Feeding and bone

Prevalence of reducing carbohydrate intake and fasted training in elite endurance athletes and association with bone injury

There are conflicting reports both within the lay media and scientific literature regarding the use and benefit of dietary practices that aim to reduce CHO intake in endurance athletes. This study aimed to determine the prevalence of intentional reduction of CHO intake and fasted training in elite endurance-based athletes using a semi-quantitative questionnaire. Bone is a nutritionally modulated tissue; therefore, this study also aimed to explore if these dietary practices are potentially associated with bone injury incidence. The reported reduction of CHO intake was prevalent (28%) with the primary motivation being maintenance or manipulation of body composition. However, discrepancies in athletes' awareness of CHO intake were identified providing a potential avenue of intervention especially within applied practice. The use of fasted training was more prevalent (38%) with athletes using this practice for both body composition manipulation and promoting a desired adaptive response. Forty-four per cent of participants had suffered a radiographically confirmed bone injury at some point in their career. There was no association between reduction in CHO intake and bone injury incidence; however, the incidence of bone injury was 1.61 times higher in those who currently use fasted training compared to those who have never used it or who have used it in the past. Although a direct causal link between these dietary practices and the incidence of bone injury cannot be drawn, it provides robust justification for future investigations of the potential mechanisms that could explain this finding.

Training with reduced carbohydrate availability affects markers of bone resorption and formation in male academy soccer players from the English Premier League

PURPOSE

To test the hypothesis that training with reduced carbohydrate (CHO) availability increases bone resorption in adolescent soccer players.

METHODS

In a randomised crossover design, ten male players (age: 17.4 ± 0.8 years) from an English Premier League academy completed an acute 90-min field-based training session (occurring between 10:30-12:00) in conditions of high (TRAIN HIGH; 1.5 g.kg-1, 60 g, 1.5 g.kg-1 and 1.5 g.kg-1 consumed at 08:00, during training, 12:30 and 13:30, respectively) or low CHO availability (TRAIN LOW; 0 g.kg-1). Participants also completed a non-exercise trial (REST) under identical dietary conditions to TRAIN LOW. Venous blood samples were obtained at 08:30, 10:30, 12:30 and 14:30 for assessment of bone resorption (βCTX), bone formation (PINP) and calcium metabolism (PTH and ACa).

RESULTS

External training load did not differ (all P > 0.05) between TRAIN HIGH and TRAIN LOW, as evident for total distance (5.6 ± 0.8; 5.5 ± 0.1 km), average speed (81 ± 9; 85 ± 12 m.min-1) and high-speed running (350 ± 239; 270 ± 89 m). Area under the curve for both βCTX and PINP was significantly greater (P < 0.01 and P = 0.03) in TRAIN LOW versus TRAIN HIGH, whilst no differences in PTH or ACa (P = 0.11 and P = 0.89) were observed between all three trials.

CONCLUSION

CHO restriction before, during and after an acute soccer training session increased bone (re)modelling markers in academy players. Despite acute anabolic effects of bone formation, the long-term consequence of bone resorption may impair skeletal development and increase injury risk during growth and maturation.

Gut hormones and bone homeostasis: potential therapeutic implications

Bone resorption follows a circadian rhythm, with a marked reduction in circulating markers of resorption (such as carboxy-terminal telopeptide region of collagen type I in serum) in the postprandial period. Several gut hormones, including glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide 1 (GLP1) and GLP2, have been linked to this effect in humans and rodent models. These hormones are secreted from enteroendocrine cells in the gastrointestinal tract in response to a variety of stimuli and effect a wide range of physiological processes within and outside the gut. Single GLP1, dual GLP1-GIP or GLP1-glucagon and triple GLP1-GIP-glucagon receptor agonists have been developed for the treatment of type 2 diabetes mellitus and obesity. In addition, single GIP, GLP1 and GLP2 analogues have been investigated in preclinical studies as novel therapeutics to improve bone strength in bone fragility disorders. Dual GIP-GLP2 analogues have been developed that show therapeutic promise for bone fragility in preclinical studies and seem to exert considerable activity at the bone material level. This Review summarizes the evidence of the action of gut hormones on bone homeostasis and physiology.

Association of a history of gestational diabetes mellitus with osteoporosis, bone mineral density, and trabecular bone score in postmenopausal women

BACKGROUND

Studies on the association of gestational diabetes mellitus (GDM) with osteoporosis, and bone mineral density (BMD) have been inconsistent. The aim of this study was to investigate the association of a history of GDM with osteoporosis, BMD, and trabecular bone score (TBS) in postmenopausal women.

METHODS

Postmenopausal women from the National Health and Nutrition Examination Survey (NHANES) between 2007 and 2010, between 2013 and 2014, and between 2017 and 2018 were retrospectively included in this cross-sectional study. The logistic regression model was used to explore the relationship between GDM and osteoporosis, and a weighted linear regression model was applied to investigate the association between GDM and total femoral BMD, femoral neck BMD, and total TBS. Subgroup analysis of the association between GDM and osteoporosis was performed according to age, body mass index (BMI), and DM (yes or no).

RESULTS

Of the 6732 women included, 253 women (3.76%) had GDM. No significant differences in total femoral BMD, femoral neck BMD, and total TBS were observed between postmenopausal women with and without a history of GDM. However, a history of GDM was associated with a higher risk of osteoporosis in postmenopausal women [odds ratio (OR): 11.18, 95% confidence intervals (CI): 3.64 to 34.27, P < 0.001]. There was no significant difference between a history of GDM and osteoporosis in postmenopausal women whom BMI is normal and overweight women. However, there was an association between a history of GDM and osteoporosis in postmenopausal obese women (OR: 26.57, 95% CI 10.23 to 68.98, P < 0.001).

CONCLUSION

A history of GDM was associated with a higher risk of osteoporosis in postmenopausal women, particularly in postmenopausal obese women.

The clinical utility of TRACP-5b to monitor anti-resorptive treatments of osteoporosis

TRACP-5b can be used to monitor the response of treatments in osteoporosis. We investigated the effect of feeding on levels of TRACP-5b and how these markers perform in a clinical setting. After feeding, there was no effect on levels TRACP-5b. It has similar diagnostic accuracy to CTX and PINP.

INTRODUCTION

Bone turnover markers (BTMs) can be used to monitor response to osteoporosis treatment. However, some are affected by food intake and are not suitable to measure in a clinical setting. An assay is available which is capable of detecting the active isoform 5b of tartrate resistance acid phosphatase (TRACP-5b) and it may have minimal biological variation. Our aims were to investigate the effect of feeding on levels of TRACP-5b and compare this to CTX and PINP and then to compare the diagnostic accuracy of TRACP-5b to CTX and PINP in patients with osteoporosis given commonly used treatments.

METHODS

Eighteen patients were recruited to investigate the effect of feeding on BTMs. Ninety-seven patients (74 females and 23 males) receiving 5 mg annual intra-venous zoledronate (mean age 70) and 97 patients receiving no treatment were recruited as group-matched controls. Sixteen patients receiving 60 mg subcutaneous denosumab every 6 months, (mean age 76) and 16 matched controls were recruited. Seventy-six patients were receiving oral bisphosphonates: 70 mg alendronate weekly, 35 mg risedronate and 150 mg monthly ibandronate (4%). Thirty of these patients had BMD measured at the total hip and lumbar spine. An estimate of compliance was not determined. Eighty patients receiving no treatment were recruited as group-matched controls. TRACP-5b (ELISA, Nittobo) and CTX and PINP were measured in serum in the non-fasting state between 0800 and 1700.

RESULTS

After feeding, there was no effect on levels TRACP-5b and significant reductions in CTX and PINP, 29% and 10%, respectively (p < 0.001). In the zoledronate and denosumab groups, there were no differences in the areas under the curves (AUCs) between TRACP-5b, PINP and CTX. In the oral bisphosphonates group, the AUCs between TRACP-5b and PINP and TRACP-5b and CTX were significantly different, p < 0.01 and p = 0.001, respectively. TRACP-5b was negatively correlated with BMD.

CONCLUSION

TRACP-5b is not affected by food intake, unlike CTX and PINP. All three BTMs correlate with change in BMD at the lumbar spine and total hip. TRACP-5b has similar diagnostic accuracy to CTX and PINP with commonly used treatments for osteoporosis with the exception of oral bisphosphonate therapy.

The circadian rhythm of calcium and bone homeostasis in Maasai

OBJECTIVES

Ethnic groups differ in prevalence of calcium-related diseases. Differences in the physiology and the endogenous circadian rhythm (CR) of calcium and bone homeostasis may play a role. Thus, we aimed to investigate details of CR pattern in calcium and bone homeostasis in East African Maasai.

