In vitro functional evidence of different neurotensin-receptors modulating the motor response of human colonic muscle strips

The direct profibrotic and indirect immune antifibrotic balance of blocking the cannabinoid 2 receptor

Cannabinoid 2 (CB2) receptors expressed on immune cells are considered to be antifibrogenic. Hepatic stellate cells (HSCs) directly interact with phagocytosis lymphocytes, but the nature of this interaction is obscure. We aimed to study the effects of CB2 receptors on hepatic fibrosis via their role in mediating immunity. Hepatic fibrosis was induced by carbon-tetrachloride (CCl(4)) administration in C57BL/6 wild-type (WT) and CB2 knockout (CB2(-/-)) mice. Irradiated animals were reconstituted with WT or CB2(-/-) lymphocytes. Lymphocytes from naïve/fibrotic WT animals and healthy/cirrhotic hepatitis C virus were preincubated in vitro with or without CB2 antagonist, evaluated for proliferation and apoptosis, and then cocultured with primary mouse HSCs or a human HSC line (LX2), respectively. Lymphocyte phagocytosis was then evaluated. Following CCl(4)-administration, CB2(-/-) mice developed significant hepatic fibrosis but less necroinflammation. WT mice harbored decreased liver CD4(+) and NK(+) cells but increased CD8(+) subsets. Naïve CB2(-/-) mice had significantly decreased T cell subsets. Adoptive transfer of CB2(-/-) lymphocytes led to decreased fibrosis in the irradiated WT recipient compared with animals receiving WT lymphocytes. Moreover, necroinflammation also tended to decrease. In vitro, a CB2-antagonist directly increased human HSC activation and increased apoptosis and decreased proliferation of mice/human T cells (healthy/fibrotic) and their phagocytosis. We concluded that CB2(-/-) lymphocytes exert an antifibrotic activity, whereas lack of CB2 receptor in HSCs promotes fibrosis. These findings broaden our understanding of cannabinoid signaling in hepatic fibrosis beyond their activity solely in HSCs.

Complex actions of neurotensin in ascending and sigmoid colonic muscle: Involvement of enteric mediators

The brain-gut peptide neurotensin has complex effects on gastrointestinal smooth muscle. Our objective was to elucidate the mechanisms underlying neurotensin contractions in human colon. Discrete concentration response curves to neurotensin were obtained in strips of circular muscle and taenia coli from "normal" ascending and sigmoid colon segments, in the presence and absence of various pharmacological inhibitors. Potency of neurotensin in all regions was similar (pD(2) ~7). Atropine and the selective muscarinic receptor antagonists, methoctramine and darifenacin, had no effect on neurotensin contractions. In ascending colon circular muscle, responses were enhanced by indomethacin (indicating inhibitory prostaglandin mechanisms) and by tetrodotoxin (TTX), hexamethonium and L-NAME, suggesting nicotinic and enteric inhibitory neurotransmission, with involvement of nitric oxide. In sigmoid circular muscle, neurotensin responses were also enhanced by TTX and hexamethonium, but were attenuated in the presence of mepyramine, MEN10627 and CP99994, suggesting inhibitory neuronal mechanisms and involvement of histamine and tachykinins, respectively; L-NAME and the GABA(B) receptor antagonist, CGP36742, were without effect. The transcripts of NTS1 and NTS3 receptors, but not NTS2 receptors, were detected in sigmoid colon circular muscle and taenia coli. No age and gender differences in NTS1 mRNA expression were found. In conclusion, neurotensin contracts circular muscle strips from ascending and sigmoid regions of the human colon via direct (muscle) and indirect (neuronal/non-neuronal mechanisms). The enteric mediators influenced by neurotensin are regionally specific. In taenia coli strips from both ascending and sigmoid colon, neurotensin contractions were unchanged in the presence of inhibitors, suggesting direct actions only.

GPCR Screening via ERK 1/2: A Novel Platform for Screening G Protein–Coupled Receptors

Discovery of novel agonists and antagonists for G protein–coupled receptors (GPCRs) relies heavily on cell-based assays because determination of functional consequences of receptor engagement is often desirable. Currently, there are several key parameters measured to achieve this, including mobilization of intracellular Ca2+ and formation of cyclic adenosine monophosphate or inositol triphosphate. However, no single assay platform is suitable for all situations, and all of the assays have limitations. The authors have developed a new high-throughput homogeneous assay platform for GPCR discovery as an alternative to current assays, which employs detection of phosphorylation of the key signaling molecule p42/44 MAP kinase (ERK 1/2). The authors show that ERK 1/2 is consistently activated in cells stimulated by Gq-coupled GPCRs and provides a new high-throughput platform for screening GPCR drug candidates. The activation of ERK 1/2 in Gq-coupled GPCR systems generates comparable pharmacological data for receptor agonist and antagonist data obtained by other GPCR activation measurement techniques.

