Sex hormone-binding globulin at the crossroad of body composition, somatotropic axis and insulin/glucose homeostasis in young healthy men.

OBJECTIVES: Sex hormone-binding globulin (SHBG) modulates the bioavailability of sex steroids at tissue level. Genetic, hormonal and lifestyle-related factors determine the SHBG levels, and low SHBG levels are a known risk factor for the development of the metabolic syndrome, diabetes and cardiovascular diseases. We investigated to what extent different determinants contribute to the variation in SHBG levels in healthy young men. DESIGN AND PATIENTS: Healthy male siblings (n = 677) aged 25-45 year were recruited in a cross-sectional, population-based study. MEASUREMENTS: Lean and fat mass were measured using dual-energy X-ray absorptiometry (DXA), and immunoassays were used to determine the serum hormonal levels. Additional information about smoking and physical activity was obtained using questionnaires. Carriers of two SHBG polymorphisms, the Asp327Asn polymorphism and the (TAAAA)(n) repeat polymorphism, were identified. RESULTS: Weight, BMI, whole body fat mass and truncal fat mass were negatively associated with SHBG levels. Body composition characteristics did not differ between SHBG genotype groups, indicating that body composition controls SHBG levels rather than the other way around. The associations may be mediated by adipokines because leptin and adiponectin were, respectively, inversely and positively associated with SHBG levels. Insulin and glucose were negatively associated with SHBG levels, as well as IGF-1 and IGF-BP3, while no associations were found with free thyroid hormone status. CONCLUSIONS: In conclusion, we found that fat mass, insulin and IGF-1 levels are important negative determinants of SHBG levels in young healthy men. The association with fat mass could be mediated by the effects of adiponectin and/or leptin on SHBG synthesis.

Birth weight in relation to sex steroid status and body composition in young healthy male siblings.

CONTEXT: Sex steroid concentrations have a strong genetic determination, but environmental factors and body composition play an important role. From studies in children with intrauterine growth restriction, low birth weight has been associated with altered gonadotropin concentrations. OBJECTIVE: We aim to investigate sex steroid concentrations in healthy young brothers in relation to birth weight (normal gestational age), body composition, and parental steroid concentrations. DESIGN AND SETTING: We conducted a cross-sectional, population-based sibling pair study with inclusion of parental data. PARTICIPANTS: A total of 677 men (25-45 yr old) were included in this study, with 296 independent pairs of brothers and 122 fathers. MAIN OUTCOMES: We measured testosterone, estradiol, leptin, adiponectin, IGF-I (immunoassays), and free steroid hormones (calculated) in relation to birth weight and changes in body composition (dual-energy x-ray absorptiometry). RESULTS: Birth weight was associated with serum testosterone (P = 0.0004) and SHBG (P = 0.0001), independent from weight, age, or fat mass, whereas no association with (free) estradiol, LH, or FSH was found. Paternal testosterone (P = 0.02), estradiol (P = 0.04), and SHBG (P = 0.0004) were associated with the respective sex steroid concentrations in the brothers. Weight increase (population rank) during life, was associated with lower testosterone (-15%; P < 0.001), independent from current weight and with higher free estradiol concentrations (+8%; P = 0.002), whereas weight decrease was associated with higher testosterone (+13%; P < 0.001). CONCLUSION: Birth weight and paternal steroid concentrations are associated with testosterone concentrations, independent from adult weight. These findings support the concept of in utero programming across the range of birth weight.

On-line microheterogeneity analysis and rapid phenotyping of haptoglobin by capillary electrophoresis using sodium dodecyl sulfate as additive.

