Effects of high and moderate non-structural carbohydrate hay on insulin, glucose, triglyceride, and leptin concentrations in overweight Arabian geldings

The objective of this study was to determine the effects of high and moderate non-structural carbohydrates (NSC) hay on insulin, glucose, triglyceride, and leptin concentrations in overweight Arabian geldings. Eight adult overweight (average BCS 7 [9-point scale]) Arabian geldings were fed each of two orchardgrass hays, high NSC (18% DM) and moderate NSC (12% DM), in a cross over design during two 28-day periods. Body weight and body condition score assessment along with blood sampling to measure insulin, glucose, leptin, and triglyceride concentrations were performed on days 0, 7, 14, 21 and 28 of each period. Effects of hay, period, day, and day*hay on plasma glucose and serum leptin were not detected. Serum insulin was influenced by hay (p = 0.001), day (p = 0.03), and day*hay (p = 0.04). Insulin concentrations were higher on day 7 in the high NSC group (15.6 μIU/ml) than the moderate NSC group (9.5 μIU/ml), but not by day 14 (p = 0.0007). Plasma triglyceride was influenced by period (p = 0.0003), day*period (p < 0.0001), and day*hay (p = 0.02). Hyperinsulinaemia was not observed in the overweight Arabian geldings fed either a moderate or high NSC hay.

Pore-forming proteins share structural and functional homology with amyloid oligomers

Degenerative diseases such as Alzheimer's, Parkinson's, and Huntington's diseases are believed to be causally related to the accumulation of amyloid oligomers that exhibit a common structure and may be toxic by a common mechanism involving permeabilization of membranes. We discovered that amyloid oligomers and the pore-forming bacterial toxin, alpha-hemolysin (alpha HL), as well as human perforin from cytotoxic T lymphocytes, share a structural and functional homology at the level of their common reactivity with a conformation-dependent antibody that is specific for amyloid oligomers, A11. The alpha HL oligomeric pores and partially folded alpha HL protomer, but not the monomer alpha HL precursor reacts with A11 antibody. A11 antibody inhibits the hemolytic activity of alpha HL, indicating that the structural homology is functionally significant. Perforin oligomers were also recognized by A11. Amyloidogenic properties of alpha HL and perforin were confirmed spectroscopically and morphologically. These results indicate that pore forming proteins (PFP) and amyloid oligomers share structural homology and suggest that PFPs and amyloid oligomers share the same mechanism of membrane permeabilization.

Calcium Dysregulation and Membrane Disruption as a Ubiquitous Neurotoxic Mechanism of Soluble Amyloid Oligomers*♦

Increasing evidence suggests that amyloid peptides associated with a variety of degenerative diseases induce neurotoxicity in their intermediate oligomeric state, rather than as monomers or fibrils. To test this hypothesis and investigate the possible involvement of Ca2+ signaling disruptions in amyloid-induced cytotoxicity, we made homogeneous preparations of disease-related amyloids (Abeta, prion, islet amyloid polypeptide, polyglutamine, and lysozyme) in various aggregation states and tested their actions on fluo-3-loaded SH-SY5Y cells. Application of oligomeric forms of all amyloids tested (0.6-6 microg ml-1) rapidly (approximately 5 s) elevated intracellular Ca2+, whereas equivalent amounts of monomers and fibrils did not. Ca2+ signals evoked by Abeta42 oligomers persisted after depletion of intracellular Ca2+ stores, and small signals remained in Ca2+-free medium, indicating contributions from both extracellular and intracellular Ca2+ sources. The increased membrane permeability to Ca2+ cannot be attributed to activation of endogenous Ca2+ channels, because responses were unaffected by the potent Ca2+-channel blocker cobalt (20 microm). Instead, observations that Abeta42 and other oligomers caused rapid cellular leakage of anionic fluorescent dyes point to a generalized increase in membrane permeability. The resulting unregulated flux of ions and molecules may provide a common mechanism for oligomer-mediated toxicity in many amyloidogenic diseases, with dysregulation of Ca2+ ions playing a crucial role because of their strong trans-membrane concentration gradient and involvement in cell dysfunction and death.

