Relationships Among the Metabolic Syndrome, Bone Mineral Density, Bone Turnover Markers, and Hyperglycemia

The role of bone in energy metabolism: A focus on osteocalcin

Understanding the mechanisms involved in whole body glucose regulation is key for the discovery of new treatments for type 2 diabetes (T2D). Historically, glucose regulation was largely focused on responses to insulin and glucagon. Impacts of incretin-based therapies, and importance of muscle mass, are also highly relevant. Recently, bone was recognized as an endocrine organ, with several bone proteins, known as osteokines, implicated in glucose metabolism through their effects on the liver, skeletal muscle, and adipose tissue. Research efforts mostly focused on osteocalcin (OC) as a leading example. This review will provide an overview on this role of bone by discussing bone turnover markers (BTMs), the receptor activator of nuclear factor kB ligand (RANKL), osteoprotegerin (OPG), sclerostin (SCL) and lipocalin 2 (LCN2), with a focus on OC. Since 2007, some, but not all, research using mostly OC genetically modified animal models suggested undercarboxylated (uc) OC acts as a hormone involved in energy metabolism. Most data generated from in vivo, ex vivo and in vitro models, indicate that exogenous ucOC administration improves whole-body and skeletal muscle glucose metabolism. Although data in humans are generally supportive, findings are often discordant likely due to methodological differences and observational nature of that research. Overall, evidence supports the concept that bone-derived factors are involved in energy metabolism, some having beneficial effects (ucOC, OPG) others negative (RANKL, SCL), with the role of some (LCN2, other BTMs) remaining unclear. Whether the effect of osteokines on glucose regulation is clinically significant and of therapeutic value for people with insulin resistance and T2D remains to be confirmed.

Effect of gut hormones on bone metabolism and their possible mechanisms in the treatment of osteoporosis

Bone is a highly dynamic organ that changes with the daily circadian rhythm. During the day, bone resorption is suppressed due to eating, while it increases at night. This circadian rhythm of the skeleton is regulated by gut hormones. Until now, gut hormones that have been found to affect skeletal homeostasis include glucagon-like peptide-1 (GLP-1), glucagon-like peptide-2 (GLP-2), glucose-dependent insulinotropic polypeptide (GIP), and peptide YY (PYY), which exerts its effects by binding to its cognate receptors (GLP-1R, GLP-2R, GIPR, and Y1R). Several studies have shown that GLP-1, GLP-2, and GIP all inhibit bone resorption, while GIP also promotes bone formation. Notably, PYY has a strong bone resorption-promoting effect. In addition, gut microbiota (GM) plays an important role in maintaining bone homeostasis. This review outlines the roles of GLP-1, GLP-2, GIP, and PYY in bone metabolism and discusses the roles of gut hormones and the GM in regulating bone homeostasis and their potential mechanisms.

Effect of Liraglutide on Osteoporosis in a Rat Model of Type 2 Diabetes Mellitus: A Histological, Immunohistochemical, and Biochemical Study

Diabetic osteoporosis (DOP) is a diabetic complication associated with a significant disability rate. Liraglutide, a glucagon-like peptide-1 receptor agonist, is a promising and innovative drug for type 2 diabetes mellitus (T2DM), with potential therapeutic implications for bone disorders. This investigation examined the impact of liraglutide on osteoporosis in rats with T2DM and studied the influence of vitamin D receptor Bsm1 polymorphism on liraglutide-induced outcomes. Thirty rats were divided into control, T2DM induced by a combination of a high-fat diet and 25 mg/kg streptozotocin, and T2DM-liraglutide (T2DM treated with 0.4 mg/kg/day liraglutide) groups. After 8 weeks of liraglutide treatment, femurs and blood samples were obtained from all rats for subsequent investigations. Diabetes induced a remarkable rise in the serum levels of receptor activator of nuclear factor kappa B ligand (RANKL) and C-telopeptide of type I collagen (CTX-1) associated with a remarkable decline in osteocalcin and osteoprotegerin (OPG). Impaired bone architecture was also demonstrated by light and scanning electron microscopic study. The immune expression of OPG was down-regulated, while RANKL was up-regulated. Interestingly, the administration of liraglutide ameliorated the previous changes induced by diabetes mellitus. In conclusion, liraglutide can prevent DOP, mostly due to liraglutide's ability to increase bone growth, while inhibiting bone resorption.

