Early changes in biochemical markers of bone turnover and their relationship with bone mineral density changes after 24 months of treatment with teriparatide.

UNLABELLED: We report the changes in biochemical markers of bone formation during the first 6 months of teriparatide therapy in postmenopausal women with osteoporosis according to previous antiresorptive treatment. Prior therapy does not adversely affect the response to teriparatide treatment. Similar bone markers levels are reached after 6 months of treatment. INTRODUCTION: The response of biochemical markers of bone turnover with teriparatide therapy in subjects who have previously received osteoporosis drugs is not fully elucidated. We examined biochemical markers of bone formation in women with osteoporosis treated with teriparatide and determined: (1) whether the response is associated with prior osteoporosis therapy, (2) which marker shows the best performance for detecting a response to therapy, and (3) the correlations between early changes in bone markers and subsequent bone mineral density (BMD) changes after 24 months of teriparatide. METHODS: We conducted a prospective, open-label, 24-month study at 95 centers in 10 countries in 758 postmenopausal women with established osteoporosis (n = 181 treatment-naïve) who had at least one post-baseline bone marker determination. Teriparatide (20 µg/day) was administered for up to 24 months. We measured procollagen type I N-terminal propeptide (PINP), bone-specific alkaline phosphatase (b-ALP), and total alkaline phosphatase (t-ALP) at baseline, 1 and 6 months, and change in BMD at the lumbar spine, total hip and femoral neck from baseline to 24 months. RESULTS: Significant increases in formation markers occurred after 1 month of teriparatide regardless of prior osteoporosis therapy. The absolute increase at 1 month was lower in previously treated versus treatment-naïve patients, but after 6 months all groups reached similar levels. PINP showed the best signal-to-noise ratio. Baseline PINP correlated positively and significantly with BMD response at 24 months. CONCLUSIONS: This study suggests that the long-term responsiveness of bone formation markers to teriparatide is not affected in subjects previously treated with antiresorptive drugs.

Investigation of keratinocyte regulation of collagen I synthesis by dermal fibroblasts in a simple in vitro model.

BACKGROUND: Hypertrophic scarring and skin graft contracture are major causes of morbidity after burn injuries. A prominent feature is excessive fibroplasia with accumulation of increased fibrillar collagen relative to normal scar tissue. The application of split-thickness skin grafts or cultured epithelial autografts to burn wounds is known to reduce scarring and contraction. OBJECTIVES: To investigate further how the keratinocyte influences underlying fibroblast behaviour by examining the influence of keratinocytes on fibroblast collagen synthesis, using a new assay for collagen synthesis never previously applied to skin cell biology. METHODS: We investigated the influence of the keratinocyte on fibroblast synthesis of type I collagen using an immunoassay for the aminoterminal propeptide of type I collagen (P1NP) in conditioned medium from monocultures and cocultures of keratinocytes and fibroblasts over 14 days. The importance of the physical presence of the keratinocyte was investigated by comparing cocultures of keratinocytes and fibroblasts against fibroblast monocultures with keratinocyte-conditioned medium. Pharmacological agents known to promote fibroblast proliferation [basic fibroblast growth factor (bFGF)], keratinocyte proliferation [insulin-like growth factor (IGF)-1], modify scarring in vivo[tumour necrosis factor (TNF)-alpha] or modify collagen biochemistry [putrescine, estrone, estradiol and beta-aminopropionitrile (beta-APN)] were then investigated for their effect on collagen synthesis in fibroblasts and in keratinocyte/fibroblast cocultures. RESULTS: Keratinocytes in coculture with fibroblasts, and keratinocyte-conditioned medium, both reduced fibroblast P1NP synthesis. Of the pharmacological agents investigated, bFGF, IGF-1, TNF-alpha and beta-APN all increased collagen synthesis both in monocultures of fibroblasts and in cocultures of keratinocytes and fibroblasts. CONCLUSIONS: Fibroblast collagen synthesis appears to be downregulated by keratinocyte-derived cytokines. Fibroblast growth factors and proinflammatory cytokines appear to be able partially to overcome this downregulation and to increase collagen synthesis.

