Antiparathyroid Antibody Research Articles

FRI697 Severe Hypocalcemia Due To Idiopathic Hypoparathyroidism In An Elderly Female

Abstract Disclosure: K.A. Chopra: None. Most cases of acquired hypoparathyroidism in adulthood occur after neck surgery or radiation. However, idiopathic cases, although rare, do occur in elderly patients and should be a diagnosis of exclusion after thorough investigation. 76-year-old female with a history of chronic kidney disease, anemia of chronic disease, and hypertension presented with fatigue. Labs showed calcium (Ca) 5.7(RR 8.4-10.2 mg/dL), albumin 3.5(RR 3.5-5 g/dL), magnesium 2(RR 1.6-2.5 mg/dL), phosphorus 7.8(RR 2.5-4.4 mg/dL), parathyroid hormone 9(RR 15-75 pg/mL), 25-hydroxyvitamin D 32(RR 12-99 ng/mL). Patient denied history of neck surgery or radiation. Patient denied nephrolithiasis, perioral numbness, paresthesias, family history of hypoparathyroidism. Physical exam notable for positive Chvostek sign. Neck ultrasound unremarkable, no evidence of infiltrative disease. Urine Ca was low at 6 mg/24 hour(RR 100-300 mg/24hr). ACE level 10 nmol/ml/min(RR<40 nmol/ml/min) and 1,25 dihydroxyvitamin D level 12(RR 18-78 pg/mL) making sarcoidosis or granulomatous disease unlikely. HIV screen negative and interferon gamma response to mycobacterium tuberculosis antigens was not detected. Ferritin elevated at 300(RR 12-150 ng/mL) but transferrin saturation was 15%(RR 15-55%), not consistent with hemochromatosis. Antiparathyroid antibodies were negative. Patient denied mucocutaneous candidiasis, however testing for underlying autoimmune polyglandular syndrome type 1 (APS type 1) and adrenal insufficiency was completed with cosyntropin stimulation test. Patient had normal response to cosyntropin with baseline cortisol 20.1 (RR 6-18.4 ug/dL) and ACTH 37.7(RR<52 pg/mL), 30 minute cortisol 27(RR 6-18.4 ug/dL) and 60 minute cortisol 37(RR 6-18.4 ug/dL). Patient was treated with Ca gluconate infusion (100 ml of 10% Ca gluconate in 1000 mL of normal saline) at 30 ml/hr and Ca level gradually improved. Once Ca level was greater than 8.0(RR 8.4-10.2 mg/dL), Ca drip was discontinued. Due to patient’s lack of prior neck surgery history, lack of evidence of infiltrative conditions, negative antiparathyroid antibodies, normal adrenal function (unlikely APS type 1), lack of family history, and low urine Ca (unlikely activating mutation of Ca sensing receptor), patient’s hypoparathyroidism was considered idiopathic. Patient was discharged on oral Ca carbonate, Ca acetate, and calcitriol tablets. On follow up, patient had Ca 8.5(RR 8.4-10.2 mg/dL) with symptom improvement. Although hypocalcemia is commonly encountered, it is rare to see severe hypocalcemia in an elderly patient due to hypoparathyroidism without a history of neck surgery or radiation. Therefore, it is vitally important to conduct a thorough investigation to rule out underlying causes before diagnosing idiopathic hypoparathyroidism as highlighted in our case to guide future treatment and optimize patient health. Presentation: Friday, June 16, 2023

Calcium-sensing receptor autoantibodies in primary hyperparathyroidism

Background Mutations in the extracellular calcium-sensing receptor ( CaSR) gene are known to be implicated in some cases of primary hyperparathyroidism. However, not all patients display such mutations and so the mechanisms of primary hyperparathyroidism are still largely unknown. An autoimmune origin has been suggested, as autoantibodies against the CaSR have been detected in some patients. The aim of our study was to investigate the presence of CaSR autoantibodies in a large cohort of patients with primary hyperparathyroidism. Methods Seventy-five patients were tested for the presence of anti-parathyroid antibodies using an immunoblotting assay with the recombinant extracellular domain of the human CaSR and an immunofluorescence technique with parathyroid adenoma. Results Five of 75 (6.7%) patients had CaSR autoantibodies. There was no statistically significant difference in the decrease of parathyroid hormone (PTH) level after surgery between patients with or without autoantibodies. Histological examination of parathyroid tissue did not show greater lymphocytic infiltration in patients with autoantibodies than in those without. Conclusions This study confirmed that some patients with primary hyperparathyroidism displayed CaSR autoantibodies. The pathophysiological role of these autoantibodies in hyperparathyroidism needs to be further elucidated.

