Osteocalcin levels in patients with hyper- and hypothyroidism

Diagnosis and therapeutic approach to bone health in patients with hypopituitarism

The results of many studies in recent years indicate a significant impact of pituitary function on bone health. The proper function of the pituitary gland has a significant impact on the growth of the skeleton and the appearance of sexual dimorphism. It is also responsible for achieving peak bone mass, which protects against the development of osteoporosis and fractures later in life. It is also liable for the proper remodeling of the skeleton, which is a physiological mechanism managing the proper mechanical resistance of bones and the possibility of its regeneration after injuries. Pituitary diseases causing hypofunction and deficiency of tropic hormones, and thus deficiency of key hormones of effector organs, have a negative impact on the skeleton, resulting in reduced bone mass and susceptibility to pathological fractures. The early appearance of pituitary dysfunction, i.e. in the pre-pubertal period, is responsible for failure to achieve peak bone mass, and thus the risk of developing osteoporosis in later years. This argues for the need for a thorough assessment of patients with hypopituitarism, not only in terms of metabolic disorders, but also in terms of bone disorders. Early and properly performed treatment may prevent patients from developing the bone complications that are so common in this pathology. The aim of this review is to discuss the physiological, pathophysiological, and clinical insights of bone involvement in pituitary disease.

Biochemical bone turnover markers in hormonal disorders in adults: a narrative review

BACKGROUND

Hormonal disorders are often associated with abnormal levels of bone turnover markers (BTMs). N-terminal propeptide of type I procollagen (PINP) and serum C-terminal cross-linking telopeptide of type I collagen (CTX-I) are the reference markers of bone formation and bone resorption, respectively.

METHODS

A comprehensive literature search within the MEDLINE and Web of Science databases was performed.

RESULTS

Acromegaly is associated with higher BTM levels, which decrease during the remission after treatment. Adult-onset growth hormone deficiency is often associated with decreased BTM levels. Growth hormone replacement therapy stimulates bone turnover and increases BTM levels. Hypothyroidism is characterized by general slowing of bone metabolism which is reflected by lower BTM levels. The replacement thyroid hormone therapy increases the bone turnover rate and BTM levels increase. Patients with thyroid cancer receive a suppressive dose of thyroid hormones and may have slightly elevated BTM levels. Patients with overt hyperthyroidism had higher BTM levels and anti-thyroid therapy induces a rapid decrease in the BTM levels. Patients with overt primary hyperparathyroidism have higher BTM levels, whereas those with asymptomatic and normocalcemic hyperparathyroidism usually have normal BTM levels. Hypoparathyroidism is characterized by slightly decreased BTM levels. Cushing's syndrome is characterized consistently by markedly decreased osteocalcin concentration, whereas data on other BTMs are discordant.

CONCLUSIONS

BTMs help us to better understand mechanisms of the impact of hormonal disorders and their treatment on bone metabolism. However, it is unknown whether BTMs may be used to monitor the effect of their treatments on bone in the clinical practice.

Quantitative computed tomography measurements of bone mineral density in prepubertal children with congenital hypothyroidism treated with L-thyroxine

Low bone density (BD) has been reported in patients with hyperthyroidism. Whether or not levothyroxine (LT4) therapy in children with congenital hypothyroidism (CH) affects BD is unclear. Medical records of 45 patients with various etiologies of CH who had at least one BD measurement (32 female, mean age 7.6 +/- 2.6 years) were reviewed. The mean LT4 dose was 3.6 +/- 0.88 microg/kg/day. Cancellous bone density (CaBD) was measured by quantitative computed tomography (CT) in all 45 patients and 20 had measurements of cortical bone density (CoBD), cross-sectional area (CSA) and cortical bone area (CBA) of the femur. TSH levels were considered partially or completely suppressed when values were <1.0 or <0.5 microIU/ml, respectively. The control group consisted of age- and gender-matched healthy children. No significant differences were found in CaBD, CoBD, CSA, or CBA between patients with CH and controls. There were no significant differences between initial and subsequent BD measurements. No correlations were found between CaBD and etiology of CH, dose or duration of LT4 therapy, or serum TSH. In pre-pubertal children with CH, LT4 appears to have no significant effect on BD. Moreover, absence or hypoplasia of the thyroid parenchyma appears to have no significant impact on bone formation within the first 10 years of life.

