Increased sclerostin and preadipocyte factor-1 levels in prepubertal rhythmic gymnasts: associations with bone mineral density, body composition, and adipocytokine values

Sclerostin and bone mass in pubertal girls: different associations between athletes and non-athletes

BACKGROUND

Rhythmic gymnasts (RG) start their heavy trainings already at early age and despite of low body fat mass, their bone parameters are higher than in untrained controls (UC). The specific role of sclerostin and preadipocyte factor-1 (Pref-1), which are the negative regulators of bone mass by inhibiting bone formation, is not well understood in puberty. The aims of the study were to compare sclerostin and Pref-1 between RG and UC, and to evaluate relationships of sclerostin and Pref-1 with bone mass.

METHODS

Study involved 32 RG and 32 UC girls aged 10-12 years. Bone mass and body composition were measured by dual-energy X-ray absorptiometry, and plasma sclerostin and Pref-1 concentrations were assessed from fasting blood samples.

RESULTS

Sclerostin was higher (P<0.0001) in RG (24.2±8.8 pmol/L) compared with UC (14.7±10.0 pmol/L1), while Pref-1 was similar between the groups. In RG, sclerostin was positively correlated with lumbar spine (LS) (r=0.44; P=0.012) and femoral neck (FN) (r=0.37; P=0.039) bone mineral content (BMC), whereas in UC, sclerostin was inversely associated with LS (r=-0.37; P=0.039) and FN (r=-0.35; P=0.048) BMC. In RG, sclerostin remained positively correlated with LS BMC independent of confounding factors (r=0.60; P=0.001). Pref-1 was not correlated with any bone mass values in both groups.

CONCLUSIONS

Early pubertal RG girls have higher plasma sclerostin levels compared UC. Sclerostin has differential associations with bone mass in RG compared to UC.

Associations of Circulating Irisin and Fibroblast Growth Factor-21 Levels with Measures of Energy Homeostasis in Highly Trained Adolescent Rhythmic Gymnasts

The aim of this investigation was to determine the associations of serum irisin and fibroblast growth factor-21 (FGF-21) with the measures of energy homeostasis, training stress and other energy homeostasis hormones in highly trained adolescent rhythmic gymnasts (RG). Thirty-three RG and 20 untrained controls (UC) aged 14−18 years participated in this study. Body composition, resting energy expenditure (REE), peak oxygen consumption, and different energy homeostasis hormones in serum, including irisin, FGF-21, leptin, and resistin, were measured. Irisin and FGF-21 were not significantly different (p > 0.05) between RG and UC groups. In RG, serum irisin was positively associated with REE (r = 0.40; p = 0.021) and leptin (r = 0.60; p = 0.013), while serum FGF-21 was related to body fat mass (r = 0.46; p = 0.007) and leptin (r = 0.45; p = 0.009). Irisin was related to FGF-21, independent of age, body fat, and lean masses (r = 0.36; p = 0.049) in RG. In conclusion, serum irisin concentration was associated with energy expenditure and serum FGF-21 level with energy availability measures in lean adolescent athletes, while no relationships of irisin and FGF-21 with energy status measures were observed in lean nonathletic adolescents.

Sclerostin as a biomarker of physical exercise in osteoporosis: A narrative review

Osteoporosis, a disease of low bone mass, is characterized by reduced bone mineral density (BMD) through abnormalities in the microarchitecture of bone tissue. It affects both the social and economic areas, therefore it has been considered a lifestyle disease for many years. Bone tissue is a dynamic structure exhibiting sensitivity to various stimuli, including mechanical ones, which are a regulator of tissue sclerostin levels. Sclerostin is a protein involved in bone remodeling, showing an anti-anabolic effect on bone density. Moderate to vigorous physical activity inhibits secretion of this protein and promotes increased bone mineral density. Appropriate exercise has been shown to have an osteogenic effect. The effectiveness of osteogenic training depends on the type, intensity, regularity and frequency of exercise and the number of body parts involved. The greatest osteogenic activity is demonstrated by exercises affecting bone with high ground reaction forces (GRF) and high forces exerted by contracting muscles (JFR). The purpose of this study was to review the literature for the effects of various forms of exercise on sclerostin secretion.

