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P Krogsgaard-Larsen

Publications and source records attributed to P Krogsgaard-Larsen.

At least 91 records · Page 5Linked to original sources
PubMed1995

Excitatory amino acid receptor ligands: asymmetric synthesis, absolute stereochemistry and pharmacology of (R)- and (S)-homoibotenic acid.

The (R)- and (S)-forms of 2-amino-3-(3-hydroxyisoxazol-5-yl)propionic acid (homoibotenic acid, HIBO) were synthesized, using (S)-BOC-phenylalanine as a chiral auxiliary and their absolute stereochemistry correlated with that of (R)-Br-HIBO. The enantiomeric excesses for (R)-HIBO (1) (> 99.5%) and (S)-HIBO (2) (99.5%) were determined using chiral HPLC. Whereas compounds 1 and 2 were equipotent inhibitors of the binding of [3H]glutamic acid in the presence of calcium chloride, 2 showed AMPA agonist activity and 1 very weak NMDA agonist activity.

Animals↗
PubMed1994

Role of GABAB receptors in intracellular Ca2+ homeostasis and possible interaction between GABAA and GABAB receptors in regulation of transmitter release in cerebellar granule neurons.

The expression of GABAB receptors in cultured mouse cerebellar granule cells was investigated in binding experiments using [3H](S,R)-baclofen as well as in functional assessment of the ability of (R)-baclofen to interact with depolarization (15-40 mM KCl) coupled changes in intracellular Ca2+ homeostasis and neurotransmitter release. In the latter case a possible functional coupling between GABAA and GABAB receptors was investigated. The binding studies showed that the granule cells express specific binding sites for (R)-baclofen. The number of binding sites could be increased by exposure of the cells to the GABAA receptor agonist THIP (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol) during the culture period. Pretreatment of the neurons with pertussis toxin showed that the GABAB receptors are coupled to G-proteins. This coupling was, however, less pronounced when the cells had been cultured in the presence of THIP. When 45Ca2+ uptake was measured or the intracellular Ca2+ concentration ([Ca2+]i) determined using the fluorescent Ca2+ chelator Fluo-3 it could be demonstrated that culturing the neurons in THIP influences intracellular Ca2+ homeostasis. Moreover, this homeostasis was found to be functionally coupled to the GABAB receptors as (R)-baclofen inhibited depolarization-induced increases in 45Ca2+ uptake and [Ca2+]i. (R)-Baclofen also inhibited K(+)-induced transmitter release from the neurons as monitored by the use of [3H]D-aspartate which labels the neurotransmitter pool of glutamate. Using the selective GABAA receptor agonist isoguvacine it could be demonstrated that the GABAB receptors are functionally coupled to GABAA receptors in the neurons leading to a disinhibitory action of GABAB receptor agonists.

Animals↗
PubMed1994

Synthesis and structure-activity studies on acidic amino acids and related diacids as NMDA receptor ligands.

The 3-isoxazolol amino acids (S)-2-amino-3-(3-hydroxy-5-methyl-4- isoxazolyl)propionic acid [(S)-AMPA, 2] and (R,S)-2-amino-2-(3-hydroxy-5-methyl-4-isoxazolyl)acetic acid (AMAA, 5a) (Figure 1) are potent and specific agonists at the AMPA and N-methyl-D-aspartic acid (NMDA) subtypes, respectively, of (S)-glutamic acid (1) receptors. A number of amino acids and diacids structurally related to AMAA were synthesized and tested electrophysiologically and in receptor-binding assays. The hydroxymethyl analogue 7c of AMAA was an NMDA agonist approximately equipotent with AMAA in the [3H]CPP-binding assay (IC50 = 7 +/- 3 microM) and electropharmacologically in the rat cortical wedge model (EC50 = 8 +/- 2 microM). In contrast to this, the tertbutyl analogue 7a of AMAA turned out to be an antagonist at NMDA and AMPA receptors. The conformational characteristics of AMAA and 7a, c were studied by molecular mechanics calculations. Compound 7a possesses extra steric bulk and shows significant restriction of conformational flexibility compared to AMAA and 7c, which may be determining factors for the observed differences in biological activity. Although the nitrogen atom of quinolinic acid (6) has very weak basic character, 6 is a, perhaps subtype-selective, NMDA receptor agonist and a potent neurotoxic agent. These aspects prompted us to synthesize and test the diacids 8a, b, in which the amino group of AMAA has been replaced by a methylthio and methoxy group, respectively. Neither compound showed significant affinity for nor depolarizing effects at NMDA receptors. The hydroxymethyl AMPA analogue 3c showed no interaction with NMDA receptors and only weak AMPA agonist effects.