Assessment of sex hormone-binding globulin and osteocalcin in patients undergoing coronary artery bypass graft surgery

OBJECTIVE

To determine sex hormone-binding globulin (SHBG) and osteocalcin (OC) levels in patients undergoing coronary artery bypass graft surgery to clarify the status of peripheral thyroid metabolism and to correlate SHBG and OC with thyroid hormones and adverse postoperative events.

DESIGN

Prospective study.

SETTING

University medical center.

PARTICIPANTS

Fifty randomly selected patients undergoing coronary artery bypass graft surgery.

INTERVENTIONS

On the morning of surgery before induction of anesthesia; 30 minutes after cross-clamping of the aorta; 2 hours and 6 hours after aortic cross-clamp removal; and on the first, second, third, and seventh postoperative mornings, blood samples were drawn and analyzed for OC, SHBG, triiodothyronine (tT3), free T3 (fT3), thyroxine (tT4), free T4 (fT4), thyroid-stimulating hormone, and thyroid-binding globulin. Adverse postoperative events were recorded.

MEASUREMENTS AND MAIN RESULTS

Mean tT3 and fT3 decreased on average by 35% and 18% but remained within the normal range perioperatively. Similarly, mean SHBG and OC remained within the normal range. More than half of the patients investigated (60%) had OC concentrations below the normal range. Patients with pathologically decreased tT3 (n = 6) and tT4 (n = 16) intraoperatively and postoperatively had SHBG and OC concentrations similar to those in patients with normal tT3 and tT4 levels. Patients with postoperative complications had significantly lower OC levels preoperatively and on the first postoperative morning than those with an uneventful postoperative recovery.

CONCLUSION

Despite significant intraoperative and postoperative decreases in levels of thyroid hormones, low T3 syndrome was rare in this patient population. Unchanged concentrations of SHBG and OC in patients with pathologically decreased tT3 or tT4 suggest normal local thyroid exposure at the tissue sites in these patients. OC may act as a predictor for postoperative outcome.

Effect of endogenous subclinical hyperthyroidism on bone metabolism and bone mineral density in premenopausal women

In this cross-sectional study, we evaluated 15 premenopausal women to elucidate whether bone turnover is increased and bone mineral density is reduced due to endogenous subclinical hyperthyroidism. Each patient had normal free thyroxine (FT4) and free triiodothyronine (FT3) levels associated with a stable suppression (<0.1 mU/L) of serum thyrotropin (TSH) levels during a period ranging between 6 and 11 months. Metabolic parameters of bone turnover (serum osteocalcin, bone specific alkaline phosphatase, procollagen I C-terminal peptide reflecting bone formation; urinary deoxypyridinoline and calcium excretion reflecting bone resorption) were assessed. Bone mineral density was measured at lumbar 1-4 vertebrae, femoral neck, and the forearm (midshaft radius and distal radius) by dual energy x-ray absorptiometry. All measurements were compared with 15 healthy age-, height-, and weight-matched premenopausal women who served as control group. Our findings suggest that endogenous subclinical hyperthyroidism is not associated with increased bone turnover, and bone mineral density is not reduced in premenopausal women, at least in the short term.

Bone mineral metabolism and thyroid replacement therapy in congenital hypothyroid infants and young children

Impairment of calcium metabolism and low bone density have been found in hypothyroid adults. We investigated the effect of thyroid replacement therapy on calcium metabolism and bone mineralization in congenital hypothyroid (CH) infants and children. One hundred and 16 Caucasian CH consecutive patients were studied and were grouped according to their age: 23 patients at diagnosis, 20 at 3 mo, 24 at 6 mo, 25 at 12 mo and 24 at 36 mo. Thyroid replacement therapy was started at an initial dose of 6-8 micrograms/kg/day of L-thyroxine, and then decreased progressively. Calcium, phosphorus, magnesium, alkaline phosphatase (AP), parathyroid hormone (PTH) and osteocalcin (BGP) were measured as calcium metabolism indices. Bone mineral content (BMC) was measured at the mid-portion of the right radius AP, PTH and BGP concentrations were significantly higher in subjects at 3 mo of age (p < 0.05). This rise coincided with the end of the period of maximum dosage of L-thyroxine. Mild asymptomatic hypercalcemia was observed in 20 patients. All the other indices did not differ between age groups. BMC values and BMC annual increment were not different from those calculated for age-matched controls. We found that L-thyroxine replacement therapy does not alter bone mineralization of CH infants and children. Only a transitory increase of osteoblastic function was observed after the first few months of therapy.

