Cyclic nucleotides and growth regulation in suspension cultures of mammalian cells

Alcohol-induced bone disease: relationship to age and parathyroid hormone levels

Alcohol abuse leads to osteopenia and fractures. Epidemiological evidence suggests that older alcoholics are at substantially greater risk of fractures than younger alcoholics. To examine the interaction of age and alcohol abuse on bone mineral homeostasis, we studied 27 subjects with a history of 10 more years of alcohol abuse ranging in age from 26-68 years. They were evaluated for disordered bone mineral homeostasis by assessing bone density (by quantitative computed tomography of the lumbar spine), histomorphometry of a transcortical biopsy from the iliac crest, serum levels of vitamin D metabolites and parathyroid hormone, and serum and urine levels of bone minerals. Seventeen of the subjects were found to have spinal compression fractures by routine radiologic procedures. The older the subject the more likely the subject was to have such a fracture. Bone densitometry indicated a marked reduction in spinal bone density with 15 subjects below 2 SD of normal aged-matched controls. Bone density fell sharply with the age of the subject. Histomorphometry of iliac crest bone biopsies revealed no evidence of osteomalacia, but total resorption surfaces were increased. Consistent with the lack of osteomalacia were the normal levels of the vitamin D metabolites. The increased total resorption surfaces were correlated with high normal or elevated levels of parathyroid hormone as indicated both by radioimmunoassay and by urinary cAMP levels. Bone formation and active bone resorption (resorption surfaces containing osteoclasts) did not correlate with parathyroid hormone levels, however, but correlated negatively with age.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of TSH bio-activity by synthetic beta TSH peptides

The in vitro bioactivity of the human beta TSH subunit was investigated utilizing eleven overlapping synthetic peptides representing the entire 112 residue sequence. The peptides were tested for both stimulatory and inhibitory activity in two sensitive bioassay systems: the first based on cAMP production in FRTL-5 rat thyroid cells, and the second based on stimulation of iodine trapping by the same continuous cell line. Peptides from three distinct regions of the beta-subunit showed concentration dependent inhibition of TSH bio-activity, including beta 1-15, beta 11-25, beta 31-45, beta 81-95, and beta 91-105 with IC50 values ranging from 150 to 304 microM. An additional peptide representing the entire sequence of the "intercysteine loop" region of beta TSH, beta 31-52, also inhibited TSH activity with somewhat higher potency than its fragment peptide beta 31-45 (IC50 of 87.5 +/- 14.7 microM for beta 31-52 versus 207 +/- 92.4 microM for beta 31-45). Three of these, beta 1-15, beta 31-45, and beta 31-52, also inhibited binding of TSH to the receptor in a radio-receptor assay, as previously reported (1), supporting their importance in receptor interaction. None of the synthetic peptides stimulated either cAMP production or iodine trapping. Two other overlapping peptides, beta 81-95 and beta 91-105, possessed bio-inhibitory activity but did not inhibit binding of labeled TSH. Computer analysis of this sequence predicted an extended turn structure for this region. This region has been referred to as the "determinant loop" as it is bounded by cysteine residues at positions 88 and 95 that many believe form a disulfide bond in the native subunit. The current data suggests the beta 88-95 region may play a role in receptor activation after initial binding of hormone to receptor.

Role of site-selective cAMP analogs in the control and reversal of malignancy

Two isoforms of cAMP receptor protein, RI and RII, the regulatory subunits of cAMP-dependent protein kinase, transduce opposite signals, the RI being stimulatory and the RII being inhibitory of cell proliferation. In normal cells RI and RII exist at a specific physiological ratio whereas in cancer cells such physiological balance of these receptor proteins is disrupted. Reversal and suppression of malignancy can be achieved when the physiologic ratio of these intracellular signal transducers of cAMP is restored as shown by the use of site-selective cAMP analogs, antisense oligodeoxynucleotides or gene transfer, suggesting new approaches to cancer control.

