Immunological Evidences for the Presence of Small Late Carboxylterminal Fragment(S) of Human Parathyroid Hormone (PTH) In Circulation in Man

Abstract

Two antisera, C-52 and C-97, raised against bovine (b)PTH(1-84) in guinea pigs, were evaluated with 125I-[tyr53] human (h)PTH(53-84) as tracer and intact hPTH(1-84) and synthetic hPTH(39-84), representative of large carboxylterminal ("C") fragments found in circulation, as standards. In both assays, hPTH(39-84) was 5-6 times more potent than hPTH(1-84) on a molar basis in displacing the tracer. With both antisera, progressive deletion at the aminoterminal end of large "C" fragments, as in hPTH(53-84) and hPTH(65-84), lead to decreased immunoreactivity, hPTH(69-84) being non-immunoreactive. The mid-carboxylterminal fragments, hPTH(44-68) and hPTH(39-68), did not react in either assay. Each antiserum measured known quantities of pure hPTH(1-84) or hPTH(39-84) standards similarly. Serum PTH values obtained with antiserum C-97 were about 3 times higher in renal failure, 1.75 times higher in normal individuals and those with primary hyperparathyroidism, while similar to values measured with antiserum C-52 in individuals with secondary hyperparathyroidism without renal failure or with pseudohypoparathyroidism. When circulating PTH taken from patients with these disorders was fractionated by gel chromatography, both antisera recognized similar peaks of intact hPTH(1-84) and of large "C" fragments while antiserum C-97 further recognized a peak of smaller "C" fragments. This explained the different clinical behavior of the latter antiserum. Our findings demonstrate the existence of small late "C" fragments in circulation. They further suggest an influence of serum calcium and of renal function on the quantity of these fragments.

Parathyroid Hormone Secretion and Action: Evidence for Discrete Receptors for the Carboxyl-Terminal Region and Related Biological Actions of Carboxyl-Terminal Ligands

“…Differences in immunoreactivity registered in assays with predominantly mid-or late-carboxyl reactivity strongly suggest the presence of multiple CPTH fragments, some of which may extend to, or close to, the C terminus of intact PTH, whereas others may have undergone substantial C-terminal cleavage to produce bitruncated "mid-carboxyl" fragments (270,318). Although most of the CPTH fragments characterized to date are at least 50 -70% as large as PTH(1-84), some small "late carboxylterminal" fragments also may exist in human plasma (335).…”

Familial Resemblance of Bone Mineral Density Between Females 18 Years and Older and Their Mothers

“…Serum PTH was evaluated with an in-house radioimmunoassay (between assay CV = 11.6%) recognizing large carboxyl terminal fragments of PTH. 37,38 Bone mineral content of the lumbar spine (BMC L ) was evaluated in all subjects by dual photon absorptiometry using Novo LAB-22B equipment. Measurements were taken on the L 2 , L 3 and L 4 vertebrae.…”

Effects of acute and chronic hypercalcemia on parathyroid function and circulating parathyroid hormone molecular forms

“…Porcine (p) parathyroid cells have been demonstrated to secrete pPTH fragments starting at positions 34 and 37 (5). Studies in humans have also outlined the existence of smaller C-PTH fragments (6) and, more recently, of larger C-PTH fragments with a partially preserved aminoterminal structure (7), called non-(1 -84)PTH. These non-(1 -84)PTH molecular form or forms have been described in humans during the analysis of normal and abnormal serum HPLC profiles using Nichol's I-PTH assay (7), the same assay as that employed by Bas et al (1) in their study.…”