Differential effects of parathyroid hormone responsive cultured human cells on biological activity of parathyroid hormone and parathyroid hormone inhibitory analogs

Abstract

We have employed parathyroid hormone (PTH) responsive human cells cultured from dermis or giant cell tumors of bone (GT) to evaluate the biological properties of a newly developed in vivo PTH inhibitor, [Tyr34]bPTH-(7-34)-amide (PTH-Inh). Short periods of incubation of cells from dermis or GT with maximal stimulatory concentrations of PTH in the presence of increasing concentrations of PTH-Inh resulted in a dose-dependent inhibition of the adenosine cyclic 3',5'-phosphate (cAMP) response (Ki = 3 X 10(-7) M and 4.2 X 10(-7) M for GT and dermal cells, respectively). In both cell cultures, PTH-Inh alone did not increase cAMP levels, and in desensitization experiments, preincubation with PTH-Inh alone did not desensitize cells to PTH. Hence, the analogue displayed no agonist properties. Unexpectedly, when PTH-Inh was incubated with dermal cells in the presence of PTH, the PTH-Inh failed to block desensitization, suggesting a loss of biological effectiveness of the inhibitor. When medium containing PTH-Inh alone was removed from dermal cells and tested for inhibition of the acute PTH response in untreated cells, there was apparent loss of inhibitory efficacy (t1/2 = 20 h). In contrast, incubation of native PTH or bPTH-(1-34) with cells did not affect the biological activity of these ligands. Unlike the dermal cells, the PTH-Inh did block desensitization to PTH in GT, and there was no loss of inhibitor efficacy when medium containing PTH-Inh was incubated with GT (48 h) and then tested in untreated cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Agonist-regulated Cleavage of the Extracellular Domain of Parathyroid Hormone Receptor Type 1

“…PTH(7-34) is a competitive antagonist to PTH(1-34) and is believed to have no intrinsic activity (22). First, we investigated the capacity of these four PTH peptides to induce PTHR internalization.…”

Inhibitory Effect of [Tyr34]bPTH-(7–34)-Amide on bPTH-(l-34) Ability to Reduce Uterine Contraction

“…However, NTA-(3-34) was found to effectively antagonize the effect of bPTH-(1-34) on uterine contraction and this ac tion was dose dependent [Shew and Pang, 1984], In the same studies a 7-34 PTH frag ment was observed to cause a dose-depen dent increase in uterine contraction [Shew and Pang, 1984). However, since these re- NTA-(3-34) has been shown to be an an tagonist of bPTH-(l-34) in vitro [Rosenblatt et al, 1977;Goldring et al, 1979], When the 1-34 PTH fragment was modified by delet ing the first 6 NH2-terminus amino acids the result was a more potent antagonist of PTH in vitro [Goldring et al, 1983[Goldring et al, , 1985 as well as in vivo [Horiuchi et al, 1983a, b] which was also devoid of PTH-like activity.…”

“…The biologically active fragment of PTH consists of the NH2-terminal 34 amino acids ] [Tre gear et al, 1973;Potts et al, 1971Potts et al, , 1982, Shortening this fragment by removing the first six amino acids from the NH2-terminus ] results in a biologically inac tive fragment [Horiuchi et al, 1983a, b]. However, bPTH-(7-34) inhibits both the calcemic effect of bPTH-(l-34) in rats [Doppett et al, 1983] and the bPTH-(l-34)-stimulated accumulation of cyclic AMP in cultured cells obtained from human giant cell tumors of bone and dermis [Goldring et al, 1983[Goldring et al, , 1985,…”

“…[Nle8, Nle18, Tyr34]bPTH-(3-34)amide ], has no PTH-Iike activity [Shew and Pang, 1984] and did not affect basal uterine tension but blocked this effect of the intact peptide. However, bPTH-(7-34) surprisingly stimulated uterine contraction [Shew and Pang, 1984], This observation was unex pected since this analogue antagonizes ef fects of PTH in other systems [Doppett et al, 1983;Goldring et al, 1983Goldring et al, , 1985. These results might suggest that there are two re ceptor domains in the PTH molecule, per haps the contractile action of bPTH-(7-34) involves a portion of the bPTH-(l-34) mole cule masked by the presences of the first 6 amino acids.…”

Inhibition of the in vivo parathyroid hormone-mediated calcemic response in rats by a synthetic hormone antagonist.

“…Certain data, such as the need for three injections of antagonist in the calcium elevation assay, suggest that the half-life of the antagonist in vivo is less than that of hPTH-(1-34). Data obtained in vitro in cell culture systems support the notion that the antagonist is rapidly degraded at a rate exceeding that of PTH (18 (19). Antagonists that are more effective than [Tyr34]bPTH-(7-34)-amide may be necessary for hormone action to be blocked continuously; the high doses of antagonist required in these studies may not be practical for either extended physiological studies or trials as a diagnostic or therapeutic agent in hypercalcemic disorders in humans.…”