Serum sclerostin concentration is associated with specific adipose, muscle and bone tissue markers in lean adolescent females with increased physical activity

OBJECTIVES

Sclerostin is an important regulator of bone mass involving the Wnt/β-catenin signalling pathway. Relatively few studies have investigated the relationships of circulating sclerostin levels with adiposity-related and muscle-related biochemical factors in individuals with increased energy metabolism. The aim of this study was to investigate the associations of circulating sclerostin with adipokines, myokines, osteokines and body composition values in lean adolescent females with increased physical activity.

METHODS

A total of 73 adolescent females who were physically active and aged 14-18 years old participated in the study. Sclerostin, leptin, resistin, tumour necrosis factor (TNF)-α, interleukin (IL)-6, irisin, osteocalcin, C-terminal telopeptide of type I collagen (CTx), insulin-like growth factor (IGF)-1 and insulin were obtained from fasting blood samples. Body composition was measured by dual-energy X-ray absorptiometry (DXA) and analyzed for body fat mass, lean body mass, bone mineral content and muscle mass.

RESULTS

Serum sclerostin (117.9 ± 60.3 pg/mL) was correlated with age, age at menarche, body fat, muscle mass, training activity, leptin, TNF-α, irisin, osteocalcin, CTx and IGF-1. Multivariate linear regression analysis demonstrated that fat mass (β = 0.434; p = 0.001), leptin (β = -0.308; p = 0.015), irisin (β = 0.227; p = 0.024) and CTx (β = 0.290; p = 0.031) were the most important predictors of serum sclerostin concentration.

CONCLUSIONS

Bone-derived sclerostin is associated with specific adipokine, myokine and osteokine values in lean adolescent females with increased physical activity. These results suggest that the interactions between bone, adipose and muscle tissues could also be associated with circulating sclerostin concentrations.

Relationships of Bone Mineral Variables with Body Composition, Blood Hormones and Training Volume in Adolescent Female Athletes with Different Loading Patterns

The aim of this investigation was to determine the relationships of areal bone mineral density (aBMD) and content (BMC) with body composition, blood hormone and training load variables in adolescent female athletes with different loading patterns. The participants were 73 healthy adolescent females (14–18 years), who were divided into three groups: rhythmic gymnasts (RG; n = 33), swimmers (SW; n = 20) and untrained controls (UC; n = 20). Bone mineral and body compositional variables were measured by dual-energy X-ray absorptiometry, and insulin-like growth factor-1 (IGF-1), estradiol and leptin were analyzed from blood samples. In addition, aerobic performance was assessed by a peak oxygen consumption test. No differences (p > 0.05) in weekly training volume were observed between rhythmic gymnasts (17.6 ± 5.3 h/week) and swimmers (16.1 ± 6.9 h/week). Measured areal bone mineral density and bone mineral content values were higher in rhythmic gymnasts compared with other groups (p < 0.05), while no differences (p > 0.05) in measured bone mineral values were seen between swimmers and untrained control groups. Multiple regression models indicated that IGF-1 alone explained 14% of the total variance (R² × 100) in lumbar spine aBMD, while appendicular muscle mass and training volume together explained 37% of the total variance in femoral neck BMC in the rhythmic gymnast group only. In swimmers, age at menarche, estradiol and appendicular muscle mass together explained 68% of the total variance in lumbar spine BMC, while appendicular muscle mass was the only predictor and explained 19 to 53% of the total variance in measured bone mineral values in untrained controls. In conclusion, adolescent rhythmic gymnasts with specific weight-bearing athletic activity present higher areal bone mineral values in comparison with swimmers and untrained controls. Specific training volume together with appendicular muscle mass influenced cortical bone development at the femoral neck site of the skeleton in rhythmic gymnasts, while hormonal values influenced trabecular bone development at the lumbar spine site in both athletic groups with different loading patterns.

