Urinary excretion of hydroxylysine and its glycosides as an index of collagen degradation

A longitudinal study of the blood and urine metabolome of Vipera berus envenomated dogs

Envenomation of dogs by the common European adder (Vipera berus) is associated with high morbidity. The cytotoxic venom of Vipera berus contains enzymes with the potential to cause acute kidney injury, among other insults, however robust biomarkers for such effects are lacking. A prospective observational follow-up study of naturally envenomated dogs and controls was conducted to fill knowledge gaps regarding canine Vipera berus envenomation, attempt to identify novel biomarkers of envenomation and related kidney injury, and elucidate potential long-term effects. Blood and urine samples were analyzed with a global metabolomics approach using liquid chromatography-mass spectrometry, uncovering numerous features significantly different between cases and controls. After data processing and feature annotation, eight features in blood and 24 features in urine were investigated in order to elucidate their biological relevance. Several of these are associated with AKI, while some may also originate from disturbed fatty acid β-oxidation and soft tissue damage. A metabolite found in both blood and a venom reference sample may represent identification of a venom component in case dogs. Our findings suggest that envenomated dogs treated according to current best practice are unlikely to suffer permanent injury.

Metabolomics and Cardiovascular Risk in Patients with Heart Failure: A Systematic Review and Meta-Analysis

The associations of plasma metabolites with adverse cardiovascular (CV) outcomes are still underexplored and may be useful in CV risk stratification. We performed a systematic review and meta-analysis to establish correlations between blood metabolites and adverse CV outcomes in patients with heart failure (HF). Four cohorts were included, involving 83 metabolites and 37 metabolite ratios, measured in 1158 HF patients. Hazard ratios (HR) of 42 metabolites and 3 metabolite ratios, present in at least two studies, were combined through meta-analysis. Higher levels of histidine (HR 0.74, 95% CI [0.64; 0.86]) and tryptophan (HR 0.82 [0.71; 0.96]) seemed protective, whereas higher levels of symmetric dimethylarginine (SDMA) (HR 1.58 [1.30; 1.93]), N-methyl-1-histidine (HR 1.56 [1.27; 1.90]), SDMA/arginine (HR 1.38 [1.14; 1.68]), putrescine (HR 1.31 [1.06; 1.61]), methionine sulfoxide (HR 1.26 [1.03; 1.52]), and 5-hydroxylysine (HR 1.25 [1.05; 1.48]) were associated with a higher risk of CV events. Our findings corroborate important associations between metabolic imbalances and a higher risk of CV events in HF patients. However, the lack of standardization and data reporting hampered the comparison of a higher number of studies. In a future clinical scenario, metabolomics will greatly benefit from harmonizing sample handling, data analysis, reporting, and sharing.

Neutrophil Adhesion and the Release of the Free Amino Acid Hydroxylysine

During infection or certain metabolic disorders, neutrophils can escape from blood vessels, invade and attach to other tissues. The invasion and adhesion of neutrophils is accompanied and maintained by their own secretion. We have previously found that adhesion of neutrophils to fibronectin dramatically and selectively stimulates the release of the free amino acid hydroxylysine. The role of hydroxylysine and lysyl hydroxylase in neutrophil adhesion has not been studied, nor have the processes that control them. Using amino acid analysis, mass spectrometry and electron microscopy, we found that the lysyl hydroxylase inhibitor minoxidil, the matrix metalloproteinase inhibitor doxycycline, the PI3K/Akt pathway inhibitors wortmannin and the Akt1/2 inhibitor and drugs that affect the actin cytoskeleton significantly and selectively block the release of hydroxylysine and partially or completely suppress spreading of neutrophils. The actin cytoskeleton effectors and the Akt 1/2 inhibitor also increase the phenylalanine release. We hypothesize that hydroxylysine release upon adhesion is the result of the activation of lysyl hydroxylase in interaction with matrix metalloproteinase, the PI3K/Akt pathway and intact actin cytoskeleton, which play important roles in the recruitment of neutrophils into tissue through extracellular matrix remodeling.

Neural crest-specific deletion of Bmp7 leads to midfacial hypoplasia, nasal airway obstruction, and disordered breathing modelling Obstructive Sleep Apnea

Pediatric obstructive sleep apnea (OSA), a relatively common sleep-related breathing disorder (SRBD) affecting approximately 1-5% of children, is often caused by anatomical obstruction and/or collapse of the nasal and/or pharyngeal airways. The resulting sleep disruption and intermittent hypoxia lead to various systemic morbidities. Predicting the development of OSA from craniofacial features alone is currently not possible and a controversy remains if upper airway obstruction facilitates reduced midfacial growth or vice-versa. Currently, there is no rodent model that recapitulates both the development of craniofacial abnormalities and upper airway obstruction to address these questions. Here, we describe that mice with a neural crest-specific deletion of Bmp7 (Bmp7ncko) present with shorter, more acute angled cranial base, midfacial hypoplasia, nasal septum deviation, turbinate swelling and branching defects, and nasal airway obstruction. Interestingly, several of these craniofacial features develop after birth during periods of rapid midfacial growth and precede the development of an upper airway obstruction. We identified that in this rodent model, no single feature appeared to predict upper airway obstruction, but the sum of those features resulted in a reduced breathing frequency, apneas and overall reduced oxygen consumption. Metabolomics analysis of serum from peripheral blood identified increased levels of hydroxyproline, a metabolite upregulated under hypoxic conditions. As this model recapitulates many features observed in OSA, it offers unique opportunities for studying how upper airway obstruction affects breathing physiology and leads to systemic morbidities.

