Reprint of Pharmacological and molecular characterization of the positive allosteric modulators of metabotropic glutamate receptor 2.

The metabotropic glutamate receptor 2 (mGlu2) plays an important role in the presynaptic control of glutamate release and several mGlu2 positive allosteric modulators (PAMs) have been under assessment for their potential as antipsychotics. The binding mode of mGlu2 PAMs is better characterized in functional terms while few data are available on the relationship between allosteric and orthosteric binding sites. Pharmacological studies characterizing binding and effects of two different chemical series of mGlu2 PAMs are therefore carried out here using the radiolabeled mGlu2 agonist 3[H]-LY354740 and mGlu2 PAM 3[H]-2,2,2-TEMPS. A multidimensional approach to the PAM mechanism of action shows that mGlu2 PAMs increase the affinity of 3[H]-LY354740 for the orthosteric site of mGlu2 as well as the number of 3[H]-LY354740 binding sites. 3[H]-2,2,2-TEMPS binding is also enhanced by the presence of LY354740. New residues in the allosteric rat mGlu2 binding pocket are identified to be crucial for the PAMs ligand binding, among these Tyr3.40 and Asn5.46. Also of remark, in the described experimental conditions S731A (Ser5.42) residue is important only for the mGlu2 PAM LY487379 and not for the compound PAM-1: an example of the structural differences among these mGlu2 PAMs. This study provides a summary of the information generated in the past decade on mGlu2 PAMs adding a detailed molecular investigation of PAM binding mode. Differences among mGlu2 PAM compounds are discussed as well as the mGlu2 regions interacting with mGlu2 PAM and NAM agents and residues driving mGlu2 PAM selectivity. This article is part of the Special Issue entitled 'Metabotropic Glutamate Receptors, 5 years on'.

Pharmacological and molecular characterization of the positive allosteric modulators of metabotropic glutamate receptor 2.

The metabotropic glutamate receptor 2 (mGlu2) plays an important role in the presynaptic control of glutamate release and several mGlu2 positive allosteric modulators (PAMs) have been under assessment for their potential as antipsychotics. The binding mode of mGlu2 PAMs is better characterized in functional terms while few data are available on the relationship between allosteric and orthosteric binding sites. Pharmacological studies characterizing binding and effects of two different chemical series of mGlu2 PAMs are therefore carried out here using the radiolabeled mGlu2 agonist 3[H]-LY354740 and mGlu2 PAM 3[H]-2,2,2-TEMPS. A multidimensional approach to the PAM mechanism of action shows that mGlu2 PAMs increase the affinity of 3[H]-LY354740 for the orthosteric site of mGlu2 as well as the number of 3[H]-LY354740 binding sites. 3[H]-2,2,2-TEMPS binding is also enhanced by the presence of LY354740. New residues in the allosteric rat mGlu2 binding pocket are identified to be crucial for the PAMs ligand binding, among these Tyr3.40 and Asn5.46. Also of remark, in the described experimental conditions S731A (Ser5.42) residue is important only for the mGlu2 PAM LY487379 and not for the compound PAM-1: an example of the structural differences among these mGlu2 PAMs. This study provides a summary of the information generated in the past decade on mGlu2 PAMs adding a detailed molecular investigation of PAM binding mode. Differences among mGlu2 PAM compounds are discussed as well as the mGlu2 regions interacting with mGlu2 PAM and NAM agents and residues driving mGlu2 PAM selectivity.

Hemodynamics, biochemical effects, and pharmacokinetics of the renin inhibitor remikiren in healthy human subjects.

INTRODUCTION: Remikiren (Ro 42-5892) is a potent and specific inhibitor of human renin in vitro. Its in vivo action on plasma renin activity (PRA), immunoreactive renin, and blood pressure has been shown in pilot studies in humans. OBJECTIVE: To investigate tolerability, hemodynamic effects, and biochemical effects of remikiren in relation to its pharmacokinetics after single ascending intravenous and oral doses in healthy humans. METHODS: In this double-blind, placebo-controlled, two-way crossover (intravenous and oral) study, single ascending doses of 10, 20, 40, 80, 160, and 320 mg (intravenous) and 100, 200, 400, 800, and 1600 mg (oral) were given; six subjects received active drug and three received placebo at each dose level. At regular intervals, blood pressure, heart rate, cardiac output, PRA, immunoreactive renin, and drug plasma levels were determined. RESULTS: The compound was well tolerated except at the 1600 mg oral dose level at which diarrhea occurred in two subjects. At neither dose were there effects on blood pressure, heart rate, or cardiac output relative to placebo. PRA and angiotensin I production rate decreased and immunoreactive renin increased dose dependently after both intravenous and oral administration. The duration of these effects was also dose dependent and was longer than 12 hours with higher doses. Systemic plasma clearance, volume of distribution, and absolute bioavailability of remikiren were in the magnitude of 900 ml/min, 70 L, and below 1%, respectively. The angiotensin I production rate correlated in a sigmoidal way with plasma drug concentrations independent of the route of administration. CONCLUSION: Remikiren is a potent inhibitor of renin in humans with long-lasting effects after both intravenous and oral administration.

Cimetidine alters the disposition kinetics of the monoamine oxidase-A inhibitor moclobemide.

The influence of cimetidine on the absorption and disposition of moclobemide was examined in eight healthy male subjects. A single 100 mg intravenous and 100 mg oral dose of moclobemide was administered before and after 2 weeks of cimetidine administration (200 mg five times a day). The data on intravenous administration indicated that cimetidine produced a statistically significant alteration in the following disposition parameters (mean values for control versus cimetidine): systemic clearance, 46.6 versus 28.3 L/hr; mean residence time, 2.1 versus 3.2 hours; elimination half-life, 1.6 versus 2.3 hours. There was no significant difference in the steady-state volume of distribution. The absolute oral bioavailability of moclobemide increased significantly after cimetidine administration (54% versus 68%), as did the maximum plasma concentration after a single oral dose (575 versus 787 ng/ml). There were no differences in the mean absorption time or time to achieve maximum concentration. The values of systemic and apparent oral clearances of moclobemide after cimetidine administration were directly related to the corresponding control values before cimetidine. In contrast, the percentage change in clearance was essentially independent of the corresponding initial control clearance value.

Effect of food intake on the relative bioavailability of moclobemide (Ro 11-1163).

Twelve healthy adult volunteers received a single 100-mg tablet of moclobemide in an open-label crossover study designed to determine the influence of food on moclobemide absorption. Moclobemide was administered 30 min after a standard breakfast as well as under fasting conditions. Moclobemide absorption was rapid in the absence of food. Bioavailability parameters obtained when drug was taken 30 min after the meal suggested that the rate of absorption was slightly decreased in the presence of food (mean Tmax 0.71 h vs. 1.14 h), while the extent of absorption of moclobemide given with food was unaltered. The decreased absorption rate in the presence of food is not expected to be of clinical significance.