The serum undercarboxylated osteocalcin level and the diet of a Japanese population: results from the Kyushu and Okinawa Population Study (KOPS)

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.

Undercarboxylated Osteocalcin and Its Associations With Bone Mineral Density, Bone Turnover Markers, and Prevalence of Osteopenia and Osteoporosis in Chinese Population: A Cross-Sectional Study

OBJECTIVE

Undercarboxylated osteocalcin (ucOC) is one form of osteocalcin lacking full carboxylation, which plays an important role in bone homeostasis, glucose homeostasis, and energy metabolism. Our aim is to obtain the profile of serum ucOC level according to gender and age and explore its associations with bone mineral density (BMD), bone turnover markers (BTMs), and prevalence of osteopenia and osteoporosis in the Chinese population.

METHODS

This is a cross-sectional study with 900 subjects, composed of 431 men and 469 women. Clinical information was collected, and BMD values of the lumbar spine (L1-4), left femoral neck, and total hip were scanned. Biochemical markers including hepatic and renal function, serum calcium, serum phosphorus, procollagen type 1 N-propeptide (P1NP) β-CrossLaps of type I collagen-containing cross-linked C-telopeptide (β-CTX) intact parathyroid hormone (PTH), 25-hydroxyvitamin D (25OHD), and ucOC were measured.

RESULTS

We found that the median ucOC level was higher in men than women [men, 2.6 ng/ml; women, 1.6 ng/ml; p < 0.001]. The profile according to age showed that ucOC levels were the lowest at the age of 40-49 years in both men [2.55 ng/ml (95% CI = 1.96-3.13 ng/ml)] and women [1.57 ng/ml (95% CI = 1.12-2.03 ng/ml)]; in patients younger than 49 years, they decreased with age; then over 50 years, they quickly increased. Furthermore, we found that a higher ucOC level was correlated with lower BMD values at the lumbar spine (men, r = -0.128, p = 0.013; women, r = -0.321, p < 0.001), femoral neck (men, r = -0.095, p = 0.062; women, r = -0.260, p < 0.001), and total hip (men, r = -0.123, p = 0.015; women, r = -0.209, p < 0.001) and higher P1NP (men, r = 0.307, p < 0.001; women, r = 0.239, p < 0.001) and β-CTX (men, r = 0.169, p = 0.001; women, r = 0.354, p < 0.001) levels in both men and women. Furthermore, we also showed that a 1 - SD increase in ucOC was associated with an odds ratio (OR) of 1.63 and 1.70 for having osteopenia or osteoporosis in men and women, respectively (men, 95% CI = 1.25-2.13, p = 0.004; women, 95% CI = 1.19-2.42, p = 0.004).

CONCLUSIONS

We first revealed the profile of serum ucOC levels according to gender and age in the Chinese population and demonstrated the associations of ucOC with BMD and BTMs and the risk of prevalent osteopenia or osteoporosis. Our findings provide a clue to elucidate the function of ucOC in bone metabolism.

Small Dense Low-Density Lipoprotein Cholesterol and Carotid Intimal Medial Thickness Progression

AIM

The association between small dense low-density lipoprotein cholesterol (sdLDL-C) levels and carotid intimal medial thickness (cIMT) progression has not been evaluated fully. We assessed specialized lipoproteins, including sdLDL-C, with regard to cIMT progression in a prospective observational study in Japan.

METHODS

Plasma total cholesterol, direct LDL-C, sdLDL-C, LDL-triglycerides (LDL-TG), high-density lipoprotein cholesterol (HDL-C), HDL2-C, HDL3-C, triglycerides, Lp(a), and adiponectin were measured in 2,030 men and women (median age 59 years, free of cardiovascular disease (CVD) and off cholesterol lowering medication). At both baseline and after a five-year follow-up, cIMT was assessed. Univariate, multivariate regression, and least square analyses were performed to examine the relationships between direct LDL-C, sdLDL-C, and other lipoproteins with cIMT progression.

RESULTS

The median cIMT at baseline was 0.63 mm and five-year progression was 0.18 mm. After adjustment for standard CVD risk factors, including age, gender, systolic blood pressure, total cholesterol, HDL-C, smoking, diabetes, and hypertension treatment, only direct LDL-C, sdLDL-C, and the sdLDL-C/LDL-C ratio were associated with cIMT progression. Even in subjects with direct LDL-C ＜100 mg/dL, who were considered at low CVD risk, elevated sdLDL-C were associated with cIMT progression (P for trend=0.009) in a model with established CVD risk factors, although the sdLDL-C/LDL-C ratio did not. Those correlations did not change by including triglycerides as a controlling factor or excluding premenopausal women from the analyzed population.

