Glucagon receptor antagonist and GIP agonist combination for diet-induced obese mice

Ablation of glucagon receptor signaling represents a potential treatment option for type 2 diabetes (T2DM). Additionally, activation of glucose-dependent insulinotropic polypeptide (GIP) receptor signaling also holds therapeutic promise for T2DM. Therefore, this study examined both independent and combined metabolic actions of desHis(1)Pro(4)Glu(9)(Lys(12)PAL)-glucagon (glucagon receptor antagonist) and d-Ala(2)GIP (GIP receptor agonist) in diet-induced obese mice. Glucagon receptor binding has been linked to alpha-helical structure and desHis(1)Pro(4)Glu(9)(Lys(12)PAL)-glucagon displayed enhanced alpha-helical content compared with native glucagon. In clonal pancreatic BRIN-BD11 beta-cells, desHis(1)Pro(4)Glu(9)(Lys(12)PAL)-glucagon was devoid of any insulinotropic or cAMP-generating actions, and did not impede d-Ala(2)GIP-mediated (P<0.01 to P<0.001) effects on insulin and cAMP production. Twice-daily injection of desHis(1)Pro(4)Glu(9)(Lys(12)PAL)-glucagon or d-Ala(2)GIP alone, and in combination, in high-fat-fed mice failed to affect body weight or energy intake. Circulating blood glucose levels were significantly (P<0.05 to P<0.01) decreased by all treatments regimens, with plasma and pancreatic insulin elevated (P<0.05 to P<0.001) in all mice receiving d-Ala(2)GIP. Interestingly, plasma glucagon concentrations were decreased (P<0.05) by sustained glucagon inhibition (day 28), but increased (P<0.05) by d-Ala(2)GIP therapy, with a combined treatment resulting in glucagon concentration similar to saline controls. All treatments improved (P<0.01) intraperitoneal and oral glucose tolerance, and peripheral insulin sensitivity. d-Ala(2)GIP-treated mice showed increased glucose-induced insulin secretion in response to intraperitoneal and oral glucose. Metabolic rate and ambulatory locomotor activity were increased (P<0.05 to P<0.001) in all desHis(1)Pro(4)Glu(9)(Lys(12)PAL)-glucagon-treated mice. These studies highlight the potential of glucagon receptor inhibition alone, and in combination with GIP receptor activation, for T2DM treatment.

4-hydroxyphenylacetic acid derivatives of inositol from dandelion (Taraxacum officinale) root characterised using LC-SPE-NMR and LC-MS techniques

The combination of hyphenated techniques, LC-SPE-NMR and LC-MS, to isolate and identify minor isomeric compounds from an ethyl acetate fraction of Taraxacum officinale root was employed in this study. Two distinct fractions of 4-hydroxyphenylacetic acid derivatives of inositol were isolated and characterised by spectroscopic methods. The (1)H NMR spectra and MS data revealed two groups of compounds, one of which were derivatives of the di-4-hydroxyphenylacetic acid derivative of the inositol compound tetrahydroxy-5-[2-(4-hydroxyphenyl)acetyl] oxycyclohexyl-2-(4-hydroxyphenyl) acetate, while the other group consisted of similar tri-substituted inositol derivatives. For both fractions the derivatives of inositols vary in the number of 4-hydroxyphenylacetic acid groups present and their position and geometry on the inositol ring. In total, three di-substituted and three tri-substituted 4-hydroxyphenylacetic acid inositol derivates were identified for the first time along with a further two previously reported di-substituted inositol derivatives.

A linear endothelin-1 analogue: solution structure of ET-1[Aib1,3,11,15, Nle7] by nuclear magnetic resonance spectroscopy and molecular modelling

Two-dimensional nuclear magnetic resonance techniques and a combination of distance geometry and molecular dynamics calculations were utilised to determine the three dimensional solution structure of an ET-1 analogue, ET-1[Aib1,3,11,15, Nle7], in a methanol-d3/water co-solvent. The modelled structure shows that the peptide folds into a consistent alpha-helical conformation between residues Ser4-His16 while the C-terminus prefers no fixed conformation. Our studies confirm that the disulphide links which are normally associated with the endothelin family of neuropeptides are not important for the formation of a helical conformation in solution. This full length, modified, synthetic linear ET-1 analogue plays a vital role towards designing endothelin receptor agonists. Structure activity relationships are discussed in terms of the conformational features of the calculated structure.

