Mechanisms of hypercalcemia in patients with head and neck cancer

Hypercalcemia associated with head and neck malignancy is not an uncommon occurrence; its causes are multiple. Eight hypercalcemic patients with head and neck malignancy were studied. Serum calcium, serum phosphorus, tubular phosphorus threshold, fasting calcium excretion, plasma 1,25-dihydroxyvitamin D, nephrogenous cyclic adenosine monophosphate (AMP), and immunoreactive parathyroid hormone were measured. Excessive dietary calcium administration in the form of an oral hyperalimentation preparation appeared to be the cause of hypercalcemia in 2 patients. Six patients demonstrated humorally mediated hypercalcemia. These patients resembled patients with primary hyperparathyroidism in having elevated nephrogenous cyclic AMP excretion and reduced proximal tubular phosphorus reabsorption, but they differed from patients with primary hyperparathyroidism by having normal levels of immunoreactive parathyroid hormone, MA rkedly increased fasting calcium excretion, and strikingly reduced mean plasma levels of 1,25-dihydroxyvitamin D. These data strongly suggest that the humoral factor responsible for hypercalcemia in patients with head and neck cancer is not parathyroid hormone, and that patients with hyperparathyroidism can now be distinguished with confidence from those with malignancy-associated hypercalcemia.     

A hypercalcemic nude rat model that completely mimics human syndrome of humoral hypercalcemia of malignancy

Summary Tumors causing humoral hypercalcemia of malignancy (HHM) were implanted to athymic nude rats. In one of these rat models transplanted with uterine cancer (UCC), a complete reproduction of human HHM syndrome was achieved: hypercalcemia, hypophosphatemia with increased urinary phosphate and cyclic AMP excretion, and suppressed serum 1,25-dihydroxy-vitamin D (1,25(OH)₂D) level. In another hypercalcemic nude rat model implanted with oral cavity cancer (OCC), all the features were similar except for markedly elevated serum 1,25(OH)₂D. Hypercalcemia disappeared by surgical removal of the tumors in both models, confirming the humoral mechanisms for causing these features. Furthermore, in UCC tumor-bearing rats, hypophosphatemia, increased renal phosphate excretion, and reduced serum 1,25(OH)₂D concentration were already present when these rats were only marginally hypercalcemic. These results raise the possibility that the changes in renal tubular phosphate handling and vitamin D metabolism in HHM are not secondary to hypercalcemia but are due to direct effects of the humoral factor(s) that cause this syndrome. Extracts of both tumors exhibited stimulation of cyclic AMP production in osteoblastlike cells, UMR 106, which could be almost completely inhibited by parathyroid hormone (PTH) antagonist, human PTH(3–34). By comparing the nature and characteristics of humoral factor(s) from UCC and OCC models, mechanisms responsible for causing these abnormalities can be explored. Thus, these nude rat models can be useful for elucidating the underlying mechanism of the development of HHM.     

Contrasting mechanisms of hypercalcemia in patients with early and advanced humoral hypercalcemia of malignancy

The mechanisms of hypercalcemia were assessed in 15 patients with humoral hypercalcemia of malignancy (HHM) who had tumors at various stages of progression. In patients with early tumors, bone biopsies were generally normal and the hypercalcemia was due to an elevation in renal tubular resorption of calcium. Conversely, osteoclastic resorption was markedly increased in patients with advanced tumors, particularly those in whom the biopsies were obtained postmortem. Osteoclast surface (Oc.S) correlated positively with the stage of tumor progression (r = 0.80, p less than 0.002), degree of immobility (r = 0.87, p less than 0.002), and level of urinary cyclic AMP excretion (r = 0.60, p less than 0.02). When compared with a group of ambulant patients with primary hyperparathyroidism (HPT), osteoblast surface (Ob.S%) in HHM was depressed (median and range): 1.2% (0-11.6%) versus 5.3% (1.1-32.0%) (p less than 0.001). However, a relatively low Ob.S (4%) and raised Oc.S (43.5%) were also seen in an immobilized patient with severe HPT. These data suggest that the PTH-related peptides currently invoked in the pathogenesis of HHM may initially cause hypercalcemia by enhancing renal tubular calcium resorption. The increase in osteoclastic activity and depression of osteoblastic activity that subsequently occurs is probably due to the combined effects of immobilization and higher circulating levels of PTHrP on the skeleton. However, the release of other bone-resorbing factors by the tumor, which have a depressant effect on osteoblastic activity, remains possible.     

