Serum bone alkaline phosphatase and calcaneus bone density predict fractures: a prospective study

The aim of this study was to assess the ability of serum bone-specific alkaline phosphatase (bone ALP), creatinine-corrected urinary collagen crosslinks (CTx) and calcaneus bone mineral density (BMD) to identify postmenopausal women who have an increased risk of osteoporotic fractures. Calcaneus BMD and biochemical markers of bone turnover (serum bone ALP and urinary CTx) were measured in 512 community-dwelling postmenopausal women (mean age at baseline 69 years) participating in the Hawaii Osteoporosis Study. New spine and nonspine fractures subsequent to the BMD and biochemical bone markers measurements were recorded over an average of 2.7 years. Lateral spinal radiographs were used to identify spine fractures. Nonspine fractures were identified by self-report at the time of each examination. During the 2.7-year follow-up, at least one osteoporotic fracture occurred in 55 (10.7%) of the 512 women. Mean baseline serum bone ALP and urinary CTx were significantly higher among women who experienced an osteoporotic fracture compared with those women who did not fracture. In separate age-adjusted logistic regression models, serum bone ALP, urinary CTx and calcaneus BMD were each significantly associated with new fractures (odds ratios of 1.53, 1.54 and 1.61 per SD, respectively). Multiple variable logistic regression analysis identified BMD and serum bone ALP as significant predictors of fracture (p = 0.002 and 0.017, respectively). The results from this investigation indicate that increased bone turnover is significantly associated with an increased risk of osteoporotic fracture in postmenopausal women. This association is similar in magnitude and independent of that observed for BMD.

Use of bone alkaline phosphatase to monitor alendronate therapy in individual postmenopausal osteoporotic women

BACKGROUND

Biochemical bone markers are sensitive to the changes in bone turnover that result from treatment of postmenopausal osteoporotic women with antiresorptive therapies. Although information is available on the use of bone markers in monitoring therapy in groups of subjects, less is known regarding how these markers perform in individual patients.

METHODS

Serum bone alkaline phosphatase (bone ALP) concentrations, measured with the Tandem(R) Ostase(R) assay, were used to monitor the biochemical response of bone in postmenopausal women with osteoporosis receiving either 10 mg/day alendronate therapy (n = 74) or calcium supplementation (n = 148) for 24 months.

RESULTS

Bone ALP decreased significantly from baseline at 3 months (P </=0.0001), reaching a nadir between 3 and 6 months of alendronate therapy. The magnitude of the bone ALP decrease in the treated osteoporotic population was consistent with normalization to premenopausal concentrations. Of the 74 alendronate-treated subjects, 63 (85.1%) demonstrated a decrease from baseline in bone ALP by 6 months that exceeded the least significant change of 25%. The bone ALP decrease from baseline exceeded 25% in 72 (97%) by the end of the study.

CONCLUSION

The bone ALP assay is a sensitive and reliable tool that may be used to monitor the reduction in bone turnover after alendronate therapy in individual postmenopausal osteoporotic women.

Monitoring antiosteoporotic treatment of postmenopausal women using biochemical markers of bone turnover

Postmenopausal osteoporosis is preventable. An increasing number of antiresorptive therapies including estrogen, selective estrogen receptor modulators (the so-called designer estrogens), bisphosphonates and calcitonins are now available as treatment options for osteoporosis. These agents reduce the level of bone turnover and consequently slow or arrest bone loss and decrease the risk of fracture. However, these therapies are only effective if they are taken as prescribed. Unfortunately, most women who initiate antiresorptive therapy are unwilling or unable to make a long-term commitment to maintain such therapy. The test for biochemical markers of bone turnover can be used to confirm a biochemical response of bone within 3-6 months of initiating therapy, far sooner than the 2 years required for bone density testing. Such information incorporates a timely assessment of the woman's physiologic response with therapeutic compliance. A test result indicating the expected response to treatment may motivate some patients to remain compliant and maintain the therapy for an extended period of time. Bone turnover markers with demonstrated efficacy in monitoring the reduction of bone turnover induced by antiresorptive therapies include bone-specific alkaline phosphatase and osteocalcin (bone formation markers), and free deoxypyridinoline, N-telopeptide and C-telopeptide (bone resorption markers).

