Characterization of vascular reactivity in dorsal hand veins after oral rosiglitazone treatment in healthy subjects.

OBJECTIVE: In clinical studies with diabetic patients thiazolidinediones have been shown to restore abnormal vascular function which might be attributed to improved blood sugar control or to restoration of vascular endothelium and smooth muscle responsiveness. The present study was undertaken to investigate whether rosiglitazone modulates vascular responsiveness to different vasoactive agents and exerts renin-angiotensin-system (RAS)-inhibiting properties in healthy subjects in vivo. METHODS: 24 healthy male subjects were randomized to receive either rosiglitazone or placebo. Venoconstrictor responses to angiotensin II (Ang II) and phenylephrine, and endothelium-dependent response to histamine and insulin, and endothelium-independent response to glyceroltrinitrate were compared using the dorsal hand vein compliance method. Effects on the RAS were investigated by plasma level determinations of Ang II and angiotensin-(1-7). Treatment effects on the systemic arterial system were investigated by standardized pulse-wave-analysis. RESULTS: Rosiglitazone significantly inhibited venoconstrictor responses to Ang II by 19% (-70% vs. -51% constriction, p = 0.034) and in the presence of rosiglitazone the ED80 for phenylephrine was increased (ED80: 317 A+/- 86 ng vs. 531 A+/- 102 ng; p = 0.010). Rosiglitazone treatment was without effect on endothelium-dependent dilation, blood pressure, pulse-wave-velocity and plasma angiotensin peptide levels. CONCLUSIONS: The data of the present study in veins of healthy subjects are consistent with data from in vitro and animal studies supporting a direct effect of rosiglitazone on venous tone by modulation of the vascular smooth muscle response via AT1-receptor-downregulation.

A novel class of amino-alkylcyclohexanes as uncompetitive, fast, voltage-dependent, N-methyl-D-aspartate (NMDA) receptor antagonists--in vitro characterization.

The fact that potent NMDA receptor channel blockers produce phencyclidine-like psychotropic symptoms in man and rodents implies that uncompetitive antagonism of NMDA receptors may not be a promising therapeutic approach. However, recent data indicate that agents with moderate affinity such as memantine and neramexane (MRZ 2/579) are useful therapeutics due to their strong voltage-dependency and rapid unblocking kinetics. Merz has developed a series of novel uncompetitive NMDA receptor antagonists based on an amino-alkylcyclohexane structure. These compounds displaced [(3)H]-MK-801 binding to rat cortical membranes with K(i) values between 1 and 100 microM and inward current responses of cultured hippocampal neurons to NMDA were antagonized in a strongly voltage-dependent manner with rapid blocking/unblocking kinetics. Three of these compounds, with similar biophysical properties to memantine, were chosen for development. MRZ 2/759 (1-ethenyl-3,3,5,5-tetramethyl-cyclohexylamine), 2/1010 (1,3,3,5-tetramethyl-6-azabicyclo[3.2.1]octane) and 2/1013 (8,8,10,10-tetramethyl-1-azaspiro[5.5] undecane) displaced [(3)H]-MK-801 binding with K(i) values of 1.18, 2.59 and 3.64 microM, respectively. They were similarly potent against NMDA-induced currents in hippocampal neurons - IC(50) values of 1.51, 3.06 and 2.20 microM, respectively. In line with their moderate affinity, all were voltage-dependent (delta = 0.86, 0.96 and 0.89, respectively) and fast, open-channel blockers (k(on) 7.90, 1.70 and 2.60 x 10(4) M(-1) sec(-1), k(off) 0.13, 0.12 and 0.24 sec(-1), respectively). These compounds are also NMDA receptor antagonists in the CNS following systemic administration and have good therapeutic indices in a variety of in vivo behavioural models where glutamate is known to play a pivotal role. In view of their relatively low affinity and associated rapid kinetics, they should prove to be useful therapeutics in a wide range of CNS disorders.

Agonist concentration dependency of blocking kinetics but not equilibrium block of N-methyl-D-aspartate receptors by memantine.

Memantine is an uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist which is registered in both Europe and the USA for the treatment of Alzheimer's disease (AD). Cultured rat hippocampal neurons were used to evaluate the potency and blocking kinetics of this therapeutically very well-tolerated agent in the presence of various concentrations of the synthetic agonist NMDA and a constant, saturating concentration of the co-agonist D-serine (10 microM). Whole-cell patch-clamp experiments at -70 mV revealed that the degree of "equilibrium" blockade of NMDA-induced currents by memantine was largely unaffected by the concentration of the agonist NMDA. The IC50 values for NMDA at 300, 100, 30 and 10 microM were 0.80+/-0.12, 1.01+/-0.08, 0.92+/-0.13 and 1.31+/-0.09 microM, respectively, giving an average IC(50) for all agonists concentrations tested of 1.01+/-0.11 microM. In contrast, and as expected, the onset and offset kinetics of blockade were clearly dependent on agonist concentration. For NMDA 300, 100, 30 and 10 microM, kon values were 10.55+/-1.41, 8.60+/-0.17, 4.90+/-0.20 and 3.22+/-0.08x10(4) M(-1) s(-1), respectively; 1/tauon values at the IC50 concentration of memantine-i.e. 1 microM-were 0.58+/-0.11, 0.28+/-0.05, 0.15+/-0.02 and 0.11+/-0.03 s(-1), respectively and koff values were 0.24+/-0.01, 0.19+/-0.01, 0.14+/-0.00 and 0.09+/-0.01 s(-1), respectively. It therefore appears that the kinetics, but not the equilibrium potency, of memantine are agonist concentration-dependent. These fast agonist concentration-dependent kinetic properties, in addition to the clear voltage-dependence of memantine, are proposed to be important for the therapeutic tolerability of this compound in the treatment of AD.

