Increased sensitivity of desensitized TRPV1 by PMA occurs through PKCepsilon-mediated phosphorylation at S800.

Important mechanisms that regulate inhibitory and facilitatory effects on TRPV1-mediated nociception are desensitization and phosphorylation, respectively. Using Ca2+-imaging, we have previously shown that desensitization of TRPV1 upon successive capsaicin applications was reversed by protein kinase C activation in dorsal root ganglion neurons and CHO cells. Here, using both Ca2+-imaging and patch-clamp methods, we show that PMA-induced activation of PKCepsilon is essential for increased sensitivity of desensitized TRPV1. TRPV1 has two putative substrates S502 and S800 for PKCepsilon-mediated phosphorylation. Patch-clamp analysis showed that contribution of single mutant S502A or S800A towards increased sensitivity of desensitized TRPV1 is indistinguishable from that observed in a double mutant S502A/S800A. Since S502 is a non-specific substrate for TRPV1 phosphorylation by kinases like PKC, PKA or CAMKII, evidence for a role of PKC specific substrate S800 was investigated. Evidence for in vivo phosphorylation of TRPV1 at S800 was demonstrated for the first time. We also show that the expression level of PKCepsilon paralleled the amount of phosphorylated TRPV1 protein using an antibody specific for phosphorylated TRPV1 at S800. Furthermore, the anti-phosphoTRPV1 antibody detected phosphorylation of TRPV1 in mouse and rat DRG neurons and may be useful for research regarding nociception in native tissues. This study, therefore, identifies PKCepsilon and S800 as important therapeutic targets that may help regulate inhibitory effects on TRPV1 and hence its desensitization.

Reduction of postoperative emetic episodes and analgesic requirements with dexamethasone in patients scheduled for dental surgery.

STUDY OBJECTIVE: To evaluate the antiemetic and analgesic effects of dexamethasone for the first 24 hours postoperatively in patients scheduled for dental surgery. DESIGN: Prospective, randomized, double-blind, placebo-controlled study. SETTING: University hospital. PATIENTS: One hundred twenty ASA physical status I and II patients (45 men, 75 women; aged 17-48 years) undergoing general anesthesia for dental surgery. INTERVENTIONS: Patients received intravenously placebo or dexamethasone at 3 different doses (4, 8, or 16 mg) at the end of the surgical procedure. A standard general anesthetic technique, including sevoflurane and nitrous oxide in oxygen, was used. MEASUREMENT AND MAIN RESULTS: Emetic episodes and analgesic requirements were evaluated. The rate of patients who were emesis free (no nausea, retching, or vomiting) during 0 to 24 hours after anesthesia was 63% with dexamethasone 4 mg (P = NS), 83% with dexamethasone 8 mg (P < .05), and 90% with dexamethasone 16 mg (P < .05), compared to placebo (60%). The need for diclofenac sodium for intolerable pain was less in patients who had received dexamethasone 8 mg or dexamethasone 16 mg than in those who had received placebo or dexamethasone 4 mg (P < .05). No clinically important adverse events were observed in any group. CONCLUSIONS: Prophylactic dexamethasone 8 mg is effective for the prevention of nausea and vomiting after dental surgery and in the management of postoperative pain. Increasing the dose to 16 mg provides no further benefit.

Nociception and TRP Channels.

Noxious thermal, mechanical, or chemical stimuli evoke pain through excitation of the peripheral terminals called nociceptor, and many kinds of ionotropic and metabotropic receptors are involved in this process. Capsaicin receptor TRPV1 is a nociceptor-specific ion channel that serves as the molecular target of capsaicin. TRPV1 can be activated not only by capsaicin but also by noxious heat (with a thermal threshold >43 degrees C) or protons (acidification), all of which are known to cause pain in vivo. Studies using TRPV1-deficient mice have shown that TRPV1 is essential for selective modalities of pain sensation and for thermal hyperalgesia. One mechanism underlying inflammatory pain which is initiated by tissue damage/inflammation and characterized by hypersensitivity is sensitization of TRPV1. In addition to TRPV1, there are five thermosensitive ion channels in mammals, all of which belong to the TRP (transient receptor potential) super family. These include TRPV2, TRPV3, TRPV4, TRPM8 and TRPA1. These channels exhibit distinct thermal activation thresholds (> 52 degrees C for TRPV2, > approximately 34-38 degrees C for TRPV3, > approximately 27-35 degrees C for TRPV4, < approximately 25-28 degrees C for TRPM8 and < 17 degrees C for TRPA1) and are expressed in primary sensory neurons as well as other tissues. Some of the thermosensitive TRP channels are likely to be involved in thermal nociception, since their activation thresholds are within the noxious range of temperatures.

