Reproductive performance of lactating dairy cattle after intrauterine administration of a prostaglandin F2α receptor antagonist 4 days after insemination

Previous research has determined that PGF2α detrimentally affects pregnancy via direct effects on early embryonic development. Because early embryonic loss is relatively prevalent in lactating dairy cows, we hypothesized that pregnancy retention (and resulting conception rates) would be improved by administering a PGF2α receptor antagonist (AL-8810) shortly after insemination. Multiparous, lactating Holstein dairy cows were randomly assigned to receive one of four intrauterine treatments: (1) control group-untreated cohort (CON; n = 93); (2) control group-vehicle infusion (CON-V; n = 90); (3) 2000 nM AL-8810 infusion (AL-2000; n = 96); or (4) 10,000 nM AL-8810 infusion (AL-10,000; n = 93). Treatments were administered transcervically 4 days after insemination in the horn ipsilateral to the CL. There was no effect of treatment on conception rate (36.6%, 38.9%, 25.0%, and 35.5% for CON, CON-V, AL-2000, and AL-10,000, respectively) or calving rate (24.7%, 24.4%, 16.7%, and 28.0% for CON, CON-V, AL-2000, and AL-10,000, respectively). There was a significant effect of treatment on return to estrus with CON-V (23.6 ± 0.6) and AL-10,000 (23.3 ± 0.6) groups having a longer interval to next estrus over the CON group (21.5 ± 0.6; P < 0.05). Prior treatment did not affect conception to the subsequent insemination. It is important to note that although the addition of AL-8810 into the uterus on Day 4 after insemination did not increase conception rates in the present experiment, it also did not have a negative impact. Furthermore, the treatment procedure itself did not impair the establishment of pregnancy (CON vs. CON-V, AL-2000, and AL-10,000). These results demonstrate that a therapeutic agent can be administered directly into the uterus on Day 4 after insemination without detrimentally affecting conception rates.

Purification of protected syntheic peptides by preparative high performance liquid chromatography on silica gel 60

A simple preparative system is described for rapid and efficient purification of protected synthetic peptides on a gram scale by high performance liquid chromatography on prepacked silica gel 60 columns. A variety of protected peptides up to tetradecapeptides have been chromatographed at pressures of 50 to 150 psi and obtained in analytically pure from within 2 to 4 h. With such commonly used protecting groups as N-benzyloxycarbonyl (Z), N-2-(p-biphenylyl)-2-propyloxycarbonyl (Bpoc), N-t-butyloxycarbonyl (Boc), O- and S-t-butyl (But), and S-acetamidomethyl (Acm), compounds were sufficiently soluble in chloroform, alcohols, acetic acid, or mixtures of these solvents for column loading. Dimethylformamide was also used as a solvent for loading. Solvent systems for column elution in isocratic, stepwise, or gradient modes were composed of chloroform, isopropanol, ethanol, or methanol and acetic acid in ratios that differed for each protected peptide depending on Rf values on t.l.c. plates. A simple chromatography is described which was self-assembled using standard instruments commonly in use in most laboratories. A shut-off valve was designed to prevent loss of material between fractions.

Fluorescamine as a terminating agent in solid phase peptide synthesis

Fluorescamine was shown to be an excellent terminating agent for blocking unreacted amino groups during solid phase peptide synthesis. A comparison of the termination efficiency of fluorescamine versus that of acetylation revealed that the former method gave superior products as assessed by peptide analysis, dansyl-amino end group determination and biological assay. In addition, fluorescamine terminated fragments were converted to non-fluorescent spirolactones during the deprotection stage. These spirolactones were stable to subsequent solid phase reaction conditions and were readily removed from the target peptide.

Synthesis of bis- and tris-branched COOH-terminal pegylating reagents: conjugation to NH-terminal peptides

In previous studies we reported an orthogonal protection scheme that was developed for the solution-phase synthesis of a family of bis- and tris-pegylating reagents which contain a free NH(2)-terminus. These pegylating reagents were coupled to the COOH-terminus of a model peptide. In the present study we report on the solution synthesis of a novel family of bis- and tris-pegylating reagents which contain a free COOH-terminus. To illustrate their general utility, conditions were developed for the coupling of these novel pegylating reagents to the NH(2)-function of a model pentapeptide. Taken together, our studies demonstrate that these pegylating reagents are well suited for conjugation to peptides and proteins that contain either free COOH- or NH(2)-functions. These reagents may have general utility in therapeutic development as branched pegylation has been shown to provide more effective protection of proteins from proteolysis by shielding the protein surface from approaching macromolecules.

Synthesis of symmetrically and asymmetrically branched pegylating reagents

A solution-phase procedure using an orthogonal protection scheme was developed for the synthesis of a novel family of multi-pegylating reagents. The procedure was exemplified by the synthesis of bis- and tris-pegylating reagents prepared by stepwise insertion of the poly(ethylene glycol) units thereby enabling the preparation of both symmetrical and asymmetrical pegylating reagents. Asymmetrical pegylation and tris-pegylation of peptides and proteins introduces new variables for use in the optimization of pegylated peptides and proteins. These reagents are ideally suited for conjugation to peptides and proteins as they possess a required functional group and will be useful intermediates for the synthesis of a new generation of pegylated products. Tris-pegylation can also provide more effective protection from proteolysis by shielding the protein surface from approaching macromolecules. To illustrate this potential, conditions were developed for the successful coupling of the tris-pegylating reagent to a model pentapeptide.

Activation barriers to structural transition determine deposition rates of Alzheimer's disease a beta amyloid

Brain amyloid composed of the approximately 40-amino-acid human beta-amyloid peptide A beta is integral to Alzheimer's disease pathology. To probe the importance of a conformational transition in Abeta during amyloid growth, we synthesized and examined the solution conformation and amyloid deposition activity of A beta congeners designed to have similar solution structures but to vary substantially in their barriers to conformational transition. Although all these peptides adopt similar solution conformations, a covalently restricted Abeta congener designed to have a very high barrier to conformational rearrangement was inactive, while a peptide designed to have a reduced barrier to conformational transition displayed an enhanced deposition rate relative to wild-type A beta. The hyperactive peptide, which is linked to a heritable A beta amyloidosis characterized by massive amyloid deposition at an early age, displayed a reduced activation barrier to deposition consistent with a larger difference in activation entropy than in activation enthalpy relative to wild-type A beta. These results suggest that in Alzheimer's disease, as in the prion diseases, a conformational transition in the depositing peptide is essential for the conversion of soluble monomer to insoluble amyloid, and alterations in the activation barrier to this transition affect amyloidogenicity and directly contribute to human disease.

The Alzheimer's peptide a beta adopts a collapsed coil structure in water

The self-assembly of the soluble peptide Abeta into Alzheimer's disease amyloid is believed to involve a conformational change. Hence the solution conformation of Abeta is of significant interest. In contrast to studies in other solvents, in water Abeta is collapsed into a compact series of loops, strands, and turns and has no alpha-helical or beta-sheet structure. Conformational stabilization is primarily attributed to van der Waals and electrostatic forces. A large conspicuous uninterrupted hydrophobic patch covers approximately 25% of the surface. The compact coil structure appears meta-stable, and because fibrillization leads to formation of intermolecular beta-sheet secondary structure, a global conformational rearrangement is highly likely. A molecular hypothesis for amyloidosis includes at least two primary driving forces, changes in solvation thermodynamics during formation of amyloid deposits and relief of internal conformational stress within the soluble precursor during formation of lower-energy amyloid fibrils.

