Molecular determinants of the species selectivity of neurokinin type 1 receptor antagonists.

Most nonpeptide neurokinin (NK)1 antagonists display a marked difference in affinity for rat versus human NK1 receptors. The molecular basis for the species selectivity of RP67580 and CP96,345 has been previously addressed [J. Biol. Chem. 267:25668-25671 (1992); J. Biol. Chem. 268:2319-2323 (1993)]. We are extending these previous results to additional NK1 antagonists, which are members of different chemical families. Included is a new perhydroisoindolol, RPR100893, which unlike its parent compound (RP67580) is human receptor selective. Chimeric rat/human NK1 receptors, as well as rat and human mutant NK1 receptors, were constructed and expressed in COS-1 cells, and affinities for substance P and the various antagonists were determined in binding studies. With human receptor-selective antagonists, the rat R290(S-->I) mutation was the most effective in increasing antagonist affinity (from 7- to 23-fold). Combination with the R116(L-->V) mutation led to an additional increase in affinity for trans-4-hydroxy-1-(1H-indol-3-ylcarbonyl)-L-prolyl-N- methyl-N-(phenylmethyl)-L-tyrosineamide (a derivative of FK888) and to nearly full human receptor affinity for RPR100893 and (+/-)-CP99,994. Based on the gains in affinities, these results confirm and extend the role of residues 116 and 290 of the NK1 receptor in the species selectivity of these three new human receptor-selective NK1 antagonists. In comparison, the affinity of RP67580, the least selective molecule, was most affected by changes at position 116, and combination with mutations at either position 97 (V-->E) or position 290 led to the human receptor phenotype. For the heterosteroid KAN610857, modifications of the rat receptor at positions 97 and 290, and to a lesser degree position 116, were the most effective in reducing affinity. Two double-mutants [R(97,290) and R(116,290)], although different from those identified for RP67580, also displayed human receptor-like affinity. Therefore, the molecular determinants of the species selectivity appear to be different, in part, between rat and human receptor-selective compounds, even between closely related chemical families.

Septide: an agonist for the NK1 receptor acting at a site distinct from substance P.

The hexapeptide [pGlu6,Pro9]substance P (SP)6-11, septide, has been shown to be an agonist as potent as SP in eliciting smooth muscle contraction in several in vitro preparations, while being a poor competitor of labeled SP binding. These results, as well as other pharmacological data, have suggested the existence of either a specific septide receptor or a septide site on the neurokinin (NK)1 receptor distinct from that for SP. We have used rat recombinant NK1 receptor expressed in COS-1 cells to address this issue. Both functional (agonist-induced inositol phosphate accumulation) and radioligand binding studies were conducted on transiently transfected cells. SP and septide elicited similar maximal increases (4-6-fold) in inositol phosphate levels in transfected cells, with EC50 values of 0.05 +/- 0.02 nM for SP and 5 +/- 2 nM for septide. No additivity of the maximal responses to the two agonists was observed, and neither agonist evoked any response in sham-transfected cells. RP 67580 was a competitive inhibitor of SP responses, with an inhibition constant (KB) of 13 +/- 2 nM, in agreement with displacement studies of [3H]SP binding to membranes and intact transfected cells (Ki values of 10 +/- 4 nM, and 1.16 +/- 0.06 nM, respectively). In comparison, septide responses were inhibited by RP 67580 in an uncompetitive fashion, with an apparent KB* value of 1.5 +/- 0.2 nM. Septide was a weak competitor of [3H]SP binding, with dissociation constants (Ki) of 2.9 +/- 0.6 microM and 3.7 +/- 0.9 microM for membranes and intact transfected cells, respectively. Similarly, septide at concentrations up to 10 microM did not affect [3H]RP 67580 binding. In conclusion, we have demonstrated that septide is a potent functional agonist of the NK1 receptor but it seems to act at a specific subsite different from that for SP. Although not ruling out the existence of selective septide receptors in some tissues, these results could explain some of the discrepancies with regard to the pharmacological properties of septide. Furthermore, a specific septide site on the NK1 receptor could represent an original pharmacological target.

Inhibition by riluzole of electrophysiological responses mediated by rat kainate and NMDA receptors expressed in Xenopus oocytes.

The effects of riluzole, an anticonvulsant and neuroprotective compound, on excitatory amino acid-evoked currents were studied in Xenopus laevis oocytes injected with mRNA from rat whole brain or cortex. Responses to kainic acid were blocked by riluzole (IC50 = 167 microM) as well as by the quinoxalinedione antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX: IC50 = 0.21 microM) and 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo[f]quinoxaline (NBQX: IC50 = 0.043 microM). Riluzole was somewhat more potent at blocking responses to N-methyl-D-aspartic acid (NMDA: IC50 = 18.2 microM); the competitive NMDA receptor antagonist 2-amino-phosphonovaleric acid (2-APV) yielded an IC50 of 6.1 microM in this system. The inhibition by both riluzole and 2-APV was reversible and did not appear to be use dependent, unlike that of the channel blocker MK-801 ([+]-5-methyl-10,11-dihydro-5H-dibenzo-[a,d]cyclohepten-5,10-imine maleate). It was impossible to demonstrate an interaction of riluzole with any of the known ligand recognition sites on either the kainate or the NMDA receptor in radioligand binding studies. These results suggest a direct but non-competitive action of riluzole on ionotropic glutamate receptors.

Inhibition of Clostridium tyrobutyricum by bacteriocin-like substances produced by lactic acid bacteria.

Lactic acid bacteria were selected for their inhibitory activity against Clostridium tyrobutyricum under conditions that eliminate the effects of lactic acid and hydrogen peroxide. Four strains were isolated belonging to the species Lactococcus lactis ssp. lactis. The sensitivity of the inhibitory substances to pronase and trypsine indicates that they are proteins or peptides different from nisin. Their resistance to phospholipase D indicates that they are also different from lactostrepcin. The inhibitory substances are produced during the exponential phase of growth. Their activity is bactericidal and directed toward some strains of Clostridium tyrobutyricum, Lactobacillus helveticus, and Streptococcus thermophilus, but strains used as dairy starters, Lactobacillus lactis, Streptococcus thermophilus, and Propionibacterium shermanii, are not all affected by the inhibition.

[Cases of prosthodontic tissue reconditioning in geriatric dentistry]. / Incidences de la remise en condition prothétique en gérodontologie.

In elderly patients, recurrent fractures of the lower denture must raise the question of a neurological deficit as cause of the occluso-prosthetic imbalance. Hypotonicity of the peri-oral mastication musculature, especially the masseters, may explain the alteration of the prosthetic supporting surface due to shriveling of the mandibular arch, along with an osseogenesis at the point of flexion of the mandible. The rest and activity muscular imbalance, resulting from unilateral mastication, may cause lingual dysfunction and deviation of the tongue at rest. If this problem is not controlled within an acceptable period of time, one should expect psychological, biological and physiological consequences affecting the patient's physical condition. The restoration of the denture fracture is insufficient. Reconditioning must be performed in order to replace the existing prosthesis in the patient's function, allowing him/her to recover a normal psychological, biological and physiological balance. In conclusion, in geriatric dentistry, the objective of reconditioning is, not only to restore a functional occlusion, but also the psychological, biological and physiological balance of the patient. This is an unvaluable advantage, especially if this contributes to maintain or restore an often precarious health.