Genetics of osteoporosis: role of steroid hormone receptor gene polymorphisms

Osteoporosis is a common skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue with a consequent increase in bone fragility and susceptibility to fracture. In the past years, twin and family study have shown that this disease recognizes a strong genetic component and that genetic factors play an important role in regulating bone mineral density (BMD). While in few isolate conditions osteoporosis can be inherited in a simple Mendelian pattern, due to single gene mutations, in the majority of cases has to be considered a multifactorial polygenic disease in which genetic determinants are modulated by hormonal, environmental and nutritional factors. Given the important role that steroid hormones play in bone cell development and in the maintenance of normal bone architecture, polymorphisms at receptor of the steroid/thyroid hormone receptor superfamily, such as estrogen receptor alpha (ERalpha) and Vitamin D receptor (VDR) have been thoroughly investigated in the last years and appeared to represent important candidate genes. The individual contribution of these genetic polymorphisms to the pathogenesis of osteoporosis remains to be universally confirmed and an important aim in future work will be to define their functional molecular consequences and how these polymorphisms interact with each other and with the environment to cause the osteoporotic phenotype. A further promising application of genetic studies in osteoporosis comes from their pharmacogenomic implications, with the possibility to give a better guidance for therapeutic agents commonly used to treat this invalidating disorder or to identify target molecules for new therapeutic agents.

Guidelines for diagnosis and therapy of MEN type 1 and type 2

This is a consensus statement from an international group, mostly of clinical endocrinologists. MEN1 and MEN2 are hereditary cancer syndromes. The commonest tumors secrete PTH or gastrin in MEN1, and calcitonin or catecholamines in MEN2. Management strategies improved after the discoveries of their genes. MEN1 has no clear syndromic variants. Tumor monitoring in MEN1 carriers includes biochemical tests yearly and imaging tests less often. Neck surgery includes subtotal or total parathyroidectomy, parathyroid cryopreservation, and thymectomy. Proton pump inhibitors or somatostatin analogs are the main management for oversecretion of entero-pancreatic hormones, except insulin. The roles for surgery of most entero-pancreatic tumors present several controversies: exclusion of most operations on gastrinomas and indications for surgery on other tumors. Each MEN1 family probably has an inactivating MEN1 germline mutation. Testing for a germline MEN1 mutation gives useful information, but rarely mandates an intervention. The most distinctive MEN2 variants are MEN2A, MEN2B, and familial medullary thyroid cancer (MTC). They vary in aggressiveness of MTC and spectrum of disturbed organs. Mortality in MEN2 is greater from MTC than from pheochromocytoma. Thyroidectomy, during childhood if possible, is the goal in all MEN2 carriers to prevent or cure MTC. Each MEN2 index case probably has an activating germline RET mutation. RET testing has replaced calcitonin testing to diagnose the MEN2 carrier state. The specific RET codon mutation correlates with the MEN2 syndromic variant, the age of onset of MTC, and the aggressiveness of MTC; consequently, that mutation should guide major management decisions, such as whether and when to perform thyroidectomy.

Genetics of menopause-associated diseases

Menopause is the permanent cessation of menstruation resulting from the loss of ovarian follicular activity. It is estimated that perhaps 50 million women worldwide will go into menopause annually. Atherosclerotic cardiovascular disease, osteoporotic fractures and Alzheimer's dementia are common chronic disorders after menopause, representing major health problems in most developed countries. Apart from being influenced by environmental factors, these chronic disorders recognize a strong genetic component, and there are now considerable clinic evidences that these disorders are related to low hormonal milieu of postmenopausal women. Here, we review up-to-date available data suggesting that genetic variation may contribute to higher susceptibility to four sporadic chronic syndromes such as osteoporosis (OP), osteoarthritis (OA), Alzheimer's disease (AD) and coronary artery disease (CAD). For these four syndromes candidate genes that today appear as major loci in genetic susceptibility encode for proteins specific of a given system, as the vitamin D receptor (VDR) gene for the skeleton and, therefore, OP or angiotensin converting enzyme (ACE) for the cardiovascular system and, therefore, CAD. The investigation of gene polymorphisms in various pathological conditions typical of postmenopause offer an explanation not only of their genetic inheritance but also of their co-segregation in given individuals. In this view, it may be possible to identify a common set of genes whose variants contribute to a common genetic background for these different disorders. Ideal candidates appear genes of the estrogen response cascade [i.e. estrogen receptor (ERs), enzymes involved in estrogen metabolism or co-activators and co-inhibitors]. All together this information may represent the basis both for future recognition of individuals at risk and for the pharmacogenetic driving of drug responsiveness.