A Longitudinal Study of Bone Mineral Accrual during Growth in Competitive Premenarcheal Rhythmic Gymnasts

The purpose of this investigation was to study whether prolonged competitive rhythmic gymnastics training influenced bone mineral accrual in premenarcheal girls. Eighty-nine girls (45 rhythmic gymnasts [RG] and 44 untrained controls [UC]) between 7 and 9 years of age were recruited and measured annually for four years (not all participants were measured at every occasion). Dual energy x-ray absorptiometry was used to assess the development of whole body (WB), femoral neck (FN) and lumbar spine (LS) bone mineral content (BMC). In addition, body composition, blood adipokine and jumping performance characteristics were obtained. For longitudinal analyses, hierarchical mixed-effects models were constructed to predict differences in the development of WB, FN and LS BMC between RG and UC groups, while accounting for differences in body composition, blood adipokine and jumping performance values. It appeared that from 8 years of age, RG had lower (p < 0.05) fat mass and leptin values, and higher (p < 0.05) jumping performance measures in comparison with UC girls. Hierarchical mixed-effects models demonstrated that RG had 71.9 ± 12.0, 0.23 ± 0.11 and 1.39 ± 0.42 g more (p < 0.05) WB, FN and LS BMC, respectively, in comparison with UC girls. In addition, WB, FN and LS BMC increased more (p < 0.05) between 7 to 12 years of age in RG girls in comparison with UC. In conclusion, these findings suggest that the prolonged exposure to competitive rhythmic gymnastics trainings in premenarcheal girls is associated with greater bone mineral accrual despite lower body fat mass and leptin values.

Sclerostin, preadipocyte factor-1 and bone mineral values in eumenorrheic adolescent athletes with different training patterns

INTRODUCTION

The specific aims of the study were to compare possible differences in sclerostin and preadipocyte factor-1 (Pref-1) between rhythmic gymnasts (RG), swimmers (SW) and untrained controls (UC), and to investigate the relationships of sclerostin and Pref-1 with bone mineral characteristics in studied groups.

MATERIALS AND METHODS

This study included 62 eumenorrheic adolescents (RG = 22; SW = 20; UC = 20). Bone mineral and body composition characteristics were measured by dual-energy X-ray absorptiometry, and sclerostin, Pref-1, osteocalcin and C-terminal telopeptide of type I collagen (CTx) were measured.

RESULTS

Sclerostin was higher (P = 0.001) in RG (129.35 ± 51.01 pg/ml; by 74%) and SW (118.05 ± 40.05 pg/ml; by 59%) in comparison with UC (74.32 ± 45.41 pg/ml), while no differences (P = 0.896) were seen in Pref-1 (RG: 1.42 ± 0.16 ng/ml; SW: 1.41 ± 0.20 ng/ml; UC: 1.39 ± 0.26 ng/ml) between groups. Osteocalcin (RG: 7.74 ± 4.09 ng/ml; SW: 8.05 ± 4.18 ng/ml; UC: 7.04 ± 3.92 ng/ml; P = 0.843) and CTx (RG: 0.73 ± 0.22 ng/ml; SW: 0.64 ± 0.16 ng/ml; UC: 0.62 ± 0.20 ng/ml; P = 0.173) were not different between groups. Sclerostin correlated (P < 0.05) with whole-body bone mineral content (r = 0.61) and lumbar spine (LS) areal bone mineral density (aBMD) (r = 0.43) in RG, and femoral neck aBMD (r = 0.45) in UC. No correlation was found between sclerostin and bone mineral values in SW, and Pref-1 was not correlated with any bone mineral characteristics in studied groups. Sclerostin was the independent variable that explained 14% of the total variance (R² × 100) in LS aBMD value only in RG.

CONCLUSIONS

Adolescent athletes have higher sclerostin compared to UC. Sclerostin was correlated with bone mineral values and predicted areal bone mineral density in RG.

The Important Role of Adiponectin and Orexin-A, Two Key Proteins Improving Healthy Status: Focus on Physical Activity

Exercise represents the most important integrative therapy in metabolic, immunologic and chronic diseases; it represents a valid strategy in the non-pharmacological intervention of lifestyle linked diseases. A large body of evidence indicates physical exercise as an effective measure against chronic non-communicable diseases. The worldwide general evidence for health benefits are both for all ages and skill levels. In a dysregulated lifestyle such as in the obesity, there is an imbalance in the production of different cytokines. In particular, we focused on Adiponectin, an adipokine producted by adipose tissue, and on Orexin-A, a neuropeptide synthesized in the lateral hypothalamus. The production of both Adiponectin and Orexin-A increases following regular and structured physical activity and both these hormones have similar actions. Indeed, they improve energy and glucose metabolism, and also modulate energy expenditure and thermogenesis. In addition, a relevant biological role of Adiponectin and Orexin A has been recently highlighted in the immune system, where they function as immune-suppressor factors. The strong connection between these two cytokines and healthy status is mediated by physical activity and candidates these hormones as potential biomarkers of the beneficial effects induced by physical activity. For these reasons, this review aims to underly the interconnections among Adiponectin, Orexin-A, physical activity and healthy status. Furthermore, it is analyzed the involvement of Adiponectin and Orexin-A in physical activity as physiological factors improving healthy status through physical exercise.

