The response of the skeleton to physical training: a biochemical study in horses

Bisphosphonates in veterinary medicine: The new horizon for use

Bisphosphonates (BPs) are characterized by their ability to bind strongly to bone mineral and inhibit bone resorption. However, BPs exert a wide range of pharmacological activities beyond the inhibition of bone resorption, including the inhibition of cancer cell metastases and angiogenesis and the inhibition of proliferation and apoptosis in vitro. Additionally, the inhibition of matrix metalloproteinase activity, altered cytokine and growth factor expression, as well as reductions in parameters of pain have also been reported. In humans, clinical BP use has transformed the treatment of post-menopausal osteoporosis, rare bone diseases such as osteogenesis imperfecta, as well as multiple myeloma and metastatic breast and prostate cancer, albeit not without infrequent but significant adverse events. Despite the well-characterized health benefits of BP use in humans, the evidence-base for the therapeutic efficacy of BPs in veterinary medicine is, by comparison, limited. Notwithstanding, BPs are used widely in small animal veterinary practice for the medical management of hyperparathyroidism, idiopathic hypercalcemia in cats, as well as for the palliative care of bone tumors which are common in dogs, and in particular, primary bone tumors such as osteosarcoma. Palliative BP treatment has also recently increased in veterinary oncology to alleviate tumor-associated bone pain. In equine veterinary practice, non-nitrogen-containing BPs are FDA-approved to control clinical signs associated with navicular syndrome in adult horses. However, there are growing concerns regarding the off-label use of BPs in juvenile horses. Here we discuss the current understanding of the strengths, weaknesses and current controversies surrounding BP use in veterinary medicine to highlight the future utility of these potentially beneficial drugs.

The Effect of a Moderate Exercise Program on Serum Markers of Bone Metabolism in Dogs

Simple Summary

In this article, we investigate the long-term (four months) effects of a 25 min moderate-intensity treadmill exercise, three times per week, on serum markers of bone metabolism (bone alkaline phosphatase and osteocalcin as bone formation markers and C-terminal telopeptide as bone resorption marker) in dogs. Twenty healthy dogs (Labrador and Golden Retrievers), median age 16.2 (11.7–24.4) months underwent the exercise program. Blood samples were collected as a baseline, mid-term (after two months) and at the end of the study. The values of bone formation markers significantly decreased following two months of exercise program; after which, bone alkaline phosphatase increased while osteocalcin concentration continued to decrease towards the end of the study. Bone resorption marker did not significantly change through the exercise duration. In overall, moderate exercise resulted in no change in bone resorption, and a mild bone formation in young developing dogs.

Abstract

The beneficial effect of physical activity on the musculoskeletal health in dogs is well recognized, but the level of intensity, duration, and frequency of exercise is not fully described. Measurement of serum markers of bone metabolism (bone alkaline phosphatase and osteocalcin as bone formation markers and C-terminal telopeptide as bone resorption marker) during four months of organized moderate-intensity physical training in Labrador retriever and Golden retriever dogs aged between 11.7–24.4 months, showed variations of bone metabolism. Dogs were included in treadmill running sessions for 25 min, three times per week. Blood samples were taken at the beginning of the program (baseline), after two months (mid-term) and at the end of the study after four months. The values of bone alkaline phosphatase and osteocalcin significantly decreased following two months of exercise program. Bone alkaline phosphatase increased by the end of four-month training cycle, but did not reach baseline value. Osteocalcin levels continued to decrease towards the end of the study. C-terminal telopeptide concentrations did not significantly change throughout the study duration. The results of this study show that aerobic exercise of moderate-intensity caused an initial decrease in bone formation followed by an increase of bone alkaline phosphatase and a further decrease of osteocalcin concentration. The response of two formation markers can be explained by the different stage of osteoblast activity that they express. In summary, moderate exercise resulted in no change in bone resorption, and a mild bone formation in young developing dogs.

Revisiting predictive biomarkers of musculoskeletal injury in thoroughbred racehorses: longitudinal study in polish population

BACKGROUND

High prevalence of musculoskeletal disorders in racehorses and its impact on horse welfare and racing economics call for improved measures of injury diagnosis and prevention. Serum biomarkers of bone and cartilage metabolism have previously shown promise in prediction of musculoskeletal injuries in horses. This study aimed to re-evaluate usability of the predictive serum biomarkers identified in North American Thoroughbred racehorses in a geographically distinct group of Polish Thoroughbreds.

RESULTS

Serum concentrations of bone and cartilage biomarkers: osteocalcin, c-terminal telopeptide of type I collagen, total glycosaminoglycans (GAG), chondroitin sulfate epitope and c-propeptide of type II procollagen (CPII) were evaluated in the beginning and the next 3 months of one racing season in a cohort of twenty-six 2-year-old Polish racehorses. Exit criteria were diagnosis of musculoskeletal injury, leading to > 5 days off training (n = 8), or completion of 3 study months with no training interruptions (n = 18). Normalized results and matching archival data from 35 2-year-old North American racehorses was used for logistic regression analysis to identify universal predictors of injury. Mean GAG and CPII levels were lower in injured group comparing to control, which is consistent with previous findings in racehorses. These biomarkers were also identified as predictors of injury in the mixed population model. Population origin had no significant effect on predictive value of evaluated biomarkers (Wald test p = 0.137). Decreased osteocalcin and increased c-terminal telopeptide of type I collagen levels in injured horses comparing to controls were specific for Polish population and signalized disruption in bone turnover homeostasis.