A Review of Current Evidence on the Relationship between Phosphate Metabolism and Metabolic Syndrome

Phosphorus, present as phosphate in biological systems, is an essential mineral for various biological activities and biochemical processes. Numerous studies have indicated that disturbed phosphate balance may contribute to the development of metabolic syndrome (MetS). However, no consistent result was found on the association between phosphorus intake and serum phosphate concentration with MetS. It is believed that both positive and negative impacts of phosphorus/phosphate co-exist in parallel during MetS condition. Reduced phosphate level contributed to the development of obesity and hyperglycaemia. Low phosphate is believed to compromise energy production, reduce exercise capacity, increase food ingestion, and impair glucose metabolism. On the other hand, the effects of phosphorus/phosphate on hypertension are rather complex depending on the source of phosphorus and subjects' health conditions. Phosphorus excess activates sympathetic nervous system, renin-angiotensin-aldosterone system, and induces hormonal changes under pathological conditions, contributing to the blood pressure-rising effects. For lipid metabolism, adequate phosphate content ensures a balanced lipid profile through regulation of fatty acid biosynthesis, oxidation, and bile acid excretion. In conclusion, phosphate metabolism serves as a potential key feature for the development and progression of MetS. Dietary phosphorus and serum phosphate level should be under close monitoring for the management of MetS.

The Impact of GLP1 Agonists on Bone Metabolism: A Systematic Review

Background and Objectives: The association between diabetes mellitus and increased risk of bone fractures has led to the investigation of the impact of antidiabetic drugs on bone metabolism. Glucagon-like peptide-1 receptor agonists (GLP1RAs) are a relatively novel and promising class of anti-hyperglycemic drugs. In addition to their blood glucose lowering action, GLP1RAs seem to have additional pleiotropic properties such as a beneficial skeletal effect; although the underlying mechanisms are not completely understood. The present systematic review summarizes current evidence about GLP1RAs and their effects on bone metabolism and fracture. Methods: An extensive literature search was conducted based on electronic databases namely, PubMed, Google Scholar and Cochrane Central Register of Controlled Trials (CENTRAL) through October 2019 to January 2020 for articles related to bone mineral density, diabetes mellitus and GLP1RAs. We included articles published in English. Finally, we included four randomized controlled trials, three meta-analyses, a case-control study and a population-based cohort analysis. Results: Based on the articles included, the animal studies indicated the salutary skeletal effects of GLP1RAs in opposition to what has been commonly observed in human studies, showing that these agents have no impact on bone mineral density (BMD) and the turnover markers. Moreover, it was demonstrated that GLP1 was not associated with fracture risk as compared to other anti-hyperglycemic drugs. Conclusions: Findings from this systematic review have demonstrated the neutral impact of GLP1RAs on BMD. Moreover, further double-blind randomized controlled trials are needed to draw more meaningful and significant conclusions on the efficacy of GLP1RAs on BMD.

The Hyperglycemia and Hyperketonemia Impaired Bone Microstructures: A Pilot Study in Rats

Though diabetes mellitus (DM) is one of the known causes of osteoporosis, it is also realized that ketogenic diet (KD), an effective regimen for epilepsy, impairs bone microstructures. However, the similarities and differences of effects between these two factors are still unknown. The purpose of this study is to identify different effects between hyperglycemia and hyperketonemia, which are manifestations of DM and KD, on bone in rats. Thirty male Sprague-Dawley rats were randomly divided into three groups: the sham, DM, and KD groups. Hyperglycemia was achieved by intravenous injection of streptozotocin in DM group, while hyperketonemia was induced by application of ketogenic diet (carbohydrates-to-fat as 1:3) in KD group. The body weight, blood ketone body, and blood glucose were recorded, and the bone turnover markers, bone length, bone microstructures, bone biomechanics and histomorphology were measured after 12 weeks intervention. Compared with the control and KD groups, a significant body weight loss was found in the DM group, and the bone lengths of tibia and femur of the group were shortened. The blood glucose and blood ketone were noticeably increased in the DM and KD rats, respectively. Microstructures and properties of cancellous bone were significantly deteriorated in both the DM and KD groups compared with the sham group, as the bone volumes were decreased and the bone trabecula structures were disturbed. Meanwhile, the thickness and strength of cortical bone was reduced more in the DM group than those in the sham and KD groups. The HE staining showed that bone trabecula was significantly decreased in both the DM and KD groups, and more adipose tissue was observed in the KD rats. The activity of osteoblasts was decreased more in both the KD and DM groups than that in the sham group, while the activity of osteoclasts of the two groups was remarkably increased. The present study indicates that both hyperglycemia and hyperketonemia have adverse effects on bone. Therefore, it is worth paying more attention to the bone status of patients with hyperglycemia and hyperketonemia in clinic.

