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The N-terminal 1-34 segment of parathyroid hormone (PTH) is fully active in vitro and in vivo and it elicits all the biological responses characteristic of the native intact PTH. Recent studies reported potent helical analogues of the PTH (1-11) with helicity-enhancing substitutions. This work describes the synthesis, biological activity, and conformational studies of analogues obtained from the most active non-natural PTH (1-11) peptide H-Aib-Val-Aib-Glu-Ile-Gln-Leu-Nle-His-Gln-Har-NH; specifically, the replacement of Val in position 2 with d-Val, l-(αMe)-Val and N-isopropyl-Gly was studied. The synthesized analogues were characterized functionally by in-cell assays and their structures were determined by CD and NMR spectroscopy. To clarify the relationship between the structure and activity, the structural data were used to generate a pharmacophoric model, obtained overlapping all the analogues. This model underlines the fundamental functional role of the side chain of Val and, at the same time, reveals that the introduction of conformationally constrained C-tetrasubstituted α-amino acids in the peptides increases their helical content, but does not necessarily ensure significant biological activity. [ABSTRACT FROM AUTHOR]

The N-terminal 1–34 segment of parathyroid hormone (PTH) is fully active in vitro and in vivo and it can reproduce all biological responses in bone characteristic of the native intact PTH. Recent studies have demonstrated that N-terminal fragments presenting the principal activating domain such as PTH(1–11) and PTH(1–14) with helicity-enhancing substitutions yield potent analogues with PTH(1–34)-like activity. To further investigate the role ofα-helicity on biological potency, we designed and synthesized by solid-phase methodology the following hPTH(1–11) analogues substituted at positions 1 and/or 3 by the sterically hindered and helix-promoting C α-tetrasubstitutedα-amino acidsα-amino isobutyric acid (Aib), 1-aminocyclopentane-1-carboxylic acid (Ac5c) and 1-aminocyclohexane-1-carboxylic acid (Ac6c): Ac5c-V-Aib-E-I-Q-L-M-H-Q-R-NH2 (I); Aib-V-Ac5c-E-I-Q-L-M-H-Q-R-NH2 (II); Ac6c-V-Aib-E-I-Q-L-M-H-Q-R-NH2 (III); Aib-V-Ac6c-E-I-Q-L-M-H-Q-R-NH2 (IV); Aib-V-Aib-E-I-Q-L-M-H-Q-R-NH2 (V); S-V-Aib-E-I-Q-L-M-H-Q-R-NH2 (VI), S-V-Ac5c-E-I-Q-L-M-H-Q-R-NH2 (VII); Ac5c-V-S-E-I-Q-L-M-H-Q-R-NH2 (VIII); Ac6c-V-S-E-I-Q-L-M-H-Q-R-NH2 (IX); Ac5c-V-Ac5c-E-I-Q-L-M-H-Q-R-NH2 (X); Ac6c-V-Ac6c-E-I-Q-L-M-H-Q-R-NH2 (XI). All analogues were biologically evaluated and conformationally characterized in 2,2,2-trifluoroethanol (TFE) solution by circular dichroism (CD). AnaloguesI– V, which cover the full range of biological activity observed in the present study, were further conformationally characterized in detail by nuclear magnetic resonance (NMR) and computer simulations studies. The results of ligand-stimulated cAMP accumulation experiments indicated that analoguesIandIIare active, analoguesIII,VIandVIIare very weakly active and analoguesIV,V,VIII–XIare inactive. The most potent analogue,Iexhibits biological activity 3500-fold higher than that of the native PTH(1–11) and only 15-fold weaker than that of the native sequence hPTH(1–34). Remarkably, the two most potent analogues,IandII, and the very weakly active analogues,VIandVII, exhibit similar helix contents. These results indicate that the presence of a stable N-terminal helical sequence is an important but not sufficient condition for biological activity. [ABSTRACT FROM AUTHOR]

To evaluate the ability of molecular dynamics (MD) simulations using atomic force-fields to correctly predict stable folded conformations of a peptide in solution, we show results from MD simulations of the reversible folding of an octapeptide rich in α-aminoisobutyric acid (2-amino-2-methyl-propanoic acid, Aib) solvated in di-methyl-sulfoxide (DMSO). This solvent generally prevents the formation of secondary structure, whereas Aib-rich peptides show a high propensity to form secondary structural elements, in particular 3[sub 10]- and α-helical structures. Aib is, moreover, achiral, so that Aib-rich peptides can form left- or right-handed helices depending on the overall composition of the peptide, the temperature, and the solvation conditions. This makes the system an interesting case to study the ensembles of peptide conformations as a function of temperature by MD simulation. Simulations involving the folding and unfolding of the peptide were performed starting from two initial structures, a right-handed α-helical structure and an extended structure, at three temperatures, 298 K, 340 K, and 380 K, and the results are compared with experimental nuclear magnetic resonance (NMR) data measured at 298 K and 340 K. The simulations generally reproduce the available experimental nuclear Overhauser effect (NOE) data, even when a wide range of conformations is sampled at each temperature. The importance of adequate statistical sampling in order to reliably interpret the experimental data is discussed. [ABSTRACT FROM AUTHOR]