Acetates↗
PubMed1994

Resolution, absolute stereochemistry, and pharmacology of the S-(+)- and R-(-)-isomers of the apparent partial AMPA receptor agonist (R,S)-2-amino-3-(3-hydroxy-5-phenylisoxazol-4-yl)propionic acid [(R,S)-APPA].

(R,S)-2-Amino-3-(3-hydroxy-5-phenylisoxazol-4-yl)propionic acid ((R,S)-APPA) is the only partial agonist at the (R,S)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) subtype of excitatory amino acid receptors so far described. In light of the pharmacological interest in partial agonists, we have now accomplished the resolution of (R,S)-APPA. (S)-(+)-APPA (5) and (R)-(-)-APPA (6) were obtained in high enantiomeric purity using (R)-(+)- and (S)-(-)-1-phenylethylamine, respectively, as resolving agents. The absolute stereochemistry of 6 was established by X-ray analysis of 6.HCl.0.25H2O. Compounds 5 and 6 were tested electropharmacologically using the rat cortical wedge preparation and in receptor-binding assays using [3H]-AMPA, [3H]kainic acid, and the N-methyl-D-aspartic acid (NMDA) receptor ligands [3H]CPP, [3H]MK-801, and [3H]glycine. Whereas 6 did not significantly affect the binding of any of these ligands (IC50 > 100 microM), compound 5 revealed affinity for only the [3H]AMPA-binding site (IC50 = 6 microM). In electropharmacological tests, 5 showed full AMPA receptor agonism (EC50 = 230 microM). This effect of 5 was insensitive to the NMDA antagonist CPP but was inhibited competitively by the non-NMDA antagonist NBQX (pKi = 6.30). Compound 6, on the other hand, turned out to be a non-NMDA receptor antagonist, inhibiting competitively depolarizations induced by AMPA (pKi = 3.54), kainic acid (pKi = 3.07), and 5 (pKi = 3.57).

Alanine↗
PubMed1994

GABAB antagonists: resolution, absolute stereochemistry, and pharmacology of (R)- and (S)-phaclofen.

Phaclofen, which is the phosphonic acid analogue of the GABAB agonist (RS)-3-(4-chlorophenyl)-4-aminobutyric acid (baclofen), is a GABAB antagonist. As part of our studies on the structural requirements for activation and blockade of GABAB receptors, we have resolved phaclofen using chiral chromatographic techniques. The absolute stereochemistry of (-)-(R)-phaclofen was established by X-ray crystallographic analysis. (-)-(R)-Phaclofen was shown to inhibit the binding of [3H]-(R)-baclofen to GABAB receptor sites on rat cerebellar membranes (IC50 = 76 +/- 13 microM), whereas (+)-(S)-phaclofen was inactive in this binding assay (IC50 > 1000 microM). (-)-(R)-Phaclofen (200 microM) was equipotent with (RS)-phaclofen (400 microM) in antagonizing the action of baclofen in rat cerebral cortical slices, while (+)-(S)-phaclofen (200 microM) was inactive. The structural similarity of the agonist (R)-baclofen and the antagonist (-)-(R)-phaclofen suggests that these ligands interact with the GABAB receptor sites in a similar manner. Thus, it may be concluded that the different pharmacological effects of these compounds essentially result from the different spatial and proteolytic properties of their acid groups.

Animals↗
PubMed1994

Molecular pharmacology of the AMPA agonist, (S)-2-amino-3-(3-hydroxy-5-phenyl-4-isoxazolyl)propionic acid [(S)-APPA] and the AMPA antagonist, (R)-APPA.

