John P. Fox

Hypoparathyroidism in the adult: epidemiology, diagnosis, pathophysiology, target-organ involvement, treatment, and challenges for future research.

Recent advances in understanding the epidemiology, genetics, diagnosis, clinical presentations, skeletal involvement, and therapeutic approaches to hypoparathyroidism led to the First International Workshop on Hypoparathyroidism that was held in 2009. At this conference, a group of experts convened to discuss these issues with a view towards a future research agenda for this disease. This review, which focuses primarily on hypoparathyroidism in the adult, provides a comprehensive summary of the latest information on this disease.

Defining a Noncarcinogenic Dose of Recombinant Human Parathyroid Hormone 1–84 in a 2-Year Study in Fischer 344 Rats

The carcinogenic potential of human parathyroid hormone 1–84 (PTH) was assessed by daily subcutaneous injection (0, 10, 50, 150 μg/kg/day) for 2 years in Fischer 344 rats. Histopathological analyses were conducted on the standard set of soft tissues, tissues with macroscopic abnormalities, selected bones, and bones with abnormalities identified radiographically. All PTH doses caused widespread osteosclerosis and significant, dose-dependent increases in femoral and vertebral bone mineral content and density. In the mid- and high-dose groups, proliferative changes in bone increased with dose. Osteosarcoma was the most common change, followed by focal osteoblast hyperplasia, osteoblastoma, osteoma and skeletal fibrosarcoma. The incidence of bone neoplasms was comparable in control and low-dose groups providing a noncarcinogenic dose for PTH of 10 μg/kg/day at a systemic exposure to PTH that is 4.6-fold higher than for a 100 μg dose in humans. The ability of PTH to interact with and balance the effects of both the PTH-1 receptor and the putative C-terminal PTH receptor, may lead to the lower carcinogenic potential observed with PTH than reported previously for teriparatide.

Hemagglutinins associated with certain human enteric viruses.

Summary 1) Monkey kidney cell culture fluids containing ECHO viruses 3, 6, 7, 10, 11 and 12 and Coxsackie B3 have been shown to be capable of agglutinating human Group O erythrocytes in relatively high dilutions. Evidence has been presented indicating that the hemagglutinating activity is specifically related to these agents, rather than to possible simian viral contaminants. 2) Preliminary findings suggest that the HA property resides in the viral particle, that it is absorbed by erythrocytes during the process of agglutination and may be eluted from them, exhausting red cell receptors during the process. Despite such similarities to the myxoviruses, additional data suggest that these agents do not belong to the myxovirus group. 3) Monkey kidney cell preparations of polioviruses 1, 2, and 3, ECHO viruses 1, 2, 5, 8, 9, 13 and 14 and Coxsackie A9 failed to agglutinate human Group O cells, whereas preparations of ECHO 4 and Coxsackie B1, B2, B4 and B5 manifested HA activity in low dilution.

Direct effects of calcium channel blockers on duodenal calcium transport in vivo

The direct effects of verapamil, diltiazem and nifedipine on duodenal calcium transport were assessed in rats by the in vivo ligated loop technique, using luminal calcium concentrations at which active and passive transport mechanisms predominate (2 and 50 mM Ca, respectively). At 2 mM Ca, addition of verapamil (0.3-10 mM) to the luminal solution caused a concentration-dependent decrease in calcium lumen-to-plasma uptake and an increase in calcium plasma-to-lumen translocation, such that at 10 mM verapamil there was a net secretion of calcium into the duodenal lumen. In contrast, nifedipine (0.3-3 mM) was without effect on calcium transport, and diltiazem reduced calcium lumen-to-plasma uptake and net calcium absorption only at 10 mM, without influencing plasma-to-lumen translocation. The verapamil-induced increase in calcium plasma-to-lumen translocation was abolished by bile duct ligation. Calcium transport was unaffected by any calcium channel blocker at 50 mM luminal calcium. Thus, verapamil can directly influence active calcium translocation in the intestine, in vivo, and may affect calcium homeostasis during chronic oral treatment with this drug.

Pharmacokinetics and pharmacodynamics of subcutaneous recombinant parathyroid hormone (1-84) in patients with hypoparathyroidism: an open-label, single-dose, phase I study.

