Ai-Niu Ma

Site‐specific PEGylation of exenatide analogues markedly improved their glucoregulatory activity

Exenatide is a 39‐amino‐acid peptide widely used to manage type 2 diabetes mellitus. However, it has a short plasma half‐life and requires a twice daily injection regime. To overcome these drawbacks we used maleimide‐polyethylene glycol to induce site‐specific PEGylation.

Role of spinal 5-HT receptors in cutaneous hypersensitivity induced by REM sleep deprivation.

Previous studies indicate that rapid eye movement (REM) sleep deprivation facilitates pain sensitivity. Since serotoninergic raphe neurons are involved both in regulation of sleep and descending pain modulation, we studied whether spinal 5-HT receptors have a role in sleep deprivation-induced facilitation of pain-related behavior. REM sleep deprivation of 48h was induced by the flower pot method in the rat. The pain modulatory influence of various serotoninergic compounds administered intrathecally was assessed by determining limb withdrawal response to monofilaments. REM sleep deprivation produced a marked hypersensitivity. Sleep deprivation-induced hypersensitivity and normal sensitivity in controls were reduced both by a 5-HT(1A) receptor antagonist (WAY-100635) and a 5-HT(2C) receptor antagonist (RS-102221). An antagonist of the 5-HT(3) receptor (LY-278584) failed to modulate hypersensitivity in sleep-deprived or control animals. Paradoxically, sensitivity in sleep-deprived and control animals was reduced not only by a 5-HT(1A) receptor antagonist but also by a 5-HT(1A) receptor agonist (8-OHDPAT). The results indicate that serotoninergic receptors in the spinal cord have a complex role in the control of sleep-deprivation induced cutaneous hypersensitivity as well as baseline sensitivity in control conditions. While endogenous serotonin acting on 5-HT(1A) and 5-HT(2C) receptors may facilitate mechanical sensitivity in animals with a sleep deprivation-induced hypersensitivity as well as in controls, increased activation of spinal 5-HT(1A) receptors by an exogenous agonist leads to suppression of mechanical sensitivity in both conditions. Spinal 5-HT(3) receptors do not contribute to cutaneous hypersensitivity induced by sleep deprivation.

The non-peptide GLP-1 receptor agonist WB4-24 blocks inflammatory nociception by stimulating β-endorphin release from spinal microglia

Two peptide agonists of the glucagon‐like peptide‐1 (GLP‐1) receptor, exenatide and GLP‐1 itself, exert anti‐hypersensitive effects in neuropathic, cancer and diabetic pain. In this study, we have assessed the anti‐allodynic and anti‐hyperalgesic effects of the non‐peptide agonist WB4‐24 in inflammatory nociception and the possible involvement of microglial β‐endorphin and pro‐inflammatory cytokines.

Intrathecal administration of a gap junction decoupler, an inhibitor of Na+–K+–2Cl− cotransporter 1, or a GABAA receptor agonist attenuates mechanical pain hypersensitivity induced by REM sleep deprivation in the rat

We studied the hypothesis that some of the spinal mechanisms that are involved in neuropathic hypersensitivity play a role in hypersensitivity induced by REM sleep deprivation (REMSD). Rats with a chronic intrathecal (i.t.) catheter had REMSD of 48h duration that induced hypersensitivity to mechanical stimulation. After REMSD, the animals were treated i.t. with carbenoxolone (a gap junction decoupler), bumetanide (a blocker of Na(+)-K(+)-2Cl(-) cotransporter 1 or NKCC1), muscimol (a GABA(A) receptor agonist), or pretreated intraperitoneally with minocycline (an inhibitor of microglia activation). Previously, all these treatments attenuated neuropathic hypersensitivity. Following REMSD, carbenoxolone, bumetanide and muscimol had a strong antihypersensitivity effect, whereas pretreatment with minocycline failed to prevent development of hypersensitivity. The results suggest that among spinal pain facilitatory mechanisms that are common to REMSD and neuropathy are NKCC1 blocker- and gap junction decoupler-reversible mechanisms. Moreover, there is a net pain inhibitory effect by spinal administration of an exogenous GABA(A) receptor agonist following REMSD as shown earlier in neuropathy. In contrast, activation of spinal microglia may not be as important for the development of hypersensitivity induced by REMSD as following nerve injury.

Interactions of the potent D-amino acid oxidase inhibitor CBIO with morphine in pain and tolerance to analgesia.

A series of experiments using technologies of gene mutation and silencing as well as chemical biology have demonstrated that spinal D-amino acid oxidase (DAAO) contributes to the development of central sensitization-mediated chronic pain and might be a potential molecular target for the treatment of chronic pain. DAAO inhibitors are now under clinical investigations for the management of chronic neuropathic pain. This study examined the interactions between morphine and the DAAO inhibitor CBIO (5-chloro-benzo[d]isoxazol-3-ol) in pain and analgesia tolerance mainly in the formalin test. Given subcutaneously CBIO acutely interacted with morphine in analgesia in an additive manner both in the acute nociception settings (the formalin acute phase nociception, hot-plate test and tail immersion test) and in formalin-induced tonic pain. Bi-daily exposure of CBIO given subcutaneously for 7 days did not produce self-tolerance to analgesia or cross-tolerance to morphine whereas 7-day subcutaneous morphine induced self-tolerance to analgesia but not cross-tolerance to CBIO. More importantly, subcutaneous co-administrations or even single dose of CBIO completely prevented or reversed morphine tolerance to analgesia (exhibited by a single dose or a dose-response curve of morphine) in both formalin-induced acute phase nociception and tonic phase pain. These results, for the first time, identified DAAO as an efficacious molecule mediating morphine tolerance, in addition to clarifying the complex interactions between morphine and DAAO inhibitors probed by CBIO, and provided a pharmacological basis for DAAO inhibitors in combination with morphine to clinically manage pain.