The heterocyclic analogue of (S)-glutamic acid, (S)-2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid [(S)-AMPA] is a potent and selective AMPA receptor agonist, whereas the enantiomeric compound, (R)-AMPA, is virtually inactive. We have previously characterized (RS)-2-amino-3-(3-hydroxy-5-phenyl-4-isoxazolyl)propionic acid [(RS)-APPA] as a partial AMPA receptor agonist showing about 60% of the efficacy of (RS)-AMPA. This partial agonism produced by (RS)-APPA is, however, only apparent, since resolution of (RS)-APPA has now been shown to provide the full AMPA receptor agonist, (S)-APPA, whereas (R)-APPA is a non-N-methyl-D-aspartic acid (non-NMDA) receptor antagonist showing preferential AMPA blocking effects. In agreement with classical theories for competitive interaction between agonists and antagonists, the efficacy of depolarizations produced by (S)-APPA in the rat cortical wedge preparation was shown to be progressively reduced with increasing molar ratios of (R)-APPA/(S)-APPA. These compounds and the competitive antagonists (RS)-2-amino-3-(3-carboxymethoxy-5-methyl-4-isoxazolyl)propionic acid [(RS)-AMOA], 6-cyano-7-nitroquinoxalin-2,3-dione (CNQX) and 6-nitro-7-sulfamoylbenzo(f)quinoxalin-2,3-dione (NBQX) were also tested in [3H]AMPA and [3H]CNQX binding systems, the latter ligand being used in the absence or presence of thiocyanate ions. On the basis of these studies it is suggested that (RS)-AMPA and the AMPA agonist (S)-APPA interact with a high-affinity receptor conformation, whereas the competitive antagonists (RS)-AMOA and (R)-APPA, derived from these agonists, preferentially bind to a low-affinity AMPA receptor conformation.(ABSTRACT TRUNCATED AT 250 WORDS)

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1994

Modulation of AMPA receptor function in relation to glutamatergic abnormalities in Alzheimer's disease.

Abnormalities in the excitatory glutamate neurotransmitter system appear to be a prominent factor in Alzheimer's disease (AD). Whereas hypoactivity of this system is observed in some areas of Alzheimer brains, hyperactivity may play a role in the degenerative processes in other brain areas. This apparently paradoxical situation makes therapeutic intervention in the glutamatergic system in AD difficult and demands the development of unique therapeutic approaches. The involvement of the (RS)-2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA) subtype of glutamate receptors in AD brain dysfunctions seems to be important, and compounds showing different modulatory activity at AMPA receptors are discussed in relation to therapeutic possibilities. Compounds enhancing excitatory activity at AMPA receptors may have beneficial effects on the learning and memory deficits observed in AD, whereas agents showing antagonistic or partial agonist profiles may block or delay the progressive neurodegeneration, which is a key phenomenon in AD. In vitro experiments with compounds capable of enhancing AMPA receptor activity have been performed. Such compounds without excitatory activity on their own may not show the excitotoxic properties characteristic of glutamate agonists. Another possibility for therapeutic intervention is the use of a partial agonist. The concept of "functional partial agonism" at the AMPA receptors is described with a specific example.

Alzheimer Disease↗
PubMed1994

Effects of GABAA receptors activation on brain glucose metabolism in normal subjects and temporal lobe epilepsy (TLE) patients. A positron emission tomography (PET) study. Part I: Brain glucose metabolism is increased after GABAA receptors activation.

Though gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the human central nervous system, the metabolic response to GABA system activation remains imperfectly known. We studied in vivo with positron emission tomography (PET) the variations of glucose metabolism in the human brain after stimulation of the GABAA receptors by systemic administration of the specific GABAA agonist, 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP). These investigations were performed in three normal volunteers and as part of presurgical evaluation for temporal lobe epilepsy in six patients. While clinical and electroencephalographic (EEG) monitoring showed a sedative effect and sleepiness after THIP administration, glucose metabolism was paradoxically increased in grey matter structures, which are known to have a high density of GABAA receptors. These findings suggest that the pharmacological activation of GABA pathways, although inhibitory and producing a decrease of vigilance, increases the energetic demand at least during a phase of GABA agonist action, probably at the synaptic or at the glial cell level.

Adult↗
PubMed1994

Effects of GABAA receptors activation on brain glucose metabolism in normal subjects and temporal lobe epilepsy (TLE) patients. A positron emission tomography (PET) study. Part II: The focal hypometabolism is reactive to GABAA agonist administration in TLE.

Positron emission tomography (PET) using [18F]fluorodeoxyglucose (FDG) was used to study the metabolic response of focal hypometabolism to the administration of a specific GABAA agonist (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol), THIP, in six temporal lobe epilepsy (TLE) patients. After THIP injection, the increase of glucose metabolism in the hypometabolic focus was larger than the mean increase reported in the whole brain (Part I; Epilepsy Res., 19 (1994) 45-54). Within the hypometabolic focus, this increase was significantly higher in regions with the lowest basal metabolic level. This metabolic response in the hypometabolic focus, observed in the absence of any epileptic discharge during FDG accumulation and PET data acquisition, suggests that GABAA receptors are up-regulated or, at least, preserved in TLE.

