Biochemical markers of nutrition in type-I and type-II osteoporosis.

We studied nutritional deficits, using as markers the levels of transferrin, retinol-binding protein, and prealbumin, in 20 women with osteoporotic hip fractures (type II), 40 women with vertebral fractures (type I), and two groups of age-matched control subjects. The concentrations of all three nutritional markers were lower in the two groups of patients than in their matched controls, and in type-I as compared with type-II osteoporosis. In the osteoporotic patients, simple linear regression showed a significant correlation between the variables which we studied (r2 ranged from 0.5 to 0.7; p < 0.001), the best correlation being between prealbumin and retinol-binding protein in type-II osteoporosis. Our results suggest that there is a more marked nutritional deficit in type-II than in type-I osteoporosis.

Biochemical markers of nutrition in elite-marathon runners.

Although diet surveys have been made in marathon runners, as far as we know their nutritional state has not been evaluated by measurement of the so-called biological markers of nutrition, such as transferrin, retinol-binding protein, and prealbumin. We measured the levels of these substances in 18 marathon runners (11 men and 7 women; mean age 26.9 +/- 4.0 years) and in 22 controls (13 men and 9 women; mean age 26.2 +/- 3.6 years). As some of these markers are zinc-dependent, serum zinc levels also were measured. Likewise, serum calcium, phosphorus, and magnesium levels were measured to ascertain the athletes' mineral status. Calcium corrected for proteins, phosphorus, magnesium, and zinc did not differ between the marathon runners and controls; likewise, there were no differences in serum ferritin and glucose levels. As regards the biological markers of nutrition, prealbumin levels were higher in athletes than in controls (31.7 +/- 4.7 vs 28.9 +/- 4.8 mg/dl, p < 0.025). There were no differences in the levels of retinol-binding protein and transferrin between runners and controls.

Zinc, biochemical markers of nutrition, and type I osteoporosis.

Having observed previously that the reduction of levels of biological markers of nutrition in postmenopausal osteoporosis may be related to zinc deficiency, we measured plasma and urinary zinc concentrations in 30 women with postmenopausal osteoporosis and in 30 healthy postmenopausal women who served as controls. Plasma zinc levels did not differ between groups, but urinary zinc excretion was significantly higher in the women with postmenopausal osteoporosis (p = 0.002). The relation between total body bone mineral content corrected for body weight (TBBMC/W) and markers of nutrition was significant (multiple regression analysis: p < 0.0001) in the women with postmenopausal osteoporosis but not in the healthy postmenopausal controls. Likewise, the relation between TBBMC/W and plasma and urinary zinc levels also was significant in the women with postmenopausal osteoporosis but not in the controls (multiple regression analysis: p = 0.0022). Neither group showed any correlation between plasma or urinary zinc concentrations and levels of biological markers of nutrition. Urinary zinc concentration correlated significantly with serum tartrate-resistant acid phosphatase level (simple linear regression analysis: r = 0.583, p < 0.001) in the women with postmenopausal osteoporosis but not in controls. TBBMC correlated with urinary zinc concentration significantly in the women with postmenopausal osteoporosis (simple linear regression: r = 0.567, p = 0.0015), but the correlation was nonsignificant in healthy postmenopausal controls. These findings indicate that the elevation of urinary zinc elimination in osteoporosis is dependent on bone resorption.

Beta 2-microglobulin in postmenopausal osteoporosis.