METHODS

Ten clinically healthy adult Maasai men and women from Tanzania were examined. Blood samples were collected every 2nd hour for 24 h. Serum levels of total calcium, albumin, parathyroid hormone (PTH), 25(OH)D, creatinine, C-terminal telopeptide (CTX), bone-specific alkaline phosphatase (BSAP), procollagen type 1 N-terminal propeptide (P1NP), and osteocalcin were measured. Circadian patterns were derived from graphic curves of medians, and rhythmicity was assessed with Fourier analysis.

RESULTS

PTH-levels varied over the 24 h exhibiting a bimodal pattern. Nadir level corresponded to 65% of total 24-h mean. CTX and P1NP showed 24-h variations with a morning nadir and nocturnal peak with nadir levels corresponding to 23% and 79% of the 24-h mean, respectively. Albumin-corrected calcium level was held in a narrow range and alterations were corresponding to alterations in PTH. There was no distinct pattern in 24-h variations of 25(OH)D, creatinine, osteocalcin, or BSAP.

CONCLUSIONS

All participants showed pronounced 24-h variations in PTH and bone turnover markers CTX and P1NP. These findings support that Maasai participants included in this study have typical patterns of CR in calcium and bone homeostasis consistent with findings from other ethnic populations.

Nutritional recommendations for patients undergoing prolonged glucocorticoid therapy

Glucocorticoid (GC) therapy is a common treatment used in rheumatic and autoimmune diseases, owing to its anti-inflammatory and immunosuppressive effects. However, GC therapy can also induce a number of adverse effects, including muscle and bone loss, hypertension, metabolic perturbations and increased visceral adiposity. We review available evidence in this area and provide nutritional recommendations that might ameliorate these adverse effects. Briefly, optimizing calcium, vitamin D, sodium and protein intake and increasing consumption of unprocessed and minimally processed foods, while decreasing the consumption of ultra-processed foods, might counteract some of the specific challenges faced by these patients. Importantly, we identify a dearth of empirical data on how nutritional intervention might impact health-related outcomes in this population. Further research is required to investigate the clinical and therapeutic efficacy of these theory-based recommendations.

Linagliptin in Combination With Metformin Ameliorates Diabetic Osteoporosis Through Modulating BMP-2 and Sclerostin in the High-Fat Diet Fed C57BL/6 Mice

BACKGROUND

Diabetic osteoporosis is a poorly managed serious skeletal complication, characterized by high fracture risk, increased bone resorption, reduced bone formation, and disrupted bone architecture. There is a need to investigate drugs that can improve bone health along with managing glycemic control. DPP-4 inhibitors and metformin have proven benefits in improving bone health. Here, we investigated the effects of linagliptin, a DPP inhibitor, and metformin alone and in combination to treat diabetic osteoporosis in high-fat-fed mice.

METHODS

C57BL/6 mice were kept on the high-fat diet (HFD) for 22 weeks to induce diabetic osteoporosis. Linagliptin (10mg/Kg), metformin (150mg/Kg), and their combination were orally administered to the diabetic mice from the 18^th-22^nd week. Femur and tibial bone microarchitecture together with bone mineral density (BMD) were evaluated using µCT and histopathological changes were assessed. Further, bone turnover biomarkers namely bone morphogenetic protein-2 (BMP-2), sclerostin, tartrate-resistant acid phosphatase (TRAP), osteocalcin, alkaline phosphatase (ALP), calcium, and pro-inflammatory cytokines were assessed. Additionally, metabolic parameters including body weight, fasting blood glucose (FBG), glucose & insulin tolerance, lipids profile, and leptin were measured.

RESULTS

HFD feeding resulted in impaired bone microarchitecture, reduced BMD, distorted bone histology, and altered bone turnover biomarkers as indicated by the significant reduction in bone ALP, BMP-2, osteocalcin, and an increase in sclerostin, TRAP, and serum calcium. Interestingly, treatment with linagliptin and its combination with metformin significantly reverted the impaired bone architecture, BMD, and positively modulated bone turnover biomarkers, while metformin alone did not exhibit any significant improvement. Further, HFD induced diabetes and metabolic abnormalities (including an increase in body weight, FBG, impaired glucose and insulin tolerance, leptin, triglycerides, cholesterol), and pro-inflammatory cytokines (TNF-alpha and IL-1β) were successfully reversed by treatment with linagliptin, metformin, and their combination.

CONCLUSION

Linagliptin and its combination with metformin successfully ameliorated diabetic osteoporosis in HFD-fed mice possibly through modulation of BMP-2 and sclerostin. The study provides the first evidence for the possible use of linagliptin and metformin combination for managing diabetic osteoporosis.

Reduced postprandial bone resorption and greater rise in GLP-1 in overweight and obese individuals after an α-glucosidase inhibitor: a double-blinded randomized crossover trial

When taken with a meal, α-glucosidase inhibitors (α-GI) reduce the rise in postprandial glucose and increase glucagon-like peptide-1 (GLP-1), and this may lower bone turnover. In this study, a salacinol-type α-GI increased GLP-1 and markedly reduced postprandial bone resorption compared to placebo, suggesting it could have implications for bone health.

INTRODUCTION

Animal and clinical trials indicate that α-glucosidase inhibitors attenuate postprandial glycemic indices and increase secretion of GLP-1. In addition, GLP-1 acts on bone by inhibiting resorption. The goal in this study was to determine if a salacinol α-GI alters postprandial bone turnover and can be explained by changes in serum GLP-1.

METHODS

In this double-blind, placebo-controlled crossover study, healthy overweight/obese adults (body mass index 29.0 ± 3.8 kg/m²; 21-59 years; n = 21) received a fixed breakfast and, in random order, were administered Salacia chinensis (SC; 500 mg) or placebo. A fasting blood sample was taken before and at regular intervals for 3 h after the meal. Serum was measured for bone turnover markers, C-terminal telopeptide of type I collagen (CTX) and osteocalcin, and for glycemic indices and gut peptides.

RESULTS

Compared to placebo, SC attenuated the bone resorption marker, CTX, at 60, 90, and 120 min (p < 0.05) after the meal, and decreased osteocalcin, at 180 min (p < 0.05). As expected, SC attenuated the postprandial rise in glucose compared with placebo, whereas GLP-1 was increased at 60 min (p < 0.05) with SC. Serum GLP-1 explained 41% of the variance for change in postprandial CTX (p < 0.05).

CONCLUSION

This study indicates that attenuating postprandial glycemic indices, with an α-GI, markedly decreases postprandial bone resorption and can be explained by the rise in GLP-1. Future studies should determine whether longer term α-GI use benefits bone health.

Analysis of Combined Indicators for Risk of Osteoporotic Hip Fracture in Elderly Women

Objective

To compare the accuracy of combined independent risk factors in assessing the risk of hip fractures in elderly women.

Methods

Ninety elderly females who sustained hip fractures (including femoral neck fractures and intertrochanteric fractures) and 110 female outpatients without a hip fracture were included in our cross‐sectional study from 24 November 2017 to 20 May 2019. The age of subjects in the present study was ≥65 years, with the mean age of 78.73 ± 7.77 and 78.09 ± 5.03 years for women with and without elderly hip fractures, respectively. Bone mineral density (BMD), Beta‐carboxy terminal telopeptide (β‐CTX), N‐terminal/mid region (N‐MID), and 25(OH)D levels were analyzed. A novel evaluation model was established to evaluate combined indicators in assessing hip fractures in elderly women.

Results

Compared with the control group, taller height (155.68 ± 6.40 vs 150.97 ± 6.23, P < 0.01), higher levels of β‐CTX (525.91 ± 307.38 vs 330.94 ± 289.71, P < 0.01), and lower levels of total hip BMD (0.662 ± 0.117 vs 0.699 ± 0.111, P = 0.022), femoral neck BMD (0.598 ± 0.106 vs 0.637 ± 0.100, P = 0.009), and 25(OH)D (15.67 ± 7.23 vs 29.53 ± 10.57, P < 0.01) were found in the facture group. After adjustment for confounding factors, logistic regression analysis revealed that 25(OH)D (adjusted OR 0.837 [95% CI 0.790–0.886]; P < 0.01), femoral neck BMD (adjusted OR 0.009 [95% CI 0.000–0.969]; P = 0.048) and height (adjusted OR 1.207 [95% CI 1.116–1.306]; P < 0.01) remained risk factors for hip fractures in elderly women. Then a model including independent risk factors was established. A DeLong test showed the area under the receiver operator characteristic (ROC) (Area under the curve [AUC]) of 25(OH)D was significantly greater than that for femoral neck BMD (P < 0.01) and height (P < 0.01). The AUC of model including 25(OH)D and height was significantly greater than that of other combinations (P < 0.01).

Conclusion

25(OH)D, femoral neck BMD and height were associated with the occurrence of hip fractures in elderly women even after adjustment for confounding factors, and a model including 25(OH)D and height could provide better associated power than other combinations in the assessment of elderly hip fractures.