Combined solid-phase/solution synthesis of a 31-residue vasoactive intestinal peptide analog: general method for repetitive coupling of fragments without isolation and purification of intermediates

A novel analog of vasoactive intestinal peptide (VIP) has been reported which exhibits high potency and enhanced duration of in vivo biological activity. This VIP analog, cyclo-(Lys21-Asp25)Ac[Glu8 Lys12 Nle17 Ala19, Asp25 Leu26,Lys27,28,Gly29,30,Thr31]-VIP, which also has a lactam bridge, has been reported to have relaxant effects that are significantly more potent than other beta-agonists such as salbutamol and salmeterol. Because it has potential use for the treatment of bronchial asthma in humans, various convergent syntheses were evaluated to enable the economic preparation of large quantities of this medium-sized hentriacontapeptide. From these studies we developed a combined solid-phase/solution synthesis which uses four protected fragments (each prepared by solid-phase synthesis with highly acid-labile resins) possessing Nalpha-9-fluorenylmethyloxycarbonyl and side-chain tert-butyl protection. Only equivalent amounts of each fragment were required to achieve near-quantitative coupling reactions using N-[(1H-benzotriazol-1-yl)(dimethylamino)methylene]-N-methylmeth anaminium hexafluorophosphate N-oxide/N-hydroxybenzotriazole. All reagents and side products were removed at each stage by simple extraction procedures. Final deprotection was carried out with 90% trifluoroacetic acid. Under these conditions only low levels of epimerization were observed (<2%). These diastereoisomers and other trace impurities were removed from the product in a single purification by preparative high-performance liquid chromatography. The procedure has been scaled up (10-g scale) and the final product obtained in an overall (nonoptimized) yield of 24%. This procedure for the repetitive coupling of fragments, without isolation of intermediates, may be generally applicable for the economic synthesis of other medium-sized and longer peptides.

Pegylated peptides. V. Carboxy-terminal PEGylated analogs of growth hormone-releasing factor (GRF) display enhanced duration of biological activity in vivo

In the present study, human growth hormone-releasing factor (hGRF) and analogs were successfully pegylated at the carboxy-terminus using a novel solid- and solution-phase strategy. Following synthesis, these pegylated hGRF analogs were evaluated for in vitro and in vivo biological activity. Specifically, hGRF (1-29)-NH2, [Ala15]-hGRF (1-29)-NH2, [desNH2Tyr1, D-Ala2, Ala15]-hGRF(1-29)-NH2 and [His1, Val2, Gln8, Ala15, Leu27]-hGRF(1-32)-OH were each C-terminally extended using a Gly-Gly-Cys-NH2 spacer (previously demonstrated not to alter intrinsic biological activity), and then monopegylated via coupling to an activated dithiopyridyl-PEG reagent. PEG moieties of 750, 2000, 5000 or 10,000 molecular weight (MW) were examined to determine the effect of polymer weight on activity. Initial biological evaluations in vitro revealed that all C-terminally pegylated hGRF analogs retained high growth hormone (GH)-releasing potencies, regardless of the MW of PEG polymer employed. Two of these pegylated hGRF analogs, [desNH2Tyr1, D-Ala2, Ala15]-hGRF (1-29)-Gly-Gly-Cys(NH2)-S-Nle-PEG5000 and [His1, Val2, Gln8, Ala15, Leu27]-hGRF(1-32)-Gly-Cys(NH2)-S-Nle-PEG5000, were subsequently evaluated in both pig and mouse models and found to be highly potent (in vivo potency range = 12-55-fold that of native hGRF). Relative to their non-pegylated counterparts, these two pegylated hGRF analogs exhibited enhanced duration of activity.

A beta deposition inhibitor screen using synthetic amyloid

The formation, growth, and maturation of brain amyloid "senile" plaques are essential pathological processes in Alzheimer's disease (AD) and key targets for therapeutic intervention. The process of in vitro deposition of A beta at physiological concentrations onto plaques in AD brain preparations has been well characterized, but is cumbersome for drug discovery. We describe here a high-through put screen for inhibitors of A beta deposition onto a synthetic template (synthaloid) of fibrillar A beta immobilized in a polymer matrix. Synthaloid is indistinguishable from plaques in AD brain (the natural template) in deposition kinetics, pH profile, and structure-activity relationships for both A beta analogs and inhibitors. Synthaloid, in contrast to current A beta aggregation screens, accurately predicted inhibitor potency for A beta deposition onto AD cortex preparations, validating its use in searching for agents that can slow the progression of AD and exposing a previously inaccessible target for drug discovery.

Point substitution in the central hydrophobic cluster of a human beta-amyloid congener disrupts peptide folding and abolishes plaque competence

Alzheimer's disease (AD) is pathologically characterized by the presence of numerous insoluble amyloid plaques in the brain composed primarily of a 40-43 amino acid peptide, the human beta-amyloid peptide (A beta). The process of A beta deposition can be modeled in vitro by deposition of physiological concentrations of radiolabeled A beta onto preexisting amyloid in preparations of unfixed AD cerebral cortex. Using this model system, it has been shown that A beta deposition is biochemically distinct from A beta aggregation and occurs readily at physiological A beta concentrations, but which regions and conformations of A beta are essential to A beta deposition is poorly understood. We report here that an active congener, A beta (10-35)-NH2, displays time dependence, pH-activity profile, and kinetic order of deposition similar to A beta (1-40), and is sufficiently soluble for NMR spectroscopy in water under conditions where it actively deposits. To examine the importance of the central hydrophobic cluster of A beta (LVFFA, residues 17-21) for in vitro A beta deposition, an A beta (10-35)-NH2 analog with a single point substitution (F19T) in this region was synthesized and examined. Unlike A beta (10-35)-NH2, the F19T analog was plaque growth incompetent, and NMR analysis indicated that the mutant peptide was significantly less folded than wild-type A beta. These results support previous studies suggesting that the plaque competence of A beta correlates with peptide folding. Since compounds that alter A beta folding may reduce amyloid deposition, the central hydrophobic cluster of A beta will be a tempting target for structure-based drug design when high-resolution structural information becomes available.

Pegylated peptides. IV. Enhanced biological activity of site-directed pegylated GRF analogs

Conditions have been developed for the site-specific pegylation (NH2-terminus, side-chain and carboxy-terminus) of a potent analog of growth hormone-releasing factor, [Ala15]-hGRF(1-29)-NH2. These pegylated peptides were prepared by solid-phase peptide synthesis using the Fmoc/tBu strategy, and were fully characterized by analytical HPLC, amino-acid analysis, 1H-NMR spectroscopy and laser desorption mass spectrometry. Biological activities of hGRF analogs were determined in vitro utilizing stimulation of growth hormone release by cultured rat pituitary cells as an index. GH-releasing potencies of the pegylated hGRF analogs were compared to a series of model analogs of [Ala15]-hGRF(1-29)-NH2 that were acetylated or protected as the ethylamides at the pegylation sites. It was found that acetylation at the NH2-terminus resulted in reduced potency, which was not further affected when the NH2-terminus was pegylated, regardless of the size of poly(ethyleneglycol) (PEG) employed (e.g. PEG2000 or PEG5000). Pegylation at Asp8 or Lys12 decreased biological potency, a situation which was exacerbated by increasing the molecular weight of PEG. Pegylation at Lys21 or Asp25 did not significantly affect biological activity. The C-terminal model peptide, [Ala15,Orn(Ac)30]-hGRF(1-29)-NH2, was the most potent analog identified in this series (ca. 4-5-fold that of hGRF(1-44)-NH2. The COOH-terminal pegylated analogs retained this increased level of biological activity independent of PEG molecular weight. These studies demonstrate that a biologically active peptide can be pegylated and retain the full in vitro potency of the peptide. However, the biological activity is highly dependent on the site of pegylation and, in some cases, the molecular weight of PEG (degree of pegylation) moiety used.