Genetics of male osteoporosis

In the past years, several epidemiological and clinical observations have underlined the importance of genetics in the pathogenesis of both female and male osteoporosis. It has been estimated that from 50 to 80% of the inter-individual variability in bone mass is genetically determined. In rare instances, osteoporosis in men could be inherited in a simple Mendelian pattern. Examples of this include familial osteoporotic syndromes due to mutations in the aromatase and ER alpha genes. Families have also been described in which high bone mass is inherited as an autosomal dominant trait, consistent with the effect of a single gene located on chromosome 11. However, except for these rare conditions, osteoporosis has to be considered a multifactorial disease in which genetic determinants are modulated by hormonal, environmental, and nutritional factors. The genetic effect on bone may also be gender- and site-specific, with different genes regulating bone density at different skeletal sites in males and females. To date, most of the work on the genetics of osteoporosis has focused on women. In some studies, polymorphisms at the IGF-I, VDR, COLI-alpha1, ER alpha, and aromatase gene have been recently shown to predict BMD variation and osteoporotic risk in males. These observations remain to be confirmed by other independent studies. Other candidate genes, are still awaiting mapping and identification.

[Use of clodronic acid in mineral metabolism conditions: state of the art in 2000]

Clodronic acid is a non-aminate bisphosphonate capable of inhibiting bone resorption. Pharmacological and clinical trials have shown the efficacy of clodronic acid in the treatment of post-menopausal osteoporosis and in all conditions of excess bone resorption, such as Paget's disease, malignant tumoral hypercalcemia and osteolytic metastases. Clodronic acid is the only bisphosphonate currently on the market available for both oral and parenteral administration. Intramuscular therapy with clodronic acid at a dose of 100 mg/week has shown significant effects on bone mineral density after 6 months treatment in patients with postmenopausal osteoporosis and these effects were maintained 3 years after the start of treatment. Increased bone mass is associated with a reduced risk of the onset of vertebral fractures. In a recent three-year study a significant increase was observed in bone mineral density associated with a 46% reduction in the incidence of vertebral fractures. The reduction in bone pain after parenteral treatment with clodronic acid is an important added value in the use of this molecule in osteopenic pathologies. Moreover the costs of parenteral clodronic acid treatment is certainly competitive compared to other drugs. Oral and parenteral clodronic acid was well tolerated in clinical trials. Gastrointestinal adverse effects were described only with high oral doses. These effects were transient and generally resolved without interrupting the treatment. Clodronic acid is an effective and well tolerated drug able to inhibit bone resorption. The low incidence of undesired effects at a gastroenteric level, the possibility of formulas for parenteral administration, the antalgic effect and low costs make clodronic acid an extremely interesting molecule for the prevention and treatment of postmenopausal osteoporosis and all conditions of excessive bone resorption, such as Paget's disease, malignant tumoral hypercalcemia, osteolytic metastasis and hyperparathyroidism.

