[Show abstract][Hide abstract] ABSTRACT: Opioids are effective analgesics for the management of moderate to severe cancer pain. Here we show that κ opioid receptor (KOR) agonists act as anti-angiogenic factors in tumors. Treatment with KOR agonists, U50,488H and TRK820, significantly inhibited human umbilical vein endothelial cell (HUVEC) migration and tube formation by suppressing VEGFR2 expression. In contrast, treatment with a μ opioid receptor agonist, DAMGO, or a δ opioid receptor agonist, SNC80, did not prevent angiogenesis in HUVECs. Lewis lung carcinoma (LLC) or B16 melanoma grafted in KOR knockout mice showed increased proliferation and remarkably enhanced tumor angiogenesis compared with those in wild type mice. On the other hand, repeated intraperitoneal injection of TRK820 (0.1-10 μg/kg, b.i.d.) significantly inhibited tumor growth by suppressing tumor angiogenesis. These findings indicate that KOR agonists play an important role in tumor angiogenesis and this knowledge could lead to a novel strategy for cancer therapy.
[Show abstract][Hide abstract] ABSTRACT: BACKGROUND:: Patients with peritoneal carcinomatosis often report abdominal pain, which is relatively refractory to morphine. It has been considered that a new animal model is required to investigate the mechanism of abdominal pain for the development of optimal treatments for this type of pain. METHODS:: To prepare a peritoneal carcinomatosis model, highly peritoneal-seeding gastric cancer cells, 60As6, were implanted into the abdominal cavity. The nociceptive modality for pain-related behavior was assessed in terms of withdrawal behavior in response to mechanical stimuli and hunching behavior. Tissue samples from mouse dorsal root ganglia and spinal cord were subject to immunohistochemistry and real-time reverse transcription polymerase chain reaction. RESULTS:: Mice with peritoneal dissemination showed significant hypersensitivity of the abdomen to mechanical stimulation and spontaneous visceral pain-related behavior. There was a significant increase in c-Fos-positive cells in the spinal cord in tumor-bearing mice. Those mice exhibited a remarkable increase in substance P-positive neurons in the dorsal root ganglia (control vs. tumor, 15.4 ± 1.1 vs. 24.2 ± 3.6, P < 0.05, n = 3). A significant decreases in μ-opioid receptor expression mainly in substance P-positive neurons was observed in tumor-bearing mice (69.3 ± 4.9 vs. 38.7 ± 0.9, P < 0.05, n = 3), and a relatively higher dose of morphine was required to significantly reverse the abdominal hypersensitivity. CONCLUSION:: Both the up-regulation of substance P and down-regulation of μ-opioid receptor seen in the dorsal root ganglia may be, at least in part, responsible for the abdominal pain-like state associated with peritoneal carcinomatosis.
[Show abstract][Hide abstract] ABSTRACT: Vagal nerves modulate not only physical homeostasis, but also pain transmission. It has been reported that subdiaphragmatic vagal dysfunction causes visceral pain. However, the functional changes in nociceptive primary afferent fibers under such visceral pain soon after subdiaphragmatic vagal dysfunction are not fully documented. The present study was designed to investigate changes in the sensitivity of primary afferent fibers in the distal colon using a Neurometer which individually stimulates C, Aδ and Aβ fibers. Under stimulation with a handmade stimulus electrode in the distal colon, the current threshold in the distal colon was recorded with high reproducibility. Subdiaphragmatic vagotomy significantly decreased the current threshold of Aδ fibers in the distal colon with no change in the sensitivity of C or Aβ fibers. These results suggest that vagal dysfunction at an early stage may cause, at least in part, hypersensitivity of visceral Aδ fibers.
[Show abstract][Hide abstract] ABSTRACT: Subdiaphragmatic vagal dysfunction causes chronic pain. To verify whether this chronic pain is accompanied by enhanced peripheral nociceptive sensitivity, we evaluated primary afferent neuronal excitability in subdiaphragmatic vagotomized (SDV) rats. SDV rats showed a decrease in the electrical stimuli-induced hind limb-flexion threshold at 250 Hz, but showed no similar effect at 5 or 2000 Hz, which indicated that lumbar primary afferent Aδ sensitivity was enhanced in SDV rats. The whole-cell patch-clamp technique also revealed the hyper-excitability of acutely dissociated medium-sized lumbar dorsal root ganglion (DRG) neurons isolated from SDV rats. The contribution of changes in voltage-dependent potassium (Kv) channels was assessed, and transient A-type K(+) (I(A) ) current density was apparently decreased. Moreover, Kv4.3 immunoreactivity in medium-sized DRG neurons was significantly reduced in SDV rats compared to sham. These results indicate that SDV causes hyper-excitability of lumbar primary Aδ afferent neurons, which may be induced along with suppressing I(A) currents via the decreased expression of Kv4.3. Thus, peripheral Aδ neuroplasticity may contribute to the chronic lower limb pain caused by SDV.