Permeabilization of Lipid Bilayers Is a Common Conformation-dependent Activity of Soluble Amyloid Oligomers in Protein Misfolding Diseases

Amyloid fibrillization is multistep process involving soluble oligomeric intermediates, including spherical oligomers and protofibrils. Amyloid oligomers have a common, generic structure, and they are intrinsically toxic to cells, even when formed from non-disease related proteins, which implies they also share a common mechanism of pathogenesis and toxicity. Here we report that soluble oligomers from several types of amyloids specifically increase lipid bilayer conductance regardless of the sequence, while fibrils and soluble low molecular weight species have no effect. The increase in membrane conductance occurs without any evidence of discrete channel or pore formation or ion selectivity. The conductance is dependent on the concentration of oligomers and can be reversed by anti-oligomer antibody. These results indicate that soluble oligomers from many types of amyloidogenic proteins and peptides increase membrane conductance in a conformation-specific fashion and suggest that this may represent the common primary mechanism of pathogenesis in amyloid-related degenerative diseases.

Common structure of soluble amyloid oligomers implies common mechanism of pathogenesis

Soluble oligomers are common to most amyloids and may represent the primary toxic species of amyloids, like the Abeta peptide in Alzheimer's disease (AD). Here we show that all of the soluble oligomers tested display a common conformation-dependent structure that is unique to soluble oligomers regardless of sequence. The in vitro toxicity of soluble oligomers is inhibited by oligomer-specific antibody. Soluble oligomers have a unique distribution in human AD brain that is distinct from fibrillar amyloid. These results indicate that different types of soluble amyloid oligomers have a common structure and suggest they share a common mechanism of toxicity.

Conformational analysis and proteolytic processing of synthetic pre-pro-GnRH/GAP protein

Homogeneous pre-pro-GnRH/GAP protein was recently synthesized in 100 mg quantities by solid-phase methods and surprisingly, the synthetic pre-pro-protein, which normally does not escape the endoplasmic reticulum, was found to inhibit the release of prolactin from cultured pituitary cells. This is the first demonstration of significant biological activity associated with a precursor protein and provides the rationale for its further study. We now report the results of our initial examination of the conformational properties of pre-pro-GnRH/GAP protein as a prelude to solving its solution phase conformation by homonuclear 1H-NMR protocols. Thermal and pH titration fluorescence and circular dichroism spectroscopies reveal that the protein is resistant to thermal-induced conformational changes but is particularly sensitive to pH-induced conformational changes; while Asp/Glu and Arg residues may contribute to structural stability, His and Lys residues predominate. Pre-pro-GnRH/GAP is about 30% helix in the range of 2-40 degrees C; however, even at 90 degrees C, the peptide retains nearly 50% of its helix character. There is no evidence for a cooperative transition; for this reason, differential scanning calorimetry failed to yield a defined transition thermogram. Pre-pro-GnRH/GAP apparently does not pass through a transition state as a function of temperature but appears to flex and retain a high percentage of helix structure, resulting in subtle changes in secondary structure. There is no discernible isodichroic point. On either side of the neutral pH range, however, there are dramatic changes in structure that result in nonreversible denaturation of the protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Total solid-phase synthesis and prolactin-inhibiting activity of the gonadotropin-releasing hormone precursor protein and the gonadotropin-releasing hormone associated peptide

The human gonadotropin-releasing hormone precursor protein, pHGnRH (Met-23-Ile69) (preproGnRH), and three of its fragment peptides, pHGnRH (Asp14-Ile69) (gonadotropin-releasing hormone associated peptide--GAP), pHGnRH (Phe38-Ile69), and pHGnRH (Ser47-Ile69), were assembled in a stepwise solid-phase cosynthesis employing Boc/Bzl tactics and an optimized acylation schedule which included recoupling steps with hexafluoro-2-propanol to help overcome the aggregation of the pendant peptide chains of the peptidoresin during difficult couplings. Reversed-phase high-performance liquid chromatography (HPLC) purification yielded products which were characterized by analytical reversed-phase HPLC, ion-exchange chromatography, capillary zone electrophoresis, SDS-polyacrylamide gel electrophoresis, and ion-spray mass spectrometry to reveal a high degree of homogeneity. Biological characterization demonstrated that only GAP stimulated luteinizing hormone and follicle-stimulating hormone release from primary cultures of rat anterior pituitary cells, while GAP, pHGnRH (Phe38-Ile69), and preproGnRH all inhibited prolactin release, with the latter being the most potent at concentrations comparable to bromocryptine. However, only GAP and pHGnRH (Phe38-Ile69) were able to displace a labeled gonadotropin-releasing hormone agonist from binding to rat pituitary membrane preparations. This first demonstration of significant biological activity with a precursor protein also suggests that the gonadotropin-releasing and prolactin release-inhibiting functions of GAP are not mediated through the same pituitary receptors.