Analysis of Body Perception, Preworkout Meal Habits and Bone Resorption in Child Gymnasts

The beneficial effects of physical activity on body image perception and bone are debated among artistic gymnasts. Gymnasts seem to be at greater risk of developing body dissatisfaction, eating disorders and osteoporosis due to inadequate nutrition and attention to the appearance of the body. The objective of this work was to investigate the association between the artistic gymnast and a more favorable body image compared to their sedentary peers and if a preworkout high-carbohydrate meal (HCM; 300 kcal, 88% carbohydrates, 9% protein, 3% fat) or high-protein meal (HPM; 300 kcal, 55% carbohydrates, 31% protein, 13% fat) is able to attenuate bone resorption in young rhythmic gymnasts. Twenty-eight preadolescent female gymnasts were examined. Self-esteem tests were used to analyze body image perception. Preworkout eating habits were examined by short food frequency questions (FFQ) validated for children. The biomarker of the bone resorption C-terminal telopeptide region of collagen type 1 (CTX) was measured in the urine (fasting, postmeal and postworkout). Gymnasts reported higher satisfaction with their body appearance compared to sedentary peers. Of the gymnasts, 30% did not have a preworkout meal regularly, and the timing of the consumption was variable. Bone resorption was decreased by the HCM, consumed 90 min before the training, with respect to the HPM. The study suggests that playing artistic gymnastics is associated with a positive body self-perception in a child. The variability in preworkout meal frequency and timing need attention to prevent inadequate eating habits in light of the ability of the HCM to reduce acute bone resorption.

Infection by CagA-Positive Helicobacter pylori Strains and Bone Fragility: A Prospective Cohort Study

Helicobacter pylori (HP) infection is a common and persistent disorder acting as a major cofactor for the development of upper gastrointestinal diseases and several extraintestinal disorders including osteoporosis. However, no prospective study assessed the effects of HP on bone health and fracture risk. We performed a HP screening in a population-based cohort of 1149 adults followed prospectively for up to 11 years. The presence of HP infection was assessed by serologic testing for serum antibodies to HP and the cytotoxin associated gene-A (CagA). The prevalence of HP infection did not differ among individuals with normal bone mineral density (BMD), osteoporosis, and osteopenia. However, HP infection by CagA-positive strains was significantly increased in osteoporotic (30%) and osteopenic (26%) patients respect to subjects with normal BMD (21%). Moreover, anti-CagA antibody levels were significantly and negatively associated with lumbar and femoral BMD. Consistent with these associations, patients affected by CagA-positive strains had a more than fivefold increased risk to sustain a clinical vertebral fracture (HR 5.27; 95% CI, 2.23-12.63; p < .0001) and a double risk to sustain a nonvertebral incident fracture (HR 2.09; 95% CI, 1.27-2.46; p < .005). Reduced estrogen and ghrelin levels, together with an impaired bone turnover balance after the meal were also observed in carriers of CagA-positive HP infection. HP infection by strains expressing CagA may be considered a risk factor for osteoporosis and fractures. Further studies are required to clarify in more detail the underlying pathogenetic mechanisms of this association. © 2020 American Society for Bone and Mineral Research (ASBMR).

Diabetes and Bone Involvement in Primary Hyperparathyroidism: Literature Review and Our Personal Experience

BACKGROUND

Primary hyperparathyroidism (PHPT) and type 2 diabetes mellitus (T2DM) are common endocrine disorders impacting on skeletal health, whose concomitant occurrence is becoming more frequent.

PATIENTS AND METHODS

We searched the PubMed database from the National Library of Medicine about the relationship between T2DM and its treatment and bone manifestations of PHPT. Thereafter, we retrospectively evaluated a consecutive series of 472 PHPT patients. Among them 55 were also affected by T2DM. At the diagnosis of PHPT we compared bone turnover markers and bone densitometry between 55 patients with and 417 without T2DM and in the former group according to antidiabetic treatment.

RESULTS

Few data are available about T2DM and PHPT bone involvement, studies about T2DM treatments and PHPT bone manifestations are lacking. Among patients with PHPT of our series, those with T2DM were older, had a lower prevalence of osteitis fibrosa cystica, higher lumbar and femoral T-scores than the remaining patients. No difference was disclosed among the diabetic patients according to ongoing antidiabetic treatment, even though modern treatments were under-represented.

CONCLUSIONS

No clinical study specifically evaluated the impact of T2DM on bone involvement in PHPT. In our experience, diabetic patients resulted more frequently "mild asymptomatic" than non-diabetic patients and showed a lower prevalence of radiological PHPT bone manifestations. The treatment of T2DM does not seem to affect the biochemical or clinical features of PHPT in our series. Further studies are needed to fully disclose the influence of T2DM and antidiabetic treatment on bone health in patients with PHPT.

The Associations of Serum Vitamin D and Bone Turnover Markers with the Type and Severity of Hip Fractures in Older Women

Purpose

Vitamin D (25[OH]D) status and bone turnover markers (BTMs) are considered important determinants of bone quality, which is associated with the risk of hip fractures, including both femoral neck and intertrochanteric fractures, in older adults; however, the exact relationship of 25(OH)D and BTMs with the type and severity of hip fractures remains unclear and the present study aimed to identify any specific associations.

Patients and Methods

According to the inclusion and exclusion criteria, 441 older female patients with hip fractures from 2015 to 2020 and 215 women without hip fractures were included in this cross-sectional study. According to Garden and AO/OTA classifications for femoral neck and intertrochanteric fractures, patients were divided into less severe (Garden I and Garden II; 31A1) and more severe (Garden III and Garden IV; 31A2 and 31A3) fracture groups. Levels of the serum osteoblast indicator, N-terminal/mid region (N-MID); the osteoclast indicator, beta-carboxy terminal telopeptide (β-CTX); and 25(OH)D were analyzed.

Results

For patients with less severe fractures, mean 25(OH)D levels were significantly higher than those with more severe fractures (17.67 vs 15.30 ng/mL, p = 0.006). Higher 25(OH)D levels were also observed in patients with less severe intertrochanteric fractures (p = 0.01). After adjustments for confounders, 25(OH)D remained a risk factor for patients with more severe fractures (p = 0.01), particularly those with intertrochanteric fractures (p = 0.011). No significant differences in BTMS were found between patients with less severe and more severe fractures.

Conclusion

Levels of 25(OH)D were significantly associated with the severity of intertrochanteric, but not femoral neck, fractures. Neither 25(OH)D nor BTMs were associated with the type of hip fracture in older women. Separate consideration of intertrochanteric and femoral neck fractures may be appropriate when investigating the clinical association between 25(OH)D and the severity of hip fractures in older women.

Nutrition and Athlete Bone Health

Athletes should pay more attention to their bone health, whether this relates to their longer-term bone health (e.g. risk of osteopenia and osteoporosis) or their shorter-term risk of bony injuries. Perhaps the easiest way to do this would be to modify their training loads, although this advice rarely seems popular with coaches and athletes for obvious reasons. As such, other possibilities to support the athletes’ bone health need to be explored. Given that bone is a nutritionally modified tissue and diet has a significant influence on bone health across the lifespan, diet and nutritional composition seem like obvious candidates for manipulation. The nutritional requirements to support the skeleton during growth and development and during ageing are unlikely to be notably different between athletes and the general population, although there are some considerations of specific relevance, including energy availability, low carbohydrate availability, protein intake, vitamin D intake and dermal calcium and sodium losses. Energy availability is important for optimising bone health in the athlete, although normative energy balance targets are highly unrealistic for many athletes. The level of energy availability beyond which there is no negative effect for the bone needs to be established. On the balance of the available evidence it would seem unlikely that higher animal protein intakes, in the amounts recommended to athletes, are harmful to bone health, particularly with adequate calcium intake. Dermal calcium losses might be an important consideration for endurance athletes, particularly during long training sessions or events. In these situations, some consideration should be given to pre-exercise calcium feeding. The avoidance of vitamin D deficiency and insufficiency is important for the athlete to protect their bone health. There remains a lack of information relating to the longer-term effects of different dietary and nutritional practices on bone health in athletes, something that needs to be addressed before specific guidance can be provided.

Consumption of nutrients and insulin resistance suppress markers of bone turnover in subjects with abdominal obesity

OBJECTIVE

Abdominal obesity and type 2 diabetes are associated with insulin resistance and low bone turnover along with an increased fracture risk. The mode of action is poorly understood. The bone resorption marker, C-terminal telopeptide type 1 collagen (CTX), and to a lesser extent, the bone formation marker, Procollagen type 1 N-terminal propeptide (P1NP) appear to be inhibited by food consumption. The link between food consumption, insulin resistance and bone turnover remains to be clarified. Primarily we aimed to compare the postprandial CTX, P1NP and PTH responses by two frequently applied methods in assessing metabolic health; oral glucose tolerance test (OGTT) and mixed meal tolerance test. Secondly, we explored the effect of insulin resistance on bone marker responses.