Is the Treatment of Hodgkin’s Disease Detrimental to the Parathyroid Gland?

The thyroid gland is often injured by supradiaphragmatic irradiation for Hodgkin’s lymphoma. The aim of the present study was to examine whether the parathyroid gland gets injured by the treatment for Hodgkin’s disease. Calcium, phosphorus and parathormone levels of 143 patients with primary treatment for Hodgkin’s disease and in complete remission for 2 years were measured as well as the presence of antiparathyroid antibody in patients having antithyroid antibody. Out of the 143 patients studied, 104 received neck irradiation (with or without chemotherapy); among them laboratory alterations were observed in 7 cases. 39 patients received only chemotherapy; 3 of them had alterations. In contrast to the injury of the thyroid gland, no damage to the parathyroid glands associated with the treatment for Hodgkin’s disease was noted. It has been concluded that the use of high-dose external radiotherapy does not mean a higher risk as regards the parathyroid gland but further follow-up studies of the patients may result in the revelation of the development of parathyroid lesions.

Enhanced visualization of parathyroid tissue by infusion of a visible dye conjugated to an antiparathyroid antibody

Background The antiparathyroid antibody BB5-G1 conjugated to cibacron blue, a blue dye, was intravenously infused to enhance parathyroid visualization. Previously, we demonstrated selective staining of human parathyroid implants in athymic nude mice after infusion of the conjugate. Methods Mice possessing implanted parathyroid tissue were randomized into the following: group I, infused with cibacron blue alone; group II, infused with the antibody/dye conjugate; and group III, infused with radiolabeled BB5-G1 alone. Implants were surgically explored. Three blinded observers ranked parathyroid visualization in the operative fields, and corresponding histologic sections were computer analyzed. Results Group II implants were easily visualized; groups I and III showed no staining. Group III showed high gamma counts. Subjective rankings and computer rankings correlated well (p < .05). Group II showed a higher mean staining intensity of 27.45 picogram protein product (PPP)/cell compared with 7.76 PPP/cell of group I (p = .002). Conclusion Cibacron blue/BB5-G1 consistently enhances visualization of implanted parathyroid tissue. © 1999 John Wiley & Sons, Inc. Head Neck 21: 111–115, 1999.

Enhanced visualization of parathyroid tissue by infusion of a visible dye conjugated to an antiparathyroid antibody.

The antiparathyroid antibody BB5-G1 conjugated to cibacron blue, a blue dye, was intravenously infused to enhance parathyroid visualization. Previously, we demonstrated selective staining of human parathyroid implants in athymic nude mice after infusion of the conjugate. Mice possessing implanted parathyroid tissue were randomized into the following: group I, infused with cibacron blue alone; group II, infused with the antibody/dye conjugate; and group III, infused with radiolabeled BB5-G1 alone. Implants were surgically explored. Three blinded observers ranked parathyroid visualization in the operative fields, and corresponding histologic sections were computer analyzed. Group II implants were easily visualized; groups I and III showed no staining. Group III showed high gamma counts. Subjective rankings and computer rankings correlated well (p < .05). Group II showed a higher mean staining intensity of 27.45 picogram protein product (PPP)/cell compared with 7.76 PPP/cell of group I (p = .002). Cibacron blue/BB5-G1 consistently enhances visualization of implanted parathyroid tissue.