To improve the detection sensitivity and determine phenotypes of haptoglobin (Hp), a prefilling technique was developed and tested in capillary electrophoresis (CE) with UV-vis absorbance detection. Adding 0.01% sodium dodecyl sulfate (SDS) to the protein sample and 0.1% SDS to the prefilling buffer solution, on-line stacking and microheterogeneity separation of Hp were achieved. In addition, the influences of pH, buffer concentration, sample and prefilling buffer SDS concentration upon resolution were examined. Under optimized conditions, Hp-microheterogeneity was well resolved and two phenotypes of Hp (Hp 1-1 and Hp 2-2) were differentiated. This method was applied to the analysis of sera from normal individuals and beta-Thalassemia patients. After the depletion of albumin (HSA) and immunoglobulin G (IgG), this method allowed to determine two phenotypes in different individuals and to detect the decrease of Hp in beta-Thalassemia patients. Featuring high efficiency, speed and simplicity, the proposed method shows great potential for use in clinical diagnosis and proteome research.

Fat mass is negatively associated with cortical bone size in young healthy male siblings.

CONTEXT: Body weight has been associated with bone mass and bone size through shared genetic determination and environmental influences. Whereas lean mass exerts a positive influence on bone size, the relationship between fat and bone remains unclear. OBJECTIVE: The objective of the present study was to investigate the individual influence of fat mass and lean mass on volumetric bone density and size in young healthy male siblings at age of peak bone mass. DESIGN: This was a cross-sectional, population-based sibling pair study. PARTICIPANTS: A total of 677 men (25-45 yr) were included in this study with 296 independent pairs of brothers. MAIN OUTCOME MEASURES: Areal and volumetric bone parameters were determined using dual-energy X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT). Body composition was determined by DXA. Sex steroids, leptin, and adiponectin were determined by immunoassay. RESULTS: Total and regional fat mass were found to be inversely associated with areal bone mass and bone size, independent from lean mass (radius periosteal circumference beta: -0.29 +/- 0.04; P < 0.001). Lean mass was positively associated with bone size but inversely with cortical density at both tibia and radius (P < 0.01). The negative association between total fat mass and bone size was independent from sex steroid concentrations. Leptin but not adiponectin was inversely associated with bone size, but this was no longer significant after adjustment for body fat. CONCLUSIONS: Increased fat mass is associated with smaller bone size, challenging the view of a high bone mass index as a protective factor for osteoporosis, whereas lean mass was a consistent positive determinant of bone size.

Guanidino compounds after creatine supplementation in renal failure patients and their relation to inflammatory status.

BACKGROUND: Specific guanidino compounds have been described as uraemic toxins and their concentrations are increased in renal failure due to dimished glomerular filtration, whereas the guanidino compound creatine is used as a performance-enhancing substance in athletes. The present study investigates the effects of creatine supplementation on plasma guanidino compounds in a chronic haemodialysis population. METHODS: Twenty male haemodialysis patients were included in a placebo-controlled cross-over trial. Patients were treated with creatine (2 g/day) or placebo during two treatment periods of 4 weeks, separated by a washout of 4 weeks. Plasma guanidino compounds and routine biochemical parameters were determined, as well as the prognostic inflammatory and nutritional index (PINI). RESULTS: Upon creatine supplementation, guanidinoacetate concentrations decreased by 15%, due to inhibition of creatine synthesis. Concentrations of alpha-keto-delta-guanidinovaleric acid increased three-fold and argininic acid concentrations doubled. Guanidinosuccinate concentrations did not change, but correlated inversely with CRP (r = -0.736; P = 0.001), PINI-score (r = -0.716; P = 0.002) and correlated positively with plasma urea concentration (r = 0.54; P = 0.02). CONCLUSIONS: Creatine supplementation in haemodialysis patients significantly altered the concentration of specific guanidino compounds. Guanidinosuccinate correlated positively with plasma urea and negatively with inflammation markers.

Biological and clinical aspects of the vitamin D binding protein (Gc-globulin) and its polymorphism.