BACKGROUNDnImpaired mineral homeostasis affecting calcium, phosphate, and magnesium is a result of parathyroid hormone (PTH) deficiency in hypoparathyroidism. The current standard of treatment with active vitamin D and oral calcium does not control levels of these major minerals. Recombinant full-length human PTH 1-84 (rhPTH[1-84]) is being developed for the treatment of hypoparathyroidism.nnnOBJECTIVEnThe goal of this study was to investigate the pharmacokinetics and pharmacodynamics of a single subcutaneous injection of rhPTH(1-84) in patients with hypoparathyroidism.nnnMETHODSnThis was an open-label, dose-escalating study of single subcutaneous administration of 50 µg and then 100 µg of rhPTH(1-84). Enrolled patients (age range, 25-85 years) had ≥12 months of diagnosed hypoparathyroidism defined according to biochemical evidence of hypocalcemia with concomitant low-serum intact PTH and were taking doses ≥1000 mg/d of oral calcium and ≥0.25 µg/d of active vitamin D (oral calcitriol). The patients prescribed dose of calcitriol was taken the day preceding but not on the day of or during the 24 hours after rhPTH(1-84) administration. Each patient received a single 50-µg rhPTH(1-84) dose, had at least a 7-day washout interval, and then received a single 100-µg rhPTH(1-84) dose. The following parameters were assessed: plasma PTH; serum and urine total calcium, magnesium, phosphate, and creatinine; and urine cyclic adenosine monophosphate.nnnRESULTSnAfter administration of rhPTH(1-84) 50 µg (n = 6) and 100 µg (n = 7), the approximate t½ was 2.5 to 3 hours. Plasma PTH levels increased rapidly, then declined gradually back to predose levels at ~12 hours. The median AUC was similar with calcitriol and rhPTH(1-84) for serum 1,25-dihydroxyvitamin D (calcitriol, 123-227 pg · h/mL; rhPTH[1-84], 101-276 pg · h/mL), calcium (calcitriol, 3.3-3.7 mg · h/dL; rhPTH[1-84], 3.3-7.6 mg · h/dL), and magnesium (calcitriol, 0.7-0.9 mg · h/dL; rhPTH[1-84], 1.3-2.8 mg · h/dL). In contrast, the median AUC for phosphate was strongly negative with rhPTH(1-84) (calcitriol, -1.0 to 0.8 mg · h/dL; rhPTH[1-84], -21.3 to -26.5 mg · h/dL). Compared with calcitriol, rhPTH(1-84) 50 µg reduced 24-hour calcium excretion and calcium-to-creatinine ratios by 12% and 23%, respectively, and rhPTH(1-84) 100 µg reduced them by 26% and 27%. There was little overall impact on urine magnesium levels. Compared with calcitriol, rhPTH(1-84) 50 µg increased urinary phosphate excretion and phosphate-to-creatinine ratios by 53% and 54%, respectively, and rhPTH(1-84) 100 µg increased them by 45% and 42%. Urine cyclic adenosine monophosphate-to-creatinine ratio increased with rhPTH(1-84) by 2.3-fold (50 µg) and 4.4-fold (100 µg) compared with calcitriol.nnnCONCLUSIONSnPTH replacement therapy with rhPTH(1-84) regulated mineral homeostasis of calcium, magnesium, phosphate, and vitamin D metabolism toward normal in these study patients with hypoparathyroidism.

What is vitamin D deficiency

Vitamin D derived from the diet or produced in the skin is converted to its active form by two sequential hydroxylation reactions (1, 2). The first occurs in the liver, forming 25-hydroxyvitamin D3 (25-(OH)D3), and the second occurs in the kidney, forming the active hormonal form 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3). The activity of the renal 25-(OH)D3-1 α-hydroxylase enzyme (1-hydroxylase), which is tightly regulated according to the calcium and phosphorus requirements of the body, is stimulated predominantly by parathyroid hormone and low plasma calcium and phosphate concentrations. 1,25-Dihydroxyvitamin D3 acts to increase intestinal active calcium transport and, in concert with parathyroid hormone, to stimulate renal tubular calcium reabsorption and bone mineral mobilization (1, 2). Vitamin D restriction by dietary deficiency and/or by reduced exposure to sunlight can lead to the development of vitamin D-deficiency rickets (2, 3). The best recognized definition of vitamin D-deficiency, i.e., bony rickets, has its origin in the evolving understanding of this bone disease and the fact that vitamin D deficiency is the most frequent cause (Table I). In more recent times, many investigators have considered animals to be vitamin D deficient if they exhibit rickets, reduced intestinal calcium transport, hypocalcemia, or “undetectable” levels of 25-(OH)D3 (Table II; 7–27). However, in a series of studies (28–30) directed toward establishing a normocalcemic rat model exhibiting vitamin D-deficiency, we realized that understanding or defining vitamin D deficiency is extremely complex. For example, most workers would probably agree that vitamin D deficiency should entail 1,25-(OH)2D3 deficiency. However, as described below, absence of 1,25-(OH)2D3 may not always be associated with absence of vitamin D or 25-(OH)D3. Conversely, physiological levels of 1,25-(OH)2D3 can exist in the presence of extremely low levels of vitamin D or 25-(OH)D3.

