Biochemical markers of nutrition in osteoporosis

Reduced prealbumin is associated with bone mineral density in women with osteoporosis

OBJECTIVES

Poor nutritional status is associated with osteoporosis (OP) in postmenopausal women. Moreover, recent studies documented that prealbumin is the best and most widely used parameter to monitor nutrition intervention and is a sensitive predictor of short-term outcome compared with albumin. Therefore, the aim of this study was to examine the association of prealbumin levels with bone mineral density (BMD) in patients with OP.

METHODS

This cross-sectional study recruited 664 women. Prealbumin levels and BMD at femoral neck and lumbar spine were measured. Multiple linear regression analysis was performed to assess the correlation between prealbumin and BMD.

RESULTS

Results of this study found that prealbumin levels dropped gradually as BMD decreased. Furthermore, partial correlation analysis revealed that prealbumin was correlated with BMD after adjusting for confounders. Multiple linear regression analysis showed that prealbumin is a significant factor for reduced BMD in women (for BMD at spine L2-4, β = 0.186, P < 0.001; for BMD at femoral neck, β = 0.180, P < 0.001).

CONCLUSION

Prealbumin was significantly correlated with BMD after adjusting for traditional cardiovascular risk factors. Further prospective research is warranted to further enhance our understanding of the important role of prealbumin in OP.

Skeletal and hormonal effects of magnesium deficiency

Magnesium (Mg) is the second most abundant intracellular cation where it plays an important role in enzyme function and trans-membrane ion transport. Mg deficiency has been associated with a number of clinical disorders including osteoporosis. Osteoporosis is common problem accounting for 2 million fractures per year in the United States at a cost of over $17 billion dollars. The average dietary Mg intake in women is 68% of the RDA, indicating that a large proportion of our population has substantial dietary Mg deficits. The objective of this paper is to review the evidence for Mg deficiency-induced osteoporosis and potential reasons why this occurs, including a cumulative review of work in our laboratories and well as a review of other published studies linking Mg deficiency to osteoporosis. Epidemiological studies have linked dietary Mg deficiency to osteoporosis. As diets deficient in Mg are also deficient in other nutrients that may affect bone, studies have been carried out with select dietary Mg depletion in animal models. Severe Mg deficiency in the rat (Mg at <0.0002% of total diet; normal = 0.05%) causes impaired bone growth, osteopenia and skeletal fragility. This degree of Mg deficiency probably does not commonly exist in the human population. We have therefore induced dietary Mg deprivation in the rat at 10%, 25% and 50% of recommended nutrient requirement. We observed bone loss, decrease in osteoblasts, and an increase in osteoclasts by histomorphometry. Such reduced Mg intake levels are present in our population. We also investigated potential mechanisms for bone loss in Mg deficiency. Studies in humans and and our rat model demonstrated low serum parathyroid hormone (PTH) and 1,25(OH)(2)-vitamin D levels, which may contribute to reduced bone formation. It is known that cytokines can increase osteoclastic bone resorption. Mg deficiency in the rat and/or mouse results in increased skeletal substance P, which in turn stimulates production of cytokines. With the use of immunohistocytochemistry, we found that Mg deficiency resulted in an increase in substance P, TNFalpha and IL1beta. Additional studies assessing the relative presence of receptor activator of nuclear factor kB ligand (RANKL) and its decoy receptor, osteoprotegerin (OPG), found a decrease in OPG and an increase in RANKL favoring an increase in bone resorption. These data support the notion at dietary Mg intake at levels not uncommon in humans may perturb bone and mineral metabolism and be a risk factor for osteoporosis.

Sevelamer restores bone volume and improves bone microarchitecture and strength in aged ovariectomized rats