The vitamin D binding protein (DBP) is the major plasma carrier protein of vitamin D and its metabolites. Unlike other hydrophobic hormone-binding systems, it circulates in a considerably higher titer compared to its ligands. Apart from its specific sterol binding capacity, DBP exerts several other important biological functions such as actin scavenging, fatty acid transport, macrophage activation and chemotaxis. The DBP-gene is a member of a multigene cluster that includes albumin, alpha-fetoprotein, and alpha-albumin/afamin. All four genes are expressed predominantly in the liver with overlapping developmental profiles. DBP is a highly polymorphic serum protein with three common alleles (Gc1F, Gc1S and Gc2) and more than 120 rare variants. The presence of unique alleles is a useful tool for anthropological studies to discriminate and to reveal ancestral links between populations. Many studies have discussed the link between DBP-phenotypes and susceptibility or resistance to osteoporosis, Graves' disease, Hashimoto's thyroiditis, diabetes, COPD, AIDS, multiple sclerosis, sarcoidosis and rheumatic fever. This article reviews the general characteristics, functions and clinical aspects of DBP.

Vitamin D binding protein, bone status and body composition in community-dwelling elderly men.

The vitamin D binding protein (DBP) is the major carrier protein for vitamin D metabolites in plasma. Polymorphisms in DBP have been described to be associated with an increased bone fracture risk and diabetes. The present study investigates the influence of both phenotypic and (TAAA)(n)-Alu repeat DBP-polymorphism and DBP-concentration on bone mineral density, body composition, bone turnover- and metabolic markers in a cohort of ambulatory elderly men. We included 211 men (>70 years) in this study. Bone mineral density (BMD) was determined by dual energy X-ray absorptiometry. Bone turnover was assessed by measurement of serum osteocalcin, serum and urinary C-terminal telopeptides of type I collagen and urinary deoxypyridinoline, together with 25(OH)-vitamin D and 1,25(OH)(2)-vitamin D concentrations. DBP-phenotypes were determined electrophoretically and the (TAAA)(n)-Alu repeat polymorphism was determined by polymerase chain reaction. Body composition was estimated using bioelectrical impedance analysis, together with handgrip and arm strength, fasting serum glucose and leptin concentrations. No differences in BMD or bone turnover markers among DBP-phenotypes or (TAAA)(n)-genotypes were observed in this study. Serum 25(OH)-vitamin D was comparable among DBP-variants and did not relate to DBP-concentrations, whereas 1,25(OH)(2)-vitamin D was different among DBP-phenotypes and was correlated positively with DBP-concentrations. DBP-concentrations related positively to body mass index, fat mass, leptin and glucose concentration. The correlation with leptin remained significant after correction for fat mass. Fasting glucose concentrations were different among DBP-phenotypes, whereas no difference was observed between (TAAA)(n)-genotypes. In conclusion, serum 1,25(OH)(2)-vitamin D concentrations are codetermined by DBP-phenotypes and DBP-concentrations. No major effect of DBP-polymorphism was demonstrated on BMD, bone turnover markers or body composition.

Serum vitamin C concentration is influenced by haptoglobin polymorphism and iron status in Chinese.

BACKGROUND: Vitamin C is a powerful antioxidant (free radical scavenger). Apart from the diet, other factors regulating its catabolism may affect its serum concentration. Haptoglobin (Hp) is a plasma protein participating in iron metabolism. It shows a genetic polymorphism which shows marked geographical differences. We investigated the relationship between vitamin C, iron status and haptoglobin polymorphism in Chinese men and women. METHODS: Iron status markers were compared according to Hp phenotypes determined by chemiluminescence detection in 110 healthy Chinese subjects. The concentration of haptoglobin was determined using an immunoturbidimetric method. Serum vitamin C was tested by a 2,4-dinitrophenylhydrazine based method. RESULTS: In Chinese, the haptoglobin phenotype distribution was 10.0% Hp 1-1, 33.6% Hp 2-1, and 56.4% Hp 2-2. In the study group, serum vitamin C concentration was associated with haptoglobin type, showing lowest values in serum from Hp 2-2 subjects in males (p=0.028, ANOVA). In contrast to Hp phenotype, Hp concentration did not affect vitamin C concentration. Hp 2-2 shows higher haptoglobin (p=0.002 (ANOVA)) than individuals with the other types. Furthermore, vitamin C was influenced by (log)ferritin levels. In Chinese, vitamin C is influenced by haptoglobin polymorphism and iron status. CONCLUSION: The present findings support the role of non-nutritional factors in vitamin C status.

