Osteocalcin as a negative regulator of serum leptin concentration in humans: insight from triathlon competitions

The effects of a 226-km ironman triathlon race on bone turnover in amateur male triathletes

BACKGROUND

The purpose of this study was to investigate the effects of an Ironman-distance triathlon on bone metabolism.

METHODS

Nine recreational male triathletes (39.7±8.2 years old) were voluntarily recruited before a 226-km Ironman triathlon race. Baseline blood samples were collected >1 hour before race. Serial post-race blood sampling time points included immediately (0hr), 1 hour (1hr), 1 day (d), 3 d, and 5 d after the Ironman race.

RESULTS

Serum muscle damage markers, serum myoglobin, creatine kinase (CK) and lactate dehydrogenase (LDH) revealed significant post-race peak values immediately, 1hr and 1d after the race, respectively. Except for the marginally higher serum CK and myoglobin at 5d (P=0.01~0.05), all post-race serum levels of muscle damage markers were significantly higher than baseline levels (P<0.01). Serum phosphorus values were significantly higher immediately (0hr) after the Ironman race. Serum osteocalcin, an index specific to bone formation, showed a significant decrease at time points 0hr and 1hr, but a significant increase 1 day after (P<0.01) and a marginal increase 3 and 5 days after (P=0.01~0.05) the race. No difference was shown in type I collagen C-telopeptide (CTX-1), a bone resorption marker. Pearson's correlation between serum osteocalcin and CTX-1 was done at each time point, and significant correlation was shown on the 5th d after the race (r=0.591, P<0.05).

CONCLUSIONS

An Ironman-distance contest induces a bone-formative-favoring turnover during the post-race period for amateur male triathletes.

Marathon Race Affects Neutrophil Surface Molecules: Role of Inflammatory Mediators

The fatigue induced by marathon races was observed in terms of inflammatory and immunological outcomes. Neutrophil survival and activation are essential for inflammation resolution and contributes directly to the pathogenesis of many infectious and inflammatory conditions. The aim of this study was to investigate the effect of marathon races on surface molecules related to neutrophil adhesion and extrinsic apoptosis pathway and its association with inflammatory markers. We evaluated 23 trained male runners at the São Paulo International Marathon 2013. The following components were measured: hematological and inflammatory mediators, muscle damage markers, and neutrophil function. The marathon race induced an increased leukocyte and neutrophil counts; creatine kinase (CK), lactate dehydrogenase (LDH), CK-MB, interleukin (IL)-6, IL-10, and IL-8 levels. C-reactive protein (CRP), IL-12, and tumor necrosis factor (TNF)-α plasma concentrations were significantly higher 24 h and 72 h after the marathon race. Hemoglobin and hematocrit levels decreased 72 h after the marathon race. We also observed an increased intercellular adhesion molecule-1 (ICAM-1) expression and decreasedTNF receptor-1 (TNFR1) expression immediately after and 24 h after the marathon race. We observed an increased DNA fragmentation and L-selectin and Fas receptor expressions in the recovery period, indicating a possible slow rolling phase and delayed neutrophil activation and apoptosis. Marathon racing affects neutrophils adhesion and survival in the course of inflammation, supporting the “open-window” post-exercise hypothesis.

Acute effects of different degrees of ultra-endurance exercise on systemic inflammatory responses

BACKGROUND

Intense physical stress might promote inflammatory responses, whereas a regular physical exercise has positive influence. Little is known on the acute metabolic and inflammatory responses to different levels of strenuous exercise in trained athletes.

AIM

To compare the short-term effect of two different ultra-endurance competitions on the inflammatory profile in male triathletes.

METHODS

We studied 14 Ironman (IR) and 13 Half Ironman (HIR) before and after their own specific race. We assessed body composition and measured blood cells, lipids, iron metabolism and plasma levels of some acute-phase cytokines and inflammatory markers.