Treatment of humoral hypercalcemia of malignancy in rats with inhibitors of carbonic anhydrase

The enzyme carbonic anhydrase has been suggested as a critical participant in osteoclast-mediated bone resorption. In humoral hypercalcemia of malignancy (HHM) intense osteoclastic bone resorption is principally responsible for the observed hypercalcemia. We therefore undertook to examine the effect of the carbonic anhydrase inhibitor acetazolamide on the hypercalcemia induced by the H500 Leydig cell tumor in Fisher rats, a well-described model of HHM. Acetazolamide treatment for 10 h at 10 mg/h resulted in a significant fall in serum calcium in the five drug-treated animals (14.2 +/- 0.9 to 11.5 +/- 0.1 mg/dl, p less than 0.05). Conversely, the six animals infused with vehicle alone showed a significant rise in serum calcium (12.5 +/- 0.5 to 13.8 +/- 0.1 mg/dl, p less than 0.05). At the end of the infusion, the acetazolamide-treated animals had a significantly lower mean serum calcium than those receiving vehicle alone (11.5 +/- 0.1 versus 13.8 +/- 0.1, p less than 0.05). There was no significant change in serum phosphorus, urine calcium, urine phosphorus, or nephrogenous cyclic AMP excretion between the two groups. Acetazaolamide and HTS 5-(3-hydroxybenzoyl)-2-thiophenesulfonamide, another carbonic anhydrase inhibitor, both significantly inhibited in vitro bone resorption induced by 5 X 10(-9) M 36Tyr(1-36)-PTHrP-amide (PTHrP, parathyroid hormone-related protein). Acetazolamide also inhibited the resorption induced by 10(-8) M (1-141)-PTHrP and 2.5 X 10(-9) M (1-74)-PTHrP. We conclude that acetazolamide is effective in lowering the serum calcium in animals with humoral hypercalcemia of malignancy. The data are consistent with the hypothesis that the mechanism of action for this effect is direct inhibition of osteoclast-mediated bone resorption.     

The effect of low calcium diet, mithramycin, and dichlorodimethylene bisphosphonate on humoral hypercalcemia of malignancy in nude mice transplanted with the canine adenocarcinoma tumor line (CAC-8)

The effect of a low calcium diet, mithramycin, or dichlorodimethylene bisphosphonate were evaluated in nude mice with humoral hypercalcemia of malignancy associated with the transplanted canine adenocarcinoma (CAC-8). Low calcium (0.01%) diet significantly reduced serum calcium levels in hypercalcemic nude mice and reduced urine calcium excretion to control levels. Mithramycin (8 mg/kg) decreased serum calcium concentration and urine calcium excretion to the range of control non-tumor-bearing nude mice at day 5 after a single injection, but there was no change in the number of tartrate-resistant acid phosphatase-positive osteoclasts in lumbar vertebrae. Osteoclasts from CAC 8-bearing nude mice after mithramycin administration were decreased in size, had small ruffled borders, and increased relative size of clear zones. Dichlorodimethylene bisphosphonate (Cl2MDP) (45 mg/kg) partially reduced serum calcium concentration of hypercalcemic tumor-bearing nude mice, decreased urine calcium excretion to control levels, and markedly reduced the numbers of tartrate-resistant acid phosphatase-positive osteoclasts in lumbar vertebrae. Osteoclasts from Cl2MDP-treated nude mice were smaller and had a reduced frequency of ruffled borders than saline-treated hypercalcemic nude mice. In vitro bone resorption induced by CAC-8 extract was significantly reduced by Cl2MDP and mithramycin. The results of these investigations suggest that the hypercalcemia and hypercalciuria associated with HHM in nude mice with CAC-8 are the combined result of altered calcium homeostasis in the bone, kidney, and intestine. Chemotherapeutic agents that specifically affect only bone or feeding a low calcium diet alone may not completely ameliorate the hypercalcemia of HHM.     