Free urinary glycosylated hydroxylysine as an indicator of altered collagen degradation in the mucopolysaccharidoses

Extracellular matrix (ECM) disruption is known to be an early pathological feature of the Mucopolysaccharidoses (MPS). Collagen is the main component of the ECM and its metabolism could act as a useful indicator of ECM disruption. We have measured the specific collagen breakdown products; urinary free hydroxylated (Lys-OH) and glycosylated hydroxylysines (Lys-O-Gal and Lys-O-GalGlc) in MPS patients using a tandem liquid chromatography tandem mass spectrometry assay. A pilot study cohort analysis indicated that concentrations of lysine and Lys-OH were raised significantly in MPS I (Hurler) disease patients. Lys-O-GalGlc was raised in MPS II and MPS VI patients and demonstrated a significant difference between MPS I Hurler and an MPS I Hurler-Scheie group. Further analysis determined an age association for glycosylated hydroxylysine in control samples similar to that observed for the glycosaminoglycans. Using defined age ranges and treatment naïve patient samples we confirmed an increase in glycosylated hydroxylysines in MPS I and in adult MPS IVA. We also looked at the ratio of Lys-O-Gal to Lys-O-GalGlc, an indicator of the source of collagen degradation, and noticed a significant change in the ratio for all pediatric MPS I, II, and IV patients, and a small significant increase in adult MPS IV. This indicated that the collagen degradation products were coming from a source other than bone such as cartilage or connective tissue. To see how specific the changes in glycosylated hydroxylysine were to MPS patients we also looked at levels in patients with other inherited metabolic disorders. MPS patients showed a trend towards increased glycosylated hydroxylysines and an elevated ratio compared to other metabolic disorders that included Battens disease, Fabry disease, Pyridoxine-dependent epilepsy (due to mutations in ALDH7A1), and Niemann Pick C disease.

Osteoporosis and the Potential of Cell-Based Therapeutic Strategies

Osteoporosis, the most common chronic metabolic bone disease, is characterized by low bone mass and increased bone fragility. Nowadays more than 200 million individuals are suffering from osteoporosis and still the number of affected people is dramatically increasing due to an aging population and longer life, representing a major public health problem. Current osteoporosis treatments are mainly designed to decrease bone resorption, presenting serious adverse effects that limit their safety for long-term use. Numerous studies with mesenchymal stem cells (MSCs) have helped to increase the knowledge regarding the mechanisms that underlie the progression of osteoporosis. Emerging clinical and molecular evidence suggests that inflammation exerts a significant influence on bone turnover, thereby on osteoporosis. In this regard, MSCs have proven to possess broad immunoregulatory capabilities, modulating both adaptive and innate immunity. Here, we will discuss the role that MSCs play in the etiopathology of osteoporosis and their potential use for the treatment of this disease.

Metabolomics reveals elevated urinary excretion of collagen degradation and epithelial cell turnover products in irritable bowel syndrome patients

INTRODUCTION

Irritable bowel syndrome (IBS), the most commonly diagnosed functional gastrointestinal (GI) disorder in developed countries, is characterized by chronic abdominal pain, and altered bowel habits.

OBJECTIVES

Accurate and timely diagnosis is challenging as it relies on symptoms and an evolving set of exclusion criteria to distinguish it from other related GI disorders reflecting a complex etiology that remains poorly understood. Herein, nontargeted metabolite profiling of repeat urine specimens collected from a cohort of IBS patients (n = 42) was compared to healthy controls (n = 20) to gain insights into the underlying pathophysiology.

METHODS

An integrated data workflow for characterization of the urine metabolome with stringent quality control was developed to authenticate reliably measured (CV < 30%) and frequently detected (> 75%) metabolites using multisegment injection-capillary electrophoresis-mass spectrometry. Complementary statistical methods were then used to rank differentially excreted urinary metabolites after normalization to osmolality that were subsequently identified by high resolution tandem mass spectrometry and their electrophoretic migration behavior.

RESULTS

Our work revealed ten consistently elevated urinary metabolites in repeat samples collected from IBS patients at two different time points (q < 0.05 after age and Benjamini-Hochberg/FDR adjustment), which were associated with greater collagen degradation and intestinal mucosal turn-over processes likely due to low-grade inflammation. IBS-specific metabolites identified in urine included a series of hydroxylysine metabolites (O-glycosylgalactosyl-hydroxylysine, O-galactosyl-hydroxylysine, lysine), mannopyranosy-L-tryptophan, imidazole propionate, glutamine, serine, ornithine, dimethylglycine and dimethylguanosine. A major limitation in this retrospective case-control study was significant co-morbidity of IBS patients with other illnesses, including depression and prescribed medications as compared to healthy controls.