METHODS

We enrolled 64 subjects with abdominal obesity. Following 10 h of fasting, subjects initially underwent a standard OGTT (300 kcal) and approximately one week later a mixed meal tolerance test (1130 kcal). Circulating CTX, P1NP and PTH were assessed on both days at time = 0, after 30 min and after 90 min for comparison of the two interventions. We analyzed glucose and insulin levels for the assessment of insulin resistance. Additionally, we measured plasma calcium levels along with the gut hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like-peptide 2 (GLP-2) in an attempt to identify possible mediators of the postprandial bone response.

RESULTS

CTX, P1NP and PTH were suppressed by OGTT and the mixed meal; the latter induced a more pronounced suppression after 90 min. Calcium levels were similar between OGTT and meal. GIP and GLP-2 levels increased after both interventions, although only the meal induced a sustained increase after 90 min. Fasting P1NP was inversely associated with insulin resistance. The meal-induced suppression of P1NP (but not CTX or PTH) was inversely associated with level of insulin resistance.

CONCLUSION

The acute postprandial suppression of bone turnover markers is extended after ingestion of a mixed meal compared to an OGTT. The response appears to be independent of gender and prompted by a reduction in PTH. The study additionally indicates a possible link between the development of insulin resistance and low bone turnover - which may be of key essence in the development of the fragile bone structure and increased fracture risk demonstrated in subjects with abdominal obesity and T2D.

GIP and the gut-bone axis - Physiological, pathophysiological and potential therapeutic implications

The influence by gut-derived hormones on bone remodelling appears increasingly important as research on the enteroendocrine-osseous axis accelerates. Glucose-dependent insulinotropic polypeptide (GIP) is secreted from the gut and potentiates insulin secretion in a glucose-dependent manner. GIP has, like the two other gut-derived hormones, glucagon-like peptide 1 and glucagon-like peptide 2, been shown to affect bone remodelling as part of the enteroendocrine-osseous axis. Observational studies have shown that a mutation in the GIP receptor causing reduced receptor signalling leads to lower bone mineral density and increased fracture risk. Rodent as well as human studies have shown that GIP causes serum levels of the bone resorption marker carboxy-terminal type 1 collagen crosslinks to decline. GIP may also increase bone formation indicating a potential uncoupling of bone resorption and formation. Here, we review past and recent discoveries elucidating the enteroendocrine-osseous axis with a special focus on GIP.

Glucagon-like peptide 1 and Glucagon-like peptide 2 in relation to osteoporosis in non-diabetic postmenopausal women

Osteoporosis results from an imbalance in bone remodeling, which is known to follow a circadian rhythm determined by a functional relationship between intestine and bone tissue. Specific intestinal peptides have been identified as mediators. Glucagon-like peptide 1 and glucagon-like peptide 2, have been associated with bone health. Our main objective was to determine whether postprandial plasma levels of glucagon-like peptide 1, glucagon-like peptide 2 and dipeptidyl-peptidase 4 activity, are associated with osteoporosis in non-diabetic postmenopausal women. We studied non-diabetic postmenopausal women with osteoporosis diagnosed by dual-energy X-ray absorptiometry (cases, n = 43) and age-matched (±1 yr) controls without osteoporosis or a history of osteoporotic fracture (n = 43). We measured postprandial plasma levels of glucagon-like peptide 1, glucagon-like peptide 2, and dipeptidyl-peptidase 4 activity, bone mineral density, and baseline levels of bone remodeling markers and analyzed the food intake using a food-frequency questionnaire. Postprandial glucagon-like peptide 1 values were lower (p < 0.001) in cases, μ (SEM) = 116.25 (2.68), than in controls, μ (SEM) = 126.79 (2.68). Glucagon-like peptide 1 was associated with reduced osteoporosis risk in the crude logistic regression analysis [OR (95% CI) = 0.724 (0.53-0.97), p = 0.031] and adjusted analysis [OR = 0.603 (0.38-0.94), p = 0.027]. We found no association of glucagon-like peptide 2, or dipeptidyl-peptidase 4 activity with osteoporosis. Postprandial glucagon-like peptide 1 levels are related to osteoporosis and osteoporosis risk in non-diabetic postmenopausal women. Further studies are required to verify these findings.

Efficacy of targeting bone-specific GIP receptor in ovariectomy-induced bone loss

Glucose-dependent insulinotropic polypeptide (GIP) has been recognized in the last decade as an important contributor of bone remodelling and is necessary for optimal bone quality. However, GIP receptors are expressed in several tissues in the body and little is known about the direct vs indirect effects of GIP on bone remodelling and quality. The aims of the present study were to validate two new GIP analogues, called [d-Ala2]-GIP-Tag and [d-Ala2]-GIP1-30, which specifically target either bone or whole-body GIP receptors, respectively; and to ascertain the beneficial effects of GIP therapy on bone in a mouse model of ovariectomy-induced bone loss. Both GIP analogues exhibited similar binding capacities at the GIP receptor and intracellular responses as full-length GIP1-42. Furthermore, only [d-Ala2]-GIP-Tag, but not [d-Ala2]-GIP1-30, was undoubtedly found exclusively in the bone matrix and released at acidic pH. In ovariectomized animals, [d-Ala2]-GIP1-30 but not [d-Ala2]-GIP-Tag ameliorated bone stiffness at the same magnitude than alendronate treatment. Only [d-Ala2]-GIP1-30 treatment led to significant ameliorations in cortical microarchitecture. Although alendronate treatment increased the hardness of the bone matrix and the type B carbonate substitution in the hydroxyapatite crystals, none of the GIP analogues modified bone matrix composition. Interestingly, in ovariectomy-induced bone loss, [d-Ala2]-GIP-Tag failed to alter bone strength, microarchitecture and bone matrix composition. Overall, this study shows that the use of a GIP analogue that target whole-body GIP receptors might be useful to improve bone strength in ovariectomized animals.

The effect of meals on bone turnover - a systematic review with focus on diabetic bone disease

INTRODUCTION

Type 2 diabetes is associated with an increased risk of bone fractures. Bone mineral density (BMD) is increased and bone turnover is low in type 2 diabetes and the increased BMD does not explain the increased fracture risk. However, the low bone turnover may lead to insufficient bone renewal with unrepaired micro-cracks and thus increase fracture risk. Ingestion of food acutely decreases bone resorption markers and the macronutrient composition of meals and meal frequency may influence bone metabolism adversely in subjects with unhealthy eating patterns, e.g., patients with type 2 diabetes.

AREAS COVERED

The treatment strategy of bone disease in type 2 diabetics is covered in this review. The current management of diabetic bone disease consists of anti-osteoporotic treatment. However, anti-resorptives may further reduce an already low bone turnover with uncertain effects. Furthermore, the acute and long-term effects of meal ingestion, weight loss alone and in combination with exercise as well as the possible underlying mechanisms are covered in this systematic review.

EXPERT COMMENTARY

Current management of diabetic bone disease is based on principles of anti-osteoporotic treatment in non-diabetic subjects. However, studies are urged to investigate whether anti-resorptives are equally beneficial in type 2 diabetes as in non-diabetic individuals.

Use of bone turnover markers in postmenopausal osteoporosis

Bone turnover comprises two processes: the removal of old bone (resorption) and the laying down of new bone (formation). N-terminal propeptide of type I procollagen (PINP) and C-telopeptide of type I collagen (CTX-I) are markers of bone formation and resorption, respectively, that are recommended for clinical use. Bone turnover markers can be measured on several occasions in one individual with good precision. However, these markers are subject to several sources of variability, including feeding (resorption decreases) and recent fracture (all markers increase for several months). Bone turnover markers are not used for diagnosis of osteoporosis and do not improve prediction of bone loss or fracture within an individual. In untreated women, very high bone turnover marker concentrations suggest secondary causes of high bone turnover (eg, bone metastases or multiple myeloma). In people with osteoporosis, bone turnover markers might be useful to assess the response to anabolic and antiresorptive therapies, to assess compliance to therapy, or to indicate possible secondary osteoporosis. Much remains to be learnt about how bone turnover markers can be used to monitor the effect of stopping bisphosphonate therapy (eg, to identify a threshold above which restarting therapy should be considered). More studies are needed to investigate the use of bone turnover markers for assessment of the bone safety of new medications.

Obesity, Type 2 Diabetes and Bone in Adults

In an increasingly obese and ageing population, type 2 diabetes (T2DM) and osteoporotic fracture are major public health concerns. Understanding how obesity and type 2 diabetes modulate fracture risk is important to identify and treat people at risk of fracture. Additionally, the study of the mechanisms of action of obesity and T2DM on bone has already offered insights that may be applicable to osteoporosis in the general population. Most available evidence indicates lower risk of proximal femur and vertebral fracture in obese adults. However the risk of some fractures (proximal humerus, femur and ankle) is higher, and a significant number fractures occur in obese people. BMI is positively associated with BMD and the mechanisms of this association in vivo may include increased loading, adipokines such as leptin, and higher aromatase activity. However, some fat depots could have negative effects on bone; cytokines from visceral fat are pro-resorptive and high intramuscular fat content is associated with poorer muscle function, attenuating loading effects and increasing falls risk. T2DM is also associated with higher bone mineral density (BMD), but increased overall and hip fracture risk. There are some similarities between bone in obesity and T2DM, but T2DM seems to have additional harmful effects and emerging evidence suggests that glycation of collagen may be an important factor. Higher BMD but higher fracture risk presents challenges in fracture prediction in obesity and T2DM. Dual energy X-ray absorptiometry underestimates risk, standard clinical risk factors may not capture all relevant information, and risk is under-recognised by clinicians. However, the limited available evidence suggests that osteoporosis treatment does reduce fracture risk in obesity and T2DM with generally similar efficacy to other patients.