CONCLUSIONS

Small dense LDL-C has a stronger relationship with cIMT progression than LDL-C does; therefore, measuring sdLDL-C may allow for the formulation of optimal therapy for CVD prevention.

Vitamin K deficiency, evaluated with higher serum ucOC, was correlated with poor bone status in women

BACKGROUND

An increase in serum undercarboxylated osteocalcin concentrations suggests vitamin K deficiency. Clinical intervention studies suggested that the vitamin K supplementation might contribute to preventing bone loss in postmenopausal women. Evidence on the relationship between serum undercarboxylated osteocalcin (ucOC) levels and bone parameters of quantitative ultrasound (QUS) is limited. We examined the correlation between serum ucOC concentrations and bone status as measured by QUS among middle-aged and older Japanese men and women.

METHODS

The subjects were community-dwelling men (n = 358) and women (n = 503) aged ≥ 40 years in Japan. Heel QUS parameters, including the stiffness index, speed of sound, and broadband ultrasound attenuation, were measured. Serum ucOC concentrations were measured by electrochemiluminescence immunoassay. Grip strength was measured in the dominant hand. Information on alcohol drinking, current smoking, exercise, and menopause in women was collected.

RESULTS

Serum ucOC concentrations were significantly associated with age in both sexes. Serum ucOC concentrations in men were higher at ≥ 80 years than those in the age groups of 40-49, 50-59, and 60-69 years. Serum ucOC concentrations in women were higher in the age groups of 50-59 and 60-69 years than those at 40-49 years. Partial correlation analysis adjusting for covariates (age, body mass index, grip strength, alcohol drinking, current smoking, and exercise in men; age, body mass index, grip strength, alcohol drinking, current smoking, exercise, and menopause in women) showed that serum ucOC concentrations were negatively significantly correlated with all QUS parameters in women. Serum ucOC concentrations were not correlated with them in men.

CONCLUSIONS

Vitamin K deficiency, evaluated with higher serum ucOC, was correlated with poor bone status in women.

Dietary Intake during 56 Weeks of a Low-Fat Diet for Lomitapide Treatment in Japanese Patients with Homozygous Familial Hypercholesterolemia

AIM

Lomitapide is an oral inhibitor of the microsomal triglyceride transfer protein used to treat homozygous familial hypercholesterolemia (HoFH); patients require a low-fat diet to minimize gastrointestinal adverse effects and dietary supplements to prevent nutrient deficiencies. We investigated the diet and nutritional status during lomitapide treatment.

METHODS

Japanese patients with HoFH, who were in a phase 3 trial of lomitapide, were instructed to start low-fat diets with supplements of vitamin E and essential fatty acids 6 weeks before starting lomitapide treatment. Dietary education was conducted by registered dietitians 16 times during the study period, which included a pre-treatment run-in phase (Weeks －6-0), a lomitapide treatment efficacy phase (Weeks 0-26) and a safety phase (Weeks 26-56). Two-day dietary records were collected at each dietary counseling session. Anthropometric and biochemical parameters were measured at Weeks 0, 26 and 56.

RESULTS

Eight patients completed the 56 weeks of lomitapide treatment. Their median energy intakes derived from lipids were 19.2% and 17.9% during the efficacy and safety phases, respectively. "Fats and oils" intakes, and "Fatty meat and poultry" intakes in two patients, were successfully reduced to achieve low-fat diets. Although intakes of energy, fatty acids and fat-soluble vitamins did not differ significantly among phases, body weight, serum fatty acid levels and vitamin E concentrations were decreased at Week 26 as compared with Week 0.

CONCLUSION

HoFH patients can adhere to low-fat diets with ongoing dietary counseling. Instructions about intakes of energy, fatty acids and fat-soluble vitamins, as well as periodic evaluations of nutritional status, are necessary.

Association between osteocalcin and glucose metabolism: a meta-analysis

This meta-analysis aimed to investigate the associations between osteocalcin (Ocn) and fasting plasma glucose (FPG) and glycated hemoglobin A1c (HbA1c). It was revealed that both total Ocn and undercarboxylated Ocn (unOcn) were negatively related with FPG and HbA1c, and the association of unOcn with FPG was more pronounced in men.

INTRODUCTION

The aim of this study was to investigate the strength of associations between Ocn and FPG and HbA1c using a meta-analysis approach.

METHODS

A search was carried out using the databases of PubMed, ISI Web of Science, and the Cochrane library from 2007 to 2014 to identify related studies. A pooled effect size with 95 % confidence intervals (CI) was derived.