Effect of age on variables relating to calcium and phosphorus metabolism in women

Lack of adequate data concerning the effect of age on biochemical variables relating to bone and mineral metabolism hampers research on age-related bone loss in women. Furthermore, to detect disease and to monitor therapy, clinical laboratories require reference values derived from an appropriate population sample. Therefore, we determined the age-specific distribution of values for serum concentrations of calcium, inorganic phosphorus, alkaline phosphatase, bone Gla protein, and parathyroid hormone; for creatinine clearance; for fasting urinary calcium:creatinine ratio; and for 24 h urinary excretion of calcium, hydroxyproline, and cyclic AMP in a population-based sample of 301 white women. From this sample, a healthy subgroup of 181 women was identified by medical record review. Age-related effects were seen in all variables except serum calcium and phosphorus. Moreover, substantial differences between the population sample and the healthy subgroup were noted in values for creatinine clearance, serum alkaline phosphatase, and 24 h urinary calcium excretion. These observations may prove useful for assessment of normality in other populations of aging white women.

Accumulation of cyclic 3',5'-adenosine monophosphate in cultured neonatal human dermal fibroblasts exposed to parathyroid hormone and prostaglandin E2

We sought to determine whether cultured human dermal fibroblasts respond to parathyroid hormone (PTH) with accumulation of cyclic 3',5'-adenosine monophosphate (cAMP) reproducibly enough for such cells to be useful in characterizing states of altered end-organ response to PTH. Thus, we cultured fibroblasts from 15 human neonatal foreskins and tested fibroblast cAMP responses to addition of synthetic human PTH-(1-34), bovine PTH-(1-34), and native bovine PTH-(1-84) at concentrations of 10(-6) to 10(-10) M. Accumulation of cAMP (cells plus medium) was significantly enhanced by PTH in only 10 of 37 experiments. In cells that had a significant cAMP response to PTH, the ratio of treated to control cAMP values ranged only from 1.27 to 2.18. No study showed a clear-cut dose-response relationship. In six of six experiments, the cells responded to prostaglandin E2 (1 microgram/ml) with markedly increased accumulation of cAMP (9.7 to 110.9-fold the basal value). We conclude that cultured human dermal fibroblast cAMP responses to PTH with use of the current methods are too small and inconsistent for that tissue to be useful in studies of reduced end-organ responsiveness to PTH such as pseudohypoparathyroidism. Nevertheless, states of hyperresponsiveness to PTH might still be detectable by this method.

Structural requirements for parathyroid hormone action in mature bone. Effects on release of cyclic adenosine monophosphate and bone gamma-carboxyglutamic acid-containing protein from perfused rat hindquarters

To determine the structural requirements for parathyroid hormone (PTH) activity in mature bone, we perfused the surgically isolated hindquarters of adult male rats with either native bovine PTH-(1-84) [bPTH-(1-84)] or the synthetic amino-terminal fragment, bovine PTH-(1-34) [bPTH-(1-34)]. Changes in the release of cyclic AMP (cAMP) and bone Gla protein (BGP) were monitored as evidence of bone-specific response to PTH; tissue specificity of the cAMP response was confirmed through in vitro examination on nonskeletal tissue response to PTH. Biologically active, monoiodinated 125I-bPTH-(1-84) was administered to determine if mature murine bone cleaves native hormone. We found that perfused rat bone continuously releases BGP, and that both bPTH-(1-84) and bPTH-(1-34) acutely suppress this release. In addition, both hormones stimulate cAMP release from perfused rat hindquarters. When examined on a molar basis, the magnitude of the cAMP response was dose-dependent and similar for both hormones, with doses yielding half-maximal cAMP responses. The response for bPTH-(1-34) was 0.5 nmol and for bPTH-(1-84) was 0.7 nmol. Moreover, biologically active 125I-bPTH-(1-84) was not metabolized in our hindquarter perfusion system. These findings indicate that PTH-(1-84) does not require extraskeletal or skeletal cleavage to an amino-terminal fragment in order to stimulate cAMP generation in, or suppress BGP release from, mature rat bone.