Cytotoxic T cells specific for glutamic acid decarboxylase in autoimmune diabetes

Insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease that results in the destruction of the pancreatic islet beta cells. Glutamic acid decarboxylase (GAD) has been recently indicated as a key autoantigen in the induction of IDDM in nonobese diabetic mice. In human diabetes, the mechanism by which the beta cells are destroyed is still unknown. Here we report the first evidence for the presence of GAD-specific cytotoxic T cells in asymptomatic and recent diabetic patients. GAD65 peptides displaying the human histocompatibility leukocyte antigen (HLA)-A*0201 binding motif have been synthesized. One of these peptides, GAD114-123, binds to HLA-A*0201 molecules in an HLA assembly assay. Peripheral blood mononuclear cells from individuals with preclinical IDDM, recent-onset IDDM, and from healthy controls were stimulated in vitro with the selected peptide in the presence of autologous antigen-presenting cells. In three cases (one preclinical IDDM and two recent-onset IDDM), we detected specific killing of autologous antigen-presenting cells when incubated with GAD114-123 peptide or when infected with a recombinant vaccinia virus expressing GAD65. These patients were the only three carrying the HLA-A*0201 allele among the subjects studied. Our finding suggests that GAD-specific cytotoxic T lymphocytes may play a critical role in the initial events of IDDM.

1H NMR of A beta amyloid peptide congeners in water solution. Conformational changes correlate with plaque competence

To begin to examine the structural basis for the deposition of soluble A beta amyloid peptide onto senile plaques in Alzheimer's disease, we have prepared A beta congeners and measured their activity in an in vitro plaque growth assay. The N-terminal fragment, A beta (1-28)-OH, was inactive at all pH values tested. While the central fragment, A beta (10-35)-NH2, and the full length peptide, A beta (1-40)-OH, were inactive below pH 4, both were active (plaque competent) between pH 5 and 9. The active and inactive fragments were studied by nuclear magnetic resonance spectroscopy in water at submillimolar concentrations at pH 2.1 and 5.6. Changes in chemical shifts, coupling constants, and nuclear Overhauser enhancements indicate a pH dependent folding transition in A beta (10-35)-NH2 as it becomes active. The conformation of the active fragment is not helical, and preliminary data indicate the presence of several turns and at least two short strands. In contrast, the inactive fragment A beta (1-28)-OH did not undergo a similar folding transition. Earlier nuclear magnetic resonance studies of amyloid peptides in fluorinated alcohols or detergent micelles at low pH described a helical conformation and proposed a helix to sheet transition in plaque formation; the present study demonstrates that no such conformations are present in water under conditions where the peptides can adhere to authentic amyloid plaques.

Rational design, synthesis, and biological evaluation of novel growth hormone releasing factor analogues

Since its initial discovery in 1982, growth hormone-releasing factor (GRF) has been the subject of intense investigation. This interest was prompted by the potential application of GRF for stimulating growth in dwarf humans and for performance enhancement in livestock. Substantial research has been focused upon the development of potent, long-acting analogs as therapeutics. Herein is described a summary of the cumulative efforts of various laboratories endeavoring in this quest. The rationale utilized in GRF analog development is discussed: 1) determination of bioactive core, 2) evaluation of secondary structure, and 3) elucidation of degradation pathways (chemical and enzymatic). Using this information, several series of linear (unnatural and natural sequence) and cyclic GRF analogs were designed, synthesized, and evaluated. Stimulated by the constraints of commercial production, innovative, alternative methods of synthesis were explored: solid-phase, solution-phase, enzymatic, and recombinant. To date, the most promising candidate for drug development is [His1, Val2, Gln8, Ala15, Leu27]-hGRF(1-32)-OH. This natural sequence analog, consisting of rodent and human sequences, incorporates the bioactive core, preferred secondary structure, resistance to chemical and enzymatic degradation; with the added benefit of amenability to large-scale recombinant synthesis.

Peptide synthesis catalyzed by the Glu/Asp-specific endopeptidase. Influence of the ester leaving group of the acyl donor on yield and catalytic efficiency

We recently described a two-step enzymatic semisynthesis of the superpotent analog of human growth hormone releasing factor, [desNH2Tyr1,D-Ala2,Ala15]-GRF(1-29)-NH2 (4), from the precursor, [Ala15,29]-GRF(4-29)-OH (1). C-Terminal amidation of 1 to form [Ala15]-GRF(4-29)-NH2 (2) was achieved by carboxypeptidase-Y-catalyzed exchange of Ala29-OH for Arg-NH2. The target analog 4 was then obtained by acylation of segment 2 with desNH2Tyr-D-Ala-Asp(OH)-OR (3) (R = CH3CH2- or 4-NO2C6H4CH2-) catalyzed by the V8 protease. In this paper we report on the use of the recently isolated Glu/Asp-specific endopeptidase (GSE) from Bacillus licheniformis, which is shown to be an efficient catalyst for the segment condensation of 2 and 3. GSE is more stable than the V8 protease under the conditions employed (20% DMF, pH 8.2, 37 degrees C). The extent of conversion of 2 into 4 is limited by proteolyses at Asp3-Ala4 and Asp25-Ile26. However, this proteolysis is virtually eliminated by use of the appropriate ester leaving group, R. A systematic study of the kinetics of the GSE-catalyzed segment condensations of 2 and a series of tripeptide esters, desNH2Tyr-D-Ala-Asp(OH)-OR (3) [R = CH3CH2- (3a), CH3- (3b), ClCH2CH2- (3c), C6H5CH2- (3d), 4-NO2C6H4CH2- (3e)] revealed that rate of aminolysis versus proteolysis, and hence the conversion of 2 into 4, increase with increasing specificity (Vmax/Km) of GSE for the tripeptide ester.(ABSTRACT TRUNCATED AT 250 WORDS)

Solid-phase synthesis of extended lactam ring systems: preparation of amino acid alpha-fluorenylmethyl esters for the synthesis of reverse-extended lactams

Conventional side-chain to side-chain cyclization between Lys/Orn and Asp/Glu side chains has the inherent shortcoming of limited variability in the ring sizes; limited by the amino acids involved in the lactamization. A novel approach to modulate the ring size has been introduced by using "spacers" (e.g., Gly, beta-Ala, gamma-Aba). General solid-phase procedures were developed that enabled the insertion of these spacers for the preparation of extended and reverse-extended lactam ring systems. Extended lactam ring systems were prepared using the Boc/Bzl strategy with Fmoc protection on the side chain of the basic residue, Lys/Orn. The spacer was introduced as the Fmoc amino acid, and chain elongation proceeded by the Boc/Bzl strategy. The acidic residue, Asp/Glu, involved in the lactam bridge was introduced with side-chain -OFm protection. Selective deprotection of the Fmoc and -OFm functions was followed by BOP cyclization, further chain elongation and HF cleavage. Reverse-extended lactam ring systems were prepared analogously using the Boc/Bzl strategy with the initial introduction of -OFm protection on the side chain of the acidic residue. In this case, amino acid alpha-fluorenylmethyl esters were used as the spacers. Amino acid alpha-fluorenylmethyl ester hydrochlorides were prepared in two steps from N-t-butyloxycarbonyl amino acids in excellent yield. These intermediates have general utility in peptide synthesis, including their specific application as "spacers" for the solid-phase synthesis of extended cyclic peptides (lactams). Using these intermediates, we prepared a model dicyclo-peptide that contains both an extended and reverse-extended lactam ring system.