Antinociceptive, hypothermic, hypotensive, and reinforcing effects of a novel neurotensin receptor agonist, NT69L, in rhesus monkeys

Neurotensin (NT) is a tridecapeptide found in the nervous system, as well as elsewhere in the body. It has anatomic and functional relationships to dopaminergic neurons in brain. NT has been implicated in the actions of antipsychotic drugs and psychostimulants, and animal studies suggest that neurotensin directly injected into brain has reinforcing effects. Previously, we showed that one of our brain-penetrating analogs of neurotensin, NT69L (N-methyl-L-Arg, L-Lys, L-Pro, L-neo-Trp, L-tert-Leu, L-Leu), has many pharmacological effects in rats including antinociception, hypothermia, and blockade of the hyperactivity caused by psychostimulants (cocaine, D-amphetamine, and nicotine). Since these studies in rats suggest that this compound may have clinical use in humans, we were interested to know what effects NT69L had in primates. NT69L caused a potent antinociceptive effect against capsaicin (0.1 mg)-induced allodynia in 46 degrees C water in rhesus monkeys, inducing 40% of the maximal possible effect at an intravenous dosage of 0.03 mg/kg; its hypotensive effects precluded evaluation of higher dosages. Core temperature measured by rectal probe was modestly reduced at 0.01 and 0.03 mg/kg. In an intravenous self-administration procedure, NT69L was without reinforcing effects at any dose, including those that caused other pharmacological effects, and did not alter cocaine-maintained behavior when administered as a pretreatment.

SR 48692, a specific neurotensin receptor antagonist, has no effect on oesophageal motility in humans

BACKGROUND

The administration of exogenous neurotensin can reduce the lower oesophageal sphincter pressure, but it is unclear whether this effect is pharmacological or physiological.

AIM

A specific neurotensin receptor antagonist (SR 48692) was used to assess the effect of endogenous neurotensin on lower oesophageal sphincter function.

METHODS

Twenty-four healthy male subjects were included in a double-blind, placebo-controlled, randomized, cross-over study designed to determine the effects of two single doses (90 and 300 mg, preceded by a loading dose) of SR 48692 on the resting lower oesophageal sphincter pressure, transient lower oesophageal sphincter relaxations, primary oesophageal peristalsis and oesophageal acid exposure. Oesophageal pH and motility recordings were performed during 1 h of fasting and 3 h post-prandially. Plasma neurotensin-like immunoreactivity release was determined by radioimmunoassay.

RESULTS

During fasting, the lower oesophageal sphincter pressure, transient lower oesophageal sphincter relaxation rate and reflux episodes were similar with the two doses of SR 48692 and placebo. Meal ingestion induced a rise in plasma neurotensin-like immunoreactivity, a decrease in lower oesophageal sphincter pressure and an increase in both the transient lower oesophageal sphincter relaxation rate and the number of reflux episodes, which were not significantly modified by SR 48692. SR 48692 did not affect oesophageal primary peristalsis.

CONCLUSION

This study shows that SR 48692, a specific neurotensin 1 receptor antagonist, has no effect on oesophageal motility in humans.

The effects of deleting the mouse neurotensin receptor NTR1 on central and peripheral responses to neurotensin

Mice deficient in the neurotensin (NT)-1 receptor (NTR1) were developed to characterize the NT receptor subtypes that mediate various in vivo responses to NT. F2 generation (C57BL6/Sv129J) NTR1 knockout (-/-) mice were viable, and showed normal growth and overt behavior. The -/- mice lacked detectable NTR1 radioligand binding in brain, whereas NTR2 receptor binding density appeared normal compared with wild-type (+/+) mice. The gene deletion also resulted in the loss of NTR1 expression as determined by reverse transcription-polymerase chain reaction and in situ hybridization. Intracerebroventricular injection of NT (1 microg) to +/+ mice caused a robust hypothermic response (5-6 degrees C) and a significant increase in hot-plate latency. These effects were absent in the -/- mice. Similar results were obtained with i.p. injections of the brain-penetrant NT analog NMe-Arg-Lys-Pro-Trp-Tle-Leu (NT-2, 1 mg/kg i.p.). NT-2 administration also impaired rotarod performance in wild-type mice, but had no effect on motor coordination in knockout mice. In vitro, NT and NT-2 at 30 nM caused predominantly contraction and relaxation in isolated distal colon and proximal ileum, respectively, from +/+ mice, but no responses were observed with tissues from -/- mice. A similar loss of the contractile effects of NT was observed in the isolated stomach fundus from the knockout mice. In vivo, NT-2 administration reduced colonic propulsion substantially in wild-type mice. In contrast, NT-2 had no effect in NTR1 null mice, whereas the hypomotility effect of clonidine was intact. These data indicate that NTR1 mediates several of the central and peripheral effects of NT.