Effects of Incretin-Based Therapies and SGLT2 Inhibitors on Skeletal Health

Anti-diabetic drugs are widely used and are essential for adequate glycemic control in patients with type 2 diabetes. Recently, marketed anti-diabetic drugs include incretin-based therapies (GLP-1 receptor agonists and DPP-4 inhibitors) and sodium-glucose co-transporter 2 (SGLT2) inhibitors. In contrast to well-known detrimental effects of thiazolidinediones on bone metabolism and fracture risk, clinical data on the safety of incretin-based therapies is limited. Based on meta-analyses of trials investigating the glycemic-lowering effect of GLP-1 receptor agonists and DPP4 inhibitors, it seems that incretin-based therapies are not associated with an increase in fracture risk. Sodium-glucose co-transporter 2 inhibitors may alter calcium and phosphate homeostasis as a result of secondary hyperparathyroidism induced by increased phosphate reabsorption. Although these changes may suggest detrimental effects of SGLT-2 inhibitors on skeletal integrity, treatment-related direct effects on bone metabolism seem unlikely. Observed changes in BMD, however, seem to result from increased bone turnover in the early phase of drug-induced weight loss. Fracture risk, which is observed in older patients with impaired renal function and elevated cardiovascular disease risk treated with SGLT2 inhibitors, seems to be independent of direct effects on bone but more likely to be associated with falls and changes in hydration status secondary to osmotic diuresis.

Boning up on DPP4, DPP4 substrates, and DPP4-adipokine interactions: Logical reasoning and known facts about bone related effects of DPP4 inhibitors

Dipeptidyl peptidase 4 (DPP4) is a conserved exopeptidase with an important function in protein regulation. The activity of DPP4, an enzyme which can either be anchored to the plasma membrane or circulate free in the extracellular compartment, affects the glucose metabolism, cellular signaling, migration and differentiation, oxidative stress and the immune system. DPP4 is also expressed on the surface of osteoblasts, osteoclasts and osteocytes, and was found to play a role in collagen metabolism. Many substrates of DPP4 have an established role in bone metabolism, among which are incretins, gastrointestinal peptides and neuropeptides. In general, their effects favor bone formation, but some effects are complex and have not been completely elucidated. DPP4 and some of its substrates are known to interact with adipokines, playing an essential role in the energy metabolism. The prolongation of the half-life of incretins through DPP4 inhibition led to the development of these inhibitors to improve glucose tolerance in diabetes. Current literature indicates that the inhibition of DPP4 activity might also result in a beneficial effect on the bone metabolism, but the long-term effect of DPP4 inhibition on fracture outcome has not been entirely established. Diabetic as well as postmenopausal osteoporosis is associated with an increased activity of DPP4, as well as a shift in the expression levels of DPP4 substrates, their receptors, and adipokines. The interactions between these factors and their relationship in bone metabolism are therefore an interesting field of study.

Osteocalcin levels on oral glucose load in women being investigated for polycystic ovary syndrome

OBJECTIVE

Osteocalcin (OC) might play a hormone-like role in energy metabolism and the regulatory circuit between the pancreas and osteoblasts. Effects of a 75-g oral glucose tolerance test (OGTT) on total OC, undercarboxylated (ucOC), and carboxylated osteocalcin (cOC) in insulin-resistant (IR) and noninsulin-resistant (nIR) premenopausal women was evaluated, and the relationships of changes in OC, ucOC, and cOC with area under the curve (AUC) insulin and the Matsuda index were examined.

METHODS

In this cross-sectional study, 105 premenopausal women underwent OGTT; 18 were IR (homeostatic model assessment of insulin resistance [HOMA-IR] > 2.6; (2 with type 2 diabetes, 2 with impaired glucose tolerance), and 87 were nIR (3 with impaired glucose tolerance). Changes in total OC, ucOC, and cOC were evaluated 60 and 120 minutes after glucose loading.

RESULTS

At baseline, IR subjects had significantly lower levels of total OC, cOC, and ucOC. In nIR women, total OC decreased by 19% from 18.0 ng/mL (14.5-24.7) at baseline to 14.6 ng/mL (10.9-17.8) after 120 minutes, ucOC decreased by 22% from 3.2 ng/mL (2.1-4.5) to 2.5 ng/mL (1.7-3.5), and cOC decreased by 26% from 14.9 ng/mL (12.1-20.4) to 11.1 ng/mL (9.0-14.5) (P < .001, respectively). No significant decreases were noted in IR subjects. The declines in OC and cOC predicted AUCinsulin (ΔOC: β = 0.301, P = .001; ΔcOC: β = 0.315, P < .001) and the Matsuda index (ΔOC: β = -0.235, P = .003; ΔcOC: β = -0.245, P = .002).

CONCLUSIONS

Glucose intake lowers levels of OC, ucOC, and cOC in nIR women, the extent of which predicts IR and insulin sensitivity in premenopausal women. OC parameters seem suppressed in IR women. There might be a differential osteoblast response to oral glucose in IR and nIR women, with OC reflecting this finding.

Diurnal Rhythms of Bone Turnover Markers in Three Ethnic Groups

CONTEXT

Ethnic groups differ in fragility fracture risk and bone metabolism. Differences in diurnal rhythms (DRs) of bone turnover and PTH may play a role.

OBJECTIVE

We investigated the DRs of plasma bone turnover markers (BTMs), PTH, and 1,25(OH)2D in three groups with pronounced differences in bone metabolism and plasma PTH.

PARTICIPANTS

Healthy Gambian, Chinese, and white British adults (ages 60-75 years; 30 per country).

INTERVENTIONS

Observational study with sample collection every 4 hours for 24 hours.

MAIN OUTCOMES

Levels of plasma C-terminal telopeptide of type I collagen, procollagen type-1 N-propeptide, N-mid osteocalcin, bone alkaline phosphatase, PTH, and 1,25-dihydroxyvitamin D were measured. DRs were analyzed with random-effects Fourier regression and cross-correlation and regression analyses to assess associations between DRs and fasting and 24-hour means of BTMs and PTH.

RESULTS

Concentrations of BTMs, PTH, and 1,25-dihydroxyvitamin D were higher in Gambians compared to other groups (P < .05). The DRs were significant for all variables and groups (P < .03) and were unimodal, with a nocturnal peak and a daytime nadir for BTMs, whereas PTH had two peaks. The DRs of BTMs and PTH were significantly cross-correlated for all groups (P < .05). There was a significant positive association between C-terminal telopeptide of type I collagen and PTH in the British and Gambian groups (P = .03), but not the Chinese group.

CONCLUSIONS

Despite ethnic differences in plasma BTMs and PTH, DRs were similar. This indicates that alteration of rhythmicity and loss of coupling of bone resorption and formation associated with an elevated PTH in other studies may not uniformly occur across different populations and needs to be considered in the interpretation of PTH as a risk factor of increased bone loss.

Glucagon-like peptide 2 and its beneficial effects on gut function and health in production animals

Numerous endocrine cell subtypes exist within the intestinal mucosa and produce peptides contributing to the regulation of critical physiological processes including appetite, energy metabolism, gut function, and gut health. The mechanisms of action and the extent of the physiological effects of these enteric peptides are only beginning to be uncovered. One peptide in particular, glucagon-like peptide 2 (GLP-2) produced by enteroendocrine L cells, has been fairly well characterized in rodent and swine models in terms of its ability to improve nutrient absorption and healing of the gut after injury. In fact, a long-acting form of GLP-2 recently has been approved for the management and treatment of human conditions like inflammatory bowel disease and short bowel syndrome. However, novel functions of GLP-2 within the gut continue to be demonstrated, including its beneficial effects on intestinal barrier function and reducing intestinal inflammation. As knowledge continues to grow about GLP-2's effects on the gut and its mechanisms of release, the potential to use GLP-2 to improve gut function and health of food animals becomes increasingly more apparent. Thus, the purpose of this review is to summarize: (1) the current understanding of GLP-2's functions and mechanisms of action within the gut; (2) novel applications of GLP-2 (or stimulators of its release) to improve general health and production performance of food animals; and (3) recent findings, using dairy calves as a model, that suggest the therapeutic potential of GLP-2 to reduce the pathogenesis of intestinal protozoan infections.