Pegylated peptides. II. Solid-phase synthesis of amino-, carboxy- and side-chain pegylated peptides

General procedures are presented for the site-specific pegylation of peptides at the NH2-terminus, side-chain positions (Lys or Asp/Glu) or COOH-terminus using solid-phase Fmoc/tBu methodologies. A model tridecapeptide fragment of interleukin-2, IL-2(44-56)-NH2, was chosen for this study since it possesses several trifunctional amino acids which serve as potential sites for pegylation. The pegylation reagents were designed to contain either Nle or Orn, which served as diagnostic amino acids for confirming the presence of 1 PEG unit per mole of peptide. NH2-Terminal pegylation was carried out by coupling PEG-CH2CO-Nle-OH to the free NH2-terminus of the peptide-resin. Side-chain pegylation of Lys or Asp was achieved by one of two pathways. Direct side-chain pegylation was accomplished by coupling with Fmoc-Lys(PEG-CH2CO-Nle)-OH or Fmoc-Asp(Nle-NH-CH2CH2-PEG)-OH, followed by solid-phase assemblage of the pegylated peptide-resin and TFA cleavage. Alternatively, allylic protective groups were introduced via Fmoc-Lys(Alloc)-OH or Fmoc-Asp(O-Allyl)-OH, and selectively removed by palladium-catalyzed deprotection after assemblage of the peptide-resin. Solid-phase pegylation of the side-chain of Lys or Asp was then carried out in the final stage with PEG-CH2CO-Nle-OH or H-Nle-NH-(CH2)2-PEG, respectively. COOH-Terminal pegylation was achieved through the initial attachment of Fmoc-Orn(PEG-CH2CO)-OH to the solid support, followed by solid-phase peptide synthesis using the Fmoc/tBu strategy. The pegylated peptides were purified by dialysis and preparative HPLC and were fully characterized by analytical HPLC, amino acid analysis, 1H-NMR spectroscopy and laser desorption mass spectrometry.

Enhanced stability and potency of novel growth hormone-releasing factor (GRF) analogues derived from rodent and human GRF sequences

Native human GRF(1-44)-NH2(hGRF44) is subject to biological inactivation by both enzymatic and chemical routes. In plasma, hGRF44 is rapidly degraded via dipeptidylpeptidase IV (DPP-IV) cleavage between residues Ala2 and Asp3. The hGRF44 is also subject to chemical rearrangement (Asn8-->Asp8, beta-Asp8 via aminosuccinimide formation) and oxidation [Met27-->Met(O)27] in aqueous environments, greatly reducing its bioactivity. It is therefore advantageous to develop long-acting GRF analogues using specific amino acid replacements at the amino-terminus (to prevent enzymatic degradation): residue 8 (to reduce isomerization) and residue 27 (to prevent oxidation). Inclusion of Ala15 substitution (for Gly15), previously demonstrated to enhance receptor binding affinity, would be predicted to improve GRF analogue potency. Substitution of [His1,Val2]-(from the mouse GRF sequence) for [Tyr1,Ala2]-(human sequence) in [Ala15,Leu27]hGRF(1-32)-OH analogues completely inhibited (24-h incubation) DPP-IV cleavage and greatly increased plasma stability in vitro. Additional substitution of Thr8 (mouse GRF sequence), Ser8 (rat GRF sequence), or Gln8 (not naturally occurring) for Asn8 (human GRF sequence) resulted in analogues with enhanced aqueous stability in vitro (i.e., decreased rate of isomerization). These three highly stable and enzymatically resistant hGRF(1-32)-OH analogues, containing His1, Val2, Thr/Gln8, Ala15, and Leu27 replacements, were then bioassayed for growth hormone (GH)-releasing activity in vitro (rat pituitary cell culture) and in vivo (SC injection into pigs). Enhanced bioactivity was observed with all three hGRF(1-32)-OH analogues. In vitro, these analogues were approximately threefold more potent than hGRF44, whereas in vivo they were eleven- to thirteenfold more potent.(ABSTRACT TRUNCATED AT 250 WORDS)

Pegylated peptides I: Solid-phase synthesis of N alpha-pegylated peptides using Fmoc strategy

The feasibility of pegylating peptides by the solid-phase procedure was examined. Although polyethyleneglycol (PEG) was shown to be partially degraded by HF, the use of TFA was fully compatible with the PEG system. Therefore, the Fmoc/tBu solid-phase strategy was utilized for the synthesis of a series of model tetra-, octa- and dodecapeptides, and the corresponding N alpha-pegylated peptides, which were prepared from common peptide-resin intermediates. PEG-OCH2-CO-Nle-OH, 3, proved to be an ideal reagent for N-terminal pegylation. This intermediate served as a diagnostic for the determination of the number of PEG units/mole of peptide. Solid-phase coupling reactions proceeded by standard procedures using BOP-activation. The authentic pegylated peptides (readily purified by conventional methods of preparative HPLC) were fully characterized by amino acid analysis, 1H-NMR spectroscopy, analytical HPLC and laser desorption ionization mass spectrometry, leading to the values that are identical with the expected structures.

Enzymatic semisynthesis of a superpotent analog of human growth hormone-releasing factor

A superpotent analog of human growth hormone-releasing factor, [desNH2Tyr1,D-Ala2,Ala15]-GRF(1-29)-NH2 (4), was prepared from the precursor, [Ala15,29]-GRF(4-29)-OH (1), by a two-step enzymatic semisynthesis. The amidated C-terminus, essential for high biological potency, was obtained via a carboxypeptidase Y-catalyzed exchange of Ala29-OH for Arg29-NH2 to produce [Ala15]-GRF(4-29)-NH2 (2). The N-terminal desNH2Tyr-D-Ala moiety, which greatly increases in vivo duration of action, was then incorporated by V8 protease-catalyzed condensation of segment 2 with desNH2Tyr-D-Ala-Asp(OH)-OR [R = CH3CH2- (3a) or 4-NO2C6H4CH2-(3b)]. The main focus of this report was to develop conditions to use the V8 protease-catalyzed coupling while avoiding a competing cleavage of the proteolytically-sensitive Asp25-Ile26 bond in GRF. Conversion of 2 to 4 in couplings employing the alpha-ethyl ester of the acyl component 3a was limited to about 60% by competing proteolysis at Asp25-Ile26. This system was adequate for preparing, isolating, and fully characterizing the target analog 4 and identifying the side products. The 4-nitrobenzyl ester 3b proved to be a superior substrate, resulting in 90% conversion of 2 to 4 with no detectable loss to proteolysis and requiring significantly lesser amounts of catalyst. These results demonstrate that enzymatic semisynthesis of a biologically-active peptide amide which contains unnatural amino acids at the N-terminus can be achieved from a biosynthetic precursor in good yield and purity.

Semisynthesis of human growth hormone-releasing factor by trypsin catalyzed coupling of leucine amide to a C-terminal acid precursor

Human growth hormone-releasing factor, GRF(1-44)-NH2, was synthesized by trypsin catalyzed coupling of Leu-NH2 to Arg43 of the precursor, GRF(1-43)-OH, prepared by solid phase peptide synthesis. The semisynthetic GRF(1-44)-NH2 was fully characterized and showed full potency in the rat pituitary in vitro bioassay. Conversion to GRF(1-44)-NH2 was limited to 60-70% in both 75% v:v N,N'-dimethylacetamide and 95% v:v 1,4-butanediol due to competing transpeptidations at Arg41 and Arg38 generating [Leu42]-GRF(1-42)-NH2 and [Leu39]-GRF(1-39)-NH2 side-products, respectively. The rates of formation and yields of GRF(1-44)-NH2 versus pH, Leu-NH2 concentration, and solvent composition were also studied.

