*4.5.1. The role of cAMP-PKA in vomiting*

and palonosetron, respectively) are combined [45], the combination significantly and in an additive manner attenuate both the frequency and the percentage of shrews vomiting in response to either FPL 64176 or 2-Methyl-5-HT. Furthermore, although nifedipine alone up to 20 mg/kg dose failed to protect shrews from acute cisplatin-induced vomiting, its 0.5 mg/kg dose, significantly potentiated the antiemetic efficacy of a non-effective (0.025 mg/kg) as well as a semi-effective (0.5 mg/kg) dose of palonosetron. In another study we also utilized a combination of non-effective doses of amlodipine (0.5 mg/kg or 1 mg/kg) with a non- or semi-

antiemetic doses produced a similar additive efficacy against vomiting induced by either FPL 64176 or cisplatin. In fact relative to each antagonist alone, the combination was at least 4 times more potent in reducing the vomit frequency and provided more protection against FPL 64176-induced vomiting. The observed additive antiemetic efficacy of a combination of

a combination should provide greater emesis protection in cancer patients receiving chemo-

both in the laboratory [144, 147] and in the clinic [148]. Although in our investigation, the mechanism underlying the additive antiemetic efficacy of combined low doses of LTCC

There are several published clinical case reports that demonstrate Ca2+ channel blockers may provide protection against several causes of nausea and vomiting. The LTCC antagonist flunarizine (**Figure 2**) was shown to reduce cyclic vomiting on acute basis in one patient [151] and prophylactically in 8 other patients [152]. Gabapentin is a gamma-aminobutyric acid (GABA) analog and is predominantly used in the clinic for the management of pain [3]. Gabapentin binds to the alpha-2/delta auxiliary subunits of voltage-gated Ca2+ channels (VGCCs) (i.e., LTCCs), and exerts inhibitory actions on trafficking and activation kinetics of VGCCs [153] (**Figure 2**). Moreover, several other reports indicate that gabapentin can also be used as a well-tolerated, less-expensive and promising anti-nausea and antiemetic agent in diverse conditions including: postoperative nausea and vomiting [154, 155], moderately or highly emetogenic chemotherapy-induced nausea and vomiting, particularly effective against delayed chemotherapy-induced nausea and vomiting [156], and both acute and delayed nausea induced by chemotherapy [157], as well as hyperemesis gravidarum [158]. When combined with dexamethasone, gabapentin can also significantly reduce the 24-h incidence of postoperative nausea and vomiting [159]. Alpha-2/delta subunits of VGCCs control transmitter release and further facilitate excitatory transmission [153]. Gabapentin's interaction with neuronal alpha-2/delta subunits of VGCCs and subsequent downregulation of neuronal Ca2+ signaling in emesis relevant sites, such as the dorsal vagal complex, is postulated to play a

to their interaction at the signal transduction level involving Ca2+ [20, 149, 150].

**4.3. Clinical use of LTCC blockers as anti-nausea/antiemetic medication**

R antagonist palonosetron (0.05 or 0.5 mg/kg) [46]. The combined


R antagonists was not directly studied, the published literature points



effective dose of the 5-HT<sup>3</sup>

120 Calcium and Signal Transduction

antagonists with 5-HT<sup>3</sup>


therapy in a manner similar to that reported between 5-HT<sup>3</sup>

critical role in its anti-nausea and anti-vomiting effects [3].

**4.4. Intracellular Ca2+ release channels: possible targets for suppression of emesis**

A functional and physical linkage between LTCCs and RyRs appears to exist and plays an important role in intracellular Ca2+ release following voltage-dependent Ca2+ entry through LTCCs

5-HT<sup>3</sup>

In mammals, cyclic AMP (cAMP) is synthesized by 10 adenylate cyclase isoforms [168]. One of the best-studied second messenger molecules downstream of selected G-protein coupled receptors is cAMP. It is an example of a transient and diffusible second messenger involved in signal propagation by integrating multiple intracellular signaling pathways [169]. cAMP activates protein kinase A (PKA) which results in phosphorylation of downstream intracellular signals. The adenylyl cyclase/cAMP/PKA signaling pathway can phosphorylate Ca2+ ionchannels found on the plasma membrane and intracellular IP<sup>3</sup> Rs [110]. These Ca2+ channels respectively increase extracellular Ca2+-influx and intracellular Ca2+-release [110]. The emetic role of cAMP has been well established (**Figure 5**), since microinjection of cAMP analogs (e.g., 8-bromocAMP) or forskolin (to enhance endogenous levels of cAMP) in the brainstem dorsal vagal complex emetic locus area postrema, not only can increase electrical activity of local neurons, but also induces vomiting in dogs [170]. Moreover, administration of 8-chlorocAMP as a potential chemotherapeutic in cancer patients can evoke nausea and vomiting [171]. Furthermore, phosphodiesterase inhibitors (PDEI) such as rolipram prevent cAMP metabolism and consequently increase cAMP tissue levels, which leads to excessive nausea and vomiting in humans [172]. In fact, one major side-effect of older PDEIs is excessive nausea and vomiting which often precludes their use in the clinical setting [173]. In addition, we have

and LTD4

serotonin 5-HT<sup>3</sup>

Ca2+ mobilization [144].

