Comparison of two solid-phase peptide syntheses of a 32-amino acid carboxyl-terminal fragment of human parathyroid hormone, hPTH-(53-84)

Solid-phase synthesis and biologic activity of human parathyroid hormone (1-84)

We have chemically synthesized the full-length, 84 amino acid, human parathyroid hormone (hPTH) on a greater than 100 mg scale by the Merrifield solid-phase technique of stepwise peptide synthesis using a benzhydrylamine support. The peptide was purified by high-performance liquid chromatography and found to be greater than 96% pure. The authenticity or the sequence of the synthetic peptide was confirmed by repetitive Edman degradation. Furthermore, tryptic digestion of hPTH generated the predicted fragments. The synthetic full-length hormone was evaluated for biologic activity in assays of PTH receptor binding and stimulation of adenylate cyclase activity (using bovine renal cortical membranes and rat and human bone cells). Synthetic hPTH (1-84) was found to be highly potent in binding to PTH receptors (Kb = 1-25 nM) and stimulating adenylate cyclase (Km = 1-14 nM). The availability of significant quantities of synthetic full-length hPTH and future analogs will permit widespread use in multiple in vitro and in vivo assays to delineate their spectrum of biologic properties. Available supplies of the synthetic hormone will also enable evaluation of the effectiveness of PTH antagonists at inhibiting the action of native sequence hormone at its receptors.

Difficult couplings in stepwise solid phase peptide synthesis: predictable or just a guess?

Stepwise solid phase peptide synthesis, Fmoc-approach, of 88 peptides varying in length from 4 to 24 amino acid residues was performed using a uniform procedure for coupling, monitoring and deprotection steps. The data of 696 couplings have been incorporated into a computer programme in order to study whether the degree of coupling can be predicted. Parameters studied are the nature of the amino acid to be coupled, the amino acid to be acylated and the length of the growing peptide chain. Using this information, prediction of "good" or "difficult" sequences, that is, peptides that can be synthesized without appreciable repeated couplings or the opposite, seems possible.

Evaluation of a parathyroid hormone antagonist in an in vivo multiparameter bioassay

The antagonist properties of a bovine parathyroid hormone analogue ([Tyr34]bPTH-(7-34] amide were quantitatively assessed in vivo in a multiparameter assay to estimate the potency of the antagonist against the major actions of PTH. The analogue inhibited PTH-stimulated urinary excretion of phosphate and adenosine 3',5'-cyclic monophosphate in vitamin D-deficient thyroparathyroidectomized rats in a dose-dependent manner. At a molar dose ratio as low as 5:1 of antagonist to PTH, partial inhibition occurred. PTH stimulates the activity of 25-hydroxyvitamin D3-1 alpha-hydroxylase in renal proximal tubules. When coinfused with PTH, this analogue completely inhibited PTH-stimulated 1 alpha-hydroxylase activity at a molar dose ratio of 25:1 of antagonist to PTH and partially inhibited the activity at a molar dose ratio of 10:1. The analogue revealed no PTH-like agonist activity for stimulation of the 1 alpha-hydroxylase. Taken together, these studies indicate that [Tyr34]bPTH-(7-34) amide is a potent antagonist of several of the parameters of PTH action in vivo and demonstrate the feasibility of designing a PTH antagonist that can interact simultaneously with all the PTH receptors responsible for the hormone's major actions in vivo.

Semi-preparative high-performance liquid chromatographic purification of a 28-amino acid synthetic parathyroid hormone antagonist

Structure-activity studies of parathyroid hormone (PTH) over the last decade have led to the design and synthesis of a peptide hormone inhibitor of PTH action in vivo, [Tyr-34]bPTH-(7-34)amide. To evaluate the biological properties of this 28-amino acid hormone analogue, sufficient amounts of the peptide needed to be prepared in a high state of purity to permit continuous infusion in groups of animals for periods of several hours. For this purpose, gel chromatography followed by semi-preparative, reversed-phase high-performance liquid chromatography (HPLC) using a lyophilizable solvent gradient system of acetonitrile in 0.1% trifluoroacetic acid was utilized. In a parallel purification scheme, gel filtration followed by ion-exchange chromatography was employed. Comparison of yields and product purity were determined by a battery of chemical analytical techniques. Semi-preparative HPLC generated a highly purified product; substantial heterogeneity was detected in the ion-exchange-purified material. The HPLC-purified product retains the biological activities of binding to PTH receptors in vitro and inhibiting PTH action in vivo.

A parathyroid hormone inhibitor in vivo: design and biological evaluation of a hormone analog

A synthetic analog of bovine parathyroid hormone (bPTH), [tyrosine-34] bPTH-(7-34)NH2, was found to inhibit parathyroid hormone action in vivo. When the analog and parathyroid hormone were infused simultaneously to rats at a molar ratio of 200 to 1, the analog inhibited the excretion of urinary phosphate and adenosine 3',5'-monophosphate. When infused alone at the same dose rate, the analog was devoid of agonist activity. The compound was prepared by following design principles developed for inhibitors of parathyroid hormone, and is believed to be the first antagonist of parathyroid hormone that is effective in vivo.

Prosomatostatin-specific antigen in rat brain: localization by immunocytochemical staining with an antiserum to a synthetic sequence of preprosomatostatin

Using an antiserum to a 15-amino acid synthetic peptide corresponding to amino acids 63-77 of rat preprosomatostatin (rat somatostatin cryptic peptide, RSCP), we have compared the distribution of immunoreactive RSCP (IR-RSCP) with that of immunoreactive somatostatin-14 in the rat brain. IR-RSCP was present in neuronal cell bodies, processes, and axon terminals in the hypothalamic tuberoinfundibular system as well as in diverse regions of the central nervous system in an identical distribution to immunoreactive somatostatin. These observations indicate that in neurons the somatostatin prohormone or the NH2-terminal extension peptide of somatostatin-28 (or both) is stored and transported intracellularly along with somatostatin 14. In addition, the presence of IR-RSCP in nerve terminals suggests that this material may be secreted as a hormone or neuromodulator and may serve as a biologic marker of somatostatin secretion.

Characterization of two anti-human parathyrin antisera

Two anti-human parathyrin antisera were raised in sheep. These were characterized by radioimmunoassay using two commercially available bovine parathyrin preparations and one synthetic human parathyrin fragment (sequence 42-55 (42-Tyr)) for radioiodination. In addition, four synthetic human parathyrin fragments (sequences 1-34, 32-43, 434-68, 53-84), one bovine parathyrin peptide (sequence 28-48) and a human parathyrin standard from a tissue culture containing the intact hormone were utilized in a competitive inhibition assay against the two radiolabelled bovine parathyrin preparations. On column chromatography, both tracers revealed a difference in molecular weight, which is believed to be related to the extraction technique. The sequence fragment 44-68 of human parathyrin had the highest affinity for the two antisera when using the smaller molecular weight tracer and there were no qualitative changes observed in the presence of plasma. Using the higher molecular weight tracer, the addition of plasma to one of the antisera resulted in a higher affinity for the sequence fragment 1-34 of human parathyrin compared to that of intact parathyrin. Antiserum from a second sheep remained specific only for the mid-region (sequence 44-68) of the parathyrin molecule independent of the tracer used. Due to the antiserum's constant characteristic, it revealed a high reliability for the discrimination between plasma parathyrin levels in normal probands and in patients with hyperparathyroidism. Our data demonstrate that the specificity of the radioimmunoassay for human parathyrin is not exclusively dependent on the antibody source, but also on the tracer preparation and the protein content of the incubation medium.