Rapid development of renal resistance to low doses of synthetic bovine parathyroid hormone fragment 1-34. Dissociation of urinary cyclic adenosine monophosphate, phosphaturic, and calciuric responses

The designing of parathyroid hormone (PTH)-renal dose-response studies in human beings is complicated by the possibility of rapid homologous receptor down-regulation, a phenomenon that is clearly shown to occur in vitro. Large amounts of PTH given to human subjects as serial injections or prolonged infusions cause decreased urinary 3',5'-cyclic adenosine monophosphate (cAMP) responses to subsequent PTH doses, but it is uncertain whether lower doses given over shorter periods similarly cause renal tachyphylaxis to PTH action. Thus, in seven water-loaded adults, we infused in ascending order 10, 30, 75, 150, and 300 U of synthetic bovine PTH fragment 1-34 (bPTH 1-34) per 70 kg body wt over 15 min on widely separated days ("separate day administration"). On another day, each subject received all five 15-min doses in ascending order at 75-min intervals ("single day administration"). Urine collection intervals were control, 0-30 min (including the PTH infusion), and 30-60 min. Peak nephrogenous cAMP (NcAMP, nmol/100 ml glomerular filtrate) response was linearly related to the dose of PTH (separate day study, r = 0.94, P less than 0.001; single day study, r = 0.88, P less than 0.001). However, the slope of NcAMP responses plotted against PTH dose for the single day study was only 36% of that derived from separate day administration of the same PTH doses (P less than 0.001). After only 40 U (10 + 30) of bPTH 1-34/70 kg, the NcAMP response to 75 U was reduced 44%, and the effect of 300 U/70 kg, when given as the last of the sequential single day infusions, was 64% less than the response to 300 U of bPTH 1-34 given alone (P less than 0.001). The phosphaturic response (fractional excretion of phosphorus, FEP [percent]) was also linearly related to bPTH 1-34 dose, but combined administration of the PTH infusions on one day increased FEP at each dose identically with the effects of separate day administration. A transient, dose-related, early hypercalciuric response to bPTH 1-34 also occurred, and was of equal magnitude in both protocols. These studies demonstrate that significant blunting of the NcAMP response to bPTH 1-34 occurs rapidly and follows brief exposure to relatively low doses of hormone. In contrast, there is no effect of recent PTH administration on the phosphaturic and early hypercalciuric actions of bPTH 1-34. This seeming dissociation of PTH effects makes unclear the physiologic importance of PTH-induced cAMP tachyphylaxis in the regulation of final PTH actions. In any case, studies of NcAMP responses in which the occurrence of tachyphylaxis would be undesirable should be designed to avoid prolonged or closely spaced administrations of the hormone.

Hypocalcemia with osteoblastic metastases in patient with prostate carcinoma. A cause of secondary hyperparathyroidism

A 68 year old man with prostatic carcinoma and extensive painful osteoblastic metastases was discovered to have hypocalcemia (serum calcium 7.1 mg/dl) without evidence of hypoalbuminemia, renal failure or malabsorption. Baseline studies revealed hypocalciuria (24 hour urine calcium less than 5 mg/day), normal serum phosphate (3.4 mg/dl), low tubular reabsorption of phosphate (68 percent), undetectable serum calcitonin, normal serum 25-hydroxyvitamin D, slightly elevated serum parathyroid hormone level and increased urinary cyclic AMP (8.87 mumol/g creatinine). These studies were compatible with secondary hyperparathyroidism. The intravenous administration of parathyroid extract produced no further change in urinary phosphate but a 25-fold increase in nephrogenous cyclic AMP. Three days administration of intramuscular parathyroid extract slowly and temporarily restored serum calcium to normal levels while increasing urinary cyclic AMP and phosphate. Chemotherapy with cyclophosphamide and 5-fluorouracil rendered the patient free of pain while reducing serum acid and alkaline phosphatase levels and restoring serum total and ionized calcium and urinary cyclic AMP excretion to normal.