TGF-beta isoform and receptor expression in giant cell tumor and giant cell lesions of bone

The authors examined the distribution of tumor growth factor-beta (TGF-beta) isoforms and receptors in 35 giant cell tumor (GCT) of bone in comparison with a group of benign giant cell-containing lesions of bone, including 5 aneurysmal bone cysts, 2 cases of brown tumor of hyperparathyroidism, 3 nonossifying fibromas, and 7 cases of giant cell reparative granuloma. The results of immunohistochemical analysis of GCT showed a complete absence of TGF-beta1 expression in both mononuclear tumor cells and giant cells. Only reactive bone present within the tumor showed an intense immunoreactivity. Transforming growth factor-beta2 and TGF-beta3 were detected in the majority of cases (97.1% and 82.8%, respectively), whereas TGF-beta receptor type I (TGF-beta RI) and type II (TGF-beta RII) were diffusely expressed in all cases. Reverse transcription-polymerase chain reaction (RT-PCR) analysis performed on 10 GCTs with specific oligonucleotide primers demonstrated the presence of mRNA transcripts for TGF-beta1, 2, 3, and for TGF-beta RI and RII. Quantitative measurements of TGF-beta1 in conditioned media from primary cultures of GCT showed undetectable or very low amounts of the cytokine (0-23 pg/mL). The results of immunohistochemical analysis showed that all giant cell-containing lesions of bone were at least focally positive for the 3 isoform of TGF-beta, with positivity present both in osteoclast-like giant cells and mononuclear cells, and diffusely positive for TGF-beta RI and RII. Reverse transcription-polymerase chain reaction analysis conducted on samples from 3 nonossifying fibromas and 1 giant cell reparative granuloma confirmed the expression of the corresponding mRNA. In conclusion, according to the current data, GCT of bone can be distinguished from other giant cell-containing lesions of bone on the basis of the absence of TGF-beta1 expression at the protein level, which appears to be the result of posttranslational regulation processes.

Polymorphism of the aromatase gene in postmenopausal Italian women: distribution and correlation with bone mass and fracture risk

Conversion of C(19) steroids to estrogens is catalyzed by the aromatase enzyme. Inactivating mutations of the aromatase gene are associated with decreased bone mineral density in both men and women. Genetic studies suggest that several genes contribute to the regulation of bone mass via interaction with the modeling and remodeling processes. Among these genes, the aromatase gene is a potential candidate to be evaluated for segregation with bone metabolism and bone mass. A tetranucleotide simple tandem repeat polymorphism in intron 4 at the human aromatase cytochrome P-450 gene has been recently described. In the present study we evaluated the distribution of this polymorphism in a cohort of Italian postmenopausal women, both normal and osteoporotic. We observed that the NN genotype was significantly more frequent in nonosteoporotic women than in osteoporotic women (72.7% vs. 27.2%), whereas the DN genotype was significantly more represented in osteoporotic women (90.48% vs. 9.5%; Pearson's chi(2) test = 42.8; df = 10; P = or < 0.01). The allele containing the longer TTTA repeats was statistically more represented in nonosteoporotic women (Pearson's chi(2) test = 19.14; df = 2; P = 0.00007). In addition, women with a high number of TTTA repeats had a significantly higher lumbar bone mineral density than women with alleles containing 8-11 TTTA repeats (P = 0.03). Finally, considering the spine fractures, a significantly higher incidence was observed in women with shorter TTTA repeats than in those with longer TTTA repeats (Pearson's chi(2) test = 7.3; df = 2; P = 0.02), equivalent to a relative risk of 4.1 (95% confidence interval, 1.19-13.87). In conclusion, the aromatase gene can be one of the several genes potentially involved in the maintenance of bone mass and in the regulation of bone mass loss.

The importance of the unsuppressed glands in the study of intact parathyroid hormone disappearance after parathyroid adenomectomy

BACKGROUND

In the usual techniques for intraoperative intact parathyroid hormone (iPTH) monitoring for primary hyperparathyroidism, the normal glands are implicitly considered suppressed. On the contrary, we believe, as do other researchers, that they are not totally suppressed.

METHODS

For this reason, we considered the introduction of an infusion from the unsuppressed normal glands (UNG), described by an influx constant (IC (pg/ml per min)), into the formulation of a two-compartment model. For the blood compartment, we have: C(t)=A.exp(-at)+B.exp(-bt)+EV, where A+B+EV=iPTH concentration at zero time (clamping), EV (equilibrium value)=IC/k, 'a' and 'b' are reciprocals of the time constants of the two exponentials and k=rate constant of elimination from the blood. The experimental data were obtained using an IRMA standard method, collecting samples in 20 patients, during and following adenomectomy.