A case report: primary hyperparathyroidism--comparison before and after parathyroidectomy by oral calcium tolerance test

To evaluate the cause of hypercalciuria, we carried out the oral calcium tolerance test before and after parathyroidectomy in a patient with primary hyperparathyroidism who had recurrent and multiple nephrolithiasis. Preoperative laboratory examination showed hypercalcemia, hypophosphetamia, hypercalciuria, decrease in % tubular reabsorption of phosphorus and strikingly elevated urinary cyclic AMP excretion. The oral calcium tolerance test indicated a significantly greater increase in serum calcium (delta serum calcium: 1.4 mg/dl vs 0.8 mg/dl) and a significantly greater suppression of urinary cyclic AMP excretion (delta U-cyclic AMP:-3.56 moles/gCre vs-1.17 moles/gCre) before parathyroidectomy than after. These results showed that hypercalciuria in this case was induced not only by the significant increase in the filtrated load of calcium but by the reduction in the resorption of calcium in the distal tubule caused by the significantly suppressed parathyroid hormone effect.     

Assessment of renal and skeletal components of hypercalcemia

The management of hypercalcemia of malignancy is guided by assessments of its various components. Since the intestine usually makes no contribution to hypercalcemia under these circumstances, the problem is to measure the net efflux of calcium out of bone and the ability of the kidneys to excrete the unwanted calcium load. Established relationships between serum and urinary calcium excretion rates allow the quantitation of the relative contribution of an impaired glomerular filtration rate, of reduced renal tubular calcium reabsorption, and of increased bone resorption. Since the renal handling of calcium is closely related to that of sodium in the proximal nephron, the rate of sodium excretion is an important variable in these measurements. A practical approach to the separation of hypercalcemia into its renal and skeletal components is described in this article. Examples of how these measurements can be used to assess the responses to various types of therapy for malignancy-associated hypercalcemia are also given.     

Influence of dietary animal protein on renal stone disease

The effect of dietary protein load on the incidence of nephrolithiasis was studied in rats and men. Three groups of adult male Wister rats were fed with a standard protein diet, a high protein diet, or a low protein diet for 4 weeks. In the high protein group, calcium excretion was significantly increased and citrate excretion was remarkably decreased. This group also exhibited low grade metabolic acidosis due to catabolism of excess amino acids, and increases in urinary cyclic AMP excretion and bone resorption. These findings indicate that protein-induced hypercalciuria is due to low grade metabolic acidosis, which directly affects renal handling of calcium. Long-term calcium loss in the urine may lead to negative calcium balance and hyperfunction of the parathyroid gland may induce bone resorption. The influence of 40 g animal protein load on urinary risk factors of calcium stone formation was investigated in 23 healthy males and 26 patients with nephrolithiasis. All subjects were given control diets each day containing 60 g protein for a week and during the next week each received an additional 40 g animal protein. In the controls, added dietary protein resulted in decreased urinary citrate and increased urinary uric acid, with no change in urinary calcium or cyclic AMP excretion. In contrast, the patients showed increased urinary calcium and cyclic AMP as well as decreased urinary citrate. Further examination of the patients revealed that the significant increases of calcium and cyclic AMP excretion occurred only in hypercalciuric patients, who seemed to be classified into renal hypercalciuria.(ABSTRACT TRUNCATED AT 250 WORDS)     