CONCLUSION

This work provides new mechanistic insights into the pathophysiology of IBS while also offering a convenient way to monitor patient disease progression and treatment responses to therapy based on a panel of urinary metabolites that avoids invasive blood sampling, colonoscopy and/or tissue biopsies.

Bone biochemical markers for assessment of bone responses to differentiated phosphorus supply in growing-finishing pigs

Phosphorus (P) is essential for building and maintaining a healthy and strong skeleton. Moreover, dietary P supply may play a role for bone turnover, and the excretion of bone turnover metabolites may be useful as markers for sufficient dietary P supply. The objective was to study the long-term effects of low, medium, and high dietary P supply on bone metabolism in terms of serum concentration and urinary excretion of bone turnover components and metabolites in healthy growing-finishing pigs compared with bone mineral content (BMC) and bone mineral density (BMD) of humerus and femur. Pigs were fed diets containing low [LP; 4.1 g/kg dry matter (DM)], medium (MP; 6.2 g/kg DM), or high dietary P (HP; 8.9 g/kg DM) from 39.7 kg body weight (BW) until slaughter at 110 kg BW. Urine and blood were collected at 40, 70, and 110 kg BW while bones were collected at slaughter. Serum was analyzed for osteocalcin (OC), bone alkaline phosphatase (BAP), and C-terminal telopeptides of type I collagen (CTX-I), whereas urine was analyzed for pyridinoline (PYD), deoxypyridinoline (DPD), CTX-I, hydroxylysine (HYL), galactosyl-hydroxylysine (GAL-HYL), glycosyl-galactosyl-hydroxylysine (GLC-GAL-HYL), and hydroxyproline (HYP). Humerus and femur were analyzed for BMC and BMD. The LP diet caused reduced OC and increased BAP and CTX-I concentrations in serum. Furthermore, BAP was increased in response to the HP diet. Urine metabolites of bone resorption were all increased in pigs fed the LP diet, but only a few responses were obtained in response to the HP diet. Furthermore, age-related decreases were identified for BAP, HYL, GAL-HYL, and GLC-GAL-HYL. Bone mineral content and BMD were markedly lowered in pigs fed the LP diet but were not affected in pigs fed the HP diet. In conclusion, OC, BAP, and CTX-I in serum have proved useful for P adequacy in growing-finishing pigs. In addition, urine bone resorption metabolites have also proved useful for P adequacy and analysis of PYD, DPD, and CTX-I was considered to be the most relevant markers due to their specificity for bone and their negative correlation with BMD, BMC, ash, calcium (Ca), and P contents. Finally, DPD may be the preferred marker in long-term P feeding assessments.

Concentrations of CTX I, CTX II, DPD, and PYD in the urine as a biomarker for the diagnosis of temporomandibular joint osteoarthritis: A preliminary study

OBJECTIVES

The aim of this study was to identify a marker for temporomandibular joint (TMJ) osteoarthritis (OA) diagnosis by comparing the concentrations of urinary pyridinoline (PYD), deoxypyridinoline (DPD), and C-terminal telopeptides type I collagen (CTX-I), and CTX-II of TMJ OA patients with those of a non-symptomatic group.

METHODS

PYD, DPD, CTX-I, and CTX-II concentrations in the urine of 36 non-symptomatic subjects and 31 TMJ OA subjects were analyzed.

RESULTS

The differences for only PYD and DPD were significant. In ROC analysis, PYD and DPD showed higher sensitivity and specificity than CTX-I and CTX-II. PYD and DPD concentrations in urine were significantly increased in TMJ OA patients and can therefore be used as a biomarker in the supplementary clinical diagnosis of TMJ OA.

DISCUSSION

The findings suggest that measurement of their concentration can be a supplementary method for clinical diagnosis of TMJ OA.

Utility of biochemical markers of bone turnover and bone mineral density in management of osteoporosis

Biochemical markers of bone turnover (bone-turnover markers) are released during bone formation or resorption and can be measured in blood and/or urine. The concentration of bone-turnover markers in serum or urine reflect bone remodeling activity and can potentially be used as surrogate markers of the rate of bone formation or bone resorption. While the diagnosis of osteoporosis is based on bone mineral density (BMD), the absolute fracture risk for a particular BMD measurement varies several fold depending on age and is also influenced by other clinical risk factors. The measurement of bone-turnover markers may be of additional value to BMD and clinical risk factors in fracture risk assessment by improving the sensitivity and specificity of prediction of future fractures. In clinical practice, bone-turnover markers may help make cost-effective treatment decisions in patients with borderline absolute risk. BMD changes following treatment cannot be detected with confidence for 12-24 months due to measurement imprecision. Bone-turnover markers, which show an early response following treatment, may be useful for monitoring therapy, identifying non-compliance and non-responders, and predicting early response to therapy. This review concludes by identifying the need for internationally agreed-upon standards for bone resorption and formation.