RESULTS

In spite of the variability among the patients, all fits were very good, thus confirming the importance of the UNG contribution to the shaping of the disappearance curve. For this reason, the relationship between the constant infusion from the UNG and the basal iPTH level at the induction of anaesthesia (BV), was studied.

CONCLUSIONS

The existence of a negative correlation, together with the determination of a regression curve (IC=6.5BV), not only confirmed our assumptions, but also revealed the theoretical possibility of a priori knowledge of the iPTH contribution from the UNG. Hence, there is a theoretical possibility of discriminating between this contribution and that of the remaining (if any) affected gland(s).

Microencapsulation of human parathyroid cells: an "in vitro" study

BACKGROUND

Patients affected by hypoparathyroidism of variable etiology are currently treated with exogenously administered vitamin D and calcium. Human parathyroid transplantation has long been investigated as a possible mean of treating these patients to prevent long-term hypocalcemia. However, the main obstacle for this treatment is represented by tissue rejection. A reliable method to efficiently protect the transplanted tissue from rejection and to allow long-term survival of the graft is the encapsulation of tissues or cells in alginate-polylysine-alginate membranes, which were successfully used for encapsulation of islets of Langerhans. The microencapsulation of parathyroid tissue fragments or of parathyroid cells becomes, therefore, a potential approach for the successful treatment of permanent symptomatic hypoparathyroidism without pharmacological immunosuppression.

MATERIALS AND METHODS

We describe microencapsulation of differentiated human parathyroid cells derived from adenoma or hyperplastic glands. Long-term viability, cell growth, and parathyroid hormone production of microencapsulated cells were evaluated together with responsiveness to extracellular Ca(2+).

RESULTS

Microencapsulated parathyroid cells maintained proliferative and differentiative properties for a long term in culture with a good response to extracellular Ca(2+) concentration.

CONCLUSIONS

These findings represent a crucial step toward the construction of functional bioartificial parathyroid organoids for the treatment of hypoparathyroidism in humans.

Genotype distribution of estrogen receptor-alpha gene polymorphisms in Italian women with surgical uterine leiomyomas

OBJECTIVE

To explore a possible association between estrogen receptor-alpha (ER-alpha) gene polymorphisms and development of uterine leiomyomas.

DESIGN

Case-control study.

SETTING

University teaching hospital.

PATIENT(S)

119 women with clinically and surgically diagnosed uterine leiomyomas.

INTERVENTION(S)

Therapeutic hysterectomy.

MAIN OUTCOME MEASURE(S)

Frequency and distribution of ER-alpha gene polymorphisms.

RESULT(S)

No statistically significant differences between controls and patients in the allele frequency and genotype distribution were found when Pvu II and Xba I restriction polymorphism sites were analyzed separately. When the two ER-alpha gene polymorphisms were analyzed in combination, five major genotypes were recognized in controls or patients; the frequency differed slightly but not significantly between groups.

CONCLUSION(S)

The Pvu II and Xba I polymorphisms in the ER-alpha gene do not produce different risks of developing uterine leiomyomas.

Physiopathological basis of bone turnover

Bone remodeling involves the continuous removal of bone (bone resorption) followed by synthesis of new bone matrix and subsequent mineralization (bone formation). The principal cells that mediate the boneforming processes of the skeleton are osteoblast cells. They are responsible for the production of the matrix constituents and the differentiation of osteoblasts from stromal cell precursors is stimulated by several hormonal and non-hormonal molecules. On the other hand, the osteoclasts are giant multinucleated cells responsible of bone resorption. They are formed in the bone marrow and mature cells are stimulated by PTH and locally acting agents such as transforming growth factor alpha (TGFalpha), tumor necrosis factor (TNF) interleukin 1 (IL-1) and interleukin 6 (IL-6). The first events during bone remodeling is osteoclast activation, followed by osteoclast formation, polarization constitution of the ruffled border, resorption and ultimately apoptosis. Osteoclast apoptosis is followed by a series of sequential changes in cells in the osteoblast lineage, including osteoblast chemotaxis, proliferation and differentiation, which in turn is followed by formation of mineralized bone and cessation of osteoblast activity. The final phase of the formation process is cessation of osteoblast activity. The resorption lacunae are usually repaired either completely or almost completely. Understanding the sequence of cellular events may be important to better know the mechanisms responsible for bone loss that occurs in age and in several pathological conditions.