The effect of weight loss on body composition, serum bone markers, and adipokines in prepubertal obese children after 1-year intervention

Purpose/Aim: The influence of weight loss on bone turnover and bone quality in childhood remains controversial, but it may implicate interactions between adiposity and bone metabolism. Therefore, we studied the relationships between bone markers and adipokines during weight loss in obese children.

MATERIALS AND METHODS

We determined serum leptin, soluble leptin receptor, adiponectin, bone alkaline phosphatase (BALP), C-terminal telopeptide of type I collagen (CTX-I), osteocalcin (OC), carboxylated-OC (Gla-OC), undercarboxylated-OC (Glu-OC), sclerostin, body composition, and bone mineral density (BMD) in 40 obese prepubertal children before and after therapy. The control group, matched for sex and age, consisted of 40 non-obese children.

RESULTS

We found that values of the total body less head-bone mineral content (TBLH-BMC) and TBLH-BMD were significantly increased, but TBLH-BMD Z-score was decreased by 25% (p = 0.002) in obese children with weight loss after therapy. We observed increases of CTX-I to OC ratio (p = 0.009), and Gla-OC concentrations (p = 0.049). Changes in TBLH-BMD Z-score in patients were positively correlated with changes in BMI Z-score (p = 0.001), percentage of fat mass (p = 0.004), and BALP activity (p = 0.01). Changes in BALP activity were negatively correlated (p < 0.001) with changes in adiponectin concentrations, while changes in sclerostin levels were positively correlated (p = 0.001) with leptin changes.

CONCLUSIONS

We suggest that alterations in adipokines metabolism were associated with a lower rate of bone mineral accrual as a result of decreased bone formation rather than increased bone resorption. The lower rate of bone mass accrual in weight losing children may be an effect of reduced BALP levels related to increase in adiponectin levels.

Exercise Early and Often: Effects of Physical Activity and Exercise on Women's Bone Health

In 2011 over 1.7 million people were hospitalized because of a fragility fracture, and direct costs associated with osteoporosis treatment exceeded 70 billion dollars in the United States. Failure to reach and maintain optimal peak bone mass during adulthood is a critical factor in determining fragility fracture risk later in life. Physical activity is a widely accessible, low cost, and highly modifiable contributor to bone health. Exercise is especially effective during adolescence, a time period when nearly 50% of peak adult bone mass is gained. Here, we review the evidence linking exercise and physical activity to bone health in women. Bone structure and quality will be discussed, especially in the context of clinical diagnosis of osteoporosis. We review the mechanisms governing bone metabolism in the context of physical activity and exercise. Questions such as, when during life is exercise most effective, and what specific types of exercises improve bone health, are addressed. Finally, we discuss some emerging areas of research on this topic, and summarize areas of need and opportunity.

Longitudinal changes in bone-testis axis and their associations with insulin resistance in 11- to 12-year-old boys

PURPOSE

Associations between osteocalcin (OCN), an osteoblast-specific hormone, and different markers of energy metabolism and insulin resistance have been reported in adults, but few studies have investigated this in children. The aim of the current study was to investigate serum OCN levels during pubertal development in normal weight (NW) and overweight (OW) boys, and to evaluate possible associations of OCN with body composition, testosterone, insulin resistance and adipocytokine values during puberty.

METHODS

Ninety 11- to 12-year-old boys were investigated at 12-month intervals over the next 2years. Boys were divided by their BMI into NW (n=60) and OW (n=30) groups. Serum OCN, testosterone, leptin, adiponectin, insulin, HOMA-IR score, and body composition were measured.