Randomized, double-blind comparison of subhypnotic-dose propofol alone and combined with dexamethasone for emesis in parturients undergoing cesarean delivery.

BACKGROUND: Nausea, retching, and vomiting are common in parturients undergoing cesarean delivery performed under regional anesthesia. Subhypnotic-dose propofol 1.0 mg/kg per hour has been used to reduce the incidence of these emetic symptoms. Dexamethasone has been shown to reduce chemotherapy-induced emesis when added to an antiemetic regimen. OBJECTIVE: The aim of this study was to examine the difference in efficacy and tolerability between subhypnoticdose propofol 1.0 mg/kg per hour alone and combined with dexamethasone 8 mg for reducing postdelivery emetic episodes in parturients undergoing cesarean delivery. METHODS: In a randomized, double-blind trial, parturients received IV placebo (saline) or dexamethasone 8 mg followed by a continuous infusion of propofol at subhypnotic dose (1.0 mg/kg per hour) immediately after clamping of the umbilical cord. Intraoperative, postdelivery emetic episodes and safety assessments were performed by an investigator. RESULTS: One hundred twenty parturients (mean [SD] age, 29 [5] years; age range, 21-38 years; mean [SD] height, 158 [7] cm; height range, 145-172 cm; mean [SD] body weight, 72 [8] kg; weight range, 54-90 kg) were enrolled in the study, 60 in each treatment group. The treatment groups were comparable with respect to maternal demographics and operative management. The rate of emetic symptoms (nausea, retching, and vomiting) in an intraoperative, postdelivery period was lower in patients who received the combination regimen than in those who received subhypnotic-dose propofol 1.0 mg/kg per hour alone (5% [3/60] vs 20% [12/60], respectively; P = 0.012). No clinically important adverse events attributable to the study drug were observed in either group. CONCLUSION: In the parturients undergoing cesarean delivery performed under spinal anesthesia in this study, the combination of subhypnotic-dose propofol 1.0 mg/kg per hour and dexamethasone 8 mg was more effective than propofol alone for reducing the incidence of postdelivery emetic symptoms.

Regulation mechanisms of vanilloid receptors.

The capsaicin receptor TRPV1 (also known as the vanilloid receptor VR1) is a non-selective cation channel and is activated not only by capsaicin but also by noxious heat or protons. Tissue damage associated with infection, inflammation or ischaemia, produces an array of chemical mediators that activate or sensitize nociceptor terminals. An important component of this pro-algeic response is ATP. In cells expressing TRPV1, ATP increased the currents evoked by capsaicin or protons through activation of P2Y metabotropic receptors in a PKC-dependent manner. In the presence of ATP, the temperature threshold for TRPV1 activation was reduced from 42 degrees C to 35 degrees C, such that normal body temperature could activate TRPV1. Functional interaction between P2Y receptors and TRPV1 was confirmed in a behavioural analysis using TRPV1-deficient mice. Direct phosphorylation of TRPV1 by PKC was confirmed biochemically and the two serine residues involved were identified. Extracellular Ca2+ -dependent desensitization of TRPV1 is thought to be one mechanism underlying the paradoxical effectiveness of capsaicin as an analgesic therapy. The Ca2+ -binding protein calmodulin binds to the C-terminus of TRPV1. We found that disruption of the calmodulin binding segment prevented TRPV1 desensitization even in the presence of extracellular Ca2+.

Activation of protein kinase C reverses capsaicin-induced calcium-dependent desensitization of TRPV1 ion channels.