A Protein Involved in Calcium Sensing of the Human Parathyroid and Placental Cytotrophoblast Cells Belongs to the LDL-Receptor Protein Superfamily

Monoclonal anti-parathyroid antibodies have been utilized to isolate a single-chain glycoprotein of 500 kDa, which apparently acts as a sensor of the extracellular calcium concentration and is expressed on the surface of human parathyroid, placental, and kidney tubule cells. The present contribution reports the isolation of a cDNA clone encoding this protein in human placenta and subsequent Northern blots confirming the mRNA expression also in human parathyroid and kidney cells. Close similarity in sequence as well as in tissue distribution is demonstrated with the rat Heymann nephritis antigen, a kidney tubule glycoprotein with calcium-binding ability. The 500-kDa protein belongs to the LDL-receptor superfamily of glycoproteins, claimed to function primarily as protein receptors and characterized by functionally important calcium-binding capacity. It is proposed that the currently identified protein constitutes part of a common structure for the sensing of extracellular calcium concentrations and influences calcium homeostasis in different organs.

Improvement in histological diagnosis of primary hyperparathyroidism with a monoclonal antiparathyroid antibody.

The monoclonal antiparathyroid antibody E11 reacts with a glycoprotein of high molecular weight, which acts as a calcium receptor on the surface of parathyroid cells and mediates calcium regulation of parathyroid hormone (PTH) release. Reduced expression of the calcium receptor has been implicated as a cause of the defect in PTH regulation in the pathological parathyroid parenchyma of patients with hyperparathyroidism (HPT). The present study evaluated the efficacy of immunostainings with the E11 antibody in comparison with routine histopathological methods including staining by the oil red O technique for histological discrimination between normal and pathological parathyroid glands. Parathyroid tissue from euparathyroid individuals invariably presented intense and homogeneous surface staining, with the antibody on virtually all chief cells, while the pathological glands from patients with HPT consistently showed heterogeneous and reduced immunostaining. Even minimally enlarged pathological glands from individuals with mild hypercalcemia and the normal-sized glands associated with adenomas displayed parathyroid chief cells with reduced antibody reactivity. The monoclonal antiparathyroid antibody should constitute a useful tool in parathyroid histopathology not only by its ability to identify the parathyroid tissue, but also by directly demonstrating the functionally normal and abnormal cells within the parathyroid tissue.

The role of the pathologist in diagnosis and surgical decision making in hyperparathyroidism

Hyperparathyroidism has been diagnosed with increasing frequency in recent decades. The concomitant awareness that the disease may be the cause of a concealed morbidity and even an increased mortality has resulted in more liberal indications for surgery. Many patients currently undergo surgery on the grounds of only mild hypercalcemia and in the absence of any apparent clinical symptoms. This policy of early surgical treatment has emphasized the importance of a histopathological parathyroid diagnosis, since many of these patients exhibit chief cell hyperplasia and minimal glandular enlargement. Light microscopic examination of frozen sections stained with hematoxylin-eosin and with stains for demonstration of cytoplasmic fat in the parathyroid chief cells, and appropriate weight estimates of the parathyroid glands, constitute the conventional, intra-operative basis for the diagnosis. The use of specific antiparathyroid antibodies is an important new tool in the histopathological parathyroid examination, mainly because of the ability to demonstrate the cause of increased parathyroid hormone release from the pathological parathyroid tissue. A careful histopathological examination in combination with gross inspection of the parathyroid glands by an experienced eye should contribute to adequate surgical treatment and minimize errors in operative management in patients with hyperparathyroidism.

Monoclonal antiparathyroid antibodies — tools for studies of the regulation of cytoplasmic calcium and function of parathyroid and other antibody-reactive cells

Monoclonal antiparathyroid antibodies — tools for studies of the regulation of cytoplasmic calcium and function of parathyroid and other antibody-reactive cells

Expression of a cell surface antigen with potential Ca 2+-sensor/receptor function in rat placenta and uterus

The reactivities of monoclonal anti-parathyroid antibodies identifying a cell surface ‘calcium sensing’ mechanism were investigated in the placenta and uterus of the pregnant rat. The rat placenta showed positively stained cells at the end of pregnancy. Staining was confined exclusively to the columnar epithelial cells lining the sinuses of Duval. In the uterus, positive staining of the epithelium lining the uterine lumen was obtained exclusively prior to and during implantation.

