Protective effect of a mitochondria-targeting peptide against paclitaxel-induced peripheral neuropathy.

Chemotherapy-induced peripheral neuropathy (CIPN) is a major side effect of several anticancer agents including paclitaxel, a chemotherapeutic drug widely used in cancer treatment. CIPN deteriorates patients' quality of life and compromises cancer treatment. Dysfunction or injury of mitochondria has been suggested to be involved in the induction of this neuropathy. SS-20 is a tetrapeptide that targets mitochondria and restores mitochondrial bioenergetics. This study was aimed to examine the protective effect of SS-20 against paclitaxel-induced peripheral neuropathy using a murine model. Repeated administration of paclitaxel to mice induced peripheral neuropathy as demonstrated by the presence of mechanical allodynia and the loss of intraepidermal nerve fibers in the hind paw. Concomitant administration of SS-20 protected against the development of the neuropathy. Our results suggest that SS-20 may be a drug candidate for the prevention of CIPN.

Protective Effect of a Mitochondria-Targeted Peptide against the Development of Chemotherapy-Induced Peripheral Neuropathy in Mice.

Several chemotherapeutic agents used for cancer treatment induce dose-limiting peripheral neuropathy that compromises patients' quality of life and limits cancer treatment. Recently, mitochondrial dysfunction has been shown to be involved in the mechanism of chemotherapy-induced peripheral neuropathy. SS-20 is a mitochondria-targeted peptide that promotes mitochondrial respiration and restores mitochondrial bioenergetics. In the present study, we examined the protective effect of SS-20 against the development of chemotherapy-induced peripheral neuropathy utilizing a murine model of peripheral neuropathy induced by oxaliplatin, a first-line chemotherapy agent for colon cancer. Weekly administrations of oxaliplatin induced peripheral neuropathy as demonstrated by the development of neuropathic pain and loss of intraepidermal nerve fibers in the hind paw. Continuous administration of SS-20 protected against the development of oxaliplatin-induced neuropathic pain and mitigated the loss of intraepidermal nerve fibers to normal levels. Our findings suggest that SS-20 may be a drug candidate for the prevention of chemotherapy-induced peripheral neuropathy.

Nonpeptide Orexin-2 Receptor Agonist Attenuates Morphine-induced Sedative Effects in Rats.

BACKGROUND: Sleepiness and decrease in attention are dose-limiting side effects of opioids. The orexin/hypocretin system plays an important role in maintaining wakefulness. This study aimed to explore the potential of a nonpeptide orexin receptor agonist to alleviate morphine-induced sedative effects. METHODS: Morphine sedative effects were evaluated as changes in electroencephalogram (EEG), locomotor activity, and acoustic startle response in rats (n = 5 to 9 per group). Effects of intracerebroventricular orexin-A and systemic orexin type-2 receptor agonist, YNT-185, on EEG changes induced by morphine were examined. Furthermore, the authors examined effects of morphine administered with or without YNT-185 on locomotor activity and on acoustic startle response. RESULTS: Morphine-induced, frequent, short epochs of increased power (total epoch duration: 0.5 [0.0 to 8.0] s/10 min during baseline vs. 74.0 [49.0 to 115.0] s/10 min during the post-morphine administration period; P = 0.012). EEG analyses revealed that morphine-induced, high-amplitude, slow activity (increase in spectral power of frequencies less than 15 Hz, baseline vs. postmorphine; P < 0.001). Orexin-A and YNT-185 attenuated these changes. Locomotor activity decreased after morphine (268 [103 to 889] ambulatory movement counts during baseline period [20 min] vs. 138 [7 to 434] counts during 40 to 59 min postadministration; P = 0.012), but did not change after morphine with YNT-185 (363 [121 to 636] vs. 864 [381 to 1092] counts, difference within morphine + YNT-185 group; P = 0.071). Startle response latency was longer after morphine (26 [20 to 28] ms) than after morphine with YNT-185 (17 [16 to 18] ms; P = 0.012). CONCLUSIONS: Orexin-A and/or YNT-185 attenuated morphine-induced sedative effects assessed by EEG changes and behavioral measures in rats. The authors' results suggest that orexin-2 receptor activation alleviates morphine-induced sedative effects.

The analgesic effect of orexin-A in a murine model of chemotherapy-induced neuropathic pain.