RESULTS

Pubertal development over the 2-year period was similar in both groups. Serum OCN was not different at the beginning of the study and increased similarly in both groups. However, at the end of the study, NW had higher OCN than OW (142.9±5.2 vs. 124.0±7.4ng/ml; p<0.05). OW had higher leptin, insulin and HOMA-IR compared to NW, and these differences remained significant through the 2-year period. Testosterone, insulin and HOMA-IR increased through the study period in both groups. In multiple regression analyses increment in OCN was associated with the increase in testosterone in NW (p<0.001) and OW (p=0.049) boys. Increment in OCN was also associated with the increase in insulin (p=0.019) and HOMA-IR (p=0.012) over the 2-year period in NW boys.

CONCLUSION

Serum OCN concentration increases in puberty and the increment is positively associated with the rise in testosterone level in both NW and OW boys. The positive association between the rise in OCN and insulin in NW boys would suggest that OCN may have a role in the development of insulin resistance.

Physical activity and hypocaloric diet recovers osteoblasts homeostasis in women affected by abdominal obesity

Obesity is a multifactorial disease linked to metabolic chronic disorders such as diabetes, and hypertension. Also, it has recently been associated with skeletal alterations and low bone mineral density. We previously demonstrated that exposure of osteoblasts to sera of sedentary subjects affected by obesity alters cell homeostasis in vitro, leading to disruption of intracellular differentiation pathways and cellular activity. Thus, the purpose of the present study has been to evaluate whether sera of sedentary obese women, subjected to physical activity and hypocaloric diet, could recover osteoblast homeostasis in vitro as compared to the sera of same patients before intervention protocol. To this aim, obese women were evaluated at time 0 and after 4, 6, and 12 months of individualized prescribed physical activity and hypocaloric diet. Dual-energy-X-ray absorptiometry measurements were performed at each time point, as well as blood was collected at the same points. Cells were incubated with sera of subjects before and after physical activity as described: obese at baseline and after for 4, 6, and 12 months of physical activity and nutritional protocol intervention. Osteoblasts exposed to sera of patients, who displayed increased lean and decreased fat mass (from 55.5 ± 6.5 to 57.1 ± 5.6% p ≤ 0.05; from 44.5 ± 1.1 to 40.9 ± 2.6% p ≤ 0.01 respectively), showed a time-dependent increase of Wnt/β-catenin signaling, versus cells exposed to sera of obese patients before intervention protocol, suggesting recovery of osteoblast homeostasis upon improvement of body composition. An increase in β-catenin nuclear accumulation and nuclear translocation was also observed, accompanied by an increase in Adiponectin receptor 1 protein expression, suggesting positive effect on cell differentiation program. Furthermore, a decrease in sclerostin amount and an increase of type 1 procollagen amino-terminal-propeptide were depicted as compared to baseline, proportionally to the time of physical activity, suggesting a recovery of bone remodeling modulation and an increase of osteoblast activity induced by improvement of body composition. In conclusion, our results show for the first time that sera of obese sedentary women who increased lean mass and decreased fat mass, by physical activity and hypocaloric diet, rescue osteoblasts differentiation and activity likely due to a reactivation of Wnt/β-catenin-pathway, suggesting that a correct life style can improve skeletal metabolic alteration induced by obesity.

Hormonal and systemic regulation of sclerostin

The Wnt/β-catenin signaling pathway plays an essential role in osteoblast biology. Sclerostin is a soluble antagonist of Wnt/β-catenin signaling secreted primarily by osteocytes. Current evidence indicates that sclerostin likely functions as a local/paracrine regulator of bone metabolism rather than as an endocrine hormone. Nonetheless, circulating sclerostin levels in humans often reflect changes in the bone microenvironment, although there may be exceptions to this observation. Using existing assays, circulating sclerostin levels have been shown to be altered in response to both hormonal stimuli and across a variety of normal physiological and pathophysiological conditions. In both rodents and humans, parathyroid hormone provided either intermittently or continuously suppresses sclerostin levels. Likewise, most evidence from both human and animal studies supports a suppressive effect of estrogen on sclerostin levels. Efforts to examine non-hormonal/systemic regulation of sclerostin have in general shown less consistent findings or have provided associations rather than direct interventional information, with the exception of mechanosensory studies which have consistently demonstrated increased sclerostin levels with skeletal unloading, and conversely decreases in sclerostin with enhanced skeletal loading. Herein, we will review the existent literature on both hormonal and non-hormonal/systemic factors which have been studied for their impact on sclerostin regulation.