Synthesis and biological activity of novel C-terminal-extended and biotinylated growth hormone-releasing factor (GRF) analogs

A series of novel hGRF(1-29)-NH2 analogs were synthesized and biotinylated. The immunological and biological activities of these analogs were then characterized. To distance the biotin moiety from the putative bioactive core, a C-terminal spacer arm consisting of -Gly-Gly-Cys-NH2 (-GGC) was added to hGRF(1-29)-NH2 (hGRF29) and analogs, with subsequent biotinylation performed at the cysteine residue. Neither addition of the C-terminal spacer arm nor biotinylation affected affinity of these analogs for GRF antibody. Relative to hGRF(1-44)-NH2 (hGRF44: potency = 1.0), the biotinylated analogs were equipotent in vitro to their nonbiotinylated, parent compounds: [desNH2Tyr1,D-Ala2,Ala15]hGRF29-GGC-(tpBiocyt in)-NH2 (4.7) = [Ala15]hGRF29-GGC-(tpBiocytin)-NH2 (3.9) greater than hGRF29-GGC-(tpBiocytin)-NH2 (0.8). Based upon cumulative GH release data in vivo (0-60 min postinjection), [desNH2Tyr1,D-Ala2,Ala15]hGRF29-GGC-(tpBiocyt in)-NH2, [Ala15]hGRF29-GGC-(tpBiocytin)-NH2, and hGRF29-GGC-(tpBiocytin)-NH2 displayed 8.6, 5.5, and 0.8 times, respectively, the potency of hGRF44. These in vivo potency values were not significantly different from the corresponding parent compounds (i.e., with or without the C-terminal spacer arm). In summary, biotinylated hGRF analogs have been developed that retain full immunoreactivity and potent bioactivity (in vitro and in vivo), thus permitting their use in GRF receptor isolation, ELISA, and histochemical procedures.

Semisynthesis of human growth hormone-releasing factors by alpha-amidating enzyme catalyzed oxidation of glycine-extended precursors

Recombinant alpha-amidating enzyme was used in the semisynthesis (1-5 mg scale) of human growth hormone-releasing factor, GRF(1-44)-NH2, by in vitro enzymatic oxidation of the glycine-extended precursor, GRF(1-44)-Gly-OH, prepared by solid-phase synthesis. The equipotent analog, GRF(1-29)-NH2, and the superactive analog, [Ala15]-GRF(1-29)-NH2, were also prepared by this route and were fully characterized. Isolated yields of about 75% were obtained, and the products each possessed full potency in an in vitro rat pituitary bioassay and full receptor-binding affinity. Methods to monitor the amidation of polypeptide substrates and analyze the final products are described, including the use of capillary zone electrophoresis. A transient alpha-hydroxyglycine intermediate, [Ala15]-GRF(1-29)-Gly(alpha-OH)-OH, was isolated and characterized. Kinetic studies with this intermediate demonstrate that the rat alpha-amidating enzyme from recombinant mouse C127 cells possesses both the monooxygenase and lyase activities needed to catalyze both steps of the amidation process.

Solution structures of cyclic and dicyclic analogues of growth hormone releasing factor as determined by two-dimensional NMR and CD spectroscopies and constrained molecular dynamics

Solution structures were determined for a linear analogue of growth hormone releasing factor (GRF), and cyclic and dicyclic analogues in which the side chains of aspartyl and lysyl residues spaced at positions i-(i + 4) were joined to form a lactam. The four analogues were [Ala15]-GRF-(1-29)-NH2 and its cyclo8-12, cyclo21-25, and dicyclo8-12;21-25 derivatives. The peptides were studied in two solvent systems: 75% methanol/25% water at pH 6.0; and 100% water at pH 3.0. CD spectroscopy was used to assess the overall alpha-helical content. Nuclear magnetic resonance spectroscopy was used to determine the structures in more detail. Nearly complete proton resonance assignments were made for each of the peptides, in both solvents. Nuclear Overhauser effects were converted into distance constraints and applied in the molecular dynamics program CHARMM to evaluate the range of low-energy structures that satisfied the nmr data. In 75% methanol, all of the peptides are comprised of a single alpha-helical segment with fraying of one to three residues at each end. The linear analogue has a tendency to kink. In water, the analogues have two helical segments with flexible regions between them and at the termini of the peptides. The linear analogue is helical at residues 7-14 and 21-28. In the cyclo8-12 analogue, the N-terminal helical region extends to include residues 7-19, while the other helical region is slightly shortened. In the cyclo21-25 analogue, the C-terminal helical region is extended to include residues 19-28, while the N-terminal helical region is destabilized. The dicyclic analogue has the largest N-terminal helix, spanning residues 7-20, but its helical segment at residues 21-28 is not well ordered. All of the analogues exhibit substantial biological activity. The cyclic and dicyclic analogues show dramatically increased resistance to degradation during incubation with human plasma. The i-(i + 4) lactam, therefore, appears to be a synthetic means of stabilizing a local alpha-helical conformation, which may be of general use in the design of active, stable peptides.

Degradation of aspartic acid and asparagine residues in human growth hormone-releasing factor

Products of the degradation of human growth hormone-releasing factor (GRF) in aqueous solutions (15-200 microM) have been isolated and fully characterized. The cleavage product, GRF(4-44)-NH2, and the isomerization product, [beta-Asp3]GRF(1-44)-NH2, from the degradation of GRF(1-44)-NH2 in acidic solution and the corresponding products, GRF(4-29)-NH2 and [beta-Asp3]GRF(1-29)-NH2, from the degradation of GRF(1-29)-NH2 have been isolated and characterized. The products, [beta-Asp8]GRF(1-44)-NH2 and [Asp8]GRF(1-44)-NH2, from the deamidation of GRF(1-44)-NH2 at pH 8.0 and the corresponding products, [beta-Asp8]GRF(1-29)-NH2 and [Asp8]GRF(1-29)-NH2, from the deamidation of GRF(1-29)-NH2 have been isolated and characterized. All the degradation products of GRF(1-44)-NH2 and GRF(1-29)-NH2 were evaluated for biological activity and found to have much lower in vitro potencies than the parent peptides. Degradation occurs at Asp3 and Asn8 and the kinetics of these various transformations versus pH and temperature have been studied. GRF is most stable at pH 4-5. At pH below the pKa of the Asp3 side-chain (pH less than 4), cleavage at Asp3-Ala4 is the major route of degradation. For pH greater than 4, isomerization of Asp3 to beta-Asp3 (iso-Asp3) predominates. The rates of cleavage and isomerization are simple first order and vary with pH, independent of buffer concentration, such that the protonated (COOH) form of Asp3 undergoes cleavage while the ionized (COO-) form isomerizes. The more rapid deamidation of Asn8 to generate beta-Asp8 and Asp8 in about a 4:1 ratio, presumably via a cyclic imide intermediate, occurs at pH greater than or equal to 5 and is general base-catalyzed. Evidence was also obtained for direct hydrolysis of protonated Asn8 in GRF(1-29)-NH2 at pH less than or equal to 2 to give exclusively [Asp8]GRF(1-29)-NH2. The deamidation of Asn8 in GRF(1-29)-NH2 at pH 8.0, 22-55 degrees C, is relatively insensitive to temperature for T less than 37 degrees C, possibly due to conformational constraints. Asp25 and Asn35 are sterically, conformationally, or otherwise hindered with respect to these changes as no degradation at these sites was observed under the conditions employed.

A sensitive and specific competition microELISA for the immunoactive polypeptide parathymosin and detection of this peptide in porcine tissues

A sensitive and specific microELISA assay is described for the immunoactive polypeptide parathymosin. Antibodies against a synthetic peptide corresponding to the rat parathymosin sequence 5-30 were raised in rabbits immunised with this peptide conjugated to keyhole limpet hemocyanin (KLH). The useful range of the assay was 0.25-30 pmol (3-330 ng) of parathymosin and the assay was specific. The related immunoactive polypeptides prothymosin alpha or thymosin alpha 1 showed no cross-reactivity. In spiking experiments the recovery of the assay was found to be greater than 92% at all concentrations tested. The intra-assay variation was 17%, whereas the inter-assay variation was 26%. Using this assay the highest concentration of parathymosin was found in porcine liver, followed by kidney, lung, thymus and spleen. This assay compares favorably with one microELISA and two RIA methods already published, in that it is more sensitive by at least an order of magnitude, and it is simpler and quicker.