Orexins are neuropeptides that are localized to neurons in the lateral and dorsal hypothalamus but its receptors are distributed to many different regions of the central nervous system. Orexins are implicated in a variety of physiological functions including sleep regulation, energy homeostats, and stress reactions. Furthermore, orexins administered exogenously have been shown to have analgesic effects in animal models. A type of intractable pain in patients is pain due to chemotherapy-induced peripheral neuropathy (CIPN). Several chemotherapeutic agents used for the treatment of malignant diseases induce dose-limiting neuropathic pain that compromises patients' quality of life. Here, we examined the analgesic effect of orexin-A in a murine model of CIPN, and compared it with the effect of duloxetine, the only drug recommended for the treatment of CIPN pain in patients. CIPN was induced in male BALB/c mice by repeated intraperitoneal injection of oxaliplatin, a platinum chemotherapeutic agent used for the treatment of advanced colorectal cancer. Neuropathic mechanical allodynia was assessed by the von Frey test, and the effect on acute thermal pain was assessed by the tail flick test. Intracerebroventricularly administered orexin-A dose-dependently attenuated oxaliplatin-induced mechanical allodynia and increased tail flick latencies. Oxaliplatin-induced mechanical allodynia was completely reversed by orexin-A at a low dose that did not increase tail flick latency. Duloxetine only partially reversed mechanical allodynia and had no effect on tail flick latency. The analgesic effect of orexin-A on oxaliplatin-induced mechanical allodynia was completely antagonized by prior intraperitoneal injection of SB-408124 (orexin type-1 receptor antagonist), but not by prior intraperitoneal injection of TCS-OX2-29 (orexin type-2 receptor antagonist). Our findings suggest that orexin-A is more potent than duloxetine in relieving pain CIPN pain and its analgesic effect is mediated by orexin type-1 receptors. Orexin type-1 receptor agonists may have potential therapeutic roles in the treatment of CIPN pain in patients.

[Perioperative Management of Patients Receiving Chronic Opioid Therapy].

Recently in Japan, more patients are receiving chronic opioid therapy for cancer pain or chronic pain, and there is an increasing number of such patients presenting for surgery. The anesthesiologist should be familiar with available opioid formulations as well as the change they induce by their chronic administra- tion, such as physical dependence, opioid tolerance and opioid-induced hyperalgesia. Physical dependence results in withdrawal symptoms when the opioid is abruptly interrupted or when the dosage is markedly reduced in a short period of time. Furthermore, these patients tend to have increased pain and increased opioid requirements postoperatively, most likely due to opioid tolerance and opioid-induced hyperalgesia. Peri- operative management of these patients require knowledge and skills to manage these phenomena.

[Understanding Oral and Nasal Mucosal Absorption of Fentanyl, and Rectal Absorption of Buprenorphine].

One of the key issues in the treatment of pain is to choose the appropriate route and dosage form of analgesics for each individual patient in pain. New drug forms of fentanyl absorbed by oral or nasal mucosa, and buprenorphine absorbed by rectal mucosa are described in this chapter. Only lipophilic opioids such as fentanyl and buprenorphine can be absorbed via the mucosa of oral or nasal cavity of the human body. The T max of rapid onset opioids (ROO) such as fentanyl buccal or sublingual tablets is the fastest among various dosage forms of opioid analgesics. However, such rapid increase in plasma concentration of fentanyl by ROO formulations may cause the risk of respiratory depression. Safe ways to use ROO analgesics are described.

Efficacy and safety of sublingual fentanyl orally disintegrating tablet at doses determined from oral morphine rescue doses in the treatment of breakthrough cancer pain.

OBJECTIVE: A randomized, crossover, double-blinded placebo-controlled and non-blinded active drug-controlled, comparative clinical trial was conducted to evaluate the efficacy and safety of sublingual fentanyl tablet. METHODS: Subjects were patients treated with strong opioids at fixed intervals for chronic cancer pain and with oral morphine as rescue medication for breakthrough pain. Sublingual fentanyl was administered at doses that were 1/25th (high dose) and 1/50th (low dose) of the dose of rescue morphine and was compared with placebo and oral morphine. The primary endpoint was pain intensity difference at 30 min after administration. (Clinical Trials Government; NCT00684632). RESULTS: Fifty-one patients were enrolled in the investigation. Their mean pain intensity in visual analog scale before rescue medication prior to the investigation was 60.96 (16.44, standard deviation) mm. Compared with placebo, the low and high doses of sublingual fentanyl showed significant analgesic effects (least squares mean difference, 4.54 and 8.49 mm; P = 0.014, P < 0.001, respectively). Adverse reactions were observed in 17.6%, the most common being constipation, nausea and somnolence. The incidence of adverse reactions during the high-dose administration period was higher than that during the low-dose and active control drug administration periods. CONCLUSIONS: Patients treated with strong opioid analgesics at fixed intervals for chronic cancer pain and with oral morphine at doses up to 20 mg as rescue medication were investigated. The doses of sublingual fentanyl to treat breakthrough pain were determined from rescue morphine doses by use of conversion ratios. In these patients, administration of sublingual fentanyl at doses determined by a conversion ratio of 1/50 was effective and safe. Further studies are needed to validate the use of this conversion method.