Effects of age and sex on osteocalcin and bone-specific alkaline phosphatase-reference intervals and confounders for two bone formation markers

Bone formation markers bone-specific alkaline phosphatase and osteocalcin are used in many clinical situations. Therefore, we calculated reference intervals for the two markers and investigated how they are influenced by several factors including sex and age. Furthermore, we established clinically relevant reference intervals for the two markers.

OBJECTIVE

The bone turnover markers (BTMs), bone-specific alkaline phosphatase (bone ALP), and osteocalcin (OC), are frequently measured formation markers. The purpose of this study was to establish reference intervals (RIs) for the two BTMs in a general adult Danish population.

METHODS

Bone ALP and OC were measured on the iSYS (IDS Plc) automatic analyzer in samples from the Danish Health2006 5-year follow-up study on serum from 2308 participants (54% women, age range 24-76). Participants with self-reported diagnosis of osteoporosis or receiving hormonal replacement were excluded from analyses while participants on hormonal contraceptives were included.

RESULTS

The geometric mean and 95%RI for bone ALP were 13.9 μg/L (7.6-25.6) for men and 13.8 μg/L (7.0-27.4) for women, while for OC 16.0 μg/L (7.5-34.4) for men and 18.6 μg/L (8.1-42.9) for women. Levels of bone ALP increased with increasing age (β 1.004, p < 0.001), while female sex had no effect. OC levels decreased with increasing age (β 0.998, p = 0.009) and increased with female sex (β 1.104, p < 0.001). Based on our findings, we propose for bone ALP and OC three clinical RIs for men based on age and three clinical RI for women based on age and menopausal status.

CONCLUSION

The RI for bone ALP and OC varies with age and sex and the BTMs are influenced differently by the two factors. Consequently, the need for establishing valid RIs is of great importance before the full potential of BTM can be used in clinical practice.

Characteristics of bone turnover markers in women with gestational diabetes mellitus

BACKGROUND

Bone turnover markers (BTMs) can be applied to the assessment of bone formation and bone resorption activity. The aim of this study was to investigate the changes in BTMs in women with gestational diabetes mellitus (GDM).

METHODS

One hundred and five women with gestational diabetes mellitus defined as the GDM group and 46 healthy pregnant women with normal glucose tolerance selected as the control group were enrolled in this study. Serum samples were collected during regular obstetric examinations and the serum levels of total procollagen type 1 N-terminal propeptide (P1NP), N-terminal midfragment of osteocalcin (N-MID), and β-C-terminal telopeptide of type 1 collagen (β-CTX) were measured. An independent-sample t-test, the Mann-Whitney U test, and a Pearson correlation analysis were performed for data analyses.

RESULTS

Serum β-CTX levels in the GDM group were significantly higher than those in the control group (296.00 [235.00-369.00] pg/mL vs. 218.5 [165.25-292.50] pg/mL, p < 0.05), while P1NP and N-MID levels did not differ between the two groups. The Pearson correlation analysis revealed that β-CTX level was correlated with blood glucose level.

CONCLUSIONS

The difference in β-CTX levels indicated that bone resorption in patients with GDM diabetes was higher than that in pregnant women with normal glucose tolerance. No obvious differences in bone formation markers P1NP and N-MID were found between the two groups.