Altered renal calcium handling in hypercalcemia of malignancy

It has been controversial whether increased renal tubular calcium reabsorption contributes to hypercalcemia in patients with malignancies. Moreover, whether this abnormality is associated with volume depletion, a parathyroid hormone-like effect, or other mechanisms has not been clarified. Eight consecutive patients with hypercalcemia due to a variety of tumor types were studied in detail. The glomerular filtration rate (iothalamate clearance) was reduced in all patients (0.98 +/- 0.10 (mean +/- SE) mL/s.1.73 m2; P less than 0.001) compared with normal controls (N = 9) (1.93 +/- 0.08 mL/s.1.73 m2), but it was similar to that in controls matched for renal insufficiency (N = 6) (1.15 +/- 0.05 mL/s.1.73 m2). During hypercalcemia produced by calcium infusion, urinary calcium excretion (millimoles of calcium per liter of glomerular filtrate) was increased in controls with renal insufficiency compared to those with normal renal function (P = 0.028). In all patients with hypercalcemia of malignancy, urinary calcium excretion was decreased compared with controls with renal insufficiency, but it was low in only five of eight patients compared with normal controls. Extracellular fluid volume (iothalamate volume of distribution) was not decreased in any patient, and urinary cAMP and/or plasma parathyroid hormone-like bioactivity were increased in six of eight patients. After treatment with an inhibitor of bone resorption, aminopropylidene 1,1 diphosphonate, abnormal renal calcium handling was not detected if the serum calcium normalized. It was concluded that increased renal tubular calcium reabsorption was consistently present in patients with hypercalcemia of malignancy compared with controls matched for renal insufficiency, but the proportion with the abnormality was underestimated if normal controls were used.(ABSTRACT TRUNCATED AT 250 WORDS)     

A model for malignancy-associated humoral hypercalcemia

Summary Tumor tissue from a patient with squamous cell carcinoma of the lung and hypercalcemia has been serially implanted into athymic mice. Tumor-bearing mice develop cachexia, hypercalcemia without bone metastases, hypophosphatemia, increased urinary cyclic adenosine monophosphate (cAMP) to creatinine ratio, and undetectable human immunoreactive parathyroid hormone levels. Radiographs of spines in the tumor-bearing mice demonstrate demineralization, suggesting skeletal resorption as the source of the hypercalcemia. Within 4–8 hours following tumor removal, hypercalcemia is reversed, suggesting that a relatively short-acting humoral substance is responsible for the hypercalcemia. The animals gain weight and become essentially normal within 4 days following tumor removal. The studies demonstrate that this animal model is similar in many aspects to human malignancy-associated humoral hypercalcemia (MAHH) and can provide a useful tool for further investigation of the pathogenesis and treatment of this syndrome.     

Evaluation of bone resorption and renal tubular reabsorption of calcium and phosphate in malignant and nonmalignant hypercalcemia

Tubular reabsorption of calcium (Ca) is becoming recognized as a determinant of malignant hypercalcemia. However, its importance as compared to increased bone resorption has not yet been widely investigated. We determined Ca fluxes of bone resorption and tubular reabsorption in 141 rehydrated patients with hypercalcemia of malignant or benign origin, before any specific treatment. Bone resorption (BRI) was evaluated by fasting urinary Ca excretion and Ca tubular reabsorption using an index (TRCaI) calculated from a nomogram relating fasting urinary Ca excretion and calcemia. The relationship between alterations in TRCaI and in the tubular capacity to reabsorb inorganic phosphate (Pi), as judged by TmPi/GFR, was also examined for each cause of hypercalcemia. Among 101 cases with malignancy, 67% had overt bone metastases, but all displayed increased BRI. Calcemia was highest in breast cancer and lowest in prostate carcinoma. BRI was markedly increased in breast cancer, lymphoma, and multiple myeloma, whereas it was slightly elevated in lung squamous cell, renal, and liver carcinomas. TRCaI was increased in 49% of malignant hypercalcemia, particularly in epidermoid (above the upper normal limit in 71% of the cases), renal, and liver carcinomas. It was elevated in 54% of breast cancer and normal in multiple myeloma and prostate cancer. In nonmalignant hypercalcemia, BRI was markedly increased in vitamin D intoxication, sarcoidosis, and immobilization. In primary hyperparathyroidism (PHP), BRI was moderately increased. TRCaI was abnormally elevated in PHP, but normal in vitamin D intoxication, sarcoidosis, and immobilization. In malignant hypercalcemia, TmPi/GFR was low in 77% of patients and in all types of tumors, except in prostate carcinoma. The index ratio [TRCaI/(TmPi/GFR)] gave a better discrimination of PHP from other causes of nonmalignant hypercalcemia than the use of either TRCaI or TmPi/GFR taken alone. Thus, in malignant hypercalcemia, increased bone resorption is associated with an elevation in tubular Ca reabsorption in half the patients surveyed, whereas low tubular Pi reabsorption is observed in more than 75%. Increased TRCaI is restricted to some types of tumor, whereas decreased TmPi/GFR is observed in all types except prostate carcinoma. In nonmalignant hypercalcemia, a significant increase in mean TRCaI was only observed in PHP, of which individual cases can be fully discriminated from other conditions by using a new index taking into account alteration in the renal transport capacity of both Ca and Pi.     