Efficacy and safety of sublingual fentanyl orally disintegrating tablet at doses determined by titration for the treatment of breakthrough pain in Japanese cancer patients: a multicenter, randomized, placebo-controlled, double-blind phase III trial.

BACKGROUND: Breakthrough cancer pain typically has a rapid onset and relatively short duration. Due to this temporal profile, it may not be adequately relieved by oral opioid analgesics. The sublingual fentanyl orally disintegrating tablet is a formulation by which fentanyl can be rapidly absorbed across the oral mucosa producing rapid-onset analgesia, and which may be effective for breakthrough pain treatment. METHODS: A multicenter, randomized, placebo-controlled, double-blind comparative study was conducted to evaluate the efficacy and safety of the sublingual fentanyl tablet at optimized doses for breakthrough pain treatment in cancer patients treated with strong opioid analgesics at fixed intervals. The optimal dose was determined by open-label dose titration. The efficacy and safety of a 12-week extended treatment were also evaluated. RESULTS: Eleven of 42 subjects who received the sublingual fentanyl tablet experienced adverse drug reactions. Common reactions were somnolence, constipation, nausea, and vomiting. No serious adverse reactions occurred. Sublingual fentanyl tablets at optimal doses and placebo were administered to 37 subjects in a double-blinded manner. A significant analgesic effect of the sublingual fentanyl tablet was present compared to placebo at 30 min after administration. The sublingual fentanyl tablet was also effective and safe during extended treatment, in which changes in basal opioid doses as well as sublingual fentanyl tablet doses were made as needed. CONCLUSION: Sublingual fentanyl tablets at doses determined by titration were effective and safe for breakthrough pain treatment in cancer patients treated with strong opioid analgesics at fixed intervals. Extended treatment up to 12 weeks was also effective and safe.

Characterization of acute and chronic neuropathies induced by oxaliplatin in mice and differential effects of a novel mitochondria-targeted antioxidant on the neuropathies.

BACKGROUND: Oxaliplatin, a chemotherapeutic agent used for the treatment of colorectal cancer, induces dose-limiting neuropathy that compromises quality of life. This study aimed to reproduce, in mice, patients' symptoms of oxaliplatin-induced neuropathy and to observe effects of SS-31, a mitochondria-targeted antioxidant on the neuropathy. METHODS: Neuropathy was induced by single or repeated injections of oxaliplatin. Cold and mechanical hypersensitivities were assessed by 15°C-cold plate, temperature preference, and von Frey tests. Morphology of peripheral nerves and dorsal root ganglions, expression of spinal cord c-Fos, density of intraepidermal nerve fibers, and levels of dorsal root ganglion-reactive oxygen/nitrogen species were examined. SS-31 was administered concomitantly or after oxaliplatin injections. RESULTS: Single injection of oxaliplatin induced cold hypersensitivity in forepaws but not in hind paws which resolved within days (maximal forepaw shakes: 28 ± 1.5 vs. 9.3 ± 1.6/150 s, mean ± SEM, P < 0.001, n = 6 per group). Oxaliplatin-administered mice disfavored 10° and 15°C plates more than control. Paw stimulation at 15°C induced c-Fos-positive cells within superficial laminae of the dorsal horn in C7-T1 segments. Weekly administrations induced gradual development of persistent mechanical allodynia in the hind paws (minimal mechanical threshold: 0.19 ± 0.08 vs. 0.93 ± 0.11 g, P < 0.001, n = 10 per group). Microscopy revealed no overt morphological changes in peripheral nerves and dorsal root ganglions. Concomitant SS-31 administration with repeated oxaliplatin administration attenuated both cold and mechanical hypersensitivity. Decrease in intraepidermal nerve fibers and increase in dorsal root ganglion-reactive oxygen/nitrogen species were also attenuated. Acute SS-31 administration after symptoms were established reversed only cold hypersensitivity. CONCLUSION: This model of oxaliplatin-induced neuropathy mimicked patients' conditions. SS-31 has potentials to prevent both acute and chronic neuropathies but is only helpful in treatment of acute neuropathy. (Anesthesiology 2014; 120:459-73).