Biochemical markers of bone turnover: part I: biochemistry and variability

With the ageing population in most countries, disorders of bone and mineral metabolism are becoming increasingly relevant to every day clinical practice. Consequently, the interest in, and the need for effective measures to be used in the screening, diagnosis and follow-up of such pathologies has markedly grown. Together with clinical and imaging techniques, biochemical tests play an important role in the assessment and differential diagnosis of metabolic bone disease. In recent years, the isolation and characterisation of cellular and extracellular components of the skeletal matrix have resulted in the development of molecular markers that are considered to reflect either bone formation or bone resorption. These biochemical indices are non-invasive, comparatively inexpensive and, when applied and interpreted correctly, helpful tools in the diagnostic and therapeutic assessment of metabolic bone disease. Part I of this article provides an overview of the basic biochemistry of bone markers, and sources of non-specific variability. Part II (to be published in a subsequent issue of this journal) will review the current evidence regarding the clinical use of biochemical markers of bone remodelling in metabolic and metastatic bone disease.

The first synthesis of glucosylgalactosyl hydroxylysine (Glu-Gal-Hyl) an important biological indicator of collagen turnover

This paper reports the first chemical synthesis of alpha-D-glucopyranosyl-(1-->2)-beta-D-galactopyranosyl-O-hydroxylysine, a glycoside of hydroxylysine important as indicator of skin and bone collagen turnover, starting with commercial compounds.

Collagen Markers Deoxypyridinoline and Hydroxylysine Glycosides: Pediatric Reference Data and Use for Growth Prediction in Growth Hormone-deficient Children

Background: In children and adolescents, markers of bone and collagen metabolism reflect the dynamics of skeletal growth and development. The aim of this study was to assess the relationship of the urinary collagen markers deoxypyridinoline (DPD) and hydroxylysine (Hyl) and its glycosides [galactosyl-Hyl (Gal-Hyl) and glucosyl-Gal-Hyl] with growth.

Methods: Urine samples from 240 apparently healthy children and adolescents (6–19 years; 124 girls) and from 51 prepubertal children with growth hormone (GH) deficiency (3–14 years; 14 girls) were analyzed. Urinary Hyl and its glycosides were quantified by HPLC, and DPD was assessed by chemiluminescence assay. Urinary concentrations of all markers were related to urinary creatinine.

Results: Multiple regression analysis revealed that only age and height velocity were independently associated with these markers in healthy children. In GH-deficient patients, the urinary excretion of both analytes after 4 weeks of GH therapy correlated significantly with the height increase during the first treatment year (r = 0.79 for Gal-Hyl; r = 0.70 for DPD; P &lt;0.001 each). In a multivariate linear regression model using Gal-Hyl concentrations at 4 weeks, baseline concentrations of insulin-like growth factor 1 and height velocity after 3 months accounted for 80% of the variability in height gain during the first treatment year. A model using DPD concentrations at 4 weeks, in place of Gal-Hyl concentrations, as well as baseline concentrations of insulin-like growth factor 1 and height velocity after 3 months accounted for 83% of the variability.

Conclusions: These urinary bone and collagen markers give some early indication of growth response, but the prediction of an individual marker is too imprecise to serve as a basis for clinical decisions. Markers of bone and collagen metabolism might be more useful as components of multivariate growth prediction models.

Assay for 5-hydroxylysine and L-lysine in human and rat urine and in bone by gas chromatography

An accurate method for the determination of collagen to study its distribution and turn-over in different tissues is described. 5-Hydroxylysine (5Hylys) is an amino acid that is apparently present in no other protein except collagen and, as it is metabolised only to a minor degree compared with 4-hydroxyproline (4Hypro), it has been suggested as a better marker of the collagen metabolism. Interest in this amino acid has increased recently because the levels of 5Hylys in urine and in different tissues may offer a new basis for detecting pathologies of the collagen molecule. This paper describes a method for the quantitative determination of 5Hylys and lysine (Lys) by gas chromatography (GC) in human and rat urine and in rat bone. The limit of detection was 350 pmol ml-1 for 5Hylys and 200 pmol ml-1 for Lys for all the biological samples. This method therefore provides a complete view of the metabolism of this amino acid and of the tissue it comes from.

Extension of phenotype associated with structural mutations in type I collagen: siblings with juvenile osteoporosis have an alpha2(I)Gly436 --> Arg substitution

Mutations in the type I collagen genes have been identified as the cause of all four types of osteogenesis imperfecta (OI). We now report a mutation that extends the phenotype associated with structural abnormalities in type I collagen. Two siblings presented with a history of back pain and were diagnosed with juvenile osteoporosis, based on clinical and radiological examination. Radiographs showed decreased lumbar bone density and multiple compression fractures throughout the thoracic and lumbar spines of both patients. One child has moderate short stature and mild neurosensory hearing loss. However, neither child has incurred the long bone fractures characteristic of OI. Protein studies demonstrated electrophoretically abnormal type I collagen in samples from both children. Enzymatic cleavage of RNA:RNA hybrids identified a mismatch in type I collagen alpha2 (COL1A2) mRNA. DNA sequencing of COL1A2 cDNA subclones defined the mismatch as a single-base mutation (1715G --> A) in both children. This mutation predicts the substitution of arginine for glycine at position 436 (G436R) in the helical domain of the alpha2(I) chain. Analysis of genomic DNA identified the mutation in the asymptomatic father, who is presumably a germ-line mosaic carrier. The presence of the same heterozygous mutation in two siblings strongly suggests that the probands display the full phenotype. Taken together, the clinical, biochemical, and molecular findings of this study extend the phenotype associated with type I collagen mutations to cases with only spine manifestations and variable short stature into adolescence.