Biosynthesis of human growth hormone-releasing hormone (hGRH) in the pituitary of hGRH transgenic mice

We have studied the posttranslational processing of prohuman GH-releasing hormone (pro-hGRH) to the mature hormones, hGRH(1-44)-NH2 and hGRH(1-40)-OH, and its carboxyl-terminal peptide (hGCTP) in pituitary cells from transgenic mice bearing a metallothionein-hGRH fusion gene after incubation with [35S]methionine. After separation on HPLC, 35S-labeled and unlabeled hGRH in medium and cell extracts were characterized by RIA and immunoprecipitation with antisera against hGRH and against hGCTP. After a 4-h pulse, unlabeled and [35S]pro-hGRH, hGRH(1-44)-NH2, and hGRH(1-40)-OH were identified in medium and cell extracts by both RIA and immunoprecipitation with anti-hGRH serum. In cell extracts, after a 0.5-h pulse, [35S]pro-hGRH and hGRH(1-44)-NH2 but not [35S]hGRH(1-40)-OH were detectable. After a 0.5-h chase, however, 35S-labeled hGRH(1-40)-OH, pro-hGRH, and [35S]hGRH(1-44)-NH2 were all measurable. After a 4-h chase, comparable levels of [35S]hGRH(1-44)-NH2 and hGRH(1-40)-OH were present, and very little intracellular 35S-pro-hGRH remained. A progressive decrease in the ratio of immunoprecipitable pro-hGRH to mature hGRH peptides and an increase in the ratio of hGRH(1-40)-OH to hGRH(1-44)-NH2 was observed in the two chase periods. In medium, [35S]hGRH(1-44)-NH2 was detectable at all times, whereas only minimal amounts of [35S]hGRH(1-40)-OH were present. Labeled and unlabeled pro-hGRH in cell extracts was also detected with anti-hGCTP serum, and another peak, which coeluted with synthetic hGCTP, was also identified. The low molar ratio of intracellular immunoreactive hGCTP to hGRH (less than 0.02) suggests a more rapid turnover rate of hGCTP than of hGRH. These results demonstrate the processing of hGRH prohormone to both mature forms of hGRH and provide evidence that hGRH(1-40)-OH is derived from hGRH(1-44)-NH2.

Effect of human growth hormone-releasing factor and a potent analog on antibody formation in African green monkeys

African Green monkeys were injected (2 x daily subcutaneously for six months) with human GRF(1-44)-NH2 (10 micrograms/kg BW) or a more potent analog, [desNH2Tyr1,Ala15]-hGRF(1-29)-NH2 (2 micrograms/kg BW) to determine the potential of each peptide to induce antibody formation. Blood samples were taken every two weeks, diluted 1:100 and tested for ability to bind radioiodinated hGRF. One animal in the hGRF(1-44)-NH2 group [N = 6] produced low-titer GRF antibodies by 6 weeks (19% binding) and continued throughout the 24 weeks of treatment (average = 50-60% binding). Similarly, one animal in the hGRF analog group [N = 6] displayed low-titer GRF antibodies by 18 weeks (14% binding), with the highest binding observed at 24 weeks (51% binding). Subsequent dilutions (1:1,000 and 1:3,000) of these bleedings confirmed that higher GRF antibody titers were not masked by antibody excess. Dialyzed sera from these two animals did not affect the abilities of hGRF(1-44)-NH2 or [desNH2Tyr1,Ala15]-hGRF(1-29)-NH2 to stimulate GH secretion by rat pituitary cells in vitro. After 20 weeks of treatment, significant GH responses (increased mean GH area under the curve 2.3-2.5 fold and GH peak 3.5-3.7 fold, that of control) were observed following hGRF or hGRF analog injection. Therefore, the low titer GRF antibodies detected in monkey sera during six months of treatment with hGRF or a potent analog were biologically non-neutralizing.

Synthesis and biological evaluation of mouse growth hormone-releasing factor

The recently described mouse growth hormone-releasing factor (mGRF) was synthesized by the solid phase procedure, purified by 2 stages of preparative high performance liquid chromatography and fully characterized. The biologic activity of the 42-amino acid peptide (H-His-Val-Asp-Ala-Ile-Phe- Thr-Thr-Asn-Tyr- Arg-Lys-Leu-Leu-Ser-Gln-Leu-Tyr-Ala-Arg-Lys-Val-Ile-Gln-Asp-Ile-Met-Asn- Lys- Gln-Gly-Glu-Arg-Ile- Gln-Glu-Gln-Arg-Ala-Arg-Leu-Ser-OH) was assessed in primary cultures of both mouse and rat anterior pituitary cells and compared to synthetic rat (rGRF) and human (hGRF) growth hormone-releasing factors. mGRF was equipotent to rGRF in mouse somatotrophs but slightly less potent in rat somatotrophs, while hGRF was 3-5 times less potent in both rodent species.

GRF analogs and fragments: correlation between receptor binding, activity and structure

GH-releasing activity in vitro was directly correlated with GRF receptor binding affinity for all hGRF analogs examined. hGRF(1-29)-NH2 analogs with Ala15-substitution (for Gly15) displayed 4-5 times higher affinity for the GRF receptor relative to hGRF(1-44)-NH2. Replacement of Gly15 with Sar15 resulted in a dramatic loss of activity and receptor binding. The present data supports the proposal that Ala15-substitution increases receptor affinity, and hence potency, due to increased amphiphilic alpha-helical interactions. Fragments of hGRF, representative of DPP-IV and trypsin-like cleavage, are inactive as a consequence of greatly diminished GRF receptor binding. These results provide a comprehensive analysis of the structural features required for both GRF receptor binding and activation.

Identification of 11,13-dihydroxy-14-octadecaenoic acid as a circulating Na+/K(+)-ATPase inhibitor

Two digitalis-like compounds (DLC) were purified to homogeneity from bovine plasma. The purification procedure consisted of organic extractions and batch chromatography followed by three subsequent separations using reverse-phase high-performance liquid chromatography. The presence of a DLC in the different fractions was monitored by their ability to inhibit (a) [3H]ouabain binding to rat brain synaptosomes, and (b) microsomal Na+/K(+)-ATPase activity. Using mass spectrometry and nuclear magnetic resonance spectroscopy the structure of one of the DLCs was identified as 11,13-dihydroxy-14-octadecaenoic acid. It is suggested that this new hydroxy, unsaturated, fatty acid derivative may regulate Na+/K(+)-ATPase activity under some physiological and pathological conditions.

In vitro stability of growth hormone releasing factor (GRF) analogs in porcine plasma

The stability of growth-hormone releasing factor (growth regulating factor; GRF) analogs in porcine plasma was examined. GRF analogs were incubated in porcine plasma at 37 degrees C, extracted and subsequently analyzed using high performance liquid chromatography (HPLC). GRF(1-29)-NH2 was rapidly broken down in the plasma with a degradation rate of t1/2 = 13 min. The primary degradation product was identified as GRF(3-29)-NH2. Substitution of Gly15 by Ala15 slightly prolonged the plasma half-life (t1/2 = 17 min) and the major degradative fragment was found to be [Ala15]GRF(3-29)-NH2. The cleavage between the 2 and 3 position of the peptide was not inhibited by trasylol at a concentration of 1,000 KIU/ml but was dramatically reduced by the combined use of diprotin A and trasylol. Absence of the free amino group at the N-terminus and/or substitution of a D-amino acid residue at the penultimate position completely prevented cleavage between the 2 and 3 position in the structural linear GRF analogs. Side-chain to side-chain cyclization between Asp8 and Lys12 amino acid residues significantly improved the stability of GRF in plasma with t1/2 greater than 2 hr. An additional stability was provided by substitution of D-Ala2 for Ala2 in the structural cyclic analog. Cyclization between Lys21 and Asp25 also improved the stability of the GRF peptide in the plasma. Stability was further enhanced by the presence of D-Ala2 or by forming a dicyclic analog through an additional linkage between Asp8 and Lys12.