[Treatment of constipation in chronic pain patients].

The treatment of chronic pain, whether of cancer or noncancer origin, frequently involves the use of opioids. Delay in GI transit and constipation are the most common and often disabling side effects of opioid analgesics. Many treatments involving laxatives and prokinetic drugs have been explored to circumvent opioid-induced bowel dysfunction, but the outcome has in general been unsatisfactory. Specific antagonism of peripheral opioid receptors offers a more rational approach to the management of the adverse actions of opioid analgesics in the gut. This goal is currently addressed by the use of opioid receptor antagonists with limited absorption such as oral naloxone and by the development of peripheral opioid receptor antagonists such as methylnaltrexone and alvimopan. These drugs hold considerable promise in preventing constipation due to treatments with opioids, whereas the analgesic action of opioids remains unabated.

Superior analgesic effect of H-Dmt-D-Arg-Phe-Lys-NH2 ([Dmt1]DALDA), a multifunctional opioid peptide, compared to morphine in a rat model of neuropathic pain.

H-Dmt-D-Arg-Phe-Lys-NH(2) ([Dmt(1)]DALDA) is a synthetic tetrapeptide with extraordinary selectivity for the mu-opioid receptor and is an extremely potent analgesic. [Dmt(1) ]DALDA is unusual in the way that the greater part of its analgesic potency appears to be produced by its actions in the spinal cord. Furthermore, [Dmt(1) ]DALDA inhibits norepinephrine re-uptake and is a mitochondria-targeted antioxidant. Such characteristics may make [Dmt(1)]DALDA particularly effective against neuropathic pain. The present study was designed to compare the effects of [Dmt(1)]DALDA and morphine on thermal hyperalgesia in an experimental neuropathic pain model. Neuropathic pain was induced in rats by surgical ligation of the L5 spinal nerve, and thermal pain thresholds were assessed by latencies of paw withdrawal to radiant heat. The increase in paw withdrawal latency was greater after the administration of [Dmt(1) ]DALDA than that of morphine in neuropathic rats at doses that were equianalgesic in naïve animals. We conclude that [Dmt(1)]DALDA is more effective than morphine against thermal hyperalgesia in this experimental model of neuropathic pain.

Endogenous endomorphin-2 contributes to spinal ĸ-opioid antinociception.

BACKGROUND/AIMS: Multiple opioid receptor (OR) types and endogenous opioid peptides exist in the spinal dorsal horn and there may be interactions among these receptor types that involve opioid peptides. In a previous study we observed that antinociceptive effects of the selective κ-opioid receptor (κOR) agonist, U50,488H, was attenuated in µ-opioid receptor (µOR) knockout mice as compared to wild-type mice when administered spinally. This suggests that an interaction between κORs and µORs exits in the spinal cord. The present study was aimed at investigating whether endogenous opioid peptides were involved in such interaction. METHODS: We examined whether the presence of antibodies to endogenous opioid peptides, endomorphin-2, met-enkephalin and dynorphin A affected the antinociceptive effects of spinal U50,488H in rats. The tail-flick test was used to assess pain thresholds. RESULTS: The increase in tail-flick latency after spinal U50,488H was attenuated when the rats were pretreated intrathecally with antiserum against endomorphin-2. Pretreatments with antisera against met-enkephalin and dynorphin A had no effect on U50,488H antinociception. The antisera alone did not affect pain threshold. CONCLUSION: The results suggest that endomorphin-2, an endogenous opioid peptide highly selective to the µOR, plays a role in antinociception induced by κOR activation in the spinal cord.

[Social pain].

This chapter focuses on what social pain is and how it should be managed. In order to understand social pain in a cancer patient, it is necessary to recognize the change in the patient's daily life after the diagnosis of cancer. Because the degree of suffering and the relationships with family members and the people he or she worked with differ from patient to patient, it is important to note that the context of social pain is different in each patient. Five points shown below are essential in managing social pain. 1. Economical suffering may be alleviated by utilization of the social security system while taking into account each patient's standard of living. 2. Burdens on family members should be lessened, such as by not having them stay at the patient's bedside every day and letting them go home occasionally. 3. The normal patterns of communication, support, and conflict in the family should be identified, and the extent to which they have been disrupted by the illness should be assessed. 4. It is important to understand the ethnic, cultural, and religious background of the patient and the potential impact of their influence on the individual and the illness. 5. Practical or emotional unfinished business that the patient has needs to be identified, and efforts should be made to support fulfillment.

Differential analgesic effects of a mu-opioid peptide, [Dmt(1)]DALDA, and morphine.