The strong propensity of 2-amino-2-methyl propanoic acid (Aib)-rich peptides to form stable helical structures is well documented. NMR analysis of the short peptide Z-(Aib)[sub 5]-L-Leu-(Aib)[sub 2]-OMe indicates the presence of a well-characterized 3[sub 10]-helix even in dimethylsulfoxide (DMSO), a solvent known to disrupt helical structures. The structure remains stable at least up to 348 K. Stereospecific assignment of the diastereotopic methyls of Aib was achieved, with the assumption of a specific helical screw sense. The methyl more eclipsed with respect to the CO vector resonates at a higher field in the carbon dimension. Molecular dynamics simulations successfully predict the [sup 3]J[sub CHNH] coupling constant of Leu[sup 6] and most of the H-bonding pattern. Discrepancies were found for Aib[sup 3] and Aib[sup 7] amide protons which can be explained by a higher sensitivity of the simulations to the helix fraying at the end of the peptide and by the presence of extended conformations for Leu[sup 6] during most of the simulations. [ABSTRACT FROM AUTHOR]

The step-by-step synthesis by solution methods of the [Ser2,5,6,9, Leu-OMe11] analog of trichogin GA IV is described. The four Ser residues have been incorporated into the sequence as replacements of the naturally occurring Gly residues to increase the amphiphilicity of the 3D-structure of the lipopeptaibol. A detailed solution conformational analysis has been performed on this undecapeptide and its prototypical [Leu-OMe11] trichogin GA IV analog using FTIR absorption and CD spectroscopies, and two-dimensional NMR under a variety of experimental conditions, including a membrane-mimetic environment. Both peptides adopt a mixed 310/α-helical structure, which in the micellar system was found to be less flexible for the Ser-containing analog. For both analogs permeability measurements revealed membrane-modifying properties comparable to those of the natural lipopeptaibol. [ABSTRACT FROM AUTHOR]

Brain MRI and multimodal evoked potentials (EPs) were obtained for 13 patients with benign multiple sclerosis and 13 patients with secondary progressive multiple sclerosis, matched for age and duration of the disease, to investigate the nature of the disability in multiple sclerosis. Patients with secondary progressive multiple sclerosis had significantly greater lesion loads for five of seven periventricular regions and for three of nine regions separate from the ventricles. Patients with secondary progressive multiple sclerosis also had more severe infratentorial atrophy scores (p = 0.04), whereas there were no differences between the two groups in number and extent of enhancing lesions. The frequencies were significantly higher and severities greater for multimodal EP abnormalities of all the modalities in patients with secondary progressive multiple sclerosis. At least one EP component was absent in 12 (92%) patients with secondary progressive multiple sclerosis but in only one patient (8%) with benign multiple sclerosis (p < 0.001). There was neurophysiological evidence for cervical cord involvement in eight (61%) patients with secondary progressive multiple sclerosis and in one with benign multiple sclerosis (p < 0.01). These data indicate that the total amount of lesions, the distribution, and the nature of the pathological process might all account for the development of disability in multiple sclerosis. [ABSTRACT FROM AUTHOR]

We describe the diffusion- weighted MRI findings and follow- up in a case of autopsy-proven Creutzfeldt-Jakob disease that revealed abnormal hyperintensity in the cortex and basal ganglia. [ABSTRACT FROM AUTHOR]

To evaluate whether hemispheric lesion distribution in multiple sclerosis is related to the uneven interhemispheric localisation of cerebral function, a 10 item self administered questionnaire evaluating hand preference and supratentorial brain MRI was obtained in 23 patients with clinically definite multiple sclerosis. The mean degree of hand preference was +74 (range -86 to +100). The median lesion volumes were 7275 (range 1045-22,440) mm3 for the left hemisphere and 5385 (range 1010-19,490) mm3 for the right hemisphere. The degree of hand preference correlated with the index of interhemispheric lesion distribution (P = 0.02). The data suggest that local events, possibly related to specialisation of hemispheric function, might be responsible for the increased vulnerability of the dominant hemisphere to the pathological process of multiple sclerosis. [ABSTRACT FROM AUTHOR]