Cellular distribution of prothymosin alpha and parathymosin in rat thymus and spleen

By means of immunohistochemical methods, we have investigated the cellular distribution of prothymosin alpha and parathymosin in rat thymus and spleen, using specific antibodies raised against thymosin alpha-1 and against parathymosin. We observed prothymosin alpha immunoreactivity in lymphoid cells both in thymus and spleen. In the thymus, prothymosin alpha staining was more marked in cortex than in medulla. In the spleen, prothymosin alpha was found in lymphocytes of the periarteriolar lymphatic sheaths and was especially prominent in the germinal centers. Parathymosin immunoreactivity in the thymus was mainly localized in the medulla; positive cells were reticuloepithelial cells from the thymic reticulum and the blood barrier. Thymocytes were negative. In spleen, parathymosin was found in reticular cells arranged in a ring between the periarteriolar lymphatic sheath and the marginal zone. Our results do not support an exclusive role for these peptides as immune system hormones or cytokines.

Localization and growth hormone (GH)-releasing activity of rat testicular GH-releasing hormone-like peptide

The testis contains many peptides originally described as originating in the central nervous system. The physiological function of these factors in the testis is generally unknown. We previously reported that the rat testis contains both a peptide with GH-releasing hormone-like immunoactivity (tGHRH-LI) and a mRNA species that cross-hybridizes with a hypothalamic cDNA for rat GHRH (rGHRH). The current study was designed to further characterize tGHRH-LI by determining its location within rat testis, and to evaluate whether tGHRH-LI and hypothalamic GHRH share similar biological and electrophoretic properties. Partially purified tGHRH is capable of stimulating GH secretion from cultured anterior pituitary cells in a dose-dependent manner. Testicular GHRH and rGHRH have different HPLC retention times and significantly different electrophoretic properties by Western gel analysis. The estimated size of tGHRH-LI is approximately 3.7 times that of synthetic rGHRH. Using immunohistochemistry, tGHRH-LI is localized to mature sperm forms in rat testis. We conclude that rat tGHRH-LI and rGHRH share some structural and functional properties and are probably related peptides. However, the difference in electrophoretic mobility and HPLC retention time indicates that they are not identical. The presence of tGHRH-LI in rat sperm, within the confines of the blood-testis barrier, which is generally impermeable to peptides, leads us to speculate that tGHRH serves a paracrine or autocrine role in testicular physiology.

The antagonism of glucocorticoid inhibition of wound healing in rats by growth hormone-releasing factor

Daily therapeutic injections of cortisone to rats will cause weight loss and impaired wound healing. Weight loss is attributed to the catabolic effect of steroid, whereas impaired healing is associated with reductions in fibroplasia and connective tissue deposition. As the major structural protein component of connective tissue is collagen, its absence is responsible for the retarded gain in wound breaking strength. Cortisone also blocks wound closure by inhibiting wound contraction. An anabolic agent such as growth hormone may antagonize the effect of cortisone on the wound healing process. Endogenous GH can be released from the pituitary by exogenous injections of growth hormone-releasing factor (GRF). Two synthetic GRF peptides, a natural 44-amino acid peptide of the human GRF sequence, GRF-44, and an N-terminally substituted analog 29 residues, GRF-29A, were studied. Each was given twice daily with a single daily injection of cortisone for a 7-day period. Concurrent administration of GRF-44 or GRF-29A and cortisone to rats had no effect on restored body weight loss or inhibited wound contraction. While GRF-44 restored collagen deposition and caused restored wound breaking strength, GRF-29A was ineffective in restoring either. GRF-44, a synthetic peptide that stimulates pituitary release of growth hormone, antagonized some of the inhibiting effect of steroid on wound repair by promoting fibroplasia and collagen deposition.

Defining minimal requirements for antibody production to peptide antigens

The role that individual determinants play in modulating the immune response of an organism to a pathogen is often obscured because of the complexity of the pathogen. In order to gain a better appreciation of the role of individual determinants in the immune response, a pathogen may be dissociated into smaller components, for example peptides representing specific epitopes. These isolated components are often poorly immunogenic and historically have required the use of adjuvants to stimulate antibody production. This report defines the minimal essential requirements for antibody production to a peptide in this system. These are the ability to stimulate both B- and T-helper lymphocytes, anchorage in a phospholipid complex and multivalency within the complex. When these conditions are met, no additional adjuvants are necessary. This procedure has allowed us to identify three distinct T-helper cell epitopes from HIV gp160. In addition, this information has been used to produce a simple, totally synthetic and highly immunogenic preparation for the production of antibodies to peptides.

Structure-activity studies with cholecystokinin: stereoisomers containing ortho-, meta- and para-tyrosine sulfate

Analogs of cholecystokinin (Ac-CCK-7) in which Tyr(SO3H) was replaced with D-Tyr(SO3H), Tyr(m-SO3H), D-Tyr(m-SO3H) Tyr(o-SO3H) and D-Tyr(o-SO3H) were prepared by solid phase peptide synthesis, characterized by amino acid analysis, MS, UV, IR and tested in vivo for their ability to suppress food intake and in vitro (receptor binding). Comparison of the binding efficacy to food intake revealed a poor correlation. Ac-[Tyr(m-SO3H)]-CCK-7 retained substantial anorectic activity, whereas Ac-[Tyr(o-SO3H)-CCK-7 was essentially inactive. Ac-[D-Tyr(SO3H)]-CCK-7 and Ac-[D-Tyr(mSO3H)]-CCK-7 retained substantial biological activity. From these studies we conclude that the position of the negative charge on Tyr (meta or para) is important for anorectic activity, but the chirality of the alpha-carbon is not important for biological activity.

A novel Fmoc-based anchorage for the synthesis of protected peptides on solid phase

A novel bifunctional compound, 9-(hydroxymethyl)-2-fluoreneacetic acid, was synthesized, coupled to benzhydrylamine-resin, and evaluated for its application to the solid phase synthesis of protected peptide fragments. Anchor-bond cleavage was achieved with 15% piperidine/DMF. A protected heptapeptide, Boc-Val-Val-Ser(Bzl)-His(Tos)-Phe-Asn-Lys-(Z)-OH, corresponding to the sequence (1-7) of rat-transforming growth factor-alpha, was synthesized using this new support with an overall yield of 46%.

Prothymosin alpha expression is associated to cell division in rat testis

Using immunohistochemical methods, we have investigated the cellular distribution of prothymosin alpha (ProT) in adult rat testis. A policlonal antibody raised against thymosin alpha 1 conjugated to keyhole limpet hemocyanin was used. ProT immunoreactivity was observed in the cytoplasm and nucleus of spermatogonia and primary spermatocytes in initial phases of the first meiotic division, preleptotene, leptotene and zygotene. However, in pachytene phase they already showed a weak or negative staining. On the other hand, secondary spermatocytes, spermatids, spermatozoa and Sertoli cells were not stained. Based on this fact we suggest that ProT is present in the proliferative cycle in the final steps of G1 phase, throughout the S and G2 phases and in initial steps of the prophase.

Dipeptidylpeptidase IV and trypsin-like enzymatic degradation of human growth hormone-releasing hormone in plasma

The plasma enzyme responsible for primary proteolytic cleavage of growth hormone-releasing hormone (GRH) at the 2-3 amino acid bond was characterized. Native GRH[GRH(1-44)-NH2 and GRH(1-40)-OH], and COOH-terminally shortened fragments [GRH(1-32)-NH2 and GRH(1-29)-NH2] were rapidly cleaved, while GRH(2-32)-NH2 was not degraded at this site. Moreover, degradation to GRH(3-44)-NH2 was unaffected by an aminopeptidase inhibitor, indicating that this metabolite was generated from a single step cleavage by a dipeptidylpeptidase (DPP) rather than sequential aminopeptidase cleavages. Conversion to GRH(3-44)-NH2 was blocked by diprotin A, a DPP type IV (DPP IV) competitive inhibitor. D-Amino acid substitution at either position 1 or 2 also prevented hydrolysis, characteristic of DPP IV. Analysis of endogenous plasma GRH immunoreactivity from a human GRH transgenic pig revealed that the major peak coeluted with GRH(3-44)-NH2. Native GRH exhibited trypsin-like degradation at the 11-12 position but cleavage at the 12-13 site occurred only with GRH(1-32)-NH2 and GRH(1-29)-NH2. Formation of these metabolites was independent of prior DPP IV hydrolysis but was greatly reduced by trypsin inhibitors. Evaluation of plasma stability of potential GRH super analogues, designed to resist degradation by these enzymes, confirmed that GRH degradation in plasma occurs primarily by DPP IV, and to a lesser extent by trypsin-like enzyme(s).