Double-blind placebo-controlled study of testosterone patch therapy on bone turnover in men with borderline hypogonadism.

Clinical studies suggest there may be a threshold concentration of serum testosterone below which replacement will result in skeletal and psychological benefit. We evaluated the response to testosterone in men with borderline hypogonadism. A randomized double-blind placebo-controlled trial in 39 men over age 40 years presenting with sexual dysfunction and a borderline low testosterone level (total testosterone <10 nmol/L or free androgen index <30%). Patients were randomized to Testoderm TTS body patch (5 mg/day, n = 20) or a placebo patch (n = 19) for 6 months, followed by open-label testosterone replacement for a further 6 months in all patients. During the placebo-controlled phase of the study serum testosterone increased significantly on testosterone vs. placebo treatment (p = 0.004); this was associated with a decrease in total body fat mass (p = 0.019) and increase in haemoglobin level (p = 0.036). There were no significant changes in lean body mass, markers of bone turnover, and measures of bone mineral density (BMD). There was evidence of difference in quality of life according to the Male Erectile Dysfunction Quality of Life questionnaire (MEDQoL score, p = 0.017), mainly accounted for by deterioration in the placebo arm. When the active treatment period was combined for placebo and testosterone groups, the within-patient analysis showed a significant effect of testosterone to decrease markers of bone resorption (uNTX/Cr, p = 0.007; iFDPD/Cr, p = 0.0006) and to increase lean body mass (p = 0.001). There was little convincing evidence from this study that testosterone replacement is likely to have major benefit in men over age 40 years with borderline hypogonadism and sexual dysfunction. However, there was evidence of suppression in bone resorption and hence longer and larger studies are needed to examine its effect on BMD.

Changes in bone mass and bone turnover following tibial shaft fracture.

INTRODUCTION: Bone loss occurs in the regional bone following tibial shaft fracture. An earlier cross-sectional study showed that measurements made at the metaphyseal region of the tibia using peripheral quantitative computed tomography (pQCT) and the ultradistal region of the tibia using dual-energy X-ray absorptiometry (DXA) were the most responsive at monitoring this bone loss. Biochemical markers of bone turnover enable us to assess the activity of bone formation and resorption during fracture healing. The aim of this longitudinal study was to determine the pattern and distribution of bone loss and bone turnover following a tibial shaft fracture treated with either plaster cast or intramedullary nail. METHODS: Eighteen subjects underwent bone mass measurements using DXA at the tibia and hip and quantitative ultrasound (QUS) at the tibia and calcaneus of both limbs at 2 weeks, 8 weeks, 12 weeks and 24 weeks following fracture, with hip and tibia DXA measurements also performed at 52 weeks. Nine of the patients treated with plaster cast had pQCT measurements at the tibia at 24 weeks. We measured three bone formation markers, bone alkaline phosphatase (bone ALP), osteocalcin (OC) and procollagen type 1 N-terminal peptide (PINP), a marker of bone resorption, serum C-telopeptides of type 1 collagen (beta-CTX) and a marker of collagen III turnover, procollagen type III N-terminal peptide (PIIINP) at 1 day, 3 days and 7 days and at 2, 4, 8, 12, 16 and 24 weeks following fracture. The greatest bone losses were observed at the ultradistal region of the tibia using DXA (28%, p <0.001) and the metaphyseal region of the tibia using pQCT (26-31%, p <0.001) at 24 weeks. In the hip, the greatest loss was in the trochanter region at 24 weeks (10%, p <0.001). The greatest loss at the calcaneus measured using QUS was for broadband ultrasound attenuation (BUA) measured using CUBA Clinical at 24 weeks (13%, p =0.01). RESULTS: At 1 year, there was a small recovery in bone loss (ultradistal tibia DXA, 20%, p <0.01; trochanter DXA 9%, p <0.001). Bone turnover increased following fracture (PINP +72+/-21%, p <0.0001, bone ALP +199+/-22%, p =0.004, beta-CTX +105+/-23%, p <0.0001, all at 24 weeks). There was a smaller +33+/-10% increase in osteocalcin at 24 weeks. PIIINP concentration peaked at week 8 (+57+/-9%, p <0.0001). The bone resorption marker beta-CTX showed an earlier rise (week 2, 139+/-33%) than the bone formation markers. CONCLUSIONS: We conclude that: (1) bone loss following tibial shaft fracture occurs both proximal and distal to the fracture; (2) the decreased BMD is largest for trabecular bone in the tibia with similar measurements using DXA and pQCT; (3) there is limited recovery of bone lost at the hip and tibia at 1 year; (4) tibial speed of sound (SOS) demonstrated a greater decrease than calcaneal SOS when comparing z -scores; (5) BUA is the QUS variable that shows the biggest decrease of bone mass at the calcaneus; (6) increase in bone turnover occurs following fracture with an earlier increase in bone resorption markers and a later rise in bone formation markers.