Association between glycosylated hemoglobin A1c and bone biochemical markers in type 2 diabetic postmenopausal women: a cross-sectional study

BACKGROUND

type 2 diabetes mellitus (T2DM) is a complicated disease that can affect bone health, but the change in bone biochemical markers caused by T2DM was controversial, so the aim of this study was to investigate whether there was a discrepancy in the levels of bone biochemical markers between postmenopausal women with T2DM and non-diabetic women and to explore the relationship between the level of glycosylated hemoglobin A1c (HbA1c) and bone biochemical markers in these subjects.

METHODS

A total of 237 type 2 diabetic postmenopausal women visiting the First Affiliated Hospital of Anhui Medical University from January 2017 to October 2018 and 93 healthy postmenopausal women were retrospectively enrolled. The differences in the levels of bone biochemical markers between patients and controls were analyzed by one-way ANOVA or chi-square test. The relationship between HbA1c and bone biochemical markers was analyzed by multivariate regression, forest plot and fitted curve.

RESULTS

Bone formation markers including N-MID osteocalcin and procollagen type 1 amino-terminal pro-peptide (PINP) were decreased in postmenopausal women with T2DM compared to controls (17.42 ± 9.50 vs 23.67 ± 7.58, p < 0.001; 48.47 ± 27.27 vs 65.86 ± 21.06, p < 0.001, respectively), but the bone resorption markers β-crossLaps (β-CTX) was no difference between the two groups (0.57 ± 0.28 vs 0.55 ± 0.21, p = 0.868). Multivariate regression showed that HbA1c was inversely associated with N-MID osteocalcin and PINP after adjusting for age, BMI, menopause's years, diabetic duration, TC, TG, HDL-c, LDL-c, creatinine, UA and eGFR. The adjusted coefficients for N-MID osteocalcin and PINP per 1% HbA1c decrease were - 0.71 (- 1.19, - 0.22) and - 1.79 (- 3.30, - 0.28), respectively. A segmentation effect was seen in the fitted curve between HbA1c and β-CTX with an inflection point at 7.4% of HbA1c, the highest quartile of β-CTX (> = 0.74 ng/ml) showed a significantly negative with HbA1c. No significant association was seen between HbA1c and other biochemical markers.

CONCLUSIONS

Our study found that bone formation was inhibited in postmenopausal women with T2DM, but bone resorption was not affected, and poor glycemic control was related to lower levels of bone formation, may increase the risk of bone fracture in postmenopausal women with T2DM.

Menopause and metabolic syndrome in the Middle East countries; a systematic review and meta-analysis study

INTRODUCTION

Metabolic syndrome (MetS) prevalence that is associated with increasing risk of diabetes and cardiovascular diseases (CVD) has accelerated with age. Since, menopause is known as a partial cause of CVD accelartion with againg among women, determining the prevalence of MetS is important in this condition. We aimed to assess critically the prevalence rate of MetS among menopaused women in the Middle East Countries in this systematic review meta-analysis study.

METHODS & MATERIALS

International webdata bases including Scopus, ISI web of Science and PubMed were systematically searched using Medical Subject Headings terms from January 2000 to February 2017. We included all cross-sectional conducted in the Middle East that reported prevalence of MetS in menopause status regardless of MetS definition. Quality assessment was considered for each included study. The pooled prevalence of MetS based on the Adult Treatment Panel III (ATP III) was estimated using random effect method due to between-study heterogeneity by STATA software, version 11.0 (StataCorp, USA).

RESULTS

Within 60 studies, 21 and 17 studies were included in qualitative synthesis and meta-analysis respectively. The prevalence of MetS among menopaused women was estimated 54.87% (95% CI: 53.76-55.97) in the Middle East countries. In sub-group analysis based on country the prevalence rate of MetS in Iran and Turkey was estimated 58.78% (95% CI: 57.54-60.02), and 39.02% (95% CI: 36.57-41.47), respectively.

CONCLUSIONS

MetS was highly prevalent as an alarming sign among menopaused women in the Middle East countries. Thus, it is an emergency requirement to promote healthy lifestyle. Also, early detection and treatment of women who reach menopause and are at great risk of developing MetS is necessary for prevention of diabetes and CVD in the region.