Interaction of monoclonal antiparathyroid antibody with Ca 2+ agonistic actions of Mn 2+ in normal human parathyroid cells

Effects of the monoclonal antiparathyroid antibodies G11 and E11 on Mn 2+ Interaction with individual normal human parathyroid cells were studied. At 0.5mM Ca 2+, 3mM Mn 2+ induced a rapid transient increase in cytoplasmic Ca 2+ [Ca 2+ i] followed by quenching of the fluorescence from the Ca 2+ indicator fura-2 as Mn 2+ entered into the cells. Whereas the antibody E11 had no effects, treatment with G11 abolished the Ca 2+ i transient and considerably delayed the entry of Mn 2+. The results support the presence of a cation-sensltive receptor mechanism on parathyroid cells and indicate that the antibody C11 not only blocks the interaction between Ca 2+ and this receptor mechanism but also that of Mn 2+.

Monoclonal antiparathyroid antibodies revealing defect expression of a calcium receptor mechanism in hyperparathyroidism.

AbstractMonoclonal antibodies were generated with a hybridoma technique after immunization of mice with intact human parathyroid cells. Three antibodies of the IgG type reacted in immunohistochemistry and immunofluorescense with parathyroid epithelial cells and proximal tubule cells of the kidney but not with a large number of other human tissues. Adenomatous and hyperplastic parathyroid glands of patients with hyperparathyroidism (HPT) demonstrated a reduced immunohistochemical reactivity with the antibodies as compared to the intense staining of normal human parathyroid tissue. Experiments with dispersed parathyroid cells from the normal and pathological glands showed that 2 of the antibodies blocked the effects of ambient calcium on cytoplasmic calcium and parathyroid hormone release. This indicates that the antibodies interfere with a newly recognized receptor mechanism of parathyroid cells involved in the sensing and gating of calcium and thereby also in the regulation of parathyroid hormone release. A reduced expression of the putative calcium receptor mechanism of abnormal parathyroid cells may, thus, be principally responsible for the hypercalcemia of HPT by causing a decreased sensitivity to extracellular calcium of the parathyroid hormone release from pathological parathyroid glands. The antibodies should improve the parathyroid histological diagnosis by their ability to identify and to distinguish between normal and abnormal parathyroid tissue.

Hyperparathyroidism is associated with reduced expression of a parathyroid calcium receptor mechanism defined by monoclonal antiparathyroid antibodies.

Parathyroid tissue from patients with hyperparathyroidism (HPT) exhibited reduced immunohistochemical reactivity with monoclonal antiparathyroid antibodies, previously shown to stain intensely the surface of normal human parathyroid cells and to interfere with a receptor mechanism of these cells which is involved in the sensing and gating of Ca2+. Parathyroid hormone (PTH) release and cytoplasmic Ca2+ concentrations (Ca2+i) of dispersed cells from the pathological parathyroid glands had right-shifted dependencies on extracellular Ca2+, and exposure to the antibodies rendered both Ca2+i and PTH release almost completely insensitive to changes in ambient Ca2+. The results suggest that reduced expression of a parathyroid calcium receptor mechanism may be an important cause for the aberrant PTH release in HPT.

Modulation of the Ca 2+-sensing function of parathyroid cells in vitro and in hyperparathyroidism

When raising the extracellular Ca 2+ concentration stepwise from 0.5 to 3.0 mM, bovine parathyroid cells reacted with initial transient and sustained elevations of the cytoplasmic Ca 2+ concentration (Ca 2+ i), as well as more than 50% inhibition of parathyroid hormone (PTH) release. Human parathyroid adenoma cells and bovine cells cultured for 1 day or exposed to a low concentration of a monoclonal antiparathyroid antibody exhibited right-shifted dependencies of PTH release and Ca 2+ i on extracellular Ca 2+ and reduced Ca 2+ i transients. The protein kinase C activator 12- O-tetradecanoylphorbol-13-acetate (TPA) further right-shifted the dose response relationship for Ca 2+ regulated Ca 2+ i of the adenoma cells, whereas the protein kinase C inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7) tended to normalize it, without affecting Ca 2+ i of normal bovine cells. In cells from an oxyphil adenoma and a parathyroid carcinoma as well as in bovine cells cultured 4 days or exposed to a high concentration of the antiparathyroid antibody, there were no Ca 2+ i transients, very small increases in steady-state Ca 2+ i and nonsuppressible PTH release. The results suggest that reduced availability of a putative Ca 2+-receptor and increased protein kinase C activity may be important factors in the decreased Ca 2+ sensitivity of abnormal parathyroid cells.