RESULTS

The meta-analysis included 39 studies involving 23,381 participants. The overall correlation was -0.16 (95 % CI, -0.19 to -0.14) between total Ocn (tOcn) and FPG and -0.15 (95 % CI, -0.20 to -0.11) between undercarboxylated Ocn (unOcn) and FPG. In the analysis of the association between Ocn and HbA1c, the pooled correlation was -0.16 (95 % CI, -0.18 to -0.14) for tOcn and -0.16 (95 % CI, -0.23 to -0.08) for unOcn. The magnitude of the correlation between unOcn and FPG is significantly higher in men than in women (r = -0.18, 95 % CI, -0.21 to -0.14; r = -0.09, 95 % CI, -0. 13 to -0.05, respectively; P for interaction < 0.05). Similar trend was also found between unOcn and HbA1c but without significance (for men, r = -0.19, 95 % CI, -0.24 to -0.14; for women, r = -0.09, 95 % CI, -0.22 to 0.04, respectively; P for interaction > 0.05). No indication of significant publication bias was found in any method.

CONCLUSIONS

This meta-analysis demonstrated that both unOcn and tOcn were similarly and negatively correlated with FPG and HbA1c in humans. The negative correlations between unOcn and glucose metabolism appear to be more pronounced in men than in women.

The association between objective tongue color and endoscopic findings: results from the Kyushu and Okinawa population study (KOPS)

Background

The relation between tongue color and gastroesophageal disease is unclear. This study was done to investigate the associations between tongue color (TC), endoscopic findings, Helicobacter.pylori infection status, and serological atrophic gastritis (SAG).

Methods

The participants were 896 residents of Ishigaki Island, Okinawa, aged 28–86 years. The tongue was photographed, esophagogastroduodenoscopy was done, and serum antibody to H.pylori was measured. SAG was defined as a serum Pepsinogen (PG)Ilevel ≤70 ng/ml and a PGI/IIratio ≤3.0. TC was measured by the device-independent international commission on Illumination 1976 L*a*b* color space standards at four points: (1) edge, (2) posterior, (3) middle, and (4) apex. We also calculated the ratio of the tongue edge to the three other measured points to examine the association between the coating of the tongue and the endoscopic and laboratory findings.

Results

Participants were excluded who had two or more endoscopic findings (n = 315) or who had SAG without seropositivity to H.pylori (n = 33). The remaining 548 participants were divided into three groups: SAG and seropositive to H.pylori (n = 67), seropositive to H.pylori alone (n = 56), and without SAG and seronegative for H.pylori (n = 425). We divided 425 residents into a single endoscopic finding positive group (n = 207) and a negative group, which served as a control (n = 218). The most frequent single endoscopic finding was esophageal hernia (n = 110), followed by erosive esophagitis (n = 35) and erosive gastritis (EG) (n = 45). EH was significantly associated with TC (2b*/1b*) (P < 0.05). EG was significantly associated with TC (3a*, 3b*) (P < 0.05). Seropositivity to H.pylori was significantly associated with TC (3 L*, 3 L*/1 L*) (P < 0.05, <0.01), and seropositivity to both H.pylori and SAG was significantly associated with TC (3 L*/1 L*) (P < 0.05). Multivariate analysis extracted TC (3a*, 3b*) as an independent factor associated with a differential diagnosis of EG (Odds ratio (OR) 2.66 P = 0.008, OR 2.17 P = 0.045).

Conclusions

The tongue body color of the middle area reflects acute change of gastric mucosa, such as erosive gastritis. Tongue diagnosis would be a useful, non-invasive screening tool for EG.

GGCX and VKORC1 inhibit osteocalcin endocrine functions

Cell-specific gene inactivation experiments delineate the functions of the enzymes required for osteocalcin modification and demonstrate that it is its uncarboxylated form that acts as a hormone.

Osteocalcin (OCN) is an osteoblast-derived hormone favoring glucose homeostasis, energy expenditure, male fertility, brain development, and cognition. Before being secreted by osteoblasts in the bone extracellular matrix, OCN is γ-carboxylated by the γ-carboxylase (GGCX) on three glutamic acid residues, a cellular process requiring reduction of vitamin K (VK) by a second enzyme, a reductase called VKORC1. Although circumstantial evidence suggests that γ-carboxylation may inhibit OCN endocrine functions, genetic evidence that it is the case is still lacking. Here we show using cell-specific gene inactivation models that γ-carboxylation of OCN by GGCX inhibits its endocrine function. We further show that VKORC1 is required for OCN γ-carboxylation in osteoblasts, whereas its paralogue, VKORC1L1, is dispensable for this function and cannot compensate for the absence of VKORC1 in osteoblasts. This study genetically and biochemically delineates the functions of the enzymes required for OCN modification and demonstrates that it is the uncarboxylated form of OCN that acts as a hormone.