Thyroid hormone suppresses the differentiation of osteoprogenitor cells to osteoblasts, but enhances functional activities of mature osteoblasts in cultured rat calvaria cells

The effects of thyroid hormone on osteoblastic differentiation and activity were studied in fetal rat calvaria (RC) cells cultured for up to 30 days in medium supplemented with thyroid hormone-depleted serum. In this condition, the cells proliferated and differentiated to form mineralized bone nodules (BN) and expressed osteoblastic markers such as alkaline phosphatase (ALP), osteocalcin (OCN), and osteopontin (OPN). The continuous presence of triiodothyronine (T3) at 10(-9)-10(-8) M in the medium inhibited the osteoblastic differentiation: 34% decrease in ALP activity on day 12 and 60% decrease in BN formation on day 15 at 10(-8) M. T3 at these doses had no effect on the DNA content of RC cells at confluence (day 6). Short-term (48-h) exposure of T3 at 10(-9) M or higher decreased ALP activity when RC cells were differentiating (days 7-11). However, when BN formation by the cells had already reached a plateau (day 28), the activity was increased by treatment with T3 at 10(-7)-10(-6) M. OCN production was increased dose dependently by this treatment with T3 (2.1-fold and 1.3-fold of control at 10(-8) M on days 11 and 28, respectively). Similar increases were observed in the levels of OCN mRNA. In addition, increases in phosphorylated OPN in the medium (day 11) and mineralized matrix (day 28) were observed (1.5-fold at 10(-8)-10(-6) M), while OPN synthesis and the level of its mRNA were depressed by T3 (60-70% of control at 10(-8) M). These results suggest that T3 regulates osteoblastic differentiation and activity depending on the state of cell differentiation: T3 suppresses the differentiation of osteoprogenitor cells to osteoblasts, but enhances the functional activity of mature osteoblasts.

Bone mineral density in patients with endogenous subclinical hyperthyroidism: is this thyroid status a risk factor for osteoporosis?

OBJECTIVE

The aim of the present study was to elucidate whether endogenous subclinical hyperthyroidism due to a solitary autonomously functioning thyroid nodule affects bone metabolism and is a risk factor for osteoporosis.

DESIGN

In a cross-sectional study measurements of bone mineral density were performed in premenopausal and post-menopausal women. Patients were categorized into non-toxic nodular goitre (n = 32), subclinical hyperthyroid (n = 37) and toxic solitary autonomous thyroid nodule (n = 22) subgroups and the results were compared with those of sex and age-matched control reference population (n = 68).

MEASUREMENTS

Lumbar spine and femoral neck bone mineral densities were measured by dual energy X-ray absorptiometry. Single-photon absorptiometry was applied to the measurement of bone mineral content in the midshaft of the radius.

RESULTS

In the non-toxic nodular goitre group, bone densities for all the scanned sites did not differ from the sex and age-matched reference population. At the L2-4 scanning site a significant decrease in the bone mineral density could be observed only in the toxic nodular goitre group and this decrease was more marked in the postmenopausal (P < 0.001) than in the premenopausal females (P < 0.05). At the femoral neck and midshaft radius the mean densitometric values were slightly, but significantly, lower only in the post-menopausal subclinical hyperthyroid group compared with the reference population (P < 0.01). The bone mineral density of the femoral neck, as well as the bone mineral content of the midshaft radius, was significantly decreased in both the premenopausal and post-menopausal patients with a toxic solitary nodule.

CONCLUSION

This study indicates that the bone mineral density of the lumbar spine, femoral neck and the midshaft of the radius are not significantly decreased in premenopausal patients with endogenous subclinical hyperthyroidism resulting from a solitary autonomously functioning thyroid nodule. Conversely, findings hint at the possibility that long-lasting endogenous subclinical hyperthyroidism may be a contributing factor to the development of osteoporosis in some post-menopausal women, mostly at sites where cortical bone preponderates.