Monoclonal antibodies with exclusive reactivity against parathyroid cells and tubule cells of the kidney.

Four monoclonal anti-parathyroid antibodies were generated after immunization of mice with intact cells from human parathyroid tissue. All four monoclonal antibodies reacted in immunohistochemistry with structures present on parathyroid epithelial cells and proximal-tubule cells of the kidney but were unreactive with all other human tissues investigated. Immunofluorescence microscopy on suspended human parathyroid cells showed that the antibodies reacted with structures present on the cell surface. Two of these antibodies efficiently blocked the increase in cytoplasmic calcium concentration of parathyroid cells that is normally associated with increased concentrations of extracellular calcium. The results indicate that these two antibodies interfere with a calcium-sensing mechanism of parathyroid cells--i.e., a potential calcium receptor by which extracellular calcium regulates cytoplasmic calcium and hormone release in these cells.

Monoclonal anti-parathyroid antibodies interfering with a Ca 2+-sensor of human parathyroid cells

Previous findings indicate that binding of Ca 2+ to an external receptor is part of the mechanism by which extracellular Ca 2+ regulates cytoplasmic Ca 2+ and hormone release of parathyroid cells. We now present evidence that two newly generated monoclonal anti-parathyroid antibodies react with structures involved in this sensing and/or gating of Ca 2+. Microfluorimetric studies of fura 2-loaded human parathyroid cells thus revealed that the antibodies competed with Ca 2+ and antagonized the rise in cytoplasmic Ca 2+ normally obtained when parathyroid cells are exposed to increasing concentrations of extracellular Ca 2+.

Antibodies cytotoxic to bovine parathyroid cells in autoimmune hypoparathyroidism.

We utilized a recently developed long-term serum-free culture system for bovine parathyroid cells to detect antibodies in seven patients with autoimmune hypoparathyroidism (AHP). Antibodies were tested by indirect immunofluorescence methods and by cytotoxicity utilizing the chromium (51Cr) release technique. Seven AHP sera caused specific lysis [57 +/- 6% release of 51Cr vs. 5 +/- 1% for 56 controls (15 normal subjects and 41 patients with diverse other conditions associated with immune dysfunction)]. The least effect of any of the AHP sera on cell lysis exceeded the greatest effect of any of the control sera. Absorption of AHP sera (two cases) with bovine pituitary, thyroid, liver, or kidney cells did not affect lysis, but absorption with adrenal or parathyroid cells caused a marked decrease in specific lysis. Cytotoxicity determined by 51Cr release increased with antiserum concentration and time of incubation. Cytotoxicity was dependent on complement. Replicating parathyroid cells provide a uniform reproducible detection method for anti-parathyroid antibodies in AHP. The autoantibodies in AHP appear to be specific for tissue (parathyroid and adrenal cortex) but not for species.

Idiopathic hypoparathyroidism and autoimmunity.

Only a small number of cases of idiopathic hypoparathyroidism linked to the presence of specific antibodies have been described until now. Serum antiparathyroid antibodies have been frequently discovered in the absence of overt parathyroid disease. This suggests either that this kind of antibody is only a marker of genetic predisposition to immunological disease or more probably that subclinical hypoparathyroidism does exist though we lack the sensitive laboratory tests to prove it.

Distribution and Half-life of131I-Labeled Parathyroid Hormone in the Rat1

The half-life and volume of distribution of radioiodinated parathyroid hormone was measured in normal and parathyroidectomized rats. The labeled hormone was detected in plasma by modified paper electrophoresis and further identified by reaction with specific antiparathyroid hormone antibody. The half-life of the labeled hormone was 22.3 min in normal rats, 24.3 min in parathyroidectomized rats and 27.6 min in parathyroidectomized rats given excess carrier parathyixnd hormone. The volumes of distribution for the hormone in the 3 groups were 36.4, 27.0 and 28.6% of the body weight, respectively. The data obtained support the conclusion, derived from physiological experiments, that circulating parathyroid hormone is rapidly destroyed. (Endocrinology 77: 198, 1965)