CONCLUSIONS

Changes in serum GAG and CPII in racehorses at risk of injury appear to be similar across distinct populations while dynamics of serum bone marker is more population-specific.

Bone turnover markers in sheep and goat: A review of the scientific literature

Bone turnover markers (BTMs) are product of bone cell activity and are generally divided in bone formation and bone resorption markers. The purpose of this review was to structure the available information on the use of BTMs in studies on small ruminants, especially for monitoring their variations related to diet, exercise, gestation and metabolic lactation state, circadian and seasonal variations, and also during skeletal growth. Pre-clinical and translational studies using BTMs with sheep and goats as animal models in orthopaedic research studies to help in the evaluation of the fracture healing process and osteoporosis research are also described in this review. The available information from the reviewed studies was systematically organized in order to highlight the most promising BTMs in small ruminant research, as well as provide a wide view of the use of sheep and goat as animal models in orthopaedic research, type of markers and commercial assay kits with cross-reactivity in sheep and goat, method of sample and storage of serum and urine for bone turnover markers determination and the usefulness and limitations of bone turnover markers in the different studies, therefore an effective tool for researchers that seek answers to different questions while using BTMs in small ruminants.

Relationship between serum biomarkers of cartilage and bone metabolism and joint injury in young Thoroughbred racehorses in training

OBJECTIVE

To compare serum concentrations of biomarkers of cartilage and bone metabolism between racehorses with a carpal or metacarpophalangeal or metatarsophalangeal (ie, fetlock) joint injury and matched uninjured control horses, determine changes in biomarker concentrations following joint injury, and establish the biomarkers' diagnostic test performance.

ANIMALS

50 Thoroughbred racehorses with a carpal or fetlock joint injury and 50 matched uninjured horses (control horses).

PROCEDURES

Serum concentrations of 2 cartilage synthesis biomarkers (carboxy-terminal propeptide of type II collagen [CPII] and chondroitin sulfate epitope 846 [CS846]), 2 cartilage degradation biomarkers (neoepitope generated by collagenase cleavage of type II collagen [C2C] and cross-linked carboxy-terminal telopeptide fragments of type II collagen [CTX-II]), and serum activity of a bone formation marker (bone-specific alkaline phosphatase [BAP]) were measured around the time of injury diagnosis and monthly thereafter for as long as possible.

RESULTS

Injured horses as a group and horses specifically with fetlock joint injuries had significantly lower serum CPII concentrations and significantly higher serum BAP activities than matched control horses. Concentrations of CTX-II were decreased between 2 and 4 months following joint injury. Measurement of CPII concentration at baseline could distinguish between injured horses and control horses with a sensitivity of 82% and specificity of 50%.

CONCLUSIONS AND CLINICAL RELEVANCE

Although significant differences in specific biomarker concentrations between horses with carpal and fetlock joint injuries and matched control horses were identified, there was no convincing evidence of the suitability of these biomarkers as diagnostic or prognostic tools in a clinical setting.

Influence of housing type and age in female pigs. 1. Effects on growth performance and fat deposition and distribution in the carcasses of female Large White × Landrace pigs grown from 5.5 to 120 kg liveweight

One hundred and sixty female Large White × Landrace pigs were obtained at 3 weeks of age, average liveweight (LW) 5.5 ± 0.08 kg, stratified on LW and allocated to four treatments in a factorial design that consisted of two housing treatments, conventional (C) or deep-litter (D), across two growth periods: early (3–13 weeks of age) and late (13–24 weeks of age). At 13 weeks of age eight pigs per treatment (n = 32) were slaughtered, and the remaining pigs (n = 128) moved to new pens where they remained until slaughter at 24 weeks of age. Moving pigs into a new housing system caused a growth reduction, as indicated by significantly lower LW (P = 0.003), compared with pigs that remained within the same housing system, regardless of whether the new system was C or D. Carcass composition results indicated that pigs finished in the D system (24 weeks of age) were not fatter than pigs raised in C housing, with pigs raised entirely in C housing tending to be the fattest (P = 0.090). There was an effect of housing on fat distribution within the carcass where pigs finished in D housing had significantly less fat in the belly primal compared with pigs finished in the C facilities (35.3 versus 31.2%, P = 0.030). These findings suggest that the strategy of moving pigs from D housing to C housing for finishing, to reduce carcass fatness and improve pig growth performance, was not successful as pigs were fatter, lighter and less efficient than pigs of the same age housed in D from wean to finish.

Serum biomarker levels for musculoskeletal disease in two- and three-year-old racing Thoroughbred horses: A prospective study of 130 horses

REASON FOR PERFORMING STUDY

Biomarkers have shown some in vivo promise for the detection of musculoskeletal injuries, but further study to assess biomarker levels in clinical orthopaedic disease is required.

OBJECTIVE

To assess 7 serum biomarkers for the detection of musculoskeletal injuries.

METHODS

Two- and 3-year-old racehorses were entered into the study (n = 238). Exit criteria were lack of training for >30 days, or completion of 10 study months. Data from horses with solitary musculoskeletal injuries and completion of >2 months were analysed. Musculoskeletal injury was considered intra-articular fragmentation (IAF), tendon or ligamentous injury (TL), stress fractures (SF) and dorsal metacarpal disease (DMD). Monthly lameness examination and serum collection were performed. Serum was analysed for glycosaminoglycan (GAG), type I and II collagen degradation (C1, 2C), type II collagen synthesis (CPII), type II collagen degradation (Col CEQ), aggrecan synthesis (CS846), osteocalcin (OC) as a marker of bone formation and (C-terminal telopeptide of type I collagen) CTX as a marker of bone degradation.