A four-season molecule: osteocalcin. Updates in its physiological roles

Osteocalcin (OC) is the main non-collagenous hydroxyapatite-binding protein synthesized by osteoblasts, odontoblasts, and hypertrophic chondrocytes. It has a regulatory role in mineralization and it is considered a marker of bone cell metabolism. Recent findings evidenced new extra-skeletal roles for OC, depicting it as a real hormone. OC shares many functional features with the common hormones, such as tissue-specific expression, circadian rhythm, and synthesis as a pre-pro-molecule. However, it has some peculiar features making it a unique molecule: OC exists in different forms based on the degree of carboxylation. Indeed, OC has three glutamic acid residues, in position 17, 21, and 24, which are subject to γ-carboxylation, through the action of a vitamin K-dependent γ-glutamyl carboxytransferase. The degree of carboxylation, and thus the negative charge density, determines the affinity for the calcium ions deposited in the extracellular matrix of the bone. The modulation of the carboxylation could, thus, represent the mechanism by which the body controls the circulating levels, and hence the hormonal function, of OC. There are evidences linking OC, and the bone metabolism, with a series of endocrine (glucose metabolism, energy metabolism, fertility) physiological (muscle activity) and pathological functions (ectopic calcification). Aim of this review is to give a full overview of the physiological roles of OC by collecting the newest experimental findings on this intriguing molecule.

Outcome of glucose homeostasis in patients with glucocorticoid-induced osteoporosis undergoing treatment with bone active-drugs

Over the last few years, there has been experimental evidence for the existence of cross-talking between bone remodeling and glucose metabolism. Whether this experimental model can be translated to humans is still debated, and it is also unclear whether the modulation of bone turnover by anti-osteoporotic drugs may lead to changes in glucose metabolism. The aim of this 12-month prospective study was to investigate whether treatment of glucocorticoid-induced osteoporosis (GIO) with bipshosphonates or teriparatide may influence serum glycated hemoglobin (HbA1c) and fasting plasma glucose. One-hundred-eleven patients (70 F, 41 M, median age 70, range: 55-89) chronically treated with glucocorticoids were evaluated for changes in serum HbA1c and fasting plasma glucose during treatment with bisphosphonates (45 cases) or teriparatide (33 cases) as compared to those occurring during treatment with calcium and vitamin D alone (33 cases). In patients treated with teriparatide, but not in those treated with bisphosphonates or calcium and vitamin D alone, a statistically significant (p=0.01) decrease in serum HbA1c was observed during the follow-up, the change being greater (p=0.01) in patients with diabetes as compared to those without diabetes. In most cases, the decrease of serum HbA1c was relatively limited and in some patients the improvement of glucose homeostasis was concomitant with implementation of anti-diabetic treatments. Fasting plasma glucose did not change significantly during either bisphosphonates or teriparatide treatments. In conclusion, currently used bone active drugs may produce limited effects on glucose metabolism in patients with GIO. Interestingly, the bone anabolic drug teriparatide was shown to be associated with some improvement in serum HbA1c in this clinical context.

Vitamin K deficiency evaluated by serum levels of undercarboxylated osteocalcin in patients with anorexia nervosa with bone loss

BACKGROUND & AIMS

Osteoporosis is a chief complication in patients with anorexia nervosa. Serum levels of undercarboxylated osteocalcin reflect serum and bone vitamin K deficiency. We investigated vitamin K status in patients with anorexia nervosa to help establish prevention and treatment recommendations for osteoporosis.

METHODS

Fifty-four female amenorrheic patients with anorexia nervosa (29 restricting-type and 25 binge eating/purging type) (age, 28.0 (26.7-31.1) (mean (95% CI)) years; body mass index, 14.8 (14.1-15.5) kg/m(2), duration of illness; 107.3 (88.5-126.0) months) and 15 age-matched healthy females were included in this study. We measured serum levels of undercarboxylated osteocalcin, biochemical and nutritional markers, and bone metabolic markers. Dietary vitamin K intake was evaluated by a questionnaire.

RESULTS

Lumbar bone mineral density and T-scores in patients with anorexia nervosa were 0.756 (0.721-0.790) g/cm(2) and -2.4 (-2.1 to -2.7), respectively, indicating bone loss. Serum levels of undercarboxylated osteocalcin in patients with anorexia nervosa were significantly higher than those of controls. The 17% of restricting type and 40% of binge eating/purging type anorexia nervosa patients, serum levels of undercarboxylated osteocalcin were higher than 4.5 ng/ml and were diagnosed with vitamin K deficiency. Serum levels of undercarboxylated osteocalcin correlated significantly and negatively with vitamin K intake in patients with anorexia nervosa.

CONCLUSIONS

Patients with anorexia nervosa had vitamin K deficiency. Since a supplement of vitamin K might be effective for maintaining bone quality, we provide recommendations regarding vitamin K intake for prevention and treatment of osteoporosis in patients with AN.