High Levels of Serum DPP-4 Activity Are Associated with Low Bone Mineral Density in Obese Postmenopausal Women

BACKGROUND

Dipeptidyl peptidase 4/CD26 (DPP-4) is a widely expressed cell surface serine protease. DPP-4 inhibitors, one of common anti-diabetic agents play a protective role in bone metabolism in recent studies. A soluble form of DPP-4 is found in serum, and exhibits DPP-4 enzymatic activity. However, the physiological role of serum or soluble DPP-4 and its relationship with DPP-4 enzymatic function remain poorly understood. The aims of current study were to determine the association between serum DPP-4 activity and bone mineral density (BMD) in postmenopausal women.

METHODS

We recruited data and serum samples from 124 consecutive healthy postmenopausal women aged >50 years. We divided study subjects into obese (body mass index [BMI] ≥25 kg/m²) and non-obese (BMI <25 kg/m²) postmenopausal women and examined the correlation between serum DPP-4 activity and clinical variables in each groups.

RESULTS

A total of 124 postmenopausal women was enrolled, with a mean age of 59.9±7.1 years. The mean BMI of the study patients was 24.4±2.8 kg/m². Regarding bone turnover markers, serum DPP-4 activity was positively correlated with serum calcium concentrations, intact parathyroid hormone, and serum C-telopeptide levels in all of the study subjects. However, there was no association between serum DPP-4 activity and BMD in the spine or femoral neck in all of the study subjects. Serum DPP-4 activity was negatively correlated (R=-0.288, P=0.038) with BMD of the spine in obese postmenopausal women.

CONCLUSION

This study demonstrated for the first time that serum soluble DPP-4 activity was negatively correlated with BMD in obese postmenopausal women.

Effects of diabetes drugs on the skeleton

Type 2 diabetes is associated with increased fracture risk and the mechanisms underlying the detrimental effects of diabetes on skeletal health are only partially understood. Antidiabetic drugs are indispensable for glycemic control in most type 2 diabetics, however, they may, at least in part, modulate fracture risk in exposed patients. Preclinical and clinical data clearly demonstrate an unfavorable effect of thiazolidinediones on the skeleton with impaired osteoblast function and activated osteoclastogenesis. The negative effect of thiazolidinediones on osteoblastogenesis includes decreased activity of osteoblast-specific transcription factors (e.g. Runx2, Dlx5, osterix) and decreased activity of osteoblast-specific signaling pathways (e.g. Wnt, TGF-β/BMP, IGF-1). In contrast, metformin has a positive effect on osteoblast differentiation due to increased activity of Runx2 via the AMPK/USF-1/SHP regulatory cascade resulting in a neutral or potentially protective effect on bone. Recently marketed antidiabetic drugs include incretin-based therapies (GLP-1 receptor agonists, DPP-4 inhibitors) and sodium-glucose co-transporter 2 (SGLT2)-inhibitors. Preclinical studies indicate that incretins (GIP, GLP-1, and GLP-2) play an important role in the regulation of bone turnover. Clinical safety data are limited, however, meta-analyses of trials investigating the glycemic-lowering effect of both, GLP-1 receptor agonists and DPP4-inhibitors, suggest a neutral effect of incretin-based therapies on fracture risk. For SGLT2-inhibitors recent data indicate that due to their mode of action they may alter calcium and phosphate homeostasis (secondary hyperparathyroidism induced by increased phosphate reabsorption) and thereby potentially affect bone mass and fracture risk. Clinical studies are needed to elucidate the effect of SGLT2-inhibitors on bone metabolism. Meanwhile SGLT2-inhibitors should be used with caution in patients with high fracture risk, which is specifically true for the use of thiazolidinediones.

Risk factors for the development of osteoporosis after spinal cord injury. A 12-month follow-up study

Spinal cord injury (SCI) has been associated with a marked bone loss after injury and a consequent increased risk of osteoporosis. The evaluation of bone mineral density shortly after SCI is a simple and effective method for predicting the development of osteoporosis during the first year after SCI.

INTRODUCTION

Spinal cord injury (SCI) has been associated with a marked bone loss after injury and a consequent increased risk of osteoporosis and fractures. The aim of this study was to analyze the factors associated with osteoporosis development short-term after SCI.

METHODS

We included patients with complete recent SCI (<6 months) evaluating bone turnover markers (P1NP, bone ALP, and sCTx), 25-OH-vitamin D (25OHD) levels, and lumbar and femoral BMD (Lunar, Prodigy) at baseline, 6 and 12 months after SCI. The risk factors for osteoporosis analyzed included the following: age, gender, BMI, toxic habits, bone turnover markers, 25OHD levels, lumbar and femoral BMD, level, severity and type of SCI, and days-since-injury. Osteoporosis was defined according to WHO criteria.

RESULTS

Thirty-five patients aged 35 ± 16 years were included, and 52 % developed osteoporosis during the 12-month follow-up. These latter patients had lower BMD values at femur and lumbar spine and higher bone turnover markers at baseline. On multivariate analysis, the principal factors related to osteoporosis development were as follows: total femur BMD <1 g/cm(2) (RR, 3.61; 95 % CI 1.30-10.06, p = 0.002) and lumbar BMD <1.2 g/cm(2) at baseline (0.97 probability of osteoporosis with both parameters under these values). Increased risk for osteoporosis was also associated with increased baseline values of bone ALP (>14 ng/mL) (RR 2.40; 95 % CI 1.10-5.23, p = 0.041) and P1NP (>140 ng/mL) (RR 3.08; 95 % CI 1.10-8.57, p = 0.017).

CONCLUSIONS

The evaluation of BMD at the lumbar spine and femur short-term after SCI is a simple, effective method for predicting the development of osteoporosis during the first year after SCI. Our results also indicate the need to evaluate and treat these patients shortly after injury.

Effect of carbohydrate feeding on the bone metabolic response to running

Bone resorption is increased after running, with no change in bone formation. Feeding during exercise might attenuate this increase, preventing associated problems for bone. This study investigated the immediate and short-term bone metabolic responses to carbohydrate (CHO) feeding during treadmill running. Ten men completed two 7-day trials, once being fed CHO (8% glucose immediately before, every 20 min during, and immediately after exercise at a rate of 0.7 g CHO·kg body mass⁻¹·h⁻¹) and once being fed placebo (PBO). On day 4 of each trial, participants completed a 120-min treadmill run at 70% of maximal oxygen consumption (V̇o_{2 max}). Blood was taken at baseline (BASE), immediately after exercise (EE), after 60 (R1) and 120 (R2) min of recovery, and on three follow-up days (FU1-FU3). Markers of bone resorption [COOH-terminal telopeptide region of collagen type 1 (β-CTX)] and formation [NH₂-terminal propeptides of procollagen type 1 (P1NP)] were measured, along with osteocalcin (OC), parathyroid hormone (PTH), albumin-adjusted calcium (ACa), phosphate, glucagon-like peptide-2 (GLP-2), interleukin-6 (IL-6), insulin, cortisol, leptin, and osteoprotogerin (OPG). Area under the curve was calculated in terms of the immediate (BASE, EE, R1, and R2) and short-term (BASE, FU1, FU2, and FU3) responses to exercise. β-CTX, P1NP, and IL-6 responses to exercise were significantly lower in the immediate postexercise period with CHO feeding compared with PBO (β-CTX: P = 0.028; P1NP: P = 0.021; IL-6: P = 0.036), although there was no difference in the short-term response (β-CTX: P = 0.856; P1NP: P = 0.721; IL-6: P = 0.327). No other variable was significantly affected by CHO feeding during exercise. We conclude that CHO feeding during exercise attenuated the β-CTX and P1NP responses in the hours but not days following exercise, indicating an acute effect of CHO feeding on bone turnover.

The role of enteric hormone GLP-2 in the response of bone markers to a mixed meal in postmenopausal women with type 2 diabetes mellitus

BACKGROUND

Type 2 diabetes mellitus (T2D) is a complex disease associated with several chronic complications, including bone fragility and high fracture risk due to mechanisms not yet fully understood. The influence of the gastrointestinal tract and its hormones on bone remodeling has been demonstrated in healthy individuals. Glucagon-like peptide 2 (GLP-2), an enteric hormone secreted in response to nutrient intake, has been implicated as a mediator of nutrient effects on bone remodeling. This study aimed to analyze the dynamics of bone resorption marker C-terminal telopeptide of type I collagen (CTX), bone formation marker osteocalcin, and GLP-2 in response to a mixed meal in diabetic postmenopausal women.

METHODS

Forty-three postmenopausal women with osteopenia or osteoporosis (20 controls - group CO - and 23 diabetic - group T2D) were subjected to a standard mixed meal tolerance test, with determination of serum CTX, plasma osteocalcin and serum GLP-2 concentrations at baseline and 30, 60, 120 and 180 minutes after the meal.