Soy protein improves tibial whole-bone and tissue-level biomechanical properties in ovariectomized and ovary-intact, low-fit female rats

BACKGROUND

Osteoporosis and related fractures, decreased physical activity, and metabolic dysfunction are serious health concerns for postmenopausal women. Soy protein might counter the negative effects of menopause on bone and metabolic health due to the additive or synergistic effects of its bioactive components.

OBJECTIVE

To evaluate the effects of ovariectomy (OVX) and a soy-protein diet (SOY) on bone outcomes in female, low-capacity running (LCR) rats selectively bred for low aerobic fitness as a model of menopause.

METHODS

At 27 weeks of age, LCR rats (N = 40) underwent OVX or sham (SHAM) surgery and were randomized to one of two isocaloric and isonitrogenous plant-protein-based dietary treatments: 1) soy-protein (SOY; soybean meal); or, 2) control (CON, corn-gluten meal), resulting in four treatment groups. During the 30-week dietary intervention, animals were provided ad libitum access to food and water; body weight and food intake were measured weekly. At completion of the 30-week intervention, body composition was measured using EchoMRI; animals were fasted overnight, euthanized, and blood and hindlimbs collected. Plasma markers of bone formation (osteocalcin, OC; N-terminal propeptide of type I procollagen, P1NP) and resorption (tartrate-resistant acid phosphatase, TRAP5b; C-terminal telopeptide of type I collagen, CTx) were measured using ELISA. Tibial trabecular microarchitecture and cortical geometry were evaluated using μCT; and torsional loading to failure was used to assess cortical biomechanical properties. Advanced glycation end-product (AGE) content of the femur was measured using a fluorimetric assay, and was expressed relative to collagen content measured by a colorimetric OH-proline assay. Two-factor ANOVA or ANOVCA was used to test for significant main and interactive effects of ovarian status (OV STAT: OVX vs. SHAM) and DIET (SOY vs. CON); final body weight was included as a covariate for body-weight-dependent cortical geometry and biomechanical properties.

RESULTS

OVX had significantly greater CTx than SHAM; SOY did not affect bone turnover markers. OVX adversely affected trabecular microarchitecture as evidenced by reduced BV/TV, trabecular thickness (Tb.Th), trabecular number (Tb.N), and connectivity density (Conn.D), and by increased trabecular separation (Tb.Sp) and structural model index (SMI). SOY increased BV/TV only in ovary-intact animals. There was no effect of OVX or SOY on tibial cortical geometry. In SHAM and OVX rats, SOY significantly improved whole-bone strength and stiffness; SOY also increased tissue-level stiffness and tended to increase tissue-level strength (p = 0.067). There was no effect of OVX or SOY on AGE content.

CONCLUSION

Soy protein improved cortical bone biomechanical properties in female low-fit rats, regardless of ovarian hormone status.

The impact of the metabolic syndrome on bone mass density: a prospective case control study

Background Obesity and metabolic syndrome (MetS) during the perimenopausal period and in menopause have been linked to altered bone mass density (BMD) in various experimental studies. However, current clinical studies provide conflicting results in this field. The purpose of the present study was to evaluate this association. Materials and methods We conducted a prospective case control study that was based on a consecutive series of menopausal women who attended the Reproductive Endocrinology Outpatient Clinic of our hospital between January 2013 and December 2016. Results One hundred and forty post-menopausal women were included in the present study. After stratifying the women in two groups according to the presence of MetS we observed that bone turnover markers remained unaffected by the presence of MetS (p > 0.05). On the other hand, both the T- and Z-scores of women with MetS were significantly higher compared to healthly postmenopausal women [T-score: 0.4 (-0.7 to 1.3) vs. -1 (-1.62 to -0.1), p < 0.001] [Z-score: 0.55 (-0.3 to 1.7) vs. -0.4 (-1.1 to 0.4), p = 0.003]. Conclusions According to the findings of our study the presence of MetS during the perimenopausal years seems to have a mild benefit on bone mass density. The pathophysiology that underlies this effect remains unclear as bone turnover markers seem to be unaffected by MetS.