AIMS: H-Dmt-D-Arg-Phe-Lys-NH(2) ([Dmt(1)]DALDA), a highly selective micro-opioid peptide, is potently analgesic after systemic and intrathecal administration but is less potent given intracerebroventricularly. This study was performed to further characterize the analgesic effects of [Dmt(1)]DALDA. METHODS: We compared the effects of [Dmt(1)]DALDA and morphine after systemic administration in two different acute pain tests, the tail flick test and the paw withdrawal test, and examined how antagonizing the spinal opioid actions would affect their analgesic effects. RESULTS: [Dmt(1)]DALDA was markedly more potent in the tail flick test than in the hot plate test, while the potencies of morphine were similar in the two tests. Intrathecal naloxone completely blocked the effect of systemic [Dmt(1)]DALDA in the tail flick test, while it only partially blocked the effect of morphine. At higher doses that produced analgesia in the hot plate test, the effect of [Dmt(1)]DALDA in this test was only partially blocked by naloxone. CONCLUSION: Systemic [Dmt(1)]DALDA has a unique analgesic property clearly different from that of morphine and it has a propensity to produce spinal analgesia.

Multiple components of the defense response depend on orexin: evidence from orexin knockout mice and orexin neuron-ablated mice.

Stressor induces not only cognitive, emotional and behavioral changes but also autonomic changes. Although research on the neural circuits underlying such autonomic changes has implicated the hypothalamus in the defense response against stressors, neurotransmitters in this multifaceted and coordinated response have not been revealed. In this brief review, here we summarize our recent discovery using orexin knockout mice and orexin neuron-ablated mice of possible contribution of orexin in the defense response and discuss future directions.

Morphine can produce analgesia via spinal kappa opioid receptors in the absence of mu opioid receptors.

Previous studies have demonstrated the virtual lack of analgesia in mu opioid receptor knockout mice after systemic administration of morphine. Thus, it has been suggested that analgesic actions of morphine are produced via the mu opioid receptor, despite its ability to bind to kappa and delta receptors in vitro. However, it is not clear whether the results of these studies reflect the effect of morphine in the spinal cord. In the present study, we report study of the analgesic actions of spinally-administered morphine and other opioid receptor agonists in mu opioid receptor knockout and wild type mice. Morphine produced a dose-dependent antinociceptive effect in the tail flick test in the knockout mice, although higher doses were needed to produce antinociception than in wild type mice. The antinociceptive effect of morphine was completely blocked by naloxone (a non-selective opioid antagonist) and nor-binaltorphimine (nor-BNI, a selective kappa-opioid receptor antagonist), but not by naltrindole (a selective delta-opioid receptor antagonist). U-50,488H (a selective kappa-opioid receptor agonist) also produced a dose-dependent antinociceptive effect in knockout mice but presented lower analgesic potency in knockout mice than in wild type mice. Analgesic effects of [d-Pen2,d-Pen5]enkephalin (DPDPE, a selective delta-opioid receptor agonist) were observed in wild type mice but abolished in knockout mice. SNC80 (a selective delta-opioid receptor agonist) was not antinociceptive even in wild type mice. The present study demonstrated that morphine can produce thermal antinociception via the kappa opioid receptor in the spinal cord in the absence of the mu opioid receptor. Lower potency of U50,488H in mu opioid receptor knockout mice suggests interaction between kappa and mu opioid receptors at the spinal level.

Differential respiratory effects of [Dmt1]DALDA and morphine in mice.

H-Dmt-D-Arg-Phe-Lys-NH(2) ([Dmt(1)]DALDA, dDAL), a highly selective mu-opioid peptide, produces potent analgesia without respiratory depression after intrathecal administration. Despite carrying 3+ net charge, dDAL is also a potent analgesic after systemic administration. We compared the respiratory effects of dDAL and morphine after subcutaneous administration in mice using whole body plethysmography. Analgesic doses of 3 and 10 times ED(50) were examined. Both drugs dose-dependently decreased respiratory frequency and minute volume in room air. Tidal volume was increased by the lower dose of morphine, while it was decreased by the higher dose of dDAL. The decrease in minute volume by dDAL and morphine was completely reversed by naloxone. No difference in ventilatory response to CO(2) was observed between dDAL and morphine at three times ED(50). Ventilatory response to hypoxia was significantly diminished by dDAL compared to morphine and saline, and this effect of dDAL was naloxone-irreversible. Thus dDAL likely reduces the sensitivity of the peripheral chemoreflex loop through a non-opioid action.