Analytical and clinical performance characteristics of Tandem-MP Ostase, a new immunoassay for serum bone alkaline phosphatase

The performance characteristics of the Tandem-MP Ostase assay, a new microplate immunoassay for bone-specific alkaline phosphatase (bone ALP; EC 3.1.3.1) in human sera, are described. Bone ALP is bound to streptavidin-coated microwells by a single biotinylated anti-bone ALP monoclonal antibody. Antigen is detected by the addition of p-nitrophenyl phosphate. The assay is performed at room temperature in <90 min. Imprecision was 2.3-6.1% with a detection limit of 0.6 microg/L. Method comparison of bone ALP measurements with the Tandem-MP Ostase assay and the mass-based Tandem-R Ostase assay (n = 285) indicated regression statistics of Tandem-MP Ostase = 1.03 Tandem-R Ostase + 0.22 microg/L, S(y/x) = 4.0 microg/L, r = 0.97. Serum bone ALP values in apparently healthy men and in pre- and postmenopausal women were also similar between the two Ostase assay formats. Liver ALP reactivity determined using the slope and heat inactivation methods was similar in both Ostase assays. Liver ALP reactivity ranged from 3 microg/L (heat inactivation) to 6 microg/L (slope method) per 100 U/L of liver ALP activity, whereas bone ALP reactivity was 37 microg/L per 100 U/L of bone ALP activity, indicating a liver ALP relative reactivity of 8.1-16.2%. Similar results were obtained with the Alkphase-B bone ALP immunoassay. The Tandem-MP Ostase bone ALP assay demonstrated increased concentrations of serum bone ALP in conditions where bone metabolism is increased and showed a rapid, temporal decrease in serum bone ALP in Paget disease patients on bisphosphonate therapy. In conclusion, the Tandem-MP Ostase assay for serum bone ALP is a rapid, simple, robust nonisotopic alternative to the Tandem-R Ostase immunoradiometric assay that provides an accurate and sensitive assessment of bone turnover.

Characteristics of a two-site immunoradiometric assay for human skeletal alkaline phosphatase in serum

This two-site IRMA includes specific monoclonal antibodies for measuring skeletal alkaline phosphatase (B-ALP) in human serum. Assay calibration is based on mass units (micrograms per liter) and was established with purified B-ALP from a human osteosarcoma cell line, SAOS-2. Precision studies demonstrated intra- and interassay CVs of 3-5% and 5-7%, respectively. Relative reactivity studies showed that the assay has a sevenfold preference for detecting B-ALP compared with the liver isoenzyme in serum. The normal reference interval for 478 healthy adults was 5-22 micrograms/L. Method comparison studies showed good correlation between this B-ALP assay (y) and commercially available electrophoretic methods (x) (y = 0.3540x + 20.5, R2 = 0.929) in a pagetic population. Temporal profiles for total ALP, this IRMA B-ALP assay, and B-ALP by electrophoresis in three pagetic patients were parallel. We conclude that this assay demonstrates good analytical performance and would be useful for the clinical assessment of metabolic bone disorders.

Characteristics of a two-site immunoradiometric assay for human skeletal alkaline phosphatase in serum

This two-site IRMA includes specific monoclonal antibodies for measuring skeletal alkaline phosphatase (B-ALP) in human serum. Assay calibration is based on mass units (micrograms per liter) and was established with purified B-ALP from a human osteosarcoma cell line, SAOS-2. Precision studies demonstrated intra- and interassay CVs of 3-5% and 5-7%, respectively. Relative reactivity studies showed that the assay has a sevenfold preference for detecting B-ALP compared with the liver isoenzyme in serum. The normal reference interval for 478 healthy adults was 5-22 micrograms/L. Method comparison studies showed good correlation between this B-ALP assay (y) and commercially available electrophoretic methods (x) (y = 0.3540x + 20.5, R2 = 0.929) in a pagetic population. Temporal profiles for total ALP, this IRMA B-ALP assay, and B-ALP by electrophoresis in three pagetic patients were parallel. We conclude that this assay demonstrates good analytical performance and would be useful for the clinical assessment of metabolic bone disorders.