A case of renal pelvic squamous cell carcinoma accompanied with humoral hypercalcemia of malignancy

A 74-year-old male was urgently admitted to our hospital because of consciousness disturbance. Laboratory data showed remarkable hypercalcemia (7.8 mEq/L), hypophosphatemia, low % TRP, low intact PTH level, normal nephrogenic cyclic AMP and normal 1,25 (OH)2D level. Serum bone Gla protein, which was thought to express osteoblastic activity, was low. Serum tartarate resistant acid phosphatase and urinary excretion of hydroxyproline, which were thought to express osteoclastic activity, were high. CT scan showed an enlarged mass in the left renal pelvis, which was found to be a squamous cell carcinoma (SCC) by biopsy through percutaneous nephroscopy. Bone scintigram appeared normal. Therefore, we diagnosed it as renal pelvic SCC with humoral hypercalcemia of malignancy (HHM) and performed left nephrectomy. After nephrectomy, serum calcium returned to normal. But after a few weeks, lung metastasis appeared and serum calcium was reelevated. As to PTH related protein (PTHrP) which was thought to induce HHM, PTHrP content of the resected tumor measured by RIA assay was 13 pmol/g wet weight of tissue, which suggested that this tumor might have been producing PTHrP.     

Altered responses in serum calcium phosphorus and parathyroid hormone to oral calcium load in symptomatic and asymptomatic members of family with idiopathic hypercalcemia

A family of idiopathic hypercalciuria (IH), 3 symptomatic and 2 asymptomatic, plus 3 normal subjects were given the 1 Gm oral calcium challenge. Biochemical parameters measured included: serum and urinary calcium and phosphate, urinary cyclic AMP, and serum intact and carboxyl-terminal parathyroid hormone. Major differences between the normal control and the family with IH include: (1) higher calcemic response in the family with IH (0.9 vs 0.4 mg/dl); (2) a fall in carboxyl-terminal PTH and urinary cyclic AMP in the IH family in contrast to control subjects in whom there were no changes; (3) a rise in serum phosphorus in the IH family (0.8 vs 0.2 mg/dl, p < 0.05). Urinary excretion of calcium, phosphorus, and sodium after the calcium challenge was minimal. The oral calcium challenge is a simple and useful test in demonstrating increased calcium absorption even in asymptomatic relatives of patients with idiopathic hypercalciuria.     

Hypercalcemia during the osteogenic phase after rat marrow ablation coincides with increased bone resorption assessed by the NTx marker

Marrow ablation is a model of bone turnover in which the excavated tibial intramedullary cavity is rapidly and reproducibly filled by osteoblasts with new woven bone (days 6-8), which is then rapidly resorbed by osteoclasts (days 10-15). We showed previously (Magnuson et al., 1997) that marrow ablation induces a dramatic hypercalcemia and hypercalciuria in rats that unexpectedly peaked at the time of maximal osteogenesis and continued throughout the subsequent resorption phase. Based upon the amount of calcium mobilized and a peak of urinary hydroxyproline, we suggested that the hypercalcemia and hypercalciuria were due to increased systemic osteoclastic bone resorption induced by marrow ablation. We now apply a new enzyme-linked immunosorbent assay for rodent alpha(2)(I) N-telopeptide (NTx), a marker of bone resorption, to the marrow ablation model to demonstrate that excretion of NTx parallels that of calcium release in the operated control group. Specifically, maximal NTx/creatinine excretion coincides with the onset of hypercalcemia on days 7-8. A peak of NTx was also observed in methylprednisolone- and deflazacort-treated ablated animals. Analyses for urinary free deoxypyridinoline crosslink failed to detect a significant ablation-induced change in excretion. Interleukin 6 activity was increased in all operated control and glucocorticoid-treated groups after marrow ablation, whereas serum parathyroid hormone remained at presurgical levels in operated controls throughout the 15-day study period. The NTx results confirm that bilateral tibial marrow ablation induces a burst of extratibial bone resorption and hypercalcemia 7-8 days later. We have estimated that the osteogenic phase of the ablation model deposits 40 mg of calcium as hydroxyapatite crystals within the intramedullary cavity on days 6-8; this represents 33%-50% of the total blood calcium content of a young rat. We hypothesize that the size and rapidity of this demand for ionized calcium is met through an extratibial bone resorption pathway of osteoclast formation and activation that anticipates and fulfills this need, and that is initiated at the time of marrow ablation.     