RESULTS

T2D women had higher body mass index as well as higher femoral neck and total hip bone mineral density. At baseline, luteinizing hormone, follicle-stimulating hormone, osteocalcin and CTX levels were lower in group T2D. In response to the mixed meal, CTX and osteocalcin levels decreased and GLP-2 levels increased in both groups. The expected CTX suppression in response to the mixed meal was lower in group T2D.

CONCLUSIONS

Bone turnover markers were significantly reduced in T2D women at baseline. Confirming the role of nutrient intake as a stimulating factor, GLP-2 increased in response to the mixed meal in both groups. Importantly, CTX variation in response to the mixed meal was reduced in T2D women, suggesting abnormal response of bone remodeling to nutrient intake in T2D.

DPP IV inhibitor treatment attenuates bone loss and improves mechanical bone strength in male diabetic rats

Dipeptidyl peptidase IV (DPP IV) modulates protein activity by removing dipeptides. DPP IV inhibitors are currently used to improve glucose tolerance in type 2 diabetes patients. DPP IV substrates not only increase insulin secretion but also affect bone metabolism. In this study, the effect of DPP IV inhibitor sitagliptin on bone was evaluated in normal and streptozotocin-induced diabetic rats. This study included 64 male Wistar rats divided into four groups (n = 16): two diabetic and two control groups. One diabetic and one control group received sitagliptin through drinking water. Tibiae were scanned every 3 wk using an in vivo μCT scanner. After 6 and 12 wk, rats were euthanized for histomorphometric analysis of bone parameters. The mechanical resistance of femora to fracture was assessed using a three-point bending test, and serum levels of bone metabolic markers were measured. Efficient DPP IV inhibition was achieved in sitagliptin-treated groups. Trabecular bone loss, the decrease in trabecular number, and the increase in trabecular spacing was attenuated through sitagliptin treatment in diabetic rats, as shown by in vivo μCT. Bone histomorphometry was in line with these results. μCT analysis furthermore showed that sitagliptin prevented cortical bone growth stagnation in diabetic rats, resulting in stronger femora during three-point bending. Finally, the serum levels of the resorption marker CTX-I were significantly lower in sitagliptin-treated diabetic animals compared with untreated diabetic animals. In conclusion, sitagliptin treatment attenuates bone loss and increases bone strength in diabetic rats probably through the reduction of bone resorption and independent of glycemic management.

Ethnic differences in calcium, phosphate and bone metabolism

The prevalence of osteoporosis and the incidence of age-related fragility fracture vary by ethnicity. There is greater than 10-fold variation in fracture probabilities between countries across the world. Mineral and bone metabolism are intimately interlinked, and both are known to exhibit patterns of daily variation, known as the diurnal rhythm (DR). Ethnic differences are described for Ca and P metabolism. The importance of these differences is described in detail between select ethnic groups, within the USA between African-Americans and White-Americans, between the Gambia and the UK and between China and the UK. Dietary Ca intake is higher in White-Americans compared with African-Americans, and is higher in White-British compared with Gambian and Chinese adults. Differences are observed also for plasma 25-hydroxy vitamin D, related to lifestyle differences, skin pigmentation and skin exposure to UVB-containing sunshine. Higher plasma 1,25-dihydroxy vitamin D and parathyroid hormone are observed in African-American compared with White-American adults. Plasma parathyroid hormone is also higher in Gambian adults and, in winter, in Chinese compared with White-British adults. There may be ethnic differences in the bone resorptive effects of parathyroid hormone, with a relative skeletal resistance to parathyroid hormone observed in some, but not all ethnic groups. Renal mineral excretion is also influenced by ethnicity; urinary Ca (uCa) and urinary P (uP) excretions are lower in African-Americans compared with White-Americans, and in Gambians compared with their White-British counterparts. Little is known about ethnic differences in the DR of Ca and P metabolism, but differences may be expected due to known differences in lifestyle factors, such as dietary intake and sleep/wake pattern. The ethnic-specific DR of Ca and P metabolism may influence the net balance of Ca and P conservation and bone remodelling. These ethnic differences in Ca, P and the bone metabolism may be important factors in the variation in skeletal health.

Feeding and bone turnover in gastric bypass

CONTEXT

Roux-en-Y gastric bypass (RYGB) is associated with high bone turnover. In healthy subjects, feeding causes acute reduction of bone resorption, which is regulated by several intestinal and pancreatic peptides.

OBJECTIVE

Our objective was to assess bone turnover after feeding in patients with RYGB.

DESIGN AND SETTING

This was a cross-sectional case-control study at a university hospital.

PARTICIPANTS

Fifteen postmenopausal women who underwent RYGB 7.4 ± 4.1 years previously were matched by age and body mass index with 15 nonoperated women (controls).

MAIN OUTCOMES

Serum PTH, calcium, phosphorus, insulin, carboxy telopeptide (CTX), procollagen type I N-terminal propeptide (P1NP), and glucagon-like peptide 2 (GLP-2) were measured while fasting and after a standard meal (SM).

RESULTS

The fasting calcium, phosphorus, and PTH were similar in both groups and exhibited similar decreases after an SM. The fasting CTX level was higher in the RYGB than in the control group (0.589 ± 0.18 vs 0.382 ± 0.11 ng/mL; P < .05) and fell to a nadir of 42.2% of the basal value in the RYGB and 53.9% in controls (P < .05). The fasting and postprandial P1NP levels were similar in both groups and fell to a nadir of 85.8% in the RYGB and 89.3% in controls. Insulin and GLP-2 levels were similar during fasting in both groups. RYGB patients had exaggerated postprandial insulin and GLP-2 response compared with the controls with the insulin and GLP-2 area under the curve being significantly higher in the RYGB group. There was a significant negative correlation between the peak of insulin levels and the CTX changes.

CONCLUSION

The acute reduction in bone resorption after feeding is preserved in RYGB and is even higher than in nonoperated subjects. This phenomenon is related to the increase of postprandial levels of insulin. These findings suggest a bone-protecting mechanism in RYGB that may counteract the elevated bone resorption that occurs during fasting.

Cytokines and Hormones That Contribute to the Positive Association between Fat and Bone

The positive association between body weight and bone density has been established in numerous laboratory and clinical studies. Apart from the direct effect of soft tissue mass on bone through skeletal loading, a number of cytokines and hormones contribute to the positive association between adipose and bone tissue, acting either locally in sites where cells of the two tissues are adjacent to each other or systemically through the circulation. The current review describes the effects of such local and systemic factors on bone physiology. One class of factors are the adipocyte-secreted peptides (adipokines), which affect bone turnover through a combination of direct effects in bone cells and indirect mechanisms mediated by the central nervous system. Another source of hormones that contribute to the coupling between fat and bone tissue are beta cells of the pancreas. Insulin, amylin, and preptin are co-secreted from pancreatic beta cells in response to increased glucose levels after feeding, and are also found in high circulating levels in obesity. A number of peptide hormones secreted from the gastrointestinal tract in response to feeding affect both fat and bone cells and thus can also act as mediators of the association between the two tissues. The current review focuses on results of laboratory studies investigating possible mechanism involved in the positive association between fat mass and bone mass.

Influence of hormonal appetite and energy regulators on bone

Nutritional status is an essential component in determining whole body energy homeostasis. The balance between energy/food intake and metabolism is governed by a range of hormones secreted from various parts of the body. Their subsequent dissemination via the blood results in a wide range of biological responses including satiety, hunger, and glucose uptake. The roles of these systemic hormones also extend to bone regulation with animal and clinical studies establishing a relationship between these regulatory pathways. This review covers the gastrointestinal hormones, ghrelin, PYY, GIP, GLP-1, and GLP-2, and the adipokines, leptin, and adiponectin and their roles in regulating bone homeostasis. Their known actions are reviewed, with an emphasis upon recent advances in understanding. Taken together, this review outlines an expanding appreciation of the interactions between bone mass and the nutritional control of whole body energy balance by gut and adipose tissue.

An association between post-meal bile acid response and bone resorption in normal subjects

Background

The mechanism surrounding bone suppression after a meal may involve several mediators, but is yet to be clarified. Bile acids (BA) function as signalling molecules in response to feeding, and may be directly involved in bone suppression acutely after a meal. The aim of this study was to test the hypothesis that BA are involved in the acute bone suppression observed after a meal.

Methods

A prospective study in which samples collected from volunteers fed a 400 Kcal test meal after an overnight fast were analysed for parathyroid hormone (PTH), BA, and carboxyterminal of type 1 collagen telopeptide (CTX). The study was carried out in 10 healthy male volunteers. Ethical approval was obtained from the Local Research and Ethics Committee at King's College Hospital.

Results

Total BA, glycine conjugated bile acids (GCBA), PTH and CTX showed a response to meal ingestion. There was a negative correlation between percentage change in PTH and CTX ( R2 = −0.82, P = 0.004), and between PTH and GCBA ( R2 = −0.39, P = 0.005).

Conclusion

This study demonstrated an association between GCBA and PTH suppression after a meal. The drop in PTH concentration after a meal may be responsible for the suppression of bone resorption as observed by the decrease in CTX concentration.