Genetic markers of osteoarticular disorders: facts and hopes

Osteoarthritis and osteoporosis are the two most common age-related chronic disorders of articular joints and skeleton, representing a major public health problem in most developed countries. Apart from being influenced by environmental factors, both disorders have a strong genetic component, and there is now considerable evidence from large population studies that these two disorders are inversely related. Thus, an accurate analysis of the genetic component of one of these two multifactorial diseases may provide data of interest for the other. However, the existence of confounding factors must always be borne in mind in interpreting the genetic analysis. In addition, each patient must be given an accurate clinical evaluation, including family history, history of drug treatments, lifestyle, and environment, in order to reduce the background bias. Here, we review the impact of recent work in molecular genetics suggesting that powerful molecular biology techniques will soon make possible both a rapid accumulation of data on the genetics of both disorders and the development of novel diagnostic, prognostic, and therapeutic approaches.

Modulation of the effects of osteoprotegerin (OPG) ligand in a human leukemic cell line by OPG and calcitonin

The discovery of osteoprotegerin (OPG), osteoprotegerin ligand (OPGL), and RANK has elucidated the mechanism by which osteoblasts and stromal cells regulate osteoclastic differentiation and function and mediate the effects exerted by other hormones and cytokines. We have investigated the effects of these novel cytokines on the preosteoclastic cell line FLG 29.1. We show that OPGL alone and in combination with macrophage colony-stimulating factor (CSF-1) dramatically reduced replication and increased tartrate-resistant acid phosphatase activity. However, although FLG29.1 cells appear to adhere to the bone surface, they are not able to form resorption lacunae. OPG and calcitonin completely abolished the differentiation induced by OPGL. RANK was detectable in FLG 29.1 and the number of positive cells was increased by OPGL/CSF-1 treatment while reduced by calcitonin. We propose that calcitonin could interact with the OPG/OPGL, and its effects on RANK may explain in part the action of this hormone in suppressing bone resorption.

[Subclinical hyperthyroidism and hypothyroidism]

Currently, technical methods to obtain precocious and reliable diagnosis of thyroid disorders are available for physicians. Therefore today, patients affected by mild hypo- or hyperthyroidism are more often diagnosed when they are still asymptomatic; these mild forms of thyroid disorder are known as subclinical hypo- and hyperthyroidism. In comparison with '80ties, over the last few years we have observed that patients come to endocrinological examination for subclinical forms of thyroid disorders (particularly for hypothyroidism) more frequently than for severe thyroid diseases. However, before to start a therapy, it is necessary for these patients to determine the causes of subclinical hypo- and hyperthyroidism. The main goals of therapy are to reduce the prevalence of cardiac arrhythmia and osteoporosis of patients with subclinical hyperthyroidism, and to slow down the course of arteriosclerotic disease (linked to hyperlipidemia and/or to hyperhomocysteinemia) of patients with subclinical hypothyroidism.

Efficacy and safety of alendronate for the treatment of osteoporosis in diffuse connective tissue diseases in children: a prospective multicenter study

OBJECTIVE

Osteopenia/osteoporosis is being increasingly reported as a complication of many chronic diseases, even in children. In this preliminary study, we evaluated the effect of an oral bisphosphonate (alendronate) on bone mass in children with diffuse connective tissue diseases.

METHODS

Thirty-eight children with low bone mass were treated with alendronate for 1 year; 38 children who had the same primary disorders as the study patients but in a less severe form served as untreated control patients. We were also able to evaluate changes in bone mass (before and after alendronate) in 16 of the treated patients whose bone mineral density (BMD) had been routinely measured before the present study was initiated.