Clodronate in hypercalcemia of malignancy

Of the many compounds belonging to the diphosphonate family, clodronate has been widely used in hypercalcemia and osteolysis of malignancy. All published reports indicate that clodronate can normalize plasma calcium in the majority of hypercalcemic, rehydrated cancer patients in whom increased bone resorption is the prevailing disturbed calcium flux. In these patients, clodronate, given intravenously either as a single infusion or as repeated daily administrations, can normalize serum calcium, usually 3–5 days after the onset of therapy. In these good responders, long-term maintenance treatment should be individually adjusted since relapse appears to depend upon the type of tumor, the extent of malignancy and the administration of anticancer therapy. In a subset of well-rehydrated hypercalcemic patients in whom increased tubular calcium reabsorption represents the prevailing disturbed calcium flux, the acute effect of clodronate on plasma calcium is incomplete, despite the normalization of bone resorption. This type of therapeutic response can be experimentally reproduced in diphosphonate-treated animals receiving a constant infusion of parathyroid hormone-related peptide, a peptide isolated from lung, kidney and breast carcinomas. This indicates that, in addition to antiosteolytic drugs, such as clodronate, patients with hypercalcemia of malignancy would benefit from the development of agents that can selectively reduce the renal tubular reabsorption of calcium. In patients displaying a good response to clodronate, the fall in plasma calcium is accompanied by an increase in the calcium-regulating hormones, parathyroid hormone and 1,25-dihydroxyvitamin D₃. This homeostatic reaction probably explains why hypocalcemia rarely occurs in clodronate-treated patients. No serious side effects have been reported in cancer patients receiving oral clodronate, except for the occasional occurrence of mild and transient gastrointestinal upset. A large number of clinical studies indicate that clodronate is a safe and efficacious drug in the treatment of hypercalcemia of malignancy, particularly in cases in which increased bone resorption is the major mechanism disturbing the homeostasis of extracellular calcium.     

Role of bone and kidney in parathyroid hormone-related peptide-induced hypercalcemia in rats

A protein responsible for the biochemical syndrome similar to primary hyperparathyroidism associated with certain tumors has been recently characterized and its effects at the level of bone and kidney reported. However, the relative role of tubular reabsorption of calcium (Ca) and bone resorption in the pathogenesis of hypercalcemia induced by this factor is still debated. We investigated the effects of a synthetic amino-terminal fragment of parathyroid hormone-related protein [PTHrP-(1-34)] administered chronically by intraperitoneal osmotic minipumps in thyroparathyroidectomized (TPTX) rats. Clearance studies performed on day 6 of treatment after a 24 h fast revealed an increase in renal tubular reabsorption of Ca and a decrease in renal tubular reabsorption of phosphate (Pi), accompanied by an increase in cAMP excretion. PTHrP-(1-34) (90 pmol/h) stimulated bone resorption as evaluated by an increment in fasting urinary Ca excretion. Although the bone resorption inhibitor aminopropylidene diphosphonate fully corrected urinary Ca excretion and reduced plasma Ca from 3.04 +/- 0.07 to 2.44 +/- 0.21 mM (p less than 0.05), this latter value remained considerably higher than in TPTX control rats (1.54 +/- 0.12 mM, p less than 0.01). In contrast, when the agent WR-2721, which is known to decrease the renal tubular reabsorption of Ca by a PTH-independent mechanism, was given, a further drop in plasma Ca and an increase in urinary Ca excretion were observed. These findings are similar to those found in animals implanted with the hypercalcemic Leydig cell tumor.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hereditary hypophosphatemic rickets with hypercalciuria: report of a new kindred