Ca2+ selective ion channels of vanilloid receptor subtype-1 (TRPV1) in capsaicin-sensitive dorsal root ganglion (DRG) neurons and TRPV1 transfected Chinese hamster ovarian (CHO) cells are desensitized following calcium-dependent tachyphylaxis induced by successive applications of 100 nM capsaicin. Tachyphylaxis of TRPV1 to 100 nM capsaicin stimuli was not observed in the absence of extracellular calcium. Capsaicin sensitivity of desensitized TRPV1 ion channels recovered on application of phorbol-12-myristate-13-acetate (PMA). PMA-induced recovery of desensitized TRPV1 was primarily due to influx of extracellular calcium observed during re-application of capsaicin following desensitization. Capsazepine blocked the re-sensitization to capsaicin by PMA. Protein kinase C (PKC) inhibitory peptide PKC fragment 19-36 also inhibited re-sensitization to capsaicin by PMA. Reversal of capsaicin-induced desensitization by PMA was prevented by a mutation of TRPV1 where phosphorylation sites serine502 and serine800 were replaced with alanine. This study provides evidence for a role of PKC in reversing capsaicin-induced calcium-dependent desensitization of TRPV1 ion channels.

DIP (mDia interacting protein) is a key molecule regulating Rho and Rac in a Src-dependent manner.

Cell movement is driven by the coordinated regulation of cytoskeletal reorganization through Rho GTPases downstream of integrin and growth-factor receptor signaling. We have reported that mDia, a target protein of Rho, interacts with Src and DIP. Here we show that DIP binds to p190RhoGAP and Vav2, and that DIP is phosphorylated by Src and mediates the phosphorylation of p190RhoGAP and Vav2 upon EGF stimulation. When endogenous DIP was inhibited by expressing dominant-negative mutants of DIP or siRNA, phosphorylation of p190RhoGAP and Vav2 upon EGF stimulation was diminished, and EGF-induced actin organization, distribution of p190RhoGAP and Vav2, and cell movement were affected. Therefore, DIP seems to transfer the complex of the three proteins from cytosol to beneath the membrane, and the three proteins, in turn, can be phosphorylated by Src. DIP inactivated Rho and activated Rac following EGF stimulation in the membrane fraction. Thus, DIP acts as a regulatory molecule causing Src kinase-dependent feedback modulation of Rho GTPases downstream of Rho-mDia upon EGF stimulation, and plays an important role in cell motility.

Reduction of emetic symptoms during cesarean delivery with antiemetics: propofol at subhypnotic dose versus traditional antiemetics.

STUDY OBJECTIVE: To evaluate the efficacy and safety of propofol (at a subhypnotic dose), droperidol, and metoclopramide in reducing emetic symptoms during cesarean delivery. DESIGN: Randomized, double-blinded, placebo-controlled study. SETTING: University hospital. PATIENTS: 100 ASA physical status I and II parturients undergoing cesarean delivery with spinal anesthesia. INTERVENTIONS: Patients received placebo (saline) followed by placebo (Intralipid(R)), placebo (saline) followed by propofol at a subhypnotic dose (1.0 mg/kg/hr), droperidol 1.25 mg followed by placebo (Intralipid(R)), or metoclopramide 10 mg followed by placebo (Intralipid(R)) intravenously (IV) immediately after clamping of the umbilical cord. MEASUREMENT AND MAIN RESULTS: The percentage of patients who were emesis-free, which was defined as experiencing no nausea, retching, or vomiting, in the intraoperative, postdelivery period was 80% with propofol, 80% with droperidol, and 78% with metoclopramide (p < 0.05), compared with placebo (40%). Severity of nausea was less inpatients who received propofol than in those who received placebo (p < 0.05), and there were no differences seen among the droperidol, metoclopramide, and placebo groups. No clinically serious adverse events as a result of the study drugs were observed in any of the groups. CONCLUSIONS: Prophylactic antiemetic efficacy of propofol at a subhypnotic dose (1.0 mg/kg/hr), droperidol 1.25 mg, and metoclopramide 10 mg is comparable in parturients undergoing cesarean delivery. Moreover, propofol at a subhypnotic dose is effective in the prevention of severe nausea.

[Molecular mechanisms of nociception].