Basic principles and clinical applications of biochemical markers of bone metabolism: biochemical and technical aspects

The interest in and the need for effective measures to be used in the screening, diagnosis, and follow-up of disorders of connective tissue, bone, and mineral metabolism has markedly grown. Next to clinical and imaging techniques, indices of bone turnover have come to play an important role in the assessment of metabolic bone disease. In osteoporosis, recent research has shown that bone markers may also be used to predict future bone loss and hip fractures (in larger cohorts of older patients), identify individuals at risk for osteoporosis, select therapy, and predict and monitor the therapeutic response in individual patients. The development of new markers of bone metabolism has greatly enriched the spectrum of serum and urine analytes used in the assessment of skeletal pathologies. Besides total alkaline phosphatase, other markers such as bone-specific alkaline phosphatase, osteocalcin, or the collagen propeptides are being used to measure bone formation. Bone resorption, previously assessed only by the measurement of urinary calcium and hydroxyproline, may now be detected more precisely by a number of new serum and urine markers. Among these, the pyridinium crosslinks and the telopeptides of collagen type I are presently considered the most specific markers of bone resorption. More recently, bone sialoprotein has also been suggested as a marker of bone resorption in serum. Tartrate-resistant acid phosphatase is now measurable by immunoassay. This article surveys the biochemistry and relevant technical aspects of the currently available markers of bone metabolism.

Development of an immunoassay for urinary galactosylhydroxylysine

Galactosylhydroxylysine (GHL) is released during bone resorption and has been shown to be elevated in subjects with metabolic bone loss. GHL is relatively specific for bone, it is not recycled or significantly metabolized during collagen turnover, and the levels are not influenced by diet. Previous measurements of GHL levels in urine have been performed using reverse-phase high performance liquid chromatography following pre-column derivatization. We produced polyclonal antibodies to GHL using GHL purified from sea sponges and developed an immunoassay that can recognize GHL in urine. The antibodies have minimal cross-reactivity with a physiological mixture of amino acids (< 1%), galactose (< 0.2%), lactose (< 0.3%), and glucosylgalactosylhydroxylysine (< 1%). This competitive immunoassay requires no dilution or pretreatment of the samples and provides a rapid and easy method for the evaluation of GHL in urine. Analysis of clinical samples from normal individuals, post-menopausal women, osteoporotic patients and individuals with Paget's disease show that the assay can discriminate between groups with differing levels of bone resorption as well as deoxypyridinoline (Dpd).

Biochemical markers of bone turnover. Applications for osteoporosis

The recent discovery of specific and sensitive biochemical markers reflecting the overall rate of bone formation and bone resorption has markedly improved the noninvasive assessment of bone turnover in various metabolic bone diseases, especially in osteoporosis. The immunoassay of human osteocalcin, recognizing the intact molecule and its major proteolytic fragment, and assays for bone alkaline phosphatase and the intact form of the N-terminal extension propeptide of type I collagen are currently the most sensitive markers for assessing bone formation. The best indices of bone resorption are the new immunoassays for pyridinoline cross-links and type I collagen-related peptides in urine and, recently, in serum. Several studies indicate that screening for these bone markers may be useful for improving the prognostic assessment of postmenopausal women in combination with bone mass measurement, that is, their risk for osteoporosis and, ultimately, for fractures and to monitor rapidly the efficacy of antiresorptive drugs.

Osteoporosis

Osteoporosis, one of the most prevalent diseases associated with aging, is characterized by a low bone mass and microarchitectural deterioration of bone tissue leading to increased susceptibility of fracture. The management of osteoporotic patients relies especially on the static measurement of bone mass as bone mineral and dynamic changes of bone turn over. New developments of bone mineral density measurement techniques and biochemical markers of bone turnover are reviewed. Their clinical uses for the management of patients with osteoporosis are discussed.

Bone markers

The recent development of specific and sensitive biochemical markers reflecting the overall rate of bone formation and bone resorption, has markedly improved the non-invasive assessment of bone turnover in various metabolic bone diseases, especially osteoporosis. The immunoassay of human osteocalcin recognizing the intact molecule and its major proteolytic fragment, along with that of bone alkaline phosphatase, are currently the most sensitive markers to assess bone formation. For bone resorption, the total urinary excretion of pyridinoline crosslinks measured by high pressure liquid chromatography has shown its superiority over all other markers for the clinical assessment of osteoporosis. The recent development of immunoassays recognizing either the free pyridinoline crosslinks or pyridinoline crosslinked-type I collagen peptides in urine and serum should allow a broad use of this sensitive resorption marker. Recent studies, some of them still in progress, define the clinical use of these markers: first, to improve the prognostic assessment of post-menopausal women in combination with bone mass measurement, i.e. their risk of developing osteoporosis and, ultimately, fractures and, second, to monitor the efficacy of anti-resorption drugs.