Serum concentrations of osteocalcin in patients with hyperthyroidism, hypothyroidism and subacute thyroiditis

Serum concentration of osteocalcin (OC) was measured in sera from untreated patients with Graves' disease, hypothyroidism due to Hashimoto's thyroiditis, and subacute thyroiditis. Serum concentration of OC in Graves' disease and hypothyroidism were 14.1 +/- 5.6 micrograms/L and 3.8 +/- 2.7 micrograms/L, respectively which were significantly different from that of healthy subjects (Graves' disease, p less than 0.001, hypothyroidism, p less than 0.01). Serum concentration of OC in patients with subacute thyroiditis was 8.0 +/- 3.5 micrograms/L which was not statistically different from age-matched normal controls. Serial measurement of serum OC for 24 mo in 15 patients with Graves' disease after initiation of antithyroid drugs disclosed that the decline of serum OC was obtained only 24 mo after antithyroid drug therapy. On the other hand, in hypothyroid patients, increased serum OC was observed after 1-2 months treatment of L-T4. Correlation coefficients between serum concentrations of OC and T3, T4, FT3 or FT4 in all the patients with thyroid disorders were 0.66, 0.51, 0.50 and 0.54, respectively, which were statistically significant (all, p less than 0.001). These results suggest that osteoblastic activity is enhanced in hyperthyroidism and suppressed in hypothyroidism. In hyperthyroid patients, despite of normalization of FT4 concentration in relatively short period (within 3-4 mo), it took 24 mo after initiation of antithyroid drugs for OC to normalize, suggesting not only thyroid hormone per se but also some unknown factor(s) participates in serum OC secretion. In contrast to thyrotoxic patients, rapid increase in serum OC after initiation of supplemental L-T4 treatment in hypothyroidism was observed, suggesting a direct effect of thyroid hormone on the osteoblasts in patients with hypothyroidism.

Determination of bone mineral density by quantitative computed tomography and single photon absorptiometry in subclinical hyperthyroidism: a risk of early osteopaenia in post-menopausal women

OBJECTIVE

There is evidence that treatment with L-thyroxine increases the risk of early osteopaenia. The aim of our study was to investigate the effect of subclinical hyperthyroidism in patients on TSH-suppressive L-thyroxine in view of the increased risk of decalcification.

DESIGN

Measurements of bone mineral density were performed in patients with subclinical hyperthyroidism at different scanning sites of varying trabecular portion. Bone mineral values as well as biochemical data were compared to those of normal controls.

PATIENTS

Fifty patients (nine men, 25 premenopausal and 16 post-menopausal women) on TSH-suppressive doses of L-thyroxine were investigated after removal of thyroid cancer.

MEASUREMENTS

Dual energy quantitative computed tomography was used for osteodensitometry in the lumbar spine. Single photon absorptiometry from a 125I source was applied to the calcaneus, midshaft radius and distal as well as proximal scanning sites of the distal radius. Normal bone mineral values for each measurement site were taken from healthy reference populations.

RESULTS

A significant decrease of bone mineral density in the calcaneus was found in 26 of 50 patients. Bone mass assessment yielded a 9.1% decrease of mean bone mineral content in all patients compared to controls (P less than 0.01). The decrease in post-menopausal women was 22% (P less than 0.001). In premenopausal women bone mineral density changes in the calcaneus were not statistically significant. Cortical measurement sites like the midshaft radius and the proximal scanning site of the distal forearm showed a 14.8% (P less than 0.05) and 10.8% (P = NS) decalcification in post-menopausal women but normal values at the distal scanning site. The lumbar spine was not affected by subclinical hyperthyroidism in either pre or post-menopausal women. In hypoparathyroid patients, bone density did not essentially differ from normals. There was no significant correlation between bone mineral values and duration of treatment or osteocalcin values.

CONCLUSIONS

Our data suggest that TSH suppressive L-thyroxine treatment has a detrimental effect on the appendicular skeleton in post-menopausal women. Additional effects of oestrogen deficiency and subclinical hyperthyroidism might lead to accelerated bone loss requiring close supervision to determine the smallest dose needed for suppression of the pituitary-thyroid axis.