RESULTS

BMD increased by a mean +/- SD of 14.9 +/- 9.8% (P < 0.002 versus baseline) in the treated patients (reaching the normal range in 13 patients), while the BMD was 2.6 +/- 5% (not significant versus baseline) in the control group (15 had a decrease). Most interestingly, there was a large increase in BMD (15.3 +/-9.9%) after alendronate therapy in the 16 children who had their BMD followed up in the year before the study, during which time they had shown little increase in BMD (1.03 +/- 6.3%), and often a decrease. Considering their condition, increases in the height of all patients was satisfactory. No new fractures were observed after alendronate therapy was initiated.

CONCLUSION

Bisphosphonates can be considered essential components of the treatment of secondary osteoporosis, not only in adults, but also in pediatric patients. Alendronate has a positive effect on secondary osteopenia/osteoporosis in children with connective tissue diseases.

Evidence of a linkage disequilibrium between polymorphisms in the human estrogen receptor alpha gene and their relationship to bone mass variation in postmenopausal Italian women

Bone mineral density (BMD), the major determinant of osteoporotic fracture risk, has a strong genetic component. The discovery that inactivation of estrogen receptor alpha (ERalpha) gene is associated with low BMD indicated ERalpha as a candidate gene for osteoporosis. We have investigated the role of three ERalpha gene polymorphisms [intron 1 PVU:II and XBA:I RFLPs and TA dinucleotide repeat polymorphism 5' upstream of exon 1] in 610 postmenopausal women. There was a strong linkage disequilibrium between intron 1 polymorphic sites and also between these sites and the microsatellite (TA)(n) dinucleotide polymorphism, with a high degree of coincidence of the short TA alleles and the presence of PVU:II and XBA:I restriction sites. No significant relationship between intron 1 RFLPs and BMD was observed. A statistically significant correlation between (TA)(n) repeat allelic variants and lumbar BMD was observed (P = 0.04, ANCOVA), with subjects with a low number of repeats (TA < 15) showing the lowest BMD values. We observed a statistically significant difference in the mean +/- SD number of TA repeats between analyzed women with a vertebral fracture (n = 73) and the non-fracture group, equivalent to 2.9 (95% CI 1.56-5.72) increased fracture risk in women with a low number of repeats (TA < 15). We conclude that in this large population sample the (TA)(n) dinucleotide repeat polymorphism at the 5' end of the ERalpha gene accounts for part of the heritable component of BMD and might prove useful in the prediction of vertebral fracture risk in postmenopausal osteoporosis.

Comparison of quantitative calcaneal ultrasound and dual energy X-ray absorptiometry in the evaluation of osteoporotic risk in children with chronic rheumatic diseases

Osteoporosis is a common complication in children with chronic rheumatic diseases (CRD). Although dual energy X-ray absorptiometry (DXA) is increasingly being used to determine bone mineral density (BMD) in children, it exposes the subject to ionizing radiation and does not provide a measure of true bone density; in fact, in growing bones the increase in BMD is mainly caused by the increase in bone size. In recent years, quantitative ultrasound techniques (QUS) have been used in radiation-free assessment of bone density and "bone quality" by measurement of the ultrasound waves attenuation by bone (BUA). In the present study we made a direct comparison of BUA in the calcaneum, determined by the pediatric contact ultrasound bone analyzer (CUBA) with lumbar BMD measured by DXA, in a group of 6-18-year-old patients with CRD. The study group consisted of 53 patients affected with juvenile rheumatoid arthritis (n = 29), systemic lupus erythematosus (n = 13), and juvenile dermatomyositis (n = 11). Mean age was 13.02 +/- 2.69 years. In 22 patients (19 girls, 3 boys) both DXA and CUBA were repeated after 1 year in order to assess the mean percentage rate of BMD and BUA change over this time. Both lumbar spine BMD and calcaneal BUA measurements were lower in the CRD patients compared with a control group (P < 0.001). Calcaneal BUA was significantly correlated (r = 0.83, P < 0.001) with lumbar spine BMD. Age and sex correction (Z-score) did not change the relationship between BUA and BMD (r = 0.80, P < 0.001). A significant correlation between the mean percentage of variation (delta%) of BMD and BUA (r = 0.76, P < 0.001) was also demonstrated in the 22 patients who were evaluated prospectively. Portability, ease of use, lower cost, and absence of radiation make CUBA a promising means of evaluating BMD in children.