RESULTS

Of the 238 horses 59 injured and 71 uninjured control horses met the analysis criteria. Based on injury no significant differences in the proportions were observed for age, gender or lesion type, although a higher proportion of injuries occurred at the beginning of the study. Of injured horses, 16 (27%) sustained an IAF, 17 (29%) a TL injury, 7 (12%) SF and 19 (32%) were diagnosed with DMD. There were significant changes seen in biomarkers based on the injury incurred when longitudinal samples were assessed. Furthermore, based on the serum biomarkers collected prior to injury, horses could be correctly classified as injured or uninjured 73.8% of the time.

CONCLUSIONS

A unique biomarker pattern occurred before each injury and this was beneficial in classifying horses as injured or uninjured.

POTENTIAL RELEVANCE

Biomarkers have the potential to be used as a screening aid prior to musculoskeletal injury.

Response of biochemical markers of bone metabolism to exercise intensity in thoroughbred horses

We studied the response of biochemical markers of bone metabolism to exercise intensity in horses. Four horses were walked on a mechanical walker for one week (pre-exercise). Then they performed low-speed exercise on a high-speed treadmill in the first week and medium-speed exercise in the second week and high-speed exercise in the third week of training. We measured two indices of bone resorption, serum hydroxyproline concentration and the urinary deoxypyridinoline/creatinine ratio, and serum osteocalcin (OC) concentration as an index of bone formation. Both indices of bone resorption gradually decreased during the experiment. Serum OC concentration did not change in the first week but was significantly lower in the second and the third weeks compared to in the pre-exercise period and in the first week. These results suggest that the low-speed exercise decreased bone resorption but did not affect bone formation, which possibly results in increasing bone mineral content and strengthening of bones. The high-speed exercise decreased bone formation and bone resorption, i.e., bone turnover was suppressed. The low-speed exercise may be preferable for increasing bone mineral content.

Analysis of biochemical markers of bone metabolism in Asian elephants (Elephas maximus)

Two human enzyme immunoassays (EIA) and one radioimmunoassay (RIA) were validated and used to measure osteocalcin (OC), bone alkaline phosphatase (BAP), and the cross-linked telopeptide domain of type I collagen (ICTP), in serum from Asian elephants (Elephas maximus). Sera from four adult females sampled on 7 consecutive days were also analyzed to assess the existence and magnitude of intraindividual day-to-day variability of the serum concentration of these markers. Sample dilution curves were parallel with assay standard curves, which demonstrated that excellent cross reactivity existed between assay antibodies and elephants marker antigens. Statistically significant inverse correlations were found between age and concentrations of all three markers: BAP, r = -0.862 (P < 0.01); OC, r = -0.788 (P < 0.002); and ICTP, r = -0.848 (P < 0.01). Strong positive correlations were found between BAP and OC (r = 0.797, P < 0.01), OC and ICTP (r = 0.860, P < 0.01), and between BAP and ICTP (r = 0.958, P < 0.01). No statistically significant intraindividual variability was found over 7 days in the four adult females for any of the markers assessed (OC: P = 0.089; ICTP: P = 0.642; BAP: P = 0.146; n=4 in each case). The overall coefficient of variability observed in this group of animals was 10.3%, 7.4%, and 5.5% for OC, BAP, and ICTP, respectively. These results suggest a potential role for biochemical markers of bone turnover in monitoring skeletal health and bone disease in Asian elephants.

Changes in synovial fluid and serum biomarkers with exercise and early osteoarthritis in horses

OBJECTIVE

To discriminate between changes in biomarkers with exercise compared to changes in biomarkers with osteoarthritis (OA) in exercising horses.

METHOD

Sixteen, 2-year-old horses were randomly assigned either to an exercise-alone (n=8) or OA-affected (also exercised) (n=8) group. All horses had both mid-carpal joints arthroscoped and OA induced in one mid-carpal joint in the OA-affected joints of OA-affected horses. Two weeks after surgery all horses commenced a strenuous exercise program on a high-speed treadmill. Clinical outcomes and synovial fluid and serum biomarkers, were evaluated weekly. Synovial and serum biomarkers evaluated were epitope CS846 (CS846), epitope CPII (CPII), glycosaminoglycans (GAGs), epitope Col CEQ (Col CEQ) (a marker of type II collagen degradation), type I and II collagen degradation fragments (C1,2C), osteocalcin, C-terminal of bone type I collagen (CTX1), type I collagen (Col I) and (synovial fluid only of cartilage) prostaglandin E2 (PGE2) levels. Horses were euthanized at day 91 and their joints assessed grossly, histopathologically, and histochemically.

RESULTS

Exercise induced a significant increase in synovial fluid CS846, CPII, GAG, Col CEQ, C1,2C, osteocalcin and Col I concentrations. There was a significant increase in synovial fluid CS846, CPII, Col CEQ, C1,2C, osteocalcin, Col I and PGE2 concentrations in OA-affected joints compared to exercise-alone joints. The concentration of serum CS846, CPII, GAG, osteocalcin, C1,2C and Col I increased with exercise. For each of these biomarkers there was also a statistically significant increase in serum biomarker levels in OA-affected horses compared to exercise-alone horses.