Increased rat femur osteocalcin mRNA concentrations following in vivo administration of thyroid hormone

Thyroid hormone has a direct resorptive effect on bone. Thyroid hormone therapy in doses that suppress pituitary TSH production result in a reduction in bone density. Osteocalcin is a bone matrix protein. Serum levels are a sensitive marker for bone turnover and are increased in hyperthyroid patients. In order to establish an animal model to study the effects of thyroid hormone on bone turnover, we measured rat femur osteocalcin mRNA following in vivo administration of thyroid hormone. Young CD rats weighing 60-90 g were given daily ip injections of T3, T4, or saline (control) for 12 days. Blood was obtained for radioimmunoassays, and RNA was extracted from femurs and analyzed by Northern blot using a 60-mer synthetic oligonucleotide probe corresponding to bases 360-420 of rat osteocalcin mRNA, labeled with [32P] ATP by 5'-end-labeling. Serum TSH concentrations were suppressed to subnormal levels by the lowest doses of T3 and T4, and to undetectable levels by the higher doses. Increases in serum T3 and T4 concentrations were proportional to the dose of each administered hormone. T3, 5 and 10 micrograms/100 g body weight, resulted in a 43% and 62% increase in osteocalcin mRNA, respectively. T4, 5, 10, and 20 micrograms/100 g body weight, resulted in a 35%, 47%, and 135% increase in osteocalcin mRNA, respectively. These data demonstrate that in vivo administration of either T4 or T3 to young rats results in a significant dose-dependent increase in femur osteocalcin mRNA concentrations.

Effect of thyroxine therapy on bone metabolism in substituted hypothyroid patients with normal or suppressed levels of TSH

The statement that pituitary hyperthyroidism reflects peripheral hyperthyroidism is still controversial. To evaluate a possible relationship between the calcium and the thyroid metabolism, 29 women with thyroxine (T4) substituted hypothyroidism were examined. They were separated into two groups, one with normal (0.15 to 6 mU/l) and one with suppressed TSH (less than 0.15 mU/l). All the women were judged euthyroid both by their T4 and T3 and by their clinics. The daily dose of T4 (median 0.15 mg in both groups) had been unchanged and TSH level had been stable during the previous six months. Bone mineral content (BMC) of the lumbar spine, bone mineral density (BMD) of left and right collum femoris, serum alkaline phosphatase activity (AP), serum concentration of osteocalcin (Ost) and urinary excretion of hydroxyproline/creatine (Hpr/crea) were similar in the two groups. Furthermore, sex- hormone-binding-globulin (SHBG) was equal in the two groups, but significantly higher than in normals (p less than 0.01). A significant positive correlation was found between serum Ost and Hpr/crea (p less than 0.05) indicating a balanced state where bone formation equals bone resorption. AP failed to correlate to Ost and Hpr/crea because the AP raises from both bone and liver of bone and liver metabolism whereas the two others predominantly reflect bone metabolism. SHBG, being a marker of liver metabolism, was elevated in both groups, probably because of the oral administration of T4. Our data suggest that euthyroid, T4 substituted patients have a normal calcium metabolism whether TSH levels are suppressed or not.

Thyroid hormone 5'-deiodinase activity, nuclear binding, and effects on mitogenesis in UMR-106 osteoblastic osteosarcoma cells

The hyperthyroid state in vivo is associated with an increase in osteoblast number and activity, suggesting that thyroid hormone may stimulate osteoblast replication and function. We therefore examined the effects of T3 (16-1170 pM) on replication rate as assessed by cell counts in UMR-106 osteoblastic osteosarcoma cells cultured for 5-10 days in medium supplemented with 10% hormone-stripped fetal calf serum (FCS). Despite the virtual absence of thyroid hormone in the control medium (total T3 concentration, 0.02 ng/ml), the addition of T3 in concentrations to 1000 pM did not increase the cell replication rate. At higher T3 concentrations, a slight decrease in growth rate was observed. No significant 5'-monodeiodinase activity was detected in UMR-106 cell homogenates. However, nuclear binding of T3 was demonstrated in intact cells. A high-affinity nuclear binding component was identified with a Ka of 2.6 x 10(10) M-1 and a maximum binding capacity of 7.7 pg T3 per mg DNA, equivalent to 51 binding sites per cell nucleus. A lower affinity nuclear T3 binding component with a Ka of 1.8 x 10(9) M-1 was also identified. Thus, despite the presence of nuclear T3 receptors, UMR-106 cells do not exhibit a mitogenic response to T3.