β-Arrestin-biased agonists are a new class of drugs with promising therapeutic effects. The molecular mechanisms of β-arrestin-biased agonists are still not completely identified. Here, we investigated the effect of angiotensin II (AngII) and [Sar1,Ile4,Ile8] AngII (SII), a β-arrestin-biased agonist, on ezrin–radixin–moesin (ERM) phosphorylation in NIH3T3 cells (a fibroblast cell line) stably expressing AngII type 1A receptor. ERM proteins are cross-linkers between the plasma membrane and the actin cytoskeleton and control a number of signaling pathways. We also investigated the role of Gαq protein and β-arrestins in mediating ERM phosphorylation. We found that AngII stimulates ERM phosphorylation by acting as a β-arrestin-biased agonist and AngII-stimulated ERM phosphorylation is mediated by β-arrestin2 not β-arrestin1. We also found that SII inhibits ERM phosphorylation by acting as a Gαq protein–biased agonist. We concluded that ERM phosphorylation is a unique β-arrestin-biased agonism signal. Both AngII and SII can activate either Gαq protein or β-arrestin-mediated signaling as functional biased agonists according to the type of the cell on which they act.
Glutamatergic dysfunction has been implicated in psychiatric disorders such as schizophrenia. Both the stimulation of the metabotropic glutamate (mGlu) 2/3 receptor and the blockade of the mGlu1 receptor have been shown to be effective in a number of animal models of schizophrenia. However, the efficacy for social cognition, which is poorly managed by current medication, has not been fully addressed. The present study evaluated the effects of an mGlu2/3-receptor agonist and an mGlu1-receptor antagonist on social memory impairment in rats. Pretreatment with an mGlu2/3-receptor agonist, (−)-2-oxa-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate (LY379268), or an mGlu1-receptor antagonist, (3,4-dihydro-2H-pyrano[2,3-b]quinolin-7-yl)-(cis-4-methoxycyclohexyl)-methanone (JNJ16259685), improved social memory impairment induced by 5R,10S-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801) without affecting the social interactions. In addition, the intraperitoneal administration of an mGlu2-receptor potentiator, 3'-[[(2-cyclopentyl-2,3-dihydro-6,7-dimethyl-1-oxo-1H-inden-5-yl)oxy]methyl]-[1,1'-biphenyl]-4-carboxylic acid (BINA), also improved the MK-801–induced impairment of social memory, which was blocked by pretreatment with an mGlu2/3-receptor antagonist, (2S)-2-amino-2-[(1S,2S)-2-carboxycycloprop-1-yl]-3-(xanth-9-yl) propanoic acid (LY341495). These findings indicate that both the stimulation of the mGlu2 receptor and the inhibition of an mGlu1 receptor improve social memory impairment elicited by MK-801, and both manipulations could be effective approaches for the treatment of certain cognitive dysfunctions observed in schizophrenic patients.
This study aims to evaluate the protective effects of Yi-Qi-Fu-Mai sterile powder (YQFM) on myocardial oxidative damage and tries to identify the active components responsible for its pharmacological benefits. YQFM and the n-butanol extract of YQFM (YQFM-Bu) were administered to ISO-induced myocardial injury mice. Left ventricle weight index and histopathological analyses were conducted. Serum enzymatic activities of lactate dehydrogenase (LDH), creatine kinase (CK) and superoxide dismutase (SOD), myeloperoxidase (MPO), and the levels of malondialdehyde (MDA) were also measured. Our results demonstrated that both YQFM and YQFM-Bu significantly restored the abnormal activities of CK, LDH, MPO, SOD, and the levels of MDA in ISO-induced myocardial injury mice, and these biochemical results were further supported by histopathological data. Our in vitro findings also confirmed that both YQFM and YQFM-Bu exhibit significant radical scavenging activity. Furthermore, the major active fractions of YQFM were identified by UPLC–MS/MS. Twenty-five ginsenosides and three lignans were identified from YQFM-Bu. These findings suggested YQFM-Bu is the major active fraction of YQFM with the ginsenosides and lignans as potential active components responsible for its protective effect against myocardial injury, and YQFM exerted its beneficial effects on myocardial injury mainly through inhibiting oxidative damage and maintaining the functional integrity of myocardial tissue.