Effects and differentiation activity of IGF-I, IGF-II, insulin and preptin on human primary bone cells

The importance of the complex interrelated regulatory pathways involving IGF factors and pancreatic hormones can be observed in several metabolic diseases, where the deregulation of these factors has a wide impact on bone health. These findings have stimulated us to compare the effect of IGF-I, IGF-II, insulin and preptin on human bone cells. The effect on cell differentiation and cell activity of osteoblasts and osteoclasts has been analysed. We have observed a significant effect by IGF-I, a modest effect by IGF-II and preptin and no effect after insulin administration on human primary osteoblast-like cells. All studied factors have shown an induction on human primary osteoclast differentiation and bone resorption activity, with IGF-I being the most potent factor. We hypothesize that these findings may be on the basis of decreased bone mass density observed in several diseases.

Effect of fasting versus feeding on the bone metabolic response to running

Individuals often perform exercise in the fasted state, but the effects on bone metabolism are not currently known. We compared the effect of an overnight fast with feeding a mixed meal on the bone metabolic response to treadmill running. Ten, physically-active males aged 28 ± 4y (mean ±SD) completed two, counterbalanced, 8d trials. After 3d on a standardised diet, participants performed 60 min of treadmill running at 65% VO(2max) on Day 4 following an overnight fast (FAST) or a standardised breakfast (FED). Blood samples were collected at baseline, before and during exercise, for 3h after exercise, and on four consecutive follow-up days (FU1-FU4). Plasma/serum were analysed for the c-terminal telopeptide region of collagen type 1 (β-CTX), n-terminal propeptides of procollagen type 1 (P1NP), osteocalcin (OC), bone alkaline phosphatase (bone ALP), parathyroid hormone (PTH), albumin-adjusted calcium, phosphate, osteoprotegerin (OPG), cortisol, leptin and ghrelin. Only the β-CTX response was significantly affected by feeding. Pre-exercise concentrations decreased more in FED compared with FAST (47% vs 26%, P<0.001) but increased during exercise in both groups and were not significantly different from baseline at 1h post-exercise. At 3h post-exercise, concentrations were decreased (33%, P<0.001) from baseline in FAST and significantly lower (P<0.001) than in FED. P1NP and PTH increased, and OC decreased during exercise. Bone markers were not significantly different from baseline on FU1-FU4. Fasting had only a minor effect on the bone metabolic response to subsequent acute, endurance exercise, reducing the duration of the increase in β-CTX during early recovery, but having no effect on changes in bone formation markers. The reduced duration of the β-CTX response with fasting was not fully explained by changes in PTH, OPG, leptin or ghrelin.

Enhanced trabecular bone resorption and microstructural bone changes in rats after removal of the cecum

The cecum, the proximal part of the large intestine, has the highest rate of calcium absorption compared with other intestinal segments. Previously, we showed that rats with the cecum surgically removed (cecectomized rats) had severe negative calcium balance, low bone mineral density (BMD), and a compensatory increase in colonic calcium absorption. Herein, we used the computer-assisted bone histomorphometric technique and microcomputed tomography (μCT) to analyze bone microstructural defects in cecectomized rats at 1 and 3 mo postsurgery compared with age-matched sham-operated control rats. Relatively low BMD as determined by dual energy X-ray absorptiometry was observed in the femora, tibiae, and lumbar vertebrae of the 3-mo cecectomized rats. μCT analysis revealed decreases in the tibial cortical thickness, periosteal and endosteal perimeters, and moment of inertia in cecectomized rats. The histomorphometric results further showed that trabecular bone volume and number were markedly decreased, whereas trabecular separation was increased in the proximal tibial metaphysis of cecectomized rats, thus leading to a decrease in trabecular volumetric BMD. Since osteoclast surface and eroded surface were increased after cecectomy, such bone loss in cecectomized rats appeared to result from an enhanced bone resorption. Moreover, decreases in bone formation rate and osteoblast surface indicated a suppression of osteoblast-mediated bone formation. In conclusion, cecectomy induced widespread osteopenia in rats presumably by enhancing the osteoclast-mediated bone resorption and suppressing bone formation. The present results underline the important role of cecum in the body calcium homeostasis.

The coordinated expression, interaction and evolution of the neuroendocrine genes

The neuroendocrine system is a complex biological system controlled by various neuropeptides and hormones. The evolution and network properties of neuroendocrine genes are analyzed along with their expression profiles. The neuroendocrine genes show very similar expression profiles and local network properties across a wide range of tissues consistent with the physiological roles of their proteins. Moreover, the coordinated evolution of 10 neuroendocrine genes involved in mammalian reproduction and homeostasis is demonstrated using several methods, such as correlated evolution, relative-rate test, relative-ratio test and codon usage bias. The neuroendocrine genes seem to evolve predominantly under similar selective strengths and regimes of purifying selection, which is well reflected in their evolutionary fingerprints. This result demonstrates for the first time a key role of natural selection in creating and maintaining a well-designed neuroendocrine system at the genomic level. It also indicates that component properties of a complex system at a higher physiological scale may determine component properties at a lower genomic scale and/or vice versa.

Bone: incretin hormones perceiver or receiver?

Novel incretin-based drugs, such as glucagon-like peptide-1 receptor agonists (GLP-1 RA) and dipeptidyl peptidase-4 inhibitors (DPP-4i), have been last introduced in the pharmacological treatment of type 2 diabetes. In the last few years, the interest on the relationship of gut hormones with bone metabolism in diabetes has been increasing. The aim of present paper is to examine in vitro and in vivo evidence on the connections between incretin hormones and bone metabolism. We also discuss results of clinical trials and metaanalysis, explore the effects of incretin drugs in vitro on osteogenic cells and osteoclasts, and speculate on the possibility of different effects of GLP-1 RA and DPP-4i on the risk of bone fractures risk in humans. Although existing preliminary evidence suggests a protective effect on the bone, at least for DPP-4i, further controlled, long-term studies with measurement of bone markers, bone density, and clinical fractures rates are needed to substantiate and confirm those findings.

Effects of vildagliptin on postprandial markers of bone resorption and calcium homeostasis in recently diagnosed, well-controlled type 2 diabetes patients

BACKGROUND

Bone metabolism is a dynamic process that is influenced by food ingestion. Endogenous incretins have been shown to be important regulators of bone turnover. The aim of the present study was to assess whether a dipeptidylpeptidase (DPP)-4 inhibitor affects markers of bone resorption and calcium homeostasis.

METHODS

The present study was a single-center, double blind, randomized clinical trail. Fifty-nine drug-naïve patients with type 2 diabetes (T2D) were randomized to either 1 year treatment with the DPP-4 inhibitor vildagliptin (100 mg, once daily; n = 29) or placebo (n = 30). Patients received a standardized breakfast after measurement of serum concentrations of cross-linked C-terminal telopeptide (s-CTx), a bone resorption marker influenced by food intake, before and after 50 weeks treatment.

RESULTS

Vildagliptin did not change postprandial s-CTx concentrations compared with pretreatment levels (between-group ratio 1.15 ± 0.17; P = 0.320). Fasting serum alkaline phosphatase, calcium, and phosphate were also unaffected y 1 year treatment with vildagliptin.

CONCLUSIONS

Treatment with vildagliptin for 1 year was not associated with changes in markers of bone resorption and calcium homeostasis in drug-naïve patients with T2D and mild hyperglycemia.

Plasma metabolomics and proteomics profiling after a postprandial challenge reveal subtle diet effects on human metabolic status

We introduce the metabolomics and proteomics based Postprandial Challenge Test (PCT) to quantify the postprandial response of multiple metabolic processes in humans in a standardized manner. The PCT comprised consumption of a standardized 500 ml dairy shake containing respectively 59, 30 and 12 energy percent lipids, carbohydrates and protein. During a 6 h time course after PCT 145 plasma metabolites, 79 proteins and 7 clinical chemistry parameters were quantified. Multiple processes related to metabolism, oxidation and inflammation reacted to the PCT, as demonstrated by changes of 106 metabolites, 31 proteins and 5 clinical chemistry parameters. The PCT was applied in a dietary intervention study to evaluate if the PCT would reveal additional metabolic changes compared to non-perturbed conditions. The study consisted of a 5-week intervention with a supplement mix of anti-inflammatory compounds in a crossover design with 36 overweight subjects. Of the 231 quantified parameters, 31 had different responses over time between treated and control groups, revealing differences in amino acid metabolism, oxidative stress, inflammation and endocrine metabolism. The results showed that the acute, short term metabolic responses to the PCT were different in subjects on the supplement mix compared to the controls. The PCT provided additional metabolic changes related to the dietary intervention not observed in non-perturbed conditions. Thus, a metabolomics based quantification of a standardized perturbation of metabolic homeostasis is more informative on metabolic status and subtle health effects induced by (dietary) interventions than quantification of the homeostatic situation. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11306-011-0320-5) contains supplementary material, which is available to authorized users.