Circadian variation in biochemical markers of bone cell activity and insulin-like growth factor-I in two-year-old horses.

Studies in humans have found circadian changes to be one of the most important sources of controllable preanalytical variability when evaluating bone cell activity using biochemical markers. It remains unclear whether similar circadian changes influence bone marker concentrations in the horse. The aim of this study was to characterize changes in serum concentrations of three biochemical markers of bone cell activity over a 24-h period in six 2-yr-old Thoroughbred mares, and to determine circadian variability in IGF-I, which regulates bone turnover. Three bone markers were measured in serum: osteocalcin, a marker of bone formation, the carboxy-terminal propeptide of type-I collagen (a marker of bone formation), and the carboxy-terminal telopeptide of type-I collagen (a marker of bone resorption). Data were analyzed using the cosinor technique, which fits a 24-h cycle to each dataset. A significant circadian rhythm was observed for osteocalcin (P = 0.028), with an estimated amplitude of 7.6% of the mean (95% confidence interval 1.3% to 16.3%), and an estimated peak time of 0900. However, the observed rhythm for the carboxy-terminal telopeptide of type-I collagen (amplitude = 7.4%) was not significant (P = 0.067), and there were no significant changes in concentrations of the carboxy-terminal propeptide of type-I collagen over the 24-h study period (P = 0.44). There was a small but significant circadian rhythm for IGF-I (P = 0.04), with an estimated amplitude of 3.4% (95% confidence interval 0.2 to 7.1%) and peak at 1730. Further studies are now required to determine the potential association between circadian changes in IGF-I and osteocalcin in the horse. Although no significant circadian variation was found in concentrations of the car-boxy-terminal propeptide of type-I collagen and the carboxy-terminal telopeptide of type-I collagen, this may in part be a result of the age of the animals that were still skeletally immature. Future studies should aim to determine whether these markers develop a circadian rhythm at a later age when growth is complete. In the meantime, consistency in time of sampling should continue to be considered best practice when measuring biochemical markers of bone turnover in the horse.

Serum osteoprotegerin as a determinant of bone metabolism in a longitudinal study of human pregnancy and lactation.

Osteoprotegerin (OPG) is a soluble decoy receptor that inhibits bone resorption by binding to receptor activator of nuclear factor kappa B ligand. Murine studies suggest that OPG is elevated in pregnancy, but its role in human pregnancy is unknown. We evaluated the relationship among OPG, bone turnover, and bone density in a longitudinal study of planned human pregnancy and lactation (n = 17; age, 20-36 yr). Samples were collected before conception; at 16, 26, and 36 wk gestation; and at 2 and 12 wk postpartum. Indexes of bone resorption included serum beta C-terminal and urinary N-terminal (uNTX) telopeptides of type I collagen. OPG increased by 110 +/- 16% (mean +/- SEM) at 36 wk (P < 0.001), followed by a rapid postpartum decline in both lactating and nonlactating women. Bone resorption was elevated at 36 wk (serum beta C-terminal telopeptides by 76 +/- 17%; urinary N-terminal telopeptides by 219 +/- 41%; P < 0.001). The tissue source of OPG in pregnancy is unknown. Human breast milk contains large amounts of OPG (162 +/- 58 ng/ml in milk vs. 0.42 +/- 0.03 ng/ml in nonpregnant serum). However, the rapid postpartum decline in serum OPG and the low serum OPG in neonates suggest a placental source. There was no correlation between change in OPG and bone turnover or bone mineral density (P > 0.05), and the physiological importance of elevated OPG in human pregnancy remains uncertain.