Serum sclerostin decreases following 12months of resistance- or jump-training in men with low bone mass

PURPOSE

We previously reported that 12months of resistance training (RT, 2×/wk, N=19) or jump training (JUMP, 3×/wk, N=19) increased whole body and lumbar spine BMD and increased serum bone formation markers relative to resorption in physically active (≥4h/wk) men (mean age: 44±2y; median: 44y) with osteopenia of the hip or spine. The purpose of this secondary analysis was to examine the effects of the RT or JUMP intervention on potential endocrine mediators of the exercise effects on bone, specifically IGF-I, PTH and sclerostin.

METHODS

Fasting blood samples were collected after a 24-h period of no exercise at baseline and after 12months of RT or JUMP. IGF-I, PTH and sclerostin were measured in serum by ELISA. The effects of RT or JUMP on IGF-I, PTH and sclerostin were evaluated using 2×2 repeated measures ANOVA (time, group). This study was conducted in accordance with the Declaration of Helsinki and was approved by the University of Missouri IRB.

RESULTS

Sclerostin concentrations in serum significantly decreased and IGF-I significantly increased after 12months of RT or JUMP; while PTH remained unchanged.

CONCLUSION

The beneficial effects of long-term, progressive-intensity RT or JUMP on BMD in moderately active men with low bone mass are associated with decreased sclerostin and increased IGF-I.

Bone mineral density is increased after a 16-week resistance training intervention in elderly women with decreased muscle strength

OBJECTIVE

Non-pharmacological interventions are important in reducing risk for osteoporotic fractures. We investigated the effects of a 16-week individualized resistance training intervention on bone mineral density (BMD), bone turnover markers and 10-year relative risk (RR) for osteoporotic fracture.

DESIGN

Interventional study with a follow-up.

METHODS

In total, 37 elderly women (mean age 71.9 ± 3.1 years) with decreased muscle strength participated in the resistance training intervention three times per week with 60 min per session for 16 weeks under the supervision of a licensed physiotherapist. Total hip BMD with quantitative CT, bone markers (sclerostin, osteocalcin, CTX, PINP, IGF-1, 25(OH)-D) and 10-year RR for osteoporotic fracture were measured at baseline, post-intervention and at 1-year follow-up after the end of the intervention. Eleven age- and sex-matched controls did not participate in the intervention but were studied at baseline and at 1-year follow-up.

RESULTS

Resistance training seemed to increase total hip BMD by 6% (P = 0.005). Sclerostin (P < 0.001) and total osteocalcin (P = 0.04) increased while other bone markers remained unchanged. A 10-year RR for major osteoporotic and hip fracture remained unchanged. At follow-up total hip BMD (P < 0.001) decreased back to the baseline level with a simultaneous decrease in serum sclerostin (P = 0.045), CTX (P < 0.001) and an increase in 25(OH)-D (P < 0.001), 10-year RR for major osteoporotic (P = 0.002) and hip fracture (P = 0.01).

CONCLUSIONS

Our findings suggest an important role of continuous supervised resistance training for the prevention of osteoporotic fractures in elderly women with decreased muscle strength.

Implications of exercise-induced adipo-myokines in bone metabolism

Physical inactivity has been recognized, by the World Health Organization as the fourth cause of death (5.5 % worldwide). On the contrary, physical activity (PA) has been associated with improved quality of life and decreased risk of several diseases (i.e., stroke, hypertension, myocardial infarction, obesity, malignancies). Bone turnover is profoundly affected from PA both directly (load degree is the key determinant for BMD) and indirectly through the activation of several endocrine axes. Several molecules, secreted by muscle (myokines) and adipose tissues (adipokines) in response to exercise, are involved in the fine regulation of bone metabolism in response to the energy availability. Furthermore, bone regulates energy metabolism by communicating its energetic needs thanks to osteocalcin which acts on pancreatic β-cells and adipocytes. The beneficial effects of exercise on bone metabolism depends on the intermittent exposure to myokines (i.e., irisin, IL-6, LIF, IGF-I) which, instead, act as inflammatory/pro-resorptive mediators when chronically elevated; on the other hand, the reduction in the circulating levels of adipokines (i.e., leptin, visfatin, adiponectin, resistin) sustains these effects as well as improves the whole-body metabolic status. The aim of this review is to highlight the newest findings about the exercise-dependent regulation of these molecules and their role in the fine regulation of bone metabolism.