Homologous Up‐Regulation of Vitamin D Receptors Is Tissue Specific in the Rat

1,25‐dihydroxyvitamin D3 (1,25(OH)2D3) receptors (VDR) are expressed in multiple tissues within the body. VDR levels are increased by 1,25(OH)2D3 in intestine and kidney and in numerous cell models. The ability of 1,25(OH)2D3 to affect VDR levels in other target tissues in vivo was studied by assessing VDR levels by the3H‐1,25(OH)2D3 binding assay under varied physiological conditions in the rat. When compared with vitamin D–deficient (−D) controls, rats raised on a normal vitamin D–sufficient (+D) diet showed elevated VDR levels in kidney (391 ± 53 vs. 913 ± 76 fmol/g of tissue; p < 0.05), but not in testis, heart, or lung. Up‐regulation of the VDR also occurred in kidney of +D rats 1 day after a single 100‐ng dose of 1,25(OH)2D3 (454 ± 43 vs. 746 ± 113 fmol/mg of DNA; p < 0.05), but no changes were seen in intestine, testis, or lung. Because 1,25(OH)2D3‐induced hypercalcemia may independently affect VDR regulation, 1,25(OH)2D3 was infused into −D rats, and normocalcemia was maintained by reduced dietary calcium intake. In this model, the renal VDR was again up‐regulated (446 ± 115 vs. 778 ± 58 fmol/mg of DNA; p < 0.05), but VDR levels in testis and lung were unaffected. Scatchard analysis and tests of 1,25(OH)2D3 dose (1–100 ng/day for 7 days) and temporal (100 ng/day for 1–7 days) responsiveness further supported the tissue‐specific nature of the homologous VDR regulation. Assay of VDR levels by l‐1‐tosylamido‐2‐phenylethyl chloromethyl ketone–3H‐1,25(OH)2D3 exchange assay ruled out differences in endogenous 1,25(OH)2D3 occupancy as the basis for the observed differences in VDR regulation. Finally, coidentity of the VDR‐like sites in kidney versus testis was confirmed by competitive binding analysis comparing their relative affinities for 25(OH)D3 versus 1,25(OH)2D3 (30.5 ± 6.4 vs. 35.6 ± 3.6 in kidney and testis, respectively) and by immunoblot analysis using a highly specific monoclonal anti‐rat VDR antibody. Thus, under a wide variety of experimental conditions, homologous up‐regulation of the VDR occurs in the rat kidney in vivo, but not in several other target tissues which do not regulate plasma calcium homeostasis. Moreover, this differential VDR regulation did not result from secondary changes in plasma calcium, from differential 1,25(OH)2D3 responsiveness in the various tissues, nor from differences in endogenous 1,25(OH)2D3 occupancy of the VDR. These studies thus establish that, in contrast to observations in vitro, the widely described phenomenon of homologous VDR up‐regulation in kidney and intestine is not a universal property of 1,25(OH)2D3 target tissues in vivo in the rat.

IMMUNIZING INFECTIONS WITH POLIOMYELITIS VIRUSES AND SEROIMMUNE PATTERNS IN SOUTHERN LOUISIANA

The relative infrequency of overt disease, as compared with infection, has long imposed a serious barrier to full understanding of the mechanisms involved in, and the factors which influence, the dissemination of poliomyelitis viruses. As less cumbersome laboratory methods have been developed, increasing efforts have been made to chart the occurrence of past infections in selected population samples by means of serologic surveys 2 , and, in a few cases, by survey of serially collected sera, to discover the frequency of immunizing infections within defined periods of time.4. Efforts have also been made to discover persons actually harboring virus. Poor environmental sanitation, low economic status, and large families have been named as factors contributing to early development of immunity? Also, much evidence has accumulated to show that the probability of harboring virus increases with proximity to known, overt cases, and is maximum in child household associates of such cases.s I The work described in this paper relates to populations in southeastern Louisiana and was divided into two parts. The first concerned itself with determining the extent of infection within the households of patients with clinically diagnosed disease occurring in late 1951 and in 1952. This project has been completed and is being reported in full detail elsewhere? The objective of the second part was to determine when, and under what circumstances, the average individual, selected without reference to overt disease, acquires his immunizing infections. A corollary development, the delineation of patterns of seroimmunity within the study group, may reflect the patterns in the communities from which the group was selected. This second project is being reported now only in preliminary fashion.