Observations on prostaglandins in normal and leukemic human lymphocytes

Prostaglandins E (PGE) and F2 alpha (PGF2 alpha) were measured in lymphocytes of normal subjects, children with acute lymphocytic leukemia (ALL), and adults with chronic lymphocytic leukemia (CLL). In ALL lymphocytes PGE increased from a normal value of 25 pgrams to 270 pgrams/10(6) cells, and PGF 2 alpha increased from a normal value of 31 pgrams to 482 pgrams/10(6) cells. In CLL lymphocytes, levels of PGE and PGF2 alpha were normal or low. When normal lymphocytes were stimulated with phytohemagglutinin (PHA), the level of PGE and PGF2 alpha fluctuated, followed by corresponding changes in the level of cyclic nucleotides. In cultured ALL lymphocytes, the level of PGE remained high, while cyclic 3':5'-adenosine monophosphate (c-AMP) level was constantly low, and the initial level of PGF2 alpha fluctuated in relation to similar oscillations of cyclic 3':5'-guanosine monophosphate (c-GMP). These values were lower, although not significantly, when ALL lymphocytes were stimulated with PHA. When CLL lymphocytes were stimulated with PHA, the level of PGE remained low (20 pgrams), as did that of c-AMP. The level of PGF2 alpha, after a brief initial increase (130 pgrams), returned to and remained at a lower level (60 pgrams) while the level of c-GMP was persistently high. These results suggest: (1) prostaglandins may indirectly influence the cell cycle, possibly through modulation of cyclase activity and levels of cyclic nucleotides; and (2) some derangement of this regulatory mechanism may be present in leukemic lymphocytes.

Skeletal responsiveness in pseudohypoparathyroidism. A spectrum of clinical disease

Three cases of pseudohypoparathyroidism with roentgenographic evidence of hyperparathyroid bone disease are described. Renal resistance to exogenous parathyroid hormone (PTH), the hallmark of pseudohypoparathyroidism, was documented by markedly blunted or absent urinary phosphate and cyclic AMP responses to parathyroid extract. At the time of diagnosis all patients were hypocalcemic and hyperphosphatemic with elevated serum alkaline phosphatase levels and subperiosteal resorption noted on skeletal films. Bone biopsy in one patient revealed a histologic appearance consistent with hyperparathyroidism. Serum PTH levels, measured in two patients while they were hypocalcemic, were elevated. None of the patients had short stature, brachydactyly, subcutaneous calcification or mental deficiency. These cases are compared to the 15 well-documented cases previously reported. The presently available information on pseudohypoparathyroidism indicates a variable skeletal response to PTH mediated by several factors extrinsic to bone and suggests that pseudohypoparathyroidism with hyperparathyroid bone disease is one extreme of a clinical spectrum of skeletal responsiveness to PTH. This disorder is part of an expanding clinical picture which makes pseudohypoparathyroidism a diagnostic consideration in any patient with unexplained hypocalcemia, hyperphosphatemia, elevated alkaline phosphatase levels or metabolic bone disease.

Effects of angiotensin II and angiotensin II antagonist saralasin on cell growth and renin in 3T3 and SV3T3 cells

Components of the renin-angiotensin system were studied in established cell culture lines of 3T3 and SV3T3 mouse fibroblasts. The renin content in 3T3 cells was significantly higher than in virus-transformed SV3T3 cells. With time after infection, renin decreased in Simian virus 40 transformed cells, while it increased steadily in mock-infected 3T3 cells. In contrast to renin, angiotensinase activity was higher in SV3T3 cells. Angiotensin II stimulated cell proliferation in 3T3 mouse fibroblasts and decreased their renin content in a dose-related manner. In contrast, saralasin, an angiotensin receptor antagonist, inhibited cell growth in 3T3 and SV3T3 cells and caused an increase of cellular renin concentration. The angiotensin fragments angiotensin (2-8) heptapeptide and angiotensin (4-8) pentapeptide had no effect on cell growth. A significant negative correlation was found between cell proliferation and renin levels in 3T3 and SV3T3 cells irrespective of the treatment. Our results indicate (1) that angiotensin II may be involved in cell growth regulation, (2) that a negative feedback exist between angiotensin II added and intracellular renin content, and (3) that virus infection causes a decrease in intracellular renin synthesis, while non-specific angiotensinase activity is increased under this condition.