Potential role of spinal TRPA1 channels in antinociceptive tolerance to spinally administered morphine

BACKGROUND Prolonged morphine treatment leads to antinociceptive tolerance. Suppression of spinal astrocytes or d-amino acid oxidase (DAAO), an astroglial enzyme catalyzing oxidation of d-amino acids, has reversed morphine antinociceptive tolerance. Since the astrocyte-DAAO pathway generates hydrogen peroxide, an agonist of the TRPA1 channel expressed spinally on nociceptive nerve terminals and astrocytes, we tested a hypothesis that the spinal TRPA1 contributes to antinociceptive tolerance to prolonged spinal morphine treatment. METHODS Nociception was assessed using hot-plate test in rats with an intrathecal (it) catheter. Drugs were administered it twice daily from day one to seven in five treatment groups: (i) Saline, (ii) Chembridge-5861528 (a TRPA1 antagonist; 10μg), (iii) morphine (10μg), (iv) Chembridge-5861528 (10μg)+morphine (10μg), (v) DMSO. Antinociceptive action of morphine was assessed at day one and eight. Additionally, mRNA for DAAO and TRPA1 in the spinal cord was determined on day 8. RESULTS Morphine treatment produced antinociceptive tolerance, which was attenuated by co-administration of Chembridge-5861528 that alone had no effect on hot-plate latencies. In animals treated with morphine only, spinal mRNA for DAAO but not TRPA1 was increased. DAAO increase was prevented by co-administration of Chembridge-5861528. CONCLUSIONS Antinociceptive morphine tolerance and up-regulation of spinal DAAO were attenuated in morphine-treated animals by blocking the spinal TRPA1. This finding suggests that spinal TRPA1 may contribute, at least partly, to facilitation of morphine antinociceptive tolerance through mechanisms that possibly involve TRPA1-mediated up-regulation of the astroglial DAAO, a generator of hydrogen peroxide, a pronociceptive compound acting also on TRPA1.

Mechanical antihypersensitivity effect induced by repeated spinal administrations of a TRPA1 antagonist or a gap junction decoupler in peripheral neuropathy.

Spinal transient receptor potential ankyrin 1 (TRPA1) channel is associated with various pain hypersensitivity conditions. Spinally, TRPA1 is expressed by central terminals of nociceptive nerve fibers and astrocytes. Among potential endogenous agonists of TRPA1 is H2O2 generated by d-amino acid oxidase (DAAO) in astrocytes. Here we studied whether prolonged block of the spinal TRPA1 or astrocytes starting at time of injury attenuates development and/or maintenance of neuropathic hypersensitivity. Additionally, TRPA1 and DAAO mRNA were determined in the dorsal root ganglion (DRG) and spinal dorsal horn (SDH). Experiments were performed in rats with spared nerve injury (SNI) and chronic intrathecal catheter. Drugs were administered twice daily for the first seven injury days or only once seven days after injury. Mechanical hypersensitivity was assessed with monofilaments. Acute and prolonged treatment with Chembridge-5861528 (a TRPA1 antagonist), carbenoxolone (an inhibitor of activated astrocytes), or gabapentin (a comparison drug) attenuated tactile allodynia-like responses evoked by low (2g) stimulus. However, antihypersensitivity effect of these compounds was short of significance at a high (15g) stimulus intensity. No preemptive effects were observed. In healthy controls, carbenoxolone failed to prevent hypersensitivity induced by spinal cinnamaldehyde, a TRPA1 agonist. TRPA1 and DAAO mRNA in the DRG but not SDH were slightly increased in SNI, independent of drug treatment. The results indicate that prolonged peri-injury block of spinal TRPA1 or inhibition of spinal astrocyte activation attenuates maintenance but not development of mechanical (tactile allodynia-like) hypersensitivity after nerve injury.

Beneficial effects of natural Jeju groundwaters on lipid metabolism in high-fat diet-induced hyperlipidemic rats

BACKGROUND Groundwater is believed to possess many beneficial effects due to its natural source of various minerals. In this study, we examined the effects of natural Jeju groundwater S1 (Samdasoo™), S2 and S3 pumped up from different locations of Jeju Island, Korea, along with local tap water, on body weight gain, serum lipids and lipoproteins, and liver histopathology in high-fat diet-induced hyperlipidemic rats. MATERIALS/METHODS Rats were randomly and equally divided into 6 groups. Different water samples were supplied to the hyperlipidemic rats as their daily drinking water and the widely-used anti-hyperlipidemic drug simvastatin was used as a positive control. Body weight, serum lipids and lipoproteins were measured weekly. Liver weight, liver index and liver histopathology were examined after the execution of the rats. RESULTS After drinking Jeju groundwaters for two months, S2 but not S3 significantly reduced weight growth and serum triglycerides levels and increased high density lipoprotein-C (HDL-C) without affecting total cholesterol or LDL-C. S1 and particularly S2 significantly reduced the severity of liver hypertrophy and steatosis. All Groundwaters had much higher contents of vanadium (S3>S2>S1>>tap water) whereas S1 and S2 but not S3 markedly blocked autoxidation of ferrous ions. CONCLUSION Jeju Groundwater S1 and particularly S2 exhibit protective effects against hyperlipidemia and fatty liver and hypothesize that the beneficial effect of Jeju Groundwaters may be contributed from blockade of autoxidation of ferrous ions rather than their high contents of vanadium.