On the use of dispersed nanoparticles modified with single layer beta-cyclodextrin as chiral selecor to enhance enantioseparation of clenbuterol with capillary electrophoresis.

A new strategy for chiral separation by capillary electrophoresis employing modified-nanoparticles as chiral selector is described for clenbuterol analysis. Nanoparticles modified with beta-cyclodextrin (beta-CD) form a large surface area platform to serve as a pseudostationary chiral phase, which can be applied for the enhancement of the enantioseparation. The application of four kinds of nanoparticles was investigated (multi-walled nanotubes (MWNTs), polystyrene (PS), TiO(2) and Al(2)O(3)) modified with single layer beta-CD as chiral selector in the enantioseparation of clenbuterol by capillary electrophoresis (CE). Successful clenbuterol enantioseparation could be achieved with the beta-CD-modified MWNTs as chiral selector. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) confirmed the beta-CD modification of the nanoparticles. The effects of nanoparticles, surfactant, chiral selector (beta-CD) and run buffer were studied in relation to the enantiomeric separation of clenbuterol. This study opens attractive perspectives for the use of modified nanoparticles for chiral separational purposes in CE.

Creatine supplementation does not decrease total plasma homocysteine in chronic hemodialysis patients.

BACKGROUND: Hyperhomocysteinemia is present in the majority of chronic hemodialysis patients. Treatment with folic acid, vitamin B12, and vitamin B6 cannot fully normalize plasma homocysteine concentrations (tHcy). Previously we have demonstrated the tHcy-lowering effect of creatine supplementation in an animal model of uremia (Kidney Int 64:1331-1337, 2003). The present study investigates the effects of creatine supplementation on tHcy in a vitamin-repleted chronic hemodialysis population. METHODS: Forty-five hemodialysis patients receiving folic acid and vitamin B6 and B12 were included. Patients were treated with creatine (2 g/day) or placebo during 2 treatment periods of 4 weeks, separated by a washout of 4 weeks. Plasma tHcy, creatine, Kt/V(urea), folic acid, vitamin B12, and routine biochemistry were determined, as well as the prognostic inflammatory and nutritional index. RESULTS: All patients had elevated tHcy concentrations (21.2 +/- 5.6 micromol/L). Creatine treatment resulted in increased plasma and red blood cell creatine levels, documenting uptake of creatine. Creatine did not affect tHcy concentrations. There was no relationship between plasma creatine concentrations and tHcy concentrations. No changes in body weight, routine biochemistry, nutritional status, folic acid, or vitamin B12 were observed during the study. CONCLUSION: Creatine supplementation at a rate of 2 g/day does not further decrease tHcy concentrations in chronic dialysis patients already treated with high dose folic acid, vitamin B6, and B12 supplementation.

Effect of dietary creatine on skeletal muscle myosin heavy chain isoform expression in an animal model of uremia.

BACKGROUND: Chronic renal failure is accompanied with muscle dysfunction and myopathy, characterized by muscle weakness and increased fatigue. Myosin heavy chain (MHC) is the principal structural protein that controls the intrinsic contractile properties of striated muscle. Creatine is widely used as an ergogenic nutritional supplement in sportsmen. This study investigates the effect of creatine supplementation on MHC expression in the setting of uremic myopathy. METHODS: Male Wistar rats were either sham operated or subtotally nephrectomized and received a control diet or creatine (2% w/w)-supplemented diet. After 4 weeks of treatment, serum creatinine, creatine, urea and creatinine clearances were determined. MHC isoforms were determined electrophoretically in the extensor digitorum longus and soleus muscles. RESULTS: Creatinine clearances were lower in nephrectomized animals, but similar in creatine-supplemented and control diet animals. Nephrectomized animals had significantly higher MHC IIb and lower MHC IIx isoform expression in the extensor digitorum longus muscle compared to sham-operated animals. In the soleus muscle, MHC IIb expression was increased in nephrectomized animals. Creatine supplementation reversed the MHC transitions observed in uremia in the soleus muscle, but not in the extensor digitorum longus muscle. CONCLUSION: We observed altered expression of MHC isoforms in uremia. In uremic animals, fast MHC IIb isoforms were increased, whereas MHC I and IIx isoforms predominate in control animals. Dietary creatine supplementation reversed the altered MHC expression during uremia in slow-twitch, but not in fast-twitch muscles.