Total chemical synthesis of a D-enzyme: the enantiomers of HIV-1 protease show reciprocal chiral substrate specificity [corrected]

The D and L forms of the enzyme HIV-1 protease have been prepared by total chemical synthesis. The two proteins had identical covalent structures. However, the folded protein-enzyme enantiomers showed reciprocal chiral specificity on peptide substrates. That is, each enzyme enantiomer cut only the corresponding substrate enantiomer. Reciprocal chiral specificity was also evident in the effect of enantiomeric inhibitors. These data imply that the folded forms of the chemically synthesized D- and L-enzyme molecules are mirror images of one another in all elements of the three-dimensional structure. Enantiomeric proteins are expected to display reciprocal chiral specificity in all aspects of their biochemical interactions.

Selective FSH-releasing activity of [D-Trp9]GAP1-13: comparison with gonadotropin-releasing abilities of analogs of GAP and natural LHRHs

We had previously shown that fragments of human gonadotropin-releasing hormone associated peptide (GAP) stimulated FSH and LH release in vivo. In particular, GAP1-13 had a preferential FSH-releasing activity. To decrease enzymatic degradation, analogs of GAP1-13 with D-amino acid substitutions were synthesized. The activities were tested in ovariectomized, estrogen-progesterone primed (OEP) rats and compared with those of GAP1-13, mammalian (m), chicken II (cII), and lamprey (1) LHRH. The peptides were injected (IV) into conscious, OEP rats and blood samples were obtained via the jugular catheter. [D-Trp9 )GAP1-13 selectively stimulated FSH release at a dose of 1 microgram. Multiple injections of this analog (10 micrograms every 30 min for 5 injections) induced a marked elevation of plasma FSH values which peaked (p less than 0.001) after the third injection. By contrast, [D-Trp9]GAP1-13 had no effect on LH and prolactin (PRL) release after either single or multiple injections. These doses of [D-Ala4]GAP1-13 had no effect on the release of FSH, LH or PRL. Both human GAP1-13 and its [D-Trp9] analog exerted a selective FSH-releasing effect at a dose of 10 micrograms, however, the [D-Trp9] analog was more potent than GAP1-13 on FSH release. The potency of [D-Trp9]GAP1-13 in releasing FSH was approximately 1/100th that of mLHRH. Chicken II LHRH had slightly selective FSH-releasing activity with a potency 1/10th that of mLHRH. Lamprey LHRH had a preferential LH-releasing activity and a potency 1000 times less than mLHRH. In conclusion. [D-Trp9]GAP1-13 is a selective FSH-releasing peptide of potential clinical value.

LH-releasing activity and receptor binding of pHGnRH 14-26 analogues

The human gonadotropin-releasing hormone (GnRH) precursor consists of the GnRH sequence followed by a cleavage and amidation site and a 56-amino acid carboxyl-terminal extension (pHGnRH - precursor human GnRH) which has been shown to stimulate gonadotropin release. This activity has been localized to a decapeptide sequence (corresponding to pHGnRH 17-26) in its amino-terminal region using human pituitary cell cultures. To further characterize the structural features required for gonadotropin release, two analogues, [D-Ala17]pHGnRH 14-26 and [D-Trp22]pHGnRH 14-26, with D-amino acid substitutions inside and peripheral to this decapeptide sequence were chemically synthesized. pHGnRH 14-26 and the D-Ala17 analogue were inactive and GnRH, pHGnRH 14-36 and the D-Trp22 analogue stimulated luteinizing hormone release from cultured rat pituitary cells in a calcium-dependent, dose-responsive manner. Experiments and receptor binding studies with the active pHGnRH peptides in conjunction with GnRH or a GnRH antagonist suggest that the active pHGnRH peptides act through the GnRH receptor.