Capsaicin, the main ingredient in 'hot' chili peppers, elicits burning pain by activating nociceptors. The cloned capsaicin receptor (TRPV1) is a nonselective cation channel with six transmembrane domains, and is activated not only by capsaicin but also by noxious heat (> 43 degrees C) or protons (acidification), both of which cause pain in vivo. Furthermore, analyses of mice lacking VR1 showed that VR1 is essential for selective modalities of pain sensation and for tissue injury-induced thermal hyperalgesia. Tissue damage produces an array of chemical mediators that activate or sensitize nociceptor terminals to elicit pain. Important components of this pro-algesic response are ATP and bradykinin. In cells expressing TRPV1, ATP or bradykinin increased the currents evoked by capsaicin or protons through activation of metabotropic P2Y or B2 bradykinin receptors. In the presence of ATP or bradykinin, the temperature threshold for VR1 activation was reduced from 42 degrees C to 30-35 degrees C, such that normally non-painful normal body temperatures were capable of activating TRPV1, thereby leading to the sensation of pain. Direct phosphorylation of TRPV1 by PKC epsilon was confirmed and the involved two serine residues were determined. This represents a novel mechanism through which ATP or bradykinin in response to tissue trauma might trigger the sensation of pain.

Structural determinant of TRPV1 desensitization interacts with calmodulin.

The capsaicin receptor, TRPV1 (VR1), is a sensory neuron-specific ion channel that serves as a polymodal detector of pain-producing chemical and physical stimuli. Extracellular Ca2+-dependent desensitization of TRPV1 observed in patch-clamp experiments when using both heterologous expression systems and native sensory ganglia is thought to be one mechanism underlying the paradoxical effectiveness of capsaicin as an analgesic therapy. Here, we show that the Ca2+-binding protein calmodulin binds to a 35-aa segment in the C terminus of TRPV1, and that disruption of the calmodulin-binding segment prevents TRPV1 desensitization. Compounds that interfere with the 35-aa segment could therefore prove useful in the treatment of pain.

Direct phosphorylation of capsaicin receptor VR1 by protein kinase Cepsilon and identification of two target serine residues.

The capsaicin receptor, VR1, is a sensory neuron-specific ion channel that serves as a polymodal detector of pain-producing chemical and physical stimuli. It has been reported that ATP, one of the inflammatory mediators, potentiates the VR1 currents evoked by capsaicin or protons and reduces the temperature threshold for activation of VR1 through metabotropic P2Y(1) receptors in a protein Kinase C (PKC)-dependent pathway, suggesting the phosphorylation of VR1 by PKC. In this study, direct phosphorylation of VR1 upon application of phorbol 12-myristate 13-acetate (PMA) was proven biochemically in cells expressing VR1. An in vitro kinase assay using glutathione S-transferase fusion proteins with cytoplasmic segments of VR1 showed that both the first intracellular loop and carboxyl terminus of VR1 were phosphorylated by PKCepsilon. Patch clamp analysis of the point mutants where Ser or Thr residues were replaced with Ala in the total 16 putative phosphorylation sites showed that two Ser residues, Ser(502) and Ser(800) were involved in the potentiation of the capsaicin-evoked currents by either PMA or ATP. In the cells expressing S502A/S800A double mutant, the temperature threshold for activation was not reduced upon PMA treatment. The two sites would be promising targets for the development of substance modulating VR1 function, thereby reducing pain.

Dose-range effects of propofol for reducing emetic symptoms during cesarean delivery.

OBJECTIVE: To evaluate the efficacy and safety of propofol at subhypnotic doses for reducing emetic symptoms in parturients undergoing cesarean delivery under spinal anesthesia. METHODS: In a randomized, double-masked trial, 80 patients received lidocaine intravenously 0.1 mg/kg (for injection pain relief) followed by either placebo or propofol at three different doses (0.5 mg/kg per hour, 1.0 mg/kg per hour, 2.0 mg/kg per hour) (n = 20 in each group) immediately after clamping of the umbilical cord. Emetic episodes and safety assessments were performed during spinal anesthesia for cesarean delivery. To estimate a sufficient sample size, it was calculated that 20 patients per group would be required with alpha =.05 and beta =.2. RESULTS: The rate of patients experiencing no emetic symptoms in an intraoperative, postdelivery period was 45% with propofol 0.5 mg/kg per hour (P =.5), 80% with propofol 1.0 mg/kg per hour (P =.011), and 80% with propofol 2.0 mg/kg per hour (P =.011), compared with placebo (40%). No clinically serious adverse events caused by the study drugs were observed. CONCLUSION: Propofol 1.0 mg/kg per hour is the minimum effective subhypnotic dose for reducing emetic symptoms during cesarean delivery. Increasing the dose to 2.0 mg/kg per hour provides no further benefit.