Effect of an oral calcium load on urinary markers of collagen breakdown

Aim of this study was to investigate whether osteoclast activity changes as a consequence of even mild physiological perturbation of plasma calcium as such induced by an oral calcium load. Osteoclast activity was determined indirectly by measuring, in spot urines at two and four hours after oral calcium load, the urinary excretion of hydroxylysylpyridinoline (Pyr), deoxylysylpyridinoline (D-Pyr), hydroxyproline (Hyp) and galactosyl-hydroxylysine (GHyl). The occurrence of the metabolic perturbation of plasma calcium homeostasis was assessed by measuring three indexes: i.e. calcemic response, PTH reduction and calciuric response at times following oral calcium loading. A significant fall of urinary D-Pyr and Pyr followed the perturbation of calcium homeostasis induced by the oral calcium load in two groups of healthy young adult and postmenopausal women. The highest mean percent reduction was observed for D-Pyr and was quantitatively similar in the two groups. Since urinary D-Pyr is the most specific bone resorption marker, it may be inferred that the perturbation of plasma calcium homeostasis induced by an oral calcium load is able to acutely inhibit osteoclast activity. This supports the view that osteoclasts are involved in the short-term error correction of plasma calcium.

Urinary output of hydroxylysine glycosides and pyridinium cross-links in detecting rat bone collagen turnover rate

Glucosylgalactosylhydroxylysine (GGHYL), galactosylhydroxylysine (GHYL), pyridinoline (PYD) and deoxypyridinoline (DPD) were measured in the urine (6 h serial specimens over 96 and 24 h urine specimens for 4 days) collected from four adult Sprague Dawley rats and in the femoral and tibia] bone as well as in the dorsal skin of the same rats. No significant daily variations were found in the urine excretion of GGHYL, GHYL, PYD and DPD but significant diurnal variations. The GGHYL/GHYL ratio in rat urine (0.46 +/- 0.1) reflected neither the bone collagen ratio (1.9 to 2.4) nor the skin collagen ratio (1.22 +/- 1.07), a finding that may reflect GGHYL conversion into GHYL. The content of both pyridinolines was very low in the skin and high in the bone collagen and the urinary PYD/DPD ratio (1.46 +/- 0.15) reflected essentially the bone collagen ratio (0.8-3.0). These results suggest the usefulness of measuring GGHYL, GHYL, PYD and DPD in 24 h urine specimen and, based on the inter-animal variations, the necessity to consider each animal as its own control when bone turnover needs to be monitored.

Galactosylhydroxylysine and pyridinium cross links in monitoring the bone response to hormone replacement therapy

Aim of the study was to compare urinary galactosyl-hydroxylysine (GHyl), deoxypyridinoline (D-Pyr) and pyridinoline (Pyr) before and after 5 to 9 months of hormone replacement therapy (HRT) in postmenopausal women. The urinary markers were measured by HPLC in the second void of fasting samples and were expressed as ratio to creatinine. GHyl was also expressed as a ratio to glucosylgalactolysyl-hydroxylysine (GGHyl). After short-term hormone replacement therapy, urinary D-Pyr fell significantly, but Pyr and GHyl, also when expressed as a ratio to GGHyl, remained unmodified. We conclude that GHyl and Pyr are not useful markers in monitoring the bone response to HRT in postmenopausal women.

New developments in biochemical markers for osteoporosis

The noninvasive assessment of bone turnover has markedly improved in the past few years with the development of sensitive and specific markers of bone formation and bone resorption. Markers of bone formation in serum include total and bone-specific alkaline phosphatase, osteocalcin, and type I collagen carboxyterminal extension peptide. Assessment of bone resorption can be achieved by measuring plasma tartrate-resistant acid phosphate and the urinary excretion (and possibly serum levels) of bone type I collagen degradation products: hydroxyproline, hydroxylysine glycosides, and, more recently, the pyridinium crosslinks (pyridinoline and deoxypyridinoline) and associated peptides. The immunoassay of human osteocalcin and bone alkaline phosphatase for formation and the pyridinoline crosslinks measured by high-pressure liquid chromatography or by immunoassay for bone resorption are currently the most sensitive and specific markers of bone turnover for the clinical assessment of osteoporosis. Using these new markers, several studies have shown that bone turnover increases after the menopause and remains elevated in late postmenopausal and elderly women. An increased bone turnover rate is related to a high rate of bone loss in postmenopausal women and to a decreased bone mass in elderly women. Recent data suggest that some of the new immunoassays for pyridinoline crosslinks could predict the subsequent risk of hip fracture in elderly women. Thus, bone markers might be used in combination with bone mass measurement to improve the prognostic assessment of postmenopausal women, i.e., their risk of developing osteoporosis and ultimately fractures. Treatment of postmenopausal women with antiresorptive drugs such as estrogens, bisphosphonates, and calcitonin induces a rapid decrease in the levels of bone markers that is correlated with the long-term effect of such treatments on bone mass. Thus, bone markers should be very useful in monitoring treatment efficacy in patients with osteoporosis.