Effect of feeding on bone turnover markers and its impact on biological variability of measurements.

Bone turnover markers are subject to day-to-day and within-day variability, which may influence clinical interpretation. We examined the effect of fasting vs. feeding on the concentration and between-day variability of several markers. Twenty healthy premenopausal women were studied on 10 consecutive weekdays. Subjects were studied either in the fasting (no breakfast) or fed (breakfast at 08:00 h) state on alternate days, and were randomized to begin either fasting or fed. Two hour urine collections were obtained each day between 08:00 h and 10:00 h, and blood samples were collected daily at 09:00 h. The N-telopeptide cross-link of type I collagen in urine (uNTX) and serum (sNTX), the C-telopeptide in urine (uCTX) and serum (sbetaCTX), and immunoreactive free deoxypyridinoline (uifDPD) in urine were measured as resorption markers. Procollagen type I N-terminal propeptide (PINP), osteocalcin (OC), and bone alkaline phosphatase (bone ALP) were measured as formation markers. All bone formation and resorption markers were significantly lower in the fed state with the exception of bone ALP. The magnitude of the decrease ranged from 3.8 +/- 0.9% for PINP (p < 0.0001) to 17.8 +/- 2.6% (p < 0.0001) for sbetaCTX. Measurement variability was partitioned into analytical variability based on replicate assays (CV(a)) and within-subject variability (CV(i)). The CV(i) was greater (p < 0.05) for some markers in the fasting state (uifDPD, uNTX, and sNTX) but greater in the fed state for other markers (OC and sbetaCTX). In conclusion, the clinical impact of feeding vs. fasting is small with the exception of sbetaCTX; however, in clinical practice, collection of samples in the fasting state may be necessary to minimize the unpredictable effects of feeding. The mechanism of the acute effect of feeding on bone turnover remains uncertain.

Prognostic value of troponin T in hemodialysis patients is independent of comorbidity.

BACKGROUND: Patients on long-term hemodialysis have a high mortality. Various clinical and biochemical markers are of prognostic value. Cardiac troponin T (cTnT) is a sensitive and specific marker for myocardial damage. Asymptomatic dialysis patients have a high prevalence of cTnT concentrations above the diagnostic threshold for myocardial damage. There is controversy over whether this represents a false positive cTnT or an underlying pathology with a poor outcome. It is not known whether cTnT reflects comorbidity in these patients. METHODS: A cohort of 73 long-term hospital hemodialysis patients had cTnT estimated once prior to a mid-week dialysis. Samples were analyzed using the second-generation cTnT assay from Boehringer Mannheim on an Elecsys 1010 analyzer. The standard diagnostic threshold for myocardial damage of 0.1 ng/mL was used. A commonly employed measure of comorbidity (Khan) was applied at the time cTnT was measured. Patients were followed for 15 months. Mortality was used as the clinical end point. Kaplan-Meier survival analysis was employed and differences between groups were assessed using the Cox-Mantel log-rank test. RESULTS: Of the 73 patients, 20 were positive for cTnT and 53 were negative, at the cut-off of 0.1 ng/mL. At fifteen months, 65% of the positive patients were dead, whereas only 15% of the negative patients were dead. Survival analysis confirmed that this difference was statistically significant (P < 0.00001), and that the effect of cTnT on survival was independent of comorbidity. CONCLUSIONS: There is a high prevalence of positive cTnT in stable hemodialysis patients. A single estimation of cTnT in this group has significant prognostic value, independent of comorbidity.

Excess paternal age in apparently sporadic osteogenesis imperfecta.