CONCLUSIONS

Six synovial fluid and serum biomarkers were useful in separating early experimental OA from exercise alone but synovial fluid CTX1 and serum Col CEQ and CTX1 were not.

High-intensity exercise induces structural, compositional and metabolic changes in cuboidal bones--findings from an equine athlete model

Fatigue fracture of cuboidal bones occurs in the human foot as well as the equine carpus. The racehorse provides a naturally-occurring model to study the effects of high-intensity exercise on the morphology and metabolism of cuboidal bones. We studied both the mineral and the collagenous matrix of the third (C(3)) and radial (C(r)) carpal bones of raced and non-raced Thoroughbred (TB) horses. We hypothesised that racehorses would show increases in the mineral component of these bones and post-translational modifications of the collagenous matrix alongside changes in markers of collagen remodelling and bone formation. C(3) and C(r) carpal bones were retrieved from raced TB horses (n=14) and non-raced TB horses (n=11). Standardised proximal-distal sections were taken from each bone and these were sliced transversely to study the proximal-distal differences in bone metabolism from the subchondral plate through to trabecular bone. Histomorphometry and bone mineral density measurements were performed in parallel with biochemical analyses including total collagen, collagen synthesis and cross-links, matrix metalloproteinases-2 and 9 and their inhibitors, calcium and phosphate, and bone alkaline phosphatase. The results of this study show that, while there is a net increase in bone formation in the racehorses, there is additionally an increase in bone collagen synthesis and remodelling, particularly within the trabecular regions of the bone. The increase in bone density would lead to greater stiffness, particularly in the cortical bone, and failure of this 'stiffer' cortical bone may result from its lack of support from the rapidly remodelling and structurally weakened underlying trabecular bone.

Joint dependent concentrations of bone alkaline phosphatase in serum and synovial fluids of horses with osteochondral injury: an analytical and clinical validation

OBJECTIVES

Validate use of a commercially available immunoassay for measurement of bone alkaline phosphatase (BAP) in equine serum and synovial fluid (SF), and investigate the effects of osteochondral (OC) injury in horses on BAP concentrations in serum and SF.

METHODS

SF was collected from 37 joints of 34 Thoroughbred (TB) racehorses undergoing arthroscopic surgery for the removal of OC fragments from either the carpal joints (n=18) or the metacarpo-/metatarsophalangeal (MP) joints (n=19). SF was also obtained from 52 joints of 16 normal TB horses, collected bilaterally from carpal joints of 10 horses (n=40), and MP joints of six horses (n=12). Blood was obtained from all 50 horses. A commercially available immunoassay was validated and subsequently used to determine equine serum and SF BAP concentrations. Correlations to radiographic and arthroscopic scores were assessed.

RESULTS

BAP concentrations were significantly lower in serum from horses with OC injury in their carpal or MP joints than in serum from normal horses. SF BAP concentrations in normal and OC injured carpal joints were significantly higher than MP joints. BAP concentrations were significantly higher in SF from OC injured carpal joints than normal. BAP concentrations were affected by joint sampled, with age having a significant interaction. Concentrations of BAP in the serum (<30U/L), SF (>22U/L) and a ratio of SF to serum > or = 0.5 were predictive of OC injury. Radiographic and arthroscopic scores significantly correlated with serum BAP concentrations, and SF:serum BAP correlated with arthroscopic scores.

CONCLUSIONS

Determination of serum and SF BAP concentrations may be beneficial in the investigation of early joint injury. Joint and injury dependent differences in BAP concentrations allowed the estimation of predictive value for identifying OC injury.

Serum osteocalcin and CTX-MMP concentration in young exercising thoroughbred racehorses

Bone responds to exercise with changes in bone (re-)modelling, which might be monitored non-invasively with biochemical bone markers. The aim of this study was to evaluate the influence of exercise on serum osteocalcin and serum carboxy-terminal cross-linked telopeptide of type I collagen generated by matrix metalloproteinases (CTX-MMP) concentration in young racehorses. Seventy-one 2 to 4-year-old Thoroughbreds were included in this prospective infield study. Blood sampling was performed six times (i.e. six sampling cycles) during a 9-month period. Serum samples were analysed with commercial osteocalcin and CTX-MMP radioimmunoassays. Two-year-old racehorses had higher serum osteocalcin and CTX-MMP values than 3-year-old horses. Gender and training amplitude did not significantly influence serum osteocalcin and CTX-MMP values. Two-year-old horses showed an increase in osteocalcin values between cycles 2 and 3 and an increase in serum CTX-MMP values between cycles 1 and 2. Serum osteocalcin and CTX-MMP concentrations decreased between cycles 4 and 5, and 5 and 6. Three-year-old horses showed an increase in serum osteocalcin levels between cycles 3 and 4 and an increase in serum CTX-MMP concentrations between cycles 1 and 2, and 3 and 4. Serum osteocalcin levels decreased between cycles 5 and 6, whereas serum CTX-MMP levels decreased between cycles 4 and 5, and 5 and 6. Two- and three-year-old horses showed a decreased osteocalcin/CTX-MMP ratio between cycles 1 and 2. Moreover, 2-year-old horses showed an increase in the osteocalcin/CTX-MMP ratio between cycles 2 and 3. Sore shin formation did not significantly influence serum osteocalcin and CTX-MMP values. Serum osteocalcin and CTX-MMP are promising bone markers for monitoring exercise induced changes in equine bone metabolism.