The so-called bone-derived growth factor, or beta 2-microglobulin, has a regulatory function in bone metabolism, stimulating osteoclastic activity. Osteoclastic activity is enhanced in postmenopausal osteoporosis, suggesting that beta 2-microglobulin concentration may also be increased in this disease. beta 2-microglobulin concentration was found to be raised (P < 0.001) in 30 women with postmenopausal osteoporosis as compared with 30 normal women of similar age; tartrate-resistant acid phosphatase concentration also was raised (P < 0.001), and total body bone mineral content was decreased (P < 0.001). Linear regression analysis revealed a highly negative correlation result between total body bone mineral content and beta 2-microglobulin (r = 0.577, P < 0.001), and a positive correlation result between beta 2-microglobulin and tartrate-resistant acid phosphatase concentration (r2 = 0.806, P < 0.001). These findings, and the stimulatory effect of beta 2-microglobulin on osteoclastic and osteoblastic activity, suggest that beta 2-microglobulin may play an important role as a local regulatory factor in the pathogenesis of postmenopausal osteoporosis.

Biochemical markers of nutrition in osteoporosis.

Thirty-six women with vertebral osteoporosis showed significantly decreased levels of biochemical markers of nutrition, transferrin (P < 0.001), prealbumin (P < 0.001), retinol binding-protein (P < 0.001), and fibronectin (P < 0.001), compared with 40 healthy women of similar age. Multiple regression analysis showed a significant (R2 = 0.509; P = 0.0068) correlation between bone mineral content and biochemical markers of nutrition in the osteoporotic patients but not in the control group. These data suggest that postmenopausal osteoporosis may be associated with a nutritional deficiency.

beta 2-Microglobulin in Paget's bone disease.

On the basis of earlier findings of increased serum beta 2-microglobulin concentration in women with postmenopausal osteoporosis, we decided to study serum beta 2-microglobulin concentration in other bone diseases. In 28 patients with untreated Paget's bone disease, serum beta 2-microglobulin concentration was normal (1.49 +/- 0.41 mg/liter versus 1.36 +/- 0.21 mg/liter in 42 control subjects, P = ns), a finding that contradicts reports in the literature. We found that serum beta 2-microglobulin concentration was related negatively and significantly (r2 = -0.154, P = 0.0354) with serum total alkaline phosphatase concentration, but not with serum tartrate-resistant acid phosphatase concentration (p = ns). Urinary elimination of beta 2-microglobulin was lower in the patients with Paget's disease than in the controls (34 +/- 28 versus 120 +/- 21 mg/liter, P < 0.001). These findings suggest that beta 2-microglobulin behaves similarly to osteocalcin (BGP) in Paget's bone disease and that its concentration remains within normal levels perhaps because of the rate of reuptake of beta 2-microglobulin in bone neoformation.

Beta-2-microglobulin in diseases with high bone remodeling.

Beta2-microglobulin has been observed to behave as a biological marker of bone remodeling. We measured beta2-microglobulin and tartrate-resistant acid phosphatase (TRAP), a specific biological marker of bone remodeling, in 225 women: healthy premenopausal controls, healthy postmenopausal control, and patients with diseases characterized by enhanced bone turnover (postmenopausal osteoporosis, primary hyperparathyroidism, primary hyperthyroidism, polyostotic Paget's bone disease), and in other Paget's group before and after calcitonin treatment. Beta2-microglobulin levels differed significantly between the healthy premenopausal women (n = 20) compared with all the other groups. However, beta2-microglobulin levels did not differ significantly between healthy postmenopausal women (n = 38) and patient's with Paget's bone disease (n = 40)(P = 0.5095), or between women with postmenopausal osteoporosis (n = 30) and women with hyperthyroidism (n = 20)(P = 0.7890). TRAP concentrations differed significantly in all the groups paired except for women with Paget's bone disease and women with either hyperparathyroidism or hyperthyroidism (P = 0.5179 and 0.6993, respectively); likewise, TRAP levels did not differ significantly between the women with hyperparathyroidism and those with hypothyroidism (P = 0.7804). After calcitonin treatment, there was a 22% increase in beta2-microglobulin, a 17% decrease in TRAP, and a 39% decrease in alkaline phosphatase, all of which were significant at P < 0.0001. Our findings indicate that serum beta2-microglobulin, like osteocalcin, behaves as a biological marker of remodeling in a number of diseases with enhanced bone remodeling but not in Paget's bone disease.