Prohepcidin accumulates in renal insufficiency.

BACKGROUND: The understanding of iron metabolism has increased substantially during the last decade. Several new transporters and iron regulating molecules have been described. Hepcidin, a small hepatic peptide has recently been proposed as a central mediator of dietary iron absorption. We have investigated the relationship between prohepcidin, the prohormone of hepcidin, and renal function and iron status. METHODS: Forty six patients, referred for 51Cr-EDTA clearance were included in this study. Renal function was assessed by determination of serum creatinine, creatinine clearance, serum cystatin C and serum beta-trace protein. Iron status was evaluated by determination of serum iron, transferrin, transferrin saturation and serum ferritin. All determinations were performed using commercial reagents (Roche Diagnostics, Dade Behring). Serum prohepcidin was determined using an ELISA kit. RESULTS: Serum prohepcidin was found to correlate with 51Cr-EDTA clearance (r = -0.44; p = 0.005), creatinine clearance, serum creatinine, beta-trace protein and cystatin C. No significant relationship was observed between serum prohepcidin concentrations and red cell count, hemoglobin concentration or hematocrit. No significant correlation was found in this population between prohepcidin concentrations and iron status. CONCLUSION: Increased serum prohepcidin concentrations were observed with declining kidney function. We observed no relationship between red cell indices or iron status and serum prohepcidin concentrations.

Creatine supplementation decreases homocysteine in an animal model of uremia.

BACKGROUND: Hyperhomocysteinemia is prevalent in more than 85% of patients with end-stage renal disease (ESRD) and is thought to contribute to the excess cardiovascular mortality and morbidity. Creatine is synthesized by methylation of guanidinoacetate with formation of S-adenosylhomocysteine and subsequently, homocysteine (Hcy). Creatine supplementation down-regulates its endogenous synthesis and, thus, may reduce Hcy production. The present study investigates the effect of creatine supplementation on Hcy concentrations in an animal model of uremia. METHODS: Male Wistar rats were either sham-operated and received a control diet (N = 8) or a 2% creatine-supplemented diet (N = 8), or underwent subtotal nephrectomy and received a control diet (N = 10) or a 2%-supplemented creatine diet (N = 10). After 2 weeks of treatment, total plasma Hcy, creatine, creatinine, folate, and vitamin B12 were determined, as well as hepatic folate and vitamin B12 concentrations. RESULTS: Plasma creatinine concentrations were higher in nephrectomized animals, but similar in creatine-supplemented and control diet-fed animals. Plasma Hcy was higher in nephrectomized animals but lower in creatine-supplemented nephrectomized animals compared to nephrectomized control diet-fed animals (12.1 +/- 2.4 micromol/L vs. 15.4 +/- 1.7 micromol/L; P < 0.01). Total plasma Hcy inversely correlated with plasma creatine concentrations (r =-0.39; P = 0.02). Plasma folate was higher in supplemented animals and hepatic tetrahydrofolate (THF) was higher in nephrectomized supplemented animals. Plasma vitamin B12 was similar in all groups, whereas hepatic vitamin B12 was higher in nephrectomized animals. CONCLUSION: Creatine supplementation can effectively lower plasma Hcy concentrations in an animal model of uremia and should be further investigated as a potential treatment for hyperhomocysteinemia in patients with ESRD.