Adult↗
PubMed1994

Neurotoxicity and excitatory amino acid antagonists.

The cytotoxic action of excitatory amino acids (glutamate, aspartate, NMDA, AMPA, and kainate) was studied in cultured neocortical neurons. It was demonstrated that all amino acids triggered an increase in the intracellular Ca2+ concentration which appeared to be prerequisite for their cytotoxic action. However, while glutamate and NMDA affected both Ca2+ influx and release from intracellular stores, AMPA and kainate preferentially stimulated influx with little (kainate) or no (AMPA) effect on the intracellular store. Using NMDA and non-NMDA receptor selective antagonists it was shown that glutamate cytotoxicity in these neurons is mediated by both receptor subtypes. using the AMPA/kainate selective antagonists AMOA and AMNH it was demonstrated that excitation and neurotoxicity may not be correlated in a simple manner. antagonist and an agonist at AMPA receptors depending on the AMPA concentration.

Animals↗
PubMed1994

Molecular pharmacology of gamma-aminobutyric acid type A receptor agonists and partial agonists in oocytes injected with different alpha, beta, and gamma receptor subunit combinations.

Using systematic combination of alpha 1, alpha 3, and alpha 5 with beta 1, beta 2, and beta 3, together with gamma 1, gamma 2, and gamma 3, we have investigated the contributions of the various alpha, beta, and gamma subunits to the pharmacology of gamma-aminobutyric acid (GABA)A agonists. We have characterized GABA, (RS)-dihydromuscimol, piperidine-4-sulfonic acid, and 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol with recombinant human GABAA receptors expressed in Xenopus oocytes. Our observations indicate that the alpha subunit is the major determinant of efficacy for partial GABAA agonists. When alpha 1 and alpha 3 or alpha 1 and alpha 5 are coexpressed, the alpha 1 subunit determines the maximum efficacy, whereas the affinity is determined by the entire combination of subunits. Thus, the results of the present study demonstrate that the pharmacology of GABAA agonists is dependent on the subunit composition of the GABAA receptor complex. Functional GABAA receptors containing two different alpha subunits show pharmacological profiles distinctly different from those of receptors containing a single alpha subtype, indicating that two different alpha subunits can be coexpressed in one functional GABAA receptor complex.

Animals↗
PubMed1993

Anticonvulsant activity of the gamma-aminobutyric acid uptake inhibitor N-4,4-diphenyl-3-butenyl-4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridin-3-ol .

The N-4,4-diphenyl-3-butenyl derivative of the glial selective gamma-aminobutyric acid (GABA) uptake inhibitor 4,5,6,7-tetrahydroisoxazolo [4,5-c]pyridin-3-ol (N-DPB-THPO), was tested for its ability to block sound-induced seizures in the audiogenic seizure-susceptible Frings mouse model of epilepsy. Following intracerebroventricular (i.c.v.) administration, N-DPB-THPO blocked tonic hindlimb extension in a dose- and time-dependent manner. At the doses tested no gross behavioral effects were noted.

Acoustic Stimulation↗
PubMed1993

The non-depolarizing D-form of bromohomoibotenic acid enhances depolarizations evoked by the L-form or quisqualate.

The D-enantiomer of bromohomoibotenic acid (Br-HIBO) was inactive in electrophysiological experiments when administered alone, but enhanced depolarizations evoked by L-Br-HIBO or quisqualate when co-administered with these agonists. In addition, quisqualate induced a long-lasting (> 120 min) sensitization of cortical wedge neurons to D-Br-HIBO. This latter effect of D-Br-HIBO was similar to, but significantly more potent and selective, than the earlier observed quisqualate-induced sensitization of cortical neurones to depolarization by (S)-2-amino-4-phosphonobutyric acid (L-AP4).

Aminobutyrates↗
PubMed1993

Conformational analysis and molecular modelling of a partial GABAA agonist and a glycine antagonist related to the GABAA agonist, THIP.