Conformational origin of a difficult coupling in a human growth hormone releasing factor analog

During the solid-phase synthesis of the human growth hormone releasing factor (GRF) analog [Ala15, Leu27, Asn28] -GRF(1-32)-OH, incorporation of Boc-Gln16 was determined to be incomplete. While aggregation of growing resin-bound peptide chains with concomitant beta-sheet formation and "precipitation" has been proposed to account in general for such "difficult coupling," no feature of sequence in the Gln16 region of this GRF analog provided an immediate rationale for this result. We now report 500 MHz 1H NMR spectra of a series of resin-bound GRF segments surrounding the Gln16 position (19-32 through 14-32), swelled in dimethylsulfoxide-d6 solutions [GRF(14-32) = Leu14-Ala-Gln-Leu-Ser(Bzl)-Ala-Arg(Tos)-Lys(CIZ)-Leu- Leu-Gln-Asp(OcHex)-Ile-Leu-Asn-Arg(Tos)-Gln-Gln-Gly32-PAM resin]. While relatively sharp spectra are observed for GRF(19-32), components with resonances broadened by an order-of-magnitude appear in spectra of the 18-32 and 17-32 peptide-resin, and the entire spectrum of 16-32 is ill-resolved and highly broadened. Subsequent spectra sharpen again (15-32, 14-32). These combined synthesis/spectroscopic experimental results, in conjunction with predictive analyses using standard Chou-Fasman 2 degrees structure parameters, suggest that the completeness of the Gln16 coupling is hindered by formation of a specific, folded beta-sheet/beta-turn structure in GRF(16-32) (with the turn located at 18-21, "upstream" of the difficult coupling site), and accompanying aggregation of peptide chains. This analysis suggests that awareness of such potential beta-sheet/beta-turn sequences can guide analog choices, and/or facilitate pre-programming of synthesis steps in anticipation of problem couplings.

Evidence for the monomeric nature of thymosins

According to gel-filtration experiments, alpha- and beta-thymosins appear to form oligomers, which are 4-5-fold larger than the corresponding polypeptides. However, on analysis by sedimentation equilibrium ultracentrifugation, prothymosin alpha and thymosin beta 4 showed relative molecular masses of 12,800 and 4600, which are close to the values calculated from their amino acid sequences, confirming their existence in solution as discrete monomeric entities.

Synthesis, biological activity and conformational analysis of cyclic GRF analogs

A novel cyclic GRF analog, cyclo(Asp8-Lys12)-[Asp8,Ala15]-GRF(1-29)-NH2, i.e. cyclo8,12[Asp8,Ala15]-GRF(1-29)-NH2, was synthesized by the solid phase procedure and found to retain significant biological activity. Solid phase cyclization of Asp8 to Lys12 proceeded rapidly (approximately 2 h) using the BOP reagent. Substitution of Ala2 with D-Ala2 and/or NH2-terminal replacement (desNH2-Tyr1 or N-MeTyr1) in the cyclo8,12[Asp8,Ala15]-GRF(1-29)-NH2 system resulted in highly potent analogs that were also active in vivo. Conformational analysis (circular dichroism and molecular dynamics calculations based on NOE-derived distance constraints) demonstrated that cyclo8,12[Asp8,Ala15]-GRF(1-29)-NH2 contains a long alpha-helical segment even in aqueous solution. A series of cyclo8,12 stereoisomers containing D-Asp8 and/or D-Lys12 were prepared and also found to be highly potent and to retain significant alpha-helical conformation. The high biological activity of cyclo8,12[N-MeTyr1,D-Ala2,Asp8,Ala15]-GRF(1-29)- NH2 may be explained on the basis of retention of a preferred bioactive conformation.

Expression of an enzymatically active Yb3 glutathione S-transferase in Escherichia coli and identification of its natural form in rat brain

Glutathione S-transferases containing Yb3 subunits are relatively uncommon forms that are expressed in a tissue-specific manner and have not been identified unequivocally or characterized. A cDNA clone containing the entire coding sequence of Yb3 glutathione S-transferase mRNA was incorporated into a pIN-III expression vector used to transform Escherichia coli. A fusion Yb3-protein containing 14 additional amino acid residues at its N terminus was purified to homogeneity. Recombinant Yb3 was enzymatically active with both 1-chloro-2,4-dinitrobenzene and 1,2-dichloro-4-nitrobenzene as substrates but lacked glutathione peroxidase activity. Substrate specificity patterns of recombinant Yb3 were more limited than those of glutathione S-transferase isoenzymes containing Yb1- or Yb2-type subunits. Peptides corresponding to unique amino acid sequences of Yb3 as well as a peptide from a region of homology with Yb1 and Yb2 subunits were synthesized. These synthetic peptides were used to raise antibodies specific to Yb3 and others that cross-reacted with all Yb forms. Immunoblotting was utilized to identify the natural counterpart of recombinant Yb3 among rat glutathione transferases. Brain and testis glutathione S-transferases were rich in Yb3 subunits, but very little was found in liver or kidney. Physical properties, substrate specificities, and binding patterns of the recombinant protein paralleled properties of the natural isoenzyme isolated from brain.

Use of osmotic pumps for subcutaneous infusion of growth hormone-releasing factors in steers and wethers

Osmotic pumps were evaluated for 7-d delivery of growth hormone-releasing factor (GRF). In Exp. 1, 12 steers weighing 253 kg received hGRF(1-29)NH2 in H2O at rates of 0, 3, 30 and 300 pmol.h-1.kg-1. Pumps were implanted s.c. on d 0 and removed at 1200 on d 7. Blood samples were drawn at 20-min intervals from 0800 to 1200 on d -1, 1, 3, 5, 7 and 9. Growth hormone levels were not altered by GRF treatment (P greater than .05). Solubility and volume limitations render hGRF(1-29)NH2 delivery via osmotic pumps problematical. Flow rate and duration of release of dimethyl sulfoxide (DMSO):H2) (1:1) from osmotic pumps incubated in vivo and in vitro were found to be consistent with manufacturer's specifications. Two hGRF(1-29) analogues, Ro23-7863 and 4SG-29, were dissolved in DMSO:H2O. In Exp. 2, six 222-kg steers had pumps implanted and blood samples were taken as in Exp. 1. Three steers received each analogue at a rate of 300 pmol.h-1.kg-1. Analogues had similar GH-releasing ability and GH levels differed (P less than 0.001) among days, being approximately fourfold higher on d 3, 5 and 7 than on d -1, 1 and 9. Residual analogue solutions retained full bioactivity after 7-d implantation, and in vitro biopotencies of Ro23-7863 and 4SG-29 were similar (Exp. 3). In Exp. 4, 15 wethers (means = 31.3 kg) received osmotic pumps delivering 0, 3, 15, 75 and 300 pmol.h-1.kg-1 Ro23-7863 in DMSO:H2O for 7 d. Lambs were bled at 0800 and 1400 from d -1 to 8. The latter two doses increased (P less than .01) mean GH levels 2.7- and 4.3-fold over those in control animals during the treatment period. Results demonstrate that increased GH secretion can be elicited in steers and wethers for 1 wk by continuous s.c. infusion of GRF analogues utilizing osmotic pumps.