Solution structure of a novel ETB receptor selective agonist ET1-21 [Cys(Acm)1,15, Aib3,11, Leu7] by nuclear magnetic resonance spectroscopy and molecular modelling

The solution structure of a biologically active modified linear endothelin-1 analogue, ET1-21[Cys(Acm)1,15, Aib3,11, Leu7], has been determined for the first time by two-dimensional nuclear magnetic resonance spectroscopy in a methanol-d3/water solvent mixture. Out of approximately one hundred linear peptide analogues tested by biological assay, this peptide, together with a dozen others, showed significant ETB selective agonist activity. Here we report the solution structure of an ETB selective agonist of a full-length, synthetic linear endothelin analogue. The calculated structures indicate that the peptide adopts an alpha-helical conformation between residues Ser5-His16, whilst both N- and C-termini show no preferred conformation. These results suggest that the disulphide bridges normally associated with endothelin and sarafotoxin peptides may not necessarily be important for either ETB receptor binding activity or the formation of a helical conformation in solution.

N alpha- and N epsilon-D-galacturonoyl-L-lysine amides: properties and possible occurrence in plant cell walls

Three representatives of a novel class of amide (isopeptide) glycoconjugates have been synthesised: N alpha-D-galacturonoyl-L-lysine and N epsilon-D-galacturonoyl-L-lysine and N epsilon-D-polygalacturonoyl-L-lysine. Galacturonoyl-lysine amide bonds were labile in 2 M trifluoroacetic acid at 120 degrees and in alkali, but relatively stable in cold acid. The amide bonds were resistant to digestion by Driselase, Pronase and trypsin. The polysaccharide backbone of N epsilon-D-polygalacturonoyl-L-lysine was hydrolysed by Driselase to yield two major ninhydrin-positive compounds which were shown by 1H and 13C NMR spectroscopy to be tri- and tetra-alpha-(1-->4)-D-galacturonoyl-L-lysines. To investigate the possible natural occurrence of N-galacturonoyl isopeptide bonds, we fed cell-suspension cultures of spinach and tomato with D-[6-14C]glucuronic acid, which radio-labels pectic polysaccharides. The radioactive cell walls were digested with, sequentially, Driselase, mild acid, and proteinases. On electrophoresis at pH 2.0, several of the radioactive digestion-products were cathodic. Some of the cathodic products yielded [14C]galacturonic acid upon complete acid hydrolysis. The existence of these products is compatible with the presence of novel N-galacturonoyl isopeptide bonds, which could serve as cross-links in plant cell walls.

Development of ET(B) selective agonists: solution structure of a linear endothelin-1 analogue, ET-1 [Cys(Acm)(1,15), Ala3, Leu7, dAsp8, Aib11]

The solution structure of a synthetic ET(B) selective agonist, ET-1[Cys(Acm)(1,15), Ala3, Leu7, dAsp8, Aib11] has been solved by 1H NMR and molecular modelling studies. Such solution structures of linear modified peptides in aqueous methanol are being used in an ongoing program of research designed to assist in an understanding of the basic structural requirements for the biological activity of vasoconstrictors. The resulting structure of this peptide is characterised by an alpha-helical conformation between residues Leu6-His16 and by N- and C-termini which assume no defined conformation. A knowledge of the solution structures of this and related peptides, which are ET(B) selective agonists, are proving to be important in the understanding of how they interact with the ET(B) receptor.

Solution conformation of an ET(B) selective agonist, ET-1[Cys(Acm)1,15,Ala3,Leu7,Aib11], in CD3OH/H2O by 1H NMR and molecular modelling

To understand the basic structural requirements for the biological activity of endothelin peptides, the solution structure of an ETB selective agonist, ET-1[Cys-(Acm)1,15, Ala3,Leu7,Aib11, was investigated by 1H NMR spectroscopy and molecular modelling. The structure is characterised by an alpha-helical conformation between residues Ser5-His16 but is undefined at both the N and C termini. To date, neither the solution structures of linear modified peptides nor the effects of a methanol/water solvent system have been examined for endothelin or endothelin-like peptides. This structure plays an important role towards the design of endothelin receptor selective agonists and antagonists.

Solution structure determination of endothelin-1 in methanol/water by NMR and molecular modelling methods

To understand the structural requirements for the biological activity of endothelin peptides and to develop receptor selective endothelin analogues further, the solution structure of the bicyclic 21 amino acid residue vasoactive peptide, endothelin-1, has been determined in methanol-d3/water using high-resolution 1H-NMR spectroscopy. To our knowledge, this solvent system has not previously been used in NMR studies of endothelin and/or endothelin-like peptides. Two-dimensional DQFCOSY, TOCSY and NOESY spectra were acquired along with a series of one-dimensional spectra. A total of 219 distance constraints and 5 angle constraints were derived from the NMR data. These were incorporated into structure calculations using distance geometry (DIANA) followed by simulated annealing and molecular dynamics. The resulting structures are characterized by an alpha-helical conformation, Lys9-His16, and residues Ser5-Asp8 form a type I beta-turn. The N-terminal region, which was not extensively constrained by NMR data, showed no preferred conformation. The C-terminal tail showed less extensive conformational averaging but no descriptive conformation could be observed. The results obtained in this study are in good agreement with previous proposals.