Urinary concentration of a specific peptide of type I collagen of bone (CrossLaps): correlation to hydroxyproline

Urinary bone resorption markers, CrossLaps and hydroxyproline are compared in a non-selected group of 93 women. The correlation between CrossLaps and hydroxyproline is satisfactory. The r value is 0.79. Furthermore, it is investigated whether CrossLaps can substitute for hydroxyproline in the estimation of bone loss, using a model based on the combination of several biochemical markers. The results indicate that the two systems reflect related or parallel events, and show that CrossLaps is suitable for use in a normal clinical chemistry laboratory.

Serum pyridinolines as specific markers of bone resorption in hemodialyzed patients

Serum levels of hydroxylysyl pyridinoline and lysyl pyridinoline were quantified in uremic patients undergoing maintenance hemodialysis and in healthy subjects. Pre-hemodialysis serum levels of hydroxylysyl pyridinoline and lysyl pyridinoline in the hemodialyzed patients were significantly higher than those in healthy subjects. Serum levels of hydroxylysyl pyridinoline and lysyl pyridinoline decreased significantly after hemodialysis with reduction rates of about 40%. Pre-hemodialysis serum levels of hydroxylysyl pyridinoline and lysyl pyridinoline correlated significantly with intact parathyroid hormone, osteocalcin and bone-specific alkaline phosphatase. Lysyl pyridinoline showed better correlations with these parameters than hydroxylysyl pyridinoline. Parathyroidectomy markedly decreased serum levels of hydroxylysyl pyridinoline and lysyl pyridinoline. These results indicate that serum pyridinolines, especially lysyl pyridinoline, may be used as specific biochemical markers of bone resorption in hemodialyzed patients.

Effect of bisphosphonate therapy and parathyroidectomy on the urinary excretion of galactosylhydroxylysine in primary hyperparathyroidism

BACKGROUND

In patients with mild or asymptomatic primary hyperparathyroidism a reliable index of bone resorption might be useful for appropriate management. Hydroxyproline is the most commonly used marker of bone resorption but its low specificity and sensitivity are known. Galactosylhydroxylysine, an amino acid mainly represented in bone collagen, has been proposed as a more suitable index of bone resorption. In this study we evaluated the sensitivity of galactosylhydroxylysine and hydroxyproline assays in following the changes of their urinary levels in 12 patients with mild primary hyperparathyroidism before and after treatment with bisphosphonate and surgery.

METHODS

Serum and fasting urine specimens were obtained from 12 women with mild primary hyperparathyroidism before and after bisphosphonate treatment (2.5 mg daily for 5 days, intravenously) and after a further 25 days; in 7 patients biochemical tests were also performed 1 and 6 days after parathyroidectomy. Galactosylhydroxylysine was assayed by an HPLC method and hydroxyproline by a RIA commercial kit.

RESULTS

Baseline galactosylhydroxylysine urinary levels were far above the normal range in all the patients whilst in 8 of them baseline hydroxyproline levels were normal. Bisphosphonate treatment significantly decreased bone turnover as shown by a significant fall in serum calcium (from 2.9 to 2.6 mmol/l; P < 0.001) and in galactosylhydroxylysine and hydroxyproline (-55 and -31% respectively). Twenty-five days after the end of treatment, resorption increased again and serum calcium and galactosylhydroxylysine, but not hydroxyproline, rose significantly towards basal levels. One day after parathyroidectomy serum calcium, galactosylhydroxylysine and PTH showed reduction below normal ranges. PTH and galactosylhydroxylysine returned to normal values at day 6 after parathyroidectomy. No changes in hydroxyproline levels were seen. Galactosylhydroxylysine, but not hydroxyproline, correlated significantly with serum calcium and PTH.

CONCLUSION

Galactosylhydroxylysine appears to be a sensitive index of bone resorption, useful in the clinical assessment of bone involvement and in the management of patients with mild primary hyperparathyroidism.

Biochemical markers of bone turnover

The noninvasive assessment of bone turnover has received increasing attention over the past few years because of the need for sensitive markers in the clinical investigation of osteoporosis. Markers of bone formation include the serum measurement of total and bone-specific alkaline phosphatase, osteocalcin, and type I collagen extension peptides. Assessment of bone resorption can be achieved with measurement of fasting urinary calcium and hydroxyproline, urinary hydroxylysine glycosides, urinary excretion of the pyridinium cross-links (pyridinoline and deoxypyridinoline), and plasma tartrate-resistant acid phosphatase activity. Several studies performed in a variety of metabolic bone diseases have shown these markers to be of unequal sensitivity and specificity. In addition, some of them are not fully characterized. For assessment of the level of bone turnover in women with vertebral osteoporosis, serum osteocalcin and urinary pyridinoline appear to be the most sensitive markers so far. Programs combining bone mass measurement and assessment of bone turnover by several markers in women at the time of menopause are being developed in an attempt to improve the assessment of the risk for osteoporosis. Efforts are being made to develop more convenient assays and to identify other markers of bone turnover. A battery of various specific markers is likely to improve the assessment of the complex and subtle abnormalities of bone metabolism that characterize metabolic bone diseases, especially the various aspects of osteoporosis.