The Impact of Glucagon-Like Peptide-1 on Bone Metabolism and Its Possible Mechanisms

The impact of antidiabetic drugs on bone metabolism is drawing increasing attention due to the discovery of a correlation between type 2 diabetes mellitus (T2DM) and osteoporosis. Glucagon-like peptide-1 (GLP-1) receptor agonists are a novel and promising class of drugs for T2DM, which may also have clinical applications in bone tissue disorders. This review examines the impact of GLP-1 on bone metabolism, including enhancement of bone mineral density and improvement of bone quality. However, the precise effect of GLP-1 on fracture risk has not been unambiguously defined. This review also summarizes our current understanding of the mechanisms by which GLP-1 affects bone metabolism. GLP-1 may act on bone by promoting bone formation, inhibiting bone resorption, and affecting the coordination of the two processes. We describe molecular pathways and proteins, such as Wnt and calcitonin, that are associated with GLP-1 and bone tissue. The specific processes and related molecular mechanisms of the effects of GLP-1 on bone metabolism need to be further explored and clarified.

Metabolic syndrome and the risk of bone fractures: A Meta-analysis of prospective cohort studies

Increasing evidence has suggested an association between metabolic syndrome (MetS) and bone fractures. However, because of controversial results it is still not clear whether this effect is protective or detrimental. Therefore, we conducted a meta-analysis of prospective studies to assess the association between them. Pertinent studies were identified by searching PubMed and EMBASE databases until the end of July 2015. Summary relative risks (RRs) and 95% confidence intervals (CIs) for associations between MetS and fracture risk were estimated with random effects models. Our meta-analysis included five prospective studies. The summarized RRs of any type of fractures for MetS were 0.76 (95%CI: 0.59-0.97, P = 0.026) with moderate heterogeneity (I(2) = 63.80%, P = 0.064). Notably, subgroup analyses by gender showed that significant inverse associations were observed only in men (summarized RR = 0.66; 95%CI = 0.51-0.86, P = 0.002; I(2) = 27.90%, P = 0.235; n = 5) but not in women (summarized RR = 0.96, 95%CI: 0.60-1.54, P = 0.866; I(2) = 83.40%, P = 0.002; n = 3). However, the difference of the pooled RRs from the two subgroups did not reach statistical significance with a test of interaction (p = 0.179 for the interaction test). When pooling the RRs of non-vertebral fractures, significant inverse associations were similarly observed in men (RR = 0.72, 95%CI: 0.52-0.99, P = 0.048) but not in women (RR = 0.99, 95%CI: 0.60-1.64, P = 0.969). There was no evidence of publication bias. Our findings demonstrated that MetS was significantly associated with a lower fracture risk. There might be gender differences in the relationship of MetS with fractures, but further confirmation is needed.

Association between basal metabolic function and bone metabolism in postmenopausal women with type 2 diabetes

OBJECTIVE

Diabetes is a risk factor for osteoporosis, and glycemic control is critical during osteoporosis treatment in patients with type 2 diabetes (T2D). However, diabetic therapies have potentially adverse effects on bone metabolism. Additionally, biomarkers for bone metabolism are directly affected by drug therapies for osteoporosis. This study examined resting energy expenditure (REE) and respiratory quotient (RQ) as indices of bone metabolism in postmenopausal Japanese women with T2D.

METHODS

Forty-six postmenopausal Japanese women with T2D were examined. Procollagen type 1 N-terminal propeptide (P1NP, a fasting serum bone formation marker) and carboxy-terminal collagen cross-links-1 (CTX-1, a resorption marker) were evaluated, along with intact parathyroid hormone, 25-hydroxyvitamin D (25[OH]D), urine microalbumin, motor nerve conduction velocity, sensory nerve conduction velocity, R-R interval, body composition, REE, RQ, and bone mineral density at the nondominant distal radius.

RESULTS

The mean T-score was low with high variance (-1.7 ± 1.6), and 18 patients (39%) met the criteria for osteoporosis. REE was positively correlated with body mass index (β = 0.517; r(2) = 0.250), serum calcium (β = 0.624; r(2) = 0.200), glycated hemoglobin A1C for the previous 6 mo (β = 0.395; r(2) = 0.137), and the serum P1NP/CTX-1 ratio (β = 0.380; r(2) = 0.144). RQ was positively correlated with serum 25(OH)D (β = 0.387; r(2) = 0.131).

CONCLUSION

The basal metabolic rate and diabetic pathophysiology are interrelated with bone turnover.