Biochemical markers of bone metabolism in animals: uses and limitations

Routine assessment of the skeleton's response to disease and injury traditionally has consisted of plain-film radiography supplemented with advanced imaging techniques, such as computed tomography, magnetic resonance imaging, nuclear scintigraphy, and bone densitometry. Although these techniques provide increased sensitivity as compared with radiography, they still are limited by the fact that they can only document the net results of past skeletal activity. In contrast, serum and urinary biomarkers of bone formation and resorption provide near real-time information about bone cell activity. In this review, I describe the scientific rationale behind the use of these markers in humans and detail the efforts that have been made to adapt this technology to veterinary medicine and animal research. Commercial assay kits that are applicable to different animal species are described, and the potential limitations of the technology are discussed. The goal of this review is to provide clinical pathologists and researchers with the information needed to decide whether the use of bone markers is likely to be helpful and to select the most appropriate marker (or panel of markers) to answer a particular question.

Evaluation of serum concentrations of biochemical markers of bone metabolism and insulin-like growth factor I associated with treadmill exercise in young horses

OBJECTIVE

To evaluate changes in serum concentrations of biochemical markers of bone metabolism and insulin-like growth factor I (IGF-I) associated with treadmill exercise in young horses.

ANIMALS

12 two-year-old Thoroughbred mares.

PROCEDURE

During a 20-week study period, 6 horses were exercised on a treadmill 3 times a week (exercise group) and 6 horses received walking exercise 6 days a week (controls). Serum concentrations or activity of biochemical markers and IGF-I were assessed biweekly. Bone mineral density and content of the first phalanx were measured by dual-energy X-ray absorbiometry (DEXA) on completion of the study.

RESULTS

Compared with values in controls, bone mineral density and content were higher and serum concentrations of osteocalcin (a marker of bone formation) and the carboxy-terminal telopeptide of type I collagen (a marker of bone resorption; ICTP) were lower in exercised horses. Serum concentration and activity of the bone formation markers carboxy-terminal propeptide of type I collagen and bone-specific alkaline phosphatase (BAP) were not different between the 2 groups. Serum IGF-I concentration was lower in the exercise group, compared with control values; there was a significant correlation between change in IGF-I values and changes in osteocalcin, ICTP, and BAP values at the end of the study.

CONCLUSIONS AND CLINICAL RELEVANCE

Treadmill exercise over 20 weeks induced adaptive changes in bones of 2-year-old Thoroughbreds; training appears to increase bone mineral density, thereby enhancing mechanical strength of bone, but decreases bone turnover. Results indicated an association between changes in serum IGF-I concentration and bone cell activity in horses.

Significant exercise-related changes in the serum levels of two biomarkers of collagen metabolism in young horses

OBJECTIVE

To identify metabolic biomarkers that can be evaluated in serum for monitoring the effects of exercise on skeletal development in mammals.

DESIGN

Sera of foals from three groups (box-stall rest, pasture and training) were serially collected over the first 5 months of life and assayed for eight biomarkers of cartilage and bone metabolism. Sub-populations from each group were sampled for an additional 6 months of identical exercise.

RESULTS

When expressed as a percentage of baseline values, lower serum levels of the carboxy-terminal propeptides of type II collagen (CPII), and higher serum levels of the cross-linked telopeptide fragments of degraded type I collagen (CTx1) were found in the trained foals compared to the other groups. Significant differences disappeared in those foals sampled during an additional 6 months of identical exercise. The most significant correlations were between serum biomarkers of bone metabolism, being positive between anabolic markers and negative between anabolic and catabolic markers. Serum levels of CTx1 and CPII significantly increased with age in all groups throughout the study.

CONCLUSIONS

We have identified two markers of collagen metabolism, CPII and CTx1, as potential serum indicators of the exercise effects on the developing skeletal system in horses. Forced exercise during the first months postpartum appeared to have a negative effect on collagen turnover when compared to levels in pastured foals. Routine monitoring of collagen biomarkers in sera of exercising young mammals may allow for the early detection of abnormalities in skeletal tissue metabolism and for subsequent intervention before permanent damage occurs.

Calcium homeostasis and intact plasma parathyroid hormone during exercise and training in young Standardbred horses

Physical exercise is known to affect calcium homeostasis in horses, but there is little information on the hormonal regulation of calcium metabolism during exercise. In order to evaluate the effects of exercise and training on calcium homeostasis and intact plasma parathyroid hormone, 7 untrained Standardbred horses were studied in a 6 week training programme. These horses were accustomed to running on the treadmill 3 weeks before onset of training and were exercised on a high-speed treadmill with an initial incremental standardised exercise test (SET 1: 6 incremental steps of 5 min duration each; first step 5 m/s, increase 1 m/s). SET 1 was followed by a lactate-guided training programme (6 weeks in total) with 2 types of exercise in alternating order with a day of rest after each work day: high-speed exercise (HSE) of 15 min duration, starting at VLa4, continuous increase in speed every 60 s by 0.3 m/s (14 incremental steps); and low-speed exercise (LSE) at a constant velocity at VLa2.5, duration approximately 60-90 min. The whole training programme consisted of 8 HSE and 8 LSE sessions. HSE and LSE were calculated to require the same energy expenditure. A final SET (SET 2) finished the training programme. Blood samples for lactate, plasma total calcium [Ca], blood ionised calcium [Ca2+], blood pH, plasma inorganic phosphorus [P(i)] and plasma intact parathyroid hormone [PTH] were collected before, during and after SETs 1 and 2, before and after the first and eighth HSE and LSE. During SETs 1 and 2, HSEs 1 and 8 there was a decrease in ionised Ca2+ and pH and a rise in lactate, intact PTH and P(i). LSEs 1 and 8 resulted in an increase in pH, whereas lactate, ionised Ca2+, total Ca, P(i) and intact PTH were not affected. No changes in calcium metabolism were detected during training. Results of this study suggest that intact PTH is a mediator in counter-regulation of exercise-induced hypocalcaemia.