The objective of this study was to examine whether parental age is associated with the occurrence of apparently sporadic osteogenesis imperfecta (OI). We compared parental age and the joint distribution of maternal and paternal age with expected distributions based on statutory birth records for each year and location of birth. The study included patients with OI based in the United Kingdom. The study was restricted to cases born in England, Wales, and Scotland between 1961 and 1998. Subgroup analysis was by clinical type [Sillence et al., 1979: J Med Genet 16:101-116] and apparent mode of inheritance based on pedigree analysis. Of 730 eligible cases, 357 were apparently sporadic. The mean age of fathers at birth of children with apparently sporadic OI was 0.87 years greater than expected (P = 0.010; 95% confidence interval = 0.21 to 1.54 years). The relative risk was 1.62 for fathers in the highest quintile of paternal age compared with fathers in the lowest quintile. The magnitude of the paternal age excess did not differ significantly between Sillence types (analysis of variance P = 0.534). In sporadic cases, paternal age was 0.51 years greater than expected, given maternal age, year, and location of birth (P = 0.033). In contrast, in familial cases, there was no significant paternal age excess, and paternal age was not significantly different from that expected given maternal age. Increased paternal age is a significant risk factor for sporadic OI. This effect is not accounted for by increasing maternal age. The magnitude of the paternal age excess is small in comparison with that in some other autosomal dominant disorders.

Asthma and Cushing's syndrome.

A female patient was treated with high-dose inhaled fluticasone propionate for her asthma. Over 2 years, she developed features of Cushing's syndrome with proximal myopathy, osteopenia, hypertension, depressive psychosis, and cushingoid appearance. She had biochemical evidence of marked adrenal suppression with a 9:00 AM serum cortisol of 20 nmol/L that returned to normal (315 mol/L) after her therapy was changed to budenoside, 0.8 mg/d. Her appearance, mental state, and myopathy also improved with no loss of asthma control. This case illustrates the potential for developing clinically relevant adverse effects of inhaled corticosteroids when given at licensed doses.

Serum galactosyl hydroxylysine as a biochemical marker of bone resorption.

BACKGROUND: Serum-based biochemical markers of bone resorption may provide better clinical information than urinary markers because direct comparison with serum markers of bone formation is possible and because the within-subject variability of serum markers may be lower. We describe a method for the measurement of free beta-1-galactosyl-O-hydroxylysine (Gal-Hyl) in serum. METHODS: The assay used preliminary ultrafiltration of serum, dansylation, and separation by reversed-phase HPLC with fluorescence detection. Healthy subjects were recruited from population-based studies of bone turnover. RESULTS: The within-run (n = 15) and between-run (n = 15) CVs were 7% and 14%, respectively, at a mean value of 48 nmol/L. In women and pubertal girls, serum free Gal-Hyl correlated with urine free Gal-Hyl (r = 0.84; P <0.001). Serum Gal-Hyl was higher during puberty and increased after menopause. The fractional renal clearance of free Gal-Hyl relative to that of creatinine was 0.90 (95% confidence interval, 0.82-0.98). Serum free Gal-Hyl decreased by 36% (SE = 4%) in 14 patients with mild Paget disease treated with an oral bisphosphonate, and this decrease was significantly (P <0. 001) greater than that seen for either serum tartrate-resistant acid phosphatase (9%; SE = 4%) or serum C-terminal telopeptide of collagen I (19%; SE = 8%). CONCLUSION: Serum free Gal-Hyl may be useful as a serum marker of bone resorption.

A longitudinal study of bone gain in pubertal girls: anthropometric and biochemical correlates.