RESULTS

After the race, IR showed reduced total body water and fat-free mass, not related with the duration of exercise, and increased white cells and platelets; high-density lipoprotein levels also increased. IR, but not HIR, showed reduced iron levels, increased ferritin and transferrin, reduced % saturated transferrin. HIR showed higher basal interleukin (IL)-6, tumour necrosis factor (TNF)-α, IL-10, IL-1β than IR; however, the post-performance rise was greater in IR. Irisin increased only in HIR and osteocalcin decreased in IR. In the whole study group, delta of white blood cells was directly related with delta of monocyte chemoattractant protein 1, and Δ ferritin was inversely related with Δosteocalcin.

CONCLUSIONS

A single ultra-endurance competition induces an inflammatory response depending on the duration of physical effort, with increased acute-phase cytokines, and an altered iron metabolism. Irisin, whose biological meaning is still uncertain, seems to be associated with acute variations of some metabolic parameters.

Higher daily physical activity is associated with higher osteocalcin levels in adolescents

BACKGROUND

Exercise stimulates bone remodeling and improves insulin sensitivity (Si), even without associated weight loss. Osteocalcin (OCN), a bone-derived protein, is associated with improved Si.

PURPOSE

We examined how daily physical activity is associated with OCN and Si.

METHODS

Physical activity was measured through questionnaires completed in Minneapolis from 2010-2012. A physical activity score (PAQsum) was calculated to quantify physical activity (range 1-5). OCN and bone specific alkaline phosphatase (BAP) were measured by ELISA. Si was measured by the insulin modified frequently sampled IV glucose tolerance test.

RESULTS

The mean PAQsum value was 2.4±0.8 in 47 participants (12-17.9 years old). PAQsum was positively associated with OCN (p= 0.006). Participants with PAQsum<2 had significantly lower OCN levels compared to participants with PAQsum>2 (p<0.02). Obesity did not modify the association between PAQsum and OCN. There was no statistically significant association between PAQsum and Si or between OCN and Si, even after adjustment for percent body fat.

CONCLUSIONS

OCN is higher in more physically active individuals. More research is needed to clarify the relationship between OCN, physical activity and Si.

The impact of triathlon training and racing on athletes' general health

Although the sport of triathlon provides an opportunity to research the effect of multi-disciplinary exercise on health across the lifespan, much remains to be done. The literature has failed to consistently or adequately report subject age group, sex, ability level, and/or event-distance specialization. The demands of training and racing are relatively unquantified. Multiple definitions and reporting methods for injury and illness have been implemented. In general, risk factors for maladaptation have not been well-described. The data thus far collected indicate that the sport of triathlon is relatively safe for the well-prepared, well-supplied athlete. Most injuries 'causing cessation or reduction of training or seeking of medical aid' are not serious. However, as the extent to which they recur may be high and is undocumented, injury outcome is unclear. The sudden death rate for competition is 1.5 (0.9-2.5) [mostly swim-related] occurrences for every 100,000 participations. The sudden death rate is unknown for training, although stroke risk may be increased, in the long-term, in genetically susceptible athletes. During heavy training and up to 5 days post-competition, host protection against pathogens may also be compromised. The incidence of illness seems low, but its outcome is unclear. More prospective investigation of the immunological, oxidative stress-related and cardiovascular effects of triathlon training and competition is warranted. Training diaries may prove to be a promising method of monitoring negative adaptation and its potential risk factors. More longitudinal, medical-tent-based studies of the aetiology and treatment demands of race-related injury and illness are needed.

Osteocalcin is inversely associated with glucose levels in middle-aged Tibetan men with different degrees of glucose tolerance

BACKGROUND

Research on the characteristics and mechanisms of diabetes in Tibetans is scant. Especially, there is no study on the relationship between osteocalcin and glucose metabolism. The objective of this study was to investigate the associations of serum total osteocalcin (tOC) and undercarboxylated osteocalcin (ucOC) with glucose and lipid metabolism in Chinese indigenous Tibetans with different degrees of glucose tolerance.