A series of 3-hydroxyisoxazoles (3-isoxazoles) substituted in the 5-position by piperidyl moieties (2-, 3-, and 4-PIOL) were studied by molecular modelling and computer graphics methods. Whereas 2-PIOL is pharmacologically inactive, 3-PIOL is a glycine antagonist and 4-PIOL a low-efficacy partial GABAA agonist. A conformational analysis of the isomeric PIOLs was performed on the basis of molecular mechanics calculations. The conformational analysis revealed a large degree of conformational freedom for all three compounds, especially of conformers having the 3-hydroxyisoxazole moiety in equatorial positions. By comparison of the PIOLs with the semi-rigid GABAA agonist THIP and the conformationally restricted glycine antagonist THAZ, the conformations relevant for GABAA and glycine receptor recognition were determined. For 2-PIOL a predicted active conformation is energetically favourable, but it exhibits considerable extra volume as compared to THIP, which may explain its lack of affinity for GABAA receptors. 3-PIOL is capable of adopting a conformation resembling that of THAZ. The GABAA receptor affinity of 4-PIOL may be explained by its ability to orientate the functional groups in space in a manner that allows a comparison with THIP. The low efficacy and affinity of 4-PIOL may reflect that not all atoms are directly involved in receptor binding. Certain steric requirements for binding to the GABAA receptor site have been identified and discussed.

Analgesics↗
PubMed1993

Conformational aspects of the muscarinic receptor interactions of bicyclic isoxazole ester bioisosteres of arecoline.

3-Methoxy-4,5,6,7-tetrahydroisoxazolo [4,5-c]pyridine (O-Me-THPO) and O,5-di-Me-THPO are conformationally restricted bioisosteres of the muscarinic agonists norarecoline and arecoline, respectively, showing partial agonist effects at muscarinic acetylcholine receptors. The 7-membered ring analogue of O-Me-THPO, 3-methoxy-5,6,7,8-tetrahydro-4H-isoxazolo[4,5-c]azepine (O-Me-THAO), shows higher affinity for muscarinic receptor sites than O-Me-THPO or O,5-di-Me-THPO. Similarly, O-Et-THAO binds much more tightly to muscarinic receptor sites than its 6-membered ring analogues, O-Et-THPO and O-Et-5-Me-THPO. Based on receptor binding data, O-Me-THPO and O-Me-THAO, and O-Et-THPO and O-Et-THAO, respectively, show similar degrees of partial agonism. They also show similar relative affinities for muscarinic M1 and M2 receptor sites. Using the semiempirical quantum mechanics programme, AM1, and the molecular mechanics programme, SYBYL, we have studied the conformational flexibility of the O-alkyl-THPO and O-alkyl-THAO ring systems. As expected, the 7-membered ring of the latter system was shown to be markedly more flexible than the piperidine rings of O-alkyl-THPO analogues. On the basis of this analysis, a common pharmacophore for these two classes of compounds was constructed.

Arecoline↗
PubMed1992

Excitatory amino acid receptor ligands. Synthesis and biological activity of 3-isoxazolol amino acids structurally related to homoibotenic acid.

The 3-isoxazolol amino acid (RS)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA, 2) and the isomeric compound (RS)-2-amino-3-(3-hydroxy-4-methylisoxazol-5-yl)propionic acid (4-methylhomoibotenic acid, 4a) are potent agonists at the AMPA subtype of central excitatory amino acid receptors. Using 4a as a lead structure, the amino acids 4c-e, in which the 4-methyl group of 4a is replaced by substituents of different size and polarity, were synthesized. Attempts to synthesize 4-(bromomethyl)homoibotenic acid (4f), a potential receptor alkylating agent, were unsuccessful. 4-Butylhomoibotenic acid (4c) and 4-(2-hydroxyethyl)homoibotenic acid (4e) were equipotent as inhibitors of [3H]AMPA binding (IC50 = 2 microM) and showed similar excitatory activity in the rat cortical slice preparation. 4d did not show significant affinity for AMPA receptor sites, but turned out to be a weak N-methyl-D-aspartic acid (NMDA) receptor antagonist. However, like 4c,e, 4d did not significantly affect the binding of the competitive NMDA antagonist, [3H]CPP, or the noncompetitive NMDA antagonist, [3H]MK-801. None of the amino acids 4c-e showed detectable affinity for [3H]kainic acid binding sites. Like the parent compound 4a (IC50 = 0.18 microM), 4c (IC50 = 0.18 microM), 4e (IC50 = 0.14 microM), and in particular 4d (IC50 = 0.02 microM) were effective inhibitors of calcium chloride-dependent [3H]glutamic acid binding, whereas AMPA is inactive (IC50 greater than 100 microM) in this binding assay. Thus, 4d is an effective and highly selective inhibitor of calcium chloride-dependent [3H]glutamic acid binding and may be a useful tool for studies of the physiological relevance and pharmacological importance of this binding affinity.

Animals↗