Biochemical markers of bone activity in young standardbred horses during different types of exercise and training

Seven untrained Standardbred horses were used in a training programme of 6 weeks to evaluate the effects of exercise and training on bone metabolism. The horses were exercised on a treadmill according to a standardized exercise test (SET 1: six incremental steps, 5 min duration each; start 5 m/s, increase 1 m/s). SET 1 was followed by a training programme of 6 weeks. In alternating order: high-speed exercise (HSE): 15 min duration, start at VLa4, continuous increase in speed every 60 s by 0.3 m/s (14 incremental steps); low-speed exercise (LSE): constant velocity at VLa2.5, duration: approximately 60-90 min (total training programme: eight HSE and eight LSE sessions). SET 2 finished the training programme and a deconditioning period of 12 weeks followed. Blood samples for lactate, total plasma protein (TPP), osteocalcin, and ICTP (cross-linked C-telopeptide of type I collagen) were collected. ICTP increased during SET 1 and SET 2, whereas osteocalcin decreased to below resting concentration 24 h after SET 1. A rise in ICTP was observed during LSE 1 and LSE 8, which was followed by a drop 24 h after exercise. No changes in osteocalcin were noted during LSE 1, but 24 h after LSE 1 osteocalcin dropped to below pre-exercise levels. LSE 8 resulted in an increase in osteocalcin, followed by a drop 24 h after LSE 8. Osteocalcin and ICTP were not affected by HSE. Baseline osteocalcin levels dropped during the course of training. The acute response of biochemical bone markers indicates a direct influence of a single bout of exercise on bone metabolism.

Serum concentrations of keratan sulfate, osteocalcin, and pyridinoline crosslinks after oral administration of glucosamine to standardbred horses during race training

OBJECTIVE

To determine the effects of orally administered glucosamine on concentrations of markers of bone and cartilage metabolism in Standardbred horses during race training.

ANIMALS

Twenty 16- to 20-month-old Standardbreds beginning race training.

PROCEDURE

Horses were randomly assigned to 2 groups. One group received glucosamine hydrochloride (4 g, PO, q 12 h), and the second (control) group received glucose (4 g, PO, q 12 h). Serum samples were obtained prior to onset of the study (baseline) and at regular intervals for 48 weeks for determination of concentrations of keratan sulfate (KS), osteocalcin (OC), and pyridinoline crosslinks (PYD).

RESULTS

Osteocalcin concentrations changed significantly with time; mean serum concentrations were significantly higher than baseline values for samples obtained at 24 to 48 weeks after onset of the study. Although a significant effect of time was observed for mean concentration of KS, concentrations did not differ significantly from baseline values at any time during the study when groups were analyzed separately. However, pooled analysis revealed significant increases of mean serum KS concentration at weeks 24 and 30. Significant changes in serum PYD concentrations were not detected. Oral administration of glucosamine did not significantly affect serum concentrations of any of the markers.

CONCLUSIONS AND CLINICAL RELEVANCE

Increased serum OC in clinically normal Standardbreds during race training may reflect bone formation that accompanies adaptive remodeling of the appendicular skeleton. For these experimental conditions, glucosamine did not appear to exert a detectable influence on serum concentrations of these 3 markers of connective tissue metabolism.

Simulation of bone adaptive remodeling using a stochastic process as loading history

In this simulation study for bone adaptive remodeling, loading conditions are described as stochastic processes to catch the unpredictable characteristics of daily physical activities, which are observed to be closely related with bone adaptive remodeling. This will not only eliminate the necessity of arbitrary choices for loading conditions, but also generate greater flexibility for simulations of bone adaptive remodeling. The sensitivity of simulation outcomes to the parameters in the simulation algorithm was examined by applying stochastic loading conditions on finite element models of simplified spine structures. In this way, the limitations induced by simplifying loading conditions into constant or cyclic loads can be avoided and, potentially, more clinical observations could be accommodated when more comprehensive finite element models are available.