that unlike other leukotrienes (e.g., LTA4

), appear to be potent emetogens [72, 149, 176, 177]. Our findings demonstrate

and LTF4

), the above discussed leukotrienes

http://dx.doi.org/10.5772/intechopen.78370

. Regarding

123

R


Role of Calcium in Vomiting

receptor antagonist

, LTB4

LTC4, the evoked vomiting was shown to be suppressed in a dose-dependent manner in the least shrew by the antiasthmatic drug pranlukast, the corresponding cysteinyl leukotrienes receptor 1 (CysLT1R) antagonist [72]. Although not available in the USA, the cost of other members of this class of drugs (montelukast and Zafirlukast) that are sold in the USA is

[72], we envisaged it may have potential utility against cisplatin-evoked emesis. Our most recent publication [178] shows the potential of pranlukast (currently used for the treatment of various respiratory disorders including asthma), as a new class of antiemetic for the suppression of the acute- and delayed- phases of cisplatin-evoked vomiting in the least shrew. An intraperitoneal (i.p.) dose of 10 mg/kg pranlukast by itself significantly reduced the mean frequency of vomits by 70% and fully protected 46% of least shrews during the delayed-phase of cisplatin (10 mg/kg, i.p.)-evoked vomiting. Although pranlukast tended to substantially reduce both the mean frequency of vomits and the number of shrews vomiting during the early-phase, these reductions failed to attain significance. When pranlukast was combined with a first (tropisetron)- or a second (palonosetron)-generation 5-HT<sup>3</sup>

antagonist, it potentiated their antiemetic efficacy during both acute- and delayed-phases of cisplatin-evoked vomiting. Moreover, pranlukast potentiated the antiemetic efficacy of

induced nausea and vomiting. In fact per hour efficacy antiemetic profile of pranlukast combined with palonosetron or tropisetron during both phases of chemotherapy-induced

netupitant (5 mg/kg) plus palonosetron (0.1 mg/kg) in the same species [144]; (ii) netupitant plus ondansetron in ferrets [179]; and (iii) ondansetron plus aprepitant in combination with dexamethasone in ferrets [179]; and (iv) palonosetron plus netupitant in combination with dexamethasone in ferrets [179]. If analogs of pranlukast such as montelukast and zafirlukast can also provide similar antiemetic potential, then clinical trials should be initiated since this class of drugs are relatively inexpensive than available effective antiemetic regimens against chemotherapy-induced nausea and vomiting. Our related biochemical data indicates the mechanisms of antiemetic action of pranlukast are linked to suppression of cisplatin-elicited PKCα/βII, ERK1/2 and PKA activation (phosphorylation) in the least shrew brainstem [178]. Moreover, suppression of these signaling molecules may be shared

When antiemetic mechanism of action of pranlukast against LTC4-induced vomiting or cisplatin-induced responses is discussed, Ca2+ is also an essential element. Montelukast and pranlukast were found to inhibit nucleotide-induced Ca2+ mobilization in a human monocytemacrophage-like cell line, DMSO-differentiated U937 [180]. CysLT1 receptors belonging to the rhodopsin family of the G protein-coupled receptor genes respond to LTD4 with a strong increase in cytosolic Ca2+ concentration partially sensitive to pertussis toxin, and with the activation of the Ras-MAPK cascade totally dependent upon Gi/o [144]. These signaling effects were totally inhibited by various specific CysLT1-receptor antagonists, and CysLT1 antagonists inhibit both the P2Y agonist-induced activation of phospholipase C and intracellular

receptor antagonists, tropisetron and palonosetron, against chemotherapy-

are effective emetogens with the following potency order: LTC4 = LTD4 > LTE4

less than one dollar per pill. Based on pranlukast's efficacy against LTC4

nausea and vomiting in the least shrew resembles those of: (i) the NK<sup>1</sup>

in the anti-inflammatory signaling pathway of pranlukast.

**Figure 5.** Summarized behavioral and biochemical evidence for intracellular signaling molecules (cAMP, PKA, CaMKII, ERK1/2, PKC) related to emesis based on the least shrew emesis model. First, cyclic AMP (cAMP) is synthesized by adenylate cyclase and cAMP activates protein kinase A (PKA) [110, 168]. The adenylyl cyclase/cAMP/PKA signaling pathway can mediate vomiting. Indeed, increased levels of endogenous cAMP can evoke vomiting in animal models [109, 170] as well as humans [171–173], which can be prevented by adenylate cyclase inhibitor SQ22536 [109]. Evoked PKA-phosphorylation is associated with peak vomit frequency during both immediate- and delayed-phases of vomiting caused by cancer chemotherapeutics including cisplatin and cyclophosphamide in the least shrew [109, 144, 149]. In addition, Ca2+/calmodulin kinase IIα (CaMKIIα) and extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) phosphorylation in the least shrew brainstem were elevated in vomiting evoked by the 5-HT<sup>3</sup> R agonist 2-Methyl-5-HT [46], thapsigargin [70], or the selective NK<sup>1</sup> R agonist GR73632 [167]. Phosphorylation of protein kinase Cα/βII (PKCα/ βII) and ERK1/2 in least shrew brainstem were also upregulated in the vomiting induced by cisplatin [144, 149].

demonstrated that increased brain cAMP levels evoke vomiting which can be prevented by SQ22536 (**Figure 5**), an inhibitor of adenylyl cyclase [109]. Moreover, PKA-phosphorylation is associated with peak vomit frequency during both immediate- and delayed-phases of vomiting caused by either cisplatin or cyclophosphamide in the least shrew [109, 144, 149] (**Figure 5**).