Biochemical markers of bone turnover. I: Theoretical considerations and clinical use in osteoporosis

The recent development of noninvasive techniques to measure bone mass and bone turnover represents a major advance in the diagnosis and management of osteoporosis. The rate of formation or degradation of the bone matrix can be assessed either by measuring a prominent enzymatic activity of the bone-forming or resorbing cells, such as alkaline and acid phosphatase activity, or by measuring bone matrix components released into the circulation during formation or resorption. Recent studies have shown that the appropriate combination of the most efficient markers of bone resorption and formation will provide a powerful tool in the clinical investigation of osteoporosis.

Galactosyl hydroxylysine and deoxypyridinoline: a methodological comparison

Galactosyl hydroxylysine and deoxypyridinoline are at present the most promising markers of bone resorption. Various studies have indeed shown that these two markers discriminate with high accuracy subjects with different rates of bone turnover and that their accuracies and discriminate power are very similar. The aim of this paper is to compare the practicality and the reproducibility of the HPLC galactosyl hydroxylysine and deoxypyridinoline assays. In summary, this review shows that the galactosyl hydroxylysine and deoxypyridinoline HPLC assays differ mainly in the need, in using deoxypyridinoline, for an acid hydrolysis and a preextraction of the urine samples. This implies two major problems for deoxypyridinoline: 1) more time is required due to the cumbersome preanalytical procedures; and 2) a lower reproducibility. Our data, in fact, show that both the intra-assay and inter-assay coefficient of variation of the deoxypyridinoline assay are almost 100% higher than those of the galactosyl hydroxylysine assay.

High-performance liquid chromatographic method for measuring hydroxylysine glycosides and their ratio in urine as a possible marker of human bone collagen breakdown

Glucosyl-galactosyl-hydroxylysine (GGHYL) and galactosyl-hydroxylysine (GHYL) are constituents of collagen protein. The ratio of the two hydroxylysine glycosides varies with the collagen type and, moreover, for a given collagen type, it also varies according to the connective tissue. For example, in type I collagen (the most abundant in the body), the GGHYL/GHYL ratio tends to be greater in soft connective tissues and lower in bone. The hydroxylysine glycosides are not recycled during collagen turnover and are excreted in the urine. Therefore, the urinary GGHYL/GHYL ratio, which reflects the proportion of the two metabolites in the various collagens, may indicate the type of connective tissue affected by pathological turnover, and may thus be a promising marker of bone metabolism. In this paper a method is described for the measurement of urinary hydroxylysine glycosides by reversed-phase liquid chromatography after purification of the sample by solid-phase extraction. The method presented is analytically reliable and suitable for routine use in a clinical laboratory.

The glycosides of hydroxylysine are final products of collagen degradation in humans

Glucosyl-galactosyl-hydroxylysine (GGHYL) and galactosyl-hydroxylysine (GHYL) are metabolites derived from collagen degradation. They are useful biochemical markers provided they are not further processed. Experiments were run to test the activity of alpha- and beta-glycosidases in human kidney cortex preparations. Results allow to exclude the presence of the specific enzymes, in contrast with what is reported for the rat kidney tissue.

Markers of bone and collagen breakdown in early inflammatory arthritis

Inflammatory arthritis has the potential to cause irreversible erosive damage to cartilage and bone. This may occur very early in the course of the disease. At present it is not possible at diagnosis to identify those patients who will develop erosive damage. If this were possible, it would enable aggressive therapy to be targeted to those patients at greatest risk. There is therefore a need for sensitive markers to detect and quantify joint damage at as early a stage as possible. In this chapter we review potential biochemical markers of such damage and assess their clinical usefulness.

Urinary excretion of pyridinium crosslinks of collagen in patients with osteoporosis and the effects of bone fracture

Values for the urinary excretion of pyridinium crosslinks of collagen, pyridinoline and deoxypyridinoline, in a group of 30 elderly women with femoral fractures associated with osteoporosis and a group of 20 women without recent fracture but with overt or suspected osteoporosis were compared with 27 control subjects matched for age. Relative to the control group, the excretion of the crosslinks was significantly higher in the group with fractures and the group with osteoporosis. Fractures contributed markedly to the excretion of pyridinium crosslinks as the patients with fractures showed significantly higher excretion of pyridinoline and deoxypyridinoline than the group without recent fractures. This was confirmed by the fact that excretion of pyridinium crosslinks in patients with accidental bone fractures was significantly higher than for healthy control subjects matched for age and sex. The crosslinks appear to provide valid indices of bone resorption, but the effects of bone fracture must be considered in the clinical application of this technique.