Sevelamer hydrochloride, a noncalcium phosphate binder, has been shown to reduce coronary artery and aortic calcification, and to improve trabecular bone mineral density in hemodialysis patients with chronic kidney disease. Here, we examined whether sevelamer given orally for 12 wk with normal food could restore bone volume (BV) and strength in aged ovariectomized (OVX) rats starting at 4 wk after OVX. Dual-energy x-ray absorptiometry, microcomputerized tomography, and bone histomorphometry analyses showed that OVX animals receiving sevelamer had increased trabecular BV (51%), trabecular number (43%), trabecular thickness (9%), cortical thickness (16%), mineral apposition rate (103%), bone formation rate (25%), and enhanced cortical and trabecular bone mechanical strength as compared with OVX rats. Sevelamer decreased collagen C telopeptide, increased osteocalcin levels, and decreased phosphate and magnesium levels without affecting calcium levels in the blood. Although sevelamer was not absorbed systemically, it stimulated osteoblast differentiation in BM-derived mesenchymal stem cell cultures, as evaluated by alkaline phosphatase positive colony-forming units, and inhibited recombinant human soluble receptor activator of nuclear factor-kappaB ligand-induced osteoclast differentiation, as evaluated by tartrate-resistant acid phosphatase positive cells in bone mineral-hematopoietic stem cell cultures. Surface enhanced laser desorption/ionization time-of-flight mass spectrometry analysis revealed that 69 proteins were differently expressed after OVX, of which 30% (20 of 69) were reversed to sham activity after sevelamer intake. PTH, fibroblast growth factor-23, and cytokine profile in serum were not significantly changed. Together, these results suggest that sevelamer in food increases the BV and improves biomechanical properties of bone in OVX rats.

Reduction of dietary magnesium by only 50% in the rat disrupts bone and mineral metabolism

INTRODUCTION

The objective of this study was to determine the effect of a moderate reduction of dietary magnesium [50% of nutrient requirement (50% NR)] on bone and mineral metabolism in the rat, and to explore possible mechanisms for the resultant reduced bone mass.

METHODS

Female rats were 6 weeks of age at the start of study. Serum magnesium (Mg), calcium (Ca), parathyroid hormone (PTH), 1,25(OH)(2)-vitamin D, alkaline phosphatase, osteocalcin, and pyridinoline were measured during the study at 3- and 6-month time points in control (dietary Mg of 100% NR) and Mg-deficient animals (dietary Mg at 50% NR). Femurs and tibias were also collected for mineral content analyses, micro-computerized tomography, histomorphometry, and immunohistochemical localization of substance P, TNFalpha, and IL-1beta at 3 and 6 months.

RESULTS

Although no significant change in serum Mg was observed, Mg deficiency developed, as assessed by the reduction in bone Mg content at the 3- and 6-month time points (0.69+/-0.05 and 0.62+/-0.04% ash, respectively, in the Mg depletion group compared to 0.74+/-0.04 and 0.67+/-0.04% ash, respectively, in the control group; p=0.0009). Hypercalcemia did not develop. Although serum Ca level remained in the normal range, it fell significantly with Mg depletion at 3 and 6 months (10.4+/-0.3 and 9.6+/-0.3 mg/dl, respectively, compared to 10.5+/-0.4 and 10.1+/-0.6 mg/dl, respectively, in the control group; p=0.0076). The fall in serum Ca in the Mg-depleted animals was associated with a fall in serum PTH concentration between 3 and 6 months (603+/-286 and 505+/-302 pg/ml, respectively, although it was still higher than the control). The serum 1,25(OH)(2)-vitamin D level was significantly lower in the Mg depletion group at 6 months (10.6+/-7.1 pg/ml) than in the control (23.5+/- 12.7 pg/ml) (p<0.01 by the t-test). In Mg-deficient animals, no difference was noted in markers of bone turnover. Trabecular bone mineral content gain was less over time in the distal femur with Mg deficiency at 3 and 6 months (0.028+/-0.005 and 0.038+/-0.007 g, respectively, compared to 0.027+/-0.004 and 0.048+/-0.006 g, respectively, in the control group; p<0.005). Histomorphometry at these time points demonstrated decreased trabecular bone volume (15.76+/-1.93 and 14.19+/-1.85%, respectively, compared to 19.24+/-3.10 and 17.30+/-2.59%, respectively, in the control group; p=0.001). Osteoclast number was also significantly increased with Mg depletion (9.07+/-1.21 and 13.84+/-2.06, respectively, compared to 7.02+/-1.89 and 10.47+/-1.33, respectively, in the control group; p=0.0003). Relative to the control, immunohistochemical staining intensity of the neurotransmitter substance P and of the cytokines TNFalpha and IL-1beta was increased in cells of the bone microenvironment in the Mg depletion group, suggesting that inflammatory cytokines may contribute to bone loss.

CONCLUSION

These data demonstrate that Mg intake of 50% NR in the rat causes a reduced bone mineral content and reduced volume of the distal femur. These changes may be related to altered PTH and 1,25(OH)(2)-vitamin D formation or action as well as to an increase release of substance P and the inflammatory cytokines TNFalpha and IL-1beta.