Absence of correlation between BMP-4 polymorphism and postmenopausal osteoporosis in Italian women

Several studies have demonstrated that bone has the power of regeneration and repair. BMPs (bone morphogenetic proteins) are involved in the determination of osteoblast phenotype and bone turnover, therefore genes coding for these proteins, like BMP-4, could be considered potential candidate genes for osteoporosis. We investigated the association of BMP-4 gene polymorphism with osteoporosis in a cohort of 72 osteoporotic, postmenopausal women and 82 unrelated controls. We failed to detect any significant association between this genetic marker and the disease.

Corticosteroid-induced osteoporosis: pathogenesis and prevention

In spite of their adverse side effects, natural and synthetic glucocorticoids (GCs) occupy a unique role in several fields of medicine. They are potent regulators of bone cell growth and differentiation and the actions on the skeleton and related tissues depend on several factors including the dose, duration of the exposure, the steroid type and the species. In humans some of the effects are indirect, such as the regulation of intestinal calcium absorption and PTH secretion. Other effects are due to the cellular response that occurs within the bone microenvironment. It has been well established in in vitro studies that GCs can promote osteoblast differentiation from mesenchymal osteoprogenitors both in rat calvarial culture and in adherent marrow stromal cells. Moreover, GCs are able to enhance expression of the mature osteoblast phenotype, increasing mineralized nodules, osteocalcin secretion, and the bone morphogenetic protein-6 message level. However, the mechanisms by which GCs affect bone metabolism are still unclear. Recent studies with GCs on bone cells suggested that the production of cytokines and growth factors and the expression of their receptors may also be influenced by GCs. In fact, GCs are able to inhibit the synthesis of cytokines, such as interleukin-1 which stimulates bone remodeling by monocytes and macrophages. Moreover, osteoprotegerin, a recently cloned member of the tumor necrosis factor receptor family, is down-regulated by GCs, offering a possible interpretation for the induction of bone resorption by GCs. GC-induced inhibition of bone resorbing cytokines may contribute to explain the therapeutic actions of GCs in several diseases such as rheumatoid arthritis and myeloma. Furthermore, GCs modulate osteoclast recruitment, even if there is no clear explanation for a direct effect of GCs on osteoclastic precursors. Sustained stimulation of matrix degradation by isolated avian osteoclasts incubated with GCs has been reported, as well as cytotoxic effects on osteoclastic cells from neonatal rat long bones.

Cardiovascular effects of parathyroid hormone: a study in healthy subjects and normotensive patients with mild primary hyperparathyroidism

The aim of the study was to evaluate: 1) the cardiovascular function and the autonomic drive to the heart in patients affected by primary hyperparathyroidism (pHPT) with no evidence of renal and cardiovascular complications; 2) the cardiovascular effects of acute administration of PTH in normal subjects. In 14 patients affected by mild asymptomatic pHPT echocardiographic assessment of cardiovascular function and of the mechanic properties of the brachial and carotid artery, heart rate variability and the dispersion of QT interval were performed before and 6 months after successful surgery. Twenty age- and sex-matched healthy subjects were included in the study. Five healthy volunteers underwent a single blind, placebo-controlled, random order, cross-over study with infusion of PTH (hPTH 1-34, 200 U in saline over 5 min) or placebo. Echocardiographic assessment of cardiovascular function, heart rate variability, and QT interval were performed between 20 and 25 min after the start of the infusion and repeated after 15 min of tilting at 60 degrees. In pHPT patients the echocardiographic parameters were normal; left ventricular isovolumetric relaxation time was always in the normal range, but significantly shorter than in control subjects, suggesting an increased sympathetic stimulation. Arterial diameters and thickness, blood pressure, and QT interval were not significantly different with respect to normal subjects and were unchanged 6 months after surgery. pHPT patients lacked the circadian rhythm of the low frequency to high frequency ratio, suggesting an increased sympathetic drive to the heart at nighttime. In normal subjects there were no significant differences in basal echocardiographic measurements during PTH infusion with respect to placebo and in the hemodynamic response to tilt. These results suggest that cardiovascular function is substantially normal in normotensive pHPT patients with mild hypercalcemia. A modulation of the adrenergic control of circulation seems to be associated with hypercalcemia and/or chronic PTH excess, but its biological relevance needs further investigations.