Optimum placement for optoelectronic multichip modules and the synthesis of diffractive optics for multichip module interconnects

Decreasing the system volume for optoelectronic (OE) planar systems is achieved by advancing computer-aided design of OE multichip modules (MCM's). It is shown that in order to minimize the volume in an OE MCM, it is necessary to minimize the maximum interconnect distance. To achieve this, we have developed placement algorithms based on the constraints of a given irregular interconnect pattern. Results are given for a twin-butterfly network for two general physical models: a transmissive MCM and a reflective MCM. We then show three different types of hologram design that can be used to implement the interconnect array. These elements are for reconstruction in the near field and are fabricated by direct-write electron-beam lithography. Both simulated and experimental reconstructions are demonstrated.

Surface glycoconjugates of cynomolgus monkey trabecular cells

Non-ionic detergent-soluble and detergent-resistant cynomolgus monkey trabecular cell surface glycoconjugates have been identified using three radiolabeling procedures and polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The cell surface glycoconjugates were radiolabeled with tritiated sodium borohydride after treatment with: (1) neuraminidase/galactose oxidase; (2) galactose oxidase; or (3) sodium metaperiodate. The non-ionic detergent soluble components were removed by treatment of the monolayer cell culture with 1% Triton X-100 in hypotonic buffer. The radiolabeled trabecular cell surface glycoconjugates in the Triton X-100 soluble and insoluble fractions were resolved by sodium dodecyl sulfate polyacrylamide gel electrophoresis under reducing conditions and visualized by fluorography. Treatment of the monkey trabecular cells with neuraminidase/galactose oxidase/tritiated sodium borohydride resulted in the radiolabeling of five components ranging in apparent molecular weight from 128,000 to 39,000 in the Triton X-100 soluble fractions, while 12 radiolabeled glycoconjugates with apparent molecular weights ranging from 240,000 to 26,000 were resolved in the Triton X-100 resistant fraction.

Studies on the glycoprotein nature of the thyrotropin receptor: interaction with lectins and purification of the bovine protein with the use of Bandeiraea (Griffonia) simplicifolia I affinity chromatography

The TSH receptor from Triton-solubilized bovine microsomal membranes was found to bind to a substantial extent to columns of the immobilized lectins Bandeiraea (Griffonia) simplicifolia I, Ricinus communis I, wheat germ, and Concanavalin A, whereas it was not retained by Dolichos biflorus. Elution of TSH receptor activity from these lectins could be achieved with the appropriate saccharides in all cases except Concanavalin A. The most extensive adsorption of the receptor occurred on B. simplicifolia I-agarose (84%), and the terminal alpha-D-galactosyl specificity of this interaction was substantiated by its susceptibility to alpha-galactosidase treatment. Whereas TSH itself was not bound to this immobilized lectin, a complex of this hormone with its receptor did interact and could be eluted with methyl-alpha-D-galactoside. Purification (800-fold) of the bovine TSH receptor was achieved by a combination of TSH and B. simplicifolia I affinity chromatographies. Polyacrylamide gel electrophoresis of the purified TSH receptor after radioiodination revealed three major components with apparent mol wt of 316,000, 115,000, and 54,000.