Vitamin A intake and osteoporosis: a clinical review

BACKGROUND

If osteoporosis is linked with vitamin A (Vit A) A consumption, millions of people could be affected.

METHODS

A MEDLINE search was performed with keywords retinol, beta-carotene, and osteoporosis.

RESULTS

Of 20 clinical studies, 3 were randomized controlled trials (RCTs), 14 were observational studies, and 3 were case reports. Most (8) observational studies were cross-sectional. Oral retinoyl palmitate (RP) in high doses induces fractures and radiographic osteoporosis in animals. Retinol intake from diet or supplements is negatively associated with lumbar, femoral neck, and trochanter bone mineral density (BMD). There is a graded increase in relative risk of hip fracture with increasing retinol intake, attributable primarily to retinol (either from diet or supplements) but not beta-carotene intake. Higher serum retinol levels are associated with higher risk of any fracture and with higher risk of hip fracture, whereas there is no evidence of harm associated with beta-carotene intake. The few RCTs involve serum markers of bone metabolism, not bone density or fracture outcomes. Observational studies are generally consistent in finding harm from either dietary or supplemental retinol intake on BMD and hip fracture risk. Total Vit A intake is more important than source in determining harm. Adverse effects may occur at a level of retinol intake that is only about twice the current recommendation for adult females.

CONCLUSIONS

It is not yet possible to set a specific level of retinol intake above which bone health is compromised. Pending further investigation, Vit A supplements should not be used with the express goal of improving bone health.

Serum fructosamine level and the risk of hip fracture in elderly women: a case-cohort study within the study of osteoporotic fractures

PURPOSE

While a high serum fructosamine level may be an indicator of undiagnosed diabetes, a low level may be indicative of poor nutrition or frailty. As malnutrition is a risk factor for osteoporosis, low serum fructosamine levels may be associated with an increased risk of osteoporotic fracture. We examined the association between serum fructosamine levels and the risk of subsequent hip and vertebral fracture.

SUBJECTS AND METHODS

We performed a case-cohort study within the Study of Osteoporotic Fractures. Subjects were elderly, ambulatory, community-dwelling, Caucasian, women. Fructosamine levels were measured in baseline serum. Incident vertebral fractures were identified by comparing baseline spinal radiographs to those obtained an average of 3.5 years later. Hip fractures were confirmed by radiograph. We randomly selected 101 women who suffered a hip fracture, 100 women who developed a vertebral fracture, and 276 controls. We compared fructosamine levels in women with subsequent osteoporotic fractures to controls. All analyses were adjusted for age, weight, and use of estrogens.

RESULTS

Women with fructosamine levels in the lowest decile (< or = 223 micromol/L) had a three-fold increase in the risk of hip fracture (95% confidence interval 1.4-6.4), compared with all other women. Adjustment for markers of frailty, including smoking, functional status, and serum albumin levels, reduced the strength of this association. No clear association was observed between serum fructosamine level and the risk of vertebral fracture.

CONCLUSION

Low serum fructosamine levels, which likely reflect frailty or malnutrition, may be a useful clinical tool to identify women at risk for hip fracture.

Parathyroid hormone increases circulating levels of fibronectin in vivo: modulating effect of ovariectomy

To explore the effect of PTH on circulating levels of fibronectin (FN), adult female Sprague-Dawley rats were implanted with Alzet minipumps prepared to deliver 7 pmol/h x kg BW of either human PTH (1-34) or human PTH (1-84). Both forms of the hormone led to significant and progressive increases in circulating levels of FN over the 72-h study period (P < 0.001). However, at every time point, circulating levels of FN with human PTH (hPTH) (1-84) infusion were significantly higher than with hPTH (1-34), such that at the end of the infusion, mean levels in the hPTH (1-34) group were 32.2 +/- 1.4 ng/ml, in the hPTH (1-84) group 93.8 +/- 5.4 ng/ml, and in the vehicle infused group 14.6 +/- 0.7 ng/ml. The greater agonist efficacy of hPTH (1-84) was not explained by differences in circulating levels of the hormones, and both forms of the hormone were equipotent at stimulating cAMP production by ROS 17/2.8 cells. However, hPTH (1-84) remained a more effective agonist than hPTH (1-34) at stimulating FN production in these cells (P < 0.001). Nephrectomy did not blunt the ability of PTH to increase circulating FN in vivo, indicating that the kidney was not the source of the FN produced in response to PTH. Pretreament with the potent bisphosphonate APD to block bone resorption also did not blunt the in vivo response to PTH. Parathyroidectomy did not blunt the response. Cultured fetal rat bones showed a significant 2.4-fold increase in FN production when treated with PTH. Consistent with our earlier in vitro studies (Endocrinology, 135: 1639-1644, 1994), estrogen deficiency, induced by ovariectomy, significantly diminished the ability of PTH to increase circulating FN levels in vivo (P < 0.001). We conclude that PTH increases circulating levels of FN in vivo and may be a physiologic regulator for the plasma form of this glycoprotein. The effects of PTH on circulating FN may reflect the anabolic properties of the hormone in bone and the blunted response following estrogen withdrawal could be a manifestation of the diminished bone formation vis-à-vis resorption seen in the estrogen deficient state.