The Lurcher mutation identifies delta 2 as an AMPA/kainate receptor-like channel that is potentiated by Ca(2+).

Neurodegeneration in Lurcher (Lc) mice results from constitutive activation of delta 2, a subunit of ionotropic glutamate receptors (GluRs) with unknown natural ligands and channel properties. Homo-oligomeric channels of GluR-delta2 with the Lurcher mutation (GluR-delta 2(Lc)) expressed in human embryonic kidney 293 cells showed a doubly rectifying current-voltage relation reminiscent of the block by intracellular polyamines in AMPA/kainate channels. Similarly, the fraction of the total current carried by Ca(2+) was approximately 2-3%, comparable with that found in Ca(2+)-permeable AMPA/kainate channels. Currents through GluR-delta 2(Lc) channels were also potentiated by extracellular Ca(2+) in a biphasic manner, with maximal potentiation occurring at physiological concentrations of Ca(2+). We examined the functional role of the Q/R site in GluR-delta 2(Lc) by replacing glutamine with arginine. Analogous to AMPA/kainate receptors, GluR-delta 2(Lc)(R) channels showed no voltage-dependent block by intracellular polyamines and were nominally impermeable to Ca(2+). The potentiation by Ca(2+), however, remained intact. Hence, GluR-delta 2(Lc) channels are functionally similar to the AMPA/kainate receptor channels, consistent with the high-sequence identity shared by these subunits within the channel-lining M2 and M3 segments. Furthermore, potentiation by Ca(2+) and a permeability to Ca(2+) comparable with that of AMPA/kainate receptors provide a possible cause for cell death in Lurcher mice and may contribute to cerebellar long-term depression under physiological conditions.

Stability and binding properties of wild-type and c17s mutated human sterol carrier protein 2.

The temperature- and solvent-induced denaturation of both the SCP2 wild-type and the mutated protein c71s were studied by CD measurements at 222 nm. The temperature-induced transition curves were deconvoluted according to a two-state mechanism resulting in a transition temperature of 70.5 degrees C and 59.9 degrees C for the wild-type and the c71s, respectively, with corresponding values of the van't Hoff enthalpies of 183 and 164 kJ/mol. Stability parameters characterizing the guanidine hydrochloride denaturation curves were also calculated on the basis of a two-state transition. The transitions of the wild-type occurs at 0.82 M GdnHCl and that of the c71s mutant at 0.55 M GdnHCl. These differences in the half denaturation concentration of GdnHCl reflect already the significant stability differences between the two proteins. A quantitative measure are the Gibbs energies DeltaG(0)(D)(buffer) at 25 degrees C of 15.5 kJ/mol for the wild-type and 8.0 kJ/mol for the mutant. We characterized also the alkyl chain binding properties of the two proteins by measuring the interaction parameters for the complex formation with 1-O-Decanyl-beta-D-glucoside using isothermal titration microcalorimetry. The dissociation constants, K(d), for wild-type SCP2 are 335 microM at 25 degrees C and 1.3 mM at 35 degrees C. The corresponding binding enthalpies, DeltaH(b), are -21. 5 kJ/mol at 25 degrees C and 72.2 kJ/mol at 35 degrees C. The parameters for the c71s mutant at 25 degrees C are K(d)=413 microM and DeltaH(b)=16.6 kJ/mol. These results suggest that both SCP2 wild-type and the c71s mutant bind the hydrophobic compound with moderate affinity.

Thermodynamic stability of annexin V E17G: equilibrium parameters from an irreversible unfolding reaction.

Conformational stability of the membrane-binding protein annexin V E17G has been determined by high-sensitivity differential scanning microcalorimetry (DSC) measurements and by isothermal, guanidinium hydrochloride (GdnHCl)-induced unfolding studies. Wild-type annexin V and the E17G mutant protein studied here are structurally almost identical. Therefore, it can be expected that the present results will not deviate significantly from the stability data of the wild-type molecule. Thermal unfolding is irreversible, while GdnHCl unfolding shows a high degree of reversibility. We were able to demonstrate that characteristic features of annexin V E17G unfolding permit us to extract from the kinetically controlled heat capacity curves thermodynamic equilibrium parameters at the high heating rates. The thermodynamic quantities obtained from the DSC studies in phosphate buffer at pH 7.0 are as follows: t1/2 = 54.7 degrees C (heating rate of 2.34 K min-1), delta H0 = 690 kJ mol-1, and delta Cp = 10.3 kJ mol-1 K-1 which correspondends to a value of delta G0D (20 degrees C) of 53.4 kJ mol-1. When compared on a per gram basis, these thermodynamic parameters classify annexin V E17G as a marginally stable protein. This conclusion is consistent with structural and functional features of the protein that require conformational adaptability for hinge-bending motions and pore formation on interaction with membranes. We observed a large difference between the change in the Gibbs energy value derived from the heat capacity studies and that determined from the GdnHCl unfolding curve. The difference appears to stem from a specific interaction of the protein with the denaturant that results in both a low half-denaturation concentration C1/2 of 1.74 M and a small slope (6.0 kJ L mol-2) of the delta Gapp versus [GdnHCl] plot. The extraordinary interaction of annexin V with GdnHCl is also manifested in the enormous depression of the transition temperature delta t1/2 (= 18 degrees C) when the GdnHCl concentration is increased from 0 to 1 M. "Regular" proteins experience an average decrease in the transition temperature of 8 +/- 2 degrees C per 1 M change in the concentration of GdnHCl.