Relative sensitivity of kidney and bone to the amino-terminal fragment b-PTH (1–30) of native bovine parathyroid hormone: Implications for assessment of bioactivity of parathyroid hormone fragments in vivo and in vitro

Abstract

Summary: Adenylate cyclase activation in renal cortical membranes is widely used to assess the potency of parathyroid hormone (PTH) and hormonal fragments. Recent studies, however, suggest that the structural requirements for biological activity of PTH in bone may differ from those in kidney. In isolated perfused canine bone, cyclic AMP production is markedly increased by syn-b-PTH (1-34) whereas intact b-PTH (1-84) has minimal effect. Furthermore, a potent inhibitor of PTH stimulated adenylate cyclase activity, NleSNle18Tyl ~4 syn-b-PTH (3-34) NH2, devoid of biological activity in kidney, is an agonist in isolated bone. The present studies examine the effects in bone and kidney of the amino-terminal fragment b-PTH (1-30), prepared by cleavage of intact b-PTH (1-84) by Cathepsin B in vitro. In basolateral canine renal cortical membranes, b-PTH (1-30) was less active than syn-b-PTH (1-34) in its ability to stimulate adenylate cyclase. Half maximal stimulation of adenylate cyclase activity by b-PTH (1-30) was 50 nM compared with 2 nM for syn-b-PTH (1-34). Maximum enzyme activation by b-PTH (1-30) reached only 50%, of the activation by syn-b-PTH (1-34). Addition of Gpp(NH)p (1 mM) increased the affinities for both peptides. The relative difference in potency, however, remained unchanged. In contrast, in isolated bone, b-PTH (1-30) and syn-b-PTH (l-34) were equipotent in increasing cyclic AMP production. These data provide further evidence for differences in the structural requirements for PTH activity in bone and kidney and suggest that bioassays of PTH and PTH fragments in kidney may not accurately reflect the effects of PTH in bone.

Advances in Our Understanding of the Mechanism of Action of Drugs (including Traditional Chinese Medicines) for the Intervention and Treatment of Osteoporosis

“…Functionally, PTH and its related protein analogs function with calcitonin in the regulation of calcium and phosphorus ion metabolism in the blood and bone cell activity ( Beutner & Munson, 1960 ; Felsenfeld, Levine, & Rodriguez, 2015 ) ( Raisz, 1963 ; Bingham, Brazell, & Owen, 1969 ). The N-terminal sequence of PTH is highly conserved in many mammals; accordingly, the main biological activities of PTH are mediated by the binding of the N-terminal to PTH1R ( Martin et al, 1983 ), while the C-terminal region is mainly involved in the regulation of bone resorption and serum calcium ions. In addition, mutations in the C-terminal sequence affects its affinity to the receptor and its own metabolic degradation rate ( Potts et al, 1971 ).…”