Vertebral and metacarpal morphometry as indicators of nutritional improvement

Because of the importance of nutrition in the development of bone mass, we studied the nutritional state, and bone state by means of metacarpal radiogrammetric measurements and vertebral morphometry in a group of 40 premenopausal women born between 1960 and 1970, mean age 29 +/- 5 years, and in another group of 40 postmenopausal women born between 1934 and 1944, mean age 55 +/- 4 years. Both groups were considered normal, the main characteristic distinguishing them being that the women born between 1934 and 1944 grew up in a period of widespread malnutrition in Spain and the women born between 1960 and 1970 grew up in a period of normal nutrition. Protein, carbohydrate and fat intake in these two periods differed significantly (p < 0.0001 in the three cases by Fischer's exact test). The values of the metacarpal measurements, anterior height of the dorsal vertebrae from T-4 to T-12, and posterior height from L-1 to L-4 between the premenopausal and postmenopausal groups of women were significantly different (p < 0.001) (Anova test). These findings show the importance of nutrition in the development of bone mass during childhood.

Assessment of plasma fibronectin in malnourished Nigerian children

BACKGROUND

Severe malnutrition is associated with septic infections. The concentrations of fibronectin, albumin, and transferrin in plasma were measured in three groups of children with protein-energy malnutrition, aged 1-3 years, each group comprising 20 children. The aim of which was to test whether plasma fibronectin, being an opsonic protein, was reduced in such children, and if it was a useful index for assessing the severity of malnutrition.

METHODS

The concentrations of fibronectin, albumin, and transferrin in plasma were studied by enzyme immunoassay/ immunoblotting, spectrophotometry and immunoturbidimetry respectively.

RESULTS

All values were significantly lower in the patients with malnutrition than in the age- and sex-matched well-nourished Nigerian reference children. Within the malnourished group, the fibronectin value was evenly reduced in all subgroups. Albumin and transferrin values were lowest in the patients with kwashiorkor, highest in the marasmic patients, and intermediate in the patients with marasmic kwashiorkor; the values correlated mutually in individual cases as well, but not with the fibronectin levels. Neither plasma fibronectin fragmentation nor tissue fibronectin was detected in any patient with malnutrition or in the reference subjects.

CONCLUSIONS

The reduced plasma fibronectin values in these patients may be due to reduced synthesis by the liver, as evidenced by the equally reduced albumin and transferrin concentrations and/or to the multiple infections characteristic of the patients.

Vitamin K nutrition and osteoporosis

Although the abundance of vitamin K-dependent proteins in bone suggests an important function, the precise role of vitamin K in skeletal health remains to be determined. Serum concentrations of vitamin K are reportedly reduced in older individuals and persons with osteoporotic fracture. Whether this is causally related to vitamin K insufficiency or simply reflects inadequate nutritional status is unclear. Circulating levels of undercarboxylated osteocalcin may be a sensitive marker of vitamin K inadequacy and have been reported to be increased in both postmenopausal women and individuals who sustained hip fracture. It is also possible that vitamin K indirectly affects the skeleton via control of renal calcium excretion. The effect of vitamin K antagonists (oral anticoagulants) on both renal calcium excretion and bone density is controversial. Thus, many of the reports implicating a role for vitamin K insufficiency in the development of osteoporosis are conflicting. This review summarizes current knowledge regarding a possible role of vitamin K insufficiency in the pathogenesis of osteoporosis.

Magnesium supplementation and osteoporosis

Among other things, magnesium regulates active calcium transport. As a result, there has been a growing interest in the role of magnesium (Mg) in bone metabolism. A group of menopausal women were given magnesium hydroxide to assess the effects of magnesium on bone density. At the end of the 2-year study, magnesium therapy appears to have prevented fractures and resulted in a significant increase in bone density.