The aim of this longitudinal study was to investigate the factors associated with bone mineral acquisition in pubertal girls. Subjects were 37 healthy, Caucasian girls aged 12.1 years (SD 0.3). Measurements were made at 6-month intervals over a period of 18 months and included total body bone mineral content (TBBMC), total body bone mineral density (TBBMD), lean mass, and fat mass by dual-energy X-ray absorptiometry, anthropometry, lifestyle factors, four biochemical markers of bone turnover, hormonal status, and fractional calcium absorption. In multiple regression analysis, correlates of relative gain in TBBMC were gain in lean mass (p < 0.001) and estradiol (p = 0.008). For TBBMD, correlates were gain in lean (p < 0.001) and fat mass (p = 0.003), estradiol (p < 0.001), dietary energy intake (p = 0.003), and parathyroid hormone (p = 0.023). Statural growth and gain in bone mass were unrelated; both height velocity and bone turnover peaked approximately 20 months prior to menarche, whereas gain in bone mass peaked at menarche. Bone turnover markers correlated with height velocity (0.40 < r < 0.62), but not with bone gain. Estradiol was independently and negatively associated with all markers of bone turnover (-0.67 < r < -0.80). We conclude that estradiol is an important determinant of bone mineral gain in pubertal girls and is probably responsible for the reduction in bone turnover in late puberty; lean mass was the body composition parameter most closely associated with bone gain; height gain and bone gain are dissociated during the period of rapid growth at puberty; and bone turnover markers are modestly related to height gain, but are not predictive of bone gain.

Response of biochemical markers of bone turnover to hormone replacement therapy: impact of biological variability.

Biochemical markers of bone turnover may be useful to monitor patients taking hormone replacement therapy (HRT). The aim of this study was to assess the utility of markers in monitoring HRT by comparing the response of a large panel of markers to HRT with their within subject variability. We measured the response of markers to transdermal estradiol in 11 postmenopausal women over 24 weeks. We measured the within subject variability of markers in 11 untreated healthy postmenopausal women over the same period. The mean decrease in markers of bone formation after 24 weeks treatment ranged from 19% for procollagen type I C-terminal propeptide (PICP) to 40% for procollagen type I N-terminal propeptide (PINP). The mean decrease in markers of bone resorption ranged from 10% for tartrate-resistant acid phosphatase (TRAP) to 67% for C-terminal cross-linked telopeptide The least significant change (LSC at p < 0.05), calculated from the within subject variability in the untreated group, was used to define response. LSC for osteocalcin was 21%, bone alkaline phosphatase 28%, PICP 24%, PINP 21%, type I collagen telopeptide 28%, TRAP 17%, urinary calcium 90%, hydroxyproline 75%, total deoxypyridinoline 47%, free pyridinoline 36%, free deoxypyridinoline 26%, N-terminal cross-linked telopeptide 70%, and C-terminal cross-linked telopeptide 132%. The greatest number of responders after 24 weeks of treatment were found using PINP and osteocalcin (9 each), and free deoxypyridinoline (8 each) and total deoxypyridinoline (8 each) and total deoxypyridinoline (7 each). Lumbar spine bone mineral density defined four patients as responders. The ability to detect a response differs between markers and is not dependent on the magnitude of response to therapy.

Manganese requirement and toxicity in patients on home parenteral nutrition.

Two patients who were receiving home parenteral nutrition complained of vague neurological symptoms of such severity that they underwent full clinical appraisal. The only positive finding was that plasma manganese concentrations were greater than twice the upper 95% confidence interval of normal (7-27|nmol/l). In the light of this result all nine patients receiving home parenteral nutrition underwent evaluation for possible manganese toxicity. One other patient had serum manganese concentrations exceeding twice the upper limit (127|nmol/l). The three patients with elevated serum Mn had evidence of manganese deposition in the brain on magnetic resonance imaging scanning. In contrast two patients with normal plasma results had negative scans. Patient susceptibility appears very variable. We suggest that current amounts of trace elements provided in nutrition solutions may be a potential source of nutrient activity. The fine tuning of supply and demand may be difficult on account of a limited range of commercially available trace element solutions.

The effect of dietary sodium on calcium metabolism in premenopausal and postmenopausal women.

