and netupitant, either alone or in combination, were effective in reducing the induced elevated pPKA levels during the delayed phase. These effects on cisplatin-related emetic signals downstream of 5-HT3- and NK1-receptors help us to better understand the intracellular basis of cisplatin-induced vomiting.

Serotonin 5-HT3 receptor-mediated vomiting occurs via the activation of Ca2+/CaMKII-dependent ERK1/2 signaling in the least shrew (Cryptotis parva)

Stimulation of 5-HT₃ receptors (5-HT₃Rs) by 2-methylserotonin (2-Me-5-HT), a selective 5-HT₃ receptor agonist, can induce vomiting. However, downstream signaling pathways for the induced emesis remain unknown. The 5-HT₃R channel has high permeability to extracellular calcium (Ca²⁺) and upon stimulation allows increased Ca²⁺ influx. We examined the contribution of Ca²⁺/calmodulin-dependent protein kinase IIα (Ca²⁺/CaMKIIα), interaction of 5-HT₃R with calmodulin, and extracellular signal-regulated kinase 1/2 (ERK1/2) signaling to 2-Me-5-HT-induced emesis in the least shrew. Using fluo-4 AM dye, we found that 2-Me-5-HT augments intracellular Ca²⁺ levels in brainstem slices and that the selective 5-HT₃R antagonist palonosetron, can abolish the induced Ca²⁺ signaling. Pre-treatment of shrews with either: i) amlodipine, an antagonist of L-type Ca²⁺ channels present on the cell membrane; ii) dantrolene, an inhibitor of ryanodine receptors (RyRs) Ca²⁺-release channels located on the endoplasmic reticulum (ER); iii) a combination of their less-effective doses; or iv) inhibitors of CaMKII (KN93) and ERK1/2 (PD98059); dose-dependently suppressed emesis caused by 2-Me-5-HT. Administration of 2-Me-5-HT also significantly: i) enhanced the interaction of 5-HT₃R with calmodulin in the brainstem as revealed by immunoprecipitation, as well as their colocalization in the area postrema (brainstem) and small intestine by immunohistochemistry; and ii) activated CaMKIIα in brainstem and in isolated enterochromaffin cells of the small intestine as shown by Western blot and immunocytochemistry. These effects were suppressed by palonosetron. 2-Me-5-HT also activated ERK1/2 in brainstem, which was abrogated by palonosetron, KN93, PD98059, amlodipine, dantrolene, or a combination of amlodipine plus dantrolene. However, blockade of ER inositol-1, 4, 5-triphosphate receptors by 2-APB, had no significant effect on the discussed behavioral and biochemical parameters. This study demonstrates that Ca²⁺ mobilization via extracellular Ca²⁺ influx through 5-HT₃Rs/L-type Ca²⁺ channels, and intracellular Ca²⁺ release via RyRs on ER, initiate Ca²⁺-dependent sequential activation of CaMKIIα and ERK1/2, which contribute to the 5-HT₃R-mediated, 2-Me-5-HT-evoked emesis.