Intraoperative parathormone measurement in patients with multiple endocrine neoplasia type I syndrome and hyperparathyroidism

Total or subtotal parathyroidectomy is considered the treatment of choice for multiple endocrine neoplasia type I (MEN-I)-associated primary hyperparathyroidism (HPT). However, persistent or recurrent HPT is frequently observed. The development of a rapid two-site immunoradiometric assay (IRMA) method for measuring intact parathormone (PTH) has provided a valuable tool for recognizing possible surgical failures. Our experience includes 16 MEN-I patients (10 females, 6 males) of mean age 35.5 years operated on between 1990 and 1996. Total parathyroidectomy (TPTX) with autotransplantation of parathyroid tissue was the standard treatment. Blood samples for PTH measurement were drawn at the induction of anesthesia (basal value), 10 and 20 minutes after the removal of each gland, and 60 minutes after TPTX. Rapid PTH measurement, which required only 15 minutes of incubation at 37 degrees C, showed a highly significant correlation (p < 0.0001) with the standard method. Circulating PTH levels exhibited a stepwise decrease during TPTX, reaching a mean value of 22.3% of the baseline 20 minutes after removal of the last gland. Two patients showed a prompt decrease of PTH after removal of the single enlarged gland, featuring the kinetics observed in the adenomas. One of these two patients was successfully treated with more conservative surgery. None of the patients showed persistence or recurrence of HPT. In our experience, intraoperative measurement of PTH seems to be a valuable adjunct in both the diagnosis of multiglandular involvement and the prediction of surgical treatment in patients with primary parathyroid hyperplasia.

Discriminant capacity of quantitative ultrasound versus dual X-ray absorptiometry to determine cancellous bone loss in ovariectomized rats

The capacity of dual x-ray absorptiometry and quantitative ultrasound to discriminate bone loss and to predict the mechanical and microarchitectural properties of cancellous bone in an animal model of osteopenia was evaluated. Thirty-five female Sprague-Dawley rats (10 months old) were randomized into three groups: baseline group, 10 rats killed at the beginning of the study; ovx group, 15 rats ovariectomized; and sham group, 10 rats sham operated. At the beginning and end of the study, all the animals underwent osteosonography to record the proximal tail (C3 vertebra) bone speed of sound. Sixteen weeks after surgery, the animals were euthanized and the L5-6 lumbar vertebrae of each rat were excised for densitometric, biomechanical (compression test), and histomorphometric studies. Significant differences were found among the groups for final speed of sound (p = 0.01). The L5 bone mineral density of the ovx group decreased by 12.1% (p = 0.049) and 12.6% (p = 0.035) compared, respectively, with baseline and sham groups. The biomechanical parameters of the ovx group decreased by 15-47% compared with the other groups, showing significant differences between the ovx and sham groups both for maximal stress (p = 0.026) and elastic modulus (p = 0.013). Histomorphometric parameters of the ovx group showed significant decreases in comparison with other groups. Logistic regression analysis showed that dual X-ray absorptiometry and quantitative ultrasound discriminate ovariectomized and healthy rats with a similar capacity, classifying correctly all rats used in the model in a range of 61-70%. This similar capacity seems to derive from two different capacities to detect bone changes. Dual X-ray absorptiometry, depending on bone mineralization and density, is able to detect modifications in bone stiffness and strength, confirmed also by the correlation with biomechanical data. On the contrary, quantitative ultrasound seems to depend more on cancellous bone microarchitecural changes because it is correlated to histomorphometric parameters.