We report a new kindred of hereditary hypophosphatemic rickets with hypercalciuria. The symptomatic child and several relatives had increased renal phosphate clearance leading to hypophosphatemia, hyperabsorptive hypercalciuria, low PTH and increased 1,25-(OH)2D serum level. However, association with vitamin D deficiency and normal urinary excretion of cyclic AMP might suggest another tubular defect in phosphate transport.     

Parathyroid hormone increases the expression level of matrix metalloproteinase-13 in vivo

Parathyroid hormone (PTH) increases serum calcium (Ca) by enhancing bone resorption and renal Ca reabsorption. However, detailed mechanisms of enhanced bone resorption by PTH remain to be elucidated. Although PTH has been shown to increase the expression level of osteoblastic matrix metalloproteinase (MMP)-13 in vitro, only limited results are available regarding the in vivo regulation of MMP expression. In the present study, we have examined expression levels of MMPs in PTH-infused rats. Infusion of 1.5 or 2.0 nmol/kg/day rat PTH(1–34) for 3 days resulted in a dose-dependent increase in serum Ca. PTH infusion also decreased serum phosphate levels and increased urinary excretion of Ca and phosphate. Infusion of PTH for 7 days resulted in less severe hypercalcemia and hypophosphatemia. Urinary Ca and phosphate excretion in rats infused for 7 days was less than that in rats infused for 3 days. Northern blot analysis showed that PTH infusion increased the expression level of MMP-13 in calvaria, although it did not affect MMP-2 expression. Furthermore, the time-course and severity of hypercalcemia and hypercalciuria correlated with the expression level of MMP-13. In situ hybridization also showed that PTH infusion increased the expression level of MMP-13 in femora. These results indicate that PTH enhances MMP-13 expression in vivo and suggest that PTH stimulates bone resorption at least partly by enhancing MMP-13 expression. Received: June 5, 2000 / Accepted: January 12, 2001     

Differential diagnosis of hypercalcemia in renal malignancy

We report a case of large cell B-cell lymphoma of the kidney associated with humoral hypercalcemia of malignancy. A 70-year-old man presented with renal failure and hypercalcemia. After the workup, the patient was thought to have renal cell carcinoma and underwent radical nephrectomy. The pathologic evaluation showed a large cell lymphoma with a B-cell phenotype. Reevaluation of the patient's serum revealed a high calcitriol level with low parathyroid hormone and parathyroid hormone-related protein levels, consistent with the final pathologic findings. The differential diagnosis of hypercalcemia in renal malignancy is presented.     

Hypercalciuria during experimental vitamin K deficiency in the rat

Summary Vitamin K promotes the formation of gamma-carboxylated glutamate (GLA) in several protein species. GLA residues have a high affinity for the Ca ion. In the present study we tested the hypothesis that experimental vitamin K deficiency in rats could induce changes in Ca metabolism. Vitamin K depletion, which was associated with a reduction in urinary GLA excretion, induced within 7 days a significant increase in cumulative urinary Ca excretion that persisted throughout the 21 days of study. The hypercalciuria of vitamin K-deficient rats was corrected on vitamin K supplementation. No concomitant changes were observed in intestinal Ca absorption determined by a balance technic or of skeletal resorption and apposition rates determined by bone histomorphometry. Plasma Ca, but not total protein concentration, of vitamin K-depleted rats showed a transient decrease at day 15 that disappeared at day 21. Plasma sodium, phosphate and 1,25 (OH)₂ vitamin D concentration, and urinary phosphate, sodium, and creatinine excretion remained unchanged. In conclusion, vitamin K deficiency in the rat induces hypercalciuria that could be of renal origin. Its possible relationship to vitamin K-dependent renal GLA protein remains to be clarified.