OBJECTIVE: To investigate the effects of high and low sodium diets on urinary calcium, bone turnover and calcium absorption in pre and postmenopausal women. DESIGN: Experimental, prospective and longitudinal study. SETTING: Samples were taken at the hospital and the diets were followed at home. SUBJECTS: Volunteers were recruited from the hospital and were either hospital staff or post-graduate students. No volunteers failed to complete the study but one was omitted from analysis due to lack of compliance. INTERVENTIONS: Eleven healthy premenopausal women aged 22-47 y and 11 healthy postmenopausal women ages 45-70 y followed a high (300 mmol/d) and a low (50 mmol/d) sodium diet for one week each. On the 7th day of each diet, blood and urine samples were taken. RESULTS: On the high sodium diet 24 h urinary sodium and calcium values relative to creatinine were significantly higher for all subjects (P < 0.05). Postmenopausal women on the high sodium diet had biochemical evidence of increased bone resorption in relation to the low sodium diet. However in premenopausal women there was no such change. Calcium absorption did not change significantly in either group. CONCLUSIONS: It appears that postmenopausal, but not premenopausal, women respond to a high sodium diet by an increase in bone resorption which may lead to reduced bone density. SPONSORSHIP: Arthritis and Rheumatism Council Project Grant R44.

The value of biochemical markers of bone turnover in osteoporosis.

A number of biochemical markers of bone turnover have been described and these reflect the activity of osteoblasts (bone formation) or osteoclasts (bone resorption). These markers have the following advantages for the measurement of bone turnover: (1) they are noninvasive; (2) inexpensive; (3) can be repeated on many occasions; (4) and reflect bone cell activity in the entire skeleton. They have disadvantages: (1) they do not provide information about the work of individual cells; (2) they do not reflect the process of mineralization; and (3) their levels may be affected by the rate of clearance. The markers have been used to study the pathogenesis of osteoporosis, identify postmenopausal women with accelerated bone loss, predict fracture independently of bone loss, predict response to therapy, and monitor response to therapy. They may also be useful in the setting of clinical trials for choosing minimal and maximal effective doses, understanding the mechanism of the changes in bone mineral density (BMD) and studying the effect and time course of changes in bone after cessation of therapy. Markers do not provide a surrogate for fracture risk or BMD. However, they do have uses in osteoporosis and can provide preliminary data in the short term that can be used in the design of longterm studies of BMD and fracture.

To determine the effects of ultraviolet light, natural light and ionizing radiation on pyridinium cross-links in bone and urine using high-performance liquid chromatography.

The aims of the study were to characterize the denaturation of urinary free and conjugated pyridinoline (Pyr) and deoxypyridinoline (Dpyr) on exposure to ultraviolet (UV) and natural light at different pH levels and to study the effects of X- and gamma-irradiation on Pyr and Dpyr in urine and in the mineralized and non-mineralized compartments of human bone. Urine samples from six normal subjects, adjusted to pH 3.0, 7.0 and 9.0 were exposed to UV light for up to 3 days. Urine collections (2 mL and 24 h) from three subjects, pH adjusted to 1.0, 2.0, 3.0, 4.0 and 5.0, were exposed to natural light for up to 1 day. Urine samples and bone slices from seven human cadaveric femurs were irradiated with increasing doses of X-rays (0-100 Gy) and high-dose gamma-radiation (28 kGy). Mineralized and non-mineralized bone were separated using a modification of a published method employing heat denaturation followed by trypsin hydrolysis and analysed for Pyr, Dpyr and hydroxyproline (Hypro). The rate of UV photolysis of urinary Pyr and Dpyr increased with pH and was faster in the free fraction (after 3 days' exposure: free Pyr and Dpyr at pH 7.0 vs. 9.0, P < 0.05, conjugated pH 3.0 vs. 9.0, P < 0.05). Exposure to natural light for 3 h did not significantly decrease urinary Pyr and Dpyr in either sample collections, but levels were reduced in the 2-mL aliquots after exposure for 1 day (P < 0.05). X-irradiation of urine and bone did not affect Pyr and Dpyr. Pyr content was similar in both bone compartments (Pyr/ Hypro = 0.12 +/- 0.004), but Dpyr was higher in the non-mineralized compartment (Dpyr/Hypro = 0.047 +/- 0.002 vs. 0.038 +/- 0.002, P < 0.001). UV light and gamma-irradiation result in denaturation of pyridinium cross-links in urine. These cross-links are present in both the mineralized and non-mineralized bone compartments but are not affected by the doses of gamma-irradiation that denature these cross-links in urine.