Mucolipidosis III beta-N-acetyl-D-hexosaminidase A. Purification and properties

Mucolipidosis III acid hydrolases possess an altered carbohydrate recognition marker needed for their lysosomal localization. As a result of this alteration, a portion of these enzymes is secreted from the cell to the extracellular spaces. The structural changes that may have occurred to one of these secreted enzymes, beta-N-acetyl-d-hexosaminidase A (EC 3.2.1.52) were investigated. Normal and mucolipidosis III urinary beta-N-acetyl-d-hexosaminidase A were purified to apparent homogeneity by using affinity [Sepharose-2-acetamido-N-(epsilon-aminocaproyl)-2-deoxy-beta- d-glucopyranosylamine] and ion-exchange (DEAE- and CM-cellulose) chromatography. Sodium dodecyl sulphate/polyacrylamide-slab-gel electrophoresis showed that both enzymes had similar subunit patterns consisting of apparent mol.wts. of 68000, 60000-58000, 55000 and 29000. Differences, however, were noted in the relative proportions of the protein bands where the normal urinary beta-N-acetyl-d-hexosaminidase A contained predominantly the smaller subunits, whereas the mucolipidosis III enzyme had a predominance of the larger subunits. The binding of mucolipidosis III beta-N-acetyl-d-hexosaminidase A to Ricinus communis lectin and concanavalin A with and without endo-beta-N-acetyl-d-glucosaminidase H treatment indicated that the mutation leads to a modification of a portion of the normally occurring high-mannose-type oligosaccharide units to the complex-type. This was further supported by carbohydrate compositional analysis, which revealed a mannose/galactose ratio of 2.1 for the mucolipidosis III beta-N-acetyl-d-hexosaminidase A compared with a ratio of 3.5 for the normal enzyme. Our results indicate that as a result of their inability to be properly localized to the lysosome the majority of the mucolipidosis III lysosomal hydrolase high-mannose oligosaccharide units are further processed to the complex-type before secretion of predominantly higher-molecular-weight subunits from the cell.

Properties of N-acetyl-beta-D-hexosaminidase from isolated normal and I-cell lysosomes

Using a combination of differential centrifugation and free flow electrophoresis (Harms, E., Kern, H., and Schneider, J. A. (1980) Proc. Natl. Acad. Sci. U. S. A. 77, 6139-6143) a single population of highly purified lysosomes was obtained from normal, I-cell disease type 1, and I-cell disease type 2 cultured fibroblasts. Our findings indicate that most of the residual acid hydrolase activities remaining within the I-cell fibroblasts are localized in the lysosomes, analogous to normal cells. Characterization of the carbohydrate-dependent properties of the lysosomal N-acetyl-beta-D-hexosaminidase revealed that the I-cell and normal enzymes do not contain a significant proportion of neuraminidase-susceptible sialic acid residues, interact poorly with the beta-galactose-specific lectin Ricinus communis and are highly sensitive to endohexosaminidase H treatment, indicating that the oligosaccharide units of both the I-cell and normal lysosomal N-acetyl-beta-D-hexosaminidase are predominantly of the high mannose type. The I-cell and normal lysosomal N-acetyl-beta-D-hexosaminidase, however, differed in their endocytotic properties. In contrast to the high rate of endocytosis of the normal lysosomal enzyme (7.8%/mg/h), the I-cell type 1 lysosomal enzyme failed to be endocytosed into Sandhoff cells indicating an absent or altered phosphohexyl recognition marker on the I-cell enzyme. Examination of the normal extracellular N-acetyl-beta-D-hexosaminidase revealed the presence of predominantly high mannose-type oligosaccharide units, similar to the corresponding lysosomal enzyme, although properties typical of complex-type oligosaccharide chains were also evident. In contrast, the secreted I-cell enzyme revealed the presence of oligosaccharide units predominantly of the complex type indicating that the I-cell N-acetyl-beta-D-hexosaminidase has had high mannose-type oligosaccharide chains modified to complex-type probably in the Golgi or GERL region prior to secretion from the cell.

Effect of tunicamycin and cycloheximide on the secretion of acid hydrolases from I-cell cultured fibroblasts

I-cell cultures fibroblasts secrete excessive amounts of N-acetyl-beta-D-hexosaminidase and alpha-L-fucosidase into the culture media as compared with normal fibroblasts. Addition of tunicamycin or cyd [14C]leucine (40--50%) into trichloroacetic acid-precipitable material decreased the secretion of these I-cell hydrolases to normal values within 24 h, but had no effect on the secretion of acid hydrolases from normal fibroblasts. These results indicate that I-cell cultured fibroblasts secrete at least two types of acid hydrolases: one is tunicamycin- and cycloheximide-sensitive and constitutes the greater proportion of the secreted hydrolases, and a smaller proportion is insensitive to tunicamycin and cycloheximide, similar t9 the acid hydrolases secreted by normal cultured fibroblasts.