PROPHYLAXIS AGAINST RABIES IN HUMANS

Measures intended to prevent rabies in man may be divided into two basic categories: those taken before and those taken after the infecting bite. Historically, since the ancient realkation of the relation of dogs to human rabies, the first category has embraced measures to avoid being hitten and, since the early Nineteenth Century, measures to control canine rabies. In the second category, local cleansing treatment of the bite wound has been practiced for centuries; acid treatment, since 1830. Specific active immunization following suspected exposure has been practiced since the time of Louis Pasteur. With two important exceptions that will be indicated shortly, the foregoing states, in broad outline, the situation today with respect to the orientation of efforts to prevent human rabies. Important refinements, of course, have been introduced in the years since Pasteur, but without change in this basic orientation. These include the development and widespread utilization of canine immunization as an aid to control, improvements in methods of diagnosing animal infections as an aid to defining more certainly the individuals a t risk, and development of a rcliable method2 for measuring vaccine potency to help ensure effeclive immunization. Despite these important technical advances, completely safe and reliable protection of man against rabies has yet to be achieved. Three recent developments, however, afford the basis for renew ed hope. The first represents another example of technical advance and consists of the possible substitution of vaccine prepared in avian embryo~-chicken~-~ or duck6. 7-f~r the conventional types of vaccine that are prepared from central nervous system (CNS) tissue of infected animals. Such a vaccine, being essentially free of CNS tissue, should not induce the tissue-specific sensitization postulated as the cause of the demyelinating reactions that too often result from the Pasteur treatment. The remaining two recent developments represent the application of new principles or orientation. One, the introduction of hyperimmune serum: belongs in the after-the-bite category and is intended to protect the recipient by passively conferred antibody, against a disease with such a short incubation period that active response would be too long delaycd. The other, which technically is still in the developmental stage, falk chiefly in the before-the-bite category and consists of the demonstration that, once induced, active immunity resulting from either conventional Pasteur treatment or a primary course of avian embryo vaccine can be recalled by a single booster i n o c ~ l u m . ~ With embryo vaccine this provides the basis for possible safe, long-term immunization initiated well before exposure in high-risk population groups. It also permits abbreviated (single-inoculation) and presumably safe postexposure treatment of those who previously have had a course of Pasteur treatment. This presentation will endeavor to describe briefly and clearly the salient

Deficiency of vitamin D metabolites directly stimulates renal 25-hydroxyvitamin D3-1-hydroxylase activity in rats

Renal 25-hydroxyvitamin D3-1-hydroxylase (1-hydroxylase) enzyme activity in rats is known to be increased by parathyroid hormone (PTH), hypophosphatemia, and hypocalcemia. Thus, enzyme activity is markedly increased in vitamin D-deficient states, but whether this stimulation is a direct response to the vitamin D deficiency or only occurs following the associated changes in plasma calcium, phosphate, or PTH is unclear. We tested whether vitamin D deficiency per se influences 1-hydroxylase activity in renal cortical slices using a normocalcemic rat model of vitamin D deficiency. Weanling male rats were fed one of the following three diets: (A) 0.8% Ca, 0.5% P, 2.2 IU vitamin D3/g; or vitamin D-deficient diets containing, (B) 0.8% Ca, 0.5% P; and (C) 2.0% Ca, 1.25% P, 20% lactose. Vitamin D-deficient rats fed diet B were hypocalcemic with elevated PTH at both test periods, and 1-hydroxylase activity was increased more than 100-fold compared with rats fed diet A. Plasma calcium, phosphate, and PTH levels were the same in groups A and C, but 1-hydroxylase activity was also substantially elevated in group C versus group A rats (104- and 17-fold increases after 10 and 19 diet weeks, respectively). These data lead to the important conclusion that severe deficiency of vitamin D metabolites per se provides a strong and independent stimulus to renal 1-hydroxylase activity in rats, perhaps due to the absence of 1,25(OH)2D3-mediated enzyme inhibition.