METHODS

In this study, 160 middle-aged Tibetan men were involved, including 46 subjects with normal glucose tolerance (NGT), 52 subjects with impaired glucose regulation (IGR) and 62 subjects with type 2 diabetes. The homeostasis model assessment (HOMA) parameters, including HOMA-IR and HOMA-B, were used to estimate insulin resistance and β-cell function, respectively. Adiponectin, leptin, testosterone, 1,25-dihydroxyvitamin D, tOC and ucOC were measured using ELISA kits.

RESULTS

After adjustment for age and body mass index, plasma tOC level was correlated negatively with fasting and 30-min post-OGTT glucose, HOMA-IR, leptin and testosterone; plasma ucOC level was correlated negatively with 30-min post-OGTT glucose, total cholesterol and 1,25-dihydroxyvitamin D; ucOC : tOC was correlated positively with leptin. The negative association between HOMA-IR and tOC remained significant after correcting for adiponectin; however, the association disappeared after correcting for leptin. HOMA-IR was correlated negatively with age, adiponectin and tOC, and positively with total cholesterol, triglyceride and leptin. Stepwise linear regression analysis revealed that total cholesterol, leptin and adiponectin were independent predictors for HOMA-IR in all subjects.

CONCLUSIONS

Our data support a link between osteocalcin and glucose metabolism in middle-aged Tibetan men. The improved glucose tolerance exerted by tOC may be related to improved insulin sensitivity rather than improved β-cell function.

Association of osteocalcin with obesity, insulin resistance, and cardiovascular risk factors in young adults

Low levels of osteocalcin (OCN), an osteoblast-specific hormone, have recently been associated with insulin resistance (homeostasis model assessment-insulin resistance (HOMA-IR)) and obesity, particularly in older adults. The aim of this study was to determine whether low levels of OCN would be associated with insulin resistance, obesity, and greater cardiovascular (CV) risk in young adults just emerging from adolescence. Undercarboxylated OCN and carboxylated OCN levels were measured on stored serum samples (total OCN = undercarboxylated OCN + carboxylated OCN) on 137 participants (67 males) at mean age 18.6 years (range 17-22 years). Insulin resistance was measured by hyperinsulinemic-euglycemic clamp (M(lbm)). Multivariable regression analyses with ln(OCN) as the independent variable were adjusted for age, sex, ethnicity, and BMI as indicated. Total OCN was inversely related to BMI, waist circumference, systolic blood pressure (SBP), interleukin (IL)-6, and directly related to M(lbm); only SBP remained significant (with M(lbm) P = 0.0560) after further adjustment for BMI. Carboxylated OCN was inversely related to BMI, waist circumference, SBP, low-density lipoprotein cholesterol (LDL-C), and directly related to adiponectin; SBP and adiponectin remained significant after further adjustment for BMI. There were no significant associations with undercarboxylated OCN. In summary, most associations with OCN were mediated via BMI. However, the significant associations of OCN with SBP, obesity, and adiponectin and borderline with M(lbm), suggest a potential role for OCN in the development of insulin resistance and CV risk that becomes more apparent with aging into older adulthood.

Osteocalcin: a new link between bone and energy metabolism. Some evolutionary clues

PURPOSE OF REVIEW

Recent findings suggest that the bone is an active regulator of energy and glucose metabolism. The purpose of this review is to summarize current evidence in humans.

RECENT FINDINGS

Both cross-sectional and longitudinal studies support osteocalcin as an active regulator of carbohydrate metabolism in humans, being the muscular load of physical activity one of the possible links between the osteoblast and the insulin axis. This axis could also have been involved in the modulation of nonalcoholic steatohepatitis. The osteoblast-to-insulin axis seems to act paradoxically in patients with increased growth hormone (acromegaly) and during bone repair. Some possible evolutionary implications are suggested.

SUMMARY

Osteocalcin may have a role in the regulation of systemic energy metabolism, given the common origin of the osteoblast with the two other cells implicated (adipocytes and muscle cells). Bioactivity of circulating human carboxylated and uncarboxylated osteocalcin should be characterized in depth, especially in those patients with increased concentrations (renal failure). Osteocalcin is one of the clues in the interaction between calcium and glucose metabolism, and the discovery of the osteocalcin receptor will aid in the study of these relationships.