Urinary lysosomal hydrolases in mucolipidosis II and mucolipidosis III

Investigation of the binding characteristics of acid beta-D-galactosidase, N-acetyl-beta-D-glucosaminidase, alpha-D-galactosidase and alpha-L-fucosidase from patients with mucolipidosis II and mucolipidosis III to concanavalin A--Sepharose 4B revealed a 2--10-fold decrease in the proportion of enzyme activities from patients with mucolipidoses II and III that adsorbed on the lectin. Neuraminidase treatment of the unadsorbed enzyme fraction did not significantly increased the proportion of enzyme activities that bound to the concanavalin A--Sepharose 4B. Characterization of acid beta-D-galactosidase from the adsorbed and unadsorbed enzyme fractions of mucolipidosis II and mucolipidosis III patients demonstrated identical apparent Km values of 0.22 mM with respect to 4-methylumbelliferyl beta-D-galactopyranoside, altered pH--activity profiles and heterogeneous isoelectric-focusing patterns. The results of this study support the suggestion of an alteration of a post-translational modification (possibly glycosylation) occurring in mucolipidosis II and mucolipidosis III common to the lysosomal hydrolases that affects the mannoserelated properties of these enzymes.

Mucolipidosis type III. Multiple elevated serum and urine enzyme activities

The clinical characteristics of a 16-year-old white girl with mucolipidosis type III included early growth retardation, severe dysostosis multiplex, restricted joint motion, tight indurated skin, swollen eyelids, late-onset hepatosplenomegaly, umbilical hernia, corneal opacities, and only slightly impaired mental and neurological development. Cultured fibroblasts contained numerous coarse perinuclear retractile inclusions. Biochemical findings indicated the following: (1) normal levels of urinary acid mucopolysaccharides, (2) deficient activities of multiple lysosomal hydrolases in cultured fibroblasts, (3) elevated activity levels of seven serum lysosomal hydrolases, and (4) elevated activity levels of four lysosomal hydrolases in urine.

Carbohydrate composition of purified serum glycoproteins in mucolipidosis II and mucolipidosis III

Mucolipidosis II (I-cell disease) and Mucolipidosis III (ML III) are inherited disorders in which the molecular defect may involve an abnormality in a common post-translational modification step (possibly glycosylation) shared by lysosomal hydrolases. We tested whether such an alteration might be a generalized defect in glycoprotein biosynthesis and, thus, be reflected in an abnormal carbohydrate composition of non-lysosomal glycoproteins. The apoprotein of low density lipoprotein (apo-LDL) and immunoglobulin G (IgG) were purified to apparent homogeneity. Gas liquid chromatographic (glc) analysis of the carbohydrate content of these glycoproteins from ML II, ML III and normal sera revealed no differences in the relative ratios and total amounts of mannose, galactose, N-acetylglucosamine and sialic acid. These results suggest that if the postulated post-translational defect in these disorders involves changes in carbohydrate composition, it is not a general defect in glycosylation and may be specific for lysosomal hydrolases.

Characterization of the acid beta-D-galactosidases from human urine

Acid beta-D-galactosidases (EC 3.2.1.23) from human urine samples have been characterized using GM1-ganglioside, asialofetuin, and 4-MU-beta-D galactopyranoside. Sepharose 6-B column chromatography of crude urine supernatant fluids resolved three forms of acid beta-D-galactosidase activity with apparent molecular weights of 500 X 10(3)--700 X 10(3) (I), 90 X 10(3)--120 X 10(3) (II), and 20 X 10(3)--27 X 10(3) (III), which hydrolyzed 4-MU-beta-D-galactopyranoside, GM1-ganglioside and asialofetuin. The crude urine supernatant fluids and the separated forms of acid beta-D-galactosidase exhibited similar apparent KM values for the respective substrates. Starch gel electrophoresis of urine samples at pH 7.0 revealed a slow anodally migrating form of acid beta-D-galactosidase which electrophoretically corresponded to form I and a faster anodally migrating form corresponding to form II. Form III migrated as a composite of forms I and II suggesting that aggregation to the larger molecular weight activity forms occurred during starch gel electrophoresis. This report represents the first characterization of urinary acid beta-D-galactosidase with respect to naturally occurring glycolipid and glycoprotein substrates. In addition, data is presented to indicate that the enzyme may be composed of an enzymatically active form with an apparent molecular weight of 20 X 10(3)--27 X10(3), which is also capable of hydrolyzing the glycolipid and glycoprotein substrates.