Biochemical markers of bone metabolism in growing thoroughbreds: a longitudinal study

This study describes longitudinal changes in serum levels of biochemical markers of bone cell activity in a group of 24 thoroughbred foals from birth to 18 months of age. The markers of bone formation included the type I collagen carboxy-terminal propeptide (PICP), the bone-specific isoenzyme of alkaline phosphatase (BAP), and osteocalcin (OC). Levels of the cross-linked telopeptide of type I collagen (ICTP), a marker of bone resorption, and the N-terminal propeptide of type III collagen (PNIIIP), a marker of soft tissue turnover, were also measured. Levels of all markers fell significantly between birth and 18 months of age (70-80 per cent); this decrease being most marked between 0 and 6 months. However, a transient increase in levels of the markers then occurred between 6 and 14 months of age. The timing of this increase was specific for each parameter. ICTP and OC concentrations increased between October and December. PICP concentrations increased between December and April whereas the increase in PIIINP was coincident with the peak in weight gain between April and June. Changes in BAP concentration were less distinct at this time. Season was shown to have significant effects on the biochemical markers independent from the effect of age. Concentrations of all markers decreased with increasing body weight and at any given age heavier horses had lower marker levels. These results show that biochemical markers of bone cell activity and soft tissue turnover follow characteristic patterns of change in growing thoroughbreds influenced by age, season and bodyweight. The demonstration that the reference ranges for the biochemical markers change from month to month means that single samples from individuals are of little value for monitoring bone cell activity in growing thoroughbreds.

Training-induced changes in peritendinous type I collagen turnover determined by microdialysis in humans

1. Acute exercise is found to increase collagen type I formation locally in peritendinous connective tissue of the Achilles' tendon in humans, as determined from changes in interstitial concentrations of collagen propeptide (PICP) and a collagen degradation product (ICTP) by the use of microdialysis catheters. However, the local collagen type I turnover response to training is unknown. 2. Nineteen young males were studied before and after 4 and 11 weeks of physical training. Microdialysis catheters with a high molecular mass cut-off value (3000 kDa), allowing the determination of PICP and ICTP, were placed in the peritendinous space ventral to the Achilles' tendon, under ultrasound guidance, in both legs. The catheters were perfused with a Ringer-acetate solution containing (3)H-labelled human type IV collagen for in vivo recovery determination (relative recovery: 79 +/- 2 %, mean +/- S.E.M.). 3. The PICP concentration in the peritendinous tissue increased in response to training (from 5 +/- 1 to 35 +/- 5 microg l(-1) (4 weeks), P < 0.05) and remained elevated throughout the training period (28 +/- 6 microg l(-1), 11 weeks). Tissue ICTP only rose transiently with training (from 2.2 +/- 0.1 to 2.8 +/- 0.2 microg l(-1) (4 weeks), P < 0.05, and 2.5 +/- 0.2 microg l(-1) (11 weeks), P > 0.05 vs. basal). Plasma PICP was unchanged whereas plasma ICTP declined by 17 % in response to training. 4. The findings indicate that physical training results in an increased turnover of collagen type I in local connective tissue of the peritendinous Achilles' region. Early in the process both synthesis and degradation are elevated, whereas later, the anabolic processes are dominating causing a net synthesis of type I collagen in tendon-related tissue in humans.

Non-invasive assessment of equine bone: an update

This paper summarizes traditional and current methods of non-invasive assessment of bone in the horse. The description and potential clinical utility of two non-invasive technologies with major development in the last decade are presented, namely, (1) serum biochemical markers for bone turnover and (2) quantitative ultrasound. Serum biochemical markers of bone formation valid in horses are osteocalcin, carboxy-terminal peptide of type I procollagen and bone-specific alkaline phosphatase. The cross-linked carboxy-terminal telopeptide of type 1 collagen c-telopeptides of type I collagen and total deoxypyridinoline are the serum markers for bone degradation. These markers respond more rapidly to skeletal changes than other bone assessment techniques, but ideally each horse needs to be compared with itself. Quantitative ultrasound is radiation free and is a well-tolerated technique for measuring bone properties in horses. This device allows bone speed of sound measurements at various sites using the axial transmission mode along the cortex and gives information about stiffness, architecture, porosity and bone mass.A combination of different non-invasive assessment techniques is recommended for the evaluation of bone biphasic modelling-remodelling activity and the mineral phase with its architecture. The potential clinical and research use of these techniques is considered.

Type I collagen synthesis and degradation in peritendinous tissue after exercise determined by microdialysis in humans

1. Physical activity is known to increase type I collagen synthesis measured as the concentration of biomarkers in plasma. By the use of microdialysis catheters with a very high molecular mass cut-off value (3000 kDa) we aimed to determine local type I collagen synthesis and degradation in the peritendinous region by measuring interstitial concentrations of a collagen propeptide (PICP; 100 kDa) and a collagen degradation product (ICTP; 9 kDa) as well as an inflammatory mediator (PGE2). 2. Seven trained human runners were studied before and after (2 and 72 h) 3 h of running (36 km). Two microdialysis catheters were placed in the peritendinous space ventral to the Achilles' tendon under ultrasound guidance and perfused with a Ringer-acetate solution containing 3H-labelled human type IV collagen and [15-3H(N)]PGE2 for in vivo recovery determination. Relative recovery was 37-59 % (range of the s.e.m. values) for both radioactively labelled substances. 3. PICP concentration decreased in both interstitial peritendinous tissue and arterial blood immediately after exercise, but rose 3-fold from basal 72 h after exercise in the peritendinous tissue (55 +/- 10 microg l-1, mean +/- s.e.m. (rest) to 165 +/- 40 microg l-1 (72 h), P < 0.05) and by 25 % in circulating blood (160 +/- 10 microg l-1 (rest) to 200 +/- 12 microg l-1 (72 h), P < 0.05). ICTP concentration did not change in blood, but decreased transiently in tendon-related tissue during early recovery after exercise only. PGE2 concentration increased in blood during running, and returned to baseline in the recovery period, whereas interstitial PGE2 concentration was elevated in the early recovery phase. 4. The findings of the present study indicate that acute exercise induces increased formation of type I collagen in peritendinous tissue as determined with microdialysis and using dialysate fibre with a very high molecular mass cut-off. This suggests an adaptation to acute physical loading also in non-bone-related collagen in humans.