[Show abstract][Hide abstract] ABSTRACT: Although the way for pain management associated with acute pancreatitis has been searched for, there are not enough medications available for it. The aim of the present study was to investigate the role of bradykinin (BK) in pain related to acute pancreatitis. After repeated injections of caerulein (50 μg/kg and 6 times), mice showed edema in the pancreas, and blood concentrations of pancreatic enzymes (amylase and lipase) were clearly elevated. A histopathological study demonstrated that caerulein caused tissue damage characterized by edema, acinar cell necrosis, interstitial hemorrhage, and inflammatory cell infiltrates. Furthermore, the mRNA levels of interleukin-1β and monocyte chemotactic protein (MCP)-1 were significantly increased in the pancreas of caerulein-treated mice. The sensitivity of abdominal organs as measured by abdominal balloon distension was enhanced in caerulein-injected mice, suggesting that caerulein caused pancreatic hyperalgesia. Moreover, repeated treatment with caerulein resulted in cutaneous tactile allodynia of the upper abdominal region as demonstrated by the use of von Frey filaments, indicating that caerulein-treated mice exhibited referred pain. Under this condition, the mRNA levels of bradykinin B1 receptor (BKB1R) and bradykinin B2 receptor (BKB2R) were significantly increased in the dorsal root ganglion (DRG). Finally, we found that des-Arg⁹-(Leu⁸)-bradykinin (BKB1R antagonist) and HOE-140 (BKB2R antagonist) attenuated the acute pancreatitis pain-like state in caerulein-treated mice. These findings suggest that the upregulation of BK receptors in the DRG may, at least in part, contribute to the development of the acute pancreatitis pain-like state in mice.
[Show abstract][Hide abstract] ABSTRACT: The opioid system (opioid peptides and receptors) regulates a variety of neurophysiologic functions, including pain control. Here we show novel roles of the κ opioid system in vascular development. Previously, we revealed that cAMP/protein kinase A (PKA) signaling enhanced differentiation of vascular progenitors expressing VEGF receptor-2 (fetal liver kinase 1; Flk1) into endothelial cells (ECs) through dual up-regulation of Flk1 and Neuropilin1 (NRP1), which form a selective and sensitive VEGF(164) receptor. Kappa opioid receptor (KOR), an inhibitory G protein-coupled receptor, was highly expressed in embryonic stem cell-derived Flk1(+) vascular progenitors. The addition of KOR agonists to Flk1(+) vascular progenitors inhibited EC differentiation and 3-dimensional vascular formation. Activation of KOR decreased expression of Flk1 and NRP1 in vascular progenitors. The inhibitory effects of KOR were reversed by 8-bromoadenosine-3',5'-cAMP or a PKA agonist, N(6)-benzoyl-cAMP, indicating that KOR inhibits cAMP/PKA signaling. Furthermore, KOR-null or dynorphin (an endogenous KOR agonist)-null mice showed a significant increase in overall vascular formation and ectopic vascular invasion into somites at embryonic day -10.5. ECs in these null mice showed significant increase in Flk1 and NRP1, along with reciprocal decrease in plexinD1, which regulates vascular pathfinding. The opioid system is, thus, a new regulator of vascular development that simultaneously modifies 2 distinct vascular properties, EC differentiation and vascular pathfinding.
[Show abstract][Hide abstract] ABSTRACT: To verify whether vagal dysfunction is associated with chronic pain, we evaluated the effects of subdiaphragmatic vagotomy (vgx) on the sensitivity toward noxious stimuli in rats. Vgx rats showed sustained hyperalgesia in the gastrocnemius muscle without tissue damage (no increase in vgx-induced plasma creatine phosphokinase or lactose dehydrogenase levels) accompanied by hypersensitivity to colonic distension. We found a dramatic increase in the levels of metabotropic glutamate receptor 5, protein kinase C (PKC) gamma and phosphorylated-PKCgamma within the spinal cord dorsal horn in vgx rats, which suggests that vgx may evoke sensory nerve plasticity. Morphine produced a dose-dependent increase in the withdrawal threshold in both vgx and sham-operated rats, but the effect of a lower dose in vgx rats was weaker than that in sham-operated rats. Muscle hyperalgesia in vgx rats was also attenuated by gabapentin and amitriptyline, but was not affected by diclofenac, dexamethasone or diazepam. These findings indicate that subdiaphragmatic vagal dysfunction caused chronic muscle hyperalgesia accompanied by visceral pain and both gabapentin and amitriptyline were effective for subdiaphragmatic vagotomy-induced pain, which are partially similar to fibromyalgia syndrome. Furthermore, this chronic muscle pain may result from nociceptive neuroplasticity of the spinal cord dorsal horn.