In the present study, we investigated the effects of angiotensin AT1–receptor blockers, KT3-671 and losartan, on the cardiac vagal neurotransmission in pithed rats. The bradycardia induced by vagal nerve stimulation (VNS, at 5 Hz) was potentiated significantly and dose-dependently by KT3-671 and also losartan. This enhancement effect of KT3-671 (10 mg/kg) was slightly potent than that of losartan (10 mg/kg). On the other hand, an angiotensin AT2–receptor blocker, PD123319 (10 mg/kg), did not affect VNS-induced bradycardia. KT3-671 and losartan did not affect the exogenous acetylcholine-evoked bradycardia. Intravenous infusion of AngII (100 ng/kg per min) attenuated the VNS-induced bradycardia. This inhibitory effect of AngII on bradycardia was restored by both KT3-671 and losartan. These results suggest that endogenous AngII can have a tonic inhibitory effect on cardiac vagal transmission by stimulating the presynaptic AT1 receptors not AT2 receptors. Suppression of this mechanism by the AT1-receptor blockers causes the facilitation of acetylcholine release from vagal nerve endings. This acceleratory effect of AT1-receptor blockers on cardiac vagal neurotransmission may contribute to the lack of reflex tachycardia following hypotension.
In clinical studies, electroconvulsive stimuli have been associated with improvements in both depression and treatment-resistant depression. In a previous study, treatment with adrenocorticotropic hormone (ACTH) for 14 days decreased adult hippocampal cell proliferation. Furthermore, electroconvulsive stimuli significantly decreased the duration of immobility following repeated administration of ACTH for 14 days in rats. The present study was undertaken to further characterize the mechanism of treatmentresistant antidepressant effects of electroconvulsive stimuli by measuring cell proliferation, brain-derived neurotrophic factor (BDNF) levels, and phosphorylated and total cyclic adenosine monophosphate (cAMP) response element–binding protein (pCREB/CREB) levels in the hippocampus of ACTH-treated rats. Electroconvulsive stimuli increased cell proliferation in both saline-treated and ACTH-treated rats. Mature-BDNF protein levels showed a tendency to decrease in ACTH-treated rats. Electroconvulsive stimuli treatment increased mature-BDNF protein levels in the hippocampus of both saline-treated and ACTH-treated rats. Furthermore, electroconvulsive stimuli increased phospho-Ser133-CREB (pCREB) levels and the ratio of pCREB/CREB in both saline-treated and ACTH-treated rats. These findings suggest that the treatment-resistant antidepressant effects of electroconvulsive stimuli may be attributed, at least in part, to an enhancement of hippocampal cell proliferation.
GABA is an inhibitory transmitter found in rat salivary gland. However, the inhibitory potential of GABA on salivary secretion is unclear. Using an in vivo cannulation method, intraperitoneal administration of GABA was ineffective in the absence of gabaculine, a GABA transaminase inhibitor, on pilocarpine-induced salivary secretion, suggesting that GABA was rendered metabolically inactive before reaching the salivary gland. We hypothesized that the action of a drug on the salivary glands could be measured directly using a submandibular gland perfusion system. The submandibular gland artery, veins, and duct were cannulated in situ so that physiological functions such as innervation would not be compromised. Hank's balanced salt solution (pH 7.4) was perfused at a rate of 0.5 ml/min together with 1 μM carbachol (CCh) over a 5-min period every 30 min. Amount of secreted saliva showed no change to the recurrent addition of CCh to the perfusate. GABA or muscimol dose-dependently inhibited CCh-induced salivary secretion. This effect was blocked by bicuculline, a GABAA-receptor (GABAA-R) antagonist, and enhanced by clonazepam, a central-type benzodiazepine-receptor agonist. These results suggest that salivary secretion is suppressed by GABAA-R in rat salivary gland and that the perfusion method used was effective in clarifying inhibitory regulation of GABAA-R.
We evaluated the effect of buprenorphine, a mixed agonist for μ-opioid receptors and nociceptin/orphanin FQ peptide (NOP) receptors, in neuropathic rats, using the paw pressure test. Buprenorphine, administered i.p. at 50, but not 20, μg/kg, exhibited naloxone-reversible analgesic activity in naïve rats. In contrast, buprenorphine at 0.5 – 20 μg/kg produced a naloxonesensitive antihyperalgesic effect in the L5 spinal nerve–injured neuropathic rats. Intrathecal injection of [N-Phe1]nociceptin(1-13)NH2, a NOP-receptor antagonist, reversed the effect of buprenorphine in neuropathic rats, but not in naïve rats. Together, buprenorphine suppresses neuropathic hyperalgesia by activating NOP and opioid receptors, suggesting its therapeutic usefulness in treatment of neuropathic pain.
An attempt was made to clarify the additive suppressive effects of pranlukast, a cysteinyl leukotriene–receptor (LTR) antagonist, in combination with chlorpheniramine, an antihistamine, on the up-regulation of histamine H1–receptor (H1R) mRNA in toluene 2,4-diisocyanate (TDI)-sensitized rats. Although pre-treatment with pranlukast partially, but significantly, suppressed TDI-induced up-regulation of H1R mRNA and nasal symptoms, pre-treatment with the combination of pranlukast and chlorpheniramine significantly suppressed them in a manner greater than either drug alone. These findings suggest that the additive therapeutic effect of the combination of LTR antagonist and antihistamine is due to their additive suppression of H1R up-regulation.