Biochemical markers of bone metabolism in draught and warmblood horses

Concentrations of the cross-linked carboxyterminal telopeptide of type I collagen (ICTP) and osteocalcin (OC) have been determined in the serum of one hundred clinically healthy adult Draught or Warmblood horses. The correlation between these two markers has been evaluated and the influence of gender, age and type of horse described. No significant variations were observed between animals of different sex, but a significant inverse correlation (P < 0.0001) with age was observed for both measured parameters. After correction for age, serum levels of OC were found to be lower in Draught [adjusted least square mean (LSM) = 6.612 micrograms.L-1] than in Warmblood horses (adjusted LSM = 8.596 micrograms.L-1), whereas levels of ICTP were higher in Draughts (adjusted LSM = 8.035 micrograms.L-1) than in Warmbloods (adjusted LSM = 6.643 micrograms.L-1). A significant correlation (P < 0.0001) was observed between OC and ICTP. This correlation was stronger if the type of horse was taken into account in the statistical model. The ratio OC:ICTP was independent of gender and age. A higher OC:ICTP ratio in Warmbloods compared to the Draught horses might reflect a higher bone remodelling level of horses submitted to regular daily work. It was concluded that ICTP and OC are influenced by the type of horse, and probably reflect a physiological difference in bone remodelling between these animals.

The functional matrix hypothesis revisited. 4. The epigenetic antithesis and the resolving synthesis

In two interrelated articles, the current revision of the functional matrix hypothesis extends to a reconsideration of the relative roles of genomic and of epigenetic processes and mechanisms in the regulation (control, causation) of craniofacial growth and development. The dialectical method was chosen to analyze this matter, because it explicitly provides for the fuller presentation of a genomic thesis, an epigenetic antithesis, and a resolving synthesis. The later two are presented here, where the synthesis suggests that both genomic and epigenetic factors are necessary causes, that neither alone is also a sufficient cause, and that only the two, interacting together, furnish both the necessary and sufficient cause(s) of ontogenesis. This article also provides a comprehensive bibliography that introduces the several new, and still evolving, disciplines that may provide alternative viewpoints capable of resolving this continuing controversy; repetition of the present theoretical bases for the arguments on both sides of these questions seems nonproductive. In their place, it is suggested that the group of disciplines, broadly termed Complexity, would most likely amply repay deeper consideration and application in the study of ontogenesis.

Effects of moderate endurance exercise on calcium, parathyroid hormone, and markers of bone metabolism in young women

We investigated the short-term (1 hour-3 days) effects of a 45 minute run on calcium, parathyroid hormone, the carboxyterminal propeptide of type I procollagen (PICP), and the immunoactive carboxyterminal telopeptide of type I collagen in serum (ICTP) in young females. Fourteen healthy young women, aged 25.2 +/- 0.6 years (mean +/- SEM) with regular menstruations, participated. The test was outdoor jogging for 45 minutes at an intensity of 50% of VO2 max. Blood samples were collected 15 minutes before the test and 1, 24, and 72 hours after the test. The measured values were adjusted for changes in plasma volume. A significant decrease of ionized calcium was observed at 1 hour (P < 0.001) and 72 hours (P < 0.05) and a significant increase of parathyroid hormone (PTH) was noted 24 (P < 0.01) and 72 hours (P < 0.05) after the test. A significant decrease of PICP at 1 hour (P < 0.05) was followed by an increase after 24 (P < 0.01) and 72 hours (P < 0.001) and a significant increase in ICTP was noted at 24 and 72 hours (P < 0.05). A strong positive correlation was found between serum levels of PICP and ICTP (r = 0. 55-0.84; P < 0.05) throughout the experiment. In conclusion, young females showed biochemical signs of increased bone collagen turnover and altered homeostasis of calcium and PTH after a single bout of moderate endurance exercise.

Measurement of bone specific alkaline phosphatase in the horse: a comparison of two techniques

For many years total alkaline phosphatase (AP) activity in serum has been used to monitor bone metabolism in different species. However, total AP lacks bone specificity because the total activity in serum is made up of several isoenzymes, of which the liver and bone isoforms predominate. The aim of the present study was to evaluate an immunoradiometric assay for measuring bone specific alkaline phosphatase (BAP) in horses. BAP, a specific marker of bone formation, was measured in sera from thoroughbred horses by using a previously characterised wheat germ lectin (WGL) precipitation assay and an immunoradiometric assay. The levels of immunoreactive BAP (iBAP) and WGL precipitated BAP (wBAP) were related to the serum levels of total AP and another marker of bone formation, the carboxy-terminal propeptide of type 1 collagen (PICP). In horses over one year old, iBAP correlated at least as strongly with total AP as with wBAP, which suggests that the immunoradiometric assay may partially cross-react with liver alkaline phosphatase in horse serum. This possibility was supported by the observation that there was a weaker correlation between iBAP and PICP than between wBAP and PICP. These data indicate that WGL precipitation is currently the most specific method for measuring bone specific alkaline phosphatase in horses.